Thermogravimetric–Fourier Transform Infrared Spectroscopy–Gas Chromatography/Mass Spectrometry Study of Volatile Organic Compounds from Coal Pyrolysis

The simultaneous use of thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy, and gas chromatography/mass spectrometry (GC/MS) with the same sample provides a unique method for studying coal pyrolysis. About 124 volatile organic compounds (VOCs) were identified by TG-FTIR-GC/MS during coal pyrolysis based on the characteristic fragments or Kovats index. These compounds included alkanes, α-olefins, benzene, toluene, ethylbenzene, xylenes, and phenols. n-Alkanes from C5 to C24 with regular one-carbon retention intervals in the GC/MS system were used to calculate the Kovats indexes of all compounds. From this study, temperature was the key factor affecting VOC release. The VOCs released below 400 °C represented only 23.1% of the total VOCs released during the pyrolysis of bituminous (coal BA). Thus, the use of thermal desorption (TD) with GC/MS to analyze coal pyrolysis provides VOC release information only below 400 °C. It would underestimate the VOC release because of the temperature limitation on the TD technique. The yields of phenolic hydrocarbons from lignite were higher than those from bituminous coal. This could be the result of a higher level of oxygen cross-linking in lignite than in bituminous coal, which was proven by the results of curve fitting and GC/MS. Thus, the release of VOCs is a function of coal rank.