JPH0332532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering (meth)acrolein and purifying methyl (meth)acrylate, and more specifically, the present invention relates to a method for recovering (meth)acrolein and purifying methyl (meth)acrylate. It also relates to recovering (meth)acrolein and purifying methyl (meth)acrylate.

Methyl acrylate or methyl methacrylate has been heavily used as a useful plastic raw material, but
In recent years, there has been rapid development in various application areas,
Quality requirements for raw material monomers are also becoming stricter. For example, impurities in methyl methacrylate for optical fibers need to be particularly limited. In addition to this, there are some cases in which highly purified methyl (meth)acrylate is required, and it is considered preferable to limit the amount of carbonyl compounds that are likely to be mixed in as impurities to 100 ppm or less.

On the other hand, the production method of methyl (meth)acrylate has also progressed, and even more advanced methods include oxidizing propylene or isobutylene to form an unsaturated aldehyde, oxidizing it again to form an unsaturated carboxylic acid, and then reacting it with methanol. It has also been proposed to produce unsaturated methyl carboxylate from unsaturated aldehyde, methanol, and oxygen all at once.

In either method, depending on the reaction method or recovery and purification method, (meth)acrolein may be contained in methyl (meth)acrylate in the stage obtained by separating crude methyl (meth)acrylate. There is. In addition, whether it is contained in the reaction raw materials or
Alternatively, carbonyl impurities may be contained due to unexpected side reactions during the reaction, and in such cases, the (meth)acrolein used as a raw material is difficult to recover and separate from methyl (meth)acrylate. It is important to prevent other carbonyl trace impurities from being mixed into the product. However, (meth)acrolein is also a carbonyl compound and is present in a larger amount than carbonyl trace impurities, and no method has yet been known to achieve the above objective under such circumstances.

Various attempts have been made to remove impurities such as aldehydes and ketones from crude (meth)acrylic acid or methyl (meth)acrylate by adding substances that react with them.
Addition of glycine (Japanese Patent Publication No. 50-14) or treatment with sodium hydrogen sulfite (Japanese Patent Publication No. 47-22374) has no effect at all because glycine and sodium hydrogen sulfite dissolve in methyl (meth)acrylate. Amines are also generally used in the form of hydrochlorides and the like, so they are similarly ineffective. Although amines and semicarbazides are quite effective, they have the disadvantage of slow reaction rates. Furthermore, as disclosed in JP-A No. 55-129239, there is a method for removing trace impurities that cause coloration by contacting them with a compound having a sulfonic acid group, but when the crude methyl (meth)acrylate is When applied, it was not possible to remove trace impurities. Moreover, the crude methyl (meth)acrylate contains a small amount of water, and when brought into contact with an acid, hydrolysis occurs, which is an unfavorable result.

In view of the above, the present inventors conducted various studies in order to achieve the above object, and found that if the crude methyl (meth)acrylate is distilled and hydrazine is supplied below the raw material supply stage, the column (Meth)acrolein can be recovered from the top with almost no loss, and at the same time a liquid with reduced carbonyl impurities is obtained from the bottom of the column, which is further distilled to produce high-purity (meth)acrylic with less than 100 ppm of carbonyl impurities. They discovered that methyl acid could be obtained and completed the present invention.

That is, in the present invention, when obtaining purified methyl (meth)acrylate from crude methyl (meth)acrylate containing carbonyl impurities together with (meth)acrolein, while distilling the crude methyl (meth)acrylate, In addition, while supplying hydrazine to the lower part from the raw material supply stage, (meth)acrolein is distilled and recovered from the top of the column, and methyl (meth)acrylate is obtained from the bottom of the column, which is distilled and purified from the top of the column. The present invention provides a method for recovering (meth)acrolein and purifying methyl (meth)acrylate, which is characterized by obtaining methyl (meth)acrylate.

The effects of the present invention are obtained by distilling while supplying hydrazine below the raw material supply stage. Only in this way can the carbonyl compound and hydrazine quickly react to form carbonyl compounds. This made it possible to reduce impurities to 100 ppm or less. If hydrazine is added without distillation, the relatively large amount of (meth)acrolein will react with hydrazine, resulting in an increase in the amount of hydrazine used, which will not only be economically disadvantageous but also cause carbonyl compounds, which are trace impurities. This makes it difficult for the reaction to proceed with carbonyl impurities
Therefore, it is not possible to reduce the concentration to less than 100ppm. Furthermore, even if hydrazine is supplied while being distilled, if hydrazine is supplied from above the raw material supply stage, as mentioned above, hydrazine reacts with (meth)acrolein present in a relatively large amount and is difficult to react with trace amounts of carbonyl compounds. Therefore, carbonyl impurities cannot be reduced to 100 ppm or less.

When hydrazine hydrate is used as the hydrazine, as in this method, the water brought in by the hydrazine added during distillation is easily distilled from the top of the column by azeotroping with methyl (meth)acrylate, and the liquid obtained from the bottom of the column is When further distilling methyl methacrylate to obtain purified methyl methacrylate, it is possible to prevent water from being mixed in, which is also one of the effects of the present invention. Furthermore, under such conditions during distillation, the water produced by the reaction between hydrazine and carbonyl compound is also easily removed.
This is considered to be one of the reasons why when hydrazine is added as in the present invention, even a carbonyl compound of 100 ppm or less reacts surprisingly quickly with a small amount of hydrazine.

The hydrazine used in the present invention may be anhydrous hydrazine or hydrated hydrazine, but since anhydrous hydrazine is difficult to handle, it is preferable to use hydrated hydrazine because it is easy to operate. The amount of hydrazine added is preferably 2 to 30 times the mole of the impurities to be treated; if more hydrazine is added than this, it will react with excess (meth)acrolein, etc., which is economically disadvantageous. Further, hydrazine may be supplied continuously or intermittently. The temperature in the distillation column at the point where hydrazine is added is preferably 50°C or higher, and preferably 130°C or lower to prevent polymerization. Distillation can be carried out under elevated pressure, normal pressure or reduced pressure, and is determined by the distillation temperature. The format of the distillation column may be a tray column, a packed column, or the like. In the distillation column for separating low-boiling components, a polymerization inhibitor can be supplied from the top of the column, and phenothiazine, hydroquinone, etc. can be used. Also, at the top of this low-boiling separation column, a small amount of methanol in the crude methyl (meth)acrylate,
(Meth)Acrolein, water, etc. are concentrated (Meth)
Distilled together with part of methyl acrylate (this is 2
By recycling this into the (meth)acrolein recovery process, it is possible to recover (meth)acrolein and methyl (meth)acrylate and reduce losses in the purification process. Furthermore, when the bottom liquid obtained in this low-boiling separation column is distilled, highly pure methyl (meth)acrylate can be obtained from the top of the column.
A packed column or the like can be used, and the polymerization inhibitor can also be added from any position in the distillation column.

Next, the method of the present invention will be specifically explained using Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In addition, % and ppm used below are unless otherwise indicated.
It is based on weight.

Example 1 An older-shot distillation column with an inner diameter of 32 mm and 60 plates, a raw material supply port on the 30th plate from the top of the column, a device capable of removing liquid under reduced pressure with a brine cooler on the top, and a liquid level gauge on the bottom of the column. The first distillation column has a device that can extract the bottom liquid under reduced pressure controlled by
The second distillation column is an older-type distillation column with a supply port that supplies the bottom liquid of the first distillation column from the top to the 30th plate with 50 plates, and a device that can remove liquid under reduced pressure at the bottom and top of the column. Using this method, crude methyl methacrylate was fed to the first distillation column at 140.4 g/hr. The crude methyl methacrylate contains 0.70% methacrolein, 1.63% water, 1.33% methanol, 1.18% methacrylic acid, 0.9% high boilers, and acetone as a trace impurity carbonyl compound.
It contained 320 ppm of diethyl ketone and two types of carbonyl compounds of unknown structure. Add hydrazine hydrate to the fifth stage from the bottom of the first distillation column every 0.5 hours.
The reflux ratio of the first distillation column was adjusted while feeding 50 μ in increments and while feeding 5% hydroquinone-methyl methacrylate solution from the top of the first distillation column at a rate of 2 ml/hr.
25, pressure 280mmHg, reflux ratio of second distillation column 2, pressure
The first distillation column and the second distillation column were connected and operated continuously at 80 mmHg. The top of the first distillation column, the raw material supply stage,
The temperatures at the bottom of the tower are 45.5℃, 72℃, and 78℃, respectively.
The temperature at the top and bottom of the second distillation column is 42
The temperature was 67°C, and an average of 10.1 g/hr of low-boiling components were distilled out from the top of the first column. Distillate composition: 9.7% methacrolein, 18.5% methanol, 22.5% water.
The contents were 0.1% acetone and 49.2% methyl methacrylate. In addition, colorless and transparent purified methyl methacrylate was distilled out from the top of the second distillation column at a rate of 119 g/hr. This fraction contains 99.9% or more of methyl methacrylate, 6 ppm of methacrolein, a total of 18 ppm of other carbonyl compounds such as acetone, diethyl ketone, and carbonyl compounds of unknown structure, and 25 ppm of methanol and 35 ppm of water. was. A liquid consisting of 18.1% methacrylic acid, 13.6% high boilers, and 69.8% methyl methacrylate was obtained from the bottom of the second distillation column at an average rate of 9.2 g/hr.

Comparative Example 1 Distillation was carried out under the same conditions as in Example 1 without supplying hydrazine hydrate, and purified methyl methacrylate obtained from the top of the second distillation column contained methacrolein.
It contained 35 ppm, and further contained 147 ppm in total of other carbonyl compounds such as acetone, diethyl ketone, and a carbonyl compound of unknown structure.

Claims (1)

[Claims] 1. When obtaining purified methyl (meth)acrylate from crude methyl (meth)acrylate containing carbonyl impurities together with (meth)acrolein, while distilling the crude methyl (meth)acrylate, the raw material is supplied. While supplying hydrazine to the lower part of the stage, (meth)acrolein is distilled and recovered from the top of the column, and methyl (meth)acrylate is obtained from the bottom of the column. ) A method for recovering (meth)acrolein and purifying methyl (meth)acrylate, which comprises obtaining methyl acrylate.