Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a process for
producing hydrogen peroxide.
It is well known that in the anthraquinone process
for producing hydrogen peroxide a 2-alkyl anthraquinone dissolved
in a solvent immiscible with water, may be catalytically hydro-
genated to the corresponding 2-alkyl anthrahydroquinone and
subsequently may be oxidized in air or in oxygen-enriched air,
the 2-alkyl anthraquinone being recovered with the formation of
hydrogen peroxide. The hydrogen peroxide is extracted with water
and the solution of 2-alkyl anthraquinone in the organic solvent
is returned to the hydrogenation stage.
In the course of successive recyclings some of the
2-alkyl anthraquinone is converted into the corresponding 2-alkyl
tetrahydroanthraquinone, which can yield hydrogen peroxide by
successive reduction and oxidation, i.e., it thus actively
participates in the cycle as a carrier reactant.
The use of tetra~substituted ureas as components of a
solvent mixture with hydrocarbons in the alkyl anthraquinone
process is disclosed in German Patent No. 2 018 686. The capacity ;
o~ the process solution for producing hydrogen peroxide was thus
substantiallv increased because said ureas have a better solubility
for alkyl anthraquinone.
However, apart ~rom a high capacity and in addition to
many other requirements, a process solution must have a high
partition coefficient with respect to aqueous hydrogen peroxide
in order to attain a high hydrogen peroxide concentration in the
extraction stage with a minimum o~ expenditure.
By partition coefficient is meant the quotient of the
hydrogen peroxide concentrations which are obtained in the
equilibrium of a two-phase mixture of water-process solution in
the aqueous phase
kg of H22
and in the organic phase
kg of H2O - 1 -
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3~ ::
kg of H22
kg of process solution.
With regard to this partition coefficient a tetra-
substituted urea which permits a high capacity of the process
solution containing it, namely, N,N-diethyl-N',N'-di-n-butyl
urea, is unfavourable.
According to the process of German Patent 1 261 838
alkyl phosphorus esters in conjunction with hydrocarbons are used
as solvents for the alkyl anthraquinone process. These process
solutions only result in practice in moderate production cap-
acities but they are distinguished by a very good partition
coefficient with respect to aqueous hydrogen peroxide.
A very high partition coefficient does have advantages
in the extraction stage but, starting from a certain value, it
can also be extremely undesirable.
The reason is as follows:
In the oxidation stage of the cyclic process for pro-
ducing hydrogen peroxide a slight decomposition of the hydrogen
peroxide being formed is unavoidable. However, even the slightest
operating trouble can increase the rate of decomposition to such
an extent that an aqueous phase is formed in addition to the
organic phase. If the corresponding process solution has a
partition coefficient which is "too goodl' with respect to the~ -
aqueous hydrogen peroxide, then the aqueous hydrogen peroxide
formed in addition to the organic phase is so highly concentrated
that the entire system evidently constitutes an explosive mixture.
Applicants experiments have shown that two-phase mix-
tures of conventional process solutions with a~ueous hydrogen
peroxide exceeding a hydrogen peroxide content of 50~ by weight
can cause detonations.
As a way out of the situation described a combination
-- 2 --
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of solvents for anthraquinone might be considered, i.e., such
that
a) the capacity of the process solution as high as
possible is attained,
b) the partition coefficient with respect to aqueous
hydrogen peroxide which does not allow the formation of an
explosive mixture in the oxidation stage but is nevertheless high
enough to produce H2O2 having the desired concentration at a
technically justifiable expenditure.
The process solutions hereafter are mixtures of this
kind.
According to the present invention there is provided in
a process for producing hydrogen peroxide by the anthraquinone
process, the improvement in which at least two hydroquinone
solvents are used for dissolving the reactant alkyl anthrahydro-
quinones.
According to applicants tests, a process solution
containing as solvents, 75 parts of a hydrocarbon mixture, 12.5
parts of trioctyl phosphate and 12.5 parts of N,N-diethyl-N',N'-
di-n-butyl urea, at a charge higher by 25%, i.e., with 12.5 g
of hydrogen peroxide per litre of process solution, only allows
the build-up of a maximum of a 47.5% by weight aqueous hydrogen
peroxide in addition to the organic phase. The resulting mixture
is outside the danger point. ~ -
Another process solution which conkains 70 parts of a
hydrocarbon mixture, 15 parts of trioctyl phbsphate and 15 parts
of N,N-diethyl-M',N'-di-n-butyl urea as solvents, at a charge of
15 g of hydrogen peroxide per litre, only allows a build-up of a
maximum of a ~7.6% by weight aqueous hydrogen peroxide.
~owever, a combination of hydroquinone solvents, i.e., ;
special solvents for alkyl hydroquinones, was by no means obvious
to persons skilled in the art since the influence of the individual
components (when applied jointly) on the entire process cannot be ~ -
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predetermined.
For example, the activity and/or the selectivity of
the hydrogenation catalyst can be varied. The behavior of the
process solution in the extraction is not predictable. Moreover
there is the risk of a negative effect on the stability and of
a possible decrease in the quality of the hydrogen peroxide
produced.
For these reasons no mixtures of hydroquinone solvents
were used in the A O process heretofore. Surprisingly enough
and contrary to apprehensions, namely trouble in the hydrogena-
tiOII stage, in the oxidation and extraction and decreases in
the quality of the product obtained, it was now found that
in the production of hydrogen peroxide by means of the anthra-
quinone process the manner of carrying out the entire process
can even be improved if a mixture of at least two solvents for
the alkyl anthrahydroquinone is used as the hydroquinone
solvent. -
Phosphorus triesters, tetra-substituted ureas, methyl -
cyclohexyl acetate, diisobutyl carbinol are particularly suitable
as solvents for the alkyl anthrahydroquinones.
These solvents can be used as components of an
individual group or as components of various groups ln mixture.
Mixtures of tetra-substituted ureas with phosphorus
triesters, primarily N,N-diethyl-N',N'-di-n-butyl urea with
trioctyl phosphate (tris-2-ethyl hexyl phosphate) are particularly
suitable and preferred.
The proportion of the individual hydroquinone solvents
can vary within wide limits. For example, it is possible to
increase very substantially the capacity of a process solution
containing only a single hydroquinone, as for example, tris-2-
ethyl-hexyl phosphate, by adding a tetra-substituted urea, such
as N,N-diethyl-N',N'-di-n-butyl urea.
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.. . . .
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Since tetraalkylated ureas usually have more
favourable density and viscosity properties than tris-2-ethyl-
hexyl phosphate, density and viscosity of the entire solution
are improved by partially replacing the phosphate by urea. The ;
improved selectivity of the hydrogenation stage showed
distinctly in the reduced formation of the very undesirable
by-product octahydro anthraquinone.
The quality of the hydrogen peroxide produced in
pilot-plant experiments and characterized by the carbon content
of the product was equally surprising. Under production
conditions in the pilot plant process solutions with the
solvent N,N-diethyl-N',N'-di-n-butyl urea/hydrocarbon mixture
yielded a 40% by weight hydrogen peroxide having a carbon
content of approximately 350 p.p.mO Process solutions with ~ -
the solvent components trioctyl phosphate and hydrocarbons
yielded hydrogen peroxide of the same concentration with
a carbon content of approximately 180 p.p.m. -
With a solvent mixture hydrocarbons-trioctyl phosphate-
N,N-diethyl-N',N'-di-n-butyl urea a 40~ by weight hydrogen
peroxide, which also had a carbon content of 180 p.p.m., could
be produced. This value thus is substantially lower than the
average value of 265 p p.m. which can be expected for this
mixture in the most favourable case.
The advance in the art of the process according to the
invention lies in that by using a mixture of at least two
solvents, so-called hydrogen peroxide solvents, process
.
solutions which assure a high deyree of safety in operation and
at the same time a high capacity for hydrogen peroxide can be
produced for dissolving the alkyl anthrahydroquinones.
Moreover, the selectivity of the hydrogenation
catalyst is distinctly changed in a positive sense and a hydrogen ~-
peroxide low in carbon is ob-tained.
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It must be particularly emphasized that by using
mixtures of hydroquinone solvents the partition coefficient
of the process solution varies within wide limits with respect
to aqueous hydrogen peroxide solutions and even a-t high ~;
capacities it can be so adjusted that particularly in the
oxidation stage of the cyclic process no dangerous hydrogen
peroxide concentrations can build up.
The invention is further illustrated by the following
Examples.
Example l -
.
In a pilot-plant apparatus adapted to operating
conditions the following process solutions were tested:
85 g of ethyl anthraquinone, 85 g of 2-ethyl-
tetrahydroanthraquinone in l litre of solvent consisting of 75
parts by volume of tetramethyl-benzene mixture, 12.5 parts by
volume of trioctyl phosphate and 12.5 parts by volume of
N,N-diethyl-N',N'-di-n-butyl urea~ This composition permitted
a production capacity of 12.5 g of hydrogen peroxide per litre
of recycle solution.
After having been run for 500 hours the hydrogenation
catalyst still showed the same activity as at the start of the
test. In the individual process stages of the cyclic process
difficulties due to the three-component solvent mixture were
not encountered.
Example 2
In the same apparatus a recycle solution having the
following composition was tested:
100 g of 2-ethyl anthraquinone, 100 g of 2-ethyl
tetrahydroanthraquinone in 1 litre of solvent consisting of
70 parts by volume of tetramethyl-benzene mixture, 15 parts by
volume of trioctyl phosphate and 15 parts by volume of N,N-
diethyl-N',N'-di-n-butyl urea.
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~39~
With this solution a production capacity of 15 g of
hydrogen peroxide per litre of recycle solution was obtained.
The 40% by weight hydrogen peroxide produced had a carbon
content of 180 p.p.m.
However, a process solution containing 30 parts of
trioctyl phosphate and 70 parts of tetramethyl-benzene mixture :
as the solvent mixture had a maximum practical production
capacity of 11.5 g per litre of process solution. . .
The hydrogen peroxide produced in this apparatus .
with a conventional recycle solution containing only the tetra-
methyl-benzene mixture and trioctyl phosphate as solvents had the
same carbon content, namely, 180 p.p~m.
Example 3
Three different recycle solutions were subjected
to a hydrogenation test at 60C and 6 atmospheres excess .
pressure (hydrogen pressure) in the presence of palladium black.
The initial solutions had the following composition: :
solution 1: 50 g of 2-ethyl anthraquinone in tetramethyl~
benzene mixture/trioctyl phosphate = 75:25 ~
solution 2: 50 g of 2-ethyl anthraquinone in tetramethyl- ~ :
benzene mixture/trioctyl phosphate/N,N-
diethyl-N',N'-di n-butyl urea = 70:15:15
solution 3: 50 g of 2-ethyl anthraquinone in te-tramethyl- ~
benzene mi.xture/trioctyl phosphatejN,N- :~
diethyl-N',N'-di-n-butyl urea = 70:25:5. : .
After 72 hours solution 1 had the following quinone
composition: 5,34% of 2-ethyl octahydroanthraquinone and ~.
94.66% of 2-ethyl tetrahydroanthraquinone, solution 2: 1.83%
of 2-ethyl octahydro anthraquinone, 90.17% of 2-ethyl tetra-
hydroanthraquinone and 8.0% of 2-ethyl anthraquinone,
solution 3: 2.67% of 2-ethyl octahydroanthraquinone, 88.83% :~... .
o~ 2-ethyl tetrahydroanthraquinone and 8.5% of 2-ethyl-anthra- .
quinone.
- 1 - : ' '
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t
Example 4
In a pilot-plant apparatus adapted to operating
conditions the following process solution was tested: ~:
85 g of 2-ethyl anthraquinone, 85 g of 2-ethyl tetra-
hydroanthraquinone in 1 litre of solvent consisting of 70 parts ;
by volume of tetramethyl-benzene mixture, 15 parts by volume :
of trioctyl phosphate and 15 parts of N,N-diethyl-N',N'-di-n-
butyl urea. :
C2H5 / 2 5
N - - C - N'
C4H / 1 \ C4Hg ;
This composition resulted in a production capacity
of 15.5 g of hydrogen peroxide per litre of recycle solution.
After having been run for 700 hours the hydrogenation
catalyst still showed the same activity as at the start of the
test. In the individual process stages of the recycle process
difficulties due to the three-component solvent mixture were
not encountered.
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