New approaches to hydroprocessing

Abstract

Heavy oil conversion adds a new dimension to refinery operations that requires the use of units to prevent high yields of coke and more beneficial yields of distillate products. Typically, heavy oil conversion involves two general routes: (1) carbon (coke) removal as a product having a low atomic hydrogen/carbon ratio and, at the same time, to produce overhead material (distillate) having a high atomic hydrogen/carbon ratio; and (2) hydrogen addition by a hydrocracking/hydrogenolysis mechanism by which the yield of coke is reduced in favor of enhanced yields of liquid products. Efficient conversion of heavy oil by fluid catalytic cracking or by hydrotreating requires serous efforts to develop adequate catalysts as well as the modification of existing, or the development of new, processes. The constituents of heavy oil are deleterious to catalyst activity and to on-stream lifetime and there is the need to develop catalysts that are tolerant to the high molecular weight and metal constituents of the feedstocks. Alternative processes include hydrotreating coupled with coking or visbreaking. Such options combine the benefits of higher liquid yields from hydrogen addition with the benefit of the added hydrogen during the thermal process. Furthermore, hydrovisbreaking is receiving some attention as a possible alternate to visbreaking and coking. Hydrovisbreaking heavy oil and thermal cracking (e.g., coking, fluid catalytic cracking) the liquid product process (coking) offers the potential for higher yields of distillate with corresponding decreases in the yield of coke. Further development of these and process other concepts are needed to enhance the conversion of heavy oils.