Influence of Cyclopentane and SDS on Methane Separation from Coal Mine Gas by Hydrate Crystallization

The influence of cyclopentane (CP) on methane separation from low-concentration coal mine gas (30% CH4, 60% N-2, and 10% O-2) by gas hydrate formation was investigated in the present work. Overpressure was used as the driving force. Experiments were carried out at 286.6 K and (2.0-5.0) MPa, and the cyclopentane concentration was fixed at 7.0 wt %. The experimental results indicated that the gas uptake increased with the increase of driving force, but the methane recovery decreased with the increase of driving force. A similar to 6% higher methane recovery was obtained under the low driving force Delta P = 1.5 MPa as compared to that obtained in the presence of tetra-n-butyl ammonium bromide (similar to 27%). Then, the anionic surfactant sodium dodecyl sulfate (SDS) was employed to enhance hydrate formation from low-concentration coal mine gas in the presence of cyclopentane. Surface tensions of the solution (H2O/CP/SDS) were measured under different SDS concentrations and reported. It was found that gas uptake and the rate of hydrate formation were dependent on SDS concentration, but the presence of SDS did not show clear influence on methane recovery. The methane recovery obtained in the presence of SDS was similar to 33.3% while that obtained without SDS was 33.1%.