JP2001348360A - Method for inhibiting polymerization of (meth)acrylic cid and ester and method for producing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively inhibiting polymerization of (meth) acrylic acid and an ester in both vapor and liquid phases in a refining column in the production process for such easily polymerizable substance (s) so as to make continuous operation for the production possible, and to provide a method for producing (meth)acrylic acid and an ester by the use of the above technique. SOLUTION: This method for inhibiting polymerization of (meth)acrylic acid and an ester thereof is characterized by comprising feeding nitroso compound into a refining column for the (meth)acrylic acid and the ester thereof at a height not higher than the point corresponding to 70% of the total theoretical plate number based on the bottom of the column. On feeding the nitroso compound, part thereof is decomposed and the compound rises inside the column and effectively inhibits the (meth)acrylic acid and the like from being polymerized. In addition to the nitroso compound, an N-oxyl compound, etc., can be used in combination therewith, thereby more effectively inhibiting the (meth) acrylic acid and the ester thereof from being polymerized in both vapor and liquid phases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for preventing polymerization of (meth) acrylic acid and its ester and a method for producing the same. More specifically, the present invention relates to a method for using a nitroso compound as a polymerization inhibitor. The present invention relates to a method for preventing (meth) acrylic acid and its ester from being polymerized, which is fed from the bottom of the column and distillation, and a method for producing (meth) acrylic acid and its ester, which includes the method for preventing polymerization in its production step.

[0002]

2. Description of the Related Art An easily polymerizable compound such as acrylic acid or methacrylic acid is an industrial raw material and a chemical substance produced in large quantities in a large-scale plant. For example, taking (meth) acrylic acid as an example, the easily polymerizable compound is produced by a catalytic gas phase oxidation reaction of propylene, isobutylene, isobutylene, t-butanol, methyl-t-butyl ether, acrolein, etc. The target gas (meta) is contained in the reaction gas obtained by the catalytic gas phase oxidation reaction.
Other by-products of acrylic acid are mixed. For example, mainly non-condensable gases, i.e., unconverted propylene, isobutylene, acrolein and water vapor having a boiling point lower than the boiling point of acrylic acid, low-boiling organic compounds such as unconverted acrolein, and formaldehyde and acetic acid produced by side reactions. Impurities and high-boiling compounds such as maleic anhydride, furfural, benzaldehyde, benzoic acid, and acrylic acid dimer having a boiling point higher than that of acrylic acid are generated. For this reason, in order to purify the reaction gas to produce the target product, it is common to absorb the reaction gas by countercurrent washing with water or a heavy solvent and then supply it to a distillation column for purification. It is a target.

[0003] On the other hand, (meth) acrylic acid and its ester are compounds which are very easily polymerized due to their structures. In addition, since the (meth) acrylic acid distillation step and the like constitute a system in which the gas phase and the liquid phase are mixed, the polymerization is performed on both the liquid phase and the gas phase in the distillation column. It is necessary to suppress the pressure effectively and enable stable continuous operation for a long time. Generally, in order to prevent such polymerization from occurring, various polymerization inhibitors are added to the monomer alone or in combination of several kinds to prevent the generation of a polymer in the production process.

[0004] For example, Japanese Patent Application Laid-Open No. 9-95465 discloses that, when using N-nitrosophenylhydroxylamine or a salt thereof as a kind of nitroso compound to prevent polymerization of a vinyl compound, N-nitrosophenylhydroxylamine or N-nitrosophenylhydroxylamine is used. There is disclosed a method for preventing polymerization of a vinyl compound, characterized in that a copper salt is present together with the salt. According to the method, by introducing both compounds simultaneously or separately to the distillation step, polymerization of acrylic acid or methacrylic acid can be effectively prevented, and the production process can be stably operated for a long time. And
In the examples, refluxing operation is performed after dissolving copper dibutyldithiocarbamate and N-nitrosophenylhydroxylamine in acrylic acid, and generation of a polymer is observed.

[0005]

However, the method described in Japanese Patent Application Laid-Open No. 9-95465 uses a copper salt as an essential component, so that water or the like containing the copper salt is discharged into the environment. Therefore, a means for processing this is newly required, which is disadvantageous.

In order to effectively prevent polymerization of (meth) acrylic acid and the like, the amount of the polymerization inhibitor to be used may be increased. This requires a step of removing the polymerization inhibitor, which is disadvantageous.

Also, low-boiling substances such as acetic acid and lower aldehyde contained in (meth) acrylic acid synthesized by catalytic gas-phase oxidation of propylene and the like and high-boiling substances such as furfural and maleic anhydride form by-products. In order to purify and separate, a (meth) acrylic acid-containing solution is subjected to methods such as distillation, stripping, extraction, and crystallization, but further simplification of the manufacturing process is required. For example, if the number of acetic acid separation columns is reduced or the number of distillation steps is reduced, it is necessary to make the distillation conditions stricter. The simplification of the manufacturing process is a social request, but for this purpose, each purification step requires more severe distillation conditions than at present. A polymer is more easily generated.
On the other hand, if a polymer is generated, continuous operation becomes impossible, and it becomes more difficult to remove the polymer in the purification tower.

[0008] Under such circumstances, in a method for producing an easily polymerizable substance such as (meth) acrylic acid, generation of a polymer in both a gas phase and a liquid phase in a refining tower is effectively prevented. Continuous operation can be achieved (meta)
A method for preventing polymerization of acrylic acid or its ester and a method for producing these are desired.

[0009]

The present inventors have studied in detail the polymerization preventing function of a nitroso compound and found that, for example, N-nitrosophenylhydroxylamine or a salt thereof is at least partially decomposed after being added to a distillation step. That the decomposition product has a polymerization inhibiting action and a polymerization promoting action, and that the compound is supplied from a specific location when introduced into the distillation column, so that It has been found that the effect of preventing polymerization can be promoted and the effect of the polymerization promoting substance can be suppressed, thereby completing the present invention. That is, the above object is achieved by the following (1) to (8).

(1) Using a nitroso compound (meth)
(A) when purifying acrylic acid and its ester in a purifying column, supplying the nitroso compound from 70% or less of the total number of theoretical plates based on the column bottom of the purifying column; And a method for preventing polymerization of the ester thereof.

(2) The method for preventing polymerization of (meth) acrylic acid and its ester as described in (1) above, wherein the nitroso compound is dissolved in a solvent.

(3) The method for preventing polymerization of (meth) acrylic acid and its ester as described in (1) or (2) above, wherein the nitroso compound is N-nitrosophenylhydroxylamine or a salt thereof.

(4) The method for preventing polymerization of (meth) acrylic acid and its ester as described in (3) above, wherein the salt of N-nitrosophenylhydroxylamine is an ammonium salt of N-nitrosophenylhydroxylamine.

(5) The method for preventing polymerization of (meth) acrylic acid and its ester according to any one of the above (1) to (4), further comprising introducing an N-oxyl compound into a purification tower. .

(6) An N-oxyl compound is characterized by coexisting an N-hydroxy-2,2,6,6-tetramethylpiperidine compound and a 2,2,6,6-tetramethylpiperidine compound. (5) The method for preventing polymerization of (meth) acrylic acid and its ester according to (5).

(7) The method for preventing polymerization of (meth) acrylic acid and its ester as described in (5) or (6) above, wherein the N-oxyl compound is introduced from above the raw material supply stage of the purification tower. .

(8) A method for preventing the polymerization of (meth) acrylic acid or an ester thereof according to any one of the above (1) to (7), wherein the method comprises the steps of: Method for producing ester.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The first aspect of the present invention is that when (meth) acrylic acid and its ester are purified by a purification tower using a nitroso compound, the nitroso compound is converted into a total starting from the bottom of the purification tower. A method for preventing polymerization of (meth) acrylic acid and its ester, characterized in that it is supplied from a position of 70% or less of the theoretical plate number.

As described above, the present inventors have found that the nitroso compound is decomposed in the distillation step of (meth) acrylic acid or the like, but when the compound is introduced from the bottom side of the purification tower, the inside of the purification tower will be decomposed. It has been found that the gas components of the decomposition products in the environment exert an action of preventing polymerization of gas-phase (meth) acrylic acid and its esters. In particular, when the nitroso compound is supplied from the bottom side of the purification tower, the gas component obtained by decomposition in the environment of the purification tower is present in a gaseous state while rising in the purification tower. Can be easily mixed with each other, whereby the polymerization of these compounds can be more effectively prevented.

In the present invention, “purification” includes:
Includes distillation and emission. Here, "distillation" is a method of heating a solution to its boiling point to separate volatile components contained therein, and "dissipating" is a method of supplying a dissipated gas and evaporating a gas or vapor dissolved in a solution. It refers to the method of phase transfer. Hereinafter, the present invention will be described in detail.

The method for preventing polymerization of (meth) acrylic acid and its ester according to the present invention prevents polymerization occurring in a purification column when purifying (meth) acrylic acid and its ester. Therefore, regardless of the name of the purification tower, the equipment used for the production of (meth) acrylic acid and its esters and for purifying or producing (meth) acrylic acid and its esters is widely used regardless of its name. Including, distillation tower, stripping tower, azeotropic separation tower, dehydration tower,
An acetic acid separation tower, a light-boiling matter separation tower, a high-boiling matter separation tower, and the like are included.

The conditions for purifying (meth) acrylic acid and its ester in these purification towers can be applied to conventionally known conditions for purifying or producing (meth) acrylic acid and its ester. However, the present invention is not limited to this.

The nitroso compound used in the present invention is not particularly limited, and includes N-nitrosophenylhydroxylamine, p-nitrosophenol, N-nitrosodiphenylamine and ammonium salts thereof.
These may be used alone or in combination of two or more. Particularly, N-nitrosophenylhydroxylamine and its ammonium salt are preferred. This is because, after the compound is decomposed under the conditions in the purification tower, the gas component is particularly excellent in suppressing the polymerization of the easily polymerizable substance.

In the present invention, this is supplied from the bottom of the purification column. As used herein, the phrase "at most 70% of the total number of theoretical plates based on the bottom side of the purification column as a base point" in the present specification refers to the inside of the purification column at a position of 70% or less of the total number of theoretical plates in the purification column and attached thereto. It means all of piping and attached equipment. Therefore, if the position is 70% or less of the total theoretical plate number, the gas phase portion in the purification tower, the bottom liquid, the reboiler attached to the purification tower, and the piping for introducing into or retrieving from the reboiler are included. Shall be included. Therefore, when a thin-film evaporator is attached to the bottom of the purification tower, the thin-film evaporator and the piping for introducing the thin-film evaporator to the thin-film evaporator are also included in the supply position of the nitroso compound in the present application. . The position is more preferably 30% or less, more preferably 10% or less of the total theoretical plate number. In particular, when a nitroso compound and an N-oxyl compound described later are used in combination, the total theoretical plate number is 50 to 50% based on the bottom side of the purification column.
When administered from the 70% position, the polymerization prevention effect in the liquid phase and gas phase is excellent.

In the present invention, the nitroso compound is supplied from a position of 70% or less of the total number of theoretical plates from the bottom of the purification column as a base point, as described above, because gaseous decomposition products are easily produced in the gas phase. This is because it has been found that some of the non-volatile decomposition products have an action of accelerating the polymerization while exhibiting the action of preventing the polymerization of the polymerizable substance. In the purification tower, distillation of trays, packings, liquid dispersion plates, flash feed liquid dispersion plates, primary liquid dispersion plates, collectors, vapor dispersion plates, packing supports, packed bed suppression plates, etc. Due to the presence of the column interior, if a non-volatile component, which is a decomposition product of a nitroso compound and adheres to these interiors, there is a possibility that polymerization of (meth) acrylic acid and the like on the surface of the interior will be accelerated. In this regard, if the position is 70% or less of the total number of theoretical plates with respect to the bottom of the purification tower as the base point, polymerization of the easily polymerizable gas can be effectively prevented in the gas phase and polymerization promotion generated on the surface of the interior material Side effects are also in an acceptable range.

It is preferable that such a nitroso compound is dissolved in a solvent and administered to a purification tower.
Specifically, a solution obtained by dissolving the nitroso compound in a suitable solvent, preferably a solvent to be charged into the reaction system, or a solvent of the same kind as the components contained in the raw material supply liquid such as water, and converting the solution into a liquid at the bottom of the purification tower Supplied from the position below 70% of the total theoretical plate number with the side as the base point. The solvent used for dissolving the nitroso compound may be appropriately selected depending on the conditions in the purification column and the chemical and physical properties such as solubility and decomposability of the nitroso compound in the solvent. Examples of the solvent include water, alcohol, hydrocarbon, ketone, ester, acid and the like.
In the case where the nitroso compound is an ammonium salt of N-nitrosophenylhydrosylamine, water is most preferable and an acid is not preferable in consideration of stability in a solvent. When a raw material supply stage is included in this position, the nitroso compound-containing solution may be mixed in the raw material supply solution, or the nitroso compound may be dissolved in the raw material supply solution and introduced into the purification tower. Alternatively, the nitroso compound-containing solution may be introduced, dropped, or sprayed from the nitroso compound supply port penetrated through the purification tower.

Although the supply amount of the nitroso compound to be added to the purification column in the present invention is not particularly limited, the compound is decomposed in the purification column. The concentration of the nitroso compound in the solution is 0.000
5 to 0.05% by mass, preferably 0.001 to 0.01
% By mass. If the amount is less than 0.0005% by mass, the effect of preventing polymerization is not sufficient. Incidentally, at least a part of the nitroso compound is decomposed under the conditions of the purification tower,
Depending on the type of the decomposition product, polymerization of (meth) acrylic acid or the like may be promoted. Therefore, the polymerization can be suppressed by setting the concentration of the nitroso compound in the bottom liquid to 0.05% by mass or less.

In the present invention, in addition to the nitroso compound, an N-oxyl compound, a 2,2,6,6-tetramethylpiperidine compound, an N-hydroxy-2,2,6,6
A tetramethylpiperidine compound, a phenol compound,
Known polymerization inhibitors such as copper salts and manganese salts can be used in combination. As described above, the polymerization may be accelerated depending on the decomposition product of the nitroso compound. Therefore, the polymerization of (meth) acrylic acid or the like particularly in the liquid phase can be prevented by using another polymerization inhibitor in combination.

The N-oxyl compound used in the present invention is not particularly limited, and any N-oxyl compound generally known as a polymerization inhibitor for a vinyl compound can be used. Among them, 2,2,6,6-tetramethylpiperidinooxyls represented by the following formula (1):

[0030]

Embedded image

(Where R ¹ is CHOH, CHC
H ₂ OH, CHCH ₂ CH ₂ OH, CHOCH ₂ OH, CH
OCH ₂ CH ₂ OH, CHCOOH, or C ＝ O, and R ² represents H or CH ₂ OH) is preferably used. Any N-oxyl compound can be used without particular limitation, but it can provide a good polymerization preventing effect.
2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl, 4,4 ′, 4 ″ -tris- (2,2,6,6 −
It is preferable to use one or more of tetramethylpiperidinooxyl) phosphites. In particular,
As the N-oxyl compound, 2,2,6,6-tetramethylpiperidinooxyl or 4-hydroxy-2,
In the case of using 2,6,6-tetramethylpiperidinooxyl, since there is no danger of metal corrosion of equipment due to the stabilizer, since it becomes a stabilizer system even if no metal is contained in the component,
Waste liquid treatment is also facilitated.

The N-hydroxy-2,2 used in the present invention
Representative examples of 2,6,6-tetramethylpiperidine compounds include 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine, 1-hydroxy-2,2,6,6
-Tetramethylpiperidine and the like.
These N-hydroxy-2,2,6,6-tetramethylpiperidine compounds can be used alone or in combination of two or more.

Specific examples of the 2,2,6,6-tetramethylpiperidine compound used in the present invention include 2,2,6,6-tetramethylpiperidine.
6,6-tetramethylpiperidine, 4-hydroxy-
2,2,6,6-tetramethylpiperidine and the like, and one or more of these can be used. Note that N
-Hydroxy-2,2,6,6-tetramethylpiperidine compound and 2,2,6,6-tetramethylpiperidine compound may be contained as impurities in commercially available N-oxyl compound products, In such a case, N-hydroxy-2,2,6,6-tetramethylpiperidine compound and 2,2,6,6-tetramethylpiperidine compound were used together with the use of a commercially available N-oxyl compound. Will be.

In the present invention, in particular, together with the nitroso compound, N
-Oxyl compounds, and additionally N-hydroxy-2,
2,6,6-tetramethylpiperidine compounds and 2,2,2
It is preferable to use a 6,6-tetramethylpiperidine compound in combination. This is because these compounds are particularly excellent in the effect of suppressing polymerization of (meth) acrylic acid and their esters in the liquid phase, so that the polymerization of both gas and liquid phases in the purification tower can be synergistically suppressed as a whole. .

When an N-oxyl compound is used in combination with such a nitroso compound, it is particularly preferable to introduce the N-oxyl compound from above the raw material supply stage of the purification tower. In the present invention, `` upper than the supply stage '' includes the case where a condenser or a distillate attached to the purification column is supplied from a storage tank or the like used when separating into an oil-water phase, and particularly preferably a column top, It is supplied from the inside of the condenser, the storage tank or the reflux liquid of the condenser or the storage tank. When these polymerization inhibitors are supplied to the purification tower, the polymerization inhibitor must exhibit sufficient solubility in the liquid phase in order to exhibit the polymerization prevention effect most effectively. In addition, in a refining tower having a different composition depending on the position in the tower, in order to supply the polymerization inhibitor while maintaining the composition, it is necessary to add a liquid composition most similar to the composition in the tower. It is required that the position of the polymerization inhibitor can be mixed most effectively with the target liquid phase.

Since the N-oxyl compound is a powder, it is preferable to supply the N-oxyl compound into the purification tower after dissolving it in a solvent. For example, the N-oxyl compound may be used by using a part of the solvent supplied into the purification tower. It is preferred to prepare a solution containing the compound. It is preferable to select a range in which the concentration of the solvent in the solution and the concentration of the solvent in the purification tower are similar to each other as a charging position of the solution containing the polymerization inhibitor, since the composition in the tower does not need to be changed. . Although these conditions cannot be uniquely determined depending on the distillation conditions, the stripping conditions, and the like in the purification column, in the case of the N-oxyl compound, the polymerization prevention effect is excellent if it is located above the raw material supply stage.

The N-oxyl compound may be supplied after being dissolved in a solvent, or may be supplied to the purification column in a solidified state or a vaporized state.

For example, as a method of acting in a dissolved state, a solution prepared by dissolving a polymerization inhibitor in a suitable solvent is supplied from the top of the purification tower and supplied to a condenser or a storage tank attached to the purification tower. May be supplied. Depending on the type of the condenser or the like, a solution containing a polymerization inhibitor may be charged inside the condenser and dissolved by blowing a gaseous distillate or pouring a liquefied distillate into the solution. . If you do this,
Polymerization in the condenser can also be effectively prevented.

As a method of acting in a solidified state, a powdery polymerization inhibitor is sprayed and dropped from the top of the purification tower or the inside of the condenser.

Further, as a method of causing the polymerization inhibitor to act in a vaporized state, a substance obtained by vaporizing or sublimating a polymerization inhibitor may be supplied to and mixed in a piping path communicating the purification tower and the condenser.

The solvent capable of dissolving the above-mentioned polymerization inhibitor is preferably a solvent supplied in the production or the like or a reflux liquid from an attached condenser as described above. As the solvent to be supplied, benzene, toluene, xylene, cyclohexane, acetone, methyl ethyl ketone, methyl isobutyl ketone, n
-Hexane, heptane and the like, and mixtures thereof. Since these solvents vary depending on the conditions in the purification column, the most preferable solvent for dissolving the polymerization inhibitor is selected based on the solvent actually used. The use of the solvent used in the purification tower is also preferable in that the mixture of the easily polymerizable substance and the polymerization inhibitor is excellent and the composition in the tower can be maintained. If different solvents are used, it is necessary to collect them separately.
In the case of separation by reflux to the reaction system, control and management of the reaction system become complicated, which is disadvantageous.

Examples of the phenol compound which can be further used in the present invention include hydroquinone and methoquinone (p-methoxyphenol). Methoquinone is preferred because it has a superior polymerization inhibitory effect to hydroquinone, particularly when used in combination with an N-oxyl compound and a phenothiazine compound. These phenol compounds may be used in combination of two kinds.

Examples of the phenothiazine compound include phenothiazine, bis- (α-methylbenzyl) phenothiazine, 3,7-dioctylphenothiazine, and bis- (α-
(Dimethylbenzyl) phenothiazine and the like, and among them, phenothiazine is particularly preferably used. Two or more of these phenothiazine compounds may be used in combination.

On the other hand, it is necessary to ensure the preservation of the environment by the metal compound salt having a corrosive action and being separated when released into the environment after use, but may be used together in the present invention. .

For example, the copper salt is not particularly limited, and may be any of an inorganic salt and an organic salt, and various ones can be used. For example, copper dialkyldithiocarbamate, copper acetate, copper naphthenate, copper acrylate, copper sulfate,
Examples thereof include copper nitrate and copper chloride. These copper salts may be monovalent or divalent. Among the above copper salts, copper dialkyldithiocarbamate is preferred from the viewpoint of effects and the like.

The copper dialkyldithiocarbamate includes, for example, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper dibutyldithiocarbamate, copper dipentyldithiocarbamate, copper dihexyldithiocarbamate, copper diphenyldithiocarbamate, copper methylethyl, Copper dithiocarbamate, copper methylpropyldithiocarbamate,
Copper methylbutyldithiocarbamate, copper methylpentyldithiocarbamate, copper methylhexyldithiocarbamate, copper methylphenyldithiocarbamate, copper ethylpropyldithiocarbamate, copper ethylbutyldithiocarbamate, copper ethylpentyldithiocarbamate, copper ethylhexyldithiocarbamate, ethylphenyldithiocarbamine Copper acid, copper propylbutyldithiocarbamate, copper propylpentyldithiocarbamate, copper propylhexyldithiocarbamate, copper propylphenyldithiocarbamate, copper butylpentyldithiocarbamate, copper butylhexyldithiocarbamate, copper butylphenyldithiocarbamate, copper pentylhexyldithiocarbamate , Copper pentylphenyldithiocarbamate, hexylfe Such as Le copper dithiocarbamate and the like. These copper dialkyldithiocarbamates are:
It may be a monovalent copper salt or a divalent copper salt. Among these, copper dimethyldithiocarbamate, copper diethyldithiocarbamate and copper dibutyldithiocarbamate are preferred from the viewpoints of effect and availability, and copper dibutyldithiocarbamate is particularly preferred.

Examples of the manganese salt compound include manganese dialkyldithiocarbamate (the alkyl group is any of methyl, ethyl, propyl and butyl, which may be the same or different), manganese diphenyldithiocarbamate, manganese formate, acetate Manganese, manganese octoate, manganese naphthenate, manganese permanganate, manganese salts of ethylenediaminetetraacetic acid and the like can be mentioned, and one or more of these can be used. Although the manganese salt compound alone has a relatively low polymerization inhibitory effect, the manganese salt compound exhibits a remarkable polymerization inhibitory effect by using the N-oxyl compound or the N-oxyl compound together with another polymerization inhibitor in the present invention. Became clear. Further, copper salts have a corrosive action, and the addition of a manganese salt is also preferable in that the corrosive action can be suppressed.

In the present invention, in order to supply the phenol compound, the copper salt and the manganese salt to the purification tower, it is preferable to introduce the phenol compound, the copper salt and the manganese salt from above the raw material supply stage of the purification tower, similarly to the N-oxyl compound. From the viewpoint of solubility of the compound in a solvent, as in the case of adding an N-oxyl compound,
This is because the mixing with the easily polymerizable compound is easy and the purification operation can be continued without changing the composition in the purification tower.
These may all be charged from the same supply location for the polymerization inhibitor used in combination, or may be charged from different supply locations. Further, the supply time is not particularly limited. Therefore, for example, the N-oxyl compound can be supplied from the top of the column, while the manganese salt can be supplied from the middle stage of the purification column. This is because, when a manganese salt that is hardly soluble in an organic solvent is used, if the concentration of the organic solvent on the top side of the purification tower is high, the composition in the tower is rarely changed by supplying from the middle of the tower. . Therefore, when the manganese salt is easily soluble in an organic solvent and hardly soluble in water, an efficient polymerization preventing effect can be obtained by supplying the manganese salt from the top of the purification tower. In any case, the most suitable supply place is selected in consideration of the solubility of the polymerization inhibitor to be added to the solvent, the environment in the purification column, particularly the composition in the column, and the like.

When the polymerization inhibitor used in the present invention is a liquid by itself, even if the composition and the mutual solubility in the column are not sufficient, the polymerization inhibitor can move through the structure in the column. If there is no obstacle in terms of viscosity, reactivity, etc., supply from the top of the column is possible.

The polymerization preventing method of the present invention can be suitably used for (meth) acrylic acid and its ester which are particularly easily polymerized among vinyl compounds. As acrylic acid esters, methyl acrylate, ethyl acrylate,
Examples of the application include butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the like. Examples of methacrylates include methyl methacrylate, butyl methacrylate, and 2-hydroxy methacrylate. Ethyl, 2-hydroxypropyl methacrylate and the like can be mentioned as applicable objects.

As a method for preventing polymerization, for example, the case of producing (meth) acrylic acid by a catalytic gas phase oxidation reaction will be described. A rectification column for (meth) acrylic acid, separation of (meth) acrylic acid and a solvent The above polymerization inhibitor is used in various distillation steps such as a column, a separation tower of (meth) acrylic acid and light boiling components such as acetic acid and the like, and various processes including a distillation operation such as strippers of light boiling components such as acrolein and methacrolein. What is necessary is just to make it coexist with (meth) acrylic acid.

The amount of the polymerization inhibitor other than the nitroso compound is appropriately adjusted according to the operating conditions, and is not particularly limited.
The total amount of the polymerization inhibitor to be used is 3 to 1500 pp with respect to the evaporation vapor amount of (meth) acrylic acid and its ester.
m (weight basis). The preferred amount of each polymerization inhibitor used is 1 to 500 ppm of the N-oxyl compound with respect to the amount of evaporated vapor of the monomer, and 1 to 200 ppm of the manganese salt compound or the copper salt compound with respect to the amount of evaporated vapor of the monomer. , 6,6-tetramethylpiperidine compound or 1-5 in the case of nitroso compound
00 ppm.

The term “evaporated vapor amount” as used herein means the total amount of monomer vapor generated in the reboiler according to the amount of heat applied to the reboiler of the distillation column. The total amount of monomer vapor can be easily calculated. It is a number that is an important factor in determining the criteria for adding the polymerization inhibitor.

In the present invention, molecular oxygen may be supplied into the purification tower as a polymerization inhibitor, and the supply of molecular oxygen may be performed by air bubbling or the like.
It may be directly mixed with acrylic acid and its ester, or may be indirectly mixed with (meth) acrylic acid and its ester while being dissolved in another solvent. The air bubbling can be easily incorporated into the manufacturing process if the gas is sent from the bottom of the purification tower or the stripper and / or from the reboiler. Molecular oxygen is (meta)
It is desirable to add about 0.1 to 1.0% by volume based on the amount of evaporated vapor of acrylic acid or its ester.

The second aspect of the present invention is a method for producing (meth) acrylic acid or an ester thereof, which comprises the above-mentioned method for preventing polymerization of (meth) acrylic acid or an ester thereof.

(Meth) acrylic acid and its ester are produced continuously, and are generally followed by a catalytic gas-phase oxidation reactor, a collecting tower, a dehydrating tower, a light-boiling substance separating tower, a high-boiling substance separating tower and an acetic acid separating tower. It is manufactured through various purification steps called towers, ester reactors, dehydration towers and the like.

The conditions of the purification tower used in these steps differ depending on the conditions of the purification towers before and after the purification tower, and cannot be uniquely defined. However,
In the present invention, in particular, an azeotropic dehydration tower for removing water from a (meth) acrylic acid-containing solution in which (meth) acrylic acid has been collected by an aqueous solvent, or a low-pressure column for separating low-boiling substances such as aldehydes and acetic acid in addition thereto. It is preferable to carry out the polymerization prevention method of the present invention in a boiling separation column. Since these are generally the most likely to cause polymerization of (meth) acrylic acid and the like, these are the rate-limiting steps in the compound production step, and the present invention is particularly effective.

In the method for producing (meth) acrylic acid at least partially including the method for preventing polymerization of the present invention, it is possible to prevent long-term continuous operation by preventing the generation of a polymer in the purification tower, and also to reduce the yield of the product. Rate can be improved.
In this regard, in the method for producing (meth) acrylic acid and esters thereof of the present invention, it is preferable that the above-described polymerization prevention method of the present invention be applied to each purification column used in the production step.

[0059]

The present invention will be described more specifically below with reference to examples.

Example 1 Acrylic acid-containing gas obtained by supplying propylene and a molecular oxygen-containing gas to a catalytic gas-phase reactor 10 and subjecting it to catalytic gas-phase oxidation was introduced into an acrylic acid collecting tower 20. Acrylic acid was collected in an aqueous solution by contact with water. This acrylic acid-containing solution contained acrolein as an impurity. The acrylic acid-containing solution was introduced into the acrolein stripping tower 30 to evaporate acrolein to obtain an acrylic acid aqueous solution containing 30% by mass of water and 3.0% by mass of acetic acid.

The acrylic acid aqueous solution was provided with a stainless steel sieve tray having 50 stages and a step interval of 147 mm, a distilling tube and a reflux liquid supply tube at the top of the column, a raw material supply tube and a polymerization inhibitor introducing tube at the center, and a bottom of the column. Was introduced into an azeotropic separation tower 40 having an inner diameter of 105 mm and provided with a bottom liquid discharge pipe and a polymerization inhibitor inlet pipe, and an acrylic acid solution was distilled using toluene as an azeotropic solvent.

The amount of the polymerization inhibitor used was 4-hydroxy-2,2,6,6-
Tetramethylpiperidinooxyl 100 ppm, 1,4
-Dihydroxy-2,2,6,6-tetramethylpiperidine, 20 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidine, and 10 ppm of ammonium salt of N-nitrosophenylhydroxylamine. The ammonium salt of N-nitrosophenylhydroxylamine was supplied from the bottom of the azeotropic dehydration tower 40 after being dissolved in water. All other polymerization inhibitors were supplied from the top of the tower after being dissolved in the reflux liquid. Further, 0.3% by volume of molecular oxygen with respect to the amount of vaporized acrylic acid was supplied to the bottom of the column. Here, the amount of vaporized acrylic acid vapor refers to the total amount of monomer vapor vaporized from the bottom of the azeotropic dehydration tower 40 corresponding to the amount of heat added from the reboiler 42.

The operating conditions during steady-state operation are as follows: the top temperature of the azeotropic separation column 40 is 50 ° C., the bottom temperature is 105 ° C., the top pressure is 170 hPa, and the reflux ratio (total moles of reflux liquid per unit time / unit time) Total number of moles of distillate per 1.20)
The supply amount of the acrylic acid aqueous solution was 9.0 liter / hour.
The liquid withdrawn from the bottom of the column contained 97% by mass of acrylic acid, 0.02% by mass of water, and 2.98% by mass of others.

When the azeotropic separation column 40 was operated continuously for 30 days under the above conditions, a stable state was always obtained. After the operation was stopped, the distillation column was inspected. Only the thing was recognized, and further continuation of the operation was possible.

Example 2 Example 2 was repeated except that the injection position of the aqueous solution of the ammonium salt of N-nitrosophenylhydroxylamine was changed from the bottom of the column to 25% of the total theoretical plate number from the bottom of the column as a base point. In the same manner as in Example 1, an azeotropic distillation operation of the acrylic acid aqueous solution was performed.

When the azeotropic separation tower 40 was continuously operated under these conditions for 30 days, the same separation state as in Example 1 was obtained.
After the operation was stopped, the inside of the distillation column was inspected, and almost no generation of a polymer was observed.

Example 3 Example 1 was repeated except that the charging position of the aqueous solution of the ammonium salt of N-nitrosophenylhydroxylamine was changed from the bottom of the column to 60% of the total theoretical plate number from the bottom of the column as a base point. In the same manner as in Example 1, an azeotropic distillation operation of the acrylic acid aqueous solution was performed.

When the azeotropic separation column 40 was continuously operated under these conditions for 30 days, the same separation state as in Example 1 was obtained.
After the operation was stopped, the inside of the distillation column was inspected. As a result, no polymer was generated.

(Example 4) In Example 1, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl, 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine and 4-hydroxy-2,2,6,
Instead of using 6-tetramethylpiperidine, instead of using 30 ppm of copper dibutyldithiocarbamate, 30 ppm of manganese acetate, 100 ppm of hydroquinone, and 100 ppm of phenothiazine, copper dibutyldithiocarbamate and phenothiazine are dissolved in a reflux solution, and manganese acetate and An azeotropic distillation operation of an aqueous acrylic acid solution was performed in the same manner as in Example 1, except that hydroquinone was dissolved in water and supplied into the tower from the 20th stage.

When the azeotropic separation column 40 was continuously operated under these conditions for 30 days, the same separation state as in Example 1 was obtained.
After the operation was stopped, the inside of the distillation column was inspected. As a result, no polymer was generated.

Example 5 Example 4 was repeated except that the injection position of the aqueous solution of the ammonium salt of N-nitrosophenylhydroxylamine was changed from the bottom of the column to 60% of the total theoretical plate number from the bottom of the column as a base point. In the same manner as in Example 4, an azeotropic distillation operation of the acrylic acid aqueous solution was performed.

When the azeotropic separation column 40 was continuously operated under these conditions for 30 days, the same separation state as in Example 4 was obtained.
After the operation was stopped, inspection of the inside of the distillation column revealed that only a small amount of polymer was found in the column, and the operation could be continued.

Example 6 Example 6 was repeated except that the injection position of the aqueous solution of the ammonium salt of N-nitrosophenylhydroxylamine was changed from the bottom of the column to 25% of the total number of theoretical plates from the bottom of the column as a base point. In the same manner as in Example 4, an azeotropic distillation operation of the acrylic acid aqueous solution was performed.

When the azeotropic separation column 40 was continuously operated under these conditions for 30 days, the same separation state as in Example 4 was obtained.
After the operation was stopped, the inside of the distillation column was inspected, and almost no generation of a polymer was observed.

Comparative Example 1 Acrylic acid aqueous solution was prepared in the same manner as in Example 1 except that the position of the aqueous solution of the ammonium salt of N-nitrosophenylhydroxylamine was changed from the bottom to the top. A boiling distillation operation was performed.

When the azeotropic separation column 40 was continuously operated under these conditions, a separation state similar to that of Example 1 was obtained at the beginning of the operation, but the pressure loss in the column started 5 days after the start of the operation. On the sixth day, it became difficult to continue driving.
When the operation was stopped and the distillation column was dismantled and inspected, generation of a large amount of polymer in the column was recognized.

Comparative Example 2 An acrylic acid aqueous solution was prepared in the same manner as in Example 4 except that the position of the aqueous solution of the ammonium salt of N-nitrosophenylhydroxylamine was changed from the bottom to the top. An azeotropic distillation operation was performed.

When the azeotropic separation column 40 was continuously operated under these conditions for 30 days, the same state of separation as in Example 4 was obtained at the beginning of operation, but the pressure loss in the column started 7 days after the start of operation. On the eighth day, it became difficult to continue driving. When the operation was stopped and the distillation column was dismantled and inspected,
Generation of a large amount of polymer was observed in the tower.

[0079]

According to the present invention, when the nitroso compound is supplied from a position of 70% or less of the total number of theoretical plates, the compound is decomposed in the distillation column, and the resulting gas component is removed from the gas in the purification column. Polymerization of the easily polymerizable substance present in the phase can be effectively prevented. Further, when an N-oxyl compound or the like is further used in combination, it is possible to particularly suppress polymerization of the easily polymerizable substance existing in the liquid phase. As the easily polymerizable substance, (meth) acrylic acid and its ester constituting the gas-liquid phase in the purification tower are used.

By carrying out the polymerization preventing method of the present invention,
When acrylic acid and its ester are produced, continuous operation is enabled by suppressing the generation of a polymer in the production process, and the product yield is improved.

[Brief description of the drawings]

FIG. 1 is a schematic flow chart showing a process for producing acrylic acid.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... propylene, 10 ... reactor, 20 ... acrylic acid collection tower, 21 ... acrylic acid collection liquid, 30 ... acrolein separation tower, 40 ... azeotropic dehydration tower, 41 ... storage tank, 42 ... reboiler, 50 ... high boiling Separation tower, 51 ... acrylic acid.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuo Okochi 992, Nishioki, Okihama-shi, Abashi-ku, Himeji-shi, Hyogo Japan Nippon Shokubai Co., Ltd. Within Nippon Shokubai (72) Inventor: Osamu Nakahara 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo F-term (reference) in Nippon Shokubai Co., Ltd.

Claims (8)

[Claims] 1. When purifying (meth) acrylic acid and its ester in a purification column using a nitroso compound, the nitroso compound is converted from a position below 70% of the total theoretical plate number with respect to the bottom of the purification column as a base point. Characterized by supplying
A method for preventing polymerization of (meth) acrylic acid and its ester. 2. The method for preventing polymerization of (meth) acrylic acid and its ester according to claim 1, wherein said nitroso compound is dissolved in a solvent. 3. The method according to claim 1, wherein the nitroso compound is N-nitrosophenylhydroxylamine or a salt thereof.
Or the method for preventing polymerization of (meth) acrylic acid and its ester according to 2. 4. The method for preventing polymerization of (meth) acrylic acid and its ester according to claim 3, wherein the salt of N-nitrosophenylhydroxylamine is an ammonium salt of N-nitrosophenylhydroxylamine. 5. The method for preventing polymerization of (meth) acrylic acid and esters thereof according to claim 1, further comprising introducing an N-oxyl compound into a purification tower. 6. An N-oxyl compound comprising: an N-hydroxy-2,2,6,6-tetramethylpiperidine compound;
The method for preventing polymerization of (meth) acrylic acid and its ester according to claim 5, wherein a 2,2,6,6-tetramethylpiperidine compound coexists. 7. The method for preventing polymerization of (meth) acrylic acid and its ester according to claim 5, wherein the N-oxyl compound is introduced from above the raw material supply stage of the purification tower. 8. A method for producing (meth) acrylic acid or an ester thereof, which comprises the method for preventing polymerization of (meth) acrylic acid or an ester thereof according to claim 1. .