Effect of phosphorus P-π bonding on the volumetric properties and vapor-liquid equilibrium of phosphorus trichloride-benzene liquid mixtures

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• The density and vapor–liquid equilibrium of PCl 3 -benzene mixture at atmospheric pressure are measured. • The attractive P-π interaction yields large negative V E , and the π-π antibonding effect causes positive V E in PCl 3 dilute solution. • V E is fitted to the Redlich-Kister equation and excess molar volumes are estimated. • VLE data are modeled by the coexistence equation and Wilson and NRTL activity coefficient models. New density and vapor–liquid equilibrium data of PCl 3 -benzene binary system at atmospheric pressure (99.7–101.3 kPa) were carefully measured to provide crucial information for their industrial reaction and separation. The experimental mixture densities show excellent linear dependence on both solution composition and temperature and a generalized empirical correlation is proposed with an average relative deviation of 0.13%. The specific attractive P-π interaction between the phosphorus atom of PCl 3 and the π cloud of benzene seems to be quite strong in solution, leading to large negative excess volumes. But the π-π antibonding effect from benzene dimers are predominant in PCl 3 highly dilute solution, where positive excess volume and excess partial molar volumes of PCl 3 were observed. Experimental bubble points of the binary mixture were corrected to those under 101.325 kPa. Two distinctive methods of coexistence equation and activity coefficient models of Wilson and NRTL equations were applied to model the VLE data, and they yielded very consistent results. Although no azeotrope were found, this mixture exhibited quite low relative volatility.