Methanol sono-pyrolysis for hydrogen recovery: Effect of methanol concentration under an argon atmosphere

A number of theoretical and experimental works showed the possibility of increasing the sonochemical production of hydrogen through the pyrolysis of methanol within the acoustic cavitation (i.e. sonolysis of aqueous methanol solution). In this study, numerical simulations have been conducted in order to reveal, for the first time, the effect of methanol concentration (in the bulk liquid) on the maximal sonochemical efficiency for hydrogen yielding, methanol conversion and the broadness of active bubbles range. The current adopted model is built on a set of ordinary differential equations that account for non-equilibrium evaporation and condensation of water vapor and methanol at the bubble wall, thermal conduction both within and outside the bubble and heat of chemical reactions. All numerical simulations were carried out for a single bubble oscillating in O2 and/or argon-saturated water with varying concentration of methanol. It was found that the variation of methanol concentration (0-100% (v/v)) affects slightly the broadness of active bubbles ranges for methanol consumption. Conversely, for hydrogen production, a gradual decrease of the active bubbles ranges is observed for methanol concentration greater than 20%. The maximal sonochemical efficiency for hydrogen yielding, methanol conversion and the broadness of active bubbles ranges (for H2 production and CH3OH conversion) is obtained at 80% of argon and for methanol concentration between 7 to 20%. The yield of hydrogen increased by 26.16 and 22.4 times at 10 and 20% (v/v) of methanol in bulk solution, respectively, whereas CH3OH conversion decreased by 13.84 and 22.3%, respectively.