Inorganic chemicals permeation

Appendix IV Permeation of Organic and Inorganic Chemicals Through Fluoroplastic Films... 

The inorganic chemical industry has a use for such brines, e.g., NF permeate (RO concentrate in Lagoon 2) for chlorine production. Another potential use is NF concentrate (Lagoon 1) for Mg production. A high market value of the brine streams from... 

A fundamental property of fluoropolymers is their resistance to organic and inorganic chemicals (Fig. 12.1). Increased content of fluorine enhances the chemical resistance of the polymer. The overwhelming majority of the applications of fluoropolymers take advantage of their inertness to chemicals. Chemical properties of fluoropolymers are not affected by fabrication conditions. Another aspect of the interaction of these plastics with chemicals is permeation. Even though a reagent may not react with a fluoropolymer, it may be able to permeate through the polymer structure. The extent and rate of permeation is dependent upon the structure and properties of the plastic article as well as the type and concentration of permeant. Temperature and pressure usually influence the permeation process. This chapter reviews chemical compatibility of fluoropolymers and their permeation behavior towards different chemicals. 

This review addresses the issues of the chemical and physical processes whereby inorganic anions and cations are selectively retained by or passed through cell membranes. The channel and carrier mechanisms of membranes permeation are treated by means of model systems. The models are the planar lipid bilayer for the cell membrane, Gramicidin for the channel mechanism, and Valinomycin for the carrier mechanism. 

The permeability data in Table 7.10 and other data show that the polarity of the substituent group on the polymer backbone (such as poly[bis(phenoxy)phosphazene] or PPOP) has a significant impact on the membrane permeability. The more polar gas (i.e. S02) the more easily it permeates a polar polymer (i.e., m-F-PPOP) and a less polar gas (i.e., CO2) exhibits a lower permeability through a more polar membrane (i.e., SO3-PPOP). This seems to provide a vast opportunity for chemically designing an inorganic polymer membrane for a particular separation application [Peterson et al., 1993]. 

Size-exclusion chromatography (SEC) differs from the other methods in that the separation is based on physical sieving processes and not on chemical phenomena. The stationary phase is chemically inert and there is selective diffusion of solute molecules into and out of the mobile phase-filled pores in a three-dimensional network which may be a gel or a porous inorganic solid. The degree of retention is dependant on the size of the solvated solute molecule relative to the size of the pore. Smaller molecules will permeate the smaller pores, intermediate-sized molecules will permeate some pores and... 

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