Separation of propionic and acetic acid by pertraction in a multimembrane hybrid system

Studies have been made on transport rates and separation of propionic over acetic acid by the solution-diffusion type pertraction in a multimembrane h ybrid system (MHS). The membrane system has been composed of two hydrophili c, strongly basic or acidic, polymer membranes separated by a hydrophobic b ulk liquid membrane. Separation of propionic and acetic acids from their aq ueous solutions (0.1-0.8 M) or real fermentation broth has been studied. Ex perimentally observed mass transfer coefficients (k) range from 3.5 x 10(-6 ) to 1.5 x 10(-5) cms with the higher values for propionic acid. In the cas e of fermented broth the fluxes were found to depend on its pH and the pret reatment of the feed. The selectivity SELAAPA evaluated as the ratio of pro pionic and acetic acid fluxes can attain values ranging from 3.5 to 5.5. Th e overall transport mechanism is consistent with a solution-diffusion mecha nism typical for liquid membranes operating without a carrier. The fluxes a nd selectivity of the membrane system in respect to acetic and propionic ac id have been found to depend on the viscosity of liquid membrane phase and solubility parameters characterizing both acids and solvents. A model based on fundamental physicochemical properties of the permeants and solvents (d iffusion coefficients, solubility parameters and molar volumes) has been el aborated, and experimentally verified. (C) 2000 Elsevier Science B.V. All r ights reserved.