Chemical Engineering Science 57 (2002) 5039–5050 www.elsevier.com/locate/ces Comparative control study of ideal and methyl acetate reactive distillation Muhammad A. Al-Arfaj, William L. Luyben * Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA Received 28 February 2002; received in revised form 11 June 2002; accepted 15 July 2002 Abstract The control of an ideal reactive distillation column is compared with that of a similar, but somewhat dierent, real chemical system, the production of methyl acetate. Similarities and dierences are observed. Three control structures are evaluated for both systems. A control structure with one internal composition controller and one temperature controller provides eective control of both systems for both high and moderate conversion designs. A two-temperature control structure is eective when the system is overdesigned in terms of number of reactive trays, holdup and/or catalyst load. Direct control of product purity for the high-conversion/high-purity design is dicult because of system nonlinearity and interaction. Tray temperature control avoids the nonlinearity problem. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: Reactive distillation; Process design and control; Methyl acetate 1. Introduction Reactive distillation combines both separation and reac- tion in one unit. It has been used in a small number of in- dustrial applications for many years, but the last decade has shown an increase in both research and applications. It can oer signicant economic advantages in some systems, par- ticularly for reversible reactions. The literature up to 1992 was reviewed by Doherty and Buzad (1992). Many papers have discussed steady-state design. Some have dealt with openloop dynamics, which in some systems feature multi- plicity. Only a small number of papers discuss the closedloop control of reactive distillation columns or the interaction be- tween design and control. The control papers up to 1999 were discussed by Al-Arfaj and Luyben (2000). Several new papers have appeared. Sneesby, Tade and Smith (2000) studied three control structures for a single-feed ETBE reac- tive distillation column. Monroy-Loperens, Perez-Cisneros and Alverz-Ramirez (2000) studied the control of ethylene glycol reactive distillation using nonlinear control. Luyben (2000) studied the economic and control eects of using excess reactant. * Corresponding author. Tel.: +1-610-758-4256; fax: +1-610-758-5297. E-mail address: wll0@lehigh.edu (W. L. Luyben). In our previous paper (Al-Arfaj & Luyben, 2000) we presented a comparison of several control structures for an ideal two-product reactive distillation system. Simple vapor– liquid equilibrium, reaction kinetics and physical properties were used so that the inherent control features of reactive distillation could be explored without clouding the picture with the complexities that can occur in some real chemical systems. All of the workable control structures used a mea- surement of a reactant composition in the reactive section of the column so that operation with exactly stoichiometric feeds could be achieved (“neat” operation). We studied several other chemical systems. In the ETBE system (Al-Arfaj & Luyben, 2002a), there are two reactants, one product and one inert. We studied single-feed and double-feed designs and several con- trol schemes were examined. The ethylene glycol system (Al-Arfaj & Luyben, 2002b) has two feeds but only one product. A control scheme where a temperature in the stripping section is controlled by the heat input was found to be eective. Olen metathesis (Al-Arfaj & Luyben, 2002c) has only one reactant and two products. A tem- perature in the stripping section is controlled by the heat input and another temperature in the rectifying section is controlled by the reux rate. This scheme was found to be eective. A plantwide owsheet that contains reactive dis- tillation column was developed for the production of TAME 0009-2509/02/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII:S0009-2509(02)00415-3