Quantitative Simulation Research On The Mechanism Of CO₂ Absorption/desorption From Coal-fired Flue Gas By Metal-doped Modified Calcium-based Adsorbent

The large-scale combustion of fossil fuels to produce CO₂is considered to be the main causes of global warming.Among them,coal-fired power plants are the main source of CO₂emissions.Therefore,effective recovery and capture of CO₂emitted by coal-fired power plants is an important ways to alleviate the greenhouse effect.Calcium-based adsorbent has the advantages of large adsorption capacity,CO₂separation at high temperature,cheap and easy-to-obtain raw materials.At present,there are few studies on the interpretation of metal elements to improve calcium-based adsorbents from the microscopic mechanism.In order to solve this problem,this paper uses the CASTEP program based on density functional theory to establish CaO and CaCO₃crystal models and modify them with metal elements to study the performance of CO₂adsorption/desorption,adsorption stability and ion diffusion.The main research contents of this paper are as follows:（1）Established a CaO crystal model to study the effect of metal doping modification on its CO₂adsorption performance and adsorption stability.The adsorption energies of CaO for CO₂and Ca₄O₄clusters are-1.53e V and-4.54e V,respectively.After the modification of metal elements,the adsorption energy of Mg,Al and Zr doped configuration all increases,which means that the adsorption performance and adsorption stability have been improved.The adsorption energy of CO₂increased significantly after Na-doping modification,but the adsorption energy of Ca₄O₄clusters decreased,which means the adsorption stability decreased.The doping modification of Ni,Sr and La didn’t improve the CO₂adsorption performance and adsorption stability.（2）Established a CaCO₃crystal model to study the effect of metal doping modification on its CO₂desorption performance.The reaction energy barrier and reaction heat of CaCO₃desorption of CO₂are 3.98e V and 3.604e V.After the modification of the metal elements on the two doped active sites,the reaction energy barrier and reaction heat of the Mg,Al,and Zr doped configurations All have decreased,indicating that the modification is beneficial to the desorption of CaCO₃.Na doping will not play a beneficial role in the process of CaCO₃desorption of CO₂.On the whole,the top side doped active site configuration has better desorption performance than the central doped configuration.（3）Study the internal O^2-and Ca²⁺diffusion behavior and the influence of metal doping modification on diffusion in the CaO crystal model.The energy barriers of O^2-and Ca²⁺diffusion in CaO are 2.931e V and 1.221e V,respectively.After the modification of metal elements,Mg,Al,and Zr can reduce the diffusion energy barriers of the two ions.O^2-diffusion is an endothermic reaction while Ca²⁺diffusion is an exothermic reaction.Therefore,O^2-diffusion is the velocity control step of the diffusion process.This paper has 22 pictures,8 tables,and 73 references.