Experimental and computational investigations on the synergistic inhibition mechanism of biphenyl quinoline quaternary ammonium and hexamethylenetetramine on the corrosion of J55 steel in 20 wt% HCl solution

Abstract

The present study involves the synthesis of a novel biphenyl quinoline quaternary ammonium salt (BDQ) and its application in combination with hexamethylenetetramine (HMT) as a compounded corrosion inhibitor for acid stimulation, aiming to effectively prevent the corrosion of J55 steel in a 20 wt% HCl solution at 60 °C. The optimized BDQ/HMT mixture (with a mass ratio of 1:3) at 0.4 wt% produced a significant decrease in the corrosion rate of J55 steel to 3.7637 g/(m²·h), much lower than the requirement of 5.0 g/(m²·h) stipulated by the standard SY/T 5404–2019. The electrochemical analysis demonstrated that the BDQ/HMT mixture exhibited a mixed-type corrosion inhibitor with predominantly anodic characteristics, retarding both the anodic oxidation and cathodic reduction reactions of J55 steel in the HCl solution. The adsorption studies revealed that BDQ conformed to a Langmuir-type adsorption isotherm on J55 surfaces, driven by a combination of physisorption and chemical interactions, with chemical interactions playing a dominant role. Additionally, quantum chemical calculations and molecular dynamics simulation were also performed to elucidate the observed synergistic effect of BDQ and HMT.