Structural analysis of a bituminous coal vitrinite by NaH pretreatment and n.m.r. spectroscopy

Abstract

A bituminous coal vitrinite (82.3%C, daf) was treated with NaH in decalin under 3 MPa hydrogen pressure at 300 °C for 6 h. The reacted vitrinite was fractionated according to its solubility in decalin, methanol, tetrahydrofuran and pyridine. The THF-soluble, but decalin- and methanol-insoluble fraction was sub-fractionated by gel permeation chromatography (g.p.c.). The fractions were characterized by elemental and phenolic group analysis, and by DD-TOSS technique for solid state 13C n.m.r. spectral editing with CH n discrimination. Average molecular mass measurements and FT 1H and 13C n.m.r. spectroscopy were also applied to the soluble fractions. Important atomic ratios and parameters, describing the average aromatic structural units of the fractions, were derived. The behaviour of various model compounds under the NaH treatment conditions was also tested. This treatment led to the removal of sulphur and 80% of the oxygen content in the vitrinite (the diarylether oxygen and substantial parts of heterocyclic and phenolic oxygen undergo reductive splitting off). Data indicate that the hydrocarbon skeleton structure of the vitrinite was preserved to a great extent in the decalin- and methanol-insoluble fractions. These fractions showed slightly lower aromaticity, ( H C ) al ratio and degree of aromatic substitution as compared with the initial vitrinite. They had rather diverse C H ratios, but the average number of aromatic unit rings varied within 1.8–3.4.