Heat Of Dissociation Research Articles

Thermodynamic phase equilibria study of Hythane (methane + hydrogen) gas hydrates for enhanced energy storage applications

Hydrogen blending with natural gas has become an effective technique for incorporating the characteristics of natural gas and facilitating the storage and transportation of hydrogen gas. The transportation of hydrogen and natural gas (methane) blend, also referred to as Hythane, presents numerous challenges, advantages, and disadvantages that differ based on the technology employed. The current research showcased a thorough examination of the thermodynamics involved in studying the three phase equilibrium analysis of gas hydrate technology for storing Hythane gas mixtures. Three different Hythane compositions varying in hydrogen percentage were selected, and the isochoric gas hydrate phase equilibria study was performed. The experimental results of phase equilibria and thermodynamic modelling using CPA EOS in software were compared. A similar study was also conducted in the presence of a 5.56 mol % THF solution to understand the reduction in the pressure requirement for the phase equilibria. Results from the mixed Hythane+THF gas hydrate findings suggested stable gas hydrate formation at much lower pressure requirements, increasing the credibility of storing Hythane mixtures in gas hydrates at moderate conditions. The gas compositions for each experiment were analyzed using gas chromatography to evaluate the presence of the desired gas in the hydrate phase. Heat exchange during the gas hydrate dissociation was analyzed using a high pressure differential scanning calorimeter (DSC). The change in the heat release temperature also indicates the stability of the gas hydrate, and with increasing hydrogen gas in the blend, the gas hydrate stability decreased. The Clausius-Clapeyron equation was employed to compute the heat of gas hydrate dissociation, and a comparison was made with the heat of dissociation obtained from the DSC study. The experimental investigations on Hythane gas hydrates were performed to find the hydrogen storage inside the gas hydrate phase and compare it with the previous studies of pure hydrogen hydrates. To demonstrate the Hythane gas transportation, Hythane gas hydrate pellets were formed, followed by their storage in a controlled environment to observeany changes in pressure and temperature. The Hythane gas hydrate pellets demonstrated exceptional stability of Hythane gas presenting an intriguing prospect for utilizing gas hydrate technology in Hythane gas transportation.

An Experimental Study on the Influence Solution Concentration and Nano-Additives on Cold Storage Performance of Tetrabutylammonium Bromide

Tetrabutylammonium bromide (TBAB) is considered a promising alternative cold energy storage material. Due to the high dissociation heat of phase transition at an atmospheric pressure of 278–293 K, which reaches 200–500 kJ/kg, this substance is considered an effective cold energy storage medium for air conditioning systems. In this paper, the cold storage crystallization process of TBAB solution with different concentrations was tested by conducting experiments and the phase transition’s temperature and latent heat were measured. Finally, the growth characteristics of TBAB hydrate crystals with different concentrations (10%, 20%, 30% and 40%) were analyzed. Considering the cold storage temperature, phase transformation temperature and latent heat, the cold storage effect is the best when 40% TBAB solution is used. Although single substance phase change materials have a long service life, they have problems with low thermal conductivity and high undercooling. Therefore, researchers usually improve the performance of phase change materials by adding other auxiliary materials, thereby enhancing their application prospects. Among these auxiliary materials, adding nano additives to phase change materials can significantly improve latent heat, thermal conductivity and nucleation ability, while also reducing undercooling. Therefore, we studied the influence of different nano-additives (Al2O3, SiC, TiO2 and ZnO) on phase change materials. The composites with excellent properties were screened by cooling step cooling curve and differential scanning calorimeter (DSC). Compared with pure TBAB solution, the phase transition latent heat of the composite phase change materials (PCMs) prepared by adding nanoparticles were significantly increased. The results show that adding nano-SiC into 40% TBAB solution can obtain better performance. This work not only provides reference for the further research, but also a sight to design the phase change materials for the application of new phase change cold storage materials.

THERMODYNAMICS OF STEPWISE DISSOCIATION OF GLYCYL-D-PHENYLALANINE IN AQUEOUS SOLUTION

Recently, more and more drugs that are derivatives of oligopeptides have been introduced to the pharmaceutical market. The structural elements of these compounds are amino acids and dipeptides. When stabilizing functional groups are introduced into the peptide structure, as well as through the use of special delivery systems, oligopeptide derivatives can be used as innovative medicines. The calorimetric method was used to determine the heat of interaction of glycyl-D-phenylalanine with solutions of nitric acid and potassium hydroxide at 298.15K and the values of the ionic strength of the solution 0.5, 0.75 and 1.0 in the presence of KNO3. Measurements were carried out on a calorimeter with an isothermal shell and automatic recording of the temperature-time curve. The unit was equipped with a reaction vessel with a volume of 60 cm3. Calibration was performed by current at T = (293.15–308.15) ± 0.01 K and P = 100.5± 0.7 kPa. A thermistor KMT-14 was used as a temperature sensor. The temperature of the calorimetric cell was controlled in a thermostat equipped with a PID controller with an accuracy of 0.002 K. The temperature sensor of the thermostat was a platinum resistance thermometer. The calorimeter was calibrated by current. The volume of the calorimetric liquid is 42.83 ml. The enthalpy of stepwise dissociation of glycyl-D-phenylalanine at zero ionic strength was found by an equation with one individual parameter. Standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°) of acid-base interaction reactions in aqueous solutions of glycyl-D-phenylalanine are calculated. The effect of the background electrolyte concentration on the dissociation heats of glycyl-D-phenylalanine is considered. Knowledge of the thermochemical characteristics of dipeptides is necessary for understanding and subsequent modeling of the process of protein biosynthesis occurring in biological systems. Data on the thermodynamic characteristics of dipeptide solutions are needed in various fields where these compounds are used: pharmacology, medicine, food and cosmetic industries, for the development, justification and optimization of technological processes involving these compounds and their complexes with metals.

Equilibrium conditions of the methane and natural gas hydrates formation in sodium bicarbonate solutions

Empirical correlations were obtained to calculate the equilibrium pressure of the methane and natural gas (the Srednevilyui gas and condensate field) hydrates formation in sodium bicarbonate solutions, the hydration numbers and dissociation heats of these hydrates were determined. The values of the hydration numbers assume that methane forms hydrates with the CS-I structure and natural gas – CS-II. The dissociation heat of the natural gas hydrates is higher than that of the methane hydrates.

Effect of Temperature on the Thermodynamics of the Stepwise Dissociation of Alanyl-Phenylalanine in Aqueous Solutions

The heats of interaction between alanyl-phenylalanine and solutions of nitric acid and potassium hydroxide at 288.15 and 308.15 K and solution ionic strengths of 0.5, 0.75, and 1.0 are determined via calorimetry with KNO3. Standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°, ΔC∘pΔ∘) of the reactions of acid–base interaction in aqueous solutions of alanyl-phenylalanine. The effect temperature has on the heats of dissociation of alanyl-phenylalanine is considered along with the relationship between the thermodynamic characteristics of the dissociation of the dipeptide and the structure of this compound.

Measurements of the Dissociation Heats of Tetrabutylammonium Acetate and Tetrabutylammonium Hydroxide Ionic Semiclathrate Hydrates

Measurements of the Dissociation Heats of Tetrabutylammonium Acetate and Tetrabutylammonium Hydroxide Ionic Semiclathrate Hydrates

Quest for optimal nanoconfinement for hydrate-based CO2 capture

CO2 capture is a viable solution for mitigating the global CO2 emission in the atmosphere. Hydrate-based CO2 capture is a promising technology. In this study, the CO2 hydrate formation thermodynamics and kinetics, along with the factors that influence CO2 capture in nanoporous silica gels (named S9, S26, and S77 with an average pore size of 9, 26 and 77 nm, respectively), with different degrees of nanoconfinement were investigated. The CO2 hydrate phase equilibrium and dissociation heat were determined by heat flow analysis. The heat flow curves revealed the formation of both confined- and bulk-phase hydrates in S9 and only bulk-phase hydrate in S26 and S77. The phase equilibrium temperature of the confined-phase hydrate was about 10 K lower than that of the bulk-phase hydrate and the dissociation heat of confined phase hydrate is 285.81 J/g in S9. According to the pressure curves, the CO2 hydrate formation time in S9 was 2–3.5 times longer than that in S26 and S77. Compared with dry silica gel, the supersaturated one was more conducive to CO2 capture. Under the same water saturation condition, the CO2 capture ability of S26 and S77 was stronger than that of S9, and the effect of water saturation was dominant over that of pressure. Thus, nanoconfinement in S9 has an adverse effect on hydrate-based CO2 capture whereas that in S26 and S77 is advantageous to it. This study provides an important fundamental basis for enhancing the hydrate-based CO2 capture ability via nanoconfinement in silica gel.

Synthesis and thermophysical properties of Tetrabutylammonium picolinate hydrate as an energy storage phase change material for cold chain

Ionic semiclathrate hydrates, the water-based phase change materials (PCMs) have potential for thermal energy storage media. There are a number of hydrates, reported in the literature, which are suitable as PCMs for air conditioning system of the required temperature range 10–15 °C. In this study, Tetrabutylammonium picolinate hydrate (TBAPi hydrate) was newly synthesized as a PCM for the cold chain, which has a lower phase equilibrium temperature than the previously reported hydrates. Thermophysical properties of TBAPi hydrate were experimentally measured. The hydrate dissociation heat was determined using a differential scanning calorimeter (DSC). The phase equilibrium temperature was measured by visually observing system with a CMOS camera and microscope. Also, the cycling test was conducted to confirm the long-term stability of thermophysical properties. The largest dissociation heat was 157.7 ± 4.9 kJ･kg−1 at a mass fraction of TBAPi aqueous solution, wTBAPi of 0.37. The highest phase equilibrium temperature of TBAPi hydrate was 5.5 °C at 0.34 ≤ wTBAPi ≤ 0.36. These thermophysical properties did not change even after 200 cycles of hydrate formation and dissociation. Based on the experimental results, TBAPi hydrate can be applied to the transport and storage of vaccines, blood packs, and perishable foods.

Effects of sodium hydroxide and calcium hydroxide on the phase equilibria of methane hydrates

Alkalis such as sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2] find lots of applications in oil and gas industry where formation of methane hydrates (and resulting flow hindrance) is a common occurrence. While many hydrate inhibitors have been identified to maintain flow assurance, effects of these alkalis on the phase stability of methane hydrate have not yet been explored in detail. In this study, the phase behaviour of methane hydrate has been investigated in the presence of aqueous solutions of NaOH and Ca(OH)2 with varying concentrations of 0.005, 0.01, 0.02, and 0.04 mass fractions in a high pressure stirred tank reactor. The phase equilibrium of methane hydrate in aqueous alkali solutions has been generated in the pressure and temperature ranges of 4.27–7.90 MPa and 276.60–283.22 K, respectively. Both the alkalis have found to exhibit inhibition of methane hydrate formation, and the inhibition effect becomes more pronounced at higher concentrations of the alkalis, with NaOH performing as a better inhibitor than Ca(OH)2. A plausible mechanism for the same has also been discussed. The heat of dissociation has been calculated to show that the presence of the alkalis does not influence the structure (sI) of methane hydrate. In addition, a simple model based on the van der Waals-Platteeuw (vdW-P) thermodynamic model consisting of single parameter has been used to predict the phase equilibrium of methane hydrate in the presence of aqueous alkali solutions. The absolute average relative deviations (AARD%) in pressure for the model were measured for the 40 experimental data points generated in this work. The predictions are well within 4 % of the experimental values, which suggests that the model can adequately predict the methane hydrate phase stability in the presence of alkalis. These alkalis are used in various operations during exploration and production of oil and gas. This study therefore will assist in designing an effective and economic thermodynamic inhibitor for methane hydrate based on alkalis for the oil and gas industry.

Measurements of phase equilibrium temperature and dissociation heat of tetrabutylphosphonium glutarate ionic semiclathrate hydrate

Thermophysical properties such as phase equilibrium temperature and dissociation heat are important to determine the performance of phase change materials targeting thermal energy storage. The phase equilibrium temperature and dissociation heat of tetrabutylphosphoniumglutarate ionic semiclathrate hydrate were measured in this study. The highest phase equilibrium temperature of tetrabutylphosphoniumglutarate hydrate was experimentally determined 287.4 K at the mass fraction 0.347 and 0.357. The largest dissociation heat was 193.3 ± 1.6 kJ/kg at the mass fraction 0.357. The measurement results in this work show that the dissociation heat can be utilized in the suitable temperature range targeting general air conditioning and data center.

Synthesis and evaluation of green phase change materials for efficient air conditioning by tetrabutylphosphonium phosphate ionic semiclathrate hydrate

A tetrabutylammonium bromide (TBAB) hydrate is the only ionic semiclathrate hydrate that has been commercialized as a medium for efficient thermal energy storage targeting general air conditioning. However, TBAB is an environmental pollutant, while liquid water and ice that have been widely used as conventional media, also have difficulty in increasing the thermal energy storage density as well as the coefficient of performance (COP) of a refrigerator to form solid. In this study, a tetrabutylphosphonium phosphate ((TBP)3PO4) hydrate was proposed as an alternative green medium. The dissociation heat and the phase equilibrium temperature, which were both crucial factors to evaluate the thermal energy storage density, and COP was experimentally determined. It was found that the maximum dissociation heat was 154.1 ± 2.0 kJ･kg−1 at the mass fraction of 0.309. The highest phase equilibrium temperature was 10.0 °C at the mass fractions of 0.290, 0.299, and 0.309. The thermal energy storage density of (TBP)3PO4 hydrates was 3.7 times larger than that of water. (TBP)3PO4 hydrates increased the COP of a refrigerator to form solid by 42% as compared with ice, indicating the potential size-reduction of conventional devices with the decrease in the power consumption of a refrigerator. The effective balance between environmental protection and the system performance through (TBP)3PO4 hydrates was also discussed.

Theoretical Study on the Electrochemical Catalytic Activity of Au-Doped Pt Electrode for Nitrogen Monoxide

In order to gradually reduce automobile exhaust pollution and improve fuel quality, the NOx sensor, which can be monitored in real time in an automobile engine’s electronic control system, has become an indispensable part of the automobile lean burn system. In these types of NOx sensors, Au-doped platinum electrodes have received great attention due to their selectivity towards NO. However, the reaction process of NO gas on the Au-doped platinum electrode in the sensor and the possible regulation mechanism is still unclear. In this paper, the density functional theory (DFT) was used to analyze the effect of Au-doped Pt electrodes on the performance of nitrogen oxide sensors in automobiles. Firstly, the adsorption energies of NO molecules on pure Pt and Au/Pt surfaces were compared. The adsorption and dissociation of NO on Pt substrates doped with Au monomers, dimers, and trimers were investigated. These results showed that Au can effectively weaken the adsorption energy of NO molecules on a Pt surface. It was noted that with the increase in the number of Au atoms on the surface of Pt(111), the adsorption capacity of NO molecules on the alloy surface becomes weaker. When observing the transition state of NO decomposition on three different alloy surfaces, the study showed that the activation energy and reaction heat of NO dissociation increased. It further showed that doping with Au increased the activation energy of NO decomposition, thereby effectively inhibiting the decomposition of NO.

Initial heat analysis in dissociation isothermal titration calorimetry: An analytical tool for thermodynamic dissection of biomolecular condensates

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.

Experimental study on the influence of brine concentration on the dissociation characteristics of methane hydrate

Brine stimulation is a common method for assisting depressurization to produce hydrate, which significantly improves the efficiency of hydrate production. In this work, to study the influence of brine concentration on the natural gas hydrate production process, a novel cylindrical hydrate production simulation experimental device was established, and investigations of hydrate dissociation experiments induced by depressurization in conjunction with brine injection were carried out. The effects of different brine concentrations on the gas production rate and heat transfer during production were studied. The distribution, flow, and concentration evolution of brine during hydrate production were analyzed. Brine injection can significantly enhance cumulative gas production during the depressurization stage, increase the sensible heat for hydrate dissociation, enhance heat transfer between the hydrate reservoir and the environment during the recovery process, and significantly improve the gas production rate of hydrate. The increase in the gas production rate caused by brine injection mainly occurs at the end of the depressurization stage and the beginning of the constant pressure stage. The injected brine is mainly located in the middle and upper areas of the reactor. In the bottom area of the reactor, the hydrate has higher saturation and longer dissociation time, which is slightly affected by the injected brine. A higher hydrate saturation is not beneficial to brine injection and does not promote hydrate dissociation. Additionally, in the experiments with brine injection, the resistance decreases more obviously during the depressurization stage due to more hydrate dissociation. The resistance also shows that in the bottom area of the reactor, there is a higher hydrate saturation and a lower brine effect on hydrate.

Optimal absorbents of CO2 hydrate formation and energy consumption analysis for district cooling application under low pressure conditions

Hydrate-based CO2 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, CO2 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 CO2 capture. Consequently, an alternative to a conventional district cooling system by replacing it with a CO2 hydrate slurry cooling system is proposed, and a sufficient reduction in energy consumption is demonstrated.

Accelerating gas production of the depressurization-induced natural gas hydrate by electrical heating

Natural gas hydrate (NGH) will be one of the major future energy sources due to its properties of clean energy and large reserves. Depressurization is proposed as an effective method to extract natural gas from hydrate, however, the gas production from hydrate dissociation may be interrupted by ice generation and hydrate re-formation due to insufficient heat supply in the single depressurization process. To solve this issue, this work conducted simulation on accelerating gas production from the depressurization-induced methane hydrate by electrical heating. The continuous heating and intermittent heating modes were employed and then the electrical heating scheme was optimized for the comprehensive effect of high energy efficiency and high gas production rate. The results show that electrical heating is conducive to gas production from hydrate dissociation at a rapid rate. In the continuous heating, a high initial hydration saturation, low initial water saturation, low specific heat capacity, and high thermal conductivity result in the high gas generation rate and efficient electrical energy utilization (a large energy efficiency ratio). The intermittent heating has a higher efficient utilization of electrical energy than continuous heating. The optimal scheme is determined as the first-half heating type with the optimized electrical heating power of 25.6 W and the heating time of 12.5 min by the gradient descent method of AdaGrad. Compared to the baseline continuous heating case, the energy efficiency ratio (10.70) of the optimal scheme is enhanced by 24.7% with the average gas production rate (2.55 SmL/s) enhanced by 18.2%. It's hoped that the findings of this work can provide some insights into extracting natural gas from gas hydrate deposits. Electrical heating is employed to provide heat for the endothermic dissociation of methane hydrate induced by depressurization for accelerating natural gas production in this work. The electrical heating scheme is optimized to achieve high-efficient utilization of electrical energy for the fast extraction of natural gas from hydrate dissociation. • Electrical heating accelerates the depressurization induced dissociation of hydrate. • The effects of phase components and porous media properties are analyzed. • Intermittent heating has higher efficiency of energy utilization than continuous heating. • The electrical heating power is optimized by the gradient descent method of AdaGrad. • The optimal scheme is first-half heating with the optimized electrical heating power.

Synthesis and thermophysical property evaluation of ionic semiclathrate hydrate formed with tetrabutylphosphonium glycine as a chilling temperature phase change material

Ionic semiclathrate hydrate, which is formed under atmospheric pressure with sustainably safe properties, has a potential for solid-liquid phase change materials(PCMs). In this study, the thermophysical property of tetrabutylphosphonium glycine(TBPGly) hydrate containing no halogen guest compound, glycine (aminoacetic acid), was investigated to evaluate the availability as an eco-efficient thermal energy storage medium. The phase equilibrium temperature was obtained through visual observation method. The heat flow rate curve behavior and dissociation heat were measured via differential scanning calorimetry(DSC). In the dissociation process, a single hydrate dissociation peak emerged, indicating TBPGly hydrate has one type of crystallographic structure. The concentration dependency of the TBPGly aqueous solution on the equilibrium temperature and the dissociation heat was confirmed. The highest equilibrium temperature of 5.8 °C was confirmed at the fraction range wTBPGly =0.368 or xTBPGly =0.0306, and the largest dissociation heat was 177.7 kJ·kg−1 at the fraction range wTBPGly =0.377or xTBPGly =0.0318. The estimated hydration number in the congruent composition was found to be in 31.2 to 32.5. In addition, based on the measured physical property, the optimum operating temperature and volume fraction of TBPGly hydrate was evaluated to determine the concentration for the practical cooling system. These data revealed TBPGly hydrate is available as a solid or slurry PCM under the operating temperature range 2 °C to 5.8 °C. The experimental data as well as the illustrative calculations contribute to accelerate the expansion in the application range, and provide the prospect in selecting the suitable composition toward the actual hydrate-based cooling system.

Production Performance Analysis of Class II Hydrate-Bearing Layers Based on an Analytic Aquifer Model

In the current numerical simulation studies, bottom water in Class II hydrate-bearing layers is represented by grids with high water saturation that significantly extends the calculation time if the volume of the bottom water is large or grid size is small. Moreover, the influence of the bottom water volume on the depressurization performance of Class II hydrate-bearing layers has not been fully investigated. In this study, the Fetkovich analytic aquifer model was coupled with a simulation model of a hydrate reservoir to accelerate the simulation of Class II hydrate-bearing layers. Then the simulation results and calculation time were compared between the coupled model and the model in which the bottom water layer is only represented by grids. Finally, the influence of the bottom water volume on the productivity of gas and water in the depressurization method was investigated and the variation of pressure, temperature, and hydrate saturation during the production process was analyzed. The results show that the coupled model can significantly reduce the simulation time of Class II hydrate-bearing layer while ensuring calculation accuracy. When the pore volume of the aquifer increases to 20 times that of the bottom water layer, the computation time of a single model in which the bottom water layer is represented by grids is 18.7 times that of the coupled model. Bottom water invasion slows down the depressurization, and therefore, the larger the aquifer, the lower the peak value of gas production, and the later it appears. However, the invading bottom water can provide heat for hydrate dissociation; therefore, the gas production rate of the hydrate-bearing layer with bottom water is higher than that of the hydrate-bearing layer without bottom water in the late development stage. Generally, the presence of bottom water reduces the cumulative gas production and increases the cumulative water production; therefore, the larger the aquifer, the more unfavorable the depressurization development of the hydrate-bearing layer.

Experimental and theoretical study on dissociation thermodynamics and kinetics of hydrogen-propane hydrate

Hydrate-based hydrogen storage is a promising technology in the clean energy field. In this study, propane was selected as the accelerator guest molecule for hydrogen storage in hydrates. Hydrogen–propane (0.67/0.33, mole ratio) hydrate dissociation properties are investigated by experiment and molecular dynamics simulation. The hydrogen–propane hydrate phase equilibrium is measured by different methods and the average dissociation heat is 77.03 J/g under 0.98–1.72 MPa. While hydrate dissociation heat flow curves show the characteristic of two-step dissociation, which is further confirmed via Raman spectroscopy. Simultaneously, hydrogen–propane hydrate dissociation driven by depressurization and heating are also investigated by Raman spectroscopy. During dissociation, the Raman peak area of hydrogen in hydrate continues to decrease, whereas it is relatively stable for propane before the hydrate dissociation complete. In addition, hydrogen–propane hydrate reformation occurs more intensely during the heating process, especially when the temperature exceeds 273 K than with depressurization. This indicates that depressurization is more feasible for continuous hydrogen releasing, a concept of recycling hydrate clathrate structure was proposed to shorten hydrate formation time and accelerates hydrogen storage rate. In addition, the molecular dynamics simulation results confirmed that the hydrogen release rate from hydrate is higher than that of propane from the microscopic view point. The results of this study provide a potential pathway of hydrogen storage using hydrates.

Thermodynamic analysis of hydrate-based refrigeration cycle

Clathrate hydrates (hydrates) have a larger dissociation heat than an evaporation heat of the working fluid of conventional refrigeration systems. This property can be applied to a novel refrigeration system. In this study, theoretical performance analysis of the refrigeration system utilizing hydrates as its working medium was conducted. We modeled the thermodynamic cycle of the hydrate-based refrigeration system composed of following processes: adiabatic compression, hydrate formation at high temperature, adiabatic expansion, and hydrate dissociation at low temperature. Based on the thermodynamic cycle, the coefficient of performance (COP) of the hydrate cycle was theoretically formulated with thermodynamic state functions of the working medium. Using the formula, COP was calculated on the three hydrate forming systems including HFC-32 + cyclopentane (CP) + water, Kr + CP + water, and HFC-41 + CP + water. The analysis based on the calculated results revealed that the dissociation heat of hydrates and the enthalpy change of guest gas were dominant factors to COP and polyatomic molecules would be appropriate for guest gas of hydrates. The maximum COP values on the hydrate cycle were comparable to those of the reversed Rankine cycle. The hydrate-based refrigeration system outperformed conventional refrigeration systems in terms of safety and environmental-friendliness.