Research on the CO2 gas uptake of different hydrate structures with cyclopentane or methyl-cyclopentane as co-guest molecules

Gas hydrate-based technology has been more important in the recent years. And the hydrate gas uptake affects the efficiency of hydrate-based gas storage and exchange exploitation technologies. In this study, this types of additives cyclopentane (CP) and methyl-cyclopentane (MCP) were investigated. The gas uptake of CO2 hydrate formation with CP or MCP in porous medium were investigated and seven experimental cases (58 cycles) with different CP or MCP molar ratios, both ranging from 0 to 0.03, were conducted. And the calculation equation of hydrate gas uptake was based on the specific volume of CO2 gas. The result indicated that the initial total gas amount affected the gas uptake and the higher pressure increases the gas uptake. CP would decrease the hydrate gas uptake gradually, while MCP increased the gas uptake. This resulted from the change of the hydrate crystal structure. CP helped form s-II CO2-CP hydrates and MCP helped form s-H CO2-MCP hydrates among s-I CO2 hydrates. The proportion of s-I CO2 hydrate and s-II CO2-CP or s-H CO2-MCP hydrates determined the double hydrates gas uptake. And we believe that the CO2 hydrate gas uptake sequence when other conditions keep constant is: s-H > s-I > s-II. We recommend that controlling to form s-H hydrate is better for CO2 capture or storage and to form s-II hydrate is better for hydrate-based technology, especially CO2-CH4 efficient exchange exploitation. (C) 2017 The Authors. Published by Elsevier Ltd.