Solvent Extraction of a South African Bituminous Coal using a Model Biomass-derived Phenolic Mixture

A model biomass-derived phenolic mixture was investigated for its solvent ability for extraction of a South African bituminous coal at temperatures of 300–360 °C. A previous study showed that phenol gave the highest extraction yield of 49.5 wt. % (daf) for bituminous coal at 360 °C, with an oil yield of 26.3 wt. % (daf). The phenolic products produced from sweet sorghum bagasse via an alkaline liquefaction process were identified and reported earlier and a model biomass-derived phenolic mixture was formulated, evaluated and results used in this study. The model mixture gave an extraction yield of 37.1 wt. % (daf) and oil yield of 16.9 wt. % (daf) at 360 °C. This solvent mixture was found to be less effective for high extraction yields when compared to phenol at mild temperatures. This could be due to phenol being a better hydrogen carrier than the solvent mixture during the internal redistribution of hydrogen in the coal. The infrared spectroscopy results of the coal and extraction products obtained using the model mixtures showed similar functional groups. These results demonstrate that the use of a model biomass-derived phenolic mixture has the potential to depolymerize coal and produce high-value chemicals from coal.