| The greenhouse effect caused by human activities is constantly threatening the human living environment.Fossil fuel combustion is the main source of CO2 emissions,accounting for about 30-40%of the global total emissions.In order to effectively control atmospheric CO2 concentration,the Intermational Energy Agency(IEA)proposed carbon capture and storage technology(CCS)for CO2 capture in coal-fired power plants.The key difficulty of this technology is to find efficient CO2 adsorbents.Mesoporous silica materials have become widely studied as CO2 adsorbents due to their high specific surface area,adjustable pore size and high stability.In this paper,mesoporous silicon MCM-41 was selected as the research object.Firstly,the preparation conditions of MCM-41 were explored.The structure properties of MCM-41 prepared with various ammonia amount were analyzed by X-ray diffraction(XRD),Fourier infrared(FT-IR)and nitrogen adsorption and desorption.The optimum preparation conditions of MCM-41 were obtained.In order to further improve the adsorption performance of MCM-41,two modification methods(grafting and impregnation method)were used to load organic amine onto the surface or pore of the material,and systematically compared the advantages and disadvantages of the two modification methods in terms of adsorption performance and stability.Meanwhile,MCM-41 with different surfactant content was firstly prepared by controlling calcination temperature in this paper,confirmed the promotion of surfactant on the adsorption performance of amine functionalized MCM-41.The diffusion coefficient of CO2 in modified MCM-41 was calculated by Fick diffusion model,and the mechanism of promoting CO2 capture by surfactant was obtained.Based on this research idea,this paper mainly carries out the following work:(1)The effects of ammonia(20,30,40 and 50g)on the structure properties of MCM-41 and the relationship between the structure and adsorption performance of MCM-41 were explored.XRD,FT-IR and nitrogen adsorption and desorption were used to test the structure properties of the samples.The data show that the pore size and specific surface area of MCM-41 are smaller when the amount of ammonia is 20g.The pore size of MCM-41 prepared with 30 and 40g of ammonia is 2.6nm.When the ammonia continues to increase.The pore size of MCM-41 is as high as 3.95nm,and the adsorption capacity of CO2 is 0.75mmol·g-1.The results show that the structure and properties of MCM-41 prepared with 50g ammonia are the best,and the CO2 adsorption capacity of MCM-41 with larger pore size is large.(2)MCM-41 was impregnated and grafted with polyethyleneimine(PEI)and 3-aminopropyltriethoxysilane(APTS)respectively with organic amine loading of 40,50 and 60w.t%.The adsorption and cyclic regeneration performance of adsorbents were studied,and the adsorption process was fitted by adsorption kinetic model.The results showed that the adsorption capacity of MCM-41 modified by 50w.t%PEI and 50w.t%APTS reached the maximum.The adsorption capacity of MCM-41 was 3.53 and 2.41mmol·g-1 at 25℃ and 1 bar,which were 4.7 and 3.2 times of that of MCM-41,respectively.The cyclic adsorption-desorption data showed that the adsorption capacity of adsorbents modified by impregnation method decreased by 14.22%after five cycles,and the adsorbents prepared by grafting method decreased by 5.19%.The Avrami model shows the highest correlation coefficient for the adsorption curve and the predicted equilibrium adsorption capacity is the closest to the experimental value.It can be seen that the adsorption mechanism of impregnated and grafted MCM-41 is the same,but the adsorption capacity of impregnated adsorbents are higher while the stability of the grafted adsorbents are better.(3)MCM-41 was calcined at 100,200,300,400 and 550℃ for 5h,and modified by 50%PEI.Structural and adsorption properties of all samples were characterized.The influence of calcination temperature on the structure properties and the effect of surfactant on the adsorption performance of MCM-41 were analyzed.The mechanism of surfactant promoting the adsorption properties of amine-functionalized MCM-41 was studied by Fick diffusion model.The structural data showed that with the increase of calcination temperature,the residual amount of surfactant decreases gradually,the pore structure performance enhances gradually,and the structure performance of MCM-41-400℃reaches the maximum.The adsorption data show that before modification,the adsorption performance of the sample is positively correlated with the mechanism performance,and after modification,the adsorption capacity of the PEI-MCM-41-100℃ with the worst structural properties is the largest,which indicates that the surfactant can improve the adsorption of the adsorbent only under the combined action of PEI and surfactant.By calculating the diffusion coefficient of CO2 at PEI-MCM-41-100/200/300/400/550℃,the diffusion resistance of CO2 at PEI-MCM-41-100℃ is the smallest,which directly proves that the adsorption performance of surfactant promoting amine-functionalized MCM-41 is achieved by reducing the diffusion resistance. |
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