Performance of Activated Carbon in Evaporative Loss Control Systems

Although activated carbons have been used successfully for approximately 20 years for control of hydrocarbon evaporative emissions from motor vehicles, the correlation of fundamental activated carbon properties, molecular scale pore size/volume characteristics, to carbon performance has not generally been available. Improvements in wood-based carbon have focused on the pore size/volume characteristics resulting in a doubling of performance, as measured by butane working capacity, over the past few years. In addition to relating the butane working capacity for different types of carbon to pore characteristics, laboratory studies using new carbons have demonstrated that the capacity for adsorption of vapors from gasoline is also related to this fundamental property. Furthermore, different types of in-use carbons from vehicle canisters have been evaluated to confirm that the key to carbon performance is pore characteristics and also, that laboratory evaluations of carbons, using proper conditions, can realistically simulate the performance of actual in-use carbons.