JPS6348257B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is a method for producing methyl methacrylate (hereinafter abbreviated as MMA) from methacrylonitrile (hereinafter abbreviated as MAN) with extremely low unreacted MAN of several tens of ppm at a high yield. Regarding.

If unreacted MAN remains in MMA, there is a concern that it will adversely affect the chromaticity and physical properties of the polymer, so it is desirable to reduce unreacted MAN as much as possible.

Conventionally, a method for producing an unsaturated carboxylic acid ester by hydrolyzing an unsaturated nitrile with a mineral acid and water and then esterifying it is known, but there is little discussion on the residual nitrile in the ester.
None discussed ppm levels.

Typical common methods for reducing unreacted nitriles include separation by distillation after esterification and reduction by setting conditions during amidation and esterification reactions. However, it is quite difficult to separate unreacted nitrile at a low concentration of several hundred to several thousand ppm by purification using ordinary distillation methods, and furthermore, it is difficult to separate unreacted nitrile at a low concentration of several hundred to several thousand ppm.
This becomes extremely difficult when the boiling points are close to each other, as in the case of

In addition, general methods for reducing unreacted nitrile through reaction include increasing the molar ratio of sulfuric acid and water;
Examples include increasing the reaction temperature and residence time. For example, in Japanese Patent Publication No. 52-6974,
As a method for reducing unreacted nitrile when producing acrylamide sulfate from acrylonitrile, a method is described in which sulfuric acid and water are used in excess of the stoichiometric amount within a range that does not cause a decrease in yield or an increase in by-products. The optimum molar ratio of sulfuric acid and water per mole of nitrile is 1.0 to 1.3.
However, as far as we can see in the example of producing MMA from MAN, unreacted MAN is
% remaining, and there is no discussion about the level of tens to hundreds of ppm. Furthermore, according to the studies of the present inventors, when the reaction was carried out under the conditions described in the above publication for the purpose of reducing unreacted MAN as much as possible, if the molar ratio of water per mole of supplied MAN was less than 1.10, the reaction temperature was lowered. Even if the reaction temperature is increased or the reaction time is increased, no reaction occurs even though some water remains in the reaction system.
It was found that there was a problem in that MAN was not reduced to 100 ppm or less, but rather the amidation yield was reduced.

Also, in Koka Magazine 69-6 (1966), from MAN
In the method of synthesizing MMA, sulfuric acid is added dropwise to a mixed solution of MAN and methanol to form a monoalkyl sulfate of methacrylic acid amide, and then methanol water is added to esterify it.
It is stated that unreacted nitrile can be reduced compared to a method in which MAN is added dropwise to form methacrylamide sulfate and then methanol is added for esterification, but according to specific examples, even in the case of the former method, unreacted nitrile can be reduced.
About 2% of MAN remains based on the supplied MAN, and it has not been possible to reduce it to a level of several tens to hundreds of ppm.

In this way, the unreacted material can be removed without reducing the yield.
The industrial technology to reduce MAN as much as possible is still incomplete.

The inventors of the present invention have conducted extensive research on the method for producing MMA using MAN as a raw material under the above circumstances, and have found that there is a kind of equilibrium phenomenon when producing methacrylamide sulfate by reacting MAN with sulfuric acid and water. They discovered that water plays an extremely important role in reducing unreacted MAN to a level of several tens of ppm, leading to the present invention. More specifically, when MAN is reacted with sulfuric acid and water, the maximum amidation yield (=actual double bond amount in the amide solution/theoretical double bond amount in the supplied MAN) increases as the reaction progresses. There is a point in time when it can be obtained, but at this point unreacted MAN still remains in the amount of several hundred to several thousand ppm and does not meet quality requirements. When continuing the reaction and reducing unreacted MAN, it is necessary to keep in mind the following points discovered by the present inventors. First, the minimum concentration of unreacted MAN is determined by the water concentration in the reaction product (see Figure 1), and second, when the reaction temperature is low, compared to when the reaction temperature is high, unresponsive
There is a tendency for the minimum concentration of MAN to decrease (see Figure 1). Thirdly, if sulfuric acid is present in equimolar or more relative to MAN, it will affect the rate of reduction of unreacted MAN, but it will reduce the amount of unreacted MAN. These are various points that are not related to the minimum concentration (see Figure 2).
Furthermore, in order to maintain the amidation yield, care must be taken not to raise the reaction temperature and not to increase the molar ratio of sulfuric acid to MAN.

The present inventors interpret the above phenomenon to be due to an equilibrium phenomenon occurring between MAN, methacrylamide, and methacrylic acid. That is, when MAN is reacted with sulfuric acid and water, methacrylamide sulfate is produced, but when water is in excess of the theoretical amount, methacrylic acid is produced through a sequential reaction.
In this case, the rate at which methacrylamide sulfate is generated from MAN, sulfuric acid, and water is faster than the rate at which methacrylic acid is generated from methacrylamide sulfate and water, so the reaction that generates methacrylamide sulfate from MAN occurs first. It is thought that the process will proceed autonomously, reaching a roughly equilibrium state between MAN and methacrylamide sulfate, followed by an equilibrium state between methacrylamide sulfate and methacrylic acid, and at this point an equilibrium between the three will be reached. It will be done. Considering this equilibrium, it is easy to understand that in the exothermic reaction of producing methacrylamide from MAN, when the reaction temperature is high, the level of unreacted MAN increases.

As mentioned above, water plays an extremely important role in reducing unreacted MAN through reaction, but if this water is present in an amount greater than the required amount, the rate of reduction of unreacted MAN decreases, leading to esterification. In this case, the by-product rate of methacrylic acid increases, and methacrylic acid
Perhaps because it has a higher boiling point and is easier to polymerize than MMA, MMA
A decrease in the total distillation yield of methacrylic acid and methacrylic acid occurs.

Therefore, the molar ratio of remaining water in the process of reducing unreacted MAN is 0.03 to 1 mole of supplied MAN.
A range of 0.3 moles is suitable. The method of setting the water molar ratio within the above range is to use the amidation process and unreacted
Either a method of dividing the amount into the MAN reduction step or a method of supplying the entire amount to the amidation step is possible.

Further, the reaction temperature in the step of reducing unreacted MAN is preferably 90 to 120° C. for two reasons: to suppress a decrease in the amidation yield and to lower the level of unreacted MAN. Further, from an industrial standpoint, it is preferable to use a tubular reactor in this step for reasons of reaction engineering. By esterifying and purifying the reaction product in which unreacted MAN has been reduced to an extremely low level in this manner by a conventional method, high-quality MMA can be obtained in good yield.

Firstly, the present invention has the advantage that, in contrast to the conventional method, which required harsh reaction conditions to reduce residual nitrile,
It is now possible to set mild conditions, eliminating unreacted products with almost no decrease in yield or increase in by-products.
MAN can be reduced. Second, it is now possible to select a relatively low sulfuric acid molar ratio compared to conventional methods.
It also contributes to reducing the amount of sulfuric acid used and the amount of by-product ammonium bisulfate. Thirdly, it is extremely simple and economical as it does not require special additives or processing agents to reduce unreacted MAN. Fourth, compared to a method in which unreacted MAN is separated by distillation in the purification process after esterification, the equipment cost is low and the amount of steam is small, making it extremely economical. In this manner, the present invention provides a process that is excellent in terms of both quality and economy.

Next, the present invention will be explained in detail by examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 7.0 ml/each of MAN and 84.5% sulfuric acid aqueous solution
min, 6.0ml/min (MAN/H ₂ SO ₄ /H ₂ O=1/
1.1/1.1) to the first tank reactor. The first tank reactor has one flask equipped with a stirrer and a condenser, and has a structure in which the mixed liquid can be continuously extracted through a measuring pipe. Adjust the oil bath temperature to bring the reaction temperature to 110℃.
Keep at ℃ and incubate for 40 minutes. The effluent from the first tank reactor is continuously supplied to the second tank reactor due to the altitude difference. The second tank reactor has the same structure as the first tank reactor, and the effluent from the first tank reactor is reacted at 120°C for 40 minutes. Next, the liquid discharged from the second tank reactor is introduced into a capillary reactor having an inner diameter of 15 mm and a length of 1.0 m due to the altitude difference, and the reactor is kept at an internal temperature of 120° C. using an oil bath and reacted for 15 minutes. Analysis of the liquid extracted from the capillary reactor revealed that the concentration of unreacted MAN was 510 ppm (molar ratio based on 1 mole of supplied MAN. From now on, the concentration of unreacted nitrile in amide is expressed in the same way), and the remaining water was 510 ppm. supply
0.05 mol per 1 mol of MAN, and the amidation yield is
It was 98.5%. Next, the liquid from the capillary reactor in the previous step is continuously introduced into a mixing tank with a residence time of 1 minute, and mixed with water supplied at a rate of 0.15 ml/min. Type reactor led to 110
After reacting at ℃ for 30 minutes, the reactor outlet liquid was analyzed and found that the unreacted MAN was 36 ppm, and the remaining water was in the supply MAN1.
0.06 mol/mol, the amidation yield was 98.2%.

Next, esterification is carried out in an esterification apparatus in which five reactors are connected in series in an overflow format. Each reactor is equipped with a stirrer and steam distillation piping, and the liquid capacity of the first to third reactors is 1000ml each.
The liquid capacity of the fourth and fifth tanks is 500 ml each. The outlet liquid from the capillary reactor in the previous step and the 61.4% methanol aqueous solution are supplied to the first esterification tank at a rate of 8.3 ml/min, and are sequentially passed through the second tank to the fifth tank to perform esterification. The reaction conditions for each tank are 90°C for the first tank, 110°C for the second tank, 120°C for the third tank, 130°C for the fourth tank, and 140°C for the fifth tank. Hot water is supplied to each of the five tanks at a rate of 1.5 g/min.

MMA, methacrylic acid, and unreacted liquid in the liquid obtained by taking the evaporated components from each tank out of the reaction system and condensing them.
As a result of analyzing MAN, supply MAN standard MMA
The yield is 94.2% and the methacrylic acid yield is 3.1%
It was hot. The weight ratio of unreacted MAN to the total weight of MMA and methacrylic acid was 29 ppm.

Example 2 The reaction product obtained by carrying out the reaction under the same conditions as in the first step of Example 1 was mixed with water supplied at a rate of 0.45 ml/min, and then introduced into a capillary reactor.
Incubate at 110°C for 120 minutes. Analysis of the resulting reaction product revealed that unreacted MAN was 16 ppm, residual water was 0.22 mol per mol of MAN supplied, and the amidation yield was
It was 97.5%. Subsequently, esterification was carried out under the same conditions as in Example 1, and the resulting distillate was analyzed.
The MMA yield based on the supplied MAN was 91.1%, and the methacrylic acid yield was 5.2%. Also, the unreacted MAN relative to the total weight of MMA and methacrylic acid
The weight ratio of was 14 ppm.

Example 3 The reaction product obtained by carrying out the reaction under the same conditions as in the first step of Example 1 was directly introduced into a capillary reactor without adding water and reacted at 110° C. for 50 minutes.
Analysis of the resulting reaction product revealed that unreacted MAN
was 75 ppm, the residual water was 0.03 mol per 1 mol of MAN supplied, and the amidation yield was 98.0%. Subsequently, esterification was carried out under the same conditions as in Example 1, and the resulting distillate was analyzed, and the yield of MMA based on the supplied MAN was 94.5%, and the yield of methacrylic acid was 2.6%. Furthermore, the weight ratio of unreacted MAN to the total weight of MMA and methacrylic acid was 62 ppm.

Example 4 7.0 ml/each of MAN and 83.3% sulfuric acid aqueous solution
min, 6.1ml/min (MAN/H ₂ SO ₄ /H ₂ O=1/
1.1/1.2) to the first tank reactor at a rate of 110
Incubate for 40 min at °C. Then in the second tank reactor 120
℃ for 40 minutes, and in a capillary reactor at 120℃ for 15 minutes. Analysis of the outlet liquid from this capillary reactor revealed that unreacted MAN was 405 ppm, and residual water was supplied.
0.09 mol per 1 mol of MAN, amidation yield 98.4%
It was hot. Next, the reactor outlet liquid from the previous step was directly introduced into a capillary reactor without being added to water, and heated at 110℃.
After reacting for 30 minutes, the resulting reaction product was analyzed and found that unreacted MAN was 38 ppm, and the remaining water was in the supplied MAN1.
0.05 mol/mol, the amidation yield was 98.1%. Subsequently, esterification was carried out under the same conditions as in Example 1, and the resulting distillate was analyzed, and the yield of MMA based on the supplied MAN was 93.9%, and the yield of methacrylic acid was 3.3%. Also, the weight ratio of unreacted MAN to the total weight of MMA and methacrylic acid is
It was 33ppm.

Comparative Example 1 7.0ml/each of MAN and 85.0% sulfuric acid aqueous solution
min, 5.95ml/min (MAN/H ₂ SO ₄ /H ₂ O=1/
1.1/1.06) to the first tank reactor at a rate of 110℃.
Incubate for 40 minutes. This was followed by 40 minutes at 120°C in the second tank reactor and 120°C in the capillary reactor.
Incubate for 15 minutes. At the outlet of the capillary reactor, unreacted MAN was 1200 ppm, and the amidation yield was 97.8
It was %. The residual water content was 0.01 mol per 1 mol of MAN supplied. Next, the reaction product from the previous step was introduced into a capillary reactor and reacted at 110°C for 30 minutes, but the unreacted MAN was at a high concentration of 790 ppm.
The amidation yield was 97.2%. Furthermore, by adding a capillary reactor, the temperature at 110℃ for 60 minutes and 90 minutes
When the reaction was carried out for 60 minutes, the amount of unreacted MAN was 805 ppm, and the amidation yield was
96.5%, no reaction when reacted for 90 minutes
MAN was 830 ppm and the amidation yield was 95.8%, which was a slight increase in unreacted MAN and a decrease in the amidation yield compared to when the reaction was carried out for 30 minutes.

Comparative Example 2 The outlet liquid from the first step of Comparative Example 1 was introduced into a capillary reactor and reacted at 130°C for 30 minutes, but no reaction occurred.
MAN was 1160 ppm, hardly reduced, and the amidation yield decreased to 96.3%. Furthermore, even when the reaction was carried out at 130°C for 60 minutes, unreacted MAN remained at 1240 ppm, and the amidation yield significantly decreased to 94.9%.

Comparative Example 3 The reaction product obtained by carrying out the reaction under the same conditions as the first step of Example 1 was mixed with water supplied at a rate of 0.9 ml/min, and then introduced into a capillary reactor.
Incubate at 110°C for 180 minutes. Analysis of the resulting reaction product revealed that unreacted MAN was 9 ppm, residual water was 0.35 mol per mol of supplied MAN, and amidation yield was 97.2.
It was %. Subsequently, esterification was carried out under the same conditions as in Example 1, and the resulting distillate was analyzed.
The MMA yield based on MAN was 86.8%, and the methacrylic acid yield was 7.5%.

[Brief explanation of the drawing]

FIG. 1 is a correlation graph between residual water content and unreacted MAN, and FIG. 2 is a correlation graph between reaction time and unreacted MAN.

[Claims]

1 General formula () [Wherein, X is the general formula (), (), (), ()
,
() or expression ()

【formula】

【formula】