Muhammad Imran Khan

Jinzhan Su
email: j.su@xjtu.edu.cn

Eric Lichtfouse
email: eric.lichtfouse@inra.fr

Liejin Guo
email: lj-guo@mail.xjtu.edu.cn

Higher efficiency of triethanolamine-grafted anion exchange membranes for acidic wastewater treatment

Keywords: Triethanolamine, Brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), Anion exchange membrane, Water uptake, Acid recovery

Acidic wastewaters are major industrial effluents that must be cleaned before release in natural waters, yet classical treatment methods are limited. Diffusion dialysis through anion exchange membranes (AEM) appears as a sustainable alternative because those membranes are cheap and highly selective, yet there is a need for improved membranes. Here we synthesized AEMs from brominated poly(2,6-dimethyl-1,4-phenylene oxide) using triethanolamine as an ion-exchange group for acid recovery. The prepared membranes were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. Acid recovery was tested with a mixture of HCl and FeCl 2 . Results show that increasing triethanolamine content into the membrane polymer matrix led to an increase of water uptake from 12% to 117%, ion exchange capacity from 1.28 to 2.29 mmol/g, and linear swelling ratio from 3.52% to 32.70%. The diffusion dialysis coefficient of acid (U H + ) reached 23 × 10 -3 m/h, which is higher than that actual membranes, of 0.37-20 × 10 -3 m/h. U H + increased with membrane triethanolamine content, which is explained by increasing H bonding of aqueous protons with membrane hydroxyl groups. U H + also increased from 23 × 10 -3 m/h at 25°C to 71 × 10 -3 m/h at 55°C due to easier ion flow. Moreover, the separation factor (S) reached 495 at 25°C, which is higher than that of actual membranes, of 73-351. The diffusion dialysis coefficient of metal (U Fe 2+ ) ranged from 0.0025 to 61 10 -3 m/h. Membranes also showed excellent thermal, chemical and mechanical stability.

Introduction

Acidic wastewaters are produced in large amounts from industrial processes such as electroplating, metallurgy, and mining. Acidic wastewaters induce two major issues, environmental pollution when effluents are discharged in rivers, and corrosion, which is costly [START_REF] Agrawal | An overview of the recovery of acid from spent acidic solutions from steel and electroplating industries[END_REF][START_REF] Xiao | Selective removal of halides from spent zinc sulfate electrolyte by diffusion dialysis[END_REF]. Common processes for wastewater treatment include neutralization, crystallization, thermal decomposition, solvent extraction, precipitation, coagulation-flocculation, distillation, and electrodialysis [START_REF] Cheng | Facile and cost effective PVA based hybrid membrane fabrication for acid recovery[END_REF][START_REF] Zhu | Exploring backbone-cation alkyl spacers for multi-cation side chain anion exchange membranes[END_REF], yet these processes have drawbacks such as cost, low selectivity, high energy and the use of toxic chemicals. Alternatively, diffusion dialysis through ion exchange membranes is actually under active research investigation because it is operationally cheaper, it consumes less energy and is potentially more efficient [START_REF] Khan | Fabrication and characterization of pyridinium functionalized anion exchange membranes for acid recovery[END_REF][START_REF] Feng | Seriesconnected hexacations cross-linked anion exchange membranes for diffusion dialysis in acid recovery[END_REF][START_REF] Khan | BPPO-based anion exchange membranes for acid recovery via diffusion dialysis[END_REF][START_REF] Mondal | Improved acid recovery performance by novel Poly(DMAEMco-γ-MPS) anion exchange membrane via diffusion dialysis[END_REF][START_REF] Khan | Porous BPPO-based membranes modified by aromatic amine for acid recovery[END_REF][START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF][START_REF] Mondal | Novel pendant benzene disulfonic acid blended SPPO membranes for alkali recovery: fabrication and properties[END_REF][START_REF] Mondal | Novel quaternized aromatic amine based hybrid PVA membranes for acid recovery[END_REF][START_REF] Emmanuel | Imidazolium functionalized anion exchange membrane blended with PVA for acid recovery via diffusion dialysis process[END_REF][START_REF] Lin | Asymmetrically porous anion exchange membranes with an ultrathin selective layer for rapid acid recovery[END_REF][START_REF] Mondal | Effect of novel polysiloxane functionalized poly(AMPS-co-CEA) membranes for base recovery from alkaline waste solutions via diffusion dialysis[END_REF][START_REF] He | Facile preparation of 1,8-diazabicyclo[5.4.0]undec-7-ene based high performance anion exchange membranes for diffusion dialysis applications[END_REF]. In particular, anion exchange membranes (AEM) are wellsuited for acid separation and recycling [START_REF] Emmanuel | Covalently cross-linked Table 2 Tensile strength (TS) and elongation at break of the prepared anion exchange membranes Membranes TEA-19 TEA-31 TEA-44 TEA-56 TS[END_REF][START_REF] Ran | Graphene oxide embedded "three-phase" membrane to beat "trade-off" in acid recovery[END_REF][START_REF] Emmanuel | Facile synthesis of pyridinium functionalized anion exchange membranes for diffusion dialysis application[END_REF][START_REF] Emmanuel | Novel synthetic route to prepare doubly quaternized anion exchange membranes for diffusion dialysis application[END_REF][START_REF] Khan | Preparation of diffusion dialysis membrane for acid recovery via a phase-inversion method[END_REF][START_REF] Bakangura | Hierarchically structured porous anion exchange membranes containing zwetterionic pores for ion separation[END_REF][START_REF] Lin | Preparation of porous diffusion dialysis membranes by functionalization of polysulfone for acid recovery[END_REF], yet the performances of actual membranes are limited.

The diffusion dialysis process is driven by a gradient of compound concentration between the two sides of the ion exchange membrane. Ion exchange membranes can Desalination and Water Treatment 197, 41-51, 2020. DOI 10.5004/dwt.2020.25966 be classified into AEM and cation exchange membranes according to the ionic group attached to the polymeric backbone. Currently, AEMs are tested for acid recovery from industrial acidic wastewater. Membranes have been synthesized from polysulfone and polystyrene, by photo-initiated polymerization of 4-vinylpyridine with varying amounts of divinylbenzene in the pores of polypropylene, by surface modification and pore filling of various polymers [START_REF] Luo | Diffusion dialysis-concept, principle and applications[END_REF][START_REF] Kim | Development of thin anion-exchange pore-filled membranes for high diffusion dialysis performance[END_REF][START_REF] Stachera | Acid recovery using diffusion dialysis with poly(4-vinylpyridine)filled microporous membranes[END_REF][START_REF] Kim | Facile surface modification of anion-exchange membranes for improvement of diffusion dialysis performance[END_REF]. Nonetheless, those membranes usually lack stability, and their hydrophobicity limits ion transfer during diffusion dialysis. Therefore, there is a need for cost-effective membranes that have long-term stability, higher selectivity, and permeation for acid recovery and wastewater treatment.

AEMs can be improved by modifying the polymeric backbone and functional groups [START_REF] Feng | Seriesconnected hexacations cross-linked anion exchange membranes for diffusion dialysis in acid recovery[END_REF][START_REF] Mondal | Novel quaternized aromatic amine based hybrid PVA membranes for acid recovery[END_REF][START_REF] Emmanuel | Imidazolium functionalized anion exchange membrane blended with PVA for acid recovery via diffusion dialysis process[END_REF][START_REF] Emmanuel | Facile synthesis of pyridinium functionalized anion exchange membranes for diffusion dialysis application[END_REF][START_REF] Yue | Influence of 2,2′,6,6′-tetramethyl biphenol-based anionexchange membranes on the diffusion dialysis of hydrochloride acid[END_REF]. Indeed, the polymeric backbone should be hydrophobic and mechanically stable. Actual polymeric backbones include poly(arylene ether ketone) [START_REF] Liu | Naphthalene-based poly(arylene ether ketone) anion exchange membranes[END_REF][START_REF] Ma | Poly(aryl ether ketone)s with bromomethyl groups: synthesis and quaternary amination[END_REF], poly(arylene ether sulfone) [START_REF] Pan | A strategy for disentangling the conductivitystability dilemma in alkaline polymer electrolytes[END_REF][START_REF] Li | Synthesis and properties of anion conductive multiblock copolymers containing tetraphenyl methane moieties for fuel cell application[END_REF][START_REF] Li | Synthesis and properties of anion conductive ionomers containing tetraphenyl methane moieties[END_REF], poly(fluorenyl ether ketone sulfone) [START_REF] Chen | Degradation of imidazolium-and quaternary ammonium-functionalized poly(fluorenyl ether ketone sulfone) anion exchange membranes[END_REF], poly(vinyl alcohol) [START_REF] Wu | Anion exchange hybrid membranes from PVA and multi-alkoxy silicon copolymer tailored for diffusion dialysis process[END_REF], poly(2,6-dimethyl-1,4-phenylene oxide) [START_REF] Lin | Alkaline polymer electrolytes containing pendant dimethylimidazolium groups for alkaline membrane fuel cells[END_REF][START_REF] Rebeck | Poly(phenylene oxide) copolymer anion exchange membranes[END_REF], and polyetherimide [START_REF] Wang | Developing a novel alkaline anion exchange membrane derived from poly(ether-imide) for improved ionic conductivity[END_REF]. Besides, the ion exchange capacity (IEC) should be high because well connected ion-conducting channels improve the diffusion dialysis coefficient [39]. The anion permeability can be controlled by the functional groups such as guanidinium [START_REF] Zhang | A novel guanidinium grafted poly (aryl ether sulfone) for high-performance hydroxide exchange membranes[END_REF][START_REF] Wang | Novel hydroxide-conducting polyelectrolyte composed of an poly(arylene ether sulfone) containing pendant quaternary guanidinium groups for alkaline fuel cell applications[END_REF][START_REF] Liu | A facile strategy for the synthesis of guanidinium-functionalized polymer as alkaline anion exchange membrane with improved alkaline stability[END_REF][START_REF] Qu | A high-performance anion exchange membrane based on bi-guanidinium bridged polysilsesquioxane for alkaline fuel cell application[END_REF], sulfonium [START_REF] Zhang | Tertiary sulfonium as a cationic functional group for hydroxide exchange membranes[END_REF] and phosphonium [START_REF] Gu | A soluble and highly conductive ionomer for highperformance hydroxide exchange membrane fuel cells[END_REF][START_REF] Gu | Self-crosslinking for dimensionally stable and solvent-resistant quaternary phosphonium based hydroxide exchange membranes[END_REF][START_REF] Gu | Engineering the van der waals interaction in cross-linking-free hydroxide exchange membranes for low swelling and high conductivity[END_REF][START_REF] Jiang | Synthesis and properties of quaternary phosphonium-based anion exchange membrane for fuel cells[END_REF][START_REF] Noonan | Phosphonium-functionalized polyethylene: a new class of base-stable alkaline anion exchange membranes[END_REF].

Membranes including quaternary ammonium are cheap and easy to synthesize [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF]. Here, a higher proton diffusion coefficient U H + of 0.033 m/h and a high separation factor S of 95.45 at 25°C has been obtained with quaternary ammonium-functionalized poly(arylene ether) (QPAE-Br) membranes [START_REF] Yue | Influence of 2,2′,6,6′-tetramethyl biphenol-based anionexchange membranes on the diffusion dialysis of hydrochloride acid[END_REF]. A diffusion dialysis coefficient U H + of 0.019 m/h and a separation factor S of 127 was reported for series-connected hexacations cross-linked membranes [START_REF] Feng | Seriesconnected hexacations cross-linked anion exchange membranes for diffusion dialysis in acid recovery[END_REF]. Quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membranes displayed IEC value of 2.07 mmol/g, diffusion coefficient U H + of 0.020 m/h and a separation factor S of 73 at room temperature [START_REF] Ul Afsar | High performance anion exchange membrane with proton transport pathways for diffusion dialysis[END_REF]. Highly charged hierarchical porous membranes increased the performance of diffusion dialysis with higher diffusion dialysis coefficient U H + of 0.0273 m/h and a separation factor S of 86.5 at 25°C [START_REF] Bakangura | Highly charged hierarchically structured porous anion exchange membranes with excellent performance[END_REF]. Poly(DMAEM-co-g-MPS) gave a diffusion dialysis coefficient U H + of 0.016-0.029 m/h and a separation factor S of 23.3-87.7 [START_REF] Mondal | Improved acid recovery performance by novel Poly(DMAEMco-γ-MPS) anion exchange membrane via diffusion dialysis[END_REF]. PPO has good mechanical properties and allows easy membrane preparation for high acid recovery at room temperature [START_REF] Khan | BPPO-based anion exchange membranes for acid recovery via diffusion dialysis[END_REF][START_REF] Khan | Porous BPPO-based membranes modified by aromatic amine for acid recovery[END_REF][START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF].

Triethanolamine (TEA) appears as a better reagent for membrane preparation, compared to other quaternary ammonium groups. Indeed triethanolamine bears three highly hydrophilic hydroxyl groups ( -OH), which act as assisting groups to improve H + transfer during dialysis [START_REF] Mondal | Novel quaternized aromatic amine based hybrid PVA membranes for acid recovery[END_REF][START_REF] Emmanuel | Imidazolium functionalized anion exchange membrane blended with PVA for acid recovery via diffusion dialysis process[END_REF]. Secondly, the low acidity of triethanolamine, with pKa of 10.75, allows higher anion permeability because anions are dissociated easier from functional groups [START_REF] He | Facile preparation of 1,8-diazabicyclo[5.4.0]undec-7-ene based high performance anion exchange membranes for diffusion dialysis applications[END_REF]. In addition, the high alkalinity of triethanolamine induces higher adsorption of water molecules on positive groups, which, in turn, facilitates the conduction of anions [START_REF] He | Facile preparation of 1,8-diazabicyclo[5.4.0]undec-7-ene based high performance anion exchange membranes for diffusion dialysis applications[END_REF].

Here we present the first attempt to employ triethanolamine as a functional group in AEMs. Membrane properties were tailored by varying the triethanolamine content of the polymeric matrix. Membranes were characterized by Fourier-transform infrared spectroscopy (FTIR), and for morphology, IEC, water uptake, linear swelling ratio (LSR), thermal, chemical, and mechanical stability. Membranes were tested for acid recovery with a mixture of HCl and FeCl 2 by diffusion dialysis. The effect of temperature on the dialysis performance was also tested.

Experimental setup

Materials

PPO from Sigma-Aldrich (Germany). Triethanolamine, chlorobenzene, ethanol, chloroform, N-methyl-2-pyrrolidone (NMP), 2,2′-azobisisobutyronitrile (AIBN), N-bromosuccinimide (NBS), sodium chloride (NaCl), silver nitrate (AgNO 3 ), sodium sulfate (Na 2 SO 4 ), potassium chromate (K 2 CrO 4 ), hydrochloric acid (HCl), ferrous chloride (FeCl 2 •4H 2 O), methyl orange (MO) from Sinopharm Chemical reagent Co. Ltd, China. Distilled water was used.

Preparation of brominated PPO

Synthesis has been described [START_REF] Li | Comb-shaped polymers to enhance hydroxide transport in anion exchange membranes[END_REF] (Fig. 1). Typically, 6 g of PPO (50 mmol) is dissolved into 50 ml chlorobenzene in a round bottom flask containing a magnetic stirrer and reflexed condenser. 4.45 g NBS (25 mmol) and 0.25 g azobisisobutyronitrile (AIBN, 1.5 mmol) are added and the solution is stirred at 135°C for 3 h. After cooling to 25°C, the reaction mixture is poured into an excess of ethanol to precipitate the polymer. The polymer is filtered, washed with ethanol, re-dissolved into 60 mL chloroform then precipitated into an excess of ethanol. The polymer is collected as a light-yellow powder and dried under vacuum for 2 d at 40°C to yield brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) with a bromination ratio of 75%.

Fabrication of AEMs

We used the solution casting method to prepare membranes [START_REF] Khan | BPPO-based anion exchange membranes for acid recovery via diffusion dialysis[END_REF][START_REF] Khan | Development of BPPO-based anion exchange membranes for electrodialysis desalination applications[END_REF][START_REF] Khan | Preparation of anion exchange membranes from BPPO and dimethylethanolamine for electrodialysis[END_REF][START_REF] Khan | Design of anion exchange membranes and electrodialysis studies for water desalination[END_REF][START_REF] Kumar | Synthesis and characterization of polyaniline membranes withsecondary amine additive containing N,N′-dimethyl propylene urea for fuel cell application[END_REF][START_REF] Khan | Comparison of different quaternary ammonium groups on desalination performance of BPPO-based anion exchange membranes[END_REF]. We prepared a 8%w solution by dissolving 0.8 g of BPPO into 10 mL of NMP. 0.15, 0.25, 0.35, or 0.45 g of triethanolamine were added to obtain membranes named TEA-19, TEA-31, TEA-44, and TEA-56 respectively, where 19, 31, 44, and 56 refer to the weight percentage (w%) of triethanolamine into the membrane matrix. The reaction mixture was stirred 12 h at 40°C then casted onto a glass plate at 60°C for 24 h. Membranes were peeled off from glass plates and cleaned with deionized water. The chemical structure of the prepared membrane is also shown in Fig. 1.

Characterization

Instrumentation

1 H-NMR (proton nuclear magnetic resonance) with DMX 300 NMR spectrometer operating at 300 MHZ was used to monitor the bromination of PPO. AEM was analysed for attenuated total reflectance with a Vector 22, Bruker, (Massachusetts, MA, USA) FTIR spectrometer at 4,000-400 cm -1 . Field-emission scanning electron microscopy (FE-SEM, Sirion 200, FEI Company, USA) and atomic force microscopy (AFM) were used to observe the membrane morphology. Membrane thermal stability was tested using a Shimadzu Corporation, (Kyoto, Japan) TGA-50H analyzer under nitrogen flow with a heating rate of 10°C/min from 25°C to 800°C. Membrane mechanical stability was measured using Q800 dynamic mechanical analyzer (DMA, TA Instruments, Kyoto, Japan) at a stretch rate of 0.5 N/min.

Ion exchange capacity

IEC of membranes was determined by Mohr's method. Typically, the dried membrane samples were immersed in 1 M NaCl for 48 h to convert the charged sites into the Cl - form. Excess NaCl was removed from membranes by careful water cleaning then immersion into 0.5 M Na 2 SO 4 for 48 h. The concentration of released Cl -was determined by titration with 0.05 M AgNO 3 using K 2 CrO 4 as an indicator, and was calculated using the following equation [START_REF] Khan | Development of BPPO-based anion exchange membranes for electrodialysis desalination applications[END_REF]:

IEC AgNO AgNO Dry = C V W 3 3 (1)
where m, V, and C depict the dry weight of the membrane sample, titer value during titration, and the concentration of AgNO 3 solution, respectively.

Water uptake and LSR

To measure water uptake of the prepared membranes, the dried membrane samples were weighed and then immersed in water for 24 h at room temperature. After removing the surface water with tissue paper, wet weight was measured. Water uptake was calculated from the mass difference before and after the complete drying of the membranes, using the following equation [START_REF] Khan | Comparison of different quaternary ammonium groups on desalination performance of BPPO-based anion exchange membranes[END_REF][START_REF] Khan | Synthesis and characterization of stable anion exchange membranes for desalination applications[END_REF]:

W W W W R WET D RY DRY % = - × 100 (2)
where W WET and W DRY depict the wet and dry weights of membrane samples, respectively. The LSR was measured at 25°C. The membranes sample was cut into a 3 cm 2 × 3 cm 2 pieces. The ratio was obtained using the following equation [START_REF] Khan | Preparation of anion exchange membranes from BPPO and dimethylethanolamine for electrodialysis[END_REF]:

LER WET D RY DRY = - ( ) × L L L 100% (3)
where L WET and L DRY denote wet and dry lengths of membrane samples, respectively.

Chemical stability

To investigate membrane chemical stability, membrane samples were immersed in HCl/FeCl 2 feed solution at 55°C. The change in weight as a function of immersion time was calculated to measure chemical stability.

Diffusion dialysis of HCl/FeCl 2

The acid recovery performance of anionic exchange membranes reported in our previous work [START_REF] Khan | Fabrication and characterization of pyridinium functionalized anion exchange membranes for acid recovery[END_REF][START_REF] Khan | Porous BPPO-based membranes modified by aromatic amine for acid recovery[END_REF]. Typically, the experiment was carried out in a two-compartment stack separated by the AEM. The effective area of the used membrane is 5.7 cm 2 . The membrane sample is conditioned in the feed solution of 0.89 M HCl and 0.25 M FeCl 2 for 5 h, which stimulates waste acid solution prior to the test. One compartment of the stack is filled up with a 100 mL feed solution, while the other side with 100 mL deionized water during the experiment. Both solutions are stirred 60 min. vigorously in order to minimize the concentration polarization. Then both feed and permeate are taken from the different compartments. The concentrations of H + in both compartments were measured by titration, while Fe 2+ concentration was measured by inductively coupled plasma spectrophotometry (ICP, Optima 7300 DV).

The dialysis coefficient U is calculated using the following equation [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF]:

U M At C = ∆ ( 4
)
where M is the concentration of the transported component in mol, A depicts the effective membrane area in m 2 , t denotes the time in h, and ∆C represents the logarithm average concentration between the two chambers in mol/m 3 . ∆C is measured as below [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF]:

∆C C C C C C C f f t d t f f t d t = - - ( ) - ( )     0 0 ln / (5)
where C f 0 and C f t are feed concentrations at time 0 and t, respectively, and C d t is the dialysate. Dialysis coefficient U H and U Fe can be measured using Eqs. ( 4) and [START_REF] Khan | Fabrication and characterization of pyridinium functionalized anion exchange membranes for acid recovery[END_REF]. The separation factor S is ratio of dialysis coefficients U of the two species present in the solution. S is calculated by [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF]:

S U U H Fe = (6)

Results and discussion

Bromination of PPO

Brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) was synthesized by the bromination of PPO by NBS as a brominating agent and AIBN as initiator. Bromination can occur either at the benzylic position or at the aromatic ring depending on the reaction condition and reagents [START_REF] Li | Comb-shaped polymers to enhance hydroxide transport in anion exchange membranes[END_REF][START_REF] Xu | Fundamental studies of a new series of anion exchange membranes: membrane preparation and characterization[END_REF]. In this research, it occurred at the benzylic position of PPO in refluxing chlorobenzene solution at 135°C. The structure and degree of BPPO were investigated by 1 H-NMR spectroscopy (Fig. 2). The benzyl bromide group is located at 4.3 ppm. The degree of bromination is 75%, it is the percentage of the integral area of the benzyl bromide group vs. the unreacted benzyl signal at 2.1 ppm.

Quaternization of brominated PPO

FTIR spectroscopy was used to check the quaternization of BPPO with triethanolamine. Fig. 3 shows the FTIR spectra of the pristine BPPO membrane and of the BPPO membrane containing 65% triethanolamine (TEA-56). The band at 1,608 cm -1 is due to C=C stretching in phenyl groups; the peak at 1,190 cm -1 is characteristic of C-O-C stretching [START_REF] Wu | New anion exchanger organic-inorganic hybrids and membranes from a copolymer of glycidylmethacrylate and -methacryloxypropyl trimethoxy silane[END_REF]. The bands at 1,446 cm -1 are attributed to -CH stretching (V and δ) [START_REF] Wu | Anion exchange hybrid membranes from PVA and multi-alkoxy silicon copolymer tailored for diffusion dialysis process[END_REF]. Symmetrical and asymmetrical stretching of C-O are at 1,200 and 1,306 cm -1 , and those of phenyl groups at 1,470 and 1,600 cm -1 respectively [START_REF] Khan | Preparation of anion exchange membranes from BPPO and dimethylethanolamine for electrodialysis[END_REF]. The band at 750 cm -1 is attributed to C-Br stretching in the pristine BPPO membrane [START_REF] Arges | Mechanically stable poly(arylene ether) anion exchange membranes prepared from commercially available polymers for alkaline electrochemical devices[END_REF].

The triethanolamine-containing membrane shows a characteristic band at 1,080 cm -1 associated with C-N stretching, thus demonstrating the successful reaction of BPPO and triethanolamine. Other characteristic bands include -OH stretching of triethanolamine at 3,435 cm -1 ; a peak at 2,940 cm -1 due to the -CH 2 group of triethanolamine attached to the BPPO backbone. Noteworthy, the signal for C-Br stretching in bromobenzyl groups at 750 cm -1 disappeared after the reaction of triethanolamine with BPPO [START_REF] Arges | Mechanically stable poly(arylene ether) anion exchange membranes prepared from commercially available polymers for alkaline electrochemical devices[END_REF][START_REF] Li | Fundamental studies of a new series of anion exchange membranes: membranes prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) and pyridine[END_REF]. Overall, our findings confirm the successful grafting of triethanolamine with the BPPO backbone.

Membrane morphology

The morphology of anionic exchange membranes prepared with 19% and 56% triethanolamine was studied by scanning electron microscopy (SEM) (Fig. 4a). Results show that membranes are free from any hole or crack in surfaces and cross-sections, thus confirming their homogeneous nature. Moreover, the membrane homogeneity is enhanced by increasing the concentration of triethanolamine into the membrane matrix. This finding is explained by higher miscibility with an increasing amount of triethanolamine into the polymer matrix. Overall, the homogeneous morphology of the membranes makes them suitable for acid recovery via diffusion dialysis. Membrane surfaces were also analyzed by AFM at room temperature (Fig. 4b). Results show again that the membranes are homogeneous without any phase separation.

Ion exchange capacity

The IEC of the prepared membranes, measured by the Mohr's method, is given in Table 1. Results show that the IEC increases from 1.28 to 2.28 mmol/g by increasing the amount of triethanolamine in the polymer matrix. The IEC depicts the number of exchangeable ion-conducting groups and thus controls the ion conductivity and swelling ratio of membranes. The IEC also provides information on the membrane charge density, which is related to their conductivity and transport properties [START_REF] Khan | Preparation of anion exchange membranes from BPPO and dimethylethanolamine for electrodialysis[END_REF]. Our results thus imply higher anion permeability and, in turn, higher performance for diffusion dialysis.

Water uptake and linear swelling ratio

Table 1 depicts the water uptake of the membranes prepared with 19%-56% triethanolamine at room temperature. Results show an increase in water uptake from 12% to 117% with triethanolamine content. This finding implies that hydrophilicity can be controlled and that ion permeability and mechanical properties can be tailored for diffusion dialysis applications. Indeed, water molecules are involved in ion transport and, as a consequence, a moderate water uptake is required for higher anion permeability [START_REF] He | Facile preparation of 1,8-diazabicyclo[5.4.0]undec-7-ene based high performance anion exchange membranes for diffusion dialysis applications[END_REF]. Nonetheless, too much water may reduce mechanical and dimensional stability. Overall, our membranes display a suitable water uptake for diffusion dialysis.

Table 1 presents linear swelling ratio (LSR) of prepared membranes. Results show that LSR increases from 3.51% to 32.70 % with increasing the amount of triethanolamine into the polymer matrix. These findings imply that the membranes exhibit excellent swelling resistance, which is required for diffusion dialysis.

Diffusion dialysis coefficient and separation selectivity

We used a mixture of HCl and FeCl 2 as a model of acidic wastewater to test the membrane performances, similarly to previous reports [START_REF] Khan | BPPO-based anion exchange membranes for acid recovery via diffusion dialysis[END_REF][START_REF] Khan | Porous BPPO-based membranes modified by aromatic amine for acid recovery[END_REF][START_REF] Emmanuel | Imidazolium functionalized anion exchange membrane blended with PVA for acid recovery via diffusion dialysis process[END_REF]. The diffusion dialysis coefficient of HCl (U H + ) and metal (U Fe 2+ ) of our membranes are shown in Fig. 5a. Results show that U H + ranges from 1.3 to 23 × 10 -3 m/h, and that U Fe 2+ ranges from 0.0025 to 0.61 × 10 -3 m/h at room temperature. Our membranes have thus higher U H + values than the commercial DF-120B membranes (4 × 10 -3 m/h) [START_REF] Khan | BPPO-based anion exchange membranes for acid recovery via diffusion dialysis[END_REF], PVA-based hybrid membranes (11-18 × 10 -3 m/h) [START_REF] Cheng | Facile and cost effective PVA based hybrid membrane fabrication for acid recovery[END_REF] and PPO-based membranes (0.37-20 × 10 -3 m/h) at 25°C [START_REF] Ul Afsar | High performance anion exchange membrane with proton transport pathways for diffusion dialysis[END_REF].

The increase of U H + and U Fe 2+ with triethanolamine content is explained by higher water uptake and IEC, leading to enhanced membrane hydrophilicity. In addition, the free hydroxyl groups of triethanolamine are assistant functional groups that accelerate the transport of H + ions through hydrogen bonding [START_REF] Mondal | Novel quaternized aromatic amine based hybrid PVA membranes for acid recovery[END_REF]. The higher values of U H + is explained by the much smaller ionic radius of H + vs. Fe 2+ [START_REF] Luo | Diffusion dialysis of hydrochloride acid at different temperatures using PPO-SiO 2 hybrid anion exchange membranes[END_REF].

The separation selectivity is calculated by the separation factor S, defined as a ratio of U H + to U Fe 2+ . Fig. 5b shows that our membranes have S ranging from 37 to 495 at room temperature. These values are much higher than that of the commercial DF-120B membrane [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF], BPAES-based Table 1 Theoretical ion exchange capacity (IEC), experimental ion exchange capacity, water uptake (W R ), and linear swelling ratio (LSR) of anionic exchange membranes prepared with 19%, 31%, 44%, and 56% of triethanolamine (TEA). Results show that all factors increase with triethanolamine amount in the polymer matrix at 25°C membranes [START_REF] Feng | Seriesconnected hexacations cross-linked anion exchange membranes for diffusion dialysis in acid recovery[END_REF] and BPPO-Im/GO membranes based membranes [START_REF] Ran | Graphene oxide embedded "three-phase" membrane to beat "trade-off" in acid recovery[END_REF]. Furthermore, our results show that S decreases with triethanolamine content (Fig. 5b). This decrease is explained by higher water uptake and swelling ratio (Table 1), which enlarges the spaces between polymer chains and, in turn, favors the permeability of Fe 2+ .

Effect of temperature

We selected the anionic exchange membrane prepared with 56% triethanolamine to test the effect of temperature, from 25°C to 55°C, on the performance of diffusion dialysis of H + and Fe 2+ (Fig. 6a). Results show an increase of U H + from 23 to 71 × 10 -3 m/h, and of U Fe 2+ from 0.61 to 4.2 × 10 -3 m/h with temperature. These findings agree with enhanced ion transport at higher temperatures [START_REF] Luo | Diffusion dialysis of hydrochloride acid at different temperatures using PPO-SiO 2 hybrid anion exchange membranes[END_REF][START_REF] Lin | Fabrication of asymmetrical diffusion dialysis membranes for rapid acid recovery with high purity[END_REF]. Further, the effect of temperature on the separation factor S is shown in Fig. 6b. Data shows that S decreases from 37 to 17 with temperature. This finding is explained by the easier transfer of Fe 2+ vs. H + at higher temperatures [START_REF] Luo | Diffusion dialysis of hydrochloride acid at different temperatures using PPO-SiO 2 hybrid anion exchange membranes[END_REF][START_REF] Lin | Fabrication of asymmetrical diffusion dialysis membranes for rapid acid recovery with high purity[END_REF]. Overall the high U H + values of our membrane imply an excellent diffusion dialysis performance at various temperatures.

Comparison of various membranes

Fig. 7 compares the performances of our membranes with reported membranes [START_REF] Cheng | Facile and cost effective PVA based hybrid membrane fabrication for acid recovery[END_REF][START_REF] Khan | BPPO-based anion exchange membranes for acid recovery via diffusion dialysis[END_REF][START_REF] Emmanuel | Covalently cross-linked Table 2 Tensile strength (TS) and elongation at break of the prepared anion exchange membranes Membranes TEA-19 TEA-31 TEA-44 TEA-56 TS[END_REF][START_REF] Wu | Anion exchange hybrid membranes from PVA and multi-alkoxy silicon copolymer tailored for diffusion dialysis process[END_REF][START_REF] Ul Afsar | High performance anion exchange membrane with proton transport pathways for diffusion dialysis[END_REF][START_REF] Luo | Diffusion dialysis of hydrochloride acid at different temperatures using PPO-SiO 2 hybrid anion exchange membranes[END_REF][START_REF] Wu | Combination of OHions and -OH groups within QPPO/PVA hybrid membranes for acid recovery[END_REF][START_REF] Wu | PVA-silica anionexchange hybrid membranes prepared through a copolymer crosslinking agent[END_REF][START_REF] Wu | Bionic multisilicon copolymers used as novel cross-linking agents for preparing anion exchange hybrid membranes[END_REF][START_REF] Pan | Anion exchange membranes from hotpressed electrospun QPPO-SiO 2 hybrid nanofibers for acid recovery[END_REF]. Two parameters are displayed, the diffusion dialysis coefficient of acid U H + and the separation factor S. Results show that our membranes have the second-highest U H + value and the highest separation factor S. Therefore our membranes are very promising for acid recovery from industrial wastewater by diffusion dialysis.

Thermal and chemical stability

We selected the AEM prepared with 56% triethanolamine to test the thermal stability from 30°C to 800°C by thermogravimetric analysis. Fig. 8a shows the thermogravimetric curves of pristine membranes and membranes prepared with 56% triethanolamine. Results show that weight loss takes place in three successive steps, corresponding to evaporation of adsorbed water at 80°C-130°C, thermal deamination, and thermal oxidation of the polymer backbone. The second step at 230°C-240°C is explained by the degradation of quaternary ammonium groups [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF].

The last step around 415°C is due to the degradation of the polymer backbone. Overall, our membranes have excellent thermal stability below 300°C.

The chemical stability of the membrane was also tested by immersion into HCl/FeCl 2 for 2 weeks at 55°C (Fig. 8b). Results show a weight loss of about 15%, in agreement with our previous reported membranes [START_REF] Khan | Preparation of pyrrolidinium-based anion-exchange membranes for acid recovery via diffusion dialysis[END_REF]. Moreover, we also observed that the color of our membrane is unchanged after two weeks of immersion in HCl/FeCl 2 feed solution at 55°C. Overall, our AEMs display good chemical stability and are thus promising for acid recovery from wastewater.

Mechanical stability

We studied membrane mechanical stability by measuring tensile strength (TS) and elongation at break (E b ) of AEMs prepared with 19%-56% triethanolamine, in the wet state (Table 2). Results show that TS ranges from 19.27 to 31.85 MPa. These values are higher than our previously reported AEM [START_REF] Khan | Synthesis and characterization of stable anion exchange membranes for desalination applications[END_REF], which implies that the membranes of this work have excellent mechanical stability. The elongation at break ranges from 12.53% to 39.47%, which are lower than hybrid AEMs [START_REF] Mondal | Novel quaternized aromatic amine based hybrid PVA membranes for acid recovery[END_REF]. TS decreases and elongation at break increases with triethanolamine content. The decrease in TS with enhanced IEC agrees with previous research [START_REF] Khan | Preparation of diffusion dialysis membrane for acid recovery via a phase-inversion method[END_REF]. The membrane prepared with 56% triethanolamine displays excellent flexibility due to lower tensile strength and higher elongation at break. By contrast, the AEM prepared with 19% triethanolamine exhibits high tensile strength and low elongation at break.

Conclusion

We prepared AEMs from PPO and triethanolamine by solution casting method. The successful synthesis was confirmed by FTIR spectroscopy. The homogeneous morphology was confirmed by SEM and AFM. Membranes exhibited optimal IEC and water uptake essential for diffusion dialysis applications. Membranes showed IEC of 1.28 to 2.29 mmol/g, water uptake of 12%-117%, LSR of 3.52% to 32.70%. The IEC, water uptake, and LSR increase with triethanolamine content into the polymer matrix. The membranes were tested for acid recovery by diffusion dialysis. Results showed that membranes exhibit high value of U H + , of 1.3-23 × 10 -3 m/h, and of separation factor, from 37 to 495, at room temperature. Membranes exhibit higher chemical, thermal, and mechanical stability. Overall, our findings reveal that the triethanolamine-functionalized AEMs are promising candidates for acid recovery from industrial acidic wastewater by diffusion dialysis.

Fig. 1 .

 1 Fig. 1. Preparation of brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)-based anion exchanged membranes. NBS: N-Bromo-succinimide; AIBN: 2,2′-azobisisobutyronitrile; TEA: triethanolamine, NMP: N-methyl-2-pyrrolidone, AEM: anion exchange membrane.

Fig. 2 .

 2 Fig. 2. 1 H-NMR spectrum of brominated poly(2,6-dimethyl-1,4-phenylene oxide) synthesized by bromination of poly(2,6-dimethyl-1,4-phenylene oxide). The presence of a peak at 4.3 ppm reveals the successful bromination at benzylic positions.

Fig. 3 .

 3 Fig. 3. Infrared spectra of pristine brominated poly(2,6dimethyl-1,4-phenylene oxide) (BPPO) and the membrane prepared with 56% triethanolamine (TEA-56), confirming successful synthesis.

Fig. 4 .

 4 Fig. 4. (a) Surface and cross-section of anionic exchange membranes prepared with 19% (TEA-19) and 56% triethanolamine (TEA-56), analyzed by scanning electron microscopy (SEM). (b) Analysis by atomic force microscopy. Results show that membrane surfaces and sections are homogeneous.

Fig. 5 .

 5 Fig. 5. (a) Diffusion dialysis coefficient of acid, U H + , and metal, U Fe 2+ , and (b) separation factor S for membranes prepared with 19%-56% of triethanolamine (TEA). Results show an increase of U and a decrease of S with triethanolamine content.

Fig. 6 .

 6 Fig. 6. (a) Diffusion dialysis coefficient of acid (U H + ) and metal (U Fe 2+ ) and (b) separation factor (S) for the membrane prepared with 56% triethanolamine (TEA-56). Results show an increase of U and a decrease of S with temperature.

Fig. 7 .

 7 Fig. 7. (a) Comparison of membrane performances. Diffusion dialysis coefficients of acid U H + and separation factor S of our membranes ('this work') vs. reported membranes employing HCl/FeCl 2 as the model acidic waste solution.

Fig. 8 .

 8 Fig. 8. (a) Thermogravimetric analysis of the pristine membrane and the membrane prepared with 56% triethanolamine (TEA-56) and (b) Weight loss of the TEA-56 membrane after immersion in HCl/FeCl 2 feed solution for two weeks at 55°C, showing high chemical stability.

Acknowledgment

The authors are highly thankful for the financial support from the Basic Science Center Program for Ordered Energy Conversion of the National Natural Science Foundation of China (51888103).


Nikolay Gromov
email: gromov@catalysis.ru

Oxana P Taran

Cyril Aymonier

Valentin N Parmon

Kinetic modeling of the multistep hydrolysis-dehydration of cellulose to platform molecules over a solid carbon acid catalyst in pure water

Keywords: Cellulose, hydrolysis-dehydration, kinetics, modeling, Sibunit, carbon catalyst

Article Highlights

 Hydrolysis-dehydration of cellulose and process intermediates into glucose and 5-HMF platform molecules was studied  Reactions were carried out over Sibunit carbon catalyst at 180 °C. 18-step kinetic model of the process was proposed  Software modeling described the cellulose hydrolysis-dehydration with a sufficient accuracy

Introduction

In the recent years research efforts have been focused on cellulose as a promising alternative raw material for chemical and fuel industries. Unlike oil, gas and coal traditional recourses, cellulose has a lot of advantages which are renewability, availability, comparatively low cost, as well as an absence of competition with the food industry for land and other resources [START_REF] Negahdar | Aqueous-phase hydrolysis of cellulose and hemicelluloses over molecular acidic catalysts: Insights into the kinetics and reaction mechanism[END_REF][START_REF] Van Putten | Hydroxymethylfurfural, A Versatile Platform Chemical Made from Renewable Resources[END_REF][START_REF] Besson | Conversion of Biomass into Chemicals over Metal Catalysts[END_REF][START_REF] Yang | Recent Developments in the Catalytic Conversion of Cellulose into Valuable Chemicals[END_REF][START_REF] Bhaumik | Solid acid catalyzed synthesis of furans from carbohydrates[END_REF]. The cellulose resources may be agricultural and wood processing wastes. Hydrolytic cellulose processing is one of the most actual fields of fine chemistry. This method of cellulose transformation, itself or combined with other processes, for example oxidation [START_REF] Gromov | Hydrolytic oxidation of cellulose to formic acid in the presence of Mo-V-P heteropoly acid catalysts[END_REF][START_REF] Wolfel | Selective catalytic conversion of biobased carbohydrates to formic acid using molecular oxygen[END_REF][START_REF] Maki-Arvela | Recent Progress in Synthesis of Fine and Specialty Chemicals from Wood and Other Biomass by Heterogeneous Catalytic Processes[END_REF] or reduction [START_REF] Maki-Arvela | Recent Progress in Synthesis of Fine and Specialty Chemicals from Wood and Other Biomass by Heterogeneous Catalytic Processes[END_REF][START_REF] Liu | Polyoxometalate-supported ruthenium nanoparticles as bifunctional heterogeneous catalysts for the conversions of cellobiose and cellulose into sorbitol under mild conditions[END_REF][START_REF] Fukuoka | Catalytic Conversion of Cellulose into Sugar Alcohols[END_REF][START_REF] Gromov | The main factors affecting the catalytic properties of Ru/Cs-HPA systems in one-pot hydrolysis-hydrogenation of cellulose to sorbitol[END_REF], is suitable for the synthesis of valuable chemicals and non-petroleum fuels [START_REF] Van Putten | Hydroxymethylfurfural, A Versatile Platform Chemical Made from Renewable Resources[END_REF][START_REF] Gallezot | Conversion of biomass to selected chemical products[END_REF][START_REF] Serrano-Ruiz | Conversion of cellulose to hydrocarbon fuels by progressive removal of oxygen[END_REF].

Cellulose hydrolysis-dehydration can be applied in the production of platform compounds: glucose, 5-hydroxymethylfurfural (5-HMF) and levulinic acid [START_REF] Van Putten | Hydroxymethylfurfural, A Versatile Platform Chemical Made from Renewable Resources[END_REF][START_REF] Bhaumik | Solid acid catalyzed synthesis of furans from carbohydrates[END_REF][START_REF] Maki-Arvela | Recent Progress in Synthesis of Fine and Specialty Chemicals from Wood and Other Biomass by Heterogeneous Catalytic Processes[END_REF][START_REF] Gallezot | Conversion of biomass to selected chemical products[END_REF][START_REF] Rackemann | The conversion of lignocellulosics to levulinic acid[END_REF]. The process proceeds efficiently in the presence of solid acid catalysts such as metal oxides [START_REF] Onda | Selective hydrolysis of cellulose into glucose over solid acid catalysts[END_REF], nanodisperse metals [START_REF] Kobayashi | Water-tolerant mesoporous-carbonsupported ruthenium catalysts for the hydrolysis of cellulose to glucose[END_REF], resins [START_REF] Onda | Selective hydrolysis of cellulose into glucose over solid acid catalysts[END_REF], and modified carbon materials [START_REF] Pang | Hydrolysis of cellulose into glucose over carbons sulfonated at elevated temperatures[END_REF]. Recently we reported solid acid catalysts based on Sibunit carbon material which demonstrated high activity in hydrolysis-dehydration of cellulose to glucose and 5-HMF [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF].

Research facilities in the field of cellulose hydrolysis-dehydration are not only aimed at the search for promising catalysts, process conditions and significant yields of the target products, but also search process mechanisms and kinetic parameters [START_REF] Negahdar | Aqueous-phase hydrolysis of cellulose and hemicelluloses over molecular acidic catalysts: Insights into the kinetics and reaction mechanism[END_REF]. The kinetic studies and modeling of cellulose depolymerization into various chemicals are not trivial task. Cellulose hydrolysisdehydration is a complex multistep process. It proceeds through a lot of pathways and a large number of intermediates can be formed [START_REF] Gromov | CHAPTER 3 Catalysts for Depolymerization of Biomass[END_REF]. Nevertheless, the simplest two-stage model of cellulose depolymerization was suggested in 1945 [START_REF] Saeman | Kinetics of Wood Saccharification -Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature[END_REF]. It included the cellulose conversion to the target products at the first stage and the decomposition of the target product at the second stage [START_REF] Jacobsen | Cellulose and hemicellulose hydrolysis models for application to current and novel pretreatment processes[END_REF][START_REF] Abasaeed | Effect of transient heat transfer and particle size on acid hydrolysis of hardwood cellulose[END_REF][START_REF] Orozco | Dilute Acid Hydrolysis of Cellulose and Cellulosic Bio-Waste Using a Microwave Reactor System[END_REF][START_REF] Mok | Productive and parasitic pathways in dilute acidcatalyzed hydrolysis of cellulose[END_REF][START_REF] Rogalinski | Hydrolysis of lignocellulosic biomass in water under elevated temperatures and pressures[END_REF][START_REF] Mosier | Characterization of acid catalytic domains for cellulose hydrolysis and glucose degradation[END_REF][START_REF] Camacho | Microcrystalline-cellulose hydrolysis with concentrated sulphuric acid[END_REF][START_REF] Malester | Kinetics of dilute acid hydrolysis of cellulose originating from municipal solid wastes[END_REF][START_REF] Franzidis | The acid hydrolysis of cellulose in refuse in a continuous reactor[END_REF]:

k 1 k 2 Polysaccharide
Decomposition products Hydrolysis products Abatzoglou and co-authors reported a more complex kinetic model which involved separate stages of polysaccharide transformation into water-soluble oligosaccharides, their hydrolysis and the decomposition of the target products [START_REF] Abatzoglou | Dilute acid depolymerization of cellulose in aqueous phase: Experimental evidence of the significant presence of soluble oligomeric intermediates[END_REF][START_REF] Sribala | Unified Kinetic Model for Cellulose Deconstruction via Acid Hydrolysis[END_REF][START_REF] Bouchard | Characterization of depolymerized cellulosic residues[END_REF]:

k 1 k 2 Oligosaccharides k 3 Polysaccharide
Decomposition products Hydrolysis products Some other models reported previously took into account amorphous and crystalline domains in cellulose structure which were respectively easy and hard to hydrolyze [START_REF] Negahdar | Aqueous-phase hydrolysis of cellulose and hemicelluloses over molecular acidic catalysts: Insights into the kinetics and reaction mechanism[END_REF][START_REF] Mok | Productive and parasitic pathways in dilute acidcatalyzed hydrolysis of cellulose[END_REF][START_REF] Xiang | A comprehensive kinetic model for dilute-acid hydrolysis of cellulose[END_REF][START_REF] Fagan | Kinetics of the acid hydrolysis of cellulose found in paper refuse[END_REF] Kinetic equations of these models are used for calculating reaction constants, activations energies of stages and pre-exponential factors of kinetic constants. When modeling kinetics, all reactions involved are usually considered as irreversible and first order [START_REF] Saeman | Kinetics of Wood Saccharification -Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature[END_REF][START_REF] Xiang | A comprehensive kinetic model for dilute-acid hydrolysis of cellulose[END_REF]. However, each kinetic model can be additionally modified for the observed experimental kinetic curves to be described more accurate. In particular, some stages can be regarded as reversible [START_REF] Abatzoglou | Dilute acid depolymerization of cellulose in aqueous phase: Experimental evidence of the significant presence of soluble oligomeric intermediates[END_REF][START_REF] Xiang | Heterogeneous aspects of acid hydrolysis of α-cellulose[END_REF], as well as side reactions of cellulose hydrolysis-dehydration can be included [START_REF] Rackemann | The conversion of lignocellulosics to levulinic acid[END_REF]. Conner and co-authors suggested a model of cellulose hydrolysis-dehydration which involved two reversible transformations of glucose into disaccharides and anhydrosugars [START_REF] Conner | Cellulose: Structure, Modification and Hydrolysis[END_REF]. Bahari et al. found kinetic parameters of β-glucosane and mannoprotein conversions to 5-HMF [START_REF] Bahari | Subcritical water mediated hydrolysis of cider spent yeast: Kinetics of HMF synthesis from a waste microbial biomass[END_REF]. Polysaccharide transformation scheme included five first-order stages [START_REF] Bahari | Subcritical water mediated hydrolysis of cider spent yeast: Kinetics of HMF synthesis from a waste microbial biomass[END_REF]. Cantero et al. studied the fast cellulose hydrolysis-dehydration in supercritical water to determine kinetic parameters and activation energies. The kinetic scheme was rather complex but they did not report the kinetic modeling of the process [START_REF] Cantero | Governing Chemistry of Cellulose Hydrolysis in Supercritical Water[END_REF]. Murzin and coauthors studied transformations of arabinogalactan polysaccharide using a scheme consisted of complex zero-order interconversions of the process intermediates. The kinetic scheme described the formation of furfural and 5-HMF as the major products via the formation of soluble oligosaccharides followed by their hydrolysis-dehydration. Several other routes of intermediate and target product transformations were also taken into consideration. The scheme was treated using a special software.

The knowledge on the mechanism and kinetic regularities are certainly helpful for better understanding of the cellulose hydrolysis-dehydration and for predicting the optimal process conditions. Kinetic investigations are useful for scaling-up the laboratory process to industry. The kinetic schemes of the production of glucose and/or 5-HMF from cellulose reported elsewhere are usually based on simple kinetic models and involve only the main products and several process stages [START_REF] Jacobsen | Cellulose and hemicellulose hydrolysis models for application to current and novel pretreatment processes[END_REF][START_REF] Abasaeed | Effect of transient heat transfer and particle size on acid hydrolysis of hardwood cellulose[END_REF][START_REF] Orozco | Dilute Acid Hydrolysis of Cellulose and Cellulosic Bio-Waste Using a Microwave Reactor System[END_REF][START_REF] Sribala | Unified Kinetic Model for Cellulose Deconstruction via Acid Hydrolysis[END_REF][START_REF] Gurgel | Dilute Acid Hydrolysis of Sugar Cane Bagasse at High Temperatures: A Kinetic Study of Cellulose Saccharification and Glucose Decomposition. Part I: Sulfuric Acid as the Catalyst[END_REF]. More complex kinetic schemes are rarely used because of the necessity of special software applications. The present study was focused on software modeling of the kinetics involving 18 stages of the cellulose hydrolysis-dehydration carried out over a solid acid catalyst based on sulfonated carbon material Sibunit.

Experimental

Chemicals

5-HMF (Sigma-Aldrich), D-fructose (Sigma-Aldrich), D-mannose (Sigma-Aldrich), Dglucose (Reahim, Moscow, Russia), D-cellobiose (Alfa Aesar), levulinic acid (Acros Organics)

were purchased and used as HPLC standards. Milli-Q water (Millipore, France) was used for all experiments. Microcrystalline pure cellulose (Vekton, Saint-Petersburg, Russia) was mechanically activated before all the experiments. The polysaccharide was milled in a discrete action planetary mill Pulverizette 5 (Fristch, Germany) as we described previously [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF]. The crystallinity of the activated sample revealed by XRD (BrukerD8 Advabced, Germany) was 37%. The measurements of crystallinity are described in detail in the Supporting Information (SI) and our previous work [START_REF] Gromov | Solid Acidic NbOx/ZrO2 Catalysts for Transformation of Cellulose to Glucose and 5-Hydroxymethylfurfural in Pure Hot Water[END_REF]. The particle size measured by optical microscopy (Zeiss -Axiostar plus microscope equipped with a photocamera, Germany) was equal to 13±6 μm. The average diameter of cellulose particles was calculated as the mean diameters of 100 particles.

Preparation of Sibunit carbon acid catalyst

The catalyst was prepared from mesoporous graphite-like carbon material (commercial name Sibunit, Omsk, Russia) via sulfonation in fuming H2SO4 as we reported previously [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF].

Before preparing the catalyst, the carbon material was washed several times with boiling Milli-Q water. Then Sibunit was grinded and sifted through several sieves. The fraction of 560-940 μm was collected and washed again several times with boiling Milli-Q water. The typical procedure for preparing catalyst was the following. 1 g. of the grinded carbon was placed into a glass vessel. 15 mL of fuming H2SO4 was added. The vessel was heated upto 200 °C. The sulfonation time was 10 h. When the treatment was finished, the flask was cooled down. The catalysts was separated from the sulfuric acid, washed with boiling Milli-Q water and air-dried [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF]. The catalyst was characterized by TEM, XRF, N2 adsorption and acid-base titration with NaOH [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF]. From TEM and low-temperature N2 adsorption data, the carbon catalyst consisted of spherical carbon globules with the specific surface area of 400 m 2 •g -1 . The catalyst surface acidity equal to 0.40 mmol•g -1 was determined by acid-base titration. Before any catalytic experiment the catalyst was treated under hydrothermal conditions to remove weakly fixed acidic groups. Analysis of the treated catalyst by XRF revealed high stability of the sulfur content in the catalyst at the temperature up to 200 °C [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF].

Catalytic tests

Hydrolysis-dehydration of cellulose over the Sibunit carbon catalyst was studied in a batch hastelloy autoclave (Autoclave Engineers, USA) at 180 °C, 1 MPa of Ar, under 1500 rpm stirring.

The scheme of the experimental setup is shown in Fig. 1. Cellulose, catalyst and deionized Milli-Q water were placed into the reactor. Both the catalyst and cellulose concentrations were 10 g•L -1 . The volume of the reaction mixture was 45 mL. The autoclave was closed, the air was replaced with argon. The reactor was heated to 180 ºC, whereupon the reaction was started. Aliquots (~1 mL) of the reaction mixture were drawn from the reactor in 0, 1, 2, 3, 5 and 7 hours for HPLC analysis [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF].

The transformations of cellulose hydrolysis-dehydration intermediates (cellobiose, glucose, fructose, 5-HMF, etc.) were also studied. Experiments in the batch reactor were carried out in the same way as cellulose transformation.

Aliquots of the reaction mixtures were analyzed by HPLC Shimadzu Prominence LC-20

(Japan) setup equipped with Rezex ROA-Organic Acids (Phenomenex, 300 mm•5.0 mm) column thermostated at 40 °C and refractive index and diode array detectors. The eluent was 1.25 mM H2SO4, the flow rate was 0.6 mL min -1 .

Product yields (Y) were calculated according to the formula (1):

 CV Y m N M Product cellucose glucan = ×100 ×( ) , (1)
where Y was a yield (%), CProduct (mol L -1 ) was the concentration of a product, V was the solution volume (L), N was a stoichiometric coefficient between a glucan unit and a product (1 for glucose and 5-HMF, 6 for formic acid etc.), mcellulose was the mass of cellulose loaded to the reactor (g), and

Mglucan was the molar mass of a glucan unit in cellulose (162 g•mol -1 ).

To evaluate cellulose consumption, the reaction was carried out without drawing down any aliquots during 1, 2, etc. hours. The solids were separated from the reaction mixture by centrifugation, dried and weighted.

Cellulose consumption was calculated as following (2):

0 0 m -m X= m , (2)
where X was cellulose consumption (%), m and m0 were masses of cellulose (g) after and before the reaction, respectively.

Results and Discussion

Hydrolysis-dehydration of cellulose and main process intermediates

Cellulose hydrolysis-dehydration was experimentally studied using a batch reactor at 180 °C under inert atmosphere (argon pressure was 1 MPa) in the presence of a solid acid carbon catalyst.

HPLC was used for analysis of the reaction mixture (Fig. 2 a). The maximal yield of glucose (45.9 %) was achieved in 2 h of the reaction. The maximal yield of 5-HMF was 18 % (5 h reaction time).

It is mentioned above that cellulose transformation is a complex multistep process involving a large number of stages and intermediates [START_REF] Feather | Dehydration Reactions of Carbohydrates°[END_REF]. In studying the complex chemical system, it is important to determine the basic process mechanism and all the reaction pathways, to identify intermediates and rate-determining stages. To model the cellulose hydrolysis-dehydration process, we proposed the kinetic scheme that took into account all the intermediates detected as well as the reactions between them (Scheme 1).

Main stages of the cellulose hydrolysis-dehydration process were separately studied.

Experiments where intermediates were substrates were carried out over the carbon catalyst in the batch autoclave. The process conditions were the same as ones for cellulose transformation (180 °C, the investigations reported previously. Thus, Saeman showed that the reaction order of hydrolytic cellulose transformations was in the range of 0.7-1.3 [START_REF] Saeman | Kinetics of Wood Saccharification -Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature[END_REF]. Bobleter and Bonn reported the first order of the cellobiose hydrolysis to glucose [START_REF] Bobleter | The hydrothermolysis of cellobiose and its reaction-product dglucose[END_REF]. Experimental data demonstrated that glucose consumption was much slower than fructose one. In case of glucose hydrolysis, fructose was practically not accumulated and converted rapidly to 5-HMF. The yield of 5-HMF achieved 33 % in the experiment where fructose was spent. This value was higher than the 5-HMF yield reached from glucose (16 %) (Fig. 2 c andd). The high yields of 5-HMF derived from fructose were reported previously [START_REF] Feather | Dehydration Reactions of Carbohydrates°[END_REF][START_REF] Ponder | Pyrolysis of inulin, glucose and fructose[END_REF]. In the experiment with fructose, 5-HMF accumulation stopped as soon as fructose was fully converted. Glucose transformation proceeded slower compared with fructose consumption and resulted in lower 5-HMF yield. This was the evidence that glucose isomerization to fructose was the limiting stage of the process while fructose dehydration to 5-HMF was a fast reaction (Scheme 1). The consumptions of glucose and fructose plotted in logarithmic coordinates had linear dependences on the process time (Fig. S2). The first reaction order of sugar conversions was reported elsewhere [START_REF] Saeman | Kinetics of Wood Saccharification -Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature[END_REF][START_REF] Wit | Enolisation and isomerisation of monosaccharides in aqueous, alkaline solution[END_REF][START_REF] Kabyemela | Glucose and Fructose Decomposition in Subcritical and Supercritical Water: Detailed Reaction Pathway, Mechanisms, and Kinetics[END_REF][START_REF] Baugh | Thermochemical pretreatment of lignocellulose to enhance methane fermentation: I. Monosaccharide and furfurals hydrothermal decomposition and product formation rates[END_REF]. According to the experimental data, mannose was formed from both glucose and fructose. The experiment with 5-HMF as a substrate revealed low stability of the compound. The conversion of 5-HMF reached 70 % in 7 h (Fig. 2 e). The formation of sugars was not observed what confirmed that dehydration of fructose to 5-HMF was an irreversible reaction.

1
On the other hand, levulinic and formic acids were not accumulated from 5-HMF in significant yields. These data confirmed the transformation of 5-HMF via alternative pathway of hightemperature polycondensation to give side products [START_REF] Bonn | Determination of the hydrothermal degradation products of D-(U-14C) glucose and D-(U-14C) fructose by TLC[END_REF][START_REF] Klinger | Influence of process parameters on the hydrothermal decomposition and oxidation of glucose in sub-and supercritical water[END_REF][START_REF] Sasaki | Cellulose hydrolysis in subcritical and supercritical water[END_REF]. When fructose and 5-HMF were used as substrates (Fig. 2 c and e), furfural was demonstrated only to form from fructose but not from 5-HMF. Minor yields of furfural equal to 1-2 % were observed. The kinetics of furfural transformation was also investigated (Fig. S1 b). Compared to 5-HMF, furfural demonstrated better stability under reaction conditions. Negligible yield of formic acid from furfural was detected, accumulation of sugars was not observed.

Kinetic modeling of the cellulose hydrolysis-dehydration

All the identified intermediates and products were added to the scheme of the reaction (Scheme 1). The constants of the reactions and chemical interactions were revealed from the experimental kinetic curves (Table 1). The kinetic modeling was based on the following assumptions. The first orders of all the stages were assumed as consumptions of all the intermediates had a linear dependence in ln(C/C0) vs time coordinates (Fig. S2). The rates of proton adsorption/desorption during cellulose dissolution in water and the diffusion rates to the surface of the Sibunit solid catalyst were high enough and the reaction constants revealed were of chemical interactions but not of diffusion.

Based on the experimental data (Scheme 1), a following system of differential equations was proposed for modeling the kinetic curves.

(I) where Cellb was Cellobiose, Glu was Glucose, Fru was Fructose, Man was Mannose, Furf -Furfural, LA was Levulinic acid, FA was Formic acid. X was a cellulose conversion applied instead of cellulose concentration. X value was used as cellulose was a insoluble compound [START_REF] Saeman | Kinetics of Wood Saccharification -Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature[END_REF][START_REF] Jiang | An improved kinetic model for cellulose hydrolysis to 5hydroxymethylfurfural using the solid SO4 2-/Ti-MCM-41 catalyst[END_REF].

0 d X(t) k (1 X(t)) dt     , (II) 01 d Olig(t) k (1 X)(t) k Olig(t) dt      , (
The constant k0 of cellulose dissolution determined from the cellulose consumption measured according to the formula (2) was equal to 16•10 -3 min -1 . The constant meaning was low enough compared to k2 determined experimentally from cellobiose transformations (0.11 min -1 ).

This indicated that cellulose transformation to water soluble oligosaccharides but not hydrolysis itself was a limiting stage of cellulose processing. When modeling cellulose hydrolysis-dehydration the value of k1 of water-soluble oligomer hydrolysis was assumed to be equal to k2 as both constants described the cleavage of the β-(1-4)-glycosidic bond (Scheme 1). Hydrolysis constant was more than other constants by an order of magnitude. Hence, hydrolysis proceeded at a very high rate. The revealed constant k3 of isomerization of glucose to fructose was lower than the observed constant k5 of fructose dehydration to 5-HMF by a factor of 2.4. That demonstrated glucose consumption to fructose was limited by isomerization to result in a decrease in the yield of 5-HMF. Constants k3 determined from kinetic experiments with glucose as a substrate was 8.0•10 -3 .

The value of k31 was evaluated from thermodynamic data. According to Tewari and Goldberg, equilibrium constant for glucose-fructose isomerization at 180 °C is 2.6 [START_REF] Tewari | Thermodynamics of the conversion of aqueous glucose to fructose[END_REF]. This came to k31=k3/K=8.0•10 -3 /2.6=3.07•10 -3 min -1 . Delidovich and co-authors reported that a certain combination of the equilibrium constants for the interconversions of monosaccharides was equal to 1 [START_REF] Delidovich | Production of keto-pentoses via isomerization of aldo-pentoses catalyzed by phosphates and recovery of products by anionic extraction[END_REF]. Thus, 3 4 43 When modeling the cellulose hydrolysis-dehydration additional degradation of glucose, fructose and mannose monosaccharides was presumed via pathways with rate constants k30, k50 and k40, respectively. Contradictory data on an existence of these side transformations were shown previously. Thus, fructose transformation to glyceraldehydes and then to pyruvaldehyde and lactic acid was revealed by some researchers [START_REF] Cantero | Governing Chemistry of Cellulose Hydrolysis in Supercritical Water[END_REF][START_REF] Kabyemela | Glucose and Fructose Decomposition in Subcritical and Supercritical Water: Detailed Reaction Pathway, Mechanisms, and Kinetics[END_REF][START_REF] Klinger | Influence of process parameters on the hydrothermal decomposition and oxidation of glucose in sub-and supercritical water[END_REF][START_REF] Aida | Reactions of d-fructose in water at temperatures up to 400 °C and pressures up to 100 MPa[END_REF][START_REF] Jr | Mechanism of formation of 5-(hydroxymethyl)-2furaldehyde from d-fructose and sucrose[END_REF]. On the other hand, some doubt of the occurrence of these routes in the presence of an acid catalyst at temperatures below 270 °C was stated [START_REF] Bonn | Determination of the hydrothermal degradation products of D-(U-14C) glucose and D-(U-14C) fructose by TLC[END_REF]. Similar to fructose, dehydration of glucose to 1,6-anhydroglucose [START_REF] Kabyemela | Glucose and Fructose Decomposition in Subcritical and Supercritical Water: Detailed Reaction Pathway, Mechanisms, and Kinetics[END_REF][START_REF] Klinger | Influence of process parameters on the hydrothermal decomposition and oxidation of glucose in sub-and supercritical water[END_REF] as well as cleavage of glucose to erythrose could take place [START_REF] Kabyemela | Glucose and Fructose Decomposition in Subcritical and Supercritical Water: Detailed Reaction Pathway, Mechanisms, and Kinetics[END_REF][START_REF] Sasaki | Cellulose hydrolysis in subcritical and supercritical water[END_REF][START_REF] Aida | Reactions of d-fructose in water at temperatures up to 400 °C and pressures up to 100 MPa[END_REF]. The modeling made in the present work confirmed the existence of fructose and glucose decomposition to side products. Thus, when the value of k50 was equated with zero kinetic modeling of hydrolysis-dehydration of cellulose, as well as calculations on the other sugars gave higher yields of 5-HMF against the experimental data (Fig. S3). The constants of sugar consumption k30, k40 and k50 were determined from the available experimental and thermodynamic data via subtraction of constant values of monosaccharide transformations via confirmed pathways from the constant values of glucose, fructose and mannose total consumption, for example 30

Glu 3 34 k k k k    .
The experimental data presented in this work demonstrated the difference of the catalytic action between the solid Sibunit carbon and soluble sulfuric acid catalysts in cellulose hydrolysisdehydration. As stated above, the kinetic investigations were carried out at 180 ºC and pH value of 2.7 in this work. The determined constant k2 (0.11 min -1 ) of cellobiose hydrolysis to glucose over solid acid carbon catalyst was lower by a factor of 3.2 than the value observed previously in the presence of H2SO4 (pH 2.1, 180 ºC) [START_REF] Bobleter | Hydrolysis of Cellobiose in Dilute Sulpuric Acid and Under Hydrothermal Conditions[END_REF]. The total constant of glucose consumption through various pathways kglu (10.6•10 -3 min -1 ) was higher than the value revealed previously in the presence of H2SO4 at pH of 2.1 and 180 ºC [START_REF] Bobleter | Hydrolysis of Cellobiose in Dilute Sulpuric Acid and Under Hydrothermal Conditions[END_REF]. J. F. Saeman reported the glucose degradation constant equal to 24.1•10 -3 under 180 ºC but pH value of ca. 1.1 [START_REF] Saeman | Kinetics of Wood Saccharification -Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature[END_REF]. The reaction constant k7 of 5-HMF hydration into levulinic and formic acids was in 25 times lower than the constant of 5-HMF degradation to side compounds (k8 = 5.1•10 -3 min -1 ). This can explain why the formation of levulinic acid is not significant over solid carbons while it is easily produced in the presence of soluble acid catalysts under close conditions (temperature and pH) [START_REF] Gromov | Hydrothermal Solubilization-Hydrolysis-Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts[END_REF][START_REF] Mukherjee | Review: Sustainable production of hydroxymethylfurfural and levulinic acid: Challenges and opportunities[END_REF][START_REF] Horvat | Mechanism of levulinic acid formation[END_REF][START_REF] Van Dam | The Conversion of Fructose and Glucose in Acidic Media: Formation of Hydroxymethylfurfural[END_REF]. Thus, the data demonstrated that solid acid catalysts seems to be more suitable than soluble ones for the production of 5-HMF from the polysaccharides.

The system of differential equations was solved by the Mathcad 15.0 software with function Odesolve based on the Runge-Kutta method with an automatic step-size for solving. The developed kinetic model provided not only qualitative but also accurate enough quantitative description of cellulose hydrolysis-dehydration, as well as transformations of intermediates of the process under study (Fig. 2). It should be noted that the proposed model is applicable not only in the case of using cellulose as a substrate. Modeled kinetics also describes accurately the experiments where other intermediates glucose, fructose, mannose, and 5-HMF are substrates (Fig. 2).

Conclusions

The kinetic model which consisted of eighteen stages was proposed to predict cellulose hydrolysis-dehydration over a solid sulfonated Sibunit carbon catalyst in a batch reactor. The model described in the paper was based on the experimental data on hydrolysis-dehydration of cellulose the main process intermediates (cellobiose, glucose, fructose, mannose, 5-HMF, furfural, levulinic acid). Kinetic parameters of the reactions were revealed. Cellulose depolymerization was established to be limiting stage of cellulose processing, while hydrolysis of β-(1-4)-glycosidic bond in cellulose and oligosaccharides was a fast reaction. The difference of the catalytic action between the solid carbon and soluble acid catalysts in cellulose hydrolysis-dehydration was demonstrated.

The degradation of 5-HMF into levulinic acid is not significant over solid carbons while it is the main reaction way in the presence of soluble acid catalysts under close conditions. Thus, solid acid carbon catalysts seems to be more suitable than soluble ones for the production of 5-HMF from sugars. The data on side conversions of monosaccharides were specified. The kinetic model of cellulose hydrolysis-dehydration was updated by adding side reactions of sugar decomposition and glucose conversion to mannose. A system of differential equations was solved using the Mathcad software. The computational model described well the chemical experimental data observed.

  MPa of Ar). Hydrolysis-dehydration of cellobiose, isomerization-dehydration of glucose, fructose and mannose, degradation of furfural and 5-HMF were separately investigated. The experimental data obtained are presented in Fig. 2 and Fig. S1. Hydrolysis-dehydration of cellobiose disaccharide made possible to determine the initial rate of hydrolysis of the β-(1-4)-glycosidic bond.Quick consumption of cellobiose was established (Fig.S1 a). The conversion of the disaccharide achieved 55 % at the beginning of the reaction. Cellobiose was spent completely in 0.5 h. This confirmed that the hydrolysis was a very fast reaction, and the overall kinetics of the cellulose hydrolysis-dehydration was limited by the cellulose depolymerization and formation of watersoluble oligosaccharides. Cellobiose hydrolysis was revealed to be an irreversible process. The kinetic model fitted the experimental data when repolymerization constant was close to zero. The first order of the β-(1-4)-glycosidic bond hydrolysis used for calculations in our study agreed with

  value of 7.4•10 -3 min -1 .

kglu the constant of glucose consumption via all the pathways 10 4

 104 Reaction conditions: [a] any substrate 10 g•L -1 , Sibunit carbon catalyst 10 g•L -1 , reaction mixture volume 45 mL, 180 ºC, Ar inert atmosphere 1 2 MPa; [b] cellobiose substrate 10 g•L -1 , H2SO4 catalyst, pH 2.1, 180 ºC; [c] glucose substrate 1 g•L -1 , H2SO4 catalyst, pH 2.5, 170 ºC; [d] glucose 3 substrate 1 g•L -1 , H2SO4 catalyst, pH 2.5, 190 ºC; [e] 1.288% H2SO4 catalyst, pH 0.85, 200 ºC; [f] 0.8% H2SO4 catalyst, pH of ca. 1.1, 180 ºC; [g] 4 mannose substrate 2 g•L -1 , H2SO4 catalyst, pH 2.5, 170 ºC; [h] mannose substrate 2 g•L -1 , H2SO4 catalyst, pH 2.5, 190 ºC; [i] 5-HMF substrate 3 g•L -1 , 5 H2SO4 catalyst, pH 2.5, 170 ºC; [k] 5-HMF substrate 3 g•L -1 , H2SO4 catalyst, pH 2.5, 190 ºC. 6 7 8

  ]:

	Easy hydrolyzable polysaccharide	k E	Hydrolysis products	k 2	Decomposition products
	Non-hydrolyzable polysaccharide	k N
	Easy hydrolyzable polysaccharide	k E	Oligosaccharides	k 2	Hydrolysis products	k 3	Decomposition products
	Non-hydrolyzable polysaccharide	k N

Table 1 .

 1 Constants of the cellulose hydrolysis-dehydration reactions 1

			Constant values, min -1
	Constant	Interaction	This work [a]	Described in literature value Ref.
	k0	cellulose dissolution	16•10 -3
	k1	Oligosaccharide hydrolysis	0.11
	k2	hydrolysis of cellobiose to glucose	0.11	0.356	[55] [b]

Acknowledgments

This work was supported by the Russian Foundation for Basic Research (Project 17-53-16027) and Russian-French GDRI "Biomass".

Funding

This work was supported by the Russian Foundation for Basic Research (Project 17-53-16027) and Russian-French GDRI "Biomass".

Availability of data and material (data transparency)

Not applicable

Code availability

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Declarations

Conflict of interest

The authors declare that they have no conflict of interest.