Possible Future Sources of i n i i t i c Hydrocarbons JOHN
M. WEISS, John M. Weiss and Co., 50 East 41st St., New York 17, Ν. Υ.
T h e r e appear t o b e o n l y t w o b a s i c w a y s to m e e t the continually i n c r e a s i n g d e m a n d s f o r b e n z e n e a n d n a p h t h a l e n e — i m p o r t s or p r o d u c t i o n f r o m p e t r o l e u m . T h e first i s a t b e s t a. t e m p o r a r y m e a s u r e w h i l e t h e s e c o n d is l a r g e l y d e p e n d e n t o n p r i é e levels JL HE growth of the plastics industry has engendered continually increasing demands for two coal-tar hydrocarbons, benzene and naphthalene, and this has been previously discussed by the writer (J, 2), The source of these hydrocarbons, the high-temperature carbonization of coal, has not expanded a t a proportionate rate, and during 1948 we experienced a condition of severe shortage and increasing prices. Although a substantial number of new by-product ovens are being installed to compensate for wartime depreciation and .to provide for increased steel production, it seems that such increase will be decidedly inadequate from the long-term standpoint of aromatics. Even if all the coke-oven tar is distilled to recover its naphthalene content, the writer believes it will prove insufficient for the needs of a prosperous chemical industry. There appear to be only two basic avenues of relief—imports from other countries, or production from petroleum, either per se or incidental to other operations. Imports can, at best, be only a temporary and evanescent palliative since the same basic economic conditions as have caused the shortage in the United States exist, in greater or lesser degree, in all parts of the world. Naphthalene, for example, has been in short supply due to the demands for phthalic anhydride. Over 1948, stimulated by a price rise for 78° C. crude from $0.03 to over $0.06 per pound, imports from Europe have been substantial and have aided in alleviating the United States shortage of this important hydrocarbon. Today, the phthalic anhydride capacity (built and building) approximates 200 million pounds per year in the United States as compared with about 130 million pounds installed capacity in 1944. Outside of the United States, the phthalic anhydride capacity for 1944 may be roughly estimated as somewhere between 30 million and 50 million pounds per year while today the capacity of plants abroad (built and building) approximates between 75 million and 100 million pounds per year with the likelihood of further expansion in the relatively near future. This will leave very little excess of naphthalene for export to the United States if the phthalic plants abroad are operated to capacity. The production of raw materials for plastics from benzene—phenol, maleic anhydride, and styrene—has not reached 972
t h e proportionate stage abroad that it has in the United States, but the tendencies are in the same direction. For a time, if benzene rises in price, imports of benzene may be available in sufficient quantity to compensate for United States deficiencies, but this can be considered only a temporary condition which will disappear as the capacity for phenol, styrene, and maleic anhydride is increased i n foreign countries. This leads to the question of what can be expected from petroleum to supply materials on which an expanding plastics market may rest. Petroleum and natural gas already form the basis of a chemical industry of no mean size, based to a very large extent on ethylene, propylene, and butylène. This subject bas been reviewed by H. B. McClure (β) in some de tail. He shows that the production of aliphatic chemicals increased from 150 million pounds in 1925 to about 9 billion pounds in 1945. (In 1947 t h e production figures of the U. S. Tariff Commission ex ceeded 10 billion pounds.) The two larg est tonnage individuals are acetic anhy dride and formaldehyde which together made up over 11 % of the 1945 total. The latter has its chief use i n plastics, and a sub stantial part of the former goes into the same field by way of cellulose acetate. Other of the aliphatics find large use in plasticizers used witb all variety of the synthetic resins, and others are used as solvents. As with tbe coal-tar products (aromatics), the petroleum and natural gas products (aliphatics) owe a large part of their spectacular growtb to the growth of plastics with a wide extension of uses and applications. The aliphatics have not been retarded by lack of raw materi als but, unfortunately, do not in general provide satisfactory substitutes for the products obtained from benzene and naph thalene. Some substitution is possible but, so far at least, this applies only to a small proportion of the applications. o-Xylene More direct relief may be afforded by the petroleum industry by the production of o-xylene which may b e used in com petition with naphthalene as a raw ma terial for phthalic anhydride. This may be produced by the so-called "hydroform ing" process used to produce aviation gas oline with a high percentage of aromatic hydrocarbons and hence a high "anti knock" rating. By a suitable combina tion of solvent extraction and distillation, CHEMICAL
the aromatic hydrocarbons can be sepa rated from the "hydroformcr" product. This was the chief source of wartime tolu ene, a t least twice as much being produced in this way as from coal-tar sources. Along with toluene, a fraction of mixed xylenes may be separated which can be further fractioned to separate the ortho isomer from the mixed meta and para products. The economies of o-xylene produc tion are highly complicated. As a con stituent of gasoline, xylenes have a base value which is a combination of its fuel value and the extent to which it in creases the "antiknock" value of the gaso line. If xylenes are to be separated, the cost of operation depends on whether the toluene is recovered and sold or whether it is returned to the gasoline fraction, thereby placing the burden of all separation costs on the xylene mixture. Further, there is a sale for the mixed xylenes in the form of solvent, so that it must be taken into ac count whether the market makes it more profitable to sell the mixture as such or further t o process it to obtain the o-xy lene. Unless the m-p-xylene can be sold as solvent or for other uses, it must be returned at its gasoline value, in which case the cost of all separation operations must be carried by the o-xylene alone. Market for Xylenes The solvent market for xylenes is by no means unlimited so that this question is a very important factor. The return for xylenes in the form of solvent is a t least twice the return in the·form of gasoline. With so many bases for figuring, it is no wonder that petroleum companies come to radically different conclusions, and it is probable that they are all correct under their own individual conditions in their determination of the price level fet which o-xylene production would be of interest to them. As a final complication, it may be noted t h a t the same "antiknock 1 ' effect in gaso line can be obtained by the use of tetraethyllead but, a t the present price of lead, the hydroforming process is cheaper for the particular grade of gasoline it pro duces. The statement has been made privately by one petroleum technologist t h a t a drop in tetraethyllead prices of 2 5 % (although unlikely in the near future) would render it uneconomic to operate hydroforming plants, in which case we would have no basis at all for o-xylene production. So far, one petroleum company, Stand ard Oil of California, is producing o-xy lene and uses it to produce phthalic an hydride at the plant of its subsidiary, AND
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Oronite Chemical Co. (4). Several other refiners with hydroforming plants have produced moderate amounts of o-xy lene for sale to producers of phthalic an hydride. The largest petroleum refiner, Standard Oil (N. J.), made a public statement (δ) that it did not produce, nor did it have any intention of producing o-xylene. The best information available appears to indicate a production per year of not over 30 million pounds of o-xylene by petroleum refiners and probably some what less than this amount so that, at most, it will not provide more than about 15% of our phthalic anhydride needs. Naphthalene Another possibility resides in the fact that high-temperature cracking of pe troleum produces a certain amount of naphthalene. Several fractions of cracked petroleum products contain appreciable amounts of this hydrocarbon. The con centration of naphthalene in these frac tions is, however, quite low and a high de gree of fractionation by distillation would be required to attain a concentration from which crude naphthalene could be sepa rated by crystallization. So far, the economies of such operations appear de cidedly unattractive. Indeed, were such operations attractive, there are coal-tar fractions which could be reworked to pro duce more naphthalene, but at the present price level it has not appeared economic to do so. Relief from this source seems unlikely. High-temperature cracking of petroleum to produce aromatics, especially benzene, is also a possibility. This is done in the production of carburetted water-gas and of oil gas, and a small proportion of the United States benzene supply comes from this source. Were it economic, such oper ations could be extended with the primary purpose of producing benzene. Yields based on oil used are, however, quite low. All published results indicate that about 10% of a petroleum fraction is all that has been obtained as actual benzene al though the total aromatics obtained are appreciably larger. Since the chief prod ucts other than aromatics are gas and carbon, which are of proportionately lower value unless the gas can find use as a city gas, it is obvious that benzene prices would have to be very substantially higher than the present selling price of around $0.21 per gallon and present high costs of plant construction would have to be reduced before there could be much in terest in such a procedure. Modified high-temperature cracking, where unsaturated hydrocarbons such as ethylene are major reaction products as well as aromatics, is more promising. De velopments along this line have been made with the "Catarole" process in Great Britain, but the real economics of such processes under U. S. conditions have not, so far, been demonstrated. Earlier partial relief is more likely VOLUME
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through the separation and utilization of cyclohexane from petroleum fractions, and this has already been done to some extent. This product can and does partly replace benzene as a raw material for producing adipic acid for use in nylon. Further, were it cheap and plentiful, it could be used as the base of synthetic phenol which is one of the very large drains on our ben zene supply. The extent to which cyclo hexane may be made available at a suit able price level is still obscure, but it is a factor which should not be neglected in any appraisal of the situation. Furfural is used as a base of adiponitrile ; it is also employed in nylon manufacture and to some extent helps the benzene situation. Increased Prices In all the foregoing discussion of possi bilities of benzene and naphthalene from a petroleum base, it appears as if a higher price level is required to stimulate activ ity by petroleum, refiners and give them some justification for the substantial capi tal requirements which such development would involve. It therefore appears reasonable to assume that growth of plas tics materials based on benzene and naph thalene beyond the supplies available from coal carbonization will necessarily involve increased prices for such raw materials as phenol, styrene, and phthalic anhydride. Such increased costs to the resin manufac turer tend to restrict the growth of the in dustry and at some point would tend to decrease sales. This tendency is evident in present conditions on phthalic anhy dride. Present prices, in excess of $0.20 per pound, have certainly prevented its use in many instances and have encour aged substitution in others. Just where the breakpoint lies is uncer tain, but there is a very grave question as to whether the price level required by our present state of technical knowledge in producing aromatics from petroleum hy drocarbons is not so great as to form a bar to any such development on a broad scale. A hope, and it is only a hope, appears to lie in improved technology of cracking or other methods of treating petroleum so as to increase the yields of aromatics to a point where operations to produce them are economic without material advance in present price levels, so that the plastics industry can be stimulated rather than retarded. When* and how such technolo gical advance will be achieved is admit tedly speculative. Another matter which has been a sub ject of consideration in the technical and popular press is the effect of the FischerTropsch process in making available new supplies of chemical raw materials. One plant to produce synthetic fuels by the Fischer-Tropsch method is now under construction, based on natural gas as raw material. It is expected to produce quite substantial quantities of by-product chemi cals, possibly as much as 150 million pounds per year. These by-products,
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however, are exclusively alcohols, alde hydes, ketones, and acids of the aliphatic series. Such products will compete with similar products now obtained by fermen tation, from carbide through acetylene, or by treatment of the unsaturated gaseous hydrocarbons of petroleum. They do not present any avenue by which our supply of aromatic hydrocarbons can be aug mented. If, however, synthesis gas for the Fischer-Tropsch process were made from coal, possibilities of aromatics are present. In general, so far, the direct production of synthesis gas from coal gives a very im pure gas. The problems involved in puri fication are such that some interests have taken the position that it is better first to coke the coal and use the coke alone for the production of the synthesis gas. If coke is used to make synthesis gas, the sulfur appears in the gas mainly in the form of hydrogen sulfide, carbon bisulfide, and carbon oxysulfide, all of which are said to be more easily removed than the organic-sulfur compounds resulting when the original fuels are employed directly in the synthesis gas operation. Others are of the opinion that preliminary coking presents no advantage. If the first school of thought prevails, tar and gas would be by-products of the Fischer-Tropsch process, and if the coking were carried on at the conventional high temperatures used for metallurgical coke, the tar and gas would yield substantial amounts of naphthalene and benzene, the two needed aromatic hydrocarbons. Car bonization operations at low temperature would not produce them in appreciable amounts. Fischer-Tropsch Process If Fischer-Tropsch based on coal should be developed to, say, 100,000 barrels per day of gasoline and fuel oil, the high-tem perature tar which could be produced would be in the neighborhood of 100 million gallons per year together with the corresponding light oil from the gas. This would afford a very welcome 14% addition to our supplies of benzene and a similar increase in naphthalene if the tar were all distilled to recover it. And 100,000 barrels per day is only a very small proportion of our oil needs. Proposals have actually been made in Washington for the establishment of a capacity of 2 million barrels of synthetic oil per day, half of this to be based on the Fischer-Tropsch method using coal as the basic raw ma terial. Although there is no expressed proposal to carbonize the coal used, it is interesting to note that such a develop ment could provide about one and one half times as much naphthalene and ben zene as is produced by the whole present coke-oven industry, thereby increasing our present supplies by a factor of three. This would certainly offer an effective solution to the problem of aromatic supply. Such development is, however, undoubt973
edly a long time in the future. From a national standpoint, our supply of good coking coal to make metallurgical coke, low in ash and in sulfur, is by no means unlimited and should be conserved. There are, however, large deposits of coking coals in various sections of the country which are so high in ash and sulfur as to be considered unsuitable for metallurgy without extensive treatment to purify them and hence available at considerably lower prices than good coking coal. In other countries, where they are the only available coals, they are used to produce metallurgical coke. Conservation of these lower grade coking coals in the United States is not as urgent as in the case of the highgrade coking coals. There are also vast amounts of lignite and noncoking subbituminous coals which, when carbonized, would give large percentages of hydrocarbon distillates rich i n aromatic hydrocarbons. In some cases, a part of the hydrogen from, the synthesis-gas side of the
cycle might be used to hydrogenate the distillates so as to increase the desirable aromatics. There is, therefore, a possible large source of aromatics if gasoline from coal is developed on a large scale. Undoubtedly, any synthetic gasoline development in the near future will be financed by the United States Government either by direct erection of plants or by subsidy to petroleum refiners or other operators. Such expenditure can today only be justified as a measure of national security. Security will be extended if at the same time we increase our supply of aromatic hydrocarbons, especially naphthalene and benzene. The military uses of aromaticbase plastics and plasticizers are numerous, and the needs are not readily, if at all, met by substitutes. It therefore appears that any Government-sponsored development of gasoline from coal should be, if possible, extended so as to treat the coal under conditions
which will give the aromatic by-products : or, if the coking process selected gives nonaromatic distillates, operations to convert these distillates to oils predominantly aromatic in character should be investigated. This may prove to be no more practical than starting with petroleum oils, but we should know the facts. It appears, from the national defense standpoint, that it is a "must" to carry our studies and pilot work to a point where all these possibilities can be adequately appraised. The expansion of our aromatic-base raw-material supply is so vital to our national welfare that avenues of approach such as those discussed must not be disregarded or lightly dismissed.
Literature Cited
