Fundamentals of coal depolymerization: an experimental and statistical correlative model of the effects of temperature and solvent on free radicals in coal. Quarterly report, October 1-December 31, 1980

Abstract

In this project we are attempting to develop information as to the nature and possible role of free radicals in the depolymerization of coal under hydroliquefaction conditions. It is generally assumed that free radical chemistry plays an important role in the liquefaction of coal. Central in our work has been the use of a specially designed high pressure/high temperature electron spin resonance cavity that allows us to quantitatively monitor free radicals in coal 2 to 4 minutes after the heating cycle is initiated. The free radical concentration has been measured quantitatively and repetitively at these various sets of conditions. The heating time has been restricted to three minutes, gas pressure to 1600 psi and the gas used is hydrogen. The main conclusions from this work include the following: in general, the coal free radicals are quenched in the naphthalene < SRC-II heavy distillate < tetralin. The observed free radical concentration depends on the competing effects of free radical formation and free radical quenching, the latter being both temperature and solvent dependent. The free radical concentration of the liquefaction slurry generally increases with increasing temperature. The rate of quenching of free radicals by SRC-II heavy distillate is closer to that of tetralin at lower temperatures and approaches that of naphthalene at the higher temperature. From the results of the full correlative model, we find that temperature, solvent and residence time and their interactions account for about 90% of the effects noted in the free radical concentration. The correlative model represents the experimental results within the reproducibility of the data.