Facilitated transport of lactic acid and its ethyl ester by supported liquid membranes containing functionalized polyorganosiloxanes as carriers

The feasibility of using hydrophobic fluid organosiloxane, Me3SiO(MeSi(OR)O)x(Me2SiO)ySiMe3 polymer (containing x = 4, 11 or 30 mol% of R = –(CH2)3NMe2 (amine); –(CH2)2OEt (ether); –(CH2)5COOEt (ester); or –(CH2)4Me (alkyl), side-arm organofunctional groups) as integrated solvent/carrier supported liquid membranes (SLMs) for the recovery from aqueous phases of lactic acid and its ethyl ester has been investigated. The carriers are capable of interacting specifically with the required product in a complex mixture. The ethyl ester of lactic acid undergoes pH driven facilitated transport through both ether and amine functionalized polyorganosiloxane/celgard K-273 SLMs resulting in a dramatic permeability enhancement compared with that displayed by the free acid. The pH driven facilitated flux of the ester is directly proportional to the substrate concentration, and it is also greatest at low amine and ether functional group loadings. Both amine and ether functionalized polyorganosiloxane/celgard SLMs were found to be stable throughout the duration of the experiments (up to 100 h).