JP2000044622A - Rectification of polymerizable liquid and rectifying column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rectification process for a polymerizable liquid to enable the rectification in high efficiency while effectively suppressing the generation of clogging of packing in the rectifying column and provide the rectifying column therefor. SOLUTION: A raw material (crude polymerizable liquid) 10 is supplied to a rectifying column 11 from its bottom to effect the vapor-liquid contact of a liquefied material (the polymerizable liquid) in the rectifying column with polymerizable liquid vapor obtained e.g. by heating the raw material 10 in a reboiler. Since the rectification is carried out essentially without causing the contact of the high-molecular component in the raw material 10 with the plates or packing in the rectifying column 11, the formation of polymer in the rectifying column is effectively suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for rectifying a polymerizable liquid and a rectification column suitably usable for the rectification method, and more particularly to a rectification column having a higher molecular weight in a rectification column. By suppressing the formation of coalescence, the accumulation of the polymer in the rectification column is effectively suppressed, and the yield of rectification (yield
The present invention relates to a method for rectifying a polymerizable liquid in which d) is greatly improved, and a rectification column for the same.

[0002]

2. Description of the Related Art Conventionally, distillation, that is, an operation of separating a liquid mixture in which two or more components become vapor when heated by utilizing the difference in volatility of each component, has been performed in a chemical plant or the like. Widely used for purification and other purposes. Among such distillations, the operation of bringing the generated steam into contact with the condensate (reflux) of the already generated vapor is called "rectification" and includes simple distillation (distillation that does not bring the generated steam into contact with the reflux). Are distinguished.

In industrial rectification, from the viewpoint of efficiency,
Usually, continuous rectification using a rectification column is often used. In this continuous rectification, conventionally, a "light component" (a component with high volatility) from the top of the rectification column and a "heavy component" (a component with low volatility) from the bottom of the rectification column.
From the viewpoint of facilitating the extraction of each raw material, the raw material has been continuously supplied near the center of the rectification column (for example, Chemical Dictionary, Vol. 4, p. 822 (19).
64) See “Distillation” in Kyoritsu Shuppan). As described above, the continuous supply of the raw material to the vicinity of the central portion of the rectification column is performed by heating the vapor of the raw material heated by the reboiler (reboiler),
Since the raw material liquid supplied to the rectification column can be efficiently brought into gas-liquid contact with the crude material liquid, there is also an advantage that efficient rectification can be performed.

[0004] For example, vinyl acetate (VAc), which is an industrially important raw material, is used as a raw material for synthesizing various polymers, but is used in the synthesis of industrial polymers (eg, ethylene-vinyl acetate; EVA). Is often
An oily low molecular weight substance containing so much VAc monomer as unreacted monomer (so-called "VAc drain") is recovered. The recovered VAc drain is used as a new raw material V
When used as an Ac monomer, it is naturally necessary to purify the drain to separate the VAc monomer. For the purpose of such purification, continuous rectification using the rectification column described above has been frequently used.

[0005]

SUMMARY OF THE INVENTION However, VA
When the above-mentioned monomer is rectified by the continuous rectification method,
The occurrence of "clogging" of the packing in the rectification column is remarkable, and in order to perform good continuous rectification, an interval of slightly more than one month (8
Dismantling and cleaning of the rectification tower).

It is an object of the present invention to provide a method for rectifying a polymerizable liquid which has solved the above-mentioned disadvantages of the prior art, and a rectification apparatus which can be suitably used in the method.

Another object of the present invention is to provide a method for rectifying a polymerizable liquid, which is capable of rectifying efficiently while effectively suppressing the occurrence of "clogging" of the packing in the rectification column. And a rectification device suitably usable for the method.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a polymerizable liquid vapor which has been vaporized by heating or the like as in conventional continuous distillation and a polymerizable liquid itself as a crude material are rectified by a rectification column. Gas-liquid contact inside the rectification column; while preventing the crude polymerizable liquid supplied to the rectification column from substantially contacting the gas-liquid contact portion (condensing portion) in the rectification column, It has been found that bringing the ionic liquid vapor into gas-liquid contact with the polymerizable liquid liquefied in the rectification column is extremely effective for achieving the above object.

The method for rectifying a polymerizable liquid of the present invention is based on the above findings. More specifically, a crude polymerizable liquid possibly containing a polymer having a higher molecular weight is prepared by using a rectification column. In the rectification, the polymerizable liquid vapor and a liquefied product of the vapor are separated without substantially bringing the crude polymerizable liquid into contact with a gas-liquid contact portion (condensing portion) in the rectification column. It is characterized by gas-liquid contact in the inside.

According to the present invention, there is further provided a rectification column including at least a distillation can and a column connected to the distillation can; and a rectified liquid supplied into the rectification column. Does not substantially contact the gas-liquid contact section (condensing section) in the rectification column, and the vapor of the liquid to be rectified is vaporized with the liquefied product of the vapor.
A rectification column characterized by liquid contact is provided.

According to the knowledge of the present inventors, when a polymerizable liquid vapor vaporized by heating or the like and a liquid polymerizable liquid as a crude material are brought into gas-liquid contact as in the conventional method, Specifically, when a crude polymerizable liquid (a raw material, for example, a drain collected from a polymer polymerization apparatus) is fed to the middle of a rectification column between a bottom portion (a heavy component concentration portion) and a top portion (a light component removal portion). Although the gas-liquid contact efficiency is high (therefore, the rectification efficiency is high), the polymerizable liquid itself containing the polymerizable monomer itself is in a gas-liquid contact portion in the rectification column (for example, the rectification column inner wall, Between packings in a rectification column, packings
It is presumed that the high molecular weight component (for example, oligomer) in the polymerizable liquid was in contact with the gas-liquid contact portion upon contact with the inner wall). As described above, the polymer in the rectification column is generated by the monomer in the polymerizable liquid further adhering or impregnating and remaining in the high molecular weight component adhered to the gas-liquid contact portion, thereby forming a polymer in the rectification column. It is estimated that "clogging" or the like has occurred.

On the other hand, in the present invention, the raw polymerizable liquid as a raw material is supplied to the gas-liquid contact section (condensing section) in the rectification column.
The polymerizable liquid vapor obtained by vaporizing the liquid by heating or the like and the liquefied product of the vapor are brought into gas-liquid contact without substantially contacting the liquid (typically, at the bottom of the rectification column). In the vicinity, a crude synthetic liquid composed of a collected drain or the like is fed), so that a high molecular weight component (for example, an oligomer of a polymerizable monomer) in the crude polymerizable liquid in the rectification column is
It is assumed that contact with packing (Raschig rings, etc.) in the rectification tower is avoided, polymer production in the rectification tower is suppressed, and thus "clogging" in the rectification tower is also effectively suppressed. Is done.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to the drawings as necessary. In the following description, “parts” and “%” representing quantitative ratios are based on weight unless otherwise specified.

In the present invention, any polymerizable liquid which may contain a polymer (oligomer, polymer, etc.) having a higher molecular weight than (crude polymerizable liquid) can be used without particular limitation. Usually, the polymerizable liquid preferably contains a monomer. In the present invention, polymer formation (monomer polymerization) based on the adhesion of high molecular weight components to the rectification column is effectively suppressed, and the monomer is usually difficult to perform atmospheric distillation due to its strong thermal polymerization property. (For example, VAc = vinyl acetate) can be suitably used.

As such a monomer, a vinyl monomer (a monomer having a vinyl group) can be suitably used. Specific examples of the vinyl monomer include VAc and acrylic acid monomers (for example, acrylic acid, methacrylic acid, and esters of acrylic acid and methacrylic acid such as methyl acrylate).

In the present invention, since the "clogging" of the rectification column is effectively prevented, the above-mentioned polymerizable liquid is
It can be suitably used also when it is a liquid recovered from various reaction devices such as a polymer production device.

(Polymerization Inhibitor) In the present invention, since the monomer polymerization in the rectification column is effectively suppressed, the use of a polymerization inhibitor is not essential. A polymerization inhibitor may be added to the crude polymerizable liquid to be fed. Even when the polymerization inhibitor is added to the crude polymerizable liquid in this way, in the present invention, "clogging" in the rectification column does not substantially occur, so that the crude polymerizable liquid accompanies the vapor of the liquid to be rectified. This effectively prevents the crude polymerizable liquid from being mixed into the rectified liquid vapor. As a result, in the present invention, it is easy to remove the polymerization inhibitor from the purified polymerizable liquid. Therefore, a long-term continuous operation of the rectifying device is facilitated by adding a polymerization inhibitor as needed. The amount of the polymerization inhibitor to be added depends on the type and properties of the crude polymerizable liquid to be fed to the rectification column, but it is usually about 200 to 1000 ppm (further, 4 ppm).
(About 00 to 600 ppm).

In the present invention, any known polymerization inhibitor (eg, a stable radical type, a type that provides a stable radical by an addition reaction or a chain transfer reaction, etc.) can be used without particular limitation. A polymerization inhibitor can be suitably used. Examples of such an addition-reaction type polymerization inhibitor include hydroquinone-based polymerization inhibitors such as hydroquinone (particularly preferable for inhibiting polymerization at low temperatures), ME.
HQ (hydroquinone monomethyl ether; particularly preferred for inhibiting polymerization at high temperatures).

(Rectification tower) In the present invention, a known rectification tower can be used without any particular limitation. Such a well-known rectification column usually comprises a distillation can and a column portion arranged on the distillation can. There are several types of the tower, such as a tray type and a packed type. In consideration of the rectification performance, throughput, and economy required for the rectification device usable in the present invention, a packed rectification column can be suitably used.

Examples of the above-mentioned tray (or tray) type tower section include a bubble bell tray, a perforated plate tray, and a valve tray. On the other hand, as the packing to be packed in the above-mentioned packed type column, for example, Raschig (Ra
schig) ring, lessing ring, pole ring and the like. In consideration of the rectification performance, the throughput, and the economy of the rectification device usable in the present invention, Raschig ring can be suitably used.

FIG. 1 is a schematic sectional view of an example of a rectification column usable in the present invention. As shown in FIG. 1, in the present invention, a polymerizable liquid vapor obtained by heating a raw material (crude polymerizable liquid) 10 with a reboiler (not shown) and the liquefaction of the vapor in a rectification column In order to bring the product (polymerizable liquid) into gas-liquid contact, the raw material is passed through the rectification column 11 from the bottom of the rectification column 11.
Is supplied within. Thereby, in the present invention, since the high molecular weight component contained in the raw material 10 is rectified without substantially contacting the plate or the packing in the rectification column 11, the rectification is performed in the rectification column. Is effectively suppressed.

On the other hand, in the conventional rectification column 20 as shown in FIG. 2, since the raw material 21 is supplied from the central portion of the rectification column 20, the Raschig ring or the Raschig ring--rectification The raw material stayed for a long time in a staying portion such as between the inner walls of the tower, and a polymer in which the monomer was polymerized was produced.

(Embodiment of VAc rectification apparatus) Next, the rectification method of the present invention is applied to the method of using VA, a vinyl monomer having high thermopolymerizability.
An example applied to the rectification of c (vinyl acetate) will be described.

First, a conventional VAc rectification apparatus will be described for comparison. FIG. 3 is a schematic sectional view showing one embodiment of a conventional VAc rectification device. With reference to FIG. 3, in this apparatus, above and below a central portion where the raw material is fed,
First rectification column 30 packed with Raschig rings (not shown)
And a second rectification tower 40. Drain 31 which is a crude polymerizable liquid containing a higher molecular weight polymer
Is fed to the center of the first rectification column 30, and the rectification action of the first rectification column 30 turns (VAc + water) into an azeotropic mixture 32 (for example, an azeotropic mixture having a boiling point of 78 ° C.). It is taken out from the top of the first rectification column 30. The heavy component (high molecular weight component + VAc) is mixed with the mixture 33 (for example, V
(Ac mixture of 60 to 80%) as the first rectification column 3
Removed from the bottom of 0.

The azeotropic mixture 32 is then fed to the center of the second rectification tower 40, and the rectification action of the second rectification tower 40 causes the light component (VAc + water) to become an azeotropic mixture 41. (Moisture-rich VAc; for example, an azeotropic mixture having a boiling point of 73 ° C.) is taken out from the top of the second rectification column 40. On the other hand, purified VAc 42 (for example, having a boiling point of 73 ° C.) is removed from the bottom of the second rectification column 40 as a heavy component.

Next, an embodiment in which the present invention is applied to a VAc rectification apparatus will be described. FIG. 4 is a diagram showing VA to which the present invention is applied.
It is a schematic cross section which shows one aspect of c rectification apparatus. Referring to FIG. 4, first rectification column 50 and second rectification column 60 filled with Raschig rings (not shown) are arranged. A drain 51, which is a crude polymerizable liquid containing a polymer having a higher molecular weight, is fed to the bottom of the first rectification column 50.

In FIG. 4, the raw material VAc is heated by the reboiler in the first rectification column 50 to become VAc vapor, and comes into contact with the packing (Raschig ring) in the first rectification column 50 to be liquefied. . At this time, the high molecular weight component (for example, VAc oligomer) contained in the raw material VAc fed from the bottom of the first rectification column 50 substantially depends on the boiling point of the first rectification column 50. Without contacting the packing therein, the production of VAc polymer in the first rectification column 50 is effectively suppressed.

On the other hand, the VAc liquid liquefied by contacting the packing in the first rectification column 50 comes into gas-liquid contact with the newly generated VAc vapor based on the reboiler heating, and the gas-liquid flows.
Rectified based on liquid contact. Such a first rectification column 50
, A light component (VAc + water) is taken out from the top of the first rectification column 50 as an azeotrope 52 (VAc rich in water; for example, an azeotrope having a boiling point of 73 ° C.). On the other hand, the roughly purified VAc53 as a heavy component is taken out from the bottom of the first rectification column 50.

The partially purified VAc 53 is then fed to the bottom of the second rectification column 60, and becomes a light component by the rectification action of the second rectification column 60 (as in the first rectification column 50). The purified VAc (for example, having a boiling point of 73 ° C.) 61 is taken out from the top of the second rectification column 60. On the other hand, a mixture 62 of a high molecular weight component and VAc (waste VAc;
c composition of 30 to 50%) is removed from the bottom of the second rectification column 60 as a heavy component.

Hereinafter, the present invention will be described more specifically with reference to examples.

[0031]

EXAMPLES Using the VAc rectification equipment having a construction shown in Example 4, ethylene - was produced in VAc recovered from synthesis facility vinyl acetate (EVA).

<Components> (Peripheral equipment of the first rectification tower) First rectification tower: 1BSUS Raschig ring (average diameter: about 25 mm) irregularly filled, 250 mm inside diameter, tower height 6,
500 mm packed tower (made of SS41).

Reboiler: Multi-tube heater type. The body side is heated with 0.35 MPa steam.

Condenser: Multi-tube cooler

(Peripheral equipment of the second rectification column) Second rectification column: 1BSUS Raschig ring (average diameter: about 25 mm) irregularly packed, inner diameter 400 mm, tower height 7,
500 mm packed tower (made of SS41).

Reboiler: Multi-tube heater type. The body side is heated with 0.35 MPa steam.

Condenser: Multi-tube cooler.

<Operation Conditions> (Operation in First Rectification Column) Referring to FIG. 4, the VAc recovered from the ethylene-vinyl acetate (EVA) synthesis equipment (not shown) was used as drain 51 as described above. It was fed to the bottom of the first rectification column 50. In the first rectification column 50, the drain (raw material) VAc51 is heated by a reboiler to produce VAc.
It was vaporized and liquefied by contacting the Raschig ring in the first rectification column 50. At this time, the high molecular weight component (VAc oligomer, etc.) contained in the raw material VAc 51 fed from the bottom of the first rectification column 50 substantially contacts the Raschig ring in the first rectification column 50 due to its boiling point. Without this, the formation of VAc polymer in the first rectification column 50 was effectively suppressed.

On the other hand, the VAc liquid liquefied by contacting the Raschig ring in the first rectification column 50 comes into gas-liquid contact with the newly generated VAc vapor based on the reboiler heating.
Rectified based on the gas-liquid contact. Due to the rectification action of the first rectification column 50, the light component (VAc + water) is converted to the azeotropic mixture 52 (VAc rich in water; for example, having a boiling point of 7).
(3 ° C. azeotrope) from the top of the first rectification column 50. On the other hand, the roughly purified VAc53 as a heavy component was taken out from the bottom of the first rectification column 50.

(Operating conditions of the first rectification column) The pressure at the top was controlled to be 0.05 kg / cm ² (gauge pressure). The control method by PCV was the same as that of the second rectification column.

Column pressure: 0.07 kg / cm ² (gauge pressure) Column top temperature: 73 ° C. Column bottom temperature: 74 ° C. Ring flow rate: 118 liter / hr (so that the ring flow rate is 100 liter / hr or more, The steam flow rate of the reboiler was adjusted.) Azeotrope discharge amount: 4 liter / hr (reference number in FIG. 4: 52) Bottom level: Controlled by a feed flow control valve to the second rectification column.

(Operation of Second Rectification Column) The crude VAc 53 obtained above is then fed to the bottom of the second rectification column 60, and the rectification action of the second rectification column 60 (second Purified VAc (boiling point: 73 ° C.) 61 as a light component (distillate) was taken out from the top of the second rectification column 60 by the same method as in the first rectification column 50). On the other hand, a mixture 62 of a high molecular weight component and VAc (waste VAc; for example, a VAc composition of 30 to 50%)
Was taken out from the bottom of the second rectification column 60 as a heavy component (can effluent). This canned liquid also contained heavy components such as lubricating oil and acetic acid.

(Operating conditions of the second rectification column) PCV was adjusted so that the top pressure was 0.15 kg / cm ^2.
It was controlled by; (and de valve which is opened at the time of pressure increase, and a opened to become N ₂ charged valve when the pressure drop pressure control valve). The differential pressure from the bottom is 0.1 kg / c
m ^{2 te} .

Tower temperature: 78 ° C. Tower temperature: 84 ° C. Tower level: Controlled by the steam flow rate of the reboiler.

Column bottom liquid temperature: The temperature was controlled to be constant by the bottoms flow rate.

Ring flow rate: 1 m ³ / hr By the above operation, the crude purified VAc: the amount of feed drain to the second rectification column was 256 liter / hr (composition: VAc
99.6%, 930 ppm of acetic acid, 11 ppm of water), as purified VAc (distillate), 168 liter / hr
(Composition: VAc 99.8%, acetic acid 12 ppm, moisture 64)
ppm) was obtained.

VAc drain composition: VAc = 50-99%, acetic acid = 200-9,000, depending on production grade
ppm, water = 100-1,000 ppm, and the amount of drain generated was also significantly changed, 50-1200 liters / hr. The rectification tower was continuously fed according to the amount of drain generated.

The output of the bottom is determined by the above-mentioned overhead pressure: 0.15 kg /
under the conditions of cm ^2, 88 Rittoru / hr (composition: VAc6
8.2%, acetic acid 9,900 ppm, moisture 42 ppm). Then, by narrowing the can output to 40 liters / hr so as to eliminate VAc loss as much as possible,
VAc content can be reduced to about 30%, and
Stable operation was possible (conventionally, when clogging of the polymer occurred, it was necessary to flow several hundred liters / hr).

As described above, the rectification method of the present invention in which the drain feed point of the VAc second rectification column was arranged near the reboiler inlet maintained the rectification performance and improved the problem of clogging. As a result, at present, VAc: 70%
Not only the following drains were discarded, but all the drains could be rectified, and the continuous operation period could be extended to two years. VA contained in drain of VAc 70% or less
About 73% of c was recovered and could be reused.

Comparative Example Using the conventional VAc rectification facility shown in FIG. 3, VAc was rectified under the following operating conditions.

<Operating conditions> (Operating conditions of the first rectification column) Top pressure: 0.15 kg / cm ² ; PCV control (same as the second rectification column in Examples) Bottom pressure: Cleaning (decomposition)・ About 0.25 kg /
cm ² , but increased with the operation time, and the differential pressure from the top reached 0.3 kg / cm ² or more. ) Top temperature: 78 ° C Bottom temperature: 84 to 90 ° C (increased with increasing differential pressure) Ring flow rate: 1 m ³ / hr Bottom level: The reboiler steam flow rate was adjusted to keep the bottom temperature constant. Controlled.

The output of the bottom: The bottom level is kept constant.
It was controlled by a bottom flow control valve.

(Operating conditions of second rectification column) Top pressure: 0.05 kg / cm ² ; PCV control (same as the first rectification column) Column bottom pressure: 0.07 kg / cm ² Top temperature: 73 ° C. Tower bottom temperature: 74 ° C. Ring flow and azeotrope discharge: No flow meter.

Column bottom level: adjusted with the discharge flow control valve of the second rectification column.

Column bottom temperature: In order to keep the column bottom temperature constant,
The reboiler steam flow was controlled.

By the operation described above, the amount of feed / drain to the first rectification column was 500 liter / hr (composition: VAc
At 86.9%, 270 ppm of acetic acid, and 210 ppm of water), 130 l / hr (composition: VA)
c76.5%, acetic acid 940 ppm, moisture 290 ppm)
370 L / hr (composition: VAc 94.0%, acetic acid 61 ppm, water content 150 ppm) was obtained as purified VAc (boiler effluent) from the second rectification column.

As a result, in the conventional equipment shown in FIG. 3, the pressure difference in the rectification tower for rectifying the heavy drain (VAc 70% or less) is increased, and the number of continuous continuous rotation is extremely short. Was. Over 70% VAc (eg, 95% VAc
) Drain was 50-60 days but VAc 70%
Less than (eg, 50% VAc) drain
It had been shortened to 30 days.

[0058]

As described above, according to the present invention, when a crude polymerizable liquid possibly containing a polymer having a higher molecular weight is rectified by using a rectification column, the crude polymerizable liquid is purified. The polymerizable liquid vapor and a liquefied product of the vapor are brought into gas-liquid contact in the rectification column without substantially contacting the gas-liquid contact section (condensation section) in the rectification column. The present invention provides a method for rectifying a polymerizable liquid.

According to the present invention, there is further provided a rectification column including at least a distillation can and a column connected to the distillation can; and a rectified liquid supplied into the rectification column. Does not substantially contact the gas-liquid contact section (condensing section) in the rectification column, and the vapor of the liquid to be rectified is vaporized with the liquefied product of the vapor.
A rectification column characterized by liquid contact is provided.

According to the present invention having the above structure, the adhesion or stagnation of the high molecular weight component in the crude polymerizable liquid on the inner wall of the rectification column or the packing (Raschig ring or the like) is avoided, and the Since polymer generation is suppressed, "clogging" in the rectification column is effectively suppressed, and efficient rectification is enabled.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a rectification column that can be used in the method of the present invention.

FIG. 2 is a schematic sectional view showing an example of a conventional rectification column.

FIG. 3 is a block diagram showing an example of a conventional rectification device.

FIG. 4 is a block diagram showing an example of a rectification device used for carrying out the method of the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Sato 5-1, Anesaki Beach, Ichihara City, Chiba Prefecture F-term (reference) in Sumitomo Chemical Co., Ltd. 4D076 AA07 AA16 AA22 AA24 BB04 BB08 BC02 CC12 DA03 DA25 EA02X EA03X EA12X EA14X EA15X EA17X EA20X FA02 FA12 FA33 GA03 HA03 JA10 4F074 AA41 AA47 EA05 EA15 EA42 EA64 4J100 AG04P AJ02P AL03P CA01 GB01 GB18

Claims (11)

[Claims] When a crude polymerizable liquid possibly containing a polymer having a higher molecular weight is rectified by using a rectification tower, the crude polymerizable liquid is supplied to a gas-liquid contact portion in the rectification tower. (Condensing part)
A method for rectifying a polymerizable liquid, comprising bringing a polymerizable liquid vapor and a liquefied product of the vapor into gas-liquid contact in a rectification column without substantially contacting the polymerizable liquid. 2. The method for rectifying a polymerizable liquid according to claim 1, wherein the polymerizable liquid vapor does not substantially contact the crude polymerizable liquid as a raw material. 3. The method for rectifying a polymerizable liquid according to claim 2, wherein the gas-liquid contact portion is a tray or a packing in a rectification column. 4. The method for rectifying a polymerizable liquid according to claim 1, wherein the polymerizable liquid is a monomer. 5. The method for rectifying a polymerizable liquid according to claim 4, wherein the monomer is a vinyl monomer. 6. The method for rectifying a polymerizable liquid according to claim 5, wherein the vinyl monomer is vinyl acetate. 7. The method for rectifying a polymerizable liquid according to claim 5, wherein the vinyl monomer is an acrylic acid monomer. 8. The method for rectifying a polymerizable liquid according to claim 1, wherein the polymerizable liquid is a liquid recovered from a polymer synthesizer. 9. The method for rectifying a polymerizable liquid according to claim 1, wherein the crude polymerizable liquid is supplied into the rectification column from near the bottom of the rectification column. 10. A rectification column comprising at least a distillation can and a column connected to the distillation can; and wherein the liquid to be rectified supplied to the rectification column is A rectification column wherein the vapor of the liquid to be rectified comes into gas-liquid contact with a liquefied vapor of the vapor without substantially contacting the gas-liquid contact section (condensing section). 11. The rectification column according to claim 10, wherein the liquid to be rectified is supplied into the rectification column from near the bottom of the rectification column.