DEVELOPMENT OF IN-SITSU MEMBRANE SEPARATION PROCESS FOR ORGANIC ACID FERMENTATION

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The aim of this research is to develop in situ membrane separation process for the fermentation of organic acid. Preparation of optically active lactic acid using fermentation has attracted much attention because the production of biodegarable poly(lactic acid) is commercialized. To reduce the level of end-product inhibition in the fermentation, many processes involving procedures to separate the products have been developed. Among the processes, solvent extraction with chemical reaction is promising from economical reason. Two critical problems in the lactic acid fermentation combined with the reactive extraction remains to be resolved. The first is the toxicity of organic solvents to microbes. To avoid the direct contact between the microbes and organic solvent, we prepared the extractant impregnated cellulose triacetate membrane or polystyrene-supported microcapsules. The permeation rate of lactic acid through the membrane was relatively fast, but the extractant leaked from the membrane or capsules and fermentation stopped because of the strong toxicity of the trace amount of extractant dissolved in the broth. The second problem is the difference in the optimum pH between fermentation and reactive extractions using less toxic extractants. To overcome this point, we developed the new synergistic extraction system of lactic acid using tri-n-octylamine and tri-n-butyphosphate. But mixed extractants could not applied to the membrane separation system was problem because cellulose triacetate was hydrolyzed by the alkaline solution used as a stripping reagent. We tried to prepare the microcapsules involving the mixed extractants. The attempt was successful and its possible to apply the microcapsules to the fermentation of lactic acid.