(CORROSIÓN INTERIOR)
DR. LORENZO MARTÍNEZ GÓMEZ
To proof the corrosion efficiency of hydroxyethyl, aminoethyl and amidoethyl imidazolines, they were evaluated by linear polarizationresistance and polarization curves in deaerated 3% NaCl + Diesel + inhibitors saturated with CO2 at 50 °C. The most efficient inhibitor was the amido ethyl imidazoline, with an efficiency of 97.88% whereas the least efficient was the hydroxyethyl imidazoline, with an efficiency of 88.8%. A theoretical study of the corrosion inhibition efficiency of these imidazoline derivatives, was carried out using density functional theory (DFT). The computational calculations were used to obtain information about their molecular structure and those properties related with the inhibition efficiency of these inhibitors. The obtained correlations and theoretical conclusions agree well with the experimental results.
Oilfield corrosion manifest itself in several forms, among which CO2corrosion (sweet corrosion) and hydrogen sulfide (H2S) corrosion (sour corrosion) in the produced fluids and oxygen corrosion in water injection system are by far the most prevalent forms of attack encountered in oil and gas production [1]. The injection of corrosion inhibitor is a standard practice in oil and gas production system to control internal corrosion of carbon steel structures. Nitrogen-based organic surfactants, such as imidazolines or their salts have been used successfully in these applications even without an understanding of the inhibition mechanism [2], [3], [4].The organic compounds have turned out to be effective inhibitors of the electrochemical corrosion [5]. This property has been attributed to their molecular structure, for example, the planarity and the presence of solitary electrons in the heteroatoms, which are important characteristics that determine, among others, the capacity of adsorption of these molecules [6]. In this way, the effect of the molecular structure on the chemical reactivity has been a subject of great interest for research [7], [8], [9], [10], [11]. During the development of novel and more efficient organic corrosion inhibitors, several quantum-chemistry studies have been performed in order to relate the inhibition efficiency to the molecular properties of the different types of compounds. The molecular structure and the electronic parameters that can be obtained through theoretical calculations, as the HOMO (higher occupied molecular orbital) energy, the LUMO (lower unoccupied molecular orbital) energy, the energy of the gap, (ΔE = ELUMO − EHOMO), are involved in the activity of the inhibitors, in addition to the reactive behavior that can be treated by means of the HSAB (Hard and Soft Acids and Bases) theory [12], [13], [14], [15], [16], [17], [18], [19], [20].Most of the studies on the inhibition mechanisms of imidazoline based inhibitors have been conduced in laboratory scale systems in brine solution in presence of CO2; such as rotating cylinder electrode (RCE) and linear polarization resistance (LPR) [2], electrochemical impedance spectrum (EIS), polarization curves and surface techniques [4], electrochemical noise (ECN), EIS and LPR were compared [21] and in brine solutions in the presence of hydrocarbon phase with saturated H2S using curves de polarization and spectroscopy impedance electrochemical (EIS) [22], [23]. Others studies the inhibition mechanism of the imidazolines has been by quantum chemical method [3].The purpose of this paper was to obtain information both on the level of corrosion activity and the type of corrosion in a system, using the electrochemical techniques LPR and potentiodynamic polarization curves. These data were used to evaluate corrosion inhibitor effectiveness. Another objective in this work was calculate the more relevant molecular properties on its action as corrosion inhibitors. These properties are: the molecular structure, the dipole moment, EHOMO, ELUMO, energy of the gap (ΔE), and those parameters that give valuable information about the reactive behavior: electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN) [5], [15], [16]. The local reactivity has been analyzed by means of the Fukui indices [24], [25], [26], [27], since they indicate the reactive regions, in the form of the nucleophilic and electrophilic behavior of each atom in the molecule.
CORROSIÓN INTERIOR, INHIBIDORES DE CORROSIÓN, INTEGRIDAD DE DUCTOS, CONTROL DE CORROSIÓN, CORROSION EN MEXICO, INNOVACIÓN Y TECNOLOGÍA, CORROSIÓN Y PROTECCIÓN.