Modifying Coal Tar Pitch By 10-undecenal Assisted By Microwave And/or Ultraviolet Light To Decrease The Toxic Polycyclic Aromatic Hydrocarbons Content

Coal tar pitch?CTP?is the largest distillation product of coal tar with an output of 8 million tons annually in China.CTP is widely used in the productionofvariouscarbonmaterialbinders,coatings,aluminum-smelting electrodes,road and buildings construction,etc.However,with the enhancement of people's environmental protection,CTP contains a large number of carcinogenic polycyclic aromatic hydrocarbons?PAHs?,and its harm to the environment and human health has become the main reason for limiting its application.Therefore,how to reduce or inhibit the release of toxic PAHs in CTP has become an urgent problem need to be solved.In this paper a CTP was modified by 10-Undecenal under catalysis of KHSO₄ to reduce the toxic PAHs content.Microwave and/or ultraviolet light were used to shorten reaction time or improve the reduction efficiency.The reaction solvents under different microwave conditions and modification process conditions were optimized.The basic properties of CTP and the variation of 16 PAHs monitored preferentially by EPA before and after modification were analyzed.The impact of CTP and modified CTP?MCTP?on the environment through CTP fume and water soluble were investigated.Finally,the reaction mechanism was explored by a series of characterizations of CTP and MCTP and related model compounds experiments.The main conclusions were obtained as follows:1)Under the microwave condition,the optimal reaction solvent is cyclohexane.The reaction efficiency is improved by microwave and UV-assisted reaction,which effectively reduces the content of 16 EPA priority PAHs in CTP.Compared with the case without auxiliary treatment,the reaction time is shortened.2)Modifying CTP assisted by microwave and/or UV are realized under microwave power of 200 W,reaction temperature 50?and heating power 88¹20 W;while assisted by ultraviolet light with power of 250 W,wavelength of 365 nm.The maximum reduction efficiency of16 priority PAHs reaches 91.59%in MCTP in 60⁹0 min assisted by microwave or ultraviolet light,2.5³ h saved compared to the reaction without microwave or ultraviolet.The total content of 16 priority PAHs in MCTP is reduced to 7.41 mg/g or less.3)After modification,the softening point of MCTP is reduced to72.6?.The toluene insoluble increases from 25.71%to 30.30%,quinoline insoluble increases from 9.96%to 11.45%,and coking value increases from 58.60%to 63.20%.The 16 PAHs in MCTP fume decreased from 262 mg/m³ to 195 mg/m³,31.3 times of the maximum allowable emission concentration of asphalt fume from building mixing stipulated in the Comprehensive Emission Standard for Atmospheric Pollutants.After modification,the 16 PAHs in MCTP water soluble increased from2.05?g/g to 52.66?g/g.By comparing acid rain with distilled water soluble,it is found that the increase of solution acidity is beneficial to the dissolution of 16 PAHs.4)Through elemental analysis,Fourier transform infrared?FTIR?spectrum,Raman spectrum,TG/DSC,¹³C nuclear magnetic resonance?NMR?spectrometers,and X-ray diffractions?XRD?for CTP and MCTP,and the model compounds of PAHs experiments,it was deduced that some PAHs in CTP react with the modifier,and some of the modifiers react with themselves to form other oxygenates,which leads to an increase in hydrogen bonding forces between CTP molecules.The PAHs extraction rate in CTP by cyclohexane decreases,but the hydrogen bonding forces are not high enough and some break during heating.The releasing rate of 16 PAHs in MCTP fume decreases slightly.The PAHs content in water-soluble increases due to the presence of a large number of hydrogen bonding,and CTP molecules are easy to form stronger hydrogen bonding forces with solvents.