DIRECT OBSERVATIONS ON THE INTERACTION OF COALS WITH PITCHES AND ORGANIC-COMPOUNDS DURING CO-PYROLYSIS

Proton magnetic resonance thermal analysis (p.m.r.t.a.) was used to monitor the pyrolysis behaviour of a variety of coals, their mixtures with four different addivites, and each of the additives alone. A model was developed to quantify the effects of small quantities of an additive on the thermoplastic and other molecular properties of coal, by measuring the difference in behaviour of the mixture from that predicted assuming no interactions between the coal and additive. This model was used to define a solvation index, which was used in turn to estimate the capacity of an additive to destabilize or 'solvate' the molecular structure of coals. It was found that (1) pitches - both coal-tar and petroleum-derived - 'solvate' bituminous coals at temperatures significantly below the coal fusion or 'softening' temperature but do not solvate subbituminous or brown coals; (2) this capacity to solvate bituminous coals is shared by the two other aromatic additives tested - decacyclene and p-quaterphenyl; and (3) the rates of coking of both pitch and decacyclene are greatly increased when they are co-pyrolysed with low-rank coals, this enhancement decreasing with increasing rank of the coal.