Production of bio‐crude from forestry waste by hydro‐liquefaction in sub‐/super‐critical methanol

Hydro‐liquefaction of a woody biomass (birch powder) in sub‐/super‐critical methanol without and with catalysts was investigated with an autoclave reactor at temperatures of 473–673 K and an initial pressure of hydrogen varying from 2.0 to 10.0 MPa. The liquid products were separated into water soluble oil and heavy oil (as bio‐crude) by extraction with water and acetone. Without catalyst, the yields of heavy oil and water soluble oil were in the ranges of 2.4–25.5 wt % and 1.2–17.0 wt %, respectively, depending strongly on reaction temperature, reaction time, and initial pressure of hydrogen. The optimum temperature for the production of heavy oil and water soluble oil was found to be at around 623 K, whereas a longer residence time and a lower initial H₂ pressure were found to be favorite conditions for the oil production. Addition of a basic catalyst, such as NaOH, K₂CO₃, and Rb₂CO₃, could significantly promote biomass conversion and increase yields of oily products in the treatments at temperatures less than 573 K. The yield of heavy oil attained about 30 wt % for the liquefaction operation in the presence of 5 wt % Rb₂CO₃ at 573 K and 2 MPa of H₂ for 60 min. The obtained heavy oil products consisted of a high concentration of phenol derivatives, esters, and benzene derivatives, and they also contained a higher concentration of carbon, a much lower concentration of oxygen, and a significantly increased heating value (>30 MJ/kg) when compared with the raw woody biomass. © 2009 American Institute of Chemical Engineers AIChE J, 2009