Fuel Processing Technology, Vol.159, 386-395, 2017
Separation and structural characterization of groups from a high-volatile bituminous coal based on multiple techniques
Although considerable progress has been made in revealing the coal macromolecular structure via solvent extraction, there remains a challenge in elucidating the coal structure due to low extraction yields of coal, poor selectivity of extraction solvents, and complexity of extracts. In this work, a high-volatile bituminous coal was successfully separated into seven groups (G(1)-G(7)) with less diversity within each class using multistep extraction followed by column chromatography. The total extraction yield (dmmf) reached up to 56% and the structural characteristics of the seven groups were identified and investigated with a series of analytical techniques. The results showed that the individual groups had a rather unique composition and their chemical properties were different in elemental composition, functional groups, aromatic cluster size, number and length of the alkyl side chains, and degree of order, which resulted in differences of their pyrolysis reactivities. Aliphatic hydrogen accounted for 99% of total hydrogen in n-heptane eluted fraction (G(4)) but the aliphatic degree in the extract residue (G(1)) was only 35.7%. The ratios of aromatic bridgehead carbon were 0.32, 0.30, and 0.27 for G(1), CCI4 insoluble fraction (G(2)), and n-heptane insoluble fraction (G(3)), respectively. Additionally, total volatiles achieved 99.8, 98.1, 98.2, 89.0, and 60.0%, respectively during pyrolysis of G4, toluene eluted fraction (G(5)), ethyl acetate eluted fraction (G(5)), methanol eluted fraction (G(7)), and G(3) at end temperature of 800 degrees C, which were substantially higher than those for G(1) and G(2). In comparison with the partition of coal structure using maceral components, the proposed separation method provides an efficient and convenient investigating for structural exploration and these data can be combined to create structures that are cognitive of the structural diversity present Through this, exploration of the complex conversion mechanism of coals would become more accessible during pyrolysis, gasification, liquefaction, and coking processes. (C) 2017 Elsevier B.V. All rights reserved.