Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for preparing cycloalkanones
and cycloalkanols by conversion of cycloalkyl hydroperoxides in the presence
of a solid heterogeneous chromium oxide catalyst.
Such a known process provides a high selectivity of conversion into
the desired products cycloalkanone and cycloalkanol, a avourably low ratio
in which the ketone and the alkanol are obtained, and a high initial rate
of conversion of cycloalkyl hydroperoxides into cycloalkanones and cyclo- -
alkanols. However the known process has the disadvantage that the activity
of the heterogeneous chromium oxide catalyst rapidly decreases during the
reaction, while the selectivity of the reaction into cycloalkanone and
cycloalkanol is also reduced. -
The invention is based on the observation that the decreasing
catalyst activity and selectivity is caused by the water that is formed as
a by-product in the reaction and accumulates in the reaction mixture as
hitherto it could not be discharged sufficiently rapidly from the reaction
mixture. In order to maintain the activity and selectivity of the catalyst
it is important that no separate aqueous phase, not even in the dispersed
state, is formed in addition to the organic phase in the conversion.
The invention provides a process for preparing cycloalkanones and
cycloalkanols by conversion of a cycloalkyl hydroperoxide in a liquid hydro-
carbon in the presence of a solid heterogeneous chromium oxide catalyst,
wherein the conversion is effected at a temperature of between 30 and 150C
and wherein during the conversion, water is stripped from the reaction mixture
with a stripping gas such that the water content of the reaction mixture re-
mains at or below the saturation concentration.
Suitable stripping gases that may be used according to the invention
are inert gases or vapours, e.g. nitrogen, argonJ carbon dioxide and vapour
from the liquid used in the reaction. When low reaction temperatures are
appliedJ air diluted with nitrogen or carbon dioxide may be used with good
effect.
The reaction mixture should as indicated above be stripped to such
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extent that the water content of the reaction mixture remains at or below ~
the saturation concentration. - :
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The catalysts used in the process according to the invention may
be supported on a carrier, e.g. silica, alumina, titanium dioxide, molecular
sieves, magnesium oxide, tin oxide and charcoal. Various modifications
oi the carriers may be used e.g. the carrier may be microporous or macroporous.
Particularly suitable silica carriers are more ob~ained under the Trade Marks
AEROSIL and KETJENSIL. The catalyst particles may be in the i'orm of globules,
saddles, or tablets or other particulate i'orm. Use is preferably made of a ;
iixed catalyst bed, but the catalyst may also be finely divided in the
reaction mixture as a suspension.
The method oi' preparation of the catalyst has a considerable effect
on the speci~ic conversion rate. The catalyst preferably used is chromium
oxide obtained by heating a suitable chromium compound, e.g. chromic hydroxide.
It is advantageous to activate the catalyst before use by heating at a
temperature in the range of 300 -500 C in an atmosphere of a gas containing
molecular oxygen, e.g. air. Particularly high speciiic conversion rates can
be obtained by means oi catalysts prepared by the method described in
Applicant's British Patent Specification 1,220,105.
When catalysts on a carrier are used, the degree of loading of the
carrier with catalytically active material is also important. Use is
prei'erably made of a low degree oi loading, e.g. not more than l5 ~ by weight
oi chromium oxide, calculated as Cr. Such a catalyst appears to have a high
activity compared with catalyst with a relatively high degree oi loading.
The chromium in the catalyst may have various valencies, e.g. it
may be trivalent or hexavalent. A very active catalyst with a long li~e in
which the chromium is contained predominantly as chromium~VI)oxide, can be
obtained by heating chromium(III)oxide at a temperature in the range
300 to 500 C in an atmosphere o~ a gas containing molecular oxygen, e.g. air.
It is also possible to prepare the catalyst ~rom a chromium compound that
changes into chromium(III)oxide when heated, e.g. chromium(III)hydroxide.
A substantially complete conversion oi chromium(III) into chromium(VI) is
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obtained in catalysts with a low degree o~ loading, particularly those
that are X-ray amorphous.
The process for preparing cycloalkanones and cycloalkanols
according to the invention is preferably effected at a temperature of
from 30 to 150 C. At temperatures below 30 C the conversion rate iq
insu~ficiently high. Non-specific thermal decomposition of peroxide usually
causes a lower yield of desired products at temperatures higher than 120 C,
unless use is made of an extremely active catalyst system. m e temperature
range o~ 60 to 110 C is a good compromise between a low reaction rate at
low temperature and a low selectivity at high temperature.
The reaction pressure is not critical. The reaction is generally
carried out with a solution o~ the cycloalkyl hydroperoxide in a liquid
vehicle, so that it will then be necessary to use a pressure at which a ~ ~ :
liquid phase is maintained in the system. A pressure oi 1 atmosphere or
slightly higher is pre~erred although lower and higher pressures may be used
e.g. in the range O.l to 20 atmospheres, depending upon the liquid vehicle
and cycloalkyl hydroperoxide used. m e peroxide concentration is usually
irom 2 to 20 % by weight.
Operable liquid vehicles are those that are inert under the reaction
conditions and also the cycloalkane corresponding to the cycloalkyl hydro-
peroxide used. The last is to be prei'erred since more than one molecule oi
cycloalkanone or cycloalkanol may then be iormed per molecule oi~ cycloalkyl
hydroxyperoxide put in. Particular examples oi' suitable inert vehicles are
aromatic hydrocarbons e.g. benzene and toluene.
In the conversion according to the invention, the-yield o~' the
desired products cycloalkanone and cycloalkanol is high, and usually amounts
to more than 100 % ii the corresponding cycloalkane is used as a vehicle.
It will remain at a high level ior a long reaction period. The reaction rate
also remains high ~'or a long reaction period. As a result, the useful life
of the catalyst may be very long, e.g. more than six months as against at
~` most two weeks in process as ~urtherto used.
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The cycloalkyl hydroperoxide can be prepared by oxidation of the
corresponding cycloalkane in the liquid phase at elevated temperature by
means of a gas containing oxygen, such as air. The process is effected at
low conversions based on the cycloalkane fed in, e.g. from 1 to 12 ~.
Suitable oxidation temperatures are in the range from 120 to 200 C,
preferably from 140 to 180 C. The operating pressure is not critical but
should be such that a liquid phase Is maintained in the system. The pressure
is usually from 4 to 50 atmospheres.
m e oxidation reaction yields a hot somewhat dilute solution of
cycloalkyl hydroperoxide in cycloalkane under pressure. It is expedient to
allow the resulting solution to expand to a lower pressure e.g. to about
1 atmosphere. If the cycloalka~e is cyclopentane, cyclohexane or cyclo-
heptane, so much cycloalkane will evaporate in this expansion that the
temperature drops to a temperature of from 60 to 100 C. It is this
temperature range that is particularly suitable for the conversion according
to the invention, so that the resulting concentrated solution of cycloalkyl
hydroperoxide can be subjected as such to the process according to the
invention. However it is useful at least partly to free the crude solution
of impurities, e.g. by washing with water, thereby inhibiting contamination
of the catalyst. It is also possible first to separate pure cycloalkyl
hydroperoxide oxidation product mixture, e.g. by extraction with an aqueous
hydroxide solution and subsequent acidification and further processing of
the extract, and to use the pure peroxide as the starting material.
The process according to the invention may be effected either
batch-wise and continuously.
The following Examples of the invention are provided, together with
comparative experiments.
Example I
In a continuous process, a solution obtained by oxidation of cyclo-
-30~ ~hexane in the liquid phase by means of oxygen from air and containing
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1.20 moles/kg of cyclohexyl hydroperoxide, 0.16 mole/kg of cyclohexanone,
0.19 mole/kg of cyclohexanol and 12 meq/kg of other cyclohexane oxidation
products (determined as acids) was passed at the rate of 55 ml~hour through
two series-connected columns of 5 mm cross-section and each partly filled
with 24 grams of catalyst tablets at a temperature of 100 C and a super-
atmospheric pressure of 1.7-2.2 atmospheres gauge. The catalyst was 3.1 %
by weight of Cr203 on silica obtained under the Trade Mark EETJENSIL.
The retention time in each column was about 30 minutes. All the water formed
was continuously removed from the reaction liquor by stripping with nitrogen.
The amount of stripping gas was varied from 2 to 15 litres/hour. Eve~y six .
hours the resulting reaction product was sampled and analyzed for cyclohexanol,
cyclohexanone, acid and peroxide. m e analyses showed that the conversion ^~
set to a substantially constant value of about 90 % after a short time and
then stayed at this value for many weeks. The yield of usei'ul cyclohexanone
and cyclohexanol products was to 108 %, based on the cyclohexyl hydroperoxide
converted.
Comparative experiment A
The process according to Example I was repeated, but no stripping
gas was used. The conversion decreased to 73 % in a short time and did not
subsequently exceed this value. The yield of cyclohexanone and cyclohexanol
based on to peroxide converted was subctantially equal to that in Example I.
Comparative experiment B and Example II
The process according to Example I was carried out except that the
temperature was 80 C, the superatmospheric pressure 0.4 atmospheres gauge,
and the throughput rate of the peroxide solution 45 ml/hour. The retention
time of the cyclohexane was 45 minutes in each column. The oxidate passed
through the columns was sampled every six hours and analyzed. The analyses
of the products sampled showed that the conversion of the cyclohexyl hydro-
peroxide soon dropped to a value of 74 % to 76 % and did not subsequently
exceed this value. After 500 hours of operation stripping the reacting
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liquor with 1.5 litres/hour of nitrogen was commenced, and the water removed
from the reaction mixture. As a result, the activity of the catalyst
increased, the conversion rising from 74 to 85 % and then stayed at this
value. Whether the stripping was used or not did not strongly affect the
yield of cyclohexanone and cyclohexanol based on cyclohexyl hydroperoxide
converted.
