MODIFICATION OF THE KUMAR-STARLING 5-PARAMETER CUBIC EQUATION OF STATE AND EXTENSION TO MIXTURES

For extending the five-parameter cubic equation of state (KS EOS) proposed by Kumar and Starling (1982) (Ind. Eng. Chem. Fundam., 21: 255-262) to polar substances, and improving the phase behavior description of heavy hydrocarbons, the generalized correlations of parameters A2 and A5 were modified, and new orientation parameters were determined. In the near critical region, transition functions for parameters A2, A3 and A5 were introduced, in which the experimental critical compressibility factor was incorporated. The parameters of the modified Kumar-Starling equation of state (MKS EOS) were determined by fitting the vapor pressure and saturated liquid density data simultaneously. The proposed MKS EOS was tested on 127 pure non-polar and polar substances. Extensive comparisons with nine other well-known cubic EOS indicate that the modified version of the KS EOS significantly improved the representation of the phase behavior of pure substances in various regions. The MKS EOS was further extended to mixtures by rearranging its form into conventional van der Waals (VDW) form, and the simple VDW one-fluid mixing rules were applied to the new EOS parameters. The test results on 97 binary and multicomponent mixtures indicate that, as compared with other equations of state, the MKS EOS predicts comparable bubble point pressures, but much more accurate saturated liquid densities.