Deep desulfurization of fuels catalyzed by surfactant-type decatungstates using H2O2 as oxidant

Oxidation of dibenzothiphene (DBT) in model oil with H2O2 using surfactant-type decatungstates Q4W10O32 (Q = (CH3)3NC16H33, (CH3)3NC14H29, (CH3)3NC12H25 and (CH3)3NC10H21) as catalysts was studied. The surfactant-type decatungstates were synthesized and characterized. The suitable reaction condition of deep desulfurization was suggested: n(DBT):n(catalyst):n(H2O2) = 1:0.01:3, 60 °C for 0.5 h, under which the DBT conversion can reach 99.6% with [(CH3)3NC16H33]4W10O32 as catalyst. The length of carbon chains of quaternary ammonium cations played a vital role in the catalytic activity of surfactant-type decatungstates, that is, the longer the carbon chain of quaternary ammonium cation of a catalyst was, the better the activity of this catalyst showed. [(CH3)3NC16H33]4W10O32 exhibited the best catalytic performance and can be recycled for six times without significant decrease in catalytic activity. Using benzothiphene (BT) and 4,6-dimethyldibenzothiphene (4,6-DMDBT) as substrates in model oil, surfactant-type decatungstates also showed high catalytic activity. During desulfurization process, BT conversion can reach 99.6% at 3.25 h, while 99.4% of 4,6-DMDBT conversion reached at 1.25 h, with the temperature of 60 °C under atmospheric pressure. The sulfone can be separated from the oil using N,N-dimethylformamide (DMF) as an extractant, and the sulfur content can be lowered from 1000 to 4 ppm. For real diesel, the sulfur removal can reach 93.5% after five times extraction.