JPS5821637A - Purification of acetaldehyde suppressing formation of paraldehyde - Google Patents

Abstract

PURPOSE:To obtain acetaldehyde with a low content of paraldehyde, by adding an aqueous solution of ammonia or its organic acid salt to acetaldehyde containing a mineral acid, organic chloride, or sulfide, followed by distillation. CONSTITUTION:In purifying acetaldehyde containing a mineral acid, organic chloride, or sulfide, an aqueous solution of ammonia or an organic acid salt of ammonia (e.g., ammonium acetate) as a neutralizing agent for the mineral acid contained in it and a mineral acid which is formed by the decomposition of an organic chloride or sulfide, and acetaldehyde is distilled. The amount of the neutralizing agent to be added is preferably 10-10,000ppm (weight) based on acetaldehyde in the feed raw material in the form of 0.1-50wt% aqueous solution, and preferably the neutralizing agent is fed to the upper plate than the feed plate for raw material of a distillation column.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying acetaldehyde that suppresses paraldehyde production. Generally, acetaldehyde is produced by the oxidation method of ethylene and the water utilization reaction of acetylene, but since a small amount of paraaldehyde is produced as a by-product in this product, conventional measures to suppress this by-product have been taken. Various studies have been made.

However, since the ethylene oxidation method uses a metal chloride as a catalyst, some chlorine is eliminated and a trace amount of hydrogen chloride is produced along with methyl chloride and ethyl chloride.

On the other hand, sulfate is used as a catalyst in the hydration reaction of acetylene, and chloride is used as a catalyst in the synthesis reaction of vinyl acetate and monovinyl acetylene using acetylene as a raw material. There are many organic chlorides, organic sulfides, and some free mineral acids are formed.

These crude acetaldehydes containing mineral acids, organic chlorides, and sulfides are finally passed through a distillation column, where the organic high-boiling substances, chlorides, and sulfides are discharged.

During this distillation process, most of the free mineral acids and the mineral acids generated by the decomposition of chlorides and sulfides are discharged from the bottom of the column, but some of them are concentrated in the middle stage of the distillation column. . For this reason, the liquid side-cut from the middle liquid of the tower is 1 to 2
Paraldehyde increases to the order of several 10% in time.

A part of the mineral acid concentrated in the middle section is distilled out from the top of the column along with the distilled acetaldehyde, causing abnormal formation of paraldehyde.

As a measure to prevent para-aldehyde formation, there is a method of side-cutting the acetaldehyde containing a large amount of mineral acid concentrated in the middle stage of the distillation column, but when this method is used, the composition distribution of impurities in the distillation column fluctuates, resulting in Since a high concentration of paraldehyde is distilled out, this method is not very preferable as a continuous removal method.

Paraaldehyde is generally produced from acetaldehyde using a mineral acid as a catalyst, but in terms of the relationship between hydrogen chloride and the amount of paraaldehyde produced, several thousand ppm of paraaldehyde is produced when 1 ppm of hydrogen chloride is added. This fact indicates that prevention of paraldehyde formation cannot be achieved simply by improving distillation operations. Additionally, once paraldehyde begins to form, it grows explosively and there is no way to control it, so if it were to form, the only way to deal with it was to quickly dispose of it.

Potassium oxide is suitable, but addition of strong alkalis such as these to neutralize hydrochloric acid in acetaldehyde is not preferred because aldol condensates are formed.

The present invention solves these drawbacks by distilling crude acetaldehyde mixed with mineral acids, organic chlorides, or sulfides, and thereby reducing the amount of acetaldehyde contained in the distilled acetaldehyde. The object of the present invention is to provide a method for producing acetaldehyde by suppressing the production of paraldehyde, which makes it possible to reduce paraldehyde to the order of several ppm.

The present invention uses ammonia or ammonia as a neutralizing agent for mineral acids produced by decomposing mineral acids, organic chlorides, or sulfides when distilling acetaldehyde containing mineral acids, organic chlorides, or sulfides. It is characterized by adding a water bath solution of an organic acid salt.

The present invention will be further explained in detail below.

The neutralizing agent used in the method of the present invention is ammonia or an organic salt of ammonia, which has a mild neutralizing effect and has no adverse effects even if added in excess. As the organic rR salt of ammonia, ammonium acetate, ammonium oxalate, ammonium tartrate, ammonium formate, and ammonium chloride are preferably used.

Even if the neutralizing agent is added directly to the distilled acetaldehyde, it has the effect of suppressing paraldehyde, but since it adds impurities to the acetaldehyde, it is preferable to add it to the distillation column. When added to a distillation column, it is effective to some extent even if added directly to the feed material, but it has no neutralizing effect on mineral acids that are decomposed and generated during distillation, so it should not be added directly to the feed material feed stage of the distillation column. It is preferable to continuously add it to the upper part in the form of a water bath liquid.

The amount of neutralizing agent added depends on the amount of chloride and sulfide in the feed material, but it should be 0.1 to 50 ppm (by weight) to the acetaldehyde in the feed material. It is preferable to add it in the form of a wt % aqueous solution. If the amount of neutralizing agent used is too small, the suppressing effect on paraldehyde will be small, and if the concentration of the aqueous solution of the neutralizing agent is too low, the amount of water added will be too large, and water and high boiling point substances will be added to the distilled acetaldehyde. It is not preferable because it contains a lot of. On the other hand, if the amount of the neutralizing agent used is too large or the concentration of the aqueous solution of the neutralizing agent is too high, an addition reaction between ammonia and acetaldehyde will occur, which is not preferable. The amount of neutralizing agent to be added is preferably determined by checking the amount of distilled acetaldehyde and the amount of paraaldehyde in the middle stage liquid of the distillation column, and adding an amount that will maintain the amount of paraaldehyde in these areas at around 1.5 ppm (by weight).

Ammonia or an organic acid salt of ammonia used as a neutralizing agent is preferably one that does not contain chlorine, sulfate radicals, alkali metals or 41 alkaline earth metals, and has a content of 10 p.
pm (weight) or less is preferably used.

Examples and comparative examples are shown below. Chi and ppm k are heavy wrinkle standards.

Example 1 60.5% acetaldehyde, 69% water and 0.0% chloride.
An acetaldehyde aqueous solution containing 21 AI- was continuously fed into the conduit 2 of the distillation column 1 shown in the attached drawing at a rate of 21 AI-.

Distillation column 1 was operated at a reflux ratio of 4.0 so that the top temperature was 19'O±0.5°C, and 10 g of ammonium oxalate aqueous solution was continuously fed into conduit 3 at a rate of 2 CJIl/hr. . Sampling the distilled acetaldehyde,
The mixture was allowed to stand for an hour under water cooling, and then analyzed for noraldehyde by gas chromatography, and the result was that it was nofalaldehyde &ma Oppm. Paraldehyde was also traced after 6 hours.

Comparative Example 1 was distilled and the distilled acetaldehyde was analyzed after being left for 1 hour. As a result, paraaldehyde was 500 ppm and 3.000 ppm after being left for 3 hours.

Example 2 Under the same acetaldehyde water bath conditions as in Example 1, 4 cc of 5% ammonium acetate aqueous solution was added to conduit 3.
Continuous feeding was carried out at a rate of /hr.

The distilled acetaldehyde was sampled, left to stand under water cooling for 1 hour, and then analyzed for tR raldehyde. As a result, valaldehyde itself was found to be 1 ppm. After 6 hours, it was 5 ppm.

Example 6 An aqueous acetaldehyde solution containing 50.7% acetaldehyde, 69% water and 0.6 Llb sulfide was continuously fed into conduit 2 of distillation column 1 in the drawing at a rate of 2 l/hr. The distillation column was sampled under the same conditions as in Example 1, left to stand under water cooling for 1 hour, and then analyzed for paraaldehyde by gas chromatography. As a result, paraaldehyde was 1 ppm. Paraldehyde after 6 hours was 3 ppnn.

Comparative Example 2 As a result of leaving it under water cooling for 1 hour, paraaldehyde was 2.
50 ppm, and 9,000 ppm after 5 hours.

In the above Examples and Comparative Examples, chloride or sulfide is the total concentration of free hydrochloric acid or a-acid and organic chloride or organic sulfide.

The neutralizing agents used here were of a certain special grade. The contents of these chlorides and sulfates were as follows.

(11 ammonium oxalate chloride (cl) % 0,0005 or less sulfate (
SOa)% 0.005 or less (2) Ammonium acetate chloride (cJ)% 0.0005 or less Sulfate radical (80
4)% o, ooi Below (3) Ammonia aqueous solution chloride (cA % 0.00003 or less total sulfur (
(as SO4) 0.0003 or less

[Brief explanation of drawings]

The drawing is a system diagram of an apparatus used in an embodiment of the present invention. 1... Distillation column, 2... Conduit for supplying raw materials, 3... Conduit for supplying neutralizing agent aqueous solution, 4... Condenser, 5
... Distillation line, 6.. Reflux line, 7.. Reboiler, 8.. Liquid extraction line. Patent applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Scope of Claims] 1. Suppression of paraldehyde production characterized by adding aqueous solution of ammonia or an organic acid salt of ammonia when distilling acetaldehyde containing mineral acids, organic chlorides, or sulfides. Method for purifying acetaldehyde. 2. Adjust the concentration of the aqueous solution of ammonia or an organic acid salt of ammonia to 0.1" to 50% by weight, so that the concentration is 10 to 10.000 ppm (by weight) relative to the acetaldehyde that feeds the ammonia or the organic acid salt of ammonia. 3. The purification method according to claim 1, wherein the aqueous solution of ammonia or an organic acid salt of ammonia is fed to the raw material feed stage and the upper stage of the distillation column. The details described in the section