Investigation of curcumin antioxidant efficiency on oxidation stability of biodiesel from soybean oil and beef tallow, contaminated with metals: Kinetic and storage studies

Abstract

Biodiesel can be produced from different raw materials or its blends, being that the soybean oil and bovine fat blend has been gaining prominence, because it guarantees good oxidative stability. However, several factors can affect its oxidative stability, such as exposure to high temperatures or contact with metals that may be present in storage and transport tanks. Thus, for its commercialization, a minimum of 8 h of Induction Period (IP) is required by the EN 14112 standard, and to reach this oxidation stability value, it is often necessary to add antioxidants to delay the oxidative process. This study aimed to evaluate the antioxidant action of curcumin in commercial biodiesel produced from soybean oil (70 %) and animal fat (30 %) blend and contaminated with metals in order to evaluate parameters such as IP, stabilization factor (F), activation energy (Ea), pre-exponential factor (A), reaction rate constant (k) and samples stability during storage in an oven at 85 °C. The samples were characterized by ultraviolet absorption spectroscopy and by Rancimat method (oxidation stability). The results showed high efficiency of the curcumin antioxidant, monitored by absorption at 425 nm. The curcumin addition in the biodiesel sample provided IP values greater than 8 h, even when contaminated with copper. The results of the kinetic studies showed for activation energy a value of 97.22 kJ mol−1 for the sample with 2000 mg kg−1 of curcumin, and 94.28 kJ mol−1 for the sample with curcumin at the same concentration and contaminated with 2 mg kg−1 copper. Even after 14 days of storage at 85 °C, the samples biodiesel with curcumin showed IP values within the required by international legislation (EN 14112 standard), showing curcumin as a promising natural antioxidant, even when biodiesel exposed to factors that intensify oxidative degradation.