SELECTIVE HYDROGENATION CATALYST DESIGNED
FOR RAW GAS FEED STREAMS
Background of Invention
Field of Invention
This invention relates to selective hydrogenation
catalysts, more particularly to improved, Group
IB-promoted palladium catalysts with high pore volume and
unique pore volume distribution. The catalysts are
designed for the selective hydrogenation of butadiene,
acetylenes, diolefins, and trace quantities of other such
highly unsaturated hydrocarbon impurities in an olefinic
feed stream, particularly in a raw gas feed stream
containing C3, C4, C5 and trace quantities of C6 and higher
hydrocarbons. This invention also relates to processes
of preparation of these catalysts.
Prior Art
The manufacture of unsaturated hydrocarbons usually
involves cracking various types of hydrocarbons. This
process often produces a crude product containing
hydrocarbon impurities that are more unsaturated than the
desired product. This is particularly a problem with raw
gas feed streams from cracking facilities containing C2,
C3, C4, C5, and trace quantities of C, and higher

hydrocarbons as well as hydrogen and methane. These raw
gas feeds can contain significant unsaturated hydrocarbon
impurities, such as 1, 3 butadiene, methyl acetylene,
propadiene, acetylene, isoprene, and trace quantities of
other such unsaturated hydrocarbon impurities.
These unsaturated hydrocarbon impurities are often
very difficult to remove completely by fractionation from
a hydrocarbon feed stream. Further, it is often
difficult, industrially, to hydrogenate these highly
unsaturated hydrocarbon impurities without significant
hydrogenation of the desired unsaturated hydrocarbons
also occurring.
Two general types of gas phase selective
hydrogenation processes for removing undesired, highly
unsaturated hydrocarbons are commonly used: "front-end"
hydrogenation and "tail-end" hydrogenation. "Front-end"
hydrogenation involves passing the crude gas from the
initial cracking step, often after removal of steam and
condensable organic material, over a hydrogenation
catalyst. The crude gas generally includes a relatively
large volume of hydrogen and a mixture of unsaturated
hydrocarbons. Among these products in raw gas feed
streams may be C2, C3, C4, and C5 and trace quantities of C6

and higher hydrocarbons and may be wet or dry.
Typically, the hydrogen gas concentration is greater than
the stoichiometric amount needed for complete
hydrogenation of the impurities that are present in the
crude gas. To minimize the risk of the excess hydrogen
gas hydrogenating ethylene in the feed stream, the
hydrogenation catalyst must be very selective. In
addition, the catalyst risks being damaged in front-end
reactions because hydrogenation of ethylene can lead to
thermal excursion, known as "run-away", whereby high
temperatures are experienced. Run-away can also result
in severe loss of ethylene.
In "tail-end" hydrogenation, the crude gas is
fractionated prior to hydrogenation resulting in
concentrated product streams. Hydrogen is then added to
these product streams, if necessary, such that a slight
excess of hydrogen is present over the quantity required
for complete hydrogenation of the impurities. In
tail-end systems there is a greater tendency for
deactivation of the catalyst, and consequently, periodic
regeneration of the catalyst is necessary. While the
quantity of hydrogen added can be adjusted to maintain

selectivity, formation of polymers is a major problem in
this process.
One catalyst that is preferred for selective
hydrogenation reactions contains palladium supported on' a
low surface area carrier, such as a low surface area
alumina. However, one' of the problems with supported
palladium catalysts is that under normal operating
conditions not only are the impurities hydrogenated, but
a substantial portion of the ethylene is also converted
to ethane. In addition, these palladium on alumina
catalysts often have relatively low stability over
extended periods of time due to the formation of large
quantities of oligomers on the catalyst surface. The
rate of oligimerization is especially high when butadiene
is present in the feedstream mixture. Further these
palladium catalysts may not perform at acceptable levels
when methyl acetylene, butadiene, isoprene, and other
highly unsaturated compounds are present. For these
reasons, these heavier compounds are normally removed by
distillation prior to contact of the feed mixture with
the catalyst.
Enhancers are often added to the palladium to
improve the catalyst's properties. Copper, silver, gold,

germanium, tin, lead, rhenium, gallium, indium, and
thallium have been proposed as enhancers or modifiers for
such palladium hydrogenation catalysts.
Acetylene hydrogenation catalysts for ethylene
purification comprising palladium with a silver additive
on a low surface area support material are disclosed in
U.S. Patent Nos. 4,404,124, 4,409,410, 4,484,015,
5,488,024, 5,489,565, 5,648,576, 6,054,409 and CN
1299858. Specifically, U.S. Patent No. 6,054,409
discloses a catalyst for selective gas phase
hydrogenation of acetylenic compounds containing two or
three carbon atoms to the corresponding ethylenic
compounds. The catalyst comprises palladium, at least
one metal from group IB, optionally at least one alkali
or alkaline-earth metal and alumina, in which at least
80% of the palladium and at least 80% of the element from
group IB are present at the periphery of the catalyst,
and wherein the IB metal/palladium ratio is 0.4 to 3 by
weight.
In addition, U.S. Patent No. 6,797,669 discloses a
catalyst for selective hydrogenation comprising palladium
and a group IB metal promoter on an inorganic oxide
support, wherein the active components are uniformly

distributed between the surface and a depth of more than
300 microns. The catalyst is particularly applicable for
feed streams containing C2 - C3 fractions, hydrogen and
CO.
In addition, U.S. Patent No. 5,648,576 discloses a
selective hydrogenation catalyst for acetylene compounds
comprising from about 0.01 to 0.5 weight percent of
palladium and from about 0.001 to 0.02 percent by weight
of silver. Eighty percent (80%) or more of the silver is
placed within a thin layer near the surface of the
carrier body.
Catalysts containing palladium and Group IB metals
(Cu, Ag, Au) on alumina used for the hydrogenation of
acetylenes and diolefins have also been suggested by G.B.
802,100 and U.S. Patent Nos. 2,802,889.
Selective hydrogenation catalysts of the prior art
comprising palladium with a silver additive often do not
exhibit the necessary selectivity and frequently cause
significant loss of valuable olefins from the feed
stream. This loss is especially a problem with prior art
selective hydrogenation catalysts used in raw gas feed
streams comprising hydrogen, methane, carbon monoxide and

C4, C5, C6 and higher hydrocarbons, which may be wet or
dry.
Accordingly, it is an object of this invention to
disclose a catalyst useful for selective hydrogenation of
a C2, C3, C4 , C5, C6 and higher olefinic feed stream
containing various acetylenic and diolefinic impurities.
It is a still further object of the invention to
disclose a selective hydrogenation catalyst containing
palladium supported on an inorganic support with a Group
IB additive having a high pore volume and a unique pore
volume distribution.
These and other objects can be obtained by the
selective hydrogenation catalyst and the process for the
preparation of the selective hydrogenation catalyst for
use in olefinic feed stream containing acetylenic and
diolefinic impurities, particularly raw gas feed streams
and particularly for front end selective hydrogenation
reactions, which are disclosed by the present invention.
Summary of the Invention
The present invention is a catalyst for the
selective hydrogenation of various highly unsaturated
hydrocarbon impurities contained in an olefin-containing

hydrocarbon feed. The catalyst comprises from 0.01 to
0.1 weight percent palladium and from 0.005 to 0.6 weight
percent Group IB metal, preferably silver, wherein the
ratio of the Group IB metal:palladium is from 0.5:1 to
6:1, incorporated into an inorganic support, wherein the
surface area of the support is from 2-20 m/g, wherein
the pore volume of the support is greater than 0.4 cc/g,
wherein at least 90%, preferably at least 95% of the pore
volume is contained in pores with pore diameters larger
than 500 A, and wherein the pore volume of the pores with
a pore diameter from 500 to 1,000 A comprise from 1 to 2%
of the total pore volume.
The present invention is also a process for the
production of a catalyst for the selective hydrogenation
of acetylenic and diolfinic impurities in a feed stream
containing these impurities comprising preparing a
carrier material in a suitable shape, wherein the surface
area of the carrier material is from 2 to 20 m2/g, wherein
the' pore volume of the carrier is at least 0.4 cc/g,
wherein at least 90% of the pore volume is contained in
pores with pore diameters larger than 500 A, and wherein
the pore volume of pores with pore diameters from 500 to
1,000 A is from 1 to 2% of the total pore volume and

impregnating the carrier with a palladium compound,
wherein the quantity of the palladium compound present in
the catalyst after reduction comprises from 0.01 to 0.1
weight percent. Preferably at least 90 percent of the
palladium is located within 250 microns of the surface of
the catalyst. The process further comprises impregnating
the palladium impregnated carrier with a Group IB metal
additive, preferably silver, wherein the amount of the
Group IB" metal additive present in the catalyst, after
reduction, comprises from 0.005 to 0.6 weight percent of
the catalyst, wherein the ratio of the Group IB metal to
the palladium is from 0.5:1 to 6:1.
The invention further comprises a process for the
selective hydrogenation of acetylenic and diolefinic
impurities, preferably in a raw gas feed stream without
separation of individual components, preferably at low
temperatures, comprising passing a raw gas feed stream,
which contains acetylenic and diolefinic impurities, over
the catalysts described above.
Detailed Description
The invention is a catalyst for the selective
hydrogenation of various impurities, such as acetylenes

and diolefins, present in an olefin-containing
hydrocarbon raw gas feed. The invention further
comprises a process for the production of catalysts that
are useful for the selective hydrogenation of these
impurities, such as acetylenes and diolefins, which are
contained in a feed stream, preferably a raw gas feed
stream.
The catalyst carrier may be any low surface area
catalyst carrier, such as alumina, silica-alumina, zinc
oxide, nickel spinel, titania, zirconia, ceria,
chromia-alumina, magnesium oxide, cerium oxide and
mixtures thereof. The preferred carrier is a low surface
area alumina carrier. To qualify as a "low surface area"
carrier, the carrier has a surface area less than 20 m2/g,
preferably from 2 to 20 m2/g, more preferably from 2 to 10
mVg, and most preferably from 3-5 m2/g, as measured
using the nitrogen method of determining surface area.
The pore volume of the carrier is preferably greater than
0.4 cc/g, more preferably greater than 0.45 cc/g, and
most preferably greater than 0.5 cc/g. In addition, the
carrier is selected such that at least 90%, preferably at
least 95%, and most preferably at least 98% of the pore
volume is contained in pores with pore diameters greater

than 500 A, wherein the pore volume of pores with pore
diameters from 500 to 1,000 A is from 1 to 2% of the
total pore volume. It is important that carrier which is
selected contain this specific pore volume and pore
volume distribution to produce catalysts with enhanced
performance, particularly enhanced selectivity and
minimal loss of desired hydrocarbons, especially for
selective hydrogenation reactions.
The catalyst carrier can be formed in any suitable
shape, such as a sphere, cylinder, trilob, tablet and the
like. In one preferred embodiment the catalyst carrier
is formed as a sphere. The catalyst carrier can also be
formed in any suitable size, preferably a sphere with a
diameter from 1 to 5 mm, and more preferably from 1-3
mm.
The palladium can be introduced into the catalyst
carrier by any conventional procedure which produces the
proper palladium loading. One preferred technique
involves impregnating the catalyst carrier with an
aqueous solution of a palladium compound, such as
palladium chloride. Preferably, the depth of penetration
of the palladium compound into the carrier is controlled
so that at least 90 percent of the palladium compound is

contained within 250 microns of the surface of the
catalyst carrier. Any suitable method can be used to
control the depth of palladium penetration, such as is
disclosed in U.S. Patent Nos. 4,484,015 and. 4,404,124,
which patents are incorporated herein by reference.
After palladium impregnation, the impregnated
material is calcined at a temperature from 100'C to
600"C, preferably for three hours or so. The palladium
compound contained in the palladium catalyst precursor is
then reduced, preferably by wet reducing, using a
suitable wet reducing medium such as sodium formate,
formic acid, hydrazine, alkali metal borohydrides,
formaldehyde, ascorbic acid, dextrose and other
conventional wet reducing agents.
Once the precursor catalyst material has been
reduced, it is washed with deionized water to remove any
halides, such as chlorides, to a level of less than about
100 ppm. The reduced catalyst composition is then dried
at 100 oC to 600°C for a sufficient period of time.
The palladium impregnated precursor catalyst is then
further impregnated with one or more Group IB metal
compounds, such as Ag, Cu and Au, as an additive or
additives. These compounds are preferably selected from

silver salts, gold salts and/or copper salts or mixtures
thereof. Preferably, the metal additive is silver
impregnated in the form of a silver salt. The Group IB
additive can be impregnated in the palladium impregnated
precursor catalyst by any conventional process, such as
by soaking or spraying the palladium impregnated
precursor catalyst with an aqueous solution of the Group
IB metal compound. For example, if the Group IB metal is
silver, in one preferred embodiment the aqueous solution
is a silver nitrate solution. After impregnation, the
palladium impregnated catalyst material with the Group IB
metal additive is then calcined at a., temperature from 100
to 600°C for three hours or so. The catalyst is then
reduced, preferably by heat treating with hydrogen for 1
hour or so at 80 - 120°C.
The amount of palladium present on the catalyst is
from 0.01 to 0.1 weight percent, preferably 0.01 to 0.05
weight percent and most preferably from 0.01 to 0.03
weight percent, based on the total weight of the
catalyst. The amount of the Group IB metal additive,
preferably silver, that may be added is from 0.005 to 0.6
weight percent, preferably 0.01 to 0.3 weight percent,
and most preferably from 0.01 to 0.12 weight percent

based on the total weight of the catalyst. The ratio of
the Group IB additive present on the catalyst to the
palladium is from 0.5:1 to 6:1, preferably 1:1 to 6:1 and
most preferably from 1:1 to 4:1.
Following final drying, the palladium catalyst with
Group IB metal additive is ready for use in a selective
hydrogenation reactor, for example for the selective
hydrogenation of impurities, such as butadiene,
acetylenes and diolefins, particularly in a raw gas feed
stream, without separation of individual components.
The palladium catalyst with a Group IB additive of
the invention is designed primarily for the selective
hydrogenation of impurities, such as acetylenes and
diolefins, in admixture with other hydrocarbons, H2 and
CO, particularly in a raw gas feed stream. When the
process is front end selective hydrogenation of a raw gas
feed stream, the feed stream without separation normally
includes substantial quantities of hydrogen, methane, C2,
C3, C1, C5 and trace quantities of higher hydrocarbons,
small quantities of carbon monoxide and carbon dioxide,
as well as various impurities, such as 1, 3 butadiene,
acetylenes and diolefins, and may be wet or dry. The
goal of the selective hydrogenation reaction is to reduce

substantially the amount of the impurities present in the
feed stream without substantially reducing the amount of
desired hydrocarbons that are present.
In use, the palladium catalyst with Group IB metal
additive is placed in a reactor. The inlet temperature
of the feed stream in the reactor is raised to a level
sufficient to hydrogenate the acetylene. Any suitable
reaction pressure can be used. Generally, the total
pressure is in the range of 600 to 6750 kPa with the gas
hourly space velocity (GHSV) in the range of 1000 to
14000 liters per liter of catalyst per hour.
The catalyst of the invention can be used for gas
phase, liquid phase or combination gas and liquid phase
applications. Regeneration of the catalyst may be
accomplished by heating the catalyst in air at a
temperature, preferably not in excess of 500oC, to burn
off any organic material, polymers or char.
The subject catalyst exhibits improved hydrogenation
of impurities, such as methyl acetylene, butadiene, and
isoprene, in comparison to prior art catalysts. The
presence of these higher acetylenes and diolefins
improves the recovery of ethylene. The improved
performance characteristics may not be obvious from the

performance testing in the absence of impurities, such as
methyl acetylene, propadiene, butadiene, isoprene and the
like.
EXAMPLES
Example 1 (Comparative)
A commercially available catalyst manufactured by
Stid-Chemie Inc. under the product name of G-83C is
obtained. Analysis shows that the catalyst contains
0.018 weight percent of palladium and 0.07 weight percent
of silver on an alumina carrier. The carrier for the
catalyst has a BET surface area of 4.3 m2/g. The carrier
has a total pore volume of 0.295 cc/g and a pore volume
distribution in A as follows:

Example 2
Specially selected alumina spheres with a BET
surface area of 3.5 m2/g using the nitrogen method are

selected as the carrier for the catalyst of the
invention. The carrier material selected has a total
pore volume of 0.519 cc/g and a pore volume distribution
in A as follows: -
Pore diameter in A Percentage
35.6 to 100 0.00%
100.0 - 300.0 0.10%
300.0 - 500.0 0.27%
500.0 - 1000.0 1.71%
Above 1000.0 97.93 %
Catalyst spheres are prepared by dipping 25 grams of the
specially selected alumina carrier spheres in a palladium
chloride solution of sufficient concentration to yield a
palladium loading of 0.018 weight percent with a
palladium depth of penetration controlled to wherein at
least 90 percent of the palladium is within 250 microns
of the surface of the spheres. After palladium
impregnation, the catalyst is calcined at 250°C for 3
hours. The catalyst is then wet reduced in a 5 percent
aqueous sodium formate solution heated to a temperature
of 170° F (76°C) for about one hour. The catalyst is

then washed free of chlorides (less than 100 ppm) with
deionized water at 160'F (71oC). The catalyst is then
dried at 250°F (121oC) for about 18 hours. The palladium
containing precursor catalyst is then impregnated with
silver by dipping the catalyst spheres in a silver
nitrate solution of sufficient concentration to yield a
silver loading of 0.05 weight percent. The catalyst is
then calcined at 454°C for three hours.
Performance Testing, part 1:
Table 1, which follows, provides a comparison of the
performance of Comparative Example 1 with Example 2 of
the invention. The Examples are compared by passing a
feed stream comprising 1448 ppm C2H2, 79 ppm C2H6, 18.3%
H2, 295 ppm CO, 35% CH4 and 45% C2H4 over the catalysts.
The catalysts are evaluated in a bench scale laboratory,
three-quarter inch i.d. reactor tube, with a laboratory
prepared, simulated front-end feed stock.
For each catalyst, the inlet temperature is varied
and the conversion and selectivity of the catalyst are
recorded. See the following Table:


In the above-referenced comparison, the catalyst
activity is evaluated over a temperature range from 45oC
to 51oC. The percentage represents the percentage of
acetylene that is converted into ethylene. As the
reactor inlet temperature increases, the hydrogenation
reaction becomes more active with a greater amount of C2H2
being hydrogenated and hence, removed from the product
stream. However, some hydrogenation of C2H4 also occurs
indicating a loss of selectivity for the reaction.
"Selectivity" of each catalyst is reported as a
percentage and is determined by the following
calculation: 100 times ((inlet C2H2 - outlet C2H2) minus
(C2H6 outlet minus C2H6 inlet))/(C2H2 inlet minus C2H2
outlet). Higher positive percentages indicate a more

selective- catalyst. Data is obtained at a moderate GHSV
(7000).
Comparisons of the conversion and the selectivity
for the prior art Catalyst of Comparative Example 1 to
the inventive catalyst of Example 2 demonstrate the
enhanced performance of the. catalysts of the invention.
Selectivity is significantly improved relative to the
prior art catalysts. Further, the catalysts of the
invention demonstrate a broader and lower temperature
range over which the catalysts are active for
hydrogenation than prior art catalysts.
The principles, preferred embodiments, and modes of
operation of the present invention have been described in
the foregoing specification. The invention, which is
intended to be protected herein, however, is not to be
construed or limited to the particular terms of
disclosure, as these are to be regarded as being
illustrative, rather than restrictive. Variations and
changes may be made by those skilled in the art.

WE CLAIM:
1. A catalyst for selective hydrogenation of acetylene comprising
a low surface area carrier, with a surface area lower than 20 m2/g,
preferably from 2 m2/g to 20 m2/g, more preferably 2 m2/g to 10 m2/g,
and most preferably 3 m2/g to 5 m2/g;
palladium; and
a Group IB metal, preferably silver,
wherein the pore volume of the carrier is greater than 0.4 cc/g,
preferably greater than 0.45 cc/g and more preferably greater than 0.5
cc/g, wherein at least 90 percent, preferably at least 95%, and most
preferably at least 98%, of the pore volume of the pores is contained in
pores with pore diameters greater than 500 A, and wherein from 1 to 2
percent of the pore volume is contained in pores with a pore diameter
from 500 to 1,000 A, and the palladium comprises from 0.01 to 0.1
weight percent of the catalyst and Group IB metal comprises from 0.005
to 0.6 weight percent of the catalyst.
2. The catalyst as claimed in Claim 1 wherein the palladium comprises
preferably 0.01 to 0.05 weight percent, and most preferably 0.01 to 0.03
weight percent, of the catalyst, and wherein the Group IB metal
comprises from preferably 0.01 to 0.3 percent, and most preferably from
0.01 to 0.12 percent, of the catalyst, and wherein the ratio of the Group
IB metal to the palladium is from 0.5:1 to 6:1, preferably 1:1 to 6:1, and
most preferably 1:1 to 4:1.
3. The catalyst as claimed in Claims 1-2 wherein the depth of penetration
of the palladium into the carrier is such that at least 90 percent of the
palladium is located within 250 microns of the surface of the catalyst

material, wherein the weight percentages are based on the total weight of
the catalyst.
4. The catalyst as claimed in any of Claims 1-3 wherein the composition
of the carrier is selected from the group consisting of alumina, silica-
alumina, zinc oxide, nickel spinel, titania, zirconia, ceria, chromia-
alumina, magnesium oxide, cerium oxide and mixtures thereof,.
preferably alumina.
5. The catalyst as claimed in any of Claims 1-4 formed in a shape
selected from the group consisting of a sphere, trihole, monolith, pellet
and tablet, preferably a sphere with a diameter from 1 millimeter to 5
millimeters, preferably from 1 millimeter to 3 millimeters.
6. A method for the manufacture of a catalyst for the selective
hydrogenation of acetylene comprising
preparing a low surface area carrier, with a surface area lower than 20
m2/g, preferably from 2 m2/g to 20 m2/g, more preferably from 2 m2/g to
10 m2/g, and most preferably from 3 m2/g to 5 m2/g, wherein the pore
volume of the carrier is greater than 0.4 cc/g, preferably greater than 0.5
cc/g, wherein at least 90 percent, preferably at least 95 percent, and
most preferably at least 98 percent, of the pore volume of the pores is
contained in pores having a pore diameter greater than 500A and from 1
to 2 percent of the pore volume is contained in pores having a pore
diameter of the pores are from 500 to 1,000 A,
impregnating the carrier with a palladium metal source,
reducing the palladium,
washing and drying the reduced palladium catalyst material,

impregnating the catalyst material with a Group IB metal additive
source, preferably a silver additive source,
reducing the Group IB metal additive source, and
washing and drying the reduced catalyst to produce the catalyst.
7. The method as claimed in Claim 6 wherein the palladium metal source
comprises from 0.01 to 0.1 weight percent of the catalyst, preferably 0.01
to 0.05 weight percent, and most preferably from 0.01 to 0.03 weight
percent, and wherein the concentration of the Group IB metal additive in
the catalyst is from 0.005 to 0.6 weight percent, preferably 0.01 to 0.3
weight percent, and most preferably from 0.01 to 0.12 weight percent,
and the ratio of the Group IB metal to the palladium is from 0.5:1 to 6:1,
preferably 1:1 to 6:1, and most preferably 1:1 to 4:1.
8. The method as claimed in Claims 6-7 wherein the depth of penetration
of the palladium into the catalyst support wherein 90 percent of the
palladium is within 250 microns of the surface of the catalyst material.
9. A process for selective hydrogenation of acetylenes and diolefins
comprising passing a row gas feed stream over the catalyst as claimed in
any of Claims 1-5 or catalysts produced by the process of Claims 6-8.

ABSTRACT
TITLE:A CATALYST FOR SELECTIVE HYDROGENATION
OF ACETYLENE
This invention relates to a catalyst for selective hydrogenation of
acetylene comprising a low surface area carrier, with a surface area lower
than 20 m2/g, preferably from 2 m2/g to 20 m2/g, more preferably 2
m2/g to 10 m2/g, and most preferably 3 m2/g to 5 m2/g; palladium; and
a Group IB metal, preferably silver, wherein the pore volume of the
carrier is greater than 0.4 cc/g, preferably greater than 0.45 cc/g and
more preferably greater than 0.5 cc/g, wherein at least 90 percent,
preferably at least 95%, and most preferably at least 98%, of the pore
volume of the pores is contained in pores with pore diameters greater
than 500 A, and wherein from 1 to 2 percent of the pore volume is
contained in pores with a pore diameter from 500 to 1,000 A, and the
palladium comprises from 0.01 to 0.1 weight percent of the catalyst and
Group IB metal comprises from 0.005 to 0.6 weight percent of the
catalyst.