Design and Control of a Complete Azeotropic Distillation System Incorporating Stripping Columns for Isopropyl Alcohol Dehydration

• Published in: Industrial & engineering chemistry research Vol. 51; no. 7; pp. 2997 - 3006
• Main Authors: Chang, Wen-Teng, Huang, Chi-Tsung, Cheng, Shueh-Hen
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 22.02.2012
• Subjects: Applied sciences; Chemical engineering; Columns (process); Dehydration; Distillation; Energy conservation; Ethyl alcohol; Exact sciences and technology; Isopropyl alcohol; Recovery; Stripping; Design; Azeotropic distillation; Stripping; Dehydration
• DOI: 10.1021/ie202021g
• ISSN: 0888-5885

As demonstrated by Pham and Doherty [Chem. Eng. Sci. 1990, 45, 1823] in an ethanol dehydration process and by Arifin and Chien [Ind. Eng. Chem. Res. 2007, 46, 2535] in an isopropyl alcohol dehydration process, a three-column heterogeneous distillation sequence which contains a preconcentrator column, an azeotropic column, and an entrainer recovery column is more energy saving than two-column and four-column sequences. The three-column sequence for the isopropyl alcohol (IPA) dehydration process, according to Arifin and Chien, is more energy-saving than the two-column sequence, but the capital cost of the entire sequence is more expensive than that of the two-column sequence. Because the reflux ratio used either in the preconcentration column or the recovery column of the three-column IPA dehydration system is quite small, these two conventional distillation columns are both replaced by a stripping column, and in this study a new separation scheme is thereby developed. The economic analysis of the proposed system shows there is more saving in energy and capital costs than the two- and three-column sequences aforementioned. Further, in developing a plant-wide control structure, a tray temperature control loop is implemented in each of the three columns which regulates reboiler duty in order to maintain the bottom product compositions for the new scheme, and ratio control of the organic reflux flow to the feed flow rate of the azeotropic column is used to reject feed rate disturbance. The purities of water achieved in the preconcentrator and entrainer recovery columns are greater than 99.88 mol %, and the IPA purity in the product stream is greater than 99.99985 mol %. Closed-loop responses to ±20% changes in fresh feed rate and feed H2O composition show that the proposed strategy has good control performance.