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Highlights • Volatiles reaction (VR) occurred at 440 °C in 1.5 s, extensive at >600 °C in 4 s. • For the columns and carriers used >50% THF or hexane solubles (HS) reside in column. • With minimal VR, the tars contain mainly HS, more for a lower rank coal tar. • VR reduced HS yield, increased pitch and coke yields, resulting in lighter HS. • VR converts some SIMDIST eluted tar to residue and increases 2-ring aromatics in HS. Abstract In coal pyrolysis, the reaction of volatiles plays an important role in determination of tar yield and composition but has not been studied in detail in the literature. This work studies the volatiles' reaction in pyrolysis of a bituminous coal (SM) and a lignite (HLBE) using a two-stage fixed-bed laboratory reactor with the second-stage temperature of 440–700 °C and the residence time of 1.5–6.9 s. The tars were characterized by solvent extraction with tetrahydrofuran (THF) and hexane, and by simulated distillation (SIMDIST) of the THF soluble matter and high performance liquid chromatography (HPLC) analysis of the hexane soluble matter. It was found that the main component of the tars was oil, which was more in the HLBE tar than in the SM tar. As much as >50 wt% oil and tar retained in the chromatograph columns. The volatiles reacted at temperatures as low as 440 °C and the rate was more pronounced at 600 °C in 4.2 s. The volatiles' reaction reduced the oil yield while increased the pitch yield. The aromatics in the hexane soluble matter were mainly 2-ring compounds and their content increased by the volatiles' reaction. The major tar fractions have boiling points of 200–538 °C and their content varied systematically in the volatiles reaction. The findings are important for design of efficient coal pyrolysis reactors. [ABSTRACT FROM AUTHOR]

Solvent extraction of coals has been practiced extensively for various purposes including the determination of coal structure. It is generally assumed that the extraction is mainly a physical process involving little change in covalent bonds. But different opinions were reported. This work studies the behavior of radicals during extraction of 3 low rank bituminous coals using 5 solvents, including hexane, toluene, tetrahydrofuran (THF), 1,2,3,4-tetrahydronaphthalene (THN), and N -methyl-2-pyrrolidinone (NMP), using electron spin resonance (ESR). The extractions are carried out at temperatures from the ambient temperature to temperatures somewhat higher than the boiling points of the solvents, as well as under ultrasound. It is found that the radical concentration of the coals changes during the extraction, and the change is influenced by temperature and varies with the solvent. The decrease in radical concentration in most solvents at temperatures lower than their boiling points is attribute to coupling of free radicals dissolved from the coals, while the increase in radical concentration at high temperatures and in NMP is attributed to the cleavage of weak bonds in coals by the solvents. [ABSTRACT FROM AUTHOR]