HELSINGIN YLIOPISTO
HELSINGFORS UNIVERSITET
UNIVERSITY OF HELSINKI
MATEMAATTIS
MATEMAATTIS-LUONNONTIETEELLINEN
TIEDEKUNTA
MATEMATISK
MATEMATISK-NATURVETESKAPLIGA
FAKULTETEN
FACULTY OF SCIENCE
Maija Hakola, Marianna Kemell, Petro Lahtinen,
Markku Leskelä, Timo Repo, Tiina Riekkola,
Pauli Wrigstedt
LIBERATION OF CELLULOSE
FROM THE LIGNIN CAGE
INTRODUCTION
Catalytic and alkaline oxidations are novel and highly efficient
methods for the isolation of cellulose and lignin from
lignocellulosic biomasses. These methods loosen the wood
matrix and liberate cellulose with a high yield. Cellulose from
these pretreatment processes is more susceptible to enzymatic
hydrolysis than that obtained with the current state of art
pretreatment technique, steam explosion.
University of Helsinki
P.O.Box 55
FI-00014 University of Helsinki, Finland
Anne Kallionen, Matti Siika-aho,
Niklas von Weymarn
VTT – Technical Research Centre of Finland
P.O.Box 1000
FI-02044 VTT, Finland
During the oxidative pretreatment the wood chips loose their
macroscopic structure. The SEM images from the isolated
cellulose fraction show that chemical pulping and the catalytic
treatment reveal cellulose fibers in a rather similar way (Figure
1). On the other hand, after steam explosion the wood matrix is
still rather similar to non-treated spruce sample, although the
macro structure of wood is affected.
a
b
c
d
CATALYTIC AND ALKALINE
OXIDATION
Catalytic and alkaline oxidations are carried out in alkaline
water solution (0.25 M Na2CO3) at elevated temperature and
under oxygen pressure. In catalytic oxidation also
copper(II)phenanthroline catalyst is applied which makes the
use of lower reaction temperatures and shorter reaction times
possible. These pretreatments are significantly effective
methods to separate cellulose from lignocellulosic biomass.
After separating the cellulose fraction from the reaction
mixture, also lignin can be isolated for further processing e.g.
by treating the filtrate with a strong acid.
These methods can be considered as an environmentally benign
concepts based on in situ catalysts and pressurized air or
oxygen as the oxidant. Also various raw materials can be
applied, e.g. bagasse, spruce, pine, eucalyptus and birch wood,
leaves/needles and bark, and wheat straw.
Figure 1. The SEM images of (a) non-treated spruce, (b) steam
exploded spruce, (c) chemical spruce pulp and (d) the filtrated
solid fraction from a catalytic pretreatment reaction.
The authors thank Tekes – the Finnish Funding Agency for
Technology and Innovation and the Academy of Finland for
financial support.
Part of the research leading to these results has also received
funding from the European Community’s Seventh Framework
Programme FP7/2007-2013 under grant agreement no CP-IP
228589-2 AFORE.
Maija Hakola, Marianna Kemell, Petro Lahtinen,
Markku Leskelä, Timo Repo, Tiina Riekkola,
Pauli Wrigstedt
LIBERATION OF CELLULOSE
FROM THE LIGNIN CAGE
University of Helsinki
P.O.Box 55
FI-00014 University of Helsinki, Finland
Anne Kallionen, Matti Siika-aho,
Niklas von Weymarn
VTT – Technical Research Centre of Finland
P.O.Box 1000
FI-02044 VTT, Finland
HYDROLYSIS EXPERIMENTS
After 20 h catalytic oxidation at 120 °C approximately 50 % of
the total mass is solubilized and the filtrated homogeneous
solid material contains more than 76 % of the original total
carbohydrates and 95 % of the original glucose. Accordingly,
most of the mass loss originates from the dissolution of lignin
and wood extractives and the dissolution of cellulose is minor
(Figure 2). By contrast to catalytic oxidation, in steam explosion
hemicelluloses are totally solubilized whereas lignin mostly
remains in the solid fraction.
The catalytic and alkaline oxidation methods produce easily
hydrolyzable cellulose and the hydrolysis rate is notably high; a
95 % yield is achieved already after 24 hours with a rather low
enzyme loading (Figure 3). After four hours catalytic
pretreatment the matrix of spruce is loosened enough for the
effective enzymatic hydrolysis and extended pretreatment time
does not substantially improve the hydrolysability. No toxic
compounds are formed and the enzymatic hydrolysis can be
done in the pretreatment solution without filtering. Also due to
the high hydrolysability of the catalytically pretreated material,
the enzyme dosages can be decreased remarkably.
Figure 3. Enzymatic hydrolysis of catalytically pretreated spruce
and steam exploded spruce (SE spruce).
CONCLUSIONS
Catalytic and alkaline oxidations are highly selective methods
to isolate cellulose from lignocellulosic materials. The obtained
solid carbohydrate material contains 95 % of the original
glucose and is well susceptible to enzymatic hydrolysis. The
solubilized lignin can be also isolated and used as raw
material for the production of various chemicals.
REFERENCES
Figure 2. Carbohydrate and lignin contents of untreated spruce,
after catalytic pretreatment (Cat.Ox.) as a function of reaction
time and after steam explosion (SE Spruce).
1. Hakola, M., Kallioinen, A., Kemell, M., Lahtinen, P.,
Lankinen, E., Leskelä, M., Repo, T., Riekkola, T., Siika-aho, M.,
Uusitalo, J., Vuorela, S., von Weymarn, N., (2010): Liberation
of Cellulose from the Lignin Cage: A Catalytic Pretreatment
Method for the Production of Cellulosic Ethanol.
ChemSusChem, 3:10, p. 1142-1145.
HELSINGIN YLIOPISTO
HELSINGFORS UNIVERSITET
UNIVERSITY OF HELSINKI
MATEMAATTIS-LUONNONTIETEELLINEN TIEDEKUNTA
MATEMATISK-NATURVETENSKAPLIGA FAKULTETEN
FACULTY OF SCIENCE