Synthesis of chemical reactor networks

Abstract

Abstract: An interesting problem in chemical reactor theory is finding bounds or targets on a given performance index in a reacting system. Moreover, performance of the reactor subsystem has a key impact on the design of other processing subsystems. It determines the recycle structure of the process, the separation sequence and has a strong influence on the energy and environmental considerations. However, this area of process synthesis has seen relatively little development when compared to heat integration and separation synthesis. As with the design of heat exchanger networks, this approach has evolved into the (discrete and continuous) optimization of network superstructures as well as the performance targeting of the optimal network prior to its construction. In this study we review both methods for reactor network synthesis but concentrate on advances with the latter approach. The targeting approach is based on geometric interpretations of reaction and mixing. It uses a constructive approach to find the attainable region; that is, it effectively captures all possible reactor structures and finds the bounds on the performance of a reacting system. The approach also generates reactor structures which are candidates for the optimal system. It is however severely limited by the dimensionality of the problem and in practice only 2 and 3 dimensional problems have been solved. Nevertheless, insights gained from this geometric approach have led to an understanding of more general properties of optimal reactor structures. In particular the reactors that make up optimal structures are parallel -- series systems of plug flow reactors, CSTR's and differential side stream reactors. Furthermore, the number of parallel structures is related to the dimensionality of the problem. In addition, these properties can be embedded within optimization formulations in order to deal with more complex In particular, we describe several formulations that incorporate simpler properties derived from attainable region concepts. At this point, this approach is not as rigorous as the geometric approach but readily extendable to more complex reaction systems. In addition, it can be integrated with other process subsystems and allows for simultaneous approaches for heat integration, separation structures and reactor network design. In this way, trade-offs resulting from different parts of the process are properly taken into account in the optimization. All of these concepts will be illustrated with numerous examples. Finally, future work will concentrate on the extension of geometric concepts to more general reactor systems as well as to separation systems. These will also lead to more compact optimization formulations and the consideration of larger and more complex process problems.