JP2010265227A - Method for producing (meth)acrylic acid and crystallization system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing (meth)acrylic acid, alleviating the temperature fluctuation of a cooling medium and a heating medium returning from a crystallizer to heat source devices, stably running the heat source devices, stabilizing the crystallization operation and/or the melting operation, and reducing the energy consumption therein, in the crystallization process and/or the melting process thereof, and a crystallization system. <P>SOLUTION: The method for producing (meth)acrylic acid including a process of crystallizing (meth)acrylic acid from a crude (meth)acrylic acid solution by feeding a cooling medium to a crystallizer 1 from a heat source device 4A; a process of discharging the cooling medium from the crystallizer 1 to return the same to the heat source device 4A; a process of melting the (meth)acrylic acid by feeding a heating medium to the crystallizer 1 from a heat source device 4B; and a process of discharging the heating medium from the crystallizer 1 to return the same to the heat source device 4B, is characterized by keeping the temperature of the cooling medium returning to the heat source device 4A within a specified range using a first buffer tank 5 and keeping the temperature of the heating medium returning to the heat source device 4B within a specified range using a second buffer tank 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing (meth) acrylic acid having a crystallization step and / or a melting step. The present invention also relates to a crystallization system.

  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 gas 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 diffused and extracted. It is purified by methods such as distillation and crystallization.

  Patent Document 1 discloses a method for purifying a crude (meth) acrylic acid solution by crystallization. When purifying a crude (meth) acrylic acid solution by crystallization, cooling is required to crystallize (meth) acrylic acid from the crude (meth) acrylic acid solution, while crystallized (meth) acrylic acid. Heating is required to obtain purified (meth) acrylic acid by melting However, Patent Document 1 does not specifically describe a cooling method or a heating method at the time of crystallization.

  Patent Document 2 discloses that cold water obtained by an absorption refrigerator is used in a crystallization step when a crude (meth) acrylic acid solution is purified by crystallization. However, Patent Document 2 does not describe a technique for reducing the energy consumption of a refrigerator used as a heat source machine and the stable operation of the refrigerator during crystallization.

JP 2008-74759 A JP 2007-277182 A

  When the crude (meth) acrylic acid solution is cooled with a cooling medium to crystallize (meth) acrylic acid, the temperature of the cooling medium discharged from the crystallizer tends to increase at the initial stage, while crystallization proceeds. Accordingly, the temperature of the cooling medium discharged from the crystallizer tends to decrease. Similarly, when the crystallized (meth) acrylic acid is melted by heating with a heating medium, the temperature of the heating medium discharged from the crystallizer tends to be low at the beginning, but as the melting proceeds, There is a tendency that the temperature of the heating medium discharged from the crystallizer rises. Therefore, when the temperature of the cooling medium or heating medium discharged from the crystallizer is adjusted by the heat source unit and supplied to the crystallizer again, the temperature of the cooling medium or heating medium returned to the heat source unit changes due to the temperature fluctuation of the heating source unit. The cooling load and heating load vary. As a result, the operation of the heat source machine becomes unstable, which in turn affects the crystallization operation, and the energy consumption of the heat source machine increases.

  The present invention has been made in view of the above circumstances, and its purpose is to alleviate temperature fluctuations of a cooling medium and a heating medium returned from a crystallizer to a heat source machine in a crystallization process and / or a melting process, An object of the present invention is to provide a method for producing (meth) acrylic acid capable of reducing the energy consumption by stabilizing the crystallization operation and / or the melting operation by operating the heat source apparatus stably. Another object of the present invention is to provide a crystallization system capable of reducing energy consumption by stabilizing the crystallization operation and / or the melting operation by operating the heat source apparatus stably.

The method for producing (meth) acrylic acid of the present invention that has solved the above-mentioned problem is that a cooling medium is supplied from a heat source device to a crystallizer, and (meth) acrylic acid is obtained from a crude (meth) acrylic acid solution. A step of crystallizing; a step of discharging the cooling medium from the crystallizer and returning it to the heat source unit; the temperature of the cooling medium returned to the heat source unit is kept constant by the following first or second adjusting means It is characterized by keeping it in range.
First adjusting means: supplying at least a part of the cooling medium returned from the crystallizer to the heat source unit to the upper part of the first buffer tank, discharging the cooling medium from the lower part of the first buffer tank and returning it to the heat source unit. .
Second adjusting means: supplying at least part of the cooling medium supplied from the heat source machine to the crystallizer and / or the cooling medium returned from the crystallizer to the heat source machine to the lower part of the first buffer tank, and The cooling medium is discharged from the upper part of the tank and returned to the heat source machine.

  According to the manufacturing method, the temperature of the cooling medium returned to the heat source machine can be maintained within a certain range by the first and second adjusting means. Therefore, in the crystallization process, the cooling load of the heat source apparatus is easily maintained within a certain range, and as a result, the heat source apparatus operates stably, the crystallization operation is stabilized, and energy consumption can be reduced.

The method for producing (meth) acrylic acid of the present invention comprises a step of supplying a heating medium from a heat source unit to a crystallizer and melting the crystallized (meth) acrylic acid; and discharging the heating medium from the crystallizer. And a step of returning to the heat source device; the temperature of the heating medium returned to the heat source device may be maintained within a certain range by the following third or fourth adjusting means.
Third adjusting means: supplying at least a part of the heating medium returned from the crystallizer to the heat source machine to the lower part of the second buffer tank, discharging the heating medium from the upper part of the second buffer tank, and returning it to the heat source machine. .
Fourth adjusting means: supplying at least a part of the heating medium supplied from the heat source machine to the crystallizer and / or the heating medium returned from the crystallizer to the heat source machine to the upper part of the second buffer tank, and The heat medium is discharged from the bottom of the tank and returned to the heat source machine.

  According to the manufacturing method, the temperature of the heating medium returned to the heat source machine can be maintained within a certain range by the third and fourth adjusting means. Therefore, in the melting step, the heating load of the heat source device is easily maintained within a certain range, and as a result, the heat source device operates stably, the melting operation is stabilized, and energy consumption can be reduced.

  The method for producing (meth) acrylic acid of the present invention comprises a step of supplying a cooling medium from a heat source device to a crystallizer, and crystallizing (meth) acrylic acid from a crude (meth) acrylic acid solution; Discharging the cooling medium from the heat source and returning it to the heat source machine; supplying the heating medium from the heat source machine to the crystallizer and melting the (meth) acrylic acid; and removing the heating medium from the crystallizer. Discharging and returning to the heat source unit; maintaining the temperature of the cooling medium returned to the heat source unit within a certain range by the first or second adjustment unit; by the third or fourth adjustment unit, The temperature of the heating medium returned to the heat source machine may be maintained within a certain range. With the above-described configuration, the heat source apparatus can stably operate in both the crystallization process and the melting process, the crystallization operation and the melting operation can be stabilized, and the energy consumption can be reduced.

  The method for producing (meth) acrylic acid of the present invention comprises a step of supplying a cooling medium from a heat source device to a first crystallizer and crystallizing (meth) acrylic acid from a crude (meth) acrylic acid solution; Discharging the cooling medium from one crystallizer and returning it to the heat source machine; supplying the heating medium from the heat source machine to a second crystallizer and melting the crystallized (meth) acrylic acid; A step of discharging the heating medium from the second crystallizer and returning it to the heat source machine; the heat source machine is a refrigerator; and the cooling heat returned to the heat source machine by the first or second adjusting means. The temperature of the medium may be kept within a certain range; the temperature of the heating medium returned to the heat source device may be kept within a certain range by the third or fourth adjusting means. However, the first and second adjusting means use the first crystallizer as the crystallizer, and the third and fourth adjusting means use the second crystallizer as the crystallizer. By adopting a refrigerator as a heat source machine, it is possible to use both the cooling and heating medium discharged from the refrigerator for the production of (meth) acrylic acid, and the energy consumed for the production of (meth) acrylic acid And (meth) acrylic acid can be efficiently produced.

  In the method for producing (meth) acrylic acid of the present invention, a predetermined amount of a cooling medium is held in the first buffer tank, a predetermined amount of the heating medium is held in the second buffer tank, and the cooling heat held in the first buffer tank It is preferable that the heating medium held in the medium and the second buffer tank has a temperature gradient in which the upper side has a high temperature and the lower side has a low temperature. According to the said structure, it becomes easy to maintain the temperature of the cooling-heat medium or warm-heating medium returned to a heat-source apparatus in a fixed range by the said 1st-4th adjustment means.

  The temperature of the cooling medium returned to the heat source machine is adjusted according to the temperature above and below the cooling medium held in the first buffer tank, and the temperature of the heating medium returned to the heat source machine is held in the second buffer tank. It is preferable to adjust the temperature according to the temperature above and below the heated medium. According to the said structure, the discharge speed | rate of the high temperature or low temperature cooling medium or heating medium from a buffer tank can be adjusted, and the effect by the said 1st-4th adjustment means can be enjoyed over a long period of time.

  The first buffer tank is provided with openings through which the cooling medium enters and exits at the top and bottom, and the length between the opening at the top and the opening at the bottom is 1 of the maximum cross-sectional length of the first buffer tank. The second buffer tank is provided with openings through which the heating medium enters and exits at the upper and lower parts, and the length between the upper opening and the lower opening is the maximum of the second buffer tank. The cross-sectional length is preferably 1 time or more. According to the above configuration, the cooling medium or the heating medium held in the buffer tank is likely to generate a temperature gradient in the height direction, and the temperature of the cooling medium or the heating medium returned to the heat source device can be maintained within a certain range. It becomes easy.

  The crystallization system of the present invention includes a crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface; and a cooling medium communicating with an inlet of the heat medium existing part A heat source device having a supply port and a cooling medium return port communicated with the outlet of the heat medium existing portion; an upper opening communicated with the outlet of the heat medium existing portion and the cold medium return port; and the cooling medium supply A lower opening communicating with the outlet and / or the outlet of the heat medium existing portion and the cooling medium return port. If the crystallization system is used, the temperature of the cooling medium returned to the heat source machine can be maintained within a certain range. Therefore, when the crystallization process is performed with the crystallizer, the cooling load of the heat source device is easily maintained within a certain range. As a result, the heat source device operates stably, the crystallization operation is stabilized, and energy consumption is reduced. become able to.

  The crystallization system of the present invention includes a crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface; and a heating medium communicating with an inlet of the heat medium existing part A heat source device having a supply port and a heating medium return port in communication with the outlet of the heating medium presence portion; and communicated with the heating medium supply port and / or the outlet of the heating medium presence portion and the heating medium return port You may have an upper opening and the lower opening connected to the exit of the said heat-medium presence part, and the said heating-medium return port. If the said crystallization system is used, the temperature of the heating medium returned to a heat source machine can be maintained in a fixed range. Therefore, when performing the melting operation with the crystallizer, the heating load of the heat source device is easily maintained within a certain range, and as a result, the heat source device can operate stably, the melting operation can be stabilized, and energy consumption can be reduced. become.

  The crystallization system of the present invention includes a crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface; and a cooling medium communicating with an inlet of the heat medium existing part A first heat source device having a supply port and a cooling medium return port communicated with an outlet of the heat medium existence part; a heating medium supply port communicated with an inlet of the heat medium existence part; and an outlet of the heat medium existence part A second heat source machine having a heating medium return port in communication with the heating medium; an upper opening in communication with the outlet of the heating medium existence unit and the cooling medium return port; the cooling medium supply port and / or the heating medium existence unit A first buffer tank having a lower opening communicating with the outlet of the cooling medium and the return port of the cooling medium; an upper opening communicating with the outlet of the heating medium supply port and / or the outlet of the heating medium and the heating medium return port And a lower opening communicating with the outlet of the heat medium existing part and the heating medium return port It may have a second buffer tank. According to the above configuration, the temperature of the cooling medium and the heating medium returned to the heat source machine can be kept within a certain range, and the heat source machine can operate stably in both the crystallization and melting operations. Becomes stable and energy consumption can be reduced.

  The crystallization system of the present invention includes a first crystallizer having a first heat transfer surface, the inside of which is divided into a first heat medium existing part and a first crystal existing part by the first heat transfer surface; A second crystallizer having a second heat transfer surface, the inside of which is divided into a second heat medium existing part and a second crystal existing part by the second heat transfer surface; A cooling medium supply port communicating with the inlet, a cooling medium return port communicating with the outlet of the first heating medium presence portion, a heating medium supply port communicating with the inlet of the second heating medium presence portion, and the second heat A refrigerator having a heating medium return port in communication with the outlet of the medium presence portion; an upper opening in communication with the outlet of the first heating medium presence portion and the cooling medium return port; and the cooling medium supply port and / or A first buffer tank having a lower opening communicating with the outlet of the first heat medium presence portion and the cooling medium return port; the second heating medium supply port and / or Is a second buffer tank having an upper opening communicating with the outlet of the heat medium existing part and the heating medium return port, and a lower opening communicating with the outlet of the second heat medium existing part and the heating medium return port It may have. By adopting a refrigerator as a heat source machine, it becomes possible to use the cooling medium discharged from the refrigerator for the crystallization operation, use the heating medium for the melting operation, and reduce the energy consumed for crystallization and melting, It becomes possible to perform crystallization operation and melting operation efficiently.

  In the first buffer tank and the second buffer tank used in the crystallization system of the present invention, the length between the upper opening and the lower opening is preferably at least one time the maximum cross-sectional length. According to the above configuration, the cooling medium or the heating medium held in the buffer tank is likely to generate a temperature gradient in the height direction, and the temperature of the cooling medium or the heating medium returned to the heat source device can be maintained within a certain range. It becomes easy.

  According to the method for producing (meth) acrylic acid and the crystallization system of the present invention, the temperature fluctuation of the cooling medium and the heating medium returned from the crystallizer to the heat source apparatus is reduced, the heat source apparatus is stably operated, The stabilization operation and / or the melting operation can be stabilized, and energy consumption can be reduced.

1 represents a crystallization system having a heat source device for supplying a cooling medium, a crystallizer, and a first buffer tank. The usage method of a 1st buffer tank when the temperature of the cold-heating medium returned to a heat source machine is high is represented. The usage method of a 1st buffer tank when the temperature of the cold-heating medium returned to a heat source machine is low is represented. 1 represents a crystallization system having a heat source device for supplying a heating medium, a crystallizer, and a second buffer tank. The usage method of a 2nd buffer tank when the temperature of the heating medium returned to a heat source machine is low is represented. The usage method of a 2nd buffer tank when the temperature of the heating medium returned to a heat source machine is high is represented. 1 represents a crystallization system having two heat source machines, one crystallizer and two buffer tanks. 1 represents a crystallization system having a refrigerator, two crystallizers and two buffer tanks. 1 represents a crystallization system having a refrigerator, three crystallizers and three buffer tanks.

[1. (Meth) acrylic acid production method]
The method for producing (meth) acrylic acid of the present invention comprises a step of supplying a cooling medium from a heat source device to a crystallizer and crystallizing (meth) acrylic acid from a crude (meth) acrylic acid solution (hereinafter referred to as “crystallization”). And / or a process of supplying the heating medium from the heat source device to the crystallizer and melting the crystallized (meth) acrylic acid (hereinafter sometimes referred to as “melting process”). Have

  In the crystallization step, the crude (meth) acrylic acid solution is cooled by a cooling medium supplied from the heat source unit to the crystallizer, and (meth) acrylic acid crystals are obtained. The obtained (meth) acrylic acid crystals may be selected or collected by any solid-liquid separation means, and may be melted by any melting method. Preferably, the crystallized (meth) acrylic acid is melted by a melting step described later.

  The crude (meth) acrylic acid solution crystallized in the crystallization step 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 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 melting step, the crystallized (meth) acrylic acid is heated and melted by the heating medium supplied from the heat source unit to the crystallizer. The crystallized (meth) acrylic acid used in the melting step may be obtained by the crystallization step or may be obtained by any crystallization method. In the present invention, preferably, the (meth) acrylic acid crystal obtained by the crystallization step is melted in the melting step.

  When the crystallized (meth) acrylic acid is melted by heating, the crystallized (meth) acrylic acid is partially melted and crystallized for the purpose of increasing the purity of the resulting (meth) acrylic acid melt. In some cases, a sweating operation is performed as an operation for washing away impurities existing on the surface or the crystal surface. In the present invention, the operation is also included in the melting step.

  In the production method of the present invention, the crystallization step and the melting step may be alternately repeated a plurality of times to obtain (meth) acrylic acid with higher purity.

  The heat source apparatus used in the production method of the present invention is not particularly limited as long as it cools the cooling medium and / or heats the heating medium. As the heat source machine, for example, a multi-tube heat exchanger in which steam or liquefied gas is used as a heat source is shown.

  The heat source machine may be one that heats the heating medium simultaneously with cooling the cooling medium. As such a heat source machine, a refrigerator can be adopted, and as a refrigerator, an absorption refrigerator (ammonia absorption type, water-lithium bromide type, etc.), a compression refrigerator, an adsorption refrigerator, etc. Can be used.

  The cooling medium and the heating medium are not particularly limited as long as they maintain a liquid state with a heat source unit and a crystallizer in producing (meth) acrylic acid. The cooling medium and the heating medium may be the same or different. For example, when the cooling medium and the heating medium are the same, examples of the cooling medium and the heating medium include an ethylene glycol aqueous solution, a glycerin aqueous solution, and a methanol aqueous solution.

  When the production method of the present invention has a crystallization step, the production method of the present invention supplies a cooling medium from a heat source device to a crystallizer and crystallizes (meth) acrylic acid from a crude (meth) acrylic acid solution. And a step of discharging the cooling medium from the crystallizer and returning it to the heat source unit. The cooling medium returned to the heat source machine is cooled by the heat source machine and supplied again to the crystallizer.

  The temperature of the cooling medium discharged from the heat source machine is not particularly limited as long as it is lower than the melting point of the crude (meth) acrylic acid solution. The melting 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 melting point is generally more than −5 ° C. and 13.5 ° C.

  The temperature of the cooling medium discharged from the heat source machine is preferably −5 ° C. or lower, more preferably −10 ° C. or lower, and −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 refrigerator only needs to be lower than the melting point of the crude (meth) acrylic acid solution, but the amount of the cooling medium required for crystallization increases excessively, In order to prevent the size of the analyzer and the cooling medium piping from becoming too large, the temperature of the cooling medium discharged from the heat source device 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.

  Although the above description is about the case where there is one kind of cooling medium discharged from the heat source machine, the cooling medium discharged from the heat source machine may be two or more kinds having different temperatures. For example, when the cooling medium discharged from the heat source machine is the first cooling medium and the second cooling medium having a temperature lower than that of the first cooling medium, the temperature of the first cooling medium is preferably −15 ° C. or higher, − The temperature of the second cooling medium is preferably −40 ° C. or higher and lower than −15 ° C. In this case, in the crystallization step, it is preferable that after supplying the first cooling medium to the crystallizer, the second cooling medium having a temperature lower than that of the first cooling medium is supplied to the crystallizer. By using the first cooling medium and the second cooling medium in this manner, the purity of the (meth) acrylic acid crystal can be easily increased, and the energy consumption of the heat source device can be further reduced.

  When the production method of the present invention has a melting step, the production method of the present invention includes a step of supplying a heating medium from a heat source device to a crystallizer, melting the crystallized (meth) acrylic acid, and the crystallizer. And a step of discharging the heat medium from the heat source and returning it to the heat source device. The heating medium returned to the heat source machine is heated by the heat source machine and supplied again to the crystallizer.

  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 crystallized (meth) acrylic acid. The temperature of the heating medium discharged from the heat source machine is preferably 20 ° C. or higher, more preferably 30 ° 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 refrigerator only needs to be above the melting point of the crystallized (meth) acrylic acid, but the amount of the heating medium necessary for melting increases, In order to prevent the size of the analyzer, the heating medium pipe, and the like from becoming too large, the temperature of the heating medium discharged from the heat source device is preferably 20 ° 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. The heat medium discharged from the heat source machine may also be two or more types having different temperatures.

  The temperature of the cooling medium or the heating medium discharged from the heat source device is preferably maintained within a certain range, and the temperature range is preferably within 3.0 ° C, more preferably within 1.0 ° C. Moreover, it is preferable that the flow rate of the cooling medium or the heating medium discharged from the heat source device is maintained within a certain range. If the temperature and flow rate of the cooling medium or the heating medium discharged from the heat source device are maintained within a certain range, the crystallization operation and the melting operation in the crystallizer are easily performed stably. In addition, as described later, the temperature of the cooling medium or the heating medium returned to the heat source device is kept in a certain range, and thus the cooling or heating load of the heat source device is easily kept in a certain range, and as a result, the heat source The machine can operate stably and energy consumption can be reduced. The flow rate of the cooling / heating medium discharged from the heat source machine is the temperature of the cooling / heating medium / heating medium discharged from the heat source machine, the amount and temperature of the crude (meth) acrylic acid solution and crystallized (meth) acrylic acid, etc. It is set appropriately according to

  When the production method of the present invention includes a crystallization step and a melting step, the heat source device used in the crystallization step and the heat source device used in the melting step may be the same or different.

  The crystallizer used in the production method of the present invention is not particularly limited as long as (meth) acrylic acid is crystallized. When the production method of the present invention has a crystallization step, a cooling medium is supplied from the heat source unit to the crystallizer, and as a result, (meth) acrylic acid is crystallized from the crude (meth) acrylic acid solution. When the production method of the present invention includes a melting step, the crystallizer is supplied with a heating medium from a heat source unit, and as a result, crystallized (meth) acrylic acid is melted.

  The crystallizer used in the production method of the present invention preferably has a heat transfer surface. In this case, the crystallizer has a portion to which a cooling medium or a heating medium is supplied (a heating medium existing portion), a crude (meth) acrylic acid solution and / or a (meth) acrylic acid crystal due to the heat transfer surface. It is preferably divided into portions (crystal existing portions). When the crystallizer has a heat transfer surface, in the crystallization process, a cooling medium is supplied to the crystallizer, and a crude (meth) acrylic acid solution is supplied to the crystallizer so that the heat transfer surface is Then, the crude (meth) acrylic acid solution is cooled by the cooling medium, and (meth) acrylic acid is crystallized. In the melting step, a heating medium is supplied to the crystallizer, and the crystallized (meth) acrylic acid is heated and melted by the heating medium through the heat transfer surface.

  As a crystallizer having a heat transfer surface, a device generally used as a heat exchanger can be employed, and it is particularly preferable to employ 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 crystal existence part are alternately arranged through the plates; Tube is arranged in a container and heat exchange is performed inside and outside the tube (shell-and-tube) heat exchanger; the inner tube is placed inside the outer tube, and heat exchange is performed inside and outside the inner tube A double-pipe heat exchanger; a coil-type heat exchanger in which a single tube is arranged in a container in a coil shape and performs heat exchange inside and outside the tube; A spiral heat exchanger or the like in which a hot plate is spirally wound and two spiral channels are formed can be employed. In addition, the cross-sectional shape of the tube used in the multi-tube heat exchanger, the double tube heat exchanger, the coil heat exchanger, and the spiral heat exchanger is not particularly limited.

  In the crystallization step, the cooling medium supplied to the crystallizer is heated by exchanging heat with the crude (meth) acrylic acid solution and receiving heat from the crude (meth) acrylic acid solution. In the crystallization process, when the temperature and flow rate of the cooling medium supplied to the crystallizer are constant, the temperature of the cooling medium discharged from the crystallizer becomes high at the beginning of the crystallization process, and the crystallization proceeds as crystallization progresses. The temperature of the cooling medium discharged from the vessel is lowered. Although the temperature of the cooling medium discharged from the crystallizer varies depending on conditions, for example, a difference of about 50 ° C. can occur. Therefore, when the cooling medium discharged from the crystallizer is returned to the heat source unit as it is, the temperature of the cooling medium returned to the heat source unit greatly fluctuates, and the cooling load of the heat source unit fluctuates. As a result, the operation of the heat source machine becomes unstable, the crystallization operation becomes unstable, and the energy consumption of the heat source machine increases.

  In the melting step, the heating medium supplied to the crystallizer is cooled by heat exchange with the crystallized (meth) acrylic acid and dissipating heat to the crystallized (meth) acrylic acid. In the melting process, when the temperature and flow rate of the heating medium supplied to the crystallizer are constant, the temperature of the heating medium discharged from the crystallizer becomes low at the beginning of the melting process, and from the crystallizer as the melting proceeds. The temperature of the discharged heat medium becomes higher. Although the temperature of the heating medium discharged from the crystallizer varies depending on conditions, for example, a difference of about 50 ° C. can occur. Therefore, when the heating medium discharged from the crystallizer is returned to the heat source machine as it is, the temperature of the heating medium returned to the heat source machine fluctuates greatly, and the heating load of the heat source machine fluctuates. As a result, the operation of the heat source machine becomes unstable, the melting operation becomes unstable, and the energy consumption of the heat source machine increases.

  The reason why the operation of the heat source machine becomes unstable or the energy consumption of the heat source machine increases due to the large fluctuations in the temperature of the cooling or heating medium returned to the heat source machine is explained as follows. Is done. In general, the heat source device has a load range in which it can be efficiently cooled or heated according to its specifications. However, when the temperature of the cooling medium or the heating medium returned to the heat source apparatus fluctuates greatly, the heat source apparatus must be operated in an inefficient load range, and the energy consumption increases. In addition, when the heat source machine is operated in an inefficient load range, the operation of the heat source machine tends to become unstable. Furthermore, the heat source device is generally selected based on the maximum value of the cooling load of the cooling medium or the heating load of the heating medium, but if the temperature of the cooling medium or the heating medium returned to the heat source device fluctuates greatly, the temperature Therefore, a high-spec heat source device with higher cooling or heating capability is required than in the case where is constant. In this case, not only the equipment of the heat source machine becomes larger, but it becomes more difficult to cope with low-load operation.

  Therefore, in the method for producing (meth) acrylic acid of the present invention, the temperature variation of the cooling medium or the heating medium returned to the heat source device regardless of the temperature variation of the cooling medium or the heating medium discharged from the crystallizer. In order to reduce the range, the following first to fourth adjusting means are provided. Specifically, in the crystallization process, a first buffer tank is provided, and the temperature of the cooling medium returned to the heat source device by the first or second adjusting means is kept within a certain range. In the melting process, the second buffer tank is installed. The temperature of the heating medium returned to the heat source device by the third or fourth adjusting means is kept within a certain range.

  In the present invention, the buffer tank that stores the cooling medium is referred to as a first buffer tank, and the buffer tank that stores the heating medium is referred to as a second buffer tank. The first buffer tank and the second buffer tank are collectively referred to as a buffer tank.

  Any buffer tank may be used as long as it can store a cooling medium or a heating medium. It is preferable that a predetermined amount of the cooling / heating medium is held in the buffer tank, and the cooling / heating medium held in the buffer tank has a temperature gradient in which the upper side has a high temperature and the lower side has a low temperature. The amount of the cooling medium or heating medium held in the buffer tank is the temperature or amount of the cooling medium or heating medium discharged from the heat source unit, the capacity of the heat source unit, the crude (meth) acrylic acid solution supplied to the crystallizer The temperature is determined as appropriate based on the temperature and amount of the liquid, the temperature of the cooling / heating medium retained in the buffer tank, and the like.

  Openings for taking in and out the cooling / heating medium are provided in the upper and lower parts of the buffer tank. In the buffer tank, the length between the upper opening and the lower opening is preferably 1 time or more, more preferably 2 times or more, and more preferably 4 times or more of the maximum sectional length of the buffer tank. More preferably, as a result, the cooling medium or the heating medium held in the buffer tank is likely to have a temperature gradient in the height direction, and the temperature of the cooling medium or the heating medium returned to the heat source unit is kept within a certain range. It is easy to keep. Details of the shape of the buffer tank will be described later.

  Hereinafter, in order to facilitate understanding of the present invention, the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments shown in the drawings.

  How to use the first buffer tank in the crystallization step, and the first adjusting means and the second adjusting means will be described with reference to FIGS.

  FIG. 1 shows a flow path connecting a heat source device, a crystallizer, and a first buffer tank. The cooling medium discharged from the heat source device 4 is supplied to the crystallizer 1, subjected to heat exchange in the crystallizer 1, discharged from the crystallizer 1, and returned to the heat source device 4. The upper opening 5 a of the first buffer tank 5 communicates with the heat medium outlet 2 b of the crystallizer 1 and the cold medium return port 4 b of the heat source device 4. Further, in the first buffer tank 5, the lower opening 5 b communicates with the cooling medium supply port 4 a of the heat source unit 4 and / or the heating medium discharge port 2 b of the crystallizer 1 and the cooling medium return port 4 b of the heat source unit 4. is doing.

  The first adjusting means will be described with reference to FIG. A 1st adjustment means is employ | adopted when the temperature of the cold-heating medium returned to a heat source machine is high in a crystallization process.

  For example, at the initial stage of the crystallization process, the temperature of the cooling medium discharged from the crystallizer 1 tends to be high, and when the cooling medium discharged from the crystallizer 1 is returned to the heat source unit 4 as it is, the heat source unit 4 has a high temperature. The cooling medium will be returned. In this case, at least a part of the cooling medium returned from the crystallizer 1 to the heat source unit 4 is supplied to the upper portion of the first buffer tank 5 through the channel 15 by reducing the flow rate of the channel 16 by a valve or the like. The first buffer tank 5 holds a predetermined amount of a cooling medium having a high temperature gradient on the upper side and a low temperature on the lower side. Therefore, when the high-temperature cooling medium is supplied from the upper opening 5 a of the first buffer tank 5. The high-temperature cooling medium is stored above the first buffer tank 5 so as to maintain the temperature gradient of the cooling medium in the first buffer tank 5. On the other hand, a low-temperature cooling medium is discharged from the lower opening 5 b of the first buffer tank 5. At this time, the amount of the cooling medium in the first buffer tank 5 is preferably kept constant. Therefore, the amount of the cooling medium discharged from the lower part of the first buffer tank 5 is the cooling medium supplied to the upper part. Is preferably equal to the amount of. The low-temperature cooling medium discharged from the lower portion of the first buffer tank 5 is returned to the heat source unit 4 alone or together with the cooling medium discharged from the crystallizer 1 carried through the flow path 16. Is done. A part of the cooling medium discharged from the heat source device 4 through the flow path 12 may be combined with the low-temperature cooling medium discharged from the lower portion of the first buffer tank 5. Therefore, the cooling medium adjusted to a lower temperature than the cooling medium discharged from the crystallizer 1 is returned to the heat source unit 4.

  The second adjusting means will be described with reference to FIG. A 2nd adjustment means is employ | adopted when the temperature of the cold-heating medium returned to a heat source machine is low in a crystallization process.

  For example, at the end of the crystallization process, the temperature of the cooling medium discharged from the crystallizer 1 tends to be low, and when the cooling medium discharged from the crystallizer 1 is returned to the heat source unit 4 as it is, the heat source unit 4 has a low temperature. The cooling medium will be returned. In this case, the flow rate of the flow path 11 is reduced by a valve or the like, and at least a part of the flow path 11 is passed through the flow path 12, so that at least a part of the cooling medium supplied from the heat source unit 4 to the crystallizer 1 Supply to the bottom of the. Alternatively, the flow rate of the flow path 13 is reduced, and at least a part of the flow path 13 is passed through the flow path 14, thereby supplying at least a part of the cooling medium returned from the crystallizer 1 to the heat source unit 4 to the lower part of the first buffer tank 5. To do. The first buffer tank 5 holds a predetermined amount of a cooling medium having a high temperature gradient on the upper side and a low temperature gradient on the lower side. Therefore, when the low temperature cooling medium is supplied from the lower opening 5 b of the first buffer tank 5. The low-temperature cooling / heating medium is stored below the first buffer tank 5 so as to maintain the temperature gradient of the cooling / heating medium in the first buffer tank 5. On the other hand, a high-temperature cooling medium is discharged from the upper opening 5 a of the first buffer tank 5. At this time, the amount of the cooling medium in the first buffer tank 5 is preferably kept constant. Therefore, the amount of the cooling medium discharged from the upper part of the first buffer tank 5 is the cooling medium supplied to the lower part. Is preferably equal to the amount of. The high-temperature cooling medium discharged from the upper part of the first buffer tank 5 is returned to the heat source unit 4 alone or together with the cooling medium discharged from the crystallizer 1 carried through the flow path 13. Is done. Therefore, the cooling medium adjusted to a higher temperature than the cooling medium discharged from the crystallizer 1 is returned to the heat source unit 4. Note that a part of the cooling medium discharged from the heat source device 4 through the flow paths 12 and 17 may be combined with the high-temperature cooling medium discharged from the upper part of the first buffer tank 5.

  According to the second adjusting means, the cooling medium supplied to the lower part of the first buffer tank 5 is at least part of the cooling medium supplied from the heat source unit 4 to the crystallizer 1 and / or from the crystallizer 1. Although it becomes at least a part of the cooling medium returned to the heat source unit 4, preferably at least a part of the cooling medium supplied from the heat source unit 4 to the crystallizer 1 is supplied to the lower part of the first buffer tank 5. Since the cooling medium supplied from the heat source unit 4 to the crystallizer 1 is lower in temperature than the cooling medium returned from the crystallizer 1 to the heat source unit 4, the unit capacity of the cooling medium stored below the first buffer tank 5 The amount of retained cold heat is further increased, and a low-temperature cold heat medium can be efficiently stored. Moreover, although the temperature of the cooling medium returned from the crystallizer 1 to the heat source unit 4 changes depending on the progress of crystallization, the temperature of the cooling medium supplied from the heat source unit 4 to the crystallizer 1 is substantially constant. It becomes easy to control the temperature of the cooling medium stored below the first buffer tank 5.

  In the crystallization process, when the temperature of the cooling medium returned to the heat source unit 4 is a temperature at which the heat source unit 4 can be efficiently operated, even if the first buffer tank 5 is not used. Good. That is, in the crystallization step, there may be a state in which the cooling medium discharged from the crystallizer 1 is directly returned to the heat source unit 4 without adopting the first and second adjusting means.

  According to the method for producing (meth) acrylic acid of the present invention, the temperature of the cooling medium returned to the heat source unit can be maintained within a certain range by the first and second adjusting means. In the production method of the present invention, the temperature variation of the cooling medium returned to the heat source machine is preferably within 3.0 ° C, more preferably within 1.0 ° C, and within 0.5 ° C. More preferably. If the temperature variation of the cooling medium returned to the heat source machine is within 3.0 ° C, the cooling load of the heat source machine is easily maintained within a certain range, and as a result, the heat source machine operates stably and consumes energy. Will be reduced.

  Next, how to use the second buffer tank in the melting step, and the third adjusting means and the fourth adjusting means will be described with reference to FIGS.

  FIG. 4 shows a flow path connecting the heat source device, the crystallizer, and the second buffer tank. The heating medium discharged from the heat source device 4 is supplied to the crystallizer 1, and is subjected to heat exchange in the crystallizer 1, then discharged from the crystallizer 1, and returned to the heat source device 4. In the second buffer tank 6, the upper opening 6 a communicates with the heating medium supply port 4 c of the heat source unit 4 and / or the heating medium discharge port 2 b of the crystallizer 1 and the heating medium return port 4 d of the heat source unit 4. Yes. Further, the second buffer tank 6 has a lower opening 6 b communicating with the heat medium outlet 2 b of the crystallizer 1 and the heat medium return port 4 d of the heat source unit 4.

  The third adjusting means will be described with reference to FIG. A 3rd adjustment means is employ | adopted when the temperature of the heating medium returned to a heat-source apparatus is low in a melting process.

  For example, at the initial stage of the melting process, the temperature of the heating medium discharged from the crystallizer 1 tends to be low, and if the heating medium discharged from the crystallizer 1 is returned to the heat source unit 4 as it is, the heat source unit 4 has a low temperature. The heating medium will be returned. In this case, by reducing the flow rate of the flow path 25 with a valve or the like, at least a part of the heating medium returned from the crystallizer 1 to the heat source apparatus 4 is supplied to the lower part of the second buffer tank 6 through the flow path 26. Since the second buffer tank 6 holds a predetermined amount of a heating medium having a high temperature gradient on the upper side and a lower temperature gradient on the lower side, when the low temperature heating medium is supplied from the lower opening 6 b of the second buffer tank 6. The low temperature heating medium is stored below the second buffer tank 6 so as to maintain the temperature gradient of the heating medium in the second buffer tank 6. On the other hand, a high-temperature heating medium is discharged from the upper opening 6 a of the second buffer tank 6. At this time, the amount of the heating medium in the second buffer tank 6 is preferably kept constant. Therefore, the amount of the heating medium discharged from the upper part of the second buffer tank 6 is the heating medium supplied to the lower part. Is preferably equal to the amount of. The high-temperature heating medium discharged from the upper part of the second buffer tank 6 is returned to the heat source unit 4 alone or together with the heating medium discharged from the crystallizer 1 conveyed through the flow path 25. Is done. Further, a part of the hot medium discharged from the heat source device 4 through the flow path 22 may be combined with the high-temperature hot medium discharged from the upper part of the second buffer tank 6. Therefore, the heating medium adjusted to a higher temperature than the heating medium discharged from the crystallizer 1 is returned to the heat source unit 4.

  The fourth adjusting means will be described with reference to FIG. A 4th adjustment means is employ | adopted when the temperature of the heating medium returned to a heat-source apparatus is high in a melting process.

  For example, at the end of the melting process, the temperature of the heating medium discharged from the crystallizer 1 tends to increase. If the heating medium discharged from the crystallizer 1 is returned to the heat source unit 4 as it is, the heat source unit 4 has a high temperature. The heating medium will be returned. In this case, the flow rate of the flow path 21 is reduced by a valve or the like, and at least a part of the flow rate is flowed to the flow path 22, so that at least a part of the heating medium supplied from the heat source unit 4 to the crystallizer 1 is supplied to the second buffer tank 6. Supply to the top of the. Alternatively, the flow rate of the flow path 24 is reduced, and at least a part of the flow path 24 is passed through the flow path 23, whereby at least a part of the heating medium returned from the crystallizer 1 to the heat source unit 4 is supplied to the upper part of the second buffer tank 6. To do. The second buffer tank 6 holds a predetermined amount of a heating medium having a low temperature gradient in the lower part and a high temperature gradient in the upper part. Therefore, when the high temperature heating medium is supplied from the upper opening 6 a of the second buffer tank 6. The high-temperature heating medium is stored above the second buffer tank 6 so as to maintain the temperature gradient of the heating medium in the second buffer tank 6. On the other hand, a low temperature heating medium is discharged from the lower opening 6 b of the second buffer tank 6. At this time, the amount of the heating medium in the second buffer tank 6 is preferably kept constant. Therefore, the amount of the heating medium discharged from the lower part of the second buffer tank 6 is the same as that of the heating medium supplied to the upper part. Is preferably equal to the amount of. The low temperature heating medium discharged from the lower part of the second buffer tank 6 is returned to the heat source device 4 alone or together with the heating medium discharged from the crystallizer 1 carried through the flow path 24. Is done. Therefore, the heating medium adjusted to a lower temperature than the heating medium discharged from the crystallizer 1 is returned to the heat source unit 4. Note that a part of the heat medium discharged from the heat source device 4 through the flow paths 22 and 27 may be combined with the low temperature heat medium discharged from the lower portion of the second buffer tank 6.

  According to the fourth adjusting means, the heating medium supplied to the upper part of the second buffer tank 6 is at least part of the heating medium supplied from the heat source unit 4 to the crystallizer 1 and / or from the crystallizer 1. Although it becomes at least a part of the heating medium returned to the heat source unit 4, preferably at least a part of the heating medium supplied from the heat source unit 4 to the crystallizer 1 is supplied to the upper part of the second buffer tank 6. The heating medium supplied from the heat source unit 4 to the crystallizer 1 is higher in temperature than the heating medium returned from the crystallizer 1 to the heat source unit 4, so the unit capacity of the heating medium stored above the second buffer tank 6 The amount of heat retention per unit increases, and a high-temperature heat medium can be efficiently stored. Moreover, although the temperature of the heating medium returned from the crystallizer 1 to the heat source unit 4 changes depending on the progress of melting, the temperature of the heating medium supplied from the heat source unit 4 to the crystallizer 1 is substantially constant. 2 Temperature control of the heating medium stored above the buffer tank 6 becomes easy.

  In the melting step, when the temperature of the heating medium returned to the heat source unit 4 is a temperature at which the heat source unit 4 can be efficiently operated, there may be a state where the second buffer tank 6 is not used. . That is, in the melting step, there may be a state in which the heating medium discharged from the crystallizer 1 is directly returned to the heat source unit 4 without employing the third and fourth adjusting means.

  According to the method for producing (meth) acrylic acid of the present invention, the temperature of the heating medium returned to the heat source device can be kept within a certain range by the third and fourth adjusting means. In the production method of the present invention, the temperature variation of the heating medium returned to the heat source machine is preferably within 3.0 ° C, more preferably within 1.0 ° C, and within 0.5 ° C. More preferably. If the temperature fluctuation of the heating medium returned to the heat source machine is within 3.0 ° C, the heating load of the heat source machine is easily maintained within a certain range, and as a result, the heat source machine operates stably and consumes energy. Will be reduced.

  The buffer tank is preferably provided with a plurality of temperature measuring means in the vertical direction so that the low-temperature and high-temperature cold medium or hot medium quantity in the buffer tank can be grasped. Then, it is preferable to adjust the temperature of the cooling / heating medium to be returned to the heat source unit according to the temperature above and below the cooling / heating medium held in the buffer tank. It is preferable to adjust the temperature of the cooling medium or the heating medium to be returned to the heat source apparatus in a range in which the operation of the heat source apparatus becomes unstable or the energy consumption does not increase extremely. The temperature measuring means may be a known temperature measuring means such as a thermometer.

  The low-temperature cooling / heating medium held in the buffer tank disappears, and the high-temperature cooling / heating medium is suddenly returned to the heat source machine, or the high-temperature cooling / heating medium held in the buffer tank disappears. If a low-temperature cooling medium or heating medium is returned to the heat source machine, the operation of the heat source machine becomes extremely unstable. Therefore, by measuring the temperature distribution in the vertical direction of the cooling medium or heating medium in the buffer tank, the temperature of the cooling medium or heating medium returned to the heat source machine is adjusted to be high before the low-temperature cooling medium or heating medium is exhausted. However, it is preferable to lower the discharge rate of the low-temperature cooling / heating medium or the heating medium from the buffer tank. Or, before the high-temperature cooling medium or heating medium runs out, adjust the temperature of the cooling medium or heating medium returned to the heat source machine to a low level so as to reduce the discharge rate of the high-temperature cooling medium or heating medium from the buffer tank. It is preferable.

  Specifically, when the temperature below the cooling / heating medium held in the buffer tank exceeds a predetermined value, the temperature of the cooling / heating medium returned to the heat source unit is adjusted to be high and held in the buffer tank. It is preferable to adjust the temperature of the cooling medium or the heating medium returned to the heat source unit to be low when the temperature above the cooling medium or the heating medium is lower than a predetermined value. As a result, the effects of the first to fourth adjusting means can be enjoyed over a longer period.

  The method for producing (meth) acrylic acid of the present invention may include the crystallization step and the melting step. In this case, the method for producing (meth) acrylic acid of the present invention includes a step of supplying a cooling medium from a heat source device to a crystallizer, and crystallizing (meth) acrylic acid from a crude (meth) acrylic acid solution; A step of discharging the cooling medium from the crystallizer and returning it to the heat source unit; a step of supplying a heating medium from the heat source unit to the crystallizer and melting the (meth) acrylic acid; Discharging the heating medium and returning it to the heat source unit. At this time, the temperature of the cooling medium returned to the refrigerator is maintained within a certain range by the first or second adjusting means, and the temperature of the heating medium returned to the refrigerator is adjusted by the third or fourth adjusting means. Is kept within a certain range. The heat source machine used in the crystallization process and the heat source machine used in the melting process may be the same or different.

  FIG. 7 shows a method for producing (meth) acrylic acid, which has a crystallization process and a melting process, and the heat source machine used in the crystallization process is different from the heat source machine used in the melting process. FIG. 7 shows a first heat source device 4A that cools the cooling medium and a second heat source device 4B that heats the heating medium. The first heat source unit 4A has a cooling medium supply port 4Aa and a cooling medium return port 4Ab, and the second heat source unit 4B has a heating medium supply port 4Bc and a heating medium return port 4Bd.

  In FIG. 7, the manufacturing method of (meth) acrylic acid of the present invention supplies a cooling medium from the first heat source unit 4A to the crystallizer 1, and crystallizes (meth) acrylic acid from a crude (meth) acrylic acid solution. A step of discharging the cooling medium from the crystallizer 1 and returning it to the first heat source unit 4A; and supplying a heating medium from the second heat source unit 4B to the crystallizer 1; A step of melting acrylic acid; and a step of discharging the heating medium from the crystallizer 1 and returning it to the second heat source unit 4B. In the embodiment shown in FIG. 7, the crystallization step and the melting step are alternately performed in the crystallizer 1. That is, the crystallizer 1 is not supplied with a cooling medium and a heating medium at the same time.

  The temperature of the cooling medium returned to the heat source unit 4A is kept within a certain range by the first or second adjusting means using the first buffer tank 5, and the temperature of the heating medium returned to the heat source unit 4B is second. The temperature is maintained in a certain range by the third or fourth adjusting means using the buffer tank 6. In FIG. 7, the second adjustment unit is omitted from the flow path for supplying at least part of the cooling medium returned from the crystallizer 1 to the first heat source unit 4 </ b> A to the lower portion of the first buffer tank 5. As for the adjusting means, a flow path for supplying at least a part of the heating medium returned from the crystallizer 1 to the second heat source unit 4B to the upper part of the second buffer tank 6 is omitted.

  In the method for producing (meth) acrylic acid of the present invention, when a refrigerator is used as a heat source unit, a cooling medium is supplied from the refrigerator to the first crystallizer, and at the same time the crystallization process is performed in the first crystallizer. The heating medium may be supplied from the refrigerator to the second crystallizer, and the melting step may be performed by the second crystallizer. This will be described with reference to FIG.

  The refrigerator 7 supplies the cooling medium from the cooling medium supply port 7a, returns the cooling medium through the cooling medium return port 7b, supplies the heating medium from the heating medium supply port 7c, and passes through the heating medium return port 7d. The heating medium is returned. In FIG. 8, the manufacturing method of the (meth) acrylic acid of this invention supplies a cooling-heat medium from the refrigerator 7 to the 1st crystallizer 1A, and crystallizes (meth) acrylic acid from a crude (meth) acrylic acid solution. A step of discharging the cooling medium from the first crystallizer 1A and returning it to the refrigerator 7; and supplying a heating medium from the refrigerator 7 to the second crystallizer 1B for crystallization ( A step of melting the (meth) acrylic acid; and a step of discharging the heating medium from the second crystallizer 1B and returning it to the refrigerator 7.

  The temperature of the cooling medium returned to the refrigerator 7 is kept within a certain range by the first or second adjusting means using the first buffer tank 5, and the temperature of the heating medium returned to the refrigerator 7 is the second buffer. The temperature is kept in a certain range by the third or fourth adjusting means using the tank 6. In FIG. 8, the second adjusting means is omitted for the fourth adjusting means, omitting the flow path for supplying at least a part of the cooling medium returned from the crystallizer to the refrigerator 7 to the lower part of the first buffer tank 5. The flow path for supplying at least part of the heating medium returned from the crystallizer to the refrigerator 7 to the upper part of the second buffer tank 6 is omitted.

  After the crystallization process is completed in the first crystallizer 1A and the melting process is completed in the second crystallizer 1B, the cooling medium is supplied to the second crystallizer 1B through the flow path 31, and the heating medium is supplied. While supplying to the 1st crystallizer 1A, the cooling medium discharged | emitted from the 2nd crystallizer 1B is returned to the cooling medium return port 7b of the refrigerator 7 by the flow path 32, and is discharged | emitted from 1st crystallizer 1A. The heated heat medium is preferably returned to the heat medium return port 7 d of the refrigerator 7. That is, the heating medium is supplied from the refrigerator 7 to the first crystallizer 1A, the melting process is performed by the first crystallizer 1A, the heating medium is discharged from the first crystallizer 1A, and returned to the refrigerator 7. The cooling medium is supplied from the refrigerator 7 to the second crystallizer 1B, the crystallization process is performed in the second crystallizer 1B, and the cooling medium is discharged from the second crystallizer 1B and returned to the refrigerator 7. Is preferred. In FIG. 8, the flow paths 31 and 32 are each provided with a cooling medium flow path and a heating medium flow path.

  According to the embodiment shown in FIG. 8, it becomes possible to use both the cooling medium and the heating medium discharged from the refrigerator 7 for the production of (meth) acrylic acid, and the consumption for the production of (meth) acrylic acid. Energy can be reduced. Moreover, (meth) acrylic acid is efficiently manufactured by combining the refrigerator 7, the first crystallizer 1A, the second crystallizer 1B, the first buffer tank 5, and the second buffer tank 6. It becomes possible.

  In the method for producing (meth) acrylic acid according to the present invention, the cooling medium may be composed of a first cooling medium and a second cooling medium having a temperature lower than that of the first cooling medium. For example, a (meth) acrylic acid may be produced by using a refrigerator that discharges the first cooling medium, the second cooling medium, and the heating medium and combining three crystallizers with the refrigerator. In this case, the crude (meth) acrylic acid solution is cooled by the first cooling medium, and the first half of the crystallization process is performed, and the (meth) acrylic acid is removed from the crude (meth) acrylic acid solution cooled by the second cooling medium. Crystallization will occur in the second half of the crystallization process. By providing the first cooling medium and the second cooling medium in this manner, energy saving in the crystallization process can be achieved. In the first half of the crystallization step, the (meth) acrylic acid may be partially crystallized by cooling the crude (meth) acrylic acid solution with the first cooling medium. This will be described with reference to FIG.

The refrigerator 7 supplies the first cooling / heating medium from the first cooling / heating medium supply port 7a _1, returns the first cooling / heating medium through the first cooling / heating medium return port 7b ₁ , and from the second cooling / heating medium supply port 7a _2. supplying a second cold medium, the second cold heat medium is returned through the second cold heat medium return port 7b _2, and supplies the heat medium from the heat medium supply port 7c, hyperthermia medium through the heat medium return port 7d Will be returned. In FIG. 9, the method for producing (meth) acrylic acid of the present invention includes the step of supplying the first cooling medium from the refrigerator 7 to the first crystallizer 1 </ b> A and cooling the crude (meth) acrylic acid solution; Discharging the first cooling medium from the first crystallizer 1A and returning it to the refrigerator 7; supplying the second cooling medium from the refrigerator 7 to the second crystallizer 1B and cooling the crude (meta) A step of crystallizing (meth) acrylic acid from the acrylic acid solution; a step of discharging the second cooling medium from the second crystallizer 1B and returning it to the refrigerator 7; and a heating medium from the refrigerator 7 Supplying the third crystallizer 1C and melting the crystallized (meth) acrylic acid; and discharging the heating medium from the third crystallizer 1C and returning it to the refrigerator 7. ing. In this case, the first crystallizer 1A performs the first half of the crystallization process, the second crystallizer 1B performs the second half of the crystallization process, and the third crystallizer 1C performs the melting process. .

  The temperature of the first cooling medium returned to the refrigerator 7 is kept within a certain range by the first or second adjusting means using the first (1) buffer tank 5 </ b> A, and is returned to the refrigerator 7. The temperature of the cooling medium is kept within a certain range by the first or second adjusting means using the first (2) buffer tank 5B, and the second buffer tank 6 is used as the heating medium returned to the refrigerator 7. The temperature is maintained within a certain range by the third or fourth adjusting means. In FIG. 9, the second adjustment means omits the flow path for supplying at least a part of the cooling medium returned from the crystallizer to the refrigerator 7 to the lower part of the first buffer tanks 5 </ b> A, 5 </ b> B. As for the means, a flow path for supplying at least a part of the heating medium returned from the crystallizer to the refrigerator 7 to the upper part of the second buffer tank 6 is omitted.

After the first half of the crystallization process is completed in the first crystallizer 1A, the second half of the crystallization process is completed in the second crystallizer 1B, and the melting process is completed in the third crystallizer 1C, the flow path 33 Thus, the second cooling medium is supplied to the first crystallizer 1A, the heating medium is supplied to the second crystallizer 1B, the first cooling medium is supplied to the third crystallizer 1C, and the flow path 34 is used. The second cooling medium discharged from the first crystallizer 1A is returned to the second cooling medium return port 7b ₂ of the refrigerator 7, and the heating medium discharged from the second crystallizer 1B is heated by the refrigerator 7. The first cooling medium returned to the medium return port 7d and discharged from the third crystallizer 1C is returned to the first cooling medium return port 7b ₁ of the refrigerator 7. As a result, the first crystallizer 1A performs the latter half of the crystallization process, the second crystallizer 1B performs the melting process, and the third crystallizer 1C performs the first half of the crystallization process. .

After the second half of the crystallization process is completed in the first crystallizer 1A, the melting process is completed in the second crystallizer 1B, and the first half of the crystallization process is completed in the third crystallizer 1C, the flow path 33 Thus, the heating medium is supplied to the first crystallizer 1A, the first cooling medium is supplied to the second crystallizer 1B, the second cooling medium is supplied to the third crystallizer 1C, and the flow path 34 is used. The heating medium discharged from the first crystallizer 1A is returned to the heating medium return port 7d of the refrigerator 7, and the first cooling medium discharged from the second crystallizer 1B is used as the first cooling medium of the refrigerator 7. The second cooling medium returned to the return port 7b ₁ and discharged from the third crystallizer 1C is returned to the second cooling medium return port 7b ₂ of the refrigerator 7. As a result, the first crystallizer 1A performs the melting process, the second crystallizer 1B performs the first half of the crystallization process, and the third crystallizer 1C performs the second half of the crystallization process. .

  In FIG. 9, the flow paths 33 and 34 are each provided with a flow path for the first cooling medium, a flow path for the second cooling medium, and a flow path for the heating medium.

  According to the embodiment shown in FIG. 9, the refrigerator 7, the first crystallizer 1A, the second crystallizer 1B, the third crystallizer 1C, the first buffer tank 5 and the second buffer tank 6 By combining the above, (meth) acrylic acid can be more efficiently produced, and the energy consumption of the refrigerator 7 can be further reduced.

  When the manufacturing method of (meth) acrylic acid of this invention has the said crystallization process, it is preferable that the manufacturing method of this invention has the process of obtaining a crude (meth) acrylic acid solution further.

  The step of obtaining the crude (meth) acrylic acid solution includes a catalytic gas phase oxidation reaction step of obtaining a (meth) acrylic acid-containing gas from a (meth) acrylic acid production raw material by a catalytic gas phase oxidation reaction, and the (meth) acrylic acid It is preferable to have a collection step of collecting the contained gas with a liquid medium. Furthermore, you may provide a refinement | purification process in the back | latter stage of the said collection process for the purpose of raising the (meth) acrylic acid content rate of the (meth) acrylic acid solution obtained at the said collection process.

  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 (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.

  When the (meth) acrylic acid content of the (meth) acrylic acid solution obtained in the collecting step is low, a purification step is provided after the collecting step, and the (meth) acrylic acid solution obtained in the collecting step May be purified by distillation or diffusion to obtain a crude (meth) acrylic acid solution for use in the crystallization step.

  When the production method of (meth) acrylic acid of the present invention has the melting step and does not have the crystallization step, the production method of the present invention further crystallizes (meth) acrylic acid by an arbitrary method. It is preferable to have the process to do.

[2. Crystallization system)
The crystallization system of the present invention will be described. The crystallization system of the present invention includes a crystallizer, a heat source device, and a buffer tank. When performing the crystallization operation in the crystallizer, the crystallization system of the present invention includes a crystallizer, a heat source device, and a first buffer tank, and when performing a melting operation in the crystallizer. The crystallization system of the present invention includes a crystallizer, a heat source device, and a second buffer tank.

  The crystallizer used in the crystallization system of the present invention has a heat transfer surface, and the inside is divided into a heat medium existing part and a crystal existing part by the heat transfer surface. A cooling medium or a heating medium is present in the heat medium existence part, and a crystal-containing liquid and / or a crystal is present in the crystal existence part. In the present invention, it is preferable that a crude (meth) acrylic acid solution and / or a (meth) acrylic acid crystal exist in the crystal existing part. The heat transfer surface is not particularly limited as long as the crystallizer is divided into two parts, a heat medium existing part and a crystal existing part, and heat exchange is performed via the heat transfer surface.

  As a crystallizer having a heat transfer surface, a device generally used as a heat exchanger can be adopted, and the heat exchanger exemplified above can be adopted.

  In the crystallizer, the cooling medium is made to exist in the heat medium existence part, and the crystal-containing liquid is made to exist in the crystal existence part, whereby the crystal-containing liquid is cooled through the heat transfer surface to generate crystals. Further, in the crystallizer, when the heating medium is present in the heat medium existing part and the crystal is present on the crystal existing part side, the crystal is heated and melted through the heat transfer surface to obtain a crystal melt. .

  The heat medium existence part has an inlet (heat medium supply port) to which the cooling medium and / or the heating medium is supplied and an outlet (heating medium outlet) from which the cooling and / or heating medium is discharged. . The crystal existence part has an inlet through which the crystal-containing liquid is supplied and an outlet through which the crystal-containing liquid and / or crystal melt is discharged.

  The heat source apparatus used in the crystallization system of the present invention is not particularly limited as long as it cools the cooling medium and / or heats the heating medium, and the heat source apparatus exemplified above can be used. Moreover, you may use the refrigerator which heats a heating medium simultaneously with cooling a cooling medium as a heat source machine.

  When the heat source machine cools the cooling medium, the heat source machine has a cooling medium supply port for supplying the cooling medium and a cooling medium return port for returning the cooling medium. The cooling medium supply port of the heat source unit communicates with the inlet of the heat medium existing part of the crystallizer, and the cooling medium is discharged from the heat source unit through the cooling medium supply port and supplied to the heat medium existing part of the crystallizer. The The cooling medium return port of the heat source unit communicates with the outlet of the heat medium existing part of the crystallizer, and the cooling medium discharged from the heat medium existing part of the crystallizer is returned to the heat source unit through the cooling medium return port. The

  When the heat source machine heats the heating medium, the heat source machine has a heating medium supply port for supplying the heating medium and a heating medium return port for returning the heating medium. The heating medium supply port of the heat source unit communicates with the inlet of the heat medium existing part of the crystallizer, and the heating medium is discharged from the heat source unit through the heating medium supply port and supplied to the heat medium existing part of the crystallizer. The The heating medium return port of the heat source unit communicates with the outlet of the heat medium existing part of the crystallizer, and the heating medium discharged from the crystallizer heat medium existing part is returned to the heat source unit through the heating medium return port. The

  The buffer tank used in the crystallization system of the present invention has two openings, an upper opening and a lower opening. The buffer tank is not particularly limited as long as it can store a cooling / heating medium or a heating / heating medium, and does not have to have a structure in particular.

  The buffer tank holds a cooling medium or a heating medium having a temperature gradient in a height direction in which the upper side is a high temperature and the lower side is a low temperature. In order to hold a cooling medium or a heating medium having a temperature gradient in the height direction in which the upper side is high temperature and the lower side is low temperature in the buffer tank, the high-temperature cooling medium or heating medium is opened from the upper opening of the buffer tank. It is sufficient to supply a low-temperature cooling / heating medium from the lower opening of the buffer tank, and by doing so, the temperature gradient in the vertical direction is naturally generated in the cooling / heating medium held in the buffer tank. Will occur.

  The shape of the buffer tank is not particularly limited, but a substantially columnar body such as a cylinder or a prism is preferable. The length between the upper opening and the lower opening of the buffer tank is preferably 1 time or more, more preferably 2 times or more, and more preferably 4 times or more of the maximum sectional length of the buffer tank. Further preferred. That is, the length of the buffer tank between the upper opening and the lower opening is preferably at least the lateral width, and by using such a shape, the cooling medium or the heating medium held in the buffer tank is A temperature gradient tends to occur in the height direction.

  The maximum cross-sectional length of the buffer tank is, for example, the diameter of the bottom circle if the buffer tank has a cylindrical shape. If the buffer tank has a quadrangular prism shape, the diagonal length of the square on the bottom surface is the maximum cross-sectional length of the buffer tank. If the buffer tank has a columnar shape except for the lower part, and the lower part has a conical shape that dents downward, the maximum cross-sectional length of the columnar part is the maximum cross-sectional length of the buffer tank. . If the buffer tank has a shape in which the vicinity of the middle in the height direction is swollen, the maximum cross-sectional length at the most swollen portion near the middle is the maximum cross-sectional length of the buffer tank.

  The upper opening and the lower opening of the buffer tank are provided so that the upper opening is located above the lower opening. By providing each opening in this manner, the cooling medium or the heating medium is held in the buffer tank so that the liquid level is located in the upper opening.

  As the upper opening and the lower opening, for example, an opening may be provided on the outer surface of the buffer tank, or a pipe that opens inside the buffer tank may be provided in the buffer tank. Preferably, as the upper opening, a pipe that opens upward in the buffer tank is provided in the buffer tank. The lower opening is preferably provided at the bottom of the buffer tank. Both the upper opening and the lower opening are preferably provided in the central portion of the cross section of the buffer tank. By providing the upper opening and the lower opening in this manner, the temperature gradient of the cooling / heating medium in the buffer tank can be easily maintained even if the cooling / heating medium or the heating / heating medium flows out of each opening.

  Next, the flow path connecting the crystallizer, the heat source device, and the buffer tank will be described with reference to FIGS.

  FIG. 1 shows a flow path when the first buffer tank is used as a buffer tank, and shows a crystallization system in the case of performing crystallization using a cooling medium. When a cooling medium is used, the crystallization system of the present invention includes a crystallizer 1, a heat source device 4, and a first buffer tank 5. The cooling medium supply port 4 a of the heat source device 4 communicates with the inlet 2 a of the heating medium existence portion 2 of the crystallizer 1, and the outlet 2 b of the heating medium existence portion 2 of the crystallizer 1 is the cooling medium return port 4 b of the heat source device 4. Communicating with As a result, a circulation path for the cooling medium is formed between the crystallizer 1 and the heat source unit 4. The cooling medium supplied from the heat source unit 4 to the heat medium existing part 2 of the crystallizer 1 is heat-exchanged in the crystallizer 1, and then discharged from the heat medium existing part 2 of the crystallizer 1. Returned to 4. Crystals are generated in the crystal existence part 3 of the crystallizer 1 by heat exchange of the cooling medium in the crystallizer 1. The cooling medium returned to the heat source unit 4 is cooled in the heat source unit 4 and discharged again from the cooling medium supply port 4 a of the heat source unit 4.

  In the first buffer tank 5, the upper opening 5 a communicates with the outlet 2 b of the heat medium existing part 2 of the crystallizer 1 and the cooling medium return port 4 b of the heat source unit 4. As a result, the cooling medium discharged from the crystallizer 1 is supplied to the upper opening 5 a of the first buffer tank 5 and the flow returned to the heat source device 4 from the upper opening 5 a of the first buffer tank 5. A path is formed.

  The first buffer tank 5 has a lower opening 5b at the cooling medium supply port 4a of the heat source unit 4 and / or the outlet 2b of the heat medium existing part 2 of the crystallizer 1 and the cooling medium return port 4b of the heat source unit 4. Communicate. As a result, the cooling medium supplied from the heat source unit 4 and / or the cooling medium discharged from the crystallizer 1 is supplied to the lower opening 5 b of the first buffer tank 5 and the first buffer tank 5. A flow path returning to the heat source unit 4 from the lower opening 5b is formed.

  FIG. 4 shows a flow path when the second buffer tank is used as the buffer tank, and shows a crystallization system when melting is performed using a heating medium. When using a heating medium, the crystallization system of the present invention includes a crystallizer 1, a heat source device 4, and a second buffer tank 6. The heating medium supply port 4 c of the heat source device 4 communicates with the inlet 2 a of the heating medium existence portion 2 of the crystallizer 1, and the outlet 2 b of the heating medium existence portion 2 of the crystallizer 1 is the heating medium return port 4 d of the heat source device 4. Communicating with As a result, a circulation path for the heating medium is formed between the crystallizer 1 and the heat source unit 4. The heat medium supplied from the heat source unit 4 to the heat medium existing part 2 of the crystallizer 1 is subjected to heat exchange in the crystallizer 1 and then discharged from the heat medium existing part 2 of the crystallizer 1 to be heat source machine. Returned to 4. When the heating medium is heat-exchanged in the crystallizer 1, the crystals in the crystal existing part 3 of the crystallizer 1 are melted. The heating medium returned to the heat source unit 4 is heated in the heat source unit 4 and discharged again from the heating medium supply port 4 c of the heat source unit 4.

  The second buffer tank 6 has an upper opening 6 a at the heating medium supply port 4 c of the heat source unit 4 and / or the outlet 2 b of the heat medium existing part 2 of the crystallizer 1 and the heating medium return port 4 d of the heat source unit 4. Communicate. As a result, the heating medium supplied from the heat source device 4 and / or the heating medium discharged from the crystallizer 1 are supplied to the upper opening 6 a of the second buffer tank 6 and the second buffer tank 6. A flow path that is returned to the heat source unit 4 from the upper opening 6a is formed.

  In the second buffer tank 6, the lower opening 6 b communicates with the outlet 2 b of the heat medium existing part 2 of the crystallizer 1 and the heating medium return port 4 d of the heat source unit 4. As a result, the heating medium discharged from the crystallizer 1 is supplied to the lower opening 6 b of the second buffer tank 6 and the flow returned to the heat source unit 4 from the lower opening 6 b of the second buffer tank 6. A path is formed.

  According to the crystallization system of the present invention, by providing a crystallizer, a heat source device, and a buffer tank, and forming a flow path as described above, the heat source device operates stably, and crystallization operation and / or Alternatively, the melting operation is stabilized and energy consumption is reduced.

  As shown in FIG. 7, the crystallization system of the present invention may have two heat source units and two buffer tanks for one crystallizer.

  The heat source machine includes a first heat source machine 4A that cools the cooling medium and a second heat source machine 4B that heats the heating medium. The first heat source unit 4A has a cooling medium supply port 4Aa that communicates with the inlet of the heating medium existence unit 2 of the crystallizer 1, and a cooling medium return port 4Ab that communicates with the outlet of the heating medium existence unit 2. The two heat source unit 4B has a heating medium supply port 4Bc that communicates with the inlet of the heating medium existence unit 2 of the crystallizer 1 and a heating medium return port 4Bd that communicates with the outlet of the heating medium existence unit 2. A cooling medium is supplied to the crystallizer 1 by the first heat source unit 4A, a crystallization operation is performed in the crystallizer 1, and a heating medium is supplied to the crystallizer 1 by the second heat source unit 4B. A melting operation is performed in the analyzer 1.

  The buffer tank includes a first buffer tank 5 that keeps the temperature of the cooling medium returned to the first heat source unit 4A within a certain range, and a second buffer tank 6 that keeps the temperature of the hot medium returned to the second heat source unit 4B within a certain range. It consists of. The flow path connecting the first buffer tank 5, the first heat source device 4A, and the crystallizer 1 is the same as FIG. 1 showing the crystallization system when crystallization is performed using a cooling medium. The flow path connecting the second buffer tank 6, the second heat source device 4 </ b> B, and the crystallizer 1 is the same as that in FIG. 4 showing the crystallization system when melting is performed using a heating medium. In FIG. 7, the flow path for supplying at least a part of the cooling medium returned from the crystallizer 1 to the first heat source unit 4A to the lower part of the first buffer tank 5 is omitted, and the second heat source unit 4B from the crystallizer 1 is omitted. The flow path for supplying at least a part of the heating medium to be returned to the upper part of the second buffer tank 6 is omitted.

  When using a refrigerator as a heat source machine, the crystallization system of this invention may have two crystallizers and two buffer tanks with respect to one refrigerator. This will be described with reference to FIG.

  The crystallizer is composed of a first crystallizer 1A and a second crystallizer 1B, and the first crystallizer 1A has a first heat transfer surface, and the first heat transfer surface causes the inside to have a first heat transfer. The second crystallizer 1B has a second heat transfer surface that is divided into a medium existence portion 2A and a first crystal existence portion 3A, and the inside is separated from the second heat transfer medium existence portion 2B by the second heat transfer surface. It is divided into the second crystal existence part 3B.

  The refrigerator 7 includes a cooling medium supply port 7a that communicates with the inlet of the first heating medium existence part 2A, a cooling medium return port 7b that communicates with the outlet of the first heating medium existence part 2A, and a second heating medium existence part 2B. And a heating medium return port 7d communicating with the outlet of the second heating medium presence part 2B.

  The buffer tank includes a first buffer tank 5 that keeps the temperature of the cooling medium returned to the refrigerator 7 in a certain range, and a second buffer tank 6 that keeps the temperature of the hot medium returned to the refrigerator 7 in a certain range. The flow path connecting the first buffer tank 5, the refrigerator 7, and the crystallizer 1 is the same as that in FIG. 1 showing the crystallization system when crystallization is performed using a cooling medium. The flow path connecting the second buffer tank 6, the refrigerator 7, and the crystallizer 1 is the same as that shown in FIG. 4 showing the crystallization system when melting is performed using a heating medium. In FIG. 8, the flow path for supplying at least a part of the cooling medium returned from the crystallizer 1 to the refrigerator 7 to the lower part of the first buffer tank 5 is omitted, and the heat returned from the crystallizer 1 to the refrigerator 7 is omitted. A flow path for supplying at least a part of the medium to the upper portion of the second buffer tank 6 is omitted.

  In the embodiment shown in FIG. 8, the flow path 31 communicated with the inlet of the heat medium existing part 2A of the first crystallizer 1A and the inlet of the heat medium existing part 2B of the second crystallizer 1B, It is preferable to provide a flow path 32 communicating with the outlet of the heat medium existing part 2A of the first crystallizer 1A and the outlet of the heat medium existing part 2B of the second crystallizer 1B. The flow paths 31 and 32 are each provided with a flow path for a cooling medium and a flow path for a heating medium.

  If a refrigerator is used as the heat source device, cooling of the cooling medium and heating of the heating medium can be performed simultaneously. Therefore, the cooling medium is supplied from the refrigerator 7 to the first crystallizer 1A, and the first crystallizer 1A. At the same time as the crystallization operation, the heating medium can be supplied from the refrigerator 7 to the second crystallizer 1B and the melting operation can be performed by the second crystallizer 1B. After the crystallization operation is completed in the first crystallizer 1A and the melting operation is completed in the second crystallizer 1B, the cooling medium is supplied to the second crystallizer 1B through the flow path 31, and the heating medium is supplied. While supplying to the 1st crystallizer 1A, the cooling medium discharged | emitted from the 2nd crystallizer 1B is returned to the cooling medium return port 7b of the refrigerator 7 by the flow path 32, and is discharged | emitted from 1st crystallizer 1A. The heated heat medium is preferably returned to the heat medium return port 7 d of the refrigerator 7. As described above, if the crystallization system shown in FIG. 8 is used, the crystallization operation and the melting operation can be performed efficiently.

  In the crystallization system of the present invention, the heat source unit may be capable of supplying the first cooling medium and the second cooling medium having a temperature lower than that of the first cooling medium. For example, a crystallization system may be used in which a refrigerator that discharges the first cooling medium, the second cooling medium, and the heating medium is used, and three crystallizers and three buffer tanks are combined. This will be described with reference to FIG.

  The crystallizer includes a first crystallizer 1A, a second crystallizer 1B, and a third crystallizer 1C. The first crystallizer 1A has a first heat transfer surface, and has a first heat transfer. The inside is divided into a first heat medium existing portion 2A and a first crystal existing portion 3A by the surface, and the second crystallizer 1B has a second heat transfer surface, and the second heat transfer surface has the second inside. The heat medium existence part 2B, the second crystal existence part 3B, and the third crystallizer 1C have a third heat transfer surface, and the third heat transfer surface existence part 2C and the second crystal existence part are formed by the third heat transfer surface. It is divided into 3C.

The refrigerator 7 includes a first cooling medium supply port 7a ₁ that communicates with the inlet of the first heating medium presence unit 2A, a first cooling medium return port 7b ₁ that communicates with the outlet of the first heating medium presence unit 2A, second and cold medium supply opening 7a ₂ that communicates with the inlet of the 2 heat medium exists portion 2B, the second and thermal medium return port 7b _2, third heat medium exists portion 2C communicating with the outlet of the second heat medium existing section 2B And a heating medium return port 7d communicating with the outlet of the third heating medium presence portion 2C.

  The buffer tank has a first (1) buffer tank 5A that keeps the temperature of the first cooling medium returned to the refrigerator 7 in a certain range, and a first that keeps the temperature of the second cooling medium returned to the refrigerator 7 in a certain range. (2) It consists of a buffer tank 5B and a second buffer tank 6 that keeps the temperature of the heating medium returned to the refrigerator 7 within a certain range. The flow path connecting the first buffer tanks 5A and 5B, the refrigerator 7 and the crystallizer 1 is the same as that in FIG. 1 showing the crystallization system when crystallization is performed using a cooling medium. The flow path connecting the second buffer tank 6, the refrigerator 7, and the crystallizer 1 is the same as that shown in FIG. 4 showing the crystallization system when melting is performed using a heating medium. In FIG. 9, the flow path for supplying at least a part of the cooling medium returned from the crystallizer to the refrigerator 7 to the lower portions of the first buffer tanks 5A and 5B is omitted, and the heating heat returned to the refrigerator 7 from the crystallizer. A flow path for supplying at least a part of the medium to the upper portion of the second buffer tank 6 is omitted.

  In the embodiment shown in FIG. 9, the inlet of the heat medium existing part 2A of the first crystallizer 1A, the inlet of the heat medium existing part 2B of the second crystallizer 1B, and the heat of the third crystallizer 1C. A flow path 33 communicating with the inlet of the medium existing part 2C, an outlet of the heat medium existing part 2A of the first crystallizer 1A, an outlet of the heat medium existing part 2B of the second crystallizer 1B, and a third crystal It is preferable to provide a flow path 34 that communicates with the outlet of the heat medium existing part 2C of the analyzer 1C. The flow paths 33 and 34 are provided with a flow path for the first cooling / heating medium, a flow path for the second cooling / heating medium, and a flow path for the heating / heating medium, respectively.

  According to the embodiment shown in FIG. 9, the crystal-containing liquid is cooled by the first cooling medium, the first half of the crystallization operation is performed, and the crystal-containing liquid cooled by the second cooling medium is crystallized, The latter half of the conversion operation will be performed. By using the first cooling medium and the second cooling medium in this way, energy saving in the crystallization operation can be achieved. In the first half of the crystallization operation, the liquid to be crystallized may be cooled by the first cooling medium and crystallized.

After the first half of the crystallization operation is finished in the first crystallizer 1A, the second half of the crystallization operation is finished in the second crystallizer 1B, and the melting operation is finished in the third crystallizer 1C, the flow path 33 Thus, the second cooling medium is supplied to the first crystallizer 1A, the heating medium is supplied to the second crystallizer 1B, the first cooling medium is supplied to the third crystallizer 1C, and the flow path 34 is used. The second cooling medium discharged from the first crystallizer 1A is returned to the second cooling medium return port 7b ₂ of the refrigerator 7, and the heating medium discharged from the second crystallizer 1B is heated by the refrigerator 7. The first cooling medium returned to the medium return port 7d and discharged from the third crystallizer 1C is returned to the first cooling medium return port 7b ₁ of the refrigerator 7. As a result, in the first crystallizer 1A, the second half of the crystallization operation is performed, in the second crystallizer 1B, the melting operation is performed, and in the third crystallizer 1C, the first half of the crystallization operation is performed. . Similarly, after the second half of the crystallization operation is completed in the first crystallizer 1A, the melting operation is completed in the second crystallizer 1B, and the first half of the crystallization operation is completed in the third crystallizer 1C. By operating the flow paths 33 and 34, the first crystallizer 1A performs the melting operation, the second crystallizer 1B performs the first half of the crystallization operation, and the third crystallizer 1C performs the crystallization operation. The second half can be done. As described above, if the crystallization system shown in FIG. 9 is used, the crystallization operation and the melting operation can be efficiently performed, and the energy consumption of the refrigerator 7 can be further reduced.

(1) When using a buffer tank Purified acrylic acid was produced from a crude acrylic acid solution using the crystallization system shown in FIG. An absorption refrigerator was used as the heat source machine. From the absorption refrigerator, the first cooling medium at 0 ° C., the second cooling medium at −30 ° C., and the heating medium at 40 ° C. were discharged at a flow rate of 300 m ³ / hour. As the crystallizer, a crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface was used.

  The crude acrylic acid solution contained 94.3% by mass of acrylic acid, 2.3% by mass of water, 2.0% by mass of acetic acid, 0.4% by mass of maleic acid, and 1.0% by mass of other impurities. The crude acrylic acid solution at 30 ° C. was supplied to the crystal existing part of the crystallizer for 20 t, and the first cooling medium at 0 ° C. was supplied to the heat medium existing part of the crystallizer to perform the first half of the crystallization process. At this time, a first (1) buffer tank in which a predetermined amount of the first cooling medium was held was used so that the temperature of the first cooling medium returned to the refrigerator was kept at 5 ° C.

When the temperature of the first cooling medium returned to the refrigerator is measured and the temperature exceeds 5 ° C., a part of the first cooling medium discharged from the crystallizer is stored in the first (1) buffer tank. While supplying the upper portion, the same amount of the first cooling medium was extracted from the lower portion of the first (1) buffer tank. The first cooling medium extracted from the lower part of the first (1) buffer tank was combined with the remaining first cooling medium discharged from the crystallizer and returned to the refrigerator. At this time, the first (1) buffer tank, 150 meters ³ / hour ~300m ³ / first cold medium is supplied when, 0 m ³ / h ~150m ³ / first cold medium is the first time (1 ) Returned to the refrigerator without passing through the buffer tank.

When the temperature of the first cooling medium returned to the refrigerator is below 5 ° C, a part of the first cooling medium at 0 ° C supplied from the refrigerator to the crystallizer is placed below the first (1) buffer tank. And the same amount of the first cooling medium was extracted from the top of the first (1) buffer tank. The first cooling medium extracted from the upper part of the first (1) buffer tank was combined with the first cooling medium discharged from the crystallizer and returned to the refrigerator. At this time, the crystallizer is supplied first cold medium 150 meters ³ / hour ~300m ³ / time, the first (1) buffer tank, 0 m ³ / h ~150m ³ / first cold medium when Was supplied.

  The first half of the crystallization process was performed for 40 minutes, and the freezing function of the refrigerator at this time was 1250 kW.

  Next, the second refrigeration medium at −30 ° C. was supplied to the heat medium existing part of the crystallizer, and the latter half of the crystallization process was performed. At this time, a first (2) buffer tank in which a predetermined amount of the first cooling medium was held was used so that the temperature of the second cooling medium returned to the refrigerator was kept at −25 ° C.

  When the temperature of the second cooling medium returned to the refrigerator is measured and the temperature is higher than −25 ° C. or lower than −25 ° C., the same as in the case of the first cooling medium, 1 (2) A buffer tank was used. The latter half of the crystallization process was performed for 40 minutes, and as a result, acrylic acid crystals were obtained. The refrigeration functional power of the refrigerator in the latter half of the crystallization process was 1250 kW.

  Next, a heating medium at 40 ° C. was supplied to the heat medium existing part of the crystallizer, and a melting step was performed. In the melting process, sweating was also performed. At this time, a second buffer tank in which a predetermined amount of the heating medium was held was used so as to keep the temperature of the heating medium returned to the refrigerator at 35 ° C.

When the temperature of the heating medium returned to the refrigerator is measured and the temperature falls below 35 ° C., a part of the heating medium discharged from the crystallizer is supplied to the lower part of the second buffer tank, and The same amount of heating medium was withdrawn from the top of the two buffer tanks. The heating medium extracted from the upper part of the second buffer tank was combined with the remaining heating medium discharged from the crystallizer and returned to the refrigerator. At this time, the second buffer tank, 150 meters ³ / hour ~300m ³ / when the heat medium is supplied to the 0 m ³ / h ~150m ³ / when the heat medium is refrigerator without passing through the second buffer tank Returned.

When the temperature of the heating medium returned to the refrigerator exceeds 35 ° C, a part of the heating medium of 40 ° C supplied from the refrigerator to the crystallizer is supplied to the upper part of the second buffer tank, and the second The same amount of heating medium was withdrawn from the bottom of the buffer tank. The heating medium extracted from the lower part of the second buffer tank was combined with the heating medium discharged from the crystallizer and returned to the refrigerator. At this time, the crystallizer is supplied with 150 meters ³ / hour ~300m ³ / time of thermal medium, the second buffer tank, 0 m ³ / h ~300m ³ / when the heat medium is supplied.

  The melting step was performed for 40 minutes, and as a result, 15 t of an acrylic acid melt (purified acrylic acid) was obtained. The freezing function power of the refrigerator in the melting step was -2500 kW. Note that the refrigeration functional power represents “amount of heat taken from an object per unit time”, the cooling side capacity is represented by “+”, and the heating side capacity is represented by “−”.

(2) When a buffer tank is used but an operation method different from that of the present invention is implemented The first cooling medium, the second cooling medium, and the heating medium discharged from the crystallizer are temporarily supplied to the corresponding buffer tank Then, the first half and the second half of the crystallization step and the melting step were performed in the same manner as in the example of (1) except that the buffer tank was continuously returned to the refrigerator. In each of the first cooling medium, the second cooling medium, and the heating medium, the temperature of each heating medium returned to the refrigerator fluctuated by about 10 ° C. within one process. As a result, it becomes difficult to operate the refrigerator stably while keeping the temperature of each heating medium supplied from the refrigerator to the crystallizer constant, resulting in unstable crystallization operation and energy consumption. Increased.

(3) When not using a buffer tank Except not using a buffer tank, the first half and the latter half of the crystallization process, and the melting | dissolving process were performed similarly to the Example of said (1). In each of the first cooling medium, the second cooling medium, and the heating medium, the temperature of each heating medium returned to the refrigerator fluctuates by 20 ° C. or more in one process, and each heat supplied from the refrigerator to the crystallizer. The refrigerator could not be operated so as to keep the temperature of the medium constant, and as a result, the crystallization operation became unstable and the energy consumption increased.

  The present invention can be used in a method for producing (meth) acrylic acid having a crystallization step and / or a melting step. Also, the crystallization system of the present invention can be used for crystallization and / or melting.

1, 1A, 1B, 1C: Crystallizer 4, 4A, 4B: Heat source machine 5, 5A, 5B: First buffer tank 6: Second buffer tank 7: Refrigerator

Claims (12)

Supplying a cooling medium from a heat source device to a crystallizer, and crystallizing (meth) acrylic acid from a crude (meth) acrylic acid solution;
Discharging the cooling medium from the crystallizer and returning it to the heat source unit;
A method for producing (meth) acrylic acid, characterized in that the temperature of the cooling medium returned to the heat source unit is maintained within a certain range by the following first or second adjusting means.
First adjusting means: supplying at least a part of the cooling medium returned from the crystallizer to the heat source unit to the upper part of the first buffer tank, discharging the cooling medium from the lower part of the first buffer tank and returning it to the heat source unit. .
Second adjusting means: supplying at least part of the cooling medium supplied from the heat source machine to the crystallizer and / or the cooling medium returned from the crystallizer to the heat source machine to the lower part of the first buffer tank, and The cooling medium is discharged from the upper part of the tank and returned to the heat source machine. Supplying a heating medium from a heat source to the crystallizer and melting the crystallized (meth) acrylic acid;
Discharging the heating medium from the crystallizer and returning it to the heat source machine;
A method for producing (meth) acrylic acid, characterized in that the temperature of the heating medium returned to the heat source unit is maintained within a certain range by the following third or fourth adjusting means.
Third adjusting means: supplying at least a part of the heating medium returned from the crystallizer to the heat source machine to the lower part of the second buffer tank, discharging the heating medium from the upper part of the second buffer tank, and returning it to the heat source machine. .
Fourth adjusting means: supplying at least a part of the heating medium supplied from the heat source machine to the crystallizer and / or the heating medium returned from the crystallizer to the heat source machine to the upper part of the second buffer tank, and The heat medium is discharged from the bottom of the tank and returned to the heat source machine. Supplying a cooling medium from a heat source device to a crystallizer, and crystallizing (meth) acrylic acid from a crude (meth) acrylic acid solution;
Discharging the cooling medium from the crystallizer and returning it to the heat source machine;
Supplying a heating medium from a heat source device to the crystallizer and melting the (meth) acrylic acid;
Discharging the heating medium from the crystallizer and returning it to the heat source machine;
The temperature of the cooling medium returned to the heat source machine is kept within a certain range by the following first or second adjusting means;
A method for producing (meth) acrylic acid, characterized in that the temperature of the heating medium returned to the heat source unit is maintained within a certain range by the following third or fourth adjusting means.
First adjusting means: supplying at least a part of the cooling medium returned from the crystallizer to the heat source unit to the upper part of the first buffer tank, discharging the cooling medium from the lower part of the first buffer tank and returning it to the heat source unit. .
Second adjusting means: supplying at least a part of the cooling medium supplied from the heat source machine to the crystallizer and / or the cooling medium returned from the crystallizer to the heat source machine to the lower part of the first buffer tank, and The cooling medium is discharged from the upper part of the tank and returned to the heat source machine.
Third adjusting means: supplying at least a part of the heating medium returned from the crystallizer to the heat source machine to the lower part of the second buffer tank, discharging the heating medium from the upper part of the second buffer tank, and returning it to the heat source machine. .
Fourth adjusting means: supplying at least a part of the heating medium supplied from the heat source machine to the crystallizer and / or the heating medium returned from the crystallizer to the heat source machine to the upper part of the second buffer tank, and The heat medium is discharged from the bottom of the tank and returned to the heat source machine. Supplying a cooling medium from the heat source unit to the first crystallizer, and crystallizing (meth) acrylic acid from the crude (meth) acrylic acid solution;
Discharging the cooling medium from the first crystallizer and returning it to the heat source machine;
Supplying a heating medium from the heat source device to the second crystallizer and melting the crystallized (meth) acrylic acid;
Discharging the heating medium from the second crystallizer and returning it to the heat source machine;
The heat source machine is a refrigerator;
The temperature of the cooling medium returned to the heat source machine is kept within a certain range by the following first or second adjusting means;
A method for producing (meth) acrylic acid, characterized in that the temperature of the heating medium returned to the heat source unit is maintained within a certain range by the following third or fourth adjusting means.
First adjusting means: supplying at least a part of the cooling medium returned from the first crystallizer to the heat source apparatus to the upper part of the first buffer tank, and discharging the cooling medium from the lower part of the first buffer tank to the heat source apparatus. Return it.
Second adjusting means: supplying at least a part of the cooling medium supplied from the heat source machine to the first crystallizer and / or the cooling medium returned from the first crystallizer to the heat source machine to the lower part of the first buffer tank, The cooling medium is discharged from the upper part of the first buffer tank and returned to the heat source machine.
Third adjusting means: supplying at least part of the heating medium returned from the second crystallizer to the heat source machine to the lower part of the second buffer tank, and discharging the heating medium from the upper part of the second buffer tank to the heat source machine. Return it.
Fourth adjusting means: supplying at least a part of the heating medium supplied from the heat source machine to the second crystallizer and / or the heating medium returned from the second crystallizer to the heat source machine, to the upper part of the second buffer tank, The heating medium is discharged from the lower part of the second buffer tank and returned to the heat source machine. A predetermined amount of cooling medium is held in the first buffer tank,
A predetermined amount of heating medium is held in the second buffer tank,
5. The (meta-meta) according to claim 1, wherein the cooling medium held in the first buffer tank and the heating medium held in the second buffer tank have a temperature gradient in which the upper part is a high temperature and the lower part is a low temperature. ) A method for producing acrylic acid. In accordance with the upper and lower temperatures of the cooling medium held in the first buffer tank, the temperature of the cooling medium returned to the heat source machine is adjusted,
The method for producing (meth) acrylic acid according to claim 5, wherein the temperature of the heating medium returned to the heat source unit is adjusted according to the temperature above and below the heating medium held in the second buffer tank. The first buffer tank is provided with openings through which the cooling medium enters and exits at the top and bottom, and the length between the opening at the top and the opening at the bottom is 1 of the maximum cross-sectional length of the first buffer tank. More than double;
The second buffer tank is provided with openings through which the heating medium enters and exits at the upper part and the lower part, and the length between the upper opening and the lower opening is 1 of the maximum cross-sectional length of the second buffer tank. It is more than twice, The manufacturing method of the (meth) acrylic acid as described in any one of Claims 1-6. A crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface;
A heat source machine having a cooling medium supply port communicating with the inlet of the heating medium existence part and a cooling medium return port communicating with the outlet of the heating medium existence part;
An upper opening communicated with the outlet of the heat medium existing part and the cooling medium return port, and a lower opening communicated with the cooling medium supply port and / or the outlet of the heat medium existing part and the cooling medium return port. And a first buffer tank. A crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface;
A heat source device having a heating medium supply port communicating with the inlet of the heating medium presence portion and a heating medium return port communicating with the outlet of the heating medium presence portion;
An upper opening communicating with the heating medium supply port and / or an outlet of the heating medium existing portion and the heating medium return port; and a lower opening communicating with the outlet of the heating medium existing portion and the heating medium return port. And a second buffer tank. A crystallizer having a heat transfer surface and divided into a heat medium existing part and a crystal existing part by the heat transfer surface;
A first heat source machine having a cooling medium supply port communicating with an inlet of the heating medium existence unit and a cooling medium return port communicating with an outlet of the heating medium existence unit;
A second heat source machine having a heating medium supply port communicating with the inlet of the heating medium presence portion and a heating medium return port communicating with the outlet of the heating medium presence portion;
An upper opening communicated with the outlet of the heat medium existing part and the cooling medium return port, and a lower opening communicated with the cooling medium supply port and / or the outlet of the heat medium existing part and the cooling medium return port. A first buffer tank having;
An upper opening communicating with the heating medium supply port and / or an outlet of the heating medium existing portion and the heating medium return port; and a lower opening communicating with the outlet of the heating medium existing portion and the heating medium return port. And a second buffer tank. A first crystallizer having a first heat transfer surface, the inside of which is divided into a first heat medium existing portion and a first crystal existing portion by the first heat transfer surface;
A second crystallizer having a second heat transfer surface, the inside of which is divided into a second heat medium existing portion and a second crystal existing portion by the second heat transfer surface;
A cooling medium supply port that communicates with the inlet of the first heating medium presence part, a cooling medium return port that communicates with the outlet of the first heating medium existence part, and a heating medium that communicates with the inlet of the second heating medium existence part A refrigerator having a supply port and a heating medium return port communicating with the outlet of the second heat medium presence part;
The upper opening communicated with the outlet of the first heat medium existing portion and the cooling medium return port, and the outlet of the cooling medium supply port and / or the outlet of the first heat medium existing portion and the cooling medium return port. A first buffer tank having a lower opening;
An upper opening communicated with the second heating medium supply port and / or an outlet of the heating medium presence portion and the heating medium return port, and an outlet of the second heating medium existence portion and the heating medium return port And a second buffer tank having a lower opening.   12. The length of the first buffer tank and the second buffer tank between the upper opening and the lower opening is one time or more of a maximum cross-sectional length. 12. Crystallization system.

Images