JP2025017229A - Method for producing methyl methacrylate - Google Patents

Abstract

The present invention provides a method for producing methyl methacrylate, which is capable of producing methyl methacrylate using MMA-containing methanol in a simpler and more cost-effective manner.
[Solution] A method for producing methyl methacrylate by reacting methacrylamide sulfate with methanol, the method comprising the step of adding a mixed liquid (1) in which the mass ratio of methanol to methyl methacrylate is 51:49 to 99:1 to methacrylamide sulfate.
[Selection diagram] None

Description

This disclosure relates to a method for producing methyl methacrylate.

The following method is known as an industrial method for producing methyl methacrylate (hereinafter, also referred to as MMA). That is, the so-called ACH method is known in which acetone cyanohydrin (hereinafter, also referred to as ACH) obtained by reacting acetone with hydrogen cyanide (prussic acid) is reacted with sulfuric acid or fuming sulfuric acid to produce methacrylamide sulfate, which is then reacted with water and methanol to produce MMA.

As shown in Patent Document 1, in the ACH method, an excess amount of methanol is used relative to methacrylamide sulfate when producing MMA, so a mixed liquid containing methyl methacrylate and methanol, together with ammonium sulfate, is obtained.

Patent Document 2 and Patent Document 3 disclose methods for distilling and purifying methyl methacrylate and methanol from a mixture containing methyl methacrylate and methanol, respectively. Patent Document 3 also discloses that the mixture is obtained by an esterification reaction of methacrylic acid with methanol, or a transesterification reaction of methyl methacrylate and alcohol.

The synthesis of (meth)acrylic acid esters of high-boiling alcohols such as polyhydric alcohols and higher alcohols is carried out by transesterification of these alcohols with lower alcohols of (meth)acrylic acid. In this production method, for example, when the lower alcohol is methanol, in addition to the (meth)acrylic acid esters of the target compounds such as polyhydric alcohols and higher alcohols, a mixture of the remaining methyl (meth)acrylate and by-product methanol is produced during purification.
Conventionally, the treatment of the mixed liquid required incineration to recover heat, or a step of adding an azeotropic solvent to separate methyl (meth)acrylate by distilling off methanol to separate methyl (meth)acrylate and a step of separating methanol and the azeotropic solvent in a decanter to isolate the components methyl (meth)acrylate and methanol (see Patent Documents 2 and 3 [Figs. 3 and 4]). Methyl (meth)acrylate that has undergone these steps becomes a product, and methanol is used, for example, in a post-step for esterification of (meth)acrylic acid or for synthesis of methyl (meth)acrylate by methanolysis of (meth)acrylamide in the presence of sulfuric acid. In the synthesis reaction of methyl (meth)acrylate in the post-step, a mixed liquid of the product methyl (meth)acrylate and the remaining methanol is produced, and a step of isolating these again is required.

Japanese Unexamined Patent Publication No. 57-156438 Japanese Patent Application Publication No. 2-17150 Japanese Patent Application Publication No. 8-268938

When MMA-containing recovered methanol is reused to produce methyl methacrylate by the ACH method, the following method can be considered, for example. That is, the MMA-containing recovered methanol is purified by distillation using an azeotropic solvent such as n-hexane by the method described in Patent Document 2 or Patent Document 3, and the purified MMA is isolated. After that, the mixture of the azeotropic solvent and the recovered methanol from which the MMA has been removed is separated by a liquid separation operation. Then, methacrylamide sulfate obtained by the ACH method is allowed to act on the recovered methanol obtained to produce methyl methacrylate.

However, when considering the case where methyl methacrylate produced using recovered methanol is to be purified again by distillation, the above-mentioned method requires two distillation purification steps. Therefore, there has been a demand for the development of a simpler and more cost-effective method for producing methyl methacrylate using MMA-containing methanol.

The present disclosure aims to provide a method for producing methyl methacrylate that can produce methyl methacrylate using MMA-containing methanol in a simpler and more cost-effective manner.

The method for producing methyl methacrylate according to the present disclosure has the following configurations [1] to [4].
[1] A method for producing methyl methacrylate by reacting methacrylamide sulfate with methanol, the method comprising the step of adding a mixed liquid (1) having a mass ratio of methanol to methyl methacrylate of 51:49 to 99:1 to methacrylamide sulfate.
[2] The method for producing methyl methacrylate according to [1] further comprises a step of adding an azeotropic solvent with methanol to the mixed liquid (2) having a mass ratio of methanol and methyl methacrylate of 1:99 to 49:51 produced in the above step, and distilling off the methanol.
[3] The method for producing methyl methacrylate according to [1] or [2], wherein the mixed liquid (1) is a product of an ester exchange reaction between a high-boiling alcohol and methyl methacrylate.
[4] The method for producing methyl methacrylate according to [1] or [2], wherein the mixed liquid (1) is a product produced in a production process of methacrylic acid.

The present disclosure provides a method for producing methyl methacrylate using MMA-containing methanol in a simpler and more cost-effective manner.

When reusing (recycling) recovered MMA-containing methanol to produce methyl methacrylate by the ACH process, it has previously been necessary to either incinerate the recovered MMA-containing methanol for thermal recovery, or to carry out the following operations to isolate methyl methacrylate and methanol. That is, an azeotropic solvent such as n-hexane is added to the recovered MMA-containing methanol and the methanol is distilled off to isolate methyl methacrylate, and the distilled off methanol and the azeotropic solvent are separated in a decanter to separate the two components. After these steps, the methyl methacrylate becomes the product, and the separated methanol is used to synthesize methyl methacrylate by methanolysis of methacrylamide in the presence of sulfuric acid.

On the other hand, in the method for producing methyl methacrylate disclosed herein (hereinafter also referred to as the present production method), a mixed liquid containing methyl methacrylate and methanol is directly subjected to methanolysis with methacrylamide without isolation and purification. Therefore, in the present production method, distillation purification of recovered methanol containing MMA can be omitted, which makes it possible to effectively use resources, reduce greenhouse gas emissions, eliminate distillation and separation processes, and reduce the amount of azeotropic solvent used.

The following describes in detail an embodiment of this manufacturing method, but the present disclosure is not limited to this embodiment. In addition, the present disclosure can be modified in any manner without departing from the spirit and scope of the present disclosure.

In the present specification, the numerical range indicated using "to" includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.
In this specification, (meth)acrylic acid means either or both of methacrylic acid and acrylic acid.

This manufacturing method is a method for manufacturing methyl methacrylate using methanol containing methyl methacrylate. More specifically, in this manufacturing method, methacrylamide sulfate is reacted with a mixed liquid containing methyl methacrylate and methanol (recovered methanol containing MMA) to produce methyl methacrylate from the methanol. In other words, this manufacturing method can be said to be a method for manufacturing methyl methacrylate using the ACH method that utilizes recovered methanol containing MMA. Note that methyl methacrylate (MMA) is used as a raw material monomer for various polymers such as polymethyl methacrylate (PMMA), which is known as a transparent resin.

Here, the above-mentioned mixed liquid may be a mixed liquid (1) containing methanol and methyl methacrylate in a mass ratio of 51:49 to 99:1, and the manufacturing method and other components contained therein are not particularly limited as long as the effects of the present disclosure can be obtained.

The mixed liquid (1) may be, for example, a reaction product of an esterification reaction between methacrylic acid and methanol, an ester exchange reaction between methyl methacrylate and an alcohol (preferably a high-boiling alcohol), or a methanolysis reaction between methacrylamide sulfate and methanol, or a product produced in a process for producing methacrylic acid that does not involve methacrylamide. In addition, the mixed liquid (1) may be a product that has been subjected to other treatment operations such as distillation purification or the like (i.e., a product derived from the reaction product) as required.

In the esterification reaction of methacrylic acid and methanol, a mixture containing methyl methacrylate, methanol, and water is obtained. In the esterification reaction, methanol is usually used in excess of methacrylic acid, so most of the methacrylic acid is consumed and there is no unreacted methacrylic acid. Therefore, the reaction liquid after the reaction is a mixture of excess methanol, the reaction product methyl methacrylate, and the reaction by-product water.

In addition, in the transesterification reaction between methyl methacrylate and a high-boiling alcohol (for example, a polyhydric alcohol having two or more hydroxyl groups in the molecule, or a higher alcohol having six or more carbon atoms), a mixed liquid (1) containing methyl methacrylate and methanol is obtained. In the transesterification reaction, an excess amount of methyl methacrylate is usually used relative to the alcohol, so most of the alcohol is consumed by the transesterification reaction. Therefore, the reaction liquid after the reaction is a mixed liquid containing methanol, which is a reaction by-product, unreacted methyl methacrylate, and an ester, which is a reaction product (a methacrylic acid ester corresponding to the alcohol used). Of these, the ester, which is a reaction product, has a large boiling point difference from methanol and methyl methacrylate, so it is relatively easy to separate, and a mixed liquid containing methanol and methyl methacrylate excluding this ester can be obtained.

The methanolysis reaction of methacrylamide sulfate with methanol may be a reaction step included in the ACH method described above.
The ACH method includes, for example, the following steps.
(a) Acetone and hydrogen cyanide are subjected to an addition reaction, for example, in the presence of an alkali catalyst, to obtain acetone cyanohydrin (ACH).
(b) ACH is subjected to an amidation reaction with sulfuric acid or fuming sulfuric acid (sulfuric acid group), optionally with heating, to obtain methacrylamide sulfate (hereinafter also referred to as MAAm).
(c) MAAm, water, and methanol are subjected to a methanolysis reaction to obtain MMA.
Here, in the step (c), an excess amount of methanol is used relative to MAAm, so that a mixed liquid containing methyl methacrylate and methanol together with ammonium sulfate is obtained. This mixed liquid obtained in the step (c) may be used as the mixed liquid (1) (recovered methanol containing MMA) in the present production method.

The detailed reaction conditions for each of the above reactions to obtain the mixed solution used in this production method are not particularly limited and may be any conventionally known reaction conditions.

For example, in step (b) of the ACH method, the reaction between ACH and sulfuric acid is usually carried out at 1.0 to 3.0 moles, preferably 1.42 to 2.1 moles, of sulfuric acid per mole of ACH. The reaction temperature is 50 to 180°C, preferably 90 to 150°C. The reaction may be carried out continuously or batchwise, with the continuous method being preferred. Reactors used in the reaction include, for example, stirred reaction tanks, continuous stirred reaction tanks, and flow-through reaction tanks, with the continuous stirred reaction tank being preferred.

In step (c), the amount of water used is usually 1 to 5 moles, preferably 2 to 3 moles, per mole of MAAm. The water may be steam, which also serves as a heating source. The amount of methanol used is usually 1 to 5 moles, but it is preferable to use an excess amount relative to MAAm. The reaction temperature is 60 to 150°C, preferably 90 to 140°C. The reaction may be carried out continuously or batchwise, but the continuous method is preferable. Examples of reactors used in the reaction include a stirred reaction tank, a continuous stirred reaction tank, and a flow-through reaction tank, but the continuous stirred reaction tank is preferable. The MMA obtained by the reaction contains water, unreacted methanol, low-boiling impurities generated by the reaction, and the like. These substances can also be removed by separation operations such as distillation and extraction. Usually, water and unreacted methanol can be removed by extraction, and low-boiling impurities can be removed by distillation.

In this production method, MMA is produced by reacting MMA and methanol in a mixed state (i.e., MMA-containing recovered methanol mixed solution (1)) with MAAm without separately performing a distillation separation operation or the like. Here, the mixing ratio of methanol to methyl methacrylate in the mixed solution (1) (MMA-containing recovered methanol) is 51:49 to 99:1, and preferably 75:25 to 99:1, from the viewpoint of preventing the reactor volume from becoming excessively large. Ammonium sulfate, residual sulfuric acid, acidic ammonium sulfate (NH ₄ HSO ₄ ), etc. contained in the product after the methanolysis reaction of MAAm are extracted from the bottom of the reactor, and MMA and the residual methanol are distilled off by distillation to obtain a mixed solution (2) containing methanol and MMA in a mass ratio of 1:99 to 49:51.

In addition, in this production method, the reaction product obtained by reacting the MMA-containing recovered methanol with MAAm (mixed liquid (2) containing MMA and methanol) may be subjected to a purification operation described below as necessary, and then reacted with MAAm again. In other words, in this production method, the operation of reacting the mixed liquid containing methyl methacrylate and methanol with MAAm may be repeated multiple times to increase the content of MMA in the mixed liquid (2).

In this production method, the mixture (2) obtained by reacting the mixture (1) (recovered methanol containing MMA) with methacrylamide sulfate may be distilled to purify methyl methacrylate. In other words, this production method may include a purification step such as distillation of the obtained reaction product.

Here, the distillation method for the above-mentioned mixed liquid (2) is not particularly limited, and a conventionally known method can be used as appropriate. For example, a process of adding an azeotropic solvent with methanol and distilling off the methanol may be used, as in the purification methods described in the above-mentioned Patent Documents 2 and 3. Examples of the azeotropic solvent include low-boiling hydrocarbon solvents that are incompatible with methanol, such as pentane, hexane, and heptane.

The following purification method may also be used. Specifically, the reaction product (crude MMA) of recovered methanol containing MMA and MAAm is fed to a distillation column. Crude MMA contains impurities with lower and higher boiling points than MMA. Examples of high-boiling impurities include ethyl methacrylate, methyl α-hydroxyisobutyrate, methyl α-methoxyisobutyrate, methyl β-hydroxyisobutyrate, methyl β-methoxyisobutyrate, methyl methacrylate dimer, and methacrylic acid. Typical high-boiling impurities and their contents are 1-2% methyl α-hydroxyisobutyrate, 1-2% methyl β-methoxyisobutyrate, and 2-8% methacrylic acid.

In the distillation operation, the purified MMA is distilled from the top of the distillation column. At least one high-boiling impurity in the distillate is selected as an indicator substance, and the column is operated so that the concentration of each is 50 ppm or less, preferably 20 ppm or less. However, in order to increase the recovery rate of MMA, the concentration of each indicator substance in the distillate is preferably 15 ppm or more. Examples of indicator substances include methyl α-hydroxyisobutyrate (boiling point at normal pressure: 137°C) and methyl β-methoxyisobutyrate (boiling point at normal pressure: 147°C). For example, if the indicator substance is methyl α-hydroxyisobutyrate and the content of methyl α-hydroxyisobutyrate in crude MMA is 1-2%, it is preferable to aim for a recovery rate of MMA in the distillation purification of 80-86%.

The type of distillation tower used in the distillation operation is not particularly limited, and examples include packed towers and tray-type towers. Examples of packing materials used in packed towers include Helipak, McMahon, and cascade mini rings. Examples of tray-type distillation towers include Oldershaw type and lift tray type. The number of theoretical plates of the distillation tower is not particularly limited, but 5 or more plates are preferable, and 10 or more plates are more preferable. In addition, 70 plates or less are preferable, and 50 plates or less are more preferable. The higher the number of theoretical plates, the higher the separation ability, and the lower the number of theoretical plates, the smaller the pressure difference in the distillation tower.

The distillation operation can be carried out under any of normal pressure (near atmospheric pressure), reduced pressure and increased pressure, but the preferred distillation pressure is 2600 to 108000 Pa (absolute pressure).
The distillation temperature (temperature inside the distillation column) cannot be generally determined because it varies depending on the distillation pressure, but is generally 40 to 110° C. When the reaction pressure is normal pressure, the distillation temperature is generally 90 to 105° C.

A polymerization inhibitor may be present in the system during the distillation. Any polymerization inhibitor may be used as long as it has a polymerization inhibitory effect on MMA. Examples of such polymerization inhibitors include phenolic compounds such as hydroquinone, paramethoxyphenol, and 2,4-dimethyl-6-t-butylphenol; amine compounds such as phenothiazine, N-phenyl-N'-isopropylparaphenylenediamine, N,N'-di-2-naphthylparaphenylenediamine, and N-phenyl-N'-(1,3-dimethylbutyl)paraphenylenediamine; and N-oxyl compounds such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, or N-oxyl compounds represented by the following general formula (1). The polymerization inhibitor may be used alone or in combination of two or more kinds.
As described above, according to the present production method, MMA, which can be purified as necessary, can be obtained from MMA-containing recovered methanol.

The present invention will be described in more detail below with reference to several examples, but the present disclosure is not limited to these examples.

<Composition analysis of mixed liquid>
A column (GL Sciences; InertCap 1 (df=0.4 μm, 0.25 mm ID×60 m)) was connected to a gas chromatograph (Shimadzu Corporation; GC-14A). Measurements were performed under the following conditions: injection temperature was 180° C., detector temperature was 180° C., and column temperature was increased from 60° C. (held for 5 minutes) to 200° C. at a rate of 10° C./min.

[Example 1]
A mixed liquid (1-1) consisting of 80% by mass of methanol and 20% by mass of MMA was obtained as a by-product by the transesterification reaction of a high boiling point alcohol with methyl methacrylate (MMA).
To the reactor, 250 parts by mass of a mixed solution of methacrylamide sulfate containing 100 parts by mass of methacrylamide and sulfuric acid, and 75 parts by mass of the mixed solution (1-1) were continuously supplied, and the reaction was carried out at 130° C. The produced acidic ammonium sulfate (NH ₄ HSO ₄ ) was extracted from the bottom of the reactor, and 155 parts by mass of a mixed solution (2-1) consisting of 15% by mass of methanol and 85% by mass of MMA was obtained as a distillate fraction.
To the mixture (2-1), n-hexane was added as an azeotropic solvent and distilled, and methanol and n-hexane were azeotropically distilled off from the top of the column, and 133 parts by mass of purified MMA was obtained from the bottom of the column.

[Example 2]
The mixed solution (1-1) was diluted 10 times with methanol to obtain a mixed solution (1-2) consisting of 98 mass% of methanol and 2 mass% of MMA. The reaction was carried out in the same manner as in Example 1, except that the mixed solution supplied to the reactor was changed to 61 mass parts of the mixed solution (1-2), and 141 mass parts of a mixed solution (2-2) consisting of 16 mass% of methanol and 84 mass% of MMA was obtained as a distillate fraction.
To the mixture (2-2), n-hexane was added as an azeotropic solvent and distilled, and methanol and n-hexane were azeotropically distilled off from the top of the column, and 119 parts by mass of MMA was obtained from the bottom of the column.

[Example 3]
The reaction was carried out in the same manner as in Example 1, except that the mixed liquid supplied to the reactor was changed to 86 parts by mass of a mixed liquid (1-3) consisting of 70 mass % of methanol and 30 mass % of MMA, and 166 parts by mass of a mixed liquid (2-3) consisting of 14 mass % of methanol and 86 mass % of MMA was obtained as a distillation fraction.
To the mixture (2-3), n-hexane was added as an azeotropic solvent and distilled, and methanol and n-hexane were azeotropically distilled off from the top of the column, and 143 parts by mass of MMA was obtained from the bottom of the column.

[Comparative Example 1]
MMA was produced in the same manner as in Example 1, except that a preliminary purification procedure was performed in which the mixed liquid (1-1) was distilled using n-hexane as an azeotropic solvent before reacting the mixed liquid (1-1) with methacrylamide sulfate in Example 1, and n-hexane and methanol distilled from the top of the column were separated in a decanter to obtain methanol.

As described above, in this production method, MMA is produced by reacting methacrylamide sulfate directly with MMA-containing recovered methanol without purification procedures such as distillation and separation. Therefore, compared to the conventional method in which the MMA-containing recovered methanol undergoes the above-mentioned purification procedures, MMA can be produced more simply and in a shorter process. The recovery rate of MMA by this production method was equivalent to that of the conventional method in which the MMA-containing recovered methanol is purified in advance. Furthermore, in this production method, the amount of azeotropic solvent such as hexane used in the distillation purification of the MMA-containing recovered methanol can be reduced, so MMA can be produced at a lower cost than by the conventional method.

According to the present disclosure, MMA can be produced more simply and at low cost, and various polymers (e.g., PMMA) using the MMA as a raw material monomer can also be produced at low cost. The present disclosure is also applicable to the production of methyl acrylate. In other words, the present production method can also be used as a method for producing methyl (meth)acrylate.

Claims (4)

A method for producing methyl methacrylate by reacting methacrylamide sulfate with methanol, comprising the steps of:
A method for producing methyl methacrylate, comprising the step of adding a mixed liquid (1) having a mass ratio of methanol and methyl methacrylate of 51:49 to 99:1 to methacrylamide sulfate. The method for producing methyl methacrylate according to claim 1 further comprises the step of adding an azeotropic solvent with methanol to the mixture (2) produced in the above step, the mixture having a mass ratio of methanol to methyl methacrylate of 1:99 to 49:51, and distilling off the methanol. The method for producing methyl methacrylate according to claim 1, wherein the mixed liquid (1) is a product of an ester exchange reaction between a high-boiling alcohol and methyl methacrylate. The method for producing methyl methacrylate according to claim 1, wherein the mixed liquid (1) is a product produced in a process for producing methacrylic acid.