Enhancement of biogenic methane production from coal using supercritical CO2

Supercritical CO 2 (ScCO 2 ) extraction could improve the bioavailability of coal for the enhancement of biogenic methane production. Here, the influence of prolonged ScCO 2 extraction on methane yield was investigated since in-situ ScCO 2 injection is time-consuming. The results showed that the enhancement of biomethane production from coal was negatively correlated with extraction time and extraction yield. With the extension of ScCO 2 extraction time from 0.5 day to 28 days, the methane yield of extracted coals increased by 20.1∼111.4% than that of raw coal. ScCO 2 mainly reacted with the organic structures on the surface of coal (such as the C-O and CH 2 -C O), rarely the skeleton structure. In the prolonged extraction, aromatics were first extracted, then oxygen-containing matters and aliphatics which reduces the methane production of extracted coal but increases the methane generation potential of extractable organic matter. Then, a conceptual model of ScCO 2 -MECBM was proposed for enhancing methane recovery in-situ.