The Tincture of Kraft Pulps Art J. Ragauskas, Tom J. Dyer Institute of Paper Science and Technology Georgia Institute of Technology
verview of Kraft Pulping + 200 year old technology Insensitive to wood species, relatively rapid Integrated system is conservative on chemicals and energy Yields a high quality product Withstands numerous challenges, mechanical pulping, soda, soda/aq, organo-solv Limitations: Yield AQ, H-factor, EA/Sulfidity dor Chemical scrubber technology Pulp color $40 60 x 10 6 bleach plant???????????? WHY
The Problem Holzer/1934: Presence of sulfur darkens the color of kraft pulp more than that of a comparable soda pulp Bard/1941: Color may be produced by adsorption or absorption of colored material from the black liquor Pigman and Csellak/1948: Among the first to pinpoint lignin and its degradation products as responsible for the bulk of the color found in kraft pulps, possible carbohydrate contribution Hartler and Norrström/1960, 70 s: verall, the contribution from carbohydrates is low throughout the cook
Possible Chromophoric Structures L M L CH 3 L rtho-quinone Para-Quinone Catechol-Metal Complex L L L H H CH 3 Hydroxy-Quinone H L L Stilbene or Enol Ether H CH 3 (Conjugated Carbonyl, Aromatic, Furan Derivatives) Alpha-Carbonyl Stilbene-Quinone Carbohydrate Derived
Research Goals To explore the fundamental nature of chromophore formation during kraft pulping To obtain a better understanding of and define the particular lignin functionalities that are responsible for color formation in kraft pulps To determine the kraft pulping parameters having the greatest impact on color formation during kraft cooking Chart color formation through the kraft pulping process
Experimental Kraft Pulping Added 100 g southern pine wood chips to individual vessels
Experimental Kraft Pulping Added 100 g southern pine wood chips to individual vessels Added mixture of NaH, Na 2 S (4:1 L/W) NaH + Na 2 S
Experimental Kraft Pulping Added 100 g southern pine wood chips to individual vessels Added mixture of NaH, Na 2 S (4:1 L/W) Vessels placed in rotating digester
Experimental Kraft Pulping Added 100 g southern pine wood chips to individual vessels Added mixture of NaH, Na 2 S (4:1 L/W) Vessels placed in rotating digester 90 min. ramp to maximum temperature Temperature ( o C) 180 160 140 120 100 80 60 40 20 0 0 50 100 150 Time (minutes)
Experimental Kraft Pulping Added 100 g wood chips to individual vessels Added mixture of NaH, Na 2 S (4:1 L/W) Vessels placed in rotating digester 90 min. ramp to 170 o C Cooled in water bath
Experimental Kraft Pulping Disintegrated wood chips
Experimental Kraft Pulping Disintegrated wood chips Thoroughly washed and screened pulps
Experimental Design x 3 Central composite design Regression equation Constant lignin content Three process variables % EA (14-21%) % Sulfidity (23-57%) Maximum temperature (162-178 C) 20 experiments x 2 x 1
806 170 40 18 20 806 170 40 18 19 806 170 40 18 18 806 170 40 18 17 806 170 40 18 16 806 170 40 18 15 806 178.4 40 18 14 806 161.6 40 18 13 646 170 56.8 18 12 1217 170 23.2 18 11 565 170 40 21.4 10 1352 170 40 14.6 9 522 175 50 20 8 929 175 50 16 7 790 175 30 20 6 1294 175 30 16 5 570 165 50 20 4 929 165 50 16 3 790 165 30 20 2 1349 165 30 16 1 H-Factor Temperature Sulfidity, % EA, % Sample
Pulping Results Lignin Content Target 4.5% lignin 4.95 Confidence interval 6 replicates Samples 15-20 ± 0.32% Lignin Content, % 4.75 4.55 4.35 4.15 All samples are statistically the same At 95% C.I. 3.95 3.75 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Sample
K-M Remission Function Use optically thick handsheets Diffuse reflectance 3 2.5 2 1.5 k/s Area under Curve = Chromophore Index Integrate k/s curve over visible region 1 Chromophore Index 0.5 0 350 400 450 500 550 600 650 700 750 Wavelength (nm)
Results Chromophore Index Chromophore Index % EA, % Sulfidity Significant parameters Max. Temperature Not significant Curvature Due to quadratic relationship 160 150 140 130 120 110
Results Chromophore Index Chromophore Index Minimal color % EA, % Sulfidity Maximum color % EA, % Sulfidity 160 150 140 130 120 110
Pulp Color Formation vs. Cooking Time 300 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Chromophore Index 250 200 150 100 50 50 70 90 110 130 Cooking Time (minutes after 100 o C)
Color Formation vs. Lignin Content Chromophore Index 300 250 200 150 100 50 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity What is the Fundamental Component Contributing to the Difference in Color for These Pulps? 0 5 10 15 20 25 Klason Lignin Content (%)
Surface Lignin ESCA Electron Spectroscopy for Chemical Analysis Bombard surface with x-rays Substrate ejects electrons Specific binding energy Depends on type of atom Measures 2-9 nm into surface X-ray source Electrons Analyser Treated paper samples Mercuric acetate Specific for lignin Westermark (1999) Heijnesson et al. (2003) Sample Channeltron detector
Surface Lignin Content vs. Bulk Lignin Surface Lignin Content (%) 80 70 60 50 40 30 20 10 0 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity R 2 = 0.99 0 5 10 15 20 25 Klason Lignin Content (%) Conclusion: Color Differences are NT Due to Difference in Surface Lignin Content ther Parameters Must Be Involved!
Color Formation vs. Surface Lignin 300 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Chromophore Index 250 200 150 100 50 0 10 20 30 40 50 60 70 80 Surface Lignin Content (%)
Residual Lignin Studies
Isolation of Residual Lignins Pulp Reflux for 2 hrs (4% cons.) in 0.1N 9:1 dioxane:hcl Filter (coarse) Filter (fine) Neutralize Remove dioxane under reduced pressure Precipitate lignin wash lignin x3 Lyophilize Spectral Characterization
Color Formation vs. Lignin Content Condition A Condition B Absorptivity (l g -1 cm -1 ) at 430 nm 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 Low Sulfidity 0 5 10 15 20 25 Klason Lignin (%) Residual lignin UV/Vis results parallel pulp results, suggesting that isolation procedure has not influenced chromophore properties 300 Condition A: Pulping with high effective alkali/low sulfidity. Condition B: Pulping with low effective alkali/high sulfidity (darker) Chromophore Index 250 200 150 100 50 0 0 0.2 0.4 0.6 0.8 1 1.2 Visible Absorbance from Lignin * klason
Characterization of Residual Lignins UV/Vis Ionization Difference εi A-1 A-4 A-7 B-1 B-4 B-9 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0-0.1-0.2 230 280 330 380 430 480 530 Wavelength (nm) 370 nm: Phenolic stilbenes 350 nm: Phenolic α-carbonyl units 250 nm Unconjugated Phenolics εi 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 250 nm 300 nm 350 nm A-1 A-4 A-7 B-1 B-4 B-9 Sample Condition A: Pulping with high effective alkali/low sulfidity. Kappa # 163, 69, 30 Condition B: Pulping with low effective alkali/high sulfidity Kappa # 152, 69, 30 Color differences in pulps A vs. B can not be due to phenolic stilbenes
Trimethylphosphite Chemistry Reaction with rtho-quinone Structures P(CH3)3 P(CH3)3 P CH3 CH3 CH3 I II III H 2 R R R=P(CH 3 )(H) or H
Typical 31 P NMR-TMP Spectrum rtho-para Quinone Adduct P Internal Standard: tri-m-tolylphosphate 0-5 -10-15 -20-25PPM
Quinones Quinone (mmol/g lignin) 0.40 0.32 0.24 0.16 0.08 0.00 Condition A Condition B Lighter 0 5 10 15 20 25 Klason Lignin (%) Condition A: Pulping with high effective alkali/low sulfidity/brighter Kappa # 163, 69, 30 Condition B: Pulping with low effective alkali/high sulfidity/darker Kappa # 152, 69, 30 Quinones Could Be a Component in Color Difference in these Pulps But Extinction Coefficients Must Differ or Not a Key Factor
19 F-NMR Aliphatic Carbonyls Condition A Condition B Aliphatic Carbonyls (mmol/g lignin) 1.0 0.8 0.6 0.4 0.2 0.0 0 5 10 15 20 25 Klason Lignin (%) Aliphatic carbonyl do not Contribute to the bserved ptical Differences in Pulp A & B
FT-IR Carbonyls % Carbonyl in Lignin 5.30 5.10 4.90 4.70 4.50 4.30 4.10 3.90 3.70 3.50 Condition A Condition B 0 5 10 15 20 25 Klason Lignin (%)
Characterization of Residual Lignins 31 P NMR CH 3 CH 3 P Cl + Lignin-H CH 3 CH 3 CH 3 CH 3 P Lignin CH 3 CH 3 P R P Me P Me P R
Residual Lignin Analysis 31 P NMR 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Aliphatic H (mmol/g lignin) 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0 5 10 15 20 25 Klason Lignin (%) Differences exist!
Residual Lignin Analysis 31 P NMR 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Phenolic H (mmol/g lignin) 1.0 0.9 0.8 0.7 0.6 0.5 0 5 10 15 20 25 Klason Lignin (%) Biphenyl H (mmol/g lignin) 0.60 0.55 0.50 0.45 0.40 0.35 Condition A Condition B 0.30 0 5 10 15 20 25 Klason Lignin (%) Condensed Phenolics Appear to Contribute to the bserved ptical Differences in Pulp A & B
Catechol In Pulp Condition A Condition B 0.18 Catechol H (mmol/g lignin) 0.16 0.14 0.12 0.10 0.08 0 5 10 15 20 25 Klason Lignin (%) Catechols do not appear to contribute to optical differences for pulps A and B
Conclusions
Conclusions verall color of kraft pulp Influenced by pulping parameters % EA, % Sulfidity are significant Maximum temperature not significant within experimental limitations Chromophore content Changes with pulping, depending on conditions More surface lignin needed for light colored pulp to obtain same chromophore content
Conclusions Lignin functional groups Provide further evidence that lignins from two different conditions are very different Quinones, Condensed Phenolics, Aliphatic hydroxyls Appear to be contributors to the color difference of kraft pulps studied Aliphatic carbonyl, Noncondensed phenolics, Catechols Do not Appear to be Important contributors to the color difference of kraft pulps studied Differences in optical properties can not be attributed to surface lignin concentration for pulps studied
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