[0001] The invention relates to a process to prepare a haze free base oil having a kinematic
viscosity at 100 °C of greater than 10 cSt from a Fischer-Tropsch wax.
Many publications are known describing processes for the conversion of gaseous hydrocarbonaceous
feed stocks, as methane, natural gas and/or associated gas, into liquid products,
especially methanol and liquid or solid hydrocarbons, particularly paraffinic hydrocarbons.
In this respect often reference is made to remote locations (e.g. in the dessert,
tropical rain-forest) and/or offshore locations, where no direct use of the gas is
possible, usually due to the absence of large populations and/or the absence of any
industry. Transportation of the gas, e.g. through a pipeline or in the form of liquefied
natural gas, requires extremely high capital expenditure or is simply not practical.
[0002] To make efficient use of such stranded gas reserves on-site Fischer-Tropsch processes
are being build. Such processes involve a synthesis gas manufacturing step using the
natural gas as feedstock and a Fischer-Tropsch synthesis step to make a heavy wax.
WO-A-02070627 describes a process for preparing a base oil having a kinematic viscosity
at 100 °C of 22 cSt from a heavy Fischer-Tropsch wax.
[0003] A problem of the prior art processes is that especially the base oils having a high
viscosity often show a haze. This haze makes the process less suitable for some applications.
However not all applications for this family of base oils require that a haze should
be absent. The object of the present invention is a process to prepare haze free base
oils in an efficient manner.
[0004] The following process achieves this object. Process to prepare a haze free base oil
having a kinematic viscosity at 100 °C of greater than 10 cSt from a Fischer-Tropsch
wax feed having a 10 wt% recovery boiling point of above 500 °C and a wax content
of greater than 50 wt% by performing the following steps,
(a) reducing the wax content of the feed to a value of below 50 wt% by contacting
the feed with a hydroisomerisation catalyst under hydroisomerisation conditions at
a remote location,
(b) transporting an intermediate product having a wax content of below 50 wt% as obtained
in step (a) from one location to another location, and
(c) solvent dewaxing the transported intermediate product to obtain the haze free
base oil at the location closer to the end-user.
[0005] The process according the invention is advantageous because step (a) is typically
performed at a remote location. Thus any low boiling by-products can be advantageously
be blended with lower boiling products of the Fischer-Tropsch process at that remote
location. Examples of such products are base oils having a lower viscosity and gas
oil. A further advantage of this process is that step (c) can be performed at a location
more close to the end users. This allows the user of this process to choose the dewaxing
technique most suited for the specific application. Thus if a haze free lubricant
is required a solvent dewaxing step according the invention is applied. If on the
other hand haze is not a major issue a less selective dewaxing technique can be used.
Thus it is not required to have two types of dewaxing technology at the remote location
and optimal use can be made of existing dewaxing facilities at the locations more
close to the end users. A further advantage is that all of the intermediate product
can be efficiently used. Because step (c) is a solvent dewaxing step an oil having
the desired viscometric properties and a valuable microcrystalline wax is obtained.
Thus all of the intermediate product can be sold as products. In contrast, if a catalytic
dewaxing is performed on the intermediate product low boiling by-products would have
been obtained which would only have a blending value at the location close to the
costumer. This value would be less than the value of these by-products if the dewaxing
had been performed at the remote location. A further advantage is that the high quality
products such as the haze free base oil as well as the wax as prepared in step (c)
do not have to be transported from the remote location to the end users.
[0006] A further advantage is that the wax feed used in step (a) may also contain the heaviest
molecules as prepared in the Fischer-Tropsch synthesis. This is advantageous because
it is now possible to prepare high viscosity grade base oils without having to perform
a deep-cut distillation in order to remove possible haze-precursors as for example
described in WO-A-03033622.
[0007] The Fischer-Tropsch wax as used in step (a) can be obtained by well-known processes,
for example the so-called commercial Sasol process, the Shell Middle Distillate Process
or by the non-commercial Exxon process. These and other processes are for example
described in more detail in EP-A-776959, EP-A-668342, US-A-4943672, US-A-5059299,
WO-A-9934917 and WO-A-9920720. The process will generally comprise a Fischer-Tropsch
synthesis and a hydroisomerisation step as described in these publications.
[0008] More preferably the wax used in step (a) is prepared according to the following process.
In this process a Fischer-Tropsch product is subjecting to a hydroisomerisation step
and a wax is isolated having a 10 wt% recovery boiling point of above 500 °C. The
feed to the hydroisomerisation step is a Fischer-Tropsch product which has at least
30 wt%, preferably at least 50 wt%, and more preferably at least 55 wt% of compounds
having at least 30 carbon atoms. Furthermore the weight ratio of compounds having
at least 60 or more carbon atoms and compounds having at least 30 carbon atoms of
the Fischer-Tropsch product is at least 0.2, preferably at least 0.4 and more preferably
at least 0.55. Preferably the Fischer-Tropsch product comprises a C20+ fraction having
an ASF-alpha value (Anderson-Schulz-Flory chain growth factor) of at least 0.925,
preferably at least 0.935, more preferably at least 0.945, even more preferably at
least 0.955.
[0009] The initial boiling point of the Fischer-Tropsch product may range up to 400 °C,
but is preferably below 200 °C. Preferably any compounds having 4 or less carbon atoms
and any compounds having a boiling point in that range are separated from a Fischer-Tropsch
synthesis product before the Fischer-Tropsch synthesis product is used in said hydroisomerisation
step.
[0010] Such a Fischer-Tropsch product can be obtained by any process, which yields a relatively
heavy Fischer-Tropsch product. Not all Fischer-Tropsch processes yield such a heavy
product. An example of a suitable Fischer-Tropsch process is described in WO-A-9934917
and in AU-A-698392. These processes may yield a Fischer-Tropsch product as described
above.
[0011] The Fischer-Tropsch product will contain no or very little sulphur and nitrogen containing
compounds. This is typical for a product derived from a Fischer-Tropsch reaction,
which uses synthesis gas containing almost no impurities. Sulphur and nitrogen levels
will generally be below the detection limits, which are currently 5 ppm for sulphur
and 1 ppm for nitrogen.
[0012] The hydrocracking/hydroisomerisation reaction of the hydroisomerisation is preferably
performed in the presence of hydrogen and a catalyst, which catalyst can be chosen
from those known to one skilled in the art as being suitable for this reaction. Catalysts
for use in the hydroisomerisation typically comprise an acidic functionality and a
hydrogenation/dehydrogenation functionality. Preferred acidic functionality's are
refractory metal oxide carriers. Suitable carrier materials include silica, alumina,
silica-alumina, zirconia, titania and mixtures thereof. Preferred carrier materials
for inclusion in the catalyst for use in the process of this invention are silica,
alumina and silica-alumina. A particularly preferred catalyst comprises platinum supported
on a silica-alumina carrier. Preferably the catalyst does not contain a halogen compound,
such as for example fluorine, because the use of such catalysts require special operating
conditions and involve environmental problems. Examples of suitable hydrocracking/hydroisomerisation
processes and suitable catalysts are described in WO-A-0014179, EP-A-532118, EP-A-666894
and the earlier referred to EP-A-776959.
[0013] Preferred hydrogenation/dehydrogenation functionality's are Group VIII metals, for
example nickel, palladium and platinum and more preferably platinum. In case of platinum
and palladium the catalyst may comprise the hydrogenation/dehydrogenation active component
in an amount of from 0.005 to 5 parts by weight, preferably from 0.02 to 2 parts by
weight, per 100 parts by weight of carrier material. In case nickel is used a higher
content will be present, optionally nickel is used in combination with copper. A particularly
preferred catalyst for use in the hydroconversion stage comprises platinum in an amount
in the range of from 0.05 to 2 parts by weight, more preferably from 0.1 to 1 parts
by weight, per 100 parts by weight of carrier material. The catalyst may also comprise
a binder to enhance the strength of the catalyst. The binder can be non-acidic. Examples
are clays and other binders known to one skilled in the art.
[0014] In the hydroisomerisation the feed is contacted with hydrogen in the presence of
the catalyst at elevated temperature and pressure. The temperatures typically will
be in the range of from 175 to 380 °C, preferably higher than 250 °C and more preferably
from 300 to 370 °C. The pressure will typically be in the range of from 10 to 250
bar and preferably between 20 and 80 bar. Hydrogen may be supplied at a gas hourly
space velocity of from 100 to 10000 Nl/l/hr, preferably from 500 to 5000 Nl/l/hr.
The hydrocarbon feed may be provided at a weight hourly space velocity of from 0.1
to 5 kg/l/hr, preferably higher than 0.5 kg/l/hr and more preferably lower than 2
kg/l/hr. The ratio of hydrogen to hydrocarbon feed may range from 100 to 5000 Nl/kg
and is preferably from 250 to 2500 Nl/kg.
[0015] The conversion in the hydroisomerisation as defined as the weight percentage of the
feed boiling above 370 °C which reacts per pass to a fraction boiling below 370 °C,
is at least 20 wt%, preferably at least 25 wt%, but preferably not more than 80 wt%,
more preferably not more than 70 wt%. The feed as used above in the definition is
the total hydrocarbon feed fed to the hydroisomerisation, thus also any optional recycle
to step (a).
[0016] One or more distillate separations are performed on the effluent of the hydroisomerisation
to obtain at least one middle distillate fuel fraction and the wax which is to be
used in step (a). Preferably the effluent is subjected to an atmospheric distillation.
The residue as obtained in such a distillation is subjected to a distillation performed
at near vacuum conditions. This atmospheric bottom product or residue preferably boils
for at least 95 wt% above 370 °C. The vacuum distillation is suitably performed at
a pressure of between 0.001 and 0.1 bara. The heavy wax for step (a) is preferably
obtained as the bottom product of such a vacuum distillation.
[0017] Step (a) may be performed using any hydroconversion process, which is capable of
reducing the wax content to below 50 wt%. The wax content in the intermediate product
is preferably below 35 wt% and more preferably between 5 and 35 wt%, and even more
preferably between 10 and 35 wt%. A minimal amount of wax will is required in order
to operate a solvent dewaxing step in an optimal manner. The intermediate product
as obtained in step (a) preferably has a congealing point of below 80 °C and more
preferably between 20 and 60 °C. Preferably more than 50 wt% and more preferably more
than 70 wt% of the intermediate product boils above the 10 wt% recovery point of the
wax feed used in step (a).
[0018] A very suitable process is the hydroisomerisation process as described above. It
has been found that the wax may be reduced to the desired level using such catalyst.
By varying the severity of the process conditions as described above a skilled person
will easily determine the required operating conditions to arrive at the desired wax
conversion. However a temperature of between 300 and 330 °C and a weight hourly space
velocity of between 0.1 and 0.5, more preferably between 0.1 and 0.3 kg of oil per
litre of catalyst per hour (kg/l/hr) are especially preferred for optimising the oil
yield.
[0019] A next suitable class of catalyst, which may be applied in step (a), is the class
of dewaxing catalysts. The process conditions applied when using such catalysts should
be such that a wax content remains in the oil. In contrast typical catalytic dewaxing
processes aim at reducing the wax content to almost zero.
[0020] The dewaxing catalyst which may be applied in step (c) suitably comprises a molecular
sieve and optionally in combination with a metal having a hydrogenation function,
such as the Group VIII metals. Molecular sieves, and more suitably molecular sieves
having a pore diameter of between 0.35 and 0.8 nm have shown a good catalytic ability
to reduce the wax content of the wax feed. Suitable zeolites are mordenite, beta,
ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 and ZSM-48. Another preferred group
of molecular sieves are the silica-aluminaphosphate (SAPO) materials of which SAPO-11
is most preferred as for example described in US-A-4859311. ZSM-5 may optionally be
used in its HZSM-5 form in the absence of any Group VIII metal. The other molecular
sieves are preferably used in combination with an added Group VIII metal. Suitable
Group VIII metals are nickel, cobalt, platinum and palladium. Examples of possible
combinations are Pt/ZSM-35, Ni/ZSM-5, Pt/ZSM-23, Pd/ZSM-23, Pt/ZSM-48 and Pt/SAPO-11.
Further details and examples of suitable molecular sieves and dewaxing conditions
are for example described in WO-A-9718278, US-A-4343692, US-A-5053373, US-A-5252527
and US-A-4574043.
[0021] A preferred class of molecular sieves are those having a relatively low isomerisation
selectivity and a high wax conversion selectivity, like ZSM-5 and ferrierite (ZSM-35).
[0022] The dewaxing catalyst suitably also comprises a binder. The binder can be a synthetic
or naturally occurring (inorganic) substance, for example clay, silica and/or metal
oxides. Natural occurring clays are for example of the montmorillonite and kaolin
families. The binder is preferably a porous binder material, for example a refractory
oxide of which examples are: alumina, silica-alumina, silica-magnesia, silica-zirconia,
silica-thoria, silica-beryllia, silica-titania as well as ternary compositions for
example silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and
silica-magnesia-zirconia. More preferably a low acidity refractory oxide binder material,
which is essentially free of alumina, is used. Examples of these binder materials
are silica, zirconia, titanium dioxide, germanium dioxide, boria and mixtures of two
or more of these of which examples are listed above. The most preferred binder is
silica.
[0023] A preferred class of dewaxing catalysts comprise intermediate zeolite crystallites
as described above and a low acidity refractory oxide binder material which is essentially
free of alumina as described above, wherein the surface of the aluminosilicate zeolite
crystallites has been modified by subjecting the aluminosilicate zeolite crystallites
to a surface dealumination treatment. A preferred dealumination treatment is by contacting
an extrudate of the binder and the zeolite with an aqueous solution of a fluorosilicate
salt as described in for example US-A-5157191 or WO-A-0029511. Examples of suitable
dewaxing catalysts as described above are silica bound and dealuminated Pt/ZSM-5,
silica bound and dealuminated Pt/ZSM-35 as for example described in WO-A-0029511 and
EP-B-832171.
[0024] The conditions in step (a) when using a dewaxing catalyst typically involve operating
temperatures in the range of from 200 to 500 °C, suitably from 250 to 400 °C. Preferably
the temperature is between 300 and 330 °C. The hydrogen pressures in the range of
from 10 to 200 bar, preferably from 40 to 70 bar, weight hourly space velocities (WHSV)
in the range of from 0.1 to 10 kg of oil per litre of catalyst per hour (kg/l/hr),
suitably from 0.1 to 1 kg/l/hr, more suitably from 0.1 to 0.3 kg/l/hr and hydrogen
to oil ratios in the range of from 100 to 2,000 litres of hydrogen per litre of oil.
[0025] Transportation in step (b) is preferably performed by means of a ship. The location
at which step (a) is performed is preferably a remote location and the location of
which step (c) is performed is preferably a location more close to the end users of
the base oil. The product is loaded into the ships containers by preferably first
purging the empty product containers in the ship with nitrogen in order to lower the
oxygen content. Purging is preferably performed for at least 5 minutes and more preferably
for at least 10 minutes. After purging the product containers are filled with the
intermediate product. Preferably nitrogen is supplied to the loaded containers to
achieve a nitrogen atmosphere in the gaseous space above the product in the product
containers. More preferably nitrogen is supplied for at least 5 minutes and more preferably
for at least 10 minutes to the loaded containers. The duration of the transport in
step (b) is typically more than 5 days.
[0026] In step (c) the haze free oil is obtained by solvent dewaxing the intermediate product
as transported in step (b). Solvent dewaxing is well known to those skilled in the
art and involves admixture of one or more solvents and/or wax precipitating agents
with the base oil precursor fraction and cooling the mixture to a temperature in the
range of from -10 °C to -40 °C, preferably in the range of from -20 °C to -35 °C,
to separate the wax from the oil. The oil containing the wax is usually filtered through
a filter cloth which can be made of textile fibres, such as cotton; porous metal cloth;
or cloth made of synthetic materials. Examples of solvents which may be employed in
the solvent dewaxing process are C3-C6 ketones (e.g. methyl ethyl ketone, methyl isobutyl
ketone and mixtures thereof), C6-C10 aromatic hydrocarbons (e.g. toluene), mixtures
of ketones and aromatics (e.g. methyl ethyl ketone and toluene), autorefrigerative
solvents such as liquefied, normally gaseous C2-C4 hydrocarbons such as propane, propylene,
butane, butylene and mixtures thereof. Mixtures of methyl ethyl ketone and toluene
or methyl ethyl ketone and methyl isobutyl ketone are generally preferred. Examples
of these and other suitable solvent dewaxing processes are described in Lubricant
Base Oil and Wax Processing, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994,
Chapter 7.
[0027] In step (c) also a wax is obtained. It has been found that such a wax is a relatively
soft microcrystalline wax, which may be used for various purposes. An additional advantage
of the present invention is that the wax is recovered from the intermediate product
at a location near the end-costumer. The soft microcrystalline wax as obtained with
the above process has preferably a congealing point as determined by ASTM D 938 of
between 85 and 120 and more preferably between 95 and 120 °C and a PEN at 43 °C as
determined by IP 376 of more than 0.8 mm and preferably more than 1 mm. The wax is
further characterized in that it preferably comprises less than 1 wt% aromatic compounds
and less than 10 wt% naphthenic compounds, more preferably less than 5 wt% naphthenic
compounds. The mol percentage of branched paraffins in the wax is preferably above
33 and more preferably above 45 and below 80 mol% as determined by C13 NMR. This method
determines an average molecular weight for the wax and subsequently determines the
mol percentage of molecules having a methyl branch, the mol percentage of molecules
having an ethyl branch, the mol percentage of molecules having a C3 branch and the
mol percentage having a C4+ branch, under the assumption that each molecule does not
have more than one branch. The mol% of branched paraffins is the total of these individual
percentages. This method calculated the mol% in the wax of an average molecule having
only one branch. In reality paraffin molecules having more than one branch may be
present. Thus the content of branched paraffins determined by a different method than
above may result in a different value.
[0028] The oil content of the wax as determined by ASTM D 721 is typically below 10 wt%
and more preferably below 6 wt%. If lower oil contents are desired it may be advantageous
to perform an additional de-oiling step. Deoiling processes are well known and are
for example described in Lubricant Base Oil and Wax Processing, Avilino Sequeira,
Jr, Marcel Dekker Inc., New York, 1994, pages 162-165. After de-oiling the wax preferably
has a oil content of between 0.1 and 2 wt%. The lower limit is not critical. Values
of above 0.5 wt% may be expected, but lower values can be achieved depending on the
method in which the wax is obtained. Most likely the oil content will be between 1
and 2 wt%. The kinematic viscosity at 150 °C of the wax is preferably higher than
8 cSt and more preferably higher than 12 and lower than 18 cSt.
[0029] The haze free base oil will preferably have a kinematic viscosity at 100 °C of above
10 cSt, preferably above 14 cSt and typically below 30 cSt. The pour point is preferably
below -18 °C, more preferably below -21 °C and even more preferably below -27 °C.
The viscosity index is suitably above 120 and preferably above 130. A haze free base
oil is determined by its cloud point. A haze free base oil according to this invention
has a cloud point as determined by ASTM D2500 of below 0 °C, preferably below -10
°C and more preferably below -15 °C.
[0030] Because of these properties applicant has found that the base oil may be advantageously
be used to prepare a lubricant composition which does not require a viscosity modifier
(VM). Applicants further found that such a VISCOSITY MODIFIER-free lubricant may be
obtained without having to add a poly-alpha olefin co-base oil as shown in WO-A-0157166.
The invention is thus also directed to prepare a VM-free lubricant composition by
blending a preferably Fischer-Tropsch derived and low viscosity base oil with the
haze free base oil as obtained in step (c) and one or more additives. The low viscosity
base oil preferably has a kinematic viscosity at 100 °C of less than 7 cSt. The haze
free base oil preferably has a kinematic viscosity at 100 °C of more than 18 cSt.
[0031] Applicants found that by blending the haze free base oil with the lower viscosity
grade base oil it is possible to achieve the properties of a so-called SAE "xW-y"
viscosity lubricant formulation without having to add a viscosity modifier. Applicants
further found that when a viscosity modifier-free lubricant is used as motor engine
lubricant in gasoline direct injection (GDI) engines no build up of residue on the
back of the inlet valve tulip occurs, which would happen if a VM is present.
[0032] It has further been found that especially SAE "xW-y" viscosity lubricant formulations
wherein y-x is greater or equal than 25 can be prepared without having to add a VM.
Based on the teaching of WO-A-0157166 one would have expected that such formulations
could only be prepared by having to add a VM.
[0033] The Fischer-Tropsch derived base oil having a kinematic viscosity at 100 °C of less
than 7 cSt preferably has a pour point of less than -18 °C, more preferably less than
-27 °C. The kinematic viscosity at 100 °C is preferably greater than 3.5 cSt and more
preferably between 3.5 and 6 cSt. The viscosity index (VI) is preferably greater than
120, more preferably greater than 130. The VI will typically be less than 160. The
Noack volatility (according to CEC L40 T87) is preferably less than 14 wt%. The low
viscosity component may be a typical API Group III base oil and more preferably a
Fischer-Tropsch derived base oil as disclosed in for example EP-A-776959, EP-A-668342,
WO-A-9721788, WO-0015736, WO-0014188, WO-0014187, WO-0014183, WO-0014179, WO-0008115,
WO-9941332, EP-1029029, WO-0118156 and WO-0157166.
1. Process to prepare a haze free base oil having a kinematic viscosity at 100 °C of
greater than 10 cSt from a Fischer-Tropsch wax feed having a 10 wt% recovery boiling
point of above 500 °C and a wax content of greater than 50 wt% by performing the following
steps,
(a) reducing the wax content of the feed to a value of below 50 wt% by contacting
the feed with a hydroisomerisation catalyst under hydroisomerisation conditions at
a remote location,
(b) transporting an intermediate product having a wax content of below 50 wt% as obtained
in step (a) from one location to another location, and
(c) solvent dewaxing the transported intermediate product to obtain the haze free
base oil at the location closer to the end-user.
2. Process according to claim 1, wherein the wax content in the feed is between 60 and
95 wt%.
3. Process according to any one of claims 1-2, wherein the 10 wt% recovery boiling point
of the feed is between 500 and 550 °C.
4. Process according to any one of claims 1-3, wherein the wax content in the intermediate
product is between 10 and 35 wt%.
5. Process according to any one of claims 1-4, wherein the intermediate product has a
congealing point of between 20 and 60 °C.
6. Process according to any one of steps 1-5, wherein more than 50 wt% of the intermediate
product boils above the 10 wt% recovery point of the feed used in step (a).
7. Process according to claim 6, wherein more than 70 wt% of the intermediate product
boils above the 10 wt% recovery point of the feed used in step (a).
8. Process according to any one of claims 1-7, wherein the hydroisomerisation catalyst
used in step (a) is a substantially amorphous based catalyst comprising a silica-alumina
carrier and a noble or non-noble Group VIII metal.
9. Process according to any one of claims 1-7, wherein the hydroisomerisation catalyst
used in step (a) is a molecular sieve based catalyst and a noble or non-noble Group
VIII metal.
10. Process to prepare a lubricant composition not containing a viscosity modifier additive
by blending a low viscosity base oil with the haze free base oil as obtained in step
(c) of the process as described in claims 1-9 and one or more additives.