A case study for reactor network synthesis: the vinyl chloride process

A key objective of the integrated reactor network synthesis approach is the development of waste minimizing process flowsheets (Lakshmanan & Biegler, 1995). With increasing environmental concerns in process design, there is a particularly strong need to maximize conversion to product and avoid gener ation of wasteful byproducts within the reactor network. This also avoids e xpensive treatment and separation costs downstream in the process. In this study, we present an application of the mixed integer nonlinear programming (MINLP)-based reactor network synthesis strategy developed by Lakshmanan a nd Biegler (1996a). Here we focus on applying these reactor network synthes is concepts to the vinyl chloride monomer production process. Vinyl chlorid e is currently produced by a balanced production process from ethylene, chl orine and oxygen with three separate reaction sections: oxychlorination of ethylene; direct chlorination of ethylene; and pyrolysis of ethylene dichlo ride. The hydrogen chloride produced in the pyrolysis reactor is used compl etely in the oxychlorination reactor. Byproducts such as chlorinated hydroc arbons and carbon oxides are generated by these reaction sections. These ar e studied using reaction kinetic models for the three reaction sections. Th e case study results in optimal reactor networks that improve the conversio n of ethylene to vinyl chloride and minimize the formation of byproducts. T hese results are used to generate an improved flowsheet for the production of vinyl chloride monomer. Moreover, an overall profit maximization, that i ncludes the effect of heat integration, is presented and a set of recommend ations that improve the selectivity of vinyl chloride production are outlin ed. Finally, the optimal reactor structures, overall conversion and annual profit are shown to be only mildly sensitive with respect to small changes in the kinetic parameters. (C) 1999 Elsevier Science Ltd. All rights reserv ed.