JP4204097B2 - Method for producing methyl methacrylate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing methyl methacrylate in which methacrolein is reacted with methanol and an oxygen-containing gas in the presence of a catalyst.
[0002]
[Prior art]
In recent years, a method of obtaining methyl methacrylate in one step by reacting methacrolein with methanol and an oxygen-containing gas in the presence of a palladium catalyst (hereinafter referred to as an oxidative esterification method) has been proposed. The reaction liquid obtained by the oxidative esterification method is generally a mixture of unreacted methacrolein and a large excess of methanol, a reaction product such as methyl methacrylate. Unreacted methacrolein is usually recovered and recycled to the reaction in consideration of economy.
[0003]
In order to recover this unreacted methacrolein without polymerization or conversion to a high boiling point product, a reaction liquid comprising methacrolein obtained by the oxidative esterification method, water, methyl methacrylate and methanol is first subjected to distillation, and distilled. A method of obtaining a methanol mixture containing methyl methacrylate substantially free of methacrolein from the tower bottom and recovering from the tower top or tower upper stage as a methanol solution having an unreacted methacrolein concentration of not more than 40% by weight, This is proposed in Japanese Patent Publication No. 2-44294.
[0004]
The methacrolein used as the raw material for the oxidative esterification process is usually produced by subjecting a gas containing tertiary butyl alcohol and / or isobutylene and molecular oxygen to gas phase catalytic oxidation in the presence of an oxidation catalyst. Various organic acids, aldehydes, ketones and the like are by-produced during the process. Acetone, one of such by-products, is difficult to completely separate from methacrolein by distillation or extraction, and is slightly contained even if methacrolein is purified to a purity of 90% or more.
[0005]
When methacrolein containing acetone is used as a raw material for the oxidative esterification method, acetone is sent as it is from the oxidative esterification reactor to the methacrolein recovery step and recovered together with unreacted methacrolein. Normally, the recovered unreacted methacrolein is recycled as a raw material for the oxidative esterification reaction, so that acetone accumulates in the reaction system, resulting in a decrease in the raw material concentration of the oxidative esterification reaction and / or a reduction in residence time. There is a risk that the conversion rate decreases.
[0006]
Japanese Examined Patent Publication No. 2-44294 discloses an example of removing low-boiling substances from the top of a distillation column in the methacrolein recovery step. However, there is no description regarding the problem of acetone as described above, and acetone is not considered 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 included in the raw material methacrolein, some of the acetone will be removed from the top. . However, depending on the operating conditions, there is a case where the accumulation amount of acetone is large, or the accumulation amount is small but a large amount of methacrolein is removed with a low boiling point, resulting in a large loss of methacrolein. Methyl cannot be produced.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for efficiently producing methyl methacrylate while suppressing accumulation of acetone and loss of methacrolein.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve such problems, the present inventors have found that methyl methacrylate can be efficiently produced by removing acetone under specific conditions, and have completed the present invention. .
[0009]
That is, in the present invention, 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 is added to one or more distillation towers. In the methacrolein recovery step, it is separated into a low boiling product, a solution containing methacrolein, and a solution containing methyl methacrylate, the low boiling product is removed out of the system, and the solution containing methacrolein is one of the raw materials for the reaction. In the process for producing methyl methacrylate to be recycled as a part, the amount of acetone D (g / h) removed out of the system as a part of low-boiling substances and the methacrolein recovery step as a part of the reaction solution per unit time It is characterized by operating so that the relationship of the amount of acetone F (g / h) sent to A may become D / F = 0.015-0.250. A method for producing methacrylic acid methyl.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the methacrolein used as a raw material for the oxidative esterification method may be any as long as it contains 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 is subjected to gas phase catalytic oxidation with molecular oxygen in the presence of an oxidation catalyst, so that high-boiling or low-boiling products are previously formed. The appropriately removed methacrolein usually contains 1 to 4% by weight of acetone, 1 to 4% by weight of acetaldehyde, and 2 to 5% by weight of water, and thus corresponds to methacrolein containing acetone in the present invention.
[0011]
Hereinafter, the present invention will be described with reference to FIG. However, FIG. 1 is 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. There is no particular limitation as long as the process includes recycling to an esterification reactor.
[0012]
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 oxidative esterification reactor (1), but they may be supplied directly to the oxidative esterification reactor (1) without mixing. As the form of the oxidative esterification reactor (1), any form 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 fed to the reactor is usually 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. For example, a reaction of air, oxygen-enriched air, oxygen, nitrogen or 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 with respect to the raw material methacrolein.
[0013]
The catalyst for the oxidative esterification reaction is not particularly limited, but a palladium-based catalyst is usually used. The amount of the catalyst used depends on the reaction conditions, the activity of the catalyst, etc., and cannot be generally stated, but is an amount necessary to achieve a predetermined conversion rate.
[0014]
The reaction temperature and reaction pressure of the oxidative esterification reaction are not particularly limited, but the reaction temperature is usually 0 to 100 ° C., and the reaction pressure may be normal pressure, reduced pressure, or increased pressure. In the oxidative esterification reactor (1), acetone supplied in the raw material methacrolein (3) is hardly lost.
[0015]
The reaction liquid (6) exiting from the oxidative esterification reactor (1) is sent to a methacrolein recovery step including one or more distillation towers. The composition of the main components of the reaction liquid (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.
[0016]
In the methacrolein recovery step, the reaction solution (6) is separated into a low boiling point product (7), a solution containing methacrolein (8), and a solution containing methyl methacrylate (9). The solution (8) containing the methacrolein is removed outside and recycled as part of the raw material for the oxidative esterification reaction, and the solution (9) containing methyl methacrylate is sent to the purification step. Here, the low boiling point substance (7) refers to a low boiling point compound and methacrolein by-produced by an oxidative esterification reaction such as acetone and methyl formate, and the solution (8) containing methacrolein refers to methacrolein, methanol and A solution containing acetone and a solution (9) containing methyl methacrylate mean a solution containing methyl methacrylate and methanol substantially free of methacrolein.
[0017]
FIG. 1 illustrates a methacrolein recovery step of recovering methacrolein using only one distillation column (2) having a side stream port. The reaction liquid 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 extracted from the bottom of the distillation column (2) and separated into methyl methacrylate and methanol by a distillation operation or the like in the purification step to obtain methyl methacrylate. The methanol recovered at the same time can be recycled as a raw material for the oxidative esterification reaction.
[0018]
Although not shown in FIG. 1, a methacrolein recovery step in which two or more distillation towers are combined may be used. For example, two distillation columns are combined, the reaction solution from the oxidative esterification reactor is supplied to the middle of the first distillation column, low boilers are removed from the system from the top of the first distillation column, A bottom liquid is supplied in the middle of the second distillation tower, and in the second distillation tower, a solution containing methacrolein is separated as a tower top distillate, and a solution containing methyl methacrylate is separated as a tower bottom liquid, and contains methacrolein. The solution is recycled to the oxidation esterification reactor in the same manner as in the case of one distillation column, and the solution containing methyl methacrylate is purified in the purification step.
[0019]
The type of the distillation column used in the methacrolein recovery step is not particularly limited, and a known type such as a shelf type or a packed column type is used. The pressure during distillation is preferably normal pressure or reduced pressure, and the temperature at the bottom of the column is preferably operated at 120 ° C. or lower in order to prevent polymerization. In the present invention, materials that are easily polymerized such as methacrolein and methyl methacrylate are handled, and it is preferable to use a known polymerization inhibitor such as methoxyquinone.
[0020]
In the present invention, the amount of acetone D (g / h) removed out of the system per unit time as part of the low-boiler is the amount of acetone (g / h) removed out of the system per unit time. Calculated by multiplying by concentration (% by weight). Further, the acetone amount F (g / h) sent to the methacrolein recovery step per unit time as part of the reaction solution is the acetone concentration in the reaction solution amount (g / h) sent to the methacrolein recovery step per unit time. Calculated by multiplying by (% by weight).
[0021]
In the present invention, D and F satisfy D / F = 0.015 to 0.250, preferably D / F = 0.020 to 0.150. The method for adjusting D and F is not particularly limited. Examples of the method for adjusting D include, for example, adjustment of the reflux ratio when distilling low-boiling substances, and the amount of recycled solution containing methacrolein recycled to the reactor. Adjustment and the like. The reflux ratio when distilling the low boilers is not particularly limited, but it is preferable to operate so as to be 40 or more.
[0022]
When the D / F decreases, the acetone concentration in the reactor increases, and the yield of methyl methacrylate tends to decrease due to a decrease in methacrolein concentration and / or a reduction in methacrolein conversion due to a reduction in residence time. . In addition, the amount of methyl methacrylate in the solution containing methacrolein recycled to the reactor increases, resulting in problems such as extra energy and large equipment. On the other hand, when the D / F increases, the amount of methacrolein removed out of the system together with low-boiling substances such as acetone tends to increase, which is economically disadvantageous.
[0023]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The weight composition of the reaction mixture was analyzed by gas chromatography. The conversion rate, distillation rate, and reflux ratio were calculated as follows.
Conversion (%) = (amount of methacrolein lost by reaction / amount of methacrolein fed to the reactor) × 100
Distillation rate (%) = (weight of liquid distilled from the top of the column / weight of liquid supplied to the distillation tower) × 100
Reflux ratio (−) = amount of liquid refluxed to the distillation column / amount of liquid withdrawn from the top of the column
[Example 1]
From the reaction product obtained by gas phase catalytic oxidation of isobutylene with a molecular oxygen-containing gas in the presence of an oxidation catalyst, low and high boilers are removed to obtain 2.3 wt% acetone and other compounds 5 The raw material methacrolein for oxidative esterification reaction containing 0.8% by weight was obtained.
[0025]
350 g of a catalyst (calcium carbonate catalyst containing 5% by weight of palladium, 1% by weight of lead, and 1% by weight of iron) is placed in a 3 L flask equipped with a reflux condenser (hereinafter referred to as a reactor), and the raw material for the above oxidative esterification reaction It was supplied at 170 g / h for methacrolein and 390 g / h for methanol, and reacted at a reaction pressure of 300 kPa (gauge pressure) and a reaction temperature of 80 ° C. while supplying air 129.5 NL / h and nitrogen 142.5 NL / h into the reaction solution. It was. The reaction liquid is supplied to the 20th stage from the top of an Oldershaw type distillation column having an inner diameter of 40 mm and 50 stages, and distilled at a reflux ratio of 70 and a pressure at the top of the column of 100 kPa to distill low-boiling substances from the top of the tower. The solution containing methacrolein was extracted from the side cut port at the 10th stage from the top of the tower and recycled to the reactor to obtain a methanol solution of methyl methacrylate substantially free of methacrolein from the bottom of the tower. The distillation column was distilled at a distillation rate of 1.6% and adjusted so that D / F was 0.031, and the operation was continued for 100 hours.
[0026]
The temperatures at the top of the distillation column, the side cut port and the bottom of the column after 100 hours of operation were 45 ° C, 54 ° C and 68 ° C, respectively. The composition of the reaction solution supplied to the distillation column was methacrolein 8.9 wt%, methanol 54.4 wt%, methyl methacrylate 23.5 wt%, water 6.0 wt%, acetone 2.6 wt%, The other compound was 4.6% by weight, and the supply rate of the reaction solution to the distillation column was 624 g / h. At this time, the acetone amount F sent to the methacrolein recovery step as a part of the reaction solution per unit time was 16.2 g / h. The composition of low boilers extracted from the top of the column was methacrolein 31.4% by weight, methanol 23.5% by weight, methyl formate 40.0% by weight and acetone 5.1% by weight. The speed was 9.8 g / h. At this time, the amount D of acetone removed from the system as a part of low boiling substances per unit time was 0.5 g / h. The composition of methacrolein extracted from the side cut port was methacrolein 40.3% by weight, methanol 45.8% by weight, acetone 10.8% by weight, and other compounds 3.1% by weight. The solution withdrawal rate was 130 g / h. The composition of the methyl methacrylate extracted from the bottom of the column is 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 extraction rate of this solution was 484 g / h.
[0027]
Thus, when D / F = 0.031, the methacrolein conversion rate was 66.4%, and methacrolein removed out of the system as a low-boiling product was 2.0% of methacrolein fed to the reactor. %Met.
[0028]
[Comparative Example 1]
The operation was performed under the same conditions as in Example 1 except that the distillation rate was about half (0.8%) of Example 1 and the reflux ratio of the distillation column was 130 so that the D / F was 0.013. .
[0029]
After 100 hours of operation, the composition of the reaction solution fed to the distillation tower was methacrolein 10.4 wt%, methanol 46.6 wt%, methyl methacrylate 22.1 wt%, acetone 10.1 wt% The supply rate of the reaction liquid to the tower was 714 g / h. At this time, the acetone amount F sent to the methacrolein recovery step as a part of the reaction solution per unit time was 72.1 g / h. The composition of the low boiler extracted from the top of the column was 21.7 wt% methacrolein, 25.8 wt% methanol, and 15.1 wt% acetone, and the distillation rate of the low boiler was 6 g / h. . At this time, the amount of acetone D removed out of the system as a part of the low boilers was 0.91 g / h. The composition of the solution containing methacrolein extracted from the side cut opening is 18.3% by weight of methacrolein, 48.5% by weight of methanol, and 17.1% by weight of acetone. The extraction rate of this solution is 400 g / h. there were. The composition of the solution containing methyl methacrylate extracted from the column bottom was 44.5% by weight of methanol and 37.6% by weight of methyl methacrylate, and the extraction rate of this solution was 309 g / h.
[0030]
Thus, when D / F = 0.013, the methacrolein conversion rate was 59.8%, and methacrolein removed out of the system as a low-boiling product was 0.74 of methacrolein fed to the reactor. %Met.
[0031]
[Comparative Example 2]
The operation was performed under the same conditions as in Example 1 except that the distillation rate was about 4.5 times (7.2%) of Example 1 so that D / F was 0.264.
[0032]
After 100 hours of operation, the composition of the reaction solution supplied to the distillation tower was methacrolein 8.8 wt%, methanol 55.2 wt%, methyl methacrylate 24.4 wt%, acetone 1.1 wt%, The supply rate of the reaction liquid to the tower was 611 g / h. At this time, the acetone amount 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 boilers extracted from the top of the column was methacrolein 49.3% by weight, methanol 37.3% by weight, acetone 4.1% by weight, and the low boilers distillation rate was 44 g / h. . At this time, the amount of acetone D removed out of the system per unit time as a part of the low boiling point was 1.79 g / h. The composition of methacrolein extracted from the side cut port was methacrolein 25.6% by weight, methanol 62.4% by weight, and acetone 7.2% by weight. The extraction rate of this liquid was 125 g / h. there were. The composition of the solution containing methyl methacrylate extracted from the column bottom was 55.0% by weight of methanol and 31.6% by weight of methyl methacrylate, and the extraction rate of this solution was 442 g / h.
[0033]
Thus, when D / F = 0.264, the methacrolein conversion was 67.1%, and methacrolein removed out of the system as a low-boiling product was 13.0 of methacrolein fed to the reactor. %Met.
[0034]
【The invention's effect】
According to the present invention, accumulation of acetone and loss of methacrolein can be suppressed, so that methyl methacrylate can be produced efficiently.
[Brief description of the drawings]
FIG. 1 shows an example of a schematic diagram of an embodiment according to the present invention.
[Explanation of symbols]
(1) oxidation esterification reactor (2) distillation column (3) methacrolein containing acetone (4) methanol (5) oxygen-containing gas (6) reaction liquid (7) low boiling product (8) including methacrolein Solution (9) Solution containing methyl methacrylate (10) Gas

Claims (1)

A methacrolein recovery step including reacting 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, and containing one or more distillation towers The solution is separated into a low-boiling product, a solution containing methacrolein and a solution containing methyl methacrylate, the low-boiling product is removed out of the system, and the solution containing methacrolein is recycled as a part of the raw material of the reaction. In the method for producing methyl acid, the amount of acetone D (g / h) removed from the system per unit time as a part of low-boiling substances and the amount of acetone sent to the methacrolein recovery step per unit time as part of the reaction solution The methyl methacrylate is operated so that the relationship of F (g / h) is D / F = 0.015 to 0.250 Manufacturing method.

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