JPS6148817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing glyoxylic acid by an oxidation method of glyoxal.

The electrolytic reduction method of oxalic acid has been known for a long time as a method for producing glyoxylic acid. As for the rate of change, there are many problems as an industrial production method, such as a decrease in selectivity and a decrease in current efficiency.

The most well-known method for producing glyoxylic acid by oxidizing glyoxal is the nitric acid oxidation method. In this reaction, selectivity is good as long as the conversion rate of glyoxal is low, but when the conversion rate is increased, oxalic acid is produced by sequential reactions, and the selectivity of glyoxylic acid obtained is significantly reduced. For example, when the conversion rate of glyoxal is increased from 70% to 90%, the glyoxylic acid selectivity decreases sharply from 90% to 70%.

Furthermore, in the nitric acid oxidation method, it takes a considerable amount of time for the added nitric acid to complete the reaction, and the reaction proceeds with nitric acid accumulated in the system. For this reason, the controllability of the reaction by adjusting the nitric acid charging rate is poor. Moreover, if nitric acid oxidation is interrupted midway, the formation after restarting, especially the selectivity, will be extremely poor. Therefore, it is not possible to carry out the first stage reaction at a low reaction rate without fear of decreasing the selectivity and then fine-tune it to the desired rate of change by adding nitric acid, or restart the reaction due to temporary inconvenience. I can't stand it.

Such inconveniences are observed not only in the reaction-interrupting solution but also in general nitric acid oxidation of glyoxal aqueous solutions containing a significant amount of glyoxylic acid.

Furthermore, a method for producing glyoxylic acid by electrolytic oxidation of glyoxal is also known (Japanese Patent Laid-Open No. 55-79884).
issue). This method maintains a selectivity of about 80% even when the conversion rate is increased to about 95%, and although it solves to some extent the drawback of the nitric acid oxidation method, which cannot obtain high selectivity at high conversion rates, it does It is difficult to react in
It also requires large fixed equipment.

Considering these problems of the conventional method, the present inventor sought an oxidation method that can produce glyoxylic acid with high selectivity even when the conversion rate of glyoxal is high, that allows easy control of the reaction, and that does not require large fixed equipment. We conducted a thorough study. As a result, it was found that by selecting chlorine as the oxidizing agent among the many oxidizing agents known in the world, the above object could be achieved very satisfactorily, and the present invention was completed. That is, the present invention is a method for producing glyoxylic acid characterized by reacting an aqueous glyoxal solution with chlorine, and the reaction formula is as follows.

The oxidizing agent used in the present invention is chlorine, which is produced in large quantities as a co-product of electrolytic soda and is commercially available, so it can be obtained very easily. For the purposes of the present invention, elemental chlorine is an oxidizing agent that is very specifically effective, and by oxidizing glyoxal with chlorine, glyoxylic acid can be obtained with a selectivity of 80% or more even at a high conversion rate of 90% or more. .

Glyoxal is usually obtained in a hydrated form as an aqueous solution, and can also be used in the present invention in the form of an aqueous solution, usually 5 to 40%.

The method of the present invention can be carried out by blowing chlorine into an aqueous glyoxal solution, but a bubble column,
It is also possible to use a packed column or other known gas-liquid reaction methods, and both batch and continuous methods are possible. The reaction in the present invention can be controlled by adjusting the chlorine supply rate, keeping the reaction temperature constant,
Fine adjustment of the amount of oxidizing agent to achieve a desired rate of change is much easier than in the case of nitric acid oxidation. The reaction is exothermic and the reaction temperature is usually maintained by appropriate heat removal means such as water cooling. Although the liquid temperature is not particularly limited, it is usually 0 to 100°C, and the reaction proceeds satisfactorily even below room temperature. However, in normal pressure and low temperature reactions, the absorption rate of chlorine is relatively low, and it takes a long time to complete the reaction. One way to shorten the reaction time is to select the reaction temperature. For example, it is possible to carry out the reaction at a temperature of 80°C, but as the reaction rate becomes high, the selectivity tends to decrease. A more preferred reaction temperature is such a moderate temperature.

A more effective means for shortening the reaction time is a pressurized reaction, and by reacting an aqueous glyoxal solution and chlorine under pressure, the reaction rate can be increased without reducing the reaction product. for example,
Example 5, which will be described later, was a normal pressure reaction, and it took 58 hours to reach a change rate of glyoxal of 91.4%, but in Example 6, which was slightly pressurized, the reaction took 36 hours and a pressure of 2 kg/cm ² gauge. In Example 7, 93 each in 14 hours.
% or more was obtained, and the selectivity to glyoxylic acid was also high.

The reaction rate can be further increased by increasing the reaction pressure, for example, 5 Kg/cm ² G or 10
Although it can be carried out at Kg/cm ² , it requires high-pressure equipment and increases the heat removal load. Even at 2 Kg/cm ² G, the time can be shortened to about 10 hours (Example 9), so a very large pressure is not required.

In order to shorten the reaction time, it is also effective to have a small amount of bromine present as a catalyst. Bromine may be added as a simple substance, but may also be added as a bromide such as KBr or hydrobromic acid. Examples of the addition mode of bromine include bromine chloride or a compound capable of producing bromine chloride under the reaction conditions of chlorine oxidation.

The amount of bromine catalyst used is relative to glyoxal.
0.1-10 mol%, preferably about 0.5-5 mol%. For example, when adding 5 mol % of bromine and applying a pressure of 2 kg/cm ² G, the conversion rate of glyoxal reaches nearly 99% in 6 hours at 30°C. Since it is not necessary to increase the glyoxal conversion rate to this extent in practice, it is possible to further reduce the reaction time, the amount of catalyst used, and the reaction pressure.

Furthermore, when the concentration of hydrochloric acid in the reaction solution is 13 to 15% or more and the reaction rate is suddenly slowed down, it is particularly advantageous to shorten the reaction time by adding bromine. For example, in Example 4, the rate of change in glyoxal was approximately 54% after 24 hours of reaction at normal pressure;
However, in Example 15, which used a combination of pressurization of 2 kg/cm ² and 5 mol% bromine, the concentration was higher than that of Example 4.
Despite using 19% glyoxal, a change rate of 82.2% was obtained in 9 hours. When bromine is used in this way, the chloride concentration in the reaction solution is 20
%, the reaction can proceed.

As is clear from the reaction formula shown above, in the method of the present invention, hydrogen chloride is produced as a by-product, and since it is in an aqueous solution, it coexists in the reaction system as hydrochloric acid, and its concentration increases as the reaction progresses. The reaction rate is also related to this hydrochloric acid concentration; for example, in a reaction at 30°C, the reaction rate becomes rapidly slow when the hydrochloric acid concentration in the reaction system exceeds 13 to 15% by weight. Therefore, if the raw material concentration is adjusted so that the hydrochloric acid concentration achieved by the hydrochloric acid by-produced in the reaction is 13 to 15% or less, the reaction can be carried out at normal pressure or even under slight pressure.
The rate of change of glyoxal can be determined with a reaction time of about 1 hour.
It can be increased to 90-95% (Example 1,
8). If the reaction pressure is further increased to 2.0 Kg/cm ² G, the reaction time can be shortened to about 9 to 10 hours (Example 9). At the same time, we discovered an unexpected fact that the reaction selectivity improved by lowering the concentration of glyoxal as a raw material and suppressing the concentration of hydrochloric acid in the reaction system (Example 8,
9).

In order to keep the hydrochloric acid concentration in the reaction solution below 15%, it may be possible to remove hydrochloric acid by other means such as extraction, electrodialysis, ion exchange resin treatment, evaporation, etc., but it depends on the glyoxal concentration of the raw material. It is the simplest and has the highest practical value.

The hydrochloric acid concentration also affects the yield relative to chlorine in the method of the present invention. That is, the present inventor noticed that the yield relative to chlorine was sometimes abnormally low at the beginning of the reaction, and in order to prevent this phenomenon, the inventor conducted a detailed study on the mechanism of the oxidation reaction.As a result, when the concentration of hydrochloric acid is low, the formula Cl It was found that hypochlorous acid produced by ₂ + H ₂ OHOCl + HCl caused a side oxidation reaction of oxalic acid or formic acid mixed into the raw material glyoxal, resulting in poor chlorine yield. They have also discovered that this side reaction can be suppressed by ensuring the concentration of hydrochloric acid in the glyoxal aqueous solution used for the reaction. In the latter stages of the reaction, there is no problem because hydrochloric acid produced by the reaction that produces glyoxylic acid is present, but in the end, the initial concentration of hydrochloric acid must be maintained by adding a small amount of hydrochloric acid to the glyoxal aqueous solution supplied at the beginning of the reaction. Bye. The concentration of hydrochloric acid added is preferably 1 to 2%. If the concentration of hydrochloric acid is too high, the reaction rate will be adversely affected as mentioned above, so it is best to maintain the concentration of hydrochloric acid in the glyoxal aqueous solution in the range of 1 to 15% when reacting with chlorine. When hydrochloric acid is added as described in Example 10, the yield of glyoxal based on absorbed chlorine is improved, and wasteful hydrochloric acid by-products due to side reactions are suppressed. As a result, when comparing at the same level, such as a glyoxal conversion rate of about 95%, the achieved hydrochloric acid concentration was only 12.8%, which is the same as when starting from zero hydrochloric acid concentration, and the addition of 1 to 2% hydrochloric acid has a lower reaction rate. There are no negative effects from

In addition, when glyoxal containing formic acid or oxalic acid as an impurity is used as a raw material, when chlorine oxidation is started from zero concentration of hydrochloric acid, the exhaust gas in the early stage of the reaction contains an extremely large amount of carbon dioxide, an inert component, at about 80% by weight. Therefore, the amount of exhaust gas removed to maintain the reaction pressure and the accompanying loss of chlorine were large, but when the reaction was carried out with an initial concentration of hydrochloric acid of 1%, the carbon dioxide gas in the initial reaction gas was 30vol%. The loss of chlorine is also very small.

In this way, it is sufficient to add hydrochloric acid to an initial concentration of about 1%; adding more hydrochloric acid than necessary will cause the concentration of hydrochloric acid to become too high when the reaction reaches a high rate of change, slowing down the reaction rate. Become. ) Reaction formation deteriorates. ) This is not preferable because hydrochloric acid is wasted.

Glyoxylic acid is used, for example, in reactions with phenols, but glyoxylic acid obtained by nitric acid oxidation requires removal of nitric acid and separation and purification because the nitric acid content in the reaction mixture is harmful.

The glyoxylic acid obtained in the present invention is obtained as an aqueous solution mixed with hydrochloric acid as a by-product, but it can be used as is in the next step as long as there is no problem.

Of course, depending on the application, it may be used after being subjected to dehydrochloric acid treatment by methods such as ion exchange resin treatment, electrodialysis, and amine extraction.

The concentration of glyoxylic acid obtained depends primarily on the concentration of the glyoxal aqueous solution, but in the case of nitric acid oxidation, it is further diluted by the water accompanying the nitric acid. Chlorine is advantageous in that it does not involve water. In order to obtain a high-concentration glyoxylic acid aqueous solution which is difficult to obtain directly as a reaction solution, the reaction solution obtained in the present invention may be concentrated using known techniques as necessary.

The present invention will be explained below with reference to Examples. % in example
are based on weight unless otherwise specified.

Example 1 Glyoxal 5.03% and glyoxylic acid 0.48
15-18 to 1850.2g of glyoxal aqueous solution containing %
Glyoxylic acid bubbled with chlorine gas for 19 hours at ℃ 5.08
%, 1984.3 g of an aqueous solution containing 0.34% glyoxal and 7.24% hydrochloric acid was obtained.

The conversion rate of glyoxal was 92.8%, and the selectivity of glyoxylic acid was 83.4%.

Example 2 Glyoxal 14.00% and glyoxylic acid
15 in 829.3g of glyoxal aqueous solution containing 1.15%
Glyoxylic acid bubbled with chlorine gas for 13 hours at ~20℃
912.7 g of an aqueous solution containing 9.29% glyoxal, 5.43% glyoxal and 10.57% hydrochloric acid was obtained. The conversion rate of glyoxal was 57.5%, and the selectivity of glyoxyl was 88.6%.

Example 3 Glyoxal 30.41% and glyoxylic acid
15 to 1850.0g of glyoxal aqueous solution containing 2.68%
glyoxylic acid by bubbling chlorine gas for 46 hours at °C.
14.68%, glyoxal 16.15% and hydrochloric acid 14.19%
2114.3 g of a reaction solution containing . By this time, 92.4% glyoxylic acid was obtained based on 3.81 mol of glyoxal converted.

Example 4 Glyoxal 14.25% and glyoxylic acid
Chlorine gas was blown into glyoxal aqueous solution 2405.19 containing 0.40% at 80°C for 24 hours to dissolve glyoxylic acid.
8.02%, glyoxal 6.07%, and hydrochloric acid 9.63%
2600.9 g of a reaction solution containing . At this time, the conversion rate of glyoxal was 53.9%, and the selectivity of glyoxylic acid was 84.6%.

If the chlorine injection was restarted, an even higher rate of change could be obtained without any effect from the interruption. That is, 32, 40, and 48 hours after the beginning, the glyoxal concentration decreased to 4.64%, 2.43%, and 0.47%, respectively, and the rate of change was
Reached 95%. During this period, the concentration of glyoxylic acid was 9.29%, 10.04%, and 10.51%, respectively, and hydrochloric acid was also
It increased by 11.6%, 12.8%, and 16.0%.

Example 5 Glyoxal 13.01% and glyoxylic acid
Chlorine was blown into 2230.6 g of glyoxal aqueous solution containing 5.18% at 30°C for 58 hours at normal pressure.
0.96%, glyoxylic acid 14.02% and hydrochloric acid 14.02%
2596.4 g of a reaction solution containing . At this time, the glyoxal conversion rate was 91.4%, and the glyoxylic acid selectivity was
The yield was 73.4%, and the yield based on the glyoxyl compound (total number of moles of glyoxal and glyoxylic acid in the raw materials) was 74.9%.

Example 6 Glyoxal 11.88% and glyoxylic acid
0.2Kg/ ^cm2 in glyoxal aqueous solution containing 6.12%
Chlorine was blown into the reactor at 30° C. under the pressure of G for 36 hours to obtain 2,854.8 g of a reaction solution containing 0.70% glyoxal, 14.13% glyoxylic acid, and 16.20% hydrochloric acid. At this time, the glyoxal conversion rate was 93.1%, the glyoxylic acid selectivity was 73.7%, and the yield relative to the glyoxyl compound was 77.6%.

Example 7 Glyoxal 12.12%, glyoxylic acid 2.51%
% glyoxal aqueous solution containing ^0.69 % glyoxal, 12.48% glyoxylic acid and hydrochloric acid.
993.4 g of a reaction solution containing 14.46% was obtained. At this time, the glyoxal conversion rate was 93.5%, the glyoxylic acid selectivity was 81.4%, and the yield relative to the glyoxyl compound was 79.5%.

Example 8 Glyoxal 9.11% and glyoxylic acid 3.60
0.2 to 2234.1g of glyoxal aqueous solution containing %
Blow in chlorine for 21 hours at 30℃ under a pressure of Kg/cm ² G.
Glyoxal 0.56%, glyoxylic acid 11.29%
2,522.1 g of a reaction solution containing 12.68% of hydrochloric acid was obtained.
At this time, the glyoxal conversion rate was 93.1%, the glyoxylic acid selectivity was 84.5%, and the yield relative to the glyoxylic acid compound was 83.7%.

Example 9 Glyoxal 9.32% and glyoxylic acid 3.46%
2.0Kg/868.9g of glyoxal aqueous solution containing %
Chlorine was blown into the mixture at 30° C. under a pressure of cm ² G for 10 hours to obtain 975.6 g of a reaction solution containing 0.65% glyoxal, 11.45% glyoxylic acid, and 12.47% hydrochloric acid. At this time, the glyoxal conversion rate was 92.2%, the glyoxylic acid selectivity was 85.8%, and the yield relative to the glyoxyl compound was 83.3%.

Example 10 Glyoxal 9.16%, glyoxylic acid 1.93%
and glyoxal aqueous solution containing 1.00% hydrochloric acid
Add 868.0g of chlorine to 868.0g at 30℃ under a pressure of 2.0Kg/cm ² G.
Time blowing, 969.4 g of reaction solution containing 0.44% glyoxal, 10.36% glyoxylic acid and 12.78% hydrochloric acid.
I got it. The glyoxal change rate at this time was 94.7
%, glyoxylic acid selectivity was 87.1%, and yield to glyoxylic acid compound was 85.0%. The rate of change up to 6 hours was 90.9%, and the selection rate was 89.2%. The yield of glyoxylic acid based on the amount of absorbed chlorine determined from the increment of hydrochloric acid before and after 8 hours of reaction is 82.1
It was %.

For comparison, when the initial concentration of hydrochloric acid was 0% and the reaction was carried out with chlorine at 30°C and under a pressure of 2.0 kg/cm ² G, the increase curve of hydrochloric acid concentration against reaction time was similar with a delay of about 2 hours. After 10 hours, both the rate of change in glyoxal and the concentration of hydrochloric acid reached almost the same values as above. The yield based on chlorine was 80.0%, indicating that the low concentration of hydrochloric acid had an adverse effect at the beginning of the reaction.

When the initial concentration of hydrochloric acid was 1.5% and 2%, the yields based on chlorine were 85.4% and 82.4%, respectively.

Example 11 Glyoxal aqueous solution (concentration 9.20) purified by electrodialysis and added with hydrochloric acid to a concentration of 1.5%
%, glyoxylic acid 0.20%) 819.8g to 2.0Kg/cm ²
Blow chlorine under the pressure of G for 9 hours at 30℃, glyoxylic acid 9.21%, glyoxal 0.28%, hydrochloric acid
916.6 g of a reaction solution containing 12.86% was obtained. At this time, the glyoxal conversion rate was 96.6% and the glyoxylic acid selectivity was 89.0%.

Example 12 To 748.6 g of the same glyoxal aqueous solution used in Example 11, 12.3 g of sodium bromide (5 mol% amount as bromine) was added, and 6 chlorine was added at 30°C under a pressure of 2.0 Kg/cm ² G. time infusion, glyoxylic acid
863.6 g of a reaction solution containing 9.37% glyoxal, 0.10% glyoxal and 13.66% hydrochloric acid was obtained. The glyoxal conversion rate was 98.7%, and the glyoxylic acid selectivity was 91.6%.

Example 13 Glyoxal 9.04% (glyoxylic acid 0.25
%, containing 1.51% hydrochloric acid) 10.4 g of bromine in 834.6 g of aqueous solution
2 kg/cm ² G at 30° C. for 6 hours to obtain 948.6 g of glyoxylic acid 9.27% (glyoxal 0.10%, hydrochloric acid 12.9%) aqueous solution. Similar to Example 12 using sodium bromide, both the change rate and selectivity were improved compared to Example 11.

Example 14 The reaction was carried out for 8 hours in the same manner as in Example 13 except that the amount of bromine added was reduced to 1.0 g, and glyoxylic acid was 9.24%.
(glyoxal 0.23%, hydrochloric acid 12.62%) aqueous solution
934.6g was obtained. With a change rate of 97.2% and a selection rate of 90.1%,
Although not as good as Examples 12 and 13, the results were better than Example 11, which did not contain any bromine.

Example 15 Glyoxal 19.9% (glyoxylic acid 0.58
22.4 g of bromine was added to 816.6 g of an aqueous solution (%, 1.51% hydrochloric acid), and chlorine was blown in at 2 Kg/cm ² G, 30°C for 9 hours, resulting in 1019.9 g of an aqueous solution of glyoxylic acid 16.68% (glyoxal 2.84%, hydrochloric acid 1.91%). I got it.
In this example, the hydrochloric acid limit was close to 20% at the end of the reaction, but a conversion rate of 82.2% was obtained in 9 hours, and the selectivity was extremely high at 97.1%.

Reference example (nitric acid oxidation method) Glyoxal 17.84% and glyoxylic acid
1500.0g of glyoxal aqueous solution containing 10.50%
742.4g of 45% nitric acid was added dropwise at 40℃ over 4 hours.
Further aging at 40℃ for 6 hours yields glyoxylic acid 17.46
% and reaction solution containing 1.10% glyoxal 2032.1
I got g. The conversion rate of glyoxal was 91.6% and the selectivity of glyoxylic acid was 63.1%.

Claims (1)

[Claims] 1. A method for producing glyoxylic acid, which comprises reacting an aqueous glyoxal solution with chlorine. 2. The production method according to claim 1, wherein the reaction is carried out under pressure. 3 The reaction occurs when the concentration of hydrochloric acid in the glyoxal aqueous solution is 1
The manufacturing method according to claim 1, which is carried out in a state of ~15%. 4. A method for producing glyoxylic acid, which comprises reacting an aqueous glyoxal solution with chlorine in the presence of bromine.