Application of thermogravimetric Fourier transform infrared spectroscopy (TG-FTIR) to the analysis of oxygen functional groups in coal

This paper attempts to relate oxygen- containing gases H2O, CO2, and CO evolved during pyrolysis of the Argonne premium coals to oxygen- containing functional groups as a function of rank. Our approach to functional group analysis of oxygen- containing species in coal has been to use a pyrolysis technique, thermogravimetric Fourier transform infrared spectroscopy ( TG- FTIR), involving thermogravimetric analysis with the measurement of the gaseous decomposition products via IR detection. Under suitable heating conditions, TG- FTIR pyrolysis of a coal sample in a stream of inert gas has been shown to expel quantitatively all of the organic oxygen in the form of H2O, CO2, and CO, and consequently, this technique can be effectively applied for determining the total oxygen content. Focusing on the Argonne premium coals, which cover a wide range in rank between lignite ( Ro = 0.25) and low- volatile bituminous ( Ro = 1.68), TG- FTIR provided complex pyrolysis profiles of oxygen- containing gases, which yield information on the sources of the different peaks observed in coal as a function of rank from a chemical- structure standpoint. Deconvolution of the complex profiles was performed to assign peaks to the different sources of oxygen- containing gases. Model polymers containing various oxygen functional groups in aliphatic and/ or aromatic molecular environments were also pyrolyzed by TG- FTIR in an attempt to assign peaks in the gas evolution profiles of the Argonne premium coals. Although complex evolution profiles were observed for the three oxygen- containing gas species H2O, CO2, and CO in the Argonne premium coals, the strength of the TG- FTIR technique in revealing both similarities and differences in profiles depending upon the coal rank was evident. The findings in this investigation are compared to data published on oxygen functional group analysis for the Argonne premium coals made with various analytical techniques.