Processes are disclosed for separating at least one gas from a gaseous feed mixture containing at least one other gas comprising passing the gaseous feed mixture to at least two permeator stages in series. Each permeator stage contains a separation membrane which has a feed side and a permeate exit side and exhibits selective permeation of the at least one gas as compared to the permeation of the at least one other gas of the gaseous mixture. A total pressure differential is maintained across the thickness of the separation membrane in each permeator stage to provide a driving force for the permeation of the at least one gas across the separation membrane. The ratio of total pressure on the feed side to total pressure on the permeate exit side of the separation membrane for at least one permeator stage is less than the ratio of total pressure on the feed side to total pressure on the permeate exit side of the separation membrane for at least one subsequent, i.e., downstream, permeator stage. The at least one gas of the gaseous feed mixture permeates through the membrane, and a permeating gas containing the at least one gas is obtained on the permeate exit side of each of the permeator stages. Between permeator stages, the non-permeating gas from one permeator stage is passed to the feed side of the next permeator stage.
Process and apparatus for the separation and purification of oxygen and nitrogen as well as a novel membrane useful therein are disclosed. The process utilizes novel facilitated transport membranes to selectively transport oxygen from one gaseous stream to another, leaving nitrogen as a byproduct. In the method, an oxygen carrier capable of reversibly binding molecular oxygen is dissolved in a polar organic membrane which separates a gaseous feed stream such as atmospheric air and a gaseous product stream. The feed stream is maintained at a sufficiently high oxygen pressure to keep the oxygen carrier in its oxygenated form at the interface of the feed stream with the membrane, while the product stream is maintained at a sufficiently low oxygen pressure to keep the carrier in its deoxygenated form at the interface of the product stream with the membrane. In an alternate mode of operation, the feed stream is maintained at a sufficiently low temperature and high oxygen pressure to keep the oxygen carrier in its oxygenated form at the interface of the feed stream with the membrane and the product stream is maintained at a sufficiently high temperature to keep the carrier in its deoxygenated form at the interface of the product stream with the membrane. Under such conditions, the carrier acts as a shuttle, picking up oxygen at the feed side of the membrane, diffusing across the membrane as the oxygenated complex, releasing oxygen to the product stream, and then diffusing back to the feed side to repeat the process. Exceptionally and unexpectedly high O.sub.2 /N.sub.2 selectivity, on the order of 10 to 30, is obtained, as well as exceptionally high oxygen permeability, on the order of 6 to 15.times.10.sup.-8 cm.sup.3 -cm/cm.sup.2 -sec-cmHg, as well as a long membrane life of in excess of 3 months, making the process commercially feasible.
In a process for the dehydration of gases by permeation through a membrane of selective permeability, the membrane comprises a bundle of hollow fibres based on polymers and open at both ends, the methane permeability of which is at least 10.sup.-5 cm.sup.3 /cm.sup.2.s.cm Hg and the water/methane selectivity factor of which is greater than about 100. The gas to be dehydrated is supplied under pressure to a chamber through which the fibres extend and water-enriched gas is withdrawn from the interiors of the fibres. The fibres have internal diameters of between 0.1 mm and 0.5 mm, lengths of between 0.5 m and 3 m and thicknesses of between 0.05 mm and 0.3 mm, the thickness of the active layer of the membrane being less than 1 .mu.m.
A process for separating and/or recovering gases from gas and/or gas vapor mixtures includes a membrane separating device to which a gas and/or gas vapor mixture is supplied, the latter being separated in the membrane separating device into a permeate, which is enriched with gas, and a retentate, which is depleted of gas. A first membrane separating device and a downstream second membrane separating device are provided, to which is supplied (at its inlet end) the retentate from the first membrane separating device, the first membrane separating device having a membrane which is selective for higher hydrocarbons in the gas and/or gas vapor mixture to be separated and in that the second membrane separating device has a membrane which is selected for gases of small molecular diameter.
Very high purity nitrogen is produced by air separation in a three stage membrane system in which the third stage permeate is recycled to the second stage and the membrane surface area is distributed between the stages to achieve high product recovery and process performance. Other gas separations, such as argon from oxygen, can likewise be achieved by thus using a three stage membrane system.
This method permits the production of at least two gaseous fluxes enriched in a permeable component from a gaseous mixture wherein the fluxes are considerably different, compared to the gaseous mixture. A first permeation unit (20) is supplied by the gaseous mixture feed. A second permeation unit (22) is supplied by the non-permeate produced by the first unit (20). The permeate produced by the second unit (22) which forms a first enriched flux is then sent to the third permeation unit (24) to form a second enriched flux.
