Comparative Study of Biomass Fast Pyrolysis and Direct Liquefaction for Bio-Oils Production: Products Yield and Characterizations

摘要

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 CO_2 (more than 99 wt %), whereas gas from fast pyrolysis is a mixture of CO, CO_2, H_2, CH_4, and light hydrocarbons.