THERMODYNAMICS OF COAL-DERIVED FLUIDS .2. VAPOR-LIQUID-EQUILIBRIA OF COAL LIQUID FRACTIONS

A thermodynamic model for prediction of vapour-liquid equilibria (VLE) in coal-derived fluids has been developed. The model uses group contr ibution methods for property evaluations and a continuous thermodynami cs approach for VLE computations. A coal fluid is defined by multiple molecular weight distributions, and each distribution is represented b y an average molecule with fixed relative proportions of different fun ctional groups. Besides the hydrocarbon group, phenolic, pyridinic and thiophenic groups are used to represent O, N and S heteroatoms. From the results it is concluded that for low-boiling coal liquid fractions the phenolic compounds need to be treated separately, as opposed to t he use of a single average molecule to define the coal liquid. Compari son with published data shows that the model is successful in predicti ng boiling ranges for low-boiling fractions. Failure of the model at h igher temperatures is attributed to the binary interaction parameters in the UNIFAC model which are regressed from low-temperature binary VL E data.