lignin complexity: fundamental and applied issues€¦ · · 2008-05-06•action of urea - breaks...
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Lignin complexity: fundamental and applied issues
Göran Gellerstedt
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Content
• The lignin structure in wood• Lignin chemistry in pulping• Technical lignins
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Content
• The lignin structure in wood• Lignin chemistry in pulping• Technical lignins
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Spruce: C9H8.62O2.48(OCH3)0.94 Phenolic OH: 20-30%Birch: C9H8.59O2.86(OCH3)1.52 Phenolic OH:
Milled Wood Lignin
Percent of total linkages Linkage
type
Dimer structure
Softwood Hardwood
β-O-4'
α-O-4'
β-5'
5-5'
4-O-5'
β-1'
β−β'
Arylglycerol-β-aryl ether
Noncyclic benzyl aryl ether
Phenylcoumaran
Biphenyl
Diaryl ether
1,2-Diaryl propane
Pinoresinol/lignan type
50
2-8
9-12
10-11
4
7
2
60
7
6
5
7
7
3
Ref., Adler, 1977
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Monomer yield on thioacidolysis(theoretical: ~4700-5500 μmol/g)
Sample Yield of the main monomer(s),
μmol/g Klason lignin
Content of phenolic OH, Number per 100 C9-units
Spruce wood
Spruce wood (preswollen)
Spruce MWL
Spruce TMP (preswollen)
Birch wood (preswollen)
Birch MWL
Aspen wood (preswollen)
Aspen MWL
1332
1682 (31%)
986
1498
672 (G) + 2318 (S) = 2990 (63%)
403 (G) + 809 (S) = 1212
866 (G) + 1942 (S) = 2808 (58%)
609 (G) + 863 (S) = 1472
n.a.
10-13 20
14
7.6
n.a.
10
n.a.
O OCH3Lignin
O
HO
R
HO
H3CO
Lignin
R
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Mechano-chemical cleavage of β-O-4 structures in milling
OOCH3
CHOH
L
CHCH2OH
O L
H3CO
OOCH3
CHOHCHCH2OH
L
OOCH3
+
L
M. E.
Δ
+H-H
OOCH3
C OCH2
CH2OH
LOH
OCH3
L
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SEC of thioacidolysis products from spruce, eucalyptusand birch wood
0
0.2
0.4
0.6
0.8
1
1.2
20 25 30 35 40
MonomersDimers
Trimers
OligomersSpruce
Eucalyptus/Birch
Time, min
Absorbance
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•Endoglucanase(Novozyme 476)
•Action of urea- Breaks down the crystallinity of the cellulose by
forming hydrogen bonds between the microfibrils
- Dissolves any material containing > ~50% lignin
- Removes enzyme contamination from the fibres
•Action of alkaline borate solution- Dissolves all remaining components
Dissolution of wood/pulp fibres by the use of enzyme
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Types of LCC isolated from sprucewood meal
Type of Lignin-Carbohydrate Complex, LCC Lignin yield, %
GalactoGlucoMannan - Lignin
Glucan - Lignin
GlucoMannan - Lignin
Xylan - Lignin
8
4
48
40
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Dimer Monomer
SEC of acetylated thioacidolysis products from spruce LCCs
Xylan-rich LCC(40% lignin on wood)
Glucomannan-rich LCC(48% lignin on wood)Response
Wood
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Suggested lignin structures in spruce wood
OH
OH
O OMe
HO
OMeO
OH
O
HO
OMe
O
OH
MeO
MeO
O
HO
O
OH
OMe
MeO
OLignin
Xylan
Linear xylan-lignin
Branched glucomannan-lignin
O
Lignin
O
O
O
O
O
OO
O
O
HO OH
OO
O
O
O
O
O
O
CHO
O
Lignin
CH2OH
O
O
O
O
O
Lignin
HO
OCH3
H3CO
OCH3
H3CO
H3CO
OCH3
OCH3
OCH3
H3CO
H3CO
H3CO
OCH3
OCH3
OCH3
H3CO
OCH3
OCH3
OCH3
H3CO
OCH3
H3CO
OCH3
OCH3H3CO
OCH3
HO
HO
HO
OH
OH
OH
OH
HO
HO
Glucomannan
HO
HO
OHHO
OH
OHOHOH
OH
OH
OHHO
HO
HO
HO
OH
OH
OH
HO
OHOH
OH
OH
OH
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S/G ratios in hardwoods
Wood species S/G-ratio Method Reference
Birch
Birch
E. globulus
E.globulus
E. grandis
3.8
3.7
5.3
4.8
3.6
Thioacidolysis
Nitrobenzene
Thioacidolysis
Pyrolysis
Pyrolysis
Gellerstedt et al, 2007
Chen, 1992
Gellerstedt et al, 2007
Gutierrez et al, 2007
Gutierrez et al, 2007
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G-units/S-units in white birch wood
Morphological Differentiation Guaiacyl/Syringyl
Fibre, S2-layer
Vessel, S2-layer
Ray parenchyma, S-layer
Middle lamella (fibre-fibre)
Middle lamella (fibre-vessel)
Middle lamella (fibre-ray)
Middle lamella (ray-ray)
12 : 88
88 : 12
49 : 51
91 : 9
80 : 20
100 : 0
88 : 12
Ref. Saka and Goring, 1988
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The lignin structure in hardwoods …
contains a high proportion of S-unitswhich results in a high percentage of linear lignin – unevenly distributed
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MS-identification of lignin fragment from E. globulus lignin
HOOCH3
H3CO
OHO
H3CO
H3COOH
OOCH3
H3COOH OH
O
O
OOH
OOCH3
OCH3
HO
OH
OH
OCH3
HO
OCH3
H3CO
Evtuguin et al, 2003
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Lignin in annual plants
Origin Lignin content H:G:S
Flax
Sisal
Wheat straw
Rice straw
2.9 (+ 1.6)
10.8 (+ 3.0)
16.0
6.1
57:33:11 (pyrolysis)
1:20:79 (pyrolysis)
5:49:46 (thioacidolysis)
15:45:40 (thioacidolysis)
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Content
• The lignin structure in wood• Lignin chemistry in pulping• Technical lignins
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Dissolution of lignin and carbohydrates in kraft pulping
Residual lignin; removed by bleaching
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Degree of delignification for different wood species
Pulp type Kappa No Lignin kappa
Delign. degree
Pine
Birch
E. globulus
28.0
16.5
15.9
24.6
4.0
5.7
94.0
98.2
97.5
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Kraft pulping of birch and E. globulusrespectively to similar kappa numbers
E. globulus
Birch
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β-O-4 structures in wood and pulp based on thioacidolysis
0
500
1000
1500
2000
2500
3000
Birch B pulp Euc E pulp
GS
Degradation product, μmol/g of lignin
Klason lignin, %: 16.6 0.6 18.3 0.9
(birch and eucalyptus)
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Size exclusion chromatography (SEC) of lignin degradation products
(no ”residual lignin” present in wood)
Methodology
•Thioacidolysis of wood/pulp•Acetylation•SEC in tetrahydrofuran
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Suggested mode of formation of radicalcoupling products in kraft pulping
OH3CO
Lignin
OOCH3
R
SS
SS
SS
SS
SS
S SSS
SS
Δ
OH3CO
Lignin
OOCH3
R
SS
SS
SS
SS
OH3CO
Lignin
OOCH3
R
OH3CO
Lignin
HOOCH3
R
OOCH3
OH3CO
H
Lignin R
H H
Low reactivity due to H-bonding
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Principles in the steam explosion process(Conditions: ~190-240 oC, 1-5 min)
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Chemical composition before and after steam explosion
Substantial removal of hemicelluloses and extractives: SO2SE > TwoSE > OneSE
0
20
40
60
80
100
Wood SO2SE OneSE TwoSE Wood SO2SE OneSE
Lignin
Extractives
(Ara)-xyl
(Gal)-Glu-man
GlucanSpruce samples Birch samples
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Lignin isolation yield (hardwoods)
SO2SE > OneSE
0
20
40
60
80
100
120
SO2SE OneSE SO2SE OneSE
Residual
Extractable,NaOH
Birch samplesAspen samples
(missing lignin from aspen highly soluble lignin)
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SEC of acetylated lignin from steamexploded aspen wood
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Degradability by thioacidolysis/SEC analysis
Condensation less degradability
Spruce
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Degradability by thioacidolysis/SEC analysis, SE aspen
SESO2SE
monomers
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Steam explosion chemistry
OOCH3
OHO
Lignin
HO
OCH3
LigninO
OCH3
HO
HO
Lignin
O
H3CO
Lignin
OOCH3
O
Lignin
HO
OCH3
Lignin
OOCH3
O
Lignin
H3CO
Lignin
Lignin
OH3CO
OH
OOCH3
OH
Lignin
OOCH3
OH
Lignin
O
High temperature
Hydrolysis, H+Condensation
Acidolysis
Stabilisation
O
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Content
• The lignin structure in wood• Lignin chemistry in pulping• Technical lignins
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Biomass tree showing the main chemical outlets
Ref. Rintekno oy, 1984
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Highest-value lignin uses to show greatestfuture rise (W. Glasser)
As structure of lignin yieldsto advances in analyticaltechniques, new markets are projected in adhesives, foams, films, coatings and plasticsRef: C&EN 1984
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The Biorefinery Concept
• Production of large volumes of ethanol will be necessary in a short term
• New separation process(es) for lignocellulosicsrequired
• New chemistry based on carbohydrates will be developed
• Lignin for fuel – and for chemicals• On a longer term, gasification of biomass to
syngas (biodiesel) will be developed
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Indicative targets for the share of biofuel in the EU
• 2005: 2% (not achieved)• 2010: 5.75% (will probably not be achieved)
-------------------• 2007: New energy policy document setting a
minimum requirement at 10% by 2020
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From biomass to liquid fuels
• Biodiesel from oils and fat; rapeseed etc – esterification with methanol
• Biochemical pathways to ethanol; 1) Sugar beet etc – sugar-fermentation2) Starch crops – hydrolysis-sugar-fermentation3) Lignocellulosics – separation-hydrolysis-sugar-
fermentation; lignin as byproduct• Thermochemical pathways to biofuels;
1) lignocellulosics – pyrolysis-bio oil-biofuels2) lignocellulosics – gasification-methanol/FT-fuels
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Feedstock sources
• Forestry waste (forest residue, bark, woodchips, thinnings)
• Agricultural residues (straw, stover, bagasse)• Energy crops (poplar, willow, switch grass)• Municipal waste (paper, packaging,..)
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Biomass composition
Structure Softwood (Picea abies)
Hardwood(Betula verrucosa)
Wheat straw
Cellulose
Hemicellulose (C6-sugars)
Hemicellulose (C5-sugars)
Lignin
Extractives
Other components
42
19
7
27
2
3
42
4
26
23
3
2
38
1
24
24
3
10
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The ideal separation of biomass
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… and the reality
• Kraft and soda pulping• Sulfite pulping• Acid hydrolysis• Steam explosion• Organosolv pulping
At present, none of these processes resultsin an efficient and cheap separation
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Elemental analysis
Sample carbon hydrogen oxygen sulfur
Kraft lignin, pine
Kraft lignin, birch
Kraft lignin, E. globulus
Soda lignin, bagasse
Steam explosion, beech
64.3
63.5
56.1
61.8
57.6
6.0
6.1
5.7
6.0
6.0
27.9
28.0
35.4
32.2
36.4
1.8
2.4
2.8
0
0
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Substance Groups in Kraft Black Liquors(kg/ton of pulp)
Fraction Pine Birch
Lignin
Hydroxycarboxylic acids
Acetic acid
Misc. products
490
320
50
200
330
230
120
170
Ref: Sjöström 1993
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Principle for manufacturing of lignin from kraft black liquor
Black liquor
Evaporation
Precipitation pH = 9
Filtration,Washing
Lignin
Flash drying
Acid:CO2 or H2SO4
Filtrate,wash water
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Solvent fractionation of softwood kraft lignin
Fraction Yield Mn Mw Mw/Mn
CH2Cl2
n-propanol Methanol
9
22 26
4.5 x 102
9.0 x 102
1.7 x 103
6.2 x 102
1.3 x 103
2.9 x 103
1.4 1.4 1.7
CH3OH/CH2Cl2
Undissolved
Unfractionated
28 14
100
3.8 x 103
5.8 x 103
1.4 x 103
8.2 x 104
1.8 x 105
3.9 x 104
22 31
28
Ref: Kringstad et al
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Lignin fractionation•Material: Industrial black liquor of softwood (pine/spruce), birch
and eucalypt respectively
•Fractionation: Ultra-filtration, 5 kD and 15 kD to remove high molecular particles / carbohydrates
•Lignin isolation: Precipitation with CO2 (pH 9), Acid washing with H2SO4 (pH 2.3), Drying
•Purification: Cation-exchange to remove traces of Me+
Permeate
Retentate
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SEC of kraft lignins before/after fractionation
0 1 2 3 4 5 6log M (relative polystyrene)
dw/d
log
M
SWL
SP5
SR5
0 1 2 3 4 5 6log M (relative polystyrene)
dw/d
log
M
EL
EP5
ER5
softwood eucalypt
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SEC-data from fractionated (5 kDa) kraft lignins
Sample/
polymer data
SW
lignin
SW
permeate
SW
retentate
Euc.
lignin
Euc.
permeate
Euc.
retentate
Mw
Mn
Polydispersity
5600
900
6.2
1800
450
3.9
6100
900
6.8
2300
530
4.4
1300
440
3.0
3400
660
5.1
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Thermal analysis of purified kraft lignins
Lignin sample/
thermal data
SW
lignin
SW
permeate
SW
retentate
Euc.
lignin
Euc.
permeate
Euc.
retentate
Tg, oC
Ts, oC
Td, oC
148
-
267
130
181
260
157
-
261
133
-
264
119
182
260
142
-
248
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Even a small lignin withdrawal can be interesting …
650,000 tonnesof pulp
… converted to 16,000 tonnes of CF
Lignin withdrawal of 10% yields 33,000 tonnes
…to support 160,000 cars with CF-composite(~40% replacement)
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Conclusions
• All native lignins are heterogeneous biopolymerslinked to polysaccharides
• Alkaline or acidic processes result in both lignin degradation and re-polymerisation
• The up-grading of technical lignins requirepurification steps
• Several options exist for an increased lignin use