SIMULATION OF MULTICOMPONENT DISTILLATION COLUMN

Abstract

This thesis presents an investigation on simulation studies of multicomponent reactive distillation column. Using the basic equations of material balance, enthalpy balance, phase equilibria and rate equation, a mathematical model has been developed. It has been solved by application of equation tearing method, which includes transforming the equations into tridiagonal matrix and using an iterative solution procedure. The model developed has been examined for ethanol-acetic acid multicomponent reactive system in a distillation column having 13 number of equilibrium stages and other specified geometrical and operating parameters. It has predicted the profiles for temperature. liquid and vapor compositions, liquid and vapor molar flow rates and extent of reaction at each equilibrium stage. Computed profiles have been compared with the reported data due to Suzuki et al., 1971. The acceptable accuracy of the ethanol-acetic acid simulations demonstrates the adequacy of the modeling process and validates its extension to other multicomponent reactive distillation columns. The model has been further updated with inclusion of activity coefficient by UNIQUAC equation in combination with Marek's equation for association in vapor phase. It takes into account the nonideal behaviour of the system. Analysis of methanol-acetic acid multicomponent reactive system has been carried out by using the above model and profiles for temperature, vapor and liquid compositions, liquid and vapor molar, .flow rates, extent of chemical reaction at each stage and percent conversion with respect to acetic acid have been determined. Effect of various parameters namely stage hold up, number of equilibrium stages, reflux ratio, feed composition, feed flow rate and column pressure on percent conversion and top ester (methyl acetate) mole fraction have been determined keeping other parameters constant. Analysis has shown that increase in stage hold up, number of equilibrium. stages, reflux ratio, feed composition and column pressure favours higher product yield but increase in feed flow rate displays reverse trend. The system has also been investigated when two feeds have been introduced at two different stages of the column. In fact, when methanol was introduced at the eleventh iii stage and acetic acid on second stage in a column of 13 equilibrium stages including a reboiler and a condenser, a maximum yield of methyl acetate was obtained. Minimum value of reflux ratio has been computed by solving differential equation for rectification and stripping column simultaneously along with the appropriate condition for minimum reflux ratio and the value so obtained has been compared with reported data due to Doherty and Barbosa, 1988. Using HYSYS software package ethanol-acetic acid multicomponent reactive distillation column has been simulated and the profiles for temperature, liquid and vapor compositions and molar flow rates have been obtained. iv