The demands of the omnivorous motorist are still far from satiated and, on top of that, aviation demand for motor fuel has grown apace. Obviously, the question of supply is highly impor tant to civilian and military aviation. In 1928 aviation gasoline was so-called straight-run gasoline of high volatility. That is, it was a regular refinery gasoline produced by straight refining and possibly by the addition of high-volatility natural gasoline. Little attention had been paid to anti-knock value, which then was in no way standardized. That year the U.S. Army Air Corps asked petroleum refinery technicians to develop a fuel of high and standardized anti-knock value. If they could obtain it in sufficient quantities, they said they could develop substantially increased power from the same sized gasoline engines then in use. They issued specifications for anti-knock gasoline of 87 octane number by existing methods of test. The petroleum refiners suc ceeded in developing the fuel, and before long U.S. military planes were giving outstanding demonstration of improved flying speed, take-off and climb, and attracting the envious attention of commercial aviation, which demanded its quota of high octane number aviation fuel. Within a few years fuel of standardized anti-knock quality ranging from 70 to 87 octane-number was available to them. This made aviation history—the establishment of long-distance commercial flying routes, the spanning of contin ents and oceans. By 1936 the power output of aircraft engines was increased a third or more due to the availability of this fuel. Not only was power output increased but fuel consumption was decreased. In other words, less fuel had to be carried, and load-carrying capacity could be increased—essentials for long distance commercial flying.
The chemists and refinery engineers did not stop with 70 and 87 octane-number motor fuel, but embarked on an era of new com mercial and experimental processing for high quality fuel, the like of which had not been seen in the petroleum industry since the early days of cracking development and expansion. From 87 octane-number, fuels of 95 and loo octane-number for military purposes were developed, and enough produced to give commercial aviation a taste of them. The development of iso-octane, an almost pure hydrocarbon, added to leaded gasoline, raised octane ratings to '00. Without this super-type motor fuel, cruising speeds of aeroplanes would have remained at from 8o to ioom.p.h. as they were in 1925, instead of 200 and 220m.p.h. attained in 1938.
It is estimated that from $25,000,000 to $35,000,000 annually have been spent in America in research and development on the processing side of petroleum refining. Catalysis and synthesis have been the instruments chiefly used, with attention concen trated on more economical production of high octane-number motor fuel. Such processes as polymerization, hydrogenation and other methods of synthesis for obtaining not only superior products for established uses but also important by-products in the chemical field, have come into more or less commercial usage. More actual production of high quality motor fuel, as well as enor mously expanded potential yield, became an accomplished fact.
The polymerization process came into use in the early 193os.
It catches petroleum refinery gases, formerly largely wasted and blown away, and converts them into liquid form. This process is the reverse of cracking. Whereas cracking breaks down the heavier molecules of fuel oil into the lighter ones of gasoline, polymeri zation combines the smaller molecules of certain gaseous by-prod ucts of refining into the chemical components of motor fuel. Installations have been rapid, and polymer gasoline may ultimately vie with cracked gasoline in volume. The hydrogenation process originated in Europe, and was technically perfected in the United States. Its effect was to lend a considerable flexibility to refining, making possible an amazing manipulation of molecular groups. It is also possible by hydrogenation to convert coal and shale into motor fuel. In 1938 announcement was made in the United States of the Houdry catalytic cracking process for petroleum refining, together with the fact that $35,000,000 would be spent in building commercial units, and that this process would be licensed generally to the entire petroleum industry.
This process apparently opened the way for large quantity sources of high octane-number aviation fuel, and caused it to be stated that not since the cracking process first came into use had there been such a change promised in the potential output of motor fuel. The process adds a catalyst in the cracking operation. In 1937-38, 7,00o,000gal. of aviation gasoline were produced by the process. The yields given showed that 33 or 34gal. of gasoline may be taken from a 42-gallon barrel of crude oil. This compares with the 1938 gasoline yield by all methods from American refinery operations of r 8 z gallons. Tests indicated that the octane-numbers of the gasoline produced by the process were somewhat higher than on gasoline produced by ordinary thermal cracking of similar oils. The finished aviation gasoline, it was revealed, would be approximately 87 to 92 octane-number, and, when used for blend ing with usual anti-knock agents, i 00 octane-number fuel, after addition of tetraethyl lead, would be produced.
In 1938 it was announced that isopropyl ether could be mixed with leaded aviation gasoline to form a fuel that could be made available in sufficient quantities for all commercial needs. Further more, a fuel with the proper concentration of this new blending agent could go right through the "ceiling" of commonly accepted methods for anti-knock measurements should there be a call for fuels above the i oo octane rating. Then in 1939 another develop ment in the field of super-fuels was the announcement in the United States of a process called alkylation, which uses waste refinery gases to make curly molecules of hydrocarbon. In the presence of sulphuric acid, it combines an olefin, or non-satur ated hydrocarbon such as butane, with a saturated branch-chain hydrocarbon like iso-butane, to produce a blending agent much like iso-octane. Thus, alkylate has been added to the list of blending agents. In view of these developments, it was generally accepted that ioo octane fuel, once considered the "gold stand ard" of aviation gasoline, had become generally available in commercial quantities.