以混合配體製備金屬有機骨架薄膜於滲透蒸發之應用

Abstract

為了降低以蒸餾方式分離混合溶液造成的工業能源消耗，本論文研究滲透蒸發的方式分離乙醇與水的混合溶液。滲透蒸發不僅可以解決蒸餾分離過程中面臨的共沸點問題，同時也節省蒸餾所需的能源消耗。本論文研究金屬有機骨架（metal-organic frameworks，MOFs）當作薄膜材料，MOF因為具有高比表面積和可調控的孔洞大小，在氣體分離和氣體儲存等領域中廣為應用。在過去的研究中，發現以MOF-303薄膜做滲透蒸發具有很好的分離表現性；在本研究中，使用MOF-303的有機配體3,5-吡唑二甲酸(H3PDC)額外摻雜配體2,5-噻吩二羧酸(H2TDC)做混合配體MOF。希望透過此方式得到之MOF材料可以同時具有兩種有機配體之優點，由H3PDC提高對水的吸附能力，H2TDC提供較大最窄孔道直徑(pore-limiting diameter, PLD)。並將合成出的混合配體MOF，命名為MOF-303(TDC/PDC)。經由XRD結合結構精修的方式計算出不同有機配體比的MOF材料之PLD，結果顯示當加入H2TDC的比例越高，材料之PLD會逐漸變大。我們也利用水吸附等溫線分析材料的吸水性質，發現原本對水沒有吸附能力的材料MOF-303-TDC，在加入H3PDC配體後吸水能力大幅增加到與純MOF-303接近。除此之外，我們也藉由in-situ FT-IR光譜與高解析XRD的鑑定技術分析水分子進入材料後的相互作用。在乙醇水溶液滲透蒸發分離表現上，我們發現在混合配體比為(50/50)的薄膜應用於乙醇及水的分離中效果是最好的。在333K的條件下對90 wt.%乙醇水溶液可以達到10000以上，且通量比MOF-303來的高。在(50/50)薄膜的長時間測試中，我們進行24小時的滲透蒸發操作，薄膜分離表現性仍然維持穩定，說明薄膜穩定性比純MOF-303高。

In order to reduce the industrial energy consumption caused by the distillation, this study adopted pervaporation for separating a mixed solution of ethanol and water. Pervaporation can address the problem of azeotropic points encountered in the distillation separation process, and also saves the energy consumption required for distillation. In the study, metal-organic frameworks (MOFs) were used as membrane materials. MOFs are widely applied in gas separation, and gas storage due to their high surface area and tunable pore sizes. In previous studies, it was found that using MOF-303 membranes in pervaporation exhibited excellent separation performance. In this study, a mixed-linker MOF based on MOF-303 was synthesized by incorporating the organic linker 3,5-pyrazoledicarboxylic acid (H3PDC) with an additional linker, 2,5-thiophenedicarboxylic acid (H2TDC). The aim of this approach is to obtain a MOF material that combines the advantages of both organic linkers, with H3PDC enhancing water adsorption capacity and H2TDC providing a larger pore-limiting diameter (PLD). The synthesized mixed-linker MOF is named as MOF-303(TDC/PDC). By combining XRD with Rietveld refinement, we calculated the PLD of MOF materials with different ratios of organic linkers. The results showed that as the proportion of H2TDC increased, the PLD of the material gradually became larger. We also analyzed the water adsorption properties of the materials using water adsorption isotherms. It was found that MOF-303-TDC, which had no water adsorption capacity, exhibited a significant increase in water adsorption ability after incorporating the H3PDC linker. Additionally, we utilized in-situ FT-IR spectroscopy and high-resolution XRD techniques to investigate the interactions of water molecules within the channel of materials.In the pervaporation separation of ethanol-water solutions, it was observed that the (50/50) mixed-linker membrane demonstrated superior performance. At a temperature of 333 K, the membrane achieved an impressive separation factor of over 10,000 for a 90 wt.% ethanol-water solution, surpassing the performance of MOF-303. Additionally, the (50/50) membrane exhibited a higher flux compared to pure MOF-303. During the 24-hour long-term testing, the MOF-303(50/50) membrane maintained a stable separation performance, indicating greater stability compared to pure MOF-303.