U.S. patent application number 16/935043 was filed with the patent office on 2021-01-07 for fischer-tropsch process using reduced cobalt catalyst.
The applicant listed for this patent is BP P.L.C.. Invention is credited to Ewen FERGUSON, Piotr KRAWIEC, Manuel OJEDA PINEDA, Alexander PATERSON, Matthew James WELLS.
Application Number | 20210001322 16/935043 |
Document ID | / |
Family ID | |
Filed Date | 2021-01-07 |
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United States Patent
Application |
20210001322 |
Kind Code |
A1 |
FERGUSON; Ewen ; et
al. |
January 7, 2021 |
FISCHER-TROPSCH PROCESS USING REDUCED COBALT CATALYST
Abstract
A process for the conversion of a feed comprising a mixture of
hydrogen and carbon monoxide to hydrocarbons, the hydrogen and
carbon monoxide in the feed being present in a ratio of from 1:9 to
9:1 by volume, the process comprising the step of contacting the
feed at elevated temperature and atmospheric or elevated pressure
with a catalyst comprising titanium dioxide and co bait wherein the
catalyst initially comprises from 30% to 95% metallic cobalt by
weight of cobalt.
Inventors: |
FERGUSON; Ewen; (Saltend,
GB) ; KRAWIEC; Piotr; (Middlesex, GB) ; OJEDA
PINEDA; Manuel; (Yorkshire, GB) ; PATERSON;
Alexander; (Yorkshire, GB) ; WELLS; Matthew
James; (Yorkshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BP P.L.C. |
London |
|
GB |
|
|
Appl. No.: |
16/935043 |
Filed: |
July 21, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15533554 |
Jun 6, 2017 |
10717075 |
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PCT/EP2015/078417 |
Dec 2, 2015 |
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16935043 |
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Current U.S.
Class: |
1/1 |
International
Class: |
B01J 37/18 20060101
B01J037/18; B01J 21/06 20060101 B01J021/06; B01J 23/75 20060101
B01J023/75; B01J 37/02 20060101 B01J037/02; C10G 2/00 20060101
C10G002/00; B01J 37/00 20060101 B01J037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2014 |
EP |
14197770.2 |
Claims
1-12. (canceled)
13. A Fischer-Tropsch catalyst comprising: i. titanium dioxide
support, and ii. cobalt wherein the catalyst comprises from 30% to
95% metallic cobalt by weight of cobalt.
14. A process for making a Fischer-Tropsch catalyst according to
claim 13, comprising the step of: reducing a catalyst composition
comprising: a) titanium dioxide support, and b) oxidic cobalt or a
cobalt compound decomposable thereto, with a reducing agent to
produce the Fischer-Tropsch catalyst.
15. (canceled)
16. A catalyst according to claim 13, wherein the catalyst
comprises from 40% to 85% metallic cobalt by weight of cobalt.
17. A catalyst according to claim 13, wherein the catalyst
comprises from 50% to 85% metallic cobalt by weight of cobalt.
18. A catalyst according to claim 13, wherein the catalyst
comprises from 70% to 80% metallic cobalt by weight of cobalt.
19. A catalyst according to claim 13, wherein the catalyst
comprises from 5% to 30% cobalt by weight of the catalyst.
20. A catalyst according to claim 13, wherein the catalyst further
comprises one or more promoters selected from chromium, nickel,
iron, molybdenum, tungestein, manganese, boron, zirconium, gallium,
thorium, lanthanum, cerium, ruthenium, rhenium, palladium,
platinum, and compounds and/or mixtures thereof.
21. A catalyst according to claim 20, wherein the promoter is
present in an amount up to 5% by weight of the catalyst.
22. A process according to claim 14, wherein the reducing is
performed by exposing the catalyst composition to a hydrogen
gas-containing stream, wherein the hydrogen gas-containing stream
comprises less than 10% carbon monoxide gas by volume of carbon
monoxide gas and hydrogen gas.
23. A process according to claim 14, wherein the reducing is
performed by exposing the catalyst composition to a carbon monoxide
gas-containing stream, wherein the carbon monoxide gas-containing
stream comprises less than 10% hydrogen gas by volume of carbon
monoxide gas and hydrogen gas.
24. A process according to claim 14, wherein the reducing is
performed at a temperature of from 200.degree. C. to 250.degree.
C.
25. A process according to claim 14, wherein the reducing is
performed at a temperature of from 220.degree. C. to 250.degree.
C.
26. A process according to claim 14, wherein the catalyst comprises
from 40% to 85% metallic cobalt by weight of cobalt.
27. A process according to claim 14, wherein the catalyst comprises
from 50% to 85% metallic cobalt by weight of cobalt.
28. A process according to claim 14, wherein the catalyst comprises
from 70% to 80% metallic cobalt by weight of cobalt.
29. A process according to claim 14, wherein the catalyst comprises
from 5% to 30% cobalt by weight of the catalyst.
30. A process according to claim 14, wherein the catalyst further
comprises one or more promoters selected from chromium, nickel,
iron, molybdenum, tungsten, manganese, boron, zirconium, gallium,
thorium, lanthanum, cerium, ruthenium, rhenium, palladium,
platinum, and compounds and/or mixtures thereof.
31. A process according to claim 14, wherein the promoter is
present in an amount up to 5% by weight of the catalyst.
Description
[0001] This invention relates to Fischer-Tropsch (FT) processes for
the conversion of a feed comprising a mixture of carbon monoxide
gas and hydrogen gas (e.g. synthesis gas (syngas)) to hydrocarbons
over a cobalt catalyst comprising a titanium dioxide (titania)
support, catalysts therefor and uses of said catalysts.
[0002] Known FT processes typically utilise a stable catalyst
composition comprising oxidic cobalt, such as cobalt(II)
dicobalt(III) oxide (also known as cobalt oxide or cobalt(II,III)
oxide, i.e. Co.sub.3O.sub.4) which may be supported on titanium
dioxide, and employ a reduction step in order to activate the
catalyst by reducing the cobalt(II,III) oxide to elemental (or
metallic) cobalt (Co.sup.0) which is understood to be the
catalytically active species. It has thus been thought desirable to
reduce as much of the cobalt present as possible in order to
improve the activity of the resultant catalyst, in other words to
obtain a degree of reduction of the cobalt as near to 100% as
possible. See Batholomew et al, Journal of Catalysis 128, 231-247
(1991). U.S. Pat. No. 7,851,404 discloses an FT process utilising a
reduced cobalt catalyst comprising a titanium dioxide support.
There remains an ongoing need to improve or maintain the properties
of such FT catalysts, most notably in relation to their activity,
i.e. enabling greater conversion of syngas to hydrocarbons for the
same temperature (or equal conversion at lower temperatures) and
enabling more desirable selectivity, such as selectivity towards
producing hydrocarbons having at least 5 carbon atoms (C.sub.5+),
or selectivity away from producing methane, especially when
operating with less energy intensive conditions (i.e. lower
temperature or lower duration). Surprisingly, it has now been found
that a limited degree (or extent) of reduction of a titanium
dioxide supported cobalt catalyst, i.e. reduction achieved to a
lower level, (commensurately the degree of reduction of the
catalyst when it is subsequently exposed to the feed), may be
utilised while still achieving at least acceptable, and even
enhanced, catalyst activity and C.sub.5+ selectivity in an FT
process.
[0003] According to a first aspect, the present invention thus
relates to a process for the conversion of a feed comprising a
mixture of hydrogen and carbon monoxide to hydrocarbons, the
hydrogen and carbon monoxide in the feed being present in a ratio
of from 1:9 to 9:1 by volume, the process comprising the step of
contacting the feed at elevated temperature and atmospheric or
elevated pressure with a catalyst comprising titanium dioxide and
cobalt wherein the catalyst initially comprises from 30% to 95%
metallic cobalt by weight of cobalt. This aspect may also desirably
include a step of pre-treating a catalyst composition comprising
titanium dioxide support and oxidic cobalt (e.g. cobalt oxide) or a
cobalt compound decomposable thereto by reduction to produce the
catalyst above.
[0004] Advantageously in the process of the present invention, the
catalyst initially comprises from 35% to 90% metallic cobalt by
weight of cobalt, preferably from 40% to 85% (or 50% to 85%)
metallic cobalt by weight of cobalt, such as from 70% to 80%
metallic cobalt by weight of cobalt. As used herein, the general
term "cobalt" includes cobalt either in metallic (elemental) form
or as part of a cobalt compound (i.e. referring to the total cobalt
present), so for example where the catalyst is referred to as
"comprising cobalt", it is intended to mean that the catalyst
comprises metallic/elemental cobalt and/or at least one cobalt
compound. Commensurately, the mass of cobalt includes the total
mass of cobalt atoms and ions present, i.e. ignoring any other ions
in any cobalt compounds. As used herein, the more specific terms
"metallic cobalt" or "elemental cobalt" mean cobalt in an oxidation
state of zero, i.e. Co.sup.0.
[0005] The percentage metallic cobalt by weight of cobalt (herein
interchangeable with the degree of reduction) of the catalyst
according to the present invention applies to the catalyst
initially, which refers to process startup, i.e. the point in time
at which the catalyst is first contacted with the feed.
Accordingly, the percentage metallic cobalt by weight of cobalt
applies to the catalyst immediately prior to, and/or substantially
at the time of, introducing the feed to the catalyst to produce
hydrocarbons, or may additionally or alternatively refer to the
degree of reduction achieved by a reduction step, especially if
such a reduction step is carried out in situ. Notably, it is thus
recognised that exposing the catalyst to the feed itself at
elevated temperature may further impact the degree of reduction,
for example to a level outside the claimed range, such as complete
reduction. However, even if further reduction of the catalyst
occurs upon, or following exposure to the feed, it has been found
that the benefits of the present invention remain, and this is
specifically included within the scope of the present
invention.
[0006] The catalyst employed in the present invention may be
obtained by pre-treating a catalyst composition comprising titanium
dioxide support and oxidic cobalt or a cobalt compound decomposable
thereto, with a reducing agent. Accordingly, a pre-treatment, or
reduction step, may be used to obtain the degree of reduction, i.e.
by reducing the catalyst. That pre-treatment is not particularly
limited by the present invention.
[0007] Suitably, a pre-treatment step which may be a gaseous
reduction, i.e. using a reducing gas stream, may be employed. If a
reducing gas stream is used, it advantageously comprises at least
25 vol. % of a reducing gas, preferably at least 50 vol. % of a
reducing gas, more preferably at least 75 vol. % reducing gas, even
more preferably at least 90 vol. % reducing gas, even more
preferably still at least 95 vol. % reducing gas and yet further
preferably is substantially entirely made up of reducing gas. Any
remainder may comprise, or be, inert diluents such as argon,
helium, nitrogen and/or water vapour, or minor components such as
hydrocarbons (e.g. methane) or carbon dioxide. The reducing gas
referred to above may particularly be carbon monoxide or
hydrogen.
[0008] Advantageously, as such gases are readily available where
processes using a feed comprising a mixture of hydrogen gas and
carbon monoxide gas are located, the catalyst may be pre-treated
using reducing gases such as a gas comprising molecular hydrogen
(hydrogen gas) and/or a gas comprising carbon monoxide (carbon
monoxide gas). If hydrogen gas is used then it is suitable that the
reducing gas stream comprises less than 10% carbon monoxide gas (by
volume of hydrogen gas and carbon monoxide gas) in order to prevent
premature reaction start-up and a resultant poorly performing
catalyst. Similarly, if carbon monoxide gas is used then it is
suitable that the reducing gas stream comprises less than 10%
hydrogen gas (by volume of hydrogen gas and carbon monoxide gas).
For the avoidance of any doubt, the upper limit of hydrogen which
may be present in the reducing gas stream as reported herein is
relative only to the volume of carbon monoxide in the gaseous
stream, and not relative to the combined volume of carbon monoxide
and any inert diluents or other components. Correspondingly, the
upper limit of carbon monoxide which may be present in the reducing
gas as reported herein is relative only to the volume of molecular
hydrogen in the gaseous stream, and not relative to the combined
volume of hydrogen and any inert diluents or other components.
[0009] Suitably, the pre-treating step may be performed at a
temperature of from 100.degree. C. to 500.degree. C., preferably
from 200.degree. C. to 350.degree. C., and/or at any desired
pressure, for instance from 10 to 5500 kPa, preferably from 20 to
3000 kPa, more preferably from 50 to 1000 kPa, and even more
preferably from 100 to 800 kPa. During this step, reducing gas
(such as hydrogen gas or carbon monoxide gas) is suitably passed
over the catalyst bed at a gas hourly space velocity (GHSV) in the
range from 100 to 10000 h.sup.-1, preferably from 250 to 5000
h.sup.-1, such as from 250 to 3000 h.sup.-1 and more preferably
from 250 to 2000 h.sup.-1, for example 1000 h.sup.-1. As used
herein, unless otherwise specified, GHSV means gas hourly space
velocity on gas volumes converted to standard temperature and
pressure based on the catalyst bed volume.
[0010] In order to efficiently obtain the desired level of metallic
cobalt in the catalyst, the pre-treating step of reducing a
catalyst advantageously occurs at a temperature of from 200.degree.
C. to 300.degree. C., preferably from 220.degree. C. to 280.degree.
C., more preferably from 230.degree. C. to 250.degree. C. These
temperature ranges particularly apply (non-exclusively) in
combination with using carbon monoxide gas and/or hydrogen gas to
reduce the catalyst. Within these temperature ranges, it is thought
to be easier to control the degree of reduction. As used herein,
temperatures may refer to feed temperatures, applied temperatures
and/or catalyst bed temperatures.
[0011] The precise duration of the pre-treatment step is important
only insofar as to obtain the desired degree of reduction.
Exemplary durations of the pre-treatment step, which may be in
combination with any of the temperature ranges specified above,
include from 0.1 to 100 hours, preferably from 1 to 50 hours, more
preferably from 5 to 35 hours, even more preferably from 7 to 20
hours, and even more preferably still from 10 to 15 hours.
[0012] For convenience, the pre-treatment step may desirably occur
in the same reactor used for the subsequent conversion of syngas to
hydrocarbons ("in situ") in order to reduce the time and effort
required loading and unloading catalysts. Reducing in situ also
mitigates the need for any steps to ensure the degree of reduction
achieved during the pre-treatment step remains present when the
conversion of syngas to hydrocarbons is commenced. The
pre-treatment step may, however, also be carried out in another
location apart from the FT reactor ("ex situ").
[0013] As used herein, the degree of reduction may be measured
using temperature programmed reduction (TPR). TPR is a technique
for the characterisation of solid materials in which a catalyst
(e.g. cobalt(II,III) oxide) is subjected to a programmed
temperature increase while a reducing gas is passed over the
sample. The effluent gas may be analysed by a thermal conductivity
detector (TCD) or mass spectrometer (MS) to determine the decrease
in reductant gas concentration or evolution of other species, such
as water.
[0014] In order to determine the degree of reduction herein, a
standard data set is produced by drying a sample and conducting TPR
through to 100% reduction of the cobalt atoms present in the
catalyst (e.g. corresponding to 100% reduction of Co.sub.3O.sub.4
to Co.sup.0). The standard data may thus be obtained in situ (i.e.
within the TPR unit) by initially exposing the sample to a drying
step including contacting the sample with argon gas at a GHSV of
1800 h.sup.-1, ramping the temperature from 20.degree. C. to
120.degree. C. at a rate of 5.degree. C./min then dwelling at
120.degree. C. for 15 min before cooling back to 20.degree. C. also
under argon gas. The TPR itself may be performed utilising 4%
H.sub.2 gas (in Argon), at a gas hourly space velocity (GHSV) of
3800 h.sup.-1 and ramping the temperature from 20.degree. C. to
800.degree. C. at a rate of 5.degree. C./min. Sample data is
generally produced by conducting the drying step as above, followed
by the reduction step desired (for example 10 hours under 100%
hydrogen gas at 240, 260, 280 or 300.degree. C. at a GHSV of 1800
h.sup.-1) and then conducting TPR through to 100% reduction. The
sample data may thus be obtained in situ (i.e. within the TPR unit)
by initially exposing the sample to a drying step including
contacting the sample with argon gas at a GHSV of 1800 h.sup.-1,
ramping the temperature from 20.degree. C. to 120.degree. C. at a
rate of 5.degree. C./min then dwelling at 120.degree. C. for 15 min
before cooling back to 20.degree. C. also under argon gas. For the
reduction step itself, 100% H.sub.2 gas may be utilised, also at a
GHSV of 1800 h.sup.-1 and the temperature ramped from 20.degree. C.
to 150.degree. C. at a rate of 2.degree. C./min followed by slower
ramping from 150.degree. C. to the desired reduction temperature at
a rate of 1.degree. C./min before dwelling at the desired reduction
temperature for 10 hours and cooling to 20.degree. C. under argon
gas. The TPR itself is then conducted as described above. Utilising
a TCD, a graph of thermal conductivity against temperature may be
produced, with the conductivity approaching a baseline value at
complete reduction. Comparison of the area under the TCD graph
(relative to the baseline) obtained in the sample TPR data against
the corresponding area of the standard TPR data allows the
calculation of the relative amount of hydrogen consumed during
pre-reduction between the sample and standard data. In practice,
this involves subtracting the integrated area under the TCD graph
obtained for the sample data from the area under the TCD graph for
the standard data, then expressing the resultant value as a
percentage of the integrated area from the standard data. Expressed
as an equation, this is:
% H 2 consumed = 100 .times. [ Area of standard TPR data ] - [ Area
of sample TPR data ] [ Area of standard TPR data ] ##EQU00001##
Equation 1: Method of Calculating Relative Hydrogen Consumption
Using TPR Data
[0015] TPR is an advantageous technique to utilise for determining
degree of reduction because the technical measurements on a sample
are made following the reduction step. Accordingly, while the %
H.sub.2 consumed is calculated via the formula above, the data
obtained is applicable even if another reducing gas (for example,
carbon monoxide) has been used, merely being expressed as the
equivalent % H.sub.2 consumed and enabling the stoichiometry from
hydrogen reduction to be used in calculating the degree of
reduction i.e. the percentage of cobalt atoms present as Co.sup.0.
This is a preferred approach because determining simply the
percentage H.sub.2 consumed may correspond to a different relative
amount of Co.sup.0 produced by reduction for different catalysts,
but Co.sup.0 is understood to be the catalytically active species
so in the context of the present invention it is desirable to
understand the actual amount of Co.sup.0 produced by reduction.
[0016] The complete reduction of cobalt oxide (Co.sub.3O.sub.4) is
a two-step process (firstly the reduction to cobalt(II) oxide, also
known as cobaltous oxide, and then the reduction of cobalt(II)
oxide to metallic cobalt) as shown by the chemical equations
below:
Co.sub.3O.sub.4+H.sub.2.fwdarw.3CoO+H.sub.2O
COO+H.sub.2.fwdarw.Co.sup.0+H.sub.2O
Equations 2 and 3: Step-Wise Reduction of Cobalt(II,III) Oxide to
Metallic Cobalt
[0017] The overall reduction may alternatively be represented as a
single stoichiometric equation:
Co.sub.3O.sub.4+4H.sub.2.fwdarw.3CoO+H.sub.2O+3H.sub.2.fwdarw.3Co.sup.0+-
4H.sub.2O
Equation 4: Overall Reduction of Cobalt(II,III) Oxide to Metallic
Cobalt
[0018] Accordingly, in the first step, 1 equivalent of H.sub.2 is
consumed without producing any metallic cobalt, while in the
second, 3 equivalents are consumed. In total, therefore, complete
reduction requires 4 equivalents of II.sub.2 to reduce the 3
equivalents Co to Co.sup.0. However, the first step is believed to
be much faster than the second so herein is assumed to proceed to
completion before any formation of Co.sup.0 occurs. The amount of
hydrogen required to produce the metallic cobalt is thus higher per
mole of metallic cobalt when the degree of reduction is lower, and
tends towards the stoichiometric ratio of 4 moles of H.sub.2 for
every 3 moles of Co as 100% reduction is approached.
[0019] Taking this into account, the degree of reduction achieved
in the sample may be calculated using the formula below:
% Degree of Reduction = 100 * ( 1 - 4 [ Area of sample TPR data ] 3
[ Area of standard TPR data ] ) ##EQU00002##
Equation 5: Calculation of Degree of Reduction from TPR Data.
[0020] More generally, for a reduction having stoichiometry whereby
x equivalents of H.sub.2 are required before the rate determining
step of the reduction, and y equivalents of H.sub.2 are required
during and after the rate determining step, the degree of reduction
may be calculated using the formula below:
% Degree of Reduction = 100 * ( 1 - ( x + y ) [ Area of sample TPR
data ] y [ Area of standard TPR data ] ) ##EQU00003##
Equation 6: General Calculation of Degree of Reduction from TPR
Data
[0021] Using TPR as described above, the degree of reduction may
thus be determined for a catalyst that has been reduced ex situ,
e.g. following any period in storage, transport or other
intermediate steps that may occur before the catalyst is used to
produce hydrocarbons, in order to be assured that the amount of
cobalt metal present by weight of cobalt remains within the range
of the present invention. If not, additional measures may be taken
in order to achieve the required degree of reduction, for example
additional reduction in situ or avoiding exposing the catalyst to
an oxidising atmosphere during storage and transport. Such
avoidance of oxidising atmospheres may be achieved by packing the
catalyst in an inert (e.g. nitrogen) atmosphere, packing the
catalyst in a reducing atmosphere (e.g. 5% H.sub.2, 95% nitrogen by
volume), passivating by creating a thin, protective oxide layer on
the surface of the catalyst, or wax-coating the catalyst for
storage and transport.
[0022] The catalyst used in accordance with the present invention
may comprise a cobalt compound intended to be reduced to metallic
cobalt. The identity of the cobalt compound is not particularly
limited except that the cobalt compound should be decomposable
(either directly or indirectly (e.g. via intermediates) to metallic
cobalt, including mixtures of such compounds. Preferably, the
cobalt compound is oxidic cobalt, a cobalt compound decomposable
thereto or mixtures thereof, for example cobalt(III) oxide,
cobalt(II,III) oxide, and/or cobalt(II) oxide, compounds
decomposable to cobalt(III) oxide, cobalt(II,III) oxide, and/or
cobalt(II) oxide, and mixtures thereof. More preferably, the cobalt
compound is cobalt(II,III) oxide, cobalt(II) oxide, a cobalt
compound that is decomposable to cobalt(II,III) oxide and/or
cobalt(II) oxide, or mixtures thereof, for example cobalt(II,III)
oxide, cobalt(II) oxide, cobalt nitrate (e.g. cobalt nitrate
hexahydrate), cobalt acetate or cobalt hydroxide. Even more
preferably, the cobalt compound is cobalt(II,III) oxide, cobalt(II)
oxide or mixtures thereof, as this removes the need for additional
calcination/oxidation/decomposition steps to prepare the oxide, and
even more preferably still the cobalt compound is cobalt(II,III)
oxide. If a cobalt compound other than oxidic cobalt is used, this
may be referred to herein as a catalyst precursor, from which the
calcination/oxidation/decomposition step used to form cobalt oxide
may be carried out in situ or ex situ with respect to the
hydrocarbon synthesis reactor or with respect to the reduction
step.
[0023] The amount of cobalt compound present in the catalyst is not
particularly limited. According to some embodiments of the present
invention, the catalyst comprises from 5% to 30%, preferably from
5% to 25% and more preferably from 10% to 20%, cobalt compound by
weight of the catalyst.
[0024] The catalyst also comprises titanium dioxide (also referred
to herein as titania) as a supporting material for the cobalt
compound. The catalyst may further comprise one or more promoters
in order to improve the activity of the catalyst. Non-limiting
examples of promoters include: chromium, nickel, iron, molybdenum,
tungsten, manganese, boron, zirconium, gallium, thorium, lanthanum,
cerium, ruthenium, rhodium, rhenium, palladium, platinum and/or
mixtures thereof. The one or more promoters may be present as the
elemental metal or as a compound, for example an oxide. In some
embodiments, the promoter comprises, or is selected from platinum,
molybdenum or mixtures thereof, for example molybdenum. Such
promoters may be present in an amount up to 15% by weight of the
catalyst but may be advantageously present in an amount of from 0%
to 5% by weight of the catalyst, from 0.1% to 3% by weight of the
catalyst, or from 0.5% to 2.5% by weight of the catalyst, such as
from 1% to 2.5% or from 1.5% to 2.25%, for example 2%.
[0025] The catalyst may be prepared by any known method, including
impregnation, precipitation or gelation. A suitable method, for
example, comprises impregnating titanium dioxide with a compound of
cobalt that is thermally decomposable to metallic cobalt (e.g. via
the oxide), such as cobalt nitrate, cobalt acetate or cobalt
hydroxide. Any suitable impregnation technique including the
incipient wetness technique or the excess solution technique, both
of which are well-known in the art, may be employed. The incipient
wetness technique is so-called because it requires that the volume
of impregnating solution be predetermined so as to provide the
minimum volume of solution necessary to just wet the entire surface
of the support, with no excess liquid. The excess solution
technique as the name implies, requires an excess of the
impregnating solution, the solvent being thereafter removed,
usually by evaporation. The impregnation solution may suitably be
either an aqueous solution or a nonaqueous, organic solution of the
cobalt compound. Suitable nonaqueous organic solvents include, for
example, alcohols, ketones, liquid paraffinic hydrocarbons and
ethers. Alternatively, aqueous organic solutions, for example an
aqueous alcoholic solution, of the thermally decomposable cobalt
compound may be employed.
[0026] Following preparation, the catalyst may also be formed by
any known technique including extrusion, pulverisation,
powderisation, pelletisation, granulation and/or coagulation.
Preferably, the catalyst is extruded, for example to enable less
pressure drop in a reactor and highly consistent diameter of the
catalyst. In extrusion, an extrudable paste may be formed, such as
from a mixture of the catalyst components in water, which is then
extruded into the desired shape and dried to form the catalyst.
Alternatively, an extrudable paste of titanium dioxide may be
formed from a mixture of powdered titanium dioxide and water. This
paste may then be extruded and typically dried and/or calcined to
form the desired shape, which may then be contacted with a solution
of a cobalt compound in order to impregnate the extruded support
material with the cobalt compound. The resultant impregnated
support material may then be dried to form the catalyst, which if
not already comprising oxidic cobalt such as cobalt(III) oxide,
cobalt(II,III) oxide or cobalt(II) oxide may also be calcined.
[0027] As indicated above, the present invention provides, in a
first aspect, a process for the conversion of a feed comprising a
mixture of hydrogen and carbon monoxide, preferably in the form of
a synthesis gas mixture, to hydrocarbons, which process comprises
contacting the feed with a reductively activated catalyst
composition as hereinbefore described.
[0028] In the hydrocarbon synthesis processes described herein, the
volume ratio of hydrogen to carbon monoxide (H.sub.2:CO) in the
feed is in the range of from 1:9 to 9:1 preferably in the range of
from 0.5:1 to 5:1, more preferably from 1:1 to 3:1, and most
preferably from 1.6:1 to 2.2:1. Such ratios especially apply as
regards the feed to the reactor, e.g. at the reactor inlet. The
feed may also comprise other gaseous components, such as nitrogen,
carbon dioxide, water, methane and other saturated and/or
unsaturated light hydrocarbons, each preferably being present at a
concentration of less than 30% by volume. The temperature of the
reaction (or reactor) is elevated, preferably in the range from 100
to 400.degree. C., more preferably from 150 to 350.degree. C., and
most preferably from 150 to 250.degree. C. The pressure of the
reaction (or reactor) is atmospheric or elevated, preferably in the
range from 1 to 100 bar (from 0.1 to 10 MPa), more preferably from
5 to 75 bar (from 0.5 to 7.5 MPa), and most preferably from 10 to
50 bar (from 1.0 to 5.0 MPa). As used herein "elevated" in relation
to conditions refers to conditions greater than standard
conditions, for example, temperatures and pressures greater than
standard temperature and pressure (STP).
[0029] The gaseous reactants (feed) for the present process may be
fed into the reactor either separately or pre-mixed (e.g. as in the
case of syngas). They may initially all contact the solid catalyst
at the same portion of the solid catalyst, or they may be added at
different positions of the solid catalyst. The ratio of hydrogen
gas to carbon monoxide gas may thus be determined from the relative
flow rates when both streams are flowing. Preferably, the one or
more gaseous reactants flow co-currently over the solid
catalyst.
[0030] The feed used for the present process may also comprise
recycled materials extracted from elsewhere in the process, such as
unreacted reactants separated from any reduction steps associated
with the process of the invention.
[0031] The mixture of hydrogen and carbon monoxide is suitably
passed over the catalyst bed at a gas hourly space velocity (GHSV)
in the range from 100 to 10000 h.sup.-1 (gas volumes converted to
standard temperature and pressure), preferably from 250 to 5000
h.sup.-1, such as from 250 to 3000 h.sup.-1, and more preferably
from 250 to 2000 h.sup.-1.
[0032] As is well known in the art, synthesis gas, which is
preferably used as the feed for the present process, principally
comprises carbon monoxide and hydrogen and possibly also minor
amounts of carbon dioxide, nitrogen and other inert gases depending
upon its origin and degree of purity. Methods of preparing
synthesis gas are established in the art and usually involve the
partial oxidation of a carbonaceous substance, e.g. coal.
Alternatively, synthesis gas may be prepared, for example by the
catalytic steam reforming of methane. The ratio of carbon monoxide
to hydrogen present in the synthesis gas may be altered
appropriately by the addition of either carbon monoxide or
hydrogen, or may be adjusted by the so-called shift reaction well
known to those skilled in the art.
[0033] The process of the invention may be carried out batch wise
or continuously in a fixed bed, fluidised bed or slurry phase
reactor. When using the catalyst as described in the present
invention in a fixed bed process, the particle size should be of
such shape and dimension that an acceptable pressure drop over the
catalyst bed is achieved. A person skilled in the art is able to
determine the particle dimension optimal for use in such fixed bed
reactors. Particles of the desired shape and dimension may be
obtained by extrusion of a paste to which optionally extrusion aids
and/or binders may be optionally added.
[0034] According to second and third aspects, the present invention
relates to uses of a catalyst comprising titanium dioxide support
and cobalt, wherein the catalyst comprises from 30% to 95% metallic
cobalt by weight of cobalt, for the conversion of a feed comprising
a mixture of hydrogen gas and carbon monoxide gas to hydrocarbons,
and to increase the selectivity and/or productivity of a process
for the conversion of a feed comprising a mixture of hydrogen gas
and carbon monoxide gas to hydrocarbons. As the catalyst so used is
in a process for the conversion of a feed comprising a mixture of
hydrogen gas and carbon monoxide gas to hydrocarbons (to which the
first aspect of the invention relates), any features of the
catalyst or any process relating to it described above in relation
to the first aspect are applicable to these second and third
aspects, either individually or in any combination.
[0035] In a fourth aspect, the present invention relates to a
Fischer-Tropsch catalyst comprising titanium dioxide support and
cobalt, wherein the catalyst comprises from 30% to 95% metallic
cobalt by weight of cobalt. As the catalyst is intended for use in
a process for the conversion of a feed comprising a mixture of
hydrogen gas and carbon monoxide gas to hydrocarbons (to which the
first aspect of the invention relates), any features of the
catalyst or any process relating to it described above in relation
to the first aspect are applicable to this fourth aspect, either
individually or in any combination.
[0036] In a fifth aspect, the present invention relates to a
process for making a Fischer-Tropsch catalyst according to the
fourth aspect, comprising the step of reducing a catalyst
comprising titanium dioxide support and oxidic cobalt or a cobalt
compound decomposable thereto to produce the Fischer-Tropsch
catalyst. As the catalyst is intended for use in a process for the
conversion of a feed comprising a mixture of hydrogen gas and
carbon monoxide gas to hydrocarbons (to which the first aspect of
the invention relates), any features of the catalyst or any process
relating to it described above in relation to the first aspect are
applicable to this fifth aspect, either individually or in any
combination.
[0037] In a sixth aspect, the present invention also provides a
product (preferably a fuel) comprising hydrocarbons obtained from a
process according to the first aspect. As the product results from
a process for the conversion of a feed comprising a mixture of
hydrogen gas and carbon monoxide gas to hydrocarbons (to which the
first aspect of the invention relates), any features of the process
described above in relation to the first aspect are applicable to
this sixth aspect, either individually or in any combination.
EXAMPLES
Examples 1-6
[0038] Cobalt oxide supported on titanium dioxide was manufactured
as a catalyst by impregnating titanium dioxide powder with an
aqueous solution of cobalt nitrate hexahydrate, followed by
extrusion of the formed paste, and then drying and calcining to
yield catalyst extrudates with a cobalt loading of 10% by weight of
catalyst and a manganese loading of 1% by weight of catalyst. 0.25
g of the catalyst was loaded into the quartz u-tube reactor of a
TPR unit and subjected to reduction under 100% hydrogen gas (at a
GHSV of 3800 h.sup.-1) for 15 hours at the temperatures in Table 1
below. As described hereinabove, the degree of reduction was
determined using TPR via comparison of the integrated areas of the
TCD graphs of the samples against a standard that had been subject
to TPR with no reduction step, in order to obtain the percentage
hydrogen consumption, and calculation of the degree of reduction as
percentage of Co present as Co.sup.0 using Equation 5 detailed
hereinabove.
TABLE-US-00001 TABLE 1 Temperature Programmed Reduction (TPR) of
cobalt oxide/manganese on titanium dioxide support Reduction
Temperature Degree of Reduction Example (.degree. C.) (% of Co as
Co.sup.0) 1 No Pre-treatment 0 2 200 28 3 220 51 4 240 74 5 260 99
6 (comparative) 300 97
Examples 7-10
[0039] The catalyst sample was cobalt oxide on titanium dioxide
support, 10 wt. % cobalt loading, 1 wt. % manganese loading. 9.6 g
of catalyst sample was loaded into a metal liner of a multi-channel
catalyst-screening microreactor. Each channel of the microreactor
underwent the same drying procedure in parallel, before the
catalysts were activated according to the following protocols under
100% H.sub.2 gas at a GHSV of 3800 h.sup.-1 and pressure of 1
atm:
Example 7 (Comparative)
[0040] From room temperature ramped to 150.degree. C. at a rate of
2.degree. C./min, then ramped to 200.degree. C. at a rate of
1.degree. C./min, before dwelling at 200.degree. C. for 15
hours.
Example 8 (Inventive)
[0041] From room temperature ramped to 150.degree. C. at a rate of
2.degree. C./min, then ramped to 240.degree. C. at a rate of
1.degree. C./min, before dwelling at 240.degree. C. for 15
hours.
Example 9 (Comparative)
[0042] From room temperature ramped to 150.degree. C. at a rate of
2.degree. C./min, then ramped to 260.degree. C. at a rate of
1.degree. C./min, before dwelling at 260.degree. C. for 15
hours.
Example 10 (Comparative)
[0043] From room temperature ramped to 150.degree. C. at a rate of
2.degree. C./min, then ramped to 300.degree. C. at a rate of
1.degree. C./min, before dwelling at 300.degree. C. for 15
hours.
[0044] The liners were then cooled, purged with nitrogen, and
temperature ramped identically under a 1.8:1 H.sub.2:CO molar
stream of syngas in 18% N.sub.2 at 30 barg total pressure at a GHSV
of 1250 h.sup.-1. Each example was operated at a temperature of
201-214.degree. C. in order to achieve the same level of
conversion, under identical operating conditions with results
presented in Table 2. The data for the inventive example shows
acceptable selectivity to C.sub.5+ and CH.sub.4 alongside a similar
temperature to reach the same CO conversion rate versus comparative
examples 9 and 10, despite the milder reduction conditions leading
to a lower degree of reduction. Example 8 also shows improved
selectivity to C.sub.5+ and CII.sub.4 alongside a lower temperature
to reach the same CO conversion rate versus example 7.
TABLE-US-00002 TABLE 2 Performance data of examples 7-10 in
conversion of syngas to hydrocarbons Example 7 8 9 10 Pre-reduction
Temperature (.degree. C.) 200 240 260 300 GHSV (h.sup.-1) 1250 1250
1250 1250 Temperature (.degree. C.) 214 201 200 198 CO Conversion
(%) 67 65 65 65 C.sub.5+ Selectivity (%) 74.8 81.8 85.0 86.8
CH.sub.4 Selectivity (%) 15.0 10.8 8.9 7.4
Examples 11-13
[0045] The catalyst sample was cobalt oxide on titanium dioxide
support, 10 wt. % cobalt loading, 2 wt. % manganese loading. Each
catalyst sample (mass provided in Table 3) was loaded into a metal
liner of a multi-channel catalyst-screening microreactor. Each
channel of the microreactor underwent the same drying procedure in
parallel, before the catalysts were activated according to the
following protocols under 100% H.sub.2 gas at a GHSV 3800 h.sup.-1
and pressure of 1 atm:
[0046] From room temperature, ramped to 150.degree. C. at a rate of
2.degree. C./min, then ramped to 240.degree. C. (example 11),
260.degree. C. (example 12) or 300.degree. C. (example 13) at a
rate of 1.degree. C./min, before dwelling at this final temperature
for 15 hours.
[0047] The liners were then cooled, purged with nitrogen, and
temperature ramped identically under a 1.8:1 H.sub.2:CO molar
stream of syngas in 18% N.sub.2 at 30 barg total pressure and a
GHSV of 1250 h.sup.-1. Each example was operated at a temperature
of 195.degree. C. under identical operating conditions with results
presented in Table 3. The data for example 11 clearly shows
improved selectivity to C.sub.5+ and similar selectivity to
CH.sub.4 alongside similar temperatures to reach the same CO
conversion rate versus the example 13, despite the milder reduction
conditions leading to a lower degree of reduction, and even despite
a lower mass of catalyst having been used, indicating improved
activity.
TABLE-US-00003 TABLE 3 Performance data of examples 11-13 in
conversion of syngas to hydrocarbons Example 11 12 13 Mass of
Catalyst (g) 8.6 8.8 9.4 Pre-reduction Temperature (.degree. C.)
240 260 300 GHSV (h.sup.-1) 1250 1250 1250 Temperature (.degree.
C.) 204 206 203 CO Conversion (%) 64 64 63 C.sub.5+ Selectivity (%)
83.7 81.0 82.5 CH.sub.4 Selectivity (%) 9.3 10.1 9.2
[0048] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0049] Every document cited herein, including any cross referenced
or related patent or application, is hereby incorporated herein by
reference in its entirety unless expressly excluded or otherwise
limited. The citation of any document is not an admission that it
is prior art with respect to any invention disclosed or claimed
herein or that it alone, or in any combination with any other
reference or references, teaches, suggests or discloses any such
invention. Further, to the extent that any meaning or definition of
a term in this document conflicts with any meaning or definition of
the same term in a document incorporated by reference, the meaning
or definition assigned to that term in this document shall
govern.
[0050] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope and
spirit of this invention.
* * * * *