Synthesis of Reactor Networks and Reactor-Separator-Recycle Systems

Abstract

This chapter discusses the application of MINLP methods in the synthesis of reactor networks with complex reactions and in the synthesis of reactor-separator-recycle systems. Despite the importance of reactor systems in chemical engineering processes, very few systematic procedures for the optimal synthesis of reactor networks have been proposed. The main reason for the scarcity of optimization strategies for reactor networks is the difficulty of the problem itself. The large number of alternatives along with the highly nonlinear equations that describe these systems have led to the development of a series of heuristic and intuitive rules that provide solutions only for simple cases of reaction mechanisms. Most of the studies considered single reactors with a specified mixing pattern and focused on investigating the effect of temperature distribution, residence time distribution, or catalyst dilution profile on its performance. In the sequel, we will briefly review the approaches developed based on their classification: (i) isothermal operation and (ii) nonisothermal operation. Trambouze and Piret (1959) proposed graphical and analytical criteria for selecting the type of reactor. Levenspiel (1962) reported heuristic rules for optimal yield and selectivity in stirred tank and tubular reactors. Aris (1964, 1969) applied dynamic programming to determine the optimal amounts of by-passes and cold streams in a multistage reaction system within a fixed structure. Gillespie and Carberry (1966) studied the Van der Vusse reaction with an intermediate level of mixing and demonstrated the potential advantages of recycle reactors for such a complex reaction. Horn and Tsai (1967) studied the effects of global and local mixing using the adjoint variables of optimization theory. Jackson (1968) proposed an algebraic structure for the reactor representation consisting of parallel ideal tubular reactors that were interconnected with side streams at various sink and source points. Different flow configurations and mixing patterns could be obtained by varying the number and the positions of the sink and source points, as well as the levels of the sidestreams. By deliberate manipulation of the flow configuration, potential improvements in the reactor performance coul be investigated. Ravimohan (1971) modified Jackson's model so as to handle cases of local mixing.