Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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' ' ' Le A 32 871
WO 99/39827 PCT/EP99/00035
A method of re~eneratin~ support catalysts coated with gold particles for the
oxidation of unsaturated hydrocarbons
This invention relates to a method of regenerating catalysts for the catalytic
production of epoxides from unsaturated hydrocarbons by oxidation with
molecular
oxygen in the presence of molecular hydrogen in the gas phase, and also
relates to the
use of these regenerated catalysts for the oxidation of unsaturated
hydrocarbons.
The direct oxidation of unsaturated hydrocarbons with molecular oxygen in the
gas
phase does not normally proceed below 200°C - even in the presence of
catalysts, and
it is therefore difficult selectively to produce oxidation products which are
susceptible
to oxidation, such as epoxides, alcohols or aldehydes for example, since
subsequent
reactions of these products frequently proceed more rapidly than the oxidation
of the
olefines themselves which are used.
As an unsaturated hydrocarbon, propene oxide constitutes one of the most
important
basic chemicals of the chemical industry. More than 60 % of this substance is
used in
the plastics sector, particularly for the production of polyether polyols for
the
synthesis of polyurethanes. In addition, propene oxide derivatives have an
even larger
share of the market in the field of glycols, particularly for lubricants and
antifreeze
compositions.
World-wide, about 50 % of propene oxide is currently synthesised by the
"chlorohydrin method". The other 50 % is obtained by "oxirane methods", and
this
trend is increasing.
In the chlorohydrin method (F. Andreas et al.; Propylenchemie, Berlin 1969),
the
chlorohydrin is first formed by the reaction of propene with HOCI (water and
chlorine), and propene oxide is subsequently formed from the chlorohydrin by
the
~0 separation of HC1 with lime. This method is costly, but when it is
optimised
appropriately it provides a high selectivity (>90 %) at high conversions.
Chlorine
losses in the chlorohydrin method, in the form of valueless calcium chloride
or
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sodium chloride solutions, have hitherto led to a search for oxidation systems
which
are free from chlorine.
Instead of the inorganic oxidising agent HOCI, organic compounds have been
selected
for the transfer of oxygen to propene (oxirane method). This indirect
epoxidation is
based on the fact that organic peroxides such as hydroperoxides or
peroxycarboxylic
acids in the liquid phase are capable of selectively transferring their
peroxide oxygen
to olefines with the formation of epoxides. In the course of this process,
hydroperoxides are converted into alcohols and peroxycarboxylic acids are
converted
into acids. Hydroperoxides and peroxycarboxylic acids are produced from the
corresponding hydrocarbon or aldehyde, respectively, by autoxidation with air
or
molecular oxygen. One serious disadvantage of indirect oxidation is the
economic
dependence of the value of propene oxide on the market value of the coupled
product.
Using titanium silicate (TS 1 ) as a catalyst (Notari et al., US 44 10 501 (
1983) and US
47 O1 428) it proved possible for the first time to epoxidise propene with
hydrogen
peroxide in the liquid phase under very mild reaction conditions with
selectivities >
90 % (Clerici et al., EP-A 230 949).
The oxidation of propene by a gas mixture consisting of molecular oxygen and
molecular hydrogen proceeds with a low yield in the liquid phase over titanium
silicates containing platinum metal (JP-A 92/352771).
The direct gas phase oxidation of propene to form propene oxide with a
selectivity of
100 % was described for the first time in EP-A 0 709 360 A1 (Haruta et al.).
This is a
catalytic gas phase oxidation with molecular oxygen in the presence of the
reducing
agent hydrogen. A special titanium dioxide comprising an anatase modification
which
is coated with nanometre-scale gold particles is used as the catalyst. The
maximum
propene conversion and yield are quoted as 1 %. The Au/Ti02 catalysts
described
,0 achieve a propene conversion of about 1 % for a very short time only.
Typical half
lives at moderate temperatures (40-50°C) are only 100-200 minutes, for
example.
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The regeneration of catalysts which are coated with gold and which are based
on
titanium silicate by dilute hydrogen peroxide solution was known hitherto
{Thiele et
al., J. Mol. Cat. 117, pages 351-356, 1997).
The possibility of efficiently regenerating the catalyst is of decisive
importance for the
development of a propene oxidation process which is of economic interest.
It has surprisingly been found that when catalysts which have become inactive
are
treated with water, dilute acids or dilute hydrogen peroxide solution,
catalytic
activities of up to 80 % of the original activity can be achieved again. The
catalysts
which have become inactive are preferably washed with dilute acids (e.g.
dilute
H2S04 or HF) at a pH of 4 to 7.5, preferably 5.5 to 6.
The present invention therefore relates to a method of regenerating support
catalysts,
which are coated with gold particles and which are based on titanium dioxide
or
hydrous titanium dioxide, for the oxidation of unsaturated hydrocarbons in the
gas
phase, wherein the catalytic activity of the catalyst is regenerated by
bringing it into
contact with water or with dilute acid or with a dilute hydrogen peroxide
solution.
?0 Treatment in the sense of the present invention can be effected at room
temperature or
at elevated temperature. In variants of the invention, elevated pressures
and/or the use
of steam can advantageously be put into effect.
Treatment can be effected separately after removing the catalyst from the
reactor, or
can also be effected in the reactor if the catalytic oxidation of propene in
the presence
of hydrogen and regeneration of the catalyst with water or hydrogen are caused
to
proceed cyclically in succession. In one embodiment of this variant, it is
advantageous
to perform the operations of catalysis and regeneration simultaneously in a
plurality of
spatially separated reactors which are connected in series. These phases can
be
~0 connected so that they operate alternately.
Agitation of the regeneration mixture may be advantageous, but is not a
requirement
of the use according to the invention.
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According to the invention, support catalysts can be regenerated which are
coated with
nanometre-scale gold particles and which are based on titanium dioxide or
hydrous
titanium oxide. These catalysts are preferably produced by the "deposition-
precipitation" method.
The concentration of dilute hydrogen peroxide solution is usually within the
range
from 1 to 10 % by weight, preferably 1 to 4 % by weight.
When catalysts which are regenerated according to the invention are used for
the
oxidation of unsaturated hydrocarbons, there is no restriction on the amount
of
catalyst which is used and on the amounts of gases which are used. The "space
velocity" of the gas stream through the catalyst bed should usually amount to
about
0.5 to 20 1/g catalyst per hour.
IS
The use according to the invention of regenerated catalysts is effected in the
presence
of the gases oxygen and hydrogen. In the presence of these gases at
150°C, the
oxygenated products propene oxide and acetone are also formed in addition to
the
main products comprising water, propane and C02. If the reaction temperature
is
reduced to <100°C, preferably to 30-60°C, the formation of water
is suppressed
considerably, and the formation of COZ is suppressed completely. At a
temperature
between 30 and 60°C only traces of the other components (about 1 % with
respect to
propene oxide) are found in addition to the main product propene oxide (yield
about
4-5 %). The proportion of water is twice the proportion of propene oxide
(molar
basis).
The composition of the gas phase, which contains propene, oxygen, hydrogen and
possibly an inert gas, is not only important as regards the space-time yield,
but is also
important as regards safety. In theory, all molar compositions of the gases
propene /
s0 oxygen / hydrogen / nitrogen / inert gas (e.g. nitrogen) can be used. The
preferred gas
ratios for the oxidation of propene are the following ratios: HZ / hydrocarbon
/ oxygen
/ nitrogen: 20-80 % / 10-50 % / 1-10 % / 0-50 %; the preferred HZ /
hydrocarbon
/oxygen / nitrogen ratio is 30-75 % / 15-40 % / 3-8 % / 0-10 %. The molecular
oxygen
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which is used for the reaction can originate from diverse sources, e.g. pure
oxygen, air
or other oxygen/inert gas mixtures.
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Exameles
Direct oxidation of propene to propene oxide
Standard reaction conditions: the reactor was a fixed bed tubular reactor
(diameter 1
cm, length 20 cm) made of double-walled glass, which was heated at a
controlled
temperature of 46°C by means of a water thermostat. A static mixing and
temperature
control section was disposed upstream of the reactor. The gold-support
catalyst was
placed on a glass frit beforehand. The catalyst loading was 1.8 1/g
catalyst/hour. The
gaseous starting materials were metered into the reactor from top to bottom by
means
of mass-flow controllers. The ratios of the gaseous starting materials
corresponded to
02 / HZ / C3H6 = 0.1 /1.3 /0.4 1/hour. The reaction gas mixture was analysed
by gas
chromatography using an FID detector (for all organic compounds containing
oxygen,
with the exception of C02) and a thermal conductivity detector (for permanent
gases,
CO, C02 and H20). The apparatus was controlled via a central data recording
system.
The gold particle size of all the catalysts was investigated by TEM
(transmission
electron microscopy).
Catalyst preparation 1
100 mg H(AuCl4), dissolved in 100 ml of deionised water, were added drop-wise
over
60 minutes at room temperature, with stirring, to a suspension of 10 g hydrous
titanium oxide (BET specific surface 380 mz/g, sulphate content 0.6 %, 12 %
water)
in 0.3 1 of deionised water. The pH was adjusted to 8 with an 0.5 molar Na2C03
solution in order to precipitate gold hydroxide. The slightly yellow
suspension was
decolorised. The suspension was stirred for 3 hours at room temperature, and
the solid
was separated and washed 4 times with 25 ml of deionised water each time. The
solid
was dried for 2 hours at 150°C and for 1 hour at 200 °C, and the
dried contact catalyst
;0 was subsequently calcined in air for 2 hours at 250°C and for 5
hours at 400°C.
A catalyst which contained 0.5 % by weight gold was obtained. Characterisation
by
TEM showed the presence of nanometre-scale gold particles with average
particle
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diameters of about 1-6 nm. The results of the catalytic reaction in accordance
with the
standard reaction conditions (Example A) are given in Table 1.
Catalyst preparation 2:
A solution of 0.104 g HAuCl4 x H20 in 400 ml distilled water was heated to
70°C and
adjusted to pH 7.5 with an aqueous 0.1 N NaOH solution. 5 g titanium dioxide
(an
anatase-rutile mixed oxide; P 25 supplied by Degussa) was added in one portion
with
intensive stirring, and the batch was stirred for a further 1 hour. The solid
was washed
5 times with 3 litres of distilled water each time, dried under vacuum at room
temperature for 12 hours, and calcined for 4 hours at 400°C . A gold-
titanium dioxide
catalyst was obtained which contained 1 % by weight gold.
The results of the catalytic reaction in accordance with the standard reaction
conditions (Example B) are given in Table 1.
Examples 1 to 10 Catalyst regeneration and catalytic activity of gold support
catalysts which had become inactive and which were
treated according to the invention with water, dilute acids
or dilute hydrogen peroxide solutions:
Example 1
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation 1, was
suspended in 100 ml H20, stirred for 1 hour at roam temperature, separated,
and dried
for 1 hour at 150°C. The contact catalyst which was thus obtained was
used for the
oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table 1.
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Example 2
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation 1, was
suspended in 100 ml H20, stirred for 1 hour at 80°C, separated, and
dried for 1 hour at
150°C. The contact catalyst which was thus obtained was used for the
oxidation of
propene by the standard procedure.
Examtlle 3
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation 1, was
suspended in 100 ml H20, stirred for 3 hours at room temperature, separated,
and
dried for 1 hour at 150°C. The contact catalyst which was thus obtained
was used for
the oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table 1.
Example 4
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation l, was
suspended in 100 ml of 3 % H202 solution, stirred for 1 hour at room
temperature,
separated, and dried for 1 hour at 150°C. The contact catalyst which
was thus obtained
was used for the oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table 1.
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Example 5
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation 1, was
~ 5 suspended in 100 ml of 6 % H202 solution, stirred for 1 hour at room
temperature,
separated, and dried for 1 hour at 150°C. The contact catalyst which
was thus obtained
was used for the oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table I .
Example 6
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation l, was
suspended in 100 ml of 3 % H202 solution, stirred for 1 hour at 50°C,
separated, and
dried for 1 hour at 150°C. The contact catalyst which was thus obtained
was used for
the oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table 1.
Example 7
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation 1, was
suspended in 100 ml H20 which had been adjusted with 0.05 molar H2S04 to pH 6,
was stirred for 3 hours at room temperature, separated, dried for 1 hour at
150°C and
calcined for 2 hours at 400°C. The contact catalyst which was thus
obtained was used
for the oxidation of propene by the standard procedure.
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Example 8
A catalyst which had become inactive due to reaction (2 g; 0.6 % propene oxide
yield), and which had been produced according to catalyst preparation l, was
suspended in 100 ml H20 which had been adjusted with 0.05 molar H2S04 to pH
6.5,
was stirred for 3 hours at room temperature, separated, dried for 1 hour at
150°C and
calcined for 2 hours at 400°C. The contact catalyst which was thus
obtained was used
for the oxidation of propene by the standard procedure.
Example 9
A catalyst which had become inactive due to reaction (2 g; 0.2 % propene oxide
yield), and which had been produced according to catalyst preparation 2, was
suspended in 500 ml water, stirred for 1 hour at room temperature, separated,
and
dried for 1 hour at 150°C. The contact catalyst which was thus obtained
was used for
the oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table 1.
Example 10
A catalyst which had become inactive due to reaction (2 g; 0.2 % propene oxide
yield), and which had been produced according to catalyst preparation 2, was
suspended in 100 ml of 3 % H202 solution, stirred for 1 hour at room
temperature,
separated, and dried for 1 hour at 150°C. The contact catalyst which
was thus obtained
was used for the oxidation of propene by the standard procedure.
The results of the catalytic reaction are given in Table 1.
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Table 1
Catalyst Time Propene oxide Propene oxide
preparation (min) yield selectivity (%)
1 (%)
Example A (active)30 5.3 >9~
Example A (inactive) Q,6
Example I 30 3.7 >9'7
Example 2 30 3.8 >9~
Example 3 30 3.8 >9'7
Example 4 30 3.9 >9~
Example 5 30 3.6 >9'7
Example 6 30 3.8 >9~
Example 7 30 4.2 >9~
Example 8 30 4.0 >9~
Catalyst Time Propene oxide Propene oxide
preparation (min) yield selectivity (%)
2 (%)
Example B (active)30 1.4 >9~
Example B (inactive) 0.2 >9'7
Example 9 30 0.9 >9'7
Example 10 30 1.0 >9'7
