Insight into the aggregation of coal derived material in solvent - an observation by size exclusion chromatography

The aggregation of coal derived material in solvents was investigated by si ze exclusion chromatography (SEC), using a polystyrene-divinylbenzene packe d column and eluting with NMP, NMP/CS2 (1:1, v/v) and NMP containing anion additives. The SEC chromatogram of coal extract using NMP as the eluent sho ws two main peaks. One appears near the exclusion limit of the column (shor ter retention time) and the other one at the longer retention time. Changin g the eluent to NMP/CS2 (1:1, v/v) mixed solvent results in the disappearan ce of the material eluted near the exclusion limit. Instead, all the fracti ons appear at longer retention time. Adding anion additives (5-10 mM), e.g. tetrabutylammonium acetate and NMP 1,1,2,3,3-pentacyanopropenide, into NMP eluent also results in the disappearance of the material eluted near the e xclusion limit. The observed changes are thought to be due to the disruptio n of coal molecular aggregation rather than changes in solvent properties. The material eluted near the exclusion limit is strongly aggregated, its si ze depends on the extent of aggregation and the solvent used. Disruption of the aggregated coal molecule was responsible for the changes in the SEC ch romatogram. In addition, the aggregation of the coal extract was found to i ncrease with decreasing coal rank. For the different extract fractions, the aggregation increases in the order: acetone soluble, pyridine soluble-acet one insoluble and pyridine insoluble-NMP/CS2 (1:1, v/v) mixed solvent solub le. (C) 2001 Elsevier Science Ltd. All rights reserved.