Research Article Incorporation of Dynamic Flexibility in the Design of a Methanol Synthesis Loop in the Presence of Catalyst Deactivation A typical methanol loop reactor is analyzed in this study. All basic equipment in the Lurgi-type methanol loop is included in the proposed model. A detailed dy- namic model described by a set of ordinary differential and algebraic equations is developed to predict the behavior of the overall process. The model is validated against plant data. A new deactivation model is proposed and its parameters are estimated using daily plant data. The interesting feature of this model is that it in- corporates the effect of carbon dioxide and carbon monoxide on the catalyst de- activation. Using the model, the effect of various factors to compensate for the re- duction of production rate due to catalyst deactivation has been examined. Some improvements can be achieved by adjusting the operating conditions. Finally, a strategy is proposed for prevention of reduced production due to catalyst deacti- vation. Keywords: Catalyst deactivation, Deactivation, Dynamic simulation, Loop reactor, Modeling Received: June 06, 2007; accepted: October 27, 2007 DOI: 10.1002/ceat.200700209 1 Introduction The nonlinearity of chemical processes results in parametric sensitivity, state multiplicity and instability of oscillatory be- havior. From the viewpoint of design and control, designs close to bifurcation varieties should be avoided. The reason is that the uncertainty of the design parameters and the distur- bances affecting the process may shift the operating point to a region where the behavior is different from that expected. Consequently, undesirable phenomena may occur, i.e., loss of stability; reaction ignition or extinction and reverse sign of the gain in control loops. In addition, high sensitivity to distur- bances is expected close to bifurcation points. Many chemical process systems consist of a reactor and a separation unit. These unit operations are considered to be the core of a chemical process. Energy supply to, and withdrawal from, the process are labeled as utilities in traditional process design [1]. The utilities include the steam system, process fur- naces, electricity generation and supply on the site, the fuel supply system for fired heaters and furnaces, process water and water treatment, etc. This article addresses the nonlinear behavior of certain reac- tor-heat exchanger-separator-recycle systems. Tubular reactors are used in a large number of chemical processes for kinetic performance reasons. The design of systems with tubular reac- tors involves recognition of the many important differences between continuous stirred-tank reactors (CSTR) and plug- flow tubular reactors (PFR). The most important distinction is the importance of the feed conditions in tubular reactor sys- tems, particularly the reactor inlet temperature. Reactor feed preheating becomes an important design parameter, which typically involves trade offs between steady-state economics and dynamic controllability. Reactor inlet concentrations are also more critical in tubular reactor systems, because of para- metric sensitivity and the potential for complex dynamics. Due to kinetic limitations, exothermic reactions are usually carried out at a high temperature where the conversion is lim- ited by chemical equilibrium. In these reactor systems, it is necessary to recycle the reactants. The product needs to be sep- arated from the recycle stream within the recycle loop. A reac- tor-separator system with recycling is also referred to as a chemical synthesis loop. Typically, the reactor effluent is first processed by the separation section and is then recycled. Hence, the composition and temperature of the recycle stream are different from the reactor effluent. Moreover, temperature controllers keep the reaction temperature constant, or for adia- batic reactors, maintain the reactor feed temperature constant. The behavior of reactor-separator-recycle systems is relevant for integrating conceptual design and plant-wide control at an © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Payam Parvasi 1 Mohammad Reza Rahimpour 1 Abdolhossein Jahanmiri 1 1 Department of Chemical and Petroleum Engineering, Shiraz University, Iran. – Correspondence: Prof. M. R. Rahimpour (rahimpor@shirazu.ac.ir) Department of Chemical and Petroleum Engineering, School of Engineering, Shiraz University, Shiraz 71345, Iran. 116 Chem. Eng. Technol. 2008, 31, No. 1, 116–132