Synthesis of New Phenolic-Schiff Base and Its Application as Antioxidant in Soybean Biodiesel and Corrosion Inhibitor in AISI 1020 Carbon Steel

Abstract

New Schiff base compound N,N'-bis-(4-hexadecanate)-salicylethylenediamine (named IM) was synthesized, and characterized via infrared and nuclear magnetic ressonance spectroscopies. IM was tested as corrosion inhibitor and antioxidant in soybean biodiesel. Corrosion studies were developed with AISI 1020 carbon steel in a three-step accelerated corrosion assay and IM inhibitory activity was evaluated using microscopic techiniques: optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). In 750 ppm concentration, IM showed better inhibitory activity compared to commercial compounds tert-butylhydroquinone and pyrogallol, reducing root-mean-square roughness (Rq) from 37.8 to 11.7 nm and peak-peak height (PP) from 454.1 to 120.2 nm after 8 days of immersion. Antioxidant studies were conducted using the PetroOXY equipment. In 250 ppm concentration, IM showed better antioxidant activity as metal chelator, reducing biodiesel oxidation induced by copper on biodiesel. In this concentration, IM increased the induction period from 3.0 to 5.8 h. Furthermore, the new Schiff base acts as an oxygen scavanger. This is a great property because it reduces oxygen concentration in biodiesel, reducing metal corrosion reactions.

Biofuels-related materials deterioration in biorefineries, transportation and internal combustion engines: a technical review

“…The high antioxidation capacity of poly-phosphorous (hydroperoxide dissociation agent), synthetic phenolic, BHT, gallic acid (GA), BHA, PG, TBHQ, pyrogallol (PY), 2,5-di-tert-butyl-hydroquinone (DTBHQ), IONOX 220, Vulkanox, ZKF, Vulkanox, BKF and Baynox as additives for Biofuels are frequently documented [48,98]. Comparing results indicates that antioxidants efficiency can be summarised as PY > PG > Ethanox-4760E > N,N′-di-sec-butyl-p-phenylenediamine > 2,2′-methyl-ene-bis-(4-methyl-6-ter-butylphenol) > BHA > TBHQ∼BHT > 2,5-di-tert-butyl-hydroquinone > α-T with special mention for binary and ternary blends like TBHQ/BHA [6,99 101] for Biofuels during consumption and caffeic acid > ferulic acid > tert-butyl-hydroquinone during storage [102,103]. The efficient biofuel corrosion inhibitor organic compounds can be chosen from nucleophile chemicals with free electrons on their heteroatoms and the ability of electron transfer into the electrophile metal surface and cohesive film-forming along the metal–medium interface via their chelate and complex compounds.…”

“…The efficient biofuel corrosion inhibitor organic compounds can be chosen from nucleophile chemicals with free electrons on their heteroatoms and the ability of electron transfer into the electrophile metal surface and cohesive film-forming along the metal–medium interface via their chelate and complex compounds. The selection of appropriate corrosion inhibitor in biofuels also relies on their effect on lubricity and combustion efficiency [100]. The natural corrosion inhibitor additives have shown high effectiveness in biofuels, such as propyl gallate (83%), stearic acid (75%), Beta-carotene with (62%) [104].…”

“…The natural corrosion inhibitor additives have shown high effectiveness in biofuels, such as propyl gallate (83%), stearic acid (75%), Beta-carotene with (62%) [104]. Corrosion inhibition against biofuels is mostly successful via chemical compounds with the ability to form adherent interface layers by pi-electron bonding [105]; film-forming agents via physical adsorption of N-containing compound which creates a protective layer over the metal surface[106]; antioxidation agents via chain termination reactions between functional groups (OH or NH) hydrogen [100] and peroxide free radical that can be easily abstracted by the [106,107]. Polar amine groups in amine-based inhibitors are capable of ionising the interfaces and adsorbing heterocyclic moiety via N atoms, which results in enhanced inhibiting properties for metal surfaces [108].…”