Method for producing readily polymerizable compound

Abstract

A method for producing a readily polymerizable compound, comprising the following polymerization prevention step: supplying a gas containing oxygen into a liquid containing the readily polymerizable compound through a gas supply unit having one or more supply ports, wherein the area S (mm2) of each of the supply ports is 2 ) is greater than 0.1 and less than 20, and a ratio V / S of a linear velocity V (m / s) of the gas at the aforementioned supply port in the anti-polymerization step to an area S is greater than 6.0.

Description

Technical Field

[0001] The present invention relates to a method for producing a readily polymerizable compound such as (meth)acrylic acid and (meth)acrylic acid ester. Background Art

[0002] Conventionally, there is known a method of supplying a gas containing oxygen to a readily polymerizable compound such as (meth)acrylic acid and (meth)acrylic acid ester to prevent the polymerization of the readily polymerizable compound. For example, Patent Document 1 discloses a method in which, during the distillation purification of acrylic acid, a gas containing oxygen is supplied to a liquid containing acrylic acid supplied to a distillation tower or to the bottom of the distillation tower. Patent Document 2 discloses a method in which, when (meth)acrylic acid and (meth)acrylic acid ester are transferred to a tank after distillation purification, a gas containing oxygen is supplied to the liquid containing (meth)acrylic acid and the liquid containing (meth)acrylic acid ester in the piping.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2003-277318

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-028108 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] When supplying a gas containing oxygen to a liquid containing a readily polymerizable compound to prevent polymerization, it is desired to reliably supply the gas containing oxygen to the liquid containing the readily polymerizable compound. For example, when supplying the gas containing oxygen to the liquid containing the readily polymerizable compound using a gas supply unit such as a nozzle, it is desired that the gas supply port of the gas supply unit does not become clogged, or that if clogged, the clogged port can be eliminated without stopping the operation.

[0009] The present invention has been made in view of the above-mentioned situation, and its object is to provide a method for producing a readily polymerizable compound, which is a method for producing a readily polymerizable compound while preventing the polymerization of the readily polymerizable compound by supplying a gas containing oxygen, and can effectively suppress and / or eliminate the clogging of the supply port of a gas supply unit for supplying a gas containing oxygen.

[0010] Solutions for solving problems

[0011] The present invention includes the following technical solutions.

[0012] [1] A method for producing a readily polymerizable compound, characterized by comprising the following polymerization prevention step: supplying a gas containing oxygen into a liquid containing the readily polymerizable compound through a gas supply unit having one or more supply ports,

[0013] The area S (mm) of each supply port 2 ) is 0.1 or more and 20 or less,

[0014] In the polymerization prevention step, a ratio V / S of a linear velocity V (m / s) of the gas at the supply port to the area S is 6.0 or more.

[0015] [2] The method for producing a readily polymerizable compound according to [1], further comprising the step of supplying gas to the gas supply means to clean the supply port,

[0016] The pressure difference across the supply port of the gas supply unit in the polymerization prevention step is 100 kPa or less.

[0017] The pressure difference of the gas supply unit across the supply port in the cleaning step is 150 kPa or more.

[0018] [3] The method for producing a readily polymerizable compound according to [1] or [2], further comprising a cleaning step of supplying a liquid to the gas supply means to clean the supply port.

[0019] [4] A method for producing a readily polymerizable compound, characterized in that:

[0020] An anti-polymerization step: supplying a gas containing oxygen into a liquid containing an easily polymerizable compound through a gas supply unit having one or more supply ports; and

[0021] Cleaning step: supplying gas to the gas supply unit to clean the supply port.

[0022] The pressure difference across the supply port of the gas supply unit in the polymerization prevention step is 100 kPa or less.

[0023] The pressure difference of the gas supply unit across the supply port in the cleaning step is 150 kPa or more.

[0024] [5] A method for producing a readily polymerizable compound, characterized in that:

[0025] An anti-polymerization step: supplying a gas containing oxygen into a liquid containing an easily polymerizable compound through a gas supply unit having one or more supply ports; and

[0026] Cleaning step: supplying liquid to the gas supply unit to clean the supply port.

[0027] [6] The method for producing a readily polymerizable compound according to any one of [1] to [5], wherein the polymerization prevention step is performed by at least one of the following methods (1) to (4).

[0028] (1) the polymerization prevention step is performed in the step of introducing the gas containing the readily polymerizable compound into a cooling tower selected from an absorption tower and a condensation tower to obtain a liquid containing the readily polymerizable compound,

[0029] The gas supply unit is provided in the cooling tower, or in a circulation line that takes out a portion of the liquid containing the easily polymerizable compound in the cooling tower and returns the liquid to the cooling tower.

[0030] (2) the polymerization prevention step is performed in the step of introducing the liquid containing the readily polymerizable compound into a vaporization separation tower selected from a distillation tower and a release tower for purification,

[0031] The gas supply unit is provided in the vaporization separation tower, a supply line for supplying the liquid containing the easily polymerizable compound to the vaporization separation tower, or a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the vaporization separation tower and returning it to the vaporization separation tower.

[0032] (3) performing the aforementioned anti-polymerization step during the step of storing the aforementioned liquid containing the readily polymerizable compound in a storage tank,

[0033] The gas supply means is provided in the storage tank, a supply line for supplying the liquid containing the easily polymerizable compound to the storage tank, or a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the storage tank and returning it to the storage tank.

[0034] (4) the polymerization prevention step is performed in the step of introducing the liquid containing the readily polymerizable compound into a reactor to react the liquid,

[0035] The gas supply unit is provided in the reactor, a supply line for supplying the liquid containing the easily polymerizable compound to the reactor, or a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the reactor and returning it to the reactor.

[0036] Effects of the Invention

[0037] According to the present invention, when producing a readily polymerizable compound while preventing polymerization of the readily polymerizable compound by supplying a gas containing oxygen, clogging of a supply port of a gas supply unit containing oxygen can be effectively suppressed and / or eliminated. DETAILED DESCRIPTION

[0038] The method for producing a polymerizable compound of the present invention has an anti-polymerization step of supplying a gas containing oxygen to a liquid containing a polymerizable compound. It is important that the polymerizable compound does not undergo an unexpected polymerization reaction during its production and treatment. As a method for preventing the polymerizable compound from polymerizing, a method of supplying a gas containing oxygen to a liquid containing a polymerizable compound is known. The supply of a gas containing oxygen to a liquid containing a polymerizable compound is carried out through a gas supply unit such as a nozzle, and it is expected that the size of the gas supply port provided in the gas supply unit will not be narrowed or the supply port will not be completely blocked. For example, if the liquid containing a polymerizable compound enters the interior of the gas supply unit from the supply port, the liquid containing the polymerizable compound will come into contact with the supply gas flow of the oxygen-containing gas, and therefore, the liquid containing the polymerizable compound will evaporate and dry, and precipitates will easily be generated and accumulated in the interior and supply port of the gas supply unit. As a result, it is possible that the size of the supply port of the gas supply unit is narrowed, or the supply port is completely blocked, and the oxygen-containing gas supplied to the liquid containing the polymerizable compound becomes insufficient. In the method for producing a readily polymerizable compound of the present invention, when supplying a gas containing oxygen to a liquid containing a readily polymerizable compound, clogging of the supply port of the gas supply means and generation and / or accumulation of precipitates can be suppressed.

[0039] The readily polymerizable compound used in the present invention is not particularly limited as long as it is a compound that easily undergoes polymerization reaction in a liquid, and examples thereof include (meth)acrylic acid or its esters, maleic anhydride or its esters, acrylonitrile, styrene, divinylbenzene, vinyltoluene, diethylene glycol monovinyl ether, etc. Among these, (meth)acrylic acid or its esters are representative. Examples of the (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, methoxyethyl (meth)acrylate, benzyl (meth)acrylate, and glycidyl (meth)acrylate. Preferred readily polymerizable compounds include (meth)acrylic acid, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxyethyl (meth)acrylate, nonyl (meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, benzyl (meth)acrylate, and glycidyl (meth)acrylate.

[0040] The liquid containing the readily polymerizable compound is obtained by a manufacturing process of the readily polymerizable compound, and is preferably a liquid containing the readily polymerizable compound. For example, when the readily polymerizable compound is (meth)acrylic acid, examples of the liquid containing the readily polymerizable compound include: a liquid containing crude (meth)acrylic acid obtained by capturing and condensing a gas containing (meth)acrylic acid obtained by a contact gas-phase oxidation reaction of a raw material for manufacturing (meth)acrylic acid and recovering it in the form of a liquid; a liquid containing purified (meth)acrylic acid obtained by purifying the aforementioned liquid containing crude (meth)acrylic acid; a process liquid obtained in the purification of the aforementioned liquid containing crude (meth)acrylic acid; a stored liquid obtained by temporarily storing the aforementioned liquid containing crude (meth)acrylic acid or the aforementioned liquid containing purified (meth)acrylic acid, etc., but are not limited thereto.

[0041] The concentration of the easily polymerizable compound in the liquid containing the easily polymerizable compound is not particularly limited, and for example, it may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more. It should be noted that, from the viewpoint of the necessity of preventing the polymerization of the easily polymerizable compound by supplying a gas containing oxygen, the concentration of the easily polymerizable compound in the liquid containing the easily polymerizable compound is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and further preferably 80% by mass or more. The upper limit of the concentration of the easily polymerizable compound in the liquid containing the easily polymerizable compound is not particularly limited, and for example, it may be 99.9% by mass or less, 99% by mass or less, or 97% by mass or less.

[0042] In the polymerization prevention step, a gas containing oxygen is supplied to the liquid containing the easily polymerizable compound through a gas supply unit having one or more supply ports. A gas containing oxygen is supplied to the liquid containing the easily polymerizable compound through a supply port of the gas supply unit.

[0043] The oxygen-containing gas is not particularly limited as long as it is a gas containing molecular oxygen, and pure oxygen gas, air, a gas having any oxygen concentration obtained by mixing nitrogen, oxygen and air, etc. can be used. The concentration of molecular oxygen in the oxygen-containing gas can be arbitrarily adjusted within the range of, for example, 1% by volume to 100% by volume.

[0044] The gas supply unit may be a nozzle, a diffuser pipe, a diffuser plate, etc., and their shapes are not particularly limited. The gas supply unit is immersed in a liquid containing a readily polymerizable compound. The supply port is arranged to face the outside of the gas supply unit and to be in contact with the liquid containing a readily polymerizable compound outside the gas supply unit. The supply port is arranged as an opening for flowing a gas containing oxygen into the liquid containing a readily polymerizable compound.

[0045] The supply port of the gas supply unit can be arranged upward, downward, or horizontally. When the gas supply unit is a unit having a gas supply pipe and the gas supply pipe is provided with a supply port, the setting direction of the gas supply pipe at the position where the supply port is provided is not particularly limited. It can be arranged in a manner extending upward, downward, horizontally, obliquely upward or obliquely downward. Taking into account the structure of the introduction part, etc., the gas supply pipe can be arranged as a straight pipe, or it can have one or more bends. It should be noted that the extension direction of the gas supply pipe (for example, whether the pipe extending in the vertical direction is upward or downward) is determined according to the gas flow direction in the gas supply pipe.

[0046] For example, when the gas supply pipe is arranged to extend upward and the supply port is arranged upward, even if the liquid containing the easily polymerizable compound flows back into the gas supply pipe, the backflowing liquid can be discharged from the lower part of the gas supply pipe, and the retention of the liquid in the gas supply pipe can be suppressed. In addition, the precipitate with a small specific gravity can be prevented from flowing into the gas supply pipe.

[0047] When the gas supply pipe is arranged to extend upward and the supply port is arranged horizontally, even if the liquid containing the easily polymerizable compound flows back into the gas supply pipe, the backflowing liquid can be discharged from the lower part of the gas supply pipe, and the retention of the liquid containing the easily polymerizable compound in the gas supply pipe (hereinafter sometimes referred to as "liquid retention") can be suppressed. In addition, it is possible to prevent the precipitate with a large specific gravity from flowing into the gas supply pipe.

[0048] When the gas supply pipe is arranged to extend downward and the supply port is arranged downward, even if the liquid containing the easily polymerizable compound flows back into the interior of the gas supply pipe, the backflowing liquid can be discharged from the lower part of the gas supply pipe, that is, the supply port, so that the retention of the liquid in the gas supply pipe can be suppressed.

[0049] When the gas supply pipe is arranged to extend downward and the supply port is arranged horizontally, even if the liquid containing the easily polymerizable compound flows back into the gas supply pipe, the backflowing liquid can be discharged from the lower part of the gas supply pipe, that is, the supply port, so that the liquid can be suppressed from being retained in the gas supply pipe. In addition, it is possible to prevent the precipitate with a large specific gravity from flowing into the gas supply pipe.

[0050] When the gas supply pipe is arranged in a manner extending in the lateral direction, a plurality of supply ports can be arranged at approximately the same height, and therefore, the liquid pressure near each supply port (i.e., the pressure based on the liquid depth of the liquid containing the easily polymerizable compound) is equal. On this basis, when the supply port is arranged upward, it is possible to prevent the precipitate with a small specific gravity from flowing into the gas supply pipe. On the other hand, when the supply port is arranged downward, even if the liquid containing the easily polymerizable compound flows back into the interior of the gas supply pipe, the backflowing liquid can be discharged from the supply port, and the retention of the liquid in the gas supply pipe can be suppressed. When the supply port is arranged horizontally, it is possible to prevent the precipitate with a large specific gravity from flowing into the gas supply pipe.

[0051] When the gas supply pipe is provided so as to extend obliquely downward and the supply port is provided upward, it is possible to prevent the precipitate having a small specific gravity from flowing into the gas supply pipe.

[0052] When the gas supply pipe is arranged to extend obliquely downward and the supply port is arranged downward, even if the liquid containing the easily polymerizable compound flows back into the interior of the gas supply pipe, the backflowing liquid can be discharged from the lower part of the gas supply pipe, that is, the supply port, so that the retention of the liquid in the gas supply pipe can be suppressed.

[0053] When the gas supply pipe is provided so as to extend obliquely downward and the supply port is provided horizontally, it is possible to prevent precipitates having a large specific gravity from flowing into the gas supply pipe.

[0054] The area S (mm) of each supply port of the gas supply unit 2 ) is preferably 0.1 or more and 20 or less. By setting the area of ​​the supply port to 0.1 mm 2 On the other hand, by setting the area of ​​the supply port to 20 mm 2 As a result, in accordance with the relationship with the linear velocity V of the gas at the supply port described later, when the oxygen-containing gas is supplied through the supply port, it is unlikely that a portion of the liquid containing the easily polymerizable compound will flow back or the liquid containing the easily polymerizable compound will enter the interior of the gas supply unit from the supply port. As a result, blockage caused by the formation of polymers or solidification of small amounts of components contained in the liquid containing the easily polymerizable compound or the like in the supply port and the gas supply unit can be suppressed. In addition, the bubble diameter of the oxygen-containing gas supplied from the supply port to the liquid containing the easily polymerizable compound will not be too large, and the oxygen-containing gas will easily dissolve in the liquid containing the easily polymerizable compound. The area of ​​the supply port is more preferably 0.3 mm 2 More preferably, 0.5 mm 2 More than 18 mm, and more preferably 18 mm 2 Below, more preferably 15mm 2 the following.

[0055] The oxygen-containing gas is preferably supplied at a ratio of the linear velocity V (m / s) of the oxygen-containing gas at the supply port to the area S (mm 2) is supplied from the supply port to the liquid containing the easily polymerizable compound in such a manner that the ratio V / S becomes 6.0 or more. That is, in order to make the ratio V / S be 6.0 or more, it is preferably set in such a manner that the linear velocity V of the oxygen-containing gas at the supply port is increased as the area S of the supply port becomes larger. By setting the ratio V / S in this way, when the oxygen-containing gas is supplied through the supply port, it is not easy for a part of the liquid containing the easily polymerizable compound to flow back and the liquid containing the easily polymerizable compound to enter the interior of the gas supply unit from the supply port. As a result, precipitates are not easy to be generated inside the gas supply unit and at the supply port, and the supply port is not easy to be blocked. The ratio V / S is more preferably 6.2 or more, and further preferably 6.4 or more. The upper limit of the ratio V / S is not particularly limited, for example, it can be less than 100, less than 60, less than 40 or less than 30.

[0056] The shape of the supply port is not particularly limited, but is preferably a shape without corners, such as a circle or an ellipse, from the viewpoint that the liquid containing the easily polymerizable compound is not easy to enter the interior of the gas supply unit from the supply port when the oxygen-containing gas is supplied through the supply port. In addition, by forming the supply port in such a shape, it is also difficult for precipitates to accumulate at the supply port.

[0057] The pressure difference across the supply port of the gas supply unit in the anti-polymerization process is preferably 100 kPa or less. Thereby, the specifications of the blower and compressor used to supply the oxygen-containing gas can be suppressed, and the equipment cost and auxiliary material cost of the blower and compressor can be reduced. The pressure difference across the supply port of the gas supply unit in the anti-polymerization process is more preferably 50 kPa or less, further preferably 20 kPa or less, further preferably 10 kPa or less, and particularly preferably 5 kPa or less. The lower limit of the pressure difference is not particularly limited within the range where the ratio V / S described above is 6.0 or more, for example, it can be 0.01 kPa or more, 0.05 kPa or more, or 0.1 kPa or more.

[0058] The gas supply unit is preferably connected to a gas supply line, and a gas containing oxygen is supplied to the gas supply unit through the gas supply line. The gas supply line is preferably provided with a flow meter and a valve, thereby adjusting the supply amount of the gas containing oxygen from the gas supply unit. The gas supply line branches into a plurality of lines, and each of the branched gas supply lines can be provided with a gas supply unit. In this case, each branched supply line is preferably provided with a flow meter and a valve, thereby adjusting the supply amount of the gas containing oxygen from each gas supply unit. By adjusting in a manner that a gas containing oxygen of more than a specified amount is supplied from each gas supply unit, the blockage of the supply port of each gas supply unit can be prevented. In addition, when the oxygen supply from a part of the gas supply unit is reduced, it can be judged that a precipitate is generated inside the gas supply unit and at the supply port, and by increasing the opening of the valve of the supply line connected to the gas supply unit, the oxygen supply can be increased to prevent the blockage of the supply port of the gas supply unit.

[0059] From the viewpoint of preventing backflow from the supply port toward the inside of the gas supply unit, the surface tension of the liquid containing the easily polymerizable compound at 20°C is preferably 10 mN / m or more, more preferably 15 mN / m or more, and further preferably 20 mN / m or more. The upper limit of the surface tension is not particularly limited, and may be, for example, 200 mN / m or less, 150 mN / m or less, or 100 mN / m or less. For example, the surface tension of acrylic acid at 20°C is 28.1 mN / m.

[0060] The liquid containing the easily polymerizable compound preferably contains a polymerization inhibitor. Thus, the effect of preventing the liquid containing the easily polymerizable compound from polymerizing is improved in tandem with the supply of a gas containing oxygen to the liquid containing the easily polymerizable compound. As the polymerization inhibitor, conventionally known polymerization inhibitors can be used, and examples thereof include quinones such as hydroquinone and p-hydroxyanisole (p-methoxyphenol); phenothiazines such as phenothiazine, bis-(α-methylbenzyl)phenothiazine, 3,7-dioctylphenothiazine, and bis-(α-dimethylbenzyl)phenothiazine; N-oxyl compounds such as 2,2,6,6-tetramethylpiperidinyl oxide, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl oxide, and 4,4',4"-tris(2,2,6,6-tetramethylpiperidinyloxy)phosphite; Compounds; copper salt compounds such as copper dialkyl dithiocarbamate, copper acetate, copper naphthenate, copper acrylate, copper sulfate, copper nitrate, and copper chloride; manganese salt compounds such as manganese dialkyl dithiocarbamate, manganese diphenyl dithiocarbamate, manganese formate, manganese acetate, manganese octoate, and manganese naphthenate; nitroso compounds such as N-nitrosophenylhydroxylamine or its salt, p-nitrosophenol, N-nitrosodiphenylamine or its salt, etc. These polymerization inhibitors can be used alone or in combination of two or more. Among these, it is preferred to use at least quinones as polymerization inhibitors.

[0061] The concentration of the polymerization inhibitor in the liquid containing the readily polymerizable compound can be appropriately set, and is, for example, preferably 1 mass ppm or more, more preferably 10 mass ppm or more, further preferably 100 mass ppm or more, further preferably 1000 mass ppm or more, and preferably 50000 mass ppm or less, more preferably 10000 mass ppm or less, further preferably 5000 mass ppm or less, further preferably 2000 mass ppm or less.

[0062] The liquid containing the readily polymerizable compound may contain other compounds such as dimers of the readily polymerizable compound, maleic acid, glyoxal, acetic acid, formaldehyde, acrolein, propionic acid, furfural, benzaldehyde or derivatives thereof if the amount is small.

[0063] The method for producing a readily polymerizable compound of the present invention preferably includes a cleaning step of the gas supply unit on the basis of an anti-polymerization step of supplying a gas containing oxygen to a liquid containing a readily polymerizable compound through a gas supply unit. In the anti-polymerization step, if the gas containing oxygen is continuously supplied to the liquid containing the readily polymerizable compound through the gas supply unit for a long period of time (e.g., several weeks), precipitates may accumulate little by little at the supply port of the gas supply unit, and the size of the supply port may be narrowed or the supply port may be completely blocked. Therefore, it is preferred that a cleaning step of the gas supply unit is provided after the supply of the oxygen-containing gas and during the supply of the oxygen-containing gas to remove precipitates attached to the inside of the gas supply unit and the supply port.

[0064] In the cleaning process, it is preferred to supply gas to the gas supply unit to clean the supply port. Hereinafter, the gas supplied in the cleaning process is referred to as "cleaning gas". The cleaning gas is supplied from the inside of the gas supply unit to the outside. At this time, the cleaning gas is supplied at a pressure higher than the supply pressure of the oxygen-containing gas in the anti-polymerization process. For example, the pressure difference across the supply port of the gas supply unit in the cleaning process is preferably set to 150kPa or more, more preferably 160kPa or more, and further preferably 180kPa or more. By supplying the cleaning gas at this pressure, the precipitate attached to the inside and the supply port of the gas supply unit can be effectively removed. On the other hand, the upper limit of the aforementioned pressure difference is not particularly limited. If the supply pressure of the cleaning gas is too high, a high-specification compressor or pressure resistance of the equipment is required. Therefore, the pressure difference is preferably below 1000kPa, and more preferably below 800kPa. It should be noted that the pressure difference across the supply port refers to the pressure difference between the inside and outside of the gas supply unit.

[0065] The type of cleaning gas is not particularly limited, but a non-condensable gas is preferably used. As the cleaning gas, for example, the oxygen-containing gas described above can be used, and an inert gas such as nitrogen can also be used.

[0066] The cleaning gas is preferably supplied in a short time. For example, the single supply time of the cleaning gas is preferably set to be less than 20 seconds, more preferably less than 10 seconds, and further preferably less than 5 seconds. In addition, it is preferred to supply the cleaning gas multiple times in such a short time. By supplying the cleaning gas in this way, the precipitates attached to the supply port of the gas supply unit can be effectively removed. The single supply time of the cleaning gas can be set to be less than 3 seconds, or less than 2 seconds or less than 1 second.

[0067] The linear velocity of the cleaning gas at the supply port of the gas supply unit can be appropriately set according to the pressure difference across the supply port, for example, preferably up to 400 m / s or more, more preferably 450 m / s or more, and further preferably 500 m / s or more. The upper limit of the linear velocity is not particularly limited, for example, it can be 2000 m / s or less, 1500 m / s or less, or 1200 m / s or less.

[0068] In the cleaning process, it is also preferred to supply liquid to the gas supply unit to clean the supply port. By supplying liquid from the inside to the outside of the gas supply unit, precipitates attached to the inside and supply port of the gas supply unit can be removed. As the liquid, it is preferred to use a liquid containing a polymerizable compound, specifically, it is preferred to use a liquid containing a polymerizable compound obtained by a manufacturing process of a polymerizable compound in which a gas supply unit is provided. By using a liquid containing a polymerizable compound as a cleaning medium, it is possible to suppress the quality variation of the liquid containing a polymerizable compound in which a gas supply unit is provided.

[0069] As the liquid containing a polymerizable compound used as a cleaning medium, it is preferred that the main component of the liquid containing a polymerizable compound be the same composition as the composition of the liquid containing a polymerizable compound circulating near the supply port. Examples thereof include a liquid containing a polymerizable compound supplied to a device having a gas supply unit, a liquid containing a polymerizable compound circulating near the supply port, and a liquid containing a polymerizable compound discharged from a device having a gas supply unit. The liquid containing a polymerizable compound used as a cleaning medium may be a liquid containing a polymerizable compound obtained from different parts of the same production line, including a product, or may be a liquid containing a polymerizable compound obtained from different production lines when there are multiple production lines.

[0070] In the cleaning process, when a liquid is used as a cleaning medium, the linear velocity at the supply port of the gas supply unit of the liquid is preferably 0.01 m / s or more, more preferably 0.05 m / s or more, and further preferably 0.1 m / s or more. Thus, the precipitate attached to the inside of the gas supply unit and the supply port can be effectively removed. On the other hand, the upper limit of the linear velocity is preferably 10 m / s or less, more preferably 5 m / s or less, and further preferably 1 m / s or less, thereby, it is possible to suppress the adverse effects on the liquid containing the easily polymerizable compound provided with the gas supply unit (for example, hindering the flow of the liquid containing the easily polymerizable compound, etc.).

[0071] The above-described polymerization prevention step and washing step may be performed in any step of the production process of the readily polymerizable compound. Hereinafter, an embodiment of the present invention will be described by taking the production process of (meth)acrylic acid as an example.

[0072] When the readily polymerizable compound is (meth)acrylic acid, the method for producing a readily polymerizable compound of the present invention (in this case, a method for producing (meth)acrylic acid) preferably comprises, for example, the following steps: a step of subjecting a raw material for producing (meth)acrylic acid to a contact gas phase oxidation reaction to obtain a gas containing (meth)acrylic acid; and a step of introducing the gas containing (meth)acrylic acid into a cooling tower selected from an absorption tower and a condensation tower to obtain a liquid containing (meth)acrylic acid.

[0073] As the raw material for producing (meth)acrylic acid supplied to the contact gas phase oxidation reaction, any raw material can be used without particular limitation as long as (meth)acrylic acid is generated by the reaction, and examples thereof include propane, propylene, (meth)acrolein, isobutylene, etc. Acrylic acid can be obtained, for example, by oxidizing propane, propylene, or acrolein in one stage or by oxidizing propane or propylene via acrolein in two stages. Acrolein is not limited to a material obtained by oxidizing propane or propylene as a raw material, and can be, for example, a material obtained by dehydrating glycerol as a raw material. Methacrylic acid can be obtained, for example, by oxidizing isobutylene or methacrolein in one stage or by oxidizing isobutylene via methacrolein in two stages.

[0074] As the catalyst used in the catalytic gas phase oxidation, a conventionally known catalyst can be used. For example, when propylene is used as a raw material for producing acrylic acid, a composite oxide catalyst containing molybdenum and bismuth (molybdenum-bismuth catalyst) is preferably used as a catalyst. When propane and acrolein are used as raw materials for producing acrylic acid, a composite oxide catalyst containing molybdenum and vanadium (molybdenum-vanadium catalyst) is preferably used as a catalyst.

[0075] As a reactor for contacting gas phase oxidation reaction, a fixed bed reactor, a fluidized bed reactor, a moving bed reactor, etc. can be used. Among them, from the viewpoint of excellent reaction efficiency, a multi-tubular fixed bed reactor is preferably used. In the case of generating (meth) acrylic acid by oxidation reaction of (meth) acrylic acid manufacturing raw materials in two stages, by combining a reactor for performing the oxidation reaction of the first stage with a reactor for performing the oxidation reaction of the second stage, or dividing the inner area of ​​a reactor into a region for performing the oxidation reaction of the first stage and a region for performing the oxidation reaction of the second stage, (meth) acrylic acid can also be generated from (meth) acrylic acid manufacturing raw materials. In the latter case, for example, in a fixed bed reactor, the inlet side (the introduction side of the (meth) acrylic acid manufacturing raw materials) of the reaction tube of the fixed bed reactor is filled with a catalyst for performing the oxidation reaction of the first stage, and the outlet side is filled with a catalyst for performing the oxidation reaction of the second stage.

[0076] The reaction of generating a gas containing (meth)acrylic acid from a (meth)acrylic acid production raw material can be carried out under known reaction conditions. For example, when propylene is subjected to a two-stage oxidation reaction to generate acrylic acid, the propylene-containing gas can be introduced into a reactor together with molecular oxygen, and the reaction temperature can be 250° C. to 450° C., the reaction pressure can be 0 MPaG to 0.5 MPaG, and the space velocity can be 300 h / min. -1 ~5000h -1 The first stage of the oxidation reaction is carried out under the conditions of 250°C to 380°C, 0MPaG to 0.5MPaG, and a space velocity of 300h -1 ~5000h -1 The second stage oxidation reaction is carried out under the conditions of .

[0077] The gas containing (meth) acrylic acid obtained by subjecting the raw materials for manufacturing (meth) acrylic acid to a contact gas phase oxidation reaction can be introduced into an absorption tower or a condensation tower to obtain a liquid containing (meth) acrylic acid. In the former case, the gas containing (meth) acrylic acid is introduced into the absorption tower to contact the capture solvent, so that the (meth) acrylic acid is absorbed by the capture solvent to obtain a liquid containing (meth) acrylic acid (capture process). In the latter case, the gas containing (meth) acrylic acid is introduced into the condensation tower and cooled, so that the (meth) acrylic acid is condensed to obtain a liquid containing (meth) acrylic acid (condensation process). It should be noted that in this specification, the absorption tower and the condensation tower are sometimes collectively referred to as a "cooling tower".

[0078] As an absorption tower, there is no particular limitation as long as the gas containing (meth) acrylic acid can be brought into contact with the capture solvent in the absorption tower. For example, by introducing the gas containing (meth) acrylic acid from the lower part of the absorption tower into the absorption tower, and simultaneously introducing the capture solvent from the upper part of the absorption tower into the absorption tower, the gas containing (meth) acrylic acid is brought into convection contact with the capture solvent during the period of rising in the absorption tower, and the (meth) acrylic acid is absorbed by the capture solvent and recovered in the form of a liquid containing (meth) acrylic acid. As an absorption tower, for example, a plate tower having a plate (sieve plate tray) in the tower, a packed tower filled with a filler in the tower, a wet wall tower supplying a capture solvent to the inner wall surface of the tower, a spray tower spraying a capture solvent into the inner space of the tower, etc. can be used.

[0079] The capture solvent is not particularly limited as long as it can absorb and dissolve (meth)acrylic acid, and examples thereof include diphenyl ether, biphenyl, a mixture of diphenyl ether and biphenyl, water, water containing (meth)acrylic acid (for example, an aqueous solution containing (meth)acrylic acid generated in a (meth)acrylic acid production process), etc. Among them, water or water containing (meth)acrylic acid is preferably used as the capture solvent, and water or water containing (meth)acrylic acid containing 50% by mass or more (more preferably 70% by mass or more, and even more preferably 80% by mass or more) of water is more preferably used.

[0080] The temperature and supply amount of the capture solvent can be appropriately set so that the (meth)acrylic acid contained in the gas containing (meth)acrylic acid is fully absorbed by the capture solvent. From the viewpoint of improving the capture efficiency of (meth)acrylic acid, the temperature of the capture solvent is preferably 0°C or higher, more preferably 5°C or higher, and preferably 35°C or lower, more preferably 30°C or lower. Regarding the supply amount of the capture solvent, the liquid-gas ratio (L / G) represented by the ratio of the amount of the capture solvent (L) supplied to the absorption tower to the amount of the gas containing (meth)acrylic acid (G) supplied to the absorption tower is preferably 2L / m 3 More preferably 3L / m 3 More preferably, 5L / m 3 More than 15L / m 3 Below, more preferably 12L / m 3 Below, more preferably 10L / m 3 the following.

[0081] The (meth)acrylic acid absorbed by the collecting solvent is taken out from the absorption tower as a liquid containing (meth)acrylic acid. The liquid containing (meth)acrylic acid can be taken out from a position below the supply position of the gas containing (meth)acrylic acid in the absorption tower (e.g., the bottom of the absorption tower).

[0082] The absorption tower preferably has a circulation line for taking out a portion of the liquid containing (meth) acrylic acid taken out from the absorption tower and returning it to the absorption tower. The circulation line is preferably arranged in a manner that connects a position lower than the supply position of the gas containing (meth) acrylic acid of the absorption tower to a position higher than the supply position of the gas containing (meth) acrylic acid and the discharge position of the liquid containing (meth) acrylic acid of the absorption tower and lower than the supply position of the capture solvent. By returning a portion of the liquid containing (meth) acrylic acid taken out from the absorption tower to the absorption tower and circulating it, the (meth) acrylic acid concentration of the liquid containing (meth) acrylic acid can be increased. In the circulation line, a heat exchanger for cooling the liquid containing (meth) acrylic acid circulating in the circulation line is preferably provided.

[0083] On the other hand, when a liquid containing (meth) acrylic acid is obtained by condensing a gas containing (meth) acrylic acid, a condensation tower is preferably used. As a condensation tower, for example, a condensation tower having a heat exchanger with a heat conducting surface can be used. By cooling the gas containing (meth) acrylic acid with the aid of a heat conducting surface, (meth) acrylic acid can be condensed from the gas containing (meth) acrylic acid, and as a result, a liquid containing (meth) acrylic acid can be obtained. As a heat exchanger, any existing known heat exchanger can be used, such as a plate heat exchanger, a multi-tube (shell and tube) heat exchanger, a shell and tube heat exchanger, a coil heat exchanger, a spiral heat exchanger, etc. can be used. By connecting a plurality of heat exchangers in series, the gas containing (meth) acrylic acid is cooled and condensed in multiple stages, thereby recovering the liquid containing (meth) acrylic acid.

[0084] As a condensation tower, a gas containing (meth) acrylic acid can be brought into contact with a condensate, and a liquid containing (meth) acrylic acid is obtained from the gas containing (meth) acrylic acid. In this case, it is preferred to set a tray (sieve tray) in the condensation tower or fill a filler in the condensation tower to improve the contact efficiency between the gas containing (meth) acrylic acid and the condensate. By using this condensation tower, the gas containing (meth) acrylic acid is introduced into the condensation tower from, for example, the lower part of the condensation tower, and is condensed during the period of moving from the lower part to the upper part in the condensation tower. At this time, for example, a liquid containing (meth) acrylic acid is taken out from the middle section of the condensation tower, a substance with a higher boiling point than (meth) acrylic acid is taken out from the lower section of the condensation tower, and a substance with a lower boiling point than (meth) acrylic acid is taken out from the upper section of the condensation tower.

[0085] The condensation tower may be provided with a circulation line for taking out a portion of the liquid (condensate) containing (meth) acrylic acid in the condensation tower and returning it to the condensation tower. The circulation line is provided in a section of the condensation tower in such a manner that the liquid containing (meth) acrylic acid is returned from the lower part of the section to the upper part. The circulation line may be provided in each section of, for example, the upper section, the middle section and the lower section of the condensation tower, or may be provided only in a part of the section. The circulation line may be provided with a heat exchanger, and the liquid containing (meth) acrylic acid taken out of the condensation tower may be cooled by the heat exchanger and then returned to the same section of the condensation tower. It should be noted that a liquid medium other than the condensate produced in the condensation tower is usually not added to the condensate returned to the condensation tower.

[0086] When a liquid containing a polymerizable compound (in the above case, a liquid containing (meth)acrylic acid) is obtained by using an absorption tower or a condensation tower, the polymerization prevention step (or further cleaning step) of the present invention can be carried out in the step of introducing a gas containing a polymerizable compound into a cooling tower selected from the absorption tower and the condensation tower to obtain a liquid containing a polymerizable compound. In this case, the gas supply unit is preferably provided in the cooling tower or the circulation line of the cooling tower, thereby preventing the clogging of the gas supply unit or the associated reduction in the supply amount of the oxygen-containing gas, and effectively suppressing the polymerization of the polymerizable compound in the cooling tower or its circulation line.

[0087] When the gas supply unit is provided as described above and the cleaning process is performed using a liquid as the cleaning medium, it is preferred to use a liquid containing a readily polymerizable compound taken out from a cooling tower as the liquid and supply it to the gas supply unit. Alternatively, the liquid containing a readily polymerizable compound may be taken out from a circulation line of the cooling tower and supplied to the gas supply unit.

[0088] The method for producing a readily polymerizable compound of the present invention may include a step of introducing a liquid containing a readily polymerizable compound into a vaporization separation tower selected from a distillation tower and a release tower for purification (hereinafter referred to as a "vaporization separation step"), and performing the polymerization prevention step of the present invention in this step. By introducing the liquid containing a readily polymerizable compound into a vaporization separation tower for purification, at least a part of components having a lower boiling point and / or a higher boiling point than the readily polymerizable compound is removed from the liquid containing the readily polymerizable compound, and a purified readily polymerizable compound can be obtained.

[0089] The liquid containing the readily polymerizable compound introduced into the vaporization separation tower of the distillation tower or the emission tower is not particularly limited as long as it is obtained by the manufacturing process of the readily polymerizable compound and contains the readily polymerizable compound. For example, in the case where the readily polymerizable compound is (meth)acrylic acid, as the liquid containing the readily polymerizable compound, there can be listed the liquid containing (meth)acrylic acid obtained by the above-described capture process and condensation process, the liquid containing (meth)acrylic acid obtained by any purification process that is earlier than the vaporization separation process, and the purified residue obtained by any purification process that is later than the vaporization separation process. As purification units that can be used in these arbitrary purification processes, crystallization, distillation (fractionation), emission, extraction, etc. can be listed, and a plurality of them can be combined.

[0090] As the distillation tower or the venting tower used as the vaporization separation tower, a plate tower (e.g., a perforated plate tower or a bubble cap tower) provided with a plate (sieve plate tray) in the tower, a packed tower filled with a filler in the tower, or other tower-type equipment can be suitably used. The vaporization separation tower has a tower top, a tower middle, and a tower bottom, and when the vaporization separation tower is divided into sections in the height direction, the height range where the plates or the filler are provided is called the tower middle, the side closer to the tower top is called the tower top, and the side closer to the tower bottom is called the tower bottom.

[0091] The position for introducing the liquid containing the readily polymerizable compound into the vaporization separation tower and the position for taking out the purified readily polymerizable compound from the vaporization separation tower may be appropriately set according to the composition of the liquid containing the readily polymerizable compound and the type of the vaporization separation tower, that is, whether the vaporization separation tower is a distillation tower or a purge tower.

[0092] When the vaporization separation tower is a distillation tower, it is preferred that the liquid containing the readily polymerizable compound is introduced into the distillation tower from the middle of the distillation tower. The extraction position of the purified readily polymerizable compound extracted from the distillation tower can be appropriately set according to the composition of the liquid containing the readily polymerizable compound introduced into the distillation tower.

[0093] For example, when a liquid containing (meth)acrylic acid is introduced into a distillation tower and purified, it is preferable to take out the purified (meth)acrylic acid from the distillation tower as follows. When the distillation tower distills the liquid containing (meth)acrylic acid obtained by the previous collection step and condensation step, the liquid containing (meth)acrylic acid contains a large amount of components having a lower boiling point than (meth)acrylic acid, and therefore, it is preferable to take out the purified (meth)acrylic acid from the middle part of the distillation tower and / or the bottom of the tower. In this case, the extraction position of the purified (meth)acrylic acid is preferably located closer to the bottom of the tower than the introduction position of the liquid containing (meth)acrylic acid. On the other hand, when the liquid containing (meth)acrylic acid contains a large amount of components having a higher boiling point than (meth)acrylic acid, such as Michael adducts and maleic acid, it is preferable to take out the purified (meth)acrylic acid from the top of the tower than the introduction position of the liquid containing (meth)acrylic acid, and more preferably from the top of the tower. In this case, the purified (meth)acrylic acid is preferably taken out as vapor.

[0094] When the gasification separation tower is a purge tower, it is preferred that a liquid containing a readily polymerizable compound is introduced into the purge tower from the middle or top of the purge tower, and the purified readily polymerizable compound is taken out from the bottom of the tower. In the purge tower, a purge gas is basically supplied from the bottom of the tower, and low-boiling-point components contained in the liquid containing a readily polymerizable compound are vaporized and separated. The purified readily polymerizable compound is preferably taken out from the purge tower in the form of a liquid.

[0095] The gasification separation tower is preferably provided with a circulation line for taking out a portion of the liquid containing the easily polymerizable compound in the gasification separation tower and returning it to the gasification separation tower. The circulation line is preferably arranged in a manner that the bottom liquid taken out from the bottom of the tower is returned to the bottom of the tower. The position of the circulation line returning to the bottom of the tower can be a position higher than the position where the bottom liquid is taken out from the bottom of the tower, or a position lower than it, or a position at the same height. The circulation line is preferably provided with a reboiler, thereby being able to increase the temperature in the gasification separation tower, and the temperature is easily adjusted, and the separation efficiency in the gasification separation tower can be improved.

[0096] When the liquid containing the easily polymerizable compound is introduced into a distillation tower or a discharge tower and purified as described above, the anti-polymerization step (or further cleaning step) of the present invention can be carried out in the step of introducing the liquid containing the easily polymerizable compound into a gasification separation tower selected from a distillation tower and a discharge tower and purifying it. In this case, the gas supply unit is preferably provided in the gasification separation tower, the supply line for supplying the liquid containing the easily polymerizable compound to the gasification separation tower, or the circulation line of the gasification separation tower, thereby preventing the clogging of the gas supply unit or the associated reduction in the supply amount of the oxygen-containing gas, and effectively suppressing the polymerization of the easily polymerizable compound in the gasification separation tower or its circulation line. When the gas supply unit is provided in the circulation line of the gasification separation tower, from the viewpoint of suppressing the polymerization of the easily polymerizable compound in the reboiler of the circulation line, it is preferred to provide the gas supply unit on the side more upstream than the reboiler of the circulation line.

[0097] When the gas supply unit is provided as described above and the cleaning process is performed using a liquid as a cleaning medium, it is preferred to use a liquid containing a readily polymerizable compound taken out from a gasification separation tower as the liquid and supply it to the gas supply unit. Alternatively, the liquid containing a readily polymerizable compound may be taken out from a circulation line of the gasification separation tower and supplied to the gas supply unit. When the gas supply unit is provided in a supply line for supplying the liquid containing a readily polymerizable compound to the gasification separation tower, the liquid containing a readily polymerizable compound removed from the supply line may be supplied to the gas supply unit.

[0098] The method for producing a readily polymerizable compound of the present invention comprises a step of storing a liquid containing a readily polymerizable compound in a storage tank, and the polymerization prevention step of the present invention may be performed in this step. For example, when the liquid containing a readily polymerizable compound is a liquid containing (meth)acrylic acid, examples of the liquid containing a readily polymerizable compound stored in the storage tank include a liquid containing (meth)acrylic acid obtained by the above-described collection step and condensation step, a purified liquid containing (meth)acrylic acid or a purified residue obtained by the above-described vaporization separation step, a liquid containing (meth)acrylic acid or a purified residue obtained by any purification step preceding or following the vaporization separation step, and a (meth)acrylic acid product.

[0099] In the storage process of the liquid containing the easily polymerizable compound, a gas supply unit may be provided in the storage tank and a supply line for supplying the liquid containing the easily polymerizable compound to the storage tank. In this way, it is possible to prevent the clogging of the gas supply unit and the associated reduction in the supply amount of the oxygen-containing gas, and effectively suppress the polymerization of the easily polymerizable compound in the storage tank. In the case where the storage tank is provided with a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the storage tank and returning it to the storage tank, the gas supply unit may be provided in the circulation line.

[0100] When a gas supply unit is provided in the storage tank, the supply line of the storage tank, or the circulation line of the storage tank as described above, and the cleaning process is performed using a liquid containing a readily polymerizable compound, it is preferred that the liquid containing a readily polymerizable compound taken out of the storage tank is supplied to the gas supply unit. Alternatively, the liquid containing a readily polymerizable compound supplied to the storage tank may be supplied to the gas supply unit, and the cleaning process may be performed.

[0101] The method for producing a readily polymerizable compound of the present invention comprises a step of introducing a liquid containing a readily polymerizable compound into a reactor and reacting the liquid, and the polymerization prevention step of the present invention may be performed in this step. For example, when the liquid containing a readily polymerizable compound is a liquid containing (meth)acrylic acid, the polymerization prevention step of the present invention may be performed in a reactor used for producing a (meth)acrylic acid derivative from (meth)acrylic acid. Representative examples of the (meth)acrylic acid derivatives include (meth)acrylates, and examples of the (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, methoxyethyl (meth)acrylate, benzyl (meth)acrylate, and glycidyl (meth)acrylate.

[0102] In the process of introducing a liquid containing a polymerizable compound into a reactor and reacting it, a gas supply unit may be provided in the reactor or in a supply line for supplying the liquid containing a polymerizable compound to the reactor. In this way, it is possible to suppress the clogging of the gas supply unit and the associated reduction in the supply amount of the oxygen-containing gas, suppress the polymerization reaction of the polymerizable compound, and appropriately carry out the desired reaction such as esterification reaction. When a circulation line is provided in the reactor to take out a part of the liquid containing a polymerizable compound in the reactor and return it to the reactor, a gas supply unit may be provided in the circulation line.

[0103] When the gas supply unit is provided as described above and the cleaning step is performed using a liquid as the cleaning medium, it is preferred to use a liquid containing a readily polymerizable compound taken out of the reactor or a liquid containing a readily polymerizable compound supplied to the reactor as the liquid and supply it to the gas supply unit.

[0104] The above is a description of the method for producing the readily polymerizable compound of the present invention, but the present invention can also be used as a method for preventing the gas supply unit from being clogged or a method for cleaning the gas supply unit. The gas supply unit at this time has one or more supply ports as described above, and is immersed in the liquid containing the readily polymerizable compound, and a gas containing oxygen is supplied to the liquid containing the readily polymerizable compound through the gas supply unit. In addition, by supplying a cleaning medium of a gas or liquid to the gas supply unit, the cleaning port of the gas supply unit can be cleaned.

[0105] This application claims priority based on Japanese Patent Application No. 2020-098799 filed on June 5, 2020. The entire contents of the specification of Japanese Patent Application No. 2020-098799 filed on June 5, 2020 are incorporated herein by reference.

[0106] Example

[0107] Hereinafter, the present invention will be described in more detail by showing examples, but the scope of the present invention is not limited to these examples.

[0108] (1) Experiment 1: Confirmation experiment of backflow into the supply pipe

[0109] (1-1) Experimental methods

[0110] A SUS304 tube with an inner diameter of 16 mm, an outer diameter of 19 mm, and a length of 1 m was prepared, and one end of the SUS tube was sealed to form a supply tube. A blower was connected to the other end of the SUS tube. In Experiment No. 1-1, a circular hole (supply port) with a diameter of 1 mm was opened near one end of the SUS tube, and the SUS tube was immersed in acrylic acid contained in a water tank with the supply port facing downward. The liquid depth from the supply port of the SUS tube to the liquid surface was about 10 cm, and the temperature of the acrylic acid was 25°C. Air was supplied to the inside of the SUS tube from the blower at 0.3 NL / min, and a fiberscope was used to observe whether acrylic acid flowed back into the inside of the SUS tube during the period, and whether there were acrylic acid droplets (foam) inside the SUS tube after the air was supplied for 10 minutes. For Experiments No. 1-2 to 1-13, the conditions of the supply port and the air supply amount were changed as shown in Table 1, and air was supplied to the inside of the SUS tube for 10 minutes in the same way as Experiment No. 1-1.

[0111] (1-2) Experimental results

[0112] The experimental results are shown in Table 1. In Experiments No. 1-2, 1-5 to 1-7, the linear velocity of air V (m / s) at the supply port and the area S (mm 2 ) ratio V / S was 1.7 to 5.5, and it was confirmed that acrylic acid flowed back into the supply pipe (droplet adhesion). In Experiments No. 1-10 to 1-11, the area S (mm) of each supply port was 2 ) was greater than 20, and acrylic acid was confirmed to flow back into the supply pipe (droplet adhesion). On the other hand, in Experiments No. 1-1, 1-3 to 1-4, 1-8 to 1-9, the area S of each supply port was 0.1 to 20, and the ratio V / S was 6.6 to 15.3, and acrylic acid was not confirmed to flow back into the supply pipe (droplet adhesion). In addition, in Experiments No. 1-12 and 1-13 with multiple supply ports, the same results as those of No. 1-2 and 1-3 with a single supply port were also confirmed.

[0113] [Table 1]

[0114]

[0115] (2) Experiment 2: Experiment to eliminate blockage of the supply port of the supply pipe by blowing air

[0116] (2-1) Experimental methods

[0117] A SUS304 tube with an inner diameter of 16 mm, an outer diameter of 19 mm, and a length of 1 m was prepared, and one end of the SUS tube was sealed to form a supply tube. In Experiment No. 2-1, a circular hole (supply port) with a diameter of 1 mm was opened near one end of the SUS tube, and the SUS tube was used as an air supply pipe for acrylic acid polymerization inhibition, and the supply port was set in the circulation line of the light boiling distillation tower of the acrylic acid production equipment for 1 month with the supply port facing downward, so that the supply port was blocked. A compressor was connected to the other unsealed end of the SUS tube with the supply port blocked, and air was supplied to the inside of the SUS tube at 52 NL / min for 0.1 second to confirm whether the blockage was eliminated. For Experiments No. 2-2 to 2-6, the conditions of the supply port and the air supply amount were changed as shown in Table 2. In addition, after the supply port was blocked in the same way as Experiment No. 2-1, air was supplied to the inside of the SUS tube to confirm whether the blockage was eliminated.

[0118] (2-2) Experimental results

[0119] The results are shown in Table 2. In Table 2, in the column "Clogging Eliminated", "○" indicates when the clogging is eliminated, and "×" indicates when the clogging is not eliminated. Regardless of the size of the supply port provided in the supply pipe, the clogging of the supply port of the supply pipe can be eliminated by supplying air to the supply pipe in such a manner that the pressure difference at the supply port becomes 200 kPa or more.

[0120] [Table 2]

[0121] No. 2-1 2-2 2-3 2-4 2-5 2-6 Supply port diameter mm 1.0 2.0 2.0 3.0 3.0 4.0 Supply port area mm- 0.8 3.1 3.1 7.1 7.1 12.6 Air supply NL / min 52 37 89 116 201 207 Air velocity at supply port m / s 548 387 949 548 949 548 Supply port pressure difference kPa 200 100 600 200 600 200 Unblocking - ○ × ○ ○ ○ ○

Claims

1. A method for producing a readily polymerizable compound, characterized in that: The method comprises the following steps of preventing polymerization: supplying a gas containing oxygen to a liquid containing an easily polymerizable compound through a gas supply unit having one or more supply ports, wherein the gas supply unit is selected from a nozzle, a diffuser pipe and a diffuser plate; The area S (mm) of each supply port 2 ) is 0.1 or more and 20 or less, In the polymerization prevention step, a ratio V / S of a linear velocity V (m / s) of the gas at the supply port to the area S is 6.0 or more.

2. The method for producing a readily polymerizable compound according to claim 1, further comprising a cleaning step of supplying gas to the gas supply unit to clean the supply port, The pressure difference of the gas supply unit across the supply port in the polymerization prevention step is 100 kPa or less. The pressure difference of the gas supply unit across the supply port in the cleaning step is 150 kPa or more. 3 . The method for producing a readily polymerizable compound according to claim 1 , further comprising a cleaning step of supplying a liquid to the gas supply unit to clean the supply port. 4 . The method for producing a readily polymerizable compound according to claim 2 , further comprising a cleaning step of supplying a liquid to the gas supply unit to clean the supply port.

5. A method for producing a readily polymerizable compound, characterized in that: It has: Anti-polymerization step: supplying a gas containing oxygen into the liquid containing the easily polymerizable compound through a gas supply unit having one or more supply ports, wherein the gas supply unit is selected from a nozzle, a diffuser pipe, and a diffuser plate; and Cleaning step: supplying gas to the gas supply unit to clean the supply port, The pressure difference of the gas supply unit across the supply port in the polymerization prevention step is 100 kPa or less. The pressure difference of the gas supply unit across the supply port in the cleaning step is 150 kPa or more.

6. The method for producing a readily polymerizable compound according to any one of claims 1 to 5, wherein The anti-polymerization step is carried out by at least one of the following methods (1) to (4), (1) the polymerization prevention step is performed in the step of introducing the gas containing the readily polymerizable compound into a cooling tower selected from an absorption tower and a condensation tower to obtain a liquid containing the readily polymerizable compound, The gas supply unit is provided in the cooling tower, or in a circulation line that takes out a portion of the liquid containing the easily polymerizable compound in the cooling tower and returns it to the cooling tower; (2) the polymerization prevention step is performed in a step of introducing the liquid containing the easily polymerizable compound into a vaporization separation tower selected from a distillation tower and a release tower for purification, The gas supply unit is provided in the gasification separation tower, a supply line for supplying the liquid containing the easily polymerizable compound to the gasification separation tower, or a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the gasification separation tower and returning it to the gasification separation tower; (3) performing the polymerization prevention step in the step of storing the liquid containing the readily polymerizable compound in a storage tank, The gas supply unit is provided in the storage tank, a supply line for supplying the liquid containing the easily polymerizable compound to the storage tank, or a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the storage tank and returning it to the storage tank; (4) the polymerization prevention step is performed in the step of introducing the liquid containing the readily polymerizable compound into a reactor to react, The gas supply unit is provided in the reactor, a supply line for supplying the liquid containing the easily polymerizable compound to the reactor, or a circulation line for taking out a part of the liquid containing the easily polymerizable compound in the reactor and returning it to the reactor.

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