Preparing ash-less coal and further converting it into
chemicals
is an efficient and promising means for lignite utilization. This
work performed depolymerization of lignite to prepare ash-less coal
(SDP) and separated it into the hexane-soluble fraction (HS), toluene-soluble
fraction (TS), and tetrahydrofuran-soluble fraction (THFS). The structure
of SDP and those of subfractions were characterized by elemental analysis,
gel permeation chromatography, Fourier transform infrared spectroscopy,
and synchronous fluorescence spectroscopy. The results show that SDP
is a mixture of aromatic derivatives containing alkyl substituents
and oxygen-containing functional groups. The number of condensed aromatic
rings, the amount of oxygen-containing functional groups, and the
molecular weight gradually increase as HS < TS < THFS. SDP was
further analyzed by 1H-NMR and 13C-NMR to calculate
its structural parameters. The macromolecule of THFS contains 15.8
total ring systems with 9.2 aromatic rings and 6.6 naphthenic rings.
On average, each THFS molecule contains 6.1 alcohol hydroxyl groups,
3.9 phenol hydroxyl groups, 1.4 carboxyl groups, and 1.0 inactive
oxygen-containing functional groups. The dominant reactions occurred
during depolymerization are the breakage of ether linkages. The average
THFS molecule consists of 3.3 structural units with aromatic nuclei
(2.8 rings on average) linked with methylene, naphthene, and so forth.