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
  • C08J3/12—Powdering or granulating
• • 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 methods for the pneumatic conveying of water-absorbing polymer particles, wherein the compressor used for pneumatic conveying has a steep characteristic.
• Water-absorbing polymers are, in particular, polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose or starch ethers, crosslinked carboxymethylcellulose, partially crosslinked polyalkylene oxide or natural products swellable in aqueous liquids, such as guar derivatives.
• Such polymers are used as aqueous solution-absorbing products for the production of diapers, tampons, sanitary towels and other hygiene articles, but also as water-retaining agents in agricultural horticulture.
• Water-absorbing polymers typically have a centrifuge retention capacity of 25 to 60 g / g, preferably of at least 30 g / g, preferably of at least 32 g / g, more preferably of at least 34 g / g, most preferably of at least 35 g /G.
• Centrifuge retention capacity is determined according to the EDANA (European Disposables and Nonwovens Association) recommended test method no. 441.2-02 "Centrifuge retention capacity".
• water-absorbing polymers are described, for example, in "Modern Superabsorbent Polymer Technology", F.L. Buchholz and AT. Graham, Wiley-VCH, 1998, pages 69 to 17.
• water-absorbing polymer particles are transported by means of pneumatic conveying systems. The inevitably occurring mechanical stress leads to undesirable abrasion. Therefore, low transport speeds and thus reduced mechanical loads should be strived for.
• Dense flow conveying (plug conveying, impulse delivery) with high pressure loss.
• the pressure delivery can work at slower delivery speeds than the suction, since the pressure reserves in the overpressure are greater than in a vacuum, and there increases with increasing pressure counselgas Why that propels the product increases.
• Too low conveying speeds in the field of strands promotion are problematic, since in the unstable region between the dense phase promotion and Strandscine no stable promotion is possible. Rather, the mechanical stresses that occur can lead to serious damage to the conveyor system, up to the tearing of the delivery lines from the brackets.
• the object of the present invention was to provide an improved process for the pneumatic transport of water-absorbing polymer particles, in particular at low conveying speeds safe operation is possible.
• the problem was solved by a method for pneumatic conveying of water-absorbing polymer particles, characterized in that the volume flow of the compressor used for pneumatic conveying at pressure rise of idle to 800 mbar falls by less than 50% and the initial gas velocity in promoting a Froude number of 10 to 18 corresponds.
• the volume flow decrease of the compressors used is preferably less than 30%, most preferably less than 20%, most preferably less than 10%.
• the volume flow decrease can either be measured or determined on the basis of the compressor characteristic curve.
• the compressors used in the process according to the invention have a steep characteristic.
• Preferred compressors are forced compressors.
• a particularly suitable forced-circulation compressor with a steep characteristic curve is a rotary piston blower.
• the optimum gas start speed for pneumatic delivery depends on the diameter of the delivery line. This dependency is best described by the Froude number:
• the Froude number in the pneumatic conveying according to the invention is preferably from 10 to 16, more preferably from 1 to 15, most preferably from 12 to 14.
• the randomlygutbeladung the pneumatic conveying is preferably from 0.5 to 20 kg / kg, more preferably from 1 to 10 kg / kg, most preferably from 2 to 8 kg / kg, wherein the strategicallygutbeladung is the quotient of strategicallygutmassenstrom and gas mass flow.
• the diameter of the pipeline, in which the pneumatic conveying is carried out is preferably from 3 to 30 cm, more preferably from 4 to 25 cm, most preferably from 5 to 20 cm. Too low pipe diameters lead to a higher mechanical load due to the pneumatic conveying and thus promote the undesirable abrasion. Too large pipe diameters allow one as well unwanted settling of the water-absorbing polymer particles in the delivery line.
• a pipeline in a pneumatic Conveyor system is the section between the feed device for the water-absorbing polymer particles and the receiving container, ie the area in which the water-absorbing polymer particles are transported in the gas stream.
• the water content of the water-absorbing polymer particles is preferably less than 10 wt .-%, more preferably less than 5 wt .-%, most preferably from 1 to 5 wt .-%, wherein the water content according to the EDANA (European Disposables and Nonwovens Association) recommended test method No. 430.2-02 "Moisture content" is determined.
• the mechanical stability of the water-absorbing polymer particles decreases with the water content, i. the unwanted abrasion increases. Too high water contents during the pneumatic conveying can lead to the plastic deformation of the polymer particles (angel hair formation) or to blockages.
• the water-absorbing polymer particles preferably have at least 90% by weight, a particle diameter of less than 1000 ⁇ m, particularly preferably at least 95% by weight, a particle diameter of less than 900 ⁇ m, very particularly preferably at least 98% by weight Particle diameter of less than 800 microns, on.
• the mechanical load during pneumatic conveying is reduced to such an extent that the proportion of polymer particles having a particle diameter of less than 150 ⁇ m by pneumatic conveying is preferably less than 1% by weight, particularly preferably less than 0 , 7 wt .-%, most preferably by less than 0.5 wt .-%, each based on the total amount of polymer particles, is increased and the permeability of the polymer particles by the pneumatic conveying preferably by less than 5x10 "7 cm 3 s / g, more preferably less than 4x10 "7 cm 3 s / g, most preferably less than 3x10" 7 cm 3 sec / g, decreases.
• the water-absorbing polymer particles which can be used in the process according to the invention can be obtained by polymerization of a monomer solution containing
• Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid. Particularly preferred monomers are acrylic acid and methacrylic acid. Very particular preference is given to acrylic 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%.
• Preferred hydroquinone half ethers are hydroquinone monomethyl ether (MEHQ) and / or tocopherols.
• Tocopherol is understood as meaning compounds of the following formula
• R 1 is hydrogen or methyl
• R 2 is hydrogen or methyl
• R 3 is hydrogen or methyl
• R 4 is hydrogen or an acid radical having 1 to 20 carbon atoms.
• R 4 Preferred radicals for R 4 are acetyl, ascorbyl, succinyl, nicotinyl and other physiologically acceptable carboxylic acids.
• the carboxylic acids can be mono-, di- or tricarboxylic acids.
• R 4 is particularly preferably hydrogen or acetyl. Especially preferred is RRR-alpha-tocopherol.
• the monomer solution preferably contains at most 130 ppm by weight, more preferably at most 70 ppm by weight, preferably at least 10 ppm by weight, more preferably at least 30 ppm by weight, especially preferably around 50 ppm by weight, hydroquinone halide, in each case based on acrylic acid, wherein acrylic acid salts are taken into account mathematically as acrylic acid with.
• acrylic acid salts are taken into account mathematically as acrylic acid with.
• an acrylic acid having a corresponding content of hydroquinone half-ether can be used to prepare the monomer solution.
• the water-absorbing polymers are crosslinked, i. the polymerization is carried out in the presence of compounds having at least two polymerisable groups which can be radically copolymerized into the polymer network.
• Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallyloxyethane, as described in EP-A-0 530 438, di- and triacrylates, as in EP-A-0 547 847, EP-A-0 559 476, EP-A-0 632 068, WO-A-93/21237, WO-A-03/104299, WO-A-03/104300, WO-A-03/104301 and DE-A-10331450, mixed acrylates which contain, in addition to acrylate groups contain ethylenically unsaturated groups, as described in DE-A-103 31 4
• Suitable crosslinkers b) are especially N, N'-methylenebisacrylamide and N 1 N'-methylenebismethacrylamide, esters of unsaturated mono- or polycarboxylic acids lyolen of Po, such as diacrylate or triacrylate, for example butanediol or ethylene glycol and also trimethylolpropane triacrylate and allyl compounds, such as allyl (meth) acrylate, triallyl cyanurate, maleic acid diallyl esters, polyallyl esters, tetraallyloxyethane, triallylamine, tetraallylethylenediamine, allyl esters of phosphoric acid and vinylphosphonic acid derivatives, as described, for example, in EP-A-0 343 427.
• esters of unsaturated mono- or polycarboxylic acids lyolen of Po such as diacrylate or triacrylate, for example butanediol or ethylene glycol and also trimethylolpropane
• crosslinkers b) are pentaerythritol di-, pentaerythritol tri- and pentaerythritol tetraallyl ethers, polyethylene glycol diallyl ether, ethylene glycol diallyl ether, glycerol di- and
• Glyceryl triallyl ether polyallyl ether based on sorbitol, and ethoxylated variants thereof.
• Useful in the process according to the invention are di (meth) acrylates of polyethylene glycols, where the polyethylene glycol used has a molecular weight between 300 and 1000.
• crosslinkers b) are di- and triacrylates of 3 to 20 times ethoxylated glycerol, 3 to 20 times ethoxylated trimethylolpropane, 3 to 20 times ethoxylated trimethylolethane, in particular di- and triacrylates of 2 to 6-times ethoxylated glycerol or trimethylolpropane, the 3-fold propoxylated glycerol or trimethylolpropane, and the 3-times mixed ethoxylated or propoxylated glycerol or trimethylolpropane, the 15-times ethoxylated glycerol or trimethylolpropane, and at least 40-times ethoxylated glycerol, trimethylolpropane lethanes or trimethylolpropane.
• Very particularly preferred crosslinkers b) are the polyethoxylated and / or propoxylated glycerols esterified with acrylic acid or methacrylic acid to form di- or triacrylates, as described, for example, in DE-A-103 19 462.
• 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 glycerin.
• the amount of crosslinker b) is preferably 0.01 to 1 wt .-%, particularly preferably 0.05 to 0.5 wt .-%, most preferably 0.1 to 0.3 wt .-%, respectively based on the monomer a).
• Examples of ethylenically unsaturated monomers c) copolymerizable with the monomers a) are acrylamide, methacrylamide, crotonamide, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminobutyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoneopentyl acrylate and dimethylaminoneopentyl methacrylate.
• water-soluble polymers d) it is possible to use polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, polyglycols or polyacrylic acids, preferably polyvinyl alcohol and starch.
• Suitable reactors are kneading reactors or belt reactors.
• the polymer gel formed in the polymerization of an aqueous monomer solution is comminuted continuously by, for example, counter-rotating stirring shafts, as described in WO-A-
• the hydrogel After leaving the polymerization reactor, the hydrogel is advantageously stored even at a higher temperature, preferably at least 50 ° C., more preferably at least 70 ° C., very preferably at least 80 ° C., and preferably less than 100 ° C., for example in isolated containers. By storage, usually 2 to 12 hours, the monomer conversion is further increased.
• the acid groups of the hydrogels obtained are usually partially neutralized, preferably from 25 to 95 mol%, preferably from 50 to 80 mol%, particularly preferably from 60 to 75 mol%, the usual neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides , Alkali metal carbonates or alkali metal hydrogencarbonates and mixtures thereof.
• the usual neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides , Alkali metal carbonates or alkali metal hydrogencarbonates and mixtures thereof.
• alkali metal salts it is also possible to use ammonium salts.
• Sodium and potassium are considered
• Alkali metals are particularly preferred, but very particularly preferred are sodium hydroxide, sodium carbonate or sodium bicarbonate and mixtures thereof.
• 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, as a melt, or preferably as a solid.
• sodium hydroxide with a water content well below 50 wt .-% may be present as a waxy mass with a melting point above 23 ° C. In this case, a dosage as general cargo or melt at elevated temperature is possible.
• the hydrogel stage it is also possible to carry out the neutralization after the polymerization at the hydrogel stage. Furthermore, it is possible to neutralize up to 40 mol%, preferably 10 to 30 mol%, particularly preferably 15 to 25 mol%, of the acid groups prior to the polymerization by adding a part of the neutralizing agent to the monomer solution and the desired final degree of neutralization is adjusted only after the polymerization at the level of the hydrogel. If the hydrogel is at least partially neutralized after the polymerization, the hydrogel is preferably comminuted mechanically, for example by means of a meat grinder, wherein the neutralizing agent can be sprayed, sprinkled or poured on and then thoroughly mixed. For this purpose, the gel mass obtained can be further gewolfft for homogenization.
• the hydrogel is then preferably dried with a belt dryer until the residual moisture content is preferably below 15% by weight, in particular below 10% by weight, the water content being determined in accordance with the test method No. 430.2- recommended by EDANA (European Disposables and Nonwovens Association). 02 "Moisture content" is determined.
• a fluidized bed dryer or a heated ploughshare mixer can be used for drying but also a fluidized bed dryer or a heated ploughshare mixer.
• the dryer temperature must be optimized, the air supply and removal must be controlled, and it is in any case to ensure adequate ventilation. The drying is naturally simpler and the product is the whiter, if the solids content of the gel is as high as possible.
• the solids content of the gel before drying is therefore preferably between 30 and 80% by weight.
• Particularly advantageous is the ventilation of the dryer with nitrogen or other non-oxidizing inert gas.
• sufficient ventilation and removal of the water vapor also leads to an acceptable product.
• Advantageous in terms of color and product quality is usually the shortest possible drying time.
• the dried hydrogel is thereafter ground and classified, wherein for grinding usually one- or multi-stage roller mills, preferably two- or three-stage roller mills, pin mills, hammer mills or vibratory mills can be used.
• Suitable postcrosslinkers e) for this purpose are compounds which contain at least two groups which can form covalent bonds with the carboxylate groups of the polymers.
• Suitable compounds are, for example, alkoxysilyl compounds, polyaziridines, polyamines, polyamidoamines, di- or polyglycidyl compounds, as described in EP-AO 083 022, EP-A-543 303 and EP-A-937 736, polyhydric alcohols, as in DE-C No. 2,314,019, DE-C-35 23 617 and EP-A-450 922, or ⁇ -hydroxyalkylamides as described in DE-A-102 04 938 and US Pat. No.
• 6,239,230 are also suitable.
• compounds having mixed functionality such as glycidol, 3-ethyl-3-oxetanemethanol (trimethylolpropane oxetane), as described in EP-A-1 199 327, aminoethanol, diethanolamine, triethanolamine or compounds which form a further functionality after the first reaction such as ethylene oxide, propylene oxide, isobutylene oxide, aziridine, azetidine or oxetane.
• cyclic carbonates in DE-A-198 07 502 2-oxazolidone and its derivatives, such as N- (2-hydroxyethyl) -2-oxazolidone, in DE-A-198 07 992 Bis- and poly-2-oxazolidinone, in DE-A-198 54 573 2-oxotetrahydro-1,3-oxazine and its derivatives, in DE-A-198 54 574 N-acyl-2-oxazolidone, in DE-A Cyclic ureas, in DE-A-103 34 584 bicyclic amide acetals, in EP-A-1 199 327 oxetanes and cyclic ureas and in WO-A-03/031482 morpholine-2,3-dione and its derivatives as suitable postcrosslinkers e) are described.
• Preferred postcrosslinkers e) are oxazolidone and its derivatives, in particular N- (2-hydroxye
• the amount of postcrosslinker e) is preferably 0.01 to 1 wt .-%, particularly preferably 0.05 to 0.5 wt .-%, most preferably 0.1 to 0.2 wt .-%, each based on the polymer.
• the postcrosslinking is usually carried out so that a solution of the crosslinker e) is sprayed onto the hydrogel or the dry polymer particles. Subsequent to the spraying, it is thermally dried, whereby the postcrosslinking reaction can take place both before and during the drying.
• the spraying of a solution of the crosslinker is preferably carried out in mixers with moving mixing tools, such as screw mixers, paddle mixers, disk mixers, plowshare mixers and paddle mixers.
• moving mixing tools such as screw mixers, paddle mixers, disk mixers, plowshare mixers and paddle mixers.
• Vertical mixers are particularly preferred, plowshare mixers and paddle mixers are very particularly preferred.
• Suitable mixers are, for example, Lödige® mixers, Bepex® mixers, Nauta® mixers, Processall® mixers and Schugi® mixers.
• the thermal drying is preferably carried out in contact dryers, more preferably paddle dryers, very particularly preferably disk dryers.
• Suitable dryers are, for example, Bepex® T rockner and Nara® T rockner.
• fluidized bed dryers can also be used.
• the drying can take place in the mixer itself, by heating the jacket or blowing hot air. Also suitable is a downstream dryer, such as a hopper dryer, a rotary kiln or a heatable screw. However, it is also possible, for example, to use an azeotropic distillation as the drying process.
• Preferred drying temperatures are in the range 170 to 250 ° C, preferably 180 to 220 ° C, and particularly preferably 190 to 210 ° C.
• the preferred residence time at this temperature in the reaction mixer or dryer is preferably at least 10 minutes, more preferably at least 20 minutes, most preferably at least 30 minutes.
• the water-absorbing polymer particles can additionally be aftertreated with at least one polyvalent cation f).
• Suitable cations f) are, for example, divalent cations, such as the cations of zinc, magnesium, calcium 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.
• trivalent cations such as the cations of aluminum, iron, chromium, rare earths and manganese
• tetravalent cations such as the cations of titanium and zirconium.
• Aluminum sulfate is preferred.
• the multivalent cation f) is used as an aqueous solution.
• concentration of the polyvalent cation f) in the aqueous solution is for example 0.1 to 12 wt .-%, preferably 0.5 to 8 wt .-%, particularly preferably 1, 5 to 4 wt .-%.
• the amount of polyvalent cation f) is preferably 0.001 to 0.25 wt .-%, more preferably 0.005 to 0.2 wt .-%, most preferably 0.01 to 0.15 wt .-%, each based on the Polymer.
• the polyvalent cations f) are preferably applied during the postcrosslinking, wherein postcrosslinker e) and cation f) are preferably metered in via separate solutions.
• the process according to the invention enables the reliable transport of water-absorbing polymer particles in the area of the strands promotion.
• the inventive method is extremely reliable and allows the pneumatic conveying at significantly lower conveyor speeds. With conventional compressors with a flat characteristic, such as fans, such a high level of operational reliability can not be achieved.
• Measurements should be taken at an ambient temperature of 23 ⁇ 2 ° C and a relative humidity of 50 ⁇ 10%, unless otherwise specified.
• the water-absorbing polymer particles are thoroughly mixed before the measurement.
• the absorption under pressure is determined according to the test method No. 442.2-02 "Absorption under pressure" recommended by the EDANA (European Disposables and Nonwovens Association). Permeability (SFC Saline Flow Conductivity)
• the permeability of a swollen gel layer under pressure of 0.3 psi (2070 Pa) is determined as described in EP-A-0 640 330, as gel-layer permeability of a quenched gel layer of superabsorbent polymer, which in the aforementioned patent application Page 19 and described in Figure 8 apparatus was modified to the effect that the glass frit (40) is no longer used, the punch (39) made of the same plastic material as the cylinder (37) and now evenly distributed over the entire support surface contains 21 equal holes , The procedure and evaluation of the measurement remain unchanged compared to EP-A-0 640 330. The flow is detected automatically.
• the permeability (SFC) is calculated as follows:
• LO is the thickness of the gel layer in cm
• d the density of the NaCl solution in g / cm 3
• A is the area of the gel layer in cm 2
• WP is the hydrostatic pressure over the gel layer in dynes / cm 2 .
• Polyethylene glycol 400 diacrylate (diacrylate of a polyethylene glycol having an average molecular weight of 400 g / mol) is used as the polyethylenically unsaturated crosslinker.
• the amount used was 2 kg per ton of monomer solution.
• the throughput of the monomer solution was 18 t / h.
• the individual components are continuously metered into a 6.3 ml 3 volume List Contikneter reactor (List, Arisdorf, Switzerland) in the following quantities:
• the reaction solution had a temperature of 23.5 ° C. at the inlet.
• the reactor was operated at a shaft speed of 38rpm.
• the residence time of the reaction mixture in the reactor was 15 minutes.
• the aqueous polymer gel was applied to a belt dryer. In total, 18.3 t / h of aqueous polymer gel having a water content of 55% by weight were dried. The gel was applied from a height of 30 cm by means of a swivel tape on the conveyor belt of the dryer. The height of the gel layer was about 10 cm.
• the belt speed of the dryer belt was 0.02 m / s and the residence time on the dryer belt was about 37 minutes.
• the dried hydrogel was ground and sieved. The fraction with the particle size 150 to 800 microns was postcrosslinked.
• the postcrosslinker solution was sprayed onto the polymer particles in a Schugi® mixer.
• the postcrosslinker solution was a 1.2% strength by weight solution of ethylene glycol diglycidyl ether in propylene glycol / water weight ratio 1: 2). Based on the polymer particles 5 wt .-% solution were sprayed. It was then dried for 60 minutes at 150 ° C. and postcrosslinked.
• the delivery line used was a smooth aluminum pipeline with a length of 153 m and an internal diameter of 108.5 mm.
• the delivery line consisted of two horizontal and two vertical sections, the sections being connected by arches. The vertical elevation totaled 10 m.
• the delivery rate was 6,400 kg / h of water-absorbing polymer particles, the delivery air volume was 1,050 kg / h and the gas velocity was 17.8 m / s at the beginning of the delivery line and 26 m / s at the delivery line end.
• the pressure in the delivery line was from +500 to 0 mbar, based on the ambient pressure.
• the transported load was 6.2 kg / kg and the Froude number at the beginning of the feed was 16.8.
• the water-absorbing polymer particles had g, an absorption under pressure of 24.9 g /, and a permeability of 40.1 x 10 "7 cm 3 s / g.
• the water-absorbing polymer particles After the pneumatic transportation, the water-absorbing polymer particles had g, an absorption under pressure of 22.4 g / and a permeability of 30,4x10 "7 cm 3 s / g.

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  • 2007-03-06 US US12/281,535 patent/US8591152B2/en not_active Expired - Fee Related
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