Synthesis And Hydrocarbon Gas Adsorption Separation Performance Of In-MOFs Based On Fluoro-Substituted Terephthalic Acid

The separation and purification of light hydrocarbon mixtures is one of the most important processes in the petrochemical industry.Absorption or distillation have been used to purify the mixture depend on their different physical and chemical properties.However,these industrial processes usually require largescale tower equipment and high energy consumption,which leads to increased costs.Therefore,many concerns have been pushing development towards an alternative technology with high-efficiency separation capabilities and simple routes currently.As a new type of organic-inorganic hybrid porous material,metal-organic frameworks(MOFs)have broad application potential in gas adsorption storage and selective separation due to their large specific surface area and functional tunability and widely have been studied.In this work,suitable metal center and functional groups have been selected and synthesized MOFs materials that can be used to purify and separate light hydrocarbon mixtures,the research contents are as follows:Firstly,two In-MOFs,[InH(BDC)2]n·2H2O·DMF(MOF-1)and[InH(FBDC)2]n·3H2O·1.5DMF(MOF-2)were successfully designed and synthesized through solvent-thermal method based on terephthalic acid(H2BDC),2-fluoroterephthalic acid(H2FBDC)and main group metal In(III)center.The structure was confirmed by X-ray single crystal diffraction data,and the basic characterization of IR,XRD and TG was carried out.Structural analysis shows that two In-MOFs are isostructural 3D frameworks with open three-way channel,and the whole framework can be regarded as a doubleinterleaved 4-connection qtz network with the topological symbol {6^4.8^2}.In addition,the porous wall contains the free F atoms in MOF-2,which will serve as potential active sites playing a vital role in the adsorption.Thermogravimetric results show that two compounds can be stable up to 400?,showing good thermal stability.Secondly,based on the characteristics of open channels in MOF-1 and MOF-2,the gas adsorption and separation performance of MOF-1 and MOF-2 was also studied.At 77 K and 1 atm,the maximum adsorption capacities of MOF-1 and MOF-2 on N2 were 190 cm3/g and 76.7 cm3/g,respectively.Both of them exhibited reversible type I adsorption behavior,but the specific surface area and adsorption capacity decreased due to the modification of F substituent in channels of MOF-2.At 273 K,298 K and 1 atm,MOFs showed high adsorption capacity of C2 gas,but extreme low adsorption capacity of CH4.The L-F model and the Virial 2 model were used to perform curve fitting and calculation of the isosteric heat of adsorption(Qst).The results show that the Qst values of C2 hydrocarbons are higher than CH4,indicating that the stronger interaction force between the framework and C2 hydrocarbons,which is mainly attributed to the inside of the pores are filled with strong negative F atoms that can serve as potential functionalization centers.At 298 K and 1 atm,the IAST selectivity of MOF-1 binary C2H2/CH4,C2H4/CH4 and C2H6/CH4 mixtures stabilized at about 6.3,6.63 and 5.49,and MOF-2 stabilized at about 13.2,10.5 and 10.0,which is mainly attributed to the inside of the pores are filled with strong negative F atoms that can serve as potential functionalization centers.