Gasoline composition containing acid anhydrides

A fuel composition containing an acid anhydride as an anti-knock additive.

BACKGROUND OF THE INVENTION 
The present invention relates to an antiknock additive for fuel 
compositions, primarily gasoline compositions. 
The petroleum industry has long recognized a need for greater fuel economy 
and efficiency in the operation of gasoline powered spark ignition 
engines. In many instances, high compression ratios are desired in order 
to provide for superior engine performance under various driving 
conditions. In order to provide high performance in high compression 
engines without the risk of knock damage, fuels which will be used in such 
engines require a high octane number and good anti-knock characteristics. 
While octane ratings of fuels can be improved by blending appropriate 
refining streams, the necessary additional refining and blending 
operations needed to obtain a fuel having the desired high octane rating 
are costly. In lieu of these various refining and blending processes the 
petroleum industry sometimes blends antiknock additives into fuels to 
increase the octane number of the fuel. For many refineries the use of 
anti-knock compounds is essential due to the lack of the refining and 
blending facilities to produce the high octane fuels. 
Numerous compounds have been suggested as anti-knock additives for fuel 
compositions. The most successful of these anti-knock compounds additives 
are organo-lead compounds. The future use of organo-lead compounds as 
anti-knock additives is severely limited by recent legislation and may be 
completely prohibited in the future. It is desirable to develop other 
anti-knock additives as replacements for organo-lead compounds. 
Numerous non-lead, anti-knock compounds have been suggested, such as rare 
earth beta-keto-enolate compounds, the lithium and sodium salts of 
organo-amino-cresols, various other organo metallic compounds, in 
particular organo-iron and organo-manganese compounds, such as iron 
pentacarbonyl and methyl cyclopentadienyl manganese tri-carbonyl. In 
addition, it is known to improve the anti-knock and octane properties of 
gasoline by blending alcohol therewith. 
These anti-knock additives have their own associated problems when blended 
into fuels for use in internal combustion engines. The numerous 
organo-iron compounds increase the potential of wear in internal 
combustion engines and the organo-manganese compounds may effect the 
catalytic converters used on most cars today to reduce air pollution for 
exhaust emissions. Fuel compositions of gasoline and alcohol have many 
problems, including separation if water is admixed with the composition 
(due to the gasoline insolubility of many alcohols). 
As can be seen, the petroleum industry has a need for gasoline additives, 
which, while having useful anti-knock properties, do not impart the known 
disadvantages of organo-metallic compounds and alcohol. 
SUMMARY OF THE INVENTION 
The present invention resides in a fuel composition having improved 
anti-knock characteristics comprising a liquid hydrocarbon fuel, 
particularly gasoline, and an anti-knock enhancing amount of a compound of 
the following formula: 
##STR1## 
wherein: 
R and R' are the same or different C.sub.1 -C.sub.20 organic radical, 
preferably a C.sub.1 -C.sub.10 substituted or unsubstituted alkyl or aryl 
radical and most preferably a C.sub.1 -C.sub.10 substituted or 
unsubstituted alkyl radical. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed to a composition comprising a major 
amount of a base fuel and an anti-knock enhancing amount of a compound of 
formula: 
##STR2## 
wherein: 
R and R' are the same or different C.sub.1 -C.sub.20 organic radical, 
usually a C.sub.1 -C.sub.10 alkyl or aryl radical, preferably a C.sub.1 
-C.sub.4 alkyl radical, more preferably a methyl radical and most 
preferably a t-butyl radical. 
Additive compounds having the above structure are generally referred to as 
acid anhydrides, such as n-butyric anhydride, acetic anhydride, propionic 
anhydride, and hexanoic anhydride, the most preferred being pivalic 
anhydride. 
Anti-knock characteristics of an additive are typically evidenced by an 
increase in the motor and research octane numbers of the base fuel when 
the additive is admixed therewith. The motor (MON) and research (RON) 
octane numbers of fuel compositions are typically measured by ASTM D 2700 
and ASTM D 2699, respectively. While motor and research octane numbers are 
themselves good indicators of the anti-knock characteristics of an 
additive, another measure of the anti-knock characteristics of an additive 
is the average of the two numbers (RON+MON)/2. This average provides a 
fairly good approximation of the octane number required by engines under 
typical driving conditions, in that MON is a more severe test, with higher 
compression and temperature, than RON. Furthermore, this average is the 
typical rating used for commercial fuel products. 
The fuel composition may be comprised of any amount of the additive 
compound of this invention which enhances the anti-knock characteristics 
of the fuel to the level desired by the end user. Usually, the anti-knock 
additive comprises a minor amount (i.e., less than 50 percent by volume) 
of the fuel composition. Preferably the fuel composition comprises from 
about 1 volume percent to about 15 volume percent of the additive compound 
of this invention, more preferably from about 5 to about 10 volume percent 
of the additive compound. 
Base fuels to which the anti-knock additive compound of this invention may 
be added to improve the anti-knock properties include all of the volatile 
liquid fuels known to be suitable for spark-ignition, internal combustion 
engines. Preferably, the base fuel composition comprises gasoline, e.g., 
liquid hydrocarbon having a boiling range from about 130.degree. F. to 
about 430.degree. F. These base fuels usually comprise straight chain or 
branch chain paraffins, cycloparaffins, olefins and substituted or 
unsubstituted aromatic hydrocarbons or any mixture of these. This fuel can 
be derived from straight-run naphtha, alkylate gasoline, polymer gasoline, 
natural gasoline, isomerized and/or hydrotreated stocks, catalytically 
cracked or thermally cracked hydrocarbons, catalytically reformed stocks 
and synthetic hydrocarbons stocks derived from the various solid 
carbonaceous materials, e.g. coal or oil shale. In general, any 
conventional, substantially hydrocarbon motor fuel base may be employed in 
the practice of this invention. 
The base fuel may contain other additives normally employed in fuels, e.g., 
anti-icing agents, detergents, demulsifiers, corrosion inhibitors, dyes, 
deposit modifiers, anti-knock, multi-purpose additives and the like, 
However, since this invention relates to anti-knock compounds useful for 
admixture into base fuels, the base fuel used will preferably be 
essentially free of other anti-knock compounds, particularly the 
organo-metallic compounds, e.g., organo-lead and organo-manganese 
compounds, and other anti-knock compounds used in base fuels, 
specifically, alcohols such as methanol. Thus the preferred composition of 
this invention comprises a major portion of a base fuel and an anti-knock 
enhancing amount of the compound of this invention, with the composition 
being essentially free of compounds such as organo-lead and 
organo-manganese compounds and completely free of alcohol. By "essentially 
free of" it is meant that the composition will comprise less than 0.05 
grams/gallon organo-lead and organo-manganese compounds, independently. 
The following examples serve to further illustrate the invention and are 
not intended to be construed as limiting thereof.

EXAMPLES 1-13 
The following Examples 1-13 illustrate the invention. Anti-knocking 
additives of this invention were blended into a base fuel at the levels 
indicated in Table 1. The base fuel was a gasoline containing 33.5 volume 
percent aromatics, 7.5 volume percent olefins and 59 volume percent 
saturants having an A.P.I. gravity of 58.4, vapor pressure of 8.6, a 
sulfur content of 296 ppm, and less than about 0.05 grams/gallon lead. 
Also indicated in Table 1 are the organic radicals of each anti-knock 
additive and the respective RON, MON and (RON+MON)/2 numbers. As can be 
seen the anti-knock additive of this invention increased the RON, MON and 
(RON+MON)/2 significantly over the value for the base fuel when used at a 
concentration of 5 volume percent. 
TABLE 1 
______________________________________ 
Ex- Vol. % 
ample In 
No. R R' Fuel RON MON (R + M)/2 
______________________________________ 
1 t-Butyl t-Butyl 1 134.4 104.5 119 
2 t-Butyl t-Butyl 5 122.5 98.5 111 
3 Ethyl Ethyl 1 94.5 34.5 65 
4 Ethyl Ethyl 5 108.5 88.5 99 
5 Phenyl Phenyl 1 54.4 84.4 69 
6 Phenyl Phenyl 5 98.5 94.5 97 
7 Methyl Methyl 1 74.4 84.4 79 
8 Methyl Methyl 5 112.5 100.5 107 
9 n-Butyl n-Butyl 1 84.4 84.4 84 
10 n-Butyl n-Butyl 5 96.5 86.5 92 
11 n-Propyl n-Propyl 1 94.5 84.4 89 
12 n-Propyl n-Propyl 5 104.5 94.5 100 
13 i-Butyl i-Butyl 1 94.5 84.4 89 
Base -- -- -- 94.4 84.1 89.25 
Fuel 
______________________________________ 
While the preferred embodiments have been described and illustrated, 
various modifications and substitutions may be made thereto without 
departing from the spirit and the scope of the present invention. The 
invention has been described by way of illustration and not limitation, 
and thus no limitation should be imposed other than those as indicated in 
the following claims.