Study On The Adsorption And Separation Performance Of Metal Organic Framework Materials For N₂O-CO₂

Nitrous oxide（N₂O）is the third largest greenhouse gas after CO₂ and CH₄,and it can seriously damage the ozone.N₂O can also be used as rocket oxidant,cream foaming agent,anesthetic,N,O atom donor in the chemical field,etc.making it have great application value.The largest source of industrial N₂O emissions is the exhaust gas produced by the cyclohexane method of producing adipic acid which is the main raw material for nylon 66 and polyurethane foam and its demand is increasing year by year,so the recovery and utilization of N₂O in the exhaust gas is of great significance for reducing greenhouse gas emissions and increasing its economic value.Besides N₂O,many impurity gases such as N₂,CO₂,O₂,H₂O,CO and NO₂exist,among which the physical properties of CO₂ and N₂O are extremely similar,so the separation of N₂O and CO₂ has great challenges.Pressure swing adsorption technology has the advantages of low energy consumption,adsorbent recyclability and simple operation,which is a common separation method in the field of gas separation and purification,and the most crucial factor is the choice of adsorbent.As a new type of adsorbent,MOFs have the advantages of large adsorption capacity and high selectivity,and have shown great application prospects in the field of gas separation.This thesis mainly focuses on the synthesis,characterization and post-modification of two rigid MOFs with unsaturated metal sites and three flexible MOFs,studies the adsorption separation properties of N₂O and CO₂,and explores their separation mechanism.The main research work is summarized as follows:（1）Based on the fact that CO₂ is an acidic gas but N₂O is not,ED-MIL-100Cr-X was successfully prepared by using different amounts of ethylenediamine modification,and their adsorption properties of CO₂ and N₂O on basic sites were studied.The results show that the adsorption of CO₂ and N₂O on MIL-100Cr is basically the same,which is 129.9 cm³/g and129.4 cm³/g,respectively,and the effective separation of CO₂/N₂O cannot be achieved.After ethylenediamine modification,the adsorption of CO₂ and N₂O decreases,but the adsorption of N₂O decreases more obviously.The adsorption capacities of CO₂ and N₂O on ED-MIL-100Cr-0.4 are 91.9 cm³/g and 44.9 cm³/g,respectively,and the adsorption amount gap was the largest.The selectivity calculated by IAST shows that the CO₂/N₂O selectivity of ED-MIL-100Cr-0.4is up to 28.0,which is much higher than that of MIL-100Cr（0.9）.The breakthrough experiment further proved that ED-MIL-100Cr-0.4 has excellent CO₂/N₂O separation performance,and multiple adsorption and desorption cycles show that the modified material has good repeatability.（2）Using flexible MOFs with different opening pressures for different gas molecules,three flexible MOFs ELM-11,ELM-12 and MIL-53Al were selected to study their N₂O and CO₂ adsorption and separation properties.The results show that the opening pressure of CO₂on ELM-11 and ELM-12 is lower than that of N₂O,but it is opposite on MIL-53Al.The gate opening pressure difference on ELM-12 and MIL-53Al is only manifested at high pressure,but ELM-11 produces this phenomenon at low pressure.The GCMC was used to explore the causes of the difference in opening pressure.The separation of N₂O and CO₂ is achieved by different high-pressure opening pressures for the first time,and the breakthrough experimental results show that MIL-53Al has a potential N₂O/CO₂ separation performance at 8 bar.Multiple adsorption-desorption cycles shows excellent stability in all three materials.（3）The effect of MIL-100Fe on the adsorption separation of N₂O/CO₂ was studied by using the characteristics of Fe²⁺unsaturated metal sites after activation at high temperature（573K）and high vacuum(1×10^-7 bar).The results show that after activating at a lower temperature（423 K）,the adsorption sites in MIL-100Fe were Fe³⁺-F^-site and Fe³⁺unsaturated metal site,and the adsorption amounts of CO₂ and N₂O were basically the same,showing no separation possibility.DFT calculation shows that Fe³⁺-F^-has strong force with CO₂ but Fe³⁺has strong interaction of with N₂O,so the adsorption amount of these two gases is basically the same.After high temperature and high vacuum activation,Fe²⁺and Fe³⁺was the main adsorption site in MIL-100Fe-300,both of which have stronger interaction forces for N₂O,so that the adsorption of N₂O is greater than CO₂.The IAST selectivity shows that the N₂O/CO₂ selectivity at 298 K,1 bar gradually increases from 1.08 of MIL-100Fe-150 to 1.84 of MIL-100Fe-300.Through the breakthrough experiment,it is further proved that MIL-100Fe-300 has a potential N₂O/CO₂ separation performance.