Comparative Study of Biomass Fast Pyrolysis and Direct Liquefaction for Bio-Oils Production: Products Yield and Characterizations
2014
Doassans-Carrère, Nicolas | Ferrasse, Jean-Henry | Boutin, Olivier | Mauviel, Guillain | Lédé, Jacques
The objective of this work is to compare two biomass-to-oil processes: fast pyrolysis and direct liquefaction, using the same biomass (beech sawdust). Fast pyrolysis is conducted in a cyclone reactor (wall temperature between 870 and 1040 K) and direct liquefaction in a 150-mL-autoclave reactor (bulk temperature between 420 and 600 K). Three fractions of pyro-oil are obtained from fast pyrolysis (heavy oil, light oil, and aerosol), whereas two fractions of liq-oil (heavy oil and water-soluble organics) are obtained from direct liquefaction. The comparison of both processes is based on the product yields and their characterization (ultimate analysis for solid and oils, oil–water content, gas and oil molecular composition, ¹H NMR for oils). For both processes, there is an optimal temperature at which the oil yield is maximum. Up to 62.6 wt % of pyro-oil are obtained at 970 K with the cyclone reactor (with 25.7 wt % of gas and 11.7 wt % of solid), whereas 47.0 wt % of liq-oil was obtained at 573 K with the batch-reactor (completed by 5.5 wt % of gas and 17.8 wt % of solid). Water content mainly explains the differences (mass yield and oxygen content) between oils from fast pyrolysis and direct liquefaction. Nevertheless, there are also some differences in organic composition: levoglucosane is a main component in pyro-oil, whereas levulinic acid is a main component in liq-oil. Finally, gas formed during direct liquefaction is mainly composed of CO₂ (more than 99 wt %), whereas gas from fast pyrolysis is a mixture of CO, CO₂, H₂, CH₄, and light hydrocarbons.
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