Fractionation of beech wood pyrolysis liquids with supercritical and gaseous CO ₂

Abstract The utilization of slow pyrolysis liquids occurring during charcoal production is limited due to their high content of acids (e.g., acetic acid) and high molecular weight substances. Supercritical carbon dioxide (scCO 2 ) extraction is an effective method to separate low and high molecular weight substances. Gaseous CO 2 is capable of removing acetic acid, which is present in significant quantities in slow pyrolysis liquids of wood. In this study, a two-step process was applied to upgrade beech wood slow pyrolysis liquid by removing high molecular weight substances and acids. First, high molecular weight substances and sugars were separated from the beech wood pyrolysis liquid using scCO 2 extraction. Then, the contents of acids and ketones in the scCO 2 pyrolysis liquid extract were reduced through treatment with gaseous CO 2 . This method led to the production of an extract with a low content of acids (1.2 wt. %) and a high content of monomeric phenolic compounds (33.7 wt. %). This upgraded extract has the potential to serve as a promising bio-based raw material for the production of phenolic resins, which are extensively utilized in the wood product industry.