Molecular weight distributions of heavy products are very important factors necessary to understand the mechanism of coal liquefaction reaction. GPC is a promising method for heavy organic materials such as preasphaltenes (benzene insoluble-pyridine soluble fractions) derived from coal. In this paper, GPC analysis was applied to characterize the preasphaltenes using N-methyl-2-pyrolidinone (NMP), which is a preferable solvent for the preasphaltenes, as an elution solvent in GPC.
In the GPC analysis of the preasphaltenes, two characteristic peaks were observed in the region of the molecular weight of 103 and 105-7 correlated by polystyrene standards. A peak corresponding to 105-7 shifted to the lower-molecular-weight region after addition of LiBr into the solvent. Besides the preasphaltenes, phenol novolak resin showed the same GPC profile using NMP as the solvent. These results suggested that the origin of the peak in the higher-molecular-weight region was the oxygen-containing polar components in the preasphaltenes. The peak separation and the peak shift after LiBr addition were also observed in the reversed phase liquid chromatography of preasphaltenes and phenol resin using NMP as the solvent. It was therefore suggested that the peak observed in the higher-molecular-weight region was ascribed to the decrease of the interaction between polar components and the column packings, because of the enhanced ionic properties of the polar components caused by NMP. Therefore, it was realized that the evaluation of the molecular weight distributions of these polar components was needed to analyze the preasphaltenes, and the phenol resin was one of the promising candidates for the standards to be used in the correlation of molecular weight.
