In a membrane separation process, which gas is primarily allowed to flow through the membrane?

In a membrane separation process, the primary gas that is allowed to flow through the membrane is typically oxygen. This is due to the design of the membranes, which are often engineered to selectively allow certain molecules or gases to pass based on their size, solubility, or affinity for the membrane material.

Oxygen has a smaller molecular size compared to some other gases and often has a higher permeability through the membrane. This selectivity is particularly useful in applications such as gas enrichment processes, where increasing the concentration of oxygen is desired without allowing larger molecules or less permeable gases, such as nitrogen, to pass through as readily.

In contrast, gases like nitrogen or carbon dioxide may be restricted by the membrane's characteristics or the specific design aimed at maximizing the flow of oxygen. Helium, while small and often used in some specific applications, is not typically the primary focus of oxygen separation processes.