RECOVERY OF CEPHALEXIN FROM DILUTE-SOLUTION IN A BULK LIQUID MEMBRANE

As a step towards the development of a liquid membrane technique; for the recovery of cephalexin from dilute solutions obtained in enzymic c onversion processes, an experimental study of the facilitated transpor t of cephalexin using aliquat-336 and a model medium has been carried out in a stirred transfer cell. A solution of the anion exchange carri er, aliquat-336 in n-butyl acetate was used as the bulk liquid membran e phase. The effect of feed and receiving phase composition and stirri ng speed on the transport rate have been systematically investigated. Cephalexin was transported from an aqueous phase of higher pH through the membrane phase to another aqueous phase of lower pH. By maintainin g an appropriate pH gradient in the aqueous phases, facilitated 'uphil l' transport and more than 90% extraction could be achieved. This is s olely attributed to the strongly pH dependent distribution coefficient of cephalexin between the membrane and aqueous phases. The effects of the chloride ion countertransport and the membrane phase carrier conc entration on the transport rate were found to be of secondary importan ce. This is the first demonstration of uphill transport by use of pH d ependence of the distribution ratio of a semisynthetic cephalosporin. (C) 1997 Elsevier Science Ltd.