Preparation And CO₂ Adsorption Performance Of Zeolites From Rice Hull Ash

Carbon dioxide is a greenhouse gas that has a significant impact on global warming,and its emissions in industrial production and atmospheric concentrations are increasing year by year.In order to cope with climate deterioration and environmental crisis,as well as address the challenges of carbon emission reduction,research on CO2 capture technology is particularly urgent.The use of solid adsorbents to capture CO2 in industrial flue gas after combustion is a well-suited technical path and can be quickly deployed due to its simple system.In this paper,various zeolite-based adsorbents were prepared by using rice husk ash as a cheap raw material,and the microstructure and adsorption properties of the materials were studied from preparation method,characterization,gas adsorption and theoretical calculation,and the application potential of CO2 adsorption and separation in industrial flue gas was discussed.The main research contents and conclusions are as follows:(1)NaA,NaX and NaZSM-5 zeolites were prepared by using SiO2 extracted from rice hull ash.Various characterization results indicated that the seed hydrothermal process was advantageous for obtaining higher crystallinity and smaller size nanoparticle zeolites.The CO2 and N2 adsorptions at 0,30,and 60? were tested and fitted perfectly by the Dual-site Langmuir isotherm model.At 0? and 101.3 kPa,the maximum CO2 equilibrium adsorption amount of NaA-RS,NaX-RS and NaZSM-5-RS were 1.46,3.12 and 2.20 mmol/g,respectively.The CO2/N2 adsorption selectivity results indicated that in order to achieve greater separation,the degree of vacuum should be increased as much as possible during the pressure swing adsorption process.The calculation results of the adsorption heat of three zeolites indicated that the heat released during the adsorption process had no obvious influence on the adsorption capacity of the adiabatic work.(2)A series of ZSM-5 zeolites with different usage amount of colloidal silica was prepared by rice husk ash and pseudo-boehmite in colloidal system.The characterization results demonstrated that the method can reduce the formation of impurity crystals and improve the pore structure.The adsorption amount of CO2 at 0 and 90? was tested,with maximum values of 55.01 and 23.08 cm3/g,respectively.The adsorption amount of N2 and O2 was tested,and the adsorption selectivity of CO2/N2 and CO2/O2 at 101 kPa was estimated to be 4-8 and 15-25,respectively.The Langmuir,Freundlich and Sips isotherms were utilized to fit the adsorption data and analyze the adsorption mechanism.The cyclic adsorption-desorption experiments of ZSM-5-25,ZSM-5-50 and ZSM-5-75 demonstrated excellent regenerative stability.(3)Four kinds of cation type M-ZSM-5(M=Na+,Li+,Mg2+,Ca2+,Cu2+,Zn2+,La3+,Ce3+)were prepared by rice husk ash as raw material,including alkali metals,alkaline earth metals,transition metals and rare earth metals.Characterization and adsorption tests of the materials indicated that the degree of ion exchange,relative crystallinity,texture property,and cation type had the effect on the adsorption performance of CO2 and N2.Cu-ZSM-5 and Zn-ZSM-5 had excellent adsorption capacity,which were 70.24 and 74.38 cm3/g at 0? and 120 kPa.The tendency of the ratio of the Henry's law constant of CO2 to N2 is the same as that of the adsorption amount under low pressure,and the tendency of the working adsorption amount is the same as the tendency of the ratio of the adsorption amount of CO2 to N2 under high pressure.(4)The ZSM-5 with mesoporous structure was loaded with TEPA for amine functional modification to verify the CO2 adsorption performance of the composite adsorbent in the condition of industrial flue gas.The characterization results showed that the crystal structure of the amine-modified zeolite was not changed,and the amine group was uniformly supported to the pores and surface of ZSM-5.The optimum CO2 adsorption temperature of ZT7 was 100?and the adsorption capacity was 1.80 mmol/g.The aminoe efficiencies of ZT7 at 80,90 and 100? were 0.311,0.342 and 0.351,respectively,which indicated the utilization extent of the amine groups.The adsorption test under the condition of 10%CO2 evaluated by ZT7,which reached the adsorption amount of 82?88%compared to pure CO2.The adsorption kinetics and adsorption thermodynamic calculation results showed that the reaction of amine functionalized zeolite with CO2 was a complex mixing process of physical adsorption and chemical adsorption.(5)A series of amine functionalized adsorbents ZSM-5-PEI-X with different PEI loadings were prepared by using rice husk ash.The CO2 adsorption experiments of various PEI loading adsorbents at different temperatures showed that ZSM-5-PEI-30 had the highest adsorption at 120?,which was 1.96 mmol/g.The Fractional-order kinetic model can be used to accurately predict the CO2 adsorption rate and saturated adsorption capacity of ZSM-5-PEI-30.The analysis of the Fractional-order kinetic model and the Dual-site Langmuir adsorption isotherm model showed that the addition of amine groups led to the main role of chemisorption in the initial stage,and then the adsorbent tended to be saturated in the subsequent physical adsorption.Excellent CO2/N2 adsorption selectivity and stable cycle regeneration performance indicated that ZSM-5-PEI-30 was an excellent solid adsorbent for adsorption and separation of CO2 in industrial flue gas.