Study On Photochemical Degradation Of Crude Oil In Seawater

In the past several decades, a large amount of petroleum has entered marine environment through various pathways, and its contamination has gradually become one of the most serious problems to the marine environment. When oil is released into seawater, immediate changes in its physical and chemical properties occur. Previous studies have demonstrated that photo-oxidation processes may play an important role in the weathering of oil and refined petroleum products. In this thesis, the photochemical degradation reaction of water-soluble fraction of crude oil(WSF) in seawater was studied. The dynamic process was investigated and the effects of light, media, heavy metal ions, anion, hydrogen peroxide and photosensitizer were discussed. Also the change of the component and pH of WSF were discussed. The results were showed as follows:(1)WSF could be degraded under different light irradiation and showed the first-order reaction kinetic behavior, and the rate constant of photo-degradion were changed when experiment condition has changed.(2)The factor which could influence WSF's photo-degradationa. Light: Compared with the reaction under dark, WSF could be degraded under the irradiation of sun and high-pressure mercury lamp(300 W and 500 W). However, the rate of photo-degradation under high-pressure mercury lamp was much higher than the rate of under sunlight, and the rate of photo-degradation under high-pressure mercury lamp of 500 W was higher than the rate of the one under 300 W, which indicated that different lights had definite effects on the degradation of WSF.b. Aquatic mediate: The photochemical degradation reactions of WSF in three mediates (distilled water, artificial seawater and natural seawater) were systematically studied under high-pressure mercury lamp of 300 W and found that the aquatic mediate could influence the degradation of WSF. Result showed that the speed of degradation in ASW was slower than in DW.Compared to the ASW, the speed of degradation in NSW[0] showed a faster rate.c. Heavy metal ion: Four metal ions, Cu2+, Hg2+, Cd2+ and Zn2+, which are familiar in natural seawater, were added in reaction solution and found that each ion showed different effect, which were mainly resulted from the interaction between ions and aquatic media. The effects of the ions were changed with the concentration increasing. Cu2+ could restrain the photo-degradation of WSF in all the mediates. However, Hg2+, Cd2+ and Zn2+ showed different effect with the concentration increasing.d. Anion: The effect of two familiar anions in seawater, CO32- and HCO3- were discussed to the photo-degradation of WSF in the experiment and found that CO32- could accelerate the photo-degradation at lower concentration but could restrain it at higher concentration. The effect of HCO3- was similar. However, in NSW[0], the effect was different from two other mediates.e. Hydrogen peroxide(H2O2): In this thesis, we found that Hydrogen peroxide could accelerate the photo-degradation of WSF and acceleration degree was grew up when the concentration of Hydrogen peroxide has grew.f. Photosensitizer: Two photosensitizers, humid acid and acetone, were discussed in this thesis. Result showed that humid acid in three mediates could restrain the photodegradation of WSF, and the restrain degree was increased with the increasing of the concentration of humid acid. However, acetone with lower concentration could accelerate the photo-degradation of WSF, and with the increasing of the concentration, the accelerate degree was decreased.(3) The component change of WSF before and after photo-degradation: The component change of WSF by GC-MS was studied and it was found that the component concentration has decreased after photo-degradation and the number of major component which could be detected has also decreased.(4) pH detection: The pH of the solution of WSF was gradually declined during the photo-degradation. But different media showed different declined degree. In NSW, the degreee was the smallest. This might caused by the reaction under illumination of some substance in NSW.