US2395976A - Tractor fuel and process of making same - Google Patents

Description

Patented Mar. 5, 1946 7M. SlEhnull TRACTOR FUEL AND PROCESS OF MAKING SAME Rodney V. Shankland. Chicago. 111.. assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana No Drawing. Application June 20, 1941,

Serial No. 398,947

4 Claims.

This invention relates to an improvement in tractor fuels and more particularly to a method of making tractor fuels by catalytic processes in which light hydrocarbons are converted at high temperatures with solid catalysts and the products are fractionated to the desired boiling range. One object of th invention is to produce a synthesized, heavy, volatile hydrocarbon fuel for use in internal combustion engines of the type employed on tractors, which fuel has less tendency to cause detonation and provides smoother operation of the tractor than do fuels ordinarily available. Another object of the invention is to convert low boiling hydrocarbon distillates into a valuable liquid tractor engine fuel having superior properties, either when used alone or when blended with other tractor fuels having an undesirable tendency toward detonation.

Tractor fuels commonly employed heretofore have been made by the distillation of crude petroleum oil or thermal cracking still products. They have had a distillation range generally overlapping the upper end of the gasoline boiling range and the lower end of the kerosene boiling range, even extending through the kerosene boillng range. Engines employing these fuels ordinarily operate at a higher temperature than gasoline engines and at a lower compression ratio, e. g., 4:1, although the compression ratio may be as high as 5:1 or 5%:1. Unlike solid injection engines, these tractor engines vaporize the fuel before ignition. For this reason the distillation characteristics of the fuel are quite important.

Tractor engines using this fuel operate with a high intake manifold temperature as a result of which they are not adapted to burning gasoline because of excessive thermal expansion which has the effect of throttling the engine. Thus, the intake manifold temperature of the tractor engine under avera e load conditions is typically in the range of 250 F. to 300 F. whereas a gasoline engine operating under the same load conditions will have an intake manifold temperature of only about 180 F. The manifold temperature of the tractor engine is consistently about 50 to 100 F. higher than that of the gasoline engine.

Recently, there has been developed for tractor engines a special fuel, herein called light tractor fuel. which is characterized by a relatively low initial boiling point and low distillation point but having about the same maximum boiling point as tractor fuels heretofore used. Following are typical A. S. T. M. distillation ranges for heavy and "light tractor fuels of the types heretofore used:

Heavy Light fuel fuel specification F. Initial boiling point 215 67 F- (minimum). 10% off 372 210 F. (maximum).

419 284 F. (minimum).

472 460 F. (maximum). End point 506 510 F. (maximum).

In one example such a heavy" fuel had an A. P. I. gravity of 42.6, an open cup flash point of 93 F. and sulfur content of about 032% to .05%. The knock rating of this fuel by the regular A. S. T. M. motor method was about 37.1 octane number. The specification for the light fuel just described also includes an octane number of at least 40 A. S. T. M. and an octane number of 50 to is frequently desired for more recent designs of engines running at higher speeds, for example. 1500 R. P. M. instead of 800 R. P. M. previously.

I have now discovered that I can prepare, by catalytic conversion methods applied to petroleum distillates, a superior tractor fuel having a much higher octane number and also a higher boiling range and lower A. P. I. gravity than tractor fuels heretofore employed. In making this fuel I prefer to convert the heavy naptha fraction of crude petroleum. The crude petroleum fraction or virgin naptha employed may have a distillation range of about 250 F. to 450 F. Considerable variation in the boiling range is permissible, however, and I may employ naptha stocks having an end point within the gasoline boiling range, for example, about 400 F., or I may employ somewhat higher boiling napthas, boiling up to about 500 F. Another naptha suitable for this purpose may have a boiling range of 300 F. to 425 F. In general, fractions boiling at least largely within the range from 250 F. to 450 F. are most suitable.

The catalytic operation is generally carried out by first vaporizing the naptha and conducting the vapors at conversion temperatures of the order of 850 F. to 1050 F. in contact with a catalyst, usually of the dehydrogenation type. For this purpose I may use a catalyst composed essentially of an oxide of a metal of the left column of the VIth group of the periodic system. preferably in combination with active alumina, although the oxide of vanadium and oxides of other metals of the left columns of the IVth and Vth grou s may also be u ed alone or in combination with each other. Molybdenum oxide and chro ium oxide are verv effective and their effectiveness is enhanced by alumina used as a su port. The With group metal oxide is preferably present in a minor proportion in the mixture. for exam le. 2 to 25%. The catal st may be made by impregnating activated bauxite or active alumina or ma nesia with ammonium chromate. ammonium molybdate. chromium nitrate or other suitable. salt and subseouently heating the catalyst mixture. The catalyst may be employed in the form of a powder or in ranular form. either suspended or maintained in a porous fixed bed through which the naptha. vapors are passed.

In processing na'p a I prefer to maintain a hydrogen pressure with n the catalyst zone and this may be. accom lished .bv l' ixin hydro en with the na'otha va ors entering the reaction chambe or by adding super ea ed r en directly to the react on chamber. H dro en for th s ur ose. may be obtained lar el f om the hydro enmws ases produced in the proc ss and if desired t se bvdro einnus ga es conta ni g about 40 to 80% of hydro en by vo ume may be dire tl recvoled fr the as Senar tm' o t e reac i n c amber, The pressure emnloved in the reac on chamber will preferab y be of the order of 50 o 450 p unds per souar inch and the amount Of hy ro en is meierahlv about 1 t 3 mole per mol of naphtha h drocar on treated.

The hydrogen pressure is insufilcient to effect hydro enation of the hvdrocarbon products and the react on occurrin a pears to he one of dehydro enat on accompanied by olyme zation and con e sa ion of t e nt rmedi te roducts to hi her boilin hydrocarbons suitable f r tractor fue s. The. rate of contact ng the na tha vapors with the catalyst is preferably about 0-2 to volumes of l ould naotha per hour p r apparent volume of catalyst (0.2 to 10 V. H. V).

As a specific exam le of catal tic nantha conversion. an East Texas strai ht run heavy naot a was subjected to the action of a catalyst containing about 10% of active molvbdena on active alumina. The na'otha feed has approximately the following characteristics:

The temperature in the reactor was 930 F. to 990 F.. vary ng somewhat with the age of the catalyst. About 2% of tractor fuel was obtained in this operation having the following characteristics:

Gravity-A. S. T. M 12 Initial boiling point F.. 430 10% .F' 461 90% F 566 After the reaction has proceeded for a period of time. generally from 1 to 20 hours. the catalyst activity is diminished by the deposition of carbonaceous matter thereon. It is accordingly desirable to divert the hydrocarbon vapors to another catalyst chamber and regenerate the spent catalyst by blowing with air or oxygen-containing gases to remove carbon by combustion. The temperature of regeneration is preferably kept below 1200 F. and generally in the range of 1000 F. to 1100 F. After regeneration the catalyst is ready for reuse and this regeneration may be repeated almost indefinitely.

The products from the catalytic operation are separated by fractionation into gas, gasoline and higher boiling synthetic fuel fractions. The heavier fractions boiling above the gasoline boiling range constitute about 2 to 10% of the naptha charged to the process. This material may have a boiling range of about 400 F. to 600 F. but the boiling range may be narrowed by redistillation to about 425 F. to 550 F. This fraction may be used directly as a tractor fuel but it is preferred to blend it with other stocks especially stocks boiling in a lower distillation range, the amount of such other stock being about 25 to of the blend. Stocks suitable for this purpose may be virgin or cracked kerosene or virgin heavy naptha. One of the characteristics of the polymer fraction is its very low A. P. I. gravity or high density which may equal or even exceed the density of water. A. P. I. gravities of 9.5 to 12 are readily obtainable, and the gravity is generally in the range of about 10 to 20 A. P. I. The high density of this fuel corresponds to a higher weight per gallon which is especially desirable for tractor operators who purchase the fuel on a volume basis. Accordingly, this fuel provides the tractor operator with a larger actual amount of fuel or power per gallon simultaneously with increased knock resistance which increases the smoothness of tractor operation.

Following are typical distillation inspections for my synthesized tractor fuel:

The refractive index of the above unblended fuel was 1.583 and the A. P. I. gravity 12.2.

One of the characteristics of my synthetic tractor fuel is its high blending value which means that when blended with ordinary tractor fuels, it improves the knock rating of that fuel to a higher degree than would be expected from the amount employed on a straight proportional basis. The following table shows the results obtained:

Octane numberA. S. T. M. ordinary tractor fuel 37.1

' 90% ordinary tractor fuel plus 10% syn- 100% synthetic tractor fuel 90 The knock rating of my synthetic fuel is above 80 and generally between 80 and A. S. T. M.

ing my relatively heavy synthetic tractor fuel with lower boiling fractions of the ordinary tractor fuel heretofore employed. Thus, a light fraction was made by distilling oil. 60% from ordinary tractor fuel. When this was blended in the ratio of 90 parts to parts of synthetic tractor fuel, the knock rating A. S. T. M. was increased from 41.9 to 48. When blended in the ratio of 80 to 20, the knock rating, the A. S. T. M., of this same light tractor fuel was increased to 54. In another example, blending 20 parts of the synthetic fuel with 80 parts of a Mid-Continent virgin heavy naptha increased the knock rating, A. S. T. M., from 25.5 to 43.2. All ratios given here for blending are in parts by volume.

The blended fuel obtained in this way has a wide boiling range which includes those light constituents of the virgin fuel having the best knock rating and the heavy high knock rating constituents of the synthetic fuel. As a result, I obtain more uniform performance with this fuel under engine operating conditions where segregation of the fuel occurs due to partial vaporizaproximately that of heavy naptha and about;

10 to per cent of a synthetic hydrocarbon polymer fraction having a higher boiling range than the boiling range of said naptha prepared by contacting a petroleum naptha at conversion temperature in the presence of added hydrogen; with a dehydrogenation catalyst and recovering from the product a polymer fraction boiling in the range of about 400 to 600 F. with an A. P. I.

gravity of about 10 to 20, and a knock rating above about A. S. T. M.

2. A light tractor fuel as described in claim 1 further characterized in that the finished tractor fuel has an initial boiling point of about 356 F. and a maximum boiling point of about 520 F.

3. The method of preparing a tractor fuel of high knock rating which comprises blending with a low knock rating heavy petroleum naptha boiling substantially within the gasoline boiling range about 10 to 40 per cent of a synthetic polymer fraction boiling in the range of about 400 to 600 F. with a gravity of about 10 to 20 A. P. 1.. derived from the conversion of a heavy petroleum naptha by contact with a dehydrogenating catalyst at conversion temperature and in the presence of added hydrogen.

4. The process of claim 3 wherein said heavy petroleum naptha is characterized by. a knock rating of about 25.5 to 42 A. S. T. M.

RODNEY V. SHANKLAND.

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