Activation energies of phenanthrene desorption from carbonaceous materials: Column studies

SummarySorption/desorption kinetics of phenanthrene from two carbonaceous samples (lignite and high-volatile bituminous coal (HC)) at different temperatures was monitored using an on-line column method. Pulverized samples (<30 μm) were equilibrated in the column for 2 months before desorption began. The desorption rates declined initially fast, followed by an extended tailing part, which could be described very well by a single parameter spherical diffusion model accounting for non-linear sorption. Desorption was carried out at stepwise increased temperatures (20–90 °C), and the apparent activation energies were calculated based on the Arrhenius relationship for each of totally three temperature steps. The apparent activation energies were in an order of 58–66 kJ mol−1 and 70–71 kJ mol−1 for lignite and HC, respectively and they did not increase significantly during the leaching procedure. At the end of the experiments desorption was almost complete and only 0.2% (lignite) and 6% (HC) of the initially sorbed phenanthrene was present after the last temperature step. Fitted diffusion coefficients as well as the comparison between the apparent activation energies and sorption/desorption enthalpies obtained for the same samples from equilibrium isotherms imply that the diffusion occurred in organic matter of the lignite and in micropores of the high-volatile bituminous coal, where higher apparent activation energies are expected.