Restricted diffusion of model sulfides over a NiMo/BK catalyst under hydrodesulfurization reaction conditions

摘要

Micro-mesoporous composite Beta-KIT-6 (BK) material with cubic Ia (3) over bard mesoporous structure was synthesized, and then a NiMo/BK hydrodesulfurization (HDS) catalyst was prepared using BK as a support. Four kinds of model sulfides with different structures and molecular sizes, including thiophene, benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene, were chosen as the reactant probe molecules. The intra-particle diffusion effects on HDS of these four different model sulfides were investigated systematically over the novel NiMo/BK micro-mesoporous-supported catalyst under HDS reaction conditions. The changing rules of the catalyst effective factor (eta) and effective diffusion coefficient (D-e) of model sulfides were investigated. The results showed that the eta values of NiMo/BK catalyst in the HDS of different reactant molecules are higher than those of the traditional NiMo/Al2O3 owing to excellent mass transfer ability of the well-ordered NiMo/BK catalyst, and the De values decreased with the increasing molecular sizes of model sulfur-containing compounds. The relationship of effective diffusion coefficient (D-e) with molecule diameter to pore diameter ratio (lambda) was further determined. Restrictive factors were correlated by F(lambda) = (1 - lambda)(3.15) for NiMo/BK and F(lambda) = (1 - lambda) 3.67 for NiMo/Al2O3 catalyst, indicating that large pore size is beneficial to the diffusion of macromolecular reactants.