Process for classifying water-absorbing polymer beads

Patent metadata

Field	Value
Publication number	US-9550213-B2
Application number	US-201414779990-A
Country	US
Kind code	B2
Filing date	Mar 18, 2014
Priority date	Mar 28, 2013
Publication date	Jan 24, 2017
Grant date	Jan 24, 2017

Abstract

A process for classifying water-absorbing polymer particles, wherein screens having different mesh sizes are used before and after surface postcrosslinking to remove the undersize (fines).

First claim

The invention claimed is:

1. A process for preparing water-absorbing polymer particles, comprising
i) classifying the water-absorbing polymer particles, undersize being removed using a screen having the mesh size m 1 ,
ii) surface postcrosslinking the classified polymer particles,
iii) classifying the surface postcrosslinked polymer particles, undersize being removed using a screen having the mesh size m 2 , and
iv) recycling the undersize from step i) and iii), wherein a throughput per hour of the water-absorbing polymer particles in the course of classification in step i) is at least 100 kg/h per m 2 of screen area and the mesh size m 1 in step i) is greater than the mesh size m 2 in step iii).

2. The process according to claim 1 , wherein a product fraction is removed in step i) and/or step iii) using at least two screens of different mesh sizes.

3. The process according to claim 1 , wherein oversize is removed in step i) and/or step iii) using at least two screens of different mesh sizes.

4. The process according to claim 1 , wherein the mesh size m 1 in step i) is at least 180 μm.

5. The process according to claim 1 , wherein the mesh size m 2 in step iii) is not more than 150 μm.

6. The process according to claim 1 , wherein the mesh size m 1 in step i) is at least 30 μm greater than the mesh size m 2 in step iii).

7. The process according to claim 1 , wherein the water-absorbing polymer particles, during the classification in step i) and/or step iii), have a temperature of from 40 to 120° C.

8. The process according to claim 1 , wherein classification in step i) and/or step iii) is effected under reduced pressure.

9. The process according to claim 1 , wherein the water-absorbing polymer particles are flowed over by a gas stream during the classification in step i) and/or step iii).

10. The process according to claim 9 , wherein the gas stream has a temperature of from 40 to 120° C.

11. The process according to claim 9 , wherein the gas stream has a steam content of less than 5 g/kg.

12. The process according to claim 1 , wherein the water-absorbing polymer particles have been obtained by polymerizing an aqueous monomer solution.

13. The process according to claim 1 , wherein the water-absorbing polymer particles comprise at least 50 mol % of at least partly neutralized polymerized acrylic acid.

14. The process according to claim 1 , wherein the water-absorbing polymer particles, before step ii), have a centrifuge retention capacity of at least 15 g/g.

Assignees

• Basf Se

Inventors

• Possemiers Karl J
• Pfeiffer Thomas
• Weismantel Matthias
• Funk Rüdiger
• Peterson Monte
• Serneels Sven
• Johnson Jeffrey
• De Kaey Ronny

Classifications

• C08L33/02

  Homopolymers or copolymers of acids; Metal or ammonium salts thereof · CPC title

• B07B1/46 Primary

  Constructional details of screens in general; Cleaning or heating of screens · CPC title

• C08F220/06

  Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof · CPC title

• C08J2333/02

  Homopolymers or copolymers of acids; Metal or ammonium salts thereof · CPC title

• A61L15/60

  Liquid-swellable gel-forming materials, e.g. super-absorbents · CPC title