Research On Methane Adsorption And Storage Characteristics In Functionalized Metal-Organic Framework Based On ZIF-8

Natural gas has the clean and non-polluting characteristics,and it occupies an important proportion in energy structure.The adsorption method for natural gas under mild conditions is a storage technology with development potential.The metal-organic framework material ZIF-8 has good adsorption capacity for methane and has certain application prospects,but there is still a certain gap compared with the ideal adsorption capacity.From the perspective of functionalized groups,ZIF-8 was selected to discuss the influence of groups with different properties on the amount of methane adsorbed in ZIF-8,and theoretically provide a basis for improving the storage capacity of methane.ZIF-8 amd methane molecular models were constructured.The functionalized ZIF-8 were modified by-NH₂-1,-Cl,-NH₂-2,-C₂H₅ and-NO₂ groups.The calculation results show that the specific surface area is ZIF-8-NH₂-1>ZIF-8>ZIF-8-Cl>ZIF-8-NH₂-2>ZIF-5-C₂H₅>ZIF-8-NO₂,this rule is consistent with the change of pore volume.At the same time,the GCMC simulation results show that under the CFF force field parameters,the adsorption behavior of ZIF-8 on methane can be accurately described.The results also found that functionalized ZIF-8 can provide more adsorption sites for methane.The order of adsorption amount is:ZIF-8-NH₂-1>ZIF-8-Cl>ZIF-8-C₂H₅>ZIF-8-NH₂-2>ZIF-8>ZIF-8-NO₂.The MD results shows that the diffusion coefficient of ZIF-8-NO₂ is the smallest,which explains why the steric hindrance caused by the functional group leads to the low adsorption capacity.Combined with the centroid distribution map,it is found that the distribution of methane in ZIF-8-NH₂-1 is the most uniform.The DFT method is used to study the adsorption mechanism of methane in the adsorbent.The electrostatic potential distribution show that the electrostatic potential distribution and potential energy value in ZIF-8-NH₂-1 are the most favorable.At the same time,the adsorption energy between methane and the adsorbent is not high.ZIF-8-NH₂-1 was used as the adsorbent for experimental synthesis.ZIF-8 was synthesized by hydrothermal method,the optimal synthesis process was determined,and ZIF-8-NH₂-1 was synthesized.Comparing with the microstructure parameters,it was found that the specific surface area of ZIF-8-NH₂-1 increased to 748.00 m²/g,and the pore volume increased to 0.29 cm³/g.The pore size distribution changes from 0.85 to 1 nm to 0.65 to 0.7 nm and 0.8 to 0.95 nm.Finally,the gas adsorption experiment device was used to carry out the experiment of methane adsorption in ZIF-8 and ZIF-8-NH₂-1.The methane adsorption capacity of ZIF-8-NH₂-1 is significantly higher than that of ZIF-8at the temperature of 25℃.When the pressure reaches 5～7 MPa,the methane adsorption capacity of ZIF-8-NH₂-1 is increased to 251.71 cm³/cm³,21.53%higher than that of ZIF-8.With the decrease of temperature,the storage capacity of ZIF-8-NH₂-1 methane is increased by 153.86%at 15℃.The isometric adsorption heat of methane in ZIF-8 and ZIF-8-NH₂-1 is calculated.The adsorption heat of methane in ZIF-8-NH₂-1 is less than the heat in ZIF-8,indicating that the energy required for regeneration of the adsorbent is not high.After multiple cycles of use,ZIF-8 and ZIF-8-NH₂-1 both have good repeated use performance,and the performance degradation of ZIF-8-NH₂-1 is lower than that of ZIF-8.ZIF-8-NH₂-1 is a good methane adsorbent,which provides theoretical guidance for the application of natural gas adsorption storage.