Effect Of Citric Acid On The Performance Of Hydrodesulfurization Catalysts

The crude oil quality is becoming worse and worse, meanwhile the environmental legislations pay more attention to confine the content of sulfur in diesel or gas oil. Thus, the deep hydrodesulfurization processes is becoming more and more important for the low sulfur gasoline and diesel. To achieve this goal, one of the most important approachs is to develop a novel high-performance hydrodesulfurization catalyst.Two kinds of Ni-Mo catalysts supported on alumina and alumina-activated carbons prepared by impregnation method with and without ctric acid (CA) have been compared. Catalytic activity of the the catalysts for the hydrodesulfurization of dibenzothiophene (DBT) have been studied with1.0wt.%DBT-decalin feed in a three-phase trickle bed reactor. The catalysts and supports were further characterized by N2adsorption, XRD, TPR, XRF techniques, so that the influence of adding CA through different ways on the activity of the catalysts and the role of citric acid in the catalysts preparation could be elucidated. The N2adsorption results show that the pore diameter of catalysts with CA mostly falls in mesoporous and the specific surface areas are slightly decreased compared with those without CA. The pore diameter of alumina-activated carbon support prepared with CA is larger then that with acetic acid. Adding CA during catalyst preparation by different ways has effectively increased the catalytic activity of the catalyst. The optimum catalyst activity is obtained at a CA/Ni mole ratio=1for the catalysts supported on alumina, and at a CA/Mo mole ratio=1for the catalysts supported on alumina-activated carbon. TPR and XRD results show that the presence of CA can properly weaken the metal-support interaction, increase the dispersion of NiMo and therefore the effective amount of NiMo components loaded on the surface of the supports. And so that the catalytic activity of the catalysts is increased.Hydrodesulfurization catalytic performance of the commercial catalyst HT-2003was carried out under the same conditions. Compared with the commercial catalysts HT-2003, the catalytic activity of the self-made catalyst NiMo-CA/A is higher.