| CO2 is one of the main greenhouse gases causing global warming.With the increasing harm of global climate change to the ecological environment,CO2 emission reduction has gradually become the global human consensus.Direct air capture(DAC)technology is an important negative carbon emission technology,and it is also one of the indispensable technical means to achieve the goal of carbon peak and carbon neutrality.Among them,the solid adsorption technology with solid amine adsorbent as the core has attracted wide attention due to its high CO2 adsorption selectivity and low regeneration energy consumption.However,the solid amine adsorbents currently have the problems of complex and expensive preparation process,low adsorption capacity of CO2 from air,and poor recycling performance.The above problems lead to high cost,thus prevent large-scale industrial applications of solid amine adsorbents.At the same time,the mechanism of CO2 adsorption and deactivation of solid amine adsorbents is still unclear.Therefore,an efficient and low-cost resin-based solid amine adsorbent was developed in this thesis.The CO2 adsorption and cycling performance were investigated,and the mechanism of CO2 adsorption and deactivation was further explored,which provided a theoretical basis for the industrial application of solid amine adsorbents.Firstly,a series of solid amine adsorbents were prepared by impregnation method using commercial solid porous materials such as macroporous adsorption resin,γ-Al2O3,fumed silica and cellulose as supports.The adsorbents were characterized by BET,SEM-EDS,FTIR and EL.The effects of organic amine type and molecular weight(TEPA,PEI Mw=600,1800,10000),amine loading(10 wt%～40 wt%)and adsorption temperature(30℃～70℃)on CO2 adsorption performance were studied by thermogravimetric analyzer.The results showed that the larger specific surface area,pore volume and pore size of the support could ensure the organic amine load and improve its dispersion characteristics.The X-5 macroporous adsorption resin loaded with 30 wt%TEPA had the highest CO2 adsorption capacity,and its adsorption capacity for pure CO2 at 30℃ could reach 6.08 mmol/g.Compared with PEI,TEPA had more significant effect on improving CO2 adsorption capacity.When the amine loading was less than 30%,the CO2 adsorption capacity increased with the increase of TEPA loading.The increase of organic amine molecular weight was not conducive to the diffusion of CO2 in the organic amine molecular layer.The adsorption of pure CO2 on 30%TEPA/X-5 was thermodynamically controlled.The fractional kinetic model and Redlich-Peterson adsorption isotherm model fitted the CO2 adsorption curve best,with R2 above 0.93 and 0.96 respectively.In-situ infrared spectroscopy analysis confirmed that the chemical reaction process of CO2 and TEPA followed the zwitterionic mechanism,and the main products of the reaction were carbamate and carbamate.When the temperature was higher than 40℃,CO2 partially reacted with TEPA to form an irreversible product urea,and the increase of temperature was beneficial to the formation of urea.The occupation of amine active sites resulting from urea was not conducive to the adsorption of CO2.Secondly,the regeneration performance and deactivation characteristics of 30%TEPA/X5 adsorbent at 60℃～120℃ in argon and air atmosphere were studied,and the mechanism of adsorbent regeneration and deactivation was analyzed by in-situ infrared technology.Compared with air purge,the regeneration of 30%TEPA/X-5 adsorbent under inert gas purge had higher stability.The TEPA on the surface of 30%TEPA/X-5 adsorbent volatilized when it was regenerated at variable temperature under argon and air purge,and the volatilization amount of TEPA increased with the increase of temperature.The adsorbent could only achieve complete CO2 desorption at 80℃ and 100℃ under argon purge.Through in-situ infrared spectroscopy analysis,it was found that the chemical reaction between the adsorbent and the gas component during the regeneration process was also one of the reasons for the deactivation.,TEPA reacted with desorbed CO2 to form during regeneration urea with argon purge,and TEPA was oxidized by O2 to form C=O or C=N structure during regeneration with air purge.Finally,the adsorption performance of 30%TEPA/X-5 adsorbent at CO2 concentration of 400 ppm was investigated in a fixed bed system.The effects of temperature(30℃～50℃)and gas composition(O2,H2O)on direct air capture performance were studied.The CO2 adsorption mechanism and reaction path under humid conditions were further clarified by DFT simulation.It was found that the CO2 adsorption capacity of the adsorbent reached a peak at 40℃ under dry conditions,and the highest CO2 adsorption capacity was 2.29 mmol/g.The presence of O2 was not conducive to CO2 adsorption,and moisture could promote the adsorption of CO2 The adsorbent after adsorption saturation under humid conditions was easier to regenerate than the adsorbent after adsorption saturation under dry conditions,and the adsorbent had a faster regeneration rate at 100℃.The 30%TEPA/X-5 adsorbent had good cycling performance under simulated actual air conditions,and the CO2 adsorption capacity only decreased by 4.6%after 5 cycles.DFT calculation results showed that H2O was more easily adsorbed by TEPA than CO2,and the adsorption was more likely to occur at the primary amine active site of TEPA.Under humid conditions,CO2 was more likely to react with H2O to form H2CO3 and then adsorb on the surface of TEPA. |
