Numerical investigation of the ultrasound-assisted biodiesel transesterification with a polyalcohol

Abstract

Ultrasound elicits chemical and physical effects that drive and intensify chemical reactions. It can assist esterification and transesterification reactions for biomass conversion. There is extensive experimental data in the literature that highlight the effects of ultrasound on these reactions, but their numerical investigations are very few. In this work, we simulated an ultrasound-assisted biodiesel transesterification to produce lubricants. We studied the acoustic reactive flow by coupling acoustic, fluid dynamics, and chemical reaction models via the finite element software COMSOL Multiphysics. The Acoustics interface in COMSOL computed the pressure field and the Reacting Turbulent Flow interface simulated the fluid velocity and the lubricant concentration profiles inside the reactor. After validating the numerical model with experimental results, we investigated the effect of the probe immersion depth and diameter, the beaker radius and the frequency of ultrasound on lubricant production. The probe immersion depth at mid-height level (at 3 cm depth) was the optimal position. It produced a higher lubricant yield than the 1 and 4 cm depths (94% versus 86% at 4 cm and 81% at 1 cm). A 1.9 cm diameter probe yielded more lubricant than a 1.3 cm probe, maintaining the ultrasound power constant (e.g., 96% lubricant versus 87%, at 62 W).