Optimization of the corrosion inhibition performance of 2-mercaptobenzothiazole for carbon steel in HCl media using response surface methodology

In this work, the corrosion inhibition performance of 2-mercaptobenzothiazole (2-MBT) was investigated for carbon steel in 1 M HCl by examining the simultaneous effects of temperature, immersion time, and inhibitor dosage. Design and optimization of the corrosion inhibition have been performed using response surface methodology (RSM). The effectiveness of the inhibitor was analyzed by determining the corrosion rate (CR) and corrosion inhibition efficiency (CIE) using the experimental weight loss method. Based on experimental data and using ANOVA (analysis of variance), two high-precision models have been established to predict CR and CIE. The results depicted that the impact of concentration and temperature on CR and CIE was stronger than immersion time. It was observed that at low concentrations (10–50 ppm), the inhibition performance of 2-MBT was not significant. Increasing the temperature from 30 to 70 °C remarkably decreased CIE by about 14–20% and increased CR by 8–14 mm/y. In addition, it was found that adding 140–160 ppm of 2-MBT at low-to-mean temperature levels (30–50 °C) has the greatest interaction effect on the inhibition performance. In this case, the CIE was more than 92% and CR less than 1 mm/y. Moreover, the process was numerically optimized to “maximize” CIE and “minimize” CR. The results of numerical optimization indicated that optimal conditions for maximum corrosion inhibition performance of 2-MBT (CIE = 94.92%, and CR = 0.72 mm/y) were obtained to be 140 ppm, 34 °C, and 70 h. Furthermore, the type of adsorption of 2-MBT has been examined in the immersion time and temperature ranges of 5–105 h and 30–70 °C. Four models of isotherm for the adsorption analysis were used: Langmuir, Freundlich, Temkin, and Flory Huggins. The best results were observed using the Langmuir isotherm.The presence of both physical and chemical adsorption of 2-MBT was detected. This finding was supported by the range of values for the free energy of adsorption, spanning from −33.72 to −37.16 kJ.mol−1.