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Perhydrous coal has advantages as a fuel source and raw material for hydrocarbon production over other coal with similar rank. Good understanding of thermal characterization of perhydrous coal can provide important information for control of the pollutants release and enhancement of the conversion rate of coal during its utilization. A perhydrous bituminous coal from Dingji Coal Mine, China was selected for the investigation of the non-isothermal pyrolysis process below 500 °C in N 2 flow by in-situ transmission FIIR. Evolutions of the main functional groups in coal, including aliphatic groups, aromatic C C and C H, carbonyl, C O and hydroxyl could be divided into several stages. The thermal characterization of each stage was discussed. The aliphatic groups and aromatic C C content decreased slightly with the volatilization of small molecules below 400 °C, while the amount of aromatic C H increased with the loss of substituent groups. The conversion of C O to C O contributes to the slight increase in the C O amount below 370 °C, and the decrease of hydroxyl was attributed to loss of water and the condensation and elimination of hydroxyl groups. The amount of all functional groups except for the aromatic C H declined rapidly with the cracking of C C bonds after 400 °C. The kinetic characterization of pyrolysis stages for three functional groups, including aliphatic groups, C O and hydroxyl, was studied with modified integral method. Activation energy of pyrolysis stages of the three functional groups increased with rising temperature. Kinetics for the different stages of functional groups were fitted with different kinetic models. The initial loss of aliphatic groups and C O was controlled by diffusion. Then, the reaction of the three functional groups fitted on the first-order or third-order reaction models. The results obtained by in-situ FTIR revealed more detail information about thermal characterization and kinetic characterization and can be expected to lead to good understanding of pyrolysis of a perhydrous coal. [ABSTRACT FROM AUTHOR]

• The thermal behavior of six functional groups in various rank coals was compared. • The decomposition of aliphatic C H contribute to the primary pyrolyisis stage. • The evolution of OH is relatively insensitive to coal rank. • The pattern of E a for pyrolysis of FGs in various temperature range was presented. Pyrolysis has widely found applications in the processes of coal conversion and utilization. Good understanding of its reaction mechanism contributes to the optimization of coal conversion process and the controlling of the emission of pollutants during coal utilization. The evolution of the six main functional groups in coal with different ranks during pyrolysis was compared based on the data from in-situ transmission FTIR. As the increase of the coal rank, the initial temperature for the primary decomposition of aliphatic group rises and the remaining proportion at the final temperature gets bigger due to the more stable aliphatic structure in the high rank coal. The evolution of methyl, methylene and methine presents more detailed information in different rank coal. For the decomposition of aromatic C H in the three relatively low rank coals, there are two stages: the decreasing stage and the increasing stage with temperature rising. The temperature range of the decreasing stage depends on the interaction of coal molecules, while the growth extent of aromatic C H in the increasing stage can indicate the degree of the substitutions at the aromatic rings. Both aromatic C C and C O in the two high rank coals decrease slower in the high temperature stage than in the low temperature stage, while the situation is opposite for the two low rank coals. The number of C O type decrease with the rising of coal rank. Among the six functional groups, OH is the most insensitive to the coal rank. For kinetics analysis, the pattern of activation energy for the loss of the four functional groups in different rank coals is presented. The activation energy for the decomposition of aliphatic groups and OH in the high temperature stage is much higher than that (<50 kJmol−1) in the low temperature stage. The decomposition of C O and C O shows relatively low activation energies in all stages. The kinetic models are mostly one way diffusion and n th order chemical reaction and the pre-exponential factor appears obvious compensation effect with the activated energy. [ABSTRACT FROM AUTHOR]

Understanding the molecular structural evolution mechanism during coal pyrolysis can help better regulate coal conversions for developing clean coal technology. This study investigated changes in functional groups and polycyclic aromatic hydrocarbons (PAHs) during pyrolysis of a perhydrous bituminous coal at temperature of 75–600 °C. Results indicated that aliphatic, C–O, C=O, OH, aromatic C=C, and aromatic C–H groups declined in relative abundance below 300 °C. These declines were attributed to cracking of hydrogen bonds and devolatilization. Meanwhile, the alkyl side chains of alkylated PAHs, i.e., alkyl-naphthalenes and alkyl-phenanthrenes, were continuously detached. Pyrolysis at 300–450 °C was characterized by elevated aromaticity, reflected by increments in the relative abundances of aromatic C–H, aromatic carbon, pyridine nitrogen, and protonated carbon. PAH evolutions at this stage exhibited relative increases of 4-–6-ring PAHs with relative decreases of 2-–3-ring PAHs. Pyrolysis at 450–600 °C was characterized by an increment of aromatic C=C and significant increases in relative abundances of 4-–6-ring PAHs in emitted particulate and gaseous phases. The elevation of pyrolysis temperature transformed coal macromolecules into more compact structure. The molecular structural units of chars were formulated as C 245 H 227 N 3 O 14 S, C 239 H 193 N 3 O 8 S, C 228 H 152 N 2 O 3 S, and C 221 H 113 NO 3 S for coal and chars produced at 300, 500, and 600 °C, respectively. Changes in three-dimensional molecular structural units reflected step-by-step intense deformation and condensed process. • The evolution behaviors of various functional groups varied at different temperature stages. • Hydrogen bond crackings, devolatilization, and dealkylation reactions occurred below 300 °C. • Aromatic and protonated carbons increased above 300 °C due to aromaticity elevation. • Changes in PAH compositions recorded dealkylation, polymerization and condensation reactions. • Molecular formulas varied from C 245 H 227 N 3 O 14 S for coal to C 221 H 113 NO 3 S for 600 °C char. [ABSTRACT FROM AUTHOR]