Characteristics Of Carbon Dioxide Adsorption Of Modified Fumarate Based Metal-Organic Frameworks

The excessive use of fossil fuel has led to a large amount of CO₂ emissions.Although the research on sustainable energy is flourishing,the energy consumption mode dominated by fossil fuel around the world will not change for a long time.Since the main source of CO₂ is fossil fuel emissions after combustion,it is important to capture CO₂ in the exhaust gas after combustion to control CO₂ emissions.Among the many post combustion CO₂ capture technologies,the adsorption method has great application prospects due to low regenerative energy consumption,easy operation,compatible new construction and already-produced power plants.Adsorption materials play a vital role in the CO₂ capture process.Metal organic frameworks（MOFs）and solid amine show great potential in post combustion CO₂ capture applications.However,MOFs are always synthesized by hydrothermal method which need tedious post treatment procedure,and the common organic ligands of traditional MOFs are very expensive.Solid amine exhibit superior CO₂ adsorption performance under post-combustion conditions,but the preparation of tranditional support material for fabricate solid amine is complicated and requires tedious pre-treatment steps.So the large scale preparation and application of these two adsorbents are limited.Based on this,this paper proposes the preparation of MOFs using cheap fumaric acid as organic ligand,and tests there CO₂ adsorption performances.Then,Material Studio soft ware was employed to study the CO₂ adsorption performances of Aluminum fumarate MOF（AlFu）before and after functional groups modification.Based on the simulation results,AlFu was used as support to prepare solid amine CO₂ adsorbents and its CO₂ adsorption performance under different synthesis and operating conditions were investigated.Finally,the CO₂ adsorption kinetics of AlFu based solid amine adsorbents were analyzed by the adsorption kinetic models and the rate limiting kinetic models.The main research contents and conclusions of this paper are as follows:（1）Zirconium fumarate MOF（ZrFu）was prepared by conventional hydrothermal synthesis using cheap fumaric acid as organic ligand.On this basis,Iron fumarate MOF（FeFu）,and Aluminum fumarate MOF（AlFu）were successfully synthesized by a rapid synthesis method at room temperature.The results show that AlFu has the best pore structure and thermal stability,its specific surface area is 828.442 m²/g.The CO₂adsorption amount of ZrFu,FeFu and AlFu at 30°C and 1 bar were 1.050 mmol/g,0.795mmol/g,and 1.610 mmol/g,respectively.（2）The CO₂ adsorption properties of the functional groups modified AlFu were studied using Material Studio software based on the grand canonical Monte Carlo method.Three kinds of functional groups of-CH₃,-OH and-NH₂ were used to modify AlFu framework.The results show that all functional groups modification will enhance the adsorption of CO₂ molecules and reduce the force between the AlFu framework and N₂molecules,which will improve the adsorption selectivity of AlFu.The adsorption amount of AlFu and modified AlFu decrease with the increase of temperature,the–NH₂functionalized AlFu shows highest CO₂ adsorption amount of 4.59 mmol/g at 50°C,1.5bar.Therefore,the modification of AlFu with functional groups is an effective method to enhance the performance of CO₂ capture after combustion.（3）Based on the above research,four kinds of solid amine adsorbents include PEI-AlFu,PEHA-AlFu,TEPA-AlFu and TETA-AlFu were prepared by introducing the amino groups into the rapid synthesized AlFu framework material at room temperature,and the post combustion CO₂ adsorption performance of these solid amine were investigated.The results show that the adsorption performance of solid amine adsorbent is much higher than that of AlFu.The optimum loading for PEI and PEHA is 50 wt%,and their CO₂adsorption amount under the optimal adsorption conditions is 2.67 mmol/g and 2.97mmol/g,respectively.The optimum loading of TEPA and TETA is 60 wt%,and the adsorption amount under the best conditions is 3.59 mmol/g and 3.06 mmol/g,respectively.The effect of CO₂ partial pressure on the adsorption performance of small molecular amine modified AlFu material is stronger than that of large molecular amine modified AlFu.The results of cyclic adsorption and desorption experiments show that PEI,PEHA and TEPA modified AlFu solid amine adsorbents have great cycle stability.（4）The CO₂ adsorption kinetics of amine modified AlFu was studied.The result show that the fractional order kinetic model can better fit the CO₂ adsorption curve,indicating that the adsorption process contains both physical adsorption and chemical adsorption.The rate limiting kinetic models were used to analyze the adsorption limiting factors of all amine modified AlFu.The results show that the adsorption rate of the large molecular weight amine modified AlFu is controlled by intraparticle diffusion due to aggregation.