Adsorption and desorption characteristics of hydrocarbons in multi-layered hydrocarbon traps

In this study, a hydrocarbon (HC) trap was developed using a multi-layered zeolite, in which zeolite A and zeolite beta was selected for the water trap and the hydrocarbon trap, respectively, with the goal of reducing hydrocarbon emissions during a cold-start. The adsorption and desorption of hydrocarbons was examined in the monolithic adsorber during a vehicle test as well as in a lab-scale micro-reactor as a powder form. The competitive adsorption of water vapor and hydrocarbons in the exhaust gas from a gasoline vehicle on the hydrocarbon adsorption sites at low temperatures caused the decrease in the HC removal efficiency during a cold-start. In a multi-layered adsorption system composed of the water trap and the hydrocarbon trap, the hydrocarbon removal efficiency was greatly improved owing to the elimination of water with the hydrophilic zeolite A in the upper layer. Furthermore, the hydrocarbon desorption can be delayed because of the latent heat of desorption of adsorbed water in the upper layer. Therefore, this double-layered zeolite-based hydrocarbon trap showed the better performance compared with the conventional hydrocarbon trap during a cold-start.