Pyrolysis of O-methylated Illinois No. 6 coal. Reaction pathways

Illinois No. 6 coal was modified by selective O-methylation. The O-methyl, O-methyl-d/sub 3/, and O-methyl-/sup 13/C coals were pyrolyzed in a wire-screen reactor at 600-850 C. The char, tar, and gas yields were measured, and the distributions of the isotopic labels in the tar and gaseous products were determined. The product and isotope distributions provide insight concerning the thermal decomposition of the O-methyl coal and the principal reaction pathways of the methyl radicals formed in these reactions. The results for the tar reveal that certain kinds of O-methyl groups are selectively decomposed. Deuterium is incorporated into benzylic and aliphatic positions of the tar. The observations for the gaseous products imply that methyl radicals abstract hydrogen atoms selectively from the coal molecules and thereby initiate an array of other reactions. The work with labeled compounds indicates that the methyl radicals also undergo substitution and addition reactions that lead to low-molecular-weight hydrocarbons and other products. Methoxy radicals also participate in the reactions. Plausible reaction pathways are discussed. 25 references, 2 figures, 8 tables.