JP2000001458A - Method for producing methyl methacrylate - Google Patents

Abstract

(57) [Problem] To provide a method for efficiently producing methyl methacrylate by suppressing accumulation of acetone and loss of methacrolein. SOLUTION: Methacrolein containing acetone is reacted with methanol and an oxygen-containing gas in the presence of a catalyst, and the resulting reaction solution containing at least methyl methacrylate, methacrolein and methanol contains one or more distillation columns. In the methacrolein recovery step, it is separated into a low-boiling substance, a solution containing methacrolein and a solution containing methyl methacrylate, and the low-boiling substance is removed out of the system. In the method for producing methyl methacrylate, which is recycled as a product, the amount of acetone D (g /
h) and the amount of acetone F (g / h) sent to the methacrolein recovery step per unit time as a part of the reaction solution is D /
Operate so that F = 0.015 to 0.250.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing methyl methacrylate by reacting methacrolein with methanol and an oxygen-containing gas in the presence of a catalyst.

[0002]

2. Description of the Related Art In recent years, a method has been proposed in which methacrolein is reacted with methanol and an oxygen-containing gas in the presence of a palladium-based catalyst to obtain methyl methacrylate in one step (hereinafter referred to as an oxidative esterification method). The reaction liquid obtained by the oxidative esterification method is generally a mixture of unreacted methacrolein and a large excess of methanol, and a reaction product such as methyl methacrylate. Unreacted methacrolein is usually recovered and recycled to the reaction for economic reasons.

[0003] In order to recover this unreacted methacrolein without polymerization or conversion to a high boiling point, a reaction solution comprising methacrolein, water, methyl methacrylate and methanol obtained by an oxidative esterification method is first subjected to distillation. Then, a methanol mixture containing substantially no methacrolein and containing methyl methacrylate is obtained from the bottom of the distillation column, and the unreacted methacrolein concentration is recovered as a methanol solution not exceeding 40% by weight from the top or the top of the column. A method is proposed in Japanese Patent Publication No. 2-44294.

Methacrolein, which is a raw material for the oxidative esterification method, is usually produced by subjecting a gas containing tertiary butyl alcohol and / or isobutylene and molecular oxygen to gas phase contact oxidation in the presence of an oxidation catalyst. In the process of oxidation, various organic acids, aldehydes, ketones and the like are produced as by-products.
Acetone, which is one of such by-products, is difficult to completely separate from methacrolein by distillation, extraction, or the like, and even if methacrolein is purified to a purity of 90% or more, it is slightly contained.

When methacrolein containing acetone is used as a raw material for the oxidative esterification method, acetone is sent from the oxidative esterification reactor to a methacrolein recovery step as it is, and is recovered together with unreacted methacrolein. Normal,
Since the recovered unreacted methacrolein is recycled as a raw material for the oxidative esterification reaction, acetone accumulates in the reaction system, and the concentration of the raw material for the oxidative esterification reaction is reduced and / or the residence time is shortened. May decrease.

Japanese Patent Publication No. 2-44294 discloses an example in which a low-boiling substance is removed from the top of a distillation column in a methacrolein recovery step. However, there is no description regarding the problem of acetone as described above, and no consideration is given to acetone in the operating conditions. However, since it is described here that low-boiling substances are removed from the top of the distillation column, if acetone is contained in the raw material methacrolein, some acetone will be removed from the top. . However, depending on the operating conditions,
There is a case where the accumulated amount of acetone is large, or a case where the accumulated amount is small but a lot of methacrolein is removed together with a low boiling point and the loss of methacrolein is large, and it is not always possible to efficiently produce methyl methacrylate. .

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for efficiently producing methyl methacrylate by suppressing the accumulation of acetone and the loss of methacrolein.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to solve such a problem, and as a result, have found that by removing acetone under specific conditions, it is possible to produce methyl methacrylate efficiently. The present invention has been completed.

That is, the present invention provides a reaction solution containing at least methyl methacrylate, methacrolein and methanol obtained by reacting methacrolein containing acetone with methanol and an oxygen-containing gas in the presence of a catalyst.
In a methacrolein recovery step including one or more distillation columns, a low-boiling substance, a solution containing methacrolein and a solution containing methyl methacrylate are separated, and the low-boiling substance is removed out of the system and contains methacrolein. In the method for producing methyl methacrylate, which is recycled as a part of the raw material for the reaction, the amount of acetone D (g / h) removed out of the system in a unit time as a part of a low boiling substance and a part of the reaction liquid Amount of acetone F (g) sent to the methacrolein recovery process per unit time
/ H) is a method for producing methyl methacrylate, which is operated so that D / F = 0.15 to 0.250.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, methacrolein used as a raw material for the oxidative esterification method may be any one containing acetone, and the concentration of acetone is not particularly limited. The method for producing methacrolein containing acetone is not particularly limited. For example, tertiary butyl alcohol and / or isobutylene are oxidized in the gas phase with molecular oxygen in the presence of an oxidation catalyst to remove high-boiling and low-boiling substances in advance. The methacrolein appropriately removed is usually 1 to 4% by weight of acetone,
Since it contains 1 to 4% by weight of acetaldehyde and 2 to 5% by weight of water, it corresponds to methacrolein containing acetone in the present invention.

Hereinafter, the present invention will be described with reference to FIG.
However, FIG. 1 shows an example of a process for carrying out the present invention. In carrying out the present invention, low boiling substances are removed from the reaction solution by distillation, unreacted methacrolein is recovered and oxidized. The process is not particularly limited as long as the process involves recycling to the esterification reactor.

A solution (8) containing methacrolein (3) containing acetone, methanol (4) and recovered methacrolein is continuously fed to the oxidative esterification reactor (1). In FIG. 1, these raw materials are mixed and then supplied to the oxidized esterification reactor (1), but may be directly supplied to the oxidized esterification reactor (1) without mixing. As the type of the oxidative esterification reactor (1), any type such as a stirred tank reactor, a bubble column reactor, a draft tube reactor and the like can be used. The molar ratio of methacrolein: methanol supplied to the reactor is usually from 1: 100 to 1: 1. The oxygen-containing gas (5) supplied to the oxidative esterification reactor (1) is not particularly limited as long as it contains molecular oxygen, and is, for example, a reaction of air, oxygen-enriched air, oxygen, nitrogen and the like. For example, air diluted with an inert gas is used. The method for supplying the oxygen-containing gas is not particularly limited, but is usually supplied into the reaction solution by bubbling or the like. Usually, the supply amount of molecular oxygen is 0.1 to 2 equivalents as oxygen atoms to the raw material methacrolein.

The catalyst for the oxidative esterification reaction is not particularly limited, but usually a palladium-based catalyst is used. Since the amount of the catalyst used depends on the reaction conditions, the activity of the catalyst, and the like, it cannot be determined unconditionally, but it is an amount necessary to achieve a predetermined conversion.

The reaction temperature and reaction pressure of the oxidative esterification reaction are not particularly limited, but the reaction temperature is usually from 0 to 100.
The reaction pressure may be normal pressure, reduced pressure, or increased pressure. Further, in the oxidized esterification reactor (1), the acetone contained and supplied in the raw material methacrolein (3) hardly disappears.

The reaction solution (6) discharged from the oxidation esterification reactor (1) is sent to a methacrolein recovery step including one or more distillation columns. The composition of the main components of the reaction solution (6) is usually 1 to 13% by weight of methacrolein, 3 to 45% by weight of methyl methacrylate, 2 to 10% by weight of water, and 45 to 90% by weight of methanol.

In the step of recovering methacrolein, the reaction solution (6) is a low-boiling substance (7), a solution (8) containing methacrolein,
The solution (9) containing methyl methacrylate is separated, the low-boiling substance (7) is removed out of the system, and the solution (8) containing methacrolein is recycled as a part of the raw material for the oxidative esterification reaction, and methacrylic acid is recycled. The solution (9) containing methyl is sent to the purification step. Here, the low-boiling substance (7) is acetone,
A low-boiling-point compound and methacrolein by-produced in an oxidative esterification reaction such as methyl formate. A solution containing methacrolein (8) is a solution containing methacrolein, methanol and acetone, and a solution containing methyl methacrylate. (9) refers to a solution containing methyl methacrylate substantially free of methacrolein and methanol.

FIG. 1 illustrates a methacrolein recovery step for recovering methacrolein using only one distillation column (2) having a side stream port. The reaction solution is supplied in the middle of the distillation column (2), and low-boiling substances containing acetone are removed from the system as low-boiling substances (7) from the top of the distillation column (2). The solution (8) containing methacrolein is withdrawn from the side stream port and recycled to the oxidative esterification reactor (1). The solution (9) containing methyl methacrylate is withdrawn from the bottom of the distillation column (2) and is separated into methyl methacrylate and methanol by a distillation operation or the like in a purification step to obtain methyl methacrylate. At the same time, the recovered methanol can be recycled as a raw material for the oxidative esterification reaction.

Although not shown in FIG. 1, a methacrolein recovery step in which two or more distillation columns are combined may be used. For example, two distillation columns are combined, and the reaction solution discharged from the oxidized esterification reactor is supplied in the middle of the first distillation column,
Low-boiling substances are removed from the top of the first distillation column to the outside of the system, and the bottom liquid is supplied to the middle of the second distillation column. In the second distillation column, a solution containing methacrolein is used as a top distillate. , The solution containing methyl methacrylate is separated as a bottom solution, the solution containing methacrolein is recycled to the oxidative esterification reactor as in the case of one distillation column, and the solution containing methyl methacrylate is purified in the purification step. Method.

The type of the distillation column used in the methacrolein recovery step is not particularly limited, and a known type such as a plate type or a packed column type may be used. The pressure at the time of distillation is preferably normal pressure or reduced pressure, and it is preferable to operate the column at a temperature of 120 ° C. or lower for preventing polymerization. In the present invention, a substance that easily polymerizes, such as methacrolein and methyl methacrylate, is used, and it is preferable to use a known polymerization inhibitor such as methoxyquinone.

In the present invention, the amount of acetone D (g / h) removed out of the system in a unit time as a part of low boiling matter is determined by the amount of low boiling matter (g / h) removed out of the system in unit time. Is multiplied by the concentration of acetone (% by weight). The amount of acetone F (g / h) sent to the methacrolein recovery step per unit time as a part of the reaction solution is determined by the amount of acetone (g / h) sent to the methacrolein recovery step per unit time. (% By weight).

In the present invention, D / F is D / F = 0.0
15 to 0.250, preferably D / F = 0.020 to
This satisfies the relationship of 0.150. The method for adjusting D and F is not particularly limited, and examples of the method for adjusting D include, for example, adjustment of a reflux ratio when distilling low-boiling substances, and a recycling amount of a solution containing methacrolein to be recycled to a reactor. And the like. The reflux ratio for distilling low-boiling substances is not particularly limited, but it is preferable to operate so as to be 40 or more.

As the D / F becomes smaller, the acetone concentration becomes higher in the reactor, and the yield of methyl methacrylate decreases due to a decrease in methacrolein concentration and / or a decrease in methacrolein conversion due to a shortened residence time. Tend. In addition, the amount of methyl methacrylate in the solution containing methacrolein to be recycled to the reactor increases, which causes problems such as the necessity of extra energy and a large device. On the other hand, when D / F increases, the amount of methacrolein removed from the system together with low-boiling substances such as acetone tends to increase, which is economically disadvantageous.

[0023]

The present invention will be described below in more detail with reference to examples and comparative examples. The analysis of the weight composition of the reaction mixture and the like was performed by gas chromatography. The conversion, the distilling rate, and the reflux ratio were calculated as follows. Conversion rate (%) = (amount of methacrolein lost by reaction / amount of methacrolein supplied to reactor) × 100 Distillation rate (%) = (weight of liquid distilled off from the top / supply to distillation column) (Liquid weight) × 100 Reflux ratio (−) = Amount of liquid refluxed to distillation column / Amount of liquid withdrawn from top of column

Example 1 A low-boiling substance and a high-boiling substance were removed from a reaction product obtained by subjecting isobutylene to gas-phase catalytic oxidation with a molecular oxygen-containing gas in the presence of an oxidation catalyst to obtain acetone. A raw material for methacrolein for oxidative esterification reaction containing 3% by weight and 5.8% by weight of other compounds was obtained.

A catalyst (5% by weight of palladium-1% by weight of lead) was placed in a 3 L flask equipped with a reflux condenser (hereinafter referred to as a reactor).
350 g of a calcium carbonate catalyst containing 1% by weight of iron) were introduced, and 170 g / h of the raw material for the oxidative esterification reaction and 390 g / h of methanol were supplied. The reaction mixture was supplied with 129.5 NL / h air and 142 nitrogen nitrogen. .5N
The reaction was performed at a reaction pressure of 300 kPa (gauge pressure) and a reaction temperature of 80 ° C. while supplying L / h. Reaction solution with an inner diameter of 40
mm, fed to the 20th stage from the top of the Older Shaw distillation column with 50 stages, reflux ratio 70, top pressure 100 kPa
And distills low-boiling substances from the top of the column.
A solution containing methacrolein was withdrawn from the side cut opening at the 0th stage and recycled to the reactor, and a methanol solution of methyl methacrylate substantially free of methacrolein was obtained from the bottom of the column. The distillation rate of the distillation column was set to 1.6%, and D
The operation was performed continuously for 100 hours while adjusting / F to be 0.031.

After 100 hours of operation, the temperature at the top of the distillation column, the side cut opening and the bottom of the distillation column were 45 ° C. and 54 ° C., respectively.
° C and 68 ° C. The composition of the reaction solution supplied to the distillation column was methacrolein 8.9% by weight, methanol 54.4.
Wt%, methyl methacrylate 23.5 wt%, water 6.0
Wt%, acetone 2.6 wt%, other compounds 4.6
%, And the supply rate of the reaction solution to the distillation column was 624 g.
/ H. At this time, the amount of acetone F sent to the methacrolein recovery step per unit time as a part of the reaction solution is 1
6.2 g / h. The composition of the low-boiling matter withdrawn from the top was 31.4% by weight of methacrolein and 2% of methanol.
3.5% by weight, 40.0% by weight of methyl formate, 5.1% by weight of acetone, and the distillation rate of low-boiling substances was 9.8 g / h.
Met. At this time, the amount D of acetone removed out of the system per unit time as a part of low-boiling substances was 0.5 g / h. The composition of the solution containing methacrolein withdrawn from the side cut opening was 40.3% by weight of methacrolein, 45.8% by weight of methanol, 10.8% by weight of acetone, and 3.1% by weight of other compounds. The withdrawal rate of the solution was 130 g / h. The composition of the solution containing methyl methacrylate withdrawn from the bottom was composed of 57.4% by weight of methanol, 29.8% by weight of methyl methacrylate, 7.7% by weight of water and 5.1% by weight of other compounds. The withdrawal rate of this solution was 484 g / h.

When D / F = 0.031, the conversion of methacrolein is 66.4%, and the methacrolein removed as a low-boiling substance out of the system is equivalent to the methacrolein supplied to the reactor. 2.0%.

Comparative Example 1 Example 1 was repeated except that the distilling rate was set to about half (0.8%) of Example 1 so that the D / F was 0.013, and the reflux ratio of the distillation column was 130. The operation was performed under the same conditions as in the above.

After 100 hours of operation, the composition of the reaction solution supplied to the distillation column was 10.4% by weight of methacrolein, 46.6% by weight of methanol, 22.1% by weight of methyl methacrylate, and 10.1% by weight of acetone. The feed rate of the reaction solution to the distillation column was 714 g / h. At this time, the amount of acetone F sent to the methacrolein recovery step per unit time as a part of the reaction solution was 72.1 g / h. The composition of the low-boiling substance withdrawn from the top was 21.7% by weight of methacrolein, 25.8% by weight of methanol and 15.1% by weight of acetone, and the distillation rate of the low-boiling substance was 6 g / h. . At this time, the amount D of acetone removed out of the system per unit time as a part of low-boiling substances was 0.91 g / h. The composition of the solution containing methacrolein withdrawn from the side cut opening is
The amount of methacrolein was 18.3% by weight, the amount of methanol was 48.5% by weight, and the amount of acetone was 17.1% by weight. The liquid was withdrawn at a rate of 400 g / h. The composition of the solution containing methyl methacrylate extracted from the bottom of the column is methanol 4
The content was 4.5% by weight and methyl methacrylate 37.6% by weight, and the withdrawal rate of this solution was 309 g / h.

When D / F = 0.013, the conversion of methacrolein is 59.8%, and methacrolein removed as a low-boiling substance from the system is the same as that of methacrolein supplied to the reactor. 0.74%.

[Comparative Example 2] An operation was performed under the same conditions as in Example 1 except that the distilling rate was set to about 4.5 times (7.2%) of Example 1 so that D / F was 0.264. Was done.

After 100 hours of operation, the composition of the reaction solution supplied to the distillation column was 8.8% by weight of methacrolein, 55.2% by weight of methanol, 24.4% by weight of methyl methacrylate,
Acetone was 1.1% by weight, and the supply rate of the reaction solution to the distillation column was 611 g / h. At this time, the amount of acetone F sent to the methacrolein recovery step as a part of the reaction solution per unit time was 6.77 g / h. The composition of the low-boiling substance withdrawn from the top was 49.3% by weight of methacrolein, 37.3% by weight of methanol and 4.1% by weight of acetone, and the distillation rate of the low-boiling substance was 44 g / h. . At this time, the amount D of acetone removed out of the system per unit time as a part of low-boiling substances was 1.79 g / h. The composition of the solution containing methacrolein withdrawn from the side cut opening is 25.6% by weight of methacrolein, 62.4% by weight of methanol and 7.2% by weight of acetone, and the withdrawal rate of this solution is 125 g / h. there were. The composition of the solution containing methyl methacrylate extracted from the bottom of the column was methanol 55.
0% by weight, 31.6% by weight of methyl methacrylate,
The withdrawal rate of this solution was 442 g / h.

As described above, when D / F = 0.264, the conversion of methacrolein is 67.1%, and methacrolein removed as a low-boiling substance out of the system is equivalent to methacrolein supplied to the reactor. 13.0%.

[0034]

According to the present invention, since accumulation of acetone and loss of methacrolein can be suppressed, methyl methacrylate can be efficiently produced.

[Brief description of the drawings]

FIG. 1 shows an example of a schematic view of an embodiment according to the invention.

[Explanation of symbols]

 (1) Oxidation esterification reactor (2) Distillation tower (3) Methacrolein containing acetone (4) Methanol (5) Oxygen-containing gas (6) Reaction liquid (7) Low boiling matter (8) Contains methacrolein Solution (9) Solution containing methyl methacrylate (10) Gas

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4H006 AA02 AC48 AD11 BA06 BA11 BA19 BA25 BA32 BC38 BD33 BD52 BE30 KA35 4H039 CA66 CC30 CD10

Claims (1)

[Claims] A reaction solution containing at least methyl methacrylate, methacrolein and methanol obtained by reacting methacrolein containing acetone with methanol and an oxygen-containing gas in the presence of a catalyst is passed through one or more distillation columns. In the step of recovering methacrolein containing low-boiling substances, a solution containing methacrolein and a solution containing methyl methacrylate, the low-boiling substances are removed outside the system, and the solution containing methacrolein is used as one of the raw materials for the reaction. In the method for producing methyl methacrylate to be recycled as a part, the amount of acetone D (g /
h) and the amount of acetone F (g / h) sent to the methacrolein recovery step per unit time as a part of the reaction solution is D /
A method for producing methyl methacrylate, which is operated so that F = 0.015 to 0.250.