Modelling sorption and diffusion in activated carbon: a novel low pressure pulse-response technique

A novel low pressure pulse-response technique, referred to as Multitrack, was applied for the simultaneous determination of the adsorption and diffusion parameters of gases in porous materials in a packed bed. Measurements were performed on two different carbons, Kureha and Sorbonorit B3, in the temperature range between 473 and 700 K. The modelling procedure of the pulse responses consisted of two parts. The transport parameters through the packed bed were determined from the pulse responses of non-adsorbing argon. Adsorption and diffusion parameters were determined for the adsorbing gases n-butane and hexafluoropropylene. As a general rule it is concluded that microporous materials must be described with a basic three-parameter model, while macroporous materials must be described with a simplified two-parameter model. The heats of adsorption, determined from the adsorption equilibrium constant, agree well with the values determined independently from uptake experiments. With Multitrack a single value for the diffusivity is obtained at a given temperature, valid for the low pressure limit, whereas with uptake a range of diffusivities is found, covering a wide concentration range. The values were of the same order of magnitude. Multitrack is a promising method for the simultaneous determination of adsorption and diffusion parameters. (C) 2001 Elsevier Science Ltd. All rights reserved.