Oxidative stability and storage behavior of soybean–macauba biodiesel blends: Experimental evaluation using GC-MS and FTIR analysis

Biodiesel is a good renewable source as a substitute of the traditional diesel, but the oxidative stability is low limiting its extensive use in storage. This analysis compares oxidative stability and storage of soybean biodiesel (BS100) and macauba biodiesel (BM100) and blends (BSM10-BSM50) at ambient temperatures during 90 days. Gas chromatography mass spectrometry (GC-MS) and Fourier-transform infrared spectroscopy (FTIR) were used to analyze the chemical composition and functional group characteristics of the newly developed products, whereas physicochemical properties such as water content, acid value, cold filter plugging point, and oxidation stability were periodically measured. The results of GC-MS showed that macauba bio-diesel is rich in saturated fatty acids (65.01%), where lauric acid (36.37%) and thus provides good oxidation resistance. Addition of macauba biodiesel to soybean biodiesel greatly enhanced the oxidative stability with 4.5 h (BS100) and 9.2 h (BM100) corresponding to induction phases. The amount of water BS100 contained increased by about 325%–363% and the acid value increased between 0.50 and 0.86 mg KOH/g during the storage period of 90 days, a fact that revealed a gradual degradation of the material. Blended fuels on the other hand did not experience the same steep rise in water content and acidity. In spite of the changes, the level of kinematic viscosity (3.0–6.0 mm²/s) and density (850–900 kg/m³) stayed at an acceptable level. The results show that, macauba biodiesel enhances the oxidative stability of soybean biodiesel within the first storage period; notwithstanding, severe deterioration causes it to be ineffective in long-term storage stability at ambient conditions. Nevertheless, the fact that the degradation becomes important after 60 days is an indication that more stabilization measures should be employed in case of long-term storage.