JP4068839B2 - Storage tank for easily polymerizable substances - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tank for storing bottoms obtained when purifying easily polymerizable substances such as (meth) acrylic acid and esters thereof with a purifier under vacuum.
[0002]
[Prior art]
In a process for producing an easily polymerizable substance such as (meth) acrylic acid or its ester, a bottomed liquid is obtained when the easily polymerizable substance is purified by distillation or the like. This bottomed liquid is usually stored in a tank, and finally transferred to a combustion device, for example, for processing.
The bottoms contain an easily polymerizable substance at a relatively high concentration. Further, the tank is often at a relatively high temperature. For this reason, there is a problem that a polymerization reaction of the easily polymerizable substance occurs in the tank. In particular, by allowing a stabilizer such as a polymerization inhibitor to coexist in the bottoms, the polymerization in the liquid phase part of the tank can be prevented to some extent, but the polymerization inhibitor concentration is not sufficient in the gas phase part, so that polymerization is not possible. It was easy to happen.
[0003]
Therefore, in order to prevent polymerization in the tank, particularly polymerization in or near the gas phase, a molecular oxygen-containing inert gas has been conventionally supplied to the gas phase in the tank ( FIG. 4). Thereby, it is said that the polymerization in the gas phase portion in the tank or in the vicinity thereof can be suppressed and oxygen is dissolved and supplied in the liquid phase, so that the polymerization in the liquid phase portion can be further suppressed.
[0004]
[Problems to be solved by the invention]
On the other hand, in a process for producing a readily polymerizable substance such as (meth) acrylic acid or its ester, when the easily polymerizable substance is purified by distillation or the like, a distillation apparatus and a reboiler are usually used. . Since this reboiler has a gas phase portion, the polymerization of the easily polymerizable substance easily occurs on the wall surface of the gas phase portion. Therefore, in order to suppress the drying of the gas phase portion of the reboiler, the bottoms in the tank are circulated and supplied to the reboiler to wet the inner wall of the reboiler (Japanese Patent Laid-Open No. 2000-300901).
[0005]
However, high-boiling easily polymerizable substances such as (meth) acrylic acid and esters thereof generally require purification under vacuum, and when the above-described circulation supply process is established, a distillation apparatus and vacuum under vacuum are used. A circulating process is constructed that includes the reboiler below. Therefore, the dissolved oxygen in the bottoms is vacuum degassed during the circulation of the bottoms, and the polymerization preventing effect is weakened. Therefore, there is a problem that the easily polymerizable substance is polymerized in the tank. . Furthermore, there is a problem that the easily polymerizable substance is polymerized in a purification apparatus such as a distillation apparatus or a reboiler.
Therefore, the problem to be solved by the present invention is to provide a storage tank capable of suppressing the polymerization of the bottoms obtained when purifying easily polymerizable substances under vacuum. . Another object of the present invention is to provide a storage tank that can suppress polymerization in a refining apparatus such as a distillation apparatus or a reboiler when a circulating supply process for supplying the retentate in the tank to the reboiler is assembled.
[0006]
[Means for Solving the Problems]
The inventor has intensively studied to solve the above problems. As a result, it has been found that the above problem can be solved by adopting a form in which the molecular oxygen-containing inert gas is directly supplied into the liquid phase in the storage tank of the bottoms.
That is, the storage tank for the easily polymerizable substance according to the present invention is a tank that stores the bottoms obtained when the easily polymerizable substance is purified by a purification apparatus under vacuum, and contains molecular oxygen in the storage tank. An outlet of a gas introduction pipe for supplying an inert gas is arranged in a liquid phase in the storage tank.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the easily polymerizable substance in the present invention include polymerizable monomers, and examples thereof include acrylic acid, methacrylic acid, maleic anhydride, acrylonitrile, and esters and derivatives thereof. It may be a solvent and a mixture containing by-products at the time of production of an easily polymerizable substance. Preferably, acrylic acid, acrylic acid ester (methyl ester, ethyl ester, butyl ester, 2-ethylhexyl ester, etc.), methacrylic acid, methacrylic acid ester (methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester , Tertiary butyl ester, cyclohexyl ester, etc.), dimethylaminoethyl (meth) acrylate, and hydroxyalkyl (meth) acrylate.
[0008]
The storage tank of the easily polymerizable substance according to the present invention is a tank for storing the bottoms obtained when the easily polymerizable substance is purified by a purification apparatus under vacuum.
Examples of the purification method include diffusion, absorption, and distillation. In particular, distillation is preferably performed in terms of purification efficiency.
Purification of the easily polymerizable substance in the present invention is performed by a purification apparatus under vacuum. The storage tank according to the present invention has a problem that the bottoms obtained when purifying an easily polymerizable substance are prone to polymerization in the storage tank or in a purifier when the purification is performed under vacuum. Because it was completed for the purpose of solving.
[0009]
As the purification apparatus, it is preferable to use a distillation apparatus and a reboiler, or to use a thin film evaporator.
Examples of the distillation apparatus include an evaporator in simple distillation and flash distillation, a plate tower such as a perforated plate tower and a bubble tower in multistage distillation, or a packed tower. A plate tower and a packed tower are preferably used.
Examples of the reboiler include a vertical thin film evaporator, a horizontal thin film evaporator, a (multitubular) vertical liquid film heat exchanger, a (multitubular) vertical thermosiphon heat exchanger, (Multi-tube) horizontal thermosiphon heat exchanger, (multi-tube) vertical forced circulation heat exchanger, (multi-tube) horizontal forced circulation heat exchanger, kettle heat exchanger, etc. Among these, a vertical thin film evaporator, a horizontal thin film evaporator, and a (multi-tubular) vertical liquid film heat exchanger are preferably used for refining the bottoms having a relatively high viscosity.
[0010]
These reboilers can be used as a purification apparatus even when not used in combination with the distillation apparatus. In particular, it is preferable to use a thin film evaporator as a purification device.
Purification of the easily polymerizable substance in the present invention is carried out under vacuum, and the degree of vacuum is preferably 0.66 to 1000 hPa, more preferably 1.33 to 666 hPa, and particularly preferably 4 to 400 hPa. If it is less than 0.66 hPa, it is not preferable in that it is difficult to condense and recover the vapor of the easily polymerizable compound, and if it exceeds 1000 hPa, the operation temperature becomes high and polymerization occurs in the purification apparatus. That is not preferable.
[0011]
As described above, the storage tank for the easily polymerizable substance according to the present invention is a tank for storing the bottoms obtained when the easily polymerizable substance is purified under vacuum, and the molecular oxygen is contained in the storage tank. The outlet of the gas introduction pipe for supplying the contained inert gas is arranged in the liquid phase in the storage tank.
For the reasons described above, conventionally, a molecular oxygen-containing inert gas has been supplied to the gas phase portion in the tank (FIG. 4). As a result, the polymerization in the gas phase portion in the tank or in the vicinity thereof can be suppressed, and since oxygen is dissolved and supplied in the liquid phase, the polymerization in the liquid phase portion can be further suppressed. . However, even if the method shown in FIG. 4 is used, as described above, the bottoms obtained when purifying the easily polymerizable substance are circulated to the purifier when the purification is performed under vacuum. As a result of the diligent study, the present inventor has eagerly studied the gas introduction pipe for supplying the molecular oxygen-containing inert gas into the storage tank. It is found that the above-mentioned new problem can be solved by arranging the outlet of the gas in the liquid phase in the storage tank and directly supplying the molecular oxygen-containing inert gas into the liquid phase in the storage tank. It came to examination of.
[0012]
A specific example of a storage tank for easily polymerizable substances according to the present invention is shown in FIG. As shown in FIG. 1, it is a feature of the present invention that the line 2 for introducing the molecular oxygen-containing inert gas is directly thrust into the liquid phase in the storage tank 1. In this way, disposing the outlet of the gas introduction pipe for supplying the molecular oxygen-containing inert gas into the storage tank in the liquid phase in the storage tank has hitherto caused a high inert gas supply pressure. In the past, the polymerization phase was concentrated at a relatively high concentration in the liquid phase in the bottoms storage tank, and in the liquid phase in the storage tank. It was thought that there was no need to supply molecular oxygen-containing inert gas directly.
[0013]
It is a feature of the present invention that the outlet of the gas introduction pipe for supplying the molecular oxygen-containing inert gas into the storage tank is disposed in the liquid phase in the storage tank as described above. When the lowermost part of the side surface of the storage tank is 0% and the uppermost part is 100%, the outlet of the gas introduction pipe is preferably arranged at 50% or less, more preferably at 40% or less, It is particularly preferable that the content is not more than%. If it is disposed above 50%, the outlet of the gas introduction pipe may appear on the liquid level when the liquid level changes, which is not preferable because the polymerization preventing effect in the storage tank is reduced. Moreover, when it arrange | positions above 50%, since the contact time with the liquid of the molecular oxygen containing inert gas supplied in the liquid falls and the oxygen concentration in a liquid becomes insufficient, it is unpreferable.
[0014]
The molecular oxygen-containing inert gas is, as the wording, an inert gas containing molecular oxygen, and examples of the inert gas include nitrogen, air, helium, neon, argon, etc. Nitrogen and air are preferably used in terms of cost.
Although the oxygen concentration in the said molecular oxygen containing inert gas is not specifically limited, For example, 0.5-21 vol% is preferable, 2-15 vol% is more preferable, 3-7 vol% is especially preferable. If it is less than 0.5 vol%, it is not preferable in that the effect of preventing the polymerization of molecular oxygen is insufficient, and if it exceeds 21 vol%, it is not preferable in that the risk of igniting the bottoms increases.
[0015]
Supply amount of the molecular oxygen-containing inert gas is not particularly limited, for example, preferably 0.001~100m ³ / h, more preferably 0.005~10m ³ / h, 0.01~5m ³ / h is particularly preferred. If it is less than 0.001 m ³ / h, it is not preferable in that the polymerization preventing effect in the storage tank is insufficient, and if it exceeds 100 m ³ / h, it is preferable in that the cost of the inert gas increases. Absent.
As shown in FIG. 1, the state in which the line for introducing the molecular oxygen-containing inert gas is directly thrust into the liquid phase in the storage tank, that is, the molecular oxygen-containing inert gas is supplied into the storage tank. The outlet of the gas inlet pipe for the liquid is placed in the liquid phase in the storage tank, and the molecular oxygen-containing inert gas is directly supplied into the liquid phase in the storage tank, Even if the oxygen concentration in the inside is sufficiently increased and purification of the easily polymerizable substance is carried out under vacuum, the oxygen concentration in the bottoms is not easily lowered, and polymerization in the storage tank can be prevented.
[0016]
The storage tank of the easily polymerizable substance according to the present invention may include a stirrer. By stirring, the composition of the bottoms in the tank can be made uniform, which is effective for further suppressing polymerization in the tank. Another advantage is that the molecular oxygen-containing inert gas can be sufficiently dissolved in the bottoms. The stirrer is not particularly limited, and examples thereof include a propeller type, a paddle type, and a turbine type, and a plurality of stirrers may be provided in multiple stages.
It is preferable to provide the waste gas outlet line 6 in the storage tank of the easily polymerizable substance according to the present invention. The boiling point of the easily polymerizable substance to be stored is low, and when it is stored at a high temperature, a condenser is provided in the waste gas outlet line to reduce the outflow of the easily polymerizable substance to the outside of the tank. It is preferable in terms of measures against ignition.
[0017]
Since the easily polymerizable substance storage tank according to the present invention has the above-described characteristics, it can be preferably applied to a form in which the bottoms in the storage tank are circulated and supplied to the purification apparatus under vacuum. Further preferred forms are a form in which the vacuum purifier is a distillation apparatus and a reboiler, and a form in which the vacuum purifier is a thin-film evaporator. Specific examples of this form are shown in FIGS.
In FIG. 2, 1 is a storage tank for easily polymerizable substances according to the present invention, 7 is a distillation apparatus under vacuum, and 8 is a reboiler under vacuum. Reference numeral 2 denotes a molecular oxygen-containing inert gas line which is a feature of the present invention. Reference numeral 3 represents a line for receiving the bottoms from the reboiler. Reference numeral 9 represents a circulation line, and 10 represents a pump for circulating and feeding the bottoms to a reboiler under vacuum. 13 represents a vapor line from the reboiler to the distillation apparatus, and 14 represents a liquid line from the distillation apparatus to the reboiler under vacuum.
[0018]
In FIG. 3, reference numeral 15 denotes a thin-film evaporator under vacuum.
In FIG. 2 and FIG. 3, the bottoms in the storage tank of the easily polymerizable substance according to the present invention are circulated and supplied to a reboiler and a thin film evaporator in a vacuum. In this way, by circulating supply to the reboiler or thin film evaporator, the inner wall of the reboiler or thin film evaporator can be wetted, and drying of the gas phase part of the reboiler or thin film evaporator can be suppressed, The polymerization of the easily polymerizable substance can be suppressed at the wall surface of the part.
In the case of using a conventional general-purpose storage tank, the oxygen concentration in the circulated bottoms was not sufficient. Therefore, when a purifier under vacuum as shown in FIG. 2 or FIG. 3 is used, Dissolved oxygen is vacuum degassed during circulation of the bottoms, and the effect of preventing polymerization is weakened. Therefore, there is a problem that easily polymerizable substances are polymerized in the tank, and easy polymerization is also performed in the purification apparatus. However, by using the storage tank for easily polymerizable substances according to the present invention, the oxygen concentration in the circulating effluent is sufficiently high even if a purification apparatus under vacuum is used. The conventional polymerization problem can be prevented.
[0019]
The amount of the circulating feed is not particularly limited, for example, preferably from 0.1 to 100 m ³ / h, more preferably ^{0.3~10m 3 / h, 0.5~5m 3 /} h are particularly preferred. If less than 0.1 m ³ / h, drying unit occurs in the reboiler and thin-film evaporation apparatus, where not preferable in that the polymer is produced, when more than 100 m ³ / h, the reboiler and the thin-film type evaporating device Since the film thickness of the liquid increases, the heat transfer capability decreases, and the liquid entrainment increases, which is not preferable.
[0020]
【Example】
Example 1
The product distillation of hydroxyethyl acrylate was carried out continuously using a liquid film falling multitubular heat exchanger as a reboiler. The bottoms were stored in a storage tank. Nitrogen gas adjusted to an oxygen concentration of 10 vol% was supplied to the storage tank at 0.5 Nm ³ / h through a nozzle directly thrust into the liquid phase in the tank. In order to secure the liquid film of the heat exchanger, the bottoms in the storage tank were circulated and supplied at 1 m ³ / h to the liquid supply port of the heat exchanger.
[0021]
When the inside of the tank was inspected after one month, no polymer was formed.
In addition, no polymer was formed inside the reboiler.
(Comparative Example 1)
Continuous distillation was performed in the same manner as in Example 1 except that nitrogen gas adjusted to an oxygen concentration of 10 vol% was supplied to the gas phase part of the tank at 0.5 Nm ³ / h.
When the inside of the tank was inspected after one month, about 2 kg of polymer was formed in the tank.
Moreover, the production | generation of the granular polymer was seen in the reboiler inside in some places.
[0022]
(Example 2)
Product distillation of hydroxyethyl acrylate was carried out continuously using a horizontal thin film evaporator as the purification device. The bottoms were stored in a storage tank. Nitrogen gas adjusted to an oxygen concentration of 10 vol% was supplied to the storage tank at 0.5 Nm ³ / h through a nozzle directly thrust into the liquid phase in the tank. In order to secure the liquid film of the heat exchanger, the bottoms in the storage tank were circulated and supplied at 1 m ³ / h to the liquid supply port of the heat exchanger.
When the inside of the tank was inspected after one month, no polymer was formed.
[0023]
In addition, no polymer was generated in the thin film evaporator.
(Comparative Example 2)
Continuous distillation was performed in the same manner as in Example 2 except that nitrogen gas adjusted to an oxygen concentration of 10 vol% was supplied to the gas phase part of the tank at 0.5 Nm ³ / h.
When the inside of the tank was inspected after one month, about 2 kg of polymer was formed in the tank.
Moreover, the production | generation of the granular polymer was seen in the thin film evaporator inside the place.
[0024]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the storage tank which can suppress superposition | polymerization inside the tank of the bottom liquid obtained when refine | purifying an easily polymerizable substance with the refiner | purifier under a vacuum can be provided. In addition, when a circulation supply process is circulated to supply the bottoms in the tank to a purification device under vacuum, polymerization in a purification device such as a distillation device, reboiler, or thin film evaporator can be suppressed. A storage tank can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic view of an example of a storage tank for easily polymerizable substances according to the present invention.
FIG. 2 is a specific example of a usage form of a storage tank of an easily polymerizable substance according to the present invention.
FIG. 3 is a specific example of a usage pattern of a storage tank of an easily polymerizable substance according to the present invention.
FIG. 4 is a schematic view of an example of a conventional storage tank for easily polymerizable substances.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Storage tank 2 Inert gas line containing molecular oxygen 3 Bottom discharge receiving line 4 Bottom discharge line 5 Stirrer 6 Waste gas outlet line 7 Distillation device 8 under vacuum Reboiler under vacuum (liquid membrane heat exchanger)
9 Circulation line 10 Circulation pump 11 Distillation feed line 12 Distillation line 13 Vapor line 14 Liquid line 15 Thin-film evaporator under vacuum

Claims (5)

In a tank for storing the bottoms obtained when purifying easily polymerizable substances with a purification apparatus under vacuum,
A storage tank for easily polymerizable substances, characterized in that an outlet of a gas introduction pipe for supplying a molecular oxygen-containing inert gas into the storage tank is disposed in a liquid phase in the storage tank. The storage tank for easily polymerizable substances according to claim 1, wherein the bottoms in the storage tank are circulated and supplied to the purification apparatus under vacuum. The storage tank for easily polymerizable substances according to claim 1 or 2, wherein the purification apparatus under vacuum is a distillation apparatus and a reboiler. The storage tank for easily polymerizable substances according to claim 1 or 2, wherein the purification apparatus under vacuum is a thin film evaporation apparatus. The easily polymerizable substance is at least one selected from acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, dimethylaminoethyl (meth) acrylate, and hydroxyalkyl (meth) acrylate. A storage tank for the easily polymerizable substance according to any one of the above.

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