Medhat Kamel,Mohamed Hegazy,Salah Rashwan,Mohamed El Kotb

1 Department of Chemistry,Faculty of Science,Suez Canal University,Ismailia 41522,Egypt

2 Egyptian Petroleum Research Institute (EPRI),Nasr City,Cairo 11727,Egypt

Keywords: Innovative Gemini surfactant Synthesis Dissolution mitigation Steel Pickling HCl media

ABSTRACT A new surfactant of Gemini-type, N,N’-((phthylbis(oxy))bis(ethane-2,1-diyl))bis(N,N-dimethyldodecan-1-aminium bromide)is prepped &confirmed.The dissolution suppression impact of the new compound on steel is performed in 1 mol·L-1 HCl environment by means of chemical and electrochemical methods.The prepared surfactant is an agreeable dissolution inhibitor for steel.The mitigation efficacy rises with the quantity of the compound.The surfactant belongs to inhibitors of mixed-type.The adsorption of the synthesized compound followed the Langmuir’s model.The negative magnitudes of both ΔG?ads and ΔH?ads indicate that the adsorption process proceeds from its own accord and exothermic.The mechanism of adsorption is elucidated by scanning microscopy.It is established that the transfer resistance (Rct) value rose,where the value of the phase element (CPE) reduced with the amount of synthesized inhibitor.According to the experimental data arrived by surface tension measurements,the prepared compound is a powerful active agent at the air/water boundary.

1.Introduction

Steel metal is inclusively applied in-store tanks,oil refineries,and so on.Inhibitors are chemical substances that dominance,lessen,or prohibit reactions between the metal and its corrosive media when added in diminutive quantities.The choice of efficient inhibitor is quite essential for an application.The inhibitors are picked out concerning what sort of metal/alloy and disintegration environment are utilized [1–4].Acid solutions are employed for eliminating the discarded scale and rust in the majority of industrial operations.The chief problem concerning with steel is the disintegration in sour media.Inhibitors are commonly utilized to lessen both the metal disintegration and the spending of acid.Utmost of the inhibitors utilized in sour media are compounds having O,S,N,and P,unsaturated bonds,and conjugated systems comprising all sorts of aromatic rings [5–7].Surface-active inhibitors possess plentiful vantages like high mitigation efficacy,simplistic production,low poisoning and least cost.Surface-active substances are molecules consist of a polar hydrophilic and a non-polar hydrophobic group.The mitigation action of a surfactant is chiefly assigned to the occurrence of physisorption or chemisorption onto the metal’s surface.The surfactant adsorption markedly ameliorates the resistance of metal to dissolution.For these causes,studying the relationship between adsorption and disintegration mitigation is markedly important [8,9].

Surfactants of the scientist Gemini are a novel class of surfaceactive agents that are received great awareness.The surfactant in this category includes 2 hydrophilic and 2 hydrophobic groups.The hydrophilic group attached to the hydrophobic group via an aromatic/aliphatic spacer.Gemini’s surfactants are greatly activating the surface and possess much lower micelle concentration(CMC) magnitudes than traditional surfactants.They are much more efficient than the corresponding classical surfactants in minimizing the surface tension of water.In addition,they show other favorable features,like increasing wetting,promoting emulsification of oil in water,enhancing dispersion of solids,and possessing a high foaming stability.They can also show better solubilizing properties,stronger tolerance to multivalent metal ions,stronger antimicrobial ability,a good mildness to skin owing to their low CMC values,safe ecology,and environmental control.Finally,some Gemini surfactants can be manufactured at a reasonable cost.Owing to their distinctive physical–chemical properties,this category of compounds keeps on interest for different applications[10–21].Recently,Gemini surfactants are utilized as the collector for the reverse flotation separation of halite from carnallite ore and phosphate ore in sustainable production of phosphate fertilizer,carnallite ore for production of potash fertilizer and quartz from phosphorite ore at low temperatures [22–25].

The goal of the current study is to prepped and characterize innovative surfactant from the Gemini-type,namely,N,N′-((phthyl bis(oxy))bis(ethane-2,1-diyl))bis(N,N-dimethyldodecan-1-aminium bromide).In addition,the given work aims to examine the surface properties of the prepped surfactant and its inhibitive impact toward the dissolution of steel in 1 mol·L-1hydrochloric acid solution by impedance spectroscopy (EIS),polarization measurements,and weight lack methods.The adsorption mechanism is elucidated by scanning microscopy and energy dispersive Xray.The thermodynamic parameters are calculated.

2.Experimental

2.1.Preparing the compound

The prepped compound that applied in this treatise is synthesizedvia2 strides.Firstly,0.05 mol of 2-dimethylaminoethanol(99.5%,Sigma-Aldrich)is reacted with 0.05 mol of dodecyl bromide(97.0%,Sigma-Aldrich).Then they are permitted to reflux in ethyl alcohol(≥99.8%,Merck)at 80C for twenty-four hours.After that,the admixture was allowed to attain room temperature.Thereafter,it was washed by diethyl ether (≥99.7%,Sigma-Aldrich) and filtered to detach the precipitate (N-(2-hydroxyethyl)-N,Ndimethyldodecan-1-aminium bromide).Secondly,the innovative surfactant was preppedviaa condensation reaction between 0.02 mol ofN-(2-hydroxyethyl)-N,N-dimethyldodecan-1-aminium bromide,and 0.01 mol of phthalic acid (>99.5%,Sigma-Aldrich) at 140 C for 8 h.The reaction is accomplished when water is completely taken away from the reaction.Moreover,the mixture is distilled beneath vacuum conditions for detaching the solvent.The output compound was crystallized two times from ethyl alcohol solvent.The structure formula of the prepped innovative cationic surfactant,N,N′-((phthylbis(oxy))bis(ethane-2,1-diyl))bis(N,Ndimethyldodecan-1-aminium bromide) (purity > 98.5%) (Fig.1),was elucidated by FTIR and1H NMR techniques.The FTIR spectrum was obtained using Thermo Scientific Nicolet iS10 spectrophotometer (Thermo Fisher scientific,USA).The1H NMR spectrum was recorded in DMSO-d6 employing Joel ECA 400 MHz NMR spectrometer (Joel,Japan).

2.2.Mass loss technique

Tests are carried out on steel coupons(3 cm×0.5 cm×6 cm)of composition (mass fraction): 98.72 % Fe,0.90 % Mn,0.007 % P,0.006 % S,0.015 % Ni,0.008 % Cr,0.20 % C,0.08 % Si,0.030 % Al,0.014 % V,0.002 % Ti and 0.020 % Cu.The coupons were abraded using emery cloth and thereafter washed totally by distilled water.The coupons were swilled by acetone solvent&subsequently desiccated.The specimens,after precisely weighed,were placed in a closed vessel comprises 1 mol·L-1HCl with and devoid of distinct quantities of the synthesized compound for twenty-four hours at 25–60C,then washed,desiccated,and weighed.

2.3.Techniques based on electrochemistry

For electrochemical experiments,a standard cell with a Ptcounter electrode and a saturated Hg2Cl2electrode (SCE) was utilized.The working electrode (low carbon steel rod) was pressure fitted into a poly tetra fluoro ethylene (PTFE) holder,showing up 0.7 cm2surface area to the corrosive media.Unmasked surface was polished by emery cloth,cleaned by acetone,distilled water,and then allowed to be desiccated.The measurements were performed at a stationary temperature using an air thermostat.The polarization curves were plotted by varying the steel potential from - 0.8 to - 0.3 VversusSCE.The scan rate is 0.2 mV·s-1.The steel electrode was placed in the plank solution at open circuit potential (OCP) for 1/2 h to reach a steady-state prior to each run.EIS data were established in a wide scope of frequency 100 kHz–50 MHz using a sine wave of 10 mV.For obtaining measurements,we used a Volta lab 40 Potentiostat PGZ 301 attached to a corrosion program.

2.4.Scanning electron microscopy (SEM)

SEM results of steel coupon in 1 mol·L-1HCl in the absence and presence of the tested surfactant at 5×10-3mol·L-1are obtained using SEM Model Quanta 250 FEG (Field Emission Gun).

2.5.Surface properties

The surface tension of aquatic solutions for the surfactant was determinedviaDu Nouy ring procedure with a Kruss K6 tensiometer at 25C.The surface characteristics of the prepped surfactant were estimated using the parameters of surface activity,like the critical micelle concentration (Ccmc),surface tension atCcmc(γcmc),utmost surface excess concentration (Γmax),effectiveness (πcmc),and minimum surface area/molecule (Amin) at the air/solution boundary.

3.Results and Discussion

3.1.Elucidation the structure of the prepped compound

The structure of the prepped compound is established by FTIR and1H NMR techniques.

3.1.1.FTIR spectra

FTIR spectrum of the prepped compound displayed the subsequent absorption bands at the following wavenumbers (cm-1):736.67 (CH rocking),1279.54 (C-O stretching),1073.19 (C-N+),1372.1 (CH3bending),1465.63 (CH2bending),1598.7 (C=C stretching),1738.26 (C=O of ester group),2854.13 (CH aliphatic non-symmetrical stretching),2923.56 (CH aliphatic symmetrical stretching),and 3372.89 (water because cationic surfactants generally are hydroscopic).The FTIR elucidated the functional groups in the prepped compound as indicated in Fig.2.

Fig.1.The chemical structure of the synthesized cationic Gemini surfactant.

Fig.2.FTIR spectrum of N,N’-((phthylbis(oxy))bis(ethane-2,1-diyl))bis(N,N-dimethyldodecan-1-aminium bromide).

3.1.2.1H NMR spectra

The1H NMR spectrum (DMSO-d6,400 MHz) of the prepped compound displayed distinct bands at δ=0.8350–0.8625 (t,6H,NCH2CH2(CH2)nCH3);δ=1.1881–1.3302(m,36H,NCH2CH2(CH3)n-CH3); δ=1.6726 (m,4H,; δ=2.9167 (m,4H,; δ=3.2790–3.4456 (s,12H,NCH3); δ=3.6 611–3.7023 (m,4H,OCH2CH2NCH2CH2(CH2)nCH3); δ=4.3091–4.3 229 (m,4H,OCH2CH2NCH2CH2(CH2)nCH3); δ=7.4791–7.5143 (m,2H,m-phthalic acid); δ=7.8093–7.8827 (m,2H,o-phthalic acid).The1H NMR proved the prospective H+allocation in the innovative compound,Fig.3.

3.2.Mass loss tests

The suppression performance of the prepped compound was evaluated using mass loss tests.The dissolution rate (k) was estimated by the subsequent relation [26,27]:

Fig.3.1H NMR specturm of N,N’-((phthylbis(oxy))bis(ethane-2,1-diyl))bis(N,N-dimethyldodecan-1-aminium bromide).

whereW1is the mass of steel before immersion andW2is the mass after immersion.Sis the area of steel coupon,andtis the exposition period.

The mitigation efficacy (ηw) was calculated as follows [28]:

whereWcorrandWocorrare the loss of the steel’s mass devoid of and with the surfactant,respectively.Mass loss information of steel in 1 mol·L-1HCl in the non-existence and existence of distinct quantities of surfactant at 25,40,and 60C are scheduled in Table 1.The dissolution mitigation of the synthesized compound increases with the compound’s amount in the media.However,it tends to diminish with raising the temperature within the range 25–60C.The loss of mitigation efficacy with rising temperatures chiefly assigned to the detachment of the compound’s molecules the steel surface at elevated temperatures.

3.3.Potentiodynamic tests

Fig.4 represents theV–Iplot of steel in 1 mol·L-1HCl devoid of& with distinct quantities of the prepped compound.The Tafel’s plot gives fruitful information about the disintegration potential(Ecorr),disintegration current (icorr) & cathodic and anodic Tafel slopes(βc),(βa),Table 2.The disintegration current increases while the disintegration rate diminishes as the content of the surfactant increases in the media.This mainly assigned to the adhesion of the compound’s molecules at the corroded surfaceviathe process of adsorption [29].The Tafel slopes are slightly changed in with the surfactant’s quantity.Thence,the prepped surfactant follows the mixed-type inhibitors.

3.4.Impedance measurements

The Nyquist and Bode graphs for steel coupons in 1 mol·L-1HCl solutions in the non-existence and existence of various amounts of the prepped surfactant are depicted in Figs.5,6,respectively.Nyquist diagram shows analogous form overall examined amounts.This proved that there is no alteration in the dissolution mechanism when the prepped compound exists in the solution.Nyquist plot possesses only a single bleak semicircle.The radius of the semicircle,get larger and larger by raising the quantity of the compound in the solution.This elucidates that the electron transfer step is the slowest one during the disintegration process.The loops at high–frequencies range are not idealistic semicircles as anticipated from the of EIS’s theory.The deviation may assign to the imperfect performance of the double-layer as a capacitor.This imperfect performance ascribed to the frequency dispersal due to the coarseness and non-homogeneity of the surface [30].Fig.7 shows the electric circuit which accustomed to verify the practical results.The circuit includes a constant phase element (CPE)attached in parallel to a resistorRct.CPE is exchanged for the capacitive element.This allows extra precise fitting because the majority of the capacitive loops are bleak semi-circles instead of orderly semi-circles [31].

Fig.4.Polarization diagram of steel in 1 mol·L-1 HCl solution devoid of and with distinct concentrations of the prepped compound at 25 C.(B) 1 mol·L-1 HCl,(1)5×10-5 mol·L-1,(2) 1×10-4 mol·L-1,(3) 5×10-4 mol·L-1,(4)1×10-3 mol·L-1,and (5) 5×10-3 mol·L-1.

For investigational results,the variables like a proportional factor(Yo),phase shift(n),Rs,andRctwere evaluated with the help of the ZSimpWin program.The impedance variables are given in Table 3.The CPE type impedance,ZCPE,was estimated from the subsequent equation [32 –34]:

Table 1Mass loss data of steel corrosion in 1 mol·L-1 HCl in the absence and presence of different concentrations of the synthesized inhibitor,at different temperatures

Table 2Potentiodynamic polarization parameters for carbon steel corrosion in 1 mol·L-1 HCl in the absence and presence of different concentrations of the synthesized surfactant at 25 C

Table 2Potentiodynamic polarization parameters for carbon steel corrosion in 1 mol·L-1 HCl in the absence and presence of different concentrations of the synthesized surfactant at 25 C

wherenis that the phase shift,that enables notification for the degree of imperfection in capacitive action,andYois a proportionality operator,j=■■■■■■■■.

Double-layer capacitance magnitudes (Cdl) obtained from CPE parameters in keeping with the subsequent relation [35,36]:

Fig.5. ZR2e versus -ZIm plots of steel in 1 mol·L-1 HCl devoid of and with distinct concentrations of the prepped compound at 25 C.

where ωmax=2πfmaxandfmaxis that the frequency when the imaginary part of the impedance is the utmost.

The mitigation efficacy of surfactant can be estimatedviathe next equation [37,38]:

whereRctandare the electron-transfer resistances magnitudes in the non-existence and existence of the prepped compound,respectively.

Fig.6 displays Bode and phase angle curves of steel in 1 mol·L-1HCl devoid of and with distinct quantities of the prepped compound.For Bode plots,at the mediate frequency range,there is a directly proportional relation between lg |Z| and lgf.The value of a slope approaches -1 and the phase angle value adjacent to-60.This confirms the non-ideal capacitive performance at mediate frequencies.It has been informed that the perfect capacitive performance is attained if the slope is -1 and the angle of phase is-90at mediate frequencies.The magnitudes of slope and phase angle in inhibited solutions are larger than ones get in uninhibited solution.This elucidates the suppression performance of the examined compound in the disintegration process of steel.Fig.6 also demonstrates the phase angle curves of the prepped compound.Increasing the amount of the prepped compound in the corroding solution ameliorates the mitigation efficacy because of the adhesion of more surfactant molecules at the metal surface at higher concentrations.

The impedance variables deduced from the Nyquist diagram and the mitigation efficacy,ηI,are illustrated in Table 3.TheRctmagnitudes were increased,whereas CPE magnitudes decreased by introducing more of the quantity of prepped compound in the solution.The diminishing in the CPE magnitudes is ascribed to the attachment of surfactant molecules with the surface of the metal.This results in diminish in the native dielectric constant and/or grow in the thickness of the double-layer.

3.5.Adsorption isotherm and thermodynamics approach

The Langmuir’s model is employed for agreeing on the practical outputs.It can be described by the subsequent relation [39–41]:

where θ is the surface covering,Csuris the surfactant’s concentricity andKadsis the equilibrium constant for adsorption.

Fig.6.Bode plot and phase plot of steel in 1 mol·L-1 HCl devoid of and with distinct concentrations of prepped compound at 25 C.

Fig.7.The proposed circuit for EIS data.

The latter is calculated from the intercept of the line in Fig.8.The correlation coefficient is ~1 and the slope approaches 1.Kadsmagnitudes that got under diverse practical conditions are given in Table 4.The prepped surfactant is facilely and hardly attached to the steel surface at depress temperatures.Otherwise,the magnitudes of the equilibrium constant diminish at elevated temperatures due to rising in the rate of detaching of the surfactant’s molecules from the surface of steel metal.Standard Gibbs free energy for adsorption,is linked to equilibrium constant(Kads) with the subsequent relation [42–44]:

whereR=8.314 J·K-1·mol-1,Tis the temperature in absolute scale,and 55.5 is the concentration of water by molarity units.

Table 3EIS parameters for corrosion of steel in 1 mol·L-1 HCl in the absence and presence of different concentrations of the synthesized surfactant at 25 C

Table 3EIS parameters for corrosion of steel in 1 mol·L-1 HCl in the absence and presence of different concentrations of the synthesized surfactant at 25 C

Table 4Standard thermodynamic parameters of the adsorption on carbon steel surface in 1 mol·L-1 HCl containing different concentrations of the synthesized inhibitor at various temperatures

Table 5Comparison between the tested cationic Gemini surfactant and other traditional organic inhibitors and monomeric surfactants reported in the literature for steel in 1 mol·L-1 HCl

Fig.8.Langmuir isotherm of steel in 1 mol·L-1 HCl in the existence of distinct concentrations of the prepped compound at different temperatures.

3.6.Scanning electron microscopy (SEM)

SEM micrographs of steel surface without and with 5×10-3mol·L-1of the cationic Gemini surfactant in 1 mol·L-1HCl are chronicled in Fig.9.SEM photo shows that steel strip in 1 mol·L-1HCl is highly damaged due to formation of soluble FeCl2and evolution of H2gas,Fig.9(a).This indicates that steel is highly corroded in the absence of inhibitor.However,steel strip in the presence of the inhibitor is smooth without any damage.This result confirms that the synthesized cationic surfactant minimizes the corrosion rate for steel dissolution.

3.7.The inhibition mechanism

The effectiveness of synthesized cationic Gemini surfactants is dependent on their chemical structure and surface properties.The synthesized cationic Gemini surfactant contains two fatty alkyl chains.These chains retard the corrosive medium on the metal surface outward.The inhibitor is adsorbed on the metal surfacevialone pairs of electrons of N,O atoms and double bond of benzene ring (chemical adsorption).In addition to the attraction between N+and Cl-ions with cathodic and anodic sites on steel surface.

Fig.10.The relation between the concentration of the prepped compound and the surface tension at 25 C.

3.8.Comparison between the tested cationic Gemini surfactant and other traditional organic inhibitors and monomeric surfactants reported in the literature

Generally,the surfactant corrosion inhibitor is more effective than the traditional organic compounds.They minimize the interfacial tension between the corrosive medium and the metal surface.On the other hand,the efficacy of the inhibitor depends on its concentration.The surfactants usually utilized concentrations less than critical micelle concentration (Ccmc).The surfactants molecules afterCcmcis attained,formed micelle in the bulk of the tested solutions.Therefore,for concentrations higher thanCcmcthere is non-increasing in the inhibition efficacy.The migration of surfactants to adsorb on steel surface is faster.Also,all surfactants molecules are adsorbed on steel surface.But,organic inhibitors diffuse almost at the equal amount in the bulk of solution and interface.Therefore,using surfactants are more effective than ordinary inhibitor.The comparison between the tested surfactant and other inhibitors reported in the literature are listed in Table 5.This comparison illustrates that the cationic Gemini surfactant is excellent inhibitor.This surfactant is more effective than traditional corrosion inhibitors.

3.9.Properties of prepped surfactant

3.9.1.Surface tension (γ)

Fig.10 displays the correlation between γ and the lgCof the surfactant.The severe decay in the value of γ is recognized as the concentration rises till approaching theCcmc,and then continues to diminish leisurely with further increase in concentration.The plot in Fig.10 was employed to estimate the purity andCcmcof theprepped surfactant.The value ofCcmcis obtainedviathe intersection points at the γ –lgCcurves and scheduled in Table 5.

Table 6Critical micelle concentration (Ccmc),the effectiveness (πcmc),the maximum surface excess (Γmax) and minimum area (Amin) values of the synthesized surfactant

3.9.2.Activity (πcmc)

The utmost value of surface pressure πcmcis calculated from the subsequent equation [55]:

where γois the tension of surface;estimated for purified water,and γcmcis the tension of surface atCcmc.The πcmcmagnitude of the prepped is displayed in Table 6.

According to the data arrived,the prepped compound is deemed as a powerful surfactant at the water/air boundary.

3.9.3.Surface excess (Γcmc)

The utmost value of surface excess of a surfactant(Γcmc)is estimatedviathe highest slope(dγ/d lgC)at the γ-lgCdiagram.When the solution is free from electrolyte,Γcmcis evaluated from the adsorption equation [56]:

where dγ/d lgCis the pressure of surface,R=8.314 J·K-1·mol-1,Tis the temperature in Kelvins,andn=3 for a dimeric surfactant as it consists of one ion(bivalent surfactant)and two bromide ions(univalent counter ions)[56].The value of Γmaxwas estimated and tabulated in Table 6.

3.9.4.The area of a molecule (Amin)

The minimum surface area per adsorbed molecule,Amin(nm2),is estimatedviathe subsequent relation [55,56]:

whereNA=6.02×1023atoms.The value ofAminwas determined and scheduled in Table 6.

4.Conclusions

A new cationic surfactant of Gemini- type is prepped & confirmedviaFT-IR and1H NMR spectra.The new prepped surfactant is used to mitigate the disintegration of CS in 1 mol·L-1HCl.The efficacy of the compound rises with raising its concentration in solution,but it heads for diminishing with the temperature.The high mitigation efficacy of the prepped surfactant ascribed to the attachment of its molecules with the steel surface.The results came close despite the use of different techniques.The synthesized surfactant belongs to the category of mixed-type.The adsorption of the prepped compound molecules satisfies Langmuir’s model.The novel surfactant possesses powerful surface properties.SEM micrograph showed that the synthesized cationic surfactant prevents the corrosion process.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.