Synthesis, Characterisation and

Application of Polymeric Scale

Inhibitors

Ali A. Al Hamzah

Master of Science (KSU)

Bachelor of Science with Honours (KSU)

(KSU) King Saud University, Riyadh, Saudi Arabia

A thesis submitted for the degree of Doctor of Philosophy of the University

of New England, Armidale, NSW, Australia

March, 2011

Declaration ii

Declaration

The work described in this thesis was carried out at the Department of Chemistry at the

University of New England under the supervision of Dr. Christopher M. Fellows.

I certify that the substance of this thesis has not already been submitted for any degree and is

not currently being submitted for any other degree or qualification.

I certify that any help received in preparing this thesis, and all sources used, have been

acknowledged in this thesis.

Signature Date: 8/3/2011

Acknowledgements iii

Acknowledgements

The submission of this thesis would not have been possible without the support and guidance

of my principal supervisor. I wish to express my deep appreciation to my supervisor Dr.

Christopher Fellows who provided me with inspiration at academic and professional levels

and without his limitless guidance and thoughtful comments I would not have achieved this

work.

I wish to extend special thanks to my co supervisor A/Prof. Trevor Brown and Prof. Stephen

Glover the head of chemistry department.

I am grateful to the Saudi government for their generously supporting my study.

I appreciate the support provided by my colleagues particularly my honest mate Mr. Andrew

Wallace, Mr. Chris East and Dr. Martijn Boerkamp.

I also wish to thank my family and most important to my daughters Sara, Hawra and Zahra

for their patience during my study. Special thanks are extended to my parents, wife, brother,

sister and sister-in-law for consistently supporting me in all my study and providing me with

encouragement to pursue further studies.

Abstract iv

Abstract

Desalination of seawater by both the evaporation (e.g. multi stage flash, MSF) and membrane

(e.g. reverse osmosis, RO) processes encounters difficulties with precipitation of sparingly

soluble inorganic salts such as calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2)

and calcium sulfate (CaSO4). These precipitate during the desalination process when their

solubility product Ksp is exceeded. To control this scaling problem, several methods for scale

prevention and control are used, such as acid and additive treatments. Scale inhibitors are

chemical additives that have gained importance in controlling scale formation and/or

deposition in recent decades. These are low molecular weight organic compounds, typically

phosphonates, or polymers of molecular weight 1000-4000, typically containing carboxylate,

sulfonate or phosphonate groups.

In Chapter one, a brief summary of the mechanism of scale formation and scale inhibitors in

desalination plants is given. The synthesis and characterisation of poly(acrylic acid) (PAA)

with different end groups and molecular mass using Atom Transfer Radical Polymerization

(ATRP) is explained in detail in Chapter two. In Chapter three the inhibition efficiency of

PAA with different end groups and molecular mass to prevent the homogenous formation of

calcium carbonate scale at low and elevated temperatures is studied. The best inhibition

efficiency was found for low molecular mass of PAA with hydrophobic middle length end

group (n-hexyl isobutryate, HIB) under most conditions.

Chapter four focuses on the effect of PAA with different end groups and molecular mass in

the thermal decomposition of bicarbonate (HCO3¯) at high temperature. Low molecular mass

PAA with hydrophobic middle length end group (HIB) and long end group (decyl-

isobutryate, DIB) was found to have the lowest rate coefficient for thermal decomposition of

bicarbonate (HCO3¯). In Chapter five a type of intrinsic exposed core optical fibre sensor

(IECOFS) was used to study the heterogeneous crystallization of CaCO3 and coprecipitation

Abstract v

of CaCO3 and CaSO4 in the absence and presence of PAA at 100 and 120 °C. The attenuation

of IECOFS and scanning electron microscope (SEM) results showed there was no

heterogeneous crystallization of CaCO3 on optical fibre surface in the presence of HIB-PAA

(Mn = 1403 g/mol) and PAA (Mn = 1687 g/mol) with the longest hydrophobic end group

(hexadecyl-isobutyrate, HDIB).

In Chapter six the homogeneous crystallization of Mg(OH)2 in the absence and presence of

low molecular mass (Mn≤ 2000 g/mol) PAA with different end groups is discussed at 100

°C. The results showed a significant decrease in crystal growth of Mg(OH)2 in the presence

of PAA with different end groups. In Chapter seven, the inhibition efficiency of PAAs to

prevent the homogeneous formation of calcium oxalate (CaC2O4) at low and high

temperatures is studied. The highest inhibition efficiency of PAA with different end groups

was at molecular masses between 1400 and 3300 g/mol. At low and high temperatures, a

strong effect of the end-group was found. PAA with hydrophilic (CMM) and longer

hydrophobic end groups (HDIB) have a performance better PAA with short (EIB) and middle

(HIB &CIB) end groups. At 80 °C however, the effectiveness of the inhibitors terminated

with middle hydrophobes was better than other end groups.

Abbreviations vi

Abbreviations

∆G Gibbs free energy

2θMc The interaction parameters of M with major cations (c) in solution

ATRP Atom Transfer Radical Polymerization

BMa , CMa The interaction parameters of M with major anions (a) in solution (ionic

strength dependence)

c, a cations and anions

CF Concentration factor of brine solution

CIB Cyclohexyl- isobutyrate

CMM Carboxymethyl-1,1-dimethyl

COD Calcium oxalate dihydrate

COM Calcium oxalate monohydrate

COT Calcium oxalate trihydrate

CGR Crystal growth rate

DIB Decyl- isobutyrate

EIB Ethyl- isobutyrate

Eq- Equation

FTIR Fourier Transform Infrared spectroscopy

Abbreviations vii

ƒγ The limiting Debye-Hückel ( a function of ionic strength)

GPC Gel permeation chromatography

HDIB Hexadecyl- isobutyrate

HIB Hexyl- isobutyrate

I Ionic strength

IE Inhibition efficiency

IECOFS Intrinsic exposed core optical fibre sensor

ITD of HCO3¯ The inhibition of thermal decomposition of HCO3

¯

K Conductivity (S.cm-1)

k rate coefficient

Ksp Solubility product

mi The molality of ion i ( number of moles per kg water)

MSF Multi Stage Flash

n The order of reaction

NMR Nuclear Magnetic resonance spectroscopy

PAA Poly(acrylic acid)

PDI Polydispersity index

Abbreviations viii

PtBA Poly(tert-butyl acrylate)

Re. Reaction

RI Refractive index

RO Reverse Osmosis

S Salinity

SEM Scanning Electron Microscope

SL Supersaturation level

TBT Top brine temperature

TDS Total dissolved solids

THF Tetra-hydrofuran

TIR Total internal reflection

XRD X-ray diffraction

β°Ma, β1Ma, β2

Ma

and CϕMa

Pitzer parameters temperature dependence

γM Activity coefficient of cation (M)

γX Activity coefficient of anion (X)

Λ The equivalent conductance

λ Limiting Equivalent conductivity

Abbreviations ix

ΨMca The interaction parameters of M with major cations (c) and anions (a) in

solution

Table of Contents x

Table of Contents

Declaration ii

Acknowledgements iii

Abstract iv

Abbreviations vi

Chapter One: Scale and Scale Inhibitor in Desalination (1-60)

Research Objectives 2

1.1 Introduction 3

1.2 Desalination Technologies 5

1.2.1 Reverse Osmosis (RO) Desalination 6

1.2.2 Multi Stage Flash (MSF) Desalination 7

1.3 The Chemistry of Seawater Scales 9

1.3.1 Seawater Composition 9

1.4 Scale Formation in Desalination 13

1.4.1 Scale Formation 13

1.4.2 Mechanisism of Alkaline Scale Formation 15

1.4.2.1 Langelier Mechanism 17

Table of Contents xi

1.4.2.2 Dooly and Glater Mechanism 19

1.4.2.3 Shams El-Din Model 19

1.4.3 Calcium Sulfate Scale 20

1.5 The activity coefficients of ions and solubility product of CaCO3 and CaSO4 23

1.5.1 The Debye-Hückel Limiting Law 23

1.5.2 The Davies Equation 24

1.5.3 The extended Debye-Hückel Model 24

1.5.4 Ion Pairing Model 25

1.5.5 Pitzer Model 26

1.5.6 The Solubility of CaCO3 and CaSO4 30

1.6 Control of Seawater Scale 33

1.6.1 Acid treatment 34

1.6.2 Mechanical cleaning 34

1.6.3 Additive Treatment as Polymeric Scale Inhibitors 34

1.6.3.1 Threshold effect 35

1.6.3.2 Dispersion effect 35

1.6.3.3 Adsorption effect 35

Table of Contents xii

1.6.3.4 Classification of Polymeric Scale Inhibitors 36

1.7 Free Radical Polymerization 40

1.7.1 Living Radical Polymerization (LRP) 42

1.7.2 Atomic Transfer Radical Polymerization (ATRP) 43

1.7.3 The limitation of using ATRP 45

1.8 Methods for the Evaluation of Scale Inhibitors 47

1.8.1 The Conductivity of ions in solution 47

1.8.2 Optical Fiber Sensor 50

1.9 Calcium oxalate scale in the sugar industry 52

References 53

Chapter Two: Synthesis and Characterisation of Poly(Acrylic Acid) 61-75

2.1 Polymer Synthesis 62

2.1.1 Purification of Reagents 62

2.1.2 Synthesis of Initiators 62

2.1.3 Synthesis of Poly (tert-butyl acrylate ) (PtBA) 63

2.1.4 Selective hydrolysis to PAA 64

2.1.5 Hydrolysis of end groups 65

Table of Contents xiii

2.2 Polymer Characterization 67

2.2.1 The Characterization of Polymer by 1H-NMR 67

2.2.2 The Characterization of PtBA by GPC 68

2.2.3 The Characterization of PAA by GPC 70

References 75

Chapter Three: Inhibition of Calcium Carbonate Homogenous

Formation 76-140

3.1 Introduction 76

3.2 Experimental Determination of Conductivity and Turbidity at 25 °C 78

3.3 Steady State and Induction Time 79

3.4 Results 81

3.4.1 Inhibition of CaCO3 Crystallization at room temperature(condition 1) 81

3.4.2 Inhibition of CaCO3 Crystallization at room temperature (condition

2) 89

3.4.3 Inhibition of CaCO3 Crystallization at 60, 80 and 90 °C (conditions 3,4 and 5)

94

3.4.4 Inhibition of CaCO3 Crystallization at 100 °C (conditions 6 and 7) 110

3.5 Discussion 115

3.6 Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and Fourier

Transform Infrared (FTIR) 118

Table of Contents xiv

3.6.1 Results 119

3.6.2 A possible mechanism of CaCO3 crystal growth 130

3.7 Conclusion 137

References 139

Chapter Four: Apparent Inhibition of Thermal Decomposition of

HCO3¯

141-205

4.1 Introduction 142

4.2 The Effect of Scale Inhibitor on the Thermal Decomposition of HCO3¯ 143

4.2.1 Walinsky and Morton (1979) 143

4.2.2 Mubarak (1998) 144

4.2.3 Shams El-Din (2002) 145

4.2.4 Thermodynamic and Kinetics Treatment of Alkaline Scale in MSF 145

4.3 The objective of this chapter 147

4.4 Advance Thermodynamic Treatment of Alkaline Scale in MSF Desalination

Plants 148

4.4.1 Pitzer Model 148

4.4.2 Calculation of Enthalpy (∆Hf° ) and Gibbs Free Energy (∆G°

f) 154

4.4.3 Estimation of Gibbs Free Energy (∆G) for the competitive reactions

under Desalination conditions 156

Table of Contents xv

4.5 The Kinetics of Thermal Decomposition of HCO3¯ at high temperature 163

4.5.1 Experiment Determination of Conductivity at 97.2 °C 163

4.5.2 Derivative of Electrical Conductivity Equation for Decomposition of

HCO3¯

164

4.6 Results and Discussion 168

4.6.1 Section one: The Kinetics Model of Thermal Decomposition of

HCO3¯ in absence of PAA

168

4.6.2 Section two: Thermal Decomposition of HCO3¯ in the presence of

PAA 172

4.6.2.1 The Conductivity of Polyacrylate (PA( n-)) at high temperature 175

4.6.2.2 The Inhibition Efficiency of PAA to Retard the Thermal

Decomposition of HCO3¯ 187

4.6.3 The Mechanism of TD of HCO3¯ by different end groups and

molecular mass of PAA 197

4.7 Conclusion 201

References 204

Chapter Five: Inhibition of Heterogeneous Crystallization of

Calcium Carbonate and Coprecipitation of Calcium Carbonate and

Calcium Sulfate at High Temperatures

206-246

5.1 Introduction 207

5.2 Optical Fiber System for high temperature 208

5.3 The Heterogeneous Crystallization of CaCO3 on Optical Fiber surface at

100°C 213

Table of Contents xvi

5.3.1 Experimental 213

5.3.2 Results and Discussion 214

5.3.2.1 In the absence of PAA (blank) 214

5.3.2.2 In the presence of PAA 216

5.4 Heterogeneous Co-precipitation of CaCO3 and CaSO4 on Optical Fiber

surface at 120°C 232

5.4.1 Experimental 232

5.4.2 Results and Discussion 233

5.4.2.1 In the absence of PAA (blank) 229

5.4.2.2 In the presence of PAA 240

5.5 Conclusion 245

References 246

Chapter Six: Inhibition of Homogeneous Formation of Magnesium

Hydroxide 247-266

6.1 Introduction 248

6.2 Experimental Determination of Conductivity at 100°C 249

6.3 Result and Discussion 250

6.3.1 In the absence of PAA (blank) 251

6.3.2 In the presence of PAA 253

Table of Contents xvii

6.3.3 The estimation of order and crystal growth rate for Mg(OH)2

formation 259

6.4 Conclusion 265

References 266

Chapter Seven: Inhibition of Homogeneous Formation of Calcium

Oxalate 267-287

7.1 Introduction 268

7.2 Experimental Determination of Conductivity and Turbidity at 23 °C 268

7.2.1 Results and Discussion 269

7.3 The Inhibition Efficiency of PAAs at 80 °C 276

7.3.1- Results and Discussion 276

7.4 Crystal Morphologies of CaC2O4 in presence of PAA at 80 °C 277

7.5 Conclusion 284

References 286

Chapter Eight: Summary 288-294

References 294

Appendix 1: Pitzer model for calcium sulfate hemihydrate

(CaSO4.1/2 H2O) A1- A12