Glassy polymers, membranes

Dual-Mode Gas Sorption and Diffusion in Glassy Polymer Membranes. 97... 

So far, it appears that the gas transport properties of glassy polymer membranes, manifested in a decreasing P(a), or increasing D(C), function can be adequately represented by the above dual diffusion model with constant diffusion coefficients Dl5 D2 (or Dtj, DX2). We now consider the implications of this model from the physical point of view ... 

The above results indicate that the general characteristics of gaseous diffusion in glassy polymer membranes can be represented reasonably well in terms of the dualmode concept. The basic reason for the observed increasing D(C) function is seen to be the concurrent increasing proportion of less strongly sorbed (and hence more easily activated) penetrant molecules. The model is, no doubt, highly idealized, but is nevertheless shown to be physically reasonable and consistent with the correspond-... 

J.Y. Park and D.R. Paul, Correlation and Prediction of Gas Permeability in Glassy Polymer Membrane Materials via a Modified Free Volume Based Group Contribution Method, J. Membr. Sci. 125, 29 (1997). 

The above-mentioned inverse selectivity/permeability relationship of polymers has been summarized by Robeson by means of log-log plots of the overall selectivity versus the permeability coefficient, where A is considered to be the more rapidly permeating gas. These plots were made for a variety of binary gas mixtures from the list He, H2, O2, N2, C02, and CH4, and for a large number of rubbery and glassy polymer membranes. Such representations, shown in Fig. 8 and Fig. 9 are often referred to as upper bound plots (Robeson, 1991). The upper bound lines clearly show the inverse selectivity/permeability relationship of polymer membranes. While these plots were prepared in 1991, only small advances have been made to push the upper bound higher since that time. 

S. The diffusion coefficients of gases in glassy polymer membranes are strong functions of the penetrant gas concentration in the membranes (or of the gas pressure), and depend also on polymer morphology (crystallinity, orientation), crosslinking, and chain mobility. The chain mobility depends, in turn, on the polymer free volume, the... 

Park, J. Y., and Paul, D. R. (1997). Correlation and prediction of gas permeability in glassy polymer membrane materials via a modified free volume based group contribution method, J. Membrane Sci. 125, 23. 

Semenova SI, Smirnov SI, and Ohya H. Performances of glassy polymer membranes plasticized by interacting penetrants. J Membr Sci 2000 172 75-89. 

M. E. Rezac, J. D. Le Roux, H. Chen, D. R. Paul, and W. J. Koros, Effect of mild solvent post-treatments on the gas transport properties of glassy polymer membranes. Journal of Membrane Science 90, 213-229 (1994). 

When the interaction between one penetrant and the polymer is not affected by the presence of another penetrant, the pure-component permeabilities of the two penetrants in the mixture can be used in Equation 7. For rubbery polymers at low penetrant partial pressures, this assumption of independent-permeation appears satisfactory (19-20). It does not, however, appear to hold in general for glassy polymer membranes (12,13,21-25). Moreover, it also has been shown that plasticization of both rubbery (26) and glassy (27) polymers can occur at higher penetrant activities. 

Huang, Y, and Paul, D. R., Effect of film thickness on the gas-permeation characteristics of glassy polymer membranes, Ind. Eng. Chem. Res., 46, 2342-2347 (2007b). 

A. Bos, High pressure CO2/CH4 separation with glassy polymer membranes, PhD Thesis, Twente, 1996. 

It is known that glassy polymer membranes can have a considerable size-sieving character, reflected mainly in the diffusive term of the transport equation. Many studies have therefore attempted to correlate the diffusion coefficient and the membrane permeability with the size of the penetrant molecules, for instance expressed in terms of the kinetic diameter, Lennard-Jones diameter or critical volume [40]. Since the transport takes place through the available free volume in the material, a correlation between the free volume fraction and transport properties should also exist. Through the years, authors have proposed different equations to correlate transport and FFV, starting with the historical model of Cohen and Turnbull for self diffusion [41], later adapted by Fujita for polymer systans [42]. Park and Paul adopted a somewhat simpler form of this equation to correlate the permeability coefficient with fractional free volume [43] ... 

D.L. Gin, R.D. Noble, Ending aging in super glassy polymer membranes, Angewandte Che-mie 126 (2014) 5426-5430. 

H2-selective rigid glassy polymer membranes (occoj/Hj =10, at room temperature) this type of glassy membrane increases the selectivity as the temperature increases at 150°C, acOj/Hj = 15 was considered. 

Poly(4-methyl-2-pentyne) [PMP] is a glassy, disubstituted, purely hydrocarbon-based polyacetylene. PMP has a density of only 0.78 g/cm and a high fractional free volume of 0.28. The polymer has very high hydrocarbon permeabilities for example, the /i-butane permeability of PMP in a mixture of 2 mol% n-butane in methane is 7,500 X lO l cm3(STP) cm/cm2 s cmHg at 25 C. In contrast to conventional, low-free-volume glassy polymer membranes, PMP is significantly more permeable to n-butane than to methane in gas mixtures. In this paper, we present the gas permeation properties of PMP in mixtures of -butane with methane. The mixed-gas permeation and physical aging properties of PMP are compared to those of poly(l-trimethylsilyl-l-propyne), the most permeable polymer known. 

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