Determination of adsorption isotherm and diffusion coefficient of toluene on activated carbon at low concentrations

Adsorption is one of the most effective technologies for indoor gas pollutant removal. To guide the design and modeling of sorbent-based air cleaners, it is necessary to characterize a sorbent material (e.g., activated carbon) in advance. A new dynamic volumetric adsorption test method was developed in this study. The adsorption capacity of toluene on activated carbon was determined in the concentration range of 0.1-100 ppm at three relative humidity conditions (20%, 50%, and 80%). The obtained adsorption isotherm was used to evaluate the validity of Langmuir model, Freundlich model and Dubinin-Radushkevich (D-R) model, respectively. Langmuir model gave the best fit. A linear adsorption isotherm was observed when the concentration was below 1.5 ppm. The measured data was then used to determine the model parameters (partition coefficient, mass transfer coefficient and diffusion coefficient) by least-square fitting to a mechanistic numerical model. Results show that the diffusion coefficient increases with increased concentration, indicating the dominating role of surface diffusion during VOC adsorption on activated carbon.