US2413262A - High-compression motor fuel - Google Patents

Description

Patented I? 1946 HIGH-COMPRESSION MOTOR FUEL Robert I. Stir-ton, Redondo Beach, Calif., assignor to Union Oil Gompany of California, Los Angeles, Califi, a corporation of California No Drawing. Application May 10, 1943, Serial No. 486,433

6 Claims. 3

This invention relates to the production of motor fuels, especially aviation gasolines, having unusual anti-detonating properties as well as stability against separation of solid material at very low temperatures.

It is well known that a gasoline of low antiknock value may be improved by the addition of a knock-suppressing additive such as tetraethyl lead, or by modification of its composition, for example, by cracking it to increase its content of aromatic-type and/or olefinic-type hydrocarbons, or by adding these hydrocarbons to the gasoline. In attempting to produce gasolines of relatively high anti-knock quality by combining these effects, however, i. e., by the use of both tetraethyl lead and olefinic and/or aromatic-type hydrocarbons, it has generally been found that the presence of such hydrocarbons reduces the efiectiveness of the tetraethyl lead markedly, so that gasolines containing moderate amounts of both tetraethyl lead and olefinic and/or aromatic hydrocarbons, for example, may even be of no lng, particularly when the gasoline is of relatively' low anti-knock quality and contains no additives such as tetraethyl lead. Such amines behave as super-aromatics in that they are generally many times as effective as the corresponding aromatics, but the prior art shows that they frequently have similarly harmful effects on lead susceptibility, or response to the addition of tetraethyl lead, and therefore have been considered of little value for use in gasolines of high anti-knock rating containing moderate to large amounts of tetraethyl lead. For example, it is shown in U. S. Patent No. 2,230,844 that when 2% of various primary amines were added to an aviation gasoline containing no tetraethyl lead and having a C. F. R. motor method octane number of about 85, the octane number was increased in all cases by about 2 to 7 points; whereas when the same amounts of the same amines were added to the same gasoline containing 2 ml. of tetraethyl lead per gallon and having an octane number of about 97, the octane number was actually reduced in most instances, the reduction amounting to nearly 2 points in three of the eight examples shown.

I have discovered that contrary to expectations based on the above described earlierobservations, the addition of small amounts of primary aromatic amines to aviation-type gasolines of -extremely high anti-knock value and containing relatively large amounts of tetraethyl lead has definitely beneficial effects on their anti-knock characteristics. Furthermore, even more unexpected improvements in anti-knock quality may be realized by the inclusion of aromatic hydrocarbons in the amine-containing blend, provided that the aromatics are present in at least a critical minimum concentration. Secondary aromatic amines have also been found to exhibit the same phenomena as the ',primary aromatic amines. It has further been discovered that the presence of both aromatic amines and aromatic hydrocarbons in the same gasoline has another beneficial efi'ect, i. e., the aromatic hydrocarbons tend to lower the "compatibility temperature" of the gasoline, as brought out below.

Since motor gasolines may be used at extremely low temperatures, as in arctic climates or at stratospheric temperatures in the case of aviation gasolines, it is necessary that they remain homogeneous mobile liquids at these low temperatures as well as at normal atmospheric tem peratures, to prevent plugging of lines, filters, etc., and to prevent loss of desirable ingredients. It has been found that many gasolines, on being subjected to low temperatures in the region of -50 F. to F., will exhibit a lack of compatibility," i. e., will show separation of substantial amounts of a second phase, usually a solid, sometimes crystalline in appearance. There is usually a fairly well defined temperature above which the gasoline will remain substantially homogeneous, but below which there may be a definite separation of a second phase, and this temperature is what is referred to herein as the compatibility temperature. It has been discovered that gasolines containing certain amines, as well as those containing certain aromatics, and those containing certain combinations of amines and aromatics, have exceptionally low compatibility temperatures. It is an object of this invention therefore to provide motor fuels containing certain amines and having exceptionally low compatibility temperatures. It is another object of this invention to provide motor fuels containing certain amines and having exceptionally good anti-detonation characteristics as well as exceptionally low compatibility temperatures.

According to this invention, gasolines of good anti-detonation characteristics, containing substantial amounts of isoparafiinic hydrocarbons, as well as tetraethyl lead and aromatic amines, are improved both in increased anti-detonation auasea characteristics and in lowered compatibility temperatures by the addition of aromatic hydrocarbons. The most suitable amines, aromatic hydrocarbons, gasoline blends, test methods, etc., are described in the following paragraphs.

The amines useful in this invention are those of the following type:

in which R1 to Rs inclusive are hydrogen or phenyl or saturated alkyl hydrocarbon groups. In order to provide for low compatibility temperatures as well as reasonable volatility, those amines containing at least '7 and preferably between about 7 and 12 carbon atoms are preferred. Among the most effective of these in improving the anti-knock quality of gasolines, are cymidines, cumidines, xylidines, and N methyl aniline. Formulas of the last named amine and of one isomer of each of the first three follow:

H II C-C-CH;

CH3- H I II C CH3 x C C HC 11 x liC CCH a H H HO OH I II I EC H 4 H I 1! 1110-0 CH CH: H 00H, HC on N N N N [I H H H H H H CH: Cymidine p-Cumidiuc 2,4 Xylidinc N Methyl aniline ness in maintaining low compatibility temperatures. It has also been observed that for aromatic amines having alkyl substituents containing 3 or more carbon atoms, the branched chain isomers'a'repreferable. For example the cumidines are preferable to the n-propyl amino 66 benzenes.

Mixtures of aromatic amines or amine isomers may be employed and are frequently more desirable, especially from a compatibility temperature standpoint, than a single isomer. effective material is a mixture of amines prepared by nitration of aromatic hydrocarbon concentrates followed by reduction of the product. In one instance such a concentrate was prepared by solvent extraction of a California crude gasoline fraction boiling in the range of about 270 to 360 F. This concentrate contained about 70% aromatic hydrocarbons having about '7 to carbon atoms and about 30% of naphthenic and parafiinic hydrocarbons, In another instance an aromatic hydrocarbon concentrate was prepared by catalytic reforming of a 200 to 260 F. boiling range fraction from a California crude at a temperature of about 950 F. in the presence of about 5000 cubic feet of hydrogen per barrel of liquid feed, employing a molybdic oxide on alumina catalyst; separating from the product a xylene fraction boiling in the range of about 270 to 290 F. and containing about 82% aromatic hydrocarbons, preponderantly xylenes, and less than about 5% of oleflns. Nitration of this frac 'tion; followed by reduction of the product as desaturated alkyl side chains, and contain at least '7 carbon atoms, and preferably from '7 to about 10 carbon atoms in the molecule. These include toluene, the xylenes, mesitylene and other trimethyl benzenes, ethyl benzene, cymene, cumenc, etc., or mixtures containing such hydrocarbons, such as aromatic hydrocarbon concentrates prepared by solvent extraction of naphtha. Aromatic hydrocarbon concentrates obtained from the products of certain types of cracking processes such as the catalytic hydroforming operation described above are also suitable in many instances, particularly if they contain no diolefins, less than about 0.05% sulfur, and a very low olefin content, such as less than about one-tenth the aromatic hydrocarbon content. The product described above is especially suitable for the purposes of this invention. Such products differ from typical cracked gasoline, since it is usually necessary to have hydrogen introduced into the catalytic reforming unit, and/or to treat the product with hydrogen, sulfuric acid, clays, etc., to remove excessive amounts of. olefins and sulfur compounds, which must not be present in the gasolines of this invention.

In the aromatic hydrocarbons, as well as the amines, there is also a wide variation in the effectiveness of the various isomers. Among the three xylene isomers, for example, the metaand paraisomers are most effective in enhancing the anti- A very e0 to asoline.

knock qualities of the gasolines containing the aromatic amines, but the metaand orthoisomers, especially the,meta-, are most effective in reducing the compatibility temperature of the Also the aromatics having branched chain substituents are in general preferable to the corresponding aromatics having the substituent carbon atoms in a straight chain.

The motor fuels of this invention are those of any conventional type which have octane numbers by the well known A. S. T. M. or C. F. R. motor method of about '75 or above, and are therefore suitable for use in high compression internal combustion engines. The invention is particularly applicable to aviation gasolines having anti-detonation characteristics equal to or superior to those of pure isooctane (2,2,4-trimethyl pentane), such as for example, the 100 octane gasoline of commerce. It is desirable that these motor fuels be resistant to deterioration in storage under severe conditions, and this requirement not only prohibits the presence of more than traces of diolefins or any substantial amounts of olefins, as described above, but also frequently makes desirable the inclusion of a small amount of an antioxidant, such as the conventional amino-phenols, etc. These motor fuels must also have certain volatility characteristics, for example, a Reid (A. S. T. M. method B32342) vapor pressure between about 5 and 12 pounds distillation range of about 80 to about 450 F.

and preferably about 100 to about 350 F. It

is preferred that they contain an anti-detonant such as tetraethyl lead. The latter may be employed in substantial amounts, such as 1 to ml. or more per gallon, preferably about 2 to 4 ml. per gallon. They generally contain large amounts of isoparaffinic material such as isopentane, isooctane, alkylate, etc. Their content of normal paratllns should be low, but there may be moderate amounts of naphthenes especially alkylated naphthenes, present as well as the aromatics described above. The anti-knock ratings of the preferred gasolines of 100+ octane num'- ber may be determined by the so-called AFB-3C rich mixture method described in U. S. Army-' Navy Specification AN-VV-F-748a.. This method utilizes commercial isooctane (S 2 reference fuel) containing tetraethyl lead as a basis for' compari: son, and the knock-rating is reported as the ml. of tetraethyl lead required to be added to the 8-2 reference fuel to match the anti-knock quality of the gasoline in question.

Since, as mentioned above, it is desirable that the gasolines of this invention remain homogeneous at all times prior to actual vaporization and combustion, it is desirable that they have low compatibility temperatures, uch as below about 50 F. and preferably below about -'76 F. The compatibility temperature may be determined by chilling a 20 ml. sample of the gasoline contained in a vacuum jacketed test tube provided with a mercury-sealed stirrer and protected from atmospheric moisture by use of a calcium chloride filled- ,drying tube, reducing the temperature at a rate of about 4 F. per minute until a temperature of -110 F. is attained, or a substantial separation of a second phase (usually a solid) takes place, then holding this minimum temperature constant for 20 minutes, and finally allowing the temperature to rise at a rate of about 1 I. per minute until substantially all of the second phase is redissolved. The mixture is stirred continuously throughout the test. The temperature at the point of substantially complete re-solution is taken as the compatibility temperature, since it has been found that super-cooling normally occurs before the separation of second phase occurs during the chilling.

It has been found possible to correlate this compatibility temperature, for the gasolines of this invention, in a general way although not rigorously, with the melting points of the added amines and aromatic hydrocarbons, higher melting points generally leading to higher compatibility temperatures. For example, blends containing meta-xylene and the amines derived therefrom have much lower compatibility temperatures than blends containing para-xylene and 3,4-xylidine. This agrees with the melting point data, since 3,4-xylidine has a melting point of +50 C., while the melting point of the mixed meta-xylidines is below ,50 C.; and similarly para-xylene has a melting point of +13 C., while meta-xylene melts at -54 C. On the basis of solubility, therefore, those aromatic amines and aromatic hydrocarbons of this invention which have low melting points, such as below about 15 C., and preferably below about 50 C. are preferred. These may be separated from the less desirable materials of higher melting point by selective crystallization of the latter and recovery of the desired non-crystallized material by conventional methods.

Inthe preparation of the gasolines of this invention, the above described amines are used in concentration of about 0.5% to about 15% or more, preferably about 1% to 5%, in the finished gasolines, which are blended to conform to the above requirements. In order to obtain the enhanced anti-knock value of the amines in the presence of the aromatic hydrocarbons described, the latter must be present in a concentration greater than a critical minimum value of about 5%, and are preferably used in concentrations above about 9%. Percent as used herein refers to percent by liquid volume at room temperature.

As specific examples of the enhanced antidetonation tendencies of gasolines containing the amines and aromatics specified in this invention, a series of basic aviation-type blends containing various amounts of aromatic-type hydrocarbons was prepared. These blends contained 22% of isopentane, 18% of California straight-run gasoline heart out containing about 5% of aromatictype hydrocarbons, and 60% of mixtures in various proportions of alkylate and the above-described aromatic hydrocarbon concentrate prepared by solvent extraction and containing about 70% of aromatics. Boiling ranges of the heart out and alkylate were approximately 100 F. to 225 F. and 100 F. to 300 F. respectively, and the alkylate was'obtained by a conventional alkylation of isobutane with butenes and pentenes in the presence of concentrated sulfuric acid. Four such blends were prepared by varying the propor;

tions of alkylat and aromatic concentrate so as 'to obtain products containing 1, 5,- 11, and 15%,

of aromatics respectively. These four contained no aniline, and a similar series of four was prepared with 3% of aniline added. All eight gasolines were leaded with 4.0 ml. tetraethyl lead per gallon and tested by the AFB-'30 rich mixture method. The following knock rating data were obtained:

3% aniline No aniline added added These data show that aniline is effective in this fuel even in the absence of an appreciable quantity of aromatics, but that its effect is remarkably enhanced when the concentration of aromatics is over about 5%, and preferably over about 9%.

Other primary and secondary aromatic amines were similarly effective in blends similar to those above containing about 15% aromatics. For example 3% of commercial mixed xylidine isomers (predominantly meta-xylene derivatives, with no ortho-xylene derivative) raised the knock rating from 0.4 to 2.4 ml.; 3% of cumidine isomers prepared from commercial cumene by nitration and reduction raised the 'knock" rating from 0.4 to 2.0; 3% of the mixed products obtained from the above 70% aromatic hydrocarbon concentrate by ntiration and reduction also raised the knock rating from 0.4 to 2.0; 3% of the mixed product from nitration and reduction of the 82% xylene concentrate above was similarly efiective; and 3% the knock rating from 0.4 to 1.0. Similar efiects may be obtained with tion gasoline.

individual alkyl-substituted aromatic hydrocarbons of this invention, such as toluene, mixed xylenes, cumene, etc. Different amounts such as about 1% of these amines and about 5% of the aromatics, were also efiective. All of the above blends of this paragraph had compatibility temperatures below about 50 F., the blends containing meta xylene or cumene having compatibility temperatures below -76 F. and exhibiting unusually good anti-detonation properties.

The process of nitration and reduction used in converting aromatic hydrocarbon concentrates to amines may be exemplified by the following procedure which was used with the above 70% aromatic concentrate. A similar procedure was employed for the 82% xylene concentrate obtained from the hydroforming operation described earlier.

To a mixture of 2100 ml. of concentrated (96%) sulfuric acid and 1200 ml.'of glacial acetic acid, cooled to about 20 F., was-added 3600 in]. (about 3000 g.) of the 70% aromatic concentrate. This mixture was cooled to about 0 F; and maintained between 0 F. and F. while adding slowly with vigorous agitation a mixture of 1050 ml. of concentrated (70% nitric acid and 2100 ml. concentrated (96%) sulfuric acid. This product mixture was then kept cold while diluting it with water sufiiciently to prevent further reaction and to permit separation into two layers, a lower aqueous acid layer, andan upper layer which consisted ,of the crude nitro-aromatics containing unreacted oil and some products of side-reactions. Half of this upper layer was reduced by adding it to 1000 g. of water, and 200 g. of concentrated (37%) hydrochloric acid, and refluxing the mixture at 180 F. to 190 F. while slowly adding 2000 g. of iron. Agitation was continued for about 45 minutes, the mixture wa'scooled, the acid was neutralized with about 100 g. of caustic 'soda dissolved in water, andthe mixture was distilled to recover about 1100 ml. of oil phase. was redistilled with rough fractionation to obtain 400 ml. of a fraction distilling between 415 F. and 4.54 F. This fraction constituted the mixed amines used in the above example. The gravity of the mixture was about 14 API at 60 F. and it was practically completely soluble in 6 N hydrochloric acid. The remaining approximately 700 ml. of product was largely unreacted oil, but contained about 18% of unrecovered amines, and could also probably be used to advantage in aviahydrocarbons of this invention. It has long been known that isopropyl ether is a very effective agent for improving tion gasolines, yet its relativ instability to oxida- The nitro-aromatics may also be reduced to amines by high pressure hydrogenathe anti-knock value of aviation has militated against its widespread use, since upon oxidation it forms dangerously explosive peroxides. According to the present invention, 1% to 5% of the aromatic amines described are used in conjunction with 1% to 20% of isopropyl ether, thereby staiblizing the ether so as to prevent the formation of explosive peroxides with the consequent hazard and loss of knock rating. This ether also is effective in reducing th compatibility temperatures of amine-containing blends. The enhanced value. of the amines in the presence of the aromatics may also be obtained in the presence of the isopropyl ether.

While I have described my invention employing I tetraethyl lead as a knock-suppressing additive,

The latter I intend to include in the invention defined in th following claims not only tetraethyl lead and other alkyl lead compounds but also other knocksuppressing additives, such as nickel carbonyl, iro-n carbonyl, iron acetonyl acetonates, organic ferroand ferri-cyanides, ferric compounds of oxymethylene camphor, heavy metal compounds of beta-diketones, etc.

There are modifications of the above described invention which will be obvious to those skilled in the art, and where these are not covered by earlier art, they are to be included in the scope of the following claims.

I claim:

1. An aviation-type gasoline having a compatibility temperature below about F., comprising a blend of about 0.5% to about 15% of an amin having 7 to 12 carbon atoms and having a structural formula as follows:

in which R1 to Rs inclusive are groups selected from the class consistin of hydrogen, phenyl, and saturated alkyl; more than about 5% of aromatic hydrocarbons having 7 to 10 carbon atoms; and a mixture of hydrocarbons boiling in the gasoline range other than said aromatic hydrocarbons having from 7 to 10 carbon atoms,

' with more than about 2 ml. per gallon of tetrathe ethyl lead, said last named mixture of hydrocarbons with tetraethyl lead having an antiknock rating at least equal to' that of 2,2,4-tri methyl pentane.

2. A gasoline according to claim 1 in which the amine is a secondary amine.

3. .A gasoline according to claim 1 in which the amine is N-methyl aniline.

4. A gasoline according to claim 1 in which amine is a primary amine.

5. A gasoline according to claim 1 in which the amine is a xylidine.

6. A gasoline according to claim 1, containing also 1 to 20% of isopropyl ether and no substantial quantity of olefins.

ROBERT I. S'I'IRTON.