EVALUATION OF RETENTATE RECYCLE EFFECT ON ENRICHMENT OF LESS PERMEABLE GAS COMPONENT IN A MEMBRANE PERMEATOR

In the present paper, a theoretical examination is made of the retenta te recycle to the permeate stream, which was verified experimentally a s an effective method for enriching the less permeable component in th e retenate stream using hollow fiber membrane permeators. The concentr ation of the less permeable gas component in the retentate was calcula ted as a function of membrane area, cut, pressure ratio, ideal separat ion factor, and the retentate recycle ratio. The concentration of the less permeable gas in the retentate had a maximum point as a function of the recycle ratio at a given operating condition (constant membrane area and pressure ratio). The recycle was more effective for obtainin g high purity of the less permeable component when a more selective me mbrane (high separation factor) rather than a less selective one was u sed. It was also more effective with a large pressure ratio than with a small pressure ratio. The evaluation of the separation efficiency by Rony's extent of separation and the tails separation factor also indi cated that the case with the retentate recycle was more effective for obtaining high purity less permeable component than the case without t he recycle, especially for a highly selective membrane and high pressu re ratio. On the other hand, the retentate recycle to the feed was fou nd to have no effect in improving the concentration in this calculatio n range.