Thermodynamics of coal-derived fluids. 3. VLE and heat capacities of coal liquid fractions

Abstract

A previously developed thermodynamic model for vapour-liquid equilibrium (VLE) properties of coal-derived liquids has been successfully revised 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 previous model, the revised model fails at higher temperatures, in part because of the limitation of the UNIFAC activity coefficient correlation, which uses binary interaction parameters regressed from low-temperature VLE and enthalpy data. To improve the applicability of the model at higher 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 distributions (phenolic and non-phenolic) are sufficient to represent the coal liquid reasonably well. However, for accurate representation of higher-boiling coal liquids, in addition to average molecular weight distribution 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 that include these functional groups.