Choice of suitable entrainer in heteroazeotropic batch distillation system for acetic acid dehydration

Abstract

Mixture containing acetic acid and water does not form azeotrope. However, because of tangent pinch on the pure water end, it is customary in industry to add an entrainer into this mixture to aid the separation via heterogeneous azeotropic distillation. When the production scale is relatively small, it is more beneficial to run the acetic acid dehydration in batch mode. In Chien et al. [Chien, I. L., K. L. Zeng, H. Y. Chao, and J. H. Liu, “Design and Control of Acetic Acid Dehydration System via Heterogeneous Azeotropic Distillation,” Chemical Engineering Science, 59, 4547 (2004)], a suitable entrainer for acetic acid dehydration operating in continuous mode was found to be iso-butyl acetate. This paper demonstrates that although iso-butyl acetate is a good entrainer for continuous heterogeneous azeotropic distillation system, it is not suitable in heteroazeotropic batch system for acetic acid dehydration. Instead, the performances of two other acetates are compared for the suggestion of better entrainer in batch operation. An extremely simple batch operating sequence for acetic acid dehydration will be demonstrated via dynamic simulation. The proposed batch operation is very robust in terms of the particular values chosen for the operating variables. This proposed batch operation gives very similar separation performance comparing to a multivessel operation and requires less process, instrumentation, and control equipments.