JP2859682B2 - Purification method and production method of methyl methacrylate - Google Patents

Description

The present invention relates to a method for purifying and producing methyl methacrylate (hereinafter abbreviated as MMA).

[Conventional technology]

MMA is produced by esterifying methacrylic acid (hereinafter abbreviated as MAA) or methacrylamide with methanol in the presence of sulfuric acid or a strongly acidic ion exchange resin.

In the crude MMA (MMA containing impurities) obtained from this esterification step, in addition to water produced by the reaction, unreacted methanol and MAA, methyl acrylate (hereinafter abbreviated as MA) caused by impurities in the raw materials. ), And a small amount of low boiling point impurities such as methyl propionate (hereinafter abbreviated as MP).

These impurities and MMA have close boiling points or form an azeotrope with each other, so that it is impossible to separate MMA by ordinary distillation.

As a method of separating MMA from coarse MMA, for example, coarse MM
A method for removing the methanol in A by azeotropic distillation using a hydrocarbon (JP-A-57-9740, 58-180457, 58-180457)
-203940) and a method for removing methanol in crude MMA by extractive distillation using water as an extractant (Japanese Patent Application Laid-Open No. 54-2481).
2) Alternatively, a method has been proposed in which MMA is extracted and separated using water and a hydrocarbon as an extractant (JP-A-54-24814).

[Problems to be solved by the invention]

In recent years, with the development of optoelectronics, methacrylic resins have been used in a large amount in this field, and high-quality qualities have been demanded not only in mechanical and chemical performance but also in optical performance. However, conventional MMA manufacturing methods are not sufficiently satisfactory in terms of process and economy, and even with these methods, it is possible to sufficiently remove impurities that are an obstacle to obtain high-purity MMA. Can not. Particularly in industrial processes, the active ingredient is usually recovered and recycled for economic reasons.Thus, even if trace amounts of impurities are not completely removed, they are gradually accumulated in the process and deteriorate in product quality unless they are completely removed. Cause

An object of the present invention is to provide an excellent MMA production method capable of obtaining high-purity MMA in a high yield as compared with a conventional MMA production method.

Another object of the present invention is to provide a method without loss of MMA.
An object of the present invention is to provide a method for purifying MMA which can remove water, methanol, low boiling impurities such as MA and MP almost completely, and a method for producing MMA having this method.

A further object of the present invention is to purify MMA having a method for recovering methanol, which enables the recovery of methanol free from impurities such as MA and MP, which are obstacles as a raw material for MMA production, and prevents the accumulation of harmful impurities in the process. And a manufacturing method.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve such a problem, and as a result, by distilling crude MMA in the presence of hexane, water, methanol, M
A, MP and other low boiling point impurities can be almost completely removed;
Furthermore, by distilling the aqueous solution containing these low-boiling impurities after alkali treatment, it is possible to collect methal that does not contain impurities such as MA and MP, which are obstacles to MMA production raw materials, preventing the accumulation of harmful impurities in the process. It has been found that the present invention can be performed and the present invention has been completed.

That is, the present invention azeotropically distills a mixture containing water, methanol, and MMA as main components and containing at least one of MA, MP, and MAA together with hexane to obtain water, methanol, MA, and MPA. And a high-boiling fraction substantially free of hexane and containing MMA as a main component, water, methanol and hexane as main components, MA and
An azeotropic distillation step of obtaining a low-boiling fraction containing at least one of MPs; a step of cooling the low-boiling fraction to obtain a condensate; a step of separating the condensate into an aqueous phase and an oil phase A step of adding an alkaline substance to the aqueous phase; a step of recovering methanol by distilling the aqueous phase to which the alkaline substance has been added; and a step of using the oil phase as a source of hexane used for the azeotropic distillation. Is a method for purifying MMA.

Further, the present invention provides a method for recovering methanol which can be suitably applied to the production of MMA, that is, a method comprising adding an alkaline substance to a mixture containing water and methanol as main components and containing at least one of MA and MP. And a method for purifying MMA including a method for recovering methanol by distilling this mixture to recover methanol.

Further, the present invention provides a method of esterifying at least one selected from the group consisting of MAA and methacrylamide with methanol, comprising water, methanol and MMA as main components, and converting at least one of MA, MP and MAA. The method also includes a method for producing MMA, in which the resulting mixture is obtained, and the mixture is subjected to a method for purifying MMA containing up to the above-mentioned recovery of methanol.

Hexane used in the present invention forms the lowest azeotrope with water and methanol in the crude MMA, thus facilitating the removal of these impurities.

When the crude MMA is distilled without using hexane, the following problems occur. That is, the MMA itself functions as an entrainer and is azeotropically distilled with water and methanol, so that the polymerizable MMA circulates through the distillation column, which is likely to cause polymerization trouble. Further, since the difference in specific gravity between the water phase and the oil phase of the condensate obtained by condensing the distillate distilled off from the top of the column is small, it becomes difficult to separate the condensate. Furthermore,
Since the proportion of impurities such as MA and MP in the condensate is distributed into the aqueous phase is small, the amount of the impurities discharged out of the system together with the aqueous phase is reduced, and the amount circulated and accumulated in the process is increased. .

These disadvantages are solved by using hexane as an entrainer. In this case, the overhead distillate is distilled at a lower temperature, and the polymerization trouble is reduced because MMA is hardly contained therein. Further, since the specific gravity difference between the aqueous phase and the oil phase of the condensate is sufficiently large, the condensate is easily separated. Furthermore, since the distribution of low boiling impurities such as MA and MP to the aqueous phase is improved in a more advantageous direction, the impurities can be easily discharged out of the system.

The aqueous phase discharged out of the distillation column system contains methanol, which is a raw material for esterification. Since methanol and MA or MP mutually form a minimum azeotrope, it is not possible to recover only methanol by distillation.

The present invention further relates to a method for effectively recovering the methanol in the aqueous phase, wherein the aqueous phase is treated with an alkaline substance and then subjected to distillation, so that methanol which does not contain impurities which are a hindrance as an MMA production raw material is not contained. Can be recovered, and MA and MP can be prevented from accumulating and circulating in the process.

 Hereinafter, the present invention will be described in more detail.

In the present invention, the crude MMA is a crude MMA component obtained by esterifying MAA or methacrylamide with methanol. The esterification is performed at 60-130 ° C. From the viewpoint of simplicity of the process and energy consumption, it is desirable to subject the crude MMA to water, methanol and MAA which have been previously or partially or mostly removed according to a known method, and subject them to the purification method of the present invention. The crude MMA used in the purification method of the present invention is water 2
~ 10% (hereinafter,% is represented by weight), methanol 2 ~
15%, MAA 2% or less, MA or MP each 1% or less and MMA75
Mixtures containing ~ 95% are preferred.

The crude MMA is distilled in the presence of hexane by a distillation means represented by a distillation column.

During this distillation, it is necessary to use a sufficient amount of hexane to distill the water, methanol, etc. contained in the crude MMA by azeotropic distillation, but it was actually separated from the low boiling fraction as described later. What is necessary is just to replenish the distillation column by refluxing the oil phase.

The amount of hexane to be replenished to the distillation column is preferably 17 to each of the weight of water and methanol supplied to the distillation column.
The range is not less than the total amount of the double amount and the triple amount, and is not more than the total amount of the 50 times amount and the 10 times amount. If the amount of hexane used is less than the lower limit, MMA is distilled off in the top distillate, which is not preferable. Although the use amount of hexane may exceed the upper limit, there is no problem, but there is no merit.

The azeotropic distillation is preferably performed under normal pressure or reduced pressure. MM
To prevent the polymerization of A, it is desirable to lower the operating pressure, but if the operating pressure is too low, the equipment becomes large, and the use of a low-temperature refrigerant is required because the condensation temperature of the low-boiling fraction decreases. Therefore, it is preferable to perform distillation in the range of 760 to 300 mmHg. The tower top temperature at this time is 63-37 ° C
It is.

A bottoms substantially free of water, methanol, MA and MP is obtained as a high-boiling fraction from the bottom of the column. This high-boiling fraction still contains a small amount of MAA and high-boiling impurities, but impurities close to MMA and boiling points near MMA.
Since water forming an azeotrope with A has already been removed, high-purity MMA can be obtained by subjecting it to distillation again.

The low-boiling fraction mainly composed of hexane is preferably 5
After being cooled and condensed at ~ 35 ° C, it is separated into an aqueous phase and an oil phase in a reflux drum. Where the raw MMA
When the water content is small, it may be difficult to separate the two layers, but an aqueous phase can be formed by pouring water into a reflux drum. Most of hexane is distributed to the oil phase, most of water and methanol are distributed to the aqueous phase, and impurities such as MA and MP are distributed to both phases according to their partition coefficients. Here, the addition of water not only facilitates two-phase separation, but also methanol, MA and oil in the oil phase.
It has the effect of lowering the concentration of MP. By refluxing the oil phase containing hexane as a main component to the distillation column, the amount of hexane used can be minimized and impurities can be efficiently removed.

By discharging the aqueous phase out of the system, low boiling impurities such as MA and MP separated from the crude MMA can be removed together with water.

The aqueous phase is treated with an alkaline substance and the methanol is recovered by further distillation. As the alkaline substance, sodium hydroxide or potassium hydroxide is preferably used. The amount of the alkaline substance used may be an amount necessary for hydrolyzing the carboxylic acid esters contained in the aqueous phase, i.e., MA, MP, etc. to form a corresponding carboxylate, and adding the carboxylic acid. It is preferred to use one to two times the molar amount of the ester. These alkali components are separated in the reflux drum and can be added at any stage before the aqueous phase is subjected to distillation for methanol recovery. The hydrolysis reaction is completed while staying in the distillation column, but in order to promote the hydrolysis of the carboxylic acid ester, the aqueous phase to which the alkaline substance has been added is preliminarily heated at normal temperature to 60 ° C. and then supplied to the distillation column. It is desirable to do. Distillation for recovering methanol is performed under normal pressure, and methanol free of MA and MP can be recovered as a low boiling fraction.

〔Example〕

One embodiment of the present invention will be described more specifically with reference to FIG. 1, but the present invention is not limited to the following embodiment.

First crude MMA containing water, methanol, MA, MP and MAA
The distillation column 1 (inner diameter 150 mm, height 10 m, filled with 1/4 inch bell saddle) is supplied from the conduit 10 to the middle stage, and the operating pressure is 500 mm Hg, the top temperature is 54 ° C., the bottom temperature is 90 ° C. Distillation was performed under the condition of total reflux. The water, methanol, MA and MP in the crude MMA of the raw material are distilled off from the top through the conduit 12 together with hexane supplied from the conduit 14, condensed in the condenser 3, and then condensed in the condenser 3, followed by the reflux drum 4 To separate two layers. The oil phase mainly composed of hexane was refluxed to the upper stage of the first distillation column 1, and the aqueous phase mainly composed of water was discharged from the conduit 15 to the next hydrolysis tank 5. From the bottom of the first distillation column 1, MMA containing a small amount of MAA and a high boiling component without water and a low boiling component is obtained through a conduit 11,
By subjecting this MMA to precision distillation (not shown), high-purity MMA could be obtained.

An aqueous solution of 20% by weight of sodium hydroxide was supplied to the hydrolysis tank 5 from a conduit 16 and maintained at a pH of 13 to 13.5 at room temperature for 30 minutes. The hydrolyzed aqueous phase is supplied through a conduit 17 to the middle stage of the second distillation column 6 (inner diameter 80 mm, height 5 m, filled with 1/4 inch bell saddle), and at normal pressure, the top temperature of the column is 64 ° C. and the bottom temperature is 10
Distillation was performed under the conditions of 0 ° C. and a reflux ratio of 4, and a methanol fraction 21 substantially free of MA and MP was recovered from the top of the column. Table 1 shows the amount of liquid in the main conduit for each component.

[Effects of the Invention] Methyl acrylate, low-boiling impurities such as methyl propionate and methanol and water which are difficult to separate by azeotropic distillation with methyl methacrylate are efficiently removed from methyl methacrylate by the method of the present invention. Can be recycled and used without accumulating in the process, and high-purity MMA can be produced efficiently.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of an embodiment of the present invention. 1: 1st distillation column, 2, 7: heater 3, 8: condenser, 4: reflux drum 5: hydrolysis tank, 6: second distillation column 9: receiving tank, 10-21: conduit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Minoru Koshibe 1-5-8 Tsutsuyamadai, Tondabayashi-shi, Osaka (56) References JP-A-57-9739 (JP, A) JP-A-2-188540 ( JP, A) JP-A-49-116014 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C07C 69/54 C07C 67/54 C07C 31/04 C07C 29/80 WPI / L (QUESTEL) CA (STN)

Claims (11)

(57) [Claims] An azeotropic distillation of a mixture comprising water, methanol and methyl methacrylate as main components and containing at least one of methyl acrylate, methyl propionate and methacrylic acid together with hexane, A high-boiling fraction essentially free of water, methanol, methyl acrylate, methyl propionate and hexane and containing methyl methacrylate as a main component, and a water-, methanol- and hexane-main component containing methyl acrylate and propionic acid An azeotropic distillation step of obtaining a low-boiling fraction containing at least one of methyl, a step of cooling the low-boiling fraction to obtain a condensate, and a step of separating the condensate into an aqueous phase and an oil phase A step of adding an alkaline substance to the aqueous phase, a step of recovering methanol by distilling the aqueous phase to which the alkaline substance has been added, and Method for purifying methyl methacrylate having a process using the oil phase as a source of hexane for use in the azeotropic distillation. 2. The method according to claim 1, further comprising the step of adding water to the condensate before the step of separating the condensate into an aqueous phase and an oil phase. 3. The method according to claim 1, wherein in the step of adding an alkaline substance to the aqueous phase, sodium hydroxide or potassium hydroxide is selected as the alkaline substance. 4. The method according to claim 1, wherein a low-boiling fraction is separated in the range of 63 to 37 ° C. in the azeotropic distillation step. 5. The azeotropic distillation step, wherein hexane is at least 17 times water and at least 3 times the amount of methanol on a weight basis;
The method according to claim 1, wherein the method is used in a range of not more than 50 times the amount of water and 10 times the amount of methanol. 6. A process for recovering methanol by distilling the aqueous phase to which the alkaline substance has been added, wherein the main component is water and methanol, and at least one of methyl acrylate and methyl propionate is contained. The method according to claim 1, wherein after adding an alkaline substance to the mixture, the mixture is distilled to recover methanol. 7. The method according to claim 6, wherein sodium hydroxide or potassium hydroxide is selected as said alkaline substance. 8. At least one selected from the group consisting of methacrylic acid and methacrylamide is esterified with methanol to form water, methanol and methyl methacrylate as main components, and methyl acrylate, methyl propionate and methacrylic acid. Obtaining a mixture containing at least one of the acids: azeotropically distilling the mixture with hexane to obtain a mixture substantially free of water, methanol, methyl acrylate, methyl propionate and hexane, and methyl methacrylate An azeotropic distillation step of obtaining a high-boiling fraction having as a main component water and a low-boiling fraction containing water, methanol and hexane as main components and containing at least one of methyl acrylate and methyl propionate; A step of cooling the low-boiling fraction to obtain a condensate; a step of separating the condensate into an aqueous phase and an oil phase Adding an alkaline substance to the aqueous phase, distilling the aqueous phase to which the alkaline substance has been added to recover methanol, and using the oil phase as a source of hexane used for the azeotropic distillation. A method for producing methyl methacrylate having a step. 9. In the azeotropic distillation step, hexane is used in a range of not less than 17 times of water and 3 times of methanol, and not more than 50 times of water and 10 times of methanol, based on weight. The method according to claim 8. 10. The process of recovering methanol by distilling the aqueous phase to which the alkaline substance has been added, wherein the main component is water and methanol, and at least one of methyl acrylate and methyl propionate is contained. The method according to claim 8, wherein after adding the alkaline substance to the mixture, the mixture is distilled to recover methanol. 11. The method according to claim 10, wherein sodium hydroxide or potassium hydroxide is selected as said alkaline substance.