An internally staged hollow‐fiber permeator for gas separation

Conventional membrane permeation of gases employ a non‐step process between the feed and the product on two sides of a membrane. By applying the overall driving force change through a two‐step process using two membranes in one device, we illustrate theoretically the possibility of achieving a much higher enrichment without any extra energy consumption. Such an internally staged permeation is experimentally carried out in a hollow‐fiber permeator with two sets of asymmetric cellulose acetate hollow fibers for the systems of O₂N₂ (air) and CO₂N₂. The superior enriching performance of the internally staged permeator over the same permeator operated in the conventional mode is demonstrated experimentally. A cocurrent flow pattern is found to be superior to a countercurrent flow pattern for the conditions employed. The simulation model incorporating fiber lumen pressure drop predicts the experimental performance quite well. A further improvement in performance can be achieved by recycling the intermediate pressure shell reject stream to the feed stream. The energy requirement in an internally staged permeator without recycle is less than that of a conventional permeator with permeate recycle.