DECONVOLUTING CHROMOPHORE FORMATION AND REMOVAL DURING KRAFT PULPING INFLUENCE OF METAL CATIONS

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Margaret Clemence Mills
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1 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

kraft pulping Characteristic red-brown color of pulp

hydroxide and sodium sulfide Varies in intensity and

2 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

absorption of colored material from the black liquor Pigman and Csellak/1948: Among

of the color found in kraft pulps, possible carbohydrate contribution Hartler and

3 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

4 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

5 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

6 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 = 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

7 Experimental Design Two central composite designs bjective 1 Constant kappa number Four variables Extractives % EA (14-21%) % Sulfidity (23-57%) Maximum temperature ( C) 40 experiments x 3 x 2 x 1

8 Experimental Parameters 100 g of southern pine wood chips Extracted vs. unextracted Pulped to H-factor From equation Disintegrated Washed thoroughly Screened

9 Experimental Results Total Pulp Color Total Color % EA, % Sulfidity Significant parameters Max. Temperature Not significant Curvature Due to quadratic relationship Pulp Color Measurements via diffuse reflectance Integrate k/s curve over visible region ( nm)

10 Experimental Results Total Pulp Color Total Color Minimal color % EA, % Sulfidity Maximum color % EA, % Sulfidity Brightness Showed similar trends

11 Impact of Extractives H 0 : µ 1 = µ 2 H 1 : µ 1 µ 2 Average Kappa # S.D. Unextracted Wood Chips Extracted Wood Chips Extracted vs. unextracted wood chips 0.06% vs. 1.80% extractives t (calculated) p-value Extracted vs. Unextracted Statistically the same kappa pulps at 95% CI Critical region: t > with ν = 10

12 Impact of Extractives Total Color Unextracted Wood Chips 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

13 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) Initial EA (mol/l) Higher EA Lower Ca Consistent with Gustavsson et al Nordic Pulp and Paper Research Journal 14(1): (1999)

14 Relationship Between Pulp Color and Ca ++ Chromophore Index no good correlation between the pulp chromophore index and the iron in the pulp Calcium Content (mg/kg pulp) How much is due to metals vs. other components

15 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

16 Relationship Between Pulp Color and Ca ++ Chromophore Index % Ca: 1080 ppm 55% Ca:1430 Before Treatment After Treatment 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

17 Charting Color Formation Through Kraft Pulping Two pulping conditions High %EA, Low % Sulfidity Low Color Low %EA, High % Sulfidity High Color

18 Color Formation vs. Time Chromophore Index % EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Brighter pulp Cooking Time (minutes after 100 o C)

19 Color Formation vs. Lignin Content Chromophore Index % EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Brighter pulp Klason Lignin Content (%)

20 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

21 Surface Lignin vs. Bulk Lignin Surface Lignin Content (%) % EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity R 2 = Klason Lignin Content (%) Conclusion: Color Differences are NT Due to Difference in Surface Lignin Content ther Parameters Must Be Involved!

22 Color Formation vs. Surface Lignin Chromophore Index % EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Brighter pulp Surface Lignin Content (%)

23 Impact of Calcium Klason Lig nin Content (% ) % EA, 23.2% Sulfidity 14.6% EA, 56.8% Sulfidity Calcium Content (ppm) Calcium Studies by Sundin & Hartler Lignin precipitation Li and Reeve Darker lignin Precipitate on surface

24 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 DTPA Acid Untreated ppm DTPA Acid Untreated Wood 0 Ca Mg Mn Fe 0 Ca Mg Kappa 30 Mn Fe

25 Impact of Metals 1. Q 2. Kraft Pulping Chromophore Index Kappa Untreated Acid Chelated

26 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??

27 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 Pulp B Washer Reg. Box Blend Chest Reel Average Kappa Number Higher kappa pulp-pulp A Tappi Brightness: 27

28 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 Washer Refiner Inlet Reg. Box Refiner utlet Blend Chest Process parameters were implemented that changed NPE s and brightness values of Pulp B were raised

29 Conclusions

30 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

31 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

32 Acknowledgements DE, USDA Member Companies of

The Tincture of Kraft Pulps. Art J. Ragauskas, Tom J. Dyer Institute of Paper Science and Technology Georgia Institute of Technology

The Tincture of Kraft Pulps. Art J. Ragauskas, Tom J. Dyer Institute of Paper Science and Technology Georgia Institute of Technology 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