Impact of diffusion at the gas/liquid interface on deep hydrodesulfurization of fluid catalytic cracking naphtha

For fluid catalytic cracking naphtha, there exists a complex co-existing gas-liquid-solid three-phase system in the catalyst bed under deep hydrodesulfurization (HDS) conditions representative of industrial practice. The system is extremely crucial and could influence and even determine the finished HDS reaction result. The paper reports that owing to the diffusion at the gas/liquid interface of the above system, thiophene rather than slow-reacting benzothiophene and its alkylated derivatives remains in the final product, which is against with common-sense knowledge about the relative reactivity of sulfur compounds. Two designed experiments which investigate impacts of solvents and sulfur-containing compounds under different temperatures further corroborate the above conclusion. Meanwhile, they reveal that elimination of the diffusion through making gas/liquid two phases into one gas or liquid phase effectively improves the efficiency of desulfurization even under the same reaction conditions. It could be concluded that for the deep HDS reaction, diffusion at the gas/liquid interface is the rate-determining step of whole reaction, which is also proved by the resulting data under conditions (production of Euro-5 gasoline).