Inhibition of carbon steel corrosion by long alkyl-chain amino acid corrosion inhibitors

183 Pages·2011·2.27 MB·English

Department of Chemical Engineering
McGill University, Montreal, Canada

Inhibition of carbon steel corrosion by
long alkyl-chain amino acid corrosion inhibitors

A Thesis submitted to McGill University in partial fulfillment of the
requirements of the degree of

Doctor of Philosophy

by

Saad Ghareba

© Saad Ghareba 2011
ABSTRACT
ABSTRACT
Carbon steel (CS) is the most commonly used material for equipment and pipes in
the oil production processes. However, presence of water/salts and carbon dioxide,
among other gases, in the oil is a serious problem due to increased corrosion rate of the
material. The most common way of mitigating this problem is by using corrosion
inhibitors. However, many common corrosion inhibitors that are in use today are health
hazards. Therefore, there is a need to develop more environmentally compatible and
biodegradable corrosion inhibitors. Bioorganic and naturally occurring molecules, such
as amino acids, are the most obvious candidates.
This work was aimed at studying the influence of some amino acids, 11-
aminoundecanoic acid (11AA) and 12-aminododecanoic acid (12AA), as corrosion
inhibitors for carbon steel (CS) in hydrochloric acid and some other electrolytes that
might be used in certain industries.
In this study the inhibiting effect of 12AA on corrosion of CS in CO -free and
2
CO -saturated 0.5 HCl was investigated as a function of various parameters: inhibitor
2
concentration, electrolyte pH, temperature, treatment time, CS surface roughness,
electrolyte flow rate and pattern, effect of electrolyte type. In addition, the interaction of
11AA with the CS surface under selected experimental conditions was also investigated.
It was found that 12AA inhibits both partial corrosion reactions, with a slightly
stronger inhibition of the anodic corrosion reaction which indicated that 12AA acts as a
mixed-type inhibitor. The corrosion protection mechanism is by formation of a surface-
adsorbed 12AA monolayer that offers a hydrophobic barrier to transport of solvated
corrosive ions to the surface yielding a maximum inhibition efficiency of ~98%. The
adsorption of 12AA onto the CS surface was described by the Langmuir adsorption
isotherm. The corresponding Gibbs energy of adsorption was calculated to be −26 and
−28 kJ mol−1 in the CO -free and CO -saturated 0.5 M HCl, respectively. This indicated
2 2
that the self assembled monolayers (SAM) formation process is spontaneous and
reversible. PM-IRRAS measurements revealed that the SAM is amorphous, which could
be attributed to the repulsion between the neighboring positively charged amine groups
and also to a high heterogeneity of the CS surface. The study showed also that the 12AA
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ABSTRACT
can be used as an effective inhibitor of CS general corrosion in several other electrolytes
including; acetic acid, perchloric acid and sodium chloride, but its application in nitric
and sulfuric acid should be avoided. The corrosion inhibition of the CS surface by 12AA
is also effective at higher pH values, although the corresponding corrosion inhibition
efficiency decreased due to a decrease in 12AA solubility. 12AA was also confirmed to
be an efficient corrosion inhibitor of a CS surface of different roughness.
The effect of flow and flow pattern of CO -saturated HCl on the corrosion
2
inhibition of CS by 12AA was also investigated in a square duct, rotating disk electrode
(RDE) and jet impingement cell configuration. 3 mM 12AA provided high corrosion
inhibition efficiency in the square duct and RDE configuration. However, in 1 mM 12AA
solution, the inhibition efficiency decreased with an increase in Reynolds number (Re),
due to desorption of 12AA from the CS surface. 12AA was found to poorly protect CS in
the impingement-jet configuration at low Re, while at high Re, acceleration of CS
corrosion was recorded.
Similar results were also obtained for inhibition of CS corrosion by 11AA. In fact,
this molecule was found to better protect CS from corrosion than 12AA. This was
attributed to the higher surface coverage of 11AA on the CS surface, i.e. the formation of
a more compact 11AA monolayer.

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RÉSUMÉ
RÉSUMÉ
L’acier au carbone est le matériel le plus couramment utilisé pour les équipements
et les pipelines reliés aux processus de production pétrolière. Toutefois, la présence de
certains éléments comme l’eau, les sels and le dioxyde de carbone dans l’huile pose
plusieurs problèmes reliés à l’augmentation du taux de corrosion du matériel. La façon la
plus répandue d’éliminer ce problème est l’utilisation d’inhibiteurs de corrosion. Il est
cependant important de mentionner que la majorité de ces inhibiteurs sont nocifs pour
l’être humain. Il est donc nécessaire de développer des composés compatibles avec
l’environnement et biodégradables et ceci peut être fait avec l’utilisation d’acides aminés.
Ce projet a pour but d’étudier l’influence des acides aminés “11-aminoundecanoic
acid’’ (11AA) et “12-aminododecanoic acid’’ (12AA) en tant que qu’inhibiteurs pour
l’acier carbone dans l’acide chlorhydrique et plusieurs autres électrolytes utilisés dans
certaines industries.
Dans cette étude, l’effet inhibiteur du 12AA sur la corrosion de l’acier carbone
dans une solution sans ou saturée en dioxyde de carbone et avec 0.5 M d’acide
chlorhydrique a été étudié. Différents paramètres tels que la concentration des inhibiteurs,
la concentration des électrolytes, le pH, la température, le temps de traitement, la rugosité
de surface, le taux de flux et les différents types d’électrolytes furent analysés pour mieux
comprendre le mécanisme de fonctionnement. De plus, l’interaction du 11AA avec la
surface de l’acier à certaines conditions fut également prise en considération.
Il fut démontré que le 12AA inhibait les corrosions partielles et démontrait une
corrosion anodique légèrement plus inhibée. Ceci nous a donc indiqué que cet inhibiteur
était de type mixte. Le mécanisme de protection de la corrosion se faisait par adsorption
de l’inhibiteur 12AA et cela procurait une protection hydrophobique contre les ions
corrosifs avec une efficacité de 98%. L’adsorption de 12AA à la surface de l’acier suit le
modèle de l’isotherme de Langmuir. L’énergie de Gibbs correspondante de cette
adsorption a été calculée comme étant environ −26 (sans CO ) et −28 kJ mol−1 (saturée
2
en CO et 0.5 M HCl). Ceci a indiqué que la formation de la couche (composée d’une
2
épaisseur) est amorphe et que cela est causé par la répulsion engendrée avec les groupes
voisins de même charge positive et par le caractère très hétérogène de la surface. L’étude
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RÉSUMÉ
a aussi démontré que le 12AA peut être très efficace contre la corrosion de l’acier
carbone et ce avec une grande variété d’électrolytes et d’acides. Il est important de
mentionner que l’inhibiteur est inefficace contre l’acide nitrique et sulfurique.
L’inhibiteur peut aussi réduire la corrosion lorsque le pH est élevé, mais voit son
efficacité réduite dans ces conditions en raison de l’augmentation de sa solubilité.
Finalement, le 12AA semble aussi performant avec toutes les rugosités.
L’effet et le type de flux d’une solution de HCl saturée en dioxyde de carbone fut
aussi étudié avec l’aide d’une électrode à disque rotatif. L’inhibiteur 12AA (3mM) se
démontra très performant à contrer la corrosion dans un espace carré et avec un électrode
à disque rotatif. Cependant, lorsque la concentration fut réduite à 1mM la performance de
l’inhibiteur diminua et son nombre de Reynolds fut augmenté. Ceci fut causé par
désorption de 12AA de la surface de l’acier. Cet inhibiteur ne fut donc pas efficace à
protéger l’acier carbone dans ces conditions.
L’étude de l’inhibiteur 11AA donna des résultats similaires. Cependant, la
protection de l’acier carbone fut plus efficace qu’avec le 12AA à cause que le 11AA est
capable de couvrir une surface plus importante tout en faisant une couche plus compacte.

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AKNOWLEDGMENTS
AKNOWLEDGMENTS

I would like to dedicate this thesis to my wife, kids, grandmother and parents and
especially my father who did not live long enough to see this day but his memories will
always be with me. I wouldn’t have been able to complete my study without the
encouragements and emotional supports of all of them.

I would like to express my sincere gratitude and deepest appreciation to my
research supervisor, Professor Sasha Omanovic, for his broad knowledge, support, kind
attitude, research guidance, suggestions and inspiration throughout the period of this
work that made possible the successful completion of this thesis.

I wish to thank all my colleagues in the research group, Arash Shahryari, Jeff
Harvey, Irshad Ali, Nehar Ullah, Hesam Dadafarin, Mahdi Dargahi, Sajad Habibzadeh,
Mario Alberto Ascencio, Diana Nakad Rodríguez, Simon Kwan, and Steven Yasmine for
all the help they provided during my research. I would like to express my sincere
gratitude to Laurent-Pierre Scheffer for his help to translate the abstract to French.

I would like to express my gratitude for the financial support from the higher
education ministry and Almergheb University (Khoms-Libya). Special thanks to all the
teachers and professors who have taught me during my study.

Finally, I would like to express my sincere thanks to all my brothers, sisters,
relatives, and friends for their continued inspiration, encouragements, and support.

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TABLE OF CONTENTS

TABLE OF CONTENTS

ABSTRACT ......................................................................................................................... i
RÉSUMÉ ........................................................................................................................... iii
AKNOWLEDGMENTS ......................................................................................................v
TABLE OF CONTENTS ................................................................................................... vi
LIST OF FIGURES ........................................................................................................... ix
LIST OF TABLES ......................................................................................................... xviii

CHAPTER 1: INTRODUCTION ........................................................................................1

CHAPTER 2: BACKGROUND AND LITERATURE REVIEW ......................................6
2.1 Corrosion...............................................................................................................7
2.1.1 Definition of Electrochemical Corrosion .................................................... 7
2.1.2 Anodic Reaction.......................................................................................... 7
2.1.3 Cathodic Reaction ....................................................................................... 8
2.2 General or Uniform Type of Corrosion ................................................................9
2.3 Corrosion in the Oil Industry ..............................................................................10
2.3.1 Sweet and Sour Corrosion in the Oil Industry .......................................... 10
2.3.1.1 Carbon Dioxide (Sweet) Corrosion ................................................... 10
2.3.1.2 Hydrogen Sulfide (Sour) Corrosion ................................................... 11
2.3.1.3 Oxygen ............................................................................................... 12
2.4 Methods of Corrosion Protection ........................................................................13
2.4.1 Proper Selection of Materials .................................................................... 13
2.4.2 Coatings, Linings and Non-Metallic Piping ............................................. 13
2.4.3 Cathodic protection ................................................................................... 14
2.4.4 Corrosion inhibitors .................................................................................. 14
2.5 Classification of corrosion inhibitors ..................................................................15
2.5.1 Anodic corrosion inhibitors ...................................................................... 15
2.5.2 Cathodic corrosion inhibitors .................................................................... 16
2.5.3 Mixed corrosion inhibitors ........................................................................ 16
2.6 Toxicity of corrosion inhibitors ..........................................................................16
2.7 Self-assembled monolayers (SAMs)...................................................................17
2.8 Environmentally friendly inhibitors ....................................................................21
2.9 Selection of the corrosion inhibitor.....................................................................22
2.10 Corrosion inhibitors in the oil industry ...............................................................23
2.11 Adsorption of corrosion inhibitors ......................................................................27
2.11.1 Adsorption isotherms ................................................................................ 28

CHAPTER 3: OBJECTIVES .............................................................................................31
3.1 Main objective ....................................................................................................32
3.2 Specific objectives ..............................................................................................32

CHAPTER 4: EXPERIMENTAL METHODS AND MATERIALS ................................34
4.1 Chemicals and solutions .....................................................................................35
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TABLE OF CONTENTS

4.2 Electrochemical/corrosion cell............................................................................36
4.2.1 Square duct................................................................................................ 37
4.2.2 Rotating disk electrode ............................................................................. 37
4.2.3 Jet impingement ........................................................................................ 38
4.3 Experimental Equipment ....................................................................................40
4.4 Experimental Methodology ................................................................................41

CHAPTER 5: RESULTS AND DISCUSSION .................................................................43
5.1 Potentiodainamic polarization of CS in 0.5 M HCl ............................................44
5.2 Interaction of 12AA with a CS surface in oxygen-free electrolytes ...................47
5.2.1 Open circuit potential measurements ........................................................ 48
5.2.2 Electrochemical impedance spectroscopy measurements ........................ 49
5.2.3 Tafel polarization measurements .............................................................. 54
5.2.4 Weight-loss measurements ....................................................................... 57
5.2.5 Compilation of EIS, Tafel and weight-loss measurements ....................... 58
5.2.6 PM-IRRAS measurements ........................................................................ 63
5.2.7 Adsorption isotherm.................................................................................. 65
5.2.8 Effect of time ............................................................................................ 68
5.2.9 Effect of HCl concentration ...................................................................... 72
5.2.10 Effect of temperature ................................................................................ 74
5.2.11 Effect of pH ............................................................................................... 78
5.2.12 Post-application of 12AA: inhibition of further corrosion of an already
corroded CS surface .................................................................................. 80
5.2.13 Effect of surface roughness ....................................................................... 82
5.2.14 Effect of corrosive solution ....................................................................... 84
5.3 Investigation of interaction of 12AA with a CS surface in carbon dioxide
containing electrolytes - “sweet corrosion” ........................................................88
5.3.1 EIS measurements ..................................................................................... 88
5.3.2 Tafel polarization measurements .............................................................. 93
5.3.3 Weight-loss measurements ....................................................................... 95
5.3.4 Influence of the presence of CO on the corrosion rate ............................ 98
2
5.3.5 12AA adsorption isotherm ...................................................................... 100
5.3.6 Effect of time on corrosion inhibition efficiency .................................... 102
5.3.7 Effect of temperature .............................................................................. 105
5.3.8 Effect of pH ............................................................................................. 109
5.3.9 Mechanism of corrosion inhibition and the surface structure of the 12AA
monolayer in the CO -containing electrolyte ......................................... 110
2
5.3.10 Application of 12AA in CO -saturated 0.5 M HCl containing 10% of
2
diesel oil .................................................................................................. 113
5.3.11 Effect of electrolyte flow on the performance of 12AA ......................... 115
5.3.11.1 Square duct ................................................................................. 115
5.3.11.2 Rotating disk electrode ............................................................... 122
5.3.11.3 Jet impingement .......................................................................... 126
5.4 Investigation of 11AA as corrosion inhibition for CS ......................................130
5.4.1 Effect of 11AA concentration ................................................................. 130
5.4.2 Effect of Time ......................................................................................... 132
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5.4.3 Effect of temperature .............................................................................. 134
5.4.4 Adsorption isotherm................................................................................ 136
5.4.5 Effect of pH ............................................................................................. 138
5.4.6 Effect of surface roughness ..................................................................... 139
5.4.7 Verification of 11AA corrosion inhibition efficiency in a carbon dioxide
containing electrolyte - “sweet corrosion” .............................................. 142
5.5 Investigation of the corrosion inhibition efficiency of a mixture of 11AA and
12AA .................................................................................................................143

CHAPTER 6: CONCLUSIONS ......................................................................................144
6.1 Summary and conclusions ................................................................................145
6.2 Original contributions .......................................................................................147
6.3 Suggestions for Future Work ............................................................................148

REFERENCES ................................................................................................................149

APPENDICES .................................................................................................................160
Appendix A ......................................................................................................................160

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LIST OF FIGURES

LIST OF FIGURES
Fig. 2.1: 11-Aminoundecanoic acid (11AA) is a typical long-chain alkyl
molecule that can form a SAM: Head group (COOH); chain
(−CH ) ; tail group (NH ). ……………………………...……...…… 18
2 10 2
Fig. 2.2: General chemical structure of imidazoline. ………………………….. 24
Fig. 4.1: 12-Aminododecanoic acid (12AA). …………………………………. 35
Fig. 4.2: 11-Aminoundecanoic acid (11AA). …………………………………. 35
Fig. 4.3: Schematics of a CS working electrode used in this work. …………... 36
Fig. 4.4: Schematics of experimental setups (configurations) used in corrosion
rate measurements under flow conditions (a) square duct, (b-1)
rotating desk electrode (RDE), and (c) jet impingement. CS = carbon
steel working electrode, MSE = reference electrode, SS = 316L
stainless steel counter electrode, PVC = polyvinyl chloride tip
(holder). (b-2) Solution flow pattern close to the RDE surface,
viewed from below and (b-3) view from the side, showing how the
solution is pumped towards the disc, and then thrown outwards. …… 39
Fig. 4.5: Schematics an in-situ electrochemical PM-IRRAS cell. …………….. 41
Fig. 4.6: Schematics of a CS coupon used in weight loss measurements. ……. 42
Fig. 5.1: Linear polarization voltammogram of the CS electrode in 0.5 M HCl
recorded at a scan rate of 10 mV s−1, in a positive-going direction.
Temperature = 295 K. ……………………………………………….. 45
Fig. 5.2: Pourbaix diagram for iron at 298 K. ………………………………… 46
Fig. 5.3: Variation of the open circuit potential (OCP) with time for a CS
electrode immersed in 0.5 M HCl, in the absence and presence of
various concentrations of 12AA. (1) 0 mM, (2) 1 mM, (3) 2 mM, (4)
3 mM, and (5) 4 mM 12AA. Temperature = 295 K. ………………… 49
Fig. 5.4: Nyquist plot of CS recorded at different 12AA concentrations in 0.5
M HCl. (◊) 0 mM, () 1 mM, (□) 2 mM, (O) 3 mM and () 4 mM
12AA. The inset shows high-frequency data of the 4 mM 12AA
spectrum. Symbols are experimental data and solid lines represent
the simulated (modeled) spectra. In the inset, the dashed line
represents a simulated spectrum obtained by using the one-time-
constant EEC in Fig. 5.5a, while the solid line represents the
simulated spectrum obtained by using the two-time-constant EEC in
Fig. 5.5b. The spectra were recorded at OCP one hour after
stabilization of the CS electrode at OCP. Temperature = 295 K. …… 50

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