Alcohol residues in biodiesel can be present even after the purification steps. It diminishes the flash point, lubricity and cetane number. The standard technique to quantify residual alcohol in biodiesel is the FID-GC with headspace sampling. NMR, although underused for quantitative analyses, requires no special sample preparation, and consumes low volume of solvent. In this work, methodologies for the residual methanol and ethanol contents in soy biodiesel by 1H-NMR in a 9.4 T (400 MHz) spectrometer by standard addition were developed and validated. Quantification limits were found equal to 0.07 and 0.08% respectively, so more than twice lower than the maximum level acceptable, which is 0.2%. Accuracy and precision were considered suitable for the alcohol content around the specification limit.

Biodiesel made from oils is rich in polyunsaturated fatty acids methyl esters, and, consequently, presents high tendency to oxidize. Biodiesel made from fats, on the other hand, is mainly comprised by saturated chains. Although it is highly stable, they easily crystalize at low temperatures. Blends from both can exhibit optimized properties. In this work, oxidative stability, expressed by induction period (IP), and cold filter plugging point (CFPP) of blends from palm, palm kernel, babassu, tallow or lard biodiesels with soy one were measured. Biodiesel samples were prepared by two steps transesterification methodology with KOH catalysis followed by H2SO4. IP increases, as the fat biodiesel content in the blend is higher, as expected. Blends comprised by 60% of fat biodiesel by volume had their IP increased from 1.5 (lard) to 2 times (palm kernel), compared to soy one. At this level, IP was found 8 h or higher, except for palm, which 80% was required. CFPP was observed at 8 °C or lower for the blends containing up to 60% of all the fat biodiesel, except for the palm one, which a 20% content must not be surpassed. Palm kernel 80% biodiesel blend reached the Brazilian specification, that is, IP higher than 12 h and CFPP lower than 5 °C.