Kinetics of ozone decomposition by granular activated carbon

The kinetics of the removal of ozone from air by granular activated carbon (GAC) has been investigated. Twenty GACs with different textural and chemical surface properties were used in this study. The kinetic experiments were carried out in an expanded bed reactor (EBR) and in a packed bed reactor (PBR). A rate equation that takes into account thermal ozone decomposition and removal of ozone by GAC due to chemisorption and catalytic decomposition has been proposed. Deactivation kinetics has also been considered in the reaction model. Intrinsic rate constants for thermal ozone removal (k(T)), chemisorption of ozone (k(1)), and GAC-catalyzed decomposition of ozone (k(2)), as well as deactivation rate constants (k(d1) and k(d2)) have been evaluated from dynamic modeling. At the conditions used in this work, ozone was thermally stable only below 323 K. Above this temperature, ozone partially decomposed even in the absence of GAC. Temperature favored the rate of ozone removal by GAC following Arrhenius behavior while air humidity had a negative effect, likely attributed to the blockage of GAC active sites by water. A relationship between k(1) and surface area, volume of pores larger than 3.5 nm, concentration of surface oxygen complexes (SOC), and ash content has been found, while k(2) depends mainly on surface area, basic SOC concentration, and metal content. The activity of the all the GAC samples used decreased with the ozone exposure time. The formation of acidic SOC due to chemisorption of ozone onto GAC has been pointed to as a major reason for the process deactivation. Effective GAC regeneration has been achieved by thermal treatment at 1123 K.