1 Introduction

Corrosion studies are very important in the natural gas and crude oil sector [1]. Hydrochloric acid is widely used in industries as a cleaning agent and pickling. Since acids are aggressive behavior, corrosion in acids is vital and this causes great problems. The chemicals used for corrosion control is expensive. The environment is destructive to C-steel in the improvement of oil and gas creation in pickling, mechanical cleaning, and descaling. Thus, the industry of petroleum is an inhibitors consumer.

Inhibitors used must have numerous favorable circumstances, for example, high hindrance effectiveness [2], easily produced on a large scale, low toxicity, and low price [3]. The activity of the surfactant in aqueous solutions may be attributed to chemisorption or electrostatic physical adsorption onto the metallic surface [4]. The improvement of surfactants dependent on common sustainable assets is an idea that is picking up recognition from different industries [5, 6]. Derivatization of fats and oils to create a wide range of surfactants for a wide scope of utilizations has a long convention and is settled. The creation of surfactants dependent on fats, oils, and sugars on a wide scale was considered [7, 8]. Considering the amphiphilic structure of a normal surfactant with a hydrophilic head and a hydrophobic tail, it has consistently been a test to join carbohydrate molecules an ideal polar head, because of its various hydroxyl group, so a fat and oil derivatives, for example, unsaturated fatty alcohol ao fatty acids [9, 10]. Generally, surfactants as corrosion inhibitors must be added with the HCl solutions to diminish the destructive effect of acid [11]. Alkylphenol ethoxylates, e.g. nonylphenol ethoxylates (NPE) are used in the oil field industry [12, 13]. NPEs have been restricted from use on account of their harmfulness. Gravimetric and electrochemical evaluations of nonionic surfactants were studied as corrosion inhibitors for mild steel in 1 M HCl solution [14,15,16,17,18]. The quaternary ammonium salts and amines are the most utilized mixes of the cationic surfactants class, where the cation is the surface-active species [19, 20]. Cationic gemini-surfactants were used as inhibitors for carbon steel in hydrochloric acid [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37]. The objective of this work is to synthesise and characterize some novel fatty alcohol surfactants and study the effect of ethoxylation and sulfonation of fatty alcohol and investigations as inhibitors.

2 Experimental

2.1 Chemicals and Materials

The reagents used were ethylene oxide gas (highest purity), purchased from air products incorporation. Potassium hydroxide (48.0–50.0% w/w) purchased from EL-Gamhoria Co., Egypt. Acetic acid (glacial), purchased from Sigma-Aldrich Co. LINEVOL 11 which is a high purity C11 primary oxo alcohol manufactured using the shell hydroformylation (SHF) process. Its specification is shown in Table 1.

Table 1 Key physical and chemical properties of LINEVOL 11
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The concentration range of the prepared surfactants as corrosion inhibitors in this study was ranging from 50 to 300 ppm.

2.2 Synthesis Procedures

2.2.1 Ethoxylation of LINEVOL 11 with 20 mol of Ethylene oxide

The synthesis of novel fatty alcohol surfactants performed in a 2L autoclave. LINEVOL 11 (R–CH2OH) where R = C10H21 as long chain. Fatty alcohol was put into a stainless steel autoclave with KOH 1 wt% at high pressure and 130 °C with incessant stirring, flowing a nitrogen gas to flush out the air for 10 min. Then, the flow nitrogen gas was stopped and exchanged by inserting 7 mol of ethylene oxide gas (EO) to prepare R–CH2O–(CH2CH2O)7–H and inserting 20 mol of ethylene oxide gas (EO) to prepare R–CH2O–(CH2CH2O)20–H [38]. The heating was stopped at the point when the pressure becomes a minimum value and the vessel substances were cooled. At this stage, the reaction completion was accepted. The product was cooled and neutralized by acetic acid. Then collected the yield, the surfactant obtained appeared as a waxy appearance. The obtained compound has the following structure and is labeled (B2).

2.2.2 Sulfonation of Ethoxylated Fatty Alcohols

R–CH2O–(CH2CH2O)7–H and R–CH2O–(CH2CH2O)20–H were reacted with oleum containing SO3 content (65% by weight) in a glass-fitted reactor. The temperature of the reactor was adjusted to 30 °C. The acidic intermediate product formed was neutralized while stirring in a receiving vessel containing a mixture of 50% sodium hydroxide and demineralized water [39, 40]. R–CH2O–(CH2CH2O)7–SO3Na and R–CH2O–(CH2CH2O)20–SO3Na surfactants obtained appeared as waxy appearance, and Label as B1 and B3 as shown in Scheme 1.

Scheme 1
scheme 1

Generalized structure of the synthesized compounds

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2.3 Composition of C-Steel

Carbon steel alloy specimens used in this investigation were cut from unused petroleum pipeline as regular edged cuboids with dimensions 2 cm × 2 cm × 0.5 cm. The chemical composition of carbon steel alloy is listed Table 2.

Table 2 Composition in wt% of C-steel
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2.4 Electrochemical Techniques

For electrochemical estimations, a traditional three-terminal cell was utilized. A platinum sheet used as a counter electrode and the reference electrode is a saturated calomel electrode (SCE). The carbon steel rod was fitted into a polytetrafluoroethylene (PTFE) holder, the exposed area to the solution in the glass cell is 1 cm2. The electrode surface was scraped by emery paper grades (320–600–800–1000–1200). Acetone is used as a degreasing solution, then the electrode is washed by water and dried [41, 42]. Tests were completed at a steady temperature (25 °C\()\) controlled by a thermostatic bath with accuracy \(\pm 0.1\)°C. The potentials of carbon steel electrodes were measured against saturated calomel electrode in 1 M HCl solution in the absence and presence of different concentrations of the inhibitors. EIS experiments frequency range expands from 100 kHz to 100 MHz with a 10 mV sine wave as the excitation signal at open circuit potential. The current–potential curves were recorded by varying the potential with a sweep rate of 5 mV/s from − 1.2 to 1.2 V [43,44,45]. The working electrode was put in the investigated solution for 30 min until the steady-state was attained. All potentials were recorded against SCE. Gamry Instrument Potentiostat/Galvanostat/ZRA (PCI4-G750) was used. All experiments were carried out at room temperature in a cell contains 100 ml of the freely aerated stagnant solutions. In each experiment, three parallel tests were conducted on samples in triplicate for (Table 2).

2.5 Surface Examination

Samples were scraped with emery paper (350–600–800–1000–1200) grade until a mirror surface is attained, degreased, washed, dried, and then dipped in solution. The electrode was dipped in HCl without and with 300 ppm of the surfactants at 25 °C for 24 h. The sample was cleaned with bidistilled water, dried then the surface of the C-steel was examined with different magnifications [45, 46] by scanning electron microscope (JEOL JSM-5500, Japan).

2.6 Surface Tension Measurements

The measurement of surface tensions was conducted for ethoxylated and sulfonated fatty alcohol surfactants with different concentrations, which its surface tension is 72 mN/m at 25 °C by using Attension Sigma 703D instrument using Du Noüy ring methods at 25 °C. The mean values of surface tension were obtained from multi repetitions CMC values of the ethoxylated and sulfonated fatty alcohol surfactants were obtained from the plotted curve of surface tension value corresponding to the concentrations of these surfactants. The critical micelle concentrations can be predicted from the phase change of surface tensions with concentrations [12, 47].

2.7 Spectroscopic Characterization of the Ethoxylated and Sulfonated Fatty Alcohol Surfactants

The chemical structures of synthesized ethoxylated and sulfonated fatty alcohol surfactants were investigated by 1H NMR spectra and FTIR spectra [12]. FTIR was performed using KBr methods at the region from 4000 to 400 cm−1 using Thermo Scientific, Nicolet iG50 FT-IR spectrophotometer. 1H NMR spectra were measured on Bruker 400 MHz (d-Acetone) using TMS as an internal standard (chemical shift in d-scale).

3 Results and Discussion

3.1 Spectroscopic Investigation of the Newly Prepared Surfactants

The chemical structure of the new ethoxylated and sulfonated fatty alcohol was founded by FTIR and 1H NMR spectroscopy.

3.1.1 FTIR Spectroscopy

Figure 1a, b, and c shows FTIR spectra of the synthesized surfactants B1, B2, and B3, respectively. The structural moieties for the newly prepared ethoxylated linear primary alcohol confirmed by infrared spectroscopy are summarized:

Fig. 1
figure 1

a FTIR spectrograms of (B1). b FTIR spectrograms of (B2). c FTIR spectrograms of (B3)

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(B1) cm−1: 2875, 2923 (CH aliphatic), 1462 (CH2), 1353, 1252 (–SO3 asymmetric, symmetric), 1104 (O–C).

(B2) cm−1: 3450 (OH), 2878 (CH aliphatic), 1467 (CH2), 1111 (O–C).

(B3) cm−1: 2858, 2925 (CH aliphatic), 1463 (CH2), 1353, 1253 (–SO3 asymmetric, symmetric), 1108 (O–C).

3.1.2 1H NMR Spectroscopy

Figure 2a, b, and c represent 1H NMR spectrograms of B1, B2, and B3 surfactants, respectively.

Fig. 2
figure 2

a 1H NMR spectra of B1 surfactant in D2O. b 1H NMR spectra of B2 surfactant in acetone-d6. c 1H NMR spectra of B3 surfactant in D2O

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(B1) Surfactant: 1H NMR (400 MHz) (D2O) δ 0.804–0.821 (t, CH3), 3.550–3.578 (m, CH2), 3.614–3.631 (t, O–CH2), 3.640–3.715 (t, O–CH2).

(B2) Surfactant: 1H NMR (400 MHz) (acetone-d6) δ 0.860–0.877 (t, CH3), 1.287 (s, OH) 3.399–3.501 (m, CH2), 3.511–3.525 (t, O–CH2), 3.580–3.617 (t, O–CH2).

(B3) Surfactant: 1H NMR (400 MHz) (D2O) δ 0.803–0.819 (t, CH3), 3.585–3.637 (m, CH2), 3.702–3.723 (t, O–CH2), 4.085–4.107 (t, O–CH2).

3.2 Surface Tension Measurements

Water surface tension (γ) is produced from hydrogen bonds between an air/water interface at the water molecules. When surfactants adsorb at the interface, it breaks the hydrogen bonds, as a result, the value of the water surface will decrease less than 72 mN/m at 25 °C. The surface tension of the current surfactants was obtained from various concentrations of current surfactants under and above the CMC [48]. Figure 3a, b, c represents plots of surface tension against concentration for the prepared surfactants B1, B2, and, B3, respectively. The surface tension curve reveals a decrease when the concentration of aqueous surfactants increases. This reveals the high adsorption of surfactant molecules at the water interface. Therefore, the surface tension values will be constant when the concentration of the surfactant molecules increased. When those two regions are interrupted [49], will give CMC value at which formed the surfactant micelles. These notices were recorded for the current surfactant up to the CMC, on the further side which no considerable changes were observed. The screening of partitioning above the aqueous CMC is important [50] (Table 3).

Fig. 3
figure 3

a The surface tension of B1 versus its concentrations in water at 25 °C. b The surface tension of B2 versus its concentrations in water at 25 °C. c The surface tension of B3 versus its concentrations in water at 25 °C

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Table 3 Surface tension (γ) and critical micelle concentration (Ccmc) of the prepared surfactants from surface tension measurements at 25 ± 1 °C
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3.3 Electrochemical Impedance Spectroscopy

Figure 4a–c show the Nyquist plots for C-steel in the absence and presence of different concentrations of surfactants (B1, B2, and B3) at 25 °C. This measurement potential is related to open circuit potentials after 30 min until reach steady-state equilibrium between Metal and Electrolytes. The impedance data fitting using the equivalent CPE circuit which gives a more accurate fit. Show in Fig. 5, which contains Rs, as electrolyte resistance and Rct, as charge transfer resistance and CPE, constant phase elements, which give us information about Cdl capacitance double layer. The result of CPE constant phase element was used instead of the capacitive element is due to the heterogeneity of electrode surface result from the adsorption of inhibitors, surface roughness, grain boundaries, dislocations, impurities, and formation of porous layers [51,52,53]. To obtain Cdl, the frequency at which the imaginary component of the impedance is maximum \(f(-{Z}_{\mathrm{image}}^{\prime\prime})\) was predicted and Cdl values were calculated from Eq. (1).

Fig. 4
figure 4

a Nyquist plots for C-steel in 1 M HCl in the absence and presence of different concentrations of B1. b Nyquist plots for C-steel in 1 M HCl in the absence and presence of different concentrations of B2. c Nyquist plots for C-steel in 1 M HCl in the absence and presence of different concentrations of B3

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Fig. 5
figure 5

Equivalent circuit model used to fit experimental EIS

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$$f \left(-{Z}_{\mathrm{image}}^{\prime\prime}\right)=\frac{1}{2} (\pi {C}_{\mathrm{dl}}{R}_{\mathrm{ct}})$$
(1)

From the charge transfer resistance values, the efficiency was calculated using the Eq. (2):

$${\text{IE \% = }}\uptheta \times {\text{100}} =\frac{{R}_{\mathrm{ct}} - {{R}_{\mathrm{ct}}^{*}}}{{R}_{\mathrm{ct}}} \times 100$$
(2)

where \(R_{{{\text{ct}}}}^{*}\) and Rct are the values of charge transfer resistance without and with surfactant, respectively. As the concentration of the surfactant increased, the Rct values increased, and the Cdl values decrease.

The decrease in the magnitude of Cdl is due to the adsorption of the compounds on the metal surface. Table 4 shows that, Rct increase with increasing the surfactant concentration, which is due to the reduction in the active surface required for corrosion reaction. The high values of Rct indicate the higher inhibition efficiencies [54]. Cdl values decrease with increasing the surfactant concentration, which supposed that surfactant molecules are adsorbed on the metal surface [55] which leads to increase θ and IE% which was in the order as B1 > B2 > B3. Because of the number of ethoxylated groups in B1 and B2, more than that is in B3 and the presence of sulfonic group in B1 and B3 and absence in B2.

Table 4 EIS data in the presence of different concentrations of surfactants
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3.4 Open-Circuit Potential Measurements

The electrode was immersed in 1 M HCl without and with different concentrations from the investigated compounds. The open-circuit potential (OCP) was recorded with time. The OCP of carbon steel electrodes was measured against saturated calomel electrode (SCE) in the absence and presence of various concentrations of the inhibitors as indicated in Fig. 6a–c. It is obvious, that the direction of the potential firstly towards more negative values for a short time. This attitude is an indication of the breakdown of the oxide film present on the surface of C-steel before immersion, then the potential is shifted to a more noble direction until the steady-state potential is established [1]. As shown from the obtained figures, the potential is shifted to the noble direction in the following order: B1 > B2 > B3. This suggests, that the kinetics of the anodic reaction of carbon steel is affected more strongly in the presence of the inhibitor (B1), than in presence of the inhibitor (B2 and B3). This is in agreements with the order of inhibition efficiencies obtained from EIS.

Fig. 6
figure 6

a Potential–time curves for carbon steel in 1 M HCl solution in the absence and presence of different concentrations of B1at 298 K. b Potential–time curves for carbon steel in 1 M HCl solution in the absence and presence of different concentrations of B2at 298 K. c Potential–time curves for carbon steel in 1 M HCl solution in the absence and presence of different concentrations of B3 at 298 K

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3.5 Potentiodynamic Polarization Technique

Figure 7a–c show the polarization curves for C-steel in 1 M HCl without and with different concentrations of surfactants. It is evident from the curves that values of current density decrease with the presence of the investigated compounds indicating that the compounds were adsorbed on the steel surface and caused corrosion inhibition. Potentiodynamic parameters as deduced from these curves, e.g., corrosion potential (Ecorr), corrosion current density (icorr), the anodic Tafel slope (ba), the cathodic Tafel slope (bc), and % IE are shown in Table 4. The value of icorr continuously decreases in presence of increasing inhibitor concentration. The maximum IE of 93.5% was observed at a concentration of 300 ppm of B1compound indicating that a higher coverage of surfactant on C-steel surface is obtained in the solution with the highest concentration of inhibitor. The magnitude of the shift in Ecorr in presence of the investigated compounds (less than 85 mV) suggests that it acts as a mixed inhibitor and affects both anodic and cathodic reactions [56]. There is no markedly change of both cathodic Tafel slopes (βc) and anodic Tafel slopes (βa), which reveals that the corrosion mechanism doesn’t change and simple adsorption mode is the way to inhibit the corrosion [57, 58].

Fig. 7
figure 7

a Polarization curves C-steel in 1 M HCl in the absence and presence of different concentrations of B1 at 25 °C. b Polarization curves C-steel in 1 M HCl in the absence and presence of different concentrations of B2 at 25 °C. c Polarization curves C-steel in 1 M HCl in the absence and presence of different concentrations of B3 at 25 °C

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The (%IE) can be calculated from the (icorr) values determined by Tafel extrapolation using Eq. (3):

$$\mathrm{IE}\%= \theta \times 100 = \frac{{i}^{^\circ }\mathrm{corr }-\mathrm{ icorr }}{{i}^{^\circ }\mathrm{corr}} \times 100$$
(3)

where icorro and icorr are the corrosion current densities in the absence and presence of the compounds respectively. IE % values were ordered as B1 > B2 > B3. Because of the number of ethoxylated groups in B1 and B2, more than that is in B3 and the presence of the sulfonic group in B1 and B3 absence in B2. Generally, increase surfactant concentration lead to an increase in inhibitions efficiency (Table 5).

Table 5 Potenitiodynamic data in the presence of different concentrations of surfactants at 25 °C
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3.6 Adsorption Isotherm

The adsorption isotherm phenomena are due to the interaction between the surface of C-steel and surfactant as inhibitors. Two main types describe the adsorption of surfactants: physical adsorption and chemical adsorption. The chemical structure influences the adsorption kind of molecules, the nature of metals, charges, and types of electrolytes. From electrochemical measurements, we can calculate the surface coverage; θ using Eq. (3). While the values of θ at different concentrations from the investigated compounds were examined by fitting to various isotherms including, Flory-Huggins, Temkin, Frumkin, and Langmuir [59]. The best fit was gained with the Langmuir isotherm is through the following equation (4):

$$\frac{C}{\theta }= \frac{1}{{K}_{\mathrm{ads}}}+C$$
(4)

where θ is the surface coverage of surfactants on the C-steel surface, C is the concentration of the surfactant and Kads is the equilibrium constant of the adsorption process.

The relation between (C/θ) versus C, for all concentrations of inhibitors, gives a straight line relationship (Fig. 7). In the present study, Langmuir adsorption isotherm was found to be suitable for the experimental data. Regression coefficient values close to unity (R2) confirmed the validity of this approach. We can calculate ΔG˚ads from Eq. (5):

$${K}_{\mathrm{ads}}= \frac{1}{55.5}{\mathrm{e}}^{\frac{-\Delta {G}_{\mathrm{ads}}^{^\circ }}{RT}}$$
(5)

R is the universal gas constant and T is the temperature in Kelvin. The slope of the obtained straight lines, nearly equal unity. The deviation from unity is attributed to the interactions between adsorbed species on the surface and changes in adsorption with the increase in the surface coverage [60, 61]. The negative values of ΔG°ads (Table 1) are firmed with the spontaneous adsorption process and the constancy of the layer on the surface of the C-steel [62]. It is known that the values of ΔG°ads up to − 20 kJ/mol indicates physisorption; the inhibition performance due to the electrostatic interaction between the charged surfactants and the charged metal surface, while the values around − 40 kJ/mol or larger, indicates chemisorption [63]. The ΔG°ads values in this study were − 18.22, − 17.1, and − 15.95 kJ/mol for B1, B2, and B3, respectively. This approves the adsorption of the physisorption of the investigated compounds (Table 6; Fig. 8).

Table 6 Adsorption parameters for B1, B2, and B3 were obtained from Langmuir at 25 °C
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Fig. 8
figure 8

Langmuir adsorption plots were obtained from the potentiodynamic polarization method for C-steel in 1 M HCl containing different concentrations from B1, B2, and B3

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3.7 Electrochemical Frequency Modulation

It is a non-destructive method that can resolve the corrosion current values without prior data of Tafel slopes, and with a small polarizing signal. These benefits of the EFM method make it a perfect technique for the examination [64]. The huge force of the EFM is the causality factors which serve as an internal check on the validity of EFM measurement. Figure 9a–c show the (current vs frequency) of C-steel in HCl solution containing different concentrations of the compounds under investigation. The corrosion current densities (icorr), the Tafel slopes, and the causality factors are calculated from the larger peaks [65]. These parameters were registered in Table 7. The addition of the investigated compounds to the corrosive solution diminishes the corrosion current density, indicating that these surfactants inhibit the corrosion of C-steel in 1 M HCl. The % IE increases by increasing the surfactant concentrations and was calculated by applying Eq. (3).

Fig. 9
figure 9figure 9figure 9

a Intermodulation spectra in the absence and presence of different concentrations from B1. b Intermodulation spectra in the absence and presence of different concentrations from B2. c Intermodulation spectra in the absence and presence of different concentrations from B3

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Table 7 Parameters got by the EFM for various solutions at 25 °C
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The % IE values were order as B1 > B2 > B3. Because of the number of ethoxylated groups in B1 and B2, more than that is in B3 and the presence of the sulfonic group in B1 and B3 and absence in B2. Generally, increasing surfactant concentrations lead to an increase in inhibition efficiency values. The slight difference between different techniques (EIS, EFM, and PP) in inhibitions efficiency IE%, maybe due to different conditions affected on the electrode surface in these measurements [66].

3.8 Scanning Electron Microscopy (SEM)

Figure 10a shows SEM for the C-steel surface image in the air without an explosion in any media. Figure 10b shows surface destroy after dipping in the aggressive medium for 24 h, a thick porous layer of corrosion product covers the entire metal surface; the surface was strongly injured. While Fig. 10c–e, present the surface in the existence of 300 ppm of the investigated compounds. The pictures show that the surface is practically liberated from harms and it is smooth, this demonstrates the nearness of a decent defensive film present on the C-steel surface, additionally affirms the most elevated IE% of the explored recently arranged surfactants.

Fig. 10
figure 10

SEM micrographs of C-steel surface a before immersion in 1 M HCl, b after 1 day of immersion in 1 M HCl and c after 1 day of immersion in 1 M HCl + 300 ppm of surfactant (B1) and d after 1 day of immersion in 1 M HCl + 300 ppm of surfactant (B2). e After 1 day of immersion in 1 M HCl + 300 ppm of surfactant (B3)

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The images show that the surface is practically liberated from harms and it is smooth, this demonstrates the nearness of a decent defensive film present on the C-Steel surface also shows the highest IE% of the investigated newly prepared surfactants [67]. The surface is slightly injured when B1 is added.

From the results obtained from different techniques, is clear that these compounds s showed high anti-corrosion action in oil fields with low dosage compared to previous studies recorded in Table 8. Consequently, aliphatic cationic surfactants can serve as a good option to mitigate corrosion problems.

Table 8 Comparison of the corrosion inhibition efficiency of the prepared cationic surfactants with some previous studies
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4 Conclusions

The current study of new ethoxylated and sulfonation fatty acid surfactant indicated the difference between B1, B2, and B3 according to its molecular weight, the number of ethoxylated groups, presence of a sulfonated group at the same hydrocarbon chain length; which lead to the corrosion inhibition of C-steel. Results obtained from different experimental techniques are in good agreement and the order in inhibitions efficiency is (B1 > B2 > B3). The adsorption of the surfactant on the surface of carbon steel inhibition the corrosion of C-steel by blocking its active sites. Polarization data shows that the investigated compounds affect both anodic and cathodic reactions. Langmuir adsorption isotherm is confirmed. B1 is more efficient, it may be attributed to its higher molecular weight and the presence of SO3H group.