Determination of water transport numbers in cation exchange membranes by an EMF (Streaming potential) method.
Onindo, Charles O.
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The work presented is an experimental determination of water transport numbers as a function of concentration of electrolytes in some cation exchange membranes. These were Permaplex C-20, BDH (Na+ form), and Nepton CR 61 AZL 065 and Nepton CR 61 AZL 183 membranes. Experimental investigation is done in the following cell with cation exchange membrane at a temperature of 25oC CATION Ag/AgCl/MCL (aqC1) /EXCHANGE/MCL (aqC1)/AgCl/Ag MEMBRANE This is done for the aqueous electrolyte solutions MCL, were M is the alkali metal cation Li+, Na+ and K+. Thus sodium chloride, Lithium Chloride and Potassium Chloride are studied. An approach based on the theory of irreversible thermodynamics is used to derive an equation of the emf of the cell. The equation is used to calculate the water transport numbers. Silver - silver Chloride electrodes are prepared and used for the measurements of the streaming potentials. On application of short hydrostatic pressure pulses lasting 4.5 seconds, the streaming potential is measured as a function of time and recorded as square pulses. The experimental water transport numbers are observed to be decreasing with increasing concentration of solutions within the concentration range of 0.1M to 1M of electrolytes studied. Attempt is made to determine water transport numbers across the thin BDH (Na+) membrane by mounting several pieces of the membranes in the cell. It is observed that the streaming potential method is yet not a good method for transport number determination in thin membranes.