Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Separation and analysis of maceral concentrates from Victorian brown coal Yuxin Yan, Ying Qi, Marc Marshall, W. Roy Jackson, Alan L. Chaffee ⁎ School of Chemistry, Monash University, Clayton, Victoria 3800, Australia ARTICLE INFO Keywords: Maceral separation Lithotypes Sink-float method Pyrolysis-GC-MS Victorian brown coal ABSTRACT Four selectively mined lithotypes and a run-of-mine coal (ROM) have been obtained from the Yallourn coal seam in the La Trobe Valley, Victoria, Australia and a partial maceral separation of each of them has been carried out using the sink-float method with centrifugal force on a laboratory scale. The yields of liptinite-rich float fractions were between 22.5 and 2.8 wt% in the order of Pale > Light > Med-light ≈ ROM > Dark. Elemental analysis and FTIR showed that the liptinite-rich float fractions had higher H/C ratios and aliphaticities than the corre- sponding vitrinite-rich sink fractions and this was confirmed by solid state 13 C NMR. Pyrolysis-GC-MS using a pyrolysis temperature of 650 °C showed little difference in the distribution of aliphatic peaks but dramatic changes in the relative abundance of triterpenoids between lithotypes and in some cases between float and sink fractions of a lithotype. Variations in yields with pyrolysis temperature suggested that the triterpenoids are loosely bound to the main coal structure. 1. Introduction Scientists classically attempt to divide a complex mixture system into individual constituents to study the properties of simpler materials, then combine the information to deduce the properties of the whole system [1]. Coal with its organic components is an example of such a complex system. The organic components of coal include plant debris derived from resins, tissues, spores, waxes and cuticles, which have decayed and gelified to varying degrees and have been chemically al- tered during the coalification process [2]. These organic components in coal have been identified as macerals [3]. The Standards Association of Australia (1986) issued a standard for maceral classification applicable to all coals. The standard defines twenty-five macerals which all belong to three maceral groups, namely vitrinite, liptinite and inertinite [4]. It would be expected that maceral groups derived from different macerals and precursors and having different optical properties would be chemically distinct. This has been demonstrated by several researchers. For example, Machnikowska et al. [5] applied diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy in the characterization of maceral groups separated from several subbituminous to anthracite coals and identified differences of functional groups between vitrinite and inertinite. They concluded that the CH ar /CH al (aromatic carbon/aliphatic carbon) ratio increased from liptinite through vitrinite to inertinite. The ratio also increased with carbon content in vitrinites and inertinite. Maroto-Valer et al. [6] de- termined the structural variation within vitrinite and inertinite maceral groups separated from a bituminous coal using single pulse excitation (SPE) solid state 13 C NMR. It was determined that the aromaticity of the vitrinite fractions was significantly lower than that of the inertinite fractions, but the aromaticity, the fraction of non-protonated aromatic carbon and the number of rings per cluster all increased with density within both maceral groups. Das [7] studied devolatilisation char- acteristics of vitrinite and inertinite using thermogravimetric analysis coupled with gas chromatography to better understand the devolatili- sation characteristics of coking coal. It was found that vitrinite-rich concentrates were characterized by a higher content of volatiles. The thermal behaviour of vitrinite-rich concentrates was significantly dif- ferent from that of inertinite-rich concentrates, with higher values of maximum rate of weight loss, higher weight loss as tar and lower weight loss as gas for vitrinites than for inertinites. The dominant maceral groups in black coals are usually vitrinite and inertinite, whereas in brown coals, vitrinite and liptinite are the most important. However, once maceral groups have been separated, the techniques used to study them are similar, as outlined below for brown coals. Turning to lignites and brown coals, Parkash et al. [8] separated Texas and North Dakota lignites into fractions of different density by a sink-float method and determined the elemental analysis, maceral analysis and liquefaction reactivity of the different fractions. Cronauer et al. [3] carried out similar separations for a Texas lignite and noted that liptinite macerals appeared in both high and low density fractions, possibly because of association between liptinite and inorganic com- ponents. Stankiewicz et al. [9] separated a range of organic materials, https://doi.org/10.1016/j.fuel.2019.01.025 Received 20 September 2018; Received in revised form 20 December 2018; Accepted 3 January 2019 ⁎ Corresponding author. E-mail address: alan.chaffee@monash.edu (A.L. Chaffee). Fuel 242 (2019) 232–242 0016-2361/ © 2019 Published by Elsevier Ltd. T