High-efficiency recovery of methane from coal bed gas via hydrate formation in emulsions

Although the hydrate-based coal bed gas (CBG) separations have been investigated, the obtained CH4 recovery ratios were not quite satisfactory. To further improve CH4 extraction, this study developed a high-efficiency CBG recovery method via hydrate formation in emulsions facilitated by an excellent anti-agglomerant. Thermodynamic promoters were introduced to lower operating pressure and the hydrate equilibrium conditions were determined. Then the effect of water-cut (40-100 vol%), initial pressure, experimental temperature, stirring rate and feed gas composition was investigated. The CH4 concentration in equilibrium gas first decreased then increased as the water-cut increased. Specifically, it decreased from 30.16 mol% to 8.23 mol% in the 60 vol% water-cut emulsions and CH4 recovery reached 88.02 % at 274.15 K and an initial pressure of 3.0 MPa, marking the highest CH4 recovery achieved in CBG separation thus far. The CH4 recovery was increased at low temperature while decreased at high pressure conditions. After a second-stage separation, the CH4 concentration in equilibrium gas decreased to 1.64 mol% from 30.16 mol%, signifying a remarkable 94.56 % recovery of CH4 from feed gas. The CH4 contents after a three-stage enrichment exceeded 87 mol%. This study furnishes valuable insights for CH4 recovery from CBG utilizing hydrate-based separation technology.