Characterization of activated carbon adsorption and deterioration in carbon canisters during vehicle refueling

Abstract

The carbon canister is adsorbing gasoline vapors under high-speed loading conditions during vehicle refueling, and ensuring the carbon canister’s working capacity is the key to controlling refueling emissions. This study analyzed carbon canister working characteristics during refueling as well as carbon canister bleeding emission components. The activated carbon deterioration curve was obtained by 300 adsorption/desorption cycle tests, and the deterioration mechanism was further analyzed by using characterization means and molecular simulation techniques. The results show that the working capacity of carbon canister decreases approximately linearly with the increase of gasoline vapor loading speed, with the working capacity at 2700 g/h loading speed being only 58.6 % − 69.6 % of that at conventional loading speed. Carbon canister bleeding emissions consist primarily of small molecule alkanes, and refueling emissions cannot be equated with bleeding emissions. The working capacity of the activated carbon showed a tendency to decrease with the increase in the number of cycles, with the most severe deterioration in the initial cycle stage and finally stabilizing. Difficulty in desorption of adsorbates at high-energy sites is the main cause of deterioration. The residuals in the activated carbon during the initial cycle stage are predominantly C4 − C6 species, followed by a gradual replacement of most C4 − C6 species by C7 − C10 species. In terms of methods to cope with the deterioration of carbon canisters, three aspects can be considered: increasing the desorption capacity, increasing the desorption temperature, and decreasing the proportion of small micropores in activated carbon.