Study On Oxidative Desulfurization Of Fuel Oil By Molybdenum Oxide/mesoporous Alumina

In recent years, with the world's increasing strict environmental regulations, fuel oil depth desulfurization has become a worldwide important topic. Oxidative desulfurization(ODS) has become the research focus, because its mild reaction conditions, the operation process is simple and it can remove the sulfides that can't be removed by hydrodesulfurization(HDS). The catalyst used in oxidative desulfurization mainly includes the homogeneous catalysts and the heterogeneous catalyst .For homogeneous catalysts, although it can achieve high desulfurization rate but it can't be seperated and recycled easily. And the heterogeneous catalyst are expected to resolve this problem. Metal oxide is one of the commonly used catalyst carrier .The mesoporous alumina not only has the ordinary alumina's excellent performance ,and the excellent properties of the mesoporous characteristics make its catalytic and adsorption performance more superior.In this paper, the alumina (MA and PA) could be obtained by different methods, using aluminum nitrate and pseudo-boehmite as the aluminum source, respectively. The characterization of N2 adsorption-desorption showed that the alumina possessed mesoporous structure. MA has the larger surface area and the more narrow pore size distribution than PA. Mesoporous alumina supported molybdenum oxide catalysts(MoO₃/MA and MoO₃/PA) used in the oxidative desulfurization (ODS) process of fuel oil , were prepared by incipient wetness impregnation of ammonium molybdate. Compared with the catalyst of MoO₃/PA, the MoO₃/MA had higher catalytic activity.Using hydrogen peroxide as the oxidant, MoO₃/MA as the catalyst, methylpyrrolidon(eNMP)as the extractant, the effects of catalyst, dosage of oxidation agent and reaction condition on desulfurization in diesel oil and model oil were investigated .The experiment results showed that MoO₃ / mesoporous Al₂O₃ catalyst can significantly improve the desulphurization rate. The loading amount of MoO₃, catalyst and oxidant dosage, reaction temperature and time could effect the desulfurization rate. The sulfur removal efficiency increased as the loading amount of MoO₃ enhanced, and then reduced a little.The optimum loading amount of MoO₃ is 20%. Inorder to reach a good desulphurization performance ,the oxidant dosage used should be higher than theory. Sulfur removal efficiency was increased with the increase of temperature, but it decreased slightly when the temperature continue to increase. Desulphurization rate could be improved gradually with the increase of catalyst dosage, but when the dosage of catalyst reached a certain amount the desulfurization rate changed a little. The optimum oxidation conditions, which were the loading of MoO₃ of 20%, the molar ratio of oxidant H₂O₂ to sulfur in diesel oil of 12,catalyst dosage of 1.0%,reaction temperature of 60℃, reaction time of 30min, were obtained .And the desulfurization rate was 68.4%.A simulated oil consisting of model sulfur compounds, such as benzothiophene (BT) , dibenzothiophene (DBT) ,4 ,6-dimethyldibenzothiophene (4 ,6-DMDBT) and thiophene (Th), and cyclohexane as solvent was employed in the oxidation desulfurization study . It was showed that the removal efficiency of DBT at 60℃was as high as 99.4% when the content of MoO₃, dosage of catalyst and the molar ratio of H₂O₂ to sulfur were 20% ,1.5% and 4, respectively. Under the optimum conditions, the oxidative activity of the model sulfur compounds follows the order of DBT > 4,6-DMDBT >BT>Th,and the removal efficiency of 4,6-DMDBT and BT could be reached 90% also.