Swelling, LEMs

Applications of liquid emulsion membranes (LEMs) to biomedical and biochemical systems are reviewed and other potential applications identified. The LEM-mediated downstream processing of small, zwitterionic biochemicals (e.g. amino acids) is examined using chloride ion counter-transport to separate and concentrate the amino acid phenylalanine from stimulated fermentation broth. The effect of agitation rate and osmotic swelling of membranes on separation is shown to be significant. 

In spite of the potential problems of swelling and breakage, LEMs have been tested on the pilot plant scale with good results (2,9,11, 12), and will soon be used for the commercial separation of zinc from Viscose wastewater from rayon and cellophane processing (13). 

Ion exchange membranes (lEMs) have recently been studied as a means for overcoming the above problems (A). The carrier is the counter ion in the lEM. The carrier is bound in the membrane by ionic charge forces. The lEM is a nonporous polymer which is swelled by the solvent. Because the lEM is nonporous, no "short circuiting" occurs if the membrane loses solvent. The carrier also remains bound in the membrane. The membrane can be resolvated and continue performing without a loss in capacity... 

Field Test 1. The copper extractions from all three solutions were very good 98.0, 95.7, and 91.6 percent, respectively. Membrane swell was only 5.3 percent for the first solution and 11.1 and 11.4 percent for the final two solutions. The higher swell in the last two solutions was related to a design flaw (too much flow resistance between the extraction units and the settler at high flow rates) that resulted in the need to operate the extraction mixers at higher than desired speeds. (This problem was corrected before the second field test.) All three of the solutions that were fed to the LEM system contained more iron than copper. For example, the Cu/Fe ratios were 0.81 for the PLS, 0.29 for the 520 ppm solution, and 0.19 for the 320 ppm solution. The same copper internal... 

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