1 research outputs found
Selective Synthesis of Phenolic Compounds from Alkali Lignin in a Mixture of Sub- and Supercritical Fluids: Catalysis by CO<sub>2</sub>
A successful selective liquefaction
of lignin has been demonstrated in the presence of a H<sub>2</sub>O–CO<sub>2</sub> mixture at 300 °C, yielding 40–50
wt % organic phenolic phase. The effect of the temperature at a constant
pressure and short residence time on the selectivity and yield of
phenolic products from the hydrothermal reforming of alkali lignin
in a mixture of sub- and supercritical fluids (H<sub>2</sub>O mixed
with CO<sub>2</sub> or N<sub>2</sub>) has been investigated. Dependent
upon the processing conditions, the lignin samples produced a homologous
series of phenols, such as guaiacol, homovanillic acid, quaiacyl carbonyls,
guaiacyl dimers, phenol, and cresol. Gas chromatography–mass
spectrometry (GC–MS), total organic carbon (TOC), and pyrolysis–GC–MS
(Py–GC–MS) were used for chemical analysis of the organic
liquid and solid phases. The results from GC–MS analysis of
the liquid organic phases demonstrated the trend of increasing the
amounts of major guaiacol products with the temperature. The thermal
carbon analysis (TCA) showed a significant increase of the readily
volatile organic carbon in the liquid fractions resulting from the
treatments at 300 and 400 °C at the expense of less volatile
organic carbon and recalcitrant pyrolyzed carbon. Evaluated for the
first time, a significant effect of CO<sub>2</sub> versus N<sub>2</sub> was demonstrated, providing both a higher yield of volatile products
and more selective synthesis of guaiacols