Hydrates-Based Separation of CH4/N2 Gas Using Copper Foam and Chemical Promoters

Hydrate-based gas separation (HBGS) offers a safe and promising route for capturing low-concentration coalbed methane (CH4). Herein, the formation behavior of CH4 hydrates promoted by 1,3-dioxolane (1,3-DIOX) and porous copper foam (CF) was systematically investigated. Experimental results demonstrated that the combined use of CF (60 PPI) and 5.56 mol % 1,3-DIOX under a coupled spraying-stirring mode markedly accelerates hydrate formation, yielding a maximum gas storage capacity of 0.1733 mol CH4 per mole H2O at 3.0 MPa, which is 10.1 times higher than that of the static pure water system. At 4.0 MPa, the maximum capacity is 0.1244 mol CH4/mol H2O, which is 3.7 times higher than that of the static pure water system. Furthermore, due to the higher thermodynamic driving force, the induction time for the 10% CH4 system is shorter than that of the 5% system. Specifically, the induction time with 0.3 wt % l-leucine was 21.31%–40.38% shorter than that of the combined CF and 1,3-DIOX system. After single-stage separation, the CH4 content was effectively enriched from 5% to 8.0%–10.25% and from 10% to 17.9%–21.7%. Compared to l-leucine, the system containing sodium lignosulfonate demonstrated a higher CH4 concentration in the hydrate phase, indicating superior selectivity. The CH4 recovery rates for the feeding gas systems with 10% and 5% CH4 were approximately 40% and 50%, respectively. Comparing to the reported results in smaller reactors of 58–1000 mL, the comparable CH4 recovery here is realized in a much larger scale reactor of 3927 mL, which is really a great improvement. These findings confirm that the proposed CF/1,3-DIOX system is an effective strategy for the enrichment of low-concentration CBM, providing a viable technical route for multistage industrial separation processes.