TECHNICAL FIELD
[0001] The present invention relates to a gas oil composition, in particular to a gas oil
composition which can be used in a very low temperature environments.
BACKGROUND ART
[0002] In general, a gas oil composition is produced by blending one or more types of blendstocks
produced by subjecting a straight gas oil or straight kerosene, produced through an
atmospheric distillation unit of crude oil to hydrorefining or hydrodesulfurization.
In particular, it is often the case that the blend ratio of the foregoing kerosene
blendstock and gas oil blendstock is controlled in order to ensure low temperature
fluidity during a winter season. If necessary, the blendstocks are blended with additives
such as cetane number improvers, detergents, and cold flow improvers.
[0003] In recent years, the use of Fischer Tropsch synthetic oil (hereinafter, referred
to as "FT synthetic oil") obtained by Fischer Tropsch synthesis using carbon monoxide
and hydrogen as feedstocks, as one of alternative fuels for a petroleum-based fuel
is considered. When gas oil for diesel fuel is produced from FT synthetic oil, gas
oil free of sulfur content can be obtained. Thus, the FT synthetic gas oil is preferable
in terms of reducing environmental impact.
[0004] However, the above-described FT synthetic oil has a relatively high content of straight-chain
saturated hydrocarbon (normal paraffin) compounds. It has been pointed out that in
particular when heavy normal paraffin compounds are contained, there is the possibility
that they would deposit in the form of wax. Further, the FT synthetic blendstock is
a hydrocarbon mixture containing predominantly the aforesaid normal paraffin and saturated
hydrocarbons having a side chain (isoparaffin) and thus generally has poor oil solubility.
Accordingly, there is a case that additives to be dissolved in fuel oils such as gas
oil, highly relying on their oil soluble groups (straight-chain alkyl group or the
like) would be hardly dissolved. With this being the situation, there has been a problem
in that gas oil derived from FT synthetic oil cannot be used in a low temperature
environment.
[0005] In order to solve the above problem, various techniques have been developed. For
example,
JP 2007-270109 A (PTL 1) discloses a technique of adding and mixing a lubrication improver and a cold
flow improver to and with a FT synthetic gas oil composition having a certain composition
to thereby improve the fluidity in a low temperature environment.
CITATION LIST
Patent Literature
SUMMARY OF INVENTION
(Technical Problem)
[0007] However, considering the use of a gas oil composition in cold climate areas such
as the Arctic Circle or the Antarctic Circle, the FT synthetic gas oil composition
obtained by the technique described in PTL 1 would not exhibit sufficient fluidity.
Therefore, it has been required to improve the low temperature performance.
[0008] Further, when the aforesaid FT synthetic gas oil is used as fuel for a diesel engine,
in order to keep favorable startability in engine combustion and stability in idling,
the kinetic viscosity at 30 °C is required to be high. On the other hand, in order
to improve the fluidity in a low temperature environment, the pour point is required
to be low. In short, since there is a trade-off between the favorable kinetic viscosity
and the favorable pour point, it has been difficult to achieve the both using conventional
techniques. Therefore, it is desirable to develop a technique making it possible to
improve the fluidity without reducing the kinetic viscosity even in a severe low temperature
environment.
[0009] The present invention was made in view of the above circumstances, and an object
thereof is to provide a gas oil composition that provides superior low temperature
performance as compared with the conventional techniques even if it contains as a
feedstock, an oil having a high normal paraffin content, such as an FT synthetic oil.
(Solution to Problem)
[0010] The inventors of the present invention made various studies on the above problem
to find that excellent fluidity in a low temperature environment can be realized without
reducing the kinetic viscosity, by optimizing the composition of a gas oil composition
and also adding a certain amount of a cold flow improver to the gas oil composition.
[0011] The invention is made based on such findings, and the summary is as follows.
- (1) A gas oil composition, wherein a sulfur content is 1 ppm by mass or less, an aromatic
content is 1 % by mass or less, a C5-C15 paraffin content is 30 % to 85 % by mass,
a C20-C27 paraffin content is 3 % to 20 % by mass, and a isoparaffin content is 50
% to 75 % by mass,
characterized in that the gas oil composition comprise a cold flow improver at 20
ppm to 1000 ppm by mass.
- (2) The gas oil composition according to (1), wherein the pour point is -70 °C to
-35 °C and the kinetic viscosity at 30 °C is 1.5 mm2/s to 4.0 mm2/s.
- (3) The gas oil composition according to (1), comprising Fischer Tropsch synthetic
oil.
(Advantageous Effect of Invention)
[0012] The present invention makes it possible to provide a gas oil composition providing
superior low temperature performance as compared with the case of using the conventional
techniques even if an oil having a high normal paraffin content is used as a feedstock.
DESCRIPTION OF EMBODIMENTS
[0013] The invention of the present application is described below in detail.
[0014] A gas oil composition of the present invention has a sulfur content of 1 ppm by mass
or less, an aromatic content of 1 % by mass or less, a C5-C15 paraffin content of
30 % to 85 % by mass, a C20-C27 paraffin content of 3 % to 20 % by mass, and an isoparaffin
content of 50 % to 75 % by mass; and contains 20 ppm to 1000 ppm by mass of a cold
flow improver.
(Sulfur content, Aromatic content)
[0015] The gas oil composition of the present invention has a sulfur content of 1 ppm by
mass or less and an aromatic content of 1 % by mass or less. In order to further reduce
particulates emitted from a diesel engine, and in terms of further improving the fuel
efficiency, the sulfur content is 1 ppm by mass or less and the aromatic content is
1 % by mass or less.
(C5-C15 Paraffin content)
[0016] The gas oil composition of the present invention has a C5-C15 paraffin content of
30 % to 85 % by mass, preferably 40 % to 70 % by mass. The C5-C15 paraffin content
is limited to 30 % by mass or more in terms of improving the startability of a diesel
engine and the stability in idling, and is limited to 85 % by mass or less in terms
of reducing the particulates emitted from the diesel engine.
(C20-C27 Paraffin content)
[0017] The gas oil composition of the present invention has a C20-C27 paraffin content of
3 % to 20 % by mass, preferably 7 % to 16 % by mass. The C20-C27 paraffin content
needs to be 3 % by mass or more for favorable solubility of the cold flow improver,
and needs to be 20 % by mass or less for favorable low temperature fluidity of the
gas oil composition.
(Isoparaffin content)
[0018] The gas oil composition of the present invention has an isoparaffin content of 50
% to 75 % by mass, preferably 60 % to 70 % by mass. In order to improve the startability
and operability at a low temperature, the isoparaffin content needs to be 50 % by
mass or more, whereas in order to obtain a gas oil composition with high yield, the
isoparaffin content needs to be 75 % by mass or less.
(Mass ratio between normal paraffin and isoparaffin)
[0019] Further, the mass ratio of the normal paraffin content with respect to the isoparaffin
content (normal paraffin content / isoparaffin content) is preferably in the range
of 0.3 to 1.0, more preferably in the range of 0.4 to 0.7. In terms of improving the
startability in the combustion and the stability in idling of a diesel engine under
very low temperature weather conditions, the mass ratio (normal paraffin content /
isoparaffin content) is preferably 0.3 or more. Since a certain amount of isoparaffin
is contained due to isomerization in order to achieve favorable startability and operability
at low temperatures, the mass ratio is preferably 1.0 or less.
(Distillation properties)
[0020] The gas oil composition of the present invention preferably has a 5 % distillation
temperature of 140 °C to 200 °C, more preferably 150 °C to 195 °C. In order to improve
the startability of a diesel engine and the stability in idling, the 5 % distillation
temperature is 140 °C or more, whereas in order to achieve favorable startability
and operability at low temperatures, the 5 % distillation temperature is preferably
200 °C or less.
[0021] Further, the gas oil composition of the present invention preferably has a 95 % distillation
temperature of 300 °C to 340 °C, more preferably 310 °C to 330 °C. In terms of improving
the specific fuel consumption of a diesel engine, the 95 % distillation temperature
is preferably 300 °C or more, whereas in terms of reducing particulates emitted from
the diesel engine, the 95 % distillation temperature is preferably 340 °C or less.
(Density)
[0022] The gas oil composition of the present invention preferably has a density at 15 °C
of 0.750 g/cm
3 to 0.780 g/cm
3, more preferably 0.760 g/cm
3 to 0.780 g/cm
3. The density at 15 °C is 0.750 g/cm
3 or more for favorable specific fuel consumption of a diesel engine, and is 0.780
g/cm
3 or less for favorable low temperature fluidity of the gas oil composition.
(Cloud point)
[0023] Further, the gas oil composition of the present invention preferably has a cloud
point of -35 °C or less, more preferably -55 °C or less so as to withstand the use
under very low temperature weather conditions. The cloud point used herein means the
pour point measured based on JIS K 2269 "Testing method for pour point and cloud point
of crude oil and petroleum products".
(Kinetic viscosity at 30 °C)
[0024] The gas oil composition of the present invention preferably has a kinetic viscosity
at 30 °C of 1.5 mm
2/s to 4.0 mm
2/s, more preferably 2.0 mm
2/s to 3.5 mm
2/s. The kinetic viscosity at 30 °C is 1.5 mm
2/s or more in terms of improving the startability of a diesel engine or the stability
in idling, and is preferably 4.0 mm
2/s or less in terms of reducing particulates emitted from the diesel engine.
(Pour point)
[0025] The pour point of the gas oil composition of the present invention is preferably
-35 °C or less. In order to achieve favorable low temperature fluidity under very
low temperature weather conditions, the pour point is preferably -35 °C or less, more
preferably -55 °C or less.
[0026] The pour point need not be lower than necessary, and the pour point is preferably
-70 °C or more, more preferably -66 °C or more in terms of the production cost of
the gas oil composition.
(Cold flow improver)
[0027] The gas oil composition of the present invention is required to contain 150 ppm to
1000 ppm by mass of a cold flow improver, the content of the cold flow improver is
preferably 150 ppm to 500 ppm by mass, more preferably 200 ppm to 300 ppm by mass.
The content (addition amount) of the cold flow improver is 150 ppm by mass or more
in order to prevent a filter of a diesel powered automobile from being plugged in
a low temperature situation, and is 1000 ppm by mass or less in terms of the effectiveness
of the cold flow improver and the economic efficiency.
[0028] As the cold flow improver, ethylene-vinyl acetate copolymer and/or a cold flow improver
having a surfactant effect are/is used. Examples of the cold flow improver having
a surfactant effect include one or more selected from copolymers of ethylene and methyl
methacrylate, copolymers of ethylene and α-olefin, chlorinated methylene-vinyl acetate
copolymers, alkyl ester copolymers of unsaturated carboxylic acids, eaters synthesized
from nitrogen-containing compounds having a hydroxyl group and saturated fatty acids
and salts of the esters, esters and amide derivatives synthesized from polyhydric
alcohols and saturated fatty acids, esters synthesized from polyoxyalkylene glycol
and saturated fatty acid, esters synthesized from alkyleneoxide adducts of polyhydric
alcohols or partial esters thereof and saturated fatty acids, chlorinated paraffin/naphthalene
condensates, alkenyl succinamides, and amine salts of sulfobenzoic acids.
(Lubricity improver)
[0029] The gas oil composition of the present invention preferably contains a lubricity
improver at a concentration of 20 mg/L to 300 mg/L, more preferably 50 mg/L to 200
mg/L. With the addition amount of the lubricity improver being within the range of
20 mg/L to 300 mg/L, the efficacy of the added lubricity improver can be effectively
exerted. For example, for a diesel engine equipped with a distributor injection pump,
increase in the driving torque of the pump in operation can be suppressed and the
wear of the pump can be reduced.
[0030] As for the type of the lubricity improver, a lubricity improver containing a compound
which comprises a fatty acid and/or a fatty acid ester and has a polar group is used.
There is no particular restriction on the specific name of the compounds and so on.
For example, any one or more selected from carboxylic acid-, ester-, alcohol- and
phenol-based lubricity improvers can be used. Out of those, carboxylic acid- and ester-based
lubricity improvers are preferred. Examples of the carboxylic acid-based lubricity
improver include linoleic acid, oleic acid, salicylic acid, palmitic acid, myristic
acid or hexadecenoic acid or a mixture of two or more of these carboxylic acids. Carboxylic
acid esters of glycerin can be given as an example of the ester-based lubricity improver.
The carboxylic acid ester may include one or more carboxylic acids. Specific examples
of the carboxylic acids include linoleic acid, oleic acid, salicylic acid, palmitic
acid, myristic acid, and hexadecenoic acid. The weight-average molecular weight of
the active component of the lubricity improver is preferably 200 or more and 1000
or less in order to enhance the solubility to the gas oil composition.
(Other additives)
[0031] In order to further enhance the properties of the gas oil compositions of the present
invention, other known fuel oil additives mentioned later (hereinafter referred to
as "other additives" for convenience) may be used alone or in combination. Examples
of the other additives include phenolic-and aminic- antioxidants; metal deactivators
such as salicyliden derivatives; anti-corrosion agents such as aliphatic amines and
alkenyl succinic acid esters; anti-static additives such as anionic, cationic, and
amphoteric surfactants; coloring agents such as azo dye; silicone-based antifoaming
agents and antifreezing agents such as 2-methoxyethanol, isopropyl alcohol, and polyglycol
ethers.
[0032] The amounts of the other additives may be set to any value. Especially, the amount
of each of the other additives is preferably 0.5 % by mass or less, more preferably
0.2 % by mass or less, on the basis of the total amount of the gas oil composition.
[0033] There is no particular restriction on the other specifications of a diesel engine
in which the gas oil composition of the present invention is used, the applications
thereof, and the environment where the gas oil composition is used.
(FT Synthetic oil)
[0034] The gas oil composition of the present invention preferably further contains Fischer
Tropsch synthetic oil (FT synthetic oil). As described above, the FT synthetic oil
contains a relatively large amount of straight-chain saturated hydrocarbon (normal
paraffin) compounds and accordingly, a gas oil derived from an FT synthetic oil cannot
be used in a low temperature environment, which has been a problem. Thus, the advantageous
effect of the present invention can be exerted most significantly.
[0035] Further, in order to suppress the consumption of oil base blendstock by using an
FT synthetic oil in terms of alternative fuels for petroleum, the gas oil composition
preferably contains an FT synthetic oil.
[0036] For example, the FT synthetic oil can be obtained by a production method including
the steps of fractionating an FT synthesis oil into a light fraction and a wax fraction,
hydroisomerizing the light fraction to obtain a hydroisomerized oil, hydrocracking
the wax fraction to obtain a hydrocracked oil, mixing the hydroisomerized oil and
the hydrocracked oil and then supplying it to a product fractionator, and adjusting
the cutting temperature at the product fractionator so as to obtain a kerosene composition
of the invention. Moreover, it is preferable to recycle a bottom oil of the product
fractionator and mix it with the wax fraction and then hydrocrack it thereby obtaining
the hydrocracked oil.
[0037] Furthermore, the light gas oil blendstock and a heavy gas oil blendstock obtained
from the product fractionator may be mixed at a predetermined ratio, thereby producing
a gas oil composition of the present invention. The light gas oil blendstock and the
heavy gas oil blendstock have a sulfur content of 1 ppm by mass or less and an aromatic
content of 1 % by mass or less. The light gas oil blendstock preferably has a density
of 0.740 to 0.760, a 5 % distillation temperature of 155 °C to 175 °C, a 95 % distillation
temperature of 230 °C to 250 °C, a C5-C15 paraffin content of 90 % to 99.9 % by mass,
and an isoparaffin content of 40 % to 55 % by mass. The heavy gas oil blendstock preferably
has a density of 0.770 to 0.790, a 5 % distillation temperature of 240 °C to 260 °C,
a 95 % distillation temperature of 330 °C to 350 °C, a C5-C15 paraffin content of
15 % to 35% by mass, and an isoparaffin content of 70 % to 85 % by mass.
[0038] In addition, it can also be prepared by being blended with a solvent or a blendstock
obtained from each unit of a petroleum refinery plant as appropriate to meet the composition
of the gas oil composition of the present invention.
EXAMPLES
[0039] The present invention will now be described in more detail with Examples; however,
the invention is not limited to any of the following Examples.
[0041] Paraffin content, Isoparaffin content: the paraffin content and isoparaffin content
per carbon atom were measured using GC-FID. The calculation was performed using values
measured using a temperature program (column oven temperature: heated at 8 °C/min
from 140 °C to 355 °C, sample injection temperature: 360 °C, detector temperature:
360 °C) at a carrier gas (helium) flow rate of 1.0 mL/min using a nonpolar column
(stainless steel capillary column ULTRA ALLOY-1) and an FID (flame ionization detector).
(Light gas oil blendstock, Heavy gas oil blendstock)
[0042] A light gas oil blendstock and a heavy gas oil blendstock were prepared in accordance
with the following procedure.
[0043] An FT synthetic oil obtained by FT synthesis was used and a light fraction of the
FT synthetic oil was subjected to hydroisomerization (LHSV: 1.8 h
-1, hydrogen partial pressure: 3.0 MPa, reaction temperature: 320 °C). After that, the
resultant hydroisomerized oil and a hydrocracked oil obtained by performing hydrocracking
(LHSV: 1.8 h
-1, hydrogen partial pressure: 4.0 MPa, reaction temperature: 310 °C) on a wax fraction
of the FT synthetic oil were mixed while recycling (recycling rate: 50 vol%) a bottom
oil (fraction at the cutting temperature: not less than 360 °C) of a product fractionator,
and the mixture was then supplied to the product fractionator. Subsequently, the mixture
was fractionated by the product fractionator, thereby obtaining the light gas oil
blendstock and the heavy gas oil blendstock. The cutting temperature of the light
gas oil blendstock and the heavy gas oil blendstock was 250 °C.
[0044] The composition of the obtained light gas oil blendstock 1 and the heavy gas oil
blendstock 1 is shown in Table 1.
(Examples 1 to 4, Comparative Examples 1 and 2)
[0045] Light gas oil blendstocks and heavy gas oil blendstocks were mixed based on the mixing
ratios shown in Table 1. A cold flow improver (Infineum R240 manufactured by Infineum
Japan Ltd.) was added at 200 ppm by mass to the mixture, thereby obtaining gas oil
compositions used as samples.
[0046] For the gas oil compositions obtained in Examples and Comparative Examples above,
after the properties were measured (note that the distillation temperature, cloud
point, flash point, and cetane index were measured only with respect to Example 2,
Comparative Example 1, and Comparative Example 2), the pour point and kinetic viscosity
were evaluated. The results are shown in Table 1.
[0047] As for the conditions suitable for use under very low temperature weather conditions,
cases where the requirements for the pour point of - 70 °C to -35 °C and the kinetic
viscosity at 30 °C of 1.5 mm
2/s to 4.0 mm
2/s were met were evaluated as "preferable (+)", whereas cases where the requirements
for the pour point of - 66 °C to - 55 °C and the kinetic viscosity at 30 °C of 2.0
mm
2/s to 3.5 mm
2/s were met were evaluated as "particularly preferable (++)". On the other hand, cases
where none of the above conditions were met were evaluated as "poor (-)".
[Table 1]
|
Example 1 |
Example 2 |
Example 3 |
Example 4 |
Comparative Example 1 |
Comparative Example 2 |
Light gas oil blnedstock |
vol% |
20 |
40 |
60 |
80 |
0 |
100 |
Heavy gas oil blnedstock |
vol% |
80 |
60 |
40 |
20 |
100 |
0 |
CFI Addition amount |
mass ppm |
200 |
200 |
200 |
200 |
200 |
200 |
5 % Distillation temperature |
°C |
|
187,5 |
|
|
252 |
165 |
50 % Distillation temperature |
°C |
|
251 |
|
|
293,5 |
197 |
95 % Distillation temperature |
°C |
|
322 |
|
|
339 |
238 |
97 % Distillation temperature |
°C |
|
329 |
|
|
346 |
242 |
Sulfur content |
ppm |
< 1 |
< 1 |
< 1 |
< 1 |
< 1 |
< 1 |
Aromatic content |
mass% |
< 1 |
< 1 |
< 1 |
< 1 |
< 1 |
< 1 |
Density |
g/cm3 |
0,776 |
0,769 |
0,762 |
0,755 |
0,783 |
0,749 |
Cloud point |
°C |
|
-56 |
|
|
-6 |
≤-25 °C |
Pour point |
°C |
-56 |
-58 |
-57 |
-53 |
-54 |
-53 |
Flash point |
°C |
|
59 |
|
|
88 |
48 |
Cetane index |
|
|
84 |
|
|
94,4 |
73,1 |
Paraffin content |
mass% |
≥ 99.5 |
≥ 99.5 |
≥ 99.5 |
≥ 99.5 |
≥ 99.5 |
≥ 99.5 |
C5-15 Paraffin content |
mass% |
40 |
55 |
69 |
84 |
26 |
99,7 |
C20-27 Paraffin content |
mass% |
14 |
11 |
7 |
4 |
17 |
0 |
Isoparaffin content |
mass% |
71 |
66 |
59 |
54 |
76 |
48 |
Normal paraffin content |
mass% |
29 |
34 |
41 |
46 |
24 |
52 |
Normal paraffin content/Isoparaffin content |
mass% |
0,4 |
0,5 |
0,7 |
0,9 |
0,3 |
1,1 |
Pour point |
°C |
-56 |
-58 |
-57 |
-53 |
-54 |
-53 |
Kinetic viscosity (30 °C) |
mm2/s |
3,2 |
2,5 |
2,1 |
1,7 |
4,1 |
1,4 |
Evaluation |
++ |
++ |
++ |
+ |
- |
- |
[0048] The results in Table 1 show that the gas oil compositions obtained in Examples had
good quality even if they were used under very low temperature weather conditions,
and in particular, Examples 1 to 3 that met the preferred ranges of the present invention
achieved better quality.
[0049] On the other hand, for the gas oil compositions obtained in Comparative Examples,
it was found that they deposited in the form of wax under very low temperature weather
conditions or their kinetic viscosity was insufficient.
INDUSTRIAL APPLICABILITY
[0050] The present invention has particularly advantageous effects in that a gas oil composition
providing superior low temperature performance as compared with the case of using
the conventional techniques can be provided and an oil having a high normal paraffin
content, such as FT synthetic oil can easily be used as a feedstock of the gas oil
composition.