Process
conditions used for solvent liquefaction of technical lignin
in mixtures of o-cresol and tetralin were explored
for optimizing the yield of phenolic monomers (PM) and liquid products.
The effects of solvent mixture, reaction temperature, solids loading,
and residence time were evaluated using a central composite response
surface statistical model. Six response variables were monitored to
evaluate the influence of the four factors. Liquid and solid yield
were tracked via mass balance. The yield of distillable products (distillate)
was determined using a thermogravimetric analyzer (TGA). Gas chromatography
(GC) was used to monitor the individual yields of phenol, guaiacol,
and 2,6-xylenol. Tetralin, which served as a hydrogen donor, was most
effective in enhancing liquid production, reducing solid products,
and increasing selectivity toward PM when present at less than 30
wt % of the solvent mixture. The interaction of solids loading and
solvent mixture further indicated o-cresol was more
effective than tetralin at solubilizing lignin and stabilizing the
liquid products. The hydrogen-donating capability of tetralin was
most beneficial at temperatures near 340 °C. Residence time was
not found to be a significant factor for experiments lasting up to
30 min. Distillate yields as high as 40 wt % from lignin on a dry,
ash-free basis indicated the ability of this process to generate low-boiling-point
PM suitable for recycle solvent. These results demonstrate this process
to be robust and effective in converting technical lignin to valuable
PM.
A method was developed
to simulate the rapid heating bio-oil fractions
will undergo if upgraded using conventional petroleum refining processes.
Bio-oil fractions were produced via fluidized bed fast pyrolysis of
southern yellow pine sawmill residue. Thermal processing of the bio-oil
fractions was evaluated at three temperatures (100, 200, and 300 °C)
and two heating times (60 and 120 s). Thermal stability was defined
as the increase in average relative molecular weight (RMW) of bio-oil
samples after thermal treatment. The effect of moisture content and
total acid number (TAN) on thermal stability was also investigated.
Changes in chemical structures were observed via Fourier transform
infrared spectroscopy (FTIR). Bio-oil fractions exhibited considerable
instability at temperatures above 100 °C with substantial increases
in average RMW for both 60 and 120 s heating times. The initial concentration
of acids, as measured by TAN and ion chromatography (IC), was found
to be the strongest predictor of thermal instability.
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