| 摘要: | 近來，氣體分離膜的技術正開始蓬勃發展，簡單、連續程序的特性，使分離膜的技術對工業用途上帶來低成本、環保和提高分離效率等優勢，其中，高分子膜對於天然氣的純化及分離另闢新興替代能源的選擇途徑。
金屬有機框架材料(metal-organic frameworks, MOFs) 作為填料並分散至高分子相中形成混合基質膜(mixed-matrix membranes, MMM)，相較於純高分子膜有更好的分離效果，再者，金屬有機框架材料的有機鏈結使其與高分子間有更好的連接性，而在此研究中，我們使用MIL-53(Al) 作為填料。由於MIL-53(Al) 在水中維持結構穩定、不同環境下可調節孔洞大小(呼吸效應)，以及對特定氣體的優異選擇性等優點，皆指出MIL-53(Al) 優良的特性並適合作為混合基質膜中的填料。
本研究利用在兩種不同溶劑、改變前驅液中高分子含量及製備混合基質膜，因而導致填料不同程度的沉降或聚集，並分析膜在氣體分離應用的潛力。混合基質膜的合成分為兩部分：以大孔(LP) 和窄孔(NP) 兩種形式的MIL-53(Al) 晶體合成，以及配製聚砜(PSF) 於不同的溶劑中，之後結合填料與高分子兩者形成最終的混合基質膜。
在此研究，MIL-53(Al)_NP 和MIL-53(Al)_LP分別展現出1153 m2 g-1, and 1231 m2 g-1的BET比面積，並皆檢測出微孔為主要組成。藉由掃描電子顯微鏡(SEM) 觀察到MIL-53(Al) 沉澱現象發生於低濃度前軀液製備而成的混合基質膜中，而由X-光繞射(XRD) 的結果證實了填料沉澱會造成峰值強度的明顯差異。此外，我們透過流變儀和差示掃描量熱分析儀(DSC) 測量的黏度和玻璃轉移溫度(Tg)之間的關係，並發現填料均勻分布使混合基質膜具有較高的玻璃轉移溫度，也與填料和高分子之間有更強的相互作用力。進一步測試MIL-53(Al)_NP作為填料的混合基質膜在氣體滲透應用上的表現，填料均勻分布並以氯仿製備的混合基質膜展現出最佳的CO2/N2選擇性22.71。另外，也觀察到滲透性質與填料分散形態的關係，填料沈積、聚集和均勻形態造成不同的氣體分子擴散路徑，也證明填料分散形態對氣體滲透有顯著的影響。;Membranes for gas separation have already become a promising field of technology. It offers a continuous and relatively simple process for industry and is also an economical, environmentally friendly and efficient separation method. Additionally, organic polymer membranes are one of the feasible options for separating natural gas from other components as an alternative energy source.
The addition of metal-organic frameworks (MOFs) to form mixed-matrix membranes (MMM) opens the door to enhanced separation performances over pure polymer systems as a result of the combined polymeric phase dispersed with hybrid fillers. MOFs interact well with the polymer due to its organic linkers, and in this work, we focus on MIL-53(Al) as a candidate filler because of several advantageous properties, including structural stability in water, breathing behavior for tunable pore opening in different environment, and outstanding selectivity for specific gases.
This research demonstrates the fabrication of mixed-matrix membranes with various contents of polymer in two different solvents to which led to different degrees of sedimentation or aggregation. Subsequent analysis investigates their potential in gas separation applications. The synthesis of MMM was divided into two parts: the synthesis of MIL-53(Al) crystals in two different forms which are large-pore (LP) form and narrow-pore (NP) form, and preparation of the polysulfone (PSF) in different solvents. Then, we combined the both resulting the final product.
In our studies, MIL-53(Al)_NP and MIL-53(Al)_LP show BET surface areas of 1153 m2g-1, and 1231 m2g-1 dominated by micropores. The morphology of the MMMs for MIL-53(Al) exhibit sedimentation of fillers at low concentration of precursor solutions which were characterized by scanning electron microscopy (SEM), while the results of X-ray diffraction (XRD) confirmed obvious discrepancy of intensity caused by sedimentation. Moreover, we investigated the relationship between viscosity and glass transition temperature (Tg) measured by rheometer and differential scanning calorimetry (DSC), respectively, where the highest Tg matched with a homogeneous morphology with stronger interaction between fillers and polymer. Further gas permeation measurements showed a promising CO2/N2 selectivity of 22.71 for homogenous membrane. Permeation properties of various preparations were also studied, revealing the influence of fillers distribution on gas permeation relating to different diffusion paths for gas molecules in sedimentation, aggregation, and homogeneous morphologies. |
