Comparison of heteroazeotropic and extractive distillation for the dehydration of propylene glycol methyl ether

Separation section often is the most energy intensive section of an industrial chemical process, even so when there is an azeotropic mixture needed to be separated. In order to further save energy in a particular azeotropic separation system, various heat integration methods were proposed. However, because of more complex nature of these heat integration methods, the operation and control of such process may be hindered. Since there are various ways which can be used to separate a particular azeotropic mixture, this paper uses an industrial relevant propylene glycol methyl ether dehydration system as an example to demonstrate that selecting the most effective separation method is crucially important in attempting to save energy of the separation system. The drawback of using heterogeneous azeotropic distillation for this separation task can easily be revealed with process understanding. A more effective separation method via extractive distillation is proposed to significantly save steam cost by 39.7% and reduce the total annual cost by 32.7%. Simple feed-effluent heat exchanger can be added in the proposed extractive distillation system to further save energy without much complication of the process design flowsheet.