Critical temperatures and pressures for hydrocarbon mixtures from an equation of state with renormalization-group theory corrections

A recently developed crossover equation of state (EOS) incorporates contrib utions from long-wavelength density fluctuations by renormalization-group t heory. This EOS can satisfactorily describe the thermodynamic properties of chain fluids both far-from and near-to the critical region; it is used her e to calculate the critical locus of a mixture. Because the calculations re quire much computation time, especially for ternary land higher) mixtures, an interpolation method is used as suggested by Redlich over 30 years ago. For a binary mixture, along the critical line that gives the critical tempe rature or critical pressure as a function of composition, the limiting slop es at the critical points of the pure components are explicitly derived fro m the criteria for a critical point. Logarithmic-hyperbolic interpolation e quations are selected to calculate the entire critical lines of the binary mixtures; this procedure is then generalized to multicomponent mixtures. Up on comparison with experimental critical data, the interpolation equations give good critical lines for binary and multicomponent type-1 mixtures of n -alkanes. (C) 2000 Elsevier Science B.V. All rights reserved.