JPH085842B2 - Process for producing 2-hydroxyalkyl (meth) acrylate - Google Patents

Description

TECHNICAL FIELD The present invention relates to the production of 2-hydroxyalkyl acrylate or 2-hydroxyalkyl methacrylate (both of which are referred to as 2-hydroxyalkyl (meth) acrylate or monomer). It is about the method.
More specifically, it relates to prevention of polymerization during the synthesis reaction or distillation of 2-hydroxyalkyl (meth) acrylate.

2. Description of the Related Art 2-Hydroxyalkyl (meth) acrylate is usually synthesized by reacting acrylic acid or methacrylic acid (both of which are referred to as (meth) acrylic acid) with an alkylene oxide in the presence of a catalyst, Then, the product is obtained as a fraction by purifying by distillation.

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

Therefore, various polymerization preventing techniques have been conventionally proposed, and various polymerization inhibitors have also been proposed.

For example, as a phenol type polymerization inhibitor, hydroquinone, hydroquinone monomethyl ether and the like, and as an amine type, N, N'-di-2-naphthyl-p-phenylenediamine (JP-A-51-8214), phenothiazine and the like are often used. Are known. In addition, inorganic salts or complex salts such as potassium nitrite or sodium nitrite (US Pat. No. 2,819,296), water-soluble alkali metal sulfite (Japanese Patent Publication No. 44-2685), copper dialkyldithiocarbamic acid (Japanese Patent Publication No. 59-12658) Is also used.

In Japanese Examined Patent Publication No. 60-43056, as a method for preventing polymerization during distillation, a vapor of the monomer is heated to prevent condensation in the column portion, and a condensation liquid obtained by precooling the vapor of the monomer is used. A method of condensing and quenching by contacting in parallel is proposed.

Problems to be Solved by the Invention However, according to the studies by the present inventors, none of the conventional proposals is sufficient in preventing polymerization during the reaction or distillation.

For example, when the above-mentioned polymerization inhibitor was used, a satisfactory polymerization inhibition effect was exhibited in the synthesis and distillation on a small test scale using a glass instrument. However, in a reactor or distillation apparatus of a commercial production facility made of stainless steel, a sufficient polymerization inhibiting effect was not obtained. According to the tests conducted by the present inventors, the method disclosed in Japanese Examined Patent Publication No. 60-43056 was found to cause the following problems.

Polymers are easily attached to the heat transfer part of the distillation can.

It is an effective polymerization prevention method to prevent the condensation by heating the vapor line of the monomer, but the distillation can liquid and the vapor are mixed, for example, the heat transfer by applying to the gas-liquid separation section. A hard polymer adheres and grows on the entire surface, and eventually it becomes impossible to operate. Further, the polymer adheres firmly to the wall surface and is difficult to remove by cleaning.

On the other hand, when the gas-liquid separation part is not heated, a part of the vapor of the monomer is condensed and becomes a droplet to start the polymerization, and the entire gas-liquid separation part is filled with the polymer in a short time, which causes the operation. It becomes impossible.

As described above, the conventionally proposed techniques have not been satisfactory in synthesizing 2-hydroxyalkyl (meth) acrylate in a commercial production facility using stainless steel and preventing polymerization during distillation.

Means and Actions for Solving Problems The present inventors have conducted diligent studies to solve the above problems, and the surface of stainless steel usually used for commercial production equipment has a very high degree of polymerization of the monomer. It was found that the surface of stainless steel is more difficult to polymerize than fluororesin, phenolic resin, glass, etc., which are considered to be inert to polymerization, by subjecting the stainless steel surface to electrolytic polishing treatment. It has been completed.

That is, 2-hydroxyalkyl (meth) of the present invention
The production method of acrylate is as follows. 2- (meth) acrylic acid and alkylene oxide are reacted with each other, and then the obtained reaction solution is distilled to obtain 2-hydroxyalkyl (meth).
When producing acrylate, 2-hydroxyalkyl (meth), characterized in that the inner wall surface of the reaction device and / or distillation device made of stainless steel is electrolytically polished.
This is a method for producing acrylate.

The object of the present invention is to prevent the occurrence of polymerization during the synthesis reaction and distillation of 2-hydroxyalkyl (meth) acrylate in a stainless steel commercial production facility by electrolytically polishing the surface of the equipment wall. .

Here, the electropolishing is a method of electrochemically polishing the surface of an object to be polished by using an object to be polished immersed in an electrolytic solution as an anode and an insoluble metal as a cathode. The methods described in Processing Handbook, pages 384-389 (1969), Industrial Book Publishing, can be used.

The method of the present invention is described below, including the embodiment for producing 2-hydroxyalkyl (meth) acrylate.

The alkylene oxide used in the method of the present invention is an alkylene oxide such as ethylene oxide or propylene oxide, or an oxirane compound such as epichlorohydrin.

A catalyst is usually used in the reaction, and as the types thereof, various amines (Japanese Patent Publication No. 44-2685), quaternary ammonium salts (Japanese Patent Publication No. 45-27083), trivalent iron compounds and co-catalysts are used. A combination of silver or mercury (Japanese Patent Publication No. 43-1889)
No. 0), chromium compounds (JP-A-57-42657) and the like are known, but any of them may be used. The catalyst amount is generally 0.01 to 10% by weight with respect to the raw material (meth) acrylic acid,
The proportion is preferably 0.03 to 3% by weight.

The synthesis reaction of 2-hydroxyalkyl (meth) acrylate is usually carried out batchwise as follows. (Meth) acrylic acid in a reactor equipped with heating and cooling functions and a stirring device,
Charge the catalyst and polymerization inhibitor, replace the gas in the space inside the reactor with an inert gas such as nitrogen gas to avoid the risk of explosion, and then raise the liquid temperature to 50-110 ° C, preferably 60-90 ° C. To do. Then, the 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, and the liquid temperature starts to rise, so that the reaction temperature is cooled to 50 to 110 ° C,
It is preferably maintained at 70 to 90 ° C. The reaction operating pressure is not particularly limited, and may be increased pressure, normal pressure, or reduced pressure.

When the supply amount of alkylene oxide to (meth) acrylic acid is 1.0 to 1.2, preferably 1.03 to 1.10, the supply of alkylene oxide is stopped and the (meth) acrylic acid concentration in the reaction solution is 1.0. The above reaction temperature is maintained and the reaction is continued until the amount becomes not more than 0.5% by weight, preferably not more than 0.5% by weight.

As the polymerization inhibitor, hydroquinone, hydroquinone monomethyl ether, catechol, phenothiazine,
N, N'-di-2-naphthyl-p-phenylenediamine,
One or two or more kinds of nitric acid or nitrates are usually used in an amount of 0.01 to 3% by weight, preferably 0.03 to 1% by weight, based on (meth) acrylic acid.

 Hereinafter, further details will be described with reference to the drawings.

The reaction solution obtained as described above is purified by distillation to obtain a product as a fraction.

The distillation device is a distillation can 6 that performs necessary heat transfer for evaporation.
It is composed of a gas-liquid separator 9 and / or a distillation column, a cooling condenser 14 and an exhaust line 16.

The model of the distillation can is a jacketed container, or
There is a type in which bottoms are circulated and heated in a multi-tube heat exchanger, but the latter type and falling liquid film type are particularly preferable because of high heat transfer coefficient.

Distillation is performed under reduced pressure. It is desirable that the operating pressure is as low as possible from the viewpoint of polymerization prevention, but it is difficult to use a low pressure of 1 mmHgabs or less in a commercial production facility.
It is usually 1 to 8 mmHgabs, preferably 3 to 6 mmHgabs.
The temperature of the distillation can 6 is 70 to 100 ° C, preferably 80 to 90 ° C.

The vapor of the monomer generated from the distillation can 6 is usually introduced to the cooling condenser 14 via the gas-liquid separator 9 and / or the distillation column.

It is desirable to provide a demister 10 in the gas-liquid separator 9 and / or the distillation column to prevent entrainment of droplets. Further, it is preferable to heat the vapor conduit 11 from the outside and keep the vapor of the monomer in an overheated state to prevent condensation, thereby preventing polymerization.

However, when the vapor of the monomer is superheated,
Since the polymerization is likely to occur when it is introduced into the cooling condenser 14, it is preferable to bring the pre-cooled condensate and steam into contact with each other for rapid cooling.

In the present invention, the above synthetic reaction operation and distillation operation,
It is carried out using an apparatus in which a part or all of the material of the portion in contact with the monomer is stainless steel. The type of stainless steel may be any of so-called austenitic, mantensite, and ferritic types, but austenitic types such as SUS-304 and SUS-316 are usually used because they are easy to obtain and process.

In the present invention, part or all of the stainless steel device wall is electrolytically polished.

As an example of the electrolytic polishing treatment conditions, Cu-Pb is used as a cathode, and an electrolytic solution having a composition of 45% phosphoric acid, 35% sulfuric acid and 3% chromic acid is used at a current of 0.20 to 0.40 A / cm ² . It is preferable.

EXAMPLES Hereinafter, the present invention will be described more specifically by way of examples.

Example 1 On the entire inner wall of a SUS-304 reactor having an internal volume of 150 l, Cu-Pb
With a cathode as the cathode and an electrolyte solution containing 45% by weight of phosphoric acid, 35% by weight of sulfuric acid and 3% by weight of chromic acid at a current density of 0.30.
Electrolytic polishing was performed for 20 minutes at A / cm ² and a temperature of 60 to 70 ° C.

66.1 kg of methacrylic acid, 410 g of chromium (II) chloride (hexahydrate) as a catalyst, and phenothiazine as a polymerization inhibitor
66 g was charged into the reactor, the internal gas was replaced with N ₂ gas, and then 8
The temperature was raised to 0 ° C and the internal pressure was adjusted to 2.2 atm. 35.1 Kg of ethylene oxide was supplied over 4 hours, and the temperature was maintained at 80 ° C for the reaction.

After completion of the supply, the temperature was raised to 90 ° C. and the reaction was continued for 3 hours. As a result, the concentration of methacrylic acid in the reaction solution was 0.28% and the concentration of ethylene oxide was 400 ppm. Immediately after cooling, the solution was withdrawn.

Then, when the inside of the reactor was inspected, formation and adhesion of a polymer was not observed.

Further, the viscosity of the reaction solution was 4.8 cst (30 ° C.), and there was no increase in viscosity, which is a sign of polymerization.

After the inspection was completed, the reaction was continued in the same manner as another batch. After the completion of 2 batches, there was no polymer formation and adhesion in the reactor, the reaction liquid obtained was normal, and its viscosity was 4.8 cst.
(30 ° C).

Comparative Example 1 The procedure of Example 1 was repeated, except that the inner wall surface of the reactor was not electrolytically polished.

After the completion of the first batch, the inside was inspected, and it was found that the viscosity of the adhered liquid in the upper part of the reactor, that is, in the vapor phase part was high and the string was pulled.

The viscosity of the obtained reaction liquid was 5.1 cst (30 ° C), which was slightly high.

Then, the reaction of the second batch was performed. Two hours after the temperature was raised to 90 ° C. after the completion of the ethylene oxide supply, the viscosity of the reaction liquid was measured and found to be as high as 7.2 cst (30 ° C.) because of polymerization, so the liquid was immediately cooled and extracted.

Next, when the inside of the reactor was disassembled and inspected, a jelly-like polymer was found to be attached to various places around the gas phase.

Example 2 Obtained by the method of Example 1 by using the distillation apparatus shown in FIG. 1 in which a falling liquid film type double-tube heat exchanger using a 1-inch tube having a length of 1 m as a heat transfer tube was used as a distillation can. The reaction liquid thus obtained was distilled. The material of the contact portion of 2-hydroxyethyl methacrylate of the distillation apparatus was SUS-304. Further, electrolytic polishing was performed in the same manner as in Example 1 from the distillation can to the gas-liquid separator, the vapor conduit and the cooling condenser to the condensate receiver below.

To the reaction solution, 200 ppm of hydroquinone monomethyl ether and 100 ppm of chromium nitrate (decahydrate) were added as stabilizers.

With the liquid flow rate in the distillation can supply line set to 100 l / Hr, heating was performed in the distillation can with steam at 100 ° C. Air was supplied at 6 Nl / Hr from the top of the distillation can.

The pressure in the gas-liquid separator was 4 mmHgabs, and the liquid temperature of the bottom liquid was 86 ° C. A Teflon mesh-shaped demister was attached above the gas-liquid separator, and the vapor conduit beyond this was heated by a heater so that the wall temperature was 100 ° C. Similarly, the cooling condenser is a falling-film double-tube heat exchanger that uses a 1-inch tube with a length of 1 m as a heat transfer tube, while flowing cooling water of 30 ° C to the shell side and a liquid temperature of 40 ~ 30 ~ 40l / Hr of condensate at 50 ℃
It was supplied from above under the conditions described above, and the vapor and the condensate were brought into countercurrent contact with each other.

In this way, 5.5 Kg of reaction solution was supplied per hour,
A 5.0 Kg / Hr distillate and a 0.5 Kg / Hr bottom liquor were constantly obtained, which was maintained for 10 days.

After that, when the distillation apparatus was disassembled and inspected, only a small amount of the polymer was found to adhere to the liquid disperser of the distillation can, and no other polymer was present.

Comparative Example 2 Distillation was performed in the same manner as in Example 2 except that electrolytic polishing treatment was not performed.

As a result, 20 hours after the start of operation, the gas-liquid separator was clogged with the polymer and the operation was impossible.

In addition, the jelly-like polymer was attached to a considerable part of the lower side of the heating surface of the distillation can about 1/3. In addition, some polymer adhesion was found around the joint of the steam conduit below the cooling condenser.

Comparative Example 3 The procedure of Comparative Example 2 was repeated except that the heating area of the steam conduit was expanded to the upper half which is the gas phase part of the gas-liquid separator. Start of operation 4
After a day, the pressure in the gas-liquid separator was 5 mmHgabs and the temperature of the bottom liquid was 91.
Since it became ℃, I stopped the operation and inspected it. As a result, the thickness of the wall of the heating area from the gas-liquid separator to the demister is increased.
A hard polymer of 5 mm to 2 cm was firmly attached. In addition, the jelly-like polymer adhered to almost the entire lower half of the heating surface of the distillation can.

Comparative Example 4 Distillation was performed in substantially the same manner as in Example 2 except that the inner wall surface of the gas-liquid separator was treated as shown in Table 1. The results are shown in Table 1.

EFFECTS OF THE INVENTION Conventionally, when 2-hydroxyalkyl (meth) acrylate was produced in a commercial production facility using stainless steel, polymerization troubles frequently occurred, and smooth production was difficult.

However, as described above, the method of the present invention enabled the prevention of polymerization on the surface of stainless steel, and thus enabled smooth commercial production of 2-hydroxyalkyl (meth) acrylate.

[Brief description of drawings]

FIG. 1 is a flow sheet of the distillation apparatus shown in Example 2. The symbols in the figure are: 1: reaction liquid inlet, 2: bottom liquid outlet 3: distillation can supply line, 4: air inlet 5: liquid disperser, 6: distillation can 7: steam inlet, 8: drain outlet 9: Gas-liquid separator, 10: demister 11: steam conduit, 12: heating part 13: bottoms circulation pump, 14: cooling condenser 15: liquid disperser, 16: exhaust line 17: cooling water inlet, 18: cooling water Outlet 19: Condensate receiver, 20: Condensate outlet 21: Condensate circulation line, 22: Condensate circulation pump.

Claims (1)

[Claims] 1. When a 2-hydroxyalkyl (meth) acrylate is produced by reacting (meth) acrylic acid with an alkylene oxide and then distilling the obtained reaction solution, a reaction apparatus made of stainless steel and / Or the inner wall surface of the distillation apparatus is electrolytically polished, a method for producing 2-hydroxyalkyl (meth) acrylate.