Membrane transport of organics. III. Permeation of some carboxylic acids through bipolar polymer membrane

Abstract

AbstractThe permeation of acetic (AA), propionic (PA), lactic (LA), oxalic (OA), citric (CA), and tartaric (TA) acids through the bipolar ion‐exchange membrane Neosepta BP‐1 (Tokuyama Corp.) was studied. It was found that the fluxes (J, mol cm−2 s−1) and mass‐transfer coefficients (k, cm s−1) increase in the following order: CA < OA < LA < TA < PA ≤ AA. The transport processes in the Neosepta BP‐1 membrane are concentration‐dependent and can be described phenomenologically using I‐Fick's law for diffusion. The permeation phenomena correspond to the solution–diffusion model similarly as to the permeation of carboxylic acids through strongly acidic cation‐exchange membranes. However, in competitive AA–PA transport experiments, typically for strongly basic membranes, the separation ability of the BP‐1 membrane with a preference toward AA was observed. The selectivity coefficients α calculated as the ratio of the respective mass‐transfer coefficients vary in the range from 1.31 ± 0.2 to 2.1 ± 0.6. These values depend on the feed composition and the system arrangement, which means that α is always higher for the system with the anion‐exchange layer is in contact with a feed solution. Rather low fluxes of PA, AA, and other acids, as compared to some monopolar membranes (Neosepta AFN‐7, Nafion‐120, Flemion), are promising for the application of the bipolar membrane in an electrodialytic separation of carboxylic acids from their aqueous solutions or mixtures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2705–2717, 2001