U.S. patent application number 11/794217 was filed with the patent office on 2008-07-03 for process to prepare a base oil from a fischer-tropsch synthesis product.
This patent application is currently assigned to SHELL OIL COMPANY. Invention is credited to Jan Lodewijk Maria Dierickx.
Application Number | 20080156697 11/794217 |
Document ID | / |
Family ID | 34930180 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080156697 |
Kind Code |
A1 |
Dierickx; Jan Lodewijk
Maria |
July 3, 2008 |
Process to Prepare a Base Oil From a Fischer-Tropsch Synthesis
Product
Abstract
Process to prepare base oils from a Fischer-Tropsch synthesis
product by (a) separating the Fischer-Tropsch synthesis product
into a fraction (i) boiling in the middle distillate range and
below, a heavy ends fraction (iii) and an intermediate base oil
precursor fraction (ii) boiling between fraction (i) and fraction
(iii), (b) subjecting the base oil precursor fraction (ii) to a
catalytic hydroisomerisation step in the presence of a catalyst
comprising a binder, zeolite Beta and a Group VIII metal and a
catalytic dewaxing step in the presence of a catalyst comprising a
binder, a medium pore size zeolite having and a Group VIII
hydrogenation component to yield one or more base oil grades, (c)
subjecting the heavy ends fraction (iii) to a conversion step to
yield a fraction (iv) boiling below the heavy ends fraction (iii)
and (d) subjecting the high boiling fraction (v) of fraction (iv)
to a catalytic hydroisomerisation and catalytic dewaxing process to
yield one or more base oil grades .
Inventors: |
Dierickx; Jan Lodewijk Maria;
(Amsterdam, NL) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Assignee: |
SHELL OIL COMPANY
Houston
TX
|
Family ID: |
34930180 |
Appl. No.: |
11/794217 |
Filed: |
December 27, 2005 |
PCT Filed: |
December 27, 2005 |
PCT NO: |
PCT/EP2005/057172 |
371 Date: |
June 26, 2007 |
Current U.S.
Class: |
208/79 |
Current CPC
Class: |
C10G 65/14 20130101 |
Class at
Publication: |
208/79 |
International
Class: |
C10G 65/14 20060101
C10G065/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2004 |
EP |
04107026.9 |
Claims
1. A process to prepare base oils from a Fischer-Tropsch synthesis
product comprising (a) separating a Fischer-Tropsch synthesis
product into a fraction (i) boiling in the middle distillate range
and below, a heavy ends fraction (iii) and an intermediate base oil
precursor fraction (ii) boiling between fraction (i) and fraction
(iii); (b) subjecting the base oil precursor fraction (ii) to a
catalytic hydroisomerisation step in the presence of a catalyst
comprising a binder, zeolite Beta and a Group VIII metal and a
catalytic dewaxing step in the presence of a catalyst comprising a
binder, a medium pore size zeolite and a Group VIII hydrogenation
component to yield one or more base oil grades; (c) subjecting the
heavy ends fraction (iii) to a conversion step to yield a fraction
(iv) boiling below the heavy ends fraction (iii); and (d)
subjecting a high boiling fraction (v) of fraction (iv) to a
catalytic hydroisomerisation and catalytic dewaxing process to
yield one or more base oil grades.
2. The process according to claim 1, wherein the heavy ends
fraction (iii) has an initial boiling point of between 500 and
600.degree. C.
3. The process according to claim 1, wherein the medium pore size
zeolite in step (b) is selected from the group consisting of
mordenite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 or ZSM-48
and combinations of said zeolites.
4. The process according to claim 3, wherein the medium pore size
zeolite in step (b) is ZSM-48.
5. The process according to claim 1, wherein the hydroisomerisation
in step (b) is performed in the presence of a catalyst comprising a
binder, zeolite Beta and platinum and a catalytic dewaxing step in
the presence of a catalyst comprising a binder, a medium pore size
zeolite and platinum.
6. The process according to claim 1, wherein step (c) is performed
as a hydrocracking/hydroisomerisation process making use of an
amorphous catalyst comprising an acidic functionality and a
hydrogenation/dehydrogenation functionality.
7. The process according to claim 1, wherein the effluent of step
(c) is provided to step (a), such that in effect steps (b) and (d)
take place simultaneously.
8. A process to prepare base oils from a Fischer-Tropsch synthesis
product by comprising (a) separating a Fischer-Tropsch synthesis
product into a fraction (i) boiling in the middle distillate range
and below, a heavy ends fraction (iii) and an intermediate base oil
precursor fraction (ii) boiling between fraction (i) and fraction
(iii); (b) subjecting the base oil precursor fraction (ii) to a
catalytic hydroisomerisation step in the presence of a catalyst
comprising a binder, zeolite Beta and a Group VIII metal and a
catalytic dewaxing step in the presence of a catalyst comprising a
binder, a medium pore size zeolite and a Group VIII hydrogenation
component to yield one or more base oil grades; and (c) subjecting
the heavy ends fraction (iii) to a conversion step to yield a
fraction (iv) boiling below the heavy ends fraction (iii) and
recycling the high boiling fraction (v) of fraction (iv) boiling in
the base oil range to step (b).
9. The process according to claim 8, wherein the fraction boiling
above fraction (v) of fraction (iv) is recycled to step (c).
Description
[0001] The present invention is directed to a process to prepare
base oils or the intermediate waxy raffinate product in a high
yield from a Fischer-Tropsch synthesis product.
[0002] Such processes are known from WO-A-9941332, U.S. Pat. No.
6,080,301, EP-A-0668342, U.S. Pat. No. 6,179,994,
U.S.-A-2004/0065581 or WO-A-02070629. These processes all comprise
some kind of hydroisomerisation of the Fischer-Tropsch synthesis
product followed by a dewaxing step of the higher boiling fraction
obtained in said hydroisomerisation.
[0003] WO-A-02070629, for example, describes a process wherein the
C5 plus fraction of a Fischer-Tropsch synthesis product is first
subjected to a hydrocracking/hydroisomerisating step in the
presence of a catalyst consisting of platinum on an amorphous
silica-alumina carrier. The effluent of this conversion step is
separated into middle distillate products and a base oil precursor
fraction and a higher boiling fraction. The base oil precursor
fraction is catalytically dewaxed in the presence of a
platinum-ZSM-5 based catalyst and the heavy fraction is recycled to
the hydrocracking/hydroisomerisating step.
[0004] Although such a process will yield excellent quality base
oils there is room for improvement. Especially the yield of base
oils relative to the Fischer-Tropsch synthesis product may be
improved. More especially for base oils having a kinematic
viscosity at 100.degree. C. of between 2 and 8 cSt an improved
yield would be welcome.
[0005] EP-A-776959 discloses a process to prepare base oil in a
high yield from a narrow boiling Fischer-Tropsch wax by first
performing a hydroisomerisation step in the presence of an
amorphous catalyst system followed by a catalytic dewaxing step
using a platinum/ZSM-23 catalyst.
[0006] U.S.-A-2004/0065581 also discloses the preparation of a base
oil in a high yield from a narrow cut Paraflint C80 wax, which is a
substantially normal paraffin wax having a melting point of about
80.degree. C., by contacting the feed with a stack of
platinum/zeolite Beta and platinum/ZSM-48.
[0007] The above two processes describe a high yield to base oils
relative to the narrow cut feed. If calculated on the entire
Fischer-Tropsch wax, which may boil well above the boiling range of
the feeds disclosed in these publications, the yield will be much
lower.
[0008] The present invention aims at providing a process, which
will make more base oils relative to the entire Fischer-Tropsch
synthesis product as boiling in the base oil range and above.
[0009] The following process achieves this object. Process to
prepare base oils from a Fischer-Tropsch synthesis product by
[0010] (a) separating the Fischer-Tropsch synthesis product into a
fraction (i) boiling in the middle distillate range and below, a
heavy ends fraction (iii) and an intermediate base oil precursor
fraction (ii) boiling between fraction (i) and fraction (iii),
[0011] (b) subjecting the base oil precursor fraction (ii) to a
catalytic hydroisomerisation step in the presence of a catalyst
comprising a binder, zeolite Beta and a Group VIII metal and a
catalytic dewaxing step in the presence of a catalyst comprising a
binder, a medium pore size zeolite having and a Group VIII
hydrogenation component to yield one or more base oil grades,
[0012] (c) subjecting the heavy ends fraction (iii) to a conversion
step to yield a fraction (iv) boiling below the heavy ends fraction
(iii) and [0013] (d) subjecting the high boiling fraction (v) of
fraction (iv) to a catalytic hydroisomerisation and catalytic
dewaxing process to yield one or more base oil grades.
[0014] Applicants have found that by directly subjecting the
fraction of the intermediate fraction (ii) of the Fischer-Tropsch
synthesis product and the high boiling fraction (v) as obtained in
step (c) to a selective isomerisation and dewaxing step a higher
yield to base oils relative to the Fischer-Tropsch synthesis
product can be obtained.
[0015] Without intending to be bound by the following theory it is
believed that the high yield to base oils is achieved in that the
present process yields more of the fraction boiling in the base oil
range, i.e. fractions (ii) and (v), as suitable feed to the
catalytic hydroisomerisation and catalytic dewaxing processes of
steps (b) and (d). In the prior art process of WO-A-02070629 the
boiling in the base oil range of the Fischer-Tropsch synthesis
product was first contacted with a catalyst which would convert a
large part to middle distillate products and lower boiling
products. By using this different line-up the conversion of
potential base oil molecules in the Fischer-Tropsch synthesis
product to middle distillate molecules is minimized. Furthermore in
the process of WO-A-02070629 the heavy fraction as obtained in the
hydrocracking/hydroisomerisating step is recycled to said step.
This results in that more potential base oil molecules are
converted to middle distillate molecules.
[0016] The Fischer-Tropsch synthesis product can be obtained by
well-known processes, for example the so-called Sasol process, the
Shell Middle Distillate Synthesis Process or by the ExxonMobil
"AGC-21" process. These and other processes are for example
described in more detail in EP-A-776959, EP-A-668342, U.S. Pat. No.
4,943,672, U.S. Pat. No. 5,059,299, WO-A-9934917 and WO-A-9920720.
Typically these Fischer-Tropsch synthesis products will comprise
hydrocarbons having 1 to 100 and even more than 100 carbon atoms.
The hydrocarbon product will comprise iso-paraffins, n-paraffins,
oxygenated products and unsaturated products. The feed to step (a)
or any fractions obtained in step (a) may be hydrogenated in order
to remove any oxygenates or unsaturated products. The process of
the present invention is especially advantageous when a substantial
part, preferably more than 10 wt %, more preferably more than 30 wt
% and even more preferably more than 50 wt % of the Fischer-Tropsch
synthesis product boils above 550.degree. C. An example of a
suitable process which may prepare such a heavy Fischer-Tropsch
synthesis product is described in WO-A-9934917.
[0017] In step (a) the Fischer-Tropsch synthesis product is
separated into a fraction (i) boiling in the middle distillate
range and below, a heavy ends fraction (iii) preferably, having an
initial boiling point between 500 and 600.degree. C. and an
intermediate base oil precursor fraction (ii) boiling between
fraction (i) and fraction (iii). Preferred base oil precursor
fractions (ii) comprise for more than 90 wt % of compounds boiling
between 370 and 600.degree. C. Suitably the Fischer-Tropsch
synthesis product is first fractionated at atmospheric pressure or
higher to obtain fraction (i) boiling in the middle distillate
range and below. Fractionation may be performed by flashing or
distillation. The middle distillate range is sometimes defined as
the fraction boiling predominately, i.e. for more than 90 wt %,
between 200 and 350.degree. C. and it comprises the gas oil and
kerosene fractions, which can be isolated from the Fischer-Tropsch
synthesis product. The residue or bottom product of the atmospheric
fractionation is further separated at near vacuum pressure to the
heavy ends fraction (iii) having an initial boiling point between
500 and 600.degree. C. and the intermediate base oil precursor
fraction (ii). More preferably the T10 wt % recovery point of the
heavy ends fraction (iii) is between 500 and 600.degree. C.
[0018] In step (b) the base oil precursor fraction (ii) is first
passed over a catalyst comprising a binder, zeolite Beta and a
Group VIII metal. The resulting intermediate product is then
further subjected to a catalytic dewaxing step. These first and
second stages can be operated as separated steps. Preferably both
stages are integrated process steps, for example cascaded. Zeolite
Beta catalysts are 12 ring acidic silica/alumina zeolites with or
without boron, wherein boron replaces some of the aluminum atoms.
Pre-sulfided Zeolite Beta is preferred when some residual sulfur in
the product is acceptable and when the base oil precursor fraction
contains some sulphur. In cases wherein part of the base oil
precursor fraction (ii) is prepared in step (c) using a sulphided
catalyst a sulphur containing base oil precursor fraction may be
suitably prepared as feed to step (b) in one of the preferred
embodiments of the present invention as illustrated in FIG. 3
wherein steps (b) and (d) are combined.
[0019] Zeolite Beta as used in the first stage catalyst preferably
has an Alpha value below 15, more preferably below 10, at least
prior to metal loading. Alpha is an acidity metric that is an
approximate indication of the catalytic cracking activity of the
catalyst compared to a standard catalyst. Alpha is a relative rate
constant (rate of normal hexane conversion per volume of catalyst
per unit time). Alpha is based on the activity of the highly active
silica-alumina cracking catalyst taken as an Alpha of 1 as
described in U.S. Pat. No. 3,354,078 and measured at 538.degree. C.
as described in the Journal of Catalysis, vol. 4, p. 527 (1965);
vol. 6, p. 278 (1966); and vol. 61, p. 395 (1980). The use of
Fischer Tropsch derived base oil precursor fraction requires a low
Alpha value of the Zeolite Beta catalyst due to minimal nitrogen
content in the feeds. Alpha values may be reduced by steaming.
Examples of suitable first stage catalysts are described in the
earlier referred to U.S.-A-2004/0065581.
[0020] The catalyst of the second stage in of step (b) compromises
a medium pore size molecular sieve. Preferably the intermediate
pore size molecular sieves are zoelites having a pore diameter of
between 0.35 and 0.8 nm. Suitable intermediate pore size zeolites
are mordenite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 and
ZSM-48 or combinations of said zeolites. Most preferred are ZSM-48,
SSZ-32, ZSM-23, ZSM-12 and ZSM-22, of which ZSM-48 is very
suitable. Another preferred group of molecular sieves are the
silica-aluminaphosphate (SAPO) materials of which SAPO-11 is most
preferred as for example described in U.S. Pat. No. 4,859,311.
[0021] The first stage or second stage catalyst of step (b)
suitably comprises 0.01-5 wt % of at least one Group VIII metal
(i.e., Fe, Ru, Os, Co, Rh, Ir, Pd, Pt, Ni). Platinum and palladium
are most preferred. Platinum or palladium blended with each other
or other group VIII metals follow in preference. Nickel may also be
blended with group VIII precious metals and is included in the
scope of the invention whenever group VIII blends, alloys, or
mixtures are mentioned. Preferred metal loading on both catalysts
are 0.1-1 wt % with approximately 0.6 wt % most preferred.
[0022] The binder of the first stage or second stage catalyst of
step (b) 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. A suitable
binder is alumina. If alumina is used the content of the binder in
the catalyst is preferably between 10 and 65 wt %. 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. If
a low acidity binder is used the content of the binder is
preferably between 60 and 95 wt %, more preferably between 65 and
90 wt %.
[0023] Catalysts comprising the low acidity binder as described
above are preferably subjected to a dealumination treatment. In
such a treatment the surface of the aluminosilicate zeolite
crystallites will be 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 U.S. Pat. No.
5,157,191 or WO-A-2000029511. Examples of suitable dewaxing
catalysts as described above are silica bound and dealuminated
Pt/ZSM-5, silica bound and dealuminated Pt/ZSM-23, silica bound and
dealuminated Pt/ZSM-12, silica bound and dealuminated Pt/ZSM-22, as
for example described in WO-A-200029511 and EP-B-832171.
[0024] The crystallite size of the medium pore size zeolite and/or
the zeolite beta may be as high as 100 micron. Preferably small
crystallites are used in order to achieve an optimum catalytic
activity. Preferably crystallites smaller than 10 micron and more
preferably smaller than 1 micron are used. The practical lower
limit is suitably 0.1 micron. It has been found that the
combination of small size crystallites and a surface dealumination
treatment, especially the AHS treatment, as described above results
in more active catalyst when compared to the same, but
non-dealuminated, catalyst. Preferable catalysts are used having a
crystallite size of between 0.05 and 0.2 .mu.m and which have been
subjected to a dealumination treatment. The size or better said the
length of the crystallite in the direction of the pores is the
critical dimension. X-ray diffraction (XRD) can be used to measure
the crystallite length by line broadening measurements.
[0025] The process conditions in both first and second stage
include a 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 0.2 to 5 kg/l/hr, more suitably from
0.5 to 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.
[0026] The first stage reaction step of step (b) involving the Beta
catalyst is preferably performed at temperatures between 200 and
370.degree. C., more preferably at between 260 and 340.degree. C.
and most preferably at 270 and 300.degree. C.
[0027] The second stage reaction step of step (b) is preferably
performed at temperatures between 260 and 430.degree. C., more
preferably at between 320 and 370.degree. C. and most preferably at
330 and 350.degree. C. The temperature at which the two stages of
step (b) are performed are preferably controlled independently. The
pressure in both stages is preferably similar to each other. In a
preferred embodiment of the invention, a cascaded two-bed catalyst
system consisting of a first bed Pt/Beta catalyst followed by a
second bed of a catalyst comprising platinum and one of the medium
pore size zeolites mentioned above allows a highly selective
process for preparing base oils from the base oil precursor
fraction (ii) with minimal gas formation. In cascading, the
intermediate product preferably directly passes from the first bed
to the second bed without inter-stage separation. Optionally, light
byproducts (e.g., methane, ethane) can be removed between the first
and second stage.
[0028] The base oil precursor fraction to step (b) may be the
fraction of the Fischer-Tropsch wax as synthesized. Such a fraction
will usually comprise for more than 95 wt % of normal paraffins.
Preferably the feed to step (b) also comprises fraction (v) as
obtained in step (c). This fraction (v) will comprise for a
substantial portion of iso-paraffins. The presence of iso-paraffins
is advantageous because these molecules require less isomerisation
as compared to the normal paraffins for achieving the desired pour
point of the base oil. The lower congealing point of this combined
base oil precursor fraction is indicative for the presence of
iso-paraffins. The congealing point is therefore preferably lower
than 80.degree. C., more preferably lower than 60.degree. C. and
even more preferably lower than 50.degree. C. The lower limit will
typically be above 0.degree. C. After performing a dewaxing step
(b) the desired base oil(s) are preferably isolated from the
dewaxed effluent in a base oil recovery step (e). In this step (e)
lower boiling compounds formed during catalytic dewaxing are
removed, preferably by means of distillation, optionally in
combination with an initial flashing step. By choosing a suitable
narrow distillation cut as feed to step (b) in step (a) it is
possible to obtain a desired base oil directly after a catalytic
dewaxing step (b) without having to remove any higher boiling
compounds from the effluent of step (b). Preferred narrow cut feeds
have a difference between its 90 % wt boiling point and its 10 % wt
boiling point (T.sub.90-T.sub.10) in the range of from 40 to
150.degree. C., more preferably from 50 to 130.degree. C. Examples
of very suitable grades are base oils having a kinematic viscosity
at 100.degree. C. of between 3.5 and 6 cSt.
[0029] It has also been found possible to make more than one
viscosity grade base oil with the process according to the
invention. By obtaining a base oil precursor fraction (ii) in step
(a) having a more broad boiling range more base oil grades may
advantageously be obtained in step (e). Preferably the difference
between the T10 wt % recovery point and the 90 wt % recovery point
in the boiling curve is larger than 100.degree. C., more preferably
larger than 150.degree. C. In this mode the effluent of step (b) is
separated into various distillate fractions comprising two or more
base oil grades. In order to meet the desired viscosity grades and
volatility requirements of the various base oil grades preferably
off-spec fractions boiling between, above and/or below the desired
base oil grades are also obtained as separate fractions. These
fractions and any fractions boiling in the gas oil range or below
may advantageously be recycled to step (a). Alternatively fractions
obtained boiling in the gas oil range or below may suitably be used
as a separate blending component to prepare a gas oil fuel
composition.
[0030] The separation into the various fractions in step (e) may
suitably be performed in a vacuum distillation column provided with
side strippers to separate the fraction from said column. In this
mode it is found possible to obtain for example a 2-3 cSt product,
a 4-6 cSt product and a 7-10 cSt product simultaneously from a
single broad boiling base oil precursor fraction (ii). The
viscosity values are the kinematic viscosity at 100.degree. C.
[0031] In step (c) the heavy ends fraction (iii) is subjected to a
conversion step to yield a fraction (iv) boiling below the heavy
ends fraction (iii). Step (c) may be performed by any conversion
process capable of converting the heavy Fischer-Tropsch wax to
lower boiling hydrocarbon compounds. If the conversion product of
step (c) is to contain a high content of olefinic compounds
preferably a conversion process is applied which operates in the
absence of added hydrogen. Examples of suitable processes which
operate in the absence of added hydrogen are the well known thermal
cracking process as for example described in U.S. Pat. No.
6,703,535 and the catalytic cracking process as for example
described in U.S. Pat. No. 4,684,759. If on the other hand the
conversion product of step (c) is to contain almost no olefins
preferably a process is applied which is performed in the presence
of added hydrogen. An example of a suitable process is the well
known hydroisomerisation/hydrocracking process. Preferably the
latter type of conversion process is preferred in the process
according to the present invention in order to minimise the olefins
content in the final base oil products.
[0032] The hydroconversion/hydroisomerisation reaction of step (c)
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 of which some will be
described in more detail below. The catalyst may in principle be
any catalyst known in the art to be suitable for isomerising
paraffinic molecules. In general, suitable
hydroconversion/hydroisomerisation catalysts are those comprising a
hydrogenation component supported on a refractory oxide carrier,
such as amorphous silica-alumina (ASA), alumina, fluorided alumina,
molecular sieves (zeolites) or mixtures of two or more of these.
One type of preferred catalysts to be applied in the
hydroconversion/hydroisomerisation step in accordance with the
present invention are hydroconversion/ hydroisomerisation catalysts
comprising platinum and/or palladium as the hydrogenation
component. A very muchpreferred hydroconversion/hydroisomerisation
catalyst comprises platinum and palladium supported on an amorphous
silica-alumina (ASA) carrier. The platinum and/or palladium is
suitably present in an amount of from 0.1 to 5.0% by weight, more
suitably from 0.2 to 2.0% by weight, calculated as element and
based on total weight of carrier. If both present, the weight ratio
of platinum to palladium may vary within wide limits, but suitably
is in the range of from 0.05 to 10, more suitably 0.1 to 5.
Examples of suitable noble metal on ASA catalysts are, for
instance, disclosed in WO-A-9410264 and EP-A-0582347. Other
suitable noble metal-based catalysts, such as platinum on a
fluorided alumina carrier, are disclosed in e.g. U.S. Pat. No.
5,059,299 and WO-A-9220759.
[0033] A second type of suitable hydroconversion/hydroisomerisation
catalysts are those comprising at least one Group VIB metal,
preferably tungsten and/or molybdenum, and at least one non-noble
Group VIII metal, preferably nickel and/or cobalt, as the
hydrogenation component. Both metals may be present as oxides,
sulphides or a combination thereof. The Group VIB metal is suitably
present in an amount of from 1 to 35% by weight, more suitably from
5 to 30% by weight, calculated as element and based on total weight
of the carrier. The non-noble Group VIII metal is suitably present
in an amount of from 1 to 25 wt %, preferably 2 to 15 wt %,
calculated as element and based on total weight of carrier. A
hydroconversion catalyst of this type which has been found
particularly suitable is a catalyst comprising nickel and tungsten
supported on fluorided alumina.
[0034] The above non-noble metal-based catalysts are preferably
used in their sulphided form. In order to maintain the sulphided
form of the catalyst during use some sulphur needs to be present in
the feed. Preferably at least 10 ppm and more preferably between 50
and 150 ppm of sulphur is present in the feed. A possible source of
sulphur are for example vacuum distillate or atmospheric residues
of crude petroleum sources. Preferred sources are gas field
condensates. These sources may be co-fed to step (c) in order to
achieve the desired level of sulphur.
[0035] A preferred catalyst, which can be used in a non-sulphided
form, comprises a non-noble Group VIII metal, e.g., iron, nickel,
in conjunction with a Group IB metal, e.g., copper, supported on an
acidic support. Copper is preferably present to suppress
hydrogenolysis of paraffins to methane. The catalyst has a pore
volume preferably in the range of 0.35 to 1.10 ml/g as determined
by water absorption, a surface area of preferably between 200-500
m.sup.2/g as determined by BET nitrogen adsorption, and a bulk
density of between 0.4-1.0 g/ml. The catalyst support is preferably
made of an amorphous silica-alumina wherein the alumina may be
present within wide range of between 5 and 96 wt %, preferably
between 20 and 85 wt %. The silica content as SiO.sub.2 is
preferably between 15 and 80 wt %. Also, the support may contain
small amounts, e.g., 20-30 wt %, of a binder, e.g., alumina,
silica, Group IVA metal oxides, and various types of clays,
magnesia, etc., preferably alumina or silica.
[0036] The preparation of amorphous silica-alumina microspheres has
been described in Ryland, Lloyd B., Tamele, M. W., and Wilson, J.
N., Cracking Catalysts, Catalysis: volume VII, Ed. Paul H. Emmett,
Reinhold Publishing Corporation, New York, 1960, pp. 5-9.
[0037] The catalyst is prepared by co-impregnating the metals from
solutions onto the support, drying at 100-150.degree. C., and
calcining in air at 200-550.degree. C. The Group VIII metal is
present in amounts of about 15 wt % or less, preferably 1-12 wt %,
while the Group IB metal is usually present in lesser amounts,
e.g., 1:2 to about 1:20 weight ratio respecting the Group VIII
metal.
[0038] A typical catalyst is shown below:
TABLE-US-00001 Ni, wt % 2.5-3.5 Cu, wt % 0.25-0.35
Al.sub.2O.sub.3--SiO.sub.2 wt % 65-75 Al.sub.2O.sub.3 (binder) wt %
25-30 Surface Area 290-325 m.sup.2/g Pore Volume (Hg) 0.35-0.45
ml/g Bulk Density.
[0039] The hydroconversion/hydroisomerisation conditions involve a
feed that 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.degree. C.,
preferably higher than 250.degree. C. and more preferably from 300
to 370.degree. 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.
[0040] The conversion in step (c) as defined as the weight
percentage of the feed boiling above 370.degree. C. which reacts
per pass to a fraction boiling below 370.degree. C. is preferably
at least 20 wt %, more preferably at least 25 wt %, preferably not
more than 80 wt %, more preferably not more than 70 wt % and even
more preferably not more than 65 wt %.
[0041] Preferably the effluent of the above combined steps (c) and
(d) is provided to the same above described base oil work up
section (step (e)). This is advantageous because the isolation of
all base oil grades, including the heavier grade, may then be
performed in the same distillation column(s).
[0042] In step (d) the high boiling fraction (v) of fraction (iv)
is subjected to a catalytic hydroisomerisation and catalytic
dewaxing process to yield one or more base oil grades. The high
boiling fraction (v) in the effluent of step (c) preferably has a
initial boiling point of between 340 and 400.degree. C. More
preferably the 10 wt % recovery point is between 340 and
400.degree. C. Preferably the fraction (v) comprises for more than
90 wt % of compounds boiling between 370 and 600.degree. C. The
final boiling point of said fraction (v) is preferably between 500
and 600.degree. C. More preferably the 90 wt % recovery point is
between 500 and 600.degree. C. The catalytic dewaxing of step (d)
may be performed using the first or second stange dewaxing
processes as described above for step (b). These processes may be
used alone or more preferably in the combination as described for
step (b). Separations are preferably performed by means of
distillation. Preferably the base oils are isolated from the
effluent of step (d) in the same base oil work-up section (step
(e)) as described above.
[0043] The fraction of the effluent of step (c) which boils above
fraction (v), i.e. the so-called unconverted part of the feed to
step (c), may be suitably recycled to step (c). Because the wax
content of this fraction is lower than the wax fraction of the feed
to step (c) it has been found possible to prepare a high viscous
base oil from said fraction. This can be done by means of catalytic
dewaxing, solvent dewaxing or combinations of said processes. A
suitable combined process includes a first reduction of the wax
content to between 5 and 40, preferably 5 and 30 wt % by means of
catalytic dewaxing, and a subsequent solvent dewaxing step of the
resultant product to obtain a haze free base oil. Catalytic
dewaxing may be performed by means of well known dewaxing
technology or by the first and second stage dewaxing processes as
described for step (b). Applicants have found that a
platinum/ZSM-12 catalyst is suitable for reducing the wax content
while maintaining a high yield to the more viscous base oils. The
kinematic viscosity at 100.degree. C. of these haze free base oils
is preferably above 10 cSt, more preferably above 14 cSt and may
range to values of 30 cSt and above.
[0044] Preferably step (b) and (d) are combined. In such an
embodiment it is preferred to provide the effluent of step (c) to
step (a). This is advantageous because it reduces the number of
distillation columns. In step (a) a mixture of fresh
Fischer-Tropsch synthesis product and step (c) effluent will be
separated simultaneously into again a fraction (i) boiling in the
middle distillate range and below, a heavy ends fraction (iii) and
an intermediate base oil precursor fraction (ii) boiling between
fraction (i) and fraction (iii). In this embodiment step (b) and
(d) are performed in the same reactor, which is also advantageous
for obvious reasons.
[0045] The Fischer-Tropsch synthesis product may contain olefins
and oxygenates which may be detrimental for the hydroconversion
catalysts used in step (b), (c) and (d). These compounds may be
removed by means of hydrogenation of the Fischer-Tropsch synthesis
product prior to performing step (a) or hydrogenation of the feeds
to the separate steps (b), (c) and/or (d). The latter is
advantageous because some of the oxygenates and/or olefins present
in the Fischer-Tropsch synthesis product will end up in the middle
distillate fraction (i) and could serve as lubricity enhancers in
the resulting gas oil or kerosene fractions. The advantages of the
presence of such compounds are for example described in
EP-A-885275.
[0046] Possible hydrogenation processes are for example described
in EP-B-668342. The mildness of the hydrotreating step is
preferably expressed in that the degree of conversion in this step
is less than 20 wt % and more preferably less than 10 wt %. The
conversion is here defined as the weight percentage of the feed
boiling above 370.degree. C., which reacts to a fraction boiling
below 370.degree. C. Examples of possible hydrogenation processes
involve the use of nickel containing catalysts, for example nickel
on alumina, nickel on silica-alumina nickel on Kieselguhr, copper
nickel on alumina, cobalt on silica-alumina or platinum nickel on
alumina. The hydrogenation conditions are typical conditions for
these type of processes, well known to the skilled person.
[0047] The invention will also be illustrated by making use of
FIGS. 1-3.
[0048] FIG. 1 illustrates a state of the art process of
WO-A-02070629.
[0049] FIG. 2 illustrates a process according to the invention.
[0050] FIG. 3 illustrates a process according to the invention.
[0052] FIG. 1 describes a state of the art process line-up
according to WO-A-02070629 illustrating a Fischer-Tropsch synthesis
process step 1 wherein a Fischer-Tropsch product 2 is prepared.
This product 2 is fed to a hydrocracking/hydroisomerisation step 3.
Product 4 is subsequently separated in an atmospheric distillation
column 5 into a naphtha product 6, a kerosene product 7, a gas oil
product 8 and a bottoms product. The bottoms product is
subsequently separated in a vacuum distillation column 9 into a
base oil precursor fraction 10 and a higher boiling fraction 17.
The fraction 10 is subsequently catalytically dewaxed 11 and the
dewaxed oil 12 is fractionated in column 13 into various base oil
products 14, 15 and 16. The higher boiling fraction 17 is recycled
to hydrocracking/hydroisomerisation step 3.
[0053] FIG. 2 illustrates an embodiment of the present invention.
In a Fischer-Tropsch synthesis process step 20 a Fischer-Tropsch
product 21 is prepared. This product 21 is separated by means of
distillation 22 in one or more middle distillate fractions 31, 38,
which may be naphtha, kerosene and gas oil, into a base oil
precursor fraction 36 and a higher boiling fraction 23.
Distillation 22 may be a atmospheric distillation and a vacuum
distillation scheme as in FIG. 1. The base oil precursor fraction
is fed to a catalytic hydroisomerisation step and a catalytic
dewaxing step as combined in 30 to perform step (b) and the dewaxed
oil 34 is fractionated in column 32 into one or more base oil
products 35, 36 and 37. The higher boiling fraction 23 is fed to a
hydrocracking/hydroisomerisation step 24 yielding a cracked product
25. From this product 25 a fraction boiling in the gas oil range
and below 38, a base oil precursor fraction 27 and a higher boiling
fraction 33 is separated in column 26. The base oil precursor
fraction 27 is catalytically dewaxed 28 and the dewaxed oil is
combined with dewaxed oil 34 to be separated in 32 as described
above wherein base oil 37 is more viscous than base oil 16 of FIG.
1.
[0054] FIG. 3 is a process as in FIG. 2 wherein the products
obtained in the hydrocracking/hydroisomerisation step 44 is
recycled to the first separation unit 42. As can be seen by
comparing FIG. 2 with FIG. 3 a considerable reduction in unit
operations is achieved. In a Fischer-Tropsch synthesis process step
40 a Fischer-Tropsch product 41 is prepared. This product 41 is
separated by means of distillation 42 in one or more middle
distillate fractions 46, 47, which may be naphtha, kerosene and gas
oil, into a base oil precursor fraction 48 and a higher boiling
fraction 43. Distillation 42 may be an atmospheric distillation and
a vacuum distillation scheme as in FIG. 1. The higher boiling
fraction 43 is fed to a hydrocracking/hydroisomerisation step 44
yielding a cracked product 45, which is recycled to distillation
42.
[0055] The base oil precursor fraction 48 is fed to a catalytic
hydroisomerisation step and a catalytic dewaxing step as combined
in 49 and the dewaxed oil 50 is fractionated in column 51 into one
or more base oil products 53 and 54. Base oil 54 will have a
comparable viscosity as base oil 16 of FIG. 1.
[0056] The gas oil product 52 as separated from the dewaxed oil is
preferably blended with the gas oil fraction 47 such to obtain a
blended product having favorable low temperature properties. The
gas oil product 52 will have a low cloud point and cold filter
plugging point (CFFP). The volume of the gas oil product 52 having
the favorable low temperature properties may be controlled by
adjusting the initial boiling point of the base oil precursor
fraction 48. Such a control allows the operator to target the low
volume of gas oil 52 and thus also the temperature properties, such
as cloud point and CFFP of the resulting blend of gas oil products
52 and 47.
[0057] The invention will be illustrated by the following
non-limiting examples.
EXAMPLE 1
[0058] A Fischer-Tropsch derived product having the properties as
listed in Table 1 was distilled into fraction boiling substantially
above 540.degree. C. (recovered 72 wt % on feed to distillation)
and a fraction boiling substantially between 350 and 540.degree. C.
(recovered as 25 wt % on feed to distillation). In addition 3 wt %
of a fraction boiling substantially below 350.degree. C. was
separated from the feed. The boiling curve data of the feed and the
main distillate fractions are listed in Table 1.
TABLE-US-00002 TABLE 1 Fischer-Tropsch derived product 350.degree.
C.-540.degree. C. 540.degree. C.+ (feed) fraction fraction (%
weight fraction boiling below listed boiling point) Sample (%
weight) 320.degree. C. 5.5 5.8 1.6 350.degree. C. 7.6 13.0 1.6
370.degree. C. 9.3 22.2 1.6 400.degree. C. 12.2 34.4 1.6
450.degree. C. 17.4 64.3 1.6 500.degree. C. 23.9 91.1 2.2
540.degree. C. 29.5 99.0 6.6 590.degree. C. 35.9 16.6 700.degree.
C. 51.6 43.6
[0059] The 540.degree. C.+fraction of Table 1 was subjected to a
hydrocracking step wherein the feed was contacted with a 0.8 wt %
platinum on amorphous silica-alumina carrier. The conditions in the
hydrocracking step were: a fresh feed Weight Hourly Space Velocity
(WHSV) of 0.9 kg/l.h, no recycle, and hydrogen gas rate=1100 Nl/kg
feed, total pressure=32 bar. The reactor temperature was varied as
listed in Table 2. The hydrocracker effluent was analysed and the
yields for the different boiling fractions are listed in Table
2.
TABLE-US-00003 TABLE 2 Example 1-a 1-b 1-c 1-d Reactor 349 344 353
358 Temperature, .degree. C. Fraction boiling 69.8 47.1 82.2 95.1
below 370.degree. C. (wt %) Fraction boiling 17.8 19.4 11.0 3.6
between 370 and 540.degree. C. (wt %)
[0060] Thus relative to the feed to the distillation step 25 wt %
of a fraction (I) boiling between 350 and 540.degree. C. comprising
substantially of n-paraffins is obtained in the distillation step
and 14 wt % of a waxy raffinate fraction (II) boiling between 370
and 540.degree. C. is obtained in the hydrocracking step. These two
fractions (I) and (II) may be combined and a base oil may be
prepared from this combined fraction by dewaxing.
[0061] To calculate the potential base oil yield on these fractions
(i) and (ii) we base ourselves on the reported base oil yields as
shown in FIG. 1 of U.S.-A-2004/0065581. The base oil yield for a
base oil having a pour point of -20.degree. C. is 60 wt % in a
process wherein a substantially normal paraffin C24-C60 wax was
dewaxed over a platinum/zeolite beta and platinum/ZSM-48 stacked
catalyst system. It should be borne in mind that these yields are
based on a substantially normal paraffin feedstock while in the
present invention a partly isomerised feedstock will be dewaxed.
Thus the 60 wt % yield on feed will provide a conservative overall
yield for Example 1.
[0062] Thus 60 wt % of the combined fraction (I) and (II) will
yield a base oil. Thus the total yield of base oil calculated on
feed is 0.6*(25 wt %+14 wt %)=23.4 wt %.
COMPARATIVE EXPERIMENT A
[0063] Example 1 was repeated except that the Fischer-Tropsch
derived product (feed) was directly submitted to the hydrocracker
step. No prior distillation was performed. The yield to the
370-540.degree. C. fraction on feed was 24 wt %. Because this
fraction is also partly hydroisomerised the same estimated base oil
yield as for example 1 may be applied. The base oil yield will then
be (0.6*24 wt %=) 14.4 wt % on feed.
[0064] As can be seen by comparing Example 1 and comparative
experiment A is that the base oil yield on Fischer-Tropsch derived
product (feed) is significantly higher for the process according to
the present invention (=23.4 wt %) as compared to a situation
wherein the prior art process line-up is used (=14.4 wt %).
* * * * *