Effect of nitrogen compounds on deactivation of hydrotreating catalysts by coke

A series of coked catalysts containing different levels of coke were prepared in a batch Autoclave by treatment of a sulfided CoMo catalyst with mixtures of vacuum gas oil (VGO) in mineral oil at 35 atm hydrogen and temperatures between 280 degrees C and 370 degrees C. A similar series of coked catalysts were prepared with acridine or carbazole added to the VGO mixture. After extraction with xylene and resulfiding, the coked catalysts were analyzed for C, N, pore volume and surface area, and tested for hydrogenation of naphthalene and carbon -nitrogen hydrogenolysis of indole. The presence of the nitrogen compound in the VGO mixture resulted in higher coke levels on the catalyst. All conversions decreased with coke content. However, for the same level of coke, the nitrogen-coked catalysts showed less deactivation as compared to the normal coked catalysts. This was attributed to strong adsorption of the nitrogen compounds on nonactive sites of the catalyst.