Chain reference system and scaling factor algorithm for perturbed hard-sphere-chain equation of state

Abstract Improvement in original perturbed hard-sphere-chain (PHSC) equation of state (EOS) [Song et al., Ind. Eng. Chem. Res. 33 (1994) 1047–1057] was realized by upgrading the reference system with chain molecule fluids. The new reference system includes four spherical molecule fluids (neon, argon, krypton, xenon), and 20 chain molecule fluids (alkanes from methane to eicosane). Two universal functions, which are needed for relating the attractive and repulsive parameters of the EOS to three PHSC segment parameters, were refitted on the new reference system by adjusting their coefficients and the PHSC segment parameters of the respective reference fluids progressively. The universal functions are single valued functions of a scaling temperature which is defined as the temperature over a non-bonded segment pair interaction energy and a scaling factor. An algorithm for calculation of the scaling factor was derived theoretically in this work, and the result of the calculation was close to the result of an empirical program compiled by Song et al. The reduced temperature ( T / T c ) applicability of the PHSC EOS was also extended, from original 0.5–0.9 to a wider range 0.25–5.73 which covers almost entire fluid state in normal use. The PHSC segment parameters of 90 normal fluids were determined from vapor pressures and saturated liquid densities. For the normal fluids, the average root-mean-square (rms) deviations of vapor pressure and saturated liquid density are 2.29 and 3.53%, respectively, from melting points to critical temperatures. The PHSC segment parameters of 36 polymers were also determined from their liquid densities. For the polymers, the average rms deviation of liquid density is 0.24%.