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

本研究旨在开发用于有机酸发酵的原位膜分离工艺。由于生物可脱脂聚乳酸的商业化生产，利用发酵法制备光学活性乳酸引起了人们的广泛关注。为了减少发酵过程中最终产物的抑制程度，已经开发了许多涉及分离产品的过程。在众多工艺中，从经济角度考虑，溶剂萃取法和化学反应法是最有前途的。乳酸发酵与反应萃取联用的两个关键问题有待解决。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，我们制备了浸渍三醋酸酯纤维素膜或聚苯乙烯支载微胶囊的萃取剂。乳酸通过膜的渗透速率较快，但由于微量萃取剂溶解在发酵液中的毒性较强，萃取剂从膜或胶囊中泄漏，发酵停止。第二个问题是使用毒性较低的萃取剂的发酵萃取物和活性萃取物之间的最佳pH差异。为了克服这一点，我们开发了三辛胺和三丁基磷酸协同萃取乳酸的新体系。但混合萃取剂不能应用于膜分离系统，因为三醋酸纤维被用作反萃剂的碱性溶液进行了水解。我们尝试制备了含有混合萃取剂的微胶囊。这一尝试是成功的，该微胶囊有可能应用于乳酸发酵。

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.