Computers and Chemical Engineering 57 (2013) 63–77 Contents lists available at SciVerse ScienceDirect Computers and Chemical Engineering jo u r n al homep age: www.elsevier.com/locate/compchemeng Design and control of a reactive-distillation process for esterification of an alcohol mixture containing ethanol and n-butanol Yi-Chang Wu a , Hao-Yeh Lee b , Chen-Yu Tsai a , Hsiao-Ping Huang a , I-Lung Chien a,∗ a Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan b Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan a r t i c l e i n f o Article history: Received 12 September 2012 Received in revised form 13 December 2012 Accepted 8 January 2013 Available online 25 January 2013 Keywords: Reactive distillation Esterification Ethyl acetate n-Butyl acetate Design and control a b s t r a c t This paper presents an economical design flowsheet and overall control strategy for simultaneous esterifications of ethanol and n-butanol mixtures with acetic acid. In this work, a difficult-to-design reactive-distillation (RD) process, classified as mixed Type-II/Type-III system, has been studied. After comparing three alternative design flowsheets, an indirect-sequence design containing a RD column, a top decanter, and a stripper gives significantly lower total annual cost and energy consumption than the other two designs. In the control strategy development, conventional inventory control with RD bot- tom level controlled by manipulating RD bottom flow shows that this process would exhibit multiple steady-states. An improved inventory control strategy with a rather unusual pairing by controlling this level using reboiler duty is proposed to alleviate this complex dynamic behavior. The dynamic results show that the proposed plant-wide control strategy is capable of holding product specifications despite disturbances from throughput and feed composition changes. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Manufacturing processes in the semiconductor and pharma- ceutical industries often produce massive organic liquid wastes including alcohol mixtures. Therefore, the esterifications of alcohol mixtures would be a beneficial step in reusing wastes from these industries to produce valuable esters. The purpose of this paper is to study the design and control of a process to reuse an alcohol mixture containing ethanol (EtOH) and n-butanol (BuOH) to react with acetic acid (HAc) to produce ethyl acetate (EtAc) and n-butyl acetate (BuAc). There are quite a few papers in the literature discussed reactive- distillation (RD) design for the esterificaton reaction with a single alcohol feed. Books by Sundmacher and Kienle (2003) and Luyben and Yu (2008) all have chapters addressing design and/or control of reactive-distillation processes involving various esterification reac- tions. Tang et al. (2005) developed different process flowsheets for the esterification of acetic acid with C1–C5 alcohols. For methanol reacted with acetic acid, a single RD column can be designed to obtain methyl acetate at the distillate and water at the column bot- toms. This RD system was classified as a Type-I system. For ethanol or isopropanol reacted with acetic acid, the RD system is more com- plicated including a RD, a decanter, and a stripper. The water is ∗ Corresponding author. Tel.: +886 2 3366 3063; fax: +886 2 2362 3040. E-mail address: ilungchien@ntu.edu.tw (I-L. Chien). obtained from the aqueous outlet of the decanter and the ethyl or isopropyl acetate is obtained from the bottoms of the stripper. There is no outlet stream at the RD column bottoms. This kind of RD system was classified as Type-II system. For n-butanol or n- pentanol reacted with acetic acid, only a single RD column with top decanter is needed with heavy ester obtained from the column bottoms and water obtained from the aqueous outlet stream. This heavy ester RD system was classified as Type-III system. The existing literature on the topic of simultaneous esteri- fications of EtOH and BuOH with acid (e.g., acetic acid) in a reactive-distillation system is relatively scarce. Cooke and Yeomans (1975) developed a process including one RD column with decanter, another distillation column with decanter, and a final col- umn to separate two main products (EtAc and BuAc). The overall conversion is at 97% and the purity of the EtAc product is relatively low at 98.2 wt%. Van Acker, Mathieu, Milner, and Pacynko (1998) further improved the above process for mixed alcohol feed with small ketone or aldehyde impurities by adding another column to the process. However, the purities of the two main products are still not pure enough. Schulz, Baucer, and Merscher (2006) developed a process with one RD, two columns, and three decanters. Although high purity products of EtAc and BuAc can be obtained, the water purity is low resulting in loss of some ethanol and ester products. In this study, the RD process with mixed EtOH and BuOH alco- hol feed will be developed with goal to have higher conversion and product purities. In Lee, Yen, Chien, and Huang (2009), mixed n- butanol and n-amyl alcohol RD process has been developed. That 0098-1354/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compchemeng.2013.01.002