processes Article Energy Optimization and Effective Control of Reactive Distillation Process for the Production of High Purity Biodiesel Syed Sadiq Ali 1 , Agus Arsad 2 , SK Safdar Hossain 1 , Avijit Basu 1 and Mohammad Asif 3, *   Citation: Ali, S.S.; Arsad, A.; Hossain, S.S.; Basu, A.; Asif, M. Energy Optimization and Effective Control of Reactive Distillation Process for the Production of High Purity Biodiesel. Processes 2021, 9, 1340. https://doi.org/10.3390/ pr9081340 Academic Editor: Chiing-Chang Chen Received: 1 July 2021 Accepted: 26 July 2021 Published: 30 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Chemical Engineering, King Faisal University, P.O. Box 380, Al-Ahsa 31982, Saudi Arabia; ssali@kfu.edu.sa (S.S.A.); snooruddin@kfu.edu.sa (S.S.H.); abasu@kfu.edu.sa (A.B.) 2 Faculty of Engineering, UTM-MPRC Institute for Oil and Gas, School of Chemical and Energy Engineering, Universiti Teknologi Malaysia, Johor Bahru 81310, Johor, Malaysia; agus@utm.my 3 Department of Chemical Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia * Correspondence: masif@ksu.edu.sa; Tel.: +966-114676849; Fax: +966-114678770 Abstract: Biodiesel is a promising renewable energy option that significantly reduces the emission of greenhouse gases and other toxic byproducts. However, a major challenge in the industrial scale production of biodiesel is the desired product purity. To this end, reactive distillation (RD) processes, which involve simultaneous removal of the byproduct during the transesterification reaction, can drive the equilibrium towards high product yield. In the present study, we first optimized the heat exchange network (HEN) for a high purity RD process leading to a 34% reduction in the overall energy consumption. Further, a robust control scheme is proposed to mitigate any feed disturbance in the process that may compromise the product purity. Three rigorous case studies are performed to investigate the effect of composition control in the cascade with the temperature control of the product composition. The cascade control scheme effectively countered the disturbances and maintained the fatty acid mono-alkyl ester (FAME) purity. Keywords: biodiesel; reactive distillation; heat integration; process control; optimization 1. Introduction The continuous depletion of non-renewable energy resources and their hazardous impact on the environment has impelled the scientific community to explore alternative energy sources. Due to consistently increasing energy demands, the need to develop renewable, non-toxic, and environmentally friendly energy options such as biofuels has grown rapidly [1–3]. Biodiesel is similar to petroleum diesel in terms of properties and is a promising alter- native to fossil fuels [4–6]. Fatty acid mono-alkyl esters (FAME) are the main component of biodiesel, which can be produced by transesterification of free fatty acids (FFA) and alcohol. The biodegradable feed stocks such as animal fats, vegetables, or cooking oils are common sources of FFA. The optimization and simplification of FFA transformation to the clean- burning biodiesel fuel is a subject of active research [7–10]. While using the conventional reactor-separation system, the reaction equilibrium limits the product yield. The generation of byproducts amplifies the backward reaction, thus limiting the reaction conversion. This limitation instigates the need for multiple separation systems in the process, involving additional capital and operational costs. A potential solution to this drawback is the de- ployment of a reactive distillation (RD) column. An RD column is a separation column with catalysts in a particular section, which enables the reaction as well as separation to occur simultaneously in the same tray. The RD process is best suited for equilibrium-limited chemical reactions, whereby the byproducts are separated immediately after their forma- tion. This causes the reaction to move forward and results in high conversion and product yield. Additionally, the RD process optimizes the plant economics, eliminating the need for extra separation processes and added utilities [11–15]. Estrada-Villagrana et al. [13] studied Processes 2021, 9, 1340. https://doi.org/10.3390/pr9081340 https://www.mdpi.com/journal/processes