Kinetics of Two Pathways for 4,6-Dimethyldibenzothiophene Hydrodesulfurization over NiMo, CoMo Sulfide, and Nickel Phosphide Catalysts

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• 作者：Jae Hyung Kim ; Xiaoliang Ma ; Chunshan Song ; Yong-Kul Lee ; and S. Ted Oyama
• 刊名：Energy & Fuels
• 出版年：2005
• 出版时间：March 2005
• 年：2005
• 卷：19
• 期：2
• 页码：353 - 364
• 全文大小：403K
• 年卷期：v.19,no.2(March 2005)
• ISSN：1520-5029

文摘

The kinetics for the initial stage of the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and dibenzothiophene (DBT) were comparatively examined over NiMoand CoMo sulfide catalysts and newly developed nickel phosphide catalysts. The HDS can proceedthrough an indirect hydrogenation (HYD) pathway and a direct desulfurization (DDS, orhydrogenolysis) pathway. The rate constants for the HYD and DDS pathways (k₁ and k₂,respectively) were estimated using a method that involved extrapolation to zero conversion forthe initial selectivity ratio of primary products. The overall rate constants (k₁ + k₂) for 4,6-DMDBTon a catalyst weight basis (in units of 10^-5 s^-1 g·cat^-1) at 573 K under a pressure of 20.4 atmincreased in the order of CoMo sulfide (34.1) < Ni₂P/USY (51.5) < Ni₂P/SiO₂ (66.4) < NiMo sulfide(83.2); however, the values based on active sites (in units of s^-1 active site^-1) ranked in a differentorder (CoMo sulfide (4.0) < NiMo sulfide (8.8) < Ni₂P/USY (15.2) < Ni₂P/SiO₂ (23.7)). The rateconstants for the HYD pathway of 4,6-DMDBT HDS at 573 K based on active sites were stronglydependent on the type of catalyst used; however, those for the DDS pathway were less sensitiveto the type of catalyst, as can be observed from the corresponding values (k₁; k₂) for CoMo sulfide(2.2; 1.8), NiMo sulfide (6.7; 2.1), Ni₂P/USY (12.7; 2.5), and Ni₂P/SiO₂ (21.6; 2.1). The NiMo sulfidecatalyst, which favored the HYD pathway, was more active than the CoMo sulfide catalyst for4,6-DMDBT. The nickel phosphide catalysts showed higher activity in 4,6-DMDBT HDS thanthe sulfide catalysts, based on rate constants normalized to active sites; they operated throughthe HYD pathway. A comparison with DBT HDS at 573 K under a hydrogen (H₂) pressure of20.4 atm showed that the presence of the methyl groups at the 4- and 6-positions dramaticallyinhibited the DDS pathway, because of steric hindrance around the S atom, and thus made theHYD pathway more important. Higher H₂ pressure further enhanced the HYD pathway, whereasincreased temperature increased the contribution of the DDS pathway for 4,6-DMDBT HDS.