The document discusses research on using novel ionic liquids for wood processing. Key findings include: 1) Wood can now be fibrillated using ionic liquids under mild conditions, removing pectins and small amounts of lignin and hemicellulose. This creates a material similar to thermo-mechanical pulp while maintaining fiber strength. 2) Ionic liquids allow for dissolution of all wood biopolymers and selective extraction of biopolymers from the wood matrix under different treatment conditions. 3) Researchers have discovered new "switchable" and "distillable" ionic liquids that can effectively process lignocellulose while being recyclable, improving sustainability over initial ionic liquids.

1. Future Biorefinery
Programme Report 2009–2011

3. Future Biorefinery
Programme Report 2009-2011

4. Content
5 Foreword
6 Introduction
12 Novel ionic liquids for wood processing
24 Hot water treatment of lignocellulose
48 Modification of xylan and galactoglucomannan
56 Hemicellulose and cellulose-based films and barriers
64 Co-polymerisation of three hydroxy acids
74 Dry-jet wet fiber spinning
– Creating a new cellulose regeneration infrastructure
84 Functional cellulose beads
96 Cellulose/polymer blends
110 Improving the extensibility and formability of paper and board
122 A novel process for the production of dialdehyde cellulose microfibers
130 Stimuli-responsive materials and their applications
142 Papermaking with hemi-lean pulp
152 Selected extractives in protection of wood products and human health
162 Immunomodulatory effects of bark and knot extract and compounds
168 Anti-carcinogenic and metabolic effects of wood-derived extracts
Copyright Forestcluster Ltd 2011. All rights reserved.
This publication includes materials protected under copyright law, the copyright for which is held by
Forestcluster Ltd or a third party. The materials appearing in publications may not be used for commercial
purposes. The contents of publications are the opinion of the writers and do not represent the official position
of Forestcluster Ltd. Forestcluster Ltd bears no responsibility for any possible damages arising from their use.
The original source must be mentioned when quoting from the materials.
ISBN 978-952-92-9718-4 (paperback)
ISBN 978-952-92-9719-1 (PDF)
4

5. Foreword
Wood is one of the most versatile biological raw materials that is available today in
large, renewable reserves around the world. Wood products have countless impor-
tant industrial applications, such as in design, furniture and construction. These ap-
plications have a bright future ahead. At the same time, chemical and mechanical
wood processing provides the basis for a growing range of globally significant fibre-
based tissue, paper and packaging applications and solutions. At the sharp end, ad-
vances in the use of the individual chemicals and polymers that make up wood are
creating the foundation for future biorefineries and helping change the shape of so-
ciety for the better.
Human use of wood reaches back thousands of years. Today’s escalating global pop-
ulation and limited natural resources, however, call for new ways of improving the ef-
ficiency of our use of this vital natural resource. This opens up significant opportuni-
ties for products based on renewable, non-food materials (‘non-food bio-products’).
In the face of current oil price and sustainability challenges, the bio-economy concept
is fast winning ground. Could an increasing share of our consumer products be pro-
duced using renewable raw materials, like wood, instead of non-renewables, like oil?
The forest-based industry sees this opportunity and believes that the industry will play
a decisive role in the development towards a bio-economy. With this goal in sight,
diversifying the product output of the primary wood refining process – pulping – is
a rational strategic starting point. The pulp mills of today are being redefined as the
biorefineries of tomorrow.
The change requires new competencies. This is happening on several levels. In Fin-
land, the foundation for this development is being laid by the joint research company
Forestcluster Ltd (www.forestcluster.fi) and especially its Future Biorefinery strategic
area (FuBio). FuBio is a 5-year undertaking with a volume of around EUR 50 million.
This programme report covers most of the main results of the first two years of FuBio,
i.e. the ‘FuBio Joint Research 1’ research programme. Most of the themes of Fu-
Bio Joint Research 1 are now being carried forward either in the continuation of
FuBio or as company-lead development projects.
Mikael Hannus
Stora Enso Oyj
Chairperson of the FuBio Joint Research 1
Research Programme Management Group
5

6. Introduction
1. Background gramme, FuBio Joint Research 1 (March
The forest-based industry is a pillar of 2009–May 2011), with a total volume
the global bio-economy. In Europe, the of about EUR 19 million financed by the
industry, including forestry, is estimat- owners of Forestcluster and the Finnish
ed to have employed approximately 4.8 Funding Agency for Technology and Inno-
million persons in 2009 (CEPI and CEI- vation (Tekes). The owners of Forestclus-
BOIS). The Public-Private Partnership For- ter include (August 2011) nine compa-
estcluster Ltd was established in 2007 to nies (Andritz, Kemira, Metso, Metsä-Bot-
accelerate the development of the Euro- nia, Metsäliitto Cooperative, M-Real, Myl-
pean knowledge-based bio-economy from lykoski, Stora Enso and UPM-Kymmene),
a Finnish perspective. The initial strategy two research organisations (the Finnish
process of Forestcluster identified three Forest Research Institute (Metla) and VTT
focus areas for R&D: ‘Forward Custom- Technical Research Centre of Finland), as
er Solutions’ strives to develop new busi- well as eight universities (Aalto Universi-
ness models and market ideas for exist- ty, Lappeenranta University of Technolo-
ing products of the pulp and paper indus- gy, University of Eastern Finland, Univer-
try. The focus of ‘Intelligent, Resource- sity of Helsinki, University of Jyväskylä,
Efficient Production Technologies’ is on University of Oulu, Tampere University of
improving the resource efficiency of pulp Technology and Åbo Akademi University).
and paper mills and modifying them for
the production of novel bio-products. ‘Fu-
ture Biorefinery’, or FuBio, is developing
the scientific and technological basis for
2. Structure
transitioning from mills’ existing markets and participants
to markets where wood-based products
currently have no or only a minimal pres- FuBio Joint Research 1 comprised five
ence. If successful, such new bio-prod- Themes (see Figure 2). A sixth Theme
ucts would replace existing petroleum- (T4) was also planned, but it did not be-
based products and thus bring consider- gin during FuBio Joint Research 1.
able sustainability benefits. FuBio is also The programme partners included the
developing pioneering processes for the owners of Forestcluster Ltd. Additional re-
fractionation of wood, thus generating en- search was also subcontracted to external
tirely new bio-materials for further pro- partners, primarily Danisco Sweeteners,
cessing and a range of new high-poten- Finex, GloCell, Pharmatest Services (Or-
tial applications. thotopix), Pöyry Management Consulting,
The Forestcluster strategy process Separation Research, University of Tam-
was continued, and in terms of FuBio, po- pere and University of Turku. Leading in-
tential target markets for the diversifica- ternational expertise was also included
tion process were identified. The outcome in the programme. Key collaborators in-
is summarised in Figure 1. cluded Karlsruhe Institute of Technolo-
FuBio is planned to run for 5 years. gy (Germany), RWTH Aachen (Germany)
It was initiated by a 2-year research pro- and FPInnovations (Canada).
6

7. Figure 1. The six target markets of FuBio.
Figure 2. Structure of the FuBio Joint Research 1 research programme
(March 2009-May 2011).
7

8. 3. Management 4. Specific research areas
FuBio Joint Research 1 was managed by The specific research areas of FuBio Joint
a Management Group (MG). The execu- Research 1 are on the following pages
tion of the programme was headed by portrayed as five concepts. The yellow
the Programme Manager together with boxes illustrate existing industrial oper-
theme-specific leaders and tutors. The ations, the green boxes are the process-
MG had the following members: es that FuBio Joint Research 1 aims to in-
• Mikael Hannus, Stora Enso, tegrate into the existing operations. The
Chairman of the MG fourth box could also be ‘Paper produc-
• Lars Gädda, Forestcluster tion’ (now ‘Board production’).
• Eeva Jernström, UPM-Kymmene
• Annaleena Kokko, VTT Technical
Research Centre of Finland, Theme
3 Leader
5. Future plans
• Jukka Leppälahti, Tekes Two new research programmes were
• Paterson McKeough, Andritz launched on June 1, 2011. The first of
• Jussi Mäntyniemi, Metso these, FuBio Joint Research 2, is pursu-
• Klaus Niemelä, VTT Technical ing four of the target markets outlined
Research Centre of Finland, Theme in Figure 1, namely ‘Structural compos-
1 Leader ites’, ‘Novel packaging and filtration ma-
• Erkki Peltonen, Myllykoski terials’, ‘Polymers, resins and chemicals’,
• Ismo Reilama, Metsä-Botnia and ‘Health-promoting products’. The
• Kari Saari, Kemira ‘Regenerated fibre and chemicals’ target
• Pekka Saranpää, Finnish Forest market is the focus of the second new
Research Institute (Metla), Theme 5 research programme, ‘FuBio Products
Leader from dissolved cellulose’. The sixth target
• Anna Suurnäkki, VTT Technical market, ‘Wood preservatives and glues’,
Research Centre of Finland, Theme is currently in the planning stage (as of
2 Leader September 2011).
• Niklas von Weymarn, VTT Technical This report summarises the results
Research Centre of Finland, of the first two years of research activity
Programme Manager within FuBio. The structure of the report
mirrors the structure of the research pro-
The tutors were Herbert Sixta, Aalto gramme itself.
University (Theme 1), Lars Gädda
(Theme 2), Ali Harlin, VTT Technical Re-
search Centre of Finland and Maija Ten-
kanen, University of Helsinki (Theme 3),
as well as Tiina Nakari-Setälä, VTT Tech-
nical Research Centre of Finland and
Bjarne Holmbom, Åbo Akademi Univer-
sity (Theme 5).
8

9. Figure 3. The concept comprises the separation of either lignin or organic acids
from black liquor and the consequent upgrading of the said components to novel
bio-products. The acids could alternatively be produced directly from wood-
based sugars (‘sugar platform’).
Water
treatment
Additives Additives
Wood Wood Pulp Board Converting
harvest handling production production & printing
Residues Bark
Knotwood Chemical Lignin sep.
recovery Moulding Composites
Acid sep.
Energy Fibre
By-products Upgrading Additives
Wood-based Fermen-
sugar tation
Chemicals
Resins
Polymers
Figure 4. The concept has two goals: i) to develop novel bio-based materials to
replace current petroleum-based materials (paper chemicals and coating), and
ii) to study ways to add mouldability to the fibre web.
Water
treatment New paper New bio-
chemicals barriers
Wood Wood Pulp Board Converting
harvest handling production production & printing
Residues Bark
Knotwood Chemical
recovery Fibre modification for
improved mouldability
Energy
By-products
9

10. Figure 5. The concept comprises the extraction of compounds from wood and
using them in different applications (from health promotion to the protection
of wood products).
Water
treatment
Additives Additives
Wood Wood Pulp Board Converting
harvest handling production production & printing
Residues Bark
Knotwood Chemical
recovery
Tall oil Energy
GGM By-products
Product Health products,
protection (food and medicine;
(high volume) high value)
Figure 6. The concept comprises the development of new
processes for cellulose dissolution and regeneration.
Water
treatment
Thermally formed
Wood Wood Pulp Dissolution & products
harvest handling production Converting Cellulose beads
Regeneration
(Textiles)
(Nonwovens)
Residues Bark
Knotwood Chemical
Derivatisation
recovery
Energy
Chemicals
By-products
10

11. Figure 7. The concept comprises the development of completely new
processes for the fractionation of wood, thus generating novel materials for
further upgrading. The processes are based on hot water treatment and/or
novel ionic liquids.
Hemicelluloses:
• Barriers
• Films
Wood/ New Cellulose/fibre
saw dust fraction. (incl. Theme 2 applications)
Lignin
On behalf of Forestcluster Ltd and myself, I extend my sincere gratitude to all partici-
pants from industry and the research community for their active efforts in getting this
programme successfully off the ground. Together, we have taken the first key step to-
wards shaping the biorefineries of the future.
Niklas von Weymarn
VTT Technical Research Centre of Finland
Programme Manager, FuBio Joint
Research 1 Research Programme
11

12. Novel ionic liquids for
wood processing
Editor Alistair W. T. King
Partners: Key researchers:
Aalto University Herbert Sixta, Michael Hummel, Lauri K. J. Hauru,
Anne Michud
Åbo Akademi University Jyri-Pekka Mikkola, Päivi Mäki-Arvela, Pasi Virtanen,
Ikenna Anugwom
University of Helsinki Ilkka Kilpeläinen, Alistair W. T. King, Pirkko Karhunen,
Jorma Matikainen, Arno Parviainen, Timo Leskinen,
Paula Järvi
12

13. Abstract
New concepts in wood processing with novel ionic liquids, as potentially environmentally benign
reaction media, are presented. These include a refinement in our understanding about the ef-
fects that these unique solvators have on woody material and examples of the new structures
under development, which offer increased process sustainability over the initial generations.
In addition to selective dissolution of purified wood biopolymers, wood can now be fibrillated
using ionic liquids, under mild treatment conditions. This can be achieved without chemical mod-
ification of the material or extracts. The process is accompanied by removal of pectins, including
small amounts of mobile lignin and hemicelluloses, which are extracted from the middle lamella.
As lignin is not extracted completely and the fibres maintain their strength, the new material is,
in a way, similar to thermo-mechanical pulp (TMP). Surprisingly from a processing point of view,
it seems that fibrillation of wood does not require chemical fragmentation of lignin and can be
achieved under relatively mild conditions using ionic liquids. In consideration to wood fraction-
ation, different ionic liquids and treatment conditions are also available that will allow for dissolu-
tion of all wood biopolymers, including wood itself and selective extraction of wood biopolymers
from the wood matrix. Systematic screening and literature review has resulted in our improved
understanding of the factors that affect these effects and phenomena.
Ionic liquid recyclability has been foremost on our minds during this research period. The re-
sult is the discovery that new classes of ‘switchable’ and ‘distillable’ ionic liquids can effective-
ly lignocellulose. This takes advantage of the electron density afforded by superbases such as
1,8 - diazabicycloundec - 7 - ene (DBU) and 1,1,3,3 - tetramethylguanidine (TMG) as bulk
chemicals. Whereas previous structures have low recyclabilities, the new structures can be con-
verted from their ‘ionic’ form into neutral species, which allows for distillation of the materials in
high yields and recovery. This increases the overall sustainability of the prospective processes,
beyond what was capable before and offers significant energy savings.
Overall we have developed understanding that makes us highly competitive, on the interna-
tional scale in the area of bioprocessing with ionic liquids.
13

14. 1. Background 2. Objectives
The main application objectives of this
Ionic liquid bioprocess work was in the development of process-
sustainability es that utilise ionic liquids:
Wood is regarded as a leading sustainable • Assess and develop the potential
resource, to replace fossil fuels. However, for fractionation of wood into its
challenges will exist in the incorporation components using ionic liquids as
of wood-based feedstocks and process- solvating media
es into, traditionally, fossil-based value • Assess and develop the potential of
chains. Therefore, new ‘tuneable’ meth- ionic liquids in the dissolution and
ods offering more varied and improved regeneration of cellulose-rich pulp
selectivities, for the fractionation and pro- to novel materials; in particular,
cessing of wood biopolymers, into materi- develop new fibre-spinning
als, chemicals and energy are necessitat- processes, based on the Lyocell
ed. The reported high efficiency in the dis- process, by dissolution of pulp
solution of cellulose by ionic liquids (ILs), into ionic liquids and subsequent
has thus afforded new processing oppor- regeneration by air-gap spinning
tunities, whereby wood itself can be ef- into water
fectively solvated and processed accord- • Develop recyclable and low toxicity
ingly. In addition, room temperature ion- ionic liquid systems to maintain
ic liquids (RTILs), such as 1-ethyl-3-me- sustainability of processing
thylimidazolium acetate ([Emim][OAc],
m.p. -45°C), offer so effective cellulose On the whole, the objectives called for
solvation capabilities that they are now both assessments of existing structures
considered to be industrially viable me- for their efficiency in the fractionation of
dia for existing and novel cellulose pro- woody material and also for the develop-
cessing applications. An important ex- ment of new ionic liquids. This was nec-
ample is in the replacement of N-methyl- essary due to the poor stability and re-
morpholine-N-oxide hydrate (NMMO·H2O) cyclability of existing structures. A gen-
in a ‘Lyocell’ process, circumventing haz- eral pre-requisite for new ionic liquids
ardous thermal stability issues. [Emim] for the above application was that they
[OAc] has been so successful in cellulose be effective at dissolving both lignin and
solvation that BASF is now producing it wood polysaccharides such as cellulose or
on a ton-scale. Publications are appear- hemicelluloses.
ing, however, that highlights the insta-
bility of [Emim][OAc], in the presence of
lignocellulosic solutes. Basic ILs such as
[Emim][OAc] are also known to have re-
3. Research approach
duced thermal stabilities. This effectively Due to the infancy of ionic liquids re-
prevents the recovery of the IL on an in- search and the structural complexity of
dustrial-scale by distillation. As such, oth- ionic liquids, in comparison to molecular
er methods of recycling or more recycla- solvents, this work package demanded a
ble structures/systems are sought. more academic approach. This was con-
ducted alongside assessment ionic liquids
for their efficacy for the processing of lig-
nocellulosics. Three main areas were fo-
cused on (Figure 1).
14

15. Figure 1. Strategy for academic development of novel and
effective ionic liquids.
The research strategy outlined in used to predict physiochemical
Figure 1 can be summarised as follows: properties of structures.
• The starting point was the synthesis • Through this understanding of
of existing imidazolium-based ionic effects, parameters and the
liquids generation of new structures,
• The next step was to further our it was possible to develop
understanding of different effects hypotheses about which structural
and phenomena that occur when features would allow for more
lignocellulosics are contacted advantageous effects (e.g. lower
with ionic liquids (e.g. dissolution viscosities or more recyclable
capabilities, fractionation efficiency, structures)
fibrillation, chemical reaction). • New series of structures were
• Develop quantitative structure synthesised with an improved
property relationships in regard understanding of physical properties
to the physical properties of and recycling issues, in particular
the ionic liquids (e.g. thermal
stabilities) and the observed Although the above strategy requires
effects and phenomena (mainly a large set of structures and data to work
biopolymer solubilities). This most efficiently, thorough literature re-
was achieved through a process view and the development of our own da-
of parameterization of effective ta resulted in the development of highly
and non-effective ionic liquids. novel structures and associated intellec-
Computational methods were also tual property.
15

16. 4. Results A new concept, called wood chip ‘fi-
brillation’, was identified for ionic liquids,
4.1 Initial ionic liquids synthesis & which are known to be highly effective
testing at solvating cellulose. Despite the abili-
A thorough literature review was per- ty of ionic liquids to dissolve wood itself,
formed looking at the solubility of ligno- under more harsh dissolution conditions,
cellulosics in current ionic liquids. This these ionic liquids were capable of reduc-
combined with additional screening of a ing wood chips into fibres. The products
range of structures (Table 1) allowed us were similar to TMP (Figure 2) and fibril-
to identify potential opportunities with re- lation was achieved under mild treatment
gard to biopolymer solubilities. conditions (110°C, 3 d, without stirring).
Table 1. Efficiency of cellulose dissolution, lignin dissolution,
and wood fibrillation for in-house ionic liquid structures.
a a a
Ionic Liquid Preparation Cellulose Lignin Fibrillation
[mmim][Me2PO4] Synthesized Dissolves +++++ +++ (Softwood)
[amim]Cl Synthesized Dissolves +++ ++ (gels) (Softwood)
[amim]Br Synthesized Dissolves - (Softwood)
[amim][Me2PO4] Synthesized Dissolves +++++ +++ (Softwood)
[emim]Cl Merck Dissolves - (Softwood)
[emim][Me2PO4] Synthesized Dissolves +++++ +++++ (Softwood)
[emim][Et2PO4] Synthesized Dissolves +++++ ++++ (Softwood)
[emim][SCN] Merck Degrades ++++ - (Softwood)
[emim][MeHPO3] Synthesized Dissolves +++++ +++++ (Softwoods)
[emim][EtHPO3] Synthesized Dissolves +++++ +++ (Softwood)
[emim][HSO4] Merck Fragments - (Softwood)
[emim][MeSO4] Iolitec Fragments +++++ - (Softwood)
[emim][OTs] Iolitec Fragments +++++ - (Softwood)
[emim][OAc] Iolitec Dissolves ++++ (Hard and Softwoods)
[emim][Me2PO3] Synthesized Dissolves +++++ - (Softwood)
[emim][OCOCF3] Iolitec - - (Softwood)
[emim][NTf2] Merck - - - (Softwood)
[eeim][Et2PO4] Synthesized Dissolves ++ (Softwood)
[mmmim][Me2PO4] Synthesized ++ (Softwood)
[emmim]Cl Synthesized - (Softwood)
[emmim][Et2PO4] Synthesized +++ (Softwood)
[prmim][Me2PO4] Synthesized +++ (Softwood)
[iprmim][Pri2PO4] Synthesized + (Softwood)
[bmim][Me2PO4] Synthesized ++ (Softwood)
[bmim][HSO4] Merck Fragments - (Softwood)
[omim][OctSO4] Merck - - (Softwood)
[hemim]Cl Iolitec - - (Softwood)
[Hmim]Cl BASF - - (Softwood)
[P4444]Cl Iolitec - ++++ - (Softwood)
[P14444]Cl Iolitec - ++++ - (Softwood)
[P14666]Cl Iolitec - ++++ - (Softwood)
[P4442][Et2PO4] Iolitec ++++ - (Softwood)
[P4441][OTs] Iolitec - (Softwood)
[mPyr][MeHPO3] Synthesized (impure) Degrades ++ (Softwood)
[DBUH][OCOC2H5] Synthesized Dissolves
a efficiency of dissolution or fibrillation: +++++ (strong effect), - (no effect)
16

17. Figure 2. SEM of Norway spruce chip ‘fibrillated’ from
1-ethyl-3-methylimidazolium dimethylphosphate ([emim]
[Me2PO4]) at 110°C for 3 d.
Of these structures, [Emim][Me2PO4] 4.2 Ionic liquid parameterization
was found to be most effective for soft- While basic imidazolium-based ionic liq-
woods such as spruce and pine. [Emim] uids (e.g. [Emim][OAc]) are known to be
[OAc] was found to be highly effective for highly effective at dissolving cellulose,
both softwoods and hardwoods such as several reports have appeared, including
birch and aspen. Wood chips were about those from FuBio, indicating that they are
2 * 2 * 0.25 cm and pre-dried by solvent capable of reacting with various lignocel-
exchange with acetone. Sugar analysis lulosic functionalities. To learn more about
and NMR analysis of the chips and resid- the various parameters that affect both
ual ionic liquid showed that mainly pec- dissolution and reactivity, two methods of
tins were removed from the middle lamel- parameterisation were chosen:
la. Small quantities of lignin and hemicel- • Kamlet-Taft solvatochromic
luloses were also removed but essential- parameterisation; prediction of
ly the fibrillation occurred, without bulk α (H-bond acidity), β (H-bond
fragmentation of removal of cellulose, basicity) and π* (dipolarity/
hemicellulose or lignin. 1-Ethyl-3-methy- polarisability). This is the most
limidazolium methylphosphonate ([Emim] comprehensive parameterization
[MeHPO3]) was also found to be very ef- strategy to date for ionic liquids
fective at fibrillating softwoods but it be- and should allow for quantitative
came apparent that the ionic liquid was understanding of how the ionic
reacting with the fibres. No reaction or liquids structural features effect
complexation with fibres was observed solvation through the development
with [Emim][Me2PO4] or [Emim][OAc]. of linear solvation energy
The discovery resulted in the filing of a relationships. An initial manuscript
patent application. is ready for submission, which more
17

18. Figure 3. The difference β-α (aggregate basicity - essentially basicity of the
anion minus the acidity of cation) plotted against β (basicity); full symbols
are effective cellulose solvents, empty symbols non-solvents, half-empty poor
solvents; LiCl/DMAc data shown in the range 20–100°C.
comprehensively demonstrates the stability. From a process of
effect of the ionic liquids H-bond measuring the thermal stability
basicity, as a requirement for of imidazolium-based ionic liquids
dissolution. This was applied to and comparison with the proton
existing ionic liquids, novel TMG- affinities for those anions, it was
based ionic liquids and traditional possible to see an approximate
molecular solvents such as LiCl/ correlation (Figure 4). It is also
DMAc and NMMO•H2O (Figure 3). known the main mechanism of
Reduction in basicity was also decomposition of basic imidazolium-
observed to be the major factor in based ionic liquids is through
the regeneration of pulp from ionic nucleophilic attack of the anion on
liquid, upon addition of water. the imidazolium alpha-positions.
This indicates that as the ability of
• Ab initio proton affinity ionic liquids to dissolve cellulose
computational calculations increases (increasing basicity),
on anions and neutral bases, their thermal stability decreases
as a measure of the enthalpy (increasing nucleophilicity). This is
of deprotonation in the gas- consistent with the fact that [emim]
phase (i.e. measure of basicity [OAc], as a basic ionic liquid, is now
or nucleophilicity); Allows for known to react with lignocellulosics.
prediction of relative inherent This also has additional implications
basicity, acidity and nucleophilicity for the recyclability sustainability
of ILs as properties predicting of processes using imidazolium-
cellulose solubility and thermal based ionic liquids as many of
18

19. Figure 4. The correlation of Figure 5. Molten acid-base conjugates,
proton affinities vs decomposition capable of dissolving cellulose,
temperatures. as the acetate salts.
them decompose under the (TMG) with proton affinities of -253.9,
practical processing conditions -244.9 and -248.9 kcal mol-1 respective-
that available for distillation of ly, all dissolve cellulose, in combination
these materials. Under some with acetic acid. When the proton affin-
circumstances this is not such an ity values of neutral bases rise above ~
issue, e.g. cellulose dissolution/ -240 kcal mol-1 the resulting ionic liquids
regeneration but for more complex formed, by stoichiometric combination
systems, including those involving with acetic or propionic acid, no longer
wood, sustainabilities can drop dissolve cellulose. Moreover, as the acid-
quickly under the wrong processing ity of the cation is only just higher than
conditions. the acidity of carboxylic acids, in the neat
ionic liquid, it was possible to distil some
4.3 ‘Distillable’ ionicliquids of the mixtures (Figure 6). Essentially by
The calculation of proton affinities for heating the sample we could dissociate
neutral bases also had the benifit of al- the conjugated acid and base, thus af-
lowing us to predict which combination of fording a vapour pressure to the system
acids and bases would be effective at dis- and allowing for distillation and recom-
solving cellulose (Figure 5). bination.
For example, [Emim][OAc] can be We recently reported a new class
thought of a combination of acetic ac- of ILs that both dissolved cellulose and
id and the 1-ethyl-3-methylimidazol- were distillable at much lower tempera-
2-ylidene carbene ([Emim]:), as the C2- tures and higher pressures than for imid-
H is the most acidic position on the im- azolium-based ILs, such as [Emim][OAc].
idazolium ring. The proton affinity for In our hands we achieved > 99% recov-
this neutral species is -262.9 kcal mol-1 ery and 99% purity of distillate which is a
at the MP2/6-311+G(d,p)//MP2/6- considerable improvement over the distill-
311+G(d,p) level of ab initio theory. Im- ability of archetypical structures (imidazo-
ino-tris(dimethylamino)phosphorane liums). Undoubtedly the electron density
(PhosP1), 1,8-diazabicycloundec-7-ene provided by the more basic neutral bas-
(DBU) and 1,1,3,3-tetramethylguanidine es allowed for formation of the ionic liq-
19

20. Figure 6. Distillation and X-ray crystallographic structure of [TMGH][CO2Et].
uids in the first place, but also preserva- ble ionic liquids. The general structures
tion of that basicity, in the media, which of which were protonated DBU cations
makes them effective solvators of cellu- with carbonate or sulphite anions. These
lose. A patent application was filed. materials were observed to dissociate
again upon heating to higher tempera-
tures or upon bubbling inert gas through
4.4. ‘Switchable’ ionic liquids the mixtures. In effect the solvents could
(SILs) be ‘switched’ between ionic and neutral
As in the case of the distillable ionic liq- species when perturbed. This has impor-
uids, superbases such as DBU allowed for tant implications concerning the proces-
the conjugation of alcohols and gases, sibility and recyclability of the system
such as carbon or sulphur dioxide. When (Figure 7).
these materials were combined in stoi- Several combinations of alcohols and
chiometric quantities, they formed sta- gases with DBU were tested and wood
Figure 7. Synthesis, use and regeneration of novel
switchable ionic liquids.
20

21. Figure 8. Birch wood chip treated with different switchable ionic liquids. (A)
Treated with (SIL #1) for 5 days at 100°C, (B) treated with (SIL #2) for 5
days at 100°C and (C) is the untreated wood. No mechanical stirring was
applied during the experiments.
was treated with the most processable 4.5 Novel imidazolium-based
structures. The result was that it was pos- ionic liquids
sible to extract hemicelluloses and selec- Since both, the fractionation trials and
tively lignin, in some cases by treatment spinning experiments demand substan-
under mild conditions (100°C). Some of tial amounts of [Emim][OAc] of high pu-
the structures even had the capability of rity, cost-effective syntheses were inves-
fibrillating wood chips under mild treat- tigated. [Emim][OAc] can be prepared in
ment conditions (Figure 8). The results excellent yields and high purity (Figure
of the research resulted in the filing of 9). This was possible through a novel me-
a patent and preparation of several re- tathesis step. Dimethylsulfite was used as
search articles. alkylating agent. The methylsulfite anion
Figure 9. Preparation of [Emim][OAc] via methylation of
imidazole with dimethylsulfite.
21

22. Figure 10. Synthesis of imidazolium O,S-dimethylphosphorothioates
via salt metathesis using sodium O,S-dimethylphosphorothioate.
formed can be hydrolyzed and expelled PCT assessment stage. Cellulose regener-
as sulphur dioxide upon addition of acetic ation activities are well under way. The in-
acid, leaving acetate remaining. Accurate frastructure is available for continuing the
control of the reaction conditions is re- research and optimizing processes. The
quired to suppress the formation of meth- major advances have been in the devel-
anesulfonate during the alkylation step. opment of recyclable structures allowing
Even though [Emim][OAc] is the for increased sustainability. This is neces-
working horse for the spinning and frac- sary for future developments. Overall un-
tionation trials, new cellulose dissolving derstanding of the area and chemistry is
ionic liquids are always of interest. In co- at a very high standard and teamwork be-
operation with Professor Herwig Schot- tween partners is now at a distinct level.
tenberger from the University of Inns-
bruck, Austria we synthesised sever-
al new ionic liquids with O,S-phosphoro-
thioate or O, Se-phosphoroselenoate an-
6. Key development
ions (Figure 10). Their structural similari- needs and future plans
ty to [Emim][Me2PO4] explains their abil-
ity to dissolve cellulose. As such, are also Increased recyclability of novel ionic liq-
potential candidates for the fibrillation of uids and ensuing intellectual property are
wood chips. An article was published this always of interest. Refinement of ionic liq-
year concerning the work. uid structures developed in FuBio - Phase
1 will be continued. More thorough ap-
plication testing is also necessary with
scale-up and feasibility analysis of the
5. Future business more defined concepts. Physiochemical
potential properties of the ionic liquids and biopoly-
mer solutions need more comprehensive
On the whole important progress by inter- study for application development. From
national standards has been made, in the an academic perspective, a better un-
area of the processing of lignocellulosics derstanding of the factors that affect the
using ionic liquids, through FuBio - Phase fractionation of lignin in particular from
1. Moderate advances have been realized wood is necessary to allow for more tu-
with the overall application-based targets. neable fractionation processes. Ionic liq-
3 Patents have been filed and are at the uids are highly effective at solvating wood
22

23. and wood biopolymers but this academic King, A. W. T., Asikkala, J., Mutikain-
challenge persists and will always be an en, I., Kilpeläinen. I. 2011 Distillable
obstacle to fractionation efficiency. Sup- Acid-Base Conjugate Ionic Liquids for Cel-
porting academic projects are intended to lulose Dissolution and Processing. Ange-
improve this situation. wandte Chemie International Edition 50,
6301-6305
King, A. W. T., Parviainen, A., Kar-
7. Publications hunen, P., Matikainen, J., Hauru, L. K.
and reports J., Sixta, H., Kilpeläinen, I. 2011. Rel-
ative and inherent nucleophilicity/basic-
ity/diffusivity of imidazolium-based ion-
Mäki-Arvela, P., Anugwom, I., Vir- ic liquids – the implications for lignocel-
tanen, P., Sjöholm, R., Mikkola, J.-P. lulose processing applications. Submitted
2010. Dissolution of lignocellulosic mate- to Green Chemistry
rials and its constituents using ionic liq-
uids-A review. Industrial Crops and Prod- Hauru, L. K. J., Hummel, M., King, A.
ucts 32(3): 175-201. W. T., Kilpeläinen, I., Sixta, H. 2011.
New insights into the requirements for
Anugwom, I., Mäki-Arvela, P., Vir- dissolution of cellulose into ionic liquids.
tanen, P., Damlin, P., Sjöholm, R., Submitted - Journal of the American
Mikkola, J.-P. 2011. Switchable ionic Chemical Society
liquids (SILs) based on glycerol and acid
gases. RSC Advances 1, 452-457. Hummel, M., Froschauer, C., Laus, G.,
Röder, T., Kopacka, H., Hauru, L. K.
Anugwom, I., Mäki-Arvela, P., Vir- J., Weber, H. K., Sixta H., Schotten-
tanen, P., Willför, S., Sjöholm, R., berger H. 2011. Dimethyl phosphoro-
Mikkola , J.-P. 2011. Dissolution of wood thioate and phosphoroselenoate ionic liq-
using novel switchable ionic liquids based uids as solvent media for cellulosic ma-
on 1,8-diazabicyclo-[5.4.0]-undec-7-ene terials. Green Chemistry 13, 2507-2517
- glycerol applying acid gases as trig-
gers. Manuscript Submitted – Carbohy- Karhunen, P., Matikainen, J., King,
drate Polymers A. W. T., Kyllonen, L., Willför, S., Kil-
peläinen, I. 2011. Ionic liquids for fibril-
Anugwom, I., Mäki-Arvela, P., Vir- lation of wood chips. Manuscript under
tanen, P., Willför, S., Sjöholm, R., preparation
Mikkola, J.-P. 2011. Selective extraction
of hemicellulose from spruce with switch- King, A. W. T., Karhunen, P., Mati-
able ionic liquids. Carbohydrate Polymers, kainen, J., Kilpeläinen, I. 2010. Pro-
in press cess for fibrillating lignocellulosic materi-
al, fibres and their use, Finnish Patent Ap-
Mikkola, J.-P., Anugwom, I., Mäki- plication 2010/5272
Arvela, P., Virtanen, P. 2010. Dissolu-
tion, fractionation and processing of ligno- King, A. W. T., Kilpeläinen, I. 2010.
cellulosic materials and polymers with bi- Method of dissolving lignocellulos-
carbonate ionic solvents formed from am- ic materials, Finnish Patent Application
ides, alcohols and carbon dioxide. Finnish 2010/5727
Patent Application 2010/6142
23

24. Hot water treatment of
lignocellulose
Editors Herbert Sixta, Marc Borrega and Lasse Tolonen
Partners: Key researchers:
Aalto University Herbert Sixta, Marc Borrega, Lasse Tolonen, Kaarlo
Nieminen, Ville Alopaeus, Juha Visuri, Susanna Kuitunen
Metla Hannu Ilvesniemi, Kaisu Leppänen, Veikko Kitunen,
Peter Spetz, Risto Korpinen
Åbo Akademi University Stefan Willför, Bjarne Holmbom, Andrey Pranovich,
Tao Song, Jens Krogell, Henrik Grenman
University of Jyväskylä Raimo Alén, Joni Lehto
VTT Technical Research Marjatta Kleen
Centre of Finland
24

25. Abstract
Treating wood, e.g. wood chips or saw dust, with hot water results in a partial deconstruction
of certain wood components into the water. Hot water treatment (HWT) processes can thus be
used for the removal of hemicelluloses from wood prior to subsequent delignification for the
production of pulp, or as a mean to extract valuable hemicelluloses for a wide range of applica-
tions. The extraction efficiency depends on several process variables, such as extraction inten-
sity (time-temperature), wood species, wood particle size, process mode (batch, flow-through)
and pH. The use of mild extraction conditions favours the recovery of water-soluble, medium-
and high-molar mass hemicelluloses in quasi-intact (close-to-native) form, but at low yield. The
water-solubility was a prerequisite for further ease of handling and usability. Increasing the ex-
traction severity increases the yield of extracted hemicelluloses, which are then recovered large-
ly as oligo- and monosaccharides. Under severe extraction conditions (above 200 °C), signifi-
cant amounts of acetic acid and degradation products, such as furfural and HMF, were recovered
from the water extracts. In this chapter, results from two different HWT sub-studies are present-
ed: i) HWT of soft- and hardwoods at temperatures up to about 200 °C, and ii) cellulose disso-
lution in near- and supercritical water treatment.
In regard to HWT, similar results were obtained by using batch and flow-through process
modes. However, the particle size (chips vs. saw dust) and the liquid-to-wood ratio had signifi-
cant effects on the extraction efficiency, presumably related to mass transfer and solubility limi-
tations, respectively. Furthermore, the influence of pH and extraction time was also found to be
critical in terms of the molar mass of the hemicelluloses obtained. Without pH adjustment, the
end-pH dropped below 3.5. This also led to autohydrolysis, which caused severe depolymeri-
sation, especially at longer extraction times. The removal of lignin increased considerably with
increasing extraction temperatures. The combination of intense HWT and mild alkaline pulping
may allow for the production of high-purity cellulosic pulps, due to the quasi-quantitative remov-
al of hemicelluloses.
In regard to near- and supercritical water treatment, literature sources suggest that cellulose
can be dissolved in near- and supercritical water as a polymer that precipitates upon cooling.
To test the concept, two reactors were built and operated at Karlsruhe Institute of Technology,
Germany. The conversion of microcrystalline cellulose under various reaction conditions was in-
vestigated. An extensive conversion occurs in ten seconds in nearcritical water at 300 °C, and in
supercritical water the conversion is complete in a fraction of a second. For instance, at 360 °C,
54 % of cellulose was converted in 0.25 seconds. Of the converted fraction, 44 % was found as
cellulose precipitate, 35 % as DP2-5 oligomers, and 5 % as glucose. The structural changes in
the cellulose residues were investigated to elucidate the conversion mechanism. Cellulose was
found to be depolymerized significantly in all trials. There were certain indications that supercrit-
ical water swells or otherwise damages cellulose crystallites.
25

26. 1. Background loring the solvent properties by shifting
the pressure at a given temperature.
The use of hot water treatment (HWT; in Given the higher ion product, and
literature also known as ‘hot water ex- therefore a higher H+ concentration, hy-
traction’, ‘autohydrolysis’ or ‘hydrother- drothermal treatment in subcritical water
molysis’) for wood fractionation is cur- has been proposed as a promising meth-
rently receiving considerable attention. od to hydrolyse biomass and cellulose. As
The hemicelluloses dissolved in the aque- an additional advantage, no acid neutral-
ous extract may be recovered and con- isation is required because the H+ con-
verted into products of high added val- centration decreases again when temper-
ue. The wood residue after the extraction, ature is reduced.
composed mostly of cellulose and lignin,
can be further subjected to pulping, using
less chemicals and shorter pulping times
than in the case of untreated wood. At an
2. Objectives
industrial scale, however, HWT is solely In terms of HWT:
utilised in the form of steam in pre-hydro- - Exploitation of the full potential
lysis-Kraft processes for the production of of HWT for the separation of
dissolving pulps. hemicelluloses (130–240°C)
HWT is often applied to hardwoods. - Effect of wood species (birch vs.
The higher amount of acetyl groups bound spruce/pine)
to the hemicelluloses and a good delig- - Effect of particle dimensions
nification efficiency, with lesser tenden- - Effect of liquor-to-wood ratio
cy for lignin condensation, make hard- (dilution)
woods more suitable to water extraction - Effect of pH
than softwoods. The temperatures used - Comparison of batch and flow-
usually range between 130°C and 240°C. through systems
The particle size of the raw material stud- - Relationship between molar mass
ied varies from industrial-size chips to fine of isolated carbohydrates (xylan or
wood meal. Due to mass and heat transfer GGM) and yield.
limitations, the larger the particle size, the - Fractionation of wood polymers as
lower is the yield of extracted products. part of a biorefinery concept
The extraction efficiency may also depend - Lignin removal and activation to
on the liquid-to-wood (L:W) ratio of the facilitate subsequent delignification
process, owing to solubility limitations. for the manufacture of pure
Temperatures closer and over 300°C cellulose pulps
offers interesting new possibilities. Cer- - Kinetic modelling of reactions
tain solvent properties of hot liquid wa- - Purification of water extracts
ter are shifted as a function of temper- - Upscaling of the HWT process
ature and pressure. For instance, densi-
ty, viscosity and surface tension are de- In terms of treatment at near- and super-
creased as temperature increases. Dielec- critical conditions:
tric constant decreases concomitantly, - Establish an international
which makes water to behave like a less collaboration with Karlsruhe
polar solvent at higher temperatures. Ion Institute of Technology (KIT) in
product is increased in subcritical temper- Karlsruhe, Germany, which has a
ature range. The effect of pressure is pro- long experience with high pressure
nounced under supercritical conditions at high temperature processes for
temperatures above 374°C, enabling tai- biomass conversion.
26

27. - Together with KIT, to build and 0.05 L to 300 L) and different conditions
evaluate a reactor system capable (L:S ratio, temperature, time, pH, etc.).
to operate under subcritical and Naturally, the question arises how
supercritical conditions using these results compare with each other?
reasonable short reaction times. The definition of an intensity factor re-
- Study the effect of raw material, lated to the quantitative extraction of
as well as process time and hemicelluloses (in particular xylan) into
temperature on the conversion of the aqueous phase was considered to be
cellulose and formation of reaction a reasonable basis for the comparative
products. evaluation of the different processes. Fur-
- Confirm the formation of cellulose ther, some simplified kinetics was com-
precipitate, and evaluate its puted to determine the rate of xylan or
potential for material applications. mannan extraction into the water phase
- Characterization of cellulose residue as a function of temperature, time and
prior and after the treatment in acidity. The experimental set-ups and re-
order to increase knowledge about action conditions of the different research
the conversion mechanism. groups are summarized in Tables 1 (for
birch) and 2 (for spruce and pine). Fur-
thermore, the influence of pH was thor-
oughly studied.
3. Research approach These tables show that the majority
Hot water treatment of experiments were done with birch and
Five research groups from Aalto Univer- spruce in batch mode. The precise condi-
sity (AALTO), Åbo Akademi University tions and experimental set-ups are com-
(ÅBO), University of Jyväskylä (JYV), Met- prehensively described in the reports of
la (METLA) and VTT (VTT) carried out ex- the individual research groups.
periments on water HWT, using different
wood species (birch, spruce and in one Near- and supercritical treatment
case pine), wood particle dimensions (fine Two reactors were used for the experi-
and coarse wood meal, wood chips), pro- ments in Karlsruhe. The first reactor, Zyk-
cess modes (batch, continuous batch and lon, was capable to operate only under
flow-through) in different scales (from subcritical conditions only, limited by the
Table 1. Overview on the different HWT reaction
conditions of birch wood.
27

28. Table 2. Overview on the different HWT
reaction conditions of spruce (S) and pine (P).
reaction time that was too long for super- proach was applied. The simplified reac-
critical temperatures. The second reac- tion scheme assumes a consecutive pseu-
tor, Mikki-reactor, reached reaction times do-first order reaction as illustrated in
down to 0.20 seconds, enabling experi- scheme 1:
ments to be carried out also under super-
critical conditions. Scheme 1.
In all the experiments, no catalyst
was added, and water alone was used as
reaction medium. Commercial microcrys-
talline cellulose from Merck was used as in which CS denotes the concentration of
cellulose substrate. In the second set of the carbohydrates in the solid residue, CL
experiments with Mikki-reactor, two oth- the concentration of the dissolved carbo-
er cellulose powders from Rettenmeyer hydrates and D the concentration of the
GmbH were used in addition to MCC from degraded carbohydrates. Other, more
Merck. complex reaction schemes have been
tested, such as scheme 2:
Scheme 2.
4. Results
PART1: HOT WATER TREATMENT
OF SOFT- AND HARDWOODS
4.1. Comparative evaluation of however, with limited success. Thus, the
different experimental concepts: following differential equations derived
Common basis of comparison from scheme 1 have been solved (Sci-
entist®):
4.1.1. Kinetic study
In an effort to compare the results origi-
nating from the participating laboratories
using different reactors, reaction condi-
tions and wood particle dimensions, the
rates of xylan and mannan extraction in-
to the water phase have been comput- [ ]
.
ed as a function of the pH. Owing to the
shortcomings of the available data base .[ ]
for kinetic evaluations a rather simple ap-
28

29. Figure 1. a (left): Experimental and calculated total xylan concentrations on
oven dry birch wood dissolved in water as a function of time, temperature
and pH. The data points reveal the experimental results, while the lines derive
from the kinetic model. b (right): Development of the pH during the dissolution
of the carbohydrates from birch wood.
where A1 and A2 are the pre-exponen- rate of xylan hydrolysis increases rapidly.
tial factors of reactions 1 and 2, EA1 and The pH reaches lower values in the flow-
EA2, the activation energies, R the uni- through mode, presumably owing to the
versal gas constant, T the absolute tem- elution of cations from the wood. Conse-
perature in Kelvin and k1 and k2 the rate quently, less buffering capacity is avail-
constants. able and thus the pH of the hydrolysate
Reaction rate k2, which describes the drops below the value in the batch hydro-
velocity of the degradation or the dehy- lysate where all cations accumulate and
dration reactions of dissolved carbohy- form a buffer system with the released
drates, is insignificant at low intensity acids. The use of sawdust in HWT batch
HWT and/or high acidity. Thus, reliable operations results in relatively flat pH pro-
results on k2 have been received only in files of generally low pH level (Fig 1b).
a few cases (Table 3). Overall, it was pos- Lower mass transfer restrictions allow a
sible to simulate the experimental results faster release of acetic acid as compared
sufficiently well as demonstrated in Fig- to the case of wood chip hot water extrac-
ure 1 and Figure 2. tions and thus accelerate the HWT pro-
Figure 1a reveals the differences be- cess. Consequently, in batch mode, the
tween the process modes: in the batch pH profiles of wood chip hot water treat-
mode the xylan dissolution starts right ments are steeper and the minimum pH
away, while it undergoes a time lag in level is reached after longer treatment
the flow-through mode which can be eas- times (or higher temperatures) as com-
ily explained by the different pH profiles pared to the hot water treatments of saw-
as illustrated in Figure 1b. In the perco- dust. As expected, the xylan concentra-
lation mode performed on birch sawdust tion increases faster when wood meal
(which has been applied in the case of (dash-dot, VTT) was used as compared
METLA), the hydrolyzed carboxylic acids to the use of chips (solid line, VTT) or
(mainly acetic acid) are not accumulated compressed chips (dash, VTT). The per-
in the reactor as in the case of the batch formance of xylan hydrolysis from wood
mode, but are eluted into the receiving chips can be largely explained by their
tank. However, after a certain period of associated pH profiles (Fig 1b), which in
time the acidity drops much faster than turn are affected by the applied lignin-to-
in the batch reactor and, accordingly, the solid ratio (L:S).
29

30. Table 3. Summary of the computed rate constant k2, expressing
the degradation rate of the solubilised xylan from birch wood at pH 3.5.
Table 4. Summary of the computed rate constant k1, expressing
the rate of xylan solubilisation from birch wood at pH 3.5.
k_internal (1) represents the hydro- that with an increasing ionic strength,
lytic rate of the cleavage of an internal as it is the case in the batch mode (see
bond in a xylo-oligosaccharide in homo- above), a general increase of the hydro-
geneous dilute sulphuric acid hydrolysis; lysis rate was observed. In other words,
k_internal (2) was derived from xylobiose the ratio of the proton concentration in-
hydrolysis in water at pH 4.0; k_Xylan hy- side the solid phase relative to that in the
drolysis originated from results obtained bulk liquid can be increased by the addi-
from the water HWT of Eucalyptus salig- tion of electrolytes.
na. Italic means that the listed values are The amount of hydrolysed xylan un-
outside the experimental range of which dergoes a maximum value of about 17
the rate constant has been determined. to 18% on odw which represents 80 to
The rate constant k1 calculated from 85% of the total xylan present in birch. In
the VTT_BC_B_30 and VTT_BC*_B_30 this respect the results from METLA (flow-
experiments are comparatively high, but through) and AALTO (batch) were pretty
are not included in the discussion since much the same. However, in both cases
the data set is too small to allow reliable very high liquor-to-wood ratios were ap-
computation of rate constants. Relative plied which favours the solubility of poly-
to their pH values the rates of xylan ex- meric xylan and counteract degradation
traction were rather low in the case of the reactions. There are clear indications that
METLA results which might be explained the solubilisation of xylan is affected by
by the Donnan effect which is caused by the liquor-to-wood ratio. It can be as-
non-diffusible cations. It has been shown sumed that the efficiency of xylan solu-
30

31. Figure 2. a (left): Experimental and calculated total mannan concentrations
on oven dry softwood dissolved in water as a function of time, temperature
and pH. The data points reveal the experimental results, while the lines derive
from the kinetic model. b (right): Development of the pH during the dissolution
of the carbohydrates from softwood.
bilisation is superior in a percolation than (ÅBO, JYV), the mannan dissolution pro-
in a simple batch reactor system. The lat- ceeds smoothly from the start of the re-
ter, however, may result in higher xylan action and peaks at 8 wt% on odw wood
concentrations in the hydrolysate which in (70% of the total mannan), while in the
turn favours process economy. The com- case of the flow-through mode it starts
bined recirculation-percolation process only after a certain time lag, accelerates
constitutes the best option since it com- fast and peaks at 10 wt% on odw (86%
bines the advantages of both batch and of the total mannan in wood). The man-
flow-through modes. nan dissolution behaviour of the differ-
The extraction of mannan from soft- ent reaction concepts can be explained
wood has been investigated by METLA, by their corresponding pH profiles. The
JVY and ÅBO. The results are depicted in low and retarded mannan dissolution of
Figure 2. METLA_SC_FT_300 as compared to that
Again, the calculated mannan dissolu- of METLA_SM_FT_0.05 both at 160°C can
tion rates fit very well to the experimen- be nicely explained by the high pH val-
tal results (Figure 2a). In the batch mode ues because the rate constants k1, ex-
Table 5. Summary of the computed rate constant k1, expressing
the rate of mannan solubilisation from softwood at pH 3.5.
31

32. Table 6. Summary of the computed rate constant k2, expressing
the rate of mannan solubilisation from softwood at pH 3.5.
trapolated to pH 3.5, are at a compara- ty factors are introduced which allow the
ble level (Table 5). As expected, the use prediction of quantitative changes of the
of chips compared to wood meal is ex- wood composition triggered by the HWT
pressed by a later onset of mannan disso- reaction.
lution and a lower rate constant k1 (MET-
LA_SC_FT_300 vs. METLA_SM_FT_300). 4.1.2. Intensity of HWT
The results from ÅBO (spruce) and The intensity of HWT is conveniently ex-
JYV (pine) obtained at 150°C show a very pressed as P-factor using an Arrhenius-
good correspondence despite the different type of expression. A value of 125.6 kJ
wood furnish. Both used a batch reactor mol-1 for the fast-reacting xylan (XF),
and a relatively low liquor-to-wood ratio. based on extensive investigations of xylan
Unfortunately, no experiments at high- hydrolysis from Eucalyptus saligna, has
er temperature have been executed with been suggested for the P-factor (P-XF)
pine as a raw material. Thus, no compre- calculation in a pre-hydrolysis kraft pulp
hensive evaluation of the HWT kinetics of mill. Overend and Chornet introduced the
this particular wood furnish is available. severity factor, R0, to quantify the inten-
The degradation of the dissolved sity of hydrothermal biomass treatment
mannan is promoted by its concentration using the following expression:
and the applied temperature (Table 6).
The results from ÅBO reveal that at low R0=t*Exp[(T-100)/14.75]
liquor-to-wood ratio the degradation of
mannan starts to become significant al- where T, the temperature, is measured in
ready at 160°C. At high dilution, the rate °C, t, the time in minutes. The logarith-
of dissolved mannan degradation remains mic plot of R0 allows the illustration of
insignificant up to 180°C as demonstrat- the data in a more condensed form. The
ed in Table 6. relationship between log(P-XF) or logR0
Water HWT affects not only the dis- with the xylan content of the wood resi-
solution and degradation of the major due, based on the initial wood, revealed
hemicellulose components in wood, but significant scattering in the high intensi-
also the minor hemicellulose components, ty HWT region, representing a xylan frac-
the side chains of the hemicelluloses, the tion of less than 0.2, which is typically de-
lignin, the cellulose and the whole wood noted as slowly-reacting or more resistant
morphology. It is obvious that the reac- xylan (XS) (Figure 3). A reassessment of
tions of the wood components are mainly the kinetics of the HWT of xylan pres-
affected by the intensity of the HWT re- ent in birch wood (Betula pendula) in the
action. In the following chapter, intensi- temperature range of 150 to 240°C yield-
32

33. ed an activation energy of 187 kJ/mol for Figure 3. Relationship between the xylan
the hydrolysis of the slowly-reacting xy- content in auohydrolysed birch wood
and HWT intensity factors, expressed as
lan fraction XS, assuming the presence of
log(P-XF), log(P-XS) and log(R0).
two types of xylan that hydrolyse via par-
allel first-order reactions. This value was
used to calculate the P-factor, P-XS, rep- 25
resenting the intensity of the HWT of the
20
resistant xylan fraction. Indeed, log(P-XS)
Xylan, % on odw
revealed a fairly well relationship with the 15 AALTO
remaining xylan content in the wood, par-
10
ticularly for the values below 5% on od
birch wood. (Figure 3). 5
The relationship between the HWT
0
intensity and the amount of sugar com- 024 6
ponents and their dehydration products Autohydrolysis Intensity
2 2 2
log(P ): r =0.980; log(P ): r =0.997; log( R0): r =0.972
(furfural and hydroxymethylfurfural) re- X
f
X
S
leased to the water phase is, however,
more precisely described by the log(P-XF)
indicating that the application of more se-
vere conditions particularly promotes the
degradation reactions.
4.2. HWT of Betula pendula appreciable rate. The release of oligomer-
ic and polymeric xylan fractions reaches a
4.2.1. Characterization of the maximum of 14.7% on odw at a log(P-XF)
extract of about 2.85, while the maximum of the
total hydrolysed xylan fraction is shifted
4.2.1.1. Sugar and acetic acid to a log(P-XF) of 3.0 and amounts about
balance 17.5% on odw. The results from AALTO,
Following the principle of autocatalysed JVY, VTT(wood meal) and those of MET-
reactions, the hydrolytic cleavage of car- LA at higher intensities show a compara-
bohydrates and the release of water sol- ble relationship with log(P-XF) (Fig. 4a).
uble fragments are initiated only when a This is quite interesting because JVY used
certain threshold value of HWT intensity wood chips, while the other research labs
(P-XF) is exceeded. The first water solu- used wood meal or sawdust. It could be
ble, polymeric xylan fractions appear at expected that wood chips require a high-
a log(P-XF) of about 1.6 in the hydroly- er log(P-XF) than wood meal to extract
sate as demonstrated in Figure 4a. With a certain amount of xylan as exemplified
increasing reaction intensity, the rate of by VTT results using wood chips (VTT_
the hydrolytic cleavage further acceler- BC_B_30, see Fig. 4a).
ates until it reaches a fairly constant val- As expected, the maximum amount
ue at log(P-XF) values between 1.9 and of bound acetyl groups in the hydroly-
2.4. Still, only polymeric and oligomeric sate equals the maximum amount of xy-
xylan fractions are released to the aque- lo-oligomers (Figure 4b). A further inten-
ous phase. The hydrolysis rate of solid xy- sification of HWT is answered by an in-
lan slightly decelerates at higher log(P- creasing yield of monomeric xylose, peak-
XF) because at the same time the gener- ing at an amount of 9.5% on odw at a
ation of xylose monomers through the hy- log(P-XF) of 3.45 (AALTO, batch mode),
drolytic cleavage of oligomers starts at an and a progressive dehydration of pentos-
33

34. Figure 4. a (left): Yield of xylan equivalents during HWT
as a function of log(P-XF); b (right): Yield of bound
acetyl groups and free acetic acid as a function of
log(P-XF).
es to furfural. The latter peaks at a log(P- At a P-factor 200 (log(P-XF) = 2.30), the
XF) of 4.24 reaching 10% of xylose equiv- total yield of the released xylan fragments
alent on odw, which slightly exceeds the in solution comprises about 10% on odw,
maximum monomeric xylose yield (Fig- which constitutes the minimum yield for a
ure 4a). The yield of monomeric xylose commercially attractive application.
is lower in the flow-through than in the The results can be divided into two
batch mode which is demonstrated by the clusters (Figure 5): The first represents
results provided by METLA. the low-Mw xylans with Mw’s lower than
The yield of free acetic acid in the 3.5 kDa derived from autohydolysis rang-
aqueous liquor is surprisingly low at ing between log(P-XF) 2.3 to 3.5, while
moderate log(P-XF) values. Thus, HWT the second displays the high-Mw xylans
in combination with SAQ pulping for the with Mw’s ranging from 4.7 to 17 kDa.
production of rayon grade pulps is not a The yield of the latter, however, is very
profitable source for the recovery of ace- low since they derive from low-intensi-
tic acid. However, high yields of acetic ty HWT, particularly applying the flow-
acid (6.5% on odw) and furfural (10% through reaction mode.
on odw) can be obtained at high inten-
sity HWT equivalent to a log(P-XF) value 4.2.1.3. Formation of furanic
of about 4.25 which, succeeded by SAQ compounds
pulping, might result in the manufacture Dehydration reactions are favoured at low
of a xylan-free dissolving pulp suitable for pH (0.05 M mineral acid) and high tem-
specialty applications. peratures (e.g. 200°C). During moderate
HWT the formation of dehydration prod-
4.2.1.2. Molar mass of sugars ucts remains insignificant. Thus, high in-
Although HWT has shown to release main- tensity HWT is necessary to initiate the
ly oligomeric and polymeric xylan frac- formation of furanic compounds (Figure
tions, the autohydrolysate from batch re- 6).
actions seems to be not a very rewarding The quantitative formation of both fu-
source for high molecular weight xylans. ranic compounds can be precisely predict-
34

35. Figure 5. Weight average molar mass reactions such as resinification or conden-
(Mw) of xylans originating from birch sation reactions.
autohydrolysates.
4.2.2. Characterization of the wood
residue
4.2.2.1. Yield and sugar composition
The yield losses of wood through HWT
are mainly attributed to the removal of
hemicelluloses up to relatively high reac-
tion intensities (Figure 7). The removal of
lignin starts from the very beginning but
becomes significant in the case of birch
wood when HWT intensity is exceeding
log(P-XS) of 3.5 (Figure 8). It is known
since a long time that HWT of hardwood
induces lignin solubility.
ed by HWT intensity expressed as log(P- Figure 8 reveals that delignification
XF) factor. The onset of furfural produc- undergoes a maximum for each reaction
tion is at log(P-XF) > 3.0, while that of time in which the maximum shifts to a
HMF is connected to severe cellulose higher degree of delignification with ris-
hydrolysis which starts at log (P-XF) > ing temperature. Unfortunately, the time
3.5. The high yields of both furanic com- range at each temperature gets narrower
pounds may be attributed to the high li- with increasing temperature owing to the
quor-to-wood ratio of 40:1. Water HWT in competing acid-catalysed re-condensation
commercial-size with liquor-to-wood ra- reactions. The cellulose fraction in the
tios below 3.0, however, would result in birch wood stays surprisingly stable un-
significantly lower yields of furanic com- til very high HWT intensities are reached
pounds owing to the onset of severe side (log(P-XS) 5.5 – 6.0). Cellulose, however,
Figure 6. a (left): Furfural formation in the birch autohydrolysate
from dehydration of pentoses. b (right): Hydroxymethylfurfural (HMF)
formation in the birch autohydrolysate from dehydration of hexoses.
35

36. Figure 7. Material balance of birch wood Figure 8. Lignin content in the birch
as a function of HWT intensity expressed residue as a function of log(P-Xs),
as log(P-XF). temperature, liquor-to-wood ratio and
wood particle dimensions.
remains not unaffected. In fact, it is sub- ter birch wood meal HWT between 180 °C
jected to severe depolymerisation reac- and 240 °C was about 8-10% (results not
tions through hydrolytic cleavage starting shown). At any extraction temperature,
in the amorphous domains, but also af- the amount of soluble lignin in the hy-
fecting the crystalline domains depending drolysate remained mostly constant, re-
on the HWT intensity. The newly created gardless of the extraction time. An insol-
reducing end groups are starting points uble fraction, mainly related to lignin frac-
for intensive peeling reactions in subse- tions precipitated during cooling, was al-
quent alkali treatments. The development so found in the hydrolysate, particularly
of effective and industrially competitive after severe HWT severities. Degradation
stabilization measures is a subject of the products from carbohydrates and/or oth-
continuation of FuBio (‘FuBio 2’). er degradation products may be attached
Figure 8 demonstrates that the ex- to the insoluble lignin fraction.
tent of delignification is decreasing with
increasing wood particle dimensions due 4.3. HWT of softwood
to mass transfer limitations and, even
more pronounced, with decreasing liquor- 4.3.1. Characterization of
to-wood ratio owing to solubility limita- the extract
tions which promote condensation reac-
tions inside the cell wall architecture. To 4.3.1.1. Sugar and acetic acid
overcome these limitations, at least part- balances
ly, the combined recirculation-percolation ÅBO and METLA performed HWT trials
process is recommended and is subject of with spruce, JYV with pine. The relation-
investigations in one of the FuBio 2 pro- ship between log(P-XF) and the extracted
grammes. amounts of C5 and C6 sugars is reason-
ably well. Figure 9 shows the above de-
4.2.2.2. Lignin balance scribed differences in the dissolution pat-
The amount of soluble lignin (as % on terns between batch and flow-through
original dry wood) in the liquid phase af- modes. The later onset of the sugar re-
36

37. Figure 9. a (left): Extracted amounts of C6 sugars from softwood as a
function of HWT intensity. b (right): Extracted amounts of C5 sugars from
softwood as a function of HWT intensity.
lease in the case of METLA’s experiments masses, Mw, are related to the intensity
in the 300 L-reactor compared to those of HWT, log(P-XF).
in the small lab-scale reactor can be ex- Figure 10 shows the expected de-
plained by the lower pH values in the lat- crease in the Mw with progressive HWT
ter. The lower pH values during pine HWT intensity. The correspondence between
compared to spruce HWT seems to be al- the data provided by METLA and ÅBO is
so the reason for the higher C5 and C6 fairly good, which is quite surprising since
sugar yields at given log (P-XF). As ex- both the process mode and the liquor-to-
pected, the flow-through mode results wood ratios differ significantly. The dis-
in higher sugar yields as compared to tinct degradation of the dissolved sugars
the batch mode. The latter shows rather at log(P-XF) below 3.0 in the case of the
low sugar yields (ÅBO) and a surprising- ÅBO batch trials is by no means reflect-
ly sharp yield decrease when exceeding
a log (P-XF) of about 3, which is presum-
ably due to the low liquor-to-wood ratio. Figure 10. Weight average molar mass
(Mw) of xylans originating from spruce
autohydrolysates.
4.3.2. Molar mass of sugars
4.3.2.1. General overview
A major aim of softwood HWT is the re-
covery of high molecular weight polysac-
charides mainly consisting of galactoglu-
comannan (GGM). METLA and ÅBO have
determined the molar masses by SEC
measurements from both the unpurified,
dissolved sugars (METLA) and the poly-
meric sugar recovered by ethanol precip-
itation (ÅBO). The weight average molar
37

38. ed in the Mw of the precipitated sugars. Figure 11. Yield of softwood as a
On the contrary, the Mw increases (again) function of HWT intensity expressed as
with increasing reaction temperature and log(P-XF).
intensity (see encircled points in Figure
10). These (conflicting) results cannot be
explained on the basis of the existing re-
sults. Also quite surprising are the very
high Mws at low log(P-XF) values which
significantly exceed the MWs of alkaline
extracted hemicelluloses following known
analytical protocols.
4.3.3. Characterization of the wood
residue
4.3.3.1. Yield and sugar composition
The yield decreased slightly with increas-
ing the extraction intensity up to a log (P-
XS) of about 3, and thereafter the yield
started decreasing significantly (Figure
11). Both pine and spruce wood show a
comparable behaviour. At higher temper- been investigated to remove both the in-
ature, extraction is more effective and soluble and the soluble lignin.
less non-cellulosic carbohydrates are left
in residuals. Therefore, by applying lower 4.4.1. XAD-4 treatment
temperature it is possible to obtain poly- Birch HWT hydrolysates were treated
meric GGM with higher molar mass with- with an Amberlite XAD-4 resin (regener-
out dramatic loss in yield. Lower tem- ated with NH4OH). The objective of the
perature is also more promising because treatment was to remove non-carbohy-
causes less degradation in residual wood. drate components from hydrolysates. As
seen in Table 7, XAD treatments did not
4.3.3.2. Lignin Balance have any significant effect on the content
The lignin content in the pine wood res- of free monosaccharides or on the total
idue after the hot water extractions was carbohydrate content. In addition, the ef-
rather similar after any extraction condi- fects on the content of volatile acids were
tions, being about 30 % of the dry wood small. However, dissolved lignin and fura-
residue (results not shown). Most of the noic compounds were efficiently removed
lignin was determined as Klason lignin, from the hydrolysates (Table 7). The pH
with only a minor amount of acid-solu- of the resin did not have any clear influ-
ble lignin. As the yield decreased with in- ence on the removal efficiency.
creasing extraction intensity, it can be ex-
pected that the residual lignin decreased 4.5. Modelling of hot water
as well. treatment
A population balance based model was
4.4. Purification of the hydrolysate developed at Aalto to describe the depo-
The concomitant release of substan- lymerisation reactions of hemicellulos-
tial amounts of very reactive lignin frac- es taking place in HWT conditions. Kinet-
tions which partly form gluey precipi- ics of the cleavage of glycosidic bonds in
tates avoids the commercialization of wa- hemicellulose was studied and two scis-
ter HWT. Thus, different measures have sion mechanisms were tested.
38

39. Table 7. Compounds content in birch hydrolysates before and after
XAD-4 extraction for various extraction intensities (P-factor).
P-factor
10 20 30 41 60 119 179 238
Total carbohydrates
- Untreated 0,91 1,35 1,78 2,63 2,75 6,87 11,41 14,68
- XAD (neutral)
- XAD (basic)
0,79 1,17 1,63 2,15 2,51 4,63 10,17 14,30
0,69 1,17 1,59 2,27 2,37 6,07 10,96 15,53
Soluble lignin
- Untreated 1,18 1,85 1,98 2,51 2,88 4,70 5,20 5,84
- XAD (neutral)
- XAD (basic)
0,86 1,13 1,47 1,77 1,62 2,63 3,51 4,00
0,82 1,22 1,56 1,65 1,63 2,70 3,51 3,69
HMF
- Untreated 1,03 1,58 2,31 3,02 4,09 6,28 10,26 16,40
- XAD (neutral)
- XAD (basic)
0,64 0,81 1,24 1,63 1,94 3,43 5,85 8,50
0,56 0,89 1,36 1,43 2,12 3,92 5,63 8,28
Furfural
- Untreated 2,78 4,78 7,62 9,74 10,98 24,98 52,52 108,58
- XAD (neutral)
- XAD (basic)
1,01 0,98 1,69 1,98 2,16 5,59 10,67 12,11
1,20 1,40 2,25 1,82 2,35 6,79 12,73 21,60
Acetic acid
- Untreated 0,23 0,36 0,46 0,67 0,60 1,16 1,84 2,17
- XAD (neutral)
- XAD (basic)
0,21 0,32 0,40 0,56 0,39 0,98 1,53 2,13
0,20 0,30 0,44 0,54 0,46 0,94 1,64 2,29
Formic acid
- Untreated 0,12 0,14 0,14 0,15 0,17 0,21 0,24 0,23
- XAD (neutral)
- XAD (basic)
0,11 0,11 0,12 0,14 0,13 0,16 0,19 0,16
0,10 0,12 0,13 0,13 0,12 0,15 0,19 0,22
The literature part of this modelling In the applied part, kinetic param-
work consisted of exploring the phenom- eters for the two scission mechanisms
ena that need to be taken into account were optimized for the depolymerisation
when HWT is modelled. The previous ki- of galactoglucomannan. The effect of hy-
netic studies were reviewed and the re- drogen ion concentration on the scission
actions taking place were identified. The rate was also studied. The experimental
modelling of depolymerisation was stud- data for galactoglucomannan reactions
ied to get an overview on the topic. Mass was received from ÅBO. The obtained ki-
transfer and thermodynamic aspects were netic parameters were compared against
also considered. the acid hydrolysis data of disaccharides.
39

40. PART2: CELLULOSE DISSOLUTION Based on the experiences with the
IN SUB- AND SUPERCRITICAL Zyklon-reactor, a new reactor named Mik-
WATER TREATMENT ki was built. Experiments were carried out
using reaction times of 0.25/0.50/0.75
4.6. Conversion kinetics and seconds, at temperatures of 280-390 °C.
reaction products The behaviour of different celluloses was
The experiments were started in autumn investigated by treating two additional
2009 in Karlsruhe with the Zyklon-reactor. cellulose powders in addition to micro-
In these first runs the goal was to study crystalline cellulose. The results are sum-
the reaction kinetics under subcritical marized in Figure 14 and Figure 15.
temperatures, and gain first-hand expe- A complete conversion of MCC was
rience of such reaction systems. The Zyk- reached at 390 °C as fast as in 0.25 sec-
lon-runs were limited to subcritical tem- ond. As expected, the high yields of cel-
peratures. The main results from these lulose precipitate were reached with the
experiments are given in Figure 12. shortest reaction times. The best yield of
These results were combined into a the precipitate was 24% on treated cellu-
simple descriptive kinetic model assum- lose. The best combined yield of precipi-
ing that cellulose dissolves as oligomers tate, oligomers, and glucose was 44% on
that depolymerize to monomeric glucose cellulose, or 84% on the solubilized part.
and further to degradation products. The The yield of precipitate was in agreement
model supported the assumption that a with reported literature values but did not
short reaction time together with a high reach the best reported values: 51% in a
temperature provides a high yield of treatment at 400°C for 0.02 second.
oligomers and glucose whereas a long The effect of raw material was sig-
time resulted in a high amount of degra- nificant (Figure 15). The used MCC was
dation products, as shown in Figure 13. much more reactive than that of the used
Figure 12. Left: Degree of conversion vs. reaction temperature using different
reaction times. White markers for unextracted and black markers for
acetone extracted samples. In ~15 s series extraction was not done. Right:
Concentration of glucose in product solution for different reaction times and
temperatures. Dashed lines according to the developed kinetic model.
40

41. Figure 13. Appearance of liquor products after the removal of
cellulose residue. a) 300 °C for 6 s. b) 287 °C for 2.5 seconds
containing white cellulose precipitate.
Figure 14. Concentrations of different compounds in the system
after hot water treatment of microcrystalline cellulose with Mikki-
reactor. More complete mass balance including C2-C5 oligosugars
was carried out for the 0.25s series.
Figure 15. Effect of raw material. The mass of quantified compuounds
in the system using a reaction time of 0.50 s. MCC: microcrystalline
cellulose from Merck, AC1: Arbocell cellulose powder, grain size 1 µm,
and AC30: Arbocell cellulose powder, grain size 30 µm.
41