Preparation And Studies Of Presulfurization-free MoNiP/Al₂O₃ Catalysts For Hydrodesulfurization

At present, for improving the activity of hydrodesulfurization catalysts, thecatalysts should be presulfided before use in most refineries. However, the presulfidedprocess will result in increasing the environment contamination and the consumptionof energy. In this paper, an improving Mo-Ni-P catalyst with high activity forthiophene hydrodesulfurization (HDS) has been developed and used under theconditions without both calcination and presulfurization. The preparation charactersof the catalysts include (1) suitable amount of polar organic substance wasincorporated into the Mo-Ni-P-O impregnation solution, and (2) the catalyst thusprepared was not calcined after drying.The composition of Mo-Ni-P-O impregnation solution was studied emphatically.On studying the preparation conditions of Mo-Ni-P-O impregnation solutions, it wasfound that there are two un-preparable regions named as UPRâ… and UPRâ…¡,and theprecipitates corresponding to UPRâ… and UPRâ…¡are molybdenum trioxide or its hydrate,and nickel phosphate respectively.The addition of polar organic substances, such as citric acid, to Mo-Ni-P-Oimpregnation solution was found to improve the HDS activities of the MoNiP/Al₂O₃catalysts thus prepared in a wide extent and to make the sulfurization of the catalystseasy．The action mechanism of citric acid was studied by FT-IR,XPS,H₂-TPR,H₂-TPD and TG techniques,the results are summarized as follows:citric acid andmetal component react to produce a complex,which is then adsorbed by supportowing to the affinity function between porlar group of citric acid and Al³⁺ of Al₂O₃support．The citric acid in this complex is decomposed in the start-up process,leadingto the formation of coke on the surface of the support. The coking of the catalyst hastwo functions:(1) weakening the strong metal-support interaction and therefore, madethe catalyst more easily be sulfurized and reduced spontaneously; (2) decreasing themoving and aggregation of the metal group, thus improving metal component dispersion, which has been proved to be in favor of improving the catalysis efficiency.The characterizations of H₂-TPR,H₂-TPD,XPS display that metal-supportinteraction would be enhanced by calcining, this directly gives rise to thedevelopment of the calcination-free technique in the preparation of the catalysts, andit is one of reasons that the catalyst has higher activity under the condition withoutpresulfrization.The effects of the variation of the contents of Mo,Ni,P in the MoNiP/Al₂O₃ catalyst containing citric acid on catalytic performances of the catalysts were investigated by means of H₂-TPR,H₂-TPR,H₂-TPR. The experiment results showthat the optimum Mo content is 1．67×10^-3 mol/gCat．；the optimum Ni／(Ni+Mo)is0．278,and corresponding,the optimum Ni content is 6．4×10^-4 mol／gCat．,theoptimum content of phosphorus is about 3．2×10^-4 mol／gCat．the optimumconcentrations of the active components in Mo-Ni-P-O impregnation solution areMo:2．78mol／L,Ni:1．07 mol／L,P:0．65 mol／L．At last,the effects of reaction conditions on the catalytic activities of thecatalysts were studied,a set of kinetics data obtain about the effects of the operatingon the conversion of thiophene were treated,and the conversion of thiophene can beexpressed as follows:whereθ,:P_H,(?),Ï„stand for relative temperature,relalive pressure,relativeLHSV,:resident time,respectively．In this paper,the above equation is with the ARD 3．97％．...