Study On Preparetion Of Ce/Mn/Al₂O₃-EG For Tetracycline Adsorption And The Regeneration By Microwave-ultraviolet Method

A novel adsorbent Ce/Mn/Al₂O₃ which with stable adsorption and catalytic propertie is designed to reuse and mineralize the adsorbed organic pollutants during thermal regeneration in this research.The catalatic propertie of adsorbent can enhace the degradation of organic adsorbate and reduce secondary pollution during adsorbent regeneration.Further more,expanded graphite is added in Ce/Mn/Al₂O₃ as microwave absorber to let the composite adsorbent can be regenerated in microwave-ultraviolet field.The regneneration of designed adsorbent can take the advantage of microwave regeneration method and further mineralize intermediate products in air phase.Ce/Mn/Al₂O₃ difunctional adsorbent is designed and synthesizd to enhance the elimination of absorbed organic pollutants.Pseudo-boehmite is used as adsorbent precursor,transition metal manganese as catalyst,cerium and polyethylene glycol 2000used as catalyst promoter and pore-forming agent respectively.Ce/Mn/Al₂O₃ is synthesized at 450 ^oC for 4 h by solid state sintering method,and the dosage of catalyst,catalyst promoter and pore-forming agent is 5 wt%,5 wt‰and 10 wt%respecitively.Tetracycline is chosed as target contaminant to evaluate the properties of synthesized adsorbent.The cowork of catalyst promoter and pore-forming agent can decrease the side effect of catalyst on adsorbent adsorption property,and the theoretical maximum adsorption capacity of synthesized adsorbent can increase from 78.04 mg/g to 196.44mg/g.In addtion,the mineralization percentage of adsorbed tetracycline increases from16.3%to 38.5%and the regeneration temperature reduces to 457?from 563 ^oC after load catalyst on Al₂O₃.The catalytic property of adsorbent can reduce both the volatile organic compounds relsease and energy consumption during regeneration.Characterization results show that catalyst promoter and pore-forming agent can restrain lattice distortion and reduce micropore blocking.The kinetics results show that adsorption process has three stages and fit second order kinetics model.The apparent activation energy of adsorption process is 63.924 KJ/mol.A multifunction composite adsorbent with microwave adsorbing ability is designed and synthesized to further eliminate organic pollutants release into the air phase.Ce/Mn/Al₂O₃-EG composite adsorbent is synthesized by microwave heating method and regenerated in microwave-ultraviolet field.Response surface methodology is used to optimize the synthesis and regeneration process of Ce/Mn/Al₂O₃-EG.Microwave absorbing agent is chosen base on the adsorption ability and temperature rising property in microwave field.Results show that only 8 wt%addition of expanded graphite can make Ce/Mn/Al₂O₃-EG temperature higher than 500 ^oC within 100 seconds with 500 W microwave suppy.Besides,the high-thermal conductivity properties of expanded graphite can reduce the local destruction caused by uneven heating of microwave.Base on the change of material adsorption and catalytic properties,the optimum synthesis condition of composite material is 6.5 min,500 W,material dose 8 g.Characterization results show that materials synthesized by two methods have similar microstructure which demonstrate microwave can synthesize Ce/Mn/Al₂O₃-EG in a few minutes and replace traditional heating method.Regeneration ratio and mineralization percentage of tetracycline are used to optimize regeneration condition,and the optimum rengeneration condition of Ce/Mn/Al₂O₃-EG in microwave-ultraviolet field is 11 min,560 W,material dose 6.5 g.The combination of novel adsorbent and regeneration technology can minearalize 71.7%tetracycline,the volatile organic compound release is significantly reduced.The mineralization mechanism of organic pollutants in the microwave-ultraviolet field is studied to further optimize adsrobent regeneration and enhance the mineralization process.Base on the effect of the input condition on the reactor internal condition and tetracycline mineralization percentage,it is detected that the microwave power,regeneration time,air mass flow and air inlet humidity are the main influence factors of mineralization process.The results reveal that the addition of electrodeless lamp enhances the mineralization of organic pollutants in the air phase.Ozone also detected during the regeneraion process and its peak concentration is among 100-200 ppm.However,ozone is not the primary factor of tetracycline mineralization.The photoreaction in reaction is inferred base on the emission wavelength of electrodeless lamp and the bond dissociation energy of compounds in reactor.Ozone,singlet oxygen and hydroxyl radical is the main active species duing mineralization process.The mineralization process of tetracycline has two stages:thermal decomposition on adsorbent surface,and mineralization in the air phase.The intermediate product analysis results and the active species in reactor show that air phase mineralization includes three parts:hotolysis,ozone oxidation and radical oxidation.Besides,Aromatic ring compounds is difficult to mineralized into inorganic compounds?water,carbon dioxide etc.?than hydrocarbon compound in the air phase of microwave-ultraviolet field.