Study of intra-particle diffusion effect on hydrodesulphurization of dibenzothiophenic compounds

In this paper, the intra-particle diffusion effect on hydrodesulphurization of dibenzothiophenic compounds in light cycle oil was experimentally studied. The catalyst effectiveness factors were determined with a full-size commercial NiMo/Al2O3 hydrotreating catalyst and its crushed catalyst particles under similar operating conditions. In the full-size commercial catalyst, significant intra-particle diffusion resistance was present, resulting in reduced sulphur removal reaction rates for all the dibenzothiophenic compounds investigated. The effectiveness factors ranged from only 0.300 to 0.822 in the temperature range of commercial importance. In the crushed catalyst, the intra-particle diffusion limitation was mostly eliminated with the corresponding effectiveness factors between 0.813 and 0.985. The DBTs with little or no steric hindrance effect, and thus with high intrinsic reactivities, had lower effectiveness factors, indicating a stronger intra-particle diffusion resistance. Those with strong steric hindrance effect, and thus with low intrinsic reactivities, had higher effectiveness factors, showing a weaker intra-particle diffusion limitation.