Research On Preparation Of MOF/porous Polymer Composite Materials And Its Performance Of CH₄/N₂ Adsorption Separation

As an important supplement of natural gas resources,coal-bed methane has high utilization value.However,the separation of CH4 and N2 in lowconcentration coal-bed methane is extremely difficult,and there is currently no any material that can be applied in industry.Some Metal-organic frameworks(MOFs)with special structures have high CH4 adsorption performance and CH4/N2 separation selectivity,but they have always had the problem of poor hydrothermal stability.In addition,the densification of MOFs microcrystalline powder during the processing and molding will cause a serious decrease in adsorption performance.This work mainly studied the in-situ growth of MOF material(Al-CDC)with trans-1,4-cyclohexanedicarboxylic acid(H2CDC)as the ligand and aluminum ion as the metal center on polyacrylamide(PAM)and hydrophobic polyacrylate(PA).Al-CDC/PAM and Al-CDC/PA composite materials were prepared and the CH4/N2 adsorption and separation performance of them were comprehensively evaluated.The main work contents are as follows:(1)PAM was prepared by a combination of emulsion polymerization and suspension polymerization,and PAM with appropriate hardness and porosity was selected as the support of Al-CDC.The methods of changing the impregnation method and increasing the concentration of precursor solution were used to control the loading and the crystal morphology of Al-CDC in the support.Finally,Al-CDC was uniformly in-situ grown in the inner pores of the polymer.The structures and properties of the composite materials were characterized,and the successful synthesis of Al-CDC in PAM support was confirmed.The prepared Al-CDC/PAM was used as adsorbent for the adsorption and separation of CH4/N2,the adsorption capacity of CH4 reached 24.4 cm3(STP)/g,and the highest selectivity reached 13.5.(2)The macroporous polymer support material is further improved,and hydrophobic PA is prepared by changing the monomer type.The water adsorption capacity of PA is only 30%of that of PAM at 298 K and 1.0 bar,showing excellent hydrophobic property.By introducing-CH3 and-NH2 functional groups to modify the characteristics of PA,and then exploring the influence of PA containing different surface groups on the Al-CDC crystal morphology.Through adjusting the crystal structures,Al-CDC in PA was converted from the original three-dimensional bulk phase to two-dimensional nanosheets with a lateral size of 100～300 nm and thickness of 10～30 nm.After reducing the size of Al-CDC to the nanometer range,the adsorption capacity of CH4 increased to 32.5 cm3(STP)/g.The sorption kinetics of the composite material were tested,and the result shows that Al-CDC/PA has excellent kinetics performance.In order to further verify its CH4 separation performance in actual application,continuous adsorption and desorption cycle tests were performed.After 50 cycles,the CH4 adsorption capacity of the composite material only decreased by 2.0%.