Hydrothermal liquefaction of beech wood using a natural calcium borate mineral

This study reports the effects of a natural calcium borate mineral, colemanite, on the hydrothermal liquefaction of beech wood biomass. Hydrothermal liquefaction experiments were performed at 250, 300 and 350 °C with and without colemanite. The highest light bio-oil yield (11.1 wt%) and the highest heavy bio-oil yield (29.8 wt%) were obtained at 300 °C with colemanite. The total bio-oil yields were 22 wt% and 41 wt% ca. at 300 °C without and with colemanite, respectively. The highest heating values were obtained from the hydrothermal liquefaction of biomass using colemanite at 350 °C: 23.81 MJ/kg for LBO and 27.53 MJ/kg for HBO. Most of the identified compounds in the light bio-oils were phenols. The light bio-oil obtained without the catalyst at 300 °C contained furfurals. However, these compounds were not observed in the run with colemanite at the same temperature. The heavy bio-oils from the runs both without and with colemanite are composed of phenols, aldehydes, ketones, acids, and benzene derivatives. 4-Methyl-3-penten-2-one was the major compound in the heavy bio-oils produced in the catalytic runs.

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► Beech wood in the form of sawdust was converted into bio-oil via hydrothermal processing at 250, 300 and 350 °C.
► The catalytic performance of the colemanite was distinct at 300 and 350 °C.
► The use of colemanite increased the total bio-oil yields at all tested temperatures.
► The majority of the identified compounds in the light bio-oils were phenols.
► The formation of carbon spheres in bio-chars obtained from both the thermal run and the run with colemanite was observed at 350 °C.