Reduction Of Polycyclic Aromatic Hydrocarbons In Coal Tar Pitch By Chemical Conversion

Coal tar pitch is the remnant of distillation process for high temperature coal tar, approximately being 50%～60%of coal tar.Coal tar pitch mainly comprises polycyclic aromatic hydrocarbons(PAHs).Coal tar pitch is a kind of greatly valuable raw material confirmed in some fields such as road construction,building sealant.But considering the carcinogenic activity of some pitch components and corresponding environmental regulation limitation,Coal tar pitch is limited in these fields,except no substitutes for coal tar pitch as electrode for aluminum smelting up to the present.Therefore,for reasonably using coal tar pitch and decreasing PAHs polluting for environment,it is necessary that pretreating coal tar pitch and reducing the content of carcinogenic PAHs.This is necessitous mission for world, especially for china where coal tar pitch is still largely being produced nowadays.The article aims to reduce carcinogenic PAHs of coal tar pitch,principally benzo[a]pyrene (BaP) which is worldwide considered to be a strong carcinogen by using different cross linking agents reacting with coal tar pitch in different conditions which emphasis on the change of temperature,reaction time and the quantity of cross linking agents.The cross linking agents include polymers and monomers.The polymers include unsaturated polyester resin(UPR) and polyethylene glycol(PEG).The monomers include 1,4-Benzenedimethanol(PXG), Divinylbenzene(DVB),and Trioxymethylene.Reaction temperature is limited in 90℃～170℃according to the progress of producing coal tar pitch and the property of cross linking agents, and the proportion of polymer is restricted in 5%～30%,reaction time is 0.5～6 hours.The results indicated that 33.99%conversion on BaP in modified pitch with 10%PEG at 170℃for 1 hours was achieved;50.48%conversion on BaP in modified pitch with 30%UPR at 160℃for 1 hours was achieved;35.60%conversion on BaP in modified pitch with 12%DVB at 130℃for 3 hours was achieved;43.35%conversion on BaP in modified pitch with 25%PXG at 120℃for 1.5 hours was achieved;88.92%conversion on BaP in modified pitch with 25% Trioxymethylene at 110℃was achieved.Besides,there are different extent reduction for other carcinogenic PAHs such as Benzo[a]anthracene,Chrysene,Benzo[g,h,i]perylene in modified pitch with DVB,PXG and Trioxymethylene.Pure BaP was blended with PEG and trioxymethylene,the c¹³ n.m.r.spectras of raws and products were determined,the mechanism probably including O-alkylation and C-alkylation.