The nature and role of free radicals in coal conversion processes as revealed by e.s.r. studies

Abstract

Dr Ladner and Professor Pines in the previous two papers demonstrated how nuclear magnetic resonance can provide significant information on the structure of coals and coal extracts. We wish to provide evidence that electron spin resonance (e.s.r.) also can yield significant information on coal structure and coal conversion processes. Free radicals in coal have been known for several years (Uebersfeld et al . 1954; Ingram et al . 1954). In our own research group, we have during the last several years carried out a systematic investigation of the nature and role of free radicals in coals, coal components and in coal conversion processes, with the use of e.s.r. techniques (Petrakis & Grandy 1978, 1980 a, b : Grandy & Petrakis 1979; Petrakis et al . 1980). For the most part, we have studied residual free radicals, but very recently we have also constructed a special cavity that allows the study of free radicals under liquefaction and pyrolysis conditions. Professor Pines indicated in the previous paper that the very observation of the carbon-13 n.m.r. spectra of solid coal is possible because of the effects that free radicals in coal have on the relaxation times of the carbon-13 nuclei. E.s.r. allows the study of the free radicals in coal as they pre-exist in coals and during and after conversion. The significant e.s.r. parameters in these studies are spin concentrations, g values, line shapes and line widths.