S Ho-Van
email: son.ho-van@emse.fr

B Bouillot
email: bouillot@emse.fr

J Douzet

S Maghsoodloo Babakhani

J M Herri

Cyclopentane hydratesa candidate for desalination?

Keywords: Review, Desalination, Clathrate Hydrates, Cyclopentane Hydrates, Seawater treatment

This article presents a systematic review on the past developments of Hydrate-Based Desalination process using Cyclopentane as hydrate guest. This is the first review that covers all required fundamental data, such as multiphase equilibria data, kinetics, morphology, or physical properties of cyclopentane hydrates, in order to develop an effective and sustainable desalination process. Furthermore, this state-of-the-art describes research and commercialization perspectives. When compared to traditional applications, cyclopentane hydrate-based desalination process could be a promising solution. Indeed, it operates under normal atmospheric pressure, lower operation energies are required, etc… However, there are some challenges yet to overcome. A decision aid in the form of a diagram is proposed for a new cyclopentane hydrates-based desalination process. Hopefully, concepts reviewed in this study will suggest new ideas to advance technical solutions in order to make commercial hydrate-based desalination processes a reality.

Introduction

Seemingly abundant, clean water is a crucial resource for life on our planet. However, due to the increasing population, industrialization, global warming, agriculture activities, the shortage of clean water has become an urgent issue in many countries, especially in the Middle East and Africa [START_REF] Pedro-Monzonís | A review of water scarcity and drought indexes in water resources planning and management[END_REF][START_REF] Lu | Review of social water cycle research in a changing environment[END_REF]. Today, more than 1 billion people are denied the right to access clean water and about 2.6 billion people lack access to adequate sanitation [START_REF] Watkins | Human Development Report 2006 -Beyond scarcity: Power, poverty and the global water crisis[END_REF][START_REF] Montgomery | Water And Sanitation in Developing Countries: Including Health in the Equation[END_REF]. Dirty water is the world's second biggest children killer [START_REF] Watkins | Human Development Report 2006 -Beyond scarcity: Power, poverty and the global water crisis[END_REF]. For instance, in the Kingdom of Saudi Arabia (KSA), 60% of water demand is provided by desalination, that is to say about 10 Mm 3 /day [START_REF] Caldera | Role of Seawater Desalination in the Management of an Integrated Water and 100% Renewable Energy Based Power Sector in Saudi Arabia[END_REF]. Expectations of KSA desalination demand in 2050 should be 60 Mm 3 /day. Therefore, while mature technologies exist, processes for clean water production need to be optimized in regard to the enormous future demand. Because of the practical unlimited supply capacity of sea-water, desalination has become an ever increasingly used method to produce fresh water [START_REF] Khawaji | Advances in seawater desalination technologies[END_REF]. A history of desalination research literature is detailed in Figure 1. As illustrated in figure, there has been a significant rise in research on desalination over the past decades. The most common studied methods have been:

Thermal distillation, Reverse osmosis, Freezing, and Electro dialysis [START_REF] Lawson | Membrane distillation[END_REF][START_REF] Wang | A conceptual demonstration of freeze desalination-membrane distillation (FD-MD) hybrid desalination process utilizing liquefied natural gas (LNG) cold energy[END_REF][START_REF] Buros | Desalination Manual[END_REF][START_REF] Subramani | Emerging desalination technologies for water treatment: A critical review[END_REF]. Recently, Clathrate hydrate-based desalination technique has attracted considerable interest [START_REF] Park | A new apparatus for seawater desalination by gas hydrate process and removal characteristics of dissolved minerals (Na + , Mg 2+ , Ca 2+ , K + , B 3+ )[END_REF][START_REF] Lee | An optimal design approach of gas hydrate and reverse osmosis hybrid system for seawater desalination[END_REF][START_REF] Kang | Evaluation of Desalination by Nanostructured Hydrate Formation and Pellet Production Process[END_REF]. Clathrate hydrates, or gas hydrates, are ice-like non-stoichiometric crystalline solid compounds that contain water molecules forming cages through a hydrogen-bonding system enclosing guest molecules, formed under high pressure and low temperature conditions [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF]. This is usually the case for gaseous guest molecules (CO 2 , CO, N 2 , CH 4 …). Other heavier guest molecules can form clathrate hydrates under atmospheric pressure (Cyclopentane (CP), Tetrahydrofuran…). Depending on size and nature of the guest molecules, water molecules can form different kind of cages that combine to form a crystal lattice according to three well-known Publications Year structures: I, II, and H. Since water is usually present in the oil and gas flowlines, gas hydrates are well known to plug pipelines [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF]. Besides, several potential applications of clathrate hydrates have been investigated, such as gas storage [START_REF] Mimachi | Natural gas storage and transportation within gas hydrate of smaller particle: Size dependence of self-preservation phenomenon of natural gas hydrate[END_REF][START_REF] Sun | Natural gas storage in hydrates with the presence of promoters[END_REF][START_REF] Burnol | Influence of impurities (nitrogen and methane) on the CO 2 storage capacity as sediment-hosted gas hydrates -Application in the area of the Celtic Sea and the Bay of Biscay[END_REF][START_REF] Veluswamy | Hydrogen storage in clathrate hydrates: Current state of the art and future directions[END_REF], carbon dioxide capture [START_REF] Duc | CO 2 capture by hydrate crystallization -A potential solution for gas emission of steelmaking industry[END_REF][START_REF] Herslund | Thermodynamic promotion of carbon dioxide-clathrate hydrate formation by tetrahydrofuran, cyclopentane and their mixtures[END_REF], gas transportation [START_REF] Mimachi | Natural gas storage and transportation within gas hydrate of smaller particle: Size dependence of self-preservation phenomenon of natural gas hydrate[END_REF][START_REF] Taheri | Natural gas transportation and storage by hydrate technology: Iran case study[END_REF], gas separation [START_REF] Herri | Enhanced Selectivity of the Separation of CO 2 from N 2 during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions[END_REF][START_REF] Babu | A review of the hydrate based gas separation (HBGS) process forcarbon dioxide pre-combustion capture[END_REF], air-conditioning [START_REF] Darbouret | Rheological study of TBAB hydrate slurries as secondary two-phase refrigerants[END_REF][START_REF] Douzet | Prototyping of a real size air-conditioning system using a tetra-n-butylammonium bromide semiclathrate hydrate slurry as secondary two-phase refrigerant -Experimental investigations and modelling[END_REF][START_REF] Ogoshi | Air-Conditioning System Using Clathrate Hydrate Slurry[END_REF], and of course seawater desalination [START_REF] Park | A new apparatus for seawater desalination by gas hydrate process and removal characteristics of dissolved minerals (Na + , Mg 2+ , Ca 2+ , K + , B 3+ )[END_REF][START_REF] Kang | Evaluation of Desalination by Nanostructured Hydrate Formation and Pellet Production Process[END_REF][START_REF] Fakharian | Desalination of high salinity produced water using natural gas hydrate[END_REF][START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF].

Here As a matter of fact, gas hydrates-based desalination has been investigated for decades [START_REF] Subramani | Emerging desalination technologies for water treatment: A critical review[END_REF][START_REF] Lee | An optimal design approach of gas hydrate and reverse osmosis hybrid system for seawater desalination[END_REF][START_REF] Colten | Hydrolysis losses in the hydrate desalination process: rate measurements and economic analysis[END_REF][START_REF] Sugi | Concentration and demineralization of sea water by the hydrate process[END_REF][START_REF] Mccormack | Build and operate clathrate desalination pilot plant[END_REF][START_REF] Mccormack | Clathrate desalination plant preliminary research study[END_REF][START_REF] Bradshaw | Desalination Utilizing Clathrate Hydrates[END_REF][START_REF] Max | Hydrate desalination for water purification[END_REF][START_REF] He | A novel conceptual design of hydrate based desalination (HyDesal) process by utilizing LNG cold energy[END_REF][START_REF] Englezos | The Freeze Concentration Process and its Applications[END_REF][START_REF] Babu | Unusual behavior of propane as a co-guest during hydrate formation in silica sand: Potential application to seawater desalination and carbon dioxide capture[END_REF][START_REF] Barduhn | The properties of some new gas hydrates and their use in demineralizing sea water[END_REF]. Despite that, hydrate-based technology is not used nowadays in desalination plants. There are several explanations: mostly energy consumption issues and technology immaturity [START_REF] He | A novel conceptual design of hydrate based desalination (HyDesal) process by utilizing LNG cold energy[END_REF].

However, a great deal of research has been done recently, and could provide a base for future hydrate-based desalination technology. In some studies, CP is suggested as an adequate guest candidate [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF][START_REF] Tohidi | Equilibrium data and thermodynamic modelling of cyclopentane and neopentane hydrates[END_REF][START_REF] Lv | Phase equilibrium and dissociation enthalpies for hydrates of various water-insoluble organic promoters with methane[END_REF][START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF][START_REF] Hong | Investigation of thermodynamic and kinetic effects of cyclopentane derivatives on CO2 hydrates for potential application to seawater desalination[END_REF][START_REF] Wang | Lattice Boltzmann modeling for hydrate formation in brine Dalian University of Technology[END_REF]. Indeed, CP forms clathrate hydrates with pure water under atmospheric pressure at 7°C. Especially, it is not miscible into water (solubility of 0.156 g/L at 25°C [START_REF] Mcauliffe | Solubility in Water of Paraffin, Cycloparaffin, Olefin, Acetylene, Cycloolefin, and Aromatic Hydrocarbons1[END_REF]).

Therefore, it can be easily recovered from water after dissociation, and recycled for the desalination/cleaning process.

Note that CP act as a hydrate promoter for other applications, such as carbon capture, as described in detail by Herri et al. [START_REF] Herri | Enhanced Selectivity of the Separation of CO 2 from N 2 during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions[END_REF], or Zheng et al. [START_REF] Zheng | Effects of cyclopentane on CO2 hydrate formation and dissociation as a co-guest molecule for desalination[END_REF]. It is a co-guest used to milder hydrate formation conditions when combined to other molecules such as N 2 [START_REF] Tohidi | Equilibrium data and thermodynamic modelling of cyclopentane and neopentane hydrates[END_REF][START_REF] Lee | Characterization of cyclopentane clathrates with gaseous guests for gas storage and separation[END_REF][START_REF] Zhao | Prediction of phase equilibrium conditions for gas hydrates formed in the presence of cyclopentane or cyclohexane[END_REF][START_REF] Jianwei | Experimental determination of the equilibrium conditions of binary gas hydrates of cyclopentane + oxygen, cyclopentane + nitrogen, and cyclopentane + hydrogen[END_REF], C 3 H 8 [START_REF] Baek | Inhibition effects of activated carbon particles on gas hydrate formation at oil-water interfaces[END_REF], CO 2 [START_REF] Lee | Characterization of cyclopentane clathrates with gaseous guests for gas storage and separation[END_REF][START_REF] Zhao | Prediction of phase equilibrium conditions for gas hydrates formed in the presence of cyclopentane or cyclohexane[END_REF][START_REF] Matsumoto | Phase equilibrium relations for binary mixed hydrate systems composed of carbon dioxide and cyclopentane derivatives[END_REF][START_REF] Herslund | Measuring and modelling of the combined thermodynamic promoting effect of tetrahydrofuran and cyclopentane on carbon dioxide hydrates[END_REF][START_REF] Zheng | Research on the CO 2 Gas Uptake of Different Hydrate Structures with Cyclopentane or Methyl-cyclopentane as Co-guest Molecules[END_REF], CH 4 [START_REF] Tohidi | Equilibrium data and thermodynamic modelling of cyclopentane and neopentane hydrates[END_REF][START_REF] Zhao | Prediction of phase equilibrium conditions for gas hydrates formed in the presence of cyclopentane or cyclohexane[END_REF][START_REF] Lv | Raman Spectroscopic Studies on Microscopic Mechanism of CP -CH 4 Mixture Hydrate[END_REF][START_REF] Mohammadi | Phase Equilibria of Clathrate Hydrates of Tetrahydrofuran+Hydrogen Sulfide and Tetrahydroduran+Methane[END_REF], or H 2 S [START_REF] Mohammadi | Phase Equilibria of Clathrate Hydrates of Tetrahydrofuran+Hydrogen Sulfide and Tetrahydroduran+Methane[END_REF]. Thus, the use of cyclopentane hydrates (CPH) for a combined gas capture and desalination process could be applicable and probably more interesting energetically.

Finally, this article provides a comprehensive, but non exhaustive, state-of-the-art review on CPH. It objective is to inform the scientific and industrial community the latest advances, and establishing the challenges to address when developing CPH-based desalination.

Phase equilibria of CPH

Phase equilibrium data of CPH in pure water and in presence of electrolytes are crucial for salt removal using CPH. Thermodynamic equilibrium data of CPH has been classified into three categories: CP+water, CP+water+electrolytes, and CP+water+other guests.

Phase equilibrium of CPH in pure water with and without surfactants

At ambient pressure, CP can form hydrate with pure water from 6.3°C to 7.7°C according to literature. The melting point varies in the literature, and can be lowered by adding surfactant such as SPAN 80. Table 1 presents literature results. Equilibrium temperatures reported at 7.7-7.8°C range were obtain by quick dissociation method [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF][START_REF] Dirdal | Can cyclopentane hydrate formation be used to rank the performance of kinetic hydrate inhibitors?[END_REF][START_REF] Sefidroodi | Investigation into the strength and source of the memory effect for cyclopentane hydrate[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Masoudi | An in situ method on kinetics of gas hydrates An in situ method on kinetics of gas hydrates[END_REF]. Unfortunately, the quick method tends to miss the correct dissociation temperature, because of the high dissociation rate. Therefore, the value of equilibrium temperature is usually overestimated.

One seemingly more reliable method is Differential Scanning Calorimetry (DSC) [START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Whitman | Investigation of factors affecting crystallization of cyclopentane clathrate hydrate[END_REF][START_REF] Zhang | Equilibrium of hydrogen + cyclopentane and carbon dioxide + cyclopentane binary hydrates[END_REF][START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF]. Equilibrium temperatures measured by DSC show a temperature range from 6.6°C to 7.2°C.

In addition, Sakemoto et al. [START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF], Mitarai et al [START_REF] Mitarai | Surfactant effects on the crystal growth of clathrate hydrate at the interface of water and hydrophobic-guest liquid[END_REF], Ho-Van et al. [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF], and Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] performed slow dissociation method and reported crystallization temperature of CPH of 7.0°C, 7.1°C and 7.2°C, respectively. The small variations could be attributed to heating rate differences. Sakemoto et al. [START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF], Mitarai et al [START_REF] Mitarai | Surfactant effects on the crystal growth of clathrate hydrate at the interface of water and hydrophobic-guest liquid[END_REF], and Ho-Van et al. [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF] used an increment of 0.1°C/hour, and 0.2°C/hour for Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF]. Hence, equilibrium temperature reported by Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] is slightly higher. In another work, Delroisse et al. [START_REF] Delroisse | Determination of thermophysical properties of cyclopentane hydrate using a stirred calorimetric cell[END_REF] reported the dissociation temperatures of 7.05°C (280.2 °K) by using a stirred calorimetric cell. Their method utilized an agitator to mix the fluid (CP+H 2 O) in a calorimetric cell instead of static condition, as in a normal DSC method. This development is believed to provide more accurate data [START_REF] Delroisse | Determination of thermophysical properties of cyclopentane hydrate using a stirred calorimetric cell[END_REF].

Martinez de Baños et al. [START_REF] Martinez De Baños | Droplet-based millifluidics as a new tool to investigate hydrate crystallization: Insights into the memory effect[END_REF] determined the equilibrium of 7.2°C which is very close to the values according to slow dissociation method [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF][START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF][START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF], and DSC method [START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Whitman | Investigation of factors affecting crystallization of cyclopentane clathrate hydrate[END_REF][START_REF] Zhang | Equilibrium of hydrogen + cyclopentane and carbon dioxide + cyclopentane binary hydrates[END_REF][START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF].

Finally, the temperature range 6.6-7.2°C seems to be the most reliable and should be considered.

Besides, Ambekar et al. [START_REF] Ambekar | Equilibrium conditions of Hydrate-forming pickering emulsions[END_REF], Zylyftari et al. [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF], Baek et al. [START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF], and Peixinho et al. [START_REF] Peixinho | Growth of Clathrate Hydrates from Water Drops in Cyclopentane[END_REF] indicated that the use of a surfactant, such as Span, can reduce CPH equilibrium temperature.

Indeed, hydrate crystallization is usually observed at the water -CP interface, while surfactant can modify the interfacial tension force. Hydrate formation is therefore affected by the surfactant [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Aman | Interfacial mechanisms governing cyclopentane clathrate hydrate adhesion/cohesion[END_REF]. Karanjkar et al. [START_REF] Karanjkar | Surfactant Effects on Hydrate Crystallization at the Water-Oil Interface: Hollow-Conical Crystals[END_REF] stated that a mushy and porous structure, showing small needle-like crystals, is formed in presence of Span compared to polycrystalline shell structure in the absence of any surfactant. This porous structure hydrate may cause a reduction in dissociation point, referred to as the Gibbs-Thomson effect [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Perez | Gibbs-Thomson effects in phase transformations[END_REF].

However, in the presence of 0.1% mass Span 80, corresponding to a concentration above Critical Micelle Concentration (CMC), the hydrate dissociation temperature is 7.7°C, according to Peixinho et al. [START_REF] Peixinho | Growth of Clathrate Hydrates from Water Drops in Cyclopentane[END_REF]. At this concentration, surfactants cover the whole water droplet and the morphology of the hydrate is hence slightly denser. Consequently, dissociation would require a higher temperature [START_REF] Peixinho | Growth of Clathrate Hydrates from Water Drops in Cyclopentane[END_REF].

In terms of pressure dependency, by applying a pressure-search method [START_REF] Fan | Hydrate Formation of CO 2 -Rich Binary and Quaternary Gas Mixtures in Aqueous Sodium Chloride Solutions[END_REF], Fan et al. [START_REF] Fan | Hydrate equilibrium conditions for cyclopentane and a quaternary cyclopentane-rich mixture[END_REF] reported that CPH formation conditions are within the temperature range of 0.21-7.07°C for a pressure range of 6.9-19.8 kPa. The measured equilibrium data are detailed in . This point is very close to the equilibrium temperature reported elsewhere [START_REF] Davidson | Clathrate Hydrates[END_REF][START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Whitman | Investigation of factors affecting crystallization of cyclopentane clathrate hydrate[END_REF][START_REF] Zhang | Equilibrium of hydrogen + cyclopentane and carbon dioxide + cyclopentane binary hydrates[END_REF][START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF][START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF] at atmospheric pressure, involving only three phases: L w -H -L cp .

In the desalination process, atmospheric pressure condition is more favorable than high pressure or even vacuum like conditions. However, the data reported by Fan et al. [START_REF] Fan | Hydrate equilibrium conditions for cyclopentane and a quaternary cyclopentane-rich mixture[END_REF] are also very useful for salt removing from seawater under vacuum especially in association with membrane [START_REF] Mericq | Vacuum membrane distillation of seawater reverse osmosis brines[END_REF] or simply vacuum distillation [START_REF] Itsuno | Vacuum Distillation System Aiming to Use Solar-Heat for Desalination[END_REF].

Under higher pressures, Trueba et al. [START_REF] Trueba | Phase equilibrium measurements of structure II clathrate hydrates of hydrogen with various promoters[END_REF] reported hydrate (H)aqueous liquid (L w ) -CP-rich liquid (L a ) phase equilibrium data. They indicated that the equilibrium temperature was nearly independent of pressure due to the low compressibility of the two fluids and the one solid phase.

This indicates that, without any gas molecule, CPH dissociation temperature is almost constant with pressure increase [START_REF] Trueba | Phase equilibrium measurements of structure II clathrate hydrates of hydrogen with various promoters[END_REF]. High pressure condition is out of the question in CPH pure baseddesalination because of a significant increase in the energy required.

Phase equilibrium of CPH in the presence of salts

Obviously, to design an actual CPH based-desalination process, it is essential to have sufficient phase equilibrium data of CPH in the presence of diverse salts [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF]. However, only few published datasets are available.

Zylyftari et al. [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF] reported a set of equilibrium data in the presence of NaCl at a wide range of concentration, from 0 up to 23% mass by using DSC method. This method was also used by Baek et al. [START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF] for CPH equilibrium at 3.5% mass NaCl concentration. There are slight variations concerning dissociation temperature at 3.5% NaCl between four studies of Han et al. [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF], Sakemoto et al. [START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF], Baek et al. [START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF], and Ho-Van et al. [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF]. Han et al. [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF] used the quick dissociation procedure leading to a higher value (6.6°C) compared to others. Among the three other data, Baek et al. [START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF] reported the lowest dissociation temperature of 4.57°C, while Ho-Van et al. [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF] and Sakemoto et al. [START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF] recorded 5.0°C and 5.5°C, respectively. This is due to the presence of SPAN surfactant, used by Baek et al. [START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF]. It decreased the equilibrium temperature due to Gibbs-Thomson effect [START_REF] Perez | Gibbs-Thomson effects in phase transformations[END_REF], as stated by Zylyftari et al. [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF].

In addition, at 3.4% NaCl, Zylyftari et al. [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF] reported that the equilibrium temperature of CPH is 5.28°C. This value is slightly higher than the value of 5.0°C at 3.5% NaCl provided by Ho-Van et al. [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF].

Phase equilibria of mixed hydrates containing CP as a co-guest

Clathrate hydrates can form in the presence of multiple guests beside CP. Therefore, some efforts used a secondary guest alongside CP for desalination process (Cha et al. [START_REF] Cha | Increasing gas hydrate formation temperature for desalination of high salinity produced water with secondary guests[END_REF], and Zheng et al. [START_REF] Zheng | Effects of cyclopentane on CO2 hydrate formation and dissociation as a co-guest molecule for desalination[END_REF]). Results show that these mixed clathrate hydrates can improve salt removal efficiency compared to pure CPH. One promising idea is to combine CP with another guest molecule, and by this mean to couple desalination to another hydrate-based application, such as gas capture, gas hydrate exploitation (CH 4 for instance), or gas separation. Hereby, energy involved in the integrated process could be optimized, and salt removal efficiency could increase [START_REF] Herslund | Thermodynamic promotion of carbon dioxide-clathrate hydrate formation by tetrahydrofuran, cyclopentane and their mixtures[END_REF][START_REF] Zheng | Effects of cyclopentane on CO2 hydrate formation and dissociation as a co-guest molecule for desalination[END_REF][START_REF] Lv | Formation of cyclopentane -methane hydrates in brine systems and characteristics of dissolved ions[END_REF].

Table 5 provides range of thermodynamic equilibrium data of the mixed hydrate containing CP as a co-guest. conditions [START_REF] Mohammadi | Phase Equilibria of Clathrate Hydrates of Tetrahydrofuran+Hydrogen Sulfide and Tetrahydroduran+Methane[END_REF][START_REF] Takeya | Phase Equilibrium for Structure II Hydrates Formed with Krypton Co-existing with Cyclopentane, Cyclopentene, or Tetrahydropyran[END_REF] . However, Kr is a very expensive gas due to costly production process, from liquid air by a fractional distillation procedure. Plus, H 2 S is a toxic, corrosive, and flammable gas. These gases cannot be considered as candidates for CPH-based desalination processes. all much harder to achieve than those of CP-CO 2 in pure water. As CO 2 is the most common and arguably famous greenhouse gas, the disposal of CO 2 has become a global concerns issue [START_REF] Burnol | Influence of impurities (nitrogen and methane) on the CO 2 storage capacity as sediment-hosted gas hydrates -Application in the area of the Celtic Sea and the Bay of Biscay[END_REF][START_REF] Duc | CO 2 capture by hydrate crystallization -A potential solution for gas emission of steelmaking industry[END_REF][START_REF] Herri | Gas hydrate equilibria for CO 2 -N 2 and CO 2 -CH 4 gas mixtures-Experimental studies and thermodynamic modelling[END_REF][START_REF] Yang | Progress in carbon dioxide seperation and capture: A review[END_REF][START_REF] Li | Synergic effect of cyclopentane and tetra-n-butyl ammonium bromide on hydrate-based carbon dioxide separation from fuel gas mixture by measurements of gas uptake and X-ray diffraction patterns[END_REF][START_REF] Herslund | Thermodynamic and Process Modelling of Gas Hydrate Systems in CO 2 Capture Processes[END_REF]. One of the ways to mitigate CO 2 emission is gas hydrate-based capture [START_REF] Zheng | Kinetic evaluation of cyclopentane as a promoter for CO 2 capture via clathrate process employing different contact modes[END_REF].

Furthermore, pressurized CO 2 streaming from CO 2 emission sources may be favorable for hydrate formation and the cost for pressurization can be decreased [START_REF] Yang | Effects of C3H8 on hydrate formation and dissociation for integrated CO 2 capture and desalination technology[END_REF][START_REF] Sarshar | Simultaneous water desalination and CO 2 capturing by hydrate formation[END_REF].

Note that CO 2 forms hydrate SI in pure water at 278.8 K at 2.33 Mpa according to the study of Zhang et al [START_REF] Zhang | Phase Equilibrium of Cyclopentane + Carbon Dioxide Binary Hydrates in Aqueous Sodium Chloride Solutions[END_REF]. In the presence of CP, the binary mixture of CP-CO 2 can form SII hydrate at milder condition (291.3 K at 2.33 Mpa in pure water [START_REF] Zhang | Phase Equilibrium of Cyclopentane + Carbon Dioxide Binary Hydrates in Aqueous Sodium Chloride Solutions[END_REF]) compared to the single CO 2 gas [START_REF] Cha | Increasing gas hydrate formation temperature for desalination of high salinity produced water with secondary guests[END_REF][START_REF] Zhang | Phase Equilibrium of Cyclopentane + Carbon Dioxide Binary Hydrates in Aqueous Sodium Chloride Solutions[END_REF]. In this case, CP occupies large cages while CO 2 molecules occupy small cages. Hence, CP-CO 2 binary can be used for both desalination [START_REF] Hong | Investigation of thermodynamic and kinetic effects of cyclopentane derivatives on CO2 hydrates for potential application to seawater desalination[END_REF][START_REF] Zheng | Effects of cyclopentane on CO2 hydrate formation and dissociation as a co-guest molecule for desalination[END_REF] and carbon capture [START_REF] Herslund | Thermodynamic promotion of carbon dioxide-clathrate hydrate formation by tetrahydrofuran, cyclopentane and their mixtures[END_REF]. Note that, in the case of flue gas, mixed CO 2 -N 2 -CP hydrates would be formed, and CO 2 -H 2 for precombustion capture. Still, more studies are needed to improve gas hydrate based desalination and CO 2 capture processes in term of energy requirement, salt removal efficiency, and CO 2 storage capacity from a gas mixture in brine.

Kinetics of CPH formation

Kinetics is one key parameter for a process design. It is, in the present case, correlated to the rate of crystallization, water conversion efficiency, and therefore the number of separating steps, and total operating cost. In this section, all published studies on kinetic of CPH formation are collected and investigated.

Table 6 lists the effects of several parameters on CPH formation kinetics in terms of nucleation and growth. In the next subsections, some details are provided to explain these phenomena. Presence of free resins, biding resins, and residual Asphaltenes NA ↓ [START_REF] Morrissy | Reduction of Clathrate Hydrate Film Growth Rate by Naturally Occurring Surface Active Components[END_REF] where ↑: increase; ↓: decrease; NA: Not Acknowledge.

Subcooling and Agitation

The rates of hydrate nucleation [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF][START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF][START_REF] Ohmura | Statistical Study of Clathrate-Hydrate Nucleation in a Water/Hydrochlorofluorocarbon System: Search for the Nature of the "Memory Effect[END_REF][START_REF] Englezos | Clathrate Hydrates[END_REF][START_REF] Kashchiev | Induction time in crystallization of gas hydrates[END_REF][START_REF] Jacobson | Nucleation pathways of clathrate hydrates: Effect of guest size and solubility[END_REF] and growth [START_REF] Masoudi | An in situ method on kinetics of gas hydrates An in situ method on kinetics of gas hydrates[END_REF][START_REF] Uchida | CO 2 hydrate film formation at the boundary between CO 2 and water: Effects of temperature, pressure and additives on the formation rate[END_REF][START_REF] Saito | Correlation of Hydrate-Film Growth Rate at the Guest / Liquid-Water Interface to Mass Transfer Resistance[END_REF][START_REF] Saito | Crystal growth of clathrate hydrate at the interface between hydrocarbon gas mixture and liquid water[END_REF][START_REF] Freer | Methane hydrate film growth kinetics[END_REF][START_REF] Peng | Hydrate film growth on the surface of a gas bubble suspended in water[END_REF][START_REF] Taylor | Macroscopic investigation of hydrate film growth at the hydrocarbon/water interface[END_REF][START_REF] Karamoddin | Water purification by freezing and gas hydrate processes, and removal of dissolved minerals (Na + , K + , Mg 2+ , Ca 2+ )[END_REF][START_REF] Davies | High-Pressure Differential Scanning Calorimetry Measurements of the Mass Subcooling[END_REF]] can be increased with the raise of the subcooling. Note that subcooling, ΔT sub , is related to the driving force for the crystallization and defined as the difference between the system and the equilibrium temperature [START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF].

Xu et al. [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF] indicated that the duration of CPH formation from salty water decreases with both the increase of subcooling and agitation speed. Martinez de Baños et al. [START_REF] Martinez De Baños | Droplet-based millifluidics as a new tool to investigate hydrate crystallization: Insights into the memory effect[END_REF] and Ho-Van et al [START_REF] Ho-Van | Crystallization mechanisms and rates of Cyclopentane Hydrates formation in Brine[END_REF] reported that the hydrate growth rate is observed to be proportional to subcooling.

Indeed these conditions enhance mass and heat transfer between water/CP and the driving force for the hydrate formation.

Masoudi et al [START_REF] Masoudi | An in situ method on kinetics of gas hydrates An in situ method on kinetics of gas hydrates[END_REF] stated that under mixing condition, the growth rate of CPH (1.9 × 10 -5 -3.9 × 10 -5 kg m -2 s -1) is much higher than only flow condition (4.5×10 -6 kg m -2 s -1). Sakemoto et al.

[64] and Kishimoto et al. [START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF] reported that the CPH nucleation location is at the CP-water interface because of the low solubility of CP in the aqueous phase. Consequently, agitation is needed to increase the kinetic of CPH formation.

Moreover, Cai et al. [START_REF] Cai | Formation kinetics of cyclopentane-methane binary clathrate hydrate[END_REF] observed that the rate of CP-CH 4 hydrate formation improves with the increase of the agitation rate. Indeed, this increase can lead to smaller CP droplets, as well as the splitting of hydrate shells covering CP droplets. Ergo, this enhances the CP-water contact area and then enhances the hydrate formation rate.

Addition of CP

Corak et al. [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF] and Lim et al. [START_REF] Lim | Morphology of carbon dioxide-hydrogencyclopentane hydrates with or without sodium dodecyl sulfate[END_REF] showed that the kinetic of CPH depends strongly not only on subcooling, but also on the quantity of CP. Faster growth was ascertained by increasing amount of CP. In fact, increasing the quantity of hydrate former improves mass transfer, diffusion and consequently escalates the number of nucleation locations for hydrate formation.

However, for desalination, CP quantity needed to be minimized in accordance with other important parameters, in order to reduce the total cost.

"Memory effect''

"Memory effect'' corresponds to the empirical reduction of induction time by using a solution that has already formed crystals. This has been observed and used in laboratories to reduce drastically the induction time, especially for crystallization without agitation in small reactors.

Some authors have investigated the influence of this phenomenon on hydrate formation [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF][START_REF] Dirdal | Can cyclopentane hydrate formation be used to rank the performance of kinetic hydrate inhibitors?[END_REF][START_REF] Ohmura | Statistical Study of Clathrate-Hydrate Nucleation in a Water/Hydrochlorofluorocarbon System: Search for the Nature of the "Memory Effect[END_REF][START_REF] Takeya | Freezing-memory effect of water on nucleation of CO 2 hydrate crystals[END_REF][START_REF] Parent | Investigations Into the Nucleation Behaviour of Methane Gas Hydrates[END_REF][START_REF] Duchateau | Laboratory Evaluation of Kinetic Hydrate Inhibitors : a New Procedure for Improving the Reproducibility of Measurements[END_REF][START_REF] Duchateau | Hydrate precursor test method for the laboratory evaluation of kinetic hydrate inhibitors[END_REF]. Sefidrood et al. [START_REF] Sefidroodi | Investigation into the strength and source of the memory effect for cyclopentane hydrate[END_REF] concluded that the "memory effect" could enhance the nucleation of CPH formation. Using a small quantity of water from dissociated CPH at a temperature 2-3°C above the equilibrium, the CPH formation rate was observed to be much faster than starting from fresh water. Consequently, in desalination, a small amount of the melted water from dissociation step can be recycled to the next CPH formation step in order to reduce the induction time. Of course, this is not a problem in case of a continuous process, or in presence of seeds.

Solid kinetic additives

Some kind of solids such as ice, silica gel, silica sand, rust, chalk, or clay have been studied to reduce hydrate nucleation time [START_REF] Babu | Unusual behavior of propane as a co-guest during hydrate formation in silica sand: Potential application to seawater desalination and carbon dioxide capture[END_REF][START_REF] Dirdal | Can cyclopentane hydrate formation be used to rank the performance of kinetic hydrate inhibitors?[END_REF][START_REF] Jensen | Inhibition of structure I and II gas hydrates using synthetic and biological kinetic inhibitors[END_REF][START_REF] Kelland | History of the Development of Low Dosage Hydrate Inhibitors[END_REF][START_REF] Xie | Gas hydrate fast nucleation from melting ice and quiescent growth along vertical heat transfer tube[END_REF][START_REF] Sloan | A Molecular Mechanism for Gas Hydrate Nucleation from Ice[END_REF]. Zylyftari et al. [START_REF] Zylyftari | Nucleation of cyclopentane hydrate by ice studied by morphology and rheology[END_REF] reported CPH formation at the ice -CPbrine phase contact line, which is believed to improve kinetics of hydrate crystallization [START_REF] Zylyftari | Nucleation of cyclopentane hydrate by ice studied by morphology and rheology[END_REF]. Karanjkar et al [START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF] observed that, in this case, there is no induction time and nucleation takes place instantaneously as ice dissociates into free water. This fresh free water is then converted totally into CPH. Moreover, Li et al [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF] indicated that addition of graphite promotes CPH formation. The graphite particles are composed of many flat carbon sheets (graphenes) that can provide heterogeneous sites for both ice and hydrate nucleation [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF]. Other studies using nanoparticules can also be found, but not in presence of CP [START_REF] Rahmati-Abkenar | Nucleation of ethane hydrate in water containing silver nanoparticles[END_REF][START_REF] Abedi-Farizhendi | Kinetic study of propane hydrate in the presence of carbon nanostructures and SDS[END_REF][START_REF] Nashed | Review the impact of nanoparticles on the thermodynamics and kinetics of gas hydrate formation[END_REF]. Nanofluids enhance crystallization kinetics as well [START_REF] Said | A study on the influence of nanofluids on gas hydrate formation kinetics and their potential: Applicatin to the CO 2 capture process[END_REF].

Influence of salts

It is known that inorganic mineral salts affects significantly not only thermodynamics of CPH but also the kinetics of hydrate formation [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF][START_REF] Uchida | CO 2 hydrate film formation at the boundary between CO 2 and water: Effects of temperature, pressure and additives on the formation rate[END_REF]. In the presence of salts, the equilibrium temperature is further shifted lower [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF][START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF][START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF][START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Martinez De Baños | Droplet-based millifluidics as a new tool to investigate hydrate crystallization: Insights into the memory effect[END_REF][START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF][START_REF] Ho-Van | Implementing Cyclopentane Hydrates Phase Equilibrium Data and Simulations in Brine Solutions[END_REF][START_REF] Sloan | Natural Gas Hydrate in Flow Assurance[END_REF]. This leads to less subcooling, reducing hydrate growth and preventing the final water-to-hydrate conversion.

Kishimoto et al. [START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF] described that the nucleation and the growth rates of CPH are slowed down with increasing salt concentrations at a given subcooling. Moreover, Cai et al [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF] reported that the mixed CP-methane hydrate growth rate in NaCl solution is systematically lower than that in pure water for any salt concentrations. Indeed, during hydrates formation in brine, ions are mostly excluded and then accumulate at the vicinity of growing solid hydrate. Therefore, it could locally lower the driving force for hydrate growth. This is called the concentration polarization effect [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF].

Finally, the quantity of accumulated salt considerably depends on the kinetic of hydrate formation and the speed of stirring. Consequently, the concentration polarization effect can be reduced by enhancing the mixing to transport salt away from the growing crystal.

Interfacial effects, surfactants

Hydrate formation kinetics is also deeply related to surface phenomena [START_REF] Englezos | Clathrate Hydrates[END_REF][START_REF] Lo | The role of surface active agents on hydrate formation[END_REF][START_REF] Nesterov | Promotion and inhibition of gas hydrate formation by oxide powders[END_REF][START_REF] Zarenezhad | Accurate prediction of the interfacial tension of surfactant/fluid mixtures during gas hydrate nucleation: The case of SDS surfactant-based systems near ethylene hydrate formation region[END_REF][START_REF] Aman | Surfactant adsorption and interfacial tension investigations on cyclopentane hydrate[END_REF][START_REF] Aman | Interfacial phenomena in gas hydrate systems[END_REF].

Interfacial tension of liquid-liquid or liquid-gas system plays a crucial role on the mass and heat transfers. Some additives, which affect the interfacial tension, can be used as a promotor while others can be used as an inhibitor for hydrate formation.

It is known that CP is a hydrophobic hydrocarbon. Hence it is immiscible with water. Therefore, complete conversion of water (or CP) into CPH is hard to achieve. This issue can be remedied by adding a small quantity of certain surfactants to the process [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Lo | Adsorption of Cationic and Anionic Surfactants on Cyclopentane Hydrates[END_REF][START_REF] Erfani | Kinetic promotion of non-ionic surfactants on cyclopentane hydrate formation[END_REF][START_REF] Li | Effect of surfactant-coated particles on clathrate hydrate formation[END_REF][START_REF] Lo | The role of surface active agents on hydrate formation[END_REF]. Of course, it is then difficult to separate fresh water from liquid CP afterward.

Erfani et al. [START_REF] Erfani | Kinetic promotion of non-ionic surfactants on cyclopentane hydrate formation[END_REF] investigated the effects of 14 surfactants and polymers on CPH formation. The results showed that the addition of surfactants can highly decrease the induction time and enhance the hydrate formation rate. Furthermore, Lauryl Alcohol Ethoxylates with 8 ethoxylate groups (LAE8EO), TritonX-100 and Nonyl Phenol ethoxylates with 6 ethoxylate groups (NPE6EO) were found to be the best additives to increase the kinetic of hydrate formation.

Erfani et al. [START_REF] Erfani | Kinetic promotion of non-ionic surfactants on cyclopentane hydrate formation[END_REF] demonstrated that surfactants generating oil in water emulsion improved the kinetic of hydrate formation better than those generating water in oil emulsion.

Lo et al. [START_REF] Lo | The role of surface active agents on hydrate formation[END_REF] declared that CPH growth rate is higher in presence of sodium dodecyl sulfate (SDS) and dodecyl-trimethylammonium bromide (DTAB) than without surfactant.

Likewise, Karanjkar et al. [START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF] and Zylyftari et al. [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF] reported that Span 80 promotes CPH formation. However, Peixinho et al [START_REF] Peixinho | Growth of Clathrate Hydrates from Water Drops in Cyclopentane[END_REF] observed the opposite. They witnessed that addition of surfactant Span 80 (0.0001, 0.01, 0.1% mass) into water, to form water in oil emulsion, decreases kinetic time for hydrate formation. According to them, surfactant Span 80 molecules cover the CP-water interface and inhibit water and CP diffusion. Thus, the CPH formation is prevented.

This variation of the influence of Span 80 on kinetics could be attributed to differences in the experimental systems. For instance, Zylyftari et al [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF] studied the CPH formation in the hydrate-forming emulsion, while Peixinho et al [START_REF] Peixinho | Growth of Clathrate Hydrates from Water Drops in Cyclopentane[END_REF] studied CPH formation in one water drop in CP phase without agitation.

Brown et al [START_REF] Brown | Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties[END_REF] reported that the CPH shell thickness is not modified when surfactants are introduced into the system. This study reveals that they have different effects on the growth rate: Dodecylbenzenesulfonic acid at a concentration of 10 -6 mol/L (DDBSA) and Tween at 10 -4 mol/L decrease slightly the growth rate, while DDBSA at 10 -4 mol/L and Tween at 10 -8 mol/L slightly increase the growth rate.

Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] and anti-agglomerants (AAs) by considering CPH formation. Their results showed that no link was found between hydrophilic-lipophilic balance (HLB) value and AA performance. In addition, it was found that anionic surfactants perform insufficiently, whilst cationic surfactants exposed favorable performances in dispersing hydrate crystals.

To sum up, in desalination, surfactants which promote hydrate formation and/or reduce the induction time such as LAE8EO, TritonX-100, NPE6EO, SDS, DTAB, Span 80, DDBSA and Tween at appropriate concentrations are advantageous. However, since their presence makes the hydrate former difficult to separate after dissociation, their use probably bring more drawbacks than advantages.

Liquid co-guests influence

Li et al. [START_REF] Li | Anti-agglomeration in cyclopentane hydrates from bioand co-surfactants[END_REF] indicated that the presence of 0.01-0.05% mass THF increases CPH formation rate. Moreover, Mohamed et al. [START_REF] Bmh Abdulkader | Cyclopentane Hydrate for Hydrate Wetting Studies[END_REF] observed that the addition of THF to the CPH system, either with or without surfactants (Span 20, Tween 20), enhances the kinetics of CHP formation.

They stated that THF, a highly soluble molecule into water, is a better kinetic additive than Span 20 or Tween 20. Unfortunately, it is difficult to separate THF from water for its reuse in desalination applications. Therefore, use of THF is not recommended in CPH-based desalination processes.

Other inhibitors

Li et al. [START_REF] Li | Anti-agglomeration in cyclopentane hydrates from bioand co-surfactants[END_REF] elucidated that Rhamnolipid bio-surfactant (product JBR 425) and Methanol inhibit CPH formation. Moreover, Baek et al. [START_REF] Baek | Inhibition effects of activated carbon particles on gas hydrate formation at oil-water interfaces[END_REF] demonstrated that activated carbon particles act as a kinetic inhibitor for the mixed hydrate of CP and propane. At 1%mass of activated carbon particles, the particle layer covers the whole interface between hydrate formers and water, preventing mass transfer and diffusion. Therefore, hydrate growth is retarded compared to pure mixed hydrate without activated carbon particles.

Finally, Morrissy et al. [START_REF] Morrissy | Reduction of Clathrate Hydrate Film Growth Rate by Naturally Occurring Surface Active Components[END_REF] indicated that free resins (FR), binding resins (BR), and residual asphaltenes (RA) in the crude oil reduce CPH film growth rate with a trend in following order:

RAs > BRs > FRs. Above a given concentration threshold, these additive species are suspected to settle at the water/CP interface. Consequently, this prevents the growth of CPH crystals [START_REF] Morrissy | Reduction of Clathrate Hydrate Film Growth Rate by Naturally Occurring Surface Active Components[END_REF].

Conclusion on kinetics

Table 6 reveals that there have been several methods to increase the hydrate formation rate such as increasing subcooling, quantity of CP, agitation speed, using memory effect, using heterogeneous nucleation by ice or graphite, and addition of appropriate surfactants.

Nevertheless, the methods of increasing subcooling and agitation speed consume much more energy than other methods. Moreover, increasing the quantity of CP is also a costly method because the huge quantity of seawater or salt water employed in a real facility. The uses of memory effect and/or heterogeneous nucleation by ice or graphite are probably favorable techniques to improve CPH kinetic due to low cost and operating simplicity. Appropriate surfactants could give the impression of being good method because of their high capability to enhance kinetics of CPH formation. However, their use is a significant issue in water/CP separation since an emulsion is formed.

Physical properties of CPH

Crystal morphology is another important aspect of hydrate-based technologies [START_REF] Saito | Crystal growth of clathrate hydrate at the interface between hydrocarbon gas mixture and liquid water[END_REF], and of course CPH-based desalination [START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF]. Indeed, CPH crystal shape strongly influences the kinetics of the formation process and it should be taken into account in designing equipment such as reactors and transportation devices. Adhesion, cohesion, rheology, interfacial tension, yield stress, and shell property are also useful common properties of hydrates. These are essential factors that affect CPH transportation in the process. In this section, morphology and physical properties of CPH in the open literature are classified and presented. Rheology [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Zylyftari | Modeling Oilfield Emulsions: Comparison of Cyclopentane Hydrate and Ice[END_REF][START_REF] Karanjkar | Rheology of cyclopentane hydrate slurry in a model oil-continuous emulsion[END_REF][START_REF] Leopercio | Kinetics of cyclopentane hydrate formation -an interfacial rheology study[END_REF][START_REF] Ahuja | Calorimetric and rheological studies on cyclopentane hydrate-forming water-in-kerosene emulsions[END_REF] Interfacial tension [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Baek | Equilibria of cyclopentane hydrates with varying HLB numbers of sorbitan monoesters in water-in-oil emulsions[END_REF][START_REF] Brown | Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties[END_REF][START_REF] Hobeika | High-Resolution Optical Microscopy of Gas Hydrates[END_REF][START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF][START_REF] Aman | Interfacial mechanisms governing cyclopentane clathrate hydrate adhesion/cohesion[END_REF][START_REF] Li | Effects of sorbitan monooleate on the interactions between cyclopentane hydrate particles and water droplets[END_REF][START_REF] Dann | Surfactant effect on hydrate crystallization at oilwater interface[END_REF][START_REF] Erfani | Kinetic promotion of non-ionic surfactants on cyclopentane hydrate formation[END_REF][START_REF] Lo | The role of surface active agents on hydrate formation[END_REF][START_REF] Aman | Surfactant adsorption and interfacial tension investigations on cyclopentane hydrate[END_REF][START_REF] Aman | Interfacial phenomena in gas hydrate systems[END_REF][START_REF] Aspenes | Adhesion force between cyclopentane hydrates and solid surface materials[END_REF][START_REF] Aman | Adhesion Force between Cyclopentane Hydrate and Mineral Surfaces[END_REF][START_REF] Aman | Interfacial Tension and Mineral Adhesion Properties of Cyclopentane Hydrate[END_REF][START_REF] Aman | Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties[END_REF] Yield stress [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Ahuja | Yield stress measurements of cyclopentane hydrate slurry[END_REF] Hydrate density [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF][START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Hobeika | High-Resolution Optical Microscopy of Gas Hydrates[END_REF][START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] Wettability [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF][START_REF] Karanjkar | Surfactant Effects on Hydrate Crystallization at the Water-Oil Interface: Hollow-Conical Crystals[END_REF][START_REF] Ho-Van | Crystallization mechanisms and rates of Cyclopentane Hydrates formation in Brine[END_REF] Shell property [START_REF] Brown | Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties[END_REF] Heat of formation [START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Delroisse | Determination of thermophysical properties of cyclopentane hydrate using a stirred calorimetric cell[END_REF][START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF][START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF][START_REF] Zhang | Differential Scanning Calorimetry Studies of Clathrate Hydrate Formation[END_REF] Heat capacity [START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF] Torque [START_REF] Delroisse | Evaluation of the Performance of a New Biodegradable AA-LDHI in Cyclopentane Hydrate and CH 4 /C 3 H 8 Gas Hydrate Systems[END_REF]

Morphology

Hobeika et al. [START_REF] Hobeika | High-Resolution Optical Microscopy of Gas Hydrates[END_REF] reported that the growth rate and morphology of CPH remarkably depends on subcooling. CPH grow slowly with some large crystals present at low subcooling, while CPH grow quicker with many small crystals under high subcooling. Furthermore, the morphologies of CPH are different when additives like PVP, PVCap, or VP/VCap are present. In this case, CPH particles are thinner, less glassy, and more fragile.

Sakemoto et al. [START_REF] Sakemoto | Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface[END_REF] and Kishimoto et al. [START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF] pointed out that the morphology of the individual CPH crystals in water, seawater and brine at any NaCl concentration are comparable at a similar subcooling. Moreover, the size of the CPH crystals are smaller at higher subcooling [START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF]. In addition, Mohamed et al. [START_REF] Bmh Abdulkader | Cyclopentane Hydrate for Hydrate Wetting Studies[END_REF] reported that the nature of surfactants affects the morphology of CPH. Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] studied the morphology of CPH at different surfactant DA 50 concentrations. Their results showed that at 0.01% mass DA 50, small hairy hydrate crystals with a large quantity of needles and some many-sided shapes were observed. At 0.1 and 1% mass DA 50, smaller hydrate crystals with many-sided, three-sided, and sword-like shaped were observed.

This was attributed to differences in the configuration of the surfactant molecules absorbed on hydrate surface, due to differences in surfactant concentration tested.

Mitarai et al [START_REF] Mitarai | Surfactant effects on the crystal growth of clathrate hydrate at the interface of water and hydrophobic-guest liquid[END_REF] elucidated that, with Span surfactant present, the individual CPH crystals had a larger size compared to those in the system without Span surfactant. Their results also indicate that Span has two effects: inhibition of hydrate agglomeration; enhancement of hydrate formation.

Lim et al. [START_REF] Lim | Morphology of carbon dioxide-hydrogencyclopentane hydrates with or without sodium dodecyl sulfate[END_REF] showed that adding SDS can modify the CPH hydrate crystal morphology.

Indeed, with SDS present, the same length rectangular tree-like or fiber-like crystals were observed from hydrate deposit.

Adhesion

Aspenes et al. [START_REF] Aspenes | Adhesion force between cyclopentane hydrates and solid surface materials[END_REF] investigated adhesion force between CPH and solid surface materials. Their results showed that the force of adhesion depend on the surface materials and the presence of water. Low free energy surface solids lead to the lowest adhesion. The hydrate-solid surface adhesion was more than 10 times stronger than hydrate-hydrate adhesion. Adding petroleum acids declined adhesion, while the presence of water-dissolved oil phase improved adhesion. In addition, water-wet solid surfaces were found to have the strongest adhesion.

Nicholas et al. [START_REF] Nicholas | Assessing the feasibility of hydrate deposition on pipeline walls-Adhesion force measurements of clathrate hydrate particles on carbon steel[END_REF] revealed that adhesion between CPH and carbon steel was found to be significantly weaker than CPH -CPH particles and were also lower than icecarbon steel.

Aman et al. [START_REF] Aman | Adhesion Force between Cyclopentane Hydrate and Mineral Surfaces[END_REF] reported that CPH adhesion forces are 5 to 10 times stronger for calcite and quartz minerals than stainless steel, and adhesive forces are strengthened by 3 -15 times when delaying surface contact time from 10 to 30 seconds. Finally, Aman et al. [START_REF] Aman | Influence of model oil with surfactants and amphiphilic polymers on cyclopentane hydrate adhesion forces[END_REF] demonstrated that hydrate adhesion drops significantly with Span 80, polypropylene glycol, or naphthenic acid mixture present in a mineral oil and CP continuous phase.

Cohesion

Brown et al. [START_REF] Brown | Cyclopentane hydrate cohesion measurements and phase equilibrium predictions[END_REF] observed that, at different temperatures, longer annealing time led to lower cohesive force. Indeed, annealing step disrupts micropores or capillaries in hydrate structures, where free water is transported from the hydrate core to the outer surface. This diminishes the water layer favorable for cohesion.

Aman et al. [START_REF] Aman | Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties[END_REF] determined cohesion force for CPH in water, hydrocarbon, and gas bulk phases. Their results showed that cohesion is different in various phases. Cohesion in gas phase is roughly twice and six times stronger than that in the hydrocarbon phase and in the water phase, respectively. Furthermore, Aman et al. [START_REF] Aman | Interfacial mechanisms governing cyclopentane clathrate hydrate adhesion/cohesion[END_REF] reported that cohesion force of the CPH particles is 9.1 ± 2.1 mN/m and 4.3 ± 0.4 mN/m at around 3°C in the gas phase (N 2 and CP vapor) and in the pure liquid CP phase, respectively.

Interfacial tension

Aman et al. [START_REF] Aman | Surfactant adsorption and interfacial tension investigations on cyclopentane hydrate[END_REF] affirmed that the interfacial tension of CPHwater and CPH -CP is 0.32 ± 0.05 mN/m and and 47 ± 5 mN/m, respectively. Brown et al. [START_REF] Brown | Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties[END_REF] indicated that the addition of Tween 80 leads to a remarkable drop in interfacial tensions at high concentrations above critical micelle concentration (CMC) in a water bulk phase. Nonetheless, dodecylbenzenesulfonic acid (DDBSA) showed no dependence of interfacial tension under concentrations below the CMC.

Moreover, Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] concluded that, in presence of DA 50, the interfacial tension between CPH and water increases while the interfacial tension between CPH and CP diminishes.

Rheology

In term of CPH rheology, Karanjkar et al. [START_REF] Karanjkar | Rheology of cyclopentane hydrate slurry in a model oil-continuous emulsion[END_REF] indicated that CPH slurry viscosity is proportional to the water volume fraction. Slurry viscosity decreases (1-3 Pa.s at 8 °C) with increasing of subcooling (below freezing ice temperature). This is explained by ice formation.

Indeed, more ice was observed in the CPH slurry system at lower temperatures (higher subcooling) than at higher temperature (lower subcooling), resulting in lower viscosity.

Moreover, at Span 80 concentrations of 0.5-5% (v/v), viscosity was found to be lower due to the accessibility of extra quantity of Span 80 molecules (oil-soluble surfactant) which can adsorb onto the CPH interface and weaken CPH-CPH interactions. Therefore, Span 80 can increase the flowability as an anti-agglomerant at high concentrations.

In addition, when introducing ice to the system to induce hydrate crystallization, Zylyftari et al. [START_REF] Zylyftari | Nucleation of cyclopentane hydrate by ice studied by morphology and rheology[END_REF] observed that the viscosity of the mixture increases faster than by introducing CPH.

Finally, since high viscous hydrate slurry requires much more energy to be transported, methods to reduce viscosity, such as the use of surfactants or especially CPH seeds, are recommended in CPH-based desalination.

Yield stress

Ahuja et al. [START_REF] Ahuja | Yield stress measurements of cyclopentane hydrate slurry[END_REF] determined that the yield stress of CPH slurry rises quickly from 5 Pa to 4600

Pa when increasing the water volume fraction (ϕ) from 16% to 30% above a critical water fraction (ϕ c ) of 15%. A power dependence of the yield stress of CPH and slurry viscosity on water volume fraction was also found, scaling as (ϕ-ϕ c ) 2.5 .

Zylyftari et al. [START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF] reported that, at low water conversions (< 27%vol), the yield stress is quite small (10 -1 Pa). At higher water conversions (42-81%vol), yield stress increases to 100 Pa. It reaches to a maximum of 145 Pa at 81%vol conversion. The behavior of yield stress as a function of the water to CPH conversion exhibits a similar tendency as the viscosity. This also illustrates the effect of capillary bridges between CPH particles. At 81% water conversion, the yield stress is maximum (145 pa), showing the optimal number of capillary bridges and CHP surface required to have the strongest network structure.

Density

Sloan et al. [START_REF] Sloan | Clathrate hydrates of natural gases[END_REF], Delroisse et al [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF], Hobeika et al. [START_REF] Hobeika | High-Resolution Optical Microscopy of Gas Hydrates[END_REF] and Nakajima et al. [START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF] indicated that CPH density is about 950 to 960 kg/m 3 . At standard conditions, this value is between the density of brine (>1000 kg/m 3 ) and CP (751 kg/m 3 ). Thus, CPH floats on water and sinks in liquid CP.

Wettability and shell properties

Delroisse et al. [START_REF] Delroisse | Effect of a Hydrophilic Cationic Surfactant on Cyclopentane Hydrate Crystal Growth at the Water/Cyclopentane Interface[END_REF] reported that CPH is CPwettable with surfactant DA 50 present. However, Karanjkar et al. [START_REF] Karanjkar | Surfactant Effects on Hydrate Crystallization at the Water-Oil Interface: Hollow-Conical Crystals[END_REF] indicated that in the presence of Span 80, CPH is waterwettable. This requires selecting the appropriate surfactants to be used in desalination to optimize hydrate separation from the aqueous and also CP phases.

Brown et al. [START_REF] Brown | Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties[END_REF] investigated the effect of surfactants on CPH shell properties. It was found that the addition of DDBSA and Tween 80 changed the CPH properties. Indeed, the CPH shells, with DDBSA and Tween 80 present, require a much lower perforation than for pure CPH. This indicates that adding these surfactants weaken the CPH shell strength.

Thermodynamic properties

Two thermodynamic parameters including heat of formation and heat capacity have been well

reported in literature [START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Delroisse | Determination of thermophysical properties of cyclopentane hydrate using a stirred calorimetric cell[END_REF][START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF][START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF][START_REF] Zhang | Differential Scanning Calorimetry Studies of Clathrate Hydrate Formation[END_REF]. These two parameters are crucial for the design and optimization of CPH-based desalination [START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF].

The value of heat of formation (kJ/mole of water) varies according to authors: 4.84 [START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF][START_REF] Zhang | Differential Scanning Calorimetry Studies of Clathrate Hydrate Formation[END_REF]; 5.098 [START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF]; 6.786 [START_REF] Delroisse | Determination of thermophysical properties of cyclopentane hydrate using a stirred calorimetric cell[END_REF]. The CPH heat capacity was firstly approximated from the heat capacities of THF and propane hydrate according to He el al. [START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF] as follows:

C P = -124.33+3.2592T+2×10 -6 T 2 -4×10 -9 T 3 where T is the absolute temperatures (K).

Torque

The agglomeration phenomena of hydrate crystals are important in hydrate-based desalination since they are related to the transport of hydrate in the desalination process. The torque value is one of the common factors that represent the agglomeration of hydrate [START_REF] Sloan | Natural Gas Hydrate in Flow Assurance[END_REF][START_REF] Abojaladi | Can cyclopentane hydrate formation be used to screen the performance of surfactants as LDHI anti-agglomerants at atmospheric pressure?[END_REF][START_REF] Kelland | History of the Development of Low Dosage Hydrate Inhibitors[END_REF][START_REF] Leopercio | Kinetics of cyclopentane hydrate formation -an interfacial rheology study[END_REF][START_REF] Cai | Desalination via formation of binary clathrate hydrates[END_REF].

Delroisse et al [START_REF] Delroisse | Evaluation of the Performance of a New Biodegradable AA-LDHI in Cyclopentane Hydrate and CH 4 /C 3 H 8 Gas Hydrate Systems[END_REF] reported that, without biodegradable anti-agglomerant (called AA-LDHI [START_REF] Delroisse | Evaluation of the Performance of a New Biodegradable AA-LDHI in Cyclopentane Hydrate and CH 4 /C 3 H 8 Gas Hydrate Systems[END_REF]) in a stirred-tank reactor, the torque of CPH increases progressively to 0.3N.m until the agitator stopped at 550 min (approximately 0.7N.m). It is because of the significant increase in viscosity after the crystallization onset, when CPH crystals agglomerated via capillary bridges. In addition of 0.1% AA-LDHI, the torque drops significantly, about ten times. Furthermore, in the presence of AA-LDHI, when CPH crystallization started, the torque grows slightly from 0.025 N.m to 0.035 N.m and then remains nearly constant. The results indicate that the added AA-LDHI disperses CPH particle (average diameter of 380 ± 150 μm [START_REF] Delroisse | Evaluation of the Performance of a New Biodegradable AA-LDHI in Cyclopentane Hydrate and CH 4 /C 3 H 8 Gas Hydrate Systems[END_REF]) and reduce their agglomeration during crystallization. Consequently, this is expected to facilitate the transport of CPH crystals in desalting processes.

Conclusion on CPH physical properties

In many cases, adding surfactants modifies morphology and physical properties of CPH in aqueous solution. The choice of appropriate kind and amount of surfactants could be favorable to the improvement of CPH kinetics and transport.

Besides, some issues on the use of surfactants should be prudently considered. Since they are soluble into water, and enhance CP solubility into water, it is very difficult to recover them by a simple physical method as decanting. Indeed, some techniques for removal surfactants from water could be applied such as nano-filtration [START_REF] Archer | Separation of an Anionic Surfactant by Nanofiltration[END_REF], activated carbon/ultrafiltration hybrid process [START_REF] Zahoor | Separation of surfactants from water by granular activated carbon/ultrafiltration hybrid process[END_REF], coagulation [START_REF] Taylor | The removal of anionic surfactants from water in coagulation process[END_REF][START_REF] Onder | An alternative method for the removal of surfactants from water : Electrochemical coagulation[END_REF], or constructed-wetland-treatment systems [START_REF] Sima | Removal of Anionic Surfactants from Wastewater Using a Constructed Wetland[END_REF]. Biosurfactants are also a good suggestion for CPH-based desalination since they promote hydrates formation and they are degradable [START_REF] Delroisse | Evaluation of the Performance of a New Biodegradable AA-LDHI in Cyclopentane Hydrate and CH 4 /C 3 H 8 Gas Hydrate Systems[END_REF][START_REF] Arora | Biosurfactant as a Promoter of Methane Hydrate Formation : Thermodynamic and Kinetic Studies[END_REF][START_REF] Rogers | Catalysis of Gas Hydrates by Biosurfactants in Seawater-Saturated Sand/Clay[END_REF]. However, the use of surfactants still needs more efforts to purify the dissociated water and increases the total operating cost. Therefore, minimizing quantity of the surfactants is one of the requirements for feasible CPHbased salt removal process.

Influence of operating conditions on CPH-based desalination efficiency

Gas hydrate formation involves high pressure conditions, and therefore appropriate equipments are required to design a hydrate-based process. Indeed, operating costs could be significantly higher compared to standard processes (distillation, reverse osmosis…). This cost drawback is the reason hydrate-based desalination has not been commercialized yet. As discussed earlier, the use of CP as guest for desalination in combination with other applications, such as gas capture/separation, or cold energy storage (see later in section 6.2), might be advantageous or profitable.

Remember that, with CP, hydrate crystallization occurs at only one bar under normal atmospheric pressure. In addition, CP can be recovered easily after hydrate dissociation since it is not miscible into water. This simplicity is an enormous advantage, and this is probably why CPH-based desalination is still of interest in the scientific community.

Recently, the use of CPH for desalination has been investigated at both laboratory and pilot scales [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF][START_REF] Cai | Desalination via formation of binary clathrate hydrates[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF][START_REF] Mottet | Method for treating an aqueous solution containing dissolved materials by crystallization of clathrates hydrates[END_REF] considering three main concerns: yield of dissociated water from CPH, water conversion to hydrate, and salt removal efficiency. The effects of mentioned considerations on CPH-based desalination process are detailed in Table 8. [ [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] [42] Salinity: 3 -5% mass NaCl range: ↑ ↓ NA ↑ [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] 0.17 -5% mass NaCl range: ↑ NA ↓ NA [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] Use of graphite ↑ NA ↑ [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF] Use of filtering NA NA ↑ [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] Use [119]

[ [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF] [ [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Cai | Desalination via formation of binary clathrate hydrates[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] [ [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] Ratio of washing water/dissociated water (g/g) 0.1 -0.

[69] [START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF] [196] Use of sweating NA NA ↑ [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF] Use of gravitational separating NA NA ↑ [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] Use of spray injecting Use of tube injecting NA NA ↑ ↑ NA NA [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] [ [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] where ↑: increase; ↓: decrease, NA: Not Acknowledge Removal efficiency, yield of dissociated water, water conversion to hydrate, ratio of washing water/dissociated water (g/g), CP concentration, and water cut were calculated as follows:

Yield of dissociated water = m 1 m o ×100% or = V 1 V o ×100% (1)
where m o /V o are the mass/volume of initial salt solution, and m 1 /V 1 are the mass/volume of melted water [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF].

Water conversion to hydrate = m c m o ×100% (2)
where m c is the mass of water converted to hydrates [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF].

Salt removal efficiency = C 0 -C 1 C 0 ×100% (3)
where C 0 is weight percent of NaCl in prepared brine and C 1 is that in dissociated water [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF].

Ratio of washing water/dissociated water =

m 2 m 1 ×100% (4)
where m 2 is the mass of water used for washing [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] CP concentration =

n CP n brine ×100% (5)
where n CP is the mole number of CP and n brine is the mole number of initially prepared brine [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF]. This is somewhat related to another parameter in the literature, the "Water cut".

Water cut = V brine V brine +V CP ×100% (6)
where V brine is the volume of initially prepared brine and V CP is the volume of CP [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] In the next sections, some details are provided to explain the effects of some considerations on the CPH-based desalination process.

Quantity of CP.

Water cut can be used to indicate quantity of CP as described by Equation [START_REF] Khawaji | Advances in seawater desalination technologies[END_REF]. When water cut increases, quantity of CP then decreases because these two parameters are inversely proportional to each other.

Table 8 illustrates that the water conversion into hydrate increases by raising the CP concentration in the system [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF]. Also, the salt removal efficiency varies irregularly from less than 70% to close to 90% when increasing CP concentration from 0.9 to 2.3 mol % [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF].

Moreover, the water cut can affect the yield of dissociated water and the salt removal efficiency differently [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF]. The yield of dissociated water first augments significantly with water cut from 20% to 60% while the removal efficiency declines inappreciably. When the water cut is in 60% -90% range, the yield tends to lessen considerably while the removal efficiency is slightly improved. To summarize, the removal salt efficiency for different water cut varies from 75% to 85%. This demonstrates that, compared to high water cut systems (>80 vol% water or <5 mol% CP [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF]), extra CP addition in brine could considerably improve the yield of dissociated water while the removal efficiency undergoes a relatively minor change.

The effect of CP quantity on the hydrate formation rate is described in elsewhere [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Lim | Morphology of carbon dioxide-hydrogencyclopentane hydrates with or without sodium dodecyl sulfate[END_REF][START_REF] Lv | Formation Kinetics of Cyclopentane + Methane Hydrates in Brine Water Systems and Raman Spectroscopic Analysis[END_REF]. It was found that excess CP can increase notably the kinetics of hydrate formation, and hence the conversion of water to hydrate and the yield of dissociated water.

Agitation

Change in flow condition, or shear rate, is observed using various stirring rates. This leads to different mass and heat transfer rates in the system. Table 8 shows that boosting the agitation rate promotes water conversion and yield of dissociated water, as examined by different authors [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF][START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF][START_REF] Nakajima | Clathrate hydrate formation from cyclopentane-inwater emulsions[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Cai | Formation kinetics of cyclopentane-methane binary clathrate hydrate[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF]. However, this comes with a decrease in salt removal efficiency [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF]. Indeed, higher agitation rates may enhance the reaction kinetic and hence cause formation of smaller hydrate crystals with larger specific surface area. As a hydrate surface is hydrophilic, more salt ions tend to attach on the crystal surfaces, leading to a difficult separation of brine from hydrate [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF].

The way CP is introduced into a system can also change the hydrate formation kinetics. Xu et al [START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] declared that, by using the CP spray injection method, higher water conversion can be achieved, due to the smaller CP droplets created by the spray injection. However, a pump is hence needed for CP injection in this case, thus more energy is required.

Operating temperature

Table 8 indicates that the operating temperature affects strongly water conversion to hydrate, yield of dissociated water, and removal efficiency. At higher operating temperature, the hydrate formation rate decreases due to decrease in the driving force (here subcooling). Thus, both water conversion and yield of dissociated water are reduced with higher operating temperature [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF].

However, two different observations in purification efficiency when increasing operating temperature were reported by Beak et. [START_REF] Corak | Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine[END_REF] and Lv et al. [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF].

One the first hand, Beak et al. elucidated that, at operating temperature of 2.4°C, the purification is less efficient than at 0.4°C. This is attributed to higher attractive force between CPH particles.

Certainly, adhesion forces between CPH particles increase linearly with rising temperature [START_REF] Ogienko | Direct measurement of stoichiometry of the structure H argon gas hydrate synthesized at high pressure[END_REF].

Thus, at higher temperatures, growing CPH crystals adhere to each other in a stronger framework than at lower temperatures. Consequently, more brine is trapped between CPH crystals, and a post-treatment method, such as centrifuging, is required.

One the second hand, Lv et al. [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] showed that the salt removal efficiency improves when increasing operating temperature from 0.95 to 3.95°C (or 274.1 -277.1K). It was found that the residual salinity is likely to be strongly related to the shapes and size of hydrate crystals.

Kishimoto et al. [START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF] specified that the size of the hydrate crystals diminished with subcooling increase.

Moreover, by using the FBRM probe, Lv et al. [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] indicated that the median chord length of CPH particles after 8h formation at 0.95 °C (274.1 K) is 22.16 μm, while, particles formed at 3.95°C (277.1 K) under the same other conditions exhibited a median chord length of 34.15 μm.

Thus, it was supposed that at higher operating temperature (or lower subcooling), hydrate particles are bigger with a smaller specific surface area favorable to salt removal [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF].

To sum up, in order to clarify the effect of operating temperature on the purification efficiency, more data at a varied range of operating temperature and salt concentration would be needed.

Salinity

Table 8 shows that the salt removal efficiency increases slightly with the salinity increase, while both water conversion to hydrate and yield of dissociated water appear to decrease considerably [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF]. Indeed, when there is uptake in salt concentration, the driving force for hydrate formation decreases [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF]. This reduces the CPH formation rate [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF][START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF]. As a result, less water converts into hydrate under higher salt concentrations.

Moreover, an enhancement in purification efficiency at high operating temperatures can be attributed the CPH crystals size change. Indeed, the hydrate formation kinetics decreases as salt concentration increases [START_REF] Cai | Formation of cyclopentane methane binary clathrate hydrate in brine solutions[END_REF][START_REF] Zylyftari | Salt effects on thermodynamic and rheological properties of hydrate forming emulsions[END_REF][START_REF] Kishimoto | Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF]. Thus, bigger hydrate particles with a smaller specific area are likely to form. Consequently, there is less brine trapped between CPH crystals.

Solid additives

As aforementioned, the addition of some solid additives can promote CHP formation [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF][START_REF] Whitman | Investigation of factors affecting crystallization of cyclopentane clathrate hydrate[END_REF][START_REF] Peixinho | Growth of Clathrate Hydrates from Water Drops in Cyclopentane[END_REF][START_REF] Zylyftari | Nucleation of cyclopentane hydrate by ice studied by morphology and rheology[END_REF][START_REF] Karanjkar | Calorimetric investigation of cyclopentane hydrate formation in an emulsion[END_REF]. Moreover, Li et al [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF] reported that the addition of graphite not only enhances CPH formation but also boosts the salt removal efficiency. They indicated that the surface functional groups of graphite improve both hydrate nucleation and growth of CPH.

Moreover, the hydrophobic surfaces of graphite could inhibit hydrate aggregation and make hydrate crystal particles more porous. Consequently, the trapped salt ions can be removed more easily by centrifuging process, thus increasing the salt removal efficiency [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF]. In addition, in presence of graphite, the prolongation of hydrate formation improved the desalting efficiency [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF]. The hydrophobic behavior of graphite is believed to play a crucial role in this improvement [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF]. These findings present interesting perspectives for the use of graphite or carbon material surfaced in the development of CPH-base desalination techniques.

Post-treatment methods

In order to remove salts trapped onto the hydrate surfaces, some post-treatment methods are introduced, such as filtration, centrifuging, sweating, gravitational separation, and washing.

Several studies concluded that all these techniques can enhance profoundly the salt removal efficiency [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF].

About 60-63% of NaCl from the feed solution was removed after CPH formation with only vacuum filtration [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF]. It means that the treated water still contained a high level of NaCl.

Obviously, this level of water purification is insufficient for desalination, so further posttreatments are needed.

Han et al. [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF] demonstrated that centrifuging can enhance salt removal efficiency up to 96%.

However, centrifuging is very expensive for mass treatment. Sweating by melting the impure zone over time can be a potential process to enhance salt removal. Nonetheless, it reduces the quantity of water retrieved. Moreover, this process is time consuming, hence an optimal time should be determined for the sweating of CPH crystal [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF].

Washing is also an effective approach to enhance salt removal [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Xu | Hydrate Desalination Using Cyclopentane Hydrates At Atmospheric Pressure[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF][START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF]. The source of the wash can be fresh, DI water, filtered water, or even brine water. The effect of washing water/produced water ratio on salt removal was remarkable. Han et al. [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF] indicated that the optimal ratio of washing water/ produced water is approximately 0.03 (g/g) with a salt removal efficiency above 90%. Lv et al. [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] suggested that this value should be 0.5 (g/g) in order to remove enough salt from CPH crystals. However, this value is extremely high for industrial scales. Therefore, more investigation is required to optimize this ratio in order to meet the requirement of water purification and reduce the costs of desalination process.

Finally, forthcoming research should combine optimization of both kinetics of CPH formation and the salt removal efficiency [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF]. Post-treatment methods may include filtration or pelletizing (squeezing) at first step [START_REF] Park | A new apparatus for seawater desalination by gas hydrate process and removal characteristics of dissolved minerals (Na + , Mg 2+ , Ca 2+ , K + , B 3+ )[END_REF][START_REF] Kang | Evaluation of Desalination by Nanostructured Hydrate Formation and Pellet Production Process[END_REF] in order to facilitate CPH separation from aqueous solution and transportation to dissociation devices. Furthermore, to meet potable water standards, several existing technologies like washing and sweating are needed to remove entrapped salt ions on the crystal surfaces. Of course, optimizations on these technologies are also required for the economy feasibility of the desalting process.

Comparison to other desalination technologies

Comparison to traditional technologies

Other processes such as multi-stage flash distillation (MSF), multiple-effect distillation (MED), solar thermal distillation (SD), freezing, reverse osmosis (RO), ecletro-dyalysis (ED), ionexchange desalination (IE), and adsorption have been investigated, and industrially used, for seawater desalination [START_REF] Khawaji | Advances in seawater desalination technologies[END_REF][START_REF] Subramani | Emerging desalination technologies for water treatment: A critical review[END_REF][START_REF] Fakharian | Desalination of high salinity produced water using natural gas hydrate[END_REF][START_REF] Englezos | The Freeze Concentration Process and its Applications[END_REF][START_REF] Sarshar | Simultaneous water desalination and CO 2 capturing by hydrate formation[END_REF][START_REF] Al-Karaghouli | Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes[END_REF][START_REF] Mahdavi | Application of Freezing to the Desalination of Saline Water[END_REF][START_REF] Ameri | Effect of design parameters on multieffect desalinationsystem specifications[END_REF][START_REF] Imbrogno | Critical aspects of RO desalination: A combination strategy[END_REF][START_REF] Ng | Adsorption desalination: An emerging low-cost thermal desalination method[END_REF][START_REF] Elimelech | The Future of Seawater and the Environment: Energy, Technology, and the Environment[END_REF][START_REF] Park | An economic analysis of desalination for potential applicaiton in Korea[END_REF][START_REF] Thu | Adorption desalination: Theory & Experiments[END_REF][START_REF] Kalogirou | Seawater desalination using renewable energy sources[END_REF][START_REF] Shannon | Science and technology for water purification in the coming decades[END_REF][START_REF] Youssef | Comparative analysis of desalination technologies[END_REF][START_REF] Javanmardi | Energy consumption and economic evaluation of water desalination by hydrate phenomenon[END_REF][START_REF] Sangwai | Desalination of Seawater Using Gas Hydrate Technology-Current Status and Future Direction, 18th[END_REF][START_REF] Fakharian | Saline Produced Water Treatment Using Gas Hydrates[END_REF][START_REF] Goh | Recent trends in membranes and membrane processes for desalination[END_REF].

Table 9 presents a comparison between diverse technologies based on four criteria: Thermal Energy consumption, electrical energy consumption, production cost, and product water salinity.

Also, note that, in the case of clathrates, different formers can be used. Therefore, there are other opportunities than CPH to consider when discussing hydrate-based desalination. Consequently, a short comparison between different clathrate formers will be presented in the next section. Table 9 illustrate of what can be expected with other clathrate than CPH.

In term of purification level, MSF, MED, RO, adsorption, or clathrate hydrate technique can produce water with salinity lower than 10 ppm. Of course, this value varies according to the procedure and technology. For hydrate-based desalination, Subramani et al. [START_REF] Subramani | Emerging desalination technologies for water treatment: A critical review[END_REF] estimated that the technique can reach 100% salt removal in theory. However, such quality should not be expected. For instance, McCormack et al [START_REF] Mccormack | Clathrate desalination plant preliminary research study[END_REF] obtained fresh water with a salinity of 100 ppm by using HCFC 141b (Dichloromonofluoroethane -CCl 2 FCH 3 ) clathrates. In a patent, Mottet [START_REF] Mottet | Method for treating an aqueous solution containing dissolved materials by crystallization of clathrates hydrates[END_REF] evaluates that the salinity for the treated water via CPH crystallization to be 1000 ppm. By using a new batch-wise displacement washing technique in CPH-based desalting process, Cai et al [START_REF] Cai | Desalination via formation of binary clathrate hydrates[END_REF] obtained fresh water with a salinity less than 10 ppm (<0.001% mass). Accordingly, in other efforts, Han et al. [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF] and Lv et al. [START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF] indicated that CPH-based desalination technology can produce water with a salinity from 700-4400 ppm. Recently, Xu et al [START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] and Li et al [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF] reported values of 700 ppm and 4008 ppm, respectively.

Note that, according to World Health Organization (WHO), the palatability of water with a total dissolved solids (TDS) level less than 600 mg/l is generally considered to be good; drinkingwater becomes significantly and increasingly unpalatable at TDS levels greater than 1000 mg/l [START_REF] Edition | Guidelines for drinking-water quality[END_REF]. Remember that seawater has an average of 35000 ppm TDS [START_REF] Youssef | Comparative analysis of desalination technologies[END_REF][START_REF] El-Dessouky | Fundamentals of salt water desalination[END_REF]. The high TDS value (here salinity) of product water via CPH-based desalination is strongly related to the salts trapped in the hydrate crystals [START_REF] Khawaji | Advances in seawater desalination technologies[END_REF][START_REF] Subramani | Emerging desalination technologies for water treatment: A critical review[END_REF][START_REF] Fakharian | Desalination of high salinity produced water using natural gas hydrate[END_REF][START_REF] Englezos | The Freeze Concentration Process and its Applications[END_REF][START_REF] Sarshar | Simultaneous water desalination and CO 2 capturing by hydrate formation[END_REF][START_REF] Al-Karaghouli | Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes[END_REF][START_REF] Mahdavi | Application of Freezing to the Desalination of Saline Water[END_REF][START_REF] Ameri | Effect of design parameters on multieffect desalinationsystem specifications[END_REF][START_REF] Imbrogno | Critical aspects of RO desalination: A combination strategy[END_REF][START_REF] Ng | Adsorption desalination: An emerging low-cost thermal desalination method[END_REF][START_REF] Elimelech | The Future of Seawater and the Environment: Energy, Technology, and the Environment[END_REF][START_REF] Park | An economic analysis of desalination for potential applicaiton in Korea[END_REF][START_REF] Thu | Adorption desalination: Theory & Experiments[END_REF][START_REF] Kalogirou | Seawater desalination using renewable energy sources[END_REF][START_REF] Shannon | Science and technology for water purification in the coming decades[END_REF][START_REF] Youssef | Comparative analysis of desalination technologies[END_REF][START_REF] Javanmardi | Energy consumption and economic evaluation of water desalination by hydrate phenomenon[END_REF][START_REF] Sangwai | Desalination of Seawater Using Gas Hydrate Technology-Current Status and Future Direction, 18th[END_REF][START_REF] Fakharian | Saline Produced Water Treatment Using Gas Hydrates[END_REF][START_REF] Goh | Recent trends in membranes and membrane processes for desalination[END_REF]. This requires efforts on post-treatment process to completely remove trapped salt and therefore achieve product water with quality that meets the WHO drinking-water criterions. [START_REF] Thu | Adorption desalination: Theory & Experiments[END_REF] 0.85 [START_REF] Park | An economic analysis of desalination for potential applicaiton in Korea[END_REF][START_REF] Javanmardi | Energy consumption and economic evaluation of water desalination by hydrate phenomenon[END_REF] 0.45-1.72 [START_REF] Al-Karaghouli | Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes[END_REF] 0.64-0.76 [START_REF] Thu | Adorption desalination: Theory & Experiments[END_REF] 35 [START_REF] Caldera | Role of Seawater Desalination in the Management of an Integrated Water and 100% Renewable Energy Based Power Sector in Saudi Arabia[END_REF][START_REF] Elimelech | The Future of Seawater and the Environment: Energy, Technology, and the Environment[END_REF] 400-500 [START_REF] Al-Karaghouli | Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes[END_REF] 10 1000 [START_REF] Mottet | Method for treating an aqueous solution containing dissolved materials by crystallization of clathrates hydrates[END_REF] 700-4400 [START_REF] Han | Enhanced efficiency of salt removal from brine for cyclopentane hydrates by washing, centrifuging, and sweating[END_REF][START_REF] Lv | Desalination by forming hydrate from brine in cyclopentane dispersion system[END_REF][START_REF] Han | Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination[END_REF] 4008 [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF] 700 [START_REF] Xu | Hydrate-Based Desalination Using Cyclopentane Hydrates at Atmospheric Pressure[END_REF] 100-500 [START_REF] Buchanan | Removing salt from sea water, US3027320A[END_REF] 7665 [START_REF] Park | A new apparatus for seawater desalination by gas hydrate process and removal characteristics of dissolved minerals (Na + , Mg 2+ , Ca 2+ , K + , B 3+ )[END_REF] 1100 [START_REF] Kang | Evaluation of Desalination by Nanostructured Hydrate Formation and Pellet Production Process[END_REF] 23270 [START_REF] Cha | Increasing gas hydrate formation temperature for desalination of high salinity produced water with secondary guests[END_REF] 8055 [START_REF] Cha | Increasing gas hydrate formation temperature for desalination of high salinity produced water with secondary guests[END_REF] * Not Acknowledge

In terms of energy consumption, Table 9

Comparison between Clathrate formers for hydrate-based process

Concerning hydrate-based approach, the kind of former is crucial. It is one of the most important factors in hydrate-based desalination since the operating conditions strongly depend on the guest molecules. With a possibility to form hydrate at temperature above 0°C from seawater, CHFC 141B has been studied for desalination in the last few decades [START_REF] Mccormack | Clathrate desalination plant preliminary research study[END_REF][START_REF] Bradshaw | Desalination Utilizing Clathrate Hydrates[END_REF][START_REF] Karamoddin | Water desalination using R141b gas hydrate formation[END_REF]. However, CHFC 141B has a solubility of 350mg/l at 15.6 o C [START_REF] Mccormack | Clathrate desalination plant preliminary research study[END_REF] higher than that for CP (156mg/l at 20°C) [START_REF] Ho-Van | Experimental Measurement and Thermodynamic Modeling of Cyclopentane Hydrates with NaCl, KCl, CaCl 2 or NaCl-KCl Present[END_REF][START_REF] Mcauliffe | Solubility in Water of Paraffin, Cycloparaffin, Olefin, Acetylene, Cycloolefin, and Aromatic Hydrocarbons1[END_REF]. Moreover, HCFC R141B is also very volatile (boiling point of 32.2 °C) [START_REF] Mccormack | Clathrate desalination plant preliminary research study[END_REF]. This leads to an ozone-depletion problem when released into the atmosphere [START_REF] Bolaji | Ozone depletion and global warming: Case for the use of natural refrigerant -A review[END_REF]. International concern over relatively high global warming potential of HCFC has caused some European countries to abandon it for many applications such as refrigerants or as a cleaning agent [START_REF] Bolaji | Ozone depletion and global warming: Case for the use of natural refrigerant -A review[END_REF]. HCFC compounds, such as R141b, are hence restricted by current environmental regulations and are no longer practical candidates for a hydrate desalination process, despite their ease of use [START_REF] Bradshaw | Desalination Utilizing Clathrate Hydrates[END_REF].

Recently, He et al [START_REF] He | A novel conceptual design of hydrate based desalination (HyDesal) process by utilizing LNG cold energy[END_REF][START_REF] He | LNG cold energy utilization : Prospects and challenges[END_REF], Nambiar et al [START_REF] Nambiar | Improved Kinetics and Water Recovery with Propane as Co-Guest Gas on the Hydrate-Based Desalination ( HyDesal ) Process[END_REF], and Chong et al [START_REF] Chong | Economic evaluation of energy e ffi cient hydrate based desalination utilizing cold energy from lique fi ed natural gas ( LNG )[END_REF], proposed a propanehydrate based desalination process using LNG cold energy. When compared to MSF, RO, and freezing techniques, Babu et al [START_REF] Babu | A Review of Clathrate Hydrate Based Desalination to Strengthen Energy-Water Nexus[END_REF] demonstrated that this technology (the HyDesal process) can be economically attractive. As shown in Table 9, this process requires a remarkably low energy (0.60-0.84 kWh/m 3 ) compared to others. The cost of potable water was found to be approximately $1.11/m3 with LNG cold energy integration [START_REF] Chong | Economic evaluation of energy e ffi cient hydrate based desalination utilizing cold energy from lique fi ed natural gas ( LNG )[END_REF]. LNG cold energy from the LNG regasification terminals replaces the external refrigeration cycle. Of course, this 8, these two parameters are usually inversely proportional to each other. There is a need to investigate the best method to transport CPH after formation. Filtration and pelletizing seem to be appropriate to facilitate this transportation step. A washing method is necessary to enhance the salt removal capacity. However, improving the ratio of washing water/dissociated water is also required to make this process economical feasible.

Utilizing LNG cold energy during the regasification process in the LNG regasification terminals for CPH-based desalination is one of the promising approaches to minimize the energy consumption and hence Strengthen Energy-Water Nexus [START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF]. Of course, this technique requires more experimental explorations before commercial readily-available in the freshwater production industry.

Furthermore, the idea of combining CO 2 capture and desalination can be advantageous when a hydrate mixture of CO 2 + CP is used. Indeed, merging two energy demanding processes can optimize energy use [START_REF] Babu | A review of the hydrate based gas separation (HBGS) process forcarbon dioxide pre-combustion capture[END_REF][START_REF] Cha | Increasing gas hydrate formation temperature for desalination of high salinity produced water with secondary guests[END_REF][START_REF] Zhang | Phase Equilibrium of Cyclopentane + Carbon Dioxide Binary Hydrates in Aqueous Sodium Chloride Solutions[END_REF]. However, this procedure is more complicated with the added requirements of higher pressure equipment.

To recap, based on the analysis of all of the articles reviewed, a diagram of CPH-based desalination, with all proposed required steps and apparatus, is proposed in Figure 4. [START_REF] Mottet | Method for treating an aqueous solution containing dissolved materials by crystallization of clathrates hydrates[END_REF])

Figure 4 presents a continuous system of water treatment. A mixing system is fed with both cooled CP and saline solution. This mixer, also called an emulsifier is critical to design as it governs the size of the CP droplets in water. The second piece of equipment is crystallizer, where the formation of CPH occurs. Since this is a continuous process; there is no induction time to consider. However, the residence time to complete hydrate formation in the crystallizer is optimized based on the device configuration design in order to reduce the process capital cost.

Saline aqueous solution

Cyclopentane

Mixing system Crystallizer Decanter

Precipitated salts

Slurry filter CPH

Concentrated solution

Decanter

Purified water

Cyclopentane

Washing

The slurry is then transferred to a decanter, allowing the growth of hydrate particles and the separation of different phases, notably the possible precipitation of the salts. Then, the slurry filter separates CPH and a concentrated solution. This concentrated solution is waste. However it can be partially re-injected to the mixing system if the aim is to produce saturated solution and precipitated salts. CPH crystals are melted with a heat exchanger and are introduced in a decanter allowing the separation of the CP (on the top) and purified water (on the bottom). The CP is then re-used at the beginning of the process in a closed loop.

A washing step can be also added to the slurry filter. This drives out the concentrated solution trapped between CPH particles. Nonetheless, a less concentrated solution is required. This can be the initial saline aqueous solution or a fraction of the purified water, depending on the rate of purification expected. Although by using a fraction of purified water, while a better purification rate can be obtained, unfortunately the yield of the system decreases.

As seen on figure 4, there are cooling and heating systems in the process. An optimization by energy recovery between the two types of heat exchangers could be considered in order to reduce the energy consumption still further.

From a technological point of view, this flow diagram summarizing all required steps and apparatus for a CPH based desalination process is inspired by the one proposed by BGH Company (France) [START_REF] Mottet | Method for treating an aqueous solution containing dissolved materials by crystallization of clathrates hydrates[END_REF].

According to Mottet [START_REF] Arora | Biosurfactant as a Promoter of Methane Hydrate Formation : Thermodynamic and Kinetic Studies[END_REF], here are some advantages to this process:

 CPH can act as both a water purifier and a concentrator of dissolved materials (salts).

Interestingly, Ho-van et al [START_REF] Ho-Van | Implementing Cyclopentane Hydrates Phase Equilibrium Data and Simulations in Brine Solutions[END_REF] reported the precipitation of salts (6% mass Na 2 SO 4 at less than 5.3°C) during CPH crystallization. As solid materials, the precipitated salts can be then removed easily by a physical method since their high density compared to others (CPH, CP, brine).

 This is a "no discharge method", since simultaneous production valorized salts and pure water  High yield, more than 95%  This technique can treat highly-salty water (impossible for RO method).

 No pressure requirement, and reasonable operating temperature from -20°C to 7°C

 Less energy consumed than both evaporation and Ice EFC (Eutectic Freeze Crystallization) methods.

 This method is technically more reliable than the Ice EFC as the crystallization of water is internal and direct when CP is added.

 This is a continuous process Obviously, before hydrate desalination becomes a practical commercial technology, the vital issues of controlled hydrate nucleation, formation rate, phase properties, amount of entrapped salt and its removal efficiency must be thoroughly understood and optimized [START_REF] Bradshaw | Desalination Utilizing Clathrate Hydrates[END_REF]. As aforementioned, CPH has been recently studied in terms of thermodynamic, kinetic, and phase properties. A relatively sufficient database of CPH for desalination is now available in the literature as provided in this present review.

Figure 1 .

 1 Figure 1. Frequency of desalination study in literature. Data from Web of Science with the keyword "desalination" (09/04/2019).

Figure 2 .

 2 Figure 2.

Figure 3 .

 3 Figure 3. Equilibrium data of mixed gas hydrates containing CP in literature

Figure 3

 3 Figure 3 also shows that CP-Kr and CP-H 2 S can form mixed hydrates at the most favorable

Figure 3

 3 Figure 3 further indicates that the hydrate formation conditions of CP-O 2 , CP-N 2 , and CP-H 2 are

+

Figure 4 .

 4 Figure 4. CPH-based desalination process diagram (inspired by[START_REF] Mottet | Method for treating an aqueous solution containing dissolved materials by crystallization of clathrates hydrates[END_REF])

8 Conclusions

 8 Numerous investigations have been being conducted on CPH for decades. Records on thermodynamic, kinetic, phase properties, and use of CPH for desalination were presented. A comparison between CPH based desalination and other techniques has also been provided. After analyzing vital factors such as energy consumption, product water quality, and economy of desalination plant, conclusions show that Clathrate hydrates present potential for new desalination technique. The use of CP as hydrate former is a promising idea, supported by recent researches in that field. While hydrate technology has not been yet fully developed in the industry, the combination of water desalination to other applications, such as cold energy storage, or even gas separation and storage, makes it again an encouraging idea compared to other competing technologies like distillation, freezing, and reverse osmosis. Of course, other clathrates formers, instead or in addition to CP molecule, could be more suitable for future water treatment applications. However, a diagram of CPH based salt removed has been suggested to illustrate future directions. Finally, some challenges, such as the best economic compromise between salt efficiency and water-to-hydrate conversion need to be addressed before industrial development and implantation.

  is how water desalination works with Clathrates. During hydrate formation, water and guest molecules are incorporated into a new solid phase. It can be separated and recovered. Moreover, salts are excluded from the crystal phase. Therefore water and guest molecules can be retrieved after dissociation. If the guest is gaseous at standard conditions, only saturated gas remains inside liquid water. Consequently, clean "desalinated" water is obtained. If the guest molecule is not under vapor phase after dissociation, clean water is obtain providing that it can be separated after dissociation. Usual guest molecules studied for desalination applications are: CH 4 , CO 2 , C 3 H 8 , HCFC R141B, and CP.

Table 1 .

 1 Equilibrium temperature of CPH in pure water at atmospheric pressure with and

		without surfactant
	Authors	Publish	Value (°C)	Method	Citation
		ed year
	Palmer et al.	1950	7.7	Quick	[57]
				dissociation
	Davidson et al.	1973	7.7	Quick	[58]
				dissociation
	Fan et al.	1999	7.07	"Pressure	[59]
				search"
				procedure
	Dendy Sloan et al.	2008	7.7	Quick	[14]
				dissociation
	Nakajima et al.	2008	6.6, 6.8, 7.1	DSC	[60]
	Whitman et al.	2008	7.0	DSC	[61]
	Nicholas et al.	2009	7.7	Quick	[62]
				dissociation
	Zhang et al.	2009	7.02	DSC	[63]

+ in the presence of surfactant, * not acknowledge, DSC: Differential Scanning Calorimetry, Uncertainty range: a ±0.1°C, b ±0.01°C, c ±0.2, d ±0.5°C.

Table

1

shows that there are actually two ranges of equilibrium temperatures in pure water: 7.7-7.8°C and 6.6-7.2°C. This can be explained by different experimental procedures used by the authors.

Table 2 .

 2 Fan et al.

indicated that the quadruple point is 7.07°C at 19.8 kPa involving four phases: liquid water (L w ) , liquid CP (L cp ), hydrate (H), and vapor CP (V cp

Table 2 .

 2 Three phase (V-L w -H) equilibrium data of CPH in pure water[START_REF] Fan | Hydrate equilibrium conditions for cyclopentane and a quaternary cyclopentane-rich mixture[END_REF]

	Phase	Temperature	Pressure
		(±0.01°C)	(±0.1kPa)
	L w -H-V cp	0.21	6.9
		1.19	8.1
		2.08	9.2
		3.34	11.2
		4.36	13.2
		5.72	16.3
		6.72	18.9
	L w -L cp -H-V cp	7.07	19.8 *

* Upper quadruple point

Table 3 .

 3 CPH phase equilibrium data at high pressure

	Phase	Temperature	Pressure (MPa)
		(±0.02°C)	(±3% of reading)
	L w -H-L a	6.75	2.55
		6.79	5.05
		6.87	7.55
		6.85	10.03
		6.88	12.55

Table 4 .

 4 Literatures on equilibrium temperature of CPH in the presence of salts

	Salts	Salt concentration	Method	Published	Citation
		range (% mass)		year
	NaCl	3.5	Slow dissociation a		[64]
	Synthetic seawater	*	Slow dissociation a		[64]
	NaCl	5-26.4	Slow dissociation a		[87]
	NaCl	0 -23	DSC a		[68]
	NaCl	3.5	Quick dissociation		[69]
	NaCl	3.5	DSC		[73]
	NaCl	0 -4	Slow dissociation b		[77]
	NaCl	0 -23	Slow dissociation a		[28]
	KCl	0 -20	Slow dissociation a		[28]
	NaCl-KCl	0 -22	Slow dissociation a		[28]
	CaCl 2	0 -25	Slow dissociation a		[28]
	Na 2 SO 4	0 -6	Slow dissociation a		[88]
	MgCl 2	0 -20	Slow dissociation a		[88]
	MgCl 2 -NaCl	0 -22	Slow dissociation a		[88]
	MgCl 2 -NaCl-KCl	0 -22	Slow dissociation a		[88]
	* 2.6518% NaCl, 0.2447% MgCl 2 , 0.3305% MgSO 4 , 0.1141% CaCl 2 , 0.0725% KCl, 0.0202%
	NaHCO 3 , and 0.0083% NaBr. Uncertainty range: a ±0.1°C, b ±0.2°C.

Table 5 .

 5 Equilibrium conditions of mixed hydrate containing CP as a co-guest Note: pure water implies distilled or only under laboratory conditions

	Hydrate formers	Aqueous solution	Temperature	Pressure range	Citation
			range (K)	(Mpa)
	Binary
	CP -CO	Simulated produced water:	280.15 -289.15	3.1	[90]
		8.95 % mass
	CP -CO	NaCl: 3.0% mass	271.89 -292.21	0.55 -3.59	[47]
	CP -CO	NaCl: 0, 3.5, 7.0, 10.0, 15,	269.8 -292.4	1.18 -3.33	[92]
		25% mass
	CP -CO	Pure water	280.16 -291.57	0.08 -4.88	[52]
	CP -CO	Pure water	284.6 -291.6	0.49 -2.58	[53]
	CP -CO	Pure water	275.5 -285.2	0.42 -0.59	[20]
	CP -CO	Pure water	284.3 -291.8	0.35 -2.52	[93]
	CP -CO	Pure water	281.55 -290.25	0.15 -1.92	[94]
	CP -CO	Pure water	283.5-287.5	0.761-1.130	[95]
	CP -CH	NaCl : 0, 3.5, 7.0, 10.0 %	284.4 -301.3	0.480 -16.344 [96]
		mass
	CP -CH	NaCl : 0, 3.5, 7.0% mass	288.5 -296.9	3.26 -1.09	[39]
	CP -CH	NaCl : 3.5% mass	283.15 -298.15	0.48 -10.15	[97]
	CP -CH	(K + , Na + , Mg 2+ , Ca 2+ )	292.68 -295.06	2.50 -2.51	[98]
		(Cl -,SO 4 2-)	293.75 -295.06	2.50 -2.51	[98]
	CP -CH	Pure water	282.8 -300.5	0.157 -5.426 [40]
	CP -CH	Pure water	284.8 -299.3	0.321 -4.651 [56]
	CP -CH	Pure water	287.5 -303.0	0.62 -8.61	[48]
	CP -CH	Pure water	286.70 -300.0	0.48 -5.69	[41]
	CP -N 2	Pure water	282.9 -289.1	0.641 -3.496 [40]
	CP -N 2	Pure water	285.9 -302.0	1.68 -24.45	[50]
	CP -N 2	Pure water	284.7-296.0	1.27-10.4	[48]

Table 5

 5 indicates that CO 2 , CH 4 , N 2 , and H 2 are the four most common gases used to study mixed CPH. As seen from Figure 3, mixed CP-CH 4 , CP-CH 4 -O 2 , CP-CH 4 -N 2 , CP-CH 4 -TMS (Trimethylene sulfide) hydrates have been studied in pure water and in brine. Indeed, CH 4 is valuable fuel. Moreover, it is flammable and dangerously explosive at high pressure, especially when air, or just O 2, is present. As a result, CH 4 is not an auspicious hydrate former for CPHbased desalination, even though the hydrate formation conditions of the mixed CP-CH 4 hydrates are systematically milder than those of the mixed CP-CO 2 , CP-O 2 , CP-N 2 , or CP-H 2 hydrates in fresh water and in brine.

Table 6 .

 6 The effects of several considerations on kinetic of CPH formation

	Considerations	Nucleation Growth	Citation
			rate
	Subcooling increase	↑	↑	[42,64,68,70-72,76,87,119-125]
	Quantity of CP	↑	↑	[42,79,119,120,126,127]
	Agitation speed increase	↑	↑	[39,60,70,119,124,125,128]
	Use of ''Memory effect''	↑	NA	[61,65,66,72]
	Solid additives	↑	NA	[43,61,75,129,130]
	Presence of salts	↓	↓	[39,45,68,72,77,87,119]
	Presence of surfactants or polymers	↑	↑	[68,71,74,126,130-136]
	Presence of surfactants or polymers	↓	↓	[65,74-77,121,131,137-140]
	Presence of THF (0.01 -0.05 % mass)	↑	↑	[139]
	Presence of MeOH	↓	↓	[139]
	Presence of activated carbon particles	↓	↓	[51]

  indicated that the average lateral growth of CPH in the presence of 0.1% and 1% of surfactant DA 50 (benzyl-dodecyl-dimethylazanium chloride, C 21 H 38 C l N) is about twice lower compared to pure water system. Furthermore, Zhang et al.[START_REF] Zhang | Adsorption of kinetic inhibitors on clathrate hydrates[END_REF] indicated that polyvinyl pyrrolidone (PVP) and polyvinylcaprolactam (PVCap) acted as inhibitors on CPH formation. In fact, PVP and PVCap prevented CP diffusion from the bulk to the hydrate surface. This hence decreases the growth rate of CPH. Hobeika et al.[START_REF] Hobeika | High-Resolution Optical Microscopy of Gas Hydrates[END_REF] showed that, with PVP, PVCap, or vinylpyrrolidone/vinyl-

caprolactam copolymer VP/VCap present, the CPH growth rate is much lower compared to pure water. Therefore larger subcooling is required. Moreover, among these three polymers, PVCap was found to be best to prevent hydrate formation.

Dirdal et al.

[START_REF] Dirdal | Can cyclopentane hydrate formation be used to rank the performance of kinetic hydrate inhibitors?[END_REF]

investigated the inhibition efficacy of various of kinetic hydrate inhibitors (KHIs) of CPH formation under atmospheric pressure. Their results exhibited that, in the range of 100-200 ppm, considerable smaller quantities of KHIs are needed to prevent CPH formation than standard gas hydrate formation. Furthermore, Abojaladi et al

[START_REF] Abojaladi | Can cyclopentane hydrate formation be used to screen the performance of surfactants as LDHI anti-agglomerants at atmospheric pressure?[END_REF]

studied the performance of surfactants (cation, non-ionic, and anion surfactants) as low dosage hydrate inhibitors (LDHI)

Table 7

 7 provides different properties of CPH in the literature. The following subsections look at different parameters in detail.

Table 7 .

 7 CPH physical properties studied in the literature

	Properties	Citation
	Morphology	[42,45,64,71,74-77,87,122,126,127,129,131,171-174]
	Adhesion	[42,62,80,175-180]
	Cohesion	[74,137,141,175,177,181,182]

Table 8 .

 8 Effect of various considerations on CPH-based desalination process

	Considerations	Yield of	Water	Salt removal	Citation
		dissociated	conversion to	efficiency
		water	hydrate
	Quantity of CP:

Table 9 .

 9 A comparison in energy consumption, production cost and product water quality

		between desalination technologies
	Desalination	Thermal energy	Electrical energy	Production cost	Water salinity
	technology	consumption	consumption	($/m 3 )	(ppm)
		(kWh/m 3 )	(kWh/m 3 )
	MSF	52.78-78.33[200] 15.83-23.5 [200]	0.52-1.75	10 [200]
				[200][217]
				1.0785 [218]
				0.77-1.64 [207]
	MED	40.28-63.89 [200] 12.2-19.1 [200]	0.52 -8.0 [200]	10 [200]
				0.87-1.95 [207]
	SD	0 [200,210]	0 [200,210]	1.3-6.5 [200]	80 [210]
				3.9 [210]
	Freezing	*	9-11[219]	0.93 [219,220]	100 [210]
	RO	4.1 [5]	4.0 [5]
			3-7 [221]
			8.2-9.0

  indicates that clathrate hydrate, adsorption, SD, or IE technology require the lowest amount of energy ( 2kWh/m 3 ), whilst MSF, MED, and Freezing consume an energy almost more than 10 kWh/m 3 . The lower energy required in clathrate techniques compared others is related to its low phase change enthalpy. As clarified in Table10,

	HCFC 141b hydrate or CPH requires a smaller energies (5.74 or 4.84 kJ/mol water, respectively)
	compared to freezing water (6.02 kJ/mol) or water evaporation (40.7 kJ/mol) [69,130,187].

Table 9

 9

	also displays that the production cost for adsorption and clathrate hydrate is much
	smaller than MSF, SD, freezing, and IE technologies. For instance, production costs for HCFC
	141b and propane hydrates are less than 0.6 $/m 3 and 1.11 $/m 3 , respectively. Otherwise, it is
	between 0.6 and 1.95 $/m 3 for RO, MED, and ED technologies.

Table 10 .

 10 Latent heat of phase change of several techniques in desalination

	Method of desalination	Latent heat of phase	Citation
		change, kJ/mol
	CPH	4.84	[69,130,187]
		57.7±1.8 to 63.6±1.8	[230]
	CO 2 hydrates	53.29	[231]
		66.8	[232]
	Propane hydrates	27 ±0.33	[233]
	Mixed hydrate CP + C 3 H 8	2.23	[51]
	Mixed hydrate CP + CH 4	131.70 -121.74	[41]
		6.19	[225,234]
	Form R141 b hydrate
		5.74	[32]
	Freezing water	6.02	[69]
	Water distillation	40.7	[69]

7 Example of CPH technological approach

  Based on the literature, hydrate-based desalination requires a relative low energy and it is theoretically more competitive economically than other standard processes (distillation, freezing, and RO technologies). To apply that at a commercial and industrial scale, there are still various challenges that need to be addressed. One of the most difficult trials concerns the improvement of two crucial limiting factors: salt removal efficiency and water to hydrate conversion. As detailed in Table

desalination technique still needs a stable LNG cold energy source. High-pressure devices (0.4 Mpa) are also required to form propane hydrate. Lastly, it should be noticed that LNG and propane are flammable and explosive gases at high pressure. Thus, although its economic feasibility, also estimated by Chong et al [START_REF] Chong | Economic evaluation of energy e ffi cient hydrate based desalination utilizing cold energy from lique fi ed natural gas ( LNG )[END_REF], an industrial-scale testing of this process is not yet available.

In addition, Table 10 process was estimated to be $6,113,751 (for 0.75 m 3 /h of pure water) which is again lower than with propane hydrates ($ 9.6 million for 1.3 m 3 /h of pure water [START_REF] Chong | Economic evaluation of energy e ffi cient hydrate based desalination utilizing cold energy from lique fi ed natural gas ( LNG )[END_REF]). Moreover, the FCI augments from $6,113,751 to $9,559,668 when decreasing the CPH formation temperature from 277.15 K to 273.15 K. Finally, He et al [START_REF] He | Techno-economic Evaluation of Cyclopentane Hydrate-Based Desalination with LNG Cold Energy Utilization[END_REF] stated that the escalation of the water recovery rate of the CPH can lead to a decline in the SEC and FCI, and to a rise in the pure water flow rate and exergy efficiency. Consequently, improving the water recovery rate of CPH is crucial to enable fresh water production from this technique. Furthermore, based on the fact that CPH-based desalination requires relatively low temperatures (less than 7°C) for hydrate nucleation and growth, this desalting technique would be more costeffective if we can use the low temperature of actual seawater instead of utilizing a cryostat. For that purpose, Li et al [START_REF] Li | Promotion e ff ect of graphite on cyclopentane hydrate based desalination[END_REF] worked with actual seawater in winter at -10°C. Their results show that the crystallization occurred rapidly over 7h, with a salt removal efficiency of 70% and a water conversation rate of 56%. This indicates one more time the economy feasibility of CPH-based desalting technique when utilizing cold seawater.