Process for producing water-absorbent polymer particles by polymerizing droplets of a monomer solution
AssigneeBASF SE
InventorsThomas Daniel, Norbert Herfert, Stephan Bauer, Katrin Baumann, Birgit Reinhard, Jürgen Freiberg, Rudolf Schliwa
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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.
Claims22
(canceled)
Polymer particles according to claim 14, wherein the heated gas phase is flowing cocurrent to the droplets through the reaction zone.
Polymer particles according to claim 14, wherein the monomer solution comprises from 0.05 to 0.15% by weight, based on monomer a), of the at least one persulfate.
Polymer particles process according to claim 14, wherein the monomer solution comprises from 0.2 to 0.5% by weight, based on monomer a), of the at least one azo initiator.
Polymer particles according to claim 14, wherein the temperature of the gas leaving the reaction zone is from 110 to 120° C.
Polymer particles according to claim 14, wherein the temperature of the gas entering the reaction zone is from 160 to 200° C.
Polymer particles according to claim 14, wherein a gas velocity inside the reaction zone is from 0.1 to 2.5 m/s.
Polymer particles according to claim 14, wherein the temperature of the water-absorbent polymer particles during the thermal posttreatment is from 60 to 80° C.
Polymer particles according to claim 14, wherein the residence time of the water-absorbent polymer particles in the fluidized bed is from 120 to 240 minutes.
Polymer particles according to claim 14, wherein a gas velocity inside the fluidized bed is from 0.3 to 2.5 m/s.
Polymer particles according to claim 14, wherein the gas entering the fluidized bed comprises from 0.02 to 0.15 kg steam per kg of dry gas.
Polymer particles according to claim 14, wherein the ethylenically unsaturated monomer which bears an acid group is an ethylenically unsaturated carboxylic acid.
Polymer particles according to claim 14, wherein the ethylenically unsaturated monomer which bears an acid group is acrylic acid.
Water-absorbent polymer particles prepared according to 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,
- c1) from 0.01 to less than 0.3% by weight, based on monomer a), of at least one persulfate,
- c2) 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.
Water-absorbent polymer particles having a bulk density of at least 0.65 g/cm3, a centrifuge retention capacity of at least 35 g/g, and a HC 60 value of at least 80.
Dependencies are inferred from the claim text.