Performance evaluation of an eco-friendly corrosion inhibitor extracted from residue of biogas plant

Purpose – The purpose of this study is to develop a new eco friendly inhibitor to protect the steel from corrosion in acidic and saline conditions. Biogas plant residue extract (BPRE) is evaluated as a green and effective inhibitor to mitigate steel corrosion. Design/methodology/approach – Two steel grades, low carbon steel (LCS) and medium carbon steel (MCS) are investigated in the 3.5% NaCl and 0.1 M H₂SO₄ solutions with and without the use of BPRE. Spectroscopic and chemical tests were performed to characterize BPRE. The efficiency of the BPRE was evaluated through gravimetric and electrochemical tests. Findings – Fourier-transformed infrared spectroscopy result confirmed the presence of -OH, -CHO, -CN, -COOH, -CO and M-O functional groups, whereas phytochemical test results confirmed the presence of organic compounds in the BPRE. The gravimetric test results showed the corrosion rate of both steels remarkably decreased with increasing inhibitor concentration in both solutions. Potentiodynamic polarization test results further confirmed that BPRE has higher corrosion inhibition capability on LCS than MCS in both solutions. The maximum inhibition efficiency of 87% was achieved in 3.5% NaCl solution, whereas the maximum inhibition efficiency of 45% was achieved in 0.1 M H₂SO₄ solution by LCS. Electrochemical impedance spectroscopy (EIS) test results suggested that BPRE molecules inhibited steels by adsorbing to the surface, potentially reduced the number of available active anodic sites and raised the charge transfer resistance of both solutions, thereby reducing the corrosion rate. EIS results also confirmed that inhibitor obeyed the Freundlich and Langmuir adsorption isotherm models. Originality/value – This study evaluated the BPRE as an effective green inhibitor for carbon steels prone to corrosion in alkaline and acidic environments.