Combined preconcentrator/recovery column design for isopropyl alcohol dehydration process

The design and control of a complete heterogeneous azeotropic distillation column system using cyclohexane (CyH) as entrainer has been presented by Chien et al. (Ind. Eng. Chem. Res. 2004, 43, 2160). In that study, the feed composition to the heterogeneous azeotropic column is assumed to be near the isopropyl alcohol (IPA) and water azeotropic composition (water at 31 mol % in that paper). However, for a typical waste IPA stream in the semiconductor industry where IPA is used as a cleaning agent, this waste stream is more diluted. Taking a typical waste IPA stream with equal molar of IPA and water as an example, design and control of the overall isopropyl alcohol dehydration process will be investigated. The resulting proposed design flow sheet is a two-column system which combines preconcentrator column and recovery column into a single column. This design adapted from Ryan and Doherty (AIChE J. 1989, 35, 1592) for their ethanol dehydration process not only minimizes the total annual cost but also is very robust when operating in the face of various fresh feed disturbances. Only one tray temperature control loop in the heterogeneous azeotropic column and another one in the combined preconcentrator/recovery column are needed in the proposed overall control strategy.