JPH0517401A - Separation of vinyl pivalate - Google Patents

Abstract

PURPOSE:To efficiently obtain vinyl pivalate by distillation separation of a mixture solution of vinyl pivalate and specified fatty carboxylic acids in the presence of water. CONSTITUTION:By distillation of a mixture composed of vinyl pivalate and formula RCOOH (R is H or lower alkyl) such as formic acid, acetic acid, propionic acid or a mixture thereof in the presence of water, vinyl pivalate can be very efficiently separated from aliphatic carboxylic acids by a low plate number or even in a distillation condition similar to single distillation because an azeotropic mixture is formed between vinyl pivalate and water. The vinyl pivalate layer obtained by separation from the distillate substantially does not contain water or aliphatic car boxylic acids and, therefor, can be used as a monomer for polymerization without further purification. On the other hand, the distilled water, after separation operation, can be recycled as an additional water to the distillation and separation system. The above- mentioned method in this invention can supply a more economical vinyl pivalate monomer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating vinyl pivalate from a mixed liquid of vinyl pivalate and a specific aliphatic carboxylic acid.

[0002]

It is known to produce an aromatic or aliphatic vinyl carboxylate by transesterifying an aromatic or aliphatic carboxylic acid with vinyl acetate in the presence of a palladium salt and a copper salt. (JP-A-63
-39835). The reaction liquid obtained by this reaction contains four components of aromatic or aliphatic carvone and vinyl acetate which are raw materials, and aromatic or aliphatic vinyl carboxylate which is a product and acetic acid. As a method for separating each component, in Example 1 of the publication, first, vinyl acetate was separated by distillation, then p-tert-butylbenzoic acid as a raw material was extracted with benzene, and then the product p- was obtained by vacuum distillation. It is described to obtain tertiary-butyl vinyl benzoate with a purity of 99.8%.

[0003]

Vinyl acetate has a lower boiling point than the other three components coexisting in the reaction solution and is relatively easy to recover by distillation. However, pivalic acid is used as the starting carboxylic acid. When used to obtain vinyl pivalate and acetic acid as products, it is extremely difficult to separate them because the boiling points of vinyl pivalate and acetic acid are close.

FIG. 1 shows vapor-liquid equilibrium data on the separation of vinyl pivalate and acetic acid. As is clear from FIG.
The composition difference of the gas-liquid part is extremely small, the azeotropic behavior of the two components is also recognized, and a distillation column having a high number of plates is required for the separation of both components, and the reflux ratio must be increased. The distillation operation must be carried out under economically unfavorable conditions with increased costs and utilities.

Therefore, an object of the present invention is to provide a mixed solution of vinyl pivalate and an aliphatic carboxylic acid represented by the general formula RCOOH represented by acetic acid (wherein R represents a hydrogen atom or a lower alkyl group). To efficiently separate vinyl pivalate from.

[0006]

The above object can be achieved by separating the mixed solution by distillation in the presence of water.

Examples of the aliphatic carboxylic acid represented by the general formula RCOOH used in the present invention include formic acid, acetic acid, propionic acid and mixtures thereof.

In the present invention, vinyl pivalate and RC
By distilling a mixed solution of an aliphatic carboxylic acid represented by OOH in the presence of water, vinyl pivalate is azeotropically mixed with water [azeotropic point: 86.5 ° C./760 mmHg, azeotropic composition: vinyl pivalate]. / H ₂ 0 = 4/1 (weight ratio)]
It is possible to separate vinyl pivalate and an aliphatic carboxylic acid very efficiently even in a low number of stages or under an evaporation condition close to simple evaporation, and the distillate from the top of the distillation column is a coexisting aliphatic compound. Substantially free of carboxylic acid,
In addition, the distillate can be separated into a vinyl pivalate layer (upper layer) containing substantially no water and an aqueous layer (lower layer) containing substantially no vinyl pivalate. The vinyl pivalate layer obtained by the liquid separation operation of the distillate is substantially water,
It does not contain an aliphatic carboxylic acid and can be used as it is as a monomer for polymerization without further purification operation, while the distillate water can be reused as added water to the distillation separation system after liquid separation. Therefore, according to the present invention, it is possible to construct a rational separation process in which both the facility cost burden and the utility usage amount are reduced, and it is possible to contribute to the inexpensive supply of vinyl pivalate monomer.

In the present invention, it is desirable to adjust the amount of water such that vinyl pivalate is present as an azeotropic mixture with water in the distillation column.
When the coexistence amount of water is small, for example, the number of distillation stages or the reflux ratio needs to be increased. On the contrary, when the coexistence amount of water is excessively large, thermal loss and reduction in volumetric efficiency are caused. Absent. The composition ratio of the vinyl pivalate / aliphatic carboxylic acid mixture to be separated becomes easier as the content of vinyl pivalate increases, but the number of distillation stages is increased to some extent or the reflux ratio is increased. As a result, vinyl pivalate and aliphatic carboxylic acid can be efficiently separated even if the content of vinyl pivalate in the mixed solution is about 1%.

The temperature in the distillation column is related to the stability in the presence of vinyl pivalate, an aliphatic carboxylic acid and water, and a range of 20 to 120 ° C. can be exemplified as a preferable range. Considering the properties, hydrolysis resistance, etc., 30 to 90 ° C, and further 40 to 70 ° C can be recommended as the internal temperature region. A temperature in the tower of 120 ° C. or higher is not preferable from the viewpoint of increasing the polymerizability of vinyl pivalate, the progress of hydrolysis in the presence of an acidic substance, and the like. The pressure in the distillation column can be appropriately selected from a reduced pressure of about 10 mmHg to a slightly increased pressure of about 2 atm in relation to the temperature inside the distillation column.

Since the distillative separation system of the present invention contains, in addition to water, an aliphatic carboxylic acid which may act as an acid catalyst in the distilling system, vinyl pivalate, which is one of vinyl esters, is used. There is a concern that the yield may decrease due to the hydrolysis of.

Certainly, among vinyl esters, vinyl acetates of primary or secondary carboxylic acids represented by vinyl acetate and vinyl isobutyrate easily cause hydrolysis, and by-products such as acetaldehyde and carboxylic acid are observed. Therefore, the distillation operation at low temperature is inevitable, including the distillation under reduced pressure. However, since the distillation separation system containing vinyl pivalate of the present invention is superior in hydrolysis resistance to vinyl pivalate, even in the distillation separation system in which an aliphatic carboxylic acid coexists, the separation operation can be performed at a high temperature, It is possible to construct an industrially suitable distillation separation system such that the distillate can be condensed without using a refrigerant.

The distillation separation method for carrying out the present invention is not particularly limited as long as it is a method for carrying out the distillation operation in the coexistence of water, but it is desirable that the gas-liquid contact is sufficiently carried out, and therefore the column tower is preferred. The countercurrent contact method of the formula is even more effective. That is, water is introduced from the upper part of the distillation column, a mixture of vinyl pivalate and an aliphatic carboxylic acid is introduced from the middle stage of the distillation column, and vinyl pivalate substantially free of an aliphatic carboxylic acid from the top of the distillation column-water. It is possible to obtain an azeotropic mixture and obtain an aliphatic carboxylic acid substantially free of vinyl pivalate from the bottom of the distillation column. Since the vinyl pivalate-water azeotrope obtained from the top of the distillation column separates into vinyl pivalate and the aqueous layer, they can be easily separated by performing a liquid separation operation.

The distillation column is a commonly used multistage distillation column,
A packed distillation column can be used as it is, and a material having corrosion resistance to an aliphatic carboxylic acid is desirable. The number of theoretical plates cannot be uniquely determined because it varies depending on the amount of water, the temperature in the distillation column, the concentration of vinyl pivalate, etc.
Steps are sufficient, and the reflux ratio is operated at 0.1 to 60. As described above, according to the method of the present invention, vinyl pivalate substantially free of an aliphatic carboxylic acid can be obtained as an azeotropic mixture with water from a mixture of vinyl pivalate and an aliphatic carboxylic acid. Since the azeotropic mixture is well separated into both layers of vinyl pivalate and water,
The vinyl pivalate can be efficiently isolated in a high yield with a purity high enough to supply it to polymerization, and the industrial significance of the present invention is extremely great.

The present invention relates to a reaction solution (pivalic acid as a raw material) produced by transesterification of pivalic acid and vinyl carboxylate represented by the general formula RCOOH = CH ₂ represented by vinyl acetate (R is the same as above). And RCOOH = CH
Vinyl carboxylate represented by _2, and a vinyl pivalate from including) the four components of the aliphatic carboxylic acid represented by vinyl pivalate and RCOOH product is particularly useful as a method for separating and purifying.

[0016]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples without departing from the gist thereof.

Example 1 A glass inner diameter of 30 mmφ equipped with a reflux head at the top,
500m with a Vigreux type reflux tube with a height of 200mmH as a distillation tube and a thermometer and sampling port at the bottom
The distillation test was carried out using an apparatus equipped with a 1-liter three-necked flask with a heating jacket. After replacing the system with nitrogen gas,
Under a nitrogen gas flow, 119 g of vinyl pivalate and 41 of acetic acid
A mixed solution of g and 72 g of distilled water was charged at the bottom of the distillation apparatus.
Start heating of the bottom under normal pressure, bottom temperature 87 ~ 92
A distillation test was carried out in the range of ° C, during which a vinyl pivalate-water azeotrope was distilled from the column top at an internal temperature of 86.5 to 87 ° C. Reflux operation was not carried out throughout the distillation period, and the distillate was directly collected in the receiver through the cooling pipe.
The distillation was stopped when the distillation temperature exceeded 87 ° C., during which 145 g of distillate was obtained, and the distillate was immediately separated into two layers [upper layer (organic layer) 118 g, Lower layer (aqueous layer) 27 g]. Gas chromatography and Karl Fischer analysis of both layers revealed that the upper layer contained 117 g of vinyl pivalate, 1 g of acetic acid and 0.1 g of water, and the lower layer contained 23 g of water and 4 g of acetic acid. Also, the bottom is 86g (vinyl pivalate 2g, acetic acid 36g,
Water 49 g), and formation of pivalic acid by hydrolysis and formation of high boiling substances by polymerization were not observed.

Example 2 50 g of 16-32 mesh granular activated carbon was immersed in 135 ml of acetic acid in which 550 mg of palladium acetate was dissolved, and allowed to stand overnight at room temperature. Then, the activated carbon was separated from the mouth and vacuum dried at room temperature. Adsorption rate 63%). This activated carbon was further immersed in 100 ml of an aqueous solution in which 2.7 g of potassium bromide and 0.77 g of cupric acetate were dissolved, and evaporated to dryness with heating to prepare a solid catalyst. 100 ml of this catalyst with an inner diameter of 3
A 0 mm U-shaped glass tube was filled, and this was placed in a thermostat at 80 ° C. to give a reaction tube. Pivalic acid 1530
g, 860 g of vinyl acetate, 20.0 g of potassium acetate, 550 mg of copper acetate, and 240 mg of potassium bromide were quantitatively fed at a flow rate of 100 g / inch for about 12 hours,
A transesterification reaction was carried out. As a result of analyzing the product liquid by gas chromatography, the product liquid was a mixed liquid containing 284 g of vinyl pivalate, 133 g of acetic acid, 235 g of vinyl acetate, and 532 g of pivalic acid. Glass inner diameter 40mmφ, height 1500 with a reflux head on top
Using a distillation column with a heating jacket of mmH, SUS31
The mixture was charged with McMahon filling No. 6 and the above mixture was distilled and separated in a distillation apparatus provided with a thermometer and a 1000 ml three-necked flask equipped with a heating jacket at the bottom. After substituting the inside of the system with nitrogen gas, 720 g of the mixed liquid was charged under the flow of nitrogen gas. The reflux ratio of the distillation system is 10, the temperature of the distillate from the top of the column is kept at 50 to 60 ° C., the low boiling point vinyl acetate is distilled off while adjusting the degree of pressure reduction and the bottom temperature, and then the vinyl pivalate-acetic acid mixed system. Was separated by distillation from pivalic acid, which has a high boiling point, to obtain 239.1 g of a mixed solution of 165.6 g of vinyl pivalate, 72.0 g of acetic acid and 1.5 g of pivalic acid. Example 1 was prepared by charging 200 g of this mixed solution and 45 g of distilled water into the distillation apparatus of Example 1.
The same distillation separation operation as above was carried out, and the temperature inside the column top was 86.5-
Distillate at 87 ° C 145 g [organic layer 118 g, water layer 27
g] was obtained. From the gas chromatography of both layers and the analysis by Karl Fisher, the composition of the organic layer was 99.2 wt% vinyl pivalate, 0.7 wt% acetic acid and 0.07 wt% water, and the composition of the aqueous layer was 88.3 wt% water.
Acetic acid was 11.7 wt%, vinyl pivalate was a trace amount, and the presence of pivalic acid was not confirmed.

Example 3 An inner diameter of 200 mmφ and a height of 3,500 mm were provided with a cooling and liquid separating device at the top of the tower and a side reboiler at the bottom of the tower.
The H column was loaded with a SUS316 McMahon packing to make a distillation separator. A mixed vapor of vinyl pivalate and acetic acid vaporized by a preheater from the middle stage of the distillation column was continuously supplied at a composition of vinyl pivalate of 100 Kg / hour and acetic acid of 47 Kg / hour, and distilled water of 24 Kg / hour was supplied from the top of the tower.
A continuous distillation test was carried out under conditions of a column top temperature of 93 ° C. and a column bottom temperature of 106 ° C. After reaching the steady state, a mixture of vinyl pivalate-water (vinyl pivalate 100 Kg / hour, water 45
(Kg / hour) is distilled out, and a water-acetic acid mixed solution is 71 kg / hour (water 24 kg / hour, acetic acid 47 kg / hour) from the bottom of the column.
Time) was obtained. The distillate was separated into a vinyl pivalate layer and an aqueous layer by a separator, and the aqueous layer was continuously refluxed to the top of the column. Acetic acid in the vinyl pivalate layer is 120
ppm and water content were 800 ppm. The amount of pivalic acid in the liquid taken out from the bottom of the column was a trace amount.

Example 4 128 g of vinyl pivalate was added to the bottom of the distillation apparatus of Example 1,
50 g of formic acid and 50 g of distilled water were charged, and vinyl pivalate and formic acid were separated by distillation by the same operation as in Example 1. The distillate from the top of the column was separated into two layers in the same manner as in Example 1 to obtain 116.1 g of an organic layer and 23.6 g of an aqueous layer. Gas chromatographic analysis of both layers and Karl Fischer analysis revealed that the organic layer was 115.7 g vinyl pivalate,
It contained 0.4 g of water and there was a trace of coexistence of formic acid. The water layer is 0.03g vinyl pivalate, 23.5g water,
It contained 0.01 g of formic acid. The distillation bottom is 88g
(Vinyl pivalate 12 g, formic acid 49.8 g, water 26.
2 g), and the formation of pivalic acid by hydrolysis and the amount of high-boiling substances were trace amounts.

Example 5 128 g of vinyl pivalate was added to the bottom of the distillation apparatus of Example 1,
Example 1 was charged with 74 g of propionic acid and 75 g of distilled water.
By the same operation as above, distillation separation of vinyl pivalate and propionic acid was carried out. The distillate from the top of the column was separated into two layers in the same manner as in Example 1, and the organic layer was 109.3 g and the aqueous layer was 21.2.
g was obtained. Gas chromatography of both layers and analysis by Karl Fischer revealed that the organic layer contained 109.1 g of vinyl pivalate and 0.2 g of water, and the coexistence of propionic acid was trace amounts. The water layer is vinyl pivalate.
It contained 1 g, 20.8 g of water and 0.3 g of propionic acid. Distillation bottom is 145.5g (vinyl pivalate 1
8.7 g, 73.3 g of propionic acid, 53.5 g of water), and the formation of pivalic acid by hydrolysis was a trace amount.

Comparative Example 1 Vinyl pivalate and acetic acid were separated by distillation in the same manner as in Example 1 except that 72 g of distilled water was not added. Charged liquid mixture (molar ratio of vinyl pivalate / acetic acid =
58/42) at the time of half-distillation (distillation temperature 109-1
The distillate up to 10 ° C) was analyzed by gas chromatography to find that the composition molar ratio of vinyl pivalate / acetic acid was 65 /
It was 35.

Comparative Example 2 Vinyl propionate 120 instead of vinyl pivalate 120
Separation of vinyl propionate and acetic acid was carried out by the same method as in Example 1 except that g was used. We were able to obtain an azeotropic mixture of vinyl propionate and water as the distillate, but propionic acid was charged in the bottom liquid of the column and 2 mol% of the propionate was detected, and the distillate was analyzed by gas chromatography. From the results, 1.8 mol% of acetaldehyde was detected on the basis of charged vinyl propionate, and it was confirmed that hydrolysis of vinyl propionate occurred.

Comparative Example 3 Vinyl acetate and formic acid were separated by the same method as in Example 4 except that 120 g of vinyl acetate was used instead of vinyl pivalate. Although an azeotropic mixture of vinyl acetate and water could be obtained as a distillate, acetic acid was charged in the bottom of the column to detect 2.5 mol% of vinyl acetate, and the distillate was analyzed by gas chromatography. Acetaldehyde was detected in an amount of 2.3 mol% based on vinyl acetate, which confirmed that hydrolysis of vinyl acetate had occurred. In addition, from the analysis of the liquid in the can, a high boiling substance assumed to be a polymer of vinyl acetate was detected in an amount of 2% by weight based on the charged vinyl acetate.

[0025]

According to the present invention, vinyl pivalate can be efficiently and highly separated from a mixed liquid of vinyl pivalate and an aliphatic carboxylic acid.

[Brief description of drawings]

1 shows vapor-liquid equilibrium data of vinyl pivalate and acetic acid.

[Explanation of symbols]

 1 Vapor-liquid equilibrium curve of vinyl pivalate and acetic acid

Claims (1)

Claim: What is claimed is: 1. A method according to claim 1, wherein vinyl pivalate and the general formula RCOOH.
(In the formula, R represents a hydrogen atom or a lower alkyl group)
A method for separating vinyl pivalate, which comprises distilling and separating vinyl pivalate in the presence of water when separating vinyl pivalate from a mixed solution with an aliphatic carboxylic acid represented by.