Theoretical Study on Clathrate Hydrate for Energy Storage and Transport
Formalism for calculating the thermodynamic properties of a clathrate hydrate with weak guest-host interactions was realized. The proposed model accounted for multiple cage occupancy, host lattice relaxation, and the description of the quantum nature of guest behavior :
- using this approach, the phase diagrams of the pure and binary hydrogen hydrates were constructed and they are in agreement with available experimental data [2-7]. In order to evaluate the parameters of weak interactions, a time-dependent density-functional formalism and local density technique entirely in real space have been implemented for calculations of vdW dispersion coefficients for atoms within the all-electron mixed-basis approach. The combination of both methods enables one to calculate thermodynamic properties of clathrate hydrates without resorting to any empirical parameter fittings . Using proposed approach, the phase diagrams of various clathrate hydrates and obtained results are in agreement with available experimental data;
- it has been found that the pure hydrogen cubic structure II (CS-II) hydrate is more thermodynamically stable than the cubic structure I (CS-I) hydrate in a wide range of p–T regions. However, at low pressure, the stabilization of the CS-I hydrate can be realized for H2–C2H6–H2O systems even with small concentrations of ethane in the gas phase. However, in this case, the amount of stored hydrogen strongly depends on the ethane concentrations in the gas phase. At low concentration of ethane, the amount of hydrogen stored, 2.5 wt%, in CS-I hydrate can be achieved at T = 250K. We believe that the present approach can be useful for understanding the thermodynamic properties of the binary hydrate and it can support the experimental exploration of novel hydrogen storage materials based on clathrate hydrates;
- it has been found that at a small methane concentration in the gas phase the stable hydrate phase has cubic structure II (CS-II) and at a methane concentration of 6% stabilizes cubic structure I, which is metastable in the case of the pure hydrogen hydrate. This is in agreement with recent experimental data. The amount of hydrogen storage depends on the methane concentration in the gas phase as well as the thermodynamic conditions of hydrate formation. Hydrogen storage up to 2.6 wt.% can be achieved in the binary H2-CH4 CS-II hydrate at T=250 K. Despite the fact that these conditions do not satisfy the criteria for onboard hydrogen storage applications, the present binary clathrate hydrate can be considered as a promising candidate for the large-scale stationary storage in urban areas or industrial complexes. In contrast to large molecules such as tetrahydrofuran (THF) or propane, the stabilization of the CS-II hydrate is forced by occupation of both the small and large cages. Therefore, four fold hydrogen occupancy can be easily achieved due to the low ratio of occupied large cavities;
- theoretical modeling of argon + hydrogen mixed hydrate phase diagram and hydrate composition has been performed. For this purpose the original approach allows to take into account multiple cage occupancy with possibility of mixed clusters as well as influence of guest molecules on the host lattice has been used. Separately, argon and hydrogen form CS-II hydrates. We considered only CS-II gas hydrates formation. It is shown that thermodynamic stability of mixed argon + hydrogen hydrates strongly depends on presence of argon in the gas phase as the heavier component. Thus, with increasing argon content in the system, hydrate stability field extends to low pressures with increasing argon fraction in the small cavities. Furthermore, we observed no mixed occupation of the large hydrate cavities by Ar + H2 clusters. It has been shown that the addition of argon, as a heavier component in the gas mixture, reduces the pressure of hydrate formation, however, this causes a decrease in hydrogen content in the hydrate. It is estimated that for large cavities of hydrate filling by clusters of four hydrogen molecules is preferable. Small cavities are more suitable for filling with argon atoms;
- thermodynamic properties hydrogen clathrate hydrates (CS-II) and ice Ih and pressure of clathrate hydrate phases immersed in the ice Ih phases have been investigated using both lattice dynamics and molecular dynamics methods with the aim to understand the existence of self-preservation effect in hydrogen hydrate in the framework of molecular–level models;
- the statistical thermodynamics model with some modifications describing host lattice relaxation, guest-guest interactions and the quantum nature of guest behavior in clathrate hydrates was applied to calculate the relative thermal expansion, i.e. ratio of volume at temperature T and pressure P0 to volume at T0, P0, of hydrogen clathrate hydrate as well as for ices. As reference points the temperature and pressure were selected as T0 = 140 K and P0 = 0.1 MPa, respectively. It was shown that hydrate phases immersed in the ice phases are stable below the three-phase ice–hydrate–gas equilibrium pressure. The hydrate phase remains thermodynamically stable under heating. The calculations show that the pressure in the hydrogen clathrate hydrate sphere immersed into the ice matrix is notably higher than the pressure inside the ice phase, but it does not lead to system distortion because of the formation of a network of hydrogen bonds between hydrate and ice phases. This is because the thermal expansion of hydrogen hydrate is larger than that of ice. Hydrate can be stay in region of its stability on phase diagram because thermal expansion of hydrate phase limited by thermal expansion of ice. Such difference of thermal expansion should lead to self-preservation effect by appearing additional pressure. From a practical point of view this effect can be used for storage and transport of hydrogen in the hydrate form .
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- Accurate description of phase diagram of clathrate hydrates at the molecular level, R.V.Belosludov, O.S. Subbotin, H.Mizuseki, Y.Kawazoe, V. R Belosludov, J.Chem. Phys. 131, 244510 1 (2009).
- Theoretical modelling of phase diagrams of clathrate hydrates for hydrogen storage applications. R. V. Belosludov, R. K. Zhdanov, O. S. Subbotin, H. Mizuseki M. Souissi, Y. Kawazoe and V. R. Belosludov, Molecular Simulation 38 773(2012).
- Theoretical investigation of the possibility of using multicomponent (N2–O2–CH4–H2O) clathrate hydrates for methane recovery from mine gas. Adamova T.P., Subbotin O.S., Chen L.-J., and Belosludov V.R. J. Eng. Thermophys. 22. 62-68 (2013).
- Theoretical investigation of structures and compositions of double neon-methane clathrate hydrates, depending on gas phase composition and pressure. Bozhko, Y.Y., Subbotin, O.S., Fomin, V.M., Belosludov, V.R., Kawazoe, Y. Journal of Engineering Thermophysics. 23(1), 9 – 19 (2014)
- Theoretical investigation of structures, compositions, and phase transitions of neon hydrates based on ices Ih and II. Bozhko, Y.Y., Subbotin, O.S., Fomin, V.M., Belosludov, V.R., Kawazoe, Y. Journal of Engineering Thermophysics. 23(1), 20 - 26 (2014).
- Stability and Composition of Helium Hydrates Based on Ices Ih and II at Low Temperatures. Belosludov R.V., Bozhko Y.Y., Subbotin O.S., Belosludov V.R., Mizuseki H.,Kawazoe Y., Fomin V.M. J. Phys. Chem. C. 118, 2587-2593 (2014).
- Theoretical study of hydrogen storage in binary hydrogen-methane clathrate hydrates. Belosludov R. V., Zhdanov R. K., Subbotin O. S., Mizuseki H., Kawazoe Y., and Belosludov V. R.. Journal of Renewable and Sustainable Energy. 6, 053132-053132-20 (2014).
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- Hydrogen hydrates: Equation of state and self-preservation effect. R.V. Belosudov , Y.Y. Bozhko, R.K. Zhdanov, O.S. Subbotin, Y. Kawazoe,V.R. Belosludov. Fluid Phase Equilibria, 413, 220-228 (2016).