Multistage gradient extractive separation and direct and indirect analysis of petroleum ether insoluble fractions from low temperature coal tar

Abstract

The composition and structure of heavy components in coal tar are very complex, which affect the further processing and utilization of coal tar. In this paper, the multistage gradient extractive separation and analysis of petroleum ether (PE) insoluble fractions from low temperature coal tar (CTPI) were performed. CTPI was separated into diethyl ether extracts (DEE) and residues (DER) by Soxhlet extraction with quartz sand. DEE was further stepwise separated into tetrachloromethane extracts (TME), toluene extracts (MBE) and residues (MBR). DER was separated into ethyl acetate extracts (EAE), tetrahydrofuran extracts (THFE) and residues (THFR). Physical and chemical characterization of the six fractions were analyzed, using GPC, Uv-fluorescence spectroscopy, FTIR, 13C CP/MAS NMR, 1H MAS NMR, XRD, TG-FTIR and Py-GC/MS, to obtain the composition and structure of these fractions. The results show that the extraction yields of TME, MBE, MBR, EAE, THFE and THFR are 29.98 wt%, 42.13 wt%, 10.93 wt%, 6.02 wt%, 6.98 wt% and 3.96 wt%, respectively. The order of the maximum molecular weights is THFE > EAE > MBE > TME > MBR. THFE has the largest polycyclic aromatic structure. THFE and EAE contain more ethers than other fractions, and they may be mainly composed of polycyclic aromatic structure with -CH2- as bridge bonds. The order of fa values is EAE > CTPI > MBR > MBE > THFE > TME. The aromatic layer spacing d002 follows the order of MBE > TME > MBR > THFE > EAE > CTPI. The final thermal weight loss rates of these fractions follow the order of TME > MBE > THFE > EAE > MBR > THFR. Oxygen-containing compounds, acid compounds and heteroatomic compounds have been enriched in the pyrolysis volatiles derived from the separated fractions (EAE, THFE and THFR) of DER. The common feature of DEE and DER is the presence of the widely distributed phenolic compounds.