Gradient separation of ≥300 °C distillate from low-temperature coal tar based on formaldehyde reactions

The high-temperature distillate of low-temperature coal tar (LTCT) is constituted of polycyclic aromatic hydrocarbon (PAHs) with a wide molecular distribution and many different functional groups. This distillate is a sort of complicated material, which is difficult to be identificated and characterized. The objective of this paper is to get more information on PAHs in the high-temperature distillate from LTCT. >= 300 degrees C distillate (300DF) of heavy tar (H-tar) from LTCT was reacted with formaldehyde under the condition of alkaline. After reaction, light oil (L-oil) and heavy oil (H-oil) samples were collected. H-oil was gradient separated with toluene (MB) and tetrahydrofuran (THF). MB soluble (MBS), THF soluble (THFS) and THF insoluble (THFR) were collected. L-oil, MBS and THFS were analyzed by gas chromatography-mass spectroscopy (GC-MS). The results show that MBS contains long chain hydrocarbons and PAHs, especially C4 alkyl phenanthrene with the content of 8.45 wt%. There is no detectable matter by GC-MS in THFS. The pyrolysis processes of THFS and THFR using thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG-FTIR) are mainly divided into 5 stages and 3 stages, the total weight losses are 56.00 wt% and 38.00 wt%, respectively. The corresponding volatiles of FTIR show that the maximum temperature of CH4 emission in THFS is higher than that in THFR. Peaks at 882 cm(-1) are due to the decomposition of mono-and multi-substituted compounds of the benzoic ring in THFR. THFR is a polymer which is mainly composed of alkyl PAHs and the -CH2- bridge. (C) 2015 Elsevier Ltd. All rights reserved.