Inhibition of retrogressive reactions in coal/petroleum co-processing. Final technical report

Abstract

The objective of this study was to examine the processes in coal/petroleum coprocessing systems which led to coke formation. Specifically, the interactions between the petroleum residue and coal, leading to retrogressive products, were investigated. Five coals were reacted with five model compounds in order to investigate the coal conversions in a variety of solvents and to determine the role of the solvent in promoting or inhibiting coal conversion. The selected model compounds range from paraffinic to fully aromatic and were chosen as representative of types of compounds that are found in petroleum residua. Coprocessing experiments were conducted using the five coals and three petroleum residua. The effect of temperature on coal conversions was crucial. The coal conversions at 350 and 400{degree}C seem to be governed by the nature of the coal and to a lesser extent by the petroleum residua. Negative coal conversions were observed above 400{degree}C indicating that retrogressive processes had occurred. At temperatures higher than 400{degree}C, the petroleum residua undergo physical and chemical transformations and the influence of the petroleum residua on coal conversions is significant. The structural features of the residues indicated that the residues were predominately coal-derived. An overall increase in aromaticity was observed with increasing temperature which was also accompanied by loss of oxygen functional groups. The retrogressive reactions with non-caking coals involve carbonyl and carboxyl group leading to a final solid characterized by a cross-linked structure. In the case of caking coal, these reactions are governed by loss of aromatic oxygen groups and loss of alkyl groups.