High-temperature extraction of lignocellulosic bio-crude by supercritical carbon dioxide

Supercritical carbon dioxide extraction was utilized for the fractionation of a pinewood derived hydrothermal liquefaction bio-crude. The experiments were performed at temperature 120 ºC and at pressure levels that correspond to CO2 density of 500, 615 and 730 kg/m3. Extraction yields of 34 to 49 % were achieved, which increased with increasing solvent density. Density was reduced for all extracts (2-10 %) while the H/C ratio increased when compared to the bio-crude. Low boiling point components such as ketones, 1-ring aromatic hydrocarbons and low molecular weight fatty acids were extracted preferentially (K-values up to 11). 1-ring phenols and benzenediols were enriched in the extracts as well (K-values 1-3). Heavy hydrocarbons and long chain fatty acids were extracted at the later stages of extraction when the lighter components were depleted.</p

Using Isopropanol as a Capping Agent in the Hydrothermal Liquefaction of Kraft Lignin in Near-Critical Water

In this study, Kraft lignin was depolymerised by hydrothermal liquefaction in near-critical water (290-335 degrees C, 250 bar) using Na2CO3 as an alkaline catalyst. Isopropanol was used as a co-solvent with the objective of investigating its capping effect and capability of reducing char formation. The resulting product, which was a mixture of an aqueous liquid, containing water-soluble organic compounds, and char, had a lower sulphur content than the Kraft lignin. Two-dimensional nuclear magnetic resonance studies of the organic precipitates of the aqueous phase and the char indicated that the major lignin bonds were broken. The high molar masses of the char and the water-soluble organics, nevertheless, indicate extensive repolymerisation of the organic constituents once they have been depolymerised from the lignin. With increasing temperature, the yield of char increased, although its molar mass decreased. The addition of isopropanol increased the yield of the water-soluble organic products and decreased the yield of the char as well as the molar masses of the products, which is indicative of a capping effect