Some imidazoline derivatives as corrosion inhibitors

Article abstract of DOI:10.1007/s11743-009-1168-9

In this study, cationic surfactants having different alkyl chain lengths were prepared by amidation of lauric, myristic, palmitic, stearic, oleic acids with diethylene triamine. The products were quaternized using chlo-roacetic acid. The chemical structure of the prepared compounds was elucidated using different spectroscopic techniques. The critical micelle concentration (CMC) and the free energy of the micellization and adsorption of these compounds were determined by surface tension and conductivity measurements. The products were evaluated as surface-active agents as well as corrosion inhibitors for steel alloy in 1 M hydrochloric and sulfuric acid, the results indicate that these materials have a high efficiency as corrosion inhibitors and as surface active agents. These results were correlated with the chemical structure of the prepared compounds. AOCS 2009.

Full text of DOI:10.1007/s11743-009-1168-9

J Surfact Deterg (2010) 13:247–254
DOI 10.1007/s11743-009-1168-9
ORIGINAL ARTICLE
Some Imidazoline Derivatives as Corrosion Inhibitors
•
Ismail Abdelrhman Aiad A. A. Hafiz
•
•
M. Y. El-Awady A. O. Habib
Received: 17 March 2009 / Accepted: 7 September 2009 / Published online: 10 December 2009
Ó AOCS 2009
Abstract In this study, cationic surfactants having dif-
ferent alkyl chain lengths were prepared by amidation of
lauric, myristic, palmitic, stearic, oleic acids with diethyl-
ene triamine. The products were quaternized using chlo-
roacetic acid. The chemical structure of the prepared
compounds was elucidated using different spectroscopic
techniques. The critical micelle concentration (CMC) and
the free energy of the micellization and adsorption of these
compounds were determined by surface tension and con-
ductivity measurements. The products were evaluated as
surface-active agents as well as corrosion inhibitors for
steel alloy in 1 M hydrochloric and sulfuric acid, the results
indicate that these materials have a high efficiency as
corrosion inhibitors and as surface active agents. These
results were correlated with the chemical structure of the
prepared compounds.
organic compounds is related to their adsorption properties.
Adsorption depends on the nature and the state of the metal
surface, on the type of corrosive medium and on the
chemical structure of the inhibitor [3]. Studies report that
the adsorption of the organic inhibitors mainly depends on
some physicochemical properties of the molecule, related
to its functional groups, to the possible steric effects and
electronic density of donor atoms; adsorption is supposed
also to depend on the possible interaction of p-orbitals of
the inhibitor with d-orbitals of the surface atoms, which
induce greater adsorption of the inhibitor molecules onto
the surface of carbon steel, leading to the formation of a
corrosion protecting film [4].
Different imidazoline derivatives are employed as steel
corrosion inhibitors. Even though they have been specially
employed in the oil industry, only recently have many
studies been undertaken to understand how they work
[5–8]. Ramachandran et al. [9], Wang et al. [10], and Cruz
et al. [11] have published important papers concerning the
use of imidazoline derivatives as corrosion inhibitors.
These gtive rise to some key questions regarding the
structure–performance relationships of imidazolines and
corresponding amines, they are: (a) the role of the hydro-
carbon chain relative to the imidazoline head group and the
pendant amine group in film formation; (b) the thickness of
the imidazoline film; (c) the stability of the imidazolines
film; (d) the solution composition and (e) hydrolysis of
imidazoline. Some authors have found that amide and
imidazoline have the same efficiency as corrosion inhibi-
tors [12].
Keywords Cationic surfactants ꢀ
Imidazoline derivatives ꢀ Corrosion inhibitors
Introduction
Corrosion of metals is one of the most important and
challenging problems in industry. Therefore, the develop-
ment of inhibiting films able to protect the underlying
metal from corrosion has been the subject of numerous
investigations [1, 2]. The corrosion inhibition efficiency of
The aim of this work was the preparation of some imi-
dazoline derivatives and evaluating them as surface active
agents and as corrosion inhibitors for low carbon steel in
acid media and correlating these properties with their
chemical structure.
I. A. Aiad (&) ꢀ A. A. Hafiz ꢀ M. Y. El-Awady
Egyptian Petroleum Research Institute (EPRI), Cairo, Egypt
e-mail: yiaiad@yahoo.co.uk
A. O. Habib
Faculty of Engineering, Ain-Shams University, Cairo, Egypt
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J Surfact Deterg (2010) 13:247–254
FirstTM V2.01 software (Egyptian Petroleum Research
Institute).
3. 1H NMR which was measured in DMSO-d6 by Spect
Varian, GEMINI 200 (1H 200 MHz). (Micro Analyt-
ical Center, Cairo University).
Materials and Experimental
Synthesis of the Imidazoline Derivatives
The imidazoline derivatives were synthesized by the
reaction of lauric, myristic, palmitic, stearic and
oleic acid, (0.1 mol) with diethylenetriamine (DETA),
(0.1 mol) in xylene (100 mL) as the solvent [13]. The
synthesis process was carried out in a three-necked flask
with thermometer, stirrer and water splitter. The reaction
mixture was refluxed at 140 °C for 2.5 h. When the
splitting water was close to the theoretically generated
amount, the solvent was removed by distillation, then the
mixture was warmed up to 200 °C and reacted for 4 h at
a constant temperature. When the splitting water was
close to the amount demanded, the mixture was cooled
down to 70 °C and 30% (wt) chloroacetic acid was
slowly dripped into the reactor. Finally, it was refluxed at
80 °C for 2 h.
Surface Properties Measurements
The CMC for various imidazoline derivatives were deter-
mined from surface tension measurements of the prepared
compounds solutions at 30 °C using a Du-Nouy tensiom-
eter (Kru¨ss K6).
Corrosion Inhibition Measurements
Two techniques were used to determine the inhibition
efficiency of the prepared compounds—the electro-polari-
zation and weight loss.
The diethylenetriamine (DETA), chloroacetic acid were
of analytical grade, and the fatty acids and the xylene were
of technical grade.
The Electro-Polarization Technique
The electro-polarization technique was employed using a
Radiometer analytical Potentiostat PGZ 3O1 (Volta Master
4). The concentration range of imidazoline derivatives
employed was 10 to 200 ppm in 1 M HCl. The corrosion
inhibition tests were carried out on electrodes cut from
sheets of low carbon steel. Steel strips containing 0.09% P,
0.38% Si, 0.01% Al, 0.05% Mn, 0.21% C, 0.05% S and the
remainding iron were used for the measurement of weight
loss and electrochemical studies. The surface preparation
of the specimens was carried out using emery paper, grades
600 and 1,200; they were degreased with ethanol and dried
at room temperature before use. The solutions (1 M HCl)
were prepared by dilution of analytical reagent grade 37%
HCl with doubly distilled water.
The fatty acids and DETA were reacted to form the
corresponding amides which were reacted with chloro-
acetic acid to generate the corresponding quaternary
ammonium salt, as shown in the following Scheme 1:
Confirmation of the Chemical Structure
The chemical structure of the synthesized compounds was
confirmed by:
1. Elemental analyses which were carried out in the
Micro Analytical Center, Cairo University.
2. FTIR spectra using an ATI Mattson Infinity seriesTM
,
Bench top 961 spectrophotometer controlled by Win
Scheme 1 Reaction sequence
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249
Weight Loss Technique
Table 1 The elemental analysis of the prepared imidazoline
compounds
A weight-loss technique [ASTM G31-72 (Reapproved
2004)] was used to measure the inhibition efficiency of the
prepared imidazoline amphiphiles for low carbon steel in
1 M HCl or 1 M H2SO4 solutions at 25 °C for 72 h. The
dissolved oxygen range was 6–8 ppm. The low carbon
steel specimen was machined into regular shapes of
55.8 cm2 cross-sectional area. The specimens were
sequentially abraded with different emery papers,
degreased with acetone, washed with distilled water and
dried. The corrosive solutions (1 M HCl or 1 M H2SO4) in
the absence and presence of the inhibitors at concentrations
ranging from 50 to 200 ppm were prepared from doubly
distilled water the average weight loss of three coupons
was recorded.
Elem. comp. C (%)
Calc.
N (%)
Cl (%)
Found Calc.
Found Calc. Found
LII
MII
PII
SII
OII
59.75 60.56
11.61 8.41
9.82
9.11
8.5
7.72
7.44
7.88
7.52
7.66
60.22 58.69
63.23 60.78
64.64 62.21
64.93 59.87
1,078 7.28
10.06 6.61
9.42
9.47
6.88
7.18
7.97
8.00
Table 2 The FTIR bands (cm-1) of the function groups of prepared
compounds
–C–H CH2,
CH3
C=N
Imidaz.
ring
N–H
bending
(CH2)n
skeletal
LII
MII
PII
SII
OII
2,922
2,919
2,915
2,922
2,916
1,631
1,635
1,636
1,637
1,640
1,601
1,602
1,602
1,600
1,602
1,549
1,549
1,548
1,546
1,540
716
717
711
716
716
Results and Discussion
Structure Confirmation
The chemical structures of the prepared imidazoline
derivatives were confirmed by different techniques.
carbon of carboxylic acid (1.59), CH2 attached to the
nitrogen of NH2 group (1.99). CH2 attached to the carbon
of the imidazoline ring (2.24 ppm), CH2 attached to the
nitrogen of the imidazoline ring (2.66, 2.75, 2.8 ppm), CH2
attached to the carbon of the imidazoline ring 2.36, 2.37
and 2.39 ppm), CH2 in the ring attached to the t nitrogen
and CH2 in the ring attached to Q nitrogen (3.61,
3.616 ppm), H of carboxylic group (5.33 ppm), H of NH2
group (7.27 ppm).
Elemental Analysis
The chemical structure of the synthesized surfactants based
on imidazoline as shown in Fig. 1 were confirmed using
micro elemental analyses, Table 1.
FTIR Spectroscopy
The prepared imidazoline derivatives showed different
FTIR bands as shown in Table 2, which indicates that they
were prepared by the right method.
Surface Parameters
Surface Tension (c) and Critical Micelle Concentration
NMR Spectroscopy
Figure 3 represents the variations of surface tension versus
the solution concentration of the synthesized surfactants
(LII, MII, PII, SII and OII) at 30 °C. It’s clear that the
surface tension decreased as the solution concentration
increased. Surfactant molecules first adsorbed at the liquid/
air interface until the surface of the solution was com-
pletely occupied. Then, the excess molecules tended to
self-aggregate in the bulk to form micelles. From the
intersection points of c versus solution concentration
curves, the critical micelle concentration (CMC) was
determined, Table 3. The highest CMC value was observed
for OII (2.5 9 10-4), while, the lowest value was observed
for MII 0.7 9 10-4 at 30 °C. This may be due to the dif-
ference in the alkyl chain lengths. It is clear that as the
alkyl chain length increased the hydrophobicity of the
molecule increased, this led to a decrease in the CMC value
As shown in Fig. 2, the 1H-NMR spectra of OII compound
show the following signals:
CH3 (0.85, 0.87 and 0.94 ppm, (CH2)n (1.26 ppm). CH2
attached to the Q nitrogen of the imidazoline ring and the
Fig. 1 The chemical structure of imidazoline derivatives (R = C11,
C13, C15, C17 and unsaturated C17)
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1
Fig. 2 The H-NMR spectra of
C18 unsaturated imidazoline
derivatives
Fig. 3 Surface tension of
aqueous solutions of different
compounds versus
concentration
of the molecule, which can be referred to the differences in
their structures where, the OII compound behave nearly the
same as PII.
distilled water is defined as its effectiveness (pcmc). The
most efficient is the one that gives the greatest lowering in
surface tension at the critical micelle concentration (CMC).
According to the values of the effectiveness shown in
Table 3, SII is found to be more efficient, it achieve the
maximum reduction of the surface tension at its CMC.
The maximum surface excess is expressed as the con-
centration of surfactant molecules at the interface per unit
area (Cmax). Meanwhile the minimum surface area is
Effectiveness (pcmc), Maximum Surface Excess (Cmax
and Minimum Surface Area (Amin
)
)
The difference between the surface tension value of the
surfactant solution at its CMC and that of corresponding
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251
Table 3 Surface properties of prepared imidazoline surfactants
Comp.
S.T. (mN/m)
CMC 9 10-4
PCMC (mN/m)
Cmax (mol cm-291010
)
Amin (nm)
ꢂDGꢃmic
ꢂDGꢃads
LII
MII
PII
SII
OII
43
45
54
56
53
1
38
1.42
1.2
1.12
1.38
2.2
23.2
24.1
21.8
21.8
20.9
25.8
26.6
24.9
24.4
24.4
0.7
1.7
2.1
2.5
31
23.5
22
0.755
0.702
0.77
2.37
2.15
27
defined as the area occupied by each molecule in nm2 at the
interface. Using the adsorption law of molecules at the
interfaces, (Cmax) values were calculated according to
the following equation.
Corrosion Inhibition
The inhibition efficiency (g) of the synthesized imidazoline
can be calculated from the weight loss in the corrosive
medium according to the following equation:
ꢀ
ꢁꢂ
dc
d log C
Cmax
¼
ð8:3 ꢁ 107 ꢁ RTÞ
ð1Þ
g ð%Þ ¼ ½ðW0 ꢂ WÞ=W0ꢄ ꢁ 100
ð5Þ
The W and W0 are the weight loss in the steel’s coupon
in the presence and absence of inhibitor, respectively.
Tables 4, 5, and 6 represent the variation of inhibition
efficiencies of the synthesized inhibitors in different acidic
media for low carbon steel with a wide range of doses
(from 50 to 200 ppm). It is clear that the inhibition
efficiency towards corrosion process increases by
increasing the inhibitor dose. The maximum corrosion
inhibition was found at 200 ppm for all the synthesized
inhibitors in 1 M HCl or H2SO4 solutions. Increasing
the inhibition efficiencies with increasing the concentration
of the targeted inhibitors is mainly due to the adsorption of
those inhibitors on the metal surface. The adsorption
where dc/d log C is the surface pressure. R, the universal
gas constant and T, the absolute temperature. Regarding the
results listed in Table 3 we can see that Cmax was decreased
by increasing the alkyl chain length so that the lowest value
is for SII which may be attributed to the dissolution of
molecules from the interface and their dissolution in the
aqueous phase [14], the OII compound behaves nearly the
same as PII.
The minimum surface area occupied by each surfactant
molecules at the air\water interface (Amin) is calculated
according to the following equation.
Amin ¼ 1=N Cmax
ð2Þ
where (Amin) values increase with the increase in the alkyl
chain length, the OII compound behaves nearly the same as
PII.
Table 4 The corrosion inhibition efficiency of the prepared imidaz-
oline surfactant at different doses (weight loss method) in 1 M HCl
Standard Free Energies of Micellization and Adsorption
À
Á
ꢂDGꢃmic; ꢂDGꢃads
Dose (ppm)
Eff. (%)
LII
MII
PII
SII
OII
Understanding the process of micellization and adsorption
are important for explaining the effects of structural and
environmental factors on the values of the CMC and to
predict the effect on the CMC of new structural and
environmental variations, ꢂDGꢃmic and ꢂDGaꢃds have played
an important role in such understanding. The ꢂDGꢃmic and
ꢂDGꢃads are given by:
50
35
60
85
89
34
56
75
86
46
62
79
84
43
68
85
94
33
57
72
79
100
150
200
ꢂDGꢃmic ¼ RT ln CMC
ð3Þ
Table 5 The corrosion inhibition efficiency of the imidazoline sur-
factants (weight loss method) in 1 M H2SO4 solution
DGꢃads ¼ DGmꢃ ic ꢂ 6:023 ꢁ 10ꢂ1pcmc Amin
:
ð4Þ
Dose (ppm)
Eff. (%)
LII
As shown in Table 3 the ꢂDGꢃmic and ꢂDGaꢃds values were
always negative, indicating the spontaneity of these two
processes. However, there was a greater increase in the
negativity of ꢂDGaꢃds than that of ꢂDGmꢃ ic, indicating the
tendency of the molecules to be adsorbed at the interface
water/air or water/metal [15].
MII
PII
SII
OII
50
33
77
85
91
61
68
83
85
22
31
32
36
9
21
36
48
–
40
52
59
100
150
200
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(FeH?)ads ? e- ? (FeH)ads
Table 6 The corrosion inhibition efficiency of compounds PII, SII
and OII in 10% ethanol 1 M H2SO4 solution (weight loss method)
(FeH)ads ? H? ? e- ? Fe ? H2
Meanwhile, amine groups are protonated in the acidic
medium forming the protonated amine (–N?H2C–) which
adsorbed physically to the negative species formed during
steel dissolution (FeCl-). The same thing occurred with
H2SO4.
Dose (ppm)
Eff. (%)
PII
10Eth
SII
10Eth
OII
10Eth
50
22
31
32
36
30
50
73
75
9
21
36
48
40
53
75
82
–
40
52
59
30
72
83
81
100
150
200
The experimental results of the corrosion processes of
the low carbon steel in the HCl media showed high inhi-
bition efficiencies of the synthesized inhibitors, which were
increased by increasing the addition dosage of the inhibitor.
The efficiency of the LII was 35, 60, 85 and 89% at con-
centrations of 50, 100, 150 and 200 ppm. Whereas, the
maximum inhibitions at concentration of 200 ppm in HCl
media were 89, 86. 84, 94 and 79%, for LII, MII, PII, OII
and SII, respectively.
mechanism of the inhibitor molecules at metal/solution
interfaces is dependent on the chemical structure of the
inhibitors and their response towards the environment and
governed by one or more of the following factors:
Analyzing the data of corrosion inhibition reveals that
the inhibitors which have unsaturated alkyl chain imidaz-
oline exhibit higher efficiencies than those obtained from a
saturated one.
1. Electrostatic attraction between the charged inhibitor
molecules and the metal surface.
2. Interaction between the p-electrons in the inhibitor
molecules and the metal.
The above results were confirmed by the thermody-
namic parameters of the micellization and adsorption
process, in which it is found that the more negative ꢂDGmꢃ ic
and ꢂDGꢃads corresponding the more corrosion efficiency.
In the case of 1 M H2SO4 as shown in Tables 5 and 6 the
efficiency of these compounds is dependent on their solu-
bility, the shorter the alkyl chain is the more water soluble
and the more efficient it is. So, for the long chain derivatives
we added 10% (V/V) ethanol to the corrosive media in order
to enhance the solubility. As shown in Table 6 addition of
the ethanol enhanced the inhibition efficiency from 36 to 75
for PII, from 48 to 82 for SII and from 59 to 81 for OII.
3. Interaction between uncharged moieties in the inhibitor
molecules and the metal surface.
The chemical structure of the synthesized inhibitors
comprises unsaturation sites (conjugation within imidazo-
line rings) and heteroatom in the amine groups.
The hydrophobic part of the alkyl fatty acid acts as the
uncharged moiety which forms the thin film preventing
chloride ions from the metal surfaces.
The proposed mechanism of the steel dissolution in the
acidic medium was described in the following equations
[16]:
Fe ? Cl- ? (FeCl-)ads
(FeCl-)ads ? (FeCl)ads ? e-
Tafel Polarization
(FeCl)ads ? FeCl? ? e-
FeCl? ? Fe?2 ? Cl-
Figure 4 show a typical record of Tafel polarization mea-
surements for low carbon steel in 1 M HCl in the absence
Fe ? H? ? (FeH?)ads
Fig. 4 The polarization curves
of compound PII at 1 M HCl
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253
Table 7 The Tafel polarization parameter values for the corrosion of mild steel in 1 M hydrochloric acid containing different concentrations of
the PII
Dose (ppm)
-Ecorr (mv)
icorr (mA/cm2)
Rp (ohm cm2)
Ba (mv)
Bc (mv)
Corr rat (lm/y)
Eff. (%)
0.0
10
512.1
529
0.052
0.0338
0.014
0.013
0.011
0.012
0.008
585.8
1,240
1,790
2,250
2,610
1,930
3,160
97.5
140.3
131.6
154.5
153
-119.9
-142.0
-139.1
-142.2
-152.9
-127
607.7
394.8
169.9
157.4
135
0.0
35
20
542.8
547.8
556.6
546.9
568.9
72
30
74
50
78
100
200
124.8
148
148.8
97.6
76
-142
84
and presence of the compound PII. As shown in Table 7 the
corrosion current density (icorr) of bare low carbon steel
electrode was 0.0520 mA cm-2 and has a corrosion rate of
607.7 lm/Y. It is clear that addition of PII to the corrosive
media decreases the corrosion current density and corrosion
rate. This decreasing is depending on the dosage of the PII.
It is clear that the addition of the PII to acid media
affected both the cathodic and anodic parts of the curves.
Therefore, these compounds behaved as mixed inhibitors.
The corrosion potential shifted to negative direction more
markedly. This shows that the effect of inhibitors on the
cathodic reaction is more observable than on the anodic
reaction. Increasing the concentration of the PII caused the
corrosion potential to be more inert.
properties against the corrosion of low carbon steel in 1 M
HCl and H2SO4 solutions at room temperature, and the
inhibition efficiency is increased by increasing the con-
centration of the inhibitors. However, the corrosion inhi-
bition of the prepared compounds depends mainly on their
solubility.
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Table 7 lists the polarization parameters for corrosion of
low carbon steel in the presence at different concentrations
of the investigated compounds. The corrosion inhibition
efficiency (gP%) is defined as:
ꢀ
ꢁ
i0corr
gP%
¼
1 ꢂ
ꢁ 100
ð6Þ
icorr
The i0corr and icorr are the corrosion current densities of
corrosive medium with and without inhibitor, respectively.
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increasing the concentration of the inhibitors. The depo-
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addition of the inhibitors indicates that not only was dis-
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oxygen (we did not try to purge the dissolved oxygen out of
the cell) was also suppressed. Therefore, the imidazoline
derivatives cause a decrease in the corrosion rate of steel in
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Amal A. Hafiz received her MSc in Organic Chemistry (1992) and
PhD in Applied Organic Chemistry (1999) from University College
for Women, Ain Shams University, Cairo, Egypt. She is an Associate
Professor at the Egyptian Petroleum Research Institute (Surfactants
Laboratory) since 2003. Her research interest focuses on the synthesis
and application of new surface active agents, particularly in
Environmental Chemistry.
15. Rosen MJ (1989) Surface and interfacial phenomena, vol 2.
Wiley, New York
16. Shokry H, Yuasa M, Sekine I, Issa RM, El-Baradie HY, Gomma
GK (1998) Corrosion inhibition of mild steel by Schiff base
compounds in various aqueous solutions: part 1. Corrosion Sci
40:2173–2186
Moshira Y. El-Awady received her BS (1978), MSc (1988) and PhD
(2000) from the College of Science at Ain Shams University, Cairo,
Egypt. She is now an Assistant Professor at the Egyptian Petroleum
Research Institute (Surfactants Laboratory).
Amro O. Habib recieved his BS (1997), MSc (2001) and PhD (2004)
from the collegue of Engineering at Ain Shams University, Cairo,
Egypt, where he is now a lecturer member of the Engineering Faculty.
Author Biographies
Ismail Abdelrhman Aiad received his PhD in Physical Chemistry
from the College of Sciences, Zagazig University, Egypt (1998). He is
a member in Board of the Chemical Services and Development
Center for Oil Field Chemicals, and an Assistant Professor at the
Egyptian Petroleum Research Institute (Surfactants Laboratory). His
research deals with the synthesis and applications of surfactant
materials.
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