Abstract
ABSTRACT Plant-based material, namely bitter kola leaf, as an additive for surface modification of mild steel in H2SO4 solution was thoroughly scrutinized using electrochemical, theoretical and optimization techniques. The functional groups, of the biomolecules of the bitter kola leaf extract, were examined using Fourier transform infrared spectrometry (FTIR) and gas chroma-tography-mass spectrophotometry (GC-MS). For clarification purpose, scanning electron microscopy (SEM) was used to inspect the texture of the degraded and inhibited steel after 21 h of immersion. For the response surface methodology (RSM), central composite design of Design-Expert Software was used to optimize the inhibition efficiency as a function of acid concentration, inhibitor concentration, temperature and time. The optimum inhibition efficiency of 93 % was obtained at 0.9 g L-1 bitter kola leaf. The mutual correlation between the considered variables and expected response was adequately interpreted by a quadratic model. The fitness of the model was justified by the following standards which include P-value (<0.0001), adjusted R2 (0.9843), R2 (0.991), adequate precision (43.14) and coefficient of variation (2.59). Bitter kola leaf extract behaved as a mixed-type inhibitor and adequately satisfied Langmuir adsorption isotherm. Furthermore, the theoretical modelling revealed the most active molecule of bitter kola leaf responsible for the overall inhibition. The experimental and theoretical results are in agreement that bitter kola leaf extract is a viable corrosion inhibitor of mild steel in H2SO4 solution. Keywords: Acid corrosion, electrochemical study, green extract, mild steel, optimization study, theoretical modelling.
Highlights
The continuous industrial development and the consequent use and generation of chemical complexes have resulted in the degradation of engineering process equipment through the corrosion process
A standard titrimetric method was used to identify the active ingredients present in the bitter kola leaf (BKL) extract. These active ingredients were seen to associate with garcinia bio-flavonoids, a mixture known as kolaviron
Phenolics are a group of compounds obtained from hydroxycinnamic and hydroxybenzoic acids that exist in dry plants or leaves containing enough gallic acid as the major constituent.[27]
Summary
The continuous industrial development and the consequent use and generation of chemical complexes have resulted in the degradation of engineering process equipment through the corrosion process. Sometimes to eliminate the formation of clogging on the inside of transportation pipelines, they are treated with mineral acids like HCl and H2SO4. These mineral acids may cause severe corrosion in the storage facilities, pipes and oil reservoirs. If the internal corrosion is not correctly monitored the effect or damage can be catastrophic. This has necessitated the development of effective corrosion inhibitor in acidizing industries that can be mixed with mineral acids during routine treatment of industrial equipment.[1] A corrosion inhibitor is any substance that retards the rate of corrosion. The corrosion inhibitors retard the partial reactions through the formation of a dense film layer which functions as an impediment between corroding and the
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