Deep Oxidative/adsorptive Desulfurization Of Diesel Fuel Based On Bi-functional Catalytic/adsorptive Materials

Due to the environmental protection and increasingly stringent regulations of sulfur content in fuel,ultra-deep desulfurization of fuel is becoming an increasingly important subject globally.Since the sulfur oxide generated from the combustion of fossil fuel is one of pollutants to atmosphere,which also contributed to acid rain and haze,the urgent need for clean fuel is now a great challenge to refineries around the world.In order to achieve ultra-deep desulfurization by an energy and cost effective way,non-hydrotreating such as oxidative desulfurization,adsorptive desulfurization,and extractive desulfurization have been developed as supplementary technologies.The combination of oxidative and adsorptive desulfurization is a potential technolygy by oxidizing and adsorbing the organosulfur compounds selectively to achieve ultra-deep desulfurization.Adsorbent regeneration is critical for a continuous adsorption-regeneration process and often underestimated.In this work,the regeneration of bifunctional Ag_xO@SBA-15 for[O]-induced reactive adsorptive desulfurization of liquid fuel were reported and further investigated.The spent Ag_xO@SBA-15 was regenerated in various types of solvents followed by calcination,and tested in multiple desulfurization-regeneration cycles.Effect of regeneration solvents was compared.The original and regenerated Ag_xO@SBA-15 were characterized by X-ray diffraction,transmission electron microscopy,energy dispersive X-ray spectroscopy,N₂ adsorption,X-ray photoelectron spectroscopy and atomic absorption spectrometer.The recovery of desulfurization capacity using various solvents follows the order of acetonitrile>C₃H₆O>EtOH>MeOH>H₂O.Owing to the complete reduction of silver species to Ag⁰ and severe agglomeration of Ag⁰,the bifunctional Ag_xO@SBA-15demonstrating>85%?2.60 mg-S/g-sorb?of sulfur removal dramatically reduced to<46%?1.56 mg-S/g-sorb?after only 1-cycle regeneration.It is suggested that polar organic species strongly adsorbed?or resided?on the spent Ag_xO@SBA-15 after solvent wash may contribute to the accelerated decomposition of Ag⁺to Ag⁰ in the following calcination step.The capacity decreased rather mildly in the later regeneration runs.Cautious choice of regeneration conditions and strategies to rationally design stabilized adsorbents are required to avert the adsorbent deactivation.In this work,a series of commercial silica gels was screened for ODS in the presence of cumene hydrogen peroxide?CHP?,with the dibenzothiophene conversion varied diversely from 1.2⁹9.8%.The best silica gel SC-2 is capable of treating>375 cm³ of simulated diesel per gram of catalyst with³ ppmw-S at 100^oC.The trend of the electron charge on the sulfur atom of different sulfur compounds was consistent with that of the ODS reactivity,which is suitable for diesel desulfurization systems with DBT and 4,6-DMDBT as the main sulfide.The apparent activation energy on the oxidation of DBT was 45.32 kJ/mol,which is obviously lower than that of SiO₂-catalyzed ODS reaction?58.1 kJ/mol?,but very close to Ti-SiO₂system?43.8 kJ/mol?and Mo-SiO₂ system?42.2 kJ/mol?.The significantly lower activation energy indicates the metal-like sites,which are likely more active than silanol groups naturally present in the SiO₂ materials,in the presence of peroxides.To recover the activity of catalysts,oxidative air treatment at 400^oC was then introduced to oxidize the strongly adsorbed species.Consequently,the S conversion was stable at¹00%even after 7 cycles.The recyclability of silica gel guarantees the sustainable development and cost efficiency of the oxidation system.This work further studied the roles played by these physical and chemical characters of silica gels,which is essential in the development of silica gel-based catalysts for oxidative desulfurization.In order to understand the effect of surface textural structure on oxidation performance,the textural properties of the silica gels were characterized by N₂ adsorption,The results implied that rather than textural properties,different active sites in those silica gels may play a more important role in determining the oxidation activity of silica gels for ODS.Fairly trace Ti species of⁰.02 wt%in silica gel was detected and quantified by ICP,which was identified as the major Lewis acidic species correlating to the high ODS conversion.In the presence of peroxide,the highly dispersed Ti impurity acts as the Lewis acidic sites and DBT molecules was preferentially adsorbed on the surface of silica gel by acid-base reaction pathway.This work also explored ultra-deep oxidative desulfurization?ODS?of real diesel using two-layer silica gels as both guard adsorbent and oxidation catalyst under mild conditions.the effects of real diesel composition,including model aromatics,olefin,oxygen fuel additive and trace organonitrogen compounds on ODS using silica gel were investigated,where nitrogen compounds such as indole was identified as a major inhibitor,even at low concentration of 150 ppmw.Accordingly,guard adsorbents were investigated for adsorptive denitrogenation in prior to ODS,the N-capacity followed the order of SC-2^AC>Al₂O₃>13X.The layered-bed combination for deep desulfurization was optimized to be 5 and 2.5 mg/ml of SC-2,respectively,as guard adsorbent and oxidation catalyst.The matrix is capable of processing deep-desulfurized diesel below 10ppm with the total sulfur capacity up to 4.2 mg-S/g.The process by using two-layer commercial silica gel beds provides a new path for ultra-deep oxidative desulfurization of diesel under mild conditions.