Abstract

A thermodynamic model for prediction of vapour-liquid equilibria (VLE) in coal-derived fluids has been developed. The model uses group contribution methods for property evaluations and a continuous thermodynamics approach for VLE computations. A coal fluid is defined by multiple molecular weight distributions, and each distribution is represented by an average molecule with fixed relative proportions of different functional 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 the use of a single average molecule to define the coal liquid. Comparison with published data shows that the model is successful in predicting boiling ranges for low-boiling fractions. Failure of the model at higher temperatures is attributed to the binary interaction parameters in the UNIFAC model which are regressed from low-temperature binary VLE data.

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