Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
  • C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
  • C02F5/10—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances

Definitions

• the invention relates to the use of copolymers of maleic acid as an inhibitor for calcium oxalate coatings.
• Calciu oxalate deposits affect processes for the production of pulp and paper and occur in particular, but not exclusively, in the bleaching stages of kraft pulp and wood pulping plants. Calcium oxalate coatings are also known from the sulfite pulp process.
• the problem of calcium oxalate is exacerbated, particularly in modern plants with a reduced amount of waste water in combination with oxygen-containing bleaches.
• the calcium oxalate deposits occur, for example, on the inner walls of pipes, on filter fabrics, on pumps, on heat exchanger surfaces e.g. from evaporator systems or in the digester.
• the deposits which often appear in combination with other inorganic deposits such as calcium carbonate or calcium sulfate, reduce the heat exchange and lead to constrictions or blockages. If parts of the covering become detached, there can be massive disruptions in the subsequent processes, e.g. of papermaking come.
• oxalic acid occurs in wood in concentrations of approx. 0.1 - 0.5 kg / t. Furthermore, oxalic acid is produced during the bleaching process by oxidative degradation of lignin and of mono-, oligo- or polysaccharides, e.g. Xylan.
• Calcium ions are brought into the system through the wood.
• Typical calcium ion concentrations in wood are e.g. 0.2-1.0 kg / t.
• Calcium oxalate deposits have formed, they are extremely difficult to remove due to their low solubility. In practice, this is usually accomplished by mechanical removal, acid washing or using complexing agents in high concentrations. Disadvantages of these processes are the loss of production, damage to the systems due to corrosion and mechanical stress, and high costs for the feed materials. Calcium oxalate deposits also appear in evaporator systems in sugar production.
• JP-A-04/018184 describes the use of copolymers of maleic acidic with lower alkyl acrylates and vinyl acetate known as a coating inhibitor in papermaking.
• US-A-4575425 describes a method for inhibiting calcium oxalate in an aqueous system, a mixture of (a) a phosphate or phosphonate and (b) an anionic water-soluble polyelectrolyte being used as the inhibitor.
• the polyelectrolytes used preferably have molecular weights in the range from 1,000 to 5,000.
• EP-A-0276464 discloses the use of copolymers of maleic acid as water treatment agents for reducing scale deposition and water hardness excretion in water-bearing systems, for example maleic acid copolymers with K values of 7 to 20 (determined in 5% strength aqueous solution) 25 ° C and pH 7) used in the desalination of sea and brackish water by distillation or membrane processes and in the evaporation of sugar juices.
• EP-A-0350985 recommends the use of a copolymer of maleic anhydride and diallyldimethylammonium chloride for controlling scale deposits.
• US Pat. No. 5,320,757 describes a method for inhibiting calcium oxalate at a pH of at least 7.0 using a hydrolyzed terpolymer of maleic acid / ethyl acrylate / vinyl acetate.
• the US-A-5409571 relates to a scale inhibitor for use in the Kraft pulp production, which is a terpolymer of Ma ⁇ leinklare / comprising acrylic acid and units of the hypophosphorous acid.
• WO-A-96 29291 From WO-A-96 29291 a blend of (a) is an anionic organic polymer, (b) a polyphosphate, and (c) an organic phosphonic acid ⁇ rule for the inhibition of inorganic coatings known.
• a terpolymer of maleic acid / acrylic acid / acrylamidopropanesulfonic acid is used as a scale inhibitor in the pulp production.
• JP-A-10/180293 discloses the use of polymers containing carboxyl groups, such as, for example, polyacrylic acid, as a scale inhibitor for calcium oxalate in the production of cellulose.
• US-A-5755971 relates to a method for preventing calcium oxalate deposits using ignin sulfonate and phosphate.
• the coating inhibitors known from the prior art are in need of improvement in terms of their effectiveness because, despite their use, the formation of calcium oxalate coatings cannot be prevented sufficiently.
• the situation is particularly unsatisfactory in aqueous systems with pH values below 7. In this pH range, massive formation of calcium oxalate deposits is frequently observed without this being able to be controlled with the products known from the prior art.
• the object of the invention is therefore to provide substances which are more effective than known inhibitors for inhibiting calcium oxalate deposits.
• copolymers contain polymerized and have a weight average molecular weight of 25,000 to 250,000, as an inhibitor for calcium oxalate deposits.
• copolymers are preferred which
• copolymerized ⁇ are sate whose weight average molecular weight is from 25,000 to 150,000.
• Methacrylic acid fumaric acid, itaconic acid, mesaconic acid, methylene malonic acid, citraconic acid, maleic acid monomethyl ester, acrylonitrile, methacrylonitrile, styrene, Acrylic acid methyl ester, acrylic acid ethyl ester, methacrylic acid methyl ester, methacrylic acid ethyl ester, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, alkyl polyethylene glycol (meth) acrylate,
• Vinylsulfonic acid allylsulfonic acid, methallylsulfonic acid, styrene sulfonic acid, 2-acrylamidomethyl propane sulfonic acid,
• N-vinylpyrrolidone N-vinylcaprolactam
• N-vinylformamide vinylphosphonic acid
• N-vinylimidazole N-vinyl-2-methylimidazoline
• diallyldimethylammonium chloride N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, vinylphosphonic acid, N-vinylimidazole, N-vinyl-2-methylimidazoline, diallyldimethylammonium chloride,
• the basic monomers can also be used in quaternized form.
• Monomer units (c) can optionally by reacting copolymers of (a) maleic acid or maleic anhydride and
• alkyl polyethylene glycol with an average degree of ethoxylation of 2 to 45 alkyl polyethylene glycol block polypropylene glycols, such as e.g. Methyl polyethylene glycol block polypropylene glycol with up to 40 ethylene oxide units and up to 5 propylene oxide units
• copolymers of maleic acid and acrylic acid are modified with monomer units (c), these units are preferably derived from methacrylic acid, vinyl sulfonate, methylpolyethylene glycol methacrylates from methylpolyethylene glycols with molecular weights from 200 to 2500 or mixtures thereof.
• monomeric groups (a), (b) and optionally containing acid groups are preferably derived from methacrylic acid, vinyl sulfonate, methylpolyethylene glycol methacrylates from methylpolyethylene glycols with molecular weights from 200 to 2500 or mixtures thereof.
• the copolymers can be partially or completely neutralized with alkali metal bases or ammonia.
• a partial Wise neutralization means that the degree of neutralization of the acid groups in the copolymerizations is, for example, 1 to 99, preferably 30 to 75%.
• the polymers used according to the invention are prepared by radical polymerization reaction of the ethylenically unsaturated monomers (a), (b) and, if appropriate, (c).
• the monomers to be polymerized can be placed in the reaction vessel or added to the reaction batch in portions or, preferably, continuously.
• the main amount and in particular at least 90% by weight of the maleic acid or the maleic anhydride are preferably introduced into the reaction vessel and the main amounts of the monomers (b) and optionally (c) are added continuously to the reaction mixture.
• the polymerization can be carried out as a substance - polymerization, solution polymerization or, if the monomers are not very soluble in the reaction medium, as an emulsion, dispersion or suspension polymerization.
• the reaction is preferably carried out as solution polymerization in water.
• the monomers containing acid groups can be present in their acid form, but also partially or completely neutralized as a salt.
• sodium hydroxide solution, potassium hydroxide solution, ammonia, triethanolamine or diethanolamine can be used as the neutralizing agent; sodium hydroxide solution is preferred.
• Such methods are known, cf. for example in EP-A-075820, EP-A-076992, EP-A-0103254, EP-A-0106111, EP-A-0106991 and WO-A-97 31036.
• Water is preferably used as the reaction medium, but mixtures of water with up to 80% by weight, based on the mixture, of a solvent containing OH groups can also be used.
• solvents are, for example, from the group C1-C4-alkanols, C2-C10-alkylene glycols, in which the alkylene chain can be interrupted by one or more, non-adjacent oxygen atoms, and ether of the C2-C10-alkylene glycols with C1-C4-alkanols.
• suitable solvents containing OH groups are methanol, ethanol, isopropanol, n-butanol, ethylene glycol, diethylene glycol, methyl diglycol, dipropylene glycol, butyl glycol, butyl diglycol, triethylene glycol, the methyl ethers of the glycols mentioned and oligomers of ethylene oxide with 4 to 6 ethylene oxide units, oligomers Propylene oxide with 3 to 6 propylene oxide units as well as polyethylene glycol-polypropylene glycol - cooligomers.
• the aqueous reaction medium can also other water-miscible solvents such as acetone, methyl contain ethyl ketone, tetrahydrofuran, dioxane, N-methylpyrrolidone, dimethylformamide etc.
• reaction medium cyclic ethers such as tetrahydrofuran or dioxane, ketones and acetone, methyl ethyl ketone, cyclohexanone, esters of aliphatic carboxylic acids with C1-C4-alkanols, such as ethyl acetate or n-butyl acetate, aromatic hydrocarbons such as toluene, xylenes, Cumene, chlorobenzene, ethylbenzene, technical mixtures of alkyl aromatics, cyclohexane and technical aliphatic mixtures.
• cyclic ethers such as tetrahydrofuran or dioxane, ketones and acetone, methyl ethyl ketone, cyclohexanone, esters of aliphatic carboxylic acids with C1-C4-alkanols, such as ethyl acetate or n-butyl acetate
• the polymerization can also be carried out as an emulsion or suspension polymerization if the monomers are poorly soluble in the reaction medium.
• Such polymerization processes are known to the person skilled in the art and can be carried out in the usual manner for the preparation of the polymers according to the invention.
• the polymers according to the invention are prepared by radical aqueous emulsion polymerization, it is advisable to add surfactants or protective colloids to the reaction medium.
• surfactants or protective colloids can be found, for example, in M Houben Weyl, Methods of Organic Chemistry, Volume XIV / 1 Macromolecular Substances, Georg Thieme Verlag, Stuttgart 1961, p. 411 ff.
• the polymerization initiators used for the radical polymerization are preferably soluble in the reaction medium. They are used in amounts of up to 30% by weight, preferably 0.05 to 15% by weight, particularly preferably 1.5 to 10% by weight, based on the monomers used in the polymerization. It follows ⁇ m polymerization a water-containing solvent-m or water, preferably water-soluble Polymerisati - onsinitiatoren such as sodium persulfate, Kaliumper ⁇ sulfate, Ammoniumpersulf t, hydrogen peroxide, tert.
• a water-containing solvent-m or water preferably water-soluble Polymerisati - onsinitiatoren such as sodium persulfate, Kaliumper ⁇ sulfate, Ammoniumpersulf t, hydrogen peroxide, tert.
• redox initiator systems can also be used as polymerization initiators.
• Such redox imiator systems contain at least one compound containing peroxides in combination with a redox co-initiator, for example reducing sulfur compounds, for example bisulfites, sulfites, thiosulfates, dthionites or tetrathionates of alkali metals and ammonium compounds, sodium hydroxymethanesulfate dihydrate and / or thiourea.
• reducing sulfur compounds for example bisulfites, sulfites, thiosulfates, dthionites or tetrathionates of alkali metals and ammonium compounds, sodium hydroxymethanesulfate dihydrate and / or thiourea.
• This is how combinations of Peroxodi - Use sulfates with alkali metal or ammonium hydrogen sulfites, e.g. ammonium peroxydisulfate
• transition metal catalysts can be used, e.g. Iron, nickel, cobalt, manganese, copper, vanadium, or chromium salts, such as iron (II) sulfate, cobalt (II) chloride, nickel (II) sulfate, copper (I) chloride, manganese (II) acetate , Vanadium-III-acetate, manganese-II-chloride.
• these transition metal salts are usually used in amounts of 0.1 to 1000 ppm. So you can use combinations of hydrogen peroxide with iron (II) salts, such as 0.5 to 30% hydrogen peroxide and 0.1 to 500 ppm Mohr's salt.
• initiators such as dibenzoyl peroxide, dicyclohexyl peroxidicarbonate, dilauryl peroxide, methyl ethyl ketone peroxide, acetylacetone peroxide are preferred.
• reac ⁇ tion mixture polymerized at the lower limit of the next for the polymerization into consideration temperature range and subsequently completed at a higher temperature, it is expedient to use at least two different initiators which decompose at different temperatures, so that in each temperature interval a sufficient concentration of radicals is available.
• the polymerization reaction takes place, for example, at temperatures in the range from 30 to 300 ° C., preferably in the range from 50 to 160 ° C. and very particularly preferably in the range from 100 to 150 ° C. It is preferably carried out in the absence of oxygen, preferably in a nitrogen stream. As a rule, the polymerization is carried out at normal pressure, but the use of lower pressures or higher pressures is also possible, in particular if polymerization temperatures are used be above the boiling point of the monomers and / or
• a molecular weight regulator i.e. a conventional chain terminating substance to polymerize.
• Suitable molecular weight regulators include, for example, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, formic acid, ammonium formate, hydroxylamine and its sulfate, chloride or phosphate; SH groups - compounds containing such as thioglycolic acid, mercapto-propionic acid, mercapotethanol, mercaptopropanol, mercaptobutanol, mercatophexanol, thiomaleic acid, thiophenol, 4-tert.
• polymerization regulators are allyl alcohol, butenol, isopropanol, n-butanol, isobutanol, glycol, glycerol, pentaerythritol, hypophosphorous acid and their salts, such as e.g. Sodium hypophosphite, phosphorous acid and its salts, e.g. Sodium phosphite.
• the polymerization regulators are used in amounts of up to 20% by weight, based on the monomers. Polymerization is preferably carried out in the presence of 0.5 to 15% by weight of a polymerization regulator containing SH groups, based on the monomers.
• Crosslinked poly ⁇ merisate are either obtainable by copolymerization of said monomers with di- or multi-ethylenically unsaturated compounds, or by subsequent crosslinking of carboxyl, anhydride or hydroxyl groups in the polymer with appropriate polyfunctional compounds. If the crosslinking is carried out by means of copolymerization with polyethylenically unsaturated compounds, these are usually present in proportions of 0.01 to 20% by weight and preferably in amounts of 0.1 to 5% by weight, based on those to be polymerized Monomers.
• Suitable two or more ethylenically unsaturated compounds include: diacrylates or dimethacrylates of at least dihydric saturated alcohols, such as, for example, ethylene glycol - diacrylate, ethylene glycol dimethylacrylate, 1,2-propylene glycol - diacrylate, 1,2-propylene glycol dimethacrylate, butanediol-1, -diacrylate Butanediol-1, 4-dimethacrylate, hexanediol diacrylate, hexanediol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 3-methylpentanediol dimethacrylate, 3-methyl-pentanediol dimethacrylate; Acrylic acid and methacrylic acid esters of alcohols with more than 2 OH groups, such as, for example, trimethylolpropane methacrylate, trimethylolpropane
• Glycidyl ethers of polyhydroxy compounds or the glycidyl esters of di- or polycarboxylic acids are particularly suitable as polyfunctional, reactive crosslinking compounds which can be used for subsequent crosslinking.
• suitable crosslinking compounds include: ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, pentaerytol tolpolyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol glycidyl ether, resorcidiglycidyl ether, o-phthalate or diglycidyl ester.
• the concentration of the monomers is usually 10 to 70, preferably 20 to 60% by weight.
• phosphonates such as e.g. 2-phosphono-l, 2, 4-t ⁇ carbonsaure, Ami notri- (methylenphosphonsaure), 1-hydroxyethylene (1, 1-d phosp- honsaure), ethylenediamm-tetramethylene-phosphonic acid, hexamethylenediamm-tetramethylene-phosphonic acid and diethylenetriamine -pentarethylene-phosphonic acid,
• ammocarboxylates such as e.g. Nit ⁇ lot ⁇ essigsaure, ethylenediammetetraacetic acid, Diethylenetriam pentaessigsaure, Hydroxyethylethylenendiam t ⁇ essigsaure and Methylglycmdi acetic acid,
• water soluble polymers e.g. Homo- and copolymers of acrylic acid with a weight average molecular weight in the range from 500 to 15,000; Homo- and copolymers of sulfo-containing monomers, such as e.g. 2-Acrylam do-2-methylpropanesulfonic acid, styrene sulfonic acid or V ylsulfonic acid with a weight average molecular weight of 500 to 15,000 as well as naphthalene sulfonic acid formaldehyde polycondensates.
• water soluble polymers e.g. Homo- and copolymers of acrylic acid with a weight average molecular weight in the range from 500 to 15,000
• sulfo-containing monomers such as e.g. 2-Acrylam do-2-methylpropanesulfonic acid, styrene sulfonic acid or V ylsulfonic acid with a weight average molecular weight of
• components (a) to (d) can optionally be used with further formulation components such as surfactants, dispersants, defoamers, corrosion inhibitors, oxygen scavengers, biocides, alkalis and / or bleaches.
• further formulation components such as surfactants, dispersants, defoamers, corrosion inhibitors, oxygen scavengers, biocides, alkalis and / or bleaches.
• the copolymers described above are used to inhibit calcium oxalate deposits. They prevent or reduce the formation of calcium oxalate deposits or the boiler separation of water-bearing systems which contain calcium ions and oxalic acid or water-soluble salts of oxalic acid.
• the copolymers are used, for example, in amounts of 1 to 2000, preferably 2 to 200 ppm, based on the aqueous system. If there are failures, there are easily washed-out excretions that are remotely distributed. This keeps the inner walls of heat exchangers, pipes or pump components free of deposits and at the same time reduces their tendency to corrode.
• the water-carrying systems are e.g. around open or closed cooling circuits, for example of power plants or chemical plants such as reactors, distillation apparatus and heat exchangers.
• the copolymers to be used according to the invention can prevent damage to the membranes by crystallizing calcium oxalate. They are also used as deposit inhibitors when evaporating sugar juices from sugar cane or from sugar beet.
• the copolymers to be used according to the invention in pulp and paper production because - as has already been explained in relation to the prior art - a considerable amount of calcium ions and oxalic acid are introduced into the aqueous system with the paper stock.
• copolymers may be used for example in the entire pH range, which is in practice of In ⁇ teresse, eg in the range 2 to 12 to the inhibitors so far used have inhibitors of the invention at pH values below of 8, preferably below 7, a sufficient effect.
• aqueous solution containing 114.5 ppm calcium chloride dihydrate, 105 ppm sodium oxalate and 10 ppm of the polymer to be tested is adjusted to the desired pH with 2% hydrochloric acid or 2% sodium hydroxide solution.
• the solution is heated in a round-bottom flask with a reflux condenser to 70 ° C. with stirring. After 3 hours the solution is cooled, 150 ml removed and filtered.
• the calcium ion concentration in the filtrate c (Ca) [ppm] is determined using Determined atomic absorption spectroscopy.
• the polymer-specific inhibition IP is calculated using the following formula:
• IP [%] (c (Ca) x 100) / 31.2
• VSNa sodium methyl sulfonate
• MPEGMA methyl polyethylene glycol methacrylate with a molecular weight of 1000.

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• 1999
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