金屬有機骨架混合基質薄膜於二氧化碳分離之應用

Abstract

混合基質薄膜(mixed matrix membranes, MMMs)以多孔材料作為填充物分散於高分子基質當中，可作為氣體分離膜。MMMs同時保有高分子良好的加工性與多孔材料優異的分離效能，亦展現出優於高分子本身的通透率與選擇性，有機會打破高分子膜在氣體分離上的效能限制。金屬有機骨架是一具有結晶性的奈米孔洞材料，由於其可調控的通道大小及內部官能基，在氣體分離領域有良好的應用潛能。根據過去文獻的報導，UTSA-280對於CO2有很好的吸附能力，因此在本研究中我們選用UTSA-280作為填充物，將其混摻入聚醚酰亞胺(Polyetherimide, PEI)高分子基質中，製備出金屬有機骨架混合基質薄膜，並應用於CO2分離。UTSA-280作為填充物的材料，其尺寸及在高分子中的分散程度會直接影響薄膜分離的效能。為了控制UTSA-280的粒徑大小，我們使用不同溶劑(水、乙醇和甲醇)合成出三種粒徑不同的UTSA-280粉體，並將其與PEI混合。接著採用刮刀塗佈法製備出MMMs。我們發現用乙醇溶劑合成出的粉體(UTSA-280_E)粒徑小且分佈集中，所製備出的PEI_E MMMs的缺陷也較少。氣體分離的結果也顯示，PEI_E MMMs在CO2/N2和CO2/CH4的分離上有較為優異的表現，CO2/N2選擇率由純PEI薄膜的5.1提升至80.8；CO2/CH4 則由4.2提升至137.5。同時我們也由分子模擬結果得知，UTSA-280結構中的四環和鍵結水與CO2產生很強的作用力，導致MMMs的CO2/N2和CO2/CH4吸附選擇率相較於純PEI有顯著的增加。

Mixed matrix membranes (MMMs) containing porous materials as fillers dispersed in a polymer matrix can be used for membrane gas separation. MMMs combine the good processability of the polymers and superior separation ability of the porous materials, and can exhibit better permeability and selectivity than the pure polymeric membranes. Metal-organic frameworks (MOFs) are crystalline nanoporous materials, which have been widely applied in gas separations due to their tunable pore size and chemical diversity. According to a previous report, UTSA-280 has high affinity to CO. In this study, we incorporated UTSA-280 into a polyetherimide (PEI) matrix to prepare MMMs for CO2 separation. The particle size of the fillers may affect the dispersion in polymer, so we used different solvents (water, ethanol, and methanol) for the synthesis of UTSA-280 particles for the subsequent fabrication of MMMs. The powder synthesized with ethanol solvent (UTSA-280_E) had a smallest particle size and a narrowest size distribution, and the prepared PEI_E MMMs had a low quantity of defects. The gas separation results also show that PEI_E MMMs exhibited higher CO2 separation performance than the pure PEI membranes. Specifically, the introduction of UTSA-280 into PEI increased its CO2/N2 selectivity from 5.1 to 80.8, and CO2/CH4 selectivity from 4.2 to 137.5. Molecular simulations suggest that the linker and the guest molecule (water) in the UTSA-280 had strong interaction to CO2, which resulted in high CO2/N2 and CO2/CH4 adsorption selectivity.