Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02342228 2001-02-28
Method For Producing a Titanium Silicate with RUT Structure
The present invention relates to a process for
preparing a titanium silicate having the RUT structure
and its use as catalyst and also to a process for
reacting organic compounds with the aid of this
catalyst.
Silicates as salts of the silicic acids are usually in
t0 the form of uniformly structured, spatially limited
acyclic or cyclic silicate anions or spatially infinite
silicate ions which are joined by means of associated
metal cations to form larger complexes. Examples of
structures of these spatially infinite silicate anions
i5 are chain, band, sheet and framework structures.
An important group of framework silicates are the
zeolites. The three-dimensional network of these
zeolites is built up of Si04 tetrahedra which are joined
20 to one another via shared oxygen bridges. The zeolites,
i.e. aluminosilicates, have ordered channel and cage
structures. The pore openings occurring here are in the
size range of >0.9 nm. An overview of the various known
structures of aluminosilicates may be found, for
25 example, in M.W. Meier, D. H. Olson and C. Baerlocher,
~~Atlas of Zeolite Structure Types", 4th Edition,
Elsevier, 1996.
Apart from the aluminosilicates, materials in which
30 titanium is present in place of silicon in the silicate
lattice are also known. Among these compounds,
particular mention may be made of titanium-containing
silicate having the MFI structure type. Such a silicate
is disclosed, for example, in US-A-4,410,501.
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Titanium silicates having the MFI structure are
typically obtained by first preparing an aqueous
mixture of an Si02 source and a titanium source. This
mixture is then reacted in a pressure vessel in the
presence of a template compound. This process is
described, for example, in US-A-4,666,692.
The present invention provides a process for preparing
a titanium silicate having the RUT structure, which
1o comprises the steps (i) and (ii):
(i) preparation of a mixture comprising at least
one Si02 source and at least one titanium
source;
(ii) crystallization of the mixture from (i) in a
pressure vessel with addition of at least one
template compound to give a crystallization
product,
wherein the template compounds used are amines or
ammonium salts which are suitable for stabilizing cages
of the silicate structure [445462] and [44566581] .
The present invention likewise provides the titanium
silicate having the RUT structure itself, able to be
prepared by a process which comprises the steps (i) and
(ii)
(i) preparation of a mixture comprising at least
one Si02 source and at least one titanium
source;
(ii) crystallization of the mixture from (i) in a
pressure vessel with addition of at least one
template compound to give a crystallization
product,
wherein the template compounds used are amines or
ammonium salts which are suitable for stabilizing cages
of the silicate structure [445462] and [44566581] .
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As Si02 source in the abovementioned process, use is
made, in particular, of esters of orthosilicic acid.
Preference is given to using tetraesters. Tetraethyl
orthosilicate is particularly preferably used in the
process of the present invention.
As titanium source in the process of the present
invention, it is possible to use, for example, titanium
dioxide. However, preference is given to using
titanates, particularly preferably orthotitanates and
in particular tetraisopropyl orthotitanate.
It is of course possible to use two or more suitable
Si02 sources and/or two or more suitable titanium
sources in the process of the present invention.
In the process of the present invention, a mixture is
prepared from the Si02 source or sources and the
titanium source or sources. Particular preference is
given to using an aqueous mixture of these components.
The order in which the components are mixed is not
critical. The way in which the components are mixed
with one another is likewise not critical. All methods
and apparatuses known from the prior art, e.g. blade
stirrers, can be used for this purpose.
In the process of the present invention, a template
compound as described above is added to the above-
described mixture. This template compound is preferably
added in an aqueous solution to the above-described
mixture. In general, the concentration of this solution
of template compound can be chosen freely. However, it
preferably has a content of template compound in the
range from 1 to 25o by weight, particularly preferably
in the range from 2 to 15% by weight and in particular
in the range from 3 to 8o by weight.
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Examples of such template compounds are
tetramethylammonium hydroxide or pyrrolidine.
In addition to the template compound, one or more
further basic compounds, e.g. hydroxides of ammonium
salts, can be added to the abovementioned mixture of
the Si02 source or sources and the titanium source or
sources in the process of the present invention.
l0 The alkali metal or alkaline earth metal content of the
suspension obtained from step (ii) in the process of
the present invention is generally < 1000 ppm,
preferably < 500 ppm and particularly preferably
c 200 ppm.
Depending on the Si02 and/or titanium sources, the
preparation of the mixture as described above may
result in formation of an alcohol by hydrolysis. This
is generally distilled from the mixture at from 90 to
100°C, but can also remain in the mixture. The residue
is transferred to a pressure vessel. If the starting
materials are chosen so that no distillation is
necessary, the mixture comprising the SiOz source or
sources and the titanium source or sources can be
transferred immediately to the pressure vessel.
The mixture is reacted in the pressure vessel at a
reaction temperature which is generally in the range
from 80 to 300°C, preferably from 120 to 250°C,
particularly preferably from 150 to 220°C. The reaction
time here is generally in the range from 3 to 15 days,
preferably in the range from 6 to 13 days, particularly
preferably in the range from 8 to 11 days.
After the reaction is complete, the crystalline product
resulting from the reaction can be separated from the
liquid phase by all customary methods of the prior art.
Depending on the application for which the product is
CA 02342228 2001-02-28
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intended, it may be necessary to wash it one or more
times with water. The solid obtained is dried in the
process of the present invention. Here too, use can be
made of all customary methods of the prior art. For
example, the solid obtained can be dried in an oven
suitable for this purpose at temperatures in the range
from 105 to 115°C. The drying time is generally from 5
to 20 hours, preferably from 7 to 15 hours.
Naturally, spray drying the crystalline product as
described above, which is present in suspension in the
liquid phase, in at least one spray-drying step is also
conceivable.
To remove the template compound added in step (ii) and
any further basic compounds, the crystalline product is
calcined at least once subsequent to drying.
The temperatures selected in the calcination or
calcinations are generally in the range from 120 to
850°C, preferably from 180 to 700°C, particularly
preferably from 250 to 550°C. Calcination is generally
carried out in an oxygen-containing atmosphere in which
the oxygen content is from 0.1 to 90o by volume,
preferably from 0.2 to 22o by volume, particularly
preferably from 0.2 to loo by volume. The pressure
selected for the calcination is generally in the range
from 0.01 to 5 bar, preferably from 0.05 to 1.5 bar.
Accordingly, the present invention also provides a
process for preparing a titanium silicate having the
RUT structure which comprises, in addition to the steps
(i) and (ii) as described above, the steps (iii) and
(iv)
(iii) drying of the crystallization product resulting
from (ii) ;
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(iv) calcination of the dried product from (iii).
To prepare the titanium silicate having the RUT
structure by the process of the present invention, as
described above, the concentrations of the SiOz source
or sources and the titanium source or sources for
preparing the mixture as described in step (i) are
selected so that the crystalline product resulting from
step (ii) or (iv) has a titanium concentration which is
generally in the range from 0.001 to 5o by weight.
However, the titanium concentrations in the titanium
silicate having the RUT structure are preferably
selected so as to be in the range from 0.002 to 1% by
weight, particularly preferably from 0.003 to 0.5o by
IS weight, more particularly preferably from 0.004 to 0.1%
by weight, very particularly preferably from 0.005 to
0.05% by weight and most preferably about 0.01% by
weight.
Accordingly, the present invention also provides a
titanium silicate having the RUT structure whose
titanium content is in the range from 0.001 to 5o by
weight.
Here, these figures for the titanium content are based
on results obtained from wet chemical analysis.
The present invention also provides a titanium silicate
having the RUT structure which displays at least the
following reflections in the X-ray diffraction pattern:
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Diffraction angle 2A Lattice plane spacing d
(0.1 nm)
10.79 8.19
13.69 6.45
14.48 6.10
20.19 4.49
22.16 4.00
23.26 3.82
27.45 3.24
A further characteristic which distinguishes titanium-
containing zeolites from zeolites which do not contain
titanium is a specific lattice vibration band in the IR
spectrum (DE 3047798). Accordingly, the present
invention also provides a titanium silicate having the
RUT structure which displays a band in the range from
955 to 970 cm-1 in the IR spectrum.
Titanium zeolites having the MFI structure are known to
be suitable as catalysts for the reaction of organic
compounds. This is disclosed, for example, in
B. Notari, Stud. Surf. Sci. Catal., Vol. 37, Amsterdam,
pages 413 to 425 (1987). The titanium silicates of the
present invention having the RUT structure have also
been found to be suitable as catalysts.
The present invention therefore also provides for the
use of a titanium silicate as defined herein as
catalyst.
For use of the titanium silicate of the present
invention having the RUT structure as catalyst,
particularly mention may be made of processes in which
CA 02342228 2001-02-28
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organic compounds are reacted. The present invention
therefore also provides a process for the reaction of
an organic compound in which the organic compound is
brought into contact with a catalyst according to the
present invention, as described above, during the
reaction.
In particular, the present invention also relates to a
process in which the organic compound is oxidized
during the reaction.
Examples of reactions are:
the epoxidation of olefins, e.g. the preparation of
IS propene oxide from propene and Hz02 or from propene and
mixtures which provide H202 in situ;
hydroxylations, e.g. the hydroxylation of monocyclic,
bicyclic or polycyclic aromatics to form
monosubstituted, disubstituted or higher-substituted
hydroxyaromatics, for example the reaction of phenol
and H202 or of phenol and mixtures which provide H202 in
situ to form hydroquinone;
the conversion of alkanes into alcohols, aldehydes and
acids;
oxime formation from ketones in the presence of H20z or
mixtures which provide H202 in situ and ammonia
(ammonoximation), for example the preparation of
cyclohexanone oxime from cyclohexanone;
isomerization reactions, e.g. the conversion of
epoxides into aldehydes;
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and also further reactions described in the literature,
as are described, for example, by W. Holderich in
"Zeolites: Catalysts for the Synthesis of Organic
Compounds", Elsevier, Stud. Surf. Sci. Catal., 49,
Amsterdam (1989), p. 69 to 93 and particularly for
possible oxidation reactions by B. Notari in Stud.
Surf. Sci. Catal., 37 (1987), pp. 413 to 425, or in
Advances in Catalysis, Vol. 41, Academic Press (1996),
pp. 253 to 334.
The term "mixture which provides H202 in situ" as used
for the purposes of the present invention means that
this mixture, which can consist of two or more
different compounds, is combined in a single-vessel
reaction with at least one compound which is to be
reacted with H202 and the H202 formed from the mixture
reacts either at the time it is formed or at a later
point in time with the compound or compounds to be
reacted.
Depending on the type of process in which the titanium
silicate of the present invention having the RUT
structure is used as catalyst, the silicate is used
either as powder or as shaped bodies.
When the catalyst is used as powder, recourse can be
made directly to the crystalline product which results
from the process of the present invention, as described
above .
If the crystalline product is shaped to form a shaped
body, it is possible to employ, for example, the dried
crystalline product from the above-described step
(iii) .
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The product obtained, for example, from a spray-drying
step is compacted to produce the shaped body in a
further step of the process of the present invention.
This processing step can be carried out in all
apparatuses known for this purpose, but preference is
given to kneaders, pan mills or extruders. For
industrial implementation of the process of the present
invention, particular preference is given to using a
pan mill.
In this shaping step, one or more viscosity-increasing
substances can be additionally added as pasting agents.
All suitable substances known from the prior art can be
used for this purpose. In the process of the present
invention, preference is given to using water or
mixtures of water with one or more organic substances
which are miscible with water as pasting agents. The
pasting agent can be removed again during the later
calcination of the shaped body.
Preference is given to using organic, in particular
hydrophilic organic, polymers such as cellulose,
cellulose derivatives such as methylcellulose,
polyvinylpyrrolidone, ammonium (meth)acrylates, Tylose,
particularly preferably methylcellulose.
As further additives, it is possible to add ammonium,
amines or amine-like compounds such as
tetraalkylammonium compounds or aminoalkoxides. Such
further additives are described in EP-A 0389041, EP-A
02002660 and WO 95/19222, the full scope of which is
incorporated by reference into the present application.
Instead of basic additives, it is also possible to use
acidic additives. Preference is given to acidic organic
compounds which can be burnt out by calcination after
CA 02342228 2001-02-28
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the shaping step. Particular preference is given to
carboxylic acids.
To influence properties of the shaped body, it is
possible to add further substances, preferably organic
compounds, in particular organic polymers, as further
additives which can also influence the formability of
the composition. Such additives are, inter alia,
alginates, polyvinylpyrrolidones, starch, cellulose,
l0 polyethers, polyesters, polyamides, polyacrylates,
polymethacrylates, polyethylenimines or polyetherols.
Of course, it is also possible for mixtures of two or
more of the abovementioned additives to be
incorporated.
The order in which the additives are added is not
critical.
If desired, the generally still pulverulent mixture can
be homogenized for from 10 to 180 minutes in a kneader
or extruder prior to compaction. This is generally
carried out at temperatures in the range from about
10°C to the boiling point of the pasting agent and at
atmospheric pressure or slightly superatmospheric
pressure. The mixture is kneaded until an extrudable
composition has been formed.
In principle, kneading and shaping can be carried out
using all conventional kneading and shaping apparatuses
or processes as are well known from the prior art and
are suitable, for example, for the production of shaped
catalyst bodies.
Preference is given to using processes in which shaping
occurs in customary extruders to form, for example,
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extrudates having a diameter of usually from about 1 to
about 10 mm, in particular from about 1.5 to about
mm. Such extrusion apparatuses are described, for
example, in "Ullmanns Enzyklopadie der Technischen
5 Chemie", 4th Edition, Volume 2 (1972), p. 295 ff. Apart
from the use of an extruder, the use of a ram extruder
is also preferred. In the case of industrial
application of the process, preference is given to
using extruders.
The extrudates are either rods or honeycombs. The
honeycombs can be of any shape. The extrudates can be,
for example, round rods, tubes or star-shaped profiles.
The honeycombs can also have any diameter. The external
shape and the diameters are generally decided by the
process engineering requirements which are determined
by the process in which the shaped body is to be used.
Before, during or after the shaping step, noble metals
in the form of suitable noble metal components, for
example in the form of water-soluble salts, can be
applied to the material. This preferably gives
catalysts containing from 0.01 to 30o by weight of one
or more noble metals selected from the group consisting
of ruthenium, rhodium, palladium, osmium, iridium,
platinum, rhenium, gold and silver.
However, in many cases it is most useful to apply the
noble metal components to the shaped bodies after the
shaping step, particularly when high-temperature
treatment of the noble metal-containing catalyst is
undesirable. The noble metal components can be applied
to the shaped body by, in particular, ion exchange,
impregnation or spraying. They can be applied by means
of organic solvents, aqueous ammoniacal solutions or
supercritical phases such as carbon dioxide.
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The use of the abovementioned methods enables a wide
variety of types of noble metal catalysts to be
produced. Thus, one type of coated catalyst can be
produced by spraying the noble metal solution onto the
shaped bodies. The thickness of this noble metal-
containing shell can be significantly increased by
impregnation, while ion exchange results in virtually
uniform distribution of noble metal across the cross
section of the catalyst particles.
l0
After extrusion has been carried out, the shaped bodies
obtained are dried at generally from 50 to 250°C,
preferably from 80 to 250°C, at pressures of generally
from 0.01 to 5 bar, preferably from 0.05 to 1.5 bar,
for from about 1 to 20 hours.
The subsequent calcination is carried out at from 250
to 800°C, preferably from 350 to 600°C, particularly
preferably from 400 to 500°C. The pressure range is
similar to that for drying. In general, calcination is
carried out in an oxygen-containing atmosphere in which
the oxygen content is from 0.1 to 90% by volume,
preferably from 0.2 to 22o by volume, particularly
preferably from 0.2 to loo by volume.
The titanium silicate of the present invention having
the RUT structure is preferably used as powder when
employed as catalyst.
The titanium silicate having the RUT structure which
has been discussed comprehensively above is
particularly suitable for the epoxidation of alkenes.
Accordingly, the present invention also provides a
process in which an alkene is reacted to form an alkene
oxide .
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Alkenes which are suitable for such a functionalization
are, for example:
ethylene, propylene, but-1-ene, but-2-ene, isobutene,
butadiene, pentenes, isoamylene, piperylene, hexenes,
hexadienes, heptenes, octenes, diisobutene,
trimethylpentene, nonenes, dodecene, tridecene,
tetradecanes to eicosenes, tripropylene and
tetraproylene, polybutadienes, polyisobutenes,
isoprenes, terpenes, geraniol, linalol, linalyl
acetate, methylenecyclopropane, cyclopentene,
cyclohexene, norbornene, cycloheptene,
vinylcyclohexane, vinyloxirane, vinylcyclohexene,
styrene, cyclooctene, cyclooctadiene, vinylnorbornene,
indene, tetrahydroindene, methylstyrene,
dicyclopentadiene, divinylbenzene, cyclododecene,
cyclododecatriene, stilbene, diphenylbutadiene, vitamin
A, beta-carotene, vinylidene fluoride, allyl halides,
crotyl chloride, methallyl chloride, dichlorobutenes,
?0 allyl alcohol, methallyl alcohol, butenols,
butenediols, cyclopentenediols, pentenols, octadienols,
tridecenols, unsaturated steroids, ethoxyethylene,
isoeugenol, anethole, isoallesafrol, unsaturated
carboxylic acids such as acrylic acid, methacrylic
acid, crotonic acid, malefic acid, vinylacetic acid,
unsaturated fatty acids such as oleic acid, linoleic
acid, palmitic acid, and also naturally occurring fats
and oils.
An advantage of the titanium silicate having the RUT
structure prepared according to the present invention
is that the crystalline product as described above
resulting from the process of the present invention has
a large specific external surface area. This is
generally in the range from 10 to 200 m2/g, preferably
in the range from 80 to 120 m2/g.
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These values for the specific external surface area are
based on results obtained by nitrogen adsorption in
accordance with DIN 66131.
Furthermore, the titanium silicate of the present
invention having the RUT structure has a particular
internal structure in which essentially no pores having
a width of > 5.5 A are present.
It is thus possible, without restricting the pore
system as in the case of zeolites having a structure
other than the RUT structure, for sterically very bulky
molecules and/or mixtures of natural materials to be
reacted catalytically on the external surface. Since
catalysis over the titanium silicate of the present
invention having the RUT structure takes place at the
external surface, relatively high molecular weight
compounds can be reacted in polymer-analogous reactions
of all the abovementioned reaction classes.
When using the titanium silicate of the present
invention having the RUT structure as catalyst in the
conversion of an alkene to an alkene oxide, it is
possible to employ all oxidants which are suitable for
this purpose. Examples which may be mentioned are
hydrogen peroxide, compositions which can generate
hydrogen peroxide in situ, or organic hydroperoxides.
An advantage of the titanium silicate of the present
invention having the RUT structure when used as
catalyst is that, in contrast to titanium-containing
zeolite catalysts of the prior art, it is possible to
use, for example, hydrogen peroxide solutions which
have a very low concentration of H202.
Preference is given to using H202 solutions whose HZOZ
concentration is in the range from 0.05 to 40% by
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weight, particularly preferably from 0.1 to 20% by
weight, in particular from 0.5 to loo by weight.
Particularly when the oxidant used is a mixture of
hydrogen and oxygen, the titanium silicate of the
invention having the RUT structure can further comprise
one or more elements selected from the group consisting
of ruthenium, rhodium, palladium, osmium, iridium,
platinum, iron, cobalt, nickel, rhenium, silver and
l0 gold in addition to titanium, silicon and oxygen.
Naturally, it is also possible in the process of the
present invention for the titanium silicate having the
RUT structure used as catalyst to be regenerated after
t5 it has become exhausted.
If the catalyst has been used in powder form, it can be
regenerated by, for example, washing it with oxidizing
mineral acids such as nitric acid and then refluxing it
20 with hydrogen peroxide.
If the titanium silicate of the present invention
having the RUT structure has been used as catalyst in
the form of a shaped body, the shaped body can be
25 regenerated in or outside the reaction arrangement
employed, e.g. a reactor, by treating it with gases
which comprise or provide oxygen, e.g. air, synthetic
air, nitrogen oxides or molecular oxygen. Here, the
catalyst is preferably heated from room temperature to
30 a temperature in the range from 120 to 850°C,
preferably from 180 to 700°C and particularly
preferably from 250 to 550°C, and air or oxygen is
added to an inert gas flowing over the catalyst in
concentrations of generally from 0.1 to 90o by volume,
35 preferably from 0.2 to 22o by volume and particularly
preferably from 0.2 to 10% by volume, based on the
total gas stream. A pressure of generally from 0.01 to
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bar, preferably from 0.05 to 1.5 bar, is generally
employed.
The following examples illustrate the process of the
5 present invention without restricting it in any way.
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EXAMPLES
Example 1
455 g of tetraethyl orthosilicate were placed in a
four-necked flask (2 1 capacity) and, while stirring
(250 rpm, blade stirrer), 15 g of tetraisopropyl
orthotitanate were added from a dropping funnel over a
period of 30 minutes. A colorless, clear mixture was
formed. Finally, 800 g of a 20% strength by weight
tetramethylammonium hydroxide solution (alkali metal
contents < 10 ppm) was added and the mixture was
stirred for another one hour. The alcohol mixture
(about 450 g) formed by hydrolysis was distilled off at
90 - 100°C. 1.5 1 of deionized water were added and the
now slightly opaque sol was transferred to a 2.5 1
stirring autoclave (stainless steel 1.4571).
At a heating rate of 3°C/min, the closed autoclave
(anchor stirrer, 200 rpm) was brought to a reaction
temperature of 175°C. The reaction was ended after 10
days. The cooled reaction mixture was centrifuged and
the solid was washed a number of times with water until
neutral. The solid obtained was dried at 100°C for 24
hours (weight: 149 g).
Finally, the template remaining in the product was
burnt off in air at 550°C for 5 hours (calcination
loss: 14o by weight).
The calcined product had a Ti content of 1.5s by weight
and a residual alkali metal content of less then
100 ppm according to wet chemical analysis. The yield
based on Si02 used was 870. The crystallites had a size
of from 0.05 to 0.25 ~m and the product displayed a
typical band at about 960 cm-1 in the IR.
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The product displays the X-ray diffraction pattern
reproduced in Figure 1. In Figure 1, the intensity I is
plotted on the ordinate.
Example 2
A 250 ml glass autoclave was charged with 36 g of
methanol and 0.5 g of titanium silicate powder from
Example 1 and the suspension was stirred by means of a
magnetic stirrer. The closed glass autoclave was then
cooled to -30°C and 10 g of propene were injected.
Subsequently, the glass autoclave was warmed to 0°C and
17 g of a 300 strength hydrogen peroxide solution were
metered in. The reaction mixture was stirred at 0°C for
5 hours under the autogenous pressure. The catalysts
was then centrifuged off and the propylene oxide
content was determined by gas chromatography. The .
propylene oxide content was 0.3% by weight.
Example 3
A 250 ml glass autoclave was charged with 36 g of
methanol and 0.5 g of titanium silicate from Example l
and the suspension was stirred by means of a magnetic
stirrer. The closed glass autoclave was then cooled to
-30°C and 20.2 g of propene were injected.
Subsequently, the glass autoclave was warmed to 0°C and
23 g of 0.5% strength hydrogen peroxide solution were
metered in. The reaction mixture was stirred at 0°C for
30 minutes under the autogenous pressure. The catalyst
was then centrifuged off and the propylene oxide
content was determined by gas chromatography. The
propylene oxide content was 0.0980 by weight.
