Renormalization-Group Corrections to a Perturbed-Chain Statistical Associating Fluid Theory for Pure Fluids Near to and Far from the Critical Region

Abstract

A perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state has been extended to include a crossover correction, based on White’s work with renormalization-group (RG) theory, that accounts for the contributions of long-wavelength density fluctuations in the critical region. In the critical region, the improved crossover equation of state provides the correct nonclassical critical exponents. Away from the critical region, the crossover equation reduces to the original PC-SAFT equation, therefore maintaining the accuracy of PC-SAFT in this region. No modifications to the original PC-SAFT molecular parameters are necessary, therefore allowing for an accurate description of thermodynamic properties from the triple point to the critical point. Excellent agreement with vapor−liquid equilibrium experimental data for the n -alkane family is obtained inside and outside the critical region, and all critical constants T c, P c, and ρ c are calculated within their respective experimental errors. The extrapolative abilities of the RG parameters are demonstrated for higher molecular weight chains. Finally, the present results are contrasted with results from other groups using alternative interpretations of White’s theory.