Binary Hydrate Research Articles

Water-in-oil emulsions as micro-reactors for achieving extremely rapid and high hydrogen uptakes into clathrate hydrates

As humanity transitions to a low-carbon future, hydrogen, with its high energy density and zero carbon emissions, is gaining prominence, and efficient hydrogen storage is thus a critical area of research. Storing hydrogen in a solid form by forming hydrates, ensuring straightforward formation and dissociation, environmental friendliness, and stability, is emerging as a new technology. In particular, the use of thermodynamic promoters such as tetrahydrofuran (THF) to form binary hydrogen hydrates enables hydrogen storage under much milder conditions compared to traditional compression and liquefaction processes. However, slow hydrate formation kinetics currently hinder commercialization, necessitating breakthroughs in this area. This study reports extremely rapid and high hydrogen uptake in binary hydrogen + THF hydrates by utilizing a water-in-oil emulsion. A hydrogen storage capacity of approximately 51.23 mmol H2/mol H2O and the hydrogen uptake rate of 91.71 mol min−1 m−3 water were achieved, significantly outperforming existing studies conducted at pressures below 15 MPa. This remarkable kinetics was achieved by controlling the distribution of THF within a ternary emulsion system composed of water, isooctane, and THF. Phase equilibrium measurements and a series of kinetic tests validated that using an excess of THF over stoichiometric amounts can lead to such high and rapid hydrogen uptake. Consequently, a hydrate formation mechanism in the emulsified system was suggested based on the results of a Raman analysis, water droplet size measurements, and 1H NMR analysis. These results will pave the way for further advances in practical hydrate-based hydrogen storage technology.

Thermodynamic phase equilibria of binary SF6–N2O hydrates and their structural analysis for the hydrate-based greenhouse gas capture

The increasing greenhouse gas (GHG) emissions from industrial activities have driven the development of efficient and environmentally safe GHG capture technologies. Clathrate hydrates, primarily composed of water, have attracted significant attention for their potential in GHG capture due to their ability to manage large emissions and their environmental advantages over materials like amine-based sorbents and metal-organic frameworks. This study investigates the hydrate-based capture of SF6 and N2O, two potent GHGs, to develop an effective GHG capture process. Phase equilibrium measurements demonstrate that binary SF6-N2O hydrates can form under moderate thermodynamic conditions, even with a small proportion of SF6, highlighting the feasibility of using hydrate-based methods to capture GHG mixtures. Furthermore, the formation of binary SF6-N2O hydrates enhances GHG volumetric storage capacity compared to pure SF6 hydrates. The guest compositions calculated for each binary SF6-N2O hydrate phase, along with spectroscopic analyses (Powder X-Ray Diffraction and Raman spectroscopy), confirm that the high GHG uptake in binary hydrates results from N2O molecules occupying the small cages of structure II hydrates, which are inaccessible to the larger SF6 molecules. These findings suggest that both the small and large cages of sII hydrates can be practically utilized for efficient capture of GHG mixture (SF6 and N2O) under mild conditions, thereby increasing the storage density of GHGs within the hydrate structure.

Rapid hydrogen enclathration and unprecedented tuning phenomenon within superabsorbent polymers

Clathrate hydrate has emerged as a potentially viable storage medium for efficient hydrogen storage, owing to its eco-friendly characteristics and high hydrogen storage capacity. However, it is essential for its practical application to address the challenges posed by harsh thermodynamic formation conditions and slow formation kinetics for hydrogen hydrate. Here, we introduce the utilization of superabsorbent polymers (SAPs) as a dispersion matrix for tetrahydrofuran (THF) solutions to develop a method for rapid hydrogen enclathration. We investigated two distinct synthetic pathways, solution-borne and hydrate-borne routes. We also explored the relationship between hydrogen uptake/storage capacity, varying THF solution concentration within SAPs, and synthetic pathways for binary THF–hydrogen hydrates. The hydrogen storage capacity after 200 min enclathration reaction was relatively low for 1.0 mol% THF cases but significant for 5.56 mol% THF cases in hydrate-borne route (around 20 mmol H2/mol water), highlighting its potential for hydrogen storage material. The spectroscopic analysis revealed that the tuning phenomenon in THF 1.0 mol% hydrate was only observed in the solution-borne route, which facilitated hydrogen enclathration in partially vacant large cages of sII hydrates. It was striking that the tuning phenomenon was also observed in THF 5.56 mol% hydrate synthesized in both solution-borne and hydrate-borne pathways. Through phase equilibria measurements, we confirmed that less than 5.56 mol% of THF participated in forming binary hydrates. The different water and THF absorbability of SAPs resulted in a non-uniform distribution of THF solution within SAPs, causing the unprecedented tuning phenomenon. These findings provide valuable insights into the potential of SAPs for rapid hydrogen enclathration media, emphasizing the importance of understanding synthetic pathways and solution absorption properties for optimized hydrogen storage.

Experimental study on supercooling performance optimization of sodium acetate trihydrate phase change energy storage materials

In response to the pressing demands for sustainable energy, the development of efficient energy storage materials and technologies has emerged as a focal point in contemporary research. Sodium acetate trihydrate (CH3COONa·3H2O, SAT), recognized for its potential as a mid-to-low temperature phase change material (PCM) in energy storage systems, encounters significant limitations due to its substantial supercooling effect and inferior thermal conductivity. Traditional approaches to enhance SAT's thermal performance often involve costly additives, which hinder their adoption on an industrial scale. This study introduces SAT as a base compound, and through a fusion blending method, binary eutectic hydrate salt composites (CPCMs) are synthesized with either sodium sulfate decahydrate (Na2SO4·10H2O, SSD) or disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O, DHPD) in varying ratios. The results demonstrate that the prepared eutectic hydrates effectively reduce the supercooling degree of pure SAT from above 35 °C to below 10 °C, with the SAT/SSD-5/5 composition exhibiting the lowest supercooling at 3.17 °C. Notably, these eutectic blends possess appreciable latent heat capacities, with SAT/SSD-9/1 delivering 196.18 J/g, and exhibit improved thermal conductivity, as seen in SAT/SSD-3/7 with a coefficient of 0.8925 W/(m·K). Furthermore, the SAT-based eutectic hydrates are devoid of expensive additives, facile to manufacture, and applicable over a broad temperature range (20–60 °C), making them highly suitable for large-scale commercial applications.

Effect of complex ionic liquid additives on the formation kinetics and separation efficiency of binary gas mixture hydrates

Rising carbon emissions worldwide have necessitated the discovery of efficient CO2 separation and capture technologies. Owing to their good CO2 selectivity, imidazolium-based ionic liquids (ILs) have been used as additives in hydrate-based gas separation (HBGS) technologies. Sodium dodecyl sulfate (SDS) can notably improve the rate of hydrate formation when used as a surfactant. However, the synergistic effect of imidazolium-based ILs and SDS remains unknown. This study aimed at investigating the synergistic effect of imidazolium-based ILs and SDS on the hydrate formation kinetics of binary gas mixtures of CO2/N2 at different temperatures. The carbon capture and storage capacity was determined, and HBGS was evaluated using pure imidazolium-based IL 1-butyl-3-methylimidazolium octyl sulfate ([BMIM] [OS]) and composites of IL and SDS as additives. Compared with pure water, [BMIM] [OS] effectively promoted gas hydrate formation and increased CO2 consumption by 107.9 %. The maximum CO2 separation factor was obtained at 273.15 K, and the mixed additive significantly enhanced gas consumption by 11.1 %. X-ray diffraction and Raman spectroscopy analysis indicated that the hydrate samples were type I structural hydrates and that [BMIM] [OS] improved the mass transfer process. The results of this study provide a theoretical basis for CO2 gas separation and capture.

Experimental investigation on the performance of binary carbon-based nano-enhanced inorganic phase change materials for thermal energy storage applications

Phase change materials (PCMs) are considered potential resources for Thermal energy storage (TES) applications. However, the PCMs are limited because of their lower thermal conductivity, resulting in a significant decrease in heat transport and energy storage capability. The foremost objective of the present research is to formulate a novel salt hydrate PCM filled with binary carbon-based nanoparticles (graphene and multi-walled carbon nanotubes) at various weight concentrations and examine the thermophysical properties. A two-step approach is used to formulate binary nanomaterials dispersed salt hydrate PCM. The formulated binary nanocomposite's thermo-physical properties like morphological behaviour, thermal stability, chemical stability, melting enthalpy, optical performance, rate of heat transfer and thermal reliability were characterized. The binary nanoparticle-enhanced nanocomposites can form a decent thermal network, resulting in a remarkable enhancement in thermal conductivity by 160 % (1.2 W/mK) compared to pure salt hydrate. Moreover, a remarkable improvement in optical absorptance and a reduction in optical transmittance by 82.55 % for 0.7 wt% graphene and 0.07 wt% MWCNT enhanced salt hydrate PCM (SAHGrM-0.07) than pure salt hydrate PCM. In addition, the formulated nanocomposites possess excellent heat storage capability, chemical and thermal stability after 300-thermal cycling. The binary carbon-based nanoparticle-enhanced salt hydrate nanocomposites offered acceptable thermal and chemical stability, thermal reliability, and heat transmission characteristics, by this means reflecting its appropriateness for medium-temperature solar TES applications.

Evaluation of a Simplified Model for Three-Phase Equilibrium Calculations of Mixed Gas Hydrates

In this study, we perform an extensive evaluation of a simple model for hydrate equilibrium calculations of binary, ternary, and limited quaternary gas hydrate systems that are of practical interest for separation of gas mixtures. We adopt the model developed by Lipenkov and Istomin and analyze its performance at temperature conditions higher than the lower quadruple point. The model of interest calculates the dissociation pressure of mixed gas hydrate systems using a simple combination rule that involves the hydrate dissociation pressures of the pure gases and the gas mixture composition, which is at equilibrium with the aqueous and hydrate phases. Such an approach has been used extensively and successfully in polar science, as well as research related to space science where the temperatures are very low. However, the particular method has not been examined for cases of higher temperatures (i.e., above the melting point of the pure water). Such temperatures are of interest to practical industrial applications. Gases of interest for this study include eleven chemical components that are related to industrial gas-mixture separations. Calculations using the examined methodology, along with the commercial simulator CSMGem, are compared against experimental measurements, and the range of applicability of the method is delineated. Reasonable agreement (particularly at lower hydrate equilibrium pressures) between experiments and calculations is obtained considering the simplicity of the methodology. Depending on the hydrate-forming mixture considered, the percentage of absolute average deviation in predicting the hydrate equilibrium pressure is found to be in the range 3–91%, with the majority of systems having deviations that are less than 30%.

Phase Equilibrium Conditions and Crystal Structure of Binary Hydrates Formed with 1-Methylpiperidine

Phase Equilibrium Conditions and Crystal Structure of Binary Hydrates Formed with 1-Methylpiperidine

Molecular study on the growth mechanism of CO2-H2 binary hydrate promoted by electric field

The storage and transportation of hydrogen (H2) are widely recognized as the main challenge of hydrogen utilization technology. The hydrate-based method is one of the safe and environmentally friendly hydrogen storage methods. However, the harsh generation conditions and slow growth rate of H2 hydrate hinder its industrial application. Therefore, exploring methods to reduce the reaction conditions of H2 hydrate and improve growth efficiency is worth further research. This study investigated the effect of different intensities of electrostatic fields (0–0.9 V/nm) on the growth of CO2-H2 binary hydrates through molecular dynamics (MD) simulation. Representative parameters such as growth configuration, number of cages, dipole moment, four body angular order parameters, mean square displacement, occupancy rate, etc. were analyzed. The T, P conditions used for the simulation were 255 K, 80 MPa, and 400 ns in duration. The results suggest that a certain range of electric field strength can increase the growth rate of CO2-H2 binary hydrates and reduce the conditions required for hydrogen hydrate formation. The growth-promoting effect of the electric field is primarily manifested in the increased growth rate of binary hydrates. Detailed analysis reveals that electric field of a certain strength can to some extent promote the multiple occupancy of H2 within cage structures, thereby enhancing the hydrate's ability to capture H2. These molecular insights are beneficial for the application of electrostatic field in hydrate-based technologies to improving the storage efficiency of H2 hydrate and the reuse of CO2.

Experimental investigation on nucleating agent for low temperature binary eutectic salt hydrate phase change material

The melting enthalpy and melting temperature have a significant impact on the latent heat that results from phase change materials (PCMs) used for thermal energy storage. Among the PCMs that are currently on the market, inorganic salt hydrates have greater thermal conductivity and latent heat than organic PCMs. However, the problem of salt hydrates' degree of supercooling limits their use in energy storage devices. Using sodium carbonate decahydrate (SCD) and sodium phosphate dibasic dodecahydrate (SPDD), a low temperature inorganic-inorganic eutectic salt hydrate PCM with a higher melting enthalpy and intended phase transition temperature is developed in this research study. The eutectic SCD/SPDD salt hydrate PCM eutectic point and the eutectic composition of salt hydrate PCMs to operate at low temperature range is numerically determined using Schrader equation. By numerical methods we obtain the 68 wt% of SCD with 32 wt% of SPDD to exhibit eutectic SCD/SPDD composite with eutectic melting temperature of 26.2 °C and melting enthalpy of 210.6 J/g. The synthesised eutectic PCM are characterised to explore their chemical stability, latent heat, melting point and their shortcoming due to degree of supercooling. A good way to get around the problem of the supercooling degree is to disperse the nucleating agents. In order to assess the type and degree of supercooling, the produced eutectic PCM composition is experimentally evaluated at 1–10% utilising borax, alumina, and sodium sulphate dodecahydrate as nucleating agents. However, for building cooling applications PCM with minimal degree of supercooling, with the ability to release low enthalpy during discharging is an advantage.

Surface modification of mesostructured cellular foam to enhance hydrogen storage in binary THF/H2 clathrate hydrate

Solid-state tuning of a mesostructured cellular foam (MCF) enhances hydrogen storage in clathrate hydrates. Grafting of promoter-like molecules (e.g., tetrahydrofuran) at the internal surface of the MCF improved the kinetics of formation of binary H2-THF clathrate hydrate.

Molecular dynamic simulation of H2-CH4 binary hydrate growth induced by methane hydrate

Hydrogen storage based on hydration is a promising technology, in which hydrogen molecules are captured in a three-dimensional cage structure formed by hydrogen bonds between water molecules. In this study, methane was selected as the accelerator guest molecule for hydrogen storage in hydrates, hydrogen-methane hydrate formation properties was investigated at 240 K and 110 MPa by molecular dynamic simulation. The combined TraPPE(CH4)-TIP4P/ice(H2O)-Diatomic(H2) force field was adopted. The molecular mechanism of the growth of CH4/H2 binary hydrates with different liquid methane concentrations (1.51–5.79 mol%) was explored, the effect of concentration on kinetic properties such as hydrate growth rate, hydrate hydrogen storage density, and properties related to cage occupancy and structural transformation were analysed. Any concentration of liquid-phase methane in this study increased hydrogen storage compared to a system without liquid methane. The growth rate of binary hydrates is related to the concentration and diffusion of liquid-phase methane: the higher the concentration of methane in liquid phase, the smaller the diffusion coefficient of hydrogen and water molecules in the solution, and the slower the growth rate of binary hydrates. The cage at the solid–liquid interface is preferentially occupied by hydrogen molecules, and the occupation process is gradually from the interface to the interior of the hydrate. At lower methane concentrations, the hydrate grows more uniformly along the interface. When the methane concentration is large, the hydrate not only grows along the interface, but also develops new nucleation sites in the liquid phase for growth, resulting in uneven growth of hydrate in the whole system. Methane acts as an accelerator to stabilize the cage while reducing diffusion. According to the hydrogen storage density of each system, it was found that hydrates have the best hydrogen storage efficiency when the concentration of methane in the liquid phase is 4.41 mol%. The transition from double-occupied cages to single-occupied cages indicated that the breakdown of the six-membered ring in the hydrate cage was the key to the passage of hydrogen molecules into and out of cages. This study will provide theoretical basis for the stable storage of H2 hydrate, and promote the industrial application of HHST technology.

Evaluating the gas storage capacity of 1,3-dioxolane–hydrogen binary hydrates via molecular simulations

H2 is a green fuel with high energy density, but its efficient storage and transportation remain challenging. Clathrate hydrates are promising materials for H2 storage. In this study, molecular simulations are conducted to evaluate the gas storage capacity of 1,3-Dioxolane (DIOX)–H2 hydrate under various thermodynamic conditions. Results reveal that the growth rates of DIOX–H2 and tetrahydrofuran (THF)–H2 hydrates exhibit similar trends to those of pure DIOX and THF hydrates with temperature, indicating that the growth processes of the binary hydrates are dominated by DIOX and THF. However, their growth rates are almost constant with pressure of 10–110 MPa at 250 K. H2 can significantly improve the growth rate of hydrates due to its small size and high mobility. Furthermore, temperature has little effect on the gas storage capacity of the binary hydrates, but an increase of pressure significantly enhances it. Although DIOX is more efficient than THF in promoting the growth of hydrates, the gas storage capacity of DIOX–H2 hydrate is weaker. The gas occupancy of 512 cages is the key factor determining the gas storage capacity of the binary hydrates. Multiple H2 occupancies can be found in 51264 cages at high pressures. This study provides molecular-level insights into the hydrate growth process, which can serve as a guide for improving the gas storage capacity of hydrates.

Tuning cyclopropanecarboxaldehyde clathrate hydrates for enhancement of methane storage

This study investigates the tuning behavior of guest molecules in gas hydrates to achieve an optimal balance between the storage capacity and moderate formation conditions for CH4 gas storage. A new structure II hydrate-forming agent, cyclopropanecarboxaldehyde (CPCAld), was examined, and the guest inclusion behavior, crystal structure, and tuning behavior of the binary (CPCAld + CH4) clathrate hydrate were analyzed using 13C solid-state nuclear magnetic resonance (NMR), Raman spectroscopy, and synchrotron powder X-ray diffraction (PXRD). The phase equilibria and CH4 storage capacity of the binary (CPCAld + CH4) clathrate hydrates were also investigated. The experimental results provide insights into the design and optimization of gas hydrate storage systems for CH4 gas and other applications. The study demonstrates the potential for tuning CH4 content in clathrate hydrates by adjusting the concentration of CPCAld from 0.5 mol% to 5.56 mol%, which enhanced the storage and transportation of CH4 gas. The CH4 storage capacity of the binary (CPCAld + CH4) clathrate hydrate at 3.0 mol% CPCAld concentration was approximately 25 % higher than that of (CPCAld + CH4) hydrate at 5.56 mol% of CPCAld concentration. Overall, the exploration of a new hydrate former, CPCAld, and the understanding of the tuning behaviors of the binary (CPCAld + CH4) hydrate provide important insights into enhancing the storage capacity and contribute to the development of efficient and safe CH4 gas storage technologies using gas hydrates.

Experimental study of the formation and decomposition of mixed gas hydrates in water-hydrocarbon system

The phase transition of gas hydrate with two or more guests is associated with gas recovery, storage and separation. In this work, the formation and decomposition of binary and ternary gas hydrates containing CH4, C2H6 and C3H8 were investigated experimentally in high-pressure reactors equipped with visual windows. The gas compositions during mixed hydrates formation and decomposition were analyzed to track the occupation of guests in hydrate structures and the release of guests from hydrate cages. It was found that of CH4 was adsorbed in the hydrate cages constructed by C2H6 and C3H8 in the initial stage. In the depressurized decomposition of CH4-C3H8 hydrates and CH4-C2H6-C3H8 hydrates slurry, CH4 and C2H6 molecules were preferentially released from hydrate structures while more C3H8 molecules were able to stay in hydrate phase, which was in accordance with the order of the diameter ratio of guest molecule to hydrate cage. The preservation of CH4-C3H8 hydrates and CH4-C2H6-C3H8 hydrates above 0 ℃ was observed under a low pressure. It was proposed that the reconstitution or reformation of hydrate layer rich of C3H8 may encrust the remaining hydrate particles, preventing hydrate from further quick decomposition. In-situ Raman spectra confirmed the enrichment of C3H8 molecules at the surface of CH4-C3H8 hydrates, which revealed that the metastable hydrate layer rich of C3H8 molecules may act as mass transfer resistance of gas release from hydrate decomposition. Differently, the decompositions of CH4-C2H6 hydrates and C2H6-C3H8 hydrates were uniform as different guests were produced concurrently without preservation. The new insights into mixed hydrates decomposition in this work may provide a new basis for mixed gas production from gas hydrate, and gas storage and separation with hydrate.

Eco-friendly coconut shell biochar based nano-inclusion for sustainable energy storage of binary eutectic salt hydrate phase change materials

Eco-friendly, stable and thermally reliable nano enhanced phase change materials (PCMs) with improved thermal property and photo absorbance are vital competencies for solar energy harnessing. In the proposed research, we develop and investigate the morphological, chemical, optical and thermal features of biochar-eutectic PCM composite for clean energy storage. Herewith, primarily coconut shell-based biochar nanoparticle (BNP) is synthesized through carbonization process in vacuum oven at 130 °C followed by wet ball milling to reduce the size. Coconut shell being a feasible candidate in terms of economical, pore structured and light weight ensures better binding, uniform dispersion and improved intermolecular attraction with PCM. The synthesized BNP is evenly spread into the surface morphology of inorganic binary eutectic PCM comprising of 62% of sodium sulphate decahydrate (SSD) and 38% of sodium phosphate dibasic dodecahydrate (SPDD). Electromagnetic spectrum absorbance in the range of infrared and visible rays increased from 0.09 to 0.84 (833%) and transmissibility has been reduced from 83.7% to 15.11% with BNP. Developed BNP composite eutectic PCM demonstrate higher thermal conductivity (0.715 W/m⋅K) on comparison with base eutectic PCM (0.464 W/m⋅K) owing to the presence of carbon element and porous nature of BNP. Heat flow curves specifies increment in melting enthalpy of eutectic PCM from 202.3 J/g to 218.1 J/g with energy storage efficiency of 71.7%. On the basis of thermophysical properties obtained, the developed BNP composite PCM is expected to contribute effectively for thermal regulation applications.

Formation and Transformation of Clathrate Hydrates under Interstellar Conditions.

ConspectusContinuing efforts by many research groups have led to the discovery of ∼240 species in the interstellar medium (ISM). Observatory- and laboratory-based astrochemical experiments have led to the discovery of these species, including several complex organic molecules (COMs). Interstellar molecular clouds, consisting of water-rich icy grains, have been recognized as the primordial sources of COMs even at extremely low temperatures (∼10 K). Therefore, it is paramount to understand the chemical processes of this region, which may contribute to the chemical evolution and formation of new planetary systems and the origin of life.This Account discusses our effort to discover clathrate hydrates (CHs) of several molecules and their structural varieties, transformations, and kinetics in a simulated interstellar environment. CHs are nonstochiometric crystalline host-guest complexes in which water molecules form cages of different sizes to entrap guest molecules. CHs are abundant on earth and require moderate temperatures and high pressures for their formation. Our focus has been to form CHs at extremely low pressure and temperature as in the ISM, although their existence under such conditions has been a long-standing question since water and guest molecules (CH4, CO2, CO, etc.) exist in space. In multiple studies conducted at ∼10-10 mbar, we showed that CH4, CO2, and C2H6 hydrates could be formed at 30, 10, and 60 K, respectively. Well-defined IR spectroscopic features supported by quantum chemical simulations and temperature-programmed desorption mass spectrometric analyses confirmed the existence of the 512 (for CH4 and CO2) and 51262 (for C2H6) CH cages. Mild thermal activation for long periods under ultrahigh vacuum (UHV) allowed efficient molecular diffusion, which is crucial for forming CHs. We also explored the formation of THF hydrate (a promoter/stabilizer for binary CHs), and a spontaneous method was found for its formation under UHV. In a subsequent study, we observed a binary THF-CO2 hydrate and its thermal processing at 130 K leading to the transportation of CO2 from the hydrate cages to the matrix of amorphous water. The findings imply that such systems possess a dynamic setting that facilitates the movement of molecules, potentially accounting for the chemical changes observed in the ISM. Furthermore, an intriguing fundamental phenomenon is the consequences of these CHs and their dynamics. We showed that preformed acetone and formaldehyde hydrates dissociate to form cubic (Ic) and hexagonal (Ih) ices at 130-135 K, respectively. These unique processes could be the mechanistic routes for the formation of various ices in astrophysical environments.Other than adding a new entry, namely, CHs, to the list of species found in ISM, its existence opens new directions to astrochemistry, observational astronomy, and astrobiology. Our work provides a molecular-level understanding of the formation pathways of CHs and their transformation to crystalline ices, which sheds light on the chemical evolution of simple molecules to COMs in ISM. Furthermore, CHs can be potential candidates for studies involving radiation, ionization, and electron impact to initiate chemical transformations between the host and guest species and may be critical in understanding the origin of life.

A model to predict the thermodynamic stability of abiotic methane-hydrogen binary hydrates in a marine serpentinization environment

Abiotic methane (CH4) and hydrogen (H2), which are produced during marine serpentinization, provide abundant gas source for hydrate formation on ocean floor. However, previous models of CH4–H2 hydrate formation have generally focused on pure water environments and have not considered the effects of salinity. In this study, the van der Waals–Platteeuw model, which considered the effects of salinity on the chemical potentials of CH4, H2, and H2O, was applied in a marine serpentinization environment. The model uses an empirical formula and the Peng–Robinson equation of state to calculate the Langmuir constants and fugacity values, respectively, of CH4 and H2, and it uses the Pitzer model to calculate the activity coefficients of H2O in the CH4–H2–seawater system. The three-phase equilibrium temperature and pressure predicted by the model for CH4–H2 hydrates in pure water demonstrated good agreement with experimental data. The model was then used to predict the three-phase equilibrium temperature and pressure for CH4–H2 hydrates in a NaCl solutions, for which relevant experimental data are lacking. Thus, this study provides a theoretical basis for gas hydrate research and investigation in areas with marine serpentinization.

On the phase behaviors of CH4-CO2 binary clathrate hydrates: Two-phase and three-phase coexistences.

We develop a statistical mechanical theory on clathrate hydrates in order to explore the phase behaviors of clathrate hydrates containing two kinds of guest species and apply it to CH4-CO2 binary hydrates. The two boundaries separating water and hydrate and hydrate and guest fluid mixtures are estimated, which are extended to the lower temperature and the higher pressure region far distant from the three-phase coexisting conditions. The chemical potentials of individual guest components can be calculated from free energies of cage occupations, which are available from intermolecular interactions between host water and guest molecules. This allows us to derive all thermodynamic properties pertinent to the phase behaviors in the whole space of thermodynamic variables of temperature, pressure, and guest compositions. It is found that the phase boundaries of CH4-CO2 binary hydrates with water and with fluid mixtures locate between simple CH4 and CO2 hydrates, but the composition ratios of CH4 guests in hydrates are disproportional to those in fluid mixtures. Such differences arise from the affinities of each guest species to the large and small cages of CS-I hydrates and significantly affect occupation of each cage type, which results in a deviation of the guest composition in hydrates from that in fluid on the two-phase equilibrium conditions. The present method provides a basis for the evaluation of the efficiency of the guest CH4 replacement to CO2 at the thermodynamic limit.

Reactivity of bis(2‐chloroprop‐2‐enyl)sulfide in the system hydrazine hydrate/alkali: A quantum chemical insight

AbstractThe reactivity of bis(2‐chloroprop‐2‐enyl)sulfide in the system hydrazine hydrate/alkali has been studied using quantum‐chemical methods. The B2PLYP‐D2//B3LYP approach shows a good agreement between the relative values of activation barriers compared to high‐precision CBS//Q‐B3. The correction for the entropy change during the transition from the gas phase to the binary solvent hydrazine hydrate is calculated. The IEF PCM model was parameterized for hydrazine hydrate solvent. The studied reaction routes includes (i) a competition between migration of the C=C bond and dehydrochlorination of bis(2‐chloroprop‐2‐enyl)sulfide; (ii) 1,3‐prototropic rearrangements of bis (allenyl)sulfide resulting from a dehydrochlorination; (iii) the possible substitution of sulfur and chlorine atoms with hydrazine. The probable formation of the thiiranium and thiirenium cations formation in the above has also been evaluated.