Hydrate-Based Methane Separation from the Drainage Coal-Bed Methane with Tetrahydrofuran Solution in the Presence of Sodium Dodecyl Sulfate

To determine the appropriate operating conditions for separating methane (CH4) from drainage coal-bed methane (CBM) mixed with air, a hydrate-based methane separation method is proposed. The amount of gas uptake, CH4 concentration in decomposed gas phase, CH4 split fraction, and CH4 separation factor are investigated at the initial operating pressure range of 1.50-4.50 MPa and 279.15 K in the presence of sodium dodecyl sulfate (SDS) with the concentration range of 0-1000 ppm in 1.0 mol % tetrahydrofuran (THF) aqueous solution. The results indicate that the 1.0 mol % THF aqueous solution with the addition of 300 ppm SDS at 2.50 MPa and 279.15 K is the optimal condition for recovering CH4 from the drainage CBM via hydrate formation. Under the condition, the final amount of the gas uptake, the CH4 concentration in decomposed gas phase, the,CH4 split fraction, and the CH4 separation factor after a one-stage hydrate-based separation are up to 0.1364 mol, 69.93 mol %, 86.44%, and 10.77, respectively. The result illustrates that the hydrate-based CH4 separation is a promising method to recover CH4 from the drainage CBM at mild conditions. Moreover, CH4 recovered from the drainage CBM can be directly utilized in industry.