Thermodynamic properties of p-xylene - chloroethans

Abstract

The importance of accurate thermodynamic data of pure substances and mixtures in research and industry hardly needs any emphasis. Apart from their utility in process design calculations, such data are useful in theoretical studies concerning molecular interactions in solutions and in the calculation of derived properties from thermodynamic relations. For example, enthalpy of vaporization of liquid mixtures for which data are not available in literature could be calculated from accurate data on vapour–liquid equilibrium, excess enthalpy and specific heats and enthalpy of vaporization of pure components. The present study is a contribution in this area.

Methods as well as the results of accurate measurements of the thermodynamic properties of liquid mixtures of three chloroethanes (1,2-dichloroethane, 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane) with p-xylene have been reported in the thesis. The following four properties have been experimentally determined: (i) excess enthalpy, (ii) vapour–liquid equilibrium, (iii) enthalpy of vaporization of pure components and their mixtures, and (iv) vapour pressures of pure components.

For the measurement of excess enthalpy values, a modified form of Tanaka’s calorimeter has been fabricated and used. A modified Brown Still has been employed for obtaining vapour–liquid equilibrium data and a variation of Stein–Martin apparatus for measuring enthalpies of vaporization. Vapour pressures have been measured in Brown and Swietoslawsky Stills.

Thermodynamic consistency of the vapour–liquid equilibrium data has been checked using the exact equation given by Van Ness. Vapour phase non-ideality has been corrected using the virial equation of state. The second virial coefficient data available in literature and cross coefficients computed from a three-term potential energy function have been used. Wilson and Redlich–Kister equations have been employed to correlate the experimental vapour–liquid equilibrium data.

The effect of alkyl substitution in benzene and its homologues on enthalpy of mixing with the same chloroethanes has been studied by comparing the present data with earlier data on benzene-, toluene-, and chloroethane systems.

After establishing the thermodynamic consistency of the isobaric vapour–liquid equilibrium data using excess enthalpy values determined experimentally, the enthalpies of vaporization of liquid mixtures have been calculated from relations available in literature, using data on vapour–liquid equilibrium, excess enthalpy, specific heats and enthalpy of vaporization of pure components. The enthalpies of vaporization of mixtures thus calculated have been compared with experimental data. This procedure helped to further establish the reliability and accuracy of the experimental data.