Aqueous organic solution permeation

Table IV presents the comparative data on the permeation rates of the three types of membranes with two different porosities for various aqueous organic solutions and for pure water as measured over the duration of the study. The data shown here represent the relative chronological order in which the samples were tested. In the beginning, even though the percent rejection of NaCl is high for PA and CAc (indicating small-size pores), the rates of permeation of pure water are higher for denser membranes than for membranes having lower percent rejection of NaCl. In the case of the PBI membrane, the reverse of this phenomenon is observed.

Figure 17.12 Comparison of simulated values with real values in permeation of aqueous organic solution.

Size exclusion chromatography (SEC), also called gel filtration when the mobile phase is aqueous, and gel permeation (GPC) when the mobile phase is organic, is based on the differing degrees of penetration of the sample molecules into the pores of the stationary phase (Fig. 7.1). These pores must have a diameter similar to the size of the species to be separated when these species are in solution in the mobile phase (Fig. 7.5). 

Knapp et al. (2009) introduced polynorbomene PV membrane film for the separation of organics (butanol) from water. Wang et al. (2005) used the carbazole-functionalized norbornene membrane for the separation of aqueous alcohol solution by PV. A higher separation factor and lower permeation rate were achieved for a higher-molecular-weight alcohol. 

Macroporous polyvinyl alcohol particles with a molecular weight cutoff of ca. 8 X 10 in gel-permeation chromatography have been prepared. The particles are produced by first dispersing an aqueous solution of polyvinyl alcohol in an organic solvent to make spheres of polyvinyl alcohol solution. Holding the dispersion in such a state that a gel will then form spontaneously will cause the gel to react with glutaraldehyde in the presence of an acidic catalyst (85). 

Size exclusion was first noted in the late fifties when separations of proteins on columns packed with swollen maize starch were observed (Lindqvist and Storgards, 1955 Lathe and Ruthven, 1956). The run time was typically 48 hr. With the advent of a commercial material for size separation of molecules, a gel of cross-linked dextran, researchers were given a purposely made material for size exclusion, or gel filtration, of solutes as described in the classical work by Porath and Flodin (1959). The material, named Sephadex, was made available commercially by Pharmacia in 1959. This promoted a rapid development of the technique and it was soon applied to the separation of proteins and aqueous polymers. The work by Porath and Flodin promoted Moore (1964) to apply the technique to size separation, gel permeation chromatography of organic molecules on gels of lightly cross-linked polystyrene (i.e., Styragel). 

Exclusion chromatography is a technique for separating molecules based on their effective size and shape in solution. The technique is often called gel permeation chromatography if used with organic solvents or gel filtration if used with aqueous solvents. 

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