Design and Control of Thermally-Coupled Reactive Distillation System for Esterification of an Alcohol Mixture Containing n-Amyl Alcohol and n-Hexanol

Semiconductor and pharmaceutical industries often produce waste alcohol mixtures. This study discusses a reactive distillation process of a mixed alcohol feed containing n-amyl alcohol and n-hexanol to react with acetic acid to produce useful esters. In an earlier paper (Lee et al. Ind. Eng. Chem. Res. 2009 48, 7186-7204), optimal design of the same Type-III mixed-alcohol reactive distillation process containing n-butanol and n-amyl alcohol was developed. In that paper, the indirect sequence containing a reactive distillation column with heavier amyl acetate bottom product and a second column to produce butyl acetate gives the lowest total annual cost. In this study, with different mixed alcohol feed (although of the same reaction type), it is found that an alternative direct sequence design is much more economically favorable with 34% reduction in total annual cost as compared to the indirect sequence. The reason for the seemingly contradictory results can be explained by differences in relative volatilities of binary pairs in the stripping sections of the reactive distillation towers. Process intensification technology is also attempted to devise a thermally coupled reactive distillation configuration to further save 13% of the operating energy. The overall control strategy using tray temperatures is also proposed to maintain high-purity products despite various disturbances.