CA1049749A - Process for manufacturing hydrogen peroxide - Google Patents

Abstract

Abstract of the Disclosure The invention relates to a process for producing hydrogen peroxide by hydrogenation of anthraquinones in the presence of a solvent and subsequent oxidation of the hydrogenation products, whereby hydrogenated solution and 50-100% oxygen are introduced into a vessel which is free from packing or similar filling. The vessel is, to the greatest extent, kept filled with solution, and the solution and gas are led continuously in substantially the same direction through the vessel. The oxidation vessel is preferably made in the form of a continuously or step-wise upwardly tapering column.

Description

~049'749 Hydrogen peroxide can be produced in a number of different ways from the classical method via barium peroxide, electric discharge, cathodic reduction, auto-oxidation of organic compounds, etc. The auto-oxidation method dates to Manchot, 1901 via ~alton and Filson, U.S. Patent 2 059 569 and the Riedl-Pfleiderer process, German Patents 649 234, 658 767, 671 318, 801 840, etc.
In this producing of hydrogen peroxide by auto-oxidation, anthraquinones or other ~uinone derivatives are used, dissolved in one or more solvents. The working solution is hydrogenated, whereby about 50% of the quinones are converted to hydro-quinones (quinolS). In a subsequent oxidation step, the solution is brought into contact with air, whereby the oxygen of the air re-oxidizes the quinols to quinones under simultaneous hydrogen peroxide formation. The hydrogen peroxide in the working solution is washed out with water, after which the working solution is returned to the hydrogenation step.
In this cyclical process hydrogen peroxide is thus produced from hydrogen and the oxygen of the air.
Oxidation with air involves many disadvantages, however.

The reaction speed is relatively low, for which reason the set of oxidation apparatus is bulky and heavy. The use of air implies that large quantities of inert gas must pass the set of apparatus and leave the same saturated with solvent vapors.
Also serious is the fact that for those reaction conditions which must be maintained under industrial drift, not only the hydrogen added during quinol formation is oxidized, but an oxidation of the solvents and anthraquinones also takes place.

10497~L9 Epoxides are formed from 1etrahydroanthraquinones present, said epoxides being wholly ineffective as reaction carriers for the hydrogen peroxide process. A plurality of processes are indeed known for recovering of active tetrahydroanthra-quinones from the epoxides, but these processes involveincreased consumption of agen-ts and energy.
In using air for the oxidation process the highest oxygen yield is obtained, as a rule, when the anthraquinone solution is led in counter-current or gradually in countPr-current against the air. This process implies, however, thatthe solution, when it contains a low proportion of quinols, is subjected to gas with the highest partial oxygen pressure and thereby the undesirable oxidation attack becomes relatively large. The ability of the solution to produce hydrogen peroxide therefore ceases after a short time if a special regeneration process is not introduced.
In order to increase the boundary surface bet~een the two phases it is, per se, advantageous to provide packing or other similar arrangements in the oxidation vessel. The large area of the packing has, however, initself a disintegrating effect on the hydrogen peroxide. The metals from group VIII
in the periodic Table, used as catalysts for hydrogenation, ~-catalyze all of the decomposition of the hydrogen peroxide and in that connection the platinum group metals have an especially high catalytic effect on this decomposition. The decomposition of the formed hydrogen peroxide in the solution implies both product loss and that the solution is subjected to a strong oxidation strain. It is difficult in practice to i ~04~49 avoid that microscopic catalyst particles accompany the solution from the hydrogenation to the oxidation. The particles can there adhere to the packing and remain there with subsequent unfavourable effect on the hydrogen peroxide yield and on the working solution.
According to the invention there is provided a cyclic process for the production of hydrogen peroxide by hydrogenation of anthraquinones in an organic solvent in the presence of a nickel catalyst, oxidation of the hydrogenated anthraquinones (quinols) in the solution after separation of the catalyst, and washina out the hydrogen peroxide product with water, which process comprises feeding the solution containing the hydrogenated anthraquinon~s continuously into an oxidation vessel concurrently with a feed of an oxidizing gas comprising from 50 to 100% free oxygen, maintaining the oxidation vessel substantially filled with the solution but free of packing or similar arrangements, and providing a residence time in the oxidation vessel sufficient to permit a degree of oxidation up to 20 about 98 to 100~.
In this way no enrichment or an insi~nificant en-richment of epoxides is obtained in the solution.
In consideration of both the decomposition of the hydrogen peroxide, which increases with increasing tem-perature, and the oxidation strain on the working sol~tion, the oxidation temperature should preferably be held to a maximum of 50C., more preferably 40-47C.
Oxidation with oxygen-enriched gas has been shown to be particularly suitable when the hydrogenation is carried out with Raney nickel which is heat-treated prior to use in an alkaline medium at a temperature of 120-160C. This catalyst ,", ~
~'S''~; - 3 -.

~049~49 causes a quite insignificant change in the composition of the solution in the hydrogenation step and nickel has a con-siderably lesser catalytic effect on the disintegration of the hydrogen peroxide than do the platinum metals.
With the use of 50-100% oxygen according to the invention an essentially 100% degree of oxidation is obtained with high oxygen yield, without l~se of high temperature and/or increased pressure. ~y degree of oxidation is meant the mole ratio between the amount of hydrogen peroxide obtained in oxidation and this amount increased by (plus) the amount of anthraquinols remaining at the termination of the oxidation process. In consideration of the life time of the working solution it can, however, be advantageous -to drive the degree of oxidation no longer than to 98-99%.
When 90-100% oxygen is introduced together with the hydrogenated solution at the bottom of the reaction vessel, the reaction speed is initially so high tha-t the quantity of gas and, therewith, the gas charge quickly decrease higher up in the vessel. If the oxidation vessel is designed as a column, it can be made so that it continuously or by steps tapers upwards.
In a cyclic process for producing hydrogen peroxide according to the anthraquinone method, the hydrogenated solution is preferably oxidized continuously with 99% oxygen in a cylindrical column wholly lacking both packing and bottoms.
The working solution i5 fed in at the bottom of the column where the oxygen is also introduced.
Under a period of 29 days, 28 m3/h, on the average, passed through the oxidation column. The corresponding time of residence for the solution in the colurnn was about 15 min.

~,~ .

~0~749 The temperature in the column was so controlled that it maximally reached 47C. The supply of oxygen gas was so regulated that on the average less than 1% of the quantity of oxygen gas conveyed -to the lower por~ion of the column 5 exited in gas form at the top of the column. In this connection a degree of oxidation of 98-99% was obtained.
During the period the experiment was in progress, each part of the circulation solution was hydrogenated, oxidized and extracted about 290 times~ and in all, after the extraction, 10 240,000 kg of 100% H202 in the form of an approximately 27.5%
aqueous solution was obtained. 12.3 kg H202 was obtained from each m3 in each cycle.
During the entire time of the experiment no special -~
measures were taken for recovering of the by~products as 15 anthraquinones or tetrahydroanthraquinones. Neither was any type of reaction carrier added during the reported period. Data pertaining to the solution prior to and after the 29 days of continuous drift are presented in the following table:-Solution Befc~re experiment After 29 days . _ . _ . . . _ . _ , . . .
Density at 40C 0.903 0.903

2-ethylanthraquinone, g/l 72 69 Tetrahydro-2-ethylanthraquinone~ g/l 90 98 T~trahydroanthraquinone, g/l 31 28 25 Evaporation residue, g/l 238 234 Under essentially the same oxidation conditions an anthraquinone solution was circulated during hydrogen peroxide production for more than one year in the same apparatus. During . . ~

~5:)49749 this time the composition of the solution was adjusted with regard to losses, for example through evapo~tion or mechancial leakage. No special regeneration of epoxides took place nor were the similar non-desirable oxidation products removed from the solution in other ways by means of special apparati. At the end of the period the solution contained about 5 g epoxide per liter.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cyclic process for the production of hydrogen per-oxide by hydrogenation of anthraquinones in an organic solvent in the presence of a nickel catalyst, oxidation of the hydrogenated anthraquinones (quinols) in the solution after separation of the catalyst, and washing out the hy-drogen peroxide product with water, which process comprises feeding the solution containing the hydrogenated anthra-quinones continuously into an oxidation vessel concurrently with a feed of an oxidizing gas comprising from 50 to 100%
free oxygen, maintaining the oxidation vessel substantially filled with the solution but free of packing or similar arrangements, and providing a residence time in the oxidation vessel sufficient to permit a degree of oxidation up to about 98 to 100%.

2. The process of claim 1, characterized in that the gas which is introduced into the oxidation vessel contains 90 to 100% by volume of oxygen.

3. The process of claim 1, characterized in that the solution in the oxidation vessel is kept at a temperature of at most 50°C.

4. The process of claims 1, 2 or 3, characterized in that the anthraquinones in the working solution included in the oxidation are produced through hydrogenation in the presence of a nickel catalyst which is heat-treated in an alkaline medium at 120 to 160°C. prior to use.

5. The process of claims 1, 2 or 3, characterized in that the oxidation is carried out in a column which continuously or by steps tapers upwardly.