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A process for producing (meth)acrylic acid, comprising a crystallizing step of supplying a cooling medium from a refrigerator to a crystallizer and returning the cooling medium from the crystallizer to the refrigerator, thereby obtaining a (meth)acrylic acid crystal from a (meth)acrylic acid-contain

A process for producing (meth)acrylic acid, comprising a crystallizing step of supplying a cooling medium from a refrigerator to a crystallizer and returning the cooling medium from the crystallizer to the refrigerator, thereby obtaining a (meth)acrylic acid crystal from a (meth)acrylic acid-containing solution; and a melting step of supplying a heating medium from a refrigerator to the crystallizer and returning the heating medium from the crystallizer to the refrigerator, thereby melting the (meth)acrylic acid crystal; wherein the crystallizing step and the melting step are respectively performed at least once, thereby producing purified (meth)acrylic acid from a crude (meth)acrylic acid solution; temperature of the cooling medium discharged from the refrigerator is maintained constant at temperature T1; temperature of the cooling medium to be returned to the refrigerator is maintained constant at temperature T2; the temperature T2 is adjusted depending on a production amount of the purified (meth)acrylic acid per unit time.

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1. A process for producing (meth)acrylic acid, comprising: a crystallizing step of supplying a cooling medium from a refrigerator to a crystallizer and returning the cooling medium from the crystallizer to the refrigerator, thereby obtaining a (meth)acrylic acid crystal from a (meth)acrylic acid-con

1. A process for producing (meth)acrylic acid, comprising: a crystallizing step of supplying a cooling medium from a refrigerator to a crystallizer and returning the cooling medium from the crystallizer to the refrigerator, thereby obtaining a (meth)acrylic acid crystal from a (meth)acrylic acid-containing solution; anda melting step of supplying a heating medium from a refrigerator to the crystallizer and returning the heating medium from the crystallizer to the refrigerator, thereby melting the (meth)acrylic acid crystal;wherein:the crystallizing step and the melting step are respectively performed at least once, thereby producing purified (meth)acrylic acid from a crude (meth)acrylic acid solution;temperature of the cooling medium discharged from the refrigerator is maintained constant at temperature T1;temperature of the cooling medium to be returned to the refrigerator is maintained constant at temperature T2 in the crystallizing step by a first adjustment operation and/or a second adjustment operation;the temperature T2 is adjusted depending on a production amount of the purified (meth)acrylic acid per unit time;the first adjustment operation is performed by feeding at least a part of the cooling medium to be returned to the refrigerator from the crystallizer into an upper part of a first buffer tank and discharging the cooling medium from a lower part of the first buffer tank to return to the refrigerator; andthe second adjustment operation is performed by feeding at least a part of the cooling medium to be supplied to the crystallizer from the refrigerator and/or the cooling medium to be returned to the refrigerator from the crystallizer into the lower part of the first buffer tank and discharging the cooling medium from the upper part of the first buffer tank to return to the refrigerator. 2. A process for producing (meth)acrylic acid, comprising: a crystallizing step of supplying a cooling medium from a refrigerator to a crystallizer and returning the cooling medium from the crystallizer to the refrigerator, thereby obtaining a (meth)acrylic acid crystal from a (meth)acrylic acid-containing solution; anda melting step of supplying a heating medium from a refrigerator to the crystallizer and returning the heating medium from the crystallizer to the refrigerator, thereby melting the (meth)acrylic acid crystal;wherein:the crystallizing step and the melting step are respectively performed at least once, thereby producing purified (meth)acrylic acid from a crude (meth)acrylic acid solution;temperature of the heating medium discharged from the refrigerator is maintained constant at temperature T3;temperature of the heating medium to be returned to the refrigerator is maintained constant at temperature T4 in the melting step by a third adjustment operation and/or a fourth adjustment operation;the temperature T4 is adjusted depending on a production amount of the purified (meth)acrylic acid per unit time;the third adjustment operation is performed by feeding at least a part of the heating medium to be returned to the refrigerator from the crystallizer into an lower part of a second buffer tank and discharging the heating medium from an upper part of the second buffer tank to return to the refrigerator; andthe fourth adjustment operation is performed by feeding at least a part of the heating medium to be supplied to the crystallizer from the refrigerator and/or the heating medium to be returned to the refrigerator from the crystallizer into the upper part of the second buffer tank and discharging the heating medium from the lower part of the second buffer tank to return to the refrigerator. 3. A process for producing (meth)acrylic acid, comprising: a crystallizing step of supplying a cooling medium from a refrigerator to a crystallizer and returning the cooling medium from the crystallizer to the refrigerator, thereby obtaining a (meth)acrylic acid crystal from a (meth)acrylic acid-containing solution; anda melting step of supplying a heating medium from a refrigerator to the crystallizer and returning the heating medium from the crystallizer to the refrigerator, thereby melting the (meth)acrylic acid crystal;wherein:the crystallizing step and the melting step are respectively performed at least once, thereby producing purified (meth)acrylic acid from a crude (meth)acrylic acid solution;temperature of the cooling medium discharged from the refrigerator is maintained constant at temperature T1;temperature of the cooling medium to be returned to the refrigerator is maintained constant at temperature T2 in the crystallizing step by a first adjustment operation and/or a second adjustment operation;temperature of the heating medium discharged from the refrigerator is maintained constant at temperature T3;temperature of the heating medium to be returned to the refrigerator is maintained constant at temperature T4 in the melting step by a third adjustment operation and/or a fourth adjustment operation;the temperatures T2 and T4 are adjusted depending on a production amount of the purified (meth)acrylic acid per unit time;the first adjustment operation is performed by feeding at least a part of the cooling medium to be returned to the refrigerator from the crystallizer into an upper part of a first buffer tank and discharging the cooling medium from a lower part of the first buffer tank to return to the refrigerator;the second adjustment operation is performed by feeding at least a part of the cooling medium to be supplied to the crystallizer from the refrigerator and/or the cooling medium to be returned to the refrigerator from the crystallizer into the lower part of the first buffer tank and discharging the cooling medium from the upper part of the first buffer tank to return to the refrigerator;the third adjustment operation is performed by feeding at least a part of the heating medium to be returned to the refrigerator from the crystallizer into an lower part of a second buffer tank and discharging the heating medium from an upper part of the second buffer tank to return to the refrigerator; andthe fourth adjustment operation is performed by feeding at least a part of the heating medium to be supplied to the crystallizer from the refrigerator and/or the heating medium to be returned to the refrigerator from the crystallizer into the upper part of the second buffer tank and discharging the heating medium from the lower part of the second buffer tank to return to the refrigerator. 4. The process for producing (meth)acrylic acid according to claim 3, wherein the temperatures T1 and T3 are fixed irrespective of the production amount of the purified (meth)acrylic acid per unit time. 5. The process for producing (meth)acrylic acid according to claim 3, wherein the temperature T2 is adjusted to be lower and the temperature T4 is adjusted to be higher when the production amount of the purified (meth)acrylic acid per unit time is decreased. 6. The process for producing (meth)acrylic acid according to claim 3, wherein a product amount of the purified (meth)acrylic acid obtained by performing the crystallizing step and the melting step at least once, respectively, is kept constant, andthe temperatures T2 and T4 are adjusted depending on a period for producing the purified (meth)acrylic acid. 7. The process for producing (meth)acrylic acid according to claim 3, further comprising the steps of: dehydrating glycerin or 2-methylglycerin to convert to (meth)acrolein; andoxidizing the (meth)acrolein to convert to (meth)acrylic acid, thereby obtaining the crude (meth)acrylic acid solution. 8. The process for producing (meth)acrylic acid according to claim 3, further comprising the step of: dehydrating hydroxypropionic acid or 2-methyl-3-hydroxypropionic acid to convert to (meth)acrylic acid, thereby obtaining the crude (meth)acrylic acid solution. 9. A process for producing a hydrophilic resin, comprising the step of: polymerizing a monomeric component(s) including the (meth)acrylic acid obtained by the producing process according to claim 3. 10. A process for producing an absorbent resin, comprising the step of: polymerizing a monomeric component(s) including the (meth)acrylic acid obtained by the producing process according to claim 3. 11. The process for producing (meth)acrylic acid according to claim 1, wherein the temperature T1 is fixed irrespective of the production amount of the purified (meth)acrylic acid per unit time. 12. The process for producing (meth)acrylic acid according to claim 1, wherein the temperature T2 is adjusted to be lower when the production amount of the purified (meth)acrylic acid per unit time is decreased. 13. The process for producing (meth)acrylic acid according to claim 1, wherein a product amount of the purified (meth)acrylic acid obtained by performing the crystallizing step and the melting step at least once, respectively, is kept constant, andthe temperature T2 is adjusted depending on a period for producing the purified (meth)acrylic acid. 14. The process for producing (meth)acrylic acid according to claim 2, wherein the temperature T3 is fixed irrespective of the production amount of the purified (meth)acrylic acid per unit time. 15. The process for producing (meth)acrylic acid according to claim 2, wherein the temperature T4 is adjusted to be higher when the production amount of the purified (meth)acrylic acid per unit time is decreased. 16. The process for producing (meth)acrylic acid according to claim 2, wherein a product amount of the purified (meth)acrylic acid obtained by performing the crystallizing step and the melting step at least once, respectively, is kept constant, andthe temperature T4 is adjusted depending on a period for producing the purified (meth)acrylic acid. 17. The process for producing (meth)acrylic acid according to claim 1, further comprising the steps of: dehydrating glycerin or 2-methylglycerin to convert to (meth)acrolein; andoxidizing the (meth)acrolein to convert to (meth)acrylic acid, thereby obtaining the crude (meth)acrylic acid solution. 18. The process for producing (meth)acrylic acid according to claim 1, further comprising the step of: dehydrating hydroxypropionic acid or 2-methyl-3-hydroxypropionic acid to convert to (meth)acrylic acid, thereby obtaining the crude (meth)acrylic acid solution. 19. A process for producing a hydrophilic resin, comprising the step of: polymerizing a monomeric component(s) including the (meth)acrylic acid obtained by the producing process according to claim 1. 20. A process for producing an absorbent resin, comprising the step of: polymerizing a monomeric component(s) including the (meth)acrylic acid obtained by the producing process according to claim 1.