(46e) Effect of Temperature and Transport on the Yield and Composition of Pyrolysis-Derived Bio-Oil

Fast pyrolysis of biomass produces bio-oil, char, and non-condensable gases. Bio-oil is the desired product in the context of converting biomass to biofuel. In addition to the yield, the chemical composition of bio-oil is also important since it governs the stability and quality of bio-oil. However, both, the yield and the composition of bio-oil are significantly affected by operating conditions, particularly temperature and transport. The effect of temperature on bio-oil yield and composition is anticipated to be different under reaction-limited and transport-limited conditions. Attaining fundamental understanding of the effect of temperature and transport on bio-oil yield and composition is challenging due to the very limited knowledge of pyrolysis chemistry and the inter-relationship between chemistry and transport. In this work, we performed thin-film and powder pyrolysis experiments to investigate the thermal decomposition of glucose (a model biomass compound) under both reaction-controlled and transport-limited operating conditions. Pyrolysis experiments were conducted in a micropyrolyzer and products were analyzed using an inline GC-MS system. In thin-film experiments, less than 10 micron size thin-film of glucose was used and the effect of temperature on pyrolysis product distribution, especially on bio-oil yield and composition, was studied. Additionally, using the thin-film data, mechanistic insights into glucose decomposition were provided and a map of reaction pathways was proposed. Decomposition of glucose in the reaction-controlled regime is initiated by dehydration reactions. With increase in the temperature, anhydrosugars, viz. levoglucosan and levoglucosenone, apparently converted into furans (hydroxymethylfurfural) and light oxygenates (formic acid/methyl glyoxal), respectively, as ring opening and fragmentation reactions became more facile. Pyrans remained relatively stable. The effect of transport was investigated by performing pyrolysis experiments with different particle size distributions of glucose. The variation in the yield and composition of bio-oil with respect to temperature and particle size was also analyzed. In the case of glucose powder, levoglucosan yield increased significantly with particle size but decreased marginally with temperature, while hydroxymethylfurfural, furfural, formic acid, and methyl glyoxal yields monotonically increased with increase in temperature and particle size. Thin-film pyrolysis of glucose produced lower yield of bio-oil and higher yield of char than that of glucose powder. The current work enabled us to systematically examine the yields of individual compounds in bio-oil with respect to pyrolysis operating conditions (i.e. temperature and particle size). Additionally, the experimental product distribution of glucose pyrolysis under reaction-controlled and transport-controlled operating regimes would be utilized to validate the in house developed particle scale model, which takes into account pyrolysis reaction chemistry (as reaction kinetics) and transport to enable us understand the reaction-transport interplay during the pyrolysis process.