Pulp Properties Influencing xygen Delignification Bleachability A.J. Ragauskas Institute of Paper Science and Technology arthur.ragauskas@ipst.gatech.edu
xygen Delignification M i l l i o n T o n s Chemical Usage of North American Bleach Plants 200 150 100 50 0 Chlorine 2 Delign. 1983 1986 1994 2000 Total Cl2 Improved environmental and operating cost performance
xygen Delignification Increased interest in one and two-stage oxygen delignification Pulp Yield, %. 50 49 48 47 46 45 44 Kraft 43 42 41 40 39 38 0 10 20 30 40 50 60 DEopD DEopD 30 () 30 ECF 50 () 40 () KAPPA Improved environmental, operating, and capital cost performance
xygen Delignification: Back ground Citations 700 600 500 400 300 200 100 0 1965-70 1970-75 1975-80 1980-85 1985-90 1990-95 1995-99 Literature 1960/70s basic engineering & chemistry 1980/early 90s process parameters, energy, environmental, pretreatments, fundamental chemistry, pulp properties Late 1990 s yield, selectivity, process parameters, lignin/carbohydrate chemistry, catalysts
Fundamentals of xygen Delignification
xygen Delignification: Back ground Lignin - NaH 2 2 H CH 3 - CH 3 CH 3 CH 3 Free Phenolic 2 2 -MeH Fragmented Lignin Acid & ketone groups C 2 - C 2 - H 3 C -
xygen Delignification: Back ground 2 + e - H + + e - H + H HH + e - H + HH + H + e - H + 2 HH oxygen perhydroxl radical hydrogen peroxide water & hydroxyl radical water H + 2 superoxide radical H + - H H + perhydroxyl anion oxoanion pka 4.8 pka 11.8 pka 11.9 Several potential bleaching agents with varying sensitivities to reactions with transitional metals
xygen Delignification: Back ground Free Phenolic R NaH 2 R 2 - R R H CH 3 CH 3 CH 3 - CH 3 Chain Fragmented Lignin Enriched with carbonyl groups
xygen Delignification: Back ground 2 CH 3 H NaH Free Phenolic H MeH H NaH 2 C - 2 (colored) C 2 -
Delignification: Lignin Structure Studies xygen delignification leads to a decrease of various types of phenolic groups in residual lignin. However, condensed phenolics survived...to a large extent Jiang & Argyropoulos, JPPS, 1999. xygen delignification does not change the residual lignin structure of kraft pulp to a large-degree Moe & Ragauskas. Holzforschung, 1999. After the oxygen stage, the isolated residual lignin seems to have a somewhat more intact and less oxidized structure than the corresponding lignin from the unbleached pulp. Gellerstedt, Heuts, & Robert, JPPS, 1999. Discrepancies exist between model compound and residual lignin studies
Delignification Research bjectives - I Examine use of standard, Pa, and aggressive * delignification conditions on high and low kappa pulps evaluated by: % Delignification Brightness Viscosity Fundamental lignin structures
Delignification: Experimental Design Bleaching Conditions Bleach Sequences 75 psig, 60 min., 6% csc High Kappa SW kraft (47) : 2% NaH, 90 o C *: 4% NaH, 105 o C Low Kappa SW kraft (24) : 1% NaH, 90 o C *: 2% NaH, 105 o C Pa: 4% Pa, ph 8, 70 o C distilled peracetic acid High Kappa SW, *, Pa, Pa*, Pa Low Kappa SW, *, Pa, Pa*
Delignification Research bjectives-ii Determine how varying and Pa-stages influences residual lignin structure and controls bleachability Lignin Analysis Techniques Isolate residual lignin Analyze residual lignin functional groups: uncondensed phenoxy free phenoxy acid groups quinones carbonyl groups-- ketones
, *, and Pa Delignification Results
-Delignification High Kappa Delignification Pa equivalent to * >> Pa or Pa* >> * Brightness increases as % delign. increases* Low Kappa Delignification Pa > * Pa treated pulps usually exhibit a higher brightness
-Delignification: Viscosity vs. Delignification Delignification (%) 100 80 60 40 20 Pa* * Pa Pa Low Kappa Pa* * Pa 0 10 15 20 25 30 35 Viscosity (cp) High Kappa Greater delignification incurs greater loss in viscosity Higher kappa pulps yield higher post viscosity
-Delignification: Viscosity vs. Brightness Brightness (% IS) 60 50 Pa* Pa Pa Pa* 40 * * Pa 30 Low kappa High kappa 20 10 15 20 25 30 35 Viscosity (cp) Higher kappa pulp yields higher brightness at a given brightness
- Delignification: Summary Pulp Results High kappa SW pulp responded very well to all treatments Pa improved performance >50% delignification is a possible target What is the Chemistry? Color Bodies CH 3 Reactive Sites CH 3 H 3 C H H H CH 3
Fate of Quinones and Carbonyl Groups After, *, & Pa
- Delignification: Quinones Quinones Lignin P(CH 3 ) 3 H 2 H 3 C H 3 C P "Quinone" Lignin 0.1 BS:47 * Pa Pa* Pa BS:24 * Pa Pa* 0.08 0.06 0.04 0.02 0 Quinone (mmol/gr lig.)
- Delignification: Quinones 19 F-NMR: Lignin IS Carbonyl + H 2 NNH CF 3 NNH CF 3 Quinone -56-57 -58-59 -60-61 -62-63ppm
- Delignification: Quinones Quinone (mmol/g Lignin) 0.6 0.5 0.4 0.3 0.2 0.1 0.0 BS(47) P31 F19 * Pa Pa* Pa D Minor increase in quinones and virtually no increase in carbonyl content of residual lignin
- Delignification: Phenoxy Groups Reactive PhH mmol/gr Lign. 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 BS:47 :27 Pa:19 Pa:19 Uncond. Phenoxy Condensed Phenoxy *14 Pa*10 :10 CH 3 H Unreactive H 3 C H H CH 3
- Delignification: Acid Groups 3 PhH mmol/gr Lign. 2.5 2 1.5 1 0.5 0 BS:47 :27 Pa:19 Pa:19 *14 Pa*10 :10 BS:24 :14 *:8 Pa*7 Generally Acid groups % delign. Pa introduces more acid groups Note: despite increased lignin solubility resistant to extraction
- Delignification: β--aryl Ether Groups PhH mmol/gr Lign. 0.22 0.2 0.18 0.16 0.14 0.12 H H Me Me Important linkage in pulping & D Not in 0.1 0.08 BS:47 :27 Pa:19 Pa:19 *14 Pa*10 :10 BS:24 :14 *:8 Pa*7 Note: PhMe does not change
- Delignification: Residual Lignin Results Primary site of oxidation is unsubstituted phenolics Substituted phenols resistant to oxidation Lignin structure enriched in acid groups Quinones/carbonyls appear not to accumulate during - delign. hence brightness gains not due to their destruction PhMe and β--aryl ether unreactive
- Delignification: Implications Enhanced -stages must activate both condensed and unsubstituted PhHs. Cleavage of β--aryl ether may improve delign. Lignin model compounds provided limited practical guidance. Mass transfer limitations could explain portions of residual lignin chemistry.
IPST Member Companies L. Allison arthur.ragauskas@ipst.edu or http://home.ipst.edu/~aragausk//