Comparison of supercritical CO ₂, liquid CO ₂, and solvent extraction of chemicals from a commercial slow pyrolysis liquid of beech wood

Innovative extraction methods with supercritical CO2 and liquid CO2 have been employed to obtain value-added chemicals from a slow pyrolysis liquid. Sequential solvent extraction with hexane and acetone was carried out for comparison. Pyrolysis liquid was first adsorbed on silica (SiO2) with weight ratios SiO2:oil of 100:40 and 100:80. Pyrolysis liquid and extracts were mainly characterized by GCeMS/FID, elemental analysis, and water content. Results show that scCO2 extraction is mainly controlled by dissolution at the first 3 h during a 6-h extraction period and by combination of dissolution and diffusion at later extraction periods. Around 60e65% of the CO2 and hexane extracts could be identified by GC compared to 49% of the starting pyrolysis liquid. GC data confirmed that, CO2 extraction effectively enriched both non-aromatics and aromatic compounds. Hexane extracts contained lower contents of organic acids. Hexane enabled a complete extraction of aromatics. Chemical composition of extracts from scCO2 and liquid CO2 are very similar. Extraction with scCO2 and liquid CO2 proves to be an effective and innovative pre-treatment process for the production of chemicals from pyrolysis liquid.