JPH0710794B2 - Method for distilling 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). Regarding the method. More specifically, it relates to a method for preventing polymerization when the vapor of the monomer is condensed and collected in the distillation purification 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 (hereinafter, both are collectively referred to as (meth) acrylic acid) and an alkylene oxide in the presence of a catalyst. Then, the product is obtained as a distillate by purifying by distillation.

The monomer has a very high polymerizability, and the polymerization is prevented by the same method as the (meth) acrylic acid ester or the (meth) acrylic acid ester obtained from this and an alcohol such as methanol or ethanol. It is very difficult to purify the monomer by distillation.

Conventionally, various polymerization inhibitors have been proposed, but even if they have a certain effect in a distillation can, they cannot prevent the polymerization of the vapor of the monomer in a conduit or a condenser.

Japanese Patent Publication No. 60-43056 discloses the following method for preventing polymerization during distillation.

Since the vapor of the monomer condenses and polymerizes when the condensate is exposed to high temperatures, the vapor conduit to the condenser keeps the vapor of the monomer superheated to prevent condensation.

In the condensation and collection of the monomer vapor, the condenser is a gas-liquid co-current direct heat exchange system, and the supercooled vapor introduced is condensed and sprayed with the liquid of the monomer that has been precooled. Rapid cooling of the condensate is essential to prevent polymerization.

However, according to a study conducted by the present inventors, by keeping the steam in the steam pipe in a superheated state to prevent condensation, the polymerization in the pipe pipe can be substantially prevented, but in the condenser, the superheated state is prevented. The vapor of the monomer in the state is much more easily polymerized than so-called saturated vapor. When the condenser type is a gas-liquid co-current direct heat exchange method for spraying such a pre-cooled condensate, the spray nozzle is exposed to high temperature by superheated steam, so that the nozzle is polymerized. It was easy to get clogged with things, and smooth continuous distillation operation was difficult.

Means and Actions for Solving Problems The inventors of the present invention have made extensive studies to solve the above problems, and use a double-tube or multi-tube heat exchanger as the type of condenser. The heat exchanger design handbook 2
As a vertical falling liquid film type condenser cooler described on pages 686 to 688 of the edition (published by Optical Book in 1982), the condensate is supplied from the upper part and made to flow down along the inner wall surface of the heat transfer tube. If the body fluid and the vapor of the monomer introduced from the lower part are brought into countercurrent contact,
The inventors have found that it is possible to condense and collect vapor in an overheated state without causing polymerization trouble, and have completed the present invention.

That is, the method for distilling 2-hydroxyalkyl (meth) acrylate of the present invention comprises reacting acrylic acid or methacrylic acid with alkylene oxide, distilling the obtained reaction solution, and distilling 2-hydroxyalkyl (meth) acrylate.
In obtaining the acrylate, a cooling condenser 14 which is a vertical double-tube type or multi-tube heat exchanger is used, and the liquid of the monomer is supplied from the upper part of the cooling condenser 14 in the heat transfer tube. It is characterized in that it is made to flow down along the wall surface and the vapor of the monomer introduced into the lower part of the cooling condenser 14 and the liquid of the monomer are countercurrently contacted to be condensed and collected while keeping the superheated state. It is a distillation method of 2-hydroxyalkyl (meth) acrylate.

An object of the present invention is to provide a means capable of condensing and collecting vapor of the monomer, which is kept in an overheated state because of the necessity of preventing polymerization in the vapor conduit, without causing polymerization trouble.

The method of the present invention will be described below, including the embodiments of the examples.

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.

The reaction is usually performed in the presence of a catalyst.

As the catalyst, various amines (Japanese Examined Patent Publication No. 44-2685), quaternary ammonium salts (Japanese Examined Patent Publication No. 45-27083), combinations of trivalent iron compounds and silver or mercury as a co-catalyst (Japanese Examined Patent Publication No. 43) -18890), chromium compound (JP-A-57-42657)
Etc. are known, but any of them may be used. The amount of the catalyst is generally 0.01 to the (meth) acrylic acid as the raw material.
The proportion is 10% by weight, 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, catalyst, and polymerization inhibitor were charged into a reactor equipped with heating and cooling functions and a stirrer, and the gas inside the reactor was replaced with an inert gas such as nitrogen gas to avoid the risk of explosion. After substitution, the liquid temperature is raised to 50 to 110 ° C, preferably 60 to 90 ° C. 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 molar ratio 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 concentration of (meth) acrylic acid in the reaction solution is 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.

As the polymerization inhibitor, usually, one or more of hydroquinone, hydroquinone monomethyl ether, catechol, phenothiazine, N, N'-di-2-naphthyl-p-phenylenediamine, sulfuric acid or nitrate, etc.,
It is 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 apparatus is composed of a distillation can 6, which performs necessary heat transfer for evaporation, a gas-liquid separator 9 and / or a distillation column, a cooling condenser 14, an exhaust line 16 and the like.

As the model of the distillation can, there are a jacketed container and a model in which the bottoms are circulated and heated by a multi-can heat exchanger. It is preferable because it has a large thermal coefficient.

Distillation is performed under reduced pressure. The operating pressure is preferably as low as possible from the viewpoint of preventing polymerization, but it is difficult to set the pressure as low as 1 mmHgabs or less in a commercial production facility, usually 1-8 mmHgabs, preferably 3-6 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. A demister 10 for the gas-liquid separator 9 and / or the distillation column.
It is desirable to prevent the entrainment of droplets by providing a.

In the present invention, in order to prevent the condensation of the vapor of the monomer in the conduit and the polymerization that occurs as a result thereof, the vapor conduit 11 is heated, and the vapor is introduced into the cooling condenser 14 in an overheated state. The temperature of the superheated steam is not limited to an excessively high temperature as long as it can prevent condensation, but is usually 0.1 to 30 ° C., preferably 1 to 15 ° C. higher than the boiling point at the operating pressure.

The monomer vapor is introduced into the cooling condenser 14. Since the monomer has a high polymerizability and is in an overheated state, it is very likely to undergo polymerization, and it is necessary to devise a great deal in terms of the operation of the cooling condenser due to its structure.

The cooling condenser 14 used in the present invention is a vertical double-tube or multi-tube heat exchanger, which is used as a vertical falling liquid film cooling condenser to collect the condensate from the upper part. Supply
By flowing down along the inner wall surface of the heat transfer tube and causing the condensate and the vapor of the monomer introduced from the lower part to come into countercurrent contact, the condensation and the condensate can be rapidly cooled.

The condensate is supplied to the upper part of the cooling condenser 14. The circulating fluid volume is
The amount of vapor of the monomer is usually 1 to 100 times by weight, preferably 3 to 30 times by weight.

The temperature of the condensed circulating liquid is 70 ° C or lower, preferably 50 ° C or lower.

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

Example 1 <Synthesis reaction> A SUS-304 reactor with an internal volume of 150 was charged with methacrylic acid at 66.1K.
g, 410 g of chromic chloride (hexahydrate) as a catalyst, 66 g of phenothiazine as a polymerization inhibitor, and 10 g of chromium nitrate (9 hydrate) were charged, and the internal gas was replaced with N ₂ gas, then at 80 ° C.
The internal pressure was raised to 2.2 atm. 35.1 kg of ethylene oxide was supplied over 4 hours, and the reaction was carried out while maintaining the temperature at 80 ° C.

After the completion of the supply, the temperature was raised to 90 ° C. and the reaction was continued for 3 hours. As a result, the methacrylic acid concentration in the reaction solution was 0.3% and the ethylene oxide concentration was 400 ppm, and then the reaction solution was cooled.

<Distillation> Obtained by the above-mentioned method using the distillation apparatus shown in FIG. 1 which uses a falling film double tube type heat exchanger having a 1-inch long 1-inch tube as a heat transfer tube as a distillation can. The reaction solution was distilled. The material of the contact portion of 2-hydroxyethyl methacrylate of the distillation apparatus was SUS-304. 200 ppm of methoxyhydroquinone was added to the reaction solution as a stabilizer.

Assuming that the liquid flow rate in the supply line of the distillation can 6 is 100 / Hr, 100
The distillation can 6 was heated with steam at ℃. Air was supplied from the upper part of the distillation can 6 at 6 N / Hr.

The pressure in the gas-liquid separator 9 was 4 mmHgabs, and the liquid temperature at the outlet of the distillation tube 6 was 86 ° C. A mesh-shaped demister 10 made of Teflon was attached above the gas-liquid separator 9, and the vapor conduit 11 further from there was heated by a heater so that the wall temperature became 100 ° C. The cooling condenser 14 is also a falling-film double-tube heat exchanger that uses a 1-inch tube with a length of 1 m as the heat transfer tube, and is a shell-side heat exchanger.
While flowing cooling water of ℃, the condensate at a temperature of 40 to 50 ℃ was supplied to the tube side from above at a temperature of 30 to 40 / Hr so as to make countercurrent contact with steam. Thus, the reaction liquid of 5.5 Kg was supplied for 1 hour, the distillate of 5.0 Kg / Hr and the bottom liquid of 0.5 Kg / Hr were constantly obtained, and the state was maintained for 10 days.

After that, when the distillation apparatus was disassembled and inspected, formation and adhesion of a polymer was not observed in the falling liquid film cooling condenser 14, its peripheral portion, the condensate circulation line 21 and the like.

Comparative Example 1 SUS-3 with a diameter of 150 mm and a height of 2000 mm as shown in FIG.
A 04 condenser was used. 800 mm from the top in the condenser
Distillation was carried out in substantially the same manner as in Example 1 except that there was a cooling jacket 4 between the two and the method was such that direct flow gas-liquid contact by the spray nozzle 7 was possible.

The liquid temperature of the spray liquid was 50 ° C. and the flow rate was 500 / Hr. In addition, cooling water having a water temperature of 30 ° C. was passed through the cooling jacket 4.

Since the spray liquid flow rate could not be maintained at 500 / Hr 3.5 days after the start of distillation, distillation was stopped and disassembly inspection was performed. As a result, about half of the nozzles were clogged with the polymer and the spray liquid stopped flowing. Further, adhesion of a polymer was found on various places on the wall of the condenser main body 13.

Effect of the Invention In the distillation of 2-hydroxyalkyl (meth) acrylate, it is essential to prevent the polymerization of the vapor of the monomer in the conduit from the viewpoint of polymerization, but the conventional technique is satisfactory from the viewpoint of polymerization prevention. There was no method for condensing and collecting superheated steam.

However, for the first time, the method of the present invention makes it possible to condense and collect superheated steam capable of sufficiently preventing polymerization, and enable smooth and continuous distillation of 2-hydroxyalkyl (meth) acrylate.

[Brief description of drawings]

FIG. 1 is a flow sheet of the distillation apparatus shown in Example 1. In the figure, each symbol is 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 section 13: Bottom liquid 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. FIG. 2 is a flow sheet of the condenser section of the distillation apparatus shown in Comparative Example 1. In the figure, each symbol is 1: superheated steam supply line, 2: superheated air inlet part 3: heating part, 4: cooling jacket 5: cooling water inlet, 6: cooling water outlet 7: spray nozzle, 8: condensate circulation Pump 9: Condensate outlet, 10: Condensate circulation line 11: Cooler, 12: Exhaust line 13: Condenser body.

Claims (1)

[Claims] 1. When a (meth) acrylic acid is reacted with an alkylene oxide and then the obtained reaction solution is distilled to obtain 2-hydroxyalkyl (meth) acrylate as a fraction, a vertical type double tube is used. Using a cooling condenser 14 which is a type or multi-tube heat exchanger, the monomer liquid is supplied from the upper part of the cooling condenser 14 to flow down along the inner wall surface of the heat transfer tube,
A 2-hydroxyalkyl (meth) which is characterized in that the vapor of the monomer introduced into the lower part of the cooling condenser 14 and the liquid of the monomer are countercurrently contacted with each other while keeping them overheated to condense and collect. )
Acrylate distillation method.