JP2003104939A - Method for producing methyl methacrylate - Google Patents

Abstract

(57) [Problem] To provide a method for industrially and efficiently producing methyl methacrylate substantially free of diketones and nitrogen compounds. SOLUTION: In the method for producing methyl methacrylate, crude methyl methacrylate containing diketones;
The aliphatic amine having a higher boiling point than methyl methacrylate is reacted in the reaction operation section, and the obtained reaction solution is distilled in the distillation operation section, and a substance having a boiling point lower than that of methyl methacrylate is first distilled off from the top of the column. The bottom liquid is distilled in the next distillation column to obtain methyl methacrylate substantially free of diketones and nitrogen compounds as a distillate, and a part of the bottom liquid withdrawn is sent to the reaction operation section. A method for producing methyl methacrylate, which is circulated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a process for producing methyl methacrylate, and more particularly to a process for producing methyl methacrylate substantially free of diketones and nitrogen compounds.

[0002]

2. Description of the Related Art Methyl methacrylate has been used as a useful raw material for plastics, and is a raw material monomer for optical materials such as optical fibers and light guide plates and cast plates that utilize transparency, which is the most important feature. The quality requirements for methyl methacrylate are becoming more stringent. In order to ensure transparency, it is considered preferable to remove the diketones, which are color-causing substances, in the raw material methyl methacrylate.

On the other hand, the method for producing methyl methacrylate has also advanced. Starting from the old ACH method with ammonium bisulfate as a by-product, a method of oxidizing isobutylene and / or t-butyl alcohol to methacrolein, reoxidizing this to methacrylic acid, and then reacting with methanol was further advanced. A method for producing methyl methacrylate at once using methacrolein, methanol, and oxygen has been industrialized. In either method, since diketones are contained in methyl methacrylate due to side reactions during the production of methyl methacrylate, it is important to remove the diketones.

As a method for removing diacetyl, which is one of the diketones contained in methyl methacrylate, conventionally, a method of treating it with a sulfite salt such as sodium sulfite to remove it as an organic sulfonate (JP-A-7-278053). Gazette), a method of treating with a non-aromatic 1,2-diamine (JP-A-8-169862), three or more primary or secondary groups.
Method of reacting with an aliphatic compound having a high-grade amino group in the molecule and then removing the reaction product (JP-A-2000-25
6265), and a method of bringing a cross-linking adsorption resin having porosity into contact with (meth) acrylic acid ester (JP 2001-122826 A) and the like are proposed.

However, a method of treating with an inorganic salt such as sodium sulfite (Japanese Patent Laid-Open No. 7-278053)
Is, since the unreacted sulfite remaining in the methyl methacrylate causes stains on the tray and reboiler of the distillation tower when the methyl methacrylate is distilled off after the treatment.
Not preferable.

The method of treating with a non-aromatic 1,2-diamine (JP-A-8-169862) requires an acid such as methacrylic acid as a catalyst for the reaction with diacetyl. Furthermore, when an amine compound such as ethylenediamine is contained in methylmethacrylate, the amine compound itself has a drawback that causes coloring of the methylmethacrylate polymer, and thus must be removed. However, the boiling point of ethylenediamine is 117 ° C. Boiling point of methyl methacrylate 100 ℃
Therefore, a large number of distillation stages and a large amount of energy are required to separate methyl methacrylate and ethylenediamine.

Further, in a method (Japanese Patent Laid-Open No. 2000-256265) in which a reaction product is removed after reacting with an aliphatic compound having three or more primary or secondary amino groups in the molecule, It is advantageous for the separation of methyl methacrylate and high boiling aliphatic compounds having an amino group in the molecule, but a large amount of a drug is required to produce methyl methacrylate of less than 0.5 ppm diacetyl, and the addition of a drug is required. If the amount is reduced, a long reaction time is required. Furthermore,
By this method, the diacetyl concentration of 0.
It was difficult to obtain methyl methacrylate with less than 1 ppm and less than 0.2 ppm of nitrogen compounds.

On the other hand, the method of treating by contacting a cross-linking type adsorbing resin (Japanese Patent Laid-Open No. 2001-122826) requires a large amount of adsorbing resin in order to remove target impurities, which is industrially and economically economical. Was not the preferred method.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for industrially and efficiently producing methyl methacrylate which is substantially free of diketones and nitrogen compounds.

[0010]

Means for Solving the Problems In order to solve such problems and achieve the object industrially and efficiently, the present inventors have conducted various studies and found that diketones contained in crude methyl methacrylate , An aliphatic amine having a boiling point higher than that of methyl methacrylate, for example, 2-aminoethanol, is reacted in the reaction part, and the reaction solution obtained by the reaction is distilled to obtain a product having a boiling point lower than that of methyl methacrylate. Distilled off,
The bottom liquid was supplied to the next distillation column, methyl methacrylate was obtained from the top of the column, and a part of the bottom extract liquid was circulated to the reaction section. It was found that the diacetyl concentration was less than 0.1 ppm and the total nitrogen amount was less than 0.2 ppm, and the present invention was completed.

That is, the present invention comprises the following (1) to (6). (1) In the method for producing methyl methacrylate, crude methyl methacrylate containing a diketone and an aliphatic amine having a boiling point higher than that of methyl methacrylate are reacted in a reaction operation section, and the obtained reaction solution is distilled. Distillation in the operating section, first distilling a substance having a lower boiling point than methyl methacrylate from the top of the column, the bottom liquid is distilled in the next distillation column,
A process for producing methyl methacrylate, characterized in that methyl methacrylate, which is substantially free of diketones and nitrogen compounds, is obtained as a distillate, and a part of the liquid extracted at the bottom of the column is circulated to the reaction operation section.

(2) A method for producing crude methyl methacrylate containing the above diketone is a method for producing methyl methacrylate by oxidatively esterifying methacrolein in a liquid phase with methacrolein, methanol and oxygen. The method for producing methyl methacrylate according to (1).

(3) The aliphatic amine having a boiling point higher than that of the methyl methacrylate is 2-aminoethanol (1)
Alternatively, the method for producing methyl methacrylate according to (2).

(4) Methyl methacrylate according to any one of (1) to (3), wherein the obtained methyl methacrylate has a diacetyl concentration of less than 0.1 ppm and a total nitrogen concentration of less than 0.2 ppm. Manufacturing method.

(5) In the reaction of the crude methyl methacrylate with the aliphatic amine, the aliphatic amine is 1 to 10 moles as the amino group in the aliphatic amine with respect to the diketones in the crude methyl methacrylate to be removed. The method for producing methyl methacrylate according to any one of (1) to (4), which is added in an amount range.

(6) Phenothiazine, di-t-butylcatechol, hydroquinone, 4-methoxyphenol and N-oxyl groups are used in the reaction operation and distillation operation of the crude methyl methacrylate containing the diketone and the aliphatic amine. The method for producing methyl methacrylate according to any one of (1) to (5), which is carried out in the presence of at least one polymerization inhibitor selected from compounds.

The present invention will be specifically described below with reference to FIGS. 1 and 2. In FIG. 1, 1 is a crude methyl methacrylate after removing high-boiling substances such as unreacted or by-produced methacrylic acid from a reaction solution containing methyl methacrylate produced in the production process of methyl methacrylate. Contains diketones. The crude methyl methacrylate is methyl methacrylate containing, in addition to diketones, impurities having a boiling point lower than that of methyl methacrylate such as methyl isobutyrate and methyl acrylate. The diketones are compounds having two adjacent ketone groups in one molecule, such as diacetyl and methylpropyl diketone. 2 is an aliphatic amine having a boiling point higher than that of methyl methacrylate. It is also possible to use an aliphatic amine having a high boiling point in which an amine compound which is contained as an impurity in the aliphatic amine and has a boiling point close to that of methyl methacrylate is previously removed by a separation means such as distillation.

Crude methyl methacrylate 1 and aliphatic amine 2
Is supplied to the reaction part A and reacted in the reaction part A. The crude methyl methacrylate 1 and the aliphatic amine 2 may be supplied to the reaction part A after being mixed, or may be individually supplied. Here, the reaction temperature is preferably 60 to 100 ° C.
The shape of the reaction part A is not particularly limited, and may be a stirring tank type or a tubular type as long as the crude methyl methacrylate 1 and the aliphatic amine 2 can be mixed. The obtained reaction liquid 3 is supplied to the distillation column B of the distillation operation section. The distillation column B has a column bottom temperature of 60 to 100 ° C., preferably 70 to
The pressure is adjusted so that the temperature is 90 ° C., and distillation is performed. A low boiling point substance such as methyl isobutyrate or methyl acrylate is withdrawn from the top of the distillation column B as a top distillate 4 together with methyl methacrylate. Of the amine compounds having a lower boiling point than methyl methacrylate contained in the added aliphatic amine 2, the residual low-boiling amine compound which has not been raised to a high boiling point by the reaction with the diketone is also contained in the overhead distillate 4, It is extracted from the top of the distillation column B. Further, even an aliphatic amine having a boiling point higher than that of methyl methacrylate is partially decomposed by a reaction operation or a distillation operation, and even when it has a lower boiling point than that of methyl methacrylate, it is withdrawn from the top of the distillation column B. Methyl methacrylate contained in the overhead distillate 4 can be recovered separately in another step.

The bottom liquid 5 is supplied to the next distillation column C, and methyl methacrylate substantially free of diketones and nitrogen compounds is obtained from the top of the column. In the present invention, "not containing diketones substantially" means that diacetyl is less than 0.1 ppm. Preferably, diacetyl 0.1 pp
It is desirable that it is less than m and less than 0.1 ppm of methyl propyl diketone. Further, the phrase "substantially free from nitrogen compounds" means that the total nitrogen content is less than 0.2 ppm. By setting the coloring-causing substances such as diketones and nitrogen compounds contained in methyl methacrylate, which is a raw material of the methyl methacrylate polymer, within the above range, a methyl methacrylate polymer having excellent transparency can be obtained. The distillation column C has a column bottom temperature of 60 to 100 ° C.,
Desirably, the pressure is adjusted to 70 to 90 ° C. and distillation is performed.

A bottom-bottom circulating liquid 7 which is a part of the bottom-bottomed liquid of the distillation tower C is circulated to the reaction section A. It may be directly supplied to the reaction part A, or may be supplied to the reaction part A after being mixed with the crude methyl methacrylate 1 and / or the aliphatic amine 2. By recirculating the column bottom withdrawal liquid to the reaction part A again, most of the unreacted aliphatic amine can be efficiently reused for the reaction with the diketones, and at the same time, the aliphatic amine The concentration can be increased to accelerate the reaction with the diketones. The flow rate of the bottom circulation liquid 7 with respect to the flow rate of the bottom extraction liquid 8 can be freely set by the amount of the diketones in the crude methyl methacrylate 1 and the addition amount of the aliphatic amine 2, and the addition flow amount of the polymerization inhibitor. However, it can be, for example, 0.1 to 10. The column bottom withdrawal liquid 8 is mainly methyl methacrylate and contains an aliphatic amine. Separately, methyl methacrylate can be recovered from the liquid 8 withdrawn from the bottom of the column in another step.

Here, the reaction operation section means the liquid hold volume of the reaction section A, the liquid hold volume of the distillation column B below the reaction liquid 3 supply section and the column bottom portion including the reboiler, and the distillation column B. It is the sum of the liquid holding volume of the piping part from the column bottom to the distillation column C and the column bottom part of the distillation column C including the reboiler. The residence time in the reaction operating part is preferably 5 minutes to 5 hours, particularly preferably 15 minutes to 3 hours. Further, the distillation operation section refers to both the upper part of the distillation column B above the reaction liquid 3 supply part and the upper part of the distillation column C above the bottom. As the model of the distillation column, for example, a plate column or a packed column can be used.

Next, FIG. 2 will be described. In FIG. 2, 9 is a crude methyl methacrylate after removing high-boiling substances such as unreacted or by-produced methacrylic acid from a reaction liquid containing methyl methacrylate produced in the production process of methyl methacrylate, Contains diketones. 10
Is an aliphatic amine. In this case, the liquid hold amount of the distillation column D lower than the feed stage of the aliphatic amine 10 and the column bottom portion including the reboiler, the piping portion from the column bottom of the distillation column D to the distillation column E, and the reboiler of the distillation column E are set. The amount of liquid held at the bottom of the column is the reaction operating part. Further, the upper part of the distillation column D above the supply stage of the aliphatic amine 10 and the upper part of the distillation column E above the bottom serve as the distillation operation part.

By arranging the feed position of the aliphatic amine 10 below the feed position of the crude methyl methacrylate 9, at least a part of diketones such as diacetyl having a lower boiling point than that of methyl methacrylate is previously prepared. The aliphatic amine can be efficiently used for the reaction with the diketones in methyl methacrylate by distilling off together with a low boiling point compound such as methyl isobutyrate or methyl acrylate in crude methyl methacrylate. Further, an impurity amine compound having a boiling point lower than that of methyl methacrylate contained in the aliphatic amine 10 can be removed by distillation. The low boiling point compound is extracted from the top of the distillation column D as a column top extraction liquid 11.
Furthermore, even an aliphatic amine having a boiling point higher than that of methyl methacrylate is partially decomposed by a reaction operation or a distillation operation, and even when it has a lower boiling point than that of methyl methacrylate, it is withdrawn from the top of the distillation column D. The bottom liquid 12 of the distillation column D is supplied to the bottom of the next distillation column E. In the distillation column E, methyl methacrylate, which is substantially free of diketones and nitrogen compounds, is withdrawn as the overhead distillate 13, and the column bottom circulating liquid 14 which is a part of the column bottom extract is a fat. It is circulated to the reaction operation section of the distillation column D together with the group amine 10. By recirculating the column bottom liquid to the reaction operation section, most of the unreacted aliphatic amine can be efficiently reused for the reaction with the diketones, and the concentration of the aliphatic amine in the reaction operation section can be increased. Can be enhanced to accelerate the reaction with diketones. Tower bottom liquid 1
The flow rate of the bottoms circulating liquid 14 with respect to the flow rate of 5 can be freely set depending on the amounts of the diketones in the crude methyl methacrylate 9 and the addition amount of the aliphatic amine 10, and the addition flow amount of the polymerization inhibitor. For example, it can be 0.1 to 10. The residence time in the reaction operating part is preferably 5 minutes to 5 hours, particularly preferably 15 minutes to 3 hours.

In the present invention, the method for producing crude methyl methacrylate is not particularly limited,
As a preferred production method, there is a method of producing methyl methacrylate by oxidatively esterifying methacrolein in a liquid phase with methacrolein, methanol and oxygen.

Examples of the aliphatic amine having a boiling point higher than that of methyl methacrylate include 2-aminoethanol, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and the like. Among them, 2-aminoethanol (boiling point 170.5 C) is preferred.

The addition amount of the aliphatic amine in the reaction of the crude methyl methacrylate with the aliphatic amine is such that the amino group of the aliphatic amine is 1 to 10 mole times the diketones in the crude methyl methacrylate to be removed. Is preferred.

Further, in order to prevent polymerization in the reaction operation of crude methyl methacrylate and the aliphatic amine and the distillation operation, phenothiazine, di-t-butylcatechol, hydroquinone, 4-methoxyphenol, and a compound having an N-oxyl group are used. Preference is given to working in the presence of at least one selected polymerization inhibitor.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method of the present invention will be specifically described with reference to Examples, but the scope of the present invention is not limited by these Examples. Percentages and ppm are by weight unless otherwise indicated.

Further, quantitative determination of diacetyl, total nitrogen analysis, coloring evaluation of methyl methacrylate and coloring evaluation of methyl methacrylate polymer were carried out as follows.

<Determination of diacetyl content> Shimadzu Gas Chromatograph 14B was used for quantitative analysis of diacetyl content.
Mold and G-950 sold by the Chemicals Inspection Association
A column was used. The lower limit of quantification was 0.1 ppm.

<Total Nitrogen Analysis> For analysis of total nitrogen in methyl methacrylate, Mitsubishi Chemical's trace total nitrogen analyzer TN-
100 was used. The lower limit of quantification of the nitrogen compound in methyl methacrylate was 0.2 ppm.

<Evaluation of Coloration of Methyl Methacrylate> The method of comparing the degree of coloring of methyl methacrylate is JIS
According to -K6716, potassium platinum chloride and cobalt chloride were dissolved in concentrated hydrochloric acid and diluted with distilled water to be used as a standard solution, and the degree of dilution was compared with the coloring degree by the number of APHA for evaluation. Distilled water in APHA
The value was set to 0, and the degree of dilution of the standard solution with distilled water was sequentially decreased to prepare standard solutions having APHA values of 5, 10, 15, and 20.

<Evaluation of Coloration of Methyl Methacrylate Polymer> When methyl methacrylate is polymerized to form a methyl methacrylate polymer, the evaluation method of coloration is as follows. The length is 55 cm, the width is 10 cm, and the thickness is 5 mm. A plate of acid methyl polymer was prepared, and the longitudinal direction was visually observed and compared with a long optical path transmission color measuring instrument. (Method for producing a plate of methyl methacrylate polymer) A gasket is sandwiched between two glass plates and clamped,
I created a uniform space with a gap. 0.05% of 2,2′-azobisisobutyronitrile was added to methyl methacrylate as a polymerization initiator and mixed. Using a funnel, methyl methacrylate mixed with a polymerization initiator was poured between the glass plates. The two glass plates were tightened with a clamp to remove air, and then sealed. 50 per glass plate
The mixture was placed in warm water of ± 1 ° C. for 6 hours and then placed in a thermostat of 115 ± 1 ° C. for 2 hours to polymerize. After allowing to cool naturally, the methyl methacrylate polymer plate was removed from the glass plate, and a plate having a length of 55 cm and a width of 10 cm was cut out. Both ends in the longitudinal direction were polished and finished with a file and buff. The long optical path transmission color measuring instrument is ASA-made by Nippon Denshoku Industries Co., Ltd.
Type 2 was used. As an evaluation index, JIS-K710
3 Described in the yellowness and yellowing test method of plastics,
The yellowness YI was expressed as a numerical value calculated from the measurement result by the long optical path transmission color measuring device and comparatively evaluated.

[0034]

Example 1 Two Oldershaw distillation columns made of glass were connected as shown in FIG. Both of them have a tray column type with an inner diameter of 2 inches and 40 plates. The distillation column D has a crude methyl methacrylate 9 supply port on the 20th stage from the top of the column and a condenser on the top of the column under reduced pressure. A device capable of draining liquid is provided, and a device for withdrawing the column bottom liquid 12 under reduced pressure controlled by a liquid level gauge and a heating facility are provided at the bottom of the column. Further, there is a feed port for the aliphatic amine 10 at the 30th stage from the top of the column. Distillation tower E is 4 from the top
A device having a feed port for the bottom liquid 12 of the distillation column D at the 0th stage, a condenser at the top of the column and a device for extracting the top distillate 13 under reduced pressure, and a liquid level gauge at the bottom of the column. It has equipment for extracting the bottom liquid under controlled decompression and heating equipment. The column bottom circulating liquid 14 which is a part of the column bottom withdrawal liquid is replaced with the aliphatic amine 10
Together with this, it was installed in the distillation column D so that it could be circulated.

200 ppm of diacetyl as diketones
1000 g of crude methyl methacrylate having ## STR3 ## was fed to the distillation column D per hour. This solution is colored yellow, and the APHA value is 20 from the visual comparison with the standard solution showing the number of colors.
That was all. 0.4 g of 2-aminoethanol was injected as the aliphatic amine 10 every hour. Distillation column D has a bottom temperature of 8
The degree of vacuum was adjusted so that the temperature became 0 ° C. 20 g of the top distillate 11 was withdrawn from the top of the column per hour, and the rest was withdrawn as a bottom liquid 12 from the bottom of the column and supplied to the distillation column E. Distillation tower E
360 g / h is withdrawn from the bottom of the tower, of which 300 g / h
Was circulated with the aliphatic amine 10 of the distillation column D. In order to prevent polymerization, the distillation columns D and E were operated by continuously adding hydroquinone to the reflux liquid at the top of the column.

As a result, 920 g of methyl methacrylate was obtained from the top of the distillation column E every hour, the diacetyl concentration was less than 0.1 ppm, and the total nitrogen concentration was 0.2 pp.
It was less than m. After continuous operation for 5 days, the concentration of diacetyl in methyl methacrylate 13 obtained from the top of distillation column E was maintained at less than 0.1 ppm and total nitrogen concentration of less than 0.2 ppm. The color was colorless and transparent, and the APHA value was 5 or less by visual comparison with a standard solution representing the number of colors. Further, there were no troubles due to polymerization such as clogging and stains. Under this condition, the molar ratio of the amino group supplied as the aliphatic amine 10 to the diacetyl contained in the crude methyl methacrylate and supplied was 2.8.

The methyl methacrylate obtained from the top of the distillation column E was polymerized to prepare a methyl methacrylate polymer plate, which was visually colorless and transparent. The yellowness YI obtained by measuring with a long optical path transmission color measuring device is 5.5.
Met.

[0038]

Comparative Example 1 In a flask equipped with a reflux condenser and a stirrer,
Methyl methacrylate 60 containing 192 ppm diacetyl
g and diethylenetriamine (boiling point 208 ° C) 2.0 wt
% Methyl methacrylate 60 g was added. Methyl methacrylate containing 192 ppm of diacetyl is colored in yellow, and the visual comparison with the standard solution showing the number of colors indicates that APH
The A value was 20 or more. Both solutions contained 4-hydroxy-2,2,6,6- which is a compound having an N-oxyl group.
Tetramethylpiperidine-N-oxyl was added as a polymerization inhibitor in an amount of 100 ppm each, and each was preheated to 80 ° C.
The temperature of the liquid in the flask was kept at 80 ° C. by an oil bath even after the addition to the flask, and the mixture was stirred. The molar ratio of amino group to diacetyl after adding both solutions is 2
It was 61. The time at which the diacetyl concentration was added was taken as the reaction start time, and the change with time of the diacetyl concentration was followed. The diacetyl concentration immediately after the addition was 110 ppm, the diacetyl concentration 10 minutes after the addition was 1.9 ppm, and the diacetyl concentration 100 minutes after the addition was 1.1 ppm. The reaction solution was distilled, and the distilled methyl methacrylate was analyzed by gas chromatography. As a result, the diacetyl concentration was 1.3 ppm, and the APHA value was 5 and 1.
It was between 0.

[0039]

Comparative Example 2 In Example 1, the withdrawal from the bottom of the distillation column E was set to 60 g per hour, and the circulation to the distillation column D was stopped. Further, the operation was performed in the same manner as in Example 1 except that diethylenetriamine was used as the aliphatic amine. as a result,
The diacetyl concentration in the methyl methacrylate 13 obtained from the top of the distillation column E was 0.4 ppm, and the APHA value was between 5 and 10 from visual comparison with the standard solution representing the color number. The value of total nitrogen was less than 0.2 ppm. Under this condition, the molar ratio of the amino group supplied as the aliphatic amine 10 to the diacetyl contained in the crude methyl methacrylate and supplied was 5.0. Example 1 was prepared by polymerizing the methyl methacrylate obtained from the top of the distillation column E to prepare a methyl methacrylate polymer plate.
When compared with the plate prepared in 1., it was clearly colored yellow. The value of yellowness YI was 10.1.

[0040]

Comparative Example 3 In Example 1, the position of addition of the aliphatic amine was changed from the position of the liquid 10 to the position of the liquid 12, and impurities in the aliphatic amine having a boiling point lower than that of methyl methacrylate were distilled. It was directly supplied to the distillation column E without being removed. The same operation as in Example 1 was carried out except that diethylenetriamine was used as the aliphatic amine and the addition amount was 1.2 g / hr. As a result, the diacetyl concentration in the methyl methacrylate 13 obtained from the top of the distillation column E was 0.1 ppm.
Was less than. The APHA value was 5 or less by visual comparison with a standard solution representing the number of colors. The value of total nitrogen is 0.6p
There was pm. A plate of a methyl methacrylate polymer was prepared using methyl methacrylate obtained from the top of the distillation column E, and when compared with the plate prepared in Example 1, it clearly had yellow coloring. The value of yellowness YI is 16.9.
Met.

[0041]

EFFECTS OF THE INVENTION According to the present invention, diketones, which are coloring-causing substances in methyl methacrylate, and nitrogen compounds, which cause coloring of methyl methacrylate polymer, can be sufficiently removed, and both monomer and polymer are excellent in transparency. Methyl methacrylate can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a specific example of a method for producing methyl methacrylate of the present invention.

FIG. 2 is a diagram showing another specific example of the method for producing methyl methacrylate of the present invention.

[Explanation of symbols]

A reaction part B, C, D, E Distillation tower 1,9 Crude methyl methacrylate 2,10 Aliphatic amine 3 reaction liquid 4 Top distillate of distillation column B 5 Bottom liquid of distillation column B 6 Top distillate of distillation column C 7 Circulating liquid at the bottom of distillation column C 8 Distillation tower C bottom liquid 11 Top distillate of distillation column D 12 Bottom liquid of distillation column D 13 Top distillate of distillation column E 14 Bottom circulation liquid of distillation column E 15 Bottom liquid of distillation tower E

Claims (6)

[Claims] 1. A method for producing methyl methacrylate, comprising: crude methyl methacrylate containing a diketone;
An aliphatic amine having a boiling point higher than that of methyl methacrylate is reacted in the reaction operation section, the obtained reaction liquid is distilled in the distillation operation section, and a lower boiling point than methyl methacrylate is first distilled from the top of the column. Then, the bottom liquid is distilled in the next distillation column to obtain methyl methacrylate substantially free of diketones and nitrogen compounds as a distillate,
A method for producing methyl methacrylate, characterized in that a part of the liquid taken out from the bottom of the column is circulated to the reaction operation section. 2. A method for producing crude methyl methacrylate containing a diketone is a method for producing methyl methacrylate by oxidatively esterifying methacrolein in a liquid phase with methacrolein, methanol and oxygen. The method for producing methyl methacrylate according to claim 1. 3. The method for producing methyl methacrylate according to claim 1, wherein the aliphatic amine having a higher boiling point than that of methyl methacrylate is 2-aminoethanol. 4. The method for producing methyl methacrylate according to claim 1, wherein the obtained methyl methacrylate has a diacetyl concentration of less than 0.1 ppm and a total nitrogen concentration of less than 0.2 ppm. . 5. In the reaction of the crude methyl methacrylate with an aliphatic amine, the aliphatic amine is used in an amount of 1 to 10 moles as an amino group in the aliphatic amine with respect to the diketones in the crude methyl methacrylate to be removed. The method for producing methyl methacrylate according to any one of claims 1 to 4, which is added within the range of. 6. A compound having phenothiazine, di-t-butylcatechol, hydroquinone, 4-methoxyphenol, and N-oxyl group in the reaction operation and distillation operation of the crude methyl methacrylate containing the diketone and the aliphatic amine. The method for producing methyl methacrylate according to claim 1, which is carried out in the presence of at least one polymerization inhibitor selected from the group consisting of: