Synthesis of Composite Corrosion Inhibitor Based on Maleic Anhydride, Monoethanolamine and Phosphate Acid

In this article, the optimum conditions for the synthesis of corrosion inhibitors based on maleic anhydride, monoethanolamine, and phosphoric acid and the inhibitory efficiency of the obtained inhibitor are studied. In this case, the mole ratio of the starting materials was 2 moles (122 g) of monoethanolamine: 1 mole (98 g) of maleic anhydride: 1 mole (98 g) of phosphoric acid, and the yield of the reaction was 92.5%. The IR spectra of the structure of this obtained inhibitor were studied. The inhibition efficiency of this corrosion inhibitor was measured by the gravimetric method according to GOST 9.506-87 in 1M HCl + 200 mg/l NaCl and 0.5 HCl + 200 mg/l NaCl environments. The inhibition efficiency was 93.15% and 92.86%, respectively. reached According to the results of the electrochemical research, the inhibition efficiency was 91.5%. In addition, Langmuir, Frumkin, and Tyomkin isotherms of the inhibition mechanism of the inhibitor were studied. The effect of the inhibitor on the steel surface was studied with a scanning electron microscope.


Introduction
Corrosion is a reversible process, which converts pure metal to different chemical compounds [1].Nowadays, corrosion is turning into a major issue in many industries, building materials, infrastructure, tools, ships, trains, vehicles, machines, and appliances [2].Carbon steel experiences extensive corrosion during the cleansing process with acids.The NACE 2016 reported shows that at the world level about 2.5 trillion U.S. dollars economic fall caused by corrosion every year total of 10% of total metal of world is lost due to corrosion which influences the economy of the nation [3].Corrosion is not only responsible for an economic loss but also associated with safety issues because it decreases the shelf life of steel [4].This problem turns into a major issue for the entire world, so researchers are trying to address this issue in various ways [5].An inhibitor is a substance which when added to an environment in small concentration [6].In the following studies, corrosion inhibitors were obtained based on methyl methacrylate, poly (methyl methacrylate-maleic anhydride) P(MMA-MAH) with different percentages methyl methacrylate and maleic anhydride were synthesized and the inhibitory potential of this inihitor on simple carbon steel in a 0.5 M HCl environment studied [7,8].A new N-heterocyclic initiator N-[2-(8-heptadecenyl)-4,5-dihydro-1H-imidazole-1-ethyl]-2-bromoisobutyramide was synthesized [9,10].

Experimental part
Synthesis of composite corrosion inhibitor.This reaction is the reverse of the above process, that is, the process proceeds with the release of a large amount of heat.It is explained that one of the main reasons for this is not only the high reaction activity due to the presence of two functional groups in the composition.Based on this property, a 500 ml flask with a flat bottom is taken, first, 2 moles (122 g) of monoethanolamine are poured into it and the system is cooled in the presence of cooling agents (mainly chilled water).While stirring the reaction mass, 1 mole (98) of maleic anhydride is slowly added to the reaction mixture.The mixture was stirred for 45 minutes and the intermediate product was obtained with a yield of 92.5%. 1 mol (98 g) of phosphoric acid is slowly added dropwise to the intermediate product obtained based on monoethanolamine and maleic anhydride and mixed (Fig. 2.1).The resulting intermediate product has the following physicochemical properties:

№
Aggregate status pH Density g/cm2 Solvent MMF-2 An interesting colored, dark substance 5,4 1,37 In hot water IR-spectrium analyses.The obtained reaction product was analyzed by IR-spectra methods.The inhibition efficiency of the obtained composite corrosion inhibitor was studied at concentrations of 75, 100, 150, and 200 mg/l, and the optimal concentration here was 200 mg/l.Based on the research results, the optimum inhibitory concentration of corrosion inhibitors was assumed to be 200 mg/l concentration [11,12].It is known from Table 3.2 that 0.5 HCl+200 mg/l NaCl was 92.86% at 333 K due to high absorption on the metal surface with increasing temperature [13]..

Electrochemical studies.
One of the most reliable methods for determining the inhibition efficiency of corrosion inhibitors is the electrochemical method.As a result of the absorption of inhibitors on the surface of the steel electrode, there is a change in the potential difference and the amount of corrosion current in the electrodes.The process of polarization occurs because the potentials at the cathode and anode do not have a constant value.
Electrochemical studies of these MMF-2 brand corrosion inhibitors were studied in Fon-1 corrosion environments at a temperature of 20 0 C. Inhibition efficiency of Fon-1(1M HCl+200 mg/l NaCl) without inhibitor at different (50, 100, 150 and 200) concentrations of St2 steel o studied.
In general, when the Tafel curves are studied in the medium with and without the inhibitor, the amount of corrosion current is higher in the medium without the inhibitor, which increases the formation of hydrogen and chloride ions in the solution and stimulates the acceleration of the dissolution of the cathode and anode.However, in environments where corrosion inhibitors are added to the corrosive environment, the Tafel curves show that the amount of corrosion current decreases, that is, the corrosion inhibitors reduce the melting of steel to a maximum level due to the slowing down of the cathode and anode dissolution.It is known from the results of the research that the concentration of the inhibitor depends on the change of the Tafel curves, which shows how much of the inhibitor molecules cover the steel surface [15].Tafel curves (Fig. 3.12) of corrosion current density (icorr), corrosion rate (  ), corrosion potential (  ),   and   slopes were obtained (Table 3.3).3.3, we can see that the amount of corrosion current is high (56.1 mA/cm2) in solutions without inhibitor, but the amount of corrosion current decreases accordingly with the introduction of an inhibitor into the system and the increase of the concentration of the inhibitor.For example: 8.63 mA/cm 2 at 50 mg/l, 6.22 mA/cm 2 at 100 mg/l, 4.13 8.63 mA/cm 2 at 150 mg/l and 2.21 at 200 mg/l reduced to mA/cm 2 .
Due to the formation of a complex with Fe 2+ ions, this MMF-1 brand corrosion inhibitor blocks cathodic reactions, reduces the release of hydrogen and prevents anode and cathode melting.Inhibition efficiency was 91.5% at 200 mg/l [16]..When smaller concentrations of the inhibitor are effectively adsorbed on the metal surface in a straight direction, its inhibition efficiency can be even higher.In conclusion, it can be said that the adsorption mechanism depends on the concentration, and with the increase in the concentration, the electrostatic repulsion and the forces between the inhibitor molecules increase with the increase of the concentration, which leads to the adsorption mechanism of a straight direction along the metal surface.
Thermodynamic and kinetic.By finding the activation energy of the obtained composite corrosion inhibitors at different concentrations and temperatures, it is possible to study the mechanism of interaction of the inhibitors with the metal surface.The corrosion rate is determined using the Arrhenius formula to determine the activation energy in solutions with and without inhibitors.
Here:  is the activation energy expressed in kJ/mol moles, R is the universal gas constant value of 8.314 J/mol×K, and T is the temperature expressed in K -exponential coefficient.
If we compare the activation energy (Ea) of the solutions with an inhibitor to the solution without the inhibitor, we can see that (Ea) increases as a result of the addition of the inhibitor to the solution, and the activation energy also increases with the increase in the concentration of the inhibitor in the solution.
A high activation energy causes physical adsorption, and if it does not change or becomes less, it causes chemical adsorption.
As the inhibitor concentration increased, the activation energy (Ea) values also increased dramatically.Therefore, in preventing corrosion, the primary function of the inhibitor is physical adsorption on the metal surface.From the large negative values of entropies, we can see that the rate-determining step of corrosion, i.e., active complex formation, is more associated than dissociated, which leads to a decrease in disorder.

Adsorption isotherm.
The process of adsorption is the desorption of water molecules by adsorbing inhibitor molecules on the metal surface, and this process can also be described as an exchange process.From this we can see that the inhibitor is adsorbed on the metal surface and covers the surface (th) as the inhibitor concentration increases, the surface is covered to a higher degree and the efficiency increases.θ is a quantity indicating the effectiveness of the inhibitor and is taken as 100.Several types of isotherms have been used to describe this process.Freundlich adsorption isotherms were obtained, which can be expressed as follows: where 0<n<1; θsurface coating; Сinhibitor concentration; Kads-equilibrium constant of the adsorption-desorption process.
The following isotherms for adsorption of these corrosion inhibitors were also studied Lengmyur: where: Сing -concentration of the inhibitor in the solution (mg/l), θthe full coverage rate, Kads-adsorption equilibrium constant.
The Langmuir isotherm provides a more complete understanding of the mechanism of interaction between the metal surface and the inhibitor.Using the Langmuir isotherm with Cing bilan Cing/θ as the adsorption equilibrium constant Kads found by ∆  0 value in the temperature range 25 o C -55 o C is found using Equation 3.7: The standard free energy of adsorption (DG°ads) is calculated by the following equation (3.8).
Here, R is the universal gas constant, T is the absolute temperature in Kelvin, and g/l.kads is the density of water in g/l.The values of cads and ΔG°ads are calculated using the above isotherm equations.
In this case, Ea values were found from the dependence of lgW on 1000/T in mediums without and with inhibitors.

Figure 3.2. Arrhenius plot g for the activation energy of MMF-1 corrosion inhibitor in Fon-1 solution
According to the results presented in Table 3.13, the value of Ea was 41.45 (kJ/mol-1) in solutions without an inhibitor, value increased with the introduction of MMF-1 brand corrosion inhibitor into the solution, and when the concentration reached 200 mg/l, it was 89.29 (kJ/mol-1).Also, the value of ∆Sa in the solution without inhibitor took a positive value of 101.25 kJ/mol, but with the addition of inhibitor to the solution, this value decreased to negative -75.21 (kJ/mol-1), the smaller this value, the corrosion depends on the concentration of the inhibitor, the association is higher than dissociation in the system, and this indicates that a stable complex is formed between the inhibitor and the metal.

Table-3.4. Values of activation parameters for steel St20 in graded water without inhibitor and in presence of green inhibitor
Ingibitor konsentratsiyasi Ea(kJ/mol -1 ) ∆Ha (kJ/mol -1 ) ∆Sa(kJ/mol The average energy difference between activation energy and enthalpy for samples without inhibitor and with different concentrations of inhibitor was approximately 2.67 which confirms the inhibition and adsorption process of St20 steel during melting.Several researchers have recognized that one of the reasons for the inhibition of the metal surface in the inhibitor solution is the absorption of the corrosion inhibitor on the surface.The presence of free ions in the composition of the corrosion inhibitor leads to the transport of charges, or the presence of functional groups binds to the metal surface through the donor-acceptor mechanism in exchange for negative charges.Langmuir, Frumkin, and Tyomkin isotherms of MMF-1 corrosion inhibitor were also studied.comparing the values of Frumkin, Tyomkin and Langmuir isotherms, the value of the Langmuir isotherm is higher than 0.99, which shows us that it matches the experimental data for the calculation of thermodynamic parameters.Langmuir, Frumkin, and Tyomkin isotherms for green corrosion inhibitors were also studied.
Available online at: https://jazindia.com-1460 -  Then the values of  were calculated based on the intersection of Langmuir isotherms.It follows from the values of  that the adsorption of MMF-1 brand corrosion inhibitor on the metal surface is superior to all desorption.Judging from the data in Table 3.14, the values of ∆G0ads were obtained in the range of 303−333 K, with results ranging from negative -23.12 kJ/mol to-28.29 kJ/mol provided, thus confirming that the adsorption of MMF-1 brand corrosion inhibitor on the metal surface occurs spontaneously [17].

Scanning electron microscope analysis.
A scanning electron microscope (SEM) uses a focused beam of high-energy electrons on the surface of solid samples to produce a variety of signals.SEM allows obtaining information such as the surface structure (external morphology), chemical composition, orientation of components, as well as the crystal structure of the sample from the signals obtained from the electron interaction of the sample.The purpose of SEM analysis is to determine the presence of an inhibitor on the steel surface.
The pre-corrosion, post-corrosion and inhibited states of the steel surface were studied using a SEM-EVO MA 10 (Zeiss, Germany) scanning electron microscope.It is known from Figure 3.6 that the SEM and elemental analysis of MMF-1 brand corrosion inhibitor in Fon-1 environment using a scanning electron microscope is presented.It is known that the inhibitor is adsorbed on the steel surface and against aggressive environments.It can also be seen from the element analysis.

Conclusion
It It is known from the results of the research that the optimal conditions for the synthesis of corrosion inhibitor based on maleic anhydride, monoethanolamine, and phosphoric acid were studied and its structure was analyzed using IR-spectra The inhibition efficiency of the obtained corrosion inhibitor was studied based on gravimetric and electrochemical methods, and the results obtained by both types of methods completely repeated each other.
The inhibition mechanism of this inhibitor was studied based on Langmuir, Frumkin, and Tyomkin isotherms from the adsorption parameters and its effect on the steel surface using a scanning electron microscope.

Figure 2 . 1 .
Figure 2.1.IR-spectra of MMF-1 composite corrosion inhibitor.From the IR spectrum analysis of the intermediate product of MMF-2 corrosion inhibitor, we can see that the valence vibrations of the OH group were observed in the broad and intense absorption region of 3059.10cm-1 .Valence vibrations of -C-N-bonds to the area of 1298.09-1182.62cm -1 , asymmetric valence vibrations of -C-O-C-bonds in the area of 1298.09cm -1 , valence, intensive vibration frequencies of -C-OH groups 1186.22 cm -1 Valence and intensity fluctuations were observed in the range of -1 field.

Figure 3 . 1 .
Figure 3.1.Polarization curves of the steel electrode in the Fon-1 solution in the presence of solutions without and with inhibitors.

Figure 3 .
Figure 3.4 of MMF-1 brand corrosion inhibitor.(a) Tyomkin (Figure 3.4 a), Frumkin (Figure 3.4 b), and Langmuir (Figure 3.4 c) isotherms are also plotted.According to the obtained results, when comparing the values of Frumkin, Tyomkin and Langmuir isotherms, the value of the Langmuir isotherm is higher than 0.99, which shows us that it matches the experimental data for the calculation of thermodynamic parameters.Langmuir, Frumkin, and Tyomkin isotherms for green corrosion inhibitors were also studied.

Figure 3 . 4 .
Figure 3.4.(a) Tyomkin, (b) Frumkin and (c) Langmuir isotherms and (d) temperature dependence of ∆G 0 ads Correlation coefficient values were obtained at different temperatures.We can see from Figures 3.7a and 3.7b that the values of the correlation coefficients the Frumkin and Tyomkin adsorption isotherms are not close to 1, indicating that the adsorption process does not follow these isotherms.

TABLE 1 . Study of determination of inhibition and protection levels of corrosion inhibitors using gravimetric method. Determination
of inhibition efficiency of composite corrosion inhibitor by gravimetric method was carried out by GOST 9.506-87.In this case, the temperature was between 30 0 C and 80 0 C, and the speed of the moving liquid was 1.1 m/s.

Table 3 .
1, we can see that 60 0C is 93.15% in a strong aggressive environment such as 1M HCl + 200 mg/l NaCl at a concentration of 200 mg/l.

Table - 3.3. The efficacy of the inhibitor is determined by the method of polarization curves in solution
with inhibitor (MMF-1) and without inhibitor.Inhibitor С, (mg/l) i, (mА/cm 2 )