A RATIONALE FOR HEATING RATE AND COAL TYPE EFFECTS ON LIQUIDS YIELDS AND SUBSTRATE MORPHOLOGY CHANGES DURING RAPID PYROLYSIS

A recent analysis by Darivakis et al. holds that during pyrolysis, liquids production is enhanced when bonds connecting liquids precursors to coal break at virtually identical rates. By analyzing coal thermal depolymerization statistics, this approach relates molecular weight (MW) distributions of primary pyrolysis liquids to coal molecular structure with known mathematical functions. Here it is shown that this analysis provides a plausible, internally consistent, and fundamentally-based rationale for several macroscopic and non-obviously related chemical and physical effects of heating rate and coal type on pyrolysis: (a) higher liquids yields from bituminous coals than from lignites; (b) increasing liquids yields and bubble concentrations in softened coal with increasing heating rate; and (c) that lignites, in contrast to bituminous coals, do not soften over wide ranges of heating rates, but can be made to soften at very high heating rates. Also presented are experimentally determined yields and number average MW's of tars from pyrolysis of a North Dakota lignite at heating rates of 1000 and 4000 degrees C/s, and temperatures of 600-1000 degrees C.