U.S. patent application number 10/323343 was filed with the patent office on 2003-06-26 for recovery of rhenium from a spent catalyst via sublimation.
This patent application is currently assigned to ConocoPhillips Company. Invention is credited to Allison, Joe D., Ramani, Sriram, Srinivasan, Nithya.
Application Number | 20030119658 10/323343 |
Document ID | / |
Family ID | 23352797 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030119658 |
Kind Code |
A1 |
Allison, Joe D. ; et
al. |
June 26, 2003 |
Recovery of rhenium from a spent catalyst via sublimation
Abstract
This invention provides a method for recovering rhenium oxide
from a material containing rhenium by itself or rhenium in
combination with some other element, such as an element
catalytically active for a catalytic process, such as
hydrogenation, oxidation, reforming, and hydrocracking. The method
includes conversion of rhenium to a sublimable oxide via oxidation,
heating in an oxidizing atmosphere to sublime the oxide as a
volatized oxide, and then isolation of rhenium from the volatized
oxide.
Inventors: |
Allison, Joe D.; (Ponca
City, OK) ; Srinivasan, Nithya; (Ponca City, OK)
; Ramani, Sriram; (Ponca City, OK) |
Correspondence
Address: |
DAVID W. WESTPHAL
CONOCOPHILLIPS COMPNAY
P.O. BOX 1267
PONCA CITY
OK
74602-1267
US
|
Assignee: |
ConocoPhillips Company
Houston
TX
|
Family ID: |
23352797 |
Appl. No.: |
10/323343 |
Filed: |
December 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60344950 |
Dec 21, 2001 |
|
|
|
Current U.S.
Class: |
502/38 ;
423/49 |
Current CPC
Class: |
C22B 11/026 20130101;
Y02P 10/214 20151101; Y02P 10/20 20151101; C22B 61/00 20130101 |
Class at
Publication: |
502/38 ;
423/49 |
International
Class: |
C22B 061/00 |
Claims
What is claimed is:
1. A method for recovering rhenium from a spent catalyst comprising
rhenium, the method comprising: heating the spent catalyst in an
oxidizing atmosphere at a temperature effective to sublime a
portion of the rhenium as a volatized oxide.
2. The method according to claim 1 wherein the atmosphere is at
standard pressure and the temperature is between about 250.degree.
C. and about 400.degree. C.
3. The method according to claim 1 further comprising: scrubbing
the volatized oxide with an aqueous medium to form a
rhenium-bearing aqueous solution.
4. The method according to claim 3 further comprising: separating
rhenium from the aqueous solution so as to form a rhenium-bearing
solid.
5. The method according to claim 1 wherein the portion comprises at
least 25% of the rhenium.
6. The method according to claim 1 wherein the spent catalyst
further comprises a second metal.
7. A method for recovering rhenium and a second metal from a spent
catalyst comprising rhenium and the second metal, the method
comprising: (a) heating the spent catalyst in an oxidizing
atmosphere at a temperature effective to sublime a portion of the
rhenium as a volatized oxide and to form a catalyst remainder; and
(b) removing at least a portion of the second metal from the
catalyst remainder.
8. The method according to claim 7 wherein the atmosphere is at
standard pressure and the temperature is between about 250.degree.
C. and about 400.degree. C.
9. The method according to claim 7 further comprising: (c)
scrubbing the volatized oxide with an aqueous medium to form an
aqueous rhenium-bearing solution.
10. The method according to claim 9 further comprising: (d)
separating rhenium from the aqueous solution so as to form a
rhenium-bearing solid.
11. The method according to claim 7 wherein the portion of the
rhenium comprises at least 25% of the rhenium.
12. The method according to claim 7 wherein step (b) comprises:
(b1) dissolving the catalyst remainder in an acid solution; and
(b2) extracting the second metal from the acid solution.
13. The method according to claim 12 wherein the portion of the
second metal comprises at least 50% of the second metal.
14. The method according to claim 7 wherein the second metal is a
metal catalytically active for a catalytic process selected from
among hydrogenation, oxidation, reforming, and hydrocracking.
15. A method for reclaiming rhenium from a spent catalyst,
comprising: (a) heating the spent catalyst in an oxidizing
atmosphere at a temperature effective to sublime a portion of
rhenium as a volatilized oxide; (b) isolating the rhenium from the
volatized oxide; and (c) incorporating the isolated metal in a
fresh catalyst.
16. The method according to claim 15 wherein the atmosphere is at
standard pressure and the temperature is between about 250.degree.
C. and about 400.degree. C.
17. The method according to claim 15 further comprising: (d)
scrubbing the volatized oxide with an aqueous medium to form a
rhenium-bearing aqueous solution.
18. The method according to claim 17 further comprising: (e)
separating rhenium from the aqueous solution so as to form a
rhenium-bearing solid.
19. The method according to claim 15 wherein the portion of rhenium
comprises at least 25% of the rhenium.
20. The method according to claim 15 wherein step (c) comprises
loading a catalyst support with the reclaimed rhenium.
Description
RELATED APPLICATIONS
[0001] The present application claims the benefit of 35 U.S.C.
111(b) provisional application Serial No. 60/344,950 filed Dec. 21,
2001, and entitled Recovery of Rhenium From A Spent Catalyst Via
Sublimation.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
FIELD OF THE INVENTION
[0003] The present invention generally relates to a process for the
recovery of rhenium from a spent catalyst. Still more particularly,
this invention relates to a method that includes heating the
catalyst in an oxidizing atmosphere at a temperature effective to
sublime a portion of the rhenium as a volatized oxide.
BACKGROUND OF THE INVENTION
[0004] Catalysts for use in facilitating chemical reactions often
contain precious metal components which aid in the function of the
catalyst. For example, rhenium is a relatively scarce and expensive
material, typically recovered from ores, which has however found
utility in certain catalysts. The most common catalytic use of
rhenium is in improved platinum-based reforming catalysts for the
production of high-octane hydrocarbons for low-lead, lead-free
gasoline. Rhenium also is known to improve hydrogenation catalysts.
In particular, rhenium has been used as a promoter for cobalt-based
catalysts in the Fischer-Tropsch reaction for the production of
multi-carbon molecules, such as hydrocarbons, from methane. In this
connection, reference is made to U.S. Pat. No. 4,801,573 and
International Publications WO 98/47618 and WO 98/47620, each hereby
incorporated herein by reference. Further, rhenium is known as a
component in some oxidation catalysts. For example, U.S. Pat. Nos.
4,042,533, 6,008,389, and 5,720,901, each hereby incorporated
herein by reference, illustrate the role of rhenium in oxidation of
unsaturated aliphatic aldehydes, preparation of epoxides, and
partial oxidation of a hydrocarbon feedstock to produce carbon
monoxide and hydrogen (synthesis gas), respectively. Still further,
rhenium is known as a component in some hydrocracking catalysts, as
disclosed in, for example, U.S. Pat. Nos. 5,494,569 and 6,235,670,
each hereby incorporated herein by reference.
[0005] In the life of a catalyst, the catalyst may lose some or all
of its activity. A catalyst may deactivate through the accumulation
of a layer of carbon deposits, or coke. Coke accumulation typically
occurs throughout the catalyst pore systems and physically blocks
access to active sites. Further, metal agglomeration may occur,
which can severely reduce catalyst activity. Still further, poisons
(e.g., lead, arsenic, sulfur) may permanently deactivate the
catalyst.
[0006] Cycles of reaction and regeneration may occur for many
years. The catalyst may be regenerated in situ or removed for ex
situ regeneration. In one strategy, a fixed bed or slurry bed
reactor unit and a regenerator unit are paired in tandem, for
simultaneous operation. After the catalyst is regenerated ex situ
it is commonly loaded back to the same or another unit. This
procedure has the advantage of reducing down time of the reactor.
Alternatively, a catalyst may continuously recirculate between an
entrained bed reactor and a regenerator. Cost savings over fresh
catalyst vary widely, but using regenerated catalyst can save
50-80% of the new catalyst cost.
[0007] A catalyst that has been through cycles of use and
regeneration may, with time, lose the ability to be regenerated to
an adequate level of activity, becoming a spent catalyst. This loss
of regenerability may be due to incompleteness of the regeneration.
For example, in an oxidative regeneration of a coked catalyst,
sulfur in the coke is typically not removed to as low a level as
coke is removed during regeneration. Further, sulfates associated
with alumina supports are typically not removed, nor are metal
poisons. Permanent loss of acceptable activity may also occur
through sintering or other structural changes.
[0008] Often a spent catalyst is discarded. However, a spent
catalyst, if discarded, represents a loss of precious material.
Further, use of landfills for such disposal is problematic. For
example, landfills have decreased in number by 75% in the past 20
years, a trend that is expected to continue. Further, environmental
liability can reach unacceptable levels if the landfill releases
toxins to the environment. Still further, the environmental
protection agency (EPA) "Land Ban" imposes restrictions on
disposal.
[0009] Thus it is desirable to have a method for reclamation of
catalyst materials. Reclamation is the process of recovering and
recycling a material. For a precious-metal-containing catalyst,
reclamation is particularly desirable for economic reasons. For
example, a single drum of spent catalyst may contain thousands of
dollars worth of valuable metals, such as platinum, palladium,
iridium, ruthenium, and rhenium.
[0010] In particular, it is desirable to have a method for
reclamation of precious metal from a spent catalyst. The costs of
an entire catalytic process could be reduced appreciably by
recovery of the precious metal, such as rhenium, from spent
catalysts and subsequent recycling of the metal.
[0011] Methods that have been used to rhenium from rhenium-bearing
sources have varied, depending in part on the nature and identity
of other substances admixed with the rhenium. It is well known from
the art of chemical analysis of materials, such as elemental
analysis, that techniques for isolation, separation, and recovery
of elements tend to vary in method or implementation with the
composition of the material.
[0012] Methods of rhenium recovery that have been applied to ores
that are the typical natural source of rhenium, such as
molybdenite, conventionally have involved oxidative roasting of the
ore and recovery of rhenium from the roaster gases by methods such
as wet scrubbing. In this connection, reference is made to U.S.
Pat. Nos. 2,414,965, 2,809,092, 3,739,549, and 3,798,306, each
hereby incorporated herein by reference.
[0013] Alternatively, solution-based methods have been used for the
recovery of rhenium from spent platinum-rhenium catalysts. In this
connection, reference is made to U.S. Pat. Nos. 3,672,874,
3,855,385, and 3,932,579, hereby incorporated herein by reference.
These methods usually involve complete dissolution of the various
rhenium-bearing source materials, such as using an acid, followed
by the use of an anion exchange resin or another chemical
separation method to isolate the rhenium. A disadvantage of
complete dissolution is the necessity for typically complex
separation of the rhenium from the solution. Further, the solvent
used for dissolution tends to vary with the material, as does the
method of separation.
[0014] In one method for selective dissolution of rhenium from a
spent platinum-rhenium catalyst, the rhenium is selectively
dissolved from the catalyst through use of a slight alkali
solution, such as NaHCO.sub.3. See, for example, T. N. Angelidis et
al., in: "Selective Rhenium Recovery from Spent Reforming
Catalysts," Ind. Eng. Chem. Res. 1999, 38, 1830-1836). This method
has the disadvantage that it relies on the insolubility of the
catalytic metal, in particular platinum, in the weak alkali
solution. Catalytic materials that are insoluble in weak alkali
solutions include for, example Al, Cd, and Zn. A survey of the
solubilities of metals from Lange's Handbook of Chemistry, J. A.
Dean, McGraw-Hill Handbooks, 15.sup.th edition (1998), Table 3.2,
Page 3.14, hereby incorporated by herein reference, lists reference
acid or weak acid solutions for dissolution.
[0015] Notwithstanding the above teachings, there remains a need
for a selective and economical method for recovering rhenium from a
spent catalyst.
SUMMARY OF THE INVENTION
[0016] A method is provided for recovering a metal from a
metal-containing source. The metal-containing source may contain
the metal present in mixed oxidation states, that is, different
metal atoms in the source may have different oxidation states. The
metal-containing source is preferably a spent catalyst. The present
method has the advantage that selective recovery of the metal may
be achieved.
[0017] The metal preferably has a desirable oxidation state that is
the oxidation state of that elemental metal when present in a
sublimable compound of the metal. The sublimable compound is
preferably a sublimable oxide. The sublimable compound preferably
sublimes to form a volatized compound. The volatized compound is
preferably one from which the elemental metal may be recovered.
[0018] According to a method of recovering a metal from a
metal-containing source, the metal-containing source is oxidized to
form the metal in the desirable oxidation state. The metal in the
desirable oxidation state is preferably recovered by heating the
source to obtain the sublimable compound. The sublimable compound
may be further treated for recovery of the metal.
[0019] In accordance with a preferred embodiment of the present
invention, a method for recovering rhenium from a spent catalyst
containing rhenium includes heating the spent catalyst in an
oxidizing atmosphere at a temperature effective to sublime a
portion of the rhenium as a volatized oxide. The spent catalyst may
contain the rhenium, by itself or in combination with at least one
other metal.
[0020] In accordance with another preferred embodiment of the
present invention, a method for recovering rhenium and a second
metal from a spent catalyst that contains rhenium and the second
metal includes heating the spent catalyst in an oxidizing
atmosphere at a temperature effective to sublime a portion of the
rhenium as a volatized oxide and to form a catalyst remainder, and
removing at least a portion of the second metal from the catalyst
remainder.
[0021] In accordance with still another preferred embodiment of the
present invention, a method for reclaiming rhenium from a spent
catalyst includes heating the spent catalyst in an oxidizing
atmosphere at a temperature effective to sublime a portion of
rhenium as a volatilized oxide, isolating the rhenium from the
volatized oxide, and incorporating the isolated metal in a fresh
catalyst.
[0022] In any one of the above-described embodiments, a catalyst,
including a spent catalyst or a fresh catalyst, may be any suitable
catalyst using rhenium, including but not limited to a catalyst
selected from among hydrogenation catalysts, oxidation catalysts,
reforming catalysts, and hydrocracking catalysts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] For a more detailed description of the preferred embodiment
of the present invention, reference will now be made to the
accompanying drawings, wherein:
[0024] FIG. 1 is a schematic flow chart illustrating a method of
rhenium recovery, according to an embodiment of the present
invention; and
[0025] FIG. 2 is a schematic flow chart illustrating an alternate
method of rhenium recovery, according to an alternate embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Rhenium Recovery
[0027] Referring initially to FIG. 1, according to a preferred
embodiment of the present invention, a method for separating
rhenium from a spent catalyst includes oxidation of the spent
catalyst. The rhenium is preferably oxidized to form a sublimable
oxide, in particular rhenium heptoxide. More preferably, at least
60% of the elemental rhenium is present as rhenium heptoxide in the
oxidized catalyst. A sublimable oxide is a compound that, when
present in a solid state, undergoes a transition to a gaseous state
upon heating. The standard sublimation temperature of a compound is
conventionally given as the sublimation temperature for standard
(i.e. atmospheric) pressure. For example, the standard sublimation
temperature of rhenium heptoxide is 250.degree. C. An advantage of
a sublimable oxide is that it may be readily isolated and separated
from other solid compounds in a source by heating the source at a
temperature effective to sublime the sublimable oxide as a
volatized oxide. Volatized oxide denotes herein the sublimable
oxide in a gaseous state.
[0028] Oxidation is conventionally any process that increases the
proportion of oxygen or acid-forming radical in a compound. An
element in a compound typically has a formal oxidation state
(herein termed oxidation state) that is increased upon oxidation
and decreased upon reduction. Reduction is conventionally any
process that decreases the proportion of oxygen or acid-forming or
radical in a compound.
[0029] Referring still to FIG. 1, the spent catalyst may include
rhenium compounds of various oxidation states, such as fully
reduced metallic rhenium, Re(III) (i.e. rhenium with a formal
oxidation state of 3), Re(IV) (i.e. rhenium with a formal oxidation
state of 4), Re(VI) (i.e. rhenium with a formal oxidation state of
6), Re(VII) (i.e. rhenium with a formal oxidation state of 7), and
combinations thereof. Exemplary rhenium oxides having at least one
of these oxidation states are indicated in Table 1. Rhenium
sesquioxide is unstable and thus would tend not to be present in a
spent catalyst. The spent catalyst preferably contains rhenium in
the form of at least one rhenium oxide compound. The spent catalyst
preferably contains any one or combination of rhenium dioxide,
ReO.sub.2, rhenium trioxide, ReO.sub.3, and rhenium heptoxide,
Re.sub.2O.sub.7. Alternately, the rhenium in the spent catalyst may
be present in coordinated complexes, including their oxides, with
other elements, such as another catalyst metal. Further, when the
catalyst includes a support, the rhenium may be found in
coordinated complexes, such as oxides, with an element included in
a support. For example, for a cobalt-rhenium catalyst supported on
alumina, the rhenium may be present in a rhenium oxide, a
metal-rhenium oxide (i.e. a composition containing cobalt, rhenium,
and oxygen), an aluminum-rhenium oxide, or an
aluminum-cobalt-rhenium oxide (i.e. a composition containing
alumina, cobalt, rhenium, and oxygen). It will be understood that
cobalt is exemplary of a catalytically active metal and aluminum is
exemplary of a support element. The various percentages of rhenium
compounds having various oxidation states in a spent catalyst may
depend on the length of time the catalyst has been in use, as well
as whether the catalyst has been exposed to air.
1TABLE 1 Rhenium Oxide Chemical Formula Re Oxidation State Rhenium
Heptoxide Re.sub.2O.sub.7 7 Rhenium Trioxide Re.sub.3O.sub.3 6
Rhenium Peroxide Re.sub.2O.sub.6 6 Rhenium Dioxide ReO.sub.2 4
Rhenium Sesquioxide Re.sub.2O.sub.3xH.sub.2O 3
[0030] It will be appreciated that the various percentages of
rhenium compounds in a spent catalyst typically differ from those
in a fresh or regenerated catalyst. The rhenium in a fresh catalyst
or regenerated catalyst mostly exists in the 0 (metallic) oxidation
state, due to reduction of the catalyst to make it active. In
contrast, the rhenium in a spent catalyst has a range of rhenium
oxidation states due to the oxidation of metallic rhenium during
its use. Further, there is typically not much rhenium in a spent
catalyst in the +7 oxidation state, due in part to the availability
of other oxides and to the reaction conditions. Thus, a spent
catalyst typically contains a greater proportion of rhenium
selected from among Re(IV) and Re(VI) than a fresh or regenerated
catalyst.
[0031] Referring still to FIG. 1, the oxidation is preferably
carried out by contacting the spent catalyst with an
oxygen-containing gas under conditions effective to oxidize at
least a portion of the rhenium in the spent catalyst. The
oxygen-containing gas may be chosen from among air, oxygen gas,
oxygen-helium mixtures and the like. Oxidation is preferably
achieved by heating the spent catalyst in an oxidizing atmosphere.
The oxidizing atmosphere preferably contains the oxygen-containing
gas. The oxidation conditions preferably include a temperature
greater than the sublimation temperature of rhenium heptoxide. The
oxidation conditions preferably include a pressure approximately
equal to atmospheric pressure. At atmospheric pressure the
sublimation temperature of rhenium heptoxide is 250.degree. C.
Thus, when the spent catalyst is heated under conditions of
atmospheric pressure, the conditions preferably further include a
temperature of at least about 250.degree. C. Heating above the
sublimation temperature of a sublimable oxide such as rhenium
heptoxide preferably effects sublimation of at least a portion of
the rhenium as a volatized oxide during oxidation. Thus, oxidation
and sublimation may occur together as one step.
[0032] Further, when the spent catalyst further contains at least
one other metal, recoverable from the solid catalyst remainder, the
conditions for oxidizing the spent catalyst by heating the spent
catalyst in an oxidizing atmosphere preferably include a
temperature less than any transformation temperature of the other
metal. Heating under conditions that include a temperature below
the lowest transformation temperature of the other metal preferably
suppresses transformations of compounds of the other metal
contained in the spent catalyst and thus suppresses conversion of
the other metal to forms that may be difficult to recover or that
may interfere with the process of recovery of rhenium from the
spent catalyst. It is preferred that the other metal remains intact
in the spent catalyst during the oxidation. In some embodiments,
the other metal is any metal catalytically active for a catalytic
process benefiting from a rhenium-bearing catalyst. Thus, in such
embodiments, the other metal may be a metal catalytically active
for hydrogenation, oxidation, reforming, hydrocracking, and the
like. A catalytically active metal is one known to be active in
suitably activated or regenerated catalyst and may be present
either in an active or an inactive state in a spent catalyst.
[0033] Still further, the conditions for oxidizing a spent catalyst
by heating the spent catalyst in an oxidizing atmosphere preferably
include a temperature less than the decomposition temperature of a
decomposable rhenium oxide. At atmospheric pressure, rhenium
trioxide decomposes at 400.degree. C. Thus, when the spent catalyst
is heated under conditions of atmospheric pressure, the conditions
preferably further include a temperature less than about
400.degree. C. Heating under conditions that include a temperature
below the decomposition temperature of a decomposable oxide of
rhenium, such as rhenium trioxide, preferably suppresses
decomposition of rhenium-bearing species contained in the spent
catalyst and thus suppresses conversion of rhenium to forms that
are not available to be oxidized to a sublimable oxide.
[0034] Still further, the above considerations for the temperature
are preferably combined, such that a method for separating rhenium
from a spent catalyst includes heating the spent catalyst in an
oxidizing atmosphere under conditions that include a temperature
greater than the sublimation temperature of rhenium heptoxide and
less than the decomposition temperature of rhenium trioxide, more
preferably a temperature between about 250.degree. C. and about
400.degree. C.
[0035] Referring to FIG. 2, in an alternate embodiment, an oxidized
catalyst is cooled to ambient temperature. After cooling the
oxidized catalyst, a method of recovering rhenium includes heating
the oxidized catalyst under conditions effective to sublime a
rhenium oxide and produce a gaseous stream containing a vaporized
rhenium oxide, preferably rhenium heptoxide. The sublimation
conditions preferably further include a pressure approximately
equal to atmospheric pressure. Thus, the sublimation conditions
preferably include a temperature of at least about 250.degree. C.
Temperature-programmed reduction indicates that reduction of
Re.sub.2O.sub.7 occurs at 280-350.degree. C. Thus, it is preferred
that the atmospheric pressure conditions of heating to effect
sublimation be maintained preferably below about 280.degree. C.
Reheating the catalyst to effect sublimation has the advantage of
increasing recovery of rhenium from the catalyst.
[0036] Referring to FIGS. 1 and 2, a catalyst solid remainder
includes the remains of the catalyst solid after oxidation and
sublimation, whether occurring together or separately. The catalyst
solid remainder preferably includes less than 70%, more preferably
less than 50%, and most preferably less than 20% of the elemental
rhenium content of the spent catalyst. Thus, a method of separating
rhenium from a spent catalyst preferably includes recovering at
least 25% of the rhenium, more preferably at least 50%, and most
preferably at least 80%.
[0037] Referring to FIGS. 1 and 2, according to a preferred
embodiment, a method of recovering rhenium from a spent catalyst
includes isolating rhenium from the volatized oxide. Isolating
rhenium from the volatized oxide preferably includes wet scrubbing
of a gaseous stream containing vaporized rhenium, preferably
rhenium heptoxide. The wet scrubbing preferably proceeds according
to conventional methods, such as disclosed in U.S. Pat. Nos.
2,414,965 and 2,809,092, which are incorporated herein by
reference. The scrubbing may be performed in conventional scrubbing
and/or absorption equipment, such as venturi scrubbers, cyclonic
scrubbers, packed towers, other gas cleaning equipment, and the
like. Rhenium heptoxide (Re.sub.2O.sub.7) is soluble in water and
forms perrhenic acid when it goes into solution. The scrubbing
produces a rhenium-bearing aqueous solution containing rhenium and
other soluble and suspension products. The resulting
rhenium-bearing aqueous solution may be concentrated, which then
allows the rhenium content to be separated by conventional methods
such as ion exchange and precipitation. In ion exchange, a portion
of the rhenium-bearing aqueous solution is passed through an ion
exchange column to obtain a column eluent and rhenium is then
precipitated from a portion of the eluent. In some embodiments, at
least 25% of the rhenium is separated.
[0038] Referring to FIGS. 1 and 2, according to a preferred
embodiment, the present method of separating rhenium from a spent
catalyst preferably additionally includes recovery of other
catalytic metals, such as cobalt, from a catalyst solid remainder.
The method of recovering the other metal(s) may depend on the
structural form of the spent catalyst. For example, for a supported
cobalt-rhenium catalyst, the cobalt is preferably recovered by a
method that includes conventional acid extraction or other methods
known to those skilled in the art. In acid extraction, the catalyst
remainder is dissolved in an acid solution and cobalt is then
extracted from the acid solution. However, it will be understood
that, according to other embodiments contemplated herein, a
catalyst solid remainder may be discarded. In some embodiments, at
least 80% of the cobalt is recovered.
[0039] Heating preferably occurs in any conventional heating zone
suitable for subliming rhenium heptoxide from a spent catalyst. The
spent catalyst is preferably maintained in the heating zone for a
sufficient period of time to effect maximum conversion of different
oxides of rhenium to rhenium heptoxide. Any of a number of heating
techniques and equipment in practice may be used and they can
operate under static or flowing conditions. Selection of suitable
techniques and equipment for heating are within the skill of one of
ordinary skill in the art.
[0040] Cooling preferably occurs in any conventional cooling zone
suitable for condensing the vapors of rhenium heptoxide. The
rhenium heptoxide is preferably maintained in the cooling zone for
sufficient period to effect the condensation of vapors. The rhenium
heptoxide preferably collects in the cooling zone (which acts as a
condenser). Any of a number of cooling techniques and equipment in
practice may be used and they can operate under static or flowing
conditions. Selection of suitable techniques and equipment for
heating are within the skill of one of ordinary skill in the
art.
[0041] Catalyst
[0042] It will be understood that the selection of a catalyst or
catalyst system requires many technical and economic
considerations. The process of selecting a precious metal catalyst
can be broken down into components. Key catalyst properties include
high activity, high selectivity, high recycle capability and
filterability. Catalyst performance is determined mainly by the
precious metal component. A metal is chosen for a catalyst based
both on its ability to activate a desired reaction and its
inability to promote an unwanted reaction.
[0043] A rhenium-bearing catalyst according to the preferred
embodiments of the present invention may include any suitable
support material. Preferably, the support is a catalyst support.
The catalyst support may be any of a variety of materials on which
a catalytically active material may be coated. The catalyst support
preferably allows for a high degree of metal dispersion. The choice
of support is largely determined by the nature of the reaction
system. The support catalyst is preferably stable under reaction
and regeneration conditions. Further, it preferably does not
adversely react with solvent, reactants, or reaction products.
Suitable supports include activated carbon, alumina, silica,
silica-alumina, carbon black, TiO.sub.2, ZrO.sub.2, CaCO.sub.3, and
BaSO.sub.4. Preferably, the catalytically active material is
supported on carbon, alumina, zirconia, titania or silica.
[0044] It will be understood that alternative choices of support
may be made without departing from the preferred embodiments of the
present invention by one of ordinary skill in the art A support
preferably favorably influences any of the catalyst activity,
selectivity, recycling, refining, material handling reproducibility
and the like. Properties of a support include surface area, pore
volume, pore size distribution, particle size distribution,
attrition resistance, acidity, basicity, impurity levels, and the
ability to promote metal-support interactions. Metal dispersion
increases with support surface area. Support porosity influences
metal dispersion and distribution, metal sintering resistance, and
intraparticle diffusion of reactants, products and poisons. Smaller
support particle size increases catalytic activity but decreases
filterability. The support preferably has desirable mechanical
properties, attrition resistance and hardness. For example, an
attrition resistant support allows for multiple catalyst recycling
and rapid filtration. Further, support impurities preferably are
inert. Alternatively, the support may contain additives that
enhance catalyst selectivity.
[0045] In rhenium-bearing catalyst according to the preferred
embodiments of the present invention, the rhenium may have
catalytic activity. Alternatively, the rhenium may be present in
combination with a second metal that is a catalytically active
metal for any suitable reaction.
[0046] Thus, a rhenium-bearing catalyst according to the preferred
embodiments of the present invention may further include any
suitable catalytically active metal. Exemplary catalytically active
metals for hydrogenation are the metals of Groups 8, 9, and 10,
combinations thereof, and the like. For hydrogenation of carbon
monoxide, also known as the Fischer-Tropsch reaction, preferred
metals are iron, nickel, and cobalt, and combinations thereof.
Exemplary catalytically active metals for oxidation include noble
metals (also termed precious metals), such as ruthenium, rhodium,
palladium, osmium, iridium, platinum, rhenium, gold, and silver,
combinations thereof, and the like. Further exemplary catalytically
active metals for oxidation include, the elements of molybdenum,
vanadium, and tungsten in combination. A molybdenum, vanadium,
tungsten catalysts may further include one or more of manganese,
iron, copper, tin, aluminum, cobalt, nickel, phosphorous, zinc,
bismuth, sliver, cadmium, niobium, arsenic, chromium, the alkali
and the alkaline earth elements. Exemplary catalytically active
metals for reforming include platinum, and the like. Exemplary
catalytically active metals for hydrocracking include platinum,
palladium, tungsten, nickel, combinations thereof, and the like.
Thus, a rhenium-bearing spent catalyst may further contain any one
or more of the above-listed catalytically active metals.
[0047] An advantage of the process of the present invention is
that, when the catalytically active metal does not have a
sublimable oxide, the catalytically active metal remains in a spent
catalyst remainder upon heating the spent catalyst in an oxidizing
atmosphere at a temperature effective to sublime a portion of the
rhenium as a volatized oxide. For example, none of the non-rhenium
nobel metals has a sublimable oxide.
[0048] The recovered rhenium is preferably recycled for use in a
fresh catalyst. The catalysts of the present invention may be
prepared by any of the methods known to those skilled in the art.
By way of illustration and not limitation, such methods include
loading a catalyst metal, in the form of a catalytic component or
precursor thereof onto a support. Catalytic components include
catalytically active metals and promoters. According to the
function of the catalyst, rhenium may be either a catalytically
active metal or a promoter. Methods of loading a support with a
catalyst metal include impregnating the catalyst metal onto a
support, extruding one or more catalyst metals together with
support material to prepare catalyst extrudates, and/or
precipitating the catalyst metal onto a support. Accordingly, the
supported catalysts of the present invention may be used in the
form of powders, particles, pellets, monoliths, honeycombs, packed
beds, foams, and aerogels.
[0049] The most preferred method of preparation may vary among
those skilled in the art, depending for example on the desired
catalyst particle size. Those skilled in the art are able to select
the most suitable method for a given set of requirements.
[0050] One method of preparing a supported metal catalyst is by
incipient wetness impregnation of the support with an aqueous
solution of a soluble metal salt such as nitrate, acetate,
acetylacetonate or the like. Another method of preparing a
supported metal catalyst is by a melt impregnation technique, which
involves preparing the supported metal catalyst from a molten metal
salt.
[0051] Without further elaboration, it is believed that one skilled
in the art can, using the description herein, utilize the present
invention to its fullest extent. The following embodiments are to
be construed as illustrative, and not as constraining the scope of
the present invention in any way whatsoever.
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