Deep Desufurization Catalyzed By Decatungstates

The sulfur in fuels could contribute to the air pollution and the acid rain, influencing the environment as well as the quality of human being life. The traditional approach for desulfurization is hydrodesulfurization (HDS), which could not yet meet the standards of legitimates. To further lower the sulfur content, many new methods towards the achievement of little-to-no sulfur fuel come into being, among which the oxidative desulfurization(ODS) has received much attention for it can effectively remove those refractory sulfur compounds which are hard to be got rid of during HDS. In this work, the catalytic oxidative and extractive system was taken, in which decatungstate were adopted as catalyst and hydrogen peroxide was the oxidant, also with the participation of the ionic liquid [Bmim]PF₆.n-Octane was used as the model oil while dibenzothiophene (DBT), benzothiophene (BT) and 4, 6-dimethyl-dibenzothiophene (4, 6-DMDBT) were chosen as the representative sulfur compounds. The aim is to achieve deep or ultra-deep desulfurization.This investigation includes three chapters as follows:First of all, ten decatungstates have been synthesized including (Omim)₄W₁₀O₃₂. These catalysts were characterized by IR, UV-vis, thermogravimetric and differential scanning (TG-DSC) and gravimetric determination (GD).In the second chapter, the catalytic activity of decatungstates with cation of quaternary ammonium with long carbon chain towards desulfurization was studied in the oxidative desulfurization system. The results indicated that the catalysts showed positive contribution to the reaction. Among the four catalysts, [(CH₃)₃NC₁₆H₃₃]₄W₁₀O₃₂ was the best with the sulfur removal of 99.6%. The optimized conditions were suggested as: n(DBT):n(catalyst):n(H₂O₂)=100:1:300, 60℃for 0.5 h. [(CH₃)₃NC₁₆H₃₃]₄W₁₀O₃₂ can be recycled for six times with the sulfur removal all over 99.0%. The decatungstates are also effective to BT and 4, 6-DMDBT. 99.4% sulfur removal of 4, 6-DMDBT could be obtained with the reaction time of 1.25 h while BT can get 99.6% removal at 3.25 h. As for the real diesel, the sulfur removal of 93.5% can be achievied after five extractive treatments.In the third chapter, six decatungstates with quaternary ammonium cation of short carbon chain and of ligands were used as catalysts in the extractive oxidative desulfurization of oil/H₂O₂/catalyst/IL. Taken [(C₄H₉)₄N]₄W₁₀O₃₂ as the representative catalyst to investigate the effects of amount of the catalyst and the oxidant, reaction time as well as the temperature on sulfur removal, the optimized conditions were suggested as: n(DBT):n(catalyst):n(H₂O₂)=100:1:300, 60℃for 0.5 h, the amount of [Bmim]PF₆ 1 mL, under which the sulfur removal can reach 98.0%.There are two different systems herein including catalytic oxidative desulfurization and extractive catalytic oxidative desulfurization with ionic liquid [Bmim]PF₆.Decatungstate perform good catalytic activity, which supports a novel way for its use in deep desulfurization.