# US 9,434,802 B2 · Method for removal of residual monomers from water-absorbing polymer particles > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,434,802 B2 - Document ID: US9434802B2 - Status: Granted - Kind: B2 - Application number: 14/762,026 - Filed: 2014-01-20 - Published: 2015-11-12 - Granted: 2016-09-06 - Earliest claimed: 2013-01-30 - Assignees: BASF SE - Applicants: BASF SE - Inventors: Stephan Bauer; Norbert Herfert; Lydia König; Yvonne Hagen; Xiana Romani Fernandez; Marcus Schöppler - Web page: https://patentgrep.com/patent/US9434802B2 ## CPC - B29B 9/16: Auxiliary treatment of granules - C08F 220/06: Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof - A61L 15/24: Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof {(A61L15/225 takes precedence)} - A61L 15/60: Liquid-swellable gel-forming materials, e.g. super-absorbents - C08F 6/005: {from solid polymers} - C08F 6/008: {Treatment of solid polymer wetted by water or organic solvents, e.g. coagulum, filter cakes} - C08L 33/02: Homopolymers or copolymers of acids; Metal or ammonium salts thereof - B29B 2009/168: {Removing undesirable residual components, e.g. solvents, unreacted monomers; Degassing} - C08L 2201/54: Aqueous solutions or dispersions - C08L 2312/00: Crosslinking - B29B: PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS - C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS - A61L: METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES (preservation of bodies or disinfecting characterised by the agents employed A01N; preserving, e.g. sterilising, food or foodstuffs A23; preparations for medical, dental or toiletry purposes A61K) - C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06) ## Abstract A process for removing residual monomers from water-absorbing polymer particles by thermally aftertreating the water-absorbing polymer particles in a mixer with rotating mixing tools at a temperature of at least 60° C. in the presence of water and of a surfactant. ## Claims ### Claim 1 A process for removing residual monomers from water-absorbing polymer particles by thermally aftertreating the water-absorbing polymer particles in a mixer having rotating mixing tools, the water-absorbing polymer particles during the thermal aftertreatment having a temperature of at least 60° C. and a water content of at least 8% by weight, with addition of water or an aqueous solution before or during the thermal aftertreatment and/or of a steam-comprising gas stream during the thermal aftertreatment, wherein process comprises performing the thermal aftertreatment in the presence of at least one surfactant, the at least one surfactant having a polar group and a nonpolar group, the polar group and the nonpolar group of the surfactant not being joined via a carboxylic ester group, and the polar group having at least one hydroxyl group, a cationic group, or an anionic group and the nonpolar group having a C4- to C20-alkyl chain. ### Claim 2 (depends on 1) The process according to claim 1, wherein the polar group is a cationic group. ### Claim 3 (depends on 1) The process according to claim 1, wherein the surfactant is a surfactant mixture. ### Claim 4 (depends on 3) The process according to claim 3, wherein surfactants in the surfactant mixture comprise different linear and/or branched alkyl chains as nonpolar groups. ### Claim 5 (depends on 1) The process according to claim 1, wherein from 0.0005 to 0.01% by weight of the at least one surfactant, based on the water-absorbing polymer particles, is used. ### Claim 6 (depends on 1) The process according to claim 1, wherein the water-absorbing polymer particles have a temperature of 80 to 110° C. during the thermal aftertreatment. ### Claim 7 (depends on 1) The process according to claim 1, wherein from 0.05 to 20% by weight of water or an aqueous solution is added before or during the thermal aftertreatment, based on the water-absorbing polymer particles. ### Claim 8 (depends on 1) The process according to claim 1, wherein the gas stream added during the thermal aftertreatment comprises from 0.05 to 1.0 kg of steam per kg of dry gas. ### Claim 9 (depends on 1) The process according to claim 1, wherein a mean residence time in the mixer is from 10 to 120 minutes. ### Claim 10 (depends on 1) The process according to claim 1, wherein a gas volume used for thermal aftertreatment in a batchwise mixer is from 0.01 to 5 m3 (STP)/h per kg of water-absorbing polymer particles, or, in a continuous mixer, from 0.01 to 5 m3 (STP)/h per kg/h of water-absorbing polymer particle throughput. ### Claim 11 (depends on 1) The process according to claim 1, wherein the thermal aftertreatment is performed in a horizontal mixer. ### Claim 12 (depends on 1) The process according to claim 1, wherein the water-absorbing polymer particles are prepared by polymerizing a monomer solution comprising 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) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a), e) optionally one or more water-soluble polymer or copolymer and f) water. ### Claim 13 (depends on 12) The process according to claim 12, wherein the monomer a) has been neutralized to an extent of at least 25 mol %. ### Claim 14 (depends on 12) The process according to claim 12, wherein the monomer a) is acrylic acid to an extent of at least 50 mol %. ### Claim 15 (depends on 12) The process according to claim 12, wherein the monomer solution comprises at least 0.1% by weight of crosslinker b), based on unneutralized monomer a).