Design In The Pressure Photocatalytic Reactor And Study On The Degradation Of Organic Compounds

In recent years, refractory organic pollutants are concerned greatly in experimental study, advanced oxidation technology is widely used due to its highly producing oxidative free radicals(·OH),meanwhile, TiO₂ photocatalytic technology is considered as a "green oxidation technology" because it can mineralize refractory organic pollutants completely. However, the role of oxygen in the reaction has been proved insufficient. It is the first time that the high pressure photocatalytic reactor is designed. And a variety of organic pollutants were researched in this reactor with TiO₂ and P25 as catalyst and UV lamp as light source.Further more, the reactive red X-3B as the target pollutant was chose for the further research.The effect of pressurization with oxygen on the degradation and decoloration of Reactive Brilliant Red X-3B was discussed and the influence of various reaction conditions (such as pH, TiO₂ dosage, as well as temperature, etc.) under high pressurization environment was also determined. The results show that the degradation and decoloration under pressurization and normal atmospheric conditions were in a similar trend. Pressurization with O2 improved the degradation and decoloration of X-3B. With N2, however, there was no obvious promotion. This indicates that promoting the activity of the solution was not due to pressurization but to the dissolved oxygen. The degradation of TOC and COD were positively correlated with decoloration. That is, the higher the decoloration was, the better the TOC and COD were removed from the water.Under the irradiation of a 250 W UV lamp, at 20℃, P25 catalytic dose was 0.5 g L^-1and pH was 6.0. Under these conditions, when the initial concentration of reactive brilliant red X-3B was 100 mg L^-1, about 99 % decolorization, as determined by UV-visible analysis, was achieved after 100 min photocatalytic reaction. Intermediates formed during reactive brilliant red X-3B were detected by gas chromatography coupled with mass spectrometry (GC/MS). On the basis of these results, we propose a tentative degradation pathway. The probable process of reactive brilliant red X-3B was that it was first adsorbed onto the surface of catalysts, where it reacted with Valence band holes and the surface-bound or adsorbed ?OH radicals as well as reactive oxygen species derived from oxygen reduction by photogenerated electrons, and then C-N and C-S bond were broken. In the condition with oxygen, small molecule organic materials maybe generated through a series of decarboxylation, hydrolysis and oxidation reaction. With the time prolonging the ring was opened and maleic acid was generated.It was found that degradation process under the condition of 5 atm completed ahead of that of 0 atm, its reaction mechanism was not changed through analysis and comparison the intermediates under different conditions. In the condition with nitrogen, however, the reactive brilliant red X-3B could not be totally degraded and mineralized, and ultimately generated the intermediate of benzoquinone.