Highly efficient tetrafluoroethylene recovery for batch polymerization system: Membrane preparation and process development

Abstract

In tetrafluoroethylene (TFE) batch polymerization, H2 is utilized to stabilize pressure and control reaction degree. TFE lost in the purge can account for about 6.0% of the loaded monomer. In this work, membrane-based separation system was presented to effectually reduce TFE loss. Polyimide asymmetric membrane with JH2 up to 196 GPU and αH2/TFE higher than 1680 was developed for the separation. A pseudo-steady process was customized to sufficiently complete TFE recovery within the 30-min idle period after batch polymerization. With the procedure that H2-enriched permeate is compressed back into the reactor, it is succeeded to overcome the limits that the purge is gradually falling in pressure and the TFE-enriched stream is hazardous in compression. In this instance, TFE recovery ratio was increased to about 90%. For a 5.0-kt/a TFE polymerization unit, the investment for the separation system is about 2.56 × 105 USD, the running payout is less than 4.35 × 104 USD/a, and meanwhile the annual gross profit can be up to 3.126 × 106 USD. On the whole, gas membrane separation is a promising technique to reduce TFE loss in the batch polymerization processes.