Preparation And CO₂/CH₄ Separation Performance Composite Membranes With Ni-Based Metal-Organic Framework Nanosheets

CO₂ separation and purification not only supply industrial economic benefits but also ameliorate the greenhouse effect on the environment.Among all the separation technologies,the membrane-based separation has become a research focus and gained great attention in the field of CO₂ separation and purification because of its low cost,high efficiency,and environmental friendliness in recent years.In this paper,different types of CO₂ separation membranes were designed and prepared to construct CO₂rapid transport passageways for improving CO₂ permeation properties.The main research contents are as follows:（1）Layered α-Ni（im）₂ crystals were synthesized by hydrothermal method with a solid mixture of nickel hydroxide and imidazole.Single or several-layer metal-organic framework（MOF）nanosheets were prepared by exfoliatingα-Ni（im）₂ precursors,which exhibited excellent preferential adsorption on carbon dioxide with application potentials in CO₂ separation and purification.（2）The exfoliated MOF nanosheets were blended with Pebax MH 1657 to fabricate mixed matrix membranes（MMMs）.The loading effects of MOF nanosheets and feed pressure on membrane separation and mechanical properties were studied.It was found that the loadings of MOF nanosheets would effectively improve the selectivity of the membrane,because the pores of MOF nanosheets could selectively sieve CO₂ and CH₄ molecules.Under 2 wt%loading ofα-Ni（im）₂ nanosheets,the CO₂/CH₄ selectivity and CO₂ permeability of the MMMs could be up to 33 and 100.6Barrer respectively,demonstrating a 72%increase in selectivity with no significant change in CO₂ permeability over pure Pebax membrane.The loadings of 2Dα-Ni（im）₂ nanosheets in MMMs could also improve the mechanical properties and stabilities of the membranes.（3）By selecting porous polyacrylonitrile（PAN）as the based membrane,α-Ni（im）₂ nanosheet as the gutter layer,commercial Pebax MH 1657 as the selective layer,defect free and continuous thin film composite membranes were prepared.The reason for the effective separation of CO₂/CH₄ component gases was that the ultrathin MOF nanosheets could significantly reduce gas diffusion resistance and prevent the penetration of selective Pebax solution into the PAN-membrane during preparation.The CO₂/CH₄ selectivity and CO₂ permeance of thin film composite membranes could reach 20.35 and 81 GPU respectively at 298 K under a transmembrane pressure of 2 bar.