Solubility selectivity glassy polymers

So far, strong interest in highly selective glassy polymer membranes has been in academic laboratories. Despite abundant reports about newly synthesized polymers showing remarkable permselectivity, most of the polymers are not yet practical for gas separation applications. Their complicated synthetic routes and poor solubilities in... 

Table 4 contains some selected permeability data, including diffusion and solubility coefficients foT flavors in polymers used in food packaging. Generally, vtuylidene chloride copolymers and glassy polymers such as polyamides and EVOH are good barriers to flavor and aroma permeation, whereas the polyolefins are poor barriers. Comparison to Table 2 shows lhat the large-molecule diffusion coefficients are 1000 or more times lower tli an the small-molecule coefficients. 

Table 4.2 illustrates the various selectivity factors for some typical rubbery polymers, that is, silicone rubber, poly(dimethyl siloxane), and natural rubber, polyiso-prene, and a glassy polymer, polysulfone. Here, we consider the important 02/N2 pair and several pairs involving C02 that will be our focus later. In all the cases, the solubility selectivity is greater than unity and there is not a large difference between rubbery and glassy polymers. For most of these pairs, the diffusion selectivity is greater than unity, but there are some exceptions for C02/02 and C02/N2 that reflect... 

Comparative Permeability of C2, C3, and C4 olefins. It is interesting to compare permeability, diffusion, and solubility coefficients of various olefins, as well as ideal olefin/paraffin selectivity in a glassy polymer. Such comparison can be made,... 

Table I Mobility and solubility contributions to the permeability and selectivity of typical glassy polymers at 35°C for a 20 atm pressure of both components based on pure component parameters.

The unique behavior of cellulose acetate was supported recently by Koros (42). He found that of all glassy polymers Investigated, cellulose acetate had the highest solubility selectivity, defined as the ratio of the solubilities of two gases C0 and CH. Its extremely high solubility value of 8.9 measured at 35°C and 20 atm exceeds the values of the other polymers listed below by factors of... 

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