Modification of coal-tar pitch with 10-Undecenal to reduce the content of environmental pollutants of polycyclic aromatic hydrocarbons

Abstract

Although there were approximate 10 million potential yields of coal-tar pitch (CTP) annually in China since 2011, plenty of environmental pollutants of polycyclic aromatic hydrocarbons (PAHs) existing in CTP limit its many applications. Reducing the content of PAHs hazardous to environment in CTP becomes an imminent problem. In the paper, CTP was modified with 10-Undecenal (UNL) over the catalysis of potassium bisulfate (KHSO4) in cyclohexane solvent to reduce the content of U.S. Environment Protection Agency (EPA) priority PAHs in CTP. The effects of modifier and catalyst quantities, reaction temperature and reaction time on the reduction efficiency of 16 EPA priority PAHs were investigated. The optimum reaction conditions were obtained as follows: UNL additive quantity 8 wt% of CTP, KHSO4 additive quantity 5 wt% of CTP, reaction temperature 50 °C and reaction time 4 h. Under these conditions, the reduction efficiency of the 16 priority PAHs in CTP reached 91.10%, Benzo[a]pyrene, a typical toxicant to environment, decreased by 93.14%. Simultaneously, the softening point of modified CTP (MCTP) dropped from 87 °C to 59 °C. The changes of structure of CTP before and after modification were investigated via thermogravimetry analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and 13C nuclear magnetic resonance (NMR) Spectrum. It was proved that the alkylation reaction generated between PAHs and UNL might reduce markedly the content of the 16 priority PAHs in CTP.