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Abstract

The invention disclosed herein relates to a polymeric microporous electrolytic cell separators for producing alkali metal hydroxide at high current efficiencies, said separator having: a. porosity of at least about 60%; b. thickness of between 8 and 130 mils; c. hysteresis of from 0.30 to 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the separator after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and d. distribution of pore sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns and at least 60% of said pores have a diameter between 0.59 and 33 microns; wherein the porosity, thickness, hysteresis, and pore size distribution are adapted to provide the separator with the property of exhibiting a high current efficiency including the property of a current efficiency of about 85% to about 98% when measured at a sodium hydroxide concentration of 150 gpl. The separator also possesses hydraulic properties which renders them suitable for use in a commercial scale cell. Also disclosed herein is a method for preparing the separators of this invention comprising the steps (a) forming a sheet comprising a fluorocarbon polymer, a pore forming additive and a fluorinated surface active agent; (b) sintering the sheet; and (c) removing the pore forming additive.

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First Claim