Abstract
The determination of asphaltenes in coal liquefaction products is strongly related to the chosen solvents, extraction time, sequence of extractive solvents, and co-solvent effects of the coal liquids. Recognizing that asphaltenes are operationally defined, the above observations raise the question of whether there are “asphaltenes” in the unseparated coal liquids or whether they are artifacts of the separation procedure, resulting from the association of unstable, reactive molecules that combine upon their concentration and isolation from the original slurry. Using preparative and analytical Gel Permeation Chromatography and solvent extraction procedures, qualitative molecular size profiles of coal liquid products have been obtained. It has been concluded that: (1) the pre-asphaltenes, asphaltenes and oils exist in the coal liquids, and are not artifacts of the separation procedures; (2) their molecular sizes follow the order pre-asphaltenes > asphaltenes > oils; (3) association—dissociation of the coal liquids is indicated and (4) coal liquid fractions obtained by different methods should not be considered equivalent.
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