One- and two-stage coprocessing of coal and petroleum residues

The potential of two atmospheric and three vacuum petroleum residues as feedstocks for coprocessing with a UK bituminous coal has been assessed. In a simulation of the British Coal Corporation's two-stage liquid solvent extraction process, the residues were first examined as prospective solvents in the extraction stage. Coal conversions varied from about 6-37%, the best yields being obtained from residues with a high asphaltene content or a high (aromatic and polar) content in the maltene-fraction. These yields compare poorly with those obtainable with coal-derived solvents. In two cases, catalytic prehydrogenation of the petroleum residue improved conversions to about 65%, but these results were not reproducible. One-stage coprocessing at 450°C and 12 MPa hydrogen pressure was much more successful. Coal conversions of about 75% were obtained at optimum conditions. Conversions under one-stage coprocessing were insensitive to the nature of the residue.