Temperature programmed desorption of coal gases – Chemical and carbon isotope composition

Fresh and stored coals from the United States (New Mexico, Colorado and Wyoming) and Czech Republic (North Bohemian and Upper Silesian Basins) were studied by the method of temperature programmed desorption. Desorbed gases were analyzed for their chemical and carbon isotope composition. Upon heating from room temperature with a constant rate of 40 °C/min, two desorption phases were observed: low temperature desorption of CH4 and CO2 with a maximum intensity between 50 and 80 °C and high temperature desorption of CO2 only between 150 and 210 °C. The desorption of (residual) primary coalbed gas was compared with the desorption of re-adsorbed gases. The δ13C values of the desorbed gases changed due to isotopic fractionation during coal degassing. Kinetic isotope effects were evaluated by comparing the gas desorption from fresh and stored coals from the same seams. Mean values of isotope enrichment during desorption are 2‰ and 1.9‰ for CO2 and CH4, respectively.