Bio-oil is a liquid fuel that can be produced from various lignocellulosic feedstocks via fast pyrolysis. It is a complex mixture comprised of hundreds of highly oxygenated organic compounds originating from lignin and carbohydrates and is recognized as a clean renewable bio-fuel, an attractive alternative to fossil fuels. It can be easily transported and used directly in boilers and modified turbines or upgraded/fractionated for drop in fuels or chemical production. Proper bio-oil characterization is important in optimizing the pyrolysis process, bio-oil upgrading and utilization, and its stabilization for long-term storage. With this in mind, research has been undertaken to develop better techniques to rapidly profile the composition of whole bio-oil samples, and an accelerated aging study performed to determine why bio-oil is unstable upon storage.
Pyrolysis-GC/MS and TLC-FID were used as tools to differentiate bio-oils of different lignocellulosic biomasses, and among thermal-cracking (upgrading) fractions. Results showed that birch bio-oil had high syringol derivatives compared to pine and barley straw bio-oils which had higher guaiacol and non-methoxy-phenolic compounds, respectively, compared with birch bio-oil. TLC-FID was successful in bio-oil differentiation, showing diagnostic chromatographic profile differences.
Direct infusion-ESI-ion trap MS and ESI-ion trap MS2 were successfully used in the analysis of forest-residue bio-oil and reference bio-oils from cellulose and hardwood lignin dissolved in methanol:water. NH4Cl can be used as a dopant to distinguish carbohydrate-derived products from other bio-oil components. NaOH and NaCl dopants resulted in the highest intensity peaks in negative ion mode and positive mode, respectively. Tandem MS, that is, ESI-Ion Trap MS2 was a successful tool for the confirmation of individual target ions such as levoglucosan and cellobiosan and for structural insight into lignin products.
In accelerated aging (at 80 °C for 1, 3 and 7 days) studies, the physical and chemical properties of bio-oil from ash wood (produced from a pilot-scale auger pyrolyzer) and birch wood (lab-scale pyrolyzer) were monitored in order to identify the factors responsible for bio-oil instability. Water content, viscosity, and decomposition temperature (by TGA) increased for both bio-oil samples with aging. Chemical analysis showed reduction in amount of most of the bio-oil components as aging progressed, typically for are olefins and aldehydes. The oils remained a single phase throughout until the 7th day
