Process optimization and extraction of acids, syringols, guaiacols, phenols and ketones from beech wood slow pyrolysis liquids with supercritical carbon dioxide at different densities

In order to enhance the usability of beech wood slow pyrolysis liquid, an optimization of the extraction process with supercritical carbon dioxide (scCO₂) has been carried out. The main goals were to minimize losses and to stabilize the extraction parameters. Different designs of extraction vessels were used to accelerate the extraction and to facilitate the extraction of slow pyrolysis liquids on silica gel as well as in its liquid state. The slow pyrolysis liquid was extracted at different scCO₂ densities and temperatures. The densities were approx. 355 and 725 kg/m³ at 313.15 and 333.15 K respectively. A high density is the primary factor in increasing the extraction yield. An elevated temperature at high density level further increased the yields. The distribution of GC-MS detectable compounds of the extracts changed distinctly, resulting in an increase of syringols and a decrease of acids, ketones and furans during extraction.