Determination of phenolic structures in low rank coals: elucidation of transformation processes of lignin at the early stage of coalification

Because lignin is considered to be a major precursor of coal vitrinite, chemical alteration studies of lignin structure are important for elucidating coalification processes as well as for understanding the chemical structure of vitrinite. Many investigators have attempted to elucidate the chemical processes in the coalification lignin. For example, Wayman et al have reported that a 100-million-year-old conifer consists of lignin-like material which is about one-third demethylated. Extensive cleavage of lignin ether linkages was also observed. Recently, based on /sup 13/C NMR study, Hatcher has concluded that the defunctionalization reactions of lignin-derived aromatic structures occur sequentially during coalification. A similar pathway has been suggested by Wilson. From a comparative NMR study of (/beta/-/sup 13/C) lignin and its coalified products, Botto has suggested that transformation of lignin is initiated by the heterolytic bond cleavage of labile /beta/-aryl ether groups. The present study continues the investigation of transformation processes of plant organic material to coal during early stages of coalification. To understand alteration of phenolic structures in lignin, and natural and synthetic coals have been characterized by using two-step depolymerization procedure of alkaline hydrolysis followed by silver oxide oxidation. In parallel experiments, lignin model compounds and a polymer have been transformed using more » thermal catalytic reaction conditions that mimic natural catagenetic metamorphism. « less