JPH0745447B2 - Method for recovering N-vinylformamide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for recovering N-vinylformamide.

[Conventional technology]

N-vinylformamide is useful as a polymerizable monomer that gives a water-soluble polymer having excellent aggregating performance, and its production method is, for example, by reacting acetaldehyde with formamide as shown in the following reaction formula. A method is known in which the obtained N- (α-hydroxyethyl) formamide is etherified with alcohol to give N- (α-alkoxyethyl) formamide, which is then pyrolyzed at high temperature to obtain N-vinylformamide. . That is, the following reaction formula: In the above method, N-vinylformamide is N
Since it is obtained by thermal decomposition of-(α-alkoxyethyl) formamide, it is recovered as a thermal decomposition mixture with alcohol as a by-product. Therefore, it is usually necessary to distill this mixture to isolate the N-vinylformamide. By the way, the method of the thermal decomposition reaction varies depending on the type of alcohol used for etherification, but usually, the above thermal decomposition mixture obtained by thermally decomposing N- (α-alkoxyethyl) formamide in the gas phase is condensed and recovered. In this case, since N- (α-alkoxyethyl) formamide is heated in a liquid phase to thermally decompose N-vinylformamide and alcohol produced by distillation, N- (α-alkoxyethyl) formamide is used in any case. -Vinylformamide will be recovered as a mixture with the alcohol.

[Problems to be solved by the invention]

However, conventionally, when N-vinylformamide is recovered by distilling a thermal decomposition mixture of N-vinylformamide and alcohol as described above, a part of N-vinylformamide is decomposed during the distillation, and N-vinylformamide is decomposed. Not only the recovery rate of N-vinylformamide decreases, but also the impurities generated by the decomposition are contained in the recovered N-vinylformamide, and this impurity also adversely affects the polymerizability of N-vinylformamide. There is a problem that it is desirable to keep the content as low as possible.

An object of the present invention is to provide a method for recovering N-vinylformamide by distilling a pyrolyzed mixture of N-vinylformamide and alcohol, which can solve the above conventional problems.

[Means for solving problems]

As a result of various studies to achieve such an object, the present inventors have found that a small amount of basic impurities are by-produced in the thermal decomposition of N- (α-alkoxyethyl) formamide, and the basic impurities are N-vinylformamide. It is present in a pyrolysis mixture with an alcohol to promote the decomposition of N-vinylformamide during the distillation time, and by contacting the pyrolysis mixture with a specific cation exchange resin in advance, a high purity N-vinylformamide can be obtained. The present invention has been achieved for the first time by discovering that vinylformamide is recovered by distillation in a high yield. That is, in the present invention, when a mixture containing N-vinylformamide obtained by thermally decomposing N- (α-alkoxyethyl) formamide is distilled to recover N-vinylformamide, the mixture is preliminarily weak acid cation. The gist is a method for recovering N-vinylformamide, which is characterized by carrying out a contact treatment with an exchange resin.

First, a conventional thermal decomposition mixture containing N-vinylformamide as a raw material for the recovery method of the present invention, that is, N- (α-hydroxyethyl) formamide as shown in the above reaction formula, was obtained by etherification reaction with alcohol. N- (α-
A general mixture of N-vinylformamide and alcohol obtained by thermally decomposing alkoxyethyl) formamide in a gas phase or a liquid phase and a distillation method thereof will be described in detail.

The etherification reaction of N- (α-hydroxyethyl) formamide with an alcohol is usually carried out at a temperature of 0 to 100 ° C., preferably 10 to 50 ° C. in the presence of a mineral acid catalyst such as sulfuric acid, hydrochloric acid or phosphoric acid. , The conversion rate of N- (α-hydroxyethyl) formamide as a raw material is 80% or more, preferably 90%
It will be implemented until the above. The alcohol used here is usually a monovalent aliphatic lower alcohol such as methanol, ethanol or propanol, or triethylene glycol, diethylene glycol, propylene glycol, 1,3-, 1,4- or 2,3-butane. Diol,
Examples thereof include dihydric aliphatic alcohols such as polyethylene glycol or polypropylene glycol having a molecular weight of 300 to 1,000. In this etherification reaction, an alcohol is usually used in an excess amount also as a solvent, but N- (α
-Hydroxyethyl) formamide is almost insoluble in the reaction system, but N- (α
Since -alkoxyethyl) formamide dissolves, a complete homogeneous mixed solution is obtained at the end of the reaction.

Then, the N- (α-alkoxyethyl) formamide obtained above is pyrolyzed to obtain a mixture containing N-vinylformamide. Depending on the type of alcohol used in the above etherification reaction, N- (α-alkoxyethyl) ) Due to the different properties of formamide, the thermal decomposition is carried out by the gas phase method or the liquid phase method, depending on this type. As a method of thermal decomposition, N- (α-alkoxyethyl) formamide is usually obtained by thermally decomposing N- (α-alkoxyethyl) formamide in a gas phase at a temperature of 200 to 400 ° C. under a reduced pressure of 200 mmHg or less, preferably 50 to 150 mmHg.
A method of condensing and recovering vapor containing vinylformamide and alcohol, or 20 mmHg or less, preferably 1 to 10
A method of heating at 90 to 200 ° C., preferably 120 to 180 ° C. under reduced pressure of mmHg, and performing thermal decomposition in a liquid phase while distilling off the produced N-vinylformamide and alcohol is mentioned.

In any case, these thermal decomposition methods produce N
-Vinylformamide is recovered as a mixture with the byproduct alcohol. Therefore, in order to isolate N-vinylformamide, it is necessary to distill these pyrolysis mixtures. This distillation is performed, for example, with N- at 3 mmHg.
Since the boiling point of vinylformamide is about 70 ° C, the conditions are appropriately selected at a temperature of 50 to 150 ° C under reduced pressure depending on the boiling point of the alcohol to be isolated.

In the recovery method of the present invention, the conventional pyrolysis mixture containing N-vinylformamide obtained as described above is used as a raw material for distillation. In the case of distillation, the raw material is previously weakly acid cation exchanged. The contact treatment with the resin is an essential requirement.

That is, a conventional pyrolysis mixture containing N-vinylformamide recovered by the above-mentioned pyrolysis contains a small amount of basic impurities, and when this is directly subjected to distillation, when it is directly subjected to distillation, The problem that not only the N-vinylformamide is partially decomposed and the recovery rate of the N-vinylformamide is lowered, but also the recovered N-vinylformamide contains a trace amount of impurities which adversely affect the polymerization. I got it. However, these problems are solved by subjecting such a conventional thermal decomposition mixture to a contact treatment with a weakly acidic cation exchange resin in advance.

As the weakly acidic cation exchange resin used in the present invention,
Usually, commercially available H-type acrylic acid-based or methacrylic acid-based cation exchange resins are mentioned, but acrylic acid-based ones are particularly preferable.

The contact treatment between the thermal decomposition mixture containing N-vinylformamide and the cation exchange resin is usually carried out by passing the thermal decomposition mixture through a resin-filled column or by adding the resin to the thermal decomposition mixture for a predetermined time. Any method of separating the resin after stirring is adopted. The contact time varies slightly depending on the processing conditions, but in the former case, the space velocity (S.
V.) 0.5 to 20, preferably 1 to 10 (converted to N-vinylformamide), and in the latter case, 5 minutes to 5 hours,
It is preferably 0.5 to 4 hours. The contact temperature is usually 0
-100 ° C, preferably 10-40 ° C.

In the present invention, when the thermal decomposition mixture is subjected to the contact treatment with the cation exchange resin, the mixture may be diluted with water, alcohol or the like, if necessary.

The thermal decomposition mixture that has been subjected to the above-mentioned contact treatment has good thermal stability by removing basic impurities, and further, for example, a small amount of potassium hydroxide, sodium hydroxide, sodium carbonate, etc. It is desirable to add the alkaline compound (1) because the thermal stability of the mixture is further improved. In this case, the alkaline compound is the pH of the pyrolysis mixture.
(PH when the pyrolysis mixture was diluted with 3 times the weight of water) was 6
It is adjusted so as to be in the range of 8 and added.

〔Example〕

Next, the present invention will be described more specifically with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist. In addition, "%" represents "wt%" unless otherwise specified.

Examples 1 to 4 and Comparative Example 1 (Production of ether body) In a 0.5 l glass reactor equipped with a stirrer and a temperature controller,
N- (α-hydroxyethyl) formamide (hereinafter abbreviated as "hydroxy form") crystal (73% purity, 0.5% formamide content, K ₂ ) obtained by reacting formamide and acetaldehyde in the presence of a potassium carbonate catalyst. 30 g of CO ₃ content 0.5%) was added, and 31.5 g of methanol (4 mol times with respect to hydroxy form) and 0.25 g of sulfuric acid (neutralization amount of K ₂ CO ₃ + 0.5 mol% with respect to hydroxy form) were added. Under stirring, the etherification reaction is carried out at a temperature of 25 to 40 ° C until the residual amount of hydroxy compound in the reaction system becomes 8% (reaction time 3 hours), and then 20% aqueous sodium hydroxide solution is added to this. The pH was brought to 7 by neutralizing the catalyst. Further, the liquid fraction was removed under reduced pressure of 50 mmHg, and then the ether was distilled and recovered under reduced pressure of 3 mmHg.

(Production of N-vinylformamide) The ether body obtained above was placed in a stainless steel tube equipped with a heater and having a diameter of 10 mm and a length of 500 mm while keeping the internal temperature at 400 ° C.
Under a reduced pressure of 0 mmHg, it is supplied at a rate of 2 g / mm, while the exhausted gas is immediately condensed to perform thermal decomposition,
23 g of distillate having the following composition was recovered.

N-Vinylformamide 67% Methanol 31% Other organic components 2% (Distillation of pyrolysis mixture containing N-vinylformamide) The distillate, which is the pyrolysis mixture obtained above, is in the form of H acid.
Ion exchange resin (trade name: Daiei, manufactured by Mitsubishi Kasei Co., Ltd.)
on WK-20) was added, and at room temperature, the following Table 1 was used.
After the contact treatment was performed under the conditions shown in, the resin was separated. Profit
Separately from each of the resulting solutions under reduced pressure of 50 mmHg, methanol.
For 30 minutes at a column top temperature of 87 ° C under a reduced pressure of 10 mmHg.
Distilling off N-vinylformamide
Recovered.

The recovery rate of the N-vinylformamide recovered here and the residual rate in the bottom of the kettle were obtained, and the polymerization test of the recovered N-vinylformamide was carried out to measure the time until the initiation of polymerization. The results are summarized in Table 1 below.

Comparative Examples 2-7 Instead of the weakly acidic cation exchange resin used in Example 3, the commercially available known adsorbent shown in Table 2 was used, and the thermal decomposition mixture was processed with Example 3. N-vinylformamide was recovered in exactly the same manner. The results are also shown in Table 2.

EFFECT OF THE INVENTION According to the method for recovering N-vinylformamide of the present invention, N
-By previously treating the pyrolysis mixture containing vinylformamide with a specific cation exchange resin,
It is possible to improve the stability of N-vinylformamide at the time of distillation and almost prevent its decomposition, and as a result, it is possible to recover N-vinylformamide in a much higher yield than before. Furthermore, conventionally, N at the time of distillation was used.
-A slight amount of impurities by-produced by the decomposition of vinylformamide was mixed in the N-vinylformamide recovered by distillation to adversely affect the polymerization reaction. However, according to the recovery method of the present invention, these impurities are hardly present. Therefore, N-vinylformamide having good polymerizability can be obtained extremely easily and in high yield.

Claims (1)

[Claims] 1. A method for distilling a mixture containing N-vinylformamide obtained by thermally decomposing N- (α-alkoxyethyl) formamide to recover N-vinylformamide, the mixture is weakly acid cation exchanged in advance. A method for recovering N-vinylformamide, which comprises contacting with a resin.