AU2012203515B1 - Descaling polymers - Google Patents

Abstract

The specification describes a method for inhibiting the formation of scale and related solids in an aqueous liquid. In the method, a polyacrylic acid having a terminal group of structure RO-G-C(R'R")- is added to the liquid. In the terminal group, R is H or 5 alkyl, R' and R" are hydrocarbon groups and G is a group, for example C=O, such that G-OH is an acidic group. The aqueous liquid is at a temperature of greater than 90*C or else has a calcium ion concentration of greater than about 200ppm or else has a magnesium concentration of greater than about 50ppm.

Description

S&F Ref: P036471 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Ali Abdrabalrasoul Mohamed Al Hamzah, of Sihat, of Applicant: Wasel 3657-32654, Eastern Provence, PO Box 6896, Saudi Arabia Actual Inventor(s): Ali Abdrabalrasoul Mohamed Al Hamzah Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Descaling polymers Associated Provisional Application Details: [33] Country: [31] Appl'n No(s): [32] Application Date: AU 2012901575 20 Apr 2012 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(6375636_1) Descaling polymers Technical Field The present invention relates to polymers for use in reducing scaling in water treatment applications. 5 Background of the Invention The economic production of fresh water from seawater has become an important goal worldwide, due to increasing urbanization and industrial development in regions with limited ground and surface water resources. A critical factor contributing to the rapid uptake of seawater desalination technologies is the successful use of scale control agents. 10 Higher through put requires working under higher brine concentrations and higher temperatures, conditions that favour the growth of scale-forming minerals. As a consequence, scale formation becomes the limiting factor in factory efficiency. In reverse osmosis (RO) plants, scale formation on the membrane surfaces not only reduces the rate of production and the quality of product water, but accelerates degradation of the is membranes. In multi stage flash (MSF), scale formation on surfaces reduces heat transfer and hence efficiency because of the lower thermal conductivity of the deposited material. The problem is usually managed by adding small quantities (ppm range) of scale inhibitors, which may be organic or inorganic compounds and either low molar mass compounds or polymers. 20 Alkaline scales such as calcium carbonate CaCO 3 and magnesium hydroxide Mg(OH) 2 are one of the main operational problems in thermal desalination of seawater such as MSF. Without effective scale control, this can make periodic shut-down of the plant for cleaning essential. Two main mechanisms have been proposed to explain the formation of alkaline 25 scale in thermal desalination plants. First is the "bimolecular mechanism" and second is the "unimolecular mechanism" In both mechanisms, the first step is the thermal decomposition of bicarbonate ion HCO 3 . Currently, it is believed that both bimolecular and unimolecular mechanisms can occur under desalination conditions. Most investigators in the desalination field believe the mechanism of alkaline scale 30 formation is a more complex process involving competitive equilibria between unimolecular and bimolecular reactions. Moreover, many parameters such as supersaturation, temperature, mixing conditions, impurities, homogenous and heterogeneous nucleation and the effect of additives on calcium carbonate and 2 magnesium hydroxide formation need to be considered and it is very difficult to separate them and investigate independently. Calcium carbonate CaCO 3 is one of the most common scales in both the evaporation and membrane desalination processes when its solubility product Ksp is 5 exceeded under certain conditions. The most important of those conditions are temperature, pH and the concentration of Ca 2 +, Mg 2 +, HC03- and S0 4 2 -. An increase in temperature, pH and the concentration of those ions can lead to enhanced scale formation. The concentrations of those ions in standard seawater (salinity = 35 g/kg) are 0.01028, 0.05282, 0.00175 and 0.02824 M respectively. 10 To overcome this problem, soluble polyelectrolytes such as poly(acrylic acid), poly(maleic acid), poly(phosphonic acid) and co-polymers of these and similar monomers have been used to control scale in desalination. One hypothesis as to the mechanism of action is that these polymers may adsorb on growing crystallite surfaces so as to prevent aggregation, inhibit growth, or alter crystal morphology and speciation, all of which can is inhibit scaling. Another commonly encountered scale in desalination applications is magnesium hydroxide Mg(OH) 2 . Magnesium hydroxide formation depends on the concentration of Mg2+ and the pH of the solution. In thermal desalination plants Mg(OH) 2 deposits usually appear at temperatures above 80 *C and predominate in alkaline scale above 100'C when 20 the concentrations of Mg 2 + and OH exceed the thermodynamic solubility product (Ks,). Two phosphonate additives (methylenephosphonic acid and N,N,N',N' ethlenediaminetetramethylenephosphonic acid) have been shown to have a significant reduction in crystal growth of Mg(OH) 2 . However, the effect of those scale inhibitors was much less for CaCO 3 and CaSO 4 . 25 There is therefore a need for improved methods for inhibiting scale formation in water purification systems, in particular in reverse osmosis systems. Object of the Invention It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. It is a further objective to at least 30 partially satisfy the above need. Summary of the Invention In a first aspect of the invention there is provided a method for inhibiting the formation of a solid inorganic group 2 metal salt in an aqueous liquid, said method 3 comprising adding a polyacrylic acid to said liquid, said polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein: R is selected from the group consisting of H and an alkyl group containing from 1 to 20 carbon atoms, s R' and R" are each, independently, a hydrocarbon of from 1 to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic ring of from 3 to 8 carbon atoms, and G is a group such that -G-OH is an acidic group. The aqueous liquid may be one in which formation of the solid inorganic group 2 1o metal salt would occur in the absence of the polyacrylic acid. The following conditions may apply to said liquid: a) the aqueous liquid may be at a temperature of greater than 90*C; b) the aqueous liquid may have a calcium ion concentration of greater than about 200ppm; c) the aqueous liquid may have a magnesium concentration of greater than about 50ppm; d) any two or more of conditions a) to c) may apply. is The following options may be used in conjunction with the first aspect, either individually or in any suitable combination. G may be, for example, -C(=0)-, -S(=0)-, -S(=0)-O-, -P(=O)-O- or -P(=0) 2 -0-. In these options, the C, S or P atom is directly attached to the C atom of the C(R'R")- group. G may be for example -C(=0)-, whereby the terminal group is RO-C(=O)-C(R'R")-. G 20 may be a group such that -G-OH has a pKa of less than about 6. The inhibiting may comprise reducing the rate of formation of the salt or it may comprise delaying the onset of formation of the salt or it may comprise both reducing the rate of formation of the salt and delaying the onset of formation of the salt. The inorganic group 2 metal salt may be, or may comprise, a group 2 metal 25 carbonate, a group 2 metal sulfate or a group 2 metal hydroxide or a mixture of any two or all thereof. It may be, or may comprise, a magnesium salt or a calcium salt or a mixture thereof. It may be, or may comprise, magnesium hydroxide or calcium carbonate or calcium sulfate or a mixture of any two or all thereof. The polyacrylic acid may have an average molecular weight of less than about 30 4000g/mol, optionally less than 2000 g/mol. It may have an average molecular weight of less than about 1500 g/mol. It may have an average degree of polymerisation of less than about 55, or less than about 30, or less than about 20, or about 10 to about 20.

4 In the terminal group, R' and R" may be the same. In an embodiment, R' and R" are both methyl. R may be an alkyl group of from about 6 to about 10 carbon atoms, or may be an alkyl group from about 10 to about 20 carbon atoms. The polyacrylic acid may be added in an amount of less than about 15ppm or less 5 than about 1Oppm, for example in an amount of between about I and about 1Oppm. It may be added in an amount of about 0.5 to 5piM. It may be added in a molar ratio of less than about 10% relative to the concentration of the inorganic group 2 metal salt, for example in a molar ratio of between about 0.5% and about 10% relative to the concentration of the inorganic group 2 metal salt. 10 The method may be conducted at between about 10 and about 100*C, or between about 10 and about 120*C, optionally greater than I 00*C or greater than 120*C, e.g. up to 150 0 C. The aqueous liquid may be a feed for a water purification process. In this case the method represents a method of reducing scale in said water purification process. The is water purification may be, or may comprise any one or more of, reverse osmosis, flash distillation, flash vacuum distillation, multistage flash distillation (evaporation), membrane distillation, ultrafiltration, multi effect distillation (MED), thermal vapour compression (TVC) or any other process which suffers from problems of scale formation. In an embodiment there is provided a method for inhibiting the formation of a solid 20 inorganic group 2 metal salt in an aqueous liquid, said method comprising adding a polyacrylic acid to said liquid, said polyacrylic acid having a terminal group of structure RO-C(=0)C(Me 2 )-, wherein R is an alkyl group containing from 6 to 16 carbon atoms, said polymer having a number average molecular weight of less than about 2000g/mol. In another embodiment there is provided a method for inhibiting the formation of a 25 solid inorganic group 2 metal salt in an aqueous liquid, said method comprising adding a polyacrylic acid to said liquid, said polyacrylic acid having a terminal group of structure RO-C(=O)C(Me 2 )-, wherein R is an alkyl group containing from 6 to 16 carbon atoms, said polymer having a number average molecular weight of less than about 2000g/mol, said polyacrylic acid being added to the aqueous liquid at about I to 15ppm. 30 In another embodiment there is provided a method for inhibiting the formation of a solid inorganic group 2 metal salt in an aqueous liquid, said method comprising adding a polyacrylic acid to said liquid, said polyacrylic acid having a terminal group of structure RO-C(=0)C(Me 2 )-, wherein R is an alkyl group containing from 6 to 16 carbon atoms, said polymer having a number average molecular weight of less than about 2000g/mol, 5 said polyacrylic acid being added to the aqueous liquid in a molar ratio of between about 0.5% and about 10% relative to the concentration of the inorganic group 2 metal salt. In a second aspect of the invention there is provided the use of a polyacrylic acid having a terminal group of structure RO-G-C(R'R")- for inhibiting the formation of a s solid inorganic group 2 metal salt in an aqueous liquid, wherein: R is selected from the group consisting of H and an alkyl group containing from I to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from 1 to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic 1o ring of from 3 to 8 carbon atoms, and G is a group such that -G-OH is an acidic group. G may be -C(=0) In a third aspect of the invention there is provided a polyacrylic acid having a terminal group of structure RO-G-C(R'R")- when used for inhibiting the formation of a is solid inorganic group 2 metal salt in an aqueous liquid, wherein: R is selected from the group consisting of H and an alkyl group containing from I to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from I to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic 20 ring of from 3 to 8 carbon atoms, and G is a group such that -G-OH is an acidic group. In an embodiment, G is -C(=O)-, R is a C6 to C16 alkyl, R' and R" are both methyl and the polyacrylic acid has a molecular weight of less than about 2000g/mol. Any one or more of the options described in respect of the first aspect may also be 25 applied to the second and/or third aspects. In a fourth aspect of the invention there is provided a polymer for inhibiting the formation of a solid inorganic group 2 metal salt in an aqueous liquid, said polymer being a polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein R' and R" are both methyl and R is any one of ethyl or hexyl or cyclohexyl or decyl or hexadecyl 30 and the polymer has a number average molecular weight of less than about 4000Da, optionally less than about 2000Da, and G is a group such that -G-OH is an acidic group. The aqueous liquid may be at a temperature of greater than 90*C or else may have a calcium ion concentration of greater than about 200ppm or else may have a magnesium 6 concentration of greater than about 50ppm, or any two or more of these conditions may apply In the polymer of the fourth aspect, if R is hexyl and G is -C(=O)-, the polymer may have a number average molecular weight of about 1400g/mol, e.g. 1403, or of about 5 3500, e.g. 3563 g/mol. If R is cyclohexyl or hexadecyl and G is -C(=O)-, the polymer may have a number average molecular weight of about 1700 g/mol, e.g. 1689 g/mol. If R is decyl and G is -C(=O)-, the polymer may have a number average molecular weight of about 2400 g/mol, e.g. 2422 g/mol. If R is hexadecyl and G is -C(=O)-, the polymer may have a number average molecular weight of about 1700 g/mol, e.g. 1687 g/mol. If R 10 ethyl, the polymer may have a number average molecular weight of about 1700 g/mol. In a fifth aspect of the invention there is provided a method of reducing the rate of thermal decomposition of bicarbonate ions in an aqueous liquid comprising adding a polyacrylic acid to said liquid, said polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein: is R is selected from the group consisting of H and an alkyl group containing from 1 to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from I to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic ring of from 3 to 8 carbon atoms, and 20 G is a group such that -G-OH is an acidic group. The various options described in respect of the first aspect, as well as the further options listed below, may be used in conjunction with the fifth aspect where appropriate, either individually or in any suitable combination. The temperature of the aqueous liquid may be from 80 to 150*C, or 80 to 100*C. 25 The polyacrylic acid may be added to the liquid in an amount sufficient to achieve a concentration of less than 15ppm. It may be added to the liquid in an amount of less than the amount of bicarbonate ion on a w/w basis. It may be added to the liquid in an amount of less than 20% of the amount of bicarbonate ion on a w/w basis. The rate of thermal decomposition of the bicarbonate ions may be less than 50% of 30 the rate under the same conditions but in the absence of the polyacrylic acid. In a sixth aspect of the invention there is provided use of a polyacrylic acid for reducing the rate of thermal decomposition of bicarbonate ions in an aqueous liquid, said polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein: 7 R is selected from the group consisting of H and an alkyl group containing from 1 to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from I to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic s ring of from 3 to 8 carbon atoms, and G is a group such that -G-OH is an acidic group. In a seventh aspect of the invention there is provided a polyacrylic acid when used for reducing the rate of thermal decomposition of bicarbonate ions in an aqueous liquid, said polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein: 10 R is selected from the group consisting of H and an alkyl group containing from I to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from 1 to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic ring of from 3 to 8 carbon atoms, and 15 G is a group such that -G-OH is an acidic group. The various options available in conjunction with the fifth aspect, as described above, may also be applied to the sixth and seventh aspects, either individually or in any suitable combination. In an eighth aspect of the invention there is provided a process for making a 20 polymer for inhibiting the formation of a solid inorganic group 2 metal salt in an aqueous liquid, said polymer being a polyacrylic acid having a terminal group of structure RO-G C(R'R")-, wherein R' and R" are both methyl and R is any one of ethyl or hexyl or cyclohexyl or decyl or hexadecyl and G is a group such that -G-OH is an acidic group and the polymer has a number average molecular weight of less than about 4000Da, or less 25 than about 2000Da, said process comprising: - polymerising an acrylate ester in the presence of Cu(I) and RO-G-C(R'R")X, wherein R' and R" are both methyl and R is any one of ethyl or hexyl or cyclohexyl or decyl or hexadecyl and G is a group such that -G-OH is an acidic group and X is a halogen, so as to form a poly(acrylate ester) having a terminal 30 group of structure RO-G-C(R'R")-; - hydrolysing the poly(acrylate ester) so as to form the polyacrylic acid having a terminal group of structure RO-G-C(R'R")-.

8 The various options described elsewhere herein for R, R', R" and G may be used in conjunction with the eighth aspect, and the following options may also be used either individually or in any suitable combination. The acrylate ester may be a t-butyl ester, whereby the poly(acrylate ester) is a s poly(t-butyl acrylate). X may be Br. The hydrolysis may be conducted in organic solution in the presence of an organic acid. The organic acid may be trifluoroacetic acid. The ratio of Cu(I) to RO-G-C(R'R")X may be about 0.9:1 to about 1.1:1, e.g. about to 1:1. The ratio of acrylate ester to Cu(I) may be about 1:1 to about 1.5:1, or about 1.1:1 to about 1.3:1, e.g. about 1.2:1. In an embodiment there is provided a process for making a polyacrylic acid having a terminal group of structure n-C 6

H

1 4 -0-C(=O)-CMe 2 -, wherein the polymer has a number average molecular weight of about 1400g/mol, said process comprising: is - polymerising t-butyl acrylate in the presence of Cu(I) and n-C 6 Hi 4 -0-C(=O) CMe 2 Br to form a poly(t-butyl acrylate), wherein the ratio of n-C 6

H

14 -0-C(=O) CMe 2 Br to t-butyl acrylate is such that the polyacrylic acid has a molecular weight of about 1400g/mol; - hydrolysing the poly(t-butyl acrylate) in an organic solvent in the presence of 20 trifluoroacetic acid so as to form the polyacrylic acid. In a ninth aspect of the invention there is provided a method for purifying water comprising adding a polyacrylic acid to said water and subsequently applying a water purification process to the water, said polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein: 25 R is selected from the group consisting of H and an alkyl group containing from I to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from 1 to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic ring of from 3 to 8 carbon atoms, and 30 G is a group such that -G-OH is an acidic group. The water purification process may comprise reverse osmosis or multistage flash distillation or multi effect distillation. The various options for the polyacrylic acid and for addition conditions (ratios etc.) are as set out elsewhere herein.

9 In a specific embodiment of the invention, the polyacrylic acid has a number average molecular weight between about 1400 and 2000, a terminal group of structure RO-C(=O)-C(Me 2 )- in which R is a hydrocarbon group (linear, branched or cyclic) of from 2 to 6 carbon atoms and the aqueous liquid has a calcium ion concentration of s greater than about 100, or greater than about 200ppm, commonly from 200 to 1000ppm. In this embodiment, the purification process may be a multistage flash distillation or it may be multi effect distillation, each being conducted at a temperature of greater than about 90*C. In another specific embodiment of the invention, the polyacrylic acid has a number io average molecular weight between about 1400 and 2000, a terminal group of structure RO-C(=O)-C(Me 2 )- in which R is OH or a hydrocarbon group (linear, branched or cyclic) of from 2 to 12 carbon atoms and the aqueous liquid has a calcium ion concentration of greater than about 200ppm, commonly from 200 to 1000ppm. In this embodiment, the purification process may be reverse osmosis conducted at a temperature of from about 20 is to about 90 0 C. In yet another specific embodiment of the invention, the polyacrylic acid has a number average molecular weight between about 1400 and 2000, or about 1400 and 4000, a terminal group of structure RO-C(=0)-C(Me 2 )- in which R is OH or a hydrocarbon group (linear, branched or cyclic) of from 2 to 12 carbon atoms and the aqueous liquid 20 has a magnesium ion concentration of greater than about 50ppm, commonly from 1000 to 2000ppm. In this embodiment, the purification process may be reverse osmosis conducted at a temperature of from about 20 to about 90 0 C or a multistage flash distillation or it may be multi effect distillation, each being conducted at a temperature of greater than about 90 0 C. 25 The present invention may be particularly useful in cases where either the aqueous liquid is at a temperature of greater than 90*C or else has a calcium ion concentration of greater than about 200ppm or else has a magnesium ion concentration of greater than about 50ppm, optionally greater than about 1000ppm, or any two or more of these conditions apply (i.e. calcium ion concentration over 200ppm and temperature of greater 30 than 90*C, or calcium ion concentration over 200ppm and magnesium ion concentration of greater than about 50ppm, optionally greater than about 1000ppm, or magnesium ion concentration of greater than about 50ppm, optionally greater than about 1000ppm, and temperature of greater than 90*C or calcium ion concentration over 200ppm and 10 magnesium ion concentration of greater than about 50ppm, optionally greater than about 1000ppm, and temperature of greater than 90'C. In a tenth aspect of the invention there is provided use of a polyacrylic acid having number average molecular weight less than about 4000g/mol, optionally less than about 5 2000g/mol, and having a terminal group of structure RO-G-C(R'R")-, wherein: R is selected from the group consisting of H and an alkyl group containing from 1 to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from I to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic to ring of from 3 to 8 carbon atoms, and G is a group such that -G-OH is an acidic group for inducing distortion in the edge of a calcium carbonate polymorph so as to affect crystal morphology of said polymorph. The use may result in reduction in the concentration of said polymer required to is retard or inhibit crystal growth of said calcium carbonate. Brief Description of the Drawings Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein: Figure IA is a scheme showing ATRP polymerization of vinyl tert-butyl acrylate. 20 Figure 1B is a scheme showing selective hydrolysis of tert-butyl groups by trifluoroacetatic acid. Figure IC is a scheme showing hydrolysis of PAA end groups. Figure 2 is an NMR spectrum of PAA with HDIB end group. Figure 3 shows a conductivity-time curve showing the determination of induction 25 time and steady state for three different experiments (dashed lines) and their average (solid line), of a solution containing Ca 2 + and C0 3 2 - ions and 1.5 ppm HDIB-PAA (M,= 17167 g/mol) under condition I by conductivity; and an absorbance-time curve showing the determination of induction time and steady state for three different experiments and their average, of a solution containing Ca 2 + and C32- ions and 1.5 ppm HDIB-PAA (M&= 30 17167 g/mol) under condition 1 by turbidity. Figure 4 is a conductivity-absorbance curve showing induction times by conductivity vs. induction times by turbidity for CaCO 3 formation under condition 1. Figure 5 shows conductivity curves of solutions containing Ca 2 + and C0 3 2 ions and 1.5 ppm CMM-PAA under condition 1. (M= 1946, 3024 and 7633 g/mol and Blank); 11 conductivity curves of solutions containing Ca 2 + and C0 3 2 - ions and 1.5 ppm EIB-PAA under condition 1. (M= 1669, 5065 and 7180 g/mol Blank); conductivity curves of solutions containing Ca 2 + and C0 3 2 - ions and 1.5 ppm CIB-PAA under condition 1. (M= 1689, 2867, 4092 and 11593 g/mol and Blank); conductivity curves of solutions s containing Ca 2 + and C0 3 2 - ions and 1.5 ppm HIB-PAA under condition 1. (M= 1403, 3563, 8928 and 12946 g/mol and Blank); conductivity curves of solutions containing Ca 2 + and C0 3 2 ~ ions and 1.5 ppm DIB-PAA and HDIB-PAA under condition 1. (Mn= 2422 and 6023 (as DIB), 1687, 2767 and 17167 (as HDIB) g/mol and Blank). Figure 6 is a curve showing % IE (inhibition efficiency) of CaCO 3 formation by 10 PAA with different end groups (M 5f 2000) under condition 1; and a curve showing % IE of CaCO 3 formation by PAA with different end groups (3000 > M < 6000) under condition 1. (e = CIB-PAA); and a curve showing % IE of CaCO 3 formation by PAA with different end groups (Me> 6000) under condition 1. (o = CIB-PAA). Figure 7 is a curve showing %IE of CaCO 3 formation by PAA with different end is groups (M, 5 2000) under condition 2; and a curve showing induction times of CaCO 3 formation on the presence of PAA with different end groups (M 5 2000) under condition 2. (e = CIB-PAA); and a curve showing %IE of CaCO 3 formation by PAA with different end groups (M, > 3000) under condition 2. (e = CIB-PAA); and a curve showing induction times of CaCO 3 formation on the presence of PAA with different end groups 20 (M, > 3000) under condition 2. (o = CIB-PAA) Figure 8 is a diagram of a system for measuring inhibition efficiency and induction time of PAA as scale inhibitor to prevent CaCO 3 crystallization in the bulk solution at 60*C, 80 *C and 90 *C. Figure 9 shows conductivity curves of solutions containing Ca2 + and C0 3 2- ions and 25 1.5 ppm CMM-PAA under condition 3. (M= 1946, 3024 and 7633 g/mol and Blank); and conductivity curves of solutions containing Ca 2 + and CO 3 ions and 1.5 ppm EIB-PAA under condition 3. (Mn= 1669 and 7180 g/mol Blank); and conductivity curves of solutions containing Ca+ and CO 3 2- ions and 1.5 ppm CIB-PAA under condition 3. (Mn= 1689, 2867 and 6210 g/mol and Blank); and The conductivity curves of solutions 30 containing Ca 2 + and C0 3 2- ions and 1.5 ppm HIB-PAA under condition 3. (M= 1403, 3563 and 8928, g/mol and Blank); and conductivity curves of solutions containing Ca 2 + and C0 3 2 - ions and 1.5 ppm DIB-PAA and HDIB-PAA under condition 3. (M= 2422 as DIB 1687 and 2767 as HDIB g/mol and Blank); 12 Figure 10 shows curves of %IE of CaCO 3 formation by PAA with different end groups (M, 5 2000) under condition 3. (e = CIB-PAA) and induction times of CaCO 3 formation on the presence of PAA with different end groups (M 2000) under condition 3. (e = CIB-PAA) 5 Figure 11 shows a curve of %IE of CaCO 3 formation by PAA with different end groups (Ma > 4000) under condition 3. (a = CIB-PAA). Figure 12 shows conductivity curves of solutions containing Ca 2 + and C0 3 2 - ions and 1.5 ppm CMM-PAA under condition 4. (M,,= 1946 and 7633 g/mol and Blank); and conductivity curves of solutions containing Ca2+ and CO 3 2- ions and 1.5 ppm EIB-PAA 1o under condition 4. (M,= 1669 and 7180 g/mol Blank); and conductivity curves of solutions containing Ca 2 + and C0 3 2 - ions and 1.5 ppm CIB-PAA under condition 4. (M,= 1689, 1852 and 3518 g/mol and Blank); and conductivity curves of solutions containing Ca 2 + and C0 3 2 - ions and 1.5 ppm HIB-PAA under condition 4. (M= 1403, 3563 and 4224 g/mol and Blank); and conductivity curves of solutions containing Ca 2 + and C0 3 2 is ions and 1.5 ppm DIB-PAA and HDIB-PAA under condition 4. (Mn= 2422 as DIB 1687 and 2767 as HDIB g/mol and Blank) Figure 13 is a graph showing %IE of CaCO 3 formation by PAA with different end groups (M < 2000) under condition 4. (o = CIB-PAA); and a graph showing induction times of CaCO 3 formation on the presence of PAA with different end groups (Mn < 2000) 20 under condition 4. (e = CIB-PAA); and a graph showing %IE of CaCO 3 formation by PAA with different end groups (Ma > 3000) under condition 4. (o = CIB-PAA). Figure 14 is a graph showing conductivity measurements of solutions contain Ca2+ and C0 3 2 - ions and 3.75 ppm PAA (M S 2000 g/mol) with different end groups under conditions 5; and a graph showing % lEof CaCO 3 formation by PAA with different end 25 groups (M 5 2000) under condition 5. (o = CIB-PAA); and a graph showing induction times of CaCO 3 formation on the presence of PAA with different end groups (Mn < 2000) under condition 5. (9 = CIB-PAA); Figure 15 is a diagram of a system for measuring inhibition efficiency and induction time of PAA as scale inhibitor to prevent CaCO 3 crystallization in the bulk solution at 30 100*C. Figure 16 shows conductivity measurements of solutions contain Ca2+ and CO 3 ions and 0.50 ppm PAA (Mn 5 2000 g/mol) with different end groups; and %IE of CaCO 3 formation by PAA with different end groups (M, 2000) under condition 6. (e = CIB

PAA).

13 Figure 17 shows conductivity measurements of solutions contain Ca2 and CO 3 ions and 6.7 ppm PAA (M 5 2000 g/mol) with different end groups under conditions 7; and %IE of CaCO 3 formation by PAA with different end groups (Mn < 2000) under condition 7. (e = CIB-PAA). 5 Figure 18 shows inhibition efficiency of CaCO 3 formation by PAA with different end groups and low molecular mass (M S 2000 g/mol). Figure 19 shows SEM micrographs of magnification (x 500) of CaCO 3 crystals in the absence of PAA under conditions 7. Figure 20 shows FTIR (Fourier transform infrared) spectra of CaCO 3 crystals in the 1o absence of PAA under conditions 7: A: aragonite and C: calcite Figure 21 shows XRD (x-ray diffraction) of CaCO 3 crystals in the absence of PAA (Blank) under conditions 7 (before subtraction of background) Figure 22 shows XRD of CaCO 3 crystals in the absence of PAA (Blank) under conditions 7 - A: aragonite and C: calcite (after subtraction of background) is Figure 23 shows SEM micrographs at magnification (x 500) of CaCO 3 crystals in the presence of PAA (M, ! 2000 g/mol) with different end groups under conditions 7. Figure 24 shows XRD of CaCO 3 crystals in the presence of CMM-PAA (M, = 2106 g/mol) under conditions 7. C: calcite. Figure 25 shows XRD of CaCO 3 crystals in the presence of DIB-PAA (M, = 2422 20 g/mol) under conditions 7 - A: aragonite, C: calcite and V: vaterite. Figure 26 shows XRD of CaCO 3 crystals in the presence of HDIB- PAA (M, = 1687 g/mol) under conditions 7 - A: aragonite, C: calcite and V: vaterite. Figure 27 shows an FTIR spectrum of CaCO 3 crystals in the absence of DIB-PAA under conditions 7 - A: aragonite, C: calcite and V: vaterite. 25 Figure 28 shows SEM micrograph under magnification (x 2000) of aragonite needle-like morphology in the absence (A) and in the presence of PAA (M - 2000 g/mol) with different end groups (B, C, D and E). Figure 29 shows SEM micrograph under magnification (x 30000) of calcite rhombohedral morphology in absence (A) and in the presence of PAA (M, ~ 2000 g/mol) 30 with different end groups (B, C, D and E). Figure 30 shows SEM micrograph under magnification (x 10000) of vaterite flower morphology in the absence (A) and in the presence of PAA (M, - 2000 g/mol) with different end groups (B, C, D and E).

14 Figure 31 shows a diagram of a system for conductivity measurement for the homogeneous crystallization of Mg(OH) 2 . Figure 32 shows a graph illustrating the decline of conductivity measurements (after normalization) for homogeneous formation of Mg(OH) 2 in the absence of PAA (blank) s for more than 3 hours. Figure 33 shows a graph of normalized conductivity measurements for solutions containing Mg2+, OH- ions and 5 ppm PAA with different end groups (M : 2000 g/mol). Figure 34 shows a graph of % IE of Mg(OH) 2 formation by PAA with different end groups (Mn S 2000). (e = CIB) -d[Mgz] 10 Figure 35 shows a plot of log dt vs. log{([Mg2+] x [OH ] 2

)

3 - (Kp)" 3 } to determine n for the crystal growth of Mg(OH) 2 in the absence of PAA. 9ff2.- 2.* Figure 35A shows a plot of 9 M 2 *1, 2 versus time (t) to determine the rate of crystal growth of Mg(OH) 2 in the absence of PAA. og'rIq 2

J--M

2 ] Figure 36 shows a plot of loMg2+3 - [M 2-] 0 1 versus time (t) to determine is the crystals growth of Mg(OH) 2 in the presence of PAA with different end groups. Figure 37 shows a diagram of an electrical conductivity system for determining thermal decomposition of HCO 3 Figure 38 shows a curve illustrating overall rate coefficient of thermal decomposition of 40 ppm HCO 3 20 Figure 39 shows a graph of free energy (AG) changes with time for the decomposition of 40ppm of bicarbonate as unimolecular mechanism and bimolecular mechanism. Figure 40 shows concentration of HCO 3 , OH and C0 3 2 for thermal decomposition of HC03- as unimolecular mechanism in the absence of PAA. 25 Figure 41 shows experimental conductivity curve (gray curve) and semi- theatrical conductivity curve (black curve) for thermal decomposition of4O ppm of HCO 3 as unimolecular mechanism in absence of PAA (Blank) Figure 42 shows an experimental conductivity curve (gray curve) and semi theatrical conductivity curve (back curve) for thermal decomposition of 40 ppm of HCO 3 30 as unimolecular mechanism in presence of 10 ppm of EIB-PAA, (M, = 7180 g/mol).

15 Figure 43 shows an experimental conductivity curve (gray curve) and semi theatrical conductivity curve (black curve) for thermal decomposition of4O ppm of HCO 3 as unimolecular mechanism in presence of 10 ppm of CIB-PAA, (M, = 9954 g/mol). Figure 44 shows a graph illustrating the relationship between the theoretical and 5 experimental values of the conductivity of PA "~ at 97.2 *C. Figure 45 shows The electrical conductivity of PA("- with different end groups (M < 2000 g/mol) at high temperature in unit of (S.cm 2 / monomol). Figure 46 shows equivalent conductance as a function of the molecular mass of PA "n. 1o Figure 47 shows equivalent conductivity as a function of the hydrophobicity ratio of end group to molecular mass of PA"~ (MneM). Figure 48 shows rate coefficient x 10-2 (min') for thermal decomposition of 40 ppm

HCO

3 Tat T = 97 ± 0.5 0 C in the presence of 10 ppm PAA with different end groups and molecular mass. is Figure 49 shows the net of reactions for thermal decomposition of HCO 3 following the unimolecular mechanism. Figure 50 shows %ITD (inhibition efficiency of thermal decomposition) of HCO 3 by 10 ppm of PAA with different end groups (M, 5 2000). (o = CIB-PAA). Figure 51 shows %ITD of HC0 3 by 10 ppm of PAA with different end groups 20 (3000 < M, 5 8000). (e = CIB-PAA). Figure 52 shows % ITD of 40 ppm HCO 3 at T = 97.2 *C by 10, 15 and 30 ppm of CMM-PAA (Mn = 2106 g/mol), HIB-PAA (M,= 1403 g/mol), HDIB-PAA (M, = 1687 g/mol) and CIB-PAA (Mn = 9954 g/mol). Figure 53 shows rate coefficient for thermal decomposition of 40 ppm HCO3 at T = 25 97.2 'C in 50 ppm of NaCI solution and presence of 10 ppm PAA with different end groups (M, < 2000 g/mol). Figure 54 shows %ITD of 40ppm HCO3 at T = 97.2 *C in 50 ppm of NaCl solution and presence of 10 ppm PAA with different end groups (M, < 2000 g/mol) (e = CIB-PAA) 30 Figure 55 shows increase in molecular mass of PAAs decreasing in % ITD. Figure 56 shows a diagram illustrating the covering of air bubbles by PAAs and the adsorption of PAA on the round bottom flask. Figure 57 shows a graph of attenuation of intensity laser light with progressive calcium carbonate crystallization on optical fibre surface in the absence of PAA.

16 Figure 58 shows a graph of attenuation with and without of PAA (M 5 2000 g/mol) with different end groups. Figure 59 shows SEM images of CaCO 3 crystals on an optical fibre surface (diameter 1000 pm) prepared in the absence of PAA at 100 C. 5 Figure 60 shows SEM images of crystallization of CaCO 3 on an optical fibre core (diameter 1000 pm) in the presence CIB-PAA at 100 *C. Figure 61 shows SEM images of heterogeneous crystallization of CaCO 3 on an optical fibre core (diameter 1000 pm) in the presence of EIB-PAA at 100 *C. Figure 62 SEM images of heterogeneous crystallization of CaCO 3 on an optical 1o fibre core (diameter 1000 pm) in the presence of CMM-PAA at 100 *C. Figure 63 SEM images of heterogeneous crystallization of CaCO 3 on an optical fibre core (diameter 1000 pm) in the presence of HIB-PAA at 100 *C. Figure 64 shows a graph of laser light attenuation in the absence of PAA (blank) with progressive co-crystallisation of calcium carbonate and calcium sulfate. is Figure 65 shows photographs of precipitation on the surface of heat transfer tubes in the absence of PAA (blank) for calcium carbonate and calcium sulfate coprecipitation (Ex-1, Ex-2 and Ex-3 respectively). Figure 66 shows SEM micrographs of an exposed optical fibre core in absence of PAA (blank) for scale clusters showing coprecipitation of calcium carbonate and calcium 20 sulfate. Figure 67 shows SEM micrographs of an exposed optical fibre core in absence of PAA (blank) for scale clusters showing coprecipitation of calcium carbonate and calcium sulfate (spherical polymorph of CaSO 4 (A) and rod-like hexagonal calcite polymorph (B)). 25 Figure 68 shows SEM micrographs of an exposed optical fiber core in the absence of PAA (blank) for single crystal formation of coprecipitation of calcium carbonate and calcium sulfate. Figure 69 shows SEM micrographs of an exposed optical fibre core (diameter 1000 pm) for coprecipitation of calcium carbonate and calcium sulfate at 120*C(in the presence 30 of HIB-PAA (A) and HDIB-PAA(B)). Figure 70 shows photographs showing the precipitation on the surface of a heat transfer tube in the absence and presence of PAA with HIB and HDIB end groups for calcium carbonate and calcium sulfate co-crystallization at 120*C.

17 Figure 71 shows plots of Ca 2 concentration vs. time (min.) for different scale inhibitors (5ppm) in seawater at 104*C Detailed Description s In the present specification the terminology XYZ-PAA is used to denote a polyacrylic acid (PAA) terminated by a group XYZ (most generally RO-G-C(R'R")-) as defined in Table 1. Thus, for example HDIB-PAA refers to a polyacrylic acid having a hexadecylisobutyrate (i.e. 2-(hexadecyloxycarbonyl)-2-propyl) end group. The polymers of the invention are polyacrylic acids which have terminal groups of io structure RO-G-C(R'R")-, where G is a group such that G-OH is acidic. The polymers may comprise no acrylic monomer units (i.e. monomer units of structure CH 2 C(R"')C=0) other than acrylic acid monomer units (i.e. monomer units of structure CH 2 CHCO 2 H). They may be homopolymers of acrylic acid. They may be acrylic acid homopolymers having RO-G-C(R'R")- endgroups. These polyacrylic acids may 15 commonly be produced by ATRP (Atom Transfer Radical Polymerisation), but may be made by any convenient method, e.g. nitroxide mediated polymerisation, RAFT (reversible addition-fragmentation chain transfer) polymerisation, other controlled polymerisation techniques etc. The polymers commonly have an average molecular weight (Mn, Mw or Mz) of less than about 4000, or less than about 2000 and may have an 20 average molecular weight of less than about 4000, 3500, 3000, 2500, 2000, 1900, 1800, 1700, 1600 or 1500, or between about 2000 and 4000, 1000 and 3000, 2000 and 3000, 1000 and 2000, or 1000 and 1700 or 1000 and 1500 or 1200 and 2000 or 1400 and 2000 or 1200 and 1800 or 1200 and 1600 or 1400 and 1600 or 1400 and 1800, e.g. about 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 25 1750, 1800, 1850, 1900, 1950, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900 or 4000. They may have a degree of polymerisation less than about 55, or less than about 50, 45, 40, 35, 30, 25, 20 or 15, or between about 10 and about 55 or about 25 and 55, 20 and 40, 10 and 25, 10 to 20, 10 to 15, 15 to 25 or 15 to 20, e.g. about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 30 20, 21, 22, 23, 24 or 25. They may have a narrow molecular weight distribution or a broad molecular weight distribution. They may have Mw/Mn of less than about 2, or less than about 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2 or 1.1, or of about I to about 2, or about I to 1.8, 1 to 1.6, 1 to 1.4, 1 to 1.2, 1.2 to 2, 1.4 to 2, 1.1.6 to 2, 1.1 to 1.5, 1.1 to 1.3 or 1.3 to 1.5, e.g. about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2. The polymers may be 18 essentially linear. They may have one end group which is RO-C(=O)C(R'R")-. The other end group may be the same or may be, and commonly is, different. The other end group may be a halogen, e.g. Br. Alternatively it may be some other end group, e.g. OH or OR"' or OC(=O)R"', where R"' is an alkyl group (e.g. CI to C6 alkyl). 5 In the terminal group RO-G-C(R'R")-, R may be H, in which the terminal group is relatively hydrophilic and comprises a carboxylic acid group, or R may be an alkyl group. Typically the alkyl group R is from I to 20 carbon atoms long, although in some instances even longer chains may be used. The alkyl group may be linear, branched, cyclic or may contain all three of these. R may have about 1 to 20 carbon atoms, or about 1 to 16, 1 to i 12, 1 to 10, 1 to 6, 2 to 20, 6 to 20, 12 to 20, 16 to 20, 3 to 16, 6 to 16, 10 to 16 or 10 to 14 carbon atoms, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18 or 20 carbon atoms. Examples of suitable R groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, n-hexyl, cyclohexyl, n-octyl, isooctyl, decyl, dodecyl, tetradecyl, hexadecyl and octadecyl. In some instances there may be more than one length is of carbon chain, particularly for carbon chains over about 10 in which the carbon chain is obtained from animal or vegetable sources. In these cases the above chain lengths may represent the mean or predominant chain length. Alternatively the R group may be aryl or heteroaryl, each being optionally substituted. It may for example be phenyl, naphthyl, pyidyl, pyrimidyl, oxazolyl or some other aryl or heteroaryl group. 20 Groups R' and R" may be the same or may be different. They may be, independently, for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, cyclopropyl, methylcyclopropyl or cyclobutyl. They may both be methyl groups. In some instances they may form a ring together with the carbon to which they are attached, e.g. a pentyl, hexyl, heptyl or octyl ring. One or both of R' and R" may be, independently, aryl 25 or heteroaryl, each being optionally substituted, e.g. phenyl, naphthyl, pyidyl, pyrimidyl, oxazolyl or some other aryl or heteroaryl group. G may be any suitable group such that -G-OH is acidic. Suitable G groups include -C(=O)-, -S(=O)-, -S(=O)-O-, -S(=0) 2 -, -P(=O)-, -P(=0) 2 - -P(=O)-O- and -P(=0) 2 -0-. In these options, the C, S or P atom may be directly attached to the C atom of the C(R'R") 30 group. G may be for example -C(=0)-, whereby the terminal group is RO-C(=0) C(R'R")-. G may be a group such that -G-OH has a pKa of less than about 6, or less than about 5.5 or less than about 5, or of about I to about 6, or about 2 to 6, 3, to 6, 4 to 6, 5 to 6, 1 to 5, 1 to 4, 3 to 5, 4 to 5 or 4.5 to 5.5, e.g. about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6. The pKa may be measured at 25*C.

19 The polymers of the invention are effective at inhibiting formation of a solid inorganic group 2 metal salt in an aqueous liquid, i.e. at preventing or reducing precipitation of such a salt from the aqueous liquid. Group 2 metals are also known as Group IIA metals, or alkaline earth metals. In the present context, an "inorganic group 2 s metal salt" is a salt in which the cation is the cation of a Group 2 metal and in which the counterion of the metal ion (i.e. the anion) is an inorganic anion. Representative inorganic anions include carbonate, sulfate and hydroxide and mixtures of these, but other inorganic ions may also be possible. For the present purposes, oxalate is not regarded as an inorganic anion and carbonate and bicarbonate are regarded as inorganic ions. Thus the io polymers may be effective at inhibiting formation of a solid inorganic group 2 metal salt, which is not an group 2 metal oxalate, in an aqueous liquid. The group 2 metal may be calcium, magnesium, strontium or barium. The term "inhibiting" may refer to reducing the rate of production of the solid inorganic group 2 metal salt (i.e. the rate of precipitation of said salt) or to introducing, or increasing, an induction delay to the is production of the solid inorganic group 2 metal salt, or to reducing the equilibrium amount of the solid inorganic group 2 metal salt produced (i.e. precipitated) or to any two or more of these. The reduction in rate or equilibrium amount may be by more than about 10%, or more than about 20, 30, 40, 50, 60, 70, 80, 90, 95 or 99%, or may be between about 10 and about 100%, or between about 10 and 90, 10 and 80, 10 and 70, 10 and 60, 20 10 and 50, 20 and 100, 50 and 100, 60 and 100, 70 and 100, 80 and 100, 90 and 100, 50 and 95, 50 and 80, 80 and 95 or 95 and 99%, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, 98, 99 or 100%, where 100% represents complete prevention of production of the solid inorganic group 2 metal salt. The increase in the induction delay may be by at least about 10%, or at least about 50, 100, 200 300, 400 or 500%, or about 10 to 500%, 25 100 to 500%, 250 to 500% or 100 to 250%, e.g. by about 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450 or 500% or may be by more than 500%. It is hypothesised that the reduction in scale formation may be due to the adsorption of the polymers on growing crystallite surfaces. This is thought to prevent or inhibit aggregation and/or growth of the crystallites. It may also affect crystal morphology and speciation of the 30 scale crystals. It should be understood that any increase in induction delay or decrease in rate or equilibrium amount is relative to the case in which no polyacrylic acid is added, or in which no other inhibitory material is added but other components are identical and in identical concentrations. In certain instances, the potential for precipitation of a solid 20 inorganic group 2 metal salt is only created when two solutions are mixed, commonly a solution containing the group 2 metal ion in solution and a second solution containing the counterion which would normally form a precipitate with the group 2 metal ion. In this case the polymer of the present invention may be added to either or both of those 5 solutions prior to mixing them, or may be added at the same time as the solutions are mixed, optionally in a third solution. The polymer of the present invention may be added to either or both of the above solutions, or to a single solution in which precipitation is expected to otherwise occur in the absence of the polymer, in an amount such that the concentration of the polymer in io either of the solutions, or in the combined solutions, or in the single solution, is about 0.5 to about 50p.M, or about 0.5 to 20, 0.5 to 10, 0.5 to 2, 0.5 to 1, 1 to 50, 5 to 50, 10 to 50, 20 to 50, 1 to 20, 1 to 10, 10 to 20, 1 to 5, 0.7 to 7, 7 to 21 or 5 to 10 pLM, e.g. about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45 or 50pM. The molar concentration may depend on the molecular weight, for example the concentration may be higher for lower is molecular weight polymers. The concentration may be such that the molar concentration of monomer groups is about 5 to about 1000 pM, or about 10 to 1000, 50 to 1000, 100 to 1000, 500 to 1000, 5 to 500, 5 to 100, 10 to 500, 50 to 500, 100 to 500 or 10 to 100 pM, e.g. about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900 or 1000 M. The polymer may be added such that 20 the concentration of the polymer relative to the Group 2 metal ion in either of the solutions, or in the combined solutions, or in the single solution, is less than about 10% on a mole basis, or less than about 5, 2 or 1% on a mol basis, or about 0.1 to 10% on a mole basis, or about 0.1 to 5, 0.1 to 2, 0.1 to 1, 0.1 to 0.5, 0.5 to 10, 1 to 10, 2 to 10, 5 to 10, 0.5 to 5, 0.5 to I or I to 5% on a mole basis, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 1, 1.5, 2, 2.5, 2, 25 2.5, 4, 4.5, 5, 6, 7, 8, 9 or 10% on a mole basis. The aqueous liquid to which the polyacrylic acid is added may be seawater. It may be diluted seawater. It may be partially desalinated seawater. It may be concentrated seawater. It may be brackish water. It may be some other aqueous solution comprising one or both of magnesium ions and calcium ions. It may be an industrial stream, e.g. an 30 industrial waste stream. It may have a calcium ion concentration of from about 100 to about 1000ppm, or about 100 to 500, 100 to 200, 200 to 1000, 500 to 1000, 500 to 600 or 500 to 550ppm, e.g. about 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 or 1000 ppm, or may have some other concentration. In some instances it may have a very low or zero concentration of calcium ions. In this case, 21 it will generally comprise magnesium ions. The aqueous liquid may have a magnesium ion concentration of about 1000 to about 3000ppm, or about 1000 to 2000, 2000 to 3000, 1500 to 2500 or 1500 to 2000ppm, e.g. about 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900 or 5 3000ppm. Alternatively the magnesium ion concentration may be lower, e.g. about 50 to about 1000ppm, or 50 to 500, 50 to 200, 50 to 100, 100 to 1000, 100 to 500 or 500 to 1000, e.g. about 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800 or 900ppm The methods of the invention may be conducted at a temperature of about 0 to about 100'C, or about 10 to 100, 15 to 100, 20 to 100, 15 to 100, 30 to 100, 40 to 100, 50 to to 100,75 to 100,0to75,0to50,0to25,0 to20,0 to 15,0 to 10, 10to90,25 to90, 10 to 50, 10 to 30, 20 to 50, 90 to 100 or 20 to 90*C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100*C, or in some cases over 100*C, e.g. 105, 110, 115, 120, 125, 130, 135, 140, 145 or 150*C, or from 90 to 110 or 95 to 110 or 95 to 105*C. It may be conducted at a temperature of over 90*C, or over 91, 95 or 100*C, e.g. up to about is 150*C (or between about 80 and 150, 100 and 150, 120 and 150 or 100 and 120 0 C). It will be appreciated that higher temperatures, commonly over 90 or 100*C, may be more suitable for multistage flash distillation although in specific cases this may also be conducted at lower temperatures as set out above. In particular, the addition of polyacrylic acid may occur at these temperatures and/or the subsequent water purification process 20 (e.g. reverse osmosis and/or multistage flash distillation) may be conducted at these temperatures. A particular application of the present invention is the prevention or inhibition of scale production in water purification processes such as reverse osmosis. The water purification may be, or may comprise, reverse osmosis, flash distillation, flash vacuum 25 distillation, multistage flash distillation (evaporation), membrane distillation, ultrafiltration or any other process which suffers from problems of scale formation, or it may comprise a combination of any two or more in series. In such processes, commonly purified water is separated from a solution, leaving a solution which has an increased concentration of ions relative to the original solution. For example in reverse osmosis, 30 water passes through a reverse osmosis membrane under pressure. As ions and certain other dissolved species are retained by such a membrane, the water that passes through (the "permeate") is purified, i.e. has a reduced concentration of ions and the other dissolved species. The portion of the original solution (the "feed") which does not pass through the membrane (the "retentate") has a higher concentration of ions and the other 22 dissolved species. If this higher concentration exceeds the solubility limit of the relevant salts, these salts can precipitate as scale, commonly on the membrane, and therefore impede the passage of water through the membrane. This is one mechanism of membrane fouling, and many attempts have been made to find a solution this problem. One such 5 solution is to add a polymer as described in the present invention to the feed. The polymer may be added in a batchwise method or may be added continuously. A similar solution may also reduce scale problems in other water purification processes, for example pervaporation, distillation, membrane distillation etc. Particularly effective polymers for use as scale inhibitors were polyacrylic acids 1o having end group C 6

H

3 0-C(=0)CMe 2 - of Mn less than about 2000g/mol, e.g. of about 1403 g/mol. Other useful scale inhibitors polyacrylic acids having end group C 16

H

33 0 C(=0)CMe 2 - of Mn less than about 2000g/mol, e.g. of about 1687 g/mol. The inventors have surprisingly found that the polymers described above may be used to inhibit the rate of thermal decomposition of bicarbonate ions in an aqueous is solution. The aqueous solution may be at an elevated temperature, i.e. above room temperature. It may be for example at a temperature of at least about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100*C, or of between about 25 and about 100*C, or between about 25 and 75, 25 and 50, 50 and 100, 75 and 100 or 90 and 100, e.g. at a temperature of about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 or, in 20 some circumstances, above 100*C, such as 105, 110, 115 or 120*C, or about 100 to about 120*C,orabout 100 to 120, 105 to 120, 110 to 120, 100to 110 or 105 to 115*C. The polyacrylic acid may be added to the aqueous liquid at a concentration of less than about 50ppm, or less than about 40, 30, 20 or 10ppm, or of from about 5 to about 50ppm, or from about 10 to 50, 20 to 50, 30 to 50, 5 to 30, 5 to 20, 5 to 10, 10 to 40, 10 to 25 20 or 20 to 40ppm, e.g. about 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50ppm. It may be added at a ratio to bicarbonate ion on a weight basis of less than about 50%, or less than about 40, 30, 20 or 10%, or from about 10 to 50, 20 to 50, 30 to 50, 5 to 30, 5 to 20, 5 to 10, 10 to 40, 10 to 20 or 20 to 40%, e.g. about 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50%. The resulting reduction in rate of thermal decomposition may be at least about 30 25%, or at least about 30, 40, 50, or 90%, or about 25 to 50%, or about 25 to 50, 25 to 30, 25 to 95, 50 to 95, 80 to 95, 30 to 80, 30 to 50 or 50 to 80% (as measured by the rate constant at the particular temperature), e.g. about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95%.

23 The aqueous liquid containing bicarbonate may be the feed for a water purification process such as reverse osmosis. Thus the addition of the polyacrylic acid to the aqueous liquid may result in a reduction of scale formation in the water purification process. The invention therefore encompasses a method for reducing scale formation in a water 5 purification process, e.g. in a reverse osmosis process, comprising adding to the feed for that water purification process a polyacrylic acid as described herein. The addition may be in the quantities or concentrations described elsewhere herein. The addition may be continuous or it may be batchwise. It may be added neat or in solution, optionally in aqueous solution. 10 The polymers used in the present invention may be made as described below. As discussed above, these polymers are polyacrylic acids having a terminal group of structure RO-G-C(R'R")-. In one embodiment of these polymers, R' and R" are both methyl and R is one or more of ethyl or hexyl or cyclohexyl or decyl or hexadecyl and G is a group such that -G-OH is an acidic group and the polymer has a number average is molecular weight of less than about 4000Da, optionally less than 2000Da. To make these polymers an acrylate ester is polymerised in the presence of Cu(I) and RO-G-C(R'R")X, wherein X is a halogen, so as to form a poly(acrylate ester) having a terminal group of structure RO-G-C(R'R")-. The acrylate (and polyacrylate) ester may be an alkyl ester. It may be a CI to C6 alkyl ester, or Cl to C3, C3 to C6 or C2 to C4 ester, e.g. Cl, C2, C3, 20 C4, C5 or C6. It may be an alkyl ester having a tertiary carbon adjacent the carboxyl function. It may for example be a t-butyl ester. The ratio of RO-G-C(R'R")X to acrylate should be chosen so as to achieve the desired molecular weight. A polyacrylic acid according to the present invention may be made by hydrolysing the poly(acrylate ester) so as to form the polyacrylic acid having a terminal group of 25 structure RO-G-C(R'R")-. The various options for R, R', R" and G have been described elsewhere. In some embodiments the acrylate ester is a t-butyl ester, whereby the poly(acrylate ester) is a poly(t-butyl acrylate). X may be Br or may be some other halogen, for example Cl or I. The hydrolysis may be conducted in organic solution in the presence of an organic 30 acid. The organic acid may be a strong organic acid. It may have a pKa of less than about 1, or less than about 0.7, 0.5, 0.3 or 0.2. The organic acid may be trifluoroacetic acid or some other suitable strong organic acid such as trichloroacetic acid, difluoroacetic acid, benzenesulfonic acid etc. The hydrolysis may be conducted under conditions under which the terminal group does not hydrolyse.

24 The ratio of Cu(I) to RO-G-C(R'R")X may be about 0.9:1 to about 1.1:1, or about 0.9:1 to 1:1, 1:1 to 1.1 to I or 0.95:1 to 1.05:1, e.g. about 0.9:1, 0.95:1, 1:1, 1.05:1 or 1.1:1. The ratio of acrylate ester to Cu(I) may be about 1:1 to about 1.5:1, or about 1.1:1 to about 1.5:1, 1.2:1 to 1.5:1, 1.3:1 to 1.5:1, 1.4:1 to 1.5:1, 1:1 to 1.4:1, 1:1 to 1.3:1, 1:1 to 5 1.2:1, 1:1 to 1.1:1 or 1.2:1 to 1.4:1 e.g. about 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1. The reaction may be conducted under an inert atmosphere, or under a non-oxidising atmosphere. It may for example be conducted under nitrogen, argon, helium or some other suitable atmosphere. It may be conducted at a suitable temperature, e.g. room temperature, or from about 15 to about 50*C, or about 20 to 50, 30 to 50, 15 to 30, 15 to 10 20 or 20 to 30*C, or about 15, 20, 25, 30, 35, 40, 45 or 50*C. In the present specification, where mention is made of a polyacrylic acid, it should be understood that under appropriate pH conditions some or all of the carboxylic acid groups on the polyacrylic acid may be ionised to carboxylate groups, and the term "polyacrylic acid" may also apply to the partially and/or fully ionised species. is The formation of scale (which may be inhibited by the polymers of the present invention) may be monitored using an intrinsic exposed-core optical fibre sensor (IECOFS). This may be used to estimate or determine the inhibition efficiency and/or effective concentration of the scale inhibitors of the present invention. Methods and apparatus for doing so are described in a separate patent application filed on the same day 20 as the present application and having the same inventor. That application is entitled "Monitoring scale formation" and is incorporated herein in its entirety by cross-reference. Examples Example 1: Synthesis and Characterisation of Poly(Acrylic Acids) A number of poly(acrylic acid)s (PAAs) with different end-groups and molecular weight 25 were synthesised by ATRP (Atom Transfer Radical Polymerisation) as shown in Table 1. The initiator to Cu(I)Br to ligand molar ratios were 1:1:1 for all polymerizations. These PAAs were characterised by nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC) to determine molecular weight and polydispersity. Purification of reagents 30 Tert-butyl acrylate (Aldrich 98%) (tBA) was washed twice with 0.05M NaOH, followed by two washes with water. After drying over CaC 2 , tBA was distilled under reduced pressure, only the middle fraction was collected. The purified monomer was stored over Calcium hydride at 0*C until required.

25 Cu(I)Br (98% Aldrich) was stirred in glacial acetic acid for 24 hrs under a N 2 atmosphere, washed with ethanol and diethyl ether, and then dried in a vacuum desiccator at 70 *C for three days. The purified Cu(I)Br, which was white in colour, was stored in a sealed container until required. s N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA:Aldrich 99%) was used as received. Synthesis of initiators In addition to ethyl 2-bromoisobutyrate which is available commercially (Aldrich, 99%) four different initiators (hexyl 2-bromoisobutyrate, cyclohexyl 2-bromoisobutyrate, decyl 10 2-bromoisobutyrate and hexadecyl 2-bromoisobutyrate were synthesized, as follows: Alcohol (7 g cetyl alcohol (BDH) / 4.6 g decanol (Aldrich) / 3.0 g hexanol (Aldrich) / 2.9 g cyclohexanol (Aldrich)) was added to 120 mL of dichloromethane (DCM, Ajax) in a 250 mL three-necked round bottomed flask. 4.4 g of triethylamine (Aldrich) was added to the reaction and the mixture was stirred for half an hour. The reaction was cooled in an 15 ice bath under a nitrogen atmosphere. 8.0 g of 2-bromoisobutyryl bromide (Aldrich) was dissolved in 40 mL DCM and added dropwise via an addition funnel over the period of an hour. The reaction was stirred in an ice bath for another hour and then allowed to warm to room temperature overnight. The product was washed consecutively with 200 mL aliquots of 0.1 M NaOH (Chem-supply), 0.1 M HCl (Chem-supply) distilled water and 20 saturated NaCl (Chem-supply) The products were dried over MgSO 4 (Chem-supply) and distilled under high vacuum using a Kugelohr. Synthesis of Poly (tert-butyl acrylate ) (PtBA) Copper (I) bromide {Cu(I)Br, 98% Aldrich} was placed in a 5 mL purpose-made reaction flask with 3 or 4 small boiling chips. t-Butyl acrylate (tBA, Aldrich), N,N,N',N",N" 25 Pentamethyldiethylenetriamine (PMDETA, Aldrich 99%), (ligand) and initiator were placed in a small beaker in that order. This mixture was then added to the reaction vessel, connected to the high vacuum (tap turned to off) and frozen in liquid nitrogen. Three freeze-pump-thaw cycles were conducted under nitrogen and the reaction vessel was then sealed with a LPG torch, thawed and mixed by a vortex mixer. Samples were placed in an 30 oil bath at 90 *C until reaction was complete (30 hours). The vessel was then opened and the product dissolved in 10 - 20 mL tetrahydrofuran (THF, Aldrich-HPLC Grade). The polymer solution was then filtered through a column packed with 50% A1 2 0 3 and 50% celite to remove the catalyst and THF was removed by evaporation. The polymer mass was dissolved by a minimum of methanol and poured into a Petri dish. The PtBA was 26 precipitated via slow addition of distilled water until cloudiness appeared in the methanol/water mixture. This was allowed to sit for at least an hour. The supernatant was decanted and the polymer placed in a freeze drier for two days. The reaction scheme for this polymerisation is shown in Fig. IA. 5 Selective hydrolysis to PAA 1.5g (PtBA) (11.5 mmol of tert-butyl ester) was dissolved in 30mL of dichloromethane (DCM). It was stirred with 5 molar excess (6.7 g, 57.5 mM) of trifluoroacetic acid (TFA) for 24 hours at room temperature. The PAA formed as an insoluble solid mass on the flask sides and stir bar. On completion, the excess DCM and TFA was decanted and 10 resulting polymer was dried using a high vacuum. Once dry the off-white polymer was powdered and stored. A selected representative set of the PAA was characterized with 1H NMR in methyl sulfoxide-d 6 (Aldrich 99.9 atom % D). The reaction scheme for this polymerisation is shown in Fig. IB. Hydrolysis of end groups is 0.5g of PAA, 2 mL of 10 M HCl and 20 mL of water were added to a 50 mL round bottom flask and setup for reflux. The mixture was refluxed for 3-4 hrs, allowed to cool and poured into a Petri dish. The mixture was allowed to slowly evaporate to dryness over several days at 35 "C. The resulting polymer was purified by redissolving in a small amount of water washing with DCM and drying under vacuum. Total hydrolysis of the 20 end groups were confirmed with 'H-NMR in dimethyl sulfoxide-d (Aldrich 99.9 atom % D). The reaction scheme for this polymerisation is shown in Fig. IC.

27 Table 1- Synthesis of Poly (Acrylic Acid) with different end groups by ATRP End Grouips Tern inated-PAA Natue ofNameand No. of Nature of Name and carbon Chemical structure phobicity symbol atoms 0 Carboxymethyl Hydrophilic -1,1 -dimethyl 4 HO (CMM) Ethyl Short isobutyrate 6 (EIB) Cyclohexyl isobutyrate 10 (CIB) Medium 00 Hexyl isobutyrate 10 (HIB) 0 Decyl isobutyrate 14 (DIB) Long 0 Hexadecyl isobutyrate 20

(HDIB)

28 Polymer Characterization The dried polymer as PtBA and PAA were characterized by 'H-NMR ('H -NMR, Bruker 300) and GPC (GPC- Waters 1525 HPLC, Waters autosampler 712 WISP and Waters 2414 RI detector) as follows: s 'H-NMR The NMR polymer peaks were integrated with respect to one of those groups to estimate the molecular mass (M,) of the PtBA and PAA as shown in Figure 2. The results for estimation of number average molecular mass (M,) of PAA are summarized in Table 2. GPC io 2 mg of the polymer sample PtBA was dissolved in Iml of THF and was allowed to stand for a minimum of 12 hrs before injection. Samples were filtered through a 0.45pm syringe filter prior to injection. GPC was performed with a Waters 1525 HPLC, Binary pump fitted with a Reodyne 50 mL manual injector and Waters 2414 RI detector. Column used was a Waters HR2 stryragel (7.8 x 300 mm) maintained at 30*C. The purified THF was 15 used as eluent at a flow rate of Iml/min. Polymers were analysed using PSS WinGPC processing software (version 6). The column was calibrated by using the results that were obtained from NMR spectrum for M, of PtBA in the range of 3100 - 14166 g/mol. The calibration curve showed a linear relationship with R2 = 0.997. 2 mg of the polymer sample PAA was dissolved in Iml of the sodium bicarbonate buffer 20 solution and was allowed to stand for a minimum of 48 hrs before injection. Samples were filtered through a 0.45pm syringe filter prior to injection. GPC was performed with a Waters 1525 HPLC, Binary pump fitted with a Reodyne 50 mL manual injector and Waters 2414 RI detector. Column used was an Ultrahydrogel Linear column (300 x 7.8 mm) maintained at 30*C. Sodium bicarbonate buffer solution was used as eluent at a flow 25 rate of 1ml/min. Polymers were analysed using PSS WinGPC processing software (version 6). The column was calibrated by using the results that were obtained from NMR spectra for M, of (PtBA) in the range of 2000- 14000 g/mol. The calibration curve showed a linear relationship R2 = 0.994. Some examples comparing between theoretical (expected) molecular mass and 30 experimental molecular mass are summarized in Table 2.2. The estimation of molecular mass averages and polydispersities by NMR and GPC for all PAA used in this study are given in Table 2A.

29 Table 2: A comparison between theoretical (expected) molecular mass and experimental molecular mass for some examples End groups MW of Theoretical Experimental terminated- Initiator Code Monomer (expected) Mn M PDI PAA M, as PAA (NMR) (GPC) CIB-6 16.65 1394 1689 1449 1.40 CIB-2 70.61 5285 5088 5693 1.39 CIB 249.14 CIB-3 138.14 10113 10988 9177 1.26 CIB-7 166.53 12203 13209 12409 1.15 HIB-1 16.65 1396 1403 HIB-2 48.57 3702 3563 3258 1.26 HIB 251.15 HIB-3 124.90 9179 8928 9658 1.12 HIB-5 166.53 12205 13094 12452 1.12 HDIB-1 18 1609 1687 HDIB-2 31 2545 2767 HDIB 391.41 HDIB-3 50.8 3987 4135 HDIB-4 106 7950 9391 HDIB-5 207.02 15948 17167 5 30 Table 2A: Estimated molecular mass averages and polydispersities by NMR and GPC for all PAA used in this stud' i. End Groups The Mn by Mn by Mw by Terminated- duration of Yield% PDI NMR GPC GPC PAA reaction (h) 2106 2203 2864 1.3 CMM - 7633 11312 1.5 - 11773 16453 1.4 >12 79 1669 1598 2091 1.3 EIB >12 94 5065 4548 6029 1.3 >12 82 7180 5242 6625 1.3 25 88 1689 1449 2035 1.4 15 65 1852 1714 2136 1.3 15 85 3518 2367 2867 1.2 22 82 5088 5693 7913 1.3 15 76 6210 3399 4092 1.2 CIB 25 82 6440 8624 10780 1.2 25 76 8400 6973 8716 1.2 25 74 10988 9177 11563 1.2 28 72 9954 6377 8226 1.3 27 83 13209 12409 14304 1.2 5 31 24.5 92 1403 >24 89 1981 1864 2177 1.2 28 83 3563 3258 4115 1.3 >24 54 4224 2879 3396 1.2 HIB 28 65 6227 5859 6738 1.2 >24 71 6723 3307 3856 1.2 25 86 8928 9658 10854 1.1 30 69 13094 12452 13946 1.1 7 82 2422 2392 3072 1.3 DIB 6 90 4472 3064 3816 1.3 26 76 6203 2717 4074 1.5 18 36 1687 25 72 2767 HDIB 25 38 4135 37.5 88 9391 38.5 67 17167 Example 2: Inhibition of Homogenous Formation of Calcium Carbonate The objective of this experiment was to determine the efficiency of PAA with different end-groups and controlled molecular mass range 1400-17000 g/mol as scale inhibitors to 5 prevent CaCO 3 crystallization in the bulk solution at room and elevated temperatures by using conductivity and turbidity measurements. To determine the inhibition efficiency of PAA as scale inhibitors to prevent CaCO 3 scaling, conductivity and turbidity measurements were collected at a pH of 9.2 under 32 seven sets of conditions and supersaturation level (SL = Qip/ Kip, more detail is given in Chapter 1), as outlined in Table 3. Table 3: The conditions to determine the inhibition efficiency of PAA Conditions 1 2 3 4 5 6 7 T*C 25 25 60 80 90 100 100 pH 9.2 [Ca 2 +] ppm 66 192 66 66 66 36 66 [C0 3 2 -] ppm 100 140 100 100 100 30 100 [Ca2+] /[C0 3 2 -] 1:1 2.1:1 1:1 1:1 1:1 1.8:1 1:1 [PAA] ppm 1.50 1.50 1.50 1.50 3.75 0.50 6.70 Ksp x 10-9 4.95 4.95 2.80 2.14 1.90 1.69 1.69 SL 556 2263 983 1284 1451 277 1629 5 Two solutions, 0.167 M (10000 ppm) of C0 3 2 - as Na 2

CO

3 and 0.413 M (16500 ppm) of Ca 2 + as CaCl 2 , were prepared. These solutions and the R/O water used were filtered and degassed using a 0.45 jim Millipore solvent filter. PAA solutions were prepared by dissolving 0.015g of PAA in 20 ml water (750 ppm) and were used after 3 days. 10 A UV-Vis spectrophotometer (Unicam spectrophotometer SP6-550) was used to measure the increase in turbidity with time by recording apparent absorption at 900 nm (where absorbance is negligible). Due to the formation of air bubbles at high temperatures which interfere with turbidity measurements, the turbidity measurements only at room temperature were used for conditions 1 and 2. is Filtered (0.45pm cellulose acetate membrane) deionized water (246 mL) was placed in a 500 mL cleaned beaker containing the conductivity probe and meter (Beta 81, CHK Engineering). Under magnetic stirring, one drop of 0.1 M NaOH, Ca 2 + as CaCl 2 solution to give a final concentration of 66 ppm and scale inhibitor solution to give 1.5 ppm were added to the beaker. After equilibration (approximately 2 min), the photodetector in the 20 spectrophotometer were zeroed. The solution was pumped continuously through a 1 cm Quartz flow cell using a Gilson peristaltic pump (Minipuls 2) with 4 mm silicon tubing 33 and then returned to the main mixture. CO 3 2 - as Na 2

CO

3 solution was added to the beaker to give a final concentration of 100 ppm and the recording of absorbance at 900 nm started 20 s later from the adding of C0 3 2 - solution. All experiments were done in triplicate and in a short period of time (two weeks) with the range of temperatures 24- 25 5 0 C. Analogue outputs from conductivity prop and spectrophotometer were digitally converted using a Picolog A/D Converter 16 (16 Bit) and Picolog recording software and data was acquired every 5 and 10 seconds. After each experiment all equipment was flushed multiple times with weak acid followed by R/O water. 1o The steady state (SS) is defined as the conductivity of the system when it is under equilibrium, that is, the measured conductivity when there is no more precipitation and conductivity value remain stable. Inhibition efficiency was determined by applying the following equation: %JE = ( J gBllrk x 100 s5 (Co - Cilland where SS is the steady state value of conductivity, CBIank is the equilibrium conductivity value of the system with no PAA under the given conditions, and Co is the conductivity value before any CaCO 3 scale formation under the given conditions. For example % IE of 20 PAA at without any CaCO 3 scale formation = 100% and IE of blank = 0%. Induction time (IT) is a measure of the time that a system takes to crystallize and was measured from the intersection of the slope of the decreasing part of the conductivity curve and the straight line of the SS conductivity as shown in Figure 3. Inhibition of CaCOp crystallization at room temperature (condition 1) 25 For further investigation, the inhibition efficiency of PAAs were determined under two different ratio of [Ca 2 ] / [C0 3 2 ] 1:1 and 2.1:1 at 25 *C. The induction times by conductivity and turbidity measurements were determined in the absence and presence of PAAs under conditions 1. For those data, t-test and F-test were calculated to determine if there is any statistically significant different at confidence 30 interval 95 % as well as the correlation coefficient as shown in Figure 4. The calculated t and F were 1.57 and 1.11 and their tabulated values at 11 degrees of freedom are 2.20 and 2.85 respectively, which indicate there is no significant different between the inductions 34 times by conductivity and turbidity measurements for CaCO 3 formation at room temperature. For condition 1, CBlak = 419 RS/cm and Co = 592 IS/cm. The inhibition efficiency, conductivity and turbidity measurements of PAA under condition I allow the PAA to be s divided into three groups. The % inhibition efficiency (% IE) results are shown graphically in Figure 5. Group One - For the lowest molecular mass of PAA with hydrophilic end group and short and medium hydrophobic end groups, such as carboxymethyl- 1,1 -dimethyl (CMM), ethyl 1o isobutyrate (EIB), hexyl isobutyrate (HIB) and cyclohexyl isobutyrate (CIB) terminated PAA, excellent % IE were obtained. No precipitation was observed and the turbidity and conductivity changed very slowly, therefore no induction time could be reported. Group Two - For decyl isobutyrate (DIB) terminated-PAA, HIB-PAA and CIB-PAA of moderate molecular mass (- 6000 g/mole), % IE were generally good as shown in Figure 15 3.10 and little precipitation was observed, with high induction times. Group Three - For the highest molecular mass of PAA (M, > 9000 g/mol) for all end groups and for all molecular mass for the longest end group hexadecyl isobutyrate (HDI, % IE is less than 50 %, with distinct induction times. 20 Table 4: Induction times and % inhibition efficiency (% IE) of PAA for CaCO 3 formation under conditions 1. (1) Group one: no precipitation and no significant change in conductivity. (2) Group two: minor precipitation with long induction times, (3) Group three: more significant precipitation and shorter induction times. End Groups F Cond.SS IT (sec) IT (sec) Mn PDI % IEGru Terminated- ( S/cm) Abs. Cond. PAA Blank 419 0 225 400 1673 1.6 592 100 - - I 2106 1.3 592 100 - - 1 CMM 1457 1.5 592 100 - - 1 7633 1.5 582 94.2 - - 2 11773 1.6 576 90.5 - - 2 35 1669 1.3 592 100 - - 1 +110 +208 EIB 5065 1.3 481 35.8 796 866 3 EIB___-225 -332 +81 +212 7180 1.3 514 54.9 460 610 3 -185 -23 1689 1.4 592 100 - - 1 1852 1.3 592 100 - - I 3518 1.2 592 100 - - 1 5088 1.4 592 84.4 - - 2 CIB 8400 1.2 560 81.5 - - 2 +40 +204 9954 1.3 497 45.1 510 749 3 -75 -25 +86 +204 10988 1.2 505 49.7 620 790 3 -160 -25 +33 +146 13209 1.1 456 21.4 318 433 3 -23 -50 End Groups Cond.SS IT (sec) IT (sec) Terminated- M, PDI % IE Group (I.S/cm) Abs. Cond. PAA HIB 1403 - 592 100 - - 1 1981 1.2 592 100 - - 1 3563 1.2 592 100 - - 1 4224 1.2 592 100 - - 1 6723 1.2 592 100 - - 1 36 +70 +15 8928 1.1 511 53.2 829 1190 3 -99 -209 +30 +103 13094 1.1 461 24.3 314 421 3 -13 -13 2422 1.3 546 73.4 - - 2 DIB 4472 1.3 530 64.2 - - 2 6203 1.5 503 48.6 - - 2 +6 +266 1687 - 491 41.6 706 959 3 -16 -239 +92 +238 4135 - 497 45.1 1095 1150 3 -397 -365 +57 +55 HDIB 2767 - 472 30.7 769 875 3 -11 -21 +40 +166 9391 - 489 40.5 609 827 3 -27 -15 +16 +104 17167 - 470 29.5 507 676 3 -35 -139 Inhibition of CaCO 3 crystallization at room temperature (condition 2) Under conditions 2, the conductivity and turbidity measurements were used to determine the %IE of PAA with different end groups and molecular mass to inhibit CaCO 3 s crystallization in bulk solution for the polymers which performed well (IE =100 %) under condition 1, as well as, for the polymers that have IE > 70 % with long induction time under those conditions. The induction times by conductivity and turbidity measurements were determined in the absence and presence of PAAs under conditions 1. For those data, t-test and F-test were 10 calculated to determine the statistic significantly different at confidence interval 95 % as well as the correlation coefficient. The calculated t and F were 1.43 and 1.87 and their tabulated values at 10 freedoms are 2.23 and 2.98 respectively, which indicate there is no significant different between the inductions times by conductivity and turbidity measurements for CaCO 3 formation at room temperature. For condition 2, CBIak = 871 Is jiS/cm and Co = 892 pS/cm. The % IE and induction time of conductivity and turbidity 37 measurements of PAA under condition 2 allow the PAA to be divided into two groups as shown in Table 5. Group One: Good %IE (-50%) with high induction times were observed for low molecular mass PAA with hydrophilic (CMM), short and medium end groups for EIB 5 PAA (M = 1669 g/mol), HIB-PAA (M = 1403 g/mol) and CIB-PAA (M =1689 g/mol) as shown in Figures 3.13 and 3.14 respectively. Group Two: Low %IE (less than 50%) with short induction times were observed for PAA of molecular mass greater than 4000 g/mol with short end groups and for lower molecular weight PAA with long end groups as shown in Figure 7. 10 Table 5: Induction times and % inhibition efficiency (% IE) of PAA for CaCO 3 formation under conditions 2. End Groups M PDI % IE IT (sec) Abs. IT (s) Cond. Group Terminated PAA Blank 0 60 75 1457 1.5 67.1 - 535 1 2106 1.3 67.4 - 425 1 CMM 7633 1.5 42.6 - 457 2 11773 1.6 40.5 - 336 2 EIB 1669 1.3 64.5 244 422 1 1689 1.4 55.9 245 381 1 1852 1.3 36.5 320 434 2 CIB 3518 1.2 57.0 178 257 1 5088 1.4 35.7 92 127 2 1403* - - 304 441 1 3563 1.2 50.9 380 456 1 HIB 4224 1.2 46.0 - 327 2 6723 1.2 0 193 248 2 38 2422 1.3 53.8 76 100 1 DIB 4472 1.3 53.7 68 120 1 3518 1.2 57.0 178 257 1 5088 1.4 35.7 92 127 2 1403* - - 304 441 1 3563 1.2 50.9 380 456 1 HIB 4224 1.2 46.0 - 327 2 6723 1.2 0 193 248 2 2422 1.3 53.8 76 100 1 DIB 4472 1.3 53.7 68 120 1 *: 11 exp. were done, however the results for 4 experiments were no significant precipitation. s Inhibition of CaCO3 crystallization at 60, 80 and 90 *C Since the CaCO 3 deposit is the predominant alkaline scale in MSF plants at 60, 80 and 90 0 C, the inhibition efficiency of PAA with different molecular mass and end groups to prevent that scale were studied at those temperatures. Under those conditions, the conductivity measurements were used to determine the % IE of PAA with different end to groups and molecular mass to inhibit CaCO 3 crystallization in bulk solution and that was for the polymers which performed well ( IE =100 %) under conditions 1. As well as, for the polymers that have IE > 50 % with long induction time under those conditions. Filtered (0.45 m cellulose acetate membrane) deionized water (98.25 mL) was placed in a clean cell containing the conductivity probe and thermometer. One drop of 0.1 M 15 NaOH, Ca 2 + as CaCl 2 solution to give a final concentration of 66 ppm and scale inhibitor solution to give 1.5 ppm were added to the cell under stirring. Recording of conductivity started when the solution reached the target temperature and 20 s later C0 3 2 ~ as Na 2

CO

3 solution to give a final concentration of 100 ppm was added to the cell. Conductivity was measured by a conductivity probe and meter (Beta 81, CHK Engineering). (Figure 8) 39 Inhibition of CaCO 3 crystallization at 60 'C (conditions 3) Under conditions 3, conductivity measurements was used to determine the % IE and induction time of PAA with different end groups and molecular mass in the range of (1400 -9000 g/mol) to inhibit CaCO 3 formation in bulk solution. 5 For conditions 3, CBIak = 453 pS/cm and CO= 650 jiS/cm. The % IE and induction time of PAA with different end groups and molecular mass allows the PAA to be divided to two groups as shown in Figure 9 and Table 6. Group one: Low molecular mass PAA with hydrophilic end group (CMM) and short and medium hydrophobic end groups, such as EIB-PAA (M = 1669 g/mol), HIB-PAA (Mn = i 1403 g/mol) and CIB-PAA (Mn =1689 g/mol) showed good inhibition efficiency (% IE ~ 50) and high induction time as shown in Figure 10. Group two: PAA with molecular mass more than 4000 g/ mol for hydrophilic end group (CMM) and short and medium hydrophobic end groups (EIB, CIB and HIB), as well as the low molecular mass with long hydrophobic end groups (DIB and HDIB) which is showed low inhibition efficiency (% IE < 30 %) and low induction time are shown in Figure 11. Table 6: Induction times and % inhibition efficiency (% IE) of PAA for CaCO 3 formation under conditions 3. End Groups Mn PDI SS (pS/cm) % IE IT (sec) Group terminated- Cond. PAA Blank 453 0.0 175 CMM 2106 1.3 588 68.3 217 +166 1 -80 7633 1.5 521 34.4 110 +12 2 -5 EIB 1669 1.3 573 61.1 202 +58 1 -61 7180 1.3 494 21.1 128 +42 2 -16 CIB 1689 1.4 600 74.4 304 +126 1 -121 5088 1.3 521 34.9 158 +41 2 -28 40 HIB 1403 - 589 68.8 250 +12 1 -90 3563 1.3 522 50.3 176 +34 1 -49 DIB 2422 1.3 503 25.5 163 +25 2 -10 4472 1.3 504 25.6 130 +26 2 -9 HDIB 1687 - 506 26.9 182 +68 2 -17 4135 - 484 15.8 188 +66 2 -29 Inhibition of CaCO 3 crystallization at 80 *C (conditions 4) Under conditions 4, conductivity measurements were used to determine the % IE and induction time of PAA with different end groups and molecular mass in the range of s (1400 -8000 g/mol) to inhibit CaCO 3 formation in bulk solution. For conditions 4, CBIak = 480 gS/cm and Co = 755 pS/cm. The inhibition efficiency and conductivity measurements of PAA under conditions 4 allow the PAA to be divided into two groups as shown in Figure 12 and Table 7. Group One: Low molecular mass PAA with hydrophilic (CMM) and hydrophobic short to and mid-length end groups, such as ElB-PAA (Mn = 1669 g/mol), HIB-PAA (M = 1403 g/mol) and CIB-PAA (Mw= 1689 g/mol) showed good inhibition efficiency (% IE ~ 50 %) and high induction time as shown in Figure 13. Group Two: PAA with molecular mass more than 4000 g/mol with hydrophobic, short and middle end groups and PAA of low molecular mass with long end groups showed 15 low induction time and poor inhibition efficiency (less than 30 %).

41 Table 7: % inhibition efficiency (% IE) and induction times of PAA for CaCO 3 formation under conditions 4. Induction time End Groups Mw by PDI % IE (s) Group NMR Cond. Blank 0.0 60 +20 2106 1.3 58.6 125 1 -4 CMM +46 7633 1.5 24.7 123 2 -29 +30 1669 1.3 48.8 125 1 -21 EIB +21 7180 1.3 22.2 90 2 -17 +24 3518 1.2 66.0 118 1 -8 CIB +5 1689 1.4 72.5 128 1 -16 +3 1403 - 57.1 134 1 HIB_ -48 HIB +35 3563 1.3 39.7 123 2 -17 +45 2422 1.3 22.6 122 2 -43 DIB +30 4472 1.3 18.6 117 2 -28 +33 1687 - 19.3 110 2 -24 HDIB +21 2767 - 19.3 96 2 -19 5 42 Inhibition of CaCO 3 crystallization at 90 'C (conditions 5) Due to the decreasing in % IE and induction time of PAA with molecular mass more than 2000 g/mol under condition 4, the lowest molecular mass of PAA with different end groups was chosen to determine its % IE under conditions 5. Moreover, the concentration 5 of PAA was increased to 3.75 ppm under conditions 5 to make the trends in % IE and induction time of PAA with different end groups more evident. For conditions 5, CBlank = 583 pS/cm and Co = 815 pS/cm. The results of conductivity measurements are represented in Figure 14 and Table 8. 1o Table 8: Induction times and % inhibition efficiency (% IE) of PAA for CaCO 3 formation under conditions 5 End Groups A % Inhibition Induction time terminated-PAA Efficiency (s) Cond. +20 CMM 2106 58.7± 1.4 109 -5 +37 EIB 1669 69.5 ±1.4 112 -31 +45 CIB 1689 72.6± 1.5 128 -20 Hydrophobic HIB 1403 71.7± 1.9 150 +47 End Groups -14 +38 DIB 2422 8.3 ±3.2 120 -32 +40 HDIB 1687 24.0 ±0.5 130 -28 Inhibition of CaCO3 crystallization at 100 *C (conditions 6 and 7) s At 100 *C the conductivity of Ca 2 + and C0 3 2 increases making the total conductivity over scale and needing the system of CaCO 3 crystallization recording changed by increasing the cell constant and the use of glass condenser at that temperature. The experiments were as follows.

43 Filtered (0.45 jm cellulose acetate membrane) deionized water (148 mL) was placed in 250 mL three necked round-bottom flask containing two platinum conductivity probes (0.5 x 0.5 cm), magnetic stirrer under a water-cooled glass condenser. Three drops of 0.05 M NaOH, Ca 2 + as CaCl 2 solution to give a final concentration of 36 and 66 ppm and scale s inhibitor solution to give 1.5 and 6.7 ppm were added to the three necked round bottom flask under stirring. Recording of conductivity started when the solution began to boil and 20 s later C0 3 2- as Na 2

CO

3 solution to give a final concentration of 30 and 100 ppm was added to that cell. Analogue outputs from conductivity prop was digitally converted using a Picolog A/D Converter 16 (16 Bit) and Picolog recording software and data was 1o acquired every 5 seconds as shown in Figure 3.37. Since the precipitation of CaCO 3 at 100 *C is very rapid (the scale is immediately formed) and the carbonate to carbon dioxide equilibrium value is very low (1.08 x 106). The experimental setup is shown in Figure 15. For conditions 6, CBIank = 746 pS/cm and CO = 848 pS/cm. The inhibition efficiency and 15 conductivity measurements of PAA were determined under conditions 6 only for the lowest molecular mass for each end group. The results are shown in Figure 16 and Table 9. Table 9: Induction times and % inhibition efficiency (% IE) of PAA for CaCO 3 formation 20 under conditions 6 End Groups terminated-PAA A % Inhibition Efficiency Blank - 0 CMM 2106 67.8 ±5.1 EIB 1669 84.3 ±6.5 CIB 1689 84.3 ±3.7 Hydrophobic HIB 1403 100 ±0.0 End Groups DIB 2422 21.6 ±15.0 HDIB 1687 12.7± 1.4 44 For conditions 7, CBlak = 896 pS/cm and Co = 984 pS/cm. The inhibition efficiency and conductivity measurements of PAA were determined under conditions 7 only for the lowest molecular weight for each end group. Moreover, increasing of concentration of s PAA to 6.7 ppm was done to make the trends in inhibition efficiency and induction time of PAA with different end groups more evident. The results are shown in Figure17 and Table 10. Table 10: Induction times and % inhibition efficiency (% IE) of PAA for CaCO 3 1o formation under conditions 7 End Groups terminated- % Inhibition PAA Efficiency Blank 0 CMM 2106 65.9 ±3.6 EIB 1669 75.3 ±2.8 CIB 1689 93.2 2.0 Hydrophobic HIB 1403 100 0.0 End Groups DIB 2422 18.2+ 17.0 HDIB 1687 45.5 5.7 The target molecular mass of scale inhibitors for good control of scale deposition was observed between 1000-3000 g/mol.In the results presented for CaCO 3 scaling, PAA in that molecular mass range were generally most effective in inhibition of CaCO 3 15 crystallization. In addition to the effect of molecular mass of scale inhibitor, the results for all conditions showed that the nature of the end groups terminating PAA played a very important role. Low molecular mass of PAA (- 2000 g/mol) with hydrophilic (CMM-4C) and short (EIB-6C) and mid-length hydrophobic (CIB and HIB- 10C) end groups had better inhibition efficiency than long hydrophobic (DIB-14C and HDIB-20C) end groups. 20 On the other hand, although the hydrophilic end group of PAA has very good inhibition 45 efficiency, it has a poor induction time in comparison with hydrophobic end groups. At 90 *C the inhibition efficiency for hydrophilic end group was very good (60%) and for long hydrophobic end groups (which are the lowest inhibition efficiency for hydrophobic end groups) were 7% and 23%. However the induction times for hydrophilic short and 5 mid-length hydrophobic and long hydrophobic end groups were 109s, and 120s and 130s respectively. Therefore, it appears that induction time is strongly affected by the hydrophobicity of end groups where the hydrophobic end groups have higher induction time than hydrophilic end groups. It is hypothesised that this is because the hydrophobic end groups discourage the PAA chains from desorbing from the nuclei of CaCO 3 as fast 1o as PAA with hydrophilic end groups, delaying the growth of the CaCO 3 nuclei. At high temperature, the kinetic energy and mobility of Ca 2 and C0 3 2 ions are expected to be greater than at room temperature and as a consequence the probability of collision together to precipitate as CaCO 3 is expected to increase. As a result of this kinetic effect, the solubility product of CaCO 3 is expected to decrease to give a greater thermodynamic is driving force for crystallization. Therefore, more rapid and less reversible adsorption of PAA to delay the crystal growth of CaCO 3 will be more required than at low temperature. This appears to be achieved by the hydrophobic end groups. The inhibition efficiency of CaCO 3 precipitation is affected by the size of the end groups for PAA. PAAs with short end groups both hydrophilic (CMM- 4C) and hydrophobic 20 (EIB- 6C) and middle hydrophobic end groups (CIB and HIB- 10 C) of PAA have excellent inhibition efficiency (100%) at room temperature and are more efficient than PAA with long hydrophobic end groups (DIB-14C and HDIB- 20C) at all temperatures investigated. At high temperature, the inhibition efficiency of middle hydrophobic end groups (CIB and HIB-IOC) of PAA remains better than the other end groups. 25 The effect of temperature on the inhibition efficiency of PAA with different molecular mass end groups was investigated. The results at 25, 60 and 80 *C showed that the inhibition efficiency of PAAs decrease with the increasing temperature as shown in Figure 18. The reason for that is thought to be that the adsorption of PAAs on CaCO 3 nuclei is exothermic process which decreases with increasing temperature (Yunxia et. al. 30 2007). In addition the supersaturation level increases (556, 983 and 1284) with increasing temperature and supersaturation has a strong inverse relationship with an induction time. It is expected that even at higher temperatures than observed in this work which are of interest in MSF desalination (T > 100 *C) the induction time of PAA terminated with hydrophobic end groups will be clearly greater than for PAA terminated with hydrophilic 46 end groups. This phenomenon is as a result of the mobility of PAA terminated with hydrophobic end groups faster than PAA terminated with hydrophilic end group in solution which was supported by conductivity measurements for both at 100 *C, where polyacrylate (PA ) terminated with hydrophobic end groups have a higher conductivity s than polyacrylate (PA) terminated with hydrophilic end group. Example 3: Scanning Electron Microscope, X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) These results are shown in Figs. 19 to 30: Figs. 19, 23 and 28 to 30 are SEM images, Figs. 20 and 27 are FTIR spectra and Figs. 21, 22 and 24 to 26 are XRD spectra. 10 The crystals of CaCO 3 in absence and presence of PAA (M, 5 2000 g/mol) under conditions 7 were collected after 1000 s and filtered through 0.45 pim pore size cellulose acetate filter paper and then characterized by SEM, ATR-FTIR and XRD. Scale samples were gold-coated and SEM images obtained using a FEI Quanta 200 Environmental SEM at an accelerating voltage of 15 kV. XRD was carried out using a Rigaku diffraction 15 camera with an X-ray generator with Cu Ka radiation of wavelength 1.5418 A at the X Ray Analysis Facility, Queensland University of Technology (Doherty, 2006). FTIR was carried out using Varian 660-IR (FT-IR Spectrometer). In the absence of PAA, the results of SEM, FTIR and XRD showed that, the CaCO 3 crystals occurred primarily as a mixture of calcite and aragonite as rod-like morphology 20 as shown in SEM image (Figure 19) with traces of rhombohedral calcite (Figure 29, A) and hexagonal florettes of vaterite (Figure 30, A). FTIR results showed two peaks at 711 cm- 1 indicating calcite polymorph and at 1082 cm- 1 indicating aragonite formation as shown in Figure 20. XRD patterns showed small peaks with high background (Figure 21) which made the 25 estimation of those peaks position difficult. That problem was solved by subtracting a polynomial equation for the background from XRD intensities for the range of 20 of interest (25 to 50) as shown in Figure 22. After background correction, XRD results showed that CaCO 3 present was a mixture of calcite and aragonite as shown in Figure 22. This results indicated that the rod-like 30 morphology consisted originally of aragonite polymorph. In the presence of the lowest molecular mass of PAA with different end groups, two points can be observed by SEM micrographs (x500) of CaCO 3 crystals results. First is the significant reduction in the population of CaCO 3 crystals in order of HIB > CIB > CMM > HDIB > DIB which is compatible with the conductivity measurements under conditions 47 7 as shown in Figures 23 and 17 respectively. Second is the distortion in crystals of the different polymorphs calcite, aragonite and vaterite in that same order. This is presumably by adsorption of PAA with different end groups on the active face of nucleus of CaCO 3 as shown in Figures 28 to 30. s The results of SEM and XRD for PAA with hydrophilic end group (CMM-4C) showed CaCO 3 crystals to be mostly calcite of rhombohedral morphology as shown in Figures 23 (A) and Figure 24 respectively. The hydrophobicity and rates of adsorption/desorption of CMM group may make the PAA affect on the growth of crystal stage more than nucleation stage and that was clear in the conductivity measurements where the io hydrophilic end group have induction time shorter than all hydrophobic end groups. This phenomenon is more evident in the distortion of edge of rhombohedral calcite in the presence of CMM-PAA. In contrast of CMM-PAA, the results of SEM, FTIR and XRD of PAA with long hydrophobic end groups (DIB and HDIB) showed that the crystals of CaCO 3 were as a 15 mixture of calcite and aragonite as rod-like morphology, vaterite flower and a few single crystals of rhombohedral calcite as shown in Figures 23 and 28 to 30. The formation of vaterite flower polymorph may be due to the adsorption of PAA on active nucleus surface of CaCO 3 to stabilize it and prevent its transformation into aragonite or calcite. The distortion in different polymorphs rod-like, vaterite and rhombohedral calcite by DIB 20 PAA and HDIB-PAA was the lowest comparing with other hydrophobic end groups of PAA. Moreover, the rod-like morphology was shorter (- 28 and 29 pm in the presence of PAA with HDIB and DIB respectively) than the same morphologies in absence of PAA (- 63 pm) as shown in Figures 28 to 30. Due to the excellent control of CaCO 3 formation by HIB-PAA and CIB-PAA, no other 25 peaks were observed on FTIR or XRD. However, there were traces of single crystals in different habits with rod-like (14 pm), rhombohedral and vaterite detected by SEM. Those images illustrated the highest distortion in different forms which may be due to the mid-length hydrophobic end groups discourage PAA chains from desorbing from the nuclei of CaCO 3 as fast as PAA with hydrophilic end groups, delaying the growth of the 30 CaCO 3 nucleus. In summary, the inhibition efficiency of PAA with different end groups and molecular masses as scale inhibitors to prevent CaCO 3 formation in bulk solution was studied over temperatures range between 25 and 100 *C by using conductivity and turbidity measurements. The results showed both molecular mass and the nature of the 48 end group of PAA affect the inhibition of CaCO 3 scale. Low molecular mass PAA with short and middle end groups have relatively high inhibition efficiency and long induction times under all conditions investigated. At room temperature, the lowest molecular mass of PAA with hydrophilic end group showed good efficiency in the inhibition of CaCO 3 5 scale making it suitable for use as a scale inhibitor in RO desalination. However, with increasing temperature, the lowest molecular mass of PAA with different middle hydrophobic end groups gave a better inhibition efficiency and induction time than PAA with hydrophilic end groups. These results suggest that the lowest molecular mass of PAA with middle hydrophobic end groups is more suitable as scale inhibitors in MSF io desalination. The nature and length of end groups of PAA have a big effect on the morphologies of CaCO 3 . Where, the highest distortion in the CaCO 3 polymorphs was for PAA with mid hydrophobic end groups. However, the lowest distortion in different CaCO 3 polymorphs was for PAA with long-hydrophobic end groups. These results were due to its rate of is adsorption/desorption on the active faces of CaCO 3 polymorphs. The conductivity and morphology results are compatible, where the %IE of CaCO 3 formation and the distortion of its morphologies have same order of HIB > CIB > CMM > HDIB > DIB. The high distortion in the edges of different CaCO 3 polymorphs (e.g. vaterite flower, rod like and rhombohedral calcite) in the presence of low molecular mass PAA (M, 5 2000 20 g/mol) with different end groups was proposed by the inventor for the first time and was named "Edge Active Scale Inhibitor Polymers". This property makes PAAs not only surface-active, but also edge-active. The effect on the edge rather than on a face is thought to alter crystal morphology and retard growth at lower concentrations of scale inhibitor, leading to a reduction in the cost of desalination process and making it more 25 environmental friendly. Example 4: Inhibition of Homogeneous Formation of Magnesium Hydroxide This aim of this experiment was to determine the efficiency of low molecular mass (M,< 2000 g/mol) PAA with different end-groups as scale inhibitors to retard the homogeneous crystallization of Mg(OH) 2 in calcium-free solutions containing non-equivalent 30 concentrations of Mg2+ and OH ions ([Mg 2 +] / [OH ]> 12) at high temperature (T = 100 'C) using conductivity measurements.

49 Experimental determination of conductivity at 100 *C A stock solution of 0.823 M (20000 ppm) of Mg2+ as MgCl 2 .6H 2 0 was prepared as well as 0.20 M of OH as NaOH solution which was prepared daily. These solutions and the RO water used were filtered and degassed using a 0.45 pm Millipore solvent filter. 5 Filtered deionized water (346.4 mL) was placed in a 500 mL three-neck vertical round bottom flask containing two platinum conductivity probes (0.3 x 0.3 cm) under a water cooled glass condenser. 1.4 mL of Mg 2 + solution as MgCl 2 .6H 2 0 was added to round bottom flask to give a final concentration of 3.292 x 10- (80 ppm) under stirring. When the solution began boiling, recording of conductivity was begun (the first sampling was 10 for the conductivity of Mg 2 + solution) and 1.75 mL of PAA solution and 0.45 mL of OH as NaOH solution were added (15 s from the second sampling) to give a final [PAA] = 5 ppm and [OH ] = 2.571 x 10 4 M respectively. Conductivity was measured by conductivity meter (CHK Engineering). Analogue outputs from conductivity prop and spectrophotometer were digitally converted is using a Picolog A/D Converter 16 (16 Bit) and Picolog recording software and data was acquired every 300 s as shown in Figure 31. The curves of conductivity with time of solutions containing of [Mg 2 +] = 3.292 x 10- M (80 ppm) and [OH] = 2. 571 x 1 0 4 M in the absence and presence of [PAA] = 5 ppm, and T = 100 *C were collected to determine the inhibition efficiency of low molecular 20 mass PAA with different end groups. At those experimental conditions, the

SL=

supersaturation level (SL) of was calculated as Mg(OH) 2 = 44.9 ( Ksp) . The inhibition efficiency (% IE) of PAAs were determined by applying the following equation: IE = 1 - "aA' ]X 100 % bl ank) 25 Where, a(pAA) and a(blank) are the a values in logarithmic equation (Y = a x ln(x) + b) for conductivity curve after normalization in the presence and absence (blank) of PAA respectively and x = t (time) as shown in Figure 32. Note that all conductivity curves in this Chapter are presented after the normalization of conductivity to initial value of one by applying the following equation: N. Conductivi ty = 30 K( 0 ) Where, K(o) and K(t) are the conductivity value at initial time (t = 0) and at any time over the experiment (t = t) respectively.

50 The results of conductivity measurements and (% IE) of homogeneous formation of Mg(OH) 2 in the absence of PAA and s in the presence of PAA will be discussed in turn. In the absence of PAA (blank) The conductivity curve of homogeneous formation of Mg(OH) 2 in the absence of PAA s showed increased conductivity for the second sampling compared to the first due to the adding of OH solution. As the experiment continued, the conductivity decreased, which indicates more formation of Mg(OH) 2 in bulk solution as shown in Figure 32. The conductivity measurements of Mg(OH) 2 formation in absence of PAAs were analysed over the period 5 - 50 min. The decline of conductivity could be fit to a 1o logarithmic curve (y= ax ln (t) +b) with a good correlation coefficient (R 2 = 0.98). However, the system did not reach the steady state even when the experiment continued more than 3 hours as shown in Figure 32, indicating Mg(OH) 2 formation is slow. In the presence of PAA All conductivity measurements in the presence of low molecular mass of PAA with 15 different end groups showed a significant decrease in the conductivity. The decreasing conductivity may be due to either or both of two reactions. First is the neutralization reaction between carboxylic acid groups in PAA with OH~ ions. Second is the complexation reaction between Mg 2 + and carboxylate groups in PA~. As the experiment continued, the conductivity decreased and the logarithmic curve indicated more formation 20 of Mg(OH) 2 in bulk solution for all PAA with different end groups as shown in Figure 33. The theoretical residual concentrations of [OH~] and [Mg 2 +] ions in the presence of 5 ppm of PAA were calculated based on the number of carboxylic acid units and their concentrations in monomol/L as shown in Table 11. The values of residual concentration of [OH-] and [Mg 2 +], A K Exp (K is the conductivity in pS/cm) for the first 5 minutes, and 25 Qip/Ksp were summarized in Table 12.

51 Table 11: The calculation of carboxylic acid units and their concentration in monomol/L unit in the presence of 5 ppm of PAA with different end groups. End Groups [PAA] [PAA] x 10~' Monomol/L Mn Units (n) (p)()x10 of PAA (ppm) (M) X 10 CMM 2106 29 5 2.374 2.410 EIB 1669 22 5 2.996 2.307 CIB 1689 21 5 2.960 2.176 HIB 1403 17 5 3.564 2.120 DIB 2422 30 5 2.064 2.168 HDIB 1687 19 5 2.964 1.971 Under the experimental conditions, the general %IE (for both complexation and 5 inhibition) of low molecular mass PAA (Mos 2000 g/mol) with different end groups to retard Mg(OH) 2 formation was calculated. The results showed the DIB-PAA has the best % IE (74 %) which was clear from the conductivity curve with time (Figure 6.5). In the presence of 5 ppm of DIB-PAA conductivity change was slowest (conductivity (pS) = 0.00287x in t ± 0.00032) compared with the other end groups of PAA. Short and middle 1o hydrophobic end groups (EIB-PAA and HIB-PAA) had approximately the same % IE (60 %). However, the lowest % IE was for CMM-PAA and CIB-PAA which were 31 % and 33 % respectively, as shown in Table 13 and Figure 34. In the results presented above, PAA with different end groups of molecular mass M, ~ 2000 g/mol generally have a good control of scale deposition of Mg(OH) 2 . In addition to is the effect of molecular mass of scale inhibitor, the results showed the hydrophobicity of the end groups terminating PAA have an important effect. All PAA with hydrophobic end groups have better inhibition efficiency than the hydrophilic end group (CMM) as shown in Figure 6.6. This may be due to the hydrophobic end groups discouraging the PAA chains from desorbing from the nuclei of Mg(OH) 2 as fast as PAA with hydrophilic end 20 groups, delaying the growth of the Mg(OH) 2 nuclei. The hydrophobic end groups terminating PAA may affect both nucleation and crystal growth, however the hydrophilic end group terminating PAA make the PAA affect on growth greater than the effect on nucleation.

52 Table 12: The residual concentration of [OH~] and [Mg2+], A KExp. and SL in the presence of 5 ppm of PAA with different end groups. End Groups M AExp. [M 2 +] [OH] SL of PAA (g/mol) N (Ko, - K 3 oo) x 10- x 104 Blank - - 3.929 2.571 45 CMM 2106 0.0139±0.0013 3.154 1.882 23 EIB 1669 0.0097 ± 0.0033 3.160 1.912 24 CIB 1689 0.0161 0.0037 3.168 1.949 25 HIB 1403 0.0104 0.0020 3.171 1.965 25 DIB 2422 0.0079 ± 0.0020 3.168 1.952 25 HDIB 1687 0.0087 ± 0.0027 3.179 2.008 26 5 Table 13: The effect of PAA with different end groups in Mg(OH) 2 formation. [Mg 2 +] 80 ppm, pH =10.28 &T= 100 *C Y=a x ln(t)+b End Groups M (g/mol) a R2 % IE of PAA Blank - -0.01102 ±0.00100 0.978 0 CMM 2106 -0.00755 ± 0.00300 0.998 31 ±12 EIB 1669 -0.00464 ± 0.00067 0.994 58 ±8 CIB 1689 -0.00733 ± 0.00296 0.983 33 ±14 HIB 1403 -0.00462 ±0.00109 0.982 58 ±14 DIB 2422 -0.00287 ± 0.00032 0.977 74 +8 HDIB 1687 -0.00573 ± 0.00274 0.985 48 +23 53 The estimation of order and crystal growth rate (CGR) for Mg(OH), formation The supersaturation level is a very important factor affecting the rates of nucleation and crystal growth. The equation below was used to estimate the order and rate of crystal growth for Mg(OH) 2 formation by analysing the conductivity data obtained in this study. 1 A -d{M92.1 SJjg21x[H] dtf ker{{g2+] x[OH -30..~ (- 3 dt kcS 2 >J2) In this model k, is the rate coefficient for crystal growth, S is a function of the number of effective sites added as seed crystals and n is the order of crystal growth with respect to supersaturation of Mg(OH) 2 . i The estimation of n was done by plotting log dt versus log{([Mg 2 +] x [OH - (Ksp)" 3 } where the slope = n, as shown in Figure 35. The rate of crystal growth for M 2 *]j - [Mg 2 . Mg(OH) 2 was determined from the plot of log ([MG2, - [Mg 2 . versus time (t) where, [Mg 2+],, [Mg 2+], and [Mg 2+] are the initial concentration, the concentration at t and the concentration at equilibrium of Mg2+ respectively. The concentration [Mg2+]i was is equal to the residual of Mg2+ ions in solution after that all OH ions reacted with Mg2+ to form Mg(OH) 2 at equilibrium stage (the equilibrium constant value of Mg(OH) 2 formation at 100 *C , Keq = 2.06x 10"). The concentration of Mg2+ at time (t) was calculated from conductivity data over the course of the experiment using ionic conductance values of Mg 2 +, OH , Cl and Na* at 100 *C which were estimated from their 20 ionic conductance values at 25 *C the equation below. .r =Ai2m [+ a(T - 25'C)] Where a is a temperature coefficient and its value for all ions ~ 0.02 *C~1 except H 3 0 (; 0.0 139 *C- ) and OH~(~ 0.018 oC~'). The results of the estimations of the order of crystal growth (n) and the crystal growth rate 25 for homogeneous formation of Mg(OH) 2 in solution containing non-equivalent concentrations of Mg2+ and OH ions in the absence and present of PAAs are summarized in Table 14. Those results showed the order (n) of Mg(OH) 2 formation with respect to supersaturation in the absence and presence of PAAs was 0.72 and 0.66 respectively. The small difference between the values may be due to the reduction in concentration of Mg2+ 30 and OH ions in the presence of PAA as a result of neutralization and complexation reactions. The rate of crystal growth for homogeneous formation of Mg(OH) 2 54 significantly decreased with different values in the presence of PAAs as shown in Figure 36. The decrease may be due to two effects. The first effect is the increase in the ratio of [Mg2+]/[OH ] in the presence of PAAs for those experiments carried out in the presence of more excess magnesium ions in solution when compared in the absence of PAA 5 (blank). The second effect is the adsorption of PAA on active nucleus surfaces of Mg(OH) 2 . This effect appeared clearly for different values of the rates of crystal growth in the presence of PAA with different end groups, where if the first effect was the only reason for the decrease in rate of crystal growth, the rate of crystal growth value would be approximately the same in all cases. The different values of the rate of crystal growth in 1o the presence of PAA with different end groups indicated that the complexation of carboxylate groups with Mg2+ in PA was not for all of them (fully) as was supposed initially. Table 14: The order (n), rate of crystal growth KcS and ratio of [Mg2+]/ [OH-] for 15 _Mg(OH) 2 crystallization End Groups of K (min-') % of retardation [Mg 2 +]/[OH~] PAA Rate of crystal growth Blank 0.72 1.491 x 10-' 0 12.8 CMM 0.65 1.015 x 10~ 32 16.8 EIB 0.65 0.613 x 10~ 59 16.5 CIB 0.65 1.012 x 10- 32 16.3 HIB 0.66 0.601 x 10~' 60 16.1 DIB 0.66 0.378 x 10~ 3 75 16.2 HDIB 0.66 0.773 x 10-3 48 15.8 The ratio of complexation (% RC) that taken place between carboxylate groups in PA with Mg2+ can be determined by applying the following equation: %RC= "" X 100 20 (AKtheor 55 Where (AKEtheor)ave. is the average theoretical reduction in conductivity when the complexation is 100% which was equal to 0.0380 and (AKExp.)ave is the average experimental reduction in conductivity for the first sampling after OH ions was added to Mg2+ solution regardless of the conductivity of OH_ ions which was equal to 0.0116. The s results suggest that more than 69 % of carboxylate groups in PA were not complexed by g2+ In summary, the inhibition efficiency of low molecular mass (Mus 2000 g/mol) PAA with different end-groups to prevent Mg(OH) 2 formation in solution containing non equivalent concentrations of Mg2+ and OH~ ions at 100 *C was studied by using 1o conductivity measurements. The results showed the hydrophobicity of the end group of low molecular mass PAA affects in the inhibition of Mg(OH) 2 deposit. Low molecular mass of PAA with long hydrophobic (DIB) end group showed the highest % IE, however the low molecular mass of PAA with hydrophilic end group (CMM) showed the lowest % IE. The conductivity data in the presence of PAAs with different end groups illustrated 15 that two consecutive reactions take place. The first reaction was the neutralization of carboxylic acid groups in PAA by OH ions. The second reaction was the complexation of carboxylate groups in PA with Mg 2 +. The order and rate of crystal growth with respect to supersaturation of Mg(OH) 2 crystallization were estimated. The results showed a significant decrease in the rate of 20 crystal growth of Mg(OH) 2 in the presence of PAA with different end groups. The decrease in crystal growth may be due to two effects. First is the increase in ratio of [Mg 2 +]/[OH ] in the presence of PAAs, whereas the rate of crystal growth decreased in the presence of excess magnesium ions. Second is the adsorption of PAA on active nucleus surface of Mg(OH) 2 which appear clearly in the different values of the rates of 25 crystal growth in the presence of PAA with different end groups. Example 5: Apparent Inhibition of Thermal Decomposition of Bicarbonate A known volume of filtered (0.45.m cellulose acetate membrane) deionized water was placed in a three neck round bottom flask containing a conductivity probe (Eco Scan con 30 6, Eutech Instruments), thermometer, magnetic stirrer under a water-cooled glass condenser. Measurements were first carried out in the absence of PAA then in the presence of PAA at concentrations of 10, 15 and 30 ppm. When the deionized water began to boil, enough HCO 3 as NaHCO 3 solution was added to ensure a concentration of 40 ppm. Conductivity data was collected from 30 s after addition of the NaHCO 3 solution 56 until the conclusion of the experiment. Figure 37 represents the system of electrical conductivity measurements for thermal decomposition of HCO 3 at high temperatures. The purpose for studying the thermal decomposition of HCO 3 in a simple system was to study and understand the mechanism of that process experimentally in the absence of the 5 additive, and then to understand the nature of the reaction between carbonic species

(HCO

3 and C0 3 2 -) and the fully characterized PAA scale inhibitors. The estimation of ions conductivity at high temperature was done using T = i.2s~c [t1 + a(T - 25*C)] Where a is a temperature coefficient and its value for all ions ~ 0.02 *C 4 except H 3 0* (~ 10 0.0139 C-') and OH-(~ 0.018 oCi) and X, is the equivalent conductivity of ion i. The derivation of electrical conductivity equation for thermal decomposition of HCO 3 at high temperature was for the cases in the absence and presence of PAA as follows. In the absence of PAA The conductivity of solution (K) in the unit of S/cm can be expressed as K Z ci z 1 15 1000 Where, X, is the equivalent conductivity of ion i in (S.cm 2 /eq), C, the molarity of ion i and Zi its charge. The total conductivity (K 7 ) at initial time (t = 0) for the thermal decomposition of HCO 3 as NaHCO 3 at high temperature (T = 97.2 *C) is given by 20 (Kr) 0 = [(K 1 fzO)+ (4pm. x [Aa*],) + (A4co x [HCO]) Where, KH20 is the conductivity of deionized water. The total conductivity (Kr) at any time over the experiment (t = t) for the systems of 2HC0 3 - C0 3 2- . 20H and the system of HCO 3 - OH at high temperature (97.2 *C) is given by 25 (KT)r = (KHo) + ( v.. x [Na+]) + (Acoi x [HCOJ, ) + (2 x Aco- x [CO2J ) -+ (lou- x [OH ~] In equations 4.33 and 4.34, the conductivity of deionized water and Na* (KH 2 0 and KNa+) are constant (C). Therefore, the equations should be written as (KT)O = c + (-e O- x [HC 0 j) 30 (Kr)t = C + x [HC o0l, )+ (2 xAcog- x [COj-], )+ (Ao,- x [OH-]) At the end of experiment (t = oc) equation (KrL = C + (AOH- x [OH -],,3 Therefore, AK = (Kr). - (KT)o = (o- x [OH-]. ) - x[f C031 0

)

57 As [HC0 ]i 0 = [OH-], AK = (Kr). - (KT)o = [HCOj , x Ia-)-- (AHco- A If the thermal decomposition of HC0 3 follow first-order kinetics, then In[(Kr). - (Kr)t] = -kt + a s In the plot of ln[(KT). - (KT)t]vs. time (t), the slope = -k (rate coefficient) In the absence of PAA, the above equation was applied to analyze the conductivity data and calculate rate coefficient by the plot of ln[(KT). - (KT)t] vs. time Q), where the slope = -k (rate coefficient) In the presence of PAA 1o In the presence of PAAs, (KT)o, (KT)t and (KT). can be written as (KT)o = (KHo)+ ( KN. ) + (KPA)+ (AHco3 X [HCOfl Over the experiment, the carboxylic acid groups in PAA were neutralized by OH that was generated as the final product of thermal decomposition of HCO 3 . Therefore, (KT)t can be written as: (KT)r = (KHZO)+ ( KNa+ ) + (KPAA) + (HCO x [HCo] ) + 2 X [C)(OH- x [0~) 15 33 3 +(LH O At the steady state, (KT)- can be written as: (KT). = (Km 2 o)+ ( Kva+ )+ (AOH- x [OH 1, )+ (A x [PA"-j)

KH

2 0 and KNa+ are constant (C) and KpA is very small and can be ignored. Therefore, AK can be written as: AK = (K7). - (KT)a = (H- x [OH-]. ) + (P= x [PAn-].)] - CO x [HCO3a )T he concentration of carboxylic acid groups at different concentration of PAA (10, 15 and 30 ppm) were calculated in the monomolar units. Therefore, the equivalent of OH which need to neutralize all of them will be known over the experiment and after that time the conductivity of PA will not change until reaching the steady state. AK is therefore given 25 by: AK = (KT)m - (KT)O = (AOH- x [OH 1W) - (AHcoS x [HCQ ) + KpA'.t If the decomposition of HC03- follow first-order kinetics, then ln[(Kr). - (Kr)o] = -kt + a The plot of ln[(K). - (KT)t] vs. time (t), the slope = -k (rate coefficient) 30 The conductivity of PA"~ ais therefore given as: KPA- = AKExp - AKBIank + KOH-(ConSUrning) This was used to calculate the conductivity (K) of PA".

58 Results and Discussion To determine the rate coefficient for thermal decomposition of HCO 3 and the inhibition of that decomposition by PAA with different end groups and molar mass, the conductivity measurements were collected under the following conditions: T= 97.2 ± 0.5 *C, [HCO 3 ] 5 = 6.557x104 M (40 ppm), and scale inhibitor concentration [PAA] =10, 15, 30 ppm with different end groups and molecular mass. Based on the experimental conductivity data, the results can be distinguished in two sections: 1) The kinetic model of thermal decomposition of HCO3~ in absence of PA A 10 Theoretically, when 40 ppm of HCO 3 converts solely to OH , the pH of the final solution should be 10.81. Under the experiment conditions employed, the final experimental pH value was found to be 10.73. Moreover, the theoretical change in conductivity (AK) for the overall system (HCO 3 - OH) of 6.557 x 104 (40 ppm) HCO 3 ~ as NaHCO 3 was calculated to AK = 228 RS/cm using Eq- 4.39. Experimentally, the value (AK = 224 ± 7 15 gS/cm) was obtained. This is an excellent agreement between theory and experiment. In absence of PAA, the mathematics described above was applied to analyze the conductivity data and determine rate coefficient by plot of ln[(KT). - (KT)t] vs. time (t), where the rate coefficient (k) = - slope. The plot (Figure 38) shows a very good linear (R 2 > 0.996, n= 52) relationship for overall reaction clearly indicating the thermal 20 decomposition of HCO 3 follows first order kinetics with k = 3.35 x 10-2 min~'. The concentration of C0 3 2 - in the system associated with the presence of HCO 3 and OH can be calculated by Co2-] = [HCO-] x [Off-] x 164 Where [co2j Kq = = 164 25 [HCO1 x [0H-1 Thermodynamic treatment for thermal decomposition of HCO 3 It is not apparent whether the thermal decomposition of HCO 3 is a unimolecular reaction or a bimolecular reaction following first-order kinetics. The two possibilities may be differentiated by considering the thermodynamics of the system. 30 AG vs. time as a first step in both bimolecular mechanism and unimolecular mechanism under experimental conditions was calculated and the results are shown in Figure 39. AG for the unimolecular mechanism is more negative and probable than AG for the bimolecular mechanism at all times.

59 In the case where the thermal decomposition of HCO 3 follows the unimolecular mechanism, the equation for first order kinetics can be applied to follow the concentration of HCO 3 during experiment (Figure 40) which is given as i 1 . *HC03] 0 = kt [H C03]t 5 Where [HCO 3 ]o and [HCO 3 ] are the initial concentration and the residual amount at time (t) of HCO 3 respectively. 2) Thermal decomposition of HCO 3 in the presence of PAA To study the effect of PAA on the thermal decomposition of HCO 3 , conductivity measurements (AK) and the pH of the 40 ppm HCO 3 solution under the same 1o experimental conditions were collected. Two points were observed in the comparison between AK and pH in the absence and presence of PAA. First, AK (IS/cm) values in the presence of PAA are higher than AK for blank solution and those values of AK decrease with increasing the concentration of PAA. Second, pH values in the presence of PAA are lower than pH value of blank solution and the pH values decrease with increasing PAA is concentration. These observations can be explained on the fact that, PAA is a weak acidic polyelectrolyte with many ionizable carboxylic acid groups and in aqueous solution at pH > 8.1, PAA is close to fully ionized and should be more conductive than the neutral polymer. The experimental results of electrical conductivity AK (pS/cm) and pH of final solution in presence of PAA with different end groups and molecular mass are 20 summarized in Table 15.

60 Table 15: The experimental results of AK (pS/cm) and pH of final solution in presence of PAA with different end groups and molecular mass End Groups of I 5 PAA Groupsof M. [PAAJ pH AK (pS/cm) s PAA Blank 10.73 223.66 ± 6.75 2106 10 10.61 239.78 ±8.30 2106 15 10.53 240.76 ±8.88 CMM 10 2106 30 10.40 202.72±3.02 7633 10 10.62 260.61 ± 2.15 1669 10 10.58 270.61 ±7.29 EIB 7180 10 10.59 270.94 11.18 1689 10 10.60 274.90 1.17 I5 6210 10 10.59 271.44 5.15 CIB 9954 10 10.56 266.16 2.84 9954 15 10.49 260.30 5.53 13209 10 10.65 254.10 5.40 20 1403 10 10.55 266.97 6.40 1403 15 10.52 262.15+6.59 1403 30 10.35 195.85 0.29 HIB 3563 10 10.58 267.12 8.41 25 8928 10 10.59 257.89 ±2.49 13049 10 10.65 259.53 ±0.70 2422 10 10.55 279.14± 3.14 DIB 6203 10 10.52 271.02 ±2.37 1687 10 10.65 273.13 ±5.19 30 1687 15 10.52 254.41 ±0.46 HDIB 4135 10 10.42 272.22 11.62 9391 10 10.54 278.05 2.75 1 _ _ _ 1 17167 10 10.65 273.20 10.32 61 The conductivity ofpolyacrylate (PA( n-)) at high temperature No data appear to have been reported regarding the conductivity of polyacrylate (PA"~) at high temperature. That makes the estimation of the conductivity for (PAn) at high 5 temperature due to the neutralization of carboxylic acid groups in PAA by OH which is the final product on the thermal decomposition of HCO 3 one of the important features of this study. The estimation of conductivity of (PA "~) at 97.2 *C was carried out by two pathways. Firstly, theoretical estimation of the conductivity of (PA n) by applying mathematics described above. The results of theoretical conductivity values are to summarized in Table 16.

62 Table 16: The theoretical conductivity values of PA "-) with different end groups and molecular mass at high temperature in the units of (iS/cm) estimated using equation 4.46 End Cond. of OH Theoretical Group of M, [PAA] [PAA]consuming Cond. PA PAA (p_ ____x___ (PS/cm) (pS/cm) 10 4.75 2.07 63.05 74.83 2106 15 7.12 3.10 94.58 107.34 CMM 30 14.25 6.20 189.16 163.88 7633 10 1.31 2.06 63.59 96.20 1669 10 5.99 1.98 60.36 102.97 EIB 7180 10 1.39 2.17 66.33 109.27 1689 10 5.92 1.87 56.93 103.83 6210 10 1.61 2.03 61.94 105.38 CIB 10 1.00 2.05 62.56 100.72 9954 15 1.51 3.07 93.84 126.14 13209 10 0.76 2.06 62.75 88.85 10 7.13 1.82 55.48 94.45 1403 15 10.69 2.73 83.22 117.37 30 21.38 5.45 166.45 134.30 HIB 3563 10 2.81 1.98 60.40 99.52 8928 10 1.12 2.05 62.57 92.46 13049 10 0.77 2.06 62.81 94.34 2422 10 4.13 1.86 56.72 107.86 DIB 6203 10 1.61 2.01 61.27 104.29 10 5.93 1.69 51.57 96.70 1687 15 8.89 2.53 77.36 103.77 HDIB 4135 10 2.42 1.92 58.69 102.91 9391 10 1.06 2.02 61.44 111.49 1 17167 10 0.58 2.05 62.42 107.62 63 Secondly, experimental conductivity of (PA"~) was estimated as follows: The concentration of HCO 3 and OH was followed during the experiment. The total conductivities of those ions at 97.2 *C corresponding to their concentration during experiment were used to regenerate a semi-theoretical conductivity curve vs. time. Based 5 on the theoretical average number of carboxylic acid units and their concentration in monomol/L, the conductivity of PA" at 97.2'C was determined by comparing the experimental conductivity curve and semi-theoretical conductivity curve which gives the best matching between them. The electrical conductivities of PA"~ with different end groups and molecular mass at 97.2 *C in the units of (pS/cm) and (S.cm 2 /monomol) were 1o listed in Table 17. The second pathway was applied first in the absence of PAA to regenerate a semi- theoretical conductivity curve for the decomposition of 40 ppm of

HCO

3 (blank semi- theoretical conductivity curve) assuming the unimolecular mechanism and then compared with the experimental conductivity curve as shown in Figure 41. is Figures 42 and 43 represent examples for estimating the conductivity of PA " at 97.2 0 C for EIB-PAA and CIB-PAA respectively. The agreement between the theoretical and experimental values of the conductivity of PA "~ was very good with the correlation coefficient R 2 = 0.98 as shown in Figure 44.

64 Table 17: The experimental conductivity values of PA"~ with different end groups and molecular mass at high temperature in the units of (pS/cm) and (S.cm 2/ monomol). End Ave. Experimental (K) Cond. of PA" Group of Units [PAA] of PA" pS/cm) (S.cm 2 PAA (n) mean RSD monomol) 10 79.87 2.76 0.58 ± 0.02 2106 29 15 109.47 4.04 0.53 ±0.02 CMM 30 165.24 2.46 0.40 + 0.01 7633 106 10 98.6 0.81 0.71 ±0.01 1669 22 10 106.77 2.88 0.81 ±0.02 EIB 7180 104 10 112.98 4.66 0.78 ±0.03 1689 21 10 104.44 0.44 0.84 ±0.01 6210 84 10 108.21 2.05 0.80 ±0.02 CIB 10 102.47 1.10 0.75 ±0.01 9954 136 15 135.26 2.87 0.66 ±0.01 13209 181 10 93.18 1.98 0.68 ±0.01 10 100.57 2.41 0.84 ±0.02 1403 17 15 121.77 3.06 0.67 ±0.02 30 138.13 0.20 0.38 ±0.01 HIB 3563 47 10 104.21 3.28 0.79 ±0.02 8928 122 10 95.65 0.92 0.70 ± 0.01 13049 179 10 97.39 0.26 0.71 ±0.01 2422 30 10 111.48 1.25 0.90 ±0.01 DIB 6203 83 10 107.04 0.94 0.80± 0.01 10 100.24 1.88 0.88 0.02 1687 19 15 104.74 0.19 0.62 ±0.01 HDIB 4135 53 10 105.10 4.42 0.82 ±0.03 9391 126 10 111.36 1.10 0.83 ±0.01 1__ _ 117167 234 10 106.32 4.02 0.77 ±0.03 65 The electrical conductivity of PA("') with different end groups and molecular mass at high temperature show clearly that the PA("~) with hydrophobic end groups have electrical conductivity values in units of (pS/cm) and (S.cm 2 /monomol) greater than PA("~) with hydrophilic end group, as shown in Figure 45. s The equivalent conductivity of PA"- with different end groups and molecular mass was calculated using the equatin below and the results were summarized in Table 18. AK N Where, N is the normality of the carboxylate groups. The results of equivalent conductivities of PA" illustrate that the molecular mass and end io groups of PA" significantly affect on the equivalent conductivities. The equivalent conductivity increased with increasing hydrophobicity ratio of end group to molecular mass of PA"~ (Met/M) and decreased with increasing molecular mass of PA"~. Figure 46 represents the curve obtained by plotting equivalent conductance against the molecular mass of PA"~ . This curve clearly shows that with an increase in molecular mass of PA" 15 equivalent conductivity decreases sharply in the range of (1400 - 3500 g/mol) then the decrease was then gradual until Mn= 17000 g/mol. The equivalent conductivity for all of PAA with different end groups and molecular mass was plotted against the ratio of (Mne/Mn) as shown in Figure 47. Figure 47 clearly shows a good relationship (R 2 = 0.93) between the equivalent conductivity of PAAs and the ratio 20 of (Mne/Mn). The deviation from that linearity was for PAA with longest end group (HDIB) and different molecular mass, and may be due to the formation of micelles. The effect of the molecular mass of PA"~ on equivalent conductivity is more than that of the corresponding end groups (MIM,). This effect is clearly seen in the comparison of equivalent conductance for the lowest molecular mass of HIB-PA"~ (M,=1386 g/mol) and 25 HDIB-PA (M=1668 g/mol). Although the ratio of M/M. = 0.187 for HDIB- PA" (which the highest ratio) is higher than the ratio for HIB-PA" (Mew/Mn= 0.124) however, the later has the highest equivalent conductance 4.941 x10- 2 (S.cm 2 /eq). 30 66 Table 18: The equivalent conductivities of PA"~ with different end groups and molecular mass. End Group of M, of PA". Mn, of end Ratio A of PA"~ (S.cm2/eq) group Mnx1. PAA (g/mol) (g/mol) Mnen x 10-2 2077 0.041 2.000 CMM 86.1 7527 0.011 0.670 1647 0.070 3.682 EIB 115.15 7076 0.016 0.750 1668 0.101 4.000 6126 0.028 0.952 CIB 169.24 9818 0.017 0.551 13028 0.013 0.376 1386 0.124 4.941 3516 0.049 1.681 HIB 171.25 8806 0.019 0.574 12870 0.013 0.397 2392 0.095 3.000 DIB 227.36 6120 0.037 0.964 1668 0.187 4.684 4082 0.076 1.547 HDIB 311.51 9265 0.034 0.659 16933 0.018 0.329 The inhibition efficiency of PAA to retard the thermal decomposition of HCO 3 s To determine the inhibition efficiency of thermal decomposition (% ITD) of HCO 3 assuming the unimolecular mechanism by different molecular mass and end groups of PAA, the equation below was used.

67 % ITD of HCO3 = (1- ) x100 Where kb is the rate coefficient for thermal decomposition of 40 ppm of HCO3 in the absence of PAA and k is the rate coefficient for thermal decomposition of 40 ppm of HCO3- in the presence of 10, 15 and 30 ppm of PAA, for the following reaction s HC0 3 * OH + C0 2 The thermal decomposition of 40 ppm HCO3~ in the presence of 10 ppm of PAA with different end groups and molecular mass The results of % inhibition of thermal decomposition (% ITD) of 40 ppm HC0 3 by 10 ppm of PAA with different end groups and molecular mass show that both end groups io and molecular mass play very important roles. For all end groups of PAA, the rate coefficient of thermal decomposition of 40 ppm HC0 3 ~ increased with increasing molecular mass, except PAA with HDIB end group as shown in Table 19 and Figure 48. The net of reactions for the thermal decomposition of HCO3 in the presence of PAA is shown in Figure 49. 15 68 Table 19: Rate coefficient of thermal decomposition of HC0 3 and % ITD by different molecular mass and end groups of PPA End Groups of [PAA] k x 10- 2 I Ma % ITD PAA ppm (min-') Blank 3.35 ±0.10 0 10 2.27 ± 0.08 32 2106 15 1.92 ± 0.07 43 CMM 30 1.84 ±0.03 45 7633 10 2.29 ±0.02 32 1669 10 2.02 ±0.05 40 EIB 7180 10 2.10 ± 0.09 37 1689 10 2.01 ±0.01 40 6210 10 2.04±0.04 39 CIB 10 2.16 ±0.02 36 9954 15 1.91 ±0.04 43 13209 10 2.31 ±0.05 31 10 1.89± 0.05 44 1403 15 1.74 ±0.04 49 30 1.79 ±0.01 47 HIB 3563 10 2.01 ±0.06 40 8928 10 2.16 ±0.02 36 13049 10 2.30 ±0.01 31 2422 10 1.93 0.02 42 DIB 6203 10 1.99 0.02 41 10 2.52 0.05 25 1687 15 2.49 0.01 26 HDIB 4135 10 2.16 0.09 36 9391 10 2.28 0.02 32 17167 10 2.47 0.09 26 69 Generally, at 10 ppm of PAA with different end groups and molecular mass, % ITD decreased and rate coefficient of decomposition of 40 ppm HCO 3 increased in the succession HIB-PAA> DIB-PAA > CIB-PAA> EIB-PAA > HDIB-PAA > CMM-PAA. 5 For example, HIB-PAA (M,=13049 g/mol) has % ITD of HCO 3 31 % however, the lowest molecular mass of PAA with CMM and HDIB end groups has % ITD of HCO 3 32 % and 25 % respectively. HIB-PAA and DIB-PAA (HIB) in the molecular mass range (M, S 2000 g/mol) have the best of % ITD of HC0 3 44 % and 42 % respectively. However, PAA with the longest hydrophobic end group (HDIB) (M,= 1687 g/mol) has the 1o lowest % ITD of HCO3 25 % comparing with all % ITD for PAA with different end groups and molecular mass as a special case. That result may be due to the ratio between hydrophobic chain (end group) and hydrophilic chain (PAA), which is the highest ratio (1:4), compared with the other PAA with different end groups and molecular mass, showing that this polymer has an active surface property. This phenomenon is very clear is when the solutions that contain 10 and 15 ppm of this material when boiled, plenty of foam was formed; therefore the % ITD of HC0 3 was the lowest one. However, in the solution that contained 10 ppm of HDIB-PAA (M >_ 4000 g/mol) that phenomena disappeared and the % ITD increased. For example, % ITD for HDIB-PAA (M, = 4135 g/mol) and (M, = 9391 g/mol) were 36 % and 32 % respectively. 20 PAA with EIB and CIB hydrophobic end groups for the molecular mass range (2000 8000 g/mol) has very close average of % ITD of HCO3 39 % and 40 % respectively. On the other hand, the comparison of % ITD of HC0 3 between PAA with EIB hydrophobic end group and PAA with CMM hydrophilic end group the result show that, PAA with EIB end group has better average than PAA with CMM hydrophilic end group (39 % and 25 32 % respectively) as shown in Figures 50 and 51. Those results represent clearly the effect of the hydrophobicity of end group on % ITD of HCO3 . Generally, PAA with CMM hydrophilic end group has the lowest % ITD of HC0 3 ~ in the range 2000-8000 g/mol of molecular mass. The thermal decomposition of 40 ppm HCO~ in the presence of 15 and 30 ppm of PAA 30 with different end groups and molecular mass The effect of increasing concentration of PAA to 15 and 30 ppm on TD of HCO 3 was studied under the same experimental conditions for the lowest molecular mass of PAA with end groups CMM, HIB and HDIB, and CIB-PAA at molecular mass M, =9954 g/mol. Onincreasing the concentration of PAA from 10 ppm to 15 ppm, % ITD of HCO 3 70 increased significantly by 11 %, 5 % and 7 % for CMM-PAA, HIB-PAA and CIB-PAA respectively. However, the change in the % ITD of HCO3 for HDIB-PAA was 1 % only as shown in Figure 52. In contrast, the changing on the % ITD of HCO 3 for CMM-PAA was 2% and for HIB-PAA was insignificant on increasing its concentration from 15 to 30 s ppm. The effect of adding 50 ppm NaCi on the ITD of HCO 3 If the action of the polymer additive is primarily by its interaction with metal ions then addition of positive ions would be expected to accelerate decomposition of bicarbonate. Accordingly, a series of experiments were repeated with an additional 50 ppm NaCl. io The purpose for doing the thermal decomposition of HCO 3 in solution containing 50 ppm NaCl was to understand the effect of adding NaCl on the ITD of HCO 3 by the lowest molecular mass of PAA with hydrophobic end groups. The results showed HIB-PAA and DIB-PAA have the best % ITD of HCO 3 36% and 34% respectively, as shown in Table 20 and Figures 53 and 54. All rate coefficients for TD of 40 ppm HCO 3 increases with 15 the addition of 50 ppm NaCl. This may be attributed either to the metal ion complexation between the PAA and Na+ or 'salting in' effect where less PAA sits on the interface in solutions of higher ionic strength. Table 20: Rate coefficient of thermal decomposition of HCO 3 and % ITD by different 20 end groups End Without NaCl with 50 ppm of NaCl Groups of M, [PAA] k x 10-2 k x 102 PAA .i %ITD % ITD Blank Blank 3.35 0 3.73 0

(HCO

3 )___ __ EIB 1669 10 2.02 40 2.72 27 CIB 1689 10 2.01 40 2.65 29 HIB 1403 10 1.89 44 2.40 36 DIB 2422 10 1.93 42 2.46 34 71 The mechanism of thermal decomposition of HCO 3 by different end groups and molecular mass of PAA To suggest a possible mechanism of the inhibition thermal decomposition of HCO 3 by 5 PAA with different end groups and molecular mass, the following observations are important: * The lowest molecular mass of HDIB-PAA, which has an active surface property, has the lowest % ITD of HCO 3 . That behavior is very clear as when the solutions that contains 10 and 15 ppm of this material when boiling, plenty of foam was formed. 1o That foam immediately disappeared when HCO 3 solution was added; but remained on the addition of similar amounts of NaCl solution. * The difference in % ITD of HCO 3 between EIB-PAA, which has 6 carbon atoms in end group as hydrophobic end group, and CMM-PAA which has 4 carbon atoms in end group as hydrophilic end group was equal to 7 %. Is * % ITD is inversely-proportional with the molecular mass of PAA as shown in Figure 55. The effect of end groups may appear in two ways. First is in their effect on the transport of PAA (common with molecular mass) in solution which clearly appears in the equivalent conductivity as explained previously. Second is the possible micelle formation, particularly for PAA with the longest end group (HDIB). The lowest 20 molecular mass of HDIB-PAA (at 10 ppm) has the lowest % ITD of HC03 (25 %). Moreover, there was no significant change in % ITD with increasing its concentration to 15 ppm, which may be due to the micelle formation. * HIB and DIB have the best % ITD of HCO 3 . * All rate coefficients for TD of 40 ppm HCO 3 increases with the addition of 50 ppm 25 NaCl. Those observations and other results of ITD of HCO 3 by PAA with different end groups and molecular mass suggest the mechanism of the inhibition of thermal decomposition of

HCO

3 by PAA with different end groups may be by preventing heterogeneous decomposition of HCO 3 on interfaces. The interface surfaces such as the water/air 30 interface of bubbles that form in bulk solution are very important in the heterogeneous decomposition of HCO3 which may provide the activation energy to decompose HCO 3 ions lower than that in the bulk solution. Another important interface is the glass/water interface as shown in Figure 56. At the end of the experiments there was some PAA adsorbed on that surface which was removed by acid flashing.

72 The coverage of liquid/gas interfaces by PAAs may increase with decreasing molecular mass of PAA. Theoretically, the concentration of PAA at 10 ppm is approximately same for all PAAs with different end group and molecular mass. However, the number of chains of PAA increases with decreasing molecular mass, which allow the low molecular 5 mass of PAA to cover a larger fraction of liquid/gas interface than high molecular mass PAA. Another pathway to the effect of the molecular mass of PAA may be the transport of polymer through solution by diffusion, whereas the low molecular mass is faster than the high molecular mass which was proposed previously. Those effects may be making low molecular mass of PAA thermal decomposition more than high molecular mass PAA. 10 An example of the effect of both end groups and molecular mass of PAA to prevent the heterogenous decomposition of HCO 3 is PAA with mid-length hydrophobic end groups (CIB & HIB). CIB-PAA (Mn = 9954 g/mol) and HIB-PAA (Mn = 8928 g/mol) have the same % ITD (36%) and very close equivalent conductivities of 5.51 x 10~3 and 5.74 x 1 03 (S.cm 2 /eq) respectively. CIB-PAA (M = 13209 g/mol) and HIB-PAA (M = 13049 is g/mol) also have the same % ITD (31%) and very close equivalent conductivities of 3.76 x10- 3 and 3.97 x10-3 (S.cm2 /eq) respectively. (Table 21). Table 21: the comparison between % ITD and equivalent conductivity for CIB-PAA and HIB-PAA. End Groups Ratio A of PA"~ (S.cm 2 /eq) of PAA M./Mn x 102 9954 0.017 0.551 36 CIB 13209 0.013 0.376 31 8928 0.019 0.574 36 HIB 13049 0.013 0.397 31 20 Conclusion Conductivity measurements were employed to follow the kinetics of thermal decomposition of HCO 3 by estimate AK (pS/cm) under the conditions T= 97.2 ± 0.5 *C, 73

[HCO

3 ] = 6.557x 104 (40 ppm), and in the absence and presence of PAA with different end groups and molecular mass ([PAA] =10, 15, 30 ppm). The conductivity data showed that the thermal decomposition of HCO 3 follows first-order kinetics in the absence of PAA. However, it is not apparent whether the thermal decomposition of HCO 3 is a 5 unimolecular reaction or a bimolecular reaction. AG was calculated during experiment then plotted against time for both mechanisms. The results showed that the AG for unimolecular mechanism is more negative than AG for bimolecular mechanism and hence the reaction is more probable. In the presence of PAAs, conductivities (AK pS/cm) values of thermal decomposition of 10 HCO 3 were higher than AK for blank solution. The reason was the neutralization of carboxylic acid groups in PAA by OH . The estimation of conductivity of (PA "~) in units of p S/cm, S.cm 2 /monomol and S.cm 2 /eq (equivalent conductivity) at 97.2 *C was carried out by two pathways. First is the estimation of the conductivity of (PA "~) by applying equation 4.47. The second was by regenerating a semi- theoretical conductivity curve for is the decomposition of 40 ppm of HCO 3 as unimolecular mechanism and then comparing with the experimental conductivity curve. The results of equivalent conductivities of PA" showed that the molecular mass and end groups of PA"~ have a significant effect on the equivalent conductivities. The plots of equivalent conductivity versus the ratio of molecular mass of end group to molecular mass of PA"~ (Me,/Mn) for HDIB-PAA showed 20 a deviation from the linearity that was observed for PAA with other end groups. This may be attributed to the micelles formation. The inhibition of thermal decomposition of HC0 3 by 10 ppm of PAA with different end groups and molecular mass showed that both end groups and molecular mass play a significant role. For all end groups of PAA, the rate coefficient of thermal decomposition 25 of 40 ppm HC0 3 increased with increasing molecular mass, except HDIB-PAA. Conductivity data was analysed and rate coefficient of the thermal decomposition of

HCO

3 at 97.2 *C determined. The result showed that the thermal decomposition of

HCO

3 follows first order kinetics with k = 3.35 x 10-2 min-'. The mechanism of the inhibition of thermal decomposition of HCO 3 by PAA with 30 different end groups was suggested. That mechanism was based on the preventing of heterogeneous decomposition of HCO 3 on the interface surfaces such as the water/air interface of bubbles that form in bulk solution and the interface surface of round bottom flask. The surrounding of bubbles by PAA should increase with decreasing molecular mass and increasing mobility of PAA.

74 Example 6 Inhibition of Calcium Carbonate on the surface. The objective of this experiment was to apply intrinsic exposed core optical fibre sensor (IECOFS) to the study of the surface crystallization of CaCO 3 at 100*C approaching the temperature range of interest for MSF - and to determine the effectiveness of low molar 5 mass poly(acrylic acid) (PAA, M, < 2000 g/mol) with different end groups in preventing surface crystallisation under those conditions. We have previously observed that changing the hydrophobicity of the end-groups of low molar mass PAA can dramatically improve scale inhibition performance and change the speciation and morphology of the formed crystals. 10 Optical fibre system The IECOFS sensor developed for elevated temperature use consists of a laser light source 5 mW He-Ne laser (X = 632.9 nm, Uniphase, CA USA), temperature controller (Novus-N480D with Thermocouple type J), optical fibre cell and photometric detector (Industrial Fibre optics). The optical fibre cell consists of optical fibre fused silica core of is length 21 cm (15 cm immersed in solution) and 1000 pim diameter (F-MBE, Newport Corporation USA and PUV-600T) of refractive index 1.457 and 70 mL cylindrical cell (Borosilicate glass 2.8cm OD x 2.3cm ID x 15cm long) open on both sides (as heat transfer tube). The heat transfer tube is sealed with 0-rings against two nylon endplates. The endplates are fitted with stainless steel inserts machined to allow the optical fibre to 20 pass through them and seal in place with locking screws and teflon olives. The cell is surrounded by an aluminium block containing two 250W elements for heating. This system is described in detail in Australian Patent Application No. 2012203109, the entire contents of which are incorporated herein by cross-reference. Optical power attenuation (A) was calculated using Eq. 1 tP 25 A = -101og a (Eq. 1) Where P 0 and P, are the intensities of light measured by the photometric detector at initial time (t = 0) and time (t) respectively. The Inhibition Efficiency (% IE) of PAA in reducing the heterogeneous crystallization of CaCO 3 on optical fibre surface was determined by applying equation (Eq. 2) 30 %1E =[1-- (A A ]x 100 Bltank) (Eq. 2) Where APAA is the final steady state attenuation value in the presence of PAA, A Blank is the final steady state attenuation value in the absence of PAA (blank) under experimental 75 conditions. Thus % IE of PAA without any surface crystallization of CaCO 3 = 100% and % IE of blank = 0%. Experimental The following low molecular mass PAA with different end-groups were tested for 5 efficiency in inhibiting CaCO 3 formation on the surface at I 00*C. Carboxymethyl- 1,1 -dimethyl-PAA (CMM-PAA, M,= 2106 g/mol and PDI = 1.3) Ethyl- isobutyrate -PAA, (EIB-PAA M, = 1669 g/mol and PDI =1.3) Cyclohexyl- isobutyrate-PAA (CIB-PAA, Mn = 1689 g/mol and PDI =1.4) Hexyl- isobutyrate-PAA (HIB-PAA, Mn = 1403 g/mol) io Hexadecyl- isobutyrate-PAA (HDIB-PAA, M = 1687 g/mol) PAA with short hydrophilic (CMM) and hydrophobic (EIB) end groups and middle and long hydrophobic end groups (CIB, HIB and HDIB) were chosen to investigate the effect of the hydrophobicity and size of end groups on the inhibition of the surface formation of CaCO 3 at elevated temperature and the morphology of any scale formed. 15 Determination of optical power attenuation Two solutions, 0.0835 M (5000 ppm) of C0 3 2 as Na 2

CO

3 and 0.0825 M (3300 ppm) of Ca2+ as CaCl 2 , were prepared. These solutions and the deionized water used were filtered and degassed using a 0.45 jtm Millipore solvent filter. 48 mL of filtered deionized water, 20 one drop of 0.05 M NaOH to give an approximate pH of 9.2 and 6.70 ppm of PAA were placed in a 70 mL cylindrical cell under magnetic stirring. When the target temperature of 100 *C was attained I mL of Na 2

CO

3 solution and 1 mL of CaCl 2 solution were injected to give final concentrations of 100 ppm C0 3 2 and 66 ppm Ca2+ The recording of laser light intensity was begun immediately on injection of solutions and 25 detected by photometric detector over 1000 s. Analogue outputs from photometric detector were digitally converted using a Picolog A/D Converter 16 (16 Bit) and Picolog recording software and data was acquired every 30 s. Attenuation calculated by Eq. 1 of solutions containing 66 ppm of Ca 2 + and 100 ppm of C0 3 2 - ions (Q,, /Ks, = 1629) in the absence and presence of 6.70 ppm of PAA (M, < 2000 g/mol) with different end groups at 30 pH = 9.2, t = 1000 s and T = 100 *C was determined. Optical fibre samples from the experiments in the absence and presence of PAA (M, 5 2000 g/mol) were collected at the end of the experiments (after 1000 s) and characterised by scanning electron microscope (SEM). These samples were gold-coated and SEM 76 images obtained using a FEI Quanta 200 Environmental SEM at an accelerating voltage of 15 kV in the electron microscopy facility of Queensland University of Technology. The conditions and concentration of PAA (6.7 ppm) used in the present study are similar to those conditions and concentration of PAA used in a previous study on CaCO 3 bulk s crystallization monitored by conductivity. This was done to easily compare the efficiency of the PAA with different end groups in preventing bulk and surface crystallization of CaCO 3 . Results and discussion In the absence of PAA (blank) 10 In the absence of any scale inhibitor, a linear attenuation response (R 2 = 0.995, n = 18) of the IECOFS sensor was obtained over the first 510 s, (Figure 57) consistent with previous reports on the formation of CaCO 3 at 25*C. The result indicates continuing heterogeneous crystallization on the optical fibre surface with an overall attenuation rate of 2.6 x 10- s . The attenuation then changed slowly as the system reached a steady state near the end of 15 the experiment as shown in Figure 57. On previous experience this attenuation profile corresponds to linear growth of a layer of deposited surface crystals in terms of average thickness, followed by a marked slowing of growth, although it cannot be related directly to explicit kinetic parameters. In the presence of PAA 20 Qualitative observations of CaCO 3 precipitation on the surface of heat transfer tubes and of turbidity in bulk solution were dramatically different in the presence of PAA with different end groups in surface crystallization of CaCO 3 system. High turbidity was seen in the bulk solution for the blank and a medium amount for HDIB-PAA, but only low turbidity in the presence of CMM-PAA, EIB-PAA and CIB-PAA and no visible 25 cloudiness with HIB-PAA. Precipitation on the walls of the tube cell was again high for the blank and low for most of the PAAs, but both HIB-PAA and HDIB-PAA gave no observable precipitation (Table 22). Quantitative attenuation results from the same experiments obtained with the IECOFS are given in Figure 58. In contrast of the linear IECOFS attenuation that was obtained in the absence of PAA, in 30 the presence of PAA curves a steady state was reached at a much lower level of attenuation, as shown in Figure 58. It is clear that IECOFS results obtained vary between PAAs in three ways. (1) The initial inhibition period was of different lengths; (2) The growth rate during the approximately linear phase was different; and (3) the final extent of attenuation also varied. These results are summarised in Table 22. The crystallization 77 of CaCO 3 in optical fibre surface in the presence of CMM-PAA, EIB-PAA and CIB-PAA can be characterized by three stages as follows Stage I was characterised by the inhibition period or inhibition time (IT). The inhibition time is a measure of the time before the onset of detectable\ crystallization and was 5 measured from the intercept of attenuation curve with the x-axis. IT in the presence of PAA with hydrophilic (CMM) and short hydrophobic (EIB) end groups was short (19 s). However, in the presence of PAA with middle hydrophobic end group (CIB), the formation of CaCO 3 in optical fibre surface did not begin until after 72 s induction time as shown in Figure 58. 10 Stage 2 was characterised by the maximum attenuation rate obtained in the presence of PAA. In this stage, there was no significant different in attenuation rate between in the absence (blank, A = 0.0027 s~') and presence of PAA with hydrophobic end groups (EIB, 0.0023 s-I and CIB, 0.0021 s'). However, the attenuation rate in the presence of PAA with hydrophilic end group (0.0039 s-') was higher than the blank as shown in Table 22 is and Figure 58. This suggests that while under these conditions of approximately equimolar cation and anion concentration the PAA terminated by hydrophobic end groups had an inhibiting influence on nucleation, it had little or no effect on growth of crystals already growing; while PAA terminated with hydrophilic groups increased the apparent rate of crystal growth. 20 Stage 3 was the steady state period where the attenuation rate value for all of PAA with those end groups was less than the attenuation rate of blank. This is most likely related to the ability of the PAA to stabilise crystals in the bulk, so that they do not affect the IECOFS, as can be seen from the turbidity qualitatively observed with HDIB-PAA. 25 Table 22- Initial and maximum attenuation rate for the crystallization of CaCO 3 on optical fibre surface in the presence of PAAs. Stage 1 Stage 2 Stage 3 End Groups MA Maximum A rate terminated-PAA IT (s) Final Attenuation Blank - 0 0.0027 ±0.0003 1.482 ±0.113 Hydrophilic End 2106 19 0.0039 ± 0.0015 0..530 ± 0.022 Group (CMM) Hydrophobic EIB 1669 19 0.0023 i 0.0006 0.534 ± 0.029 78 End Groups CIB 1689 72 0.0021 ± 0.0016 0.477 ± 0.025 HIB 1403 >360 s 0 0 HDIB 1687 > 360 s 0 0 Calcium carbonate polymorph SEM micrograph of the optical fibre surface in the absence of PAAs after 1000 s of crystallization showed crystals of CaCO 3 occurring primarily in a rod-like morphology of s average crystal length 8 pm, with some single crystals of rhombohedral calcite (Figure 59). The rod-like morphology is most likely to consist originally of aragonite polymorph which grows with the longest crystal axis displaying { 110) twinning crystal plane. SEM images in the presence of PAA with a mid-length hydrophobic end group (CIB) showed crystals of CaCO 3 present in vaterite polymorph as shown in Figure 60. Vaterite io polymorph may have six active surfaces ({010}, {001}, {110), {0l1}, (001) and {I11)). The first four phases are terminated with calcium atoms (positive charge) and they will be strongly inhibited by PAA. The images with CIB-PAA illustrated the highest distortion in the floral vaterite polymorph which may be due to the strong adsorption of CIB-PAA on all active faces (terminated with calcium atoms) of the growing CaCO 3 nucleus. is In the presence of PAA with short-length hydrophobic (EIB), crystals of CaCO 3 occurred primarily as a mixture of distorted vaterite florettes with a few rod-like crystals and trace of rhombohedral calcite as shown in Figure 61. However, the SEM micrograph of CaCO 3 crystals in presence of PAA with hydrophilic end group (CMM) showed a distorted rhombohedral calcite as shown in Figure 62. The distortion in rhombohedral calcite may 20 be due to the adsorption of CMM-PAA on the positively charged face {110} which is the fastest growing face in the crystal of rhombohedral calcite and the neutral face { 104). With increasing hydrophobicity on increasing length of end groups of PAA, the amount of the less thermodynamically stable vaterite polymorph increases. Ostwald's rule of stages suggests that the vaterite is formed first, with the calcite formed by dissolution and 25 re-precipitation of vaterite. Inhibition efficiency PAA with HIB and HDIB hydrophobic end groups fully retarded surface precipitation under the experimental conditions, with no significant change in attenuation of IECOFS obtained. Those results were reinforced by the SEM micrograph for optical fibre core 30 samples in the presence of HIB-PAA and HDIB-PAA which showed no visible crystals 79 (Figure 63). Although there was significant crystallization of CaCO 3 in the bulk solution in the presence of HDIB-PAA, the surface of the optical fibre and heat transfer tube were clean. These results are a good evidence that the response of IECOFS only for the surface crystallization. 5 The significant difference in the efficiency of HDIB-PAA in inhibiting CaCO 3 crystallization in the bulk solution and the surface can be explained by its higher surface activity, as it is the polymer with the greatest ratio of hydrophobic end-group to hydrophilic chain. This phenomenon could be clearly seen when solutions that contained 10 and 15 ppm of this material were boiled, as large quantities of foam formed. This 1o result suggests that HDIB-PAA may work as a scale inhibitor primarily by dispersing suspended crystals. As well as that, PAA with other hydrophobic end groups may have same effect with different degree of stabilisation of the crystals in suspension. The inhibition efficiency of PAA with different end groups to prevent surface is crystallization of CaCO 3 in order of decreasing % IE was HIB > CIB > EIB > CMM, which was the same order for crystallization in bulk solution reported in our previous study (Table 23). The inhibition efficiency of HDIB-PAA, however is significantly different, having % IE 100 and 45 for surface and bulk crystallization of CaCO 3 respectively. This suggests strongly that the deposition of crystals on the fibre surface is a 20 two-stage process. The predominant mechanism for the inhibition of CaCO 3 formation in bulk solution is most likely by the adsorption of PAA on the active faces of CaCO 3 crystals, but PAA can also act as a dispersant and prevent the adsorption of CaCO 3 crystals to the fibre surface: it is reasonable that this dispersing effect would be most significant for the PAA with the most hydrophobic end groups. The structural factors 25 leading to efficient inhibition by these two mechanisms are not the same and point to different strategies for optimal PAA scale inhibitor design. Table 23- Inhibition efficiency of PAA with different end groups to prevent surface and bulk crystallization (SC and BC respectively) of CaCO 3 . End Groups terminated- A % E for SC of % IE for BC of PAA CaCO 3 CaCO 3 Blank - 0.0 0.0 80 Hydrophilic End Group 2106 64.3 65.9 (CMM) EIB 1669 64.0 75.0 Hydrophobic CIB 1689 67.9 93.0 End Groups HIB 1403 100.0 100.0 HDIB 1687 100.0 45.5 Conclusion The crystallization of CaCO 3 at 100 *C were studied using an Intrinsic Exposed Core 5 Optical Fibre Sensor (IECOFS). The effect of PAA (Mn S 2000 g/mol) with different end groups on surface crystallization of CaCO 3 at 100 *C was found to be significant. The results showed that the end groups of PAA play important roles, with mid-length (HIB) and long (HDIB) hydrophobic groups giving excellent inhibition efficiency to prevent the surface deposit of CaCO 3 . Moreover, the results of PAA with short hydrophilic (CMM) io and hydrophobic (EIB) and middle hydrophobic (CIB) showed the inhibition efficiency increasing with increasing hydrophobicity of the end group. The low molar mass PAA with long hydrophobic end group (HDIB) showed markedly different inhibition efficiency for surface and bulk precipitation which may due to inhibition precipitation on the optical fibre surface by stabilisation of crystals in the bulk is phase as well as inhibition of crystal nucleation and growth.The IECOFS sensor was found to have advantages over other conventional methods for monitoring scale precipitation. First, its response is only to surface crystallization on its surface. Second, it can be used at high temperatures and ionic strengths - such as seawater and brine solution under conditions similar to those of thermal desalination plants. Third, the sensor fibres 20 are inexpensive and can be easily removed for microscopic analysis. Example 7 Inhibition of co-precipitation of Calcium Carbonate and Calcium Sulfate on the surface. The objective of this experiment was to apply intrinsic exposed core optical fibre sensor 25 (IECOFS) to the study of the surface co-crystallization of CaCO 3 and CaSO 4 at 120*C 81 approaching the temperature range of interest for MSF and to determine the effectiveness of low molar mass poly(acrylic acid) (PAA, M, < 2000 g/mol) with different end groups in preventing surface crystallisation under those conditions. Experimental 5 Three solutions, 0.5 M (48000 ppm) of S0 4 2 as Na 2

SO

4 , 0.0625 M (3750 ppm) of C0 3 2 as Na 2

CO

3 and 0.15 M (6000 ppm) of Ca2+ as CaCl 2 , were prepared. These solutions and the R/O water used were filtered and degassed using a 0.45 m Millipore solvent filter. 48 mL of deionized water containing S0 4 2 - as Na 2

SO

4 to give a final concentration of 5760 ppm in the absence and presence of 10 ppm of PAA was placed in a 70 mL cleaned 10 cell under magnetic stirring. When the solution reached the target temperature (120 *C), 1 mL of C0 3 2 as Na 2

CO

3 solution and I ml of Ca 2 + as CaCl 2 solution were added to the cell to give a final concentration of 75 ppm and 120 ppm respectively (Qi, /K,, (CaCO 3 )= 2752). Recording of received laser light intensity was begun immediately on injection and is detected by photometric detector over 3000 s. Analogue output from the photometric detector was digitally converted using a Picolog A/D Converter 16 (16 Bit) and Picolog recording software and data was acquired every 5 seconds. Optical fibre samples containing deposits of CaCO 3 and CaSO 4 formed in the absence and presence of PAA (M, 2000 g/mol) were collected at the end of each experiment and 20 characterized by SEM. Results and Discussion Attenuation of solutions containing 5760 ppm of S042- as Na 2

SO

4 , 75 ppm of C0 3 2 as Na 2

CO

3 and 120 ppm of Ca 2 + as CaCl 2 , and in the absence and presence 10 ppm of PAA (M, : 2000 g/mol) with different end groups at pH = 9.0, t = 50 min and T = 120 *C was 25 determined in the absence of PAA (blank) and in the presence of PAA as follows. In the absence of PAA (blank) A linear attenuation response (R2 = 0.980, n = 52) by optical fibre sensor as IECOFS was obtained in the absence of PAA for the period of (0 - 260 s) as shown in Figure 64. In that period, the overall attenuation rate was 0.0039 ± 0.0004 s- , suggesting continuous 30 heterogeneous crystallization on the optical fibre surface. After that period, the change in attenuation was slow (A= 0.0010 t + 0.7266 s-1) until 465 s (Figure 64) then the system reached the steady state until the end of experiment. At the end of experiment, there was a large amount of precipitation on the surface of heat transfer tubes as shown in Figure 65.

82 This was largely loose material, presumably generated by homogeneous crystallization and precipitated on the surfaces (settled scale). Under the same experimental conditions, the change in attenuation for single heterogeneous precipitation of CaSO 4 was very slow, even though precipitation was 5 observed in the bulk solution. This indicates that the rate of heterogeneous deposition of CaSO 4 is very slow or that it is weakly adherent on the optical fibre surface. Therefore, the predominant deposit in the first period (0 - 260 s) of the heterogeneous coprecipitation of CaCO 3 and CaSO 4 is most likely to be CaCO 3 , which forms more rapidly and adheres more strongly than CaSO 4 . In heterogeneous coprecipitation, it is 10 probable that CaCO 3 formed first then bonded the CaSO 4 deposit layer to the optical fibre surface, as was proposed to occur on a heated stainless steel surface by Bramson et al., (1996). SEM micrographs of the optical fibre surface (Figure 66) showed that the crystals were a mixture of CaCO 3 and CaSO 4 , mostly in scale clusters consisting of CaSO 4 as a spherical is polymorph and CaCO 3 as a rod-like hexagonal calcite as shown in Figures 67, with some single crystals of rhombohedral calcite as shown in Figure 68. The polymorphs of CaCO 3 crystals seem to be affected by CaSO 4 deposition, in that the rod-like polymorph of CaCO 3 was the main polymorph in single precipitation of CaCO 3 , but in coprecipitation of CaCO 3 and CaSO 4 the predominant scale morphology was as clusters. 20 This result agrees with the results of earlier work in which it was proposed that the presence of one scale can affect the structure of the other scale. Moreover, the scale layer formation results are consistent with the a two-stage process suggested by the attenuation results in this study. In the presence of PAA 25 No significant change in attenuation of IECOFS sensor in the presence of 10 ppm of CMM-PAA, EIB-PAA, CIB-PAA, HIB-PAA and HDIB-PAA was obtained during the experiments. These results indicated the excellent control of heterogeneous coprecipitation of CaCO 3 and CaSO 4 by PAA with different end groups under those conditions. The SEM of optical fibre core samples in the presence of PAA with different 30 end groups showed that the optical fibre core were largely clean, in agreement with attenuation results. While there were some deposits on the surface of optical fibre as shown in Figure 69 (A, B) they do not look like calcite and calcium sulfate dihydrate crystals, and Electron Dispersion Spectroscopy (EDS) showed that the deposit contains a high level of Na, C and S and a low level of Ca which suggests that the deposit was 83 Na 2

SO

4 and Na 2

CO

3 , and is only starting material generated by drying of solution containing a large amount of dissolved species onto the fibre. HIB-PAA and HDIB-PAA also significantly reduced the coprecipitation of CaCO 3 and CaSO 4 on the surface of heat transfer tubes (Figure 70). s Example 8 The aim of this experiment was to determine the efficiency of novel scale inhibitors based on poly(acrylic acid) PAA for prevention of scale formation in treated concentrated seawater at 104*C and to compare the efficiency of these novel scale inhibitors with 10 commercial scale inhibitors that have been shown to have good efficiency in controlling scale formation used in desalination plants of Saline Water Conversion Corporation (SWCC), Saudi Arabia. Selection of novel poly(acrylic acid) PAA scale inhibitors with different molecular mass is and end groups. From our earlier studies, two suitable scale inhibitors to prevent scale formation in bulk solution are PAA with medium hydrophobic end groups (HIB-PAA, M = 1403 g/mol and CIB-PAA, M,= 1689 g/mol). Both scale inhibitors were chosen to determine their efficiency to prevent scale formation in actual seawater. Low molecular mass PAA with 20 long end group (HDIB-PAA Mn= 1689 g/mol) which showed excellent inhibition efficiency on the surface was also chosen. PAA with medium hydrophobic end groups (HIB-PAA, M = 3563 g/mol) was also chosen so as to study the effect of molecular mass in inhibition process. 25 Selection of commercial Scale inhibitors Three commercial scale inhibitors were selected based on their performances in MSF plants as follows. Albrivap@ DSB(M) phosphonate base scale inhibitor. This scale inhibitor has been used for a long time in MSF plants in Saudi Arabia and is still used. 30 BELGARD@ EV2030 based on polycarboxylic and polymalic acid (copolymers) Sokalan® EPIOi based on polycarboxylic and polymalic acid (copolymers). Trials of these scale inhibitors in MSF were carried out at Doha West and the AI-Zour power generation and water production station. The results showed that Albrivap@ 84 DSB(M) is quite effective and successful in controlling scale formation at top brine temperature (TBT) of 103 0 C and dose rate of 3.0 ppm, Belgard@ EV2030 at TBT of 105 0 C and dose rate of 1.5 ppm and Sokalan@ EPIOi at a TBT of 105 0 C and dose rate of 1.5 ppm during the 3 months test period. 5 Primary trial test was initially performed in SWCC's Saline water Desalination Research Institute (SWDRI) MSF pilot plant for one month at TBT of 112 *C and dose rate of 2 ppm and then in the Jeddah IV commercial plant for six months at TBT of 110 *C at the same dose rate. The results showed that Belgard@ EV 2030 was effective in controlling 1o scale in brine heater tubes but no outstanding improvement was shown in reducing demister pads fouling. In fact, total blockage of the first stage demister pads was quite pronounced while the successive stages showed lesser amount of scale deposits. These conditions of demister pads fouling could allow the plant to operate for one full year, considering that demister pads of the first stage were replaced at the end of the one year Is operating period. Based on this evaluation Belgard@ EV 2030 was approved for using as scale inhibitor in MSF plants. Experimental A solution of 0.167 M (10000 ppm) of C0 3 2 - as Na 2

CO

3 (Analar®) was prepared by 20 adding 17.702 g of Na 2

CO

3 to a 1 L volumetric flask. PAA solutions were prepared by dissolving 0.010g of PAA in 20 ml water (500 ppm) and were used after 3 days. These solutions and the RIO water used were filtered and degassed using a 0.45 jim Millipore solvent filter. Commercial scale inhibitor solutions were prepared by dissolving 1 g of their commercial solution in 1L distilled water (500 ppm: the concentration of 25 commercial solution of scale inhibitor is usually 50% w/w). Treated concentrated seawater Filtered (0.45prm cellulose acetate membrane) 5L raw seawater was treated with HCl (2 M) to remove the carbonic acid species (HCO 3 and C0 3 2 -) and the pH was reduced from 30 8.2 to 4.5. Then the pH was increased to 8.2 by adding NaOH (IM) and the seawater covered to avoid the absorption of atmospheric CO 2 . Analysis of the treated seawater is shown in Table 24. Table 24: Treated seawater composition 85 Concentration Ions (ppm) TDS 45325 pH 8.2 Sodium (Na') 13200 Calcium (Ca 2 +) 546 Magnesium (Mg2+) 1635 Potassium (K*) 521 Bicarbonate (HCO 3 ) 39 Sulfate (S042) 3321 This treated seawater water (245 g) was placed in a 500 mL three necked round bottomed flask containing magnetic stirrer and thermometer under a water-cooled glass condenser. When the solution began to boil (1 04'C), scale inhibitor solution (5 ppm) and s C0 3 2 - solution (200 ppm as Na 2

CO

3 ) were added to the three necked round bottomed flask under stirring and time noted. The solution (5 mL each time) was withdrawn from 2+ 2+ the reaction vessel at 2, 5, 10, 15 and 20 min to analyze the concentration of Ca . Ca concentration was analysed by ICP OES (Perkin Elmer, Optima@& 2100 DV) with SlO Auto sampler. 10 Results and discussion The concentration of Ca 2 over experiment in the absence and presence scale inhibitors are summarized in Table 25. The plots of Ca 2 + concentration vs. time (min.) for different scale inhibitors at same experimental conditions are shown in Figure 57. It is very clear 15 from the plots that the inhibition efficiency for HIB-PAA (M= 1403 g/mol) and CIB PAA (Mn= 1689 g/mol) is better than for other inhibitors and HIB-PAA shows the best efficiency. It is to be noted from the plots that HIB-PAA with higher molecular weight (Mn= 3563 g/mol) showed lower efficiency, consistent with the observation from earlier work. The inhibition efficiency of two commercial inhibitors (Belgard@ EV 2030 and 20 Albrivap@ DSB (M)) was lower than both HIB and CIB, though Belgard® EV 2030 showed better efficiency than DSB (M) and showed efficiency very close to CIB up to around 12 minutes of the reaction time. These results suggest that the lowest molecular 86 mass of PAA with middle hydrophobic end groups is more suitable as scale inhibitors in thermal desalination plants. Another observation on the plots was the very close proximity in the efficiency of the commercial inhibitor (Sokalan@ PM 10i) and low molecular mass PAA with long 5 hydrophobic end group (HDIB-PAA, M = 1687 g/mol). Both these inhibitors showed the lowest inhibition efficiency in the bulk solution. The results of HDIB-PAA in this experiment are compatible with its results in inhibition of CaCO 3 formation in the bulk solution. It appears that HDIB-PAA (Mn = 1687 g/mol) has surface active properties and an excellent ability to prevent surface crystallization. It is believed from the above 1o observation that the commercial inhibitor (Sokalan@ PM 10i) has same surface active property as that of HDIB-PAA. Table 25: The concentration of Ca 2 over experiment in the absence and presence scale inhibitors The average Ca 2 + concentration in (ppm) over the Scale Inhibitors ::xperiment (t = min) 0 2 5 10 15 20 461 455 450 439 431 Blank ±3.32 ±2.90 ±0.37 ±4.67 ±0.43 479 476 455 442 437 Sokalan PM 10i ±0.42 ±2.37 ±4.56 ±3.73 ±6.92 CIB-PAA (Mn= 1689 511 509 506 505 499 g/mol) ±13.26 :1.34 ±1.76 ±7.13 ±1.47 529 504 488 477 477 Albrivap DSB (M) 546 ±6.58 ±21.37 ±3.42 ±5.12 ±5.06 HIB-PAA (M= 1403 ±0.42 523 519 515 510 508 g/mol) ±6.18 ±13.89 ±3.58 ±9.64 ±6.18 517 513 507 505 489 Belgard EV 2030 ± 12.97 ±13.36 ±7.34 ±4.96 ±4.66 HDIB-PAA (M,= 1687 476 472 456 447 446 g/mol) ±1.38 ±4.45 ±6.63 ±5.20 ±1.98 HIB-PAA (M= 3563 494 487 481 475 469 g/mol) ±0.65 ±5.22 ±4.32 ±1.22 3.65 15

Claims (24)

1. A method for inhibiting the formation of a solid inorganic group 2 metal salt in an aqueous liquid, said method comprising adding a polyacrylic acid to said liquid, said polyacrylic acid having a terminal group of structure RO-G-C(R'R")-, wherein: R is selected from the group consisting of H and an alkyl group containing from 1 to 20 carbon atoms, R' and R" are each, independently, a hydrocarbon of from 1 to 4 carbon atoms or R' and R" together with the carbon atom to which they are both attached form a carbocyclic ring of from 3 to 8 carbon atoms, and G is a group such that -G-OH is an acidic group and wherein either the aqueous liquid is at a temperature of greater than 90'C or else has a calcium ion concentration of greater than about 200ppm or else has a magnesium concentration of greater than about 50ppm, or any two or more of these conditions apply.

2. The method of claim 1 wherein G is -C(=O)-.

3. The method of claim 1 or claim 2 wherein said inhibiting comprises reducing the rate of formation of said salt and/or delaying the onset of formation of said salt.

4. The method of any one of claims 1 to 3 wherein said inorganic group 2 metal salt is a group 2 metal carbonate or a group 2 metal sulfate or a group 2 metal hydroxide or a mixture of any two or all thereof.

5. The method of any one of claims 1 to 4 wherein said group 2 metal salt is a magnesium salt or a calcium salt or a mixture thereof.

6. The method of claim 5 wherein the salt is magnesium hydroxide or calcium carbonate or calcium sulfate or a mixture of any two or all thereof.

7. The method of any one of claims 1 to 6 wherein the polyacrylic acid has an average molecular weight of less than about 4000Da, optionally less than about 2000Da.

8. The method of claim 7 wherein the polyacrylic acid has an average molecular weight of less than about 1500Da. 88

9. The method of any one of claims 1 to 8 wherein the polyacrylic acid has an average degree of polymerisation of less than about 55, optionally less than about 30.

10. The method of claim 9 wherein the polyacrylic acid has an average degree of polymerisation less than about 20.

11. The method of claim 10 wherein the polyacrylic acid has an average degree of polymerisation of about 10 to about 55, optionally of about 10 to about 20.

12. The method of any one of claims I to 11 wherein R' and R" are the same.

13. The method of claim 12 wherein R' and R" are both methyl,

14. The method of any one of claims I to 13 wherein R is an alkyl group of from about 6 to about 10 carbon atoms.

15. The method of any one of claims I to 14 wherein R is an alkyl group from about 10 to about 20 carbon atoms.

16. The method of any one of claims 1 to 15 wherein the polyacrylic acid is added in an amount of less than about 1Oppm.

17. The method of claim 16 wherein the polyacrylic acid is added in an amount of between about 1 and about 10ppm.

18. The method of any one of claims 1 to 17 which is conducted at between about 10 and about 120'C, optionally at between about 10 and about 100 0 C.

19. The method of any one of claims I to 18 wherein the polyacrylic acid is added in an amount of about 0.5 to 50pM.

20. The method of any one of claims 1 to 18 wherein the polyacrylic acid is added in a molar ratio of less than about 10% relative to the concentration of the inorganic group 2 metal salt. 89

21. The method of claim 20 wherein the polyacrylic acid is added in a molar ratio of between about 0.5% and about 10% relative to the concentration of the inorganic group 2 metal salt.

22. The method of any one of claims 1 to 21 wherein the aqueous liquid is a feed for a water purification process, whereby the method represents a method of reducing scale in said water purification process.

23. The method of claim 22 wherein the water purification process comprises reverse osmosis.

24. The method of claim 22 wherein the water purification process comprises multistage flash distillation and/or multi-effect desalination. Ali Abdrabalrasoul Mohamed Al Hamzah Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON