COAL SURFACE-PROPERTIES - SPECIFIC AND NONSPECIFIC INTERACTIONS FOR POLAR-MOLECULES AND SURFACE TENSIONS FOR HYDROCARBONS AT THE SURFACE OF ILLINOIS NO-6 COAL

The isosteric adsorption enthalpies of polar molecules on Illinois No. 6 coal have been measured by inverse gas chromatography (IGC), and the measured values have been separated into specific and van der Waals contributions by using adsorption heats on graphitized carbon black as a model for the van der Waals contributions. The specific adsorption heats of seven organic bases on Illinois No. 6 coal are identical to heats of hydrogen-bond formation with p-fluorophenol, suggesting that the bases hydrogen-bond to pendant phenol groups on the coal surface. Alcohols, amines, and pyridine have more exothermic specific adsorption heats on original (17% ash) compared to demineralized (2% ash) coal, while organic oxygen bases have similar adsorption heats on both coals. All of these adsorbates have similar adsorption heats on citric acid demineralized and HF-HCl demineralized Illinois No. 6 coal, demonstrating that pyridine, alcohols, and amines interact more strongly with carbonate and/or ion-exchangeable mineral matter, while oxygen bases interact preferentially with the organic component of the coal surface. Carbon dioxide and carbon disulfide both interact specifically (approximately 2 kcal/mol) with the Illinois No.6 coal surface. IGC data for hydrocarbons have been used to calculate reasonable values for the dispersive solid surface tension of Illinois No. 6 coal. Extracting Illinois No. 6 coal or heating it to 250-degrees-C causes a decrease in the dispersive surface tension.