THE SONOLYSIS OF METHANOL IN DILUTED AQUEOUS-SOLUTIONS - PRODUCT YIELDS

Diluted aqueous methanol solutions (0.001-0.5 M) were exposed to 724 k Hz ultrasound irradiation under argon atmosphere at 26 +/- 3-degrees-C . As measured with the argon-saturated Fricke dosimeter, the gamma-equ ivalent dose rate of ultrasound in the sonochemical cell was 2.6 kGy/h (1.6 x 10(22) eV dm-3 h-1). The yields of the following products were measured: H-2, H2O2, CO, CH2O, ethylene glycol, CH4, C2H2, C2H4, C2H6 . It was found that over the entire investigated concentration range t he yield of methane was strictly proportional to the methanol concentr ation, the yields of CO and H-2 increased and that of H2O2 decreased w ith increasing the concentration of methanol in the solutions. In very diluted solutions the yields of formaldehyde and ethylene glycol were measured to be, respectively, 1.5 and 0.64 molecules per 100 eV chemi cally active acoustic energy and did not depend upon the concentration of methanol unless that reached 0.02 M in case of formaldehyde and 0. 1 M in case of ethylene glycol. On the further increase of the concent ration their yields started to grow. An examination of the concentrati on dependences of the product yields leads to the assumption that in t he sonolysis of methanol in very diluted aqueous solutions the H atoms and OH radicals generated inside the imploding cavitation bubbles fro m thermal water decomposition causes the transformations of methanol. In doing so, H atoms pass into the bulk and react with methanol to for m formaldehyde and ethylene glycol, whereas .OH radicals probably cann ot escape from the hot region; they react there with methanol to give CO or recombine to give H2O2. At higher methanol concentrations the de composition of methanol due to the thermolysis of its vapors in the ca vitational hot-spots becomes significant. The experimental data are di scussed in terms of distinction and similarity between the sonolysis a nd the radiolysis of methanol in aqueous solutions.