Análise da ação de antioxidantes na estabilidade oxidativa de biodiesel de soja, babaçu e blend: uma análise via rancimat, FTIR, UV-Vis e parâmetros de qualidade

Abstract

Biodiesel is susceptible to oxidation, which is aggravated by light, oxygen, and heat. According to ANP Resolution n° 920/2023, the addition of antioxidants is mandatory, and the production chain is responsible for selecting compounds that ensure a minimum induction period (IP) of 13 h. In this context, this study aimed to evaluate the action of the antioxidants butylated hydroxytoluene (BHT), tris(dimethylaminomethyl)phenol (DMP30), and natural Cashew Nutshell Liquid (CNSL) on the oxidative stability of soybean biodiesel (SB100), babassu biodiesel (BB100), and their blend (SB50:BB50) through accelerated and non- accelerated oxidation. The antioxidants were added at 1000 mg·kg⁻¹. The samples followed three distinct paths, simultaneous testing by Rancimat (accelerated oxidation) according to EN 14112, a bench-scale accelerated oxidation system for 14 h at 110 ± 5 °C with air bubbling, and long-term storage for 180 days (non-accelerated oxidation). The antioxidant action was assessed using Rancimat, FTIR (1620–1860 cm⁻¹), UV-Vis (200–500 nm), and quality parameters including Acid Index (EN 14104), Peroxide Index (AOCS Cd 8-53), Kinematic Viscosity (ASTM D7042), and Density (ASTM D4052). Finally, Analysis of Variance (ANOVA) and Tukey's test were applied to the collected data. Rancimat results indicated that all samples containing DMP30 met the minimum IP of 13 h required by ANP Resolution n° 920/2023, with the efficiency order being DMP30 > BHT > CNSL. The highest IP was observed for the BB100 sample (26.93 h), followed by SB100 (19.42 h) and the SB50:BB50 blend (18.27 h). FTIR analysis did not reveal a consistent efficiency pattern among antioxidants to allow direct comparison with Rancimat data. Regarding the other analyses, DMP30 outperformed BHT, CNSL, and the control samples, showing efficiency consistent with Rancimat results. This can be attributed to the aromatic amine groups in DMP30, which inhibit secondary oxidation products more effectively than phenolic antioxidants such as BHT. In contrast, CNSL composed mainly of anacardic acid, can generate reactive species that promote biodiesel oxidation. Therefore, the results confirm the superior efficiency of DMP30 and support the feasibility of developing protocols that correlate Rancimat results with alternative methods such as UV-Vis, acid index, and peroxide index, among others. Such protocols would combine accessible techniques to guide the selection of new antioxidants, reducing costs by prioritizing only those with potential to enhance the oxidative stability of biodiesel.