Composite hollow fiber gas–liquid membrane contactors for olefin/paraffin separation

Gas–liquid membrane contactors frequently suffer from undesired wetting of the microporous membrane by the absorption liquid. Stabilization layers at the liquid-side of the microporous membrane potentially prevent this wetting. We apply such stabilized membranes in a membrane contactor using AgNO3 solutions as absorption liquid, to separate paraffins and olefins. Hollow fiber membrane modules with an effective surface area of 101.8cm2, containing 10 composite membranes with an 8μm thick, defect free ethylene propylene diene terpolymer (EPDM) top layer are prepared. An absorption and desorption module operated continuously in a membrane contactor process for more than 20 weeks without any change in membrane performance. In the absorber, transport of ethylene is highly enhanced by the chemical reaction and desorption turned out to be the limiting step in this separation process. The influence of feed pressure, liquid flow rate, and AgNO3(aq) concentration is investigated and the results are evaluated in terms of ethylene productivity and ethylene over ethane selectivity. Ethylene productivities range from 2.1×10−6 to 6.1×10−6cm3/cm2scmHg and gas mixture selectivities range from 72.5 to 14.7.