Preparation Of Pebax/Functionalized MOF Mixed Matrix Membranes And Study Of CO₂ Gas Separation Performance

Bio-Natural Gas（BNG）is a kind of green,clean and renewable resources（the main component is CH₄containing a small amount of CO₂ and other impurities）,and the separation and purification process of CO₂is a key step in the preparation of BNG.Gas membrane separation technology is one of the most promising technologies for CO₂ separation due to its environmental friendliness,low cost and low energy consumption.In this paper,Pebax was used as the polymer matrix,and the functional design based on MOFs fillers（including the regulation of chemical microenvironment,the regulation of pore and structure,and the construction of functional defect pore structure）was used to improve the transport mechanism of CO₂ in the mixed matrix membrane（MMMs）,so as to achieve the efficient separation of CO₂/CH₄in the functionalized MOF-based mixed matrix membrane.Specific research contents are as follows:（1）The functionally-modified IL@PEG-g-ZIF-8（IL@PZIF for short）filler was designed and prepared,and was mixed into Pebax matrix to prepare Pebax/IL@PZIF MMMs for the study of CO₂/CH₄ separation performance.The abundant ether-oxygen groups and high CO₂ capacity[Bmim][Tf₂N]in IL@PZIF improve the solubility of CO₂ in the membrane,and thus improve the CO₂ permeability.The functionalized IL@PZIF still retains the ZIF-8 microporous structure,providing additional CO₂diffusion channels in the membrane,thereby improving CO₂ permeability and CO₂/CH₄ selectivity.In addition,the introduction of IL@PZIF increased the chain spacing of Pebax in MMMs and improved the permeability of CO₂.The CO₂ permeability of Pebax/IL@PZIF-4 MMM is 325.69±7.39Barrer（91.01%higher than that of pure membrane）and the CO₂/CH₄ selectivity is 40.26±0.37（33%higher than that of pure membrane）under the condition of gas mixture humidification.（2）H-ZIF-8 with hydrophilic micropores and hollow structures was designed and prepared,and it was mixed into Pebax matrix to prepare Pebax/H-ZIF-8 MMMs for CO₂/CH₄ separation.The surface of H-ZIF-8 is attached with high hydrophilic tannic acid,which makes H-ZIF-8 have high hydrophilicity.Therefore,H-ZIF-8 can form a water channel with low resistance in the MMMs,and improve the permeability of CO₂.The retained pore structure of H-ZIF-8 improves the selectivity of CO₂/CH₄.The hollow structure inside H-ZIF-8 provides a fast transmission channel for CO₂with low resistance,thereby increasing the permeability of CO₂ in the MMMs.Pebax/H-ZIF-8-5 MMM in dry mixture ensures CO₂/CH₄ selectivity,and CO₂permeability reaches 239.9±2.0 Barrer,which is 124.7%higher than that of pure Pebax membrane.In wet Pebax/H-ZIF-8-5 MMM,the permeability of CO₂ is 412.4±3.7Barrer（85.4%higher than that of pure membrane）and the selectivity of CO₂/CH₄ is 36.3±0.1（21.4%higher than that of pure membrane）.（3）Li-HKUST-1-R（Li-HK for short）with Li⁺functional defect Pore was designed and prepared,and Li-HK was mixed into Pebax matrix to prepare Pebax/Li-HK MMMs for CO₂/CH₄ separation.Due to the layered ring structure of Li-HK,it can be intertwined with Pebax chain,so that Li-HK can be stably dispersed in the membrane.Li⁺has a high affinity with CO₂,which increases the solubility of CO₂ and CO₂/CH₄selectivity in membranes.The additional mesoporous pores generated by Li⁺exchange can provide additional low-resistance transport channels for CO₂,which increases the diffusion of CO₂ in the film.The CO₂permeability of Pebax/Li-HK-1 MMM is 335.44±2.85Barrer（68.58%higher than that of pure membrane）and the CO₂/CH₄ selectivity is 37.47±0.05（16.24%higher than that of pure membrane）under the condition of wet mixture.