Inhibitory Effect Of Aldehyde Group Chemically Modified Coal Tar Pitch On Toxic Polycyclic Aromatic Hydrocarbons

Coal tar pitch(CTP)is widely used,especially in road paving,it is an ideal substitute for petroleum asphalt.However,because it contains the carcinogen PAHs,which limits its application,it is necessary to study the inhibition of toxic polycyclic aromatic hydrocarbons(TPAHs)with CTP.This paper studies the effect of reaction of CPT with aldehyde modifiers(37% formaldehyde solution,benzaldehyde and furfural)on the reduction of TPAHs content in CPT under the condition of acidic catalyst by the method of chemical modifacation.Firstly,CPT extracted from low temperature coal tar after its basic properties were determined.The CPT was modified by aldehydes,the effects of different factors on the reduction rate of TPAHs in CPT were investigated and optimized.Then,the properties of CTP before and after modification were measured and characterized.By comparative analysis,the reaction mechanism of aldehydes with TPAHs in CTP was explored preliminarily with the design of modification mechanism.Finally,through the reactions between model compound Pyrene and modifiers in paraffin system by means of FT-IR,TG-DTG,GPC and Uv-fluorescence,the exploration and verification of the reaction mechanism.The results show that CTP mainly contains polycyclic aromatic hydrocarbons,light aromatic hydrocarbons,aliphatic hydrocarbons,acidic compounds and a small amount of heteroatom compounds.It has been detected that CTP contains 10 TPAHs,mainly in tricyclic and tetracyclic,of which the typical carcinogen benzo[a]pyrene content was 9.02 mg/g.The CTP was modified by formaldehyde,benzaldehyde and furfural,the total content reduction rate of 10 kinds of TPAHs was 84.63 %,74.14 % and 81.68 % respectively after optimization,and the reduction rate of TPAHs in modified CPT increased with the increase of aromatic ring number.Through the characterization of CTP and three aldehyde modifiers before and after modification,FT-IR and TG analysis,the chemical reaction between TPAHs in the CTP and three modifiers was preliminarily speculated,and the thermal stability of CTP was improved,and macromolecular and stable substances were produced.Gas FT-IR analysis,compared with coal tar pitch before and after modification,the products of each component showed a trend of increasing with the increase of temperature.GPC analysis shows that the order of the maximum molecular weight of the products before and after modification is formaldehyde modification,furfural modification,benzaldehyde modification and CPT decreasing in turn,which indicates that the reaction produces the substances with larger molecular weight.Uv-fluorecence analysis showed that there were more aromatic rings in formaldehyde modified products,and furfural modified products,benzaldehyde modified products and coal tar pitch decreased in turn,indicating that the reaction produced more aromatic rings.The reaction of the model compound with the modifier in the paraffin system was studied.The products were characterized by FT-IR,TG,GPC and Uv-fluorescence.It was further verified that the reaction occurred by electrophilic substitution crosslinking reaction,and the stability of the product was improved,the molecular weight was increased,and the number of aromatic rings was increased.