Polyoxyethylene sorbitan trioleate surfactant as an effective corrosion inhibitor for carbon steel protection

Colloids and Surfaces A 579 (2019) 123636

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Polyoxyethylene sorbitan trioleate surfactant as an effective corrosion inhibitor for carbon steel protection

T

Valeriya N. Ayukayevaa, Galina I. Boikoa, Nina P. Lyubchenkoa, Raushan G. Sarmurzinab, ⁎ Rashida F. Mukhamedovaa, Uzakbay S. Karabalinb, Sergey A. Dergunovc, a

Faculty of Chemical and Biological Technologies, Satbayev University, 22 Satpaev St., Almaty, 050013, Kazakhstan «KazEnergy» Association, Qabanbay Batyr Ave 17, Astana 010000, Kazakhstan c Department of Chemistry, University of Connecticut, 55 North Eagleville Rd, Storrs, CT 06269-3060, United States b

GRAPHICAL ABSTRACT

ARTICLE INFO

ABSTRACT

Keywords: Nonionic surfactant Corrosion inhibitor Corrosion protection Inhibition efficiency Temperature

Corrosion of metals is a significant economic problem globally. The use of corrosion inhibitors, particularly those based on surfactants, is one of the most effective ways of protecting metal surfaces against corrosion. This study addresses the synthesis of a non-ionic oligomeric surfactant and its application as a corrosion inhibitor. The synthesis is a simple and scalable for accomplishing under mild conditions by catalytic esterification of maleic anhydride with polyoxyethylene sorbitan, and further modification of the ether with diethanolamine. The ability of inhibitor to protect a steel sample was evaluated in a solution that simulates compositions of formation waters, and found to be quite effective. The inhibitory behavior of non-ionic polyoxyethylene sorbitan trioleate surfactant (MA/TWEEN-DEA) on ST3 steel corrosion was examined using weight loss and SEM techniques. The compound inhibited the corrosion of carbon steel in a model solution simulating compositions of formation waters, and the extent of inhibition was dependent on temperature and concentration of compound. MA/ TWEEN-DEA at 200 ppm exhibits an inhibition efficiency of 80% at 30 °C and 62% at 70 °C. Thermodynamic and kinetic parameters for ST3 steel corrosion and inhibitor adsorption were determined and discussed. The quantum chemical parameters were used to study the reactivity and adsorption behavior of surfactant. The results of experimental studies and the theoretical investigation well complimented each other.

⁎

Corresponding author. E-mail address: [email protected] (S.A. Dergunov).

https://doi.org/10.1016/j.colsurfa.2019.123636 Received 26 April 2019; Received in revised form 1 July 2019; Accepted 1 July 2019 Available online 09 July 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.

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1. Introduction

across a wide range of temperatures has been examined using ST3 steel in a model solution simulating compositions of formation waters. In order to develop the corrosion inhibition mechanism, the associated activation energy of corrosion, entropy and enthalpy of activation, and thermodynamic parameters, such as standard free energy and entropy of adsorption and the equilibrium constant were determined. For theoretical explanation of the corrosion inhibitive behavior of MA/ TWEEN-DEA and to correlation between corrosion inhibition efficiency and its molecular structure quantum chemical parameters based on the density functional theory method were investigated.

Corrosion is a significant economic problem globally across all segments of the production, processing and transportation of many commercial products and equipment [1,2]. According to the United States Cost of Corrosion Study conducted by NACE International in 2001, the US oil and gas exploration and production industry spends 1.4 billion dollars on corrosion. In detail, 0.6 billion dollars is attributed to surface pipeline and facilities cost, 0.5 billion dollars to downhole tubing and 0.3 billion dollars to capital expenditures related to corrosion [3,4]. In order to maximize the economic viability of the oil and gas industry, it is important to improve corrosion inhibition techniques [15–8]. Iron alloys are used regularly in production, processing, and distribution of refined products, and are highly susceptible to corrosion in different aggressive media [9–12]. A recent increase in the number of developing oil, gas, and gas condensate fields containing corrosionactive components, combined with the increasing workload of oilfield equipment under intensive methods of extraction, transport and processing of products has made the issue of corrosion more acute [13–15]. Use of corrosion inhibitors in the petroleum industry has the potential to extend the life of equipment and pipelines. [16–,17,18,19] A large number of surfactants (cationic, anionic, non-ionic and zwitterionic) have found application as corrosion inhibitors in various media [20–25] and in different conditions. [26,28], Aliphatic and aromatic amines and their salts, aminoalcohols, amino acids, and nitrogen or oxygen-containing five-membered and six-membered heterocycles show a good protective effect [27–34]. However, some values in the application of these compounds as inhibitors include solubility (dispersibility) of the inhibitor in the formation fluids, the low degree of its compatibility with the reservoir waters, and the incorrect selection of the reagent for specific conditions affects the inhibitor performance [35,36], Increasing inhibitor dose can solve some of these problems, but has not always proved to be effective [37]. Even in the conditions of a single petroleum production plant or a field at a different site, performance can vary significantly [38–40]. It is apparent that no one surfactant is going to solve the problem of corrosion of metals permanently. However, currently, industry uses a large number of different surfactants to minimize the effect of corrosion of oilfield equipment [41]. For example, to protect carbon steel from corrosion, El Attari et al. [42] employed n-surfactant polyethylene glycol methyl ether (PEGME), which had an inhibition efficiency of up to 90% at 80 ppm (1 N HCl at 30 °C), whereas Xia [43] showed that S-allyl-O,O’-dialkyldithiophosphates could achive inhibition efficiency up to 98% by using up to 100 mg L−1 of inhibitor in 1 N HCl. Branzoi et al. [44] shows data on application of Tween 60 and 80 as protective reagents. In 0.5 M H2SO4, TWEEN 80 achieved 87–91% inhibition efficiency with a concentration range of 20–1000 ppm, while TWEEN 60 achieved an inhibition efficiency of 93–95%. Li at al. [45] tested TWEEN 85 as a corrosion inhibitor, and showed that a maximum IE was about 92% for 100 mg L−1 in 1.0 M HCl. Additionally, critical micelles concentration (CMC) is one of the primary parameters for surfactant effectiveness as corrosion inhibitors, [46] and surfactants should have a low CMC values as the effectiveness of inhibition decreases as the CMC value increases [47]. In this paper, modified polyoxyethylene sorbitan trioleate (MA/ TWEEN-DEA), a non-ionic surfactant (Fig. 1), has been evaluated as a corrosion inhibitor. Its surface activity, and corrosion inhibition effect

2. Experimental section 2.1. Reagents and characterization Maleic anhydride, diethanolamine, polyoxyethylene sorbitan trioleate (TWEEN-85), pyridine, N,N-dimethylformamide, sodium chloride, magnesium chloride (VI), sodium bicarbonate, calcium chloride, anhydrous acetone, filter paper, distilled water, grinding materials obtained from Sigma Aldrich, all chemicals used without further purification. The tested material was commercially obtained ST3 steel, with the chemical composition (wt. %), as analyzed by optical emission spectrometer, was as follows: C-0.14, Si-0.15, Mn-0.4, Ni0.3, S-0.05, P-0.04, Cr-0.3, N-0.0008, Cu-0.3, As-0.08 and Fe-98.24. The steel was cut into 5 cm × 2.5 cm × 0.2 cm samples for weight loss measurements. Then the samples were grated consistently with 400#, 600# and 1200# abrasive papers in turn, rinsed with double distilled water and degreased with acetone, dried, weighed (accurate to 0.0001 g) and stored in desiccator. 2.2. Synthesis of polyoxyethylene sorbitan trioleate- maleic anhydridediethanolamine non-ionic surfactant, MA/TWEEN-DEA Fig. 1 shows the two-step synthetic route for the surfactant. In the first step, a catalytic esterification of polyoxyethylene sorbitan trioleate was prepared by reacting maleic anhydride (0.5 g, 0.005 mol, 1 eq) in DMF (5 ml) with TWEEN-85 (6.5 g, 0.005 mol, 1 eq) in 7.5 ml of DMF (added drop wise) under mild alkaline conditions with pyridine (0.4 g, 0.005 mol, 1 eq) solution. The mixture was refluxed for 5 h. In the second step, diethanolamine (0.8 g, 0.005 mol, 1 eq) is added to the mixture and the reaction is continued for another 5 h. After that, the process was stopped, cooled to room temperature and the solvent was removed by evaporation. The yield of the desired product was 80–85%. The structure of the synthesized organic inhibitor was confirmed by FT-IR (Fig. S1) and 1H NMR (Fig. S2). FT-IR (Agilent Cary 660, KBr, cm−1): 3382 (vibrations of the OH group), 2921, 2878 (aliphatic eCH2 asymmetric and symmetrical vibrations), 1724 (vibrations in the C]O bond of the ester), 1640 (amide bond (NeC]O, amide I), 1168 (asymmetric vibration of CeOeC in the ester bond (OeC]O). 1 H-NMR (Bruker Avance 300 MHz, D2O, ppm): δ = 0.85–0.9 (t, 6 H,−2 × CH3, alkyl chain), 1.1–1.4 (m, 36 H, −2 × (CH2)14, alkyl chain), 1.51–1.71 (m, 4 H, −2 × NCH2CH2−), 3.01 (s, 12 H, −2 × N +(CH3)2), 3.61 (s, 4 H, −2 × CH2O), 4.21 (s, 4 H, −2 × N + CH2), 6.39–6.67 (m, CH]CH). Fig. 1. Pathway for the synthesis of MA/TWEEN-DEA surfactant.

2

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2.3. Preparation of model solution

2.8. Computational

Model formation waters were prepared by mixing equal volumes of two solutions of salts: solution A and solution B in the ratio 1:1. Solution A: calcium chloride 1100 mg L−1 and magnesium chloride (hexahedral) 380 mg L−1. Solution B: sodium chloride 14045 mg L−1 and sodium bicarbonate 976 mg L−1.

For estimation of molecular properties related to reactivity a quantum chemical study was carried out using the density functional theory (DFT) method and B3LYP/6-31 G basis set as implemented in Gaussian 09 revision D.01. [49–51] Electronic properties such as the energies of the lowest unoccupied molecular orbital (ELUMO) and the highest occupied molecular orbital (EHOMO), the energy gap (ΔE = ELUMO − EHOMO), ionization potential (I = - EHOMO), the electron affinity (A=− ELUMO), the dipole moment (μ), were obtained. Electronegativity (χ, the power of an atom to attract electrons towards itself), hardness (η, resistance to a charge transfer), softness (δ, ability to receive electrons) were calculated using Eqs. (3),(4) and (5), respectively [52]

2.4. Weight loss measurements ST3 steel specimens were suspended in a model solution simulating compositions of formation waters in the absence and presence of different concentrations of MA/TWEEN-DEA at 30, 40, 50, 60 and 70 °C (Fig. S3). The tests were carried out in corrosion cells in a STANHOPE-SETA thermostat. After at least 5 h immersion, the ST3 steel specimens were cleaned with a bristle brush, washed in double-distilled water and acetone, air-dried, and then reweighed (Fig. S4). The specimens were removed and treated according to the method described in the ASTM G1-03(2017)e1 standard [48]. All samples were transferred to desiccator to prevent additional corrosion. In each experiment, at least three parallel tests were conducted on samples in triplicate for each test. The corrosion rate (CR, mg cm−2 h-1) and inhibition efficiency (IE) at different concentrations were calculated using Eqs. (1) and (2), respectively. Where W is the weight loss before and after immersion in solution, W0 and Wi represent weight loss in the absence and presence of inhibitor respectively, A the area of immersed metal coupon and t time in hours.

W CR = A×t IE =

W0

Wi W0

1 (I + A) 2

(3)

=

1 (I 2

(4)

=

A)

1

2 EHOMO

(5)

ELUMO

3. Results and discussion 3.1. Effect of concentration and temperature The corrosion rate and inhibition efficiency for ST3 steel in model formation waters in the absence and presence of different concentrations of MA/TWEEN-DEA are summarized in Table 1. The corrosion rate (CR) decreased with increasing MA/TWEEN-DEA concentrations due to the increased surface coverage of inhibitor at the interface of steel and solution. The subsequent IE efficiency of each concentration of surfactants was also calculated (Table 1). Table 1 shows that inhibition efficiency of ST3 steel increases with the increase of inhibitor concentration. At the highest concentration tested IE reached 80% at 30 °C. As the temperature increases, the

(1)

·100

=

(2)

2.5. Electron microscopy images To prepare the sample for SEM analysis (Quanta 3D 200i, working voltage of 15 kV), a dry sample was taken from desiccator and immediately was placed on SEM pin stub specimen mount covered with double coated conductive carbon tabs and all measurements were examined under vacuum without coating.

Table 1 Corrosion parameters obtained from weight loss of carbon steel in solution containing various concentrations of MA/TWEEN-DEA at different temperatures.

2.6. X-Ray diffraction characterizations The carbon steel specimens were immersed in model formation water in the absence and presence of corrosion inhibitor MA/TWEENDEA (200 ppm) for a period of 5 h. After 5 h, the specimens were taken out and dried. The nature of the surface film formed on the surface of the carbon steel specimen was examined using an X-ray diffractometer (X’Pert Pro PANalytical, Netherlands).

T, ˚C

MA/TWEEN-DEA (ppm)

30

0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200

40

2.7. Polarization measurements

50

Polarization curves were measured using Autolab PGSTAT302n (Metrohm Autolab, The Netherlands) in a three-electrode glass cell at two temperatures 30 °C and 40 °C. Platinum electrode was used as the counter electrode and silver chloride electrode (Ag/AgCl) as the reference electrode. Polarization curves were conducted from cathodic potential of −250 mV to an anodic potential +250 mV. Measurements were performed in modelling water formations containing different concentrations of the tested inhibitor. Corrosion current density (Icorr, A/cm2) and corrosion potential (Ecorr,V) values were obtained using the Tafel extrapolation method whereby the estimated corrosion current, Icorr, obtained from the intercept of the two linear segment of the Tafel slope from the cathodic and anodic polarization plots.

60

70

3

Inhibition efficiency, %

44.9 66.0 71.3 79.9 41.0 50.9 58.1 71.3 41.4 49.3 54.4 67.1 41.2 49.2 52.9 67.0 34.4 42.9 50.0 62.1

Corrosion rate, (mg/cm2·h) 0.0209 0.0115 0.0071 0.0060 0.0042 0.0148 0.0123 0.0105 0.0072 0.0292 0.0171 0.0148 0.0133 0.0096 0.0376 0.0221 0.0191 0.0177 0.0124 0.0522 0.0342 0.0298 0.0261 0.0198

θ

0.44 0.66 0.73 0.79 0.41 0.50 0.58 0.71 0.41 0.49 0.54 0.67 0.41 0.49 0.52 0.67 0.34 0.42 0.50 0.62

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corrosion rate (CR) increases and inhibition efficiency decreases. At 40, 50, 60 and 70 °C, maximum inhibition efficiencies of 71.3%, 67.1%, 67.0% and 62% were obtained in model formation waters containing 200 ppm of MA/TWEEN-DEA, respectively. The study of the temperature range on the inhibition effectiveness is important for clarifying the mechanism and kinetics of its action. The chemisorption phenomenon usually enhances inhibition efficiency with rise in electrolyte temperature while the reverse is often associated with physisorption [53]. To determine the impact of temperature on the ability of surfactant to inhibit the corrosion of ST3 steel, weight loss experiments were done at 30, 40, 50, 60 and 70 °C in the absence or presence of MA/TWEEN-DEA at different concentrations. Analyzing data of the temperature dependence on corrosion speed reveals that corrosion rate increases with increasing temperature (from 30 to 70 °C), in a linear fashion as predicted by the Arrhenius equation [54]. 3.2. Surface analysis by scanning electron microscopy (SEM) studies Scanning electron microscopy (SEM) was employed to study the surface morphologies of a freshly polished carbon steel surface incubated in corrosive solution with or without inhibitor at 30 °C and 50 °C. Images are shown in Fig. 2. The freshly polished steel sample shows a smooth, non-corroded surface with polishing scratches (see Fig. 2a). The SEM photographs of the steel after contact with the corrosive solution without the inhibitor shows a heavily corroded surface with a large number of pits on the surface of the metal (Fig. 2 b). However, steel samples treated with inhibitor are only slightly corroded with a much smaller number of pits on the metal surface (Fig. 2 c). It clearly indicates the formation of passive layer on the metal surface. Therefore, the corrosion rate decreased in the presence of inhibitor. SEM results (Fig. 3) indicate that specimens in the uninhibited solution are highly damaged due to aggressive media of salts by oxygen (Fig. 3a, c). Additionally free carbon dioxide CO2 lowers the pH of the water due to its dissociation that lead to increased rate of corrosion. From the other hand, in the presence of inhibitor (Figs. 3b and d), carbon steel surface is not as damaged as in the case of uninhibited acidic solution. A close look at the result presented indicates that in the absence of the inhibitor, the carbon steel was seriously corroded, demonstrating a significantly deteriorated morphology. It is shown that the quantity of deposits decreases, also the roughness of the carbon steel surface reducing sharply in comparison with the blank solution when these inhibitors are added; this fact may be explained on the basis of creation adsorbed film of the inhibitor MA/TWEEN-DEA at steel surface. Film prevents the corrosion solution from reaction with carbon steel. These experimental results are also consistent with adsorption and thermodynamic considerations. XRD analysis was used to determine film formation of carbon steel in in model formation waters in the absence and presence of 200 ppm of MA/TWEEN-DEA. Peaks due to iron oxides FeO(OH) appear at 2θ = 14.7°, 27.3°, 36.5° and 44.6° (Fig. 4a). This shows that in the water solution without corrosion inhibitor carbon steel specimen has incurred corrosion leading to the formation of magnetite and lepidocrocite. [55,56] The surface of the carbon steel specimen in presence of MA/TWEEN-DEA is shown in Fig. 4b. It was observed that the quantity of peaks due to oxides of iron FeO(OH) reduced. This confirms that the metal surface is more protected from corrosion with the addition of inhibitor. [57–62]

Fig. 2. SEM images of carbon steel: polished specimen before immersion (a) and steel specimen in model solution simulating compositions of formation waters at 30 °C in the absence (b) and presence (c) of 100 ppm MA/TWEENDEA.

Vcor = exp( W=

RT exp Nh

Ea ) RT Sa0 exp ( R

(6)

Ha0 ) R

(7)

where Ea is activation energy, λ is the pre-exponential factor, R is the universal gas constant, T is the absolute temperature, h is the Planck’s constant, and N is Avogadro’s number. Typical graphs based on data received from equations for ST3 steel corrosion in a model formation waters with and without MA/TWEENDEA at various temperatures are illustrated in Figs. 5 and 6 and summarized in Table 2. Results show that the values of Ea in the presence of the MA/ TWEEN-DEA are higher than those in the uninhibited acid solution indicating the physical adsorption mechanism on the metal surface [63–65]. These results are in good agreement with previously reported studies [65–69]. According to Eq. (3), it can be seen that higher Ea is correlated with a lower corrosion rate (Vcor). For example, for the corrosion process at a surfactant concentration of 50 ppm, Ea is 22.15 kJ

3.3. Kinetic considerations The relationship between the corrosion rate (mg/cm2·h) of the steel plate in a neutral medium and the temperature, and thermodynamic parameters such as entropy of activation (ΔSa), enthalpy of activation (ΔHa) and the activation energy (Ea) can be described using the Arrhenius Eq. (6) and its alternative Eq. (7) [54,63]. 4

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Fig. 3. SEM images of carbon steel in model solution simulating compositions of formation waters at 30 °C (a, b) and 50 °C (c, d) in the absence (a, c) and presence (b, d) of 200 ppm MA/TWEEN-DEA.

Fig. 5. Arrhenius plot for ST3 steel in model water solution with and without MA/TWEEN-DEA. Fig. 4. XRD spectrum of St3 steel corrosion in the (a) absence and (b) presence of MA/TWEEN-DEA.

adsorption for the surfactant when temperature is rising. The value of ΔHa is lower than Ea, which means inhibitor has formed a stable layer on the steel surface [74]. These results reflect that MA/TWEEN-DEA inhibitor showed 80% efficiency of corrosion protection in a neutral mineralized medium at a temperature of 30 °C and a reagent concentration of 200 ppm.

mol−1. Ea increases to 31.52 kJ mol−1 as surfactant concentration increased. At an inhibitor concentration of 0.2 g L−1, Ea reached maximum, and plateaued. That is, the apparent activation energy acts as a function of inhibitor concentration [70,71], Increasing inhibitor concentration also lead to an increase in enthalpy and is explained by the fact that the decrease in the corrosion rate of steel is mainly controlled by kinetic activation parameters [72]. The effectiveness of organic substances as corrosion inhibitors can be attributed to the interaction between polar groups and metallic surface [73]. The metal surface in the aqueous solution is always covered with adsorbed water due to the strong dipoles. The polar groups of the organic substances compete with water to adsorb to the metal surface in a quasi-substitution process [73]. Positive values of the enthalpy of Na indicate the endothermic nature of the corrosion process [73], which means it is good for

3.4. Adsorption and thermodynamic considerations The choice of the adsorption isotherm equation depends on the convergence of the obtained data with the trend line. In the current study, we used the equation of the Langmuir adsorption isotherm:

Cinh

=

1 ads

+ Cinh

(8)

where, Cinh is surfactant concentration, Kads is adsorption constant, and θ is the fraction of steel surface covered by the adsorbed molecules. 5

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Table 3 Values of the adsorption-desorption equilibrium constant Kads and the summary Gibbs energy ΔGаds. T (oC)

Кads, *10 3 mol−1

ΔGads, kJ/mol

30 40 50 60 70

0.9567 1.0757 1.2067 1.2281 1.1769

−27,3 −28.6 −29.8 −30.8 −31.8

Fig. 6. Alternative Arrhenius plot for St3 steel in model water solution with and without MA/TWEEN-DEA. Table 2 Activation parameters for corrosion of ST3 steel in a model solution simulating compositions of formation waters in the absence and presence of corrosion inhibitor. C, g/l

Ea, (KJ/mol)

ΔHa, (KJ/mol)

ΔSa, (KJ/mol⸱K)

0 0.05 0.1 0.15 0.2

19.205 22.15 28.61 29.97 31.52

16.51 19.48 25.93 27.3 28.84

−25,6 −20.76 −2.55 0.62 2.59

Fig. 8. Polarization curves for ST3 steel in model water solution at 30 °C containing different concentrations of MA/TWEEN-DEA.

is free energy of adsorbtion, and the constant is the molar concentration of water in solution. Negative values of ΔGads indicate [75] the stability of the adsorbed film on the surface of the steel plate. A decrease in ΔGads (more negative values) with increasing temperature indicates the presence of an endothermic process, which also confirms the mechanism of physical adsorption of the reagent. 3.5. Potentiodynamic polarization studies Polarization behavior of carbon steel in model formation water at 30 °C in the absence and presence of different concentrations of MA/ TWEEN-DEA is shown on Fig. 8 (Figure S5 shows behavior at 40 °C). Electrochemical parameters such as the corrosion potential (Ecorr), corrosion current density (Icorr), Tafel slopes βa (βc) are listed in Table 4. The inhibition efficiency (IE%) is obtained from the intersection of the anodic and cathodic Tafel lines of the polarization curve at Ecorr. IE% values were calculated from the following equation:

Fig. 7. Langmuir adsorption isotherm plots for ST3 steel in a model solution simulating compositions of formation waters containing various concentrations of MA/TWEEN-DEA at 30–70 °C.

IE %=

The diagram of the dependence of Cinh / θvs. Cinh relating the adsorption of MA/TWEEN-DEA on ST3 steel was approximated by Langmuir adsorption isotherm (8) and is shown in Fig. 7. Table 3 shows adsorption parameters derived from the plots of Fig. 7. The Kads values rise with increasing temperature (Table 3), suggesting the strong adsorption ability of MA/TWEEN-DEA on the ST3 steel surface. The equilibrium constant for the adsorption process (Kads) is related to the standard Gibbs free energy of adsorption (Gads) by the following equation:

K ads =

1 exp 55.5

ads

RT

i 0 corr icorr ·100 i 0 corr (i0corr)

(10)

and (icorr) are the corrosion current density it the absence where and presence of MA/TWEEN-DEA, respectively. The polarization measurements clearly illustrate the fact that the corrosion current density decreased with the increasing concentrations of the corrosion inhibitor [76]. This point can be explained by the adsorption of corrosion inhibitor molecules on the sample surface and forming a protective carbon steel surface. As expected the anodic Tafel slope (βa) and the cathodic Tafel slope (βc) had changed with the addition of the corrosion inhibitors (Table 4 and Table S1 for 30 and 40 °C) [78,79]. This shows that the corrosion inhibitor influences the anodic and cathodic reactions. The maximum displacement in Ecorr in our study was about 15 mV, suggesting that inhibitor acts as a mixed cathodic and anodic type [77–79]. Additionally, increasing the

(9)

where, R is the universal gas constant, T is absolute temperature, ΔGads 6

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all four arms (Fig. 9c) suggesting the strongest ability to interact with the charged sites of metal surface to form protective layer on the metal surface [83,84]. Moreover, physical adsorption process and a good electrostatic interaction with the metal surface also suggested by global hardness and softness values and dipole moment. Results showed that the electronegativity of MA/TWEEN-DEA molecule is lower than the work function of Fe (110) (4.5 Vs 4.8 eV), and predicts that inhibitor molecules are adsorbed on the metal surface by the transfer of electrons from the metal orbitals to the suitable vacant inhibitor orbitals. Therefore, results from quantum chemical calculations are correlate with the experimental data and show that MA/TWEEN-DEA favors the physical adsorption on the metal surface.

Table 4 Polarization parameters for ST3 steel in model water solution at 30 °C containing different concentrations of inhibitor. Concentration (ppm)

Ecorr (V vs. SCE)

icorr (μA/cm [2])

βa (mV/dec)

βc (mV/dec)

IE (%)

blank 50 100 150 200

−0.603 −0.611 −0.631 −0.613 −0.618

0.007 0.005 0.004 0.003 0.002

79.8 81.3 93.07 153.1 189.3

170.7 130.5 132.4 133.7 88.1

– 28.6 42.9 57.1 71.4

concentration of the inhibitor gives rise to a consistent decrease in anodic and cathodic current densities, indicating that MA/TWEEN-DEA acts as a mixed-type inhibitor. As shown in Table 4 (and Table S1), the corrosion current density (icorr) became lower and the inhibition efficiency (IE) increased with increasing concentrations of the corrosion inhibitor MA/TWEEN-DEA.

4. Conclusions In summary, an inexpensive surfactant inhibitor was developed using simple processes and low-cost and scalable for accomplishing under mild conditions by catalytic esterification of maleic anhydride with polyoxyethylene sorbitan, and further modification of the ether with diethanolamine. In this study, it has shown that MA/TWEEN-DEA is an effective corrosion inhibitor that can be applied for protection of carbon steel. Also this inexpensive inhibitor potentially can be easily applied on the inside and outside surfaces of steel pipes for exploitation in different aggressive media, and also outside surface of steel architecture. Weight loss and SEM techniques were used to confirm corrosion inhibition in a model solution simulating compositions of formation waters. It was found, that the percentage inhibition efficiency depends on the concentration of surfactant and temperature of the formation waters. The inhibition efficiency of MA/TWEEN-DEA increases with the increase of inhibitor concentration, but decreases with increasing temperature. The adsorption of the investigated reagent on a carbon steel surface in a model water solution follows the Langmuir adsorption isotherm. The negative values of ΔGads confirm the stability of the adsorbed film on the surface.

3.6. Quantum chemical calculations Fig. 9 represents HOMO and LUMO frontier molecular orbitals and Mulliken charge distributions of the optimized structure of the MA/ TWEEN-DEA. Moreover, the quantum chemical parameters are listed in Table 5. In calculations, all twenty alkoxy-groups of the core were evenly distributed in all arms of surfactant. Analysis of HOMO and LUMO parameters and distribution of charges suggest that MA/TWEENDEA molecule could adsorbed to metal surface by different centers. The HOMO and LUMO of MA/TWEEN-DEA could bond with the partially filled 3d and 4 s orbitals of iron atom, respectively [80]. Additionally, small value of energy gap (ΔE) suggest high affinity of surfactant and that a molecule could potentially be adsorbed more easily on a metal surface due to increasing of the reactivity of a molecule towards a metal surface [81,82]. The population of the electron density is focused on heteroatoms in

Fig. 9. Quantum chemical results of MA/ TWEEN-DEA molecule obtained by DFT method at B3LYP with 6–31 G basis set: (a) LUMO and (b) HOMO* (combined HOMO, HOMO-1, HOMO-2 with identical energies as shown in Fig. S6) of optimized molecular structure, (c) Mulliken charges (red: positive, blue: negative) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

7

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Table 5 Quantum chemical parameters of MA/TWEEN-DEA calculated at the B3LYP with 6–31 G basis set level of theory. EHOMO (eV)

ELUMO (eV)

ΔEgap (eV)

I (eV)

A (eV)

χ (eV)

η (eV)

δ (eV)

μ (D)

−6.363

−2.679

3.684

6.363

2.679

4.531

1.842

0.543

1.188

Author contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

[20]

Acknowledgements

[21]

This work was financially supported by grant funding for scientific and (or) scientific and technical research from the Committee of Science of the Ministry of Education and Science of Republic of Kazakhstan for 2018-2020 № AP05130541. We would like to express our gratitude to Céline Frochot, Ludovic Colombeau and Philippe Arnoux for their hospitality and creation working conditions in the Laboratoire Réactions et Génie des Procédés, Université de LorraineCNRS.

[22] [23]

[24]

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Appendix A. Supplementary data

[26]

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.colsurfa.2019.123636.

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