Courtesy, Mas B . Miller & Company, Inc.
SOLVENT EXTRACTION PLANT USINGTHE DUO-SOLPROCESS
J. BENNETT HILL
But, amazing as are these contrasts, they EVENT”-SEVEN years Sun Oil Company, are not nearly so impressive as the revolution ago, in 1858, the petroMarcus Hook, Pa. leum industry may be which has taken place in the industry within the past fifteen years. Until the advent of said to have been born. In that year the cracking in 1912, development in the petroleum industry had Seneca Oil Company was organized for the purpose of drilling wells for “rock oil” in the belief that in this way larger and more been principally a growth in size. Small stills, agitators, and commercial quantities could be obtained than by the old practanks had been replaced by bigger ones, but there were no radical changes in processing. Even the first cracking stills tice of merely collecting the small quantities which seeped to the surface of the ground. They started operations on a tract were merely the old conventional shell stills with a valve on the vapor line to control the pressure, for the science of chemia t Titusville, Pa., and in 1859 the famous Drake well struck oil cal engineering which has now so altered the industry did not and produced it a t a rate of about 25 barrels a day. It is a far cry from that small beginning to the petroleum industry make its appearance in the petroleum field until the early of today, which in the United States alone produces and re1920’s. Nevertheless, the production of gasoline from gas fines more than 900,000,000 barrels annually, employs in its oil by the cracking process marks the beginning of an epoch, various ramifications about 1,100,000 men, and has an insince it is the first example of deriving from a petroleum stock vested capital of about $12,000,000,000. This industry, in products which could not previously be made from it by any value of products according t o the census reports, ranks third known process. The realization that there was a t least one among the industries of the country, being surpassed only by new thing under the sun was undoubtedly a potent factor the meat packing and steel industries. in stimulating research, both engineering and chemical, to In the early days of the industry the primary interest was uncover new fields. in illuminating oils; even lubricating oils were of secondary Cracking importance. Today the interest is principally in motor fuels and lubricating oils but extends over the whole range from The cracking process today is an outgrowth of a number gas to asphalt and from medicinal oils and paraffin wax to of developments, in each of which the oil to be cracked was heavy fuel oils. heated to a desired temperature in a continuous stream in a
Q S
519
INDUSTRIAL AND ENGINEERING CHEMISTRY
520
Distillation
r
Experts will disagree as to whether the developments in cracking or in distillation have been of more far-reaching importance in the petroleum industry. The old horizontal shell still, running crude to coke, fuel oil, or lubricating oil, has almost vanished in favor of the modern pipe still. These stills, which are commonly built now with capacities of 10,000 to 20,000 barrels per day, provide for heating the oil in a continuous pipe coil to a temperature sufficiently high to vaporize the desired portion, leading the heated oil into the base of a fractionating tower, generally of bubble-plate design, and drawing off the desired fractions from various points in the tower. In some installations the crude is distilled in the first stage only as far as the gas oil and the lubricating oil is distilled from the bottoms in a second stage o p e r a t e d under vacuum or in other equipment. In other installations the lubricating oil also is taken overhead as a distilIate in the first operation, and the entire distillation is therefore carried out in one stage. The pipe still has resulted in large savings in l a b o r a n d f u e l a n d in elimination of the excessive amount of rerunning that was necessary with the old shell stills. Typical figures are a reduction of rerunning from 90 per cent with the old stills to 10 per cent with pipe stills. In order to avoid local overheating and consequent decomposition of the lubricating oils, stills have been
THEPETROLEUM INDUSTRY IN
VOL. 27, NO. 5
1870
pipe etill and was given a “soaking” time a t this temperature to allow the cracking reaction to take place. These various developments differed from each other in the temperature of heating, the pressure of the system, the time and type of vessel for soaking, and other factors, and therefore produced different yield and quality results. It has come to be realized that the proper conditions for the optimum results vary with the particular character of the stock charged and that the process must be designed either to perform a definite service or to be sufficiently flexible to handle different services. C r a c k i n g units have recently been i n s t a l l e d to handle as much as 30,000 b a r r e l s per day of total charge. They have been so arranged that the heavy tarry part of the stock is cracked a t a fairly low temperature to minimize trouble with coke deposition, and the light clean fractions a t high temperature under vapor-phase conditions to give a gasoline of the highest possible octane number. Such units are integrally equipped with the proper fractionating equipment to separate these various portions of the charge and products and send them to the proper point for most efficient cracking. T h e l a r g e q u a n t i t i e s of gas produced in cracking and its comparatively low dollars and cents value form an invitation for research work, and considerable success has recently been attained in polymerizing the olefins in the gas t o liquid hydrocarbons boiling within the gasoline range. Even newer processes are planned to decompose the paraffis in the gas to olefins and t o polymerize these olefins.
BATTERY OF CRACKING UNITS OF FIFTEEN YEARSAGO Courtesy, Continental Oil Company
REF~NING APLA4
THE MOSTIMPORTANT PRODUCING AREASA X D REFININGCENTERSIN 1935
MAY, 1935
521
INDUSTRIAL AND EKGINEERING CHEMISTRY
Courtesy, The
.If. W. Kellop Company
MODERN COMBINATION CRACKIXG UNITWITH A CAPACITY OF 15,000 BARRELS OF CRUDEOIL AND 5000 BARRELS OF PIPESTILLBOTTOMS PER DAY
designed and are in use in which the heating is indirect, through the medium of vapors of diphenyl, mercury, or other highboiling substances.
Dewaving Until recently it ha- been general practice to employ different types of processei for removing the wax from light and heavy lubricating oil. This practice arose on account of the different crystalline habit. of the way in the two portions of the crude. The lighter oils contained waxes which cryatallized readily in large plates and which were therefore well adapted for filter-pressing. This “wax distillate” or “paraffin dktillate” has therefore been dewaxed by chilling and pressing. The heavier and more viscous oils contain other types of waxes which yield only crystals of undetermined form and such small size that this wax was formerly regarded as amorphous. These oils, even when their viscosity was reduced by naphtha dilutions, did not respond to filter-pressing. In old practice they were dewaxed by the lengthy process of diluting, chilling, and “cold-settling” for a week or more, the wax-free oil solution being decanted from the settled wax slurry a t the bottom of the tank. More recently, centrifugal dewaxing of this type of stock has largely replaced coldsettling. The chilled diluted oil is fed continuously through the bowl of a high-speed centrifuge, and the wax slurry and dewaxed oil solutions are separately discharged. Just as the pressing operation would not handle the heavier oil with its finely crystalline wax, so these processes would not handle the coarsely crystalline wax of the lighter oils. It has been necessary therefore to make a division between the two classes of oils and process them separately. Developments within the past few years threaten to upset this picture. These are the solvent dewaxing processes. It has been shown that, if the oil is diluted with certain solvents, all of the types of wax come out in sufficiently large crystals to permit ready filtration, even on a conventional continuous .filter. While numerous solvent combinations have been
proposed, the most important ones are liquid propane, a mixture of acetone and benzene, and trichloroethylene. In the case of liquid propane, chilling is accomplished by autorefrigeration by evaporation of a portion of the propane. Since these processes are applicable to any kind of stock, they permit dewaxing of cuts from the pipe still which were previously regarded a i hybrid between light and heavy oils and which could not be dewaxed by either of the old types of processes. Theye new processes a. they develop will probably be capable of producing in a reasonably oil-free condition the higher melting and higher boiling waxes which have not previously been isolated to any considerable extent. We may therefore look for an extension of the range of properties available in paraffin wax.
Hydrogenation One of the most discussed recent developments in the industry is hydrogenation. In this process the oil is heated in a continuous stream with hydrogen in the presence of a catalyst. The entrance of hydrogen into the molecule takes place either with or without thermal decomposition or cracking, depending on the results desired and the temperaturetime conditions employed. Thus a saturated gasoline of high octane number may be obtained by hydrogenating a gas oil under drastic conditions. a high grade of kerosene may be obtained from a poor grade by applying rather mild conditions, or a high grade of lubricating oil may be made from a low-grade residuum or tar. The latter is probably the most important application of the process today. Hydrogenation has not found ready acceptance in the industry today, primarily on account of the high initial cost of the plant equipment. -4s the process has been developed this high cost is being reduced, so that with any decrease in the present abundance of crude and the consequent necessity of larger yields of high-quality products, hydrogenation will probably come in for more general serious consideration. It is probably the most radical major development which has been made.
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VOL. 27, NO. 5
Courtesy, Union Oil Company of California
PLANTFOR DEASPHALTIZING AND DEWAXING BY LIQUID PROPANE
Solvent Refining
remove the aromatic and other naphthenic compounds and so improve the burning quality of the product. This process has been in commercial use for many years. the general composition of petroleum oils is essential. While More recently the solvent extraction idea has been exas yet no exact knowledge of the constituents of the fractions tended to lubricating oils to replace sulfuric acid treatment, above gasoline is available, it is known that the petroleum in contrast to which solvent extraction permits the complete oil contains a considerable number of different series of hydrorecovery of the portion of the oil which is removed. Another carbons ranging from the straight-chain paraffins down purpose of solvent extraction is to increase the paraffinicity of through various series embodying probably one or more ring the oil and so obtain a lower coefficient of viscosity change structures and having lower with temperature, o r a higher hydrogen-to-carbon ratios. viscosity index. -4considerCrude petroleums probably able group of widely diverse differ from one another, not solvents has been employed by c o n t a i n i n g d i f f e r e n t for solvent extraction. Comseries of hydrocarbons, but mercial installations are now s i m p l y by the proportions in operation u s i n g s u l f u r of the v a r i o u s s e r i e s t o dioxide, a mixture of sulfur each other. Thus a “parafdioxide and benzene, phenol, f i n i c ” o r a “naphthenic” Chlorex (P,P’-dichloroethyl oil m e a n s simply that the ether), nitrobenzene, a comformer a p p r o a c h e s m o r e bination of p r o p a n e a n d closely in c o m p o s i t i o n to cresylic acid, and furfural. the paraffin series than the In practice the oil charged is latter. Physical properties passed countercurrent to the of oils vary, and it is the solvent either in a tower or r u l e t h a t t h e more naphin a series of agitators and thenic (or the less paraffinic) settlers, and there is drawn the oil for the same boiling off from one end of the system point, the higher will be its the refined oil or raffinate conspecific g r a v i t y , refractive taining dissolved solvent and index, viscosity, and rate of from the other end the soluchange of viscosity with temtion of the extract in solvent. perature. The solvent is distilled from Solvent refining is essenboth products. tially a fractional separation A n o t h e r q u i t e different of the constituents of the oil commercial development in b y s o l u t i o n in a solvent. solvent refining is the procIts first important applicaess involving the treatment Courtesy, Fader Wheeler Corporation tion was the Edeleanu process f o r e x t r a c t i n g low-grade MODERN ATMOSPHERIC-VACUUM TWO-STAGE PIPE STILLUNIT of oils with liquid propane. This solvent has the effect of FOR DISTILLATION OF CRUDEPETROLEUM kerosene with liquid sulfur dissolving the oil but precipi- , dioxide to dissolve out and (By contrast, a battery of old-type shell stills appears in the foreground.)
For a proper understanding of solvent refining, a concept of
MAY, 1935
INDUSTRIAL, AND ENGINEERIKG CHEMISTRY
523
Courtesy, Alco Products, Inc.
MODERNIZED COMPLETE REFINERY WITH CAPACITY OF 10,000
TO
12,000 BARRELSOF CRUDEPER
DAY
(A battery of old type shell stills appears in the center background.)
tating the asphaltic dark-colored substances, and therefore offers a means of deasphaltizing a tarry residual oil to produce a clean lubricating oil. Furthermore, since propane a t ordinary temperaturea is so close t o its critical condition (critical temperature 212" F.), a slight change in temperature makes a large difference in its physical properties, including its solvent power. By raising the temperature, therefore, more of the heavier portions of oil may be thrown out with the asphalt, or the operation may be carried out in two or more steps, in the first of which the asphalt is precipitated and in the second the temperature raised and a part of the heavy portion of the oil precipitated. Considering further the fact that dewaxing may be accomplished in propane solution, it is obvious that a great number of interesting refining sequences are possible with the use of this solvent.
Liquefied Gases As is explained later, propane and, beyond certain limits, butane are objectionable in present specification gasoline on account of their high vapor pressures. On the other hand the fact that they can be shipped as liquids and easily vaporized to a permanent gas a t the point of their use makes them of special value for certain fuel purposes, such as rural domestic use. The commercial large-scale production of liquefied propane and butane is a development of the last fifteen years.
These products were first separated from natural gas but more recently, as refinery gas has been produced in greater quantity with the growth of cracking, refineries have also been equipped for their manufacture. Both the gas and gasoline are stripped of these components, the gas generally by absorption, and the gasoline by reboiling in a fractionating tower. The product from these two sources is then combined and fractionally distilled under pressure to yield commercial propane and butane.
Gasoline Along with the major process changes which have been outlined there has been a corresponding development in the basic knowledge as to what constitutes good gasoline or good lubricating oil and an improvement in product to meet these requirements as established. The tendency of gasoline to detonate has received considerable attention and, while much is yet t o be learned scientifically of the cause and mechanism of detonation, methods of measuring this property have been worked out and considerable knowledge gained as t o how to improve gasoline in this respect. The detonation quality, or octane number, has become one of the most important specifications for gasoline. In the last ten years the octane number of commercial gasolines has been raised to such an extent that automobile manufacturers can produce automobile engines of much higher compression ratios and
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INDUSTRIAL AND ENGINEERING CHEMISTRY
hence higher efficiencies. Whereas the average compression ratio in passenger cars of ten years ago was about 4.4,in the 1935 cars it is about 6.0. Part of this improvement is in better engine design which tends to eliminate detonation, but a large part of it is actual improvement in the gasoline. The most important factors of this improvement are (1) a control of cracking conditions in making the gasoline so as to give maximum octane number and (2) the development of tetraethyllead which is added t o gasoline to suppress knocking. The question of proper gasoline volatility has been difficult, since inherently easy-starting characterics and freedom from vapor lock are opposed to one another. Easy starting in cold weather requires a certain amount of easily vaporizable material in the gasoline; on the other hand, these volatile hydrocarbons tend to cause vapor lock-that is, vaporization in the intake system of the car and consequent upsetting of the proper metering of the carburetor and irregular operation or stopping of the engine. This situation has been improved by sharply eliminating from gasoline the extremely volatile hydrocarbons, such as ethane and propane, since these compounds cause vapor-locking difficulty out of all proportion to their value in making starting easier. Even with an ideal gasoline it was impossible, however, some years ago to obtain in some cars easy starting on the cold days of a month and freedom from vapor lock on the warm days. This condition is subject to improvement by proper design of the automobile, and some automobile manufacturers have now taken steps in this direction. In order to avoid gumming troubles of highly cracked gasoline on account of polymerization in the intake passages of the car of some unsaturated constituents, gum inhibitors have been developed which retard the initial oxidation of the unsaturated compounds, the first step in gum formation. These inhibitors are generally phenolic compounds-for example, catechol, a-naphthol, and benzyl-p-aminophenol.
Lubricating Oil Similar progress has been made and is being made in lubricating oils, particularly for automobile lubrication. One of the principal efforts has been t o minimize the difference in viscosity between crank case oils a t operating temperatures and a t low temperatures where starting must be effected. This means a lower coefficient of change of viscosity with temperature, or a higher viscosity index as it is commonly expressed. Oils of low viscosity index may be improved in this respect by hydrogenation or solvent extraction, both expensive processes if used for this end alone. Interesting developments have been made recently along the line of raising viscosity index by dissolving certain compounds of very high molecular weight, such as a highly polymerized hydrocarbon, in the oil. Any method of improving viscosity index without great expense will be welcomed. Small quantities of wax in a crank case oil cause the oil to set t o a semi-solid mass a t low temperatures. A crank case oil in this condition will not feed to the oil pump in the engine until it is sufficiently warm to flow, and the engine therefore runs for a time without adequate lubrication. This wax may be eliminated by complete dewaxing, but substances have recently been made and marketed which, when added to an incompletely dewaxed oil, poison the crystal growth of the wax and keep the oil fluid and pumpable far below the temperature where it would normally solidify. Present design of automobiles is demanding far greater load-carrying capacity of the lubricant than formerly. This is particularly true in the hypoid gear now used in some rear axles, where the tooth loads and rubbing speeds are such that a pure petroleum lubricant will not maintain a lubricant film between the surfaces and scoring and seizure resuIts. A de-
VOL. 21, NO. 5
mand has therefore come into existence for an “extremepressure” lubricant for this type of service. The situation has been met so far by adding to the oil an only moderately stable sulfur or chlorine compound or a combination of the two. What appears to happen is that, a t the high temperature between the teeth, the compound reacts chemically with the metal and forms a very thin film of iron sulfide or chloride which does the lubricating. The problem of extreme-pressure lubricants is a t present an active one.
Chemicals from Petroleum Probably the greater part of the development of chemicals from petroleum has taken place outside the petroleum industry. The developments are, however, important. They have utilized principally as their raw materials the unsaturated hydrocarbons of low molecular weight, such as ethylene, acetylene, propylene, and isobutylene, and have produced acetic acid, alcohols, higher hydrocarbons, a whole series of solvents related t o ethylene glycol, and other compounds. Chemical developments have also produced synthetic lubricating oils, synthetic motor fuels, and synthetic waxes.
What of the Future? I t is safe to say that the petroleum industry will always be influenced by the changing demands of the automotive industry, because whatever may have been the start of the industry, its principal business has become supplying fuels and lubricants for the internal-combustion engine. If, therefore, it is shown a t some time in the future that engines can utilize sugar as a fuel more economically than gasoline it will become the job of the petroleum industry to make sugar. Just now the development of the Diesel engine with its specific fuel requirements is absorbing a great deal of attention. Another prediction which it is safe to make is that development in the future will be along the line of complete utilization of crude petroleum by making every part of it a desirable and marketable product. -4considerable part of the products from petroleum today have a market value lower than that of the crude. Research effort will certainly be directed toward rectifying this condition. The basic need, of the industry today for further radical advances is a better basis of fundamental research on the chemistry and physics of petroleum and its compounds. This foundation ten years ago was almost nonexistent. During the last ten years, influenced undoubtedly by the grants to such research work in petroleum from a fund established by two generous donors and administered by the Sational Research Council and the American Petroleum Institute, a large amount of fundamental research work has been carried out in the universities of this country. A count of the number of articles on petroleum compounds in the Journal of the American Chemical Society reveals only two for the year 1924 and over fifty for the year 1934. The situation is encouraging but pressing. This raw material, ranking in tonnage production in this country as one of the most important, is still so unknown to our chemists that, for example, we do not know one single compound which is present in petroleum lubricating oil, Whatever the future course of the industry may be, the need for more fundamental information on our material is obvious. RECEIYED March 22, 1935.
