JP2725593B2 - 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
-Disclosed is a polymerization inhibitory effect when hydroxypiperidine-1-oxyl is used alone or in combination with hydroquinone, indicating that the effect is higher than when copper dibutyldithiocarbamate and hydroquinone are used in combination.

However, the present inventors have studied the polymerization inhibitor system using the N-oxyl compound alone or the N-oxyl compound in combination with hydroquinone. As a result, under the following conditions, the polymerization inhibitory effect is not satisfactory. I found that there was.

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 of the present invention, which has achieved the above objects, there is provided a method for inhibiting polymerization of (meth) acrylic acid and its ester, which comprises 2,2,6,6-tetramethylpiperidinooxyl, -Hydroxy-2,2,6,6-tetramethylpiperidinooxyl and 4,4 ', 4''-tris- (2,2,6,6-
Where at least one N-oxyl compound selected from the group consisting of tetramethylpiperidinooxyl) phosphites, at least one phenol compound selected from the group consisting of hydroquinone and methoquinone, and a phenothiazine compound Have a gist.

[0009]

In the method for preventing polymerization of the present invention, it is essential to use a specific N-oxyl compound, a phenol compound and a phenothiazine compound in combination as a polymerization inhibitor. These compounds alone have a polymerization preventing effect but are insufficient, and even if two or more components are used in combination, a sufficient polymerization preventing effect is not necessarily obtained. The present inventors, by using a three-component system of a specific N-oxyl compound, a phenol compound and a phenothiazine compound as a polymerization inhibitor, provide a remarkable polymerization prevention which has not been obtained by a single or two-component system. It has been found that the effect appears as a synergistic effect, leading to the present invention. Hereinafter, the present invention will be described in detail.

In the present invention, 2,2,6,6-tetramethylpiperidinooxyl and 4-hydroxy-2,2,6,6-tetramethylpiperidyl which can provide a good polymerization inhibitory effect as an N-oxyl compound. Nooxyl, 4,4 ', 4 "-tris- (2,2,6,6
-One or more of tetramethylpiperidinooxyl) phosphites are used. In particular, when 2,2,6,6-tetramethylpiperidinooxyl or 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl is used as the N-oxyl compound, The metal-free stabilizer system eliminates the risk of metal corrosion of equipment due to the stabilizer, and facilitates disposal of waste liquid.

The phenol compounds used in the present invention include hydroquinone and methoquinone (p-methoxyphenol). Methoquinone, in particular,
-It is preferable because the polymerization inhibitory effect when used in combination with an oxyl compound and a phenothiazine compound is superior to hydroquinone. These phenol compounds may be used in combination of two kinds.

The phenothiazine compound used in the present invention includes phenothiazine, bis- (α-methylbenzyl) phenothiazine, 3,7-dioctylphenothiazine, bis- (α-dimethylbenzyl) phenothiazine, and the like. Among them, phenothiazine is particularly preferably used. Two or more of these phenothiazine compounds may be used in combination.

In the present invention, a remarkable effect of preventing polymerization can be achieved by using the above-mentioned three-component polymerization inhibitor of N-oxyl compound, phenol compound and phenothiazine compound. If molecular oxygen is used in combination as required, 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, 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.

In the method for preventing polymerization of the present invention, a three-component polymerization inhibitor 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,
The three components 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. However, the total amount of the above-mentioned three components of the polymerization inhibitor is determined by the evaporation of (meth) acrylic acid and its ester. The amount is preferably 2 to 1000 ppm (by weight) based on the amount of steam. The preferred amount of each polymerization inhibitor is 0.1 to 100 ppm based on the amount of vaporized vapor of the monomer in the case of the N-oxyl compound, and 1 to 500 ppm based on the amount of vaporized vapor of the monomer in the case of the phenol compound.
In the case of a phenothiazine compound, the amount is 1 to 500 ppm based on the amount of vaporized vapor of the monomer. In particular, the amounts of the phenol compound and the phenothiazine compound are desirably the same.

[0018] The term "evaporated vapor amount" as used herein means the total amount of monomer vapor evaporated from the bottom of the distillation column, corresponding to the amount of heat added from the reboiler of the distillation column. It is a number that is an important factor in determining the criteria for adding the polymerization inhibitor.

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 be introduced in an amount of about 0.1 to 1.0% by volume based on the amount of vaporized vapor of (meth) acrylic acid. The polymerization prevention method of the present invention exerts an excellent polymerization prevention effect also during transportation and storage of (meth) acrylic acid and its ester.

[0020]

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 had been previously removed 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 1 (units in the table are ppm; the same applies hereinafter) was added to prepare a control solution.
Nos. 1 to 11 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 100 ° C., and the polymerization time was measured visually. Table 1 shows the results. In the following examples, compound names are abbreviated as follows.

TEMPO: 2,2,6,6-tetramethylpiperidinooxyl 4H-TEMPO: 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl TRIS-TEMPO: 4,4 ', 4 "-Tris- (2,2,6,6
-Tetramethylpiperidinooxyl) phosphite DTBNO: ditertiary butyl nitroxide HQ: hydroquinone MQ: methoquinone BQ: benzoquinone PTZ: phenothiazine

[0023]

[Table 1]

As is clear from Table 1, Comparative Examples Nos. 1 to 8 in which the polymerization inhibitor was a single system or a two-component system were all shorter in polymerization time than Nos. 12 to 17 of the present invention. It turns out that the polymerization prevention effect is inferior. In particular, N of the present invention example
o. Nos. 14 to 15 have a longer polymerization time than Nos. 5 to 8 even though the total amount of the polymerization inhibitor is small. Therefore, even if any one component of the three-component system is missing, the polymerization time is shortened, and it is understood that the use of the three-component system is suitable. Comparative Example No. 9 using BQ instead of HQ or MQ, and Comparative Example Nos. 10 to 11 using DTBNO outside the scope of the present invention as an N-oxyl compound.
Shows that the polymerization time is shorter than that of Nos. 12 to 13 of the examples of the present invention, and even if a three-component system is used, the polymerization inhibitory effect is inferior.

Example 2 Acrylic acid aqueous solution was subjected to azeotropic separation using a packed tower provided with a distillation 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 2 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 2 shows the results.
Shown in

[0026]

[Table 2]

As is evident from Table 2, a large amount of polymer is generated even if any one of the three-component system is missing, and No. 23 to 24 to which the polymerization preventing method of the present invention is applied have a small amount of produced polymer. You can see that.

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 3 was added to prepare a control solution. Nos. 25 to 27 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 3 shows the results.

[0029]

[Table 3]

As is apparent from Table 3, Comparative Examples Nos. 25 to 27 in which the polymerization inhibitor was a two-component system were all N
o. It can be seen that the polymerization time is shorter than that of 28 to 31, and the polymerization prevention effect is inferior. Nos. 29 and 31 of the present invention had a longer polymerization time than Nos. 25 to 27 even though the total amount of the polymerization inhibitor was small, and exhibited an excellent polymerization prevention effect.

Example 4 The following acrylic acid ester from which the polymerization inhibitor had been removed in advance by distillation was used as a test blank. 30 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 preparation. Next, after reducing the pressure in the test tube, while immersing in an oil bath maintained at the following temperature,
The liquid temperature of the sample was measured, and the time at which heat generation due to polymerization was started is shown in Table 4 as the polymerization time.

The oil bath temperature was 70 ° C. for methyl acrylate (AM), 90 ° C. for ethyl acrylate (AE), and 90 ° C. for butyl acrylate (AB) and octyl acrylate (AO). The oil bath temperature was kept at 120 ° C.

[0033]

[Table 4]

As can be seen from Table 4, Comparative Experiments Nos. 32 to 34 in which the polymerization inhibitor was a two-component system showed that the polymerization time was longer for all types of acrylate esters than for Nos. 35 to 38 of the present invention. Is short, and the polymerization inhibitory effect is inferior.

Example 5 The following methacrylic acid ester from which the polymerization inhibitor had been removed in advance by distillation was used as a test blank. 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 control solution. The polymerization time was measured in the same manner as in Example 4 and is shown in Table 5. The oil bath temperature was 90 ° C. for methyl methacrylate (MMA) and 120 ° C. for butyl methacrylate (BMA).

[0036]

[Table 5]

As is apparent from Table 5, Comparative Experiments Nos. 39 to 41 in which the polymerization inhibitor was a two-component system showed that the polymerization time of any methacrylic acid ester was longer than that of Nos. 42 to 45 of the present invention. It can be seen that the polymer was short and the polymerization prevention effect was inferior.

Example 6 The following (meth) acrylate ester from which the polymerization inhibitor had been removed in advance by distillation was used as a test blank. 30 ml of this blank solution was placed in a test tube, and a polymerization inhibitor having the composition and concentration shown in Table 6 was added to prepare a control solution. 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 100 ° C. The time at which heat generation due to polymerization was started is shown in Table 6 as the polymerization time. HEA: 2-hydroxyethyl acrylate HPA: 2-hydroxypropyl acrylate HEMA: 2-hydroxyethyl methacrylate HPMA: 2-hydroxypropyl methacrylate

[0039]

[Table 6]

As is evident from Table 6, the examples of the present invention have excellent polymerization preventing effects. Example 7 A 50-stage stainless steel sieve tray was installed at a step interval of 147 mm, and a distilling tube was provided at the top, and an inner diameter was provided with a raw material supply tube at the center.
Using a distillation column of 05 mm, continuous operation of azeotropic separation of aqueous acrylic acid solution was performed. As a polymerization inhibitor component, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl (4H-TEMP
O), hydroquinone (HQ), phenothiazine (PTZ) and oxygen gas were used. 4H-TEMPO 30ppm, HQ 100ppm, PT
Z was added to and dissolved in 100 ppm (each amount of vaporized acrylic acid) of methyl isobutyl ketone and introduced from the top of the column, and oxygen was supplied to the bottom of the column at 0.3 vol% with respect to the vaporized amount of acrylic acid.

Acrylic acid containing 30% by weight of water and 2.5% by weight of acetic acid obtained by catalytic gas phase oxidation reaction from propylene as a feedstock, and methyl isobutyl ketone as a reflux liquid were used. The bottom temperature is 97 ° C, the top pressure is 110mmHg, the bottom pressure is 152mmHg, the feed rate is 37. Water phase 3.94 l / hr, distillate oil phase 19.74 l / hr
Distilled at hr, R / D = 0.92 (on a molar basis).

In the steady state, the composition of the liquid discharged from the bottom of the column is 97.2% by weight of acrylic acid, 0.5% by weight of acetic acid and 2.3% by weight of others, and the composition of the distillate aqueous phase is 90.8% of water, 0.4% by weight of acrylic acid and 6.5% by weight of acetic acid. %, Methyl isobutyl ketone 2.3% by weight, and the distillate oil phase composition is methyl isobutyl ketone 8
The content was 6.7% by weight, water 3.9% by weight, acrylic acid 1.4% by weight, acetic acid 6.5% by weight, and other 1.5% by weight. The effect of preventing polymerization was confirmed by pressure loss in the tower, flooding or dismantling inspection of the tower.

Under these conditions, a stable state was always obtained after continuous operation for about 14 days. After the operation was stopped, the inside of the distillation column was inspected. As a result, no polymer was generated.

COMPARATIVE EXAMPLE 1 The polymerization inhibitor system used in Example 7 was replaced with the same system as in Example 7 except that PTZ was removed from the polymerization inhibitor system to form a two-component system, the amount of HQ added was 200 ppm, and the total amount of the polymerization inhibitor was the same as in Example 7. An experiment was performed under the same conditions as in Example 7. Under these conditions, pressure loss in the tower was observed two days after the start of operation, and it was difficult to continue the operation. When the operation was stopped and the dismantling inspection was carried out, it was found that popcorn polymer was formed in the tower. From this, N-
It was found that the oxyl compound and the phenol compound alone had low polymerization inhibitory effects.

COMPARATIVE EXAMPLE 2 The polymerization inhibitor used in Example 7 was replaced by a two-component system except HQ, except that the amount of PTZ was 200 ppm and the total amount of the polymerization inhibitor was the same as in Example 7. An experiment was performed under the same conditions as in Example 7. Under these conditions, pressure loss in the tower was observed 4 days after the start of operation, and it was difficult to continue the operation. When the operation was stopped and the dismantling inspection was carried out, it was found that popcorn polymer was formed in the tower. From this, N-
It was found that only the oxyl compound and phenothiazine had a low polymerization inhibitory effect.

[0046]

The method for preventing polymerization according to the present invention is constituted as described above, and these compounds can be used alone or in combination with a specific N-oxyl compound, a phenol compound and a phenothiazine compound. As compared with the case where the component is used, the effect of preventing polymerization is remarkably improved, and the polymerization of these monomers can be prevented beforehand even under conditions where (meth) acrylic acid and its ester are very easily polymerized. Accordingly, the production apparatus for (meth) acrylic acid and its ester can be operated continuously for a long period of time, and at the same time, an excellent polymerization-preventing effect can be exhibited even during transportation and storage of (meth) acrylic acid and its ester.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoji Akazawa One of 992, Nishioki, Okihama, Himeji-shi, Hyogo Prefecture Nippon Shokubai Himeji Works Co., Ltd. (72) Inventor: Masao Baba 1 Himeji Works, Nippon Shokubai Co., Ltd.

Claims (1)

(57) [Claims] 1. As a polymerization inhibitor of (meth) acrylic acid and its ester, 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidyl Nooxyl and 4,4 ', 4 "-tris- (2,2,6,6
-One or more N-oxyl compounds selected from the group consisting of-(tetramethylpiperidinooxyl) phosphite, one or more phenol compounds selected from the group consisting of hydroquinone and methoquinone, and a phenothiazine compound A method for preventing polymerization of (meth) acrylic acid and esters thereof.