CYCLIC OPERATION OF FORCED FLOW ELECTROKINETIC SEPARATION FOR SIMULTANEOUS SEPARATION AND CONCENTRATION OF CHARGED MOLECULES

A new cyclic operation of membrane separation in the presence of an electric field is developed. The microporous membrane/filter acts as a barrier between two adjacent solutions (i.e., the solution in the membrane cell and in the permeate). An electric field is applied across the membrane to induce electromigration of charged molecules whose molecular weights are much smaller than the molecular weight cutoff of the membrane used. The charged molecules move freely through pores of the membrane without hindrance. In the presence of an electric field, the concentration of charged molecules in the permeate stream is determined by the electromigration velocity and the permeation flow rate through the membrane. The permeation rate is controlled by the applied pressure drop, and the electromigration velocity can be controlled by the electric field strength applied. By applying a high electric field and a low pressure drop, the concentration in the permeate stream can be increased, thus resulting in enrichment of the charged molecules in the permeate. By applying an electric field such that the electromigration is in the opposite direction to the permeation flow, the permeate is depleted of the charged molecules. A continuously supplied feed stream to the membrane cell can be processed into a concentrated solution and a depleted solution by alternating the polarity of an electric field. This paper presents the experimental results of a cyclic operation for the simultaneous separation/recovery and concentration of acetate, phenylalanine, glycine, and aspartic acid.