Asymmetric cellulose acetate hollow fibers: Studies in gas permeation

Gas separation behavior of permeators containing asymmetric cellulose acetate hollow fibers with the dense skin on the outside, facing the feed gas, has been investigated experimentally and theoretically using a sweep gas technique. Two systems were studied: CO₂‐N₂, and O₂‐N₂ (air). If the membrane structure is assumed to be symmetric or homogeneous, the model complies with the present data much better, compared to the assumption that the membrane is asymmetric. Separation was carried out with the high‐pressure feed outside the fibers as well as inside the fibers. In both cases the data were well predicted by the homogeneous model. No concentration polarization effects were found when the feed flowed inside the fibers. The inherent membrane separation capability appeared practically the same whether the feed was inside or outside the fibers. Internal pressurization did not damage the membrane performance for the low pressure range used. These findings enable the operation of asymmetric hollow‐fiber permeators with the feed inside the fiber lumen, which gives better separation in high stage cut situations.