AN EQUATION OF STATE FOR ASSOCIATING FLUIDS

An equation of state (EoS) suitable for describing associating fluids is presented. The equation combines the simplicity of a cubic equation of st-ate (the Soave-Redlich-Kwong), which is used for the physical p art and the theoretical background of the perturbation theory employed for the chemical (or association) part. The resulting EoS (Cubic Plus Association) is not cubic with respect to volume and contains five pu re compound parameters which are determined using vapor pressures and saturated liquid densities. Excellent correlations of both vapor press ures and saturated liquid volumes are obtained for primary-alcohols (f rom methanol up to 1-tridecanol), phenol, tert-butyl alcohol, triethyl ene glycol, and water. Moreover, excellent prediction of saturated liq uid volumes may be obtained from parameters which have been estimated by regressing only vapor pressures. Finally, we suggest a method for r educing the number of adjustable parameters for alcohols to three whil e maintaining the good correlation of vapor pressures and saturated li quid volumes. We investigate the possibility of using the homomorph ap proach for estimating the EoS parameters and explain the problems obse rved. The estimated pure compound parameters have been tested in the p rediction of second virial coefficients with satisfactory results.