JPH0239496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously producing acrylic ester or methacrylic ester from acrylic acid or methacrylic acid and a lower aliphatic alcohol using a strongly acidic cation exchange resin as a catalyst.

More specifically, in the present invention, when producing an acrylic ester or a methacrylic ester by reacting acrylic acid or methacrylic acid with a lower aliphatic alcohol using a strongly acidic ion exchange resin as a catalyst, the esterification reactor is used for the first reaction. In a steady state, the first reactor uses the new acrylic acid or methacrylic acid and alcohol in a molar ratio of 1.1:1 to 11.1 to achieve a reaction conversion rate of 60 to 90. %, and the resulting first reactor reaction product is directly sent to the recovery and purification system to recover acid and alcohol in an amount greater than the amount of unreacted acrylic acid or methacrylic acid and alcohol in the first reactor. is circulated between the recovery and purification system and the second reactor, and the reaction conversion rate in the second reactor is 40 to 70%.
(recycled acrylic acid or methacrylic acid standard),
The reaction temperature for both the first reactor and the second reactor is 60~
Production of acrylic ester or methacrylic ester, characterized by reacting substantially 100% of acrylic acid or methacrylic acid and alcohol supplied to a first reactor by reacting at 110°C for a residence time of 0.3 to 3 hours. It is about the method.

The recovery and purification system in the present invention refers to a reaction product separation and purification process such as an acrylic acid or methacrylic acid recovery process, a lower aliphatic alcohol recovery process, an extraction process, and a dehydration process.

Furthermore, in the present invention, the molar ratio of acrylic acid or methacrylic acid and alcohol in the first reactor is
The range is 1.1:1 to 1:1.1, but this is not only when using equimolar moles of alcohol to acrylic acid or methacrylic acid, but also when alcohol or acid (acrylic acid or This refers to the use of a slight excess (up to 10% excess) of alcohol or acid to supplement methacrylic acid.

When carrying out the esterification reaction, the method of using a strongly acidic cation exchange resin as a catalyst is suitable for column-type flow reaction, and it is easy to operate continuously and does not mix the catalyst acid into the reaction solution, making the subsequent purification process advantageous. This is a preferred method because it is easy to implement. On the other hand, the esterification reaction is a reversible reaction, and in order for the reaction to proceed sufficiently, the produced water or ester must be removed from the reaction system, or one of the raw materials, acid or alcohol, must be used in large excess. However, a one-pass reaction cannot increase the reaction rate sufficiently.

Therefore, various improvements have been proposed for industrial implementation of column flow reactions in which it is difficult to remove reaction products from the reaction system. That is, a method in which unreacted acrylic acid or methacrylic acid from the reaction solution is recycled to the first reactor or the reaction is further advanced in the second reactor (Japanese Patent Publication No. 48-1369, Publication No. 54-106412, Publication No. 55- 62047), method of using in combination with ordinary acid catalysts such as sulfuric acid (Japanese Patent Publication No. 49-38254),
There is a method in which the reaction system is made into a gas-liquid mixed phase, and the produced water and ester are vaporized to shift the equilibrium and the reaction proceeds (Publication Publication No. 55-122740). However, in order to carry out the esterification reaction industrially advantageously, it is necessary to have a high conversion rate of the raw material acrylic acid or methacrylic acid to ester, to reduce and recover the amount of alcohol used, to be easy to reuse, to use a solvent, etc. The methods described in the above-mentioned patents have advantages and disadvantages, such as not using any chemicals, simple steps, and easy operation.

The inventors of the present invention have taken these matters into consideration and have made extensive studies. By functionally combining the esterification reaction system and the recovery and purification system, the present inventors have achieved a high conversion rate of acrylic acid or methacrylic acid to ester, and the use of alcohol. We have invented an advantageous method for producing acrylic esters or methacrylic esters, which has features such as reduced quantity, ease of recovery and reuse, and no use of components other than reaction-related substances. This will be explained in detail below. For convenience, the following explanation will be made regarding acrylic esters, but the same applies to methacrylic esters. Note that methacrylic acid was specifically explained in Examples.

According to the present invention, the esterification reactor includes a first reactor and a second reactor. The esterification reactor is of a tubular type and is filled with a strongly acidic ion exchange resin as a solid acid catalyst. The reaction is carried out at elevated temperature. First, novel acrylic acid and alcohol are fed to the first reactor in a molar ratio of 1.1:1 to 1:1.1.
The reaction conversion rate varies depending on the type of ester, but 60
~90%. The reactant is combined with a reactant in a second reactor, which will be described later, and processed in a recovery and purification system. The recovered acrylic acid and alcohol are separated into their respective components in the recovery and purification system, and are circulated to the second reactor, where the reactants are combined with the reaction liquid in the first reactor and treated in the recovery and purification system, as described above.

In other words, the gist of the present invention can be summarized as follows.

(1) The molar ratio of acrylic acid and alcohol supplied to the first reactor is substantially 1 (1.1:1 to 1:1.1)
It is.

(2) The reactants in the first reactor and second reactor are combined and treated in a recovery and purification system.

(3) The recovered unreacted acrylic acid and alcohol as well as the accompanying ester and water are
Feed to reactor.

To explain in more detail, in the first reactor, the molar ratio of acrylic acid and alcohol is substantially 1 (1.1:1).
Since the reaction conversion rate is fixed at ~1:1.1), the reaction conversion rate can be set freely within the range of the equilibrium conversion rate, but it is set at 60 to 90% in consideration of aging properties and deterioration of the ion exchange resin. Set. In the second reactor, the equilibrium conversion rate is determined by the amount of alcohol and the ratio of the recovered acrylic acid to the four components of ester and water that are inevitably accompanied when the alcohol and acrylic acid are recovered. Conversely, the required amount of alcohol is determined by determining the conversion rate in the second reactor. This is the aim of the present invention. That is, the acrylic acid and equimolar amount of alcohol supplied to the first reactor are substantially
In order to generate ester and water through 100% reaction, it is necessary to convert unreacted acrylic acid and alcohol in the first reactor into ester and water in the second reactor. However, since the conversion rate in the second reactor cannot be 100%, accumulation of circulating acrylic acid and alcohol occurs in the early stages of operation, but becomes constant in steady state. I will explain in detail.

The conversion rate in the first reactor is set to 70%, the conversion rate in the second reactor is set to 50% (based on circulating acrylic acid),
If the amount of acrylic acid (and alcohol) supplied to the first reactor is 1 mole, the amount of unreacted acrylic acid (and alcohol) is 0.3 mole. In order for 0.3 mol of unreacted acrylic acid (and alcohol) to completely react in the second reactor, the following equation holds true, assuming that the amount of circulating (accumulated) acrylic acid (and alcohol) is X mol.

0.3=X×0.5 ∴X=0.6 In other words, for every 1 mole of acrylic acid (and alcohol) supplied to the first reactor, 0.6 mole of acrylic acid (and alcohol) is supplied to the second reactor ~
It will be circulated through the recovery and purification system. Here, the amount of alcohol to achieve 50% conversion in the second reactor is the amount of acrylic acid supplied to the first reactor because of the ester and water that inevitably accompany the recovery and purification system. Since equimolar amounts of alcohol are insufficient, it is necessary to use an excess amount. This excess alcohol is only added at the beginning of operation, and in steady state it is circulated from the second reactor to the recovery and purification system. However, if alcohol is lost due to side reactions such as ether or distillation loss, it may be added at any time. The amount of alcohol added in excess can be determined by trial and error based on liquid-liquid equilibrium, distillation conditions, etc. of the amount of ester and water entrained from the recovery and purification system.

The features of the present invention have been described above, and the advantages of the present invention can be listed as follows.

(1) Since the acrylic acid and alcohol supplied to the first reactor are essentially 100% reacted, the raw materials supplied to the first reactor can always be fresh, so they are stable. It is possible to operate the plant by doing so.

(2) In the present invention, the acrylic acid and alcohol recycled to the second reactor may be accompanied by ester and water to some extent. Since the presence of ester and water, which are reaction products, is disadvantageous in the equilibrium reaction,
In the esterification production process in which an azeotrope is formed between each reaction liquid composition, separation of each component is extremely difficult and has become an important problem.

(3) Less alcohol consumption.

As mentioned above, the conversion rate in the second reactor can be set freely, but if the conversion rate is increased too much, the amount of alcohol used will increase. On the other hand, lowering the conversion rate too much is inappropriate because the amount of acrylic acid circulated increases. It has been found that the amount of alcohol used can be extremely reduced by setting the reaction conversion rate in the second reactor to 40 to 70% (based on circulating acrylic acid). It is clear that the use of less alcohol has significant benefits in subsequent purification steps.

In carrying out the present invention, a polystyrene-based sulfonic acid type cation exchange resin or the like can be used as the strongly acidic ion exchange resin as the esterification catalyst. Examples include Amberlite (manufactured by Rohm and Haas), Dowex (manufactured by Dow Chemical Company), and Diaion (manufactured by Mitsubishi Chemical Corporation).

The reaction temperature for the esterification reaction is preferably low from the viewpoint of stability of the ion exchange resin, polymerization of monomers, and reduction of by-product formation, but it is not preferable to make it too low from the viewpoint of reaction rate, so it is usually
A temperature of 60 to 110°C, particularly 70 to 100°C, gives preferable results.

The reaction pressure is usually sufficient to keep the reaction system in a liquid state at the reaction temperature used, but depending on the type of ester, the reaction system can be mixed into a gas-liquid phase at normal pressure or reduced pressure in cases where the resin does not deteriorate. In this case, the reaction conversion rate can be greatly improved, so it may be preferable.

The esterification reaction is carried out in the presence of a polymerization inhibitor. As the polymerization inhibitor, phenothiazine, hydroquinone, hydroquinone monomethyl ether, etc. are used. The amount used is usually 0.001 to 1% by weight based on acrylic acid.

The reaction time is 0.3~ for both the first reactor and the second reactor.
The duration is 3 hours, preferably 0.5 to 2 hours.

The reaction conversion rate of each reactor is 60 to 90 in the first reactor.
%, and in the second reactor it is set at 40-70% (based on circulating acrylic acid). Each reactor has a constant residence time in order to maintain a constant production volume, but by adjusting the reaction temperature it is possible to easily achieve a set conversion rate.

The reactants in the first reactor and the second reactor are combined and treated in an acrylic acid recovery distillation column to recover unreacted acrylic acid. In this case, by operating the distillation column appropriately, a bottoms consisting of almost all of the unreacted acrylic acid and a small amount of water is collected from the bottom of the column, and from the top of the column, ester, alcohol, and water containing almost no acrylic acid are collected. A mixed liquid consisting of the following can be distilled out. It is preferable that the amount of water left at the bottom of the column is such as to bring the liquid temperature to 75 to 110°C at the operating pressure.
The acrylic acid collected from the bottom of the column is recycled to the second reactor for reuse, but a portion of it is treated with a vacuum evaporator, such as a film evaporator, to remove by-products and polymers from the system. The mixed solution of ester, alcohol, and water distilled from the top of the column is washed with water in an extraction device, and the alcohol content is separated as an aqueous alcohol solution containing the ester corresponding to the three-component liquid-liquid equilibrium.

This aqueous alcohol solution is distilled in an alcohol recovery column, and alcohol containing some ester is recovered from the top of the column and recycled to the second reactor for reuse. Of the water obtained from the bottom of the column, an amount corresponding to the amount produced in the esterification reaction is removed from the system as waste water, and the remaining amount of water is recycled and reused as water for washing in the above-mentioned extraction device.

The ester liquid from which the alcohol has been separated contains an amount of water equivalent to its solubility, and after being dehydrated in a dehydration tower using a conventional method,
The product is distilled in a purification tower to obtain the product ester.

Examples of lower aliphatic alcohols used in the present invention include methanol and ethanol.

One embodiment of the method of this invention will be explained with reference to FIG. A mixture of acrylic acid and alcohol is fed into the first reactor R-1 through channel 1 to undergo an esterification reaction, and the reactant is discharged through channel 2. This reactant is combined with the reactant flowing out from the second reactor R-2 through the channel 4, and is introduced into the acrylic acid recovery column T-1 through the channel 5. In T-1, almost the entire amount of unreacted acrylic acid is discharged from the bottom of the column through a flow path 7 through rectification along with a small amount of water. Most of this is circulated to the second reactor R-2 through the flow path 8, and
In order to remove by-products and polymer components, the acrylic acid and water are treated in a vacuum evaporator V-1 through a channel 9 to evaporate and circulated through a channel 10 to the second reactor. By-products and polymers are discharged from the channel 11 and incinerated. A mixed solution of ester, alcohol and water containing almost no acrylic acid is distilled from the top of the column T-1, and this is supplied to the bottom of the water washing column T-2 through a channel 6. Channel 1 from the top of T-2 tower
Water for washing is supplied through 6. Due to the countercurrent contact between the ester liquid and water in T-2, the alcohol in the ester liquid is transferred to water and flows out from the bottom of the T-2 column through channel 13 as an alcohol aqueous solution to the alcohol recovery distillation column T-3. The alcohol introduced and concentrated by rectification is distilled out from the top of the T-3 column via flow path 14, and is combined with the recovered acrylic acid coming from the aforementioned flow paths 8 and 10, and is then transferred from flow path 3 to the second reactor R-2. is introduced to carry out the esterification reaction. From the bottom of T-3, water containing almost no alcohol is obtained as bottom product through channel 15, and the amount equivalent to the water produced in the esterification reaction passes through channel 17 and is discharged outside the system as waste water. The remainder is supplied as washing water to the top of the T-2 column via the flow path 16 as described above.

Ester containing water equivalent to the solubility is obtained from the top of T-2 and passed through channel 12 to dehydration distillation tower T-4.
supply to.

An azeotropic mixture of ester and water is distilled from the top of the T-4 column, and this is decanted and separated, and the ester phase is refluxed to the top of the column. The aqueous phase may be discarded as is or may be recycled to T-2 for recovery of useful components. A dehydrated ester is obtained from the bottom of the T-4 column, which is fed through a flow path 18 to the purification distillation column T-5. The product is rectified in T-5, and the product ester is obtained from the top of the column through channel 19, and the bottoms are obtained from the bottom of the column via channel 20. This involves evaporating and recovering the ester using vacuum evaporator V-2.
It is circulated through the flow path 21 to the T-4 raw material supply line, and high-boiling components, mainly polymers, are discharged through the flow path 22 and incinerated.

The method of this invention will be explained in more detail with reference to examples below, but the invention is not limited to the following examples.

Example 1 A first reactor having a jacket and filled with polystyrene-based sulfonic acid type cation exchange resin 6,
0.01% by weight of acrylic acid in the reaction stock solution consisting of 3 kg of acrylic acid and 1.92 kg of ethyl alcohol per hour.
was supplied in the presence of hydroquinone corresponding to
The temperature inside the reactor is maintained at 90°C through hot water inside the jacket.
It was maintained at ℃. In this first reactor, 65% of the acrylic acid in the feed stock was converted to ethyl acrylate. The reaction liquid flowing out from the first reactor is
It is supplied to the acrylic acid recovery distillation column together with the reaction liquid flowing out from the reactor.

The acrylic acid recovery distillation column is a perforated plate column consisting of 20 stages, and the reaction liquid is supplied to the center from the first reactor and the second reactor at a rate of 9.52 kg/hour. This tower has a top pressure of
Operated at 200mmHg reflux ratio 0.5. 2 from the bottom of the tower
2.90% of water and acrylic acid containing high boilers per hour
Kg is extracted, and an amount equivalent to 10% of this is recycled to the second reactor together with the remaining 90% after high boiling point substances are removed in a vacuum evaporator and reacted. The distillate from the top of the distillation column is 6.62 kg per hour, and its composition is ester 66.
%, alcohol 20%, water 13%, other 1%, and acrylic acid was trace. This distillate is supplied to the bottom of the water washing tower. The water washing tower is a 30-stage perforated plate type extraction tower, and the distillate is brought into countercurrent contact with washing water supplied from the top of the tower to separate ethyl alcohol. The ratio of the distillate to the washing water used was 1:1.

Ethyl alcohol aqueous solution is obtained from the bottom of the water washing tower at a rate of 9.15 kg/hour. This contains 3% ester. This ethyl alcohol aqueous solution
Reflux ratio of 3 in a 30-stage perforated plate alcohol recovery distillation tower
A mixture consisting of ester, alcohol, and some water is distilled out from the top of the column at a rate of 1.72 kg per hour, which is combined with the above-mentioned recovered acrylic acid and fed to the second reactor for reaction. The second reactor uses the same type as the first reactor, and uses ion exchange resin 5
and operate at a reaction temperature of 90°C. In the second reactor, 60% of the acrylic acid feed was converted to ethyl acrylate.

Water containing almost no organic matter is extracted from the bottom of the alcohol recovery tower at a rate of 7.43 kg per hour.
0.70Kg is removed from the system as waste water, and the remainder is supplied to the top of the water washing tower as water for washing the water washing tower.

From the top of the water washing tower, 4.22 kg of ester containing solubility water flows out per hour, and this is treated in a dehydration distillation tower together with the recovered ester, which will be described later.

The dehydration distillation tower is a 30-stage perforated plate type distillation tower.The water in the raw material is distilled from the top of the tower as an azeotropic mixture with the ester.This is separated by decantation, and the ester phase is refluxed to the top of the tower, and the water is distilled off from the top of the tower. The phase is removed from the system as wastewater. 4.36 kg of ester containing almost no water is extracted every hour from the bottom of the dehydration distillation tower and supplied to the purification distillation tower.

The purification distillation tower is a 20-stage perforated plate distillation tower with a reflux ratio.
Operated in 0.2. From the top of the tower, 4.07 kg of ethyl acrylate that meets product specifications is distilled out per hour. Ester containing a polymer is obtained from the bottom of the column, and the ester component is recovered by vacuum evaporation, and the residue in the can is incinerated. The recovered ester component is supplied to a dehydration distillation column.

Example 2 Methyl acrylate is produced using the same method and equipment as in Example 1.

3.60 kg of acrylic acid and 1.60 kg of methyl alcohol per hour into the first reactor filled with 4.5 ion exchange resin
is supplied and an esterification reaction is carried out at a reaction temperature of 80°C, converting 69% of the acrylic acid into methyl acrylate, and this reaction liquid is supplied to the acrylic acid recovery distillation column together with the reaction liquid from the second reactor. This tower has a top pressure of
Operated at 250 mmHg and reflux ratio 0.5. Acrylic acid containing 3% water and high boiling point substances is extracted from the bottom of the tower every hour.
4.49Kg was extracted, 10% of which was used in a vacuum evaporator to remove high-boiling substances, and the remaining 90% was fed to the second reactor. Distillate from the top of the tower is produced every hour.
6.22Kg, its composition is 74% ester, alcohol
11% and water 15% with traces of acrylic acid. This distillate has an organic phase of 5.49 kg (per hour),
The aqueous phase is composed of 0.73 kg (per hour), of which the organic phase is fed to the bottom of the washing tower and brought into countercurrent contact with washing water fed from the top of the tower to separate methyl alcohol. The ratio of this distillate to the washing water used was 3:1.

From the bottom of the water washing tower, aqueous methyl alcohol solution is obtained at a rate of 2.92 kg/hour. This contains 8.5% ester. This alcohol aqueous solution and the acrylic acid recovery tower distillate aqueous phase are combined and supplied to the alcohol recovery distillation tower. This column has a reflux ratio of 2, and 1.05 kg of a mixed solution of methyl alcohol and ester is distilled out from the top of the column per hour, which is combined with the above-mentioned recovered acrylic acid and fed to the second reactor for reaction. The second reactor is of the same type as the first reactor, filled with ion exchange resin 5, and the reaction temperature is 80°C.
Operate with. In the second reactor 50% of the acrylic acid fed
% was converted to methyl acrylate. 2.61 kg of water containing almost no organic matter is extracted from the bottom of the alcohol recovery distillation tower every hour, of which 0.88 kg is removed from the system as waste water every hour, and the remainder is supplied to the top of the washing tower as water for washing the water washing tower.

From the top of the water washing tower, 4.40 kg of ester containing solubility water flows out per hour, and this is treated in a dehydration distillation tower together with the recovered ester, which will be described later.

Water is distilled from the top of the dehydration distillation column as an azeotropic liquid mixture with ester, which is separated by decantation, the ester phase is refluxed to the top of the column, and the aqueous phase is supplied to the top of the washing column as washing water. do.

4.67 kg of ester containing almost no water is obtained from the bottom of the dehydration distillation tower every hour, and this is fed to the purification distillation tower. Methyl acrylate that meets product specifications is distilled from the top of the refining column at a rate of 4.20 kg per hour. Since the ester containing the polymer is obtained from the bottom of the column, the ester component is recovered by vacuum evaporation, and the recovered ester component is supplied to the dehydration distillation column.

Example 3 Methyl methacrylate is produced using the same method and equipment as in Example 1.

4.47Kg of methacrylic acid and 1.66Kg of methyl alcohol per hour to the first reactor filled with ion exchange resin 7.0
Kg is supplied, and the esterification reaction is carried out at a reaction temperature of 80°C, and 60% of the methacrylic acid is converted to methyl methacrylate, and this reaction liquid is supplied to the methacrylic acid recovery distillation column together with the second reactor reaction product liquid.

The methacrylic acid recovery distillation column is operated at a top pressure of 200 mmH and a reflux ratio of 0.5, and 3.12 kg of methacrylic acid containing 2% water is extracted from the bottom of the column per hour.
The high boiling point substances are removed using a vacuum evaporator, and the remaining 90
% to the second reactor.

The distillate from the top of the column was 7.46 kg per hour and had a composition of 72% ester, 15% alcohol and 13% water, with traces of methacrylic acid. This distillate contains 6.33Kg (per hour) of the organic phase and 1.13Kg (per hour) of the aqueous phase.
This is separated into two phases, and the organic phase is brought into countercurrent contact with the washing water supplied from the top of the washing tower to separate methyl alcohol. The ratio of distillate to washing water used was 1:0.3.

An aqueous methyl alcohol solution is obtained from the bottom of the water washing tower at a rate of 3.00 kg/hour. This contains 3.4% ester. This alcohol aqueous solution and the aqueous phase of the acrylic acid recovery distillation tower distillate are combined and supplied to the alcohol recovery tower. This column is operated at a reflux ratio of 2, and 1.36 kg of a mixed solution of methyl alcohol and ester is distilled out from the top of the column per hour, which is combined with the above-mentioned recovered methacrylic acid and fed to the second reactor for reaction. The second reactor is filled with ion exchange resin 5 and operated at a reaction temperature of 90°C. In the second reactor, 60% of the methacrylic acid feed was converted to methyl methacrylate.

2.77 kg of water containing almost no organic matter is extracted from the bottom of the alcohol recovery distillation tower every hour, of which 0.87 kg is extracted every hour.
Kg is removed from the system as waste water, and the remainder is supplied to the top of the washing tower as water for washing the washing tower.

5.23 kg of ester containing solubility water flows out from the top of the water washing tower every hour, and is treated in the dehydration distillation tower.

Thereafter, the same procedure as in Example 1 was carried out to obtain 5.07 kg of methyl methacrylate per hour, which met the product specifications.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of an embodiment of the present invention. R-1...First reactor, R-2...Second reactor, T-1...Acid recovery tower, T-2...Water washing tower, T
-3...Alcohol recovery tower, T-4...Dehydration tower,
T-5... Refining tower.

Claims (1)

[Claims] 1. In producing acrylic ester or methacrylic ester by reacting acrylic acid or methacrylic acid with a lower aliphatic alcohol using a strongly acidic ion exchange resin as a catalyst, the esterification reactor consists of a first reactor and a second reactor. In the steady state, the first reactor contains the novel acrylic acid or methacrylic acid and alcohol in a molar ratio of 1.1:1.
〜1:1.1 and the reaction conversion rate is
The reaction product obtained in the first reactor is directly sent to the recovery and purification system to remove an amount greater than the amount of unreacted acrylic acid or methacrylic acid and alcohol in the first reactor. Acid and alcohol are circulated between the recovery and purification system and the second reactor, and the reaction conversion rate in the second reactor is 40 to 70% (based on circulating acrylic acid or methacrylic acid).
An acrylic acid ester characterized in that substantially 100% of the acrylic acid or methacrylic acid and alcohol supplied to the first reactor are reacted by reacting at a reaction temperature of 60 to 110°C and a residence time of 0.3 to 3 hours in both reactors. Or a method for producing methacrylic acid ester.