Jignesh Gangadwala

Dynamics of reactive distillation processes with potential liquid phase splitting based on equilibrium stage models

Abstract A dynamic reactive distillation (RD) column model is developed for highly non-ideal systems with potential phase splitting. Dynamic simulations and non-linear dynamic analysis are performed for recovery of acetic acid from waste waters by esterification with n -butanol, which is an interesting alternative to non-reactive separation processes. Two alternative RD column designs were tested with respect to their open loop transient responses to process disturbances. One parameter continuation with eigenvalue calculations reveals existence of multiple steady states with stable and unstable branches. These steady states were found to have totally different phase splitting behavior of the original liquid phase inside the column. Conclusions are drawn for process operation.

Computer aided design of reactive distillation processes for the treatment of waste waters polluted with acetic acid

A theoretical study of reactive distillation processes to remove acetic acid from its 30 wt% aqueous solution by esterification with n-butanol is presented. Two different column structures were identified rendering theoretically close to 100 percent conversion of acetic acid. A model capable of precisely predicting the potential phase split is used. Total costs for the new processes are estimated and compared with estimated costs of nonreactive separation process. It is shown that more than 56 percent costs can be reduced by using the new processes. The dynamic behavior of both the processes are studied through a series of dynamic simulation runs.

Global analysis of combined reaction distillation processes

Abstract Polyhedral relaxation is a powerful tool for determining global bounds on optimal solutions in chemical process synthesis. Combined reaction distillation processes are considered as a challenging application example. To reduce complexity of the resulting mixed integer linear optimization problems, model reduction by means of wave functions is proposed, and polyhedral relaxations of sigmoidal wave functions in two variables are derived. It is shown that these relaxations provide better approximation quality than approximating the composed functions individually. Further, the concave envelope of such functions is characterized and (nonlinear) convex underestimators are derived. The approximation results are employed in the computation of lower bounds on the vapor flow of a combined reaction distillation process with a metathesis reaction 2 B ⇋ A + C . We restrict computations to a domain around a known local optimum, trading computation time for some of the globality. This still proves a bound on the vapor flow, but for restricted operating conditions of the column.

Optimal Process Design for the Synthesis of 2,3-Dimethylbutene-1

Abstract This paper is concerned with the computer-aided optimal design of reaction-distillation processes. The production of solvent 2,3-dimethylbutene-1 by isomerization of 2,3-dimethylbutene-2 is considered as an innovative benchmark problem. Possible process candidates are a reactive distillation column, a reactor coupled to a nonreactive distillation column or a reactive reboiler with a nonreactive distillation column on top. Local MINLP optimization indicates that the reactive distillation has the lowest total annualized costs. However, due to the non-convexity of the underlying mathematical problem better solutions for the other process candidates cannot be excluded. For this purpose a new global approach is proposed which is based on discrete optimization of the underlying model equations and which proves globally that reactive distillation is the best option.

Dynamics of Reactive Distillation Processes with Potential Liquid Phase Splitting

Abstract A dynamic reactive distillation (RD) column model is developed for highly nonideal systems with potential phase splitting. Dynamic simulations and nonlinear dynamic analysis are performed for recovery of acetic acid from waste waters by esterification with n-butanol, which is an interesting alternative to nonreactive separation processes. Two alternative RD column designs were tested with respect to their open loop transient responses to process disturbances. One parameter continuation with eigenvalue calculations reveals existence of multiple steady states with stable and unstable branches. These steady states were found to have totally different phase splitting behavior of the original liquid phase inside the column. Conclusions are drawn for process operation.

Global bounds on optimal solutions in chemical process design

In this paper a new approach for computing global bounds on optimal solutions of mixed-integer nonlinear programs is presented. These type of problems frequently arise in optimal design of chemical processes. The approach is based on a hierarchy of polyhedral relaxations leading to mixed-integer linear programs, which can be solved rigorously. Application is demonstrated for the optimal design of combined reaction distillation processes and for feasibility studies of simulated moving bed chromatographic processes.