Comparison of Unimodal Versus Bimodal Pore Catalysts in Residues Hydrotreating

Abstract

Catalyst pore structure is a critical factor influencing the performance of residues hydroprocessing catalysts. The effect is reflected in both hydrodesulfurization activity of the catalyst and its rate of deactivation. In this paper, the pore size distributions of two categories of catalysts, unimodal and bimodal, were systematically varied. Performance evaluation tests in a fixed bed reactor using vacuum residues under conditions comparable to typical refinery operations were conducted. Two series of unimodal and bimodal catalyst extrudates were prepared starting from boehmite gel, whereby the pore structure was systematically varied using hydrothermal treatment and organic additives. For the unimodal catalysts, the pore maxima ranged between 50 and 500 {angstrom} with 70--80% of the pore volume in the desired pore diameter range. The bimodal catalysts had narrow pores with pore diameters less than 100 {angstrom} and wide pres with pore diameter around 5,000 {angstrom}. For bimodal catalyst, an increase in the average wide pore diameter, while maintaining the narrow pore constant, had no significant effect on the catalyst performance. For monomodal catalyst, the activity of the catalyst was noted to have an optimum between 150--350 {angstrom} diameter. Furthermore, the performance of the catalyst concerning its desulfurization activity and deactivation was superior tomore » that of the bimodal catalysts.« less