JP5368673B2 - Method for producing (meth) acrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining a solution containing (meth)acrylic acid in high concentration in high yield by suppressing the formation of a Michael addition product. <P>SOLUTION: The method for producing the (meth)acrylic acid involves a collecting step for collecting a (meth)acrylic acid-containing gas obtained by a catalytic vapor-phase oxidation method by an absorption column by bringing the gas into contact with a collecting solvent. The crude (meth)acrylic acid solution is extracted from an extraction port positioned between a feed position of the (meth)acrylic acid-containing gas and a feed position of the collecting solvent in the collecting step, and is fed to the following step. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a method for producing (meth) acrylic acid. In the present invention, “(meth) acrylic acid” means acrylic acid or methacrylic 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. For example, acrylic acid is industrially produced by catalytic vapor phase oxidation of propylene and / or acrolein. Patent Documents 1 to 4 collect acrylic acid gas obtained by the catalytic vapor phase oxidation method. A method of obtaining purified acrylic acid through a distillation and crystallization process after absorption in a solvent to obtain an acrylic acid-containing solution is disclosed, and Patent Documents 5 to 7 disclose, directly from an acrylic acid-containing gas by fractional condensation. A method for obtaining crude acrylic acid is disclosed.

In these production methods, various improvements are made to efficiently produce acrylic acid. In particular, in the technology employing solvent collection, in order to obtain purer acrylic acid, a method for adding a polymerization inhibitor used in the separation / purification process (see Patent Document 1) and the collection rate of acrylic acid are set. A method of enhancing the acrylic acid (see Patent Document 2), a method of simply purifying acrylic acid using a high-concentration acrylic acid-containing solution (see Patent Document 3) has been proposed. A method for efficiently producing acrylic acid in a catalytic gas phase oxidation reaction has been proposed.
Special table 2001-520213 gazette JP 2004-359614 A JP 2004-359615 A JP-T-2005-511776 JP 2001-516737 A Special Table 2002-539104 Special table 2002-509903 gazette

  The above method exhibits a certain effect for improving the production efficiency of acrylic acid, but there is room for further improvement when solvent collection is employed. In particular, acrylic acid is a substance that is easily polymerized, and Michael adducts such as dimers, trimers, and oligomers are easily generated by the reaction between acrylic acids. Such a by-product not only lowers the yield of acrylic acid, but also increases the viscosity of the acrylic acid-containing solution, clogs the piping in the production apparatus, and also reduces production operability.

  In addition, since the reaction which a Michael adduct produces | generates from acrylic acid is a reversible reaction, the decomposition | disassembly process of a Michael adduct is provided as a part of an acrylic acid manufacturing process, and the method of collect | recovering as acrylic acid is also proposed. However, the installation of a new process requires further capital investment and results in an increase in the production cost of acrylic acid. Moreover, even if the decomposition step is provided, it is difficult to completely decompose the Michael adduct, and it is difficult to prevent the loss of acrylic acid.

  In addition, by-products that are simultaneously generated during the synthesis of (meth) acrylic acid include those having boiling points that are equal to or higher than (meth) acrylic acid. Such high-boiling components complicate the separation and purification process. In addition, it has been difficult to remove completely.

  The present invention has been made by paying attention to the situation as described above, and the object thereof is a (meth) acrylic acid-containing solution having a low (by-product) content and a high (meth) acrylic acid concentration as described above. It is to provide a method of obtaining.

  In view of the above problems, the present inventors have reduced the amount of Michael adduct by-produced during the production of (meth) acrylic acid for the purpose of providing a more efficient method for producing (meth) acrylic acid. As a result, the inventors have reached the invention method shown below.

  That is, the method for producing (meth) acrylic acid of the present invention that has solved the above-mentioned problem is that a (meth) acrylic acid-containing gas obtained by a contact gas phase oxidation method is brought into contact with a collection solvent in an absorption tower. Including a collection step of collecting as a crude (meth) acrylic acid solution, and in the collection step, from above the supply position of the (meth) acrylic acid-containing gas and from below the supply position of the collection solvent. The crude (meth) acrylic acid solution is extracted and supplied to the next step.

  Usually, when performing solvent collection, (meth) acrylic acid absorbed in the collection solvent in the absorption tower is accumulated at the bottom of the absorption tower as a (meth) acrylic acid solution, and is extracted as the bottom liquid. The liquid is sent to the next process. Therefore, the bottom of the absorption tower contains the above-mentioned high-boiling components and by-products together with the target product (meth) acrylic acid, and these components are extracted from the bottom of the absorption tower. This was one of the causes for reducing the (meth) acrylic acid concentration in the bottom liquid.

  Therefore, the present inventors have repeatedly studied, and the crude (meth) acrylic acid solution generated in the absorption tower is placed above the (meth) acrylic acid gas supply position and below the collection solvent supply position from the side of the absorption tower. It was found that the amount of by-products such as Michael adducts can be remarkably reduced if it is extracted as a stream and supplied to the next step, thereby completing the method of the present invention.

  That is, a component having a higher boiling point than (meth) acrylic acid contained in the (meth) acrylic acid-containing gas is condensed or absorbed by the collection solvent at a relatively low position of the absorption tower, and the bottom of the absorption tower To flow down. On the other hand, gaseous (meth) acrylic acid rises in the absorption tower and is absorbed by the collection solvent at a position higher than the position where the high boiling point component is absorbed by the collection solvent in the absorption tower. Therefore, by extracting the (meth) acrylic acid solution as a side stream from the absorption tower, a (meth) acrylic acid solution having a high (meth) acrylic acid concentration with a low content of Michael adducts and high-boiling components can be obtained. It is.

  In the said manufacturing method, it is preferable that the (meth) acrylic acid density | concentration in the said (meth) acrylic acid solution extracted from an absorption tower is 80 mass% or more. The next step of supplying the crude (meth) acrylic acid solution is a step of separating and purifying (meth) acrylic acid from the crude (meth) acrylic acid solution obtained in the collecting step. This is a preferred embodiment. Further, the separation and purification step preferably includes a crystallization step and / or a distillation step. It is recommended to use water as the collecting solvent.

  According to the production method of the present invention, since a (meth) acrylic acid solution in which the content of high-boiling components and solids is suppressed to a low level is obtained, the process following the collection process can be performed efficiently. Moreover, since the production amount of the Michael adduct is also reduced, (meth) acrylic acid produced in the reaction step can be recovered with a higher yield. Therefore, if the manufacturing method of this invention is employ | adopted, the process of processing by-products, such as a high boiling point component and a Michael adduct, can be simplified, for example in a refinement | purification process.

  The method for producing (meth) acrylic acid according to the present invention is a method in which a (meth) acrylic acid-containing gas obtained by a contact gas phase oxidation method is brought into contact with a collection solvent in an absorption tower to obtain a crude (meth) acrylic acid solution. And collecting the crude (meth) acrylic acid solution from the extraction port located between the supply position of the (meth) acrylic acid-containing gas and the supply position of the collection solvent. It is characterized in that it is supplied to the next process.

  The reason why a high-concentration (meth) acrylic acid solution can be obtained by the method of the present invention is as described above, but the present inventors further inevitably performed the method of the present invention at the time of producing (meth) acrylic acid. It has been found that it is also effective in reducing the loss of (meth) acrylic acid resulting from the production of the Michael adduct that is produced.

  That is, in the conventional method of extracting the (meth) acrylic acid-containing solution from the bottom of the absorption tower, the Michael adduct is considered to be generated and increased mainly while staying at the bottom of the absorption tower. Yes. Therefore, if the (meth) acrylic acid solution is extracted as a side stream of the absorption tower, the amount of (meth) acrylic acid extracted from the bottom of the absorption tower is reduced, so that the amount of Michael adduct can be reduced.

  Moreover, if the crude (meth) acrylic acid solution is withdrawn as a side stream of the absorption tower as in the present invention method, the amount of the bottom liquid withdrawn per unit time is reduced, and the residence time of the bottom liquid in the absorption tower is become longer. However, since the production of the Michael adduct is an equilibrium reaction, the production rate of the Michael adduct is high in the initial stage of the residence of the bottom liquid, but the production rate decreases as the Michael adduct increases. Therefore, even if the residence time of the column bottom liquid becomes long, the amount decreases in terms of the amount of Michael adduct produced per unit time. The reason why the loss of (meth) acrylic acid can be reduced by adopting the present invention is considered to be due to the above reason.

Below, the manufacturing method of the (meth) acrylic acid of this invention is demonstrated.
[Synthesis of (meth) acrylic acid]
First, a method for synthesizing (meth) acrylic acid according to the present invention will be described.

  As described above, in the production method of the present invention, the (meth) acrylic acid-containing gas generated in the reaction step is absorbed by the collection solvent by the absorption tower, and then the supply position and the capture position of the (meth) acrylic acid-containing gas are collected. Since the crude (meth) acrylic acid solution is extracted as a side stream of the absorption tower from the extraction port located between the supply position of the solvent collection and supplied to the next step, the other steps are The method is not limited and a conventionally known method can be adopted. That is, (meth) acrylic acid may be synthesized by a conventionally known catalytic gas phase oxidation method. For example, when synthesizing acrylic acid, a raw material gas is prepared by mixing an acrylic acid raw material such as propylene and / or acrolein, a molecular oxygen-containing gas such as air, and a dilution gas. Next, when the raw material gas is supplied to a reactor filled with a catalytic gas phase oxidation catalyst and a catalytic gas phase oxidation reaction is performed, an acrylic acid-containing gas can be obtained. In the case of synthesizing methacrylic acid, isobutylene and / or t-butyl alcohol or the like is used as a raw material, a raw material gas is prepared in the same manner as in the case of acrylic acid synthesis, and a catalytic gas phase oxidation reaction is performed.

  The conditions for the catalytic gas phase oxidation reaction are not particularly limited, and conventionally known conditions may be employed. In addition, you may use the recycle gas produced | generated in the (meth) acrylic acid absorption tower mentioned later for the said raw material gas. The reactor for performing the catalytic gas phase oxidation reaction is not particularly limited, but a multitubular reactor is preferably used in terms of excellent reaction efficiency. Further, the catalytic gas phase oxidation reaction may be an embodiment in which a two-stage reaction is performed in a single reactor or an embodiment in which two different reactors are connected in series.

[Collection process]
Next, the collection process according to the present invention will be described. As described above, in the collection step, the (meth) acrylic acid-containing gas obtained by the contact gas phase oxidation method is brought into contact with the collection solvent in the absorption tower and collected as a crude (meth) acrylic acid solution. It is a process.

  In the present invention, the (meth) acryl-containing gas is introduced from the bottom of the absorption tower, and the collection solvent for absorbing the (meth) acrylic acid gas is introduced from the top of the absorption tower. The (meth) acrylic acid-containing gas introduced into the absorption tower is absorbed by the collection solvent while rising in the tower, and a crude (meth) acrylic acid solution is generated. In the present invention, in the process in which the crude (meth) acrylic acid solution descends to the bottom of the absorption tower, the crude (meth) acrylic acid solution is roughly removed from the extraction port located between the (meth) acrylic acid-containing gas supply position and the collection solvent supply position. The (meth) acrylic acid solution is withdrawn as a side stream of the absorption tower.

  Previously, Michael adducts that reduced the yield of (meth) acrylic acid and deteriorated the operability of (meth) acrylic acid production, and were the cause of blockage and contamination of piping in the equipment (meth) It is considered that solid contents such as an acrylic acid polymer are generated mainly at the bottom of the absorption tower while the (meth) acrylic acid solution is retained. Therefore, by adopting the production method of the present invention for extracting a crude (meth) acrylic acid solution as a side stream of the absorption tower, the amount of by-products as described above can be reduced, and (meth) acrylic acid is efficiently recovered. It becomes possible to do.

  In addition, since the high boiling point component contained in the (meth) acrylic acid-containing gas is introduced into the absorption tower, it is condensed or absorbed by the collection solvent prior to the (meth) acrylic acid gas. By providing the extraction position of the crude (meth) acrylic acid solution above the supply position of the (meth) acrylic acid-containing gas, mixing of high-boiling components into the crude (meth) acrylic acid solution can also be suppressed. .

  In the present invention, “high boiling point component” means a component having a higher boiling point than (meth) acrylic acid in the standard state, and “low boiling point component” means higher than (meth) acrylic acid in the standard state. It means a component with a low boiling point.

  The absorption tower that can be used in the present invention is not particularly limited as long as it can sufficiently contact the (meth) acrylic acid-containing gas and the collection solvent for collecting (meth) acrylic acid, For example, conventionally known absorption towers such as a plate tower, a packed tower, a wet wall tower, and a spray tower can be used.

  The method of contacting the (meth) acrylic acid-containing gas and the collection solvent in the absorption tower is not limited. For example, a cross flow using a bubble bell tray, a uniflat tray, a perforated plate tray, a jet tray, a bubble tray, or a venturi tray Contact: Any of the conventionally known contact methods such as turbo grid tray, dual flow tray, ripple tray, kittel tray, gauze type, sheet type, grit type regular packing, and countercurrent contact using irregular packing Can also be used.

  In order to efficiently make contact with the (meth) acrylic acid-containing gas, the supply position of the collection solvent is preferably provided at the top of the absorption tower, but for absorbing the (meth) acrylic acid-containing gas. If there is no hindrance, it is preferable to provide in the range of 1 to 30% of the total number of theoretical plates starting from the tower top to the tower bottom from the tower top. The position is more preferably 1 to 20%, and still more preferably 1 to 10%.

  On the other hand, the supply position of the (meth) acrylic acid-containing gas is 50% to 100% of the total number of theoretical plates starting from the tower top side to the tower bottom part of the absorption tower (that is, intermediate in the height direction of the absorption tower). Part to the tower bottom side; for example, if the tower top is one stage and the tower bottom is 100 stages, the position is 50 to 100 stages), more preferably 70% to 100%, still more preferably 90% to 100 % Is preferable.

  In addition, the extraction port of the crude (meth) acrylic acid solution may be between the supply position of the (meth) acrylic acid-containing gas and the collection solvent input port. From the viewpoint of efficiently carrying out the purification step, as shown in FIG. 1 showing a representative example of the production method of the present invention, the outlet of the crude (meth) acrylic acid solution 35 is (meth) acrylic. It is preferably provided on the column top side from the supply position of the acid-containing gas 25. On the other hand, if the position of the extraction port is too high, the (meth) acrylic acid concentration of the crude (meth) acrylic acid solution decreases and the amount of (meth) acrylic acid gas discharged from the top of the absorption tower increases. (Ie, increased loss rate of (meth) acrylic acid). The gas discharged from the top of the absorption tower is usually used as a recycle gas during the synthesis of (meth) acrylic acid, or after cooling, the condensable substances contained in the gas are trapped. It is used in absorption towers as part of the solvent collection. However, when the loss rate of (meth) acrylic acid is high, the load in the absorption tower, the reactor, and the cooling process increases, which is disadvantageous in terms of capital investment and utility. Accordingly, the outlet of the crude (meth) acrylic acid solution is preferably provided in a range of 20 to 99% in terms of the total number of theoretical plates starting from the tower top side to the tower bottom part of the absorption tower, more preferably 50 It is in the range of -99%, more preferably 70-99%, and most preferably 80-99%. By providing the outlet of the crude (meth) acrylic acid solution in the above range of the absorption tower, the content of the Michael adduct and the polymer of (meth) acrylic acid is small and contained in the solution (meta ) A crude (meth) acrylic acid solution having a high acrylic acid concentration is obtained. Furthermore, the content of high-boiling components (maleic acid, benzaldehyde, furfural, protoanemonin, etc.) produced as a by-product during the catalytic gas phase oxidation reaction can be suppressed to a low level. In order to reduce the loss rate of (meth) acrylic acid, it is preferable to provide the outlet for the crude (meth) acrylic acid solution in the above range.

  In order to efficiently extract the crude (meth) acrylic acid solution, it is preferable to provide a liquid collector at the crude (meth) acrylic acid solution outlet.

  The amount of the crude (meth) acrylic acid solution withdrawn as a side stream of the absorption tower is 20% by mass or more based on the amount of the solution withdrawn from the absorption tower (that is, the total amount of the side stream and the bottom liquid). Preferably it is 50 mass% or more, More preferably, it is 75 mass% or more, and it is preferable to set it as 96.0 mass% or less. In order to reduce the amount of Michael adduct produced, it is preferable that the extraction amount is large, but if the extraction amount is too large, solid components that are difficult to dissolve in the high boiling point component and the collection solvent are accumulated at the bottom of the column. In some cases, the viscosity of the tower bottom liquid becomes high, or piping in the apparatus is blocked, making it difficult to continue the operation of the absorption tower.

  In addition, it is preferable that the (meth) acrylic acid density | concentration of the crude (meth) acrylic acid solution extracted from an absorption tower is 80 mass% or more, More preferably, it is 85 mass% or more, More preferably, it is 90 mass% or more.

  The collection solvent is not particularly limited as long as it can absorb and dissolve (meth) acrylic acid. For example, diphenyl ether, diphenyl, a mixture of diphenyl ether and diphenyl, water, from the purification step of (meth) acrylic acid Water containing organic acid that is generated (for example, a condensate obtained by cooling a gas discharged from the top of an absorption tower (that is, a recycle gas) and condensing a condensable substance contained in the gas) A conventionally well-known thing can be used widely. Among these, it is preferable to use water and / or water containing an organic acid generated from the purification step of (meth) acrylic acid.

  In this specification, among the gases discharged from the top of the absorption tower, the exhaust gas to be circulated to the reactor ((meth) acrylic acid synthesis) is “recycle gas”, and the system is discharged from the top of the absorption tower to the outside of the system. The discharged gas is called “waste gas”.

  The method for cooling the recycle gas is not limited, and an apparatus that can condense condensable substances contained in the recycle gas may be used. For example, multi-tube heat exchangers, finned tube heat exchangers, air-cooled heat exchangers, double-tube heat exchangers, coil heat exchangers, direct contact heat exchangers, plate heat exchangers, etc. Can be used. The condensate produced by cooling the recycle gas often contains a polymerizable substance such as (meth) acrylic acid. For example, if a cooling method combining a cooling tower and a cooler is employed, polymerization is performed. It is preferable because the inhibitor can be easily supplied.

  Although there is no restriction | limiting in the cooling temperature of recycle gas, It is preferable that the water concentration in the raw material gas whole quantity supplied to a reactor shall be 0-10 volume%, More preferably, it is 0-7 volume%, Especially 0-6 volume% It is recommended that the total acid concentration be 0 to 0.2% by volume, more preferably 0 to 0.1% by volume. It is preferable that the condensable substance is condensed by cooling so that the amount of water contained in the source gas falls within the above range. When air is used as the molecular oxygen-containing gas, the air contains moisture. In such a case, the water content after cooling the recycle gas is obtained from the preferable water concentration of the raw material gas and the blending amount of the raw material gas and air, and cooled to a suitable water concentration. As a guideline for the cooling temperature, it is preferable to cool the temperature of the recycle gas to 1-50 ° C., more preferably 2-40 ° C., particularly preferably 3-30 ° C. lower than the temperature of the waste gas.

  In the present invention, the “condensable substance” means a substance that is liquid at 20 ° C. and standard atmospheric pressure.

  The mass of the collection solvent supplied to the absorption tower may be appropriately determined depending on the concentration of the target crude (meth) acrylic acid solution. In order to efficiently purify (meth) acrylic acid, (meth) The acrylic acid concentration should be as high as possible. From this viewpoint, the mass flow rate of the collection solvent introduced into the absorption tower is preferably 0.1 times or more of the mass flow rate of (meth) acrylic acid contained in the (meth) acrylic acid-containing gas, and more preferably. Is 0.15 times or more, preferably 1.5 times or less, more preferably 1.0 times or less (more preferably 0.8 times or less). If the mass flow ratio of the collection solvent is too small, it may cause an extreme reduction in efficiency of the (meth) acrylic acid absorption tower. On the other hand, if the mass flow rate of the collection solvent is too large, It may be difficult to obtain a (meth) acrylic acid solution.

  The temperature of the collecting solvent introduced into the absorption tower is usually preferably 0 to 60 ° C. More preferably, it is 10-50 degreeC. In addition, in order to set the collection solvent at a suitable temperature, a multi-tube heat exchanger, a double-tube heat exchanger, a spiral heat exchanger, a plate heat exchanger, etc. are used as necessary. Also good.

  For the purpose of preventing polymerization of the polymerizable substance in the absorption tower, a polymerization inhibitor may be added to the collection solvent. Examples of the polymerization inhibitor include N-oxyl compounds, phenol compounds, manganese salts such as manganese acetate described in JP-A Nos. 2001-348360, 2001-348358, and 2001-348359, and copper dibutylthiocarbamate. And one or more compounds selected from the group consisting of dialkyldithiocarbamate copper salts, nitroso compounds, amine compounds and phenothiazines.

  The (meth) acrylic acid absorption tower is preferably operated at a tower top pressure (gauge pressure) of 0 to 0.4 MPa, more preferably 0.1 MPa or less, and further preferably 0.03 MPa or less. Is done. When the pressure at the top of the column is too low, a pressure reducing device is required, which increases equipment costs and utility costs. On the other hand, if the tower top pressure is too high, it is necessary to raise the temperature of the absorption tower in order to discharge low-boiling substances from the top of the absorption tower, and the collection efficiency of (meth) acrylic acid may be reduced. . The top temperature of the absorption tower is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, preferably 85 ° C. or lower, more preferably 80 ° C. or lower.

  Since the bottom liquid staying at the bottom of the absorption tower in the collection step is rich in high-boiling components, it may be discarded, but may contain (meth) acrylic acid or Michael adduct, so (meth) For the purpose of improving the acrylic acid yield, a part of the column bottom liquid may be supplied to a step of performing distillation or decomposition of Michael adduct. Moreover, you may cool or heat a part of tower bottom liquid, and you may return to an absorption tower.

  On the other hand, the crude (meth) acrylic acid solution extracted as a side stream of the absorption tower in the collection step is supplied to the next step. For example, the crude (meth) acrylic acid solution may be supplied as it is to the esterification reaction step as a raw material for (meth) acrylic acid ester, or in the separation and purification step to obtain higher purity (meth) acrylic acid. You may supply.

  The production method of the present invention is characterized by the (meth) acrylic acid collection step, and the steps other than the collection step are not particularly limited. The method can be implemented with appropriate modifications.

[Next Step Example 1-Esterification Step]
First, the case where esterification is performed as a next step will be described. The method of esterification is not particularly limited, and a conventionally known method can be employed. For example, a method of esterifying the crude (meth) acrylic acid solution and alcohol obtained in the collection step in the presence of an acidic catalyst, and a crude (meth) acrylic acid solution and an alkylene oxide in the presence of a catalyst. And the like.

  Examples of the alcohol include saturated or unsaturated aliphatic alcohols having 1 to 12 carbon atoms, alicyclic alcohols having 3 to 10 carbon atoms, and aromatic alcohols having 6 to 10 carbon atoms. Among these, aliphatic alcohols having 1 to 12 carbon atoms and alicyclic alcohols having 3 to 10 carbon atoms are preferable, and typical examples thereof include methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, and sec-butanol. , T-butanol, 1-pentanol, 2-pentanol, 3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, cyclohexanol, 1-heptanol, 2-heptanol, 3-heptanol 1-octanol, isooctanol, 2-ethylhexanol, isononyl alcohol, lauryl alcohol and the like. These alcohols may be used alone or in combination of two or more.

  As an alkylene oxide, a C2-C6 alkylene oxide is mentioned, for example. Representative examples include ethylene oxide, propylene oxide, butylene oxide and the like.

  As an acidic catalyst, a cation exchange resin can be illustrated, for example. As long as it is a cation exchange resin, it is not limited by the resin physical properties such as the resin structure and the degree of crosslinking, and for example, a porous or gel type strongly acidic cation exchange resin is preferably used. As typical examples of porous type strongly acidic cation exchange resins, MSC-1 (manufactured by Dow), PK-208, PK-212, PK-216, PK-220, PK-228 (above, Mitsubishi Chemical Corporation) ), Amberlist-16 ("Amberlist" is a registered trademark of Rohm and Haas), IR-116, IR-118, IR-122, C-26, C-26TR, C-264 C-265 (manufactured by Rohm and Haas), SPC-108, SPC-112 (manufactured by Bayer), KC-470 (manufactured by Sumitomo Chemical), and the like. Moreover, as a representative example of the gel type strongly acidic cation exchange resin, HCR-S, HCR-W2, HGR-W2 (above, manufactured by Dow), SK-1B, SK-106, SK-110 (above, (Mitsubishi Chemical Corporation), Duolite C20H, C255LFH (above, manufactured by Rohm and Haas, “Duolite” is a registered trademark of Rohm and Haas), K1221, K1431 (above, Bayer) ) And the like. Of course, it is not limited to these, You may use weak acid cation exchange resins and inorganic acids, such as a sulfuric acid. These cation exchange resins and inorganic acids may be used alone or in combination of two or more. Further, when the (meth) acrylic acid solution and the alkylene oxide are subjected to an esterification reaction, a metal catalyst containing chromium or iron is used. In addition, what is necessary is just to set suitably about conditions, such as a specific method of esterification process, and reaction temperature, and it does not restrict | limit in particular.

  Following the esterification step, the product is a product of (meth) acrylic acid alkyl ester or (meth) after passing through distillation, stripping, crystallization, extraction, partial condensation, filtration or separation / purification process appropriately combining these. A hydroxyalkyl ester of acrylic acid is obtained.

[Next Step Example 2-Purification Step]
Next, the case where purification is performed in the next step following the collection step will be described. As a purification method of (meth) acrylic acid, distillation, diffusion, crystallization, extraction, partial condensation, and a method of appropriately combining these can be employed. Moreover, when using water as a collection solvent at a collection process, the refinement | purification process may include the azeotropic dehydration process in a part of distillation process. Note that the crude (meth) acrylic acid solution supplied to the purification step has a high concentration of (meth) acrylic such that the (meth) acrylic acid concentration is 70% by mass or more, preferably 80% by mass or more, more preferably 85% by mass or more. In the case of an acid solution, it is preferable to purify (meth) acrylic acid by employing a crystallization method.

  For example, when performing purification by crystallization, there are no restrictions on the crystallization methods that can be used, and either continuous or batch processes can be employed, and the crystallization operation is performed in one or more stages. May be.

  The continuous crystallizer includes a tower-type BMC crystallizer (Backmixing Column Crystallizer, manufactured by Nippon Steel Chemical Co., Ltd.), a crystal unit, a solid-liquid separation unit, and a crystal purification unit. Conversion unit (for example, CDC crystallizer (Cooling Disk Crystallizer, manufactured by GMF GOUDA)), solid-liquid separation unit (for example, belt filter, centrifuge, etc.), and crystal purification unit (for example, KCP purification unit (Kureha) Crystal Purifier, Kureha Techno Engineering Co., Ltd.) etc.) can be used.

  As the batch crystallization apparatus, for example, a layer crystallization apparatus (dynamic crystallization apparatus) manufactured by Sulzer Chemtech, a static crystallization apparatus manufactured by BEFS PROKEM, or the like can be used.

  The operating conditions and the number of crystallizations of the crystallizer may be appropriately determined according to the concentration of crude (meth) acrylic acid supplied to the crystallizer, the purity of the target purified (meth) acrylic acid, and the like. .

  When purifying by distillation, for example, in one distillation column, the low-boiling components contained in the crude (meth) acrylic acid solution are removed from the top of the column, and the high-boiling components are removed from the bottom of the column. Various modes such as a mode for obtaining product (meth) acrylic acid or a mode for obtaining purified (meth) acrylic acid by separately providing distillation towers for the purpose of removing low boiling point components and high boiling point components. Can be adopted. Examples of the distillation tower that can be used in such a purification method include a plate tower provided with a plurality of trays in the tower, a packed tower filled with a packing, and the like. In addition, the tray provided in a plate tower at this time, and the packing packed into a packed tower can use the same thing as the absorption tower used at a collection process. In addition, (meth) acrylic acid refine | purified with the distillation tower may be used as a product as it is, and may refine | purify further by the crystallization method.

  Note that the distillation column 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 operation conditions of the distillation column are not limited, and may be determined as appropriate according to the concentration of the crude (meth) acrylic acid solution supplied and the purity of the target purified (meth) acrylic acid. For example, the top pressure (absolute pressure) of the distillation column is preferably 20 to 400 hPa, more preferably 30 to 300 hPa, still more preferably 30 to 200 hPa; the top temperature is preferably 30 to 70 ° C., more preferably 40 It is recommended that the column bottom temperature is preferably 70 to 120 ° C, more preferably 80 to 110 ° C.

  Residual mother liquor (crystallization method) and distillation column bottom liquid (distillation method) discharged as a residue in the purification process may be discharged out of the system as a waste solution, but useful components contained in the residue are recovered. You may supply to the process to do. 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.

  As described above, since the production method of the present invention is a production method in which Michael adducts are not easily generated, the decomposition process can be made smaller and simpler than the conventional method.

  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, apparatuses that can be employed in the decomposition process include a thin film evaporator equipped with a thermal decomposition tank, and a distillation apparatus that distills decomposition products simultaneously with decomposition of the Michael adduct. In addition, what is necessary is just to supply the (meth) acrylic acid obtained by the decomposition | disassembly process or the distillation process to an absorption tower (namely, collection process) or a refinement | purification process.

  Here, with reference to FIG. 1, a typical manufacturing process of the method for manufacturing (meth) acrylic acid according to the present invention will be described. In addition, the manufacturing method of this invention is not limited to this representative example, In the range which does not inhibit the effect of this invention, it can add and change suitably.

  A raw material gas obtained by mixing a (meth) acrylic acid raw material 1 such as propylene and / or acrolein, a molecular oxygen-containing gas 3 such as air, and a dilution gas 5 is supplied to a reactor 20 filled with a catalytic gas phase oxidation catalyst 10. Then, the (meth) acrylic acid-containing gas 25 is obtained by a catalytic gas phase oxidation reaction. The obtained (meth) acrylic acid gas 25 is supplied from the bottom of the absorption tower 30, and this gas 25 is brought into contact with the collection solvent 33 supplied from the top of the absorption tower 30 to obtain a crude (meth) acrylic acid solution. Get. In FIG. 1, a distillate 71 from a distillation column 70 (which will be referred to as a high boiling point separation column) to be described later is supplied to the absorption column 30. A part of the discharged liquid 71 may be discharged out of the system. Further, the exhaust gas from the top of the absorption tower 30 may be circulated to the reactor 20 as a recycle gas. At that time, after cooling, the condensable components contained in the exhaust gas are separated and then condensed. The component (in the form of condensate) and the collection solvent 33 may be mixed and supplied to the absorption tower 30 (not shown).

  Next, the crude (meth) acrylic acid solution 35 is extracted from above the supply position of the (meth) acrylic acid-containing gas 25 in the absorption tower 30 and from below the supply position of the collection solvent 33. If the obtained crude (meth) acrylic acid solution 35 is supplied to the crystallizer 50 and purified, the product (meth) acrylic acid 60 is obtained.

  On the other hand, the total amount of the residual mother liquor from the crystallizer 50 may be discharged out of the system (not shown), but a distillation column 70 together with the column bottom liquid 37 discharged from the absorption tower 30 with a part or all of it as 51. May be supplied. Of course, all the column bottom liquid 37 may be supplied to the distillation column 70 (referred to as a high boiling point separation column in this case), but a part or all of it may be discharged out of the system (not shown). Further, as shown in FIG. 1, a part thereof may be cooled by the heat exchanger 39 and circulated through the absorption tower 30. Further, the crystallization residual mother liquor 51 from the crystallizer 50 may be mixed with the distillate 71 of the distillation tower 70 and supplied to the absorption tower 30. Preferably, it is recommended that the crystallization residual mother liquor 51 is mixed with the bottom liquid 37 of the absorption tower 30 and supplied to the distillation tower 70 for separating the high-boiling components.

  In the distillation tower 70, the low-boiling components and (meth) acrylic acid contained in the bottom liquid 37 of the absorption tower 30 and the crystallization residual mother liquor 51 are distilled off from the top of the tower, and the distillate 71 is circulated to the absorption tower 30. . On the other hand, the high-boiling component contained in the bottom liquid of the distillation column 70 contains Michael adduct, and this is retained in the thermal decomposition tank 75 via the thin film evaporator 73 and thermally decomposed into (meth) acrylic acid. (Ie, Michael adduct decomposition step). When the produced (meth) acrylic acid is returned to the thin film evaporator 73, it is distilled from the top of the distillation column 70 to become a distillate 71, and if this is circulated to the absorption tower 30, the final product (meta) is obtained. It can be recovered as acrylic acid 60.

  In the Michael adduct decomposition process, the decomposition reaction of the Michael adduct and the (meth) acrylic acid produced are promoted so that the equilibrium shifts in the direction of increasing the amount of (meth) acrylic acid production. A reactive distillation method may be employed in which the distillation of the water occurs at the same time. For example, as shown in FIG. 2, the bottom liquid of the distillation tower 70 is supplied to the reactive distillation apparatus 80 to decompose the Michael adduct and to distill the produced (meth) acrylic acid. The column top liquid containing (meth) acrylic acid is circulated to the distillation column 70, and the column bottom liquid containing a high boiling point component is discharged out of the system as waste oil.

  1 and 2 show an example in which a crystallization method is employed as a purification step, a purification step other than the crystallization method may be employed, and an esterification step is provided as a pre-step of the purification step. It may be a thing.

  Since the present invention is characterized in that the crude (meth) acrylic acid solution is withdrawn as a side stream of the absorption tower as described above, the tower bottom of this absorption tower has a high content containing Michael adducts. Boiling components (that is, components having a boiling point higher than (meth) acrylic acid) are easily collected. In addition, since the Michael adduct can be recovered as (meth) acrylic acid by decomposition, the production method of the present invention may be provided with a step of decomposing the bottom liquid of the absorption tower (that is, a decomposition step). . A decomposition process is not restricted to the above methods, Even if it is a case where (meth) acrylic acid is manufactured using another method, it is employable. For example, when high-boiling components are concentrated at the bottom of the absorption tower depending on the production conditions of (meth) acrylic acid and the operating conditions of the absorption tower, the bottom liquid of the absorption tower is withdrawn and the Michael adduct is decomposed. The aspect which decomposes | disassembles at a process becomes a preferable embodiment.

  Normally, the process of decomposing Michael adducts or treating high-boiling components is installed near the final step of the refining process and decomposes waste oil that has passed through the high-boiling separation tower (for example, (Kaihei 11-12222, etc.) or the high-boiling components after the (meth) acrylic acid and high-boiling components are separated from the bottom liquid discharged from the azeotropic dehydration tower (for example, JP 2004-51489). On the other hand, the above process is a process of decomposing the Michael adduct contained in the bottom liquid of the absorption tower without going through a purification process, and in particular, high-boiling components are collected at the bottom of the absorption tower. When it is easy, (meth) acrylic acid can be more efficiently produced by adopting such a process.

  When the bottom liquid of the absorption tower, that is, the crude (meth) acrylic acid solution is withdrawn as a side stream of the absorption tower, the bottom liquid collected at the bottom of the absorption tower is separated from the distillation step (that is, the high-boiling components are separated). After the step), it may be supplied to the decomposition step. The bottom liquid of the absorption tower that has undergone the decomposition step may be circulated to the absorption tower directly or via a high boiling point separation tower. Thus, (meth) acrylic acid purified by decomposition of the tower bottom liquid of the absorption tower is absorbed by the collection solvent together with (meth) acrylic acid derived from the reaction step, and the absorption tower is obtained as a crude (meth) acrylic acid solution. It will be extracted from.

  The step of decomposing the bottom liquid of the absorption tower (that is, the decomposition treatment of Michael adduct) is carried out by a high boiling point separation tower as shown in JP-A No. 11-12222, in addition to a thin film evaporator and a thermal decomposition tank. It may be performed in an installed process (see, for example, FIG. 1), or decomposition of Michael adduct and distillation of (meth) acrylic acid after decomposition as disclosed in JP-A-2003-171342. You may carry out by the process (for example, refer FIG. 2) which employ | adopts the reactive distillation format performed simultaneously. Among these processes, acrylic acid can be efficiently recovered from the bottom liquid of the absorption tower. Therefore, in addition to the thin film evaporator and the thermal decomposition tank, the reaction distillation system is adopted rather than the process in which the high boiling point separation tower is installed. The process is more preferable. In either case, a polymerization inhibitor may be blended as necessary.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

[Experimental Examples 1 and 2: Collection of acrylic acid]
Acrylic acid was collected according to the following method. In Experimental Example 1, the extraction position of the crude acrylic acid solution is fixed at a specific position (that is, the position of 89% of the total number of theoretical plates starting from the tower top to the tower bottom from the tower top). In this example, the extraction amount of the crude acrylic acid solution was changed. In Experimental Example 2, the extraction position of the crude acrylic acid solution was changed, and the extraction amount of the crude acrylic acid solution was fixed to a predetermined amount (that is, extraction). Amount 6 kg).

Experimental example 1
As the absorption tower, a gas outlet at the top of the absorption tower and an outlet for the liquid at the bottom of the tower were used, and the packing was packed so that the calculated theoretical plate number was 18. In the absorption tower, the supply port for the acrylic acid-containing gas is provided below the lowermost stage of the packing, and the inlet for the collection solvent and the liquid disperser for dispersing the collection solvent in the absorption tower are the uppermost stage of the packing. It was provided above. In addition, a collector is installed at 89% of the total number of theoretical plates from the top of the absorption tower to the bottom of the tower, starting from the top of the tower (that is, 16 theoretical plates counted from the top of the packing). The crude acrylic acid solution was extracted from here.

  Acrylic acid was collected by controlling the tower top temperature of the absorption tower to 69.6 ° C. and the tower top pressure of 0.015 MPa. The temperature control of the absorption tower was performed by cooling a part of the tower bottom liquid and circulating it.

Acrylic acid-containing gas obtained by catalytic gas phase oxidation (composition: acrylic acid 7.1 vol%, water 13.9 vol%, nitrogen 74.2 vol%, oxygen 1.5 vol%, others (propylene, propane , COx, acetic acid, aldehyde, etc.) 3.3% by volume) at 270 ° C., 34.9 Nm ³ / hour, and an acrylic acid gas supply port (total from the top of the absorption tower to the bottom of the tower. It is introduced into the absorption tower from the position of 100% of the theoretical plate number, that is, 18 theoretical plates, and the collection solvent (water: acrylic acid: acetic acid: others = 95: 2: 2: 1, acrylic from the collection solvent inlet. Absorbed by introducing 4.5 kg / hour of TEMPO (containing 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl) equivalent to 200 mass ppm with respect to acrylic acid in the acid-containing gas. Gas-liquid contact in the tower The collection solvent absorbs the acrylic acid-containing gas, and the crude acrylic acid solution is added to the tower bottom side from the middle stage of the absorption tower (that is, from the tower top to the tower bottom, the total theoretical plate number starting from the tower top side) (The position of 89%) was extracted from the absorption tower via a liquid collector.

  The composition of the obtained crude acrylic acid solution and the amount of extraction are shown in Table 1 together with the composition of the bottom liquid of the absorption tower. In Table 1, “side flow” means the position of 89% of the total number of theoretical plates from the center of the absorption tower to the tower bottom (that is, from the top to the bottom of the absorption tower, based on the tower top, ie, It means the crude acrylic acid solution extracted from the theoretical plate number of 16), “column bottom liquid” means the extracted liquid extracted from the bottom of the absorption tower, and “dimer” means that two molecules of acrylic acid react. It means the resulting Michael adduct (acrylic acid dimer). The “ratio of the side stream withdrawal amount” indicates the ratio of the mass of the side stream (that is, the crude acrylic acid solution) to the total amount of the mass of the side stream and the bottom liquid. The “column top loss rate” is the ratio of the amount of acrylic acid-containing gas discharged from the absorption tower without being absorbed by the collection solvent to the amount of acrylic acid gas introduced into the absorption tower. is there.

  Experimental Example 1-1 to Experimental Example 1-6 are examples in which the crude acrylic acid solution was extracted from the tower side of the absorption tower, and Experimental Example 1-7 was performed using the crude acrylic acid solution as the tower bottom liquid of the absorption tower. This is an extracted example. In Examples 1-1 to 1-6, acrylic acid was collected under the same conditions except for the amount of the crude acrylic acid solution extracted.

  The acrylic acid concentration and dimer concentration in Experimental Example 1-7 indicated by * in Table 1 indicate the acrylic acid concentration and dimer concentration in the bottom liquid, respectively.

  From the results in Table 1, it can be seen that even when the crude acrylic acid solution is taken out as a side stream of the absorption tower, a crude acrylic acid solution having a high concentration equal to or higher than that taken out as the bottom liquid is obtained. Moreover, since the solids and acrylic acid dimer are not contained in the side flow of the absorption tower, the solid content is removed by adopting a method of taking out the crude acrylic acid solution as a side flow of the absorption tower. The process of decomposing the filter and acrylic acid dimer can be omitted or simplified.

  Further, from the results of Table 1, in Experimental Examples 1-1 to 1-6 in which the crude acrylic acid solution was extracted as a side stream of the absorption tower, in the case of Experimental Example 1-7 in which the crude acrylic acid solution was extracted as the tower bottom liquid It can be seen that the amount of acrylic acid dimer produced at the bottom of the column can be reduced to 87% by mass or less, and the amount of acrylic acid dimer produced decreases with an increase in the amount of side stream extracted ( That is, Experimental Example 1-1: 0.117 kg / hour (86.7% of Experimental Example 1-7), Experimental Example 1-2: 0.099 kg / hour (73.2%), Experimental Example 1-3: 0.075 kg / hr (55.6%), Experimental Example 1-4: 0.067 kg / hr (49.8%), Experimental Example 1-5: 0.058 kg / hr (42.9%), Experimental Example 1-6: 0.047 kg / hr (34.5%)). In addition, when the extraction amount per unit time of the side stream exceeds 8.0 kg / hour (96.9% by mass with respect to the total of the side stream and the bottom liquid extracted from the absorption tower), the tower of the absorption tower The piping at the bottom was blocked, making it impossible to continue the operation of the absorption tower.

  That is, by removing the crude acrylic acid solution as a side stream of the absorption tower, the amount of acrylic acid dimer produced can be reduced compared with the case where it is withdrawn as the bottom liquid. Acrylic acid can be recovered at a high rate.

Experimental example 2
In Experimental Example 2, the amount of the crude acrylic acid solution withdrawn as a side stream is 6 kg, and the extraction position of the crude acrylic acid solution is based on the tower top side from the tower top to the tower bottom as shown in Table 2. Except having changed to the position of 28 to 89% of the total theoretical plate number, it carried out similarly to Experimental example 1, and extracted the crude acrylic acid solution (Experimental examples 2-1 to 2-5).

  The composition of the obtained crude acrylic acid solution and the composition of the bottom liquid of the absorption tower are shown in Table 2 together with the position of the extraction port. Table 2 also shows the results of Experimental Example 1-7 in which the crude acrylic acid solution was extracted as the bottom liquid of the absorption tower.

  In Table 2, the numerical value described in the column of the extraction stage indicates the extraction opening of the crude acrylic acid solution in the number of theoretical plates, and the numerical value in parentheses indicates the extraction opening from the top of the absorption tower to the bottom of the tower. It is shown as a percentage of the total number of theoretical plates starting from the tower top side. In addition, the acrylic acid concentration and dimer concentration in Experimental Example 1-7 indicated by * in Table 2 indicate the acrylic acid concentration and dimer concentration in the column bottom liquid, respectively.

  From the results in Table 2, the higher the outlet of the crude acrylic acid solution is at the upper stage (that is, the tower top side of the absorption tower), the smaller the amount of acrylic acid dimer produced, but the acrylic acid concentration of the crude acrylic acid solution It can also be seen that the loss rate of acrylic acid-containing gas from the top of the absorption tower tends to increase. In addition, by providing an extraction port for the crude acrylic acid solution between the supply position of the acrylic acid-containing gas and the supply position of the collection solvent, it is possible to remove acrylic acid solution as compared with the case where the crude acrylic acid solution is extracted as the bottom liquid. It turns out that the production amount of a monomer can be reduced.

[Experimental Example 3: Purification of crude acrylic acid solution]
6 kg of a crude acrylic acid solution produced under the same conditions as in Experimental Example 1-3 was purified by a crystallization purification method or a distillation purification method.

Experimental Example 3-1 Crystallization Purification Method Dynamic crystallization was performed using a crystallization purification apparatus according to the crystallization apparatus described in JP-B-53-41637. The crystallizing and purifying apparatus is composed of a metal pipe having a length of 6 m and an inner diameter of 70 mm, equipped with a reservoir in the lower part. The liquid in the reservoir is transferred to the upper part of the pipe by a circulation pump, and the liquid falls on the inner wall of the pipe film). The outer surface of the tube is composed of a double jacket, which is controlled by a thermostat so as to have a constant temperature. A crude acrylic acid solution (composition: acrylic acid 92.75% by mass, water 4.99% by mass, acetic acid 2.50% by mass, other impurities 0.16% by mass) is supplied to this reservoir at 6 kg / hour. According to the following procedure, dynamic crystallization was performed. The following procedure shows one dynamic crystallization operation.

  1. Crystallization: The crude acrylic acid solution supplied to the reservoir is poured into the inner wall surface of the pipe by a circulation pump in the form of a falling film, the jacket temperature is lowered below the freezing point of acrylic acid, and the crude acrylic acid solution supplied to the reservoir is supplied. About 60 to 80% by mass of acrylic acid contained in was crystallized on the inner wall surface of the tube.

  2. Sweating: The circulation pump was stopped, the jacket temperature was raised to the vicinity of the freezing point of acrylic acid, and about 2 to 5% by mass of the crystallized acrylic acid was sweated. After sweating, the crude acrylic acid solution and sweat solution remaining in the reservoir were pumped out.

  3. Melting: The temperature of the jacket was raised above the freezing point of acrylic acid to melt the crystals and pumped them out.

  The above operation was repeated 4 times to obtain purified acrylic acid. In the above operation, the temperature and the freezing point depended on each process to be performed.

  By the dynamic crystallization operation as described above, acrylic acid having a purity of 99.91% by mass was obtained at 2.92 kg / hour. At this time, the water contained in the acrylic acid crystal was 248 ppm by mass, and acetic acid was 602 ppm by mass.

Experimental Example 3-2: Distillation Purification Method A non-weired perforated plate tray corresponding to 18 theoretical plates is provided, and condensable components in the gas discharged from the distillation tower are condensed at the top of the tower and introduced again into the absorption tower. A crude acrylic acid solution was supplied to a distillation column equipped with a reflux line at 6 kg / hour to purify acrylic acid. The distillation column used in this purification step is equipped with a condenser at the top of the column, has a crude acrylic acid solution supply port at the 9th stage of the theoretical plate from the top of the column, and is drained from the column at the 17th level of the theoretical plate from the top of the column. It was equipped with a mouth and a condenser, and was equipped with a reboiler at the bottom of the tower.

  From the crude acrylic acid solution supply port of the distillation tower, the crude acrylic acid solution (composition: 93.10% by mass of acrylic acid, 1.88% by mass of acetic acid, 4.87% by mass of water, 0.04% by mass of acrolein, other 0.8% by mass). 11 mass%) was fed at 6 kg / hr, and a polymerization inhibitor (40 mass ppm of copper dibutyldithiocarbamate, 100 mass ppm of phenothiazine [vapour amount of evaporated acrylic acid]) was introduced from the reflux line at the top of the column. At this time, the inside of the distillation column is depressurized by a steam ejector so that the column top operating pressure becomes 100 hPa (absolute pressure), and between the column side stream outlet and the vacuum device provided downstream of the outlet. And the differential pressure between the tower side and the tower top is controlled to 95 hPa, and the flow rate ratio of the amount of steam withdrawn from the tower side stream outlet and the effluent from the tower top is 4: 1. In addition, the bottom liquid was withdrawn at 0.8 kg / hour, and purified acrylic acid vapor was obtained at 4.3 kg / hour from the outlet of the tower side stream. At this time, acrylic acid vapor was supplied by a reboiler provided at the bottom of the distillation column to control the liquid level of the column bottom, and the reflux ratio in the distillation column was set to 3.4.

  The purified acrylic acid obtained at this time has a purity of 99.82%, and contains impurities of 100 mass ppm of water, 1300 mass ppm of acetic acid, 1 mass ppm of acrolein (detection limit) or less, and 400 mass ppm of others. It was.

  From the result of Experimental Example 3, in the collection step, the production method of the present invention in which the crude acrylic acid solution is extracted from the extraction port located between the supply position of the acrylic acid-containing gas and the supply position of the collection solvent is adopted. Thus, it can be seen that high-purity acrylic acid can be obtained efficiently regardless of the type of purification method.

[Experimental example 4: decomposition process]
Acrylic acid was recovered by distillation of the bottom liquid containing the high boiling point component obtained under the same conditions as in Experimental Example 1-3 and decomposition of the Michael adduct.

Experimental Example 4-1 A process in which a high boiling point separation tower is installed in addition to the thin film evaporator and the thermal decomposition tank. Absorption tower bottom liquid (composition: 87.7 mass% acrylic acid, 2.0 mass% water, Acetic acid 1.1%, maleic acid 1.5% by mass, acrylic acid dimer 6.2% by mass, other impurities 1.5% by mass) and a perforated plate tray corresponding to 20 theoretical plates and a reboiler. Then, 2.25 kg / h (acrylic acid dimer 0.075 kg / h) was fed to the middle stage of the distillation column (that is, the high boiling point separation column). At this time, the distillation column was controlled under the conditions of an operating pressure of 93 hPa and a reflux ratio of 0.3. In the pyrolysis tank, the Michael adduct is pyrolyzed under the conditions of a pyrolysis tank temperature of 170 ° C. and a residence time of 30 hours, and the thin film evaporator is controlled so that the tower bottom temperature is 95 ° C. Acrylic acid was recovered under conditions of 33 hPa and a reflux ratio of 1.5. At this time, the conversion rate of the Michael adduct was 65%, the acrylic acid selectivity was 75%, and 48.8% (0.037 kg / h) acrylic acid could be recovered from the acrylic acid dimer. .

Experimental Example 4-2: Step of Adopting Reactive Distillation Format In the Michael adduct decomposition step, a reactive distillation apparatus with a column tower equipped with an external heat exchanger of forced circulation type as shown in FIG. 2 was used. The same operation as in Experimental Example 4-1 was performed. The reactive distillation apparatus thermally decomposed the Michael adduct under the conditions of a thermal decomposition temperature of 170 ° C., a residence time of 4 hours, and a pressure of 266 hPa. At this time, the conversion rate of the Michael adduct was 82% and the acrylic acid selectivity was 98%, and 80.4% (0.060 kg / h) of acrylic acid could be recovered from the acrylic acid dimer. .

  From the results of Experimental Example 4, in order to efficiently recover acrylic acid from the bottom liquid of the absorption tower, in addition to the thin film evaporator and the pyrolysis tank, the reactive distillation format was changed from the process in which the high boiling point separation tower was installed. It can be seen that the process adopted is more preferable.

It is process drawing which shows an example of the preferable aspect of this invention. It is process drawing which shows the other example of the preferable aspect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Propylene and / or acrolein 3 Air 5 Diluted gas 10 Catalytic gas phase oxidation catalyst 20 Reactor 25 (Meth) acrylic acid-containing gas 30 (Meth) acrylic acid absorption tower 33 Collection solvent 35 Crude (meth) acrylic acid solution 37 Absorption Column bottom liquid 39 Heat exchanger 50 Crystallizer 51 Crystallization residual mother liquor 60 Product (meth) acrylic acid 70 Distillation column 71 Distillation column distillate 73 Thin film evaporator 75 Pyrolysis tank 80 Reactive distillation apparatus

Claims (6)

A method for producing (meth) acrylic acid,
A collection step of collecting the (meth) acrylic acid-containing gas obtained by the contact gas phase oxidation method with a collection solvent in an absorption tower and collecting it as a crude (meth) acrylic acid solution;
In the collection step, it is located between the supply position of the (meth) acrylic acid-containing gas and the supply position of the collection solvent, and from the tower top to the tower bottom of the absorption tower, the total number of theoretical plates starting from the tower top The crude (meth) acrylic acid solution is withdrawn from the outlet of the absorption tower in the range of 50 to 99% and supplied to the next step .
The crude (meth) (meth) acrylic acid concentration in the acrylic acid solution is characterized in der Rukoto least 80 wt% (meth) acrylic acid withdrawn from the withdrawal outlet of the absorption tower. The next step is the crude (meth) acrylic acid solution from the (meth) according to claim 1 Symbol placement of a process of separating and purifying the acrylic acid (meth) acrylic acid. The method for producing (meth) acrylic acid according to claim 2 , wherein the separation and purification step includes a crystallization step and / or a distillation step. The method for producing (meth) acrylic acid according to any one of claims 1 to 3 , wherein the collection solvent is water and / or water containing an organic acid generated from a purification step of (meth) acrylic acid. . The supply position of the (meth) acrylic acid-containing gas is in the range of 50 to 100% in terms of the total theoretical plate number,
The method for producing (meth) acrylic acid according to any one of claims 1 to 4 , wherein a supply position of the collection solvent is in a range of 1 to 30% in terms of the total number of theoretical plates. The amount of crude (meth) acrylic acid solution withdrawn as a side stream of the absorption tower from the withdrawal outlet is any one of claim 1 to 5, 20 mass% or more relative to the amount of the solution withdrawn from the absorption tower The manufacturing method of the (meth) acrylic acid of description.

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