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Subcritical Water Reactions of a Hardwood Derived Organosolv Lignin with Nitrogen, Hydrogen, Carbon Monoxide, and Carbon Dioxide Gases
- Hill Bembenic, Meredith A., Burgess Clifford, Caroline
- Energy & Fuels 2012 v.26 no.7 pp. 4540-4549
- biorefining, carbon dioxide, carbon monoxide, catalysts, flame ionization, fuels, gas chromatography-mass spectrometry, gases, hardwood, hydrogen, lignin, methanol, nitrogen, nuclear magnetic resonance spectroscopy, phenolic compounds, solid phase microextraction, solubility, temperature, thermal conductivity, value-added products
- Subcritical H₂O at 365 °C is considered for lignin conversion, because H₂O exhibits unusual properties at higher temperatures (i.e., decreased ion product and static dielectric constant), such that there is a high solubility for organic compounds. This high solubility for organic compounds is expected to apply to lignin for its conversion into high value transportation fuels, which may prove the effectiveness of integrated biorefineries. Experiments were conducted with hardwood derived Organosolv lignin, subcritical H₂O (defined here as H₂O at 365 °C and autogenous pressure), and various industrial gases (N₂, H₂, CO, and CO₂ at a cold pressure of 500 psi) for 30 min to determine both lignin’s potential to generate value-added products (e.g., monomer compounds and methanol) without the need for a catalyst and the roles (if any) of the H₂O and the gases in the reactions. The behavior of H₂O at temperature (365 °C) and pressure within this research is expected to be similar to the behavior of supercritical H₂O (374 °C and 3205 psi), without the need to maintain supercritical conditions. Different characterization techniques were used for the products collected including primarily gas chromatography with flame ionization detection and thermal conductivity detection (GC/FID-TCD) of the evolved gases, GC/MS analysis of the organic liquids, solid phase microextraction analysis of the recovered H₂O, and solid state ¹³C NMR analysis of the solid residues. The reactor pressure at temperature was shown to influence the outcome of products, and the highest conversions (≈54–62%) were obtained when adding gas. The collected solids from the N₂, H₂, and CO reactions appeared to be the most reacted (i.e., the most changed from the unreacted lignin) according to solid state ¹³C NMR analysis, and the widest variety of products (methoxy-substituted phenolic compounds) were also obtained when using CO, according to GC/MS analysis.