Hydrogenation by CoMo/Al2O3 catalyst. (Part 5). Effect of H2S on the hydrodenitrogenation of quinoline.

Abstract

The hydrodenitrogenation (HDN) of quinoline (Qn) was studied over sulfided CoMo/Al2O3 catalysts, using a trickle bed reactor, at 400°C, 5MPa, in a stream of H2 or in flowing H2S/H2. The main products observed in the reaction were 1, 2, 3, 4-tetrahydroquinoline (4HQn), 5, 6, 7, 8-tetrahydroquinoline (4H'Qn), decahydroquinoline (10HQn), o-propylaniline (OPA), propylcyclohexane (PrCH), and propylbenzene (PrBz). The contact time dependency of the product distribution of reactions in a stream of H2 showed that the ring hydrogenation of Qn to 4HQn occurred readily, and that the HDN of Qn proceeded via aromatic and/or heteroring saturation. The conversion of HDN in a stream of H2 was about 5-15%. When the reaction was carried out in a stream of 5mol% H2S/H2, the conversion of HDN increased greatly (about 50%). From the results of reactions of several hydrogenated inteimediates observed in the reaction path of the HDN of Qn, the increase in the conversion of HDN of Qn due to H2S addition seems to be effected by the promotion of the aliphatic C-N bond-cleavage leading to nitrogen elimination. The addition of H2S was also effective to enhance the HDN activity of the catalyst which was exposed to the reaction atmosphere in a stream of H2 for a certain period of time. The HDN activity of variously pretreated catalysts was in the following order: presulfided>prereduced-then-sulfided>prereduced under H2S/H2 atmosphere. This order was consistent with the IR-absorption intensity of nitric oxide (NO) adsorbed on Co sites. The effects of Mo and Co were evaluated by performing the test runs over a series of laboratory prepared CoMo/Al2O3, CO/Al2O3, and Mo/Al2O3. In a stream of 5mol% H2S/H2, it was found that HDN activity of CoMo/Al2O3 was much higher than the sum of the activities of Co/Al2O3 and Mo/Al2O3. The maximum HDN activity was obtaind at r(Co/(Co+Mo))=ca. 0.5. The present results allow us to consider that the promoting effect of the H2S addition is strongly related with both Mo and Co species.