ALKALI SAPONIFICATION REACTION OF CELLULOSE TRIACETATE MEMBRANE IN HETEROGENEOUS SYSTEM AND PERVAPORATION WITH THE REACTION

Abstract

In heterogeneous system, the alkali saponification reaction of cellulose triacetate (CTA) membrane in the mixture of ethanol and water advanced with sharp moving boundary of reacted layer with a linear relationship of the thickness with the reaction time as in the case of ethylene-vinyl acetate copolymer membrane. Sorption and diffusion of H2O and C2 H5 OH under the pervaporation with the reaction were examined, and results were obtained as follows. Experimental values of permeation rates of H2O and C2H5OH through a partially saponified membrane agreed with those calculated by assuming the membrane to be a lamination of two layers of cellulose and CTA. For the pervaporation with the reaction, an equation was obtained. Where F is over all permeation rates for water or ethanol, k is the moving rate of the boundary front, l is the membrane thickness before the reaction and Pcell and PCTA are permeability constants for cellulose and CTA membrane, respectively. Plots of 1/F vs. t showed linear relationships for ethanol and water, respectively. From the results, the permeation constants for H2O and C2H5OH under the heterogeneous reaction were obtained. Diffusivity of alkali ion in the cellulose membrane was found 120 times larger than that in CTA membrane. Summarizing these results, it was concluded that the alkali saponification reaction under pervaporation advanced with a controlling step of boundary reaction. An analogy may be found between the reaction and the Case II type diffusion.