JPS5939844A - Preparation of glyoxal - Google Patents

Abstract

PURPOSE:To prepare glyoxal in high yield, by contacting ethylene glycol with fine silver powder having a specific particle diameter in the presence of a specific amount of phosphorus or a phosphorus compound, thereby effecting the vapor-phase oxidation reaction of ethylene glycol. CONSTITUTION:Glyoxal is prepared by the vapor-phase oxidation of ethylene glycol. In the above process, a gas containing ethylene glycol and molecular oxygen is brought into contact with a silver catalyst having a particle diameter of <=1X10<-3>mm. at a high temperature of about 450-650 deg.C in the presence of phosphorus or a phosphorus compound (preferably methyl phosphite, ethyl phosphite, methyl phosphate, ethyl phosphate, etc.). EFFECT:The reaction stability can be improved, and the amount of unreacted ethylene glycol and the production of glycol aldehyde (a reaction intermediate) can be remarkably suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas phase oxidation reaction of ethylene glycol, and more specifically, the present invention is characterized by bringing ethylene glycol into contact with fine silver of a specific particle size in the presence of a predetermined amount of phosphorus or a phosphorus compound. This is a gas phase oxidation method that yields glyoxal in high yield.

There are various proposals regarding methods for producing glyoxal by oxidizing ethylene glycol. For example, copper and/or
Or a method of oxidizing with oxygen using an oxidation catalyst consisting of silver and phosphorus (Japanese Patent Publication No. 1364/1982), in the presence of a catalyst containing phosphorus and copper, phosphorus and silver, or phosphorus, copper and silver, the conversion rate of ethylene glycol There is an oxidation method (Japanese Patent Laid-Open No. 17408/1983) in which a bromine compound is mixed into the raw material mixture gas in an amount that does not reduce the amount of bromine to about 90 or less. Also, a method using a catalyst containing copper (U.S. Pat. No. 2,339,282
No. 1), a method using a CuCu-5i alloy and oxidizing a copper-containing catalyst in the coexistence of a halogen compound has been proposed. However, methods using these alloy catalysts are not very advantageous industrially because they are difficult to prepare, have a short lifespan during which high reaction performance can be maintained, and require complicated catalyst regeneration treatment. Ta.

Furthermore, as a method by oxidation of ethylene glycol,
A method of oxidizing in the presence of chain crystals with a constant particle size (0.1 to 2.5 mm) (Japanese Patent Application Laid-Open No. 103809/1983);
A method of oxidizing using a copper-containing catalyst in the coexistence of a phosphorus compound that vaporizes under the reaction conditions (Japanese Patent Application Laid-Open No. 55-55129)
etc. have also been proposed. However, the yield of glyoxal by these methods is not very high;
Therefore, this method could not compete with the nitric acid oxidation method of acetaldehyde, which is practiced industrially.

However, compared to the nitric acid oxidation method of acetaldehyde, the production method of glyoxal using the gas phase oxidation method of ethylene glycol uses ethylene glycol, which is a conductor of ethylene oxide, as a raw material source, and uses cheap natural gas as the raw material source. It was advantageous in this respect as it was economically efficient.

Therefore, the present inventors have conducted intensive studies to overcome the drawbacks of the conventional method in a method for producing glyoxal by gas-phase oxidation of ethylene glycol.

As a result, they discovered that the reaction performance was dramatically improved by using finely powdered silver with a particle size of 1 x 10-3 or less as a catalyst in the presence of a trace amount of phosphorus or a phosphorus compound.
Based on this knowledge, we have completed the present invention.

That is, the present invention involves producing glyoxal by gas-phase oxidation of ethylene glycol, in which a gas containing ethylene glycol and molecular oxygen is oxidized to a particle size of 1 x 10-3 at high temperature in the coexistence of phosphorus or a phosphorus compound. The present invention provides a method for producing glyoxal, which is characterized by carrying out oxidation by bringing it into contact with the following silver catalyst.

In the present invention, phosphorus or a phosphorus compound may be mixed in a predetermined amount with ethylene glycol before being subjected to the reaction, or may be added to the reaction system separately from ethylene glycol, either alone or as a solution. Examples of phosphorus compounds include inorganic phosphorus compounds such as ammonium orthophosphate, ammonium phosphorus Fllwater IA, ammonium dihydrogen orthophosphate, and dihydrate ammonium sulfite, and primary to tertiary phosphines such as mono-, di-, or trimethylphosphine. , phosphorous acid esters such as methyl phosphite and ethyl phosphite, dimethyl methyl phosphonate, and diethyl ester ethyl phosphonate. However, phosphorus compounds with high boiling points require the evaporator temperature to be particularly high, or these phosphorus compounds stay in the evaporator and decompose and accumulate, causing corrosion of equipment materials and iron rust that occurs. etc. may fly into the reaction layer and adversely affect the reaction, which is not preferable. Therefore, it is more preferable to use relatively low 1! Organic phosphorus compounds having an Ili point, such as methyl phosphite, ethyl phosphite, methyl phosphate, and ethyl phosphate, are used.

The amount of phosphorus or phosphorus compound added is suitably in the range of 1 to 50 ppnl in terms of phosphorus relative to ethylene glycol. By adding this phosphorus or phosphorus compound,
Compared to the case where these are not added, the production of oxidation products such as -carbon oxide and carbon dioxide and decomposition products such as formaldehyde is significantly suppressed, and the yield of glyoxal, which is the target product, is significantly improved. In addition, when the addition of phosphorus or a phosphorus compound is temporarily interrupted in the method of the present invention, the production rate of carbon oxide, carbon dioxide, or formaldehyde immediately increases. This determines that the added phosphorus or phosphorus compound acts effectively in the gas phase rather than accumulating and acting on the catalyst.

Trace amount of phosphorus or phosphorus compound and particle size lXl in the present invention
The characteristics of the combined use of a finely divided silver catalyst of less than 0% are that the advantages and disadvantages of the action exhibited by phosphorus or a phosphorus compound itself are mutually contradictory with those of the action exhibited by the finely divided silver catalyst itself. By combining the two, the strengths of both can be successfully interacted with, resulting in a dramatic effect.

In other words, if the amount of phosphorus compound added is increased without using a finely divided silver catalyst, the amount of carbon dioxide, carbon oxide, and formaldehyde produced decreases, and glyoxal selectivity improves, but glycolaldehyde, which is a reaction intermediate, decreases. and unreacted ethylene glycol. On the other hand, in the absence of phosphorus or phosphorus compounds, approximately 0
．． Compared to the case where silver crystals with a particle size of 1 mm or more are used as a catalyst, when the gas phase oxidation reaction of ethylene glycol is performed using fine powder silver with a particle size of 1 x 10-3 mg or less as a catalyst, the oxidation is Although the activity is extremely high, many decomposition and oxidation products such as carbon monoxide and carbon dioxide are generated, so the yield of glyoxal, which is the target product, is not so good.

On the other hand, in the coexistence of phosphorus or a phosphorus compound and a powdered silver catalyst, the increase in glycolaldehyde and unreacted ethylene glycol is significantly suppressed.

On the other hand, when a phosphorus compound is added in an amount of about 50 ppm or more in terms of phosphorus to ethylene glycol in the presence of an ordinary chain crystal catalyst with a rod diameter of about 0.1 rrm or more, carbon dioxide, carbon oxide, formaldehyde, etc. Although the production of decomposition oxidation products is reduced and glyoxal selectivity is improved, unreacted ethylene glycol and glycolaldehyde, which is a reaction intermediate, increase, making this process undesirable.

Moreover, it is not practical because reaction deactivation occurs due to a decrease in reaction temperature and reaction stability is significantly impaired. However, by combining fine powder silver with a predetermined particle size as a catalyst according to the present invention, the reaction stability in particular is significantly improved, and the production of unreacted ethylene glycol and glycolaldehyde, which is a reaction intermediate, is significantly suppressed. Ru.

If the amount of phosphorus or phosphorus compound added is less than 1 ppm in terms of phosphorus relative to ethylene glycol, the effect obtained will be small and it is not practical.

Further, if more than 50 ppm of phosphorus or a phosphorus compound is added in terms of phosphorus, various reaction-inhibiting effects will appear to such an extent that the reaction cannot be maintained even in the presence of a finely divided silver catalyst, which is not practical.

Next, in the present invention, the fine powder silver having a particle size of 1×10 g1i or less is chemically produced fine powder silver, such as that obtained by an alkali precipitation method, or what is generally called a gas evaporation method. A fine powder obtained by various heating methods in an inert gas or a fine powder obtained by a vacuum evaporation method can be used regardless of its preparation method.

In the present invention, the finely divided silver catalyst can be used alone or in combination with crystalline silver particles having a particle size of 0.1 square centimeters or more. For example, in the case of a reactor in which the reaction gas flow is downward, crystalline silver particles with a particle size of about 0.1 mm or more, which are commonly used, are placed on a copper wire mesh with a suitable mesh, and then A method of filling a finely divided silver catalyst with a particle size of 1×10'm or less is an example of a practical method without scattering loss. In addition, instead of silver particles with a particle size of 0.1 nm or less, inert carriers with small specific surface areas such as α-alumina or steatite spheres can be used, but the reaction results obtained are better than when using silver particles. is somewhat low. This is because silver has excellent thermal conductivity.

Copper metal powder can also be used, but iron-based materials cannot be used as they are catalyst poisons. Furthermore, it goes without saying that the combination with silver having a grain size of about 100 ml is effective in the presence of fine chain crystals having a grain size of less than 1X10''.

In the present invention, as molecular oxygen, pure oxygen or air may be used, but economically it is preferable to use the latter.

Furthermore, in order to obtain glyoxal in high yield, ethylene glycol and molecular oxygen are diluted with an inert gas to carry out the reaction. As the inert gas, nitrogen, helium, rare gas such as argon, carbon dioxide gas, water vapor, etc. are used.

For the gas phase oxidation of the method of the present invention, a reaction temperature of 450 to 650°C is appropriate.

The reaction gas reacted as described above must be cooled as quickly as possible after leaving the catalyst layer. Excessive retention in the high temperature region will only lead to decomposition of unstable aldehydes. The cooled gas undergoes partial condensation as necessary to recover unreacted ethylene glycol. If it does not contain unreacted ethylene glycol, or if there is a trace amount of ethylene glycol remaining that does not pose a problem for the product and there is no need to remove it, it is cooled and condensed in a heat exchanger and then subjected to normal absorption operations. Separates from gas phase components.

The glyoxal aqueous solution thus obtained contains organic acids and trace amounts of formaldehyde as impurities. This formaldehyde is simply removed by a conventional stripping operation with steam injection, during which time some of the low-boiling organic acids such as formic acid and acetic acid are also removed. Furthermore, an aqueous glyoxal solution obtained by oxidizing ethylene glycol using a finely divided silver catalyst contains almost no glycolaldehyde, which is a reaction intermediate, compared to a glyoxal solution obtained by oxidizing ethylene glycol using a finely divided silver catalyst. Furthermore, the amount of organic acid contained in the glyoxal aqueous solution subjected to the bomaldehyde stripping treatment is an appropriate amount of acid necessary to maintain the stability of the product, so no further separation treatment is necessary. Therefore, it is sufficient to perform decolorization treatment and treatment with a cation exchange resin as necessary.

Thus, according to the present invention, glyoxal can be produced from ethylene glycol in a high yield by suppressing the production of by-products, and the stability of the gas phase oxidation reaction is excellent. Therefore, the present invention is suitable as an industrial method for producing glyoxal.

Next, the present invention will be explained in more detail based on examples.

Example 1 In the bottom layer of the reactor, 17 g of silver particles with a particle size of 0.84 to 1.5 mm obtained by electrolysis of an aqueous silver nitrate solution were placed on top of 17 g of silver particles with a particle size of 0.35 to 0.84 mrtr. Furthermore, 8 g of silver particles with a particle size of 0.16 to 0.35 mm were placed on top of that, and as a top layer, an average particle size of about 7 x 1 O-
511I+, finely powdered silver obtained by vacuum evaporation method was 1.0
I laid down g. The packed bed height was approximately 30 mrx.

To this reactor, 162 g/hr of ethylene glycol, 162 g/hr of water vapor, and 2804 g/hr of air were supplied to the reactor through an evaporator and a preheater. The reaction was carried out at a reaction temperature of 521°C by supplying nitrogen at a rate of 800/hr in a downward flow. After cooling the reaction gas, the product was separated and collected in a water absorption tower.

The results were that the ethylene glycol conversion rate was 100%, the glyoxal selectivity was 44.396%, and the polardehyde selectivity was 12.4%.

Next, triethyl phosphite 2 for ethylene glycol
When 6.8 ppm (5 ppm as phosphorus) was added and reacted, the reaction temperature was 502°C. Ethylene glycol conversion rate: 100 or more Glyoxal selectivity: 8
The formaldehyde selectivity was 0.1% and the formaldehyde selectivity was 2.1, but the production of glycolaldehyde, which is a reaction intermediate, was poor.

Comparative Example 1 A reactor was filled with 38 g of a silver particle catalyst obtained by electrolysis of an aqueous silver nitrate solution. First, fill the bottom layer with 20 g of silver particles with a particle size of 0.84 to 1.5 mm obtained by sieving K. On top of that, 10 g of silver particles with a particle size of 0°35 to 1.84 y + m, Similarly, the particle size is 0.16 to 0.35i.
8g of silver particles of AT were laid down and the height of the filling was about 30cm.

When a raw material gas having the same composition as in Example 1 was passed through the reactor under the same conditions as in Example 1 except that triethyl phosphite was not added and the reaction temperature was 510°C, the ethylene glycol conversion rate was 100 cm, and glyoxer + g was selected. The yield was 53%, and the selectivity for polyaldehyde was 5.296.

Comparative Example 2 Triethyl phosphite 26% compared to ethylene glycol.
The reaction was carried out under the same reaction conditions as in Comparative Example 1, except that 8 ppm (5 ppm as phosphorus) was added and the reaction temperature was 501°C.

The ethylene glycol conversion rate was 100%, the glyoxal selectivity was 80.4%, and the formaldehyde selectivity was 2.5%, but glycolaldehyde, a reaction intermediate, was produced as a by-product with a selectivity of 1.3%. .

Next, when the addition of triethyl phosphite was stopped and the product was separated and collected and analyzed, the reaction temperature was 509°C, the ethylene glycol conversion rate was 100%, the glyogysal selectivity was 53.5%, and the formaldehyde selectivity was 5. At .4%, no formation of glycolaldehyde was observed.

Comparative Example 3 Triethyl phosphite 53.5% compared to ethylene glycol.
The reaction was carried out at 496° C. under the same reaction conditions as in Comparative Example 1 except that 6 pprrl (10 ppm as phosphorus) was added.

Ethylene glycol conversion rate 98.9%, glyoxal selectivity 84.6%, formaldehyde selectivity 1.0%,
Although the glycolaldehyde selectivity was 4.5, the reaction temperature was not constant due to slight disturbances in the supply of raw materials, which caused concerns about new reactors and caused operational problems in terms of long-term stable operation.

Example 2 Triethyl phosphite vs. ethylene glycol 53.
adding 6 ppm (10 ppm as phosphorus);
The reaction was carried out under the same reaction conditions as in Example 1 except that the reaction temperature was 497°C.

Ethylene glycol conversion rate 99.9%, glyoxal selectivity 84.1%, formaldehyde selectivity 0.9%,
The addition of the finely powdered Sushi catalyst and phosphorus compound was found to be effective in improving the reaction results, with a glycolaldehyde selectivity of 0.4%, which resulted in less by-product formation and an extremely high selectivity to the desired product, glyoxal. Furthermore, in terms of operational performance, there was no fluctuation in reaction temperature as in Comparative Example 3, and excellent stability was observed.

Example 3 39 g of silver nitrate was dissolved in 140 ml of pure water, and while stirring, an aqueous solution of 20 g of NaOH dissolved in 30 ml of pure water was slowly added dropwise. The obtained brown precipitate was suction filtered and thoroughly washed with pure water. This precipitate was washed with 180% pure water.
The suspension was suspended in 100 mA, and while stirring vigorously, 12 ml of a 30% formalin aqueous solution was added, and at the same time, a 5 N NaOH aqueous solution was added to maintain the K pH at 8 to 12. After stirring for 30 minutes, the resulting gray precipitate was suction filtered, thoroughly washed with pure water, and then dried at 110°C. Average particle size approximately 0.25
25 g of μm (2500 A) silver was obtained.

In the bottom layer of the reactor, 17 silver particles with a particle size of 0.84 to 1.5 mm obtained by electrolysis of an aqueous silver nitrate solution were placed in the same manner as in Example 1.
．． 5g, and the same particle size 0.35-0.84ff1
10g of M silver particles, and on top of that, the same particle sizes of 0 and 1
8 g of silver particles with a size of 6 to 0.35 mm were spread, and finally 1.0 g of fine powder silver obtained by the above-mentioned alkali precipitation method was spread. The filled bed height was approximately 301 nIn.

Triethyl phosphite versus ethylene glycol 26.
501 by adding 8 ppm (5 ppm as phosphorus)
When the reaction was carried out in the same manner as in Example 1 at ℃, the ethylene glycol conversion rate was 100% and the glyoxal selectivity was 81.0.
%, the formaldehyde selectivity was 2.3%, and there was no trace of glycolaldehyde, which is a reaction intermediate.

Claims (1)

[Claims] (1) To produce glyoxal by gas-phase oxidation of ethylene glycol, a gas containing ethylene glycol and molecular oxygen is oxidized at high temperature in the coexistence of phosphorus or a phosphorus compound with a particle size of 1 x 10 mm or less. contact with a silver catalyst,
A method for producing glyoxal, which comprises performing oxidation.