JPS5939843A - Preparation of glyoxal - Google Patents

Abstract

PURPOSE:To prepare glyoxal in high yield, by the vapor-phase oxication of ethylene glycol in the presence of a catalyst comprising a silver catalyst and a reaction inhibitor comprising phosphorus or a phosphorus compound. CONSTITUTION:Glyoxal is prepared by the vapor-phase oxidation of ethylene glycol. The process is performed by contacting a gas containing ethylene glycol and molecular oxygen with a silver catalyst (preferably crystalline silver having a particle size of 0.1-2.5mm. and obtained by electrolysis) 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.). The amount of the phosphorus or phosphorus compound is preferably 1- 50ppm expressed in terms of phosphorus.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of glyoxal by gas phase oxidation of ethylene glycol, and more specifically, to the production of glyoxal by gas phase oxidation of ethylene glycol.
This relates to a method in which a silver catalyst is used as a catalyst and phosphorus or a phosphorus compound is present as a reaction inhibitor to obtain the desired glyoxal in a high yield.

Generally known methods for producing glyoxal include oxidation of acetylene or ethylene, oxidation of acetaldehyde with nitric acid, and oxidation of ethylene glycol. However, industrially, the method of oxidizing acetaldehyde with nitric acid is mainly used.

In this nitric acid oxidation method of acetaldehyde, as an oxidizing agent,
Since nitric acid is required in an amount at least equimolar to the acetaldehyde to be reacted, contamination of unreacted nitric acid is unavoidable.
Another drawback is that a relatively large amount of organic acid as an impurity is produced as a by-product, and therefore a complicated separation and purification process is essential.

On the other hand, there are various proposals regarding methods for producing glyoxal by oxidizing ethylene glycol. For example, a method of oxidizing with oxygen using an oxidation catalyst consisting of copper and/or silver and phosphorus (Japanese Patent Publication No. 48-1, I64), a catalyst containing phosphorus and copper, phosphorus and silver, or phosphorus, copper and silver. There is an oxidation method (Japanese Patent Application Laid-open No. 17408/1983) in which a bromine compound in the cap is mixed into the raw material mixture in the presence of ethylene glycol in a range that does not reduce the conversion rate of ethylene glycol to about 90% or less.

Additionally, a method using a catalyst containing copper (U.S. Pat. No. 2.33
No. 9,282), a method of oxidizing a copper-containing catalyst in the coexistence of a halogen compound using a Cu-Si-Mn alloy reaction tube 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.

Sara, as a method by oxidation of ethylene glycol,
A method of performing oxidation in the presence of silver crystals with a fixed particle size (0.1 to 2.5 + u) (Japanese Patent Application Laid-open No. 103809/1983),
Method C of carrying out oxidation 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;
This was not a satisfactory industrial manufacturing method.

However, compared to the nitric acid oxidation method of acetaldehyde, the method for producing glyoxal using the gas phase oxidation method of ethylene glycol uses ethylene glycol, a derivative of ethylene oxide, as a raw material source, and uses cheap natural gas as the raw material source. It has excellent economic efficiency and is advantageous as an industrial manufacturing method.

Therefore, the present inventors conducted extensive research into a method for producing glyoxal by gas-phase oxidation of ethylene glycol (D) in order to overcome the drawbacks of the conventional method. It was discovered that the reaction results were dramatically improved by adding it as an inhibitor, and based on this knowledge, the present invention was completed.

That is, the present invention involves producing glyoxal by gas-phase oxidation of ethylene glycol, and oxidizes by contacting a gas containing ethylene glycol and molecular oxygen with a silver catalyst 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 the following steps.

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 hydrogen phosphate, ammonium dihydrogen orthophosphate, ammonium dihydrogen phosphite, primary to tertiary phosphines such as mono-, di- or trimethylphosphine, and phosphorus. Examples of organic phosphorus compounds that can be effectively used include phosphorous acid esters such as methyl acid and ethyl phosphite, dimethyl methyl phosphonate, and diethyl ester ethyl phosphonate. However, phosphorus compounds with a high boiling point require a particularly high evaporator temperature, or these phosphorus compounds stay in the evaporator and decompose and accumulate, causing corrosion of equipment materials and corrosion of iron rust, etc. This is not preferable because it may fly into the reaction layer and adversely affect the reaction. Therefore, it is more preferable to use organic phosphorus compounds with relatively low boiling points, such as methyl phosphite, ethyl phosphite, methyl phosphate, and ethyl phosphate.

The amount of phosphorus or phosphorus compound added is suitably in the range of 1 to 50 ppm in terms of phosphorus relative to ethylene glycol. The addition of phosphorus or phosphorus compounds significantly suppresses the production of oxidation products such as carbon oxide and carbon dioxide, and decomposition products such as formaldehyde, compared to the case where these are not added, and the production of oxidation products such as carbon oxide and carbon dioxide and decomposition products such as formaldehyde are significantly suppressed, and the production of target products. The yield of glyoxal 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. Therefore, this suggests that the added phosphorus or phosphorus compound is acting effectively in the gas phase rather than accumulating and acting on the catalyst.

The amount of phosphorus or phosphorus compound added is 5
If it exceeds 0 ppm, the amount of glycoaldehyde as a reaction intermediate increases, the conversion rate of ethylene glycol decreases, and unreacted ethylene glycol increases, which is not preferable. Further, if the amount added is less than 1 ppm, the effect will be insufficient and the purpose of the present invention will not be achieved. The use of a reaction inhibitor for such a silver catalyst system is described, for example, in the above-mentioned Japanese Patent Application Laid-Open No. 54-103809.
Examples of glyoxal or hydrogen halides have been disclosed, but compared to these, the effect of adding phosphorus or phosphorus compounds of the present invention is remarkable, and in view of the high yield of improved glyoxal, industrial The advantages as a manufacturing method are very large.

Next, in the method of the present invention, it is preferable to use molecular oxygen at a ratio of 0.7 to 2.0 moles per mole of ethylene glycol. The presence of more than 2 moles of oxygen significantly increases oxidation products such as carbon dioxide, -carbon oxide, and decomposition products such as formaldehyde, reducing the yield of glyoxal. Furthermore, if the amount of oxygen is less than 0.7 mol, the amount of oxidized products decreases, but unreacted ethylene glycol increases, which is economically unfavorable. Moreover, it is not practical because it becomes difficult to maintain a stable reaction due to the decrease in reaction temperature. As molecular oxygen, pure oxygen or air may be used, but economically it is better to use the latter.

In the present invention, in order to obtain glyoxal in high yield, 5-ethylene glycol and molecular oxygen are diluted with an inert gas to carry out the reaction. As the inert gas, known rare gases such as nitrogen, helium, and argon, carbon dioxide gas, water vapor, and the like are used. Furthermore, the exhaust gas from this reaction can be recycled and used. Dilution with an inert gas is carried out by mixing at least 5 moles per mole of ethylene glycol. When the amount of inert gas is less than 5 moles, oxidation products such as carbon dioxide and carbon oxide increase, and the yield of glyoxal decreases.

For the gas phase oxidation of the method of the present invention, a reaction temperature of 450 to 650°C is suitable. At a reaction temperature of less than 450° C., the conversion rate of ethylene glycol is low, and a large amount of unreacted ethylene glycol must be separated, recovered, and recycled. Furthermore, the amount of glycolaldehyde produced increases. On the other hand, if the reaction temperature exceeds 650°C, carbon dioxide and carbon oxide as oxidation products increase, which is not preferable.

Next, as a catalyst, all kinds of crystalline silver can be used, but the particle size obtained by electrolysis is 0.1 to 2.5.
Preferably, a chain crystal of u is used.

The method of the present invention can be carried out by passing a gas containing the raw material ethylene glycol and oxygen through the silver catalyst layer in a downward flow from above. At this time, the silver catalyst layer should be at least 3 cm depending on the particle size.
It is preferable to use one packed in layers. That is, the top layer contains 10 to 30% by weight of silver particles with a particle size of 0.1 to 0.3511a+, and the next layer contains 10 to 30% by weight of silver particles with a particle size of 0.35 to 0.
．． It is preferable that 85 mg of silver particles be filled in an amount of 35 to 65% by weight, and the lowermost layer be filled with 5 to 55% by weight of silver particles having a particle size of o and 85 to 2.5n. Alternatively, the number of layers may be further increased and filling may be performed with the distribution changed so that the silver particles become coarser from the top to the bottom in the same manner as described above.

Preferably, the residence time of the reaction gas in this silver catalyst layer does not exceed 0.03 seconds. If the residence time is longer than this, oxidation products such as carbon dioxide, -carbon oxide and decomposition products such as formaldehyde will increase.

The reaction product gas leaving the catalyst layer is cooled as quickly as possible. That is, if residence in a high temperature region extends for a long time, decomposition of glyoxal will proceed, which is undesirable. The cooled gas is subjected to partial condensation as necessary, and unreacted ethylene glycol is recovered. If it does not contain ethylene glycol or has a trace amount of ethylene glycol that does not pose a problem as a product, and there is no need to remove it, it is cooled and condensed in a heat exchanger, and then separated from the gas components by normal water absorption. . The glyoxal aqueous solution thus obtained contains organic acids and trace amounts of formalin as impurities. However, formalin is easily removed by conventional steam stripping methods. At this time, a portion of low-boiling organic acids such as formic acid and acetic acid are also removed.

The organic acid contained in the aqueous glyoxal solution obtained in this way has the appropriate amount necessary to maintain the stability of the product. In this way, it is possible to omit treatment with an anion exchange resin for removing organic acids, as in the case of an aqueous glyoxal solution obtained by the nitric acid oxidation method of acetaldehyde. Therefore, all that is left to do is to perform decolorization treatment and treatment with a cation exchange resin as necessary.

Note that the previously separated gas components are either discharged as gas (7) or recycled and utilized in the main reaction as an inert gas.

As described above, according to the method of the present invention, glyoxal can be obtained in high yield by oxidizing ethylene glycol. It also has the advantage that the product separation and purification process can be simplified. Therefore, the method of the present invention is suitable as an industrial method for producing glyoxal.

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

Example 1 Silver particles obtained by ordinary electrolysis were placed in a reactor as follows:
8g was filled. For the packed layer, first, 20 g of silver particles with a particle size of 0.84 to 1.5 obtained by sieving were placed in the bottom layer, then 10 g of silver particles with a particle size of 0.35 to 0.84 were placed in the same layer, and the same particles were placed in the top layer. 8 g of silver particles having a diameter of 0.16 to 0.35+u+ were spread, and the height of the packed layer was formed in order of about 30.

Ethylene glycol 162 g/hr - water vapor 162
g/hr1 has a composition of 280 t/h air and 800 t/hr nitrogen, and 26.8 ppp relative to ethylene glycol.
A gas containing triethyl phosphite (5 ppm as P) was supplied in a downward flow, and the reaction was carried out at a reaction temperature of 501°C. After cooling the reaction gas, the product was collected with a water absorption group.

The results were that the conversion rate of ethylene glycol was 100% and the yield of glyoxal was 80.4%.

Next, during the reaction, phosphorous acid is added to the raw material gas!・When the addition of ethyl was stopped and the product was separated, collected, and analyzed, the reaction temperature was 509°C, and the ethylene glycol conversion rate was 10.
At 0 g, the glyoxal yield decreased to 53.5 g.

Comparative Example 1 Instead of triethyl phosphite, 50 ppm of ethylene dichloride (3 as chlorine) was added to ethylene glycol.
The reaction was carried out in the same manner as in Example 1, except that 5.8 ppm) was added and the reaction temperature was 498°C.

As a result, the ethylene glycol conversion rate was 60.896, and the glyoxal yield was 60.896.

Comparative Example 2 Instead of triethyl phosphite, 50 ppm of bromoform (47 ppm of bromine) was added to ethylene glycol.
The reaction was carried out in the same manner as in Example 1, except that 1 ppm) was added and the reaction temperature was 505°C.

As a result, the conversion rate of ethylene glycol was 100% and the yield of glyoxal was 62.1%.

Example 2 Triethyl phosphite 48.3 to ethylene glycol
ppm (9 ppm as P) and the reaction temperature was increased to 49
The reaction was carried out in the same manner as in Example 1 except that the temperature was 8°C.

As a result, the ethylene glycol conversion rate was 99.1% and the glyoxal yield was 84.3%, indicating that the addition of the phosphorus compound significantly improved the glyoxal yield.

Example 3 Trimethyl phosphate to ethylene glycol 22.7
The reaction was carried out in the same manner as in Example 1, except that 5 ppm (as P) was added and the reaction temperature was 497°C.

As a result, the ethylene glycol conversion rate was 99.0% and the glyoxal yield was 77.8%, which was a significant improvement in the glyoxal yield.

Example 4 Ethylene IJ: ``C(C2H50
) 2 POCH2COOC2H536,2ppm (
5ppm) was added as P.

The reaction was carried out in the same manner as in Example 1 except that the reaction temperature was 500°C.

As a result, the ethylene glycol conversion rate was 99.9%, and the glyoxal yield was si, o*.

Example 5 Niammonium hydrogen phosphate ((NH4)2HPO4) 12.8 ppm (P
The reaction was carried out in the same manner as in Example 1, except that 3 ppm) was added and the reaction temperature was 505°C.

As a result, the ethylene glycol conversion rate was 100% and the glyoxal yield was 70.2%.

Example 6 Triethylphosphine 719 for ethylene glycol
．． The reaction was carried out in the same manner as in Example 1, except that 1 ppm (5 ppm as P) was added and the reaction temperature was 505°C.

As a result, the ethylene glycol conversion rate was 100%, and the glyoxal yield was 70.7%.

Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (2)

[Claims] (1) When producing glyoxal by gas-phase oxidation of ethylene glycol, oxidation is carried out by bringing a gas containing ethylene glycol and molecular oxygen into contact with a silver catalyst at high temperature in the coexistence of phosphorus or a phosphorus compound. A method for producing glyoxal, characterized by: (2) The method for producing glyoxal according to claim 1, wherein phosphorus or a phosphorus compound is present in an amount of 1 to 50 pI)m in terms of phosphorus relative to ethylene glycol.