Desorption Kinetics of Naphthalene and Acenaphthene over Two Activated Carbons via Thermogravimetric Analysis

Activated carbon (AC) is a promising sorbent for adsorption removal of polycyclic aromatic hydrocarbons (PAHs) because of its cost effectiveness. The desorption kinetics of two-ring PAHs, naphthalene and acenaphthene, over bituminous-coal-based (AC_WY) and coconut-shell-based (AC_NT) activated carbons were investigated. The desorption kinetics were studied over the temperature range of 400-800 K at different heating rates (8-20 K/min) using thermogravimetric analysis techniques. The activation energy, pre-exponential factor, and kinetic model for each sorbate-sorbent pair were determined by applying analytical methods to the non-isothermal data. The Johnson-Mehl-Avrami (JMA) rate equation, g(α) = [-ln(1 - α)]ⁿ (in integral form, where α is fractional completion), following the nucleation and growth model, was found to best describe the PAH desorption from both sorbents. Strong molecular sieving effects were found to influence both adsorption capacity and desorption rates. AC_WY, with less micropore (<0.7 nm) volume and more larger pores (0.7-2 nm) compared to AC_NT, favors PAH adsorption and desorption rates, leading to different values of the kinetic exponent (n) and other kinetic parameters. Likewise, the sieving effects favor adsorption and desorption of naphthalene (kinetic diameter of 0.62 nm) over acenaphthene (kinetic diameter of 0.66 nm) for both carbons.