Preparation Of FeOOh And Catalytic Ozonation Of Nitrobenzene Wastewater By High Gravity Method

Nitrobenzene（NB）wastewater is one of the most common industrial wastewaters which is difficult to biodegrade.The degradation of organic wastewater by heterogeneous catalytic ozonation has the advantages of high catalytic activity,reuse and no secondary pollution.At present,FeOOH as an iron-based catalyst,has been widely used in heterogeneous catalysis because of its stable properties and high catalytic efficiency.However,the traditional preparation process has problems of uneven crystal nucleation and growth,wide particle size distribution and long preparation process.At the same time,in the process of catalytic ozone degradation NB wastewater,the rate control step of the reaction is ozone liquid film mass transfer,ozone low solubility in water and insufficient gas-liquid contact with ordinary stirring,resulting in low ozone utilization ratio and the degradation efficiency of organic matter is poor.Based on the above problems,combined with the characteristics of high gravity technology to enhance mass transfer and mixing,the idea of preparing FeOOH catalytic ozone degradation of nitrobenzene wastewater by high gravity method is put forward.Nano-sized FeOOH particles with narrow particle size distribution,small particle size and good dispersion were prepared by the Impinging Stream-Rotating Packed Bed（IS-RPB）.And the problem of low ozone solubility and low mass transfer efficiency in heterogeneous catalytic ozone degradation organic compounds was solved by using the Rotating Packed Bed（RPB）.This paper systematically studies the preparation of nano-sized FeOOH、O₃/FeOOH degradation NB wastewater,loading FeOOH preparation and degradation wastewater under high gravity environment,and explores its influencing factors,degradation mechanism and degradation pathway.The main results are as follows:（1）The optimum preparation conditions of the FeOOH were investigated by using the Fe SO₄·7H₂O and NaOH as raw materials and the IS-RPB which can enhanced liquid-liquid phase mass transfer as the reactor,the performance evaluation was carried out by catalytic ozonation degradation NB,the optimum conditions are as follows: C_FeSO4=C_NaOH=0.1 mol/L,Q_O2=0.5 L/min,r=1000 r/min,V_L=65 L/h,under which condition the FeOOH preparation can be completed less than 4 min,and the best product can be obtained after aging 9 h.The asprepared IS-RPB-FeOOH nanoparticles are shown to be α-FeOOH with a specific surface area of 246.717 m²/g,a surface hydroxyl density of 8.043 mmol/g,a length of 30 nm,and a narrow particle size distribution.Compared with conventional oxidation method,IS-RPB-FeOOH nanoparticles show larger specific surface area and higher surface hydroxyl density,and has a good catalytic effect on the process of ozonation degradation of NB.（2）Using the RPB which enhanced the gas-liquid two-phase contact process as the reactor and the FeOOH as the heterogeneous catalyst to explore the optimal conditions for the high gravity enhanced heterogeneous catalytic ozone oxidation degradation NB wastewater.The results show that the RPB-O₃/FeOOH system has high degradation efficiency and wide application range under different p H environments.The suitable experimental conditions were obtained: high gravity factor β=40,C_NB=100 mg/L,C_O3=40 mg/L,Q_O3=60 L/h,pH=7,L=60L/h,the degradation rate of NB reaches 100% after 20 min and the removal rate of COD reaches94 % after 40 min.The COD removal rate of RPB-O₃/FeOOH system is 25% higher than ordinary stirred catalytic oxidation system,which indicates that the RPB-O₃/FeOOH system can degrade NB wastewater quickly and efficiently.Tertiary butyl alcohol（TBA）is added to trap hydroxyl radicals,and the results show that the oxidation by hydroxyl radicals plays a dominant role in the degradation of NB.（3）To reduce the loss and secondary pollution of FeOOH in practical use,a combined process of preparing loaded FeOOH/Al₂O 3 catalyst by high gravity method and using it as filler to catalyze ozone degradation NB was proposed.The influence between preparation conditions and degradation performance was investigated,and the following conclusions were drawn: The surface area of the FeOOH/Al₂O₃ prepared under suitable operating conditions is 253.103 m²/g,the surface hydroxyl density is 1.5 mmol/g,the FeOOH load is 1.52%.The optimum technological conditions for degradation NB of RPB-FeOOH/Al₂O₃/O₃ system are as follows:T=25℃,C_NB=100 mg/L,FeOOH/Al₂O₃=40 g,V_L=100 L/h,C_O3=50 mg/L,pH=7,t=40 min,Taging=12 h,reaction 30 NB degradation completely and the TOC removal rate reached 98.33.The degradation rate of the FeOOH/Al₂O₃ catalyst was 96.54% after 7 cycles,which proves that it has good stability and reuse.An electron paramagnetic resonance spectrometer（EPR）was used to verify the indirect oxidation mechanism of the reaction process.The NB degradation process intermediates analyzed by gas chromatography-mass spectrometry（GCMS）mainly include phenol,acetic acid,nitrophenol and so on.the possible degradation pathways were inferred.