Olefin-selective membranes in gas-liquid membrane contactors for olefin/paraffin separation

The application of olefin-selective membrane materials in gas-liquid membrane contactors for the separation of paraffins and olefins using a silver nitrate solution as the absorption liquid turned out to be very successful, especially with respect to the olefin/paraffin selectivity obtainable. Composite hollow-fiber membranes with a top layer of a highly permeable block copolymer of poly(ethylene oxide) (PEO) and poly(butylene terephthalate) (PBT) are prepared and applied in a gas-liquid membrane contactor for the separation of paraffins and olefins using a silver nitrate solution as the absorption liquid. The water present in the absorption liquid swells the hydrophilic polymer sufficiently. This prevents drying out of the layer and enables the partitioning of silver ions into the polymer matrix, making it olefin-selective. Ethylene permeabilities obtained are comparable to the values found for membranes with nonselective, elastomeric top layers (40-50 barrer). Selectivities, however, are more than 20 times higher. Independent of the liquid flow rate, a selectivity of 165 is obtained for PEO/PBT-coated membranes. This makes the application of olefin-selective membranes in a membrane contactor for olefin/paraffin separations very attractive

Super selective membranes in gas-liquid membrane contactors for olefin/paraffin separation

In the present paper, selective composite membranes containing sulfonated poly(ether ether ketone) (SPEEK) layers on top of a hydrophobic, polypropylene support are applied as absorber and desorber in a gas¿liquid membrane contactor system for the separation of paraffins and olefins. The water present in the absorption liquid swells the hydrophilic polymer sufficiently, making the membranes olefin-selective. As a result, even at high liquid velocities where the membrane determines the selectivity of the process, high selectivities can be obtained in combination with high productivities. Continuous contact between the absorption silver nitrate solution and the SPEEK layer prevents the layer from drying out and subsequent loss of selectivity. Previously, unknown high ethylene/ethane selectivities (>2700) are obtained in combination with reasonable ethylene productivities (7.6×10¿10 cm3/cm2 s Pa (1×10¿6 cm3/cm2 s cmHg))