Gas oil (law451)

A gas oil according to the present invention comprises a gas oil fraction, and has a sulfur content not higher than 0.05 wt %, and either or both of (1) a content of bicyclic and higher aromatic hydrocarbons in a range of from 3.5 wt % to 15 wt %, bicyclic and higher aromatic hydrocarbons having at least one side-chain C.sub.3-11 alkyl group amounting to at least 80 wt % of said first-mentioned bicyclic and higher aromatic hydrocarbons, and (2) a content of nitrogen-containing heterocyclic compounds in a range of from 80 ppm to 500 ppm, nitrogen-containing heterocyclic compounds having at least one side-chain alkyl group accounting for at least 90 wt % of said first-mentioned nitrogen-containing heterocyclic compounds. The gas oil according to the present invention, as a diesel fuel, can impart anti-wearing properties by simply adjusting its components without the need for incorporation of an additive such as an anti-wearing agent. It does not cause wearing of a fuel injection pump, has excellent storage stability and can be furnished as an economical gas oil. It can also be furnished as a gas oil suited for use especially in cold districts.

FIELD OF THE INVENTION 
The present invention relates to a gas oil, which has a low sulfur content 
and excellent lubricity and is suited for use especially in cold 
districts. 
Diesel engines have better gas mileage and lower fuel cost and are more 
durable than gasoline engines, so that they are mounted on trucks, buses, 
watercraft, construction machinery and the like. Keeping step with changes 
in the social environment, diesel engines tend to increase year by year. 
However, sulfur contained in gas oil (diesel fuel) has induced very serious 
social problems and at the meeting of the Central Council for 
Environmental Pollution Control held in December, 1989, it was advised 
that as a short-term target the sulfur content of gas oil be reduced to 
0.2 wt % or lower in 1992 and in the long run to cut it down further to 
0.05 wt % or lower by 1998. A reduction in the sulfur content of gas oil 
is therefore a theme which requires urgent attention. 
A reduction in the sulfur content of gas oil is generally achieved by 
purification, especially catalytic hydrogenation. A reduction in the 
sulfur content of gas oil however leads to a reduction in the lubricity of 
gas oil itself, thereby developing the problem that an injection system of 
a diesel engine may be damaged. Especially, a sulfur content of 0.2 wt % 
or lower causes wearing of an injection pump (in particular, a rotary pump 
and a pump injector) and the extent of its wearing increases in proportion 
to the reduction in the sulfur content. It is therefore known for an 
anti-wearing agent to be added, for example, a fatty acid ester or the 
like. Problems associated with gas oil added with such an additive however 
include high price and poor storage stability. 
An object of the present invention is therefore to provide a gas oil having 
excellent anti-wearing properties by specifying properties of a gas oil 
fraction without the need for addition of an anti-wearing agent. 
DESCRIPTION OF THE INVENTION 
The present invention therefore provides a gas oil comprising a gas oil 
fraction and having a sulfur content not higher than 0.05 wt %, and either 
or both of (1) a content of bicyclic and higher aromatic hydrocarbons 
(hereinafter called "polycyclic aromatic hydrocarbons") in a range of from 
3.5 wt % to 15 wt %, bicyclic and higher aromatic hydrocarbons having at 
least one side-chain C.sub.3-11 alkyl group (hereinafter called 
"long-chain-alkyl-substituted polycyclic aromatic hydrocarbons") amounting 
to at least 80 wt % of said first-mentioned bicyclic and higher aromatic 
hydrocarbons, and (2) a content of nitrogen-containing heterocyclic 
compounds in a range of from 80 ppm to 500 ppm, nitrogen-containing 
heterocyclic compounds having at least one side-chain alkyl group 
accounting for at least 90 wt % of said first-mentioned 
nitrogen-containing heterocyclic compounds. 
The gas oil according to the present invention comprises a gas oil fraction 
which has been obtained by subjecting crude oil, especially a paraffin or 
mixed-base crude oil, to atmospheric distillation and then purifying the 
resultant distillate by hydrogenation. It has distillation properties of 
330.degree. C. or lower in terms of 90% distillation temperature (boiling 
points and distillation temperatures are those measured according to JIS K 
2254) and satisfies the standard for gas oil specified in JIS K 2204. 
The gas oil according to the present invention satisfies these standards 
and its sulfur content has been reduced to 0.05 wt % or lower. Further, it 
contains either or both of (1) specific aromatic hydrocarbon components 
and (2) particular nitrogen-containing heterocyclic compound components in 
the prescribed amounts, respectively. 
The aromatic hydrocarbon content of gas oil after hydrogenation is 
generally in a range of from 20 wt % to 30 wt % although it varies 
depending on the extent of the hydrogenation. It can be broken down into 
12 wt % to 27 wt % of monocyclic compounds and 2 wt % to 15 wt % of 
polycyclic compounds. In the gas oil according to the present invention, 
the content of polycyclic aromatic hydrocarbons in the gas oil is limited 
to 3.5 wt % to 15 wt %, preferably 3.5 wt % to 10 wt %. A content of 
polycyclic aromatic hydrocarbons higher than 15 wt % will lead to exhaust 
gas containing more particulates and is not preferred. On the other hand, 
a content of polycyclic aromatic hydrocarbons lower than 3.5 wt % will 
result in a gas oil having inferior anti-wearing properties. 
Concerning the distribution of aromatic hydrocarbons as broken down 
depending on the carbon numbers of their substituent akyl groups, a 
distribution substantially in the form of a normal distribution curve is 
drawn with those having one or more side-chain C.sub.5-7 alkyl groups 
forming a peak (their proportion ranging from 35 wt % to 50 wt %). Those 
having one or more C.sub.1-2 substituent alkyl groups approximately 
account for 5 wt % to 15 wt %. Further, those having one or more C.sub.12 
or higher alkyl groups are practically not found in ordinary gas oil. 
In the gas oil according to the present invention, the preferred number of 
carbon atoms in each side-chain alkyl group ranges from 3 to 11. A carbon 
number smaller than 3 is not effective for lubricity, while a carbon 
number greater than 11 leads to thermal instability. 
Polycyclic aromatic compounds contain those having one or more C.sub.3-11 
alkyl groups in a proportion of 80 wt % or higher, preferably 90 wt % or 
higher. Owing to this feature, the gas oil can exhibit superb lubricity 
despite it having a sulfur content as low as 0.05 wt % or less. 
Although detailed reasons have not been elucidated yet, a monocyclic 
aromatic hydrocarbon is presumed to give no significant contribution to 
the lubricity of a gas oil even if it contains one or more alkyl groups as 
substituent groups because the van der Waals force of the aromatic ring is 
so small that no substantial interaction takes place between molecules 
under high load. On the other hand, polycyclic aromatic hydrocarbons 
containing 80 wt % or more of long-chain-alkyl-substituted polycyclic 
aromatic hydrocarbons are believed to have strong interaction between 
molecules under high load and hence to show high viscosity owing to 
tangling of molecules, thereby presumably showing excellent lubricity. 
Further, the lubricity is presumed to be affected by the length of 
side-chain substituent groups rather than the number thereof. 
The content of polycyclic aromatic hydrocarbons in a gas oil and the 
distribution thereof as broken down depending on their carbon numbers can 
be determined by providing 5 g of the gas oil as a sample, extracting its 
saturated components with n-hexane, subjecting the residue to 
column-chromatographic separation chromatographic column: 25 
mmf.times.900 mm, chromatographic gel: 200 g (40 g/gram of sample) of 
silica gel ("#12", product of Fuji Silysia Chemical Ltd.), solvent: 600 ml 
(3 ml/gram of gel) of toluene! and then subjecting the thus-obtained 
aromatic components to mass spectrometry, by the fragment ionization 
method. 
A description will next be made about the nitrogen-containing heterocyclic 
compounds. 
Concerning the total content of nitrogen-containing heterocyclic compounds 
in general gas oil, it ranges from 20 ppm to 500 ppm in a gas oil fraction 
obtained in a straight ran. After hydrogenation, however, it is generally 
decreased to 10 ppm to 200 ppm although it varies depending on the extent 
of the hydrogenation. Nitrogen-containing heterocyclic compounds contained 
in such a gas oil are mostly carbazole compounds but also include indole 
compounds in trace proportions. Further, side-chain alkyl groups are those 
containing 0 to 4 carbon atoms and those containing 5 or more carbon atoms 
are practically not found in gas oil. In general, side-chain alkyl groups 
having 1 to 3 carbon atoms are predominant. 
In the gas oil according to the present invention, the sulfur content has 
been reduced to 0.05 wt % or lower and the content of nitrogen-containing 
heterocyclic compounds has been controlled to 80 ppm to 500 ppm, 
preferably 100 ppm to 500 ppm. A content of nitrogen-containing 
heterocyclic compounds greater than 500 ppm will lead to reduced 
low-temperature fluidity and is not preferred. On the other hand, a 
content smaller than 80 ppm will result in inferior anti-wearing 
properties. 
Further, as nitrogen-containing heterocyclic compounds, those containing 
one or more alkyl groups as side-chain substituent groups are preferred. 
It is also preferred that nitrogen-containing heterocyclic compounds 
containing one or more side-chain alkyl groups as substituents account for 
90 wt % or more of all the nitrogen-containing heterocyclic compounds 
present. This feature can provide excellent lubricity despite the sulfur 
content being as low as 0.05 wt % or less. 
Although detailed reasons for this advantage have not been fully elucidated 
yet, it is presumed that a nitrogen-containing heterocyclic compound 
having no substituent group does not contribute to the lubricity of a gas 
oil but a nitrogen-containing heterocyclic compound having one or more 
alkyl groups as side-chain substituent groups exhibits oiliness owing to 
adsorption of a nitrogen atom in the molecule on a metal surface and shows 
excellent lubricity owing to interaction of the substituent alkyl groups. 
The content of nitrogen-containing heterocyclic compounds in a gas oil and 
the distribution thereof as broken down depending on their carbon numbers 
can be determined by providing 5 g of the gas off as a sample, extracting 
its saturated components with n-hexane and its aromatic hydrocarbon 
components with toluene, subjecting the residue to column-chromatographic 
separation chromatographic column: 25 mmf.times.900 mm, chromatographic 
gel: 200 g (40 g/gram of sample) of silica gel ("#12", product of Fuji 
Silysia Chemical Ltd.), solvent: 600 ml (3 ml/gram of gel) of methanol! 
and then subjecting the thus-obtained polar components to mass 
spectrometry (by the fragment ionization method). 
The followings are the compositions of illustrative gas oils obtained by 
hydrogenation and desulfurization: 
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(1) 
Sulfur content 0.03 wt % 
Polycyclic aromatic hydrocarbon content 
1.0 wt % 
Bicyclic aromatic hydrocarbon content 
2.9 wt % 
Percentage of long-chain-alkyl-substituted 
86 wt % 
polycyclic aromatic hydrocarbons in polycyclic 
aromatic hydrocarbons 
Content of nitrogen-containing heterocyclic 
11 ppm 
compounds 
Percentage of nitrogen-containing heterocyclic 
92 wt % 
compounds containing one or more alkyl 
groups as side chains in nitrogen-containing 
heterocyclic compounds 
(2) 
Sulfur content 0.03 wt % 
Polycyclic aromatic hydrocarbon content 
1.3 wt % 
Bicyclic aromatic hydrocarbon content 
1.5 wt % 
Percentage of long-chain-alkyl-substituted 
72 wt % 
polycyclic aromatic hydrocarbons in polycyclic 
aromatic hydrocarbons 
Content of nitrogen-containing heterocyclic 
20 ppm 
compounds 
Percentage of nitrogen-containing heterocyclic 
82 wt % 
compounds containing one or more alkyl groups 
as side chains in nitrogen-containing heterocyclic 
compounds 
(3) 
Sulfur content 0.2 wt % 
Polycyclic aromatic hydrocarbon content 
3.5 wt % 
(including bicyclic aromatic hydrocarbon content) 
Bicyclic aromatic hydrocarbon content 
2.9 wt % 
Percentage of long-chain-alkyl-substituted 
60 wt % 
polycyclic aromatic hydrocarbons in polycyclic 
aromatic hydrocarbons 
(4) 
Sulfur content 0.01 wt % 
Polycyclic aromatic hydrocarbon content 
1.7 wt % 
(including bicyclic aromatic hydrocarbon content) 
Bicyclic aromatic hydrocarbon content 
1.5 wt % 
Percentage of long-chain-alkyl-substituted 
75 wt % 
polycyclic aromatic hydrocarbons in polycyclic 
aromatic hydrocarbons 
(5) 
Sulfur content 0.01 wt % 
Content of nitrogen-containing heterocyclic 
14 ppm 
compounds 
Percentage of nitrogen-containing heterocyclic 
88 wt % 
compounds containing one or more alkyl groups 
as side chains in nitrogen-containing heterocyclic 
compounds 
(6) 
Sulfur content 0.05 wt % 
Content of nitrogen-containing heterocyclic 
60 ppm 
compounds 
Percentage of nitrogen-containing heterocyclic 
93 wt % 
compounds containing one or more alkyl groups 
as side chains in nitrogen-containing heterocyclic 
compounds 
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The gas oil according to the present invention can be prepared, for 
example, by blending gas oils--which have a high aromatic hydrocarbon 
content and contain nitrogen-containing heterocyclic compounds in a large 
amount, respectively--to a hydrogenated and desulfurized gas oil as 
needed. As a gas oil rich in aromatic components, it is possible to use, 
for example, a catalytically-cracked gas oil which has been obtained by 
subjecting heavy oil, a straight run fraction of crude oil, to catalytic 
cracking. 
Further, the gas oil according to the present invention can be added with a 
pour-point lowering agent, a cetane number improving agent and the like as 
needed. 
The gas oil according to the present invention can impart anti-wearing 
properties owing only to the adjustment of its components without the need 
for incorporation of an additive such as an anti-wearing agent. It is an 
economical fuel oil having excellent storage stability and can be provided 
as a gas oil suited for use especially in cold districts.

EXAMPLES 
A description will next be made about a wear test which was adopted in 
Examples. 
The wear test adopted in the present invention is specified under ISO/TC 
22/SC7 N595. Using high frequency reciprocating rig equipment ("HFRR", 
manufactured by PCS Company), the test is conducted under the 
below-described test conditions to measure a wear scar diameter (.mu.m). 
According to this measuring method, a gas oil excellent in anti-wearing 
properties results in a smaller wear scar diameter but conversely, a gas 
oil inferior in anti-wearing properties leads to a greater wear scar 
diameter. 
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Oil volume 1 .+-. 0.20 ml 
Stroke length 1 .+-. 0.02 mm 
Frequency 50 .+-. 1 Hz 
Oil temperature 25 .+-. 2.degree. C., or 60 .+-. 2.degree. C. 
Load 200 g 
Testing time 75 .+-. 0.1 minutes 
Oil surface area 6 .+-. 1 cm.sup.2 
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Example 1 
A gas oil fraction having the properties and composition shown in Table 1 
was obtained as Sample Oil 1, which was a fuel oil according to the 
present invention, by mixing a gas oil base material having high aromatic 
properties with a gas oil fraction obtained by atmospheric distillation of 
crude oil and desulfurized to a sulfur content of 0.05 wt %. 
Example 2 
A gas oil fraction having the properties and composition shown in Table 1 
was obtained as Sample Oil 2, which was a fuel oil according to the 
present invention, by adjusting the aromatic components of a gas oil 
fraction, which had been obtained by atmospheric distillation of crude oil 
and desulfurized to a sulfur content of 0.05 wt %, as in Example 1. 
Example 3 
A gas oil fraction having the properties and composition shown in Table 1 
was obtained as Sample Oil 3, which was a fuel oil according to the 
present invention, by adding isopropylnaphthalene and 
di-tert-butylnaphthalene to Comparative Oil 1, which had been obtained by 
atmospheric distillation of crude oil, desulfurized to a sulfur content of 
0.01 wt % and shown below in Table, 1, so that the contents of 
isopropylnaphthalene and di-tert-butylnaphthalene became 0.8 wt % and 1.0 
wt %, respectively. 
Comparative Example 1 
A gas oil shown below in Table 1 was provided as Comparative Oil 1. 
Comparative Example 2 
Prepared as Comparative Oil 2 was a gas oil fraction obtained by 
atmospheric distillation of crude oil, desulfurized to a sulfur content of 
0.2 wt % and having the properlies and composition shown in Table 1. 
Sample Oils 1 to 3 and Comparative Oils 1 to 2, which had been prepared as 
described above were subjected to a wear test at 60.degree. C. The results 
are also shown below in Table 1. 
TABLE 1 
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Comparative 
Examples Examples 
1 2 3 1 2 
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Density (g/cm) 
0.83 0.82 0.82 0.82 0.82 
Cetane index 60 63 63 67 63 
Viscosity (30.degree. C., mm/s) 
3.64 3.44 3.40 3.37 3.51 
Sulfur content (wt %) 
0.05 0.05 0.01 0.01 0.2 
IBP (.degree.C.) 
176 157 153 153 157 
T20(.degree.C.) 
240 233 232 232 239 
T50(.degree.C.) 
278 275 276 274 277 
T90(.degree.C.) 
327 326 330 324 326 
Content of polycyclic 
8.4 3.6 3.5 1.7 3.5 
aromatic hydrocarbons 
(wt %) 
Ratio of polycyclic 
90 85 93 75 60 
aromatic hydrocarbons 
with long-chain alkyl 
substituents to 
polycyclic aromatic 
hydrocarbons (wt %) 
HFRR value (.mu.m) as 
420 440 430 620 580 
wear tests result 
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As is appreciated from the table, the fuel oils according to the present 
invention are excellent in anti-wearing properties. 
Example 4 
A fuel oil having the properties and composition shown in Table 2 was 
obtained as Sample Oil 4 according to the present invention by mixing a 
gas oil base material, which contained nitrogen-containing heterocyclic 
compounds in a large amount, with a gas oil fraction obtained by 
atmospheric distillation of crude oil and desulfurized to a sulfur content 
of 0.05 wt % and hence adjusting the content of the nitrogen-containing 
heterocyclic compounds. 
Example 5 
A fuel oil having the properties and composition shown in Table 2 was 
obtained as Sample Oil 5 according to the present invention by adjusting 
the content of nitrogen-containing heterocyclic compounds in a gas oil 
fraction, which had been obtained by atmospheric distillation of crude oil 
and desulfurized to a sulfur content of 0.05 wt %, as in Example 4. 
Example 6 
A fuel oil having the properties and composition shown in Table 2 was 
obtained as Sample Oil 6 according to the present invention by adding 
methylcarbazole and ethylcarbazole to Comparative Oil 3, which had been 
obtained by atmospheric distillation of crude oil, desulfurized to a 
sulfar content of 0.01 wt % and shown below in Table 2, so that the 
contents of methylcarbazole and ethylcarbazole became 26 ppm and 40 ppm, 
respectively. 
Comparative Example 3 
Prepared as Comparative Oil 3 was the gas oil which was a gas oil fraction 
obtained by atmospheric distillation of crude oil and desulfurized to a 
sulfur content of 0.01 wt % and which had the properties and composition 
shown in Table 2. 
Comparative Example 4 
Prepared as Comparative Oil 4 was a gas oil fraction obtained by 
atmospheric distillation of crude oil, desulfurized to a sulfur content of 
0.2 wt % and having the properties and composition shown in Table 2. 
Sample Oils 4 to 6 and Comparative Oils 3 to 4, which had been prepared as 
described above were subjected to a wear test at 60.degree. C. The results 
are also shown below in Table 2. 
TABLE 2 
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Comparative 
Examples Examples 
4 5 6 3 4 
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Density (g/cm) 
0.83 0.82 0.83 0.82 0.82 
Cetane index 60 63 64 67 63 
Viscosity (30.degree. C., mm/s) 
3.64 3.44 3.40 3.37 3.51 
Sulfur content (wt %) 
0.05 0.05 0.01 0.01 0.2 
IBP (.degree.C.) 
176 157 153 153 157 
T20(.degree.C.) 
240 233 232 232 239 
T50(.degree.C.) 
278 275 276 274 277 
T90(.degree.C.) 
327 326 330 324 326 
Content of nitrogen 
116 84 80 14 60 
containing heterocyclic 
compounds (ppm) 
Ratio of nitrogen- 
93 94 94 88 93 
containing heterocyclic 
compounds with side 
chain alkyl substituents 
to nitrogen-containing 
heterocyclic compounds 
(wt %) 
HFRR value (.mu.m) as 
420 440 430 620 580 
wear tests result 
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As is appreciated from the table, the fuel oils according to the present 
invention are excellent in anti-wearing properties. 
Example 7 
A fuel oil having the properties and composition shown in Table 3 was 
prepared as Sample Oil 7 according to the present invention by mixing a 
gas oil base material, which had high aromatic properties and contained 
nitrogen-containing heterocyclic compounds in a large amount, with a gas 
oil fraction obtained by atmospheric distillation of crude oil and 
desulfurized to a sulfur content of 0.4 wt % and hence adjusting the 
aromatic hydrocarbon components and nitrogen-containing heterocyclic 
compound components. 
Example 8 
A fuel oil having the properties and composition shown in Table 3 was 
prepared as Sample Oil 8 according to the present invention by adjusting 
the aromatic hydrocarbon components and nitrogen-containing heterocyclic 
compound components in a gas oil fraction, which had been obtained by 
atmospheric distillation of crude oil and desulfurized to a sulfur content 
of 0.01 wt %, as in Example 7. 
Comparative Example 5 
Prepared as Comparative Oil 5 was a gas oil which was a gas oil fraction 
obtained by atmospheric distillation of crude oil and desulfurized to a 
sulfur content of 0.03 wt % and which had the properties and composition 
shown in Table 3. 
Comparative Example 6 
Prepared as Comparative Oil 6 was a gas oil fraction obtained by 
atmospheric distillation of crude oil, desulfurized to a sulfur content of 
0.03 wt % and having the properties and composition shown in Table 3. 
The Sample Oils 7 to 8 and Comparative Oils 5 to 6, which had been prepared 
as described above were subjected to a wear test at 60.degree. C. The 
results are also shown below in Table 3. 
TABLE 3 
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Comparative 
Examples Examples 
7 8 5 6 
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Density (g/cm) 0.81 0.81 0.80 0.80 
Cetane index 53 52 55 55 
Viscosity (30.degree. C., mm/s) 
1.81 1.82 1.74 1.74 
Sulfur content (wt %) 
0.04 0.01 0.03 0.03 
IBP (.degree.C.) 
139 140 140 141 
T20(.degree.C.) 188 184 186 187 
T50(.degree.C.) 216 214 213 213 
T90(.degree.C.) 289 290 279 277 
Content of polycyclic aromatic 
5.0 4.0 1.0 1.3 
hydrocarbons (wt %) 
Ratio of polycyclic aromatic 
85 90 86 72 
hydrocarbons with long-chain 
alkyl substituents to polycyclic 
aromatic hydrocarbons (wt %) 
Content of nitrogen-containing 
83 122 11 20 
heterocyclic compounds (ppm) 
Ratio of nitrogen-containing 
91 95 92 82 
heterocyclic compounds with 
side chain alkyl substituents to 
nitrogen-containing 
heterocyclic compounds (wt %) 
HFRR value (.mu.m) as wear tests 
410 430 610 590 
result 
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