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

本研究的目的是开发有机酸发酵的原位膜分离工艺。生物降解聚乳酸的工业化生产使发酵法制备光学活性乳酸受到广泛关注。为了降低发酵中终产物抑制的水平，已经开发了许多涉及分离产物的程序的方法。其中，溶剂萃取结合化学反应法从经济上讲是一种很有前途的方法。乳酸发酵与反应萃取相结合的两个关键问题尚待解决。首先是有机溶剂对微生物的毒性。为了避免微生物与有机溶剂的直接接触，我们制备了萃取剂浸渍的三醋酸纤维素膜或聚苯乙烯支撑的微胶囊。乳酸通过膜的渗透速率较快，但由于发酵液中溶解的微量提取剂毒性较强，导致提取剂从膜或胶囊中泄漏，发酵停止。第二个问题是发酵和使用毒性较小的提取剂的反应性提取之间的最佳pH值的差异。为了克服这一点，我们开发了一种新的协同萃取体系，用三正辛胺和磷酸三丁酯萃取乳酸。但由于三醋酸纤维素作为反萃剂时会被碱性溶液水解，使混合萃取剂不能应用于膜分离系统。我们尝试制备包含混合萃取剂的微胶囊。该尝试是成功的，为微胶囊在乳酸发酵中的应用提供了可能。

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.