Advanced oxidation processes for the degradation of p-hydroxybenzoic acid 1: photo-assisted ozonation

摘要

The oxidation of p-hydroxybenzoic acid in aqueous solution by UV radiation and by photo-assisted ozonation (UV+O_3) has been studied. The effects of temperature (10,20,30 and 40 deg C), pH (2,5,7 and 9) and ozone partial pressure (0.10-0.38 kPa) on the conversion of p-hydroxybenzoic acid were established. Experimental results indicated that the kinetics for both oxidation processes fit pseudo-first-order kinetics well. In the combined process, the overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidtion by free radicals (mainly OH~(centre tod)) generated in the system. The importance of these two reaction paths for each specific value of ozone partial pressure, temperature and pH was quantified. Lastly, a general expression is proposed for the reaction rte which takes into account the two reaction pathways and is a function of known operating variables.