Thermal\nReactivity of Bio-Oil Produced from Catalytic\nFast Pyrolysis of Biomass

Catalytic fast pyrolysis\n(CFP) of biomass is a versatile thermochemical\nprocess for producing a biogenic oil that can be further upgraded\nto sustainable transportation fuels, chemicals, and materials. CFP\noil exhibits reduced oxygen content and improved thermal stability\ncompared to noncatalytic fast pyrolysis oil. However, some level of\nreactive oxygenates remain in CFP oils, and reactions between these\nspecies can result in molecular weight growth and increased viscosity,\nleading to the potential for challenges during transportation, storage,\nand downstream processing. Previous research has provided considerable\ninsight into the reactivity of noncatalytic fast pyrolysis oils, but\nCFP oils have yet to be studied in a similar fashion. Consequently,\nthe degree of catalytic upgrading that is necessary to effectively\nstabilize CFP oils has yet to be established, and little is known\nabout the mechanistic details underlying the process. The current\nstudy addresses this knowledge gap by controlling the CFP reaction\nconditions to systematically vary the oxygen content of the resulting\noil. Accelerated thermal reactivity studies were then performed, and\nthe CFP oils were analyzed using gas chromatography–mass spectrometry\n(GC-MS), Fourier transform ion cyclotron mass spectrometry (FT-ICR\nMS), gel permeation chromatography (GPC), and viscometry to evaluate\nthe impact of heating on their physical and chemical properties. The\nresults revealed that short chain carbonyls, anhydrosugars, and lignin\nderivatives with conjugated vinyl groups likely play a role in the\nthermal reactivity of CFP oils. Additionally, experiments performed\nacross a wide variety of feedstocks revealed relatively low thermal\nreactivity for CFP oils with oxygen contents of <20 wt %. However,\nabove this threshold value, the thermal reactivity grew exponentially\nas a function of oxygen content, resulting in large increases in viscosity\nand molecular weight. These results serve to deepen the mechanistic\nunderstanding of CFP oil thermal reactivity and help inform the development\nof quality specifications for catalytic upgrading to effectively stabilize\nCFP oils.