Design and Control of a Reactive-Distillation Process for Esterification of an Alcohol Mixture Containing Ethanol and n-Butanol

摘要

The objective of this study is to present a feasible design and control structure for the esterifications of ethanol (EtOH) and n-butanol (BuOH) mixtures with acetic acid (HAc). This alcohol mixture is frequently obtained in semiconductor industry as a waste by-product, thus a detailed study of how to re-use this stream to produce high-value ester products is a worthy research. In our previous paper, the design and control of mixed-alcohol reactive-distillation process, categorized as Type-II system, has been developed. In this study, a new more difficult to design reactive-distillation process, categorized as mixed Type-II/Type-III system, will be studied. After comparing several alternative design sequences, an indirect design sequence containing a reactive distillation column and a stripper gives the lowest total annual cost (TAC). In the control strategy, a traditional inventory control structure shows that this process would exhibit multiple steady states. An improved inventory control strategy is proposed to alleviate this complex dynamic behavior. The most important inventory control loop is the bottom liquid level of the reactive distillation column. A rather unusual inventory control strategy which manipulates the reboiler duty should be used. The dynamic results show that the proposed plant-wide control structure is capable of holding product specifications despite disturbances from throughput and feed composition changes. Overall control strategy with tray temperature control loops are proposed for the plant-wide control structure.