Modeling of reactive distillation for acetic acid esterification

Abstract

Reactive distillation is the combination of unit operations reactor and distillation column into one unit. Reactive distillation offers higher conversions, reacting away azeotropes , heat integration, product selectivity and significant capital saving. Reactive distillation is industrially applied for many reactions. Equilibrium and non-equilibrium models are commonly used for modeling of reactive distillation. The equations used for modeling are called MESH equations. M-material E-equilibrium S-summation H-enthalpy. The model equations were developed for a reactive distillation unit consisting of a batch reactor and one stage distillation unit. The model was applied in an ethanol and acetic acid esterification reaction considering homogeneous and heterogeneous reaction kinetics. Nineteen modelling equations were developed with 22 variables and three variables being specified. The differential equations were converted into algebraic equations by applying forward Euler method. Bubble point program is used to find equilibrium vapour composition and temperature. The initial composition of the reactor and the condenser as 45% acetic acid 45% ethanol,1% water. The holdups are assumed as 5000moles and 100moles respectively. Simulations for solving of algebraic equations and bubble point temperature calculation were developed in matlab environment. Simulation results were observed for different 0.825 to 0.99L0/V1 ratios. Dynamics of reactor and condenser compositions and ethyl acetate purity in the accumulated distillate were simulated for different L0/V1 ratios. Maximum ethyl acetate percentage in the accumulated distillate increases with increase in L0/V1 ratio. The dynamics of reactor temperature and conversion of acetic acid show high conversions of acetic acid in higher reflux ratios. Further the reactor heat load and batch time also increase with increase in L0over V1 ratio. Average production rate reduces with increasing L0/V1 ratio. The simulation was also done for heterogeneous reaction kinetics using Langmiur-Hinshelwood kinetic model. The variation of condenser composition, ethyl acetate percentage in the accumulated distillate, dynamics of reactor temperature and conversion of acetic acid were studied with time. Modelled results show that increase in theL0/V1 ratio increase the reactor batch time, although no variation in the average production rate is observed.