Pollution Characteristics And Influencing Factors Of Persistent Organic Pollutants In Chlorinated Hydrocarbon Production

Persistent organic pollutants(POPs)have the characteristics of high toxicity,persistence,bioaccumulation and long-distance migration,and have potential hazards to the global environment and human health.They have attracted widespread attention worldwide.Unintentional emissions from industrial processes are considered to be the main source of POPs.Current research has focused on the generation and emission characteristics of POPs in industrial processes such as waste incineration,steel production,and recycled metal sme lting.The production and use of chemicals is also an important source of POPs.Trace POPs generated in the chemical production process will enter the environment and even the human body in the form of by-products of chemical products such as pesticides,dry cleaning agents,pharmaceutical intermediates,etc.However,there are still few studies on the emission level,emission characteristics and formation mechanism of POPs in the chemical production process.Therefore,it is necessary to study the current situation of POPs emissions in the chemical production process,which can provide data support for the improvement of the global POPs emission inventory,and provide a basis for the pollution prevention and reduction of POPs in the chemical industry.Chlorinated hydrocarbons such as chlorobenzene and chlorophenol are important precursors of POPs such as dioxins.This study selected four typical chlorinated hydrocarbon production chemical plants in China as the research object to clarify the concentration levels,characteristics and influencing factors of POPs unintentionally generated in different chemical production process stages.And put forward the product emission factors of POPs in the chemical production process.The five POPs of dioxins(PCDD/Fs),polychlorinated biphenyls(PCBs),pentachlorobenzene(PeCBz),hexachlorobenzene(HxCBz)and hexachlorobutadiene(HCBD)in the production of chlorinated hydrocarbons were studied.The influencing factors and formation mechanism of new POPs(HCBD)in the production process of chlorinated hydrocarbons were discussed.The main results are summarized below:(1)The concentration and pollution characteristics of POPs in chemical samples were clarified.The concentration ranges of PCDD/Fs,dl-PCBs(dioxin-like polychlorinated biphenyls),PeCBz,HxCBz,HCBD in all chemical samples were 46.49～929631 pg mL-1,19.18～152869 pg mL-1,0.02～12.63 μg mL-1,0.09～3.71 μg mL-1,0.0004～243000 μg mL-1,respectively.The distribution characteristics of PCDD/Fs congeners showed that OCDF,1234678-HpCDF,OCDD and 1234678-HpCDD were the four dominant congeners in chemical samples.The distribution characteristics of dl-PCBs showed that CB-77,CB-126 and CB-118 were the dominant congeners;TeCBs,PeCBs,OcCBs and NoCBs were the dominant homologues.Comparing and analyzing the concentration of POPs in the production process of chlorobenzene,trichloroethylene and tetrachloroethylene,it is found that the concentration of POPs in the production process of trichloroethylene and tetrachloroethylene is higher than that in the production process of chlorobenzene,indicating that the production process of trichloroethylene and tetrachloroethylene is more prone to produce POPs,which needs further attention.(2)A gas chromatography-mass spectrometry analysis method for HCBD in chemical samples was established,and important factors and mechanisms of HCBD formation in the chemical production process were put forward.Optimized the instrument conditions such as chromatography and mass spectrometry,and established a method for analyzing HCBD in chemical samples.The detection limit of the method is 0.049 ng mL-1,the recovery rate is 81.79%～93.11%,and the precision is less than 6%,which were satisfactory for determination.The established method was applied to analyze the HCBD in the samples of chemical plants,and it was found that the concentration of HCBD in the chemical samples of different process sections were from high to low in the order of bottom residue>intermediate product>product>raw material.The concentration of HCBD in trichloroethylene and tetrachloroethylene plants is much higher than that in chlorobenzene plants.Raw materials,chlorine sources and temperature are important factors affecting the formation of HCBD in the chemical production process.Benzene,carbon tetrachloride,and acetylene are the main raw materials or precursors for the formation of HCBD in the chemical production process.(3)The product emission factors of POPs in the production process of chlorinated hydrocarbons were proposed,and the correlation between POPs in the chemical production process was analyzed.The average product emission factors of the four chemical plants were PeCBz>HxCBz>HCBD>PCDD/Fs>dl-PCB s,which were 1487.65 mg t-1、748.47 mg t-1、79.69 mg t-1、0.22 mg t-1、0.08 mg t-1,respectively.According to the annual output data of chemical plants,the annual emissions of POPs from four chemical plants were estimated.The annual emissions of PeCBz,HxCBz and HCBD were 125 kg,119 kg and 21 kg respectively,which were much higher than those of PCDD/Fs(33.19 g)and d1-PCBs(19.16 g).The correlation analysis result of the concentration showed that there was a significant positive correlation between PCDD/Fs and dl-PCBs,PeCBz and HCBD.It is speculated that POPs have similar formation mechanism in the chemical production process.