Ozonized (2-Hydroxypropyl)-β-cyclodextrins (Oz-HPbCDs) were produced by direct gas/solid reaction between gaseous ozone (O3) and solid HPbCD. The solid materials obtained were first characterized using physical and chemical methods and compared to the initial HPbCD. The main process parameters of the synthesis were studied independently to assess their effect on the oxidizing power of Oz-HPbCDs. The ability of the Oz-HPbCDs to retain their oxidative properties over time was evaluated, at different storage temperatures, for a period of at least two months. Lastly, aqueous solutions of HPbCD and Oz-HPbCD at different concentrations were contacted with bacterial strains of Escherichia coli and Streptococcus uberis to see whether these materials might have bactericidal properties. Since normal bacterial growth was noted with HPbCD, the antimicrobial efficiency of Oz-HPbCDs was clearly demonstrated on these two types of bacteria.

Identifying the characteristic properties of gas hydrates - including thermo-physical properties - is essential for determining their formation condition and in turn, controlling their yield/growth-rate for/in various applications/environments. Gathering these properties, during in-situ crystallization of gas hydrates, is rather challenging due to the harsh conditions they form and limited by the lack of co-existence of multiple characterization techniques. Owing to these limitations, crystallization process of some sII type gas hydrates and their characteristic properties are ill-defined. Therefore to unveil the complete picture of crystallization process of sII type gas hydrates, in this study, in-situ formation of a model system "cyclopentane hydrate" was monitored using a customized DSC sample holder with a transparent window on top. To this end, in-situ crystallization of cyclopentane hydrate was simultaneously followed by coupling optical microscopy along with scanning calorimetry. Further, we show that the cyclopentane hydrate formed by consuming a part of fresh water appearing after the fusion of ice instead of at a very low temperature <= -20 degrees C. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Organic clathrates formed by hydroquinone (HQ) and gases such as CO2 and CH4 are solid supramolecular host-guest compounds in which the gaseous guest molecules are encaged in a host framework of HQ molecules. Not only are these inclusion compounds fascinating scientific curiosities but they can also be used in practical applications such as gas separation. However, the development and future use of clathrate-based processes will largely depend on the effectiveness of the reactive materials used. These materials should enable fast and selective enclathration and have a large gas storage capacity. This article discusses the properties and performance of a new composite material able to form gas clathrates with hydroquinone (HQ) deposited on alumina particles. Apart from the general characterization of the HQ-alumina composite, one of the most remarkable observations is the unexpected formation of a guest-free clathrate structure with long-term stability (>2 years) inside the composite. Interestingly enough, in addition to a slight improvement in the enclathration kinetics of pure CO2 compared to powdered HQ, preferential capture of CO2 molecules is observed when the HQ-alumina composite is exposed to an equimolar CO2/CH4 gas mixture. In terms of gas capture selectivity toward CO2, the performance of this new composite exceeds that of pure HQ and HQ-silica composites developed in a previous study, opening up new opportunities for the design and use of these novel materials for gas separation.

A novel prototype of a microcalorimetric cell with in-situ stirring has been developed to perform DSC measurements under atmospheric or pressure conditions. After a brief technical description of the apparatus, preliminary tests are presented which analyzed the influence of the stirrer rotation on the heat-flow signal. Experiments were then performed with complex fluids such as ice slurries and clathrate hydrates formed with cyclopentane and with carbon dioxide. They took place in stirred and non-stirred conditions and the results obtained were then compared. It was proven that the rotation of the microstirrer in the measuring cell does not disrupt the heat-flow signal during the analysis. As regards the practical applications tested, the in-situ stirrer efficiently reduces crystallization metastability, increases the water-to-hydrate conversion, and reduces the amount of time needed for analysis. The dissociation enthalpy of cyclopentane (CP) hydrates was measured at atmospheric pressure; it is effectively very difficult to analyze this system with non-stirred calorimetry techniques because the two liquid phases are immiscible. The experimental results, in good agreement with other data found in the literature, showed complete water-to-CP hydrate conversion within a short period of time using a simple protocol. Experiments were also performed under pressure to demonstrate that CO2 hydrate phase equilibrium data could be obtained rapidly and easily. It is therefore our opinion that the potential of this novel technology has been thoroughly demonstrated.

Abstract The main objective of this work is to evaluate the performance of a readily biodegradable anti- agglomerant, called AA-LDHI, not harmful for the environment following the European legislation. It was tested in cyclopentane (CP) hydrate and methane (CH4)/propane (C3H8) hydrate systems. The performance of AA-LDHI was first tested in a batch reactor by torque measurements with the two hydrate systems in oil-dominated conditions (70 vol%). The experiments were performed for a subcooling of 6 °C for the CP-hydrate and up to 17 °C for the gas hydrate. The impact of AA-LDHI on hydrate growth pattern and on hydrate crystal morphology were investigated by microscopic observations at the water/CP interface for the CP-hydrate system, and at a water/(n-octane + CH4/C3H8) interface for the gas hydrate system. Then, AA-LDHI was evaluated in a semi-industrial flow loop. Without surfactant, the hydrate formed a polycrystalline shell at the water/oil interface. With AA- LDHI, large conical hydrate crystals with the vertex pointing to the aqueous phase grew at the interface before sinking in the aqueous phase. The results obtained with both CP and gas hydrates are consistent amongst themselves. In the batch reactor experiments without surfactant, hydrate crystallization led to a significant increase in the torque value and finally to the blockage of the agitator. With AA-LDHI, the torque remained almost constant at the baseline showing that this AA presented good anti-agglomeration performance. The microscopic observation in a CP phase of CP-hydrate particles formed in the reactor showed large water-wettable particles (about 400 μm) gathered in clusters but not agglomerated. AA performance of AA-LDHI was also evaluated in a semi-industrial flow loop (1-inch diameter & 35.6 m total length) in similar conditions with CH4/C3H8 mix gas but using real condensate. This experiment proved that the AA-LHDI is fully efficient in transporting safely hydrates.

Organic clathrates, particularly those formed by hydroquinone (HQ) and gas mixtures, have been far less studied than other inclusion compounds, such as gas hydrates. In this study, experiments and molecular dynamics simulations were performed on mixed (CO2 + CH4)-HQ clathrates. Single crystals were synthesized using gas mixtures with different compositions, ranging from pure CO2 to pure CH4. The crystal structure, the guest occupancy in the clathrates, and the variation of the crystal lattice parameters according to clathrate composition were obtained by X-ray diffraction measurements. In addition, molecular dynamics simulations were performed on the same systems, with state-of-the-art molecular models and force fields. The experimental results obtained and the molecular dynamics simulation estimations were in good agreement. The clathration selectivity was also calculated on the basis of experimental results, and the composition of the solid phase was correlated with the composition of the gas phase at equilibrium. These new insights into these structures will be useful from both a fundamental and a practical point of view, particularly for further developing innovative gas separation techniques using HQ clathrates.

Organic clathrates formed by combining hydroquinone (HQ) and CO2 could offer very interesting prospects in the near future, particularly in the field of CO2 capture and storage. However, one of the main limitations hindering the large-scale deployment of this type of clathrate-based technology is the slow enclathration kinetics. Our experiments, performed at different pressures (1.5, 3.0, and 4.5 MPa) and temperatures (298, 323, and 348 K), with HQ in different forms (HQ powder, HQ pellets, and HQ-silica composites, each different in nature and in terms of pore size and HQ content) demonstrated that (i) an increase in both pressure and temperature enhances the enclathration rate, (ii) the textural properties of HQ significantly impact kinetics, and composite materials remain the most efficient for improving HQ clathrate formation kinetics.

The cyclopentane hydrate, formed by combination of cyclopentane (CP) and water, is frequently used as a model system for clathrate hydrate compounds as it can form at atmospheric pressure and at temperatures below about 280 K. However, due to the immiscibility of CP and water, the dissociation enthalpy is challenging to obtain experimentally because total conversion of water to hydrate is difficult to achieve in quiescent conditions. Only two dissociation enthalpy values are available in literature, and a difference of 25 kJ.mol(-1) between them clearly indicates a discrepancy. In this study, a stirring calorimetric cell was used with a Tian-Calvet heat-flow calorimeter, to measure phase change properties. The technical system made it possible to form pure CP-hydrate with complete conversion of water to hydrate. The dissociation temperature and dissociation enthalpy of the CP-hydrate (with max 5 wt% of residual liquid CP) were measured at 280.2 +/- 0.5 K and 115,400 +/- 7600 J.mol(-1) of CP (377 +/- 27 J.g(-1) of water; 307 +/- 21 J.g(-1) of hydrate), respectively. This high enthalpy value opens new ways for using CP-hydrates in cold storage and refrigeration applications. (C) 2018 Elsevier Ltd.

Hydroquinone (HQ) clathrates have recently been identified as promising candidates for selective gas capture and storage processes. This study evaluates the effectiveness of HQ clathrates in the separation of CO2 from CO2/CH4 gas mixtures, through direct gas/solid reactions in a fixed-bed reactor. The influence of the process operating parameters (i.e. reaction time, pressure, temperature and feed gas composition) on the CO2 capture kinetics, selectivity towards CO2, and transient storage capacity were investigated. The experiments were performed using either pure HQ or HQ-based composite materials, with temperatures ranging from about 283 to 343 K, pressures from 3.0 to 9.0 MPa, and CO2 mole fraction in the gas mixture ranging from 0.2 to 1. The experimental results show that over the range of gas composition investigated, the enclathration reaction is selective to CO2. This preferential CO2 capture is enhanced at high CO2 mole fractions, low temperatures and high pressures. Regarding gas capture kinetics, it was confirmed that the composite material is much more efficient than pure HQ crystals. The CO2 enclathration rate increases with temperature, pressure and CO2 fraction in the feed gas. For the first time, the feasibility of such gas separation techniques using HQ clathrates was demonstrated at bench scale.

High pressure differential scanning calorimetry (HP-DSC) is of importance in several fields involving gas hydrates, such as oil and gas production, flow assurance, carbon dioxide capture and storage, CO2 hydrates reversible formation/dissociation for refrigeration loops. However, the technique suffered for some limitations linked to the fact that the gas hydrate formation in the calorimetric cell occurs at the gas-liquids interface, leading to problems such as inefficient gas dissolution, formation of a hydrate crust covering the gas/liquid interface, low hydrate to water conversion, and difficulties to crystallize these compounds even at low temperature. It is for example rather difficult to determine accurately the heat capacities and the enthalpies of formation/dissociation of several systems involving gas hydrates. To overcome such limitations, we present two prototypes of calorimetric cells equipped with an in-situ mechanical agitation system, which allow performing experiments under pressure (150 bar max). The first one is called MIXCEL®, and was developed for macro-calorimetry analysis (experiments carried out with a BT 2.15 Calvet Calorimeter from SETARAM Instrumentation). The second one, called MICROMIXCEL®, was developed for micro-calorimetry analysis (experiments carried out using a microDSC7 evo from Setaram Instrumentation). In this study, technical details of the two cells and results obtained both at macro and micro scales will be presented, and compared to the case with no agitation. Thermophysical properties of the cyclopentane hydrate (phase change enthalpy, and specific heat) will be given and commented. The use of such novel calorimetric cells opens a wide range of possibilities for complex systems, such as gas hydrates, which must be analysed in both pressurized and agitated conditions.

Hydroquinone (HQ) is known to form organic clathrates with some gaseous species such as CO2 and CH4. This work presents spectroscopic data, surface and internal morphologies, gas storage capacities, guest release temperatures, and structural transition temperatures for HQ clathrates obtained from pure CO2, pure CH4, and an equimolar CO2/CH4 mixture. All analyses are performed on clathrates formed by direct gas–solid reaction after 1 month’s reaction at ambient temperature conditions and under a pressure of 3.0 MPa. A collection of spectroscopic data (Raman, FT-IR, and 13C NMR) is presented, and the results confirm total conversion of the native HQ (α-HQ) into HQ clathrates (β-HQ) at the end of the reaction. Optical microscopy and SEM analyses reveal morphology changes after the enclathration reaction, such as the presence of surface asperities. Gas porosimetry measurements show that HQ clathrates and native HQ are neither micro- nor mesoporous materials. However, as highlighted by TEM analyses and X-ray tomography, α- and β-HQ contain unsuspected macroscopic voids and channels, which create a macroporosity inside the crystals that decreases due to the enclathration reaction. TGA and in situ Raman spectroscopy give the guest release temperatures as well as the structural transition temperatures from β-HQ to α-HQ. The gas storage capacity of the clathrates is also quantified by means of different types of gravimetric analyses (mass balance and TGA). After having been formed under pressure, the characterized clathrates exhibit exceptional metastability: the gases remain in the clathrate structure at ambient conditions over time scales of more than 1 month. Consequently, HQ gas clathrates display very interesting properties for gas storage and sequestration applications.

The main objective of this work was to evaluate and compare the AA performance of surfactants of different affinity in cyclopentane (CP) hydrate and gas (methane – propane mixture) hydrate systems. The study was performed with two surfactants: Noramium® DA 50 and Inipol® AH 81, which are respectively water-soluble and dispersible in water. Their AA performance was evaluated and compared without or with 4 wt% NaCl. A comparative study of the effect of the surfactants on the water/CP interfacial activity was carried out by surface pressure measurements. The impact of the surfactants on hydrate formation and morphology was observed by microscopic observations at the water/CP interface. Lastly, the AA performance of DA 50 and AH 81, was evaluated at the macroscopic scale in a batch reactor under agitation. The experiments in reactor were performed in oil-dominated systems (70 vol%) with CP as the oil phase in the CP hydrate system, and n-octane in the gas hydrate one.

Hydroquinone (HQ) can form a gas clathrate in specific pressure and temperature conditions in the presence of CO2 molecules. This study presents experimental data of clathrate phase equilibrium and storage capacity for the CO2-HQ system in the range of temperature from about 288 to 354 K. Intercalation enthalpy and entropy are determined using the obtained equilibrium data and the Langmuir adsorption model. On a kinetic point of view, CO2-HQ clathrate formation by solid/gas reaction revealed a non-negligible effect of textural parameters on enclathration rate. Introduction Gas clathrates are inclusion compounds formed with host molecules self-associating and forming cages, able to retain low molecular-weight guest molecules of gas, which have recently been highlighted as an alternative way for gas storage, transportation and separation [1-2]. Gas hydrates show high gas storage capacity. However, for potential industrials applications, the hydrate-based processes require a non-negligible energetic cost as gas hydrates are usually formed at low temperature, typically a few degrees above 273 K, and high pressure of several MPa [3]. To overcome this problem, hydroquinone (HQ) has been pointed out because of its capability to form organic clathrates over a wide range of temperature and at moderate pressure (a few MPa) [4-6]. The stable form of HQ at ambient conditions of pressure and temperature is the -HQ. Whereas, the clathrate form is the -HQ. The maximum storage capacity of HQ is defined by its ideal stoichiometry of 1 molecule of gas per 3 molecules of HQ, if all the cavities are filled by one guest molecule [7]. Thus, for CO2-HQ clathrates the maximum theoretical quantity of gas which can be stored is 67.8 L (STP) / kg. This work presents experimental data on phase equilibria and kinetics of CO2-HQ clathrate formation. Such results could be of interest for potential gas storage, transportation, or separation applications that could be developed with this compound. The equilibrium curve, the clathrate occupancy and the intercalation enthalpy and entropy are determined in the range of temperature from about 288 to 354 K. Ways for kinetic improvements are proposed and discussed. Interestingly, the use of HQ-silica composite materials as reactive medium has shown that the kinetic of HQ clathrate formation can be significantly improved. Experimental section Materials HQ with purity of 99.5 mol% is provided by Acros Organics. The solvents used for the titration and impregnation experiments are butyl acetate and absolute ethanol (purities higher than 99 mol%). CO2 gas used for the experiments (mole fraction purity of 99.995%) is purchased from Linde Gas SA. The porous supports are analytical grade spherical silica particles (SiliaSphere®) sizing 200-500 μm with pore size of 100 nm provided by SiliCycle. Apparatus and Procedures The experimental apparatus used for determining equilibrium conditions of clathrates is composed by a jacketed and stirred high pressure crystallizer connected to a gas storage tank, a solvent container, and a vacuum pump [8]. This experimental set-up allows achieving isothermal titration [8], which is the method used to determine both the HQHQ-CO2 equilibrium curve and the clathrate occupancy. The capture kinetic and the gas storage capacity measurements are performed by a gravimetric method [9] at 3.0 MPa and 323 K, using a Rubotherm magnetic suspension balance. For these measurements, the HQ is conditioned in two ways in an attempt to increase the clathrate formation kinetics. Pure HQ is ground or deposited on porous support. The HQ deposition on porous silica support is performed in fluidized bed in a dry impregnation process [10]. This method consists in intermittently spraying a warm fluidized bed of porous silica particles with a HQ solution, allowing the coupling of the HQ solution penetration in the particle porosity and the solvent evaporation. Results and discussion Phase Equilibria and occupancies The experimental equilibrium data for the CO2−HQ systems are obtained in this work from isothermal titration experiments [8]. The equilibrium curve and the clathrate occupancies at these equilibrium conditions are shown in Figure 1. Compared to the CO2 hydrates equilibrium curve [11-12], it can be noted that the CO2-HQ clathrates can be formed over a wide range of temperature and at pressures not exceeding 1 MPa for temperatures close to 360 K. Regarding the obtained clathrate occupancies, it is obvious that these ones are temperature dependent. The CO2−HQ clathrate occupancy decreases with temperature, as already pointed out in literature for other HQ clathrates [13]. Figure 1: Equilibrium data for CO2-HQ system: , clathrate equilibrium curve; , clathrate occupancies as a function of temperature. As there is an analogy between enclathration and adsorption, the gas-clathrate equilibrium obey a Langmuir type isotherm [13-15], where the involved reaction, given by Equation 1, corresponds to the liberation of the CO2 guest molecules from the -HQ host lattice. θ CO2 ∙ 3 HQβ ⇋ 3 HQβ + θ CO2 (1) The Langmuir constant Clang related to this reaction (i.e. the thermodynamic equilibrium constant) depends on clathrate occupancy θ and equilibrium pressure Peq, as described by Equation 2. Clang = Peq ∙ (1 − θ) θ ⁄ (2) Thus, the intercalation enthalpy and entropy can be determined from the slope and the intercept of the linear fit of the logarithm of the Langmuir constant as a function of the inverse of equilibrium temperature (Figure 2) [13-14]. The obtained enthalpy is 42.3 ± 4.0 kJ/mol (14.1 ± 1.3 kJ/mol) and the associated entropy is 235 ± 11 J/mol/K (78 ± 4 J/mol/K). To determine the total dissociation enthalpy of the CO2-HQ clathrate, it is necessary to consider the enthalpy of the reversion of the residual -HQ to the -HQ structure of about -0.67 kJ/mol [16]. As a result, these data indicate that the CO2 can be recovered more easily from CO2-HQ clathrates than from CO2 hydrates as the dissociation enthalpy is about 60.6 ± 1.8 kJ/mol (10.0 ± 0.3 kJ/mol) between the quadruples points Q1 and Q2 of this system [17]. Figure 2: Linear fit of the logarithm of the Langmuir constants of CO2-HQ clathrates as a function of the inverse of temperature. Kinetic aspects When the gas clathrate is formed by direct gas/solid reaction between the CO2 and the HQ, the clathrate formation kinetics seems to be enhanced by increasing the gas/solid contact area [4-6]. Thus, working on the HQ conditioning (i.e. the increase of the specific area of the media and the improvement of the contact area between the CO2 and the HQ) is very important to achieve rapid enclathration kinetics. In this work, we have tested and compared the kinetic performances of HQ powder and of a HQ-silica composite material. The grinding of HQ gives a powder with a particle size of about 100 μm. The HQ deposition on porous silica support allows developing a composite material having the HQ content of 0.44 g/g. As shown in Figure 3 by SEM images of the obtained composite, it appears clearly that HQ coats uniformly the external surface of the silica particle. Moreover, HQ crystals could be present in the 100 nm pores. Indeed, as suggested by Hemati et al. [10] the growth phenomenon does not arise before the full filling of internal porosity. Figure 3: SEM images of HQ-silica composite material: (a) full particle and (b) external surface. The native, ground, and impregnated HQ are evaluated as media in CO2 capture experiments. The amount of CO2 captured by enclathration as a function of time is shown in Figure 4. For HQ-silica composite materials, the amount of CO2 likely to be adsorbed on native silica (i.e. 0.34 mol/kg) has been deduced from the total CO2 gas captured. It is worth noting that the two conditionings improve the kinetic of clathrate formation, which highlights the importance of CO2/HQ contact area. Figure 4: Molar quantity of CO2 captured by enclathration as a function of time normalized by mass of HQ: (full line) native HQ, (dashed line) ground HQ, and (dotted line) HQ impregnated on silica particles. Table 1 presents the kinetic criteria deduced from the gas capture measurements: (i) the reaction rate for the CO2 solubilization in the -HQ, (ii) the induction time, (iii) the enclathration reaction rate, and (iv) the characteristic time at which the clathrate occupancy is 50%. Compared to native HQ, although grinding of HQ seems kinetically interesting, it is obvious that the HQ-silica composite material is the most efficient medium for enclathration. Indeed, for this reactive medium there is no induction period, the enclathration reaction rate is increased by a factor 52, and the time to fill 50% of the clathrate cavities is decreased by a factor 55 compared to native HQ. Moreover, for HQ-silica composite material, the system reaches an equilibrium value of clathrate occupancy of 0.89 after approximately 3.5 days, whereas the clathrate occupancies are 0.18 and 0.34 for native and ground HQ, respectively at the same time. After about 1 month of reaction, it is found occupancies of 0.63 and 0.71 for native and ground HQ, respectively. These values are in agreement with the ones previously found for CO2-HQ clathrates monocrystals synthesized by crystallization from solvent [18]. Table 1: Kinetic data on the CO2 capture by HQ clathrate formation. Conclusion This study brings some information on the potentiality of HQ clathrates for CO2 capture and storage process. The measured equilibrium conditions suggest the possibility to overcome specific process limitation, as CO2-HQ clathrates can be formed in a wide range of temperature (reaching at least 354 K) and at moderate pressure (few MPa). Furthermore, on a kinetic point of view, it is shown that the enclathration kinetic can be improved by a specific conditioning of HQ allowing to increase the gas/solid contact area. The induction period can be avoided with a nonnegligible incr

This study addresses both the preparation of a reactive medium composed of porous particles impregnated with hydroquinone (HQ), an organic compound capable of forming gas clathrates, and an evaluation of the kinetic performance of these composite materials for CO2 capture. Two types of porous silica particles of different sizes and pore diameters were tested. The porous particles were impregnated with HQ by a dry impregnation (DI) method in a fluidized bed, and by a wet impregnation (WI) method. The impregnation effectiveness of the two methods is discussed, and the reactivity of the composite materials formed in terms of CO2 capture and storage capacity is studied experimentally. The experimental results showed that the HQ adheres well on the silica without any chemical modification of the deposit’s structure. We demonstrated that the impregnation technique plays a very important role in the kinetics of CO2 capture. A series of experiments performed using a magnetic suspension balance at 3.0MPa and 323K showed that the silica-based impregnated particles reversibly capture and store CO2, and that the CO2 capture kinetics are significantly enhanced compared to the results obtained with pure powdered HQ. Finally, we demonstrated that CO2 capture is faster with dry-impregnated particles.

Hydroquinone (HQ) is known to form organic clathrates with different gaseous species over a wide range of pressures and temperatures. However, the enclathration reaction involving HQ is not fully understood. This work offers new elements of understanding HQ clathrate formation and dissociation mechanisms. The kinetics and selectivity of the enclathration reaction were also investigated. The focus was placed on HQ clathrates formed with CO2 and CH4 as guest molecules for potential use in practical applications for the separation of a CO2/CH4 gas mixture. The structural transition from the native form (α-HQ) to the clathrate form (β-HQ), as well as the reverse process, were tracked using in situ Raman spectroscopy. The clathrate formation was conducted at 323 K and 3.0 MPa, and the dissociation was conducted at 343 K and 1.0 kPa. The experiments with CH4 confirmed that a small amount of gas can fill the α-HQ before the phase transition from α- to β-HQ begins. The dissociation of the CO2-HQ clathrates highlighted the presence of a clathrate structure with no guest molecules. We can therefore conclude that HQ clathrate formation and dissociation are two-step reactions that pass through two distinct reaction intermediates: guest-loaded α-HQ and guest-free β-HQ. When an equimolar CO2/CH4 gas mixture is put in contact with either the α-HQ or the guest-free β-HQ, the CO2 is preferentially captured. Moreover, the guest-free β-HQ can retain the CO2 quicker and more selectively.

Hydroquinone (HQ) clathrates seem to be promising inclusion compounds for selective CO2 capture from gas mixtures. However, to date no phase equilibrium data are known in literature for mixed-gas HQ clathrates. This study presents experimental equilibrium pressures obtained within a range of 298343 K for different CO2/CH4 gas mixtures. The clathrate composition is given for each equilibrium point. The capture selectivity is calculated from the molar composition of the CO2/CH4 gas mixture in the clathrate and in the gas phase. The results obtained reveal that CH4 molecules in the CO2/CH4 mixtures are preferentially captured at equilibrium conditions. Our experimental data are compared against numerical predictions obtained from thermodynamic modeling using the Conde's model. Very good agreement is found between the calculated and experimental data in terms of clathrate phase equilibria. (C) 2017 Elsevier Ltd.

Secondary refrigeration and thermal energy storage are promising solutions to enhance the performance of refrigeration systems and reduce the impact of refrigerants on the environment. To improve the energy efficiency of secondary refrigeration loops, phase change material (PCM) slurries with a high energy density, such as CO2 hydrate slurries, can be used as a secondary refrigerant. In addition, hydrate-based processes could be an innovative option to capture CO2 from flue gas. In both applications, the rheological properties of the CO2 hydrate slurry have to be controlled. In the present study, CO2 hydrate slurry in the presence of Sodium Dodecyl Sulfate (SDS) was studied in a dynamic flow loop. The results show that SDS used at concentrations of 1500–2000ppm significantly decreases agglomeration and improves the flow properties of the slurry. Moreover, SDS helps decrease the viscosity of the CO2-hydrate slurry at high fraction (>10vol%) and therefore could be suitable for use in industrial applications such as secondary refrigeration, in which hydrate slurries must be easy to handle.