Production of phenolic-rich slow pyrolysis liquid extracts by supercritical carbon dioxide fractionation

To produce biogenic phenolic-rich liquids, which could be of great interest to the adhesive, wood preservation and coating industry, beech wood slow pyrolysis liquid (SPL) was extracted with supercritical CO2 (scCO2). To this end, a scCO2 extraction plant was extended with a separation unit with three separators. A stepwise depressurisation of the scCO2 in the separators enabled various fractions of the extracted SPL, with differing compositions, to be collected. During depressurisation, the density of the scCO2 (724 kg/m3-2 kg/m3) and, thus, the solubilities of the extracted substances in scCO2 were reduced in three separators. At a density of 261 kg/m3 in the second separator, extracts with a content of up to 41.1 wt.% GC-detectable monomeric phenolic substances were produced. At lower scCO2 densities in the subsequent separator, the proportion of better scCO2-soluble substances, such as acids, ketones and furans, increased in the extracts.