Mixed-gas permeation

Implications of the Dual-Mode Sorption and Transport Models for Mixed Gas Permeation... 

When the gas or vapor feed stream contains a component that is highly soluble in the polymer membrane and causes plasticization, then the selectivity as defined by Equation 4.6 will depend on the partial pressure or the amount of the plasticizing component sorbed into the membrane. Furthermore, pure-gas permeation measurements are generally not a good indicator of the separation performance, and mixed-gas permeation measurements will be needed [21-23]. Often, the mixed-gas selectivity is less than predicted from pure-gas measurements [8] however, the opposite has been observed [24], Competitive sorption effects can also compromise the prediction of mixed-gas behavior from pure-gas measurements [25], For gas pairs where each component is less condensable than C02, like 02/N2, it is generally safe to conclude that the selectivity characteristics can be accurately judged from pure-gas permeabilities at all reasonable pressures. When the gas pair involves a component more condensable than C02, plasticization is likely to be a factor and pure-gas data may not adequately reflect mixed-gas selectivity. When C02 is a component, the situation depends on the partial pressures and the nature of the polymer. 

Chem RT, Koros WJ, Sanders ES, Chen SH, and Hopfenberg HB. Implications of dual mode sorption and transport for mixed gas permeation. In Whyte T, Yon CM, and Wagener EH, eds. ACS Symposium Series 223 on Industrial Gas Separations. Washington DC American Chemical Society, 1983, pp. 47-73. 

Javaid A and Ford DM. Solubility-based gas separation with oligomer-modified inorganic membranes. Part II Mixed gas permeation of 5 nm alumina membranes modified with octadecyltrichlorosilane. J. Membr. Sci. 2003 215 157-168. 

Pinnau I and He Z. Pure- and mixed-gas permeation properties of polydimethylsiloxane for hydrocarbon/methane and hydro-carbon/hydrogen separation. J Membr Sci 2004 244 227-233. 

R. T. Chem, "Measurements and Modeling of Mixed Gas Permeation through Glassy Poly-... 

Fig. 12.11 SEM image of PdAu membrane GTC-31 after several hundred hours of pure and mixed gas permeation testing...

A scanning electron microscope image of the surface of membrane GTC-30 after several hundred hours of pure and mixed gas permeation testing is shown in Fig. 12.16. The EDAX spectrum and tabulated composition data for this membrane is shown in Fig. 12.17. The composition of GTC-30 is 94mass% Pd and 6mass% Cu. 

Table 7.5 Mixed gas-permeation properties of PTMSP and PMP. Feed 2% butane in methane, feed pressure 10 bar, permeate pressure atmospheric, temperature 25 °C. From I. Pinnau et al. In Polymer Membranes for Gas and Vapor Separation, ACS Symposium Series 733 (1999), 56-67.

Thomas S, Pinnau I, Du N et al (2009) Hydrocarbon/hydrogen mixed-gas permeation properties of PIM-1, an amorphous microporous spirobisindane polymer. J Membr Sd 338 1 ... 

Equation (17-8) is the operating equation for the well-mixed gas permeator. The ratio 0 = (Fp/F. known as the cut, is an important operating parameter. The RT Eq. fl7-6al and the operating Eq. (17-8) are the two equations needed to solve problems with perfectly mixed, binary gas permeators. This is illustrated in Example 17-1 when yp is known and in Example 17-2 when 0 is specified. 

A perfectly mixed gas permeation module is separating carbon dioxide from nitrogen using a poly (2,6 - dimethylphenylene oxide) membrane. The feed is 20.0 mol% carbon dioxide and is at 25 °C. The module has 50.0 m of membrane. The module is operated with a retentate pressure of 5.5 atm and a permeate pressure of 1.01 atm. We desire a permeate that is 40.0 mol% carbon dioxide. The... 

Figure 17-7. Solution for well-mixed gas permeation system for Example 17-2...

Exanq)le 17-3. Multicoiiq)onent, perfectly mixed gas permeation... 

A perfectly mixed gas permeation unit is separating a mixture that is 20 mol% carbon dioxide, 5 mol% oxygen and 75 mol% nitrogen using a poly(dimethylsiloxane) membrane at 25°C. Feed flow rate is 20,000 cm (STP)/s. The membrane thickness is 1 mil (0.00254 cm). Pressure on the feed side is 3.0 atm and on the permeate side is 0.40 atm We desire a cut fraction = 0.225. Find the membrane area needed, and the outlet mole fracs of permeate and retentate. 

For moderate transmembrane pressure difference, that is, up to about 650 kPa, and for temperatures not higher than 400°C the microstructured metallic plate having straight channels 200-500 pm wide provided good mechanical support even for the thinnest membranes tested. Moreover, mixed gas permeation experiments revealed that concentration polarization effects are expected to be subordinate [129]. 

J. Xia, T.-S. Chung, D.R. Paul, Physical aging and carbon dioxide plasticization of thin polyimide films in mixed gas permeation. Journal of Membrane Science 450 (2014) 457-468. 

Swaidan et al. investigated the mixed gas permeation through the TR-PBO membranes (Figure 5.53). In their investigation, they used polyimide with... 

Although extensive data for mixed-gas permeation in the plasticization regime are not available, good pure-gas values are available and illustrate some important points. The permeability of CO2 in various substituted polycarbonates shown in Figure 28 (111) increases with pressure above a certain characteristic value for each of the polymers. The shapes of the permeability curves are like the curve shown schematically in Figure 21. Plasticization occurs despite the fact that the downstream pressure is maintained at a vacuum of less than 1330 Pa (10 mm Hg). To determine when true transport plasticization occurs, the local diffusion coefficient Dap(Ca), which measures the ability of a penetrant to move through the membrane at a point where the local concentration of penetrant is equal to Ca, must be considered. The sorption isotherms for CO2 in the various materials are shown in Figure 29 (111), and application of the standard... 

Mixed gas permeation is shown in Fig.7. Sample A has high permeation rate of... 

Figure 8.15a, b displays the density profiles in the M-region (region shadowed gray) for (a) pure and (b) mixed gas permeation throngh the pore A of the DP carbon membrane (see Fig. 8.12a). There are three peaks that correspond to the deepest potential energy regions shown in Fig. 8.13a The peaks for (broken line) is higher...

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