Simulation and response surface analysis for the optimization of a three-phase catalytic slurry reactor

Chemical Engineering and Processing xxx (2004) xxx–xxx

Simulation and response surface analysis for the optimization of a three-phase catalytic slurry reactor
Salah D.M. Hasan a,∗ , Delba N.C. Melo b , Rubens M. Filho b
a

School of Chemical Engineering, West of Parana State University - UNIOESTE, Rua da Faculdade, 645, CEP 85903-010, Toledo-PR, Brazil b School of Chemical Engineering,State University of Campinas - UNICAMP, P.O. Box 6066, 13081-970, Campinas, SP, Brazil Received 23 May 2003; received in revised form 17 March 2004; accepted 14 May 2004

Abstract Factorial design and response surface analysis techniques were used in combination with modeling and simulation to optimize an industrial hydrogenation process. A three-phase reactor for the production of cyclohexanol byhydrogenation of phenol in the presence of the catalyst Ni/SiO2 , with a six-stage cooling system for temperature control was considered. The model equations form a system of ordinary differential equations derived from kinetic laws and steady-state balances for mass and energy for both reactants and coolant system. Initially, screening design was used to evaluate the process variables which wererelevant to the cyclohexanol yield. Two statistically significant parameters (rates of hydrogen-QH and catalyst-QNi ) were selected and used in response surface methodology for process optimization. An improvement of 5.5% in cyclohexanol yield was observed for the optimized variables (QH = 259 kg/h, QNi = 53 kg/h). © 2004 Elsevier B.V. All rights reserved.
Keywords: Three-phase reactor;Hydrogenation; Steady-state modeling; Simulation; Response surface analysis; Optimization; Catalytic

1. Introduction Nowadays, the control and safety of reactors are important features in the design as well as in the operation of industrial processes that carry out complex reactions with constraints of thermal stability and/or selectivity as, for example, exothermic hydrogenation reactions [1]. Thedevelopment of efficient and reliable models for multiphase reactors is a difficult task because it involves many aspects like hydrodynamics, gas–liquid and liquid–solid mass transfer, heat transfer, pore diffusion, and reaction and deactivation kinetics. Model assessment has mostly been reported for a single reaction, or for reactions obeying simplified kinetic laws under isothermal conditions.Nevertheless, exothermic reactions undergoing a multi-step reaction scheme with complex kinetics are industrially of a main interest, and rigorous comparisons of the performances of several multiphase reactors for such reactions have hardly ever been published [2]. This claims for the development of detailed models. On the other hand, an important issue

∗

Corresponding author. Tel.: +55 45 3797090;fax: +55 45 3797000. E-mail address: salah@unioeste.br (S.D.M. Hasan).

to be considered is to have a robust model as simple as possible so that extensive simulation does not make for too large a computational load. With computational advances, process simulation has become an important tool for study and optimization of complex processes that normally involve a large number of variables [3]. Formost multivariable processes, e.g. with three-phase reactors, in which numerous potentially influential factors are involved, it is not always obvious to determine which are the most important. Hence, it is necessary to submit the process to an initial screening design prior to optimization [4]. The methodology of Plackett and Burman [5] is a tool for this initial screening, since it makes itpossible to determine the influence of various factors with only a small of number of trials, instead of using more extensive factorial design, which would give more complete information, but may involve unfeasible complexity. If, for example, there are 10 variables on two levels (210 ) the situation implies 1024 trials. If, however, the process is subjected to initial screening, response surface...