Abstract
The inhibition of the corrosion of N80 steel in 3.5 wt. % NaCl solution saturated with CO2 by four porphyrins, namely 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin (HPTB), 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin (T4PP), 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrakis(benzoic acid) (THP) and 5,10,15,20-tetraphenyl-21H,23H-porphyrin (TPP) was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electrochemical microscopy (SECM) and scanning electron microscopy (SEM) techniques. The results showed that the inhibition efficiency, η% increases with increasing concentration of the inhibitors. The EIS results revealed that the N80 steel surface with adsorbed porphyrins exhibited non-ideal capacitive behaviour with reduced charge transfer activity. Potentiodynamic polarization measurements indicated that the studied porphyrins acted as mixed type inhibitors. The SECM results confirmed the adsorption of the porphyrins on N80 steel thereby forming a relatively insulated surface. The SEM also confirmed the formation of protective films of the porphyrins on N80 steel surface thereby protecting the surface from direct acid attack. Quantum chemical calculations, quantitative structure activity relationship (QSAR) were also carried out on the studied porphyrins and the results showed that the corrosion inhibition performances of the porphyrins could be related to their EHOMO, ELUMO, ω, and μ values. Monte Carlo simulation studies showed that THP has the highest adsorption energy, while T4PP has the least adsorption energy in agreement with the values of σ from quantum chemical calculations.
Highlights
Corrosion is a major problem in oil and gas industries and many factors have to be taken into account when attempting to solve the corrosion problems facing these industries [1]
Four porphyrin derivatives were investigated for their corrosion inhibition potential toward N80 steel corrosion in CO2-saturated 3.5% NaCl solution using electrochemical impedance spectroscopy (EIS), polarization, scanning electrochemical microscopy (SECM), scanning electron microscopy (SEM), quantum chemical calculations, quantitative structure activity relationship (QSAR) and Monte Carlo simulation approaches
(2) The shift in Ecorr (
Summary
Corrosion is a major problem in oil and gas industries and many factors have to be taken into account when attempting to solve the corrosion problems facing these industries [1]. Porphyrins find numerous applications as ligands for the spectrophotometric determination of cations, stationary phases in high-pressure liquid chromatography (HPLC), biosensors, catalysis, photovoltaic cells and membrane components for ion selective electrodes [10,11,12,13] Their applications as corrosion inhibitors for carbon steel in aqueous mineral acid have been reported [14,15,16]. A number of reports on the corrosion inhibition properties of different porphyrin molecules have revealed that porphyrin molecules can reconfigure the electron distribution of their conjugated aromatic rings in order to create ordered molecular layers on electrode surfaces These molecular layers serve as the protective film, which prevents the diffusion of electroactive species towards the metal surface.
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