Optimal design and dynamic transitions of multitask catalytic distillation columns: A Discrete-Steepest Descend Framework

Abstract

This work presents the optimal design and operation of catalytic distillation (CD) units considering discrete and continuous design and operation variables combined with rigorous non-linear dynamic process models. The key novelty in this work is that optimal process design and dynamic transitions between different product grades in CD units are simultaneously intensified using a deterministic optimization framework. The proposed optimization method is based on a Discrete-Steepest Descent Algorithm (D-SDA), which enables the designer to improve an initial feasible design, while providing local optimality guarantees. The D-SDA has been effective to handle the optimal steady-state design of CD columns. The present study brings dynamic transitions into consideration thus providing theoretical foundations regarding the optimal design of CD columns in the transient domain. The production of ethyl tert-butyl-ether (ETBE) is considered as a case study, where dynamic transitions between different grades of ETBE coupled with design considerations are investigated. This work shows that a single CD unit can be optimally designed to produce multiple ETBE grades, while simultaneously optimizing its dynamic performance to attain different steady states. Accordingly, this study provides new insights regarding the economic and operational benefits of performing the simultaneous optimal design of multitask CD columns with dynamic transitions.