Liquefaction of wood in hot compressed water: Part 1 — Experimental results

• We studied the liquefaction of wood particles of different sizes in a batch reactor.
• Hydrothermal conditions always led to more liquid products than pyrolysis.
• At lower temperatures, the products of hydrolysis were mostly water-soluble.
• The obtained water-soluble products were stable products, not reacting any further.
• Small spherical particles were found on the surface of the charred wood.

The dissolution of wood in subcritical water in the context of a hydrothermal biomass gasification process is studied in order to provide insight into the effects of the operating parameters during the liquefaction step on the product distribution. Batch experiments were conducted at temperatures of 250–350 °C and pressures of 15–30 MPa and at various holding times. The product yields showed that the early product-forming reactions are very fast, and to go to completion within the heating stage for the experimental setup used. A hydrolysis experiment using the water-soluble products as feedstock confirmed the obtained water-soluble products to be final, as they did not undergo further hydrolysis to other products. The conversion of wood to liquid and gaseous products as well as the carbon content of the solid residue increased with increasing temperature. At lower temperatures, the reaction products of hydrolysis were mostly water-soluble, while with increasing temperature the methanol-soluble products were most abundant. The hexane-soluble products were negligible in almost all cases, and the gas products were predominantly composed of CO2. The experiments provide information about the yields of different products at different temperatures, their composition, and the effect of the operating conditions on the formation of primary and secondary char and on the limitations imposed on the primary product formation.

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