Selectivity engineering with single-feed hybrid reactive distillation columns Shabih Ul Hasan, Ranjan Malik, Sanjay Mahajani n Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India HIGHLIGHTS  Synthesis and design of hybrid RD systems that are capable of offering higher selectivities in multiple reaction systems.  The procedure leads to multiple feasible configurations giving the desired selectivity.  The algorithm allows one to choose the best design based on the energy and catalyst requirement. article info Article history: Received 14 September 2012 Received in revised form 4 April 2013 Accepted 30 April 2013 Available online 21 May 2013 Keywords: Hybrid reactive distillation Attainable region Design Selectivity Reactor Feasible stage composition region abstract Reactive distillation (RD) can be advantageously used to improve the selectivity of the desired product in the multi-reaction system. Process synthesis and design of RD systems to attain the desired selectivity is a challenging task. Our previous work in this field (e.g. Amte et al., 2011, 2012) was restricted to fully reactive RD models and their networks. In this work, we examine the potential of a hybrid reactive distillation column, with both reactive and non-reactive sections, through an example of a single reactant complex reaction scheme (e.g. van de Vusse reaction) in which reactant is intermediate boiling. An algorithm for conceptual design of such columns is presented. It is based on the boundary value method (BVM) that utilizes the concept of operation leaves of rectifying and stripping sections; the overlap of which indicates the potential feasible split. Based on the desired selectivity, we determine the locus of reactive stage compositions in the RD column. Its intersections with the non-reactive stage composition lines (SCL) allow rapid screening of feasible designs of hybrid reactive distillation (HRD) columns. The approach generates multiple designs and allows one to compare them in terms of energy and catalyst requirement. The proposed method is applicable to single reactant single-feed hybrid columns, and because of its graphical representation, it cannot be directly used for systems with a large number of components. More work is therefore necessary to extend this approach to the multi-reactant double-feed hybrid configurations. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Reactive distillation, due to its well known advantages, is a promising alternative to conventional processes. It offers reduced capital cost, less energy consumption, avoidance of azeotropes, higher reaction rates and selectivity improvements in the case of multiple reactions. Selectivity engineering is an important applica- tion of reactive distillation wherein, one can cleverly manipulate composition profiles in the column in favor of the desired reaction by changing the distillation attributes. Because of the interaction between reaction and distillation in the combined unit, the synthesis and design of reactive distillation column is challenging. Simulations that are based on equilibrium-stage or non equilibrium-stage models are widely used for designing an appropriate RD configuration (Taylor and Krishna, 2000; Slava et al., 2009; Luo et al., 2009). However, this approach may be, at times, tedious and undesirable in the early stage of process synthesis due to the existence of multiple feasible design alternatives. In some cases, the desired performance may not be feasible due to non-ideality of the mixture or complexity of the reaction scheme. It is therefore necessary that one first identifies the maximum achievable performance (e.g. product com- position, selectivity) and the conceptual design associated with it. This design can be further fine-tuned with the help of rigorous simulation and optimization studies. The conceptual design techni- ques such as the one based on attainable region approach and the boundary value methods are well suited for such tasks in the early stages of design exercise. These techniques have also been proved to Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ces.2013.04.054 n Corresponding author. Tel.: +91 22 2576 7246/2578 2545; fax: +91 22 2572 6895. E-mail address: sanjaym@iitb.ac.in (S. Mahajani). Chemical Engineering Science 99 (2013) 324–334