THE FORMATION OF ASYMMETRIC HOLLOW FIBER MEMBRANES FOR GAS SEPARATION, USING PPE OF DIFFERENT INTRINSIC VISCOSITIES

A range of intrinsic viscosities of poly (2,6-dimethyl-1,4-phenylene ether) (PPE) has been used to produce skinned asymmetric hollow fibre membranes for gas separation and to study the effect of intrinsic viscosity on membrane properties. With all the PPE samples used it proved possible to produce asymmetric hollow fibre membranes with an oxygen over nitrogen selectivity of 4 to 5 at room temperature. It is shown that a clear relation exists between the intrinsic viscosity of the PPE and the attainable apparent minimal thickness of the selective layer, the skin. When using a higher intrinsic viscosity of the polymer, the minimal skin thickness of the membrane is reduced. The minimal skin thickness ranges from more than 20-mu-m using PPE with an intrinsic viscosity of 0.25 (dl/g) to less than 0.2-mu-m using PPE with an intrinsic viscosity of 1.4 (dg/l), while the selectivity remains the same. As yet, the reason of the effect of intrinsic viscosity on membrane formation is not clearly understood. However, it can not be ascribed to the viscosity of the spinning dope. If the viscosity of the spinning dope is increased by an increasing polymer concentration or a higher solvent/non-solvent ratio, the resulting hollow fibres have poor membrane properties. However, if the viscosity of the spinning dope is increased by increasing the intrinsic viscosity of the polymer, the resulting fibres have improved properties.