Membrane liquid emulsion, amino acid

In order to develop the liquid membrane techniques, i.e., emulsion Hquid membrane (ELM), supported liquid membrane (SLM), non-dispersive extraction in hollow fiber membrane (HFM), etc., for practical processes, it is necessary to generate data on equilibrium and kinetics of reactive extraction. Furthermore, a prior demonstration of the phenomena of facilitated transport in a simple liquid membrane system, the so-called bulk liquid membrane (BLM), is thought to be effective. Since discovery by Li [28], the liquid membrane technique has been extensively studied for the separation of metal ion, amino acid, and carboxyHc acid, etc., from dilute aqueous solutions [29]. 

Solvent extraction of penicillin from fermentation broths has been well documented in the literature. Penicillin G and penicillin V can be efficiently extracted with amyl acetate or butyl acetate at pH 2.5-3.0 and at 0° to 3°C.33 Schiigerl1 systematically reviewed solvent extraction of different forms of penicillin from fermentation broths. Figure 1 shows an integrated process for the extraction of penicillin G from clarified broth of Penicillium chryso-genurn fermentation.1 Penicillin G is converted to 6-amino penicillanic acid and phenylacetic acid at pH 8 in a 10 L Kiihni extractor by penicillin G-amidase immobilized in an emulsion liquid membrane. The 6-amino penicillanic acid is subsequently converted to ampicillin at pH 6 and the enzyme is recycled. 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

Thien, M. P. " Separation and Concentration of Amino Acids Using Liquid Emulsion Membranes", Doc. of Sci. Thesis, M.I.T., 1988. 

Dzygiel, P. and Wieezorek, P. (2000). Extraction of amino acids with emulsion liquid membranes using industrial surfactants and lecithin as stabilizers. J. Membr. Sci., 172, 223-32. 

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. 

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). 

Amino Acid Recovery Using Liquid Emulsion Membranes... 

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. 

A recent study with biotechnology applications relates to amino acid extraction. Schugerl and co-workers (71 ) used a quaternary ammonium carrier in an emulsion liquid membrane system for enzyme catalyzed preparation of L-amino acids. Frankenfield et al. (72) discuss a wide variety of biomedical ELM applications including enzyme encapsulation, blood oxygenation, and treatment of chronic uremia. 

Thien MP, Hatton TA, Wang DIG (1988) Separation and concentration of amino acids using liquid emulsion membranes. Biotechnol Bioeng 32 604 - 615... 

Various substances such as amino acids, organic acids, NaOH, NaCl, carbon dioxide, oxygen, metals, and various ions, such as Cd(II), Cu(II), Co(II), and Fe(III), can be separated by using suitable carrier agents in liquid or solid composite membranes. Liquid membranes behave like double liquid-liquid extraction systems where the usage of organic solvent is minimized. Such devices are generally prepared as bulk liquid, emulsion liquid, and supported liquid membranes. 

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