25th International Meeting on Organic Geochemistry IMOG 2011

P-004
Preliminary study of acid degradation of lignin using microwave
energy
Béatrice Allard, Sylvie Derenne
BIOEMCO CNRS/UPMC, Paris, France (corresponding author:beatrice.allard@upmc.fr)
Lignin is a heterogeneous and highly cross-linked
macromolecule particularly resistant to
biodegradation. This complex macromolecule is
composed of methoxylated phenol units linked by
ether and carbon bonds. It has long been known that
arylglycerol-�-O-aryl ether linkages are the most
abundant linkages in lignin. Acid-catalyzed
degradation generally cleaved these ether bonds
providing structural information on ether-linked units
in lignin.
Microwave irradiation has been successfully applied
in organic chemistry with reported more rapid
reactions, higher yields and improved product purities.
Microwaves are high frequency electromagnetic
waves which are strongly absorbed by polar
molecules. Absorption results in rapid and intensive
dielectric heating. Microwave systems using closed
vessels can operate at high temperature and pressure
and the temperature of solvent can be raised above
its theoretical boiling point.
In this preliminary study we explored the influence of
microwave irradiation on acid degradation of lignin.
Two types of lignin, namely hydrolytic (LHE) and
organosolv (LOS), were submitted to HCl 1N
degradation under microwave irradiation. The
investigated parameters were, the power of the
microwave source (100 and 300 W) and the nature of
the solvent (dioxane and 2-propanol). Due to their low
and high microwave absorbing capacities,
respectively, these solvents exhibit different efficiency
in the conversion of electromagnetic energy into heat
energy. Lignin monomeric and dimeric products
released under these conditions were analysed using
GC-MS.
The relative proportions of cinnamyl, guaiacyl and
syringyl units in the monomeric fraction depends on
the origin of the lignin. The composition of this fraction
does not appear to depend on the solvent and on the
delivered power. Acid degradation of LHE in dioxane
resulted in very low amounts of dimers whatever the
power used. On the other hand, an increase in the
relative proportions of dimers is observed when 2propanol
is used. These dimers consist mainly of
stilbene- and pinoresinol-related structures.
In contrast, acid degradation of LOS yielded high
amounts of dimers, even in dioxane. This indicates
the high level of ether linkages in this lignin. Stilbene-
and pinoreresinol-like substructures largely dominate
the dimer fraction.
This degradation technique could be a valuable
method for the analysis of lignin in complex sample
matrix such as soils and sediments.
GC-MS total ion chromatograms of products
recovered following acid degradation of LHE and LOS
in dioxane and 2-propanol.
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