PNNL

Abstract

A power flow scheme applicable to probe-type ultrasound reactors is presented, that has been deduced from both experimental measurements employing an unjacketed vessel and theoretical predictions. Under typical conditions for water, 77% of the electrical power is converted into mechanical motion of the probe, that in turn is dissipated to both acoustic power (~12%) and cavitational heating (~88%). Approximately 92% of the mechanical power of the probe was converted into heat, with the remaining power presumably converted into audible acoustic and/or mechanical motion. Heterogeneous catalysis experiments have been performed at 298 K in an isothermal (i.e., jacketed) reaction vessel comparing chemistry in conventional (e.g., thermal) versus ultrasound-assisted systems. Both product state distribution and reaction rate measurements have been performed for the hydrogenation (using hydrogen gas) of aqueous 3-buten-1-ol solutions employing Pd-black powder. Products from the heterogeneous catalysis include isomerization to cis and trans 2-buten-1-ol, as well as hydrogenation to 1-butanol. Based on the observed differences in cis- to trans- 2-buten-1-ol ratios in conventional experiments, employing untreated and pre-reduced catalysts, it has been determined that a kinetic effect controls the observed product state distribution. In addition, differences in the ratio between cis- plus trans- 2-buten-1-ol to 1-butanol, comparing ultrasound-assisted to conventional catalysis, reveal a ~5-fold enhancement in isomerization relative to the more energetically favored hydrogenation due to application of ultrasound. Finally, the product formation rates for 1-butanol, as well as isomerization plus hydrogenation, revealed that conventional and ultrasound experiments showed both a non-linear dependence with applied ultrasound power and no differences between untreated and pre-reduced catalysts. The observed reaction rate enhancements were 1:36:183 for the conventional, 90 W ultrasound, and 190 W ultrasound experiments, respectively.