Thermal and chemical regeneration of spent activated carbon and its adsorption property for toluene

This paper describes the influence of thermal and chemical treatment on the adsorption characteristics of spent activated carbons (ACs). For this purpose, we applied three different treatments: (1) thermal air (200 and 300°C), (2) acid aqueous washing (C ₂H ₂O ₄ and H ₂SO ₄), and (3) two-step treatment (acid aqueous washing followed by thermal air treatment). Structural and chemical characteristics of the spent AC and the regenerated AC analyzed and compared by nitrogen adsorption isotherm, energy distribution function, and temperature programmed desorption. It has been found that a two-step regeneration treatment of the spent ACs with thermal air (200°C) and oxalic acid aqueous washing is more efficient in recovering the textural properties of the spent AC than other regeneration treatments. In addition, the adsorption equilibrium amounts of organic compounds on the AC are highly dependent on their textural properties rather than the surface oxygen groups. Adsorption equilibrium isotherms for toluene obtained from the breakthrough curves are well correlated by Freundlich and Sips equations. An isothermal dynamic model based on linear driving force mass transfer satisfactorily predicts the adsorption breakthrough curves experimentally obtained at different conditions. The column dynamic analysis of cycles with adsorption, desorption and electrical heating clearly indicates that the AC treated with thermal air (200°C) and oxalic acid aqueous can be reapplied for removing organic substances without significant loss of its adsorption ability.