In this study, novel binary and ternary organosolv pretreatments are conducted and the resulting solid residue and lignin isolate are analyzed through compositional analysis, gas phase chromatography, NMR spectroscopy, FTIR and UV-Vis (photo)spectroscopies, and x-ray and neutron-scattering. Using a natural Populus variant, lignin was extracted from both milled wood (20 – 100 mesh) and chips of similar sizes (~10 mm x ~10 mm x 1.3 mm). The pretreatments took place in five parallel 100 mL Parr reactors for 30 min each at temperatures 120 °C, 150 °C, and 180 °C. Two different acid (H₂SO₄) concentrations (10 mM and 50 mM) were used, and solvent systems ranged from simple aqueous co-solvent combinations, such as ethanol-water (80 wt%), to ternary solutions at varying mass ratios (i.e. THF:GVL:H₂O @ 1:1:1, 2:1:1, 1:2:1, 2:2:1). In the ternary aqueous organosolv pretreatments, the lignin precipitated from pretreatment liquor exhibits characteristics that are not representative of corresponding binary pretreatments but rather distinct as if a different solvent completely is being implemented. Preliminary results have shown that an extracted lignin S/G ratio increases by ~180% (compared to cellulolytic enzyme lignin (CEL)) through a ternary-aqueous pretreatment with tetrahydrofuran and -valerolactone, whereas an ~50% and ~80% increase was observed in the binary-aqueous pretreatments with these solvents, respectively. Further analysis of the pretreatment solids and extracted lignin will provide insight into how other characteristics (i.e. lignin hydroxyl content, molecular weight, and cellulose interfibrillar spacing) respond to ternary organosolv pretreatments. The preliminary results alone from this study will impact biorefinery operations and biomaterial design – the S/G ratio of lignin is not dependent on severity conditions such as temperature or time, so solvent selection is the only means in which this ratio can be manipulated (assuming a constant biomass substrate). Ternary solvent systems could pose as a new tool used to produce technical lignin with desired characteristics, reducing the need for post-processing.

Hugh O'Neill

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