Thermodynamic properties of vapours
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
A new method (Couldwell et al., 1978) has been developed for the measurement of the second virial coefficients of condensable gases. This method evaluates the second virial coefficients in terms of three pressure measurements (temperature maintained constant) and avoids the difficult volume calibration associated with former p-V-T-n and other volumetric methods. Measurements are reported for n-hexane at temperatures of 323.15, 328.15, 338.15, 348.15, 358.15 amd 373.15 K, and for benzene and cyclohexane at temperatures of 323.15, 348.15 and 373.15 K. The influence of surface adsorption of the vapours on the measurement of second virial coefficients is observed. It is suggested that future measuremets be made for loading pressure less than 0.34 to 0.4 times the saturation vapour pressure of the gases, corresponding to a region of monolayer adsorption. The influence of the third virial coefficient is determined, thus enabling the estimations of the "true" second virial coefficients which are at variance with the literature values (Dymond and Smith, 1980). Reasons are advanced to explain this anomaly. The results interpreted in the same manner, as the literature values, are in agreement with the latter. In a parallel study. an existing apparatus (McElroy et al., 1980) has been modified to measure unlike interaction second virial coefficients (Battino et al., 1983). The excess second virial coefficients (B12ōB11+B22)/2) for benzene, cyclohexane and n-hexane vapour binary mixtures have been measured at the temperatures 298.15, 323.15. 348.15, 373.15 and 398.15 K. The method permits the interaction second virial coefficients, B12 , to be determined with an accuracy three times better than that can be obtained from measurement of second virial coefficients of the mixtures. The lower temperature measurements are affected by surface adsorption. A postulated mathematical model (Shannon, 1976) has been checked to calculate a correction for surface adsorption. The interaction virial coefficient values, for benzene + cyclohexane. Are compared with B12 values in the literature and the values obtained from empirical correlations.