Kinetic, thermodynamic and adsorption mechanism of RH inhibitors on St3 carbon steel in H2S medium

• R.E. Azizov¹, G.R. Gurbanov², A.V. Gasimzade³, A.J. Rahimli⁴ and R.A. Eyvazli⁴

¹ Azerbaijan State Oil and Industry University, Baku, AZ1010, Azerbaijan
² Department of Chemistry, Faculty of Chemical Technologies, Azerbaijan State Oil and Industry University, Baku, AZ1010, Azerbaijan
³ Department of Petrochemical Engineering, Faculty of Chemical Technologies, Azerbaijan State Oil and Industry University, Baku, AZ1010, Azerbaijan
⁴ Azerbaijan State Oil and Industry University (ASOIU), Baku, AZ1010, Azerbaijan

Abstract: The adsorption behavior, kinetic characteristics, and thermodynamic aspects of two newly synthesized aryloxy alcohol inhibitors, RH-1 and RH-2, were investigated for the corrosion protection of St3 carbon steel in H2S-containing medium. The molecular structures of the synthesized compounds were confirmed by FTIR, ¹H NMR, and ¹³C NMR spectroscopy. Corrosion experiments were performed using St3 carbon steel over the temperature range of 25–50°C and inhibitor concentrations of 10–30 ppm. Both inhibitors significantly reduced the corrosion rate, while the inhibition efficiency increased with increasing inhibitor concentration and decreased slightly with increasing temperature. The maximum inhibition efficiencies of 97% for RH-1 and 94% for RH-2 were achieved at 30 ppm and 25°C. Arrhenius and transition-state analyses revealed that the presence of the inhibitors increased the apparent activation energy of the corrosion process, indicating the formation of an effective protective adsorption layer on the steel surface. Adsorption of both inhibitors was best described by the Temkin adsorption isotherm, and the calculated adsorption equilibrium constants together with the negative values of the standard free energy of adsorption (ΔG⁰_ads) confirmed the thermodynamic favorability of the adsorption process. The adsorption parameters demonstrated that RH-1 possesses stronger adsorption affinity than RH-2. The superior performance of RH-1 is attributed to the presence of the propargyl moiety containing a C≡C triple bond, which provides higher electron density and promotes stronger donor–acceptor interactions with the St3 carbon steel surface than the allyl functionality of RH-2. These findings demonstrate that RH-1 is a promising corrosion inhibitor for protecting St3 carbon steel in H₂S-containing oil and gas environments.

Int. J. Corros. Scale Inhib., 2026, 15, no. 4, 267-300
doi: 10.17675/2305-6894-2026-15-4-11

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