US2586660A - Leaded fuel composition - Google Patents

Description

Patented Feb. 19, 1952 assesco' LEADED FUEL oo PosI'rIoN.

William Q. Howell, Jr., Union,.N. J., assignor topmentr Company, a corpo- Standard Oil Develo ration of Delaware No Drawing. Application'March'l, 1950, Serial No. 147,139 7 This invention relates to improved leaded motor fuels containing compounds known as lead scavenging agents. In accordance with the present invention the leaded fuel composition incorporates small quantities of lead scavenging agents consisting of a combination of halogenated hydrocarbons and tin alkyl compounds.

When fuels containing lead anti-knock agents are burned in internal combustion engines, at least a portion of the lead anti-knock agent is convertedinto a deposit of non-volatile lead compounds which accumulates on various parts of the engine. This deposit of non volatile lead compounds contains a large proportion of lead oxide. Deposits of this nature, due directly to the presence of the lead anti-knock agent in the fuel, are very undesirable, causing corrosion of the valves, failure of spark plugs, and general deterioration of the engine parts affected. To reduce this tendency of leaded fuels to form deposits on combustion, it has been conventional practice to incorporate a lead scavenging agent in the fuel. The mechanism apparently is that the scavenging agent consisting of one or more halogenated hydrocarbons causes formation of relatively volatile lead halides during combustion which are largely removed from the combustion chamber through the exhaust port of the engine.

Heretofore the scavenging agents which have been employed have been chosen from a wide variety of halogenated hydrocarbons. U. S. Patent 1,575,444 suggests that the scavenger may consist of any halogen compound capable of combining with the lead during combustion; U. S. Patent 2,364,921 suggests that two to five carbon atom hydrocarbons containing three halogen atoms are suitable;

and more recently, U. S. Patents bons including hydrocarbons of 3 to 8 carbon time the scavengers which are commercially emfployed in fuels consist of ethylene 'dibromide and ethylene dichloride.

of scavenger, in the case of aviation fuels, and not more than One and one-half theories for automotive fuels. One theory as defined as the quantity ofscavenger required to stoichiometrically combine with the lead present. Whilethe quantity of scavenger in some cases has been increased to as much as one and one-half theories 1 which vwill not reduce. atoms having from 2 to 3 bromine atoms and.

having a particular volatility. At the present 6 Claims. (Cl. 44-69) '2 I for aircraft fuels also, it has been found'unde sirable to employ more than one theory of scavenging agent in fuels of this type. This is true for the reason that additional quantities increase the corrosion which occurs on engine parts, presumably due to the presence of halogen acids. For thesomewhat less critical conditions encountered in automotive service, one and one-half theories of scavenging agent are in general permissible, although even in this type of fuel it is undesirable to use more than one and one-half theories. Furthermore, all scavenging agents heretofore discovered, including those described in the aforementioned patents, cause a distinguishable decrease in the anti-knock rating of the fuels in which the scavengers are incorpo rated. This proknock efiect of the scavenging agent becomes more and more marked as the quantity of scavenger increases, so that because of this factor again it is practically undesirable to employ more than one or one and one-half theories of the conventional halogenated hydro:

carbons as-scavenger agents.

Because of this circumstance; that is, that the quantity of scavenging agent which may be em ployed is limited; scavenging efiects obtained are also limited, leaving much to be desired. Thus in the case in which the, mostefiective halogen scavenging agent is employed in normal .concenof lead compounds are still encountered. 'f

It is, therefore, the principal object of this invention to provide a new and novel type of scav enging composition which will permit. utilization trations, substantial engine deposits consisting of more than.theQ-bonventional quantityof scavringing-"agent, and which .will more effectively.

freduc 2,479,900, U. S. 2,479,901, and U. S. 2,479,902 disclose preferred types of halogenated hydrocaremploying scavenging: agents.

the, fuel to the extent normally encountered'when ancewith this invention-is to complement in the' action of a conventional.sc'av-' enger "wit/1 1 a olatile--'tin compound. ffFOlfexmample; a 'fue' l rnpolsitio n' chosen with regard to -:-this concept,'rnaycontainlone theory ofragcon'fventionalhalogen scavenging agent together with analkyl tin compound in such concentration as to give about 0.5 to. 1 /2-atoms of tin per atom of lead; It is presently'hypothesized. that on combustion, lead 'halidesfiare' formed due to; the halogen scavenging-agent, but that formation of lead oxide is minimized by the preferential lead deposits formed in an engine. burn v w I Itis a further object of this 'f invention provide. ia scavengingcorr' p'osition e 1 anti-knock rating, ofi

,-.'rn *manner'byiwh cn theseobjectives areobvtainecl,".;in accord oxidation of the tin compound. Consequently, the conventional halogen scavenging agent, and the alkyl tin scavenging agent act together to reduce lead deposits by forming the maximum quantity of lead halide due to the suppression of lead oxide formation. It is important to note that neither the tin compound nor the halogen compound by itself is capable of providing the best lead scavenging action but that both materials must be present together to obtain the desired eifect.

As indicated the halogenated scavenging agents to be employed in compositions of this invention may be chosen from the long list of suitable compounds indicated by patents such as those described. For example, the conventional ethylene di-chloride and/or ethylene dibromide may be employed, brominated xylenes may be employed, or other types of brominated aliphatic and aromatic hydrocarbons may be used. It is preferred that the quantity of the conventional halogenated scavenging agent be about one theory, although somewhat more or less than this amount can be used. However, one theory of the conventional scavenging agent is the quantity best adapted to provide optimum lead scavenging with a minimum of engine corrosion due to the presence of the scavenger.

The tin compound to be employed may be deilned as a volatile tin compound. Beyond the fact that the tin compound should be reasonably volatile. for example having about the same volatility as the lead anti-knock compound, choice of the tin compound is not presently thought to be particularly critical. However, a preferred class of tin compounds are the alkyl tin compounds having two to four alkyl groups, and having alkyl radicals containing one to five carbon atoms. More specifically, the tin compound is preferably a tin alkyl compound having a volatility in the range of about 300. F. to 500 F. This limitation as to the nature of the tin compound is a stringent limitation set by the distribution characteristics required in a multicylinder engine.

Thus it is well known that the quantity of lead anti-knock agent which reaches a particular cylinder of a multicylinder engine may vary appreciably from the quantity reaching a different cylinder of the engine. For this reason it is important to select a tin compound having a volatility closely similar to that of the lead antiknock agent in order that a constant proportion of tin to lead may be maintained in all cylinders. It is presently contemplated that preferred tin compounds to be used in the practice of this invention comprise those represented by the following structural formula:

where R1, R2, R3, and R4, represent a hydrogen atom or alkyl groups having from one to four carbon atoms, and the total number of carbon atoms is not less than 8 and not more than 16. Thus, the following compounds typify but do not include all of those compounds conforming to the foregoing formula; tetraethyl tin, tetrapropyl tin, tetrabutyl tin, dimethyl dipropyl tin, diethyl dibutyl tin, dimethyl ethyl propyl tin, diethyl dibutyl tin. Other alkyl tin compounds having less than four alkyl substituents per molecule may also be used in the practice of this invention, as, for example, diethyl tin, triethyl tin, dipropyl tin. dibutyl tin, etc.

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While, as thus far described, the present inventlon has been concerned with the addition of a volatile tin compound and a volatile halogen compound as separate substances, it is visualized that both the tin and'halogen compound may be incorporated in the same molecule, such as, for example, a halogenated tin alkyl or a tin haloalkyl. Thus, the trialkyl tin bromides and dialkyl tin dibromides, as well as the trialkyl tin chlorides and dialkyl tin dichlorides, would also be suitable for the practice of this invention. Materials of this type may be represented by th formula:

Roi-X pounds of this type include dimethyl tin (ii-- bromide, dimethyl tin dichloride, diethyl tin dibromide, diethyl tin dichloride, diethyl propyl tin bromide, diethyl propyl tin chloride, dibutyl tin dibromide, dibutyl tin dichloride, triethyl tin bromide, triethyl tin chloride, diethyl isobutyl tin bromide, and diethyl isobutyl tin dichloride.

Similar halogen-containing bivalent or trivalent tin compounds may likewise be employed, such as ethyl tin bromide, diethyl tin bromide, ethyl propyl tin bromide, dibutyl tin chloride, ethyl propyl tin chloride, etc.

The other constituents of the fuel compositions of this invention are conventional. Thus, the base fuel may consist of virgin; thermally cracked; catalytically cracked; polymerized or alkylated hydrocarbons and mixtures thereof boiling in the gasoline boiling range. Any gasoline type fuel may be employed. The lead antiknock agent to be incorporated in the fuel again may consist of any of the conventionally recognized lead anti-knock agents. At the present time tetraethyl lead is the compound which is generally employed, but other alkyl lead compounds may be used, such as lead tetramethyl; lead trimethyl ethyl; lead dimethyl diethyl; lead methyl triethyl, or lead triethyl normal propyl. The quantity of lead anti-knock agent is the quantity ordinarily used which is generally in the range of about 0.5 to 4.6 cc. per gallon of fuel. In addition to these fuel constituents, other fuel additives may be employed such as gum flux agents; solvent oils; dyes; gum inhibitors; lead stabilizers, etc.

As an example of the effectiveness of the concept of employing a tin compound to complement the action of a conventional lead scavenger, data were obtained in actual engine tests to determine the amount of combustion chamber and engine deposits encountered when burning conventional fuels, and when burning fuel compositions of this invention. The conventional scavengers employed were those which are presently used in commercial fuels, ethylene dichloride and ethylene dibromide. The motor gasoline employed was selected from commercial stocks and consisted of a blend of straight run, thermally cracked, and catalytically cracked naphtha, having a boiling range of about 108 F, to 378 F., and having an ASTM Motor Method octane number of 68, to which was'added 4 cc. per gallon of pure tetraethyl lead. A single cylinder Lauson engine was employed in the tests, and runs were made for 40 hours. At the end of the test period the total deposit found in the combustion chamber was carefully removed and weighed. The portion of this deposit which consisted of lead was quantitatively determined by analytical methods. Runs were made employing the base fuel and respectively one theory of ethylene dichloride; one theory of ethylene dichloride plus one atom of tin (as tetrabutyl tin) per atom of lead; one theory of ethylene dibromide; and two theories of ethylene dichloride. The results of these tests are indicated in the table.

per gallon of fuel. From 0.5 to 1.5 theories, and preferably about 1.0 theory of a halogenated scavenging agent are utilized, and from 0.5 to 1.5 atoms, and preferably about 1.0 atom of tin is provided per atom of lead. The upper limit of tin concentration is particularly critical since a. greater concentration would exhaust the halogenated scavenging agent, resulting in an increase rather than a decrease in the amount of lead oxide deposit.

What is claimed is:

1. A leaded gasoline fuel containing in combination about 0.5 to 1 theories of a halogenated hydrocarbon scavenging agent and a volatile alkyl tin compound, said volatile alkyl tin compound being present in suflicient proportions to provide from 0.5 to 1.5 atoms of tin per atom of lead.

2. The composition defined by claim 1, in which TABLE Eflect of tetrabutyl tin on lead scavenging eificzency l l'lltllileolry of I l 'lheory i l Theory of 2 Theories of Deposit ll eights. Ethvlene D1chlor1de+l Em ylene Ethylene Grams Dichloridc 2,5 2 Dibromide Dichloride Total Combustion (hamhcr l2. 5 7. 5 ll. 3 7. 7 Load in Combustion (hamher (By analysis) 7. 3 4. 6 G. 4 5. 2

l 0.17 vol. per cent tin tetrabntyl.

As indicated, by the data in the table, the presence of the alkyl tin compound decreased the total combustion chamber deposit by and promoted 37% more scavenging of lead than in the case in which ethylene dichloride alone was employed. It is particularly significant that the combustion chamber deposit was materially decreased when the tin compound was employed, as compared to the case when ethylene dibromide alone was used, since ethylene dibromide represents one of the most potent of scavenging agents when used alone. The results obtained with the fuel containing the tin compound were also appreciably better than those obtained when employing two theories of ethylene dichloride, where the combustion chamber deposit was 7.7 grams total and 5.2 grams of lead. It should be appreciated that the use of such a high proportion of ethylene dichloride or ethylene dibromide is detrimental to engine life. For example, increasing the proportion of ethylene dibromide from 1.0 to 1.5 theories has been reported (ASTM bulletin No. 154:53-6 (1948)) to increase spark plug failures in aviation engines by 115% andto cause severe corrosion of exhaust valves and valve seats. The test on the fuel containing the volatile tin compound, on the other hand, showed that no appreciable increase in harmful spark plug and exhaust valve deposits occurred, nor was any other condition of the engine adversely affected 5 by inclusion of the tin compound.

As indicated, therefore, the compositions of this invention embrace conventional motor gasoline fuels containing lead anti-knock agents, a conventional halogenated hydrocarbon, and a volatile tin compound. This fuel composition is suited for use in internal combustion engines to permit minimum deposit formation. Preferably about 0.5 to 5.0 m1. of tetraethyl lead, or other lead alkyl anti-knock compound, are employed the volatile tin compound has the general formula:

tetraethyl lead, 0.5 to 1.5 theories of a halogenated hydrocarbon selected from the group consisting of C3 to C3 mono and dibromo hydrocarbons, and an alkyl tin compound having a boiling point in the range of 300m 500 F. and present in a quantity to provide from 0.5 to 1.5 atoms of tin per atom of lead.-

4. The composition defined by claim 3 in which the said alkyl tin compound is selected from the group consisting of alkyl tin compounds having 2 to 4 alkyl radicals, containing a total of 8 to 16 carbon atoms.

5. The composition defined by claim 3 in which the said tin compound is tetrabutyl tin.

6. A leaded gasoline fuel containing about 1 theory of halide and about 1 atom of tin per atom 5 of lead.

WILLIAM C. i-IOWELL. JR.

REFERENCES orrEn The following references are of record in the 0 file of this patent:

UNITED STATES PATENTS Number Name 7 Date I 1,575,444 Midgley Mar. 2, 1926 2,151,432 Lyons et a1 Mar. 21, 1939 Calingaert et a1. Aug. 23. 1949

Claims (1)

1. A LEADED GASOLINE FUEL CONTAINING IN COMBINATION ABOUT 0.5 TO 1 THEORIES OF A HALOGENATED HYDROCARBON SCAVENGING AGENT AND A VOLATILE ALKYL TIN COMPOUND, SAID VOLATILE ALKYL TIN COMPOUND BEING PRESENT IN SUFFICIENT PORPORTIONS TO PROVIDE FROM 0.5 TO 1.5 ATOMS OF TIN PER ATOM OF LEAD.