Dependence of coal liquefaction behaviour on coal characteristics. 7. Structural differences between coals of different rank and the asphaltenes derived from them

Aslphaltenes are difficult to characterize by any procedure that involves chromatography. In an attempt to obtain useful information on unfractionated asphaltenes and their structural relations to their parent coals, asphaltenes from a set of eight coals of hvA rank and different coalification history have been studied by ¹ H n.m.r. In addition, structural features in the coals and their asphaltenes were compared by g.c.-m.s. analysis of the products of oxidation by pertrif luoroacetic acid. Protons α to a benzene ring are the most abundant in the asphaltenes, and their relative concentration changes little with the rank of the parent coal. Protons in the β-position are abundant, however, and may be associated with aliphatic junctions linking two or more aromatic ring systems. Whereas malonic and ethane-trioic acids are the major aliphatic di-and tri-acids from oxidation of the coals, succinic and propane-or butane-tricarboxylic acids are the corresponding products that dominate the distributions from the asphaltenes. These and other differences help to define the structural changes caused by liquefaction. In addition, the results indicate the nature of structural changes with increasing rank, which are manifest in the oxidation products from the asphaltenes as well as from the coals.