JP5606692B2 - Method for producing (meth) acrylic acid - Google Patents

Description

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

  Conventionally, as a method for industrially synthesizing (meth) acrylic acid, a method of catalytic vapor phase oxidation of a (meth) acrylic acid production raw material is known. The (meth) acrylic acid-containing gas produced by catalytic vapor phase oxidation of the (meth) acrylic acid production raw material is collected, for example, in a liquid medium, recovered as a crude (meth) acrylic acid solution, and further distilled and diffused. The product is purified by a method such as extraction or crystallization.

As a method for purifying a crude methacrylic acid solution by crystallization, for example, Patent Document 1 discloses a method for purifying a crude methacrylic acid solution by crystallization and melting. In Patent Document 1, melting is performed in two steps, the melt obtained in the first melting is discharged out of the system, and the melt obtained in the second melting is recovered as purified methacrylic acid. Yes.
It is disclosed.

Japanese Patent Laid-Open No. 7-278045

  In the method disclosed in Patent Document 1, purified methacrylic acid is produced from a crude methacrylic acid solution by a crystallization step, a sweating step, and a melting step. However, although the purified methacrylic acid obtained by the method is purified, it contains slight impurities. Therefore, it is more preferable if purified methacrylic acid with higher purity can be obtained.

  This invention is made | formed in view of the said situation, The objective is to provide the manufacturing method of (meth) acrylic acid from which purified (meth) acrylic acid of higher purity is obtained.

  In the present invention, in the method for producing (meth) acrylic acid including a crystallization step, a sweating step, and a melting step, the cooling medium discharged from the crystallizer is cooled before the sweating step without cooling the crystal. It has been clarified that purified (meth) acrylic acid with higher purity can be obtained by providing an adjustment step for returning to the analyzer. That is, the method for producing (meth) acrylic acid according to the present invention that has solved the above-mentioned problem is to supply a cooling medium cooled by a heat source machine to a crystallizer, and from a crude (meth) acrylic acid solution ( A crystallization step for obtaining a (meth) acrylic acid crystallized product; an adjustment step for returning the cooling medium discharged from the crystallizer to the crystallizer without cooling; and a heating medium supplied to the crystallizer. A sweating step of discharging a melt obtained by melting a part of the crystallized (meth) acrylic acid out of the system; supplying a heating medium to the crystallizer; and the (meth) acrylic acid crystal It is characterized in that the melting step of melting the compound to obtain purified (meth) acrylic acid is performed in this order.

  By providing the adjustment step, the temperature of the cooling medium at the outlet and the inlet of the crystallizer is made uniform, and the temperature of the cooling medium within the crystallizer is made uniform. As a result, the temperature of the (meth) acrylic acid crystallization product in the crystallizer is made uniform. Therefore, in the present invention, in the subsequent sweating process, the (meth) acrylic acid crystallization product is partially partially melted to effectively remove impurities existing between the crystals and on the crystal surface. Purified (meth) acrylic acid is obtained.

  In the adjustment step, it is preferable that the cooling medium discharged from the crystallizer is returned to the crystallizer without using a heat source device. By the said structure, the temperature difference of the cooling medium until it discharges | emits from a crystallizer and returns to the said crystallizer can be made small.

  The adjustment step is preferably performed for 1 minute to 10 minutes. By performing the adjustment step for 1 minute or longer, the temperature of the cooling medium in the crystallizer is sufficiently uniformed, and by adjusting the adjustment step to 10 minutes or less, (meth) acrylic acid can be used without greatly reducing production efficiency. Can be manufactured.

  In the adjustment step, the temperature difference of the cooling medium until it is discharged from the crystallizer and returned to the crystallizer is preferably within 1.0 ° C. When the temperature difference is within 1.0 ° C., the temperature of the cooling medium in the crystallizer is sufficiently uniform, and it becomes easier to finally obtain purified (meth) acrylic acid with higher purity.

  According to the method for producing (meth) acrylic acid of the present invention, purified (meth) acrylic acid with higher purity can be obtained.

The example of the crystallizer used for the manufacturing method of this invention is represented.

  The method for producing (meth) acrylic acid according to the present invention includes a crystallization step of supplying a refrigeration medium cooled by a heat source machine to a crystallizer, and obtaining a (meth) acrylic acid crystallized product from a crude (meth) acrylic acid solution. An adjustment step in which the cooling medium discharged from the crystallizer is returned to the crystallizer without cooling; a heating medium is supplied to the crystallizer, and a part of the (meth) acrylic acid crystallized product A sweating step of discharging the melt obtained by melting the solution out of the system; supplying a heating medium to the crystallizer, melting the crystallized (meth) acrylic acid, and purifying the purified (meth) acrylic acid Obtaining a melting step. In the present invention, the crystallization step, the adjustment step, the sweating step, and the melting step are performed in this order (hereinafter, the operation from the crystallization step to the melting step may be referred to as “crystallization operation”), and rough ( Purified (meth) acrylic acid is obtained from a (meth) acrylic acid solution.

  In the crystallization process, the cooling medium cooled by the heat source machine is supplied to the crystallizer. The heat source machine used in the crystallization step is not particularly limited as long as it cools the cooling medium. Examples of the heat source device include a multi-tube heat exchanger in which steam or liquefied gas is used as a heat source. Moreover, you may use the refrigerator which can supply both a cold-heating medium and a heating medium as a heat source machine. As the refrigerator, an absorption refrigerator (ammonia absorption type, water-lithium bromide type, etc.), a compression refrigerator, an adsorption refrigerator, or the like can be used.

  The cooling medium is not particularly limited as long as it maintains a liquid state with a heat source machine and a crystallizer. The cooling medium means a heating medium cooled by a heat source machine. The cooling medium may be the same as or different from the heating medium used in the sweating process or the melting process. As the cooling medium, an ethylene glycol aqueous solution, a glycerin aqueous solution, a methanol aqueous solution or the like can be used.

  The temperature of the cooling medium discharged from the heat source machine is not particularly limited as long as it is lower than the freezing point of the crude (meth) acrylic acid solution. The freezing point of the crude (meth) acrylic acid solution varies depending on the (meth) acrylic acid concentration and the impurity composition. For example, in the case of a crude acrylic acid solution having an acrylic acid concentration of 80% by mass to 95% by mass and most other impurities are water, the freezing point is generally more than −5 ° C. and 13.5 ° C. or less.

  The temperature of the cooling medium discharged from the heat source device is preferably adjusted as appropriate according to the freezing point of the (meth) acrylic acid solution to be used in the crystallizer. For example, in the case of a solution having an acrylic acid concentration of 80% by mass to 95% by mass, −5 ° C. or lower is preferable, −10 ° C. or lower is more preferable, −40 ° C. or higher is preferable, and −30 ° C. or higher is more preferable. As described above, the upper limit of the temperature of the cooling medium discharged from the heat source device may be lower than the freezing point of the crude (meth) acrylic acid solution, but it is discharged from the heat source device from the viewpoint of efficient crystallization. The temperature of the cooling medium is preferably −5 ° C. or lower. On the other hand, when the temperature of the cooling medium discharged from the heat source device is lower than −40 ° C., the cooling load in the heat source device increases, and a high-spec heat source device may be required, or the energy consumption of the heat source device may increase. Therefore, the temperature of the cooling medium discharged from the heat source machine is preferably −40 ° C. or higher.

  In the crystallization step, the temperature of the cooling medium supplied to the crystallizer may be appropriately adjusted according to the progress of crystallization. Two or more types of cooling medium having different temperatures may be used. For example, two types of refrigeration medium in the range of -10 ° C to -5 ° C and refrigeration medium in the range of -30 ° C to -15 ° C may be used. However, when a small-scale crystallizer is used, a cooling medium having a desired temperature may be extracted from the heat source unit and supplied to the crystallizer at that temperature.

  The crystallizer is not particularly limited as long as it can crystallize a crude (meth) acrylic acid solution. As a crystallizer, what has a heat-transfer surface is preferable. In this case, the crystallizer has a portion (heat medium existing portion) to which a cooling medium or a heating medium is supplied by a heat transfer surface inside, a crude (meth) acrylic acid solution and / or (meth) acrylic acid crystallized product. It is preferable to be divided into a portion (crystallized product existing portion) in which is present.

  As a crystallizer having a heat transfer surface, a device generally used as a heat exchanger can be adopted, and it is particularly preferable to adopt a device used as a heat exchanger that performs heat exchange between liquids. For example, a plate-type heat exchanger in which one plate is arranged, or a plurality of plates are laminated at intervals, and a heat medium existence part and a crystallized substance existence part are alternately arranged via the plates; A multi-tube type (shell and tube type) heat exchanger in which the tubes are arranged in a container and exchange heat inside and outside the tube; the inner tube is placed inside the outer tube, and heat is exchanged inside and outside the inner tube. A double pipe heat exchanger or the like that performs the exchange can be employed. In addition, the cross-sectional shape of the tube used in the multi-tube heat exchanger or the double-tube heat exchanger is not particularly limited.

  The crystallizer used in the production method of the present invention is preferably a crystallizer capable of so-called dynamic crystallization, in which a crude (meth) acrylic acid solution is crystallized while flowing into a film (Falling Film format). As such a crystallizer, for example, Sulzer Chemtech's Swiss layer crystallizer can be used.

  In the crystallization step, a cooling medium is supplied to the crystallizer, and a crude (meth) acrylic acid solution is supplied to the crystallizer. As a result, the crude (meth) acrylic acid solution is cooled by the cooling medium, and a (meth) acrylic acid crystallized product is generated. In the crystallization step, the crude (meth) acrylic acid can be crystallized by circulating between the crystallized substance existing part of the crystallizer and a circulation channel connecting the inlet and the outlet of the crystallized substance existing part. Preferably, as a result, crystallization can be performed efficiently.

  The crude (meth) acrylic acid solution is not particularly limited as long as it is a liquid containing (meth) acrylic acid and other impurities. Examples of the impurities include unreacted (meth) acrylic acid production raw material, collection liquid medium (such as water), acetic acid, propionic acid, maleic acid, acetone, acrolein, furfural, formaldehyde and the like. The crude (meth) acrylic acid solution used in the production method of the present invention preferably has a (meth) acrylic acid concentration of 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. When the (meth) acrylic acid concentration is 80% by mass or more, it is easy to crystallize the crude (meth) acrylic acid solution. The upper limit of the (meth) acrylic acid concentration is not particularly limited.

  In the crystallization process, the cooling medium cooled by the heat source machine is supplied to the crystallizer, heat-exchanged with the crude (meth) acrylic acid solution, heated, and discharged from the crystallizer. Therefore, the temperature of the cooling medium is higher at the outlet than at the inlet of the crystallizer. In the crystallization process, (meth) acrylic acid is purified by crystallizing (meth) acrylic acid from the crude (meth) acrylic acid solution and keeping the liquid state without causing impurities to crystallize as much as possible. In the crystallization step, not all of the crude (meth) acrylic acid solution is crystallized. Therefore, the temperature of the cooling medium is higher at the outlet than at the inlet of the crystallizer in the entire crystallization process. This means that the (meth) acrylic acid crystallized product generated in the crystallizer in the crystallization step has a non-uniform temperature distribution.

  In the crystallization process, for example, as the crystallization progresses, the temperature of the cooling medium supplied to the crystallizer is gradually lowered, and when a predetermined amount of crystallized product is obtained, the crystallization process is completed, or The cooling medium supplied to the analyzer is operated so as to keep the temperature of the cooling medium constant. In the crystallization process, the temperature difference between the cooling medium at the inlet and outlet of the final crystallizer is generally about 2 ° C to 5 ° C.

  In the crystallization process, the cooling medium discharged from the crystallizer is returned to the heat source machine, cooled, and supplied to the crystallizer again. In the crystallization process, it is preferable to circulate and use the cooling medium by cooling the cooling medium that has received heat by the crystallizer and the temperature is increased again by the heat source unit.

  The crude (meth) acrylic acid solution that remains without being crystallized in the crystallization process (hereinafter sometimes referred to as “residual mother liquor”) is removed from the system at the end of the crystallization process, in the adjustment process, or in the sweating process. Discharge. When the residual mother liquor is discharged out of the system in the sweating process, it is efficient to discharge it out of the system together with the melt generated in the sweating process.

  In the case of obtaining purified (meth) acrylic acid from a crude (meth) acrylic acid solution by a crystallization method, it is common to proceed to a sweating step immediately after the crystallization step. The sweating process means a process of discharging the obtained melt from the system by melting a part of the (meth) acrylic acid crystallized product. Impurities existing between the crystals and on the crystal surface are washed away by the sweating process, and purified (meth) acrylic acid with higher purity can be obtained in the subsequent melting process. However, as described above, in the crystallization step, the (meth) acrylic acid crystallized product generated in the crystallizer has a non-uniform temperature distribution. Specifically, the temperature of the (meth) acrylic acid crystallized product is lowered on the cooling medium inlet side of the crystallizer, and the temperature of the (meth) acrylic acid crystallized product is increased on the cooling medium outlet side of the crystallizer. As described above, when the (meth) acrylic acid crystallized product has a non-uniform temperature distribution in the crystallizer, if the (meth) acrylic acid crystallized product moves to the sweating step immediately after the crystallization step, Melting is not performed uniformly, and the high-temperature (meth) acrylic acid crystallized product is preferentially melted. As a result, high-temperature (meth) acrylic acid crystallized material melts to high-purity (meth) acrylic acid crystallized material, and conversely (meth) acrylic acid crystallized material exists between crystals or on the crystal surface. Impurities are not sufficiently removed.

  Therefore, in the production method of the present invention, an adjustment step is provided between the crystallization step and the perspiration step, in which the cooling medium discharged from the crystallizer is returned to the crystallizer without being cooled. By returning the cooling medium discharged from the crystallizer to the crystallizer without cooling, the temperature of the cooling medium at the inlet and outlet of the crystallizer is ideally uniform, The temperature of the cooling / heating medium will be made uniform. As a result, the temperature of the (meth) acrylic acid crystallization product in the crystallizer is considered to be uniform. Therefore, by performing the sweating process following the adjustment process, the (meth) acrylic acid crystallized material is partially melted uniformly regardless of the crystallization position in the crystallizer, and impurities present between the crystals or on the crystal surface. Can be effectively removed. As a result, purified (meth) acrylic acid with higher purity can be obtained by the melting step.

  In the adjustment step, as a method of returning the cooling medium discharged from the crystallizer to the crystallizer without cooling, for example, a short-circuit channel connecting the outlet and the inlet of the crystallizer is provided, and the short-circuit channel The cooling medium discharged from the crystallizer can be returned to the crystallizer. Moreover, you may return the cooling medium discharged | emitted from the crystallizer to the crystallizer through the heat source machine which is not operating.

  In the adjustment process, it is not actively heated or cooled unless heat is inevitably transferred from a pipe or a pump. Even when heat is inevitably transferred, it is preferable that the amount transferred is as small as possible. For example, when the cooling medium discharged from the crystallizer is returned to the crystallizer through a heat source machine that is not in operation, the cooling medium may be cooled by the cold heat remaining in the heat source machine. It is preferable that the cooling medium discharged from the vessel is returned to the crystallizer without passing through the heat source unit.

  In the adjustment step, it is preferable that the temperature difference of the cooling medium at the outlet and inlet of the crystallizer is small. That is, it is preferable that the temperature difference of the cooling medium until it is discharged from the crystallizer and returned to the crystallizer is small. Specifically, the temperature difference is preferably within 1.0 ° C., and more preferably within 0.5 ° C. When the temperature difference is within 1.0 ° C., the temperature of the cooling medium in the crystallizer is sufficiently uniform, and it becomes easier to finally obtain purified (meth) acrylic acid with higher purity.

  In order to reduce the temperature difference of the cooling medium between the outlet and the inlet of the crystallizer, it is preferable that the cooling medium discharged from the crystallizer is returned to the crystallizer through the shortest path possible. Specifically, it is preferable to provide a short-circuit channel connecting the outlet and the inlet of the crystallizer, and return the cooling medium discharged from the crystallizer through the short-circuit channel to the crystallizer. You may provide the short circuit flow path with the pump for returning a cooling medium to a crystallizer as needed.

  The adjustment step is preferably performed for at least 1 minute, and more preferably for 2 minutes or more. By performing the adjustment process for 1 minute or more, the temperature of the cooling medium in the crystallizer is sufficiently uniformed, and the cooling medium and the (meth) acrylic acid crystallized product are heat-exchanged in the crystallizer, thereby crystallizing. The temperature of the (meth) acrylic acid crystallized product in the vessel is easily made uniform. On the other hand, the adjusting step is preferably performed for 10 minutes or less, more preferably 5 minutes or less. Even if the adjustment step is performed for more than 10 minutes, the temperature of the refrigeration medium and the (meth) acrylic acid crystallized product in the crystallizer is not more uniform, and the production efficiency is lowered due to the longer adjustment step time.

  In the adjustment process, in the initial stage of the process, the temperature of the cooling medium discharged from the crystallizer and returned to the crystallizer is approximately equal to the temperature of the cooling medium discharged from the crystallizer in the final stage of the crystallization process. However, as the adjustment process proceeds, the cooling medium generally receives heat from a pipe, a pump, or the like, and the temperature of the cooling medium increases. In this case, the time of the adjustment step is appropriately adjusted so that the temperature of the cooling medium falls within the range below the melting point of the (meth) acrylic acid crystallized product. Preferably, the temperature of the cooling medium discharged from the crystallizer and returned to the crystallizer is maintained in a temperature range lower by 5 ° C. than the melting point of the (meth) acrylic acid crystallized product.

  Following the adjustment step, a sweating step is performed. In the sweating step, a heating medium is supplied to the crystallizer, and a melt obtained by melting a part of the (meth) acrylic acid crystallized product is discharged out of the system.

  The heating medium means a heating medium heated by a heat source machine. The heating medium is not particularly limited as long as it maintains a liquid state with a heat source machine and a crystallizer. As the heat source machine, the heat source machine exemplified above can be used, and a refrigerator may be used. As the heating medium, the substances exemplified as the cooling medium can be used.

  The temperature of the heating medium discharged from the heat source machine is not particularly limited as long as it exceeds the melting point of the (meth) acrylic acid crystallized product. The temperature of the heating medium discharged from the heat source machine is preferably 15 ° C or higher, more preferably 25 ° C or higher, preferably 45 ° C or lower, more preferably 40 ° C or lower. As described above, the lower limit of the temperature of the heating medium discharged from the heat source machine may be above the melting point of the crystallized (meth) acrylic acid, but it is discharged from the heat source machine from the viewpoint of efficient melting. The temperature of the heating medium is preferably 15 ° C. or higher. On the other hand, when the temperature of the heating medium discharged from the heat source machine exceeds 45 ° C., a polymerization reaction of (meth) acrylic acid occurs in the crystallizer, and it becomes difficult to continue the operation or (meth) acrylic obtained. The purity and yield of the acid may be reduced. Moreover, the heating load in the heat source device may increase, and a high-spec heat source device may be required, or the energy consumption of the heat source device may increase. Therefore, it is preferable that the temperature of the heating medium discharged from the heat source machine is 45 ° C. or less.

  In the sweating step and the melting step described later, the temperature of the heating medium supplied to the crystallizer may be appropriately adjusted according to the progress of melting. Comparing the sweating process with the melting process described later, the temperature of the heating medium supplied to the crystallizer is preferably higher in the melting process than in the sweating process.

  In the sweating step, a heating medium is supplied to the crystallizer, the (meth) acrylic acid crystallized product is heated, and a part of the (meth) acrylic acid crystallized product is melted. As a result, impurities existing between the crystals of the (meth) acrylic acid crystallized product or on the crystal surface are removed, and purified (meth) acrylic acid with higher purity can be obtained in the subsequent melting step.

  In the sweating step, it is preferable to melt 1% by mass to 10% by mass of the (meth) acrylic acid crystallized product. By partially melting the (meth) acrylic acid crystallized substance at the above ratio, the purity and yield of purified (meth) acrylic acid obtained in the melting step can be effectively increased.

  The melt obtained by melting a part of the (meth) acrylic acid crystallized product is discharged out of the system. Note that discharging out of the system means discharging from the crystallizer once. The melt discharged out of the system may be used as a crude (meth) acrylic acid solution to be subjected to another crystallization step, or may be returned to an arbitrary step prior to crystallization. The residual mother liquor generated in the crystallization process and discharged out of the system may be handled in the same manner as the melt discharged out of the system.

  After the sweating process, a melting process is performed. In the melting step, a heating medium is supplied to the crystallizer, the (meth) acrylic acid crystallized product is melted, and purified (meth) acrylic acid is obtained. The heating medium used in the melting process is as described for the heating medium used in the sweating process, and it is efficient to use the same material as the heating medium used in the sweating process. By the melting step, purified (meth) acrylic acid having a higher purity than the crude (meth) acrylic acid solution is obtained. According to the production method of the present invention, purified (meth) acrylic acid with higher purity can be obtained by providing an adjustment step.

  In the melting process, the melt that has melted first with the supply of the heating medium is circulated between the crystallized product existing part of the crystallizer and the circulation channel that connects the inlet and the outlet of the crystallized product present part, and remains. It is preferable to promote melting of the (meth) acrylic acid crystallized product. Moreover, it is preferable to supply a polymerization inhibitor to the crystallized substance presence part of a crystallizer from the point of polymerization prevention of (meth) acrylic acid.

  In the production method of the present invention, the crystallization step, the adjustment step, the sweating step, and the melting step may be performed a plurality of times in this order. In this case, the purified (meth) acrylic acid obtained in the melting step is again supplied to the crystallization step as a crude (meth) acrylic acid solution. Thus, purified (meth) acrylic acid with higher purity can be obtained by repeating the crystallization operation from the crystallization step to the melting step a plurality of times. Preferably, the crystallization operation is repeated 3 to 5 times.

  In the production method of the present invention, a plurality of crystallizers may be used and the crystallization operations may be performed in parallel. For example, assuming that two crystallizers are used, the sweating process and the melting process are performed in the other crystallizer while the crystallizing process and the adjusting process are performed in one crystallizer. It is preferable to do. In this case, since a cooling medium is supplied to one crystallizer and a heating medium is supplied to the other crystallizer, a refrigerator is used as a heat source for supplying the cooling medium and the heating medium. For example, both hot and cold generated from the refrigerator are used in any step of the crystallization operation, which is efficient.

  The method for producing (meth) acrylic acid of the present invention preferably further includes a step of obtaining a crude (meth) acrylic acid solution. The step of obtaining a crude (meth) acrylic acid solution includes a contact gas phase oxidation reaction step of obtaining a (meth) acrylic acid-containing gas from a (meth) acrylic acid production raw material by a contact gas phase oxidation reaction, and the (meth) acrylic acid-containing step. It is preferable to have a collection step of collecting gas with a liquid medium. Moreover, you may have the condensation process which condenses the said (meth) acrylic acid containing gas instead of the said collection process. Furthermore, for the purpose of increasing the (meth) acrylic acid content of the (meth) acrylic acid solution obtained in the collecting step or the condensing step, a purification step may be provided after the collecting step or the condensing step. Good.

  In the catalytic gas phase oxidation reaction step, propane, propylene, (meth) acrolein, isobutylene, or the like is used as a raw material for producing (meth) acrylic acid, and this is subjected to catalytic gas phase oxidation with molecular oxygen to produce a (meth) acrylic acid-containing gas. Get. The catalytic gas phase oxidation reaction is preferably performed using a conventionally known oxidation catalyst.

  In the collection step, the (meth) acrylic acid-containing gas obtained in the catalytic gas phase oxidation reaction step is collected with a liquid medium in a collection tower to obtain a (meth) acrylic acid solution. As the liquid medium, water, (meth) acrylic acid-containing water, a high boiling point solvent (such as diphenyl ether or diphenyl), or the like can be used. In the present invention, the (meth) acrylic acid solution obtained in the collecting step may be subjected to a crystallization step as a crude (meth) acrylic acid solution. Further, the (meth) acrylic acid solution obtained by condensing the (meth) acrylic acid-containing gas may be subjected to a crystallization step as a crude (meth) acrylic acid solution.

  Next, an example of an embodiment of the production method of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiment shown in the drawings.

  FIG. 1 shows a crystallizer used in the production method of the present invention. The crystallizer 1 includes a crystallizer tube 2 that functions as a heat transfer surface. The crystallizer 1 has a heat medium existence part 3 to which a cooling medium or a heat medium is supplied, a crude (meth) acrylic acid solution and / or a (meth) acrylic acid crystallized substance on the inner and outer surfaces of the crystallization tube 2. The crystallized substance existing part 4 is divided.

  In the crystallization process, the cooling medium cooled by the heat source machine is supplied to the heating medium existence part 3 of the crystallizer 1 through the inlet 3a, and the cooling medium supplied to the crystallizer 1 passes through the outlet 3b. And discharged from the crystallizer 1. In the crystallization process, the valves 11 and 12 on the heat medium line are open, and the heat entering the inlet 3a by opening and closing the valve 6 provided in the short-circuit channel 5 connecting the inlet 3a and the outlet 3b of the crystallizer 1. The temperature of the medium is adjusted to a desired value. However, when a small-scale crystallization apparatus is used to extract a cooling medium at a desired temperature from the heat source unit and supply it to the crystallizer at that temperature, the valve 6 may be closed in the crystallization step. A predetermined amount of the crude (meth) acrylic acid solution is supplied to the crystallized substance existing part 4 of the crystallizer 1 through the inlet 4a and cooled in the crystallizing tube 2, so that a (meth) acrylic acid crystallized substance is generated. The crude (meth) acrylic acid solution which has flowed down to the lower part of the crystallizer 1 without being crystallized in the crystallizer 2 passes through the circulation channel 8 connecting the outlet 4b and the inlet 4a, and is again crystallized. To be supplied. The crude (meth) acrylic acid solution remaining without being crystallized in the crystallization step is stored in the lower part of the crystallizer 1 as a residual mother liquor. In the crystallization process and the adjustment process, the valve 9 of the flow path 10 is closed.

  In the adjustment process, the valves 11 and 12 on the heating medium line are closed, the valve 6 of the short circuit channel 5 is opened, and the cooling medium discharged from the crystallizer 1 through the outlet 3 b is passed through the short circuit channel 5. And returned to the crystallizer 1 by the pump 7. Since a cooling means such as a heat source machine is not provided in the flow path from the outlet 3b of the crystallizer 1 to the inlet 3a of the crystallizer 1, the cooling medium is returned to the crystallizer 1 without being cooled. It will be. By the adjusting step, the temperature of the cooling medium at the inlet 3a and outlet 3b of the crystallizer 1 is made uniform, and as a result, the temperature of the (meth) acrylic acid crystallized product formed on the inner surface of the crystallizer 2 is made uniform. The

  In the sweating process, the valves 11 and 12 on the heating medium line are opened, the heating medium is supplied to the heating medium existing portion 3 of the crystallizer 1, and the (meth) acrylic acid crystallized product generated on the inner surface of the crystallization tube 2. Melt a part of. In the sweating process and the melting process, the valve 6 provided in the short-circuit channel 5 is closed. In the perspiration process, the valve 9 of the flow path 10 is opened, and the (meth) acrylic acid melt generated in the perspiration process is discharged out of the system through the flow path 10 together with the residual mother liquor.

  In the melting step, a heating medium is supplied to the heating medium existing part 3 of the crystallizer 1 to melt the (meth) acrylic acid crystallized product generated on the inner surface of the crystallization tube 2 to obtain purified (meth) acrylic acid. . The purified (meth) acrylic acid can be efficiently melted by returning the purified (meth) acrylic acid to the crystallizer 1 again through the circulation channel 8. The purified (meth) acrylic acid obtained is recovered by being discharged out of the system through the channel 10 by opening the valve 9 of the channel 10.

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

Example 1
A reaction gas obtained by the catalytic gas phase oxidation reaction of propylene was introduced into a collection tower and brought into contact with an aqueous solution for collection. From the bottom of the collection tower, acrylic acid 90.0% by mass, water 3.2% by mass, acetic acid 1.9% by mass, maleic acid 0.6% by mass, acrylic acid dimer 1.5% by mass, furfural A crude acrylic acid solution having a composition of 0.07 mass%, benzaldehyde 0.27 mass%, formaldehyde 0.06 mass%, hydroquinone 0.1 mass%, and other impurities 2.3 mass% was recovered. The temperature of the crude acrylic acid solution recovered from the collection tower was 91 ° C.

  The obtained crude acrylic acid solution was subjected to a crystallization operation after cooling. The crystallizer was provided with three metal crystallizing tubes having a length of 6 m and an inner diameter of 70 mm in the upper part, and had a double jacket structure capable of cooling and heating from the outer surface of the crystallizing tube.

  In the crystallization step, the cooling medium cooled by the heat source machine was supplied to the outside of the crystallization tube, and the crude acrylic acid solution was supplied to the inside of the crystallization tube from above. The crude acrylic acid solution caused the inner surface of the crystallization tube to flow down into a film, and as a result, an acrylic acid crystallized product was formed on the inner surface of the crystallization tube. The cooling medium was circulated between the heat source machine and the crystallizer. As the crystallization progressed, the temperature of the cooling medium was lowered, and the crystallization process was completed when a predetermined amount of crystallized acrylic acid was obtained. In the crystallization step, the temperature of the cooling medium was finally lowered to −15 ° C., and the final temperature difference between the inlet and outlet of the crystallizer was about 5 ° C.

  Subsequently, as an adjustment step, the cooling of the cooling medium in the heat source machine was stopped and the cooling medium was continuously supplied to the crystallizer. As a result, the temperature difference of the cooling medium at the crystallizer inlet and outlet was within 0.2 ° C. The adjustment process was performed for 5 minutes.

  Subsequently, a heating medium was supplied to the crystallizer as a sweating process. The temperature of the heating medium was adjusted to the crystallizer so that the temperature at the crystallizer outlet was close to the melting point of the crystallized acrylic acid. In the sweating process, about 2 to 5% by mass of the acrylic acid crystallized product was melted, and the obtained melt was discharged from the crystallizer together with the residual mother liquor in the crystallization process.

  Subsequently, as a melting step, a heating medium at 37 ° C. was supplied to the crystallizer, and the acrylic acid crystallized product was completely melted to obtain purified acrylic acid. At this time, the purified acrylic acid was extracted from the lower part of the crystallizer, and returned to the upper part of the crystallizer tube for circulation.

  The purified acrylic acid obtained in the melting step was again subjected to a crystallization step as a crude acrylic acid solution, and further a second crystallization operation from the adjustment step, the sweating step, and the melting step was performed. Similarly, the third and fourth crystallization operations were performed. In the third and fourth melting steps, a 5% by mass acrylic acid solution of p-methoxyphenol was added as a polymerization inhibitor.

  Purified acrylic acid obtained through four crystallization operations contains 99.94% by mass of acrylic acid, in addition to water 85 mass ppm, acetic acid 420 mass ppm, maleic acid 2 mass ppm, furfural 0.2 mass ppm. Benzaldehyde 0.1 mass ppm, formaldehyde 0.0 mass ppm, acrylic acid dimer 47 mass ppm.

Comparative Example 1
Except not having performed the adjustment process, the same operation as Example 1 was performed and purified acrylic acid was obtained. Purified acrylic acid obtained through four crystallization operations contains 99.92% by mass of acrylic acid, and in addition, water 123 mass ppm, acetic acid 530 mass ppm, maleic acid 3 mass ppm, furfural 0.2 mass. ppm, benzaldehyde 0.2 mass ppm, formaldehyde 0.0 mass ppm, and acrylic acid dimer 85 mass ppm. The impurity content of the purified acrylic acid obtained in Comparative Example 1 was higher than that in Example 1.

1: Crystallizer 2: Crystallization tube 3: Heat medium existing part 4: Crystallized substance existing part 5: Short-circuit flow path 8: Circulation flow path

Claims (4)

A crystallization process for supplying a crystallized product of (meth) acrylic acid from a crude (meth) acrylic acid solution by supplying a cooling medium cooled by a heat source machine to the crystallizer;
An adjustment step in which the cooling medium discharged from the crystallizer is returned to the crystallizer for 1 minute or longer without being cooled;
A sweating step of supplying a heating medium to the crystallizer and discharging a melt obtained by melting a part of the crystallized (meth) acrylic acid out of the system;
(Meth) acrylic acid characterized in that a heating medium is supplied to the crystallizer, and the (meth) acrylic acid crystallized product is melted to obtain purified (meth) acrylic acid in this order. Manufacturing method.   The method for producing (meth) acrylic acid according to claim 1, wherein in the adjusting step, the cooling medium discharged from the crystallizer is returned to the crystallizer without using a heat source device.   The manufacturing method of the (meth) acrylic acid of Claim 1 or 2 which performs the said adjustment process 1 minute or more and 10 minutes or less.   The (meta) according to any one of claims 1 to 3, wherein in the adjustment step, a temperature difference of the cooling medium until it is discharged from the crystallizer and returned to the crystallizer is within 1.0 ° C. A method for producing acrylic acid.

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