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Pyrolysis bio-oil from biomass is a promising intermediate for producing transportation fuels and platform chemicals. However, its instability, often called aging, has been identified as a critical hurdle that prevents bio-oil from being commercialized. The objective of this research is to explore the bio-oil aging mechanism by an accelerated aging test of fractionated bio-oil produced from loblolly pine. When water soluble (WS), ether insoluble (EIS), and pyrolytic lignin (PL) fractions were aged separately, the increased molecular weight (Mw) was observed with increasing aging temperature and the presence of acids. WS and EIS fractions had high Mw brown solids formed after aging. Adjusting the pH of WS and EIS fractions from 2.5 to 7.0 significantly reduced the tendency of a Mw increase. Similar Mw rise was also observed on a PL fraction with an elevated temperature and acid addition. Formaldehyde was found to react with the PL fraction in the presence of any acid catalysts tested, i.e., 8-fold Mw increase in acetic acid environment, while other bio-oil aldehydes did not significantly promote lignin condensation. To better understand bio-oil stability, a potential bio-oil aging pattern was proposed, suggesting that bio-oil can be aged within or between its fractions.

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The objective of this paper is to investigate the biomass torrefaction effect on bio-oil stability by comparing the physicochemical and compositional properties of aged bio-oils. Two aging methods, accelerated aging (held at 80°C for 24 h) and long-term natural aging (12-month storage at 25°C), were employed to produce aged bio-oils for such comparison. The results indicate that bio-oils made from heat-treated wood had similar aging behavior in terms of increase of water content, acid content, molecular weight, and viscosity. The increase rate, however, was found to be different and dependent on the aging method. The accelerated method found parallel water and total acidity number (TAN) increments between raw and torrefaction bio-oils, while the natural aging method found torrefaction bio-oils, especially those made from heavily treated wood, had much slower water and acid accumulation than that of raw bio-oil. As a negative effect, both methods identified the viscosity of torrefaction bio-oils increased more significantly than that of raw bio-oil, while their molecular weights were unexpectedly lower. The correlation study showed that bio-oil viscosity is more tied to the content of bio-oil−water insoluble fraction rather than its average molecular weight. In addition, the characterization of aged bio-oils using NMR, GC/MS, and solvent fractionation indicated that torrefaction bio-oils had less compositional alternation after accelerated aging than the raw bio-oil. Also, they were more stable during the first 6 months of storage at room temperature. During the long-term storage, the raw bio-oil completely phase-separated after 6 months. However, two distinct torrefaction bio-oils (LP-280T and LP-330T) had enhanced phase stability, as a stable uniform oil phase without gum formation can be maintained during the entire 12-month storage.

A simple method is described combining solid phase microextraction (SPME) and infrared (IR) spectroscopy for determining volatile organic compounds (VOCs) in water. The solid phase consists of a small square of Parafilm (130 µm thick) that is used to selectively extract the VOCs from the water. Infrared transmission spectroscopy is used to detect the extracted VOCs directly in the Parafilm. Ten VOCs (e.g., benzene, chlorobenzene, toluene, chloroform, and p-chlorotoluene) are chosen to evaluate the SPME-IR procedure. Preliminary experiments show that detection limits are in the 66 ppb-1.3 ppm range for spiked solutions, and linear dynamic calibration ranges extend nearly to the water solubility limits for all VOCs examined. Although the formal equilibration times are determined to be 30-200 min for these VOCs, we demonstrate that reproducible extractions can also be performed at 30 min. The application of SPME-IR to a real water sample shows no significant matrix interferences. Finally, the potential for determining individual compounds in mixtures is investigated by extracting aromatic components from water samples contaminated with gasoline.