became possible through the» action of :i catalyst a substance which will greatly accélérâte a reacti«»n without itself changing. Although a catalyst can be anything, each reaction can be stimulated only by a specific substance, and most of the time of the chemists who tried to solve the aviation gasoline problem \v:is spent searching for the substances which cause hydrocarbons to condense. Hundreds of catalysts and their actions on various hydrocarbons were studied in the laboratories, and out of this work came the simultaneous discoveries of polymerization and alkylation. A short time later another important reaction was discovered—isomenzation—in which any straight-chain hydrocarbon could be changed into its isomeric form. This has become an extremely important reaction in the production of aviation gasoline. Each of these reactions uses different catalysts; some reactions can be stimulated by several catatysts. One of the most important of these, that used in polymerization, is the solid phosphoric acid catalyst developed by the Universal Oil Products Co. Its importance can be best judged by the following facts: In the United States the thermal cracking process produces 300 billion cubic
feet of \v:iste gas yearly containing up to 20 per cent unsaturated hydrocarbons which, by t h e help of catalytic polymerization, can be converted into polymer gasoline of octane number 82. Several scores of petroleum refineries in the United States are producing polymer gasoline in quantities of several million barrels a year from these waste gases. This is *not only a tremendous economy over the old practice of burning the gas to get rid of it, but a great step forward in the motor fuel problem. A t the present time methods are being developed whereby the gasoline produced by polymerization may be converted into high aviation gasoline of octane numbers over 100. As mentioned before, aviation gasoline is also obtained by the alkylation of paraffins and olefins in the presence of various catalysts. The discovery of this reaction in the United States had a great scientific as well as practical significance and amazed the entire chemical world. Previously i t had always been assumed that paraffins, the most inert of all organic substances, could not react with other hydrocarbons, and it was not until certain catalysts were found that the "impossible" was performed and paraffins were combined wit h olefins. Now tens of thousands
of barrels of gasoline of octane numbers between 90 and 100 are produced daily by this method. In such a short article the development of catalytic reactions in the petroleum industry cannot be outlined. Those who wish to acquaint themselves with t h e subject should refer to the article on "The Problem of Rational Utilization of Petroleum ami of Petroleum Distillates" The speed with which American industry has been able to take these reactions and almost overnight put them t o work on a large scale is indeed amazing. These feats owe a* much of their success to America's highly developed engineering technique—the best in the world—as to her creative inventiveness; and in t h e history of the petroleum industry, America's contribution will stand out as one of the greatest and most important. T h e fact that we are at war multiplies the value of these processes a hundredfold for it will be on our aviation gasoline that t h e Allies will fight—and win—this war. Literature Cited
(1) Ipatieff, V. N.. Proc. Am. Petroleum Inst., Sect. Ill, 17, 13-16 (1936).
Cracking J. Β Ε Ν Ν Ε Π H I L L , Sun O i l Co., 1608 Walnut St., Philadelphia, Penna. /"^RACKING, in the petroleum industry, ^_>^ may be dennc»d as the breaking down of the hydrocarbon molecules into smaller ones, with attendant polymerization and other side reactions. The science of cracking is distinctly an American development and its commercial application an American achievement. When cracking by heat was first recognized, its only commercial significance was as a possibility of producing more kerosene from crude» oil. Cracking was stimulated by the advent of the automobile and a consequent commercial demand for gasoline, but it was not until World War I that it acquired any considerable commercial importance. The first commercially sucées*·fui cracking stills, operated by W. M. Uurton at Whiting, Ind., were simply batch stills, throttled so that they could be operated under pressure. Cracking was therefore a thermal reaction taking place in the liquid phase. As petroleum distillation became a continuous instead of a batch process in the early 1920's, cracking followed the same course and cracking stills became a combination of pipe still, pressure reaction chamber, and fractionating tower. The Cross, Dubbs, Holmes-Manley, tube and tank, and other processes developed during this time were all combinations of the same essential
1368
elements b u t differed widely in engineering design. The success of these processes established cracking as a practical and essential procedure for making gasoline and marked the first major period of the development — a period of liquid phase thermal cracking. During this first period the production of cracked gasoline increased from 1,500,000 barrels during 1914, or 5 percent of the total gasoline produced, t o 122,000,000 barrels in 1928, or 3 2 per cent of the total gasoline. But it was only during the latter part of this period that it was realized «Tacked gasoline was something more than an additional quantity of a n inferior product, that it had in fact the advantage over straight-run gasoline of what we call today higher "octane number". This realization brought cracked gasoline o u t of the red-headed stepchild class, washed its face, and sent it t o school to learn to be an even better boy. Out of this realization of the possibility of better octane numbers through cracking came the side-by-side development of the highcompression, high-economy automobile engines and the high-octane gasoline t o operate them. There was ushered in t h e second phase of cracking development, a development for quality and not for quantity alone. Although the first phase of cracking
CHEMICAL
development was largely engineering, the quest for quality in the second phase has been largely a matter of chemical research, followcnl by engineering. Since research showed that high temperature favored the production of better octane fuels, the first steps were to raise the temperature of the liquid phase processes or to go beyond them and crack at high temperature in the vapor phase as had been done during World War I to produce aromatics. T h e most important commercial processes resulting from the vapor phase idea are the deFlorez and Gyro processes, the latter being an outgrowth of the earlier Ramage process. While the vapor phase processes produced a higher octane product they also gave a product rich in unsaturated hydrocarbons and suffering thereby in stability. Most of the development in recent years has been along the line of catalytic cracking. By means of suitable catalysts the desired reactions have been made to progress at lower temperature and the effect of the undesirable high-temperature reactions has been minimized. Using an alumina-silica catalyst made either by activation of a natural clay or synthetically, a cracked product is produced which is low in normal paraffins, high in isoparaffins and aromatics, and low in olefins. Such a product has excellent octane num-
AND
ENGINEERING
NEWS
bers. T h e f i r s t s u c h c o m m e r c i a l process of catalytic cracking is the Houdry process in which the heavy hydrocarbon vapors are passed through a fixed bed of the catalyst, beds being alternately regenerated by blowing with air. Although Houdry is himself French-born, the process has been developed in this country. I t is being used extensively at the present time. More recently new processes of catalytic cracking have been developed which make the operation entirely continuous. The fluid catalyst process suspends the finely divided solid catalyst in the vapor stream and later separates it, regenerates it, and returns it. The Thermofor catalytic process uses a catalyst bed which moves downward through a tower, the catalyst
being continuously removed from the bottom for regeneration. Although no substantial commercial experience on
these processes is yet available, extensive commercial installations are beiiirf made. The gasoline from all of the catalytic processes may be retreated with catalysi, resulting in virtual elimination of the olefins and increase in the aromatics. For many years cracking, by one method or another, has been used on a comparatively small scale to make certain special products other than gasoline, as, for example, ethylene or aromatics. Recently the dem a n d for i s o b u t a n e , butènes, and butadiene has focused attention on these other materials. The wide cracking knowledge and e x p e r i e n c e possessed by technical men in this country are making the solution of these problems immeasurably easier.
Nitroparaffins Η . Β. Η ASS, Purdue University, Lafayette, Ind. T ^ H B first nitroparaffin was reported in 1872 by Meyer and Stiiber who reacted amyl iodide with silver nitrite. Eight years later Beilstein and Kurbatov treated a heptane fraction with nitric acid in liquid phase and obtained a mixture of isomeric nitroheptanes. In the half cen tury between 1880 and 1930 numerous investigations were carried out in Russia,
VOLUME
2 0, N O .
Germany, and the United States to dis cover a method of utilizing this reaction for the commercial production of nitro paraffins, but in spite of approximately six thousand literature references on the aliphatic nitro compounds, none had reached commercial production. In 1930 work was started at Purdue on the assumption that isobutane, the
21-NOVEMBER
10,
1942
nitration of which had not been reported, might, because of its unique structure— nine relatively unreactive primary hydro gen atoms and one easily sμbstituted tertiary hydrogen—make it possible to obtain better yields of mononitroparafnn than had resulted from the other alkanes. Reaction was slow until the critical tem perature of isobutanc had been exceeded.
1369
