Dependence of liquefaction behaviour on coal characteristics: 10. Structural characteristics of a set of high-sulphur coals and the asphaltenes derived from them

Abstract

Yields of a number of products of the liquefaction of a set of 26 high-sulphur coals having already been reported, structural characteristics of the derived asphaltenes and their parent coals are now presented. Data on ultimate analyses, hydroxyl contents, quantitative treatments of FT-i.r. spectra and distributions of products from trifluoroperoxyacetic acid have been determined both for the same coals and for their asphaltenes. 1H n.m.r. and 13C n.m.r. spectra are reported for asphaltenes, with derived aromaticities and other structural parameters. Aromaticities of the coals have been published, and their lack of correlation with carbon contents indicates that the sample set is considerably more heterogeneous than had been expected. In fact no satisfactory bivariate correlations between liquefaction yields and structural features of the coals were found, and no factor analysis of marked significance emerged from a multivariate statistical study. Asphaltenes appear to contain long-chain aliphatic moieties as part of their chemical structure, which are presumably inherited from the macromolecular network of coals. Asphaltenes are more homogeneous than coals in general structural character. Asphaltenes differ in a number of respects from the coals: benzene rings are more highly substituted, and the content of methyl is greater. The distributions of aliphatic structures and patterns of substitution in benzene rings is different. Products of oxidation of side chains and hydroaromatic rings dominate when asphaltenes are the substrate, and acids derived from aromatic rings are the most important in products from coals. These findings help to define the chemical processes involved in liquefaction.