Hydrodesulfurization process employing a guard chamber

A process for hydrodesulfurization of a metal- and sulfur-containing residual oil comprising passing said oil and hydrogen downwardly through both a guard chamber and a reaction zone in series at a temperature in the range of 600.degree. to 900.degree. F. and a hydrogen pressure of 500 to 5,000 psi, said guard chamber and reaction zone each containing a fixed bed of hydrodesulfurization catalyst granules comprising supported Group VI-B and Group VIII metals, terminating the catalyst cycle while the upper portion of the catalyst in the reaction zone has a relatively high level of metals deposits and the lower portion of the catalyst in the reaction zone has a relatively low level of metals deposits, removing deactivated catalyst from the guard chamber, removing the catalyst from said reaction zone by gravity funnel flow through a bottom opening of the reaction zone so that said upper portion of the catalyst is removed before said lower portion and separated therefrom by discharging said upper portion of the catalyst from said process, passing at least a part of said lower portion of catalyst to said guard chamber, inserting fresh catalyst in said reaction zone, and resuming passage of residual oil and hydrogen downwardly through said guard chamber and reaction zones in series.