Method for removing metal impurities

Patent metadata

Field	Value
Publication number	US-9803033-B2
Application number	US-201013266181-A
Country	US
Kind code	B2
Filing date	Apr 19, 2010
Priority date	Apr 30, 2009
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

A process for removing metallic impurities from a product mass flow comprising water-absorbing polymer particles by means of bar magnets, wherein the water-absorbing polymer particles comprise a surfactant and have direct contact with the bar magnets.

First claim

The invention claimed is:

1. A process for producing water-absorbing polymer particles by polymerizing a monomer solution or suspension comprising
a) at least one ethylenically unsaturated monomer which bears an acid group and may be at least partly neutralized,
b) at least one crosslinker,
c) at least one initiator,
d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer specified under a), and
e) optionally one or more water-soluble polymer,
metallic impurities being removed from a product mass flow comprising water-absorbing polymer particles by a magnetic separator, the magnetic separator being formed from bar magnets, the bar magnets consisting of an austenitic steel sleeve and a magnetic material present within the sleeve, and the sleeve being bonded to the magnetic material in an undetachable manner, wherein the sleeves have direct contact to the water-absorbing polymer particles and the water-absorbing polymer particles comprise at least one surfactant,
wherein the moisture content of the water-absorbing polymer particles is increased upstream of the magnetic separator.

2. The process according to claim 1 , wherein the product mass flow has a temperature of 30 to 90° C.

3. The process according to claim 1 , wherein the water-absorbing polymer particles in the product mass flow have a moisture content of 1 to 20% by weight.

4. The process according to claim 1 , wherein an areal loading of the magnetic separator is 2 to 15 g/cm 2 s.

5. The process according to claim 1 , wherein the bar magnets have a diameter of 5 to 30 mm.

6. The process according to claim 1 , wherein a distance between the bar magnets is from 5 to 30 mm.

7. The process according to claim 1 , wherein at least 95% by weight of the water-absorbing polymer particles have a particle size of at least 150 μm.

8. The process according to claim 1 , wherein at least 95% by weight of the water-absorbing polymer particles have a particle size of at most 600 μm.

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

10. The process according to claim 1 , wherein the water-absorbing particles are surface postcrosslinked and the surfactant is added to the water-absorbing particles with a surface postcrosslinker.

11. The process according to claim 10 , wherein an amount of the surfactant, based on the water-absorbing polymer particles, is 0.001% to 0.1%, by weight.

12. A process for producing water-absorbing polymer particles by polymerizing a monomer solution or suspension comprising
a) at least one ethylenically unsaturated monomer which bears an acid group and may be at least partly neutralized,
b) at least one crosslinker,
c) at least one initiator,
d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer specified under a), and
e) optionally one or more water-soluble polymer,
metallic impurities being removed from a product mass flow comprising water-absorbing polymer particles by a magnetic separator, the magnetic separator being formed from bar magnets, the bar magnets consisting of an austenitic steel sleeve and a magnetic material present within the sleeve, and the sleeve being bonded to the magnetic material in an undetachable manner, wherein the sleeves have direct contact to the water-absorbing polymer particles and the water-absorbing polymer particles comprise at least one surfactant,
wherein an areal loading of the magnetic separator is 2 to 15 g/cm 2 s.

Assignees

• Funk Rüdiger
• Schröder Jürgen
• Pfeiffer Thomas
• Bitzer Emil
• Basf Se

Inventors

• Funk Rüdiger
• Schröder Jürgen
• Pfeiffer Thomas
• Bitzer Emil

Classifications

• B03C2201/18

  Magnetic separation whereby the particles are suspended in a liquid · CPC title

• B03C1/286

  disposed at the inner circumference of a recipient, e.g. magnetic drain bolt · CPC title

• C08F6/02

  Neutralisation of the polymerisation mass, e.g. killing the catalyst (short-stopping C08F2/42 ){also removal of catalyst residues} · CPC title

• C08F2/10 Primary

  Aqueous solvent · CPC title

• C08L33/02

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