Improving sonochemical efficiency by pulsing cylindrically converging acoustic waves

Abstract

Sonochemistry is considered a green alternative for chemical synthesis, water treatment, and hydrogen production. There are several steps for sonochemical reactions. First, the nucleation of a bubble must occur through the application of an intense acoustic pressure field. After further ultrasonic irradiation, the bubble must grow to a diameter beyond a certain threshold so that it undergoes inertial collapse during the compressional phase of the acoustic field. Finally, this inertial collapse must achieve a quasi-adiabatic compression to cause pyrolysis of the gas or vapour molecules into radicals, which is the basis of sonochemical reactions. Conventional sonochemical reactors have sub-optimal acoustic fields and therefore require long reaction times to produce meaningful yields. We present a novel sonochemical reactor design that generates cylindrically converging waves into a reaction vessel. To determine the sonochemical efficiency (SE) of our design, we measured the hydroxyl radical yield under different operating conditions dosimetrically. We also compare the SE from an ultrasonic bath, immersed horn, and cup-horn reactor. These comparisons indicate that our reactor had a SE 200-fold, 3-fold, and 70-fold higher than the conventional reactors, respectively.