Hydrate Phase Equilibria and Structure Identification of the CH4 + CO2 + Thermodynamic Hydrate Promoter Systems for Application to CO2 Capture from Natural Gas

Abstract

Some natural gas fields located in Southeast Asia contain high levels of CO2 content which can reduce energy density and increase production cost. Gas hydrate-based separation can be a good candidate for capturing CO2 from natural gas because the gas is obtained from high pressure reserviors. In this study, thermodynamic and structural analyses of the CH4 + CO2 hydrate were conducted in the presence of various thermodynamic hydrate promoters (THPs) such as tetrahydrofuran (THF), neohexane (NH), and tetra-n-butyl ammonium chloride (TBAC) in order to investigate CO2 capture characteristics depending on the structure. Three-phase (H-LW-V) or four-phase (H-LW-LNH-V) equilibria of the CH4 (50%) + CO2 (50%) + THP hydrates were measured to determine hydrate stability conditions. The phase equilibrium results showed that the addition of TBAC to the system resulted in the most significant thermodynamic promotion. Powder X-ray diffraction (PXRD) and Raman spectroscopy revealed that for the CH4 (50%) + CO2 (50%) gas mixture the addition of TBAC, THF, and NH induced the formation of semiclathrate, sII, and sH hydrate, respectively.