Preparation Of Aldehyde Resin-based Spherical Carbon And Research On Its Desulfurization And Denitrification Performance

The oil resources in the world are decreasing and the quality of crude oil is declining.So,the content of sulfur and nitrogen compounds in crude oil is gradually increasing.The combustion products of the sulfur and nitrogen compounds will seriously pollute the environment.Therefore,with the emphasis on environmental protection of the worldwide and the current stringent regulations on the quality of transportation fuels,as well as the potential application of fuel cells,countries around the world have promulgated a series of fuel regulations to limit the content of sulfur in the fuel.The conditions of the method of hydrodesulfurization(HDS)in industry are harsh.Because it needs to be carried out under high temperature and pressure,and it is difficult to meet new environmental requirements in the world.So it is necessary to find new and economically effective alternatives.At the same time,although there is no limited of the content of nitrogen compounds in the fuel,the existence of nitrogen compounds will inhibit the removal of sulfur compounds.So the nitrogen compounds must also be removed.Among various alternative methods,adsorptive desulfurization is considered to be the most promising method due to its mild operational temperature and pressure,regenerative availability and low energy consumption.Studies indicated that the combination of sulfur-selective adsorption and the conventional HDS can realize the deep desulfurization of fuels.Activated carbon is widely studied as the most valuable adsorbent.In this paper,extended Stober method was adopted to prepare modified phenolic-resin based carbon spheres.The model oils with single sulfur or nitrogen component and multicomponent were prepared using indole,quinoline and dibenzothiophene(DBT)as target adsorbents.The adsorption properties of spherical carbon for sulfur and nitrogen compounds in model fuels were studied.The structural properties,specific surface area,microtopography and phase constitution of the prepared spherical carbons were determined by nitrogen adsorption-desorption,scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray powder diffraction(XRD)technologies.Furthermore,the adsorption mechanism of spherical carbon was analyzed.Firstly,the phenolic-resin based carbon spheres were successfully synthesized by extended Stober method.Polyethylene glycol(PEG)with different adding amount and molecular weight were introduced in the synthesis process to modify the structure of prepared carbon samples.The effect of PEG modification on the adsorptive performance of carbon spheres was investigated.The results show that carbon spheres adding 17.6 wt.%amount of PEG2000 have more developed microporous structure.The specific surface area of modified carbon sphere could reach as high as 625 m2/g.Also,the micropore volume increased to 0.235m3/g.The performance of desulfurization and denitrification is the best,corresponding to the highest adsorptive capacity of 1.93 mmol/g for sulfur and nitrogen compounds.At the same time,the thermodynamic and dynamic behaviors of this carbon sample were investigated.The Freundlich model is more suitable to describe the adsorption of indole,quinolone and DBT.The pseudo second-order model well describes the adsorption of sulfur/nitrogen compounds.Besides,the internal diffusion process of particles was controlling step of adsorption for DBT.In the adsorption process for N compounds indole and quinoline,the intra-particle diffusion is not the only rate controlling step,film diffusion may also influence the N uptake.Secondly,phenolic-resin based carbon spheres with supported transition metal were prepared by two methods.(1)(Cu,Ni,Fe,Ag,Co)-phenolic-resin based carbon sphere were prepared by pore volume impregnation method using phenol-resin based carbon spheres as precursors.The capacity of desulfurization and denitrogenation was investigated.The results show that the introduction of transition metal is beneficial to improve the capacities of phenolic-resin based carbon spheres.The influence of transition metal on capacity follows the sequence:Cu>Co>Fe>Ag>Ni.The adsorption performances of phenolic-resin based carbon spheres with different content of copper were investigated.The results show that the spherical carbon supported 5 wt.%copper nitrate in the precursor has the bestadsorption capacity and the mount of adsorption is 2.58 mmol/g.(2)In another method,copper supported phenolic-resin based carbon spheres were prepared by precursor blending method in which different amounts of copper nitrate were adding to the mixture of reactant to synthesize resin spheres.The desulfurization and denitritication performance were investigated.The results show that the optimum blending amount of copper nitrate was 3 wt.%,the adsorption capacity of copper/phenolic-resin based carbon sphere was the best and the mount of adsorption is 2.34mmol/g.Compared to PEG-modified phenolic-resin based carbon spheres,the adsorption capacity of phenolic-resin based carbon spheres prepared by these two methods is higher.Finally,the adsorption selectivity of copper/phenolic-resin based carbon spheres was studied.The results show that the synthesized copper/phenolic-resin based carbon sphere adsorbed only littlearomatic hydrocarbons and selectively adsorbed sulfur/nitrogen compounds when they have equal concentrations.Furthermore,the adding of transition metal improved the adsorption selectivity for sulfur compounds.Thirdly,the regenerativity of phenolic-resin based carbon spheres were studied by thermal,ultrasonic and solvent regeneration methods.The results show that the solvent regeneration method is superior to the other two methods.Two kinds of renewable solvents of toluene and dimethyl fonnamide(DMF)were investigated.The results show that the adsorption capacity of spherical carbon decreased gradually with the regeneration cycles.After 5 cycles,the adsorption capacity for indole and quinoline rarely decreased.After 6 cycles,the adsorption capacity for DBT was almost unchanged.The DMF solvent regeneration was better than the toluene solvent regeneration for restore of adsorptive capacity.