Hydroxyl radical formation in batch and continuous flow ultrasonic systems

Abstract

The creation of free radicals by ultrasonic cavitation is the main mechanism that leads to chemical degradation of target pollutants and the process is considered an alternative advanced oxidation technology. The goal of this study was to compare the effects of batch and continuous flow ultrasonic systems on the formation of hydroxyl radicals. Ultrasonic batch experiments were conducted in two reactors (small and large) using a standard 20kHz catenoidal titanium horn at varying amplitudes and sonication times. The effect of saturating gas was also investigated by introducing helium and air at 1Lmin(-1) into the larger 100mL reactor. In the continuous flow system, the experiments were conducted with a 20kHz, 3.3kW ultrasonic systems using a titanium "donut" horn at varying volumetric flow rates and amplitudes. Formation of hydroxyl radicals was determined using terephthalic acid dosimetry measurements. At the same energy densities, higher hydroxyl radical concentrations were formed in the batch system than in the continuous flow system. Sonication time appeared to be the main factor that influenced the results in batch and continuous flow systems. The two gases (helium and air) did not increase the hydroxyl radical formation at any amplitude or sonication time tested.

Influence of cavitation and high shear stress on HSA aggregation behavior

“…The oscillating tip of the ultrasonic homogenizer resulted in a 90-times higher signal due to the high local energy input [36]. Converting the fluorescence signals to moles of hydroxyl radicals using the calibration curve, we found that 0.124 nmol/(L min) was generated by the microorifice, whereas the ultra-sonication sonotrode was capable of generating 11.25 nmol/(L min) which is in good agreement with expectations from the literature [37]. We expected that the same amount of hydroxyl radicals will result in similar levels of protein aggregation.…”

Influence of high power ultrasound on Brettanomyces and lactic acid bacteria in wine in continuous flow treatment

“…There are also commercially available types of horns with a special geometry that are suitable for pipeline installation (e.g. radially vibrating donut horns) [32].…”

Analysis of apple beverages treated with high‐power ultrasound: a quality function deployment approach

“…Several chemical reactions occur, like pyrolysis of water, oxidative species, reactive oxidative species and reactive nitrogen species reactions , . Degradation/changes of chemical molecules during ultrasonic processing could be related to oxidation reactions, promoted by the interaction of free radicals such as hydroxyl ( · OH) formed during sonication following the reaction (H 2 O → · OH + H · ) . An example is degradation of anthocyanins, chemical decomposition by opening of rings and formation of chalcone.…”

“…28,29 Degradation/changes of chemical molecules during ultrasonic processing could be related to oxidation reactions, promoted by the interaction of free radicals such as hydroxyl ( · OH) formed during sonication following the reaction (H 2 O → · OH + H · ). [30][31][32] An example is degradation of anthocyanins, 22 rings and formation of chalcone. Sonication results in a modification of macromolecular structures and a decrease of molecular weight.…”