NAMS 2002 Workshop - ICOM 2008

Biomedical and Biotechnology II – 6
Wednesday July 16, 12:15 PM-12:45 PM, Honolulu/Kahuku
Supported Liquid Membranes with Strip Dispersion for the Recovery of
Cephalexin
M. Vilt (Speaker), The Ohio State University, Columbus, Ohio, USA
W. Ho, The Ohio State University, Columbus, Ohio, USA - ho@chbmeng.ohio-state.edu
Cephalexin is an important and widely used semi- synthetic cephalosporin.
Cephalosprorins along with penicillins are Beta-lactam antibiotics, which account
for the majority of the antibiotic world market. Cephalexin is traditionally produced
by a 10-step chemical synthesis. An enzymatic synthesis for Cephalexin has
been developed, and offers several advantages over the classical route. The
enzymatic synthesis reduces energy and solvent waste, but has been used in
industrial production on a limited basis. The enzymatic reaction mixture contains
Cephalexin, side products, and unconverted reactants, which are similar in
structure, are difficult to separate. Liquid membranes, in particular supported
liquid membranes (SLMs), are a promising solution to the separation. Reactive
extraction with the quaternary ammonium compound Aliquat 336 has been
demonstrated for Cephalexin and other semi-synthetic cephalosporins. SLMs are
still not used industrially, as they still plagued with problem of long term
instability. The SLM with strip dispersion has been a recent development to solve
the issue of stability.
SLM with strip dispersion can be described when an aqueous strip solution is
dispersed in an organic membrane solution by a mixer, and passed on one side
of a membrane support. When a microporous hydrophobic support is used, the
organic phase of the dispersion becomes imbedded in the pores of the support,
forming a stable SLM. Stability is maintained by having a constant supply of
organic membrane solution to the pores.
In this study, Cephalexin has been separated and concentrated from an aqueous
solution using the SLM with strip dispersion. Experiments used a Liqui-Cel®
hollow fiber module as a microporous support. The organic membrane solution of
the SLM consisted of Aliquat 336, Isopar L (isoparaffinic hydrocarbon solvent),
and 1- decanol. The aqueous strip solution was composed of potassium chloride
and citrate buffer. The following key parameters were investigated: feed and strip
dispersion flowrate, strip dispersion mixing rate, carrier concentration, counter ion
concentration, pH, and volume of aqueous strip solution. High extraction and
recovery rates were achieved when maintaining a proper pH in the aqueous strip
solution combined with an excess of potassium chloride. An enrichment factor of
up to 3.2 was observed in the aqueous strip solution while achieving over 99%
extraction and 96.2% total recovery. In this case, the aqueous feed solution of