New Sintanyl Phosphonates for Protection of Oil and Gas Pipelines from Steel Corrosion

Many corrosion inhibitors are economically disadvantageous or toxic to the environment. Additionally, there are certain requirements for corrosion inhibitors. Therefore, the development of new corrosion inhibitors is one of the important problems in the oil-producing and oil-refining industry. The purpose of this work is the synthesis of new corrosion inhibitors with high inhibitory activity, the establishment of the structure of the compounds obtained and the determination of the anti-corrosion effect with respect to aggressive media. This paper presents the results of research on the development of new iron corrosion inhibitors. New α-aminophosphonates were synthesized based on the Kabachnik-Fields reaction. Formalin, morpholine, phosphite containing residues of industrial non-ionic surfactants syntanols as radicals were used as a raw material. The compounds obtained were isolated in high yield. The structure of the compounds obtained is established by modern methods of physico-chemical analysis. The protective effect of the compounds obtained was studied by a gravimetric method for 6, 24, 72 hour exposure and an inhibitor concentration of 10, 25, 50, 100 ppm. As an aggressive medium, a highly mineralized medium containing СО2 and Н2S was used in simulated formation water. The dynamics of changes in the protective effect of the resulting aminophosphonate from time to time, at dosages of 2.5-100 ppm, were studied using electrochemical analysis methods. The protective effect of syntanyl-O-ethyl(N-morpholinyl) methylphosphonate obtained at 25 ppm and a shutter speed of 6 hours is 73-82%. The article shows that with increasing concentration, an increase in the protective effect is observed. The greatest protective (89.6) effect showed O-2[2[2[2[2[2[2[2[2[2(dodecyloxy) ethoxy] ethoxy] ethoxy] ethoxy] ethoxy] ethoxy] ethoxy] ethoxy] ethoxy] ethyl-Oethyl(N-morpholinyl) methylphosphone at a dosage of 100 ppm.


Introduction
Corrosion is a common problem in the oil and gas industry.Oil and gas pipelines, refineries and petrochemical plants have serious problems with corrosion.Corrosion in the oil and gas industry is often caused by water, carbon dioxide (CO2) and hydrogen sulfide (H2S), and can also be enhanced by microbiological activity [1].The fight against corrosion in the oil and gas industry is of paramount importance, since the economic losses in these industries due to corrosion are extremely high [2].The use of a corrosion inhibitor is one of the best and most cost-effective methods among various methods of dealing with corrosion in the oil and gas industry [3,4].
Despite the great diversity of existing metal corrosion inhibitors, there is the problem of expanding their range by creating new inhibitors [14].
It is known that α-aminophosphonates are among the active inhibitors of iron corrosion in acidic media containing HCl and sulfuric acid [15][16][17].
The Kabachnik-Fields reaction is a simple multicomponent organic reaction from aldehydes, amines and dialkyl phosphites, as a result of which the amino phosphonatescompounds with the P (O) -C -N bond [18] are formed.Recently, the synthesis of α-aminophosphonates has attracted much attention due to the structural analogy with α-amino acids and significant biological activity.They are used as HIV protease inhibitors [19].The α-amino phosphonate based on 4-hydrazino-quinazoline has antimicrobial activity against Escherichia coli, Salmonella sp., Staphylococcus aureus, Saccharomyces cerevisiae [20].β-lactam derivatives are antitumor agents that are particularly anti-leukemic [21].
Tα-Aminophosphonates have complexing properties that are used as carriers of metals through the membrane [22].
They are used to extract valuable metals from their solutions, in particular gadolinium [23].Aminocarboxyphosphonate ligand complexes can be used as radiopharmaceuticals [24].

Materials and Methods
As corrosion inhibitors, we synthesized compositions based on α-amino phosphonation reaction products containing an О -organic substituent based on a long chain of various industrial fractions of synthanols and several active centers of phosphorus, nitrogen, and oxygen.Synthesis of corrosion inhibitors was carried out according to the Kabachnik-Fields reaction in the three component medium without using a solvent and a catalyst according to the following reaction equation scheme [25] (Equation 1).The 31 Р NMR spectra were recorded on a Bruker Avance-400 instrument (161.94MHz for 31 Р and 400.05 MHz for 1 Н).The 13 С NMR spectra are recorded on a Bruker Avance-600 instrument with an operating frequency of 150 MHz.The IR spectra were recorded on a Tenzor 27 spectrometer (Bruker, Germany) on KBr plates in the range of 0-1200 cm -1 .Mass spectra were recorded on an AmazonX instrument, electrospray ionization.Elemental analysis performed on the instrument Carlo-Erba brand EA 1108.
According to the corrosion tests of the compounds obtained, the protective effect Z %, was calculated using the Equation 1: Where Δm1, Δm2 is the mass loss of the sample after the test in non-inhibited and inhibited media, g.; Δm3 is weight loss of the sample after as a result of treatment with an etching solution.
Anticorrosion studies by an electrochemical method were carried out on a P-45X potentiostat-galvanostat produced by Elins in a highly mineralized medium (corresponding to the model described above) with a СО2 content of 250 g/m 3 , Н2S -20 g/m 3 .The electrochemical method for determining the anticorrosion activity consists in obtaining polarization curves that transmit the relationship between the potential of the electrode under study and the current density during polarization from an external source of direct electric current, followed by an assessment of the protective ability of the inhibitor by current density in inhibited and non-inhibited media.
The electrochemical cell (V = 1 l) consisted of working electrodes (metal rods made of steel grade 3.30 mm long and 5 mm in diameter) of an auxiliary platinum electrode, silver chloride reference electrode, magnetic stirrer, a tube for passing carbon dioxide through a medium, a valve for removal of excess gas and temperature sensor.
Carbon dioxide was passed through the solution to obtain the desired concentration, and then the calculated amount of Н2S solution was added.The rotation speed of the stirrer was 300 rpm.
The density of the corrosion current, proportional to the corrosion rate of the metal was determined by extrapolating the Tafel section to the value of the corrosion potential on the polarization curves.
The protective effect was determined by the Equation 2: Where: Icoring -Corrosion rate of metal with inhibitor, mA/cm 2 ; Iblank -Corrosion rate of metal with no inhibitor, mA/cm 2 .

Results and Discussion
Collate As a result of the synthesis by the Kabachnik-Fields reaction, new synthanol-O-ethyl-(N-morpholinyl) methylphosphonates 4a-c were synthesized.

O-[2-(2-dodecylcyloxy
) ethoxy] ethyl-O-ethyl phosphate 1a reacts with formaldehyde and morpholine at 80°C without solvent for 4 hours to form the corresponding phosphonates 4a.In the NMR 31 P-{ 1 H} spectra of the reaction products, the signals of the phosphorus atom shift to weaker fields and appear at 23.84; 24.33; 24.79 ppm in the ratio of 1: 1.6: 1.The manifestation of such a large number of signals of the reaction products occurs due to the formation of a mixture of products.Since we used compounds with a total content of ethoxylated groups n = 2 as the starting phosphite.According to the ESI mass spectrum, it was found that the main aminophoanates contain, as a synthanol radical, С12H25ОСН2СН2-(m/z=422.4); С12H25(ОСН2СН2)2-(m/z=446.5); (С12H25(ОСН2СН2)3-(m/z=510.5);С12H25(ОСН2СН2)4-(m/z =555.4);(С12H25(ОСН2СН2)6-(m/z + Na + =606.6)groups.Similarly, in the spectra NMR 31 P -{ 1 H}, the reaction products 4b and 4c signals of the phosphorus atom appear as three singlets 23.9; 24.46; 24.93 (2: 2.8: 1) and 23.74; 24.24; 24.71 (1.7: 2.4: 1) respectively.The presence of a doublet from methylene protons of the region δ = 3.46 ppm, with a constant of 2 JHР = 10.6 Hz in the spectra NMR 1 H of products 4a, confirms the formation of a РСН2N phosphonate bond.Signals of methylene protons from РОСН2 groups of ethyl and synthanol radicals due to the presence of several compounds in the product appear as multiplets in the region δ = 4.10 -4.25 ppm.
The signals of methylene protons СН2ОСН2 of the morpholinyl radical group appear as a triplet δ = 2.61 with the characteristic constant 3 JHH = 4.4 Hz.In the spectra NMR 13 С { 1 H}, the carbon atom signals of the РСН2N bond appear as a doublet with a characteristic constant 1 JРС 189.27 in the region δ = 48.67,which in the spectra NMR 13 С are transformed into a doublet of triplets with characteristic constant 1 JСH 134.6, 1 JРС 189.27 Hz.In the IR spectra of compounds 4a-c in the region of  = 1117-1119 cm -1 , signals from the P = O groups appear.Elemental analysis of the compounds obtained is slightly different theoretical.In products 4a carbon is more than 3% calculated, and agrees well with the data of the mass spectra, according to which the main content of the products obtained is shifted towards longer molecules compared to the theoretical one.In products 4b and 4c, the difference in elemental composition between the obtained and calculated calculations is insignificant, and is shifted towards obtaining lower molecular weight products than calculated ones.According to the mass spectra of 4b, phosphonates containing syntanyl radicals are present СnH2n+1(ОСН2СН2)m, where n= 9.12; m=5-9 and 4c СnH2n+1(ОСН2СН2)m, where n= 9.12; m=6-12.
All compounds are readily soluble in benzene, alcohols.4a is highly soluble in water, 4b and 4c are poorly soluble.Therefore, compounds for anticorrosion research were introduced in the form of solutions in isopropanol.
Data of gravimetric studies of compounds 4a-b are presented in Table 1.4a and 4b exhibits a maximum protective effect after 6 hours of exposure (82.3 and 80.9%).In contrast to 4а,b, compound 4с after 6 hours of exposure exhibits the least activity (73.2%).This is due to the slow adsorption of the inhibitor on the metal surface.In our case, the smaller the molecule, the faster the protective film is formed.Further, with increasing exposure time, the protective effect of compounds 4a, 4b decreases.The inhibitor activity for 4a drops by 20%, the decrease for 4b is insignificant (4%).During this time, a dense adsorption layer is formed on the metal surface.Further, the activity of the inhibitor smoothly decreases.This may be due to a decrease in the concentration of the inhibitor in the solution when the inhibitor molecules interact with iron ions, adsorption of the inhibitor on the walls and details of the cell, or a change in the adsorption-desorption equilibrium.It should be noted that during long-term experiments, black precipitate of iron corrosion products transferred by the flow of corrosive medium from the sample surface to the solution begins to appear in the solution.Loose sediment particles, representing a mixture of varying composition of carbonates and iron sulfides, can adsorb inhibitor molecules and reduce their concentration in solution, which leads to a decrease in the protective effect.
The anticorrosive activity of compound 4c slowly increases with increasing time from 73.2% (at 6 hours) to 76.2 (72 hours).This is due to the slow adsorption of the inhibitor and the formation of a stable protective layer, due to the presence of an inhibitor in the long radical in the molecule.
With an increase in the concentration of inhibitors at 24 h exposure, an increase in the protective effect is observed in all cases.Already at 10 mg/l, the protective effect of inhibitors is above 50.The greatest protective effect appears at 100 mg/l of compound 4c (89.6%), which is comparable to the indices of industrial inhibitors.For example, INCORGAZ-01ON and INCORGAZ-11ON exhibits a protective effect of 82-88% under similar conditions [26].Inhibitors representing the product of the interaction of N'N-tetramethyl diaminomethane and alkenyl chlorides exhibit a protective effect of 89-91% [27], mixtures of imidazolines and amidoamines exhibit a protective effect of 85-99% [28], Sulfadoxine -Pyrimethamine show a protective effect of 75-77% [29].The dependence of the inhibitory activity of the composition 4a-c on the concentration of the inhibitor at 40° C by the electrochemical method was investigated.Figure 2 shows a graph of the polarization resistance for different concentrations of the 4d inhibitor.According to the graph, it can be noted that the curves reach a maximum after 8-9 hours from the start of the inhibitor injection, that is, the full activity of the inhibitor is manifested after 8-9 hours, which then persists.At a dosage of 25 ppm, the protective effect of compound 4c (67.68%) is inferior to 4a and 4b (74.5% and 75.4%), but according to Figure 1, an increase in polarization resistance is observed with time and suggests that they will become equal over time.

Conclusion
As a result of the conducted research, three new complexes of syntanyl-O-ethyl-(N-morpholinyl) methylphosphonate were synthesized, containing ethoxylated dodecyl alcohol with ethoxylation number for 4a 1-5, for 4b 5-8, for 4c 6-12 as a syntanyl group.The compounds obtained possess high anticorrosion activity in model environments of formation water containing СО2 and Н2S.As a result of gravimetric tests, it was revealed that the protective effect of the inhibitors depends on the degree of oxidation of the syntanyl radical.Low degree of oxyethylation contribute to a high protective effect with a short holding time.Further, with increasing time, a significant decrease in anti-corrosion activity is observed.With a high degree of oxyethylation, the protective effect increases with time, remains stable for 72 hours.With an increase in the dosage of the inhibitor, the protective effect increases.According to the data of electrochemical tests, inhibitors have been established to reach the peak of activity 8-9 hours after the inhibitor has been injected.The protective effect of 50% is achieved already at a dosage of 2.5 ppm.At 25 ppm of 4a-c inhibitors, the protective effect is 64.38 -82.3% for different duration of the experiment.Composition 4c was found to exhibit the greatest inhibitory activity of 89.6% at a dosage of 100 mg /l at 24 hours exposure.

Figure 1 .
Figure 1.Dynamics of changes in polarization resistance for different concentrations of inhibitor 4c and 25 mg/l 4a, b at 40°C