Gas separation membrane system

The more permeable component is called the fast gas, so it is the one enriched in the permeate stream. Permeabihly through polymers is the product of solubility and diffusivity. The diffusivity of a gas in a membrane is inversely proportional to its kinetic diameter, a value determined from zeolite cage exclusion data (see Table 20-26 after Breck, Zeolite Molecular Sieves, Wiley New York, 1974, p. 636). Tables 20-27, 20-28, and 20-29 provide units conversion factors useful for calculations related to gas-separation membrane systems. 

In the 1940s to 1950s, Barrer [2], van Amerongen [3], Stem [4], Meares [5] and others laid the foundation of the modem theories of gas permeation. The solution-diffusion model of gas permeation developed then is still the accepted model for gas transport through membranes. However, despite the availability of interesting polymer materials, membrane fabrication technology was not sufficiently advanced at that time to make useful gas separation membrane systems from these polymers. 

How well economically a gas separation membrane system performs is largely determined by three parameters. The first parameter is its permselectivity or selectivity toward the gases to be separated. Permselectivity affects the percentage recovery of the valuable gas in the feed. For the most part, it is a process economics issue. The second is the permeate flux or permeability which is related to productivity and determines the membrane area required. The third parameter is related to the membrane stability or service life which has a strong impact on the replacement and maintenance costs of the system. 

Gas separation membrane systems offer several advantages, these are reliability, flexibility, high efficiency, low cost, quiet, reliable and simple operation over broad operating conditions (temperature up to 90 °C and pressure up to 8000 kPa). 

One unique appHcation area for PSF is in membrane separation uses. Asymmetric PSF membranes are used in ultrafiltration, reverse osmosis, and ambulatory hemodialysis (artificial kidney) units. Gas-separation membrane technology was developed in the 1970s based on a polysulfone coating appHed to a hoUow-fiber support. The PRISM (Monsanto) gas-separation system based on this concept has been a significant breakthrough in gas-separation... 

In the system N2/O2, the ABS membrane shows a high selectivity. This property makes this polymeric material attractive as a gas separation membrane for N2 and O2 at moderate temperatures. 

FIGURE 9.3 Dependence of Henry s solubility coefhcient on Van der Waals volume of penetrant molecules for the systems of natural mbber/hydrocarbons. (From Semenova, S.I., Membranes in Russian), 13, 37, 2002 Baker, R.W. and Wijmans, J.G., Membrane separation of organic vapors from gas streams. In Paul D, Yampolskii Yu, Eds., Polymeric Gas Separation Membranes. CRC Press, 1994 353-397 Crank, J. and Park, G., Ed., Diffusion in Polymers. London, Academic Press, 1968.)... 

Ishida, T. et al., R D of compact detritiation system using a gas separation membrane module for the secondary confinement, Fus. 

Ultrafiltration (UF) and microfiltration (MF) membranes can be made on less sophisticated supports. The simplest MF tubular membrane consists of an extruded porous tube (layer 1) as a support coated on the inside or outside with a macroporous layer (layer 2) which serves as the functional filtration layer. The support system shown in Fig. 6.3 is in fact a sophisticated UF or Knudsen gas separation membrane. For less demanding applications a 2-layer support could also be used. 

The hydrogen dissociation rate for some oxides of relevance to hydrogen gas separation membranes is presented as a function of the inverse absolute temperature in Fig. 1.8. Data for the H2 dissociation rate on Ni is included for comparison. As seen from the systems where both doped and undoped materials have been measured, doping generally increases the rate of dissociation. 

D.R. Paul and Yuri P. Yampol skii, Polymeric Gas-separation Membranes, Chapter 8, R.W. Baker and J.G. Wij-MANS, Membrane Separation of Organic Vapors from Gas Systems., CRC Press, 1994, p. 353 397. 

---