Photochemical Transformation Of Petroleum Pollutants On Soil Surface

To understand photochemical transformation of petroleum pollutants in soil,photoreactions of crude oil on soil surface in simulated natural conditions were studied, whichis available to investigate its transfer and transformation regulations among the soil-water-airphases as well as its ecological risks. The main work is as follows:(1) Photoreaction experiments of petroleum on soil surface were operated according tothe amended classical approach which effectively reduces the volatilization loss. The resultsshow that photoreactions of petroleum occur on soil surface under xenon light exposure.The influence of the initial oil concentration in soil, soil types and pH on photoreactionof petroleum was investigated. Changes in loWer oil concentrations affect the photochemicalprocesses of petroleum slightly. However, the higher oil concentration reduces thephotoreaction rate distinctly. The photolysis rate of petroleum on soil surface decreases whenthe content of organic matter in soil increases. Different soil pH results in similar reactionrates of petroleum. Kinetic analyses illustrate that photochemical degradation of petroleum onsoil surface, in the initial 60 h, follows pseudo first-order kinetics well under differentexperimental conditions.(2) Photolytic regulations of different petroleum fractions were investigated throughvarious quantitative analyses including UV-Visible, IR Spectrometer and GasChromatography.UV-Vis Spectrometer mostly reflects the photolytic processes of aromatic hydrocarbonswith the highest phototransformation ratio of petroleum. IR Spectrometer responds totalpetroleum hydrocarbons with the medium phototransformation ratio. The lowestphototransformation ratio of petroleum is determined by GC-FID, which reveals thephotochemical rules of saturated hydrocarbons. These results indicate that aromatichydrocarbons of petroleum are readier to photodegrade than saturated ones.(3) Two petroleum hydrocarbons, hexadecane and anthracene, were selected asrepresentative compounds of saturated and aromatic hydrocarbons and then photoreactions oftypical petroleum hydrocarbons were evaluated to speculate on photolytic regulations ofdifferent petroleum components.After 60 h irradiation, the phototransformation ratio of hexadecane on the soil surface islower than that of anthracene obviously. This result also reveals that it is easier for aromatichydrocarbons to degrade under irradiation than saturated ones. In addition, the photolysis rate of hexadecane is higher than that of the whole saturated hydrocarbons in crude oil.Furthermore, the photolysis rate of anthracene is consistent with that of the whole aromatichydrocarbons in petroleum.(4) UV-Vis, GC-FID, FTIR and GC-MS were used for the characterization of petroleumhydrocarbons in the photochemical processes to review phototransformation regulations ofpetroleum on soil surface.Experimental results indicate that absorption peak shapes of the extract from soil almostremain the same in UV-Vis Spectra, but the peak intensities change. GC-FID analyses showthat, after 50 h irradiation, most chromatogram peaks of aromatics are weakened or disappear.Moreover, the content of saturated hydrocarbons with longer chain decreases, while theproportion of shorter chain ones increases slightly. In addition, direct comparison between.unknown compounds and the standard series of n-C₁₀～n-C₄₄ is performed for qualitativeanalysis. After 60 h photolysis, the appearance of carbonyl compounds in FTIR spectra of theextract from soil demonstrates that petroleum is gradually oxidized in the photolytic process.The results demonstrate that photooxidation is one of the important photodegradationmechanisms of petroleum, and the photooxidation products of petroleum exhibit moreecological risks.