CA1089631A

CA1089631A - Process for producing hydrogen peroxide

Info

Publication number: CA1089631A
Application number: CA257,531A
Authority: CA
Inventors: Gunter Giesselmann; Gerd Schreyer; Rudolf Wagner
Original assignee: Deutsche Gold und Silber Scheideanstalt
Current assignee: Evonik Operations GmbH
Priority date: 1975-07-23
Filing date: 1976-07-22
Publication date: 1980-11-18
Also published as: FR2318820B1; AR217242A1; TR19375A; DE2532819A1; BE844424A; SE418489B; IT1063139B; SE7608379L; CH618946A5; ATA540276A; SU676158A3; DE2532819C3; AT354976B; NL184942B; JPS5231998A; DE2532819B2; BR7604689A; FR2318820A1; GB1524883A; NL7606456A

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides in a process for pro-ducing hydrogen peroxide by the anthraquinone process, the improvement in which at least two hydroquinone solvents are used for dissolving the reactant alkyl anthrahydroquinones.

Description

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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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 ~ ,3~
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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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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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.
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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. :

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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 anthrahydroquinone, one of said solvents being a tetra-substituted urea and the other of said solvents being at least one member selected from a phosphoric acid triester, a tetra-substituted urea different from said one solvent, methyl cyclohexyl acetate and diisobutyl carbinol.

2. A process accoxding to Claim 1, in which at least two components of different substance classes are used for dissolving the alkyl anthrahydroquinone.

3. A process according to Claim 1, in which a mixture of tetrasubstituted urea and phosphonic acid triester is used for dissolving the alkyl anthrahydroquinone.

4. A process according to Claim 1, in which a mixture of tetraalkylurea and phosphonic acid triester is used for dissolving the alkyl anthrahydroquinone.

5. A process according to Claim 1, in which a mixture of N, N-diethyl-N', N'-di-n-butyl urea and trioctyl phosphate is used as the solvent.