CY
T enation an
Hydrogenation of the aromatic constituents in refractory, catalytically cracked, cycle stocks to their corresponding naphthene derivatives results in improved catalytic-cracking feed stocks which are superior even to the original virgin gas oils. Higher conversions are obtained under similar cracking conditionsj less carbon and more gasoline result for a given degree of cracking. Gasoline octane numbers are at least as good as those obtained with virgin feed stocks. Hydrogenation conditions used are generally the same as for the conventional high-pressure destructive hydrogenation of gas oils directly to gasoline except for the catalyst which, similarly, is sulfur resistant. Yields of hydrogenated cycle stock are 100% or more in all cases, with little change in boiling range and virtually complete sulfur removal. A combination of catalytic cracking with hydrogenation of all cycle stock and recracking t o ultimate gasoline yield combined with fullest utilization of light hydrocarbons (Car Cd, Cs) by isomerization, alkylation, etc., is shown by calculation to result in an over-all volumetric yield OF over 90% of 100-octane gasoline. Lower pressures (750 compared to 3000 Ib. sq. in. gage) result in partial saturation of aromatics with rather complete desulfurization.
8
furirat ion
A?*
ESSO LABORATORIES, STANDARD OIL COMPANY OF NEW JERSEY, BATON ROUGE, LA.
will be apparent, particularly in conjunction with catalytic cracking. The process is also a case of simple hydrogenation, although not restricted t o olefins, but rather directed principally to the saturation of aromatics, especially the refractory condensed-ring molecules prevalent in catalytically cracked cycle stocks. The destructive hydrogenation of virgin or cracked kerosenes and gas oils gives directly aviation or motor gasoline. I n contradistinction, the simple hydrogenation of these same feed stocks results in negligible production of gasoline; the principal effect is the sat,uration of aromatics and incidental olefins, together with the elimination of sulfur, without significant change in the boiling range of the feed. Here again is another instance of the versatility of the hydrogenation process; the same feed stock and the same range of operating conditions are employed as for dest,ructivehydrogenation, and only the catalyst is changed to accomplish the desired selective simple hydrogenation. However, even the catalysts for the two processes have considerable similarity in that they are both sulfur resistant and rugged as to physical and chemical life. I n the case of the simple hydrogenation of aromat’ics,as in destructive hydrogenation, high pressures are preferable from thermodynamic considerations (4). However, wit’h sufficiently active catalysts, it is possible t o get appreciable hydrogenation and extensive desulfurization at moderate pressures. The data discussed in this paper are principally those obtained at the conventional high pressure of about 3000 pounds per square inch gage a t reaction temperatures of 550” t’o 750” F, However, a limited amount of data is also given for hydrogenation at 750 pounds in approximately the same temperature range. To avoid needless repetition, the ensuing discussion in referring t o hydrogenation will mean simple or saturation hydrogenation unless stated otheririse. Virgin gas oils can obviously be improved as Diesel fuels by saturation of aromatics t o improve cetane number and by eliminat,ion of sulfur. I n the case of cracked gas oils, the margin of improvement by hydrogenation is much greater, and excellent Diesel fuels can be prepared from very poor material. However, the broadest field in the future for the saturation hydrogenation of gas oils may be in the upgrading of catalytically cracked cycle st,ocks for further catalytic cracking; hence the data to be discussed refer principally to this application. The catalytic cracking process is an efficient and satisfactory means of producing high quality aviation and motor gasolinos from virgin gas oils. Throughout the war period the commercial catalytic cracking units were devoted t o the production of aviation base stock together with large quantities of butanes and butylenes that are alternatively used (a)t o make alkylate as a high-
HE high pressure hydrogenation of petroleum with sulfurresistant catalysts has had many and varied applications, which have been described in the literature over the past several years. The production of aviation fuels by high pressure hydrogenat,ion was discussed by Murphree, Gohr, and Brown (S), and more recently the same authors summarized the hydrogenation of petroleum with particular reference to the production of aviation gasoline, motor fuel, aviation blending agents, and Diesel fuel (8). During the war the high pressure hydrogenation process made a valuable cont’ribution t o the 100-octane aviation gasoline program in the following three types of operation: ( a ) production of commercial iso-octane from polymers of isobutylene and normal butylenes; ( b ) saturation of catalytically cracked aviation base stock t o improve stability and leaded octane number; and (c) direct manufacture of high quality aviation base from virgin and cracked kerosene fractions of predominantly cyclic character. Operations (a)and ( b ) involve merely the addition of hydrogen to convert olefins t o paraffins. This is called “simple” or “saturation” hydrogenation. I n the case of the catalytically cracked, aviation base stock it is important to restrict the hydrogen addition t o the olefins without permitting saturation of the aromatics to naphthenes. Fortunately this is readily accomplished by choice of catalyst and control of operating condit’ions. These two olefin hydrogenation processes, (a)and ( b ) , are also amenable to the low pressure techniques; and commercial low pressure hydrogenation plants XikeJTise contributed valuable production to the 100-octane program. The direct manufacture of aviation base from kerosene fractions, process (c), is an example of destructive hydrogenation since it involves a combination of simple hydrogenation and other catalytic reactions, such as cracking and isomerization, The purpose of the present paper is t o discuss briefly another adaptation of the hydrogenation process, which has not yet been commercially applied but whose potentialities for the future
T
136
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1946
octane aviation blending agent, or ( b ) for synthetic rubber raw materials. Postwar, these same plants will be largely devoted to the production of motor gasoline. In either case, one of the characteristics of the catalytic cracking process is the fact that the byproduct cycle stocks are considerably more resistant to further cracking than the original virgin feed stock, This is necessarily so, since the more easily cracked part of the virgin feed is the first to be converted, and since some aromatic formation is bound to occur in the absence of favorable hydrogenation conditions. I n fact, it is axiomatic in catalytic cracking that the cycle stock becomes progressively more refractory with increasing conversion. If recycle catalytic cracking is to be used to obtain maximum yield of gasoline from a given charge stock, it becomes desirable to consider methods for upgrading the cycle stocks to improve their quality. How this can be accomplished by hydrogenation is discussed below.
ing process. At that time (prewar) the emphasis was largely on motor gasoline production. The integration of hydrogenation with this type of operation, as illustrated below, is equally applicable where the Fluid Catalyst technique is used for the cracking step. A virgin heavy gas oil, distilled from a mixture of East Texas, Van Zandt, and Talco crude oils, was catalytically cracked for motor gasoline production in a large pilot fixed-bed unit, and the cycIe stock obtained was subjected to simple hydrogenation to obtain both partial and rather complete saturation of the cycle stock. The results of these experiments are summarized in Table I.
TABLE I. HYDROGENATIOK OF CYCLESTOCK FROM FIXED-BED CATALYTICCRACRINQOF EAST TEXAS-VAN ZANDT-TALCO MIXEDHEAVYGASOIL Unhydrogenated Cycle Stock
HIGH PRESSURE HYDROGENATION
The standard type of small pilot unit for high pressure hydrogenation used in these studies is shown in simple diagrammatic form in Figure 1. The feed stock t o be hydrogenated is introduced into the system by a high pressure feed pump. After mixing under pressure with excess hydrogen, it is preheated to the reaction temperature in a coil and then passed through the catalyst bed in the reactor. The products are cooled, the liquid and excess gas are separated, and the excess gas is recycled to the high pressure Jystem by means of a compressor. Fresh hydrogen is continuously added to replace that consumed by chemical reaction end that lost from the system by solubility in the liquid product. The product from the high pressure separator, after reduction in pressure t o atmospheric conditions, is separated from dissolved gases in a low pressure separator. As already stated, the principal object in high pressure hydrogenation of catalytically cracked cycle stocks has been to improve these materials for subsequent catalytic cracking. A considerable amount of data has been obtained both with respect to the hydrogenation operation and to the catalytic cracking of the hydrogenated cycle stock. Catalytically cracked cycle stocks from a variety of virgin feeds have been studied, and the hydrogenated products have been tested as catalytic cracking stocks for the production both of motor gasoline and aviation gasoline These cracking experiments have been obtained on pilot plants both of the fixed bed and Fluid Catalyst type. Carlsmith and Johnson ( 1 ) recently described the Fluid Catalyst pilot plants. EAST TEXAS-VAN ZANDT-TALC0 GAS OIL
Before the development of Fluid Catalyst cracking, considerable work was done at these laboratories on the fixed-bed crack-
COOLER
R E ACTOR
I
Figure 1.
--'-
I
Laboratory High Pressure Hydrogenation Unit
137
Degree of hydrogenation Pressure lb./sq. in. gage Feed ratk, vol./vol./hr. Yield, vol 7 on feed Gravity Ao.P.1. Distillaiion, F. 1%
3 2
.... .. ... ...
27.2
Hydrogenated Cycle Stock Almost Partial complete
3000 2 104 31.0
430 470
Over
550
7%?0ver a t 700° F. Color (Saybolt) Aniline point, O F. Diesel index Bromine No., cg./gram Suliur, wt. % Hydrogen, wt. % Refractive index, Sp. dispersion a t 30" C., (nF nc)lO'/d Aromatic rings, wt. %
600 650 85 .t18 !Sl 63 2 0.06 13.7
ny
-
3000 2 110 35.0
1.4692
170 22
125 14
I12 6
The yields of hydrogenated product were over 100 volume yo and there was comparatively little formation of light ends even a t the more complete saturation level. The sulfur content of the feed stock was reduced from 0.78% to as low as O.OG% for the more highly saturated product. The extent of saturation of the hydrogenated products from the two runs is shown particularly by their low aromatic contents, high Diesel indices, high hydrogen percentages, and low specific dispersions as compared with the corresponding properties of the unhydrogenated cycle stock. The percentage of aromatics represents the proportion of carbon that occurs in aromatic rings and was determined by the method of Vlugter, Waterman, and van Westen (6). The relatively high space velocity employed in these runs (namely, 2 volumes of liquid feed per volume of catalyst per hour) is indicative of high catalyst activity. From general experience in high pressure hydrogenation in other applications on the large scale units, i t is expected that the life of the catalyst would be from six months t o more than a year, before it would have to be discharged from the reactors for reworking. Catalytic cracking results were obtained in small fixed-bed pilot units on the unhydrogenated cycle stock as well as on the hydrogenated cycle stocks produced a t the two levels of saturation. These cracking runs were made at the same conditions as employed on the virgin gas oil. in order to give a direct comparison among the various feed stocks. Synthetic silica-alumina catalyst was employed a t a cracking temperature of 850' F., a feed rate of 1.8 volumes of feed per volume of catalyst per hour, and cracking periods lasting 20 minutes between regenerations. Atmospheric pressure was used. The cracking data are summarized in Table 11. Conversion is expressed as 100% minus the volume percentage of liquid distilling above the motor gasoline range, and excess C, represents that portion of the total butane produced which is beyond that required to make B gasoline of 10-pound Reid vapor pressure.
INDUSTRIAL AND ENGIMEEHING CHEMISTRY
138 6.0 5.0
$
4.0
m z
4 3.0
V
8
'
0 2 ' 0 t ~ R R : > A T 1 0 N
I
FOR VIRGIN GAS O I L
-
35
40
45 50 55 60 VOLUME 70 CONVERSION ( I O O - T o GAS O I L YIELD)
65
70
Id vs. Feed
Conversion for Fixad-Bed East Texas-Van Zandk-Taleo Mixed Oil with Synthetic Catalyst
The conversions obtained at cyuwalent conditions indicate that both of the hydrogenated cycle stocks are much lesa rerracLory than the unhjrdrogenated cycle stock, and are even less refractory than the virgin gas oil. This is particularly true of the more completely hydrogenated cyclc ktcck, which is shovn to be a remarkable feed stock for catalytic cracking. Yield of 10pound Reid vapor pressure motor gasoline is also highest for thc more completcly'hydrogenaled cycle stock and lowest €or the unhydrogenated cycle stock. Both the conversion and the gasoline yield from these various feed stocks increase with decreaqing aromaticity, as indicated by lower specific dispersion. It is well known in catalytic cracking that the yield of various products from a given feed stock is a function of the conversion obtained at a specified cracking temperature on any particular catalyst. Thus, as conversion is raised, the yields of gas and carbon increase. With increasing conversion the gasoline yield a t first grows larger, reaches a maximum, and finally begins to decrease at excessively high conversions due to recrscking. Table I1 shows merely the results obtained at a given feed rate and
Vol. 38, No. 2
IC lcngth. T!hc convcrsioas arc directly iridicativc of the rclaivc ease of cracking of the feed stocks; but the corn! [he product distribution from the -various iccds could bc more accurately shown by obtaining results at the same conversion levci. i t is obvious that the more completely hydrogenated cycle stock gives much lolyer carbon than the virgin gas oil, because t h o carbon yield is lover (2.8 compared t o 3.8y0)even though the converbion is higher (67.7 compared l o 49.8'74). I n the case of thc less completely hydrogenat'ed cycle stock, it is diEicu1t l o tcll from Table I1 mhet.her the carbon-forming tendency 01this m:iterial is less than that of the virgin gas oil because, although t h r x carbon yield is higher (4.5 compared t o 3.87,), so is the convcisiori (58.5 compared to 49.8%). I n order t o bring out molc clearly the relative carbon-producing tendencies of the various feed stocks, bhe data on carbon formation in Table TI arc plottod :igiiinet tlie coniwsions for comparison with a correlation available for thc virgin gas oil; Figure 2 indicates that t,hc lcss cornpletely hydrogenated cycle stock has a lower carbon-forming tendency tham the virgin feed. I t is interesting to observe iii Table XI the quality of gasolincs produccd by catalytic cracking of the various feed stocks. Dospite the differences in the aroinaticity of the four charging stocks, thcre is no discernible difference in the octane numbers of thc catalytically cracked gasolines. As indicated by aniline points, the gusolines from tlie hydrogenated cycle stocks, even from tlrc more completely saturated product, appear to bc just as aromatic as that from the unhydrogenated cycle stjock, LOUISIANA AND REFUOIO GAS OILS
Virgin gas oils from Southwest Louisiana crude and from Reiugio (Texas Coastal) crude are among the many feed stocks that have been catalytically cracked in the 100-barrel-per-day fluid cat,alystpilot unil at, 975 ' F. and 60% conversion to produce aviation gasoline and Cd hydrocarbons for alkylat'ion and for synthctic rubber ran- materials. The hydrogenation results on the cgcle stocks from these two feeds are discussed below as illust,rative of the possibilities of the hydrogenation technique. The hydrogenated products are compared in Table I11 with the unhydrogenated cracked material. The hydrogenation operations xere carried out a t 3000 pounds pressure with sulfur-resistant catalysk in the st'andard hydroTABLE11. FIXED-BEDCATALYTIC CRACKING WITI-I SYGTHETIC genation pilot unit. Again, the liquid yields were in excess of CATALYST OF FEEDSTOCKS DBRIVED FROM EASTTEXAS-VAN loo%, and there was comparatively little fortnation of light ends. ZANDT-TALCO MIWURE These hydrogenation runs were made to give complete saturaCracked Virgin tion of the aromatics as indicated by specific dispersions on the -Gas Oil Cycle Stock Feed hydrogenated product of 106 and 99, and aromatic ring contents of .. Degree of hydrogenation 160 64 Vol. yo on virgin gas oil 3 and 0% by weight. The high degree of refinement of the hydro26.9
Gravity, A.P.I. Distillation, % 401-10 F. ._.
700" F.
Mid-boiling point, 0 r'. Aniline point, O F. Diesel index Sulfur, wt. 9% Hydrogen wt. 70 Sp. disperaian a t 30" C., (ng
-n,x~OV~
0 30
1
2
4 85 600 181 53
51 1.10 12.9
640 156 42 0.78 12.2
s3 620 165 51 0.21 13.0
133
170
126
112
49.8 42.5 50.2 8.8 4.5 3.8
43.2 33.7 5G.S 6.9 4.1 5.2
58.5 413.6 41.5 10.5 5.7 4 .3
67.7 25.4 32.3 13.0 6.4 2.9
780
ias
61.2 31 52 65 371 406 53 92 / s a .in. 10
Octane "0.. A.S.T.M. Motor method 80.2 A.S.T.M. nIotor mothod i86..j 3 cc. T.E.L./gal. ra-E.%
27.2
77
0.06
13.7
59, D
59.0
60. 8
2s 4s 59 370 407 40 90
24 47
10
38 372 403 28 87 10
28 52 62 399 391 30 90 10
80.0
80.6
80.4
87.0-88.6
90.1
90.1
111.
H I G I I PRESSURE HYDROGEXATION O F CYCLE S T O C K S 13'ROM FLUID CATALYST CRBCKING Southwest La. Refugio Liptit \Tide-Cut Gas Oil , Gas Oil Hydi o Hydro Cycle cycle Cycle cycle stock stock stock stock ... 1oa Yield, vu; % on feed ... 110 38 0 Gravity, A.P.I. 31.1 29.7 40. Y Distillation, O F. 370 390 410 340 570 over 390 410 360 420 10% 450 470 450 410 30% i.x. n. 500 520 440 50% 540 470 560 310 70% 530 590 610 Z30 00% Final ~J.I>. 640 660 GOO 14 Robinson 270 .22 19 Robinson 7-30 Color (Saybolt) 119 157 1.57 Aniline point, F. 106 Diesel index GO 64 32 37 Rsornine KO., c g , j g r a n i 1 1 S 0 02 0.01 Sulfur, W t . 70 0.14 13 S 1-i.0 Hydrogen, wt. 76 11.8 Refractive index, n2,? 1 4597 I , 4496 1 , '49R;i TaRI,E
__.
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1946
139 52.7 B B L
-AVIAT'oN BASE EXCESS C 5 n A r u tlri P
C Y C L E- S T O C K
I
l l
J
HYDROGENATION
FLUID CATALYST CRACKING
---c
-
I
C3ALKYLATE
6.9 BBL
EXCESS PROPENE GAS CARBON
TETRAETHYL LEAD
0.1 BBL
AVIATION G A S O L I N E Figure 3. Wide-Cut
'
Aviation Gasoline from Southwest Louisiana
Gas Oil by Catalytic Cracking plus Hydrogenation
gennted products is further indicated by their excellent colors (+30 and 1-22 Saybolt). In these operations the cycle stock being hydrogenated represented the total cracked product boiling above the aviation gasoline, because it was of interest t o find the maximum yield of aviation gasoline and C4 hydrocarbons that could be obtained by combining catalytic cracking of the virgin feed stock with catalytic cracking of the hydrogenated cycle stock. To accomplish this, the hydrogenated products indicated in Table I11 were catalytically cracked in a small Fluid Catalyst pilot unit; previous operation had shown that this unit
'FABLE
Ilr.
F L U I D CATALYST (:RACKING WITH SYNTHETIC C.4T.4LYST
Southwest La.
500 640 157 60 0.02 13.8
Refugio Light Gas Oil IlydroVirgin cycle gas oil stock 51 100 40 9 31.4 4 0 440 520 570 630 142 I57 64 45 0 01 0 11 12 7 14.0
122 10
106 3
120 10
99
59.3 27.9 40.7 6.3 21.0 11.3 4.2
65.6 35.9 34.4 4.7 21.7 11.0 2.2
53.8 26.6 46.2 3.6 17.2 11.9 3.3
69.8 31.9 30.2 7.5 23.3 14.4 2.9
59.0
57.0
54.5
54.2
13 29
8
8
Wide-Cut Gas Oil _____
Sp. dispersion a t 20' C., (TLF TLc)lO'/d Aromatic rings, wt. %
-
Aviation base Gravity ' A.P.I. Distillath, % 140' F. 158' F. 2120 I?. 2210 F.
+
79y0 over.
2
0
288 320 71 62
50 55 70 292 316 43 38
8 19 45 49 66 294 316 28 60
7.0
7.0
7.0
7.0
83.0
79.3
83.9
82.5
90.1
92.6
92.1
92.5
64
2.570 Ti -.
Hydrocycle stock 44 38.0
21 46 52 68 292 318 27 71
.59
90% over, F. Final b.p., F. Bromine No., cg./gram Aniline point F. Reid vapor bressure, lb./ eq. in. Octane No. (raw gasoline) A.S.T.M. motor method Aviation rnet,liod 4 cc. T.E.L./gal. a
Virgin gas oil 100 32.2 0 620 700Q 176 57 0.27 13.4
76 ."
'E 23.1 BBL
-
PROPENE
-c
CYCLE STOCK
-
I-
f I S O B UTAN EC
,-
9.5 B B L
-EXCESS C 5
22 ~~
I O 0 OCTANE A S T M AVIATION METHOD t 4.0 CC. T.E.L./GAL 7.2 LBS. R E I D VAPOR
produces cracking results similar to those of the 100-barrel-perday Fluid Catalyst plant when run a t comparable conditions. The same type of synthetic silica-alumina catalyst and the same cracking temperature (975' F.) used with the original virgin feeds were employed a t a cracking severity level sufficient to produce a cycle stock of essentially the same hydrogen content as that of the original unhydrogenated cycle stock. Table IV summarizes the comparative cracking data on virgin feeds and hydrogenated cycle stocks. The hydrogenated cycle stocks in both cases, being virtually free of aromatics, are considerably better feed materials than the virgin gas oils. This is shown by the cracking yields. (In this case, since aviation gasoline is produced rather than motor fuel, the conversions represent 100% minus the volume percentage of liquid distilling above the aviation gasoline range. Excess C b represents that portion of the total pentane produced which cannot be included in the gasoline because of vapor pressure specifications-7-pound Reid vapor pressure.) For example, the hydrogenated cycle stocks give higher aviation gasoline yields and the same or higher total Cq despite lower carbon formation. Also, the leaded octane numbers of the raw aviation gasoline (92.6, 92.5) are as good as or better than those obtained from the virgin feeds (90.1, 92.1). Table IV indicates that a very efficient combination process for obtaining high yields of high-octane aviation gasoline could be established by combining catalytic cracking with simple hy drogenation of the cracked cycle stock. In this process the firstpass cycle stock from high temperature, high conversion Fluid Catalyst cracking would undergo simple hydrogenation for saturation of aromatics and olefins and would then be catalytically cracked with return of cycle stock for further hydrogenation and catalytic cracking in a recycle type of operation to ultimate yield of aviation gasoline. Experimentally the recycle process has been demonstrated in stages and not as an integrated operation. However, the estimates for ultimate yield should be reasonably firm, as they are based on second-pass cracking results where the cycle oils from the cracking of the hydrogenated cracked cycle stocks had nearly the same characteristics (same hydrogen content) as the original first-pass cracked cycle stocks before hydrogenation. Accordingly, calculations have been made to show the yield and quality of aviation gaRoline obtainable by this integrated recycle catalytic cracking process, involving hydrogenation of the catalytically cracked cycle stock. These estimates for total aviation base yield and quality include fullest utilization of the light
INDUSTRIAL AND ENG INEERLNG CHEMISTRY
140
TABLE v. DESULFURIZATION O F HIGHSULFUR GAS OILS BY LOW PRESSURE HYDROGENATION
Vol. 38, No, 2
genation runs were conducted for a sufficient time t o give evidence of satisfactory catalyst life. CONCLUSION
mock
Yield, vol. % on feed Gravity, A.P.I. Initial b: p., O F. Distillation, F. Over
l;g
30% 507
;:g
Final b.p. Color (Robinson) Aniline point, a F. Diesel index Bromine No., cg./gram Sulfur, wt. % Hydrogen, wt. % Refractive index, n20 " Sp. dispersion a t 20' C., ( n p - nc)lO:/d Aromatic rings, wt. %
... 23.3 470
510 520 550 590 640 700 700"
stock 100 27.3 430
West Texas Light Gas Oil Virgin Hydro gas oil gas oil 101 31.9 34. a 390 360
...
30 18 1.42 11.2 1.5174
480 500 540 580 630 700 700a 8 133 36 9 0.15 12.0 I ,5012
480 500 540 580 610 660 700 9 I53 49 0.95 13.0 1.4817
460 490 530 570 600 650 690 19 161 56 3 0 07 13 5 I . 4725
180 27
145 24
127 15
118 12
it8
11
90% over.
hydrocarbons (Ca, G, and C5)- The small quantity of n-butane (about 2094 of the saturated butanes) is isomerized, and the total isobutane is alkylated with butylenes, any excess isobutane being employed to alkylate propylene. The Cj out from catalytic cracking is utilized as a vapor pressure blending agent. For further improvement in octane number, the catalytically cracked aviation base stock is subjected to simple hydrogenation to saturate olefins. These calculations indicate that such a process would give from the virgin gas oils (Southwest Louisiana or Refugio) an over-all volumetric yield of over 90% of 100-octane gasoline. The ease for the Southwest Louisiana feed stock is shown diagrammatically in Figure 3. LOW PRESSURE HYDROGENATION
As mentioned earlier, it is possible to hydrogenat'e catalytically cracked cycle stocks a t lower pressures v i t h the Pame type of sulfur-resistant catalyst employed for simple hydrogenation a t 3000 pounds pressure. Obviously conditions are less favorable for complete saturation a t l o w x pressures; but an appreciable degree of hydrogenation is obtainable at conditions consistent with adequate catalyst life. The process is especially effective where the principal object, is desulfurization. Ysturally, low pressure hydrogenation may also be applied to desulfuring and saturating virgin feed stocks; and in this case desulfurization is easier because of the less refractory character of the sulfur-containing molecule. By way of illussration, hydrogenation data a t 750 pounds per square inch gage on a high-sulfur virgin gas oil and a high-sulfur catalytically cracked cycle stock, both derived from '&'est Texas crude, are presented in Table V. These results were obtained in a pilot uiiit similar t o that shovn in Figure 1 except, for a smaller catalyst capacity and once-through gas operation. The yields are high, and there is comparatively little change in boiling range on hydrogenation. The various indices of aromaticity (specific dispersion, aniline point, hydrogen content, Diesel index, weight per cent aromatic rings) indicate appreciable hydrogenation of aromatic rings. But the most conspicuous improvement is shown in the sulfur content of the hydrogenated products. Thus the catalytically cracked cycle stock is reduced in sulfur from 1.42 to 0.15% and the virgin gas oil from 0.95 to 0.07'%0. This degree of desulfurization is especially notable in the case of the cracked cycle stock because the sulfur-containing molecules in such materials are very refractory. These low pressure hydro-
This paper has shown that simple hydrogenation of cntalytically cracked cycle stocks a t 3000 pounds pressure improves greatly the quality of these materials to the point where they are much more desirable cracking stocks than the original virgin ieeds. The potentialities of this type of operation are apparent as a conservation measure to obtain the highest possible yield of gasoline from virgin charging stocks. Moreover, this increase in yield is secured TTithout any sacrifice in the quality of thc gasoline produced. The economics of such an operation mill obviously depend t o a l u g e extent on the differential in value between the virgin charging stock and the by-product cycle stock. Low pressure hydrogenation, TThich is cheaper than high pressure, can do ai1 intermediate job on the hydrogenation of cycle stocks and can do a rat,her complete job on their desulfurization. I n certain cases it may also be desirable to apply low pressure hydrogenation t o desulfurization and partial saturation of virgin gas oil. The choice between low pressure and high pressure hydrogenat,ion viill depend on local situations and the general price structure for petroleum and its products, xyhich hinges on thc cost and scarcity of crude oil and the relation of coal and fuel oil prices. As a means of conserving petroleum supplies from a standpoint of national policy, the hydrogenation of catalytically cracked cycle stocks should command thoughtful attention. LITERATURE CITED
(1) Carlsmith, L. E., a n d J o h n s o n ,
F. Re, IND.ENQ.CHEIvL,
37, 451
(1945).
(2) Murphree, E. V., Brown, C.
Id.?a n d Gohr, E. J., Ibid.,32, 1203
(1940).
( 3 ) Murphree, E. V., Gohr, E. J., a n d Brown, C. L., Ibid., 31, 1083 (1939). (4) Sweeney, W. J., a n d Voorhies, 1., Jr., I b i d . , 26, 195 (1934). (5) Vlugter, J. C., W a t e r m a n , H. I., a n d Westen, R.A. van, J. Inst. Petroleum Tech., 21, 661-76 (1935). PEEYEXT,ED on t h e program of t h e Division of Petroleum Chemistry of the I 946 LIeeting-in-Prini, ERICAX AX CHEMICAL 8ocrrxu.
s e h e Recovery Plant af Standard ilCompany(N.J.)at Baton Rouge,La.
,
