Experimental study on hydrate-based gas separation of mixed CH4/CO2 using unstable ice in a silica gel bed

Abstract

The reduction of energy consumed in the hydrate formation process has attracted a great attention in many fields, such as renewable energy resources and environmental issues. In this work, the water and the ice were investigated by powder X-ray diffraction (PXRD) and cryo-scanning electron microscope (SEM) in the silica gel, and the hydrate-based gas separation of CH4/CO2 mixtures was studied at four different pressures (2.6, 3.7, 4.6 and 5.2 MPa) and three different temperatures (271.1, 268.1 and 263.1 K) in silica gel bed. The results showed that water was transformed into discontinuous unstable hexagonal ice crystals on silica gel surface, which was in favor of hydrate formation. Water conversion to hydrate and normalized gas consumption were up to 100% and 0.151 (mol/mol) at 263.1 K and above 4.2 MPa, respectively. CO2 proportion in hydrate, split fraction of CH4 in equilibrium gas and separation factor were up to 99.60%, 99.8% and 257.34 at 2.6 MPa and in the temperature range of 268.1–271.1 K, respectively. It will be of practical interest in relation to losing methane of multistage hydrate-based biogas purification technology.