Vapour-Liquid equilibria at Low Concentration of One Component

Abstract

This thesis details experimental work performed on the development of a total pressure apparatus to acquire isothermal vapour-liquid equilibrium data for binary mixtures. The method has been demonstrated to be capable of producing up to 30 data points from one experimental run and provide data at very low concentrations of one component (< 10-4mole fraction). A literature survey is presented critically reviewing existing methods, particularly total pressure techniques. The survey also reviews theoretical models and correlations for predicting the non-ideal behaviour of mixtures. The theoretical basis of the correlations based on the "local mole-fraction" concept and their adaptability to "infinite dilution" prediction are discussed. The performance of the present apparatus has been tested using the binary mixtures; methanol-water, ethanol-water over the temperature range 25°C to 65°C. Data obtained has been compared with literature values, when available, and the behaviour of the mixtures approaching infinite dilution shown to correspond to that expected from Henry's Law. A computer program has been developed to analyse the raw data. The data from both systems has been fitted to some of the more commonly used correlations for predicting x-y behaviour. The difficulties met in fitting the data by the use of optimisation techniques are discussed.