Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~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.
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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
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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
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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.
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~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
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~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.
