Scaled-up sonochemical microreactor with increased efficiency and reproducibility

Abstract

Bubbles created with ultrasound from artificial microscopic crevices can improve energy efficiency values for the creation of radicals; nevertheless it has been conducted so far only under special laboratory conditions. Limited reproducibility of results and poor energy efficiency are constraints for the sonochemistry and ultrasonics community to scale-up applied chemical processes. For the first time, using conventional ultrasonic bath technology, the numbering-up and scale-up of a microfluidic sonochemical reactor has been achieved. Sonochemical effects such as radical production and sonochemiluminescence were intensified by the modification of the inner walls of a novel Cavitation Intensification Bag. While 25 times bigger than the previous microreactor, a reduction of 22 % in standard deviation and an increase of 45.1 % in efficiency compared to bags without pits were obtained. Mechanical effects accompanying bubble collapse lead to two distinct types of erosion marks observed in the bags.Cavitation, the formation and collapse of bubbles in liquids, has been used as a green energy-focusing tool to produce chemical effects (notably production of free radicals), enhanced luminescence, mechanical activation of heterogeneous systems, physicochemical modifications of inert materials as well as water remediation, water splitting, and bioenergy applications. [1] These effects can all be harnessed in applied domains, from cleaning to water treatment and nanochemistry. However, a main barrier for sonochemical and ultrasonic reactors to be uti-lized for industrial purposes and other uses is the lack of reproducibility, along with a low energy efficiency. [2] Employing the same ultrasonic equipment, glassware, chemicals and experimentalist person, is no guarantee that the standard deviations of an expected result will be small. This lack of reproducibility is because creating bubbles with ultrasound closely resembles a stochastic process, depending on physical-chemical factors difficult to control at once. [3] The first is the nucleation sites from which bubbles are created. Once bubbles are nucleated, liquid-gas concentration, frequency and amplitude of ultrasound signal, etc. have a significant influence on the overall cavitation process. These parameters influence the "unitary" reactor that a bubble itself represents, and determine the generation of plasma conditions, sonoluminescence, shockwaves, jetting, and radical production, upon collapse. [4] Despite all these useful phenomena available at ambient pressure and room temperature, industrial applications have been hindered due to a meager~10 À6 -10 À5 (kg/kJ) energy efficiency of cavitation reactors. [5] The present work is motivated by the challenge in scalingup a microfluidic sonochemical reactor while increasing its results reproducibility. [6] The energy efficiency of that system was calculated as the product of radical formation rate and the energy required for the formation of OH . radicals divided by the electric power absorbed by the transducer. Wit...

Cleaning of used rotary nickel‐titanium files in an ultrasonic bath by locally intensified acoustic cavitation

“…Taking into account that this cavitation intensifying method has been tested and found to provide advantages under different conditions (Verhaagen et al . , Gomes et al . , van Zwieten et al .…”

“…Moreover, the formation of cavitation bubbles is very unpredictable in both space and time and resembles a random process (Verhaagen et al . ). Cleaning of root canal files could be enhanced by introducing a novel sonochemical reactor into the ultrasonic bath which could intensify the cavitation locally in a well‐defined manner (Verhaagen et al .…”

“…Cleaning of root canal files could be enhanced by introducing a novel sonochemical reactor into the ultrasonic bath which could intensify the cavitation locally in a well‐defined manner (Verhaagen et al . ). This reactor has been recently realized in the form of a polypropylene bag (Cavitation Intensifying Bag, BuBclean, Borne, the Netherlands) (Fig.…”

“…) having micropits onto its inner surface (diameter 100–500 μm, depth 100–200 μm) that provide artificial nucleation sites for cavitation bubbles (Verhaagen et al . , ) and it appears to be useful for emulsification and for improving the reproducibility of micron‐sized object cleaning and exfoliation of nanomaterials (Gomes et al . , van Zwieten et al .…”

Parametric Investigations of the Induced Shear Stress by a Laser-Generated Bubble

“…Additional advantages of cavitation surface cleaning include micro-jetting penetrating in surface crevices 12 , thus achieving deep cleaning and contaminant removal. The violent collapse of bubbles is known to produce high temperatures and pressures, resulting to chemical reactions (hence the name sonochemical) and the production of free radicals 13,14 . These free radicals can further enhance cleaning capacity, by neutralizing harmful substances or microbes.…”