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Hydrocracking: a review
Hydrocracking: S. Mohanty*,
D. Kunzru
a review and D. N. Saraf
Department of ChemicalEngineering, Indian Institute of Technology, Kanpur-208076, (Received 24 October 1989; revised 17 September 7990)
India
kinetics, chemistry and reactor modelling of hydrocracking have been reviewed. While it is intended to provide a general overview of the recent advances in this process, greater emphasis has been given to technology and reactor modelling because of their industrial importance. Over ninety references have been cited. In this article the technology,
(Keywords: hydrocracking;
hydrocarbon;
petroleum)
Hydrocracking is practised in modern petroleum refineries for converting various hydrocarbons of higher boiling ranges into more valuable products such as gasoline, diesel and jet fuel’. Even though product projections show decreasing demand for gasoline and increasing demand for middle distillates, gasoline remains the most important product in the USA. Hydrocracking is a highly flexible petroleum refining process which can take feedstocks ranging from light naphthas to deasphalted vacuum residue’. Other applications of this process include upgrading of petrochemical feedstocks3, improvement of gasoline octane number4, and production of high quality lubricants. In addition, very heavy hydrocarbon deposits such as tar sands and shale oil can be upgraded by hydrocracking’. The process upgrades the original stock by increasing its overall hydrogen-to-carbon ratio and decreasing the average relative molecular mass. The operating conditions and catalysts for hydrocracking may vary, depending upon the end product required. The progress of hydrocracking has largely depended on the development of catalysts with improved activity and selectivity. Earlier, unsupported tungsten sulphide was used as a presaturation catalyst, but it has subsequently been replaced by supported catalysts such as nickel-tungsten sulphide on alumina and cobalt molybdate on alumina. These changes contributed to the production of aromatic gasoline of higher octane number6. All hydrocracking catalysts have dual functions7*8, consisting of hydrogenation metal(s) on an acidic cracking base. Commonly used hydrogenation components include cobalt, molybdenum, tungsten, nickel, platinum and palladium. The cracking component is an acidic carrier, which may consist of amorphous silica-alumina of various compositions or crystalline supports such as cation exchanged faujasites X and Yg. A desirable feature of the hydrocracking process is that the liquid yield is about l&15 mass % higher than that from delayed coking. Recently a new technology, termed mild hydrocracking, has been introduced. Its advantage is that it can use existing hydrotreaters for hydrocracking by increasing the severity of operation. The product is mainly middle * Present address:
Regional
001~2361/90(121467~7 ,c 1990 Butterworth-Heinemann
Engineering
Ltd
College,
Rourkela,
India
which is an excellent quality diesel oil blendstock. The process is steadily gaining importance, with 76% of the units in Japan and 42% of those in Western Europe practising this technique at presentlO. Recent developments made in the hydrocracking processes have been reviewed by Choudhary and Saraf' ‘, Maxwell” and Kriz et al.‘.
distillate,
PROCESSES A wide variety of feedstocks ranging from light naphthas to residual oil can be hydrocracked to obtain lighter products. One or more stages may be required, depending on the nature of the feedstock used and the end products desired. A typical two-stage hydrocracker is shown in Figure 1. In the first stage 4@-50 ~01% of the feed is hydrocracked, and the first stage also acts as a hydrotreater where poisonous nitrogen and sulphur compounds are partially hydrogenated. The eflluent from the first stage reactor passes through heat exchangers to a high pressure separator where hydrogen-rich gases are separated and recycled. The liquid from the separator is fed to a fractionating tower and the tower bottoms form the feed to the second stage13. This mode of operation is known as extinction recycle hydrocracking; there is no purge stream to remove the refractory compounds present in the feed and hence the severity of the process has to be increased to enforce the conversion. A hydrocracker reactor generally operates in the temperature range 530-700 K and at pressures in the range 6.5-13.5 MPa. Except for the H-oil and Hy-C processes, which were codeveloped by Cities Service Research and Development Co. and Hydrocarbon Research, Inc., fixed-bed reactors with liquid downflow are used13,14. Details of the reaction conditions and product yields for the major commercial hydrocracking processes are available’ 5. In addition to these processes, several investigations on hydrocracking have been reported. Sikonia2 developed a process which can hydrocrack any fraction from naphtha to demetallized oil (DMO) to yield the desired products. During hydrocracking most of the sulphur, nitrogen and oxygen are removed and the olefins saturated, so that the product obtained is a mixture of pure paraffins, naphthenes and aromatics. The catalysts
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Hydrocracking:
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S. Mohanty
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Hz recycle
c
A -Naphtha
Flashgas
P
-Wliesel
Hz recycle
blend
stock
Feed
Furnace Figure
1
Schematic
Reactor diagram
Furnace
of hydrocracking
Reactor
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Fractionator
process
are chosen to be selective towards producing distillate products. The process can be carried out in a single stage, two stages or series flow to meet various objectives of hydrocracking. A higher octane gasoline is obtained by first reforming a gasoline (boiling range 335453 K) followed by hydrocracking16. Nasution17 obtained optimum yields of middle distillates by subjecting Kuwait vacuum distillates to hydrocracking at 0.88 h-r space velocity, 683 K temperature and 10 MPa pressure, with a hydrogen to feed volume ratio of 1OOO:land Co-Mo/Al,O, catalyst. Radchenko et al.” used a two-stage process for hydrocracking of vacuum distillate; in the first stage a desulphurizing catalyst, Ni-Mo/Al,O,, was used and in the second stage Mg silicate. The products were winter diesel and jet fuel when the operating pressures were 10 and 15 MPa, respectively. Recently Kukes et a1.19 have described a two-catalyst hydrocracking process with improved product selectivity. The feedstock reacts first on a Ni-W/molecular sieve catalyst and subsequently with MO supported on an alumina-molecular sieve mixture. Hydrocracking of residual oils obtained from vacuum or atmospheric distillation of various crudes was carried out by Sakabe and Yagi2’ and Ukegawa et a1.21, using spent catalyst from a desulphurization unit. With a spent Co-Mo/Al,O, catalyst, Ukegawa et ~1.~~ obtained recoveries of oil fractions (b.p. < 773 K) of 50.7-68.3 wt% and 70.1-94.7 wt% for the residual oils from vacuum and atmospheric distillation, respectively, Kotowski” investigated the hydrocracking of a deasphalted and demetallated atmospheric residue from Ramashkino crude in a flow reactor at 685-705 K and with a catalyst concentration of 7-9 wt%; the yield of fuel oil decreased with increasing flow rate. A review of hydrocracking of light Arabian vacuum gas oil over a zeolite catalyst, for maximum conversion
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Separators
to middle distillates, is given by Light et a1.23. Sasaki et a1.24 reported the hydrocracking of a heavy oil with high metal content over an aqueous vanadyl oxalate catalyst at 715 K and 10 MPa hydrogen pressure. A two-stage hydrocracking process carried out by Kotowskiz5 involved the thermal treatment of a mixture of coal and heavy oil, so as to aromatize the fuel oil and depolymerize the coal, followed by catalytic hydrocracking in two stages to give C,-C, gases, naphtha, diesel oil and fuel oil. A sour crude was first diluted with recycle oil and then hydrocracked over a fixed bed of Ni-Mo/Al,O, catalyst at 725 K, 3 MPa and 2 h-l space velocity by Katsobashvili and Teplyakova26, and the products obtained were gasoline, diesel fuel and fuel oil. To overcome the problem of catalyst deactivation, several processes, which utilize once-through catalysts, are under development. These include Aurabon, HFC, Residue HC, M-Coke and VEBA Combi Crackingz7. The Aurabon process (developed by UOP) is suitable for extremely heavy oils and uses oil metals as catalysts. In the HFC process (hydrocracking with fine catalyst) the catalyst, consisting of coke and metals (Ni, V) from hydrotreating, is suspended in the feed. The Residue HC process (developed by Idemitsu Kasan Co., Japan) uses a novel long-life proprietary catalyst in a fixed bed reactor. The process is suitable for hydrocracking of atmospheric residue and the operating conditions are similar to those for hydrodesulphurization. In the M-Coke process (Exxon), the catalyst is formed in situ from dispersed or dissolved metals such as molybdenum and coke precursors. The powdered catalyst in the VEBA process is either a waste product of the alumina industry (‘Bayer mass’) or lignitic coke; this process includes liquid phase hydrogenation of the feed followed by gas phase hydrotreating of the products. Mild hydrocracking, a process which has been gaining importance in recent years, has been discussed by a
Hydrocracking:
number of authors’0*28,29. These workers used existing vacuum gas oil desulphurizers for conversion of vacuum gas oil to middle distillates. In the study of Sonneman et al.“, the overall conversion was ~36% at operating pressures below 7 MPa; the middle distillate formed was about 26 ~01% of the feed, heavy naphtha 2.3 vol%, and lighter products 2 wt%.
CHEMISTRY Although there are a number of reactions taking place simultaneously during hydrocracking, the mechanism of hydrocracking is similar to that of catalytic cracking with hydrogenation superimposed. The catalyst activity is maintained at a high level because of lower coke deposition. With sulphided nickel catalyst support on silica-alumina, excessive splitting produces large amounts of low molecular weight paraffins with a high iso/normal ratio. Platinum on silica-alumina, which has a much higher hydrogenation activity, gives more intermediate than low molecular weight paraffins, thus minimizing the ratio of gas to liquid products. With a more active hydrogenation catalyst such as metallic nickel or platinum, the ratio of iso/normal light paraffins may be low. The product distribution for some n-paraffins using zeolite catalyst is given by Steijns et ~1.~ and Vansina et than al.*. Olelins are more readily hydrocracked parafhns6. The cracking reaction is endothermic whereas hydrogenation is exothermic; since the heat required for cracking is less than the heat released during hydrogenation, the overall hydrocracking process is exothermic and the temperature is maintained by injecting cold hydrogen into the reactor. Generally hydrocracking reactions take placer4 at temperatures between 560 and 690 K and pressures between 8 and 13.6 MPa. Before cracking, both intermolecular and intramolecular rearrangements take place, so that it is not possible to predict the final product spectrum obtainable from a given feed. With nonacidic or weakly acidic catalysts, the reactions are generally less complex and take place on the hydrogenation sites of the catalyst; very little isomerization or structural rearrangement takes place and the reaction products are generally simple fragments of the original reactant. By using a catalyst which is intermediate between acidic and nonacidic, cracking occurs on both the acidic and the hydrogenation components of the catalyst and the products are also intermediate in character6. Langlois and Sullivan3’ reviewed the chemistry of the catalytic hydrocracking of hydrocarbons in detail; the available information indicates that hydrocracking of normal paraffins involves scission of carbon-carbon bonds at different sites. For of instance, the products from the hydrocracking n-decane can be represented as follows:
C 10
/1
c5+c5
-+
c,+c4
L
c,+c,
The amounts of C, and lighter paraffins are generally negligible. The normal paraffins formed during the cracking step can also be converted to isoparaffins by hydroisomerization. The proportion of normal to iso-paraffins depends on various factors such as the acidity of the catalyst, conversion level, and temperature.
a review: S. Mohanty
et al.
When normal paraffins are hydrocracked over a strongly acidic catalyst, the products consist mainly of isoparaffins; small amounts of n-paraffins are isomerized without cracking3’. Other studies on the hydrocracking reactions of paraffins have been carried out by Archibald et u~.~I, Flinn et a1.32, Coonradt and Garwoodj3, El-Kady et al. 34, Rabinovich et a1.35,Panchenkov et ~1.~~ and Gol’dfarb et ~1.~~. Reactions of cycloparaffins over strongly acidic catalysts were studied by Egan et ~1.~~. Sullivan et ~1.~~hydrocracked alkyl aromatics with side chains on a strongly acidic catalyst, producing paraffins and benzene; they also studied complex reactions of polycyclic aromatics over acidic hydrocracking catalysts. Schneider et aL4’ studied the hydrocracking reactions of petroleum vacuum distillate, and from spectroscopic analysis, chromatographic separation and structural analysis of the products concluded that hydrogenation and cleavage of aromatic rings are the main reactions involved. CATALYSTS The type of catalyst used varies with the feedstock being processed. COO-MOO,-Al,O, has been widely used for hydrocracking of heavy feedstocks such as residual raffinate, solvent deasphalted residual oil and vacuum residue’7~41~42.The catalyst activity decreases and the selectivity changes with age, and more gas than naphtha is produced as the catalyst temperature is raised to maintain the conversion, Regeneration is necessary when catalyst poisoning due to deposition of coke and other materials reaches a limiting level, and is usually accomplished by burning off the deposits. Kelly and Ternan studied the activity of COO-MOO,-Al,O, catalyst promoted with sodium, potassium or lithium; lithium showed the best results as regards conversion and removal of pitch, oxygen, sulphur and nitrogen. NiiMo, Ni-W and NiiCo have also been used as hydrocracking catalysts. E1-Kady44, Jaeckh et ~1.‘~ and Nasution4’ employed Mo-Ni/SiO,-Al,O, catalyst for hydrocracking of vacuum distillates. Katsobashvili and Teplyakovaz6 used the same metals on alumina for hydrocracking of a sour crude. Nishijima et ~1.~~reported the effect of distribution and dispersion of MO ions in NiO-Coo-MoO,/Al,O, catalysts; more highly dispersed MO ions gave higher hydrogenation activity whereas agglomeration of MO ions resulted in a higher hydrocracking activity. Nat47 recommended the use of Ni-Mo-zeolite catalyst for maximizing gasoline production and NiW-zeolite catalyst for maximum gas oil manufacture. In their study on hydrocracking of heptane on Ni-Mo/HY ultrastable zeolites, Isabel et al. 48 found that the atomic ratio, Ni/(Ni + MO), had a strong influence on the activity and selectivity of the catalyst. Ghosa14” hydrocracked straight run vacuum gas oil using a Ni-Mo on Y zeolite catalyst containing rare earth elements. Yan13 developed a new dual catalyst, NiW/REX-Ni/SiO,-A1203 for extinction hydrocracking. The Ni-W-impregnated rare earth (RE)-exchanged X-type zeolite was found to be more resistant to nitrogen, more selective towards a desirable naphtha product and structurally more stable, whereas Ni/SiO,-A1203 helped in the extent of conversion of heavy, polynuclear compounds in the feed. This catalyst can be used for hydrocracking heavy feeds of wide boiling range. LaX and NIX catalysts were used
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for the hydrocracking of Assam crude by Choudhary and Saraf ‘O, who reported that NiX had a lower activity. Kotowski and Benbenek” used Co-Ni on a Y zeolite carrier for hydrocracking vacuum distillates. Swift and Black” studied synthetic mica-montmorillonite with Ni or Co incorporated into the lattice structure; the activity was found to be greater than that of Pd-rare earth-Y zeolites or Pd-H-modernite. Xus3 studied the stability towards sulphur of ZSMS zeolite and found that catalysts with Pd on ZSMS showed greater total acidity and higher sulphur stability. He explained this relation between sulphur stability and acidity by the electron transfer theory. Shell Internationals4 has developed a NiW/zeolite Y82 catalyst in which Ga is incorporated by ion exchange. The presence of Ga seems to improve the catalyst activity and selectivity to C, products. Koepke and Abdos5 reported that use of NiO-Nb,O,/Al,O,-zeolite Y82 catalyst produced gasoline of enhanced octane number as compared with NiO-MoO,/Al,O,-zeolite Y82 catalyst. Tests carried out by Kondo et ~1.‘~ on hydrocracking of heavy oil from different sources showed that Ni-V/ Al,O, catalyst was more active than either CO-MO or Ni-Mo, and that spent catalyst from a desulphurization unit could be used for hydrocracking. Aqueous vanadyl oxalate prepared from V,O, and (C02H)2 (1:4 mole ratio) was found to be very effective for hydrocracking heavy oils with high metal content24. Sasaki et al.” prepared a catalyst from heavy oil, known as Ash Catalyst, which had a high vanadium content, and used it for hydrocracking of heavy oils. Although the activity of this catalyst was lower than that of Co-Mo/Al,O,, it produced the same level of liquid products. Coke formation decreased, whereas metal removal increased, with an increase in the amount of Ash Catalyst. Kotowski2’ used a two-step process to hydrocrack a coal-heavy fuel oil mixture, the first step being an initial thermal treatment to depolymerize the coal. In the second step, the mixture was catalytically hydrocracked in a two-stage process to yield gases (8.9 wt%), naphtha (14.6 wt%) and diesel oil (35.7 wt%). Morita et ~1.‘~ investigated the effect of zinc chloride catalyst supported on silica, silica-alumina or alumina on hydrocracking of anthracene. The catalyst prepared by impregnating silica-alumina with aqueous zinc chloride and drying at 413 K was found to be the most active, but rapidly became deactivated. When the catalyst was prepared by drying at a higher temperature, the catalyst life was increased. Frank and Le Pages9 prepared a number of sulphided catalysts containing Ni or Co and MO or W on silica-alumina carriers and studied their relative activity and selectivity. With toluene as the feed, for each pair of sulphides the activity passed through a maximum when the atomic ratio Ni (or Co)/(Ni (or Co)+ MO (or W)) was about 0.25. The hydrogenation activities of the various catalysts decreased in the order Ni-W > Ni-Mo > CO-MO > Co-W. This order of activity was also found to be valid for other hydrocarbons such as heavier aromatics and paraffins. With vacuum gas oil as feed, increasing the support acidity increased the activity but lowered the selectivity with respect to production of middle distillates. Aboul-Gheit6’ studied the hydrocracking of vacuum gas oil (VGO) on NiMo/Al,O,-SiO,-zeolite HY catalysts. Several workers have shown the importance of the pore
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diameter of a catalyst in its activity, selectivity and rate of deactivation6’-64. Arahata et ~1.~~3~~ reported that a catalyst with a smaller mean pore diameter was more effective in cracking, desulphurization and denitrogenation, whereas a catalyst with a larger mean pore diameter resulted in higher activities for deasphalting and demetallation. A Japanese patent6’ recommends the use of medium pore size zeolites for hydrocracking. The use of pillared interlayered clay supports has been reported to improve catalyst performance during hydrocracking 66-69. For instance, for the same conditions, a VGO hydrocracked over a NiMo-impregnated pillared clay catalyst gave a product with an APl gravity of 37.1”, versus 28.8” for the corresponding products using metal-impregnated unpillared clays. KINETICS Hydrocracking of petroleum feedstocks proceeds through a network of complex reactions involving a large number of components, which makes the kinetic study of these reactions extremely difficult. For simplification, the reaction steps and products are combined into groups. Some of the kinetic models developed have been reviewed by Sue and Sugiyama7’. Steinberg et ~1.‘~ have given an overview of the research and development work carried out at the Leuna (East Germany) petrochemical complex, on hydrocracking of n-alkanes to branched alkenes over zeolite catalysts. For hydrocracking of light hydrocarbons, Bernard0 and Trimm72 postulated a Langmuir-Hinshelwood type of kinetic model which accounted for the effect of carbon formation on a nickel catalyst. Raseev and El Kharashi’j studied the kinetics of hydrocracking of naphtha and calculated the heat of adsorption and activation energy of the surface reactions. Arayici and Deymer74 studied the kinetics of hydrocracking of naphtha over Pt/SiO,Al,O, with chloroform added during the process. A kinetic model for hydrocracking of middle distillate was developed by Grendele”. Mikshina et a1.76 studied the kinetics of hydrocracking of n-alkanes. The hydrocracking of n-decane, n-undecane and n-dodecane over Pt/Al,O, and Ni-Mo/Al,O, was investigated by Gol’dfarb et ~1.~‘; for their kinetic study the products obtained from n-decane were combined into methylnonanes, dimethyloctanes and cracked products. Steijns and Froment” developed kinetic models for hydroisomerization and hydrocracking of n-decane and n-dodecane over zeolite catalysts. They assumed that the pores were completely filled, which leads to a pseudo-zero order behaviour. The concentration of the reacting molecules at the active sites was determined by the physical adsorption process. The model was found to be superior to those which did not account for physical adsorption. Marin and Froment” considered the possible intervention of hydrogen through a Rideal mechanism for the hydrocracking of C, hydrocarbons. The kinetics of hydroisomerization and hydrocracking of n-octane over a zeolite catalyst were modelled by Baltanas et ~1.‘~ using the assumption made by Steijns and Froment7’ that the concentration of the reacting molecules at the active sites is determined by the physical adsorption process. The rate of hydroisomerization followed the same trend as for n-decane and n-dodecane. They assumed a Langmuir-Hinshelwood mechanism for chemisorption and used a Langmuir isotherm to express
Hydrocracking:
the hydrocarbon concentration at the catalyst surface. Several models were developed and compared statistically. The kinetics of hydrocracking of n-heptane over Pt/Al,O, catalysts containing various additives were studied by Sokolov and Zaidman*O. El-Kady et a1.*l carried out hydroisomerization of n-heptane over Pt/SiO,-Al,O, catalyst and reported that at low and/or moderate temperatures (600-675 K) the balance of cracking versus hydrogenation was shifted more towards hydrogenation, but under severe conditions the shift was more towards cracking. Rabinovich et ~1.~~ and Panchenkov et a1.36studied the kinetics of hydrocracking of heptane over a polymetallic platinum-containing reforming catalyst. The kinetics of hydrocracking of gas oil and vacuum distillate have been studied by Qader and Hill** and El-Kady44, respectively. These authors found the rate of hydrocracking to be first order with respect to feed concentration. Nasution4’ made a kinetic study of hydrocracking of vacuum distillate over a Ni-Mo/Al,O,-SiO, catalyst for production of middle distillate; the apparent activation energy for hydrocracking was determined to be 108 MJ kmol-‘. The above kinetic studies on model systems show that there is no simple method of predicting the product distribution. However, with most feeds the production of C, and lighter hydrocarbons is negligible. These studies indicate that although the kinetics of hydrocracking of pure alkanes are satisfactorily represented using Langmuir-Hinshelwood models, such models are difficult to apply for petroleum fractions. For such complex systems, it may be more practical to use pseudohomogeneous kinetics83,84. REACTOR MODELLING Several models which have been suggested for hydrocracking reactors are summarized below. Strangeland developed a three-parameter model for predicting the product distribution in a hydrocracker. These parameters account for the reactivity of the feed, the product selectivities, and the yield of products lighter than butane. According to Strangeland the parameters were dependent largely on the parafinicity of the feed; however, other feedstock properties may also affect them, and hence they have to be determined experimentally for each feedstock. Jaffe85 developed a model which accounts for the hot spots that are generated due to the rapid reaction in the regions of low flow, and the temperature drop due to mixing of cooler fluid from the surrounding region. The reactions were modelled by identifying combined species, and a kinetic model was developed to account for the conversion of combined reactant species to combined product species. Gerdes et aI.” developed a model for a fixed bed hydrocracker which took into consideration four classes of reactions; hydrocracking, saturation, desulphurization and denitrogenation. The catalyst bed was divided into horizontal tanks of specified thickness. Each stirred tank consisted of three regions: a solid region consisting of catalyst matrix, the pore volume, and the external void space. The model assumes that as the liquid flows down it fills the pore volume; excess liquid flows down to the tank below by undergoing reaction and subsequent vaporization. The external void is also filled with liquid, leaving space for vapour flow, and is represented by the external hold-up. The excess liquid cascades to the tank
a review: S. Mohanty
et al.
below. Simple phase equilibrium calculations were made and it was assumed that if the equilibrium liquid was insufficient to fill the pores, they were filled by condensation of heavy hydrocarbon components. A simple kinetic model was assumed, with reaction rate being proportional to the density of the reacting species and to the hydrogen partial pressure. Since under normal hydrocracking conditions diffusional resistance is not limiting, it was not included in this model. Yan’ developed a model to study the dynamic behaviour of an adiabatic trickle-bed reactor without and with gas or liquid quenching. He assumed that the fluid flow pattern was plug flow, temperature and concentration across the cross section were uniform, heat capacities and heats of reaction of the liquid and gas were constant, reaction took place at the catalyst surface, vapour behaved as an ideal gas, and liquid and vapour were in equilibrium. This model gave the required location, starting time and amount of quenching to prevent excess heating of the bed. Panchenkov et ~1.~’ modelled an industrial reactor which produced diesel fuel of low pour point from gas oil by hydrocracking and isomerization over a zeolite catalyst. A model for a CANMET process, based on a kinetic scheme, was developed by Patmore and Pruden8s. The experimental data agreed closely with the simulated results in the ranges 570-670 K and 10.44-17.34 MPa. Panaitescu and Dumitrescu89990 suggested a model for hydrocracking of petroleum fractions, and thus obtained optimal conditions for steady state operation of a hydrocracking reactor. To take account of change in catalyst activity the model constants were re-evaluated from time to time. A model for hydrocracking of vacuum gas oil, developed by Lauxgl, was based on product distribution versus boiling point index and structure index determined by the type of hydrocarbon product. The rate of hydrocracking could be determined from the change in these indices and the product distribution. A model developed by Mikshina et ~1.~’ for hydrocracking of gasoline in a fixed catalyst bed consists of 33 equations including heat and material balances; it was tested against pilot plant results and found to be satisfactory. Krishna and Saxena’” developed a two-parameter axial dispersion model to describe hydrocracking kinetics; this model does not consider temperature increase due to exothermic hydrocracking reactions explicitly, and hence is of limited utility. CONCLUSIONS This review highlights the technology, chemistry, kinetics and reactor modelling of hydrocracking processes. Although considerable information has been published on the hydrocracking of pure hydrocarbons, very few studies have been reported on the kinetics and reactor modelling of petroleum fractions. More detailed kinetic studies on each hydrocarbon type, of narrow boiling-range, should be undertaken to investigate the effects on the activity, selectivity and stability of the catalyst. Very meagre information is available on the kinetics of catalyst deactivation, and studies should be conducted to bridge this gap. The reactor models published in the open literature are not capable of predicting the composition of different homologues in the various product streams; for this more detailed models, which subdivide the feed with respect
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to both boiling range and hydrocarbon type, would be required. Most industrial hydrocrackers are trickle-bed reactors, but often these are approximated as of plug flow type. In such reactors, particularly with heavy feeds, the wetting characteristics of the catalyst can affect the reactor performance. Models which include realistic hydrodynamics need to be developed. REFERENCES
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15 16 17 18 19 20 21 22 23 24 25 26 21 28 29 30 31 32 33 34 35 36 37
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Yan, T. Y. Can. J. Chem. Eng. 1980, 58, 259 Sikonia, J. G. Hydrocarb. Proc. 1980, 59(6), 73 Mavity, V. T., Ward, J. W. and Whitebread, K. E. Hydrocarb. Proc. 1978, 57(11), 157 Chen, N. Y., Maziuk, J., Schwartz, A. B. and Weisz, P. B. Oil & Gas J. 1968, 66(47), 154 Kriz, J. F., Ternan, M. and Denis, J. M. J. Can. Per. Tech. 1983, 22, 29 Voohries Jr., A. and Smith, W. M. in ‘Advances in Hydrocracking’ Advan. Pet. Chem. and Relining, Vol. VIII (Ed. J. J. McKettaJr.), Interscience, New York, USA, 1964, p. 169 Steiins, M.. Froment. G. F.. Jacobi. P. and Uvtherhoeven. J. 1nd.OEng. ihem. Prod. Res. Dev. 1981, 20(4), 654 Vansina, H., Baltanos, M. A. and Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 526 Ward, J. W., Hansford, R. C., Reich& A. D. and Sosnowski, J. Oil & Gas J. 1973, 71(22), 69 Sonnemans, J. W. M., Plantenga, F. L., Desai, P. H. et al. ‘Mild Hydrocracking of Heavy Oils in the Eighties’, Natl. Pet. Refiners Assoc. Tech. Paper, AM-84-60, 1984 Choudhary, H. and Saraf, D. N. Ind. Eny. Chem. Prod. Res. Dev. 1975, 14, 74 Maxwell, I. E. Zngenieursbhzd 1983, 52, 53 Yan, T. Y. Ind. Eng. Chem. Proc. Des. Dev. 1983, 22, 154 Gary, J. H. and Handwerk, G. E. in ‘Petroleum Refining: Technology and Economics’ Marcel Dekker, Inc., New York, USA, 1975 ‘Relining Process Handbook’ Hydrocurb. Proc. 1986,65(9) Shipikin, V. V., Bortov, V. Y., Georgievskii, V. Y. et al. Neftepererub. Neftekhim. (Moscow) 1983, 8, 3 Nasution, A. S. ‘Proc. 3rd Pac. Chem. Eng. Congr.‘, 1983,2,232 Radchenko, E. D., Gorshtein, A. B., Shkol’nik, B. L. and Shtein, V. I. Sb. Nuuchn. Tr.-Vses. 1983, 44, 100 Kukes, S. G., Miller, J. T. and Gutberlet, L. C. US Pat. No. 4875991 1989 Sakabe, T. and Yagi, T. Hydrocurb. Proc. 1979,58(12), 103 Ukeaawa. K.. Oiima. T.. Kondo. T. et al. Sekivu Gukkuishi 1980: 23,280’ Kotowski, W. Naftu (Katowice, Pol.) 1982, 38, 232 Light, S. D., Bertam, R. V. and Ward, J. W. Hydrocurb. Proc. 1981, 60(5), 93 Sasaki, Y., Ojima, Y., Kondo, T. et al. Sekiyu Gakknishi 1983, 26, 412 Kotowski, W. Chem. Tech. (Leipzig) 1983, 35, 22 Katsobashvili, Y. R. and Teplyakova, G. A. Khim. Tekhnol. Topl. Musel. 1984, 8, 8 Schuetze, B. and Hofmann, H. Hydrocurb. Proc. 1984,63(2), 75 Gembicki, V. A., Andermann, R. E. and Tajbl, D. G. Oil & Gas J. 1983, 81(8), 116 Jaeckh, C., Dreyer, H. D., Himmel, W. F. et al. 9th Actas Simp. Iberoam. Catal. 1984. 2, 1226 Langlois, G. E. and Sullivan, R. F. in ‘Chemistry of Hydrocracking’ Adv. Chem. Ser. No. 9, 1970 Archibald, R. C., Greensfelder, B. S., Holzman, G. and Rowe, D. H. Ind. Eng. Chem. 1960,52, 745 Flinn, R. A., Larson, 0. A. and Beuther, H. Ind. Eng. Chem. 1960,52, 153 Coonradt, H. L. and Garwood, W. E. Ind. Eng. Chem. Proc. Des. Dev. 1964, 3, 38 El-Kady, F. Y. A., Menoufy, M. F. and Hassan, H. A. Ind. J. Tech. 1983, 21, 293 Rabinovich, G. B., Borisevich, Y. P., Levinter, M. E. and Rodionov, A. V. Khim. Technol. 1983, 26(6), 214 Panchenkov, G. M., Gorlov, S. G., Belov, N. N. and Kolesnikov, I. M. Zh. Fiz. Khim. 1983, 57(10), 2479 Gol’dfarb, Y. Y., Katsobashvi1i.Y. R. and Rozental. A. L. Kinef. Kural. 1981, 22, 668
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38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 51 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76
77 78 79 80 81 82 83 84 85 86
Egan, C. J., Langlois, G. E. and White, R. J. J. Am. Chem. Sot. 1962,84, 1204 Sullivan, R. F., Egan, C. J. and Langlois, G. E. J. Catal. 1964, 3, 183 Schneider, W., Mueller, E., Zschocke, R. and Onderka, E. Chem. Tech. (Leipzig) 1981, 33, 508 Kondo, T., Ojima, Y., Ukegawa, K. et al. Kogai Shiyen Kenkyusho Iho 1982, II,41 Chesnokov, A. A., Kogan, L. D., Kozlova, N. M. and Chesnokova, N. Z. Khim. Technol. Topl. Muse1 1985. 4, 32 Kelly, J. F. and Ternan, M. Can. J. &em. Eny. 1979, 57, 726 El-Kadv. F. Y. A. Ind. 3. Tech. 1979. 17. 176 Nasutidn, A. S. ‘Proc. 5th Int. Semin. New Dev. Engine Oils, Ind. Oils, Fuels Addit., 1985 Nishijima, A., Shimada, H., Sato, T. et al. Sekiyu Gukkaishi 1988, 31, 109 Nat, P. J. Erdoel Kohle, Erdgus, Petrochem. 1989,42,447 Isabel, V. M., Escardino, A. and Corma, A. Ind. Eng. Chem. Res. i987,26, 1495 Ghosal, G. K. Chem. Eng. World 1985, 20(9), 83 Choudhary, N. and Saraf, D. N. Ind. Eng. Chem. Prod. Res. Deu. 1978, 17, 196 Kotowski, W. and Benbenek, S. Nuftu (Kutowice, Pal.) 1981, 37, 209 Swift, H. E. and Black, E. R. Ind. Eng. Chem. Prod. Res. Deu. 1974, 13, 106 Xu, Y. Chem. Abstr. 1990, 112, 3938Oc Klazinga, A. H. Eur. Pat. Appl. EP 288112 1988 Koepke, J. W. and Abdo, S. F. lJS Pat. No. 4 777 157 1988 Kondo. T.. Oiima. Y.. Ukeaawa. K. et al. Koaui Shiaen Kenkyusho Hokuku. 1984, 33, i Sasaki, Y., Ojima, Y., Kondo, T. et al. Sekiyu Gakkaishi 1983, 26, 144 Morita, M., Hirosawa, K., Sato, T. and Ouchi, K. J. Jap. Pet. Inst. 1980, 23, 52 Frank, J. P. and Le Page, J. F. ‘Proc. 7th International Congress in Catalysis’, Tokyo, Japan, 1981, p. 792 Aboul Gheit, A. K. Erdoel. Erdgus. Kohle 1987, 103(10), 441 Clement, C. Pet. Tech. 1986, 328, 32 Weber, M., Becker, K., Berrouschot, H. D. ef al. German Put. (East) DO266 924 1989 Arahata, Y., Tsukada, Y., Imamura, 0. et al. Sekiyu Gukkaishi 1989, 32, 306 Arahata, Y., Tsukada, Y., Imamura, 0. et al. Sekiyu Gakkuishi 1989,32, 312 Union Oil Co. Japanese Patent JP 6245688 1987 Hamilton Jr., D. M. US Put. No. 4640 764 1987 Battiste, D. R. and Harris, J. R. US Par. No. 4637991 1987 Gortsema, J. P., McCauley, J. R., Pellet, R. J. et al. PCT Inr. Appi. WO 8806614 1988 Kirker, G. W. and Varghese, P. Eur. Put. Appl. EP284 278 1988 Sue, H. and Sugiyama, H. Petrotech (Tokyo) 1982, 5, 942 Steinberg, K. H., Becker, K. and Nestles, K. H. Acru. Phys. Chem. 1985,31,441 Bernardo, C. A. and Trimm, D. L. Rev. Port. Quim. 1977,19,369 Raseev, S. D. and El Kharashi, S. Rev. Chim (Bucharest) 1978, 29, 1140 Arayici, S. and Deymer, J. Chim. Actu. Turc. 1979, 7, 213 Grendele, G. V. 7th Simp. Iberoam. Catal. (Trab.), 1980,~. 469 Mikshina, V. S., Hofman, N., Martynenko, V. G. et al. Materialy 3-i Vses. Konf. po Kinet. Geterogen. Katalitich. R-Tsii, Kalinin, 1980, 2, 302 Steijns, M. and Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 660 Marin, G. B. and Froment, G. F. Chem. Eng. Sci. 1982,37,759 Baltanas, M. A., Vansina, H. and Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 531 Sokolov, V. P. and Zaidman, N. M. Kinet. Katul. 1983, 24(4), 898 El-Kady, F. Y. A., Menoufy, M. F. and Hassan, H. A. Ind. J. Tech. 1983, 21, 300 Qader, S. A. and Hill, G. R. Ind. Eng. Chem. Proc. Des. Dev. 1969, 8(l), 98 Strangeland, B. E. Ind. Eng. Chem. Proc. Des. Dev. 1974,13,71 Mohanty, S. Ph.D. Thesis Indian Institute of Technology, Kanpur, India, 1989 Jaffe, S. B. Ind. Eng. Chem. Proc. Des. Dev. 1976, 15,410 Gerdes, K. F., Strangeland, B. E., Chen, G. T. S. and Gumerman, R. J. paper presented at the Annual Meeting of AIChE, 1977
Hydrocracking: 87
88
Panchenkov, G. M., Laz’yan, Y. I., Rogov, S. P. ef al. Nauchn. Osn. Pererab Nefti Gaza Neftekhim., Tezisy Dokl. Vses Konf., 1977, pp. 104105 Patmore, D. J. and Pruden, B. B. ‘Thermal Hydrocracking of Athabasca Bitumen: Comparison of Computer Simulated Values of Feed and Product Vaporization with CANMET Pilot Plant Data’, CANMET Report 80-23E, Canada Centre for Mineral and Energy Technology, 1980
89
a review: S. Mohanty
et al.
Panaitescu, G. and Dumitrescu, S. Rec. Chim. (Bucharest) 1982, 33,453
91 92
Panaitescu, G. and Dumitrescu, S. Rev. Chits. (Bucharesr) 1983, 34, 724 Laux, H. Chem. Tech. (Leipzig) 1983, 35, 8 Mikshina, V. S., Martynenko, V. G. and Taganov, I. N. Khim.
93
Krishna, R. and Saxena, A. K. Chem. Eny. Sci. 1989, 44, 703
90
Technol (Kiev) 1984, 5, 8
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1473
D. Kunzru
a review and D. N. Saraf
Department of ChemicalEngineering, Indian Institute of Technology, Kanpur-208076, (Received 24 October 1989; revised 17 September 7990)
India
kinetics, chemistry and reactor modelling of hydrocracking have been reviewed. While it is intended to provide a general overview of the recent advances in this process, greater emphasis has been given to technology and reactor modelling because of their industrial importance. Over ninety references have been cited. In this article the technology,
(Keywords: hydrocracking;
hydrocarbon;
petroleum)
Hydrocracking is practised in modern petroleum refineries for converting various hydrocarbons of higher boiling ranges into more valuable products such as gasoline, diesel and jet fuel’. Even though product projections show decreasing demand for gasoline and increasing demand for middle distillates, gasoline remains the most important product in the USA. Hydrocracking is a highly flexible petroleum refining process which can take feedstocks ranging from light naphthas to deasphalted vacuum residue’. Other applications of this process include upgrading of petrochemical feedstocks3, improvement of gasoline octane number4, and production of high quality lubricants. In addition, very heavy hydrocarbon deposits such as tar sands and shale oil can be upgraded by hydrocracking’. The process upgrades the original stock by increasing its overall hydrogen-to-carbon ratio and decreasing the average relative molecular mass. The operating conditions and catalysts for hydrocracking may vary, depending upon the end product required. The progress of hydrocracking has largely depended on the development of catalysts with improved activity and selectivity. Earlier, unsupported tungsten sulphide was used as a presaturation catalyst, but it has subsequently been replaced by supported catalysts such as nickel-tungsten sulphide on alumina and cobalt molybdate on alumina. These changes contributed to the production of aromatic gasoline of higher octane number6. All hydrocracking catalysts have dual functions7*8, consisting of hydrogenation metal(s) on an acidic cracking base. Commonly used hydrogenation components include cobalt, molybdenum, tungsten, nickel, platinum and palladium. The cracking component is an acidic carrier, which may consist of amorphous silica-alumina of various compositions or crystalline supports such as cation exchanged faujasites X and Yg. A desirable feature of the hydrocracking process is that the liquid yield is about l&15 mass % higher than that from delayed coking. Recently a new technology, termed mild hydrocracking, has been introduced. Its advantage is that it can use existing hydrotreaters for hydrocracking by increasing the severity of operation. The product is mainly middle * Present address:
Regional
001~2361/90(121467~7 ,c 1990 Butterworth-Heinemann
Engineering
Ltd
College,
Rourkela,
India
which is an excellent quality diesel oil blendstock. The process is steadily gaining importance, with 76% of the units in Japan and 42% of those in Western Europe practising this technique at presentlO. Recent developments made in the hydrocracking processes have been reviewed by Choudhary and Saraf' ‘, Maxwell” and Kriz et al.‘.
distillate,
PROCESSES A wide variety of feedstocks ranging from light naphthas to residual oil can be hydrocracked to obtain lighter products. One or more stages may be required, depending on the nature of the feedstock used and the end products desired. A typical two-stage hydrocracker is shown in Figure 1. In the first stage 4@-50 ~01% of the feed is hydrocracked, and the first stage also acts as a hydrotreater where poisonous nitrogen and sulphur compounds are partially hydrogenated. The eflluent from the first stage reactor passes through heat exchangers to a high pressure separator where hydrogen-rich gases are separated and recycled. The liquid from the separator is fed to a fractionating tower and the tower bottoms form the feed to the second stage13. This mode of operation is known as extinction recycle hydrocracking; there is no purge stream to remove the refractory compounds present in the feed and hence the severity of the process has to be increased to enforce the conversion. A hydrocracker reactor generally operates in the temperature range 530-700 K and at pressures in the range 6.5-13.5 MPa. Except for the H-oil and Hy-C processes, which were codeveloped by Cities Service Research and Development Co. and Hydrocarbon Research, Inc., fixed-bed reactors with liquid downflow are used13,14. Details of the reaction conditions and product yields for the major commercial hydrocracking processes are available’ 5. In addition to these processes, several investigations on hydrocracking have been reported. Sikonia2 developed a process which can hydrocrack any fraction from naphtha to demetallized oil (DMO) to yield the desired products. During hydrocracking most of the sulphur, nitrogen and oxygen are removed and the olefins saturated, so that the product obtained is a mixture of pure paraffins, naphthenes and aromatics. The catalysts
FUEL, 1990, Vol 69, December
1467
Hydrocracking:
a review:
S. Mohanty
et al.
Hz recycle
c
A -Naphtha
Flashgas
P
-Wliesel
Hz recycle
blend
stock
Feed
Furnace Figure
1
Schematic
Reactor diagram
Furnace
of hydrocracking
Reactor
FUEL,
1990,
Vol 69, December
Fractionator
process
are chosen to be selective towards producing distillate products. The process can be carried out in a single stage, two stages or series flow to meet various objectives of hydrocracking. A higher octane gasoline is obtained by first reforming a gasoline (boiling range 335453 K) followed by hydrocracking16. Nasution17 obtained optimum yields of middle distillates by subjecting Kuwait vacuum distillates to hydrocracking at 0.88 h-r space velocity, 683 K temperature and 10 MPa pressure, with a hydrogen to feed volume ratio of 1OOO:land Co-Mo/Al,O, catalyst. Radchenko et al.” used a two-stage process for hydrocracking of vacuum distillate; in the first stage a desulphurizing catalyst, Ni-Mo/Al,O,, was used and in the second stage Mg silicate. The products were winter diesel and jet fuel when the operating pressures were 10 and 15 MPa, respectively. Recently Kukes et a1.19 have described a two-catalyst hydrocracking process with improved product selectivity. The feedstock reacts first on a Ni-W/molecular sieve catalyst and subsequently with MO supported on an alumina-molecular sieve mixture. Hydrocracking of residual oils obtained from vacuum or atmospheric distillation of various crudes was carried out by Sakabe and Yagi2’ and Ukegawa et a1.21, using spent catalyst from a desulphurization unit. With a spent Co-Mo/Al,O, catalyst, Ukegawa et ~1.~~ obtained recoveries of oil fractions (b.p. < 773 K) of 50.7-68.3 wt% and 70.1-94.7 wt% for the residual oils from vacuum and atmospheric distillation, respectively, Kotowski” investigated the hydrocracking of a deasphalted and demetallated atmospheric residue from Ramashkino crude in a flow reactor at 685-705 K and with a catalyst concentration of 7-9 wt%; the yield of fuel oil decreased with increasing flow rate. A review of hydrocracking of light Arabian vacuum gas oil over a zeolite catalyst, for maximum conversion
1468
Separators
to middle distillates, is given by Light et a1.23. Sasaki et a1.24 reported the hydrocracking of a heavy oil with high metal content over an aqueous vanadyl oxalate catalyst at 715 K and 10 MPa hydrogen pressure. A two-stage hydrocracking process carried out by Kotowskiz5 involved the thermal treatment of a mixture of coal and heavy oil, so as to aromatize the fuel oil and depolymerize the coal, followed by catalytic hydrocracking in two stages to give C,-C, gases, naphtha, diesel oil and fuel oil. A sour crude was first diluted with recycle oil and then hydrocracked over a fixed bed of Ni-Mo/Al,O, catalyst at 725 K, 3 MPa and 2 h-l space velocity by Katsobashvili and Teplyakova26, and the products obtained were gasoline, diesel fuel and fuel oil. To overcome the problem of catalyst deactivation, several processes, which utilize once-through catalysts, are under development. These include Aurabon, HFC, Residue HC, M-Coke and VEBA Combi Crackingz7. The Aurabon process (developed by UOP) is suitable for extremely heavy oils and uses oil metals as catalysts. In the HFC process (hydrocracking with fine catalyst) the catalyst, consisting of coke and metals (Ni, V) from hydrotreating, is suspended in the feed. The Residue HC process (developed by Idemitsu Kasan Co., Japan) uses a novel long-life proprietary catalyst in a fixed bed reactor. The process is suitable for hydrocracking of atmospheric residue and the operating conditions are similar to those for hydrodesulphurization. In the M-Coke process (Exxon), the catalyst is formed in situ from dispersed or dissolved metals such as molybdenum and coke precursors. The powdered catalyst in the VEBA process is either a waste product of the alumina industry (‘Bayer mass’) or lignitic coke; this process includes liquid phase hydrogenation of the feed followed by gas phase hydrotreating of the products. Mild hydrocracking, a process which has been gaining importance in recent years, has been discussed by a
Hydrocracking:
number of authors’0*28,29. These workers used existing vacuum gas oil desulphurizers for conversion of vacuum gas oil to middle distillates. In the study of Sonneman et al.“, the overall conversion was ~36% at operating pressures below 7 MPa; the middle distillate formed was about 26 ~01% of the feed, heavy naphtha 2.3 vol%, and lighter products 2 wt%.
CHEMISTRY Although there are a number of reactions taking place simultaneously during hydrocracking, the mechanism of hydrocracking is similar to that of catalytic cracking with hydrogenation superimposed. The catalyst activity is maintained at a high level because of lower coke deposition. With sulphided nickel catalyst support on silica-alumina, excessive splitting produces large amounts of low molecular weight paraffins with a high iso/normal ratio. Platinum on silica-alumina, which has a much higher hydrogenation activity, gives more intermediate than low molecular weight paraffins, thus minimizing the ratio of gas to liquid products. With a more active hydrogenation catalyst such as metallic nickel or platinum, the ratio of iso/normal light paraffins may be low. The product distribution for some n-paraffins using zeolite catalyst is given by Steijns et ~1.~ and Vansina et than al.*. Olelins are more readily hydrocracked parafhns6. The cracking reaction is endothermic whereas hydrogenation is exothermic; since the heat required for cracking is less than the heat released during hydrogenation, the overall hydrocracking process is exothermic and the temperature is maintained by injecting cold hydrogen into the reactor. Generally hydrocracking reactions take placer4 at temperatures between 560 and 690 K and pressures between 8 and 13.6 MPa. Before cracking, both intermolecular and intramolecular rearrangements take place, so that it is not possible to predict the final product spectrum obtainable from a given feed. With nonacidic or weakly acidic catalysts, the reactions are generally less complex and take place on the hydrogenation sites of the catalyst; very little isomerization or structural rearrangement takes place and the reaction products are generally simple fragments of the original reactant. By using a catalyst which is intermediate between acidic and nonacidic, cracking occurs on both the acidic and the hydrogenation components of the catalyst and the products are also intermediate in character6. Langlois and Sullivan3’ reviewed the chemistry of the catalytic hydrocracking of hydrocarbons in detail; the available information indicates that hydrocracking of normal paraffins involves scission of carbon-carbon bonds at different sites. For of instance, the products from the hydrocracking n-decane can be represented as follows:
C 10
/1
c5+c5
-+
c,+c4
L
c,+c,
The amounts of C, and lighter paraffins are generally negligible. The normal paraffins formed during the cracking step can also be converted to isoparaffins by hydroisomerization. The proportion of normal to iso-paraffins depends on various factors such as the acidity of the catalyst, conversion level, and temperature.
a review: S. Mohanty
et al.
When normal paraffins are hydrocracked over a strongly acidic catalyst, the products consist mainly of isoparaffins; small amounts of n-paraffins are isomerized without cracking3’. Other studies on the hydrocracking reactions of paraffins have been carried out by Archibald et u~.~I, Flinn et a1.32, Coonradt and Garwoodj3, El-Kady et al. 34, Rabinovich et a1.35,Panchenkov et ~1.~~ and Gol’dfarb et ~1.~~. Reactions of cycloparaffins over strongly acidic catalysts were studied by Egan et ~1.~~. Sullivan et ~1.~~hydrocracked alkyl aromatics with side chains on a strongly acidic catalyst, producing paraffins and benzene; they also studied complex reactions of polycyclic aromatics over acidic hydrocracking catalysts. Schneider et aL4’ studied the hydrocracking reactions of petroleum vacuum distillate, and from spectroscopic analysis, chromatographic separation and structural analysis of the products concluded that hydrogenation and cleavage of aromatic rings are the main reactions involved. CATALYSTS The type of catalyst used varies with the feedstock being processed. COO-MOO,-Al,O, has been widely used for hydrocracking of heavy feedstocks such as residual raffinate, solvent deasphalted residual oil and vacuum residue’7~41~42.The catalyst activity decreases and the selectivity changes with age, and more gas than naphtha is produced as the catalyst temperature is raised to maintain the conversion, Regeneration is necessary when catalyst poisoning due to deposition of coke and other materials reaches a limiting level, and is usually accomplished by burning off the deposits. Kelly and Ternan studied the activity of COO-MOO,-Al,O, catalyst promoted with sodium, potassium or lithium; lithium showed the best results as regards conversion and removal of pitch, oxygen, sulphur and nitrogen. NiiMo, Ni-W and NiiCo have also been used as hydrocracking catalysts. E1-Kady44, Jaeckh et ~1.‘~ and Nasution4’ employed Mo-Ni/SiO,-Al,O, catalyst for hydrocracking of vacuum distillates. Katsobashvili and Teplyakovaz6 used the same metals on alumina for hydrocracking of a sour crude. Nishijima et ~1.~~reported the effect of distribution and dispersion of MO ions in NiO-Coo-MoO,/Al,O, catalysts; more highly dispersed MO ions gave higher hydrogenation activity whereas agglomeration of MO ions resulted in a higher hydrocracking activity. Nat47 recommended the use of Ni-Mo-zeolite catalyst for maximizing gasoline production and NiW-zeolite catalyst for maximum gas oil manufacture. In their study on hydrocracking of heptane on Ni-Mo/HY ultrastable zeolites, Isabel et al. 48 found that the atomic ratio, Ni/(Ni + MO), had a strong influence on the activity and selectivity of the catalyst. Ghosa14” hydrocracked straight run vacuum gas oil using a Ni-Mo on Y zeolite catalyst containing rare earth elements. Yan13 developed a new dual catalyst, NiW/REX-Ni/SiO,-A1203 for extinction hydrocracking. The Ni-W-impregnated rare earth (RE)-exchanged X-type zeolite was found to be more resistant to nitrogen, more selective towards a desirable naphtha product and structurally more stable, whereas Ni/SiO,-A1203 helped in the extent of conversion of heavy, polynuclear compounds in the feed. This catalyst can be used for hydrocracking heavy feeds of wide boiling range. LaX and NIX catalysts were used
FUEL, 1990, Vol 69, December
1469
Hydrocracking:
a review: S. Mohanty
et al.
for the hydrocracking of Assam crude by Choudhary and Saraf ‘O, who reported that NiX had a lower activity. Kotowski and Benbenek” used Co-Ni on a Y zeolite carrier for hydrocracking vacuum distillates. Swift and Black” studied synthetic mica-montmorillonite with Ni or Co incorporated into the lattice structure; the activity was found to be greater than that of Pd-rare earth-Y zeolites or Pd-H-modernite. Xus3 studied the stability towards sulphur of ZSMS zeolite and found that catalysts with Pd on ZSMS showed greater total acidity and higher sulphur stability. He explained this relation between sulphur stability and acidity by the electron transfer theory. Shell Internationals4 has developed a NiW/zeolite Y82 catalyst in which Ga is incorporated by ion exchange. The presence of Ga seems to improve the catalyst activity and selectivity to C, products. Koepke and Abdos5 reported that use of NiO-Nb,O,/Al,O,-zeolite Y82 catalyst produced gasoline of enhanced octane number as compared with NiO-MoO,/Al,O,-zeolite Y82 catalyst. Tests carried out by Kondo et ~1.‘~ on hydrocracking of heavy oil from different sources showed that Ni-V/ Al,O, catalyst was more active than either CO-MO or Ni-Mo, and that spent catalyst from a desulphurization unit could be used for hydrocracking. Aqueous vanadyl oxalate prepared from V,O, and (C02H)2 (1:4 mole ratio) was found to be very effective for hydrocracking heavy oils with high metal content24. Sasaki et al.” prepared a catalyst from heavy oil, known as Ash Catalyst, which had a high vanadium content, and used it for hydrocracking of heavy oils. Although the activity of this catalyst was lower than that of Co-Mo/Al,O,, it produced the same level of liquid products. Coke formation decreased, whereas metal removal increased, with an increase in the amount of Ash Catalyst. Kotowski2’ used a two-step process to hydrocrack a coal-heavy fuel oil mixture, the first step being an initial thermal treatment to depolymerize the coal. In the second step, the mixture was catalytically hydrocracked in a two-stage process to yield gases (8.9 wt%), naphtha (14.6 wt%) and diesel oil (35.7 wt%). Morita et ~1.‘~ investigated the effect of zinc chloride catalyst supported on silica, silica-alumina or alumina on hydrocracking of anthracene. The catalyst prepared by impregnating silica-alumina with aqueous zinc chloride and drying at 413 K was found to be the most active, but rapidly became deactivated. When the catalyst was prepared by drying at a higher temperature, the catalyst life was increased. Frank and Le Pages9 prepared a number of sulphided catalysts containing Ni or Co and MO or W on silica-alumina carriers and studied their relative activity and selectivity. With toluene as the feed, for each pair of sulphides the activity passed through a maximum when the atomic ratio Ni (or Co)/(Ni (or Co)+ MO (or W)) was about 0.25. The hydrogenation activities of the various catalysts decreased in the order Ni-W > Ni-Mo > CO-MO > Co-W. This order of activity was also found to be valid for other hydrocarbons such as heavier aromatics and paraffins. With vacuum gas oil as feed, increasing the support acidity increased the activity but lowered the selectivity with respect to production of middle distillates. Aboul-Gheit6’ studied the hydrocracking of vacuum gas oil (VGO) on NiMo/Al,O,-SiO,-zeolite HY catalysts. Several workers have shown the importance of the pore
1470
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diameter of a catalyst in its activity, selectivity and rate of deactivation6’-64. Arahata et ~1.~~3~~ reported that a catalyst with a smaller mean pore diameter was more effective in cracking, desulphurization and denitrogenation, whereas a catalyst with a larger mean pore diameter resulted in higher activities for deasphalting and demetallation. A Japanese patent6’ recommends the use of medium pore size zeolites for hydrocracking. The use of pillared interlayered clay supports has been reported to improve catalyst performance during hydrocracking 66-69. For instance, for the same conditions, a VGO hydrocracked over a NiMo-impregnated pillared clay catalyst gave a product with an APl gravity of 37.1”, versus 28.8” for the corresponding products using metal-impregnated unpillared clays. KINETICS Hydrocracking of petroleum feedstocks proceeds through a network of complex reactions involving a large number of components, which makes the kinetic study of these reactions extremely difficult. For simplification, the reaction steps and products are combined into groups. Some of the kinetic models developed have been reviewed by Sue and Sugiyama7’. Steinberg et ~1.‘~ have given an overview of the research and development work carried out at the Leuna (East Germany) petrochemical complex, on hydrocracking of n-alkanes to branched alkenes over zeolite catalysts. For hydrocracking of light hydrocarbons, Bernard0 and Trimm72 postulated a Langmuir-Hinshelwood type of kinetic model which accounted for the effect of carbon formation on a nickel catalyst. Raseev and El Kharashi’j studied the kinetics of hydrocracking of naphtha and calculated the heat of adsorption and activation energy of the surface reactions. Arayici and Deymer74 studied the kinetics of hydrocracking of naphtha over Pt/SiO,Al,O, with chloroform added during the process. A kinetic model for hydrocracking of middle distillate was developed by Grendele”. Mikshina et a1.76 studied the kinetics of hydrocracking of n-alkanes. The hydrocracking of n-decane, n-undecane and n-dodecane over Pt/Al,O, and Ni-Mo/Al,O, was investigated by Gol’dfarb et ~1.~‘; for their kinetic study the products obtained from n-decane were combined into methylnonanes, dimethyloctanes and cracked products. Steijns and Froment” developed kinetic models for hydroisomerization and hydrocracking of n-decane and n-dodecane over zeolite catalysts. They assumed that the pores were completely filled, which leads to a pseudo-zero order behaviour. The concentration of the reacting molecules at the active sites was determined by the physical adsorption process. The model was found to be superior to those which did not account for physical adsorption. Marin and Froment” considered the possible intervention of hydrogen through a Rideal mechanism for the hydrocracking of C, hydrocarbons. The kinetics of hydroisomerization and hydrocracking of n-octane over a zeolite catalyst were modelled by Baltanas et ~1.‘~ using the assumption made by Steijns and Froment7’ that the concentration of the reacting molecules at the active sites is determined by the physical adsorption process. The rate of hydroisomerization followed the same trend as for n-decane and n-dodecane. They assumed a Langmuir-Hinshelwood mechanism for chemisorption and used a Langmuir isotherm to express
Hydrocracking:
the hydrocarbon concentration at the catalyst surface. Several models were developed and compared statistically. The kinetics of hydrocracking of n-heptane over Pt/Al,O, catalysts containing various additives were studied by Sokolov and Zaidman*O. El-Kady et a1.*l carried out hydroisomerization of n-heptane over Pt/SiO,-Al,O, catalyst and reported that at low and/or moderate temperatures (600-675 K) the balance of cracking versus hydrogenation was shifted more towards hydrogenation, but under severe conditions the shift was more towards cracking. Rabinovich et ~1.~~ and Panchenkov et a1.36studied the kinetics of hydrocracking of heptane over a polymetallic platinum-containing reforming catalyst. The kinetics of hydrocracking of gas oil and vacuum distillate have been studied by Qader and Hill** and El-Kady44, respectively. These authors found the rate of hydrocracking to be first order with respect to feed concentration. Nasution4’ made a kinetic study of hydrocracking of vacuum distillate over a Ni-Mo/Al,O,-SiO, catalyst for production of middle distillate; the apparent activation energy for hydrocracking was determined to be 108 MJ kmol-‘. The above kinetic studies on model systems show that there is no simple method of predicting the product distribution. However, with most feeds the production of C, and lighter hydrocarbons is negligible. These studies indicate that although the kinetics of hydrocracking of pure alkanes are satisfactorily represented using Langmuir-Hinshelwood models, such models are difficult to apply for petroleum fractions. For such complex systems, it may be more practical to use pseudohomogeneous kinetics83,84. REACTOR MODELLING Several models which have been suggested for hydrocracking reactors are summarized below. Strangeland developed a three-parameter model for predicting the product distribution in a hydrocracker. These parameters account for the reactivity of the feed, the product selectivities, and the yield of products lighter than butane. According to Strangeland the parameters were dependent largely on the parafinicity of the feed; however, other feedstock properties may also affect them, and hence they have to be determined experimentally for each feedstock. Jaffe85 developed a model which accounts for the hot spots that are generated due to the rapid reaction in the regions of low flow, and the temperature drop due to mixing of cooler fluid from the surrounding region. The reactions were modelled by identifying combined species, and a kinetic model was developed to account for the conversion of combined reactant species to combined product species. Gerdes et aI.” developed a model for a fixed bed hydrocracker which took into consideration four classes of reactions; hydrocracking, saturation, desulphurization and denitrogenation. The catalyst bed was divided into horizontal tanks of specified thickness. Each stirred tank consisted of three regions: a solid region consisting of catalyst matrix, the pore volume, and the external void space. The model assumes that as the liquid flows down it fills the pore volume; excess liquid flows down to the tank below by undergoing reaction and subsequent vaporization. The external void is also filled with liquid, leaving space for vapour flow, and is represented by the external hold-up. The excess liquid cascades to the tank
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below. Simple phase equilibrium calculations were made and it was assumed that if the equilibrium liquid was insufficient to fill the pores, they were filled by condensation of heavy hydrocarbon components. A simple kinetic model was assumed, with reaction rate being proportional to the density of the reacting species and to the hydrogen partial pressure. Since under normal hydrocracking conditions diffusional resistance is not limiting, it was not included in this model. Yan’ developed a model to study the dynamic behaviour of an adiabatic trickle-bed reactor without and with gas or liquid quenching. He assumed that the fluid flow pattern was plug flow, temperature and concentration across the cross section were uniform, heat capacities and heats of reaction of the liquid and gas were constant, reaction took place at the catalyst surface, vapour behaved as an ideal gas, and liquid and vapour were in equilibrium. This model gave the required location, starting time and amount of quenching to prevent excess heating of the bed. Panchenkov et ~1.~’ modelled an industrial reactor which produced diesel fuel of low pour point from gas oil by hydrocracking and isomerization over a zeolite catalyst. A model for a CANMET process, based on a kinetic scheme, was developed by Patmore and Pruden8s. The experimental data agreed closely with the simulated results in the ranges 570-670 K and 10.44-17.34 MPa. Panaitescu and Dumitrescu89990 suggested a model for hydrocracking of petroleum fractions, and thus obtained optimal conditions for steady state operation of a hydrocracking reactor. To take account of change in catalyst activity the model constants were re-evaluated from time to time. A model for hydrocracking of vacuum gas oil, developed by Lauxgl, was based on product distribution versus boiling point index and structure index determined by the type of hydrocarbon product. The rate of hydrocracking could be determined from the change in these indices and the product distribution. A model developed by Mikshina et ~1.~’ for hydrocracking of gasoline in a fixed catalyst bed consists of 33 equations including heat and material balances; it was tested against pilot plant results and found to be satisfactory. Krishna and Saxena’” developed a two-parameter axial dispersion model to describe hydrocracking kinetics; this model does not consider temperature increase due to exothermic hydrocracking reactions explicitly, and hence is of limited utility. CONCLUSIONS This review highlights the technology, chemistry, kinetics and reactor modelling of hydrocracking processes. Although considerable information has been published on the hydrocracking of pure hydrocarbons, very few studies have been reported on the kinetics and reactor modelling of petroleum fractions. More detailed kinetic studies on each hydrocarbon type, of narrow boiling-range, should be undertaken to investigate the effects on the activity, selectivity and stability of the catalyst. Very meagre information is available on the kinetics of catalyst deactivation, and studies should be conducted to bridge this gap. The reactor models published in the open literature are not capable of predicting the composition of different homologues in the various product streams; for this more detailed models, which subdivide the feed with respect
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to both boiling range and hydrocarbon type, would be required. Most industrial hydrocrackers are trickle-bed reactors, but often these are approximated as of plug flow type. In such reactors, particularly with heavy feeds, the wetting characteristics of the catalyst can affect the reactor performance. Models which include realistic hydrodynamics need to be developed. REFERENCES
11 12 13 14
15 16 17 18 19 20 21 22 23 24 25 26 21 28 29 30 31 32 33 34 35 36 37
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Yan, T. Y. Can. J. Chem. Eng. 1980, 58, 259 Sikonia, J. G. Hydrocarb. Proc. 1980, 59(6), 73 Mavity, V. T., Ward, J. W. and Whitebread, K. E. Hydrocarb. Proc. 1978, 57(11), 157 Chen, N. Y., Maziuk, J., Schwartz, A. B. and Weisz, P. B. Oil & Gas J. 1968, 66(47), 154 Kriz, J. F., Ternan, M. and Denis, J. M. J. Can. Per. Tech. 1983, 22, 29 Voohries Jr., A. and Smith, W. M. in ‘Advances in Hydrocracking’ Advan. Pet. Chem. and Relining, Vol. VIII (Ed. J. J. McKettaJr.), Interscience, New York, USA, 1964, p. 169 Steiins, M.. Froment. G. F.. Jacobi. P. and Uvtherhoeven. J. 1nd.OEng. ihem. Prod. Res. Dev. 1981, 20(4), 654 Vansina, H., Baltanos, M. A. and Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 526 Ward, J. W., Hansford, R. C., Reich& A. D. and Sosnowski, J. Oil & Gas J. 1973, 71(22), 69 Sonnemans, J. W. M., Plantenga, F. L., Desai, P. H. et al. ‘Mild Hydrocracking of Heavy Oils in the Eighties’, Natl. Pet. Refiners Assoc. Tech. Paper, AM-84-60, 1984 Choudhary, H. and Saraf, D. N. Ind. Eny. Chem. Prod. Res. Dev. 1975, 14, 74 Maxwell, I. E. Zngenieursbhzd 1983, 52, 53 Yan, T. Y. Ind. Eng. Chem. Proc. Des. Dev. 1983, 22, 154 Gary, J. H. and Handwerk, G. E. in ‘Petroleum Refining: Technology and Economics’ Marcel Dekker, Inc., New York, USA, 1975 ‘Relining Process Handbook’ Hydrocurb. Proc. 1986,65(9) Shipikin, V. V., Bortov, V. Y., Georgievskii, V. Y. et al. Neftepererub. Neftekhim. (Moscow) 1983, 8, 3 Nasution, A. S. ‘Proc. 3rd Pac. Chem. Eng. Congr.‘, 1983,2,232 Radchenko, E. D., Gorshtein, A. B., Shkol’nik, B. L. and Shtein, V. I. Sb. Nuuchn. Tr.-Vses. 1983, 44, 100 Kukes, S. G., Miller, J. T. and Gutberlet, L. C. US Pat. No. 4875991 1989 Sakabe, T. and Yagi, T. Hydrocurb. Proc. 1979,58(12), 103 Ukeaawa. K.. Oiima. T.. Kondo. T. et al. Sekivu Gukkuishi 1980: 23,280’ Kotowski, W. Naftu (Katowice, Pol.) 1982, 38, 232 Light, S. D., Bertam, R. V. and Ward, J. W. Hydrocurb. Proc. 1981, 60(5), 93 Sasaki, Y., Ojima, Y., Kondo, T. et al. Sekiyu Gakknishi 1983, 26, 412 Kotowski, W. Chem. Tech. (Leipzig) 1983, 35, 22 Katsobashvili, Y. R. and Teplyakova, G. A. Khim. Tekhnol. Topl. Musel. 1984, 8, 8 Schuetze, B. and Hofmann, H. Hydrocurb. Proc. 1984,63(2), 75 Gembicki, V. A., Andermann, R. E. and Tajbl, D. G. Oil & Gas J. 1983, 81(8), 116 Jaeckh, C., Dreyer, H. D., Himmel, W. F. et al. 9th Actas Simp. Iberoam. Catal. 1984. 2, 1226 Langlois, G. E. and Sullivan, R. F. in ‘Chemistry of Hydrocracking’ Adv. Chem. Ser. No. 9, 1970 Archibald, R. C., Greensfelder, B. S., Holzman, G. and Rowe, D. H. Ind. Eng. Chem. 1960,52, 745 Flinn, R. A., Larson, 0. A. and Beuther, H. Ind. Eng. Chem. 1960,52, 153 Coonradt, H. L. and Garwood, W. E. Ind. Eng. Chem. Proc. Des. Dev. 1964, 3, 38 El-Kady, F. Y. A., Menoufy, M. F. and Hassan, H. A. Ind. J. Tech. 1983, 21, 293 Rabinovich, G. B., Borisevich, Y. P., Levinter, M. E. and Rodionov, A. V. Khim. Technol. 1983, 26(6), 214 Panchenkov, G. M., Gorlov, S. G., Belov, N. N. and Kolesnikov, I. M. Zh. Fiz. Khim. 1983, 57(10), 2479 Gol’dfarb, Y. Y., Katsobashvi1i.Y. R. and Rozental. A. L. Kinef. Kural. 1981, 22, 668
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38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 51 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76
77 78 79 80 81 82 83 84 85 86
Egan, C. J., Langlois, G. E. and White, R. J. J. Am. Chem. Sot. 1962,84, 1204 Sullivan, R. F., Egan, C. J. and Langlois, G. E. J. Catal. 1964, 3, 183 Schneider, W., Mueller, E., Zschocke, R. and Onderka, E. Chem. Tech. (Leipzig) 1981, 33, 508 Kondo, T., Ojima, Y., Ukegawa, K. et al. Kogai Shiyen Kenkyusho Iho 1982, II,41 Chesnokov, A. A., Kogan, L. D., Kozlova, N. M. and Chesnokova, N. Z. Khim. Technol. Topl. Muse1 1985. 4, 32 Kelly, J. F. and Ternan, M. Can. J. &em. Eny. 1979, 57, 726 El-Kadv. F. Y. A. Ind. 3. Tech. 1979. 17. 176 Nasutidn, A. S. ‘Proc. 5th Int. Semin. New Dev. Engine Oils, Ind. Oils, Fuels Addit., 1985 Nishijima, A., Shimada, H., Sato, T. et al. Sekiyu Gukkaishi 1988, 31, 109 Nat, P. J. Erdoel Kohle, Erdgus, Petrochem. 1989,42,447 Isabel, V. M., Escardino, A. and Corma, A. Ind. Eng. Chem. Res. i987,26, 1495 Ghosal, G. K. Chem. Eng. World 1985, 20(9), 83 Choudhary, N. and Saraf, D. N. Ind. Eng. Chem. Prod. Res. Deu. 1978, 17, 196 Kotowski, W. and Benbenek, S. Nuftu (Kutowice, Pal.) 1981, 37, 209 Swift, H. E. and Black, E. R. Ind. Eng. Chem. Prod. Res. Deu. 1974, 13, 106 Xu, Y. Chem. Abstr. 1990, 112, 3938Oc Klazinga, A. H. Eur. Pat. Appl. EP 288112 1988 Koepke, J. W. and Abdo, S. F. lJS Pat. No. 4 777 157 1988 Kondo. T.. Oiima. Y.. Ukeaawa. K. et al. Koaui Shiaen Kenkyusho Hokuku. 1984, 33, i Sasaki, Y., Ojima, Y., Kondo, T. et al. Sekiyu Gakkaishi 1983, 26, 144 Morita, M., Hirosawa, K., Sato, T. and Ouchi, K. J. Jap. Pet. Inst. 1980, 23, 52 Frank, J. P. and Le Page, J. F. ‘Proc. 7th International Congress in Catalysis’, Tokyo, Japan, 1981, p. 792 Aboul Gheit, A. K. Erdoel. Erdgus. Kohle 1987, 103(10), 441 Clement, C. Pet. Tech. 1986, 328, 32 Weber, M., Becker, K., Berrouschot, H. D. ef al. German Put. (East) DO266 924 1989 Arahata, Y., Tsukada, Y., Imamura, 0. et al. Sekiyu Gukkaishi 1989, 32, 306 Arahata, Y., Tsukada, Y., Imamura, 0. et al. Sekiyu Gakkuishi 1989,32, 312 Union Oil Co. Japanese Patent JP 6245688 1987 Hamilton Jr., D. M. US Put. No. 4640 764 1987 Battiste, D. R. and Harris, J. R. US Par. No. 4637991 1987 Gortsema, J. P., McCauley, J. R., Pellet, R. J. et al. PCT Inr. Appi. WO 8806614 1988 Kirker, G. W. and Varghese, P. Eur. Put. Appl. EP284 278 1988 Sue, H. and Sugiyama, H. Petrotech (Tokyo) 1982, 5, 942 Steinberg, K. H., Becker, K. and Nestles, K. H. Acru. Phys. Chem. 1985,31,441 Bernardo, C. A. and Trimm, D. L. Rev. Port. Quim. 1977,19,369 Raseev, S. D. and El Kharashi, S. Rev. Chim (Bucharest) 1978, 29, 1140 Arayici, S. and Deymer, J. Chim. Actu. Turc. 1979, 7, 213 Grendele, G. V. 7th Simp. Iberoam. Catal. (Trab.), 1980,~. 469 Mikshina, V. S., Hofman, N., Martynenko, V. G. et al. Materialy 3-i Vses. Konf. po Kinet. Geterogen. Katalitich. R-Tsii, Kalinin, 1980, 2, 302 Steijns, M. and Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 660 Marin, G. B. and Froment, G. F. Chem. Eng. Sci. 1982,37,759 Baltanas, M. A., Vansina, H. and Froment, G. F. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 531 Sokolov, V. P. and Zaidman, N. M. Kinet. Katul. 1983, 24(4), 898 El-Kady, F. Y. A., Menoufy, M. F. and Hassan, H. A. Ind. J. Tech. 1983, 21, 300 Qader, S. A. and Hill, G. R. Ind. Eng. Chem. Proc. Des. Dev. 1969, 8(l), 98 Strangeland, B. E. Ind. Eng. Chem. Proc. Des. Dev. 1974,13,71 Mohanty, S. Ph.D. Thesis Indian Institute of Technology, Kanpur, India, 1989 Jaffe, S. B. Ind. Eng. Chem. Proc. Des. Dev. 1976, 15,410 Gerdes, K. F., Strangeland, B. E., Chen, G. T. S. and Gumerman, R. J. paper presented at the Annual Meeting of AIChE, 1977
Hydrocracking: 87
88
Panchenkov, G. M., Laz’yan, Y. I., Rogov, S. P. ef al. Nauchn. Osn. Pererab Nefti Gaza Neftekhim., Tezisy Dokl. Vses Konf., 1977, pp. 104105 Patmore, D. J. and Pruden, B. B. ‘Thermal Hydrocracking of Athabasca Bitumen: Comparison of Computer Simulated Values of Feed and Product Vaporization with CANMET Pilot Plant Data’, CANMET Report 80-23E, Canada Centre for Mineral and Energy Technology, 1980
89
a review: S. Mohanty
et al.
Panaitescu, G. and Dumitrescu, S. Rec. Chim. (Bucharest) 1982, 33,453
91 92
Panaitescu, G. and Dumitrescu, S. Rev. Chits. (Bucharesr) 1983, 34, 724 Laux, H. Chem. Tech. (Leipzig) 1983, 35, 8 Mikshina, V. S., Martynenko, V. G. and Taganov, I. N. Khim.
93
Krishna, R. and Saxena, A. K. Chem. Eny. Sci. 1989, 44, 703
90
Technol (Kiev) 1984, 5, 8
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