JP5998063B2 - Method for producing (meth) acrylic acid - Google Patents

Description

  The present invention relates to a method for producing (meth) acrylic acid.

  Acrylic acid and methacrylic acid are useful raw materials widely used as raw materials for chemical products, and various production methods have been proposed in recent years. For example, acrylic acid is produced industrially by catalytic gas phase oxidation of propylene and / or acrolein, and methacrylic acid is industrially produced by catalytic gas phase oxidation of isobutylene and / or methacrolein. The (meth) acrylic acid-containing gas obtained by the contact gas phase oxidation method is purified by, for example, distillation or crystallization after the (meth) acrylic acid-containing gas is absorbed into the collection solvent or condensed to form a solution. .

  However, since (meth) acrylic acid is an easily polymerizable substance, it is easily polymerized, and in particular, polymerization in the collection step in which the (meth) acrylic acid-containing gas is absorbed by the collection solvent has been a problem. When a polymer is generated in the collection process, the collection tower must be frequently cleaned to remove the produced polymer, which requires a large amount of maintenance.

  In the past, the present inventors have applied for an invention described in Patent Document 1, for example, as a technique focusing on this collection step. In the production of acrylic acid described in this document, a desired amount of a polymerization inhibitor is added to each of two types of solutions introduced from other than the collection solvent used in the collection step and the collection solvent supply stage, and these are collected. It is thrown into the collection tower from other than the solvent supply stage and the collection solvent supply stage.

JP 2004-51489 A

  However, in the method described in Patent Document 1, it is necessary to input a large amount of a polymerization inhibitor in order to prevent polymerization in the collection tower. For this reason, it is difficult to reduce the amount of the polymerization inhibitor in the collection solvent, and when the amount of the polymerization inhibitor is reduced, a polymer is generated, and maintenance is troublesome.

  In addition, when distillation is adopted in the purification of (meth) acrylic acid, the bottom of the distillation tower is heated in the distillation tower, so that (meth) acrylic acid in the solution is easily polymerized at the bottom of the tower. It has become. Furthermore, polymerization may occur in the column as it is purified by fractional distillation.

  Under such circumstances, in the present invention, (meth) acrylic that can suppress the production of polymer due to polymerization of (meth) acrylic acid in the collection tower or distillation tower and can stably operate for a long period of time. An object was to provide a method for producing an acid.

  As a result of the study by the present inventors, it was found that there is a region (hereinafter sometimes referred to as “polymerizable region”) in which the (meth) acrylic acid is easily polymerized in the collection tower or distillation tower. It was.

  For example, in the collection tower, the collection solvent is usually supplied from a collection solvent inlet at the top of the collection tower, but dissolves in the collection solvent as the collection solvent moves to the bottom of the tower ( Since the amount of (meth) acrylic acid increases, the concentration of the polymerization inhibitor in the collection solvent for (meth) acrylic acid decreases. Therefore, from the center of the collection tower to the bottom of the tower, the concentration of the polymerization inhibitor is lowered, and (meth) acrylic acid is easily polymerized to form a polymer.

  Further, when the present inventors examined a distillation column, even if a polymerization inhibitor was sufficiently added to the feed liquid (crude (meth) acrylic acid solution), although there were some differences depending on the operating conditions, the crude (meta) It was found that (meth) acrylic acid was easily polymerized immediately above the stage where the acrylic acid solution was supplied. This is because, in the case of the distillation column, the temperature inside the column increases as it approaches the bottom of the distillation column, just above the stage for supplying the (meth) acrylic acid solution. This is probably because acrylic acid is easily reacted.

  As a result of intensive studies, the present inventors have found that if a polymerization inhibitor is further introduced from the upper part of the polymerizable region in order to suppress the polymerization reaction of (meth) acrylic acid in this polymerizable region, The polymerization reaction of (meth) acrylic acid in the region can be suppressed, and as a result, the amount of polymer produced in the tower can be reduced, and (meth) acrylic acid can be produced by continuously operating for a long period of time. The present invention has been completed.

That is, in the method for producing (meth) acrylic acid according to the present invention, the (meth) acrylic acid-containing gas is obtained from a (meth) acrylic acid production raw material, and the (meth) acrylic acid-containing gas is obtained. From the collection step of obtaining a crude (meth) acrylic acid solution, the collection tower used in the collection step includes a gas supply port for supplying a (meth) acrylic acid-containing gas, and a polymerization inhibitor A first supply port and a second supply port for introducing the solution, and a collection solvent introduction port for introducing the collection solvent are present in order from the bottom of the tower in the height direction. A polymerization inhibitor-containing solution is introduced from both the first supply port and the second supply port.
In addition, it is desirable that the collection tower is a packed tower, and the second supply port is present on the top side of the first supply port at a theoretical plate number of 0.5 to 10 stages away. If the distance between the supply ports is within the above range, (meth) acrylic acid can be efficiently collected and the polymerization preventing effect can be improved.
In the present invention, it is preferable that the polymerization inhibitor-containing solution is introduced from a polymerization inhibitor-containing solution supply pipe that is branched and connected to the first supply port and the second supply port. Stable quality control can be carried out by branching the supply pipe and introducing the polymerization inhibitor-containing solution into the tower.
Further, the polymerization inhibitor-containing solution is a solution containing (meth) acrylic acid, and the (meth) acrylic acid solution is obtained by mixing (i) product (after purification) (meth) acrylic acid with a solvent. A solution prepared to a predetermined concentration, (ii) a solution containing (meth) acrylic acid obtained in the production step of (meth) acrylic acid, and (iii) obtained in a production process of (meth) acrylic acid of another system It is desirable to include at least one selected from the (meth) acrylic acid-containing solution corresponding to (i) or (ii) above.
The polymerization inhibitor-containing solution preferably contains a (meth) acrylic acid solution having a (meth) acrylic acid concentration of 30% by mass or more and less than 99% by mass. By using a (meth) acrylic acid solution as a polymerization inhibitor-containing solution, a decrease in the concentration of the (meth) acrylic acid solution in the collection tower can be suppressed, and the (meth) acrylic acid solution after the collection step can be made higher. It is possible to make it a concentration.
In addition, the present invention includes a distillation step of purifying a (meth) acrylic acid solution by a distillation operation, and a distillation column used in the distillation step includes a first supply port for introducing a polymerization inhibitor-containing solution and a second supply port. 2 supply ports and a reflux solution supply port for introducing the reflux solution are present in order from the bottom of the column in the height direction. In the distillation step, the polymerization inhibitor is supplied from both the first supply port and the second supply port. Also included is a method for producing (meth) acrylic acid, which is characterized by introducing a containing solution.
The polymerization inhibitor-containing solution is preferably introduced from a polymerization inhibitor-containing solution supply pipe that branches and connects to the first supply port and the second supply port. It is preferable to branch the supply pipe and introduce the polymerization inhibitor-containing solution into the tower because stable quality control can be performed.
The distillation column is preferably a high boiling point material separation column having a discharge port for distilling purified (meth) acrylic acid on the top side of the reflux liquid supply port. In the production of (meth) acrylic acid, when using a high-boiling-point substance separation tower, specifically, it is often used when recovering purified (meth) acrylic acid, especially for the separation of high-boiling substances. For this reason, the inside of the column tends to be relatively hot during distillation. In such a high-temperature atmosphere, (meth) acrylic acid is more easily polymerized. Therefore, in the scene of using a high-boiling-point substance separation column as a distillation column, in particular, the method for producing (meth) acrylic acid according to the present invention is It is valid.
Further, it is desirable that the distillation column is a plate column, and the second supply port is present on the column top side separated from the first supply port by the number of trays within 1 to 20 stages. When the distance between the supply ports is within the above range, (meth) acrylic acid can be efficiently separated and the polymerization preventing effect can be improved.
The polymerization inhibitor-containing solution is a solution containing (meth) acrylic acid, and the (meth) acrylic acid solution is obtained by mixing (i) product (after purification) (meth) acrylic acid with a solvent. A solution prepared to a predetermined concentration, (ii) a solution containing (meth) acrylic acid obtained in the production step of (meth) acrylic acid, and (iii) obtained in a production process of (meth) acrylic acid of another system It is preferable that at least one selected from (meth) acrylic acid-containing solutions corresponding to the above (i) or (ii) is included.
Moreover, it is preferable that the said polymerization inhibitor containing solution contains (meth) acrylic acid whose (meth) acrylic acid density | concentration is 30 to 99 mass%. By using a (meth) acrylic acid solution as a polymerization inhibitor-containing solution, the concentration reduction of the (meth) acrylic acid solution in the distillation tower can be suppressed, and the purity of the obtained (meth) acrylic acid is maintained at a high level. it can.
The collection solvent and the reflux liquid contain a polymerization inhibitor, and the polymerization inhibitor contained in the collection solvent or the reflux liquid may differ from the type of polymerization inhibitor contained in the polymerization inhibitor-containing solution. desirable. By using a combination of a plurality of different types of polymerization inhibitors, the polymerization prevention effect may be further improved (synergistic effect).

  According to the present invention, the polymerization inhibitor-containing solution is introduced from a plurality of supply ports existing in the column, particularly from a plurality of supply ports including a supply port existing on the column top side of the polymerizable region in the column. The polymerization reaction in the polymerizable region in the tower can be suppressed, the amount of polymer produced in the tower can be reduced, and (meth) acrylic acid can be stably produced. Further, according to the present invention, since the polymerization inhibitor-containing solution is supplied aiming at the polymerizable region in the tower, it is possible to reduce the polymerization inhibitor to be contained in the collection solvent or the supply solution to the distillation tower. It also leads to reduction of the production cost of (meth) acrylic acid.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a process diagram showing an example of a preferred embodiment of the present invention. FIG. 2 is a process diagram showing an example of a preferred embodiment of the present invention. FIG. 3 is a diagram showing an example of a preferred embodiment for the collection tower of the present invention. FIG. 4 is a diagram showing an example of a preferred embodiment for the distillation column of the present invention.

<Method for producing (meth) acrylic acid>
The method for producing (meth) acrylic acid according to the present invention comprises a (meth) acrylic acid-producing step for obtaining a (meth) acrylic acid-containing gas from a (meth) acrylic acid production raw material, and the (meth) acrylic acid-containing gas. A collection step of obtaining a (meth) acrylic acid solution is included.

  In order to purify the crude (meth) acrylic acid solution obtained in the collection step and take it out as a product, it is possible to perform a crystallization step of (meth) acrylic acid after the collection step. In addition, since the residual solution (crystallization residue) in the crystallization step contains (meth) acrylic acid, after the crystallization step, the crystallization residue is left as it is or (meta) in the crystallization residue. ) It is desirable to carry out a recycling process that recovers acrylic acid and supplies it again to the collection process.

  Alternatively, after the collecting step, water and low-boiling substances are removed from the crude (meth) acrylic acid solution obtained in the collecting step to obtain a (meth) acrylic acid solution, and the (meth) acrylic is further obtained. It is also possible to carry out the step of separating the (meth) acrylic acid and the high-boiling substance-containing liquid by removing the high-boiling substance from the acid solution. Since the high-boiling substance-containing liquid obtained by removing high-boiling substances contains (meth) acrylic acid oligomers, the oligomers are thermally decomposed to recover (meth) acrylic acid, and the recovered solution is collected again. It is economical to carry out a recycling process that supplies the tower. Below, the manufacturing method of the (meth) acrylic acid of this invention is explained in full detail.

[(Meth) acrylic acid production process]
First, the method for producing (meth) acrylic acid according to the present invention will be described. In the present invention, (meth) acrylic acid means methacrylic acid, acrylic acid and a mixture thereof.

  In the (meth) acrylic acid production step, a (meth) acrylic acid-containing gas is produced from the (meth) acrylic acid production raw material. The (meth) acrylic acid production raw material used in the (meth) acrylic acid production step is not particularly limited as long as it produces (meth) acrylic acid by a reaction. For example, propane, propylene, (meth) acrolein And isobutylene.

  Acrylic acid can be obtained in the reactor, for example, by oxidizing propane, propylene or acrolein in one stage, or by oxidizing propane or propylene in two stages via acrolein. Acrolein is not limited to those obtained by oxidizing propane or propylene as a raw material, and may be obtained by dehydrating it using glycerin as a raw material, for example. Methacrylic acid can be obtained, for example, by oxidizing isobutylene or methacrolein in one stage or by oxidizing isobutylene in two stages via methacrolein. These oxidation reaction and dehydration reaction are preferably performed in the presence of a catalyst, and a known oxidation catalyst or dehydration catalyst for producing (meth) acrylic acid may be used.

[Collection process]
Next, the collection process according to the present invention will be described. Hereinafter, although the manufacturing method of the (meth) acrylic acid of this invention is demonstrated concretely, referring FIG. 1, this invention is not necessarily limited to the example of illustration from the first.

  In the collection step, an object is to obtain a crude (meth) acrylic acid solution by bringing the (meth) acrylic acid-containing gas obtained in the (meth) acrylic acid production step into contact with the collection solvent. The (meth) acrylic acid-containing gas obtained in the (meth) acrylic acid production step is discharged from the reactor 1 and then sent to the collection tower 2.

  The collection tower 2 used in the collection step has a gas supply port 11 for supplying a (meth) acrylic acid-containing gas and a first supply for introducing a polymerization inhibitor-containing solution on the side surface of the collection tower 2. The port 12 and the second supply port 13 are present in order from the bottom in the height direction. Further, the collection tower 2 has a collection solvent introduction port 14 for introducing the collection solvent on the tower top side from the second supply port 13. In the collecting step according to the present invention, the polymerization inhibitor is introduced from a plurality of inlets of the first supply port 12 and the second supply port 13 other than the (meth) acrylic acid-containing gas supply port 11 and the collection solvent introduction port 14. It is characterized in that the contained solution is introduced.

  In addition, a gas discharge port 15 for discharging the gas in the collection tower exists above the collection tower 2. Further, at the lower part (preferably the bottom part) of the collection tower 2, there is a tower bottom liquid discharge port 10 for extracting the crude (meth) acrylic acid solution obtained in the collection process. The crude (meth) acrylic acid solution extracted from the tower bottom liquid discharge port 10 may be subjected to a (meth) acrylic acid distillation step or a crystallization step in order to purify it to an appropriate purity thereafter.

  In the collection tower 2, a (meth) acrylic acid-containing gas is introduced from the gas supply port 11. On the other hand, the collection solvent is supplied from a collection solvent introduction port 14 existing at the upper part of the collection tower 2. The (meth) acrylic acid-containing gas introduced from the gas supply port 11 moves from the tower bottom side of the collection tower 2 toward the tower top side, and the collection solvent introduced from the collection solvent introduction port 14 is: It moves from the tower top side of the collection tower 2 toward the tower bottom side along the gravity. When the introduced (meth) acrylic acid-containing gas comes into countercurrent contact with the collection solvent, (meth) acrylic acid contained in the gas dissolves in the collection solvent. In the present invention, as described later, it is preferable that the collection solvent contains a polymerization inhibitor. In this case, the collection solvent dissolves in the collection solvent as it moves to the bottom of the column. Since the amount of (meth) acrylic acid increases, the concentration of the polymerization inhibitor in the collection solvent for (meth) acrylic acid is relatively lowered.

  Here, when a solution containing a polymerization inhibitor (hereinafter also referred to as “polymerization inhibitor-containing solution”) is introduced from the first supply port 12, a solution in which (meth) acrylic acid is dissolved in the collection solvent; Since the polymerization inhibitor-containing solution is mixed, a decrease in the concentration of the polymerization inhibitor relative to (meth) acrylic acid in the mixed solution is suppressed, and polymerization in the crude (meth) acrylic acid solution at the bottom of the column hardly occurs. Thus, the crude (meth) acrylic acid solution can be stably extracted.

  On the other hand, in the upper part of the first supply port 12, since the concentration of the polymerization inhibitor with respect to (meth) acrylic acid is lowered, a region where the polymerization reaction easily proceeds (that is, the polymerizable region 16) is likely to occur. Therefore, in the present invention, in order to suppress the polymerization reaction of (meth) acrylic acid in the polymerizable region 16, the second supply that is present on the side of the collection tower 2 and closer to the top of the tower than the first supply port 12 is provided. A polymerization inhibitor-containing solution is also introduced from the mouth 13. By introducing the polymerization inhibitor-containing solution also from the second supply port 13 on the side surface of the collection tower, a decrease in the concentration of the polymerization inhibitor in the polymerizable region 16 can be suppressed.

  The collection tower 2 is not particularly limited as long as it is a tower having the first supply port 12 and the second supply port 13 on the side surface. For example, a plate tower, a packed tower, a wet wall tower, a spray tower, etc. Various collection towers can be used. In the present invention, it is desirable to use a packed tower because the collection efficiency is good.

  The position of the second supply port 13 in the collection tower 2 is not particularly limited as long as it exists on the tower top side of the first supply port 12, but the tower bottom of the collection tower 2 serves as a base point, For example, the total length of the collection tower 2 when the top is the end point is preferably in the range of 45 to 90%, more preferably 45 to 80%, and still more preferably 45 to 75%. It is preferable to set the position of the second supply port 13 within the above range because the polymerization preventing effect in the polymerizable region 16 is enhanced.

  On the other hand, the position of the first supply port 12 in the collection tower 2 is, for example, 20 to 45% in the entire length of the collection tower 2 when the tower bottom is the base point and the top is the end point. It is preferable to provide in the range, more preferably 25 to 45%, still more preferably 30 to 40%. It is preferable to set the position of the first supply port 12 within the above range because the polymerization reaction on the column bottom side of the first supply port 12 can be suppressed.

  When a packed tower is used as the collection tower 2, although depending on the scale of the apparatus, the second supply port 13 may be present on the tower top side that is 0.5 or more theoretical plates away from the first supply port 12. Preferably, it is present on the tower top side separated by one or more stages, more preferably 10 stages or less, more preferably 5 stages or less, and further preferably 3 stages or less. By setting the distance between the first supply port 12 and the second supply port 13 within the above range, the effect of preventing polymerization in the polymerizable region 16 is enhanced, and (meth) acrylic acid can be efficiently collected. preferable. When the distance between the second supply port 13 and the first supply port 12 approaches 0.5 stages in terms of the theoretical plate number, the position of the second supply port 13 becomes lower than the polymerizable region 16, and the second supply port 13. Since there is a possibility that the polymerizable region 16 may exist at the upper part, the polymerization preventing effect by introducing the polymerization inhibitor-containing solution from the second supply port 13 may not be sufficiently exhibited. Further, if the number of theoretical plates exceeds 10, the distance between the second supply port 13 and the polymerizable region 16 is increased, so that the decrease in the concentration of the polymerization inhibitor in the polymerizable region 16 may not be sufficiently suppressed. In some cases, the polymerization preventing effect due to the introduction of the polymerization inhibitor-containing solution may not be sufficiently exhibited.

  The flow rate of the polymerization inhibitor-containing solution introduced from the first supply port 12 and the second supply port 13 is not particularly limited. For example, the flow rate of the polymerization inhibitor-containing solution introduced from the second supply port 13 is not limited. The flow rate is preferably 0.001 times or more, more preferably 0.002 times or more, and more preferably 0.003 times or more with respect to the flow rate of the polymerization inhibitor-containing solution introduced from the first supply port 12. More preferably. Further, the flow rate of the polymerization inhibitor-containing solution introduced from the second supply port 13 is preferably, for example, 1 time or less with respect to the flow rate of the polymerization inhibitor-containing solution introduced from the first supply port 12, More preferably, it is 0.6 times or less, More preferably, it is 0.5 times or less. When the flow rate of the polymerization inhibitor-containing solution introduced from the second supply port 13 is less than 0.001 times, the amount of polymerization inhibitor in the polymerization inhibitor-containing solution is small, and in the polymerizable region 16 in the collection tower. Since there exists a possibility that the polymerization prevention effect may not fully be exhibited, it is unpreferable.

  The concentration of the polymerization inhibitor in the liquid between the first supply port 12 and the second supply port 13 of the collection tower 2 is specifically preferably 20 ppm or more, more preferably 50 ppm or more, and 100 ppm or more on a mass basis. Is more preferable. The upper limit of the concentration of the polymerization inhibitor in the liquid between the first supply port 12 and the second supply port 13 of the collection tower 2 is not particularly limited, but is preferably 600 ppm or less, for example, 550 ppm or less. Even if it exists, the polymerization reaction prevention effect is exhibited and 500 ppm or less may be sufficient. By controlling the concentration of the polymerization inhibitor in the liquid within the above range, the polymerization reaction in the polymerizable region 16 can be suppressed.

  In the present invention, the total amount of the polymerization inhibitor in the polymerization inhibitor-containing solution introduced from the first supply port 12 is larger than the total amount of the polymerization inhibitor in the polymerization inhibitor-containing solution introduced from the second supply port 13. It is desirable to do. In the collection tower 2, the closer to the tower bottom side, the more (meth) acrylic acid absorbed by the collection solvent, so the concentration of the polymerization inhibitor in the resulting solution is lower. Therefore, it is preferable to add a larger amount of the polymerization inhibitor from the first supply port 12 located on the bottom side of the tower because the polymerization reaction can be suppressed according to the concentration of the polymerization inhibitor in the solution in the collection tower 2.

  Regarding the method for introducing the polymerization inhibitor-containing solution, the introduction method is not particularly limited as long as the polymerization inhibitor-containing solution is introduced from the first supply port 12 and the second supply port 13. Either or both of the first supply port 12 and the second supply port 13 are, for example, a supply pipe for passing the bottom liquid extracted from the bottom liquid discharge port 10 of the collection tower 2; A supply pipe for supplying a distillate obtained by distilling a residue generated in a crystallization step performed after the process; or a supply pipe for passing a (meth) acrylic acid solution generated by a separate system process; It is preferable to be connected to. In the present invention, since the polymerization inhibitor and (meth) acrylic acid in the solution can be reused, either the first supply port 12 or the second supply port 13 is extracted from the tower bottom liquid discharge port 10. It is desirable to be connected to a supply pipe for passing the column bottom liquid; or a supply pipe for supplying a distillate obtained by distilling the residue generated in the crystallization step.

  In the present invention, the “separate process” refers to a series of production processes of (meth) acrylic acid including the collection tower 2 (that is, production and collection of (meth) acrylic acid). In the invention relating to the distillation column 22 to be described later, a series of production processes of (meth) acrylic acid including the distillation column 22 (that is, production of (meth) acrylic acid). , Processes including collection and purification).

  Particularly in the present invention, the polymerization inhibitor-containing solution is introduced into the collection tower through the polymerization inhibitor-containing solution supply pipe 9 connected by branching to both the first supply port 12 and the second supply port 13. Good. “Connected by branching to both the first supply port 12 and the second supply port 13” means that the pipe for supplying the polymerization inhibitor-containing solution has at least one branch point. That is, the end of the pipe (pipe) positioned downstream is connected to each of the first supply port 12 and the second supply port 13. Furthermore, the pipe for supplying the polymerization inhibitor-containing solution has one branch point, and the ends of the two pipes downstream from the branch point are the first supply port 12 and the second supply port 13. It is connected to each of. In this way, by introducing the polymerization inhibitor-containing solution from the first supply port 12 and the second supply port 13 through the branched polymerization inhibitor-containing solution supply pipe 9, quality control is simplified, ) The quality of acrylic acid can be stabilized.

  As the polymerization inhibitor-containing solution supply pipe 9, for example, a tower bottom liquid supply pipe connected to the tower bottom liquid discharge port 10 of the collection tower shown in FIG. And a supply pipe (supply pipe A) connected to the second supply port 13; polymerization from the crystallization process after the collection process shown in FIGS. 3B and 3C or a separate system to the collection tower 2 A supply pipe (supply pipe B) branched from the supply pipe for passing the inhibitor-containing solution and connected to the first supply port 12 and the second supply port 13; shown in FIG. A branch pipe from a tower bottom liquid supply pipe connected to the tower bottom liquid discharge port 10 and a supply for passing a polymerization inhibitor-containing solution from the crystallization process after the collection process or a separate system to the collection tower 2 Examples include a supply pipe (supply pipe C) that joins the first supply port 12 and the second supply port 13 when the pipes merge and the pipe downstream from the junction is branched. .

  For example, as shown in FIGS. 3B and 3D, the polymerization inhibitor-containing solution supply pipe 9 has a junction 9a with another supply pipe (or “pipe”). The position of the junction 9a is not particularly limited.

  As the polymerization inhibitor used in the polymerization inhibitor-containing solution, conventionally known polymerization inhibitors can be used, for example, quinones such as hydroquinone and hydroquinone monomethyl ether; phenothiazine, bis- (α-methylbenzyl) phenothiazine. Phenothiazines such as 3,7-dioctylphenothiazine, bis- (α-dimethylbenzyl) phenothiazine; 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6-tetra N-oxyl compounds such as methylpiperidinooxyl, 4,4 ′, 4 ″ -tris- (2,2,6,6-tetramethylpiperidinooxyl) phosphite; copper dialkyldithiocarbamate, copper acetate, naphthene Copper salt compounds such as acid copper, copper acrylate, copper sulfate, copper nitrate, copper chloride; dialkyldithioca Manganese salt compounds such as manganese rubamate, manganese diphenyldithiocarbamate, manganese formate, manganese acetate, manganese octoate, manganese naphthenate; N-nitrosophenylhydroxylamine and its salt, p-nitrosophenol, N-nitrosodiphenylamine and its salt These polymerization inhibitors may be used alone or in combination of two or more thereof Among these polymerization inhibitors, quinones, phenothiazines, copper salt compounds and At least one selected from the group consisting of manganese salt compounds is preferably used.

  In the present invention, the above-mentioned polymerization inhibitor-containing solution is preferably a solution containing (meth) acrylic acid (hereinafter also referred to as “(meth) acrylic acid solution”). The (meth) acrylic acid solution may be used as a solvent for dissolving the polymerization inhibitor. If it is a (meth) acrylic acid solution containing a polymerization inhibitor, it should be used as it is as a polymerization inhibitor-containing solution. Can do. By using a (meth) acrylic acid solution as the polymerization inhibitor-containing solution, it is possible to suppress a decrease in the (meth) acrylic acid concentration in the solution in the collection tower, and the crude (meth) acryl after the collection step. It becomes possible to maintain the density | concentration of an acid solution in a higher state.

  The (meth) acrylic acid concentration in the (meth) acrylic acid solution (polymerization inhibitor-containing solution) used in the collecting step is, for example, preferably 30% by mass or more, more preferably 50% by mass or more. More preferably, it is 80% by mass or more, preferably less than 99% by mass, more preferably 97% by mass or less, and still more preferably 95% by mass or less. If the (meth) acrylic acid concentration is within the above range, when the solution is introduced from both the first supply port 12 and the second supply port 13, the (meth) acrylic acid in the solution in the collection tower This is preferable because the change in density can be reduced.

  As said (meth) acrylic acid solution, as long as it contains (meth) acrylic acid, the various solutions produced during manufacture can be used. Specifically, for example, (i) a solution prepared by mixing (meth) acrylic acid of a product (after purification) with a solvent to a predetermined concentration, (ii) obtained in the production process of (meth) acrylic acid (meta ) A solution containing acrylic acid (for example, a column bottom liquid extracted from the column bottom liquid discharge port 10 of the collection tower 2, that is, a crude (meth) acrylic acid solution; a crystallization step performed after the collection step And (iii) (meth) acrylic acid corresponding to the above (i) or (ii) obtained in the production process of another (meth) acrylic acid A (meth) acrylic acid solution such as a containing solution can be used. In particular, as shown in (ii), when the residue generated during the production of (meth) acrylic acid is purified and used, (meth) acrylic acid in the solution can be recovered again, which is economical. In addition, the (meth) acrylic acid solution mentioned above may be used by 1 type, and may mix 2 or more types.

  Next, the collection solvent used in the collection step will be described. As the collection solvent, water or a high-boiling solvent (diphenyl ether, biphenyl, etc.) having (meth) acrylic acid dissolving ability may be used. Furthermore, (meth) acrylic acid-containing water can also be used as a collection solvent. Usually, the gas discharged from the gas discharge port 15 present at the upper part of the collection tower contains (meth) acrylic acid production raw material and uncollected (meth) acrylic acid. Therefore, it is preferable from an economical viewpoint that uncollected (meth) acrylic acid is separated using a cooler, a vacuum distillation apparatus or the like, mixed with a collection solvent and supplied to the collection tower 2. The separated (meth) acrylic acid production raw material may be supplied again to the reactor.

  Since (meth) acrylic acid is easily polymerized in the collection tower, the collection solvent of the present invention preferably contains a polymerization inhibitor. As the polymerization inhibitor, the compounds exemplified in the polymerization inhibitor may be used. Of these, quinones are preferably used. In addition, these polymerization inhibitors may be used independently and may use 2 or more types together.

  In the present invention, the type of polymerization inhibitor contained in the collection solvent and the type of polymerization inhibitor contained in the polymerization inhibitor-containing solution may be the same or different. By using a combination of a plurality of different types of polymerization inhibitors, the polymerization prevention effect may be further improved (a synergistic effect may be exhibited).

  When the collection solvent is introduced into the collection tower 2 and the contact between the (meth) acrylic acid-containing gas and the collection solvent proceeds, (meth) acrylic acid to the collection solvent as the solution moves to the tower bottom side. Therefore, the concentration of the polymerization inhibitor in the solution gradually decreases as compared with the concentration in the collection solvent when the collection tower is charged.

  In the present invention, the concentration of the polymerization inhibitor in the collection solvent at the time of charging the collection tower is preferably 100 ppm or more, more preferably based on the mass of the (meth) acrylic acid component in the (meth) acrylic acid-containing gas. Is 200 ppm or more, more preferably 400 ppm or more, preferably 2000 ppm or less, more preferably 1500 ppm or less, still more preferably 1200 ppm or less.

  In the present invention, a solution containing a polymerization inhibitor is introduced from the first supply port 12 and the second supply port 13 of the collection tower 2. That is, in the present invention, as described above, since the polymerization inhibitor-containing solution is introduced also from the second supply port 13 located on the column top side from the polymerizable region 16, the polymerization inhibitor-containing solution is contained only from the first supply port 12. Compared to the case of introducing a solution, the amount of the polymerization inhibitor used in the collection solvent can be reduced. This is desirable because it leads to a reduction in production cost of (meth) acrylic acid.

  The collection tower 2 is preferably operated at a tower top pressure (absolute pressure) of 1000 to 4000 hPa, more preferably 3000 hPa or less, and further preferably 2000 hPa or less. When the pressure at the top of the column rises, it is necessary to raise the temperature of the collection column 2 in order to discharge low boiling point substances from the top of the collection column 2, and the collection efficiency of (meth) acrylic acid may decrease. is there. The top temperature of the collection tower 2 is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, preferably 85 ° C. or lower, more preferably 80 ° C. or lower.

As the packing material of the collection tower 2, one that has durability against pressure and high temperature and that does not easily react with the components in the residual mother liquor is preferable. From this viewpoint, it is made of metal such as alumina or stainless steel. Is recommended. Moreover, it is preferable that the shape of the packing is difficult to increase the pressure loss of the collection tower 2. As the filler, a known filler may be used as appropriate. For example, Raschig ring, Lessing ring, Pole ring, Flexi ring, Cascade mini ring (registered trademark), Raschig super ring (registered trademark), Interlocks・ Random packing such as metal tower packing, interlock saddle, etc .; Sruzer Packing (Sulzer Chemtech), Techno Pack (Sanso Techno), MC Pack (Matsui Machine), Mera Pack (Sulzer Chemtech), Various fillers such as regular fillers such as Flexigrid (Coke) can be exemplified. All of these packing materials are preferable because they have a high packing surface area per 1 m ³ and a high porosity, so that mass exchange can be performed efficiently and pressure loss can be reduced. These packings may be used alone or in combination of two or more, but in the present invention, in particular, the irregular packing and the regular packing are used in combination. The most preferable irregular packing is Cascade Mini Ring (registered trademark), and the most preferable packing is sulzer packing.

[Crystalling process]
Next, the crystallization process will be described. The method for producing (meth) acrylic acid of the present invention may include a crystallization step as a purification step for (meth) acrylic acid after the collecting step. In the crystallization step, the crude (meth) acrylic acid solution obtained in the collecting step is introduced into the crystallizer 3, and the (meth) acrylic acid is purified from the crude (meth) acrylic acid solution in the crystallizer 3. The process to do. By the crystallization step, purified (meth) acrylic acid of the crystal and a low-purity crystallization residue are obtained.

  It is preferable that the (meth) acrylic acid crystallized by a cooling operation or the like in the crystallization step is then melted to obtain a (meth) acrylic acid melt, which is recovered as purified (meth) acrylic acid. In addition, for the purpose of increasing the purity of the (meth) acrylic acid obtained, the crystallized (meth) acrylic acid is first partially melted to wash away impurities present between the crystals and on the crystal surface (also called a sweating process). ) And then the remaining crystallized (meth) acrylic acid is preferably melted to recover the purified (meth) acrylic acid. The residue obtained when the crystallized (meth) acrylic acid is partially melted is preferably discharged from the crystallizer 3 as a crystallization residue.

  The crystallizer 3 is not particularly limited as long as it can crystallize a (meth) acrylic acid-containing solution such as a crude (meth) acrylic acid solution, and has, for example, a heat transfer surface, Examples thereof include a crystallizer that crystallizes and melts a (meth) acrylic acid-containing solution by heat exchange. In such a crystallizer, by supplying a cooling medium to one side of the heat transfer surface and supplying a (meth) acrylic acid-containing solution to the other side, (meth) acrylic is obtained by heat exchange via the heat transfer surface. The acid-containing solution is cooled and (meth) acrylic acid crystallizes. The crystallized (meth) acrylic acid supplies a heating medium to one side of the heat transfer surface, and is heated by heat exchange via the heat transfer surface, whereby a (meth) acrylic acid melt is obtained.

  As a crystallizer having a heat transfer surface, an apparatus generally used as a heat exchanger can be employed. Examples of the heat exchanger include a plate heat exchanger, a multi-tube (shell and tube) heat exchanger, a double tube heat exchanger, a coil heat exchanger, and a spiral heat exchanger.

  When the (meth) acrylic acid-containing solution is crystallized, the temperature of the heat transfer surface (if a cooling medium is used, the temperature of the cooling medium) is not particularly limited as long as it is lower than the freezing point of the (meth) acrylic acid-containing solution. However, in order to efficiently crystallize the (meth) acrylic acid-containing solution, the temperature is preferably 0 ° C. or lower, and is preferably −5 ° C. or lower. In addition, the minimum of the said temperature is not specifically limited.

  When melting crystallized (meth) acrylic acid, the temperature of the heat transfer surface (if using a heating medium, the temperature of the heating medium) is particularly limited as long as it exceeds the melting point of the crystallized (meth) acrylic acid. However, in order to efficiently melt (meth) acrylic acid, the temperature is preferably 20 ° C. or higher, more preferably 25 ° C. or higher. On the other hand, the upper limit of the temperature is preferably 45 ° C. or less, preferably 40 ° C. or less, from the viewpoint of suppressing the polymerization reaction of (meth) acrylic acid and increasing the purity and yield of the resulting (meth) acrylic acid melt. More preferred.

  In the crystallization step, crystallization and melting may be alternately repeated a plurality of times to obtain purified (meth) acrylic acid with higher purity. That is, after crystallizing and melting a (meth) acrylic acid solution to obtain a (meth) acrylic acid melt, the obtained (meth) acrylic acid is further crystallized and melted one or more times, ( Meta) acrylic acid may be purified.

[(Meth) acrylic acid recovery process in crystallization residue]
Next, the process for recovering (meth) acrylic acid will be described. In the present invention, after the crystallization step described above, (meth) acrylic acid is recovered from the crystallization residue obtained in the crystallization step and supplied to the collection tower 2. Is also possible. Since the crystallization residue contains (meth) acrylic acid and a polymerization inhibitor, a solution obtained by collecting (meth) acrylic acid and the polymerization inhibitor in the crystallization residue is supplied to the collection tower 2 as a polymerization inhibitor-containing solution. This is desirable from an economic standpoint.

  As a method for recovering (meth) acrylic acid in the crystallization residue, distillation is preferably exemplified, and it is particularly preferable to carry out distillation (high boiling separation) for separating a high boiling point substance. According to the high boiling separation, the yield of (meth) acrylic acid can be improved, and at the same time, impurities having a high boiling point in the crystallization residue and (meth) acrylic acid can be separated.

  When performing high boiling separation, it is good to use the high boiling separation tower 5 which can extract and collect the liquid which contains (meth) acrylic acid in high concentration from the tower top part. The (meth) acrylic acid-containing distillate withdrawn from the top of the high-boiling separation column 5 is the above-described (meth) acrylic acid solution, both the first supply port 12 and the second supply port 13, or the first It is desirable to supply to the collection tower 2 through one of the supply port 12 and the second supply port 13 and reuse it.

  In addition, the bottoms discharged from the bottom of the high boiling separation column 5 may contain oligomers such as a dimer of (meth) acrylic acid. Therefore, in the present invention, the bottoms discharged from the high-boiling separation tower 5 can be supplied to the (meth) acrylic acid recovery tower 6 to perform the dimer decomposition step. A part of the liquid after the dimer decomposition is reused together with the crystallization residue, and the remaining liquid is preferably discarded together with impurities having a high boiling point.

  In the distillation step and the dimer decomposition step that are performed in the recovery step, the temperature in the apparatus during the operation increases, so that (meth) acrylic acid is easily polymerized. Therefore, it is desirable to appropriately add a polymerization inhibitor to the high boiling separation column 5 and the (meth) acrylic acid recovery column 6. As the polymerization inhibitor, the above-described compounds can be used. In order to add a polymerization inhibitor to the high boiling separation tower 5 or the (meth) acrylic acid recovery tower 6, for example, a solution containing a desired amount of the polymerization inhibitor is added to the high boiling separation tower 5 or the (meth) acrylic acid recovery tower. It is preferable to supply to the top capacitor of the tower 6, and further, by providing a plurality of supply ports for introducing the polymerization inhibitor-containing solution of the present invention in each tower, and introducing the polymerization inhibitor-containing solution from the supply port, This is preferable because polymerization in the column is suppressed.

[Distillation process]
Next, the distillation process according to the present invention will be described. The purpose of this distillation step is to purify (meth) acrylic acid.

  Any distillation column may be used as long as it is used for the purpose of removing various impurities contained in the (meth) acrylic acid-containing solution by a distillation operation and purifying it. For example, an electrode such as (meth) acrolein or acetone is used. Stripping tower for separating low boiling point impurities; Light boiling point material separating tower for separating low boiling point impurities such as acetic acid; Azeotropic dehydration tower for mainly separating water using an azeotropic solvent; High boiling point substance And a high-boiling-point substance separation tower for recovering purified (meth) acrylic acid from the tower top side. In the present invention, it is particularly preferable to use a high boiling point substance separation column. In the production of (meth) acrylic acid, when using a high-boiling point material separation tower, specifically, it is often used when recovering the final purified (meth) acrylic acid. Therefore, the inside of the column tends to be relatively hot during distillation. Since the (meth) acrylic acid is easily polymerized in the high-temperature distillation column, the production of the (meth) acrylic acid according to the present invention is particularly used in a scene where a high-boiling point substance separation column is used as the distillation column. The method is effective. Hereinafter, with reference to FIG. 2, an example of a high-boiling-point material separation column as a distillation column according to the present invention will be specifically described with reference to FIG. 2 regarding the method for producing (meth) acrylic acid of the present invention.

  The distillation column 22 used in the distillation step has a first supply port 12, a second supply port 13, and a reflux liquid supply port 27 for supplying the polymerization inhibitor-containing solution in order from the bottom in the height direction. ing. Further, when the distillation column is a high boiling point substance separation column, a discharge port 26 for distilling the purified (meth) acrylic acid is provided on the column top side from the reflux liquid supply port 27.

  The (meth) acrylic acid solution (liquid to be distilled) to be introduced into the distillation column 22 is not particularly limited. For example, it may be a crude (meth) acrylic acid solution obtained through the collection step according to the present invention, may be subjected to a crystallization step after the collection step, and A (meth) acrylic acid solution obtained by condensing a reaction gas containing (meth) acrylic acid may be used.

  In the distillation column, even if the polymerization inhibitor is sufficiently added to the feed liquid (crude (meth) acrylic acid solution), the stage for feeding the crude (meth) acrylic acid solution is slightly different depending on the operating conditions. It was found that (meth) acrylic acid is an environment in which (meth) acrylic acid is easily polymerized (that is, polymerizable region 16). This is because, in the case of the distillation column, the temperature inside the column increases as it approaches the bottom of the distillation column, just above the stage for supplying the (meth) acrylic acid solution. This is probably because acrylic acid is easily reacted. Therefore, in the present invention, a polymerization inhibitor-containing solution is introduced from both the first supply port 12 and the second supply port 13 existing in the distillation column 22 in order to suppress polymerization of (meth) acrylic acid in the polymerizable region 16. To do. As in the present invention, by introducing a solution containing a polymerization inhibitor from a plurality of inlets, it is possible to suppress the polymerization reaction in the polymerizable region 16.

  The method for introducing the liquid to be distilled into the distillation column 22 is not particularly limited. For example, the liquid to be distilled is introduced through a supply port existing between the bottom of the distillation column and the first supply port 12. It may be introduced from the first supply port 12 and / or the second supply port 13, or may be introduced through a supply port existing between the first supply port 12 and the second supply port 13.

  The distillation column 22 is not particularly limited as long as it is a column having the first supply port 12 and the second supply port 13 on the side surface of the distillation column 22. For example, a shelf provided with a plurality of trays in the column. Any of a column tower (tray tower); a packed tower filled with packing; a wet wall tower; a spray tower; and the like can be preferably used. In the present invention, it is preferable to use a plate column because of its high purification efficiency. Moreover, when using a packed tower as the distillation tower 22, the packing illustrated to the column of the collection tower 2 can be used for the packing packed to a packed tower.

  When a tray column is used as the distillation column 22, although depending on the scale of the apparatus, the second supply port 13 is preferably present at the top of the column separated from the first supply port 12 by one or more trays, It is more preferable that the distance is 5 or more, and it is more preferable that the distance is 7 or more. In addition, the distance between the first supply port 12 and the second supply port 13 is preferably 20 or less in terms of the number of trays, more preferably 17 or less, and even more preferably 15 or less. If the distance between the second supply port 13 and the first supply port 12 is closer than one stage, the position of the second supply port 13 may be lower than the position where the polymerizable region 16 exists. In some cases, the polymerization preventing effect due to the introduction of the polymerization inhibitor-containing solution from the second supply port 13 is not sufficiently exhibited. Moreover, since the distance of the 2nd supply port 13 and the polymeric area | region 16 will leave | separate if it exceeds 20 steps | paragraphs, the polymerization inhibitory effect by introduce | transducing a polymerization inhibitor containing solution may not fully be exhibited.

  The position of the second supply port 13 in the distillation column 22 is not particularly limited as long as it exists on the column top side of the first supply port 12. In the full length of the distillation column 22 when it is set as the end point, it is preferable to provide in the range of 25-90%, for example, More preferably, it is 25-80%, More preferably, it is 30-75%. It is preferable to set the position of the second supply port 13 within the above range because the polymerization preventing effect in the polymerizable region 16 is enhanced.

  Further, the position of the first supply port 12 in the distillation column 22 is provided in the range of 0% or more and less than 25% in the entire length of the distillation column 22 with the bottom of the distillation column 22 as the base point and the top of the column as the end point. It is preferably 0 to 15%, more preferably 0 to 5%. By making the position of the 1st supply port 12 in the said range, since the polymerization prevention effect of (meth) acrylic acid in a tower bottom liquid increases and the purification efficiency of (meth) acrylic acid by distillation operation improves, it is preferable. .

  The flow rate of the polymerization inhibitor-containing solution introduced from the first supply port 12 and the second supply port 13 is not particularly limited. For example, the flow rate of the polymerization inhibitor-containing solution introduced from the second supply port 13 is not limited. The flow rate is preferably 0.01 times or more, more preferably 0.5 times or more, and more preferably 2 times or more the flow rate of the polymerization inhibitor-containing solution introduced from the first supply port 12. More preferably. The flow rate of the polymerization inhibitor-containing solution introduced from the second supply port 13 is preferably 40 times or less, for example, relative to the flow rate of the polymerization inhibitor-containing solution introduced from the first supply port 12, More preferably, it is 20 times or less, More preferably, it is 10 times or less. When the flow rate of the polymerization inhibitor-containing solution introduced from the second supply port 13 is less than 0.01 times, the polymerization inhibitor amount in the polymerization inhibitor-containing solution is small, and the polymerization in the polymerizable region 16 in the distillation column is performed. This is not preferable because the prevention effect may not be sufficiently exhibited.

  According to the present invention, since the concentration of the polymerization inhibitor in the liquid to be distilled between the first supply port 12 and the second supply port 13 of the distillation column 22 can be controlled within a certain concentration range, the polymerization reaction in the polymerizable region 16 is performed. Can be suppressed. Specifically, the concentration of the polymerization inhibitor in the liquid to be distilled between the first supply port 12 and the second supply port 13 of the distillation column 22 is preferably 20 ppm or more, more preferably 25 ppm or more, and more preferably 30 ppm or more on a mass basis. Further preferred. The upper limit of the concentration of the polymerization inhibitor in the liquid to be distilled between the first supply port 12 and the second supply port 13 of the distillation column 22 is not particularly limited, but is preferably 600 ppm or less, for example, 550 ppm or less. Even if it is, the polymerization reaction prevention effect is exhibited and 500 ppm or less may be sufficient. By controlling the polymerization inhibitor concentration within the above range, the polymerization reaction in the polymerizable region 16 can be suppressed.

  The concentration of the polymerization inhibitor in the polymerization inhibitor-containing solution introduced from the second supply port 13 at the time of introduction of the distillation column is preferably 100 ppm or more, more preferably 120 ppm or more, and further preferably 150 ppm or more, on a mass basis. It is preferably 700 ppm or less, more preferably 500 ppm or less, still more preferably 400 ppm or less.

  Regarding the method for introducing the polymerization inhibitor-containing solution, the introduction method is not particularly limited as long as the polymerization inhibitor-containing solution is introduced from the first supply port 12 and the second supply port 13.

  In the present invention, as in the case of the collection tower 2, the polymerization inhibitor-containing solution is connected to the polymerization inhibitor-containing solution supply pipe 9 by branching to both the first supply port 12 and the second supply port 13. It is good to introduce into the distillation column 22 through. “Connected by branching to both the first supply port 12 and the second supply port 13” means that the pipe for supplying the polymerization inhibitor-containing solution has at least one branch point. That is, the end of the pipe (pipe) positioned downstream is connected to each of the first supply port 12 and the second supply port 13. Furthermore, the pipe for supplying the polymerization inhibitor-containing solution has one branch point, and the ends of the two pipes downstream from the branch point are the first supply port 12 and the second supply port 13. It is connected to each of. Thus, by branching the polymerization inhibitor-containing solution supply pipe 9 and introducing it from the first supply port 12 and the second supply port 13, the quality control becomes simple and the quality of (meth) acrylic acid is stabilized. Can be made.

  As the polymerization inhibitor-containing solution supply pipe 9, for example, a pipe for passing the polymerization inhibitor-containing solution from the same or different system process to the distillation column 22 shown in FIGS. , A supply pipe (supply pipe D) connected to the first supply port 12 and the second supply port 13; a tower bottom liquid supply pipe connected to the tower bottom liquid discharge port of the distillation column 22 shown in FIG. And the pipe through which the polymerization inhibitor-containing solution passes from the same or different process to the distillation column 22 join, and the pipe downstream from the joining point branches to form the first supply port 12 and Supply pipe (supply pipe E) connected to the second supply port 13; the bottom liquid supply pipe connected to the bottom liquid discharge port of the distillation column 22 shown in FIG. Examples thereof include a supply pipe (supply pipe F) connected to the supply port 12 and the second supply port 13.

  For example, as shown in FIG. 4D, the polymerization inhibitor-containing solution supply pipe 9 may have a junction 9a with another supply pipe (or “pipe”). The position is not particularly limited.

  Moreover, this invention introduce | transduces only the liquid to be distilled sent from an upstream into either one of the 1st supply port 12 or the 2nd supply port 13, and introduce | transduces the liquid obtained by another series into the other ( That is, the pipe for supplying the polymerization inhibitor-containing solution is connected to the distillation column 22 without branching). A more preferable supply method introduces only the liquid to be distilled sent from the upstream side to the first supply port 12, and introduces the polymerization inhibitor-containing solution obtained by the same or different process to the second supply port 13. It is a method to do.

  As the polymerization inhibitor used in the polymerization inhibitor-containing solution, the polymerization inhibitors exemplified above may be used as appropriate, and among them, at least selected from the group consisting of quinones, phenothiazines, copper salt compounds and manganese salt compounds. One type is preferably used.

  Also in this distillation step, the polymerization inhibitor-containing solution described above is particularly preferably a (meth) acrylic acid solution containing (meth) acrylic acid. The (meth) acrylic acid solution may be used as a solvent for dissolving the polymerization inhibitor. If it is a (meth) acrylic acid solution containing a polymerization inhibitor, it should be used as it is as a polymerization inhibitor-containing solution. Can do. By using a (meth) acrylic acid solution as a polymerization inhibitor-containing solution, it is possible to suppress a decrease in the concentration of the (meth) acrylic acid solution in the distillation tower, and the purity of the obtained (meth) acrylic acid is high. Can be maintained.

  The (meth) acrylic acid concentration in the (meth) acrylic acid solution (polymerization inhibitor-containing solution) used in the distillation step is preferably 30% by mass or more, more preferably 50% by mass or more, and still more preferably. Is 80% by mass or more, preferably less than 99% by mass, more preferably 97% by mass or less, and still more preferably 95% by mass or less. If the (meth) acrylic acid concentration is within the above range, when the solution is introduced from both the first supply port 12 and the second supply port 13, the concentration change of the (meth) acrylic acid solution in the distillation column is changed. Since it can be made small, it is preferable.

  As said (meth) acrylic acid solution, as long as it contains (meth) acrylic acid, the various solutions produced during manufacture can be used. Specifically, (i) a solution prepared by mixing (meth) acrylic acid of the product (after purification) with a solvent to a predetermined concentration, (ii) (meth) acrylic obtained in the production process of (meth) acrylic acid A solution containing an acid (for example, a tower bottom liquid extracted from the bottom of the distillation tower 22, a recovered liquid such as a solution obtained by subjecting the tower bottom liquid to a recovery step described later, a tower of the collection tower 2) (I) or (i) obtained in the production process of (meth) acrylic acid in a different system, (iii) tower bottom liquid (ie, crude (meth) acrylic acid solution) etc. extracted from the bottom liquid discharge port 10 A (meth) acrylic acid solution such as a (meth) acrylic acid-containing solution corresponding to (ii) can be used. In particular, when the residue generated during the production of (meth) acrylic acid is used as in the recovered liquid (ii), it is economical because (meth) acrylic acid in the solution can be recovered again. In addition, the (meth) acrylic acid solution mentioned above may be used by 1 type, and may mix 2 or more types.

  The operation conditions of the distillation column 22 are not limited, and may be determined as appropriate according to the concentration of the supplied (meth) acrylic acid solution and the purity of the target purified (meth) acrylic acid. For example, the top pressure (absolute pressure) of the distillation column 22 is preferably 20 to 400 hPa, more preferably 30 to 300 hPa, and still more preferably 30 to 200 hPa. When the column top pressure is too high, it is necessary to increase the column bottom temperature in order to recover (meth) acrylic acid. In this case, the denatured product increases due to heating, resulting in (meth) acrylic acid. There is a risk that the yield of the product will decrease. The top temperature of the distillation column 22 is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, preferably 85 ° C. or lower, more preferably 80 ° C. or lower.

  The distillation column 22 may be provided with a reboiler for adjusting the temperature in the column, a condenser for cooling or refluxing the vapor flowing out from the top of the column, a vacuum device, and the like as necessary.

  The (meth) acrylic acid purified by the distillation tower 22 may be used as a product as it is, or may be further purified by various purification methods such as crystallization. A part of the (meth) acrylic acid purified by the distillation column 22 may be introduced into the distillation column 22 from the reflux liquid supply port 27 as a reflux liquid by being cooled by the condenser 28. The reflux ratio is, for example, preferably 0.5 to 2, more preferably 0.7 to 1.7, and still more preferably 0.9 to 1.5. The reflux ratio of the distillation column 22 is defined by the flow rate of the reflux liquid per unit time / the flow rate of the distillate per unit time.

  A polymerization inhibitor may be added to the reflux liquid. As the polymerization inhibitor, the compounds exemplified in the polymerization inhibitor may be used. Of these, quinones and copper salt compounds are preferably used, and hydroquinone monomethyl ether and copper dialkyldithiocarbamate are particularly preferable. These polymerization inhibitors may be used alone or in combination.

  In the present invention, the type of polymerization inhibitor contained in the reflux liquid and the type of polymerization inhibitor contained in the polymerization inhibitor-containing solution may be the same or different, but different. It is desirable that Since the (meth) acrylic acid concentration in the reflux liquid tends to be high, the reflux liquid and the distillation column 22 are changed by changing the kind of the polymerization inhibitor and adding a polymerization inhibitor having a higher polymerization prevention effect to the reflux liquid. It is possible to further increase the effect of preventing polymerization inside. By using a combination of a plurality of different types of polymerization inhibitors, the polymerization prevention effect may be further improved (synergistic effect).

  In the present invention, the distillate may be subjected to azeotropic dehydration in order to remove water and low-boiling substances in the distillate before being introduced into the distillation step.

  In the azeotropic dehydration tower 19, dehydration distillation for separating mainly water (top) and (meth) acrylic acid (column bottom) from the (meth) acrylic acid aqueous solution is performed. Usually, water and (meth) acrylic are used. Since the acid has a low relative volatility, it is difficult to separate by a simple distillation method. Therefore, an aqueous (meth) acrylic acid solution is distilled using an azeotropic solvent, and a water-azeotropic solvent mixture is distilled from the top of the column. Thus, azeotropic distillation for separating (meth) acrylic acid is performed. The separated (meth) acrylic acid is extracted from the bottom of the column. Moreover, the mixture of the distilled water and the azeotropic solvent is separated by the oil / water separator 20 and the azeotropic solvent may be reused.

  The azeotropic solvent is desirably poorly water-soluble from the viewpoint of enhancing the ease of separation and recovery. As such an azeotropic solvent, an azeotrope containing at least one selected from the group consisting of C6-C8 aliphatic hydrocarbons such as heptane, and C6-C8 aromatic hydrocarbons such as toluene, in particular. A solvent is recommended. Preferred examples of the azeotropic solvent include toluene, xylene, hexane, heptane, cyclohexane and the like, and one kind or a mixture of two or more kinds may be used, and they may be appropriately combined depending on the purpose.

  As the azeotropic dehydration tower 19, a known apparatus such as a plate tower or a packed tower can be used as long as it can perform dehydration distillation. Further, the configuration of the azeotropic dehydration tower 19 is not particularly limited, but those having 10 or more theoretical plates are preferable.

  Further, it is recommended to supply the polymerization inhibitor via an optional supply means (not shown) as required. Even in such a case, the method of the present invention can be suitably employed.

  Any polymerization inhibitor may be used as long as it has an effect of preventing the polymerization of (meth) acrylic acid. Hydroquinone, methoquinone, phenothiazine, copper dibutyldithiocarbamate, manganese acetate, 4-hydroxy-2,2,6,6-tetramethyl Examples are polymerization inhibitors such as piperidinooxyl, 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine, 4-hydroxy-2,2,6,6-tetramethylpiperidine, and nitrosophenol. . The amount of these polymerization inhibitors used, the combination of polymerization inhibitors, and the like are appropriately adjusted according to the operating conditions.

  The (meth) acrylic acid solution obtained by the azeotropic dehydration step is then introduced into the distillation column 22. The (meth) acrylic acid solution obtained by the azeotropic dehydration step can be temporarily stored in the tank 21 before being introduced into the distillation column 22.

[Step of recovering (meth) acrylic acid in the bottom liquid extracted from the distillation column]
On the other hand, the column bottom liquid extracted from the distillation column 22 may be discharged out of the system as a waste liquid as it is, but may be supplied to a step of recovering useful components contained in the residue. The recovery step is not particularly limited, and examples thereof include a distillation step for recovering (meth) acrylic acid remaining in the residue, a step for decomposing the Michael adduct and recovering it as (meth) acrylic acid, and the like.

  A decomposition process will not be specifically limited if a Michael adduct can be decomposed | disassembled and it can collect | recover as (meth) acrylic acid, Any conventionally well-known method and apparatus can be employ | adopted. For example, as an apparatus that can be used in the decomposition process, a (meth) acrylic acid recovery tower 23 provided with a thermal decomposition tank 25 in a thin film evaporator 24, or a distillation apparatus capable of distilling decomposition products simultaneously with decomposition of Michael adducts. Etc. In addition, what is necessary is just to supply the (meth) acrylic acid obtained at the decomposition | disassembly process to the distillation column 22 again as the (meth) acrylic acid solution mentioned above.

  Moreover, manufacture of (meth) acrylic acid can also be implemented combining the collection process and distillation process of this invention which were mentioned above. That is, after the (meth) acrylic acid-containing gas is generated from the (meth) acrylic acid production raw material, the first of the collection tower 2 is used using the collection tower 2 including the first supply port 12 and the second supply port 13. By introducing a polymerization inhibitor-containing solution from the supply port 12 and the second supply port 13 to collect (meth) acrylic acid to obtain a crude (meth) acrylic acid solution, this crude (meth) acrylic acid is obtained. In the distillation step for obtaining (meth) acrylic acid from the solution, the first supply port 12 and the second supply port 13 of the distillation column 22 are introduced into the distillation column 22 having the first supply port 12 and the second supply port 13. To (meth) acrylic acid by distillation while introducing a polymerization inhibitor-containing solution.

<(Meth) acrylic acid>
According to the present invention, as described above, even if the amount of the polymerization inhibitor used is reduced, it is possible to suppress the polymerization reaction in the collection tower or distillation tower. A small amount of high purity (meth) acrylic acid is obtained. If (meth) acrylic acid with a small amount of impurities such as a polymerization inhibitor produced according to the present invention is used as a raw material when producing a (meth) acrylic acid (co) polymer such as a hydrophilic resin, etc. Since the polymerization reaction is less likely to be inhibited or delayed, various polymer products can be stably produced.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention. In the following, “part” means “part by mass” and “%” means “mass%” unless otherwise specified.

<When using a collection tower having a second supply port>
Reference example 1
Below, it examined using the process shown in FIG.
Acrylic acid-containing gas obtained by catalytic vapor phase oxidation (composition: acrylic acid 7.1 vol%, acetic acid 0.3 vol%, water 11.6 vol%, others (nitrogen, oxygen, propylene, propane, carbon dioxide 81% by volume) was introduced from the gas supply port 11 of the collection tower at 15.2 Nm ³ / min.

As the collection tower 2, a packed tower having a gas outlet 15 at the top of the collection tower and a bottom liquid outlet 10 at the bottom of the tower was used. In the packed tower, six support plates (backing support) for placing the packing material are provided, and the support plates are hereinafter referred to as the first section, the second section, They are called Section 3, Section 4, Section 5, Section 6. CMR (Cascade Mini Ring (registered trademark) 3P manufactured by Matsui Machine Co., Ltd.), which is an irregular packing, was used as the packing.
A gas supply port 11 for supplying the gas discharged from the reactor exists between the column bottom liquid discharge port 10 and the lowermost stage (Section 6) on the side surface of the collection tower 2, and the collection solvent The collection solvent introduction port 14 for introducing gas is present between the uppermost stage (first section) and the gas discharge port 15 at the top of the tower.
Furthermore, the supply port for introducing the polymerization inhibitor-containing solution (that is, the acrylic acid solution containing the polymerization inhibitor) is between the fourth and fifth nodes from the top of the column (corresponding to the second supply port 13). ) And between the fifth and sixth nodes (corresponding to the first supply port 12).
Specifically, the second supply port 13 is present at a position that is 50% of the total length of the collection tower, and the first supply port 12 is present at a position that is 32% of the total length of the collection tower when the tower bottom is used as a reference. To do.
During the operation of the collection tower, the acrylic acid solution was extracted from the bottom of the collection tower 2 through the bottom liquid discharge port 10.
Acrylic acid was collected by controlling the tower top temperature of the collection tower 2 to 68.5 ° C. and the tower top pressure to 1120 hPa abs (absolute pressure). The temperature control of the collection tower 2 was performed by cooling a part of the tower bottom liquid and circulating it.

While supplying acrylic acid-containing gas, the collection solvent was introduced at 117 kg / h from the collection solvent introduction port 14 of the collection tower 2. In the collection tower, the collection solvent and the acrylic acid-containing gas were brought into gas-liquid contact so that the collection solvent absorbed the acrylic acid-containing gas. The crude acrylic acid solution was extracted from the tower bottom liquid outlet 10 at 358 kg / h. The composition of the crude acrylic acid solution was 94.5% acrylic acid, 1.9% acetic acid, 2.4% water, and 1.2% other components.
The collection solvent is prepared by adding water and hydroquinone as a polymerization inhibitor to a part of the effluent generated from the selective cooling tower 8 and the distillation tower vacuum generator (not shown). The composition in the collection solvent is 1.5% acrylic acid and 2.3% acetic acid, and the polymerization inhibitor hydroquinone has a concentration of 1,500 ppm with respect to acrylic acid in the acrylic acid-containing gas. It has been added.

  The crude acrylic acid solution withdrawn from the collection tower 2 was then introduced into the crystallizer 3 and subjected to crystallization operation to obtain acrylic acid crystals (product) at 201 kg / h. The purity of the acrylic acid of the product was 99.9%.

  The crystallization residue was introduced into the storage tank 4 and then supplied to the high boiling separation tower 5 at 160 kg / h. A liquid containing acrylic acid was recovered at 152 kg / h from the top of the high boiling separation tower 5 (reflux ratio was 0.2). The composition in the recovered liquid is 88.6% acrylic acid, 4.4% acetic acid, 5.9% water, and 1.1% other components. The obtained recovered liquid was once introduced into the storage tank 7. In addition, the bottom liquid extracted from the bottom of the high boiling separation tower 5 was supplied to the acrylic acid recovery tower 6.

The acrylic acid-containing solution taken out from the top of the acrylic acid recovery tower 6 was introduced into the storage tank 4 for storing the crystallization residue, and the liquid taken out from the bottom of the acrylic acid recovery tower 6 was disposed as waste oil.
A condenser (not shown) is connected to the high boiling separation column 5, and an acrylic acid solution containing a polymerization inhibitor (dibutyldithiocarbamate copper salt, hydroquinone monomethyl ether, phenothiazine, manganese acetate) is introduced into the condenser. Is done. The addition amount of the polymerization inhibitor is adjusted so that the total concentration of these polymerization inhibitors in the reflux and distillate of the high boiling separation column 5 is 380 ppm. The entire amount of the recovered liquid obtained from the top of the high boiling separation tower 5 and stored in the storage tank 7 was supplied to the collection tower 2 through the first supply port 12. A recovery liquid flow pipe connected to the first supply port 12 circulates and recovers a part of the crude acrylic acid solution from a flow pipe through which the crude acrylic acid solution extracted from the collection tower 2 flows. It joins with the supply pipe supplied to the collection tower 2 from the first supply port.

It was operated for 1 month under these operating conditions. After the operation for one month, the formation of polymer was not confirmed even when the section (polymerizable region) in the fifth section from the top of the collection tower 2 was inspected. Further, the liquid flowing down from the packing placed in Section 5 at this time was extracted, and the concentration of hydroquinone and the concentration of the polymerization inhibitor other than hydroquinone in the liquid were measured. The results are shown in Table 1.
In Table 1, the state of the polymerizable region was evaluated at the following stages.
◎: No polymer is produced. ○: Small amount of polymer is produced. △: About 5L of polymer is produced.

Reference Example 2, Comparative Example 1
Acrylic acid was produced under the same conditions as in Reference Example 1 except that the concentration of hydroquinone added to the collection solvent was reduced to the amount shown in Table 1. One month later, the inside of the collection tower was inspected in the same manner as in Reference Example 1.

Example 1
Of the recovered liquid 152 kg / h supplied from the storage tank 7 through the first supply port 12, 5 kg / h was introduced into the collection tower 2 from the second supply port 13. Acrylic acid was produced under the same conditions as in Reference Example 1 except that the concentration of hydroquinone added to the collection solvent was reduced to the amount shown in Table 1. One month later, the inside of the collection tower was inspected in the same manner as in Reference Example 1.

Examples 2-5
Except for changing the flow rate of the acrylic acid solution introduced into the collection tower 2 from the second supply port 13 and the concentration of hydroquinone added to the collection solvent to the amounts described in Table 1, they are the same as in Example 1. Acrylic acid was produced under the conditions. One month later, the inside of the collection tower was inspected in the same manner as in Example 1. The results are shown in Table 1.

As shown in Reference Example 1, when a solution containing a polymerization inhibitor is not introduced from the second supply port 13, if the amount of hydroquinone in the collection solvent is 1500 ppm, no polymer is produced even after one month of operation. . On the other hand, when a solution containing a polymerization inhibitor is introduced from the second supply port 13, even if the amount of hydroquinone in the collection solvent is reduced to 1200 ppm, the same degree of polymerization suppression effect as in Reference Example 1 is exhibited. (Example 1). It can also be seen that when the amount of solution supplied from the second supply port 13 is increased, the polymerization inhibitory effect similar to that of Reference Example 1 is exhibited even if the amount of hydroquinone in the collection solvent is further reduced (Examples). 3, Example 5).
Also, from the results of Example 2 and Example 4, even if the amount of hydroquinone in the collection solvent is reduced, if the polymerization inhibitor-containing solution is introduced from the second supply port 13, the solution is supplied from the second supply port 13. It can be seen that the same degree of polymerization suppression effect as that of Reference Example 2 which is not introduced is exhibited.
In addition, when not introduce | transducing a polymerization inhibitor containing solution from the 2nd supply port 13, when the quantity of the hydroquinone in a collection solvent is reduced to 1000 ppm, it turns out that a polymer produces | generates abundantly (Comparative Example 1).

<When using a distillation column having a second supply port>
Reference example 3
Below, it examined using the process shown in FIG.
Acrylic acid-containing gas obtained by catalytic gas phase oxidation method (composition: acrylic acid 7.1 vol%, acetic acid 0.3 vol%, water 14.7 vol%, others (nitrogen, oxygen, propylene, propane, carbon dioxide Aldehyde, etc.) was introduced into the collection tower 2 at 338 Nm ³ / min.

As the packing for the collection tower 2, CMR (Cascade Mini Ring (registered trademark) 3P, manufactured by Matsui Machine Co., Ltd.), which is an irregular packing, was used. Further, acrylic acid was collected by controlling the tower top temperature of this collection tower 2 to 62 ° C. and the tower top pressure to 1100 hPa abs (absolute pressure).
From the top of the collection tower 2, the collection solvent was supplied at 2720 kg / h. The collection solvent (composition: acrylic acid 1.5%, acetic acid 5.4%) is a part of the separated water generated from the azeotropic dehydration tower and part of the effluent generated from the distillation tower vacuum generator (not shown). It is prepared by adding water and hydroquinone as a polymerization inhibitor.
In addition, a part of the exhaust gas at the top of the tower was circulated to the oxidation reactor, and the rest was discharged out of the system as waste gas. From the tower bottom of the collection tower 2, a tower bottom liquid (crude acrylic acid solution) was obtained at 8050 kg / h. The tower bottom liquid extracted from the collection tower 2 is further guided to the stripping tower 17 to remove aldehydes such as acrolein and acetone, and an acrylic acid-containing aqueous solution (composition: acrylic acid 70% from the tower bottom of the stripping tower 17). Acetic acid 3.4%, maleic acid 0.3%). The obtained acrylic acid-containing aqueous solution was then introduced into the storage tank 18 and cooled to 40 ° C. by a cooler attached to the storage tank 18.

  Next, the cooled acrylic acid-containing aqueous solution was supplied to the middle stage of the azeotropic dehydration tower 19 provided with 50 stages of non-weired perforated plates. The top pressure of the azeotropic dehydration tower 19 is controlled to 190 hPa abs (absolute pressure) and a reflux ratio of 1.0 (flow rate of reflux liquid per unit time / flow rate of distillate per unit time), using toluene. An azeotropic separation operation was performed. The liquid at the top of the azeotropic dehydration tower 19 was introduced to the oil / water separator 20 together with the waste water of the steam ejector, which is a vacuum generator, and separated into an organic phase and an aqueous phase. Dibutyldithiocarbamic acid copper salt and hydroquinone monomethyl ether were used as polymerization inhibitors for the azeotropic dehydration tower 19. These polymerization inhibitors were put into the tower by dissolving them in a reflux solution in advance. The column bottom liquid extracted from the azeotropic dehydration column 19 was then introduced into a tank and cooled to 40 ° C. by a cooler attached to the tank.

  Next, the cooled solution was supplied to the bottom (45 stages, that is, the first supply port) of the distillation tower 22 (high boiling point material separation tower) equipped with a 45-stage non-weir perforated plate. Acrylic acid was distilled by controlling the pressure at the top of the column to 45 hPa abs (absolute pressure) and a reflux ratio of 1.4. Dibutyldithiocarbamic acid copper salt and hydroquinone monomethyl ether were used as the polymerization inhibitor for the distillation column 22. The amounts of these polymerization inhibitors were appropriately adjusted so that the concentration in the reflux liquid was 200 ppm. Acrylic acid was obtained at 5120 kg / h from the top of the distillation column 22. Further, a column bottom liquid (composition: acrylic acid oligomer 31%, maleic acid 5%) was extracted from the column bottom of the distillation column 22.

  The tower bottom liquid extracted from the distillation tower 22 was supplied to the middle stage of the acrylic acid recovery tower 23 equipped with a 10-stage non-weir perforated plate. The acrylic acid recovery tower 23 includes a thin film evaporator 24 and a thermal decomposition tank 25 at the bottom of the tower. The acrylic acid recovery tower 23 was operated by controlling the tower top pressure to 45 hPa abs (absolute pressure) and a reflux ratio of 0.5. 400 kg / h of acrylic acid containing 0.5% maleic acid was obtained from the top of the acrylic acid recovery tower 23 and introduced into the storage tank 21. In the storage tank 21, the bottom liquid extracted from the bottom of the azeotropic dehydration tower 19 is mixed, and this solution is mixed with the distillation tower 22 from the bottom of the distillation tower 22 (that is, the first supply port 12). Introduced in.

  On the other hand, the bottom liquid of the acrylic acid recovery tower 23 was introduced into a pyrolysis tank 25 equipped with a thin film evaporator 24, and pyrolyzed at a temperature of 150 ° C. and a residence time of 40 hours in the pyrolysis tank 25. An oligomer such as an acrylic acid dimer is thermally decomposed in the thermal decomposition tank 25, and the generated acrylic acid is returned to the acrylic acid recovery tower 23 through the thin film evaporator 24 and finally purified in the distillation tower 22. Dibutyldithiocarbamic acid copper salt, hydroquinone monomethyl ether, phenothiazine, and manganese acetate were used as the polymerization inhibitor for the acrylic acid recovery tower 23. These polymerization inhibitors were previously dissolved in acrylic acid, and charged into a condenser (not shown) by spraying. Waste oil (composition: acrylic acid 5.5%, acrylic acid oligomer (acrylic acid dimer and trimer) 39%) was discarded from the pyrolysis tank 25 at 170 kg / h.

When operating for one month under these operating conditions, the pressure loss in the distillation column increased. In addition, after operating for about 3 months under these operating conditions and after about 3 months of operation, the system was stopped and the internal inspection was performed. As a result, polymer formation was observed on the 40-45 stage porous plate of the distillation column 22. It was. The results are shown in Table 2. In Table 2, the fluid introduction amount (kg / h) from the first supply port 12 means the amount of fluid introduced from the acrylic acid recovery tower 23 to the storage tank 21.
In Table 2, the state of the polymerizable region was evaluated at the following stages.
◎: No polymer is produced. ○: A small amount of polymer is produced on the 40-45 plate perforated plate of the distillation column. Δ: About 5 L of polymer is produced on the 40-45 plate perforated plate of the distillation column. X: 40-45 plate of the distilling column. About 100L or more of polymer is produced on a perforated plate

Example 6
Of the 400 kg / h recovered from the top of the acrylic acid recovery tower 23, 100 kg / h is divided into the middle stage of the distillation tower 22 (35 stages, 35 stages, That is, it was introduced into the distillation column from the second supply port). After about 3 months of operation, the system was stopped and the internal inspection was performed. As a result, no polymer was observed in the distillation column.

Example 7 to Example 10
Except for changing the total amount of the polymerization inhibitor in the reflux liquid in the distillation column and the amount of the reflux liquid supplied to the middle stage of the distillation tower (35 stages, that is, the second supply port) to the amount described in Table 2. Acrylic acid was produced under the same conditions as in Example 6. The evaluation of the distillation tower was performed in the same manner as in Example 6.

  As shown in Reference Example 3, when a solution containing a polymerization inhibitor is not introduced from the second supply port 13, a large amount of polymer is generated in the tower when operated for 3 months. On the other hand, when a solution containing a polymerization inhibitor was introduced from the second supply port 13, no polymer was produced even when the total amount of the polymerization inhibitor was the same as in Reference Example 3 (Example 6). It can also be seen that when the amount of solution supplied from the second supply port 13 is increased, the polymerization inhibitory effect is exhibited even if the total amount of the polymerization inhibitor is further reduced (Examples 7 to 10).

DESCRIPTION OF SYMBOLS 1 Reactor 2 Collection tower 3 Crystallizer 4 Storage tank 5 High boiling-point separation tower 6 (Meth) acrylic acid recovery tower 7 Storage tank 8 Selective cooling tower 9 Polymerization inhibitor containing solution supply pipe 9a Junction point 10 Column bottom liquid discharge Exit 11 Gas supply port 12 First supply port 13 Second supply port 14 Collection solvent introduction port 15 Gas discharge port 16 Polymerization region 17 Stripping tower 18 Storage tank 19 Azeotropic dehydration tower 20 Oil-water separator 21 Storage tank 22 Distillation tower 23 (meth) acrylic acid recovery tower 24 Thin layer evaporator 25 Pyrolysis tank 26 Discharge port 27 Reflux supply port 28 Condenser

Claims (11)

A method for producing (meth) acrylic acid, in which a (meth) acrylic acid-containing gas is obtained from a (meth) acrylic acid production raw material, and a (meth) acrylic acid-containing gas, Including a collection step of obtaining a (meth) acrylic acid solution,
In the collection tower used in the collection step, a gas supply port for supplying a (meth) acrylic acid-containing gas, a first supply port and a second supply port for introducing a polymerization inhibitor-containing solution, and There is a collection solvent inlet for introducing the collection solvent in order from the bottom in the height direction,
In the said collection process, the polymerization inhibitor containing solution is introduce | transduced from both the said 1st supply port and the said 2nd supply port, The manufacturing method of the (meth) acrylic acid characterized by the above-mentioned.   2. The (meta) according to claim 1, wherein the collection tower is a packed tower, and the second supply port is present on the tower top side separated from the first supply port by a theoretical plate number within 0.5 to 10 plates. A method for producing acrylic acid.   The (meth) acrylic acid according to claim 1 or 2, wherein the polymerization inhibitor-containing solution is introduced from a polymerization inhibitor-containing solution supply pipe that branches and connects to the first supply port and the second supply port. Production method. The polymerization inhibitor-containing solution is a solution containing (meth) acrylic acid, and the (meth) acrylic acid solution is
(I) a solution prepared by mixing (meth) acrylic acid of a product (after purification) with a solvent to a predetermined concentration;
(Ii) a solution containing (meth) acrylic acid obtained in the production process of (meth) acrylic acid, and (iii) the above (i) or (ii) obtained in a production process of (meth) acrylic acid of another system (Meth) acrylic acid-containing solution corresponding to
The manufacturing method of the (meth) acrylic acid of any one of Claims 1-3 containing at least 1 selected from these.   The (meth) acrylic acid according to any one of claims 1 to 4, wherein the polymerization inhibitor-containing solution contains (meth) acrylic acid having a (meth) acrylic acid concentration of 30% by mass or more and less than 99% by mass. Production method. A method for producing (meth) acrylic acid, comprising a distillation step of purifying a (meth) acrylic acid solution by distillation operation,
In the distillation column used in the distillation step, a first supply port and a second supply port for introducing a polymerization inhibitor-containing solution, and a reflux liquid supply port for introducing a reflux solution are provided in the height direction from the bottom of the column. And the distillation column is a high-boiling-point substance separation column having a discharge port for distilling purified (meth) acrylic acid on the column top side from the reflux liquid supply port,
In the said distillation process, the polymerization inhibitor containing solution is introduce | transduced from both the said 1st supply port and the said 2nd supply port, The manufacturing method of the (meth) acrylic acid characterized by the above-mentioned.   The method for producing (meth) acrylic acid according to claim 6, wherein the polymerization inhibitor-containing solution is introduced from a polymerization inhibitor-containing solution supply pipe branched and connected to the first supply port and the second supply port. . The (meta) according to claim 6 or 7 , wherein the distillation column is a tray column, and the second supply port is present at the top of the column separated from the first supply port by the number of trays within 1 to 20 stages. A method for producing acrylic acid. The polymerization inhibitor-containing solution is a solution containing (meth) acrylic acid, and the (meth) acrylic acid solution is
(I) a solution prepared by mixing (meth) acrylic acid of a product (after purification) with a solvent to a predetermined concentration;
(Ii) a solution containing (meth) acrylic acid obtained in the production process of (meth) acrylic acid, and (iii) the above (i) or (ii) obtained in a production process of (meth) acrylic acid of another system The method for producing (meth) acrylic acid according to any one of claims 6 to 8 , comprising at least one selected from a solution containing (meth) acrylic acid corresponding to The (meth) acrylic acid according to any one of claims 6 to 9 , wherein the polymerization inhibitor-containing solution contains (meth) acrylic acid having a (meth) acrylic acid concentration of 30% by mass or more and less than 99% by mass. Production method. The collection solvent and the reflux liquid contain a polymerization inhibitor,
The (meth) acrylic acid according to any one of claims 1 to 10 , wherein a polymerization inhibitor contained in the collection solvent or the reflux liquid is different from a polymerization inhibitor contained in the polymerization inhibitor-containing solution. Manufacturing method.

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