Lignin complexity: fundamental and applied issues

Transcription

1 complexity: fundamental and applied issues Göran Gellerstedt

2 Content The lignin structure in wood chemistry in pulping Technical lignins

3 Content The lignin structure in wood chemistry in pulping Technical lignins

4 Milled Wood Spruce: C 9 H (CH 3 ) 0.94 Phenolic H: 20-30% Birch: C 9 H (CH 3 ) 1.52 Phenolic H: Linkage type β--4' α--4' β-5' 5-5' 4--5' β-1' β β' Dimer structure Arylglycerol-β-aryl ether Noncyclic benzyl aryl ether Phenylcoumaran Biphenyl Diaryl ether 1,2-Diaryl propane Pinoresinol/lignan type Percent of total linkages Softwood Hardwood Ref., Adler, 1977

5 Monomer yield on thioacidolysis (theoretical: ~ μmol/g) Sample Spruce wood Spruce wood (preswollen) Spruce MWL Spruce TMP (preswollen) Birch wood (preswollen) Birch MWL Aspen wood (preswollen) Aspen MWL Yield of the main monomer(s), μmol/g Klason lignin (31%) (G) (S) = 2990 (63%) 403 (G) (S) = (G) (S) = 2808 (58%) 609 (G) (S) = 1472 Content of phenolic H, Number per 100 C9-units n.a n.a. 10 n.a. H H R R CH 3 H 3 C

6 Mechano-chemical cleavage of β--4 structures in milling H 3 C CH 2 H CH CHH L CH 2 H CH CHH L L CH 3 M. E. Δ L CH 3 + CH 3 -H +H CH 2 H CH 2 C L L CH 3 H CH 3

7 SEC of thioacidolysis products from spruce, eucalyptus and birch wood Absorbance ligomers Trimers Dimers Monomers Spruce Eucalyptus/Birch Time, min

8 Dissolution of wood/pulp fibres by the use of enzyme 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

9 Types of LCC isolated from spruce wood meal Type of -Carbohydrate Complex, LCC yield, % GalactoGlucoMannan - Glucan - GlucoMannan - Xylan

10 SEC of acetylated thioacidolysis products from spruce LCCs Dimer Monomer Xylan-rich LCC (40% lignin on wood) Response Glucomannan-rich LCC (48% lignin on wood) Wood

11 Suggested lignin structures in spruce wood CH H H H Me H Me H H 3 C H H CH 3 H 3 C H H 3 C H H H CH 3 CH 3 H CH 3 H Me Linear xylan-lignin H Me Xylan H Me H Me Me H Branched glucomannan-lignin H 3 C H H H H CH 3 H H 3 C H H H H H 3 C CH 3 H H H CH 3 H CH 3 H 3 C CH 3 H 3 C CH 2 H H H 3 C H 3 C H Glucomannan H H H H H CH 3 H CH 3 H H CH 3 CH 3 CH 3 H H H H CH 3

12 S/G ratios in hardwoods Wood species S/G-ratio Method Reference Birch Birch E. globulus E.globulus E. grandis Thioacidolysis Nitrobenzene Thioacidolysis Pyrolysis Pyrolysis Gellerstedt et al, 2007 Chen, 1992 Gellerstedt et al, 2007 Gutierrez et al, 2007 Gutierrez et al, 2007

13 G-units/S-units in white birch wood Morphological Differentiation 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) Guaiacyl/Syringyl 12 : : : : 9 80 : : 0 88 : 12 Ref. Saka and Goring, 1988

14 The lignin structure in hardwoods contains a high proportion of S-units which results in a high percentage of linear lignin unevenly distributed

15 MS-identification of lignin fragment from E. globulus lignin CH 3 H CH 3 H H CH 3 H H 3 C H H 3 C H 3 C CH 3 H H H 3 C H H 3 C CH 3 H H CH 3 Evtuguin et al, 2003

16 in annual plants rigin content H:G:S Flax Sisal Wheat straw Rice straw 2.9 (+ 1.6) 10.8 (+ 3.0) :33:11 (pyrolysis) 1:20:79 (pyrolysis) 5:49:46 (thioacidolysis) 15:45:40 (thioacidolysis)

17 Content The lignin structure in wood chemistry in pulping Technical lignins

18 Dissolution of lignin and carbohydrates in kraft pulping Residual lignin; removed by bleaching

19 Degree of delignification for different wood species Pulp type Kappa No kappa Pine Birch E. globulus Delign. degree

20 Kraft pulping of birch and E. globulus respectively to similar kappa numbers E. globulus Birch

21 β--4 structures in wood and pulp based on thioacidolysis (birch and eucalyptus) Degradation product, μmol/g of lignin G S Birch B pulp Euc E pulp Klason lignin, %:

22 Size exclusion chromatography (SEC) of lignin degradation products (no residual lignin present in wood) Methodology Thioacidolysis of wood/pulp Acetylation SEC in tetrahydrofuran

23 Suggested mode of formation of radical coupling products in kraft pulping S S S S S S S S S S S S S S S S R H 3 C R CH 3 H 3 C H R H 3 C Δ S S S S S S S S CH 3 H 3 C H H R CH 3 H 3 C H CH 3 R CH 3 Low reactivity due to H-bonding

24 Principles in the steam explosion process (Conditions: ~ o C, 1-5 min)

25 Chemical composition before and after steam explosion Spruce samples Birch samples Wood S2SE nese TwoSE Wood S2SE nese Extractives (Ara)-xyl (Gal)-Gluman Glucan Substantial removal of hemicelluloses and extractives: S2SE > TwoSE > nese

26 isolation yield (hardwoods) Residual Extractable, NaH 20 0 Birch samples Aspen samples S2SE nese S2SE nese S2SE > nese (missing lignin from aspen highly soluble lignin)

27 SEC of acetylated lignin from steam exploded aspen wood

28 Degradability by thioacidolysis/sec analysis Spruce Condensation less degradability

29 Degradability by thioacidolysis/sec analysis, SE aspen monomers S2SE SE

30 Steam explosion chemistry H H H High temperature CH 3 H 3 C Stabilisation CH 3 H H CH 3 CH 3 Hydrolysis, H + H Condensation CH 3 H 3 C H H 3 C CH 3 CH 3 Acidolysis H CH 3

31 Content The lignin structure in wood chemistry in pulping Technical lignins

32 Biomass tree showing the main chemical outlets Ref. Rintekno oy, 1984

33 Highest-value lignin uses to show greatest future rise (W. Glasser) As structure of lignin yields to advances in analytical techniques, new markets are projected in adhesives, foams, films, coatings and plastics Ref: C&EN 1984

34 The Biorefinery Concept Production of large volumes of ethanol will be necessary in a short term New separation process(es) for lignocellulosics required New chemistry based on carbohydrates will be developed for fuel and for chemicals n a longer term, gasification of biomass to syngas (biodiesel) will be developed

35 Indicative targets for the share of biofuel in the EU 2005: 2% (not achieved) 2010: 5.75% (will probably not be achieved) : New energy policy document setting a minimum requirement at 10% by 2020

36 From biomass to liquid fuels Biodiesel from oils and fat; rapeseed etc esterification with methanol Biochemical pathways to ethanol; 1) Sugar beet etc sugar-fermentation 2) Starch crops hydrolysis-sugar-fermentation 3) Lignocellulosics separation-hydrolysis-sugarfermentation; lignin as byproduct Thermochemical pathways to biofuels; 1) lignocellulosics pyrolysis-bio oil-biofuels 2) lignocellulosics gasification-methanol/ft-fuels

37 Feedstock sources Forestry waste (forest residue, bark, wood chips, thinnings) Agricultural residues (straw, stover, bagasse) Energy crops (poplar, willow, switch grass) Municipal waste (paper, packaging,..)

38 Biomass composition Structure Softwood Hardwood Wheat straw (Picea abies) (Betula verrucosa) Cellulose Hemicellulose (C6-sugars) Hemicellulose (C5-sugars) Extractives ther components

39 The ideal separation of biomass

40 and the reality Kraft and soda pulping Sulfite pulping Acid hydrolysis Steam explosion rganosolv pulping At present, none of these processes results in an efficient and cheap separation

41 Elemental analysis Sample carbon hydrogen oxygen sulfur Kraft lignin, pine Kraft lignin, birch Kraft lignin, E. globulus Soda lignin, bagasse Steam explosion, beech

42 Substance Groups in Kraft Black Liquors (kg/ton of pulp) Fraction Pine Birch Hydroxycarboxylic acids Acetic acid Misc. products Ref: Sjöström 1993

43 Principle for manufacturing of lignin from kraft black liquor Black liquor Acid: C 2 or H 2 S 4 Evaporation Precipitation ph = 9 Filtration, Washing Filtrate, wash water Flash drying

44 Solvent fractionation of softwood kraft lignin Fraction Yield M n M w M w /M n CH 2 Cl x x n-propanol x x Methanol x x CH 3 H/CH 2 Cl x x Undissolved x x Unfractionated x x Ref: Kringstad et al

45 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 Permeate Retentate isolation: Precipitation with C 2 (ph 9), Acid washing with H 2 S 4 (ph 2.3), Drying Purification: Cation-exchange to remove traces of Me +

46 SEC of kraft lignins before/after fractionation softwood eucalypt SWL EL SP5 EP5 dw/d log M SR5 dw/d log M ER log M (relative polystyrene) log M (relative polystyrene)

47 SEC-data from fractionated (5 kda) kraft lignins Sample/ SW SW SW Euc. Euc. Euc. polymer data lignin permeate retentate lignin permeate retentate M w M n Polydispersity

48 Thermal analysis of purified kraft lignins sample/ SW SW SW Euc. Euc. Euc. thermal data lignin permeate retentate lignin permeate retentate T g, o C T s, o C T d, o C

49 Even a small lignin withdrawal can be interesting 650,000 tonnes of pulp withdrawal of 10% yields 33,000 tonnes converted to 16,000 tonnes of CF to support 160,000 cars with CF-composite (~40% replacement)

50 Conclusions All native lignins are heterogeneous biopolymers linked to polysaccharides Alkaline or acidic processes result in both lignin degradation and re-polymerisation The up-grading of technical lignins require purification steps Several options exist for an increased lignin use