The Study On Gas Adsorption And Separation Properties Of Flexible Metal Organic Framework Materials

In this paper,the structures of the MIL-53(M)[M=Cr,Al,Fe,Sc]series of flexible metal organic framework materials are optimized by the first principles and molecular dynamics.The adsorption and separation properties of MIL-53(Al)and MIL-53(Fe)are simulated and calculated by the Grand Canonical Monte Carlo(GCMC)and Ideal Adsorbed Solution Theory(IAST).The results show that:(1)The four materials of MIL-53(M)[M=Cr,Al,Fe Sc]have a similar framework structure.The crystal structures of materials are obviously different under different synthetic conditions.Annealing can effectively improve the crystal structure.The density affects the pore volumes and the specific surface areas of the same type of material.The framework structures of MIL-53 will change while the environment temperature changes.Especially at high temperature,the pore structures will expand remarkably.(2)The maximum adsorption properties at 77K of MIL-53(Al)and MIL-53(Fe)for four kinds of gas from high to low are N2>H2S>CO2>CH4.At 298K,the adsorption properties for four kinds of gas are in the order of CO2>H2S>CH4>N2.The adsorption property of MIL-53(Al)is better than MIL-53(Fe).MIL-53 materials show good adsorption ability to CO2 and H2S which can be separated from a mixed system.In atmospheric environment,the harmful gas H2S can be separated by the MIL-53 materials.The annealed MIL-53 materials have better adsorption properties and adsorption selectivities than MIL-53 materials under other synthetic conditions.(3)Because the adsorption is an exothermic process,the adsorption properties of MIL-53 materials will decrease with the increase of the temperature.In the adsorption process,the gas is adsorbed by-OH of the metal clusters in the structure.In MIL-53 materials,which play the role of adsorption are the metal clusters not the organic chain structures in the framework.The isosteric heats of MIL-53 materials for the gases are in the order of CO2>H2S>CH4>N2.When the isosteric heat is greater,the interaction force between gases and adsorbents becomes stronger.