JPH0416501A - Production of hydrogen peroxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved process for producing hydrogen peroxide by direct reaction of oxygen and hydrogen in the presence of a catalyst in a reaction medium. More specifically, the present invention relates to a method for effectively suppressing elution of the Pd catalyst into the reaction medium in the above reaction.

(Prior Art) The main method for producing hydrogen peroxide currently being carried out industrially is an autoxidation method using an alkylanthraquinone as a medium.

Problems with this method include that processes such as reduction, oxidation, water extraction and separation, purification, and concentration are complicated, and equipment costs and operating costs are high. Furthermore, there are also problems such as loss due to deterioration of alkylanthraquinone and deterioration of the hydrogenation catalyst.

In order to improve these problems, methods other than the above-mentioned production method have been attempted, one of which is to directly react oxygen and hydrogen in the reaction medium in the presence of a catalyst to produce hydrogen peroxide. There is a way to do it. A method for producing hydrogen peroxide from oxygen and hydrogen using a platinum group metal as a catalyst has already been proposed, and it has been shown that hydrogen peroxide can be produced at a very high concentration (Japanese Patent Publication No. 56-47121). , Special Public Service 1987-18
646, JP 123401, JP 63-1560
05). In all of these, an aqueous solution is used as the reaction medium. Furthermore, an acid or an inorganic salt is dissolved in the reaction medium which is an aqueous solution. In particular, by including halogen ions in the reaction medium, the catalyst activity is controlled and the decomposition of the generated hydrogen peroxide is greatly suppressed. Unexamined Japanese Patent Publication 1986
Publication No. -156005- describes a method for producing hydrogen peroxide from oxygen and hydrogen under pressure in an acidic aqueous solution using a platinum group catalyst, by coexisting halogen ions such as bromide ions in the aqueous solution. It is disclosed that high concentration hydrogen peroxide can be selectively produced.

(Problems to be Solved by the Invention) In a method for producing hydrogen peroxide by directly reacting oxygen and hydrogen in a reaction medium in the presence of a catalyst, when the operation is performed continuously, the activity decreases. Take out a part of the catalyst and
Fresh or activated catalyst must be supplied. Even when the operation is not carried out continuously, it is necessary to add a catalyst before starting the reaction, and furthermore, after the reaction is completed, the reaction medium must be newly filled with catalyst or separated and recovered. In this manner, the catalyst is generally handled in a suspended state in an aqueous solution as a reaction medium, not only during the reaction but also during operations before and after the reaction.

In this case, the problem is that the catalyst metal elutes into the reaction medium. In particular, when halogen ions as described above are present, the amount of elution increases in proportion to the concentration of halogen ions (Figure 1).

Elution of catalytic metal results in a decrease in the amount of catalyst, resulting in a decrease in activity of the catalyst and a reduction in catalyst life. Furthermore, the metals eluted into the aqueous solution degrade the quality of the hydrogen peroxide product, and since it is extremely difficult to recover low-concentration metals, the leaching of expensive catalytic metals causes economic losses, which is a major problem. becomes.

(Means and Effects for Solving the Problems) The present inventors have solved the problem by preventing the metal used as a catalyst from eluting into the reaction medium even in the presence of halogen ions that promote the elution of metal ions. As a result of continued investigation into a method that can be easily operated, it was discovered that this objective could be achieved by maintaining the catalyst surface in the reaction medium in a reducing atmosphere. That is, the present invention provides a method for producing hydrogen peroxide by directly reacting oxygen and hydrogen in the presence of a catalyst in a reaction medium, in which the surface of the catalyst contained in the reaction medium is always kept in a reducing atmosphere. Pd from Pd catalyst by
This is a method for producing hydrogen peroxide, which is characterized by suppressing the elution of hydrogen peroxide.

In the present invention, maintaining the catalyst surface in a reducing atmosphere means making hydrogen gas or a mixed gas containing hydrogen gas exist under normal pressure or pressurization on the surface of the catalyst metal in the reaction medium. The pressure is 0.001Kg/cm"0 or more, preferably 0.OIK.

g/cm"0 or more so as to exist so as to cover the upper gaseous phase of the reaction medium containing the catalyst.Reaction gas used during the reaction As long as the gas contains a predetermined amount of hydrogen gas, there is no problem even if the gas contains oxidizing oxygen gas.

Therefore, in the process for producing hydrogen peroxide directly from oxygen and hydrogen in the presence of a catalyst in the reaction medium, the conditions according to the invention are met in the vessel during the reaction, and the catalytic metal is transferred into the reaction medium. The elution of is suppressed.

Generally, in an oxidizing atmosphere, the catalytic metal dissolves into the aqueous solution that is the reaction medium. The reaction medium is colored by the eluted metal ions. In order to demonstrate the remarkable effectiveness of the present invention, when hydrogen gas is passed through this colored reaction medium at room temperature and pressure, it is confirmed that the coloring immediately disappears and metal precipitates.

Handling of the reaction medium containing the catalyst according to the method of the invention can be used regardless of pressure or temperature.

In a method for producing hydrogen peroxide by directly reacting oxygen and hydrogen in the presence of a catalyst in a reaction medium, generally:
In addition to the reaction operation, the following operations are performed. That is, these operations include adjusting the reaction solution, adding the catalyst into the system, and separating and recovering the catalyst from the reaction medium after the reaction has stopped. When performing these operations other than reaction operations, it is customary to use an inert gas containing no hydrogen gas for -i.

That is, in the reaction liquid adjustment operation, before aerating the reaction gas containing hydrogen gas, a reaction medium and a catalyst of a predetermined composition are placed in a reaction vessel, and the system is purged with an inert gas such as nitrogen gas. After that, a reaction gas containing hydrogen gas is introduced at a predetermined pressure. That is, in operations normally carried out in boat fishing, the Pd catalyst is present in the reaction medium before the catalyst surface is maintained in a reducing atmosphere, and elution of Pd is unavoidable. When the method of the present invention is used, only a reaction medium having a predetermined composition is placed in a reaction vessel, and after the inside of the system is purged with an inert gas, a reaction gas containing hydrogen gas is introduced. Thereafter, by adding a catalyst using the method of the present invention described below, the surface of the catalyst can be kept in a reducing atmosphere at all times, and elution of Pd can be prevented.

In the operation of supplying the catalyst into the reaction system, the following operations are usually performed: Put the reaction medium into the catalyst charging tank,
A predetermined amount of Pd catalyst is suspended therein, and after purging the charging tank with an inert gas such as nitrogen gas, the reaction medium containing the Pd catalyst is pressurized into the reaction vessel with the inert gas. In this method, Pd elution occurs in the catalyst charging tank. When the method of the present invention is used, a reaction medium is placed in a catalyst charging tank, and after replacing the charging tank with an inert gas, hydrogen gas or a gas containing hydrogen gas is introduced. After that, the Pd catalyst is placed in the charging tank, and the catalyst slurry is pressurized into the reaction vessel using an inert gas or a gas containing hydrogen gas, so that the surface of the Pd catalyst can always be kept in a reducing atmosphere. It can prevent the elution of Pd.

In addition, in the operation of separating the catalyst from the reaction medium after the reaction has stopped, after lowering the pressure in the reactor to a predetermined pressure, first fill the space inside the reaction vessel with nitrogen gas in order to avoid hydrogen gas being entrained outside the system. Replace with inert gas such as The catalyst is then filtered off using a suitable commonly used procedure. In this case, at the same time as hydrogen gas in the space is replaced with inert gas, the reducing atmosphere on the catalyst surface is gradually lost.
Elution of Pd progresses. By using the method of the present invention, the catalyst slurry is extracted from the reaction vessel into a catalyst filtration tank maintained in a reducing atmosphere while maintaining the gas composition inside the reactor in a state where the reaction has stopped and adjusting the pressure to a predetermined level. By filtering, the surface of the Pd catalyst can be kept under a reducing atmosphere at all times, and elution of Pd can be prevented. Handling of the Pd catalyst separated from the reaction medium by filtration does not need to be carried out under a reducing atmosphere.゛The reaction medium used in the method of the present invention is usually an aqueous solution of a mineral acid such as sulfuric acid or an acid aqueous solution containing a halide, and the concentration of the mineral acid is 0.01 to 2. It is ON.

In addition, halogen ions are 10'mol/l ~ 0.2 m
It is used in the range of ol/I.

The reaction temperature of this reaction is usually 0°C to 50°C, and the reaction pressure is 3Kg/cm2 ・G to 150Kg/cm"
・Implemented in G.

The Pd catalyst used in the method of the present invention may be a supported Pd catalyst supported on various carriers or a known Pd catalyst such as Pd black.
Catalysts may be used.

Further, a co-catalyst such as sodium bromate can also be used in combination.

As described above, according to the method of the present invention, hydrogen peroxide can be efficiently produced without loss of Pd.

(Example) Hereinafter, Examples and Comparative Example S: The present invention will therefore be described. The analytical values of the gas composition used in the Examples are the analytical values obtained by gas chromatography. The metal ion concentration in the solution was measured using inductively coupled plasma emission spectrometry using a 120OVR analyzer manufactured by Seiko Electronics. It was done according to 2.

Example l Glass container 22 with an internal volume of 50 ml, 0.1 mol/I of sulfuric acid and 8 mmol/I of sodium bromate as reaction medium
Aqueous solution prepared so that f! , 20 g was added.

This water-soluble K1. Then, a mixed gas having a composition of 4% by volume of hydrogen gas, 40% by volume of oxygen gas, and 56% by volume of nitrogen gas was bubbled through for 15 minutes. Next, a commercially available Pd black catalyst i o Omg was added to this aqueous solution, and the glass container was quickly placed in an autoclave with a volume of <100 ml and pressurized to 100 kg/cm2-G with a gas having the same composition as the ventilation gas. 2. While keeping the temperature at 10°C. OOOrpm
The mixture was stirred for 3 hours. After the stirring was completed, the catalyst was filtered off under a reaction gas atmosphere. The hydrogen peroxide concentration in the aqueous solution is 2.9%,
The hydrogen selectivity was 84%, and the palladium elution concentration at this time was 0.9 ppm.

Hydrogen selectivity (%) = [(Amount of hydrogen peroxide produced by reaction mo 1) ÷ (Amount of hydrogen peroxide produced in a chain mol calculated from the amount of hydrogen consumed)) x Example 2 Gas used Except that the composition is 1% by volume of hydrogen gas, 10% by volume of oxygen gas, and 89% by volume of nitrogen gas,
The same operation as in Example 1 was performed.

After 3 hours, the hydrogen peroxide concentration in the aqueous solution was 0.6%, the hydrogen selectivity was 80%, and the palladium elution concentration at this time was 1.0 ppm.

Example 3.4 Pressure pressure is 10 kg/cm2・G and 1 kg/cm2
．． The same operation as in Example 1 was performed except for G. The elution concentrations of palladium in the aqueous solution after 3 hours were 1.2 ppm and 1.0 ppm, respectively.

Example 5 The same operation as in Example 1 was performed except that the catalyst was 300 mg of 5χPa/c (commercially available). After 3 hours, the hydrogen peroxide concentration in the aqueous solution was 2.6%, and the hydrogen selectivity was 7.
1%, and what about palladium at this time? The discharge concentration was 0.6 ppm.

Comparative Examples 1 to 5.

The same operations as in Examples 1 to 5 were performed except for the treatment after the stirring was completed. After the stirring was completed, the pressure was released to the atmosphere, and the glass container was taken out from the autoclave and left in the atmosphere for 30 minutes. The palladium concentration in the aqueous solution after filtering off the catalyst was as follows.

Comparative example 1 21.3ppm 2 20.4ppm 3 19.8ppm 4 21.2ppm 5 15.8ppm

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between sodium bromate concentration and palladium elution amount. Patent Applicant Mitsubishi Gas Chemical Co., Ltd. Representative Patent Attorney Sadafumi Kobori (Effects of the Invention) Compared to the comparative example, the elution of palladium was significantly suppressed in the example in which the catalyst surface was treated while being kept in a reduced state. . According to the method of the present invention, palladium elution is efficiently suppressed even when the concentration of sodium bromate is relatively high. As described above, by using the present invention, it is possible to suppress the elution of palladium metal from the catalyst into the aqueous solution, and to efficiently produce hydrogen peroxide.

Claims (5)

[Claims] (1) In a method for producing hydrogen peroxide by catalytically reacting oxygen and hydrogen with a Pd catalyst in a reaction medium, Pd A method for producing hydrogen peroxide, characterized by suppressing the elution of Pd from a catalyst. (2) The manufacturing method according to claim 1, wherein the substance used to maintain the system in a reducing atmosphere is hydrogen gas. (3) The manufacturing method according to claim 1, wherein the reaction medium is an aqueous solution. (4) The production method according to claim 1, wherein the reaction medium is an acidic aqueous solution or an acidic aqueous solution containing an inorganic salt dissolved therein. (5) The production method according to claim 1, wherein the catalyst is in the form of a carrier or metal powder.