Compressibility of Gas Hydrates

Abstract

Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0-2 GPa), xenon (cubic structure I, pressure range 0-1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0-3 GPa) are presented. Approximation of the data using the cubic Birch-Murnaghan equation, P=1.5B(0)[(V(0)/V)(7/3)-(V(0)/V)(5/3)], gave the following results: for ethane hydrate V(0)=1781 Å(3) , B(0)=11.2 GPa; for xenon hydrate V(0)=1726 Å(3) , B(0)=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V(0)=5323 Å(3) , B(0)=8.8 GPa. In the last case, the approximation was performed within the pressure range 0-1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch-Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86% of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen-bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones.

Supramolecular Organization in Confined Nanospaces

“…Indeed, hydrates are often studied in this harsh regime, and for very good reasons: first of all, their pressure‐induced stability increase. This allows hydrates to reach temperatures around 10 °C (higher than ice melting point) at pressures of 0.1 GPa ,. Some hydrates, however, do not need high pressure to survive – like hydrogen sulfide hydrate, which can exist at ∼1 atmosphere and 273 K…”

“…This allows hydrates to reach temperatures around 10 8C (higher than ice melting point) at pressures of 0.1 GPa. [288,289] Some hydrates, however, do not need high pressure to survive -like hydrogen sulfide hydrate, which can exist at~1 atmosphere and 273 K. [32] Most hydrates crystallize in sI or sII structures, and the structure type is determined mainly -but not exclusively -by the size of the guests. Whereas sI is often formed with small molecules (e. g., methane), sII can contain larger guests (Figure 11b).…”

Measurements of diffusion coefficient of methane in water/brine under high pressure

“…Natural gas hydrate is considered to be a potential unconventional energy resource . The thermodynamic properties of natural gas hydrate have been extensively explored, such as phase boundary (Van Der Waals and Platteeuw 1958;Barrer and Ruzicka 1962a;Dalmazzone et al 2002;Anderson et al 2009;Hsieh et al 2012;Chu et al 2015Chu et al , 2016Juan et al 2015), volumetric properties (Hester et al 2007;Manakov et al 2011;Ning et al 2015), and dissociation enthalpies (Handa 1986;Rydzy et al 2007;Gupta et al 2008). Other physical properties of hydrate had been systematically reviewed (Sloan 1998;Gabitto and Tsouris 2010).…”

Modeling Thermodynamic Properties of Propane or Tetrahydrofuran Mixed with Carbon Dioxide or Methane in Structure-II Clathrate Hydrates

“…The conclusion is that thermal conductivity and thermal expansion coefficient are related to the crystal type, guest type and size, as well as the occupancy [19][20][21][22][23][24][25][26] . Large quantities of experimental results exist for the thermal expansion coefficient 20,[27][28][29][30][31][32] , compressibility 17,[33][34][35][36] or bulk modulus, and heat capacity 17,[37][38][39] of clathrate hydrates. Unfortunately, these experimental values are mostly available in a limited and insufficient temperature -and pressure range.…”