Molecular recognition combined with sequential extraction of aromatics from high-temperature coal tar pitch for separating chemicals: A comprehensive study of experiment and quantum chemistry

Developing the strategy of selectively separating heavy carbon from high-temperature coal tar pitch (HTCTP) to achieve efficient utilization is still the focus of current research. The cumulative extraction yield of HTCTP is 55.2wt% by ultrasonic-assisted extraction with petroleum ether and ethyl acetate. The slope of the fitting curve of extraction kinetics in the second stage is larger, which is 29.46 and 18.38 times of those in the first and third stages, respectively. A total of 276 organic compounds detected from gradient extracts (En) can be divided into 65 group components. The relative contents of aromatic rings (ARs) in each extract are 43.76% (3 ARs, E5), 36.44% (4 ARs, E11), 13.26%, 21.72%, 6.91%, and 4.08% (5-8 ARs, E19), respectively. Moreover, the main aromatics are reconstructed based on the basic structure of virtual molecules. The hydrogen bond in the extract is mainly OH···N formed by the lone pair peak on N in pyridine compounds and the H of OH in arenols, followed by OH···OH self-association. C-H···π-based van der Waals interaction exists between H in n-hexane or ethyl acetate and ARs in typical compounds. Compared with naphtho[7,8,1,2,3-nopqr]tetraphene, benzo[ghi]perylene, and rubicene, petroleum ether is easier to dissolve acenaphthene, phenanthrene, and fluoranthene with higher relative content and lower molecular weight. Both the dispersion interaction and total energy of n-hexane-rubicene system are the highest, which are -79.09 kJ mol-1 and -47.29 kJ mol-1, respectively, while the highest bond energy of n-hexane-naphtho[7,8,1,2,3-nopqr]tetraphene system is -34.42 kJ mol-1. Combining molecular identification with sequential extraction reveals a feasible scheme for selective separating aromatics from HTCTP for chemicals, which is also expected to be used to separate other value-added aromatics from coal derivatives.