Chromatographic Separation of Coal Bitumens

Abstract

INTEREST has long been focused on the so-called soluble coal bitumens, since Bone and Fischer demonstrated their influence on the coking characteristics of bituminous coals. Attention was specially directed towards the Fractions III and IV (Bone) of the high-pressure benzene extracts from coals. We need not recount the literature existing on the subject: but it is well known that there is no definite knowledge about the molecular nature of the coal bitumens except that they are complex mixtures. Recently, interest has been revived in the subject by Prof. H. L. Riley. From X-ray diffraction studies he suggests¹ that "the bitumen of the coal is responsible for the systematic variation in the c dimensions of the crystallites formed during carbonisation", and "It is therefore possible that the systematic variation of the c dimension is connected in some way with the coking phenomena". His researches have led him to investigate the carbonization characteristics of substances of known polycyclic structure. However that may be, it is clear that investigations on the constituents of the coal bitumens themselves would lead to a greater understanding of the subject if it were possible to isolate or at least resolve them into groups of substances of similar nature. Orthodox chemical methods have so far failed to resolve the components of coal bitumen. Although adsorption methods have been tried by some workers, it appears that no systematic application of the chromatographic technique (with all its vast elasticity) has yet been carried out. The only published example is recorded by Zechmeister and Frehden², who isolated a substance of the triterpene class from the light petroleum extract of a Hungarian lignite.