Preparation Of MnO₂/N-3DG Aerogel Catalyst And Simulation Of Optimal Design Of Ozone Catalystic Reactor

Bezafibrate（BZF）is a typical pollutant of pharmaceutical and personal care products（PPCPs）,when BZF is discharged into the environment,it could do long-term potential harm to the surrounding environment.Traditional sewage treatment process is difficult to remove BZF completely in wastewater,while the catalytic ozonation technology can remove refractory organic matter in water quickly and effectively,whici is of great benefit to water environment.As the core of catalytic ozonation technology,the catalyst determines the removal efficiency of organic matter.In this study,a manganese dioxide supported nitrogen-doped three-dimensional graphene（MnO₂/N-3DG）catalyst was prepared by in-situ synthesis and impregnation.The catalyst prepared by in-situ synthesis processes a higher catalytic activity.And the infrared spectroscopy characterization of the catalyst showed that nitrogen element on the surface of 3DG was in the form of-NH₂,and MnO₂ supported on the surface of N-3DG was connected by Mn-O-C chemical bond.As the carrier of MnO₂,N-3DG can adsorb BZF in water effectively and has a good synergy with MnO₂.Using the MnO₂/N-3DG catalyst prepared by in-situ synthesis method,the reaction efficiency of catalytic ozonation to BZF and TOC reached 100% and 75% in 90 minutes,respectively.By analyzing the chemical structure of BZF and the mechanism of ozone catalytic oxidation,it is believed that 14 intermediate products may be generated during the catalytic degradation of BZF.The OH· produced by ozone on the surface of MnO₂/N-3DG catalyst is the key to complete degradation of BZF.The Fluent software was used to simulate the flow field inside the catalytic ozonation reactor.By comparing the changes of the flow state and gas phase distribution with or without the the guide tube in the reactor,it was found that the fluid state in reactor was better after the guide tube was installed in the reactor,which was more conducive to the contact between catalyst and ozone-liquid phase;And the average gas content of the flow field increased by about 30.6%,which means the utilization efficiency of ozone was greatly improved.The structure of catalytic ozonation reactor with a guide tube was simulated and optimized.The results showed that the flow field inside the reactor can form a stable and sufficient circulation under the conditions that the distance between the aeration plate and the bottom is 0.025 m,the height of the guide tube is 0.425 m,and the diameter of the guide tube and the reactor is 0.65.Which maked the average gas content increase by 14.8%,and enhance the utilization efficiency of ozone.In addition,the influence of intake air flow and initial bubble diameter on the flow field was explored.The study found that increasing the intake air flow can effectively increase the average gas content of the flow field,thereby increasing the ozone concentration in the reactor.When the intake air flow reaches 0.3 L·min^-1,the amount of ozone gas sinking with the circulation reaches the limitation,and the diversion tube’s diversion function is fully exerted.The increase of the initial bubble diameter in the range of 0-2 mm can increase the fluid velocity,and the fluid velocity gradually stabilizes at 0.2 m·s^-1 when bubble diameter is bigger than 2 mm.In addition,the average gas content of the flow field and the gas-liquid phase contact area both decrease with the increase of the initial bubble diameter,resulting in a decrease in the ozone utilization efficiency.The simulation results provide theoretical basis and technical support for the optimal design of the ozone catalytic oxidation reactor.