Hydrogenation Catalyst
Cross Reference to Related Applications
[001] This application claims priority to U.S. Provisional Patent Application 60/645,431
filed on January 20,2005, which is incorporated herein in its entirety by reference.
Background
[002] The present development relates to a catalyst composition for hydrogenation
processes and to a method for preparing the catalyst. The catalyst comprises iridium,
palladium and, optionally, at least one of the elements selected from the group consisting of
silver, gold, copper, zinc and tin. As reported herein, the catalyst may be used for
hydrogenation reactions such as the selective hydrogenation of acetylene.
[003] Processes producing unsaturated hydrocarbons usually involve cracking of various
types of hydrocarbons and often produce a crude product containing hydrocarbon impurities
that are more unsaturated than the desired product. These unsaturated hydrocarbon
impurities are often difficult to separate from the desired product. For example, it is desirable
that polymer grade ethylene has an acetylene content of less than about five (5) parts per
million by weight. However, it can be difficult to separate the ethylene from the acetylene
when the acetylene content is greater than five parts per million.
[004] One technique that has been used for reducing the amount of acetylene in ethylene
is to selectively hydrogenate the acetylene using a catalyst comprising palladium supported
on a carrier like alumina. In the hydrogenation process, it is highly desirable to remove the
undesired highly unsaturated acetylene without hydrogenating the desired ethylene to ethane.
However, it has been difficult to develop a catalyst that can perform this selective
hydrogenation process for an extended period. For example, palladium on gamma-alumina
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catalysts have been reported as effective selective hydrogenation catalysts, but the selectivity
has diminished rapidly in less than 100 hours on stream. (See, for example, GB Patent
916,056; J. Mol. Catal. A 173 (2001) 185-221; Catal. Today 24 (1997) 181-197; J. Catal. 158
(1996) 227-278; Appl. Catal. 10 (1984) 369.)
[005] Because presently known supported Pd-containing catalysts deactivate with time
on stream, there exists a need to develop catalysts and processes for hydrogenating acetylene,
which offer improved stability of the performance over time. What is especially important is
that the selectivity to ethylene remains high and that the selectivity to the undesired ethane
stays lower than presently achievable with state-of-the art catalysts.
[006] Accordingly, it is an object of the present invention to disclose a catalyst
composition for use in a process for the selective hydrogenation of acetylene, wherein the
catalyst remains selective for the hydrogenation of acetylene, and does not promote the
hydrogenation of ethylene, more effectively than observed with prior art catalysts.
Summary of the Invention
[007] The present development relates to a catalyst composition for the selective
hydrogenation of acetylene and to a method for preparing the catalyst. In contrast to the
catalysts of the prior art, including for example, palladium / silver catalysts, the catalyst of the
present invention exhibits high selectivity and an improved stability of the catalytic
performance over an extended period of time.
[008] The catalyst comprises from about 0.001 wt% to about 1.5 wt%, indium, from
about 0.005 wt% to about 0.5 wt% palladium and, optionally, at least one of the elements
selected from the group consisting of silver, gold, copper, zinc and tin, at a concentration of
up to about 0.5 wt%. In a preferred embodiment, the catalyst is prepared such that the
palladium is located within the first 250 micrometers of the surface of the catalyst carrier.
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Detailed Description of the Preferred Embodiment
[009] The present invention is a catalyst for the selective hydrogenation of acetylene for
ethylene purification. The invention further comprises a process for the production of the
catalyst that is useful for the selective hydrogenation of acetylene for ethylene purification
and a process of hydrogenation of the acetylene for ethylene purification using the catalyst of
the invention.
[0010] The catalyst of the invention is primarily designed for the selective hydrogenation
of acetylene in an ethylene stream. Ethylene feed streams typically contain impurities such
as hydrogen, methane, ethane, carbon monoxide and acetylene. The goal of the selective
hydrogenation is to reduce the amount of the acetylene impurity present in the feed without
substantially reducing the amount of ethylene that is present in the feed.
[0011] As is known in the art, catalysts are used in the selective hydrogenation of
acetylene process. However, deactivation of the catalyst may occur. This deactivation
manifests itself as a decreasing selectivity to the desired ethylene and an increasing
selectivity to the undesired ethane. Moreover, deactivation can reduce the activity of the
catalyst used in the process.
[0012] The catalyst of the present invention comprises iridium ("Ir") and palladium
("Pd") and, optionally, a promoter ("M"), on an inorganic carrier. The catalyst carrier may
be any carrier generally known in the art for use in hydrogenation catalysts. For example, the
carrier may be metal alummates, such as calcium aluminate, magnesium aluminate, barium
hexaluminate, nickel aluminate, and alumina, silica, silica-alumina, activated carbon, ceria,
zirconia, chromia-alumina, titania, magnesium oxide, and mixtures thereof. In an exemplary
embodiment, without limitation, the carrier is an alumina having a surface area of from about
30 m2/g to about 50 m2/g. In an alternative embodiment, the carrier is an alpha-alumina.
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[0013] The catalyst of the present invention has the general stoichiometric formula
IrxPdyMz, wherein the indium concentration is from about 0.001 wt% to about 1.5 wt% and
the palladium concentration is from about 0.005 wt% to about 0.5 wt% and the promoter
concentration is up to about 0.5 wt%. In an exemplary embodiment, without limitation, the
catalyst comprises indium at a concentration of from about 0.01 wt% to about 0.06 wt% and
palladium at a concentration of from about 0.01 wt% to about 0.06 wt% and the promoter at a
concentration of up to about 0.2 wt%. Palladium catalysts are generally known in the art as
effective hydrogenation catalysts. However, indium appears to be a key component for
achieving long-term stability and for suppressing deactivation. As is further known in the art,
a promoter ("M") may be added to a catalyst to reduce deactivation and to reduce green-oil
formation. In the present development, the promoter is selected from the group consisting of
silver, gold, copper, zinc, tin and combinations thereof.
[0014] The catalyst may be prepared by any procedure known in the art. In an exemplary
embodiment, aqueous solutions of metal chlorides are used as precursors for all metals,
except for Ag for which AgNO3 can be used, and the metals are deposited by either excess
solution impregnation or incipient wetness impregnation techniques. The catalysts are then
dried and calcined. In a preferred embodiment, the catalyst is prepared such that the
palladium is located within the first 250 micrometers of the surface of the catalyst carrier.
Such methods are taught in U.S. Patents 4,484,015 and 4,404,124, both of which are
incorporated in their entirety by reference.
[0015] The catalyst is intended for use in hydrogenation reactions, and may further be
useful in oxidation reactions. For example, the catalyst may be useful for the hydrogenation
of acetylenes, including substituted acetylenes such as, without limitation, methyl acetylenes
or methyl acetylenes / propadienes (MAPD). Alternatively, the catalyst may be used for
oxidation reactions, such as, without limitation, the oxidation of vinyl acetate.
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[0016] The catalyst of the present invention differs from catalysts of the prior art by
including iridium with palladium and a promoter, thereby producing a more stable catalyst
than catalysts of the prior art. It is understood that the catalyst of the present invention may
be prepared by other methods than disclosed herein and may be supported on carriers other
than those specified herein without exceeding the scope of this development.
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What is claimed is:
1. A catalyst for the selective hydrogenation of acetylene comprising iridium
("Ir") and palladium ("Pd") and a promoter ("M") on an inorganic carrier, wherein said
promoter is selected from the group consisting of silver, gold, copper, zinc, tin and
combinations thereof, and wherein said inorganic carrier is selected from the group consisting
of alumina, silica, silica-alumina, activated carbon, ceria, zirconia, chromia-alumina, titania,
magnesium oxide, metal aluminates, calcium aluminate, magnesium aluminate, barium
hexaluminate, nickel aluminate and mixtures thereof.
2. The catalyst of Claim 1 wherein said iridium is present at a concentration of
from 0.001 wt% to 1.5 wt%.
3. The catalyst of Claim 2 wherein said iridium is present at a concentration of
from 0.01 wt% to 0.06 wt%.
4. The catalyst of Claim 1 wherein said palladium is present at a concentration of
from 0.005 wt% to 0.5 wt%.
5. The catalyst of Claim 4 wherein said palladium is present at a concentration of
0.01 wt% to 0.06 wt%.
6. The catalyst of Claim 1 wherein said promoter is present at a concentration of
up to0.5wt%.
7. The catalyst of Claim 6 wherein said promoter is present at a concentration of
up to 0.2 wt%.
8. The catalyst of Claim 1 wherein said carrier is an alumina having a surface
area of from 30 m2/g to 50 m2/g.
9. The catalyst of Claim 1 wherein said carrier is alpha-alumina.
10. A catalyst for the selective hydrogenation of acetylene comprising an
inorganic carrier and from 0.001 wt% to 1.5 wt% iridium ("Ir") and from 0.005 wt% to 0.5
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wt% palladium ("Pd") and up to 0.5 wt% of a promoter ("M"), wherein said promoter is
selected from the group consisting of silver, gold, copper, zinc, tin and combinations thereof.
11. The catalyst of Claim 10 wherein said carrier is selected from the group
consisting of alumina, silica, silica-alumina, activated carbon, ceria, zirconia, chromia-
alumina, titania, magnesium oxide, metal aluminates, calcium aluminate, magnesium
aluminate, barium hexaluminate, nickel aluminate and mixtures thereof.
12. The catalyst of Claim 11 wherein said carrier is an alumina having a surface
area of from 30 m2/g to 50 m2/g.
13. The catalyst of Claim 11 wherein said carrier is alpha-alumina.
14. The catalyst of Claim 10 wherein said indium, said palladium and said
promoters are deposited by excess solution impregnation techniques.
15. The catalyst of Claim 10 wherein said indium, said palladium and said
promoters are deposited by incipient wetness impregnation techniques.
16. The catalyst Claim 10 wherein said iridium is present at a concentration of
from 0.01 wt% to 0.06 wt%, and said palladium is present at a concentration of 0.01 wt% to
0.06 wt%.
17. A catalyst for the selective hydrogenation of acetylene comprising iridium
("Ir") and palladium ("Pd") on an inorganic carrier, and wherein said palladium is located
within the first 250 micrometers of the surface of the catalyst carrier.
18. The catalyst of Claim 17 wherein said catalyst comprises said iridium at a
concentration of from 0.001 wt% to 1.5 wt%, and said catalyst comprises said palladium at a
concentration of from 0.005 wt% to 0.5 wt%.
19. The catalyst of Claim 17 further comprising up to 0.5 wt% of a promoter
("M") selected from the group consisting of silver, gold, copper, zinc, tin and combinations
thereof.
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20. The catalyst of Claim 19 wherein said catalyst comprises said indium at a
concentration of from 0.01 wt% to 0.06 wt%, and said catalyst comprises said palladium at a
concentration of from 0.01 wt% to 0.06 wt%, and said catalyst comprises said promoter at a
concentration of up to 0.2 wt%.
21. The catalyst of Claim 17 wherein said carrier is selected from the group
consisting of alumina, silica, silica-alumina, activated carbon, ceria, zirconia, chromia-
alumina, titania, magnesium oxide, metal aluminates, calcium aluminate, magnesium
aluminate, barium hexaluminate, nickel aluminate and mixtures thereof.
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The present development relates to a catalyst composition for the selective hydrogenation of acetylene and to a
method for preparing the catalyst. The catalyst comprises iridium, palladium and, optionally, at least one of the elements selected
from the group consisting of silver, gold, copper, zinc and tin. In a preferred embodiment, the catalyst is prepared such that the
palladium is located within the first 250 micrometers of the surface of the catalyst carrier. In contrast to the catalysts of the prior art,
including for example, palladium / silver catalysts, the catalyst of the present invention exhibits high selectivity and an improved
stability of the catalytic performance over an extended period of time.