Introduction to Gas Separation Membrane Technology

Gas separation membranes are a rapidly developing new technology in recent years. Different polymer membranes have varying permeability and selectivity for different types of gas molecules, allowing for the selective separation of specific gases from gas mixtures. Examples include collecting oxygen from air, recovering hydrogen from ammonia synthesis tail gas, and separating hydrogen and carbon monoxide from petroleum cracking mixtures. Chemists at UCLA have created a thin film using a conductive organic material called polyaniline. This polymer can be doped with charged atoms, and the permeability of the membrane can be altered by adjusting the amount of dopant. Oxygen passes through this membrane faster than nitrogen, carbon dioxide faster than methane, and hydrogen faster than nitrogen, making the production of oxygen and nitrogen using this membrane inexpensive. These membranes may also be used to remove pollutants from automotive and industrial exhaust. Currently, research on gas separation membranes mainly focuses on oxygen-enriched membranes. The polymers used in oxygen-enriched membranes must possess both high permeability and high selectivity. General Electric uses a copolymer of polycarbonate and silicone as a separation membrane, achieving 40% oxygen-enriched air after a single stage of separation. Replacing ordinary air with oxygen-enriched air would significantly improve the efficiency of various combustion devices and reduce pollution. A new underwater breathing apparatus is being developed abroad, a diving device that extracts dissolved oxygen directly from seawater. It works by immersing oxygen-carrying heme from a person in a polyurethane sponge. As the heme absorbs oxygen from the seawater, a weak electric current releases the oxygen, allowing for underwater breathing. A single diving device containing 900 grams of heme could sustain a person in seawater for extended periods.