Adsorption thermodynamics and desorption properties of gaseous polycyclic aromatic hydrocarbons on mesoporous adsorbents

Performances of mesoporous materials in removal of polycyclic aromatic hydrocarbons (PAHs) from hot gases were evaluated systematically. The adsorption and desorption natures for PAHs with different aromatic rings, naphthalene (Nap), phenanthrene (Phe) and pyrene (Pyr) on mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3, were studied. Adsorption equilibria were well described by Langmuir or Freundlich model, giving the order of adsorption capacity of CMK-3 > SBA-15 > MCM41 and Pry > Phe > Nap. Temperature programmed desorption exhibited the order of ease of desorption of SBA-15 > MCM-41 > CMK-3, along with desorption kinetic triplet determined by combined model fitting analysis. The Johnson-Mehl-Avrami (JMA) rate equation was found to well describe PAH desorption kinetics, except for Phe/ SBA-15 and Pyr/CMK-3 due to potential blockage and strong binding, respectively. MCM-41 with simple 1-D mesoporous structure provided smooth diffusion and consistent behavior but very low adsorption capacity for each PAH. SBA-15 with micropores/small mesopores as interconnectivity between primary mesopores not only showed high sorption capacities but also diffusion advantages in desorption. CMK-3 with great microporosity facilitated the adsorption at low concentrations due to micropore-filling, and with surface hydrophobicity rendered high affinities especially for the bulkier Pyr.