Mathematical evaluation of a dynamic method for determining V-L equilibria



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A dynamic method proposed by Prengle and Curtice to determine the vapor-liquid equilibrium data at constant pressure for a binary mixture using only the initial composition and the temperature-liquid weight data has been explored and proved feasible. The method obviates the necessity of having to determine experimentally the liquid or vapor composition. By combining the equations proposed with the Rayleigh equation an integral equation is produced. The value of the integral can be calculated from the liquid weight at any instant and initially. The lower limit of the integral is the initial weight fraction of the more volatile component and which is a known value. The upper limit is the weight fraction at any instant which is to be determined. A computer program was written using Gauss' quadrature numerical method for solving the integral equation. Ramalho and Tiller's experimental data for Rayleigh distillation of methanol-water system at 760 mm Hg, including measured liquid composition data, were used to check the method. The results obtained indicate good agreement. Extension of the dynamic method into an experimental procedure is discussed. The average excess enthalpy was determined from literature experimental constant pressure V-L data and found to be in good agreement with individually measured excess enthalpy data.