Solubilization of Illinois bituminous coal: the critical importance of methylene group cleavage

Abstract

The extent of solubilization of an Illinois bituminous coal achieved by hydroliquefaction at various temperatures with and without catalyst was determined. The coal was also solubilized by treatment in suspension in THF with potassium in the presence of naphthalene. The original coal was also extracted with THF without prior treatment. After removal of solvent the soluble fractions were examined by 1H n.m.r. spectroscopy. It is concluded that there are two temperature regimes which affect coal conversion: in the 350–400 °C region, hydroliquefaction proceeds principally by ether cleavage; whereas in the 400–450 °C range, hydroliquefaction results in additional cleavage of methylene groups joining aromatic or heteroaromatic units. Comparison of solubilization by hydroliquefaction with solubilization achieved with potassium in THF seems to indicate the initial degradation of coal by both techniques proceeds by ether cleavage and that further degradation is achieved in both cases by attack at the methylene bridge. The n.m.r. studies on hydroliquefaction products indicate that Illinois bituminous coal is structurally quite homogeneous because the product composition is largely independent of the degree of solubilization. Thus, solubilization results from molecular weight degradation rather than from preferential-degradation to different structural units.