Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to the hydrogenation of
phenol and, more particularly, to the promotion of the
hydrogenation of phenol to cyclohexanone in the presence
of a promoted palladium catalyst.
In the hydrogenation of phenol employing a
palladium catalyst, the activity of the catalyst, and
hence the rate of hydrogenation, decreases with continued
use of the catalyst due to impurities present in the
hydrogenation reaction mixture which poison the catalyst.
While processes, such as those disclosed in U.S. Patents
3,692,845 and 3,187,050, have been developed to purify
organic compounds such as phenol to be hydrogenated,
the poisoning of metallic catalysts has not been en-tirely
eliminated in large scale commercial processes due to
long-term accumulation of impurities, such as those
impurities which are introduced with the phenol and
the hydrogen gas, and those impurities which are produced
during the processing.
To avoid the economically prohibitive alter-
natives of discarding poisoned catalyst or continuing
to use the poisoned catalyst at a reduced rate of
hydrogenation, it is desirable to promote the rate of
hydrogenation, thereby overcoming the disadvantages
of continued use of such poisoned palladium catalysts.
The hydrogenation of phenol to cyclohexanone has been
promoted by the use of "promoted palladium-on-carbon
catalysts", i.e., catalysts which have been treated
prior to their addition to the hydrogenation reaction
mixture, to incorporate on the catalysts a material which
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enhances their activity. Thus, in U.S. Patent
3,076,810, cyclohexanone is produced by hydrogenating
phenol using a sodium-promoted catalyst, i.e., a
palladium catalyst which has been modified prior to its
introduction to the reaction mixture, to incorporate
sodium thereon. Alkaline reacting agents in limited
amounts are also disclosed as being added to assist in
promotion when the sodium-promoted catalysts of that
reference are employed. However, such catalyst systems
have not been entirely satisfactory, and research has
continued to develop an improved process and/or catalyst.
Surprisingly, the present invention provides
significantly improved catalyst selectivity and activity
in the hydrogenation of phenol to cyclohexanone;
moreover, it is applicable to present commercial plants.
Further, the present invention provides an improved
process that will produce less by-products and can be
operated at a lower temperature than present commercial
plants without sacrificing production rate. Obviously,
reaction at relatively low temperature is highly
desirable as a factor increasing safety of the overall
operation.
SUMMARY OF THE INVENTION
.
In accordance with the present invention, we
provide a process for producing cyclohexanone comprising
hydrogenating phenol by passing hydrogen in contact
with phenol in the presence of a palladium catalyst,
preferably promoted by sodium in an amount of at least
1000 ppm, based on the weight of the catalyst, at a
30 temperature of 135C. to 185C., preferably 145C. to
185C., sald catalyst being further characterized
in that it is composed of palladium coated carbon
particles, said carbon particles having diameters
of 3 to 300 mierons and a surface area of 100 to 2000
m /gram, said phenol containing a small amount of an
ln situ promoter selected from the group consisting of
alkali metal hydroxides, carbonates, phenates,
bicarbonates and nitrates, said amount being 10 to 300
ppm, preferably 11 to 150 ppm, in terms of alkali metal
of said promoter.
Although in U.S. Patent 3,076,810, it was said
that higher concentrations, i.e., more than 10 ppm,
of an alkaline reacting compound in the phenol favored
the formation of eyclohexanol, we have found that in
the presenee of our improved palladium-on-earbon eatalyst,
not only is the reaction rate enhaneed but also the
produetion of cyclohexanol is redueed by operating
within the range of 10 to 300 ppm of alkali metal in
the phenol. The reason for this surprising discovery
is not known with certainty, but it is believed that the
unexpected element of the present invention involves
the apparent interaction of the in situ promoter with
the present unique eatalyst, together with eareful
eontrol of the reaetion temperature as specified
hereinabove.
The palladium catalysts useful in the present
invention contain palladium, in either its elemental
or combined form, as a catalytically active metal.
Preferably, 30 to 75 percent of the total palladium is
present as elemental palladium, i.e., as palladium zero.
The palladium is desirably absorbed or coated on the
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surface of a support consisting of carbon particles,
said carbon particles having diameters of 3 to 300
microns and a surface area o~ 100 to 2000 m2/gram.
It is preferred that the catalyst have about 95 to
98 weight percent of the particles between 4 and 150
microns in diameter. While the amount of palladium
incorporated on the selected support may vary widely,
the catalyst preferably contains from about 0.1 to
50 weight percent palladium, and most preferably from
about 0.2 to 10 weight percent. A satisfactory and
readily prepared catalyst contains 1 to 5 weight percent
palladium on charcoal. In addition, the palladium
catalysts useful in the present invention may contain
catalytically active metals in addition to palladium.
Such additional catalytically active metals which may
be employed are those selected from the group consisting
of elements of the platinum series. Exemplary of
platinum series elements which may be employed are
ruthenium, rhodium, osmium, iridium, platinum and
mixtures thereof.
The preferred promoters of the present invention
are members selected from the group consisting of sodium
hydroxide, sodium carbonate, sodium phenate, and mixtures
thereof. Particularly preferred as promoters in the
present invention are sodium hydroxide and sodium
phenate, with sodium phenate being especially preferred.
The selected promoter may be added to the hydrogenation
reaction mixture as a phenol slurry containing up to
about 25 weight percent, and preferably from about 1 to
10 weight percent, of the selected promoter.
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Alternatively, the promoter may be added to the
hydrogenation reaction mixture as an aqueous solution.
The phenol which may be employed in the present
invention may be obtained from conventional sources,
such as by the oxidation of cumene to form cumene
hydroperoxide and the decomposition of the resulting
hydroperoxide. However, the phenol treated in
accordance with the process of the present invention
will generally contain no more than about 100 ppm sulfur
impurities, and preferably not greater than about 10 ppm
sulfur impurities containing divalent sulfur, not greater
than about 20 ppm sulfur impurities containing tetra-
valent sulfur and not greater than about 80 ppm, and
most preferably not greater than about 40 ppm, sulfur
impurities containing hexavalent sulfur.
The phenol also preferably contains not greater
than 2 ppm, and most preferably not greater than 1 ppm,
iron values (calculated as elemental iron); and
preferably not greater than 100 ppm, and most preferably
not greater than 50 ppm, acetol (i.e., hydroxy-2-
propanone).
The phenol hydrogenated in accordance with the
process of the present invention may also contain a
wide variety of other impurities. These impurities
include, for example, halogen compounds and deleterious
nitrogen compounds, i.e., nitrogen-containing compounds
which inhibit the hydrogenation of phenol to cyclo-
hexanone employing palladium catalysts. Typical
deleterious nitrogen compounds include aromatic amines,
ammonium salts, polyamines, and tertiary and primary
amines. Preferably, the phenol contains less than 10
ppm halogen and less than 50 ppm of nitrogen as
deleterious nitrogen compounds. Continuous or batch
techniques can be used in this improved process for
S hydrogenating phenol to cyclohexanone, the equipment
used being that which is usual in such processes.
The selected promoter may be introduced to
the hydrogenation reaction mixture either prior to
hydrogenation or during hydrogenation. Thus, the
conditions of temperature under which the promoter
may be added to the hydrogenation mixture are not
critical and may vary widely. For example, the
temperature at which the promoter is added to the
hydrogenation reaction mixture may vary from about
25C. to about 185C. and the pressure may vary from
about atmospheric to 300 psig. While an improved rate
of hydrogenation is generally observed immediately
upon addition to the hydrogenation reaction mixture
of a promoter of the present invention, even more
improved resul~s may be obtained where the hydro-
genation reaction mixture is maintalned at a temperature
within the range of about 135C. to 185C. and a
pressure of 80-200 psig. for a period of 15 to 30
minutes after addition thereto of the selected promoter.
The selected in situ promoter may be added to
the hydrogenation reaction mixture and the reaction
product may be withdrawn from the hydrogenation vessel
either continuously or batchwise. Upon withdrawal of
the hydrogenation product from the reaction vessel,
the palladium catalyst may be recovered from the product
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stream and returned to the vessel for hydrogenation
of additional phenol. The recovery of the catalyst
from the product stream may be effected by any standard
solids separation pxocedure, e.g., centrifugation,
vacuum filtering, and the like.
Vessels which may be employed during the
hydrogenation are conventional, and include the typical
hydrogenation apparatus such as, for example, the
apparatus described in U.S. Patent 3,076,810.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is further illustrated
by reference to the following examples wherein parts
and percentages are by weight unless otherwise indicated.
The improved catalyst and the improved rates of
hydrogenation achieved by the process of the present
invention are especially significant in view of the
large tonnages of palladium catalysts used annually by
industry in the hydrogenation of phenol to cyclohexanone.
Furthermore, the in situ promoters of the present
invention have been unexpectedly found to promote the
hydrogenation of phenol to cyclohexanone while
appreciably decreasing the amount of cyclohexanol
produced by the further hydrogenation of the desired
cyclohexanone hydrogenation product. Thus, recovery
of cyclohexanone from the hydrogenation product stream,
as by distillation, is not further complicated by the
formation of substantial amounts of undesired products,
i.e., cyclohexanol.
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EXAMPLE 1
PART A: About 1000 parts of phenol containing
less than 1 ppm of soluble iron, less than 2 ppm of
sulfur, less than 5 ppm of halogen, less than 40 ppm
of nitrogen as deleterious nitrogen compounds and 0.23
part of sodium carbonate is mixed with 10 parts of
sodium-promoted, palladium-on-carbon catalyst having
a sodium content of 0.32 percent, said catalyst being
further characterized in that it is composed of about
0.93 percent palladium coated on carbon particles having
diameters of about 4 to 150 microns and a surface area
of 500 to 1500 m2/gram. The mixture is heated in a
reaction vessel under nitrogen to 160C., then agitated
at that temperature while hydrogen is admitted through
a diffuser located near the bottom of the vessel and
at a rate sufficient to maintain a pressure of 80 psig.
Periodically, the reaction mixture is sampled and
analyzed. Results are tabulated in Table 1.
TABLE 1
Hydrogenation Cyclohexanol, Cyclohexanone, Phenol,
Time, M _ tes Percent Percent Percent
62 0 38.5 61.5
0 53.8 ~6.2
120 0.5 65.6 33.8
25150 0.6 74.9 24.4
180 0.8 82.3 16.9
210 1.1 87.5 11.4
Less than 0.1 percent of cyclohexyl-cylcohexanone is
found in the reaction mixture. At the end of the
experiment, the catalyst is recovered and is found
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to contain 0.93 percent palladium (60 percent to 75
percent of total as elemental palladium) and 0.76 percent
sodium.
PART B: The procedure of Part A is repeated
with the exception that no sodium carbonate is added
to the phenol. The results are tabulated in Table 2.
TAB~E 2
Hydrogenation Cyclohexanol, Cyclohexanone, Phenol,
Time, Minu es _ Percent Percent Percent
0.3 28.1 71.6
120 0.6 48.4 50.9
210 1.4 65.9 32.5
300 2.2 77.4 20.1
390 3.2 84.3 12.1
450 3.9 88.6 7.0
In addition, about 0.47 percent of cyclohexyl-
cyclohexanone is found in the reaction mixture at the
end of the experiment.
By comparison of Part A and Part B, it is clear
that while in the prior art the in situ addition of an
alkali metal promoter above a level of 10 ppm based on
phenol caused loss of selectivity, the catalyst of the
present invention continued to improve in selectivity
with addition of sodium carbonate to the phenol at 230
ppm, which corresponds to 100 ppm of sodium. The
unexpected element of the present invention lies in the
apparent interaction of the promoter with the present
unique catalyst in combination with the relatively low
reaction temperature.
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EXAMPLE 2
The procedure of Example 1, Part A, is repeated
with the exception that 100 ppm of sodium in the form
of sodium hydroxide is added to the reaction mixture
in place of the sodium carbonate. Results obtained
are similar to those obtained in Example 1, Part A.
EXAMPLE 3
The procedure of Example 1, Part A, is repeated
with the exception that 100 ppm of sodium in the form
of sodium phenate is added to the reaction mixture in
place of the sodium carbonate. Results obtained are
similar to those obtained in Example 1, Part A.
EXAMPLE 4
This example demonstrates one effective method
of preparing the catalyst of the present invention.
However, the method of this example is relatively
expensive as compared with the procedure of Example 5.
About 150 parts of a commercially available
5 percent palladium-on-carbon catalyst is used as
starting material. A slurry of the commercially
available palladium catalyst in an aqueous solution
of sodium hydroxide is prepared and the slurry is then
evaporated to dryness in accordance with the procedure
of U.S. Patent 3,076,810. The resulting catalyst
preferably contains 2,500 - 10,000 ppm of sodium. About
150 parts of the sodium-promoted, palladium-on-carbon
catalyst is thoroughly mixed with 1850 parts of
cyclohexanone and this mixture is passed at the rate
of 2000 parts per hour through a continuous centrifuge
which operates at 3800 revolutions per minute. In
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accordance with this procedure, part of the catalyst
consisting of the finer particles passes out of the
centrifuge with the cyclohexanone. The catalyst
collected in the centrifuge has a size distribution of
98 to 99 percent greater than 4 microns, with
substantially all particles in the range 4 to 150
microns; the palladium content is 0.6 to 1.2 percent,
and the sodium content is 0.25 to 0.40 percent. This
catalyst is suitable for use in the process of this
invention. The finer catalyst particles may be recovered
from the cyclohexanone by conventional procedures; the
finer catalyst particles are unsuitable for use in
the process of this invention.
EXAMPLE 5
About 150 parts of commercially available charcoal
catalyst support having particle size distribution of
30 percent less than 10 microns, 67 percent in the
range 10 to 100 microns, and 3 percent greater than
100 microns is thoroughly mixed with 1850 parts of
cyclohexanone, and this mixture is passed through a
continuous centrifuge which operates at 3800 revolutions
per minute. By this procedure, part of the charcoal
particles consisting of the finer particles, passes
out of the centrifuge with the cyclohexanone. The
- 25 charcoal particles collected in the centrifuge, after
drying, consist of about 100 parts of particles having
diameters of 10 to 100 microns and a surface area of
about 1000 m2/gram. To 100 parts of the resulting
charcoal is added 1000 parts of aqueous palladium
chloride solution containing 5 parts palladium and
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3 parts hydrochloric acid. The solution is gradually
neutralized with a sodium carbonate solution up to
pH = 1.5. The mixture is stirred and then filtered.
The solids are dried at 100C. for 8 hours following
which they are impregnated with 80 parts of a solution
containing 5 parts of sodium carbonate. After drying
at 100-120C. the solids are placed into a cylindrical
reactor which is flushed with hydrogen at 140C. This
catalyst is suitable for use in the present invention.
EXAMPLE 6
This example demonstrates the feasibility of
continuously operating the hydrogenation process of
the present invention. The phenol used was similar to
that used in Example 1.
The first of a series of five a~itated hydro-
genation vessels is charged with 45,694 parts per hour
of phenol, 1.3 to 2.0 parts of sodium carbonate, and
1,200 parts per hour of a sodium-promoted, palladium-on-
carbon catalyst ha~ing a sodium content of 0.25 - 0.40
percent, said catalyst containing about 0.93 percent
palladium on carbon particles having diameters of about
5 to 150 microns and a surface area of about 1000 m /gram.
About 67 percent of the palladium on the catalyst is
present as elemental palladium. Each hydrogenation vessel
is connected in series so that the reaction mixture flows
throu~h the five vessels in about 3.1 hours, the hydrogen
being charged to the first vessel. The pressure is
between 80 and 200 psig. The temperature in each vessel
is as follows: 179C. in the first vessel; 168C. in the
second vessel; 166~C. in the third vessel; 164C. in the
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fourth vessel, and 162C. in the fifth vessel. It is
noteworthy for reasons of safety that the temperature
in each vessel is less than 10C. above the atmospheric
boiling point of the reaction mixture present in the
vessel. About 24,570 parts per hour of distillate,
primarily cyclohexanone, is separated from the last
three vessels; this distillate is rectified to provide
substantially pure cyclohexanone. The reaction mass
flowing from the fifth reaction vessel is fed to a
continuous centrifuge, wherein the catalyst is separated
from the crude cyclohexanone; the catalyst is recycled
in the process. The crude cyclohexanone is rectified
to recover substantially pure cyclohexanone which may
be combined with the cyclohexanone recovered as described
above.
In this continuous operation carried out for
several days, cyclohexanone recovery is 42,856 parts
per hour. Also recovered is 684 parts per hour of
cyclohexanol~ 1481 parts per hour of phenol, and 211
parts per hour of higher boiling by-products. Only 3
parts per hour of make-up catalyst is required in the
process. Similar results are obtained when an equivalent
amount of sodium as sodium hydroxide or sodium phenate
is substituted for the sodium carbonate added to the
process in the phenol.
EX~MPLE 7
The procedure of Example 6 is followed except
that the reaction temperature in each of the reaction
vessels is further reduced for reasons of increased
safety, i.e., the reaction temperature is reduced to
173C. in the first vessel, 166C. in the second vessel,
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162C. in the third vessel, 159C. in the fourth vessel,
and 156C. in the fifth vessel. Regarding safety in
operation, it is important that the temperature in each
reactor is maintained at or below the atmospheric boiling
point of the reaction mixture present in the reactor.
The phenol is fed to the first vessel at a rate of
45,550 parts per hour~ together with 2 parts per hour
of sodium carbonate and 1,200 parts per hour of a sodium-
promoted palladium-on-carbon catalyst having a sodium
content of about 0.35 percent, said catalyst containing
about 0.9 percent palladium on carbon particles having
diameters of about 3 to 32 microns and a surface area
of about lO00 m2/gram. A commercially available sodium-
promoted palladium-on-carbon catalyst containing about
l percent sodium and about 5 percent palladium is added
to the recycled catalyst as make-up catalyst at the
rate of about 2.5 parts per hour. The make-up catalyst
contains about 16.5 volume percent of particles finer
than 3 microns in diameter, but most of these finer
particles are removed from the process in the crude
cyclohexanone recovered in the centrifuge. A sample
of the make-up catalyst has the following size analysis.
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Size Range, Percent of
Microns Total Volume
1.26 to 1.59 l.S
1.59 to 2.00 2.0
2.00 to 2.52 4.0
2.52 to 3.17 9.0
3.17 to 4.00 11.5
4.00 to 5.04 13.5
5.04 to 6.35 12.5
6.35 to 8.00 14.0
8.00 to 10.08 13.0
10.08 to 12.7 10.0
12.7 to 16.0 5.0
16.0 to 10.2 2.5
20.2 to 25.4 1.0
25.4 to 32.0 0.5
In this example/ average yield of cyclohexanone
over a one month test period is 98 percent of theory
based on phenol fed to the process. Cyclohexanol is
produced at a very low rate of about 610 parts per hour.
At the end of the test period, the recycling catalyst
contains about 0.45 percent sodium and about 0.9 percent
palladium. A sample of the recycling catalyst has the
following size analysis.
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Size Range, Percent of
Microns Total Volume
. .
1.26 to 1.59 0.5
1.59 to 2.00 0.5
2.0C to 2.52 0.5
2.52 to 3.17 0.5
3.17 to 4.00 1.5
4.00 to 5.04 11.0
5.04 to 6.35 24.0
6.35 to 8.00 23.5
8.00 to 10.08 16.5
10.08 to 12.7 10.0
12.7 to 16.0 6.0
16.0 to 10.2 3.5
20.2 to 25.4 1.5
25.4 to 32.0 0.5
It will be noted that the make-up catalyst shows a
fairly normal distribution in size range while the
recycling catalyst shows a shift toward larger particles
and a skewed distribution. We postulate that said shift
toward larger catalyst particles in combination with the
in situ promoter tend to promote rapid and selective
hydrogenation of the phenol to cyclohexanone, i.e.,
produces high yields of cyclohexanone and low yields
of cyclohexanol and other by-products.
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