International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(8), pp. 166-178, 2013 Available online at http://www.ijsrpub.com/ijsres

ISSN: 2322-4983; ©2013 IJSRPUB

http://dx.doi.org/10.12983/ijsres-2013-p166-178

166

Full Length Research Paper

Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the

Corrosive Performance of Carbon Steel in CO2-Saturated Brine

Vagif M. Abbasov1, Hany M. Abd El-Lateef

1, 2*, Sevinc A. Mamedxanova

1, Leylufer. I. Aliyeva

1, Teyyub A.

Ismayilov1, Musayev J. Ilham

1, Orkhan A. Aydamirov

1, Fariz A. Amirov

1

1Mamedaliev Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, AZ1025 Baku, Azerbaijan

2Chemistry Department, Faculty of Science, Sohag University, 82524 Sohag, Egypt

*Corresponding Author: Hany_shubra@yahoo.co.uk

Received 26 April 2013; Accepted 07 June 2013

Abstract. Two surfactants [sodium and potassium salts of naphthenic acids] were synthesized by liquid-phase oxidation

process of the naphtha fraction of the Baku crude oil and their chemical structure was confirmed by FT-IR spectroscopy. The

surface tension at 298K was measured; the critical micelle concentration (CMC) and some surface active parameters were

calculated. The inhibition efficiency (η%) of these surfactants has been studied by both Linear polarization resistance corrosion

rate and Potentiodynamic polarization measurements at 50 °C. The data showed that, the presence of investigated inhibitors

results a high decrease in the corrosion rate. The inhibition efficiency increases with an increase in the inhibitor dose, getting

maximum inhibition efficiency 99.48% at 100 ppm of potassium salt. The Tafel polarization results indicate that the inhibitors

act as mixed inhibitors. Tafel slopes are approximately constant and independent on the inhibitor concentration. The adsorption

of the inhibitors on the carbon steel surface obeys Langmuir’s adsorption isotherm. The thermodynamic parameters of

adsorption revealed a strong interaction between the inhibitors and the corroding carbon steel surface.

Key words: Petroleum acids, Carbon Steel, surfactants, corrosion inhibition, Carbon Dioxide Corrosion.

1. INTRODUCTION

Corrosion of carbon steel is a significant problem in

the oil and gas production and transportation systems

and causes significant economic loss (Okafor et al.,

2009). CO2 corrosion of carbon steels has been one of

the most common corrosion problems in oil and gas

industry. Carbon dioxide dissolves in the presence of

a water phase, forming carbonic acid, which is

corrosive to carbon steel (Lo´pez et al., 2003a). The

understanding of CO2 corrosion mechanisms under

the effects of many mechanical and environmental

factors, such as flow, temperature, pressure, oil–water

ratio, pH, solution chemistry, and corrosion product

layer, has been of great concern in corrosion field

(Yin et al., 2009).

The use of inhibitors is one of the most practical

methods for protection against corrosion. The

inhibitors, which reduce corrosion on metallic

materials, are inorganic inhibitors, organic inhibitors,

surfactant inhibitors and mixed material inhibitors. Surfactants are special type of organic compounds and

exhibit unique properties due to their amphiphilic

molecule. This is the reason of their wide application

in the field of inhibition of metals against corrosion. A

molecular layer of surfactants is formed as a result of

this attraction with the construction of a hydrophobic

barrier, which prevent the contact of the metal surface

with the environment. The surfactant inhibitors have

many advantages such as high inhibition efficiency,

low price, low toxicity and easy production (Abbasov

et al., 2013a; Abbasov et al., 2013b; Abd El-Lateef et

al., 2012a; Stoyanova et al., 1997; Abdallah et al.,

2009; Joseph and Rajendran, 2001). The adsorption of

the surfactant on the metal surface can markedly

change the corrosion-resisting property of the metal

(Abd El-Lateef et al., 2012b), and so the study of the

relationship between the adsorption and corrosion

inhibition is of great importance.

Salts of naphthenic acids, which are naphthenates,

are widely used as hydrophobic sources of metal ions

in diverse applications. Metal naphthenates

are coordination complexes. They have the formula

M(naphthenate)2 or are basic oxides with the formula

M3O(naphthenate)6. The naphthenates are highly

soluble in organic media, such as paints. They have

industrial applications including

synthetic detergents, lubricants and corrosion

inhibitors (Nora et al., 2005).

In this study, two surfactants (sodium and

potassium salts of naphthenic acids) were synthesized

by liquid-phase oxidation process of

the naphtha fraction of the Baku crude oil. The surface

activities of these surfactants were determined. The

applicability of these surfactants as corrosion

inhibitors for carbon steel were estimated by Linear

polarization resistance corrosion rate and

Abbasov et al.

Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the Corrosive Performance of Carbon Steel

in CO2-Saturated Brine

167

Potentiodynamic polarization measurements in CO2-

saturated 1% NaCl solution at 50 °C.

2. MATERIALS AND METHODS

2.1. Chemical composition of carbon steel alloy

The rotating disk working electrodes for tests were

made of carbon steel grade 080A15 and have an area

of 4.55 cm2

with a chemical composition (wt%) C

0.18%, Si 0.17%, Mn 0.70%, P 0.011%, S 0.03%, Ni

0.0%, Cr 0.01% and Fe balance. The data was

provided by European Corrosion Supplies Ltd

2.2. Synthesis of Surfactant inhibitors

The surfactants used as inhibitors were synthesized in

our laboratory based on petroleum acids. The new

series of the complex surfactants were synthesized

from naphthenic acids isolated from light oil fractions

(Tb= 180-350 °C) (Abbasov et al, 2012c). Two types

from inhibitors were synthesized in high purity by the

following compositions: [R-COONa (I) and R-COOK

(II)]. The chemical structure of the synthesized

surfactants was characterized by using FT-IR,

Spectrum BX spectrometer using KBr disks.

2.3. Preparation of solutions

The aggressive solution, 1% NaCl, was prepared by

dissolving of analytical grade NaCl in distilled water.

The concentration range of the prepared surfactants

was from 25 to 100 ppm used for corrosion

measurements. All inhibitors solutions were prepared

using distilled water.

2.4. Corrosion measurements

The measurements were performed on the rotating

cylinder electrode. This electrode was used for one

time. The reference electrode was Ag/AgCl Electrode

to which all potentials are referred.

Before beginning the experiment, the prepared 1%

- of sodium chloride solution was stirred by a

magnetic stirrer for 60 min in 1000 ml cell. Then this

cell was thermostated at 50 º C for 1 hour under a CO2

pressure of 0.9 bars. The solution was saturated with

carbon dioxide. To remove any surface contamination

and air formed oxide, the working electrode was kept

at−1500 mV (Ag/AgCl) for 5 min in the tested

solution, disconnected shaken free of adsorbed

hydrogen bubbles and then cathodic and anodic

polarization was recorded. ACM Gill AC instrument

connected with a personal computer was used for the

measurements.

2.4.1. Potentiodynamic polarization measurements

The extrapolation of cathodic and anodic Tafel lines

was carried out in a potential range ±100 mV with

respect to corrosion potential (Ecorr) at scan rate of 1

mV/s.

2.4.2. Linear polarization resistance corrosion rate

The LPR method is ideal for plant monitoring offering

an almost instantaneous indication of corrosion rate,

allowing for quick evaluation of remedial action and

minimizing unscheduled downtime. The prepared 1%

- of the solution sodium chloride was stirred by a

magnetic stirrer for 60 min in 4000 ml. The prepared

solution poured into the 4 glass beakers (1000 ml for

each one). Then these beakers were placed on a heater

at 50 º C for 1 hour under a pressure of 0.9 bars. The

solution was saturated with carbon dioxide. After

that, the electrodes were placed in the medium and are

connected through a potentiometer ACM GILL AC.

The surface of working electrode is cleaned by

acetone before using, these electrodes are using for

one time. After 1 hour, except for 1 beaker, the

remaining 3 is fed with the suitable amount of

inhibitor and continued supply of CO2 under pressure

of 0.9 bar until the end of the experiment.

The potential of the working electrode was varied

by a CoreRunning programme (Version 5.1.3.)

through an ACM instrument Gill AC. The

CoreRunning programme converts a corrosion current

in mA/cm2 to a corrosion rate in mm/year. A

cylindrical carbon steel rod of the composition

080A15 GRADE STEEL was used as a working

electrode. Gill AC technology allows measure DC and

AC signals using standard Sequencer software. A

small sweep from typically –10 mV to +10 mV at 10

mV/min around the rest potential is performed.

2.5. Surface tension measurements

The surface tensions were determined by DuNouy

Tensiometer, Kruss Type 8451 and the temperature

was maintained precisely at 25 °C. Critical micelle

concentration (CMC) values of surfactants were

determined, according to the break points in plots of

the surface tension versus ln molar concentration of

investigated surfactants.

3. RESULTS AND DISCUSSION

3.1. Chemical structure of the synthesized

surfactants

The FT-IR spectrum of the naphthenic acid, shows a

broad OH stretch found at 3200-2700 cm-1

; the strong

International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(8), pp. 166-178, 2013

168

signal at 1712 cm-1

was due to a carbonyl group

(C=O). The strong signal at 1289 cm-1

was due to a C-

O stretch; the signal at 1369 cm-1

was due to a C-O-H.

The FT-IR absorption spectra of inhibitor II

confirmed that, the disappearance of OH band of acid

(broad band), this confirmed that, the replacement of

H atom in carboxylic group by K atom to form –

COOK. FTIR spectra confirmed the expected

functional groups in the synthesized anionic

surfactant.

3.2. LPR corrosion rate

The linear- polarization-resistance (LPR) corrosion

rate bubble-test method involves evaluating the

corrosion of a given metal in simulated brine saturated

with CO2 at a temperature equivalent to that in the

field. During the test, CO2 gas is sparged continuously

into the test solution. The rate of corrosion is

determined instantaneously with the LPR corrosion

rate technique, in which a small direct-current voltage

is applied to a pair of identical electrodes and the

resultant current is measured.

Figure 1 shows that, the change in corrosion rate

(CR) with time for carbon steel in CO2-saturated 1%

NaCl solution containing different concentrations

form inhibitor II (K-salt) at 50 °C. The inhibitor was

added after 1 hour of exposure because at this time the

corrosion potential got stable, allowing the

measurement of the CR prior the injection of the

inhibitor. The initial corrosion rate, without inhibitor,

was measured to be between 3.45 and 5.03 mm y-1

. It

can be observed from Figure 1 that, the CR, in the

absence of inhibitor, tends to increase with time. The

increase in CR has been attributed to the galvanic

effect between the ferrite phase and cementite (Fe3C)

which is a part of the original steel in the non-oxidized

state and accumulates on the surface after the

preferential dissolution of ferrite (α-Fe) into Fe2+

(Staicopolus, 1963). Fe3C is known to be less

active than the ferrite phase. Therefore, there is a

preferential dissolution of ferrite over cementite,

working the former as the anode and latter as the

cathode, favoring the hydrogen evolved reaction

(HER) during the corrosion process (Crolet et al.,

1998; Videm et al., 1996).

Variation of the corrosion rate for inhibitor II at

different concentrations is presented in Figure 1.

Corrosion parameters were calculated on the basis of

LPR corrosion rate test. The inhibition efficiency (η

%) and surface coverage (θ) were calculated

according to the following equations:

where CRo is the corrosion rate without inhibitor

and CRi is the corrosion rate when inhibitor is present.

It can be seen that the presence of inhibitors results a

high decrease in the rate of corrosion. In the case of

these inhibitors, the corrosion rate decreases as the

inhibitor concentration increases, getting maximum

inhibition efficiency ranged between 98.49 and

99.48% at 100 ppm after 20 hour of exposure (Table

1). This trend may results from the fact that

adsorption and surface coverage increase with the

increase in concentration; thus the surface is

effectively separated from the medium (El-Sayed et

al., 2010).

Table 1 shows the calculated values of corrosion

rates, the inhibition efficiencies and the surface

coverage in the absence and presence of different

concentrations of different inhibitors at 50 °C. A

general trend is observed in presence of the studied

inhibitors, a decrease in the corrosion rate of carbon

steel in presence of these surfactants compared to the

blank (inhibitor free solution). By increasing the

concentration of the surfactants, a further decrease in

corrosion rate of carbon steel was observed. The

maximum inhibition efficiency (η%) was obtained at

100 ppm of inhibitors.. This indicates that the

inhibitory action of the inhibitors against carbon steel

corrosion can be attributed to the adsorption of these

molecules on the metal surface, limits the dissolution

of carbon steel, and the adsorption amounts of

surfactants on carbon steel increase with

concentrations in the corrosive solutions (Taleb and

Mohamed, 2011).

Figure 2 shows the variation of the corrosion rate

with time for carbon steel in CO2-saturated brine

containing 100 ppm from different surfactants at 50

°C. This plot indicates that, the presence of different

inhibitors decreases the rate of corrosion. The data

indicate that, the inhibition efficiency of carbon steel

in CO2-saturated brine in the presence of inhibitor II

(K-salt) more than that obtained of inhibitor I (Na-

salt).

The high inhibition efficiency obtained in CO2-

saturated solution in the presence of studied inhibitors

can be attributed to the formation of a protective film

of iron carbonate (FeCO3) as follows (Lo´pez et al.,

2003b):

Abbasov et al.

Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the Corrosive Performance of Carbon Steel

in CO2-Saturated Brine

169

The anodic dissolution for iron in carbonic acid

solutions gives ferrous ions (Ogundele and White,

1986).

Fe ↔ Fe2+

+ 2e- (7)

According to these processes, a corrosion layer

was formed on the steel surface. The properties of the

formed layers and its effect on the corrosion rate are

important factors to take into account when studying

the corrosion of steels in CO2 environments. Ogundele

and White suggested that, iron carbonate, FeCO3, may

be important in the formation of protective layers on

steel surface (Ogundele and White, 1986). The

formation of iron carbonate can be explained by using

the following Eq. (Migahed et al, 2006).

Fe2+

+2

3CO → FeCO3 (8)

3.3. The extrapolation of cathodic and anodic Tafel

lines

The inhibiting effect of the synthesized compounds on

the corrosion reaction of carbon steel in CO2-saturated

NaCl solution was investigated using the

electrochemical polarization method. The polarization

technique was adopted to determine both cathodic and

anodic polarization curves. It is also used to calculate

the corrosion currents from the extrapolation of Tafel

lines to pre-determined open circuit potential. This is

achieved by measuring the potential–current

characteristics of the metal/solution system under

consideration with the aid of a potentiostat.

Figure 3 shows the influence of inhibitor I

concentrations on the Tafel cathodic and anodic

polarization characteristics of carbon steel in CO2-

saturated solution at scan rate 1 mV/s and at 50 °C.

Corrosion parameters were calculated on the basis of

cathodic and anodic potential versus current density

characteristics in the Tafel potential region (Tremont

et al, 2000; Schultze and Wippermann, 1987). Steady

state of open circuit corrosion potential (Ecorr) for the

investigated electrode in the absence and presence of

the studied inhibitor was attained after 45–60 min

from the moment of immersion. Corrosion current

density (Icorr) of the investigated electrodes was

determined (El-Sayed, et al, 2011), by extrapolation of

cathodic and anodic Tafel lines to corrosion potential

(Ecorr). The inhibition efficiency expressed as percent

inhibition (η%) is defined as:

Where Iuninh. and Iinh. are the uninhibited and

inhibited corrosion currents. The inhibited corrosion

currents are those determined in the presence of the

studied surfactants used in this investigation. The

uninhibited corrosion currents were determined in

pure (inhibitor free) CO2-saturated 1% NaCl solution

at the same temperature. It can be seen that the

presence of surfactants molecule results a marked

shift in both cathodic and anodic branches of the

polarization curves towards lower current densities.

This means that, the inhibitors affect both cathodic

and anodic reactions. It was found that, both anodic

and cathodic reactions of carbon steel electrode

corrosion were inhibited with increasing concentration

of synthesized inhibitors. These results suggest that

not only the addition of synthesized inhibitors reduce

anodic dissolution but also retard the hydrogen

evolution reaction.

The electrochemical parameters Ecorr, Icorr,

inhibition efficiency (η%), anodic and cathodic Tafel

slopes (βa , βc) obtained from the polarization

measurements were listed in Table 2. The data

exhibited that, the corrosion current density (Icorr)

decreases, and the inhibition efficiency (η%) increases

as the concentration of inhibitors is increased. These

results suggest that retardation of the electrodes

processes occurs, at both cathodic and anodic sites, as

a result of coverage of these sites by surfactants

molecules. The results also indicate that, the

percentage inhibition efficiency (η %) of the inhibitor

(II) is greater than that of the inhibitor (I), thereby;

firmly agree with aforementioned results of LPR

corrosion rate.

International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(8), pp. 166-178, 2013

170

Fig. 1: Variation of the Corrosion rate with time for carbon steel in CO2-saturated 1 % NaCl solution containing different

concentrations of inhibitor II (K-salt) at 50 °C.

Fig. 2: Variation of the Corrosion rate with time for carbon steel in CO2-saturated 1% NaCl solution containing 100 ppm of

different inhibitors at 50 °C.

The corrosion potential Ecorr values of all

synthesized inhibitors were shifted slightly toward

both cathodic and anodic directions and did not show

any definite trend in CO2-saturated brine. This may be

considered due to the mixed-type behaviour of the

studied inhibitors. It can be observed, the shift in Ecorr

that is characteristic of anodic and anodic/cathodic

inhibitor (López et al, 2005). It was explained that this

shift in Ecorr is due to active sites blocking effect that

occurs when an inhibitor is added (Cao, 1996). In the

case of CO2 corrosion the anodic and cathodic

reactions are the oxidation of iron and the reduction of

hydrogen, respectively (Nordsveen et al., 2005). If it

is considered that the active sites on the metal surface

are the same for both reactions before adding the

inhibitor, it is logical the change in Ecorr when the

inhibitor is present because its adsorption change

those active sites and therefore the anodic and

cathodic reaction rates (Farelas and Ramirez, 2010).

The fact that the slopes of the cathodic (βa) and

anodic (βc) Tafel lines in Table 2 remain almost

unchanged upon addition of the inhibitors. These

results indicate that this inhibitor acts by simply

blocking the available surface area. In other words,

the inhibitor decreases the surface area for corrosion

of the investigated metal, and only causes inactivation

Abbasov et al.

Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the Corrosive Performance of Carbon Steel

in CO2-Saturated Brine

171

of a part of the surface with respect to corrosive

medium. On the other hand, the cathodic Tafel slopes

(βc) are also found to be greater than the respective

anodic Tafel slopes (βa). These observations are

correlated with the fact that the cathodic exchange-

current density values are less than those of the anodic

counter parts. It can be concluded that the overall

kinetics of corrosion of carbon steel alloy in CO2

saturated solution are under cathodic control.

For all studied inhibitors, the common ground was

that the corrosion current density decreased and the

inhibition efficiency increased with increasing

inhibitors concentration. The highest inhibition

efficiency was 98.49 % for inhibitor II (K-salt) at100

ppm.

Table 1: The corrosion parameters obtained from LPR corrosion rate measurements for carbon steel electrode in CO2-

saturated brine in the absence and presence of various concentrations of investigated surfactants at 50 °C.

Fig. 3: Tafel polarization curves for carbon steel in CO2-saturated 1% NaCl solution containing different concentration of

inhibitor (I) at 50 °C.

International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(8), pp. 166-178, 2013

172

Table 2: Corrosion parameters obtained from Tafel polarization for carbon steel in CO2-saturted 1% NaCl solution

in the absence and presence of different concentrations of the prepared surfactants at 50 °C.

3.4. Surface tension and surface active properties

The values of surface tension (γ) were measured at

303 K for various concentrations of the synthesized

surfactants. The measured values of (γ) were plotted

against ln of the surfactant concentration, ln C (Fig.

4). The intercept of the two straight lines designates

the CMC, where saturation in the surface adsorbed

layer takes place. The plot showed that the surfactant

was molecularly dispersed at low concentration

leading to a reduction in surface tension. This

reduction increases with increasing concentration. At

high concentration, however, when a certain

concentration was reached (CMC), the surfactant

molecules form micelles, which were in equilibrium

with the free surfactant molecules (Migahed et al.,

2006).

The surface active properties of the surfactant,

effectiveness (πcmc), maximum surface excess (Γmax),

and minimum area per molecule (Amin) were

calculated using the following equations (Rosen,

1978):

Where ∂γ/∂lnC is maximum slope, γ0 is the surface

tension of pure water, γcmc the surface tension at

critical micelle concentration, NA is the Avogadro’s

number (6.023 ×1023

molecules/mol), R is the molar

gas constant (R= 8.314 J/(mol K)) and T is the

absolute temperature = (t°C+273), o

micG is the Gibbs

free energy of micellization, 0

adsG is the Gibbs free

energy of adsorption (Badawi et al., 2007).

The data presented in Table 3 show some of the

surface active properties for the investigated

surfactants. The results indicate that, the consequent

increase in of Γmax leads to crowding at the interface,

which causes a decrease in Amin values. The values of

effectiveness (πcmc) at 298 K indicate that the prepared

compounds gives large reduction of surface tension at

CMC, so that, these compounds acts as effective

corrosion inhibitors for carbon steel in CO2- saturated

1% NaCl solutions.

The free energy changes of micellization and

adsorption showed negative sign showing the

spontaneity of the two processes at 25 °C (Table 3).

Moreover, 0

adsG increase in negativity thano

micG .

That showed the higher tendency of these surfactants

towards adsorption rather than micellization. Then the

adsorption will be accompanied with micellization at

last. The tendency towards adsorption was referred to

Abbasov et al.

Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the Corrosive Performance of Carbon Steel

in CO2-Saturated Brine

173

the interaction between the aqueous phases and the

hydrophobic chains which pump the surfactant

molecules to the interface (Alsabagh et al., 2006).

Table 3: The critical micelle concentration and surface parameters of the synthesized surfactants

3.5. Adsorption isotherm and thermodynamic

parameters

Basic information on the interaction between the

inhibitor molecules and metal surfaces could be

provided from the adsorption isotherms. The values of

surface coverage (θ) which were defined as in the

following equation:

A correlation between θ and inhibitor

concentration in the corrosive medium can be

represented by the Langmuir adsorption isotherm (Tao

et al., 2009).

Where Kads is the equilibrium constant of the

inhibitor adsorption process and Cinh. is the inhibitor

concentration.

Plots of Cinh/ θ versus Cinh yielded a straight line as

shown in Fig. 5, which suggested that at 323 K the

adsorption of investigated inhibitors on metal surface

obeyed Langmuir adsorption isotherm model. This

isotherm assumed that the adsorbed molecules

occupied only one site and there was no interaction

with other molecules adsorbed. The linear regression

coefficients (r) and the slopes parameter were shown

in Table 4. All correlation coefficient (r > 0.997)

indicated that the inhibition of carbon steel by studied

surfactants was attributed to the adsorption of

inhibitors on the metal surface. However, the slopes of

the Cinh/ θ versus Cinh plots were close to 1 and

showed a little deviation from unity which meant non-

ideal simulating (Badawy et al., 2006) and unexpected

from Langmuir adsorption isotherm. They might be

the results of the interactions between the adsorbed

species on the metal surface (Migahed et al., 2003;

Azim et al., 1974).

Kads values could be calculated from the intercepts

of the straight lines on the Cinh/ θ-axis, the Kads was

related to the standard free energy of adsorption, o

adsG ; with the following equation (Flis and

Zakroczymski, 1996):

The value 55.5 in the above equation was the molar

concentration of water in solution in mol/L (Azim et

al., 1974). The relatively high value of the adsorption

equilibrium constant (Kads; Table 4) reflects the high

adsorption ability of these surfactants on the metal

surface (Abd El-Lateef et al., 2012c). It is also noted

that, the high value of Kads for inhibitor II indicate

stronger adsorption on the carbon steel surface than

the inhibitor I. Large values of Kads imply more

efficient adsorption hence better inhibition efficiency

(Refay et al., 2004).

The high and negative values of free energy of

adsorption (o

adsG ) indicate spontaneous adsorption

and strong interaction of the inhibitor molecule with

the carbon steel surface. Generally, values of o

adsG

International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(8), pp. 166-178, 2013

174

up to -20 kJ mol-1

are consistent with physisorption,

while those around -40 kJ mol-1

or higher are

associated with chemisorption as a result of the

sharing or transfer of electrons from organic

molecules to the metal surface to form a coordinate

bond (Farhat and Quraishi, 2011). In the present

study, the o

adsG values obtained for the surfactants I

and II on carbon steel in CO2-saturated 1 % NaCl

solution are -44.71 and -45.92 kJ mol-1

, respectively.

This indicates that the adsorption of studied inhibitors

is typical chemisorption.

Fig. 4: Change of surface tension (γ) with the concentration of the surfactants at 25 °C.

Fig. 5: Langmuir plots for inhibitors I and II in CO2-saturated brine obtained from the extrapolation of cathodic and anodic

Tafel lines at 50 ºC.

4. CONCLUSION

In this research, Linear polarization resistance

corrosion rate and Potentiodynamic polarization

measurements were used to study the corrosion

inhibition of carbon steel in CO2-saturated 1% NaCl

solution using sodium and potassium salts of

naphthenic acids as corrosion inhibitors. The results

can be summarized as follows.

a) The synthesized surfactant acts as an effective

corrosion inhibitor for carbon steel in CO2-saturated

1% NaCl solution.

b) The inhibition efficiency increased with

increasing concentration of the inhibitor.

Abbasov et al.

Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the Corrosive Performance of Carbon Steel

in CO2-Saturated Brine

175

c) The inhibition efficiency (η%) reached to 99.48

% at 100 ppm of the inhibitor II.

d) Polarization measurements showed that the

inhibitors act as mixed inhibitor.

e) The adsorption of the inhibitors on the metal

surface obeys Langmuir adsorption isotherm.

f) The higher value of the equilibrium adsorption

constant (Kads. = 3.65× 105) reflects the high

adsorption ability of the inhibitors molecules on the

surface of carbon steel.

Table 4: Thermodynamic parameters for the adsorption of inhibitors I and II in CO2-saturated brine on the

carbon steel surface at 323 K

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Prof. Dr. Vagif Maharram Abbasov, Doctor of chemical sciences (DSC), Azerbaijan National Academy

of Sciences, Institute of Petrochemical Processes, Director of Institute of Petrochemical Processes. He

is a Member of the Editorial Board of "Processes of Petrochemistry and oil refining journal" (Chief

Secretary). He is a Member of the American Chemical Society. He is an author on 250 papers in

international journals and more than 35 books. V. M. Abbasov has carried out the thorough researches

in the field of synthesis of antistatic additives to hydrocarbon liquids including to jet fuels. He for the

first time proposed the possibility for producing the displaced complexes of nitroalkanes and organic

acids with the transition metals, developed on their basis the high efficient and polyfunctional antistatic

additive. This additive was tested and commercialized in perm plant of aircraft engines. V. M. Abbasov

with coworkers has created in 1997 the polyfunctional waxy deposit corrosion inhibitor "Parkorin-1",

the commercial tests have been carried out in the Azerbaijan oil fields, jointly exploited by Turkish- Azerbaijan and by

TSNIIKP (Moscow city) has been recommended for application.

Dr. Hany M. Abd El-Lateef was born in Sohag, Egypt, in 1982. He received the master degree in

physical chemistry from the University of Sohag, Sohag, Egypt, in 2009, since that has worked in

different projects in the field of corrosion science. In 2010, he joined the department of chemical

resistance of materials and corrosion protection, institute of petrochemical processes, Azerbaijan

National Academy of Sciences, as a PhD student. He is one of the Editorial board of Chemistry Journal.

He is an author on 30 papers in international journals and two books. Hany is one of NACE

membership.

Dr. Sevinc A. Mamedxanov, Doctor of chemical sciences, Azerbaijan State Oil Academy. She is an

author on 50 papers in international journals. She obtained degree in Master of Science in

Petrochemistry from Azerbaijan State Oil Academy. She received his first degree in applied chemistry

from Azerbaijan State Oil Academy. Her research is focused on the Synthesis of various surfactants,

compounds soluble in oils and fuels, and their investigation as corrosion inhibitors, additives to fuels,

oils, polymeric stabilizers, development of theoretical bases for selecting corrosion inhibitors and

additives.

Prof. Dr. Leylufer Imran Aliyeva Doctor of Technical Sciences, Azerbaijan National Academy of

Sciences, Institute of Petrochemical Processes, Head of department. She is a Member of the Editorial

Board of "Processes of Petrochemistry and oil refining journal". She is an author on 180 papers in

international journals and more than 18 books. Her work focused on the synthesis of nitroalkanes

metallocomplexes, high-molecular amines and creation of polyfunctional antistatic additives, corrosion

inhibitors, inhibitor-bactericides and study of their action mechanism. She has created the high efficient

polyfunctional sulfurated hydrogen corrosion inhibitors based on α-olifins with working capacity in the

media with H2S, CO2 content more than 25% vol.

International Journal of Scientific Research in Environmental Sciences (IJSRES), 1(8), pp. 166-178, 2013

178

Dr. Teyyub A. Ismayilov, Doctor of chemical sciences, Azerbaijan National Academy of Sciences,

Institute of Petrochemical Processes. He is an author on 50 papers in international journals. T. A.

Ismayilov has carried out the thorough and extensive researches in the field of creation of the corrosion

inhibitors and obtained the following important results: on the basis of carbamide and amines there has

beer created a new method for synthesis of phosphate complexes and organized on their basis the

production and application of polyfunctional corrosion inhibitors.

Musayev Javidan Ilham is a Ph.D student in the sphere of quality control at the State Economic

University of Azerbaijan. He received his first degree from The State Economic University in 2009

awarded with Bachelor of Science. He obtained Master degree of Science from The State Economic

University in 2012. His current research is focuses on synthesis and the review in quality of sulfonation

of acids and saline acids on plant origin.

Orkhan A. Aydamirov obtained his first degree from the Baku State University in chemistry in 2011.

He is junior researcher in Petrochemical Institute of Azerbaijan National Academy of Sciences. His

current research is focuses on corrosion inhibitors and conservation fluids. To date, he has published

several scientific articles related to corrosion inhibitors. He also interests in alternative energy sources

and biomass.

Dr. Fariz A. Amirov is an Assistant Professor in Azerbaijan State Oil Academy. He has more than 22

year’s research experience in the field of Petrochemistry. He has published over 70 refereed articles in

professional journals/proceedings. Dr. F. A. Amirov research has focused on alleviating problems

associated with oil industry issues from corrosion. He is editor and reviewer of some international

journals.