Process for producing water-absorbent polymer particles by polymerizing droplets of a monomer solution

Patent metadata

Field	Value
Publication number	US-9790304-B2
Application number	US-201314442501-A
Country	US
Kind code	B2
Filing date	Nov 11, 2013
Priority date	Nov 21, 2012
Publication date	Oct 17, 2017
Grant date	Oct 17, 2017

Abstract

The present invention relates to a process for producing water-absorbent polymer particles by polymerizing droplets of a monomer solution comprising less than 0.3% by weight of persulfate and at least 0.05% by weight of azo initiator and thermal aftertreatment of the formed polymer particles at less than 100° C. in a fluidized bed for 60 to 300 minutes.

First claim

The invention claimed is:

1. A process for producing water-absorbent polymer particles by polymerizing droplets of
a) at least one ethylenically unsaturated monomer which bears an acid group and optionally is at least partly neutralized,
(b) at least one crosslinker,
c l ) from 0.01 to less than 0.3% by weight, based on monomer a), of at least one persulfate,
c 2 ) at least 0.05% by weight, based on monomer a), of at least one azo initiator,
d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a),
e) optionally one or more water-soluble polymer, and
f) water,
in a surrounding heated gas phase in a reaction zone and thermal posttreatment in a fluidized bed, wherein a temperature of a gas leaving the reaction zone is less than 150° C., a temperature of the water-absorbent polymer particles during the thermal posttreatment is less than 100 ° C., and a residence time of the water-absorbent polymer particles in the fluidized bed is from 60 to 300 minutes.

2. A process according to claim 1 , wherein the heated gas phase is flowing cocurrent to the droplets through the reaction zone.

3. A process according to claim 1 , wherein the monomer solution comprises from 0.05 to 0.15% by weight, based on monomer a), of the at least one persulfate.

4. A process according to claim 1 , wherein the monomer solution comprises from 0.2 to 0.5% by weight, based on monomer a), of the at least one azo initiator.

5. A process according to claim 1 , wherein the temperature of the gas leaving the reaction zone is from 110 to 120° C.

6. A process according to claim 1 , wherein the temperature of the gas entering the reaction zone is from 160 to 200° C.

7. A process according to claim 1 , wherein a gas velocity inside the reaction zone is from 0.1 to 2.5 m/s.

8. A process according to claim 1 , wherein the temperature of the water-absorbent polymer particles during the thermal posttreatment is from 60 to 80° C.

9. A process according to claim 1 , wherein the residence time of the water-absorbent polymer particles in the fluidized bed is from 120 to 240 minutes.

10. A process according to claim 1 , wherein a gas velocity inside the fluidized bed is from 0.3 to 2.5 m/s.

11. A process according to claim 1 , wherein the gas entering the fluidized bed comprises from 0.02 to 0.15 kg steam per kg of dry gas.

12. A process according to claim 1 , wherein the ethylenically unsaturated monomer which bears an acid group is an ethylenically unsaturated carboxylic acid.

13. A process according to claim 1 , wherein the ethylenically unsaturated monomer which bears an acid group is acrylic acid.

14. A process according to claim 1 , wherein the monomer solution comprises from 0.1 to 0.15% by weight, based on monomer a) of the persulfate.

Assignees

• Basf Se

Inventors

• Daniel Thomas
• Herfert Norbert
• Bauer Stephan
• Baumann Katrin
• Reinhard Birgit
• Freiberg Jürgen
• Schliwa Rudolf

Classifications

• C08F220/06 Primary

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

• C08F6/005

  from solid polymers · CPC title

• A61L15/42

  Use of materials characterised by their function or physical properties (liquid bandages A61L26/00) · CPC title

• C08L33/02

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

• B01J20/267

  Cross-linked polymers · CPC title