Sonolysis of Carbon Dioxide, Nitrous Oxide and Methane in Aqueous Solution

Abstract

Water was irradiated with ultrasonic waves under an argon atmosphere which contained small amounts of carbon dioxide, nitrous oxide or methane. The yield of the products was measured as a function of the composition of the gas atmosphere. Maximum yields were observed at a few per cent of the added polyatomic gas. No chemical effects occurred in the irradiation under an atmosphere of pure CO2 , N2O or CH4. It is concluded that the gas mixture in the tiny gas bubbles, in which the chemical effects are brought about, is not in Henry’s equilibrium with the aqueous gas solution. The main product of the sonolysis of CO2 is CO, a small amount of formic acid also being formed. The sonolysis is explained by both the attack of H atoms from the sonolysis of water and direct decomposition of CO2 due to the high temperatures existing in compressed gas bubbles. The main products of the sonolysis of N2O are nitrogen, nitrite and nitrate. N2O enhances the rate of various oxidations such as that of iodide, nitrite and propanol-2. In the methane containing solution, a lot of hydrogen is produced, the main oxidation products being ethane, ethylene, C3- and C4-hydrocarbons and carbon monoxide. A mechanism is postulated which involves both the attack on methane by radicals from the decomposition of water and thermal decomposition of methane. The local radical concentrations are so high that a methane molecule may undergo multiple radical attack. The similarity between sonolytic reactions and reactions occurring in flames is emphasized