Preparation,modification And CO₂ Adsorption Of ZSM-5/KIT-6 Composite Molecular Sieves

At present,the pollutant emissions from fossil fuel power plants and manufacturing plants have caused serious harm to the environment.Among them,CO₂ emitted from the massive burning of fossil fuels has contributed most to climate change and global warming.Adsorption and separation of CO₂ is a way to reduce CO₂ emission,and it is also an effective way to store carbon resources.The porous solid adsorption method has been widely used because of its advantages of low cost,high efficiency and low energy consumption.In this paper,micro-/mesoporous composite molecular sieve ZSM-5/KIT-6（ZK）was fabricated,modified by amines,characterized by X-ray diffraction（XRD）,thermal gravimetric and differential thermal gravimetric analysis（TGA/DTG）,Fourier transform infrared spectra（FTIR）,Brunauer–Emmett–Teller（BET）,scanning electron microscopy（SEM）and elemental analysis methods,and then was carried out the investigation of the CO₂ adsorption performance and mechanism.In this paper,ZSM-5/KIT-6 was synthesized via assembly procedure using tetrapropylammonium hydroxide（TPAOH）and nonionic three block copolymer P123 as directing agents.The mechanical mixtures with different ZSM-5 contents（25、50、75%）and pure ZSM-5 as well as pure KIT-6 were prepared for comparison.Among the composite samples,ZK has the largest specific surface area（749.9 m²/g）,total pore volume（1.11cm³/g）and mesoporous volume（1.04 cm³/g）.At 60°C,ZK exhibited the highest CO₂adsorption capacity（1.22 mmol/g）.ZK was impregnated by tetraethylenepentamine（TEPA）or polyethyleneimine（PEI）with the mass percentage of 50,60,70 and 80%,followed by the investigation of CO₂adsorption performance at 30,45,60,75 and 90°C.At 60°C,as amine loading was 60%,ZK-TEPA-X exhibited the optimum adsorption capacity of 5.32 mmol/g and amine efficiency of 0.38,and ZK-PEI-X also exhibited the optimum adsorption capacity of 4.49mmol/g and amine efficiency of 0.35.For ZK-TEPA-60,the optimum adsorption temperature was 60°C and the adsorption capacity was 5.32 mmol/g.While for ZK-PEI-60,the optimum adsorption temperature of 75°C with an adsorption capacity of 4.59 mmol/g was observed.ZK was double functionalized using 50%N¹-（3-trimethoxysilylpropyl）diethylenetriamine（TMPTA）as grafted component and TEPA or PEI with 30,50 and 60%loading as impregnated component followed by the investigation of CO₂ adsorption performance at 60,75 and 90°C.At 60°C,the grafted sample AZK demonstrated an adsorption capacity of 2.08 mmol/g with an amine efficiency of 0.42.TEPA-loaded samples still had high adsorption capacity of 5.91 mmol/g even at 60%loading,while the optimum loading was 50%for PEI-loaded samples with an adsorption capacity of 4.19 mmol/g.The optimum adsorption temperature was 75°C for both AZK-T60 and AZK-P50.AZK-T60demonstrated an adsorption capacity of 6.28 mmol/g with an amine efficiency of 0.423;while for AZK-P50,the adsorption capacity was 4.69 mmol/g and the amine efficiency was0.42.TEPA-loaded samples had higher adsorption capacity,amine efficiency and adsorption enthalpy than PEI-loaded samples and the properties were better after double functionalization.The fitting results of pseudo-first-order,pseudo-second-order and Avrami kinetic models showed that the adsorption for ZK was physical adsorption while for amine modified samples it was synergetic adsorption of physical and chemical adsorption.Six samples were carried out the five-adsorption-desorption cycle experiments and the results showed that they have stable adsorption performance.