PHOTO COURTESY OF ESSO RESEARCH & E N O I N E E R I N O 0 0 .
PART I
Catalytic activity of
TUNGSTEN C. H. KLINE
V. KOLLONITSCH
Petroleum processing application of tungsten catalysts is the subject of this first in a two part series of articles highlighting progress in this area ungsten compounds, particularly the oxides, sulfides, and heteropoly complexes, form T active, rugged, stable catalysts for a variety of commercially important chemicaI processes. They have been widely used on an industrial scale in Europe for over thirty years. Until recently, catalytic use of tungsten in the United States has been limited. However, the growing use of hydrocracking and severe hydrotreating of petroIeum is expected to increase greatly the consumption of tungsten catalysts in the next five years. Although there is an enormous body of scientific and patent literature on individual VOL. 5 7
NO. 7 J U L Y 1 9 6 5
53
Tungsten catalysts played a key role in hydrocracking history catalysts containing tungsten, no over-all analysis of the catalytic activity of this element has been available. This article is the first of a two-part series intended to review critically the functions, applications, advantages, and limitations of tungsten as a catalyst raw material. The series is based on evaluation of selected articles and patents referred to in the bibliography. T h e first part in the two-part series is directed at applications in petroleum processing. Petroleum processing represents the major field of application for tungsten catalysts. T h e principal processes for which application of tungsten catalysts has been studied are hydrocracking, hydrotreating, dehydrogenation, isomerization, reforming, and polymerization. Hydrocracking
This process is one of destructive hydrogenation of materials of high molecular weight in which carboncarbon bonds are broken and saturated with hydrogen. Hydrocracking is used to upgrade heavy, high-boiling fractions low in hydrogen and high in carbon to lighter, lower-boiling fractions of enriched hydrogen content. Typical feedstocks were originally coal, coal tars, shale oil, and creosote. More recently, heavy petroleum fractions and middle distillates, otherwise valuable only as fuel oils, have been used. T h e end products of hydrocracking are gasolines, kerosines, diesel oils, liquefied petroleum gases, and upgraded stocks for further processing. Hydrocracking was first developed in Germany during the 1930’s to produce liquid fuels from coal. The German plants were converted after World War I1 to hydrocrack heavy petroleum stocks. I n England a similar process was used to produce aviation gasoline during the war. Hydrocracking has also been used on a small scale to upgrade coal tars, creosote, and shale oil. The process was first studied extensively in the United States in the late 1930’s when it was feared that crude oil supplies were approaching exhaustion. However, widespread use of the process started only in the late 1950’s when the availability of relatively cheap hydrogen as a by-product of catalytic reforming helped to make it economically feasible. Under present conditions hydrocracking has become a n extremely versatile refining process, capable of producing a wide variety of products-for example, more gasoline in the summer and more distillate fuel oils in the winter. I n crude-deficient areas, such as the west coast of the United States, hydrocracking makes possible the production of a greater proportion of gasoline from each barrel of crude. Hydrocracked gasoline and kerosine are free of smog-producing and gum-forming olefins. T h e gasoline has a high content of high-octane isoparaffins. Tungsten catalysts have played a leading role in the development of hydrocracking. T h e first commercial processes developed in Germany in most cases consisted of two steps: ( a ) presaturation of the feed over un54
INDUSTRIAL A N D ENGINEERING CHEMISTRY
supported pelleted tungsten sulfide (catalyst 5058) and ( b ) hydrocracking on 10% tungsten sulfide supported on a HF-treated clay of the montmorillonite type (catalyst 6434). Later, a catalyst containing 25% tungsten sulfide and 5% nickel sulfide on activated alumina (catalyst 8376) replaced the unsupported tungsten sulfide in the presaturation stage. When the bombed-out German plants were rebuilt after World Mrar I1 to process petroleum residues, new catalysts were developed which contained oxides or sulfides of molybdenum, tungsten, or other heavy metals supported on synthetic aluminum silicates. These catalysts were more resistant to nitrogen poisoning than catalyst 6434 or iron on clay (catalyst 231) developed in England for processing creosote. Accordingly, the Germans used a less drastically prehydrogenated charge with a higher aromatic content, such as can be obtained over nickel-tungsten sulfide on alumina or cobalt molybdate on alumina. The new catalysts were applicable for processing the entire tar-free portion of the product from liquid-phase hydrogenation, as well as the relatively light middle oil of end point 680’ F. They gave gasoline fractions of considerably greater aromatic content and substantially higher octane numbers than the original nonselective catalysts 5058 and 6434. The improvement in these properties, obtained by replacing nonselective with selective catalysts in both the presaturation and hydrocracking stages, is shown in Table I ( 3 7 ) . These catalysts were the immediate ancestors of the presently used hydrocracking catalysts containing nickel plus molybdenum, cobalt plus molybdenum, nickel plus tungsten, nickel, or platinum on synthetic silica-alumina supports. I n petroleum hydrocracking plants recently built or still under construction, molybdenum catalysts are apparently most widely used, followed by tungsten, platinum, and possibly nickel, in that order. All these catalysts make possible the production of higher quality products under conditions less drastic than those originally necessary. Hydrocracking of heavy stocks involves two major reactions : ( a ) partial or, less desirably, complete hydrogenation of large polycyclic aromatic compounds, and ( b ) splitting of the hydrogenated ring. Thus, the reaction requires a dual-function catalyst which com-
Charles H . Kline is President, and Valerie Kollonitsch is Technical Information Specialist of Charles H. Kline @ Co. of Pompton Plains, A’. J . They have co-authored several articles on catalytic activity of metals including “Rhenium Catalysts’’ (I&EC, April 1962, p @ . 16-22); and “Catalytic Activity of Selenium” (I&EC, December ?963, pp. 78-26). T h e authors express thanks to the Mining @ Metals Division of Union Carbide Cor$. for permission to publish this review, which was originally prepared under its sponsorship. AUTHORS
TABLE I .
CATALYST SELECTIVITY I N TWO-STAGE HYDROCRACK IN G
PRESATURATION
Selective
Nonselective
HYDROCRACKING
Nonselective
1 1
CATALYSTS Presaturation Hydrocracking NAPHTHA PROPERTIES Aromatics, wt. % Octane No., motor Clear 1.5 cc. TEL/gal. Octane No., research Clear 1 . 5 cc. TEL/gal.
wzE:yb ..
I
Selective
Selective
1 1
j
W JE:/syn.
I
18
+
73
+
75 85
Co-Mo/AleOs W or Mo/syn.
29
Feed : Middle oil from liquid-phase hydrogenation of cracked petroleum residuum. Process: Two-stage presaturation and hydrocracking, 2900-4350 p.s.i.; 715750° F.; space-time yield, 1-1.5 kg./l. hr. Catalyst 6434; 70% tungsten suljde on a Catalyst 5058; pelleted tungstm sulfde. Tungsten or molybdenum oxides on synmontmorillonite pretreated with hydrofluoric acid. thetic aluminum silicate.
TABLE II. COMPARATIVE PERFORMANCE OF TUNGSTEN, NICKEL, AND NICKEL-TUNGSTEN CATALYSTS IN HYDROCRACKING
I
1 Charge
Gravity, API Viscosity, SUV, sec., 100' F. Sulfur, Braun-Shell, 7% Bromine number
15.0 6320 4.13%
Catalytic M e t d
(IS
Oxide
12% NiW 70% Ni 72% w 29.9 26.0 32.2
76.6 1.68% 16.9
...
51.8 l.05~o 12.0
39.9 1.18% 13.0
22 %
232
1
Yield, vol. % Carbon deposition
LOO 2% 215%
i
288O F. 102.6% 2.10%
102 1 % 324%
Feed: 50% Kuwait bottoms. Conditions: 830" F., 1000 p.s.i., VHSV 1.0, Hzrecycle, 10,250-10,600 Catalyst support: H-42 alumina.
CU.
ft./bbl.
TABLE Ill. PROMOTING EFFECT OF MOLYBDENUM O N T U NGSTEN HY D ROCRACK I NG CATALYSTS
I
I
Charge
Product
CATALYST
...
W
W-Mo
PROPERTIES Naphtha, vol. % Octane No. Phenol, % Bases. as "3, mdl.
... ...
30 69 0.03 0.3
55 71 0.01 0.3
4.8 1190
Feed : Composite medium oil from coal hydrogenation and petroleum distillates. Boiling range, 175-356' C. Midpoint, 270' C. Conditions: 3000 p.s.i., 460' C., hydrogen-oil ratio 3000:1, space velocity VHSV 4.0 for W catalyst, 1.0 for W-Mo catalyst. Product: Naphtha, 38-185' C. Catalyst: W, 20% WOa on synthetic aluminum silicate; Wo-Mo, 7.38% W o s f 7.45% MoOa on synthetic aluminum silicate.
TABLE IV. PROMOTING EFFECT OF TUNGSTEN AND VANAD IU M I N M 0 LY BDENU M HYDROCRACK I NG CATALYSTS Promoter as Oxide
Product,
w.%
Gas Light oil Heavy oil Unconverted wax
I
Nom
2.0
4;': 42.0
I 1
Feed: Petroleum wax stock. Condition: 725' F., 900 p.s.i. Basic catalyst: 9 % Mo, as MoOa, on alumina.
3%"
3.1
:"6:
21.4
I
1
3%V 2.5
20.7 55.0 21.8
bines hydrogenation and cracking activity. Hydrogenation activity is provided by such materials as tungsten, nickel, and molybdenum oxides or sulfides, or by the noble metals, chiefly platinum. The cracking base is provided by an acidic support: silica gel, alumina, synthetic silica-aluminas, natural clays, and, more recently, synthetic zeolites of the molecular sieve type. With the exception of platinum, the hydrogenating metal compounds are generally used with promotersfor example, cobalt or nickel for molybdenum, and nickel for tungsten. The combined metal content of the promoted catalysts ranges from 3 to 25%. The promoter increases the hydrocracking activity, selectivity, or stability of the catalysts. Nickel has long been the preferred promoter for tungsten. The early German workers determined that, for hydrogenation, the optimum atomic ratio of nicke) to tungsten was about 0.6 (74). Higher contents of nickel gave only slight increases in activity. However, recent patents disclose ratios of nickel to tungsten of 1.0 (4, 75,22,32),1.2 (33),or as high as 4.0 ( 76)* The promoting effect of nickel is shown in Table I1 (22), which compares nickel oxide, tungsten oxide, and a mixed nickel-tungsten oxide (1:1) on alumina for the hydrocracking of heavy bottoms high in sulfur. The nickel-tungsten catalyst had greater desulfurizing activity and lower carbon deposition. Although its cracking activity was initially lower, as shown in Table 11, it maintained its activity over long periods, while the unpromoted tungsten catalyst lost its activity after a few cycles (22). Other transition elementssuch as molybdenum alone or combined with nickel, cobalt, zinc, manganese, iron, or chromium-can be used as promoters. As shown in Table I11 (42), molybdenum increases considerably the activity of tungsten and the quality of the gasoline in the hydrocracking of middle oils. The preferred atomic ratio of molybdenum to tungsten is 1.5 (35). Conversely, the addition of about 15 atom yotungsten increases the activity of molybdenum in the hydrocracking of wax, as demonstrated in Table I V (23). Vanadium has a similar promoting effect ( 7 7). At the present time supported tungsten catalysts are used in Germany (37), the United States, and elsewhere to hydrocrack medium and heavy stocks to gasoline and other more valuable light products. I n Germany, mixtures of middle and heavy oils are split at 7500-9000 p s i . and 860' F. over fixed-bed catalysts composed of molybdenum or tungsten as the principal metal component on synthetic or natural silicates. I n oncethrough operation about 50y0 gasoline is obtained. The conversion is increased by recycling. Middle oils alone are split under less drastic conditions, generally 3000-4500 p.s.i. and 740-790' F. The exact nature of the catalysts used in the major U. S. hydrocracking processes has not been disclosed. However, indications of current commercial interest in tungsten hydrocracking catalyst may be obtained from the more recent patent literature, some of which is summarized in Table V. A wide variety of feeds, from medium oils to residual stocks, can be processed at 500VOL. 5 7
NO. 7
JULY 1965
55
3000 p.s.i. and 500-1000° F. I n many cases, removal of oxygen, sulfur, and nitrogen (hydrotreatment) occurs simultaneously with cracking. This combination of hydrorefining and hydrocracking in one step is an important advantage of tungsten and molybdenum over the precious metal catalysts. Tungsten catalysts for hydrocracking are generally made by impregnating the support with an aqueous solution of ammonium paratungstate or some other soluble salt (75, 23, 32, 33). The promoter, where used, is also added in a soluble form such as nickel nitrate. After calcination at about 1000° F., the catalyst can be reduced in hydrogen for two hours (23). The type and quality of the support are as important or even more important than the catalytic metals, since the acidity of the support profoundly influences cracking activity. T h e exact mode of preparation of the support greatly affects the performance of the finished catalyst. For example, the hydrocracking activity of a tungstenmolybdenum catalyst is higher when the support is prepared by separate precipitation of silica and alumina than when it is prepared by coprecipitation (42). There is much discussion and no agreement regarding the best metal or catalyst composition for hydrocracking. As Voorhies and Smith have stated, “The optimum catalyst for a given process will depend largely upon the process environment and the properties desired in the hydrocracking products” (48). For example, the preferred catalyst composition for hydrocracking naphthas to liquefied petroleum gases may be markedly different from that for hydrocracking tar bottoms to gasoline stocks and middle distillates. Tungsten catalysts generally have less hydrogenating and isomerizing activity than platinum or metallic nickel. For many operations this is an advantage-for example, in hydrocracking to gasoline stocks where high contents of isoparaffins and aromatics are desirable. As shown in Table VI (8))platinum may isomerize isoparaffins to near equilibrium values and hydrogenate all aromatics to naphthenes. By contrast, the less active tungsten oxide gives high ratios of isoparaffins to normal paraffins and leaves nearly all the aromatics in the feed stock unhydrogenated (8). The lower cracking activity of tungsten sulfide in relation to platinum and nickel is shown in the comparative studies of Table VI1 (73). Unfortunately the tungsten catalyst used in this work was a duplication of the now outmoded German catalyst 6434, while both the platinum and nickel catalysts were of more modern types. Both tungsten and molybdenum oxide and sulfide catalysts are more stable under hydrocracking conditions than platinum and metallic nickel. Platinum is readily poisoned, especially by nitrogen, and often requires pretreatment of feedstocks (8). Cobalt-molybdenum oxide catalysts are particularly stable after regeneration (34). Among the metal oxide catalysts differences are relatively slight. Nickel-tungsten oxide and sulfide catalysts on suitable supports are apparently superior in de56
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
sulfurization and in severe hydrocracking. They are therefore particularly suitable for hydrocracking heavy, high-sulfur crudes and residues to light stocks. Comparative studies of supported nickel-tungsten oxide and cobalt-molybdenum oxide on two supports are summarized for a heavy, high-sulfur Kuwait stock in Table VI11 (22) and for a desalted West Texas crude in Table IX ( 4 ) . In both cases the nickel-tungsten catalyst showed higher hydrocracking activity and slightly higher desulfurizing activity. I n the case of the West Texas crude, the nickel-tungsten catalyst aged better. The wartime tungsten catalysts, particularly the supported nickel-tungsten catalyst 8376, are apparently still used for refining coal tars and middle oils in some continental European plants, especially those in the Russian zone (77, 27). A variation of the German coal hydrogenation processes is the TTH low-temperature coal tar process operated in the liquid phase at 4500 p s i . and up to 660’ F. (27). Pelleted tungsten sulfide (5058) was the original catalyst, but was later replaced by supported nickeltungsten sulfide (8376). The T T H process is used mainly to produce diesel oils and lubricating oils, particularly from lignite tar. High-energy jet fuels of superior quality can be produced by hydrogenating coal-tar fractions at 780-81 0’ F. and about 3000 p.s.i. over catalyst 8376 or supported molybdenum sulfide, using a recently developed French process (26). Shale can be hydrogenated much as the middle oils were in German coal hydrogenation technology. For example, the TTH process with nickel tungsten sulfidealumina has been used in a postwar Spanish shale-oil plant (38). T h e feasibility has also been demonstrated of hydrogenating U. S. shale oil over unsupported nickeltungsten sulfide to a “synthetic crude” for further processing by conventional petroleum refining techniques (47). The U. S . Bureau of Mines has investigated the onestage hydrogenation of shale oil to gasoline or naphtha reformer stocks (70). Of 17 catalysts tested under similar conditions, tungsten sulfide gave the highest gasoline yield, but not the highest octane rating. Molybdenum oxide on alumina and cobalt tungstate on alumina also performed well. Recent reviews of hydrocracking include those by Voorhies and Smith (48) and Beuther (8). The early hydrogenation work was also reviewed in considerable detail (74). Hydrotreating
The broad term hydrotreating covers a wide range of mild hydrogenation processes. I n contrast to hydrocracking, hydrotreating involves no scission of carboncarbon bonds. The boiling range of the products is thus essentially the same as that of the feedstocks. T h e original nickel-tungsten hydrotreating catalysts used in the United States were similar to the German catalysts 5058 and 8376 developed for pretreatment of middle oils before hydrocracking. The Shell vapor-
SOME TUNGSTEN CATALYSTS FOR HYDROCRACKING
TABLE V.
Use and Conditionr
Catalyst PROMOTED WITH NICKEL Supported 4.5 % WOa-1.5 % NiO on AIzOa or SiOz-AIzOa
Reference
Residue to naphtha and gas oil. Desulfurization. 800-850" F., 5001000 p.s.i., sp. veloc., weight 0.8 Residues and c cle stocks t o cracking feed. Desulfurization. 1000 p.s.i., 445' C., 1 V?HSV Texas crude to valuable stocks. Desulfurization. 862' F., 500 p.s.i., 0.84 LHSV Cycle stocks to jet fuel. 754' F., 700 p.s.i., 1.52 LHSV Deas halted lube oil to bright stocks. 500-775O F., 2000-3500 p.s.i., 0.!5-2.0 LHSV Residue to lube oil. 730' F., 3000 p.s.i., 0.5 VHSV Residual oil to gas oil. 750-850° C., 500-1500 p.8.i. Texas crude to naphtha and gas oil. Desulfurization. 850' F., 1500 p s i . , sp. veloc., weight 2.0
9 % WOa-3 % NiO on AlzOa 4.2% WOs-1.7% NiO on SiOz-A1208 7.5 % WOa-2.5 % NiS on SiOa-AlzOa 17.4% WOs-5.5% NiO on A h 0 8 WSz-NiS, promoted with F on SiOz-AlzOa WOs-NiO on AlzOa 9 % WOa-3 % NiO on SiOz-+lzOa
U. S.Patent 2,700,014 (1955), Gulf U. S. Patent 2,801,208 (1957), Gulf
U. S. Patent 2,865,869 (1958), Gulf U. S. Patent 2,956,002 (1960), Pure Oil U. S. Patent 3,053,760 (1962), Gulf U. S. Patent 3,046,218 (1962), Gulf U. S. Patent 3,043,769 (1962), M. W. Kellogg U.
S. Patent 2,791,546 (1957), Gulf
Unsupported Residues to lube oil. 730' F., 3000 p.s.i., 0.5 LHSV Asphalt to naphtha. 850° F., 5000 p.s.i., 0.4 LHSV Heavier oil to lighter stocks. Desulfurization. 645-745 0.5 LHSV
WSa-NiS WSz-NiS W-Ni oxide or sulfide PROMOTED WITH MOLYBDENUM 13.5 % MoOa-3.7 % wo8 on &Oa 7.38 % WOa-7.45 % Moos on SiOZ-AlzOs
F., 3000 p.s.i.,
U. S. Patent 2,847,358 (1958), Calif. Research B r p h Patent 899,684 (1962), Leuna Werke Walter Ulbricht" U. S. Patent 2,908,633 (1959), Sun Oil
Wax to oil. 725' F., 900 p.8.i. Medium oils to gasoline. 2800 p.s.i., 460' C., 1 VHSV
0 . 5 % WOa-0 .5 % MoOa-oxide of Ni, Co, Mn, Fe, or Cr on clay
U. S. Patent 3,017,368 (1962), Gulf U. S. Patent 2,973,313 (1961), Texaco U. S. Patent 3,078,221 (1963), Gulf
Residues to naphtha and gas oil
UNPROMOTED
WOa or MoOa on SiOz-AlzOs
Heavy and middle oils to naphtha.
Up to 860' F., up to 9000 p.8.i.
8% ' WSz on SiOz-AlzOa
Residues to naphtha and diesel oil.
460' C., 3800 p.s.i,
TABLE VI. SELECTIVITY OF TUNGSTEN AND PLATINUM HYDROCRACKING CATALYSTS FOR ISOPARAFFINS AND AROMATICS Ratios, iso- to n-Para$nr Catalyst
I
c 4
Platinum on silica-alumina Tungsten oxide on silicaa 1u m in a Equilibrium values Feed stock
cs 4.0
0.0
6.7 0.7
28.0 2.7
13.2
...
TABLE V I I I . COMPARATIVE PERFORMANCE OF COBALT-MOLYBDENUM AND NICKEL-TUNGSTEN CATALYSTS I N HYDROCRACKING Catalytic Metals as Oxides
Aromatics vel. % in' Liquid Product
2.9
...
Proc., 4th World Petrol. Congr., Rome, 1955, Sect. 111, p. 517 German Patent 933,826 (1955), Badische Aniline & Soda Fabrik
...
15.5
Feed: Heavy straight-run naphtha. Conditions: 650' F., 750 p.8.i.
Gravity, API Viscosity, SUV, sec., looo F. Sulfur, Braun-Shell, % Distillation, % at: 392' F. 500' F. 590' F. 10% at Yield, vol. %
Charge
CO-MO
W-Ni
10.2 306 4.83
20.4 154 2.38
22.1 94.5 2.34
0
13 27 43 356 100.0 100.0
4 24 536
...
I
I
23 34 46 224 99.0 99.0
I
Feed: 70% Kuwait vacuum tower bottoms f 29% light cycle oil from catalytic cracking. Conditions: 830° F., 1000 p.s.i., VHSV 1.04.9. Catalyst: 10% metals (l:l), as oxides, on H.42 alumina.
~~
TABLE V I I . COMPARATIVE PERFORMANCE OF PLATINUM, TUNGSTEN SULFIDE, AND NICKEL CATALYSTS I N HYDROCRACKING 70% WSz on
0.5270 P t on SiOa-AIzOa
Temperature, OF. Conversion, 650" F., vol.
778
%
Dry gas, Wt. % Yields, vol. yo c 4
Light naphtha Heavy na htha ~ i g l i fuePoi1 t Cycle stock, over 650° F. Total product c 4+
CS+
8.1 14.8 54.4 40.4 1.1 118.8 110.7
I
Clay, HFTreated (6434)
5% N i on SiOz-Alios
802 72.4 4.4
820 95.0 7.5
6.9 9.7 16.2 47.0 27.6
19.7 23.8 45.0 20.6
107.4 100.5
114.1 94.4
Feed: Guico heavy gas oil. Conditions: 1500 p.8.i.; 0.5 LHSV; 14,500 SCF Hi/bbl.
5.0
TABLE IX. COMPARATIVE PERFORMANCE OF COBALT-MOLYBDENUM AND NICKEL-TUNGSTEN CATALYSTS I N H Y D ROCRACK1N G
Property Cumulative throughput, g./ g. Gravity, API Sulfur, % Distillation, % 392' F. 500' F. 590' F. Carbon log, wt. %laydown
I 1
Feed
I I Period I I
Period 6
36:3 1.39
23.5 49.7 0.076
143.9 42.9 0.151
. ..
I .. . I
28.8
Y.6% Co-Mo Oxide
1 I
72% N i - W Oxide (.I : 7). Period 7
I Period 6
23.4 58.1 0.067
137.7 47.8 0.046
1 I 1 I I I
I
.. .
1
16.4
Feed: Desalted West Texas crude. Conditions: 814-820' F., 1500 p.s.i., WHSV 1.0, Ha 16,500-20,000 scf./bbl. Support: Silica-alumina microspheres.
VOL 57
NO. 7 J U L Y 1 9 6 5
57
Hydrotreating, dehydrogenation, isomerization, reforming, phase hydrodesulfurization process used unsupported, pelleted nickel-tungsten sulfide, with an atomic Ni : W ratio of 2.0 instead of 0.5 as in the German catalysts. Over this catalyst, above 500 p.s.i. and below 700' F., considerable removal of conjugated dienes and sulfur could be obtained without cracking, polymerization, or undue loss of octane by saturation of aromatics and nionoolefins. High octane ratings were maintained in part by isomerization of a- to p-olefins, which have higher octane numbers ( 7 , 7 7 , 72, 30). A number of supported catalysts have also been developed and are apparently more generally used today. Preferred supports are y-alumina, alone or stabilized with 476 silica. Addition of the silica increases the acidity somewhat and so causes slight hydrocracking. Magnesia, silica, and other supports are occasionally claimed in patents. Optimum levels of tungsten and nickel vary widely in supported catalysts. A level of 10% tungsten nickel (atomic ratio 1.0) is generally preferred in catalysts intended for combined hydrotreating and mild hydrocracking (7). Some examples of the combined processes are given in Table V. Tungsten hydrotreating catalysts can be used for refining a great variety of feedstocks ranging from wax to naphthas. Typical conditions for these processes are pressures of 100-1000 p.s.i., temperatures of 450-800' F., liquid hourly space velocities of 0.2-24, and hydrogen recycle rates of 300-6000 cu. ft. per bbl. Sulfur and olefin removal may be carried out under the milder conditions in these ranges. However, saturation of aromatics and removal of nitrogen require more severe treatment. Catalyst compositions, feedstocks, and conditions of hydrotreatment are listed in Table X. For mild hydrotreating, cobalt molybdate on alumina is preferred over tungsten catalysts because its lower activity makes it more selective (31). I n mild hydrotreating of naphthas it is desirable to remove sulfur, nitrogen, and oxygen and to saturate diolefins but not monoolefins or aromatics, both of which are desirable for their high-octane ratings. T h e tungsten catalysts are most active for desulfurization, but less selective in hydrogenation. They give lower retention of monoolefins and of aromatics than cobalt molybdate does. O n the other hand, in more severe hydrotreating where some hydrocracking is desirable, the tungsten and tungsten-nickel catalysts are preferable because of their greater activity (7). Tungsten catalysts are also advantageous in hydrotreatment of distillate oils, diesel fuels, and lubricating oils, in all of which olefins and aromatics are undesirable. Unsupported tungsten hydrotreating catalysts are generally made by coprecipitation of the metal oxides and posttreatment with hydrogen sulfide. Supported catalysts are prepared by impregnating the support and calcining at 1000' F. or higher. Hydrotreating has been thoroughly reviewed by McKinley (37), and less comprehensively by Bradley and co-workers (9) and Gwin (78).
+
58
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Dehydrogenation
All hydrogenation catalysts may also be used as dehydrogenation catalysts under proper conditions. Thus, Shell's nickel-tungsten sulfide catalyst was used during World War I1 to dehydrogenate methyl cyclohexane concentrates to toluene. Operating conditions were around 840' F., 750 p s i , and liquid hourly space velocities of seven. Nickel-tungsten sulfide, which is a more active hydrogenating catalyst than cobalt molybdate on alumina, is likewise a more active dehydrogknating catalyst. I t converts cyclohexane to benzene practically quantitatively at 790' F. and 225 p.s.i. By contrast, cobalt molybdate on alumina causes considerable isomerization to methyl cyclopentane and cracking to paraffins. Nickel-tungsten sulfide is also much more resistant than cobalt molybdate on alumina to addition of thiophene to the feed (20). Isomerization
The ability of tungsten catalysts to isomerize paraffin hydrocarbons was noted in the early work on hydrocracking. Recent Soviet research has shown that unsupported tungsten disulfide (29) and nickel-tungsten sulfide on alumina (catalyst 8376) (2, 36) are good catalysts for the isomerization of normal hexane (29) and higher normal paraffins (2, 36) to the corresponding branched isomers at 750-840' F. and hydrogen pressures to 750 p s i . The isomerized products of the higher paraffins are useful as lubricating oils. Both nickeltungsten and cobalt-molybdenum catalysts are effective and stable in these processes, while platinum rapidly loses activity because of sulfur poisoning ( 2 ) . Tungsten can also be used as a promoter for nickel in the isomerization of normal paraffins in naphthas for octane improvement. Addition of 1 mole of tungsten sulfide to 20-80 moles of nickel sulfide (supported on silica-alumina) doubles the life of the catalyst (39). Other isomerizations include the conversion of propylene oxide to propionaldehyde over chromic and tungstic oxide (28) and the isomerization of meta-xylene to a mixture rich in the para isomer over oxides of tungsten and molybdenum on silica-alumina (40). Reforming
Because of their ability to dehydrogenate naphthenes to aromatics and to isomerize normal paraffins, tungsten catalysts have occasionally been considered for the reforming of naphthas to products with higher contents of aromatics and isoparaffins. Some examples are shown in Table XI. T h e tungsten and other metal oxide catalysts are more resistant to poisons than the standard platinum reforming catalysts. Accordingly, they do not need feedstocks purified by previous hydrotreatment, as platinum often does. However, their activity is not high enough to make them competitive with platinum. As shown in Table XII, tungsten can be a promoter for
and polymerization processes utilize tungsten catalysts ticularly by workers of the European Shell group, have shown that heteropolytungstic acids are very effective catalysts for these reactions in comparison with the liquid phosphoric acid commonly used. T h e principal heteropoly acids investigated for these processes are silico-12-tungstic acid, H4SiW12040.xH20 ; phospho-12-tungstic acid, HgPW12040.xH20 ; and silico6-molybdo-6-tungstic acid, H ~ S ~ W ~ M O ~ O ~ ~T .h X e H~O. acids are prepared in water solution from soluble salts of tungsten and the heteroelement. T h e solutions are acidified, and the acid is extracted with ether, purified, and crystallized (35). T h e nature of the heteroelement does not appear to be critical. Either phosphorus or silicon may be used.
the platinum catalysts. Addition of 0.03-0.l% by weight of tungsten increases both catalyst life (lower carbon deposition) and reforming activity (higher aromatic content) of platinum on alumina (79). Higher tungsten contents promote hydrocracking and decrease catalyst life. Polymerization
When the gaseous lower olefins are polymerized over suitable tungsten catalysts, they are converted to dimers, trimers, and other liquid polymers of low molecular weight. These polymers are useful as fuels or as intermediates for such products as detergents of the alkyl benzene sulfonate type, Recent investigations, par-
TABLE X.
SOME TUNGSTEN CATALYSTS FOR HYDROTREATING Use and Condition
Catalyst
Reference
PROMOTED WITH NICKEL WSz-NiSQ WSz-NiSa
Cracked naphtha; over 500 p.s.i., up to 700' F. Cracked naphtha; 500" F., 100 p.s.i.
Petrol. Refner 34 (6), 118 (1955) U. S. Patent 2,694,671 (1954), S.O., N.J. U. S. Patent 2,717,861 (1954), S.O., N.J.
WSz-NiP WSz-NiSa 25 % WSZ-3 % NiS on Altos 27 % WSz-3 % NiS on AlzOa WSz-NiSQ WSZ-NiS on Mg0-Ah03
Straight run gasoline; 860° F., 750 p.s.i. Cracked naphtha; 500' F., up to 200 p.s.i., 3-18 LHSV Middle oil; 390' C., 3600 p s i . Gas oil; 400' C., 560 p.8.i. Alkylation feedstock; 200-300° C., low p.s.i., 0.7-1 .O LHSV Cycle stock; 400' C., 420 p.s.i.
WSz-NiS WSz-NiS WSz-NiSa WSz-NiS WSz-NiS, up to 10% FeS WSz-NiS WSz-NiSQ
Lubricating oil; 635" F., 3000 p.s.i. Lubricating oil; 850' F., 500-3000 p.s.i. Lubricating oil; 700° F., 2500 p.s.i., 0 . 2 VHSV Wax: 700" F., 3000 p.s.i., 0.5 LHSV Wax Wax; 320' C., 1400 p s i . , sp. veloc., weight 1 . O Shale oil; 750-800° F., 1000-2250 p.s.i., 0 . 5 VHSV
25% Wsz-3% NiS on AlzOa WSrNiS P R O M O T E D WITH OTHER METALS 6.3 yo WOs-14.1% Moos on AlzOa-5 % Si02 2 % Wos-2 % MoOa-2 % CrzOa on A1208 1 . 9 % WOa-7.7% Fe on C 12 % Moos-3 % Ni0-8 % WOa on Ah08
Shale oil Shale oil; 700' F., 3000 p.s.i.
U. S. Patent 2,406,200 (19461, Shell Petrol. Refner 36 (6), 179 (1957) U. S. Patent 2,839,450 (1955) BASF Acad. Chim. Sci. Hung. 14, 133 (1958) IND. END.CHEM.40, 2295 (1948) U. S. Patent 2,853,429 (19581, Comp. Fran. de Raffinage U. S. Patent 2,879,223 (1959), Texas Co. U. S. Patent 2,967,146 (1961), 'rexaco U. S. Patent 2,554,282 (1951), S.O., Del. U. S. Patent 2,998,377 (19611, Gulf British Patent 911,813 (1962), Shell British Patent 945,914 (1964), Shell U. S. Patent 3,025,231 (1962), Texaco U. S. Patent 3,111,494 (1963), Texaco Erdoel Kohie 11, 18 (1958). U. S. Patent 2,692,226 (19541, S.O., Del.
UNPROMOTEDe 100% WSZ 5 % WOs on AlzOa 100% WSZ 100 % wsz
Mole ratio 7:2.
Mole ratio 0.75:l.
TABLE X I . Catalyst
Cycle stock; 750' F., 700 p.s.i., 1 . 5 LHSV Crude naphthalene; 750' Shale oil; 830' F., 2250 p.s.i., 0 . 5 VHSV Straight run naphtha; 750O F., 800 p s i .
U. S. Patent U. S. Patent U. S. Patent U. S. Patent Oil
Gas oil; 400' C., 560 p.s.i. Crude naphthalene; 750" C. Water gas; 480' C., 3200 p s i . Lubricating oil
Acad. Chim. Sci. Hung. 14, 133 (1958) U. S. Patent 2,916,533 (1959), Koppers German Patent 975,067 (1961) h e r b . K h i m . Zh. 1962 ( Z ) , p. 25; C . A . 57 15410 (1962)
Mole ratio 7:75.
Purification without Hz addition.
SOME TUNGSTEN REFORMING CATALYSTS
I
Condition
7 . 5 % WSs-0.5% F on Alios Moos-WOs-VzOsCrzOs on clay WSz-NiS-
