Mass Transfer Kinetics of Ultrasound-Assisted Steam Distillation for the Extraction of Cinnamon Oils

Ultrasound-assisted steam distillation (USD) increased the yield of cinnamon oils extracted from cinnamon leaves by fitting a mass transfer kinetic model during the distillation process. A response surface optimization experiment was conducted to optimize the experimental conditions, which revealed that the order of factors was particle size, ultrasound power, ultrasound time, and pulse ratio. The optimal conditions were determined to be a 40 mesh particle size, 286 W ultrasound power, 31 min ultrasound time, and 7:3 pulse ratio, resulting in a 2.36% yield of cinnamon oils. The yield of cinnamon oils was 0.57% greater in USD than that of steam distillation (SD). The nonsteady-state diffusion model was the most suitable model for the distillation process. The washing coefficient b value of USD was 0.0210, indicating that cinnamon oils were enriched on the particle surface during the initial stages. The diffusion coefficient k of the USD was 0.1770, 40.36% higher than that of the SD, indicating a higher mass transfer efficiency. The main components in cinnamon oils were cinnamaldehyde, coumarin, and 2-methoxycinnamaldehyde. Compared with those of SDs, USDs increased the diffusion coefficient k values of these components increased by 48.51%, 77.67%, and 82.43%, respectively. Ultrasound cavitation improved the mass transfer efficiency of the distillation process, allowing components such as 2-methoxycinnamaldehyde to be more easily enriched in cinnamon oils than in other oils.