Separation And Purification Of Nitrogen-Containing Mixtures By Metal-organic Framework Materials

Metal-Organic Frameworks(MOFs)are porous materials with periodic network structures that are self-assembled by inorganic metal centers(metal ions or metal clusters)and bridge-connected organic ligands,whose pores are easy to modulate and whose surfaces connect to different types of functional groups.MOFs show good application prospects in many fields due to their large surface area,high porosity and manageable chemical properties.In recent years,the application of MOFs in the field of energy is one of the current research hotspots.As the main greenhouse gases SF6 and CH4,direct emission in the air will cause global warming and environmental pollution,and in practical application,they are always mixed with N2.In order to reduce emissions,it is necessary to adsorb and purify the mixed gases.The main work contents are as follows:1.Sulfur hexafluoride(SF6)is one of the powerful greenhouse gases,which cannot be directly discharged into the air.For SF6/N2 gas mixture in industrial application,in order to improve the gas separation selectivity at low concentration,calcium-based MOF(SBMOF-1)with chemical stability of aromatic functionalization channel and specific binding site is selected to separate SF6/N2.The channel is mainly composed of four aromatic rings with low polarity,with an average size of 6.703x 7.840 A,which is equivalent to the kinetic diameter of SF6(5.49 A)and makes the SF6 has the best force with the channel in the pore.The gas selectivity in actual ratio was calculated by the single-component adsorption isotherms of SF6 and N2,and the information of binding energy and adsorption site was obtained by experiment and calculation method.The mixed gas breakthrough experiment also verified the potential application of SBMOF-1 in separating low concentration SF6/N2 mixture gas.2.Methane(CH4)is a clean and cheap energy,and its greenhouse effect is 21 times that of carbon dioxide.The separation of CH4 and N2 from poor-quality coal bed gas can reduce the release of CH4 into the atmosphere and produce fuel gas at the same time.In order to improve the adsorption capacity of CH4,1-H-benzimidazole-5carboxylic acid(HBIC)was added into the reaction system to synthesize a 3D-MOF material Ni(BIC)2·2.5H2O(JUC-86).HBIC,as a hybrid ligand,has two imidazole ring nitrogen atoms with an angle of about 1400 and two carboxyl oxygen atoms.The obtained material is composed of three infinite spiral chains arranged in parallel and has a one-dimensional channel with an aperture of about 4.5×4.5 ?.The experimental results of single-component adsorption isotherms show that the material has good separation performance and maintains high CH4 adsorption capacity,with an adsorption capacity of 42.5 cm3/g,which is in the forefront among the reported adsorbents.Besides,the material shows good thermal stability,which provides a new choice for separation of CH4/N2.3.MOFs are usually powder states of nanocrystalline or microcrystalline structures,their particle size is very small,and it is difficult to achieve solid-liquid separation when MOFs are put into water.At the same time,when large-scale industrial gas separation is applied,the powdery MOFs material has some problems such as inconvenient recovery and large loss.Based on this,we used the anti-ion gel method to solidify the material Al-CDC with excellent performance of separating CH4/N2.Adjusting the addition ratio of sodium alginate and MOFs material,and testing the internal structure,specific surface area and methane adsorption performance of the composite bead material,it is proved that the synthesized composite bead basically keeps the structure and performance of the original powder material,and has good application potential,which is helpful to promote the further industrial application of MOFs material.