U.S. patent application number 10/511127 was filed with the patent office on 2005-11-17 for method to increase the cetane number of gas oil.
Invention is credited to Clark, Richard Hugh, Kalghatgi, Gautam Tavanappa, Liney, Eleanor Mair.
Application Number | 20050256352 10/511127 |
Document ID | / |
Family ID | 29225719 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050256352 |
Kind Code |
A1 |
Clark, Richard Hugh ; et
al. |
November 17, 2005 |
Method to increase the cetane number of gas oil
Abstract
A method to increase the cetane number of a gas oil product
based on a petroleum derived gas oil to a target cetane number Y by
adding to the petroleum derived gas oil an amount of a
Fischer-Tropsch derived gas oil having a higher cetane number, B,
than the petroleum derived gas oil of cetane number, A, wherein the
amount of added Fischer-Tropsch derived gas oil is less than the
amount which would be added if linear blending is assumed.
Inventors: |
Clark, Richard Hugh;
(Cheshire, GB) ; Kalghatgi, Gautam Tavanappa;
(Cheshire, GB) ; Liney, Eleanor Mair; (Cheshire,
GB) |
Correspondence
Address: |
Shell Oil Company
Intellectual Property
PO Box 2463
Houston
TX
77252-2463
US
|
Family ID: |
29225719 |
Appl. No.: |
10/511127 |
Filed: |
October 13, 2004 |
PCT Filed: |
April 15, 2003 |
PCT NO: |
PCT/EP03/03927 |
Current U.S.
Class: |
585/14 |
Current CPC
Class: |
C10L 1/08 20130101 |
Class at
Publication: |
585/014 |
International
Class: |
C10M 101/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2002 |
EP |
02252637.0 |
Claims
1. A method of increasing the cetane number of a gas oil product
based on a petroleum derived gas oil to a target cetane number Y
comprising: adding to the petroleum derived gas oil a volume amount
of a Fischer-Tropsch derived gas oil having a higher cetane number,
B, than the petroleum derived gas oil of cetane number, A, wherein
the volume amount of added Fischer-Tropsch derived gas oil is less
than the volume amount which would be added if linear blending is
assumed.
2. The method of claim 1, wherein the volume fraction of
Fischer-Tropsch gas oil is less than x, wherein x is the volume
fraction that would be added if linear blending assumptions would
have been made according to the following equation: Y=A+x(B-A),
3. The method of claims 1, wherein a volume fraction x is added as
Fischer-Tropsch derived gas oil in order to increase the cetane
number to target value Y, wherein Y and x are related according to
the following equation: Y=A+(B-A)(-px.sup.2+qx), where p and q are
constants such that 1.4>q>1.9 and p=q-1 and wherein A is the
cetane number of the petroleum derived gas oil and B the cetane
number of the Fischer-Tropsch derived gas oil.
4. The method of claim 3, in which x is greater than 0.02 and less
than 0.7.
5. The method of claim 4, in which x is less than 0.5.
6. The method of claim 1, of which the cetane number, A, of the
petroleum derived gas oil is greater than 40 and less than 70.
7. The method of claims 1, of which the cetane number of the
petroleum derived gas oil is measured using near infrared
spectroscopy.
8. The method of claim 2, in which a volume fraction x is added as
Fischer-Tropsch derived gas oil in order to increase the cetane
number to target value Y, wherein Y and x are related according to
the following equation: Y=A+(B-A)(-px.sup.2+qx), where p and q are
constants such that 1.4>q>1.9 and p=q-1 and wherein A is the
cetane number of the petroleum derived gas oil and B the cetane
number of the Fischer-Tropsch derived gas oil.
Description
[0001] The invention is directed to a method to increase the cetane
number of a gas oil product based on a petroleum derived gas oil by
adding to the petroleum derived gas oil an amount of a
Fischer-Tropsch derived gas oil.
[0002] Commercially available blends of petroleum derived gas oil
and Fischer-Tropsch derived gas oil are known. For example
commercial transportation fuel formulations have been on the
market, which comply with the requirements of the California Air
Resources Board (CARB), and which formulations are based on a blend
of gas oil as obtained in the Shell MDS Fischer-Tropsch process
operating in Bintulu (Malaysia) and petroleum derived gas oils.
[0003] It is furthermore known that petroleum derived gas oils have
generally a lower cetane number than gas oils derived from a
Fischer-Tropsch process.
[0004] From various publications it is assumed that the cetane
number of the final blend will comply with linear blending rules.
See for example recent patent publication WO-A-0183648. This
publication discloses that Fischer-Tropsch fuels can "upgrade"
conventional fuels as predicted from simple, linear blending of the
fuel parameters, i.e., as specified in "Fischer-Tropsch Wax
Characterization and Upgrading Final Report" by P. P. Shah, G. C.
Sturtevant, J. H. Gregor and M. J. Hurnbach, US Department of
Energy, Subcontract DE-AC22-85PC80017, Jun. 6, 1998. Furthermore
from the results, as illustrated in above referred to WO-A-0183648,
one would conclude linear blending rules with regard to cetane
number.
[0005] If one intends to increase the cetane number of a petroleum
derived gas oil by blending with a Fischer-Tropsch derived gas oil
and one assumes linear blending rules one can calculate the
required volume of Fischer-Tropsch gas oil to be added.
[0006] A problem with Fischer-Tropsch derived gas oil is that they
are not widely available and that the cost of preparing such gas
oils is believed to be higher than the cost of preparing petroleum
derived gas oil for the foreseeable future. There is thus a
continuous drive to minimize the amount of Fischer-Tropsch derived
gas oil in such a blend while meeting the different final product
specifications.
[0007] Applicants have now surprisingly found the following more
optimised method to upgrade a petroleum derived gas oil to a gas
oil blend having a target cetane number using Fischer-Tropsch
derived gas oil.
[0008] Method to increase the cetane number of a gas oil product
based on a petroleum derived gas oil to a target cetane number Y by
adding to the petroleum derived gas oil an amount of a
Fischer-Tropsch derived gas oil having a higher cetane number, B,
than the petroleum derived gas oil of cetane number, A, wherein the
amount of added Fischer-Tropsch derived gas oil is less than the
amount which would be added if linear blending is assumed.
[0009] Applicants have surprisingly found that the cetane number of
a blend of petroleum derived gas oil and Fischer-Tropsch derived
gas oil, in contrast to general opinion, cannot be determined by
making use of linear blending assumptions. In contrast the addition
of a certain volume of Fischer-Tropsch derived gas oil to a
petroleum derived gas oil results in a higher cetane number than
would be expected based on linear blending rules. Thus it is
possible to add less Fischer-Tropsch derived gas oil to a petroleum
derived gas oil to increase the cetane number of the petroleum
derived gas oil to a certain target cetane number. This finding
makes it possible to minimize the volume of Fischer-Tropsch gas oil
in such a gas oil blend while avoiding so-called product give away
with respect to cetane number.
[0010] It is clear that the above method would also be applicable
when a blend is formulated to a certain property, which is
equivalent to cetane number.
[0011] The reason why this non-linear blending property was not
shown in earlier publications could be because the illustrated
cetane number of the blends and/or of the blending components were
never actually measured. For some prior art results it is believed
that the cetane number of the blends were simply calculated by
applying linear blending rules on the cetane number contributions
of the individual blending components.
[0012] The volume fraction of Fischer-Tropsch gas oil, which is
added in the method according to the invention, will be less than
x, wherein x is the volume fraction that would be added if linear
blending assumptions would have been made according to the
following equation:
Y=A+x(B-A).
[0013] The fraction x will be a value between 0 and 1 and
preferably greater than 0.02. The invention is in particular
directed to blends wherein the fraction x of Fischer-Tropsch
derived gas oil is less than 0.7 and more preferably less than 0.5
and most preferably between 0.05 and 0.3.
[0014] If a certain target cetane number Y is desired the volume
fraction x is suitably determined by making use of the following
non-linear blending rule, wherein Y and x are related according to
the following equation:
Y=A+(B-A)(-px.sup.2+qx),
[0015] wherein p and q are constants such that 1.4>q>1.9 and
p=q-1 and wherein A is the cetane number of the petroleum derived
gas oil and B the cetane number of the Fischer-Tropsch derived gas
oil.
[0016] The cetane number of the petroleum derived gas oil and the
Fischer-Tropsch derived gas oil as used in the method according the
invention may be measured according the normal ASTM D613 method.
Because such a method is cumbersome when performing the blending
method according to the invention in a refinery environment a more
preferred method is by measuring the cetane number by near infrared
spectroscopy (NIR) as for example described in detail in U.S. Pat.
No. 5,349,188. Such measurements will include the use of a
correlation between the measured spectrum and the actual cetane
number of the sample. The underlying model is made by correlating
the cetane number according to ASTM D613 of a wide variety of
petroleum derived samples, Fischer-Tropsch derived gas oil samples
and/or their blends with their near infrared spectral data.
[0017] Preferably the method according to the invention is embedded
in an automated process control of the blending operation in for
example a refinery environment. Such a process control may use
so-called quality estimators which will provide, by making use of a
model, a real time prediction of the cetane number of the resulting
blend from readily available raw process measurements, such as for
example the cetane numbers as measured by NIR and the volumetric
flows. Even more preferably such a quality estimator is calibrated
on-line by making use of for example the method described in detail
in WO-A-0206905.
[0018] The Fischer-Tropsch derived gas oil may be any gas oil,
which is prepared from the synthesis product of a Fischer-Tropsch
synthesis. The gas oil product may be obtained by fractionation of
such a Fischer-Tropsch synthesis product or obtained from a
hydroconverted (hydrocracking/hydroisomerisation) Fischer-Tropsch
synthesis product. Examples of Fischer-Tropsch derived gas oils are
described in EP-A-583836, WO-A-9714768, WO-A-9714769, WO-A-011116,
WO-A-011117, WO-A-0183406, WO-A-0183648, WO-A-0183647,
WO-A-0183641, WO-A-0020535, WO-A-0020534, EP-A-1101813 and U.S.
Pat. No. 6,204,426.
[0019] Suitably the Fischer-Tropsch derived gas oil will consist of
at least 90 wt %, more preferably at least 95 wt % of iso and
linear paraffins. The weight ratio of iso-paraffins to normal
paraffins will suitably be greater than 0.3. This ratio may be up
to 12. Suitably this ratio is between 2 and 6. The actual value for
this ratio will be determined, in part, by the hydroconversion
process used to prepare the Fischer-Tropsch derived gas oil from
the Fischer-Tropsch synthesis product. Some cyclic-paraffins may be
present. By virtue of the Fischer-Tropsch process, the
Fischer-Tropsch derived gas oil has essentially zero content of
sulphur and nitrogen (or amounts which are no longer detectable).
These hereto-atom compounds are poisons for Fischer-Tropsch
catalysts and are removed from the synthesis gas that is the feed
for the Fischer-Tropsch process. Further, the process does not make
aromatics, or as usually operated, virtually no aromatics are
produced. The content of aromatics as determined by ASTM D 4629
will typically be below 1 wt %, preferably below 0.5 wt % and most
preferably below 0.1 wt %.
[0020] The Fischer-Tropsch derived gas oil will suitably have a
distillation curve which will for its majority be within the
typical gas oil range: between about 150 and 400.degree. C. The
Fischer-Tropsch gas oil will suitably have a T90 wt % of between
340-400.degree. C., a density of between about 0.76 and 0.79
g/cm.sup.3 at 15.degree. C., a cetane number greater than 70,
suitably between about 74 and 82, and a viscosity between about 2.5
and 4.0 centistokes at 40.degree. C.
[0021] The petroleum derived gas oils are gas oils as obtained from
refining and optionally (hydro)processing of a crude petroleum
source. The petroleum derived gas oil may be a single gas oil
stream as obtained in such a refinery process or be a blend of
several gas oil fractions obtained in the refinery process via
different processing routes. Examples of such different gas oil
fractions as produced in a refinery are straight run gas oil,
vacuum gas oil, gas oil as obtained in a thermal cracking process
and light and heavy cycle oil as obtained in a fluid catalytic
cracking unit and gas oil as obtained from a hydrocracker unit.
Optionally a petroleum derived gas oil may comprise some petroleum
derived kerosene fraction.
[0022] The straight run gas oil fraction is the gas oil fraction,
which has been obtained in the atmospheric distillation of the
crude petroleum refinery feedstock. It has an Initial Boiling Point
(IBP) of between 150 and 280.degree. C. and a Final Boiling Point
(FBP) of between 320 and 380.degree. C. The vacuum gas oil is the
gas oil fraction as obtained in the vacuum distillation of the
residue as obtained in the above referred to atmospheric
distillation of the crude petroleum refinery feedstock.
[0023] The vacuum gas oil has an IBP of between 240 and 300.degree.
C. and a FBP of between 340 and 380.degree. C. The thermal cracking
proces's also produces a gas oil fraction, which may be used in
step (a). This gas oil fraction has an IBP of between 180 and
280.degree. C. and a FBP of between 320 and 380.degree. C. The
light cycle oil fraction as obtained in a fluid catalytic cracking
process will have an IBP of between 180 and 260.degree. C. and a
FBP of between 320 and 380.degree. C. The heavy cycle oil fraction
as obtained in a fluid catalytic cracking process will have an IBP
of between 240 and 280.degree. C. and a FBP of between 340 and
380.degree. C. These feedstocks may have a sulphur content of above
0.05 wt %. The maximum sulphur content will be about 2 wt %.
Although the Fischer-Tropsch derived gas oil comprises almost no
sulphur it could still be necessary to lower the sulphur level of
the petroleum derived gas oil in order to meet the current
stringent low sulphur specifications. Typically the reduction of
sulphur will be performed by processing these gas oil fractions in
a hydrodesulphurisation (HDS) unit.
[0024] Gas oil as obtained in a fuels hydrocracker has suitably an
IBP of between 150 and 280.degree. C. and a FBP of between 320 and
380.degree. C.
[0025] The cetane number of the (blend of) petroleum derived gas
oil (fractions) as described above is preferably greater than 40
and less than 70. Apart from increasing this cetane number of the
petroleum derived gas oil other properties of the blend need to
meet the required specifications. Examples of such properties are
the Cloud Point, CFPP (cold filter plugging point), Flash Point,
Density, Di+-aromatics content, Poly Aromatics and/or distillation
temperature for 95% recovery.
[0026] Preferably the final blended gas oil product comprising the
Fischer-Tropsch and the petroleum derived gas oil will have a
sulphur content of at most 2000 ppmw (parts per million by weight)
sulphur, preferably no more than 500 ppmw, most preferably no more
than 50 or even 10 ppmw. The density of such a blend is typically
less than 0.86 g/cm.sup.3 at 15.degree. C., and preferably less
than 0.845 g/cm.sup.3 at 15.degree. C. The lower density of such a
blend as compared to conventional gas oil blends results from the
relatively low density of the Fischer-Tropsch derived gas oils. The
above fuel composition is suited as fuel in an indirect injection
diesel engine or a direct injection diesel engine, for example of
the rotary pump, in-line pump, unit pump, electronic unit injector
or common rail type.
[0027] The final gas oil blend may be an additised
(additive-containing) oil or an unadditised (additive-free) oil. If
the fuel oil is an additised oil, it will contain minor amounts of
one or more additives, e.g. one or more additives selected from
detergent additives, for example those obtained from Infineum
(e.g., F7661 and F7685) and Octel (e.g., OMA 4130D); lubricity
enhancers, for example EC 832 and PARADYNE 655 (ex Infineum), HITEC
E580 (ex Ethyl Corporation), VELTRON 6010 (ex Infineum) (PARADYNE,
HITEC and VELTRON are trademarks) and amide-based additives such as
those available from the Lubrizol Chemical Company, for instance LZ
539 C; dehazers, e.g., alkoxylated phenol formaldehyde polymers
such as those commercially available as NALCO EC5462A (formerly
7D07) (ex Nalco), and TOLAD 2683 (ex Petrolite)(NALCO and TOLAD are
trademarks); anti-foaming agents (e.g., the polyether-modified
polysiloxanes commercially available as TEGOPREN 5851 and Q 25907
(ex Dow Corning), SAG TP-325 (ex OSi), or RHODORSIL (ex Rhone
Poulenc))(TEGOPREN, SAG and RHODORSIL are trademarks); ignition
improvers (cetane improvers) (e.g., 2-ethylhexyl nitrate (EHN),
cyclohexyl nitrate, di-tert-butyl peroxide and those disclosed in
U.S. Pat. No. 4,208,190 at column 2, line 27 to column 3, line 21);
anti-rust agents (e.g., that sold commercially by Rhein Chemie,
Mannheim, Germany as "RC 4801", a propane-1, 2-diol semi-ester of
tetrapropenyl succinic acid, or polyhydric alcohol esters of a
succinic acid derivative, the succinic acid derivative having on at
least one of its alpha-carbon atoms an unsubstituted or substituted
aliphatic hydrocarbon group containing from 20 to 500 carbon atoms,
e.g., the pentaerythritol diester of polyisobutylene-substituted
succinic acid); corrosion inhibitors; reodorants; anti-wear
additives; anti-oxidants (e.g., phenolics such as
2,6-di-tert-butyl-phenol, or phenylenediamines such as
N,N'-di-sec-butyl-p-phenylenediamine); and metal deactivators.
[0028] The additive concentration of each such additional component
in the additivated fuel composition is preferably up to 1% w/w,
more preferably in the range from 5 to 1000 ppmw, advantageously
from 75 to 300 ppmw, such as from 95 to 150 ppmw.
[0029] The invention will be illustrated by means of the following
non-limiting examples.
EXAMPLE
[0030] In this Example use is made of a petroleum derived-gas oil
and two Fischer-Tropsch derived gas oils in the absence of any
additives (FT1 and FT2) having the properties as listed in Table 1.
The cetane number was measured according to the CFR Cetane Engine
method, ASTM D 613.
1 TABLE 1 Fischer-Tropsch Petroleum derived gas derived oils
PROPERTIES gas oil FT1 FT2 DENSITY @ 15.degree. C. (IP365/ASTM
D4052) g/cm.sup.3 0.8503 0.776 0.7782 DISTILLATION (IP123/ASTM D86)
IBP .degree. C. 201.0 183.5 186.5 10% 244.0 214.1 216.5 20% 259.5
228.4 234.0 30% 270.5 243.6 247.0 40% 281.0 259.5 261.0 50% 290.0
275.4 273.0 60% 299.5 291.2 285.0 70% 309.5 306.9 297.5 80% 321.0
322.9 310.5 90% 337.5 340 324.5 95% 351.0 351.3 333.5 FBP 363.5 359
339.5 CETANE NUMBER ASTM D613 51.1 77.3 75.8 Kinematic viscosity at
100.degree. C. (cSt) 3.103 2.665 (IP71/ASTM D445) SULPHUR (IP373)
ppm M 400 0 <5 CARBON wt % 86.9 84.9 84.6 HYDROGEN wt % 13.2 15
15
[0031] In order to increase the cetane number of 51.1 of the
petroleum derived gas oil to a target cetane number Y as listed in
Table 2 different amounts of Fischer-Tropsch derived gas oil FT1
had to be added. From Table 2 it is clear that this amount is less
than the volume, which would have been added if linear blending
were assumed.
2TABLE 2 Fraction x of FT1 Fraction of FT1 Target cetane added to
petroleum added if linear number Y derived gas oil blending was
assumed 59.6 0.15 0.31 63.3 0.30 0.47 69.3 0.50 0.69 73.1 0.7
0.84
[0032] From the results shown in Table 2 it is clear that by using
the method according to the present invention considerably less
Fischer-Tropsch derived gas oil needs to be added to a petroleum
derived gas oil when blending such gas oils to reach a certain
target cetane number. This effect is especially pronounced at
values for x smaller than 0.5.
[0033] Similar results were obtained when the second
Fischer-Tropsch derived gas oil (FT2) was used to increase the
cetane number of the blend (see Table 3).
3TABLE 3 Fraction x of FT2 Fraction of FT2 Target cetane added to
petroleum added if linear number Y derived gas oil blending was
assumed 57.3 0.15 0.23 62.3 0.30 0.44 65.4 0.5 0.56 68.8 0.7
0.7
* * * * *