Crosslinking reactions in coal pyrolysis

Abstract

During coal pyrolysis, the break up of the coal macromolecular network is controlled by the relative rates of bond breaking, crosslinking and mass transport. Crosslinking reactions are important because the ultimate tar yield and tar molecular weight distribution are dependent on the extent of these reactions. Crosslinking, as measured by solvent swelling experiments, is observed to be rank dependent, with lignites crosslinking at lower temperatures than bituminous coals. In a recent study of crosslinking, Suubert et al. observed that the crosslinking rate appeared to correlate with the evolution of CO{sub 2}. This correlation was confirmed by Solomon et al. It appears that crosslinking may be related to the decomposition of carboxyl groups (whose concentration is rank dependent) to form CO{sub 2}. Recent research has also demonstrated that substantial reductions in the crosslinking reactions can be achieved by ultra rapid heating. The high heating rate conditions for lignites produce melting and swelling of char, higher yields of soluble products, and product molecular weight distributions previously seen only for melting, easily soluble coals.