JP2002234858A - METHOD FOR PREVENTING POLYMERIZATION OF alpha,beta-UNSATURATED CARBOXYLIC ACID AND ITS ESTER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent method for preventing the polymerization of an α,β-unsaturated carboxylic acid and its ester. SOLUTION: This method for preventing the polymerization of the α,β-unsaturated carboxylic acid and its ester is characterized by allowing an N-oxyl compound represented by general formula (1) (R1 is CH2, CHOH, C=O, CHOCOCH3, CHNHCOCH3 or CHOCH3) and a hydroxylamine compound represented by general formula (2) (R2 is CH2, CHOH, C=O, CHOCOCH3, CHNHCOCH3 or CHOCH3) to coexist in the α,β-unsaturated carboxylic acid and/or the α,β-unsaturated carboxylic acid ester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for preventing the polymerization of α, β-unsaturated carboxylic acids and esters thereof.

[0002]

2. Description of the Related Art α, β-unsaturated carboxylic acids and esters thereof are very easily polymerized, and frequently polymerize due to factors such as heat during the production process, storage and transportation. Therefore, conventionally, as a polymerization inhibitor for α, β-unsaturated carboxylic acids and esters thereof, quinones such as hydroquinone, phenols such as p-methoxyphenol and derivatives thereof, nitrosos, diphenylamine, p-phenylenediamine Amines and their derivatives are known.

On the other hand, in the distillation step for producing an α, β-unsaturated carboxylic acid by a gas phase contact reaction, polymerization of the α, β-unsaturated carboxylic acid extremely occurs due to coexisting water, acetic acid and aldehydes. In the worst case, the operation of the distillation column may occur because during the distillation, a polymer is formed on the heat transfer surface of the reboiler, and this scaling significantly deteriorates the heat transfer or deposits the polymer on a tray in the distillation column. Will be impossible. And in this case,
Even if a normal amount of a polymerization inhibitor that prevents polymerization of the monomer during storage cannot be used, polymerization cannot be prevented.
Hitherto, various proposals have been made for a method of preventing polymerization in the production process of an α, β-unsaturated carboxylic acid.

For example, in the case of using an N-oxyl compound, Japanese Patent Application Laid-Open No. 54-3853 discloses a polymerization inhibitor for producing methacrylic acid from methacrolein using an oxygen-containing gas in an organic solvent. , 2,2,6,6-
Tetramethyl-4-hydroxypiperidine-1-oxyl or 2,2,6,6-tetramethylpiperidine-
A method using 1-oxyl is disclosed. JP-A-58-46496 discloses 2,2,5,5-tetramethyl-3-oxopyrrolidine-1-oxyl or 2,2,6,6-tetramethylpiperidine-1-oxyl. The method used is disclosed.

In a multi-component system, Japanese Patent Application Laid-Open No. 5-320
No. 217 discloses 2,2,6,6-tetramethyl-4.
A method for coexisting an N-oxyl compound such as -acetoxypiperidine-1-oxyl with a phenothiazine, an aromatic amine or a phenol compound is disclosed in JP-A-6-345681. JP-A-8-48650 discloses a method in which an N-oxyl compound such as tetramethylpiperidinooxyl and a phenol compound are used in combination with a phenothiazine. A method using a compound, a 2,2,6,6-tetramethylpiperidine compound and a nitroso compound is disclosed in
JP-A-316026 discloses a method in which an N-oxyl compound and a phosphorus compound are used in combination as a polymerization inhibitor.
No. 0-175912 discloses a method in which an N-oxyl compound and a cobalt compound such as cobaltous acetate are used in combination.

[0006]

However, the polymerization prevention method proposed in this manner has a low polymerization prevention effect at a high temperature such as a distillation step in a process for producing an α, β-unsaturated carboxylic acid and its ester. Due to the small size, a polymer is generated, which causes a problem that a long-term continuous operation of a production apparatus including a distillation column becomes impossible. In addition, a large amount of a polymerization inhibitor must be added in order to exert the polymerization inhibitory effect, which is not satisfactory in industrial practice. An object of the present invention is to provide a method for preventing polymerization of α, β-unsaturated carboxylic acids and esters thereof which is superior to the prior art.

[0007]

Means for Solving the Problems The present inventors have proposed α, β-
As a result of intensive studies on methods for preventing the polymerization of unsaturated carboxylic acids and their esters, the coexistence of an N-oxyl compound and a hydroxylamine compound with respect to the α, β-unsaturated carboxylic acid and its ester allows The present inventors have found that a remarkable polymerization preventing effect that cannot be obtained can be exhibited as a synergistic effect, and have completed the present invention.

That is, the present invention provides, as a polymerization inhibitor,
The following general formula (1)

[0009]

Embedded image

(Wherein R ¹ is CH ₂ , CHOH, C ＝ O,
CHOCOCH ₃ , CHNHCOCH ₃ or CHOCH
₃ ) and an N-oxyl compound represented by the following general formula (2)

[0011]

Embedded image

(Wherein R ² is CH ₂ , CHOH, C ＝ O,
CHOCOCH ₃ , CHNHCOCH ₃ or CHOCH
Α, β-unsaturated carboxylic acid, characterized by coexisting with a hydroxylamine compound represented by ( ₃ ) in an α, β-unsaturated carboxylic acid and / or an α, β-unsaturated carboxylic acid ester. And a method for preventing polymerization of the ester.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The N-oxyl compound used in the present invention is represented by the formula (1)

[0014]

Embedded image

Wherein R ¹ is CH ₂ , CHOH, C ＝ O,
CHOCOCH ₃ , CHNHCOCH ₃ or CHOCH
₃ , 2), 2,2,6,6-tetramethylpiperidine-1-oxyl. As a specific example,
2,2,6,6-tetramethylpiperidine-1-oxyl, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 2,2,6,6-tetramethyl-4-oxo Piperidine-1-oxyl, 2,2
6,6-tetramethyl-4-acetylpiperidine-1-
Oxyl, 2,2,6,6-tetramethyl-4-acetamidopiperidine-1-oxyl, 2,2,6,6-tetramethyl-4-methoxypiperidine-1-oxyl, and one or more of these. Can be used.

The hydroxylamine compound used in the present invention is represented by the formula (2)

[0017]

Embedded image

(Wherein R ² is CH ₂ , CHOH, C ＝ O,
CHOCOCH ₃ , CHNHCOCH ₃ or CHOCH
₃ represented by the illustrated) N- hydroxy-2,2,6,6
-Tetramethylpiperidines, specifically, N-
Hydroxy-2,2,6,6-tetramethylpiperidine, 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine, N-hydroxy-2,2,6,6-tetramethyl-4-oxo Piperidine, N-hydroxy-
2,2,6,6-tetramethyl-4-acetylpiperidine, N-hydroxy-2,2,6,6-tetramethyl-
4-acetamidopiperidine, N-hydroxy-2,
2,6,6-tetramethyl-4-methoxypiperidine, and one or more of these can be used. These hydroxylamine compounds are described, for example, in E.I. G. FIG.
Rozantsev and V.A. A. It can be produced by reducing the corresponding N-oxyl compound with phenylhydrazine according to the method of Golubev.

In the present invention, the amount of the polymerization inhibitor added is N
-Oxyl compound, 1 to 1000 mass ppm based on α, β-unsaturated carboxylic acid and its ester.
Is preferable, and 5-500 mass ppm is more preferable. The hydroxylamine compound is preferably from 1 to 3000 ppm by mass, more preferably from 5 to 500 ppm by mass, based on the α, β-unsaturated carboxylic acid and its ester. In the present invention, the N-oxyl compound and the hydroxylamine compound are used in coexistence, and the ratio of both is preferably from 1: 100 to 100: 1 by mass ratio, more preferably from 1: 1.
The range of 0 to 10: 1 is more preferable. It is preferable to set the N-oxyl compound and the hydroxylamine compound in the above ranges from the viewpoint of achieving both the polymerization inhibitory effect and economy.

In the present invention, a remarkable anti-polymerization effect is exhibited by using at least two components of the above-mentioned N-oxyl compound and hydroxylamine compound. May be used in combination. Known polymerization inhibitors include hydroquinone,
Methoquinone, phenothiazine, p-phenylenediamine, diphenylamine, p-nitrosophenol, N-
Nitrosophenylhydroxyamine ammonium salts and the like.

The method for preventing polymerization of the present invention can be applied to the prevention of polymerization of α, β-unsaturated carboxylic acids, α, β-unsaturated carboxylic esters, and mixtures thereof.

As the α, β-unsaturated carboxylic acid, it can be particularly applied to acrylic acid and methacrylic acid which are easily polymerized.

The acrylate can be applied to methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the like.

As the methacrylate, it can be applied to methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, cyclohexyl methacrylate and the like.

In the present invention, the method for coexisting an N-oxyl compound and a hydroxylamine compound in an α, β-unsaturated carboxylic acid and / or an α, β-unsaturated carboxylic acid ester is not particularly limited. The oxyl compound and the hydroxylamine compound may be mixed with an α, β-unsaturated carboxylic acid and / or an α, β-unsaturated carboxylic acid ester. For example, in the case of producing methacrylic acid by a gas phase contact reaction, each polymerization inhibitor may be directly added in the form of a solid or powder, or may be added as a solution or an aqueous solution of another organic solvent. May be.

The timing of addition is not particularly limited, and the polymerization inhibitors may be added individually or simultaneously, for example, in the form of one solution. These can be added, for example, immediately after the production of methacrylic acid, but it is preferable to add them immediately before performing distillation.Industrially, they are dissolved in a stock solution of methacrylic acid supplied to a distillation apparatus or in a reflux liquid. It can also be supplied.

When the polymerization inhibitor composition of the present invention is used in combination with molecular oxygen, the polymerization inhibitory effect is further improved, and the production apparatus can be operated for a long period of time. Regarding the supply method of molecular oxygen, it may be directly mixed into α, β-unsaturated carboxylic acid and its ester by air bubbling or the like,
Alternatively, it may be indirectly mixed with an α, β-unsaturated carboxylic acid and its ester in a state of being dissolved in another solvent. When gas is supplied from the bottom of the distillation column or stripper, or from the reboiler, air bubbling can be easily incorporated into the production process. Molecular oxygen is α, β-
It is desirable to supply about 0.05 to 1% by volume based on the distillation vapor amount of unsaturated carboxylic acid and its ester.

[0028]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. In the following examples, ppm is the mass p
pm, and the compound name of the polymerization inhibitor is omitted as shown below. TEMPO: 2,2,6,6-tetramethylpiperidine-1-oxyl HO-TEMPO: 2,2,6,6-tetramethyl-4
-Hydroxypiperidine-1-oxyl OX-TEMPO: 2,2,6,6-tetramethyl-4
-Oxopiperidine-1-oxyl AM-TEMPO: 2,2,6,6-tetramethyl-4
-Acetamidopiperidine-1-oxyl AC-TEMPO: 2,2,6,6-tetramethyl-4
-Acetylpiperidine-1-oxyl ME-TEMPO: 2,2,6,6-tetramethyl-4
-Methoxypiperidine-1-oxyl NHA: N-hydroxy-2,2,6,6-tetramethylpiperidine HO-NHA: 1,4-dihydroxy-2,2,6,6
-Tetramethylpiperidine OX-NHA: N-hydroxy-2,2,6,6-tetramethyl-4-oxopiperidine AM-NHA: N-hydroxy-2,2,6,6-tetramethyl-4-acetamidopiperidine AC-NHA: N-hydroxy-2,2,6,6-tetramethyl-4-acetylpiperidine ME-NHA: N-hydroxy-2,2,6,6-tetramethyl-4-methoxypiperidine The above hydroxylamine The compound was prepared by the following method.

(Preparation of HO-NHA) 500 with thermometer
Using the corresponding HO-TEMPO3
While stirring a solution of 7 g of phenylhydrazine in 20 ml of methanol in a solution of 1.0 g in 50 ml of methanol while stirring with a magnetic stirrer,
The solution was added dropwise over 1 hour while cooling with an ice bath. After the completion of the dropwise addition, stirring was continued for another 1 hour in an ice bath. After adding 300 ml of water to the obtained reaction solution, the mixture was extracted with ether. After separating the ether layer with a separating funnel, sodium sulfate was added to the ether layer and dried. After the ether layer was concentrated by an evaporator, the concentrated solution was added to a solution obtained by mixing water and methanol at a volume ratio of 1: 1 and by-products were removed by crystallization. Ether was added to the filtrate from which by-products had been removed, and the ether layer was separated using a separating funnel, and sodium sulfate was added and dried. After concentrating the ether layer with an evaporator, the concentrate was added to a solution in which heptane and chloroform were mixed at a volume ratio of 1: 1 to precipitate the desired product. As a result, 14.2 g of HO-NHA (yield 4
6%).

(Preparation of OX-NHA) In the same manner as in the preparation of HO-NHA, OX-TEMPO was prepared from 30.6 g to obtain 16.0 g of OX-NHA (52% yield).

(Preparation of NHA) In the same manner as in the preparation of HO-NHA, NHA was prepared from 28.1 g of TEMPO.
A17.0 g (yield 60%) was obtained.

(Preparation of AM-NHA) In the same manner as in the preparation of HO-NHA, 18.6 g (yield: 45%) of AM-NHA was obtained from 38.6 g of AM-TEMPO.

(Preparation of AC-NHA) In the same manner as in the preparation of HO-NHA, AC-NHA was prepared from 38.4 g of AC-TEMPO to obtain 18.9 g of AC-NHA (yield 49%).

(Preparation of ME-NHA) ME-TEMPO was prepared from 33.5 g of ME-TEMPO in the same manner as in the preparation of HO-NHA to obtain 13.4 g of ME-NHA (yield: 40%).

[Examples 1 to 10 and Comparative Examples 1 to 12] Take 5 ml of methacrylic acid into a test tube, add a predetermined amount of a polymerization inhibitor into the test tube, tightly seal with a silicon stopper, and control the temperature to 120 ° C. The sample was immersed in a shaker-equipped oil bath, and the time required for the sample to become cloudy with the start of polymerization, that is, the polymerization start time was measured. Table 1 shows the results.

[0036]

[Table 1]

From Table 1, it is apparent that when the N-oxyl compound and hydroxylamine coexist, an excellent polymerization preventing effect is exhibited.

[Examples 11 to 16, Comparative Examples 13 to 22]
Use acrylic acid instead of methacrylic acid, and set the temperature to 10
The same experiment as in Example 1 was performed except that the temperature was set to 0 ° C. Table 2 shows the results.

[0039]

[Table 2]

From Table 2, it can be clearly seen that, in the case of acrylic acid, when an N-oxyl compound and hydroxylamine coexist, an excellent polymerization inhibitory effect is exhibited.

[Examples 17 to 25, Comparative Examples 23 to 40]
Methyl methacrylate (MMA), butyl methacrylate (BMA), cyclohexyl methacrylate (CH) as α, β-unsaturated carboxylic acid ester instead of methacrylic acid
MA), methyl acrylate (MA) and acrylic acid 2-
Using hydroxypropyl (HPA), the temperature was MMA,
The same experiment as in Example 1 was performed except that BMA and CHMA were set to 120 ° C., and MA and HPA were set to 100 ° C. Table 3 shows the results.

[0042]

[Table 3]

From Table 3, it is apparent that even in the case of α, β-unsaturated carboxylic acid esters, an excellent polymerization inhibitory effect is exhibited when an N-oxyl compound and hydroxylamine coexist.

Example 26 A tower diameter of 35 m was provided with a decanter and a distilling pipe at the top of the tower and a feed port at the center.
The methacrylic acid extract was subjected to distillation separation by using a 10-stage glass-made Oldshaw distillation column with m stages. As a polymerization inhibitor, 50 ppm of HO-TEMPO and HO-N
HA was 100 ppm (each based on methacrylic acid in the bottoms) 70% by mass of toluene and 30% of methyl methacrylate
% By mass and added through a reflux line of a distillation column. Oxygen was supplied from the bottom of the column at a rate of 0.3% by volume based on the amount of methacrylic acid vapor.

As a feedstock, an aqueous solution containing 23.5% by mass of methacrylic acid and 8.8% by mass of acetic acid obtained by absorbing crude methacrylic acid obtained by a gas phase catalytic oxidation reaction of isobutylene with water was used. Height 760mm, 4 steps
3.15 kg / h from the top of the 0-stage rotating disk type extraction tower
r, and a solvent of 67.2% by mass of toluene, 27.7% by mass of methyl methacrylate, 4.1% by mass of acetic acid, and 1.0% by mass of water as an extractant was added from the bottom of the column at 1.74 kg /%.
30.8% by mass of methacrylic acid, 3.2% by mass of acetic acid, 1.5% by mass of water, 45.6% by mass of toluene, 45.6% by mass of toluene, methyl methacrylate A methacrylic acid extract containing 18.9% by mass was used.

The operating conditions were an operating pressure of 14.0 kP
a, tower top temperature 52 ° C, kettle temperature 92 ° C, feed liquid 2.54k
g / hr, distillate (organic phase) 1.62 kg / hr, distillate (aqueous phase) 0.03 kg / hr, bottoms 0.89 kg / hr
hr and the reflux ratio was 0.5.

The composition of the distillate (organic phase) in the steady state was 0.18% by mass of methacrylic acid, 3.0% by mass of acetic acid,
67.7% by mass of toluene, 28.1 of methyl methacrylate
% Of water and 1.0% by weight of water. The composition of the distillate (aqueous phase) was 0.50% by weight of methacrylic acid, 24.5% by weight of acetic acid, 0.14% by weight of toluene, and 1.14% by weight of methyl methacrylate.
The composition of the bottoms was 87.7% by mass of methacrylic acid, 2.8% by mass of acetic acid, 6.7% by mass of toluene, 2.8% by mass of methyl methacrylate, and 2.8% by mass of methyl methacrylate.
% By mass and 0.0% by mass of water.

The effect of preventing polymerization was confirmed by visually checking the presence or absence of a polymer in the kettle and in the tower. In addition,
To confirm a viscous polymer that is difficult to confirm by visual observation, take 10 ml of saturated saline solution into a test tube, add a small amount of the bottom liquid into the test tube, shake the mixture, and visually inspect for the presence or absence of polymer precipitation (hereinafter referred to as “the presence of polymer”). , Polymer check method).

Under these conditions, during a driving time of 32 hours,
No turbidity due to polymer formation was observed in the kettle and the tower. Further, as a result of sampling the bottom liquid and conducting a polymer check, no polymer was found.

Comparative Example 41 Example 26 was repeated except that N-hydroxy-2,2,6,6-tetramethyl-4-hydroxypiperidine was not used as a polymerization inhibitor.
As a result of conducting the same experiment as above, 7 hours after the start of distillation, the solution in the kettle became cloudy, and the formation of a polymer was observed. Also, at this point, part of the tower is in a flooding state,
After the distillation was completed, the location of the flooding was examined, and it was confirmed that the polymer was attached to the tray.
From this, it was found that the polymerization inhibitory effect was low only by the N-oxyl compound.

[Comparative Example 42] As a polymerization inhibitor,
Example 26 except that 2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl was not used.
As a result of the same experiment as in the above, 5 hours after the start of distillation, the solution in the kettle became cloudy, and formation of a polymer was observed. Also, at this point, part of the tower is in a flooding state,
After the distillation was completed, the location of the flooding was examined, and it was confirmed that the polymer was attached to the tray.
This indicates that the hydroxylamine compound alone has a low polymerization inhibitory effect.

[0052]

According to the method of the present invention, the polymerization is carried out by using an N-oxyl compound and hydroxylamine in the presence of an α-, β-unsaturated carboxylic acid and its ester as a polymerization inhibitor. Thus, the generation of a polymer can be prevented even in a high temperature state such as a distillation step, and a long-term continuous operation can be performed.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomomichi Hino 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory F-term (reference)

Claims (3)

[Claims] 1. A polymerization inhibitor represented by the following general formula (1): (Wherein R ¹ is CH ₂ , CHOH, C ＝ O, CHOCOC
H ₃ , CHNHCOCH ₃ or CHOCH ₃ ) and an N-oxyl compound represented by the following general formula (2): (Wherein R ² is CH ₂ , CHOH, C ＝ O, CHOCOC
A hydroxylamine compound represented by H ₃ , CHNHCOCH ₃ or CHOCH ₃ ) in α, β-unsaturated carboxylic acid and / or α, β-unsaturated carboxylic acid ester. For preventing polymerization of α, β-unsaturated carboxylic acids and esters thereof. 2. The method according to claim 1, wherein the N-oxyl compound is the α, β-
The hydroxylamine compound is present in an amount of 1 to 1000 ppm by mass based on the total amount of the unsaturated carboxylic acid and the α, β-unsaturated carboxylic acid ester, and
-1 to 3000 ppm by mass based on the total amount of the unsaturated carboxylic acid and the α, β-unsaturated carboxylic acid ester, and the mass ratio of the N-oxyl compound to the hydroxylamine compound is 1 : 100-100: 1
The method according to claim 1, wherein the compound is present at a ratio of: 3. The method according to claim 1, further comprising coexisting molecular oxygen.
Or the method of 2.