Guest enclathration and structural transition in CO2 + N2 + methylcyclopentane hydrates and their significance for CO2 capture and sequestration

Abstract

The phase equilibria, structural transition, gas uptake, and composition of CO2 + N-2 + methylcyclopentane (MCP) hydrates were investigated for their potential applications in CO2 capture and sequestration. Thermodynamic stability conditions indicated that flue gas could form sH hydrates in the presence of MCP at a reduced pressure and an elevated temperature. Powder X-ray diffraction (PXRD) and Raman analyses revealed that the structural transition of CO2 + N-2 + MCP hydrates occurs from sH to sI with increasing CO2 concentration and that both sH and sI coexist at a boundary composition of CO2 (20%) +N-2 (80%). In situ Raman spectroscopy provided direct evidence of the enclathration of CO2 and MCP in cages of sH hydrates under highly N-2-rich conditions. The sH CO2 + N-2 + MCP hydrates demonstrated slightly lower gas uptakes and CO2 selectivity in the hydrate phase than corresponding sI CO2 + N-2 hydrates, despite their thermodynamic advantages. The overall experimental results obtained in this study can help create a better understanding of guest enclathration and structural transition in sH hydrates and thus provide new insights into sH hydrate-based CO2 capture and sequestration using flue gas.