Group contribution methods for coal liquids: vapour pressures

A group contribution method has been used to estimate the vapour pressures of coal liquids from the solvent refined coal II (SRC-II) and Wilsonville integrated two stage liquefaction (ITSL) processes. The concentrations of the functional groups used in the model were determined directly from structural data available for the coal liquids, and the group contributions were taken from the literature. Thus, the model contained no adjustable parameters. Predictions of the vapour pressure were in reasonable agreement with experimental measurements for the low boiling (< 550 K) distillates but the agreement was poor for heavier distillates. There appear to be at least two potential causes of the failure of the group contribution method for the heavier distillates. One source of error is the difficulty in obtaining accurate estimates of bridgehead carbon concentrations. A second source of error is the use of group contributions that have been based largely on low temperature (< 550 K) data.