WO2003078015A1

WO2003078015A1 - Apparatus and method for purifying easily polymerizable substance

Info

Publication number: WO2003078015A1
Application number: PCT/JP2003/003319
Authority: WO
Inventors: Seiji Miyazaki; Yasuhiro Kabu; Yoshiyuki Taniguchi
Original assignee: Mitsubishi Rayon Co., Ltd.
Priority date: 2002-03-20
Filing date: 2003-03-19
Publication date: 2003-09-25
Also published as: JPWO2003078015A1

Abstract

An apparatus (10) and a method for purifying an easily polymerizable substance equipped with a rectifying column (11) for purifying the easily polymerizable substance by continuous distillation thereof, wherein an introduction port for a first polymerization inhibitor (27) is provided in an intermediate portion (26) of the rectifying column (11), preferably at a position such that a theoretical plate number (H2) from the introduction port (27) for the polymerization inhibitor to the top (15) of the column satisfies the formula: 0.1 × H1 ≤ H2 < (H1) wherein (H1) represents the theoretical plate number from an introduction port(25) for the easily polymerizable substance to the top (15) of the column. The apparatus and the method allow the prevention of both the polymerization within the rectifying column and the incorporation of the polymerization inhibitor into a distillate of the rectification, which results in the production of a high quality product.

Description

TECHNICAL FIELD The present invention relates to an apparatus and a method for purifying an easily polymerizable substance such as a vinyl-type polymerizable monomer.

This application is based on Japanese Patent Application No. 2002-79369, the contents of which are incorporated herein. BACKGROUND ART When easily polymerizable substances such as vinyl-type polymerizable monomers are purified by distillation in a purification tower, they are very easily polymerized in the purification tower. A method of introducing a polymerization inhibitor to purify by distillation has been proposed. For example, a method is known in which a polymerization inhibitor such as hydroquinone, phenols, amines, phenothiazine, N-oxyl type compound, etc. is introduced into a purification column, and several types of the above-mentioned polymerization inhibitors are used in combination. Methods have been proposed.

Proposals for introducing the polymerization inhibitor include a condenser that condenses the vapor of the easily polymerizable substance discharged from the purification tower, a pipe that returns the condensed easily polymerizable substance to the purification tower, and the top of the purification tower. Have been. These methods were very effective in preventing polymerization in the purification tower.

However, in any of the above-described positions where the polymerization inhibitor was introduced, a part of the polymerization inhibitor was distilled out of the purification tower together with the easily polymerizable substance, and the polymerization inhibitor was sometimes mixed into the product of the easily polymerizable substance. As a result, the polymerization inhibitor sometimes causes coloring of products of easily polymerizable substances due to coloring. In addition, since the polymerization inhibitor is mixed, the polymerizability of the easily polymerizable substance when a product of the easily polymerizable substance is polymerized into a polymer changes, and it is difficult to obtain a stable polymer. Had become. As a method for introducing a polymerization inhibitor, a method has been proposed in which a polymerization inhibitor is added to an unpurified easily polymerizable substance introduced into a purification tower. However, while this method can prevent the polymerization inhibitor from distilling out, it is observed that a polymer is generated near the top of the purification column, and the polymerization in the purification column cannot be sufficiently suppressed. Was. It is also conceivable to simultaneously introduce a polymerization inhibitor at a position where the unpurified easily polymerizable substance is introduced into the purification tower, but this method adds a polymerization inhibitor to the unpurified easily polymerizable substance. Of the invention, in which polymerization in the purification tower could not be sufficiently suppressed.

The present invention has been made in view of the above circumstances, and when distilling and purifying easily polymerizable substances, it is possible to prevent polymerization in the purification column and to remove the polymerization inhibitor from the purification column more than necessary. It is an object of the present invention to provide an apparatus and a method for purifying an easily polymerizable substance, which can obtain a high-quality product by suppressing the distillation of water.

The apparatus for purifying an easily polymerizable substance according to the present invention is an apparatus for purifying an easily polymerizable substance, comprising: a purification tower for continuously distilling and purifying the easily polymerizable substance, wherein the easy polymerizable substance introduction section includes a purification tower. Separately from this, a polymerization inhibitor introducing section for introducing the first polymerization inhibitor into the purification tower is provided in an intermediate portion of the purification tower.

Here, the intermediate part of the purification tower is a part from the introduction part of the easily polymerizable substance to the top of the tower. The easily polymerizable substance introduction section is a section for introducing an unpurified easily polymerizable substance into a purification tower.

In the apparatus for purifying an easily polymerizable substance of the present invention, the relationship between the theoretical plate number H1 from the top of the purification tower to the introduction section of the easily polymerizable substance and the theoretical plate number H2 from the top of the purification tower to the polymerization inhibitor introduction section is defined as follows. It is preferable that an easily polymerizable substance introduction part and a polymerization inhibitor introduction part are provided at positions satisfying the following formula (1).

0. 1 X H 1≤H 2 <H 1 (1)

Further, in the apparatus for purifying an easily polymerizable substance of the present invention, it is preferable that the easily polymerizable substance is (meth) acrylic acid or (meth) acrylate. Further, in the method for purifying an easily polymerizable substance of the present invention, the easily polymerizable substance introduction section is provided in the purification tower, and the polymerization inhibitor introduction section is separately provided in the middle section of the purification tower. A method for purifying an easily polymerizable substance using a purification tower, in which an easily polymerizable substance is continuously introduced from an easily polymerizable substance introduction section, and a first polymerization inhibitor is purified from the polymerization inhibitor introduction section. The step of introducing

In the method for purifying an easily polymerizable substance of the present invention, the purification tower has a theoretical plate number H 1 from the top of the purification tower to the introduction section of the polymerizable substance and a theoretical plate number H from the top of the purification tower to the polymerization inhibitor introduction section H It is preferable that the purification column is provided with an easily polymerizable substance introduction part and a polymerization inhibitor introduction part at a position where the relationship with 2 satisfies the following formula (1).

0. 1 X H 1 ≤H 2 <H 1 (1)

In the method for purifying an easily polymerizable substance of the present invention, it is preferable that the easily polymerizable substance is (meth) acrylic acid or (meth) acrylate.

The method for purifying an easily polymerizable substance of the present invention may further include a step of adding a second polymerization inhibitor different from the first polymerization inhibitor to the purified easily polymerizable substance obtained from the top of the tower. it can. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an example of the apparatus for purifying an easily polymerizable substance of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The apparatus for purifying an easily polymerizable substance of the present invention will be described with reference to FIG. The apparatus for purifying easily polymerizable substances 10 includes a purification tower 11 for continuously distilling and purifying easily polymerizable substances, and an easily polymerizable substance for supplying unpurified easily polymerizable substances to the purification tower 11. Substance supply pipe 12, polymerization inhibitor supply pipe 13 that supplies the first polymerization inhibitor to purification tower 11, and condenser 1 4 that condenses the easily polymerizable substance vapor discharged from purification tower 11 And has a schematic configuration You.

Further, the purification tower 11 has a tower top outlet pipe 16 for discharging the vaporized easily polymerizable substance from the tower top 15, and a reflux pipe 17 for refluxing from the condenser 14 to the tower top 15. A bottom outlet pipe 19 for drawing out the easily polymerizable substance from the bottom 18 of the purification tower 11; and a reboiler 20 for heating a part of the easily polymerizable substance sent through the bottom guide pipe 19. The reintroduction pipe 21 for reintroducing the vapor of the easily polymerizable substance generated in the reboiler 20 into the purification tower 11 and the remaining of the easily polymerizable substance sent through the bottom outlet pipe 18 An impurity discharge pipe 22 for discharging a part is attached.

Further, the condenser 14 is provided with a next-step liquid sending pipe 23 for sending the liquid to the next step.

The purification column 11 is not particularly limited as long as it can purify the easily polymerizable substance by distillation. For example, a tray column type purification column, a packed column type purification column, and the like are used. Further, the pressure in the purification tower 11 can be reduced.

An easily polymerizable substance introduction part 25 to which an easily polymerizable substance supply pipe 12 is connected is provided at an appropriate position of the purification tower 11. The position of the easily polymerizable substance introduction section 25 should be determined by calculating the theoretical number of plates HI from the easily polymerizable substance introduction section 25 to the tower top 15 based on the type and amount of impurities to be separated in the easily polymerizable substance. Can be. That is, the purification tower 11 is provided with a tray or a packed bed having a theoretical plate number H 1 required for separating impurities between the easily polymerizable substance introduction section 25 and the tower top 15.

In order to prevent the polymerization of the easily polymerizable substance in the purification tower 11, a polymerization inhibitor supply pipe 13 is connected to an intermediate portion 26 of the purification tower 11, A polymerization inhibitor introduction section 27 for introducing the polymerization inhibitor into the purification tower 11 is provided. The position where the polymerization inhibitor introduction section 27 is provided depends on the performance of the purification tower 11, the liquid properties of the easily polymerizable substance to be treated, the distribution of the polymerization inhibitor in the vertical direction of the purification tower 11, and the like. It is appropriately determined within the range of the intermediate part 26 of 1, but it is necessary that the theoretical plate number H 2 from the polymerization inhibitor introduction part 27 to the tower top part 15 satisfies the following formula (1). preferable.

0. 1 xH 1≤H 2 <H 1 (1) (Here, HI indicates the number of theoretical plates from the easily polymerizable substance introduction section 25 to the top section 15 of the purification tower 11.)

In particular, the polymerization inhibitor introduction section 27 is preferably provided at a position where the theoretical plate number H 2 from the polymerization inhibitor introduction section 27 to the top 15 of the purification tower satisfies the following formula (2). .

0.2 xH 1≤H 2≤ 0.7 .x x 1 (2)

When the polymerization inhibitor introduction section 27 is provided at a position satisfying 0.1 x H 1> H2, the number of theoretical plates from the polymerization inhibitor introduction section 27 to the tower top 15 is small, and 1 The polymerization inhibitor may be discharged from the purification tower 1 1 and satisfies H 1 ≤ H 2

When the polymerization inhibitor introduction section 27 is provided at the same level as the easily polymerizable substance introduction section 25 or at a position lower than the same, the top section 15 in the purification column 11 Insufficient amount of polymerization inhibitor in the vicinity may cause polymerization of easily polymerizable substances.

An easily polymerizable substance is a substance having a polymerizable functional group. The easily polymerizable substance is not particularly limited as long as it is an easily polymerizable substance that can be purified by distillation.

(Meth) acrylic acid or (meth) acrylic acid ester is preferred, and among them, methyl ester of (meth) acrylic acid or (meth) acrylic acid, ethyl ester, n-propynoleesterol, and isopropyl ester are preferable. Noreesutenore, n one-butyl ester Honoré, Lee Seo-butyl ester Honoré, t one-butyl ester, 2 - Echiru hexyl ester, cyclohexyl ester to consequent opening, n, n '- dimethyl § Mino E Chino les esters are more preferred _c As the first polymerization inhibitor to be supplied into the purification tower 11, any known polymerization inhibitor can be used arbitrarily, depending on the type of easily polymerizable substance, the operating conditions of the purification tower 11, and the like. Selected. Specific examples of the first polymerization inhibitor include, for example, hide-mouth quinone, benzoquinone, hydroquinone monomethyl ether, force tecole, 2,4-dimethinole 6-tert-butyl phenol, 2,6-ditertyl butyl Phenols such as 4-methylphenol, N-isopropyl-N'-phenol-para-phenylenediamine, N, N'-diphen-nor-para-phenylenediamine, N, N'-diene Amines such as 2-naphthyl-para-phenylenediamine; N-hydroxyl such as 4-hydroxy 2,2,4,4-tetramethylpiperidine-N-oxyl And phenoxythiazine. These can be used in combination of two or more as necessary.

In the apparatus for purifying an easily polymerizable substance described above, a polymerization inhibitor introduction section 27 for introducing a first polymerization inhibitor is provided in an intermediate section 26 of a purification tower. Since the polymerization inhibitor is introduced into the purification tower 11 from the polymerization inhibitor introduction section 27, the polymerization inhibitor can be present in almost the entire portion of the purification tower 11, and the polymerization of the easily polymerizable substance can be prevented. At the same time, since the polymerization inhibitor introducing section 27 is not provided at the tower top section 15, it is possible to prevent the first polymerization inhibitor from distilling more than necessary from the tower top outlet pipe 16. Therefore, it is possible to prevent the product of the easily polymerizable substance from being colored due to the polymerization inhibitor. In addition, by adding a new polymerization inhibitor to the easily polymerizable substance distilled out of the purification device 10, the concentration of the polymerization inhibitor in the easily polymerizable substance product can be easily made constant, thereby improving the quality. be able to.

If the polymerization inhibitor introduction section 27 is provided at a position satisfying the above formula (1), polymerization in the purification tower 11 can be prevented and the polymerization inhibitor introduction section 27 is separated from the outlet pipe 16. Distillation of the first polymerization inhibitor from the purification tower 11 more than necessary can be more reliably prevented.

Further, when the easily polymerizable substance is (meth) acrylic acid or (meth) acrylic acid ester, since the production amount is large, the effect of suppressing the polymerization and the effect of improving the quality in the purification tower 11 are enormous.

Next, an example of the method for purifying the easily polymerizable substance of the present invention will be described. In this method for purifying an easily polymerizable substance, the above-described apparatus for purifying an easily polymerizable substance 10 is used. First, an unpurified easily polymerizable substance is supplied to a purification tower 1 by an easily polymerizable substance supply pipe 12. Introduced into the easily polymerizable substance introduction section 25 of 1. At the same time, the first polymerization inhibitor is introduced into the polymerization inhibitor introduction section 27 of the purification tower 11 through the polymerization inhibitor supply pipe 13. At that time, it is preferable that the first polymerization inhibitor is a solution of an easily polymerizable substance. When the first polymerization inhibitor is a solution of an easily polymerizable substance, it can be easily introduced into the purification tower 11.

The introduced liquid easily polymerizable substance flows down to the bottom 18 of the purification tower 11, and a part of the easily polymerizable substance reaching the bottom 18 is sent to the reboiler 20 via the bottom outlet pipe 19. Introduced Is heated and vaporized. Next, the easily polymerizable substance vaporized by the reboiler 20 is again introduced into the purification tower 11 through the reintroduction pipe 21 and rises inside the purification tower 11. As the liquid polymerizable substance flows down and the vapor-like polymerizable substance rises in this manner, gas-liquid comes into contact, and mass transfer and heat transfer in gas-liquid are repeated. 5, the easily polymerizable substance, which is a low-boiling component, is concentrated.

Next, the vapor-like easily polymerizable substance that has reached the tower top 15 is introduced into the condenser 14 via the tower outlet pipe 16, cooled, condensed, and liquefied. Next, a part of the easily polymerizable substance liquefied in the condenser 14 is refluxed to the top 15 through the reflux pipe 17 to flow down the purification tower 11 內, and liquefied in the condenser 14 內. The remaining part of the easily polymerizable substance thus obtained is sent to the next step through the next step liquid sending pipe 23 in order to be used as a product. On the other hand, impurities that are high-boiling components are concentrated in the bottom part 18 of the purification tower 11, and these impurities are purified together with some easily polymerizable substances through the bottom outlet pipe 18 and the impurity discharge pipe 22. It is discharged out of the device 10.

Further, the easily polymerizable substance discharged from the purification device 1 0, the purpose is to prevent polymerization in during transportation or storage, in which case _c it is the addition of a second polymerization inhibitor, the aforementioned purified In the method, a different first polymerization inhibitor from the second polymerization inhibitor can be used as the first polymerization inhibitor introduced into the purification tower 11. If the first polymerization inhibitor and the second polymerization inhibitor are different, a polymerization inhibitor suitable for the purpose can be appropriately used. For example, a second polymerization inhibitor added to a product of an easily polymerizable substance may have an insufficient effect of suppressing the polymerization in the purification tower 11. Those having a high suppression effect can be used. In addition, the first polymerization inhibitor having a high polymerization inhibitory effect often causes coloring, and as the second polymerization inhibitor, a substance which does not easily color a product of an easily polymerizable substance can be used.

If the polymerization in the purification tower 11 can be suppressed, the first polymerization inhibitor may be of the same type as the second polymerization inhibitor, but the first polymerization inhibitor may be used as the first polymerization inhibitor. If it is discharged from step 1, it becomes difficult to keep the concentration of the polymerization inhibitor in the product constant, and the quality of the product may deteriorate. It is preferable to distill the first polymerization inhibitor more than necessary from the refining tower even if it is the same. Absent.

In the above-described method for purifying an easily polymerizable substance, since the purification device 10 is used, polymerization of the easily polymerizable substance in the purification tower 11 can be prevented. In addition, since the first polymerization inhibitor does not distill more than necessary from the purification tower 11, it is possible to prevent the polymerization inhibitor, which causes coloring, from being mixed into the easily polymerizable substance product. In addition, since the second polymerization inhibitor can be newly added to the purified easily polymerizable substance, the concentration of the polymerization inhibitor in the product of the easily polymerizable substance can be easily made constant. Therefore, the quality of the easily polymerizable substance product can be improved.

Example :

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the embodiment shows one embodiment of the present invention, and does not limit the present invention in any way. In the following Examples and Comparative Examples, the apparatus for purifying easily polymerizable substances shown in FIG. 1 was used. The amount of the polymerization inhibitor was measured by liquid chromatography (quantification limit: 0.5 ppm).

(Example 1)

Methyl methacrylate (MM A), which is an easily polymerizable substance, was purified using a purification column 11 (10 theoretical plates) having 180 trays and a diameter of 180 O mm. The unpurified MMA used for the purification was synthesized from methacrylic acid and methanol in the presence of a catalyst and hydroquinone, and unreacted methacrylic acid, excess methanol and water were removed in advance.

In the purification of MMA, first, under the reduced pressure of 200 hPa, the pressure at the top of the column 15 was not transferred to the 20th tray (counting from the top of the polymerizable substance introduction section 25) counted from the top. Purified MMA was introduced at 8250 L / h. At the same time, a first polymerization inhibitor N- Isopuropi Lou New '-. Hue Nino rate para-Hue two Renjiamin 3 8 mass ^_0/0 counted from the top of the MM Alpha of 1 0 stage containing trays ( 6.2 L / h was introduced into the polymerization inhibitor introduction section 27). Then, the MMA was allowed to flow down, the MMA was sent to the reboiler 20 from the bottom 18 of the purification tower 11, and MMA vapor was generated in the reboiler 20, and the steam was reintroduced into the purification tower 11 . In this way, mass transfer and heat transfer between gas and liquid are repeated, MMA, a low-boiling component, was concentrated at the top 15.

Next, the MMA vapor led out through the outlet pipe 16 at the top was introduced into the condenser 14 using water at 4 ° C as a refrigerant, and was condensed. Next, of the condensed MMA, 1000 L / h was returned to the top 15 of the purification tower 11 as a reflux liquid by a reflux pipe 1 Ί through a reflux pipe 1 、, and the remaining liquid was passed through the next-step liquid feed pipe 23. Distilled out of the purification apparatus 10 through the apparatus.

As a result, MMA was obtained as a distillate from the purification device 10 at a rate of 7950 L / h. No hydroquinone was detected in the distilled MMA. When the MMA product was exposed to sunlight for 4 hours, there was no change in appearance, and N-isopropyl-N'-phenyl-/-para-phenylenediamine was not contaminated.

(Example 2)

Butyl methacrylate (BMA) was purified using a purification column 11 (5.5 theoretical plates) with 70 trays and a diameter of 70 O mm. The unpurified BMA used for the purification was synthesized from ΜΜΑ and butanol in the presence of the catalyst and N-isopropinole Ν'-pheninoleparaphenylenediamine, from which excess ΜΜΑ and butanol had been removed in advance. .

In this purification process, unpurified BMA was added hourly to the 18th shelf (easy polymerizable substance introduction section 25), counting from the top, under the reduced pressure of 80 hPa at the top of the column at a pressure of 15 hPa. Introduced at 1200 L. At the same time, 2 first is a polymerization inhibitor, 4-dimethyl one 6 - tertiary butyl and Honoré phenol 0.3 wt ^_0/0 containing BMA, counted from the top of the 5-stage tray (polymerization inhibitor It was introduced at 5 L / h into the introduction section 27). Then, the BMA was allowed to flow down, the BMA was sent to the reboiler 20 from the bottom 18 of the purification tower 11, and BMA steam was generated in the reboiler 20, and the steam was re-introduced into the purification tower 11. In this way, mass transfer and heat transfer were repeated between gas and liquid, and BMA, which is a low-boiling component, was concentrated at the top 15 of the tower.

Next, the BMA vapor led out through the tower top outlet pipe 16 was introduced into a condenser 14 using 4 ° C water as a refrigerant to condense. Next, 150 L / h of the condensed BMA was returned to the top 15 of the purification tower 11 as a reflux liquid by the reflux pipe 17 as a reflux liquid, and the remaining liquid was passed through the next step liquid supply pipe 23. It was distilled out of the purification device 10. As a result, BMA could be obtained as a distillate from the purification device 10 at a rate of 950 L / h. 2,4-Dimethyl-6-tert-butylphenol was not detected in the distilled BMA product. Also, the product was exposed to sunlight for 4 hours without any change in appearance.

(Comparative Example 1)

MMA containing 3.8% by weight of N-isopropyl-1-N'-phenylparaphenylenediamine as the first polymerization inhibitor is returned from the condenser 14 to the top 15 of the purification column 11 and refluxed. The MMA was purified in the same manner as in Example 1, except that it was introduced at 6.2 L / h into the reflux liquid in the tube 17.

As a result, MMA could be obtained as a distillate from the purification device 10 at 7480 L / h. No hydroquinone was detected in the distilled MMA. However, when the MMA product was exposed to sunlight for 1 hour, the colorless and clear liquid turned red, and it was found that N-isopropyl-N'-phenyl-para-phenylenediamine was mixed into the distilled MMA. INDUSTRIAL APPLICABILITY According to the present invention, the polymerization inhibitor introducing section for introducing the first polymerization inhibitor is provided in the middle of the purification tower, and the polymerization inhibitor is introduced into the purification tower from the polymerization inhibitor introducing section. Since the first polymerization inhibitor is introduced, the first polymerization inhibitor can be present in almost all parts in the purification tower, and polymerization of the easily polymerizable substance in the purification tower can be prevented. At the same time, since the polymerization inhibitor introduction section is not located at the top of the tower, it is possible to prevent the first polymerization inhibitor from distilling out of the purification tower more than necessary, and to facilitate the polymerization of the polymerization inhibitor, which causes coloring. Can be prevented from being mixed into a product with a chemical substance. Also, by adding a new polymerization inhibitor, the concentration of the polymerization inhibitor in the easily polymerizable substance product can be easily made constant, so that the quality can be improved.

Claims

The scope of the claims

1. In an apparatus for purifying an easily polymerizable substance having a purification tower for continuously distilling and purifying the easily polymerizable substance, an easy polymerizable substance introduction section is provided in the purification tower. An apparatus for purifying easily polymerizable substances, wherein a polymerization inhibitor introduction section for introducing the polymerization inhibitor into the purification tower is provided in an intermediate portion of the purification tower.

2. The apparatus for purifying an easily polymerizable substance according to claim 1, wherein the number of theoretical stages H1 from the top of the purification tower to the introduction section of the easily polymerizable substance and the theory from the top of the purification tower to the introduction section of the polymerization inhibitor. An apparatus for purifying an easily polymerizable substance, wherein an easily polymerizable substance introduction section and a polymerization inhibitor introduction section are provided at positions where the relationship with the number of stages H2 satisfies the following formula (1).

0. 1 X H 1≤H 2 <H 1 (1)

3. The apparatus for purifying an easily polymerizable substance according to claim 1 or 2, wherein the easily polymerizable substance is (meth) acrylic acid or (meth) acrylate.

4. An easily polymerizable substance introduction section is provided in the purification tower. Separately, a polymerization inhibitor introduction section is provided by a purification tower provided in an intermediate portion of the purification tower. A step of continuously introducing an easily polymerizable substance from the easily polymerizable substance introduction section and introducing the first polymerization inhibitor into the purification tower from the polymerization inhibitor introduction section. Purification method.

5. The method for purifying an easily polymerizable substance according to claim 4, wherein the purification tower comprises: a theoretical plate number H 1 from the top of the purification tower to the introduction section of the easily polymerizable substance; and a polymerization inhibitor introduced from the top of the purification tower. A method for purifying an easily polymerizable substance, which is a purification tower provided with an easily polymerizable substance introduction section and a polymerization inhibitor introduction section at a position where the relationship with the theoretical plate number H2 up to the part satisfies the following formula (1).

0.1 XH 1≤H 2 <H 1 (1)

6. The method for purifying an easily polymerizable substance according to claim 4 or 5, wherein the easily polymerizable substance is (meth) acrylic acid or (meth) acrylic acid ester. .

7. The method for purifying an easily polymerizable substance according to claim 4, wherein a second polymerization inhibitor different from the first polymerization inhibitor is added to the purified easily polymerizable substance obtained from the tower top. A method for purifying an easily polymerizable substance, further comprising a step of adding.