Oxidative Desulfurization Of Diesel Catalyzed By Mo-P-O/SiO₂Catalysts

Sulfur compounds of diesel are converted into SOX on combustion, which causes serious environmental problems. As a consequence, increasingly stringent regulations have been established worldwide to limit the sulfur content of diesel. Oxidative desulfurization (ODS) has received great attention from academia and industry due to its mild operating conditions and no consumption of H2. In the dissertation work, the effects of P on the the structure and ODS performance of P-modified MoO3/SiO2catalysts were studied. Then Na was introduced to improve the ODS performance of MoP1.0O/SiO2. Removal of sulfones from pre-oxidized diesel by extraction with ionic liquid instead of dimethyl formamide (DMF) was investigated as well.P-modified MoO3/SiO2catalysts (MoPxO/SiO2, x=P/Mo molar ratio) were prepared by incipient impregnation method and evaluated in the oxidation of dibenzothiophene (DBT) by cumene hydroperoxide (CHP) in fixed bed reactor. MoP1.0O/SiO2exhibited the highest oxidation activity in comparison with other P/Mo molar ratios. MoP1.0O/SiO2showed better performance than H3PMo12O40/SiO2, whereas the latter one had a longer induction period. Compared to MoO3/SiO2, the leaching of Mo species from MoP1.0O/SiO2were negligible. The structure of Mo and P species were characterized by XRD, Raman and31P MAS NMR. The total acidic number and the distribution of Lewis (L) and Bronsted (B) acid sites were characterized by NH3-TPD and FT-IR of pyridine adsorption, respectively. The characterization results indicated that after MoP1.0O/SiO2reacted with CHP the active peroxo intermediates formed on the surface of the catalyst, which is responsible for the induction period.A series of Na-modified MoP1.0O/SiO2(Nay-MoP1.0O/SiO2, y=Na/Mo molar ratio) was prepared by incipient impregnation method and characterized by XRD, Raman, BET, NH3-TPD and FT-IR of pyridine adsorption. Compared to MoP1.0O/SiO2, the medium strong B acid sites of the Nay-MoP1.0O/SiO2are greatly reduced. The sample of Nay-MoP1.0O/SiO2with Na/Mo molar ratio of0.2(Na0.2-MoP1.0O/SiO2) exhibited the best catalytic performance. Combining characterization and experimental results, the functions of L and B acid sites were discussed. The Na0.2-MoP1.0O/SiO2catalyst modified by different Na precursor was investigated as well. Furthermore, the kinetics of the oxidation of DBT and4,6-dimethyl dibenzothiophene (4,6-DMDBT) on MoP1.0O/SiO2and Na0.2-MoP1.0O/SiO2were discussed. Effects of quinoline, indole and carbazole on the oxidation of DBT over Na0.2-MoP1.0O/SiO2were investigated. Moreover, the oxidation of model diesel containing BT, DBT, and4,6-DMDBT was examined over Na0.2-MoP1.0O/SiO2catalyst.MoP1.0O/SiO2and Na0.2-MoP1.0O/SiO2catalysts were tested in the ODS of hydrogenated diesel followed by DMF extraction. The sulfur content of the diesel can be reduced to less than10ppmw. Also, ionic liquids [BMIM][BF4] and [BMIM][PF6] were synthesized and applied in the extraction of sulfones in pre-oxidized diesel, and the results were compared with DMF extraction results.