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I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Vol. 19, No. 10
Motor Fuels By J. B. Hill THEATLANTICREFINING COMPANY, PHILADELPHIA, PA.
Chemistry’s Contribution to Quantitative Production
F THE materials used in motor cars, gasoline has been shown to be quantitatively the most important. The weight of gasoline going into the automobile industry is more than five and a half times that of its nearest competitor, iron and steel. I n fact, more than twice as much gasoline is used than all other materials combined. I n the early days of the automobile industry it was predicted that of the three methods of automobile propulsionelectricity, gasoline, and steam-the use of electricity would be limited to short-radius operation, the use of the gasoline engine could not be expanded on account of the limited supply of gasoline, and the automobile of the future would be steam-driven. How far this prediction has fallen short of realization is due in no small part to the contribution of chemistry to gasoline. It is true that we are producing more crude petroleum than formerly, and therefore should be producing more gasoline, but during the last fifteen years, when motor vehicle registration has increased twenty-two times, the production of crude petroleum has increased only three times. It is true again that, owing to various factors, including more efficient fuel utilization, gasoline consumption per car per year is only about half what it was in 1912, but the fact still remains that, as against a 12 per cent yield of gasoline from crude in 1912, the yield last year was 37 per cent and is still climbing. EXTENSION OF BOILING POINT RANGE-It is unfortunately impossible to claim all of this increased yield as a contribution of chemistry. Part of it is due to the fact that the gasoline boiling range has been lengthened to include less volatile compounds. This change was stimulated by necessity and not by chemistry. But even here chemistry has made its contribution in recent years through a study of the vapor pressure and equilibrium vaporization relations and by indicating how far the lengthening of the cut could be carried and the specifications which must be met to insure satisfactory service from such a wider boiling gasoline. RECOVERY OF CASINGHEAD GAsoLIm-The second factor in the increased yield of gasoline is more directly attributable to the chemist and chemical engineer. It consists of the recovery of the very volatile portion of the gasoline which was formerly lost or wasted, the most important single item being the natural gasoline recovered from gas by compression or absorption processes. The natural, or casinghead, gasoline recovered from this source now represents approximately 10 per cent of the total motor gasoline production. IMPROVED FRACTIONATING EQUIPMENT-A third factor, also a chemical and chemical engineering development, is the design and adoption of improved fractionating equipment. With the old type of stills provided with inadequate means for fractionation of vapors, it was necessary to make the cut-out of gasoline earlier than was otherwise required in order to meet the end-point specification. There remained in the crude 2 or 3 per cent of a material capable of being blended into satisfactory gasoline, but which could not be distilled out as a close enough fraction to give the required end point when blended. It has been possible by fractional distillation to include this portion in the gasoline cut. DECREASED REFINERYLossEs-One of the more recent increases in yield, for which the chemist is wholly responsible, is caused by the cutting down of refinery losses. A large
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part of the gasoline production was formerly treated with strong sulfuric acid for the primary purposes of improving the color and odor of the product and of eliminating gummy impurities. The difficulty with the sulfuric acid treatment is that it not only removes the objectionable bodies, but also attacks the unsaturated compounds such as the olefins. These compounds are not only harmless, but on the contrary have been shown to be highly desirable. Attempts to supplant the treatment with strong sulfuric acid, with its consequent high loss amounting frequently to several per cent, have resulted in numerous processes. These include dilute acid treatment, acid treatment a t low temperatures, and a process of treatment with fuller’s earth in the vapor phase. It is claimed that by the fuller’s earth treatment the objectionable impurities are removed with a treating loss amounting to only a few tenths of a per cent and an important resultant saving. This general problem is still an active subject of petroleum research. CRACKING-BY far the largest item in the increased gasoline yield is cracking. It would be fruitless to claim the discovery of cracking as a contribution of chemistry. Probably the still man back in 1861, who left his still and came back several hours later to find that cracking had taken place, hardly knew what chemistry was. At the same time, the chemist and chemical engineer have made cracking a commercial process and have been responsible for the conspicuous success attained by the more modern cracking processes. A large amount of work has been done on the cracking reaction and it has given valuable information on the nature of the cracking produced at different conditions of temperature, pressure, and time. The primary objects have been to set these conditions so as to procure minimum productions of gas and coke with a maximum production of gasoline. Catalysts have also been successfully invoked in order to eliminate the necessity for extreme conditions for satisfactory cracking. As a result of the developments in the science of cracking, the process has become so generally used that it is estimated that in 1927 the production of cracked gasoline in the United States will nearly equal the production of the straight-run gasoline produced by distillation of crude. We can thus see that without the aid of chemistry in increasing the quantity of motor fuel available for automotive transportation it would have been quite impossible for the automobile industry to have reached its present proportions. Chemistry’s Contribution to Quality of Motor Fuel
The contributions of chemistry to the quality of motor fuel have been equally important, I n the early days when most of the gasoline was produced from Pennsylvania crude, when yield was no object, when automobile engines were of low compression, and when the only requirements were color and gravity, quality was a comparatively simple matter. Today these conditions are reversed and the maintenance and improvement of quality demands the application of chemical knowledge. Thus, the production of highsulfur crudes in greater proportion has presented a difficult problem and a glance at the programs of petroleum technical societies will show how intensively chemistry is being called on for its solution. Similarly, the advent of cracked gasoline brought in with it the question of gummy impurities. A few scattered instances of trouble from this source have attracted to this problem rather more than its share of
October, 1927
INDUSTRIAL A X D ENGINEERING CHEMISTRY
attention, and ha\-e glven to cracked gasoline a bad reputation which has only recently been overcome. This distinctly chemical problem of gum is, however, a real one and is likely to become still more important if there is a trend toward higher temperature cracking. The contributions of chemistry to its solution thus far have already been mentioned. REDUCTION OF KNocmm-The most discussed property of gasoline today is its tendency to detonate or knock, and i t is in this field that chemistry has made its most important contribution to motor fuel. This property has become of tremendous importance in recent years on account of the trend in engine design toward higher compression ratios. Detonation has been shown to increase with compression and, whereas the old type of gasoline was satisfactory in the low-compression-ratio engines, it has become unsatisfactory in the modern engine. This condition has been even more emphasized in the airplane engine, in which even higher compression ratios are used. It was observed in the very early stages of the study of detonation that benzene in admixture with the gasoline lowered its tendency to knock. It was also observed that certain other substances, such as aniline, had the effect to an even more marked degree. A search was consequently made for a compound which could be mixed with gasoline in only very small proportions and which would have the effect of so lowering its tendency to knock that it could be used satisfactorily a t much higher compression. The work of Midgley and Boyd iesulting in the discovery of tetraethyl lead is classic. The commercial utilization of tetraethyl lead for high-compression gasoline has already given an a t least temporary solution to the detonation problem. Following the observation that benzene imparted valuable antiknock properties to gasoline, it was observed that gasolines differed from one another in this property, the antiknock quality being largely dependent upon the source. It was observed, for example, that a gasoline produced from typical California crude would withstand a considerably higher compression without knocking than a corresponding straight-run gasoline from midcontinent crude, and was, in fact, equivalent in antiknock quality to a blend of about 25 per cent benzene with this gasoline. It became further evident that cracked gasolines were more valuable in this respect than straight-run. These observations led to an investigation of the detonation properties of the various series of hydrocarbons, the result of which was to show that the straight-chain paraffin hydrocarbons were the worst offenders on knocking, that the olefins and iiaphthenes were much better, and the aromatic hydrocarbons better yet. I n a still more recent and highly interesting piece of work, Edgar has gone even further to show that the isomeric paraffin hydrocarbons vary from one another in this property. The branched-chain octane which he has developed is far superior, even to benzene, in its antiknock quality. The information acquired from the study of gasolines from different sources with respect to detonation has already led to a very marked change in the antiknock quality of gasoline as it is being marketed. For example, omitting fuel containing tetraethyl lead, the average antiknock quality of the commercial gasoline on the Atlantic seaboard on July 1, 1927, was a t least 10 per cent benzene better than that on July 1, 1926. Chemical effort is at present being vigorously directed along the line of producing a gasoline which has in itself a high antiknock value. The cracking reaction seems to hold a means of accomplishing this end. I t has been shown, for example, that by increasing the temperature of cracking
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a larger proportion of the series of hydrocarbons having a high antiknock value may be obtained. On account of this fact the whole subject of vapor-phase cracking a t much higher temperatures than the ordinary liquid-phase processes has been reopened. Before antiknock quality became important, vapor-phase cracking had been practically dropped because of mechanical difficulties and high gas loss, and practically all the commercial processes today are liquidphase processes operating a t temperatures below 925” F. The aim of present investigations of cracking is to produce a gasoline which is not only sufficiently high in antiknock value to enable the automobile manufacturers to carry their compression ratios to their desired limits, probably in the neighborhood of 6 9 , but which will permit the badly knocking straight-run gasoline which will also be produced to be blended with it and still give this desired result. This problem is probably, a t present, the most important for the improvement of the quality of motor fuel. While progress has been made in this direction, v e must look to much greater progress in the future. A 5 a result of the scientific investigation of quality, gasoline is today judged by totally different standards than formerly. Instead of judging gasoline by color, gravity, and doctor test, as formerly, the criteria of quality are rapidly becoming volatility and antiknock value. S u b s t i t u t e s for Gasoline
Probably the most vital problem tor the application of chemistry in the future is that of producing a substitute for gasoline. While there is no immediate prospect of serious gasoline shortage, it is nevertheless certain that the petroleum resources of the world are not inexhaustible and that the time will come when we must have another source of motor fuel to supplement or replace gasoline. This problem, so far, has not been of such vital interest to chemists in this country as it has abroad, particularly in Germany, where several processes for a synthetic motor fuel have already been devised. The most important of these a t present are those of Bergius and Fischer, both using coal as the raw material. The Bergius process consists of a hydrogenation of coal under pressures of the order of 3000 pounds per square inch. He obtains a liquid oil resembling petroleum from which a satisfactory motor fuel may be produced in a yield of about 40 gallons per short ton of coal. His process has already passed the semi-works stage and is operating in Germany in large-scale installations. The Fischer process is an outgrowth of the process for the manufacture of synthetic methanol from water gas. Fischer has found that by operating a t atmospheric pressure and a t lower temperatures in the presence of a catalyst, such as a finely divided iron-cobalt mixture, a reaction takes place between the carbon monoxide and the hydrogen with the formation of a liquid oil consisting principally of hydrocarbons which he has called “Synthol.” The process has not yet been reduced to a commercial scale. While we in America do not need to worry a t present about gasoline substitutes, we should look with a great deal of interest to these developments in Germany, since they constitute the groundwork of the major problem of the motor-fuel chemist for the future. The United States District Court for the Southern District of Texas decided recently that natural gasoline is not patentable as a new product when it differs from other gasoline merely in containing more butane, the difference being in degree only, with a sharp separation of chemical constituents of the gas and a sharp discarding of some of them. The patents in suit have to do with the treatment of raw gasoline to reduce its vapor tension.
