Method for inhibiting unwanted radical polymerisation 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 furfural in an amount that results in a furfural content in the range from 25 to 1000 ppmw based on the weight of the acrylic acid present in P. 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 25 to 1000 ppmw of furfural in each case based on the weight of the acrylic acid present in P.

Claims

1. A process for inhibiting the undesired free-radical polymerization of acrylic acid present in a liquid phase P, comprising providing 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, admixing the liquid phase P with furfural in an amount that results in a furfural content in the range from 25 to 1000 ppmw based on the weight of the acrylic acid present in P, and inhibiting the free-radical polymerization of acrylic acid present in a liquid phase P.

2. The process according to claim 1, wherein the acrylic acid content of P is at least 30% by weight.

3. The process according to claim 1, wherein the acrylic acid content of P is at least 50% by weight.

4. The process according to claim 1, wherein the liquid phase P comprises in the range from 50 to 500 ppmw of glyoxal based on the weight of the acrylic acid present in P and the liquid phase P is admixed with furfural in an amount that results in a furfural content in the range from 50 to 500 ppmw based on the weight of the acrylic acid present in P.

5. The process according to claim 1, wherein the liquid phase P comprises in the range from 50 to 1000 ppmw of phenothiazine based on the weight of the acrylic acid present in P.

6. The process according to claim 1, wherein the liquid phase P comprises in the range from 50 to 1000 ppmw of methylhydroquinone based on the weight of the acrylic acid present in P.

7. The process according to claim 1, wherein said process is performed in the absence of oxygen.

8. The process according to claim 1, wherein the liquid phase P has a temperature in the range from 50° C. to 150° C.

9. The process according to claim 1, wherein said process is performed in a column for distillative recovery of acrylic acid.

10. The process according to claim 1, 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.

11. The process according to claim 1, 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 up to 80% by volume of n-propane.

12. The process according to claim 11, wherein the C.sub.3-precursor compound is propylene, acrolein or n-propane.

Description

INVENTIVE AND COMPARATIVE EXAMPLES

Experimental Procedure

(1) Preheat oil bath to 103° C.

(2) 100.0 g of acrylic acid (with appropriate additives) are filled into a 250 ml glass bottle (tared) (magnetic stirrer).

(3) N2 is passed through the acrylic acid for 30 min (about 70 I/h).

(4) After 30 min the N2 stream is only passed over the acrylic acid and reduced to 14-18 I/h.

(5) Subsequently immerse the bottle in the preheated oil bath to the fill height (internal temperature 100° C.)

(6) Stir at 100° C. for 2 h. Then lower the oil bath.

(7) After achieving an internal temperature of 50° C. the remaining acrylic acid is decanted off. Amount of polymerized acrylic acid in % by weight based on initial weight.

EXAMPLES

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

(9) TABLE-US-00001 Furfural content Glyoxal Polymer [ppm] [ppm] [%] Example 1 200 ppm MeHQ 0 0 2.9 Example 2 200 ppm MeHQ 500 0 4.4 Example 3 200 ppm MeHQ 0 50 35.7 Example 4 200 ppm MeHQ 50 50 11.1 Example 5 200 ppm MeHQ 100 50 7.3 Example 6 200 ppm MeHQ 200 50 8.2 Example 7 200 ppm MeHQ 500 50 6.5 Example 8 200 ppm MeHQ 0 100 68.1 Example 9 200 ppm MeHQ 50 100 41.4 Example 10 200 ppm MeHQ 100 100 31.4 Example 11 200 ppm MeHQ 200 100 20.5 Example 12 200 ppm MeHQ 300 100 24.8 Example 13 200 ppm MeHQ 400 100 13.0 Example 14 200 ppm MeHQ 500 100 7.4 Example 15 200 ppm MeHQ 0 175 60.7 Example 16 200 ppm MeHQ 50 175 36.7 Example 17 200 ppm MeHQ 100 175 24.3 Example 18 200 ppm MeHQ 200 175 15.9 Example 19 200 ppm MeHQ 500 175 7.9 Example 20 200 ppm MeHQ 0 250 88.1 Example 21 200 ppm MeHQ 50 250 43.8 Example 22 200 ppm MeHQ 100 250 21.4 Example 23 200 ppm MeHQ 200 250 14.1 Example 24 200 ppm MeHQ 500 250 9.8 Example 25 200 ppm MeHQ 0 500 100.0 Example 26 200 ppm MeHQ 50 500 52.6 Example 27 200 ppm MeHQ 100 500 35.6 Example 28 200 ppm MeHQ 200 500 19.9 Example 29 200 ppm MeHQ 500 500 9.0 Example 30 250 ppm PTZ 250 94 41.0 Example 31 250 ppm PTZ 850 94 15.0 ppm values are in ppmw % values are in % by wt.