Study on the Synthesis of a New Mannich Base Quaternary Ammonium Salt and Its Synergistic Corrosion Inhibition Performance in a High-Temperature Acidic Environment

A novel Mannich base quaternary ammonium salt (MIB) was synthesized via a two-step method using imidazole, acrylamide, and benzyl bromide as primary raw materials. Its corrosion inhibition performance for N80 carbon steel in 20% HCl solution was investigated through weight loss and electrochemical experiments, and the synergistic effects between MIB and different additives were evaluated. MIB demonstrated potential as a temperature-resistant inhibitor, exhibiting a corrosion rate of 6.04 g·m^-2 ·h^-1 and an inhibition efficiency (<i>IE</i>) of 99.3% at 363 K with the addition of 1% MIB. A notable synergistic effect was observed when MIB was used in conjunction with KI. Under more severe conditions (433 K, 3 MPa, 20% HCl), the system maintained a corrosion rate of 59.12 g·m^-2·h^-1 while still achieving a high <i>IE</i> of 95%. Adsorption kinetics and thermodynamics studies revealed that the adsorption of MIB on the N80 steel surface followed the Langmuir adsorption model, increasing the energy barrier of the corrosion reaction and thereby making the process more difficult to occur. Theoretical calculations and surface analysis indicated that both neutral and protonated forms of MIB possess electron-donating and electron-accepting capabilities, which facilitate their adsorption onto the metal surface. Under high-temperature conditions, iodide ions (I^-) not only adsorb onto the metal surface, filling the gaps between MIB molecules, but also form a negatively charged layer. This negative layer subsequently attracts the positively charged quaternary ammonium cations of MIB, thereby enhancing the adsorption capability of MIB on the metal surface in high-temperature environments.