Design and Optimization of the Methanol-to-Olefin Process. Part II: Comparison of Different Methods for Propylene/Propane Separation

Design and optimization of different methods for propylene/propane separation in the downstream of the methanol-to-olefin process are investigated. Since propylene and propane have similar boiling points, a large number of trays and high energy are required when separating by a traditional single column with industrial low-pressure steam as reboiler heat source (TRA-LPS case). Some alternatives are studied, including the traditional column using waste hot water as heat resource (TRA-HW), implementation of a vapor recompression cycle (VRC) configuration, and extractive distillation (ED) with acetonitrile solution as entrainer. Compared to TRA-LPS, the total annual cost can be reduced significantly for TRA-HW and ED and to a minor extent for VCR. The required number of trays for separation is also clearly reduced for the three cases. It can be concluded that TRA-HW and ED are both promising alternatives for this separation.