The Chemistry of Wood and Kraft Pulping ragauskas@hotmail.com 1
Typical Composition of Wood Cellulose (41-53%) Hemicellulose (25-41%) Lignin (16-33%) Extractives (2-5%) Inorganics (<1%) Nitrogen compounds (traces) ragauskas@hotmail.com 2
Compositions of Several North American Pulpwood Species Species Cellulose, % Hemicelluloses, % Lignin, % Balsam Fir 44 27 29 Eastern Hemlock 42 26 33 Eastern White Cedar 44 25 31 White Spruce 44 29 27 Jack Pine 41 30 29 Tamarack 43 28 29 Typical Softwood 43 28 29 Beech 42 36 22 Trembling Aspen 53 31 16 White Elm 49 27 24 Red Maple 41 35 24 White Birch 41 40 19 Yellow Birch 40 39 21 Typical Hardwood 46 34 20 ragauskas@hotmail.com 3
Cellulose (1) ne sugar Linear Long Reducing and nonreducing ends Partly crystalline ragauskas@hotmail.com 4
Cellulose (2) H H H H 4 H H 1 H H H H H H -Cellulose n ragauskas@hotmail.com 5
Hemicelluloses More than one sugar Branched or substituted Short Reducing and nonreducing ends Generally not crystalline ragauskas@hotmail.com 6
Xylan (1) Primary hemicellulose in hardwoods Linear chain backbone of xylose units Substituents are 4--methylglucuronic acid, acetate groups and, in some, arabinose Substituents prevent crystallization, but may be removed during pulping and bleaching ragauskas@hotmail.com 7
Xylan (2) H 4 H H 3 C HC H 1 α β H 1 4 1 H H HH 2 C 4 1α 3 H 1 H 4 H 1 β H 4-β D-Xylp-1 4-β D-Xylp-1 4-β D-Xylp-1 4-β D-Xylp-1 2 3 4-β D-Xyp-1 5 1 4--Me-α D-Glc pa 2 1 α-l-araf ragauskas@hotmail.com 8
Glucomannan (1) Chief hemicellulose component of softwoods Straight chain backbone of mannose units and a smaller number of glucose units More vulnerable than xylan to chemical degradation ragauskas@hotmail.com 9
Glucomannan (2) HH 2 C 4 H H R β 1 4 6 R 1 HH 2 C 4 R R 1 R 4 HH 2 C R 1 β H HH 2 C H H 1 α 4-β D-Glcp-1 4-β D-Manp-1 4-β D-Manp-1 4-β D-Manp-1 6 2,3 1 α-d-galp Ac ragauskas@hotmail.com 10
Lignin Native lignin is a polymer of coniferyl alcohol, sinapyl alcohol, and p-coumaryl alcohol H R 2 β 6 5 γ α 1 4 H 2 3 R 1 Coniferyl alcohol/guaiacyl: R 1 =Me, R 2 =H Sinapyl alcohol/ syringyl: R 1 =R 2 =Me pcoumaryl alcohol: R 1 =R 2 =H A heterogeneous, branched and cross-linked polymer with phenylpropane units linked by C-C and C- bonds Cross-linked with polysaccharide chains ragauskas@hotmail.com 11
Beta--4 Linkage SW: 50% HW: 60% ragauskas@hotmail.com 12
Alpha--4 Linkage SW: 2-8% HW: 7% ragauskas@hotmail.com 13
5-5 Linkage 5-20% ragauskas@hotmail.com 14
4--5 Linkage SW: 4% HW: 7% ragauskas@hotmail.com 15
Beta-5, Beta-1 and Beta-Beta Linkages SW: 9-12% HW: 6% SW: 7% HW: 7% SW: 2% HW: 3% ragauskas@hotmail.com 16
Lignin Reactions During Kraft Pulping Fragmentation Alpha- and beta- aryl ether cleavage in free phenolic units Enol ether formation Alpha- and beta- aryl ether cleavage in etherified units C-C bond cleavage Condensation Bonding to carbohydrates ther reactions ragauskas@hotmail.com 17
Alpha-Aryl Ether Cleavage in Free Phenolic Unit ragauskas@hotmail.com 18
Beta-Aryl Ether Cleavage in Free Phenolic Units ragauskas@hotmail.com 19
Enol Ether Formation ragauskas@hotmail.com 20
Beta-Aryl Ether Cleavage in Etherified Units ragauskas@hotmail.com 21
C-C Bond Cleavage ragauskas@hotmail.com 22
Condensation: Competitive Addition of Nucleophiles to QM s ragauskas@hotmail.com 23
Condensation with Formaldehyde ragauskas@hotmail.com 24
Kraft Pulping Resistant Structures ragauskas@hotmail.com 25
Quinone Formation During Kraft Pulping ragauskas@hotmail.com 26
Lignin Carbohydrates Bonds ragauskas@hotmail.com 27
ther Reactions: Formation of Stilbenes and Enol Ethers ragauskas@hotmail.com 28
Residual Lignin Structure Phenolic hydroxyl groups Beta-aryl ethers C-C bonds Condensation products Functional group analysis Linkages to carbohydrates ragauskas@hotmail.com 29
Phenolic Hydroxyl Groups in Dissolved and Residual Lignins 3.2 Phenolic hydroxyl content (mmol/g) 3.0 2.8 2.6 2.4 2.2 2.0 Kraft lignins Residual lignins 30 25 20 15 Unbleached kappa number 10 Phenolic hydroxyl content of various kraft (from black liquor) and residual lignins versus unbleached kappa number Froass, Peter M.; Ragauskas, Arthur J.; Jiang, Jian E. NMR studies. Part 3. Analysis of lignins from modern kraft pulping technologies. Holzforschung (1998), 52(4), 385-390. Froass, Peter M.; Ragauskas, Arthur J.; Jiang, Jian-er. Nuclear Magnetic Resonance Studies. 4. Analysis of Residual Lignin after Kraft Pulping. Industrial & Engineering Chemistry Research (1998), 37(8), 3388-3394 ragauskas@hotmail.com 30
Beta-Aryl Ethers in Residual and Dissolved Lignins Cγ in β--4 (per aromatic unit) 0.22 0.20 0.18 0.16 0.14 0.12 0.10 Residual lignins Kraft lignins 30 25 20 Unbleached kappa number 15 10 Content of Cγ in β--4 structures for various kraft (from black liquor) and residual lignin versus unbleached kappa number ragauskas@hotmail.com 31
Functional Groups in Lignin Wood/Pulp Froass, Peter M.; Ragauskas, Arthur J.; Jiang, Jian-er. Chemical structure of residual lignin from kraft pulp. Journal of Wood Chemistry and Technology (1996), 16(4), 347-365. ragauskas@hotmail.com 32
Hexenuronic Acid Formation MeGlcA HexA H 3 C H H C 2 H H Kraft pulping H H H 2 C H + CH 3 - xylan Xylan ragauskas@hotmail.com 33