Study of pyrolysis kinetics and characterization using TG-FTIR, GC, and BET using high ash Indian sub-bituminous coal

Abstract

ABSTRACTIn the present investigation pyrolysis of high ash Indian coal is performed in N2 ambiance using thermo-gravimetric analyzer under non-isothermal heating condition. The presence of various functional groups in low-grade high ash sub-bituminous coal is characterized by an FTIR analyzer. The absorbance spectra are categorized into four distinct zones, and functional groups are detected by the technique of curve-fitting. The evolved volatiles are analyzed by in-line Fourier Transform Infrared Spectrometry (FTIR) to identify the presence of various gaseous species (H2O, CO2, CO, COS) during thermal degradation of coal. Three different kinetic models – single reaction kinetic model (SRKM), single reaction and the distributed activation energy model (DAEM) are employed to estimate the activation energy and pre-exponential factor. Further, the single reaction model is extended with a multi-stage kinetic model (MKM) at various temperature ranges to evaluate the kinetic constants and is found to fit the experimental findings well. The evolution of CO2 and CH4 significantly depends upon the presence of the carboxylic group and aliphatic chains in low-grade coal. The quantification of evolved volatiles is also performed in Gas Chromatographic (GC) Analyzer, and the results confirm the presence of individual gaseous species as detected in the FTIR analyzer. The residual char obtained at a higher heating rate during pyrolysis exhibits a gradual rise in the BET surface area, resulting in the formation of more porous char.