JPH0764788B2 - Method for producing 2-hydroxyalkyl (meth) acrylate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing 2-hydroxyalkyl (meth) acrylate. For more details,
The present invention relates to prevention of polymerization during synthesis or distillation of 2-hydroxyalkyl (meth) acrylate.

2. Description of the Related Art 2-Hydroxyalkyl (meth) acrylate is generally produced by reacting acrylic acid or methacrylic acid with alkylene oxide in the presence of a catalyst, and then purifying by distillation to obtain a product as a fraction. Is the law.

2-Hydroxyalkyl (meth) acrylate is a vinyl monomer that is very easily polymerized, and it is difficult to prevent the trouble of polymerizing during the reaction or during the distillation.

Various polymerization inhibitors have been proposed in order to prevent polymerization. For example, phenol-type polymerization inhibitors such as hydroquinone and hydroquinone monomethyl ether, and amine-type polymerization inhibitors such as N, N'-di-2-naphthyl-p. -Phenylenediamine (JP-A-51-8214), phenothiazine and the like are well known. In addition, inorganic salts such as potassium nitrite or sodium nitrite (US Patent No. 2.819.296), water-soluble alkali metal sulfite (Japanese Patent Publication No. 44-2685), and dialkyldithiocarbamic acid copper salt (Japanese Patent Publication No. 59-12658). ,
Alternatively, complex salts are also used.

Problems to be Solved by the Invention According to the studies by the present inventors, the above-mentioned polymerization inhibitor exhibited a satisfactory polymerization-inhibiting effect for synthesis and distillation on a small test scale using a glass instrument. . However, in a reactor or a distillation apparatus of a commercial production facility made of steres steel, a sufficient polymerization inhibiting effect was not obtained.

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and the device wall made of stainless steel is deeply involved in the occurrence of polymerization of 2-hydroxyalkyl (meth) acrylate. The inventors have found that nitrates have a markedly greater effect of preventing polymerization than the conventional polymerization inhibitors in preventing such polymerization, and have completed the present invention.

That is, the method for producing 2-hydroxyalkyl (meth) acrylate of the present invention uses a reaction apparatus and a distillation apparatus made of stainless steel to react acrylic acid or methacrylic acid with an alkylene oxide in the presence of a catalyst,
Then, when purified by distillation to produce 2-hydroxyalkyl (meth) acrylate, the reaction and / or the distillation are performed in the presence of nitrate.
-A method for producing hydroxyalkyl (meth) acrylate.

The reactor used in the present invention is a container in which a part or all of the material of the reactor is made of stainless steel, and is usually equipped with heating and cooling functions and a stirring device.

The synthesis reaction of 2-hydroxyalkyl (meth) acrylate is usually carried out batchwise as follows. That is, the reactor was charged with (meth) acrylic acid, a catalyst and a polymerization inhibitor, and the space inside the reactor was replaced with an inert gas such as nitrogen gas to avoid the risk of explosiveness, and then the liquid temperature was 50 to 110 ° C. The temperature is preferably raised to 60 to 90 ° C. Then, alkylene oxide is supplied to the reactor in a gaseous or liquid state to start the reaction. The reaction starts when the alkylene oxide is supplied,
Since the liquid temperature starts to rise, the reaction temperature is kept at 50 to 110 ° C, preferably 70 to 90 ° C by cooling.

The supply of alkylene oxide was stopped at the time when the supply amount of (meth) acrylic acid became 1.0 to 1.2, preferably 1.03 to 1.10, and the (meth) acrylic acid concentration in the reaction solution was 1.0% by weight. The above reaction temperature is maintained and the reaction is continued until the amount becomes preferably 0.5% by weight or less.

The alkylene oxide used in the present invention includes an oxirane compound such as epichlorohydrin in addition to an alkylene oxide in a narrow sense such as ethylene oxide and propylene oxide.

As the catalyst, various amines (JP-B-44-2685), quaternary ammonium salts (JP-B-45-27083), trivalent iron compounds (JP-B-43-18890), and chromium compounds (JP-A-57-18) −4
No. 2657) is known, but any of them may be used. The amount of catalyst is generally 0.01 to 10% by weight, preferably 0.03 to 3% by weight, based on the (meth) acrylic acid as a raw material.

The synthetic reaction solution thus obtained is then distilled in a distillation apparatus in which a part or all of the material of the apparatus is similarly made of stainless steel to obtain a product of 2-hydroxyalkyl (meth) acrylate as a fraction.

The distillation apparatus is composed of a heater, the above piping, a condenser, a vacuum generator, and the like. Distillation is carried out under reduced pressure, the operating pressure is preferably as low as possible from the viewpoint of polymerization prevention, but it is 1 to 8 mmHg, usually 3 to 6 mmHg, and the liquid temperature in the heating / evaporating section is 70 ° C. to 100 ° C., usually Is 80 ° C to 90 ° C.

The type of stainless steel used as the material of the reactor and the distillation apparatus may be so-called austenite type, martensite type, ferritic type, but austenitic type such as SUS-304, 316 from the viewpoint of availability and processing. Normally used.

In the present invention, nitrate is added as a polymerization inhibitor to the reaction and / or distillation described above. The type of nitrate used here is not particularly limited, but ammonium, sodium,
It is selected from salts of potassium, magnesium, calcium, copper, aluminum, iron, chromium, cobalt, nickel and the like. The amount used is 10 to 5000 ppm, preferably 50 to 500 ppm, based on 2-hydroxyalkyl (meth) acrylate.

Nitrate exerts a sufficient effect by itself, but other polymerization inhibitors such as phenothiazine, hydroquinone and hydroquinone monomethyl ether may be used in combination. Further, at the time of distillation, it is preferable to introduce an oxygen-containing gas such as air to prevent the polymerization of the gas phase portion.

Effect of the Invention When 2-hydroxyalkyl (meth) acrylate is produced in a commercial production facility using stainless steel, polymerization troubles frequently occur because the surface of the stainless steel vessel wall is very active for polymerization, and it is smooth. Production was difficult.

However, the method of the present invention makes it possible to prevent the polymerization caused by the stainless steel surface, which has been difficult with the conventionally known polymerization inhibitors, and thus the smooth commercial productivity of 2-hydroxyalkyl (meth) acrylate. Became possible.

Further, 2-hydroxyalkyl (meth) acrylate causes polymerization trouble not only when it is produced but also when it is stored in a stainless steel storage facility. By storing in the presence, such polymerization can be prevented.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

Example 1 661 g of methacrylic acid, 4.10 g of chromic chloride (hexahydrate) as a catalyst, and 0.66 g of sodium nitrate as a polymerization inhibitor.
Was charged into a 1.5-volume SUS-304 autoclave equipped with a stirrer, and after the inside was replaced with N ₂ gas, the temperature was raised to 80 ° C. 351 g of ethylene oxide was supplied over a period of about 2.5 hours, and the temperature was maintained at 80 ° C. during the reaction. After the supply was completed, the temperature was raised to 90 ° C. and the reaction was continued for 3 hours, and when the residual methacrylic acid reached 0.30%, the liquid was cooled. The lid of the autoclave was removed and the inside was inspected, but no formation of a polymer was observed. Then, the autoclave was used as a distillation pot, and a vacuum distillation apparatus comprising a SUS-304 lid, a vertical column having a diameter of 1.5 inches and a length of 30 cm, a cooling condenser, and a condensate receiver was constructed. Asbestos tape was used to maintain sufficient heat from the lid to the condenser inlet.

The distillation is heated in an oil bath at 130 ° C., under reduced pressure of 5-6 mmHg, 90
Distillation was carried out at a kettle liquid temperature of ℃ to 95 ℃ while supplying air to the kettle liquid portion at 10 ml / min.

When 720 g of distillate was obtained over 4 hours, distillation was stopped, and the equipment was disassembled and inspected. As a result, there was no noticeable thickening, which was a sign of polymerization, in the residual liquid in the kettle, and only a small amount of polymer was found in several places in the empty column. Only the adhesion was observed, and there was no other product formation adhesion of the polymer.

Comparative Example 1 The procedure of Example 1 was repeated, except that sodium nitrite was replaced by 0.66 g instead of sodium nitrate as the polymerization inhibitor. As a result, in the inspection after completion of the reaction, some adhesion of the polymer was found on the stirring blade and the vessel wall of the autoclave.

Next, when distillation was carried out, the fraction after 2 hours from the start was 36 g.
When it was obtained, the entire kettle liquid was polymerized and distillation was not possible.

Example 2 When the reaction and distillation were performed in the same manner as in Example 1 except that the autoclave and the distillation apparatus were made of SUS-316, the same results as in Example 1 were obtained.

Example 3 Except that 0.66 g of phenothiazine was used as a polymerization inhibitor in place of sodium nitrate at the start of the synthetic reaction, and 0.20 g of chromium nitrate (9-hydrate) was added to the reaction solution before distillation after the completion of the reaction. The same procedure as 1 was performed. As a result, in the inspection after completion of the reaction, some adhesion of the polymer was found on the stirring blade of the autoclave. After the end of the distillation, as in Example 1, there was no significant thickening or polymerization in the bottom liquid, and there was no formation or adhesion of a polymer other than a few adhesion of a few polymerization products in the empty column.

Comparative Example 2 After completion of the reaction, phenothiazine was replaced with 0.66 instead of chromium nitrate.
Example 3 was repeated except that g was added. 2.5 hours after the start of distillation, when 420 g of a distillate was obtained, the whole kettle liquid was polymerized and distillation could not be performed.

Comparative Example 3 Comparative Example 2 except that the distillation apparatus was changed to stainless steel and a vacuum distillation apparatus composed of a glass-made 1.5 flask, empty column, Liebig type condenser, and eggplant type flask was used.
Reaction and distillation were carried out in the same manner as in.

Distillation took 6 hours, and when 860 g of a distillate was obtained, the stopper was disassembled and inspected. As a result, there was no sign of polymerization in the residual liquid in the kettle, and there was no deposition of polymer in the apparatus.

Example 4 Using the same reaction and distillation apparatus as in Example 1, 16.7 g of tetramethylammonium chloride as a catalyst or Fecl ₃ -6H ₂ O 4.16 g as a main catalyst and CrCl ₃ as a cocatalyst were used.
Reaction and distillation were carried out using 0.40 g of -6H ₂ O, 0.66 g of hytroquinone as a polymerization inhibitor and the nitrates shown in Table 1.

The results are shown in Table 1.

Claims (1)

[Claims] 1. A 2-hydroxyalkyl (meth) which is purified by reacting acrylic acid or methacrylic acid with an alkylene oxide in the presence of a catalyst using a reaction apparatus and a distillation apparatus made of stainless steel, followed by distillation. A method for producing 2-hydroxyalkyl (meth) acrylate, which comprises reacting and / or distilling in the presence of a nitrate in producing the acrylate.