U.S. patent application number 11/977360 was filed with the patent office on 2009-04-30 for direct epoxidation process using improved catalyst composition.
Invention is credited to Roger A. Grey.
Application Number | 20090112006 11/977360 |
Document ID | / |
Family ID | 40456349 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090112006 |
Kind Code |
A1 |
Grey; Roger A. |
April 30, 2009 |
Direct epoxidation process using improved catalyst composition
Abstract
Catalysts useful for the direct epoxidation of olefins are
disclosed. The catalysts comprise a noble metal, lead, bismuth, and
a titanium or vanadium zeolite. The noble metal, lead, and bismuth
may be supported on the titanium or vanadium zeolite. The catalyst
may also be a mixture comprising the titanium or vanadium zeolite
and a supported catalyst comprising the noble metal, lead, bismuth,
and a carrier. The invention includes a process for producing an
epoxide comprising reacting an olefin, hydrogen and oxygen in the
presence of the catalyst. The process results in significantly
reduced alkane byproduct formed by the hydrogenation of olefin.
Inventors: |
Grey; Roger A.; (West
Chester, PA) |
Correspondence
Address: |
LyondellBasell Industries
3801 WEST CHESTER PIKE
NEWTOWN SQUARE
PA
19073
US
|
Family ID: |
40456349 |
Appl. No.: |
11/977360 |
Filed: |
October 24, 2007 |
Current U.S.
Class: |
549/533 ; 502/60;
502/64; 502/66; 502/74; 549/523 |
Current CPC
Class: |
C07D 301/10 20130101;
C07D 301/08 20130101 |
Class at
Publication: |
549/533 ; 502/60;
502/64; 502/66; 502/74; 549/523 |
International
Class: |
C07D 301/04 20060101
C07D301/04; B01J 29/068 20060101 B01J029/068 |
Claims
1-9. (canceled)
10. A process for producing propylene oxide comprising reacting
propylene, hydrogen and oxygen in the prsence of a titanium zeolite
and a supported catalyst comprising palladium, lead, bismuth, and a
carrier.
11. The process of claim 10 wherein the titanium zeolite is a
titanium silicalite.
12. The process of claim 10 wherein the supported catalyst contains
0.01 to 10 weight percent palladium, 0.01 to 10 weight percent
lead, and 0.001 to 5 weight percent bismuth.
13. The process of claim 10 wherein the carrier is selected from
the group consisting of carbon, titania, zirconia, niobia, silica,
alumina, silica-alumina, tantalum oxide, molybdenum oxide, tungsten
oxide, titania-silica, zirconia-silica, niobia-silica, and mixtures
thereof.
14. The process of claim 10 wherein the reaction is performed in
the presence of a solvent comprising methanol.
15. The process of claim 14 wherein the reaction is performed in
the presence of a buffer.
16. A catalyst comprising palladium, lead, bismuth, and a titanium
or vanadium zeolite.
17. The catalyst of claim 16 wherein the titanium or vanadium
zeolite is a titanium silicalite.
18. (canceled)
19. A catalyst mixture comprising a titanium or vanadium zeolite
and a supported catalyst comprising palladium, lead, bismuth, and a
carrier.
20. The catalyst mixture of claim 19 wherein the titanium zeolite
is a titanium silicalite.
21. (canceled)
22. The catalyst mixtur of claim 19 wherein the carrier is selected
from the group consisting of carbon, titania, zirconia, niobia,
silica, alumina, silica-alumina, tantalum oxide, molybdenum oxide,
tungsten oxide, titania-silica, zirconia-silica, niobia-silica, and
mixtures thereof.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a catalyst and its use in the
production of epoxides from hydrogen, oxygen, and olefins.
BACKGROUND OF THE INVENTION
[0002] Many different methods for the preparation of epoxides have
been developed. Generally, epoxides are formed by the reaction of
an olefin with an oxidizing agent in the presence of a catalyst.
Ethylene oxide is commercially produced by the reaction of ethylene
with oxygen over a silver catalyst. Propylene oxide is commercially
produced by reacting propylene with an organic hydroperoxide
oxidizing agent, such as ethylbenzene hydroperoxide or tert-butyl
hydroperoxide. This process is performed in the presence of a
solubilized molybdenum catalyst, see U.S. Pat. No. 3,351,635, or a
heterogeneous titania on silica catalyst, see U.S. Pat. No.
4,367,342.
[0003] Besides oxygen and alkyl hydroperoxides, hydrogen peroxide
is also a useful oxidizing agent for epoxide formation. U.S. Pat.
Nos. 4,833,260, 4,859,785, and 4,937,216, for example, disclose
olefin epoxidation with hydrogen peroxide in the presence of a
titanium silicate catalyst.
[0004] Much current research is conducted in the direct epoxidation
of olefins with oxygen and hydrogen. In this process, it is
believed that oxygen and hydrogen react in situ to form an
oxidizing agent. Many different catalysts have been proposed for
use in the direct epoxidation process. Typically, the catalyst
comprises a noble metal and a titanosilicate. For example, JP
4-352771 discloses the formation of propylene oxide from propylene,
oxygen, and hydrogen using a catalyst containing a Group VIII metal
such as palladium on a crystalline titanosilicate. The Group VIII
metal is believed to promote the reaction of oxygen and hydrogen to
form a hydrogen peroxide in situ oxidizing agent. U.S. Pat. No.
6,498,259 describes a catalyst mixture of a titanium zeolite and a
supported palladium complex, where palladium is supported on
carbon, silica, silica-alumina, titania, zirconia, and niobia.
Other direct epoxidation catalyst examples include gold supported
on titanosilicates, see for example PCT Intl. Appl. WO
98/00413.
[0005] One disadvantage of the described direct epoxidation
catalysts is that they are prone to produce non-selective
byproducts such as glycols or glycol ethers formed by the
ring-opening of the epoxide product or alkane byproduct formed by
the hydrogenation of olefin. U.S. Pat. No. 6,008,388 teaches that
the selectivity for the direct olefin epoxidation process is
enhanced by the addition of a nitrogen compound such as ammonium
hydroxide to the reaction mixture. U.S. Pat. No. 6,399,794 teaches
the use of ammonium bicarbonate modifiers to decrease the
production of ring-opened byproducts. U.S. Pat. No. 6,005,123
teaches the use of phosphorus, sulfur, selenium or arsenic
modifiers such as triphenylphosphine or benzothiophene to decrease
the production of propane. U.S. Pat. No. 7,026,492 discloses that
the presence of carbon monoxide, methylacetylene, and/or propadiene
modifier gives significantly reduced alkane byproduct. In addition,
co-pending U.S. pat. appl. Ser. No. 11/489,086 discloses that the
use of a lead-modified palladium-containing titanium or vanadium
zeolite reduces alkane byproduct formation.
[0006] As with any chemical process, it is desirable to attain
still further improvements in the epoxidation methods and
catalysts. We have discovered a new catalyst and its use in olefin
epoxidation.
SUMMARY OF THE INVENTION
[0007] The invention is a catalyst comprising a noble metal, lead,
bismuth, and a titanium or vanadium zeolite. In one embodiment, the
catalyst is a mixture comprising a titanium or vanadium zeolite and
a supported catalyst comprising a noble metal, lead, bismuth, and a
carrier. The catalyst is useful in olefin epoxidation. Thus, the
invention also includes an olefin epoxidation process that
comprises reacting olefin, oxygen, and hydrogen in the presence of
a catalyst comprising a titanium or vanadium zeolite, a noble
metal, lead, and bismuth. This process surprisingly gives
significantly reduced alkane byproduct formed by the hydrogenation
of olefin compared to the process using catalyst systems that do
not contain bismuth and lead.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The catalyst of the invention comprises a titanium or
vanadium zeolite, a noble metal, lead, and bismuth. Titanium or
vanadium zeolites comprise the class of zeolitic substances wherein
titanium or vanadium atoms are substituted for a portion of the
silicon atoms in the lattice framework of a molecular sieve. Such
substances, and their production, are well known in the art. See
for example, U.S. Pat. Nos. 4,410,501 and 4,666,692.
[0009] Suitable titanium or vanadium zeolites are those crystalline
materials having a porous molecular sieve structure with titanium
or vanadium atoms substituted in the framework. The choice of
titanium or vanadium zeolite employed will depend upon a number of
factors, including the size and shape of the olefin to be
epoxidized. For example, it is preferred to use a relatively small
pore titanium or vanadium zeolite such as a titanium silicalite if
the olefin is a lower aliphatic olefin such as ethylene, propylene,
or 1-butene. Where the olefin is propylene, the use of a TS-1
titanium silicalite is especially advantageous. For a bulky olefin
such as cyclohexene, a larger pore titanium or vanadium zeolite
such as a zeolite having a structure isomorphous with zeolite beta
may be preferred.
[0010] Particularly preferred titanium or vanadium zeolites include
the class of molecular sieves commonly referred to as titanium
silicalites, particularly "TS-1" (having an MFI topology analogous
to that of the ZSM-5 aluminosilicate zeolites), "TS-2" (having an
MEL topology analogous to that of the ZSM-11 aluminosilicate
zeolites), "TS-3" (as described in Belgian Pat. No. 1,001,038), and
Ti-MWW (having an MEL topology analogous to that of the MWW
aluminosilicate zeolites). Titanium-containing molecular sieves
having framework structures isomorphous to zeolite beta, mordenite,
ZSM-48, ZSM-12, SBA-15, TUD, HMS, and MCM-41 are also suitable for
use. The titanium zeolites preferably contain no elements other
than titanium, silicon, and oxygen in the lattice framework,
although minor amounts of boron, iron, aluminum, sodium, potassium,
copper and the like may be present.
[0011] Preferred titanium zeolites will generally have a
composition corresponding to the following empirical formula
xTiO.sub.2 (1-x)SiO.sub.2 where x is between 0.0001 and 0.5000.
More preferably, the value of x is from 0.01 to 0.125. The molar
ratio of Si:Ti in the lattice framework of the zeolite is
advantageously from 9.5:1 to 99:1 (most preferably from 9.5:1 to
60:1). The use of relatively titanium-rich zeolites may also be
desirable.
[0012] In one embodiment of the invention, the noble metal, bismuth
and lead are supported on the titanium or vanadium zeolite. In
another embodiment of the invention, the noble metal, bismuth and
lead are supported on a carrier to form a supported catalyst which
is then mixed with the titanium or vanadium zeolite.
[0013] Thus, the catalyst of the invention optionally comprises a
carrier. The carrier is preferably a porous material. Carriers are
well-known in the art. For instance, the carrier can be inorganic
oxides, clays, carbon, and organic polymer resins. Preferred
inorganic oxides include oxides of Group 2, 3, 4, 5, 6, 13, or 14
elements. Particularly preferred inorganic oxide carriers include
silica, alumina, silica-aluminas, titania, zirconia, niobium
oxides, tantalum oxides, molybdenum oxides, tungsten oxides,
amorphous titania-silica, amorphous zirconia-silica, amorphous
niobia-silica, and the like. The carrier may be a zeolite, but is
not a titanium or vanadium zeolite. Preferred organic polymer
resins include polystyrene, styrene-divinylbenzene copolymers,
crosslinked polyethyleneimines, and polybenzimidizole. Suitable
carriers also include organic polymer resins grafted onto inorganic
oxide carriers, such as polyethylenimine-silica. Preferred carriers
also include carbon. Particularly preferred carriers include
carbon, silica, silica-aluminas, zirconia, niobia, and titania (in
particular anatase titanium dioxide).
[0014] Preferably, the carrier has a surface area in the range of
about 1 to about 700 m.sup.2/g, most preferably from about 10 to
about 500 m.sup.2/g. Preferably, the pore volume of the carrier is
in the range of about 0.1 to about 4.0 mL/g, more preferably from
about 0.5 to about 3.5 mL/g, and most preferably from about 0.8 to
about 3.0 mL/g. Preferably, the average particle size of the
carrier is in the range of about 0.1 to about 500 .mu.m, more
preferably from about 1 to about 200 .mu.m, and most preferably
from about 10 to about 100 .mu.m. The average pore diameter is
typically in the range of about 10 to about 1000 .ANG., preferably
about 20 to about 500 .ANG., and most preferably about 50 to about
350 .ANG..
[0015] The catalyst of the invention also comprises a noble metal,
lead, and bismuth. The noble metal, lead, and bismuth may be added
to the catalyst in any of a variety of ways, including: (1) noble
metal, lead, and bismuth may be supported on the titanium or
vanadium zeolite; and (2) noble metal, lead, and bismuth may be
supported on the carrier to form a supported catalyst, which is
then mixed with titanium or vanadium zeolite to form the
catalyst.
[0016] While any of the noble metals can be utilized (i.e., gold,
silver, platinum, palladium, iridium, ruthenium, osmium), either
alone or in combination, palladium, platinum, gold, a
palladium/platinum, or a palladium/gold combination are
particularly desirable. Palladium is most preferred. The typical
amount of noble metal present in the catalyst will be in the range
of from about 0.01 to 10 weight percent, preferably 0.01 to 4
weight percent. There are no particular restrictions regarding the
choice of noble metal compound used as the source of the noble
metal. For example, suitable compounds include the nitrates,
sulfates, halides (e.g., chlorides, bromides), carboxylates (e.g.
acetate), oxides, and amine complexes of the noble metal.
[0017] Similarly, the oxidation state of the noble metal is not
considered critical. The noble metal may be in an oxidation state
anywhere from 0 to +4 or any combination of such oxidation states.
To achieve the desired oxidation state or combination of oxidation
states, the noble metal compound may be fully or partially
pre-reduced after addition to the catalyst. Satisfactory catalytic
performance can, however, be attained without any pre-reduction. To
achieve the active state of the noble metal, the catalyst may
undergo pretreatment such as thermal treatment in nitrogen, vacuum,
hydrogen, or air.
[0018] The catalyst of the invention also contains lead. The
typical amount of lead present in the catalyst will be in the range
of from about 0.01 to 10 weight percent, preferably 0.01 to 5
weight percent. Preferably, the weight ratio of noble metal to lead
in the catalyst is in the range of 0.1 to 10. While the choice of
lead compound used as the lead source in the catalyst is not
critical, suitable compounds include lead carboxylates (e.g.,
acetate), halides (e.g., chlorides, bromides, iodides), nitrates,
cyanides, oxides, and sulfides.
[0019] The catalyst of the invention also contains bismuth. The
typical amount of bismuth present in the catalyst will be in the
range of from about 0.001 to 5 weight percent, preferably 0.01 to 2
weight percent. Preferably, the weight ratio of noble metal to
bismuth in the catalyst is in the range of 0.1 to 10. While the
choice of bismuth compound used as the bismuth source in the
catalyst is not critical, suitable compounds include bismuth
carboxylates (e.g., acetate, citrate), halides (e.g., chlorides,
bromides, iodides), oxyhalides (e.g., oxychloride), carbonates,
nitrates, phosphates, oxides, and sulfides.
[0020] Any suitable method may be used for the incorporation of the
noble metal, lead, and bismuth into the catalyst. For example, the
noble metal, lead, and bismuth may be supported on the zeolite or
the carrier by impregnation, ion-exchange, or incipient wetness
techniques. For example, the noble metal may be supported on the
zeolite or the carrier by impregnation or by ion-exchange with, for
example, palladium tetraammine chloride. If the lead, bismuth, and
noble metal are added to the titanium or vanadium zeolite (or are
added to the carrier), the order of addition is not considered
critical. However, it is preferred to add the lead and bismuth
compounds at the same time that the noble metal is introduced.
[0021] After noble metal, lead, and bismuth incorporation, the
catalyst is isolated. Suitable catalyst isolation methods include
filtration and washing, rotary evaporation and the like. The
catalyst is typically dried prior to use in epoxidation. The drying
temperature is preferably from about 50.degree. C. to about
200.degree. C. The catalyst may additionally comprise a binder or
the like and may be molded, spray dried, shaped or extruded into
any desired form prior to use in epoxidation.
[0022] After catalyst formation, the catalyst may be optionally
thermally treated in a gas such as nitrogen, helium, vacuum,
hydrogen, oxygen, air, or the like. The thermal treatment
temperature is typically from about 20.degree. C. to about
800.degree. C. It is preferred to thermally treat the catalyst in
the presence of an oxygen-containing gas at a temperature from
about 200.degree. C. to 700.degree. C., and optionally reduce the
catalyst in the presence of a hydrogen-containing gas at a
temperature from about 20.degree. C. to 600.degree. C.
[0023] The epoxidation process of the invention comprises
contacting an olefin, oxygen, and hydrogen in the presence of the
catalyst. Suitable olefins include any olefin having at least one
carbon-carbon double bond, and generally from 2 to 60 carbon atoms.
Preferably the olefin is an acyclic alkene of from 2 to 30 carbon
atoms; the process of the invention is particularly suitable for
epoxidizing C.sub.2-C.sub.6 olefins. More than one double bond may
be present, as in a diene or triene for example. The olefin may be
a hydrocarbon (i.e., contain only carbon and hydrogen atoms) or may
contain functional groups such as halide, carboxyl, hydroxyl,
ether, carbonyl, cyano, or nitro groups, or the like. The process
of the invention is especially useful for converting propylene to
propylene oxide.
[0024] Oxygen and hydrogen are also required for the epoxidation
process. Although any sources of oxygen and hydrogen are suitable,
molecular oxygen and molecular hydrogen are preferred.
[0025] Epoxidation according to the invention is carried out at a
temperature effective to achieve the desired olefin epoxidation,
preferably at temperatures in the range of 0-250.degree. C., more
preferably, 20-100.degree. C. The molar ratio of hydrogen to oxygen
can usually be varied in the range of H.sub.2:O.sub.2=1:10 to 5:1
and is especially favorable at 1:5 to 2:1. The molar ratio of
oxygen to olefin is usually 2:1 to 1:20, and preferably 1:1 to
1:10. A carrier gas may also be used in the epoxidation process. As
the carrier gas, any desired inert gas can be used. The molar ratio
of olefin to carrier gas is then usually in the range of 100:1 to
1:10 and especially 20:1 to 1:10.
[0026] As the inert gas carrier, noble gases such as helium, neon,
and argon are suitable in addition to nitrogen and carbon dioxide.
Saturated hydrocarbons with 1-8, especially 1-6, and preferably
with 1-4 carbon atoms, e.g., methane, ethane, propane, and
n-butane, are also suitable. Nitrogen and saturated C.sub.1-C.sub.4
hydrocarbons are the preferred inert carrier gases. Mixtures of the
listed inert carrier gases can also be used.
[0027] Specifically in the epoxidation of propylene, propane or
methane can be supplied in such a way that, in the presence of an
appropriate excess of carrier gas, the explosive limits of mixtures
of propylene, propane (methane), hydrogen, and oxygen are safely
avoided and thus no explosive mixture can form in the reactor or in
the feed and discharge lines.
[0028] The amount of catalyst used may be determined on the basis
of the molar ratio of the titanium contained in the titanium
zeolite to the olefin that is supplied per unit time. Typically,
sufficient catalyst is present to provide a titanium/olefin per
hour molar feed ratio of from 0.0001 to 0.1.
[0029] Depending on the olefin to be reacted, the epoxidation
according to the invention can be carried out in the liquid phase,
the gas phase, or in the supercritical phase. When a liquid
reaction medium is used, the catalyst is preferably in the form of
a suspension or fixed-bed. The process may be performed using a
continuous flow, semi-batch or batch mode of operation.
[0030] If epoxidation is carried out in the liquid (or
supercritical or subcritical) phase, it is advantageous to work at
a pressure of 1-100 bars and in the presence of one or more
solvents. Suitable solvents include any chemical that is a liquid
under reaction conditions, including, but not limited to,
oxygenated hydrocarbons such as alcohols, ethers, esters, and
ketones, aromatic and aliphatic hydrocarbons such as toluene and
hexane, nitriles such as acetonitrile, liquid CO.sub.2 (in the
supercritical or subcritical state), and water. Preferable solvents
include water, liquid CO.sub.2, and oxygenated hydrocarbons such as
alcohols, ethers, esters, ketones, and the like, or mixtures
thereof. Preferred oxygenated solvents include lower aliphatic
C.sub.1-C.sub.4 alcohols such as methanol, ethanol, isopropanol,
and tert-butanol, or mixtures thereof, and water. Fluorinated
alcohols can be used. It is particularly preferable to use mixtures
of the cited alcohols with water.
[0031] If epoxidation is carried out in the liquid (or
supercritical or subcritical) phase, it is advantageous to use a
buffer. The buffer will typically be added to the solvent to form a
buffer solution. The buffer solution is employed in the reaction to
inhibit the formation of glycols or glycol ethers during
epoxidation. Buffers are well known in the art.
[0032] Buffers useful in this invention include any suitable salts
of oxyacids, the nature and proportions of which in the mixture,
are such that the pH of their solutions may range from 3 to 10,
preferably from 4 to 9 and more preferably from 5 to 7. Suitable
salts of oxyacids contain an anion and cation. The anion portion of
the salt may include anions such as phosphate,
monohydrogenphosphate, dihydrogenphosphate, sulfate, carbonate,
bicarbonate, carboxylates (e.g., acetate, phthalate, and the like),
citrate, borate, hydroxide, silicate, aluminosilicate, or the like.
The cation portion of the salt may include cations such as
ammonium, alkylammoniums (e.g., tetraalkylammoniums, pyridiniums,
and the like), alkali metals, alkaline earth metals, or the like.
Examples include NH.sub.4, NBu.sub.4, NMe.sub.4, Li, Na, K, Cs, Mg,
and Ca cations. More preferred buffers include alkali metal
phosphate and ammonium phosphate buffers. Buffers may preferably
contain a combination of more than one suitable salt. Typically,
the concentration of buffer in the solvent is from about 0.0001 M
to about 1 M, preferably from about 0.001 M to about 0.3 M. The
buffer useful in this invention may also include the addition of
ammonia gas to the reaction system.
[0033] The following examples merely illustrate the invention.
Those skilled in the art will recognize many variations that are
within the spirit of the invention and scope of the claims.
EXAMPLE 1
PREPARATION OF Pd-Bi-Pb/TiO.sub.2, Pd-Bi/TiO.sub.2, and
Pd-Au/TiO.sub.2 CATALYSTS
[0034] Catalyst 1A (Pd-Bi-Pb/TiO.sub.2):
[0035] Lead nitrate (0.69 g) and an aqueous solution of disodium
palladium tetrachloride (1.11 g, 19.7 wt. % Pd) are added to a
solution of bismuth nitrate (0.3 g Bi(NO.sub.3).sub.3 dissolved in
15 mL, 2.56 M solution of nitric acid, 16.6% by volume of 70%
HNO.sub.3) with mixing. The Pd-Bi-Pb solution is then added by
incipient wetness to spray dried titania (20 g, 30 micron size, 40
m.sup.2/g, calcined in air at 700.degree. C.). The solids are
calcined in air in a muffle furnace by heating at 10.degree. C./min
to 110.degree. C. for 4 hours and then at 2.degree. C./min to
300.degree. C. for 4 hours. These calcined solids are then washed
with an aqueous sodium bicarbonate solution (40 mL, containing 2.25
g NaHCO.sub.3), followed by deionized water (40 mL, four times).
The washed solids are vacuum dried (20 torr) at 50.degree. C. for
16 hours and then calcined in a muffle furnace by heating at
10.degree. C./min to 110.degree. C. for 4 hours and then heating at
2.degree. C./min to 600.degree. C. for 4 hours. The solids are then
transferred to a quartz tube and treated with a 4 vol. % hydrogen
in nitrogen stream at 100.degree. C. for 1 hour (100 cc/hr),
followed by nitrogen for 30 minutes while cooling from 100.degree.
C. to 30.degree. C. to produce Catalyst 1A. Catalyst 1A contains
0.83 wt. % Pd, 0.5 wt. % Bi, 1.6 wt. % Pb, 57 wt. % Ti and less
than 100 ppm Na.
[0036] Comparative Catalyst 1B (Pd-Au/Ti0.sub.2):
[0037] Aqueous sodium tetrachloro aurate (16.54 g, 19.95 wt. % Au)
and aqueous disodium tetrachloro palladate (27.86 g, 19.74 wt. %
Pd) are added to 1.2 L of deionized water with swirling in a
round-bottom flask. To this solution, sodium bicarbonate (12.5 g)
is added as a powder, followed by spray dried TiO.sub.2 (500 g, 35
micron average size, 43 m.sup.2/g, air calcined at 700.degree. C.).
The pH of the slurry is adjusted to 7.3 by adding solid portions of
sodium bicarbonate (approximately 100 g is required) and the
reaction slurry is agitated by rotation of the flask at 25 rpm at a
45 degree angle for 18 hours at 23.degree. C. The solids are then
filtered, washed once with deionized water (1.2 L), and calcined in
air in a muffle furnace by heating at 10.degree. C./min to
110.degree. C. for 4 hours and then at 2.degree. C./min to
300.degree. C. for 4 hours. These calcined solids are then washed
with deionized water (1.2 L) eight times. The washed solids are
calcined in a muffle furnace by heating at 10.degree. C./min to
110.degree. C. for 4 hours and then heating at 2.degree. C./min to
600.degree. C. for 4 hours. The solids are then transferred to a
quartz tube and treated with a 4 vol. % hydrogen in nitrogen stream
at 100.degree. C. for 1 hour (100 cc/hr), followed by nitrogen for
30 minutes while cooling from 100.degree. C. to 30.degree. C. to
produce Comparative Catalyst 1B. Comparative Catalyst 1B contains 1
wt. % Pd. 0.6 wt. % Au, 58 wt. % Ti and less than 20 ppm Cl.
[0038] Comparative Catalyst 1C (Pd-Bi/Ti0.sub.2):
[0039] An aqueous solution of disodium palladium tetrachloride
(1.11 g, 19.7 wt. % Pd) is added to a solution of bismuth nitrate
(0.35 g Bi(NO.sub.3).sub.3 dissolved in 15 mL, 2.56 M solution of
nitric acid, 16.6% by volume of 70% HNO.sub.3). The Pd-Bi solution
is then added by incipient wetness to spray dried titania (20 g, 30
micron size, 40 m.sup.2/g, calcined in air at 700.degree. C.). The
solids are calcined in air in a muffle furnace by heating at
10.degree. C./min to 110.degree. C. for 4 hours and then at
2.degree. C./min to 300.degree. C. for 4 hours. These calcined
solids are then washed twice with an aqueous sodium bicarbonate
solution (40 mL, containing 0.9 g NaHCO.sub.3), followed by
deionized water (40 mL, five times). The washed solids are vacuum
dried (20 torr) at 50.degree. C. for 16 hours and then calcined in
a muffle furnace by heating at 10.degree. C./min to 110.degree. C.
for 4 hours and then heating at 2.degree. C./min to 600.degree. C.
for 4 hours. The solids are then transferred to a quartz tube and
treated with a 4 vol. % hydrogen in nitrogen stream at 100.degree.
C. for 1 hour (100 cc/hr), followed by nitrogen for 30 minutes
while cooling from 100.degree. C. to 30.degree. C. to produce
Catalyst 1C. Catalyst 1C contains 0.94 wt. % Pd, 0.64 wt. % Bi, 58
wt. % Ti and less than 100 ppm Na.
EXAMPLE 2
EPOXIDATION REACTION USING CATALYSTS FROM EXAMPLE 1
[0040] A 300 cc stainless steel reactor is charged with the
supported noble metal catalyst (0.07 g of 1A, 1B, or 1C), TS-1
powder (0.63 g), methanol (.about.100 g), and a buffer solution (13
g of 0.1 M aqueous ammonium phosphate, pH=6). The reactor is then
charged to 300 psig with a feed consisting of 2% hydrogen, 4%
oxygen, 5% propylene, 0.5% methane and the balance nitrogen (volume
%) for runs utilizing a 2:1 O.sub.2:H.sub.2 ratio or a feed
consisting of 4% hydrogen, 4% oxygen, 5% propylene, 0.5% methane
and the balance nitrogen (volume %) for runs utilizing a 1:1
O.sub.2:H.sub.2 ratio. The pressure in the reactor is maintained at
300 psig via a backpressure regulator with the feed gases passed
continuously through the reactor at 1600 cc/min (measured at
23.degree. C. and one atmosphere pressure). In order to maintain a
constant solvent level in the reactor during the run, the oxygen,
nitrogen and propylene feeds are passed through a two-liter
stainless steel vessel (saturator) preceding the reactor,
containing 1.5 liters of methanol. The reactor is stirred at 1500
rpm. The reaction mixture is heated to 60.degree. C. and the
gaseous effluent is analyzed by an online GC every hour and the
liquid analyzed by offline GC at the end of the 18 hour run.
Propylene oxide and equivalents ("POE"), which include propylene
oxide ("PO"), propylene glycol ("PG"), and propylene glycol methyl
ethers (PMs), are produced during the reaction, in addition to
propane formed by the hydrogenation of propylene.
[0041] The epoxidation results (see Table 1) show that a TS-1 and
Pd-Bi-Pb/TiO.sub.2 mixed catalyst shows a significant increase in
propylene selectivity resulting from reduced propane make, compared
to TS-1 and Pd-Bi/TiO.sub.2 or TS-1 and Pd-Au/TiO.sub.2 mixed
catalysts.
TABLE-US-00001 TABLE 1 Epoxidation Results O.sub.2:H.sub.2 Catalyst
Propylene Catalyst Ratio Productivity.sup.1 Selectivity (%).sup.2
1A 2 0.34 93 1A 1 0.57 88 1B* 2 0.39 81 1B* 1 0.7 68 1C* 2 0.45 89
1C* 1 0.41 86 .sup.1Productivity = grams POE produced/gram of
catalyst per hour. .sup.2Propylene Selectivity = 100 - (moles
propane/(moles POE + moles propane)) .times. 100. *Comparative
Example
* * * * *