Reactive distillation (RD) combines reaction and separation in a single unit to reduce energy consumption and capital investment. Despite of potential advantages, the reactive distillation may suffer from maintenance/design problems such as catalyst deactivation/replacement and hardware design (for catalyst packing), especially for heterogeneous catalyst such as ion exchange resin. In this work, an alternative design, side reactor configuration, is sought and the process of interest is the production of the ethyl acetate (EtAc) via esterification [1]. The reactive distillation study in [1] reveals that almost 90% conversion takes place in the column base of the RD and the rest of the 10% conversion occurs in the 10 reactive trays. This naturally leads to a coupled reactor/distillation configuration where all of the catalyst is packed in the bottoms base, denoted as Single Reactive Tray reactive distillation (SRT) hereafter. This mitigates the maintenance problem associated with conventional RD. However, simulation results show that, with the same amount catalyst loading (Wcat,RD), the SRT configuration cannot achieve the same performance as the RD (~93% conversion). In order to achieve the same conversion, the optimized design for SRT indicates that the catalyst loading should be 8.5 times of that for the reactive distillation while the heat input also increases by a factor of 24%. The cost is simply too much from maintenance perspective. Another alternative is then sought by adding external reactors to the Single Reactive Tray distillation column. This is termed as the Side Reactor Configuration (SRC) which has been proposed almost a decade ago [2-4]. Unlike conventional re active distillation design, the SRC design is less clear and design variables include: catalyst loading in the column base (Wcat,bot), % of equilibrium conversion for side reactor (X), sidestream withdrawn and return trays (Nss,r), side stream flow rate (Fss). A systematic design procedure is devised for the SRC design and the objective function to be minimized is the total annual cost (TAC). The results show that adding an external reactor decreases Wcat,bot substantially (from 8.5*Wcat,RD to 1.67*Wcat,RD) while the heat input is almost the same as that of the conventional reactive distillation and the TAC of the SRC only increases by a factor of 5% as compared to that of the RD. Considering the ease of catalyst replacement, the Side Reactor Configuration offers an attractive alternative to conventional reactive distillation.

References 1. Tang, Y. T.; Chen, Y. W.; Huang, H. P.; Yu, C. C.; Hung, S. B. ; Lee, M. J., “Design of reactive distillations for acetic acid esterification” AIChE Journal, 2005, 51, 6, 1683-1699. 2. Schoenmakers, H.; Buhler, W., “Distillation column with external reactors - an alternative to the reaction column” Chemie Ingenieur Technik, 1982, 54, 2, 163-163. 3. Jakobsson, K.; Pyhalahti, A.; Pakkanen, S.; Keskinen, K. ; Aittamaa, J., “Modelling of a side reactor configuration combining reaction and distillation” Chemical Engineering Science, 2002, 57, 9, 1521-1524. 4. Baur, R.; Krishna, R., “Distillation column with reactive pump arounds: An alternative to reactive distillation” Chemical Engineering and Processing, 2003, 43, 3, 435-445.