JPH0686407B2 - Method for producing methacrylic acid ester - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a methacrylic acid ester. More specifically, the present invention relates to a method for producing a methacrylic acid ester, which comprises reacting methacrylic acid with a lower aliphatic alcohol having 5 to 8 carbon atoms or an alicyclic alcohol.

[Prior Art] Conventionally, in the continuous production of ethacrylic acid methacrylic acid, a methacrylic acid and an alcohol were used in a reactor with a mineral acid such as sulfuric acid or phosphoric acid or an esterification catalyst of a strongly acidic cation exchange resin. After the reaction, the reaction product is distilled in a light-boiling substance separation column to obtain a high-boiling-point component containing reaction methacrylic acid ester as a main component and a low-boiling-point component containing unreacted alcohol, methacrylic acid, and produced water as main components. While separating and purifying methacrylic acid ester from the former, unreacted alcohol and methacrylic acid are recovered from the latter and circulated to the reactor.

In the method of using a mineral acid such as sulfuric acid or phosphoric acid as an esterification catalyst, since a highly corrosive mineral acid is used, it is necessary to select a corrosion-resistant equipment material, which makes the equipment expensive and is contained in the waste liquid. The waste liquid treatment for detoxifying the mineral acid also has a drawback that it becomes complicated.

On the other hand, in the method of using a strongly acidic cation exchange resin as an esterification catalyst (Japanese Patent Publication No. Sho 62-39150), if the conversion rate decreases with the deterioration of the resin, esterification is required to ensure the yield of methacrylic acid ester. The amount of unreacted alcohol and methacrylic acid recovered and circulated gradually increased as the supply to the reactor increased, and finally the operation was stopped when the distillation capacity of the equipment reached the limit and the catalyst was removed. Exchange is taking place. This method does not have the drawbacks of the above-mentioned method using a mineral acid as an esterification catalyst. However, as the amount of unreacted alcohol and methacrylic acid recovered and circulated increases, the liquid composition in the esterification reactor also changes, and the resin swells or shrinks, and in some cases cracks occur, This is also a factor that shortens the life of the resin.

[Problems to be Solved by the Invention] An object of the present invention is to remedy the drawbacks of the conventional methods. That is, it is an object of the present invention to provide a method for producing methacrylic acid ester by using inexpensive equipment materials, reducing waste liquid treatment costs, and maintaining resin life so that continuous operation for a long period of time is possible.

[Means for Solving the Problems] As a result of earnest studies, the present inventors have found that methacrylic acid and carbon number 5
When the lower aliphatic alcohol or alicyclic alcohol of ~ 8 is subjected to an esterification reaction using a strongly acidic cation exchange resin as a catalyst, the reaction temperature is adjusted so that the conversion rate of methacrylic acid is always constant, and Of the raw material liquid newly supplied to the esterification reactor of methacrylic acid and alcohol and the circulating liquid from the light boiling point separation column so that the liquid supply amount to the esterification reactor is always substantially constant. By carrying out the esterification reaction, the light-boiling substance separation column can be operated in a stable state, the amount of circulating liquid circulating in the esterification reactor is stable, and the inlet liquid composition of the reactor is also stable. I have found that I can achieve it. That is, in the present invention, methacrylic acid and a lower aliphatic alcohol having 5 to 8 carbon atoms or an alicyclic alcohol are supplied to an esterification reactor, and the esterification reaction is carried out in the reactor using a strongly acidic cation exchange resin as a catalyst. Then, the obtained reaction product is introduced into a light-boiling substance separation column, and a liquid containing substantially all of the methacrylic acid ester is withdrawn from the bottom of the light-boiling substance separation column, while the light-boiling substance separation column is removed. When alcohol, methacrylic acid and water are distilled from the top to separate them into an aqueous phase and an organic phase containing alcohol and methacrylic acid, and the organic phase is circulated as a circulating liquid in an esterification reactor to produce a methacrylic acid ester. In addition, (a) the composition of the feed liquid to the esterification reactor consisting of the raw material liquid newly fed to the methacrylic acid and alcohol esterification reactor and the above circulating liquid is substantially uniform. And (b) adjusting the reaction temperature in the esterification reactor in the range of 50 to 110 ° C. to maintain the conversion of methacrylic acid substantially constant. It is a manufacturing method. The present invention will be described in more detail below.

The methacrylic acid used in the present invention may be either crude methacrylic acid or purified methacrylic acid, and the unreacted methacrylic acid recovered from the light boiling point separation column after the esterification reaction is also recycled.

Specific examples of the lower aliphatic alcohol or alicyclic alcohol having 5 to 8 carbon atoms include 2-ethyl-hexanol,
Examples thereof include cyclohexanol, which may be linear or branched. Also,
After the esterification reaction, the unreacted alcohol recovered from the light boiling point separation column is recycled.

In the present invention, a strongly acidic cation exchange resin is used as a catalyst for the esterification reaction. A porous or gel type resin can be used, but a porous type resin is preferably used. Particularly when crude methacrylic acid is used, it is preferable to use a porous type resin having excellent resistance to organic contamination. As a porous strong cation exchange resin, the degree of crosslinking is 2
〜16%, porosity 0.1〜1.0ml / g, average pore size 100〜600
Å can be preferably used, and C-26C is a specific example.
(Duolite), PK-208, PK-216, PK-228 (Mitsubishi Kasei), MSC-1,88 (Dow), Amberlystow
16 (made by Rohm and Haas), SPC-108, SPC-112
(Manufactured by Bayer) and the like.

The esterification reaction is carried out while monitoring the conversion rate of methacrylic acid by analyzing the composition of the inlet liquid and the outlet liquid of the reactor and adjusting the reaction temperature so that the conversion ratio is always constant. The conversion rate is preferably within ± 5%, and more preferably within ± 3% based on the conversion rate of methacrylic acid when the operation is started and reaches a steady state.

The esterification reaction is usually carried out in the range of 50 to 110 ° C, although it varies depending on the desired esterification reaction. Also,
The esterification reaction is carried out in the liquid phase, and the reaction type may be either a fluidized bed or a fixed bed.

In the esterification reaction, as is usually done,
A polymerization inhibitor can be used. Examples of the polymerization inhibitor used include hydroquinone, methoxyhydroquinone, phenothiazine, hydroxylamine, and phenylenediamine. If the reaction is carried out in the presence of molecular oxygen, the effect of the polymerization inhibitor can be further enhanced.

The esterification reaction product thus obtained is introduced into a light-boiling substance separation column for distillation, and a high-boiling point component containing substantially the entire amount of the produced methacrylic acid ester as a main component is extracted from the bottom of the column for further purification step. To obtain a methacrylic acid ester product.

On the other hand, from the top of the light-boiling substance separation column, a low-boiling point component containing unreacted alcohol, methacrylic acid, and produced water as main components is distilled and condensed to form an aqueous phase and an organic phase containing alcohol and methacrylic acid as main components. To separate. The organic phase is recovered and circulated as a circulating liquid to the reactor. Here, in order to promote the esterification reaction, it is more advantageous for the composition of the circulating liquid to decrease the amount of methacrylic acid ester and water and increase the amount of alcohol and methacrylic acid. Therefore, although the circulating liquid varies depending on the target ester and reaction conditions, the sum of the concentrations of alcohol and methacrylic acid is 50% by weight or more, more preferably 60% by weight or more, and the concentration of water is 5% by weight or less. It is preferably 2% by weight or less. Further, if the amount of the circulating liquid circulated in the esterification reactor is too large or too small, the amount of resin necessary for the esterification reaction increases, which is not preferable. The circulating liquid amount is appropriately 1 to 5 times the new supply amount.

A polymerization inhibitor can also be used in the light boiling point separation column. As the polymerization inhibitor used, the same ones as exemplified for the esterification reaction can be mentioned. Similarly, the effect of the polymerization inhibitor can be further enhanced by carrying out in the presence of molecular oxygen.

Next, a more detailed description will be given with reference to FIG. 1, which illustrates a preferred embodiment of the present invention.

Methacrylic acid from line 1, alcohol from line 2,
An esterification reactor 10 in which a circulating liquid is supplied from a line 7 and these mixtures are filled with a porous strong acid cation exchange resin.
Supply to 1. In the esterification reactor 101, the liquid at the inlet 3 and outlet 4 of the reactor is analyzed to monitor the conversion rate of methacrylic acid, and the esterification reaction is performed while adjusting the reaction temperature so that the conversion rate is always constant. .

An esterification reaction product composed of the produced ester, unreacted methacrylic acid, unreacted alcohol and produced water is extracted from the outlet 4 of the esterification reactor 101, and the light boiling point separation column 102 is provided.
And then distilled. A liquid containing substantially all of the produced methacrylic acid ester is withdrawn from the bottom of the light-boiling substance separation column 102, and introduced through a line 5 to a purification step (not shown) to obtain a methacrylic acid ester product.

On the other hand, unreacted alcohol, methacrylic acid and generated water are distilled and condensed from the top of the light boiling point separation column 102, and the receiver 10
At 3, the water phase and the organic phase mainly composed of alcohol and methacrylic acid are separated into two phases. The organic phase is circulated to the esterification reactor 101 through line 7 as a circulating liquid. The water phase is extracted from the line 6 and sent to an alcohol recovery process or a wastewater treatment process (not shown).

In the present invention, the esterification reaction is carried out so that the conversion rate of methacrylic acid is always constant, so that the composition of the esterification reaction product is stable and the light boiling point separation column 102
The operating conditions of are stable. That is, the operating temperature of the light boiling point separation column 102 is constant, and the composition and amount of the organic phase circulated in the reactor as a circulating liquid are also constant.

[Examples] Further, the present invention will be described in detail by the following examples.
Each Example was carried out using the apparatus shown in FIG. 1, and the conversion rate of methacrylic acid was calculated according to the following formula by analyzing the methacrylic acid concentrations of the esterification reactor inlet liquid and outlet liquid.

Example 1 Using the apparatus shown in FIG. 1, starting from methacrylic acid having a purity of 99.8% and 2-ethylhexanol as a raw material, the esterification reactor was filled with 15 l of a porous cation exchange resin to give 2-ethyl methacrylate. Kisil was manufactured. The conditions at the start of operation (when the operation started and reached a steady state) and seven months after the start of operation were as shown in Table 1.

During the operation, the reaction temperature was gradually increased as the resin deteriorated with time in order to keep the conversion rate of methacrylic acid in the reactor constant. As a result, the reaction temperature after continuous operation for 7 months was 100 ° C. During this period, the rate of increase in reaction temperature was almost constant. During the operation, the conversion rate of methacrylic acid, the composition of the esterification reaction product, the bottom temperature of the light boiling point separation column, the composition and amount of the circulating liquid were stable.

The total amount of 2-ethylhexyl methacrylate produced per unit catalyst was 849 kg / 1.

Comparative Example 1 2-Ethylhexyl methacrylate was produced in the same manner as in Example 1 except that the reaction temperature was kept at 100 ° C during the operation. As a result, deterioration of the resin over time occurred and the conversion rate of methacrylic acid gradually decreased. As the amount of unreacted alcohol and methacrylic acid recovered and circulated increased, the bottom temperature of the light boiling point separation column gradually increased, and the continuous operation had to be stopped for 4.5 months. The methacrylic acid conversion rate is 7 when the steady state is reached after the start of operation.
Although it was 4.9%, it decreased to 36.5% when the operation was stopped, the resin life was clearly shorter than that in Example 1, and the total production amount of 2-ethylhexyl methacrylate per unit resin volume was 607 kg / 1. It wasn't too much. However, since the liquid composition at the inlet of the reactor gradually changes, it does not mean that the conversion rate decreases and the production amount per unit time decreases, and the production amount per unit time was the same as that in Example 1. .

[Effect of the Invention] According to the present invention, the composition of the feed liquid to the esterification reactor consisting of the above-mentioned new raw material liquid of methacrylic acid and alcohol and the above-mentioned circulating liquid is kept constant, and in the esterification reactor, By adjusting the reaction temperature of 50 to 110 ° C. in order to make the conversion of methacrylic acid constant, the composition of the reaction liquid in the esterification reactor becomes substantially constant, The following effects can be obtained.

(1) Problems such as swelling, shrinkage, and cracking of the ion exchange resin as a catalyst can be prevented, and the catalyst life can be maintained for a long time.

In the present invention, the catalyst life is set at the time when the temperature in the esterification reactor reaches a specified temperature, and the catalyst exchange is performed. However, since the catalyst life becomes long as described above, the unit catalyst (resin) The total production of methacrylic acid ester increases.

Specifically, the total production amount of 2-ethylhexyl methacrylate per unit catalyst in Example 1 is 849 kg / 1, whereas the total production amount of 2-ethylhexyl methacrylate per unit catalyst in Comparative Example 1 is Is only 607kg / 1.

(2) Since the liquid composition can always be operated with a constant liquid composition, the operating conditions of the light boiling point separation column are stable, and the increase of polymer due to the rise of the bottom temperature in the light boiling point separation column can be prevented.

[Brief description of drawings]

FIG. 1 represents a flow sheet diagram illustrating a preferred embodiment of the present invention. 101 ... Esterification Reactor 102 ... Light Boiling Separation Tower 103 ... Receiver 1 ... Methacrylic Acid Supply Line 2 ... Alcohol Supply Line 3 ... Esterification Reactor Inlet 4 ... Esterification Reactor Outlet 5 ... Light Boiling Separation Tower Bottom liquid extraction line 6 ... Water phase extraction line 7 ... Circulating liquid supply line

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masao Baba Inventor Masao Baba 1 992 Nishi-oki, Okihama, Aboshi-ku, Himeji-shi, Hyogo Ichirara Karaki (56) -39150 (JP, B2) JP-B-59-12102 (JP, B2) "Chemical Experimental Method" (1960-5-1) Tokyo Kagaku Dojin, 210-212, "Catalyst Engineering Course 3 Catalytic Equipment and Design" (Sho 42-7-10) Jishin Shokan, 367, “Separate Volume Chemical Industry 26-8 Progress in Catalytic Chemistry-Effective Utilization and Practical Use-” (Sho 57-5-1) Kagaku Kogyosha, 33,

Claims (1)

[Claims] 1. Methacrylic acid and a lower aliphatic alcohol having 5 to 8 carbon atoms or an alicyclic alcohol are fed to an esterification reactor, and the esterification is carried out in the reactor using a strongly acidic cation exchange resin as a catalyst. The reaction product obtained by the reaction is introduced into a light-boiling substance separation column, and a liquid containing substantially all of the methacrylic acid ester is withdrawn from the bottom of the light-boiling substance separation column, while the light-boiling substance separation column is used. Alcohol, methacrylic acid, and water are distilled from the top, coagulated and separated into an aqueous phase and an organic phase containing alcohol and methacrylic acid, and the organic phase is circulated as a circulating liquid in an esterification reactor to produce a methacrylic acid ester. (A) The composition of the feed liquid to the esterification reactor consisting of the raw material liquid newly fed to the methacrylic acid and alcohol esterification reactor and the above circulating liquid is substantially Methacrylic acid, and the conversion temperature of the methacrylic acid is maintained substantially constant by adjusting the reaction temperature in the esterification reactor in the range of 50 to 110 ° C. Method for producing ester.