面向低浓度生物乙醇/水分离的高性能沸石分子筛膜的结构设计与制备

The concentration of bioethanol produced by fermentation is usually very low. Before used to manufacture ethanol gasoline, the bioethanol should be concentrated by the traditional distillation technology. The novel membrane pervaporation technology possesses several advantageous, such as low energy consumption and simple operation. Pure silica zeolite MFI membrane, ascribed to its strong hydrophobicity and chemical/thermal stability, exhibits high ethanol selectivity for the separation of ethanol/water mixtures. Unfortunately, the ideal membrane microstructure for this separation process is unclear, resulting in an average performance of the synthesized MFI membrane. In this study, we designed two MFI membrane structure types with different micro-pattern and asymmetrical character, towards two membrane evaluation indicator of ethanol selectivity and membrane flux respectively. Based on the successful preparation of MFI membranes and their pervaporation data, we will demonstrate the relationship between membrane structure and ethanol selectivity as well as flux. Then, the preparation methods and conditions of these two synthesis routes will be reconciled to prepare MFI membrane with special composite structure. The separation mechanism of this membrane for the ethanol/water separation will be elaborated. The current proposed strategy is hopefully to reveal the ideal MFI membrane structure for the separation of ethanol/water system. This study may provide us a new perspective for the preparation of high performance zeolite membranes. We believe that the results and conclusions obtained through this project have great theoretical and practical significance.

发酵法制备的生物乙醇浓度很低，在用于生产乙醇汽油之前，需要用传统的蒸馏法预先浓缩富集。新型的膜法渗透汽化分离工艺相比蒸馏法，具有能耗低、操作简单等优点。全硅的MFI型分子筛膜具有很强的疏水性且化学和热稳定性好，表现出很好的透醇性能，非常适合用于分离低浓度的乙醇/水混合物。但目前对于分离该体系的理想的膜层微观结构并不清楚，导致制备的MFI膜总体分离性能不高。本项目提出针对乙醇透过选择性和膜通量两个重要评价指标，分别设计制备具有不同微观形态和不对称结构的MFI分子筛膜，建立膜的结构与乙醇选择性和通量之间的关系。在此基础上，协调两条路线的合成方法和合成条件，制备具有特殊复合结构的MFI分子筛膜，并阐明其对乙醇/水体系的分离机制。本项目的研究将从本质上明确分离乙醇/水体系的MFI膜的理想微观结构，为制备高分离性能的分子筛膜提供新的研究视角，具有重要的理论意义和应用价值。

低浓度有机物与水混合物体系，特别是乙醇/水的分离，是生物发酵工艺中的一个重要步骤。全硅MFI型分子筛膜由于其疏水性和适当的孔道尺寸，对乙醇/水体系具有良好的分离潜力。本项目围绕高分离性能MFI膜的制备，开展了如下几个方面的研究：硅源控制释放法制备MFI型分子筛取向膜，邻苯二酚存在下取向MFI晶种的生长过程探究，取向MFI分子筛纳米片膜的制备，多孔支撑体上制备MFI膜及其乙醇/水分离性能测试。结果表明，通过在二次合成液体系中加入苯二酚的异构体，可以调控MFI分子筛膜的优先取向，并可推广应用于MFI纳米片膜的制备。通过对制备方法-膜层结构-分离性能三者之间的协调，制备得到了具有较好分离性能的MFI膜，其对5wt.%的乙醇/水体系的最佳分离因子为55，通量为1.54 kg m-2 h-1，并分析了影响分离性能的关键因素。