Experimental Study On Removal Of Toluene From Simulated Coal Flue Gas By MnO_x-CuO_x Modified Activated Coke

In recent years,volatile organic compounds（VOCs）pollution from anthropogenic sources has become an increasingly alarming problem.It can not only cause serious air pollution,but also further endanger human health.Among them,as a representative VOC,toluene is widely believed to cause serious chronic diseases and“mutagenic-teratogenic-carcinogenic”effect even after long-term exposure to a very low concentration of toluene-containing atmosphere.Therefore,in addition to the need for more stringent legislation to regulate and limit the emission o f volatile organic compounds,it is also necessary to develop catalysts with high toluene removal efficiency.This task is not only of great significance,but also imminent.This paper introduces the physicochemical properties,existing forms and hazards of toluene;it also discusses the source of VOCs and the main technical methods for VOCs pollution control at home and abroad.Then,the properties of actived coke（AC）and its application in industry have also been stated.Mn O_x is widely regarded as a promising toluene-removing active phase because of its polymorphism and polyvalence.However,due to the interaction or synergism between the structure or electrons of composite metal oxides,the oxidation effect of composite metal oxides on toluene is often higher than that of individual metal oxides.Due to the largeπbond in the aromatic ring of phenyl VOCs is easily complexed with Cu to be activated.Therefore,Cu O_x was selected as another metal for co-load.Based on the above viewpoints,a series of Mn_xCu_y/AC composite metal oxides were prepared by ultrasound-assisted equivalent volume impregnation method.In addition to discussing their catalytic oxidation properties,the physicochemical properties of the samples were characterized by XRD,SEM,BET,XPS,H₂-TPR,O₂-TPD and DRIFT,and the catalytic oxidation process of toluene on the samples was also briefly discussed.The main research contents and conclusions are as follows:A series of Mn_x/AC and Mn_xCu_y/AC oxides were synthesized by ultrasound-assisted equivalent volume impregnation method.The effect of different mass fraction of Mn on toluene removal efficiency was investigated,and the best Mn loading was selected to determine the optimal Cu loading on samples.It is found that the activity order of different wt.%Mn loading is Mn₆/AC≥Mn₈/AC>Mn₄/AC,so Mn₆/AC was chosen as the basis to determine the optimum copper contents to be added on.Finally,it is concluded that Mn₆Cu₅/AC,that is,when the load of Mn is 6%and the load of Cu is 5%,shows the highest toluene removal efficiency and higher than Mn₆/AC,which indicates that there may be a synergism between the composite metal oxides.The analysis of Mn ₆Cu₅/AC with higher activity was obtained according to the results of the previously mentioned characterizations.The performance enhancement of Mn₆Cu₅/AC was probably ascribed to the synergistic interaction between manganese oxide and copper oxide,which lead to the homogeneous distribution and morphology（XRD and SEM）,the large specific surface area（BET）,the strong reducibility（H₂-TPR）and the good oxygen mobility ability（O₂-TPD）.Moreover,the XPS results indicated that due to the synergistic effect between Mn O_x and Cu O_x,more active oxygen species were formed,as well as the greater quantities of monovalent copper ions and tetravalent mangane se ions,which were favorable to the removal of toluene.The effects of reaction temperature and flue gas components（O₂,SO₂,NO and H₂O）on toluene removal were determined.The results show that Mn₆Cu₅/AC had outstanding performances with99.38%toluene removal efficiency at 270℃ and presented satisfactory reusability and durability under simulated flue gas.SO₂ and NO played a hindering role in the removal of toluene in the absence of O₂ due to the competitive adsorption of active sites,whereas the negative effect would be reduced due to the introduction of O₂.It was concluded that gas-phase O₂ could replenish the consumed surface active oxygen,which played a crucial role in the oxidation of toluene.Besides,the introduction of H₂O in the feed had no significant influence on toluene removal.Finally,the possible reaction process of toluene oxidation on Mn₆Cu₅/AC was studied by DRIFT characterization.The reaction process shows that toluene can be rapidly adsorbed and activated on the surface of Mn₆Cu₅/AC to form benzaldehyde and maleic anhydride species,and finally oxidized to CO₂ and H₂O.