Synergistic effects of water and methanol mixed solvents on the liquefaction of Northeastern Indian coals: Insights from product analysis

The study explored the synergistic effect of methanol as a co-solvent during the hydrothermal liquefaction of three coals from Northeastern India: Bokolia (AB), Bapung (MB), and Margherita (MG). Lignite and sub-bituminous grade coals were tested at reaction temperatures ranging from 350–400 ℃ and 30–60 min residence times, using varying ratios of methanol and water. The products included gas, oil, asphaltenes, preasphaltenes, and char. The best results were achieved with AB coal at 375 ℃ for 60 min with a water-to-methanol ratio of 1:1, yielding 41.7 wt% conversion and 13.8 wt% oil (d.a.f basis). Synergistic effects enhanced oil yield, with maximum values of 53.8 % for AB, 15.9 % for MB, and 23.6 % for MG at optimal conditions. Notably, CO in gaseous products was present in higher concentrations (5–16 vol%) across all coal types at 375 ℃, while MG oil was found to be primarily paraffinic.