Screening of ionic liquids for extraction of polycyclic aromatic hydrocarbons from high-temperature coal tar pitch based on COSMO-SAC model

Abstract

In this work, polycyclic aromatic hydrocarbons (PAHs) in high-temperature coal tar pitch (HCTP) were extracted using ionic liquids (ILs). The COSMO-SAC model was used to calculate the infinite dilution activity coefficient and to select the suitable ILs for extractants. The representative phenanthrene, fluoranthene, pyrene and benzo[a]pyrene among the 16 PAHs under the priority regulation of the U.S. EPA were selected as the research objects, and σ-profile database containing 35 IL anions and 44 IL cations is established. The result showed that the solubility properties of ILs consisting of [Cl]⁻ were obviously better than other anions. The 1,3-dimethylimidazolium chloride ([MMIM]Cl), N-ethylpyridinium chloride ([EPY]Cl) and N-propyl-N-methylpyrrolidinium chloride ([C₃MPYR]Cl) were selected for extraction of PAHs due to the best efficiency. In addition, the predicted results were verified with experiments, and optimise the process conditions of ILs extraction of PAHs from HCTP. The experimental results showed the reliability of COSMO-SAC screening. The optimum extraction process conditions were the experimental temperature of 333.15 K, stirring time of 30 min, and HCTP/ILs mass ratio of 1:20. Under these conditions, the total concentration of 16 PAHs in the HCTP is 97.223 mg/g, compared to toluene extraction, there was an increase of 2.43 %. Independent gradient model based on Hirshfeld partition was used to revealed the interactions between [MMIM]Cl and PAHs. These results can improve the high value-added utilization of HCTP, at the same time, provide a theoretical basis for separation of important chemical raw materials such as PAHs from CTP, then realize the conversion and utilization of harmful substances in HCTP.