Development of Analytical Methods for Bio‑Oil Characterization

Biomass is a major renewable source of carbon that can partially replace the use of fossil-based raw materials for the production of chemicals and fuels. The building blocks in biomass can be made available through the fast pyrolysis process. The major product of the process is bio-oil, which can be used to produce value-added chemicals or upgraded into advanced fuels. The bio-oil is highly variable in its chemical and physical properties, partly owing to variations in the chemical composition of the biomass feedstocks and in the pyrolysis process conditions used to produce the bio-oil. Thus, knowledge of the detailed chemical composition of the bio-oil is vital to maximize its utilization. Direct analysis of the crude bio-oil using existing analytical tools, such as Gas Chromatography-Mass Spectrometry (GC-MS), does not provide sufficient information about its physical and chemical characteristics. Thus, improving or devising methods for better analysis of bio-oil is crucial for a detailed understanding of its physical and chemical properties. This thesis aims to improve methods for characterizing bio-oil by first fractionating the crude bio-oil, then analyzing the different fractions using state-of-the-art analytical tools. Ethyl acetate (EtOAc) and water (H2O) were used as solvents to fractionate the pine wood crude bio-oil into EtOAc-soluble and H2O-soluble fractions. The two fractions were then analyzed using various analytical methods. Karl Fischer and potentiometric titrators were employed to determine the water content and total acid number (TAN) of the bio-oil, respectively. A CHNS(O) organic elemental analyzer and an Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) were used to analyze the elemental composition of the bio-oil. Additionally, the various compounds in the bio-oil were analyzed using High-Performance Size-Exclusion Chromatography (HP-SEC), Carbon-13 Nuclear Magnetic Resonance (13C NMR), Phosphorus-31 (31P NMR), Gas Chromatography-Flame Ionization Detector (GC-FID), and GC-MS. Results of these analyses provided detailed information on the bio-oil properties. The results show that the bio-oil was successfully fractionated into H2O-soluble and EtOAc-soluble fractions, with minimal bio-oil loss and an almost even distribution between the two fractions: 43.4 and 50.9, respectively, on a wt.% water-free bio-oil basis. Unlike for the crude bio-oil, better separation of chromatographic peaks from HP-SEC, NMR, GC-FID, and GC-MS analyses was observed for the two fractions. Most of the aromatic and phenolic compounds in the bio-oil were found in the EtOAc-soluble fraction, while the carbohydrates, alcohols, and carbonyls were dominant in the H2O-soluble fraction. Carboxylic acids were almost evenly distributed between the two fractions, and aliphatic hydrocarbons were present in both fractions in significant levels, with the levels in the EtOAc-soluble fraction being twice as high as those in the H2O-soluble fraction.