Homogeneous Catalytic Ozonation For Degradation Of Acid Nitrobenzene Wastewater In Rotating Packed Bed

Nitrobenzene is an important chemical raw material,a great deal of nitrobenzene wastewater will be produced during the production of nitrobenzene or other chemical products,nitrobenzene has teratogenic,carcinogenic and mutagenic properties.Nitrobenzene is hard to be degraded,because of the strong electron withdrawing effect of nitrobenzene enhanced the stability of nitrobenzene.Acidic organic wastewater is a kind of wastewater which is difficult to be controlled,and the O₃/H₂O₂ oxidation can be achieved by changing the p H value of wastewater.The cost of wastewater treatment increase by adding alkali to adjust the p H value of wastewater.Therefore,it is of a great practical significance and application to find a technology which can realize the degradation of acidic organic wastewater economically and efficiently.O₃/H₂O₂ technology is a kind of advanced oxidation technology,which has high efficiency,no pollution to the environment.Under acidic conditions,the oxidation performance of the technology decrease,and the transition metal ions(Mn²⁺,Ti⁴⁺)are added into the O₃/H₂O₂ system,which can significantly improve the oxidation performance and realize the rapid degradation of organic compounds.The application of O₃/H₂O₂ advanced oxidation technology in the application of has some defects that the lower mass transfer efficiency of ozone from gas phase to liquid phase.High gravity technology is a new kind of process intensification technology,which has a unique advantage in enhancing gas-liquid mass transfer.The material is affected by the strong centrifugal force,at the same time,the two pathways of mass transfer,molecular diffusion and interphase mass transfer can be significantly enhanced in a Rotating Packed Bed.The liquid is packed into droplets,stretching,broken wire,small liquid film,the high-speed rotation of the filled gas liquid two phase interface at the same time to speed up the update rate of the contact area can be improved effectively,strengthen the ozone from the gas phase to the liquid phase,increasing the amount of ozone dissolved in the liquid phase for the follow-up to produce more hydroxyl radical lay the theoretical foundation.The transition metal ions(Mn²⁺,Ti⁴⁺)are used as catalysts to cooperate with the high gravity technology and advanced oxidation technology of O₃/H₂O₂ in this paper.The acid wastewater containing nitrobenzene as the object to study two kinds of metal ions(Mn²⁺,Ti⁴⁺)under the catalysis effect on the removal of nitrobenzene and the operating parameters by adding free radical scavenger on nitrobenzene degradation mechanism.Finally,the degradation intermediates of nitrobenzene are measured by GC-MS and the possible degradation pathway of nitrobenzene are inferred according to the intermediates.The main results are as follows:?1?.The optimal operation parameters of RPB-Mn²⁺/H₂O₂/O₃ process for treatment of nitrobenzene: ?=40,liquid flow rate is 120 L/h,the initial p H is 2.5,the concentration of Mn²⁺ is 1.8 mmol/L,adding 5 mmol/L of hydrogen peroxide,the gas flow is 75 L/h,the mass concentration of ozone is 40 mg/L and cycling 25 min,the removal rate of nitrobenzene reach 99.82%,the removal rate of TOC reach 59.24%,the concentration of nitrobenzene is 0.27 mg/L in wastewater,up to the national emission standard?GB 8978-1996?.Compared with the conventional reactor,the removal rate of nitrobenzene and TOC increase by 31.54%,42.56% in rotating packed bed respectively.The removal rate of nitrobenzene and TOC increase by the addition of Mn²⁺.Compared with RPB-O₃/H₂O₂,the removal rate of nitrobenzene and TOC increase by 21.43%,21.08% respectively by RPB-Mn²⁺/H₂O₂/O₃.?2?The optimal operation parameters of RPB-Ti⁴⁺/H₂O₂/O₃ process for treatment of nitrobenzene: the gas flow is 75 L/h,the liquid flow rate is 120 L/h,ozone mass concentration is 40 mg/L,Ti⁴⁺ concentration is 0.50 mmol/L,the initial p H is 4,?=40,adding 0.4 mmol/L of hydrogen peroxide,recycling 30 min,the removal rate of nitrobenzene reach 97.17%.The removal rate of nitrobenzene by RPB-Ti⁴⁺/H₂O₂/O₃,RPB-H₂O₂/O₃ and RPB-Ti⁴⁺/O₃ are 97.17%,77.8%,and 39.74%,respectively.In the concentration range,the addition of CO₃2-has little effect on the removal rate of nitrobenzene.The addition of tert butyl alcohol could affect the removal rate of nitrobenzene,and the more amount of tert butyl alcohol,the lower removal rate of nitrobenzene.The results show that ·OH is the main active material of nitrobenzene oxidation degradation in the process of RPB-Ti⁴⁺/H₂O₂/O₃.?3?Nitrobenzene is through two ways of direct oxidation of ozone and ·OH indirect oxidation in the process of RPB-Mn²⁺/H₂O₂/O₃ and RPB-Ti⁴⁺/H₂O₂/O₃,the degradation intermediates of nitrobenzene are phenol,catechol,resorcinol,maleic acid,oxalic acid measured by GC-MS.