The Square-Well equation of state developed by Haghtalab and Mazloumi [A. Haghtalab, S.H. Mazloumi, Fluid Phase Equilib., 280 (2009) 1–8.] is extended for chain like molecules using a generalized van der Waals partition function for polyatomic fluids suggested by Donohue and Prausnitz [M.D. Donohue, J.M. Prausnitz AICHE J., 24 (1978) 849-860.]. The proposed EOS has three physical parameters per each pure fluid that are close-packed volume, characteristic temperature and one-third of external degree of freedom of the molecule. Here in, the parameters of the new EOS for a selection of pure fluids containing normal alkanes from C1 up to C20 are reported that are obtained by correlating saturated vapor pressure and liquid density of the fluids. Then, using proper mixing rules, vapor-liquid equilibrium calculation of a number of binaries are successfully carried out. The comparisons of the results with SPHCT EOS demonstrate the good accuracy of the new EOS.

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