Study On Adsorptive Desulfurization Performance Of Amine-modified Silica Hybrid Aerogels With Doping Ag

Hydrocarbon fuel is an ideal hydrogen feedstock for fuel cell systems,however,the high content sulfides in gasolines are poisonous to the reforming catalysts as well as electrodes in fuel cell stacks.Burning of sulfides in hydrocarbon fuels emits sulfur oxides resulting in severe acid rain.The current hydrodesulfurization?HDS?is highly efficient for removing sulfides,disulfides and mercaptans,while less effective for thiophenic compounds,so it is difficult to achieve the production of zero sulfur hydrocarbon fuel.Adsorption desulfurization?ADS?is widely considered as a deep desulfurization technology owing to the lower production cost,simple regeneration operation,and higher selectivity,especially it can remove thiophenics effectively.Developing adsorbents with high capacity,high selectivity,and good regeneration performance is critical for adsorptive desulfurization technology.Aerogels are three-dimensional?3D?network porous materials formed via aggregation of interconnected nanometer particles,applied widely in the adsorption fields,because of the large surface area,high porosity as well as adjustable framework structure.In our previous works,Ni O-SiO₂,Cu₂O-SiO₂,Ag/SiO₂aerogels based on?-complexation,displayed a superior adsorption performance for thiophenics.However,the sulfur uptake capacity of?-complexation adsorbent was significantly reduced in the presence of aromatics and olefins,and the loss of transition metal ions in solvent washing regeneration resulting in the poor regeneration performance.In this work,the amine-modified SiO₂ hybrid aerogel adsorbents?SiO₂-NH₂?were synthesized via the sol-gel method followed by ambient drying technique.The structure and physicochemical properties of sample were characterized by XRD,XPS,SEM,in-situ FT-IR,XRF,N₂ adsorption-desorption and contact angle experiment.Adsorptive desulfurization performance of SiO₂-NH₂ adsorbent was studied by batch experiments and breakthrough adsorption experiments.The results indicated that the adsorption capacity of SiO₂-NH₂ for thiophene was much higher than that of SiO₂ due to the hydrogen bond interaction between thiophenics and amino groups.Among them,SiO₂-NH₂-8 performed best,owing to it possessed a higher content of surface amino groups and larger specific surface area at the same time.The adsorption capacities for thiophene,benzothiophene and dibenzothiophene of SiO₂-NH₂-8 were 10.2,9.5,and 6.8 mg-S/g_ads,respectively.The equilibrium adsorption data was well fitted by the Freundlich model,implying multilayer adsorption occurred on the heterogenetic surface of SiO2-NH2-8.Sirapidly adsorb thiophenics within 5 min,which could correlate properly with pseudo-second-order kinetic model,indicating rate-controlling steps involve surface adsorption.The adsorption of SiO₂-NH₂-8 for TP was not affected by the toluene and cyclohexene in model gasoline.Heating at 393 K for 12 h could completely recover the adsorption performance of SiO₂-NH₂-8 for TP.In order to reduce the shrinkage and damage of the pore structure on the aerogel surface caused by capillary stress during atmospheric drying process,the hydrophobic methyl groups were introduced in SiO₂ to obtain SiO₂-CH₃-NH₂ hybrid aerogels.Compared with SiO₂-NH₂-4.0,SiO₂-CH₃-NH₂-4.0 with the same Si/N molar ratio exhibited a larger specific surface area,pore size and pore volume.Among them,SiO₂-CH₃-NH₂-4.0 had the best desulfurization adsorption performance,and the adsorption capacities of thiophene,benzothiophene and dibenzothiophene were 7.8,9.5,and 10.9mg-S/g_ads,respectively.The equilibrium adsorption data of SiO₂-CH₃-NH₂-4.0 for thiophene from model gasoline was well fitted by the Freundlich model,and the kinetic data was correlated properly with pseudo-second-order kinetic model.The adsorption process of thiophene from model gasoline over SiO₂-CH₃-NH₂-4.0 was an endothermic process with reduced chaotic and spontaneous.SiO₂-NH₂-8 exhibited an excellent adsorption selectivity for thiophene and regeneration performance,however,a low adsorption capacity could not be ignored.Therefore,Ag/SiO₂-NH₂ was obtained through the coordination between-NH₂ of SiO₂-NH₂-8 and Ag ions.Ag/SiO₂-NH₂removed thiophenics from model gasoline via hydrogen bond and?-complexation interaction,simultaneously.Compared with Ag₂O/SiO₂,the actual incorporated Ag content of Ag/SiO₂-NH₂ was significantly increased,and the loss rate of Ag was further reduced during the solvent washing process.Among them,Ag/SiO₂-NH₂-50 performed best,the adsorption capacities for thiophene,benzothiophene,and dibenzothiophene were 10.2,11.6 and 12.9 mg-S/gads,respectively.The equilibrium adsorption data of Ag/SiO2-NH2-50 for thiophene from model gasoline was well fitted by the Freundlich model,and the kinetic data was correlated properly with pseudo-second-order kinetic model.The adsorption process of thiophene from model gasoline over Ag/SiO2-NH2-50 was an endothermic process with reduced chaotic and spontaneous.