Biochemical separations, LEMs

In terms of the amount of literature developed, biochemical separations have been largely ignored by those in the field of LEM-mediated separations. One application that has enjoyed some experimental scrutiny is that of the use of LEMs in drug delivery and overdose prevention systems. They have been used to separate or release several different types of drugs including acetylsalicyclic acid (18), phenobarbital (19), and several barbiturates (20,21). 

LEM systems have also been shown to be successful in separating commodity-type biochemicals such as propionic acid (10) and acetic acid (10,22) and have been used for the preparation of L-amino acids from racemic D,L mixtures by means of enzymatic hydrolysis of amino acid esters (23). In addition to biochemical separations, the work of Mohan and Li showed that enzymes could be encapsulated in liquid emulsion membranes with no deleterious effect on enzyme action (24). Later work by these authors indicated that encapsulated live cells could remain viable and function in the LEM interior phase for period as long as five days (25). 

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. 

It should be noted that these pilot plant studies indicated that LEM processes were as economically advantageous, if not more so, than currently employed solvent extraction and conventional ion exchange techniques. Unfortunately, LEM-mediated separations of biochemicals have not been carried out on a pilot plant scale. 

These various uses of liquid emulsion membranes show the versatility of LEM-mediated separations and point to possible applications of liquid emulsion membranes in the biochemicals field. 

The versatility of LEMs is clear. From the encapsulation of living cells to the removal of toxic or inhibiting substances, and in their use as a downstream process, liquid emulsion membranes remain a powerful and, as of yet, virtually untapped resource for biochemical engineers. The ability of LEMs to separate and concentrate amino acids demonstrated here gives strength to this observation, and it is anticipated that these systems will enjoy increasing attention in the years to come. 

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