Performance evaluation of methane separation from coal mine gas by gas hydrate formation in a stirred reactor and in a fixed bed of silica sand

Coal mine methane (CMM) gas is a sort of unconventional natural gas that can be used as a clean supplementary energy resource when methane is purified. In this work, methane separation from a low-concentration CMM gas (30 mol% CH4, 60 mol% N2, and 10 mol% O2) was investigated using gas hydrate formation in a stirred reactor and in a fixed bed of silica sand with the presence of tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS). The concentration of THF and SDS was fixed at 1.0 mol% and 500 ppm, respectively. The experiments were carried out in batch operation with the initial pressure fixed at 3.6 MPa, and the temperature was set at 277.15 K. The results indicated that gas hydrate formation in the stirred reactor and in the fixed bed of silica sand were both promoted by adding SDS in THF solutions. It was found that the hydrate-based separation process for CH4 recovery from the CMM gas mixture performed better in the stirred reactor as compared to the fixed bed of silica sand employed in this work. The CH4 recovery obtained at 1.0 mol% THF and 500 ppm SDS in the stirred reactor was about 40.5%, which was much higher than those obtained in TBAB solutions (26.2%) and cyclopentane/SDS solutions (33.3%).