US3063818A

US3063818A - Gasoline composition

Info

Publication number: US3063818A
Application number: US18256A
Authority: US
Inventors: Reid E Sutton; John L Bame
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1960-03-29
Filing date: 1960-03-29
Publication date: 1962-11-13
Anticipated expiration: 1979-11-13
Also published as: IT649910A; BE601843A; GB915218A

Description

3,063,818 GASOLEIE CGMPOSTTIQN Reid E. Sutton and .lohn L. Barns, East Alton, Ell, assignors to Shell @ii (Iornpany, New Yorlr, N.Y., a corporation of Delaware No Drawing. Filed Mar. 2?, 1960, Ser. No. 18,256 @laims. (Cl. 446) This invention relates to improved hydrocarbon fuel compositions and particularly to improved motor gasoline fuel compositions having high octane numbers.

Recent automotive design trends have been toward engines having greater power for the same size engine and more eflicient utilization of the gasoline fuel. Engine designers have accomplished this largely by steadily raising the compression ratios of automotive engines, which has necessitated the use of fuels having increased resistance to knock. There is also an increased demand for aviation fuels having greater anti-knock properties. It has heretofore been possible to manufacture such fuels from crude petroleum by the development and utilization of new hydrocarbon conversion and synthesis processes such as cracking, reforming, polymerization, and alkylation. The resistance to knock of the fuels from these processes is even further augmented by the addition of antiknock agents such as tetraethyllead (TEL), and, recently, methyl cyclopentadienyl manganese tricarbonyl. Resistance to spark knock is, of course, evaluated as octane number. Therefore, the demand for fuels having greater resistance to spark knock is manifested in the constantly increasing octane number of premium fuels. However, as the octane number of modern gasoline fuels has been raised, there has been a concomitant decrease in the susceptibility of such fuels to octane number im provement by addition of organo-metallic antiknock agents. It becomes less economical, therefore, to obtain greater resistance to spark knock by this means With higher octane number fuels. In addition, the amount of organo-metallic additive which is added to motor fuels may also be limited by consideration of the degree of toxicity imparted to the fuel containing such materials. For this reason, the maximum amount of tetraethyllead which may be added to commercial gasoline motor fuels is 3 or 4 cc./gal. (U.S.) and 6 cc./gal. (U.S.) for automotive and aviation fuels, respectively. Consequently, the degree of octane number improvement which can be obtained in this manner is limited. Organo-metallic antiknock additives are difiicult to synthesize and are expensive. Their addition to fuels is thus limited to small concentrations by considerations of economics as well. Yet another limitation on the use of such antiknock additive-containing fuels is the tendency of the antiknock additives therein to lay down large quantities of deposits in the combustion chamber of the engine, which may contribute to an increase in the octane number requirement of the engine. Because of these limiting factors on the use of conventional organometallic antiknock additives, the octane number obtainable from gasoline fuels made by conventional refining processes has also been limited.

There have been many attempts to solve this problem by the use of two or more antiknock agents. However, in most of these situations, the incremental increase in octane number obtained by adding the second antiknock agent has been considerably less than the octane number increase obtainable when the supplemental antiknock agent is added to the gasoline by itself. That is, the antiknock activity of the supplemental antiknock agent or of both antiknock agents is less, on the basis of the volume added, than either by itself. Consequently, even though significant increases in octane number are obtainable, it has heretofore been uneconomical to oh- Patented N ov. 13, 1 962 tain higher octane number motor gasoline in this manner.

It is therefore an object of this invention to provide improved gasoline fuel compositions. -It is also an object of the invention to augment the eflicacy of tetraethyllead as an antiknock additive in gasoline. It is a further object of the invention to provide higher antiknock quality in gasoline in an economical manner. It is still another object to provide hydrocarbon compositions which enhance the efiiciency of antiknock additives added thereto. Another object is to attain the foregoing objects without detrimental side effects in theuse of the fuel in gasoline engines. A still further object of the invention is to provide an improved antiknock additive concentrate composition.

The attainment of these and other objects will be apparent from the detailed description of the invention which is a gasoline motor fuel composition containing a tetraalkyllead compound as a primary antiknock agent and small but critical amounts of certain organic silicon compounds which by themselves exhibit no primary antiknock activity.

The use of organo-metallic compounds as primary antiknock agents has long been known, and countless numbers of these materials have been suggested, tried, and used with various degrees of success. The most Widely used for many reasons, including availability, economy, and antiknock activity, are the tetraalkylleads, particularly tetraethyllead. However, it has now been found that certain organic silicon compounds, which possess essentially no primary antiknock activity when they are added to gasoline containing no other antiknock agent, nevertheless when added to leaded gasolines of selected composition as to hydrocarbon type and boiling range possess an extraordinary and unexpected co-antiknock activity. By co-antiknock activity, it is here meant that the secondary or eo-antiknock agent causes the octane number of the gasoline containing both primary and secondary antiknock additives .to be raised significantly above the level which is obtained by the primary antiknock agent alone, the co-antiknock effect being the result of co-action of the secondary with the primary additive rather than any primary antiknock properties of the secondary additive alone.

The addition of very small amounts of organic silicon compounds to gasoline fuels containing tetraalkyllead primary antiknock agents has been found to raise the octane number of the total mixture by as much as 3 octane numbers. Organic silicon compounds which have been found to be effective in this manner are represented by the following molecular formula:

(RO Si In the foregoing formula R is a monovalent organic radical, the single available valence bond of which is contained on a carbon atom, having from 1 to 15 carbon atoms and consisting only of carbon, hydrogen, oxygen and nitrogen.

Examples of organic silicon compounds within the above class which are effective as co-antiknock agents are as follows:

Tetracyclohexyl silicate Tetradodecyl silicate Tetra(tetrahydrofurfuryl) silicate Tetra-Z-ethyl-butyl silicate Tetramethylamyl silicate Tetra-C-pyrryl silicate Tetra-Z-pyrrolenyl silicate Tetra-3-pyrrolenyl silicate Tetra-C-pyrodyl silicate Tetrafuryl silicate Dihexyl diisobutyl silicate 3 Tetra-2-hydroxyl-t-butyl silicate Tetra pyranyl silicate .ganic silicon materials may be observed by reference to the following example.

EXAMPLE I Tetraoctyl silicate was added to a concentration of approximately 15 millimoles per gallon (U.S.) to one of two samples of commercial olefin-isobutane alkylate containing 3 cc. of tetraethyllead (TEL) per gallon (U.S.). The octane number of each of the samples was then determined by the research method (ASTM test designation D-357-53). The octane number of the sample containing TEL and the organic silicon co-antiknock agent was a full two octane numbers higher than the sample which contained only the TEL. Though the above test shows that large increases in octane number may be obtained from the addition of extremely small amounts of organic silicon materials to leaded gasoline, none of the compounds according to the invention are effective as primary antiknock' agents, that is, they have no antiknock activity in the absence of tetraalkylleads. Not only is the presence of tetraalkyllead necessary in order to obtain antiknock benefits from these materials but the ratio of co-antiknock agent to primary antiknock agent is also an important factor. This may be seen by reference to the following example.

EXAMPLE 11 Table I EFFECT OF CO-ANTIKNOCK CONCENTRATION ON OCTANE NUMBER ENHANCEMENT Co-autiknock Concentration Octane Number Enhancement Millimoles/ Grams of Si/ (A R-3) gallon gram Pb From the above tabulation, it is apparent that the concentration and consequently the ratio of co-antiknock to tetraethyllead is critically important. This ratio may be represented by the term metal ratio which is defined and used hereinafter as the weight ratio of elemental silicon in the co-antiknock agent to the elemental lead metal contained in the tetraethyllead. The foregoing data show that co-antiknock benefits may be obtained over a wide range of metal ratios, that is, from as little. as about 0.01

a to as high as 0.25 and even greater. However, superior results are obtained when the metal ratio lies between 0.03 and 0.2. It is still further preferred however that the metal ratio lie within the range of 0.035 to 0.175.

As long as the metal ratio is maintained between the foregoing broad limits, the concentration of tetraethyllead in the gasoline is not by itself particularly critical, that is, the co-antiknock agents are effective with any octane number-improving amount of tetraethyllead when they are used in accordance with the invention. Though the tetraethyllead concentration per se is not particularly critical it is nevertheless of considerable importance; for the co-antiknock compounds are even more effective at higher concentrations of tetraethyllead so long as the metal ratio is maintained within the above defined limits. Though the TEL is normally employed at concentrations not exceeding 3 or 4 and 6 cc. per gallon (U.S.) for motor gasoline and aviation fuels, respectively, the co-antiknock agents are nevertheless effective at even higher concentrations of TEL, for example, as high as 2 cc. TEL/gallon. From the preceding data it is of course apparent that the silicon-containing co-antiknock agents are highly effective in isoparaffinic hydrocarbons. However, their use as co-antiknock agents is not limited thereto. The composition of the base fuel to which they are added does however exert a profound effect on their activity as co-antiknock agents with tetraethyllead.

EFFECT OF ISO AND NORMAL PARAFFINS ON CO-ANTIKNOCK ACTIVITY The use of light isoparalrlns, i.e., those having less than 8 carbon atoms per molecule, is beneficial to the action of the co-antiknock agent. However, the addition of heavier isoparailins reduces the co-antiknock effect considerably. It is therefore preferred that the gasoline compositions in accordance with the invention not contain greater than about 20% by volume of isoparaflins boiling over about 300 F. It is even further preferred that the gasoline composition contain no more than about 10% by volume of isoparafiins boiling above about 300 F.

Because of the detrimental effect of normal paraflins in reducing the octane number, the gasoline compositions in accordance 'with the invention preferably contain essentially no normal paraffins having 7 or more carbon atoms per molecule and only small amounts, preferably not over 10%, of normal paratiins havingS or 6 carbon atoms per molecule. Fuel compositions containing essentially no normal parafilns having 5 or more carbon atoms per molecule are particularly preferred. Normal paraffins having less than 5 carbon atoms per molecule, for example normal butane, having high octane numbers, are useful to provide the gasoline with proper vapor pressure and are not deleterious to the action of the co-antiknock agents.

EFFECT OF CYCLOPARAFFINS (NAPHTHENES) EFFECT OF OLEFINS ON CEO-ANTIKNOCK ACTIVITY The incorporation of up to about 10% of lighter olefins, especially those which are branched, is actually beneficial to the co-action of the co-antiknock agents with tetraethyllead. Moreover, the gasoline compositions of the invention can advantageously contain up to 30% by volume olefins, but larger quantities are deleterious and should be avoided.

EFFECT OF AROMATICS Aromatics boiling below about 300 F., i.e., C aromatic hydrocarbons and lighter, have been found to be not exceed about 20% by volume of the total gasoline blend. In fact, in order to obtain more practical benefits from the co-antiknock agent, it is preferred that the gasoline of the invention contain no more than about 10% by volume of aromatics boiling above 300 F., and no more than 30% by volume of total aromatics.

Though the deleterious etfect of high boiling aromatics on the effectiveness of the co-antiknock additives is quite unfortunate, it has been found that a very surprising retionship exists between the effect of heavy aromatics and the presence of light naphthenes. That is, light naphthenes suppress the deleterious effects of heavy aromatics. In accordance with the application of Reid E. Sutton and John L. Bame, Serial No. 18,255, filed concurrently here with, it is possible to have substantial amounts of arematics boiling above 300 F. in a base gasoline and still obtain large benefits from co-antiknock additives, as long as light naphthenes, i.e., naphthenes boiling below about 300 F., are also incorporated in the base gasoline.

Relatively high response is obtained in light naphthenes even in the presence of heavy aromatics. In general it appears that one volume percent of light naphthenes can overcome completely the deleterious effect of one volume percent of heavy aromatics. However, since practical benefits are obtained up to 10% and 20% by volume heavy aromatics even in the absence of naphthenes, it is not necessary always to have present as much light naphthenes as would be needed to completely cancel the effect of the heavy aromatics. The light naphthenes can be used to obtain even greater benefits from the co-antiknock additives in gasolines which must contain aromatics boiling above 300 F. to have proper volatility distribution of high octane number components. To take advantage of light naphthenes in accordance with this preferred aspect of the invention, it is desirable that the base gasoline contain at least A by volume, or preferably at least At% by volume, of naphthenes boiling below 300 F. for each 1% by volume of aromatics boiling above 300 F. in excess of 10% by volume of such aromatics, and preferably such amounts of light naphthenes for each 1% by volume of all of such aromatics.

The adverse effect of each of the deleterious or antagonistic components, that is, aromatics, olefins, C plus normal parafiins and heavy naphthenes, is not, however, independent. Even with the use of naphthenes in accordance with above, the presence of two or more of such antagonists in maximum concentrations can result in a fuel having little or no response to the action of the coantiknock agents. Such non-responsive hydrocarbon compositions may be avoided, however, if the compositions meet the following empirical correlation which constitutes a limitation on the total equivalent amount of coantiknock antagonists (A which may be present in the hydrocarbon blend:

A =percent by volume of aromatics boiling below 300 F A =percent by volume of aromatics boiling above 300 F.

A =percent by volume of olefins A =percent by volume of C plus normal paraffins and naphthenes boiling above 300 F.

N =percent by volume of naphthenes boiling below Summing up its broad aspects, the invention therefore resides in the discovery that the organic silicon compounds as defined hereinbefore are effective as co-antiknock agents with tetraethyllead when both are added to gasoline blends containing essentially no normal paratlins containing 7 or more carbon atoms, no more than 10% by volume of C to C normal paratfins, no more than 6 2 0% by volume of isoparafiins boiling above 300 F., no more than 10% by volume of naphthenes boiling above 300 F., no more than 30% by volume olefins, no more than 50% by volume of total aromatics and no more than 20% by volume of aromatics boiling above 300 F., the composition of the gasoline blend also being within the limits defined by the empirical relationship A =A +1.3A +O.7Ao+0.25A 50=+0.75N In the foregoing examples in which TEL was used as primary anti-detonant, the TEL was added in the form of the commercial motor mix which has the following composition:

Component: Percent by weight Tetraethyllead 61.48 Ethylene dibromide 17.86 Ethylene dichloride 18.81 Dye 0.0 6 Kerosene and impurities 1.79

It is to be understood that the order of mixing the various constituents of the compositions of the invention is immaterial. For example, the co-antiknock compound may be added to a gasoline which already contains the tetraethyllead primary antiknock material. Likewise, the co-antiknock and primary antiknock compounds may be first mixed, stored, and handled as a concentrate, and added to the gasoline at a later time. A gasoline additive concentrate of this latter type may also contain halogen scavenger and spark plug antifouling compound. Under other circumstances, it may be desirable to mix the halogen scavenger and the primary antiknock compound, or the primary antiknock and co-antiknock compounds, in the desired relative proportions and handle or store this mixture, with or without stabilizers, anti-fouling compounds, inhibitors, etc., as a concentrate for incorporation with the other components of the ultimate fuel composition.

When an additive concentrate of this latter type is employed, it is preferred that it contain an optimum or near optimum metal ratio. Such a concentrate will therefore contain from 0.0 1 to 0.25 gram of metal in the co-antiknock agent per gram of lead in the tetraethyllead. Preferably, such a concentrate contains from about 0.03 to about 0.175 gram of metal per gram of lead.

A typical additive concentrate in accordance with the invention and containing both TEL motor mix and phosphorus compound for ignition control as well as co-antiknock agent has the following composition:

Component: Percent by weight Tetraethyllead 51.4-58.9 Ethylene dibromide 14.9-17.1 Ethylene dichloride 15.8-18.1 Phosphorus (as tricresyl phosphate) 3.8-13.1 Silicon (as tetra-(Z-ethylbutyl) silicate) 0.4 3.3 Kerosene, dye, impurities 1.5-11.7

We claim as our invention:

1. A gasoline composition consisting essentially of a mixture of hydrocarbons having an ASTM boiling range below about 400 R, an octane number-improving amount of tetraethyllead, and an organic-silicon co-antiknock agent having the structural formula (RO) Si wherein R is a monovalent organic radical, the available valence bond of which is contained on a carbon atom, having from 1 to 15 carbon atoms per molecule and consisting only of carbon, hydrogen and oxygen, the amount of co-antiknock agent corresponding to from about 0.01 to about 0.25 gram of silicon metal contained in the co-antiknock agent per gram of lead metal contained in the tetraethyllead, said mixture of hydrocarbons being comprised of (1) no more than 50% by volume aromatics, (2) no more than about 30% by volume olefins, (3) no more than about 20% by volume each of isoparafiin and aromatics boiling above about 300 F., (4) no more than about 10% by volume each of normal parafiins having 5 to 6 carbon atoms per molecule and naphthenes boiling above about 300 F., and (5) essentially no normal paraifins having greater than 6 carbon atoms per molecule, and further characterized as having an equivalent amount of co-antiknock antagonists (A not exceeding 50+0.75N wherein A and N are defined as hereinbefore in the specification.

2. The fuel composition of claim 1 which is comprised of (1) no more than about 30% by volume of aromatics, (2) no more than about 20% by volume each of olefins and aromatics boiling above about 300 F., (3) no more than about 10% by volume each of isoparaffins boiling above about 300 F. and naphthenes boiling above about 300 F. and (4) essentially no normal parafiins having greater than 4 carbon atoms per molecule, and further characterized as having an equivalent amount of co-antiknock antagonists (A not exceeding 50+0.75N wherein A and N are defined as hereinbefore in the specification.

3. The gasoline composition of claim 1 in which the co-antiknock agent is tetra-Z-ethyl butyl silicate.

4. The gasoline composition of claim 1 in which the co-antiknock agent is tetra-Z-ethyl hexyl silicate.

5. A gasoline additive concentrate composition consisting essentially of a mixture of tetraethyllead and a co-antiknock agent having-the structural formula Ronsr wherein R is a monovalent organic radical, the available valence bond of which is contained on a carbon atom, having from 1 to 15 carbon atoms per molecule and consisting only of carbon, hydrogen and oxygen, the amount of co-antiknock agent corresponding to from about 0.01 to about 0.25 gram of silicon metal contained in the co-antiknock agent per gram of lead metal contained in the tetraethyllead.

References Qited in the file of this patent UNITED STATES PATENTS l 2,398,282 Bartholomew Apr. 9, 1946 2,818,417 Brown et al. Dec. 31, 1957 2,901,336 Brown Aug. 26, 1959 2,913,413 Brown Nov. 17, 1959 FOREIGN PATENTS 574,644 Canada Apr. 21, 1959 746,036 Great Britain Mar. 7, 1956 780,581 Great Britain Aug. 7, 1957 OTHER REFERENCES Aviation Gasoline Manufacture, by Van Winkle,

First Ed. 1944, McGraw-Hill Book Co., pages 43-63 and 197-211.

Improved Motor Fuels Through Selective Blending, by Wagner et al., Paper Presented Before the 22nd Annual Meeting of the American Petroleum Institute, November 7, 1941, vol. 22 (III), pages 89.

Claims

1. A GASOLINE COMPOSITION CONSISTING ESEENTIALLY OF A MIXTURE OF HYDROCARBONS HAVING AN ASTM BOILING RANGE BELOW ABOUT 400*F., AND OCTANE NUMBER-IMPROVING AMOUNT OF TETRAETHYLLEAD, AND AN ORGANIC-SILICON CO-ANTIKNOCK AGENT HAVING THE STRUCTURAL FORMULA