ORIGINAL ARTICLE

Enhancing of Corrosion Inhibition and the Biocidal Effectof Phosphonium Surfactant Compounds for Oil Field Equipment

Ismail A. Aiad • Salah M. Tawfik • Samy M. Shaban •

Ali A. Abd-Elaal • Mohamed El-Shafie

Received: 15 April 2013 / Accepted: 10 July 2013

� AOCS 2013

Abstract It is well known that tetra hydroxymethyl

phosphonium sulfate (THPS) is commonly used in oil

fields as a biocide for sulfate-reducing bacteria (SRB), but

it has low corrosion inhibition. In this study, four phos-

phonium surfactant compounds were synthesized via a

coupling reaction between THPS and different fatty acids

namely: decanoic, dodecanoic, palmitic and stearic acids to

produce the corresponding surfactants. The chemical

structure of the synthesized surfactants was confirmed

using FTIR and 1H-NMR spectroscopy. The surface

activity of the prepared compounds was determined by

surface tension measurements. The critical micelle con-

centration (CMC) of each surfactant compound was

determined. The corrosion inhibition of the synthesized

compounds on carbon steel in 0.5 M HCl was studied by

weight loss measurements, potentiodynamic and electro-

chemical impedance spectroscopy. The effect of the

inhibitor concentration and hydrophobic chain length on

the their efficiency was also studied. It was found that the

CMC of each compound depends on its chemical structure.

It was also found that the corrosion inhibition efficiency

depends on both of concentration and molecular structure

of the inhibitors. Polarization curves revealed that the

inhibitors used represent mixed-type inhibitors, which

hinder the cathodic and anodic parts of the corrosion

reaction in acidic media. Adsorption of used inhibitors

leads to a reduction in the double layer capacitance and an

increase in the charge transfer resistance. Also the biocidal

effect of these compounds was enhanced.

Keywords Cationic surfactants � Surface properties �Applications

Introduction

Carbon steel is widely used in storage tanks, petroleum

refineries, and so on. The main problem of using carbon

steel is its dissolution in acidic solutions. In the chemical

industry, acid solutions are generally used for removal of

undesirable scales and rusts on steel surfaces, and also

widely applied to enhance oil/gas recovery through acidi-

fication in the oil and gas industry. These operations usu-

ally induce serious corrosion of equipment, tubes and

pipelines made of steel. Inhibitors are generally used in

these processes to control metal dissolution as well as

consumption of acid [1, 2]. It is well known that tetra

hydroxymethyl phosphonium sulfate (THPS) is used as a

water treatment broad-spectrum biocide in oil fields, to

inhibit the growth of algae, bacteria, yeasts and fungi in

process waters. THPS is effective in both acid and alkaline

environments. It is especially effective against sulfate-

reducing bacteria (SRB) which are particularly trouble-

some in enhanced oil recovery operations, such as injection

water treatment, top-side systems, pipeline protection and

storage.

Microbiologically influenced souring (MIS) is the pro-

duction of H2S through the metabolic activities of the

sulfate-reducing bacteria (SRB). A better chance for miti-

gating MIS in some down-hole environments using bio-

cides may be possible if the problem is detected early in the

Electronic supplementary material The online version of thisarticle (doi:10.1007/s11743-013-1512-y) contains supplementarymaterial, which is available to authorized users.

I. A. Aiad (&) � S. M. Tawfik � S. M. Shaban �A. A. Abd-Elaal � M. El-Shafie

Applied Surfactants Laboratory, Petrochemicals Department,

Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt

e-mail: yiaiad@yahoo.co.uk

123

J Surfact Deterg

DOI 10.1007/s11743-013-1512-y

souring process. However, if the H2S-producing creatures

are allowed to spread into subsurface regions that are less

accessible to biocides (profuse-stage MIS), the problem

becomes less possible to mitigate by conventional methods.

The corrosion process plays an important role in the field

of economics and safety. Various types of steel including

stainless steel used in different industries (chemical and

electrochemical industries, medical, nuclear, petroleum,

power, and food production), and also in daily life. However,

it suffers from a certain type of corrosion within some

environments. For this reason, the electrochemical properties

of stainless steel are the subject of many studies. Hydro-

chloric and sulfuric acids are widely used as aggressive

solutions to remove unwanted scale, such as the rust or mill

scale formed during the manufacture of steels and ferrous

alloys. Due to the aggressiveness of acids, corrosion can be

reduced by the addition of corrosion inhibitors in small

concentrations [3, 4]. Corrosion inhibitors are used in acidic

solutions to decrease the dissolution of the metallic materials.

Most commercial acid inhibitors are organic compounds

containing heteroatoms such as sulfur, oxygen, nitrogen [5],

and phosphorous. Inhibitor molecules are adsorbed onto the

metal surface, thus resulting in film formation.

The adsorbed film acts as a barrier, which separates the

metal surface from the corrosive medium and consequently

decreases the extent of corrosion. In general, the adsorption

of inhibitor molecules on the metal surface depends on the

nature and the surface charge of the metal, the adsorption

mode, chemical structure and type of electrolyte solution.

The inhibition efficiency of inhibitors increases in the order

of O \ N \ S \ P [6]. Many heterocyclic compounds

containing nitrogen atoms have been used as effective

inhibitors of the corrosion of steel in acidic media [7]. In

this work, four cationic surfactant compounds were syn-

thesized and their chemical structures were confirmed

using different spectra tools; their surface activity was

studied, and they were investigated as corrosion inhibitors

of carbon steel in 0 0.5 M HCl on the basis of weight loss,

potentiodynamic polarization and electrochemical imped-

ance spectroscopy measurements. The behavior and the

relation between molecular structure, surface properties,

and the inhibitive effects of these compounds on corrosion

inhibition of carbon steel in solution were investigated.

Our presented research is aimed at enhancing the

activity of THPS by modifying it to become surface active

agents, through a chemical reaction with fatty acids; the

surface activity of the synthesized phosphonium surfactants

and their antimicrobial activities against sulfate-reducing

bacteria was determined. We also aimed at enhancing the

inhibition mechanism against the corrosion of carbon steel

in acidic medium. The inhibition performance of the

studied inhibitors was evaluated by gravimetrical and

electrochemical methods.

Experimental

Chemicals

Commercially available tetrakis (tetra) hydroxymethyl phos-

phonium sulfate abbreviated THPS, was purchased from El

Goumhoria Trade Pharmaceuticals and Chemicals Company,

Cairo, Egypt. Decanoic, dodecanoic, palmitic and stearic acids

were analytical grade chemicals obtained from Merck.

Synthesis of Phosphonium Surfactants

A mixture of THPS (0.1 mol) and fatty acid (0.11 mol of

either decanoic, dodecanoic, palmitic and stearic) was

reacted. The reaction was carried out in a one-necked flask

connected to a Dean-Stark apparatus in the presence of

xylene as a solvent (100 mL). The reaction was continued

under reflux with stirring until the water produced by the

reaction (1.8 mL) was removed. The reaction mixture was

cooled and vacuum distilled to remove the solvent and the

excess acids. The surfactants produced were designed as I,

II, III and IV according to the fatty acid chain length.

Surface Measurements

Surface Tension

Surface tension measurements were carried out using a Du

Nouy tensiometer with a platinum ring. Freshly prepared

aqueous solutions of the synthesized phosphonium sur-

factants were measured over a concentration range of

0.01–0.000005 mL-1 at 25 �C. Apparent surface tension

values were taken as the average of three readings for each

sample with 2 min intervals between each reading.

Corrosion Measurements

The corrosion inhibition of prepared compounds was

determined using three techniques.

Weight Loss Measurements

The weight loss experiments were performed with carbon

steel specimens having a composition of (wt%): 0.21 C, 0.035

Si, 0.025 Mn, 0.082 P and the remainder Fe. The carbon steel

sheets of 2.5 9 2.0 9 0.6 cm were abraded with a series of

emery papers (grade 320, 500, 800 and 1,200) and then

washed with acetone and distilled water. After weighing

accurately, the specimens were immersed in a closed flask

contained 250 mL of a solution of 0.5 M HCl without and

with the tested inhibitors I, II, III and IV at different concen-

trations (25, 50, 100, 200, 400 and 800 ppm by weight) for

24 h at 25 �C. Then, the specimens were taken out, washed,

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123

dried and weighed accurately. The test was performed for

three specimens and the weight was the average of the three

specimens. The coupons were polished with a hard plastic

brush, first with hot water then with ethanol to remove the

corrosion products. The corrosion rate (R) and the inhibition

efficiency (IE %) were calculated using Eqs. (1, 2) [8, 9]:

R ¼ W=At ð1ÞIE % ¼ R0 � R½ Þ=R0� � 100 ð2Þ

where W is the average weight loss of three parallel carbon

steel sheets, A the total surface area of the specimen, t is

immersion time, R0 and R are the values of the corrosion

rate without and with addition of the inhibitor, respectively.

Polarization Measurements

The polarization measurements were carried out using a lab-

oratory potentiostat (Volta lab 40 PGZ 301 in a conventional

three-electrode cell system, from France). The working elec-

trode was immersed in the test solution for 30 min until the

open circuit potential was reached. After that the working

electrode was polarized in both the cathodic and anodic

directions. The values of corrosion current density (icorr) were

calculated from the extrapolation of Tafel lines to the pre-

determine open circuit potential [10]. A standard ASTM glass

electrochemical cell was used and a platinum electrode was

used as an auxiliary electrode. All potentials were measured

against a saturated calomel electrode (SCE) as a reference

electrode. The potential increased at a rate of 30 mV min-1

starting from -900 to -250 mV and the inhibition efficiency

(IE %) was calculated from Eq. (3)

IE % ¼ 1� I=I0½ � � 100 ð3Þ

where I and I0 are the current density values obtained from

the potentiostat without and with inhibitors.

Electrochemical Impedance Spectroscopy (EIS)

EIS measurements were carried out using a Voltalab 40

Potentiostat PGZ 301 using a Voltamaster software pro-

gram. The measurements were carried out using AC signal

(10 mV) peak to peak at the open circuit potential (OPC) in

the frequency range of 100 kHz to 30 MHz. The inhibition

efficiencies (g %) of the tested inhibitors were calculated

from the Rt values at (25, 50, 100, 200,400 and 800 ppm by

weight) at 298 K using the following Eq. [11]:

O� 100 ð4Þ

Antimicrobial Activity Measurements

The inhibition activity on the growth of SRB at different

doses of synthesized compounds was measured using the

dilution method.

SRB-contaminated water from Qarun Petroleum Co.

(West Desert, Egypt) was used for the test conducted

according to ASTM D4412-84. The prepared water was

subjected to growth of about 10,000,000 bacteria cell/ml.

Two biocide samples (I, II, III and IV) were tested by dose

of (50, 100, 200 and 400 ppm by weight) and the system

was incubated to contact time 3.0 h; each system was

cultured in SRB specific media for 21 days at 37 �C.

Results and Discussion

Structure Confirmation

The chemical structures of the synthesized phosphonium

surfactants (I, II, III and IV) Scheme 1 were confirmed

using FTIR and 1H-NMR spectroscopy as follows (compound

I was taken as a representative sample for the synthesized

surfactants): FTIR spectra of the synthesized compounds

(Fig. 1) showed the following absorption bands:

3,381.71 cm-1 (OH), 2,924 cm-1 (CH3), 2,870.79 cm-1

(CH2), 1,733.92 cm-1 (C=O), 1,462 cm-1 (C-P), 1,351.52

cm-1 (S=O), 1,118.74 cm-1 (C-O).

1H-NMR Spectra

1H-NMR spectra of the synthesized compounds in CDCl3,

(Fig. 2) showed signals at: 0.81 ppm (t, 3H, CH3),

1.27 ppm (m, nH, CH2), 2.14 ppm (m, 2H, CH2CH2COO),

2.46 ppm (t, 2H, CH2CH2COO), 3.69 ppm (s, 2H,

OCOCH2P?), 3.74 ppm (d, 2H, OHCH2P?), 5.19 ppm

(t, 1H, OHCH2P?) disappeared by the deuteration.

Surface Activity

The surfactant molecules consist of two characteristic

parts: the hydrophobe (organic) and the hydrophilic part

(polar) [12]. When surfactant molecules dissolved in the

aqueous medium, they organized themselves in the solution

with the hydrophilic part directed to the water phase.

However, the hydrophobe is located on the interface to

reduce the repulsion generated from the water phase.

Increasing the amount of surfactants added to the solution

decreases the surface tension values of the water gradually.

The decrease in the surface tension values indicates the

Scheme 1 The synthesized phosphonium surfactants (n = 7, 9, 13

and 15)

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123

tendency of surfactant molecules to adsorb at the liquid

interface. At a certain concentration, surfactant molecules

covered the water interface completely [12]. Then, sur-

factant molecules aggregate in the bulk of the solution to

form the micelles.

The surface tension versus the -log C relationship of

the synthesized phosphonium surfactant at 25 �C is shown

in Fig. 3 (compound I was taken as representative for the

tested compounds). It is clear that there are two distin-

guishable regions, the first at a low concentration range and

characterized by a fast decrease in the surface tension

values, (i.e., high slope) with surfactant concentration. The

second region (at higher surfactant concentrations), the

surface tension variation remains almost constant by

increasing the surfactant concentration, i.e., the slope is

almost constant. The concentration at the break point of

these two regions was taken as the critical micelle con-

centration (CMC).

It is clear from the data in Table 1 that the CMC values

were decreased gradually by increasing the alkyl chain

Fig. 1 IR spectrum of

compound I

Fig. 2 1H-NMR spectrum of

compound I

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123

length (hydrophobic chains). This could be due to

increasing the interaction forces between these chains and

the polar medium (H2O), which directs the surfactant

molecules towards the air/water interface. Hence, the CMC

values decrease gradually, due to the increase in the

repulsion forces between the various prepared compounds

and the water molecules [13–15].

The CMC values of the studied phosphonium surfac-

tants are relatively low compared to the conventional cat-

ionic surfactants [16]. The depression of the CMC values

of the prepared surfactant in their solutions indicates their

tendency towards adsorption at the air/water interface [17].

Effectiveness (pCMC) and Efficiency (Pc20)

pCMC is the effectiveness (the effectiveness is the differ-

ence in the surface tension values of bidistilled water (co)

and the surfactant solution at the critical micelle concen-

tration (cCMC), as follows:

pCMC ¼ co � cCMC ð5Þ

While, Pc20 is the surfactant concentration which

provides a 20 mN m-1 reduction in surface tension of

the surfactant solution.

The effectiveness and efficiency values of the synthe-

sized surfactants are listed in Table 1. These two variables

determine the activity of surfactant molecules at the air/

water interface. Table 1 shows the effectiveness and effi-

ciency values of the synthesized surfactants I, II, III and IV

in their solutions at 25 �C. Obviously, phosphonium

derivatives exhibited an increasing trend in both pCMC and

Pc20 with longer hydrophobic chain, reaching the maxi-

mum activity corresponding at the octadecyl derivative

(IV) at 25 �C.

Maximum Surface Excess (Cmax) and Minimum

Surface Area (Amin)

Cmax describes the accumulation of surfactant molecules at

the air–water interface, and can be calculated according to

Rosen [18] using (qc/qlog C) term. This term represents the

slope of the surface tension -log C curve at the pre-micellar

region (low concentration regions) and is called the surface

pressure, which describes the change in the surface tension

of the solution by a finite change of the surfactant con-

centration. Increasing the surface pressure of the system is

an indication for the high accumulation of surfactant

molecules at the interface. Cmax values of the surfactants

under investigation were calculated at 25 �C according to

Gibb’s adsorption equation (Eq. 6) using Rosen method-

ology [18] (Table 1).

Cmax ¼ 1=2:303 RT oc=o log Cð Þ ð6Þ

The maximum surface excess values were used to

calculate the average area occupied by surfactant

molecules (Amin) at aqueous-air interface using the

following equation [19, 20]:

Amin ¼ 1016=NACmax ð7Þ

Where NA is Avogadro’s number and Cmax is the

maximum surface excess of phosphonium surfactants.

By inspection of the data it can be concluded that

increasing the alkyl chain length of the hydrophobe

decreases the maximum surface excess values (Cmax),

probably because of the increase of hydrophilicity of the

molecules by the presence of an hydroxyl group in their

structure. From the data in Table 1, it is clear that there is a

gradual increase in Amin by increasing the alkyl chain

length as expected by the increase of hydrophobicity of the

molecules.

Standard Free Energies of Micellization and Adsorption

The behavior of the surfactant at the interface and in the

bulk of their solutions depends on the thermodynamic

parameters of micellization and adsorption. The thermo-

dynamic parameters including standard free energy were

calculated using Gibbs equations as follows [15], and data

are summarized in Table 1:

DGmic ¼ n RT ln CMC ð8ÞDGads ¼ DGmic � ð0:6� pCMC � AminÞ ð9Þ

Where n is equal to the number of the ionic species in

the solution (n = 2), R is the universal gas constant

(=8.314 J mol K-1), T is the absolute temperature.

It is clear that the free energies of micellization and

adsorption (DGmic, DGads) for the synthesized surfactants,

Fig. 3 Surface tension versus -log concentration of compounds I, II,

III and IV surfactants at 25 �C

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123

have a negative sign, indicating that the two processes are

spontaneous. Comparing the two values showed a slight

increase of DGads with respect to DGmic. This indicates that

the adsorption tendency is more favorable than the micel-

lization. That is attributed to the proper arrangement of

their molecules at the interface, which decreases the

repulsion due to the aqueous phase. Increasing the alkyl

chain length in the surfactant molecules decreases DGmic

more than DGads. This is likely to be due to a higher

interaction between the hydrophobic chains and the polar

medium. Hence, the adsorption is the most favorable

phenomenon, owing to their low interaction, which is also

stabilized by the anchoring points (polar groups) at the

interface [21].

Corrosion Measurements

Weight Loss Technique

The values of the corrosion rate, surface coverage and

inhibition efficiency in the presence and absence of the

synthesized surfactants at 25 �C, are listed in Table 2. The

doses of the tested inhibitors were 25, 50, 100, 200, 400

and 800 (ppm by weight) and were obtained from weight

loss measurements using Eqs. (1–3). From the data in

Table 2, it is clear that I, II, III and IV inhibitors retard the

dissolution of carbon steel in 0.5 M HCl solution for the

used concentrations (Table 1, supplementary file). Fur-

thermore, the inhibition efficiencies of the inhibitors were

increased to reach the maximum value in presence of the

different inhibitors at 800 (ppm by weight). The corrosion

rates decrease by increasing the concentration of the tested

inhibitor as shown in Fig. 4. On the other hand, the alkyl

chains attached to the inhibitors play an important role in

the inhibition efficiencies for the dissolution reaction of

carbon steel and also on the corrosion rate of this reaction.

Increasing the alkyl chain length decreases the corrosion

rate of the carbon steel and therefore the inhibition effi-

ciency of the inhibitor increases, Fig. 5. That can be

attributed to the increase of the adsorption tendency of

these inhibitors [22–25]. Increasing the inhibitor concen-

tration and the alkyl chain length increases the amount

of adsorbed inhibitor molecules at the metal/solution

interface. The adsorbed molecules act as an isolating sur-

face which decreases the contact between the corrosive

medium and the metal surface [26]. As a result, the dis-

solution reaction decreases. The adsorption of the corrosion

inhibitor molecules on the metal surface increases with the

presence of one pair of electrons of heteroatoms (O, S, and

P) and the presence of a phosphonium salt. The investi-

gated inhibitors give a good performance as corrosion

inhibitors, which can be related to the presence of a high

electron density of hetero atoms (O, S, and P) in addition to

the hydrophobic chain length. These atoms are adsorbed

onto the positive centers on the metal surface, while the

alkyl chains arrange themselves at the metal surface, and

this prevents contact between the metal surface and the

corrosive medium and consequently decreases the rate of

the dissolution reaction.

Potentiodynamic Polarization

The polarization profiles of a carbon steel electrode in

0.5 M HCl solution at 25 �C in the absence and presence of

synthesized inhibitors with compound I taken as a repre-

sentative sample for the synthesized surfactants is shown in

Fig. 6, while compounds II, III and IV are shown in Fig-

ure 1–3, in the supplementary file. The electrochemical

parameters including corrosion potential (Ecorr), corrosion

current density (icorr), anodic and cathodic Tafel slopes (ba,

bc) were obtained from the polarization curves and are

listed in Table 3 (and Table 2, in the supplementary file).

The anodic and cathodic current–potential curves are

extrapolated up to the intersection point where corrosion

current density (icorr) and corrosion potential (Ecorr)/SCE

are obtained [27]. Inspecting the polarization data, it is

clear that increasing the inhibitor concentration decreases

the corrosion current density (icorr) and increases the inhi-

bition efficiency (g %) which suggests that the tested

inhibitors are good corrosion inhibitors for carbon steel in

0.5 M HCl. From the polarization data listed in Table 3

(Table 2 supplementary file), it is obvious that both

cathodic and anodic reactions were hindered when the

inhibitors were added to the solution [28]. Furthermore, the

anodic and cathodic Tafel slopes (ba, bc) were found to

change with inhibitor concentration. This may be explained

from the viewpoint of thermodynamics, as the inhibitor

Table 1 Critical micelle concentration (CMC), effectiveness (pCMC), efficiency (Pc20), maximum surface excess (Cmax), minimum surface area

(Amin), free energy of adsorption (DGads) and free energy of micellization (DGmic) of the synthesized phosphonium surfactants at 25 �C

Compound CMC, mM pCMC, mNm-1 Pc20, mM Cmax 9 10-11, mol cm-2 Amin, nm2 mol-1 DGmic, kJ/mol DGads, kJ/mol

I 15.8 31.4 5.10 1.16 143.5 -10.28 -12.98

II 12.5 30.6 5.25 1.01 165.9 -11.41 -14.45

III 10 29.8 5.35 0.94 176.0 -12.56 -15.71

IV 8.91 28 6.00 0.81 183.7 -14.13 -18.01

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molecules are adsorbed onto the carbon steel surface and

these restrain the acid attack on the metal surface [29]. In

acidic solutions, the anodic reaction of corrosion is the

dissolution of Fe2? ions into the solution, and the cathodic

reaction is the discharge of hydrogen ions to hydrogen gas

(H). It is apparent from Table 3 (Table 2, supplementary

file) that the addition of the inhibitors shifts the corrosion

potentials (Ecorr) towards anodic (ba) and cathodic (bc)

direction, which indicates the inhibition of both cathodic

and anodic reactions [30, 31]. The parallel cathodic Tafel

curves in Fig. 6 (Figure 1–3, supplementary file) reveal

that the hydrogen evolution is activation controlled and

also not affected by the presence of the inhibitors [32]. It is

also clear that the values of anodic Tafel slope (bc) remain

almost unchanged (except for some points being moder-

ately changed) in the presence of the different inhibitors.

This suggests that the inhibitors were adsorbed onto the

metal surface and blocking the reaction sites of the metal

surface without affecting the anodic reaction mechanism

[33–35]. It is seen that icorr values decrease with increases

in the concentration of the inhibitors from 25 to 800 ppm.

This is due to adsorption of the inhibitor molecules onto the

metal surface and their forming a thin film that acts as a

barrier between the metal surface and corrosive surround-

ings. The film formed becomes thicker when the inhibitor

concentration is increased, and icorr decreases considerably.

The results obtained from the polarization technique in

acidic solution were in good agreement with those obtained

from the weight loss method.

Electrochemical Impedance Spectroscopy (EIS)

The EIS diagrams for the MS in 0.5 M HCl solution in the

absence and presence of various concentrations of the

tested inhibitors are given in Fig. 7 (compound I inhibitor

was taken as a representative sample), which indicates that

the Nyquist plot yields lightly depressed semicircles. The

depressed nature of the semicircle is due to the presence of

micro roughness and other inhomogeneities of the elec-

trode formed during the corrosion process [36, 37]. This

implies that corrosion of the carbon steel in 0.5 M HCl

solution is mainly controlled by a charge transfer process

Table 2 Weight loss, corrosion rate, surface coverage and corrosion

inhibition efficiency of synthesized inhibitors at 298 K

Inhibitor Dosage

(ppm by

weight)

Corrosion rate

(mg cm-2 h-1)

Surface

coverage

(h)

Efficiency

(g %)

Blank 0 0.313 – –

THPS 800 0.223 0.2852 28.52

I 800 0.065 0.7926 97.26

II 800 0.055 0.8246 82.46

III 800 0.053 0.8303 83.03

IV 800 0.046 0.8539 85.39

Fig. 4 Effect of inhibitor dosage (ppm by weight) on the corrosion

rate of carbon steel at 25 �C

Fig. 5 Effect of inhibitor dosage (ppm by weight) on the inhibition

efficiency (%) of the different inhibitors I, II, III and IV at 25 �C

Fig. 6 Current–potential relationships (cathodic and anodic) for

carbon steel in 0.5 M HCl in the presence of different concentrations

of compound I (ppm by weight) at 25 �C

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123

[38–42]. The difference in real impedance at lower and

higher frequencies on Nyquist plots is commonly consid-

ered as a charge transfer resistance. The charge transfer

resistance (Rct) must correspond to the resistance between

the metal and outer Helmholtz layer. The difference in real

impedance at lower and higher frequencies in Nyquist plots

increased in the presence of compound I inhibitor. This

increase was more pronounced with the increase in con-

centration of the inhibitors, an effect which may be

attributed to the formation of a protective layer at the metal

surface, which acts as a barrier to the corrosive ions and the

electrons. The EIS data were analyzed by fitting the

equivalent circuit model shown in Fig. 8 which matches

the experimental results. The circuits comprise a solution

resistance Rs, in series with the circuit comprising a charge

transfer resistance (Rct) and a constant phase element CPE.

The Nyquist plots presented in Fig. 7 are not perfect

semicircles as supposed in EIS theory. The Nyquist plots

obtained in the real system represent a general behavior

where the double layer on the interface of the metal/solu-

tion does not behave as a real capacitor. On the metal side,

electrons control the charged distribution, whereas on the

solution side, it is controlled by ions. As ions are much

larger than the electrons, the ions equivalent to the charge

on the metal will occupy quite a large volume on the

solution side of the double layer [43]. Therefore, CPE is

used in place of double layer capacitance, Cdl, to represent

the non-ideal capacitive behavior of the double layer. The

data obtained from the above-mentioned equivalent circuit

are presented in Table 4. The data show that the Rct value

is increased from 95.4 X cm2 for the blank to 262.1, 295.1,

380.1, 526.7, 708.9 and 750.1 X cm2 after the addition of

25, 50, 100, 200, 400 and 800 ppm by weight of compound

I, respectively. The increase in Rct values is attributed to

the formation of an insulating protective film at the metal/

solution interface. The decrease in Cdl values can be

attributed to a decrease in the local dielectric constant and/

or to an increase in the thickness of the electrical double

layer, suggesting that the inhibitor molecules are adsorbed

at the metal/solution interface [44–47]. The double layer

between the charged metal surface and the solution is

considered as an electrical capacitor. The adsorption of the

inhibitor molecules onto the carbon steel surface decrease

the electrical capacity because they displace the water

molecules and ions originally adsorbed onto the surface

[47–49]. Moreover, the decrease in this capacity with the

increase in the concentrations may be attributed to the

formation of a protective layer on the electrode surface

[50].

Antimicrobial Activity of the Studied Cationic

Surfactants Against Sulfate-Reducing Bacteria (SRB)

Sessile bacteria accelerate corrosion processes in several

ways. They accelerate the pitting corrosion by removing

the corrosion byproduct atomic hydrogen from the cathode

surface. In removing hydrogen, bacteria depolarize the

surface and allow corrosion reactions to continue.

Sulfate-reducing bacteria (SRB) produces H2S which

increases the corrosiveness of brine, causing metals to

crack and blister. In addition, bacterially (biogenically)

produced H2S reacts with iron that is solubilized from the

anode, thereby removing another corrosion byproduct to

accelerate the corrosion process. Acid-producing bacteria

produce acids that remove passivating oxide films from

surfaces.

Operational problems that are typically caused by bac-

teria are an increasing frequency of corrosion failures, H2S

concentrations, reservoir souring, rapid production decline,

metal sulfide scales, failure of downhole equipment due to

metal sulfide deposits, inefficiency of oil/water separation,

inefficiency of heat exchange, black water, black powder in

gas transmission lines, filter plugging and loss of injectiv-

ity. Bacterially produced FeS causes plugging problems in

production wells, downhole equipment, pumps, surface

facilities, filters, and at sand faces in injection wells. As

discussed above, SRB produce H2S that can react with

dissolved metals such as iron, zinc, and lead to the pro-

duction of insoluble metal sulfides. The metal sulfide par-

ticles collect throughout production facilities, but are

notable for being responsible for failures of down hole

pumps, frequent replacements of cartridge and sand filters

in surface facilities, and loss of the quantity of injected and

disposal water.

Table 3 Polarization parameters obtained for the carbon steel in 0.5 M HCl solution in the absence and in concentration (800 ppm by weight) of

inhibitor compounds I, II, III and IV at 298 K

Inhibitor Dosage, ppm -Ecorr (mV) icorr (mA/cm2) ba (mV/dec) -bc (mV/dec) h g %

Blank 0 513.1 0.107 154.7 137.6 – –

I 800 512.0 0.0171 120.3 160.5 0.840 84.01

II 800 512.5 0.0150 102.3 230.1 0.859 85.98

III 800 513.1 0.0148 75.4 130.7 0.861 86.16

IV 800 509.5 0.0137 75.3 140.4 0.871 87.19

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123

Plugging of injection and disposal wells is a problem

that is often underestimated by many production personnel.

Bacterial cells, biofilm fragments, and metabolic byprod-

ucts, such as iron sulfide, constitute a large percentage of

the total suspended solids that are filtered or injected into a

formation. The result is a solid mass of organic and inor-

ganic matter that can significantly reduce injectivity [51].

As a result of the numerous problems caused by bacteria

in oil and gas production operations, energetic measures

have been taken to monitor and control bacterial popula-

tions. Measures to monitor bacteria are not usually

considered until after corrosion failures point to MIC

(microbially induced corrosion). By the time that MIC is

discovered, extensive and costly damage to the operating

systems has often already occurred. Monitoring is often

conducted in sweet systems with no hint of bacterial con-

tamination to ensure that bacterial populations are under

control and that operating costs and risks (health, safety,

environmental, and mechanical failures) cannot be lowered

by initiating an effective biocide program [52].

The antimicrobial activity of the four studied biocides (I,

II, III and IV) against SRB was determined by a serial

dilution method at dosages of (50, 100, 200 and 400 ppm

by weight) and the results are listed in Table 5. The four

studied cationic surfactants were applied as biocides

against sulfate-reducing bacteria (Desulfomonas pigra)

showed imposing results due to their relatively high effi-

ciency against this type of bacteria. The tested compounds

I, II, III and IV have low efficiency at the lowest concen-

trations (50, 100 ppm by weight). In the relative high

dosages (200 and 400 ppm by weight), they have high

efficiency; the activity of the prepared compounds is

dependent on the alkyl chain length which determines the

compound solubility in the water, so that when the alkyl

chain length increases, the solubility of the compounds

decreases, with an increase in their activity. As shown in

Table 5, the most effective compound is compound (I).

This activity slightly decreases for compound (II). In all

cases, the four compounds have a biocidal effect at a

dosage of 200 ppm by weight.

It is believed from the recent studies on cationic sur-

factants, that they have excellent bactericidal activity [53,

54]. This activity depends on the hydrophobic chain length,

surface activities and the dosage, where, due to the

amphiphilic nature of the surfactants, causes them to

adsorb onto the outer cell membrane. In addition to the

similarity between the hydrophobic chains, the lipid layers,

i.e., the building units of the cell membranes, the mono-

saccharides in these compounds facilitates the adsorption.

With complete coverage, the molecules penetrate it. Fur-

thermore, the positive charges in the cationic molecules

neutralize the negative charges on the bacterial cell mem-

branes. Accordingly, the selective permeability which

characterizes the outer cellular membrane is completely

Fig. 7 Nyquist plots for carbon steel in 0.5 M HCl in the presence of

different concentrations of compound I (ppm by weight) at 25 �C

Fig. 8 Equivalent circuit for the corrosion behavior of the studied

systems

Table 4 Impedance parameters obtained for the carbon steel in

0.5 M HCl solution in the absence and in the presence of various

concentrations of C10 inhibitor at 298 K

Inhibitor Conc. (ppm by

weight)

Rs,

ohm cm2Cdl,

F cm-2Rct,

ohm cm2g %

Blank 0.0 3.6 210.1 95.4 –

I 25 12.0 79.6 262.1 57.62

50 7.6 75.5 295.1 67.67

100 8.8 66.1 380.1 74.90

200 7.8 38.1 526.7 81.88

400 10.9 31.3 708.9 86.54

800 9.1 28.1 750.1 87.28

Table 5 Biocidal effect of prepared compounds against SRB

Dosage, ppm by weight 50 100 200 400

Type of inhibitors

I 102 Nil Nil Nil

II [103 10 Nil Nil

III [103 103 102 Nil

IV [103 103 102 Nil

J Surfact Deterg

123

deactivated hence; the vital transportation of essential

components for cell bioreactions and activities is disturbed,

causing death to these microorganisms.

Conclusions

From the above results the following conclusions can be

drawn:

1. The synthesized compounds exhibit a good surface

activity in solution as good surfactants.

2. Transformation of THPS to surface active compounds

enhancing corrosion inhibition.

3. Polarization curves revealed that the inhibitors used

represent mixed-type inhibitors.

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Author Biographies

Ismail Abdelrhman Aiad received his Ph.D. in physical chemistry

from the Faculty of Science, Zagazig University 1998 where he is the

vice head of the Petrochemical Department. He is a member of the

board of the Chemical Services and Development Center for Oil Field

Chemicals, and he is a professor at the Egyptian Petroleum Research

Institute surfactants laboratory, Cairo, Egypt. He has been working on

the synthesis and applications of surfactants materials.

Salah M. Tawfik He is an assistant researcher in the petrochemicals

department of the Egyptian Petroleum Research Institute. He earned

his M.Sc. in organic chemistry in 2010 from Helwan University. He is

interested in the synthesis and application of novel surfactants

containing heterocyclic rings and their application as corrosion

inhibitors and biocides.

Samy M. Shaban Received his M.Sc. from Zagazig University in

2009. He is an assistant researcher in the surfactants laboratory at the

Egyptian Petroleum Research Institute, and he is a member in board

of the Chemical Services and Development Center for Oil Field

Chemicals.

Ali A. Abd-Elaal Received his B.Sc. (2004) and his M.Sc. in organic

chemistry (2010) from the chemistry department in the Faculty of

Science, Zagazig University. He worked as a research assistant from

2007 and as an associate researcher since 2010 in the Petrochemicals

Department, Egyptian Petroleum Research Institute, Cairo, Egypt. He

is interested in the synthesis of organic compounds and their

application.

Mohamed El-Shafie Received his B.Sc. from Zagazig University, his

M.Sc. from Al-Azhar University (2004), and his Ph.D. from Alazhar

University (2008). He is a researcher in the Petroleum Applications

Division, Egyptian Petroleum Research Institute (EPRI), Cairo,

Egypt.

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