Study On The Degradation Of Chlorobenzene/Chlorophenol In Reducing Atmosphere At High Temperatures

With the development of cities,the amount of municipal solid waste（MSW）is increasing rapidly in China.The traditional disposal technology of MSW has been unable to cope with this situation.Because of its harmless,reducing and resources disposal of garbage,MSW incineration technology has become a better choice for us.However,dioxin and other toxic pollutants are easy to be produced in the process of MSW heat treatment,it is necessary to initiate further study on it.Some scholars have found that the emission of dioxins from MSW pyrolysis and gasification process is much less than that from incineration.Further research speculates that the reducing gases（H2,CO,etc.）produced by pyrolysis and gasification process can inhibit the synthesis of dioxins.In view of these,the effects of reducing atmosphere on the C-Cl bond and C-O bond of benzene ring were systematically studied by taking 1,2,4-trichlorobenzene（1,2,4-TrCBz）and 4-chlorophenol（4-CP）as the research objects.This paper provides a theoretical reference for further study on the degradation of dioxin and its precursors.Firstly,the high temperature degradation characteristics of 1,2,4-TrCBz and 4-CP were studied.The results show that temperature has a great influence on the fracture of C-Cl bond and ether bond C-O bond of benzene ring.With the increase of temperature,the yield of key cleavage products increases continuously,and the relative ratio of Cl and OH groups removal reaction is hardly changed by temperature.But at the same time,the ratio of solid products in degradation products is higher and higher.The effects of reducing atmosphere on the high temperature degradation characteristics of1,2,4-TrCBz and 4-CP were studied.The results show that H₂ promotes the production of dechlorination and deoxidation products in reducing atmosphere,and inhibits the migration of degradation products to solid phase.At the same time,H₂ increases the relative ratio of OH group removal and reduces the relative ratio of Cl group removal.CO alone is not involved in the removal of Cl and OH groups.For Cl group,the mixed atmosphere of H₂ and CO still promotes the yield of Cl group removal products and inhibits the migration of degradation products to solid phase,but the effect is not as good as the same concentration of H₂.For OH group,the mixed atmosphere has better effect than same concentration of H₂.The reaction path and mechanism of single component reducing gas（H₂,CO）with 1,2,4-TrCBz and 4-CP were analyzed.The results show that H₂ reduces the activation energy of C-Cl bond fracture about 70 k J/mol and reduces the activation energy of C-O bond fracture about 90k J/mol.Therefore,H₂ promotes the formation of dechlorination and deoxidation products,simultaneously,does not change the ratio of dechlorination products of 1,2,4-TrCBz,but increases the proportion of chlorobenzene in the degradation products of 4-CP.The free energy of the functional group degradation reaction with CO is a positive number,which explains the nature of CO does not participate in the degradation reaction.The reaction path and mechanism of multicomponent reducing gases（H₂ and CO）with 1,2,4-TrCBz and 4-CP were analyzed.The results show that when CO and H₂ are mixed,the activation energy of CO is lower than that of H₂ to functional groups,and the product can further react with H₂ due to the instability of acid chloride end groups.The mixed atmosphere increases the activation energy of C-Cl bond fracture about 20 k J/mol and decreases the activation energy of C-O bond fracture about 15 k J/mol.Therefore,the mixed atmosphere of H₂ and CO promoted the yield of dechlorination products and inhibited migration of degradation products to solid phase,but the effect is not as good as the same concentration of H₂.For OH group,the mixed atmosphere has better effect than same concentration of H₂.The reaction path and mechanism of multicomponent reducing gases（H₂ and O₂）with 1,2,4-TrCBz and 4-CP were analyzed.The results show that when H₂ and a small amount of O₂ are mixed,H₂ is activated by O₂ to form H group.H group greatly reduces the activation energy of the degradation of functional groups,and further accelerated the qualitative migration of Cl and O to inorganic compounds.