JP3345985B2 - Method for producing methyl methacrylate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing methyl methacrylate from methacrylic acid and methanol. Specifically, the present invention relates to an improvement in a method of esterification using an ion exchange resin.

[0002]

2. Description of the Related Art As a method for producing methyl methacrylate from methacrylic acid and methanol, a method using sulfuric acid or a strongly acidic ion exchange resin as a catalyst is known.
Among these, the method using a strongly acidic ion exchange resin has a lower conversion rate of methacrylic acid than the method using sulfuric acid, but does not require a treatment process for sulfuric acid mixed into the oil layer. Therefore, it is considered that this method is advantageous in view of the overall situation.

Hitherto, the production of methyl methacrylate using a strongly acidic ion exchange resin as a catalyst has been performed using a fixed-bed reactor. However, since there is an equilibrium in this esterification reaction, the conversion of methacrylic acid at the reactor outlet cannot be significantly increased when the reaction is carried out in a fixed-bed reactor. In order to shift the equilibrium to the production side, usually, the molar ratio of methanol to methacrylic acid is increased (Japanese Patent Publication No. 61-4378). In this case, a method is used in which unreacted methacrylic acid and methanol are separated from the reaction solution and then recycled to the reactor (Japanese Patent Publication No. 48-1369).

[0004]

In a conventional method using a fixed bed reactor, the molar ratio of methanol to methacrylic acid is 1.2 to 2.0, and the conversion of methacrylic acid is 30 to 90%. In practice, a large excess of methanol is recovered by distillation, and thus there is a problem that the recovery energy is increased. In addition, the impurities contained in the raw materials and the polymer of methacrylic acid precipitate, so that the reaction solution does not flow uniformly throughout the ion exchange resin layer, or the catalyst performance is deteriorated due to contamination of the ion exchange resin surface, and the life is shortened. There was a problem that it became extremely short.

As a method for solving these problems, it is conceivable to use a stirring tank or a fluidized bed as a reaction tank instead of a fixed bed in order to keep the ion-exchange resin in a fluid state at all times. Inability to achieve a significant increase in methacrylic acid conversion as compared with the method, and the boiling point of methyl methacrylate and methanol azeotrope is lower even if the product methyl methacrylate and water are distilled off while reacting Therefore, there is a problem that methanol is distilled out preferentially as compared with water, so that the equilibrium cannot be shifted to the production side, and the dewatering operation cannot be performed because the distillate does not separate.

Under such circumstances, the present inventors have conducted intensive studies on a method for producing methyl methacrylate from methacrylic acid and methanol using a strongly acidic ion exchange resin, and as a result, an apparatus comprising a plurality of continuous reaction sections and a distillation section has been studied. It has been found that methyl methacrylate can be efficiently produced by continuously performing reactive distillation in multiple stages by using, and the present invention has been achieved.

[0007]

That is, the present invention relates to a method for producing methyl methacrylate by reacting methacrylic acid and methanol in the presence of a strongly acidic ion exchange resin. Using an apparatus consisting of a reaction section and a distillation section, methacrylic acid is supplied to the first reaction section, methanol is supplied to the reaction section downstream of the first reaction section, and the reaction solution of the previous stage is sequentially supplied to the reaction section of the downstream, The steam generated from the reaction section is sequentially sent to the preceding reaction section, the reactive distillation is continuously performed in each reaction section, and the steam generated from the first reaction section is distilled in the distillation section to separate methyl methacrylate. A method for producing methyl methacrylate, characterized in that:

The strongly acidic ion exchange resin used in the present invention is not particularly limited, and a commercially available strongly acidic ion exchange resin can be used. However, from the viewpoint of strength and reaction rate, Duolite (registered trademark) C -26C (manufactured by Rohm and Haas), Diaion (registered trademark) SK-1B (manufactured by Mitsubishi Kasei Kogyo), Nafion (registered trademark) NR-50 (manufactured by DuPont) and the like are preferably used.

The apparatus used in the present invention, which comprises a plurality of continuous reaction sections containing a strongly acidic ion exchange resin and a distillation section, is constituted by a tray and comprises a plurality of reaction sections containing a strongly acidic ion exchange resin and a distillation section. And a device comprising a distillation column and a multi-stage continuous reaction tank composed of 2 to 5 tanks containing a strongly acidic ion exchange resin.

A case where a reactive distillation column comprising a plurality of reaction sections containing a strongly acidic ion exchange resin and a distillation section, which is constituted by a tray, will be described below. In this case, a reactive distillation column composed of a plurality of reaction sections containing a strongly acidic ion exchange resin and a distillation section is used, and methacrylic acid is added to the upper reaction section, and methanol is added to the lower reaction section. And a part of the bottom liquid is heated and evaporated by the reboiler of the reactive distillation column, and the vapor generated from the lower reaction section is sequentially transferred to the upper reaction section, and the reaction liquid of the upper reaction section is sequentially transferred to the lower reaction section. The ion-exchange resin is fluidized and vaporized by the steam rising from the lower reaction section on the shelf of each reaction section, and reactive distillation is performed. The gas is distilled in the distillation section, and methyl methacrylate is distilled off from the top of the reactive distillation column and separated to produce methyl methacrylate.

The reactive distillation column used in the present invention can be used as long as it is a common tray column. In the case of a sieve tray or a ripple tray, stainless steel or Teflon is used to prevent the strongly acidic ion exchange resin from leaking from the tray. It is desirable to lay a net made of steel.

An embodiment of the present invention will be described with reference to FIG. The reactive distillation column 1 has a plurality of trays, and the portion of the trays becomes a plurality of reaction sections 6. Methacrylic acid is supplied from the line 9 to the shelf in the upper reaction section, and the line 1 is supplied to the shelf in the lower reaction section.
From 0 methanol is supplied. Methanol and / or methacrylic acid is supplied as a liquid or a part or all of the liquid as a gas. Part of the bottom liquid is reboiler 2 of the reactive distillation column.
Heat and evaporate. A plurality of reaction units in which a strongly acidic ion exchange resin is present are provided below the methanol supply position.

In the shelf of the reaction section in which the strongly acidic ion exchange resin is present, a mixed liquid of the raw material and the product flows down from the shelf of the upper reaction section via the downcomer, and the shelf of the lower reaction section. The strongly acidic ion exchange resin flows by the mixed vapor of the raw material and the product rising from the stage, and the reaction and the distillation are simultaneously performed. This is performed continuously in multiple stages. The produced methyl methacrylate and water rise sequentially and distill from the uppermost reaction section.

In order to prevent methacrylic acid from distilling out from the uppermost reaction section, it is preferable to provide a distillation section having 3 to 10 theoretical plates above the uppermost reaction section. In order to prevent low-boiling substances such as methanol and water from leaking to the bottom of the column, it is preferable to provide a distillation section 8 having 2 to 4 theoretical plates below the lowermost reaction section. The remainder of the bottom liquid is evaporated in the evaporator 3, high boilers are taken out from the line 14, and evaporated components mainly composed of methacrylic acid are recycled from the line 13 to the upper reaction section.

A distillate gas mainly consisting of methyl methacrylate and water, which are distilled out of the distillation section, is condensed in a condenser 4 and separated in an oil / water separator 5 to separate oil and water.
Extracted from 1. A part of the oil phase (ester phase) is refluxed to the top of the column, and the remainder is taken out of the line 12 as product methyl methacrylate. Usually, this is further purified by distillation or the like to obtain a final product.

As the number of stages in the reaction section increases, the liquid residence time of the entire apparatus can be shortened, but as the number increases, this is not necessarily better. More than about 20 stages is practically meaningless. This is because the concentration of either methanol or methacrylic acid in the liquid in the reaction section becomes sufficiently small, and the reaction rate becomes almost zero. Usually, it is performed in about 15 to 20 stages.

Further, the supply position of methanol is preferably higher than the last stage of the reaction section. When the reaction section has 20 stages,
Assuming that the methacrylic acid supply stage is the first stage, the methanol supply stage is preferably the 14th to 17th stages. When the methanol stage is fed before this stage, the methanol content becomes substantially zero near the final stage, and the reaction stage When the feed is fed to a stage subsequent to that stage, the reaction speed near the foremost stage decreases, and the overall reaction amount is suppressed. If the number of reaction sections is 5 or more, the optimum supply stage of methanol exists other than the last stage. Methanol may be supplied to two or three reaction sections.

Next, the case where an apparatus comprising a multi-stage continuous reaction tank composed of 2 to 5 tanks and a distillation column is used will be described below. In this case, using a device consisting of a multi-stage continuous reaction tank composed of 2 to 5 tanks in which the strongly acidic ion exchange resin is fluidized and a distillation column, methacrylic acid is added to the first reaction tank, Also, methanol is supplied to the subsequent 1 to 4 reaction tanks, the first reaction tank sequentially feeds the first reaction liquid to the second reaction tank, and the steam generated from the second reaction tank sequentially receives the first reaction tank. At the same time as performing reactive distillation in each reaction tank, supplying the distillate generated from the first reaction tank to the distillation column, circulating the bottom liquid to the first reaction tank, and methacrylic acid from the top of the tower. Methyl is separated to produce methyl methacrylate.

As the distillation column used in the present invention, a commonly used distillation column such as a packed column, a perforated plate column and a tray column can be used, and the type of column is not particularly limited.
As for the reaction tank, if it is a tank having a device capable of flowing a strongly acidic ion exchange resin, a stirring tank, a type such as a fluidized tank,
Can be used regardless of shape. In the stirring tank, in order to reduce the crushing of the strongly acidic ion exchange resin, a stirring blade with a smooth edge, for example, an anchor blade made of glass lining,
Faudler blades and the like are preferably used. The fluidized bed is a system in which the ion exchange resin is fluidized by an inert gas such as nitrogen, air or methanol vapor, or an ascending flow generated by a pump circulating flow.
The shape is not limited.

Hereinafter, the present invention will be described with reference to FIG. 2 showing one embodiment of the present invention. In the case of FIG. 2, it is composed of two reaction vessels and a distillation column, and the reaction vessels 6a and 6b have stirring blades 6a 'and 6b'. A distillation column 7 is connected to the reaction tank 6a, and methacrylic acid is supplied to the reaction tank 6a from a line 9 and methanol is supplied to the reaction tank 6b from a line 10. Methanol and / or methacrylic acid are supplied as a liquid or a part or all of the liquid as a gas. The reaction tank has external heaters or jackets 2a and 2b (in FIG. 2, external heaters are shown), and the reaction solution is heated to a predetermined temperature to boil and evaporate. The inside of the reaction tank is a gas-liquid-solid three-phase system including a strongly acidic ion exchange resin, and a predetermined power is applied to bring into a mixed fluid state by stirring.

From the bottom of the reaction tank 6a, only the reaction solution is extracted through a filter (not shown), and sent to the reaction tank 6b through a line 15. At this time, the supply position may be the gas phase portion or the liquid phase portion. On the other hand, the vapor generated in the reaction tank 6b is supplied to the liquid in the reaction tank 6a in gaseous form through the line 16. By performing these two transfers at the same time, gas-liquid countercurrent contact is achieved between the two tanks. From the bottom of the reaction tank 6b, a predetermined extraction is performed by a line 17 through a filter (not shown). The extracted liquid is mainly composed of methacrylic acid as a raw material and methyl methacrylate as a product and contains a small amount of high-boiling by-products. Therefore, after cutting high-boiling components, the remaining liquid is recycled to the reaction tank 6a ( (Not shown).

From the reaction tank 6a, methyl methacrylate and water are supplied to the distillation column 7 in gaseous form. In order to prevent methacrylic acid from distilling out from the top of the distillation column, it is preferable to operate the distillation column at about 3 to 10 theoretical stages and at a reflux ratio of 1.0 or more. A distillate gas containing methyl methacrylate, which is a product distilled from the top of the column, and water as main components is supplied to the condenser 4
And the oil-water separator 5 separates the oil and water, and the aqueous phase is extracted from the line 11. A part of the oil phase (ester phase) is refluxed to the top of the column and the remainder is withdrawn from line 12 as the product methyl methacrylate. Usually, this is further purified by distillation or the like to obtain a final product.

As the number of reaction vessels increases, the residence time of the entire vessel can be shortened, but as the number increases, it is not always better. More than 20 tanks is practically meaningless. This is because the reaction rate becomes almost zero because the concentration of either methanol or methacrylic acid as a raw material in the liquid in the reaction tank becomes small. In practice, it is usually carried out in 2 to 5 tanks in consideration of equipment costs. FIG. 3 shows an example of an apparatus including four reaction tanks and a distillation column.

When the reaction is carried out in a plurality of reaction vessels, methanol is supplied to one or more reaction vessels at a stage subsequent to the first reaction vessel for supplying methacrylic acid. When methanol is supplied to one place, the reaction tank at the last stage is not always good. For example, when the number of reaction tanks is five, the supply position of methanol is most preferably the fourth tank from the first reaction tank. This is because there is a difference in the reaction rate of the entire system depending on the supply position of methanol, and the reaction rate in the fourth tank is the largest. Methanol must not be supplied to the reaction tank 6a connected to the distillation column. This is because the liquid phase of the reaction vessel 6a has a methanol-rich composition, and the vapor generated therefrom is an azeotropic mixture of methanol and methyl methacrylate, which makes it impossible to drain water from the system. It is. Therefore, as a matter of course, dehydration cannot be achieved even if it is performed in only one tank. Also, the withdrawn liquid from the last reaction tank is recycled to the first reaction tank after removing high boiling substances as necessary. Although not particularly limited, it is usually recycled to the first reaction tank to which methacrylic acid is supplied.

The operation of the reactor is not particularly limited, but usually, a predetermined amount of methacrylic acid and methanol are supplied, the pressure of the distillation column is set, and the amount of heat required for the predetermined cooking is reacted. The addition is carried out while being adjusted to the tanks, and the amount of liquid withdrawn from each reaction tank is controlled so that the liquid level in each reaction tank becomes constant. The supply amounts of methacrylic acid and methanol are appropriately increased or decreased while controlling the distillation amount and the controllability of the liquid level.

In the process of the present invention, the reaction pressure and temperature are not particularly limited, but usually, the pressure at the top of the distillation column is about 500 Torr to normal pressure, the temperature is about 70 to 90 ° C.,
The reaction is performed at a temperature of about 80 to 120 ° C.

[0027]

According to the method of the present invention, the conversion of methacrylic acid is increased to 90 to 99.9% even when the molar ratio of methanol to methacrylic acid is as low as 1.01 to 1.2. Thus, methyl methacrylate can be produced efficiently.

[0028]

Hereinafter, the present invention will be described in detail with reference to Examples.
The present invention is not limited to these.

Example 1 Methyl methacrylate was produced from methacrylic acid and methanol using the same multi-stage reactive distillation column as in FIG. The reactive distillation column has an inner diameter of 0.1 m, and has a reaction section having 20 theoretical plates, 5 distillation sections above the reaction section and 2 distillation sections below the reaction section, and each stage of the reaction section has a strongly acidic ion exchange resin. 0.1 L of Duolite C-26C (manufactured by Rohm and Haas). 1.0 kg / h of methacrylic acid was added from the upper stage to the sixth stage (first stage in the reaction section) and methanol 0.41 kg / h.
h was supplied as a liquid to the 19th stage (14th stage in the reaction section) (molar ratio of methanol to methacrylic acid was 1.1), the pressure at the top of the column was 500 Torr, the temperature was 74 ° C., and the pressure at the bottom of the column was 600 Torr. At a temperature of 86 ° C. In addition,
Half of the bottom liquid was evaporated and returned to the bottom of the column to carry out heating for reactive distillation. After removing high boiling substances, the remaining bottom liquid was returned to the first stage of the reaction section in the gas phase. In the tower, the 19th stage had the lowest temperature of 73 ° C, and the 6th stage had the highest temperature of 114 ° C. The residence time of the liquid in the reaction section was 0.43 hours.

The steam cooked by the reboiler rises in the tower, and the strongly acidic ion exchange resin is in a fluid state. When the vapor from the top is condensed, its composition is water 8.
9 wt%, methanol 2.3 wt%, methyl methacrylate 88.3 wt%, and methacrylic acid 0.35 wt%. The mixture was separated into an oil phase (ester phase) and an aqueous phase at 40 ° C. by an oil-water separator. The aqueous phase was withdrawn at 0.21 kg / h, half of the oil phase was refluxed to the upper part of the distillation section, and the remaining 1.14 kg / h was obtained as a product.

The composition of the ester phase is 2.0 wt% of water, 1.9 wt% of methanol, 95.7 wt% of methyl methacrylate.
% And methacrylic acid 0.36 wt%. The substantial residual amount of methacrylic acid was only contained in the ester phase extracted from the top of the tower, and the conversion of methacrylic acid in this reactive distillation was 99.6%.

Example 2 Methyl methacrylate was produced from methacrylic acid and methanol using an apparatus comprising two reaction tanks and a distillation column shown in FIG. However, the liquid in the reaction tank was heated by a jacket. The reaction tank used two 2.2-liter glass separable flasks. In the first reaction tank 6a, 7.1 g of methanol, 14 g of water, 500 g of methyl methacrylate,
480 g of methacrylic acid and a strongly acidic ion exchange resin (Duolite (registered trademark) C-26C manufactured by Rohm and Haas Company)
: Density 400 dry-g / L), and 400 g of the same ion exchange resin as 11 g of methanol, 11 g of water, 374 g of methyl methacrylate, and 604 g of methacrylic acid were charged into the second reaction tank 6b. The distillation column 3 is a packed column of five theoretical stages in which a glass column having an inner diameter of 30 mm is filled with a filler.

The stirring was carried out by a glass anchor blade at a required stirring power of 0.25 kw / m ³ . 283 methacrylic acid.
8 g / h, methanol was supplied to the reaction tank 6 a connected to the distillation tower at a rate of 116.2 g / h as a liquid to the reaction tank 6 b (the molar ratio of methanol to methacrylic acid was 1.1.
), And an esterification reaction was performed.

The reaction was continued at a pressure of 650 Torr at the top of the distillation column. After 50 hours, the temperature at the top of the distillation column is 80
° C, the liquid temperature of the reaction tank 6a was 95.6 ° C, and the liquid temperature of the reaction tank 6b was 102.8 ° C. At this time, the withdrawal amount of the content liquid from the reaction tank 6b was 57.0 g / h (residence time was 5.03 h), and the aqueous phase from the oil-water separator was 59.6 g / h.
Then, half of the oil phase is refluxed to the upper part of the distillation column, and the remaining oil phase 3
08.4 g / h was obtained as a product.

The composition of the condensate obtained by condensing the distillate gas from the top was 9.2% by weight of water, 4.1% by weight of methanol, 86.7% by weight of methyl methacrylate, and 340 ppm of methacrylic acid. The composition of the oil phase was 2.3% by weight of water, 3.3% by weight of methanol, 94.4% by weight of methyl methacrylate, and 350 ppm of methacrylic acid. The conversion of methacrylic acid was 93.2%.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing a second example of the embodiment of the present invention.

FIG. 3 is a diagram showing a third example of the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactive distillation tower 2 Reboiler 2a-2d Heater 3 Evaporator 4 Condenser 5 Oil-water separator 6 Reaction part 6a-6d Reaction tank 6a'-6d 'Stirrer 7 Distillation part 8 Distillation part 9 Methacrylic acid supply line 10 Methanol Supply line 11 water phase extraction line 12 oil phase (ester phase) extraction line 13 extraction line from reaction tank 14 high boiling matter extraction line 15 reaction liquid extraction line 16 generated steam supply line 17 reaction liquid extraction line

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C07C 67/08 C07C 69/54

Claims (9)

(57) [Claims] Claims: 1. A method for producing methyl methacrylate by reacting methacrylic acid and methanol in the presence of a strongly acidic ion exchange resin, comprising: an apparatus comprising a plurality of reaction units containing a strongly acidic ion exchange resin and a distillation unit. Using, methacrylic acid is supplied to the first reaction section, methanol is supplied to the reaction section subsequent to the first reaction section, and the reaction liquid of the first step is sequentially supplied to the subsequent reaction section, and the steam generated from the second reaction section is sequentially supplied. Methyl methacrylate, which is sent to the former reaction section and continuously performs reactive distillation in each reaction section, and distills steam generated from the first reaction section in the distillation section to separate methyl methacrylate. Production method. 2. An apparatus comprising a plurality of reaction sections containing a strongly acidic ion exchange resin and a distillation section, comprising a shelf, and a reactive distillation comprising a plurality of reaction sections containing a strongly acidic ion exchange resin and a distillation section. The method for producing methyl methacrylate according to claim 1, wherein the apparatus comprises a distillation column or a column or a multi-stage continuous reaction tank composed of 2 to 5 tanks containing a strongly acidic ion exchange resin. 3. A method for producing methyl methacrylate by reacting methacrylic acid and methanol in the presence of a strongly acidic ion-exchange resin, comprising a plurality of reaction units comprising a shelf and containing a strongly acidic ion-exchange resin. Using a reactive distillation column consisting of a distillation section, methacrylic acid is supplied to the upper reaction section tray and methanol is supplied to the lower reaction section tray, and a portion of the bottom liquid is heated and evaporated by a reboiler of the reaction distillation column, The steam generated from the lower reaction section is sequentially sent to the upper reaction section, and the reaction solution in the upper reaction section is sequentially sent to the lower reaction section, and the ion exchange is performed by the steam rising from the lower reaction section on the shelf of each reaction section. The resin is fluidized and reactive distillation is performed, and this is continuously performed in multiple stages.The generated gas from the uppermost reaction section is distilled in the distillation section, and methyl methacrylate is distilled from the top of the reactive distillation column, Separating A method for producing methyl methacrylate, comprising: 4. The method for producing methyl methacrylate according to claim 3, wherein the number of the reaction sections comprising the plate containing the strongly acidic ion exchange resin in the reactive distillation column is 15 to 20. 5. The method for producing methyl methacrylate according to claim 3, wherein a distillation section is provided at an upper portion and / or a lower portion of the reaction section. 6. The method for producing methyl methacrylate according to claim 3, wherein a reaction section comprising a shelf in which a strongly acidic ion exchange resin is present is provided below the methanol supply position. 7. A method for producing methyl methacrylate by reacting methacrylic acid and methanol in the presence of a strongly acidic ion exchange resin, comprising a multistage tank comprising 2 to 5 tanks in which the strongly acidic ion exchange resin is fluidized. Using a device consisting of a continuous reaction tank and a distillation column, methacrylic acid in the first reaction tank,
Methanol is supplied to the first to fourth reaction tanks after the first reaction tank, the first reaction liquid is sequentially supplied from the first reaction tank to the second reaction tank, and the steam generated from the second reaction tank is sequentially supplied to the second reaction tank. At the same time as sending to the previous reaction tank and performing reactive distillation in each reaction tank,
A distillate generated from the first reaction vessel is supplied to a distillation column, a bottom liquid is circulated to the first reaction vessel, and methyl methacrylate is separated from the top of the column to produce methyl methacrylate. Method. 8. The method for producing methyl methacrylate according to claim 7, wherein the reaction tank is a stirred tank or a fluidized bed. 9. The method for producing methyl methacrylate according to claim 1, wherein the molar ratio of methanol to methacrylic acid is 1.01 to 1.2.