Some observations respecting reaction paths in coal liquefaction: 1. Reactions of coal-tetralin slurries

Results of 30 min liquefaction experiments at 400 °C and 14 MPa with six low-rank coals slurried in tetralin show that compositionally very similar coals could differ markedly in their initial reaction rates and sometimes approached their ‘end-of-test’ conversion levels via transient but quite pronounced regressive reactions. Also, conversion to toluene-soluble ‘primary liquids’ (+co-produced water and gas) in most cases continued when the reaction product mixtures were slowly cooled to room temperature. These findings are difficult to reconcile with a hypothetical reaction mechanism that considers dissolution of coal as entirely dependent on thermal generation and rapid H-capping of radicals; they suggest instead that substantial proportions of potentially useful ‘primary liquids’ can be generated by 1. (1) dispersal of physically entangled molecules constituting the coal matrix, and 2. (2) secondary changes which continue to transform preasphaltenes to asphaltenic and smaller molecular species at temperatures far below 400 °C. In either case, free radical processes would contribute to conversion but would not necessarily be the governing ones.