INFLUENCE OF COAL LITHOTYPE COMPOSITION ON THE OXIDATIVE HYDROTHERMAL DISSOLUTION (OHD) PROCESS

The influence of petrographic composition on the Oxidative Hydrothermal Dissolution (OHD) process was examined using lithotypes from the Springfield (No. 5) Coal seam and the Brazil Block seam, focusing on petrography, conversion, and final products. OHD is a coal conversion technique that reacts coal with minor amounts of molecular oxygen (introduced in the form of peroxide) in liquid water at 300°C to result in a mild oxidation of the sample. This effectively breaks up the macromolecular structure to release low-molecular-weight organic products. Coal lithotype samples including vitrain, clarain, fusain, and cannel were run in the OHD reactor for 8, 16, and 30 minutes each. The petrography and conversion percentage were determined on the residue (material remaining in the reactor) whereas the liquid product was analyzed by GCMS. Petrographic analysis of the vitrain, clarain, and cannel showed development of devolitization vacuoles, distinct reaction rims, and an associated increase in reflectance for the vitrinite macerals. Liptinite macerals started to disappear indicating its ready dissolution in the reaction whereas the fusain sample showed only a slight increase in reflectance of the inertinite macerals. For the 8-minute runs, similar conversion rates were seen (23 to 27%), and this conversion increased with increased reaction time. All four lithotypes produced a similar suite of products but relative abundances were different. Major families of products included di-substituted methoxy benzenes, mono-substituted methoxy benzoic acids, hydroxyl-substituted benzoic acids, methyl-substituted benzoic acids, disubstituted carboxylic acids, and tri-substituted carboxylic acids. The most abundant peak in all four samples, 3-methoxy benzoic acid was the largest in the cannel followed by the vitrain, fusain and clarain.