JPS5938244B2 - Continuous production method of acrylonitrile polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved industrial method for producing acrylonitrile-based polymers.

More specifically, the present invention relates to a method for continuously producing an acrylonitrile polymer having excellent thermal stability with high productivity. In general, in the production of acrylonitrile polymers used in the production of acrylic fibers, in addition to organic initiators such as azobisisobutyronitrile, so-called redox catalysts consisting of a combination of an oxidizing agent and a reducing agent are often used. It is being

On the other hand, many studies have already been conducted on the polymerization of acrylonitrile in an aqueous medium, and it is believed that the redox catalysts mentioned above are industrially useful in terms of polymerization rate and dyeability of polymers. It has been.

However, using such a redox catalyst,
Polymers obtained in aqueous media do not necessarily satisfy the high whiteness and good thermal stability that are particularly required as raw material polymers for acrylic fibers. For example, heat coloring resistance largely depends on the type of catalyst and basic polymerization conditions.

Analysis of the causes of thermal coloring of acrylonitrile polymers and countermeasures based on the results have been clarified in many documents, but these methods include the addition of extremely expensive color inhibitors and processes ranging from polymerization to fiber manufacturing processes. This method is limited to methods that inevitably lead to a decrease in productivity, such as trying to reduce the thermal history by using heat, and is often unrealistic. From this viewpoint, an object of the present invention is to continuously produce an acrylonitrile polymer having excellent thermal stability with high productivity.

The present inventors have conducted intensive studies on the production of acrylonitrile polymers suitable for the production of acrylic fibers, paying particular attention to polymerization catalysts, and have found that persulfate, nitrous acid or its salts, and reducing sulfoxy compounds. In continuous polymerization in an aqueous medium using a redox catalyst consisting of as a polymerization initiator, the above objective can be effectively achieved by adding an alkyl mercaptan that is sparingly soluble in water under predetermined polymerization conditions. I discovered that.

That is, the gist of the present invention is to continuously carry out polymerization of acrylonitrile or copolymerization of acrylonitrile with other unsaturated monomers copolymerizable with acrylonitrile in an aqueous medium, using persulfate and nitrous acid or its like as a polymerization catalyst. The purpose is to use a redox catalyst consisting of a salt and a reducing sulfoxy compound, and to satisfy the following basic conditions (1) and (2).

(1) The monomer concentration in the polymerization reaction system is expressed as a monomer/water ratio and is in the range of 1/4 to 1/1 by weight. (2) Adding an alkylcaptan having 4 to 12 carbon atoms to the polymerization system. In the present invention, first, a redox containing persulfate as an oxidizing agent is used as a catalyst.

Specifically, potassium persulfate or ammonium persulfate is preferred as the persulfate. On the other hand, as the reducing agent, a reaction product of nitrous acid or a salt thereof and a reducing sulfoxy compound is used. Although the reaction between the two has not yet been fully elucidated, it is thought that sodium hydroxylamine mono- or disulfonate is produced as the main product, and this combines with persulfate in a redox system to increase polymerization activity. There is. Therefore, it is desirable to mix and react the reducing agent components in advance before supplying them to the polymerization reaction tank, but since the reaction proceeds to some extent even in the polymerization reaction system, both may be supplied separately. However, in order to increase the polymerization activity, the former method, that is, the method of reacting both components in advance, is advantageous.
．． It is desirable to conduct the reaction continuously so that the reaction time is constant within the range of 5.5 or 5.0 to 6.5.The reaction temperature is 10 to 50°C, and the reaction time depends on the temperature. A range of 5 to 120 minutes is appropriate. Of course, it is preferable to carry out the reaction in the form of an aqueous solution, and after the reaction, the solution is fed directly to the polymerization tank at a predetermined rate. Common mineral acids are used as pH regulators, but sulfuric acid is most suitable. The reason why the pH range mentioned above is divided into two is that when alkaline sodium nitrite and particularly preferred strong acid sulfuric acid are mixed, a neutralization reaction system is instantaneously generated, and the P at the initial stage of mixing is
This is because it is very difficult to adjust H within the range of 3.5 to 5.

The best nitrite is sodium nitrite. on the other hand,
Specific examples of the reducing sulfoxy compound include sulfite, sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, ammonium bisulfite, ammonium metabisulfite, and sodium metabisulfite. It has been discovered that by using the above catalyst in polymerization, the polymerization proceeds smoothly and, at the same time, surprisingly, the viscosity of the polymerization slurry becomes abnormally low, making the stirring operation extremely easy.

As a result of further studies to achieve the above-mentioned object of the present invention, the inventors of the present invention have found that the monomer concentration in the polymerization reaction system, in other words, the ratio of supplied monomer/water, has been greatly improved, and the polymerization rate is high. It has been found that sufficient polymerization operation is possible even if the rate of polymerization is maintained at, for example, 80 to 90% per hour.

That is, the basic condition in the present invention is that the monomer/water ratio to be supplied is in the range of 1/4 to 1/1 by weight. If this ratio is less than 1/4, it is preferable because not only the polymerization productivity will be low but also troubles such as clogging of the cloth will occur in the post-processing of the polymerization slurry, especially during the overflow of the polymer. However, if the monomer/water ratio exceeds 1/1, the viscosity of the polymerization slurry increases rapidly, and scale tends to adhere to the inner wall of the polymerization pot or the stirring blade, so it is not practical. Such a high monomer/water ratio range is a surprising result that has not been found in conventional aqueous precipitation polymerization of acrylonitrile, and can directly contribute to a dramatic improvement in polymerization productivity.

On the other hand, the degree of polymerization of the polymer produced under the above conditions is generally high, and in order to freely obtain a polymer having a suitable degree of polymerization required for fibers, it is preferable to use a degree of polymerization regulator.

As a result of further investigation from this point of view, the second aspect of the present invention
We have discovered special alkyl mercaptans that simultaneously satisfy the objective of improving the thermal stability of polymers. That is, the second condition in the present invention is that the number of carbon atoms is 4 to 12.
of alkyl mercaptans to the polymerization system.

Mercaptans having 3 or less carbon atoms are highly volatile and have a bad odor, so they are not practical. The mercaptans selected here are characterized by being poorly soluble in water, and specifically include butyl mercaptan, hexyl mercaptan, n-octyl mercaptan, 2-ethylhexyl mercaptan, n- and tert-lauryl mercaptan, and Examples include thiophenol. Such mercaptans are used in an amount of 0.02 to 0.5%, preferably 0.1 to 0.3%, based on the total monomers, and are mainly used dissolved in the monomers to be fed. Mercaptans that are easily soluble in water, such as β-mercaptoethanol, are not preferred because they not only lower the degree of polymerization but also significantly lower the polymerization rate.

However, as a result of the study, the addition of the above-mentioned mercaptans that are sparingly soluble in water made it possible to freely adjust the degree of polymerization without causing a decrease in the polymerization rate. It was found that the thermal stability of the compound was significantly improved, making the present invention even more important industrially. Additional conditions for carrying out the invention are described below. In the case of copolymerization, other copolymerizable unsaturated monomers include vinyl acetate, methyl acrylate, methyl methacrylate, methacrylonitrile, acrylamide and methacrylamide or their derivatives, acrylic acid, methacrylic acid, itacon. Acids or their salts, or monomers containing basic or strongly acidic groups used for the purpose of improving dyeability, such as sodium vinylbenzenesulfonate, sodium methallylsulfonate, sodium allylsulfonate, vinylpyridines, dimethyl Known monomers such as aminoethyl methacrylate and halogen-containing monomers such as vinylidene chloride and vinyl bromide can be mentioned.

One or more of these monomers can be freely selected depending on the purpose, but the polymer used in the present invention is mainly composed of acrylonitrile. The amount of the polymerization catalyst used is not particularly different from that in the case of ordinary redox systems, and is in the range of 0.1 to 1.5%, preferably 0.3 to 1%, based on the monomer.

In order to promote the decomposition of the polymerization catalyst, it is desirable to use a metal salt such as iron or copper in combination, for example, ferrous sulfate is added in combination. In this case, the amount of ferrous ion in the polymerization system should be about 0.1 to 1 ppm relative to the monomer to sufficiently exhibit its effect. Polymerization is carried out by continuously feeding the above catalyst components, monomers and water into a polymerization tank at a predetermined rate.

Preferably, the polymerization is carried out in an atmosphere of an inert gas such as nitrogen. The pH of the polymerization system is preferably 1.5 to 3.5,
It is more desirable to keep it constant within the range of 2.0 to 3.0.

Usual inorganic acids or inorganic bases, specifically sulfuric acid, nitric acid and sodium bicarbonate, are used as pH regulators.
These may be contained in the above-mentioned feed water. The polymerization temperature is generally 40 to 60°C, preferably 45 to 55°C, and the average residence time of the reactants in the polymerization tank is usually 60 minutes to 60 minutes from the viewpoint of stirring operability to remove polymerization heat and control of polymer quality. Adopt 120 minutes.

On the other hand, for the purpose of removing polymerization heat or preventing scale adhesion at the start of polymerization, the monomer/water ratio at the initial stage of polymerization was adjusted to 1/1 in the steady state of the present invention in order to facilitate the stirring operation.
It is also desirable to make the monomer/water ratio smaller than the range of 4 to 1/1, and for example, a monomer/water ratio of 1/8 to 1/4 is practical.

It is also possible to make the polymerization tank multistage with two or more stages. In order to further improve the effects of the present invention, a commonly used whiteness improver may be further added in combination.

The polymer slurry that is continuously extracted from the polymerization tank can be obtained as a polymer powder by performing normal post-treatments such as washing, filtration, and drying, or it can be obtained as a polymer powder by omitting the drying step and retaining moisture. The acrylonitrile polymer is dissolved in a solvent and introduced into the fiber manufacturing process by a method such as directly preparing a spinning dope, either as it is or after distilling off the water.

As explained above, in the production of acrylonitrile polymers in aqueous media using specific catalysts, it is possible to achieve high thermal stability by specifying the basic conditions for continuous polymerization and by adding mercaptans that are poorly soluble in water. The industrial value of the present invention is extremely large in that it has become possible to produce a polymer with extremely high productivity. The present invention will be explained in more detail below using specific examples.

Reference Example 1 A sulfuric acid aqueous solution was added to a mixture of acrylonitrile and methyl acrylate, a potassium persulfate aqueous solution, a sodium nitrite aqueous solution, and a sodium bisulfite aqueous solution while blowing nitrogen gas into a continuous polymerization tank with an internal volume of 7.5 mm. PH3. Acrylonitrile was copolymerized by continuously and individually feeding O water.

When preparing the reducing agent aqueous solution of this reference example, first, a sodium nitrite aqueous solution and a sodium bisulfite aqueous solution were mixed continuously at a predetermined speed.

The mixing ratio of both was equimolar. Add 5N to this mixture
of sulfuric acid was added continuously, the mixture was reacted at 30° C. for 30 minutes, and the mixture was continuously supplied to the polymerization tank. At this time, the pH of the feed liquid is 2
．． It was set to 0. The polymerization conditions were as follows. Monomer: Acrylonitrile/methyl acrylate = 92/8 (
Weight %) Potassium persulfate: 0.50% by weight based on monomer Sodium nitrite: Potassium persulfate and equimolar ferrous sulfate:
0.5 ppm relative to monomer as Fe++ Polymerization temperature:
Average residence time at 50℃. 70 minutes In this reference example, polymerization was carried out under the above polymerization conditions by changing the monomer/water ratio in the steady state.

The polymerization results are shown in Table 1. Run Black 1 had very good operability in the polymerization tank, but the overflow slurry had extremely poor filtration and washing properties, and the slurry was abnormally cloudy.

On the other hand, when a high monomer concentration was applied as in Run Black 5, uniform stirring for removing polymerization heat became impossible within about 3 to 4 hours after the start of polymerization. Clearly, there is an optimal range of monomer concentration for polymerization operations.

On the other hand, the monomer concentration range of the present invention (Rurl 2, 3, 4
) and polymer specific viscosity (polymer 0.17) reached in 100 ml of dimethylformamide (DMF
) and measured at 25℃, the same applies hereafter) is extremely high,
In particular, the preferable specific viscosity range of the polymer required for fibers is 0.
16-0.18, it can be seen that when the monomer concentration is increased, the specific viscosity of the polymer shifts to a slightly higher specific viscosity side, and the spinning operability etc. decreases. Example 1 Under the conditions of Reference Example 1 and Run Black 3, β-methcaptoethanol (reference example) and n-octyl mercaptan (invention) were each added in an amount of 0.2% by weight based on the monomer.
and polymerization was carried out.

Claims (1)

[Claims] 1. Acrylonitrile alone or a mixture of acrylonitrile mainly consisting of acrylonitrile and an unsaturated monomer copolymerizable with persulfate, nitrous acid or its salt, and a reducing sulfoxy compound as catalyst components. A method for continuously producing an acrylonitrile polymer, characterized in that the following conditions (1) and (2) are satisfied during continuous polymerization in an aqueous medium. (1) The weight ratio of monomer/water to be supplied to the polymerization system is from 1/4 to
The range is 1/1. (2) Adding an alkyl mercaptan having 4 to 12 carbon atoms to the polymerization system.