JP4404191B2 - Glyoxal manufacturing method - Google Patents

Description

  The present invention relates to a method for producing glyoxal that can maintain a high conversion rate of ethylene glycol and can maintain a high yield of glyoxal even if it is continuously produced for a long time.

  A method for producing glyoxal by oxidizing ethylene glycol in the presence of a silver catalyst is known, and such a silver catalyst has a relatively good ethylene glycol conversion rate (ratio of oxidation) compared to other catalysts. It is one of the most practical oxidation methods for practical implementation. However, since a large amount of labor is required for purification if ethylene glycol remains, if the reaction is carried out at a high temperature to further increase the conversion rate of ethylene glycol, the yield of glyoxal may be lowered and the life of the catalyst may be shortened. There was a problem of becoming.

In order to solve such a problem, a method of oxidizing ethylene glycol under a certain condition of temperature, residence time and inert gas concentration in the presence of a silver catalyst having a particle size of 0.1 to 2.5 mm (for example, patent Reference 1) and a method of oxidizing a gas containing ethylene glycol and oxygen in the presence of phosphorus, a phosphorus compound, or a silver catalyst (for example, see Patent Document 2) have been proposed.
JP-A-54-103809 JP 59-39843 A

  However, in the technique of the above-mentioned Patent Document 1, since the conversion rate of ethylene glycol is not so high, the yield of glyoxal is good at the beginning of the reaction, and adhesion of carbonized products to the silver catalyst surface or agglomeration due to melting occurs. Although there was no reaction, agglomeration started to occur when the reaction was continued for a long time, and there was a problem that the conversion rate of ethylene glycol and the yield of glyoxal were lowered. In the technique of Patent Document 2, the ethylene glycol conversion rate and glyoxal yield at the beginning of operation are good, but when the reaction is continued for a long period of time, agglomeration begins to occur, and the ethylene glycol conversion rate and glyoxal yield react. There was a problem that it was significantly reduced compared to the initial period.

Accordingly, the present inventors have conducted extensive studies in view of such circumstances, and as a result, in producing glyoxal by vapor-phase oxidation of ethylene glycol, the inventors made contact with a silver catalyst having a bulk density of 3 g / cm ³ or less. It has been found that the above problems can be solved by performing gas phase oxidation, and the present invention has been completed.

  The method for producing glyoxal of the present invention can maintain a high conversion rate of ethylene glycol and can maintain a high yield of glyoxal even when continuous production is performed for a long time.

Hereinafter, the present invention will be described in detail.
In the present invention, glyoxal is produced by gas-phase oxidation of ethylene glycol. Such gas-phase oxidation is usually carried out in an inert gas, and oxygen or air is used as an oxidizing agent.
Nitrogen, argon, helium, carbon dioxide or the like is used as the inert gas, and the amount of the inert gas used is 1 time mol or more, preferably 1 to 50 times mol with respect to oxygen in the oxidation reaction system. Degree. If the amount used is less than 1 mole, the reaction system may be within the explosion limit value due to oxygen, which is not preferable.

Further, the amount of the oxidizing agent used is preferably the theoretical equivalent or more, that is, 1.0 times mole or more, more preferably 1 to 2 times mole, particularly 1.0 to 1.5 times mole with respect to ethylene glycol. If the amount is less than 1.0 times mol, a large amount of unreacted raw material may remain, which is not preferable.
Furthermore, water may be used in combination with water in order to facilitate the post-treatment of the reaction product gas during vapor phase oxidation or to control the explosion limit value due to oxygen as in the case of the inert gas described above. Is preferably less than 1.5 times the weight of ethylene glycol, and if it exceeds 1.5 times the concentration of glyoxal (aqueous solution), the concentration step is required to produce a product, which is not preferred.

In the present invention, the greatest feature is that vapor phase oxidation is performed by contacting ethylene glycol with a silver catalyst having a bulk density of 3 g / cm ³ or less, and the bulk density is preferably 0.5 to ³ g / cm ³ , 1 to 2 g / cm ³ .
If the bulk density is greater than 3 g / cm ^3, the distance between the silver catalysts will be shortened, and the gaps will be filled by melting and adhering carbonization, leading to an increase in pressure loss of the system, and the conversion rate of ethylene glycol and glyoxal in a short period of time. The yield is lowered and the object of the present invention cannot be achieved.

In order to make the bulk density of the silver catalyst within such a range, the shape of the silver catalyst may be devised, for example, a shape having a tree shape, a fiber shape, a needle shape, a wool shape, a scale shape, or the like may be used. Even if it is a normal spherical one having a hollow part or groove part, it is preferable to use a tree shape or a needle shape, and in order to prepare a silver catalyst having such a shape, silver is electrolyzed. This can be achieved by adjusting the acid solution concentration, the amount of current, the type of electrode, and the like during production. For example, in the above electrolysis method, the crystal is grown over time by reducing the concentration of the acid solution, or the silver crystal is grown while passing a minute current or changing the minute current value at regular intervals. A method is mentioned.
In the case of a tree-like or needle-like silver catalyst, the catalyst having the longest size (long side) of about 0.5 to 2 mm is preferable, and if it is less than 0.5 mm, the life of the catalyst may be reduced and may exceed 2 mm. And unreacted raw materials may remain, which is not preferable.
In the present invention, not only a silver catalyst having the above bulk density but also a copper catalyst can be used in combination as required.

Furthermore, in order to suppress the formation of oxidation products such as carbon monoxide and carbon dioxide and decomposition products such as formaldehyde, it is preferable that a cocatalyst such as phosphorus or a phosphorus compound (preferably a phosphorus compound) coexist. .
Phosphorus compounds include mono-, di- or trimethylphosphine and other primary to tertiary phosphines, phosphoric acid esters such as methyl phosphate and ethyl phosphate, methyl phosphite, dimethyl phosphite, trimethyl phosphite, phosphorous acid Examples include phosphoric acid esters such as ethyl acid, diethyl phosphite, triethyl phosphite, methylphosphonic acid dimethyl ester, ethylphosphonic acid diethyl ester, etc., which cause corrosion by staying in the equipment and decomposing and accumulating. A relatively low boiling point organic phosphorus compound such as methyl phosphite, ethyl phosphite, diethyl phosphite, triethyl phosphite, methyl phosphate and ethyl phosphate is preferred.

The coexistence amount of phosphorus or phosphorus compound is preferably 1 to 100 ppm in terms of phosphorus with respect to ethylene glycol. If the coexistence amount is less than 1 ppm, the coexistence effect may be poor, and if it exceeds 100 ppm, a large amount of unreacted raw materials may remain. It is not preferable.
Such phosphorus or phosphorus compound may be mixed with the raw material in advance and used for the reaction, or may be added to the reaction system alone or as an aqueous solution separately from the raw material.

In the present invention, ethylene glycol is passed through a packed bed filled with a silver catalyst having the above-described bulk density to perform gas phase oxidation. As such packed layers, a plurality of packed beds filled with silver catalysts having different bulk densities are used. Is preferable because the life of the silver catalyst is prolonged.
In the case where a plurality of packed beds are provided, the layer configuration may be such that the bulkiness of the packed layers decreases sequentially as ethylene glycol is passed through.
The filling amount of the silver catalyst in each layer is not particularly limited, but each layer may be disposed so as to be about 1 to 10 times the weight of the layer having the smallest weight.

  In performing the gas phase oxidation in the packed bed, ethylene glycol, the inert gas and the oxidizing agent, and water as necessary are supplied to the evaporator and the preheater in the above-described proportions. It is supplied to the packed bed after being heated to about ~ 200 ° C.

The supply amount at this time is such that the NSv value defined by supply amount per hour (L · hr ⁻¹ ) / catalyst amount (L) is 3,600 to 360, 0 ° C. and 0.1 MPa. 000 hr ⁻¹ is preferable, and 12,000 to 360,000 hr ⁻¹ is more preferable. If the NSv value is less than 3,600 hr ⁻¹ , the decomposition reaction of glyoxal may proceed, and if it exceeds 360,000 hr ⁻¹ , unreacted raw materials may remain, such being undesirable.

The gas phase reaction temperature is preferably 300 to 700 ° C, particularly 530 to 650 ° C. If the gas phase reaction temperature is less than 300 ° C., a large amount of unreacted raw material remains, and if it exceeds 700 ° C., the decomposition reaction of glyoxal may proceed, which is not preferable.
The pressure during the gas phase reaction is close to normal pressure, and the partial pressure of ethylene glycol as a raw material is usually supplied so as to be 50,000 Pa or less, and preferably 1,000 to 10,000 Pa. When the partial pressure is 50,000 Pa or more, a large amount of unreacted raw material may remain, which is not preferable.

The reaction gas exiting the packed bed may be cooled as quickly as possible. In particular, when the temperature of the reaction gas exceeds 500 ° C., it is preferably cooled to 500 ° C. or less in 0.05 seconds or less. If it exceeds 0.05 seconds, decomposition of glyoxal may proceed, which is not preferable.
The cooled gas is shrunk as necessary, and unreacted ethylene glycol is recovered. At this time, when ethylene glycol is not contained or a trace amount of ethylene glycol that does not cause a problem as a product is contained, it is cooled and condensed by a heat exchanger, and then separated from a gas component by a normal water absorption operation. The aqueous solution of glyoxal thus obtained contains organic acids such as formic acid and acetic acid and a small amount of formalin as impurities, but such formalin is easily removed by the stripping method by normal steam blowing, Part of the organic acid is also removed. Thereafter, a decoloring process, a process using an ion exchange resin, and the like are performed as necessary.

In the production method of the present invention, no increase in the pressure loss of the catalyst is observed for a long time even when continuously operated, but the pressure loss is about 3,000 to 5,000 mmH ₂ O (29 × 10 ³ to 49 × 10 ⁵ Pa). If the operation is continued after the occurrence of the catalyst, the yield may decrease. Therefore, it is preferable to replace the silver catalyst with this as a guideline. If the catalyst layer is composed of multiple layers, replace only the layer with the higher bulk density of the catalyst. It is also possible to continue continuous operation.

Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified, “%” indicates a weight standard.
Example 1
10 g of silver catalyst (tree-like crystal, long side: 1.4 to 2.0 mm, manufactured by NanoChem) having a bulk density of 1.6 g / cm ^{3 in} the lower layer of a stainless steel reactor having a diameter of 24 mm, and a bulk density of 1 in the intermediate layer .7g / cm ³ of a silver catalyst (tree-like crystals, long side 1.0 to 1.4 mm, manufactured by NanoChem Co.) 20g, silver catalyst bulk density 1.8 g / cm ³ in an upper layer (tree-like crystals, the length 14 g of sides having a side of 0.5 to 1.0 mm (manufactured by NanoChem) were sequentially filled (the height of the packed bed of silver catalyst was 54.6 mm).
Next, ethylene glycol 150 g (2.4 mol) / hr, water 150 g (8.3 mol) / hr and air 312 L (13.9 mol) / hr, nitrogen 618 L (27.8 mol) / hr, ethylene glycol Then, 50 ppm of triethyl phosphite in terms of phosphorus was heated with an evaporator and preheater at 140 ° C., then supplied from the top of the reactor at NSv 30,000 hr ⁻¹ and reacted at a reaction temperature of 590 ° C. (ethylene glycol (Partial pressure 5,000 Pa). One hour after the start of the reaction, the reaction gas discharged from the lower part of the reactor was immediately cooled (cooled to 500 ° C. or less in 0.02 seconds), and then the product was dissolved in water and collected. When this aqueous layer was analyzed, the conversion of ethylene glycol was 99.99% and the yield of glyoxal was 88%.
When the reaction was continued using this catalyst, the pressure loss of the system became 3,000 mmH ₂ O (29 × 10 ³ Pa) on the 180th day. The conversion rate and yield after 1 hour from the start of the reaction up to this point Was maintained.

Example 2
In Example 1, a silver catalyst having a bulk density of 1.6 g / cm ³ (tree-like crystal, long side of 1.4 to 2.0 mm, manufactured by NanoChem) was used for any of the upper layer, the intermediate layer, and the lower layer. Was carried out in the same manner as in Example 1.
Analysis of the aqueous layer collected by dissolving the gas discharged 1 hour after the start of the reaction in water revealed that the conversion of ethylene glycol was 99.96% and the yield of glyoxal was 85%. When the reaction was continued using this catalyst, the pressure loss of the system became 3,000 mmH ₂ O (29 × 10 ³ Pa) on the 140th day. The conversion and yield after 1 hour from the start of the reaction up to this point Was maintained.

Comparative Example 1
In Example 1, it carried out like Example 1 except having arrange | positioned the silver catalyst of bulk density 3.5g / cm < ³ > (spherical crystal whose particle diameter is 1 mm) to all the upper layer, the intermediate | middle layer, and the lower layer.
Analysis of an aqueous layer collected by dissolving the gas discharged 1 hour after the start of the reaction in water revealed that the conversion of ethylene glycol was 99.95% and the yield of glyoxal was 80%. When the reaction was continued using this catalyst, the pressure loss of the system reached 3,000 mmH ₂ O (29 × 10 ³ Pa) on the 10th day, and the reaction results up to this point were the conversion rate and yield 1 hour after the start of the reaction. However, the reaction was continued as it was, and on the 15th day from the start of the reaction, the pressure loss of the system became 6,000 mmH ₂ O (58 × 10 ³ Pa), and the conversion rate at this point was 92.85. %, The yield dropped to 65%.

The present invention relates to a method for producing glyoxal that can maintain a high conversion rate of ethylene glycol and can maintain a high yield of glyoxal even if it is continuously produced for a long time.

Claims (2)

A method for producing glyoxal, characterized by contacting a silver catalyst having a bulk density of 3 g / cm ³ or less when producing glyoxal by vapor phase oxidation of ethylene glycol. The method for producing glyoxal according to claim 1, wherein a silver catalyst having a bulk density of 0.5 to ³ g / cm ³ is used.