GB2436107A

GB2436107A - Inhibiting silica and silicate scale in aqueous systems

Info

Publication number: GB2436107A
Application number: GB0506275A
Authority: GB
Inventors: Daniel Joubert; Gary Woodward; Keith Philip Davis
Original assignee: Rhodia UK Ltd
Current assignee: Solvay Solutions UK Ltd
Priority date: 2005-03-29
Filing date: 2005-03-29
Publication date: 2007-09-19
Also published as: GB0506275D0; WO2006103203A1

Abstract

A method of inhibiting silica and silicate scale in aqueous systems, comprises addition to the aqueous system a scale-inhibiting amount of a grafted co-polymer comprising at least three moieties of distinct chemical nature, said moieties being: <SL> <LI>i) a moiety for anchoring onto solid particles; <LI>ii) a hydrophobic moiety; <LI>iii) a hydrophilic moiety; </SL> wherein one of the moieties forms the principal chain, and the others form side chains; the grafted copolymer further comprising a number of functional groups as shown in claim 1. Fig. 4 shows an example of the polymer. Also disclosed is the use of such a composition.

Description

USE OF GRAFT CO-POLYMERS IN SILICA SCALE INHIBITION

This invention relates to a method of inhibiting fouling by silica and silicates in aqueous systems and, in particular, to the use of graft co-polymers comprising at least three sequences of distinct chemical nature to inhibit the deposition of silica and silicate scales on surfaces.

Scale inhibitors are used to treat a variety of aqueous systems such as boiler water, industrial process water, cooling water and water in central heating and air conditioning systems, to prevent deposition of calcium carbonate, or other alkaline earth metal scale from hard water systems. * *

However, although other types of scale, for example calcium carbonate or barium sulphate scale, are well controlled, silica is now a major fouling problem in aqueous systems. Silica is difficult to inhibit as it assumes low solubility forms depending on the conditions in the aqueous system. *..*

For example, below pH 7 monomeric silica tends to polymerize to form ** oligomeric or colloidal silica. At a pH of above 7, for example, pH 9.5, silica can form a monomeric silicate ion. As conversion of silica into these various forms can be slow, various forms of silica can co- exist in an aqueous system at any one time, depending on the history of the system.

Silicate ions can react with polyvalent cations, such as magnesium and calcium, to produce salts with limited solubility. Thus in aqueous systems it is common for a mixture of forms of silica to be present: monomeric, oligomeric and colloidal silica; magnesium silicate, calcium silicate and other silicate salts.

It is also possible for a variety of other types of scales to co-exist with silica or silicate scales in a water system. For example there may also be present scales based around calcium, magnesium, aluminium and iron in the same water system.

It is an object of the present invention to ameliorate silica and/or silicate fouling of aqueous systems. The applicants have now found that grafted co-polymers comprising at least three sequences of distinct chemical nature are beneficial in the control of silica and silicate fouling in aqueous systems.

Accordingly, in a first embodiment the present invention provides a method of inhibiting silica and silicate scale in aqueous systems, which method comprises the addition to the aqueous system of a scale inhibiting amount of a grafted co-polymer comprising at least three sequences of distinct chemical nature, the co-polymer comprising: * a principal chain onto which are directly grafted at least two side chains, S.,. * S S

the grafted copolymer further comprising: at least three sequences of distinct chemical nature, wherein (i) a first sequence of the at least three sequence of distinct chemical nature is a sequence for anchoring onto solid particles, (ii) a second sequence of the at least three sequences of distinct chemical nature is a sequence of hydrophobic character, and (iii) a third sequence of the at least three sequences of distinct chemical nature is a sequence of hydrophilic character; wherein one of the at least three sequences of distinct chemical nature forms said principal chain and the other two of the at least three sequences of distinct chemical nature form said side chains; the grafted copolymer further comprising: 1 to 80% by mass of the sequence for anchoring onto solid particles consisting of an anchoring straight hydrocarbon chain, cycloalkyl or aromatic, comprising basic nitrogenous groups selected from the groups consisting of: heterocyclic, -NH2, -NH-, -NHR, -NR2, -CONH2, -CONHR, and -CONR2, where R is an alkyl radical (C1-C6) that may be substituted by one or more groups selected from the groups consisting of: -OH, -COO-, -CO-, - 0-, and -SO3H, wherein the anchoring chain may comprise groups -COO-, and has a * molar mass included between 150 and 10000, wherein the percent by mass of basic nitrogenous monomers in the anchoring chain is 30% minimum, and at least 10% by mass of the sequence of hydrophobic character consisting of an hydrophobic straight hydrocarbon chain, cycloalkyl or aromatic, which may comprise groups *.

selected from the groups consisting of -COO-, -S-, -F, and -*.. : Si(OR')(R'')2-where R' and R' represent (Cl-do) alkyl or (Ci-ClO) aryl radicals, and n = 0 to 2, wherein the hydrophobic chain is formed by monomer units having a parameter of solubility less than or equal to 21.5 J"2/cm312, and wherein the hydrophobic chain has a molar mass included between 250 and 10000, and at least 10 to 90% by mass of the sequence of hydrophilic character consisting of an hydrophilic straight hydrocarbon chain comprising groups selected from the groups consisting of -0-, -OH, -COO-, -COOH-, -S-, and -SOH, wherein the hydrophilic chain is formed by monomer units having a parameter of solubility greater than 22 J"2/cm312, and wherein the hydrocarbon chain has a molar mass included between 250 and 10000.

Also provided, in a second embodiment of the invention, is use of a scale inhibiting amount of a grafted co-polymer comprising at least three sequences of distinct chemical nature, the co-polymer being as defined in the first embodiment of the invention, in the inhibition of silica and silicate scale formation in aqueous systems.

In relation to the co-polymer the anchoring chain may be the principal chain. Alternatively the hydrophobic chain may be the principal chain.

As a third alternative the hydrophilic chain may be the principal chain.

The co-polymer may be in the form of one of its salts, obtained by.: quaternization or neutralization of the basic functions.

The anchoring chain may comprise basic nitrogenous groups introduced from one or more compounds selected from the groups consisting of: * ..*

S -

a) vinylpyridines, including 2-vinylpyridine, 3-vinyl-pyridine, -: : : vinylpyridine or 2-methyl-5-vinylpyridine, vinylimidazole, 2-methyl-N-vinylimidazole, vinyl-carbazole, N-vinylpyrrolidone, 3-methyl-N-vinylpyrazole, 4-methyl-5-vinylthiazole, N-vinylcaprolactam, ethylimidazolidone methacrylate, (meth)acrylamides, including (meth)acrylamide, N-methyl-acrylamide, N-isopropylacrylamide and N,N-dimethylacrylamide, N-methylol (meth) acrylamide, N, N-dimethylol (meth) -acrylamide, 2-acrylamido-2-methyl-1 -propanesulfonic acid, diacetone acrylamide, methyl-2-acrylamido.2methoxyacetate, N-tris(hydroxymethyl)methacrylamjde and aminoalkyl(meth)acrylates of formula CH2CR1COO(CH2),NR2R3, wherein R1 is an atom of hydrogen or an alkyl radical (C1-C4), R2 and R3, are identical or different and each represent an alkyl radical (C1-C6) and n=0 to 6, said nitrogenous groups being in this first case a) introduced by radical copolymerization of one or more unsaturated ethylene monomer(s), and b) N-N-diethyl-1, 4-butanediamine, 1-(2-aminoethyl) -piperazine, 2-(1- pyrrolidyl) -ethylamine, 4-amino-(2-methoxy-pyrimidine, 2- dimethylamino-ethanol, 1-(2-hydroxyethyl) -piperazine, 4-(2- hydroxyethyl) -morpholine, 2-mercapto-pyrimicijne, 2- mercaptobenzimidazole, N, N-dimethyl-1, 3-propane-diamine, 4-(2- aminoethyl) -pyridine, N-N-diallylmelamine, 3-amino-1,2, 4-triazole, 1-(3-aminopropyl-imidazole, 3-mercapto-1,2, 4-triazole, said nitrogenous groups being in this second case b) fixed by reaction on a preformed chain comprising reactive functions.

The anchoring chain preferably comprises groups selected from the groups consisting of dialkylaminoethyl (meth) acrylate, N-N-dimethyl-acrylamide, 2 -vinylpyridine, 4-vinylpyridine groups, and mixtures thereof, one or more poly(ethylene oxide) hydrophilic grafts, and one or more hydrophobic grafts based on alkyl (meth)-acrylates, vinylic esters alone or copolymerized with styrene or alkyistyrene derivatives, ***".

fluorinated monomers (trifluoroethyl)methacrylate) or (trimethoxysilyl)propyl methacrylate.

The hydrophobic chain is preferably constituted from monomer units selected from the groups consisting of: esters of (meth)acrylic acid including methyl (meth)-acrylate, ethyl (meth)acrylate, propyl (meth)-acryl ate, ethyihexyl-(meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, isodecyl (meth) acrylate, lauryl-(meth) -acrylate, steryl- (meth) acrylate, pentadecyl-(meth)acrylate, cetyl (-meth)acrylate, behenyl (meth) acrylate, 3-(trimethoxysilyl) propyl (meth) acryl ate, the vinylic esters including vinyl acetate, vinyl propionate, vinyl butyrate, vinyl sorbate, vinyl hexanoate, vinyl ethylhexanoate, vinyl laurate, vinyl stearate, styrene and alkyistyrenes including -methyistyrene, vinyl-toluene, tertiobutylstyrene, dienes including butadiene, isoprene, which may be hydrogenated after polymerization, alkylenes including ethylene, propylene, siloxanes including dimethylsiloxane, diphenylsiloxane, methyiphenylsiloxane, and fluorinated compounds including trifluoroethyl (meth) acrylate, pentafluoropropyl (meth) acrylate, pentadecafluorooctyl (meth) acrylate, eicosafluoroundecyl (meth)acrylate, vinyl fluoride, tetrafluoroethylene.

The hydrophilic chain is preferably constituted from monomer units selected from the groups consisting of:ethylene oxide, (meth) acrylic acids, maleic acid, fumaric acid, itaconic acid, ethyleneimine, vinylic alcohol, vinylpyrrolidone, vinylmethyloxazolidone, vinylsulfonate, sodium methallylsulfonate, and glycerol methacrylate. .

The grafted co-polymer used in the method of the present invention, and its method of manufacture, is described in detail in US Patent No 6 362 274. * * * S *5 **

The co-polymer may be added to the aqueous system at a concentration of from between 0.1 to l000ppm. Preferably 1 -l0Oppm, most preferably *5' -50ppm.

The aqueous system may be, for example: (1) used in a cooling tower; (2) used in a boiler; (3) used in the production of sugar; (4) used in enhanced oil recovery; (5) used in geothermal processes; (6) used in detergent applications; or (7) used in the desalination of water.

(8) used in membrane processes, such as reverse osmosis and hyperfiltration; (9) used in paper mills; (10) used in mining and mineral processing; (11) used in the manufacture or processing of chemicals.

The method and use may also include the use of other known scale inhibitors and/or polymeric dispersants to act on and inhibit other types of scale present in the system.

These other scale inhibitors and br polymeric dispersants may be present in the aqueous system in an amount of from 0.1 to 1000 ppm.

Also provided in a third embodiment of the invention is a composition for the inhibition of one or more scales in an aqueous system comprising a. :; co-polymer as described in relation to the first aspect of the invention and at least one further scale inhibitor and/or a polymeric dispersant. S *

Preferably one of the scales to be inhibited is a silica or silicate scale. S... * S**

Preferably the further scale inhibitor is a scale inhibitor for the inhibition.. : of scales such as magnesium, barium, calcium, aluminium and iron based scales.

The co-polymer and the further scale inhibitor and/or dispersant can be present in the composition added to the aqueous system as a mixture.

Alternatively the components of the composition can be added to the aqueous system separately and mix to form the composition in situ in the aqueous system.

The present invention will now be described, merely by way of example, with reference to the examples and figures, which are as follows: Figure 1 shows in graphical form silica retention levels against time in water of a predetermined composition having no added scale inhibitors; Figure 2 shows in graphical form silica retention levels against time in water of a predetermined composition having present Acumer 5000 silica scale inhibitor; Figure 3 shows in graphical form silica retention levels against time in water of a predetermined composition having present a graft co-polymer in accordance with the present invention; and Figure 4 shows the structural formula of the graft co-polymer used in the example and whose results are shown in Figure 3. * S I

Evaluation of Grafted Co-polymer as Silica/Silicate Scale Inhibitor S... * S I... S...

The following test was employed to demonstrate the improved property of..

silica and silicate scale inhibition of the grafted co-polymers, in accordance with the present invention, compared with a control and other scale inhibitors. In particular, comparison was made between the use of a grafted co-polymer in accordance with the present invention and a control system containing no silica scale inhibitor and a system containing a known silica scale inhibitor (an industrial standard silica scale inhibitor known as Acumer 5000).

Method This test simulates conditions in an evaporative cooling system. Under these test conditions, the scale formed is found to be predominantly silica (with traces of calcium and magnesium).

A silica-containing water, whose composition is set out in Table 1 below, is heated, to a temperature of 55 C, and water is evaporated by bubbling air through it. The natural tendency of the pH to rise, as CO2 is purged from solution, is countered by periodic injections of CO2 as directed by a pH controller to maintain the pH at the desired value A level controller is used to maintain a constant volume of water in the apparatus by adding more feed water of the composition in Table 1. The increase in concentration of the solutes owing to the evaporation of the water is followed by analysis of the level of solutes.

When the target levels have been achieved (typically two to three days) . the temperature of the water is reduced to 28 C to encourage the precipitation of amorphous silica. The make-up water supply is changed to deionised water to maintain an otherwise constant composition.

Analytical monitoring continues for a further seven days, at which point the test is terminated. *::::*

S S S

S

Table 1 -Target Water Composition Ion Concentration (mg/i) Initial Water Feed water Target ____________ ________________ Composition Ca21 72 36 169 Mg2 24 12 56 Na 136 68 319 L C1 128 64 300 S042-304 152 713 Si02 128 64 300 HCO3-104 52 244 PO43 0.8 0.4 1.9 N.B. For inhibited runs, typically 5Oppm (active) scale inhibitor is dosed into the initial water. S.. S S *

lppm of HEDP is also added to inhibit calcium carbonate formation. * S * S * S. **

pH value is 8.3 @25C **.. * *.. * S S *

The results of the above test are shown in Figures 1 to 3 and discussed below in detail.

In relation to the Figures the silica retention level (Si retention(%)) is a measure of the percentage of the silica still in solution. The total amount indicated is the total amount of silica retained in the test medium and includes the amount of silica dispersed but not dissolved, in addition to that dissolved. The dissolved amount indicated is defined as the amount of silica detected after passing the solution through a 0.2 micron filter.

Figure 1 shows the results, tabulated in Table 2, of the above described method being carried out on a water sample not having any scale inhibitor added to it. From days 1 to 3 it can be seen that the level of retained silica gradually drops as the water is evaporated and the solutes concentrated. After day 3 there is a fairly dramatic drop in the level of retained silica as the temperature of the water is decreased from 55 C to 28 oc and an amount of silica crashes out of solution. By day 10 it can be seen that there is about 69% total silica retained in the solution in a combination of dissolved and dispersed form and of that about 48% is in dissolved form. This means that about 22% of the silica has precipitated out of the solution and furthermore is not dispersed in the solution at all and is therefore stuck to the vessel holding the water as silica scale.

Table 2 S. S

% Si Retained in Solution: ..

S S

Day Total Dissolved 0 100 102 * * S 1 90 90 ** ..

* ** S 2 91 91 3.08 89 89 **.* : 3.167 76 75 4 76 69 6 71 56 7 68 51 8 66 47 9 65 46 69 48 Figure 2 shows the results, tabulated in Table 3, of the above described method being carried out on a water sample having Acumer 5000, an industry standard silica scale inhibitor added to it. From days 1 to 3 it can be seen that the level of retained silica generally gradually drops as the water is evaporated and the solutes concentrated. After day 3 there is a fairly dramatic drop in the level of retained silica as the temperature of the water is decreased from 55 C to 28 C and an amount of silica crashes out of solution. By day 10 it can be seen that there is about 55% total silica retained in the solution in a combination of dissolved and dispersed form and of that about 50% is in dissolved form. This means that about 45% of the silica has precipitated out of the solution and furthermore is not dispersed in the solution at all and is therefore stuck to the vessel holding the water as silica scale.

Table 3

% Si Retained in Solution Day Total Dissolved 0 100 102 1 87 89 2 82 80 S.... S..

3.08 89 82 3.167 69 70 4 68 69 6 64 60 7 57 51 8 55 50 9 52 46 55 49 Figure 3 shows the results, tabulated in Table 4, of the above described method being carried out on a water sample having a graft co-polymer in accordance with the present invention, and whose formula is shown in Figure 4, added to it. From days 1 to 3 it can be seen that the level of retained silica gradually drops as the water is evaporated and the solutes concentrated. After day 3 there is a slight drop in the level of retained silica as the temperature of the water is decreased from 55 0C to 28 oc.

By day 10 it can be seen that there is about 92% total silica retained in the solution in a combination of dissolved and dispersed form and of that about 92% is in dissolved form. This means that about 8% of the silica has precipitated out of the solution and furthermore is not dispersed in the solution at all and is therefore stuck to the vessel holding the water as silica scale. Furthermore there is little, if any, retained silica that is not dissolved in solution present in the water sample.

Table 4 .. .

% Si Retained in Solution Day Total Dissolved 0 100 98 0 0* 1 92 91 0 IS I...

2 94 90 3.24 94 94 3.32 91 91 4 94 94 7 94 94 8 94 94 9 97 92 92 92 The comparison of the results shown in Figures 1 to 3 clearly shows the benefits of the use of a co-polymer in accordance with the present invention in the inhibition of silica scale formation. Figure 3 shows that the use of the co-polymer in accordance with the present invention ensures that almost all of the silica remains in solution and therefore does not form silica scale. It can be seen that with no scale inhibitor present about 22% of the silica is not retained in the solution and therefore giving rise to the formation of silica scale. It also seems that with the industry standard scale inhibitor, Acumer 5000, the situation is even worse with 44% of the silica not being retained in solution and therefore giving rise to adherent silica scale formation. 4. * * I * .. * . * I I. * * I * I 1 *I 1_I * I *SI4 I.,. * I

Claims

CLAIMS

1. A method of inhibiting silica and silicate scale in aqueous systems, which method comprises the addition to the aqueous system of a scale inhibiting amount of a grafted co-polymer comprising at least three sequences of distinct chemical nature, the co-polymer comprising: a principal chain onto which are directly grafted at least two side chains, the grafted copolymer further comprising: at least three sequences of distinct chemical nature, wherein (i) a first sequence of the at least three sequence of distinct chemical.

nature is a sequence for anchoring onto solid particles, (ii) a second sequence of the at least three sequences of distinct chemical * S* I. nature is a sequence of hydrophobic character, and SI'S * S..

(iii) a third sequence of the at least three sequences of distinct chemical nature is a sequence of hydrophilic character; wherein one of the at least three sequences of distinct chemical nature forms said principal chain and the other two of the at least three sequences of distinct chemical nature form said side chains; the grafted copolymer further comprising: 1 to 80% by mass of the sequence for anchoring onto solid particles consisting of an anchoring straight hydrocarbon chain, cycloalkyl or aromatic, comprising basic nitrogenous groups selected from the groups consisting of: heterocyclic, -NH2, -NH-, -NHR, -NR2, -CONH2, -CONHR, and -CONR2, where R is an alkyl radical (C1-C6) that may be substituted by one or more groups selected from the groups consisting of: -OH, -COO-, -CO-, - 0-, and -SO3H, wherein the anchoring chain may comprise groups -COO-, and has a molar mass included between 150 and 10000, wherein the percent by mass of basic nitrogenous monomers in the anchoring chain is 30% minimum, and at least 10% by mass of the sequence of hydrophobic character consisting of an hydrophobic straight hydrocarbon chain, cycloalkyl or aromatic, which may comprise groups selected from the groups consisting of -COO-, -S-, -F, and -Si(OR')(R)2-where R' and R'' represent (Cl-dO) alkyl or (Ci-ClO) aryl radicals, and n=0 to 2, wherein the hydrophobic chain is formed by monomer units having a.: parameter of solubility less than or equal to 21.5 J"21cm312, and wherein the hydrophobic chain has a molar mass included between 250 and 10000, : and at least 10 to 90% by mass of the sequence of hydrophilic character S.., consisting of an hydrophilic straight hydrocarbon chain comprising groups * : ::: selected from the groups consisting of -0-, -OH, -COO-, -COOH-, -S-, and -SO3H, wherein the hydrophilic chain is formed by monomer units having a parameter of solubility greater than 22 J"2/cm312, and wherein the hydrocarbon chain has a molar mass included between 250 and 10000.

2. A method according to Claim 1 wherein the anchoring chain is the principal chain.

3. A method according to Claim 1 wherein the hydrophobic chain is the principal chain.

4. A method according to Claim 1 wherein the hydrophilic chain is the principal chain.

4. A method according to any preceding claim wherein the co-polymer is in the form of one of its salts, obtained by quaternization or neutralization of the basic functions.

5. A method according to any preceding claim wherein the anchoring chain comprises one or more basic nitrogenous group introduced from one or more compounds selected from the groups consisting of: a) vinylpyridines, including 2-vinylpyridine, 3-vinyl-pyridine, 4- vinylpyridine or 2-methyl-5-vinylpyridine, vinylimidazole, 2-methyl-N- vinylimidazole, vinyl-carbazole, N-vinylpyrrolidone, 3-methyl-N-vinylpyrazole, 4-methyl-5-vinylthiazole, N-vinylcaprolactam, ethylimidazolidone methacrylate, (meth)acrylamides, including (meth) acrylamide, N-methyl-acrylamide, N-isopropylacrylamide and N, N-dimethylacrylamide, N-methylol (meth) acrylamide, N, N-dimethylol (meth) -*: ** * acrylamide, 2-acrylamido-2-methyl-1 -propanesulfonic acid, diacetone acrylamide, methyl-2-acrylamido-2-methoxyacetate, N-. tris(hydroxymethyl)methacrylamide, and aminoalkyl(meth)acrylates of. : formula CH2CRICOO(CH2)NR2R3, wherein R1 is an atom of hydrogen or an alkyl radical (C1-C4), R2 and R3, are identical or different and each represent an alkyl radical (C1-C6) and n=0 to 6, said nitrogenous groups being in this first case a) introduced by radical copolymerization of one or more unsaturated ethylene monomer(s), and b) N-N-diethyl-1, 4-butanediamine, 1-(2-aminoethyl) -piperazine, 2-(1- pyrrolidyl) -ethylamine, 4-amino-(2-methoxy-pyrimidine, 2- dimethylamino-ethanol, 1-(2-hydroxyethyl) -piperazine, 4-(2- hydroxyethyl) -morpholine, 2-mercapto-pyrimidine, 2- mercaptobenzimidazole, N,N-dimethyl-1, 3-propane-diamine, 4-(2- aminoethyl) -pyridine, N-N-diallylmelamine, 3-amino-i, 2, 4-triazole, 1-(3-aminopropyl-imidazole, 3-mercapto-1,2,4-triazole, said nitrogenous groups being in this second case b) fixed by reaction on a preformed chain comprising reactive functions.

6. A method according to any preceding claim wherein the anchoring chain comprises one or more groups selected from the groups consisting of dialkylaminoethyl (meth) acrylate, N-N-dimethyl-acrylamjde, 2-vinylpyridine, 4-vinylpyridine groups, and mixtures thereof, one or more poly(ethylene oxide) hydrophilic grafts, and one or more hydrophobic grafts based on alkyl (meth)-acrylates, vinylic esters alone or copolymerized with styrene or alkyistyrene derivatives, fluorinated monomers (trifluoroethyl) methacrylate) or 3-(trimethoxysilyl) propyl methacrylate.

7. A method according to any preceding claim wherein the hydrophobic chain is constituted from monomer units selected from the groups consisting of: esters of (meth)acrylic acid including methyl (meth)-acrylate, ethyl (meth)acrylate, propyl (meth)-acrylate, ethyihexyl-(meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, isodecyl *. S...

(meth) acrylate, lauryl-(meth) -acrylate, steryl-(meth) acrylate, pentadecyl-* : ::: (meth) acrylate, cetyl (-meth) acrylate, behenyl (meth) acrylate, 3- (trimethoxysilyl)propyi (meth)acrylate, the vinylic esters including vinyl acetate, vinyl propionate, vinyl butyrate, vinyl sorbate, vinyl hexanoate, vinyl ethylhexanoate, vinyl laurate, vinyl stearate, styrene and alkyistyrenes including -methylstyrene, vinyl-toluene, tertiobutyistyrene, dienes including butadiene, isoprene, which may be hydrogenated after polymerization, alkylenes including ethylene, propylene, siloxanes including dimethylsiloxane, diphenylsiloxane, methylphenylsiloxane and fluorinated compounds including trifluoroethyl (meth)acrylate, pentafluoropropyl (meth)acrylate, pentadecafluorooctyl (meth) acrylate, eicosafluoroundecyl (meth) acrylate, vinyl fluoride, tetrafluoroethylene.

8. A method according to any preceding claim wherein the hydrophilic chain is constituted from monomer units selected from the groups consisting of:ethylene oxide, (meth) acrylic acids, maleic acid, fumaric acid, itaconic acid, ethyleneimine, vinylic alcohol, vinylpyrrolidone, vinylmethyloxazolidone, vinylsulfonate, sodium methallylsulfonate, and glycerol methacrylate.

9. A method according to any preceding claim wherein the co-polymer is added to the aqueous system at a concentration of from between 0.1 to l000ppm.

S

10. A method according to Claim 9 wherein the co-polymer is added to the aqueous system at a concentration of from between 1 -lOOppm. 5: 11. A method according to Claim 9 or 10 wherein the co-polymer is..: added to the aqueous system at a concentration of from between 5 -S...

5oppm. S...

S S. S

12. A method according to any preceding claim wherein the aqueous system is: (1) used in a cooling tower; (2) used in a boiler; (3) used in the production of sugar; (4) used in enhanced oil recovery; (5) used in geothermal processes; (6) used in detergent applications; or (7) used in the desalination of water.

(8) used in membrane processes, such as reverse osmosis and hyperfiltration; (9) used in paper mills; (10) used in mining and mineral processing; or (11) used in the manufacture or processing of chemicals.

13. A method according to any preceding claim wherein the method includes the use of one or more other known scale inhibitors and/or polymeric dispersants to act on and inhibit other types of scale present in the aqueous system.

14. A method according to claim 13 wherein the or each other scale inhibitors and /or polymeric dispersants are present in the aqueous system in an amount of from 0.1 to 1000 ppm.

S * S S.

15. Use of a scale inhibiting amount of a grafted co-polymer comprising at least three sequences of distinct chemical nature, the co-polymer comprising: S... * S S...

a principal chain onto which are directly grafted at least two side chains, : the grafted copolymer further comprising: at least three sequences of distinct chemical nature, wherein (i) a first sequence of the at least three sequence of distinct chemical nature is a sequence for anchoring onto solid particles, (ii) a second sequence of the at least three sequences of distinct chemical nature is a sequence of hydrophobic character, and (iii) a third sequence of the at least three sequences of distinct chemical nature is a sequence of hydrophilic character; wherein one of the at least three sequences of distinct chemical nature forms said principal chain and the other two of the at least three sequences of distinct chemical nature form said side chains; the grafted copolymer further comprising:

1 to 80% by mass of the sequence for anchoring onto solid particles consisting of an anchoring straight hydrocarbon chain, cycloalkyl or aromatic, comprising basic nitrogenous groups selected from the groups consisting of: heterocyclic, -NH2, -NH-, -NHR, -NR2, -CONH2, -CONHR, and -CONR2, where R is an alkyl radical (C1-C6) that may be substituted by one or more groups selected from the groups consisting of: -OH, -COO-, -CO-, - 0-, and -SO3H, wherein the anchoring chain may comprise groups -COO-, and has a.: molar mass included between 150 and 10000, wherein the percent by mass of basic nitrogenous monomers in the anchoring chain is 30% minimum, and at least 10% by mass of the sequence of hydrophobic character consisting of an hydrophobic straight,"** S..

hydrocarbon chain, cycloalkyl or aromatic, which may comprise groups.:::., selected from the groups consisting of -COO-, -S-, -F, and -S1(OR')(R''))-where R' and R'' represent (Ci-ClO) alkyl or (Ci-ClO) aryl radicals, and n=0 to 2, wherein the hydrophobic chain is formed by monomer units having a parameter of solubility less than or equal to 21.5 Ju2/cm3/2, and wherein the hydrophobic chain has a molar mass included between 250 and 10000, and at least 10 to 90% by mass of the sequence of hydrophilic character consisting of an hydrophilic straight hydrocarbon chain comprising groups selected from the groups consisting of -0-, -OH, -COO-, -COOH-, -S-, and -SO3H, wherein the hydrophilic chain is formed by monomer units having a parameter of solubility greater than 22 Ju2/cm3/2, and wherein the hydrocarbon chain has a molar mass included between 250 and 10000 in the inhibition of silica and silicate scale formation in aqueous systems.

16. A composition for the inhibition of one or more scales in an aqueous system comprising a grafted co-polymer comprising at least three sequences of distinct chemical nature, the co-polymer comprising: a principal chain onto which are directly grafted at least two side chains, the grafted copolymer further comprising: at least three sequences of distinct chemical nature, wherein (i) a first sequence of the at least three sequence of distinct chemical nature is a sequence for anchoring onto solid particles, ...

(ii) a second sequence of the at least three sequences of distinct chemical nature is a sequence of hydrophobic character, and

S

S *...

(iii) a third sequence of the at least three sequences of distinct chemical 5...

nature is a sequence of hydrophilic character; wherein one of the at least three sequences of distinct chemical nature forms said principal chain and the other two of the at least three sequences of distinct chemical nature form said side chains; the grafted copolymer further comprising: 1 to 80% by mass of the sequence for anchoring onto solid particles consisting of an anchoring straight hydrocarbon chain, cycloalkyl or aromatic, comprising basic nitrogenous groups selected from the groups consisting of: heterocyclic, -NH2, -NH-, -NHR, -NR2, -CONH2, -CONHR, and -CONR2, where R is an alkyl radical (C1-C6) that may be substituted by one or more groups selected from the groups consisting of: -OH, -COO-, -CO-, - 0-, and -SO3H, wherein the anchoring chain may comprise groups -COO-, and has a molar mass included between 150 and 10000, wherein the percent by mass of basic nitrogenous monomers in the anchoring chain is 30% minimum, and at least 10% by mass of the sequence of hydrophobic character consisting of an hydrophobic straight hydrocarbon chain, cycloalkyl or aromatic, which may comprise groups selected from the groups consisting of -COO-, -S-, -F, and -Si(OR!)(Rt)2 where R' and R'' represent (Ci-ClO) alkyl or (Ci-ClO) aryl radicals, and n=0 to 2, wherein the hydrophobic chain is formed by monomer units having a parameter of solubility less than or equal to 21.5 J"2/cm312, and wherein the hydrophobic chain has a molar mass included between 250 and 10000, * * Qtlrl. * * U ** ** at least 10 to 90% by mass of the sequence of hydrophilic character S...

consisting of an hydrophilic straight hydrocarbon chain comprising groups selected from the groups consisting of -0-, -OH, -COO-, -COOH-, -S-, ** and -SO3H, wherein the hydrophilic chain is formed by monomer units having a parameter of solubility greater than 22 J"2/cm312, and wherein the hydrocarbon chain has a molar mass included between 250 and 10000 and at least one further scale inhibitor and/or a polymeric dispersant.

17. A composition according to Claim 17 wherein at least one of the or each further scale inhibitors is a scale inhibitor for the inhibition of scales such as magnesium, barium, calcium, aluminium and iron based scales.

18. A composition according to Claim 16 or Claiml7 wherein the co-polymer and the or each further scale inhibitor and/or dispersant are present in the composition added to the aqueous system as a mixture.

19. A composition according to Claim 16 or Claim 17 wherein the co-polymer and the or each further scale inhibitor and/or dispersant are added to the aqueous system separately and mix to form the composition in situ in the aqueous system.

20. A method of inhibiting silica and silicate scale in aqueous systems substantially as described herein and with reference to the examples.

21. Use of a scale inhibiting amount of a grafted co-polymer substantially as described herein and with reference to the examples.

22. A composition for the inhibition of one or more scales in an aqueous system comprising a grafted co-polymer and at least one further scale inhibitor and br a polymeric dispersant substantially as described herein and with reference to the examples.

S S S...

S S S. *