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

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.