Insights in the phenomena involved in deactivation of industrial hydrocracking catalysts through an accelerated deactivation protocol.

• An accelerated deactivation protocol at the pilot plant scale was developed to study hydrocracking catalyst deactivation in a short time of 30 days. • The organic nitrogen content of the feedstock to the hydrocracking process deactivates the catalyst acid function permanently by coke deposition. In contrast, nitrogen compounds have just an inhibitory effect on the metal function. The deactivation of the metal function is mainly due to nickel depromotion. • The balance in the ratio of the metal/acid sites determines the amount and the type of formed coke. The lower the ratio, the higher the coke production rate with a more aromatic structure. • Along the catalytic bed, the metal/acid balance decreases from bed inlet to bed outlet, the bed outlet contains a higher amount of coke, which is more aromatic. A representative accelerated experimental deactivation procedure was developed to understand the activity loss of bifunctional vacuum gasoil (VGO) hydrocracking catalysts over time. Experiments were performed in an up-flow fixed-bed pilot unit with a typical vacuum gas oil feedstock. The deactivation was measured by tracking the decrease of VGO conversion (370 °C+) with time on stream. The catalyst consisted of nickel-molybdenum sulfide particles dispersed on a carrier containing USY zeolite. The impact of temperature, liquid hourly space velocity (LHSV), hydrogen to hydrocarbon (H 2 /HC) ratio and organic nitrogen (N org) on the catalyst deactivation rate was first studied. The variables with the most significant impact on conversion loss were temperature and space velocity. Temperature directly influences the production rate of coke precursors, whereas space velocity affects the local concentration of feed contaminants along the reactor. Based on these results, the following operating conditions were selected to establish the final accelerated deactivation experimental protocol: T = 418 °C, LHSV = 3 h−1, H 2 /HC = 1500NL/L, P = 14 MPa, organic nitrogen content (Norg) = 150 ppm weight, total nitrogen content = 2500 ppm weight and a total time on stream of 30 days. Spent samples from this procedure presented similar properties to some industrial catalysts submitted to cycle lengths between 12 and 18 months. Both types of samples yield similar values of surface area and pore volume loss as well as a similar amount and nature of coke deposits. These results led to the qualitative validation of the protocol representativeness. This experimental procedure was then used to get more insight into the deactivation phenomenon. It was found that the organic nitrogen content of the feedstock is crucial, as it determines the ratio between available metal and acid sites. This ratio determines the reactions that take place and, therefore, the type of coke produced. [ABSTRACT FROM AUTHOR]