Method for the agglomeration of superabsorber particles

Abstract

A process for agglomerating superabsorbent particles, wherein polymer particles having a particle size of 250 m or less are dispersed in a hydrophobic organic solvent, the dispersed polymer particles are mixed with an aqueous monomer solution, the total amount of water applied to the dispersed polymer particles being at least 100% by weight, based on the dispersed polymer particles, and the monomer solution is polymerized.

Claims

1. A process for agglomerating superabsorbent particles comprising (A) polymerizing a first aqueous monomer solution comprising a) at least one ethylenically unsaturated monomer which bears an acid group and optionally at least partly neutralized, b) optionally one or more crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a), and e) optionally one or more water-soluble polymer to provide polymer particles, optionally drying and/or comminuting the polymer particles, removing polymer particles having a particle size of 250 m or less, dispersing the polymer particles having a particle size of 250 m or less in a hydrophobic organic solvent, mixing the dispersed polymer particles with a second aqueous monomer solution comprising a) at least one ethylenically unsaturated monomer which bears an acid group and optionally at least partly neutralized, b) optionally one or more crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a), and e) optionally one or more water-soluble polymer, wherein the first aqueous monomer solution and the second aqueous monomer solution may be the same or different and a total amount of water applied to the dispersed polymer particles with the second aqueous monomer solution being at least 100% by weight, based on the dispersed polymer particles, and polymerizing the second aqueous monomer solution to provide agglomerated particle superabsorbent.

2. The process according to claim 1, wherein polymer particles having a particle size of 200 m or less are removed and dispersed in the hydrophobic organic solvent.

3. The process according to claim 1, wherein polymer particles having a particle size of 150 m or less are removed and dispersed in the hydrophobic organic solvent.

4. The process according to claim 1, wherein the amount of water applied with the second monomer solution is at least 150% by weight, based on the dispersed polymer particles.

5. The process according to claim 1, wherein the amount of water applied with the second monomer solution is at least 175% by weight, based on the dispersed polymer particles.

6. The process according to claim 1, wherein the second monomer solution comprises from 0.01 to 0.50 mmol of crosslinker b), based on 1 mol of monomer a).

7. The process according to claim 1, wherein the second monomer solution comprises from 0.02 to 0.25 mmol of crosslinker b), based on 1 mol of monomer a).

8. The process according to claim 1, wherein the second monomer solution comprises from 0.05 to 0.15 mmol of crosslinker b), based on 1 mol of monomer a).

9. The process according to claim 1, wherein the first monomer solution is polymerized by dropletizing polymerization.

10. The process according to claim 9, wherein the polymer particles are removed from an offgas of the dropletizing polymerization by means of a filter or cyclone.

11. The process according to claim 1, wherein the first monomer solution is polymerized by suspension polymerization and the resulting polymer particles are dried.

12. The process according to claim 1, wherein the first monomer solution is polymerized by solution polymerization and the resulting polymer particles are dried and comminuted.

13. The process according to claim 11, wherein the polymer particles are removed by means of a sieve having a mesh size of 250 m or less.

14. The process according to claim 11, wherein the polymer particles are removed by means of a sieve having a mesh size of 200 m or less.

15. The process according to claim 11, wherein the polymer particles are removed by means of a sieve having a mesh size of 150 m or less.

16. The process according to claim 12, wherein the polymer particles are removed by means of a sieve having a mesh size of 250 m or less.

17. The process according to claim 12, wherein the polymer particles are removed by means of a sieve having a mesh size of 200 m or less.

18. The process according to claim 12, wherein the polymer particles are removed by means of a sieve having a mesh size of 150 m or less.

19. A process for agglomerating superabsorbent particles comprising: (a) providing superabsorbent particles having a particle size of 250 m or less; (b) dispersing superabsorbent particles in a hydrophobic organic solvent; (c) mixing the dispersed superabsorbent particles with an aqueous monomer solution comprising: i) at least one ethylenically unsaturated monomer which bears an acid group and optionally at least partly neutralized, ii) optionally one or more crosslinker, iii) at least one initiator, iv) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under i), and v) optionally one or more water-soluble polymer, wherein a total amount of water applied to the dispersed superabsorbent particles with the aqueous monomer solution being at least 100% by weight, based on the dispersed polymer superabsorbent particles, and polymerizing the second monomer solution to provide agglomerated superabsorbent particles.

20. The process of claim 19 comprising providing superabsorbent particles having a particle size of 200 m or less.

Description

EXAMPLE 1

(1) A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 896.00 g of cyclohexane and 6.00 g of ethyl cellulose, and this initial charge was heated to 75 C. while stirring under nitrogen.

(2) A monomer solution 1 prepared from 150.00 g (2.082 mol) of acrylic acid, 129.00 g (1.613 mol) of 50% by weight aqueous sodium hydroxide solution, 136.80 g of water, 0.0375 g (0.243 mmol) of N,N-methylenebisacrylamide (MBA) and 0.50 g (1.850 mmol) of potassium peroxodisulfate was subsequently introduced into a feed vessel and purged with air. Monomer solution 1 was added dropwise at a stirrer speed of 450 rpm within 60 minutes. Monomer solution 1 was inertized with nitrogen immediately prior to the dropwise addition.

(3) After feeding had ended, the mixture was stirred at 75 C. for a further 60 minutes. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

(4) The suspension present was cooled to 60 C. and the resultant polymer particles were filtered off with suction using a Bchner funnel with a paper filter. The further drying was effected at 45 C. in an air circulation drying cabinet and optionally in a vacuum drying cabinet at 800 mbar down to a residual moisture content of less than 15% by weight.

(5) The resultant polymer particles had a centrifuge retention capacity (CRC) of 40.9 g/g, a free swell rate (FSR) of 0.09 g/gs, and a moisture content of 2.9% by weight.

EXAMPLE 2

(6) A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 500.00 g of cyclohexane, 1.88 g of Span 20 (sorbitan monostearate) and 60.00 g of superabsorbent particles from example 1, and this initial charge was heated to 70 C. while stirring under nitrogen.

(7) A monomer solution 2 prepared from 50.00 g (0.694 mol) of acrylic acid, 43.00 g (0.538 mol) of 50% by weight aqueous sodium hydroxide solution, 45.60 g of water, 0.0125 g (0.081 mmol) of N,N-methylenebisacrylamide (MBA) and 0.167 g (0.618 mmol) of potassium peroxodisulfate was introduced into a feed vessel and purged with air. Monomer solution 2 was added dropwise at a stirrer speed of 400 rpm within 30 minutes. Monomer solution 2 was inertized with nitrogen immediately prior to the dropwise addition.

(8) After feeding had ended, the mixture was stirred at 70 C. for a further 60 minutes. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

(9) The suspension present was cooled to 60 C. and the resultant polymer particles were filtered off with suction using a Bchner funnel with a paper filter. The further drying was effected at 45 C. in an air circulation drying cabinet and optionally in a vacuum drying cabinet at 800 mbar down to a residual moisture content of less than 15% by weight.

(10) The properties of the resultant polymer particles are summarized in table 1.

EXAMPLE 3

(11) A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 500.00 g of n-heptane, 0.92 g of sucrose stearate (Ryoto Sugar Ester S-370, Mitsubishi Chemical Europe GmbH, Dsseldorf, Germany) and 60.00 g of superabsorbent particles, and this initial charge was heated to an internal temperature of 70 C. while stirring under nitrogen, until the sucrose stearate had dissolved fully.

(12) The superabsorbent particles were produced according to example 1 of WO 2014/079694 A1 and separated out of stream (8) in FIG. 1.

(13) A monomer solution 2 prepared from 50.00 g (0.0694 mol) of acrylic acid, 43.00 g (0.538 mol) of 50% by weight aqueous sodium hydroxide solution, 45.60 g of water, 0.0125 g (0.081 mmol) of N,N-methylenebisacrylamide (MBA) and 0.167 g (0.618 mmol) of potassium peroxosulfate was subsequently introduced into a feed vessel and purged with air. Monomer solution 2 was added dropwise at a stirrer speed of 400 rpm within 30 minutes. Monomer solution 2 was inertized with nitrogen immediately prior to the dropwise addition.

(14) After feeding had ended, the mixture was stirred at 70 C. for a further 60 minutes. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

(15) The suspension present was cooled to 60 C. and the resultant polymer particles were filtered off with suction using a Bchner funnel with a paper filter. The further drying was effected at 45 C. in an air circulation drying cabinet and optionally in a vacuum drying cabinet at 800 mbar down to a residual moisture content of less than 15% by weight.

(16) The properties of the resultant polymer particles are summarized in table 1.

EXAMPLE 4

(17) The procedure was as in example 3, except that a monomer solution 2 prepared from 50.00 g (0.694 mol) of acrylic acid, 43.00 g (0.538 mol) of 50% by weight aqueous sodium hydroxide solution, 75.60 g of water, 0.0125 g (0.081 mmol) of N,N-methylenebisacrylamide (MBA) and 0.167 g (0.618 mmol) of potassium peroxodisulfate was used.

(18) The properties of the resultant polymer particles are summarized in table 1.

EXAMPLE 5

(19) The procedure was as in example 3, except that a monomer solution 2 prepared from 50.00 g (0.694 mol) of acrylic acid, 43.00 g (0.538 mol) of 50% by weight aqueous sodium hydroxide solution, 93.60 g of water, 0.0125 g (0.081 mmol) of N,N-methylenebisacrylamide (MBA) and 0.167 g (0.618 mmol) of potassium peroxodisulfate was used.

(20) The properties of the resultant polymer particles are summarized in table 1.

(21) TABLE-US-00001 TABLE 1 Properties of the agglomerated superabsorbents Moisture Water CRC FSR content Example Superabsorbent % by wt. bop g/g g/gs % by wt. 2 suspension 128 16.9 1.25 5.3 polymerization 3 dropletizing 128 24.2 0.78 3.3 polymerization 4 dropletizing 178 29.6 0.41 3.6 polymerization 5 dropletizing 208 36.6 0.23 5.0 polymerization bop based on superabsorbent particles (polymer)