JPH0138404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously saponifying an ethylene-vinyl acetate copolymer using a multi-stage column.

Using a multi-stage column, a methanol solution of ethylene-vinyl acetate copolymer and an alkali catalyst are supplied from the upper part of the column, while methanol vapor is blown from the lower part of the column or the bottom of the column to form a homogeneous liquid phase in the column to produce ethylene. - Methods for saponifying vinyl acetate copolymers are known from Japanese Patent Publications No. 14958/1980, No. 40547/1982, and 38558/1972. However, in these methods, when trying to increase the degree of saponification of the ethylene-vinyl acetate copolymer to 99 mol% or more, saponified products tend to precipitate and clog the perforated plate in the middle of the column. When a vinyl copolymer with a relatively low ethylene content, for example, one with an ethylene content of less than 33 mol %, is used, the column tends to become clogged before the degree of saponification becomes high. Such troubles can be resolved by increasing the temperature inside the tower (e.g. 96 to 135 degrees Celsius) and the pressure inside the tower (e.g. 3 to 9.5 atm), but this makes it difficult to operate when starting and stopping the operation. On the other hand, high temperatures adversely affect the quality of the obtained polymer, and high pressures are undesirable from the standpoint of safety and equipment cost.

The present invention uses a specific mixed solvent,
That is, by using a mixed solvent in which the weight ratio of polyhydric alcohol/lower aliphatic alcohol is 1/99 to 65/35, the above-mentioned problems can be completely solved.

That is, in the present invention, (1) the target ethylene-vinyl acetate copolymer has an ethylene content in a wide range of 15 to 60 mol%, but in particular ethylene content, which has traditionally been difficult to implement because it tends to precipitate during the saponification reaction; A smooth saponification reaction can be carried out for ethylene-vinyl acetate copolymers having a content of 15 to 33 mol%, especially 15 to 23 mol%.

(2) Highly saponified products with a degree of saponification of 99 mol% or more can be easily obtained.

(3) As reaction conditions, mild conditions such as a relatively low temperature inside the column of 75°C or less and a substantially normal pressure can be adopted.

(4) Even under the above reaction conditions, a homogeneous solution state can be maintained throughout the entire process of the saponification reaction, so the reaction operation is easy.

(5) As a result, a high-quality saponified product with little thermal history can be obtained.

This can have a remarkable effect.

In the present invention, an ethylene-vinyl acetate copolymer having an ethylene content of 15 to 60 mol % is used as the raw material polymer. If the ethylene content is outside this range, the oxygen barrier properties of the compound may be poor, and therefore they are not the object of the present invention. Among the above compositions, the ethylene content is 15 to 33 mol%, especially 15
Conventionally, it was thought that ethylene content of ~23 mol% could not be saponified by a multistage column at normal pressure, but in the present invention, even with ethylene content of 15 to 33 mol%, saponification degree of 99 mol% or more can be achieved under normal pressure. It is possible to saponify to a high degree of saponification.

The ethylene-vinyl acetate copolymer is supplied to the upper part of the multistage column in the form of a mixed solvent solution of polyhydric alcohol/lower aliphatic alcohol.

Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, glycerin, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, Examples include hexamethylene glycol. Among these, ethylene glycol is most suitable.

Examples of lower aliphatic alcohols include methanol,
Examples include ethanol, propanol, butanol, and methanol is particularly preferred from an industrial standpoint.

The ratio of polyhydric alcohol to lower aliphatic alcohol is 1/99 to 65/35, preferably 2.98 to 65/35 by weight.
If the ratio of polyhydric alcohol is too small, saponified particles may precipitate during the saponification reaction and cause blockage of the tower, while if the ratio of polyhydric alcohol is too large, the saponification will be delayed. The speed becomes slow, which is disadvantageous for industrial use. In relation to the ethylene content of the ethylene-vinyl acetate copolymer, it is desirable to increase the proportion of polyhydric alcohol within the above range as the ethylene content is smaller.For example, for a copolymer with an ethylene content of 24 to 33 mol%, teha22/
A range of 78 to 65/35 is desirable.

Along with the mixed solvent solution of the ethylene-vinyl acetate copolymer, an alkali catalyst is also supplied from the upper part of the column. It is desirable that both be mixed in advance before being supplied to the tower.

As the alkali catalyst, alkali hydroxides such as sodium hydroxide and potassium hydroxide, alcoholates of alkali metals, and the like are used.

Note that multi-stage towers include ordinary plate towers such as perforated plate towers and bubble bell towers, as well as packed towers.

Next, lower aliphatic alcohol vapor is blown into the lower part of the column or from the bottom of the column. As the lower aliphatic alcohol, those mentioned above are used, and methanol is particularly important.

A homogeneous liquid phase is formed within the tower, and the saponification reaction of the ethylene-vinyl acetate copolymer proceeds. The acetate ester produced by saponification rises together with the lower aliphatic alcohol, and is usually distilled off continuously from the top of the column.
It is continuously taken out from the bottom of the column in the form of a solution of a mixed solvent of lower aliphatic alcohols.

Although the degree of saponification can be determined arbitrarily, the feature of the present invention is that saponified products do not precipitate in the column even if the degree of saponification is increased to more than 99 mol% to nearly 100 mol%.

In order to precipitate the saponified product from the obtained saponified product solution, it is sufficient to add a non-solvent for the saponified product to this solution, and such a non-solvent may be, for example, acetate/lower aliphatic alcohol distilled from the column section. It is industrially advantageous to use a distillate of
Of course, other non-solvents such as acetic acid esters and ketones may also be used.

Although some polyhydric alcohol remains in the precipitated saponified product, this residual polyhydric alcohol can be easily removed by washing the saponified product with water or a solvent. However, when the saponified product is subjected to melt molding, the moldability will be better if it contains some polyhydric alcohol, so in such a case, an appropriate amount of the polyhydric alcohol may remain in the saponified product.

The temperature and pressure conditions inside the tower during the saponification reaction were 75℃.
It is sufficient to use a low temperature and normal pressure below this level, and it is not necessary to raise the temperature or pressure higher than this.

Next, the method of the present invention will be further explained with reference to Examples. Hereinafter, "%" means % by weight unless otherwise specified.

Example 1 150 kg of 50% methanol solution of ethylene-vinyl acetate copolymer with ethylene content of 26.7 mol%, 42.3 kg of ethylene glycol and 7% of sodium hydroxide
After mixing 13.4 kg of methanol solution in a mixer, it was charged into the upper part of a plate column with 36 plates at a rate of 205.7 kg/hr, while methanol vapor was charged from the bottom of the column at a rate of 150 kg/hr below the boiling point. The temperature inside the tower is 68 at the bottom of the tower.
℃, the top of the column was 58℃, and the column pressure was 1050 mmH ₂ O.
35 minutes after the start of charging, the reaction solution was taken out from the bottom of the tower at a rate of 192 kg/hr, and methyl acetate/
Distillate with methanol weight ratio of 24/76 is 163.4
It was distilled at a rate of Kg/hr.

The reaction liquid obtained from the bottom of the column was a completely transparent homogeneous solution, and its composition was 22.0% saponified ethylene-vinyl acetate copolymer, 0.9% methyl acetate, 22.0% ethylene glycol, 55.1% methanol, and 55.1% ethylene-vinyl acetate copolymer. The degree of saponification of vinyl acetate units in the saponified vinyl copolymer was 99.4 mol%.

This reaction solution was mixed with 5 times its weight of methyl acetate/
Saponified particles were precipitated by continuously feeding methanol into a mixed solvent with a weight ratio of 5/5, then pulverized, solid-liquid separation was performed using a centrifuge to reduce the volatile content to 55%, and then the mixture was heated at a temperature of 80°C. After drying for 2 hours, translucent saponified chips containing 4.5% ethylene glycol were obtained.

By supplying this saponified product as it is to a commonly used molding machine such as an injection molding machine or an extrusion molding machine without any special post-treatment, the cylinder temperature can be increased.
A molded product with no coloration could be obtained at 210°C.

When the wet particles after solid-liquid separation were poured into water at 25° C., washed once at a bath ratio of 20, and then dried, saponified particles containing no ethylene glycol were obtained.

Control example When a saponification reaction was carried out under the same conditions as described in Example 1 except for ethylene glycol, the column pressure suddenly increased 15 minutes after the start of charging.
It became impossible to continue the preparation. After disassembling the tower and inspecting it after stopping the charging, it was found that the perforated plate in the middle of the tower was clogged with precipitated particles. The degree of saponification of the precipitated particles was 98.1 mol%.

Example 2 Saponification was carried out in the same manner as in Example 1 except that glycerin was used instead of ethylene glycol.
Saponification proceeded smoothly, and a reaction solution having a composition of 22% saponified ethylene-vinyl acetate copolymer, 0.4% methyl acetate, 22% glycerin, and 55.6% methanol was taken out from the bottom of the tower. The degree of saponification of vinyl acetate units in saponified ethylene-vinyl acetate copolymer is 99.3 mol%
It was hot.

Example 3 After mixing 150 kg of a 50% methanol solution of ethylene-vinyl acetate copolymer with an ethylene content of 32.4 mol%, 26 kg of ethylene glycol, and 17.2 kg of a 7% methanol solution of sodium hydroxide, the mixture was poured into the upper part of a tray column.
Charged at a rate of 193.2Kg/hr, while 180kg was charged from the bottom of the tower.
Methanol vapor was charged at a rate of Kg/hr under heating to boiling point. In steady state, the temperature inside the column is 66
℃, the top of the column was 58℃, the column pressure was 840 mmH ₂ O, the reaction liquid was taken out from the bottom of the column at a rate of 217 Kg/hr, and the weight ratio of methyl acetate/methanol was 27/2 from the top of the column.
73 distillates were distilled at a rate of 156.2 Kg/hr.

The reaction liquid obtained from the bottom of the tower was a completely transparent homogeneous solution, and its composition was 20% saponified ethylene-vinyl acetate copolymer, 0.08% methyl acetate, and ethylene glycol.
12.0%, methanol 68.0%, and ethylene-
The degree of saponification of vinyl acetate units in the saponified vinyl acetate copolymer was 99.7 mol%.

This reaction solution was continuously fed into methyl acetate in an amount three times its weight to precipitate saponified particles, and when the liquid was removed and washed with water, a white powdery saponified product containing no ethylene glycol was obtained. It was done.

Claims (1)

[Claims] 1. Ethylene content of 15 to 60 mol% in the upper part of the multistage column
An ethylene-vinyl acetate copolymer solution and an alkali catalyst are supplied, vapor of lower aliphatic alcohol is blown into the lower part of the column or the bottom of the column, and the acetate ester produced by the saponification reaction is distilled together with the lower aliphatic alcohol from the top of the column. In this method, a solution of the saponified ethylene-vinyl acetate copolymer is taken out from the bottom of the tower by forming a homogeneous liquid phase in the tower and proceeding with the saponification reaction of the ethylene-vinyl acetate copolymer. saponified ethylene-vinyl acetate copolymer, characterized in that a mixed solvent of polyhydric alcohol/lower aliphatic alcohol with a weight ratio of 1/99 to 65/35 is used as a solvent for the ethylene-vinyl acetate copolymer. Manufacturing method. 2. Claim 1, wherein the ethylene content is 15 to 33 mol% as an ethylene-vinyl acetate copolymer.
The method described in section.