Process for the continuous production of hydrogen peroxide

Details Process for the continuous production of hydrogen peroxide Process for the continuous production of hydrogen peroxide

2001-06-01

2003-11-18

Langel, Wayne A. (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Peroxide

C423S403000, C423S415100, C549S531000, C564S259000, C568S803000

Reexamination Certificate

active

06649140

ABSTRACT:

The present invention relates to a process for the continuous production of hydrogen peroxide (H
2
O
2
)
More specifically, the present invention relates to a process for the continuous production of alcoholic or hydro-alcoholic solutions of hydrogen peroxide and their direct use in oxidation processes.
In particular, oxidation processes using hydrogen peroxide as oxidizing agent, are known in the art, in which the use of alcoholic or hydro-alcoholic solutions object of the present invention have proved to be useful.
Examples of these processes are those using titanium silicalite as catalysts, such as the epoxidation of olefins (EP-100,119), the ammoximation of carbonyl compounds (U.S. Pat. No. 4,794,198), the oxidation of ammonia to hydroxylamine (U.S. Pat. No. 5,320,819) and the hydroxylation of aromatic hydrocarbons (U.S. Pat. No. 4,369,783).
The industrial production of aqueous solutions of H
2
O
2
by means of a complex two-step process, is known. In this process a solution of an anthraquinone, such as butylanthraquinone or ethylanthraquinone, in an organic medium immiscible with water is first hydrogenated and then oxidized with air to produce H
2
O
2
which is subsequently extracted in aqueous phase.
This process is expensive owing to the high investment costs necessary for the complex production unit involved and the necessity of separating and disposing of the by-products generated during the oxidation phase and purifying and reintegrating the anthraquinone solution before being re-used.
For these reasons, processes for the direct synthesis of hydrogen peroxide from H
2
and O
2
have been studied and seem attractive from a technical and economic point of view.
These processes generally use a catalytic system consisting of a noble metal, particularly metals of the platinum group or their mixtures, in the form of salts or as supported metals, reacting the two gases in a solvent consisting of an aqueous medium or an aqueous-organic medium.
The embodiment of these processes however has proved to be difficult on an industrial scale for the following reasons:
A) the use of mixtures of H
2
and O
2
in concentrations within the explosivity range, as the mixture becomes explosive when the concentration of H
2
exceeds a value which, depending on the pressure and concentration of O
2
, varies from 4.5 to 6% by volume:
B) even when operating outside the explosivity range of H
2
—O
2
mixtures, the use of high concentrations of O
2
is risky to handle and not very compatible with the presence of flammable organic solvent mediums;
C) the use in the reaction medium of high concentrations of promoters, for example acid, halogenated promoters and/or other additives, makes the catalytic system or H
2
O
2
solution unstable. This makes it necessary to add stabilizers with costly purification operations of the H
2
O
2
solution produced before its use;
D) low productivity and selectivity of the reaction or the production of H
2
O
2
solutions which are too dilute for economic industrial exploitation;
E) low stability of the catalytic system under the reaction conditions.
For example, U.S. Pat. Nos. 3,361,533, 4,009,252 and 4,661,337 describe processes for the preparation of H
2
O
2
which use gaseous mixtures of H
2
and O
2
which are typically included in the explosivity range.
To avoid these safety problems, some processes use ingenious and complex reactor solutions.
U.S. Pat. No. 5,194,242 describes a continuous process for the preparation of H
2
O
2
in aqueous solution which comprises the use of a suitable reactor and a mixture of H
2
and O
2
in ratios with each other within the explosivity range in the feeding to the reactor, but outside this range in the gaseous stream leaving the reactor.
U.S. Pat. No. 5,641,467 describes a continuous process for the preparation of H
2
O
2
from H
2
and O
2
which operates within the explosivity range of H
2
/O
2
mixtures using a reaction apparatus suitable for producing a series of gas bubbles sufficiently small and sufficiently dispersed and separate from each other in the liquid reaction medium as to avoid any possible explosion in the reactor.
These processes however are complex from an industrial point of view and their intrinsic safety is doubtful.
Numerous other processes describe, on the other hand, the use of mixtures of H
2
and O
2
poor in hydrogen, i.e. with concentrations of H
2
of less than 4-5% by volume with respect to the gaseous mixture, for the same purpose, i.e. to avoid safety problems deriving from the use of explosive H
2
—O
2
mixtures.
These processes, however, use extremely high concentrations of O
2
, whose use is only possible when operating in an aqueous solvent medium and they are therefore normally directed towards the production of aqueous H
2
O
2
solutions, excluding the presence of organic mediums.
For example, U.S. Pat. No. 5,500,202 describes a continuous process for the preparation of aqueous solutions of H
2
O
2
from H
2
and O
2
which operates in a “trickle bed” reactor using, in the feeding, a gaseous mixture of H
2
/O
2
/N
2
containing 4.6-6.2% by volume of H
2
and 57-62% by volume of O
2
, so that the mixture leaving the reactor is outside the explosivity range.
U.S. Pat. No. 4,279,883 describes a continuous process for the preparation of aqueous solutions of H
2
O
2
from H
2
and O
2
characterized by a particular pre-treatment of the solution and catalyst with H
2
and in which the mixtures of gases at the outlet of the reactor is kept with the volume composition of 3% H
2
and 30% O
2
, the remaining percentage being N
2
.
International patent application WO 93/14025 describes a process for the preparation of aqueous solutions of H
2
O
2
from H
2
and O
2
characterized by the use of particular catalysts and stabilizers of the catalytic activity and carried out in the presence of gaseous mixtures kept outside the explosivity limits of H
2
, with O
2
being fed in pure form or preferably mixed with N
2
to obtain a preferred H
2
/O
2
/N
2
composition equal to 3.2%/86.8%/10.0% respectively by volume.
International patent application WO 92/15520 describes a process for the preparation of aqueous solutions of H
2
O
2
from H
2
and O
2
characterized by the use of particular catalysts and stabilizers of the catalytic activity and carried out in the presence of gaseous mixtures kept outside the explosivity limits of H
2
, with O
2
being fed in pure form without inert gases.
European patent application EP-627,381 describes a process for the preparation of aqueous solutions of H
2
O
2
from H
2
and O
2
characterized by the use of particular catalysts and carried out in the presence of gaseous mixtures kept outside the explosivity limits of H
2
in the presence of inert gases such as nitrogen so as to obtain a preferred H
2
/O
2
/N
2
composition equal to 3%/47%/50% respectively by volume.
In all these processes high concentrations of O
2
are used, which are scarcely compatible with the use of flammable organic reaction solvent mediums.
In other cases, the use of mixtures of H
2
and O
2
outside the explosivity range and using low concentrations of O
2
prove to have a low reaction productivity and selectivity or to produce H
2
O
2
solutions which are too dilute for an economic industrial exploitation.
For example U.S. Pat. No. 5,082,647 describes a process for the preparation of aqueous solutions of H
2
O
2
from H
2
and O
2
characterized by the use of particular catalysts and carried out in a trickle bed reactor, feeding a gaseous mixture containing 3% of H
2
by volume in air. In the example described, after 5 hours the solution re-circulated through the reactor contained 0.3% of H
2
O
2
.
From what is specified above, the objective of setting up a process for the direct synthesis of H
2
O
2
from H
2
and O
2
which can be used on an industrial scale under safety and economically advantageous conditions, does not appear to have been reached as yet.
In particular, the objective of producing stable solutions of H
2
O
2
in aqueous-organic mediums with a concentration suitable for d

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