CH4-N2在MOFs结构材料中的吸附分离性能

针对甲烷氮气的分离难题,通过溶剂热法大量合成了6种典型的由单齿、多齿与多元配体构建的金属有机框架材料,并利用单组分静态与双组分动态吸附法分别研究了甲烷与氮气在材料中的吸附行为。研究结果表明,MOFs材料相对较弱的极性,致使其甲烷氮气的分离选择性明显优于Si/Al分子筛;多齿配体MOFs材料因配体较长,孔道较大,具有与活性炭相当的甲烷氮气分离选择性;MOFs中的不饱和金属位增大了孔道极性,不利于分离性能的提高;单齿甲酸配体构建的超微孔Ni₃(HCOO)₆]框架具有非常优异的CH₄/N₂分离性能,其选择性高达7.0,是Si/Al分子筛与活性炭的2倍。这为高效甲烷氮气分离材料的设计提供了新的参考依据。

Adsorption and separation of CH4-N2 with different structural MOFs

For CH₄-N₂ separation with high-efficiency, several typical MOFs based on different ligands with high surface areas were synthesized in large scale via the simple solvothermal method, and their CH₄/N₂ separation performance was investigated experimentally by pure gas adsorption and binary gas breakthrough experiments. The results show that the adsorptive separation selectivity of most MOFs is much higher than that of Si/Al zeolites owing to their lower polarity, and the selectivity of MOFs with multidentate ligands are similar with that of high-quality activated carbon because their wide pore sizes resulted from the long linkers are not good for the separation of CH₄/N₂. In addition, the open metal sites in MOFs increase channel polarity, which is not conducive to improving the separation selectivity of CH₄/N₂ mixtures. Fortunately, the ultra-microporous adsorbent (0.5 nm) based on monodentate ligand, namely Ni₃(HCOO)₆] synthesized by the short linker of HCOO^- and Ni²⁺, has a much higher selectivity up to 7.0, twice that of conventional adsorbents, such as Si/Al zeolites and actvited carbons. In a word, the knowledge obtained in this work provides a foundation for the design of new nanoporous materials towards the CH₄/N₂ separation with high-efficiency.