Binary gas adsorption/desorption isotherms: effect of moisture and coal composition upon carbon dioxide selectivity over methane

The effect of coal moisture content and composition upon methane/carbon dio xide mixed gas adsorption characteristics is investigated. Separation facto rs are used to quantify the relative adsorption of carbon dioxide and metha ne. Experimental data indicate that carbon dioxide separation factors vary slightly between coal lithotypes, but the effects of variable coal composit ion and moisture upon selective adsorption are difficult to isolate. Model predictions based upon single-component isotherms show that although some v ariability in carbon dioxide selectivity exists for different coal types, t here is no clear relationship between coal composition and carbon dioxide s electivity. Model predictions also indicate that coal moisture decreases ca rbon dioxide selectivity. The ideal adsorbed solution (IAS) theory and the extended Langmuir model differ substantially in their ability to predict bi nary gas adsorption behaviour. Comparison of model predictions to experimen tal data demonstrates that IAS theory, in conjunction with the Dubinin-Asta khov single-component isotherm equations are more accurate for the predicti on of mixed gas desorption isotherms collected in this study than the exten ded Langmuir. IAS predictions, however, are strongly dependent upon the cho ice of pure gas isotherm equation. (C) 2000 Elsevier Science B.V. All right s reserved.