Low Temperature Adsorption VersusPore Size in Activated Carbons

Activated carbons have been used for a long time at low temperature for cryogenic applications. The physisorption properties depend on the pore geometry and size: this feature can be used to optimize the carbon structure for a specific application. In this work, we report on the lowtemperature adsorption properties of He, H2, and N2, using three activated carbons: a carbon monolith (sample A), a granular carbon (sample B) and a pelletized carbon (sample C) with different pore size distributions. Adsorption measurements were performed between 0.1 mbar and 1 bar and in the range 10 K to 100 K for He, 15 K to 300 K for H2, and 70 K to 300 K for N2. The isosteric heat of adsorption was obtained: it increases with decreasing pore diameter, as expected from the enhanced solid-fluid interaction potential in smaller pores. The characteristics curves, P(T) at constant loading, were compared to help choose the correct porosity that meets the requirements (pressure, temperature) of a specific application.