Effect of Feed Impurity on the Design of and Control of Heterogeneous Azeotropic Distillation for Acetic Acid Dehydration(II)

• Main Authors: Tang-Kai Gau, 高堂凱
• Other Authors: 黃孝平
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/91469088610076171102

碩士 === 國立臺灣大學 === 化學工程學研究所 === 93 === In this study, effect of feed impurity on the design and control of heterogeneous azeotropic distillation for acetic acid dehydration is investigated. Although acetic acid and water do not form azeotrope, using simple distillation to separate these two components is not practical. The reason is because the system has tangent pinch on the pure water end, thus it is more customary in industry to use an entrainer via a heterogeneous azeotropic distillation column system for the separation. The entrainer used for this system to enhance the acetic acid and water separation is isobutyl acetate. The impurity, p-Xylene, during normal operation will not leave the column system through outlet stream from either aqueous phase of top decanter or column bottom . A side stream purge is proposed to solve the problem of p-Xylene accumulation. Optimum design of acetic acid dehydration system is determined by total annual cost (TAC). But the controlability of the optimal design system is not good. Increasing entrainer flow rate is proposed to improve the controlability. Since the optimal flow rate of the side stream is quite small, it is not easy to control the flow rate. A practical automatic purging strategy is proposed instead. This automatic purging strategy does not rely on any on-line composition measurement but just on some tray temperature measurements. Closed-loop dynamic simulation demonstrates that the proposed purging strategy can successfully keep both top and bottom product purities at their specifications.