Study On Deep Desulfurization Of Fuel Oil By Catalytic Ozonation With Polyoxometalates As Catalysts

Sulfur-containing compounds in transportation fuels, are the most notorious and undesirable contaminants because they are converted to toxic sulfur oxides (SOx) through combustion that result in air pollution and acid rain, poison the oxidation catalysts in the emission control system and reduce their effectiveness for the removal of harmful nitric oxide (NOx), hydrocarbons and carbon monoxide. Thus, ultra-deep desulfurization from transportation fuels has become an increasingly important subject worldwide, due to urgently environmental problems and increasingly stringent regulations. Oxidative desulfurization (ODS) combined with extraction is considered to be one of the most promising processes since mild conditions as ambient temperature and atmospheric pressure are employed and the refractory sulfur-containing compounds can be readily removed in ODS.Hydrogen peroxide (H2O2) in aqueous solution is the commonly used oxidant in ODS, but the use of H2O2suffers from some shortcomings, such as emulsion-separation with fuels and the low utilization efficiency of H2O2. Ozone (O3) may be an alternative green oxidant in ODS since it has a very high oxidation potential,2.07V in acid solution, and is low cost and environmentally friendly.In this paper, catalytic ozonation process combined with extraction was firstly applied in desulfurization. Keggin-type Heteropoly compounds (HPCs), a new kind of multi-functional catalytic materials, were employed as catalysts and acetonitrile was used as extractant. Excellent catalysts for ODS were selected. Meanwhile, main factors affecting the process were investigated to determine the optimum reaction conditions by contrast experiments.The paper included four sections.In the first section, the ultrasonic-assisted desulfurization of dibenzothiophene (DBT) by heteropolyacids was evaluated. Results showed that H3PMo6W6O40was the best catalyst for the desufuriztion of DBT, and the optimum conditions were as follows: reaction temperature,0℃; H3PMo12O40dosage, equivalent to2.5%of the feed mass of n-octane; and ultrasonic irradiation; DBT can be effectively removed from simulated diesel oil with initial sulfur content≤500ppm to ultra-low level. The oxidation products of DBT were analysed, and SO42-was confirmed as the main species. Moreover, the reused catalyst exhibited good catalytic activity in recovery experiments.In the second section, the ultrasonic-assisted desulfurization of DBT by metal salts of Keggin-type heteropolyacids was evaluated. Results showed that Fe0.8H0.6PW12O40exhibited the best catalytic activity, and the optimum conditions were as follows: reaction temperature of50℃; catalyst dosage of3.0%of simulated diesel oil; and ultrasonic irradiation, and that a desulfurization efficiency of up to99.7%was achieved under these optimum conditions. It was assumed that hydroxyl radicals might be generated in ultrasound enhanced catalytic ozonation process with Fe0.8H0.6PW12O40as catalyst, and that they showed positive effect on the removal of DBT, for the presence of t-butanol decreased desulfurization. Refractory organosulfur compounds with higher electron density on the sulfur atoms, including4,6-DMDBT, DBT and BT, were easier removed than TH with lower electron density. The oxidation products of DBT were analysed, and SO42-was confirmed as the main species. Moreover, the Fe0.8H0.6PW12O40catalyst was recoverable and the recovered catalyst demonstratesd quite close catalytic activity to that of the fresh.In the third section, the desulfurization of DBT by transition metal-modified lacunary Keggin heteropolycompounds was evaluated. Results showed that Na5[PW11O39Mn] was the best catalyst, and the optimum conditions were as follows: reaction temperature of20℃, catalyst dosage of1.0%of simulated diesel oil and sulfur content of500ppm, and that a desulfurization efficiency of up to100%was achieved under these optimum conditions. Refractory organosulfur compounds with higher electron density on the sulfur atoms, including4,6-DMDBT, DBT and BT, were easier removed than TH with lower electron density. Moreover, the Nas[PW11O39Mn] catalyst was recoverable and the recovered catalyst demonstrated quite close catalytic activity to that of the fresh.In the fourth section, Fe0.8H0.6PW12O40and Nas[PW11O39Mn] were applied in desulfurization of real oils under individual favorable conditions. Results showed that and Nas[PW11O39Mn] were both effective for desulfurization of real oils. Meanwhile, through desulfurization exterior color of real oils became shallow, and the odor of real oils was reduced.