Produccion de cloroetileno

Computers and Chemical Engineering 23 (1999) 479 – 495

A case study for reactor network synthesis: the vinyl chloride process
A. Lakshmanan, W.C. Rooney, L.T. Biegler *,1
Chemical Engineering Department, Chemical Mellon Uni6ersity, Pittsburgh, PA 15213, USA Received 11 February 1998; received in revised form 3 July 1998

Abstract A key objective of the integrated reactor network synthesisapproach 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 generation of wasteful byproducts within the reactor network. This also avoids expensive treatment and separation costs downstream in the process. In this study, wepresent an application of the mixed integer nonlinear programming (MINLP)-based reactor network synthesis strategy developed by Lakshmanan and Biegler (1996a). Here we focus on applying these reactor network synthesis concepts to the vinyl chloride monomer production process. Vinyl chloride is currently produced by a balanced production process from ethylene, chlorine and oxygen with three separatereaction sections: oxychlorination of ethylene; direct chlorination of ethylene; and pyrolysis of ethylene dichloride. The hydrogen chloride produced in the pyrolysis reactor is used completely in the oxychlorination reactor. Byproducts such as chlorinated hydrocarbons and carbon oxides are generated by these reaction sections. These are studied using reaction kinetic models for the threereaction sections. The case study results in optimal reactor networks that improve the conversion of ethylene to vinyl chloride and minimize the formation of byproducts. These results are used to generate an improved flowsheet for the production of vinyl chloride monomer. Moreover, an overall profit maximization, that includes the effect of heat integration, is presented and a set of recommendations thatimprove the selectivity of vinyl chloride production are outlined. 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. © 1999 Elsevier Science Ltd. All rights reserved.

1. Introduction In most chemical processes the selective conversion of raw materials in the reactordetermines the composition and the amount of waste products produced, and the reactor network has a significant influence on the recycle structure and downstream processing steps. Hence, reaction systems and reactor design often determine the character of the flowsheet and better performance of the reactor system improves the performance of the entire process. In the past decade, several researchers haveworked on problems of reactor network synthesis and reactor design. This problem involves nonlinear reaction models, uncertain rate laws and numerous possible reactor types and networks. Hence, researchers in this area have achieved limited success. Motivated by these thoughts Lakshmanan and Biegler (1996a) proposed a
* Corresponding author. 1 Present address: Aspen Technology, Cambridge, MA02141,USA.

reactor network synthesis strategy that combines principles developed for MINLP optimization of prepostulated reactor superstructures and geometric techniques for establishing the reactor network. In particular, geometric techniques construct an attainable region, which represents the limits that can be achieved by the processes of reaction and mixing. This region includes the performance ofany reactor network structures in terms of conversion of raw materials to desired products and the amount of waste products that are produced. Glasser, Crowe and Hildebrandt (1987) and Hildebrandt, Glasser and Crowe (1990) proposed constructive techniques to map the attainable region for reactor network synthesis problems in two or three dimensions. These techniques are useful to develop new...