WAR DEVELOPMENTS
THE PETROLEUM Standard 0 1 1Development Company, N e w York, N. Y.
HE petroleum industry's contributions to the war effort have been numerous and varied. Undoubtedly, the most important of its contributions along manufacturing lines are production of synthetic toluene, of large quantities of high-octane aviation gasoline, and of raw materials for synthetic rubber. These processes give either pure chemical compounds or mixtures of definite types of chemical compounds and, therefore, represent organic chemical synthesis on an enormous scale. Table I gives an over-all picture of the new process developments and their relation to oil refining. A typical crude oil is broken down into various fractions which are then processed to obtain the products used in high-octane aviation gasoline or synthetic rubber raw materials. Table I shows that the Cd fraction can be converted into aviation gasoline through the alkylation process, using fractionation or isomerization or both. As an alternative, the butane fraction after separation of isobutane can be catalytically dehydrogenated by successive steps to give butadiene. The Cg, CC,, and C? fractions (boiling up to 200" E".) can be used directly in aviation gasoline, or selected fractions of these cuts can be isolated by fractionation and used in aviation gasoline. The low octane number fractions discarded in the fractionation can be isomerized into fractions of higher octane number. The fraction boiling from 200" to 290' F. contains most of the potential as well as the actual C7 and Cs aromatic compounds, such as toluene and the xylenes. This fraction is preferably processed by hydroforming to convert potential aromatics into actual aromatics. The hydroformed material can be used directly in aviation gasoline, or the aromatics can be isolated by extraction. The heavy naphtha boiling from 290" to 350" F. can be subjected to severe thermal cracking or reforming to yield butadiene and other desirable materials directly, or this fraction can be hydroformed. The gas oil fraction boiling from 350" E'. to crude bottoms is best processed by catalytic cracking to yield aviation gasoline and raw materials for synthetic rubber. The lighter portion of this fraction can be subjected to severe thermal cracking to yield butadiene and other desirable products. The crude bottoms can be utilized in fuel oil. Most of the processes discussed in Table I represent new tools developed in the last few years, and many of them are recent developments just now beginning to be applied. The vast amount of new equipment being installed for carrying out these processes represents an investment of nearly a billion dollars.
T
SUPERFRACTIONATION
Distillation is the oldest process for separating petroleum into its constituents. Application of fractional distillation to give extremely narrow-cut fractions is, however, a commercial development of rather recent application in petroleum refining and has been termed "superA Thermofor C a t a l y t i c Cracking Plant under Confractionation". By careful analysis struotion by Soconyof the lighter fraction of crude oil it Vacuum Oil Company, Inc. has been found that certain con(See t e x t page 626) 623
INDUSTRIAL AND ENGINEERING CHEMISTRY
624
TABLE I. PROCESSING OF CRUDEOIL yo on Crude
Fraction
0.7
Gas
1.7
c 4
cs
CS
Processes Used
E n d Use
Fractionation] Direct
Fuel
Isomerization Alkylation
Aviation gasoline
Dehydrogenation
Butadiene
Direct Fractionation Isomerization
Aviation gasoline
C, (200' F.)
4.3
20Oo-29O0 F. 29Oo-35O0 F.
11 2 7:0}
Direct Hydroforming Severe thermal cracking
350' F., crude bottoms
57.6
Catalytic craoking Severe thermal cracking
!
Bviation gasoline Synthetic aromatics Butadiene
]
Aviation gasoline Butadiene Isobutylene for Butyl rubber
stituents, particularly the is0 or branched-chain compounds, have higher octane number or antiknock properties than others. Furthermore, isobutane is one of the raw materials for the alkylation process. Fractionation is applied for isolating isobutane from the CI fraction. Isopentane has a considerably higher octane number than n-pentane and is therefore being isolated in many cases by fractionation from the C, fraction.
The n-butane introduced with the feed is discarded, and the alkylate produced is separated from a small amount of polymer of higher molecular weight. Alkylation is carried out on a large scale today for production of high-octane aviation gasoline blending agent. The isobutane required is fractionated from the butane fraction in crude oil production or in refining operations, or produced by isomerization of the n-butane obtained in this way. The olefins used as raw material for alkylation are obtained from cracking, primarily from operations involving catalytic cracking; for example, one catalytic cracking process, operated under normal conditions, will yield about 31 volume per cent of Cp through Csolefins, based on the gas oil charged, ISOMERIZATIO&
Isomerization involves rearrangement of a compound without change in molecular weight. Its most important commercial application in the petroleum field is the conversion of n-butane to isobutane. This reaction is carried out normally with aluminum chloride as catalyst. Owing t o equilibrium limitations, only part of the n-butane is con-
RECYCLE
19
I S O B U TANE
I
?.
n4UTANE
c
SETTLER
COOLER
Q
c
BOTTOMS
HCL
f
L
ALKYLATION
Alkylation is a process of relatively reeent origin by which isoparaffins are combined with olefins t o give higher molecular weight compounds of branched-chain structure. From a commercial standpoint the isoparaffin used is isobutane which can be combined with propylene or C d or Cg olefins. The reactions involved, the major products obtained, and the octane number of part of the product known as aviation alkylate which can be used in aviation gasoline are shown in Table 11. A catalyst is used in the alkylation reaction; for the CS, C4, and C6olefins, sulfuric acid or hydrofluoric acid may be employed. A flow sheet for alkylation of Cd olefins with isobutane is shown in Figure 1.
VoP. 35, No. 6
NORMAL B U
d
- STRIPPER
V
HCL
verted to isobutane per pass. The isobutane obtained can either be isolated by fractionation or directly fed t o an alkylation process. By combining isomerization of n-butane with alkylation, some saving is achieved by the use of common fractionation equipment. Figure 2 indicates the flow in such an isomerization plant. C j and higher straight-chain hydrocarbons can be isomerized to branched-chain hydrocarbons; this treatment improves their antiknock properties. Isopentane, isohexane, and isoheptane are valuable compounds for use in high-octane aviation gasoline. I n the case of the Cr and higher hydrocarbons, there is a tendency for cracking to occur during isomerization, and the olefins produced form complexes with the aluminum chloride. These complexes are very active, particularly for cracking, but have little selectivity for isomerization. For this reason it is desirable to carry out the isomerization of the Cr and higher hydrocarbons under conditions where the olefin complexes are suppressed.
Figure 1. hllcglation Process
HYDROFORMING
The fresh feed consisting of isobutane and C4olefins, which may contain some n-butane, is introduced into a reaction medium consisting of an emulsion of hydrocarbon and sulfuric acid. This emulsion circulates continuously through a reactor and then through a heat exchanger to remove the heat of reaction. Hydrocarbon fraction roughly equivalent in volume to the feed is drawn off to a fractionation system which separates the isobutane and returns it to the reaction system.
Catalytic dehydrogenation is effective for converting C S and higher normal paraffins and six-carbon ring naphthenes into aromatics. When applied to fractions of naphtha from crude, catalytic dehydrogenation yields large quantities not only of aromatics but also of coke, and the cost of equipment involved in burning off coke from the catalyst is high. To decrease coke formation, dehydrogenation is carried out under hydrogen partial pressure. This operation, involving catalytic dehydrogenation in the presence of hydrogen, is known as hydroforming.
June, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
625
Robert Yarnell Richie photograph
ALKYLATION TOWER, STANDARD OIL COMPANY O F LOUISIANA
INDUSTRIAL AND ENGINEERING CHEMISTRY
626
LIGHT
I
HZ R E C Y C L E
f
9"A S c
d(i COOLER
I
c
u)
0
c 0
24
aik
z
5!
-E
0' 4
EXTRACTION
-
NAPHTHA
FEED FURNACE
Figure 3.
Hydroforming Process
In its present commercial application, naphtha vapor along with recycled hydrogen is passed through a fixed catalyst bed for a certain time. During this dehydrogenation operation] there is a net production of hydrogen. Coke deposition on the catalyst is not completely eliminated] so that the catalyst must be periodically regenerated by burning with air or oxygen-containing flue gas. Normally two or more reactors are provided; one reactor is used for dehydrogenation while a second is being regenerated. Figure 3 is a typical flow sheet. Naphtha vaporized in a furnace is mixed with hot recycled gas which contains a high percentage of hydrogen. This mixture flows through the reactor and then to condensing equipment where the product is removed. The cooled gas is recycled back to the feed end of the system. Excess gas is removed by purging and can be used for certain types of hydrogenation. Some cracking occurs in the dehydrogenation operation] and the products are separated by fractionation. If it is desired to isolate pure aromatics, the proper fraction of hydroformed material is subjected to extraction. Hydroforming produces aromatics primarily by dehydrogenation of Canaphthenes and is not effective for obtaining aromatics from paraffins. As an example, toluene is produced by dehydrogenation of methylcyclohexane; xylenes are obtained by catalytic dehydrogenation of dimethylcyclohexane:
In addition, certain amounts of toluene and xylenes may be produced by cracking higher alkylated aromatics, either present in the feed or produced during hydroforming. There is also some formation of aromatics from alkylated C5 naphthenes which presumably are first isomerized into Cs naphthenes. The first major wartime application of hydroforming has been to produce synthetic toluene for TNT. The first commercial plant, which has been in operation for a considerable time, is making toluene at a rate equivalent t o about twice that produced by the \?-hole coal tar industry. Rithout the hydroforming process, this country would be in a serious position in regard to toluene supplies. Additional plants for synthetic toluene hay-e been installed. (A new toluene plant of Standard Oil Company of California is shown on the Contents page of this issue.) When the proper naphtha fraction is used, the hydroforming process will produce high quality aviation gasoline and will probably be widely utilized for this purpose. CATALYTIC CRACKING
Cracking has been described as a process for making little ones from big ones-that is, for converting higher into lower molecular weight hydrocarbons. Cracking can be accomplished by heat alone (thermal marking) or by the action of a catalyst under conditions which give negligible thermal cracking (catalytic cracking). The catalyst not only accelerates but also directs the course of the cracking reaction to give better yields of higher quality products. During the course of a cracking reaction, the catalyst becomes fouled and must be revivified by removal of the tar or coke by burning with air. TABLE 11.
A4LKYL.%TION REACTIONS
Raw Material
c-c-c
A
+ c-c=c
Isobutane
Main Products -3
Propylene
c-c-c
d
Isobutane
p-Dimethylcyclohexane
CHs
I
C
p-Xylene
87-89
+ 2-Butene
+ c-c=c Isoblt c ylene
93-95
j
b b
12,3,3-Trimethylpentane
I c-c-c-c-c
j c:
A&
2 ,a-Dimethylpentane
A i :
I
CHs H I
c-c-c-c-C
2,4-Dimethylpentane
C Isobutane
Toluene
A. S. T. M. Octane No. of Aviation Alkylate
c-c-c-c-c
c-c-c
Methylcyclohexane
Vol. 35, No. 6
&A&
2,3,4-Trimethylpentane
Three types of catalytic cracking are being widely appliedthe Houdry, the Fluid Catalyst, and the Thermofor processes. The Houdry process utilizes the conventional fixed-bed principle. Oil vapor is passed through a fixed catalyst bed where cracking occurs. The cracked products are separated into desired constituents by fractionation. After cracking has been carried out for a certain time in one reactor, the oil vapor stream is switched to another reactor while the first reactor is regenerated by burning the coke off the catalyst with air. Generally several reactors are used. By switching the oil vapor stream from one reactor t o another, cracking is continuous. The reactors are treated intermittently through alternate cycles of cracking and regeneration.
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
lune, 1943 C R A C K I M O SLOTION
RCQLNCRATIOY S E C T I O N
f
Figure 4.
The Fluid Catalyst operation represents a new industrial method of handling solids and of controlling the temperatures of gaseous or vapor reactions. The catalyst is used in the form of powder, maintained in a free-flowing or fluid condition at all times. Circulation of catalyst in large quantities between the reaction or cracking vessel and the regeneration vessel is accomplished without moving parts, by application of the gas lift principle for handling liquids. Pressure to promote catalyst circulation is built up by a standpipe containing catalyst of high density which provides a gravity fluid head against a catalyst leg of lower density. The amount of pressure that can be built up depends only on the height of the standabe. Figure ‘4’ shows the principle of the Fluid Catalyst process. Catalyst from a standpipe is introduced into the oil vapor entering the system and is carried by the oil vapor up into a reaction vessel of relatively large cross section. The mixture of catalyst and cracked products flows from the top of the reaction vessel into a cyclone separator where the bulk of the catalyst is separated from the products. The cracked products pass on to fractionation equipment. The spent catalyst, which contains some coke deposited from the cracking reaction, flows from the cyclone separator to a hopper and then down a standpipe where a high density is maintained to build up pressure. From the standpipe the spent catalyst flows by gravity into an air stream and is blown up into the regeneration vessel, which is also relatively large in cross section. The mixture of flue gas and regenerated catalyst flows from the top of the regeneration vessel into a cyclone separator where the bulk of the catalyst is separated from the flue gas. The
VENTFLUE GAS
Catalyst Flow i n Fluid Cracking Process
In the Fluid Catalyst and Thermofor processes, catalyst is continuously circulated through a reaction vessel, then to a regeneration vessel, and back to the reaction vessel. These processes are truly continuous. The Thermofor process uses catalyst in the form of coarse granules and mechanical conveyors for circulation. I n the Fluid Catalyst process, circulation is accomplished by principles not previously applied commercially. In both processes, oil normally in the form of vapor is passed through the reactor where cracking occurs, and cracked products are sent to suitable fractionation equipment. Air is blown through the regenerator for burning the coke deposited on the catalyst. Both the Houdry and Thermofor processes have already been discussed ( I , 9) rather fully. FLUE
627
GAS
w
PRODUCT FRACTIONATOR GASOLINE
1
- UEATING
-_ HEAVY _ _ __ _ _
OIL
~
CATALYST
RErVnrrEorO
*/ REGEI).
,
~
MOWER
OIL FEEb
GAS OIL
BOTTOMS VAPORIZING FURNACES
Figure 5.
Fluid Catalyst Cracking Plant
*
628
Figure 6.
less extremely turbulent; in many aspects it resembles a boiling liquid, and therefore, very uni-
Vol. 35, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
Commercial Fluid Catalyst Unit
MOTOR GGSOLINE FRACTIONS
a -
L I G H T FULL O I L S 3 5 BBLS.
3 Y p t
the catalyst mass in these vessels. Figure 5 gives a flow sheet of one type of design for a Fluid Catalyst cracking plant,which is s i m i l a r i n principle t o Figure 4. Oil is vaporized in a furnace and enters the c a t a l y t i c sect i o n of t h e plant. Regenerated catalyst flowing down a standpipe is introduced i n t o the oil v a p o r stream and is blown up into t h e reaction vessel, in which a relatively high c a t a l y s t density is maintained owing to the settling act i o n of t h e catalyst against the vapor flow. C a t a I y s t and c r a c k e d products pass to a series of three cyclone separators where es-
~
21.5 B B L S 4
VIRGIN N A P H T H A S
% .
CC. TETRA ETHYL LEAD PER GALLON I GO QN. PRODUCJ
stream, which carries it into the regenerator. Owing to the slipping action of the catalyst, a high relative density of catalyst is maintained in the regenerator. The mixture of flue gas and catalyst from the regeneration vessel passes first
+ Butadiene Plant Now in Opera tion Courtesy, Standard Oil Company of
Louisiana
DEHYDROGENATION
DEHYDROGENATI ON
N NORMAL B " r 4 R E A C T o R k
N
REACTOR
i 4
SOLVENT EXTRACT1ON UNIT
P b 8
RECYCLE
Y
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
630
After 500 hours on high-quality mineral oil
Figure 9.
After 1000 hours on oil containiDg detergent
Pistons from Laboratory Single-Cylinder Diesel Test Engine
jected to further processing before such use. The catalyst carried over by the cracked products is collected at the bottom of the primary fractionation tower, and may be pumped back to the catalyst system as a slurry in cycle gas oil or be returned to the catalytic system by other means. Three large Fluid Catalyst cracking units are now in successful commercial operation, and a large number are being erected. Figure 6 is a photograph of one unit. The Fluid Catalyst principle has a n important application to controlling the temperatures of vapor or gaseous reactions, whether a catalyst is required or not. Where no catalyst is desired, a n inert powder may be used to replace it. I n vessels such as the reactor or regenerator in a cracking unit, the relatively high-density catalyst is in a n extremely turbulent state. Because of this turbulence, the temperatures throughout the vessel are essentially identical. For example, in the regenerator of a typical large commercial unit, the heat liberated will be 120,000,000 B. t. u. per hour. With this high degree of heat liberation, the maximum difference found a t different points of the vessel has been less than 5" F.; this probably reflects inaccuracies of measurement rather than any real difference in temperature. The catalyst or inert powder gives the mixture in the vessel heat capacity and thus guards against rapid temperature fluctuations. Heat can be removed or added to the system by circulation of catalyst through heat exchangers, as used on the regenerator in Figure 5 . The Fluid Catalyst principle can be applied here whether or not the catalyst needs revivification and even if no catalytic effect is desired. One application would be for controlling the reaction temperature in the oxidation of aromatic compounds, particularly for the production of phthalic anhydride from naphthalene. It is believed that the Fluid Catalyst principle may be applicable in metallurgical processes for reducing ores and other operations, and to all types of reactions involving temperature control of gases, vapors, or solids. AVIATION GASOLINE
An indication of the source of high-octane aviation gasoline is given in Table I, which indicates means for processing virgin naphtha and gas oil for aviation gasoline. In general, virgin naphthas from certain types of crudes are of sufficiently high octane number to be used directly in aviation gasoline. Virgin naphtha of lower octane number can be isomerized or further processed to give naphthas of sufficiently high octane
Vol. 35. No. 6
number to go into aviation gasoline. Hydroforming may be applied to a virgin naphtha fraction having a boiling range of, say, 200' to 300" F. for preparation of an aromatic blending agent to be used in aviation gasoline. To convert gas oil into aviation gasoline and aviation gasoline raw materials, such as isobutane and butylenes, catalytic cracking has most general applications. Figure 7 illustrates the application of one type of catalytic cracking to aviation gasoline production. From 100 barrels of gas oil charged plus 9.7 barrels of isobutane, 56.9 barrels of aviation gasoline are produced. This gasoline is considerably higher in octane number than existing specifications require; it is possible to blend in 21.5 barrels of virgin naphtha, which is not sufficiently high in octane number for direct use, to give a total of 78.4 barrels of aviation gasoline meeting 100-octane specifications for each 100 barrels of gas oil cracked. This operation involves alkylation of olefins and some further processing of a portion or all of the catalytic naphtha. In addition to the 78.4 barrels of aviation gasoline 6.6 barrels of heavy naphtha are produced for motor gasoline and 35 barrels of cycle gas oil. The latter may be further processed or used as light fuel oil. Catalytic cracking is essential for the large quantities of high-octane gasoline required for the war. In addition to catalytic cracking, hydrogenation is being applied on a limited scale for production of aviation gasoline from gas oils. In general, where new equipment is involved, hydrogenation is not so attractive as catalytic cracking. Hydrogenation is also being applied for converting certain olefinic polymers to high-octane saturated compounds suitable for use in aviation gasoline. BUTADIENE
Butadiene for synthetic rubber is being produced both from n-butane obtained from natural gas fields or refinery operations and from n-butylenes obtained from cracking, particularly catalytic cracking. In addition, a certain amount of butadiene is being obtained from severe thermal cracking. The latter is part of the so-called quick butadiene program.
. .
-. ..
I
b
Treated
Figure 10.
Untreated
Water-Soaked Gravel Coated with Asphalt after 20-Hour Immersion Test
Butadiene from butane is really a two-step operation involving, first, the production of n-butylene from n-butane and then the conversion of n-butylene to butadiene. Both steps are carried out in the presence of a catalyst. Production of butadiene from refinery butylenes involves, first, the segregation of n-butylenes and then the conversion of n-butylenes to butadiene through the use of a catalyst. The processes being applied for converting n-butane to butadiene were developed
June, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
by Universal Oil Products Company, Phillips Petroleum Company, and Houdry Corporation. The process for conversion of refinery n-butylene to butadiene was developed by Standard Oil Development Company. Schematic flow sheets of the processes starting with n-butane and with refinery butylenes are shown in Figure 8. Starting with field butane, the n-butane must first be isolated. It is then converted in two catalytic stages into butadiene; the conversion per pass, however, is incomplete. Lighter products are separated between both steps; they are hydrogen and cracked products. The Cd fraction isolated after the second catalytic step is subjected to extraction to remove butadiene. Unconverted C4 fraction is recycled. Where refinery butylenes are the starting material, n-butylenes must first be segregated, although in this step it is not essential to produce a fraction of high purity. This nbutylene fraction is then subjected to catalytic dehydrogenation; some cracking occurs and the conversion is not complete. The product is fractionated to give a Cd fraction containing the butadiene. This fraction is then extracted to remove the butadiene, and the unconverted material is recycled. Equipment is being installed to produce butadiene from both raw materials on a relatively large scale. The major portion of butadiene from oil will, however, be made from refinery butylenes. The synthetic rubber program involves production of Butyl rubber on a relatively large scale. The main raw material for Butyl rubber is isobutylene which can be extracted from refinery C4fraction. The bulk of isobutylene for Butyl rubber will originate from catalytic cracking.
63I
petroleum industry has been successful in meeting these requirements. Production of synthetic ethyl, isopropyl, and higher alcohols, as well as their derivatives, is continuing on a n increasing scale. Naphthenic acids, phenols, and vanadium are being obtained from petroleum. Many new organic developments are based on petroleum. The future holds great promise in this field.
OTHER DEVEWPMENTS
Much of our military equipment requires lubricating oils with detergent properties contributed by special addition agents. Oils containing these agents tend to keep carbon and lacquer deposits from forming on various parts of the engine. Figure 9 shows engine parts after tests on the same base oil under the same conditions, with and without an addition agent. The difference in cleanliness is striking. Movement of parts of aeroplanes, cannon, and other military equipment is controlled by transmission of pressure by a fluid generally called a “hydraulic oil”. Since the equipment is subjected to widely varying temperatures, especially to very low temperatures, hydraulic oils must have a slow change of viscosity with temperature. Straight petroleum oils have too great a viscosity variation with temperature, but certain substances can be added to give the desired property. Addition agents are also used to produce an asphalt suitable for construction of roads and runways of airports under wet conditions. Normally asphalt, when mixed with wet aggregate, will not give a bond that adheres; hence roads or runways built in wet weather mill probably disintegrate. Addition of small amounts of certain materials alters the asphalt so that i t will adhere to wet aggregate. Figure 10 shows results of coating tests on wet aggregate, with and without an addition agent after immersion in water for 20 hours. Military equipment must be shipped by water for long distances. Without suitable protection it will corrode and reach its destination in an unusable condition. The industry has met the need for rust-preventive coatings with petroleum oils containing special agents to give adhering films and t o prevent rust. Many of these oils have the property of displacing water from metal surfaces. Results on exposure of two metal rods, one coated with a rust-preventive oil and the other with straight mineral oil, to hot moist air in a laboratory test are shown in Figure 11. Developments in military equipment have made necessary new types of greases and of process and industrial oils. The
Rust-preventive oil
Straight mineral oil
Figure 11. Effect of Coating on Protection against Corrosion
Strides have been made in the use of petroleum as an offensive weapon along two lines-the production of new or improved equipment for applying petroleum, and the conversion of petroleum into forms more suitable for use. Through research carried out by the petroleum industry in cooperation with the Chemical Warfare Service and the Office of Scientific Research and Development, destructive incendiary bombs have been developed. Improvements have been made in chemical and smoke bombs. The effectiveness of flame throwers has been greatly increased. Smoke generators of outstanding efficiency have been produced. Many of the processes discussed are the result of cooperative developments. The petroleum industry is working together as a team. I n meeting war problems the industry has freely exchanged information on new processes and new products through the facilities provided by the Petroleum Administration for War. I n this way the experience of any one unit in the industry has been shared by all. LITERATURE CITED
(1) Houdry, Burt, Pew, and Peters, PTOC. A m . Petroleum Inst., 111, 19, 133 (1938). (2) Simpson, Evans, Hornberg, and Payne, Ibid., 111, 23, 59-66 (1942).
