Process synthesis for reactive separations

doi:10.1016/S0255-2701(02)00087-9

Chemical Engineering and Processing: Process Intensification

Volume 42, Issue 3, March 2003, Pages 179-189

https://doi.org/10.1016/S0255-2701(02)00087-9 Get rights and content

Abstract

The integration of reaction and separation in one single process unit proved to lead to enormous savings in capital as well as in operating costs. This paper provides a systematic framework to consider reactive separations in the early stages of process development. It highlights a process synthesis procedure guaranteeing that processes like reactive distillation, reactive crystallization, reactive extraction or reactive stripping will not be overlooked during conceptual flowsheet development. First step of this procedure is the analysis of the chemical reaction system. In case a separation of one or more products, by-products or solvents seems to be beneficial for the performance of the reactor the physical separation behavior of the components has to be checked. The chemical reaction, the physical separation and the design on the apparatus need a defined operation window. Only when an overlap of these windows can be identified a reactive separation process is feasible and might lead to advantages in the overall process performance. The paper finally demonstrates that the integration of reaction and separation in one unit does not necessarily lead to economic benefits as the overall performance of the total chemical process has to be considered.

Introduction

The integration of chemical reaction and physical separation in one single unit often leads to a significant reduction in investment and operating costs. The economic benefit may be caused by a reduction of raw material use, diminution of recycle streams by higher rates of conversion, improvements in selectivity and/or energy integration.

Due to this potential economic benefit there is a need to evaluate integrated reactive separations at a very early stage of the development of chemical processes. Unfortunately, a systematic evaluation of reactive separation units during process synthesis has not been established as common procedure.

Although knowledge has been generated and published about the synthesis of dedicated reactive separations like reactive distillation a general approach to the synthesis problem has not been addressed so far [1], [2].

One major reason might be that due to the combination of two or more physical and chemical phenomena the degrees of freedom to obtain a feasible and economic operating point of the process unit are limited. Besides the traditional considerations of process selection this requires an additional evaluation whether the chemical and physical needs allow the use of a reactive separation. Due to this increased complexity most of the research work published refers to single integrated reaction and separation units (IRS units). Moreover, authors rather focus on the design of stand-alone IRS units than on the whole process in which these reactive separations are used. However, in order to evaluate the real benefit of an IRS unit the whole process including all additional process steps (e.g. additional separations) has to be designed and economically assessed.

The aim of this paper is to present on the one hand a strategy to integrate the evaluation of IRS units in a process synthesis environment. On the other hand it introduces a general process synthesis procedure which is independent from specific separation effects applied in the unit.

Section snippets

Stand-alone synthesis and design of IRS units

In order to rate the potential advantage of using a reactive separation in a chemical process two steps have to be performed. At first the chemical reaction system has to be analyzed whether an IRS unit may improve the performance of the reaction unit only. Then the designer has to check whether the use of such a unit enhances the whole chemical process. This section deals with the process synthesis of reactive separations disregarding any effect on the other down- or upstream-process steps.

Synthesis of IRS units in the framework of conceptual design of total flowsheets

Regarding the overall performance of a chemical process the introduction of an IRS unit might contribute to the economics by addressing different effects:

•
Chemical reaction aspects
•
Separation aspects
•
Energy integration aspects

Improving the chemical reaction by increasing the conversion rate and/or the selectivity affects all up-stream and down-stream units. On the one hand the throughput might be lowered while producing the same amount of desired products in the plant. On the other hand the

Conclusion

The process synthesis procedure presented does not guarantee to find the one single optimal flowsheet operated at the optimal conditions. But its pragmatism leads to feasible and economic flowsheet options in a limited amount of time. It allows the designer to evaluate the performance of IRS units in a very early step of process development when often only qualitative information about the chemical and physical behavior of the chemical components are available. The method presented might

Acknowledgements

The authors like to thank the Deutsche Forschungsgemeinschaft for the financial support of the research work reported here.

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Process synthesis for reactive separations

Abstract

Introduction

Section snippets

Stand-alone synthesis and design of IRS units

Synthesis of IRS units in the framework of conceptual design of total flowsheets

Conclusion

Acknowledgements

Chem. Eng. Sci.

Chem. Eng. Sci.

Reactive distillation by design

Trans. J. Chem.

High-purity methyl-acetate via reactive distillation

Chem. Eng. Prog.

Entwicklung membranunterstiltzter Reaktionsprozcssc

Chem. Ing. Tech.

Phase equilibrium chemical engineering

Chemical reaction engineering