Vapour Liquid Equillibrium Modeling Using UNIFAC Group Contribution Method And Its Application In Distillation Column Design And Steady State Simulation

Abstract

For efficient design of distillation equipment or any other separation processes which are diffusional in nature requires quantitative understanding of vapour liquid equilibria. In VLE phases are expressed through vapour phase fugacity coefficients and the liquid phase activity coefficients. At low or modest pressures fugacity coefficient can be estimated easily for very simple mixtures or ideal solutions, but for non-ideal mixtures, estimation of liquid phase activity coefficient is quite difficult. Experimental mixture data are required to calculate activity coefficient. Since the variety of chemical species is separated out in chemical process industry and it is not necessary to every physicochemical and VLE experimental data are available in open database. In this regard researchers developed a new ‘group contribution model which is able to predict the VLE data. The concept of group contribution method provide a correlation which correlate limited experimental data in such a way with confidence of activity coefficients of those mixtures where little or experimental data are not available. In this concept we have to know only about the each functional group of each molecule. Each molecule is considered as the sum of the functional groups which constituent that molecule; the thermodynamic properties of a solution are then correlated in terms of the functional groups which comprise the mixture. The particular promising method for calculating activity coefficient from group contributions method is provided by UNIFAC (universal quasi chemical functional group activity coefficient model). This method is a consequence of a model for activity coefficients called UNIQUAC (universal quasi chemical). The word UNIFAC stands for UNIQUAC functional group activity coefficients. The activity coefficients of binary mixtures were successfully calculated by using UNIFAC model. And using these activity coefficients the design of distillation column was done for the separation of these binary mixtures.