Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—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 a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/04—Acids; Metal salts or ammonium salts thereof
  • C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof

Definitions

• the present invention relates to a process for the preparation of water-absorbing polymer particles by polymerization of an aqueous monomer solution or suspension having at least one ethylenically unsaturated, acid group-carrying monomer which is at least partially neutralized by adding a neutralizing agent, wherein the neutralizing agent is filtered before addition ,
• concentrated sodium hydroxide solution is preferably used to neutralize the acrylic acid.
• This can be contaminated with traces of iron or iron compounds, with an average solution having impurities in the range of 3-10 ppm. Since even such small amounts of iron compounds can influence the polymerization process and have a negative effect on the product quality, as already described in the monograph "Modern Superabsorbent Polymer Technology", FL Buchholz and AT Graham, Wiley-VCH, 1998, pages 71-72 , it is necessary to remove or at least reduce these impurities.
• DE 10217096 describes the use of an electrolysis bath for purifying alkaline solutions.
• the metal content (without alkaline earth and alkali metals) of the purified solutions is a maximum of 10 ppb.
• EP 1 808 412 describes the purification of aqueous alkaline solutions, in particular for use in printed circuit board production by activated carbon fibers.
• the activated carbon fibers are packed in a column and the solution to be purified is passed over it.
• the cleaning effect depends on the fiber used, however, the content of metal compounds in the alkaline solution can be reduced to a few ppb.
• the object has been achieved by a process for preparing water-absorbing polymer particles by polymerization of a monomer solution or suspension comprising a) at least one ethylenically unsaturated, acid group-carrying monomer which may be at least partially neutralized by adding at least one neutralizing agent,
• the neutralizing agent may be, for example, an aqueous solution of at least one alkali metal hydroxide, wherein the alkali metal hydroxide is preferably potassium hydroxide, more preferably sodium hydroxide.
• the filtration can be done by means of a paper filter.
• a suitable paper filter has a cellulose content of at least 90%, preferably of at least 95% and more preferably of at least 97%.
• viscose fibers preferably modal fibers or lyocell fibers.
• modal fibers preferably modal fibers or lyocell fibers.
• Both the surface filtration and the depth filtration or a combination of both methods are suitable for use in the method according to the invention.
• Filters suitable for depth filtration are particularly suitable, such as, for example, filter layers, filter cartridges, filter cartridges, filter mats made of the abovementioned materials, with cellulose being particularly suitable.
• filters with a mesh size of 1 -6 ⁇ preferably 1, 4 to 4 ⁇ , more preferably 1, 5 to 2 ⁇ .
• the removal of iron compounds can be improved by adding a filtration aid to the neutralizing agent prior to filtration.
• Suitable filtration aids are, for example, carbonate compounds, MgCl 3 and / or CaCO 3 being particularly suitable.
• the preparation of the water-absorbing polymer particles is explained in more detail below:
• 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, i. the solubility in water at 23 ° C. is typically at least 1 g / 100 g of water, preferably at least 5 g / 100 g of 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 the monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%. It is very particularly preferred that the monomer a) is neutralized to at least 90 mol% of acrylic acid and / or the monomer a) to 30 to 80 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, more preferably at least 30 ppm by weight, in particular by 50% by weight ppm, hydroquinone halide, 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.
• 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 can be radically copolymerized into the polymer chain, and functional groups which 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 A
• 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 0.3 to 0.6 wt .-%, each based on Monomer a).
• the centrifuge retention capacity decreases and the absorbance under a pressure of 21.0 g / cm 2 (AUL 0.3 psi) goes through a maximum.
• initiators c) it is possible to use all compounds which generate free 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.
• thermal initiators and redox initiators are used, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid.
• the reducing component used 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.
• Such mixtures are available as Brüggolite® FF6 and Brüggolite® FF7 (Brüggemann Chemicals; Heilbronn; DE).
• 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 ie monomer solutions with excess monomer a), for example sodium acrylate.
• 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 aqueous polymer gel formed in the polymerization of an aqueous monomer solution or suspension is continuously comminuted by, for example, counter-rotating stirring shafts, as described in WO 2001/038402 A1.
• the comminuted aqueous polymer gel obtained by means of a kneader may additionally be extruded.
• the polymerization on the belt is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928.
• an aqueous polymer gel is formed, which must be comminuted in a further process step, for example in an extruder or kneader.
• the acid groups of the resulting aqueous polymer gels are at least 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.
• the degree of neutralization is preferably from 20 to 85 mol%, more preferably from 30 to 80 mol%, most preferably from 40 to 75 mol%, whereby the usual neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal bicarbonates and their mixtures.
• 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 aqueous polymer gel is at least partially neutralized after the polymerization, the aqueous 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 use of sodium hydroxide solution as a neutralizing agent is preferred.
• the filters preferably have a mesh size of 1 to 6 ⁇ preferably 1, 4 to 4 ⁇ , more preferably 1, 5 to 2 ⁇ on.
• the filters are preferably paper filters.
• Suitable paper filters have a cellulose content of at least 90%, preferably at least 95% and particularly preferably at least 97%.
• viscose fibers preferably modal fibers or lyocell fibers.
• modal fibers preferably modal fibers or lyocell fibers.
• filters may have any suitable shape. They can be designed, for example, as pleated filters, round filters, filter fleece, band filters, pressure belt filters, filter bags, filter mats, filter plates, filter layers, bag filters, filter cartridges or candle filters.
• Filters suitable for depth filtration are particularly suitable, such as, for example, filter layers, filter cartridges, filter cartridges, filter mats made of the abovementioned materials, with cellulose being particularly suitable. Filter plates are used for example in filter presses.
• the iron content of the neutralizing agent can thus be reduced depending on the mesh size of the filter paper used.
• the iron content of the neutralizing agent can be reduced to at most 5 ppm, preferably at most 2 ppm, more preferably below 2 ppm, so that the neutralizing agent is suitable for use in the production of water-absorbent polymers of high product quality.
• the filter material has an influence on the reduction of the iron content of the neutralizing agent.
• Particularly preferred for reducing the iron content is cellulose but also related compounds, such as viscose are well suited. It is assumed that filter materials with a high content of OH groups on the surface are generally suitable for use in the process according to the invention.
• the filtration effect can also be improved if a filtration aid is added to the neutralizing agent before filtration. This may be at least one carbonate compound, with MgCO 3 and CaCO 3 or mixtures of both carbonates being preferred as filtration aids.
• the iron content of the neutralizing agent can be reduced to a maximum of 2 ppm, preferably at most 1 ppm, more preferably below 1 ppm after filtration.
• filter cascades made up of a plurality of filters located one behind the other, with the mesh size of the filter paper decreasing from the present filter to the cascade in the cascade.
• filter cascades can also be combined with the use of filtration aids.
• the aqueous polymer gel is then dried with a circulating air belt dryer until the residual moisture content is preferably 0.5 to 15% by weight, particularly preferably 1 to 10% by weight, very particularly preferably 2 to 8% by weight, the residual moisture content being is determined by the EDANA (European Disposables and Nonwovens Association) recommended test method no. WSP 230.2-5 "Moisture Content". If the residual 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 residual moisture content is too low, the dried polymer gel is too brittle and in the subsequent comminution steps undesirably large quantities of polymer particles with too small particle size ("fines") are produced.
• the solids content of the gel before drying is preferably from 25 to 90% by weight, particularly preferably from 35 to 70% by weight. %, most preferably from 40 to 60 wt .-%.
• the dried polymer gel is then 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.
• 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 test method No. WSP 220.2-5 "Particle Size Distribution" recommended by the EDANA (European Disposables and Nonwovens Association), in which the mass fractions of the sieve fractions are cumulatively applied and the average particle size is determined graphically.
• the mean particle size here is the value of the mesh size, which results for accumulated 50 wt .-%.
• the proportion of particles having a particle size of at least 150 ⁇ m is preferably at least 90% by weight, more preferably at least 95% by weight, very particularly preferably at least 98% by weight.
• Too small polymer particles are therefore usually separated and recycled to the process. This is preferably done before, during or immediately after the polymerization, i. before drying the aqueous polymer gel.
• the too small polymer particles can be moistened with water and / or aqueous surfactant before or during the recycling.
• the too small polymer particles are preferably added during the last third of the polymerization.
• the polymer particles which are too small are added very early, for example already to the monomer solution, this lowers the centrifuge retention capacity (CRC) of the water-absorbing polymer particles obtained. However, this can be compensated for example by adjusting the amount of crosslinker b). If 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 excessively small polymer particles are difficult to incorporate into the resulting aqueous polymer gel. Insufficiently incorporated too small polymer particles, however, dissolve again during the grinding of the dried polymer gel, are therefore separated again during classification and increase the amount of recycled too small polymer particles.
• CRC centrifuge retention capacity
• the proportion of particles having a particle size of at most 850 ⁇ m is preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 98% by weight.
• 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 polymer gel.
• the sized polymer particles can be surface postcrosslinked to further improve the properties.
• Suitable surface postcrosslinkers are compounds which contain groups which can form covalent bonds with at least two carboxylate groups of the polymer particles.
• 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.
• 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.
• 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.
• chloride bromide, sulfate, hydrogen sulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate, dihydrogen phosphate and carboxylate, such as acetate, citrate and lactate, are possible.
• Aluminum sulfate 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 so that a solution of the surface postcrosslinker is sprayed onto the dried polymer particles. Following spraying, the surface postcrosslinker coated polymer particles are thermally dried, the surface postcrosslinking reaction taking place both during and after drying.
• the spraying of a solution of the surface postcrosslinker is preferably carried out 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.
• horizontal mixers such as paddle mixers
• vertical mixers very particularly preferred are vertical mixers.
• horizontal mixer and vertical mixer via the storage of the mixing shaft ie horizontal mixer have a horizontally mounted mixing shaft and vertical mixer have a vertically mounted mixing shaft.
• Suitable mixers are, for example, Horizontal Pflugschar® mixers (Gebr.
• the surface postcrosslinkers are typically used as an 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.
• solvent 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 thermal drying is preferably carried out in contact dryers, particularly preferably felt dryers, most preferably disk dryers.
• Suitable dryers are, for example, Hosokawa Bepex® Horizontal Paddle Dryer (Hosokawa Micron GmbH;
• Paddle Dryer NARA Machinery Europe, Frechen, Germany.
• fluidized bed dryers can also be used.
• the drying can take place in the mixer itself, by heating the jacket or blowing hot air.
• a downstream dryer such as a hopper dryer, a rotary kiln or a heatable screw. Particularly advantageous is mixed and dried in a fluidized bed dryer.
• Preferred drying temperatures are in the range 100 to 250 ° C, preferably 120 to 220 ° C, more preferably 130 to 210 ° C, most preferably 150 to 200 ° 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, and usually at most 60 minutes.
• the water-absorbing polymer particles are cooled after the thermal drying.
• the cooling is very particularly preferably in contact coolers, particularly preferably blade coolers
• Disc coolers performed. Suitable coolers are, for example, Hosokawa Bepex® Horizontal Paddle Coolers (Hosokawa Micron GmbH, Leingart, Germany), Hosokawa Bepex® Disc Coolers (Hosokawa Micron GmbH, Leingart, Germany), Holo-Flite® coolers (Metso Minerals Industries, Inc., Danville, USA ) and Nara Paddle Cooler (NARA Machinery Europe, Frechen, Germany).
• fluidized bed coolers can also be used.
• 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 rehydrated to further improve 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 agglomerate and water evaporates appreciably at higher temperatures.
• 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-humidification is carried out in the cooler after the thermal drying.
• Suitable coatings for improving the swelling rate and the permeability 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, 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 test method No. WSP 230.2-5 "Moisture Content" recommended by the EDANA (European Disposables and Nonwovens Association).
• the water-absorbing polymer particles according to the invention have a centrifuge retention capacity (CRC), a swelling rate (FSR) and a permeability (SFC) which are the conditions
• the water-absorbing polymer particles prepared according to the method 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, up.
• the centrifuge retention capacity (CRC) of the water-absorbing polymer particles is usually less than 60 g / g.
• the centrifuge retention capacity (CRC) is determined according to the test method No. WSP 241.2-5 "Centrifuge Retention Capacity" recommended by the EDANA (European Disposables and Nonwovens Association).
• the water-absorbing polymer particles according to the invention have a permeability (SFC) of at least 80 ⁇ 10 -7 cm 3 s / g, preferably of at least 100 ⁇ 10 -7 cm 3 s / g and very particularly preferably of at least 130 ⁇ 10 -7 cm 3
• the permeability is usually less than 500 ⁇ 10 -7 cm 3 s / g.
• the permeability (SFC) of a swollen gel layer under pressure load of 0.3 psi (2070 Pa) is, as described in EP 0 640 330 A1, determined as a gel-layer permeability of a swollen gel layer of water-absorbing polymer particles, wherein the in aforementioned patent application on page 19 and in Figure 8 was modified to the effect that the glass frit (40) is no longer used, the punch (39) of the same plastic material as the cylinder (37) and now evenly distributed over the entire support surface 21 equal holes contains. The procedure and evaluation of the measurement remains unchanged compared to EP 0 640 330 A1. The flow is automatically detected.
• SFC fluid transfer
• the iron content was 1.6 ppm.
• Example 2 100 ml of the 3.4 ppm iron-contaminated sodium hydroxide solution (50% by weight NaOH) were filtered at room temperature through a Blauband filter from Macherey-Nagel (MN 640d, diameter 150 mm, retention range 2-4 ⁇ ).
• MN 640d Macherey-Nagel
• the iron content of the supernatant was 0.7 ppm.
• Each 20 ml of a 50% sodium hydroxide solution A (50 wt.% NaOH) was filtered under a nitrogen atmosphere to avoid reaction with the CO2 of the air. At this time, the 50% sodium hydroxide solution was dropped through a funnel-shaped folded filter paper which was in a funnel overlaid with nitrogen gas in a 25 ml receiver, which was also overlaid with nitrogen gas.
• the iron content of the 50% sodium hydroxide solution was determined by inductively coupled plasma mass spectroscopy (ICP-MS) before and after filtration.
• the iron content of the 50% sodium hydroxide solution was determined by inductively coupled plasma mass spectroscopy (ICP-MS) before and after filtration.
• the iron content of the sodium hydroxide solution did not change as a result of the filtration by means of a glass fiber filter which, with a pore size of 1.6 ⁇ m, had a slightly finer pore size than the fine-pored paper filter in these test series with 2 ⁇ m.
• the result is shown in Table 1.
• the experimental procedure is the same as in experiments 4 to 8. Deviating from this, a 50% sodium hydroxide solution B (50% by weight NaOH) was used which was stored for 14 days (overlaid with nitrogen gas) over heavily rusted iron sheets. The undissolved iron fractions were filtered after storage through a glass fiber filter (Schleicher Schull GF8) to a visually clear solution. This clarified solution was used for the experiments (Comparison B and Experiments 9-13). The respective filtrations were carried out with 20 ml of 50% sodium hydroxide solution B under a nitrogen atmosphere in order to avoid a reaction with the CO2 of the air. The iron content of the 50% sodium hydroxide solution was determined by inductively coupled plasma mass spectroscopy (ICP-MS) before and after filtration.
• ICP-MS inductively coupled plasma mass spectroscopy
• the iron content of the sodium hydroxide solution did not change as a result of the filtration by means of a glass fiber filter which, with a pore size of 1.6 ⁇ , was slightly more porous than the fine-pored paper filter in these test series with 2 ⁇ .

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=47631439

Family Applications (1)

Country Status (4)

Families Citing this family (1)

Citations (44)

Family Cites Families (8)

• 2013
  • 2013-02-01 WO PCT/EP2013/052003 patent/WO2013117496A1/de active Application Filing
  • 2013-02-01 CN CN201380008334.7A patent/CN104093753A/zh active Pending
  • 2013-02-01 EP EP13702226.5A patent/EP2812365A1/de not_active Withdrawn
  • 2013-02-01 JP JP2014556013A patent/JP2015506406A/ja not_active Withdrawn

Patent Citations (45)

Non-Patent Citations (3)

Also Published As

Similar Documents

Legal Events