LIQUEFACTION OF BLACK-THUNDER COAL .1. PETROGRAPHIC EXAMINATION OF RESIDUES

Residues from the liquefaction of Black Thunder subbituminous and Illi nois No. 6 bituminous coals in an autoclave and a bench unit were exam ined petrographically. Optical microscopy proved valuable for ranking the samples on the basis of overall coal conversion and presence of vi troplast, granular residue and inertinite. It was observed that in the autoclave that runs on Black Thunder coal, K2CO3 was a superior water gas shift reaction catalyst to NaAlO2, or a combination of CS2 and Fe or Mo catalysts. The amount of vitroplast showing vacuoles and cenosp heric morphology in the residues was inversely related to the CO conve rsion, indicating that the mechanism of vitroplast dissolution is link ed to the availability of active CO intermediates (e.g. formate ion, H COO-). A GO-steam mixture was more effective than syngas or pure H-2 a nd N-2 in increasing Black Thunder coal conversion, and resulted in gr eater morphological changes to the coal particles. In contrast, for Il linois No. 6 coal pure H-2 had a greater effect on coal solubilization and overall conversion than pure CO at the same temperature; this was attributed to the absence of carboxylates to react with the formate i ons. Higher mesophase and coke contents were detected in some bench un it runs on Black Thunder coal that were operated in counterflow mode. Higher severity, poorer mixing, longer residence time and a reduction in pressure by almost 3.5 MPa are believed to be responsible for the r etrogressive reactions forming mesospheres in these cases.