The chemical nature of asphaltenes from some coal liquefaction processes

Average chemical structures of asphaltenes from three coal liquefaction processes, namely hydroliquefaction (SRC-II), hydrogen-donor solvent extraction (HDS) and supercritical gas extraction (SCG), have been deduced using a structural analysis scheme in which data from ¹H and ¹³C NMR are combined with those from elemental, molecular weight and functional group analyses. Compared with SRC-II and HDS asphaltenes, SCG asphaltenes contain less-condensed aromatic nuclei which can be largely represented by 1- and 2-ring structures. They also contain more oxygen groups and slightly larger aliphatic substituents. CH₃ accounts for between 30 and 40% of the aliphatic carbon in all the asphaltenes investigated. Small amounts of long alkyl chains are present in the SCG asphaltenes but not in the SRC-II and HDS asphaltenes. SCG extraction is chemically less severe than the SRC process and HDS extraction since neither hydrogen nor HDS are employed and, as a result, SCG extracts are considered to be much more representative of the organic matter in the parent coals.