Characterization of soybean biodiesel: Influence of alcohol type and molar ratio on speed of sound

Ultrasound techniques are widely used for monitoring chemical reactions and characterizing liquids. While the speed of sound in pure fatty acid esters (methyl and ethyl) is reasonably well established, the influence of molar ratio and alcohol type on the speed of sound in biodiesel across different frequencies remains unexplored. This study investigates the ultrasonic characterization of soybean biodiesel produced using different alcohols and molar ratios at frequencies of 1 MHz, 5 MHz, 7.5 MHz, and 10 MHz. The speed of sound in biodiesel samples was measured using the pulse–echo technique, with the expanded uncertainty determined at a 95 % confidence level. The results show that biodiesel samples produced with different alcohols at the same molar ratio exhibit distinct speed of sound values. Additionally, biodiesel synthesized at a 6:1 molar ratio demonstrated the lowest speed of sound. The findings confirm that ultrasound effectively differentiates biodiesel samples based on speed-of-sound measurements. This study highlights ultrasound as a promising technique for identifying biodiesel production pathways, offering a non-invasive and efficient analytical tool for quality assessment.