Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
  • C08J3/245—Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
  • B01J8/08—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with moving particles
  • B01J8/10—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with moving particles moved by stirrers or by rotary drums or rotary receptacles or endless belts
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F5/00—Elements specially adapted for movement
  • F28F5/02—Rotary drums or rollers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
  • B01J2208/00008—Controlling the process
  • B01J2208/00017—Controlling the temperature
  • B01J2208/00106—Controlling the temperature by indirect heat exchange
  • B01J2208/00168—Controlling the temperature by indirect heat exchange with heat exchange elements outside the bed of solid particles
  • B01J2208/00212—Plates; Jackets; Cylinders
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
  • B01J2208/00008—Controlling the process
  • B01J2208/00017—Controlling the temperature
  • B01J2208/00389—Controlling the temperature using electric heating or cooling elements
  • B01J2208/00407—Controlling the temperature using electric heating or cooling elements outside the reactor bed
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
  • B01J2208/00008—Controlling the process
  • B01J2208/00017—Controlling the temperature
  • B01J2208/00389—Controlling the temperature using electric heating or cooling elements
  • B01J2208/00415—Controlling the temperature using electric heating or cooling elements electric resistance heaters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
  • B01J2208/00008—Controlling the process
  • B01J2208/00548—Flow
  • B01J2208/00557—Flow controlling the residence time inside the reactor vessel
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
  • C08J2333/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof

Definitions

• the present invention relates to a process for the thermal surface postcrosslinking of water-absorbing polymer particles, wherein the polymer particles are coated with an aqueous solution, the deagglomerated polymer coated particles and the deagglomerated polymer particles are thermally surface postcrosslinked by means of a drum heat exchanger with inverse helix.
• Water-absorbing polymer particles are used in the manufacture of diapers, tampons, sanitary napkins and other sanitary articles, but also as water-retaining agents in agricultural horticulture.
• the water-absorbing polymer particles are also referred to as superabsorbers.
• the properties of the water-absorbing polymer particles can be adjusted, for example, via the amount of crosslinker used. As the amount of crosslinker increases, the centrifuge retention capacity (CRC) decreases and the absorption under a pressure of 21.0 g / cm 2 (AUL 0.3 psi) goes through a maximum.
• CRC centrifuge retention capacity
• water-absorbing polymer particles are generally surface postcrosslinked.
• the degree of crosslinking of the particle surface increases, whereby the absorption under a pressure of 49.2 g / cm 2 (AUL0.7 psi) and the centrifuge retention capacity (CRC) can be at least partially decoupled.
• This surface postcrosslinking can be carried out in aqueous gel phase.
• dried, ground and sieved polymer particles base polymer
• Crosslinkers suitable for this purpose are compounds which can form covalent bonds with at least two carboxylate groups of the water-absorbing polymer particles.
• EP 1 757 645 A1 and EP 1 757 646 A1 disclose the surface postcrosslinking of water-absorbing polymer particles in a rotary tube.
• DE 10 2007 024 080 A1 teaches the after-treatment of water-absorbing polymer particles, for example with water, in a rotating container.
• the object of the present invention was to provide an improved process for producing water-absorbing polymer particles, in particular an improved surface postcrosslinking.
• the object was achieved by processes for thermal surface postcrosslinking of water-absorbing polymer particles, wherein the water-absorbing polymers by polymerization of an aqueous monomer solution or suspension containing a) at least one ethylenically unsaturated, acid group-carrying monomer which may be at least partially neutralized,
• optionally one or more water-soluble polymers are prepared, characterized in that the polymer particles coated with an aqueous solution, deagglomerated the coated polymer particles and the deagglomerated polymer particles are thermally surface postcrosslinked by means of a drum heat exchanger with inverse screw helix.
• the coating and the deagglomeration are advantageously carried out in a horizontal mixer or the coating in a vertical mixer and the deagglomeration in a horizontal mixer.
• the coated polymer particles are dried or heated during deagglomeration.
• the filling height of the drum heat exchanger is preferably 30 to 100%, particularly preferably 40 to 95%, very particularly preferably 65 to 90%, in each case based on the height of the screw helix.
• the temperature of the water-absorbing polymer particles in the drum heat exchanger is preferably from 120 to 220 ° C, more preferably from 150 to 210 ° C, most preferably from 170 to 200 ° C, and / or the residence time of the water-absorbing polymer particles in the drum heat exchanger is preferably from 10 to 120 minutes, more preferably from 20 to 90 minutes, most preferably from 30 to 60 minutes.
• the drum heat exchanger is usually heated electrically or by steam, preferably indirectly. Indirectly heated means that the heating takes place via the wall of the rotating drum.
• Another object of the present invention are suitable for carrying out the method according to the invention suitable devices. These are, in particular, a device for thermal surface postcrosslinking of water-absorbing polymer particles, comprising a heatable horizontal mixer and a drum heat exchanger with inverse spiral screw, and a device for thermal surface postcrosslinking of water-absorbing polymer particles, comprising a vertical mixer, a heatable horizontal mixer and a drum heat exchanger with inverse spiral screw.
• Heatable horizontal mixer and drum heat exchanger or vertical mixer, heatable horizontal mixer and drum heat exchanger are preferably connected directly in series.
• the drum heat exchanger is followed directly by a coolable horizontal mixer.
• the present invention is based on the finding that the result of the thermal surface postcrosslinking is very strongly influenced by the residence time.
• the permeability of the swollen gel bed (SFC) undergoes a pronounced maximum.
• the thermal surface postcrosslinking in a drum heat exchanger with inverse screw helix allows a continuous thermal surface postcrosslinking with a narrow residence time distribution, a backmixing between the individual helices does not practically take place with proper loading.
• the proportion of water-absorbing polymer particles with too low and too high residence time and thus insufficient quality can be minimized.
• the water-absorbing polymer particles are prepared by polymerization of a monomer solution or suspension and are usually water-insoluble.
• the monomers a) are preferably water-soluble, ie the solubility in water at 23 ° C. is typically at least 1 g / 100 g of water, preferably at least 5 g / 100 g Water, more preferably at least 25 g / 100 g of water, most preferably at least 35 g / 100 g of water.
• Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, and itaconic acid. Particularly preferred monomers are acrylic acid and methacrylic acid. Very particular preference is given to acrylic acid.
• Suitable monomers a) are, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
• sulfonic acids such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
• AMPS 2-acrylamido-2-methylpropanesulfonic acid
• a suitable monomer a) is, for example, an acrylic acid purified according to WO 2004/035514 A1 with 99.8460% by weight of acrylic acid, 0.0950% by weight of acetic acid,
• the proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, very particularly preferably at least 95 mol%.
• the monomers a) usually contain polymerization inhibitors, preferably hydroquinone half ethers, as storage stabilizer.
• the monomer solution preferably contains up to 250 ppm by weight, preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight, preferably at least 10 ppm by weight, particularly preferably at least 30 ppm by weight, in particular by 50% by weight .
• ppm hydroquinone half ether, in each case based on the unneutralized monomer a).
• an ethylenically unsaturated, acid group-carrying monomer having a corresponding content of hydroquinone half-ether can be used to prepare the monomer solution.
• hydroquinone half ethers are hydroquinone monomethyl ether (MEHQ) and / or alpha tocopherol (vitamin E).
• Suitable crosslinkers b) are compounds having at least two groups suitable for crosslinking. Such groups are, for example, ethylenically unsaturated groups which are incorporated in the Polymer chain can be radically copolymerized, and functional groups that can form covalent bonds with the acid groups of the monomer a). Furthermore, polyvalent metal salts which can form coordinative bonds with at least two acid groups of the monomer a) are also suitable as crosslinking agents b).
• Crosslinkers b) are preferably compounds having at least two polymerizable groups which can be incorporated in the polymer network in free-radically polymerized form.
• Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallylammonium chloride, tetraallyloxyethane, as described in EP 0 530 438 A1, di- and triacrylates, as in EP 0 547 847 A1, EP 0 559 476 A1, EP 0 632 068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO 2003/104301 A1 and DE 103 31 450 A1, mixed acrylates which, in addition to acrylate groups, contain further ethylenically unsaturated Groups, as described in DE 103 31 456
• Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, 15-tuply ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate and triallylamine.
• Very particularly preferred crosslinkers b) are the polyethyleneglyoxylated and / or propoxylated glycerols esterified with acrylic acid or methacrylic acid to form diioder triacrylates, as described, for example, in WO 2003/104301 A1.
• Particularly advantageous are di- and / or triacrylates of 3- to 10-fold ethoxylated glycerol.
• diacrylates or triacrylates of 1 to 5 times ethoxylated and / or propoxylated glycerol.
• Most preferred are the triacrylates of 3 to 5 times ethoxylated and / or propoxylated glycerol, in particular the triacrylate of 3-times ethoxylated glycerol.
• the amount of crosslinker b) is preferably from 0.05 to 1, 5 wt .-%, particularly preferably 0.1 to 1 wt .-%, most preferably 0.2 to 0.6 wt .-%, each based on Monomer a).
• initiators c) it is possible to use all compounds which generate radicals under the polymerization conditions, for example thermal initiators, redox initiators, photoinitiators.
• Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite.
• mixtures of thermal initiators and redox initiators are used, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid.
• a reducing component but is preferably a mixture of the sodium salt of 2
• Hydroxy-2-sulfinatoacetic acid the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite used.
• Such mixtures are as Brüggolite® FF6 and Brüggolite® FF7 (Brüggemann Chemicals, Heilbronn, Germany).
• acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate are ethylenically unsaturated monomers d) which are copolymerizable with the ethylenically unsaturated acid group-carrying monomers a).
• water-soluble polymers e it is possible to use polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified cellulose.
• an aqueous monomer solution is used.
• the water content of the monomer solution is preferably from 40 to 75% by weight, more preferably from 45 to 70% by weight, most preferably from 50 to 65% by weight.
• monomer suspensions i.
• the monomer solution may be polymerized prior to polymerization by inerting, i. Flow through with an inert gas, preferably nitrogen or carbon dioxide, are freed of dissolved oxygen.
• an inert gas preferably nitrogen or carbon dioxide
• the oxygen content of the monomer solution before polymerization is reduced to less than 1 ppm by weight, more preferably less than 0.5 ppm by weight, most preferably less than 0.1 ppm by weight.
• Suitable reactors are, for example, kneading reactors or belt reactors.
• the polymer gel resulting from the polymerization of an aqueous monomer solution or suspension is continuously comminuted by, for example, counter-rotating stirring shafts, as in
• WO 2001/038402 A1 The polymerization on the belt is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928.
• a polymer gel is formed, which must be comminuted in a further process step, for example in an extruder or kneader.
• the comminuted polymer gel obtained by means of a kneader can additionally be extruded.
• the process steps polymerization and drying can be summarized, as described in WO 2008/040715 A2, WO 2008/052971 A1 and WO 201 1/026876 A1.
• the acid groups of the polymer gels obtained are usually partially neutralized.
• the neutralization is preferably carried out at the stage of the monomers. This is usually done by mixing the neutralizing agent as an aqueous solution or preferably as a solid.
• the degree of neutralization is preferably from 25 to 95 mol%, particularly preferably from 30 to 80 mol%, very particularly preferably from 40 to 75 mol%, wherein the customary neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or Alkalimetallhydrogenkarbonate and mixtures thereof.
• alkali metal salts and ammonium salts can be used.
• Sodium and potassium are particularly preferred as alkali metals, but most preferred are sodium hydroxide, sodium carbonate or sodium bicarbonate and mixtures thereof.
• the polymer gel is at least partially neutralized after the polymerization, the polymer gel is preferably comminuted mechanically, for example by means of an extruder, wherein the neutralizing agent can be sprayed, sprinkled or poured on and then thoroughly mixed in. For this purpose, the gel mass obtained can be extruded several times for homogenization.
• the polymer gel is then preferably dried with a belt dryer until the moisture content is preferably 0.5 to 15 wt .-%, particularly preferably 1 to 10 wt .-%, most preferably 2 to 8 wt .-%, wherein the Moisture content according to the EDANA recommended test method No. WSP 230.2-05 "Mass Loss Upon Heating". If the moisture content is too high, the dried polymer gel has too low a glass transition temperature T g and is difficult to process further. If the moisture content is too low, the dried polymer gel is too brittle and in the subsequent comminution steps undesirably large amounts of polymer particles having too small a particle size ("fines") are produced.
• the average particle size of the polymer fraction separated as a product fraction is preferably at least 200 ⁇ m, more preferably from 250 to 600 ⁇ m, very particularly from 300 to 500 ⁇ m.
• the average particle size of the product fraction can be determined by means of the EDANA recommended test method No.
• WSP 220.2-05 Particle Size Distribution
• the mean particle size is the value of the mesh size, which results for accumulated 50 wt .-%.
• the proportion of particles having a particle size of greater than 150 ⁇ m is preferably at least 90% by weight, particularly preferably at least 95% by weight, very particularly preferably at least 98% by weight.
• Polymer particles with too small particle size lower the permeability (SFC). Therefore, the proportion of too small polymer particles ("fines") should be low, so too small polymer particles are usually separated and recycled to the process, preferably before, during or immediately after the polymerization, ie before drying the polymer gel
• Polymer particles can be moistened with water and / or aqueous surfactant before or during the recycling process It is also possible to separate small polymer particles in later process steps, for example after surface postcrosslinking or another coating step. For example, if a kneading reactor is used for the polymerization, the polymer particles which are too small are preferably added during the last third of the polymerization.
• the polymer particles which are too small are added very late, for example only in an apparatus downstream of the polymerization reactor, for example an extruder, then the polymer particles which are too small can only be incorporated into the resulting polymer gel with difficulty. Insufficiently incorporated too small polymer particles dissolve during the grinding again from the dried polymer gel are therefore separated again during classification and increase the amount of polymer particles which are too small to be recycled.
• the proportion of particles having a particle size of at most 850 pm is preferably at least 90 wt .-%, more preferably at least 95 wt .-%, most preferably at least 98 wt .-%.
• the proportion of particles having a particle size of at most 600 ⁇ m is preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 98% by weight.
• Polymer particles with too large particle size reduce the swelling rate. Therefore, the proportion of polymer particles too large should also be low. Too large polymer particles are therefore usually separated and recycled to the grinding of the dried Polymergeis.
• the polymer particles are surface-post-crosslinked to further improve the properties.
• Suitable compounds are, for example, polyfunctional amines, polyfunctional amidoamines, polyfunctional epoxides, as described in EP 0 083 022 A2, EP 0 543 303 A1 and EP 0 937 736 A2, di- or polyfunctional alcohols, as described in DE 33 14 019 A1, DE 35 23 617 A1 and EP 0 450 922 A2, or ⁇ -hydroxyalkylamides, as described in DE 102 04 938 A1 and US Pat. No. 6,239,230.
• DE 40 20 780 C1 cyclic carbonates in DE 198 07 502 A1 2-
• Oxazolidinone and its derivatives such as 2-hydroxyethyl-2-oxazolidinone, in DE 198 07 992 C1 bis- and poly-2-oxazolidinone, in DE 198 54 573 A1 2-oxotetrahydro-1, 3-oxazine and its derivatives, in DE 198 54 574 A1 N-acyl-2-oxazolidinones, in DE 102 04 937 A1 cyclic ureas, in DE 103 34 584 A1 bicyclic amidoacetals, in EP 1 199 327 A2 oxetanes and cyclic see ureas and in WO 2003/031482 A1 morpholine 2,3-dione and its derivatives are described as suitable surface postcrosslinkers.
• Preferred surface postcrosslinkers are ethylene carbonate, ethylene glycol diglycidyl ether, reaction products of polyamides with epichlorohydrin and mixtures of propylene glycol and 1,4-butanediol.
• Very particularly preferred surface postcrosslinkers are 2-hydroxyethyl-2-oxazolidinone, 2-oxazolidinone and 1, 3-propanediol.
• surface postcrosslinkers which contain additional polymerizable ethylenically unsaturated groups, as described in DE 37 13 601 A1
• the amount of surface postcrosslinker is preferably 0.001 to 2 wt .-%, more preferably 0.02 to 1 wt .-%, most preferably 0.05 to 0.2 wt .-%, each based on the polymer particles.
• polyvalent cations are applied to the particle surface in addition to the surface postcrosslinkers before, during or after the surface postcrosslinking.
• the polyvalent cations which can be used in the process according to the invention are, for example, divalent cations, such as the cations of zinc, magnesium, calcium, iron and strontium, trivalent cations, such as the cations of aluminum, iron, chromium, rare earths and manganese, tetravalent cations, such as the cations of Titanium and zirconium.
• divalent cations such as the cations of zinc, magnesium, calcium, iron and strontium
• trivalent cations such as the cations of aluminum, iron, chromium, rare earths and manganese
• tetravalent cations such as the cations of Titanium and zirconium.
• hydroxide, chloride, bromide, sulfate, hydrogensulfate, carbonate, hydrogencarbonate, nitrate, phosphate, hydrogenphosphate, dihydrogenphosphate and carboxylate, such as acetate, citrate and lactate are possible.
• salts with different counterions for example basic aluminum salts, such as aluminum monoacetate or aluminum monolactate.
• Aluminum sulfate, aluminum monoacetate and aluminum lactate are preferred.
• polyamines can also be used as polyvalent cations.
• the amount of polyvalent cation used is, for example, 0.001 to 1.5% by weight, preferably 0.005 to 1% by weight, particularly preferably 0.02 to 0.8% by weight. in each case based on the polymer particles.
• the surface postcrosslinking is usually carried out by coating the dried polymer particles with an aqueous solution of the surface postcrosslinker, for example by spraying the solution onto the polymer particles.
• the polymer particles coated with surface postcrosslinkers are subsequently deagglomerated and thermally surface postcrosslinked.
• the coating with the solution of the surface postcrosslinker is preferably carried out in mixers with moving mixing tools, such as screw mixers, disk mixers and paddle mixers. Suitable mixers are, for example, Horizontal Pflugschar® mixers (Gebr.
• Deagglomeration is also preferably performed in mixers with agitated mixing tools, such as screw mixers, disc mixers, and paddle mixers.
• agitated mixing tools such as screw mixers, disc mixers, and paddle mixers.
• Advantageous suitable mixers are, for example, horizontal Pflugschar® mixers (Gebr. Lödige Maschinenbau GmbH, Paderborn, Germany), Vrieco-Nauta Continuous Mixer (Hosokawa Micron BV; Doetinchem; Netherlands) and Processall Mixmill Mixer (Processall Incorporated; Cincinnati, USA).
• the water-absorbing polymer particles When coated with aqueous solutions, the water-absorbing polymer particles tend to clump together (agglomerate). In a vertical mixer, the water-absorbing polymer particles have a lower tendency to agglomerate during coating. The coating is therefore advantageously carried out in a vertical mixer. Furthermore, the resulting agglomerates can be redissolved by moderate mechanical stress. For this purpose, horizontal mixers are better suited due to the higher residence time. It is therefore also possible to perform coating and deagglomeration in a horizontal mixer.
• the distinction between horizontal mixer and vertical mixer is made by the storage of the mixing shaft, i. Horizontal mixers have a horizontally mounted mixing shaft and vertical mixers have a vertically mounted mixing shaft.
• the surface postcrosslinkers are used as aqueous solution. The penetration depth of the surface postcrosslinker into the polymer particles can be adjusted by the content of nonaqueous solvent or total solvent amount.
• the solvent it is advantageous to add a surfactant. As a result, the wetting behavior is improved and the tendency to clog is reduced.
• solvent mixtures for example isopropanol / water, 1,3-propanediol / water and propylene glycol / water, the mixing mass ratio preferably being from 20:80 to 40:60.
• the water-absorbing polymer particles are dried and / or heated prior to the thermal surface postcrosslinking. This advantageously already takes place during deagglomeration, preferably in contact dryers, such as paddle dryers and disk dryers.
• Suitable contact dryers are, for example, Hosokawa Bepex® Horizontal Paddle Dryer (Hosokawa Micron GmbH, Leingart, Germany), Hosokawa Bepex® Disc Dryer (Hosokawa Micron GmbH, Leingart, Germany), Holo-Flite® dryers (Metso Minerals Industries, Inc., Danville, USA ) and Nara Paddle Dryer (NARA Machinery Europe, Frechen, Germany).
• Coating with the aqueous solution increases the water content of the water-absorbing polymer particles. This relatively high water content precludes thermal surface postcrosslinking at higher temperatures. Therefore, it is advantageous to dry the water-absorbing polymer particles before the thermal surface postcrosslinking and to heat to the reaction temperature.
• the water content of the coated and deagglomerated polymer particles before thermal surface postcrosslinking is preferably less than 5% by weight, more preferably less than 2% by weight, most preferably less than 1% by weight.
• the optionally dried and / or heated polymer particles are transferred to the thermal surface postcrosslinking in a drum heat exchanger with inverse screw helix.
• a drum heat exchanger with inverse spiral screw is a heated, horizontal and rotatable drum, wherein in the inner wall of the drum an inverse screw spiral for positive conveyance of the product is integrated.
• the drum can be heated indirectly via the drum wall.
• the heating takes place electrically or with steam.
• Various wall temperatures can be set in the drum via several independent heating zones along the drum longitudinal axis.
• a direct product heating in the interior of the drum heat exchanger by installing a burner or the introduction of hot flue gases is usually not used here.
• radial mixing elements e.g., in the form of cam lobes or flights
• radial mixing elements may be installed on the circumference of the drum inner wall in addition to the inverse screw flight. These support the radial mixing of the product within the separate zones, which form due to the inverse screw flight and are used in particular when working with large drum diameter and high filling height or height of the screw flight.
• Figure 1 shows a drum heat exchanger with indirect heating
• FIG. 2 shows a section through the drum heat exchanger
• heating zone 1 (electric or steam)
• heating zone 2 (electric or steam)
• Heating zone 3 (electric or steam)
• the drum preferably has a length of from 3 to 30 m, more preferably from 5 to 25 m, most preferably from 7 to 20 m.
• the inner diameter of the drum is preferably from 0.3 to 10 m, more preferably from 0.4 to 5 m, most preferably from 1 to 3 m.
• the screw helix has a height of preferably 0.05 to 1 m, more preferably from 0.1 to 0.8 m, most preferably from 0.2 to 0.6 m.
• the pitch of the screw flight is preferably 0.05 to 0.5 m, more preferably from 0.1 m to 0.4 m, most preferably from 0.15 to 0.3 m.
• the height of the screw helix is the distance between the drum inner wall and the highest point of the helix in the direction of the axis of rotation.
• the pitch of the helix is the displacement of the helix in the longitudinal direction in one full turn.
• the peripheral speed of the drum is preferably from 0.02 to 0.5 m / s, more preferably from 0.03 to 0.3 m / s, most preferably from 0.04 to 0.15 m / s.
• the maximum filling height of the drum heat exchanger with inverse spiral screw is the filling level at which barely any product reaches the next coil through the height of the screw spiral.
• Figure 2 shows the maximum fill level. This filling level corresponds to a filling level of 100%.
• the inclination of the longitudinal axis of the drum heat exchanger with inverse helix relative to the horizontal is preferably +10 to -10 °, more preferably +5 to - 5 °, most preferably +1 to -1 °, the positive sign having a rising tendency in the conveying direction and the negative sign mean a slope sloping in the conveying direction.
• the water-absorbing polymer particles are cooled after the thermal surface postcrosslinking.
• the cooling is preferably carried out in contact coolers, such as blade coolers and disc coolers.
• Suitable coolers are, for example, Hosokawa Bepex® Horizontal Paddle Cooler (Hoorkawa Micron GmbH, Leingart, Germany), Hosokawa Bepex® Disc Cooler (Hosokawa Micron GmbH, Leingart, Germany), Holo-Flite® coolers (Metso Minerals Industries, Inc., Danville ; USA) and Nara Paddle Cooler (NARA Machinery Europe; Frechen; Germany).
• the water-absorbing polymer particles to 20 to 150 ° C, preferably 30 to 120 ° C, more preferably 40 to 100 ° C, most preferably 50 to 80 ° C, cooled. Subsequently, the surface-postcrosslinked polymer particles can be classified again, wherein too small and / or too large polymer particles are separated and recycled to the process.
• the surface-postcrosslinked polymer particles can be coated or post-moistened for further improvement of the properties.
• the post-wetting is preferably carried out at 30 to 80 ° C, more preferably at 35 to 70 ° C, most preferably at 40 to 60 ° C. If the temperatures are too low, the water-absorbing polymer particles tend to clump together and at higher temperatures water is already noticeably evaporating.
• the amount of water used for the rewetting is preferably from 1 to 10 wt .-%, particularly preferably from 2 to 8 wt .-%, most preferably from 3 to 5 wt .-%.
• the post-moistening in the cooler is advantageously carried out after the thermal surface post-crosslinking.
• Suitable coatings for improving the swelling rate and the permeability of the swollen gel bed (SFC) are, for example, inorganic inert substances, such as water-insoluble metal salts, organic polymers, cationic polymers, and di- or polyvalent metal cations.
• Suitable coatings for dust binding are, for example, polyols.
• Suitable coatings against the unwanted caking tendency of the polymer particles are, for example, zinc oxide, zinc carbonate, fumed silica, such as Aerosil® 200, and surfactants, such as Span® 20.
• the water-absorbing polymer particles produced by the process according to the invention have a moisture content of preferably 0 to 15 wt .-%, particularly preferably 0.2 to 10 wt .-%, most preferably 0.5 to 8 wt .-%, wherein the Moisture content according to the EDANA recommended test method No. WSP 230.2-05 "Mass Loss Upon Heating".
• the water-absorbing polymer particles produced by the process according to the invention have a proportion of particles having a particle size of from 300 to 600 ⁇ m, preferably at least 30% by weight, more preferably at least 50% by weight, very particularly preferably at least 70% by weight.
• the water-absorbing polymer particles produced according to the process of the invention have a centrifuge retention capacity (CRC) of typically at least 15 g / g, preferably at least 20 g / g, preferably at least 22 g / g, more preferably at least 24 g / g, most preferably at least 26 g / g, on.
• the centrifuge retention capacity (CRC) of the water-absorbing polymer particles is usually less than 60 g / g.
• Centrifuge Retention Capacity (CRC) is determined according to the EDANA recommended Test Method No. WSP 241.2-05 "Fluid Retention Capacity in Saline, After Centrifugation".
• the water-absorbing polymer particles produced by the process according to the invention have an absorption under a pressure of 49.2 g / cm 2 of typically at least 15 g / g, preferably at least 20 g / g, preferably at least 22 g / g, particularly preferably at least 24 g / g, most preferably at least 26 g / g, on.
• the absorption under a pressure of 49.2 g / cm 2 of the water-absorbing polymer particles is usually less than 35 g / g.
• the absorption under a pressure of 49.2 g / cm 2 is determined analogously to the EDANA recommended test method no. WSP 242.2-05 "Absorption Under Pressure, Gravimetric Determination", wherein instead of a pressure of 21, 0 g / cm 2 a Pressure of 49.2 g / cm 2 is set.
• the residual monomer content of the water-absorbing polymer particles is determined according to the EDANA-recommended test method WSP No. 210.2-05 "Residual Monomers”.
• Centrifuge Retention Capacity is determined according to the EDANA recommended Test Method No. WSP 241.2-05 "Fluid Retention Capacity in Saline, After Centrifugation".
• the content of extractable constituents of the water-absorbing polymer particles is determined according to the EDANA-recommended test method No. WSP 270.2-05 "Extractable".
• the permeability (SFC) of a swollen gel layer under pressure of 0.3 psi (2070 Pa) is determined, as described in EP 0 640 330 A1, as gel layer permeability of a swollen gel layer of water-absorbing polymer particles.
• the punch (39) consists of the same plastic material as the cylinder (37) and now over the entire Support surface evenly distributed 21 holes of equal size. The procedure and evaluation of the measurement remains unchanged compared to EP 0 640 330 A1. The flow is automatically detected.
• SFC The permeability
• a base polymer was prepared in a DC spray dryer with integrated fluidized bed (27) and external fluidized bed (29) according to Figure 1 of WO 201 1/026876 A1.
• the cylindrical part of the spray dryer (5) had a height of 22 m and a diameter of 3.4 m.
• the internal fluidized bed (IFB) had a diameter of 3.0 m and a weir height of 0.4 m.
• the external fluidized bed (EFB) had a length of 3.0 m, a width of 0.65 m and a weir height of 0.5 m.
• the drying gas was supplied via a gas distributor (3) at the tip of the spray dryer.
• the drying gas was partially passed through a fabric filter (9) and a wash column (12) returned (cycle gas).
• the drying gas used was nitrogen having an oxygen content of 1 to 5% by volume.
• the plant was purged with nitrogen to an oxygen content of less than 5% by volume.
• the amount of gas in the cylindrical part of the spray dryer (5) was 16,170 kg / h.
• the pressure inside the spray dryer was 4 mbar below the ambient pressure.
• the exit temperature of the spray dryer was measured at three points at the lower end of the cylindrical part as described in FIG. 3 of WO 201 1/026876 A1.
• the three individual measurements (47) were used to calculate the mean starting temperature.
• the cycle gas was warmed up and the metering of the monomer solution was started. From this point on the average starting temperature was regulated by adjusting the gas inlet temperature via the heat exchanger (20) to 1 16 ° C.
• the product was collected in the internal fluidized bed (27) up to the height of the weir. Drying gas at a temperature of 132 ° C. was fed via the line (25) to the internal fluidized bed (27). The amount of gas in the internal fluidized bed (27) was 10,000 kg / h.
• the exhaust gas of the spray dryer was fed via the fabric filter (9) of the wash column (12).
• the liquid level within the wash column (12) was kept constant by pumping off excess liquid.
• the liquid within the scrubbing column (12) was cooled by means of the heat exchanger (13) and countercurrently conveyed through the nozzles (1 1) so that the temperature inside the scrubbing column (12) was regulated to 45 ° C.
• the liquid in the wash column (12) was rendered alkaline by the addition of sodium hydroxide solution.
• the exhaust gas of the scrubbing column was divided into lines (1) and (25).
• the temperatures were controlled by means of the heat exchangers (20) and (22).
• the heated drying gas was fed to the spray dryer via the gas distributor (3).
• the gas distributor consisted of a number of plates and, depending on the amount of gas, had a pressure drop of 5 to 10 mbar.
• the product was transferred from the internal fluidized bed (27) by means of the rotary valve (28) in the external fluidized bed (29). Via the line (40) the external fluidized bed (29) drying gas at a temperature of 60 ° C was supplied. Drying gas was air. The amount of gas in the external fluidized bed (29) was 2,500 kg / h.
• the product was conveyed from the external fluidized bed (29) by means of the rotary valve (32) on the sieve (33).
• the sieve (33) particles having a particle size of greater than 3,000 ⁇ m (agglomerates) were separated off.
• acrylic acid was first mixed with triply ethoxylated glycerol intriacrylate (crosslinker) and then with 37.3% strength by weight aqueous sodium acrylate.
• crosslinker triply ethoxylated glycerol intriacrylate
• the temperature of the monomer solution kept at 10 ° C.
• Umpump Vietnamese was behind the pump, a filter with a mesh size of 150 ⁇ .
• the initiators were added via lines (43) and (44) before the static mixers (41) and (42) to the monomer solution.
• a Vertropferenheit consisted as described in Figure 5 of WO 201 1/026876 A1 from an outer tube (51) and a Vertropferkassette (53).
• the dropper cassette (53) was connected to an inner tube (52).
• the inner tube (52) had a PTFE gasket (54) at the end and could be pulled out for service during operation.
• FIG. 6 of WO 201 1/026876 A1 describes the internal structure of the dropletizer cassette.
• the temperature of the dropletizer cassette (61) was controlled to 25 ° C by means of cooling water in the channels (59).
• the dropper cassette had 256 holes.
• the holes had a diameter of 2.5 mm at the entrance and at the exit a diameter of 170 ⁇ .
• the holes were arranged in 6 rows, with the distance between the holes of a row 12.38 mm and the order of the rows was 14 mm.
• the dropletizer cassette (61) had a dead-space free flow channel (60) for homogeneously distributing the premixed monomer solution and the initiator solutions to the two dropletizer plates (57).
• the holes were distributed on two dropletizer plates (57), each with 128 holes, i. the two drip plates (57) each had three rows of holes.
• the two Vertropferplatten (57) had an angled arrangement with an angle of 3 °.
• Each dropletizer plate (57) was made of stainless steel (# 1 .4571 material) and had a length of 530 mm, a width of 76 mm and a thickness of 15 mm.
• the feed to the spray dryer contained 10.25% by weight of acrylic acid, 32.75% by weight of sodium acrylate, 0.035% by weight of trisubstituted ethoxylated glycerol triacrylate (about 85% by weight).
• the resulting base polymer had a bulk density of 74.4 g / 100 ml, an average particle diameter of 392 ⁇ m, a particle diameter distribution width of 0.48, an average sphericity of 0.91, a centrifuge retention capacity (CRC) of 21.4 g / g , an absorption under a pressure k of 49.2 g / cm 3 (AUL0.7 psi) of 17.9 g / g and a residual monomer content of 2.75% by weight.
• CRC centrifuge retention capacity
• the product temperature was raised to 185 ° C and the reaction mixture held for a total of 150 minutes at that temperature and a shaft speed of 60 revolutions per minute. After different times, samples were taken. All samples were sieved prior to analysis to a particle size of 150 to 850 ⁇ .
• the product temperature was raised to 180 ° C. and the reaction mixture was kept at this temperature for a total of 120 minutes at a shaft speed of 60 revolutions per minute. After different times, samples were taken. All samples were sieved prior to analysis to a particle size of 150 to 850 ⁇ .
• Examples 2 and 3 show the considerable influence of the residence time on the result of the surface postcrosslinking.
• the permeability (SFC) goes through a pronounced maximum.
• the residence time distribution was determined in an apparatus hitherto used for thermal surface postcrosslinking.
• the speed was 37 rpm and the weir height 87% (at 100%, the weir is at the same height as the upper edge of the blade).
• the throughput of Hysorb® M7055 was 60 kg / h.
• At the entrance of the paddle dryer specially colored particles of the product Hysorb® M7055 (BASF SE, Ludwigshafen, Germany) were added for this experiment and the time distribution of the colored particles at the outlet of the paddle dryer was analyzed.
• the frequency distribution has been determined by integra- tion determines the cumulative frequency distributions ⁇ , ⁇ 5 ⁇ and T90 ( ⁇ corresponds to 10% of the cumulative frequency distribution, etc.).
• the mean residence time ( ⁇ 5 ⁇ ) was 42 minutes.
• the mean residence time ( ⁇ 5 ⁇ ) was 34 minutes.
• Example 4 The procedure was as in Example 4. The degree of filling was reduced by reducing the weir height from 87 to 62%.
• the mean residence time ( ⁇ 5 ⁇ ) was 31 minutes.
• Example 4 The procedure was as in Example 4. Instead of a paddle dryer, a drum heat exchanger with inverse spiral screw was used.
• the drum heat exchanger had an inner diameter of 700 mm, a length of 6,000 mm and 60 helical turns.
• the spiral turns had a height of 100 mm and a pitch of 100 mm.
• the speed was 0.9 rpm, the throughput was 108 kg / h and the filling level was 100% of the height of the screw helix.
• the mean residence time ( ⁇ 5 ⁇ ) was 52 minutes.
• Example 7 The procedure was as in Example 7. The speed was increased from 0.9 rpm to 2.5 rpm. The throughput was increased from 108 kg / h to 224 kg / h. The fill level was 72% of the helix height. The following widths of the frequency distribution were determined:
• the mean residence time ( ⁇ 5 ⁇ ) was 24 minutes.
• Examples 4 to 8 prove the much closer residence time distribution of the drum heat exchanger with inverse spiral screw.

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