DECNVLUTING CHRMPHRE FRMATIN AND REMVAL DURING KRAFT PULPING INFLUENCE F METAL CATINS Thomas J. Dyer, Art J. Ragauskas Institute of Paper Science and Technology School of Chemistry and Biochemistry Georgia Institute of Technology
Research bjective To contribute to our understanding of the fundamental nature of chromophore formation during kraft pulping Characteristic red-brown color of pulp obtained by cooking wood with a liquor containing sodium hydroxide and sodium sulfide Varies in intensity and shade according: - Wood species - Cooking technology - Cooking parameters
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
Proposed sources Extractives Tannins Kraft Pulp Color Lignin and its reaction products Carbohydrate degradation products Lignin and its degradation products Found to be most responsible for color in kraft BL Pigman and Csellak (1948) Non process elements Calcium Iron Copper, Aluminum, Magnesium
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
Transition Metal Complexes Transition metals May form complexes with catechols 6-7/100 C 9 units in kraft lignin Trace in residual lignin H 2 M H 2 Ferric Ion Complexes λ max = 500-550 nm Addition NPE Studies Jameson and Wilson, 1972; Ghosh, A. and Y. Ni, (1997) Gellerstedt, G. and W. W. Al-Dajani (2001); Sundin, J. and N. Hartler (2000) M
Experimental Design Two central composite designs bjective 1 Constant kappa number 30 27.6 30.9 Four variables Extractives % EA (14-21%) % Sulfidity (23-57%) Maximum temperature (162-178 C) 40 experiments x 3 x 2 x 1
Experimental Parameters 100 g of southern pine wood chips Extracted vs. unextracted Pulped to H-factor From equation Disintegrated Washed thoroughly Screened
Experimental Results Total Pulp Color Total Color % EA, % Sulfidity Significant parameters Max. Temperature Not significant Curvature Due to quadratic relationship 160 150 140 130 120 110 Pulp Color Measurements via diffuse reflectance Integrate k/s curve over visible region (400 700 nm)
Experimental Results Total Pulp Color Total Color Minimal color % EA, % Sulfidity Maximum color % EA, % Sulfidity Brightness Showed similar trends 160 150 140 130 120 110
Impact of Extractives H 0 : µ 1 = µ 2 H 1 : µ 1 µ 2 Average Kappa # S.D. Unextracted Wood Chips 29.42 1.06 Extracted Wood Chips 28.66 1.05 Extracted vs. unextracted wood chips 0.06% vs. 1.80% extractives t (calculated) p-value 1.24 0.19 Extracted vs. Unextracted Statistically the same kappa pulps at 95% CI Critical region: t > 2.228 with ν = 10
Impact of Extractives Total Color 150 140 130 120 110 100 90 80 Unextracted Wood Chips 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Sample Extracted Wood Chips Total Color Extracted vs. unextracted ANVA Indicates the two are significantly different Brightness Extracted vs. unextracted ANVA Indicates the two are not significantly different
Impact of Transition Metals Ca 2+ vs. EA Potential contributors Fe, Mg, Al, Mn, Ca, etc. Which are important?? Measured metals ICP Most other metals had a significant amount of variation when compared against pulping conditions, except S and Ca. Higher cooking sulfidity higher S in pulp Calcium (mg/kg pulp) 2000 1800 1600 1400 1200 1000 800 600 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 Initial EA (mol/l) Higher EA Lower Ca Consistent with Gustavsson et al Nordic Pulp and Paper Research Journal 14(1): 71-81 (1999)
Relationship Between Pulp Color and Ca ++ Chromophore Index 150 140 130 120 110 100 90 80 70 no good correlation between the pulp chromophore index and the iron in the pulp 60 800 1000 1200 1400 1600 1800 2000 Calcium Content (mg/kg pulp) How much is due to metals vs. other components
Examining The Relationship Between Color and Pulp Metals Experimental Procedure ph 3.0, 4ºC 48 hour Ca, Mg, Mn All reduced 77-88% Fe, Al Typically 10 30% H H 2 C H H H Decrease in HexA 2-5% Xylan
Relationship Between Pulp Color and Ca ++ Chromophore Index 150 140 130 120 110 100 90 80 70 60 50 47% Ca: 1080 ppm 55% Ca:1430 Before Treatment After Treatment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Sample verall 48% reduction in color Sample 2 high effective alkali (20%), moderate sulfidity (30%) Sample 7 low effective alkali (16%) and a high sulfidity (50%) Principle component analysis examined source of variation in chromophore index 98% of the variation in chromophore index could be accounted through Mn, Mg, Ca at constant kappa number
Charting Color Formation Through Kraft Pulping Two pulping conditions High %EA, Low % Sulfidity Low Color Low %EA, High % Sulfidity High Color
Color Formation vs. Time Chromophore Index 300 250 200 150 100 50 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Brighter pulp 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 Brighter pulp 0 5 10 15 20 25 Klason Lignin Content (%)
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 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 Chromophore Index 300 250 200 150 100 50 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Brighter pulp 0 10 20 30 40 50 60 70 80 Surface Lignin Content (%)
Impact of Calcium Klason Lig nin Content (% ) 25 20 15 10 5 0 21.4% EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity 900 1400 1900 2400 2900 3400 3900 Calcium Content (ppm) Calcium Studies by Sundin & Hartler Lignin precipitation Li and Reeve Darker lignin Precipitate on surface
D T P A A c id U n tre a te d D T P A A c id U n tre a te d Impact of Metals 1. Q (Acid or DTPA) 2. Kraft Pulping ppm 600 500 400 300 DTPA Acid Untreated ppm 2000 1500 1000 DTPA Acid Untreated 200 100 500 Wood 0 Ca Mg Mn Fe 0 Ca Mg Kappa 30 Mn Fe
Impact of Metals 1. Q 2. Kraft Pulping Chromophore Index Kappa 30 154 152 150 148 146 144 142 140 138 136 134 Untreated Acid Chelated
DECNVLUTING CHRMPHRE FRMATIN For the Pulps Examined Non process elements are a major contributor to color Ca, Mg, Mn are key contributors Wood NPE pre-extraction is important But is it important??
Mill Pulp Properties Two pulp mills Similar products Similar pulping conditions Same wood source bservations Lower kappa pulp-pulp B Tappi Brightness: 18 Pulp A Washer Refiner Inlet Refiner utlet Reel Average Kappa Number 73.0 77.7 79.7 83.9 Pulp B Washer Reg. Box Blend Chest Reel Average Kappa Number 55.1 59.8 64.9 65.6 - Higher kappa pulp-pulp A Tappi Brightness: 27
Mill Pulps Transition Metals Pulp A Ca Mn Mg Fe Pulp B Ca Mn Mg Fe (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) Washer 1202 128 285 19 Washer 3033 57 490 37 Refiner Inlet 1507 140 355 29 Reg. Box 2403 40 439 32 Refiner utlet 1517 143 331 23 Blend Chest 2470 44 513 33 Process parameters were implemented that changed NPE s and brightness values of Pulp B were raised
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 Differences in optical properties can not be attributed to surface lignin concentration for pulps studied Non Process Elements: Ca, Mg, Mn significant contributor to pulp color BUT Prior EWLP reported studies 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
Acknowledgements DE, USDA Member Companies of IPST@GT