Accelerated deactivation studies of hydrotreating catalysts in pilot unit

Abstract

In the present paper, a methodology of accelerated deactivation was employed to study the activity loss by coke deposition in short time duration experiments. The loss of activity as function of time is an inherent problem in hydrotreating (HDT) processes. Deactivation at normal operation conditions occurs slowly because of coke formation, commercial catalysts take on average 2–3 years to be replaced. Thus, the accelerated deactivation appears as an instrument capable of providing relevant information on the deactivation phenomenon in reduced time tests. A pilot plant with diesel as feedstock was used under similar conditions to those of industrial units with commercial HDT catalysts. Reaction kinetics was applied to evaluate the deactivation by coke deposition instead of the traditional characterization of residual catalysts. Normalized reaction temperature was related to the initial and residual activities for hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) reactions. The reaction temperature of 420°C in the accelerated deactivation step provided a satisfactory level of deactivation. The catalyst bed configuration proved to be a key factor in order to preserve the residual activity. HDN and HDA activities were more affected than HDS activity by coke deposition in the experimental runs. HDA reaction could reach the thermodynamic equilibrium state when using less severe operating conditions. Finally, the employed methodology led to a proper representation of the industrial HDT deactivation phenomenon.