Catalytic hydrodeoxygenation of crude bio-oil over an unsupported bimetallic dispersed catalyst in supercritical ethanol

Catalytic hydrodeoxygenation of the crude bio-oil derived from hydrothermal liquefaction of cornstalk using bimetallic ammonium nickel molybdate as a dispersed catalyst precursor at different temperatures (280-370 °C) was conducted under supercritical ethanol with initial 4 MPa H2, 60 min reaction time. Results showed that the yield of upgraded bio-oil was decreased from 26.7 to 16.3 wt.% with an increase in temperature. The water content and viscosity of upgraded bio-oil were decreased from 25.6 wt.% and 37.3 mm2/s to 1.6 wt.% and 8.8 mm2/s, respectively, and the heating value was increased from 32.1 to 38.3 MJ/kg. Compared with crude bio-oil, the upgraded bio-oil at 370 °C has minimum molar ratio of O/C (0.05) and the highest degree of deoxygenation (74.24%). FT-IR and GC-MS analysis found that the acids were almost removed via esterification; the phenols and esters decreased gradually, whereas hydrocarbons significantly increased and the functional groups and compositions were retuned. In addition, the esters produced at lower temperature were cracked into intermediates for further reactions to obtain the valuable hydrocarbons at higher temperature, for obtaining a potential transportation fuel after further refining.