Analysis and Refinement of the TRC-QSPR Method for Vapor Pressure Prediction

Various aspects associated with the use of the TRC-QSPR method (Shacham et al., Ind. Eng. Chem. Res. 49, 900-912, 2010, Ref. (1)) for the prediction of vapor pressure are investigated using a test set of 12 compounds from the n- alkane series. This test set is used to check the consistency of the parameter values of the Wagner and Riedel equations and the resulting vapor pressure values in the full range between the triple point and critical point. Inconsistency has been detected in the parameters of the commonly used version of the Riedel equation as well as the calculated vapor pressure values near the critical point, TR >0.9. Vapor pressures prediction studies are carried out for the cases of interpolation, short and long range extrapolation and using either the acentric factor (�), or number of C atoms (nC ), or the VEA1 descriptor in the TRC-QSPR equation. It is concluded that the prediction error is the lowest and within the experimental error limits over the entire temperature range, using the Wagner's equation andwithin the TRC-QSPR framework. Replacingby nC or by the descriptor VEA1 increases the prediction error, however good prediction accuracy is retained in the regions where experimental data are available for the predictive compounds. It is demonstrated that reliable vapor pressure predictions can be obtained using only nC for characterization of the target compound.