Method for producing water-absorbing polymer particles by suspension polymerisation

1. A process for producing water-absorbing polymeric particles from a reaction mixture by a suspension polymerization in a hydrophobic solvent, comprising:

i) metering a monomer solution using at least one feed line into a stirred reactor,

ii) removing the hydrophobic solvent from the resulting water-absorbing polymeric particles, and

iii) recycling the removed hydrophobic solvent into the process, wherein the hydrophobic solvent is a mixture of branched and unbranched saturated aliphatic hydrocarbons and is at least partly replaced by fresh hydrophobic solvent, the fresh hydrophobic solvent is at least partly a hydrocarbon mixture and the hydrocarbon mixture comprises 2.5% to 80% by weight of branched saturated aliphatic hydrocarbons.

2. The process according to claim 1 wherein a recycle fraction of the hydrophobic solvent is 70% to 95% by weight.

3. The process according to claim 1 wherein a recycle fraction of the hydrophobic solvent is 50% to 99% by weight.

4. The process according to claim 1 wherein the hydrocarbon mixture comprises 5% to 50% by weight of branched aliphatic hydrocarbons.

5. The process according to claim 1 wherein a recycle fraction of the hydrophobic solvent is 80% to 90% by weight.

6. The process according to claim 1 wherein the hydrocarbon mixture comprises 10% to 20% by weight of branched saturated aliphatic hydrocarbons.

7. The process according to claim 1 wherein the water-absorbing polymeric particles have a Centrifuge Retention Capacity of at least 15 g/g.

8. The process according to claim 1 wherein the monomer solution comprises at least 35% by weight of monomers.

9. The process according to claim 1 wherein the water-absorbing polymeric particles comprise less than 0.1% by weight of an interpolymerized crosslinker.

10. The process according to claim 1 wherein the water-absorbing polymeric particles comprise at least 50 mol % of at least partially neutralized polymerized acrylic acid.

11. The process according to claim 1 wherein the suspension polymerization is carried out continuously.

12. The process according to claim 1 wherein the reaction mixture is azeotropically dewatered, postcrosslinked, azeotropically dewatered again, filtered, and dried.

13. The process according to claim 1 wherein the reaction mixture is azeotropically dewatered, filtered, dried, and postcrosslinked.

14. The process according to claim 1 wherein the reaction mixture is supplementarily reacted in at least one further stirred reactor.

15. The process according to claim 1 wherein a dispersing assistant is used in the suspension polymerization.

16. The process according to claim 1 wherein a feed line in the stirred reactor ends below a liquid surface.

17. The process according to claim 1 wherein less than 80% by weight of the recycled hydrophobic solvent is distillatively purified during or after the removing ii) and before the recycling iii).

18. The process according to claim 1 wherein the hydrocarbon mixture boils in the range from 50 to 150° C.