EP1986960A2

EP1986960A2 - Control of the thickening of silicate-containing aqueous systems

Info

Publication number: EP1986960A2
Application number: EP07726257A
Authority: EP
Inventors: Alexander Göthlich; Stephan Nied; Karl-Heinz Buechner; Frank Klippel; Gunnar Schornick
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2006-02-08
Filing date: 2007-01-30
Publication date: 2008-11-05
Also published as: CN101379000A; JP2009525858A; CN101379000B; US8002119B2; WO2007090757A3; WO2007090757A2; JP5174680B2; US20090025896A1; WO2007090757A8; CA2639923A1

Abstract

The invention relates to a method for controlling the thickening of aqueous, silicate-containing systems, characterized in that at least one copolymer having an average molecular weight (Mw) of at least 3000 g/mol and not more than 60000 g/mol is added to said aqueous system and that the copolymer is, essentially statistically, made of monoethylenically unsaturated monocarboxylic acids, monoethylenically unsaturated dicarboxylic acids and eventually ethylenically unsaturated comonomers. The method is also characterized in that the polymerization is carried out in the presence of 0.01 to 100 mol-%, in relation to the total amount of all COOH groups of the mono- and dicarboxylic acids, of at least one base for producing the copolymer, the indicated amounts in wt.-% each referring to the total amount of all used monomers.

Description

Control of the thickening of silicate-containing aqueous systems

Description:

The present invention relates to a process for controlling the thickening of aqueous systems containing silicates by means of at least one copolymer. The invention further relates to thickened aqueous systems containing copolymers as well as the uses of the thickened aqueous systems. Further embodiments of the present invention can be taken from the claims, the description and the examples. It is understood that the features mentioned above and those yet to be explained of the subject matter according to the invention can be used not only in the particular concretely specified combination but also in other combinations without departing from the scope of the invention.

Many technical processes involve the concentration of dissolved ingredients in aqueous systems. This concentration is called thickening. Frequently, the efficient and safe operation of technical systems is only guaranteed if the thickening can be controlled in a predefined area. The aqueous system, for example, cooling water, is often used multiple times. For this purpose, measures must be taken to ensure stable operation of the plants, with the highest possible circulation. The control of the thickening is usually done by a combination of technical and chemical measures.

A technical measure to avoid excessive thickening is the addition of water into the thickened aqueous system. The nachgespeiste water is called additional water. Due to an often occurring, permanent tendency to thickening and the therefore necessary supply of make-up water, the thickening in the aqueous system is continuously increased by ingredients contained in the make-up water. From the thickened, up to the technically possible limit aufkon- centered aqueous system is discarded a sufficient amount and replaced by non-thickened additional water until the technically maximum permissible thickening limit is reached.

This maximum permissible limit depends significantly on the type and amount of dissolved ingredients present in make-up water. Make-up water with only small amounts of dissolved ingredients usually allows a higher thickening and vice versa. As "thickening-limiting" factors occur both ingredients that can cause encrustations and deposits, as well as corrosion-inducing / corrosion-enhancing ingredients on. In this context, the carbonate hardness present in the aqueous system (deposit-forming) and the chloride content present in the aqueous system (initiation / enhancement of corrosion processes) must be mentioned.

Chemical water treatment methods for controlling the carbonate and chloride contents are known to the person skilled in the art. For example, carbonate and chloride contents can be reduced by ion exchangers. The formation of sparingly soluble precipitates of carbonate ions and polyvalent cations, such as magnesium or calcium ions, can be suppressed by anti-settling compounds. As is known to the person skilled in the art, these compounds are often polyacrylates / acrylic acids or copolymers of acrylic acid and maleic acid or complexing agents for polyvalent cations, such as EDTA. Often, however, after carbonate and chloride levels are under control, other ingredients of the water are in the focus of chemical water treatment, which can not be adequately controlled with the known compounds. Depending on the technical design of the plants, sulfates, phosphates, fluorides, oxalates and, above all, silicates can be thickening and problem-causing.

The control of thickening in aqueous systems containing silicates often proves difficult despite the known chemical water treatment methods.

Substances that prevent deposits of silicates and their production processes are known in principle.

WO 04/78662 discloses a method for preventing silicate deposits in aqueous systems with the aid of linear phosphorus-containing copolymers and oligomers having phosphorus-containing groups at the molecular ends.

EP 0 459 661 A1 discloses a process for preventing silicate deposits in aqueous systems with the aid of (meth) acrylic acid or maleic acid-containing copolymers having an average molecular weight M w (weight average) in the range from 1000 to 25,000 g / mol. As a further method to prevent silicate deposits in the cooling water is the use of polyacrylic acids or polymaleic with a Mw of 1000 to 25000 g / mol, described in conjunction with aluminum or magnesium ions. No. 3,684,779 A1 discloses copolymers of maleic acid, acrylic acid and alkenyl phosphonate monomers, as well as derivatives of the individual monomers. The molecular weights of the polymers, as determined by intrinsic viscosity measurements, are in the range of 5,000 to 50,000. The prevention of deposits of sparingly soluble salts is mentioned in the specification.

No. 5,124,047 A1 discloses a method for preventing deposits in aqueous systems with the aid of copolymers containing allyl phosphonate monomers. The copolymers have Mw values in the range of 500 to 1,000,000 g / mol.

The object of the invention was to provide an improved method for controlling the thickening of aqueous systems, in particular those containing silicates. One aim was to find such a method that allows control of thickening in a given range. A further object of the invention was to increase the stability of thickened aqueous systems against the precipitation of dissolved salts, impurities and particles, which lead to deposits and encrustations. An additional object of the invention was to allow savings of make-up water with simultaneous protection and high availability of technical systems. Further sub-tasks of the invention were the control of the biological growth in the aqueous systems, the use of as few biocides or corrosives with the same efficiency, as well as the mobilization (dispersion) of sludge and silt in the aqueous system. Furthermore, it should be achieved that the thickening can be maintained over a long service life in the technically required range. Furthermore, the control of the thickening of aqueous systems should be achieved through cost-effective and environmentally friendly measures of chemical water treatment. In particular, the copolymers used should have low residual contents of monomers.

Accordingly, a method for controlling the thickening of aqueous systems containing silicates has been found by controlling the thickening by adding at least one copolymer having a weight average molecular weight Mw of at least 3000 g / mol to at most 60,000 g / mol in a given range is possible. The copolymers used in the process according to the invention are constructed essentially statistically from the following monomeric units:

(A) from 20 to 99.98% by weight of at least one monoethylenically unsaturated monocarboxylic acid,

(B) 0.01 to 70 wt.% Of at least one monoethylenically unsaturated dicarboxylic acid of the general formula (HOOC) R ¹ C = CR 1 COOH) (I), and / or

R ¹ R ² C = C (- (CH ₂ ) _n -COOH) (COOH) (II),

or the corresponding carboxylic acid anhydrides and / or other hydrolyzable derivatives, where R ¹ and R ² independently of one another are H or a straight-chain or branched, optionally substituted alkyl radical having 1 to 20 C atoms, or in the case of (I) R ¹ and R ² together represent an optionally substituted alkylene radical having from 3 to 20 carbon atoms, and n is an integer from 0 to 5, as well as

(C) 0.01 to 40% by weight of at least one further ethylenically unsaturated comonomer other than (A) and (B),

wherein the polymerization for the preparation of the copolymer in the presence of 0.01 to 100 mol% of at least one base, based on the total amount of all

COOH groups of the mono- and dicarboxylic acids, and wherein the quantities in% by weight are based in each case on the total amount of all monomers used.

The term "polymerization" refers to the further polymerization of the monomers (A), (B) and (C) for the preparation of the copolymer.

The structure and the preparation of the copolymers which are used in the process according to the invention is described analogously to the construction and production of closely related copolymers in the as yet unpublished application DE 102004041 127.1, to which reference is expressly made.

In addition to water, the aqueous system contains at least one substance dissolved in the water. The solute or solutes may be either molecular or ionic or may be in dispersed or emulsified form. In particular, the aqueous system contains silicates. In addition to silicates, the aqueous systems frequently contain anions, for example carbonates, chlorides, sulfates, phosphates, fluorides, oxalates and polyvalent cations. The aqueous systems may contain both monovalent and polyvalent cations. The multivalent cations are usually ions of the elements: Ca, Mg, Fe, Cu, Co, Al, Zn, Mn, Ba, Sr, Mo, Ce, Zr or, in particular, ions of Ca or Mg. Mixtures of the abovementioned ions are also frequently encountered. In addition to the main constituent water, the aqueous system may also contain fractions of water-miscible organic solvents.

Depending on the conditions in the aqueous system, silicates exist as compounds of differing difficulty in their solubility. At pH values below 7, silicates tend to condense to form oligomeric or colloidal silicates. In the pH range greater than 9.5, the monomeric silication is formed. The conversion between the different forms of silicates is often kinetically inhibited and different forms of silicates can exist in parallel in aqueous solution. The various silicates can react with polyvalent cations to form sparingly soluble salts. The composition of the aqueous, silicate-containing solutions is heavily dependent on the history of the system. However, there are often side by side monomeric, oligomeric and colloidal silicates, as well as magnesium and calcium silicates and other silicate salts. These systems are referred to herein as aqueous systems containing silicates. The term "silicates" is used to represent silicates (salt or anion) or silicas.

Surprisingly, it has been found that the process of the invention with the copolymers described above, an effective control of the thickening of aqueous systems containing silicates allowed. Of course, the copolymers used in the process according to the invention, in principle also in aqueous systems which do not contain silicates, can permit effective control of the thickening.

The molecular weight Mw of the copolymers added in the process according to the invention is preferably in the range from 3000 g / mol to 60000 g / mol. It may be, for example, from 5000 g / mol to 60000 g / mol. For example, Mw can be in the range from 5000 g / mol to 55000 g / mol, for example from 7000 g / mol to 55000 g / mol. In particular, Mw may be from 7000 g / mol to 50,000 g / mol. In one of the preferred embodiments, the molecular weight is at least 10,000 g / mol to 50,000 g / mol. Mw values are determined by gel permeation chromatography (GPC). The GPC is calibrated using a widely distributed Na-PAA mixture (Na-PAA: sodium salt of polyacrylic acid), the integral molecular weight distribution curve of which is determined by SEC laser exclusion chromatography (SEC), according to the calibration procedure of MJR Cantow et al. (J. Polym. Sci., A-1, 5 (1967) 1391-1394), but without the concentration correction proposed therein. The molecular weight of the copolymers is adjusted by the skilled person according to the desired application. The copolymers used in the process according to the invention are composed of units which are derived from monoethylenically unsaturated mono- (A) and dicarboxylic acids (B) and additionally, to a lesser extent, from other monoethylenically unsaturated monomers (C).

In the context of this invention, the term "copolymer" is used differently and in the context of this invention denotes polymers having three or more different types of monomers, in particular terpolymers constructed from three monomer types which contain monoethylenically unsaturated mono- and dicarboxylic acids, and only to a minor extent, monoethylenically unsaturated monomers (C).

The monomer (A) is at least one monoethylenically unsaturated monocarboxylic acid or its hydrolyzable derivatives. It is of course also possible to use mixtures of a plurality of different ethylenically unsaturated monocarboxylic acids. Preferably, the monomer (A) is a monoethylenically unsaturated monocarboxylic acid.

Examples of suitable monoethylenically unsaturated monocarboxylic acids (A) include acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid or C1-C4-half esters of monoethylenically unsaturated dicarboxylic acids. The term Ca-Cb designates in the context of this invention chemical compounds having a certain number of carbon atoms. The number of carbon atoms can be selected from the entire range from a to b, including a and b, a is at least 1 and b is always greater than a. Further specification of the chemical compounds is made by expressions of the form Ca-Cb-V. V here stands for a chemical compound class or substituent class, for example for alkyl compounds or alkyl substituents.

Preferred monomers (A) are acrylic acid and methacrylic acid, acrylic acid being particularly preferred.

There are used from 20 to 99.98 wt.% Of the monomer (A), wherein the amount is based on the total amount of all monomers used for the polymerization. From 30 to 90% by weight of the monomer (A) is particularly preferred preferably from 30 to 85% by weight and very particularly preferably from 35 to 80% by weight.

The monomer (B) is at least one monoethylenically unsaturated dicarboxylic acid of the general formula (HOOC) R ¹ C = CR ² (COOH) (I) or R ¹ R ² C = C (- (CH ₂ ) _n -COOH ) (COOH) (II).

It is also possible to use mixtures of several different monomers (B). In the case of (I), it may be the ice and / or the trans form of the monomer. The monomers can also be used in the form of the corresponding carboxylic anhydrides or other hydrolyzable carboxylic acid derivatives. If the COOH groups are arranged in the cis position, it is particularly advantageous to use cyclic anhydrides.

R ¹ and R ² independently of one another are H or a straight-chain or branched, optionally substituted alkyl radical having 1 to 20 C atoms. It may be preferred that the radicals R ¹ and R ^{2 are} longer-chain alcohols and, for example, have ten or more carbon atoms. In another preferred embodiment, the alkyl radical is shorter chain. The alkyl radical preferably has 1 to 4 C atoms. R ¹ or R ² is particularly preferably H and / or a methyl group. The alkyl radical itself can also optionally have one or more substituents, provided that these have no negative influence on the application properties of the copolymer in the process according to the invention.

In the case of the formula (I) R ¹ and R ² may furthermore together represent an alkylene group having 3 to 20 C-atoms, which may be further substituted also optional. Preferably, the ring formed from the double bond and the alkylene radical comprises 5 or 6 carbon atoms. Examples of alkylene radicals include, in particular, a 1,3-propylene or a 1,4-butylene radical which may also have further alkyl groups as substituents. N is an integer from 0 to 5, preferably from 0 to 3 and most preferably 0 or 1.

Examples of suitable monomers (B) of the formula (I) include maleic acid, fumaric acid, methylfumaric acid, methylmaleic acid, dimethylmaleic acid and optionally the corresponding cyclic anhydrides. Examples of formula (II) include methylenemalonic acid and itaconic acid. Preference is given to using maleic acid or maleic anhydride or itaconic acid or itaconic anhydride. It can also be mixtures of Maleic acid or maleic anhydride are used with itaconic acid or itaconic anhydride.

There are used from 0.01 to 70 wt.% Of the monomers (B), wherein the amount is based on the total amount of all monomers used for the polymerization. Preference is given to using from 1 to 60% by weight of the monomer (B), more preferably from 5 to 55% by weight and very particularly preferably from 10 to 45% by weight.

In addition to the monomers (A) and (B), an ethylenically unsaturated monomer (C) or more ethylenically unsaturated monomers (C) is also used. In addition, no other monomers are used.

The monomers (C) serve to fine-tune the properties of the copolymer. Of course, several different monomers (C) can be used. They are selected by the skilled person depending on the desired properties of the copolymer. The monomers (C) are also free-radically polymerizable.

In special cases, however, small amounts of monomers with several polymerizable groups can also be used. As a result, the copolymer can be crosslinked to a small extent.

The monomers (C) may be either acidic or basic or neutral monomers or else mixtures of these monomers. They are preferably neutral monomers or acidic monomers or mixtures of neutral and acidic monomers.

Examples of suitable monomers (C) include, in particular, monomers which have phosphoric acid or phosphonic acid groups. Particular mention should be made here of vinylphosphonic acid. Furthermore, 3-butenylphosphonic acid can be used. Further preferred monomers are dimethyl vinylphosphonate, (phosphonoxyethyl) acrylate or phosphonoxyethyl methacrylate. Allylphosphonic acid may be an, although not preferred, monomer (C). Other examples include esters of phosphoric acid such as monovinyl phosphoric acid, monoesters of phosphoric acid. Mono (3-butenyl) phosphoric acid, mono- (4-vinyloxybutyl) phosphoric acid, mono (- 2-hydroxy-3-vinyloxypropyl) phosphoric acid, phosphoric mono (1-phosphonoxymethyl-2-vinyloxy-ethyl ) ester, phosphoric acid mono- (3-allyloxy-2-hydroxy-propyl) ester, or phosphoric acid mono-2- (allylox-1-phosphate) phonoxymethyl-ethyl) esters. Further examples of suitable monomers (C) are 2-hydroxy-4-vinyloxymethyl-1,3,2-dioxaphosphol or 2-hydroxy-4-allyloxymethyl-1,3,2-dioxaphosphole. It is also possible to use salts or esters or mixtures of salts and esters, in particular C 1 -C 8 -mono-, di- or trialkyl esters of phosphoric acid or phosphonic acid-containing monomers. Of course, mixtures of the above monomers can be used. Vinylphosphonic acid, its salts and / or esters are particularly preferred.

Also suitable are monomers containing sulfonic acid groups, such as methallylsulfonic acid, styrenesulfonate, allyloxybenzenesulfonic acid, or 2- (methylacryloyl) ethylsulfonic acid or its salts and / or esters. Preference is given to using allylsulfonic acid, vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid or salts and / or esters thereof.

Other acidic monomers include e.g. Maleinsäurehalbamide.

Examples of substantially neutral monomers (C) include, unless already used as monomers (A), C 1 to C 1 alkyl esters or C 1 to C ₄ hydroxyalkyl esters of (meth) acrylic acid, such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate or butanediol -1, 4-monoacrylate. Other neutral monomers are (methyl) styrene, maleimide or maleic acid N-alkylimide.

Also suitable are vinyl or allyl ethers, e.g. Methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, vinyl cyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2- (diethylamino) ethyl vinyl ether, 2- (di-n-butyl-amino) ethyl vinyl ether or methyl diglycol vinyl ether or the corresponding allyl compounds. Also used may be vinyl esters such as vinyl acetate or vinyl propionate.

Examples of basic monomers include acrylamides and alkyl-substituted acrylamides, e.g. Acrylamide, methacrylamide, N-tert-butylacrylamide or N-methyl (meth) acrylamide.

It is also possible to use alkoxylated monomers, in particular ethoxylated monomers. Especially suitable are alkoxylated monomers which are derived from acrylic acid or methacrylic acid and have the general formula (III) Ff ^μ C = CR- R ⁵ -O- R ° (IM)

in which the variables have the following meaning:

R ^{3 is} hydrogen or methyl;

R ^{4 is} - (CH ₂ ) XO-, -CH ₂ -NR ⁷ -, -CH ₂ -O-CH ₂ -CR ⁸ R ⁹ -CH ₂ -O- or -CONH-; COO

(Ester)

R ⁵ identical or different C ₂ -C ₄ -alkylene radicals which may be arranged in blocks or randomly, wherein the proportion of ethylene radicals is at least 50 mol%;

R ^{6 is} hydrogen, C 1 -C ₄ -alkyl, -SO ₃ M or -PO ₃ M ₂ ;

R ^{7 is} hydrogen or -CH ₂ -CR ¹ = CH ₂ ;

R ⁸ -O- [R ⁵ -O] _n -R ^6, wherein the groups - [R ⁵ -0] _n - ^[5 -0 R] _n - - may be different from the other enthalte- nen in formula I residues ;

R ^{7 is} hydrogen or ethyl;

M is alkali metal or hydrogen, preferably hydrogen, m is 1 to 250, preferably 2 to 50, particularly preferably 3 to 10; x O or i.

Examples of crosslinking monomers include molecules having a plurality of ethylenically unsaturated groups, for example di (meth) acrylates such as ethylene glycol di (meth) acrylate or butanediol-1,4-di (meth) acrylate or poly (meth) acrylates such as trimethylolpropane tri (meth) acrylate or else di (meth) acrylates of oligo- or polyalkylene glycols such as di-, tri- or tetraethylene glycol di (meth) acrylate. Further examples include vinyl (meth) acrylate or butanediol divinyl ether.

The person skilled in the art will make a suitable choice among the monomers (C) depending on the desired properties of the copolymer as well as the desired application of the copolymer. For example, in the process for the stabilization of thickened, aqueous systems containing silicates, the monomer (C) used is preferably phosphonic acid or phosphoric acid-containing monomers, in particular vinylphosphonic acid or its hydrolyzable derivatives.

The amount of monomers (C) is from 0.01 to 40% by weight, based on the total amount of all monomers used for the polymerization. After one of the The preferred embodiment is the amount, preferably from 0.01 to 30% by weight. In another preferred embodiment, the amount is from 0.1 to 27% and most preferably from 1 to 20% by weight. If crosslinking monomers (C) are present, their amount as a rule should not exceed 5% by weight, preferably 2% by weight, based on the total amount of all monomers used for the process.

A surprisingly high performance has been found in copolymers of acrylic acid (A), itaconic acid (B) and vinylphosphonic acid (C) or acrylic acid (A), maleic acid (B), and vinylphosphonic acid (C). Copolymers are suitable for use in the process according to the invention for example from 20 to 99.98% by weight of acrylic acid (A) and from 0.01 to 70% by weight of itaconic acid (B) and from 0.01 to 40% by weight of vinylphosphonic acid ( C). Copolymers are preferably suitable from 40 to 90% by weight of acrylic acid (A) and from 5 to 40% by weight of itaconic acid (B) and from 0.1 to 30% by weight of vinylphosphonic acid (C). Particularly preferred copolymers are from 50 to 80 wt.% Acrylic acid (A) and from 10 to 35 wt.% Itaconic acid (B) and from 0.5 to 25 wt.% Vinylphosphonic acid (C). Copolymers are very particularly preferably suitable from 55 to 75% by weight of acrylic acid (A) and from 15 to 30% by weight of itaconic acid (B) and from 1 to 20% by weight of vinylphosphonic acid (C).

Other suitable copolymers are, for example, from 20 to 99.98% by weight of acrylic acid (A) and from 0.01 to 70% by weight of maleic acid (B) and from 0.01 to 40% by weight of vinylphosphonic acid (C). Copolymers are preferably suitable from 40 to 90% by weight of acrylic acid (A) and from 5 to 40% by weight of maleic acid (B) and from 0.1 to 30% by weight of vinylphosphonic acid (C). Particularly preferred copolymers are from 50 to 80 wt.% Acrylic acid (A) and from 10 to 35 wt.% Maleic acid (B) and from 0.5 to 25 wt.% Vinylphosphonic acid (C). Copolymers are very particularly preferably suitable from 55 to 75 wt.% Acrylic acid (A) and from 15 to 30 wt.% Maleic acid (B) and from 1 to 20 wt.% Vinylphosphonic acid (C).

The total amount of monomers (A), (B) and (C) used is 100% by weight.

The copolymers used in the process according to the invention are preferably obtained from the monomers by free radical polymerization in aqueous solution. The microstructure of the copolymers is given by a statistical distribution of the monomers. The term "aqueous solution" in the context of free-radical polymerization means that the solvent or diluent used in the preparation of the copolymers comprises water as the main constituent, but also amounts of water-miscible organic solvents may be present during the polymerization This may be advantageous in order to improve the solubility of certain monomers, in particular of the monomers (C) in the reaction medium.

The solvent or diluent used in the free-radical polymerization accordingly has at least 50% by weight of water with respect to the total amount of the solvent. In addition, one or more water-miscible solvents can be used. These include, in particular, alcohols, for example monoalcohols, such as ethanol, propanol or isopropanol, dialcohols, such as glycol, diethylene glycol or polyalkylene glycols or derivatives thereof. Preferred alcohols are propanol and isopropanol. The proportion of water is preferably at least 70% by weight, more preferably at least 80% by weight, particularly preferably at least 90% by weight. Most preferably, only water is used.

The amount of the monomers used in each case is selected by the person skilled in the art such that the monomers are soluble in the particular solvent or diluent used. Accordingly, less soluble monomers are used by the skilled person only to the extent that they can be dissolved. Optionally, small amounts of emulsifiers may be added to increase the solubility.

The polymerization is carried out in the presence of a base, for example of alkali metal hydroxides, such as NaOH or KOH, alkaline earth metal hydroxides, NH 3 or organic amines. Likewise, compounds can be used which react in the reaction medium to form a base. Examples could be alkali or alkaline earth oxides. Furthermore, N-heterocycles can also be used.

In particular, the polymerization is carried out in the presence of an organic amine. "Organic amines" are referred to hereinafter as amines The content of base is generally from 0.01 to 100 mol%, for example from 1 to 80 mol%, or from 1 to 50 mol%, in particular from 2 to 19, 9 mol%, preferably in the range from 3 to 15 and more preferably from 5 to 10 mol% The above quantities in mol% refer to the total amount of all COOH groups of the monocarboxylic acid (A) and of the dicarboxylic acids (B) Copolymer, other acidic groups which may be present are disregarded. In other words, the COOH groups are partially neutralized. Of course, a mixture of two or more bases can be used.

The amines used as base may have one or more primary and / or secondary and / or tertiary amino groups and the corresponding number of organic groups. The organic groups may be alkyl, aralkyl, aryl or alkylaryl groups. Preference is given to straight-chain or branched alkyl groups. They may also have other functional groups. Such functional groups are preferably OH groups and / or ether groups. It is also possible to use amines which are not per se water-soluble, because in contact with the acidic monomers the formation of ammonium ions advantageously increases the water solubility. The amines can also be ethoxylated.

Examples of suitable amines include linear, cyclic and / or branched C 1 -C 8 mono-, di- and trialkylamines, linear or branched C 1 -C 5 -mono-, di- or trialkanolamines, in particular mono-, di- or trialkanolamines, linear or branched C 1 -C 8 -alkyl ethers of linear or branched C 1 -C 8 -mono-, di- or trialkanolamines, oligo- and polyamines, for example diethylenetriamine.

The amines may also be heterocyclic amines, for example morpholine, piperazine, imidazole, pyrazole, triazoles, tetrazoles, piperidine. Particularly advantageous such heterocycles can be used which have corrosion inhibiting properties. Examples include benzotriazole and / or tolyltriazole.

Furthermore, it is also possible to use amines which have ethylenically unsaturated groups, in particular monoethylenic amines. Such amines can perform a dual function as an amine for neutralization as well as a monomer (C). For example, allylamine can be used.

The person skilled in the art will make a suitable choice among the amines.

Preference is given to amines having only one amino group. Further preferred are linear or branched C 1 -C 8 mono-, di- or trialkanolamines, particular preference is given to mono-, di- and triethanolamine and / or the corresponding ethoxylated products. Very particular preference is given to N, N-dimethylethanolamine, N, N-diethylethanolamine and triethanolamine. The amount of amine used is preferably from 0.01 to 100 mol%, for example from 1 to 80 mol%, or from 1 to 50 mol%, in particular from 2 to 19.9 mol%. Preference is given to working in the range from 3 to 15 and more preferably from 5 to 10 mol%. The above amounts in mol% refer to the total amount of all COOH groups of the monocarboxylic acid (A) and the dicarboxylic acids (B) in the copolymer.

The base, for example the amine, can be added before or during the polymerization. It is preferably added already before or at the latest at the beginning of the polymerization. In this case, the base, such as amine, either at once or in a time interval which corresponds to a maximum of the entire reaction time can be added. The base, such as, for example, the amine, can here be added to the monomer feed, either the monocarboxylic acid, the dicarboxylic acid or both, and metered in with them. In other words, the carboxylic acids can thus be partially added in the form of the corresponding ammonium salts. Preferably, the base, for example the amine, is metered directly into the original. In order to carry out the polymerization, it has proved useful in this case to initially introduce the dicarboxylic acid or, if appropriate, its cyclic anhydride and then to meter in the base, such as amine, before adding further monomers and / or initiator without the preparation of those used in the process according to the invention Polymers should be set to this approach.

Monoethylenically unsaturated dicarboxylic acids usually react significantly slower than monocarboxylic acids in the course of radical polymerization. Therefore, copolymers of monoethylenically unsaturated mono- and dicarboxylic acids often contain more or less large amounts of non-polymerized dicarboxylic acids. High residual contents of dicarboxylic acids are undesirable for many applications because, for example, free residual dicarboxylic acid can be leached out again.

Theoretically, there is the possibility of post-purification of the polymers. This is cumbersome and uneconomical. It is known in the art to neutralize the COOH groups of the monomers used in the course of the polymerization wholly or partly with bases. As a result, the proportion of unpolymerized dicarboxylic acid can be reduced. Surprisingly, it has been found that by using amines as the base, in the range from 2 to 19.9 mol%, based on the total amount of all COOH groups in the mono- and dicarboxylic acid units, copolymers are obtainable which have a low degree of neutralization but nevertheless also have a low residual content of unpolymerized dicarboxylic acid. It can be obtained copolymers with a very high proportion of copolymerized dicarboxylic acids. Even if relatively small amounts of amines are used as the base, the polymerization still leads to copolymers which have only small amounts of non-polymerized dicarboxylic acids.

The residual amount of unpolymerized dicarboxylic acids in the product when using amines is in the range of 2 to 19.9 mol%, based on the total amount of all COOH groups in the mono- and dicarboxylic, is lower than using other bases, such as NH3 or NaOH.

The residual content is generally no more than 2.5% by weight with respect to the copolymer, even in the case of copolymers with relatively large dicarboxylic acid contents.

The residual content of monocarboxylic acids (A) is also very low, it is usually not more than 0.1% by weight with respect to the copolymer.

As a rule, the copolymers, by the use of a base such as an amine, during the polymerization, a degree of neutralization of the carboxyl groups of all mono- and dicarboxylic acid units from 0.01 to 100 mol% with respect to the total amount of all carboxyl groups (COOH Groups) in the mono- and dicarboxylic acid units. As a rule, the degree of neutralization results simply from the amount of base originally added, for example of the amine. Depending on the type of base, e.g. Amine, in particular their volatility and basicity, but also small amounts of the base, for example of the amine, in the course of polymerization and / or work-up can be lost. When using basic monomers (C), the degree of neutralization may also be higher than that resulting from the amount of the base, for example the amine. The amines are usually present in the product as ammonium ions. Depending on the basicity of the amine, however, certain proportions of the amine may be present unprotonated in the product.

The free-radical polymerization is preferably started by the use of suitable thermally activatable polymerization initiators. Alternatively, however, it can also be triggered by suitable radiation, for example. The free-radical initiators should be soluble in the solvent of the reaction, preferably water-soluble.

Among the thermally activatable polymerization initiators are initiators having a decomposition temperature in the range from 30 to 150.degree. C., in particular from 50 to 130.degree. vorzugt. This temperature refers as usual to 10h half-life. Examples of suitable thermal initiators are inorganic peroxo compounds, such as peroxodisulfates, in particular ammonium and preferably sodium peroxodisulfate, peroxosulfates, percarbonates and hydrogen peroxide; organic peroxy compounds, such as diacetyl peroxide, di-tert-butyl peroxide, diamyl peroxide, dioctanoyl peroxide, didecanyl peroxide, dilauroyl peroxide, dibenzoyl peroxide, bis (o-toloyl) peroxide, succinyl peroxide, tert-butyl peracetate, tert-butyl permalate, tert Butyl perisobutyrate, tert-butyl perpivalate, tert-butyl peroctoate, tert-butyl perodecanoate, tert-butyl perbenzoate, tert-butyl peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, tert-butyl peroxy-2-ethylhexanoate and diisopropyl peroxydicarbamate; Azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), azobis (2-amidopropane) dihydrochloride, and azo (bisisobutylamidine) dihydrochloride. Other suitable azo compounds that are soluble in organic solvents are 2,2'-azobis (4-methoxy-2,4-dimethyl-valeronitrile), dimethyl 2,2'-azobis (2-methylpropionate), 1, 1 ' Azobis (cyclohexane-1-carbonitrile), 1 - [(cyano-1-methylethyl) azo] formamide, 2,2'-azobis (N-cyclohexyl-2-methylpropionamide), 2,2'-azobis (2,4-dimethyl valeronitrile), 2,2'-azobis [N- (2-propenyl) -2-methylpropionamide], 2,2'-azobis (N-butyl-2-methylpropionamide). Preference is given to using water-soluble compounds, such as. 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propanedisulfate dihydrate, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride , 2,2'-Azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] , 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis (2-methylpropionamide) dihydrochloride, 2,2'-azobis [2- (3,4, 5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane], 2,2'-azobis {2-methyl-N- [2- (1-hydroxybuthyl)] propionamide. Particular preference is given to sodium peroxodisulfate, hydrogen peroxide, 2,2'-azobis (2-methylpropionamide) hydrochloride. It is also possible to use mixtures of the initiators.

These initiators can be used in combination with reducing compounds as starter / regulator systems. Examples of such reducing compounds include phosphorus-containing compounds, such as phosphorous acid, hypophosphites and phosphinates, and sulfur-containing compounds, such as sodium hydrogen sulfite, sodium sulfite and sodium formaldehyde sulfoxilate.

In combination with the initiators or the redox initiator systems, it is additionally possible to use transition metal catalysts, for example salts of iron, cobalt, nickel, copper, vanadium and manganese. Suitable salts are, for example, iron (II) sulfate, cobalt (II) chloride, nickel (II) sulfate, copper (I) chloride. The reducing transition metal salt is usually used in an amount of 0.1 to 1000 ppm, based on the sum of the monomers. For example, combinations are particularly advantageous of hydrogen peroxide and iron (II) salts, such as a combination of 0.5 to 30 wt .-% hydrogen peroxide and 0.1 to 500 ppm FeSO ₄ x 7H ₂ O, in each case based on the sum of the monomers. Also preferred are combinations of sodium peroxodisulfate with FeSO ₄ .7H ₂ O or a mixture of sodium peroxodisulfate and hydrogen peroxide with FeSO ₄ .7H ₂ O. It is preferred to use from 1 to 450 ppm, more preferably from 10 to 400 ppm FeSO ₄ .times.7 H ₂ O.

Examples of suitable photoinitiators include acetophenone, benzoin ethers, benzyl dialkyl ketones and their derivatives.

Preference is given to using thermal initiators, inorganic peroxo compounds, in particular hydrogen peroxide and above all sodium peroxodisulfate, and mixtures of hydrogen peroxide and sodium peroxodisulfate being preferred. Very particular preference is given to the mixture of hydrogen peroxide and sodium peroxodisulfate.

Of course, mixtures of different initiators can be used, provided they do not adversely affect. The amount is determined by the skilled person depending on the desired copolymer. As a rule, from 0.05% by weight to 30% by weight, preferably from 0.1 to 15% by weight and particularly preferably from 0.2 to 8% by weight, of the initiator are used with respect to the total amount of all monomers.

In addition, suitable regulators, for example mercaptoethanol, can also be used in a manner known in principle. Preferably, no controllers are used.

By suitable choice of the temperature, the molecular weight M w of the copolymers can also be set between 3000 g / mol and 60 000 g / mol. The polymerization is generally carried out at a temperature of more than 60 ° C, for example, the polymerization temperature in a range of 65 to 130 ° C, preferably from 70 to 120 ° C, more preferably from 80 to 1 10 ° C and in particular chosen from 90 to 105 ⁰ C.

Apart from that, the temperature may be varied within a wide range by those skilled in the art depending on the type of monomers used, the initiator and the desired copolymer. The temperature can be kept constant during the polymerization or temperature profiles can also be run. The polymerization can be carried out in conventional free-radical polymerization apparatus. If one works above the boiling point of the water or the mixture of water and other solvents, working in a suitable pressure vessel, otherwise it can be operated without pressure.

In the polymerization, it has proven itself regularly to submit the dicarboxylic acid or corresponding anhydrides in aqueous solution. Thereafter, a base, such as amine, is conveniently added as an aqueous solution. In aqueous solution, especially in the presence of the amine, the carboxylic anhydrides hydrolyze more or less rapidly to the corresponding dicarboxylic acids. Thereafter, the monocarboxylic acid, optionally further monomers (C) and the initiator, expediently also be metered in aqueous solution. Inlet times of from 0.5 h to 24 h, preferably from 1 h to 12 h and more preferably from 2 to 8 h, have proven useful. In this way, the concentration of the more reactive monocarboxylic acids in the aqueous solution is kept relatively low. This reduces the tendency of the monocarboxylic acid to react with itself and results in a more uniform incorporation of the dicarboxylic acid units into the copolymer. After the feed of all monomers may also follow a post-reaction time, for example, from 0.5 to 3 hours. This ensures that the polymerization reaction proceeds as completely as possible. The completion can also be achieved by post-dosing polymerization initiator again. Inlet times and post-reaction time can vary over a wide range depending on the boundary conditions of the polymerization, such as the structure of the reactor.

Of course, the skilled person can also carry out the polymerization in other ways.

Not only carboxylic acid anhydrides but also other monomers used which have hydrolyzable groups, for example esters, may under some circumstances hydrolyze wholly or partly, depending on the polymerization conditions. The copolymers then contain the monomers copolymerized with the acid group resulting from the hydrolysis or else both unhydrolyzed groups and hydrolyzed groups next to one another. The synthesized copolymers can be isolated from the aqueous solution by conventional methods known to those skilled in the art, for example by evaporation of the solution, spray drying, freeze drying or precipitation.

However, particularly preferably, the copolymers are not isolated at all from the aqueous solution after the polymerization, but the resulting preparation solutions are used as such.

Partially neutralized, carboxylate-rich copolymers are obtainable by the polymerization. The composition of the copolymers essentially corresponds to the ratio of the monomers (A), (B) and (C) used.

If hydrolyzable derivatives of the monomers (B) were used, the copolymer may also contain portions of unhydrolyzed monomers, depending on the rate of hydrolysis and the conditions.

The pH of the preparation solution is generally less than 5, preferably less than 4, and more preferably less than 3.

The copolymers used in the process according to the invention are soluble or at least dispersible in water or at least 50% by weight of water-containing aqueous solvent mixtures, and copolymer solutions are obtained. It is known to the person skilled in the art that the solubility of carboxylate-rich copolymers can be strongly pH-dependent. The term "water-dispersible" means that although the solution is not very clear, the copolymer is homogeneously dispersed throughout and does not settle out, preferably copolymers that are water-soluble.

The copolymers are used according to the invention for controlling the thickening of aqueous systems, for example those containing silicates. For this purpose, the copolymers can be used as such in various dosage forms, for example as powder, gel, granules or tablets. These dosage forms may contain other auxiliaries and additives, in other words constitute a solid formulation. The copolymers can also be used as described above in the form of their preparation solution. In particular, the copolymers can be used as components of liquid formulations, for example as components of formulations for chemical water treatment. For the preparation of liquid formulations, the co-formulants present in solid dosage form are usually used. received polymers in a solvent or diluent. It is preferably an aqueous solvent. If the copolymers are present in the form of their preparation solution, the desired formulation can be obtained by adding further solvents or diluents. The pH of the formulations can be controlled by acid or base addition or by buffer. Suitable bases for adjusting the pH are the bases already described in the presence of which the polymerization of the copolymer is carried out. Preference is given to using as bases for adjusting the pH, NaOH, KOH or ammonia. Furthermore, corrosion inhibitors, biocides, surfactants, phosphonates, as well as builders and co (builders) and possibly also other auxiliaries may also be present in the formulations.

The method for controlling the thickening can in principle be applied to any aqueous systems, preferably those containing silicates, in any plant. The thickening in the aqueous system is characterized by the so-called thickening number. The thickening factor (EDZ) can be given, for example, by the ratio of the volumes of the aqueous system at two times t1 and t2 (t2> t1), given a constant amount of the solutes M (t1) = M (t2). EDZ = V (t1) A / (t2). If, for example, the volume of the aqueous system at a certain point in time t has dropped to half its initial value V (O) by evaporation, for example, and the amount of dissolved substances remains constant, we obtain an EDZ = V (0) A / (t ) In case of constant volumes, V (t1) = V (t2), the EDC is given by the ratio of the quantities of solutes EDZ = M (t2) / M (t1). In the general case, the EDC corresponds to the ratio of the solute concentrations at times t1 and t2, EDZ = c (t2) / c (t1).

A simple measurement of the EDC is possible by determining the electrical conductivity in the aqueous system. The electrical conductivity of the aqueous system depends directly on the type and amount of dissolved in the water ingredients. The EDC results roughly by the ratio of the conductivity in the aqueous system to that in the make-up water. By measuring the conductivity, a reliable control of the thickening by the method according to the invention is possible. Of course, the measurement of the EDC can also be carried out by other methods, for example, samples can be taken from the aqueous system and the determination of the concentration of the dissolved substances, in particular the silicate concentration, can be carried out with physical or chemical measuring methods known to the person skilled in the art.

The control of EDC in a certain predetermined range is carried out according to the invention by appropriate addition of the copolymers or a solid or liquid formulation containing the copolymers to the aqueous system. The dosage can be either at certain times or continuously. The first There may be, for example, at a time prior to the actual startup of the plant in which the aqueous system is located. The concentration of the copolymers in the aqueous system in the practice of the method according to the invention after addition of the appropriate dosage form or formulation to the aqueous system is generally in the range of 0.5 to 800 ppm, preferably in the range of 2 to 500 ppm. The pH of the formulation prior to addition to the aqueous system is preferably in the basic range, but may also be in the acidic range, while the pH of the thickened aqueous system in the acidic, neutral, or even basic range. In particular, the pH of the thickened aqueous system is in the range of 7 to 10.

The chemical treatment of water influences the thickening limiting factors to allow a higher thickening than in untreated water. The greatest effect is achieved with the method according to the invention, depending on the specific application, often with an EDZ of 1.1 to 8, preferably with an EDC in the range of 1.5 to 8, particularly preferably with an EDZ of 2 to 5, especially with an EDC in the range of 3 to 5. At a high EDZ, the efficiency of the process no longer increases so much with the increase in EDZ. Since an EDZ larger than 10 barely brings any further water savings and frequently introduced dirt particles must be discharged, this value will generally hardly exceed this value.

Especially silicates containing aqueous systems with uncontrolled high EDC are often triggers for problems, the cause of which does not seem to have directly to do with the deposits. For example, heat exchangers coated with silicate layers only insufficiently dissipate the energy. This leads to overheating of machines and units. The use of the method according to the invention leads to a reduction of the silicate coating, for example in heat exchangers, thus preventing overheating. The reduction achieved by the process according to the invention can vary within wide limits. This depends, for example, on the flow rate, the temperature or the residence time. The reduction by the process according to the invention can be from 20 to 90% compared to the process without control of the EDC. This extends the service life of the aqueous system in systems in which silicates are the thickening limiting factor many times over. In particular, service life extensions are achieved by a factor of 2 to 5.

The reduction of the silicate coating by controlling the EDZ also leads to an improved effect of the corrosion inhibitors contained in the formulation for chemical water treatment by using the method according to the invention. Corrosion inhibitors often do not reach the surfaces of the system components more if it is covered by a silicate layer. It comes to massive corrosion processes under the layer, which are visible only when corrosion damage is present. Just like corrosion inhibitors, biocides can hardly reach the seed nests that are under deposits. Treatment with biological control products will be unsuccessful because the circulation will be "infected" again and again after treatment has been completed, and the control of the EDC will allow more efficient and effective use of biocides In particular, it is often possible to reduce the biocide level by up to 30% In all applications, the control of biological growth in the plants may be an important factor, especially if contamination of the human by contact with the aqueous system or in the aquatic environment Cleaning the equipment is to be feared.

Systems which benefit from a controlled increase in the EDZ, according to the process of the invention, in aqueous systems containing silicates are, for example, systems whose function is essentially based on thermal effects in the aqueous system or depends on thermal effects in the aqueous system , Examples are cooling systems, such as open or closed cooling water circuits; Heating systems, such as water heaters, boilers, boilers; Heat exchanger; Water desalination plants or humidifiers. In these systems, evaporation of water often causes a constant tendency to increase EDC. For example, by controlling an elevated EDC, according to the method of the invention, the range in which a stable and efficient operation of a heat exchanger is ensured can be extended. Even with an increased EDZ, the method according to the invention prevents the deposition of silicate coatings on the heat exchanger, which would otherwise lead to a reduced heat transfer. Furthermore, systems that are based in the broadest sense on filtration systems, operate more efficiently with the inventive method. Examples are water desalination plants, reverse osmosis (RO) systems, hyper- and nano-filtration plants and dialysis machines in medical technology. Filtration processes can be carried out more efficiently by the inventive method even at a higher EDZ, since a stabilization of the aqueous system takes place against the formation of solid coatings that would clog or destroy the filter. The process according to the invention is likewise of interest for use in household appliances, for example in washing machines or dishwashers, since silicates, also as zeolites, are frequently present in the corresponding cleaning agents. Here you can realize water savings while avoiding silicate coatings on laundry or dishes.

Further, the control of EDC, according to the method of the present invention, plays a role in geothermal processes for generating electricity or heat Processes of oil extraction, sugar production, or papermaking. All these methods have in common that enormous amounts of water are used with many additives. The water used is often heated strongly in some steps of these processes. This heating leads to the evaporation of water and an increase in EDC. If the increase in the EDC uncontrolled, it comes to increased deposits, especially of silicates in the plants, which can be removed only by decommissioning and cleaning. This uncontrolled increase in EDC is avoided by the method according to the invention.

For example, in oil extraction processes, large amounts of water are pumped through silicate-containing rock under pressure, thereby taking up large quantities of silicates that can form uncontrolled coatings in subsequent process steps in pipelines leading to clogging and pressure drop. The controlled increase of the EDZ, with the method according to the invention, in particular suppresses the formation of silicate coatings and thus prevents clogging and pressure drop in the pipelines.

In papermaking, the inventive method can be used for example in the bleaching of wood pulp (PuIp). As chlorine-free bleaching agents peroxide, such as hydrogen peroxide (H2O2) or sodium peroxide (Na2Ü2) are often used. Peroxide bleaching is used, among other things, for bleaching pulp or wood pulp. Peroxide bleaching is also used for the removal of the printing inks contained in waste paper (deinking). Peroxides, especially under the catalytic action of heavy metals, can undesirably decompose. Among others, heavy metals such as manganese, especially in wood pulp present. Another source of heavy metals are the processing plants. Therefore, in addition to or as an alternative to complexing agents, such as DTPA (diethylenetriaminepentaacetic acid) or EDTA (ethylenediaminetetraacetic acid), water glass is used to stabilize the peroxides. Water glass is a soluble sodium silicate. Furthermore, the compounds of polyvalent cations, such as magnesium compounds, also have an advantageous effect on the stability of the peroxide bleach. Despite this stability-endangering combination of silicates and polyvalent cations, such as magnesium, which tend to form silicate coatings such as magnesium silicate, the method of the present invention allows the control of EDC in papermaking within a given range. This ensures the stable operation of the plants even at higher silicate concentrations and concentrations of polyvalent cations, such as magnesium.

For economic and ecological reasons, it is very often the case for larger technical installations that groundwater or surface water are used as cost-effective means of aging. native to drinking water. Depending on the source of the water more or less large amounts of dissolved ingredients are included, which accumulate during the thickening process in the water. The non-problematic ingredients present in non-concentrated water in their natural concentration can lead to very serious technical problems if they are highly concentrated and the EDC becomes too large. The inventive method allows the control of EDC even with the use of silicate-rich groundwater or surface water with a silicate content of 1 CH to 10 " ² mol / l Si, for example, with a content of 10 ³ to 10 ² mol / l Si.

Particularly advantageous method of the invention in the operation of cooling towers is used, which dissipate heat by evaporation of water. The operation of a cooling tower is characterized in that the water to be cooled is trickled through a distribution system with nozzles from above via cooling tower internals, which produce a large water surface. When descending, the water is flowed through by cooling air and evaporation heat is released into the air via the evaporation process. The water is cooled according to the energy dissipation. The predominant cooling capacity is usually obtained to more than 85% only from the necessary energy for the evaporation process. In practical operation of, for example, cooling towers, natural, not specially treated water is used in most cases. Evaporation causes thickening of the remaining water. By using the method according to the invention, in particular unwanted silicate coatings in the various parts of the plant, such as the above-mentioned nozzles, which would otherwise occur with progressive evaporation, are pushed back. For example, with the method according to the invention, the silicate coatings in the pipes or the evaporators are avoided, which would otherwise lead to blockages or reduced heat transfer. With the method according to the invention, a higher EDZ can be achieved, in which there is still a stability of the thickened system against the formation of the undesired silicate coatings. The demand for required make-up water is lowered in accordance with the higher allowable EDC.

Another embodiment of the method according to the invention is the control of the thickening in evaporative coolers. Evaporative coolers are usually referred to as open cooling towers, but also similar systems, for example, sprinkled or pre-moistened air coolers, and hybrid cooling towers as a combination of evaporative cooling towers with air coolers.

An open cooling circuit can only be thickened to a technically sensible upper limit. Above this limit, interference or damage occurs. conditions of the cooling system. An optionally automatically controlled bleed valve ensures a short-term water exchange when the upper limit of the maximum possible thickening is exceeded, it is drained from the aqueous system via the bleed valve desalination and fed to the aqueous system make-up water. By using the method according to the invention, by controlling the EDC in the range of 1.1 to 8, preferably in the range of 2 to 5, the lowest possible volume of desalting water is achieved.

Other advantageous effects of the method according to the invention are the optimal Wasserverrieselung in the cooling tower by controlling biological growth and in conjunction with the use of biocides the protection of persons from pathogenic germs in the spray water by biological control.

In particular, the inventive method can also be used in the operation of reverse osmosis (RO) systems. If solutions of different concentrations, e.g. aqueous systems with different salt contents separated by a semipermeable membrane, the more concentrated solution tends to dilute. Through the membrane, water molecules enter the concentrated solution, which increases its volume. This process, called osmosis, lasts until the osmotic balance is reached. The osmotic balance is a dynamic balance between the dilution effort on the one hand and the hydrostatic pressure due to the increase in volume on the other hand. This hydrostatic overpressure corresponds to the difference between the osmotic pressures of the differently concentrated solutions and is essentially dependent on the concentration of the substances dissolved in the liquid. In reverse osmosis, the direction of this natural osmotic flow is reversed. A pressure is exerted on the raw water which is located on one side of a semipermeable, water-permeable membrane. Since this pressure is significantly higher than the osmotic pressure difference, the water molecules penetrate the semipermeable membrane from the side of the higher salt concentration to the side of the lower concentration. RO is in addition to distillation and ion exchange a way to obtain deionized (VE) water. Depending on the process, in a RO plant, in addition to demineralised water, the concentrated raw water also accumulates with an EDC, which can vary over a wide range. For example, the EDZ is in the range of 1, 1 to 8, in particular in the range of 1, 1 to 5.

The use of the process according to the invention in RO plants prevents the uncontrolled thickening of the raw water and thus reduces the deposits on the membrane that block them and endanger the continuous operation of the plant. that would. To protect the membrane from blocking may optionally be carried out a pretreatment of the raw water. The pretreatment depends on the quality of the raw water. This pretreatment can be achieved by technical measures, eg. B. filtration, or softening done. In addition to the water hardness (carbonate hardness), silicates play an important role in the blocking of the membrane. The selection of a suitable formulation has to be done very carefully. The compatibility with the existing membranes must be ensured. By the method according to the invention, the cost of pretreatment of the raw water can be reduced. By saving other compounds for the chemical pretreatment of the raw water, the selection of a suitable formulation for the respective membrane is facilitated.

Alternatively or in combination with technical measures, the method according to the invention is available for controlling the EDZ in aqueous systems, which in particular contain silicates, for any system. The stability of thickened aqueous systems against the precipitation of dissolved substances, which lead to deposits or encrustations, is increased by the process according to the invention. Water savings are realized by the method according to the invention, which controls biological growth in aqueous systems and facilitates the mobilization of sludge and silt. The amounts of biocides and corrosives can be reduced with the same efficiency of chemical water treatment. Furthermore, the method according to the invention makes it possible to keep the thickening in the technically required range over a long service life. The copolymers used in the process according to the invention have a very low residual content of monomers due to the partially neutralized production process.

Examples:

Magnesium silicate inhibition:

The determination of the increased silicate concentration in the aqueous system (magnesium silicate inhibition) was carried out by means of turbidity titration.

Reagents: Test Solution A: 9.06 g / L Na ₂ SiO 3 * 5 H ₂ O

Test solution B: 12.55 g / l MgCl ₂ .6H ₂ O

Sodium hydroxide: 0.2 mol / l

Hydrochloric acid: 0.5 mol / l Procedure: The appropriate amount of copolymer calculated on solids weight (FG) was weighed directly into the titration vessel. Subsequently, 50 ml of test solution A and 48 ml of demineralized water were added. The pH of the titration solution was adjusted to about pH 10 with HCl 0.5 mol / l or NaOH 0.25 mol / l. The pH was kept constant during the titration. The test solution B was titrated incrementally at intervals of 0.25 ml each until permanent turbidity. At max. 75% transmission or consumption> 1 OmL, the titration was aborted automatically. Each copolymer was measured twice.

The SiÜ2 content was calculated according to: _{ß (sjθ2) =} V (MgCb). ß (MgCb). M (SiQ ₂ ) M (Mg) V (sample)

X mL * 1.5 mg / mL * 60.09 g / mol. _" Mg IS (oiu ₂ ) = in -

24.3 g / mol * 0.05 L L

The error limit is: max. +/- 5%.

Mw values are determined by gel permeation chromatography (GPC). The calibration of the GPC is carried out with a widely distributed Na-PAA mixture whose integral molecular weight distribution curve is determined by SEC laser light scattering coupling, according to the calibration method of M.J.R. Cantow et al. (J. Polym. Sci., A-1, 5 (1967) 1391-1394), but without the concentration correction proposed therein.

The K values were measured according to H. Fikentscher, Cellulose-Chemie, Vol. 13, pp. 58-64 and 71-74 (1932) in 1% strength by weight aqueous solution at 25 ° C. at uncorrected pH.

Example 1: Copolymers with maleic acid

The copolymers are characterized by their composition, their molecular weight Mw and the K value. The degree of magnesium silicate inhibition is given by the β (SiO 2) value, higher β (SiO 2) values correspond to an improved effect.

test results:

ITS: itaconic acid, AS: acrylic acid, VPS: vinylphosphonic acid

MS: maleic acid (used as anhydride), AS: acrylic acid, VPS: vinylphosphonic acid, ^* : comparative example Example 2: Comparison with commercial products.

The copolymers are characterized by their composition, their molecular weight Mw and the K value. The degree of magnesium silicate inhibition is given by the β (SiO 2) value, higher β (SiO 2) values correspond to an improved effect. The dosage of the copolymers is in all cases 400 ppm FG. For the determination of the zero value (0 value) no copolymer is used.

test results:

ITS: itaconic acid, AS: acrylic acid, VPS: vinylphosphonic acid, MS: maleic acid (used as anhydride)

Accumer®, Goddrite® and Versaflex® are registered trademarks of Rohm & Haas, Noveon and Nalco.

Claims

claims:

1. A method for controlling the thickening of aqueous systems containing silicates, characterized in that at least one copolymer of an average molecular weight Mw of at least 3000 g / mol to at most 60000 g / mol is added to the aqueous system and the copolymer substantially statistically composed of the following monomeric units:

(B) 0.01 to 70 wt.% Of at least one monoethylenically unsaturated dicarboxylic acid of the general formula (HOOC) R ¹ C = CR ² (COOH) (I), and / or

R ¹ R ² C = C (- (CH ₂ ) _n -COOH) (COOH) (II),

or the corresponding carboxylic acid anhydrides and / or other hydrolyzable derivatives, wherein

R ¹ and R ² independently of one another are H or a straight-chain or branched, optionally substituted alkyl radical having 1 to 20 C atoms, or in the case of (I) R ¹ and R ² together are an optionally substituted one

Alkylene radical having 3 to 20 carbon atoms, and

n is an integer from 0 to 5,

such as

and that the polymerization is carried out to produce the copolymer in the presence of 0.01 to 100 mol% of at least one base, based on the total amount of all COOH groups of the mono- and dicarboxylic acids, wherein the amounts in wt.% Each on the total amount all monomers used are based.

2. The method according to claim 1, characterized in that monomer (A) is acrylic acid or its hydrolyzable derivatives or mixtures thereof.

3. The method according to any one of claims 1 to 2, characterized in that monomer (B) is maleic acid, itaconic acid or their hydrolyzable derivatives or mixtures thereof.

4. The method according to any one of claims 1 to 3, characterized in that monomer (C) is vinylphosphonic acid or its hydrolyzable

Derivatives or mixtures thereof.

5. The method according to any one of claims 1 to 4, characterized in that an amine is used as the base during the polymerization for the preparation of the copolymer.

6. The method according to any one of claims 1 to 5, characterized in that a thickening number of 1, 1 to 8 is maintained in the aqueous system.

7. The method according to any one of claims 1 to 6, characterized in that the concentration of the copolymer or copolymers in the aqueous system in the range of 0.5 to 800 ppm.

8. The method according to any one of claims 1 to 7, characterized in that the pH of the thickened aqueous system is in the neutral or basic range.

9. A thickened aqueous system which has a thickening factor of 1: 1 to 8, comprising at least one copolymer having an average molecular weight Mw of at least 3000 g / mol to at most 60,000 g / mol with a substantially random structure of the copolymer comprising the following units:

(A) 20 to 99.98% by weight of at least one monoethylenically unsaturated monocarboxylic acid, (B) 0.01 to 70% by weight of at least one monoethylenically unsaturated dicarboxylic acid of the general formula (HOOC) R ¹ C = CR ² ( COOH) (I), and / or R ¹ R ² C = C (- (CH ₂ ) n -COOH) (COOH) (II),

R ¹ and R ² independently of one another are H or a straight-chain or branched, optionally substituted alkyl radical having 1 to 20 C atoms, or in the case of (I) R ¹ and R ² together for an optionally substituted alkylene radical having 3 to 20 C Atoms stand, and

n is an integer from 0 to 5,

such as

10. Use of the thickened aqueous system according to claim 9, in plants whose function is based essentially on thermal effects in the aqueous system or depends on thermal effects in the aqueous system or in installations based on filtration systems.

1 1. A process for the operation of plants whose function is based essentially on thermal effects in the aqueous system or depends on thermal effects in the aqueous system or of plants based on filtration systems, characterized in that the aqueous system is a thickened aqueous System according to claim 9.

12. Use of the thickened aqueous system according to claim 9, in the oil extraction or in geothermal processes.

13. Use of the thickened aqueous system according to claim 9, for the operation of desalination plants.

14. Use of the thickened aqueous system according to claim 9, in papermaking.

15. Use of the thickened aqueous system according to claim 9, for the operation of reverse osmosis systems.