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Effects of kinetics on reactive distillation

Ganesh Venimadhavan, University of Massachusetts Amherst


In the last decade, there has been growing success at developing commercial processes which combine reaction and separation. This technology offers the potential of significantly improved economics, reduced emissions and direct energy integration between the reaction and separation processes in the system. In this dissertation, we develop tools to analyze and design reactive distillation systems with multiple kinetically controlled chemical reactions. Residue curve maps are a useful tool in the conceptual design of distillation systems. They are the trajectories on a phase plane of the composition in a still during a simple distillation or open evaporation experiment. We derive a system of equations to model kinetically controlled reactive simple distillation. From these equations we define a dimensionless parameter, the Damkohler number, which is a measure of the amount of reaction in the system. A Damkohler number of zero implies a non-reactive system while a Damkohler number approaching infinity implies a system in which there is simultaneous reaction and phase equilibrium. The structure of the residue curve map determines whether a reactive distillation is feasible, and the structure changes with the Damkohler number. A good knowledge of the reaction kinetics is important for the analysis and design of kinetically controlled reactive distillation systems. Closed batch isothermal kinetic experiments and binary non-reactive adsorption experiments were performed for the esterification of acetic acid with methanol on the heterogeneous Amberlyst 15W catalyst. The kinetic data were then fitted with a Langmuir-Hinshelwood/Hougen-Watson model and the model was used to predict the course of simple distillation experiments. The structure of a residue curve map is determined by the composition and temperature of the solutions of the simple distillation equations. We developed a systematic way of studying the effect of kinetics on the structure of the residue curve maps by performing a bifurcation analysis of the simple distillation equations as a function of the Damkohler number starting with the non-reactive case where the singular points are the pure components and the non-reactive azeotropes. Batch reactive distillation combines the advantages of reactive distillation and batch processes. We have developed a simplified model that can be used to quickly screen through design alternatives and operating strategies to develop estimates for the number of stages, distillate policies, the initial feed ratios in the still, etc. Once promising designs and policies have been identified, a more detailed simulation at a finite reflux and with a finite holdup in the column can be performed for the conditions of interest. This model was applied to the study of the esterification of acetic acid and butanol to produce butyl acetate. For this process, we have suggested a new operating policy which will increase the purity of the main product without introducing additional purification steps. The results were also compared to those from a more detailed model.

Subject Area

Chemical engineering|Chemistry

Recommended Citation

Venimadhavan, Ganesh, "Effects of kinetics on reactive distillation" (1998). Doctoral Dissertations Available from Proquest. AAI9909230.