Lipase-facilitated separation of organic acids in a hollow fiber contained liquid membrane module

A lipase-facilitated selective and continuous separation of difficult-to-separate mixtures of organic acids has been developed in a hollow fiber contained liquid membrane (HFCLM) device. The device consists of a well-mixed two-fiber-set hydrophobic microporous polypropylene hollow fiber membrane module where lipase from Candida rugosa (CRL) and lipase from porcine pancreas (PPL) were immobilized on the internal diameter of two identical sets of hollow fibers, respectively. The module shell side contained 20 v/v% octanol in n-heptane acting as the organic liquid membrane between the two commingled fiber sets. Two systems of model acid mixtures were selected to demonstrate this technique: (1) phenylacetic acid (PAA) and mandelic acids (MAs); (2) PAA and 6-aminopenicillanic acid (6-APA). Aqueous feed solution containing the acid mixtures and ethanol flowed through one fiber set, a stripping aqueous solution flowed through the second fiber set and was highly enriched in PAA. The separation factors of PAA over MAs and PAA over 6-APA were as high as 20 and 10, respectively. The esterification kinetics of PAA and ethanol catalyzed by CRL in batch experiment yielded V_max and K′_m values to be 0.139 mmol/(h(mmol) CRL) and 62.2 mM, respectively. Much higher enzyme activities and enzyme stability were achieved in the HFCLM device due to immobilization of the lipases on the hydrophobic membrane surface where the organic-aqueous interface was immobilized and the ester produced was simultaneously transferred into the organic liquid membrane. The transport rate of PAA in the HFCLM device was 224 times higher than the V_max measured in batch experiments.