KINETICS OF THE DIRECT REACTION BETWEEN OZONE AND PHENOLIC ALDEHYDES

The kinetics of the ozonation of four phenolic aldehydes is investigat ed from ozone absorption experiments in a semi-continuous reactor. Aft er the evaluation of the stoichiometric ratios for the individual reac tions between ozone and each aldehyde, the single oxidation of vanilli n aldehyde (4-hydroxy-3-methoxy benzaldehyde) by ozone is performed in a first stage. The influence of the operating variables on the degrad ation process is established, and the application of a mass transfer w ith chemical reaction model based on the film theory leads to the dete rmination of the reaction orders and kinetic rate constants. The exper imental absorption rates obtained agree well with those calculated the oretically. In a second stage, a mixture of protocatechuic aldehyde (3 ,4-dihydroxybenzaldehyde), p-hydroxybenzaldehyde, vanillin aldehyde an d syringaldehyde (4-hydroxy-3,5-dimethoxy benzaldehyde) is ozonated un der different experimental conditions. The kinetic study is performed by means of a competitive method that takes vanillin aldehyde as refer ence compound. The application of that model allows the determination of the kinetic rate constants for each aldehyde, which are correlated as a function of pH and temperature. The results obtained support the fact that the kinetic regime of absorption is fast and pseudo-first or der with respect to ozone, a condition required by the competitive met hod to be used. (C) 1998 SCI.