Diffusivities of Hydrocarbons in the Fresh and Aged Hydrotreating Catalysts Studied by Zero-Length Column Method

Abstract

Diffusivities of a series of hydrocarbons with different configurations in two zeolites (ZSM-5 and SBA-15) and a hydrotreating catalyst (NiMo/Al 2 O 3 ) were determined by the zero-length column technique. The results revealed that the molecular configuration of hydrocarbons has a significant effect on the diffusion property in zeolites. In addition, the aromatics show surface diffusion effect in the mesoporous SBA-15 and NiMo/ Al 2 O 3 . The diffusion characteristic of 1,3,5-triisopropylbenzene (TiPB) was applied to evaluate the change of diffusion properties of a mesoporous-scale hydrotreating catalyst with 2000 h of deactivation. Arrhenius plots of the diffusional time constants show two distinct linear fitting regions for both the fresh and aged catalysts. The reduction degree in diffusivity over the aged catalyst shows an increasing tendency at low temperatures but gradually decreases at high temperatures. A correlation between pore size and diffusivities was established to reveal the influence of structure on its diffusion property.

Evaluation of Time-on-Stream Deactivation Models with Effectiveness Factors for Industrial Feedstock Hydrotreating in Bench-Scale Tests

“…21 Particle shapes (sphere, cylinder, trilobe, and tetralobe) and pore structures (pore diameter and porosity) are equally important for improving internal diffusion limitations on HDT reactions. 22,23 To simplify the estimation of η in the HDT, it is possible to focus only on the solid phase (catalyst particle), neglecting liquid and gas phases. This approach allows analyzing the influence of parameters, such as particle radius and temperature, on the effectiveness factor.…”

“…Incomplete wetting and the formation of stagnant liquid zones at particles are associated with a decrease in the catalyst effectiveness factor. − To add a wettability effect, Dudukovic proposed the concept of approximating the global effectiveness factor (η o ), considering a weight-averaged function of wetting efficiency and particle effectiveness . Particle shapes (sphere, cylinder, trilobe, and tetralobe) and pore structures (pore diameter and porosity) are equally important for improving internal diffusion limitations on HDT reactions. , To simplify the estimation of η in the HDT, it is possible to focus only on the solid phase (catalyst particle), neglecting liquid and gas phases. This approach allows analyzing the influence of parameters, such as particle radius and temperature, on the effectiveness factor. , The transient characteristics of the effectiveness factor may also provide relevant data for reactions on porous catalysts.…”