Design and characterization of a multi-frequency semi-pilot ultrasonic reactor: Application to the extraction and oxidation of flaxseed-gum

Abstract

The aim of this study was to design and study a new multi-frequency ultrasonic semi-pilot tank by evaluating the operational parameters with respect to calorimetric efficiency and sonochemical activity. The device was then applied to the extraction of flax-gum from the seeds and its oxidation by TEMPO method. The ultrasonic tank was used in single and multi-frequency modes (20 kHz, 40 kHz and 100 kHz). It has been shown that in single mode, the geometry and location of the ultrasonic transducers had a direct impact on the energy transfer efficiency and that the immersed radial probes gave transfer rates in the range of 66.9–82.8%. The production rate of molecular iodine was found to be better at a frequency of 100 kHz whatever the output powers used. The extraction of polysaccharides from flax seeds is proportional to the power density and can be done under mild conditions to preserve the integrity of macromolecules. Ultrasound assisted oxidation is efficient and we have highlighted that this could be done at low acoustic powers thank to the 100 kHz frequency. Thus, the results show that ultrasonic vessels are relevant for the scaling up of pretreatment of biomass and chemical processes.