JP2021191738A - Method for producing easily polymerizable compounds - Google Patents

Abstract

To provide a method for producing easily polymerizable compounds that includes the step of purifying easily polymerizable compounds with a vaporization separation column provided with a column bottom liquid circuit including a reboiler, whereby the polymerization of the easily polymerizable compounds in the reboiler can be suppressed.SOLUTION: A method for producing easily polymerizable compounds includes the step of introducing an easily polymerizable compound-containing liquid into a vaporization separation column selected from a distillation column and an evaporation column to purify the liquid under reduced pressure. The vaporization separation column is provided with a circuit for returning the extracted liquid, which is at least partial extract of the column bottom liquid, to the vaporization separation column. The circuit is provided with a reboiler including a heating part. Upstream of the reboiler, provided is a feed port for feeding an oxygen-containing gas. The feed port is provided below the heating part by 0.5 m or more. The oxygen-containing gas is fed from the feed port to the extracted liquid.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing an easily polymerizable compound, which comprises a step of purifying an easily polymerizable compound such as (meth) acrylic acid or a (meth) acrylic acid ester by distillation.

Conventionally, a method of purifying an easily polymerizable compound such as (meth) acrylic acid or (meth) acrylic acid ester by using a vaporization separation column such as a distillation column is known. The vaporization separation column may be provided with a circulation path for extracting at least a part of the bottom liquid and heating it with a reboiler to return it to the vaporization separation column. Easy-to-polymerize substances are easy to polymerize, and in the manufacturing process thereof, polymerization may occur and the apparatus may be forced to stop, and various measures to prevent the polymerization have been studied.

For example, in Patent Document 1, when distilling an easily polymerizable compound or a liquid containing an easily polymerizable compound using a distillation column provided with a reboiler, a reboiler having a predetermined size is used to reduce the liquid level in the distillation column. A method for distilling an easily polymerizable compound or a liquid containing an easily polymerizable compound that is maintained within a predetermined range is disclosed. Patent Document 2 describes a method for producing a (meth) acrylic acid ester, which comprises a step of introducing a process liquid stream containing a (meth) acrylic acid ester into a distillation column to perform distillation, wherein the distillation column is the bottom of the column. It is a reaction distillation column equipped with a extraction pump and a column bottom circulation line. The discharge liquid of the column bottom extraction pump is branched to extract the process liquid, and the extraction liquid and the oxygen-containing gas are mixed in a static mixer to mix gas and liquid. Disclosed is a method for producing a (meth) acrylic acid ester, which is a flow and supplies the gas-liquid mixed phase flow into a bottom circulation line of a reaction distillation column or a bottom liquid.

Japanese Unexamined Patent Publication No. 2000-239229 Japanese Unexamined Patent Publication No. 2014-162783

When the easily polymerizable compound-containing liquid is purified using the vaporization separation column, it is also required to suppress the polymerization of the easily polymerizable compound not only in the vaporization separation column but also in the circulation path. In the heating section installed in the circulation path, the extraction liquid from which at least a part of the bottom liquid of the vaporization separation tower has been extracted is heated, and the polymerization reaction of the easily polymerizable compound is easily promoted. Preventive measures are important.

The present invention has been made in view of the above circumstances, and an object thereof is an easily polymerizable compound including a step of purifying an easily polymerizable compound using a vaporization separation tower provided with a circulation path provided with a heating portion. The present invention is to provide a method for producing an easily polymerizable compound, which can suppress the polymerization of the easily polymerizable compound in a heating unit.

The present invention includes the following inventions.
[1] A method for producing an easily polymerizable compound, which comprises a step of introducing an easily polymerizable compound-containing liquid into a vaporization separation column selected from a distillation column and a diffusion column and purifying the mixture under reduced pressure.
The vaporization separation tower is provided with a circulation path for returning the extracted liquid from which at least a part of the bottom liquid is extracted to the vaporization separation tower.
In the circulation path, a supply port for supplying oxygen-containing gas and a reboiler provided with a heating portion are provided in order from the upstream side.
The supply port is arranged below the height difference of 0.5 m or more with respect to the inlet of the heating unit.
A method for producing an easily polymerizable compound, which comprises supplying an oxygen-containing gas to the extract from the supply port.
[2] The method for producing an easily polymerizable compound according to [1], wherein the pressure of the withdrawal liquid in the vicinity of the supply port is 30 kPa or more higher than the gas pressure on the upper surface of the bottom liquid.
[3] The method for producing an easily polymerizable compound according to [1] or [2], wherein the withdrawal liquid has an average residence time of 2 seconds or more from the supply port of the circulation passage to the heating portion.
[4] The method for producing an easily polymerizable compound according to any one of [1] to [3], wherein the circulation path is provided with a bent portion between the supply port and the heating portion.
[5] The method for producing an easily polymerizable compound according to any one of [1] to [4], wherein the supply port is provided in a horizontal portion where the circulation path extends in a substantially horizontal direction.
[6] The method for producing an easily polymerizable compound according to [5], wherein the average residence time of the bottom liquid flowing through the circulation path in the horizontal portion is 0.5 seconds or more.
[7] The method for producing an easily polymerizable compound according to any one of [1] to [6], wherein a widening portion is provided at a connection portion between the circulation path on the upstream side of the heating portion and the heating portion.
[8] The reboiler provided with the heating unit is composed of a plate heat exchanger, a multi-tube heat exchanger, a double-tube heat exchanger, a coil heat exchanger, or a spiral heat exchanger [ 1] The method for producing an easily polymerizable compound according to any one of [7].
[9] The method for producing an easily polymerizable compound according to any one of [1] to [8], wherein the oxygen-containing gas is supplied as microbubbles.
[10] The method for producing an easily polymerizable compound according to any one of [1] to [9], wherein the easily polymerizable compound is (meth) acrylic acid or (meth) acrylic acid ester.

The method for producing an easily polymerizable compound of the present invention includes a step of purifying the easily polymerizable compound-containing liquid under reduced pressure using a vaporization separation tower, and is located upstream of the reboiler of the withdrawal liquid circulation path of the vaporization separation tower. Therefore, the oxygen-containing gas supply port is provided at a position below the inlet of the heating portion of the reboiler with a height difference of 0.5 m or more. As a result, oxygen-containing gas can be supplied to the extract in a higher pressure state, and the supplied oxygen can be quickly dissolved in the extract, or more oxygen can be dissolved in the extract. Become. As a result, the effect of preventing polymerization in the circulation path is enhanced, and the polymerization of the easily polymerizable compound in the heated portion of the reboiler, in which the polymerization reaction is likely to occur, can be suppressed.

An example of a system around a vaporization separation column used in the method for producing an easily polymerizable compound of the present invention is shown. Another example of the system around the vaporization separation column used in the method for producing an easily polymerizable compound of the present invention is shown.

The method for producing an easily polymerizable compound of the present invention includes a step of introducing an easily polymerizable compound-containing liquid into a vaporization separation column selected from a distillation column and a diffusion column and purifying under reduced pressure. By introducing the easily polymerizable compound-containing liquid into the vaporization separation tower and purifying it, at least a part of the components having a lower boiling point and / or a higher boiling point than the easily polymerizable compound is removed from the easily polymerizable compound-containing liquid and purified. The resulting easily polymerizable compound can be obtained. Hereinafter, the step of introducing the easily polymerizable compound-containing liquid into the vaporization separation column for purification is referred to as a “vaporization separation step”.

The easily polymerizable compound is not particularly limited as long as it is a compound that easily polymerizes when heated in a vaporization separation column, and is, for example, (meth) acrylic acid and its ester, maleic anhydride and its ester, acrylonitrile, styrene, and divinyl. Examples thereof include benzene, vinyl toluene, diethylene glycol monovinyl ether and the like. Among these, typical easily polymerizable compounds include (meth) acrylic acid and its esters. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, and 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, trimethyl propandi (meth) acrylate, Examples thereof include trimethylolpropane tri (meth) acrylate, 2- (2-vinyloxyethoxy) ethyl (meth) acrylate, methoxyethyl (meth) acrylate, benzyl (meth) acrylate, and glycidyl (meth) acrylate. As the easily polymerizable compound, (meth) acrylic acid, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and 2-hydroxyethyl (meth) are preferable. Acrylate, 2-hydroxypropyl (meth) acrylate, methoxyethyl (meth) acrylate, nonyl (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethyl propandi (meth) acrylate, tri Examples thereof include methylol propantri (meth) acrylate, 2- (2-vinyloxyethoxy) ethyl (meth) acrylate, benzyl (meth) acrylate, and glycidyl (meth) acrylate.

The easily polymerizable compound-containing liquid introduced into the vaporization separation tower of the distillation column or the diffusion column is obtained in the process for producing the easily polymerizable compound, and is not particularly limited as long as it is a liquid containing the easily polymerizable compound. For example, when the easily polymerizable compound is (meth) acrylic acid, the easily polymerizable compound-containing liquid is a (meth) acrylic acid-containing liquid obtained in a collection step or a condensation step prior to the vaporization separation step. Specifically, the (meth) acrylic acid-containing liquid recovered from the (meth) acrylic acid-containing gas as a liquid), the (meth) acrylic acid-containing liquid obtained by an arbitrary purification step prior to the vaporization separation step, and the vaporization separation step. Examples thereof include purification residues obtained in an arbitrary purification step in the subsequent stage. Examples of the purification means that can be used in any of these purification steps include crystallization, distillation (fractional distillation), emission, extraction, and the like, and a plurality of these may be combined.

The concentration of the easily polymerizable compound in the easily polymerizable compound-containing liquid introduced into the vaporization separation column in the vaporization separation step is not particularly limited, but the easily polymerizable compound can exert the effect of the present invention more remarkably. The concentration of the easily polymerizable compound in the contained liquid is, for example, preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. preferable. The upper limit of the concentration of the easily polymerizable compound in the liquid containing the easily polymerizable compound is not particularly limited, but is, for example, 97% by mass or less.

Distillation towers and dissipative towers used as vaporization separation towers include shelf-stage towers (for example, perforated plate towers and bubble bell towers) provided with shelf plates (sheave trays) in the towers and fillings filled in the towers. Tower-type equipment such as a tower is preferably used. The vaporization separation tower has a tower top, a tower middle part, and a tower bottom, and when the vaporization separation tower is divided in the height direction, the range in the height direction in which the shelf or the filling is provided is referred to as the tower middle part. The tower top side is called the tower top, and the tower bottom side is called the tower bottom.

The position of introduction of the easily polymerizable compound-containing liquid into the vaporization separation tower and the position of extraction of the purified easily polymerizable compound extracted from the vaporization separation tower are the composition of the easily polymerizable compound-containing liquid and the type of the vaporization separation tower. That is, it may be appropriately set according to the above, that is, depending on whether the vaporization separation column is a distillation column or a dissipation column.

When the vaporization separation column is a distillation column, it is preferable to introduce the easily polymerizable compound-containing liquid into the distillation column from the central part of the distillation column. The extraction position of the purified easily polymerizable compound extracted from the distillation column may be appropriately set according to the composition of the easily polymerizable compound-containing liquid to be introduced into the distillation column. For example, when a (meth) acrylic acid-containing liquid is introduced into a distillation column for purification, it is preferable to extract the purified (meth) acrylic acid from the distillation column as follows. When the distillation column distills the (meth) acrylic acid-containing liquid obtained in the collection step or the condensation step in the previous stage, the (meth) acrylic acid-containing liquid has a lower boiling point than the (meth) acrylic acid. Purified (meth) acrylic acid is preferably extracted from the middle and / or bottom of the distillation column because it contains a large amount of components. In this case, the extraction position of the purified (meth) acrylic acid is preferably located on the bottom side of the column rather than the introduction position of the (meth) acrylic acid-containing liquid. On the other hand, when the (meth) acrylic acid-containing liquid contains more components having a higher boiling point than the (meth) acrylic acid such as Michael adduct and maleic acid, the purified (meth) acrylic acid is a (meth) acrylic acid-containing liquid. It is preferable to extract from the tower top side rather than the introduction position, and it is more preferable to extract from the tower top. In this case, it is preferable to extract the purified (meth) acrylic acid as vapor.

When the purified (meth) acrylic acid is extracted from the central part of the column, the purified (meth) acrylic acid may be extracted as a liquid or as a vapor. In order to extract purified (meth) acrylic acid as a liquid from the central part of the column, for example, in a shelf column, an extraction port may be provided at the position of the shelf, or a chimney or the like may be provided on the shelf. By extracting as a liquid, purified (meth) acrylic acid can be supplied to the next step without performing additional operations such as condensation. When purified (meth) acrylic acid is extracted as vapor, it becomes easy to obtain purified (meth) acrylic acid having a relatively low content of impurities. In the distillation column, the reflux liquid flows down from the top of the column to the bottom of the column, and a part of the reflux liquid exists on the shelf stage. , It becomes easy to preferentially extract purified (meth) acrylic acid in the form of vapor by suppressing the extraction of the reflux liquid.

When the purified (meth) acrylic acid is extracted from the bottom of the column, the purified (meth) acrylic acid is purified by connecting a conduit for extracting the purified (meth) acrylic acid to the extraction liquid circulation channel described later. The (meth) acrylic acid may be extracted, or a conduit for extracting the purified (meth) acrylic acid may be directly connected to the bottom of the distillation column separately from the extraction liquid circulation path. In this case, it is preferable to extract the purified (meth) acrylic acid as a liquid.

When the vaporization separation column is a dissipative column, it is preferable to introduce the easily polymerizable compound-containing liquid into the dissipating column from the center or the top of the dissipating column and extract the purified easily polymerizable compound from the bottom of the column. In the dissipating column, a dissipating gas is basically supplied from the bottom of the column, and low boiling point components contained in the easily polymerizable compound-containing liquid are vaporized and separated. It is preferable to withdraw the purified easily polymerizable compound as a liquid from the dissipation column. In this case, a conduit for extracting the purified easily polymerizable compound-containing liquid may be provided in the extraction liquid circulation channel described later, and the liquid may be extracted. A conduit for extracting the purified easily polymerizable compound-containing liquid separately from the liquid circulation passage may be directly connected to the bottom of the distillation column.

The vaporization separation tower is provided with an extraction liquid circulation path for returning the extraction liquid obtained by extracting at least a part of the bottom liquid accumulated at the bottom of the column to the vaporization separation tower. A reboiler provided with a heating unit is provided in the withdrawal liquid circulation path. The withdrawal liquid circulation path raises the temperature inside the vaporization separation tower and facilitates temperature control by heating the withdrawal liquid extracted from the bottom of the tower with a reboiler and returning it to the vaporization separation tower. It is a means to improve the separation efficiency in. Therefore, as long as these can be achieved, the connection type between the vaporization separation tower and the withdrawal liquid circulation path and the structure of the withdrawal liquid circulation path are not particularly limited. However, a liquid level gauge or the like that cannot achieve the above is not referred to as a drainage liquid circulation path in the present invention.

As the withdrawal liquid circulation passage, one withdrawal liquid circulation passage may be provided for one vaporization separation tower, or a plurality of withdrawal liquid circulation passages may be provided for one vaporization separation tower. , One withdrawal liquid circulation passage may be provided for a plurality of vaporization separation towers. When one extraction liquid circulation path is provided for a plurality of vaporization separation towers, the extraction liquids of the plurality of vaporization separation towers can be collected and heated, and then returned to the respective vaporization separation towers. From the viewpoint of increasing the separation efficiency in the vaporization separation column and enabling more precise control, it is preferable to provide a plurality of extraction liquid circulation paths for one vaporization separation column. However, if the required accuracy can be obtained, it is convenient and preferable to provide one extraction liquid circulation path for one vaporization separation column.

The circulation path is preferably provided so as to return the bottom liquid extracted from the bottom of the tower to the bottom of the tower. This facilitates temperature control inside the vaporization separation tower. The return position of the bottom liquid circulation path to the bottom of the tower may be higher than the position where the bottom liquid is discharged from the bottom, may be lower, or may be at the same height. May be good. In the following, the withdrawal liquid flowing in the circulation passage may be referred to as “circulation liquid”.

As the reboiler, it is preferable to use a heat exchanger provided with a heat transfer surface, which facilitates temperature control of the circulating fluid. In this case, the heat transfer surface becomes the heating part of the reboiler. A known heat exchanger may be used as the heat exchanger. For example, one plate is arranged, or a plurality of plates are laminated at intervals, and the heat medium presence part and the circulating liquid presence part are plates. Plate heat exchangers arranged alternately via a multi-tube (shell and tube) heat exchanger in which multiple tubes are arranged inside the container to exchange heat inside and outside the tubes; outer tubes. A double-tube heat exchanger in which an inner tube is arranged inside and exchanges heat inside and outside the inner tube; a coil type in which one tube is arranged in a coil shape inside the container and exchanges heat inside and outside the tube. Heat exchanger: A spiral heat exchanger or the like in which two heat transfer plates are spirally wound around a central tube whose cross section is divided into two and two spiral flow paths are formed can be used. The cross-sectional shape of the pipe used in the multi-tube heat exchanger, the double-tube heat exchanger, the coil heat exchanger, and the spiral heat exchanger is not particularly limited. From the viewpoint of heat transfer efficiency and ease of maintenance, a plate heat exchanger or a multi-tube heat exchanger in which a circulating liquid flows in a tube is preferable, and the latter is particularly preferable.

The heating portion of the reboiler is preferably installed so that the circulating fluid flows from the lower side to the upper side in the vertical direction. As will be described later, in the present invention, since the oxygen-containing gas supply port is provided at a position lower than the inlet of the heating section of the reboiler, the oxygen-containing gas supplied to the circulating fluid stays in the heating section, or oxygen is generated in the heating section. In order to prevent the contained gas from flowing unevenly, it is preferable that the heating unit is installed so that the circulating fluid flows from the lower side to the upper side in the vertical direction. From the same viewpoint, when a heat exchanger is used as the reboiler, it is preferable to use a plate heat exchanger or a multi-tube heat exchanger. When a heat exchanger is used as the reboiler, the inlet of the heating unit refers to the portion located most upstream on the heat transfer surface of the heat exchanger. For example, in the case of a multi-tube heat exchanger in which a circulating liquid flows in a tube, the surface of the tube plate on the upstream side corresponds to the inlet of the heating portion.

In the vaporization separation step, it is desirable to suppress the polymerization of easily polymerizable substances. Therefore, it is preferable that the easily polymerizable compound-containing liquid introduced into the vaporization separation column contains a polymerization inhibitor, or that the polymerization inhibitor is added in the vaporization separation column. In particular, since the temperature is high at the bottom of the vaporization separation column and the polymerization reaction easily proceeds, it is preferable that the bottom liquid contains a polymerization inhibitor.

As the polymerization inhibitor, a conventionally known polymerization inhibitor can be used, for example, quinones such as hydroquinone and methquinone (p-methoxyphenol); phenothiazine, bis- (α-methylbenzyl) phenothiazine, 3,7-. Phenothiazines such as dioctylphenothiazine, bis- (α-dimethylbenzyl) phenothiazine; 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl , 4,4', 4 "-Tris- (2,2,6,6-tetramethylpiperidinooxyl) N-oxyl compounds such as phosphite; copper dialkyldithiocarbamate, copper acetate, copper naphthenate, acrylic acid Copper salt compounds such as copper, copper sulfate, copper nitrate and copper chloride; manganese salt compounds such as manganese dialkyldithiocarbamate, manganese diphenyldithiocarbamate, manganese formate, manganese acetate, manganese octanate, manganese naphthenate; N-nitrosophenylhydroxyl Examples thereof include amines and salts thereof, p-nitrosophenols, N-nitrosodiphenylamines and nitroso compounds such as salts thereof. These polymerization inhibitors may be used alone or in combination of two or more. Among them, it is preferable to use at least quinones as the polymerization inhibitor.

The concentration of the polymerization inhibitor in the bottom liquid may be appropriately set, but from the viewpoint of appropriately exerting the polymerization inhibitory effect in the vaporization separation column, for example, 1 mass ppm or more is preferable, and 10 mass ppm or more is preferable. More preferably, 100 mass ppm or more is further preferable, and 1000 mass ppm or more is particularly preferable. The upper limit of the concentration of the polymerization inhibitor in the bottom liquid is not particularly limited, but from the viewpoint of reducing the amount of the polymerization inhibitor added, it is preferably 50,000 mass ppm or less, more preferably 10,000 mass ppm or less, and further preferably 5,000 mass ppm or less. It is preferably 2000 mass ppm or less, and particularly preferably 2000 mass ppm or less.

In the vaporization separation column, it is preferable to perform vaporization separation at a temperature as low as possible from the viewpoint of suppressing the polymerization of the easily polymerizable compound. Therefore, in the present invention, the pressure in the vaporization separation tower is set lower than the atmospheric pressure. In order to preferably perform separation and purification in the vaporization separation column, it is preferable to control the pressure in the vaporization separation column so that the pressure at the bottom of the column> the pressure at the center of the column> the pressure at the top of the column.

By the way, in the vaporization separation tower, the temperature tends to be higher toward the bottom side, and especially in the reboiler of the withdrawal liquid circulation path, the withdrawal liquid is heated and the polymerization reaction of the easily polymerizable compound easily proceeds. In the reboiler of the withdrawal liquid circulation path, it is important to take measures to prevent the polymerization of easily polymerizable compounds. When the polymerization reaction of the easily polymerizable compound proceeds in the heating part of the reboiler, the polymer adheres to and accumulates in the heating part, and the flow path in the heating part may be blocked.

Therefore, a supply port for supplying oxygen-containing gas is provided on the upstream side of the reboiler of the circulation path, and the oxygen-containing gas is supplied to the withdrawal liquid (circulation liquid) flowing in the circulation path from the supply port. As a result, the effect of preventing polymerization in the circulation path is enhanced, and the polymerization of the easily polymerizable compound in the heated portion of the reboiler, in which the polymerization reaction is likely to occur, can be suppressed. As the oxygen-containing gas, pure oxygen gas, air, a gas obtained by mixing nitrogen, oxygen and air to an arbitrary oxygen concentration, process waste gas and the like can be used.

When oxygen-containing gas is supplied to the circulating fluid to suppress polymerization in the reboiler heating section as described above, the supplied oxygen circulates until the oxygen-containing gas is supplied to the circulating fluid and reaches the heating section of the reboiler. It is desirable to dissolve as much as possible in the liquid. For that purpose, it is desirable to supply the oxygen-containing gas to the circulating fluid under the highest possible pressure. On the other hand, from the viewpoint of suppressing the polymerization of the easily polymerizable compound in the vaporization separation column, it is desirable to be able to set the temperature required for vaporization separation low. Purification takes place. However, in this case, the bottom liquid of the vaporization separation column has a very low content of oxygen having a polymerization preventing effect, and polymerization in the reboiler heating portion is likely to occur. That is, since the gas pressure on the upper surface of the bottom liquid of the vaporization separation tower is less than the normal pressure, the saturation concentration of the gas dissolved in the bottom liquid is low.

Therefore, in the present invention, the oxygen-containing gas is supplied at a place where the oxygen saturation concentration in the circulating liquid on the upstream side of the reboiler is high and the liquid pressure is high. Specifically, the oxygen-containing gas supply port is provided in the circulation path where the height difference is 0.5 m or more below the inlet of the heating part of the reboiler, thereby dissolving more oxygen in the circulating fluid. I try to let you. This will be described with reference to the drawings.

1 and 2 show a schematic diagram of the system around the vaporization separation tower. The vaporization separation column 1 is provided with a circulation path 2 for extracting at least a part of the bottom liquid 3 and returning it to the vaporization separation column 1, and the circulation path 2 is provided with a reboiler 4 provided with a heating unit 5. At the same time, a supply port 7 for supplying oxygen-containing gas is provided on the upstream side and below the heating unit 5. In the vaporization separation tower 1, the gas pressure on the upper surface of the bottom liquid is set to less than normal pressure, whereby the vaporization temperature of the easily polymerizable compound-containing liquid can be lowered, and the easily polymerizable compound in the vaporization separation tower 1 can be lowered. Polymerization can be suppressed. On the other hand, by providing the oxygen-containing gas supply port 7 at a position below the inlet of the heating portion 5 of the reboiler 4 with a height difference of 0.5 m or more, the oxygen-containing gas is supplied to the circulating fluid under a higher pressure. be able to. In the drawing, the difference in height between the inlet of the heating portion 5 of the reboiler 4 and the oxygen-containing gas supply port 7 is indicated by an arrow h. By providing the oxygen-containing gas supply port 7 at such a position, the supplied oxygen can be quickly dissolved in the circulating liquid, or more oxygen can be dissolved in the circulating liquid. In this case, in the oxygen-containing gas supply port 7, in addition to the liquid head pressure at the inlet of the heating unit 5 of the reboiler 4, the liquid head pressure difference between the oxygen-containing gas supply port 7 and the inlet of the heating unit 5 of the reboiler 4 Since it takes 5 kPa or more, the oxygen-containing gas can be supplied under a higher pressure. Further, it is possible to secure a sufficient time for the supplied oxygen to dissolve in the circulating liquid before the oxygen-containing gas is supplied from the supply port 7 to the circulating liquid and reaches the heating unit 5 of the reboiler 4. By supplying the oxygen-containing gas to the circulating liquid in this way, the polymerization reaction of the easily polymerizable compound can be suppressed in the heating unit 5, and the supplied oxygen dissolves in the circulating liquid to prevent the polymerization in the heating unit 5. Uneven distribution of effects can also be suppressed.

The pressure at the bottom of the vaporization separation tower 1, that is, the gas pressure (absolute pressure) at the top of the bottom liquid is the temperature dependence or temperature-vapor pressure of the polymerization reaction of the easily polymerizable compound or the composition containing it in the vaporization separation tower. It may be appropriately set from the viewpoint of correlation, and usually, for example, 50 kPa or less is preferable, 40 kPa or less is more preferable, and 30 kPa or less is further preferable. By setting the gas pressure on the upper surface of the bottom liquid to 50 kPa or less, the temperature required for vaporization of the easily polymerizable compound can be lowered. The lower limit of the gas pressure on the upper surface of the bottom liquid may be appropriately set in consideration of the cost for depressurizing, the durability of the vaporization separation tower, and the like, and usually, for example, 5 kPa or more is preferable, and 8 kPa or more is more preferable. 10 kPa or more is more preferable.

The position where the supply port 7 is provided is preferably such that the height difference is 1.0 m or more below the inlet of the heating portion 5 of the reboiler 4 from the viewpoint of supplying the oxygen-containing gas to the circulating fluid under a higher pressure. More preferably, it is 5.5 m or more below. The upper limit of the value is not particularly limited, but considering the practical installation mode of the vaporization separation tower 1 and the reboiler 4, the height difference is preferably 8.0 m or less, more preferably 6.0 m or less, and 4 It is more preferably within 0.0 m.

The pressure of the circulating liquid (extraction liquid) at the supply port 7 is preferably 30 kPa or more higher than the gas pressure on the top surface of the bottom liquid of the vaporization separation tower 1, more preferably 40 kPa or more, and further higher than 50 kPa. preferable. This makes it possible to more effectively suppress the polymerization of the easily polymerizable compound in both the vaporization separation column 1 and the reboiler 4. The upper limit of the differential pressure between the pressure of the circulating liquid at the supply port 7 and the gas pressure on the top surface of the bottom liquid of the vaporization separation tower 1 is not particularly limited, but considering the practical installation mode of the vaporization separation tower 1 and the reboiler 4, The differential pressure is preferably 100 kPa or less, more preferably 90 kPa or less, still more preferably 80 kPa or less. The pressure of the circulating fluid in the supply port 7 means the pressure in a state where it is not affected by the oxygen-containing gas supplied from the supply port 7, for example, the supply port 7 in a state where the oxygen-containing gas is not supplied from the supply port 7. It can be obtained by measuring the pressure of the circulating fluid in. Alternatively, the pressure of the circulating fluid is measured at a position away from the supply port 7, and the obtained pressure value is the pressure from the supply port 7 to the measurement position calculated based on the pipe shape of the circulation path 2, the flow velocity of the circulating fluid, and the like. The pressure of the circulating fluid at the supply port 7 may be obtained by correcting for the loss.

Only one supply port 7 may be provided in the circulation path 2, or a plurality of supply ports 7 may be provided. When a plurality of supply ports 7 are provided, it is preferable that the differential pressure between the pressure of the circulating liquid and the gas pressure on the upper surface of the column bottom liquid in at least one supply port is within the above range. Further, the amount of oxygen-containing gas supplied from the supply ports arranged at the above differential pressure is preferably 50% or more, preferably 70% or more of the total amount of oxygen-containing gas supplied from all the supply ports. Is more preferable, and 80% or more is further preferable. Particularly preferably, the differential pressure between the pressure of the circulating liquid and the gas pressure on the upper surface of the bottom liquid at all the supply ports is within the above range.

The flow rate of the circulating fluid in the circulation path 2 may be set arbitrarily, but if the Reynolds number in the circulation path 2 is high, the circulating fluid will be in a turbulent state and the dissolution rate of the oxygen-containing gas will be high, so that the Reynolds number is 2300. The above is preferable. The Reynolds number of the circulating fluid is more preferably 5,000 or more, still more preferably 10,000 or more, still more preferably 50,000 or more, and particularly preferably 100,000 or more.

Examples of the method of flowing the discharged liquid in a predetermined direction in the circulation path include a self-circulation method using the principle of a thermosiphon and a forced circulation method using a liquid feed pump or the like. In the latter method, when the supply port 7 is provided on the downstream side (discharge side) of the liquid feed pump, the oxygen-containing gas can be supplied to the circulating liquid under a higher pressure by the discharge pressure of the liquid feed pump. .. On the other hand, when the supply port 7 is provided on the upstream side (suction side) of the liquid feed pump, the dissolution of oxygen can be promoted by stirring in the pump. If the oxygen-containing gas is excessively supplied on the suction side of the liquid feed pump, cavitation may occur and the liquid feed amount may become unstable. In this case, set the oxygen-containing gas supply amount appropriately. Is preferable. The supply port 7 may be provided on both the upstream side and the downstream side of the liquid feed pump. The suction side of the liquid feed pump is connected to the bottom of the vaporization separation tower 1, and the bottom liquid is extracted by this liquid feed pump, heated by the reboiler 4, and then returned to the bottom of the tower again.

The average residence time of the circulating fluid (extracted liquid) from the supply port 7 of the circulation path 2 to the inlet of the heating unit 5 of the reboiler 4 is preferably 2 seconds or longer, more preferably 3 seconds or longer, still more preferably 4 seconds or longer. .. As a result, the supplied oxygen is easily sufficiently dissolved in the circulating liquid between the time when the oxygen-containing gas is supplied to the circulating liquid and the time when the reboiler 4 reaches the heating unit 5. The upper limit of the average residence time is not particularly limited, but since it is not particularly necessary to install the circulation path 2 excessively long, it may be, for example, 60 seconds or less, 30 seconds or less, or 15 seconds or less. .. The average residence time of the circulating fluid from the oxygen-containing gas supply port of the circulation path to the inlet of the heating part of the reboiler is the volume (m ³ ) from the oxygen-containing gas supply port of the circulation path to the inlet of the heating part of the reboiler. It can be calculated by dividing by the flow rate of the circulating fluid flowing through the circulation path (m ^{3 / sec).} The average residence time can be appropriately adjusted by adjusting the position of the supply port or changing the diameter of the circulation path.

As shown in FIG. 1, the supply port 7 may be provided in a portion where the circulation path 2 extends upward (for example, vertically upward or diagonally upward), and as shown in FIG. 2, the circulation path 2 may be provided in the horizontal direction. It may be provided on an extending horizontal portion. Alternatively, the supply port 7 may be provided at the bent portion of the circulation path 2. When a plurality of supply ports 7 are provided, the average residence time from the supply port 7 of the circulation path 2 to the inlet of the heating unit 5 of the reboiler 4 is set based on the supply port that is 50% or more of the total oxygen supply amount. Will be done.

It is preferable that the circulation path 2 is provided with a bent portion between the supply port 7 and the heating portion 5 of the reboiler 4. By providing the bent portion in the circulation path 2, the oxygen-containing gas is well mixed with the circulating liquid when the circulating liquid passes through the bent portion, and oxygen is easily dissolved in the circulating liquid. The bent portion may, for example, change a horizontal flow into a vertical flow, or may change a horizontal flow in one direction into a horizontal flow in the other direction. In FIG. 2, a bent portion 8 that changes a horizontal flow into a vertical flow is provided between the supply port 7 and the heating portion 5 of the reboiler 4.

As the bent portion, a so-called elbow tube or bend tube can be used. The bending angle of the bent portion is preferably 40 ° or more, more preferably 55 ° or more, further preferably 70 ° or more, still more preferably 125 ° or less, further preferably 110 ° or less, still more preferably 95 ° or less. The bending angle of the bent portion means the angle difference between the pipe axis extending direction on the upstream side and the pipe shaft extending direction on the downstream side of the bent portion, and the bending angle is 0 ° in the straight pipe portion.

From the viewpoint of increasing the mixing efficiency of the oxygen-containing gas and the circulating fluid, it is preferable that the widening portion 6 is provided at the connection portion between the circulation path 2 on the upstream side of the heating portion 5 of the reboiler 4 and the heating portion 5. Since the widening portion 6 is formed so that the cross-sectional area of the flow path through which the circulating liquid flows spreads from the upstream side to the downstream side, a turbulent flow is formed by the circulating liquid passing through the widening portion 6, and the oxygen-containing gas is formed. Is well mixed with the circulating fluid, making it easier for oxygen to dissolve in the circulating fluid. Further, since the linear velocity of the circulating fluid is slowed down in the widening portion 6, it is possible to increase the residence time from the supply port 7 to the inlet of the heating portion 5 and increase the amount of oxygen dissolved in the circulating fluid. Be done. Further, even when a part of the oxygen-containing gas supplied to the circulating liquid passes through the widening portion 6 in the form of a gas, the oxygen-containing gas is mixed with the circulating liquid in the widening portion 6 to contain oxygen in the heating portion 5. Uneven distribution of gas can be suppressed. The widening portion may be provided independently, or a heat exchanger having the widening portion may be used as a reboiler.

In the widening portion 6, the cross-sectional area of the flow path through which the circulating fluid flows is preferably expanded by 1.2 times or more, more preferably 1.5 times or more, further preferably 2 times or more, and preferably 50 times or less, and 30 times or more. The following is more preferable, and 20 times or less is further preferable.

As shown in FIG. 2, it is preferable that the oxygen-containing gas supply port 7 is provided in a horizontal portion where the circulation path 2 extends in a substantially horizontal direction. For example, when the supply port 7 is provided in a portion where the circulation path 2 extends in the vertical direction, the oxygen-containing gas may rise regardless of the flow direction of the circulating liquid at that point, and as a result, circulation occurs. The flow of the liquid may be impaired, or the contact time between the oxygen-containing liquid gas and the circulating liquid may be shortened. However, by providing the supply port 7 in the horizontal portion of the circulation path 2, the oxygen-containing gas and the circulation liquid can be left for a longer time under high pressure in a coexisting state, and oxygen can be more efficiently dissolved in the circulation liquid. It becomes possible. In this case, the average residence time of the circulating fluid in the horizontal portion is preferably 0.5 seconds or longer, more preferably 1 second or longer.

The horizontal portion of the circulation path 2 may be provided in a portion between the supply port 7 and the inlet of the heating portion 5 that does not include the supply port 7, and in this case as well, the effect of the above horizontal portion can be obtained. A plurality of horizontal portions may be provided between the supply port 7 and the inlet of the heating portion 5. Therefore, the total average residence time of the circulating fluid in all the horizontal portions from the supply port 7 to the inlet of the heating portion 5 is preferably 0.5 seconds or more, and more preferably 1 second or more.

It is preferable that the circulation path 2 does not have a portion extending downward (including diagonally downward) from the upstream side to the downstream side from the supply port 7 to the heating portion 5 of the reboiler 4. As a result, the oxygen-containing gas easily moves to the reboiler 4 side by riding on the flow of the circulating fluid, and it is less likely that the oxygen-containing gas stays in a part of the circulation path 2 and obstructs the flow of the circulating fluid. .. When a horizontal portion is provided in the circulation path 2, a bending portion 8 is provided on the downstream side of the horizontal portion, and the circulation path 2 is configured to extend upward (for example, vertically upward or diagonally upward) on the downstream side of the bending portion. It is preferable that it is.

The amount of oxygen-containing gas supplied to the circulating fluid may be appropriately set according to the dissolved oxygen concentration of the circulating fluid at the inlet of the heating unit 5 of the reboiler 4. The dissolved oxygen concentration of the circulating fluid at the inlet of the heating unit 5 of the reboiler 4 is preferably, for example, 5% by mass or more.

As the supply port 7 for supplying the oxygen-containing gas, for example, a nozzle can be used. As the nozzle, for example, a ring-shaped nozzle, a cylindrical nozzle, or any other nozzle having one or a plurality of holes having a diameter of 0.1 mm to 10 mm can be used. Further, a sintered filter may be used in order to increase the bubble surface area of the oxygen-containing gas supplied to the circulating liquid.

Oxygen-containing gas may be supplied to the circulating fluid as microbubbles so that oxygen can be dissolved in the circulating fluid more quickly. Since the microbubbles have a smaller bubble diameter than the normal bubbles, when the supply amount of the oxygen-containing gas is the same, the total surface area of the bubbles becomes large in the microbubbles, and it becomes easier to dissolve in the circulating liquid more quickly.

The microbubbles may contain so-called nanobubbles, and those having a bubble diameter at the time of generation of 0.1 μm to 100 μm are preferably used. As the microbubble generator, a known device may be used. As a method for generating microbubbles, a gas-liquid two-phase flow swirling method (for example, swirling flow method, static mixer method, mechanical shearing (rotation) method) in which a vortex or shear flow is generated by water flow or mechanical stirring to subdivide the bubbles. ), A pressure-dissolving method that re-vaporizes the gas dissolved in the liquid to be treated as microbubbles by dissolving the gas in the liquid to be treated in a pressurized state and then reducing the pressure. Venturi method that breaks up bubbles by being compressed and depressurized when flowing and passing through the throat part, the static pressure is locally lowered to vaporize a part of the liquid to generate steam bubbles. A cavitation nozzle method that recovers pressure in a short time to subdivide steam bubbles, a filter method that allows gas to pass through a filter with a nanoporous part and subdivides it, etc. are adopted. You may.

In the present invention, as the easily polymerizable compound-containing liquid to be introduced into the vaporization separation step, the easily polymerizable compound-containing liquid obtained in the previous step can be used. For example, when the easily polymerizable compound is (meth) acrylic acid, a (meth) acrylic acid-containing liquid obtained in a collection step, a condensation step, or the like can be used. Hereinafter, a method for obtaining a (meth) acrylic acid-containing liquid to be introduced into the vaporization separation column will be described by taking the (meth) acrylic acid production process as an example.

When the easily polymerizable compound is (meth) acrylic acid, the method for producing the easily polymerizable compound of the present invention (in this case, the method for producing (meth) acrylic acid) is in contact with the (meth) acrylic acid production raw material. A step of obtaining a (meth) acrylic acid-containing gas by a vapor phase oxidation reaction, and by contacting the (meth) acrylic acid-containing gas with a collecting solvent and / or by cooling and condensing the (meth) acrylic acid-containing gas ( It is preferable to have a step of obtaining a meta) acrylic acid-containing liquid.

The (meth) acrylic acid production raw material to be subjected to the catalytic vapor phase oxidation reaction can be used without particular limitation as long as it produces (meth) acrylic acid by the reaction, and for example, propane, propylene, (meth) acrolein, and the like. Isobutylene and the like can be mentioned. 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 that obtained by oxidizing propane or propylene as a raw material, and may be obtained by dehydrating glycerin as a raw material, for example. Methacrylic acid can be obtained, for example, by oxidizing isobutylene or methacrolein in one step, or by oxidizing isobutylene via methacrolein in two steps.

A conventionally known catalyst can be used as the catalyst used for the catalytic gas phase oxidation. For example, when propylene is used as a raw material for producing acrylic acid, it is preferable to use a composite oxide catalyst (molybdenum-bismuth-based catalyst) containing molybdenum and bismuth as the catalyst. When propane or acrolein is used as a raw material for producing acrylic acid, it is preferable to use a composite oxide catalyst containing molybdenum and vanadium (molybdenum-vanadium-based catalyst) as the catalyst.

As the reactor for performing the contact gas phase oxidation reaction, a fixed bed reactor, a fluidized bed reactor, a moving bed reactor and the like can be used. Above all, it is preferable to use a multi-tube fixed bed reactor because of its excellent reaction efficiency. When the (meth) acrylic acid production raw material is oxidized in two stages to produce (meth) acrylic acid, a reactor that performs the first-stage oxidation reaction and a reactor that performs the second-stage oxidation reaction may be combined. Even if (meth) acrylic acid is produced from the (meth) acrylic acid production raw material by dividing the inside of one reactor into a region where the first-stage oxidation reaction is performed and a region where the second-stage oxidation reaction is performed. good. In the latter case, for example, in a fixed bed reactor, the inlet side (the introduction side of the (meth) acrylic acid production raw material) of the reaction tube of the fixed bed reactor is filled with a catalyst for performing the first-stage oxidation reaction, and the outlet. The side may be filled with a catalyst for performing a second-stage oxidation reaction.

The reaction for producing the (meth) acrylic acid-containing gas from the (meth) acrylic acid production raw material may be carried out under known reaction conditions. For example, when propylene is oxidized in two stages to generate acrylic acid, a propylene-containing gas is introduced into the reactor together with molecular oxygen, and the reaction temperature is, for example, 250 ° C. to 450 ° C. and the reaction pressure is 0 MPaG to 0.5 MPaG. The first-stage oxidation reaction is carried out under the conditions of space velocity 300h ^{-1 to} 5000h ^-1 , then reaction temperature 250 ° C to 380 ° C, reaction pressure 0 MPaG to 0.5 MPaG, space velocity 300h ^{-1 to} 5000h ^-1 . The second-stage oxidation reaction may be carried out under the conditions.

The (meth) acrylic acid-containing gas obtained by subjecting the (meth) acrylic acid production raw material to a catalytic gas phase oxidation reaction is (meth) by contacting with a collecting solvent and / or by cooling and condensing. Meta) Acrylic acid-containing liquid can be obtained. In the former case, by introducing the (meth) acrylic acid-containing gas into the collection tower and bringing it into contact with the collection solvent, the (meth) acrylic acid is absorbed by the collection solvent and a (meth) acrylic acid-containing liquid is obtained. (Collecting process). In the latter case, the (meth) acrylic acid-containing gas is introduced into the condensing column and cooled to condense the (meth) acrylic acid to obtain a (meth) acrylic acid-containing liquid (condensation step).

The collection tower is not particularly limited as long as it can bring the (meth) acrylic acid-containing gas into contact with the collection solvent in the collection tower. For example, by introducing the (meth) acrylic acid-containing gas into the collection tower from the lower part of the collection tower and introducing the collection solvent from the upper part of the collection tower into the collection tower, the (meth) acrylic acid is introduced. While the contained gas rises in the collecting tower, it comes into countercurrent contact with the collecting solvent, and the (meth) acrylic acid is absorbed by the collecting solvent and recovered as a (meth) acrylic acid-containing liquid. Examples of the collection tower include a shelf tower in which a shelf plate (sheve tray) is provided in the tower, a packed tower in which the tower is filled with a filler, and a wet wall tower in which a collecting solvent is supplied to the inner wall surface of the tower. , A spray tower or the like in which the collecting solvent is sprayed into the space inside the tower can be adopted.

The collecting solvent is not particularly limited as long as it can absorb and dissolve (meth) acrylic acid, and is, for example, diphenyl ether, diphenyl, a mixture of diphenyl ether and diphenyl, water, and water containing (meth) acrylic acid (meth). For example, an aqueous solution containing (meth) acrylic acid produced in the (meth) acrylic acid production process) can be used. Among them, water or (meth) acrylic acid-containing water is preferably used as the collecting solvent, and contains 50% by mass or more (more preferably 70% by mass or more, still more preferably 80% by mass or more) of water. It is more preferable to use (meth) acrylic acid-containing water or water.

The temperature and supply amount of the collecting solvent may be appropriately set so that the (meth) acrylic acid contained in the (meth) acrylic acid-containing gas is sufficiently absorbed by the collecting solvent. The temperature of the collecting solvent is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, more preferably 35 ° C. or lower, and even more preferably 30 ° C. or lower, from the viewpoint of increasing the collecting efficiency of (meth) acrylic acid. The supply amount of the collection solvent is the liquid gas ratio (L) indicated by the ratio of the supply amount (L) of the collection solvent to the collection tower (G) to the supply amount (G) of the (meth) acrylic acid-containing gas to the collection tower. L / G) is preferably at 2L / m ³ or more, 3L / m ³ or more, more preferably, 5L / m ³ or more, and also 15L / m ³ or less, and is 12L / m ³ or less More preferably, 10 L / m ³ or less is further preferable.

The (meth) acrylic acid absorbed by the collection solvent is extracted from the collection tower as a (meth) acrylic acid-containing liquid. The (meth) acrylic acid-containing liquid may be extracted from, for example, a position below the supply position of the (meth) acrylic acid-containing gas in the collection tower (for example, the bottom of the collection tower).

In the collection tower, a part of the (meth) acrylic acid-containing liquid discharged from the collection tower is collected from the supply position of the (meth) acrylic acid-containing gas and the discharge position of the (meth) acrylic acid-containing liquid in the collection tower. It is preferable to have a circulation path for returning the liquid to a position above and below the supply position of the collecting solvent. A part of the (meth) acrylic acid-containing liquid extracted from the collection tower is returned to the collection tower and circulated through the circulation channel to increase the (meth) acrylic acid concentration of the (meth) acrylic acid-containing liquid. be able to. It is preferable that the circulation path is provided with a heat exchanger for cooling the (meth) acrylic acid-containing liquid passing through the circulation path.

On the other hand, when a (meth) acrylic acid-containing liquid is obtained by condensing a (meth) acrylic acid-containing gas, it is preferable to use a condensing tower. As the condensing tower, for example, a heat exchanger provided with a heat transfer surface is used. Can be used. By cooling the (meth) acrylic acid-containing gas through the heat transfer surface, (meth) acrylic acid can be condensed from the (meth) acrylic acid-containing gas, and as a result, the (meth) acrylic acid-containing liquid can be condensed. can get. As the heat exchanger, a conventionally known heat exchanger may be used. For example, a plate heat exchanger, a multi-tube (shell and tube) heat exchanger, a double-tube heat exchanger, or a coil heat exchanger may be used. Exchangers, spiral heat exchangers, etc. can be adopted. The heat exchanger may recover the (meth) acrylic acid-containing liquid by cooling the (meth) acrylic acid-containing gas in multiple stages by connecting a plurality of them in series and separately condensing them.

The condensing column may be one in which a (meth) acrylic acid-containing gas is brought into contact with the condensed liquid to obtain a (meth) acrylic acid-containing liquid from the (meth) acrylic acid-containing gas. In this case, it is preferable to provide a shelf plate (sheave tray) in the condensing tower or to fill the condensing tower with a filler so as to improve the contact efficiency between the (meth) acrylic acid-containing gas and the condensed liquid. By using such a condensing column, the (meth) acrylic acid-containing gas is introduced into the condensing column from the lower part of the condensing column and is separated and condensed while moving from the lower part to the upper part in the condensing column. At this time, for example, the (meth) acrylic acid-containing liquid is extracted from the middle stage of the condensing column, and the substance having a boiling point higher than that of (meth) acrylic acid is extracted from the lower stage of the condensing column, and has a boiling point lower than that of (meth) acrylic acid. The substance is extracted from the upper part of the condensing tower. A part of the condensed liquid may be taken out from the condensing column at each stage, cooled by a heat exchanger or the like, and then returned to the same stage of the condensing column. In general, no liquid medium other than the condensed liquid generated in the condensed liquid is added to the condensed liquid returned to the condensed tower.

When the (meth) acrylic acid-containing liquid is obtained from the (meth) acrylic acid-containing gas, a polymerization inhibitor may be added in the collection tower or the condensing tower in order to suppress the polymerization of the (meth) acrylic acid. As the polymerization inhibitor, the polymerization inhibitor described above can be used.

In the present invention, the (meth) acrylic acid-containing liquid thus obtained can be subjected to the vaporization separation step described above. In this case, a distillation column can be adopted as the vaporization separation column because it becomes easy to obtain purified (meth) acrylic acid of higher purity, and in this case, the distillation column functions as a light boiling separation column. Those are preferable. The light boiling separation tower is provided with a drainage liquid circulation path at the bottom of the column.

In the light boiling separation column, purified (meth) acrylic acid can be obtained by removing at least a part of the low boiling point fraction from the (meth) acrylic acid-containing liquid. The low boiling point fraction means a fraction on the lower boiling point side than the purified (meth) acrylic acid, that is, a fraction extracted from the column top side of the purified (meth) acrylic acid in the light boiling separation column. Low boiling point fractions include compounds with a lower boiling point than (meth) acrylic acid, such as water and acetic acid.

In the light boiling separation column, it is preferable to introduce the (meth) acrylic acid-containing liquid into the light boiling separation column from the central part of the light boiling separation column. The (meth) acrylic acid-containing liquid is preferably introduced from a position in the range of 5% or more and 75% or less of the total number of theoretical plates with the tower top side as the base point from the top to the bottom of the light boiling separation column, for example. The range is more preferably 10% or more, further preferably 15% or more, still more preferably 70% or less, still more preferably 65% or less.

In the light boiling separation column, the low boiling point fraction is extracted from the column top side (preferably the column top) from the supply position of the (meth) acrylic acid-containing liquid. The low boiling point fraction is preferably extracted from a position in the range of 0% or more and less than 5% of the total number of theoretical plates with the tower top side as the base point from the top to the bottom of the light boiling separation column. It is preferable that the low boiling point fraction distilled from the light boiling separation column is returned to the collection column or the condensation column in the previous stage. When returning to the collection tower, it is not particularly limited, but for example, the collection tower when the base point (0%) is the base point (0%) and the end point (100%) is the top of the collection tower. It is preferable to return the product in the range of 20% or more and 90% or less in terms of the total length, and it is more preferable to return the product in the range of 30% or more and 80% or less.

On the other hand, the purified (meth) acrylic acid is extracted from the extraction port at the center of the column and / or the bottom of the light boiling separation column. The outlet for the purified (meth) acrylic acid is preferably located on the bottom side of the column with respect to the supply position of the (meth) acrylic acid-containing liquid. It is preferable that the range is 20% or more and 100% or less of the total number of theoretical plates, 25% or more is more preferable, and 35% or more is further preferable. It is preferable that the extraction port for purified (meth) acrylic acid is provided in the central part of the column. In this case, the column bottom liquid containing a large amount of high boiling point components is extracted from the bottom of the column. It becomes easy to increase the concentration of (meth) acrylic acid in (meth) acrylic acid. In this case, the extraction port for purified (meth) acrylic acid is preferably provided in a range of 90% or less, preferably 80% or less, of the total number of theoretical plates from the top of the light boiling separation tower to the bottom of the column with the top side as the base point. Is more preferable, and 70% or less is further preferable.

In the light boiling separation column, distillation may be performed under conditions under which a low boiling point fraction containing a collecting solvent, acetic acid, etc. and (meth) acrylic acid can be separated, and light boiling is possible so that such distillation is possible. It is preferable to adjust the temperature and pressure in the separation column as appropriate. For example, the tower top pressure (absolute pressure) is preferably 2 kPa or more, more preferably 3 kPa or more, more preferably 50 kPa or less, more preferably 40 kPa or less, still more preferably 30 kPa or less. The tower top temperature is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, more preferably 70 ° C. or lower, and even more preferably 60 ° C. or lower. The column bottom temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, more preferably 120 ° C. or lower, and even more preferably 110 ° C. or lower. By performing distillation under such conditions, it becomes easy to obtain purified (meth) acrylic acid having a reduced collection solvent and acetic acid concentration (for example, both water concentration and acetic acid concentration are 1% by mass or less).

In the distillation of the (meth) acrylic acid-containing liquid, an azeotropic solvent may or may not be used. When the (meth) acrylic acid concentration of the (meth) acrylic acid-containing liquid is 80% by mass or more, it becomes easy to separate the low boiling point fraction without using an azeotropic solvent. , It is preferable not to use an azeotropic solvent.

The (meth) acrylic acid concentration of the purified (meth) acrylic acid obtained from the light boiling separation column is not particularly limited as long as it is higher than the (meth) acrylic acid-containing liquid, but is preferably 80% by mass or more, for example, 85. By mass or more is more preferable, 90% by mass or more is further preferable, and 92% by mass or more is particularly preferable. The upper limit of the (meth) acrylic acid concentration of the purified (meth) acrylic acid is not particularly limited, but is usually less than 99.5% by mass.

In the production method of the present invention, the bottom liquid obtained from the light boiling separation column may be subjected to the vaporization separation step described above. In this case, it is preferable to use a distillation column that functions as a high boiling separation column as the vaporization separation column. The bottom liquid of the light boiling separation tower contains a considerable concentration of (meth) acrylic acid, and also contains more components with a higher boiling point than (meth) acrylic acid such as michael adduct and maleic acid. By introducing the bottom liquid of the separation tower into the high boiling separation tower and distilling it, a (meth) acrylic acid-containing distillate having a reduced high boiling point component can be obtained. In this case, the bottom liquid of the light boiling separation column becomes the (meth) acrylic acid-containing liquid, and the (meth) acrylic acid-containing distillate becomes the purified (meth) acrylic acid. The (meth) acrylic acid-containing distillate is preferably returned to the light boiling separation column, which can increase the yield of (meth) acrylic acid in the entire process.

At the bottom of the high boiling separation column, a column bottom liquid in which high boiling point components such as Michael adducts are concentrated is generated. It is preferable that this column bottom liquid is extracted from the column bottom of the high boiling separation column and introduced into a (meth) acrylic acid dimer decomposition apparatus. Since the Michael adduct contained in the bottom liquid of the high boiling separation tower can be converted back to (meth) acrylic acid by thermal decomposition, the bottom liquid was introduced into the (meth) acrylic acid dimer decomposition device. It is preferable that the decomposition liquid is thermally decomposed and the obtained decomposition liquid is returned to the high boiling separation column again.

The (meth) acrylic acid dimer decomposition device is composed of a thermal decomposition tank, and the bottom liquid of the high boiling separation tower is heated in the thermal decomposition tank at a temperature of 120 ° C. or higher and 220 ° C. or lower (preferably 140 ° C. or higher and 200 ° C. or lower). By heating, the Michael adduct contained in the bottom liquid can be decomposed. In order to promote the decomposition of the Michael adduct, a decomposition catalyst such as an alkali metal salt, an alkaline earth metal salt, and an N-oxyl compound described in JP-A-2003-89672 may be added to the thermal decomposition tank. preferable. In particular, when an N-oxyl compound is used as a polymerization inhibitor in a light boiling separation column or a collection column or a condensation column in front of it, it is preferable because it can also act as a decomposition catalyst for Michael adduct.

In the high boiling separation column, at least a part of the bottom liquid in which the high boiling point component is concentrated can be extracted, heated by a reboiler provided in the extraction liquid circulation path, and returned to the high boiling separation column. When the Michael adduct contained in the bottom liquid is decomposed by the (meth) acrylic acid dimer decomposition device, the decomposition liquid may be returned to the high boiling separation column via the reboiler, or the column heated by the reboiler. The withdrawal liquid of the bottom liquid may be introduced into a (meth) acrylic acid dimer decomposition apparatus (pyrolysis tank).

The purified easily polymerizable compound obtained in the vaporization separation step may be subjected to another purification step, may be handled as a product without further purification, or may be used as a raw material for producing other compounds. In the former case, it is preferable to employ crystallization in the purification step because it is easy to obtain a higher-purity easily polymerizable compound while suppressing the polymerization of the easily polymerizable compound.

The crystallization may be carried out by a batch method or a continuous method. As the crystallization device used in the crystallization operation, for example, a crystallization device having a heat transfer surface and capable of crystallizing and / or melting an easily polymerizable compound by heat exchange on the heat transfer surface can be used. A liquid containing a purifying easily polymerizable compound by heat exchange through the heat transfer surface by supplying a cold heat medium to one side of the heat transfer surface and supplying the purifying easily polymerizable compound obtained in the vaporization separation step to the other side. Is cooled and the easily polymerizable compound crystallizes. In the batch crystallization operation, the crystallized easily polymerizable compound supplies a heat medium to one side of the heat transfer surface and is heated by heat exchange through the heat transfer surface to melt the easily polymerizable compound. Liquid is obtained. The easily polymerizable compound may be melted by heating the same heat transfer surface as that used for crystallization, or the crystallized easily polymerizable compound may be recovered and used for crystallization. The recovered crystals of the easily polymerizable compound may be heated through a heat transfer surface different from that of the above.

In the batch crystallization operation, the easily polymerizable compound is crystallized by cooling the purified easily polymerizable compound obtained in the vaporization separation step, and the easily polymerizable compound is melted by melting the crystallized easily polymerizable compound. A containing melt is obtained. At this time, for the purpose of increasing the purity of the obtained melt of the easily polymerizable compound, the crystals of the easily polymerizable compound are first partially melted (sweat) to wash away impurities existing between the crystals and on the crystal surface. After that, it is preferable to melt the remaining crystals of the easily polymerizable compound to obtain a melt of the easily polymerizable compound. It is preferable that the uncrystallized residue obtained by crystallizing the easily polymerizable compound and the sweating liquid obtained by partially melting the crystals of the easily polymerizable compound are discharged from the crystallizer as a crystallization residue. As the crystallization apparatus used in the batch crystallization operation, for example, a layer crystallization apparatus (dynamic crystallization apparatus) manufactured by Sulzer Chemtech, a static crystallization apparatus manufactured by BEFS PROKEM, or the like can be used.

In the continuous crystallization operation, for example, the purified easily polymerizable compound obtained in the vaporization separation step is continuously supplied to the crystallizer and cooled to crystallize the easily polymerizable compound, and the crystal of the easily polymerizable compound and the mother liquor are used. The slurry can be continuously discharged from the crystallizer, further supplied to the washing column, and continuously separated from the mother liquor while washing the crystals of the easily polymerizable compound. Examples of the crystallization device used in the continuous crystallization operation include a crystallization device in which a crystallization unit, a solid-liquid separation unit, and a crystal purification unit are integrated (for example, a BMC (Backmixing Colon Crystallizer) type crystallization device). , Crystallization unit (for example, CDC (Cooling Disk Crystallizer) crystallizer manufactured by GOUDA, DC (Drum Crystallizer) crystallizer manufactured by GEA), solid-liquid separator (for example, belt filter, centrifuge) and A crystallization device combined with a crystal purification unit (for example, a KCP (Kureha Crystal Purifier) purification device manufactured by Kureha Engineering Co., Ltd. or a WC (Wash Colon) purification device manufactured by GEA) can be used.

It is preferable that the crystallization residue generated in the crystallization step is returned to the vaporization separation step in the previous stage, particularly to the light boiling separation column. On the other hand, the high-purity easily polymerizable compound obtained in the crystallization step may be further purified by any purification means, but it can be handled as a product or used as a raw material for producing other compounds without further purification. It is preferable to use it.

Hereinafter, the present invention will be described in more detail by showing examples, but the scope of the present invention is not limited thereto.

(Example 1)
Acrylic acid-containing liquid (crude acrylic acid) containing hydroquinone and hydroquinone monomethyl ether was supplied to the distillation column for distillation purification. The distillation column was provided with a circulation path for the bottom liquid, and the circulation path was provided with a reboiler having a vertical multi-tube heat exchanger. The bottom liquid of the distillation column was heated by extracting a part of the bottom liquid of the distillation column, heating it with a reboiler, and returning it to the distillation column. The distillation column is operated under the conditions that the pressure at the bottom of the column is 23 kPa, the pressure at the inlet of the reboiler heating unit is 62 kPa, and the temperature at the bottom of the column is 95 ° C to 105 ° C. It had a composition of 250 ppm. An oxygen nozzle was installed in the circulation path on the upstream side of the reboiler, and oxygen gas was injected into the circulation liquid flowing in the circulation passage at ^{9 Nm 3 / h (gas volume / circulation liquid volume = 13%).} The supply port of the oxygen nozzle is installed 1850 mm below the heat exchanger (heating section) inlet, the pressure of the circulating fluid at the supply port of the circulation path is 80 kPa, and the pressure from the supply port of the circulation path to the inlet of the reboiler heating section. The average residence time of the circulating fluid was 5.1 seconds. After about 6 months of operation, the operation was stopped and the inside of the distillation column and heat exchanger was inspected, but no polymer was found.

(Comparative Example 1)
In Example 1, the oxygen nozzle supply port was installed 250 mm below the heat exchanger inlet, and the operation was performed under the condition that the pressure of the circulating fluid at the supply port was 64 kPa. After about 6 months of operation, the operation was stopped and the inside of the distillation column and heat exchanger was inspected, but more than 70% of the total number of heat exchanger tubes of the heat exchanger was blocked by the polymer. ..

(Example 2)
Acrylic acid-containing liquid (crude acrylic acid) containing hydroquinone and hydroquinone monomethyl ether was supplied to the distillation column for distillation purification. Distillation purification was performed. The distillation column was provided with a circulation path for the bottom liquid, and the circulation path was provided with a reboiler having a vertical multi-tube heat exchanger. The bottom liquid of the distillation column was heated by extracting a part of the bottom liquid of the distillation column, heating it with a reboiler, and returning it to the distillation column. The distillation column is operated under the conditions that the pressure at the bottom of the column is 15 kPa, the pressure at the inlet of the reboiler heating unit is 54 kPa, and the temperature at the bottom of the column is 80 ° C to 90 ° C. It had a composition of 250 ppm. An oxygen nozzle was installed in the circulation path on the upstream side of the reboiler, and oxygen gas was injected into the circulation liquid flowing in the circulation passage at ^{3 Nm 3 / h (gas volume / circulation liquid volume = 5%).} The supply port of the oxygen nozzle is installed 1750 mm below the heat exchanger (heating section) inlet, the pressure of the circulating fluid at the supply port of the circulation path is 71 kPa, and the pressure from the supply port of the circulation path to the inlet of the reboiler heating section. The average residence time of the circulating fluid was 5.2 seconds. After about 6 months of operation, the operation was stopped and the inside of the distillation column and heat exchanger was inspected, but no polymer was found.

(Comparative Example 2)
In Example 2, the oxygen nozzle supply port was installed 250 mm below the heat exchanger inlet, and the operation was performed under the condition that the pressure of the circulating fluid at the supply port was 57 kPa. After about 6 months of operation, the operation was stopped and the inside of the distillation column and heat exchanger was inspected, but more than 50% of the total number of heat exchanger tubes of the heat exchanger was blocked by the polymer. ..

(Example 3)
Acrylic acid-containing liquid (crude acrylic acid) containing hydroquinone was supplied to the distillation column for distillation purification. Distillation purification was performed. The distillation column was provided with a circulation path for the bottom liquid, and the circulation path was provided with a reboiler having a vertical multi-tube heat exchanger. The bottom liquid of the distillation column was heated by extracting a part of the bottom liquid of the distillation column, heating it with a reboiler, and returning it to the distillation column. The distillation column is operated under the conditions of a column bottom pressure of 14 kPa, a reboiler heating unit inlet pressure of 53 kPa, and a column bottom temperature of 80 ° C. to 90 ° C., and the column bottom liquid has a composition of 90% or more of acrylic acid and 1300 ppm of hydroquinone. Was. An oxygen nozzle was installed in the circulation path on the upstream side of the reboiler, and oxygen gas was injected into the circulation liquid flowing in the circulation passage at ^{3 Nm 3 / h (gas volume / circulation liquid volume = 10%).} The supply port of the oxygen nozzle is installed 1800 mm below the heat exchanger (heating section) inlet, the pressure of the circulating fluid at the supply port of the circulation path is 71 kPa, and the pressure from the supply port of the circulation path to the inlet of the reboiler heating section. The average residence time of the circulating fluid was 5.3 seconds. After about 6 months of operation, the operation was stopped and the inside of the distillation column and heat exchanger was inspected, but no polymer was found.

(Comparative Example 3)
In Example 3, the oxygen nozzle supply port was installed 400 mm below the heat exchanger inlet, and the operation was performed under the condition that the pressure of the circulating fluid at the supply port was 58 kPa. After about 6 months of operation, the operation was stopped and the inside of the distillation column and heat exchanger was inspected, but more than 40% of the total number of heat exchanger tubes of the heat exchanger was blocked by the polymer. ..

1: Vaporization separation tower 2: Circulation passage 3: Tower bottom liquid 4: Reboiler 5: Heating part 6: Widening part 7: Supply port (of oxygen-containing gas) 8: Bending part

Claims (10)

A method for producing an easily polymerizable compound, which comprises a step of introducing a liquid containing an easily polymerizable compound into a vaporization separation column selected from a distillation column and a dissipating column and purifying the mixture under reduced pressure.
The vaporization separation tower is provided with a circulation path for returning the extracted liquid from which at least a part of the bottom liquid is extracted to the vaporization separation tower.
In the circulation path, a supply port for supplying oxygen-containing gas and a reboiler provided with a heating portion are provided in order from the upstream side.
The supply port is arranged below the height difference of 0.5 m or more with respect to the inlet of the heating unit.
A method for producing an easily polymerizable compound, which comprises supplying an oxygen-containing gas to the extract from the supply port. The method for producing an easily polymerizable compound according to claim 1, wherein the pressure of the withdrawal liquid at the supply port is 30 kPa or more higher than the gas pressure on the upper surface of the bottom liquid. The method for producing an easily polymerizable compound according to claim 1 or 2, wherein the withdrawal liquid has an average residence time of 2 seconds or more from the supply port of the circulation path to the inlet of the heating unit. The method for producing an easily polymerizable compound according to any one of claims 1 to 3, wherein a bent portion is provided in the circulation path between the supply port and the heating portion. The method for producing an easily polymerizable compound according to any one of claims 1 to 4, wherein the supply port is provided in a horizontal portion where the circulation path extends in a substantially horizontal direction. The method for producing an easily polymerizable compound according to claim 5, wherein the average residence time of the withdrawal liquid in the horizontal portion is 0.5 seconds or more. The method for producing an easily polymerizable compound according to any one of claims 1 to 6, wherein a widening portion is provided at a connection portion between the circulation path on the upstream side of the heating portion and the heating portion. The revoir provided with the heating unit is composed of a plate heat exchanger, a multi-tube heat exchanger, a double-tube heat exchanger, a coil heat exchanger, or a spiral heat exchanger. 7. The method for producing an easily polymerizable compound according to any one of 7. The method for producing an easily polymerizable compound according to any one of claims 1 to 8, wherein the oxygen-containing gas is supplied as microbubbles. The method for producing an easily polymerizable compound according to any one of claims 1 to 9, wherein the easily polymerizable compound is (meth) acrylic acid or (meth) acrylic acid ester.

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