PROCESS FOR INHIBITING THE UNDESIRED FREE-RADICAL POLYMERIZATION OF ACRYLIC ACID PRESENT IN A LIQUID PHASE P

Abstract

Process for inhibiting the undesired free-radical polymerization of acrylic acid present in a liquid phase P, wherein the acrylic acid content of P is at least 10% by weight, the liquid phase P comprises in the range from 25 to 1000 ppmw of glyoxal based on the weight of the acrylic acid present in P and the liquid phase P is admixed with protoanemonine in an amount that results in a protoanemonine content in the range from 0.5 to 100 ppmw based on the weight of the acrylic acid present in P, and a liquid phase P, wherein the acrylic acid content of P is at least 10% by weight and the liquid phase P comprises in the range from 25 to 1000 ppmw of glyoxal and in the range from 0.5 to 100 ppmw of protoanemonine, in each case based on the weight of the acrylic acid present in P.

Claims

1.-15. (canceled)

16. A process for inhibiting the undesired free-radical polymerization of acrylic acid present in a liquid phase P, wherein the acrylic acid content of the liquid phase P is at least 10% by weight, the liquid phase P comprises in the range from 25 to 1000 ppmw of glyoxal and the liquid phase P is admixed with protoanemonine in an amount that results in a protoanemonine content in the range from 0.5 to 100 ppmw, in each case based on the weight of the acrylic acid present in P.

17. The process according to claim 16, wherein the acrylic acid content of the liquid phase P is at least 30% by weight or at least 50% by weight.

18. The process according to claim 16, wherein the liquid phase P comprises at least 100 ppmw of propionic acid based on the weight of the acrylic acid present in P.

19. The process according to claim 16, wherein the liquid phase P comprises in the range from 50 to 500 ppmw of glyoxal and/or in the range from 1 to 50 ppmw of protoanemonine, in each case based on the weight of the acrylic acid present in P.

20. The process according to claim 16, wherein the liquid phase P comprises in the range from 50 to 1000 ppmw of phenothiazine and/or methylhydroquinone, in each case based on the weight of the acrylic acid present in P.

21. The process according to claim 16, wherein the liquid phase P has a temperature in the range from 50° C. to 150° C.

22. The process according to claim 16, wherein said process is performed in a column for distillative purification of acrylic acid.

23. The process according to claim 16, wherein the acrylic acid present in the liquid phase P is the product of a heterogeneously catalyzed partial oxidation of a C.sub.3-precursor compound of acrylic acid, wherein the starting mixture comprising the C.sub.3-precursor compound used for the partial oxidation comprises, based on the molar amount of the C.sub.3-precursor compound present therein, a molar total amount of C.sub.2-compounds in the range from 100 to 10 000 molar ppm.

24. A liquid phase P, wherein the acrylic acid content of the liquid phase P is at least 10% by weight and the liquid phase P comprises in the range from 25 to 1000 ppmw of glyoxal and in the range from 0.5 to 100 ppmw of protoanemonine, in each case based on the weight of the acrylic acid present in P.

25. The liquid phase P according to claim 24, wherein the acrylic acid content of the liquid phase P is at least 30% by weight or at least 50% by weight.

26. The liquid phase P according to claim 24, wherein the liquid phase P comprises at least 100 ppmw of propionic acid based on the weight of the acrylic acid present in P.

27. The liquid phase P according to claim 24, wherein the liquid phase P comprises in the range from 50 to 500 ppmw of glyoxal and/or in the range from 1 to 50 ppmw of protoanemonine, in each case based on the weight of the acrylic acid present in P.

28. The liquid phase P according to claim 24, wherein the liquid phase P comprises in the range from 50 to 1000 ppmw of phenothiazine and/or methylhydroquinone, in each case based on the weight of the acrylic acid present in P.

29. The liquid phase P according to claim 24, wherein said phase has a temperature in the range from 50° C. to 150° C.

30. The liquid phase P according to claim 24 wherein said phase is located in a column for distillative purification of acrylic acid.

Description

INVENTIVE AND COMPARATIVE EXAMPLES

General Experimental Procedure

[0131] 100.0 g of acrylic acid (with appropriate additives) are filled into a 250 ml glass bottle (magnetic stirrer bar). Nitrogen is then passed through for 30 minutes (about 70 l/h). The amount of nitrogen is then reduced (14-18 l/h) and only passed over the acrylic acid. The glass bottle is subsequently immersed in an oil bath preheated to 103° C. up to the fill height of the glass bottle (internal temperature 100° C.). Stirring is carried out at 100° C. (internal temperature) for 2 hours. The oil bath is then lowered. After achieving an internal temperature of 50° C. the remaining acrylic acid is decanted off.

[0132] The amount of polymerized acrylic acid is calculated based on initial weight.

EXAMPLES

[0133] The following examples with acrylic acid (purity >98% by weight) were carried out analogously with the above-described experimental procedure using different amounts of protoanemonine/anemonine and glyoxal. Each experiment was repeated 2 to 6 times and the average values obtained are reported.

TABLE-US-00001 TABLE 1 Addition of protoanemonine and 200 ppm of hydroquinone monomethyl ether (MEHQ) Glyoxal Protoanemonine Polymer Example [ppmw] [ppm] [% by weight] 1 0 0 2.9 2 500 0 100 3 500 6 24.7 4 500 12 7.3 5 500 30 3.0 6 500 500 1.0

TABLE-US-00002 TABLE 2 Addition of protoanemonine and 200 ppm of phenothiazine (PTZ) Glyoxal Protoanemonine Polymer Example [ppmw] [ppm] [% by weight] 7 500 0 24.4 8 500 50 7.5

TABLE-US-00003 TABLE 3 Addition of anemonine and 200 ppm of hydroquinone monomethyl ether (MEHQ) Glyoxal Anemonine Polymer Example [ppmw] [ppm] [% by weight] 1 0 0 2.9 2 500 0 100 9 500 2 47.2 10 500 10 13.6 11 500 25 5.2 12 500 50 3.8 13 500 500 1.0 14 250 0 100 15 250 5 22.8 16 250 25 3.8 17 100 0 35.5 18 100 5 15.7 19 100 25 3.0