Extraction of value-added chemicals from pyrolysis liquids with supercritical carbon dioxide

Fast pyrolysis is an effective way to convert sustainable biomass into pyrolysis liquids which could provide both energy and chemicals. Supercritical carbon dioxide (scCO2) has been used to extract valuable chemicals from both slow and fast pyrolysis liquids. Experiments were carried out in a 600 ml scCO2 extraction system under 15, 20 and 25 MPa at 60 °C. Properties and chemical compositions were analyzed for all starting pyrolysis liquids, extracts and residues by water determination, elemental analysis, higher heating value (HHV), gas chromatography coupled with mass spectrometry and flame ionization detector (GCMS/FID) and gel permeation chromatography (GPC). The extraction yield of water free slow pyrolysis was in the range of 40.42-51.75 wt%, while for fast pyrolysis liquids 7.34-12.02 wt% were obtained. Water content in the extracts could be reduced significantly. Extracts are mostly composed of volatile low molecular components while residues show much higher molecular weight compared with original pyrolysis liquids. GC detectable compounds for original pyrolysis liquids and extracts were similar but with different concentrations. Most of the compound groups could be enriched in the extracts such as acids, aldehydes, ketones, furans and aromatic compounds. scCO2 extraction proves to be an innovative and advanced method for the extraction of valuable chemicals from pyrolysis liquids.