Hydrothermal liquefaction of wheat straw in hot compressed water and subcritical water-alcohol mixtures

Hydrothermal liquefaction of lignocellulosic biomass (wheat straw) into bio-oil has been investigated under subcritical conditions (temperature up to 350 degrees C, pressure up to 200 bar) in water and water-alcohol mixtures using ethanol and isopropanol in a continuously operated tubular reactor. The effect of different reaction parameters such as temperature, pressure and water-alcohol ratio on the biomass conversion, cracking products yield and the higher heating value (HHV) of the received bio-oil was studied. The water-ethanol mixture was found to be a very reactive medium showing a complete biomass conversion and >30 wt% yield of high caloric oil (HCO). A maximum HHV of 28 MJ/kg for HCO was achieved. In addition, Ru (5 wt%) on H-Beta support was used as catalyst in a run with hydrogen in the feed showing deeper deoxygenation of reaction intermediates and highest HHV of the product oil (30 MJ/kg). This work demonstrated the usability of water-ethanol mixtures for an effective depolymerization of lignocellulosic biomass to bio-oils under subcritical reaction conditions with more than doubled HHV compared to the feedstock, in particular using a catalyst and the presence of hydrogen for further deoxygenation. (C) 2014 Elsevier B.V. All rights reserved.