Chemical structure of heavy oil from coal hydrogenation 1. Hydrogenation with zinc chloride catalyst

Abstract

Oil product from the hydrogenolysis of a high-volatile bituminous coal was separated by solubility, fractionated by gel permeation chromotography and characterized by structural analysis. The average structural unit in the hexane-soluble, aromatic oil fraction consists of 1–3 aromatic rings with 0.3-0.5 of the ring carbons substituted by alkyl groups and oxygen containing groups. Molecular weights vary from 200 to 500. The larger molecular weight fractions have longer alkyl chains and lower carbon aromaticities. The molecules are mainly of single unit structures. The average structural units in asphaltene fractions contain from 2.5-4 aromatic rings, are of higher carbon aromaticities and contain shorter alkyl groups. The asphaltene molecules consist of two or more structural units, crosslinked together, and have molecular weights of 300–1400. The oxygen content of the fractions decreases with decreasing molecular weight. Increasing the amount of ZnCl 2 catalyst during hydrogenolysis resylts in an increased yield of lower-molecular-weight material, but no change in the structural properties of the product. This is interpreted to mean that ZnCl 2 is active in the scission of covalent bonds between structural units during liquefaction and that the hydrogenolysis reaction is mostly cleavage of crosslinks between structural units with minimal reaction of the units themselves.