Research On Reducing The Content Of Toxic Polycyclic Aromatic Hydrocarbons In Coal Tar Pitch By Alkylation

Coal tar pitch（CTP）is one of the deep-processed products of coal tar.It is a mixture of various hydrocarbons.It is a black high-viscosity semi-solid or solid at room temperature.CTP is used as a binder and impregnant in the carbon industry,and is widely used in industries such as aluminum smelting,steelmaking,refractory materials,building materials,and road construction.It is a resource with great application and potential value.However,because CTP is rich in carcinogenic polycyclic aromatic hydrocarbons（PAHs）,it has greater harm to the environment and human body,which is the main reason why CTP is restricted in its application.Therefore,how to reduce the content of PAHs in CTP is a big problem.This article explores the possibility of CTP modification through the reaction of model compounds.Firstly,the modifiers and catalysts were screened.Anthracene,one of the 16 PAHs,and then the reaction conditions were optimized,combined with GC-MS and infrared analysis and characterization,the products were analyzed,and the reaction mechanism was inferred;then under the optimized conditions five model compounds were selected to explore the law of reaction changes;the catalyst was modified to try to increase the conversion rate of anthracene.Finally,CTP was used to modify under optimized conditions,through product characterization and analysis of the modification effect.The following conclusions were obtained:（1）Through the screening of modifiers and catalysts,HY molecular sieve was selected as the catalyst and 1-octene was the modifier.The optimal conditions were:the addition amount of HY was 8%（relative to the mass of anthracene）,mass ratio of solvent cyclohexane to 1-octene of 1:4,in the reactor at 180°C,2 MPa,and 2 h.Under these conditions,the conversion rate of anthracene was 55%,and the target product yield was 28.6%.The alkylation reaction of anthracene and alkene is an electrophilic substitution reaction involving carbocations,and is accompanied by side reactions.（2）Using the controlled variable method to calculate the kinetic rate equation under the optimal conditions,at 4 different temperatures,4 time points correspond to the conversion rate of anthracene.The related linear relationship was simulated by origin,and according to the Arrhenius equation the calculated reaction activation energy was 28.582 k J·mol^-1.（3）Under optimized conditions,five model compounds such as naphthalene,phenanthrene,fluoranthene,pyrene and benzo[a]pyrene were selected,and HY molecular sieve as the catalyst to explore the feasibility of the reaction.Five kinds of catalysts,including sulfonic acid,βmolecular sieve,USY catalyst and anhydrous Al Cl₃,were used to study the reaction effect.The higher the number of aromatic rings,the higher the reactivity.（4）6 metal-loaded molecular sieves including Zn,Fe,Cu,Ca,Al,and Pb were used.After modification,the catalytic activity of HY molecular sieve decreases.It may be that the metal-supported molecular sieve destroys the orderliness of the molecular sieve structure and shields the strong acid.The center is not conducive to the progress of the reaction.（5）The optimal conditions for the alkylation reaction of anthracene and olefins are applied to the modification of coal tar pitch.When the mass ratio of cyclohexane to 1-octene is 1:4,the total amount of 16 PAHs in the cyclohexane extracts decreased from 85.134 mg/g to 59.455mg/g,and the total reduction rate was 30.2%;when the mass ratio of toluene to 1-octene was1:4,the total content of 16 PAHs in the toluene extract decreased from 98.586 mg/g To 74.178mg/g,the total reduction rate is 25%.Through a series of characterization and analysis of CTP before and after modification,olefins reacted with some substances in CTP,which changed the structure of CTP.