ABSTRACT
Waste coca cola plastic bottles were subjected to depolymerization by aminolysis using mono ethanol amine (MEA) in the presence of sodium acetate as catalyst, the product bis(2-hydroxy ethylene terephthalate amide (BHETA) was compared with sodium dichromate (Na2Cr2O7) as corrosion inhibitors for mild steel in 0.5M HCl and 0.5M H2SO4 at ambient temperature. Results indicated that the rate of corrosion of the mild steel increased in the absence of both inhibitors and decreased with increase in concentration. The effect of temperature on the corrosion behavior of mild steel in the presence of 571, 1142, 1714 and 2285ppm inhibitor concentrations was also studied. The associated activation energy of corrosion and other thermodynamic parameters such as enthalpy of adsorption (ΔHads), adsorption equilibrium constant (Kads) and standard free energy of adsorption (ΔGads) were calculated. Highest inhibitor efficiency of BHETA was 84.5% in HCl and 82.9% in H2SO4 at 303K and 1714ppm concentration; lowest inhibitor efficiency of 74.8% in HCl and 61.8% in H2SO4 was recorded at 333K and 571ppm respectively. Na2Cr2O7 had highest inhibitor efficiency of 95.4% in HCl and 79.8% in H2SO4 at 303K and concentration of 1714ppm. Lowest inhibitor efficiency of 64.5% in H2SO4 and 84% in HCl was recorded at 333K and inhibitor concentration of 571ppm. Inhibitor efficiency increased with increasing concentration and decreased with increasing temperature. The values of activation energy (Ea) and free energy of adsorption indicated that the type of adsorption on the surface of mild steel is physically controlled, exothermic and spontaneous. Optical microscope (OMS) was used to study the surface morphology of mild steel in the absence and presence of both inhibitors. BHETA however surpassed Na2Cr2O7 in its corrosion inhibition ability in H2SO4, while the corrosion inhibition ability of Na2Cr2O7 in HCl was better than BHETA. Nevertheless, BHETA is a good substitute for Na2Cr2O7 and it is recommended on the basis of low operational hazard and better inhibition in H2SO4