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Fluorinated gases (F-gases), such as CHF3 and C2F6, which are used in the semiconductor industry and have considerable global warming potential, can be recovered after use through a gas hydrate-based separation method to prevent their release into the atmosphere. In this study, the guest distributions and dissociation enthalpy (ΔHd) of F-gas (CHF3 or C2F6)+N2 hydrates with different F-gas concentrations (CHF3: 20%, 80%, and 100% and C2F6: 20%, 60%, 80%, and 100%) were experimentally investigated using a powder X-ray diffractometer and a high-pressure micro-differential scanning calorimeter, respectively. At high N2 concentrations in the feed gas, the occupancy of N2 in the small (512) cages of the F-gas+N2 hydrates increased significantly. As a result, the F-gas+N2 hydrates exhibited reduced hydration numbers at high N2 concentration. The ΔHd values (in kJ/mol gas) of the F-gas (CHF3 or C2F6)+N2 hydrates decreased with increased N2 concentration. The overall experimental results provide useful insights into the design and operation of gas hydrate-based F-gas separation processes. [ABSTRACT FROM AUTHOR]

• We report new data on dissociation pressure of CO 2 hydrate in sulfate solutions. • Sulfate solutions exhibit thermodynamic inhibition effects on CO 2 hydrate. • CuSO 4 solutions show slight inhibition effects on CO 2 hydrate. • The predicted dissociation pressure agrees reasonably well with the measured data. • The dissociation enthalpies depend on temperature and sulfate salt concentration. Carbon capture and storage (CCS) has been a popular strategy to mitigate climate change and has attracted significant attention from both industry and academia. CO 2 can be stored in the form of CO 2 hydrate in deeper locations in an ocean, which makes it a potential option for CO 2 sequestration. Dissolved salts in the ocean brine can significantly affect the dissociation pressure of CO 2 hydrate. Sulfate salts are one of the most common salt species in the oceanic brine. Although various experimental studies have been conducted to investigate the phase behavior of CO 2 hydrate in brine, few studies focus on the effect of sulfate salts on the dissociation pressure of CO 2 hydrate. In this study, we build an in-house experimental setup to investigate the effect of monovalent and divalent sulfate salts on the dissociation pressure of CO 2 hydrate. The dissociation pressure of CO 2 hydrate in Na 2 SO 4 , K 2 SO 4 , MgSO 4 , and CuSO 4 aqueous solutions is measured using the isochoric pressure search method at different concentrations over the temperature range of 274.36 – 282.15 K and the pressure range of 1.50 – 4.03 MPa. A hybrid methodology incorporating the Soave-Redlich-Kwong Equation of State (SRK EOS), the van der Waals-Platteeuw (vdW-P) model, and the Pitzer model is applied to predict the dissociation pressure of CO 2 in sulfate solutions. In addition, the dissociation enthalpies of CO 2 hydrate in these sulfate solutions are calculated using the Clausius-Clapeyron equation based on the measured dissociation points. The experimental results show that the dissociation pressure of CO 2 hydrate in Na 2 SO 4 , K 2 SO 4 , and MgSO 4 solutions is higher than that in pure water, and the dissociation pressure of CO 2 hydrate in sulfate solutions increases with an increasing salt concentration. Conversely, CuSO 4 barely affects the dissociation pressure of CO 2 hydrate, which is mainly attributed to the lower molar concentration of the ions compared with the other salt solutions and the ion specificity of Cu2+. The prediction results are in alignment with the experimental data measured in this study, which proves the feasibility of the thermodynamic model in predicting the dissociation pressure of CO 2 hydrate in sulfate solutions. Additionally, the calculated dissociation enthalpies of CO 2 hydrate show a dependence on both temperature and salt concentration. It is also revealed that Cu2+ exhibits ion specificity in affecting the dissociation enthalpy of CO 2 hydrate, likely due to its more distinct ability to impact the cage occupancy of CO 2 hydrate than the other ions. These findings enhance our understanding of the impact of sulfate salts on the dissociation behavior of CO 2 hydrate and offer valuable insights for CO 2 sequestration. [ABSTRACT FROM AUTHOR]

Due to high storage capacity, high dissociation enthalpy, and the appropriate melting point of gas hydrates, these compounds have a potential for many industrial applications. Tetra n-butylammonium halides are typical guest molecule involved in the formation of semiclathrate hydrates. In this manuscript, the dissociation enthalpy of methane/carbon dioxide/nitrogen + Tetra n-butylammonium Chloride semiclathrate hydrates is evaluated using the Clausius-Clapeyron equation. The equilibrium data are measured in a 460 cm3 stirred batch reactor using an isochoric pressure-search method. The dissociation enthalpy data were evaluated in the temperature range of (275.15 to 304.75) K and the pressure range of (0.36 to 10.57) MPa at (0 - 0.36) mass fraction of Tetra n-butylammonium Chloride. The results showed that the utilization of Tetra n-butylammonium Chloride increases the amount of dissociation enthalpy of semiclathrate hydrates per mole of the hydrated gas. By increasing the mass fraction of Tetra n-butylammonium Chloride, the amount of dissociation enthalpy per mole of hydrated gas increased.

As a promising new energy source, natural gas hydrates (NGHs) have attracted wide attention. The thermophysical properties of NGHs are of great significance to their exploitation. This work summarizes the progress of laboratory measurements and models of NGH thermophysical parameters, such as phase equilibrium, thermal conductivity, dissociation enthalpy, thermal diffusivity, and specific heat capacity. The advantages and disadvantages of measurement methods, numerical models, typical experimental data, and characteristics are discussed. The measurement accuracy of hydrate phase equilibrium is closely related to the estimation (or prediction) of the temperature (pressure), at which gas hydrate may decompose, as well as the heating rate, pores, residual water, ice and additive, etc., affect the sample quality as well as the thermal conductivity. The randomness of hydrate nucleation and growth leads to the uncertainty of hydrate distribution in sediments, which directly affects the accuracy of thermophysical property prediction models. Moreover, some future perspectives are suggested.

Semiclathrate hydrate formers such as tetra-n-butylammonium bromide (TBAB), chloride (TBAC) and fluoride (TBAF) are promising compounds that mild the thermodynamic conditions of gas hydrates, considerably. The Clausius-Clapeyron equation is employed in this manuscript to calculate the dissociation enthalpies of methane/carbon dioxide/nitrogen + TBAF semiclathrate hydrates. A 460 cm3 stirred batch reactor was used to measure the phase equilibria of gas + TBAF semiclathrate hydrates at various concentrations of tetra-n-butylammonium fluoride. The dissociation P-T data were obtained using an isochoric pressure-search method in the temperature range of 275.15 to 304.7 K and the pressure range of 0.53 to 10.24 MPa at 0.0 - 0.4482 mass fraction of TBAF. Investigating the obtained dissociation data showed that the addition of TBAF to the solution increases the amount of dissociation enthalpy of semiclathrate hydrates per mole of the hydrated gas. Increasing the mass fraction of tetra-n-butylammonium fluoride, showed a straight relation with the amount of dissociation enthalpy per mole of hydrated gas.

Due to high storage capacity, high dissociation enthalpy, and the appropriate melting point of gas hydrates, these compounds have the potential for many industrial applications. Tetra-n-butylammonium halides are molecules that can form semiclathrate hydrates. This manuscript employed the Clausius Clapeyron equation to evaluate the dissociation enthalpy of methane/nitrogen/carbon dioxide + tetra-n-butylammonium chloride (TBAC) semiclathrate hydrates (SCHs). Phase equilibrium data are measured in a batch reactor with an effective volume of 460 cc. The data of dissociation enthalpy were evaluated in the temperatures of (275.15 to 304.75) K and the pressures of (0.36 to 10.57) MPa at (0 - 0.36) mass fraction of TBAC. The results showed that the utilization of TBAC increases the amount of dissociation enthalpy of semiclathrate hydrates per mole of the hydrated gas. By increasing the amount of TBAC in the system, the quantity of dissociation enthalpy per mole of hydrated gas increased. [ABSTRACT FROM AUTHOR]

Multi-domain proteins or intrinsically disordered proteins (IDPs) often undergo liquid-liquid phase separation (LLPS) and form membraneless organelles or protein condensates. Such compartmentalization is considered critical in many cellular processes dynamically modulated by various external signals. However, molecular mechanisms underlying potential regulatory functions of the protein condensates remain obscure due to a limited understanding of the driving forces for their assembly. Here we propose isothermal titration calorimetry (ITC) as an efficient analytical tool to dissociate condensates and measure the corresponding dissociation heat. Subsequent analysis of the initial dissociation heat as a function of total protein concentration allows simple and accurate determination of the thermodynamic parameters for cooperative condensate formations including the dissociation (or condensation) enthalpy and the critical protein concentration. By performing systematic simulations, we further demonstrate that the initial heat analysis is sufficiently robust to quantitatively dissect protein condensates with a broad range of thermodynamic properties. Therefore, our proposed method analyzing the initial heat measured in dissociation ITC provides opportunities to further scrutinize the thermodynamic quantities as functions of solution variables to explore the molecular driving forces of LLPS. • Simulation of isothermal titration calorimetry dissociating biomolecular condensates. • Initial heat analysis for thermodynamic dissection of biomolecular condensates. • Utilization of ITC experiments at various concentrations of a protein stock. • Reliable quantification for a broad range of phase separation thermodynamics. [ABSTRACT FROM AUTHOR]

An elaborated statistical mechanical theory on clathrate hydrates is applied to exploration of their phase equilibria and dissociation enthalpies. The experimental dissociation pressures of methane, ethane, acetylene, and propane hydrates are well recovered by the method we have proposed. We estimate water/hydrate and hydrate/guest two‐phase coexisting conditions in the temperature, pressure, and composition space in addition to three‐phase equilibrium conditions. It is shown that the occupancy of guest molecules and the two‐phase boundaries in the phase diagram vary depending sensitively on its size. Enthalpy components arising from the host and guest interactions are separately calculated from the temperature dependence of the corresponding free energy values. This enables to evaluate the dissociation enthalpy at any stable and metastable thermodynamic state taking account of the phase transition in the coexisting phase such as melting of ice, notably that along the three‐phase equilibrium line. [ABSTRACT FROM AUTHOR]

As human society has advanced, nuclear energy has provided energy security while also offering low carbon emissions and reduced dependence on fossil fuels, whereas nuclear power plants have produced large amounts of radioactive wastewater, which threatens human health and the sustainability of water resources. Here, we demonstrate a hydrate-based desalination (HBD) technology that uses methane as a hydrate former for freshwater recovery and for the removal of radioactive chemicals from wastewater, specifically from Cs- and Sr-containing wastewater. The complete exclusion of radioactive ions from solid methane hydrates was confirmed by a close examination using phase equilibria, spectroscopic investigations, thermal analyses, and theoretical calculations, enabling simultaneous freshwater recovery and the removal of radioactive chemicals from wastewater by the methane hydrate formation process described in this study. More importantly, the proposed HBD technology is applicable to radioactive wastewater containing Cs + and Sr 2+ across a broad concentration range of low percentages to hundreds of parts per million (ppm) and even subppm levels, with high removal efficiency of radioactive chemicals. This study highlights the potential of environmentally sustainable technologies to address the challenges posed by radioactive wastewater generated by nuclear technology, providing new insights for future research and development efforts.

The enthalpies of l-carnosine interaction with solutions of hydrochloric acid have been measured by calorimetric method in the presence of NaCl at 298.15 K and ionic strength as high as 0.25, 0.50 and 0.75 mol dm−3. The enthalpies of acid dissociation have been determined from the obtained data. The effect of a background electrolyte concentration on the dissociation enthalpy of peptide has been considered. Standard thermodynamic quantities (ΔdisH°, ΔdisG°, ΔdisS°) of the acid dissociation of the dipeptide in aqueous solutions have been determined on the basis of the obtained thermochemical results and available data on the acid dissociation constants corrected for the zero-order ionic strength. Ability to acid dissociation of amino acids in a free state is compared with those for amino acid residues involved in the dipeptide linkage. The alteration of acidity has been connected with variation in hydration of reactivity centers. [ABSTRACT FROM AUTHOR]

Here, we introduce CO 2 hydrate-based desalination (CHBD) technology for freshwater recovery from radioactive wastewater, for water particularly containing Cs and Sr. The hydrate equilibrium curves of CO 2 hydrates shift towards lower temperature and higher pressure regions as the concentrations of CsCl and SrCl 2 increase. X-ray diffraction and Raman spectroscopy measurements found that neither CsCl nor SrCl 2 can affect the structure of CO 2 hydrates. The high-pressure micro-differential scanning calorimetric results demonstrate that CO 2 hydrates in the presence of CsCl and SrCl 2 started to dissociate at lower temperatures due to the enrichment of CsCl and SrCl 2 in the remaining solutions. The formation kinetics results indicate that increases in the concentrations of the radioactive chemicals lead to a decrease in the initial reaction rate and sub-cooling temperature. Solid-state nuclear magnetic resonance spectroscopy was utilized to confirm the exclusion of radioactive isotopes from solid gas hydrates. Importantly, the CHBD technology proposed in this study is applicable to radioactive wastewater containing Cs+ and Sr2+ across broad concentration ranges, spanning from a percent to hundreds of parts per million (ppm), and even sub-ppm levels, with comparable recovery efficiency. This study presents new insights into the potential of environmentally sustainable technologies to overcome the challenges posed by radioactive wastewater. [Display omitted] • The thermodynamic stability of CO 2 hydrates in the presence of CsCl and SrCl 2 was investigated. • The presence of Cs+, Sr2+, and Cl− ions had no impact on the crystal structure of CO 2 hydrates in the sI hydrate structure. • Dissociation enthalpy of CO 2 hydrates in the presence of CsCl and SrCl 2 was experimentally and theoretically investigated. • Formation kinetics of CO 2 hydrates in the presence of CsCl and SrCl 2 was investigated. • The ion exclusion from solid hydrate phases was confirmed by solid-state NMR measurements. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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In this work, a high pressure micro-differential scanning calorimeter (HP µ-DSC) was employed to measure the phase equilibrium data and dissociation enthalpies of tetra- n -butylammonium chloride (TBAC) semiclathrate hydrate formed in the presence of CO 2 , CH 4 , and CO 2 + CH 4 . The TBAC concentration varied from 1.0 mol% to 5.0 mol%, and the operating pressure changed from 1.0 MPa to 5.0 MPa. It was found that the phase boundary of TBAC semiclathrate hydrate formed at 3.3 mol% TBAC was lower than that obtained at 1.0 mol% and 5.0 mol% TBAC in the presence of CO 2 + CH 4 , and the hydrate dissociation enthalpy obtained at 3.3 mol% TBAC was larger than that obtained at 1.0 mol% and 5.0 mol% TBAC. This result indicates that TBAC semiclathrate (TBAC·29.7H 2 O) formed at the stoichiometric concentration (3.3 mol%) was more stable than that formed at 1.0 mol% and 5.0 mol% TBAC in the presence of CO 2 + CH 4 . In addition, pure TBAC semiclathrate hydrate and the mixed TBAC + CO 2 + CH 4 semiclathrate hydrate were found to coexist at 1.0 mol% TBAC. The hydrate dissociation enthalpy for the mixed TBAC + CO 2 + CH 4 semiclathrate hydrate formed at 3.3 mol% TBAC was found to increase with the increase of pressure. This is probably because a larger amount of the CO 2 + CH 4 gas mixture was incorporated into the TBAC semiclathrate hydrate at a higher pressure. [ABSTRACT FROM AUTHOR]

The dissociation enthalpy of methane hydrate is an important thermal parameter for hydrate-related work. In this paper, the dissociation enthalpies of methane hydrate in various salt solutions are calculated using the previously measured H-L W -V equilibrium data by the Clapeyron equation and the Clausius-Clapeyron equation, respectively. The calculated results by the Clapeyron equation do not show temperature dependence and the order of the dissociation enthalpy of methane hydrate in different salt solutions is 0.5NaCl>0.5MgCl 2 >0.5CaCl 2 > 1.0NaCl >1.0CaCl 2 >2.0NaCl>1.0MgCl 2 , the corresponding value of which is 52.6 ± 0.1 kJ/mol, 51.3 ± 0.3 kJ/mol, 50.4 ± 0.5 kJ/mol, 49.4 ± 0.3 kJ/mol, 46.0 ± 0.2 kJ/mol, 45.1 ± 0.2 kJ/mol and 44.0 ± 0.3 kJ/mol. Both the values and the errors calculated by the Clausius-Clapeyron equation are bigger than those by the Clapeyron equation. Moreover, the calculated values obtained by the Clausius-Clapeyron equation decrease with the temperature increase. Cations have less effect on the dissociation enthalpy than anions due to the different ability in affecting the ambient water networks. However, how the two effects (the colligative effect and the salting out effect) combine to influence the dissociation enthalpy of hydrate needs to be investigated further. [ABSTRACT FROM AUTHOR]

This paper presents a series of experimental and modelling studies on the thermodynamic inhibition effects of four ionic liquids on the methane hydrate formation. The investigated ionic liquids are 1-methyl-3-octylimidazolium chloride [MOIM-Cl], 1-methylimidazolium hydrogen sulfate [H-MIM-HSO 4 ], tetraethylammonium iodide [TEA-I], and 1-hexyl-3-methylimidazolium iodide [HMIM-I]. The impact of 0.1 mass fraction concentration ionic liquids on the methane hydrate phase boundary was evaluated by measuring the dissociation temperature of methane hydrate in the pressure range of 5.1–11.1 MPa, using a high pressure differential scanning calorimeter. The molar dissociation enthalpy of methane hydrates was calculated using the Clausius–Clapeyron equation. The density was measured for 0.10 mass fraction of aqueous solutions of ionic liquids at 293.15 K, and then compared to the commercially available gas hydrate inhibitors. The results demonstrated that 1-methylimidazolium hydrogen sulfate [H-MIM-HSO 4 ] has the highest inhibitory performance among the four ionic liquids considered. Moreover, the Dickens and Quinby-Hunt (electrolyte) model was applied to predict the phase equilibrium data of the studied ILs. The predicted data is in agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The CH 4 -CO 2 replacement occurring in sII natural gas hydrates for CH 4 recovery and CO 2 sequestration was investigated with a primary focus on thermodynamic, microscopic, and kinetic aspects. The guest-exchange behavior during replacement and the end-state composition analysis of replaced hydrates demonstrated that the extent of the replacement after CO 2 injection into the sII CH 4 + C 3 H 8 hydrate was significantly enhanced with an increase in the injected CO 2 pressure ( P CO2 ). The structure identification using powder X-ray diffraction (PXRD) suggested that the higher extent of replacement at higher P CO2 was closely related with the higher portion of sI hydrate after replacement. 13 C NMR spectroscopy confirmed that most of the CH 4 molecules resided in the small cages of the replaced sII hydrate while small amount of them also existed in the CO 2 -rich sI hydrate after replacement. The dissociation behavior and dissociation enthalpies of the replaced hydrates examined using an HP μ-DSC also verified the structural coexistence of sI and sII hydrates after replacement. The overall results can offer the first experimental evidence of the relationship between the replacement efficiency and the partial structure-transition in the CH 4 + C 3 H 8 − CO 2 replacement, and can provide further insights into the cage-specific occupation of external gas molecules and thermal property changes for the actual replacement occurring in sII natural gas hydrates. [ABSTRACT FROM AUTHOR]

The CO 2 hydrate with tetrahydrofuran (THF) is used to study the kinetics of CO 2 hydrate dissociation. The experiments are conducted at temperature (279–280) K and moderate pressures (0.3, 0.4 and 0.5 MPa), which are suitable for the cooling application. These experimental conditions can also make sure that there is no dissociation of the THF hydrate. No kinetic model and experimental correlation to calculate the activation energy and dissociation rate of the CO 2 hydrate with THF has been found. From this study, it is found that the dissociation rate strongly depends on the temperature. A kinetic model is developed to predict the activation energy for CO 2 -THF (5.56 mol%) hydrate, which fits well the experimental data with the error bands of ±8.2%. An experimental correlation for CO 2 -THF hydrate dissociation rate is developed with the error bands of ±26.0%, which can be used to calculate the dissociation rate for estimation of cooling load for district cooling application. It is found that the activation energy ΔE for CO 2 hydrate with THF is estimated as 193.6 kJ/mol and the enthalpy of the CO 2 -THF hydrate is measured to be 263.5 kJ/kg-H 2 O. Based on the results, the CO 2 hydrate district cooling system with CO 2 –THF hydrate slurry is simulated for 5000 RT, and the COP is estimated as 14.3. [ABSTRACT FROM AUTHOR]

CO 2 conversion by gas hydrate is considered one of most practical technologies in the fields of Carbon Capture, Utilization and Storage (CCUS). In this study, the effects of hydrate formation pressure and concentration of tetrahydrofuran (THF) on the CO 2 + THF hydrate formation and dissociation performance are investigated, and the reduction of CO 2 emission by applying the CO 2 + THF hydrate for district cooling system is also evaluated. The CO 2 capture ratio tends to increase with increasing the hydrate formation pressure and THF concentration. It is found that the CO 2 regeneration rate increases with decreasing the formation pressure and the increasing rate decreases with time. It is concluded that the optimum conditions for the CO 2 + THF hydrate formation and dissociation are 1.5 MPa, THF 1.5 mol% to use hydrate slurry as the working fluid for district cooling application. Also, the dissociation enthalpy of CO 2 + THF hydrate was measured by using the high pressure micro-differential scanning calorimeter. The cycle simulation of hydrate cooling system is conducted, and the COP is estimated as 11.55. Finally, it is estimated that 20,684 tons of CO 2 emission could be reduced per year if the CO 2 + THF hydrate technology is applied to the district cooling system of 51,600 RT. [ABSTRACT FROM AUTHOR]

The CH 4 -flue gas replacement that occurs in structure H (sH) hydrates was investigated, with a primary focus on thermodynamic phase behavior, structure identification, heat flow monitoring, and dissociation enthalpy, for its dual function of CH 4 recovery and CO 2 sequestration. The significant shift in the equilibrium line of the CH 4 + neohexane (2,2-dimethylbutane, NH) hydrates replaced with CO 2 (10%) + N 2 (90%) and CO 2 (20%) + N 2 (80%) indicates that CH 4 molecules in the sH hydrates were significantly exchanged with flue gas mixtures. Furthermore, 13 C NMR spectroscopy revealed that replacement using flue gas occurs without a structural transition, and that CO 2 molecules preferentially attack CH 4 molecules occupied in the medium 4 3 5 6 6 3 cages of sH hydrates. The extent of the CH 4 + NH – flue gas replacement was approximately 74%. During CH 4 – flue gas replacement in sH hydrates, there was no significant change in heat flow associated with the dissociation and subsequent reformation of gas hydrates. Dissociation enthalpies of gas hydrates before and after replacement, measured using a high-pressure micro-differential scanning calorimeter (HP μ -DSC), also supported isostructural replacement with the high extent of reaction. This study reports the first experimental evidence of isostructural CH 4 – flue gas replacement occurring in sH hydrates, and thus, might contribute to extending the potential fields of CH 4 exploitation using a flue gas replacement, into sH natural gas hydrate reservoirs. [ABSTRACT FROM AUTHOR]

In present work, the phase equilibrium of methane + cyclopentane (CP) + timethylene sulfide (TMS) hydrate were measured in NaCl solution at the temperature range from 286.42 to 303.77 K and the pressure varying from 1.16 to 12.49 MPa. The experimental data were measured with an isochoric T-cycle method. The phase equilibrium pressure of organic compounds (V CP :V TMS = 4:1) + CH 4 hydrate increases with the temperature and the NaCl concentration. When the temperature was higher, the effect of temperature and NaCl concentration on the phase equilibrium pressure was more remarkable. The dissociation enthalpies of organic compounds (V CP :V TMS = 4:1) + CH 4 hydrate in 3.5, 5.0, 7.0, 10% (mass fraction) NaCl solution were calculated through the Clausius−Clapeyron equation based on the phase equilibrium data. The dissociation enthalpy decreases with the increase of either the temperature or the NaCl concentration. The crystal structure of organic compounds (V CP :V TMS = 4:1) + CH 4 hydrate was determined by using Raman spectroscopy. Methane was present only in the small sII cavity, cyclopentane and timethylene sulfide were all in the large sII cavities. [ABSTRACT FROM AUTHOR]

This paper reports ice + vapor + hydrate three-phase equilibrium condition measurements in CO 2 + H 2 O system at the temperatures from 199.1 K to 247.1 K. The phase equilibrium pressures measured in the present study are from 34.3 kPa to 406.6 kPa. The measurements were performed using the batch, isochoric method. The results of the present measurements complement the lack of the literature data on the phase equilibrium conditions at the above temperature range and contribute to CO 2 hydrate-related environmental issues and technologies below the water freezing temperature such as Martian environment, fire extinguisher and working media of power generation system. [ABSTRACT FROM AUTHOR]

The experimental study on phase equilibrium conditions for semi-clathrate hydrates formed in the systems of CH 4 /N 2 gas mixture and tetra-butyl-ammonium fluoride (TBAF) with different ratios (0.210, 0.293 and 0.500 mol%) to water was conducted in this paper. The experiments were carried out under the conditions of 281.15–291.15 K and 0.30–3.70 MPa. The structures of the hydrates were characterized using in-situ Raman spectroscopy at 276.15 K and 2.50 MPa. At a certain given pressure, the equilibrium temperature of the semi-clathrate hydrates formed in the systems with 0.500 mol% TBAF is significantly higher than that of semi-clathrate hydrates formed the systems with 0.210 or 0.293 mol% TBAF, and even higher than that of structure II hydrates formed in the systems with THF-SDS. Moreover, TBAF has more positive influence on enhancing dissociation enthalpies of the hydrates than THF. Due to the quite weak signal of N–N triple bond vibration or/and seldom N 2 molecules encaged into the cavities, only CH 4 molecules could be determined clearly in the mixed hydrates. In addition, the crystal morphology of the semi-clathrate hydrates is affected by the ratio of TBAF to water. [ABSTRACT FROM AUTHOR]

The thermodynamic phase behaviors, dissociation enthalpies, and Raman spectra of N 2 + tetra-n-butyl ammonium chloride (TBAC) + water systems were measured in order to investigate the enclathration of N 2 in TBAC semiclathrates. The three-phase (H-L w -V) equilibria of the N 2 + TBAC (1.0, 3.3, and 5.0 mol%) semiclathrates measured using a high pressure vessel as well as a high pressure micro-differential scanning calorimeter (HP μ-DSC) indicated that the N 2 + TBAC semiclathrates have significant stability in the thermodynamic equilibrium compared with the N 2 gas hydrate and that they also exhibit maximum thermodynamic stability at 3.3 mol%, which corresponds to the stoichiometric concentration of TBAC·29.7H 2 O. The dissociation enthalpies of the N 2 + TBAC semiclathrates were determined from the endothermic dissociation thermograms of a HP μ-DSC under pressure. The Raman spectroscopic results clearly demonstrated that N 2 molecules are enclathrated in the cages of the TBAC semiclathrate. From the overall experimental results, TBAC is expected to be an effective semiclathrate former that can reduce the equilibrium dissociation pressure or enhance the equilibrium dissociation temperature for enclosing N 2 molecules as a guest in the vacant cages of TBAC semiclathrates. [ABSTRACT FROM AUTHOR]

Phase equilibria, structure identification, and dissociation enthalpies of HFC-134a hydrates in the presence of NaCl are investigated for potential application in desalination. To verify the influence of NaCl on the thermodynamic hydrate stability of the HFC-134a hydrate, the three-phase (hydrate (H) - liquid water (L) - vapor (V)) equilibria of the HFC-134a+NaCl (0, 3.5, and 8.0 wt%)+water systems are measured by both a conventional isochoric (pVT) method and a stepwise differential scanning calorimeter (DSC) method. Both pVT and DSC methods demonstrate reliable and consistent hydrate phase equilibrium points of the HFC-134a hydrates in the presence of NaCl. The HFC-134a hydrate is identified as sII via powder X-ray diffraction. The dissociation enthalpies (ΔH) of the HFC-134a hydrates in the presence of NaCl are also measured with a high pressure micro-differential scanning calorimeter. The salinity results in significant thermodynamic inhibition of the HFC-134a hydrates, whereas it has little effect on the dissociation enthalpy of the HFC-134a hydrates. The experimental results obtained in this study can be utilized as foundational data for the hydrate-based desalination process. [ABSTRACT FROM AUTHOR]

In this study, the thermodynamic behaviors, cage-specific guest distributions, structural transition, and dissociation enthalpies of sH hydrates with CO 2 + N 2 gas mixtures were investigated for their potential applications to hydrate-based CO 2 capture and sequestration. The stability conditions of the CO 2 + N 2 + water systems and the CO 2 + N 2 + neohexane (2,2-dimethylbutane, NH) + water systems indicated that the gas mixtures in the range of flue gas compositions could form sH hydrates, thereby mitigating the pressure and temperature required for gas hydrate formation. Structure identification using powder X-ray diffraction (PXRD) revealed the coexistence of sI and sH hydrates in the CO 2 (40%) + N 2 (60%) + NH system and the hydrate structure transformed from sH into sI as the CO 2 concentration increased. In addition, the Raman analysis clearly demonstrated that CO 2 molecules were enclathrated into the cages of sH hydrates in the N 2 -rich systems. It was found from direct CO 2 composition measurements that CO 2 selectivity in the sH hydrate phase was slightly lower than that in the corresponding sI hydrate phase. Dissociation enthalpy (Δ H d ) measurements using a high-pressure micro-differential scanning calorimeter (HP μ-DSC) indicated that the Δ H d values could also provide valuable information on the structural transition of sH to sI hydrates with respect to the CO 2 concentration in the feed gas. This study provides a better understanding of the thermodynamic and physicochemical background for CO 2 enclathration in the sH hydrates and its significance in gas hydrate-based CO 2 capture and sequestration. [ABSTRACT FROM AUTHOR]

Protocatechuic acid, a major metabolite of antioxidant polyphenols found in green tea, has been shown to prevent carcinogenesis or antitumor growth in vitro and in vivo studies. The dilution enthalpies Δ dil H m , dissociation enthalpies Δ dis H m and thermodynamic dissociation constants K a for protocatechuic acid in aqueous NaCl or KCl solutions were simultaneously determined by mixing-flow microcalorimetry at T = 298.15 K. In order to verify the reliability of the fitted dissociation parameters, the values of dissociation enthalpies and thermodynamic dissociation constants were also determined by isothermal titration calorimetry and electrical conductivity methods. The K a values obtained through the proposed method agree well with those reported in literatures and obtained by other techniques. Enthalpic interaction coefficients ( h 2 , h 3 and h 4 ) were computed according to the McMillan–Mayer model. The trends of h 2 and Δ dis H m for protocatechuic acid with increasing salt molality in both the salt solutions were obtained. The different influence of KCl and NaCl on the values of h 2 and Δ dis H m were discussed in terms of (solute + solute) and (solute + solvent) interactions. The results showed that it is possible to perform in a single calorimetric experiment the simultaneous determination of dilution enthalpies, dissociation enthalpies and constants in a given solvent. [ABSTRACT FROM AUTHOR]

In this work, the performance of nine ionic liquids (ILs) as thermodynamic hydrate inhibitors is investigated. The dissociation temperature is determined for methane gas hydrates using a high pressure micro deferential scanning calorimeter between (3.6 and 11.2) MPa. All the aqueous IL solutions are studied at a mass fraction of 0.10. The performance of the two best ILs is further investigated at various concentrations. Electrical conductivity and pH of these aqueous IL solutions (0.10 mass fraction) are also measured. The enthalpy of gas hydrate dissociation is calculated by the Clausius–Clapeyron equation. It is found that the ILs shift the methane hydrate (liquid + vapour) equilibrium curve (HLVE) to lower temperature and higher pressure. Our results indicate 1-(2-hydroxyethyl) 3-methylimidazolium chloride is the best among the ILs studied as a thermodynamic hydrate inhibitor. A statistical analysis reveals there is a moderate correlation between electrical conductivity and the efficiency of the IL as a gas hydrate inhibitor. The average enthalpies of methane hydrate dissociation in the presence of these ILs are found to be in the range of (57.0 to 59.1) kJ ⋅ mol −1 . There is no significant difference between the dissociation enthalpy of methane hydrate either in the presence or in absence of ILs. [ABSTRACT FROM AUTHOR]

Recently, the CO 2 hydrate as cold storage medium draws much attention and some thermodynamic promoters are proposed to moderate its hydrate formation condition for reducing energy consumption. In this study, the hydrate phase equilibrium conditions of CO 2 in the presence of tetrahydrofuran (THF), cyclopentane (CP), tetrabutylammonium bromide (TBAB) were measured with the isochoric pressure searching method. The hydrate dissociation enthalpies were calculated with Clausius-Clapeyron equation base on the measured data sets. The results showed that the hydrate phase equilibrium temperature of CO 2 in the aqueous solution containing promoters increased at least 12 K at 1.5 MPa compared to that of CO 2 in the pure water system. The hydrate dissociation enthalpies of (CO 2 +CP+H 2 O), (CO 2 +THF+H 2 O), (CO 2 +TBAB+H 2 O) reached 136.16, 147.07, 205.75 kJ . mol−1, respectively, which significantly increased than that of (CO 2 +H 2 O) (64.93 kJ . mol−1). A thermodynamic framework was proposed to prediction the hydrate phase equilibria of CO 2 in the presence of promoters. The Chen-Guo (C-G) model was used to calculate the fugacity of hydrate phase, the NRTL and developed PMZH models were used to calculate the activity of liquid phase. The CO 2 solubility was calculated by the modified Henry's law, and the effect of volatile component in aqueous phase on the composition of gas phase was investigated. The predictions of our proposed model agree well with the measured data in this work as well as literature values. [ABSTRACT FROM AUTHOR]

Natural gas hydrate creates a lot of problems during its transportation and production by plugging gas pipelines and process equipment. This work envisages the effect of electrolytes (NaCl and CaCl2) at different concentrations on methane hydrate formation and dissociation. Extensive observations on equilibrium pressure and temperature during hydrate formation and dissociation have been made. The experiments were conducted in the temperature range of 261 to 270 K and pressure range of 2.6 to 3.0 MPa. Both sodium chloride and calcium chloride salts were found to have significant inhibiting effects on hydrate formation and dissociation with the latter having stronger effects. Gas consumption was found to vary with the progress of the hydrate formation as well as the concentration of salts in the hydrate cell. The dissociation enthalpies of methane hydrates in the presence of the above salts were also determined using the Clausius-Clapeyron equation based on the phase equilibrium data. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined the structure and dissociation enthalpies of CO2 +N2 hydrates. [•] The μ-DSC provided reliable hydrate phase equilibrium data. [•] The structural transition was not observed in the range of flue gas compositions. [•] The ΔHd of CO2 +N2 hydrates increased with an increase of CO2 composition. [ABSTRACT FROM AUTHOR]

• Magnetic field promotes CO 2 hydrate formation in water or NaCl solution. • Magnetic field enhances the phase equilibrium temperature of CO 2 hydrate. • Magnetic field affects the dissociation enthalpy of CO 2 hydrate. The formation kinetic parameters, phase equilibrium and dissociation enthalpy of carbon dioxide hydrate in the presence of static magnetic field were investigated in this work. The experiments were carried out in pure water and (0.029, 0.056 and 0.110, mass fraction) sodium chloride (NaCl) aqueous solution with a magnetic field of 0.39 T. The experimental results showed that the induction time of carbon dioxide hydrate nucleation was shortened, the consumption amount and rate of carbon dioxide were significantly increased with the magnetic field. This phenomenon is mainly attributed to the fact that the magnetic effect decreases the contact angle between water and solid surface to reduce the critical size and critical free energy of hydrate nucleation. Moreover, the phase equilibrium of carbon dioxide hydrate in both pure water and NaCl aqueous solution shifted to lower pressure or higher temperature with the magnetic field, and the equilibrium temperature in pure water decreased by 3.0 K, which is due to the change of the hydrogen bond in small clusters and ions mobility by magnetic effect. In addition, the dissociation enthalpies of carbon dioxide hydrate in pure water and (0.029, 0.056 and 0.110) NaCl solution calculated by Clausius-Clapeyron equation were 91.5, 91.4, 62.8 and 52.0 kJ·mol−1, respectively, in the magnetic field, which is related to the movements of ions caused by magnetic effect and heat absorption. [ABSTRACT FROM AUTHOR]

Abstract: A study of the (fluoromethane+water) system was conducted at temperatures between 255K and 298K, and pressures from 0.09 to 2.6MPa. The solubility of fluoromethane in liquid water was measured from 280K to 298K, at pressures up to the hydrate formation pressure. The p–T behavior of the liquid+hydrate+vapor (LHV) three-phase equilibrium was measured from 273K to 295K. The p–T behavior of the ice+hydrate+vapor (IHV) three-phase equilibrium was measured from 251K to 273K. The intersection of the LHV and IHV curves was used to find the lower quadruple point, Q1, at T =272.55K and p =0.2442MPa. Solubility-corrected enthalpies of dissociation were determined at the lower quadruple point using the Clapeyron equation. The de Forcrand method was used to determine the hydration number of the hydrate at Q1. The results show that not all of the cages in the SI hydrate structure are filled. [Copyright &y& Elsevier]

RuCp (ruthenocene) and RuCpPy (cyclopentadienyl pyrrolyl ruthenium) complexes are used in ruthenium (Ru) atomic layer deposition (ALD) but exhibit a markedly different reactivity with respect to the substrate and co-reactant. In search of an explanation, we report here the results of a comparative study of the heterolytic and homolytic dissociation enthalpy of these two ruthenium complexes, making use of either density functional theory (DFT) or multiconfigurational perturbation theory (CASPT2). While both methods predict distinctly different absolute dissociation enthalpies, they agree on the relative values between both molecules. A reduced heterolytic dissociation enthalpy is obtained for RuCpPy compared to RuCp, although the difference obtained from CASPT2 (19.9 kcal/mol) is slightly larger than the one obtained with any of the DFT functionals (around 17 kcal/mol). Both methods also agree on the more pronounced stability of the Cp ligand in RuCpPy than in RuCp (by around 9 kcal/mol with DFT and by 6 kcal/mol with CASPT2). [ABSTRACT FROM AUTHOR]

The phase behaviour of the system water-tri- n-butylmethylammonium chloride (TBMAC)-CO was investigated by pressure-controlled differential scanning calorimetry in the range 0-10 mol% TBMAC in water and at CO pressures ranging from 0 to 1.5 MPa. In the absence of CO, an incongruent melting hydrate, which estimated composition corresponds to TBMAC·30HO, crystallizes at temperatures below −13.6 °C and forms with ice a peritectic phase at approximately 3.9 mol% TBMAC. In the presence of CO at pressures as low as 0.5 MPa, curves evidenced the presence of an additional phase exhibiting congruent melting at temperatures that are strongly pressure dependent and significantly higher than those of hydrates obtained without CO. This new phase, whose enthalpy of dissociation and CO content increase slightly with CO pressure, was identified as a mixed semi-clathrate hydrate of TBMAC and CO of general formula: (TBMAC + xCO)·30HO. [ABSTRACT FROM AUTHOR]

The dissociation constants of protonated 2-amino-1-ethanol (MEA), diethanol amine (DEA), triethanol amine (TEA), methyldiethanol amine (MDEA), 2-amino-2-methyl-1-propanol (AMP), 3-dimethylamino-1-propanol (DMAP), tris(hydromethyl)aminomethane (THAM), 2-[2-(dimethylamino)ethoxy]ethanol (DMAEOE) and, 1,2-bis(2-aminoethoxy)ethane (DiAEOE) were determined in the temperature range 293.15 to 343.15 K using a potentiometric titration method. The experimental technique was first validated using as reference the available literature data of MDEA. The dissociation enthalpies of amines were derived from their dissociation constants using the Van't Hoff equation. Experimental dissociation constants and dissociation enthalpies were discussed in term of amine structure and compared with literature values when available. [ABSTRACT FROM AUTHOR]

Abstract: A study of the (difluoromethane+water) system was conducted at temperatures between (255 and 298)K, and pressures from (0.06 to 1.30)MPa. The solubility of difluoromethane in liquid water was measured from (280 to 298)K, at pressures up to the hydrate formation pressure. The (p, T) behavior of the (liquid+hydrate+vapor) three-phase equilibrium was measured from (274 to 292)K. The (p, T) behavior of the (ice+hydrate+vapor) three-phase equilibrium was measured from (257 to 273)K. Solubility-corrected enthalpies of dissociation were determined at the lower quadruple point (Q1) using the Clapeyron equation. The de Forcrand method was used to determine the hydration number of the hydrate at Q1. The results show that not all of the cages in the SI hydrate structure are filled. [Copyright &y& Elsevier]

Tetra- n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N2 and CO2 and gases mixtures such as N2 + CO2 and CH4 + CO2 were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N2 for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26. [ABSTRACT FROM AUTHOR]

Tetra- n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N2 and CO2 and gases mixtures such as N2 + CO2 and CH4 + CO2 were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N2 for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26. [ABSTRACT FROM AUTHOR]

Ethylene oxide (EO), 1,3-propylene oxide (PO), tetrahydrofuran (THF), 1,3-dioxolane (1.3-DX), 1,4-dioxane (1,4-DX) and 1,3,5-trioxane (s-TO) were selected to investigate their thermodynamic promotion effects on CO 2 hydrate formation. New hydrate phase equilibrium data of carbon dioxide + epoxy heterocycles + water systems were determined employing an isochoric temperature-search method in the temperature range of (273.15 to 295.35) K and the pressure range of (0.4 to 4.5) MPa. Results showed that the presence of epoxy heterocycles significantly increased the hydrate formation temperature substantially compared with that of pure CO 2 hydrate. Under the same conditions, the phase equilibrium temperature of CO 2 hydrate under the action of the additive was from low to high: PO < 1,4-DX < 1,3-DX < s-TO < EO < THF. CO 2 hydrate dissociation enthalpies with different epoxy heterocycles were also calculated from Clausius–Clapeyron equation to infer their stabilities and the structures formed. It was found that the estimated enthalpy of dissociation was consistent with the superiority sequence obtained from the phase equilibrium data, illustrating that the water-soluble sII clathrate former of THF had the highest hydrate promoting effect. Moreover, Chen-Guo model, associated with a modified Joshi empirical activity model and PR equation of state was proposed further to predict hydrate phase equilibrium. Satisfactory agreement was observed between predictions and experimental data. Analysis of the results confirmed that the proposed thermodynamic model worked well in describing phase behavior of complex hydrates and the maximum relative error of the pressure was less than 8.5%. [ABSTRACT FROM AUTHOR]

Hydrate-based CO 2 capture technology is considered one of the most applicable methods for carbon capture, utilization, and storage, owing to its vast potential and cost effectiveness. Hydrate slurries with an appropriate solid fraction guarantee applicable flowing conditions, and their high dissociation enthalpy permits their use for cold thermal energy transportation. Nevertheless, the required conditions for hydrate formation make the direct capture and subsequent utilization of hydrate slurries challenging. Thus, thermodynamic promoters have been introduced to the hydrates to alleviate the formation conditions and facilitate their practical application. Tetrahydrofuran and tetra-n-butylammonium bromide are selected because of their inherent interaction with water molecules during hydrate formation. Hydrate formation using the pure promoters as well as a mixture of the two is evaluated based on various perspectives. The induction time, hydrate growth period, CO 2 capture ratio, and exothermic behavior of each absorbent are assessed under varying concentration and formation conditions. These key parameters provide considerable insight for determining optimal conditions for hydrate slurry-based cold thermal transportation. Based on the performance evaluation, three cases of single promoters and three mixed promoters under the condition of 3 bar are selected for the measurement of dissociation enthalpy. The results reveal that under 3 bar formation conditions, a 3:1 (THF mol%: TBAB mol%) concentration is suitable for ensuring a sufficiently high heat of dissociation and rapid hydrate slurry formation to permit considerable CO 2 capture. Consequently, an alternative to a conventional district cooling system by replacing it with a CO 2 hydrate slurry cooling system is proposed, and a sufficient reduction in energy consumption is demonstrated. • Mixed THF and TBAB are evaluated by essential aspects for CO 2 hydrate utilization. • Impact of TBAB is dominant for exothermic behavior and reducing the induction time. • Higher THF concentration accounts for higher CO 2 capture. • THF 3 mol%: TBAB 1 mol% is selected for the optimal condition for utilization. • Cycle simulation results reveal 7.41% of total energy consumption reduction. [ABSTRACT FROM AUTHOR]

The article presents a study of the Lw-H-V equilibrium conditions, the dissociation enthalpy and the CO2hydration number of a clathrate hydrate formed from THF/CO2/water mixtures using a differential scanning calorimetry (DSC) method. New equilibrium values have also been obtained in the present study together with hydrate dissociation enthalpy. It also compares the new equilibrium measurements with modeling results based on a model combining Van der Waals and Platteeuw approach with a predictive equation of state.

Abstract: The present work investigates equilibrium conditions and dissociation enthalpy of hydrates formed from CO2–TBAB (tetra-n-butylammonium bromide)–water mixtures. Differential Thermal Analysis (DTA) was used for hydrate–liquid–vapour (H–L–V) equilibrium condition determination in a TBAB concentration range from 4.43 to 9.01wt% and in a CO2 pressure range from 0.3 to 2.5MPa. The results showed that the presence of TBAB allowed decreasing the formation pressure of CO2 hydrate by approximately 74 and 87% at 283 and 279K, respectively. Moreover, pressure reductions were dependent on the TBAB concentration. The dissociation enthalpy and the composition of double hydrate formed from 9.01wt% TBAB solution were determined by both the DTA and Clapeyron equation. The DTA method resulted in 313.2kJkg−1 of hydrate for the dissociation enthalpy and 2.51CO2 ·TBAB·38H2O for composition of the double hydrate. For the use of Clapeyron equation, the volume change was defined by taking into account the gas solubility in the liquid phase. The calculation results showed a discrepancy with the experimental data obtained by DTA, suggesting the limited application of Clapeyron equation in the CO2–TBAB–water system. [Copyright &y& Elsevier]