Hydrogen separation polyimide membranes

Labrune, D. et al.. Separation of hydrogen isotopes from nitrogen with polyimide membrane, Fus. Technol, 28, 676, 1995. 

Du Pom, a leader in reverse osmosis technology built aronnd a unique class of tailored aromeik polyamides, was also an early leeder in the gas separation field.27,1 14,16 Molecuiariy engineered arometic polyimides were found by Du Pont to provide extraordinarily good flux and selectivity properties For hydrogen separations.27 Posttreataiem processes for these membranes were not reported. 

Since 1983, newer systems for hydrogen separations have appeared. Ube Industries, Ltd. announced the development of a polyimide resin in hollow fiber membrane form for H2 /Ci separations.11 12 Commercial production of this membrane and the engineering of skid mounted units were to begin in the fall of 1985.13... 

The polyimide membrane is reported to be capable of operating at temperatures up to 150°C compared to upper limits of 100°C for PR ISM separators and 60°C for cellulose acetate.46 Permeabilities increase with temperature while selectivities normally drop. The second way to overcome the lower permeabilities is to operate the Ube system at higher temperatures than possible with polysulfone or cellulose acetate. Even at the high temperatures, the polyimide selectivity will remain high enough for the abovementioned hydrogen separations. Thus, one expects the Ube system to be competitive with PRISM separators for many hydrogen applications. 

In the past, the available membranes lost a significant fraction of their selectivity when operated at these high temperatures. They also became plasticized by absorbed heavy hydrocarbons in the feed gas. As a consequence, a number of early hydrogen-separation plants installed in refineries had reliability problems. The development of newer polyimide and polyaramide membranes that can safely operate at high temperatures has solved most of these problems and the market for membrane-based hydrogen-recovery processes in refineries is growing. 

Commercial membranes for CO2 removal are polymer based, and the materials of choice are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-erimide [12]. The most tested and used material is cellulose acetate, although polyimide has also some potential in certain CO2 removal applications. The properties of polyimides and other polymers can be modified to enhance the performance of the membrane. For instance, polyimide membranes were initially used for hydrogen recovery, but they were then modified for CO2 removal [13]. Cellulose acetate membranes were initially developed for reverse osmosis [14], and now they are the most popular CO2 removal membrane. To overcome state-of-the-art membranes for CO2 separation, new polymers, copolymers, block copolymers, blends and nanocomposites (mixed matrix membranes) have been developed [15-22]. However, many of them have failed during application because of different reasons (expensive materials, weak mechanical and chemical stability, etc.). 

Monsanto and Ube (Japan) developed membrane processes for purification of hydrogen gas mixtures. This process is based on the selective diffusion of hydrogen through semi-permeable membranes in the form of hollow fibers. The Monsanto PRISM separator process (owned by Air Products as of 2004) uses a polysulfone fiber whereas Ube uses an aromatic polyimide fiber.46... 

Aromatic polyimides, containing trifluoromethyl groups, have been used to separate hydrogen over carbon monoxide, with a-values of 26-66 and hydrogen over methane with a-valves of 73-380.160 An a-valve of 22 was obtained with a membrane of a copolymer of methyl methacrylate and tris (trimethylsiloxy) y (met ha cry loxy)propyl] silane, in a process estimated to cost only 40% of the cost of the present cryogenic distillation.161... 

A number of woiks published recently concern the application of polymeric GS manbranes for separation of hydrogen isotopes, with particular consideration of tritium compounds (HT, HTO) [202-212]. For this purpose, membranes manufactured from glassy and amorphous polymers are applied, mainly polyimide and polycarbonate membranes, as well as polyphenylene oxide membranes assembled in modules of different configuration (e.g., McGeneron Inc., type B210 ... 

Hosseini, S.S. and Chung, T-S. 2009. Carbon membranes from blends of PBI and polyimides for N2/CH4 and CO2/CH4 separation and hydrogen purification, 328 ... 

Since the early 1980s, membrane technology has advanced rapidly and continues to advance. In addition to cellulose acetate and polysulfone, the polymers used in making gas separation membranes include polyimides, polyamides, polyaramid, polydimethylsiloxane, silicon polycarbonate, neoprene, silicone rubber, and others. Today membranes can be designed to withstand a 2,000 psi pressure differential. Membranes used in hydrogen or carbon dioxide applications operate at temperatures up to 200°F, while those used in solvent applications can operate at temperatures up to about 400°F (Baker, 1985). 

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