Publications Details
High tar yields from low-rank coals in non-catalyzed hydropyrolysis
Hydropyrolysis is potentially an attractive means for the production of synthetic fuels and chemical feedstocks from coals. It offers a simpler process configuration than traditional direct liquefaction with a higher throughput and avoids problems with liquid (tar)-solids (residue) separation. Recent evaluations of coal liquefaction processes have concluded that, provided 50% or more distillable liquids can be produced, hydropyrolysis will be a viable alternative to the traditional vehicle solvent-based processes. For low-rank coals, hydrogenation catalysts are much less effective than for their bituminous counterparts with the increases in tar yields being typically less than 10% daf coal{sup 6}. Nonetheless, without catalyst, the tar yields of 40--50% at 150 bar pressure are appreciably higher than for bituminous coals. In this investigation, tests have been conducted at temperatures up to 600{degrees}C and using an extremely low heating rate of 5{degrees}C/min on the Wyodak Argonne Premium Coal Sample (APCS) and the high-sulfur Mequinenza and Rasa lignites to ascertain whether tar yields could be further increased without catalyst. It was initially considered that the tar yields for low rank coals are limited by the fact that retrogressive reactions, particularly those involving phenolic and carboxylic moities, are more prevalent than for bituminous coals. Data obtained indicates that low heating rates do, in fact, improve the conversion for low-rank coals.