Equilibrium and dynamic vapour water sorption properties of biochar derived from apple wood

The water vapour sorption properties of biochar derived from apple wood (Malus sp.) have been studied. The biochar used in the study were formed from wood samples taken from different parts of the trunk and they exhibited different cell wall densities and surface area values when charred under identical conditions. The water vapour adsorption and desorption characteristics of the biochar were investigated over the relative pressure range P/Po = 0-0.95 in a dynamic vapour sorption apparatus and the kinetics was analysed in terms of the parallel exponential kinetics (PEK) model. The PEK model comprises two exponential sorption kinetic terms which are termed fast and slow sorption processes. The fast process is attributed to a linear driving force mass transfer diffusion model, while the slow process is attributed to a relaxation-limited kinetic process. Markedly different sorption behaviour was found between the biochar samples, which had been produced under identical conditions.