JP4300224B2 - Acrylic acid production method - Google Patents

Description

  The present invention relates to a method for producing acrylic acid, and more particularly to a method for producing acrylic acid in high yield in a method for producing acrylic acid.

  In the method of producing acrylic acid by catalytic vapor phase oxidation of propylene and / or acrolein, during the catalytic vapor phase oxidation reaction, acids such as water, propionic acid, acetic acid, maleic acid, acetone, acrolein, furfural, formaldehyde, etc. In addition to aldehydes, it is known that Michael adducts such as dimers and pentamers of acrylic acid and oligomers are generated as by-products due to the action of heat and catalyst in the purification process. These by-products hinder the stable operation of acrylic acid production and cause a reduction in the yield of the target acrylic acid. In addition, since acrylic acid is an easily polymerizable substance, problems such as production of acrylic acid polymer in the synthesis process involving heating and purification processes such as distillation cause clogging in the apparatus and decrease in product yield. was there. Various techniques have been proposed for the purpose of solving such problems and producing acrylic acid efficiently and stably.

  Patent Documents 1 to 4 employ a distillation purification method in which gaseous acrylic acid obtained by a catalytic gas phase oxidation method is collected as an acrylic acid solution, and by-products contained in the solution are removed by distillation. In these techniques, a method for suppressing the polymerization of acrylic acid and a method for decomposing the Michael adduct and recovering it as acrylic acid are proposed.

For example, in Patent Document 1, a polymerization inhibitor is supplied from a specific position of a collection tower or a distillation tower so that the polymerization inhibitor is uniformly dispersed, or a cooler is installed between the steps. A method is described in which the generation of polymer is suppressed by cooling the feed liquid, and acrylic acid is recovered by decomposing acrylic acid oligomer (Michael adduct) using a thin film evaporator and a thermal decomposition tank. Yes. Patent Documents 2 and 3 propose a method for recovering acrylic acid by decomposing Michael adducts using a reactive distillation apparatus, a distillation column equipped with a thin film evaporator, and a thermal decomposition tank. Patent Document 4 describes a method for improving the yield of acrylic acid by decomposing and recovering acrylic acid multimers (Michael adducts) contained in the bottom liquid of a purified acrylic acid tower to acrylic acid. ing.
JP 2004-51489 A Japanese Patent Laid-Open No. 11-12222 JP 2003-160532 A JP 2003-246765 A

  In the above-mentioned patent documents, it is also pointed out that maleic acid by-produced in the production process of acrylic acid reduces the yield of acrylic acid or hinders stable operation of production. Maleic acid is a by-product of acrylic acid synthesis, depending on the composition in the process (water-containing) maleic acid (in an environment where water is present at low temperature) or maleic anhydride (in an environment where water is not present at high temperature) Exists. In particular, maleic acid has a low solubility in acrylic acid and thus tends to precipitate, and a copolymer with acrylic acid is easily formed.

  However, in the acrylic acid production process as described above, it is difficult to completely remove the water generated in the synthesis process and the water used in the collection process from the system, and in such an environment where water exists. In this case, maleic acid is hardly dehydrated and is likely to precipitate. Furthermore, maleic acid is easily transferred to fumaric acid when heated, but since maleic acid and fumaric acid are more likely to precipitate than maleic anhydride, the viscosity of the acrylic acid solution is increased to add Michael. This may reduce the efficiency of disassembling objects and may cause clogging or contamination of piping in the manufacturing apparatus.

  Regarding such a problem concerning maleic acid, Patent Document 1 describes that a maleic acid separation tower is used to reduce the amount of maleic acid in the decomposition solution after thermal decomposition (decomposition of Michael adduct). In Patent Documents 2 and 3, the reaction temperature and operation pressure during the decomposition reaction of the Michael adduct are controlled to reduce the amount of maleic acid recovered simultaneously with acrylic acid, and maleic acid and maleic anhydride are recovered. It is described to avoid accumulating within.

  However, there is a limit to reducing the contents of maleic acid and maleic anhydride only by such optimization of decomposition and recovery conditions, and the accumulated amount of maleic acid in the system may increase during continuous operation. is there.

  Moreover, in patent document 4, prior to decomposition of the Michael adduct, or a method in which maleic acid is precipitated and separated by positively adding water or a water-insoluble solvent to the recovered liquid after decomposition of the Michael adduct. Is described. However, the installation of a new process requires further capital investment and results in an increase in the production cost of acrylic acid. Also, an increase in the amount of solvent used is not preferable from the economic and environmental viewpoints.

  The present invention has been made paying attention to the above circumstances, and its purpose is to recover acrylic acid from a high-boiling component containing a Michael adduct separated from acrylic acid in the purification process, particularly in the acrylic acid production process. At the same time, problems such as clogging of maleic acid (for example, clogging of pipes and equipment, pressure increase in the equipment, etc.) and troubles such as deterioration of properties of liquids containing high-boiling components are suppressed, and the Michael adduct is efficiently decomposed. It is to provide a method for producing acrylic acid in high yield.

  As a result of intensive studies focusing on the above problems, the present inventors, in the method for producing acrylic acid, in particular, decomposed the Michael adduct contained in the high-boiling component separated from acrylic acid to produce acrylic acid. As a result of reducing the amount of hydrous maleic acid contained in the high-boiling component to a specific amount or less, it is caused by precipitation of maleic acid in the subsequent decomposition step, formation of a copolymer with acrylic acid, etc. It has been found that troubles such as dirt, viscosity increase, and pressure loss in the tower can be remarkably suppressed. That is, although it is difficult to reduce the total amount of maleic acid by-produced in the reaction step, the proportion of maleic acid (hydrated) that has become hydrated due to the presence of water in the purification step is reduced, and this is further reduced to anhydrous. It has been clarified that troubles derived from maleic acid in the decomposition step can be suppressed and acrylic acid can be efficiently recovered if it is made into (Maleic anhydride).

  The method for producing acrylic acid according to the present invention that has solved the above problems is to collect the acrylic acid-containing gas obtained by vapor-phase oxidation of the raw material gas as a crude acrylic acid-containing liquid, and collect the collected crude acrylic acid. A method for producing acrylic acid for purifying a solution, wherein the step of purifying the crude acrylic acid-containing solution includes a high-boiling component separation step for separating a high-boiling component in a distillation tower, In a high-boiling component supplied from the high-boiling component separation step to the decomposition step, including a decomposition step of decomposing the Michael adduct contained to generate acrylic acid, and a recovery step of recovering the acrylic acid generated in the decomposition step The ratio of the amount of maleic acid is 70% or less (which is a value calculated from the following formula, and is the ratio of the amount of maleic acid when the total of maleic acid and maleic anhydride is 100%). And it has a gist to the filtrate.

  As described above, maleic acid has a low solubility in acrylic acid and is more likely to precipitate than maleic anhydride. Therefore, if the amount of maleic acid supplied to the decomposition step is reduced in advance, maleic acid is used in the decomposition step. And acrylic acid copolymer and maleic acid are difficult to precipitate. In general, since the high-boiling components supplied to the decomposition step have already been removed from the low-boiling components such as water, water is desorbed from maleic acid during the decomposition treatment. Since maleic anhydride produced at this time has a lower melting point than maleic acid, it can be present in a high-boiling component in a solution state.

  Therefore, the method of the present invention, that is, the amount of the hydrated maleic acid contained in the high-boiling component and the amount of the hydrated maleic acid relative to the maleic anhydride are set to a specific amount or less, thereby blocking the piping. Stable Michael adduct decomposition and efficient recovery of acrylic acid can be performed without causing an increase in pressure in the apparatus.

  In the high boiling point component separation step, the bottom temperature of the distillation tower is 90 to 130 ° C., the residence time of the bottom liquid is 2 to 30 hours, and the mass B of the liquid extracted from the distillation tower is supplied to the distillation tower. It is preferable that the ratio F of the liquid mass “F / B” (hereinafter, “F / B” may be referred to as a concentration ratio) be 5 to 20. Moreover, it is preferable that the density | concentration of the Michael adduct in the high boiling point component supplied to the said decomposition process shall be 20-60 mass%, and performing the said decomposition process by the reactive distillation form is recommended. In particular, it is a preferred embodiment of the present invention to perform the decomposition step in a plate-type distillation column, and at this time, the reflux ratio is preferably 0.5 to 6. Further, as the above-mentioned plate type distillation column, it is preferable to use a distillation column having three or more theoretical plates, and 70 to 100% of the total theoretical plate based on the top side of this plate type distillation column. It is preferable to heat the part to 125 ° C. or lower. Moreover, as a tray type distillation tower, what was equipped with the tray which has an opening with a hole diameter of 10-50 mm is preferable.

  The decomposition step uses a forced circulation heat exchanger, heats the high boiling point component supplied to the decomposition step to 155 to 220 ° C., and heat source of the forced circulation heat exchanger, and the forced circulation type It is recommended that the temperature difference with the high boiling point component heated by the heat exchanger be 15 to 80 ° C.

  Furthermore, it is recommended that the decomposition step be performed in the presence of an N-oxyl compound.

  In the present specification, the “low boiling point substance” means a substance having a boiling point lower than that of acrylic acid in a standard state (25 ° C., under atmospheric pressure), and the “high boiling point substance” means a substance having a lower boiling point than acrylic acid in the standard state. Refers to a substance with a high boiling point.

  The “Michael adduct” refers to a multimer of acrylic acid represented by the following formula (1). As such a Michael adduct, for example, in the case of an acrylic acid dimer, β-acryloxypropionic acid and salts thereof are included.

(In the formula (1), n represents an integer of 1 to 5, and —X— represents —CH ₂ CH ₂ — or —CH (CH ₃ ) —, where n is 2 or more. In some cases, a plurality of -X- may be the same or different.)

  Furthermore, “purification” includes distillation, stripping, crystallization, extraction, absorption and the like. Here, “distillation” is a method in which a solution is heated to its boiling point to separate volatile components contained therein, and “crystallization” means to separate the target product as crystals.

  In the present specification, “maleic acid” means “hydrous maleic acid” unless otherwise specified, and is used separately from maleic anhydride.

  According to the production method of the present invention, in the decomposition process of the Michael adduct, troubles such as precipitation of maleic acid and a pressure increase in the decomposition apparatus derived from this hardly occur. Thus, acrylic acid can be produced efficiently and stably.

  The acrylic acid production method of the present invention is an acrylic that collects an acrylic acid-containing gas obtained by vapor-phase oxidation of a raw material gas as a crude acrylic acid-containing liquid, and purifies the collected crude acrylic acid-containing solution. A method for producing an acid, comprising a step of purifying the crude acrylic acid-containing solution, a high-boiling component separation step of separating a high-boiling component in a distillation column, and further, a Michael adduct contained in the high-boiling component. The ratio of the amount of maleic acid in the high boiling point component supplied from the high boiling point component separation step to the decomposition step, including a decomposition step for decomposing and generating acrylic acid, and a recovery step for recovering the acrylic acid generated in the decomposition step Is 70% or less (a value calculated by the following formula, which is a ratio of the amount of maleic acid when the total of maleic acid and maleic anhydride is 100%). Than is.

  As described above, if the ratio of the amount of maleic acid in the high-boiling component supplied to the decomposition step (the ratio of hydrated maleic acid to the total amount of maleic acid [hydrated maleic acid + maleic anhydride]) is within the above range, Since the generation of precipitates and pressure increase in the apparatus can be suppressed in the decomposition step, the Michael adduct can be efficiently decomposed and acrylic acid can be stably produced.

  The proportion of maleic acid in the high boiling point component calculated by the above formula is preferably 50% or less, more preferably 40% or less, and of course, the proportion of maleic acid is most preferably 0%. Needless to say.

  However, in order to reduce the maleic acid content to 0%, strict operating conditions may be adopted for a specific process (the stable operability of the production process may be impaired), or the production efficiency of acrylic acid may be sacrificed. You may have to. Therefore, it is difficult in actual operation to set the ratio of the amount of maleic acid calculated by the above formula to 0%, which is not preferable from an economical viewpoint. In general, the lower limit of the proportion of the amount of maleic acid calculated by the above formula is a value greater than 0%. Specifically, the lower limit of the ratio of the maleic acid amount is 5%, more specifically 10%, and further 20%.

  The high boiling point component includes a component having a boiling point higher than that of acrylic acid, and includes by-products during the production of acrylic acid including Michael adducts. It is an object of the present invention to recover acrylic acid from such a high boiling point component to further improve the production efficiency of acrylic acid. As described above, the present invention is characterized in that the amount of maleic acid in the high boiling point component supplied to the decomposition step is reduced to a specific amount or less. Therefore, in the present invention, the method for synthesizing acrylic acid is not limited at all, and any method can be adopted as long as it is a conventionally known method for producing acrylic acid. For example, the liquid containing the high-boiling component may be discharged from the purification process (for example, the distillation, emission, crystallization, extraction, absorption, etc.), or optionally after the purification process, if necessary. What is isolate | separated from the acrylic acid used as a product in the further refinement | purification process provided is mentioned. Of course, the liquid containing the high boiling point component may contain acrylic acid. Typical examples include distillation column bottom liquid and residual mother liquor generated by crystallization purification.

  As an industrial method for producing acrylic acid, a method of catalytic vapor phase oxidation of propylene and / or acrolein is common. Therefore, in the present specification, a specific example will be described in which a contact gas phase oxidation method is employed as a method for synthesizing acrylic acid.

  First, an acrylic acid raw material such as propylene and / or acrolein, a molecular oxygen-containing gas such as air, and a dilution gas are mixed to prepare a raw material gas. This raw material gas is supplied to a reactor filled with a catalytic gas phase oxidation catalyst, and an acrylic acid-containing gas is obtained by a catalytic gas phase oxidation reaction (synthesis process).

  Next, the obtained acrylic acid-containing gas is brought into contact with a collection solvent and supplied to a collection tower that collects it as an acrylic acid-containing solution (collection step). The collection tower is not particularly limited as long as it can sufficiently contact the acrylic acid gas and the collection solvent for collecting acrylic acid. For example, a plate tower, a packed tower, a wet wall A known collection tower such as a tower or a spray tower can be used.

  The collection solvent is not particularly limited as long as it can absorb and dissolve acrylic acid. For example, diphenyl ether, diphenyl, o-dimethyl phthalate, a high-boiling organic solvent such as a mixture of diphenyl ether and diphenyl, water, Conventionally known materials such as water containing an organic acid generated from the acrylic acid purification process, an acrylic acid solution, and ejector wastewater can be widely used.

  The acrylic acid-containing gas is supplied from the bottom of the collection tower, while the collection solvent is supplied from the top of the collection tower. At this time, the contact method between the acrylic acid-containing gas and the collection solvent is not limited. For example, cross flow contact using bubble bell tray, uniflat tray, perforated plate tray, jet tray, bubble tray, venturi tray; turbo Any known contact method such as grid tray, dual flow tray, ripple tray, kittel tray, gauze type, sheet type, grit type regular packing, and countercurrent contact using irregular packing can be used.

  Next, the acrylic acid-containing solution obtained in the collection tower is extracted from the bottom of the collection tower and supplied to the purification step. The purification step is not particularly limited, and conventionally known purification methods such as distillation purification method, crystallization purification method, membrane separation method, chemical treatment method and the like can be used alone or in combination.

  In addition, when adopting the above-mentioned distillation purification method, an azeotropic separation method (azeotropic separation step) in which a crude acrylic acid solution is obtained from an acrylic acid-containing solution by distillation in the presence of an azeotropic solvent is employed. Also good. As a distillation column usable in the azeotropic separation method, a known column such as a plate column, a packed column, a wet wall column, or a spray column can be used. Examples of the azeotropic solvent include toluene, heptane, dimethylcyclotoluene, methyl isobutyl ketone, ethyl acrylate, methyl methacrylate, hexane, and butyl acetate.

  The operating conditions of the acrylic acid synthesis step, acrylic acid gas collection step, azeotropic separation step, and purification step are not particularly limited, and the composition of the generated acrylic acid gas, the acrylic acid-containing solution, and the crude acrylic acid solution What is necessary is just to adjust, considering a composition etc. suitably.

  In the present invention, in addition to the above steps, a high boiling point component separation step for separating high boiling point components in a distillation column, a decomposition step for decomposing Michael adducts contained in the high boiling point components to produce acrylic acid, and the decomposition step A recovery process for recovering the acrylic acid produced in step 1 is employed. The recovery process may be any process that can recover the acrylic acid generated in the decomposition process. For example, a preceding process such as a collection process or a purification process may be used as the recovery process. In terms of product quality, it is preferable to recover in the high boiling point component separation step in the previous step.

  The high boiling point component separation step employed in the present invention may be included in the purification step. Moreover, the said decomposition | disassembly process and collection | recovery process may be provided as a process different from a refinement | purification process, even if included in a refinement | purification process. As a preferred embodiment of the present invention, the high boiling point component-containing liquid separated from the target product acrylic acid in the purification step (high boiling point component separation step) and discharged is subjected to a decomposition step and a recovery step, The aspect which collect | recovers acrylic acid is mentioned.

  Next, a preferred embodiment of the present invention will be specifically described with reference to the process shown in FIG.

[High boiling point component separation process]
A distillation column for separating a high-boiling-point component through a line L-1 from a high-boiling-component-containing liquid supplied to a purification step (not shown) through a synthesis step and a collection step and separated from acrylic acid in the step. 1 (high boiling point component separation tower) (high boiling point component separation step).

  This high boiling point component separation step may be a step of separating acrylic acid and high boiling point components in the purification step (not shown), and is included in the high boiling point component-containing liquid separated from acrylic acid in the purification step. Any of the process of isolate | separating the high boiling point component and acrylic acid and other low boiling point components which are contained in the said high boiling point component containing liquid may be sufficient. The separated acrylic acid is distilled from the top of the distillation column 1 and condensed in the condenser E-1 through the line L-2, and then supplied as a product or further purification process. To collect for. At this time, a part of the acrylic acid introduced into the line L-2 may be circulated to the distillation column 1 and used as a reflux liquid.

  On the other hand, the bottom liquid (high boiling point component) of the distillation column 1 is supplied to the reaction device (distillation column) 2 (decomposition step) through the line L-3. Moreover, although all the high boiling components introduced into the line L-3 may be supplied to the next step, a part thereof is passed through the heat source E-2 on the line L-3, and then again to the distillation column 1. It may be circulated. The distillate distilled off from the distillation column 1 and the discharged bottom solution are passed through a strainer before being supplied to the next step to remove insoluble components contained in the distillate or the bottom solution. Also good.

  Here, the high boiling point component means a by-product or a starting material during the production of acrylic acid, and includes a component having a boiling point higher than that of acrylic acid in a standard state. Specific examples of the high boiling point component include Michael adducts (such as dimers of acrylic acid), furfural, protoanemonin, maleic acid, and maleic anhydride.

  Examples of the apparatus that can be used as the distillation tower (high boiling separation tower) in the high boiling point component separation step include a packed tower and a plate tower (tray tower). As the packing to be packed in the packed tower, any of those exemplified as the packing in the decomposition step described later can be used, and the tray provided in the tray tower is a tray illustrated in the decomposition step described later. Can be used. Of course, the above filling and tray may be used in combination. In addition, it is preferable to employ | adopt a plate tower from a viewpoint of reducing the mixing of maleic acid into a distillate (acrylic acid). For example, the theoretical plate number of the plate column is preferably 2 to 20, more preferably 4 to 12, and the reflux ratio is preferably 0.2 to 4, more preferably 0.4 to 4. 2.

  The operating conditions of the distillation tower (high boiling point component separation tower) are not particularly limited as long as acrylic acid and high boiling point components can be separated, and the acrylic acid concentration and water concentration of the high boiling point component (crude acrylic acid solution) to be introduced, It can be appropriately selected depending on the acetic acid concentration and the like. For example, the column bottom temperature is preferably 90 ° C. or higher, more preferably 95 ° C. or higher, preferably 130 ° C. or lower, more preferably 125 ° C. or lower, and further preferably 120 ° C. or lower. On the other hand, the top temperature of the distillation column is usually preferably 40 to 90 ° C, more preferably 50 to 80 ° C. The residence time of the column bottom liquid is preferably 2 to 30 hours. More preferably, it is 4 to 25 hours. Furthermore, the ratio “F / B” (hereinafter, F / B is referred to as the concentration ratio) of the mass F of the liquid supplied to the distillation column to the mass B of the liquid extracted from the distillation column (column bottom liquid) is 5-20. Preferably, it is 8-15. In addition, it is preferable that tower top pressure (absolute pressure) shall be 1.0-40 kPa, More preferably, it is 1.5-30 kPa, More preferably, it is 2.0-20 kPa. If the pressure at the top of the column is in the above range, it is not necessary to increase the size of the distillation column, the condenser installed in the distillation column or the vacuum apparatus, and there is little possibility of polymerization of acrylic acid or the like.

  The heat source E-2 of the distillation tower (high boiling distillation tower) is a heat exchanger such as a multi-tube heat exchanger, a plate heat exchanger, a spiral heat exchanger, a forced circulation heat exchanger, or a thin film evaporator. Or a reboiler can be used.

  During distillation, a polymerization inhibitor may be added to the reflux liquid in order to prevent polymerization of a polymerizable substance such as acrylic acid. Examples of such a polymerization inhibitor include manganese such as N-oxyl compounds, phenol compounds, and manganese acetate described in JP-A-2001-348360, JP-A-2001-348358, and JP-A-2001-348359. Examples thereof include one or more compounds selected from the group consisting of a salt, a copper salt of dialkyldithiocarbamate such as copper dibutylthiocarbamate, a nitroso compound, an amine compound and phenothiazine.

  The distillate obtained in the above distillation step may be used as a product (acrylic acid) or supplied to a further purification step. Of course, the distillate from the distillation column (high-boiling separation column) may be supplied as an acrylic acid-containing liquid to a collection step, an azeotropic dehydration step, etc., which are upstream of the distillation step ( Recovery).

  On the other hand, the bottom liquid of the distillation tower 1 (high boiling separation tower) is supplied to the reaction apparatus 2 (reactive distillation tower) through the line L-3, and the valuables contained in the bottom liquid are decomposed to produce acrylic. Acid is generated (decomposition step).

  In the method of the present invention, the ratio of the amount of maleic acid is 70% or less when the total amount of maleic acid and maleic anhydride contained in the high boiling point component supplied to the decomposition step is 100% by mass. The total maleic acid concentration (total concentration of maleic acid and maleic anhydride) at this time is 3 to 25% by mass in 100% by mass of the liquid (high-boiling component-containing liquid) supplied to the decomposition step. preferable. More preferably, it is 5-20 mass%, More preferably, it is 7-14 mass%. Moreover, it is preferable that the density | concentration (with respect to 100 mass% of high boiling component containing liquids) of the Michael adduct contained in the high boiling component supplied to a decomposition process shall be 20-60 mass%. More preferably, it is 25-55 mass%, More preferably, it is 30-50 mass%. In order to make the amount of maleic acid in the high boiling point component within the above range, the bottom temperature of the distillation column, the residence time, the concentration factor, the number of theoretical plates of the distillation apparatus used, the reflux ratio, etc. in the high boiling point component separation step These operating conditions may be controlled as described above. In addition, the distillation (column bottom) temperature, residence time, concentration rate, reflux ratio, tower temperature, etc. of the decomposition step described later are controlled and distilled using the distillate (circulated liquid) from the decomposition step. The amount of hydrated maleic acid or the amount of Michael adduct in the high boiling point component supplied to the tower may be adjusted.

  Thus, in accordance with the adjustment of the amount of maleic acid in the high-boiling component-containing liquid, it is a preferred embodiment of the present invention to adjust the amount of the Michael adduct to a specific range. This can further reduce problems such as blockage of piping derived from maleic acid in the decomposition step, which will be described later, deposits, and increased viscosity of waste oil.

[Disassembly process]
In the distillation step, the high-boiling components extracted from the bottom of the distillation column 1 (high-boiling component separation column) are supplied to the reactor 2 (distillation column 2) that decomposes the Michael adduct through the line L-3. To do. The high-boiling components include Michael adducts such as acrylic acid dimer, acrylic acid trimer, and acrylic acid oligomer, which can be recovered as acrylic acid by decomposition. That is, the decomposition step according to the present invention is a step in which a high-boiling component is heated and a valuable material such as a Michael adduct contained in the high-boiling component is decomposed to generate acrylic acid (decomposition step).

  As shown in FIG. 1, the acrylic acid produced in the reactor 2 is distilled from the top of the reactor 2 and through the line L-4 and the line L-1 connected to the high boiling separation column, Alternatively, it is circulated directly from the line L-4 to the distillation column 1 (not shown). On the other hand, the residual liquid in the reactor 2 may be discharged out of the system through the line L-5. Of course, a part of the residual liquid may be circulated to the heat exchanger E-3 and returned to the reaction apparatus 2. In addition, in FIG. 1, the example which uses a forced circulation type heat exchanger as a heat exchanger is shown.

  In the present invention, it is preferable that the decomposition step adopts a reactive distillation method that can simultaneously decompose the Michael adduct and evaporate or distill the decomposition product (acrylic acid). Here, the reactive distillation format means a method in which the decomposition product is distilled off by distillation while decomposing the Michael adduct. The reaction in which the Michael adduct is formed from acrylic acid is an equilibrium reaction. Therefore, by adopting the reactive distillation method, if the acrylic acid, which is the decomposition product, is distilled away at the same time as the decomposition reaction of Michael adduct, the equilibrium shifts in the direction of increasing the amount of acrylic acid produced. The reaction is accelerated and the Michael adduct can be efficiently decomposed.

  The embodiment of the reactive distillation is not limited and can be any of batch, semi-continuous and continuous, but it is preferable to adopt a continuous method. There are no particular restrictions on the type of the reactor, and a simple reactor such as a single distiller, a distillation column or a packed column, a distillation column provided with a tray (shelf) in the reactor, a reactor and a rectification column. A general reactive distillation apparatus such as an apparatus combining the above and a reactor equipped with a stirrer can be used.

  From the viewpoint of preventing contamination in the column and efficiently separating maleic acid and by-products having a boiling point close to that of acrylic acid (for example, benzaldehyde and furfural), a plate-type distillation column is used. preferable. In this case, for example, the theoretical plate is preferably 2 or more, more preferably 3 or more, preferably 15 or less, more preferably 10 or less, and the reflux ratio is 0.5 to 6, more preferably 0. 7 to 4 is preferable. Since the distillation of furfural and benzaldehyde can be suppressed by setting the theoretical plate and the reflux ratio within the above ranges, the product quality can be kept good. Furthermore, by controlling the composition in the tower and the liquid depth per tray, the concentration and precipitation of maleic acid in the tower and the generation of a copolymer with acrylic acid are further suppressed. Troubles such as an increase in pressure loss and increase in utilities such as operating costs can be suppressed. The distillate may be supplied as a circulating liquid to a preceding process such as a synthesis process or a collection process. If maleic acid is contained in the circulating liquid, water is present in the preceding process. In this process, maleic acid may become hydrated again. In such a case, the amount of hydrous maleic acid in the feed liquid to the decomposition step may increase. Therefore, it is desirable to reduce the maleic acid concentration in the distillate as much as possible in order to further reduce the amount of hydrated maleic acid in the feed solution to the decomposition step. It is preferable to do.

  Examples of the tray (tray) provided in the decomposition reaction apparatus include a cross flow contact using a bubble bell tray, a uniflat tray, a perforated plate tray, a jet tray, a bubble tray, and a venturi tray; a turbo grid tray and a dual flow tray , Ripple tray, kittel tray and so on. As described above, a tray having an opening with a pore diameter of 10 to 50 mm (more preferably 12 to 30 mm) is employed from the viewpoint of preventing the concentration and precipitation of maleic acid in the column and the accumulation of a copolymer with acrylic acid. Is preferred. Moreover, you may use combining a tray and a filler.

The filler is preferably one that has durability against pressure and high temperature and does not easily react with the components in the residual mother liquor. From this point of view, one made of metal such as alumina or stainless steel is recommended. The shape of the packing is preferably such that it is difficult to increase the pressure loss of the reactive distillation apparatus. Such packings include known Raschig rings, Lessing rings, pole rings, flexi rings, cascade mini rings (Dotwell), Raschig Super Rings, Interlocks Metal Tower Packing (Norton) and Interlocks saddle (manufactured by Norton), chemical engineering handbook (6th edition, page 604, FIGS. 11 and 13), Merapack (manufactured by Sumitomo Heavy Industries, Ltd.), Gempack (Chiyoda Corporation) ), Techno Pack (manufactured by Sancool Techno Co., Ltd.), Monz Pack (manufactured by Monz), Interlocks High Performance Structured Packing (manufactured by Norton), and other chemical engineering manuals (Chemical Engineering Association, 6th edition) Examples include mold rule filling. Depending on the size of reactor used, supply amount of residual mother liquor, temperature conditions, pressure conditions, number of theoretical plates, pressure loss, minimum liquid flow rate, and other factors, the diameter and shape to be used can be selected. Good. Among the packings mentioned above, the Raschig ring, Lessing ring, Pole ring, Flexi ring, Cascade mini ring, Raschig super ring, Interlocks metal tower packing and Interlocks saddle are all filled surface area per m ^3. Moreover, since the porosity is high, mass exchange is performed efficiently and pressure loss can be reduced. Most preferred is a cascade mini-ring.

  When a plate-type distillation column is employed as the reaction apparatus, it is preferable to heat a portion of 70 to 100% of the total theoretical plate starting from the column top side to 125 ° C. or lower. More preferably, it is 90-120 degreeC, More preferably, it is 95-115 degreeC. In addition, "the part of 70 to 100% of the total theoretical plate from the tower top side" means any part of 70 to 100% of the total theoretical plate number when the tower top is counted as the first stage. It corresponds to the lower part in the height direction of the plate-type distillation column. This part corresponds to the position where the reaction liquid (high boiling point component) heated by the heat exchanger is supplied, so the temperature is likely to rise in the distillation apparatus. This is one of the places where precipitation of hydrated maleic acid and acrylic acid is likely to occur. Moreover, when the temperature of this position is too low, it may be difficult to proceed with the decomposition reaction of the Michael adduct. Therefore, by making the temperature of the said part into the said range, the production | generation of a polymer can be suppressed and the decomposition reaction of a Michael adduct can be advanced more smoothly.

  The residence time (based on the extracted liquid) of the reaction liquid (high boiling point component) in the reaction apparatus may be appropriately set according to the tower bottom temperature. For example, it is preferably 0.2 to 30 hours, more preferably 0.5 to 15 hours, more preferably 1 to 10 hours. If the temperature is too high or the residence time is too long, the decomposition reaction proceeds, but the properties of the reaction solution such as an increase in viscosity may be deteriorated, or dirt may be deposited in the reaction apparatus. On the other hand, if the temperature is too low or the residence time is too short, the Michael adduct may not be sufficiently decomposed. In addition, when employing an azeotropic dehydration step, maleic acid in the high boiling point component is often present as hydrous maleic acid, and troubles such as precipitation are likely to occur. By heating to a temperature at which the decomposition reaction of the adduct reaches equilibrium and shortening the residence time, the Michael adduct can be decomposed more efficiently and without deteriorating the properties of the reaction solution.

  As the heat source E-3 of the reactive distillation apparatus, a multi-tube heat exchanger, a plate heat exchanger, a spiral heat exchanger, a forced circulation heat exchanger, a thin film evaporator, a reboiler, or the like can be used. In particular, when the decomposition target has a high viscosity or when it is necessary to keep the tower bottom of the reaction apparatus at a high temperature, it is preferable to employ a forced circulation heat exchanger among the above heat exchangers. The forced circulation heat exchanger is equipped with a circulation pump, and adopts a configuration in which a part of the bottom liquid in the reaction apparatus is continuously taken out, heated, and returned to the reaction apparatus. Compared with the case of heating through the wall surface in the reaction apparatus, the generation and adhesion of polymer and precipitate in the apparatus are reduced. As the forced circulation heat exchanger, for example, as described in Japanese Patent Application Laid-Open No. 09-110778, a squeezed structure may be provided in the middle of the piping. This is because the liquid overheated state can be maintained, and the energy required for boiling and vaporization can be efficiently supplied into the reactor. In addition, since troubles due to dirt and property deterioration are also suppressed, the decomposition reaction can be performed promptly.

When a forced circulation heat exchanger is used, the decomposition temperature (column bottom temperature, high boiling point component temperature) is preferably operated at 155 to 220 ° C, more preferably 160 to 200 ° C. At this time, the temperature of the heat source of the forced circulation heat exchanger is preferably adjusted so that the difference between the decomposition temperature (column bottom temperature) and the temperature of the heat source is 15 to 80 ° C., more preferably the difference. Is recommended to be 20-60 ° C. By making the difference between the decomposition temperature (column bottom temperature) and the heating temperature within the above range, it is possible to suppress the deterioration of properties such as dirt on the heat exchanger and increase in viscosity of waste oil. The difference between the decomposition temperature (column bottom temperature) and the heating temperature is more preferably in the above range. The circulation rate of the bottom liquid in the forced circulation heat exchanger is preferably 100 to 300 m ³ / hr, more preferably 140 to 250 m ³ / hr. By setting the amount of circulation within the above range, sufficient thermal efficiency can be obtained and adhesion of dirt to the heat exchanger can be suppressed, which is preferable for stable operation over a long period of time.

  Further, in order to reduce dirt and property deterioration troubles in the reaction apparatus, a liquid splash collision plate or the like may be provided in the apparatus. Thereby, when supplying the feed liquid into the reactor in the distillation column, the liquid splash from the liquid surface is cut, so that troubles caused by the formation of polymer and precipitates above the collision plate are reduced. Can do.

  The pressure at the time of the decomposition reaction can evaporate most of the useful components such as acrylic acid generated by the decomposition reaction and acrylic acid contained in the feed liquid that is the raw material of the decomposition reaction, and is the equilibrium reaction Michael It is preferable to employ a pressure that allows the decomposition of the adduct to proceed more rapidly. For example, the tower top pressure (gauge pressure) of the reactor is preferably 6.7 to 64 kPa (50 to 480 torr), more preferably 13.3 to 40 kPa (100 to 300 torr), and still more preferably 20 to 33.32. 3 kPa (150 to 250 torr) is recommended (operation pressure). The column top temperature is preferably 60 to 150 ° C, more preferably 80 to 130 ° C, and still more preferably 90 to 120 ° C. By setting the tower top pressure and tower top temperature within the above ranges, protoanemonin, which is a high boiling component in the by-product, furfural having a boiling point close to that of acrylic acid, benzaldehyde, and the like are distilled together with acrylic acid. Since it can suppress, even if it supplies the distillate of a decomposition process to the collection tower (collection process) of acrylic acid gas, or a high boiling separation tower (distillation process), product quality can be maintained favorable. Moreover, since the high temperature is not required for the decomposition reaction of the Michael adduct as in the case where the tower top pressure or the tower top temperature is too high, the property of the reaction solution is hardly deteriorated and the decomposition rate is hardly lowered.

  In the decomposition step, in order to promote the decomposition of the Michael adduct, as a catalyst, inorganic acid such as Lewis acid, Lewis base, sulfuric acid, phosphoric acid, alkali metal, alkaline earth metal, methanesulfonic acid, p-toluenesulfonic acid One or more selected from organic acids such as N-oxyl compounds and amines may be used. Among the decomposition catalysts, it is preferable to employ N-oxyl compounds. Circulating liquid in which the N-oxyl compound is circulated to the decomposition step, that is, the distillate distilled from the reactive distillation column to other steps, for example, the collection step of acrylic acid gas or the distillation step (high boiling separation column 1). This is because it can also act as a polymerization inhibitor for acrylic acid if it is contained therein.

  The addition amount of the catalyst is preferably 0.05 to 3% by mass, more preferably 0.1 to 1% by mass with respect to the bottom liquid of the reactor. The catalyst only needs to be present at the time of decomposition, and the timing of addition of the catalyst is not limited to the decomposition step. For example, the collection column and various distillation columns in the acrylic acid collection step, and further the decomposition You may add when supplying a high boiling point component containing liquid to the reactor used at a process.

[Recovery process]
Acrylic acid produced by the decomposition of the Michael adduct in the decomposition step is recovered from the top of the reactor 2 (distillation column in the decomposition step), and is collected through the line L-4 to collect the acrylic acid (not shown). It is sent to the distillation column 1. At this time, the maleic acid concentration in the distillate extracted from the top of the reactor 2 is preferably as low as possible, but is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and still more preferably Is 1.5% by mass or less, more preferably 0.6% by mass or less. This reduces maleic acid concentration troubles and can reduce the amount of hydrated maleic acid in the feed liquid from the high boiling point component separation tower in the previous step, reducing the maleic acid concentration in the distillate. For example, the operating conditions such as the number of theoretical plates of the reactor used as the reaction apparatus and the reflux ratio may be set within the above range.

  Moreover, in order to prevent polymerization of acrylic acid contained in the distillate, oxygen or a gas containing oxygen may be added to the distillate distilled off from the reactor 2. Such an oxygen-containing gas may be introduced into the gas phase portion or the liquid phase portion at the bottom of the reactive distillation apparatus. Examples of the oxygen-containing gas include pure oxygen, a mixed gas obtained by diluting oxygen with an inert gas (such as nitrogen), and air. The addition amount is preferably such that the oxygen concentration is 0.01 to 5% by volume, more preferably 0.02 to 3% by volume, with respect to the volume of gas distilled from the top of the reactor 2. And more preferably 0.05 to 1% by volume. When the oxygen concentration in the distillate gas is within the above range, the polymerization preventing effect can be sufficiently obtained. In addition, the amount of the active ingredient discharged outside the system accompanying oxygen or an oxygen-containing gas can be suppressed to a low level, and the pressure control in the decomposition process is facilitated.

  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.

[Percentage of maleic acid]
In this example, the proportion of maleic acid in the high-boiling component supplied from the separation step of the high-boiling component to the decomposition step is measured by the mass of maleic acid and maleic anhydride contained in the bottom liquid of the high-boiling separation column. Then, the ratio of the maleic acid amount was calculated by substituting the obtained value into the following formula.

  In addition, the mass of the maleic acid measured the mass of the monomethyl maleic acid produced | generated by making the maleic acid contained in a tower bottom liquid react with methanol by gas chromatography, and converted the obtained value into the mass of maleic acid. At this time, maleic anhydride does not react with methanol.

On the other hand, the mass of maleic anhydride was determined by measuring the total mass of maleic acid and maleic anhydride contained in the column bottom liquid by liquid chromatography, and subtracting the mass of maleic acid from this value. Mass.
[Percentage of maleic acid content (%)]

[Conversion rate]
The mass of the Michael adduct contained in the high-boiling component-containing liquid supplied to the decomposition step and the distillate after the decomposition step was measured by gas chromatography, and the conversion rate of the Michael adduct was calculated from the following formula.

[Selection rate]
The mass of Michael adduct in the high boiling point component-containing liquid supplied to the decomposition step, the mass of acrylic acid, and the mass of acrylic acid contained in the distillate after the decomposition step are measured by gas chromatography. From this, the selectivity of the decomposition reaction was calculated.

[Synthesis of acrylic acid]
The acrylic acid-containing gas obtained by the propylene catalytic gas-phase oxidation method is brought into contact with a collection solvent and collected as an acrylic acid-containing solution (collection step), and then the acrylic obtained in the provided azeotropic separation step A low-boiling component was removed from the acid-containing solution to obtain a crude acrylic acid solution containing a high-boiling component. The composition of the obtained crude acrylic acid solution was acrylic acid: 96.05 mass%, maleic acid: 0.49 mass%, maleic anhydride: 0.33 mass%, acrylic acid dimer (Michael adduct): 3% by mass, furfural: 0.03% by mass, benzaldehyde: 0.03% by mass, protoanemonin: 0.02% by mass, and water: 0.05% by mass.

[Experimental Example 1-1]
Acrylic acid was recovered according to the process chart shown in FIG. In Experimental Example 1, a high-boiling separation column (number of stages: 50 plates, unweired perforated plate distillation column) is used as the distillation column 1 in the high-boiling component separation step, and a reactive distillation column with a step column is used as the reaction device 2 in the decomposition step. (Number of stages: 20 stages, no weir perforated plate distillation tower 2) was used. In addition, a forced circulation heat exchanger (“E-3” in FIG. 1) is used as a heat exchanger in the decomposition process, and a strainer is used to supply each feed liquid to the high boiling separation tower and the reactive distillation tower. (Z-1 to Z-6) were passed through after removing insoluble matters in the liquid. At this time, the decomposition temperature in the decomposition step (bottom temperature of the reactive distillation column) is 170 ° C., and the temperature of the site where the total number of theoretical plates in the reactive distillation column is 80% (the 16th plate of the 20th theoretical plate) is 120 ° C. The ratio was 4. The temperature of the heat source of the forced circulation heat exchanger was 220 ° C., and the temperature difference (ΔT) between the decomposition temperature and the heat source of the forced circulation heat exchanger was 50 ° C.

  First, the crude acrylic acid solution obtained by the synthesis of acrylic acid was introduced into the distillation column 1 (high boiling separation column) together with the distillate from the decomposition step described later. The distillation column 1 is operated at an operating pressure of 46.7 hPa (mmhg), a column bottom temperature of 98 ° C., operated at a reflux ratio of 0.9, a residence time of the column bottom liquid of 5 hours, and acrylic acid from the column top. And other low-boiling components were distilled off to obtain a high-boiling liquid (high-boiling component) containing Michael adducts from the bottom of the column. The ratio of the amount of maleic acid contained in the high boiling point liquid obtained at this time (value calculated by the above mathematical formula) was 38%. Moreover, 42 mass% of Michael adduct was contained.

  Next, the obtained high-boiling liquid was introduced into the reaction apparatus 2 (reactive distillation tower with a plate column) at 10 kg / hr, and the Michael adduct was decomposed and recovered. Table 1 shows the operating conditions and results of the reactor 2 (decomposition step) at this time.

  Although the Michael adduct decomposition operation was continued for 2 weeks, no troubles such as contamination and pressure increase in the reactor occurred, and the viscosity of the waste oil (the bottom liquid of the reactor 2) was low. The Michael adduct could be decomposed stably. The value of the waste oil viscosity was measured at a constant temperature (100 ° C.) using a vibration type viscometer.

  At this time, the conversion rate of the Michael adduct was 85%, and the yield of acrylic acid based on the supplied Michael adduct was 83.3%.

[Experimental example 1-2]
In the synthesis of acrylic acid as a high-boiling content liquid supplied to the distillation tower 1 (high-boiling separation tower), the residual mother liquor of the crystallization process obtained by performing crystallization purification after the collection process is used as a crude acrylic acid solution. Acrylic acid was recovered in the same manner as in Experimental Example 1 except that it was used. The composition of the crude acrylic acid solution thus obtained was acrylic acid: 87.1% by mass, maleic acid: 0.72% by mass, maleic anhydride: 0.1% by mass, acrylic acid dimer (Mikael). Adduct): 3.1% by mass, furfural: 0.03% by mass, benzaldehyde: 0.03% by mass, protoanemonin: 0.02% by mass, water: 8.9% by mass.

  The above crude acrylic acid solution was supplied to the distillation column 1 and the distillation column 1 was operated under the conditions shown in Table 1 to obtain a high-boiling liquid containing Michael adduct from the bottom of the distillation column 1. The high-boiling liquid obtained at this time contained 62% maleic acid with respect to the total amount of maleic acid and maleic anhydride (ratio of the amount of maleic acid calculated by the above formula, the following experiment) The same applies to the example). The Michael adduct was 42% by mass.

  The obtained high-boiling liquid was supplied to the reactor 2 and the reactor was operated under the same conditions as in Experimental Example 1-1 to decompose and recover the Michael adduct. The results are shown in Table 1.

  Although the Michael adduct decomposition operation was continued for two weeks, the reactor and other ancillary equipment were free from problems such as contamination and pressure rise in the reactor, and the waste oil had a low viscosity and was operating stably. .

  At this time, the conversion rate of the Michael adduct was 82%, and the yield of acrylic acid relative to the supplied Michael adduct was 80%.

[Experimental Example 1-3]
Acrylic acid was recovered in the same manner as in Experimental Example 1-2, except that the operating conditions of the distillation column 1 (high boiling point component separation column) were changed to the conditions shown in Table 1. At this time, the high-boiling liquid supplied to the reactor 2 contained 80% maleic acid with respect to the total amount of maleic acid and maleic anhydride.

  When the Michael adduct was decomposed, it was confirmed that dirt was attached to the heat exchanger E-3. Moreover, since the waste oil viscosity increased and the internal pressure of the reactor 2 increased, the operation was stopped in one week. At this time, the conversion rate of the Michael adduct was 72%, and the yield of acrylic acid based on the supplied Michael adduct was 58%. The results are shown in Table 1.

  In addition, the high-boiling-containing liquid used in Experimental Example 1-3 is a residual mother liquor separated from the product after crystallization purification similar to Experimental Example 1-2. Therefore, the water content of the residual mother liquor is slightly larger than the crude acrylic acid solution of Experimental Example 1-1 obtained through the azeotropic separation process, and the high boiling point component separation process employed in Experimental Example 1-3. Under the above conditions (the column bottom temperature is slightly lower than that of Experimental Examples 1-1 and 1-2 and the F / B is small), maleic anhydride is hydrated maleate at the column bottom (in the column bottom liquid) of the distillation column 1. It is thought that the environment was prone to acid. The reason why the ratio of the amount of maleic acid in Experimental Example 1-3 was slightly higher than in Experimental Examples 1-1 and 1-2 is considered to be due to the above reason.

  From the results of Experimental Example 1-1 to Experimental Example 1-3, if the amount of maleic acid contained in the high-boiling liquid supplied to the decomposition step is reduced in advance, the increase in solution viscosity and the generation of polymer are suppressed. It can be seen that the Michael adduct can be efficiently decomposed and recovered.

[Experimental example 2-1]
A high-boiling liquid was obtained in the same manner as in Experimental Example 1-1 except that the operating conditions of the distillation column 1 (high-boiling component separation column) were changed as shown in Table 1. The resulting high-boiling liquid contained 62% maleic acid based on the total amount of maleic acid and maleic anhydride. Moreover, 20 mass% of acrylic acid dimers (Michael adduct) were contained in the high boiling content liquid.

  The above high-boiling liquid was supplied to the reactor 2 (reactive distillation column), and the decomposition operation of the Michael adduct was continued for 2 weeks. However, no contamination was observed on the reactor or its incidental equipment. In addition, troubles such as pressure rise in the equipment did not occur, and the viscosity of the waste oil was low and it operated stably. At this time, the conversion rate of the Michael adduct was 70%, and the yield of acrylic acid based on the supplied Michael adduct was 63%. The results are shown in Table 1.

[Experimental example 2-2]
A high-boiling liquid was obtained in the same manner as in Experimental Example 1-1 except that the operating conditions of the distillation column 1 (high-boiling component separation column) were changed as shown in Table 1. The obtained high boiling point liquid contained 63% by mass of acrylic acid dimer (Michael adduct), and contained 62% maleic acid with respect to the total amount of maleic acid and maleic anhydride.

  The high-boiling content liquid was supplied to the reactor 2 and the Michael adduct was decomposed. In addition, the high boiling content liquid supplied at this time had a little amount of Michael adduct compared with Experimental Example 2-1. When two weeks had passed since the start of the decomposition operation, the separation tower and the incidental facilities were checked. Although the amount was small, dirt was attached to the heat exchanger, and an increase in the viscosity of the waste oil was confirmed. The degree of adhesion of dirt and increase in viscosity of the waste oil was such that the decomposition operation could be continued once. The conversion rate of the Michael adduct at this time was 82%, and the yield of acrylic acid based on the supplied Michael adduct was 72%. The results are shown in Table 1.

  From the results of Experimental Example 2-1 and Experimental Example 2-2, in addition to the amount of maleic acid in the high boiling point liquid supplied to the decomposition step, the concentration of the Michael adduct is within the preferred range of the present invention (high boiling point component containing liquid 100 From 20 to 60% by mass), it can be seen that an increase in solution viscosity and generation of a polymer are suppressed, and the decomposition process can be performed more stably.

[Experimental example 3-1]
The temperature of 80% of the total theoretical stage (the 16th stage of the 20th theoretical stage, hereinafter referred to as the “lower stage”), starting from the top of the reactive distillation column with a column used as a reactor, is 140 ° C. Except that, the high boiling point component separation step and the decomposition step were performed in the same manner as in Experimental Example 1-1, and acrylic acid was recovered. The high-boiling liquid supplied to the reactor at this time contained 42% by mass of Michael adduct, and further contained 78% maleic acid with respect to the total amount of maleic acid and maleic anhydride. Table 1 shows the operating conditions at this time.

  During the operation of the reaction apparatus 2, the distillate from the top of the reaction apparatus 2 and the staying liquid in the middle stage of the reaction apparatus were analyzed. As a result, the total amount of maleic acid and maleic anhydride was 8% by mass in the distillate. The staying liquid in the middle column of the distillation column contained 70% by mass of maleic acid and maleic anhydride in total.

  Although the operation of the reaction apparatus 2 was continued, the operation was stopped in one week because the pressure in the apparatus increased. At this time, the conversion rate of the Michael adduct was 85%, and the yield of acrylic acid with respect to the supplied Michael adduct was 78%. The results are shown in Table 1.

  In Experimental Example 3-1, the temperature in the vicinity of the lower stage of the reactive distillation column in the decomposition process (the 16th stage in 20 theoretical stages and 80% of the total theoretical stage) was set to Example 1-1 (120 ° C.). It was set to 140 ° C., which is slightly higher than that. As a result, it is considered that maleic acid is concentrated in the vicinity of the lower stage in the reactive distillation column, and precipitation of hydrous maleic acid and a copolymer with acrylic acid are easily generated. In addition, since the amount of maleic acid contained in the high-boiling liquid was large, it is considered that the amount of maleic acid distilled from the top of the reactive distillation column was increased by heating. That is, in Experimental Example 3-1, although the same acrylic acid-containing liquid as in Experimental Example 1-1 was used, the amount of maleic acid contained in the recovered acrylic acid (distillate from the decomposition step) was large. It is considered that the amount of maleic acid in the high-boiling liquid supplied to the decomposition process was increased.

[Experimental example 3-2]
Acrylic acid was recovered according to the same procedures and steps as in Experimental Example 1-1. However, the reactor (reactive distillation column with a column tower) was operated at a temperature of 110 ° C. at the lower stage (the 16th stage of the 20th theoretical stage) and a reflux ratio of 3 in the reactive distillation tower. At this time, the distillate from the reactive distillation column contains 2% by mass of maleic acid and maleic anhydride in total, and the staying liquid at the lower stage of the reactive distillation column contains 35% by mass of maleic acid and maleic anhydride in total. It was. Table 1 shows the operating conditions of the reactor.

  The operation of the reactive distillation column was continued for 2 weeks, but no contamination was confirmed in the reactor 2 and its associated equipment. Moreover, troubles such as an increase in pressure in the apparatus did not occur, and the waste oil viscosity of the reaction apparatus 2 (reactive distillation tower) was low and operated stably. At this time, the conversion rate of the Michael adduct was 86%, and the yield of acrylic acid based on the supplied Michael adduct was 84%. The results are shown in Table 1.

  In Experimental Example 3-2, since the temperature near the lower stage of the reactive distillation column was operated at a slightly lower temperature (110 ° C.) than in Experimental Example 3-1, and the reflux ratio was increased, the precipitation of maleic acid and the polymer It is considered that the problems such as the formation of bismuth and distillation of maleic acid from the top of the reactive distillation column were suppressed.

[Experimental Example 3-3]
Acrylic acid was recovered according to the same procedures and steps as in Experimental Example 1-1. However, the reaction apparatus (reactive distillation column with a column tower) was operated with the temperature of the lower stage (the 16th stage of the 20th theoretical stage) controlled to 120 ° C. and the reflux ratio in the reactive distillation tower set to 0.3. The high-boiling liquid supplied to the reaction apparatus at this time contained 42% by mass of the Michael adduct, and contained 72% maleic acid with respect to the total amount of maleic acid and maleic anhydride. The distillate from the reactive distillation column contains 6% by mass of maleic acid and maleic anhydride in total, and the staying liquid at the lower stage of the reactive distillation column contains 65% by mass of maleic acid and maleic anhydride in total. It was. Table 1 shows the operating conditions of the reactor.

  Although the operation of the reactor 2 was continued, the operation was stopped in one week because the pressure in the reactor 2 increased. At this time, the conversion rate of the Michael adduct was 75%, and the yield of acrylic acid relative to the supplied Michael adduct was 62%. The results are shown in Table 1.

  From the results of Experimental Example 1-1 and Experimental Example 3-1 to Experimental Example 3-3, the temperature of the middle stage of the reactive distillation column in the cracking process was controlled, and the reflux ratio was adjusted. It can be seen that the amount of maleic acid and maleic anhydride contained can be effectively reduced. This also contributes to reducing the amount of maleic acid in the high-boiling component-containing liquid supplied to the decomposition step to a specific amount or less, so by adopting the above-described conditions in the decomposition step, acrylic acid It can be seen that it can be recovered more efficiently.

[Experimental example 4-1]
Acrylic acid was recovered in the same manner as in Example 1-1 except that the operating pressure of the reactive distillation column was 46 hPa (35 torr), the decomposition temperature (column bottom temperature) was 140 ° C., and the reflux ratio was 1.2. Table 2 shows the operating conditions of the distillation column 1 and the reaction apparatus 2 (reactive distillation column).

  At this time, the high boiling point liquid supplied to the reactive distillation column 2 contained 74% maleic acid with respect to the total amount of maleic acid and maleic anhydride (42% by mass of Michael adduct). Moreover, when the composition of the distillate was analyzed during the operation of the reactive distillation column 2, the distillate contained 10% by mass of maleic acid and maleic anhydride.

  Although the operation of the reactor 2 was continued, the operation was stopped in one week because the pressure in the device increased. Dirt was gradually recognized in the tower and in ancillary equipment such as heat exchangers. At this time, the conversion rate of the Michael adduct was 68%, and the yield of acrylic acid relative to the supplied Michael adduct was 64%. The results are shown in Table 2.

[Experimental example 4-2]
Acrylic acid was obtained in the same manner as in Experimental Example 4-1, except that the operating pressure of the reactive distillation column was 467 hPa (350 torr), the decomposition temperature (column bottom temperature) was controlled at 210 ° C., and the reflux ratio was 1.2. Was recovered. Table 2 shows the operating conditions of the distillation column 1 and the reaction apparatus 2 (reactive distillation column).

  At this time, the high-boiling liquid supplied to the reactive distillation column 2 contained 50% maleic acid with respect to the total amount of maleic acid and maleic anhydride (42% by mass of Michael adduct). Further, when the composition of the distillate was analyzed during the operation of the reactive distillation column 2, the distillate contained 8% by mass of maleic acid and maleic anhydride in total.

  The decomposition operation of Michael adduct was continued for 2 weeks, but no noticeable contamination was observed in the reactive distillation column and its associated equipment. In addition, the pressure in the tower did not increase, and the viscosity of the waste oil was low and it operated stably. The conversion rate of the Michael adduct at this time was 80%, and the yield of acrylic acid relative to the supplied Michael adduct was 61%. The results are shown in Table 2.

  From the results of Experimental Example 1-1 and Experimental Examples 4-1 and 4-2, by changing the operating pressure and reaction temperature of the reactive distillation column to appropriate conditions, The amount of maleic acid can be reduced to a specific amount or less, the amount of maleic acid and maleic anhydride contained in the reactive distillation column distillate can be effectively reduced, and acrylic acid can be prevented while precipitating maleic acid in the column. It can be seen that can be recovered more efficiently.

[Experimental Example 5]
A distillation step and a decomposition step were performed in the same manner as in Example 1-1, except that a single distiller (an apparatus combining a distillation can and a condenser) was used as the reaction device 2 in the decomposition step. Table 2 shows the composition of the feed liquid and the operating conditions for each step.

  When the composition of the distillate from the reactor 2 was analyzed at this time, the distillate contained 18% by mass of maleic acid and maleic anhydride in total.

  When the decomposition operation of the Michael adduct was continued for one week, contamination was confirmed in the incidental equipment such as the reactor and the heat exchanger. The solution viscosity in the reactor was also very high. At this time, the conversion rate of the Michael adduct was 83%, and the yield of acrylic acid relative to the supplied Michael adduct was 71%. The results are shown in Table 2.

[Experimental Example 6]
Acrylic acid was recovered according to the process shown in FIG. In Experimental Example 6, as a distillation column 1 (high boiling separation column), a non-weired perforated plate distillation column having 50 plates, and as a reaction apparatus 2 in the decomposition step, a reactive distillation column with a column (20 plates, no weir) A thin film evaporation type heat exchanger E-4 equipped with a decomposition tank V-1 was used as a heat source for the reaction apparatus 2.

  An acrylic acid-containing solution was obtained in the same manner as in Experimental Example 1-1, and this was introduced into the distillation column 1. The operation pressure of the distillation column 1 is controlled to 46.7 hPa (35 mmHg), the column bottom temperature is 98 ° C., the reflux ratio is 0.9, the column bottom liquid residence time is 5 hours. A boiling liquid was obtained. Moreover, crude acrylic acid was obtained from the tower top.

  Next, the obtained high-boiling liquid is introduced into the reaction apparatus 2 (decomposition step) with a column tower at 10 kg / hr, and acrylic acid and other low-boiling components are evaporated by the thin film evaporator E-4. 2, while the bottom liquid of the thin film evaporator E-4 was introduced into the decomposition tank V-1. The decomposition tank V-1 was operated at 150 ° C. (decomposition temperature), normal pressure, and a residence time of 30 hours. The decomposition solution heated and decomposed in the decomposition tank V-1 was circulated to the thin film evaporator E-4 by a pump, and the Michael adduct decomposition reaction and the generated acrylic acid were recovered.

  When the Michael adduct decomposition operation was continued for 3 weeks, it was at a level where continuous operation was possible, but there was an increase in solution viscosity in the reactor 2 and some contamination on the auxiliary equipment such as the reactor 2 and heat exchanger was confirmed. It was done. At this time, the conversion rate of the Michael adduct was 70%, and the yield of acrylic acid relative to the supplied Michael adduct was 60%. The decomposition conditions and results at this time are shown in Table 2.

[Experimental Example 7]
An aqueous solution (50% by mass aqueous solution) containing 4H-TEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl) was used as a decomposition catalyst for the Michael adduct from the top of the distillation column 1. Acrylic acid was recovered in the same manner as in Experimental Example 1-1 except that it was introduced at 0.06 kg / hr.

  The decomposition operation of the Michael adduct was continued for 2 weeks, but no contamination was observed in the distillation column 2 and other incidental facilities, and no increase in pressure in the column occurred. Moreover, the waste oil viscosity was low, and the reactive distillation column was operating stably. In particular, compared with other experimental examples, there was less adhesion of the polymerization product in the system, and the waste oil viscosity was also low. At this time, the conversion rate of the Michael adduct was 88%, and the yield of acrylic acid with respect to the Michael adduct supplied to the decomposition step was 86%. The decomposition conditions and results at this time are shown in Table 2.

[Experimental Example 8]
Reactive distillation under the conditions that the decomposition temperature (column bottom temperature) is 170 ° C, the temperature of the heat source of the forced circulation heat exchanger is 220 ° C, and the temperature difference (ΔT) between the decomposition temperature and the heat source of the forced circulation heat exchanger is 100 ° C. Acrylic acid was recovered in the same manner as in Experimental Example 1-1 except that the tower (reaction apparatus 2) was operated.

  When the decomposition operation was continued for 2 weeks, contamination was confirmed on the heat transfer surface of the heat exchanger. At this time, the addition rate of the Michael adduct was 82%, and the yield of acrylic acid relative to the supplied Michael adduct was 78%. The results are shown in Table 2.

  In Tables 1 and 2, “F / B (* 1)” means the flow rate of feed liquid (kg / hr) to the distillation process / flow rate of extracted liquid (column bottom liquid) (kg / hr). “Percentage of hydrous maleic acid (* 2)” means the proportion of maleic acid calculated by the above formula, and “Total amount of maleic acid (* 3)” means the total amount of hydrous maleic acid and maleic anhydride. , “Residence time (* 4)” is a value calculated by [retentate liquid mass (kg) / extracted liquid flow rate discharged from reactor (kg / hr)], “lower stage (* 5)” This means the 16th stage (80% of the total theoretical stage starting from the top of the tower) of the reactive distillation column with 20 theoretical stages.

  According to the production method of the present invention, in the decomposition process of the Michael adduct, troubles such as precipitation of maleic acid and a pressure increase in the decomposition apparatus derived from this hardly occur. Thus, acrylic acid can be produced stably and efficiently.

It is process drawing which shows an example of the process of acrylic acid manufacture concerning this invention. It is process drawing which shows the other example of the process of acrylic acid manufacture concerning this invention.

Explanation of symbols

1 Distillation tower (high boiling point separation tower)
2 Reactor E-1 Condenser E-2 Reboiler E-3 Forced circulation heat exchanger E-3 Thin film evaporator L-1 to L-6, L-5 ′, L-5 ″ line (pipe)
V-1 Decomposition tank Z-1 to Z-6 Strainer

Claims (5)

An acrylic acid-containing gas obtained by vapor-phase oxidation of a raw material gas is collected as a crude acrylic acid-containing liquid, and a method for producing acrylic acid for purifying the collected crude acrylic acid-containing solution,
The step of purifying the crude acrylic acid-containing solution includes a high boiling point component separation step of separating a high boiling point component in a distillation column,
The high-boiling point is obtained by a reactive distillation method using a plate-type distillation column having three or more theoretical plates and a forced circulation heat exchanger, with a non-weir perforated plate having an opening with a pore diameter of 10 to 50 mm as a shelf. Decomposing process that decomposes Michael adducts contained in the ingredients to produce acrylic acid,
Including a recovery step of recovering acrylic acid generated in the decomposition step,
The decomposition step is performed with the heat source of the forced circulation heat exchanger so that the ratio (%) of the amount of maleic acid in the high boiling point component supplied from the high boiling point component separation step to the decomposition step satisfies the following formula: The temperature difference from the high boiling point component heated by the forced circulation heat exchanger is set to 15 to 80 ° C., the high boiling point component supplied to the decomposition step is heated to 155 to 220 ° C., and the above-mentioned plate distillation 70 to 100% of the sites of total theoretical stages as a base point the overhead side of the column and 125 ° C. or less, for controlling the operation conditions of the more the high-boiling component separated Engineering while operating at a reflux ratio of 0.5-6 that A process for producing acrylic acid, characterized in that

As the proportion of maleic acid amount in the high-boiling component represented by the above formula (%) becomes 10% or more, in claim 1 for controlling the operating conditions of the high boiling point component separation step and decomposition step The manufacturing method of acrylic acid of description.   In the high boiling point component separation step, the bottom temperature of the distillation tower is 90 to 130 ° C., the residence time of the bottom liquid is 2 to 30 hours, and the distillation tower is supplied to the distillation tower with respect to the mass of the extracted liquid from the bottom of the distillation tower. The method for producing acrylic acid according to claim 1 or 2, wherein the mass ratio of the liquid is 5 to 20.   The manufacturing method of acrylic acid in any one of Claims 1-3 which makes the density | concentration of the Michael adduct in the high boiling point component supplied to the said decomposition process 20 to 60 mass%. The method for producing acrylic acid according to any one of claims 1 to 4 , wherein the decomposition step is performed in the presence of an N-oxyl compound.

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