Hydro-liquefaction of rice stalk in supercritical ethanol with in situ generated hydrogen

- Al was studied during rice stalk ethanolysis to provide in situ H2via its oxidation.
- The in situ formed γ-Al2O3 could act as catalyst for ethanol reforming reactions.
- A higher energy recovery of 75% from rice stalk to bio-crude oil was achieved.
- Hydrogen involved reactions favored the formation of low-boiling-points compounds.

Bio-crude oil derived from sub- and supercritical liquefaction of lignocellulosic biomass has received considerable interests, but it cannot be directly used as a fuel because of its high oxygen content. In this work, a novel hydro-liquefaction process with the hydrogen generated in situ during the oxidation of aluminum by supercritical ethanol was investigated. X-ray diffraction analyses showed that η-, κ-, θ-, and α-Al2O3 mixtures were formed as a result of aluminum oxidation. Proposed reaction pathways revealed that ethanol reforming reactions occurred with additional hydrogen produced. A maximum energy recovery around 75% from feedstock to bio-crude oil was achieved with the addition of aluminum. Investigation on the chemical composition showed that liquefaction of rice stalk in the presence of aluminum decreased the yield of aldehyde, acid, and nitrogenous groups, and increased the yield of bicyclic phenolics, ketones, and hydrocarbons in the oil. In addition, the volatile fraction of the oil was increased. Overall, aluminum assisted liquefaction significant increase in the degree of deoxygenation, and may be a promising way to convert lignocellulosic into biofuels.

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