Note: Descriptions are shown in the official language in which they were submitted.
13~01~
The present invention is related to a process
for upgrading a distillate feedstock material. More
particularly, the present invention is related to a
process for producing diesel and jet fuels.
A well known source of distillate feedstock,
particularly synthetic crude oil, for the production of
fuel products is bitumen, which is typically upgraded by
coking processes. These coking processes result in the
production of polycyclic aromatic ring structured
materials which are then: cracked to a lighter product;
fractionated to produce coker distillates and upgraded
further by severe hydrotreating which ~erves to remove
sulphur and nitrogen while simultaneously saturating
olefins and some aromatics. The distillate streams
which are thus produced through partial upgrading are
then blended to produce a synthetic crude oil.
~ Synthetic crude oil generally comprises a
mlddle distillate fraction having a boiling point range
of from about 140 to about 350 C. The boiling point
range of this middle distillate fraction embodies that
of diesel fuels, Jet fuels (also known as kerosene) and
light fuel oils. Unfortunately, this synthetic crude
middle distillate fraction is of low quallty and thus,
iR not useful for the production of these fuels and oils
becauso it possesses a high concentration of aromatic
hydrocarbons (eg. as much as 45 percent by weight~
subsc~uent to bitumen upgrading. A hi~h aromatic
hydrocarbon content is undesirable in both diesel and
jet fuels since it has a deleterious affact on the
ig~ition and combustion qualities of these fuels.
Diesel and ~et fuels heretofore produced from
conventional crude oil generally contain a lower
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concentration of aromatic hydrocarbons (eg. less than
about 30 percent by weight).
A key property of diesel fuel which i9 usually
assessed in determining whether the ~uel is suitable for
use ls the cetane number, which ls a measure o~ the
ignition quality of the fuel. The cetane number is
determined by a comparative test using a standard test
engine which measures the delay period between fuel
in~ection and ignitien for a blend of reference fuel-~,
and also for the fuel under test. The refarence fuels
are n-cetane (excellent diesel ignition propert~es~ and
heptamethylnonane (poor diesel ignition properties),
which are blended to produce a fuel having the same
ignition delay period as the test fuel. On the cetane
numbsr scale, pure n-cetane and heptamethylnonane are
arbitrarily assigned 100 and 15, raspectively. Thus,
the cetane number of the blend is a function of the
percentage of n-cetane which is given by:
cetane # = % n-cetane + 0.15(~ heptamethylnonane)
~igher cetane numbers are synonymous with short ignition
delay periods and generally good fuel ignition
properties. Low cetane numbers usually result in poor
engine perPormance and problematic environmental
emissions.
The most lmportant characteristics relating to
the quality of Jet fuel are those in~luenclng energy
content and combustion ch~racteristics. These
characteristics determine the vverall performance of the
Jet engins when the fuel is burned in the gas turbine.
The combustion charac~eristics of jet fuel are
particularly related to its hydrogen/carbon (hereinafter
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referred to as H/C) ratio. Generally, fuels which are
hydrogen deficient, such as those with a high
concentration of aromatic hydrocarbons, are more
difficult to burn than those which are richer in
paraffins (ie. straight and branched hydrocarbon
chains). Further, fuels having a low H/C ratio burn
with more radiant flames which tends to raisa combustor
liner tamperatures and thereby shorten engine life. The
combustion performance of jet fuel is usually deined by
one of the following standard tests: measurement of
luminometer number (ASTM D1740); smoke point test (ASTM
D1322); and smoke point plus maximum naphthalenes
content (ASTM D1840).
The percenta~e by mass of the various
hydrocarbon groups contained in a typical middle
distillate fraction of synthetic crude oil are provided
in Table 1. For comparison, the percentage by mass of
the various hydrocarbon groups contained in a typical
middle distillate fraction of conventional crude oil are
also provided in Table 1.
TABLE 1
Hydrocarbon Synthetic Crude Conventional Crude
Group Oil, mass ~ Oil, mass~
. ., _ . .
paraffins 17 39
naphthenes 37 34
alkylbenzenss 36 18
2 ring aromatic~ 8 8
3-ring aromatic 2
- _ _
cetane number of
fuel produced 31 4
.. _ .... _ _
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1~201~
As illustrated, a typi~al middle distillate fraction of
synthetic crude oil is low in paraffins and high in
aromatics when compared to a typical middle distillate
fractlon of convantional crude oil. Hydrocarbon groups with
the most favourable cetane numbers are paraffins having long
straight chains up to about C20. Branched chain paraffins
yield lower cetan~ numbers which decrease with increassd
branching. Napthenes (eg. cycloparaffins), which generally
have lower cetane numbers than paraffins, have better
lgnition properties than aromatics, which generally have the
lowest cetane numbers. The deficiencies of processes known
heretofore to produce diesel fuel from synthetic crude oil
are e~emplified by a comparison of the cetane numbers shown
in Table 1.
Thus, it would be desirable to have an efflclent
process which could be used to upgrade a low grade
distillate feedstock, more particularly the middle
distillate fraction of synthetic crude oil, such that the
upgraded product possessed the necessary properties to
enable it to be used as diesel or jet fuals.
It is an obJect of the present invention to
obviate or mitigate the above-mentioned disadvantages.
~ Accordingly, the present invention provides a
process for upgrading a distillate feedstock material which
compri~es:
i) hydrogenating the distillate ~eedstock material
in the presenca of a hydroganation catalyst thereby
producing from about 90 to about 95 percent by weight of a
hydrogenatad product comprising paraffins and naphthenes,
and from ~bout 4 to about 10 percent by weight of residual
refractory aromatic compounds; and
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ii) removing substantially all of said residual
refractory aromatic compounds by an extraction technique.
Thus, the process of the present invsntion may be
used to improve the cetane number of diesel fuels by
removing the refractory aromatic compounds contained
therein. Moreover, the process disclosed herein may be used
to further improve the cetane number of diesel fuels by
removing at least a pvrtion oP the naphthenes (ie. cyclic
hydrocarbons) which would otherwise be formed through
hydrogenatlon of their aromatic precursors.
Although embodiments of the invention relating to
upgrading the middle distillate of synthetic crude oil to
proAuce diesel fuel will be disclosed hereinafter, Appllcant
believes that the scope of the present invention may be
applicable to the upgrading of a variety of distillate
materials.
Pre~erably, the distillate feedstock material
suitable for use is synthetic crude oil middle distillate
derived from the conversion o a material selected from the
group comprising heavy patroleum oil, coal and mixtures of
coal and an oil of petroleum origin. Further, heavy
petroleum oils may chosen rom the group comprising
petroleum oils known as bitumens, heavy crude oils and
refinery residual oils. For the purpose of the present
process, the above-mentioned conversion may be performed by
techniques known in the art, namely: coking, hydrocracking
and ~oking/hydrocracking in the casa of heavy petroleum oil;
direct liquefication in th~ case of coal; and coprocessing
in the case of mixt~res of coal and an oil of petroleum
orlgin. A typical middle distillate fraction of synthetic
crude oil has a boiling point in the ~ange of from about
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140 to about 350 C and may be derived as described
hereinbefore.
The hydrogenation catalyst suitable for use in the
process of the present application is preferably selected
fxom i) conventional sulphides of molybdenum or tungsten
comprising an inert support compound (also known as
conventional hydrotreating catalysts) and ii) non-sulphided
transition metals comprising an inert support compound.
Non-limiting examples of inert support compounds suitable
for use with either type of hydrogenation catalyst are
alumina and silica~alumina.
Non-limiting examples of conventional
hydrotreating catalysts suitable for use in the procesq of
the present invention may be selected from sulphides of the
group comprising Co-Mo, Ni-Mo and Ni-W. Because these
catalysts are relatively inactive toward saturating aromatic
hydrocarbons, vigorous reaction conditions are usually
employed such that hydro~enation of the aromatic
hydrocarbons is thermodynamically favoured. Typical
reaction conditions which are used with thase catalysts are:
reaction temperature of from about 340 to about 420 C and
hydrogen pressure of at least about 10 MPa, more preferably
from about 10 MPa to about 15 MPa. The use of such severe
reaction conditions necessitates the use of ralatively hi~h-
cost reactors. However, the use of such catalyst systems
and reaction conditions enhances the removal of refractory
arom tic hydrocarbons which results in an improvement in the
cetane number of the dieqel fuel.
Although, conventional hydrotreating catalysts
will be oparative in the process of the present invention,
the most preferred catalysts are the non-sulphided
transition metals. Non~limiting examples of non-sulphided
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~32~167
transition metals suitable for use in the process of the
present invention are nickel, palladium and platinum. The
advantage of using this type of catalyst is that only
relatively mild reaction condltions are required to achieve
hydrogsnation o~ the distillate feedstock material. Typlcal
reaction conditions which would be required using thl~ type
of catalyst are reaction temperature of from about 160 to
about 300 C and a hydrogen pressure of at least about 1.5
MPa, more preferably from about 2.5 to about 3.5 MPa. Thus,
the use of non-qulphided transition metals as hydrogenation
catalysts enables the process of the present invention to be
carried out in relatively inexpensive reactors due to the
mild reaction conditions which are required~
The hydrogenation o~ the distillate feedstock
material results in the production of from about 90 to about
96 percent by weight of hydrogenated hydrocarbons. Thus,
the re~ractory aromatic compounds are present in an amount
of from about 4 to about 10 percent by weight.
The hydrogenated distillate feedstock material is
then subJected to extraction which serves to remove
substantially all of the remaining refractory aromatic
compounds. Examples of suitable extraction techniques
include solvent extraction~ sulphonation, sorption
extraction, membrane extraction and extraction with salts.
The preferred extraction technique is one of
solvent extraction and sulphonation.
If solvent extraction is used to remove the
re~ractory aromatic hydrocarbons, the preferred solvents may
be selected from the group comprising sulphur dioxide,
~ulfolane and glycols.
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., .,,, ... , = , .
,
2~6~
Sulphonation involves treating the hydrogenated
distillate feedstock material with oleum (concentrated H2 S04
comprising S03 in solution as an oily corrosive liquid).
The sulphonated refractory aromatic compounds so-produced
may then be removed from the desired fuel product using
standard separa-tory techniques.
Embodiments of the present invention will now be
illustrated in the following non-limiting example with
refersnce to the accompanying drawing in which:
Figure 1 is a plot of aromatic content (mass %)
versus cetane number for a number of upgraded distillate
materials.
EXAMPLE
A middla dlstillate fraction of synthetic crude
oil was derived from Athabasca bitumen by fluid coking. The
distillate undarwent primary hydrotreating prior to
synthetlc crude blending and plpelining. Some of the
properties o~ the middle distillate fraction are provided in
Table 2.
TABLE 2
Relative Density, 15/15C 0.862
Carbon content, ~ by weight 87.2
Hydrogen aontent, ~ by weight 11.7
Sulphur content, ppm 97
Nitrogen content, ppm 37
Ave. molecular weight 200
Aromatic carbon, ~ 16.9
Cetane number 31
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Hydrogenation of the middle distillate fr~ction
was conducted using a supported elemental nickel
hydrogenation catalyst and a bench-scale continuous-10w
hydrotreating unit. The reactor volume was 100 cm3 and the
nickel catalyst loading was 84.4 g. The reactor was
operated in the up-flow mode, the liquid feed and hydrogen
were mixed, passed through a preheater and then over the
fixed catalyst bed. The hydro~enation wa~ carried out at a
reaction temperature of 160 to 300 C, liquid space
velocities of 0.75 to 2.25 h~1 and a hydrogen flow rate at
standard temperature and pressure of 530 L (hydrogen) L~1
(feedstock). A11 runs were performed at a hydrogen pressure
of 3.5 MPa and the hydrogen was vented without recycle.
A series of synthetic diesel fuel products were
analyzed using low resolution mass spectrometry. The
samples were also analyzed by a W method in thosa cases
where the aromatics were at low concentrations (less than
~). Analysis for aromatic carbon content was also done by
C-13 NMR.
Extraction of refractory aromatic hydrocarbons
from the hydrogenated middle distillate samples was achieved
using sulphonation. Quantities of 700 mL of the ~amples
were treated with 30 mL portions of 15-20~ oleum at room
temperature. After removal of the sulphonated aromatics
u~ing a separatory funnel, the oil layer was washed with
concentrated sulphuric acid and then neutralized with a
mlxture of sodium hydroxide and isopropy~ alcohol. Excess
sulphonates and water were ramoved by shaking the mixture in
a saparatory funnel and removing the bottom layers. Tha
remaining solvent wa~ str~pped in a rotary e~aporator and
the emul ified naphthenic oil was treated with 15 g of
activated alumina, stirred vigorously us1ng the W method.
Compositional analysis was carried out by mass spectrometry
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to confirm the selectivity of aromatics sepaxation from the
hydrogenated product. Analysis of the latter provided
absolute yields of paraffins and naphthenes.
Cetane numbers for two series of fuel products
(hydrogenated and extracted samples) were datermined by
means of an engine test using the standard Cooperative Fuels
Research ( CFR ) test engine.
Figure 1 illustrates the relationship between
aromatic hydrocarbon content (mass %) and cetane number for
the diesel fuel samples. The solid, left-hand curvs is
referred to as the Hydrogenation Line and is representative
of fuel samples which were sub;ected to hydrogenation only
using the narrow hydroprocessing range described above. The
curvature of the Hydrogenation Line is believed to be a
unique feature of the middle distillate raction of
synthetic crude which was used and indicates that cetane
numbsr improvement is related to the types o~ aromatics
removed and their resistance to hydrogenation. A3 indlcated
by the decraasing aontent of aromatics in the fuel samples
with increasing cetane number, it is apparent that a
significant amount of the rafractory aromatic hydrocarbons
have heen converted to their naphthene analogs, which have
generally higher cetane numbers than the aromatic
hydrocarbons. However, in order to ensure ~ery low
concentrations of aromatic hydrocarbons in the fuel, the
~everity o~ the hydrogenation process must be increased.
Accordingly, an essential feature of the process
is the inclusion of an extraction stsp after hydrogenation
of the di~till~te ~eedstsck material. Because extrac~on
will remove the refractory aromatic hydrocarbons, it is
actualIy desirable not to allow their removal by conversion
to naphthenes at the hydrogenation stage of the process.
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Rather, it is desirabls to have from about 4 to about 10
percent by weight of refractory aromatic hydrocarbons in the
feedstock prior to the extraction step. Thus, not only are
the aromatics removed but also the naphthenes which would
have otherwisa been formed during hydrogenation. The
Extraction Line is shown in Figure 1 as the broken, right-
hand curve and is representative of a series of hydrogenated
fuel samples which where subsequently subjected to an
extraction step using the sulphonation step as described
above.
To illustrate the co~parlson of propertie betwsen
hydrogenated (only) and hydrogenated/axtractad fuel samples,
both were plotted on the same axis as shown in Figure 1.
The Extraction Line was constructed by plotting the aromatic
hydrocarbon contant of the hydrogenated fuel samples (prior
to extraction) against their cetane numbers which were
determined after extraction. Accordingly, the e~traction
line is "imaginary" in terms of the aromatic hydrocarbon
content since the hydrogenated/extracted samples did not
contain any aromatic hydrocarbons. As an example, Figure 1
show~ that a distillate material upgraded to a cetane number
of 40 has an aromatic hydrocarbon content of about 4 mass %.
The extraction of these refractory aromatic hydrocarbons
re ults in a product having a cetane number of about 45,
which would not have been attainable (according to Figure l)
using hydrogenation alone.
Thus, the 2-step process o~ the present invention
is useful in producing improved diesel (and ~et) fuels which
have higher cetane numbers than those which are subjeGted
only to severe hydro~enation. While not wishing to be bound
by any partiaular theory, Applicant believes that the
extraction step results not only in the removal of the
refractory aromatic hydrocarbon component in the ~eedstock
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~2~1~7
but also the corr0sponding naphthene which would otherwise
remain if a hydrogenation step alone was used. Since
naphthenes generally have cetane numbers which intermediate
between normal hydrocarbon paraffins and aromatlcs, their
removal would, conceivably, enhance further the cetane
number of diesel fuel.
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