JPH0733360B2 - Acrylic monomer distillation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for distilling an acrylic monomer, and more specifically, to a mono N-substituted acrylamide and / or a mono N-substituted methacrylamide (hereinafter simply referred to as mono N-). And a method for preventing polymerization during distillation of substituted acrylic amides).

(Prior Art) Generally, an alkylamide-based monomer is a useful monomer that is polymerized and used as a flocculant or a wastewater treatment agent, and is manufactured by various methods. Since it does not become a coagulant or a wastewater treatment agent with low performance, it is usually purified by a means such as distillation to obtain a high-purity monomer and then used for polymerization.

However, mono-N-substituted acrylic amides are extremely easy to polymerize, and often polymerize due to heat, light, and other factors during the manufacturing process, storage, and transportation, and especially under heating conditions such as distillation and concentration processes. Insoluble polymer with original structure (hereinafter referred to as popcorn polymer)
Is generated rapidly. (Hereinafter referred to as popcorn polymerization.) Such a polymer is more likely to be produced in the gas phase part than the liquid phase part in the distillation system, and sometimes the distillation column, the pipe, etc. are blocked,
It may ignite spontaneously due to the heat of polymerization.

Hydroquinone, anthraquinone, hydroquinone monomethyl ether, phenothiazine, paraphenylenediamine, and copper metal salts which are conventionally known as inhibitors for such polymerization have almost no effect, and mono N-
Substituted acrylic amides have not been produced on an industrial scale.

(Problems to be Solved by the Invention) In the situation as described above, the present inventors have previously proposed to use a nitroso compound and radicals as a polymerization inhibitor for acrylic monomers. (Japanese Patent Application No. 61-28911
issue). However, although these polymerization inhibitors have the effect of preventing popcorn polymerization, they are not sufficient in terms of toxicity and cost, and in some cases, they may contribute to coloring of products. It was wanted.

(Means for Solving Problems) As a result of intensive studies to solve the above problems, it was found that the inducer of popcorn polymerization was air, but air was completely removed from the distillation system. The thing is
In particular, it is actually difficult in an industrial apparatus, and as a result of considering such factors, addition of N-nitrosophenylhydroxylamine salt to the vapor phase of the distillation system of mono-N-substituted acrylic amides suppresses popcorn polymerization. The present invention has been completed by finding out that the above can be achieved.

That is, the present invention relates to a distillation method characterized by adding 1 ppm to 20000 ppm of at least N-nitrosophenylhydroxylamine salt as a polymerization inhibitor to the gas phase when distilling mono N-substituted acrylamides.

Examples of the substituent of the mono-N-substituted acrylamides to be distilled in the present invention include an alkyl group having 1 to 5 carbon atoms, an aminoalkyl group having 1 to 5 carbon atoms, or a mono- or dialkyl (having 1 to 5 carbon atoms). 3) N-substituted aminoalkyl groups and the like can be mentioned.

Examples of the polymerization inhibitor N-nitrosophenylhydroxylamine salt to be added to the gas phase in the present invention include ammonium salt and ethanolamine, but are not particularly limited thereto.

The above-mentioned polymerization inhibitor used in the present invention is 1 to 20000 ppm with respect to the mono-N-substituted acrylamides in the gas phase, and practically 10 to
It is effective to add about 1000 ppm to the gas phase of the distillation apparatus, specifically, for example, a packed column section provided with Raschig rings or the like.

If the addition amount is less than 1 ppm, there is substantially no polymerization inhibiting effect,
Further, even if it exceeds 20,000 ppm, the effect does not increase and it becomes an economical loss.

The method of addition is not particularly limited, but for example, a product obtained by diluting and dissolving the same acrylic amide as the substance to be distilled in a predetermined amount with respect to the substance to be distilled in the gas phase according to the distillation rate is used. It is preferable to add continuously.

Further, in the present invention, it goes without saying that the above-mentioned polymerization inhibitor has a liquid-phase polymerization inhibiting effect when added to the liquid phase, and the polymerization inhibitor added to the gas phase has been conventionally used as a polymerization inhibitor. Known substances such as phenothiazine may be used in combination.

(Functions and Effects) In the distillation of mono N-substituted acrylamides by the method of the present invention, a salt such as ammonium salt of N-nitrosophenylhydroxylamine or ethanolamine salt is added to the gas phase as a polymerization inhibitor. It was possible to prevent popcorn polymerization that could not be prevented, and it became possible to industrially efficiently produce highly pure mono-N-substituted acrylamides.

(Examples) Next, the present invention will be described in more detail with reference to Examples, but the invention is not limited to these Examples. In the following examples, parts and% are parts by weight and% by weight unless otherwise specified.

[Examples 1 to 7 and Comparative Examples 1 to 5] 30 parts of various monomers represented by the general formula (1) and Examples 1 to 1
As shown in Table 1 for 7 and Comparative Examples 1 to 5, a predetermined amount of each polymerization inhibitor was placed in a color ampoule having a volume of 50 ml, and the pressure was reduced (0.5 mmHg or less) while cooling in a dry ice methanol bath. After sufficient deaeration, the ampoule was sealed with a gas fire under reduced pressure. When nitric oxide was used as a polymerization inhibitor, high-purity nitric oxide was blown into the monomer for 30 minutes under normal pressure, placed in an ampoule, and under normal pressure in a nitric oxide atmosphere, sealed. . Then, the mixture was heated in a 100 ° C. oil bath for 20 hours, and the presence or absence of polymerization was visually checked.
Moreover, the degree of coloring of the sample and the presence or absence of impurities were also checked with the naked eye and a gas chromatograph, respectively.

The experimental conditions and results are summarized in Table 1.

As is clear from the results shown in Table 1, when the conventional polymerization inhibitor was used under deaeration or under the nitric oxide atmosphere, the target monomer did not polymerize, but a large amount of impurities were generated. However, when the polymerization inhibitor of the present invention was used, not only did the target monomer not polymerize,
Generation of impurities was not observed.

[Example 8 and Comparative Example 6] N containing 2500 ppm of phenothiazine added to a 500 ml glass flask equipped with a Raschig ring packed column equipped with a reflux condenser.
-Preparing 300 g of methyl acrylamide, performing a reflux operation under the conditions of a bath temperature of 103 ° C, a column top temperature of 51 to 57 ° C, and an internal pressure of 0.39 to 0.78 mmHg, while N-nitroso was added to N-methylacrylamide in the packed column. The presence or absence of polymerization was checked while continuously adding the ammonium salt as a 1000 ppm solution of N-methylacrylamide so that the ammonium salt of phenylhydroxylamine was maintained at an amount equivalent to 50 ppm. As a result, polymerization did not occur even when operated for 16 hours under the same conditions, and the color of the solution in the flask was light yellow and transparent. Further, a part of the reflux liquid was sampled and checked for the presence or absence of the polymerization inhibitor by a gas chromatograph, but no mixture of the polymerization inhibitor was observed. Further, a part of the solution in the flask was sampled and checked for the presence of impurities by a gas chromatograph, but it was not observed at all.

On the other hand, as Comparative Example 6, 2500 ppm of 1-nitroso-2-naphthol based on N-methylacrylamide was placed in the flask instead of the ammonium salt of N-nitrosophenylhydroxylamine in the flask in the same amount as in Example 8 (2500 ppm) of phenothiazine. A reflux operation was performed under the conditions of a bath temperature of 103 ° C. and a system internal pressure of 0.39 to 0.78 mmHg while blowing nitric oxide gas into the flask through a glass capillary.

When operated for 16 hours under the same conditions, no polymerization was observed, but the inside of the flask was colored reddish brown and the middle part of the packed column was colored yellow. Moreover, as a result of sampling a part of the reflux liquid and observing the presence or absence of coloring with the naked eye, and checking the generation of impurities with a gas chromatograph, the reflux liquid was colored slightly pale yellow, and impurities were generated near 3000 ppm. .

Furthermore, part of the solution in the flask was sampled and the presence or absence of impurities was checked with a gas chromatograph.
It occurred near m. Next, when comparing the polymerizability of the monomer samples obtained by extracting the reflux liquid in this example and this comparative example, in the case of this example, the polymerization induction time was 10 minutes, whereas in the case of this comparative example The polymerization induction time was 35 minutes, which was extremely poor in polymerization property.

The polymerization test was carried out using 20 parts of the monomer as a test, adding 0.5% of a polymerization initiator (2,2′-azobis-2-amidisopropane dihydrochloride), and immersing it in a constant temperature water bath at 40 ° C., It was carried out by measuring the time until the initiation of polymerization.

It is clear that the polymerization inhibitor of the present invention is not only excellent in the polymerization inhibiting effect but also extremely effective in the impurity generation inhibiting effect.

[Example 9 and Comparative Example 7] A Raschig ring packed column equipped with a reflux condenser was attached to a 500 ml glass flask to 100 p with respect to N-methylacrylamide.
A flask was charged with 300 g of a solution containing pm of N-nitrosophenylhydroxyamine ammonium salt, and the bath temperature was 103
℃, the tower top temperature 51 ~ 57 ℃, the system pressure 0.39 ~ 0.78mmHg under the conditions of reflux operation while N-nitrosophenylhydroxylamine ammonium in the packed tower N-methyl acrylamide equivalent to 50ppm. Was continuously added as a solution containing 1000 ppm in N-methylacrylamide, and the presence or absence of polymerization was checked. Even if operated for 16 hours under the same conditions, polymerization in the distillation column did not occur at all,
The content liquid in the flask was only slightly thickened. Further, a part of the reflux liquid was sampled and the presence or absence of the polymerization inhibitor was checked by a gas chromatograph, but the polymerization inhibitor was not detected at all. Further, a part of the solution in the flask was sampled and checked for the presence of impurities by gas chromatography, but it was not observed at all.

Further, as Comparative Example 7, the same apparatus as in Example 9 was used, and N
-Phenothiazine against methylacrylamide, 5000
300 g of a solution to which ppm was added was charged, and reflux operation was performed under the same temperature and pressure as in Example 1. After starting the reflux operation, 30
After a minute, popcorn polymer was generated in the packed column, and after 35 minutes, the distillation system was completely closed.

In addition, when a part of the reflux liquid was sampled and checked by a gas chromatograph for the presence or absence of a polymerization inhibitor and the presence of impurities, the presence of a polymerization inhibitor was not recognized, but about 50 ppm of impurities were found.

Next, when comparing the polymerizability of the monomer samples obtained by extracting the reflux liquids of Example 9 and Comparative Example 7, the polymerization induction time was 10 minutes in the case of Example 9, but in the case of Comparative Example 7,
The polymerization induction time was 22 minutes, which was a very poor polymerization property.

[Comparative Example 8] N-Methylacrylamide was refluxed under the same conditions as in Example 9 except that no N-nitrosophenylhydroxylammonium salt was added from the middle stage of the packed column. Approximately 4 hours after the start of the reflux operation, popcorn polymer was generated in the packed column, and after about 5 hours, the packed column was completely closed.

Claims (2)

[Claims] 1. At the time of distillation, at least 1 ppm of N-nitrosophenylhydroxylamine salt as a polymerization inhibitor is added to the gas phase as a polymerization inhibitor.
A method for distilling mono-N-substituted acrylamides and / or mono-N-substituted methacrylamides, which comprises adding 20,000 ppm. 2. The distillation method according to claim 1, wherein during the distillation, at least 100 ppm to 20,000 ppm of phenothiazine as a polymerization inhibitor is added to the liquid phase.