INFLUENCE OF DISSOLVED-OXYGEN TO THE DECO MPOSITION OF FORMIC-ACID BYUV IRRADIATION IN THE PRESENCE OF HYDROGEN-PEROXIDE

The irradiation of aqueous solutions containing both formic acid and h ydrogen peroxide has been carried out in the presence and in the absen ce of dissolved oxygen. Experiments were carried out under batch condi tions in a cylindrical reactor equipped with a low-pressure mercury va pour lamp which emits a monochromatic radiation at 253.7 nm. When diss olved oxygen is present, the concentration of hydrogen peroxide remain s constant during irradiation and the kinetics of the decomposition of formic acid is zero order. The reaction between formic acid and hydro xyl radicals resulting from the photolysis of hydrogen peroxide leads to the formation of CO2.-/.COOH radicals which react with oxygen to gi ve HO2. and then H2O2. In the absence of dissolved oxygen a chain reac tion is initiated by 253.7 nm light absorbed by hydrogen peroxide. The CO2.-/.COOH radicals produced from the reaction between the OH. radic als and formic acid react with hydrogen peroxide yielding OH. and thus feed the chain decomposition of both formic acid and hydrogen peroxid e. For 200-1750 muM formic acid and hydrogen peroxide, a chain length of 11.1 +/- 1.2 was found.