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Alkali lignin was subjected to depolymerization in subcritical water at 265 °C, 6.5 MPa for reaction times between 1–6 h in a batch reactor and in the presence of formic acid (FA) and Pd/C catalyst.

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Glucose, as a representative biomass model compound, was gasified under supercritical water conditions in a batch reactor. The influences of temperature in the subcritical and supercritical regimes of water, oxidant concentration, glucose concentration, and residence time were examined in relation to the yield and composition of the product gases and oils. The product gases were analyzed by packed-column gas chromatography, and the oils were extracted using solid-phase extraction and analyzed by coupled gas chromatography/mass spectrometry. The main gases produced were carbon dioxide, carbon monoxide, methane, and hydrogen, and there was significant production of oil and char. As the temperature was increased, there was an increase in the yield of gas; similarly, gas yield also increased as the concentration of the oxidant, hydrogen peroxide, was increased. The influence of residence time on the yield of products was small, with a slight decrease in oil yield and an increase in char yield. The oils were composed of a range of oxygenated compounds, including cyclopentanone, methoxybenzene, acetic acid, furfural, acetophenone, phenol, benzoic acid, and their alkylated derivatives. A reaction mechanism is proposed that describes a possible reaction route for the formation of the characteristic compounds found in the oils.

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