JPS6216937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention produces acetaldehyde dimethyl acetal from acetaldehyde and methanol.
This invention relates to a method for continuously producing methyl vinyl ether. More specifically, in the first reaction step (acetalization), the present invention allows acetaldehyde and methanol to react only up to an equilibrium reaction, and then distills and separates an azeotrope of acetaldehyde dimethyl acetal and methanol from the reaction solution. By supplying methyl vinyl ether as is to the second reaction step (pyrolysis), the target product, intermediates, by-products, and unreacted raw materials can be effectively separated, recovered, and recycled for recycling. The present invention provides a continuous method for producing methyl vinyl ether.

Methyl vinyl ether is used as a synthetic resin and adhesive, and is also an extremely useful compound as a raw material for organic synthesis. For example, glutaraldehyde, which has uses in disinfectants, leather tanning agents, and crosslinking agents, is a derivative of methyl vinyl ether.

Acetaldehyde dimethyl acetal, which is an intermediate of methyl vinyl ether, is synthesized from acetaldehyde and methanol according to the following reaction formula ().

CH ₃ CHO + 2CH ₃ OHCH ₃ CH (OCH ₃ ) ₂ + H ₂ O () This reaction is an equilibrium reaction, and the conversion rate does not exceed the equilibrium composition.

Conventionally, methods for producing acetal from aldehyde and alcohol are known, and examples include using a dehydrating agent such as calcium chloride to increase the conversion rate, and separating the produced water using an inert solvent. There are examples (French Patent No. 868182, US Patent No. 2566559). However, when a dehydrating agent such as calcium chloride is used, a large amount of calcium chloride is required, which inevitably causes pollution problems in the wastewater, and has drawbacks such as the complexity of handling large amounts of calcium chloride. Furthermore, the use of an inert solvent such as toluene is not an advantageous method because it requires an additional separation step from the solvent.

Further, in these methods, the acetal produced is azeotropically distilled with methanol, so if methanol remains in the reaction, highly pure acetal cannot be obtained.
Conventionally, in order to advance the reaction to the right, it has been difficult to remove the water produced.

On the other hand, methyl vinyl ether is synthesized from acetaldehyde dimethyl acetal according to the following reaction formula ().

CH ₃ CH (OCH ₃ ) ₂ → CH ₂ = CHOCH ₃ + CH ₃ OH () Methanol is produced as a by-product at the same time in this reaction.

Conventionally, acetal was thermally decomposed in the gas phase to produce α and β-
Methods for producing unsaturated ethers are known (Japanese Patent Publication No. 41-5376, US Pat. No. 3,285,967).

In producing methyl vinyl ether from acetaldehyde and methanol via acetaldehyde dimethyl acetal, the present inventor changed the perspective and solved the problems of the acetalization process, which is the previous step, by combining it with the next step, the thermal decomposition step. tried to solve it. First, after conducting extensive research on the thermal decomposition reaction of the intermediate acetaldehyde dimethyl acetal, we found that it was easy to separate the product methyl vinyl ether and methanol by distillation.
We also discovered that methyl vinyl ether can be synthesized in the same yield as when pure acetaldehyde dimethyl acetal is used, even when an azeotrope of acetaldehyde dimethyl acetal and methanol is used as a raw material.

Next, the present inventor conducted further intensive studies on the acetalization reaction between acetaldehyde and methanol, and adopted the simplest equilibrium reaction that does not forcefully increase the conversion rate for the acetalization reaction. It has been found that applying a distillation separation step consecutive to dehydration, deacetaldehyde, and azeotropic distillation simplifies the process and is industrially extremely advantageous.

As described above, the method of the present invention improves industrial production techniques that were not necessarily satisfactory in the past, and makes it possible to economically advantageously produce methyl vinyl ether. That is, in the present invention, when producing methyl vinyl ether from acetaldehyde and methanol via acetaldehyde dimethyl acetal, (1) supplying acetaldehyde and methanol in an amount of 1 to 3 times the mole of acetaldehyde to a first reactor; Reaction is carried out at a temperature of 0 to 60°C in the presence of an acid catalyst (first step). (2) The resulting reaction liquid is led to the first distillation column, and the by-produced water is separated from the bottom of the column. A mixture consisting of acetaldehyde, methanol and acetaldehyde dimethyl acetal is extracted from the top (second step), and (3) the liquid extracted from the top of the first distillation column is extracted from the top of the first distillation column.
(4) At the bottom of the second distillation column, unreacted acetaldehyde is recovered from the top of the column, and a mixture of acetaldehyde dimethyl acetal and methanol is extracted from the bottom of the column (third step). Add the extracted liquid to the third
A part of unreacted methanol is recovered from the bottom of the column, and an azeotropic mixture of acetaldehyde dimethyl acetal and methanol is obtained from the top of the column (fourth step); The azeotropic mixture obtained from the top of the distillation column is fed to a second reactor, and reacted in the gas phase at a temperature of 200 to 400°C in the presence of a solid catalyst to produce methyl vinyl ether (fifth Step), (6) The obtained reaction liquid is led to a fourth distillation column, methanol by-produced is recovered from the bottom of the column, and methyl vinyl ether is obtained from the top of the column (sixth step). This is a continuous production method for methyl vinyl ether.

By the way, a method can be considered in which the azeotrope of acetaldehyde dimethyl acetal and methanol is not directly used in the thermal decomposition process of acetaldehyde dimethyl acetal, but is used after separating acetaldehyde dimethyl acetal from methanol. Extractive distillation or azeotropic distillation may be considered as one method for such separation, but these are of little practical value since there is no suitable third component. Another possible separation method is to combine pressurized distillation and normal pressure or reduced pressure distillation by changing the operating pressure and taking advantage of the fact that the ratios of both in the azeotropic composition are different. However, because their boiling points are close to each other, the number of plates and reflux ratio of each distillation column must be extremely large, which requires high operating costs for many distillation columns as well as high distillation column design technology and equipment costs. Therefore, it is undesirable.

Next, the method of the present invention will be explained in more detail based on drawings showing typical examples.

In Figure 1, A, E are reactors, B, C, D,
F indicates a distillation column, and solid line (dotted line) and 1 to 1
2 indicates the flow of material.

First step (acetalization): The raw material acetaldehyde is recovered from the top of the second distillation column C, and the acetaldehyde 6 is replenished with a new required amount of acetaldehyde 1, and the raw material methanol is fed to the third distillation column D. Methanol 8 recovered from the bottom of the column and methanol 11 recovered from the bottom of the fourth distillation column F are replenished with a new required amount of methanol 2, and are continuously supplied to the first reactor A. .

The charge ratio (molar ratio) of acetaldehyde/methanol is theoretically 1/2 according to reaction formula ().
However, considering the equilibrium reaction, there is no problem in charging at any ratio. However, in order to obtain an appropriate space-time yield and to reduce the amount of recycled raw material in consideration of the entire process, it is generally 1/1 to 1/3.
A range of is desirable.

There are no particular restrictions on the acid catalyst,
For example, hydrochloric acid, phosphoric acid, sulfuric acid, toluenesulfonic acid, cation exchange resins, and the like can be used by known methods. In this case, the acid concentration of the former is 0.1
Appropriately, the concentration of the ion exchange resin is approximately 1 to 5 wt%.

The reaction temperature is selected from the range of 0 to 60°C,
If the temperature is lower than this, the reaction rate will be slow, and if the temperature is higher than this, the boiling point of the raw material mixture will be exceeded, or high-boiling substances will be produced as by-products, which is disadvantageous. The reaction pressure only needs to be high enough to maintain the liquid phase, and is usually normal pressure, but may be pressurized depending on the composition of the raw materials and the reaction temperature.

Second step; the reaction solution 3 is led to the first distillation column B,
It is distilled under normal pressure, and by-product water 4 of the reaction system is separated from the bottom of the column.

It is expected that an azeotrope will be formed between the water by-produced in the reaction and the acetaldehyde dimethyl acetal produced in the second distillation step, but the coexistence of unreacted acetaldehyde will disrupt the azeotropic composition and easily It can be dehydrated, and the reverse reaction of reaction formula () can also be effectively suppressed by continuous dehydration.

Third step: The liquid 5 extracted from the top of the first distillation column B is led to the second distillation column C, where it is distilled under normal pressure or increased pressure, and unreacted acetaldehyde 6 is distilled from the top of the column. To separate. If necessary, the low-boiling components may be removed from the reactant, and the reactant may be reused as a part of the first reaction raw material.

Fourth step: The liquid 7 extracted from the bottom of the second distillation column C is led to the third distillation column D, where it is distilled under normal pressure, and methanol 8 is separated from the bottom of the column. This can be reused as is as part of the first reaction raw material.

Note that if the methanol in the composition of the feed liquid 7 is less than the azeotropic composition with acetaldehyde dimethyl acetal (former/latter = 25/75 in weight ratio), the third distillation column D may be cut off 7'.

Fifth step (thermal decomposition): The liquid 9 extracted from the top of the third distillation column D has an azeotropic composition of acetaldehyde dimethyl acetal and methanol;
is continuously fed to reactor E.

In the reaction of the fifth step, methanol is produced as a by-product in the reaction formula () and is also an inert substance, so the amount of methanol diluted does not essentially affect the reaction.

The solid catalyst is not particularly limited, and includes, for example, phosphates, sulfates, or those supported on a carrier, activated carbon, activated alumina,
Silica gel, acid clay, molecular sieve, etc. can be used by known methods. Appropriate contact time is about 5 to 20 seconds.

The reaction temperature is selected from the range of 200 to 400°C, preferably from 250 to 350°C. At low temperatures, the reaction rate is slow, and at high temperatures, the by-product of high-boiling substances becomes significant, which is disadvantageous. Further, the reaction pressure is usually carried out at normal pressure, but increased pressure may be used.

The reactor used in the first and fifth steps may be either a tank type or a column type depending on the type and condition of the catalyst used, and may be a hollow type, a packed type, a fixed bed type, a fluid bed type, etc. Can be selected as appropriate.

Sixth step: The reactor 10 is led to the fourth distillation column F, where distillation is carried out under normal pressure or increased pressure, and methanol 11, a by-product of the reaction, is recovered from the bottom of the column. This is done by cutting off high-boiling components as necessary and
can be reused as part of the reaction raw materials.
In this way, the target methyl vinyl ether 12 is obtained from the top of the fourth distillation column F.

Note that the distillation column in the second, third, fourth, and fifth steps may be appropriately selected from plate columns, packed columns, and the like.

In the method of the present invention, (a) in the acetalization reaction, an equilibrium reaction is adopted that does not forcibly increase the conversion rate, so third components such as dehydrating agents and inert solvents are not used, and the accompanying excess (b) It is easier to design and operate the distillation column than the conventional method of combining complicated distillations to break down the azeotrope of acetaldehyde dimethyl acetal and methanol; (c) The heat In the decomposition reaction, a practically sufficient yield can be obtained even when methanol coexists in the reaction system, so the azeotrope of acetaldehyde dimethyl acetal and methanol can be used as a raw material as is. It has many excellent industrial advantages, such as the ability to effectively separate, recover, and recycle living organisms and unreacted substances.

Hereinafter, the method of the present invention will be explained in detail by way of examples.

Example 1 First step; 1 equipped with stirrer and condenser
Acetaldehyde is added to the glass reactor A every hour.
484g (11.0mol), methanol 705g
(22.0 mol) and 1.2 g of concentrated sulfuric acid were continuously charged, and a constant amount of the reacted liquid was drawn out of the reaction system every hour by an overflow method. The reaction temperature was controlled to be 40°C. The resulting reaction solution produced 228 g (5.18 mol) of acetaldehyde and 333 methanol per hour.
g (10.4 mol), acetaldehyde dimethyl acetal 522 g (5.79 mol), produced water 104 g
(5.78 mol). The conversion rate of acetaldehyde was 52.9%, and the yield of acetaldehyde dimethyl acetal based on acetaldehyde was 99.5%.

Second step: The reaction solution obtained in the first step was
It was charged into the 20th stage from the bottom of the φ40 plated distillation tower B. Continuous distillation at normal pressure with a reflux ratio of 1 produces 224 g (5.09 mol) of acetaldehyde and 333 g of methanol per hour from the top of the column (temperature 52°C).
(10.4 mol) and 517 g (5.74 mol) of acetaldehyde dimethyl acetal were obtained, and 104 g of water was produced per hour from the bottom of the column (temperature 100°C).
(5.78mol) was obtained.

Third step: The distillate obtained from the top of the distillation column in the second step is transferred to a 20-plate distillation column C with an inner diameter of 30 mmφ.
Continuously charged from the bottom of the tower to the 10th stage. By carrying out continuous distillation at normal pressure with a reflux ratio of 2,
224 g (5.09 mol) of acetaldehyde is obtained per hour from the top of the column (temperature 20℃), and from the bottom of the column (temperature 60℃).
℃), 517 g (5.74 mol) of acetaldehyde dimethyl acetal and 333 g of methanol per hour.
A mixture consisting of (10.4 mol) was obtained.

Fourth step: The mixture obtained from the bottom of the distillation column in the third step was continuously charged into the 10th stage from the bottom of a 20-plate distillation tower D having an inner diameter of 30 mmφ. By performing continuous distillation at normal pressure with a reflux ratio of 2, 517 g (5.74 mol) of acetaldehyde dimethyl acetal and 172 g of methanol are produced every hour from the top of the column (temperature 58°C).
g (5.37 mol) of azeotrope was obtained, and 161 g of methanol was produced per hour from the bottom of the column (temperature: 65°C).
(5.02mol) was obtained. The yield of acetaldehyde dimethyl acetal from the first step to the fourth step was 97.1% based on acetaldehyde.

Fifth step: Lithium phosphate supported on silica 5
630ml of tablet-shaped catalyst of mmφ x 5mmH was packed into a stainless steel tubular reactor E with an inner diameter of 28mmφ, and 517g of acetaldehyde dimethyl acetal was added per hour onto the catalyst heated to 325℃.
(5.74 mol) and methanol 172 g (5.37 mol) were fed. The resulting reaction solution produced 353g of methanol per hour.
(11.0mol), methyl vinyl ether 317g
(5.45 mol) and 15.5 g (0.17 mol) of unreacted acetaldehyde dimethyl acetal. The conversion rate of acetaldehyde dimethyl acetal was 97.0%, and the yield of methyl vinyl ether based on acetaldehyde dimethyl acetal was 97.9%.

Sixth step: Pour the reaction solution obtained in the fifth step into a tube with an inner diameter of 30 mm.
It was charged into the 20th stage from the bottom of a φ, 40-stage plate distillation column F. Purity is increased every hour from the top of the column (temperature 6°C) by continuous distillation at normal pressure with a reflux ratio of 1.
99.5% or more methyl vinyl ether 317g
(5.45 mol) was obtained, and 353 g (11.0 mol) of methanol and 15.5 g (0.17 mol) of acetaldehyde dimethyl acetal were obtained from the bottom of the column (temperature 65°C) per hour.
A mixture of was obtained. The consistent yield of methyl vinyl ether from the first step to the sixth step was 95.1% based on acetaldehyde.

Example 2 First step: Instead of concentrated sulfuric acid in Example 1, a strongly acidic ion exchange resin (manufactured by Rohm and Haas,
The same procedure as in Example 1 was carried out except that 12 g of Amberlyst 15) was used. A wire mesh was attached to the outlet of the reaction solution to prevent the ion exchange resin from flowing out of the reaction system during the reaction, and the reaction temperature was controlled at 50°C. The reaction solution obtained is acetaldehyde every hour.
182g (4.13mol), methanol 265g
(8.27mol), acetaldehyde dimethyl acetal 617g (6.85mol), produced water 123g
(6.85 mol). The conversion rate of acetaldehyde was 62.5%, and the yield of acetaldehyde dimethyl acetal based on acetaldehyde was 99.7%.

Second to fourth steps: The same procedure as in Example 1 was carried out, and the distillation in the fourth step yielded 614 g (6.81 mol) of acetaldehyde dimethyl acetal per hour as an azeotrope with methanol. The yield of acetaldehyde dimethyl acetal from the first step to the fourth step is based on acetaldehyde.
It was 99.1%.

Fifth step: The same procedure was carried out except that 630 ml of Molecular Sieves-3A (manufactured by Union Carbide Co., Ltd.) was used in place of the lithium phosphate catalyst in Example 1. 421g (13.2mol), methyl vinyl ether
It consisted of 366 g (6.31 mol) and 18.5 g (0.21 mol) of unreacted acetaldehyde dimethyl acetal. The conversion rate of acetaldehyde dimethyl acetal was 97.0%, and the yield of methyl vinyl ether based on acetaldehyde dimethyl acetal was 95.0%.

Sixth step: The same procedure as in Example 1 was carried out, and 366 g (6.31 mol) of methyl vinyl ether with a purity of 99.5% or more was obtained per hour by distillation. The consistent yield of methyl vinyl ether from the first step to the sixth step was 94.1% based on acetaldehyde.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the flow in an apparatus implementing the method of the invention. A, E: Reactor, B, C, D, F: Distillation column.

Claims (1)

[Claims] 1. When producing methyl vinyl ether from acetaldehyde and methanol via acetaldehyde dimethyl acetal, (1) acetaldehyde and methanol in an amount of 1 to 3 times the mole of acetaldehyde are fed into a first reactor. and react at a temperature of 0 to 60°C in the presence of an acid catalyst (first step). (2) The resulting reaction liquid is led to the first distillation column, and the by-produced water is separated from the bottom of the column. Then, a mixture consisting of acetaldehyde, methanol and acetaldehyde dimethyl acetal is extracted from the top of the first distillation column (second step), and (3) the liquid extracted from the top of the first distillation column is extracted from the top of the first distillation column.
(4) At the bottom of the second distillation column, unreacted acetaldehyde is recovered from the top of the column, and a mixture of acetaldehyde dimethyl acetal and methanol is extracted from the bottom of the column (third step). Add the extracted liquid to the third
A part of unreacted methanol is recovered from the bottom of the column, and an azeotropic mixture of acetaldehyde dimethyl acetal and methanol is obtained from the top of the column (fourth step); The azeotropic mixture obtained from the top of the distillation column is fed to a second reactor, and reacted in the gas phase at a temperature of 200 to 400°C in the presence of a solid catalyst to produce methyl vinyl ether (fifth Step), (6) The obtained reaction liquid is led to a fourth distillation column, methanol by-produced is recovered from the bottom of the column, and methyl vinyl ether is obtained from the top of the column (sixth step). Continuous production method of methyl vinyl ether.