Evaluation and modification of group contribution methods for critical properties of organic compounds

One of the challenges in estimating physical properties is selecting an appropriate estimation method. The group contribution methods for the estimation of normal boiling point critical properties were evaluated and modified with reference data. Firstly, the group contribution methods were evaluated by comparing the average relative error and relative error distribution of different methods. The results showed that the element and chemical bond 2 method was the most accurate for estimating the critical temperature, with an average relative error of 2.98 %. The Joback method was more accurate than the other methods for the estimation the critical pressure and critical volume, with the average relative error of 4.31 % and 4.83 %, respectively. Secondly, silicon-containing groups were added in the Constantinou-Gani method, and the contribution values of groups were fitted. The accuracy of the group contribution value was verified with the experimental data that not involved in the regression. The average relative errors of normal boiling point, critical temperature, critical volume and critical pressure were 3.08 %, 2.95 %, 3.37 % and 2.45 %, respectively. The results indicated that the divided groups were reasonable and the regressed contribution values of groups were accurate. The modified Constantinou-Gani method is a good way for the estimation of the critical properties of silica-containing organic compounds.