Polyimide membrane system for tetrafluoroethylene recovery: Industrial plant, optimal operation and economic analysis

This is a continuation of the development of polyimide membrane for tetrafluoroethylene (TFE) recovery [Sep.Purif.Technol.124(2014)89-98]. A industrial membrane plant has been designed and constructed after cryogenic acetone absorption to enhance TFE recovery for the first time. Specific to the 10-kt/a TFE synthesis plants, the nominal process capacity is set as 20 Nm3/h. The vacuum mode (−0.08 MPaG) is executed for the permeate side to increase the feed/permeate pressure ratio and enhance separation performance under low feed pressure. In response to the drastic fluctuation in feed flow rate and composition, owing to the unsteady cracking reaction, the adaptive control of membrane area is customized technically for the operation strategy. In detail, one or two modules can be shut down by the automatic response while the stream into membrane plant is lower in flow rate or higher in TFE content, and vice versa. In comparison to the ordinary mode under inflexible operation, whose TFE recovery ratio is about 84.5%, the adaptive control strategy behaved better with the recovery ratio up to 87.6%. According to the three-month running result, the membrane recovery plant with adaptive membrane area control can efficiently decrease TFE loss from 130 to 17 t/a, and the annual gross profit was about 1.264 million US dollar, with the payback period less than 4 months. It is undoubted that the polyimide membrane plant is practicable and cost-efficient for TFE recovery in the synthesis.