Synthesis of reactor networks in overall process flowsheets within multilevel MINLP approach

Abstract

This paper describes the superstructure-based mixed-integer non-linear programming (MINLP) approach to the synthesis of reactor networks in an equation-oriented environment. The approach is an extension to the MINLP synthesis procedure of plug flow reactor (PFR) networks (Pahor and Kravanja, 1995) upgraded with the multilevel-hierarchical MINLP approach (Kravanja and Grossmann, 1997). The model comprises a general superstructure in which the exact formulation of the recycle reactor (RR)—a train of differential PFRs with a common recycle stream, and a continuous stirring tank reactor (CSTR) are embedded and can easily be extended for N elements so as to enable a different feeding (cross flow, side stream), recycling and bypassing. The reactor arrangement is capable of representing several reactor systems such as a pure CSTR, pure PFR, pure RR and their combinations. Further, it is possible to represent a cross flow reactor (CFR). The superstructure is a suitable either for isothermal or non-isothermal, simple or complex reactor network. Since it is simple, it can by means of heat integration simultaneously be incorporated into an overall process synthesis, which favours simple results. With the multilevel—hierarchical strategy, it is possible to postulate the superstructure at different levels of representation of flowsheet alternatives. Therefore, the superstructure is optimized more effectively and reliably. The approach has been applied to a complex non-isothermal reaction problem—an industrial example of a production of allyl chloride.