Supported liquid membrane acidic extractants

The production process for (S)-phenylalanine as an intermediate in aspartame perpetuates the principle of reracemization of the nondesired enantiomer (Figure 4.5) in a hollow fiber/ liquid membrane reactor. Asymmetric hydrolysis of the racemic phenylalanine isopropylester at pH 7.5 leads to enantiopure phenylalanine applying subtilisin Carlsberg. The unconverted enantiomer is continuously extracted via a supported liquid membrane [31] that is immobilized in a microporous membrane into an aqueous solution of pH 3.5. The desired hydrolysis product is charged at high pH and cannot, therefore, be extracted into the acidic solution [32]. 

T0174 Commodore Separation Technologies, Inc., Supported Liquid Membrane T0176 Concurrent Technologies Corporation, Acid Extraction Treatment System (AETS)... 

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]. 

Knutsson M, Lundh J, Mathiasson L, Jdnsson JA, and Sundin P. Supported liquid membranes for the extraction of phenolic acids from circulating nutrient solutions. Anal. Lett. 1996 29 1619-1635. 

Shen Y, Grbnberg L, and Jonsson JA. Experimental studies on the enrichment of carhoxylic acids with tri- -octyphosphine oxide as extractant in a supported liquid membrane. Anal. Chim. Acta 1994 292 31-39. 

Supported liquid membranes comprised the bulk of the published literature on the transport studies of metal ions across thin polymeric films [16,56-59]. Several literature reports on actinide transport across supported liquid membranes using various types of extractants viz., acidic extractants, neutral extractants and amine extractants are discussed below. 

Ho, W.S. and Wang, B., Inventors Commodore Separation Technologies Inc., Assinee. Combined supported liquid membrane/stripping dispersion process for removal and recovery of metals Dialkyl monothiophosphoric acids and their use as extractants, US Patent... 

Dzygiel, P., Wieczorek, P., Mathiasson, L., Jonsson, J. A. (1998). Enrichment ofamino acids by supported liquid membrane extraction using Aliquat 336 as a carrier. Anal. Lett., 31, 1261-74. 

Zhao, G., Liu, J.-F., Nyman, M., Jonsson, J. L. (2007). Determination of short-chain fatty acids in serum by hoUow fiber supported liquid membrane extraction coupled with gas chromatography. J. Chromatogr. B, 846, 202-8. 

Schafer, A., Hossain, M. M. (1996). Extraction of organic acids from kiwifruit juice using a supported liquid membrane process. Bioprocess Biosyst. Eng., 16, 25-33. 

Rathore, N. S., Leopold, A., Pabby, A.K., Fortuny, A., Coll, M.T., Sastre, A. M. (2009). Extraction and permeation studies of Cd(II) in acidic and neutral chloride media using Cyanex 923 on supported hquid membrane. HydrometaUurgy 96 81-87. Uedee, E., Ramakul, P., Pancharoen, U., Lothongkum, A. W. (2009). Performance of hoUow fiber supported liquid membrane on the extraction of mercury(n) ions. Korean Journal of Chemical Engineering 25 1486-1494. 

Supported- liquid membrane extraction SLM Aq/org/aq lonizable e.g. phenolic acids in nutrient solution (27,28), triazine herbicides in fruit Juices (24). 

LIX 64N hes been used to separate nickal ions as well as copper.20 22 The chemistry of extraction in the two cases is the same [see Eqs. (19.4-3) and (19.4-4)]. However, data on transport throngh supported liquid membranes suggest that the copper flux across the membrane to fonr times that of nickal and selective extraction of copper can be achieved.22 The compound di-Q-elhylhexyl) phosphoric acid also has besn proposed for die essraciion of nickel II using liquid membranes,35... 

Nitric acid removal from an aqueous stream was accomplished by continuously passing the fluid through a hollow fiber supported liquid membrane (SLM). The nitric acid was extracted through the membrane wall by coupled transport. The system was modeled as a series of (SLM)-continuous stirred tank reactor (CSTR) pairs. An approximate technique was used to predict the steady state nitric acid concentration in the system. The comparison with experimental data was very good. 

We have Investigated the transfer of americium and, to some extent, plutonium from aqueous nitrate wastes using supported liquid membranes of the blfunctlonal organophosphorus extractants DHDECMP and 0()D(1B)CMP0 (+TBF). The results show good transfer and removal If the nitric acid In the feed Is first neutralized to O.IOM to minimize acid transfer and subsequent back transfer of the metal Ion. 

Microemulsions have not been employed to any significant extent as liquid membranes in SLMs. Although it is not absolutely clear whether microemulsions have been placed within the pores of a solid microporous membrane support to serve as a liquid membrane, a study reported in one publication came very close to doing so. Osseo-Asare and Chaiko [14] used an extractant, dinonylnaphthalenesulfonic acid (HDNNS), to separate cobalt selectively from a multicomponent aqueous stream. In the presence of water, the HDNNS forms a microemulsion. Thus, the authors concluded that their supported liquid membrane, which was initially impregnated with HDNNS, was indeed a microemulsion (supported) liquid membrane once it contacted the aqueous feed and receiving phases. 

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. 

Hollow fiber-based extraction can be used for the determination of freely dissolved phenols or total concentration of phenols in environmental water samples. Liu et al. [199] applied hollow fiber-based supported liquid membrane (SLM) coupled with HPLC to the determination of freely dissolved chlorophenols in water samples. In this equilibrium sampling through membranes, freely dissolved chlorophenols were successfully determined in model solutions of humic acids and at low-ppb levels in river and leachate waters. 

For the removal of americium from nuclear waste streams, Muscatello and Navratil (61) employed dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP) as the extractant without a diluent in a supported liquid membrane. They removed more than 95% of americium from the waste streams. The DHDECMP extractant and a surfactant, e.g., SPAN 80 or LMS-2, with 0.25M oxalic acid as the internal phase could constitute an effective ELM system for americium removal. 

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