U.S. patent application number 11/016053 was filed with the patent office on 2006-06-22 for epoxidation catalyst.
Invention is credited to Roger A. Grey, Kun Qin, Peter J. Whitman.
Application Number | 20060135795 11/016053 |
Document ID | / |
Family ID | 35610239 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060135795 |
Kind Code |
A1 |
Qin; Kun ; et al. |
June 22, 2006 |
EPOXIDATION CATALYST
Abstract
Titanium or vanadium zeolites are pretreated by contacting with
an amino polyacid compound, such as ethylenediaminetetraacetic acid
or a salt thereof, prior to use in olefin epoxidation with hydrogen
peroxide.
Inventors: |
Qin; Kun; (Chadds Ford,
PA) ; Grey; Roger A.; (West Chester, PA) ;
Whitman; Peter J.; (Glen Mills, PA) |
Correspondence
Address: |
LYONDELL CHEMICAL COMPANY
3801 WEST CHESTER PIKE
NEWTOWN SQUARE
PA
19073
US
|
Family ID: |
35610239 |
Appl. No.: |
11/016053 |
Filed: |
December 17, 2004 |
Current U.S.
Class: |
549/531 |
Current CPC
Class: |
B01J 29/04 20130101;
C07D 303/04 20130101; B01J 2229/37 20130101; C07D 301/12 20130101;
B01J 2229/20 20130101; B01J 29/89 20130101; B01J 37/0045 20130101;
B01J 37/0203 20130101 |
Class at
Publication: |
549/531 |
International
Class: |
C07D 301/12 20060101
C07D301/12 |
Claims
1. An epoxidation process which comprises reacting an olefin with
hydrogen peroxide in the presence of a titanium or vanadium
zeolite, wherein the zeolite is pre-treated by contacting with an
amino polyacid compound.
2. The process of claim 1 wherein the zeolite is a titanium
silicalite.
3. The process of claim 1 wherein the zeolite is TS-1.
4. The process of claim 1 wherein the olefin is a C.sub.2-C.sub.6
olefin.
5. The process of claim 1 wherein the amino polyacid compound is
selected from the group consisting of amino polycarboxylic acids,
amino polyphosphonic acids, amino polysulfonic acids, and mixtures
thereof.
6. The process of claim 1 wherein the amino polyacid is selected
from the group consisting of ethylenediaminetetraacetic acid,
ethylenediaminetriacetic acid, nitrilotriacetic acid, iminodiacetic
acid, and mixtures thereof.
7. The process of claim 1 wherein reaction of olefin and hydrogen
peroxide is performed in a solvent selected from the group
consisting of water, C.sub.1-C.sub.4 alcohols, supercritical
CO.sub.2, and mixtures thereof.
8. The process of claim 1 wherein the hydrogen peroxide is formed
by the in situ reaction of hydrogen and oxygen in the presence of a
noble metal catalyst.
9. The process of claim 8 wherein the noble metal catalyst
comprises a noble metal and a support.
10. The process of claim 9 wherein the noble metal is selected from
the group consisting of palladium, platinum, and gold.
11. The process of claim 9 wherein the support is selected from the
group consisting of carbon, titania, zirconia, ceria, niobium
oxides, silica, alumina, silica-alumina, tantalum oxides,
molybdenum oxides, tungsten oxides, titania-silica,
zirconia-silica, ceria-silica, niobia-silica, polystyrene,
styrene-divinylbenzene copolymers, crosslinked polyethyleneimines,
polybenzimidazole, and mixtures thereof.
12. An epoxidation process which comprises reacting an olefin,
hydrogen and oxygen in the presence of a noble metal-containing
titanium or vanadium zeolite catalyst comprising a noble metal and
a titanium or vanadium zeolite, wherein the zeolite is pre-treated
by contacting with an amino polyacid compound.
13. The process of claim 12 wherein the olefin is a C.sub.2-C.sub.6
olefin.
14. The process of claim 12 wherein the amino polyacid compound is
selected from the group consisting of amino polycarboxylic acids,
amino polyphosphonic acids, amino polysulfonic acids, and mixtures
thereof.
15. The process of claim 12 wherein the amino polyacid is selected
from the group consisting of ethylenediaminetetraacetic acid,
ethylenediaminetriacetic acid, nitrilotriacetic acid, iminodiacetic
acid, and mixtures thereof.
16. The process of claim 12 wherein reaction of olefin, hydrogen
and oxygen is performed in a solvent selected from the group
consisting of water, C.sub.1-C.sub.4 alcohols, supercritical
CO.sub.2, and mixtures thereof.
17. A process comprising contacting a titanium or vanadium zeolite
with an amino polyacid compound selected from the group consisting
of amino polycarboxylic acids, amino polyphosphonic acids, amino
polysulfonic acids, and mixtures thereof.
18. The process of claim 17 further comprising heating the
contacted titanium or vanadium zeolite at a temperature greater
than 350.degree. C.
19. The process of claim 17 further comprising washing the
contacted titanium or vanadium zeolite.
20. The process of claim 17 wherein the amino polyacid is selected
from the group consisting of ethylenediaminetetraacetic acid,
ethylenediaminetriacetic acid, nitrilotriacetic acid, iminodiacetic
acid, and mixtures thereof.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an epoxidation process to produce
epoxides from olefins and hydrogen peroxide using a titanium or
vanadium zeolite catalyst that has been pre-treated by contacting
with an amino polyacid compound, such as ethylenediaminetetraacetic
acid or a salt thereof.
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.
The production of propylene oxide from propylene and an organic
hydroperoxide oxidizing agent, such as ethylbenzene hydroperoxide
or tert-butyl hydroperoxide, is commercially practiced technology.
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. Another commercially practiced technology is the direct
epoxidation of ethylene to ethylene oxide by reaction with oxygen
over a silver catalyst. Unfortunately, the silver catalyst has not
proved useful in commercial epoxidation of higher olefins.
[0003] Besides oxygen and alkyl hydroperoxides, another oxidizing
agent useful for the preparation of epoxides is hydrogen peroxide.
U.S. Pat. Nos. 4,833,260, 4,859,785, and 4,937,216, for example,
disclose the epoxidation of olefins 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 of higher olefins. Typically, the
catalyst comprises a noble metal that is supported on 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. 5,859,265 discloses
a catalyst in which a platinum metal, selected from Ru, Rh, Pd, Os,
Ir and Pt, is supported on a titanium or vanadium silicalite. 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 by-products such as
glycols or glycol ethers formed by the ring-opening of the epoxide
product or alkane by-product formed by the hydrogenation of olefin.
U.S. Pat. No. 6,417,378 describes a direct olefin epoxidation
process in which the selectivity for the reaction of olefin,
oxygen, and hydrogen in the presence of a noble metal-containing
titanium zeolite is enhanced by contacting the titanium zeolite
with a leaching agent such as lactic acid.
[0006] As with any chemical process, it is desirable to attain
still further improvements in the epoxidation methods and
catalysts. We have discovered an effective, convenient process to
form an epoxidation catalyst and its use in the epoxidation of
olefins.
SUMMARY OF THE INVENTION
[0007] The invention is a process for producing epoxides from
olefins and hydrogen peroxide using a pre-treated titanium or
vanadium zeolite catalyst, wherein the zeolite catalyst is
pre-treated by contacting with an amino polyacid compound. The
process of the invention results in higher selectivity to the
desired epoxide.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The epoxidation process of the invention utilizes a titanium
or vanadium zeolite. 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), and "TS-3" (as described in Belgian Pat. No. 1,001,038).
Titanium-containing molecular sieves having framework structures
isomorphous to zeolite beta, mordenite, ZSM-48, ZSM-12, 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] The synthesis of titanium or vanadium zeolites is well known
in the art. Titanium or vanadium zeolite synthesis typically
comprises reacting a titanium or vanadium compound, a silicon
source, and a templating agent at a temperature and for a time
sufficient to form a titanium or vanadium zeolite. After the
reaction mixture is formed, it is reacted at a temperature and a
time sufficient to form a molecular sieve. Typically, the reaction
mixture is heated at a temperature of about 100.degree. C. to about
250.degree. C. for a period of about 0.5 hours to about 96 hours in
a sealed vessel under autogenous pressure. Preferably, the reaction
mixture is heated at a temperature range from about 125.degree. C.
to about 200.degree. C., most preferably from about 150.degree. C.
to about 180.degree. C. After the desired reaction time, the
titanium or vanadium zeolite is recovered. Suitable zeolite
recovery methods include filtration and washing (typically with
deionized water), rotary evaporation, centrifugation, and the like.
The titanium or vanadium zeolite may be dried at a temperature
greater than about 20.degree. C., preferably from about 50.degree.
C. to about 200.degree. C. Preferably, the titanium or vanadium
zeolite is heated at temperatures greater than about 400.degree.
C., typically from about 450.degree. C. to about 1000.degree. C.,
and preferably from about 475.degree. C. to about 600.degree. C.,
in order to decompose the templating agent contained in the pores.
However, for the process of the invention it is not necessary for
the titanium or vanadium zeolite to be heated prior to
pre-treatment with the amino polyacid compound. If the
as-synthesized titanium or vanadium zeolite is produced in the form
of a powder, it may be spray dried, pelletized or extruded prior to
pre-treatment with the amino polyacid compound. If spray dried,
pelletized or extruded, the titanium or vanadium zeolite may
additionally comprise a binder or the like and may be molded, spray
dried, shaped or extruded into any desired form prior to or after
the pre-treatment with amino polyacid compound.
[0013] The process of the invention utilizes a pre-treated titanium
or vanadium zeolite. The pre-treated titanium or vanadium zeolite
is formed by contacting a titanium or vanadium zeolite with an
amino polyacid compound. An amino polyacid is any compound that
contains at least one amine functionality and two or more acid
functionalities such as a carboxylic, phosphonic, or sulfonic
acids; three or more acid functionalities are preferred; and four
or more acid functionalities are most preferred. Amino polyacids
include amino polycarboxylic acids, amino polyphosphonic acids, and
amino polysulfonic acids. Amino polyacids also include the related
salts of the amino polyacids, for instance the alkali, alkaline
earth metal, or ammonium salts of the amino polyacids.
[0014] Preferred amino polycarboxylic acids include alkylenediamine
polyacetic acids, nitrilotriacetic acid, and iminodiacetic acid.
Preferred alkylene diamine polyacetic acids include
ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, and
the like, and their salts thereof. Preferred amino polyphosphonic
acids include aminodiphosphonic acids such as
(dimethylamino)methylenediphosphonic acid and
(aminoethylene)diphosphonic acid, and their salts. Preferred amino
polysulfonic acids include amino disulfonic acids such as
2-methylaminobutane-1,4-disulfonate,
1-amino-8-naphthol-3,6-disulfonic acid,
4,4'-diamino-1,1'-bianthraquinonyl-3,3'-disulfonic acids, and the
like, and their salts. Particularly preferred amino polyacids are
the amino polycarboxylic acids, and especially preferred include
the alkylenediamine polyacetic acids, and the salts thereof.
Mixtures of amino polyacids may also be contacted with the titanium
or vanadium zeolite.
[0015] The titanium or vanadium zeolite is contacted with a
solution of an amino polyacid compound. The solution is typically
an aqueous solution, but may be any other solvent that dissolves
the amino polyacid compound. Any conventional contacting procedure
is suitable. The contacting temperature is not crucial to the
invention, however lower temperatures may require a longer contact
period. Preferably, the titanium or vanadium zeolite is contacted
with the amino polyacid compound at a temperature greater than
20.degree. C. More preferred wash temperatures are greater than
40.degree. C., most preferably from 40.degree. C. to 80.degree. C.
Pressures of from 0 to 1000 psig are generally useful for purposes
of this invention. Preferably, the pressure is sufficient to
maintain the solution substantially as a liquid phase when elevated
temperatures are used.
[0016] The contacting procedure may be carried out in a continuous
or a batch-type process. In a fixed bed embodiment of the
invention, it is preferred to pass the contacting amino polyacid
compound solution through the titanium or vanadium zeolite as a
flowing stream such that solution effluent is continually carried
away from the fixed bed. The contacting solution may preferentially
be recirculated. Liquid hourly space velocities in the range of
from 0.1 to 24 are generally satisfactory. When the contacting is
performed as a batch-type process, the titanium or vanadium zeolite
may be contacted with amino polyacid compound solution by agitating
the solution and removing the supernatant solution. The contacting
time is preferably in the range of from about 1 hour to 30
days.
[0017] Contacting preferentially also encompasses separating the
amino polyacid compound solution from the contacted zeolite. For
instance, after contacting, the titanium or vanadium zeolite may be
collected by filtration, centrifugation, decantation, or other such
mechanical means prior to use in the epoxidation reaction of the
invention. After contacting and collecting the zeolite by
filtration, centrifugation, decantation, or other such mechanical
means, the titanium or vanadium zeolite may also be dried. The
drying may be performed under vacuum, with heating, or a
combination. Preferably, the titanium or vanadium zeolite is heated
at a temperature greater than 350.degree. C. in the presence of an
oxygen-containing atmosphere or an inert gas to calcine or pyrolyze
the zeolite after the contacting step. Alternatively, the titanium
or vanadium zeolite may be pyrolyzed by heating at a temperature
greater than 350.degree. C. in the presence an inert gas following
the contacting step. The contacted titanium or vanadium zeolite may
also be washed by any suitable washing procedure. Preferable wash
solvents include water, alcohols, ketones, and the like.
[0018] After contacting the zeolite with the amino polyacid
compound, the titanium or vanadium zeolite may be used in the
epoxidation process as a powder or as a large particle size solid.
If the pre-treated titanium or vanadium zeolite is still in the
form of a powder, it may preferably be spray dried, pelletized or
extruded prior to epoxidation. If spray dried, pelletized or
extruded, the titanium or vanadium zeolite may additionally
comprise a binder or the like and may be molded, spray dried,
shaped or extruded into any desired form.
[0019] The epoxidation process of the invention comprises
contacting an olefin and hydrogen peroxide in the presence of the
pre-treated titanium or vanadium zeolite 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.
[0020] The hydrogen peroxide may be generated prior to use in the
epoxidation reaction. Hydrogen peroxide may be derived from any
suitable source, including oxidation of secondary alcohols such as
isopropanol, the anthraquinone process, and from direct reaction of
hydrogen and oxygen. The concentration of the aqueous hydrogen
peroxide reactant added into the epoxidation reaction is not
critical. Typical hydrogen peroxide concentrations range from 0.1
to 90 weight percent hydrogen peroxide in water, preferably 1 to 5
weight percent.
[0021] The amount of hydrogen peroxide to the amount of olefin is
not critical, but most suitably the molar ratio of hydrogen
peroxide:olefin is from 100:1 to 1:100, and more preferably in the
range of 10:1 to 1:10. One equivalent of hydrogen peroxide is
theoretically required to oxidize one equivalent of a
mono-unsaturated olefin substrate, but it may be desirable to
employ an excess of one reactant to optimize selectivity to the
epoxide.
[0022] The hydrogen peroxide may also be generated in situ by the
reaction of hydrogen and oxygen in the presence of a noble metal
catalyst. Although any sources of oxygen and hydrogen are suitable,
molecular oxygen and molecular hydrogen are preferred.
[0023] While any noble metal catalyst can be utilized (i.e., gold,
silver, platinum, palladium, iridium, ruthenium, osmium metal
catalysts), either alone or in combination, palladium, platinum and
gold metal catalysts are particularly desirable. Suitable noble
metal catalysts include high surface area noble metals, noble metal
alloys, and supported noble metal catalysts. Examples of suitable
noble metal catalysts include high surface area palladium,
colloidal palladium, and palladium alloys. However, particularly
preferred noble metal catalysts are supported noble metal catalysts
comprising a noble metal and a support.
[0024] For supported noble metal catalysts, the support is
preferably a porous material. Supports are well-known in the art.
There are no particular restrictions on the type of support that
are used. For instance, the support can be inorganic oxides,
inorganic chlorides, 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 supports include
silica, alumina, titania, zirconia, ceria, niobium oxides, tantalum
oxides, molybdenum oxides, tungsten oxides, amorphous
titania-silica, amorphous zirconia-silica, amorphous niobia-silica,
ceria-silica, and the like. Preferred organic polymer resins
include polystyrene, styrene-divinylbenzene copolymers, crosslinked
polyethyleneimines, and polybenzimidazole. Suitable supports also
include organic polymer resins grafted onto inorganic oxide
supports, such as polyethylenimine-silica. Preferred supports also
include carbon. Particularly preferred supports include silica,
silica-aluminas, titania, zirconia, ceria, niobia, and carbon.
[0025] Preferably, the support has a surface area in the range of
about 10 to about 700 m.sup.2/g, more preferably from about 50 to
about 500 m.sup.2/g, and most preferably from about 100 to about
400 m.sup.2/g. Preferably, the pore volume of the support 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 support 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.. In one
preferred embodiment of the invention, the supported noble metal
catalyst comprises a noble metal supported on the pre-treated
titanium or vanadium zeolite. The supported noble metal catalyst
may also comprise a mixture of noble metal-containing titanium or
vanadium zeolite and noble metal-free titanium or vanadium zeolite.
The noble metal-free titanium or vanadium zeolite is a titanium or
vanadium-containing molecular sieve that is free of added noble is
metal.
[0026] The supported noble metal catalyst contains a noble metal.
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 and gold are particularly
desirable, and palladium is especially preferred. Typically, the
amount of noble metal present in the supported catalyst will be in
the range of from 0.001 to 20 weight percent, preferably 0.005 to
10 weight percent, and particularly 0.01 to 5 weight percent. The
manner in which the noble metal is incorporated into the catalyst
is not considered to be particularly critical. For example, the
noble metal may be supported on the zeolite by impregnation,
adsorption, precipitation, or the like. Alternatively, the noble
metal can be incorporated into the zeolite by ion-exchange with,
for example, tetraammine palladium dichloride or tetraammine
palladium dinitrate.
[0027] There are no particular restrictions regarding the choice of
noble metal compound or complex used as the source of the noble
metal in the supported catalyst. For example, suitable compounds
include the nitrates, sulfates, halides (e.g., chlorides,
bromides), carboxylates (e.g. acetate, trifluoroacetate), and amine
complexes of noble metals. 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 pyrolyzed,
calcined, reduced, or a combination thereof. Satisfactory catalytic
performance can, however, be attained without any pre-reduction. To
achieve the active state of noble metal, the supported noble metal
catalyst may undergo pretreatment such as thermal treatment in
oxygen, nitrogen, vacuum, hydrogen, or air.
[0028] In one preferred embodiment of the invention, the
epoxidation of olefin with hydrogen and oxygen is carried out in
the presence of a noble metal-containing titanium or vanadium
zeolite which comprises a noble metal and the pre-treated titanium
or vanadium zeolite. In this particular embodiment, the titanium or
vanadium zeolite may be pre-treated with amino polyacid either
prior to or following incorporation of the noble metal. Preferably,
the titanium or vanadium zeolite has been pre-treated with amino
polyacid prior to noble metal incorporation. If the titanium or
vanadium zeolite is pre-treated with amino polyacid prior to noble
metal incorporation, the pre-treated titanium or vanadium zeolite
should be heated at a temperature greater than 350.degree. C. in
order to remove the amino polyacid prior to introduction of noble
metal. If heated, the pre-treated titanium or vanadium zeolite is
heated at temperatures greater than 350.degree. C., and more
preferably from about 375.degree. C. to about 800.degree. C. The
high temperature heating may be conducted in inert atmosphere which
is substantially free of oxygen, such as nitrogen, argon, neon,
helium or the like or mixture thereof. By "substantially free of
oxygen", it is meant that the inert atmosphere contains less than
10,000 ppm mole oxygen, preferably less than 2000 ppm. Also, the
heating may be conducted in an oxygen-containing atmosphere, such
as air or a mixture of oxygen and an inert gas. Alternatively, the
catalyst may also be heated in the presence of an inert gas such as
nitrogen prior to heating in an oxygen-containing atmosphere. The
heating process may be conducted such that the gas stream (inert,
oxygen-containing, or both) is passed over the pre-treated titanium
or vanadium zeolite. Alternatively, the heating may be performed in
a static manner. The zeolite could also be agitated or stirred
while being contacted with the gas stream.
[0029] The noble metal-containing titanium or vanadium zeolite
catalyst may also comprise a mixture of palladium-containing
titanium or vanadium zeolite and palladium-free titanium or
vanadium zeolite. The palladium-free titanium or vanadium zeolite
is a titanium or vanadium zeolite that is free of added palladium.
The addition of a palladium-free titanium or vanadium zeolite has
proven beneficial to productivity of the palladium that is present
in the catalyst. Preferably, the palladium-free titanium or
vanadium zeolite is also pre-treated with amino polyacid.
[0030] 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.
[0031] If epoxidation is carried out in the liquid (or
supercritical) 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, but are not limited to, alcohols, water,
supercritical CO.sub.2, or mixtures thereof. Suitable alcohols
include C.sub.1-C.sub.4 alcohols such as methanol, ethanol,
isopropanol, and tert-butanol, or mixtures thereof. Fluorinated
alcohols can be used. It is preferable to use mixtures of the cited
alcohols with water.
[0032] If epoxidation is carried out in the liquid (or
supercritical) 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.
[0033] 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 8. Suitable
salts of oxyacids contain an anion and cation. The anion portion of
the salt may include anions such as phosphate, 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. The process of the invention
may be carried out in a batch, continuous, or semi-continuous
manner using any appropriate type of reaction vessel or apparatus
such as a fixed-bed, transport bed, fluidized bed, stirred slurry,
or CSTR reactor. The catalyst is preferably in the form of a
suspension or fixed-bed. Known methods for conducting
metal-catalyzed epoxidations of olefins using an oxidizing agent
will generally also be suitable for use in this process. Thus, the
reactants may be combined all at once or sequentially.
[0034] 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 0-150.degree. C., more
preferably, 20-120.degree. C. Reaction or residence times of from
about 1 minute to 48 hours, more preferably 1 minute to 8 hours
will typically be appropriate. It is advantageous to work at a
pressure of 1 to 100 atmospheres.
[0035] 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
Edta Treatment of TS-1 Catalyst
[0036] TS-1 can be made according to any known literature
procedure. See, for example, U.S. Pat. No. 4,410,501, DiRenzo, et.
al., Microporous Materials (1997), Vol. 10, 283, or Edler, et. al.,
J. Chem. Soc., Chem. Comm. (1995), 155.
[0037] Catalyst 1A: Spray dried TS-1 (15 g, 80% TS-1, silica
binder, 2.0 wt. % Ti, calcined at 550.degree. C. in air) is
suspended in a saturated aqueous ethylenediaminetetraacetic acid
(EDTA) solution (150 mL of 0.5 wt. % EDTA) solution and stirred at
60.degree. C. for 18 hours. After filtration and washing (3 times
with 100 mL water), the obtained solid is air-dried at 110.degree.
C., and calcined in air at 550.degree. C. for 4 hours. Catalyst 1A
contains 1.8 wt. % Ti.
[0038] Catalyst 1B: Spray dried TS-1 (20 g, 80% TS-1, silica
binder, 2.0 wt. % Ti, calcined at 550.degree. C. in air) is
suspended in an aqueous dipotassium ethylenediaminetetraacetic acid
dihydrate (K.sub.2EDTA) solution (300 g of 3 wt. % K.sub.2EDTA
solution) and stirred at 60.degree. C. for 18 hours. After
filtration, the collected solid is washed with water (3 times with
100 mL). The washed solid is then refluxed in an acetic acid
solution (100 mL of 0.1 M acetic acid) for 1 hour. After filtration
and washing (3 times with 100 mL water), the obtained solid is
air-dried at 110.degree. C., and calcined in air at 550.degree. C.
for 4 hours. Catalyst 1B contains 1.8 wt. % Ti.
EXAMPLE 2
Epoxidation of Propylene with Hydrogen Peroxide
[0039] Spray dried TS-1 (as a comparative example), Catalysts 1A
and 1B are used in batch epoxidation of propylene with hydrogen
peroxide according to the following procedure:
[0040] A solution of methanol, water and hydrogen peroxide (40 g of
solution, 84% MeOH, 11% H.sub.2O, and 5% H.sub.2O.sub.2) is added
to a 125-mL PARR reactor equipped with a stirring bar. The catalyst
(0.15 g) is suspended in the reaction solution, and the reactor is
charged with propylene (20 g). The closed system is then heated at
50.degree. C. for 30 minutes. The concentration of unreacted
hydrogen peroxide is determined by titration (sodium thiosulfate
method) and the products are analyzed with GC.
[0041] The results are shown in Table 1.
EXAMPLE 3
Preparation of Pd/TS-1 Catalysts
[0042] Comparative Catalyst 3A: Spray dried TS-1 (16 g, 80% TS-1,
silica binder, 2.0 wt. % Ti, calcined at 550.degree. C. in air) is
slurried in water (14 g). An aqueous solution of tetra ammine
palladium dinitrate (0.299 g aqueous solution containing 5.37 wt. %
Pd) is then added, and the slurry is stirred at 30.degree. C. for
10 minutes. The pH is adjusted to 7.0 with 30 wt. % ammonium
hydroxide and the slurry is stirred at 30.degree. C. for an
additional 35 minutes before adjusting the pH to 7.6. The slurry is
filtered and the filter cake is washed with water (100 mL, three
times). The solids are vacuum dried at 55.degree. C. for 6 hours,
then calcined in air at 300.degree. C. for 4 hours. The calcined
solids are then transferred to a quartz tube, heated to 100.degree.
C. and treated with 5 vol. % hydrogen in nitrogen (100 cc/min) for
1 hour. The dried solid contains 0.1 wt. % Pd and 2.0 wt. % Ti.
[0043] Catalyst 3B: Catalyst 3B is made according to the procedure
of Comparative Catalyst 3A, except that Catalyst 1A (16 g) is used
in place of the spray dried TS-1. The dried solid contains 0.1 wt.
% Pd and 1.8 wt. % Ti.
[0044] Catalyst 3C: Catalyst 3C is made according to the procedure
of Comparative Catalyst 3A, except that Catalyst 1B (16 g) is used
in place of the spray dried TS-1. The dried solid contains 0.1 wt.
% Pd and 1.8 wt. % Ti.
EXAMPLE 4
Direct Epoxidation of Propylene with Hydrogen and Oxygen
[0045] To evaluate the performance of the catalysts prepared in
Example 3, the epoxidation of propylene using oxygen and hydrogen
is carried out. The following procedure is employed.
[0046] A 0.1 M ammonium phosphate buffer solution is prepared by
dissolving ammonium dihydrogen phosphate
((NH.sub.4)H.sub.2PO.sub.4, 11.5 g) in deionized water (900 g).
Aqueous ammonium hydroxide (30% NH.sub.4OH) is added to the
solution until the pH reads 6 via a pH meter. The volume of the
solution is then increased to exactly 1000 mL with deionized
water.
[0047] A working solution is then prepared by diluting 125 g of the
0.1 M ammonium phosphate buffer solution with a further 125 g of
deionized water, and mixing with methanol (750 g).
[0048] The reaction system consists a 300-cc stainless steel CSTR
type reactor. Gas and liquid feeds enter the reactor, and exit
through an outlet filter. Catalyst (6 g) and working solution (100
mL) are added to the reactor as a slurry. The slurry in the reactor
is heated to 60.degree. C. under about 300 psig, and is stirred at
1000 rpm. Additional working solution is pumped through the reactor
at a rate of about 30 g/hr. The gas flow rates were about 4500 sccm
(standard cubic centimeters per minute) of 5 vol. % oxygen in
nitrogen, 280 sccm propylene, and 135 sccm hydrogen. Propylene
oxide and equivalents ("POE"), which include propylene oxide
("PO"), propylene glycol, and glycol ethers, are produced during
the reaction. The products coming out of the reactor (in both vapor
and liquid phase) are analyzed by GC. The results of the GC
analyses are used to calculate the selectivities shown in Table 2.
TABLE-US-00001 TABLE 1 BATCH EPOXIDATION RESULTS WITH HYDROGEN
PEROXIDE USING TREATED AND UNTREATED CATALYSTS H.sub.2O.sub.2
Conver- PO POE Ti Productivity PO/POE sion produced produced (mol
POE/ Selectivity Catalyst (%) (mmol) (mmol) mol Ti/min) (%) .sup.1
TS-1 * 68.2 0.233 0.251 20.1 92.8 1A 65.6 0.232 0.245 21.8 94.5 1B
51.0 0.186 0.194 17.2 96.0 * Comparative Example .sup.1 PO/POE
Selectivity = moles PO/(moles PO + moles glycols + moles glycol
ethers) * 100.
[0049] TABLE-US-00002 TABLE 2 CONTINUOUS DIRECT EPOXIDATION RESULTS
PO/POE Catalyst Wt. % Pd Productivity .sup.1 Selectivity (%) .sup.2
3A * 0.1 0.48 85 3B 0.1 0.55 89 3C 0.1 0.45 90 * Comparative
Example .sup.1 Productivity = grams POE produced/gram of catalyst
per hour. .sup.2 PO/POE Selectivity = moles PO/(moles PO + moles
glycols + moles glycol ethers) * 100.
* * * * *