Patent Description:
The use of anti-scaling additives in aqueous systems to inhibit the deposition of scale formed from the salts of divalent metals such as calcium and magnesium is standard practice in a number of industries. The reduction in the build-up of scale, which can be achieved, is beneficial in reducing fouling of the system and the frequency with which the system must be closed down in order to remove scale deposits.

Numerous anti-scaling additives have been proposed as useful additives to aqueous systems including certain polyphosphates, polyacrylic acids, polymethacrylic acids, lignin sulphonic acids and their salts, tannin, naphthalene sulphonic acid formaldehyde condensation products, polyphosphates such as tripolyphosphate and hexametaphosphate, phosphonic acids, polymaleic acids and hydrolysed copolymers and terpolymers of maleic anhydride and the salts of these acids. The use of these anti-scaling additives, particularly the acrylic acid and maleic acid polymers, is widely recognised as being effective in inhibiting the build-up of calcium carbonate and calcium sulphate scale.

In seawater desalination plants, including thermal seawater desalination plants and reverse osmosis desalination units, Mg(OH)<NUM>, CaCO<NUM> and CaSO<NUM> are the main deposits to be mitigated. They impair the function by precipitating on the desalination equipment surface causing performance loss and in case of thermal desalination plants reduction in the heat transfer. As a result, water production is reduced, and additional maintenance is required. Using proper additives would inhibit their formation and promote smooth operations. <NPL> and <NPL> give a review on scale inhibition in seawater desalination units.

While the formation of scales based on CaCO<NUM> and CaSO<NUM> can be mitigated with the abovementioned anti-scaling additives, the formation of Mg(OH)<NUM> containing scale, hereinafter also referred to as brucite containing scale, is still a serious problem in water treatment units, where the Mg concentration of the water to be treated contains at least <NUM> ppm Mg, calculated as Mg<NUM>+. As the solubility of Mg(OH)<NUM> decreases with increasing pH and also with increasing temperature, a particular risk for the formation of magnesium hydroxide containing scale exists at a pH of at least pH <NUM> and/or at temperatures of above <NUM>. Conditions which favour the formation of magnesium hydroxide containing scale are usually met in seawater desalination plants. The problem of the formation of Mg(OH)<NUM> containing scale may also occur in greywater treatment units, where the concentration of magnesium salts in the water to be treated is often considerably high and which are usually operated at high pH values.

Unfortunately, numerous anti-scaling additives, which efficiently reduce the formation of calcium carbonate scale, including polyacrylic acids and polymaleates, fail to efficiently reduce magnesium hydroxide containing scale. Other anti-scaling additives, which may reduce the formation of magnesium hydroxide containing scale may be inefficient at high salinity of the water to be treated, as for example in seawater or brackish water. Frequently, combinations of polymaleic acids and phosphorous containing anti-scaling agents are required in order to achieve acceptable scale control in seawater desalination plants. In recent years, however, the phosphor discharge is the main issue in desalination industry and thus limiting the use of phosphorous-based anti-scaling agents is of particular importance.

<CIT> suggests using a copolymer of <NUM> to <NUM> mole% of maleic acid or maleic acid anhydride and <NUM> to <NUM>% of allyl sulfonic acid for inhibiting scaling due to the formation of magnesium hydroxide in evaporative desalination units. Due to the high price of allyl sulfonic acid, the anti-scaling agents are not attractive from a commercial perspective.

<CIT> discloses a combination of polymaleic acid, a phosphonic acid salt, such as <NUM>-hydroxyethylidene-<NUM>,<NUM>-diphosphonic acid or diethylene triamine penta(methylenephosphonic acid), and an iron sequestrant, such as citric acid or gluconic acid, and suggests this combination for reducing mixed scale formation in thermal or reverse osmosis desalination units.

<CIT> suggests using a combination of polymaleic acid having a weight average molecular weight of from <NUM> to <NUM> and a phosphino acrylic acid telomere having a weight average molecular weight of from <NUM> to <NUM> for inhibiting the formation of a magnesium hydroxide containing scale. The anti-scaling agents still contain considerable amounts of phosphorous.

<NPL> investigate certain commercial anti-scaling agents with regard to their capability of inhibiting Mg(OH)<NUM>, CaCO<NUM> and CaSO<NUM> scales in thermal seawater desalination units.

<NPL> describe novel anti-scaling agents based on modified polyacrylic acids having hydrophobic end groups. These novel anti-scaling agents provide good inhibition of CaCO<NUM> scales.

<CIT> suggests copolymers of <NUM> - <NUM>% by weight of acrylic acid and <NUM> - <NUM>% by weight of one or more C<NUM>-C<NUM>-alkyl acrylates or C<NUM>-C<NUM>-alkyl methacrylates having a molecular weight between <NUM> and <NUM>/mol as scale inhibitors for CaCO<NUM>, CaSO<NUM> scale. The copolymers disclosed therein show performance against CaCO<NUM>, CaSO<NUM> crystal formation inhibition and dispersing capability against kaolin and calcium carbonate particles.

<CIT> relates to a method for preventing the formation of scale in distillation and evaporation apparatuses using essentially linear co- and terpolymers formed from at least one monomer containing acid groups or precursors thereof, such as acrylic acid, methacrylic acid, the salts thereof, or maleic acid (anhydride). A specific example is a copolymer obtained from <NUM>% ethyl acrylate and <NUM>% acrylic acid. The molecular weights of the copolymers are in the range of <NUM>,<NUM> to <NUM>,<NUM>, preferably from <NUM>,<NUM> to <NUM>,<NUM>. The acrylic acid/ethyl acrylate copolymer used in the examples has a molecular weight of <NUM>,<NUM> and is used against Mg(OH)<NUM> and CaCO<NUM> scale. The effect of the copolymer on the scale-forming matter in sea water and other hard water is shown indirectly by measurements of the heat transfer coefficient. An effect of said copolymer on the inhibition of the formation of brucite could however not be confirmed by the present inventors. In any case there is room for improvement.

<CIT> relates to a process for inhibiting or preventing the deposit of scale, in particular of alkaline earth metal scale such as magnesium hydroxide, in desalination processes using maleic anhydride copolymers as scale inhibitor. In the examples, the dispersive effect of maleic anhydride copolymers (i. a maleic anhydride/diisobutylene copolymer) in alkalinized sea water is examined and compared with that of an acrylic acid/ethyl acrylate copolymer with a molar ratio of acrylic acid and ethyl acrylate of <NUM>:<NUM> and a molecular weight of <NUM>. It is not indicated whether the molecular weight is the number-average (Mn) or the weight average (Mw) molecular weight; nor is it indicated whether the molecular weight relates to the polymer in its acid or in its salt form. This comparative acrylic acid/ethyl acrylate copolymer is said to have a very weak dispersive effect on the magnesium hydroxide-containing scale.

While the maleic anhydride copolymers of <CIT> as well as the comparative acrylic acid/ethyl acrylate copolymer show a dispersing effect on Mg(OH)<NUM> particles and possibly other scale matter not explicitly identified in the examples of this document (this effect being only weak in case of the comparative acrylic acid/ethyl acrylate copolymer), meaning that the copolymers used in this document disperse already present solid matter and thus reduce the deposition thereof on surfaces, it is desirable to avoid the formation of magnesium hydroxide-containing solid matter from the outset. In other words, it is desirable not only to keep already formed solid matter in dispersion and avoid its deposition, but additionally or alternatively to suppress the formation of magnesium hydroxide-containing crystals or amorphous forms.

It is an object of the present invention to provide an anti-scaling agent, which efficiently reduces or even inhibits the formation of magnesium hydroxide containing scale without requiring phosphorous containing compounds. The anti-scaling agent should also reduce or even inhibit the formation of other calcium- and magnesium-containing scales, in particular calcium-containing scales, such as the typically occurring CaCO<NUM> or CaSO<NUM> scales. In particular, the anti-scaling agent should not be limited to a dispersing effect, but instead or at least additionally suppress the formation of magnesium hydroxide-containing solid matter from the outset.

It was surprisingly found that certain copolymers, which consist of at least <NUM>% by weight, based on the total weight of the copolymer in its acid form, of a combination of polymerized units of acrylic acid and polymerized units of a C<NUM>-C<NUM> alkyl acrylate, efficiently reduce or even inhibit the formation of magnesium hydroxide containing scale in water bearing systems, where the formation of magnesium hydroxide containing scale is to be expected, if the amount of polymerized units of the C<NUM>-C<NUM> alkyl acrylate is in the range from <NUM> to <NUM>% by weight, based on the total weight of the copolymer in its acid form, and if the copolymer in the form of its sodium salt has a weight average molecular weight Mw in the range from <NUM> to <NUM>/mol, as determined by gel permeation chromatography.

Therefore, a first aspect of the present invention relates to the use of the copolymers as defined herein for reducing or even inhibiting the formation of magnesium hydroxide containing scale, as defined in claim <NUM>.

A second aspect of the present invention also relates to a method for reducing the formation of magnesium hydroxide containing scale in water-treatment units for processing Mg containing water, which comprises the addition of a copolymer as defined herein to the Mg containing water to be treated in the water-treatment unit, as defined in claim <NUM>.

Without being bound by theory, it is believed that the copolymers as defined herein hamper the crystallisation of magnesium hydroxide, i.e. Mg(OH)<NUM>, from the Mg containing water and thereby reduce or inhibit the formation of insoluble Mg(OH)<NUM>. The copolymers as described herein may additionally have a dispersing effect for insoluble Mg(OH)<NUM> and thus prevent the formation of large-area magnesium hydroxide containing deposits.

The present invention is associated with several benefits. First of all, the copolymers as defined herein provide for efficient reduction or inhibition of the formation of magnesium hydroxide containing scale in water bearing systems, where formation of insoluble magnesium hydroxide is likely to occur. While it is possible to apply the copolymers defined herein in combination with one or more further anti-scaling agents, in particular with a scale dispersant, the copolymers defined herein do not require phosphorous containing anti-scaling agents that are normally required for achieving efficient reduction or inhibition of the formation of magnesium hydroxide containing scale. Apart from that, the copolymers defined herein have a high calcium tolerance, as they do not form insoluble complexes with calcium salts. Rather, they also provide efficient inhibition of the formation of other scales, in particular Ca scales, e.g. scales based on CaCO<NUM> and/or CaSO<NUM>. Furthermore, they show a good inhibition of magnesium hydroxide containing scale at high salinity and thus can be used for the treatment of water having high salinity, such as seawater or brackish water. Moreover, the copolymers of the present invention are easily prepared from readily available and inexpensive monomers by standard copolymerization techniques.

Here and in the following, magnesium hydroxide containing scale refers to scale which contains crystalline magnesium hydroxide. In particular, the magnesium hydroxide containing scale predominately contains crystalline magnesium hydroxide or essentially consists thereof. This crystalline magnesium hydroxide is typically present in the brucite form. Thus, the Mg content in magnesium hydroxide containing scale, calculated as elemental Mg, is frequently at least <NUM>% by weight based on the dry scale. Magnesium hydroxide containing scale can usually be identified by one or more of the characteristic reflections of brucite present in a powder X-ray diffractogram, in particular by one or more reflections, quoted as 2θ values (<NUM> and Cu-Kα radiation) at: <NUM> ± <NUM>°, <NUM> ± <NUM>°, <NUM> ± <NUM>° and <NUM> ± <NUM>°.

Here and in the following, the term "C<NUM>-C<NUM> alkyl" refers to methyl, ethyl, n-propyl and isopropyl.

Here and in the following, the phrase "reduction or inhibition of the formation of magnesium hydroxide containing scale" means that the formation of magnesium hydroxide containing scale, in particular brucite containing scale, in a water bearing system is significantly reduced by at least <NUM>%, in particular by at least <NUM>% or at least <NUM>% compared to a water bearing system without anti-scaling agent.

Here and in the following, water-treatment unit(s) means any device or arrangement of devices, wherein water is treated and where internal surfaces are in contact with the water to be treated.

Unless specified otherwise, where the amounts or concentrations of components are given as "ppm", this corresponds to <NUM> of component per <NUM>,<NUM>,<NUM> of reference substance. If the unit "ppm" is used to define the concentration of a component in water, given the density of water as close to <NUM>/l, <NUM> ppm can also be understood as <NUM> of the component per <NUM><NUM> of water.

The copolymers of the present invention have a weight average molecular weight MW in the range from <NUM> to <NUM>/mol, in particular in the range from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol; more preferably in the range from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol and preferably <NUM> to <NUM>/mol; especially in the range from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol or preferably <NUM> to <NUM>/mol; and very specifically ><NUM> to <NUM>/mol, more specifically ><NUM> to <NUM>/mol and most specifically ><NUM> to <NUM>/mol, as determined by gel permeation chromatography of the sodium salt in buffered water at pH <NUM>. The number average molecular weight MN of the copolymers of the present invention in the form of their sodium salts is frequently in the range from <NUM> to <NUM>/mol, in particular in the range from <NUM> to <NUM>/mol, more preferably in the range from <NUM> to <NUM>/mol and especially in the range from <NUM> to <NUM>/mol, as determined by gel permeation chromatography. Frequently, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the copolymer in the form of its sodium salt, i.e. the ratio MW/MN is in the range from <NUM> to <NUM>, in particular in the range from <NUM> to <NUM>.

Both weight average molecular weights (Mw) and number average molecular weights (Mn) as referred herein relate to the molecular weight of the sodium salt of the respective copolymer, which is determined by gel permeation chromatography, in the following abbreviated as GPC. Gel permeation chromatography is usually carried out by using crosslinked acrylate copolymers of defined pore size as stationary phase, water buffered to pH <NUM> as the eluent and polyacrylic acid sodium salts as standards. Further details on GPC are given below in the experimental part.

With regard to the use of the copolymers for reduction or inhibition of the formation of magnesium hydroxide containing scale, the amount of polymerized units of the C<NUM>-C <NUM> alkyl acrylate is preferably in the range of <NUM> to <NUM>% by weight, in particular in the range of <NUM> to <NUM>% by weight, based on the total weight of the copolymer in the form of its sodium salt. Particular preference is also given to copolymers, where the amount of polymerized units of the C<NUM>-C<NUM> alkyl acrylate is preferably in the range of <NUM> to <NUM>% by weight or in the range of <NUM> to <NUM>% by weight or in the range from <NUM> to <NUM>% by weight, based on the total weight of the copolymer in the form of its sodium salt.

The molar ratio of polymerized acrylic acid to the polymerized C<NUM>-C<NUM> alkyl acrylate is usually in the range from <NUM>:<NUM> to <NUM>:<NUM>, in particular in the range from <NUM>:<NUM> to <NUM>:<NUM> and especially in the range from <NUM>:<NUM> to <NUM>:<NUM>. Particular preference is also given to copolymers, where the molar ratio of polymerized acrylic acid to the polymerized C<NUM>-C <NUM> alkyl acrylate is in the range from <NUM>:<NUM> to <NUM>:<NUM> or in the range from <NUM>:<NUM> to <NUM>:<NUM> or in the range from <NUM>:<NUM> to <NUM>:<NUM>.

Preference is given to copolymers, where the polymerized C<NUM>-C<NUM> alkyl acrylate monomer is ethyl acrylate or a mixture thereof with another C<NUM>-C<NUM> alkyl acrylate. Particular preference is given to copolymers, where the polymerized C<NUM>-C<NUM> alkyl acrylate is ethyl acrylate or comprises at least <NUM>% by weight or ethyl acrylate, based on the total amount of polymerized C<NUM>-C<NUM> alkyl acrylate.

Besides polymerized acrylic acid and the polymerized C<NUM>-C<NUM> alkyl acrylate, the copolymers may comprise up to <NUM>% by weight, especially at most <NUM>% by weight and at least at most <NUM>% by weight, or even <NUM>% by weight, based on the total amount of monomers forming the copolymer, of one or more polymerized monomers, which are different from acrylic acid and the C<NUM>-C<NUM> alkyl acrylate. Examples of such monomers include, but are not limited to, monoethylenically unsaturated monocarboxylic acids having <NUM> to <NUM> carbon atoms, such as methacrylic acid, monoethylenically unsaturated dicarboxylic acids having <NUM> to <NUM> carbon atoms, such as maleic acid, or the anhydrides thereof, such as maleic anhydride, water-soluble neutral monoethylenically unsaturated monomers having a solubility in deionized water of at least <NUM>/L at <NUM>, including the amides of monoethylenically unsaturated monocarboxylic acids having <NUM> to <NUM> carbon atoms, such as acrylamide or methacrylamide, the hydroxy-C<NUM>-C<NUM>-alkyl esters of monoethylenically unsaturated monocarboxylic acids having <NUM> to <NUM> carbon atoms, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, or hydroxypropyl methacrylate. In particular, the copolymers of the present invention do not contain any ethylenically unsaturated monomer having a phosphor containing functional group or a sulfur containing functional group.

Particular preference is given to copolymers which do not contain more than <NUM> ppm of phosphorous, in particular less than <NUM> ppm of phosphorous.

Particular preference is given to copolymers, which consist to at least <NUM>% by weight, in particular at least <NUM>% by weight and especially at least <NUM>% by weight, based on the total weight of the polymerized monomers of acrylic acid and ethyl acrylate, where the molar ratio of polymerized acrylic acid to the polymerized ethyl acrylate is preferably in the range from <NUM>:<NUM> to <NUM>:<NUM>, in particular in the range from <NUM>:<NUM> to <NUM>:<NUM> and especially in the range from <NUM>:<NUM> to <NUM>:<NUM>. Particular preference is also given to copolymers, which consist to at least <NUM>% by weight, in particular at least <NUM>% by weight and especially at least <NUM>% by weight, based on the total weight of the polymerized monomers of acrylic acid and ethyl acrylate, where the molar ratio of polymerized acrylic acid to the polymerized ethyl acrylate is preferably in the range from <NUM>:<NUM> to <NUM>:<NUM> or in the range from <NUM>:<NUM> to <NUM>:<NUM> or in the range from <NUM>:<NUM> to <NUM>:<NUM>.

Even more preference is given to copolymers, which consist to at least <NUM>% by weight, in particular at least <NUM>% by weight and especially at least <NUM>% by weight, based on the total weight of the polymerized monomers of acrylic acid and ethyl acrylate, where the molar ratio of polymerized acrylic acid to the polymerized ethyl acrylate is preferably in the range from <NUM>:<NUM> to <NUM>:<NUM>, in particular in the range from <NUM>:<NUM> to <NUM>:<NUM> and especially in the range from <NUM>:<NUM> to <NUM>:<NUM>, and where the weight average molecular weight MW of the copolymer in the form of its sodium salt ranges from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol; preferably from <NUM> to <NUM>/ mol, such as <NUM> to <NUM>/mol or <NUM> to <NUM>/mol; in particular from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol or <NUM> to <NUM> or <NUM> to <NUM>/mol; specifically from ><NUM> to <NUM>/mol, more specifically from ><NUM> to <NUM>/mol, very specifically from ><NUM> to <NUM>/mol, as determined by gel permeation chromatography in buffered water at pH <NUM>, where the number average molecular weight MN of the copolymers in its sodium form is in the range from <NUM> to <NUM>/mol, in particular in the range from <NUM> to <NUM>/mol, especially in the range from <NUM> to <NUM>/mol, as determined by gel permeation chromatography in buffered water at pH <NUM>, and where the ratio MW/MN is in the range from <NUM> to <NUM>, in particular in the range from <NUM> to <NUM>. Even more preference is also given to copolymers, which consist to at least <NUM>% by weight, in particular at least <NUM>% by weight and especially at least <NUM>% by weight, based on the total weight of the polymerized monomers of acrylic acid and ethyl acrylate, where the molar ratio of polymerized acrylic acid to the polymerized ethyl acrylate is preferably in the range from <NUM>:<NUM> to <NUM>:<NUM> or in the range from <NUM>:<NUM> to <NUM>:<NUM> or in the range from <NUM>:<NUM> to <NUM>:<NUM>, and where the weight average molecular weight MW of the copolymer in the form of its sodium salt ranges from <NUM> to <NUM>/ mol, such as <NUM> to <NUM>/mol; preferably from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol or from <NUM> to <NUM>/mol; in particular from <NUM> to <NUM>/mol, such as <NUM> to <NUM>/mol or <NUM> to <NUM> or <NUM> to <NUM>/mol; specifically from ><NUM> to <NUM>/mol, more specifically from ><NUM> to <NUM>/mol, very specifically from ><NUM> to <NUM>/mol, as determined by gel permeation chromatography in buffered water at pH <NUM>, where the number average molecular weight MN of the copolymers in its sodium form is in the range from <NUM> to <NUM>/mol, in particular in the range from <NUM> to <NUM>/mol, especially in the range from <NUM> to <NUM>/mol, as determined by gel permeation chromatography in buffered water at pH <NUM>, and where the ratio MW/MN is in the range from <NUM> to <NUM>, in particular in the range from <NUM> to <NUM>.

While the copolymers of the present invention may have any molecular architecture, they are preferably statistical copolymers. Statistical copolymers are understood as copolymers, in which the distribution of the two monomers, here acrylic acid and the C <NUM>-C<NUM> alkyl acrylate, in the chain follows a statistical distribution. In other words, the ratio of the monomers in a section corresponds to the molar ratio of the monomers (random distribution). The copolymers may have a linear or branched structure, but preferably they are essentially linear. The copolymers are in particular statistical copolymers having a linear structure. In one precautionary embodiment, the copolymer is not an acrylic acid/ethyl acrylate copolymer having a molar ratio of acrylic acid to ethyl acrylate of <NUM>:<NUM> and a weight average molecular weight MW of <NUM>,<NUM>/mol (the MW relating either to the copolymer in the form of its sodium salt or in form of the free acid), as determined by gel permeation chromatography (i.e. in an embodiment the copolymer is not the acrylic acid/ethyl acrylate copolymer possibly used in the comparative example of <CIT>).

The copolymers of the present invention can be prepared by copolymerization acrylic acid and at least one C<NUM>-C<NUM> alkyl acrylate by analogy to known methods for copolymerizing ethylenically unsaturated monomers as described e.g. in "<NPL>) and <NPL>" and the literature cited therein.

Preferably, the copolymer is obtainable by a free-radical solution copolymerization of acrylic acid and at least one C<NUM>-C<NUM> alkyl acrylate. More preferably, the copolymer is obtainable by a free-radical aqueous solution copolymerization of acrylic acid and at least one C<NUM>-C<NUM> alkyl acrylate. The term "free-radical polymerization" means that the polymerization of the ethylenically unsaturated monomers, here acrylic acid and the C<NUM> -C<NUM> alkyl acrylate, is performed in the presence of a polymerization initiator, which, under polymerization conditions, forms radicals, either by thermal or photolytic decomposition or by a redox reaction. "Solution polymerization" means that in the polymerization reaction the monomers are present in solution in a solvent which is also capable of dissolving the copolymer. A free-radical solution copolymerization is thus a polymerization performed in solution and in the presence of a polymerization initiator forming radicals under polymerization conditions. "Aqueous solution polymerization" means that solvent comprises or consists of water.

Suitable solvents for performing the solution polymerization include water and polar organic solvents and mixtures thereof with water. Suitable polar organic solvents are those, which are at least partially miscible with water and which preferably are miscible with water to an extent of at least <NUM>/L at <NUM> and ambient pressure. Suitable organic solvents include, but are not limited to C<NUM>-C<NUM>-alkanols, such as methanol, ethanol, propanol, isopropanol (= <NUM>-propanol), n-butanol, sec-butanol (= <NUM>-butanol) or isobutanol, glycols, such as ethylene glycol or diethylene glycol, dimethyl sulfoxide, dimethyl formamide, tetrahydrofuran or the dioxans. Preferred organic solvents are selected from C<NUM>-C<NUM>-alkanols, such as methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol or isobutanol, preferably isopropanol or sec-butanol. In particular, solvents for performing the solution polymerization are selected from water and mixtures of water and at least one polar organic solvent, preferably from water and mixtures of water and one or more C<NUM>-C<NUM>-alkanols. Especially, the solvent used for the copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate contains at least <NUM>% by volume, in particular at least <NUM>% by volume, based on the total amount of solvent.

If the copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate is conducted as a solution polymerization, the concentration of the monomers in the polymerization reaction may vary. In particular, the weight ratio of the monomers and the solvent will be in the range from <NUM>:<NUM> to <NUM>:<NUM>, in particular in the range from <NUM>:<NUM> to <NUM>:<NUM> and especially in the range from <NUM>:<NUM> to <NUM>:<NUM>.

The copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate is preferably a free-radical copolymerization and thus triggered by means of a free-radical polymerization initiator (free-radical initiator). These may in principle be peroxides or azo compounds. Of course, redox initiator systems may also be used.

Suitable peroxides may, in principle, be inorganic peroxides, such as hydrogen peroxide or peroxodisulfates, such as the mono- or di-alkali metal or ammonium salts of peroxodisulfuric acid, for example the mono- and disodium, -potassium or ammonium salts, or organic peroxides, e.g. peroxy acids and esters of peroxy acids, such as diisopropyl peroxydicarbonate, t-amyl perneodecanoate, t-butyl perneodecanoate, t-butyl perpivalate, t-amyl perpivalate, bis(<NUM>,<NUM>-dichlorobenzoyl) peroxide, diisononanoyl peroxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide, bis(<NUM>-methylbenzoyl) peroxide, disuccinoyl peroxide, diacetyl peroxide, dibenzoyl peroxide, t-butyl per-<NUM>-ethylhexanoate, t-butyl-<NUM>-ethylhexanoate, bis(<NUM>-chlorobenzoyl) peroxide, t-butyl perisobutyrate, t-butyl permaleate, <NUM>,<NUM>-bis(t-butyl peroxy)cyclohexane, t-butyl peroxyisopropylcarbonate, t-butyl perisononanoate, t-butyl peracetate, t-amyl perbenzoate, <NUM>-(t-butylperoxy)-<NUM>-phenylphthalide or t-butyl perbenzoate, alkyl and cycloalkyl peroxides such as <NUM>,<NUM>-bis(t-butyl peroxy)-<NUM>,<NUM>,<NUM>-trimethylcyclohexane, <NUM>,<NUM>-bis(t-butylperoxy)butane (di-t-butyl peroxide), <NUM>,<NUM>-bis-<NUM>-(t-butylperoxy)propane, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-bis(t-butylperoxy)hexane, di(t-amyl) peroxide, α,α'-bis(t-butylperoxyisopropyl)benzene, <NUM>,<NUM>-bis(t-butylperoxy)-<NUM>,<NUM>-dimethyl-<NUM>,<NUM>-dioxolane, di(t-butyl) peroxide, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-bis(t-butylperoxy)hexyne, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-hexamethyl-<NUM>,<NUM>,<NUM>,<NUM>-tetraoxacyclononane, p-menthane hydroperoxide, pinane hydroperoxide, aromatic peroxides such as dicumyl peroxide, diisopropylbenzene, mono-α-hydroperoxide or cumene hydroperoxide. A suitable peroxide may also be hydrogen peroxide.

Typical azo initiators are, for example, <NUM>,<NUM>'-azobis-<NUM>-cyanovaleric acid (ACVA), <NUM>,<NUM>'-azobis(<NUM>-methylpropionamidine) dihydrochloride, <NUM>,<NUM>'-azobis(<NUM>-methylpropionitrile) (AIBN), <NUM>,<NUM>'-azobis(<NUM>-methylbutanenitrile), <NUM>,<NUM>'-azobis(<NUM>,<NUM>-dimethylvaleronitrile), <NUM>,<NUM>'-azobis(cyanocyclohexane), <NUM>,<NUM>'-azobis(N,N-dimethylformamide), <NUM>,<NUM>'-azobis(<NUM>-methylbutyronitrile), <NUM>,<NUM>'-azobis(<NUM>-methoxy-<NUM>,<NUM>-dimethylvaleronitrile), <NUM>,<NUM>'-azobis(<NUM>,<NUM>,<NUM>-trimethylpentane), <NUM>,<NUM>'-azobisisobutyronitrile, <NUM>,<NUM>'-azobis(<NUM>-methylbutyronitrile), <NUM>,<NUM>'-azobis(<NUM>,<NUM>-dimethylvaleronitrile), <NUM>,<NUM>'-azobis(<NUM>-methoxy-<NUM>,<NUM>-dimethylvaleronitrile), <NUM>,<NUM>'-azobis(<NUM>-cyclohexanecarbonitrile), <NUM>,<NUM>'-azobis(isobutyramide) dihydrate, <NUM>-phenylazo-<NUM>,<NUM>-dimethyl-<NUM>-methoxyvaleronitrile, dimethyl <NUM>,<NUM>'-azobisisobutyrate, <NUM>-(carbamoylazo)isobutyronitrile, <NUM>,<NUM>'-azobis(<NUM>,<NUM>,<NUM>-trimethylpentane), <NUM>,<NUM>'-azobis(<NUM>-methyl propane), <NUM>,<NUM>'-azobis(N,N'-dimethyleneisobutyramidine), <NUM>,<NUM>'-azobis(N,N'-dimethyleneisobutyramidine) hydrochloride, <NUM>,<NUM>'-azobis(<NUM>-amidinopropane), <NUM>,<NUM>'-azobis(<NUM>-amidinopropane) hydrochloride, <NUM>,<NUM>'-azobis(<NUM>-methyl-N-[<NUM>,<NUM>-bis(hydroxymethyl)ethyl]propionamide), azobis(<NUM>-amidopropane) dihydrochloride or <NUM>,<NUM>'-azobis(<NUM>-methyl-N[<NUM>,<NUM>-bis(hydroxymethyl)-<NUM>-hydroxyethyl]propionamide).

Typical redox initiators are, for example, mixtures of an oxidizing agent, such as hydrogen peroxide, peroxodisulfates or aforementioned peroxide compounds, and a reducing agent. Corresponding reducing agents, which may be used are sulfur compounds with a low oxidation state, such as alkali metal sulfites, for example potassium and/or sodium sulfite, alkali metal hydrogensulfites, for example potassium and/or sodium hydrogensulfite, alkali metal metabisulfites, for example potassium and/ or sodium metabisulfite, formaldehydesulfoxylates, for example potassium and/or sodium formaldehydesulfoxylate, alkali metal salts, specifically potassium and/or sodium salts of aliphatic sulfinic acids and alkali metal hydrogensulfides, for example potassium and/or sodium hydrogensulfide, salts of polyvalent metals, in particular Co(II) salts and Fe(II) salts, such as iron(II) sulfate, iron(II) ammonium sulfate or iron(II) phosphate, but also dihydroxymaleic acid, benzoin and/or ascorbic acid, and reducing saccharides, such as sorbose, glucose, fructose and/or dihydroxyacetone.

Preferably, the free-radical polymerization initiator comprises an inorganic peroxide, in particular a peroxodisulfate, such as the mono- or di-alkali metal or ammonium salts of peroxodisulfuric acid. In particular, the free-radical polymerization initiator is a redox initiator, which comprises an inorganic peroxide, in particular a peroxodisulfate, such as the mono- or di-alkali metal or ammonium salts of peroxodisulfuric acid as the oxidizing agent. In these redox initiators, the reducing agent is preferably selected from the group of sulfur compounds with a low oxidation state, such as alkali metal sulfites, for example potassium and/or sodium sulfite, alkali metal hydrogensulfites, for example potassium and/or sodium hydrogensulfite, alkali metal metabisulfites, for example potassium and/or sodium metabisulfite, formaldehydesulfoxylates, for example potassium and/or sodium formaldehydesulfoxylate, alkali metal salts, specifically potassium and/or sodium salts of aliphatic sulfinic acids and alkali metal hydrogensulfides, for example potassium and/or sodium hydrogensulfide. In these redox initiators, the molar amount of the reducing agent will exceed the molar amount of the oxidizing agent. In particular, the molar ratio of the reducing agent to the oxidizing agent is in the range from <NUM>:<NUM> to <NUM>:<NUM> and in particular in the range from <NUM>:<NUM> to <NUM>:<NUM>.

The molecular weight of the copolymer can be adjusted by choosing a proper relative amount of the free-radical polymerization initiator with respect to the monomers to be polymerized. As a rule of thumb, increasing the relative amount of the free-radical polymerization initiator will result in a decrease of the molecular weight, while decreasing the relative amount of the free-radical polymerization initiator will result in an increased molecular weight. If the free-radical polymerization initiator is selected from redox initiators, an increase of the molar ratio of the reducing agent to the oxidizing agent will likewise result in a decreased molecular weight and vice versa. Typically, the amount of the free-radical polymerization initiator is in the range of <NUM> to <NUM> mmol, in particular <NUM> to <NUM> mmol per <NUM> mol of monomers to be copolymerized. In case of redox initiators, these ranges refer to the oxidizing agent.

The copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate is usually conducted at temperatures in the range from <NUM> to <NUM>. Temperatures employed are frequently in the range from <NUM> to <NUM>, in particular in the range from <NUM> to <NUM> and especially in the range from <NUM> to <NUM>.

The copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate can be carried out at a pressure of less than, equal to or greater than <NUM> atm (atmospheric pressure), and so the polymerization temperature may exceed <NUM> and may be up to <NUM>. Polymerization of the monomers is normally performed at ambient pressure, but it may also be performed under elevated pressure. In this case, the pressure may assume values of <NUM> to <NUM> bar (absolute) or even higher values. Frequently, the free-radical polymerization of the invention is conducted at ambient pressure (about <NUM> atm) with exclusion of oxygen, for example under an inert gas atmosphere, for example under nitrogen or argon.

The copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate can be polymerized e.g. by a batch or semi-batch procedure or by a continuous procedure. In the batch procedure, the monomers to be polymerized and optionally the solvent used in the polymerization procedure is charged to a reaction vessel, while the majority or the total amount of the polymerization initiator is added to the reaction vessel in the course of the polymerization reaction. In a semi batch procedure, at least a portion or the total amount of the free-radical polymerization initiator and solvent and optionally a small portion of the monomers are charged to the reaction vessel, and the majority of monomers to be polymerized are added to the reaction vessel in the course of the polymerization reaction. In a continuous process, the monomers and polymerization initiator and the solvent are continuously added to a reaction vessel, and the obtained copolymer is continuously discharged from the polymerization vessel. Preferably, the copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate is carried out as a semi-batch procedure. In particular, at least <NUM>% of the monomers to be polymerized are added to the reaction vessel in the course of the polymerization reaction.

The copolymerisation of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate may also include a step where any residual monomers are removed, e.g. by physical means, such as distillation or by chemical means, i.e. by forced radical polymerization, e.g. by using a second free-radical polymerization initiator, which is added to the polymerization reaction after at least <NUM>% of the monomers to be polymerized have been reacted. Preferably, the second free-radical polymerization initiator is an organic hydroperoxide, such as tert-butyl hydroperoxide.

The copolymer can typically be isolated from the resulting polymerization mixture by means of relatively customary methods, e.g. by means of precipitation or distillation. However, it is also possible to use the solution of the copolymers as obtained by solution polymerization of acrylic acid and the C<NUM>-C<NUM> alkyl acrylate, in particular, if the solvent is water or contains water. Frequently, the concentration of the copolymer in such solutions is in the range from <NUM> to <NUM> wt. -%, in particular in the range from <NUM> to <NUM> wt.

The copolymers of the present invention are particularly useful for inhibiting or reducing the formation of magnesium hydroxide containing scale, in particular brucite containing scale, in water bearing systems, in particular in water-treatment units, which are in permanent contact with Mg containing water and where thus a high risk exists that magnesium hydroxide containing scale will form.

Therefore, the present invention also relates to a method for reducing or inhibiting the formation of magnesium hydroxide containing scale, in particular brucite containing scale, in a water-treatment unit for processing Mg containing water, which comprises the addition of a copolymer as defined to the Mg containing water to be treated in the water-treatment unit, as defined in claim <NUM>.

As mentioned above, a risk particularly exists in any water bearing system, in particular in water treatment units, where the Mg concentration of the water to be treated contains at least <NUM> ppm Mg, in particular at least <NUM> ppm Mg, or at least <NUM> ppm Mg or at least <NUM> ppm Mg, calculated as Mg<NUM>+. As the solubility of Mg(OH)<NUM> decreases with increasing pH and also with increasing temperature, a particular risk for the formation of magnesium hydroxide containing scale exists if the water-treatment unit is operated at pH values of at least pH <NUM>, e.g. in the range of pH <NUM> to pH <NUM>, as determined at <NUM>, and/or the water-treatment unit is operated at temperatures of at least <NUM>, in particular at least <NUM>. Therefore, according to particular embodiments of the invention, relate to the use and method of the invention, where at least one of the following conditions are met:.

For effectively reducing or inhibiting the formation of magnesium hydroxide containing scale, the copolymer will be usually added to the Mg containing water to be treated in the water-treatment unit, such that a concentration of the copolymer in the Mg containing water to be treated in the water-treatment unit is at least <NUM>/m<NUM>, in particular at least <NUM>/m<NUM>, e.g. in the range from <NUM> to <NUM>/m<NUM>, preferably in the range of from <NUM> to <NUM>/m<NUM>, in particular in the range of from <NUM> to <NUM>/m<NUM>, e.g. from <NUM> to <NUM>/m<NUM> or from <NUM> to <NUM>/m<NUM>. In a specific embodiment, the copolymer will be added to the Mg containing water to be treated in the water-treatment unit, such that a concentration of the copolymer in the Mg containing water to be treated in the water-treatment unit is in the range of from <NUM> to <NUM>/m<NUM> or very specifically from <NUM> to <NUM>/m<NUM>.

In a particular group of embodiments, the water treatment unit is a seawater desalination unit, in particular a seawater desalination unit, which includes a multi effect distillation unit and/or a multi-stage-flushing distillation unit, or a seawater desalination unit having a reverse osmosis unit. The water to be processed in the seawater desalination unit may be seawater or brackish water. The copolymer may be dosed into the treatment unit at any state of the process, e.g. in the seawater or brackish water to be treated or in the distillation units or into the reverse osmosis unit.

In a particular group of embodiments, the water treatment unit is a greywater treatment unit, wherein greywater from a syngas process is treated. In a syngas process, the greywater cycle is a cycle, which is used to wash and cool the syngas in a two-step process and therefore contains a lot of suspended solids and has a high concentration of both Mg and Ca ions. The greywater system is sensitive to scaling and deposits due to the high suspended solids content and high hardness in the water. In particular, serious scaling can occur in the washing tower and nozzles as well as in the water return line to the sedimentation basin. Adding the copolymers of the present invention to the greywater cycle at the above dose rates will efficiently reduce scaling due to its capability of inhibiting the formation of both magnesium hydroxide and CaCO<NUM> scales.

The copolymers as defined herein are compatible with the anti-scaling agents, which are commonly used for reducing or inhibiting the formation of magnesium hydroxide containing scale, in particular in seawater desalination units or in greywater treatment units. Therefore, the copolymers as defined herein can be used in combination with a further anti-scaling agent, in particular with a scale dispersant, i.e. anti-scaling agents, which assist in dispersing insoluble inorganic material, which may form in the water-treatment unit. The use of the copolymers of the present invention may also be combined with conventional mechanical cleaning, such as sponge ball cleaning.

GPC was performed by using an Agilent 1200er Series equipped with a PSS Security Degasser and a column oven adjusted to <NUM> and a detection system measuring the refractive index. Columns used (in the direction of flow):.

As an eluent, ultrapure Water (Merck Millipore) which supplemented with <NUM> NaNO<NUM> and <NUM> NaH<NUM>PO<NUM>/Na<NUM>HPO<NUM> buffer to adjust pH <NUM> was used. Prior to use, the eluent was filtered over a <NUM> cellulose acetate filter membrane.

Polymer samples were diluted in a ratio of <NUM>/<NUM> with deionized water and adjusted to pH <NUM> by addition of <NUM>% sodium hydroxide solution.

Samples were diluted with the eluent containing the internal standard ethylene glycol to reach a polymer concentration of <NUM>-<NUM>/liter. The samples are filtered with <NUM> cellulose acetate (or hydrophilized PTFE) syringe filters prior to measurement.

For calibration narrowly dispersed poly(acrylic acid) sodium salt standards of PSS (Polymer Standard Service GmbH Germany) with the following peak molecular weights in Dalton were used:.

For calibration purposes, the GPC curves of the narrowly dispersed standard were analysed with regard to the retention volume of their refractive index intensity peak using the Win GPC UniChrom software from PSS (Polymer Standard Service GmbH Germany). A calibration correlation curve was created by means of polynomial fit (Polynomial <NUM>).

The viscosity of the polymer solutions was measured at <NUM> ± <NUM>°C by using a Brookfield digital viscosimeter (Brookfield Engineering Laboratories, Inc. ) with spindle <NUM> at a rotational speed of <NUM> rpm.

pH was determined by direct measurement at <NUM> ± <NUM>°C using a Mettler Toledo In lab routine pH electrode connected to a WTW <NUM> pH meter (WTW Germany) calibrated by WTW buffer solutions.

The following polymerization reactions were carried out in a <NUM> double jacket glass reactor connected to heating bath circulation thermostat, equipped with a <NUM> stainless steel stirrer, a condenser connected to a bubble counter outlet, fitted with a thermocouple and two additional necks for charging and dosing liquids. Except for the outlet of the condenser, the reactor is sealed gas tight.

A mixture of water (<NUM>) and <NUM>% b. sulfuric acid (<NUM>) was added to the reactor and heated to <NUM> with stirring.

The initiator mixtures were prepared, charged into disposable PP syringes equipped with PTFE tubes (<NUM> inner diameter) and mounted to syringe pumps:.

A mixture of acrylic acid (<NUM>) and ethyl acrylate (<NUM>) was charged into a glass cylinder connected to a double piston pump.

Once the internal temperature of the reactor reached at least <NUM>, about <NUM>% of the aqueous sodium bisulfite solution (about <NUM>) was charged to the reactor. The reactor temperature was set to automatic control with a target temperature of <NUM>. Feeds of monomer and initiator solutions (Syringes <NUM> and <NUM>) were started simultaneously within <NUM> minutes from this point at the respective feed rates. The feeds were dropped through separate dozing nozzles.

The feed/dosing times of the separate solutions were.

<NUM> minutes after the end of the last feed (sodium persulfate solution), a chaser solution of <NUM>% b. butyl hydroperoxide (<NUM>) in water (<NUM>) was gradually added by means of a syringe pump within <NUM> minutes, while cooling to <NUM> to reduce potential residual monomer. <NUM> minutes after the end of the addition of the chaser solution, the polymerization mixture was cooled to <NUM>. Then water was added (<NUM>). After the internal temperature of the reactor had dropped below <NUM>, <NUM>% b. aqueous NaOH (<NUM>) was added with a funnel while keeping the temperature below <NUM>.

Remaining NaOH in the funnel was flushed with water (<NUM>) into the reactor. Residual bisulfite/SO<NUM> was determined iodometrically and converted by oxidation with an equimolar amount of hydrogen peroxide <NUM>% (<NUM>), and the product was further cooled to <<NUM>. Water was added to adjust the solution to a total mass of <NUM>.

The resulting polymer solution had the following properties:.

The polymers of preparation examples <NUM> to <NUM> and of comparative examples C4 to C7 were prepared by analogy to the protocol of preparation example <NUM>. The amounts of monomers and initiators are summarized in the following table <NUM>. The properties of the resulting polymer solutions are summarized in table <NUM>.

A mixture of water (<NUM>) and <NUM>% b. sulfuric acid (<NUM>) was added to the reactor and heated to <NUM> with stirring (Stirrer speed: <NUM> rpm).

The initiator solutions were prepared, charged into disposable PP syringes equipped with PTFE tubes (<NUM> inner diameter) and mounted to syringe pumps:.

Acrylic acid (<NUM>) was charged into a glass cylinder connected to a double piston pump.

<NUM> minutes after the end of the last feed (sodium persulfate solution), the polymerization mixture was cooled to <NUM>. Then water was added (<NUM>). After the internal temperature of the reactor had dropped below <NUM>, <NUM>% b. aqueous NaOH (<NUM>) was added with a funnel while keeping the temperature below <NUM>.

Remaining NaOH in the funnel was flushed with water (<NUM>) into the reactor.

Residual bisulfite/SO<NUM> was determined iodometrically and converted by oxidation with an equimolar amount of hydrogen peroxide <NUM>% (<NUM>), and the product was further cooled to <<NUM>. Water was added to adjust the solution to a total mass of <NUM>.

The polymers of comparative examples <NUM> and <NUM> were prepared by analogy to the protocol of comparative example C1. The amounts of monomers and initiators are summarized in the following table <NUM>. The properties of the resulting polymer solutions are summarized in table <NUM>.

The solutions of the respective copolymer solutions obtained in the above examples were diluted to a concentration of <NUM>/L and used as stock solutions.

A test solution containing <NUM> mol/m<NUM> Mg<NUM>+ was prepared by dissolving a proper amount of magnesiumsulfate heptahydrate (MgSO<NUM> * <NUM><NUM>O) in deionized water. Then, <NUM> of the prepared solution was filled in a <NUM> Schott flask. Then, a defined amount of the polymer stock solution to give <NUM> ppm of active substance was added with stirring.

For each test series, a blank sample (without polymer) was tested. The pH of the respective test solution (also of the blank sample) was adjusted with <NUM> HCl to pH <NUM> ± <NUM>, and <NUM> of <NUM>% b. aqueous NaOH was added with stirring. The pH of the solution was <NUM>. Then, the flask was closed and left for <NUM> at <NUM>. Thereafter, the samples were shaken in order to distribute the precipitate evenly, and <NUM> of the sample was taken out, and the turbidity in FNU units of each sample was measured immediately by means of a turbidity meter (Hach). To check whether the experiment was carried out when a steady state had been reached, two blank samples were kept for a total of <NUM> at <NUM> and the turbidity of these samples was determined both after <NUM> and after <NUM>. The turbidity after <NUM> was essentially unchanged as compared to that after <NUM>, meaning that latest after <NUM> scale formation had reached a steady state. The degree of stabilization was calculated as follows: <MAT>.

From the thus obtained stabilization values, turbidity measurements at <NUM> ppm of active concentration are given in table <NUM>. The turbidity of the blank had <NUM> FNU.

To show that the copolymers according to the present invention also work as scale inhibitors for CaCO<NUM> as the most common scale type, some representative polymers were tested and compared to prior art scale inhibitors.

Evaluation of dynamic calcium carbonate scale inhibition was conducted in a test apparatus, which comprises a beaker (<NUM>) for test water, which is connected to a hose pump (<NUM>), a vertically mounted, thermostated glass cooler (<NUM>) with a helical internal glass tube and a cooling jacket (Fa. Normag; Art. : GSG <NUM><NUM>, <NUM> loops), where the helical tube is connected via the bottom inlet to the hose pump (<NUM>) and via its upper outlet to a measuring cylinder (<NUM>). A test solution of the composition according to Table <NUM> was prepared. First CaCl<NUM> • <NUM><NUM>O and MgSO<NUM> • <NUM><NUM>O were mixed, then the inhibitor in a concentration of <NUM> ppm was added, and sodium hydrogen carbonate solution was introduced as last. Over a two hour period <NUM> of the test solution was pumped at a constant flow rate of <NUM>/h through the helical glass tube heated by water of <NUM>. Then the water left in the cooler was pumped back with a reduced flow rate to avoid removal of loose precipitate. The exact amount of collected water was determined with a measuring cylinder. The calcium carbonate precipitated on the glass surface of the glass tube was dissolved with <NUM> % hydrochloric acid (<NUM>% HCI with deionized water, diluted <NUM>:<NUM>), and flushed into a <NUM> measuring flask. To remove hydrochloric acid residues, the glass cooler was flushed with <NUM> of deionized water which was collected in the same measuring flask. Deionized water was added to this flask to obtain a total volume of <NUM>. <NUM> of the solution were pipetted in an Erlenmeyer flask for titration which was then filled-up with <NUM> of deionized water. This solution was mixed with <NUM> of <NUM> % KOH and then titrated with an EDTA complexation solution using the indicator Calcon carboxylic acid. Comparison against a blind sample provided the relative calcium carbonate inhibition of the tested compound.

Following sources for the ionic components of the test water were used:.

Based on the consumption of the EDTA solution the calcium carbonate stabilization can be calculated by the following equation.

From the thus obtained stabilization values, for each tested copolymer measurements at <NUM> ppm of polymer concentration were taken and given in table <NUM>.

For assessing the stabilization of CaSO<NUM> <NUM> of solution with the composition mentioned in table <NUM> is prepared.

Then, the flasks were observed visually with regard to the precipitation of calcium sulfate for <NUM>. The dispersed calcium sulfate forms a white cloud in the solution. For each copolymer concentration <NUM> replications of this test are carried out.

For each replication, the formation of calcium sulfate is ranked for the first five hours (each hour) and then <NUM> after by the degree of cloudiness by the following grades:.

Preparations are done with including the copolymers (<NUM> ppm) and as blank.

If the blank solution does not become cloudy within <NUM>, the test is repeated.

The data are evaluated as follows: For each concentration of the copolymer, the grade of cloudiness after <NUM> is multiplied by <NUM> and summed up with the grades of cloudiness after <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. The obtained value is divided by <NUM>. The average of the thus obtained values for the <NUM> replications multiplied by <NUM> is the degree of stabilization in % at the given concentration of the copolymer.

Claim 1:
The use of a copolymer, which consists of at least <NUM>% by weight, based on the total weight of the copolymer in its acid form, of a combination of polymerized units of acrylic acid and polymerized units of a C<NUM>-C<NUM> alkyl acrylate, where the amount of polymerized units of the C<NUM>-C<NUM> alkyl acrylate is in the range from <NUM> to <NUM>% by weight, based on the total weight of the copolymer in its acid form, and where the copolymer in the form of its sodium salt has a weight average molecular weight Mw in the range from <NUM> to <NUM>/mol, as determined by gel permeation chromatography in buffered water at pH <NUM>, for reducing the formation of magnesium hydroxide containing scale.