Studies On Degradation And Dehalogenation Of Halogenated Aromatics By Mechanochemical Treatment

Because of strong persistence,high toxicity and degradation-resistant,etc,halogenated aromatic organic pollutants have attracted great attention.A large amount of halogenated aromatic organic pollutants contained in pesticide,medicine,and electronic products were emitted to environment,when the products were produced,used,and discarded.Halogenated aromatic organic pollutants emitted would polluted the environment of air,water and soil seriously.Also reproductive toxicity,endocrine toxicity,neurotoxicity and three induced effects of halogenated aromatic organic pollutants would bring serious threat to human health and safety.There were lots of methods to treat halogenated aromatic organic pollutants,but the application of these methods were limited for some factors in environmental purification,such as harsh reaction conditions,unsafe operation conditions,complex process program,expensive processing cost,poisonous and harmful secondary pollution,etc.It carried out a study of mechanochemical technology to treat4-bromochlorobenzene,a typical halogenated aromatic organic substance.It focuses on the exploration of dehalogenation efficiency and degradation efficiency during mechanochemical milling process.High-efficiency gas chromatograph?GC?and ion chromatograph?IC?was employed to monitor the concentrations of the substrate and inorganic halogen ions in the mechanochemical process,respectively.Besides,it investigated the influence of rotational speed,grinding time,ratio of balls to materials and materials ratio to dehalogenation efficiency and degradation efficiency.It presented the optimum parameters of mechanochemical milling process.What was more,intermediates and final products were characterized by X-ray diffraction?XRD?,Fourier infrared spectrometer?FTIR?,efficient gas phase mass spectrometry?GC-MS?,Raman spectrometer and other testing means.The mechanochemical milling reaction mechanism and the destruction ways were also represented here.The results of this study were as follows:?1?In the condition of selected rotational speed range and gradient,dehalogenation efficiency and degradation efficiency at 600 rpm were obviously better than other rotational speeds.After 8 h milling,it obtained the best removal efficiencies,while the dechlorination efficiency,debromination efficiency and degradation efficiency were 91.2%,93.8%and 99.9%.?2?In the experimental groups of studying the influence of the ratio of balls to materials and materials ratio,the experimental data show dehalogenation efficiency increased with the increase of materials ratio and the ratio of balls to materials.Take energy consumption,substance use and removal efficiency into consideration,the optimum ball material ratio and material ratio were determined to be 12.6:1 to 102:1.CaO acted as a dehalogenation agent during mechanochemical dehalogenation through the comparison of several kinds of dehalogenation agents.?3?Ca?OH?₂ and CaCO₃ were detected by XRD and FTIR,from which we speculated the generation of H₂O and CO₂ in the mechanochemical milling process.Besides the absorption peak of benzene ring always existed,which was not strong.Carbonyl affected by chlorine radicals was detected.In the spectrogram of gas phase mass spectrum,3-bromochlorobenzene,4-bromochlorobenzene and several kinds of PCBs were characterized.Graphite and amorphous carbon were detected by Raman spectroscopy analysis,from which we speculated elemental carbon as the final products.?4?Three pathways were inferred to remove 4-bromochlorobenzene:dehalogenation,benzene rings scission,and polymerization reaction.benzene rings scission accounts for a considerable proportion of all consumption of the substrate,which reached the purpose of harmless.Because of mild reaction conditions,simple operation,safe and reliable process,widely used process,no secondary pollution and easy to control etc,Mechanochemical technology is used in the field of metallurgy,synthetic and so on,the technology is more and more mature.Mechanochemical technology own unique advantages in terms of purification process of halogenated aromatic hydrocarbons.It is a promising technology,which is worthy of further study.It present a new method in the degradation process of halogenated aromatic pollutants.