Process intensification (PI) has become an important tool for novel process designs featuring drastic improvements in process performance. While miniaturization, use of alternative energy sources and discovery of multifunctional materials are examples for activities leading to intensification, integration of several operations in a single equipment have been one of the most successful PI strategies in terms of their industrial acceptance [1-2]. Specifically, reactive distillation (RD) units, which combine reaction and distillation operations in a single column, have seen a marked increase in their industrial adoption since 1980s [2]. Wider utilization of this technology requires systematic design procedures suggesting optimal intensified designs at the early design stage. Several methods have been suggested in the past for the synthesis of reactive distillation operations [3-4]. In this work, we use building block-based representation [5-8] to provide a systematic procedure for the synthesis and optimization of reactive separation processes. This novel representation can suggest non-intuitive intensified configurations with its unique outlook towards process design. The representation is based on collection of blocks positioned on a two-dimensional grid which can be used to represent several physical and chemical phenomena. Each building block has several physical attributes, i.e. temperature, pressure, phase, composition, and can stand for a unit use of a material, e.g. catalyst. While reaction operations can be represented within a single block, separation related phenomena require at least two blocks with different phases. Vapor-liquid equilibrium, for instance, requires one vapor and one liquid block sharing a common boundary through which phase transition can take place. When reaction operation is assigned into one of these neighboring blocks, a reactive vapor-liquid contact stage can be obtained. Collection of these building blocks in a grid formation yields building block superstructure which is modeled with a Mixed Integer Non-linear Programming (MINLP) model. Continuous variables are used to quantify the material and energy flow between the blocks and integer variables are utilized to assign different phenomena at different positions on the grid. This results in a generic representation and synthesis method for reactive separation processes. We will demonstrate the applicability of the proposed method with several example problems including ideal and non-ideal reactive systems and show that cost-optimal intensified designs can be realized through building-block based approach.
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[6] Li, J., Demirel, S.E. and Hasan, M.M.F. (2018). Process synthesis using block superstructure with automated flowsheet generation and optimization. AIChE Journal, 64(8), 3082-3100.
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