Adsorption And Separation Properties Of Gas Mixtures On Ni-MOF-74 In The Presence Of Water Vapor

The adsorption-based separation technology plays a crucial role in the modern chemical industry,while the properties of adsorbents determine the efficiency in the separation processes.In the past decade,metal-organic frameworks(MOFs)as adsorbents have been extensively investigated,showing potential application in some adsorption-based separations.MOFs have high BET specific surface areas,large pore volumes,adjustable pore sizes,and a wide diversity of structures and compositions.Ni-MOF-74 has a three-dimensional network with a pore size of ca.1.1 nm.The residual solvent in the synthesis can be easily removed after post-treatment.The most important characteristic of Ni-MOF-74 is that there is a high concentration of the coordinatively unsaturated metal sites in the framework.This thesis research was focused on investigating the adsorption and separation properties of Ni-MOF-74,and the main results are summarized as follows:1.Ni-MOF-74 was synthesized by a hydrothermal method using Ni2+ and 2,5-dihydroxyterephthalic acid(H4DOBDC)as metal node and organic ligand,respectively,and the mixture solution of N,N-dimethylformamide(DMF),ethanol,and water as reaction solvent.The synthesized solid sample was then washed with DMF and methanol,respectively,the so-called two-step process.The synthesized sample has a BET surface area of 1450 m2·g-1 and a total pore volume of 0.59 cm3·g-1,in which the microporous pore volume is 0.54 cm3·g-1.The XRD characterization confirms that the synthesized material is Ni-MOF-74.In addition,the result from the SEM characterization shows that the synthesized sample consists of crystallite agglomerates to form particles with an average size larger than 10 ?m.2.A volumetric method was used to measure the isotherms of CO2,N2,CH4,C3H6,and C3H8 on Ni-MOF-74 at 298;323,and 348 K.Then the dual-site Langmuir and Langmuir isotherms were separately used to describe the measured isotherms by means of a combined fitting method.The results show that the dual-site Langmuir or the Langmuir model can describe the measured isotherms very well.In addition,under the same conditions,the adsorbed amounts for CO2 are much higher than those for CH4 or N2,and,the Imeasured adsorption isotherm data of C3H6 are higher than those of C3H8.This could be due to the strong specific interactions between the coordinatively unsaturated metal sites in the framework and CO2 or C3H6.Moreover,the ideal adsorbed solution theory(LAST)was used to predict the binary isotherms and selectivities,and the corresponding results will be discussed.3.Finally,the break:through-column technique was used to investigate the separation performance of C3H6/C3H8,CO2/N2,and CO2/CH4 mixtures on Ni-MOF-74.Furthermore,the coexistence of water vapor on the separation performance was carried out.The results indicate that Ni-MOF-74 can effectively separate C3H6/C3H8,CO2/N2,and CO2/CH4 mixtures under a dry condition,and the coexisting water vapor has a less effect on CO2/N2 mixtures,a moderate effect on CO2/CH4,and a significant effect on C3H6/C3H8 mixtures.