JP2725638B2 - Method for preventing polymerization of (meth) acrylic acid and its ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing polymerization of (meth) acrylic acid monomers and (meth) acrylic acid ester monomers (hereinafter abbreviated as (meth) acrylic acid and its esters).

[0002]

2. Description of the Related Art It is generally known that (meth) acrylic acid and its ester have a property of being easily polymerized by light or heat. Therefore, in order to prevent polymerization during storage, various kinds of polymerization inhibitors are added to (meth) acrylic acid and its ester alone or in combination of several kinds.

Attempts have been made to use N-oxyl compounds as one of the above polymerization inhibitors. For example, Japanese Patent Publication No. 45-1054 discloses tertiary butyl nitroxide or 2,2,6,6-tetramethyl-4 as a stabilizer for acrylic acid.
-It has been disclosed that N-oxy radicals such as hydroxypiperidine-1-oxyl are used alone to exhibit a polymerization inhibitory effect superior to those conventionally known, such as hydroquinone, phenothiazine and cupric chloride. No. 3853 discloses, as a polymerization inhibitor when 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-1
-Methods using oxyl are disclosed.

Further, Japanese Patent Publication No. 58-46496 discloses 2,2,5,5-
Tetramethyl-3-oxopyrrolidine-1-oxyl, 2,2,
A method using a compound such as 6,6-tetramethyl-4-acetoxypiperidine-1-oxyl is disclosed. further,
Chinese Patent CN1052847A has 2,2,6,6-tetramethyl-4 as a method for preventing polymerization of acrylic acid and acrylates
-It discloses the effect of preventing polymerization when hydroxypiperidine-1-oxyl is used alone or in combination with hydroquinone.

However, the present inventors have studied the polymerization inhibitor system using the N-oxyl compound alone or the N-oxyl compound in combination with the above compound such as hydroquinone. It turned out that there was a problem in the prevention effect.

That is, by the catalytic gas phase reaction,
In the distillation step when producing acrylic acid, an aqueous solution of (meth) acrylic acid is distilled in an azeotropic separation tower (water separation tower).
At this time, the feed composition contains water, acetic acid and aldehydes, and the polymerization of (meth) acrylic acid is extremely easy to occur. For this reason, even if the above-mentioned polymerization inhibitor is used in a normal addition amount, no inhibitory effect is exhibited, and a popcorn polymer or a viscous polymer is generated during the distillation, and long-term continuous operation of the production apparatus including the distillation column is not possible. The problem is that it will be possible. Further, in order to exert the polymerization preventing effect, a large amount of a polymerization inhibitor is required, and it has been difficult to use it in an actual device.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and exhibits a polymerization preventing effect even in a process in which (meth) acrylic acid and its ester are easily polymerized with a small amount. The aim is to find a method for preventing the polymerization to be obtained.

[0008]

According to the method for preventing the polymerization of (meth) acrylic acid and its ester according to the present invention which has achieved the above object, a manganese salt compound, a copper salt compound and a N-oxyl compound are used as polymerization inhibitors. The gist lies in that at least one selected from the group consisting of a 2,2,6,6-tetramethylpiperidine compound and a nitroso compound is used. The N-oxyl compound is 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl and 4,4 ′, 4 ″ -tris-
It is a preferred embodiment of the present invention that it is at least one selected from the group consisting of (2,2,6,6-tetramethylpiperidinooxyl) phosphite.

[0009]

The method for preventing polymerization according to the present invention comprises the steps of using a specific N-oxyl compound as a polymerization inhibitor and one of a manganese salt compound, a copper salt compound, a 2,2,6,6-tetramethylpiperidine compound or a nitroso compound. It is an essential requirement to use more than one species together. These compounds alone have an effect of preventing polymerization but are insufficient. The present inventors have found the above compound capable of exhibiting, as a synergistic effect, a remarkable polymerization-preventing effect, which has not been obtained by itself, in combination with an N-oxyl compound, leading to the present invention. . Hereinafter, the present invention will be described in detail.

In the present invention, an N-oxyl compound is used as an essential component of the polymerization inhibitor. Any N-oxyl compound can be used without particular limitation, but can provide a good polymerization inhibitory effect 2,2,6,6-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) phosphite.

In the present invention, manganese salt compounds, copper salt compounds, 2,2,6,6-tetramethylpiperidine compounds, nitroso compounds are exemplified as compounds which exhibit an excellent polymerization inhibitory effect in combination with the above-mentioned N-oxyl compound. And any one of these must be used with the N-oxyl compound. Of course, even when one or more of these four types of compounds are combined with an N-oxyl compound to form a combination system of three or more components, the same or higher polymerization inhibitory effect than that of a two-component system can be obtained.

As the manganese salt compound, manganese dialkyldithiocarbamate (the alkyl group is any of methyl, ethyl, propyl and butyl, which may be the same or different), manganese diphenyldithiocarbamate, manganese formate, acetic acid 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. The manganese salt compound alone has a relatively low polymerization inhibitory effect, but it is clear that the N-oxyl compound or the N-oxyl compound in combination with another polymerization inhibitor exhibits a remarkable polymerization inhibitory effect in the present invention. It became.

Examples of the copper salt compound include copper dialkyldithiocarbamate (the alkyl group is any of methyl, ethyl, propyl and butyl, which may be the same or different), copper diphenyldithiocarbamate, and the like. Two or more kinds may be used in combination.

Specific examples of the 2,2,6,6-tetramethylpiperidine compound include 2,2,6,6-tetramethylpiperidine and
4-hydroxy-2,2,6,6-tetramethylpiperidine, 1-hydroxy-2,2,6,6-tetramethylpiperidine, 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine, etc. And one or more of these can be used.

Examples of the nitroso compound include p-nitrosophenol, N-nitrosodiphenylamine and ammonium salts of N-nitrosophenylhydroxyamine, and two or more nitroso compounds may be used.

In the method of the present invention, at least a two-component polymerization inhibitor of the N-oxyl compound and a compound selected from the group consisting of a manganese salt compound, a copper salt compound, a tetramethylpiperidine compound and a nitroso compound is used. Although a remarkable polymerization inhibitory effect can be achieved by this, a combination of three or more components may be used by using other known polymerization inhibitors. Known polymerization inhibitors include hydroquinone,
p-methoxyphenol (methquinone), cresol,
t-butylcatechol, diphenylamine, phenothiazine, tetraalkylthiuram disulfide (the alkyl group has the same meaning as described above), methylene blue and the like. Further, if molecular oxygen is used in combination as needed, the effect of preventing polymerization is further improved, and a long-term continuous operation of the production apparatus becomes 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, when producing (meth) acrylic acid by a catalytic gas phase oxidation reaction, a rectification column of (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.

In the method of preventing polymerization of the present invention, the polymerization inhibitor of two or more components may be added in the above-mentioned various steps, and the method of addition is not particularly limited. It may be added directly in the form of a solid or powder, or may be added as a solution or aqueous solution of another organic solvent. Also, 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. For example, in the case of a distillation step or the like during the production of the (meth) acrylic acid, it may be dissolved in a supply liquid or a reflux liquid and introduced into the various steps.

The amount of the polymerization inhibitor used is appropriately adjusted according to the operating conditions and is not particularly limited, but the total amount of the polymerization inhibitor used is determined based on the amount of vaporized vapor of (meth) acrylic acid and its ester. The content is preferably 3 to 650 ppm (weight basis). The preferred amount of each polymerization inhibitor used is 1 to 100 ppm of the N-oxyl compound with respect to the amount of vaporized vapor of the monomer, and 1 to 50 pp with respect to the amount of vaporized vapor of the manganese salt compound or copper salt compound.
In the case of m, 2,2,6,6-tetramethylpiperidine compound or nitroso compound, the concentration is 1 to 500 ppm.

[0021] The term "evaporated vapor amount" as used herein means the total amount of monomer vapor generated in the reboiler in accordance with 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.
Further, the polymerization prevention method of the present invention can be applied to storage of a monomer. In this case, it is recommended to add the above amount to the liquid weight of (meth) acrylic acid and its ester.

The molecular oxygen used as necessary may be directly mixed into (meth) acrylic acid and its ester by air bubbling or the like.
Alternatively, it may be indirectly mixed with (meth) acrylic acid and its ester while being dissolved in another solvent.
Air bubbling can be easily incorporated into the production process if gas is sent from the bottom of the distillation column or stripper and / or from the reboiler. It is desirable that the molecular oxygen is added in an amount of about 0.1 to 1.0% by volume based on the amount of vaporized vapor of (meth) acrylic acid.

The method for preventing polymerization of the present invention exhibits an excellent polymerization preventing effect even during transportation and storage of (meth) acrylic acid and its esters.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which do not limit the present invention.
Modifications and alterations that do not depart from the spirit described below are all included in the technical scope of the present invention. The unit ppm in the following Examples and Comparative Examples is based on weight.

Example 1 Acrylic acid from which a polymerization inhibitor was previously removed by distillation was used as a test blank. 2 ml of this blank solution was placed in a test tube, and the composition and concentration shown in Tables 1 and 2 (units in the table are p
pm. The same was applied hereinafter) to prepare a control solution. Nos. 1 to 10 are comparative examples. Next, the pressure in the test tube was reduced, and the test tube was immersed in an oil bath kept at 100 ° C., and the time until the test solution became cloudy due to the polymer (polymerization time) was visually measured. Table 1 and Table 2 show the results.
Shown in In the following examples, compound names are omitted as shown below.

PO: 2,2,6,6-tetramethylpiperidinooxyl 4H-PO: 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl T-PO: 4,4 ', 4 "-tris- (2,2,6,6-tetramethylpiperidinooxyl) phosphite MnAc: manganese acetate CB: copper dibutyldithiocarbamate 4HTMP: 4-hydroxy-2,2,6,6-tetramethylpiperidine DHTMP: 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine PNP: p-nitrosophenol NNDPA: N-nitrosodiphenylamine NPH: ammonium salt of N-nitrosophenylhydroxyamine

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from Table 1, Comparative Experiments Nos. 1 to 10 in which the polymerization inhibitor was a single system each had a polymerization time longer than Nos. 11 to 29 of a two to five component system in the present invention. It can be seen that the polymer was short and the polymerization prevention effect was inferior. In addition, all of the present invention examples are comparative experimental examples of the single systems No. 2, 4,
Although the total amount of the inhibitor was the same (10 ppm) as in 6, 8, and 10, a large difference was observed in the polymerization time, and it is clear that the synergistic effect of the combined use of the polymerization inhibitor was exhibited. In particular, a synergistic effect when a manganese salt compound is used is remarkable. Further, as shown in Table 2, three- and four-component systems (Experiment Nos. 30 to 34) obtained by adding other known polymerization inhibitors to the two-component system defined in the present invention (Experiment No. 11). Also in this case, it can be seen that the same polymerization prevention effect can be obtained without impairing the effects of the present invention.

Example 2 Acrylic acid aqueous solution was subjected to azeotropic separation using a packed tower provided with a distilling tube at the top and a raw material supply tube at the center. As a feedstock, an aqueous solution of acrylic acid containing 30% by weight of water and 2.5% by weight of acetic acid obtained by a catalytic gas phase reaction of propylene was used. Methyl isobutyl ketone was used as a refluxing liquid, an operating pressure was 160 mmHg, and a top temperature was 49%. ℃, tower bottom temperature 97 ℃
Was distilled under the following conditions. The polymerization inhibitor in the amount shown in Table 3 was added to and dissolved in the reflux liquid and charged into the column, and oxygen gas was supplied to the bottom of the column. The standard of the input amount of the polymerization inhibitor and oxygen is the amount based on the amount of vaporized acrylic acid vapor. The composition of the bottoms withdrawn in a steady state was 97% by weight of acrylic acid, 0.5% by weight of acetic acid, and 2.5% by weight of others. The reflux liquid was obtained by recycling the distillate oil phase. The polymer generated in the tower during an operation time of 8 hours was dried under reduced pressure to a constant weight, and the measurement was carried out. Table 3 shows the results.
Shown in

[0031]

[Table 3]

As is clear from Table 3, Nos. 40 to 43 to which the polymerization preventing method of the present invention was applied showed a very small amount of produced polymer and exhibited an excellent polymerization preventing effect.

Example 3 Methacrylic acid from which a polymerization inhibitor had been removed in advance by distillation was used as a test blank. 2 ml of this blank solution was placed in a test tube, and a polymerization inhibitor having the composition and concentration shown in Table 4 was added to prepare a control solution. Nos. 44 to 48 are comparative experimental examples.
Next, the pressure in the test tube was reduced, and the test tube was immersed in an oil bath maintained at 130 ° C., and the polymerization time was measured visually. Table 4 shows the results.

[0034]

[Table 4]

As apparent from Table 4, No. 4 of the present invention example
In Nos. 9 to 62, although the same amount of the polymerization inhibitor was used as in Comparative Experimental Examples Nos. 44 to 48, the time until the start of polymerization was extremely long, and the polymerization prevention synergistic effect in the combined system appeared. ing.

Example 4 Four types of acrylates from which a polymerization inhibitor had been previously removed by distillation were used as test blanks. This blank liquid 30
ml of the mixture was placed in a test tube, and a polymerization inhibitor having the composition and concentration shown in Table 5 was added to prepare a preparation. Next, the pressure in the test tube was reduced, and then the sample was measured for the liquid temperature while being immersed in an oil bath maintained at the following temperature. The time at which heat generation by polymerization started was shown in Table 5 as the polymerization time. The oil bath temperature was 70 ° C for methyl acrylate (AM), 90 ° C for ethyl acrylate (AE), and oil bath temperature for butyl acrylate (AB) and octyl acrylate (AO). Was kept at 120 ° C.

[0037]

[Table 5]

As is clear from Table 5, Nos. 68 to 71 of the present invention, in which the polymerization inhibitor is a two-component system, exhibited an excellent polymerization inhibitory effect on any acrylate.

Example 5 Two kinds of methacrylic esters from which a polymerization inhibitor had been previously removed by distillation were used as test blanks. This blank liquid 3
0 ml was placed in a test tube, and a polymerization inhibitor having the composition and concentration shown in Table 6 was added to prepare a preparation. The polymerization time was measured in the same manner as in Example 4 and is shown in Table 6. The oil bath temperature was 90 ° C. for methyl methacrylate (MMA) and 120 ° C. for butyl methacrylate (BMA).

[0040]

[Table 6]

As is clear from Table 6, Nos. 77 to 80 of the present invention, in which the polymerization inhibitor was a two-component system, exhibited an excellent polymerization inhibitory effect on any methacrylic acid ester.

Example 6 The following acrylates and methacrylates from which the polymerization inhibitor had been removed in advance by distillation were used as test blanks. 30 ml of this blank solution was placed in a test tube, and a polymerization inhibitor having the composition and concentration shown in Table 7 was added to prepare a control solution. Next, the pressure in the test tube was reduced, and the temperature of the sample was measured while being immersed in an oil bath maintained at 100 ° C .. The time at which heat generation due to polymerization was started is shown in Table 7 as the polymerization time. HEA: 2-hydroxyethyl acrylate HPA: 2-hydroxypropyl acrylate HEMA: 2-hydroxyethyl methacrylate HPMA: 2-hydroxypropyl methacrylate

[0043]

[Table 7]

As is clear from Table 7, it is understood that the polymerization preventing effect of the examples of the present invention is excellent.

[0045]

The polymerization preventing method of the present invention is constituted as described above, and includes a manganese salt compound, a copper salt compound, a 2,2,6,6-tetramethylpiperidine compound, a nitroso compound, together with an N-oxyl compound. By using at least one compound in combination, the effect of preventing polymerization is significantly improved as compared with the case where these compounds are used alone, and these monomers can be used under the condition that (meth) acrylic acid and its ester are very easily polymerized. Can be prevented beforehand. Therefore, while enabling long-term continuous operation of the production equipment for (meth) acrylic acid and its esters,
It has become possible to prevent polymerization for a long time even during transportation or storage of (meth) acrylic acid and its esters.

Continued on the front page (72) Inventor Yoji Akazawa Nippon Shokubai Co., Ltd. One of 992, Nishioki, Okihama-shi, Abashiri-ku, Himeji-shi, Hyogo Nippon Shokubai Co., Ltd. Inside

Claims (2)

(57) [Claims] 1. As a polymerization inhibitor, together with an N-oxyl compound, at least one selected from the group consisting of a manganese salt compound, a copper salt compound, a 2,2,6,6-tetramethylpiperidine compound and a nitroso compound. A method for preventing polymerization of (meth) acrylic acid and its ester, which is used. 2. The N-oxyl compound is 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,
6-tetramethylpiperidinooxyl and 4,4 ', 4 "-
Tris- (2,2,6,6-tetramethylpiperidinooxyl)
The method for preventing polymerization according to claim 1, wherein the method is one or more compounds selected from the group consisting of phosphites.