Evaluation of hydrodeoxygenation reactivity of pyrolysis bio-oil with various Ni-based catalysts for improvement of fuel properties

Abstract

Three Ni-based catalysts were prepared for hydrodeoxygenation (HDO) of bio-oil with three different support materials (active carbon, SBA-15 and Al-SBA-15) and their catalytic effects were tested with crude bio-oil at 300 °C and under 3 MPa H2 pressure for 60 min. After the HDO reaction, gas, liquid phase (light oil and heavy oil) and char were obtained as the primary products. Heavy oil was produced at a yield of 45.8-48.1 wt%, with no significant differences among the three catalysts. Mesoporous silica-supported catalysts (Ni/SBA-15 and Ni/Al-SBA-15) produced large amounts of char (16.3-18.6%), while Ni/C yielded 8.5 wt% char. Active carbon-supported catalysts (Ni/C) yielded more gas (27.7%) than the Ni/SBA-15 and Ni/Al-SBA-15 catalysts (6.6-8.9%), due to high surface area and low char deposition on the active carbon-supported catalysts. The HDO reaction led to improvement in the fuel properties of crude bio-oil. The water content, acidity, viscosity and oxygen content decreased via de-moisturization, i.e., dehydration, as well as dehydroxylation, resulting in an increase in heating value. The heavy oil obtained from HDO with Ni/Al-SBA-15 exhibited a low water content (9.3 wt%), while that of Ni/SBA-15 revealed a high HHV (22.8 MJ kg-1), energy efficiency (62.8%), and degree of deoxygenation (54.9%). A major factor of bio/oil instability is unstable oxygen-containing compounds, such as acetic acid, furfural, vanillin and levoglucosan, which were obviously reduced in the heavy oil in this study.