U.S. patent application number 09/993008 was filed with the patent office on 2002-08-22 for fischer-tropsch catalyst enhancement (jss-0113).
Invention is credited to Daage, Michel A., Koveal, Russell John, Krylova, Alla Jurievna, vovich Lapidus, Albert L?apos, Sineva, Lilia Vadimovna.
Application Number | 20020115733 09/993008 |
Document ID | / |
Family ID | 24622785 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020115733 |
Kind Code |
A1 |
Lapidus, Albert L?apos;vovich ;
et al. |
August 22, 2002 |
Fischer-tropsch catalyst enhancement (JSS-0113)
Abstract
A process of enhancing both the activity and the methane
selectivity of a particulate Dispersed Active Metal ("DAM")
hydrogenation catalyst is disclosed wherein the DAM undergoes low
temperature oxidation in a slurry phase to form a stable, unique
oxidized catalyst precursor that is subsequently reduced to form an
enhanced catalyst by treatment with hydrogen-containing gas at
elevated temperature, wherein one or more promoter metal oxides of
chromium, lanthanum and manganese are added to the DAM. Precursors
of the promoter metal oxides may be combined with the DAMs prior to
or during formation of the initial slurry, during the oxidation
step or between recovery of the oxidized catalyst precursor and
treatment of it with hydrogen-containing gas to reactivate the
catalyst. Conversion of the precursors to the promoter metal oxides
is carried out prior to the treatment with hydrogen-containing gas
unless said treatment itself produces the conversion.
Inventors: |
Lapidus, Albert L?apos;vovich;
(Moscow, RU) ; Krylova, Alla Jurievna; (Moscow,
RU) ; Sineva, Lilia Vadimovna; (Moscow, RU) ;
Koveal, Russell John; (Baton Rouge, LA) ; Daage,
Michel A.; (Baton Rouge, LA) |
Correspondence
Address: |
ExxonMobil Research and Engineering Company
P.O. Box 900
Annandale
NJ
08801-0900
US
|
Family ID: |
24622785 |
Appl. No.: |
09/993008 |
Filed: |
November 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09993008 |
Nov 19, 2001 |
|
|
|
09653915 |
Sep 1, 2000 |
|
|
|
Current U.S.
Class: |
518/714 ;
502/324 |
Current CPC
Class: |
B01J 25/00 20130101;
C10G 2/331 20130101; B01J 37/12 20130101 |
Class at
Publication: |
518/714 ;
502/324 |
International
Class: |
C07C 027/00; C07C
027/06; B01J 023/32 |
Claims
What is claimed is:
1. A process for the formation of an enhanced dispersed active
metal (DAM) catalyst for conducting hydrogenation reactions
comprising: a) forming a slurry in a suitable fluid of particulate
DAM catalyst comprising metals characterized by the capacity to
form more than one oxide; b) contacting the particulate DAM
catalyst in the slurry with an oxidizing agent at temperatures
below 200.degree. C. for a time such that the metals no longer
exhibit uncontrollable pyrophoricity, thereby forming an oxidized
catalyst precursor comprising said metals and at least one of
hydroxides thereof and oxides thereof, wherein at least a portion
of said hydroxides and oxides are in the lower oxidation state of
the metals; c) adding to said oxidized catalyst precursor a
solution in a suitable solvent of one or more precursors of
promoter metal oxides selected from the group consisting of
chromium, lanthanum and manganese oxides; d) recovering and drying
said mixture of said oxidized catalyst precursor and said oxide
precursor formed in step c); and e) treating said mixture to form
said one or more promoter metal oxides from the precursor therefor;
and f) forming an active catalyst from said oxidized catalyst
precursor by treating the said mixture with hydrogen at elevated
temperature.
2. A process in accordance with claim 1, wherein in step e) said
mixture is heated to a temperature sufficient to decompose said one
or more precursors to form said promoter metal oxides.
3. A process in accordance with claim 1, wherein heating of said
mixture with hydrogen at elevated temperature forms said promoter
metal oxides from the precursors therefor and said steps e) and f)
are carried out simultaneously.
4. A process in accordance with claim 1, wherein said precursors of
promoter metal oxides are nitrate salts that are added to said
slurry in step a) and are reacted during the oxidization in step b)
to form said promoter metal oxides and step b) and step e) are
carried out simultaneously.
5. A process in accordance with claim 4, wherein the fluid utilized
to form said slurry of the dispersed active metals is the solution
of said one or more precursors of promoter metal oxides.
6. A process in accordance with claim 4, wherein the solution of
said one or more precursors of promoter metal oxides is added to
the slurry in step b).
7. A process in accordance with claim 1, wherein the gaseous
oxidant contains a member selected from the group consisting of
oxygen, ozone and nitrogen oxides.
8. A process in accordance with claim 1, wherein the fluid forming
the slurry comprises water and the oxidized catalyst precursor
includes hydroxides of the dispersed active metals.
9. A process in accordance with claim 1, wherein the oxidant is
contained within the slurry fluid is selected from the group
consisting of nitric acid, an inorganic nitrate and a peroxide.
10. A process in accordance with claim 9, wherein the oxidant is an
inorganic nitrate and is at least partially provided by said
precursors of promoter metal oxides wherein said precursors are
nitrate salts and are added step a).
11. A process in accordance with claim 1, wherein step b) is
carried out at a temperature below 100.degree. C.
12. A process in accordance with claim 1, wherein the fluid forming
the slurry is a mixture of hydrocarbons or a supercritical
fluid.
13. A process in accordance with claim 1, wherein in step d) said
precursor is dried under an inert atmosphere.
14. A process in accordance with claim 1, wherein in step d) said
precursor is dried in air at a temperature above 100.degree. C. for
at least one hour.
15. A process in accordance with claim 1, wherein step e) is
heating said mixture in air to a temperature of about 400.degree.
C. for a time sufficient to form the promoter metal oxide from said
one or more precursors thereof.
16. An enhanced catalyst formed by the process of claim 1.
17. An enhanced catalyst in accordance with claim 15, wherein said
promoter metal oxide is chromium oxide.
18. An enhanced catalyst in accordance with claim 15, wherein said
promoter metal oxide is lanthanum oxide.
18. An enhanced catalyst in accordance with claim 15, wherein said
promoter metal oxide is manganese oxide.
19. A process for producing higher hydrocarbons by the
hydrogenation of carbon monoxide by reaction with hydrogen at
reaction conditions in the presence of an enhanced catalyst
according to claim 16.
20. A process in accordance with claim 19, wherein at least a
portion of the hydrocarbons formed are upgraded to more valuable
products by at least one of fractionation and conversion
operations.
Description
[0001] This invention relates to a process for the activation of
dispersed active metal catalysts that enhances their activity and
selectivity in the production of higher hydrocarbons from synthesis
gas.
BACKGROUND OF THE INVENTION
[0002] The production of higher hydrocarbon materials from
synthesis gas, i.e. carbon monoxide and hydrogen, commonly known as
the Fischer-Tropsch ("F-T") process, has been in commercial use for
many years. Such processes rely on specialized catalysts. The
original catalysts for the Fischer-Tropsch synthesis were nickel.
Nickel is still the preferred catalyst for hydrogenation of fats
and specialty chemicals. Over the years, other metals, particularly
iron and cobalt, have been preferred in the Fischer-Tropsch
synthesis of higher hydrocarbons whereas copper has been the
catalyst of choice for alcohol synthesis. Cobalt is particularly
preferred for Fischer-Tropsch synthesis due its high productivity
and comparatively low methane selectivity. As the technology of
these syntheses developed over the years, the catalysts became more
refined and were augmented by other metals and/or metal oxides that
function to promote their catalytic activity. These promoter metals
include the Group VIII metals, such as platinum, palladium,
rhenium, ruthenium and iridium. Metal oxide promoters include the
oxides of a broader range of metals, such as molybdenum, tungsten,
zirconium, magnesium, manganese and titanium. Those of ordinary
skill in the art will appreciate that the choice of a particular
metal or alloy for fabricating a catalyst to be utilized in
Fischer-Tropsch synthesis will depend in large measure on the
desired product or products.
[0003] Particularly suited for the production of hydrocarbons by
Fischer-Tropsch synthesis from synthesis gas are Dispersed Active
Metals ("DAM") which are primarily, i.e. at least about 50 wt. %,
preferably at least 80 Wt. %, composed of one or a mixture of
metals such as described above and are, without further treatment,
capable of catalyzing Fischer-Tropsch synthesis. DAM catalysts may
be prepared by any of a number of art-recognized processes.
[0004] In 1924, M. Raney prepared a nickel hydrogenation catalyst
by a process known today as the Raney Process. For purposes of
simplicity, the term "Raney" will be utilized herein as a generic
term to describe the process, alloys and catalysts obtained
thereby. This specific synthesis, in essence, comprises forming at
least a binary alloy of metals, at least one of which can be
extracted, and extracting it thereby leaving a porous residue of
the non-soluble metal or metals that possesses catalytic activity.
The residue, or non-extractable, catalyst metals are well known to
those skilled in the art and include Ni, Co, Cu, Fe and the Group
VIII noble metals. Likewise, the leachable or soluble metal group
is well known and includes aluminum, zinc, titanium and silicon,
typically aluminum. Once alloys are formed of at least one member
of each of these groups of metals, they are ground to a fine powder
and treated with strong caustic, such as sodium hydroxide, to leach
the soluble metal.
[0005] There exist many variations of the basic preparation of
Raney catalysts such as, for example, deposition of alloys onto a
performed support by flame spraying, (U.S. Pat. No. 4,089,812),
formation of the alloy by surface diffusion of aluminum on a
non-leachable metal substrate (U.S. Pat. No. 2,583,619), and
forming pellets from the powdered alloys for use in fixed bed
reactions vessels (U.S. Pat. No. 4,826,799, U.S. Pat. No. 4,895,994
and U.S. Pat. No. 5,536,694). These developments have made possible
the use of shaped Raney catalysts in fixed bed reaction
vessels.
[0006] A preferred reactor carrying out for Fischer-Tropsch
reactions utilizing DAM catalysts is the slurry bubble column
developed by Exxon Research & Engineering Company. This
reactor, which is ideally suited for carrying out highly
exothermic, three-phase catalytic reactions, is described in U.S.
Pat. No. 5,348,982. In such reactors, the solid phase catalyst is
dispersed or held in suspension in a liquid phase by a gas phase
that continuously bubbles through the liquid phase. The catalyst
loading in slurry bubble reactors can vary within a broad range of
concentrations, but must remain short of the so-termed "mud limit"
where the concentration becomes so high that mixing and pumping of
the slurry become so difficult that practical operation is no
longer possible. The use of high metal-loading catalysts or bulk
metal catalysts is preferred in slurry bubble reactors in order to
maximize the productivity of both catalyst and reactor.
[0007] An extensive review of process of forming DAM catalysts can
be found in "Active Metals", Edited by Alois Furstner, published by
VCH Verlagsgesellschaft mbH, D-6945 1 Weinheim (FRG) in 1996 and
the references cited therein. Methodologies described therein
include the Reike method, the use of ultrasound, reduction of metal
salts, colloids, nanoscale cluster and powders. Other relevant
references include, for example, the preparation of amorphous iron
catalyst by high intensity sonolysis of iron pentacarbonyl, Suslick
et al., Nature, Vol. 353, pp 414-416 (1991) and the formation of
single domain cobalt clusters by reduction of a cobalt salt with
hydrazine, Gibson et el., Science, Vol. 267, pp 1338-1340, (1998).
Finally, intermetallic alloys, particularly those known for forming
metal hydrides, such as LaCo.sub.5, can be formed into a fine
powder by the application of hydrogen adsorption/desorption cycles.
DAM catalysts can also be prepared by thermal or chemical
decomposition of metal formates or oxalates. These methods are
given as examples and are not intended in any way to limit the term
"DAM" as utilized in the context of the present invention.
[0008] One of the primary characteristics of DAM catalysts is that,
in their dry form, they are generally pyrophoric. For this reason,
they are generally stored and shipped in airtight containers,
typically as a slurry in an appropriate solvent, such as water or
oil, or coated with a removable protective layer of an
air-impervious material, such as wax. We are not aware of any DAM
catalysts that are not used as they are formed, i.e. without any
further treatment following extraction of the leachable metal and
subsequent drying steps as described above. On the opposite end of
the cycle, the manufacturers of DAMs recommend that spent
catalysts, i.e. those no longer economically effective, must
undergo deactivation in order that they may be safely disposed of.
Such deactivation is generally achieved via oxidation of the metal
by air oxidation or treatment with dilute bleach solution.
[0009] It will be appreciated that a means of enhancing the
activity of the catalyst would greatly increase its value in the
process. Another important aspect of the value of a catalyst is its
selectivity which is the ratio of the percent of feed material
converted to desired higher hydrocarbons to that of short chain
hydrocarbons produced, primarily methane, commonly referred to as
"methane selectivity". In copending patent application Docket No.
33737 there is disclosed and claimed a process called slurry low
temperature oxidation whereby the activity and methane selectivity
of a DAM catalyst are significantly enhanced. In accordance with
the present invention, it has been found that a modification of the
slurry low temperature oxidation further enhances the activity and
methane selectivity of DAM catalysts.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, Dispersed Active
Metal ("DAM") Fischer-Tropsch catalysts are enhanced both in
activity and methane selectivity by low temperature oxidative
deactivation in a slurry phase to form an oxidized catalyst
precursor comprising said metals and at least one of hydroxides
thereof and oxides, which differs compositionally from that
obtained by conventional high temperature oxidation utilizing an
oxygen-containing gas. The activity and methane selectivity of the
DAM catalyst is further enhanced by the addition of one or more of
the oxides of chromium, lanthanum, or manganese, known os promoter
metals for the catalytic activity of the DAMs. One or mores
precursor of these promoter metal oxides is added to the DAM
catalyst prior to, during or subsequent to the oxidation, and the
mixture is treated to form the oxides therefrom. The active
catalyst is then formed by reductive reactivation with hydrogen at
elevated temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0011] It is well known to those skilled in the art of
Fischer-Tropsch synthesis chemistry that Group VIII metal surfaces
exhibit higher activities for catalytic reactions such as
hydrogenation, methanation and Fischer-Tropsch synthesis when
subjected to a high temperature oxidation-reduction (O-R) cycle.
Such "activation" techniques are reviewed in Applied Catalysis, A.
General 175, pp 113-120 (1998) and citations therein. A series of
patents, e.g. U.S. Pat. Nos. 4,492,774; 4,399,234; 4,585,789 and
4,670,414 disclose activation of a cobalt catalyst by a
reduction/oxidation/reduction (R-O-R) cycle. So far as we are
aware, all such oxidation/reduction and
reduction/oxidation/reduction cycles described in the literature
are effected by treating a solid catalyst with an oxygen-containing
gas at high temperatures. This treatment results in the formation
of the most stable oxide of the metal, i.e. in the instance of
cobalt, Co.sub.3O.sub.4. All DAMs treated in accordance with the
invention are characterized by the capacity to form more than one
oxide. Heretofore, those practicing the process described above
have sought to completely oxidize such DAMs to the highest
oxidation state oxide, which corresponds to the most stable
oxide.
[0012] In the activation treatments described above, the oxygen
content of the treating gas in the oxidation step varies from as
low as 15 ppm to pure oxygen and the temperatures typically are
between about 200.degree. C. to 600.degree. C. Several publications
dealing with these activation methodologies also stress the
importance of controlling the exothermicity of the reaction to
avoid sintering of the cobalt oxide particles since that may be
detrimental to the activity of the final catalyst. We have found
that this latter observation is even more critical with regard to
the oxidation of DAM catalysts because of their high metal content,
particularly those that may also contain active hydrogen species as
in Raney catalysts or metal hydrides.
[0013] Significant enhancement in both the activity and methane
selectivity for Fischer-Tropsch synthesis is realized by treating a
DAM catalyst with an oxidation/reduction cycle wherein the
oxidation is carried out in a slurry phase at low temperature. By
low temperature is meant a temperature below 200.degree. C.,
preferably below 100.degree. C. The oxidation is effected by
bubbling a gaseous oxidant through a slurry of the DAM catalyst, or
by the slurry itself formed from or combined with an aqueous
solution of a suitable oxidant. Typical conditions for the
oxidative deactivation of a DAM catalyst utilizing an oxidative gas
are as follows: ratio of liquid to DAM by volume--at least about
3:1, preferably at least about 5:1; temperature--from about
25.degree. C. to 100.degree. C., preferably from about 50.degree.
C. to 80.degree. C.; total pressure--from about 15 to 300 psia,
preferably from about 15 to 100 psia; contact time for the DAM in
the slurry--at least one hour, preferably until the DAM has lost
pyrophoricity; and gas flow rate--at least 100 cc/min. Typical
oxidative gases in addition to oxygen include ozone and nitrogen
oxides, i.e. nitrous oxide and nitric oxide all of which may be
utilized in pure form, but typically are mixed with one or more
inert diluent gases. Wherein oxygen is utilized, for example,
typically air is caused to flow into the slurry. Alternatively,
pure oxygen can be mixed with an inert gas in from about 1 to 50%,
preferably from about 5 to 25% by volume.
[0014] Wherein the oxidative treatment is carried out utilizing a
dilute solution of an oxidant, the oxidant is chosen so as not to
introduce substances into the slurry that are recognized as being
permanent poisons of the Fischer-Tropsch synthesis, e.g. ionic
forms of chlorine, bromine, phosphorus and sulfur. Included within
the scope of oxidants in solution are solutions of compounds that
form oxidants in situ upon contact with air, for example, certain
alcohols will form hydroperoxides upon contact with air. Preferred
oxidants include nitric acid and inorganic nitrates, for example,
ammonium nitrate, hydrogen peroxide, and art-recognized organic
peroxides or hydroperoxides. Those skilled in the art will
appreciate that the concentration of individual oxidants will vary
according to their oxidizing capacity. In general, the amount of
the oxidant in the slurry and the duration of the oxidation are
sufficient to insure oxidation to a point such that the resulting
dry DAM material would not exhibit uncontrollable pyrophoric
responses upon exposure to ambient air and moisture but not so
great as to cause unwanted secondary reactions such as dissolution
or extraction of the active metal ions in the catalyst.
[0015] The liquid utilized to form the slurry is preferably water,
however, other organic solvents may be utilized provided that they
do not introduce any known poison of the Fischer-Tropsch synthesis
and that are non-reactive with the conditions of the oxidation
treatment. Hydrocarbons, particularly those derived from the
Fischer-Tropsch synthesis itself are appropriate and may be used
with either an oxygen-containing gas or dilute solution of the
oxidants named above that are soluble therein, such as the organic
peroxides. Further, mixtures of water and organic solvents miscible
therewith can be utilized as well. Mixtures of water with
immiscible solvents can also be utilized in combination with
suitable dispersing or emulsifying agents present to form a
continuous phase, i.e. an emulsion. Other suitable liquids include
dense fluids, for example, supercritical fluids such as liquid
phase light, i.e. C3-5 alkanes, cyclopentane and the like.
Preferred mixed liquids include, without any intended limitation,
water/ lower alkanols, water/Fischer-Tropsch products, and
water/alkanols/alkanes. Solutions of the precursors of the subject
promoter metal oxides may be utilized in whole or in part to form
the slurry as will be described below.
[0016] The oxidative treatment described herein may be carried out
in any reactor apparatus suitable for slurry reactions including,
with no limitation intended, fixed bed reactors, moving bed
reactors, fluidized bed reactors, slurry reactors, bubbling bed
reactors and the like. Irrespective of whether the slurry reactor
is operated as a dispersed or slumped bed, the mixing conditions in
the slurry will typically be somewhere between the theoretical
limiting conditions of plug flow and complete back mixing.
[0017] The product of the low temperature oxidation treatment of a
DAM catalyst as described above is a mixture of metallic and oxidic
species. This is the result of the fact that the metals in the DAMs
can exist in more than one oxidation state and, in the subject
treatment, a significant portion of the active metal of the DAM is
oxidized to a lower oxidation state. In contrast, the prior art
high temperature oxidation treatments result in complete oxidation
of the active metal to the highest, and most stable, oxidation
state. For example, in the subject treatment, a significant portion
of cobalt metal is oxidized to CoO and/or Co(OH).sub.2 rather than
Co.sub.3O.sub.4, iron metal is oxidized to FeO and/or Fe(OH).sub.2
rather than Fe.sub.3O.sub.4. Additionally, when the slurry in which
the treatment is effected contains water, hydroxides of the metals
will be formed as part of the mixture referred to above. This
mixture is in fact an oxidized catalyst precursor wherein, on a
mole percent basis, not more than 50% of the active metal present
is in the form of the oxide of the highest oxidation state, and the
highest oxidation state of the metal in combination with the amount
in the metallic state does not exceed 85% of the active metal
present, the remainder being lower oxidation state oxides and/or
hydroxides. Preferably, not more than 25% of the active metal
present is in the form of the oxide of the highest oxidation state,
and the highest oxidation state of the metal in combination with
the amount in the metallic state does not exceed 60% of the active
metal present, the remainder being lower oxidation state oxides
and/or hydroxides.
[0018] The oxidative treatment is regarded as complete when the DAM
no longer exhibits uncontrollable pyrophoricity. By not exhibiting
uncontrollable pyrophoricity is meant that, upon filtering the DAM
in air, the temperature should not rise above 200.degree. C. The
oxidized catalyst precursor is then processed to further enhance
the properties thereof as described below. Optionally, if it is
desired to complete the process of the present invention at another
time or place, since the oxidized catalyst precursor is stable, it
may be recovered and dried under vacuum or under an inert
atmosphere at a temperature of from about 50.degree. to 150.degree.
C. Preferably, the oxidized catalyst precursor is dried under air
flow at a temperature above 100.degree. C. for at least one
hour.
[0019] We have found that the activity of a DAM catalyst, already
enhanced by slurry low temperature oxidation as described above,
can be further improved by the addition thereto of small amounts of
certain metal oxides that are recognized by those of ordinary skill
in the art as promoters for cobalt DAMs. It is considered
unexpected that the promoter metal oxides utilized in the subject
process enhance the desirable properties of the DAM catalyst
particles because, of the group of metal oxides commonly recognized
as promoters for DAM catalysts, only the oxides of chromium,
lanthanum and manganese have been found to be beneficial. By this
is meant that only those metal oxides added to the oxidized
catalyst precursor as described herein have been found to improve
at least one performance characteristic of the DAM catalyst.
[0020] In accordance with the present invention, one or more of the
metal oxides is added to the DAM in an amount sufficient to
provide, in total, from about 0.01 to about 20, preferably from
about 0.1 to about 10 percent by weight of the desired metal oxide,
based on the catalyst metal in the DAM, in the final enhanced
catalyst. By precursor of the subject promoter metal oxides is
meant a compound that will form the desired metal oxide in the
oxidation step, a heating step carried out after the oxidation step
is completed, or in the treatment with hydrogen at elevated
temperatures. Precursors of the subject promoter metal oxides are
utilized since the oxides themselves possess very poor solubility.
Suitable precursors possess sufficient solubility in solvents that
are suitable for forming the oxidative slurry, or are miscible with
the fluids used to form the slurry, and that do not introduce any
incompatibility or poisons into the final enhanced catalyst. As
examples of precursors there can be mentioned salts, such as the
nitrates, and organic salts or complexes, such as the acetates,
carbonyls, chelates and the like. The nitrates are of particular
advantage in the subject process in that they can form at least a
part of the oxidizing agent for the oxidation step as described
above. In this instance, the precursor would be added to the DAM
catalyst prior to forming the slurry, or to the slurry after it was
formed, or the solution of the precursor would constitute the fluid
for the slurry. Wherein the precursor would be at least part of the
oxidizing agent, the step of converting the precursor to the
desired promoter metal oxide would be carried out simultaneously
with the oxidation step.
[0021] The solution of the precursor of the subject metal oxides
may be added to the DAM prior to formation of the slurry, to the
slurry after it is formed, during the oxidation step itself, or
subsequent to completion of the oxidation. In all instances, the
resultant mixture of the oxidized catalyst precursor and promoter
metal oxide precursor, or metal oxide where the precursor has been
at least a part of the oxidizing agent, are recovered and dried. In
the event that an oxidant was utilized in carrying out the slurry
low temperature oxidation that results in an alkaline slurry, the
oxidized catalyst precursor should be rinsed prior to combining it
with the solution of the one or more precursors for the promoter
metal oxides. Recovery of the mixture of the oxidized catalyst
precursor and one or more precursors for the promoter metal oxides
is generally by physical separation such as by filtering, decanting
and the like. Drying may take place under vacuum or under an inert
atmosphere at a temperature of from about 50.degree. to 150.degree.
C. Preferably, the mixture is dried under air flow at a temperature
above 1 00.degree. C. for at least one hour.
[0022] The mixture is then treated to convert the promoter metal
oxide precursor to the metal oxide and deposit it onto the oxidized
catalyst precursor. In general, this entails heating the mixture to
a temperature sufficiently high to cause decomposition or
transformation of the precursor to the desired oxide. Typically,
this temperature would be about 300.degree. to 500.degree. C.,
preferably about 400.degree. C. Wherein the precursor gives off
volatile compounds in connection with forming the oxide, such as
the degradation of an organic salt or complex, the heating can be
carried out under vacuum to promote removal of such products. The
heating step is carried out for a time sufficient to ensure that
the conversion to the oxide is complete. Those of ordinary skill in
the art will appreciate that there are various techniques, such as
the detection of a volatile by-product, that can serve as an
indicator that this has taken place.
[0023] The oxidized catalyst precursor is then converted to the
active catalyst by reduction with hydrogen-containing gas at
temperatures of from about 200.degree. C. to 600.degree. C.,
preferably from about 300.degree. C. to 450.degree. C., most
preferably from about 340.degree. C. to 400.degree. C. Hydrogen
partial pressure during the reduction would range from about 1 to
100 atmospheres, preferably from about 1 to 40 atmospheres. In
those instances where the precursor of the promoter metal oxide by
the above-described reduction with hydrogen at elevated
temperature, the conversion step and the reduction step are carried
out simultaneously. Typical Fischer-Tropsch activities of DAM
catalysts activated in accordance with the process of the present
invention are at least 120%, more frequently at least 150% of that
of the original DAM. By the same token, methane selectivity of the
DAMs are reduced by the present process to below 80%, more
frequently below 60% of the original DAM. As those of ordinary
skill in the art are aware, methane selectivity is enhanced when
the percentage is reduced, hence a reduction in methane selectivity
is a significant improvement.
[0024] The catalysts formed from DAMs in accordance with the
activation process of the invention are used in synthesis processes
for the formation of higher hydrocarbons wherein liquid and gaseous
products are formed by contacting a syngas comprising a mixture of
hydrogen and carbon monoxide with shifting or non-shifting
conditions, preferably the latter in which little or no water gas
shift takes place. The process is carried out at temperatures of
from about 160.degree. C. to 260.degree. C., pressures of from
about 5 atm to about 100 atm, preferably from 10 to 40 atm, and gas
space velocities of from about 300 V/Hr/V to about 20,000 V/Hr/V,
preferably from about 1,000 V/Hr/V to about 15,000 V/Hr/V. The
stoichiometric ratio of hydrogen to carbon monoxide is about 2.1:1
for the production of higher hydrocarbons. This ratio can vary from
about 1:1 to 4:1, preferably from 1.5:1 to 2.5:1, more preferably
from 1.8:1 to 2.2:1. These reaction conditions are well known to
those skilled in the art and a particular set of reaction
conditions can readily be determined from the parameters given
herein. The reaction may be carried out in virtually any type of
reactor, e.g. fixed bed, moving bed, fluidized bed and the like.
The hydrocarbon-containing products formed in the process are
essentially sulfur and nitrogen free.
[0025] The hydrocarbons produced in a process as described above
are typically upgraded to more valuable products by subjecting all
or a portion of the C5+ hydrocarbons to fractionation and/or
conversion. By "conversion" is meant one or more operations in
which the molecular structure of at least a portion of the
hydrocarbon is changed and includes both non-catalytic processing,
e.g. steam cracking, and catalytic processing, e.g. catalytic
cracking, in which the portion, or fraction, is contacted with a
suitable catalyst. If hydrogen is present as a reactant, such
process steps are typically referred to as hydroconversion and
variously as hydroisomerization, hydrocracking, hydrodewaxing,
hydrorefining and the like. More rigorous hydrorefining is
typically referred to as hydrotreating. These reactions are
conducted under conditions well documented in the literature for
the hydroconversion of hydrocarbon feeds, including hydrocarbon
feeds rich in paraffins. Illustrative, but non-limiting, examples
of more valuable products from such feeds by these processes
include synthetic crude oil, liquid fuel, emulsions, purified
olefins, solvents, monomers or polymers, lubricant oils, medicinal
oils, waxy hydrocarbons, various nitrogen- or oxygen-containing
products and the like. Examples of liquid fuels includes gasoline,
diesel fuel and jet fuel, while lubricating oil includes automotive
oil, jet oil, turbine oil and the like. Industrial oils include
well drilling fluids, agricultural oils, heat transfer oils and the
like.
[0026] It is understood that various other embodiments and
modifications in the practice of the invention will be apparent to,
and can be readily made by, those of ordinary skill in the art
without departing form the scope and spirit of the invention as
described above. Accordingly, it is not intended that the scope of
the claims appended hereto be limited to the exact description set
forth above, but rather that the claims be construed as
encompassing all of the features of patentable novelty that reside
in the present invention, including all the features and
embodiments that would be treated as equivalents thereof by those
skilled in the art to which the invention pertains. The invention
is further described with reference to the following experimental
work.
[0027] Example 1: Treatment of Cobalt Catalyst by Slurry Low
Temperature Oxidation
[0028] A slurry of about 1200 grams of commercial cobalt catalyst
(Raney.RTM. 2700) in water was placed in a 4 liter beaker and
stirred with a Teflon.RTM.-coated stirring blade. A total of 1320
cc of 0.5N nitric acid solution was added to the slurry by slow
addition. During the addition, the temperature of the slurry rose
to about 60.degree. C. and a strong ammonia odor developed. The
slurry was stirred for an additional hour following completion of
the addition. During the oxidation of the catalyst, the pH of the
slurry became basic due to the reduction of the nitrate ions to
ammonium ions. The total amount of nitrate ions added was adjusted
in order to achieve a complete consumption of the hydrogen
dissolved in the catalyst and the native hydrogen generated by the
acidic oxidation of the metal in the catalyst. Further addition of
nitric acid would result in a dissolution of cobalt ions into the
solution, evidenced by a pink coloration, which is undesirable. The
deactivated catalyst was filtered, washed three times with
deionized water recovered by filtration. During the filtration, the
solids were again washed three times with deionized water. The
solids were dried overnight in a vacuum oven at 60.degree. C. The
catalyst was further treated in flowing air at 120.degree. C. to
complete passivation. The passivated catalyst was stored as is
without additional storage precautions, yield 946.6 grams of dried,
enhanced Raney cobalt catalyst.
[0029] Example 2: Preparation of Metal Oxide Promoted Raney Cobalt
Catalyst
[0030] An appropriate quantity of the nitrate salt of the metal
promoters to be tested to provide a three percent by weight of the
metal oxide on 30.0 grams of passivated Raney cobalt catalyst was
dissolved in 12 ml of distilled water. The resulting solution was
added to 30.0 grams of the passivated catalyst prepared in Example
1 and stirred for 10 minutes. The material was then dried for 45
minutes on a steam bath and mixed with 30-40 ml of 3-4mm sized
quartz particles. The mixture was placed into a reactor. Air was
passed through the reactor and it was heated to 400.degree. C. and
held for five hours. The mixture was removed from the reactor and
the quartz particles and catalyst were separated by sieving.
[0031] Example 3: Catalyst reduction
[0032] Catalyst from Example 2 (20 ml) was mixed with 70 ml of 1-2
mm quartz particles. The mixture was place into a 25 mm ID quartz
reactor. The mixture was held in place with a layer of about 10 ml
of the 1-2 mm quartz particles at the bottom of the reactor. The
catalyst/quartz mixture was placed into the reactor one layer at a
time with the individual layers being about 0.5 to 0.7 cc thick,
until the entire volume of catalyst plus quartz was in the reactor.
Hydrogen was passed through the reactor at ambient temperature and
pressure at a gas hourly space velocity (GHSV) of 100 hr.sup.-1 for
15 minutes. Prior to being admitted to the reactor, the hydrogen
was passed through a column of potassium hydroxide pellets to
assure removal of impurities. The reactor temperature was increased
to 400.degree. C. over about 45 minutes, held for five hours, and
allowed to return to ambient, all under flowing hydrogen. The
hydrogen flow was then replaced with a 2:1 blend of hydrogen and
carbon monoxide synthesis gas at 100 hr.sup.-1 GHSV for 15 minutes
at atmospheric pressure. The synthesis gas was also passed through
KOH pellets prior to being admitted to the reactor. The valves were
then closed to the reactor thereby storing the catalyst under the
synthesis gas blend.
[0033] Example 4: Catalyst Testing
[0034] The flow of synthesis gas was resumed into a reactor as in
Example 3 and the reactor temperature increased from ambient to
140.degree. C. over about 40 minutes and the held for five hours.
The temperature was allowed to return to ambient under flowing
synthesis gas and the catalyst stored as in Example 3. Testing was
resumed the next day by repeating the procedure with the exception
of raising the temperature 10.degree. C. This procedure was
repeated until the optimum operating temperature was determined.
The optimum operating temperature was that where the yield of C5+
products was maximized by measuring the grams of C5+ products
produced per standard cubic meter of synthesis gas blend fed into
the reactor. A decline in the yield of C5+ products produced
indicated that the previous temperature was the optimum operating
temperature. Catalyst performance was determined by measuring the
gas contraction, products gas composition by gas chromatography and
C5+ liquid product yield. The C5+ products were recovered from the
reactor effluent using two traps. The first trap was water-cooled
and the second cooled with dry ice/acetone (-80.degree. C.). The
C5+ product in the first trap was weighed directly. The product in
the second trap was warmed to room temperature to volatilize C4-
components and then weighed. The combined weights from the two
traps was the yield. The C5+ product form the optimum temperature
was further analyzed to determine hydrocarbon type and carbon chain
length distribution. At random intervals, the C5+ products from the
non-optimum temperature tests were combined and analyzed. The
results are shown in the Table. In the Table, the Schultz-Flory
Alpha determination is an indication of the tendency of the
synthesis to produce a higher molecular weight hydrocarbon product.
Higher numbers are desirable. Methane yield, therefore, is the
opposite, i.e. since higher molecular weight products are
desirable, a lower methane yield and conversion are positive
results. It will be seen by the Table that, among metal oxides
recognized as promoters, only chromium, lanthanum and manganese
unexpectedly produce an increase in at least one of the desirable
parameters measured in the test.
1TABLE Metal CO Yield, g/cu meter Selectivity % of Oxide Optimum
Conversion of Syngas CO Converted Schultz-Flory Promoter Temp
.degree. C. % CH4 C5+ CH4 C5+ Alpha None 180 88 11 139 6 84 0.85
Cr2O3 170 75 8 152 4 93 0.87 La2O3 180 72 9 146 5 92 0.85 CeO2 180
73 12 136 6 84 0.85 Mn2O3 180 66 7 133 4 92 0.89 ZrO2 170 77 10 128
6 84 0.84 TiO2 180 76 20 124 10 78 0.81 ZnO 190 68 20 98 13 74
0.82
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