PROCESS FOR THE EPOXIDATION OF OLEFINS
Prior Art
From EP-A 100 119 it is known that propene can be converted by hydrogen
peroxide into propene oxide if a titanium-containing zeolite is used as
catalyst.
Unreacted hydrogen peroxide cannot be recovered economically from the
epoxidation reaction mixture. Furthermore, unreacted hydrogen peroxide
involves additional effort and expenditure in the working up of the
reaction mixture. The epoxidation of propene is therefore preferably
carried out with an excess of propene and up to a high hydrogen peroxide
conversion. In order to achieve a high hydrogen peroxide conversion it
is advantageous to use a continuous flow reaction system. Such a
reaction system may comprise either one or more tubular flow reactors or
an arrangement of two or more flow mixing reactors connected in series.
Examples of flow mixing reactors are stirred tank reactors, recycle
reactors, fluidized bed reactors and fixed bed reactors with recycling
of the liquid phase.
Furthermore the epoxidation of olefins with hydroperoxides is like most
oxidation reactions highly exothermic. Thus precautions have to be taken
to ensure sufficient removal of the heat generated by the exothermic
reaction in order to control the reaction. This problem is especially
pronounced in continuos flow systems using fixed bed reactors. Moreover
conversion and product selectivity in epoxidation reactions with the
effect that efficient temperature control is off uppermost importance.
According to a considerable number of patent disclosures as exemplified
by EP-A 230 349, EP-A 568 336, EP-A 712 852,
EP-A 757 045, JP-A 2-166636, WO 97/47613 and US-A 5,591,875 the

epoxidation reaction of olefins with hydrogen peroxide is performed in a
slurry of titanium containing zeolites as catalyst. In this reaction
mode temperature control is less difficult and thus a wide range of
suitable reaction temperatures from -20°C to 150°C are reported in these
documents whereby in the examples temperatures between 0°C and 85°C were
used.
EP-A 100 119 discloses in addition to reaction in catalyst slurry the
use of a tubular continuous flow reactor with a fixed catalyst bed that
is immersed in a cooling bath thermostated at 15° to 20°C.
In WO 97/47614 in example 8 reaction of propene with hydrogen peroxide
using a fixed bed tubular reactor having a cooling jacket is described.
The temperature of the cooling medium is controlled by a thermostat to
be in the range between 0° - 5°C. Yield and product selectivity are
still insufficient for commercial purposes.
As far as the applicants are aware all of the prior art documents
referring to epoxidation of olefins with hydrogen peroxide in tubular
fixed bed reactors equipped with cooling means disclose only the
temperature of the cooling medium without providing any information with
respect to the actual temperature within the reactor. As is known for
example from Walter Brotz et.al., Technische Chemie I, Weinheim, 1982,
pp 283; the temperature profile with respect to the cross-section of a
tubular reactor is parabolic with increasing temperature from the
periphery to the center of the reactor in case of exothermic reactions.
Additionally the temperature may vary along the axis of the tubular
reactor.
EP-A 659 473 describes an epoxidation process wherein a liquid mixture
of hydrogen peroxide, solvent and propene is led over a succession of
fixed bed reaction zones connected in series in down-flow operation. No

temperature control means are present within the reactor to remove the
generated heat from the single reaction zones. Thus each reaction zone
can be considered as an independent adiabatic reactor. In each reaction
zone the reaction is performed to a partial conversion, the liquid
reaction mixture is removed from each reaction zone, is led over an
external heat exchanger to extract the heat of reaction, and the major
proportion of this liquid phase is then recycled to this reaction zone
and a minor proportion of the liquid phase is passed to the next zone.
At the same time gaseous propene is fed in together with the liquid feed
stock mixture, is guided in a parallel stream to the liquid phase over
the fixed bed reaction zones, and is extracted at the end of the
reaction system in addition to the liquid reaction mixture as an oxygen-
containing waste gas stream. Although this reaction procedure enables
the propene oxide yield to be raised compared to conventional tubular
reactors without the temperature control described in EP-A 659 473, it
nevertheless involves considerable additional costs on account of the
complexity of the reaction system required to carry out the process.
From US-A 5 849 937 a process for epoxidation of propene using
hydroperoxides especially organic hydroperoxides is known. The reaction
mixture is fed to a cascade of serially connected fixed bed reactors in
down-flow regime with respect to each single reactor. Similarly to the
teaching of EP-A 659 473 in each reactor only partial conversion is
accomplished and the reactors are not equipped with heat exchange means.
Like in EP-A 659 473 the reaction heat is removed by passing the
effluent from each reactor through heat exchangers prior to introducing
the reaction mixture to the next fixed bed reactor in series thereby
adding to the complexity of the reaction system.
The disadvantages of the reaction systems as discussed in EP-A 659 473
and US-A 5 849 937 are the complexity and thus the increased costs for
investment.

In view of the cited prior art the object of the present invention is to
provide a process for the epoxidation of defines that results in
improved conversion and product selectivity compared to WO 97/47614
which can be carried out using conventional reaction systems.
Subject of the Invention
This object is achieved by a process for the catalytic epoxidation of
olefins with hydrogen peroxide in a continuous flow reaction system,
wherein the reaction mixture is passed through a fixed catalyst bed
within a reactor equipped with cooling means while maintaining a
temperature profile within the reactor such that the cooling medium
temperature of the cooling means is at least 40°C and the maximum
temperature within the catalyst bed is 60°C at the most.
The present inventors have surprisingly discovered that by conducting
the epoxidation reaction in such a way to fulfill the inventive
temperature profile requirement an optimized balance between conversion
and selectivity can be achieved with a standard reaction system. Thereby
now a process for epoxidation of olefins with high hydrogen peroxide
conversion and product selectivity at low investment costs is available
thus improving the overall economics of the process. Due to the
considerably high activation temperature for the epoxidation reaction
the process has to be conducted at a certain minimum temperature to
achieve economically reasonable conversion. But on the other hand the
heat generated by the exothermic reaction has to be effectively removed
from the reactor since at increased temperatures unwanted side reactions
take place with the result that product selectivity is decreased. While
maintaining the temperature profile in the reactor within the inventive
very narrow range both goals could be simultaneously achieved.

EP-A-659 473 discloses that in conventional tubular reactors temperature
rise in the catalyst bed exceeds 15°C whereas according to the examples
in EP-A-659 473 the temperature rise is 8°C at the most and in the
preferred embodiment 5½°C. Thus according to the teaching of EP-A-
659 473 temperature rise within the catalyst bed has to be kept as low
as possible in order to achieve high yields of propylene oxide. This
reduced temperature rise could only be achieved according to EP-A-
659 473 by conducting the reaction in a single reaction zone to only a
partial conversion with the result that the majority of the reaction
mixture has to be recycled, and by intermediate cooling the reaction
mixture.
But contrary to this expectation, as will be shown in more detail below
in the examples better overall yields based on hydrogen peroxide
comparable to the most preferred embodiments in EP-A-659 473 are
obtainable although a conventional reactor system without intermediate
external cooling is used according to the present invention.
Detailed Description of the Invention
In the practice of the present invention any reactor having a fixed
catalyst bed and cooling means can be used. Preferably, tubular, multi-
tubular or multi-plate reactors are used. Most preferably, tubular
reactors having a cooling jacket are applied since they are standardly
available at relatively low cost. As cooling medium that is pumped
through the cooling means, preferably the cooling jacket, all standard
cooling media like oils, alcohols, liquid salts or water can be used.
Water is most preferred.
According to the present invention the temperature profile within the
reactor is maintained such that the cooling medium temperature of the

cooling means of the tubular reactor is at least 40°C and the maximum
temperature within the catalyst bed is 60°C at the most, preferably
55°C. By preference the temperature of the cooling medium is controlled
by a thermostat.
The maximum temperature within the catalyst bed is measured with a
plurality of suitable temperature measurement means like thermocouples
or Pt-100 arranged approximately along the axis of the preferably
tubular reactor in suitable distances with respect to each other.
Whereby number, position within the reactor and distances between the
temperature measurement means are adjusted to measure the temperature of
the catalyst bed within the entire reactor as exact as necessary.
The maximum temperature of the catalyst bed can be adjusted by different
means. Depending on the selected reactor type the maximum temperature of
the catalyst bed can be adjusted by controlling the flow rate of the
reaction mixture passing through the reactor, by controlling the flow
rate of the cooling medium passing through the cooling means or by
lowering the catalyst activity, for instance by diluting the catalyst
with inert material.
The flow rate of the cooling medium is preferably adjusted to keep the
temperature difference between entry of the cooling medium into the
cooling means and exit below 5°C, preferably below 3°C, most preferably
2°C.
According to another preferred embodiment the reaction mixture is passed
through the catalyst bed with a superficial velocity from 1 to 100 m/h,
preferably 5 to 50 m/h, most preferred 5 to 30 m/h. The superficial
velocity is defined as the ratio of volume flow rate/cross section of
the catalyst bed. Consequently the superficial velocity can be varied in

a given tubular reactor by adjusting the flow rate of the reaction
mixture.
Additionally it is preferred to pass the reaction mixture through the
catalyst bed with a liquid hourly space velocity (LHSV) from 1 to 20 h1.
preferably 1.3 to 15 h1.
The process of the present invention can be conducted in down-flow or
up-flow operation mode, whereby down-flow operation mode is more
preferred. In a preferred embodiment of the present invention the
process is conducted to maintain the catalyst bed in a trickle bed
state.
Contrary to the teaching of EP-A 659 473 conducting conversion within a
single reactor or reaction zone to a limited extent is not required and
also not preferred according to the present invention. But in order to
be able to operate the process continuously when changing and/or
regenerating the epoxidation catalyst, two or more tubular flow reactors
may if desired also be operated in parallel or in series in the before-
described manner.
Crystalline, titanium-containing zeolites especially those of the
composition (Ti02)x(Si02)a.x where x is from 0.001 to 0.05 and having a MFI
or MEL crystalline structure, known as titanium silicalite-1 and
titanium silicalite-2. are suitable as catalysts for the epoxidation
process according to the invention. Such catalysts may be produced for
example according to the process described in US-A 4.410.501. The
titanium silicalite catalyst may be employed as a shaped catalyst in the
form of granules, extrudates or shaped bodies. For the forming process
the catalyst may contain 1 to 99* of a binder or carrier material, all
binders and carrier materials being suitable that do not react with
hydrogen peroxide or with the epoxide under the reaction conditions

employed for the epoxidation. Extrudates with a diameter of 1 to 5 mm
are preferably used as fixed bed catalysts.
When practicing the present invention it is preferred that the overall
feed stream to the reactor comprises an aqueous hydrogen peroxide
solution, an olefin and an organic solvent. Thereby these components may
be introduced into the reactor as independent feeds or one or more of
these feeds are mixed prior to introduction into the reactor. The feed
stream(s) to the reactor is (are) preferably adjusted to a temperature
that differs from the temperature of the cooling medium by less than X
°C, preferably to a temperature that is about the same.
Using the process according to the invention any olefins can be
epoxidized in particular olefins with 2 to 6 carbon atoms. The process
according to the invention is most particularly suitable for the
epoxidation of propene to propene oxide. For economic reasons it would
be preferred for an industrial scale process to use propene not in a
pure form but as a technical mixture with propane that as a rule
contains 1 to 15 vol.1 of propane. Propene may be fed as a liquid as
well as in gaseous form into the reaction system.
The hydrogen peroxide is used in the process according to the invention
in the form of an aqueous solution with a hydrogen peroxide content of 1
to 90 wt.%, preferably 10 to 70 wt.% and particularly preferably 30 to
50 wt.%. The hydrogen peroxide may be used in the form of the
commercially available, stabilised solutions. Also suitable are
unstabilised, aqueous hydrogen peroxide solutions such as are obtained
in the anthraquinone process for producing hydrogen peroxide.
The reaction is preferably carried out in the presence of a solvent in
order to increase the solubility of the olefin, preferably propene, in
the liquid phase. Suitable as solvent are all solvents that are not

oxidized or are oxidized only to a slight extent by hydrogen peroxide
under the chosen reaction conditions, and that dissolve in an amount of
more than 10 wt.% in water. Preferred are solvents that are completely
miscible with water. Suitable solvents include alcohols such as
methanol, ethanol or tert.-butanol; glycols such as for example ethylene
glycol, 1,2-propanediol or 1,3-propanediol; cyclic ethers such as for
example tetrahydrofuran, dioxane or propylene oxide; glycol ethers such
as for example ethylene glycol monomethyl ether, ethylene glycol
monoethyl ether, ethylene glycol monobutyl ether or propylene glycol
monomethyl ether, and ketones such as for example acetone or 2-butanone.
Methanol is particularly preferably used as solvent.
The pressure within the reactor is usually maintained at 5 to 50 bar,
preferably at 15 to 25 bar.
The olefin is preferably employed in excess relative to the hydrogen
peroxide in order to achieve a significant consumption of hydrogen
peroxide, the molar ratio of olefin, preferably propene, to hydrogen
peroxide preferably being chosen in the range from 1.1 to 10. When
adding a solvent the amount of solvent is preferably chosen so that only
a liquid phase is present in the reaction mixture. The solvent is
preferably added in a weight ratio of 0.5 to 20 relative to the amount
of hydrogen peroxide solution used. The amount of catalyst employed may
be varied within wide limits and is preferably chosen so that a hydrogen
peroxide consumption of more than 90#, preferably more than 95#, is
achieved within 1 minute to 5 hours under the employed reaction
conditions.
The present invention will be explained in more detail referring to the
following examples:

Examples 1 and 2 and Comparative Examples 1-6
A titanium-silicate catalyst was employed in all examples. The titanium-
silicate powder was shaped into 2 mm extrudates using a silica sol as
binder in accordance with example 5 in EP 00 106 671.1. The Hz02 employed
was prepared according to the anthrachinone process as a 40 wt-% aqueous
solution.
Epoxidation is carried out continuously in a reaction tube of 300 ml
volume, a diameter of 10 mm and a length of 4 m. The equipment is
furthermore comprised of three containers for liquids and relevant pumps
and a liquid separating vessel. The three containers for liquids
comprised methanol, the 40% H202 and propene. The 40% H202 was adjusted
with ammonia to a pH of 4.5. The reaction temperature is controlled via
an aqueous cooling liquid circulating in a cooling jacket whereby the
cooling liquid temperature is controlled by a thermostat. The reactor
pressure was 25 bar absolute. Mass flow of the feeding pumps was
adjusted to result in a propene feed concentration of 21.5 wt-#, a
methanol feed concentration of 57 wt-# and an H202 feed concentration of
9.4 wt-#. The reactor was operated in down-flow operation mode.
When performing the examples and comparative examples the cooling jacket
temperature (Tcool) and the total mass flow were varied and the maximum
Temperature (T,.ax) measured as indicated in Table 1. The flow rate was
adjusted to achieve comparable conversions. Product output was
determined by gas chromatography and the H202 conversion by titration. On
the basis of the gas chromatographical analysis of the hydrocarbons the
selectivity was calculated. It results from the amount of propene oxide
formed relative to the amount formed of all oxygen containing
hydrocarbons.


The data as given in Table 1 demonstrate that an optimized balance of
conversion and product selectivity is achieved within the narrow limits
of cooling medium temperature and maximum temperature in the catalyst
bed as defined by the present invention.

WE CLAIM
1. A process for the catalytic epoxidation of olefins with hydrogen peroxide in
a continuous flow reaction system, wherein the reaction mixture is passed
through a fixed catalyst bed within a reactor equipped with cooling means
while maintaining a temperature profile within the reactor such that the
cooling medium temperature of the cooling means is at least 40°C and the
maximum temperature within the catalyst bed is 60°C at the most and the
molar ratio of olefin to hydrogen peroxide is in the range from 1.1 to 10.
2. The process as claimed in claim 1, wherein the temperature profile within
the reactor is maintained such that the maximum temperature within the
catalyst bed is 55°C at the most.
3. The process of any of the preceding claims, wherein the reactor is a
tubular reactor and the cooling means is a cooling jacket.
4. The process of any of the preceding claims, wherein the reaction mixture
is passed through the catalyst bed in down-flow operation mode.
5. The process of any of the preceding claims, wherein the fixed catalyst bed
is maintained in a trickle bed state.
6. The process of any of the preceding claims, wherein the reaction mixture
is passed through the catalyst bed with a superficial velocity from 1 to 100
m/h, preferably 5 to 50 m/h, most preferably 5 to 30 m/h.

7. The process of any of the preceding claims, wherein the reaction
mixture is passed through the catalyst bed with a liquid hourly space
velocity (LHSV) from 1 to 20 h-1, preferably 1.3 to 15 h-1.
8. The process of any of the preceding claim, wherein the pressure within
the reactor is maintained at 5 to 50 bar, preferably at 15 to 25 bar.
9. The process of any of the preceding claims, wherein a titanium-
containing zeolite of the composition (TiO2)x(SiO2)1-x where x is from
0.001 to 0.05 is used as catalyst.
10. The process of any of the preceding claims, wherein the overall feed
stream to the reactor comprises an aqueous hydrogen peroxide
solution with a hydrogen peroxide content of 1 to 90 wt.%.
11. The process of claim 10, wherein the organic solvent is methanol.
12. The process of any of the preceding claims, wherein the olefin is
propene.

A process for the catalytic epoxidation of olefins with hydrogen peroxide in a
continuous flow reaction system, wherein the reaction mixture is passed through
a fixed catalyst bed within a reactor equipped with cooling means while
maintaining a temperature profile within the reactor such that the cooling medium
temperature of the cooling means is at least 40°C and the maximum temperature
within the catalyst bed is 60°C at the most and the molar ratio of olefin to
hydrogen peroxide is in the range from 1.1 to 10.