Diesel fuel composition

The invention relates to diesel fuel containing the nitric acid ester of 1-phenyl ethanol as cetane improver.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to improvement in the cetane rating of diesel 
fuel by the addition of a small but effective amount of the nitric acid 
ester of 1-phenyl ethanol herein called methyl benzyl alcohol nitrate 
(MBAN). 
2. Description of the Prior Art 
Diesel engines operate by compression ignition. They have compression 
ratios in the range of 14:1 to 17:1 or higher and for this reason obtain 
more useful work from a given amount of fuel compared to an Otto cycle 
engine. Historically, diesel engines have been operated on a 
petroleum-derived liquid hydrocarbon fuel boiling in the range of about 
300.degree.-750.degree. F. 
One major factor in diesel fuel quality is cetane number. Cetane number is 
related to ignition delay after the fuel is injected into the combustion 
chamber. If ignition delays too long, the amount of fuel in the chamber 
increases and upon ignition results in a rough running engine and 
increased smoke. A short ignition delay results in smooth engine operation 
and decreases smoke. Commercial petroleum diesel fuels generally have a 
cetane number of about 40-55. 
Through the years, many types of additives have been used to raise the 
cetane number of diesel fuel. These include peroxides, nitrites, nitrates, 
nitrosocarbonates and the like. Alkyl nitrates such as amyl nitrate, hexyl 
nitrate and mixed octyl nitrates have been used commercially with good 
results. 
Two main factors determine the commercial potential of a compound for use 
as a cetane improvement additive. These are the ease of handling the 
material and the cost/performance ratio relative to other suitable 
materials. Many nitrate esters have been described that are more effective 
cetane improvement additives than both the nitrate ester described in this 
invention and the commonly used commercial material, 2-ethylhexyl nitrate. 
However, most of these materials are too unstable to be of use in typical 
commercial applications. U.S. Pat. Nos. 4,473,378 and 4,536,190 teach that 
2-methyl-2-nitropropanol nitrate requires stabilization do to its 
shock-sensitive nature. The shock sensitivity of this compound is typical 
of dinitrates from glycols. This shock sensitivity makes this compound 
unsuitable for commercial use. U.S. Pat. No. 4,705,534 teaches that the 
dinitrates prepared from a series of ethyl glycols are also unstable and 
require stabilization. While various stabilization techniques can be used 
to stabilize these nitrates, they are still considered too unstable for 
commercial use. Mononitrates are typically more stable than the 
polynitrates, therefore are more suitable for commercial applications. 
Numerous mononitrates have been reported that produce a larger increase in 
cetane number than the nitrate ester described in this invention. However, 
these compounds are prepared from alcohols more costly than a-phenylethyl 
alcohol, which is used to prepare the nitrate of this invention. Examples 
of such compounds are 4-morpholine ethanol nitrate (U.S. Pat. No. 
4,421,552), tetrahydro-2H-pyran-3-ol nitrate (U.S. Pat. No. 4,405,333), 
1-methyl-3-piperidinol nitrate (U.S. Pat. No. 4,405,334), 
1,3-dioxolane-4-methanol nitrate (U.S. Pat. No. 4,457,763) and 
tetrahydrofuranol nitrate (U.S. Pat. No. 4,406,665). Due to its lower 
cost, the nitrate ester described in this invention has a better 
performance to cost ratio than the nitrate esters described here. 
The performance of mononitrate esters prepared from simple alkanols is 
similar to the performance of the nitrate ester described in this 
invention. The increase in cetane number obtained by adding 1.5% of some 
of these nitrate esters to a base diesel fuel are listed below: 
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Butyl Nitrate 16.8 
Isopropyl Nitrate 17.9 
Primary Amyl Nitrate 13.0 
Secondary Hexyl Nitrate 17.6 
n-Heptyl Nitrate 14.8 
n-Nonyl Nitrate 13.3 
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U.S. Pat. No. 4,723,963 describes improving the cetane rating of diesel 
fuels by adding to the fuels alkyl aromatics having an oxygenate 
functionality in the benzylic position. We are not aware of prior art 
showing the use of nitrate esters of such materials in diesel fuel. 
The preparation of methyl benzyl alcohol nitrate is known. One such 
preparation involves the reaction of the methyl benzyl halide with silver 
nitrate. See Olah, G. A.; Malhotra, R; Narang, S. C.; "Nitration, Methods 
and Mechanisms", VCH Publishers, New York, p. 270 (1989), Heggs, B; J. 
Chem. Soc., 1955, 616, and Komblum, N.; Hardies, D. E.; J. Amer. Chem. 
Soc., 88, 1707 (1966). 
The nitric acid ester can also be produced from the corresponding alcohol, 
1-phenyl ethanol (methyl benzyl alcohol) using either N-nitropyridinium 
tetrafluoroborate or N-nitrocollidium tetrafluoroborate. See Olah, G. A.; 
Malhotra, R.; Narang, S. C.; "Nitration, Methods and Mechanisms", VCH 
Publishers, New York, p. 271 (1989), and Olah, G.; Narang, S. C.; Pearson, 
R. L.; Cupas, C. A.; Syn, 1978, 452. 
Commercial processes for the production of nitric acid esters from 
corresponding alcohols typically use a mixture of nitric acid and sulfuric 
acid. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the invention, improved cetane ratings are achieved with 
diesel fuel having incorporated therein an effective amount of the nitrate 
ester of 1-phenyl ethanol having the formula:

DETAILED DESCRIPTION 
The hydrocarbon based diesel fuels utilized in the practice of this 
invention are comprised in general of mixtures of hydrocarbons which fall 
within the diesel fuel boiling range, typically about 160.degree. to about 
370.degree. C. The fuels are often referred to as middle distillate fuels 
since they comprise the fractions which distill after gasoline. The diesel 
fuels of the invention have a low sulfur content, i.e. not more than 500 
ppm by weight, preferably not more than 100 ppm and preferably not more 
than 60 ppm sulfur by weight. Aromatic content is in the range of 10-50% 
by volume, preferably 20-35% by volume. 
The MBAN is incorporated in the diesel fuel in a small but effective amount 
to improve the cetane rating thereof. The diesel fuel formulations of the 
present invention comprise at least 85% by volume diesel fuel hydrocarbons 
and 0.01 to about 3 volume % of MBAN, preferably about 0.1 to about 2 
volume % MBAN. 
Conventional additives and blending agents for diesel fuel may be present 
in the fuel compositions of this invention in addition. For example, the 
fuels of this invention may contain conventional quantities of 
conventional cetane improvers, friction modifiers, detergents, 
antioxidants, heat stabilizers and the like. The following example 
illustrates the invention. 
EXAMPLE 
a) Preparation of nitric acid (1-phenyl ethanol ester) 
a-Phenylethyl bromide, 18.5 g, is added dropwise to a suspension of silver 
nitrate, 25.6 g, in 150 ml of diethyl ether. The resulting suspension was 
allowed to stir for approximately sixteen hours at room temperature under 
a nitrogen atmosphere. The solution was then filtered and twice washed 
with 50 ml of diethyl ether. The solution was concentrated under vacuum. 
The resultant liquid was then carefully distilled under vacuum, 65.degree. 
C. at 2 torr. The pure product gave the following C.sup.13 NMR spectra in 
CDCl.sub.3 : 20.7, 82.5, 126.7, 129.2, 129.4, 139.2. 
b) Cetane Improvement Tests 
In order to determine the effectiveness of nitric acid (1-phenyl ethanol 
ester) as a cetane improvement additive, the nitrate ester was added in 
varying proportions to a base diesel fuel having a cetane number of 43, an 
aromatic content of 31% and a sulfur level of 370 ppm. In addition to the 
blends containing the nitrate ester of this invention, blends were 
prepared using the same concentrations of the commercial cetane improver, 
2-ethylhexyl nitrate. The samples of the diesel fuel compositions 
containing the nitrate ester of this invention or the commercial material 
were tested for cetane number under the standard test as outlined in ASTM 
D613. 
This test compares the ignition quality of an unknown fuel to that of 
reference fuels under the same operating conditions. The test is conducted 
using a single cylinder test engine with a variable compression ratio. The 
compression is varied to obtain the same time delay between injection and 
ignition for both the test fuel and the reference fuel. The cetane number 
rating of the test fuel is calculated by comparing the compression ratios 
of the test and reference fuels. 
The following results were obtained by this method: 
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Cetane 
Add. Level Cetane Number Net Change 
(vol. %) EHN MBAN EHN MBAN 
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0.0 42.2 42.2 -- -- 
0.5 52.0 50.4 +9.8 +8.2 
1.0 58.3 52.4 +16.1 +10.0 
1.5 63.4 57.4 +21.2 +15.2 
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While the nitrate ester of this invention is slightly less effective than 
the commercial material, it has a cost advantage over the currently 
commercial material. The cost advantage is due to the comparably lower 
cost of starting alcohol, 1-phenyl ethanol. The 1-phenyl ethanol is a 
major product produced during the commercial production of propylene oxide 
from the reaction of ethyl benzene hydroperoxide with propylene.