The Kinetic And Reaction Mechanism Of Gasoline Hydrodesulfurization Over Co-Mo/γ-Al₂O₃Catalyst

There is a large amount of organic sulfur in gasoline, and the sulfur will pollute the environment when burns into sulfur dioxide. The’Chinese Standard Ⅳ’ demands the sulfur content in gasoline lower than50ppm. Dibenzothiophene (DBT) is the key compound in deep desulfurization, and hydrodesulfurization (HDS) is the main way to remove DBT from gasoline. DBT hydrodesulfurization is difficult, and is caused by the steric hindrance between DBT and the catalyst. Increasing the reaction temperature can improve the HDS activity, however, will also promote the olefin hydrogenation, leading to a further reduction of octane number and influence the quality of gasoline. Hence, increase the catalyst HDS activity while decrease the octane number loss in order to increase the HDS selectivity, has recently attracted many attentions.In this work, FGH-31catalyst supplied by Fushun Petrochemical Institute is employed, and is used to evaluate the DBT hydrodesufurization activity and build up the DBT HDS kinetics. The L-H equation has a high fit degree with the experiment result, and L-H equation can accurately predict the DBT conversion under different conditions. The DBT HDS apparent activation energy and adsorption energy is56.2and-20.7kJ/mol respectively.The olefin conversion and selectivity over FGH-31catalyst is tested under different experimental conditions, and the results show that the selectivity of diphenyl (BP) is much higher than phenylcyclohexane (CHB). Therefore, the DDS routine which generates BP is the main way to eliminate the sulfur over FGH-31catalyst. More importantly, the DBT conversion has an opposite variation trend to the octene conversion, and octene activity is inhibited seriously when thiophene is added to the model gasoline. Therefore, two types of active site exist on the catalyst surface and competitive adsorption of H2S on the hydrogenation active site is the main factor that influences the HDS selectivity.Three kinds of γ-Al2O3cluster with different acidity are used as the carrier of HDS catalyst. The active phase is the same as FGH-31catalyst. The catalyst activity is evaluated and compared with FGH-31. XRD and Raman are used to analyze the catalyst, and Co-Mo-S model is used to illustrate the difference in activities. The result shows that the surface of all catalysts has Co-Mo-O phase before pre-sulfurization, and Co3O4is absent on the surface of the catalyst with the highest activity.