Hybrid Separation Scheme for Azeotropic Mixtures –Sustainable Design Methodology

Abstract

Distillation has been the first choice among the numerous separation techniques employed by chemical industries, primarily because of its inherent advantages. About 80% of industrial separations involving vapour – liquid phases are performed by distillation, in spite of its low thermal efficiency and highly energy intensive nature. More than 50 % of the total energy consumed in distillation, is spent for enriching the product purity from 80-90% to close to 100 %. However, a conventional distillation process operating at normal conditions is ineffective for separating azeotropic mixtures. In this work, a methodology has been proposed to explore the possibility of integrating distillation with membrane separation technique to separate azeotropic mixtures. These units will be operated at their maximum driving force for separation in the proposed hybrid schemes. The designed optimal hybrid schemes result in energy efficient separations compared to conventional distillation processes. The effectiveness of the proposed methodology is demonstrated with the help of two case studies. In the first case study, a well-known example of benzene - cyclohexane separation is presented, while production of 99.9 mole % pure acetonitrile from an ethanol ammoxidation process is discussed in the second case study. Both these systems form azeotropes at atmospheric pressure.