Extraction of pectin from tomato wastes by ultrasound assisted method and evaluation of its performance as an ecofriendly corrosion inhibitor

This study aimed to extract pectin from tomato waste in a new way and to investigate its anti-corrosion properties. In this regard, pectin using ultrasonic extraction method under different conditions of solvent type, extraction temperature, and extraction time was done. The highest yield was obtained with citric acid at a temperature of 40 ˚C and 30 min equal to 18.5%. The degree of esterification, the amount of methoxyl group, and galacturonic acid of extracted pectin were measured as 53, 25, and 45%, respectively. To evaluate its inhibitory effect on corrosion, a sample of low carbon steel in hydrochloric acid solution was used. The mechanism of inhibition was discussed by electrochemical tests and surface analysis. Electrochemical polarization test was performed after 1 h immersion of carbon steel in 1 M hydrochloric acid containing different concentrations of pectin and at different temperatures. The results showed that with increasing temperature from 20 ˚C to 40 ˚C, the inhibition efficiency decreased from 94% to 77%. Also, the activation energy of corrosion rate decreased with increasing pectin concentration from 2% to 4% w / w from 1.76% to 0.64%. The results of the corrosion potential and current density showed that pectin is a mixture-type inhibitor and its inhibition is due to the geometric blocking of chemical inhibitors adsorbed on the metal surface. In addition, examination of the morphology and roughness of the steel sample surface by field diffusion scanning electron microscopy and atomic force microscopy analyzes showed that pectin was adsorbed on the steel surface and a stable protective layer was formed on the surface to prevent corrosion. The results of element composition analysis by X-ray diffraction spectroscopy showed the absence of corrosive elements on the surface of carbon steel confirmed the effectiveness of pectin in preventing corrosion.