Study Of Photochemical Degradation And Reaction Mechanism Of Phthalic Acid Esters

Phthalates are widely used as plasticizers in different resins, especially PVC resins.As a consequence, phthalates are released into the natural environment during manufacture, used, disposal and leaching from plastic materials. Phthalates have been detected in air,natural waters, waterworks, soil and foods.More and more research groups have focused their attention on the degradation of phthalates.Photo catalytic redox reactions used in degrading pollution organics have gained wide interest because of their simplicities, economic advantages and without the second pollution.The photochemical degradation of PAEs (DMP, DEP, DBP) in water was investigated under a variety of reaction conditions using hydrogen peroxide as oxidant. All experiments were conducted under artificial UV light (high pressure Hg lamp).The results showed that DMP was more effectively degraded by UV/H2O2 system than by UV light only and the initial concentration of DMP presented relative effect to the photodegradation rate. The degradation rate of DMP displayed faster in neutral medium than in acid or alkali medium. The rate of degradation of DMP increased when increasing concentration of H2O2,but it decreased at high level of H2O2 because high concentration of H2O2 could remove the-OH in UV/H2O2 system.More than 90% of DMP degraded when a solution of DMP of 10.0 mg·L-1 was radiated under UV for 45 minutes in the presence of hydrogen peroxide of 20.0 mg-L" by the Technology of UV/H2O2. The effects of initial concentration of the phthalates and hydrogen peroxide,the time of UV radiation and pH on the degradation process have been studied in order to provide the necessary basis for practical application of this method.To understand the degradation and the environmental fate of phthalic acid esters in water, the photodegradation process of dimethyl, diethyl and dibutyl phthalates (DMP, DEP, DBP) in an aqueous solution under UV radiation were investigated. The results showed that the degradation of the three tested phthalates follows the first-order kinetics. The degradation intermediates were identified with GC/MS,finded that the chain was degraded firstly,then the Hydroxy free radical which was excited from UV-light, attacked the band of C-C which link the aromatic ring and chain ester group.with the band of C-C disconnect,the PAEs were degraded for small molecule.the primary intermediates was benzoic acid ester.A plausible mechanism was suggested for degradation of these compounds.