Evaluation of Adding Natural Gum to Pectin Extracted from Ecuadorian Citrus Peels as an Eco-Friendly Corrosion Inhibitor for Carbon Steel

The production and use of eco-friendly corrosion inhibitors allows valuable compounds contained in plant waste to be identified and repurposed while reducing the use of polluting synthetic substances. Pectin extracted from Tahiti limes (Citrus latifolia) and King mandarin (Citrus nobilis L.) in addition to natural gums—xanthan gum and latex from the “lechero” plant (Euphorbia laurifolia)—were used to create an eco-friendly corrosion inhibitor. The optimal extraction conditions for pectin were determined from different combinations of pH, temperature, and time in a 2(3) factorial design and evaluated according to the obtained pectin yield. The highest pectin extraction yields (38.10% and 41.20% from King mandarin and lime, respectively) were reached at pH = 1, 85 °C, and 2 h. Extraction of pectic compounds was confirmed using Fourier-transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry analyses. Subsequently, a simplex-centroid mixture design was applied to determine the formulation of extracted pectin and natural gums that achieved the highest corrosion inhibitor effect (linear polarization and weight loss methods in NACE 1D-196 saline media using API-5LX52 carbon steel). Impedance spectroscopy analysis showed that the addition of xanthan gum to pectin (formulation 50% pectin–50% xanthan gum) improved the corrosion inhibitor effect from 29.20 to 78.21% at 400 ppm due to higher adsorption of inhibitory molecules on the metal surface.