Studies On The Preparation And Modification Of Coal Gangue Based Porous Silica Materials And Its Application Of CO₂ Adsorption

Coal gangue is a hazardous solid waste of coal production in the excavation and washing processes.Based on the unique way of energy consumption,a large quantity of coal gangue pile causes a severe social,environmental,and economic problems;however,the main aluminosilicate component of gangue has high value-added potential.At the same time,the absorption of low concentration CO₂ has also received extensive attention and the solid adsorbents pay more attention to the low corrosion of the equipment and the small energy consumption of the regeneration.Therefore,a solid adsorbent with mesoporous structure was prepared for the low concentration CO₂ adsorption.Then,more research on enhencing the low concentration CO₂ adsorption amount was studied by surface modification.The main contents of the study include:1)the CO₂?8%Vol?adsorption in simulated flue gas on the mesoporous SiO₂ material?M-SiO₂?from coal gangue was studied.The M-SiO₂ structure was characterized systermly by the technologies of specific surface area test?BET?,X ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X ray photoelectron spectroscopy?XPS?,fourier transform infrared spectroscopy?FTIR?,and thermogravimetric analysis?TG-DSC?.After preparation of SiO₂ porous silicon material from coal gangue,single factor and orthogonal experiment were used to optimize the preparation conditions of the material.And the optimal preparation conditions were as follows:[CTAB]=0.25 g/10 mL H2O,T=393.15 K,[HCl]=2.5 mol/L,and t=20 h.Based on the orthogonal test,the maximum and minimum influence factors of material preparated were determined:range?hydrothermal temperature=1.280?>range?[HCl]=1.164?>range?[CTAB]=1.013?>range?hydrothermal time=0.256?.2)The CO₂ adsorption amount of the M-SiO₂ was improved by surface amino group modification.Different modifiers:ethylenediamine?EDA?,diethanolamine?ETA?,two ethanol?DEA?,triethanolamine?TEA?,and tetraethylenepentamine?TEPA?were applied to systemly analyze the effect of single amine and polyamine on the modification,and the effect of short chain amines and long chain of amine on the modification.Ethylenediamine was ensured as the best modifier,and the best modification conditions were as follows:M-SiO₂:EDA=2:1,t?immersion time?=10 h,and T?drying temperature?=343.15 K.The composition and modification results of M-SiO₂ and EDA-M-SiO₂ were analyzed by means of FTIR,XPS,TG,TEM,SEM and other characterization methods.The results showed that the main components of M-SiO₂ and EDA-M-SiO₂ were SiO₂ with a little adsorptive water,crystalline water and trace organic components.Besides,EDA-M-SiO₂contained amino groups.The surface channel of M-SiO₂ material was accumulated by a large number of uniform small particles,whose average pore size was 7.35 nm,the specific surface area was 156.639 m²·g^-11 and the pore volume was 0.2878 m³·g^-1.After modification,the surface microstructure of EDA-M-SiO₂ changed,but its basic structure did not change.Its specific surface area changed to 31.66 m²·g^-11 and pore volume was0.1257 m³·g^-1.After modified by impregnation,The EDA was ensured as the best modifier.At 298.15K,the adsorption amount of modified material on 8%CO₂ increased from 9.61 mg/g to83.5 mg/g,and the efficiency of amine CO₂ capture was as high as 58%.3)The adsorption phase equilibrium,kinetics and thermodynamics of CO₂ adsorption on M-SiO₂ were studied.Applying breakthrough curve and the LDF linear dynamic fitting model to determine that the increase of the adsorption temperature would decrease the CO₂adsorption amount.The adsorption isotherms at different temperatures for CO₂ adsorption on the M-SiO₂ determined that with the increase of temperature,the CO₂ adsorption of M-SiO₂ decreased;and then Langmuir and Freundlich fitting model of the adsorption isotherms determined that the distribution of CO₂ adsorption sites on M-SiO₂ was heterogeneous distribution and adsorption belonged to monolayer adsorption.Besides,the adsorption thermodynamics analysis of CO₂ adsorption on M-SiO₂ determined that the adsorption process belonged to the exothermic process and the adsorption was mainly physical adsorption.The cycle regeneration performance determined that M-SiO₂ has good regenerative property.