Kinetic Mechanism Of CO₂ Adsorption On Macroporous Ionic Polymer

Climate change is a major global challenge facing human beings today.Human CO₂emissions aggravate global warming.And extreme climate events are increasingly frequent,which pose a threat to the ecosystem and human survival.China upholds the concept of a community of common destiny and puts forward an independent contribution goal of"achieving peaking carbon dioxide emissions by 2030 and carbon neutrality by 2060".In order to achieve the long-term goal of deep decarbonization or carbon neutralization,breakthrough technical support is needed.Direct air capture（DAC）is one of the most potential carbon"negative emissions"technologies in the future,which can effectively capture and process the CO₂ emitted from distributed sources without the limitation of emission sources and flexibly match carbon storage.The key of DAC technology is to develop efficient and low-cost adsorbents.The moisture swing technology uses the free energy generated by water evaporation as the main energy source,and completes the CO₂ adsorption-desorption cycle by adjusting the partial pressure of water vapor in ambient,and low-grade energy can be used to achieve cascade utilization of energy.Based on moisture swing,dissertation develops a kind of macroporous ionic polymer material with good adsorption performance,and establishes the CO₂ adsorption kinetics model of macroporous ionic polymer material.Furthermore,the CO₂ adsorption kinetics of adsorbent was systematically studied by combining theoretical and experimental research.In this paper,four kinds of quaternary ammonium based anion exchange porous resins（D290,D261,D262,D280）were used as the research objects.Macroporous ionic polymer materials with controllable interface structure and adjustable functional groups were prepared by phase inversion method.The surface morphology,specific surface area and pore volume of adsorbent and porous resin were characterized by scanning electron microscope（SEM）and automatic specific surface analyzer.The results show that the surface of heterogeneous adsorbent is rich in pores,and the particle size distribution of resin is uniform,which is conducive to the mass transfer of CO₂ and improves the adsorbent rate.The kinetic model of CO₂ adsorption by macroporous ionic polymer was established,and four basic diffusion control equations were deduced and established:loading layer diffusion,pore diffusion,solid diffusion and chemical reaction.The model accurately described the actual diffusion reaction process of CO₂ adsorption by macroporous ionic polymer,and revealed the adsorption behavior of adsorbent and the constraints of adsorption rate It provides a theoretical basis for optimizing the performance of adsorbent.The study on the kinetics mechanism of adsorption of CO₂ by macroporous ion polymer materials.The experimental system with rotating bed reactor was built to study the CO₂adsorption kinetics of D290/PES,D261/PES,D262/PES,D280/PES under different resin particle size,relative humidity and temperature.The results show that the particle size of resin is an important factor affecting the adsorption kinetics of CO₂,and the mass transfer resistance of resin particle side accounts for a large proportion.With the decrease of particle size,the surface area exposed to CO₂ atmosphere will increase,which will eventually promote the adsorption of CO₂.Relative humidity has a significant effect on the reaction and diffusion of CO₂ adsorption process,the adsorption rate of CO₂ decreases rapidly with the increase of relative humidity in the range of 21.2%to 84.7%,while D261/PES is relatively less affected by relative humidity.Temperature is a key factor affecting the CO₂ adsorption kinetics.In the range of 10℃to 30℃,the CO₂ adsorption rates of the four adsorbents increase significantly with the increase of temperature.Under the same conditions,the adsorption properties of the four macroporous ionic polymer materials are compared.The results showed that D290/PES and D262/PES had faster adsorption rates of 9.0E-3 and 6.3E-3 1/s,but smaller adsorption capacities of 0.51 and 0.50 mmol/g,respectively.D261/PES and D280/PES had larger adsorption capacities of 0.84 and 0.85 mmol/g,but slower adsorption rates of 1.5E-3 and 0.32E-3 1/s,respectively.Therefore,in order to obtain better CO₂ adsorption performance,a balance between specific surface area,pore size and porous structure should be exploerd.Quantum chemical simulation of CO₂ adsorption on macroporous ionic polymer materials.In this paper,the quaternary ammonium functional groups in the adsorption materials were taken as the research object,and the potential mechanism of CO₂ adsorption process of quaternary ammonium functional groups was studied by using density functional theory（DFT）method and quantum chemistry calculation software under the theoretical level of B3LYP/6-311++G**.The results show that CO₂ molecules preferentially react with anions.Bound water plays an important role in the process of CO₂ adsorption by macroporous ionic polymer materials.For macroporous ionic polymer materials paired with CO₃^2-anions,the interface bound water first transfers protons to form OH^-anions,and then interacts with CO₂ reaction.