Detoxification of coal-tar pitch by alkylation method and toxicity evaluation by chemical index, fumes and water-soluble substances

Abstract

Coal-tar pitch (CTP) output in China has consistently exceeded 7 million tons annually since 2011. CTP contains 16 toxic polycyclic aromatic hydrocarbons (PAHs) that are preferentially monitored by the American Environmental Protection Agency (EPA). As a result, the widespread and extensive use of CTP is restricted. Consequently, finding ways to reduce the toxicity of CTP has become an urgent concern. In the paper, the reaction conditions were optimized using model compounds (naphthalene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, benzo [a]pyrene) of CTP. Subsequently, the CTP was modified through alkylation reaction using 1-dodecene, and the detoxification effect was evaluated based on chemical index, fumes, and water-soluble substances. The total content of 16 toxic PAHs in the modified CTP (MCTP) decreased by 75.56% compared to the original CTP. The toxicity equivalent quotient (TEQ) of the MCTP was reduced by more than 65% according to different environmental standards. The content of the 16 PAHs detected in MCTP fumes released at 140 °C decreased by 80.89%, while in water-soluble substances it decreased by 64.04% and 76.67% at 30 °C and 60 °C, respectively. These results strongly indicate the effectiveness of the alkylation method in reducing the toxicity of CTP. However, in order to develop more environmentally-friendly materials, it is necessary to explore more efficient catalysts and cheaper modifiers, which will be the focus of our future research. Novelty StatementThis study investigated the toxicity inhibition of CTP to reduce the content of PAHs by alkylation method. The modification process was analyzed using model compounds to understand the potential reaction pathways. The objective of toxicity inhibition was achieved by creating low-toxicity and long-chain alkyl substitutes. Additionally, the toxicity of CTP and MCTP was assessed by introducing fumes and water-soluble substances.