Nonradical reactions during coal conversion. A search for synchronous 1,4-hydrogen addition as a precursor to radical reactions

Previous studies on the relative reactivity of H₂ and tetralin have shown greater hydrogen transfer from H₂ to coal than from tetralin to coal at 350°C. These results are not consistent with a radical pathway for hydrogen addition and require the existence of a nonradical route. We explored the possibility that this nonradical route is synchronous 1,4-H₂ addition, which could occur either with acenes or with dihydroxybenzenes. Reactions of Illinois No. 6 coal with added phenanthrene, anthracene, or m-dihydroxybenzene provide no evidence in support of this addition reaction. The 1,4-addition of H₂ to phenols produces carbonyl compounds. Reactions of Wyodak coal, which should have a higher population of phenolic groups than Illinois No. 6, show no evidence for a correlation of CO production with H₂ utilization or for changes in carbonyl group population that would be consistent with 1,4-addition to phenols. In light of these negative findings, the likely nonradical pathway would then seem to be catalysis by mineral matter. This possibility was probed by comparing reactions of untreated and demineralized Wyodak. The untreated coal, in the absence of solvent, gives higher liquid yields and proportionately more oils and asphaltenes at the expense of preasphaltenes than does the demineralized coal. This indicates a role for the mineral matter in H₂ utilization.