Application of perturbation theory to chain and polar fluids: Pure alkanes, alkanols and water

Based on the chain theory and the anisotropic perturbation theory, a modified equation of state for chain and polar fluids is developed. The expressions of Helmholtz free energy and equation of state are given in explicit form. For non-associating fluids, the thermodynamic properties of the systems are the sum of contributions of hard sphere, chain formation, dispersion, dipole–dipole and induction. For associating fluids, multipole terms are accounted for associating interaction through an effective quadrupole moment. By simultaneously fitting vapor pressures and liquid densities, temperature independent parameters are obtained: the segment number m, the segment diameter σ and the dispersion energy ε/k for non-associating fluids, and the effective quadrupole moment Q in addition for associating fluids. This theoretical model is rather simple with good accuracy, and can be used to alkanes, alkanols and water.