Methane Recovery from Coalbed Gas by Forming sII Hydrate with the Aid of a Novel Eco-Friendly Promoter

The recovery of CH4 from coalbed gas (CBG) is significant for improving energy utilization and mitigating the greenhouse effect. In this study, CH4 was separated from CBG by forming sII hydrate with 5.56 mol % 1,3-dioxolane (DIOX) solution assisted by an eco-friendly promoter sodium lauroyl glutamate (SLG). The effects of SLG concentration, initial pressure and temperature, stirring rate, and CBG composition were systematically investigated. The results revealed that the addition of SLG notably diminished the hydrate induction time and reaction durations. The presence of 500 ppm of SLG decreased the CH4 concentration to 15.50 mol % from the initial 30.23 mol %, and the CH4 recovery and separation factor reached 81.70% and 3.34, respectively. Comparative analyses with other eco-friendly surfactants highlighted the substantial advantages of SLG. The CH4 concentration in the residual gas first decreased and then increased with the augmentation of the initial pressure, temperature, and stirring rate. An inverse pattern was observed in the variations of CH4 recovery and separation factor. This indicated that there existed an optimal initial pressure, temperature, and stirring rate for CBG separation. The CH4 content in the hydrate was increased to 91.59% after a fourth-stage enrichment, meeting the standards for the direct injection of CBG into natural gas pipelines. These findings provide valuable insights for CH4 separation from CBG by forming sII hydrate with eco-friendly promoters.