Application of foam fractionation to wood

Foam fractionation is a part of the adsorptive bubble separation methods and is a simple, gentle and rapid method for the extraction and accumulation of surface-active substances out of biomass. To assess whether the method is applicable to wood, two different device sizes were compared and two gases (N₂ and CO₂) were dispersed into the wood meal/water suspensions of several tropical wood species or into their respective water extracts. Furthermore, two tensides (Tween20 and SDS) were tested as supporting foaming agents. The compounds accumulated in the so-called spumates of these samples were compared to conventional water extracts of the respective woods and analyzed by FTIR, sugar analysis and GC/MS to examine whether an accumulation of extractives was achieved. Results show that the method is applicable to wood meal and water extracts from wood, but the conditions have to be adjusted to the targeted extractives of the wood species. Furthermore, it was observed that it is suitable for extraction of saponins without the need to separate them from other extractives, but it is not an alternative to a comprehensive analysis of water extractable compounds. The presented method can be applied using wood species that contain sufficient amounts of surface-active substances to be “self-foaming”, but for a more versatile application, it needs to be further refined. However, if the application of additives is required in order to achieve sufficient foaming, it could be shown that the use of Tween20 was not successful, whereas SDS allowed several experiments. Nevertheless, a more effective way for complete separation and recovery of the tenside has to be developed, in particular, when the targeted extractives shall be used in subsequent biorefinery processes.