Similarity coefficient

In the present study a new parameter is presented, namely similarity coefficient. This parameter can be used for estimating critical pressure and critical temperature. Group contribution technique is applied and twelve groups for hydrocarbons are offered here. For this purpose, 280 multi-functional compounds are tabulated and multiple linear regression is used with discrete definition of each group contribution while other groups’ contributions are held constant. Satisfactory results of estimated similarity coefficients indicate that, this parameter can be further investigated. By combination of Ambroseʹs critical temperatures with similarity coefficient, critical pressures for hydrocarbons are estimated. The results show that the new method is more accurate than the Ambrose, Jalowka–Daubert and Constantinou–Gani methods in both maximum of error and average absolute deviation. In addition, the predictions are made for the ideal-gas heat capacity at constant pressure and 298.15 K for n-alkanes and the results are compared with existing methods.