Elliot Scuiller

Patrick Dutournié
email: patrick.dutournie@uha.fr

Mohamed Zbair

Simona Bennici

Thermo-physical properties measurements of hygroscopic and reactive material (zeolite 13X) for open adsorptive heat storage operation

Keywords: Thermo-physical properties, Heat storage, Thermal conductivity, Specific heat capacity, Zeolite 13X

The determination of the thermo-physical properties (density, specific heat capacity, and thermal conductivity) of hygroscopic and reactive solid materials, as those applied in sorption thermochemical heat storage systems, is not trivial. Lack of precision in the measurement and contradictory results make it difficult to enter these thermal parameters in the programs used for simulating the functioning and operating scenarios of thermochemical heat storage devices. For this reason, different techniques have been applied and compared in order to improve the accuracy of the measurement. In particular, there was a difference in thermal conductivity (about 30%) between the hot disc experiments and the others, as well as a higher dispersion of the experimental data (MAD > 19%). The same was found for specific heat capacity (MAD ≈14%). Hence, the transient hot disk method is not suitable for estimating thermal conductivity and the specific heat capacity of this type of material. Nevertheless, this technique enables a good estimation of the thermal effusivity. The thermal conductivity and the specific heat capacity were investigated by the hot wire method and by TG-DSC, respectively. A slight increase in specific heat with temperature was observed, but in the range of 70 -95 °C, this value is constant at 913 J kg -1 K -1 .

The applied methodology was validated by comparing the experimental and calculated thermal effusivity values.

Introduction

Material characterizations are key contributions to the global development effort in the field of adsorptive heat storage and transformation [START_REF] Uddin | Specific heat capacities of carbon-based adsorbents for adsorption heat pump application[END_REF][START_REF] Qiu | Zeolite 4A: heat capacity and thermodynamic properties[END_REF]. Adsorptive heat storage cycles are based on reversible ad/desorption reactions [START_REF] Hauer | Sorption theory for thermal energy storage[END_REF][START_REF] Gordeeva | Adsorptive heat storage and amplification: New cycles and adsorbents[END_REF]. Basically, the discharging phase corresponds to the adsorption of an adsorbate on an adsorbent (exothermic reaction). The major aim of this technology is to release an important amount of energy (2-3 times more than the latent heat of water) that can be stored at room temperature for a long time [START_REF] Nagel | Multi-physical continuum models of thermochemical heat storage and transformation in porous media and powder beds-A review[END_REF][START_REF] Yu | Sorption thermal storage for solar energy[END_REF][START_REF] Lehmann | Water loading lift and heat storage density prediction of adsorption heat storage systems using Dubinin-Polanyi theory-Comparison with experimental results[END_REF]. When the heat is discharged, the temperature of the material (adsorbent) is expected to increase significantly, which can damage the material and or the operating equipment. Using simulation tools has been just the safest way to minimize the risks. Indeed, a simulation program allows to test different configurations and operating conditions and can be used for scaling-up. Hong et al., [START_REF] Ye | Research on melting and solidification processes for enhanced double tubes with constant wall temperature/wall heat flux[END_REF] for example, successfully used numerical simulation to investigate the melting and solidification heat transfer characteristics in double tubes with varying numbers of fins and inner tube wall boundary conditions.

A necessary and inevitable step is to know the thermo-physical properties precisely to ensure reliable simulated results, namely the isosteric heat of adsorption, sorption equilibrium, heat capacity, bulk density, and thermal conductivity [START_REF] Aristov | Adsorptive transformation of heat: Principles of construction of adsorbents database[END_REF]. The first one is the heat generated in the material due to water adsorption [START_REF] Iupac) Tiu | Isosteric enthalpy of adsorption[END_REF][START_REF] Azahar | Improved model for the isosteric heat of adsorption and impacts on the performance of heat pump cycles[END_REF]. It can be easily estimated with precision from TG-DSC investigations [START_REF] Brancato | Experimental Methods for the Characterization of Materials for Sorption Storage[END_REF]. For the correct design and sizing in terms of heat storage and supply, it is required to know precisely the material density. The thermal inertia of a material is characterized by the product of its specific heat capacity and density. In a heat storage application for home heating, the heat supply can be significantly delayed by a variation in thermal inertia. The last one (bulk thermal conductivity of the material) manages thermal gradients in the reactor and hot points.

Numerical simulations of heat and mass transfer in heat storage reactors [START_REF] Semprini | Experimental and numerical investigations of an adsorption water-zeolite heat storage for refrigeration applications[END_REF][START_REF] Li | Performance analysis of consolidated sorbent based closed thermochemical energy storage reactor for environmental sustainability[END_REF] show significant thermal gradients in the reactor (proportional to the bulk thermal conductivity). High temperatures can damage the material, thus degrading the operation of the heat storage system. These different properties are functions of temperature and water content [START_REF] Dawoud | On the effective thermal conductivity of wetted zeolite under the working conditions of an adsorption chiller[END_REF][START_REF] Freni | Thermal conductivity of selective water sorbents under the working conditions of a sorption chiller[END_REF][START_REF] Rocky | Experimental investigation of the specific heat capacity of parent materials and composite adsorbents for adsorption heat pumps[END_REF].

The material used in this application is hygroscopic and reactive, which is the main problem for the thermal properties estimation [START_REF] Tanashev | Thermal conductivity of composite sorbents "salt in porous matrix" for heat storage and transformation[END_REF][START_REF] Liu | Fast simple and accurate measurement of zeolite thermal conductivity[END_REF]. Indeed, most classical techniques applied to the thermal properties investigation are based on a temperature difference in the material [START_REF] Bird | Thermal properties of thermochemical heat storage materials[END_REF]. In the present case, a change in temperature modifies the water content (sorption equilibrium) and consequently generates heat [START_REF] Vučelić | The heat capacity of water near solid surfaces[END_REF][START_REF] Schwamberger | Estimating the Heat Capacity of the Adsorbate-Adsorbent System from Adsorption Equilibria Regarding Thermodynamic Consistency[END_REF][START_REF] Berezin | Heat capacity of the H2O/KNaX zeolite adsorption system[END_REF]. As pointed out by Aristov [START_REF] Aristov | Adsorptive transformation of heat: Principles of construction of adsorbents database[END_REF], a computational approach does not allow to assess thermodynamic parameters with sufficient accuracy. Direct measurement is the main alternative so far. He proposed an empirical model for the apparent specific heat capacity of the zeolite 4A-water pair [START_REF] Aristov | Adsorptive transformation of heat: Principles of construction of adsorbents database[END_REF]. Nevertheless, the respective contributions of the dry adsorbent and the adsorbed phase are not detailed. Concerning the zeolite 13X-water pair, Simonot-Grange et al. [START_REF] Simonot-Grange | Proprietes physico-chimiques de l'eau adsorbee dans les zeolithes 13X et 4A. II. Capacites thermiques de l'eau adsorbee, du systeme zeolithe-eau et de la zeolithe anhydre[END_REF] measured its apparent specific heat capacity at several combinations of temperature and water content (from 16 °C to 350 °C). The results are summarized in Table 1. They reached the conclusion that the influence of adsorbed water is not negligible at low uptakes. However, data for a given temperature are limited to a single value at a single water content, and the experimental methodology appears to be worthwhile. Hirasawa and Urakami [START_REF] Hirasawa | Study on Specific Heat of Water Adsorbed in Zeolite Using DSC[END_REF] measured the specific heat capacity of dried zeolite 13X in the temperature range of -50 -50 °C. It shows a slow linear increase with temperature. They also measured the specific heat capacity of the adsorbed water. By analyzing the results, it is not obvious to confirm if the assumption that "the heat capacity of the adsorbed phase is an intermediate value between that of the gaseous state and that of the liquid state" is true [START_REF] Chakraborty | Specific heat capacity of a single component adsorbentadsorbate system[END_REF].

The values of specific heat capacity available in the literature (Table 1) are significantly different.

For example, at  = 50 °C, the specific heat of dry material is 910, 690, 1026, and 880 J kg -1 K -1 , respectively, for a range of 336 J kg -1 K -1 (relative uncertainty higher than 30%). Literature data for other materials (for example, zeolite 4A) is more consistent, but with the same variability and uncertainty [START_REF] Qiu | Zeolite 4A: heat capacity and thermodynamic properties[END_REF][START_REF] Aristov | Adsorptive transformation of heat: Principles of construction of adsorbents database[END_REF][START_REF] Vučelić | The heat capacity of water near solid surfaces[END_REF][START_REF] Berezin | Heat capacity of the H2O/KNaX zeolite adsorption system[END_REF][START_REF] Simonot-Grange | Proprietes physico-chimiques de l'eau adsorbee dans les zeolithes 13X et 4A. II. Capacites thermiques de l'eau adsorbee, du systeme zeolithe-eau et de la zeolithe anhydre[END_REF][START_REF] Tatlıer | A novel approach to enhance heat and mass transfer in adsorption heat pumps using the zeolite-water pair[END_REF].

Unlike specific heat capacity (an intrinsic property), the bulk thermal conductivity and the density are functions of the size and shape of the particles. Several studies successfully applied the "hot wire" method [START_REF] Dawoud | On the effective thermal conductivity of wetted zeolite under the working conditions of an adsorption chiller[END_REF][START_REF] Freni | Thermal conductivity of selective water sorbents under the working conditions of a sorption chiller[END_REF][START_REF] Tanashev | Thermal conductivity of composite sorbents "salt in porous matrix" for heat storage and transformation[END_REF][START_REF] Liu | Fast simple and accurate measurement of zeolite thermal conductivity[END_REF][START_REF] Griesinger | Measurements and theoretical modelling of the effective thermal conductivity of zeolites[END_REF] to measure the apparent thermal conductivity of hygroscopic materials. According to Freni et al. [START_REF] Freni | Thermal conductivity of selective water sorbents under the working conditions of a sorption chiller[END_REF], the temperature increasing during the transient measurement does not change the water uptake of the material [START_REF] Freni | Thermal conductivity of selective water sorbents under the working conditions of a sorption chiller[END_REF]. In the same way, another transient method (transient plane source, also known as "hot disk") [START_REF] Hu | Analysis for composite zeolite/foam aluminum-water mass recovery adsorption refrigeration system driven by engine exhaust heat[END_REF] can be applied. In theory, this technique was designed to simultaneously estimate the thermal conductivity and the specific heat capacity of a material (via the thermal diffusivity and the effusivity) [START_REF] Log | Transient plane source (TPS) technique for measuring thermal transport properties of building materials[END_REF][START_REF] Krapez | Mesure de l'effusivité thermique -Méthodes par contact[END_REF]. The possibility to measure several thermo-physical parameters at once with a quick procedure is appealing.

Pinheiro et al. [START_REF] Pinheiro | Adsorption heat pump optimization by experimental design and response surface methodology[END_REF] used it to measure zeolite 13X's heat conductivity in the temperature range of 25-115 °C and found it lower than 0.3 W m -1 K -1 . However, the "hot disk" technique is known to face limits when applied to such low-conductivity materials [START_REF] Zheng | Analysis and improvement of the hot disk transient plane source method for low thermal conductivity materials[END_REF]. This is especially the case when applied to the granular structure of the zeolite bed with a substantial void fraction. For this reason, the packing density of the bed also has to be taken into account. To the author's knowledge, few data about the zeolite 13X-water pair is available, with high variability, ranging from 76 to 400 mW m -1 K -1 [START_REF] Liu | Fast simple and accurate measurement of zeolite thermal conductivity[END_REF][START_REF] Pinheiro | Adsorption heat pump optimization by experimental design and response surface methodology[END_REF][START_REF] Aittomäki | Determination of effective thermal conductivity of adsorbent bed using measured temperature profiles[END_REF][START_REF] Wang | Heat Transfer Enhancement on the Adsorber of Adsorption Heat Pump[END_REF]. For this reason, their values must be used with care. Thus, performing original measurements of the thermal conductivity along with the apparent density of the packed bed is relevant.

Overall, the thermophysical parameters (density, specific heat capacity, and thermal conductivity) of hygroscopic and reactive solid materials, such as those used in sorption thermochemical heat storage systems, are difficult to determine. It is difficult to enter these thermal parameters into programs that simulate the working and operation scenarios of thermochemical heat storage devices because of the lack of precision in measurement and contradictory findings. For this reason, in this work, different methods have been applied and compared in order to improve the accuracy of the measurement. In this study, we focused on the working pair "zeolite 13X-water" under atmospheric pressure. The temperature range being investigated corresponds to the operating conditions of a low-grade adsorptive heat storage device, i.e. 20 -95 °C.

Material and methods

The material used in this study is a commercial zeolite 13X "Zeolum F-9 14-20#" from Tosoh Europe B.V., Amsterdam, Netherlands. The diameter of the spherical particles (beads) is in the range of 0.85 mm-1.18 mm. The textural properties of the material were investigated by N2 adsorption experiments. The isotherm is of type I at low relative pressure, which is characteristic of a microporous material. The porous volume is 0.28 cm 3 g -1 .

Three thermo-physical properties are investigated in this study: the apparent thermal conductivity of the material bed λ (W m -1 K -1 ), the specific heat Cp (J kg -1 K -1 ) and the apparent density of the material ρ (kg m -3 ).

Density

The apparent density of the material bed (bulk density) is measured under a controlled atmosphere (T and relative humidity, RH). Several samples of material (150.00 g of zeolite) are taken at room conditions, and the volume is measured in a 250 mL graduated cylinder. The samples are dehydrated in an oven at 300 °C for 3 days and then rehydrated at the desired moisture content. In a glove box, the samples are weighted again. To take into account the influence of graduated cylinder filling, the results are presented according to the chosen samples.

To estimate the void fraction (inter-granular porosity), the intrinsic density of the material is calculated by weighing and measuring 4-5 beads with a microbalance and an electronic slide gauge (repeated several times).

Thermal conductivity

The estimation of the material's thermal properties required the use of several techniques owing to intricate balances between temperature, humidity, and reaction heat of sorption. The apparent thermal conductivity of the material was first investigated by using a transient line source (hot-wire method). The apparatus is a TLS-100 (Thermtest Inc., Fredericton, NB, Canada), with a 100 mm long probe. The diameter of the tested sample is greater than 50 mm and its depth is 120 mm, in agreement with the manufacturer's recommendations. The probe heats the sample at constant power and records its temperature. The apparent thermal conductivity is calculated assuming onedimensional heat transfer in an infinite solid.

Second, a custom guarded hot plate setup (Delta Lab ET 100, Carcassonne, France) is also used to measure the apparent thermal conductivity of the bed. The sample dimensions are 300 × 250 × 24 mm (length × width × depth). It is placed between two aluminium plates (up and down). The bottom plate is placed on 96 mm of expanded polystyrene (λps) and heated by joule effect (P0) to the required (constant) temperature. The two plates are instrumented with 3 thermocouples each (average temperature: Tb and Tt). Once the steady state is reached, the thermal conductivity is calculated according to one-dimensional Fourier's law, taking into account heat transfer in the insulation (equation 1).

𝜆 = 𝑃 0 • 𝑑 (𝑇 𝑏 -𝑇 𝑡 ) -𝜆 𝑝𝑠 (𝑇 𝑏 -𝑇 𝑜 ) 4(𝑇 𝑏 -𝑇 𝑡 ) (1)
A transient plane source technique is also used to measure the thermal conductivity of the material.

It consists of a Hot Disk M1 thermal constants analyser (Hot Disk AB, Gothenburg, Sweden) with a "Kapton 8563 F1" sensor (disc radius: a = 9.868 mm). It also provides the estimation of the thermal diffusivity (𝛼 = 𝜆 𝜌 𝐶 𝑝 , m 2 s -1 ), the thermal effusivity (E = (𝜌 𝐶 𝑝 𝜆) 1 2 , J K -1 m -2 s -0.5 ), and the specific heat (ρ Cp, in J m -3 K -1 ). The sample is in a cubic box (thickness: 60 mm, side length: 70 mm). The probe is horizontally placed in the middle of the bed and heats the material at constant power P0 (W) and records its temperature increase ΔT for a few minutes.

Heat capacity

As previously described, the heat capacity can be deduced from experiments with the transient plane source ("hot disk"). These tests can be conducted only at room temperature and in a glove box to avoid material moisture variation. To investigate the effects of both "temperature" and "water content", a two-in-one thermo-gravimetric and differential scanning calorimetry analyzer (Setaram Sensys evo TG-DSC, Kep Technologies, Caluire, France) is used.

A typical sample is constituted of approximately 10 mg of material (10 beads) contained in an aluminium crucible. It is suspended on a microscale along with another empty crucible. To control their temperature, both crucibles are enclosed in furnaces. The differential heat-flow signal is recorded thanks to a Calvet sensor. The atmosphere in the chamber is a flow of synthetic air, which mass flow, temperature, and humidity are controlled by a humidity generator (Setaram Wetsys, Kep Technologies, Caluire, France).

First, the sample is dehydrated at 300 °C with synthetic air (30 mL min -1 airflow rate pulsed by the humidity controller) for 8 h. The duration of 8 h allows to reach mass stability, such as dm/dt < 0.006 % min -1 , following the stability criterion employed by Son et al. [START_REF] Son | Equilibrium Adsorption Isotherms for H 2 O on Zeolite 13X[END_REF]. The sample is then cooled and rehydrated to the required temperature and moisture by adjusting the air humidity.

Following its pre-treatment, the sample is heated up to 110 °C at a constant heating rate while maintaining the mass of the sample constant. For this, the air humidity is continuously adjusted.

Heat capacity is continuously calculated using equation 2:

𝐶𝑝 = [( 𝑑𝑞 𝑑𝑡 ) 𝑠𝑎𝑚𝑝𝑙𝑒 -( 𝑑𝑞 𝑑𝑡 ) 𝑏𝑙𝑎𝑛𝑘 ] • 1 𝑚 0 • 𝑑𝑇 𝑑𝑡 (2

𝑁

Results and discussion

Preliminary tests

Data available in the literature on the thermo-physical properties of reactive and hygroscopic materials is uncertain and even minimal for zeolite 13X. Under these conditions, the first step is to investigate the different characterization techniques in order to assess the feasibility, reliability, and quality of measurements. For this, the thermo-physical properties of zeolite 13X were investigated with different techniques at room humidity and temperature conditions. The thermophysical properties of the material in equilibrium with air at room temperature and humidity are shown in Table 2. According to the theory, the thermal conductivity and the specific heat are simultaneously estimated by fitting the experimental temperature of the sensor with equation 3. In practice, this equation is not used in the calculation, because of its complexity [START_REF] Krapez | Mesure de l'effusivité thermique -Méthodes par contact[END_REF][START_REF] Malinarič | Contribution to the Transient Plane Source Method for Measuring Thermophysical Properties of Solids[END_REF][START_REF] Malinarič | Concentric Circular Strips Model of the Transient Plane Source-Sensor[END_REF]. Indeed, after a comparison between the calculations carried out by the software and our calculations, it was observed that the software used the solution of a one-dimensional heat transfer problem. The system (material and heat source) is assumed to be a 1D half-space unsteady problem subjected to a constant heat flux. The solution to this problem leads to a temperature profile in the material bed as follows (eq. 4):

∆𝑇 =

𝑇(𝑥, 𝑡) = 𝑇(𝑡 = 0) + 𝑃 0 𝜆𝑆 √𝐷𝑡 [ 1 √𝜋 𝑒 -𝑥 2 4𝐷𝑡 - 𝑥 2√𝐷𝑡 𝑒𝑟𝑓𝑐 ( 𝑥 2√𝑎𝑡 )] (4)
Starting from this equation the sensor temperature is (x = 0):

𝑇(𝑥 = 0, 𝑡) = 𝑇(𝑡 = 0) + 𝑃 0 𝜆𝑆 √𝐷𝑡 [ 1 √𝜋 ] (5)
The thermo-physical properties are estimated first by fitting the experimental sensor temperature with a function of the square root of time. The slope of the linear curve of T(t) versus √𝑡 is directly proportional to the material effusivity 𝐸 = √ 𝜌𝐶 𝑝 𝜆. The study of the different temperature profiles

shows good linearity and explains that the estimation of E is given with low dispersion.

Second, the thermal conductivity is estimated by minimizing a quadratic criterion between the sensor temperature (experimental) and equation 3 after significant simplifications. For this, the three integrals are substituted by a polynomial function of τ (the polynomial coefficients are previously pre-calculated from equation 3).

For this material, the obtained thermal conductivity is different from the ones measured with hotwire and hot plate techniques. Moreover, we observe a significant dispersion of the results.

The same conclusions are observed for specific heat and thermal diffusivity because they are deduced from calculations of effusivity and thermal conductivity.

From these results and observations, we can conclude that the transient plane source technique is not well suited for measuring the thermal conductivity and heat capacity of this material.

Consequently, the thermal diffusivity is affected by a large uncertainty. Only the material effusivity can be estimated accurately.

Starting from these preliminary results, the material properties were investigated by using a hot wire for thermal conductivity, TG-DSC for specific heat, and a hot disk for effusivity.

Thermo-physical properties of zeolite 13X

Material density was measured at room temperature for different moisture contents according to the protocol detailed in the previous section. This methodology was applied owing to the influence of material placement operations. The results are shown in Fig. 1. The thermal conductivity is low and can be explained by the important void fraction (around 30%)

and the porous volume that represents two thirds of the volume. The presence of adsorbed water in the pores improves the conductive heat transfer inside the beads. These results are in good agreement with the results of A. Aittomaki and A. Aula [START_REF] Aittomäki | Determination of effective thermal conductivity of adsorbent bed using measured temperature profiles[END_REF]. The thermal conductivity of a dry bed of zeolite 13X (diameter of particles 2-3 mm) is 0.076 W m -1 K -1 . The dependence on temperature of the bulk thermal conductivity is very complicated to investigate owing to the relationship between temperature and water content. Additional tests performed on a guarded hot plate (up to 50 °C) do not show a change with temperature. This would be expected since air (void fraction) is mainly responsible for the low thermal conductivity. Indeed, the thermal conductivity of dry air slightly increases with temperature (from 26 to 31 mW m -1 K -1 in the range of 20-90 °C).

Fig. 3 specific heat of dried zeolite 13X versus temperature

The specific heat of the material is estimated by using a differential scanning calorimetry analyzer.

The experiments were carried out at temperatures ranging from 65 to 140 °C for the dried material and from 60 to 90 °C for the material at different water contents. Figure 3 shows the specific heat of the dried material. A slight increase in specific heat with temperature is observed, but in the range of 70 -95 °C, this value is constant at 913 J kg -1 K -1 . This result is indeed quite different from the specific heat obtained by Simonot-Grange [START_REF] Simonot-Grange | Proprietes physico-chimiques de l'eau adsorbee dans les zeolithes 13X et 4A. II. Capacites thermiques de l'eau adsorbee, du systeme zeolithe-eau et de la zeolithe anhydre[END_REF] for anhydrous zeolite 13X.

Fig. 4 specific heat of zeolite 13X for different water contents

The same experiments are repeated for different water contents. For this, the air humidity is controlled to have a constant mass of material. Figure 4 shows the specific heat of the material at different moisture content. The specific heat seems to vary linearly with water content. Results

show that the experimental error increases with the water content due to the difficulty of controlling a constant mass of material.

From the linear approximation, the specific heat of the dried material Cp(db) is 910 J kg -1 K -1 (max = 916, min = 905 J kg -1 K -1 ), which is close to 913 J kg -1 K -1 (obtained for dried material). The slope is 2191  217 J kg -1 K -1 .

For this material type, many authors assumed a linear variation with water content. A linear rule of mixing (equation 7) can be applied to calculate the specific heat of the hydrated material.

𝐶𝑝 = 𝐶𝑝(𝑑𝑏) + 𝑤[𝐶𝑝(𝐻 2 𝑂) -𝐶𝑝(𝑑𝑏)] (7)
With this assumption, the specific heat capacity of water in the material is about 3100 J kg -1 K -1 (max = 3323, min = 2878 J kg -1 K -1 ).

This result is in good agreement with data available in the literature [START_REF] Hirasawa | Study on Specific Heat of Water Adsorbed in Zeolite Using DSC[END_REF]. Indeed, Hirasawa et al.

conclude that the specific heat of adsorbed water is about 3000 to 5000 J kg -1 K -1 . This value is an intermediate value between the liquid and vapor specific heats of water (i.e. 4190 and 1830 J kg -1 K -1 , respectively).

In order to verify the relevance of the properties estimations, calculated effusivity values are compared to results from hot disk experiments.

Calculated and experimental results are in good agreement, validating the applied methodology.

Conclusion

A precise estimation of the thermo-physical properties of adsorbent and reactive materials is a necessary and inevitable step for the development of heat storage systems. In this work, different techniques were used and compared to improve the measurement accuracy. In particular, results

show that the transient hot disk method is not suitable for estimating the thermal conductivity and the heat capacity of this type of material. There was a significant difference in thermal conductivity (approximately 30%) between the hot disc studies and the other methods, as well as a greater dispersion of the experimental results (MAD > 19%). The same was discovered for specific heat capacity (MAD ≈14%). Nevertheless, this technique enables a good estimation of the thermal effusivity. Thermal conductivity and heat capacity were investigated by hot wire and TG-DSC, respectively. There was a little rise in specific heat with temperature, although this value remains constant at 913 J kg -1 K -1 between 70 and 95 °C. Experimental and calculated thermal effusivity values from independent characterization validate the applied methodology. These results allow to obtain the thermo-physical properties of a reactive and hygroscopic material as a function of temperature and water content in a larger range of operating conditions than those reported up to now in the literature. These data are required as key input data for simulating thermochemical heat storage operations.

  20-350 260+8.6 (T-273) 1510 (w = 26 kg kg -1 , T = 289 K)

  during the sample and the blank tests, respectively. m0 is the mass of the sample (maintained constant) and 𝑑𝑇 𝑑𝑡 the heating rate.The quality of experimental results (yi) was examined using three criteria (range, mean absolute deviation, and standard deviation) and their respective relative values (divided by average value 𝑦 ̅):Range: R = max(yi)min (yi)

  P0 is the power input, I0 represents the 0 order modified Bessel functions and 𝜏 = √ 𝐷𝑡 𝑟² . With t the time measured from the start of the experiment, D is the thermal diffusivity of the material and r is the radius of the hot disk.

Fig. 1 Fig. 2 Fig. 2 .

 122 Fig. 1 Material apparent density as a function of water content

Fig. 5

 5 Fig. 5 material effusivity (experimental and calculated) as a function of water content

Table 1

 1 Specific heat capacity of zeolite 13X from the literature

Table 2

 2 Preliminary tests performed with the material in equilibrium (thermal and water balances)

	with the ambiance
		value tests	R	R(%) MAD MAD(%) SD SD(%)
	w /kg kg -1	0.193	8	0.027 13.9 0.014	7.0	0.015	8
	 /Kg M -3	794	38	78	9.9	16	2.1	20.8	3
	 /mW m -1 K -1 (Hot Wire) 94.5	8	6	6.3	1	1.5	1.7	2
	 /mW m -1 K -1 (Hot disk)	120.8 22	33	27.6	23	19.1	7.3	7
	 /mW m -1 K -1 (Hot Plate) 93.9	9	23	24.4	6	6.8	7.3	7

%). The same holds true for the specific heat capacity (MAD ≈ 14 %). Moreover, the heat capacity is low in comparison with the literature and the results obtained by thermo-gravimetric investigations.

The authors would like to thank the company Thermoconcept, Mérignac, France for additional testing with transient plane source; the Association Nationale Recherche Technologie (ANRT) for the funding of this work under agreement Cifre n° 2019/0620 (E. Scuiller grant); the Region Grand Est for providing funding for the acquisition of the TG-DSC equipment within the "STOCKFATAL" project; the Carnot MICA institute for funding part of this study in the frame of the STOCKENER project; IS2M for the postdoctoral grant of M. Zbair in the frame of the "Projets Structurants" call.

Consent to participate: Not applicable.

Funding

This research was supported by the Association Nationale Recherche Technologie (ANRT) under agreement Cifre n° 2019/0620 (E. Scuiller grant); the Region Grand Est (providing funding for the acquisition of the TG-DSC equipment within the "STOCKFATAL" project); the Carnot MICA institute (funding part of this study in the frame of the STOCKENER project); IS2M (postdoctoral grant of M. Zbair in the frame of the "Projets Structurants" call).

Availability of data and material

The material and the data are available upon request.

Code availability: Not applicable.

Ethics approval: Not applicable.

Declarations:

Conflicts of interest

The authors declare that they don't have any conflict of interest.

As expected, the bulk density of zeolite 13X is linearly proportional to the water mass fraction.

The difference in Y-intercept is due to the difference in material placement in the column. This difference is about 50 kg m -3 . The density of the dried material is about ρ0 = 662 kg m -3 . The best fitted equations for the studied samples are consistent with the theory, i.e. 𝜌 = 𝜌 0 (1 + 𝑤). The intrinsic density of the material is 1160 kg m -3 at w = 0.235 kg kg -1 . The void fraction is estimated to be in the range of 26 -32 %. Additional tests at different temperatures (up to 90 °C) reveal the same behavior. The bulk density does not appear to be dependent on temperature, but only on filling ways.


Enzo Nobile

Thomas Castanheiro

Tatiana Besset
email: tatiana.besset@insa-rouen.fr

phenylsulfonyl)difluoromethylation of (hetero)arenes with a newly designed reagent

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Introduction

Organofluorine chemistry is a research area of paramount importance as fluorinated molecules are prevalent derivatives in material science, agrochemical and pharmaceutical industries. 1 More than 40% of pharmaceuticals approved by the FDA in 2019 contain at least one fluorine atom, 2 which could be explained since the incorporation of a fluorine atom or a fluorinated moiety drastically impact the properties of the corresponding molecules. 3 Therefore, over the year, the field of organofluorine chemistry has been revolutionized by impressive advances including original and efficient transformations along with the discovery and design of potent fluorinated groups, which have opened wider the chemical space of fluorinated compounds. [START_REF] Kirk | For a selection[END_REF] Whilst special attention was paid to the HCF2 group, 5 the design of FGCF2 moiety has emerged as an interesting lead to be followed. Among them, the PhSO2CF2 residue proved to be of high importance and had aroused the interest of the scientific community. [START_REF] Prakash | For a selection of reviews[END_REF] Found in the analog of Fluconazole with antifungal activities, 7 this fluorinated group is a real synthetic handle. Indeed, it is easily converted into other valuable difluorinated moieties such as the difluoromethyl (HCF2), the difluoromethylene (-CF2-), and the difluoromethylidene (=CF2) groups. These later were found in drugs such as Eflornithine 8 and Seletracetam, 9 for instance. Main synthetic pathways to build up a C-CF2SO2Ph bond relied on the use of nucleophilic sources of (phenylsulfonyl)difluoromethyl residue or via a radical process. [START_REF] Prakash | For a selection of reviews[END_REF] In sharp contrast, methodologies involving electrophilic reagents are restricted to two major contributions from key players in the field, namely the groups of Hu 10 and Shibata. 11 They designed two electrophilic sources based on an hypervalent iodine and a sulfonium salt, respectively (Scheme 1). While the group of Hu showcased that its source was very efficient for the functionalization of thiols as well as for the copper-catalyzed allylic and vinylic (phenylsulfonyl)difluoro-methylation reaction, Shibata and co-workers successfully applied their reagent for the functionalization of C(sp 3 ) centers with -ketoesters, -diketones and dicyanoalkylidenes. Although those reagents served as a proof-of-concept, we wondered whether it would be possible to synthesize a new electrophilic reagent, which will 1) be easily accessible on a large scale, 2) not require ozone depleting reagents for its synthesis and 3) react with a large panel of nucleophiles. Such reagent will definitely facilitate the access to difluoromethylated compounds.

Scheme 1. State of the art.

By analogy with the Umemoto's reagent and its analogs, 12 we anticipated that the backbone of the reagent will be important to reach a good reactivity. Therefore, we imagine to synthesize a S- ([phenylsulfonyl]difluoromethyl)dibenzothiophenium salt. Herein, we disclosed a simple and straightforward synthesis of an electrophilic source of PhSO2CF2 group and its broad applications in various transformations.

Results and Discussion

With these considerations in mind, we embarked on the preparation of the reagent I. This newly designed reagent was synthesized in a three steps/one purification sequence in 51% overall yield starting from the commercially available or easy-to-synthesize biaryl disulfide 1a [START_REF]Note that the disulfide 1a was easily prepared from the 2-phenylaniline after four-steps synthesis (no purification) on several grams (until 50 g)[END_REF] and the (difluoromethyl)sulfonylbenzene. [START_REF]PhSO2CF2H was prepared in two steps from thiophenol when not purchased, see supporting information[END_REF]15 First, the (phenylsulfo-nyl)difluoromethylation of the disulfide 1a under basic conditions provided 1b in 74% yield. The selective oxidation of the sulfane with mCPBA furnished 1c in 90% yield, without any purification. Finally, upon treatment with triflic anhydride, the sulfoxide 1c was converted into the corresponding dibenzothiophenium salt I in 76% yield. The structure of I was further ascertained by a X-ray analysis. 15 The reagent turned out to be air-and moisture-tolerant, bench-stable and was kept for more than three months at room temperature under air with no alteration of its reactivity. Remarkably, its transition metal-free synthesis did not require any ozone depleting fluorinated reagents and was conveniently scalable as the reagent I was obtained in 46% overall yield on 48 mmol scale. Scheme 2. Synthesis of the reagent I. Reaction performed on 5 mmol scale. See the Supporting Information for more details.

Having this reagent in hand, we first explored its reactivity towards the (phenylsulfonyl)difluoromethylation of aniline derivatives with a complete selectivity towards the formation of a C(sp 2 )-CF2SO2Ph bond (Scheme 3). When aniline 2a was reacted with the reagent I, the compound 3a was obtained in a high yield as an easy-to-separate mixture of ortho and para regioisomers, the ortho isomer being the major one. 15,[START_REF]For a similar selectivity in case of trifluoromethylation with the Umemoto reagent, see[END_REF] As these fluorinated molecules might be of high interest for medicinal chemistry and drug discovery, the access to both regioisomers in one transformation might constitute a substantial advantage. Then, a panel of original and diversely para-substituted (phenylsulfonyl)difluoromethylated anilines was synthesized. Both anilines substituted with electron-donating groups (2b-2d), halogens (2e-2f) and electron--withdrawing groups (2g-2h) were suitable substrates, the transformation being more efficient with electron-rich compounds. The reaction was tolerant to various functional groups such as ketone (3g) and ester (3h). When the 3-chloroaniline 2i reacted with the reagent I, the functionalization occurred on both ortho positions, the major isomer, resulting from the (phenylsulfonyl)difluoromethylation at the less sterically hindered position, was preferentially obtained as ascertained by NMR experiments and a X-ray analysis (CCDC 2084629). 15 In case of the 2-methylaniline, a 1:1 mixture of both orthoand parasubstituted products (3j) was obtained in 83% yield as confirmed by 2D-NMR experiments. Interestingly, the 2,6-xylidine 2k, a key scaffold found in several anesthetic such as Lidocaine, Bupicaine, Mepivacaine and Etidocaine, was smoothly functionalized in 84% yield. It is worth mentioning that heteroarylamines (2l and 2m) were also functionalized in good yields. 15 The methodology was not restricted to the functionalization of primary aniline as the N-methylaniline was reacted and 3n was isolated in 48% for the ortho isomer. e 4 days. f The product was isolated with an inseparable impurity. g Only this isomer was isolated in 48% yield.

Encouraged by these results, we turned our attention to the electrophilic (phenylsulfonyl)difluoromethylation of electron-rich (hetero)arenes (Scheme 4). First indoles (4a-4e), a key scaffold for medicinal chemistry, were studied. Non-protected and N-protected 3-substituted indoles (4a-4c) were smoothly functionalized at the C2 position. When the Nmethylindole 4d was used as the substrate, the expected product 5d was obtained as a mixture of regioisomers. Interestingly, the C2-functionalization of pyrroles was efficiently achieved, except in case of 5h, which was isolated in a modest 27% yield. The (phenylsulfonyl)difluoromethylation of phenol and anisole derivatives (4i-4l) provided the corresponding products in decent to good yields. The late-stage functionalization of bioactive molecules such as Melatonin (4e), "the Sleep Hormone", and Propofol (4j), a potent anesthetic, went smoothly. The expected products (5e and 5j) were obtained with a complete regioselectivity in 74% and 70%, respectively. To further demonstrate the potential of the reagent I, the functionalization of C(sp 3 )-centered nucleophiles was studied (Scheme 5). Pleasingly, in the presence of DBU, -ketoesters 6 and dicyanoalkylidene 8 were efficiently functionalized at low temperature (-78 °C or -42 °C) and the corresponding (phenylsulfonyl)difluoromethylated products 7a-7b and 9 were isolated in good to excellent yields with a complete selectivity for the C-functionalization: a valuable alternative to the pioneering work from Shibata. 11 Due to the recent interest to the (phenylsulfonyl)difluoromethyl sulfanyl group, 10a,17 we explored the possibility to access to PhSO2CF2S-containing derivatives by reacting S-nucleophiles with the reagent I (Scheme 6). The transformation proceeded smoothly with structurally diverse thiophenol derivatives (10a-10c) including the 2benzothiazolethiol 10c under mild reaction conditions (50 °C, no base). Interestingly, in case of the 4-mercaptophenol 10b, a complete selectivity was observed for the formation of a S-CF2SO2Ph bond over a C(sp 2 )-CF2SO2Ph bond. Scheme 6. Synthesis of (phenylsulfonyl)difluoromethylthio-containing molecules from thiol derivatives. Reaction conditions: 10 (3 equiv.), I (0.3 mmol, 1 equiv.), DMSO (0.15 M), 50 °C, 16 h, argon. Isolated yields were given.

To further showcase the synthetic utility of the reagent I, the straightforward synthesis of a PhSO2CF2-analog of Lidocaine 12, an anesthetic, was achieved in 63% overall yield after the following sequence: (phenylsulfonyl)difluoromethylation of the commercially available 2,6xylidine (3k, 84% yield), followed by an amidation with the chloroacetyl chloride and reaction with diethylamine under basic conditions in a one pot process (75% yield, Scheme 7). Pleasingly, this fluorinated group was then converted into the valuable HCF2 moiety. 5 Indeed, in the presence of Mg and using a catalytic amount of I2, the difluoromethylated product 13 was obtained in 80% yield starting from 12.

Scheme 7. Synthesis of the PhSO2CF2-Lidocaine and post-functionalization reaction.

Conclusion

In summary, a straightforward synthesis of a bench-stable PhSO2CF2 reagent I was developed. This transition metal-free protocol was convenient, efficiently scalable and did not require any use of ozone depleting fluorinated reagents. Pleasingly, access to unprecedented fluorinated scaffolds was possible under simple and practical reaction conditions, as illustrated with the synthesis of PhSO2CF2-containing aniline derivatives and electron-rich (hetero)arenes in moderate to excellent yields. Moreover, the reagent I was also applied to the functionalization of C(sp 3 ) centers and for the preparation of valuable PhSO2CF2S-containing derivatives. The PhSO2CF2 residue was efficiently converted into the high-value added HCF2 group, which highlighted the versatility of this fluorinated group. The late-stage functionalization of bioactive molecules into their corresponding PhSO2CF2-containing analogs further demonstrated the synthetic utility of the novel reagent, particularly appealing in the quest of interesting scaffolds for medicinal chemistry. This newly-designed electrophilic source is distinguished by its straightforward and practical synthesis and its wide scope, thus offering a new platform to introduce the PhSO2CF2 motif on various skeletons. We believe that this original tool will enlarge the current toolbox of electrophilic reagents, will open new routes for functionalizing complex molecules and will be useful for the discovery of new bioactive molecules.

Scheme 3 .

 3 Scheme 3. (Phenylsulfonyl)difluoromethylation of anilines 2. Reaction conditions: 2 (3 equiv.), I (0.3 mmol, 1 equiv.), CH2Cl2 (0.15 M), 21 °C, 24 h, argon. Isolated yields are given. In case of regioisomers, combined isolated yields were provided and the ratio of regioisomers, in parenthesis, was determined by19 F NMR of the crude reaction mixture using the -trifluoro-acetophenone as an internal standard. a The minor isomer was isolated with an inseparable impurity. b 8 days. c 10 days. d 12 days. e 4 days.f The product was isolated with an inseparable impurity. g Only this isomer was isolated in 48% yield.

Scheme 4 .

 4 Scheme 4. Electrophilic (phenylsulfonyl)difluoromethylation of electron-rich (hetero)arenes. Reaction performed on 0.3 mmol scale. Isolated yields are given. a A combined isolated yield was provided and the ratio of regioisomers was determined by 19 F NMR of the crude reaction mixture using the trifluoroacetophenone as an internal standard. The C3-regioisomer of 5d was isolated with traces of the C4-regioisomer. b Reactions performed using 3 equivalents of 4 in DMSO, 50 °C, 16h, argon. c 5l was isolated with 13% of remaining 4l.

Acknowledgements

This work has been partially supported by University of Rouen Normandy, INSA Rouen Normandy, the Centre National de la Recherche Scientifique (CNRS), European Regional Development Fund (ERDF), Labex SynOrg (ANR-11-LABX-0029), Carnot Institute I2C, the graduate school for research XL-Chem (ANR-18-EURE-0020 XL CHEM), and by Region Normandie. E.N. and T.B. thank the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 758710). E.N. thanks the Region Normandy for a doctoral fellowship.