The
understanding of lignin softening and pyrolysis is important
for developing lignocellulosic biorefinery in order to produce carbon
fibers, polymers additives, green aromatics, or biofuels. Protobind
lignin (produced by soda pulping of a wheat straw) was characterized
by thermogravimetry, calorimetry (for glass transition temperature
and heat of pyrolysis reactions), in situ
1H NMR (for the analysis of the mobility of protons upon lignin thermal
conversion), and solution-state 13C and 31P
NMR (determination of functional groups in lignin). In situ rheology reveals the real-time viscoelastic behavior of lignin as
a function of temperature. Upon heating, lignin undergoes softening,
through glass transition overlapped with depolymerization, and is
followed by the solidification of the softened material by cross-linking
reactions. The lignin residues were quenched within the rheometer
at the midpoint temperatures of softening and solidification regions
and were further analyzed by elemental analysis, GPC-UV of acetylated
THF soluble fractions, FTIR, solid 13C NMR, and laser desorption
ionization (LDI) combined with very high-resolution mass spectrometry
(HRMS). We present the first report on lignin biochars analysis by
LDI-HRMS. NMR and FTIR analyses provide the evolution of functional
moieties in lignin residues. 13C NMR, GPC-UV, and LDI FTICRMS
analyses depict the depolymerization mechanism combined with cross-linking
and demethoxylation reactions. An overall physical and chemical mechanism
for the thermal conversion of alkali lignin is proposed based on these
complementary analyses.
The real-time analysis of volatiles
(primary tar) produced during the fast pyrolysis of biomass in a microfluidized
bed reactor (MFBR) is achieved by online single photoionization mass
spectrometry (SPI-MS). The effect of biomass composition (Douglas
fir, oak, and miscanthus), particle shape and size (cylinder, lamella,
or powder), bed temperature, and fluidizing gas flow-rate on primary
tar composition is studied. Principle component analysis is conducted
on the major ions analyzed by SPI-MS to evidence the significant differences
between conditions. The variance in obtained SPI-MS spectra reveals
the important effect of biomass composition and temperature on volatiles
composition. The effect of particle size on volatiles composition
is clearly evidenced. Typical pyrolysis regimes are defined according
to specific markers which are key chemical compounds to characterize
biomass fast pyrolysis. SPI-MS combined with a MFBR is an interesting
tool to unravel the effects of biomass composition and of heat and
mass transfers on biomass fast pyrolysis processes.
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