J. W. S C O T T
J. R. KITTRELL
Trends in the Development of the Modern Hydrocracking Process Industrial demandsfor improved catalytic capabilities should bring continuing- advances in hydrocracking-. This paper examines some new developments in theJield ntroduction of the modern hydrocracking process took
I place just 10 years ago. T h e first plant, an isocracking unit in the Richmond Refinery of Standard Oil of California, was a response to increasing excesses of refractory cycle oils produced by then-conventional processes. I n the intervening years, worldwide hydrocracking capacity has grown by a factor of a thousand, from 1000 to around 1,000,000 barrels per day. This growth occurred because continuing research and development led to new applications and new responses to changes in the world’s petroleum supplies and markets. I t is appropriate after a decade of growth that the situation today be assessed on the occasion of a symposium honoring Alex Oblad. He, with his coworkers at Houdry and now Kellogg, played a large part in the development of processes which have permitted the industry to respond to technical challenges, past and present. We will consider the present, as it relates to hydrocracking, and identify trends important during the next decade. Evolution and development of the hydrocracking process continue in response to changes within the industry and its markets. Among the most noticeable changes is the rapid growth of demand for kerosene turbine fuels; the effect this will have upon process selection during the next decade is examined. T h e interrelationship between hydrocracking and other 18
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refining processes, the use of hydrocracking for production of lubricating oils, and its use for residuum conversion and desulfurization is discussed. Progress being made in the continuing development of hydrocracking and hydroprocessing catalysts also is considered. Response to Jet Fuel Demand
The domestic refining industry is increasingly affected by greater demand for jet fuel (Figure 1). Growth is primarily in the civilian, kerosene-type turbine fuel sector. Since the gasoline market is growing less rapidly, the jet/gasoline ratio is increasing with time (Figure 2). This increase is large, and most extreme in the West, District V, which accounts for 15yoof domestic gasoline, and 30Y0 of domestic jet fuel. High jet/gasoline ratios have, consequently, affected process choice in the West, and are partly responsible for the extensive use of hydrocracking in that area. The future refining problem is intensified because incremental new capacity must satisfy incremental product demands. New processing installations should be able to attain jet/gasoline ratios substantially above the average. I n some local situations, ratios in excess of 1.5 may be desired. T h e impact on process selection is evident from Figure 3 which compares jet and gasoline production for four hypothetical coking refineries process-
Figure 1. Jet fuel demand trend, domestic United States
ing 29" API crude oil. T h e refineries are balanced to maximize light products, satisfying gasoline demand and a t the same time making as much kerosene jet fuel as possible. T h e coking-fluid catalytic cracking refinery produces four times as much gasoline as jet fuel, which is primarily straight run material recovered by distillation from crude oil. T h e coking-fluid catalytic cracking-Isomax combination produces nearly 0.7 volume of jet fuel per volume of gasoline. This process combination has been chosen recently by many Western refiners. Since catalytic cracking does not produce kerosene jet, the substitution of more hydrocracking allows a substantial increase in jet fuel production. The case for a coking-Isomax combination is indicated by production of 1.2 volumes of jet fuel per volume of gasoline, a 75% increase over the previous case. Still higher yields of jet fuel may be obtained if the hydrocracker employs more selective catalysts. A refinery with this type of processing, designated as coking-Jet Isomax, should produce 1.5 volumes of kerosene jet fuel per volume of gasoline. Although the technology for this type of operation is available, economics are marginal at present jet fuel prices. Either higher product prices or improved hydrocracking catalysts or both will support future commercial applica-
Figure 2.
Jet-to-gasoline ratio demand trend, domestic United States
Figure 3. Efect of process selection on j e t and gasoline production
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tion. Hydrocracking development will continue to respond to needs for a process capable of attaining high jet/gasoline ratio. Relationship with Other Refinery Processes
The petroleum industry is giving increasing attention to the optimum relationships between hydrocracking and the other refinery processes. Consider the important process advances occurring in recent years. Hydroprocessing is now in general use, and new zeolitic cracking catalysts have permitted large increases in conversion capacity of existing catalytic crackers. A new catalytic reforming process (7) is available permitting higher yields of gasoline and hydrogen; hydrogen manufacture has become a major refinery process. Trends in the development of hydrocracking must, therefore, be considered in the light of both changes in supplies and markets and changes in processing techniques within the refineries. T h e relationship of hydrocracking with catalytic cracking was affected by the availability of improved zeolitic cracking catalysts, permitting refiners to enjoy increased conversion from existing catalytic cracking plants, as noted, and to defer investment in new conversion equipment. The impact of this trend now has been felt, and new investments must again be considered to satisfy light product demands. I n view of trends toward reduction in fuel oil and large increases in kerosene turbine fuels, hydrocracking will comprise an important part of new conversion capacity installed during the next decade. T h e relationship between hydrocracking and catalytic reforming recently has been clarified (21, and this too will have an impact upon process selection. The chemical and economic considerations are interesting. Hydrocracking and catalytic reforming catalysts both employ a hydrogenation-dehydrogenation component on an acidic support ; and, depending on reaction conditions, each can, to some extent, do both jobs. Hydrocracking can produce aromatic, high octane gasolines that are usually the products of a reforming step. This ability might be exploited to reduce the need for reforming hydrocracked gasolines. Examination of available data indicates that optimum results are more likely if the hydrocracker is operated to obtain maximum liquid yields, and octane improvement is relegated to a modern catalytic reformer. Figure 4 illustrates the relationship between the yield of finished gasoline, produced by the combination of separate hydrocracking and reforming steps, and the octane number of the heavy hydrocracked naphtha. The case considered is for conversion of aromatic light 20
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Figure 4. E j e c t of hydrocracker operation on combined reformer and hydrocracker gasoline yield Midcontinent light cycle oil
cycle oils and is perhaps most favorable to the direct production of high octane gasoline at the hydrocracker. High values of the hydrocracked naphtha octane number, obtained at high hydrocracking severities, eliminate the need for reforming. High octane numbers are accompanied by low liquid yields. If, on the other hand, the hydrocracker is operated to produce lower octane naphtha which is upgraded in a separate reforming step, the yields of gasoline are substantially improved and net hydrogen demands are minimized. With straight run feeds, the maximum finished gasoline yields and minimum hydrogen requirements occur at even lower octane numbers than are shown to be optimal in Figure 4. Furthermore, if jet fuel is to be produced simultaneously, its yield and properties are likewise optimized under these conditions. Therefore, the strong acidity designed into hydrocracking catalysts and hydrocracking process conditions are inappropriate for the isomerization and dehydrogenation reactions employed in catalytic reforming. An all-hydrocracking refinery, previously described, requires relatively few major refinery units: crude distillation, coking (if necessary), hydrocracking, low-pressure reforming, and hydrogen manufacture. This refinery, despite its simplicity, will produce high yields of high quality light products and a wide range of jet/ gasoline ratios. The authors believe there will be a strong trend toward this type of refinery during the next decade. lube Oil Production by Hydrocracking
Another trend is toward the use of hydrocracking for production of lubricating oils ( 3 ) . This is a response to the declining availability of high-quality lube crudes in
some areas. Hydrocracking is capable of producing a complete line of high-viscosity index lube blend stocks, from neutral oils to bright stock, from rather ordinary crude oils. T h e chemistry involves an interesting catalytic separation process. Cyclic molecules, which possess low viscosity indices, are cracked more rapidly than other feed components. Consequently, higher viscosity index molecules tend to remain in the higher boiling products. Costs are comparable with the costs for conventional solvent extraction of high-quality lube crudes. Viscosity indices may, if desired, be much higher than is now usual. Further declines in availability of lube crudes, increases in base stock prices, demands for higher viscosity indices, or the need to retire older solvent extraction units should lead to the installation of hydrocracking facilities adapted to lube manufacture. Residuum Conversion and Desulfurization
T h e need for residuum conversion arisesfrom significant shifts in demand patterns away from traditional residual fuels and toward low sulfur fuels and light distillates. T h e chemical solution is simple: add hydrogen. The physical-chemical environment, however, poses formidable problems. Reacting molecules are large, and concentrations of catalyst poisons are high. Active and selective catalysts are required to minimize equipment and hydrogen costs. Catalyst plugging and deactivation due to organometallic feed constituents are dominant factors in reactor design. I n extreme cases, the preferred reaction system is not yet apparent. Despite complications, several commercial residuum hydrocracking units are operating. These take advantage of special circumstances, processing an especially clean residuum or one cleaned up by solvent deasphalting. However, most residuum conversion requirements of the domestic industry are being met by coking installations since subtracting carbon offers another solution to the problem. As long as coke and crude oil prices are appropriate, residuum hydrocracking will remain in a state of continuing development. Appreciable changes in these economic factors will be followed promptly by
AUTHORS J . W . Scott and J . R. Kittrell are with the Chevron Research Co., Richmond, Calif. 94802. This paper was jirst presented before the Murphree Award Symposium: Catalytic Process DeLlelopment, 157th National Meeting, ACS, Minneapolis, Minn., April 1969.
hydrocracking installations because of the higher liquid yields inherent in this type of processing. Meanwhile, much of the technology developed for residuum hydrocracking is being applied to the important problem of fuel oil desulfurization. T h e technical problem is somewhat less severe since cracking conversion is not a prime objective. T h e economic problem more than compensates, however, since the desulfurized products are still fundamentally low-value materials. Furthermore, the variety of target sulfur levels and the large effects of specific crude oil properties result in a proliferation of possible processing routes. It helps to divide these routes into two categories, direct and indirect. Direct desulfurization routes process a whole residuum and must reckon with the problems arising from organometallic feed constituents. Since the whole residuum is processed, low sulfur levels may be attained in the final product. Indirect desulfurization routes employ a separation process, such as vacuum distillation, solvent deasphalting, or visbreaking, to recover low metal-content oils. These oils are hydrodesulfurized using straightforward process techniques and improved catalysts. T h e desulfurized product is then blended back with the remainder of the residuum to achieve an intermediate degree of desulfurization. Figure 5 illustrates the economic relationship between a number of these desulfurization routes for two high
Figure 5. Fuel oil sulfur reduction Basis:
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sulfur Arabian crudes. T h e lines trace minimum cost for desulfurization to a given sulfur level; the points are the minimum practical sulfur level for each process route. This suggests that it is about as costly to remove a given amount of sulfur from either crude, and that the highly developed indirect route can achieve a satisfactory sulfur level when applied to the lower sulfur crude. However, desulfurization to the 0.5% level requires direct desulfurization and is difficult and expensive for either crude. T h e industry may be expected to use indirect desulfurization routes, crude oil blending, and product segregation to meet intermediate sulfur targets. Low sulfur levels will probably be met by direct desulfurization of selected lower sulfur and lower metal-content crudes. Even in these cases, the present differential between crude and fuel oil prices will not support an economic desulfurization project. There is little prospect that process improvements will alter the situation. While it is difficult to put the continuing improvement in catalysts employed in connection with hydro-
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Figure 7. Improvements realized i n hydrocracking catalyst performance
cracking in proper perspective from the literature, large improvements are clearly evident to those working in the field. An example from the Chevron Research laboratories illustrates the point. Figure 6 shows comparative performance of four generations of first-stage Isocracking catalysts. Large improvements in activity and stability are evident, and the point for an experimental catalyst gives hope that the trend will continue. Improved catalytic capability is usually exploited by designing for increasingly difficult feeds ( 4 ) ,so that catalytic progress is obscured by the demands of more severe service. Occasionally, however, a commercial comparison can be made which highlights real progress. Figure 7 relates reactor volumes in comparable sections of the large Richmond and El Segundo Isomax units. Although the plants are generally similar in capacity, the El Segundo feed is appreciably more difficult to process. Despite this, reactor volume is about one third of that required in the plant based on earlier catalysts. So, a final expected trend will be the continuing, spectacular improvements in catalysts. New catalysts launched modern hydrocracking 10 years ago and have played a dominant role in its development and adaptation. I t is certain that catalysts will continue to dominate our responses to the challenge and change of the 1970’s. REFERENCES (1) Jacobson R . L Kluksdahl, H. E McCoy, C. S and Davis, R. W., “Platinum-
Rhenium batal&s: A Major N& Catalytic Reforming Development,” 34th Midyear API Meeting, Chicaon. b _ , Mnv , 1969.
Figure 6. Improvements in hydrocracking catalyst performance 22
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(2) Kctrell, J. R., Langlois, G. E., and Scott, J. W., Hydrocarbon Proccss., 4 8 (5), 116 (1969). (3) Oil Gas J. Newsletter, 67 (20), 1 (1969). (4) Scott, J. W., and Paterson, N. J., “Advances in Hydrocracking,” 7th World
Petroleum Congress, Mexico City, September 1966.
