Isomer separation supported liquid membrane

The use of two types of liquid membranes is described in [302] liquid emulsion membranes (LEMs), and supported liquid membranes (SLMs), where isoparaffin or kerosene and their mixtures were used as organic phases. A surfactant of the type of Span 80 served as emulsifier. LEMs are used, for example, for selective separation of L-phenylalanine from a racemic mixture of L-leucine biosynthesis as well as conversion of penicillins to 6-APA (6-aminopenicillanic acid). SLMs have a higher stability. A number of their commercial applications have been studied, e.g. in separation of penicillin from fermentation broth, as well as in the recovery of citric acid, lactic acid and some aminoacids. Compared with other separation methods (ultrafiltration, ultracentrifugation and ion exchange), LEMs and SLMs are advantageous in the separation of stereospecific isomers in racemic mixtures. 

The separation has proved to be difficult, although methods based on supported liquid membranes with chiral selectors [165] and selective enzymatic oxidation to pyruvic acid have been reported [166]. Either the enantiomer selectivity is too low or the loss of raie of the lactate isomers is limiting. To overcome this, our group... 

Viji unya also studied the effect of some diol isomers as the liquid fillers in mixed-matrix membranes for gas separation. They incorporated 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and 2,3-butanediol liquid fillers into silicone rubber coating on top of the porous polysulfone support membrane. Similar to PEG liquid filler, it was found that 1,2-butanediol and 2,3-butanediol could improve propylene over propane selectivity. However, the selectivity of propylene over propane was not enhanced when 1,3-butanediol and 1,4-butanediol were added to silicone rubber. In PEG, the hydroxyl group is attached to each carbon atom on carbon backbones. A portion of 1,2- and 2,3-butanediol molecules are similar to PEG in which the hydroxyl groups are attached to the adjacent carbon atoms. In contrast, the hydroxyl groups in 1,3- and 1,4-butanediol molecules are not attached to the adjacent carbon atoms. Therefore, it was proposed that the position of hydroxyl groups of the butanediols plays an important role for the improvement of propylene over propane selectivity. 

Supported membrane concepts that were studied in the past 10 years include 5-p.m-thick dense Pd on supported y-alumina (Pacheco Tanaka et al., 2006), 10-p m-thick dense Lao.sSro.sCoOa.g for O2 purification (van der Haar, 2001), 60-nm thin amorphous silica for small gas molecule separation and water pervaporation (de Vos and Vetweij, 1998), >1 xm-thick MFI zeolite membranes for parajortho-xyicnc isomer separation (Caro et al., 2000), 0.4-2-p.m thick mesoporous y-alumina (Yu et al., 2006), and 4 p,m mesoporous C0AI2O4 for nanofiltration of liquids (Condom et al., 2006). 

We conclude from these results that the chiral structure of chitosan gels containing hydrophobic groups is effective in the hydrophobic separation and the resolution of optical isomers of D,L-amino acids. Further work will be applied to the separation of D,L-amino acids and peptides by liquid column chromatography, using chemically modified chitosan as stationary phase. In addition, the information about equilibrium sorption obtained from the present investigation is to be expected for supports of immobilized enzymes and separation membranes. 

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