(404a) Supported Liquid Membranes for Recovery of Cephalexin

I am very pleased to have this opportunity to speak in a session in honor of Professor DB Bhattacharyya.  This presentation covers three configurations of supported liquid membranes (SLMs): (1) SLM with strip dispersion (SLM-SD), (2) SLM with feed dispersion (SLM-FD), and (3) SLM with organic dispersion (SLM-OD), for simultaneous removal and recovery of the antibiotic, Cephalexin, from aqueous feed solutions using a commercially available hollow-fiber module and the carrier Aliquat 336.  In SLM-SD, the strip dispersion, formed by dispersing the strip solution in the organic membrane solution with a mixer, flowed through the shell side of the module, forming the SLM in the nanoporous hollow fibers.  In SLM-FD and SLM-OD, the feed dispersion and the organic dispersion, formed by dispersing the feed solution in the organic membrane solution and a small amount of organic membrane solution in the feed solution, respectively, using a mixer, flowed through the shell side of the module, forming the SLM in the nanoporous hollow fibers.  These three configurations can all ensure the stability of SLMs.  For SLM-SD, Cephalexin has been extracted and concentrated with high recovery.  Initial results from a 4-component feed mixture derived from its enzymatic synthesis have shown selective Cephalexin recovery possible.  This allows Cephalexin recovery from the aqueous strip solution through complexation, without enzyme deactivation, which commonly occurs when complexation is conducted in enzymatic reaction mixtures.  A mass transfer analysis has shown that the mass transfer resistance from the extraction reaction is dominant.  To minimize this resistance, SLM-FD experiments were conducted, showing that the overall mass transfer coefficient obtained was significantly larger than (1.6 times) that attained by using SLM-SD.  The mass transfer process of SLM-FD was elucidated, and a mathematical model was developed to describe the process.  Based on this model, both the theoretical and experimental overall mass transfer coefficients were obtained as a function of Aliquat 336 concentration.  These mass transfer coefficients were in reasonably good agreement.  The mass transfer mechanism of the SLM-OD was also elucidated, and a mathematical model was developed to calculate the overall mass transfer coefficient.  The overall mass transfer coefficient increased with an increase of organic-to-feed volume ratio or increase of Aliquat 336 concentration, but reduced with the increase of initial Cephalexin concentration.  Among these SLMs, the reaction resistances were in the order: SLM-SD > SLM-OD > SLM-FD, and the overall mass transfer coefficients were: K_SD : K_OD : K_FD = 1 : 1.3 : 1.6, showing that SLM-FD and SLM-OD decreased the reaction resistances and thus had greater mass transfer than SLM-SD.