Study On Adsorptive Desulfurization Employing Metallic Silver And Oxidative Desulfurization Using Peroxide For Fuel Oils

Exhaust gas generated from the combustion of sulfur-containing fuel oils hasbeen one of the main polluting sources of ambient air and the removal of thiophenicsulfur has been of great importance and difficulties. Selective adsorption hasdemonstrated minimal influence on the quality of aromatics containing fuelscomparing with other desulfurization pathways. Considering the exposed exterior offibers for mass transfer, metallic silver was supported on adsorbent cotton fibers and anovel adsorbent was prepared by aqueous reduction-dehydration method with virtuessuch as extra low silver loading （0.2wt%）, facile preparation, low energy consumptionand no toxics emission.On the basis of adsorption tests, thermo gravimetric analysis （TG）/differentialthermal analysis （DTA） and energy-dispersive X-ray spectroscopy （ESEM-EDX）, it isfirstly confirmed that the active component of adsorption is Ag⁰instead of Ag⁺. It isattributed to the distinct polarities of thiophene-octane （model oil） and AgNO₃thatthese molecules repulse with each other, while thiophene-octane and Ag⁰contactmutually on account of similar polarity. Superficial polarity congruity mechanismabout coordinative adsorption was proposed firstly.During adsorption tests, model oil （500ppmw sulfur） was pressed into anadsorption column without solvent for degassing to avoid the interference ofsulfur-free solvent. Temperature and retention time dependences of capacity wereinvestigated below60℃and at flow rates of0.2and0.3ml/min. The phenomenonthat sulfur removals increased as the declination of silver loadings has been elucidatedby Field Emission Scanning Electron Microscopy （FESEM）. The adsorption issubstantially coordinative reaction in view of the adsorption rate elevating as theimprovement of temperature. Higher capacities were determined at50℃in2h withan average sulfur removal of27.6%and the sulfur removal declined at above60℃.Adsorption isotherm was drawn on the basis of static adsorption tests at30℃. As canbe seen from the isotherm curve, the coordinative adsorption was constrained byeither the concentration of thiophene or the density of adsorption sites, andsilver/cotton is adaptive to deal with model oil with sulfur contents above500ppm. The bed pressure drop of per gram of silver/cotton is0.62KPa/g, while thepressure drops of alumina and silica are2.35and3.73KPa/g respectively, which are3.8and6.0times the amount of that of silver/cotton. Bed pressure drops of aluminaand silica with a loading height of56cm are58.2KPa and63.8KPa respectively,while that of silver/cotton is only5.3KPa. The pressure drops of alumina and silicawith a unit of loading height are11and12times the amount of that of silver/cotton.The open dimensional structure of fiber adsorbents with characteristics and lowloading density both contribute to the low pressure drop to some extent.The simple regeneration of silver/cotton was conducted via removing oil usingevaporation at100℃for0.5h. A recovery route of silver by concentration-electrolysiswas proposed.Oxidative desulfurization using peroxide has been investigated. Intenseemulsification effect on oil-water system resulting from pulsed ultrasound results inthe decrease of extractive efficiency, which is a disadvantage to oxidation-extractiondesulfurization.The oxidative desulfurization system comprising tungstophosphoric acid, reversemicelles catalyst and DMF extraction can reach an average sulfur removal of84.6%at60℃. A regeneration scheme of DMF and solid acid has been proposed.