Removal Of CVOCs With Catalytic Oxidation Technology

Catalytic oxidation technology is one of the effective techniques for degrading VOCs,especially for the treatment of large-flow,low-concentration CVOCs in the petrochemical industry.In this paper,chlorobenzene（CB）was selected as the model molecule of CVOCs,and research was carried out by catalytic oxidation technology on the degradation performance of low concentration.Various detection and characterization methods were used in the experiment to study the catalytic activity and by-product formation of the catalyst.In the study,Pd-M/Al₂O₃（M=Ce/La）series powder catalysts were prepared by impregnation method.The effect of catalysts on the catalytic activity of low concentration CB was studied.The nitrogen isotherm,SEM and H₂-TPR and O₂-TPD were used to characterize and analyze the structure and chemical properties of the catalyst.The effects of calcination temperature,noble metal content and additive amount on the catalytic activity of Pd/Al₂O₃ catalyst were studied.The catalytic activities of the catalyst under different working conditions（including CB concentration and space velocity）were investigated.The results showed that the prepared 1%Pd/Al₂O₃ and 0.75%Pd/Al₂O₃ catalyst had the best catalytic activity,but considering the noble metal,Ce was introduced on the 0.5%Pd/Al₂O₃ catalyst to improve the low temperature of the catalyst.It is catalytically active and improves the dispersibility of Pd on the surface of the catalyst.The Pd/TiO₂ series powder catalysts were prepared by impregnation method,and the activity for CB oxidation were explored and characterized.It was found that among the Pd catalysts,the catalyst had the best CB oxidation when the loading was0.2%and 0.3%.The rare earth element Ce was introduced to the 0.2%Pd/TiO₂catalyst to study the catalytic loading of Ce on the catalyst.The optimum loading ratio of Pd-Ce/TiO₂ series catalysts was obtained by the influence of CB performance,namely 0.2%Pd-0.5%Ce/TiO₂ catalyst.Then,different transition metal oxide catalysts with TiO₂ as support were prepared and CB oxidition was catalyzed.It was found that Fe/TiO₂ catalyst and Cu/TiO₂ catalyst had better catalytic performance,and the difference between them was explored.The effect of Fe or Cu loading on Fe/TiO₂catalyst,and the optimum loading ratio of Fe-Cu/TiO₂ catalyst were discussed.As a result,it was found that 5%Fe/TiO₂,5%-7%Cu/TiO₂ and 3%Fe-2%Cu/TiO₂ had better catalytic performance.The noble metal series monolithic catalyst was prepared and tested.The experimental conditions of the powder catalyst were evaluated.The preparation process of the monolith catalyst was investigated,including the silica sol coating step and dosage,the coating method,the coating times.Different coating roasting processes were carried out to compare the coating effect and catalytic activity exhibited by different processes to determine the optimal monolith catalyst preparation process,and the overall catalyst activity was compared with the powder catalyst catalyzed CB oxidition.As a result,it was found that the T₅₀ of 0.5%Pd-2.5%Ce/Al₂O₃ powder catalyst was about 340℃,which of 0.5%Pd-2.5%Ce/Al₂O₃/COR catalyst T₅₀ was increased at about 410℃.The T₅₀0 of 0.2%Pd-0.5%Ce/TiO₂ catalyst was around 270℃,which of 0.2%Pd-0.5%Ce/TiO₂/COR catalyst T₅₀ was around400℃.The by-product formation of different catalysts was studied,including the absorption and selectivity calculation of Cl^-,the formation and selectivity of CO_x（CO₂,CO）,combined with the CB activity and product analysis of different types of catalysts.catalyze The CB catalytic performance of different catalysts was analyzed.It was found that the detected Cl^-selectivity was very low,less than 20%.The Cl^-selectivity of the catalyst supported by TiO₂ was higher than that of the catalyst supported by Al₂O₃.In addition,the selectivity of CO was relatively low.Moreover,with the increase of catalytic temperature,the selectivity of CO increased firstly and then decreased.The selectivity of CO of Fe/TiO₂ catalyst was significantly higher,reaching about 18%at 350℃;over the entire temperature range.The noble metal catalyst had the highest CO₂ selectivity,and the COx selectivity reached 80%-90%at400-450℃,while the transition metal oxide catalyst had a lower CO_x selectivity,which was basically 40%-60%,especially The Fe/TiO₂ catalyst had high catalytic efficiency in the low temperature range but the lowest CO₂ selectivity,indicating that the catalytic reaction of CB in the low temperature section was incomplete.