Hydrodesulfurization process involving blending high boiling streams

Abstract

A process is described for fixed bed hydrodesulfurizing a non-asphaltic oil feed blend for a zeolitic FCC riser cracking system in which cracking occurs at a space velocity sufficiently high to prevent formation of a catalyst bed. It is shown that sulfur dioxide emissions from the zeolite catalyst regenerator associated with the riser are reduced to a lower extent than total sulfur removal from the feed oil. This indicates uneven sulfur removal in the hydrodesulfurization step whereby a smaller portion of sulfur is removed from the heavy portion of the feed from which the coke is derived than from the lighter portion of the feed. The present invention demonstrates a synergistic effect upon sulfur removal from the heavy portion of the feed by widening the boiling range of the feed and this synergistic effect is converted to practical advantage by reducing the amount of hydrodesulfurization catalyst in proportion to said synergistic effect, thereby keeping hydrocracking to a specified low level. The boiling range of the feed is widened by adding to the higher boiling portion of the feed a portion of a second stream to lower the average boiling point of the hydrodesulfurization feed whereby the sulfur content of the remaining portion of the second stream is sufficiently low that the second stream does not require desulfurization. The further discovery is demonstrated herein that the ratio of gasoline to total conversion during the subsequent riser cracking step of the hydrodesulfurizer effluent is enhanced by reducing the amount of the hydrodesulfurization catalyst as permitted by said synergistic effect.