Investigation of the ultrasonic based hydrogen production process: Sonohydrogen

Abstract

The present work carries out various sets of numerical investigations to link the primary effect of the acoustic parameters with the secondary effect of developing a chemical reaction mechanism for water vapor dissociation into hydrogen and radicals. The first set of numerical modeling predicts the acoustic pressure distribution inside a typical geometry cylindrical sonoreactor. The study validates the acoustic pressure according to different geometrical and acoustical parameters. Secondly, the analysis and assessments give access to the sonication process's acoustic streaming. The second set validates the acoustic streaming result according to the velocity profile and streamlines, which gives an excellent agreement with the literature's experimental data. Analysis of variance ANOVA investigates the performance of 27 different configurations for the sake of optimization and determines the most influential factors for the design of a sonoreactor. Nevertheless, the chemical reaction module develops a chemical kinetics model and simulates the sonohydrogen process. The reaction kinetics mechanism consists of 19 reversible reactions and investigates the effect of the acoustic bubble temperature and the dissolved gases on the hydrogen production rate. The study quantifies the amount of hydrogen produced from the sonohydrogen process successfully and reveals the energy consumption to produce one μmol of hydrogen per kWh. The chemical kinetics results reveal that the higher the bubble temperature, the higher the chemical reaction rate. In the case of the H2O/O2 bubble, the energy consumption ranges between 1.05-1.63 μmol/kWh, with a maximum hydrogen yield of 4% and a maximum energy efficiency of 2% depending on the bubble’s temperature. However, in the H2O/Ar bubble, the hydrogen production shows an outstanding improvement with energy efficiency in the range 20-30 μmol/kWh with a maximum hydrogen yield of 35% and a maximum overall efficiency of 15%. The theory beyond this finding lies in the lower thermal conductivity, higher heat capacity, and lower thermal diffusivity of water vapor and carbon dioxide composition. We find this study is promising as a start for a new technique for hydrogen production.