Separation of a helium‐methane mixture in permeators with two types of polymer membranes

The separation of a HeCH 4 mixture containing 9.95 mol% He in permeator modules that incorporate two different types of polymer membranes was studied theoretically and experimentally. The membranes were symmetric dense capillaries of silicone rubber and asymmetric hollow fibers of cellulose triacetate. These membranes exhibit reverse selectivities for He and CH 4 , silicone rubber being more permeable to CH 4 , and cellulose triacetate more permeable to He. The simultaneous use of these two types of membranes in a permeator enhances the enrichment and recovery of He compared to the levels obtained with a single‐membrane permeator utilizing either membrane alone. The experimental results were found to confirm the theoretical predictions, the agreement being better at the lower stage cuts.