THERMODYNAMICS OF COAL-DERIVED FLUIDS .3. VLE AND HEAT-CAPACITIES OF COAL LIQUID FRACTIONS

A previously developed thermodynamic model for vapour-liquid equilibri um (VLE) properties of coal-derived liquids has been successfully revi sed and extended to compute calorimetric properties of these liquids. The revised model, which is based on the modified UNIFAC correlation, predicts accurately the phase coexistence and calorimetric properties of low-temperature fractions (b.p. < 600 K). However, like the previou s model, the revised model fails at higher temperatures, in part becau se of the limitation of the UNIFAC activity coefficient correlation, w hich uses binary interaction parameters regressed from low-temperature VLE and enthalpy data. To improve the applicability of the model at h igher temperatures, high-temperature VLE and liquid enthalpy data for coal model compounds are necessary. In agreement with previous results , the revised model shows that for low-boiling fractions, two distribu tions (phenolic and non-phenolic) are sufficient to represent the coal liquid reasonably well. However, for accurate representation of highe r-boiling coal liquids, in addition to average molecular weight distri bution and functional group constitution, experimental data on actual molecular types are necessary, providing information on the functional groups that contain heteroatoms and distribution of molecular types t hat include these functional groups.