METHOD FOR BREAKING DOWN MICHAEL ADDUCTS CONTAINED IN A FLUID F AND FORMED DURING THE PREPARATION OF ACRYLIC ACID

Abstract

The present invention relates to a method of redissociating Michael adducts of acrylic acid present in a liquid F in a redissociation apparatus comprising at least one separating column K, an evaporator V and a pump P, wherein, in the event of an unwanted rise in the viscosity of the residue R in the bottom space of the separating column K, the feed of the liquid F into the redissociation apparatus is stopped, the residue R in the bottom space of the separating column K is diluted and cooled with a solvent 1, and the bottom space of the separating column K is emptied.

Claims

1.-15. (canceled)

16. A method of redissociating Michael adducts of acrylic acid that are present in a liquid F and have been formed in the preparation of acrylic acid, in which the liquid F comprises at least 10% by weight of Michael adducts of acrylic acid, based on the liquid F, in a redissociation apparatus comprising at least one separating column K which consists, from the bottom upward, of a bottom space, a separating space that comprises separating internals and adjoins the bottom space, and a top space adjoining the latter, and in which the pressure in the gas phase decreases from the bottom upward, an evaporator V and a pump P, in which Michael adducts present in the liquid F are split at a temperature of 130° C. to 240° C. and removed by distillation, and the remaining residue R is discharged, which comprises, in the event of an unwanted rise in the viscosity of the residue R in the bottom space of the separating column K, stopping the feed of the liquid F into the redissociation apparatus, diluting and cooling the residue R in the bottom space of the separating column K with at least 10% by volume of a solvent 1, based on the total volume of the residue R in the bottom space of the separating column K, and emptying the bottom space of the separating column K, where the solvent 1 has a boiling point at 1013 hPa of at least 150° C. and a solubility in water at 25° C. of at least 10 g per 100 g of water.

17. The method according to claim 16, wherein the liquid F comprises at least 40% by weight of Michael adducts of acrylic acid, based on the liquid F.

18. The method according to claim 16, wherein the Michael adducts present in the liquid F are split at a temperature of 155 to 180° C.

19. The method according to claim 16, wherein the solvent 1 has a boiling point at 1013 hPa of at least 210° C.

20. The method according to claim 16, wherein the solvent 1 has a solubility in water at 25° C. of at least 40 g per 100 g of water.

21. The method according to claim 16, wherein the solvent 1 is an alcohol, a carboxamide, a sulfoxide and/or a sulfone.

22. The method according to claim 16, wherein the solvent 1 is selected from ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, 2-ethoxyethanol, sulfolane, N,N-dimethylacetamide, N-methylacetamide, dimethyl sulfoxide and/or N,N-dimethylformamide.

23. The method according to claim 16, wherein the solvent 1 is a residue from the oxo process.

24. The method according to claim 16, wherein the residue R in the bottom space of the separating column K is diluted with at least 40% by volume of solvent 1, based on the total volume of the residue R in the bottom space of the separating column K.

25. The method according to claim 16, wherein the viscosity of the residue R in the bottom space of the separating column K at a temperature of 100° C. is less than 12 Pa s.

26. The method according to claim 16, wherein a stripping gas is guided into the splitting apparatus above the bottoms liquid and below the lowermost separating internals of the separating column K.

27. The method according to claim 26, wherein, in the event of an unwanted rise in the viscosity of the residue R in the bottom space of the separating column K, the feed of stripping gas into the splitting apparatus is stopped.

28. The method according to claim 16, wherein the discharged residue R is diluted with a solvent 2.

29. The method according to claim 28, wherein the solvent 2 is a residue from methanol production.

30. A diluted residue R obtained by the method of claim 16.

Description

EXAMPLES

[0083] For examples 1 and 2, a residue R produced in the separating column K according to the example of WO 2010/066601 was used.

Example 1

[0084] 500 g of residue R was heated to 170° C. in a 1 I round-bottom flask and stirred. After 6 hours, the mixture was diluted with 500 g of ethylene glycol and cooled down while stirring.

[0085] Samples were taken during the experiment, and the viscosity was measured at 100° C.

TABLE-US-00001 TABLE 1 Dilution with ethylene glycol Time [h] Viscosity [Pa s] 0 1.12 2 2.43 4 5.22 6 6.86 7 0.04

Example 2

[0086] 500 g of residue R was heated to 170° C. in a 1 I round-bottom flask and stirred. After 6 hours, the mixture was diluted with 500 g of propylene glycol and cooled down while stirring.

[0087] Samples were taken during the experiment, and the viscosity was measured at 100° C.

TABLE-US-00002 TABLE 2 Dilution with propylene glycol Time [h] Viscosity [Pa s] 0 3.46 6 16.3 7 0.04

Example 3

[0088] The product gas mixture from a two-stage heterogeneously catalyzed partial gas phase oxidation of (chemical grade) propylene to acrylic acid, which was conducted as described in the illustrative execution of WO 2008/090190, was subjected to a fractional condensation as in the illustrative execution of WO 2008/090190 in order to separate the acrylic acid present in the product gas mixture from the partial oxidation therefrom.

[0089] As described in the illustrative execution of WO 2008/090190, high-boiling liquid was removed from the bottom region of the condensation column and was fed to a redissociation apparatus as in the illustrative execution of WO 2010/066601.

[0090] The temperature in the bottom space of the separating column K was 168° C. The amount of residue R in the bottom space of the separating column K was about 25 m.sup.3. After 4 days, the viscosity at 120° C. rose from fluid to very viscous.

[0091] The feed of high-boiling liquid and stripping gas to the separating column K is stopped. The reflux to the separating column K is likewise stopped. Subsequently, the residue R in the bottom space of the separating column K is diluted with about 20 m.sup.3 of ethylene glycol. The diluted residue R is discharged and incinerated.