INFLUENCE OF COAL LITHOTYPE AND MACERAL 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), Herrin (No. 6), Murphysboro, and the Brazil Block coal seam; focusing on petrography, conversion, and final products. OHD is a coal conversion technique that reacts coal with small 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, 30, and 70 min each. The 70-min runs were completion runs (i.e., no coal residue left in the reactor). The petrography and conversion percentage were determined on the residue (material remaining in the reactor) whereas the liquid product was analyzed by GC-MS. Petrographic analysis of the vitrain, clarain, and cannel residues from the 8, 16, and 30 min runs showed development of devolatilization vacuoles, distinct reaction rims, and an associated increase in reflectance in the vitrinite macerals. Liptinite macerals began to alter, but did not breakdown completely. The inertinite macerals in the fusain sample displayed a slight reaction rim and increase in reflectance. The conversion rates of 8-min runs were generally around 25%, approximately 50% in 16-min runs, and nearly 90% in 30-min runs. The No. 6 seam was further split into macerals (vitrinite, liptinite, and fusinite) using density-gradient centrifugation. The separated macerals were run individually in the OHD reactor for 45 min. All lithotypes and macerals produced a similar suite of products but in different relative abundances. Major families of products included phenols, diphenols, monocarboxylic acids, dicarboxylic acids, and tricarboxylic acids.