US3098470A - Motor fuel - Google Patents

Description

3,098,470 Patented July 23, 1963 fiice 3,998,470 MOTOR FUEL Fred K. Kawahara, Park Forest, 111., assignor to Standard Oil Company, Chicago, 11]., a corporation of Indiana No Drawing. Filed Feb. 27, 1959, Ser. No. 795,893 9 Claims. (Cl. 123-1} This invention relates to motor fuels characterized by their ability to suppress surface ignition in the operation of internal combustion engines. More particularly, the invention provides an improved motor fuel which is effective in suppressing surface ignition or preignition.

Current emphasis on high compression ratios and other high-performance design features in gasoline engines of the internal combustion type has created a situation Where random knock from surface ignition, often referred to as preignition," has become a limiting factor in engine design and operation. Knock induced by surface ignition appears to be a result of the use of organo-lead compounds, particularly tetraethyl lead, as the anti-knock agent in high octane number fuels. When leaded motor fuels are burned in internal combustion engines, deposits of carbonaceops material and lead salts are continuously formed on the combustion chamber walls. Apparently surface ignition, that is, the ignition of the fuel-air mixture either before or after passage of the spark, is caused by glowing of carbon in the deposits. It is generally believed that the presence of lead compounds in the deposits causes the carbon to glow at a significantly lower temperature than the glow point of carbon alone.

'It is well known that the addition of certain organic compounds of phosphorus, such as tricresylphosphate, to leaded fuels results in reducing surface ignition. Unfortunately, phosphorus compounds vary widely in effectiveness, and those that are most effective often have the undesirable property of lowering the octane number of the fuel. With petroleum refiners spending millions of dollars annually to raise the octane numbers of premium motor fuels, any substantial decrease in octane number is of course intolerable.

In accordance with the invention, an additive for use with leaded motor fuels has now been discovered which is extremely effective in reducing surface ignition or preignition," yet, when employed in proper quantities, does not substantially reduce the octane number of the fuel. Specifically, it has now been discovered that thioesters of a cyclic dithiophosphoric acid, having the formula wherein the Y groups are each hydrogen atoms or alkyl radicals of 1-4 carbon atoms each, and X is an alkyl, aryl, aralkyl, or alkaryl radical having up to about 15 carbon atoms per radical, are outstanding preignition suppressant additives when incorporated into leaded gasolines in an amount sufficient to provide a mol ratio of phosphorus to lead of from about 0.01 to about 1.0. Preferably, the molar ratio of phosphorus to lead (MR P/Pb) is in the range of 0.020.20.

It has further been discovered, contrary to experience with most other organic compounds of phosphorus, that the inventive additives act as effective gasoline antioxi dants, and hence reduce the tendency of the motor fuel to form gums in storage. In addition, they do not cause fuel induction system deposits and they virtually eliminate sticking of engine intake and exhaust valves.

The motor fuel of the invention may contain tetraethyl lead equivalent to a concentration of from about 0.5 ml. to about 5 ml. or more per gallon of the hydrocarbon motor fuel; the concentration of tetraethyl lead may be varied as is usual with the engine and its use.

The hydrocarbon component which constitutes the base of the fuel will preferably be gasoline but may be any other combustible liquid of suitable volatility commonly employed as fuel for internal-combustion spark ignition engines, including parafiinic, naphthenic and aromatic hydrocarbons, pure hydrocarbons such as isooctane, and mixtures of isooctane with other suitable liquid hydrocarbons. These fuels may be derived, in whole or in part, by distillation of crude oil, catalytic or thermal cracking of gas oils, alkylation of isoparaliins with olefins, polymerization of olefins, etc. The boiling point of such fuels should be in the range of about F to about 500 F. and preferably in the range of about F. to about 400 F. Motor fuels may also contain anti-oxidants, stabilizers, dyes, antiicing agents, halogen-type lead scavenging agents and/or other compounds which are commonly employed in leaded motor fuels.

There can also be provided, in accordance with the invention, an additive concentrate suitable for incorporation into leaded motor fuels which contains a substantial amount (1-l00%) of the above described thioester of disubstituted thiophosphoric acid. Thioester concentrations of 5-85 wt. percent are preferred. The additive concentrate may also contain an inert solvent, such as a refined hydrocarbon oil, and also desirable amounts of tetraethyl lead (to provide an MR P/Pb in the range of (101-11)), halo-hydrocarbon lead scavenging agents, dyes, and the like.

The defined additives, which are thioesters of a cyclic disubstituted dithiophosphoric acid, may be prepared by any of the conventional means known for preparing analogous thioesters. Thus, appropriate diols, having two carbinol groups separated by a single carbon atom, may be reacted with phosphorus pentasulfide (P 8 to form a cyclic dithiophosphoric acid, and then reacted with a halide of the radical (X) to be introduced. Typical examples of appropriate diols include 2-methylpentanediol-2,4, propanediol-l,3, butanediol-l,3, 2-ethylhexanediol-L3, pentanediol-2,4, etc. Although the Y groups on the previously-defined structural formula may be hydrogen atoms or alkyl radicals of l-4 carbon atoms, it is preferred that there be at least one alkyl radical of l-3 carbon atoms on at least two of the carbon atoms which ultimately form the cyclic structure. For instance, 2-methylpentanediol- 2,4 reacts with P 8 to form 1,1,3-trimethyl cyclo trimethylene thiophosphoric acid, which can then be reacted with, say, benzyl chloride to form the benzyl dithiophosphate. This method is especially suitable for aryl and aralkyl groups such as phenyl, tolyl, ethylphenyl, etc.

It is preferred, for reasons of convenience and economy, to react the cyclic dithiophosphorie acid with an olefinic hydrocarbon having up to 15 carbon atoms per molecule to form the inventive additive. As previously mentioned, the X group may be alkyl, aryl, aralkyl, or alkaryl, and accordingly the olefinic hydrocarbon can be any compound which alfords such group. Among the suitable compounds which can form the X group of the defined formula are ethylene, propylene, i-butylene, heXene-l, heptene-l, i-octenes, decenes, cyclopentene; styrene, amethyl styrene, dimethyl-B-methyl styrene, p-t-butyl styrene, and other aralkenes of 7-15 (more desirably 7-10) carbon atoms. Using the styrenes, it is believed that the sulfur atom attaches to the or carbon atom of the styrene.

As specific embodiments of the invention, the following examples are given. It is to be understood that these are by way of illustration only and are not intended as a limitation of the invention:

3 EXAMPLE I In this example, 1,1,3-trimethyl cyclo trimethylene aphenylethyl dithiophosphate was prepared in a one-step process. To a mixture of styrene (1.1 mols) and 2-methylpentane diol-2,4 (1.2 mols), phosphorus pentasulfide (0.5 mol) was added gradually at l65-l90 F. over a 1- hour period. The mixture then was permitted to react for 2 hours at 210 F. and was then purified by filtration through filter paper. Cryoscopic examination of the product after water washing and drying at reduced pressure showed it to be essentially the monomer.

Analysis.-Calcd.: phosphorus, 8.95 wt. percent; sulfur, 18.3%. Found: phosphorus, 8.80 wt. percent; sulfur, 16.93%.

EXAMPLE II In this example, a two-step reaction was employed to prepare 1,1,3-trimethyl cyclo trimethylene a-phenylethyl dithiophosphate. The reaction was conducted by adding 111 grams (0.5 mol) of P 5 to 130 grams (1.11 mols) of 2-methylpentanediol-2,4 gradually during two hours, and then adding 124 grams (1.2 mols) of styrene in 1% hours at 195 F. The mixture was then diluted with 88 grams of 5-W oil and 200 grams of xylene solvent.

EXAMPLE III In this example, l-methyl cyclo trimethylene a-phenylethyl dithiophosphate was prepared. To a mixture of 216 grams (2.4 mols) of butanediol-l,3 and 228.8 grams (2.2 mols) of styrene, there was added 222 grams (1 mol) P 5 at 170190 F. over a one-hour period. The reaction mixture was then heated at 220 F. for a five-hour period. 633.3 grams of product was recovered; it analyzed 9.81 wt. percent phosphorus.

EXAMPLE IV In this example, 1,1,3-trimethyl cyclo trimethylene heptyl dithiophosphate was prepared. To a mixture of 141 grams (1.2 mols) Z-methyl pentanediol-2,4 and 216 grams (2.2 mols) of technical or mixed heptenes, there was added 111 grams (0.5 mol) P 5 gradually over a 55- minute period at l58-168 F. The reaction mixture was then heated at 190-l95 F. for three hours. 442 grams of product was recovered; it analyzed 7.04% P, 14.8% S,

and had an acid number of 9 (mg. KOH/g.).

EXAMPLE V Test duration 50 hours.

Coolant temperature 148 F. Oil temperature 160 F. Air to fuel ratio 13/1. For this test the engine is cycled as follows:

Cycle Conditions 45 135 600 900 None Full Surface ignition prevention effectiveness was determined using a premium fuel having 3 cc. of TEL per gallon and incorporated therewith the inventive additive and other phosphorus compounds.

EFFECTIVENESS IN SUPPRESSING SUFACE IGNITION CFILF HEAD ENGINE Concentration, MR PJPb Additive 1 A hydrocarbon dithiophosphate.

The test data in the above table demonstrate the superiority of the present additive over other phosphorus compounds with respect to surface ignition control. It will be noted that the additive may be employed at onefourth to one-half the concentration of hitherto well known preignition suppressants.

It was previously indicated that a major advantage of the inventive additive is in its ability to be incorporated into high octane gasolines without substantially reducing the octane number of said gasolines. To demonstrate this, tests were made in a CFRL head engine at various concentrations of several additives in a 9394 octane number motor fuel, containing 3.0 cc. TEL per gallon. The following results were observed.

A surprising benefit attendant with the present additives is their ability to function as antioxidants to prevent oxidative gum formation in the gasoline on long term storage. This was demonstrated by testing motor fuels at accelerated storage conditions of 212 F. and p.s.i.g. oxygen pressure, and noting the time (induction period) before rapid oxygen consumption occurred. The following results were observed with the additive of Example I:

Additive concentration: Induction period, minutes Nil 325 0.13 MR P/Pb 390 0.33 490 The additive of Example I was also tested for its equilibrium octane performance in a 1953 Oldsmobile V8 engine having special 10:1 compression ratio heads, under the following conditions:

Speed, r.p.m 1500 Load, B.H.P 9.5 Coolant Temp. F 175 Oil temp., F 165 Air-intake temp., F 100 Air-fuel ratio 13:1 Spark advance, BTDC 11 Once each hour the engine was operated at full-throttle, 1500 r.p.m.80 B.H.P. for 15 seconds. The equilibrium octane requirements and octane requirement increase (ORI) of the engine were determined after hours and after 300 hours of operation and are shown below.

OOTANE REQUIREMENT INCREASE The inventive compositions are outstanding with respect to their ability to prolong exhaust valve life, in marked contrast to the deleterious elicct which many other phosphorus compounds have. To illustrate this, tests were made on 1953 Chevrolet engines having a 216 cubic inch displacement and operated under the following conditions:

Speed, r.p.m 2,500 Load, B.H.P 25-45 Coolant temperature, F 165 Oil temperature, F 200 Air-fuel ratio 16:1 Spark advance, BTDC 32 Spark gap, inches 0.040 Exhaust valve clearance, inches 0.020 Manifold vacuum, inches Hg 7 At the end of 50 hours of testing, the engines were examined and the following results observed:

EXHAUST VALVE INSPECTION Additive Concentration Exhaust valve condition None Four stuck. Example 1 0.13 MB P/Pb All good.

The engines were disassembled and visually inspected for induction system deposits; both passed.

The additive of Example I was exposed to the copper strip test, which consists of placing a clean copper strip in a sample of motor fuel containing the additive at 122 F., and examining the strip after three hours. At concentrations of 0.13 and 0.33 MR P/Pb, the strip had the same good color as the blank (zero additive concentration).

The additive of Example I also exerts a powerful action on maintaining spark plugs in clean, unfouled condition. In tests on an Oldsmobile engine, the following results were observed:

SPARK PLUG LIFE The percentages given herein and in the appended claims are weight percentages unless otherwise noted.

While the invention has been described by reference to specific embodiments thereof, the same are given by way of illustration. Modifications and variations will be apparent to those skilled in the art.

We claim:

1. A hydrocanbon motor due] of the gasoline boiling range adapted for spark-ignition internal-combustion engines, containing a minor amount of tetraethyl lead and, in combination therewith, in an amount sufficient to provide a mol ratio of phosphorus to lead of from about 0.01 to about 1.0, a thioester of a cyclic dithiophosphoric acid having the formula wherein the Y groups are each selected from the group consisting of hydrogen atoms and alkyl radicals of 1-4 carbon atoms each, and X is seiected from the group consisting of alkyl, aryi, aralkyl, and alkaryl radicals having up to about 15 carbon atoms.

2. The fuel of claim 1 wherein the minor amount of tetraiethyl lead is in the range of about 0.5 to about 5.0 cc. per gallon of incl.

3. The fuel of claim 1 wherein Y Y and Y are methyl radicals and Y Y and Y are hydrogen atoms.

4. The fuel of claim 1 wherein X is a phenylethyl radical.

5. The fuel of claim 1 wherein X is a heptyl radical.

6. The fuel of claim 1 wherein X is a di-i-butylene radical.

7. A hydrocarbon mot-or fuel of the gasoline iboiling range adapted for spark-ignition internal-combustion en- .gines containing from 0.5 to 5.0 cc. tetraethyl lead per gallon of fuel, and, in an amount sutficient to provide a mol ratio of phosphorus to lead of from about 0.01 to about 1.0, 1,1,3 trimethyl cyclic trimethylene phenylethyl dithiophosphate.

8. An additive concentrate composition suitable for incorporation in leaded hydrocarbon motor fuels of the gasoline boiling range adapted for spark-ignition internal-combustion engines, said additive concentrate composition consisting essentially of tetraethyl lead and a substantial amount of a thioester of a cyclic dithiophosphoric acid having the formula wherein the Y groups are each selected from the group consisting of hydrogen atoms and alkyl radicals of 1-4 carbon atoms each, and X is selected from the group consisting of alkyl, aryl, aralkyl, and alkaryi radicals up to about 15 carbon atoms.

9. In the method of operating sparkignition internal combustion engines, the improvement which comprises supplying to said engines a hydrocarbon motor fuel of the gasoline lbioiling range containing a minor amount of rtctraethyl lead and, in combination therewith, in an amount suliicient to provide a mol ratio of phosphorus to lead of from about 0.01 to about 1.0, a tthi-oester of a cyclic dithiophosphoric acid having the formula wherein the Y groups are each selected from the group consisting of hydrogen atoms and alkyl radicals of 1-4 carbon atoms each, and X is selected from the group consisting of alkyl, aryl, aralkyl, and alkaryl radicals having up to about 15 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 2,737,932 Thomas Mar. 13, 1956 2,794,719 Bartleson June 4, 1957 2,794,720 Bartleson June 4, 1957 2,892,691 Howell June 30, 1959 2,892,863 Lanham June 30, 1959 2,894,016 Laniham July 7, 1959 2,897,071 Gilbert July 28, 1959 2,902,983 Patbeng Sept. 8, 1959

Claims (1)

1. 9. IN THE METHOD OF OPERATING SPARK-IGNITION INTEGRAL COMBUSTION ENGINES, THE IMPROVEMENT WHICH COMPRISES SUPPLYING TO SAID ENGINES A HYDROCARBON MOTOR FUEL OF THE GASOLINE BOILING RANGE CONTAINING A MINOR AMOUNT OF TETRAETHYL LEAD AND, IN COMBINATION THEREWITH, IN AN AMOUNT SUFFICIENT TO PROVIDE A MOL RATIO OF PHOSPHORUS TO LEAD OF FROM ABOUT 0.01 TO ABOUT 1.0, A THISOESTER OF A CYCLIC DITHIOPHOSPHORIC ACID HAVING THE FORMULA