Binary Adsorption Equilibrium and Breakthrough of <i>n</i>-Butyl Acetate and <i>p</i>-Xylene on Granular Activated Carbon

Compared with abatement methods (regenerative thermal oxidizer, regenerative catalytic oxidizer, etc.), the adsorption–desorption combined method has been considered as a sustainable way to treat and recover volatile organic compounds (VOCs) from off-gases in painting or coating industries. It also helps to reduce the production of waste adsorbents compared with the traditional single-adsorption process. Herein, n -butyl acetate and p -xylene are selected as the representatives of oxygenated volatile organic compounds and nonmethane hydrocarbons of automotive coating solvents, respectively, to test their adsorption behaviors on coal-based granular activated carbon. The single-component adsorption tests show that both the VOCs are adsorbed on the activated carbon surface as a monolayer model. Compared with single-component adsorption, it is found that a competitive adsorption happens between n -butyl acetate and p -xylene when they are mixed together for adsorption. Results clearly show that the displacement of weakly adsorbed n -butyl acetate by strongly adsorbed p -xylene results in less uptake of n -butyl acetate in binary adsorption (0.265 g·g –1 ) than in single-component adsorption (0.333 g·g –1 ). The dynamic adsorption of a binary mixture on activated carbon is found to be well-fitted mathematically by the extended Langmuir model and ideal adsorbed solution theory with average relative error less than 7% and 12%, respectively. After the adsorption model of the typical binary VOCs was obtained, the operational conditions were further optimized to understand the adsorption mechanism. It is shown that increasing the inlet concentration or feed flow rate is observed to be favorable for adsorption capacity and competitive behavior of the binary mixture. Finally, a simple adsorption mechanism for the binary mixture on activated carbon has been proposed. These findings will provide fundamental information for the recovery of VOCs through adsorption–desorption processes.