Introduction

Today, the use of strong acids is an important source of promoting petroleum well productivity1. Hydrochloric acid (HCl) is injected into the N80 C-steel pipe to remove the scale layers from the pipe surface2. During acid washing, the strong acid causes severe corrosion in the steel pipe wall, reducing the pipe's strength and resulting in material destruction3, 4. During the cleaning process, corrosion inhibitors are mixed with the acids as a first line of defence5,6,7,8. The most important source of corrosion protection for steel pipes is a group of various corrosion inhibitors such as organic compounds, inorganic compounds, and heterocyclic compounds9,10,11,12,13,14. Indeed, the toxic effects of these compounds compelled many researchers to use nontoxic alternatives to control corrosion in the petroleum industry.

Surfactants have recently been used to replace traditional corrosion inhibitors, providing minimal risk and mitigating environmental impacts15,16,17. In comparison to other reported corrosion inhibitors such as organic and inorganic inhibitors, the use of Gemini surfactants (GS) is the most practical additive due to many advantages such as low toxicity, no irritating odor, good thermal stability, and high efficacy.

Presently, GS is capable of corrosion inhibition in different media with very high efficacy18, 19. GS is composed of two head groups (hydrophilic) and two tails (hydrophobic) tied with the spacer20. Therefore, the likely role of GS in the control of corrosion will be more effective than the conventional surfactants .Moreover; the cationic GS would provide increased anti-corrosion properties due to its antibacterial effects against the bacteria in the petroleum field.

The novelty in this work is the exploring for the first time the anti-corrosion properties of cationic Gemini surfactant, 1,2-bis(dodecyl dimethylammonio) ethane dibromide (DMAEB), for N80 C-steel pipe in the acid washing solution (15% HCl). Although many works have been conducted in the field, there is still a lack in the theoretical and mechanistic approaches. In this work, we used both experimental (chemical, electrochemical and surface inspections) and theoretical approaches to explain the mechanism of inhibition efficiency of DMAEB.

Materials and methods

Materials

An Egyptian steel company supplied N80 C-steel pipe (composition: ≈ 0.33% C, 0.24% Si, 1.45% Mn, 0.05% Nb, 0.05% V, the balance Fe). Sigma-Aldrich provided the 1,2-bis(dodecyldimethylammonio) ethane dibromide (DMAEB) (purity 98%) and HCl (purity 37%). Figure 1 depicts the molecular structure of DMAEB.

Figure 1
figure 1

Molecular structure of 1,2-bis(dodecyldimethylammonio) ethane dibromide (DMAEB).

Full size image

Methods

The surfaces of the N80 C-steel specimens were prepared before each experiment according to ASTM G1-0321, 22. ASTM G31—72(2004) standard method was used to conduct the mass loss experiments and evaluating corrosion rate23, 24.

The polarization experiments were recorded using a three-electrode cell (working electrode = N80 C-steel, reference electrode = SCE, counter electrode = Pt) and potentiostat instrument (EG/G Model 273A). The polarization experiments were conducted in the potential range ± 250 mV vs. OCP and using a scan rate of 1.0 mV s−1.

All measurements (potentiodynamic polarisation, gravimetry) were carried out three times under identical conditions. The averages of all data points were recorded.

The critical micelle concentration (CMC) of the DMAEB in the pure water was determined by surface tension measurements using Tensiometer (KRÜSS Scientific).

The surface morphology investigations (SEM and EDX) were conducted using ZEISS/EVO Scanning Electron Microscope fitted with EDX analyzer. FT-IR spectra were recorded via FT-IR spectrophotometer (Shimadzu: IRTracer™-100).

Quantum chemical calculations were studied using the VAMP module in Materials Studio-6.0-software from Accelrys Inc.

Results and discussion

anti-corrosion properties of DMAEB

The mass loss method and electrochemical technique (i.e. polarization test) have been used to investigate the anti-corrosion capabilities of DMAEB for N80 C-steel pipe in the acid washing solution (15% HCl).

Table 1 shows the corrosion rate (CR) from mass loss measurements, as well as the inhibition efficiency (Ew%), for N80 C-steel pipe in 15% HCl solution with increasing concentrations of DMAEB at 303 K.

Table 1 Corrosion parameters obtained from mass loss method for N80 C-steel pipe in 15.0% HCl solution without (blank) and with DMAEB at 303 K.
Full size table

The following relationships were used to calculate the CR and Ew%25, 26:

$$C_{\text{R}} = {\text{M}}/{\text{t}} \times {\text{A}},$$
(1)
$$E_{\text{W}} \% = \frac{{C_{{\text{R0}}} - C_{\text{R}} }}{{C_{{\text{R0}}} }} \times 100$$
(2)

M is the mass loss in N80 C-steel specimen, t is the time of immersion, A is the surface area, CR0 is the corrosion rate for blank solution and CR is the corrosion rate for inhibited solution.

According to Table 1, the acid solution treatment with DMAEB resulted in a decrease in CR values. The change in DMAEB concentrations had a significant impact on the CR values. This means that increasing DMAEB concentrations causes a decrease in CR values.

The addition of 100 mg/l of DMAEB results in the highest inhibition efficiency (Ew% = 96.8) (Table 1). There was no significant change in the Ew% value above 100 mg/l.

Because the CMC of Gemini surfactant is important in determining a surfactant's inhibition efficiency27, the CMC value of DMAEB was determined by surface tension measurements, as shown in Fig. 2. According to Fig. 2, the CMC value of DMAEB is 111 mg/l. This indicates that DMAEB's maximum performance was achieved near its CMC value. At the C-steel/solution interface, a complete monolayer of DMAEB was formed at CMC value. There are no spaces available for the adsorption of additional surfactant molecules in this case. This refers to the direct relationship between the surfactant's CMC value and corrosion inhibition.

Figure 2
figure 2

Variation of the surface tension with concentrations of DMAEB at 303 K.

Full size image

These findings show that the cationic Gemini surfactant DMAEB has a high efficacy (96.8%) in inhibiting corrosion of N80 C-steel pipe in 15.0% HCl solution at a low concentration (100 mg/l).

The electrochemical parameters of N80 C-steel pipe were evaluated using the polarization method in both 15.0% HCl solution and blank solution treated with Gemini surfactant DMAEB. As shown in Fig. 3, the treatment of 15.0% HCl solution with DMAEB resulted in a reduction of both anodic and cathodic lines. The change in the polarization curves was found to be dependent on DMAEB concentration.

Figure 3
figure 3

Polarization curves of N80 C-steel pipe in 15.0% HCl solution without (blank) and with DMAEB at 303 K.

Full size image

When DMAEB was added to a 15.0% HCl solution, the corrosion potential (Ecorr.) shifted to the positive direction (Table 2). At 150 mg/l, the maximum shifting in Ecorr. was less than 85 mV. DMAEB was identified as the mixed-type corrosion inhibitor based on these findings28, 29. Furthermore, the addition of DMAEB resulted in a significant decrease in corrosion current density (icorr) (Table 2). While icorr decreases, the changes in both Tafel line slopes (ba for anode and bc for cathode) remain nearly constant (Table 2). This discovery supports DMAEB's inhibitory mechanism, which involves blocking the anodic and cathodic sites by surfactant molecules30, 31.

Table 2 Electrochemical parameters obtained from polarization curves of N80 C-steel pipe in 15.0% HCl solution without (blank) and with DMAEB at 303 K.
Full size table

The following relationship can be used to calculate the inhibition efficiency Ep% values based on polarization measurements32, 33:

$$E_{\text{P}} \% = \frac{{i_{{\text{corr(0)}}} - i_{{\text{corr}}} }}{{i_{{\text{corr(0)}}} }} \times 100.$$
(3)

icorr(0) is the corrosion current density for blank solution).

The increase in DMAEB concentration is directly proportional to Ep% values. The highest DMAEB concentration, 100 mg/l, resulted in a 97% reduction in corrosion rate (Table 2).

Figure 4 depicts a histogram comparing the inhibition percentages of the two techniques (polarization and mass loss) for the same conditions. It appears that no significant differences in inhibition percentage values are observed regardless of the techniques used. The inhibition percentages obtained by mass loss measurements were found to be slightly lower than those obtained by polarization measurements. This is because the surface of N80 C-steel is exposed to the acidic solution for a longer period of time when using the mass loss method34.

Figure 4
figure 4

Comparison of inhibition efficiency% values obtained from mass loss and polarization methods.

Full size image

The main mechanism of the Gemini surfactant's anti-corrosion properties is based on its adsorption capability on the surface of the N80 C-steel pipe35, 36. Because the surface of the steel in acidic solution has a positive charge, the adsorption of Cl- ions from the solution on the steel surface is facilitated37. The steel surface was changed to a negatively charged surface in this case. This situation promotes electrostatic interactions between positively charged DMAEB molecules and the steel surface, resulting in the formation of the DMAEB surface layer. This surface layer protects the N80 C-steel pipe's surface from the corrosive acid solution, resulting in a low corrosion rate38. The short spacer group connects the two head groups in GS. This facilitates the hydrophobic interaction between the DMAEB's two alkyl tails, lowering the CMC value. Furthermore, the short spacer group promotes the formation of more rigid molecules. This prevents DMAEB molecules from desorbing from the metal surface, resulting in increased inhibition efficiency39. Additionally, the long two alkyl chains help to cover the surface of the N80 C-steel pipe40. The schematic illustration of the inhibition mechanism is shown in Fig. 5.

Figure 5
figure 5

Schematic illustration of inhibition mechanism of DMAEB for N80 C-steel corrosion in 15.0% HCl solution.

Full size image

DMAEB has a higher efficiency in a more corrosive solution when compared to previous works for other corrosion inhibitors of the same family in the literature41,42,43,44,45 (see Table 3).

Table 3 Comparison of the inhibition efficiency of DMAEB with other inhibitors of the same family for carbon steel in HCl solution reported in the literature.
Full size table

Temperature dependence and activation energy

The CR values of the N80 C-steel pipe in 15.0% HCl solution containing 100 mg/l of DMAEB were recorded at temperatures ranging from 303 to 333 K to predict the stability of Gemini surfactant DMAEB at high temperatures (Table 4). The highest temperature (333 K), as shown in Table 4, reduced the Ew% of DMAEB to 92.5%. This finding confirms DMAEB's high stability at high temperatures. Two factors contribute to the slight decrease in Ew% of DMAEB at high temperatures. The first factor is an increase in the corrosion rate of steel as temperature rises46. The second factor is the high-temperature desorption of some DMAEB molecules from the steel surface (i.e. physical adsorption)47.

Table 4 Corrosion parameters obtained from mass loss method for N80 C-steel pipe in 15% HCl solution without and with 100 mg/l DMAEB at different temperatures.
Full size table

The relationship between corrosion rate CR and activation energy (Ea) is expressed by the Arrhenius formula (see Eq. 4) 48.

$$C_{R} = A\exp \left( {\frac{{ - E_{a} }}{RT}} \right).$$
(4)

The Ea was calculated using the Arrhenius plot (straight-line gradient) (see Fig. 6).

Figure 6
figure 6

Arrhenius plot for N80 C-steel pipe in 15.0% HCl solution without and with 100 mg/l DMAEB.

Full size image

The calculated Ea for the corrosion reaction in 15.0% HCl solution containing 100 mg/l of DMAEB is 36.74 kJ/mol, which is comparable to the calculated Ea in 15.0% HCl solution (13.08 kJ/mol). This finding confirms that the presence of DMAEB in a 15.0% HCl solution raises the energy barrier for corrosion, resulting in a low corrosion rate49,50,51.

Adsorption isotherm studies

Because the effectiveness of Gemini surfactant DMAEB is dependent on DMAEB molecules' adsorption capability on the steel surface, it is critical to investigate the adsorption isotherm in this section. The Langmuir adsorption isotherm (Eq. 5) is the best fitting isotherm that describes the adsorption process of DMAEB molecules based on mass loss measurements52.

$$\frac{{C_{{\text{inh}}} }}{\theta } = \frac{1}{{K_{{\text{ads}}} }} + C_{{\text{inh}}} .$$
(5)

θ is the surface coverage = Ew%/100, Cinh is the DMAEB concentration, Kads is the equilibrium constant).

The linear correlation coefficient (R2) is very close to one in the Langmuir isotherm plot (Fig. 7), confirming the validity of this isotherm53. The DMAEB's Kads was determined to be 1.72 × 104 M−1.

Figure 7
figure 7

Langmuir isotherm plot for N80 C-steel pipe in 15.0% HCl solution containing 100 mg/l DMAEB at 303 K.

Full size image

Gibbs free energy change (∆G°ads) was calculated from the following relation54:

$$\Delta {\text{G}}^\circ_{{{\text{ads}}}} \, = - RT{\text{ln }}\left( {{55}.{5}K_{{{\text{ads}}}} } \right).$$
(6)

The ∆G°ads for the DMAEB was identified to be − 34.62 kJ/mol. A negative ∆G°ads value confirms the spontaneity of DMAEB adsorption on the steel surface55. The value of ∆G°ads (i.e. − 34.62 kJ/mol) refers to DMAEB physisorption on the surface of the N80 C-steel56.

Surface analysis

The morphological analysis (SEM and EDX) of the N80 C-steel in the blank solution (15.0% HCl) and inhibited solution (15.0% + 100 mg/l DMAEB) are presented in Figs. 8 and 9. In the blank solution, the surface morphology of the N80 C-steel revealed a damaged structure and dense surface roughness (Fig. 8a). The N80 C-steel EDX spectrum in the blank solution (Fig. 8b) revealed characterized signals for N80 C-steel composition and corrosion products (i.e. O, Cl, C, Mn, Si, and Fe).

Figure 8
figure 8

(a) SEM image and (b) EDX spectra for N80 C-steel pipe after immersion in the blank solution (15.0% HCl).

Full size image
Figure 9
figure 9

(a) SEM image and (b) EDX spectra for N80 C-steel pipe after immersion in the inhibited solution (15.0% HCl + 100 mg/l DMAEB).

Full size image

In the presence of 100 mg/l DMAEB, the N80 C-steel has a smooth surface and is free of corrosion products (Fig. 9a). The presence of characterized DMAEB signals is revealed by the EDX spectrum of N80 C-steel in inhibited solution (Fig. 9b) (i.e. N and C). Furthermore, Cl signals have vanished.

The FT-IR spectra of pure DMAEB and the film formed on the surface of N80 C-steel in the inhibited solution (15.0% HCl + 100 mg/l DMAEB) were analyzed and shown in Fig. 10. The characteristic peaks for C–H stretch, CH2 bending, CH3 bending, C–C stretch, C–N, and long-chain CH2 groups can be seen in the FT-IR spectrum of pure DMAEB.

Figure 10
figure 10

FT-IR spectra of pure DMAEB and film formed on the surface of N80 C-steel in the inhibited solution (15.0% HCl + 100 mg/l DMAEB).

Full size image

The FT-IR spectra of the film formed on the surface of N80 C-steel in the inhibited solution showed three changes. The first is a shift in some peaks, such as C–H stretch, CH2 bending, CH3 bending, and C–C stretch. The second change is the absence of C–N. The presence of new peaks related to Fe–N bonds at 645–450 cm−1 is the third change. All of these studies support the adsorption of DMAEB molecules on N80 C-steel.

Quantum chemical calculations

Quantum chemical calculations were used to support the experimental results. Figure 11a,b show that HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) regions are concentrated on ammonium groups. This demonstrates that the ammonium groups in DMAEB molecules are the active components in the adsorption process31. The high value of the HOMO energy (EHOMO = 8.939 eV) refers to the DMAEB molecule's ability to link with the steel surface57. Also, the low LUMO energy (ELUMO = 1.577 eV) refers to the DMAEB molecule's ability to gain electrons from the filled Fe d-orbital58. Furthermore, the low energy gap (ΔE = ELUMO − EHOMO, 7.362 eV) refers to DMAEB molecules' high inhibition performance59. It was discovered that the electron density was distributed throughout the entire DMAEB molecule (see Fig. 11c). This means that DMAEB molecules are adsorbing on the Fe surface in flat-lying orientations60.

Figure 11
figure 11

(a) HOMO, (b) LUMO and (c) total electron density distribution for DMAEB molecule. "Computational results obtained using software programs from Accelrys Software Inc. The ab initio calculations were performed with the DMol3 program, and graphical displays generated with Materials Studio".

Full size image

DMAEB's high dipole moment (i.e. μ = 6.94 Debye) indicates a strong electrostatic interaction between DMAEB molecules and the C-steel surface61.

The electronegativity (χ) and global hardness (η) parameters for DMAEB are calculated from the following relations:

$$\chi = \, 0.{5} \times \left( {{\text{I}} + {\text{A}}} \right),$$
(7)
$$\eta = \, 0.{5} \times \left( {{\text{I}} - {\text{A}}} \right),$$
(8)

where I is the ionization potential = − EHOMO and A is the electron affinity = − ELUMO.

The calculated values of χ and η are 5.258 eV and 3.681 eV, respectively.

The high χ value for DMAEB molecules indicates a high ability to attract electrons and, as a result, a high adsorption efficiency62. Furthermore, the low η value for DMAEB molecules indicates a strong interaction between the metal surface and inhibitor molecules63.

Conclusions

In summary, we investigated the anti-corrosion properties of cationic Gemini surfactant, 1,2-bis(dodecyldimethylammonio) ethane dibromide (DMAEB), for N80 C-steel pipe in the acid washing solution (15% HCl).

It is worth noting that the Gemini surfactant DMAEB has a high efficacy (96.8%) in inhibiting corrosion of N80 C-steel pipe in 15.0% HCl solution at a low concentration (100 mg/l). DMAEB's anti-corrosion properties were investigated using mass loss, polarization, SEM, EDX, and FT-IR tools. DMAEB acts as a mixed-type corrosion inhibitor, as evidenced by the polarization curves. The high temperature (333 K) slightly reduced DMAEB efficacy to 92.5%, confirming DMAEB's high stability at high temperatures. Furthermore, the presence of DMAEB in a 15.0% HCl solution raises the energy barrier for corrosion, resulting in a low corrosion rate. The Langmuir adsorption isotherm accurately described the adsorption of DMAEB molecules. The ∆G°ads was − 34.62 kJ/mol, indicating physisorption behavior. SEM, EDX, and FT-IR analysis confirmed the adsorption of DMAEB molecules on the surface of N80 C-steel. To back up the experimental findings, quantum chemical calculations were used.