Cashew nut shell liquid (CNSL) residue as a greener corrosion inhibitor: Experimental and DFT studies of intensifier effect

Abstract

Industrial applications such as acid pickling and descaling justify the need for corrosion inhibitors. Among biomass derived inhibitors, there is the distillation residue of the cashew nut shell liquid (CNSL), which consists of a polyaromatic structure. The purpose of this work was to evaluate the synergistic effect of CNSL residue with KI through experimental (15 % HCl) and DFT studies. Three theoretical models were used with different radicals drawn from the experimental chemical characterization of the CNSL residue (CNSL/phenyl, CNSL/n-butyl and CNSL/tert-butyl substituents). The formulation containing intensifier, B1 + KI, achieved 89.84 % efficiency when compared to B1 (83.52 %) by linear polarization resistance. The concentration effect of formulation B1 was also evaluated, and the highest efficiency was achieved by B1 (6.0 % v/v) at 333 K (96.49 %). The presence of inhibitory film was confirmed by EDS, and a more uniform surface was observed in the presence of the corrosion inhibitor formulations. The DFT studies revealed that the proposed CNSL residue model has the potential to be used as a corrosion inhibitor, especially the CNSL/phenyl inhibitor. In acid medium, it was demonstrated that the corrosion inhibitor properties were intensified. Finally, the analysis of the interaction of chloride and iodide ions with the CNSL/phenyl compound showed that the presence of halides can improve the inhibitory properties by increasing the dipole moment values.