Estimation of critical properties with group contribution methods

Abstract

Currently available group-contribution methods for T,, P,, and V, were evaluated using the Ambrose (1980) critical property data compilation. The Ambrose estimation methods were found to be the most accurate. Linear regression methods were also employed to develop alternate estimation methods which were found to have an accuracy comparable to those of Ambrose.K. M. KLINCEWICZ SCOPECritical properties (T,, P,, V, ) are often required when using generalized property estimation methods. Due to the paucity of experimental values, one must often estimate these properties, and a group-contribution approach is generally used. The method developed by Lydersen (1955) is the most widely employed. However, many new experimental critical properties have become available since the Lydersen report and several alternate estimation schemes have been proposed. In the first portion of this paper, a few methods have been briefly reviewed and evaluated for accuracy using the currently available data.With the rapid advances in linear regression programming, it was felt to be of value to use this methodology to optimize the coefficients and group contributions utilizing a number of objective functions involving T,, P,, or V,. In this manner, one can rapidly test a number of objective functions, selected group-contribution substructures, auxiliary variables, etc. to obtain the least error method of estimation. CONCLUSIONS AND SIGNIFICANCEEvaluating all available estimation methods for T,, P,, and V, , it was shown that the methods of Ambrose (1979Ambrose ( , 1980b were the most accurate. These methods employ Tb/( T, -Tb), (MW/Pc)l12, and V, as objective functions (Q) with the equation forms given in Table 1 and the necessary group contributions in Table 3. The statistics relating to expected errors are shown in Table 5.Linear regression techniques also provided group estimation methods close in accuracy to those of Ambrose but with a simpler set of structural subgroups. In this type of analysis, multicollinearity was identified as a serious problem and the final choice of subgroups minimized the difficulties encountered.The new proposed estimation equations are given as Eqs. 10 through 12 with group contributions in Table 6. Expected errors are shown in Table 7.Models not involving the concept of group contributions were able to explain a large portion of the variance in the critical property data. Reasonably accurate estimation methods could be found where T,, (MW/P,)112, and V, were correlated only with Tb, molecular weight and the number of atoms in the compound. These preliminary results suggest that factor analysis may provide a viable alternate route to group-contributions in the estimation of critical properties.The properties of one material are often related to properties of another by assuming the respective intermolecular potentials of both are similar if the energy and separation variables are scaled appropriately. Materials that behave in this manner are called conformal substances (Rowlinson, 1969). Utilizing relation...

Modelling solubility of phenolics of mango ginger extract in supercritical carbon dioxide using equation of state and empirical models

“…A recent review analyzed various aspects and types of group contribution methods available in literature (Kolska et al 2012). Only well known Lydersen (Lydersen 1955), Ambrose (Ambrose 1978), Joback (Joback 1984) and Klincewicz-Reid (Klincewicz and Reid 1984) methods have been used for estimation of critical temperature, critical pressure and critical volume in the present study. Equations pertaining to all the four methods for predicting critical properties are given in Table. 1.…”

Kinetics of Slurry Phase Fischer-Tropsch Synthesis

“…Experimental data Marano and Holder, 1997Gao et al, 2001Ambrose, 1979Lydersen, 1955Joback, 1984, 1987Klincewicz and Reid, 1984 Figure B.3. Predictions of the critical temperature for n-paraffins.…”

Kinetics of Slurry Phase Fischer-Tropsch Systhesis

“…We have used two group contribution methods to calculate the critical temperature: Joback (Joback, 1984;Joback and Reid, 1987) and Klincewicz's method (Klincewicz and Reid, 1984). …”

“…Besides the boiling point and the structure of molecule, this method requires a molecular weight of the compound: Ambrose, 1979Lydersen, 1955Joback, 1984, 1987Klincewicz and Reid, 1984 Figure B.3. Predictions of the critical temperature for n-paraffins.…”

“…Experimental data are designated with triangular points, whereas solid lines are predictions. Ambrose (1979), Lydersen (1995), Joback (Joback, 1984;Joback and Reid 1987) and Klincewicz's (Klincewicz and Reid, 1984) are group contribution methods and can be used for prediction of properties of different types of hydrocarbons. Marano and Holder (1997) and Gao et al (2001) are ABC (asymptotic behavior correlation) methods that can be used only for n-paraffins.…”