电渗析过程中弱电解质迁移强化策略研究

Electrodialysis technology has a unique advantage in desalination of fermentation liquid, separation and extraction of organic acids and amino acids from broth. However, slow migration and high energy consumption of organic weak electrolyte have limited more widespread application of electrodialysis in fermentation industry. Most of the available migration intensification methods are proposed based on the electrodialysis process of inorganic strong electrolyte and simple system with one or two component. The intensification methods according to organic weak electrolyte characteristic and depending on electrodialysis process of multicomponent system needs to be established. The transfer performance of weak electrolyte is seriously affected by low degree of dissociation, small charge-mass ratio and variable electrical property of them. In this work, the reaction of water molecule dissociation generating H+ and OH- is utilized and ion-exchange resins are added into electrodialysis desalting compartments to enlarge the areas of this reaction. By this way, the endogenous pH regulation in compartments of electrodialyzer is realized, which can intensify weak electrolyte dissociation and promote their migration during electrodialysis process. The influence factors and action laws of migration intensification of weak electrolyte by ions-exchange resins is investigated systematically to reveal the mechanism of weak electrolyte transfer through ion-exchange membranes. Next, the resins are fixed on network of spacers or ion-exchange membranes in compartments of electrodialyzer to overcome the problems of membrane stack seal and resins renewal caused by free-moving resins. Furthermore, spacers with ion-exchange network or ion-exchange membranes with uneven surface is trial-manufacture, which can be apply to deal with fermentation liquid.

电渗析技术在发酵料液脱盐、有机酸和氨基酸产品分离回收等方面具有独特的优势，但弱电解质迁移困难、过程能耗高、产品难以兼顾收率和纯度等问题限制了电渗析的工业化应用。现有电渗析迁移强化手段多针对无机离子和一元或二元离子简单体系的电渗析过程提出，亟需针对复杂体系（发酵料液）中弱电解质迁移建立有效的迁移强化策略。解离度低、荷质比小、电性可变是限制有机酸/氨基酸离子电渗析迁移的重要因素。本项目利用过极限电流密度下水分子解离产生H+和OH-的作用，并通过填充离子交换树脂增大水解离发生的界面面积，实现膜堆内原位调节pH值，促弱电解质解离，强化其迁移。通过对树脂强化氨基酸迁移的作用机制和规律的系统研究，揭示弱电解电渗析过程中跨膜迁移的机制；通过将树脂固定于膜堆隔板网或离子膜上，解决填充游离树脂难密封、难更换的问题；并进一步试制离子交换隔板网或表面凸凹离子膜，研发适用于发酵料液体系的新型电渗析膜器或离子膜。

本项目针对电渗析分离提取氨基酸/有机酸时存在膜通量低、能耗高的问题，探索了其电渗析迁移限制因素，并提出了有效的迁移强化手段，对强化多种氨基酸/有机酸的电渗析迁移均获得较好效果。主要研究内容和结果如下：.（1）研究了电渗析中氨基酸（盐）和有机酸（盐）的迁移特性，发现阻碍电渗析中氨基酸和有机酸迁移的两个关键因素是：a. H+/OH-（包括溶液本身固有的和边界层极化水解离产成的）对氨基酸离子和有机酸负离子（OAn-）跨膜迁移形成竞争；b. 氨基酸和有机酸分子自身解离程度低（溶液电导率偏低），荷质比小，在电场中迁移能力弱。.（3）探索了在电渗析器隔室内装入离子交换树脂，对电渗析过程离子迁移的影响。结果表明，脱盐室填充树脂后，氨基酸（Glu和Lys）的电渗析迁移过程膜通量显著提高，能耗显著下降，而且201×4的效果优于001×4。研究了树脂强化氨基酸迁移的作用机制，发现树脂除了通过盐桥作用强化氨基酸迁移之外，还存在其他的作用机制：a、阴树脂的季胺基自降解生成的叔胺可通过质子与去质子化反应促进氨基酸的解离；b、填充树脂可调节膜面边界层水解离强度，改变脱盐室H+/OH-浓度（pH值），从而影响其与氨基酸的竞争迁移。.（5）制备了导离子树脂隔板网和导离子纤维隔板网替代离子交换树脂，使电渗析器隔室厚度减小70%，且与装入树脂相比，获得更高的Glu电渗析迁移通量和更低的能耗。与常规非导离子隔板网相比，本实验自制的导离子纤维隔板网对多种氨基酸和有机酸的电渗析迁移均有强化效果。.（6）对比考察了S-AET和S-CET对氨基酸（盐）和有机酸（盐）迁移的影响及作用机制。发现酸性条件下，S-CET强化氨基酸和有机酸迁移的效果优于S-AET；中性和碱性条件下，S-AET效果优于S-CET。分析导致该结果的原因是，碱性条件下S-AET可结合OH-，削弱OH-与氨基酸负离子（AAn-）和有机酸根（OAn-）的竞争；酸性条件下S-CET可结合H+，削弱H+与氨基酸正离子AAn+和有机酸根（OAn-）的竞争；中性条件下S-AET上叔胺基可催化氨基酸解离，促进其迁移。