HE Fluid Catalyst process represents a new chemical engineering technique which has wide application to industrial operations, both catalytic and noncatalytic. This development has been successfully applied to the catalytic cracking of petroleum fractions and as a resdt has become an essential part of the national wartime economy. The present paper is concerned primarily with this application of the fluid catalyst technique. The oil industry’s quest for more efficient utilization of petroleum fractions led to the field of catalysis in 1931 with the commercial application of hydrogenation. More recently work has centered on development of other catalytic processes for producing gasoline from petroleum. Inasmuch as the catalytic decomposition of hydrocarbons in the absence of hydrogen is accompanied by the formation of cokelike deposits on the catalytic surfaces, which in turn reduce the activity of the catalyst, the utilization of such reactions depended on the successful revivification or regeneration of the catalyst. The Houdry process, the first to be commercially applied, accomplishes regeneration with a. conventional multireactor system. The oil vapors are passed through a stationary bed of catalyst during the cracking cycle. At periodic intervals the oil stream is switched from one reactor to another; the first reactor then enters into a regeneration cycle where the carbon is burned off the catalyst with air. The operation is thus continuous, but in terms of the reactors containing the catalyst, the operation is intermittent. Hydroforming is another commercial process operating in this manner.
The most recent developments in this field, the Fluid Catalyst and the Thermofor processes, are characterized by a continuous flow of both catalyst and oil. The Thermofor method circulates coarse granular catalyst continuously between separate cracking and regenerating zones by mechanical conveyors. The Fluid process also operates on the principle of continuous catalyst flow but with no mechanical handling of catalyst a t any stage in the process. Because of the vital part played by the Fluid Catalyst process in making war products, it has been necessary to omit detailed information and data a t many points in the paper.
T
PRINCIPLES OF THE PROCESS
The Fluid Catalyst process fundamentally represents a new technique in handling solid materials. The solid material, in powder form, is maintained in a fluid or freely flowing condition a t all times, and can thus be handled in much the same way as a liquid. A fluidized mass can be circulated by application of the gas lift principle-that is, by balancing a downflowing stream of high-solids density against an upfloming stream of low-solids density. I n other words, the required pressure differential for circulation is obtained in much the same way as water would be transferred by balancing a column of water against a water-gas mixture. The basic equipment involved is illustrated in Figure 1, which illustrates the application of the process to petroleum cracking. The operation is divided into two primary zones, a cracking and a regeneration zone. The principal apparatus 768
July, 1943
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INDUSTRIAL AND ENGINEERING CHEMISTRY
When oils are cracked, carbon is deposited on the catalyst, reduces its activity, and makes necessary its removal by burning with air. In the Fluid Catalyst cracking process the catalyst is handled as a fine powder and is kept in a fluidized condition so that it may be handled substantially as a liquid. The catalyst is conveyed through the reactor by the oil vapor and is separated in dust recovery equipment; then the product vapor flows to distillation apparatus. The carbonized catalyst flows down a standpipe in a high-density condition. Its pressure is thus increased sufficiently to permit injection into a stream of air, which carries it to the regenerator where the carbon is burned off. The catalyst is separated, the flue gas is vented to the atmosphere, and the regenerated catalyst passes down a second standpipe and is injected into the oil vapor going to the reactor. The process is thus completely continuous as regards oil, air, and catalyst flow. Information is available on production of motor gasoline from a variety of charge stocks. The gasoline has a clear octane number of 92-94 by the CFR Research method. Operating conditions may be adjusted to produce high-octane aviation fuel, butylenes, and toluene. Gasoline fractions from the operation may be used directly as aviation base or may be reprocessed in the fluid catalyst unit or hydrogenated. Aviation fuels produced by these methods have low alkylate requirements, and after addition of tetraethyllead, they meet the highest specihations.
I
is the same in each zone-standpipe, reaction vessel, and dust separator. Oil vapor is contacted with regenerated catalyst delivered by gravity from a standpipe, and the mixture flows in suspension into the cracking reactor where the reaction occurs. The mixture of cracked products and catalyst flows through dust recovery equipment where the catalyst is recovered. The separated spent catalyst is collected in a hopper, flows a t high density down a standpipe, and is injected into a stream of air used for regeneration. This air carries the spent catalyst to the regeneration vessel, and it then passes into dust collecting equipment where essentially all the catalyst is removed from the flue gas. The recovered catalyst is collected in a hopper, flows down through a standpipe, and is injected into the oil vapor stream; the cycle is thus completed. The flow characteristics of gases carrying solid particles have been carefully investigated; it has been found possible by suitable adjustment of gas or vapor velocities to build up
769
relatively high concent rations of solids where desirable-for example, in reaction and regeneration vessels. The densities which can be attained are functions of the solids feed rate, composition, and particle size, as well as the vapor or gas velocity. Pressure drop due to friction is quite small, the main pressure drop in the system being due to static heads. Although high concentrations of solids may be obtained in reaction vessels, the solid-gas mixture is extremely turbulent and resembles a boiling liquid in many respects. Owing to this high turbulence with consequent rapid circulation of solids, the temperature throughout the solids mass is surprisingly uniform, varying less than 5" F. from bottom to top in large vessels in catalytic cracking. The extreme turbulence of solids in vessels of this type offers many advantages in temperature control in catalytic or other processes. DESCRIPTION OF A CRACKING PLANT
A simplified flow diagram illustrating the first commercial design of a Fluid Catalyst cracking plant is presented in Figure 2 to show in more detail the application of the Fluid technique to the cracking of oil. (More recent designs represent definite improvement and simplification over that indicated by Figure 2.) Regenerated catalyst from a storage hopper flows by gravity through a standpipe and is injected into the fresh oil feed vapor which carries it to the crachng reactor. The velocity in the reactor is low so as to maintain a high concentration of catalyst, and cracking occurs with a subsequent deposition of carbon on the catalyst. The mixture of cracked products and spent catalyst from the cracking zone are separated in dust recovery equipment; the cracked products flow to fractionating equipment for separation into desired components. The spent catalyst drops into a storage hopper, flows down a standpipe, is picked up by an undiluted air stream, and is carried to the regenerator in which car-
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 35, No.
bonaceous deposits are removed by combustion. C R A C K I N O SECTION R L Q E N E R A T I O N SECTION The mixture of flue gas and catalyst from the CRACKED PRODUCT regenerator are separated, the catalyst dropping into the regenerated catalyst hopper, to complete its cycle. The heat evolved in burning the carbon deposit on the catalyst is greater than can be absorbed as sensible heat by the catalyst for a reasonable temperature rise. It is therefore necessary to have an additional means of absorbing regeneration heat. This is accomplished by circulating regenerated catalyst through shell-and-tube heat exchangers, using a separate standpipe circuit as shown in Figure 2. The cooling medium applied to the heat exchangers in the unit described is fresh oil feed to the plant. However, the heat absorbed by this oil is ordinarily more than that required Figure 1. Catalyst Flow in Fluid Cracking Process to bring it to proper temperature, and a further dissipation of this heat is made to produce steam. rnally between 1000" and 1200" F. The depth of cracking is Operation of the fluid cracking plant is entirely autogoverned by both the amount of catalyst in the reaction matic. The ratio of catalyst flow to oil flow, for example, is zone and the ratio of catalyst to oil flow. This flexibility is controlled by a mechanism actuated by changes in the denimportant in that the character of products is considerably sity of the catalyst-oil mixture. Flow of catalyst to regeneraaffected by both the temperature and the conversion level tion is ensured by automatic control of the level of the catalyst in the spent catalyst hopper. Similarly, regeneration employed. The pressure level can also be held a t any desired point. temperature is governed by automatic regulation of the I n most present applications for gas oil cracking, the pressure quantity of catalyst circulated through the heat exchangers. at the top of the reaction vessel is in the order of 10 pounds The flexibility of the Fluid process is demonstrated by the per square inch, and the pressure a t the top of the regenerafact that operations can be carried out over a wide range of tion vessel is substantially atmospheric. cracking and regeneration temperatures, as well as depth of cracking. Reaction temperatures can be varied both by MOTOR GASOLINE PRODUCTION amount of heat applied to the oil in the furnaces and of hot Initial work on the Fluid Catalyst process, begun well catalyst circulated. Normal reactor temperatures lie in the before the present war, was directed toward the production range 800" to 1000" F. Theregeneration temperatures can be varied over a relatively wide range and are maintained norof high quality motor gasoline. Exploratory work was carried out in small Fluid Catalvst pilot units having a capacity of approximately 2 barrels oi fresh feed per day. Subsequent development work was conducted in a semicomTABLEI. MOTORGASOLINEPRODUCTION AND QUALITY FROM mercial pilot unit with a nominal capacity of 100 barrels per FLUIDCATALYTIC CRACKING OF GASOILS day. Typical results on a variety of feed stocks available in East West Texas Texas Coastal the Mid-continent, Gulf, and Eastern Seaboard areas are Wide Wide Texas wide presented in Table I. The results obtained on the pilot Cut Cut Heavy Cut plants have been substantially checked by three large - comFeed properties 31.7 27.3 Gravity, ' A. P. I. 2:,7 2fi; hercia1 units recently put intdoperation. Aniline point, ' F. 180 169 825 781 Motor gasoline is normally produced by contacting disA. S. T. h l . 50y0 distn., ' F. 680 710 0.43 1.80 Sulfur, wt. % 2.49 0.63 tillate stocks with catalyst at moderate temperatures in a 46,0 46,2 single-pass operation. The yield data in Table I are based 45.0 43.2 51.2 51.2 51.2 51.2 on a conversion of about 49 per cent of feed gas oil (100 2.0 4.0 4.3 3.0 5.6 5.4 minus volume per cent cracked gas oil); a t this level high 4.3 6.3 3.1 4.1 3.4 2.6 yields of specification motor gasolines ranging from 43 to 46 Motor gasoline b.properties 58,2 57,0 per cent are obtained from a variety of feed stocks. The 60.5 58.2 Gravity, A. P. I. 10.0 10.0 Reid vapor pressure, lb./sq. in. 10.0 10.0 conversion of feed gas oil to gasoline and other products can A . S. T. hl. distillation be varied over a wide range, the optimum level being deterDistillate + loss, Yo 25.5 18.5 At 158' F. ;: 2::; mined by economic considerations. 47.0 42.0 A t 212' F. 401 406 406 400 Final B. P.. F. The high quality of the motor fuel is indicated by octane 97.5 87.5 97.5 97.0 Recovery, % number ratings (Table I) which range from 91.3 to 94.3 82 71 85 76 Aniline point, ' F. 0.03 0.18 Sulfur, wt. % CFR Research ('39) clear. Coastal (more naphthenic) feed 159 162 Acid heat F. 9 14.5 13 10 Breakdokn, hr. stocks are preferable from the standpoint of octane number Octane No. 77.9 80.5 and gasoline yield. At some sacrifice in yield, gasolines of 80.5 79.4 CFR-M clear 84.6 83.0 CFR-M + 1 . 5 00. TELC higher octane number than shown in Table I can be ob92.0 91.9 CFR-R ('39) clear 97.0 95.9 CFR-R ('39) + 1 . 5 cc. T E L C 95.3 98.1 tained by higher temperature operation. High stability of Ckacked gas oil b properties the gasolines is indicated by the breakdown test. No finish22.7 22.0 30.0 21.7 GraT-ity A P I. 605 563 ing treatment is normally required aside from a light caustic 572 605 A. S: T.'&!. 50% distn.. ' F. 144 129 .4niline point, F. 124 96 or soda wash and addition of an inhibitor. The sulfur conReid vapor pressure, 10 Ib./sq. in.: end point, 400' F. tent of the material obtained from cracking the high sulfur b Inspections on product as produced without further treatment. West Texas feed is somewhat above specifications but can e Tetraethyllead. be improved by a light acid treatment.
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INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
July, 1943
Other desirable products from the motor gasoline operation are (a) heating oil which can be cut directly from the gas oil as a finished product, and ( b ) propylene, butylene, and isobutane fractions which are desirable raw materials in the production of high quality aviation components and butadiene.
TABLE 11. TYPICAL PRODUCT QUALITY
CATALYTIC AVIATIONCOXPONENTS
Single-Stage High-Temp. Production
Gravity O A. P. I. Reid v&:ppr pressure, lb./sq. in. Aniline point F. Sulfur wt. 7'
WAR PRODUCTS OPERATION
OF
771
As produced 60.2 7.0 66 0.03 63 \135
Hydro &t fraction + raw heavy fraction 62.7 7.0 102 0.03 8 13
Two-Stage Production In feed Product 60.2 56.6 7.0 G6 0.03 63 135
7.0 64 0.03 13 27
Single-Pass Low-Temp. Production Naphthenic Paraffinio feed stock feed stock 57.6
67.7
7.0 85 0.014 10 24
7.0 122
Work on the production of motor gasoline 0.01 as a primary objective was discontinued some ~ ~ ~ $ ' ~ ~ 2 . time before the United States entered the war, A. s. T,M. distillation F and emphasis was placed on the operation of p. 121 110 121 108 114 114 Fluid Catalyst plants to make war products-in 141 139 141 139 140 141 190 189 190 210 IS9 Over particular, high-octane aviation gasoline, raw 292 288 292 293 273 '03 274 materials for synthetic rubber, and synthetic %?bB. P. 338 340 338 324 300 316 toluene. No major revisions in basic equipment 0 ~ Et2clear 2 ~ 80.5 79.1 80.5 83.1 81.6 77.9 or design were necessary. Through the use of a AFD-ic + 4 TEL 90.6 96.0 90.6 97.0 96.0 93.3 and by more cracking at a Modified Francis method, centigrams per gram. higher temperatures, a more desirable product in the aviation gasoline range could be produced, along with increased quantities of the butane fractions used in the synthesis of high quality aviation blending duces, in addition to high yields of olefins and isobutane for components and synthetic rubber. Only a general discussionof alkylation, a gasoline containing fairly large amounts of operations and quality of products can be given at this time. toluene, xylenes, and the higher aromatics. Typical compoAviation fuel by Fluid Cracking can be obtained in a sitions of fractions in the aviation gasoline range, obtained number of ways, depending on the local situation and the from a paraffinic gas oil a t a conversion IeveI of 65 per cent, aviation specifications to be met. The first-pass catalytic are as follows: cracking conditions can be adjusted, or suitable portions of the first-stage product can be reprocessed by further catalytic treatment or other means. Table I1 gives typical qualities Range, BoilinogF. Aromatioa Composition, Naphthenes Vol. To Acylics Y&lefina Total of the catalytic aviation components which may be derived c8-200 3 16 81 43 from such operations. 200-225 9 40 51 50 225-250 59 16 25 26 SINGLE-STAGE HIGH-TEMPERATURE OPERATIONS.Crack68 13 19 19 250-335 ing with a suitable catalyst a t elevated temperatures pro335-350 87 5 8 12
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PROWCT FRACTIONATOR
CATALYST
RETURWEDIO
R E C E ~ .I~OPPER
OIL FEED
k
VAPORZING FURNACES
Figure 2.
-
Fluid Catalyst Cracking Plant
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INDUSTRIAL AND ENGINEERING CHEMISTRY
772 R A W MATERIALS
NAPHTHA
ALKYLATION
ALKYLATE
100 O.N. AVIATION
n
\,
LINE FRACTIONS
Y
21.5 BBLS.
Figure 3.
VIRGIN N A P H T H A S
Aviation Gasoline Production by Fluid Catalytic Cracking
Vol. 35, No. 7 r e s u l t s o n t h e aviation gasoline obtained by such treating are summarized in Table 11. The increase in product quality from roughly 90 to 97 octane number is obtained partly through the s a t u r a t i o n a n d e l i m i n a t i o n of the lower boiling olefins, and putly through the cancentr:ition of aromatics in the h i g h e r hoi 1 ing fractions. This operation has partirular merit in situations where hydrogenation equipment is not available and where supply of natural light blending naphthas is limited. The aviation gasoline produced is quite aromaticandof highquality.
L OW - T EM P E R A T U R E Eecause of their relatively low olefin content, the heavier fractions of the above gasolines are valuable as aviation blending agents, either with or without further treatment. On the other hand, the material boiling below 250' F. is high in olefin content and may be treated further for use in aviation blends. Hydrogenation of this light material results in a quality product which, when blended with the higher boiling aromatic fractions, gives a base rating 96.0 A. S. T. M. aviation' with specification lead added. As an alternate, the whole aviation gasoline may be hydrogenated to an A. 6. T. M. aviation octane number of 97.0-98.0. This compares with a 90.6 A. S. T. M. aviation quality for the material of similar boiling range as produced (Table 11). As an alternate to utilizing the light fraction through hydrogenation, a virgin naphtha can be blended with the heavy cut.
TABLE111. COMPARISON O F COMXERCIAL AND PILOT-PL.4NT CRACKIXG O F PARAFFIKIC Gas OIL T O OBTAINMOTORGASOLINE Yields on feed 10-lb. Reid-vapor-pressure gasoline, vol. Excess butane, vol. % Gasoline butane, vol. 70 Gas oil, vol. % Dry gas, wt. % Carbon, wt. %
+
Color Aniline point, ' F. Sulfur, % ' Bromine No. Octane rating A. S. T. M. alear CFR-R ('39) clear CFR-R ('39) 1 . 6 CC. TEL
+
9%
Commercial Scale
Pilot Plant
42.8 7.3 60.1 50.0 5.8 2.5
45.6 4.8 50.4 50.0 4.4 3.2
60.3
60.4
101 5.5 22.5 45.0 64.0 92.5 385 0.03 66
95 6.0 24.0 46.0 61.5 90 o 400 +20 87 0.04 75
79.2 92.9 97.3
79.7 92.0 97.0
+
;;
TWO-STAGEOPERATIONS. Aviation gasoline of high quality may also be produced by subjecting the material from the first stage t o a further catalytic treatment, for which the primary cracking plant can be used, if desired. Typical 1
4.S. T. M. Designation D G 14-42T, also referred t o as AFD-1C.
SINGLE-STAGE OPERATIONS, Cracking operations with this catalyst may also be carried out at relatively low temperatures to produce an aviation gasoline which may be used directly without further processing in aviation blends. The quality of this material when produced from commonly available paraffinic gas oils is inferior in certain aspects to that produced from higher temperature operations. Leaded A. S. T. M. aviation octane numbers of 91-94 are normally obtained with 4 cc. of tetraethyllead per gallon of fuel. However, certain naphthenic gas oils adapt themselves readily to these cracking conditions and result in a specification product high in leaded octane number (96.0 A. S. T. M. aviation). Typical products from this type operation are presented in Table 11. An inherent disadvantage to cracking a t these conditions lies in the low quantities of olefins made available for the production of aviation alkylate. INTEGRATED OPERATIONS FOR AVIATION PRODUCT1 ON. Although a number of methods of utilizing Fluid Catalyst cracking for the production of high quality aviation base have been discussed, there are other methods of application which may be attractive to certain locations. It should be emphasized, moreover, that the Fluid Cracking process is not solely a producer of aviation base, but produces raw material for alkylation simultaneously. A typical illustration of the manner in which this process fits into the production of 100octane aviation gasoline is outlined in Figure 3. Assuming that 100 barrels of paraffinic heavy gas oil are fed to a Fluid Catalyst unit, it is possible to produce 78.4 barrels of 100 octane aviation fuel meeting present specifications. Extraneous quantities of isobutane are utilized in this integrated operation owing to the fact that the isobutane produced in the catalytic unit is not sufficient to alkylate all the Cd and C6 olefins produced. Sufficient isobutane is available, however, to alkylate substantially all the butylenes. Since the blend of aviation gasoline constituents from the catalytic cracking operation is higher in octane number than specifications require, readily available light virgin naphthas are utilized in Figure 3 t o increase gasoline volume while still meeting specifications. In addition to the aviation product, the following by-products are obtained: Fuel gas Motor fuel cut Heating oil cut Fuel oil
38.8 million cu. ft. 6 . 6 barrels 23.0 barrels 12.0 barrels
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Unloading a Finely Powdered Catalyst from Freight Cars into a Hopper, from Which I t Is Delivered to the Catalytic Cracking Unit; Here I t Circulates with Products Being Manufactured, to Control Intricate Chemical Reactions.
COMMERCIAL OPERATIONS
Three large commercial Fluid Catalyst plants are now in operation; photographs of one of these units are shown on pages 768 and 769. A considerable number of these plants of improved design are being constructed for refiners in the petroleum industry. When this program is completed, the installed capacity of Fluid Catalyst cracking will probably exceed that of any other catalytic cracking process. The present commerical experience with large Fluid Catalyst plants has been gratifying. The first unit was placed in operation on May 25, 1942, with surprisingly little difficulty. Initial operations were conducted for motor gasoline on heavy wide-cut gas oils since the catalyst required for the war products operation was not available. Smooth performance has been obtained; yields, product quality, and operating conditions were found to be in good agreement with the semicommercial pilot plant, as shown in Table 111. More recently the first commercial plant has operated continuously for five months with a suitable catalyst for aviation gasoline production. Maintenance of catalyst activity was satisfactory; at the end of the run the catalyst was entirely suitable for future operations, and its use in the unit was continued. The plant was in good mechanical condition following this run, and this indicated that maintenance requirements will be low. The recovery of catalyst has been satisfactory, in general, despite periods in which high losses were experienced because of faulty mechanical conditions in the dust collecting equipment. Over the five-month period of operation actual catalyst loss averaged 2.27 tons per day, or about 0.41 pound per barrel of feed. This figure includes somewhat high losses in the starting up of the unit, which will be preventable in the future. Small mechanical changes are being made in the dust collecting system to ensure dependability of operation, and it is expected that with these changes catalyst loss from a large commercial Fluid Catalyst unit will be nearer 1 ton per day. OTHER APPLICATIONS
The Fluid Catalyst technique has wide application to many industrial operations which may or may not involve catalyst reactivation. This technique is particularly adaptable as a temperature control means for gas- or vapor-phase reactions since the powdered solid circulates rapidly within a vessel and ensures uniform temperature throughout. At the same time the powdered solid in the vessel imparts heat capacity to the reacting vapors or gases and thus guards against rapid temperature changes. Heat can be either added t o or removed from the system by circulation of the powder through suitable heaters or coolers. Application is not confined to catalytic processes, since a powdered material of noncatalytic properties may be employed. In a still broader sense, the Fluid Catalyst technique undoubtedly has application to many industrial processes involving direct handling of solid materials such as treatment of ores, coking of coal, etc.
ACKNOWLEDGMENT
The Fluid Catalyst process represents a contribution of the Standard Oil Development Company to a cooperative study on catalytic refining participated in by' the refining organizations of Standard Oil Company of New Jersey and by Anglo-Iranian Oil Company, Ltd., M. TV. Kellogg Company, Shell Oil Company, Standard Oil Company (Indiana), Texas Company, and Universal Oil Products Company. The views of the Fluid Catalyst plant on pages 768, 769, and 773 were photographed by Robert Yarnell Richie. P R E ~ S E N before T ~ D the Division of Petroleum Chemistry Of the AMERICAN CHEMICAL SOCIETY, Detroit, Mioh.
rtt the
105th Meeting
