Hydrothermal liquefaction of barks into bio-crude - Effects of species and ash content/composition

Liquefaction of barks of white pine, white spruce and white birch was performed in ethanol-water (50:50, v/v) co-solvents under the initial N ₂ pressure of 2.0 MPa at 300 C for 15 min. It was found that the liquefaction efficiency, in terms of bark conversion and bio-crude yield, varied significantly with bark species and ash content/composition. As far as the bark conversion was concerned, the order follows: white spruce bark (92%) > white birch bark (89%) > white pine bark (68%), which is also in good agreement with the ash content of the barks: white spruce bark (3.07%) > white birch bark (2.68%) > white pine bark (1.07%). Bio-crude yield reduced in the following order: white birch bark (67%) > white spruce bark (58%) ≫ white pine bark (36%). Effects of ash content on bark liquefaction were investigated by comparing the liquefaction efficiencies between crude bark and de-ashed bark. Deashing pre-treatment of barks in 0.5 M nitric acid efficiently decreased ash content in barks of white pine, white spruce and white birch form 1.07%, 3.07%, 2.68% to 0.67%, 0.33% and 0.32%, respectively. The de-ashing of bark decreased both bark conversion rate and bio-crude yield for all barks, suggesting that the ash of the bark play catalytic roles in the bark liquefaction, which was confirmed by the addition of K₂CO₃ and Ca(OH)₂ into de-ashed barks. The bark-derived bio-crude oils are aromatic/phenolic in nature with HHVs of 25-39 MJ/kg. The obtained bio-crude oils also have relatively lower molecular weights (M_n = 320-600 g/mol, M_w = 800-1700 g/mol, PDI = 2.2-2.9), which makes the bio-crude oils promising in the applications for either bio-fuel or as a phenol substitute in bio-phenolic resins. © 2013 Published by Elsevier Ltd.