JPS636051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying impure alcohol, mainly containing ethanol and butanol. Specifically, the present invention mainly contains ethanol and butanol, and contains 2,4-dimethyl-1, as an impurity.
By adding ethyl acrylate to impure alcohol containing 3-dioxane and distilling it,
This invention relates to a method for purifying impure alcohol, which is characterized by obtaining a fraction having a composition consisting essentially of ethanol and ethyl acrylate, which does not contain 2,4-dimethyl-1,3-dioxane.

By aldol condensation of acetaldehyde, 1.
When 3-butylene glycol is produced, ethanol and butanol are mainly produced as by-products, and 2,4-dimethyl-1,3-dioxane (hereinafter referred to as DMDO) is produced as an impurity. 1・3
-Recovered impure alcohol obtained by purifying butylene glycol contains DMDO, which is the impurity mentioned above, in addition to these ethanol and butanol. Its composition is usually 70-90% by weight of ethanol, 10-30% by weight of butanol, and 0.5-1.5% by weight of DMDO.

It is extremely difficult to separate each component of this impure alcohol by distillation. The boiling point of DMDO is 120°C, which is almost the same as butanol. However, its volatility is higher than that of butanol, so when attempting to distill ethanol that does not substantially contain DMDO from this impure alcohol using normal distillation operations, a considerable amount of DMDO will be mixed into the ethanol fraction. Therefore, in order to fully achieve the purpose, a large number of stages are required and a distillation operation that requires utility is indispensable.

The present invention provides a distillation method for extracting ethanol from such impure alcohol with a simple operation, and particularly aims to obtain an ethanol-containing fraction that does not entrain DMDO.

Accordingly, the present invention is specified as follows.

(1) Contains mainly ethanol and butanol, with 2,4-dimethyl-1,3- as an impurity.
Impure alcohol containing dioxane is distilled together with ethyl acrylate to produce DMDO as a fraction.
A method for purifying impure alcohol, characterized by obtaining a mixture of ethyl acrylate and ethanol that does not substantially contain ethyl acrylate.

(2) The composition of the distillate is 70 to 80% by weight of ethanol, preferably 72 to 77% by weight, and 20 to 20% of ethyl acrylate.
The method according to (1) above, characterized in that ethyl acrylate is added to the distillation system in an amount of 30% by weight, preferably in the range of 23 to 28% by weight.

The present invention is carried out based on the following findings.

It was found that when ethyl acrylate was distilled in the presence of the above impure alcohol, the DMDO volatility changed and decreased considerably. In other words, the boiling point of ethanol is 78.3℃, while the azeotropic point of ethanol and ethyl acrylate is 77.5℃ (ethyl acrylate content is 27.3% by weight: Literature Azeotropic Data
), and although there is almost no difference in boiling point, the presence of ethyl acrylate in the distillation system makes it possible to obtain a fraction in which DMDO is almost completely removed. Therefore, this phenomenon is not a known simple azeotropic phenomenon, but is caused by the presence of ethyl acrylate in the distillation column near the azeotropic point.
It is presumed that this is due to the large change in the volatility of DMDO.

On the other hand, when water that forms an azeotropic composition with ethanol is used instead of ethyl acrylate, the azeotropic point of ethanol and water is 78.3°C (water content 4.0% by weight: refer to the literature Azeotropic Data), and the ethyl acrylate Although it is almost the same as in the case of , DMDO is also distilled out, and it has been found that this is almost the same as in the case of distillation without additives.

Thus, by adding ethyl acrylate to the impure alcohol and distilling it, the distillate contains
It can be said that it is a truly surprising effect that virtually no DMDO is mixed in.

Specifically, the present invention is carried out as follows.

As already mentioned, the impure alcohol targeted by the present invention is an impure alcohol containing impurities such as ethanol, butanol, and DMDO, which are inevitably generated industrially.

This impure alcohol is fed to a conventional distillation column, ie, one with about 15 to 40 theoretical plates. Although the distillation operation can be performed under reduced pressure or increased pressure, it is usually operated at normal pressure. Ethyl acrylate has a distillate composition of 70 to 80% by weight of ethanol, preferably
72-77% by weight, ethyl acrylate 20-30% by weight,
It is preferably mixed in an amount of 23 to 28% by weight. If the amount of ethyl acrylate added is too small, the ethyl acrylate in the distillate will be less than 20% by weight and DMDO will be distilled out, whereas if it is too large, ethyl acrylate will be added to the bottom liquid. Since it remains undesirably, controlling its input amount is extremely important. Ethyl acrylate may be supplied directly to the raw material impure alcohol, or may be supplied to the middle to upper stages of the distillation column. The distillation column liquid that essentially contains DMDO and butanol can be obtained.

The ethanol-ethyl acrylate mixed liquid fraction obtained from the top of the column contains substantially butanol and DMDO.
Since it does not contain any substances, it is advantageously supplied to the next step.
In particular, this mixed fraction can be further mixed with acrylic acid and subjected to an esterification step, which is advantageous because ethyl acrylate can be produced as it is and manufactured into a product. The esterification reaction is usually carried out in the presence of an acid catalyst, etc., and the contamination of the impurity DMDO into the esterification process is
This causes a decomposition reaction and generates acetaldehyde and other high-boiling substances, complicating the ester purification operation after the esterification process, and causing not only polymerization problems in the purification process but also negative effects on the polymerization performance and purity of the obtained ester. This is to have a positive impact. According to the findings of the present inventors, it has been found that the permissible amount of DMDO should be 0.02% by weight or less, preferably 0.01% by weight or less relative to ethanol.

Hereinafter, the method of the present invention will be explained in more detail by showing Examples and Comparative Examples, but it goes without saying that the present invention is not limited only to these Examples.

Example 1 Impure alcohol was distilled at a reflux ratio of 2 under normal pressure using an Older Schott distillation apparatus (inner diameter 32 mmφ) having 15 stages of concentration section and 15 stages of recovery section. The feed impure alcohol composition is ethanol 84.8% by weight, butanol 14.4% by weight, DMDO 0.80% by weight,
The feed rate was 214 g/hour. Ethyl acrylate was added at 61 g/hour to the impure alcohol feed section.
This amount is such that an almost azeotropic composition can be formed with the ethanol added. As distillate from the top of the tower
242g/hour was obtained, and DMDO was contained in this distillate.
0.0076% by weight was detected, with traces of butanol. Ethyl acrylate in the fraction was 25.2% by weight.

On the other hand, 33 g/hour of bottom liquid was obtained from the bottom of the tower.
This contains 5.2% by weight of DMDO and 0.035% of ethanol.
% by weight, 0.085% by weight of ethyl acrylate, and the remainder was butanol.

Comparative Example 1 The distillation operation of Example 1 was repeated except that ethyl acrylate was not added, the reflux ratio was 2, and the amount of impure alcohol supplied was 270 g/hour. 230g/hour was obtained as ethanol distillate from the top of the column.
0.52% by weight of DMDO was detected in this, and traces of butanol. On the other hand, the bottom liquid from the bottom of the column was 40 g/hour and contained 2.4% by weight of DMDO and 0.076% by weight of ethanol.

Comparative Example 2 In the distillation operation of Example 1, water was added at a rate of 10 g/hour instead of ethyl acrylate at a feed rate of 255 g/hour of impure alcohol to give a reflux ratio of 2, but the procedure was the same except for the same procedure. The ethanol-water fraction from the top of the column is 227 g/hour, which contains 0.35 DMDO.
% by weight detected, butanol traces, water as
It contained 4.4% by weight. On the other hand, the bottoms from the bottom of the column was 38 g/hour and contained 3.3% by weight of DMDO, 0.091% by weight of ethanol, and 0.067% by weight of water.

Claims (1)

[Claims] 1. Impure alcohol containing mainly ethanol and butanol and 2,4-dimethyl-1,3-dioxane as an impurity is distilled together with ethyl acrylate, and the distillate is 2,4-dimethyl-1,3-dioxane. A method for purifying impure alcohol, characterized by obtaining a mixture of ethyl acrylate and ethanol substantially free of 1,3-dioxane. 2. The method according to claim 1, wherein ethyl acrylate is introduced into the distillation system so that the composition of the distillate is in the range of 70 to 80% by weight of ethanol and 20 to 30% by weight of ethyl acrylate.