Preparation And Desulfurization Performance Of Pd/SiO₂-GO And Pd/SiO₂-APTES Aerogel Composite Adsorbents

After the combustion of sulfides in hydrocarbon fuels,sulfur oxides are emitted,resulting in serious environmental pollution.Currently,the sulfur content in fuels is restricted by environmental regulation all over the word.Conventionally,the hydrodesulfurization（HDS）was effective for the removal of mercaptans,sulfides,and disulfides from fuels but ineffective to remove thiophenic compounds that can cause a decrease in the octane number of fuels.Among various ultradeep desulfurization techniques,adsorptive desulfurization（ADS）technology had received much attention because of the moderate operation conditions,low energy consumption,and no need for hydrogen.The core of adsorption desulfurization technology is the adsorbent.Research and development of adsorbent with mesporous structure,diverse surface active centers and highly dispersition is the main research trend.Aerogel,a three-dimensional porous network structure material formed by the aggregation of nanoparticles,has been widely used in the field of adsorption because of the low density,high porosity and high specific surface area.By doping Ag,Cu and Ni species to SiO₂ aerogels,our group tried to prepare a series ofπ-complex aerogel desulfurization adsorbents such as Ag₂O-SiO₂-50,Cu₂O-SiO₂-50 and NiO-SiO₂-23.But these adsorbents possesed a high loss rate of active components during the prepation process,and the competitive capacity was poor.Pd/SiO₂-GO aerogel composites with different graphene oxide content and Pd/SiO₂-APTES aerogel composites with different Si/Pd mole ration were synthesized by a sol-gel method followed by drying in the atmosphere.A series of characterization methods such as BET,XRD,FT-IR,SEM,XRF,etc.,were used to research the relevant factors affecting the performance of the adsorbent.Meantime,the adsorption performance,regeneration performance and competitive adsorption performance of the adsorbents for thiophenics were investigated through the static and dynamic adsorption penetration experiments.GO was the structural enhancer of SiO₂ aerogel.The Pd/SiO₂-GO aerogel composites did not change the inherent characteristics of the SiO₂ aerogel.When the incorporation rate of GO is 1.0wt‰,the capacity of Pd/SiO₂-GO-1.0‰was the highest,8.89 mg S/gads.In the presence of olefins,aromatic hydrocarbons,nitrides and water,the interference of pridine is most and the methyl tert-butyl ether is least.Compared with the Langmuir model,the Pd/SiO₂-GO adsorption process is more in line with the Freundlich model and belongs to the pseudo-second-order kinetic model,and the intraparticle diffusion is not the only rate control steps.The adsorption process of thiophene by Pd/SiO₂-GO is an exothermic,spontaneous process,and the low temperature is conducive to the adsorption process.By comparing the two regeneration methods of solvent elution（n-heptane-benzene）and atmospheric drying,the solvent elution is more conducive to the regeneration of Pd/SiO₂-GO,attributed to the reduction of its specific surface area and the loss of Pd²⁺.As another modification method to improving the desulfurization performance,the SiO₂-NH₂ is grafted on the surface of SiO₂ aerogel to further improve the transition metal Pd incorporation rate.The Pd/SiO₂-APTES composite aerogel adsorbent is still a three-dimensional network-like mesoporous solid material.When the amount of Pd incorporated is 0.03g,the Pd/SiO₂-APTES composite aerogel has the best desulfurization performance.The adsorption capacities of thiophene,benzothiophene and dibenzothiophene are 10.7mg-S/g_ads 11.6mg-S/g_ads and 13.1mg-S/g_ads,respectively.Both Langmuir and Freundlich models can fit the adsorption process of the Pd/SiO₂-APTES composite aerogel adsorbent well,indicating that the physical and chemical changes exist in this process,and also belong to the pseudo-second-order kinetic model.The intraparticle diffusion is not the only rate control steps.Combied with thermodynamic results,it can be found that the low tempreature was favorable for the adsorption of thiophene.By comparing the two regeneration methods of solvent elution（n-heptane-benzene）and atmospheric drying,the atmospheric drying is more conducive to the regeneration of Pd/SiO₂-APTES.The adsorption capacity was recovered to be 100%of the fresh one after four regenerations.