Hydrogenation process and catalyst therefor

A supported catalyst composition, which is effective as a diolefin hydrogenation catalyst, comprises palladium, silver and alkali metal fluoride. This catalyst composition is employed in the selective hydrogenation of C.sub.4 -C.sub.10 diolefins (preferably 1,3-butadiene) with hydrogen gas to the corresponding monoolefins.

BACKGROUND OF THE INVENTION 
In one aspect, this invention relates to a supported noble metal catalyst 
composition. In another aspect, this invention relates to a selective 
diolefin (diene) hydrogenation process employing a supported noble metal 
catalyst composition. In still a further aspect, this invention relates to 
a process for the selective hydrogenation of 1,3-butadiene to butenes 
employing a supported noble metal catalyst composition. 
Catalysts comprising palladium, silver and a support material are known 
diene hydrogenation catalysts. For instance, U.S. Pat. No. 4,409,410 
discloses the use of a Pd/Ag/Al.sub.2 O.sub.3 catalyst for the selective 
hydrogenation of butadiene to butenes. Even though supported Pd/Ag 
catalysts are effective hydrogenation catalysts, there is an ever present 
need for further improvements (e.g., for enhanced selectivity to 
monoolefins and/or increased catalyst life.). The present invention is 
directed to an improved, modified catalyst compositions and its use in 
processes for the selective hydrogenation of diolefins to monoolefins, 
preferably of 1,3-butadiene to butenes. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved 
palladium/silver-containing catalyst composition. It is another object of 
this invention to employ this improved catalyst composition in the 
selective hydrogenation of diolefins to monoolefins. It is a further 
object of this invention to employ this improved catalyst composition in 
the selective hydrogenation of 1,3-butadiene to butenes. Other objects and 
advantages will be apparent from the detailed description and the appended 
claims. 
In accordance with this invention, a catalyst composition is provided which 
comprises (a) at least one palladium-containing material selected from the 
group consisting of palladium metal and palladium compounds, (b) at least 
one silver-containing material selected from the group consisting of 
silver metal and silver compounds, (c) at least one alkali metal fluoride, 
and (d) at least one inorganic support material. In a preferred 
embodiment, the inorganic support is alumina and the alkali metal fluoride 
is potassium fluoride. 
Also in accordance with this invention, an improved process for selectively 
hydrogenating C.sub.4 -C.sub.10 diolefins with hydrogen gas to the 
corresponding C.sub.4 -C.sub.10 monoolefins is carried out with the 
catalyst composition of this invention. In a preferred embodiment, 
1,3-butadiene (more preferably present in small amounts in 
butene-containing gas streams) is selectively hydrogenated with hydrogen 
gas to at least one butene in the presence of the catalyst composition of 
this invention. 
DETAILED DESCRIPTION OF THE INVENTION 
The composition of matter of this invention comprises (preferably consists 
essentially of) (a) palladium metal and/or at least one palladium compound 
(preferably palladium oxide), (b) silver metal and/or at least one silver 
compound (preferably silver oxide), (c) at least one alkali metal fluoride 
(preferably potassium fluoride), and (d) an inorganic support material 
selected from the group consisting of alumina, silica, titania, zirconia, 
aluminosilicates, zinc aluminate, zinc titanate, and mixtures of two or 
more than two of these compounds, preferably alumina, more preferably 
alpha-alumina. Generally, the catalyst composition comprises 0.01-2 
(preferably about 0.05-0.6) weight-% Pd, about 0.02-10 (preferably about 
0.1-5) weight-% Ag, and about 0.05-10 weight-% (preferably about 0.2-5) 
weight-% alkali metal (preferably K). The catalyst particles can have any 
suitable shape (spherical, cylindrical, trilobal and the like), and are 
preferably either spheres or cyclindrical extrudates. The catalyst 
particles can have any suitable particle size, and generally have a size 
of about 1-10 mm (preferably about 2-6 mm). The catalyst particles can 
have any suitable surface area (measured by the BET method by Bruhauer, 
Emmett and Teller employing N.sub.2), and generally have a surface area of 
about 1-200 (preferably about 10- 100) m.sup.2 /g. 
The catalyst particles can be prepared by any suitable means. The promoter 
components (a), (b) and (c) can be deposited onto and/or incorporated into 
the inorganic support material by any suitable means and in any suitable 
order. For instance, the alkali metal fluoride can be incorporated into 
the support material, followed by impregnation of the fluoride-containing 
support material with Pd and Ag compounds (such as H.sub.2 PdCl.sub.4 and 
AgNO.sub.3), sequentially in any order or simultaneously, followed by 
drying and calcining of the thus-impregnated composition. Or a supported 
palladium catalyst composition (preferably a Pd/Al.sub.2 O.sub.3 
composition which is commercially available, e.g., from Mallinckrodt 
Specialty Chemicals Company, Erie, Pa.) can be impregnated with a silver 
compound and an alkali metal fluoride, either sequentially in any order or 
simultaneously, followed by drying and calcining of the thus-impregnated 
composition. Mainly for economic reasons, it is presently not preferred to 
prepare the catalyst composition by a method which includes an additional 
low-temperature wet-reduction step (i.e., treatment with a reducing agent 
dissolved or dispersed in a liquid medium, at a temperature of up to about 
60.degree. C.). Preferably, the catalyst composition of this invention is 
prepared by incorporating alkali metal fluoride into a supported 
Pd/Ag-containing base catalyst, as described below. 
The preferred starting material (also referred to as "base catalyst") which 
is to be improved in accordance with this invention by incorporation of 
alkali metal fluoride therein, can be any supported palladium- and 
silver-containing composition. The base catalyst composition can be a 
fresh butadiene hydrogenation catalyst; or it can be a used and thereafter 
oxidatively regenerated butadiene hydrogenation catalyst composition; or 
it can be a butadiene hydrogenation catalyst composition which has 
previously been treated with a wet-reducing agent (such as dissolved 
formaldehyde, formic acid, ascorbic acid, dextrose, hydrazine, alkali 
metal borohydride and the like), at a low temperature of up to about 
60.degree. C. (preferably about 10.degree.-50.degree. C.), as has been 
described in Example I. Broadly, the base catalyst can contain about 
0.01-2 (preferably about 0.05-0.6) weight-% Pd, about 0.02-10 (preferably 
about 0.1-5) weight-% Ag and a suitable solid inorganic support material, 
preferably alumina (more preferably alpha-alumina). Preferably, the Ag:Pd 
weight ratio in the catalyst is about 1:1 to about 20:1, more preferably 
about 2:1 to about 10.1. The supported Pd/Ag base catalyst particles can 
have any suitable shape, and preferably are spherical pellets or 
cylindrical extrudates. The size of these supported Pd/Ag base catalyst 
particles generally is about 1-10 mm, preferably about 2-6 mm, and its 
surface generally is about 1-200 m.sup.2 /g. 
In the preferred method of preparing the catalyst composition of this 
invention, a Pd/Ag-containing base catalyst (described above) is contacted 
with a solution (preferably aqueous) of at least one alkali metal fluoride 
(preferably KF) at such conditions as to incorporate about 0.05-10 
(preferably about 0.2-5) weight-% of alkali metal (preferably potassium) 
into the catalyst composition. Generally, the concentration of the alkali 
metal fluoride in the contacting (impregnating) solution is about 0.1-10 
mol/l (preferably about 0.2-3 mol/l). The preferred contacting method is 
"incipient wetness impregnation", i.e. essentially completely filling the 
pores of the base catalyst with the alkali metal fluoride solution. 
Generally, the weight ratio of the solution to the solid base catalyst 
composition is in the range of about 0.2:1 to about 2:1, preferably about 
0.4:1 to about 1:1 (depending on the fluoride concentration of the 
impregnating solution and the desired alkali metal fluoride level in the 
catalyst composition of this invention). Thereafter, the catalyst 
composition is substantially dried (preferably at about 
50.degree.-150.degree. C. for about 0.5-20 hours) and calcined (preferably 
in an oxidizing gas atmosphere, more preferably air) at a temperature of 
about 300.degree.-600.degree. C. (preferably about 300.degree.-500.degree. 
C.) for about 0.2-20 hours (preferably about 1-8 hours). 
The catalyst composition of this invention is preferably employed in the 
selective hydrogenation of diolefins containing 4-10 carbon atoms per 
molecule to the corresponding monoolefins containing 4-10 carbon atoms per 
molecule, particularly of 1,3-butadiene to primarily butenes (butene-1, 
butene-2). The calcined catalyst composition of this invention can be 
employed directly in this selective hydrogenation process. However, it is 
preferred to first treat the catalyst with a reducing gas such as 
hydrogen, because the optimum operation of the selective hydrogenation 
does not begin until there has been a substantial reduction of the 
catalytic metals. Typically, the reduction is carried out at a temperature 
in the range of about 10.degree. C. to about 100.degree. C. for at least 
10 minutes (preferably about 1-10 hours). 
Non-limiting examples of suitable diolefins containing 4-10 carbon atoms 
per molecule which can be hydrogenated in the process of this invention 
include 1,2-butadiene, 1,3-butadiene, isoprene, 1,2-pentadiene, 
1,3-pentadiene, 1,2-hexadiene, 1,3-hexadiene, 1,4-hexadiene, 
1,5-hexadiene, 2-methyl-1,2-pentadiene, 2,3-dimethyl-1,3-butadiene, 
heptadienes, octadienes, nonadienes decadienes, cyclopentadiene, 
cyclohexadiene, methylcyclopentadienes, cycloheptadienes, 
methylcyclohexadienes dimethylcyclopentadienes, ethylcyclopentadienes, 
octadienes, methylheptadienes, dimethylhexadienes, ethylhexadienes, 
trimethylpentadienes, methyloctadienes, dimethylheptadienes, 
ethylheptadienes, trimethylheptadienes, and mixtures of one or two of 
these diolefins. Presently preferred are diolefins containing 4-6 carbon 
atoms per molecule. 
The diolefin-containing feed for the hydrogenation process of this 
invention can also contain other hydrocarbons, in particular, monoolefins. 
Non-limiting examples of such monooefins which can be present in the feed 
at a level of at least 30 volume-% include ethylene, propylene, 1-butene, 
2-butene, isobutylene, 1-pentene, 2-pentene, methyl-1-butenes (such as 
2-methyl-1-butene), methyl-2-butenes (such as 2-methyl-2-butene), 
1-hexene, 2-hexene, 3-hexene, methyl-1-pentenes, 2,3-dimethyl-1-butene, 
1-heptene, 2-heptene, 3-heptene, methyl-1-hexenes, methyl-2-hexenes, 
methyl-3-hexenes, dimethylpentenes, ethylpentenes, octenes, 
methylheptenes, dimethylhexenes, ethylhexenes, nonenes, methyloctenes, 
dimethylheptenes, ethylheptenes, trimethylhexenes, cyclopentene, 
cyclohexene, methylcyclopentenes, cycloheptene, methylcyclohexenes, 
dimethylcyclopentes, ethylcyclopentenes, cyclooctenes, 
methylcycloheptenes, dimethylcyclohexenes, ethylcyclohenenes, 
trimethylcyclohexenes, methylcyclooctenes, dimethylcyclooctenes, 
ethylcylcooctenes, and mixtures of two or more than two of these 
monolefins. Presently preferred are monolefins containing 4-6 carbon atoms 
per molecule. 
The fluid feed (which may be liquid or gaseous at the hydrogenating 
conditions of this process) generally contains about 0.01-70 mole-% of at 
least one diolefin, preferably about 0.01 to about 10 mole-% of at least 
one diolefin. Generally, the fluid feed comprises at least one diolefin 
and additionally at least one monoolefin, preferably about 30-99.9 mole-% 
of at least one monoolefin. However, it is within the scope of this 
invention to employ feeds which contain more than about 70 mole-% of at 
least one diolefin, or even to employ feeds which consist essentially of 
at least one diolefin. Also, the feed can contain small amounts (generally 
less than about 0.01 mole-%) of sulfur compounds (such as H.sub.2 S, 
mercaptans, organic sulfides) and/or carbon monoxide (also generally less 
than about 0.01 mole-%) as impurities. 
The selective hydrogenation process of this invention is generally carried 
out by contacting a feed stream containing at least one diolefin and 
molecular hydrogen with the catalyst (generally contained in a fixed bed). 
Generally, about 1-10 moles of hydrogen are employed for each mole of 
diolefin. The temperature necessary for the selective hydrogenation 
process of this invention depends largely upon the activity of the 
catalyst and the desired extent of diolefin hydrogenation. Generally, 
temperatures in the range of about 35.degree. C. to about 200.degree. C. 
are used. A suitable reaction pressure generally is in the range of about 
20 to 2,000 pounds per square inch gauge (psig). The liquid hourly space 
velocity (LHSV) of the hydrocarbon feed can vary over a wide range. 
Typically, the space velocity of the feed will be in the range of about 3 
to about 100 liters of hydrocarbon feed per liter of catalyst per hour, 
more preferably about 20 to about 80 liter/liter/hour. The hydrogenation 
process conditions should be such as to avoid significant hydrogenation of 
monoolefins (formed by hydrogenation of diolefins and/or being initially 
present in the feed) to paraffins. 
In the preferred embodiment of the selective hydrogenation process of this 
invention, a hydrocarbon feed stream containing 1,3-butadiene and 
molecular hydrogen are contacted with the catalyst (generally contained in 
a fixed bed). Frequently, the hydrocarbon feed contains butenes as the 
primary components (comprising in excess of about 50 weight-%) and 
1,3-butadiene as a minor component (present at a level of about 0.01 to 
about 10 weight-% butadiene). Preferably, this hydrogenation process 
employs about 1-2 moles H.sub.2 per mole 1,3-butadiene. The reaction 
temperature necessary for the selective hydrogenation of 1,3-butadiene 
depends largely upon the activity of the catalyst and the desired extent 
of the 1,3-butadiene hydrogenation, and generally is in the range of about 
35.degree. C. to about 100.degree. C. Any suitable reaction pressure can 
be employed. Generally, the total pressure is in the range of about 50 to 
1,000 pounds per square inch gauge (psig). The liquid hourly space 
velocity (LHSV) of the hydrocarbon feed can also vary over a wide range. 
Typically, the space velocity will be in the range of about 3 to about 100 
liters of hydrocarbon feed per liter of catalyst per hour, more preferably 
about 20 to about 80 liter/liter/hour. The hydrogenation process 
conditions should be such as to avoid significant hydrogenation of butenes 
to butane. 
Regeneration of the catalyst composition of this invention (after it has 
been employed in a diolefin hydrogenation process) can be accomplished by 
heating the catalyst in an oxidizing gas, preferably air, at a temperature 
preferably not in excess of 700.degree. C. (preferably at a temperature 
about 500.degree.-650.degree. C.) for a time period in the range of about 
10 minutes to about 20 hours, to burn off any deposited or adsorbed 
organic matter (e.g., polymeric substances) or char. The regenerated 
catalyst can be reemployed in the selective hydrogenation process of this 
invention, generally after reduction with hydrogen, as described above.

The following examples are presented to further illustrate this invention 
and should not be construed as unduly limiting the scope of this 
invention. 
EXAMPLE I 
This example illustrates the preparation of various palladium-containing 
catalysts and their use in the selective hydrogenation of 1,3-butadiene to 
butenes. 
Catalyst A1 (Control) was a Pd/Ag/Al.sub.2 O.sub.3 catalyst, which had been 
provided by the Calsicat Catalyst Division of Mallinckrodt Specialty 
Chemicals Company, Erie, Pa. This catalyst had a BET/N.sub.2 surface area 
of 35 m.sup.2 /g, a bulk density of 0.90 cc/g, and a particle size of 8-14 
mesh. It contained 0.28 weight-% Pd and 1.85 weight-% Ag. 
Catalyst A2 (Control) was prepared in a R&D laboratory of Phillips 
Petroleum Company, Bartlesville Okla. by the following procedure: 20.03 
grams of a Pd/Al.sub.2 O.sub.3 catalyst (1/16 inch spheres containing 
about 0.3 weight-% Pd, marketed by Calsicat under the product designation 
of "E-143 SDU") were soaked for about 1 hour in 22 cc of an aqueous 
solution containing 1.03 gram of AgNO.sub.3. Thereafter, excess solution 
was drained off, the soaked catalyst was dried at 190.degree. F. for 
several hours, and the dried catalyst was calcined in air at 370.degree. 
C. for 5 hours. This catalyst contained 0.35 weight-% Pd and 3.0 weight-% 
Ag. 
Catalyst B (Invention) was prepared by soaking 80.17 grams of Calsicat 
E-143SDU (described above) with an aqueous solution of 4.08 grams of 
AgNO.sub.3 in 72.3 grams of H.sub.2 O for about 1.5 hours. Excess liquid 
was drained from the Ag-impregnated catalyst, which was then dried at 
180.degree. F. for several days and calcined for 4.5 hours at 370.degree. 
C. in air. Then 20.07 g of this Pd/Ag/Al.sub.2 O.sub.3 catalyst material 
was soaked in 30 cc of a formaldehyde solution containing about 37 
weight-% of formaldehyde, about 17 weight-% of methanol, and about 46 
weight-% of water. About 0.5 g solid KOH was added to this mixture of 
catalyst and formaldehyde solution which was then stirred for 45 minutes. 
Thereafter, another aliquot of about 0.5 g solid KOH was added to this 
mixture. After soaking for 20 minutes, excess liquid was drained off, the 
catalyst was washed twice with methanol and then twice with distilled 
water (until the filtrate had a pH of about 7). This wet-reduced, 
catalyst, from which KOH had been removed by the above washing procedure, 
was dried overnight at 180.degree. F. The dried catalyst was then 
impregnated with a solution of 0.441 g KF in 14.15 g H.sub.2 O. A large 
portion of water was removed from the mixture by heating at 180.degree. F. 
(without prior draining of excess liquid). The obtained KF-impregnated 
Pd/Ag/Al.sub.2 O.sub.3 catalyst was then dried overnight at 132.degree. C. 
and calcined in air at 370.degree. C. for 3 hours. Catalyst B contained 
about 0.28 weight-% Pd, about 2.6 weight-% Ag and about 1.3 weight-% K. 
The above-described catalyst materials were tested in the selective 
hydrogenation of 1,3-butadiene by the following procedure. About 20 cc of 
each catalyst was placed into a stainless steel reactor tube having an 
inner diameter of 0.5 inch and a length of about 18 inches. Thermocouples 
were inserted into the top and bottom regions of the catalyst bed, which 
was heated by an external furnace. The hydrocarbon feed was liquid and 
contained about 5.1 mole-% 1,3-butadiene, about 16.4 mole-% cis-butene-2, 
about 27.4 mole-% trans-butene-2, about 44.1 mole-% butene-1, about 6.8 
mole-% n-butane, and about 0.1 weight-% C.sub.6 + hydrocarbons. Hydrogen 
gas was fed with the liquid hydrocarbon feed so as to provide a H.sub.2 
/butadiene mole ratio of about 1:1. The total pressure in the reactor was 
maintained at about 500 psig. The product gas was analyzed every 1-3 hours 
by means of a gas chromatograph. Pertinent process parameters and test 
results are summarized in Table I. 
TABLE I 
__________________________________________________________________________ 
Feed Rate of 
Feed Rate 
Average 
% 
Liquid of Hydrogen 
Reaction 
Conversion 
% % 
Hydrocarbons 
Gas Temp. 
of Selectivity 
Selectivity 
Catalyst 
(cc/minute) 
(cc/minute) 
(.degree.F.) 
Butadiene 
to Butenes 
to Butane 
__________________________________________________________________________ 
A-1 9 104 106 73.7 64.1 35.8 
(Control) 
9 104 104 76.2 67.9 32.2 
9 104 104 78.4 70.9 29.1 
9 104 107 77.6 71.2 29 
9 104 108 78.6 74.6 25.4 
9 104 106 78.5 74.4 25.8 
9 104 108 78.9 75.8 24.3 
18 217 111 84.7 82.7 17.2 
18 217 108 83.9 84.9 15.5 
18 217 107 84.7 85.6 14.7 
18 217 106 84.7 84.9 15.4 
18 217 108 84.1 86 14.4 
A2 18 218 84 73.1 72.2 27.3 
(Control) 
18 218 97 85.1 83.7 15.4 
18 218 97 84.6 83.9 15.2 
18 218 104 84.8 83.4 15.7 
18 218 122 76.0 54.6 46.0 
18 218 123 75.4 60.8 39.8 
18 218 138 74.5 60.1 40.5 
18 218 141 74.0 70.4 30.1 
B 9 104 130 89.0 90.4 9.7 
(Invention) 
9 104 122 90.4 91.7 8.4 
9 104 119 89.8 92.4 7.7 
9 104 117 88.6 92.5 7.5 
9 104 118 89.9 91.6 8.6 
9 104 100 88.6 93.5 6.6 
9 104 98 87.0 94.0 6.0 
9 104 99 87.1 94.0 6.1 
9 104 98 87.0 94.3 5.7 
9 104 107 88.9 92.1 7.8 
9 104 106 86.8 92.7 7.4 
9 104 89 85.2 93.7 6.5 
9 104 90 83.6 94.2 5.8 
9 104 88 82.4 94.1 5.7 
9 104 94 88.1 95.1 5.1 
9 104 90 85.2 95.0 5.1 
9 104 88 84.0 95.5 4.6 
9 104 91 84.5 95.4 4.7 
9 104 98 84.4 95.4 4.6 
9 104 100 85.2 95.0 5.1 
9 104 100 85.4 95.1 5.0 
__________________________________________________________________________ 
Test data in Table I clearly show that the promotion of a Pd/Ag/Al.sub.2 
O.sub.3 catalyst with KF (resulting in Catalyst B) had a consistent 
beneficial effect on attained 1,3-butadiene conversion and selectivity to 
butenes (combined yields of butene-1 and butene-2 divided by butadiene 
conversion) versus control catalysts A1 and A2 (Pd/Ag/Al.sub.2 O.sub.3 
which had not been treated with KF). These test data also show that during 
the invention test, which lasted about 24 hours, Catalyst B exhibited good 
catalytic stability, as evidenced by a rather small drop in butadiene 
conversion and actually a slight increase in selectivity to the desired 
butenes. Thus, the butene yield (conversion times selectivity to butenes) 
remained approximately constant. Additional test data (not described 
herein) showed that the promotion of control catalyst A1 (Pd/Ag/Al.sub.2 
O.sub.3) with another potassium compound, KOH, resulted in a catalyst 
which exhibited unsatisfactory stability in a lengthy butadiene 
hydrogenation test, as evidenced by a significant decrease in catalytic 
activity and by process control (especially temperature control) problems. 
EXAMPLE II 
This example further illustrates the use of another KF-treated 
Pd/Ag/Al.sub.2 O.sub.3 composition as a catalyst in the selective 
hydrogenation of 1,3-butadiene. 
Catalyst C (Invention) was prepared by soaking 20.15 g Catalyst A1 
(Pd/Ag/Al.sub.2 O.sub.3, disclosed in Example I) with an aqueous solution 
of 1.448 g of KF in 14.3 g of distilled water. The obtained material was 
dried at 180.degree. F. for several hours and calcined at 235.degree. C. 
for 1.5 hour. 
Catalyst C was tested as a catalyst in the selective hydrogenation of 
1,3-butadiene to butenes, substantially in accordance with the procedure 
described in Example I, except that the liquid hydrocarbon feed contained 
36.4 mole-% 1,3-butadiene, 13.1 mole-% trans-butene-2, 13.2 mole-% 
cis-butene-2, 30.2 mole-% butene-1, 7.2 mole-% n-butane, and 0.01 mole-% 
C.sub.6 + hydrocarbons. The total reactor pressure was about 500 psig. The 
feed rate of the liquid hydrocarbon feed ranged from about 1.5 cc/minute 
(during the first two days) to about 3.0 cc/minute (during the last day), 
and the feed rate of H.sub.2 gas ranged from about 140 cc/minute (during 
the first day) to about 320 cc/minute (during the last day). A portion of 
the product was recycled to the reactor so as to attain a 3-6:1 
recycle:feed volume ratio. The reaction temperature in the center of the 
catalyst bed was about 90.degree.-100.degree. F. during the entire test 
which lasted about 5 days. When the reaction had reached a steady state 
(after about 12 hours), the 1,3-butadiene content in the product ranged 
from about 6.0 mole-% to about 4.5 mole-% (during the last day), and the 
n-butane content in the product ranged from about 8.8 to about 8.2 mole-%. 
Thus, Catalyst C exhibited good catalytic activity and selectivity (to 
butenes). Furthermore, the fact that the catalyst performance did not 
deteriorate toward the end of the test (but actually improved in terms of 
feed conversion) indicates good stability of Catalyst C. 
Reasonable variations, modifications and adaptations for various usages and 
conditions can be made within the scope of the disclosure and the appended 
claims, without departing from the scope of this invention.