New Insights into Eucalyptus Lignin & Pulping Chemistry

Transcription

1 New Insights into Eucalyptus Lignin & Pulping Chemistry Anderson Guerra, Ilari Filpponen, Lucian A. Lucia and Dimitris S. Argyropoulos rganic Chemistry of Wood Components Laboratory Department of Forest Biomaterials Science & Engineering North Carolina State University Raleigh, North Carolina, USA

2 Eucalyptus Becoming a species of extreme significance A species about which we need to accumulate knowledge Eucalyptus is Here to Stay

3 BJECTIVES To isolate lignin from Eucalyptus in high yield and purity To provide new insights into the structure of lignins from Eucalyptus grandis and globulus To compare and contrast how green liquor interacts with lignin isolated from Eucalyptus and selected softwoods

4 UTLINE bjectives Lignin Isolation from Eucalyptus and Selected Softwoods Discuss Functional Group Chemistry amongst Different Species Chemical Effects of Green Liquor Impregnation Conclusions

5 LIGNIN ISLATIN FRM EUCALYPTUS AND SELECTED STWDS Part I:

6 WD SPECIES Eucalyptus globulus Eucalyptus grandis White fir Redwood

7 WD Lignin Isolation Procedures Wiley mill Extraction Ball Milling Soluble Extraction with dioxane:h 2 Insoluble Enzymatic Hydrolysis Insoluble Residue Soluble Purification Enzymatic Hydrolysis Mild acidolysis MWL CEL Purification Extraction with dioxane:h 2 EMAL Guerra et al., J. Agric. Food Chem., 2006, 54,

8 Yields (%) Gravimetric yields MWL CEL EMAL Redwood White fir E. globulus Different wood species offer different yields when isolated with the same method The combination of enzymatic hydrolysis and mild acid hydrolysis offer significant improvements over the traditional procedures for isolating lignin

9 Part I: Determination of Units Bearing Free Phenolic Hydroxyl Groups

10 Quantitative 31 P-NMR with reagent II RH + Cl - P CH3 CH3 CH3 CH3 Pyridine CDCL 3 R - - P CH3 CH3 CH3 CH3 + HCl 2-Chloro-4,4,5,5,-tetramethyl-1,3,2-dioxaphospholane Granata and Argyropoulos. J. Agric. Food Chem., 1995, 43 (6),

11 H 2 CH H C H 3 C H 3 C CH H C HC H C H 2 H 3 C 1 H C H HCH C H 2 H 5 6 H C H HC C H C CH C H H 2 C ( 4 C H 3 H 3 C H CH H C H 2 C H 3 H C H C H HC H C H 2 C H 3 C H 2 CH 10 H C H 3 H 3 C H C CH C H 2 H 9 C H 2 CH C H 7 C C H CH 2 C H 3 H 13 H 2 CH C H H C H 2 CH H 3 C C H HC 8 12 H 2 CH C H H C H H 3 C C H 3 H H 3 C H ( P o l y s a c c ha r i de s ) H C H 2 CH 15 C H HC H 2 CH C H HCH C H H 2 CH 14 C H 2 HC H C H 17 H H 2 CH H C HCH 20 HC H C C H 3 C H 2 CH 2 C H 3 H 2 C H C H C H 3 CH C H 19 C H 3 Sakakibara, A. Wood Science Technology, 1980, 14,

12 Quantitative 31 P NMR of EMAL from E. globulus using reagent II Internal Standard Aliphatic H S-H G-H CH H-H ppm Granata and Argyropoulos. J. Agric. Food Chem., 1995, 43 (6),

13 Hydroxyl Groups (mmol/g) Uncondensed phenolic units Syringyl units Guaiacyl units p-hydroxyphenyl units Total uncondensed PH White fir Redwood E. globulus E. grandis E. grandis and globulus have lower total phenolic hydroxyl contents than the examined softwoods The total uncondensed PhH within EMAL from E. globulus is higher than in E. grandis The S/G ratio calculated for E. globulus (1.78) was higher than for E. grandis (1.46)

14 Quantitative 31 P-NMR with reagent I RH + Cl - P H H H H Pyridine CDCL 3 R - - P H H H H + H Cl 2 - Chloro - 4,4,5,5, tetramethyl - tetramethyl - 1,3,2 dioxaphospholane - 1,3,2 - Argyropoulos, D. S. J. Wood Chem. Technol., 1994,

15 Quantitattive 31 P NMR of EMAL from E. globulus using reagent I Erythro N-Hydroxynaphthalimide --4 S-H Threo G-H ppm Argyropoulos, D. S. J. Wood Chem. Technol., 1994,

16 Quantitative 31 P NMR of EMAL from Redwood by using reagent I N-Hydroxynaphthalimide Aliphatic H --4 G-H Erythro Threo H-H CH Argyropoulos, D. S. J. Wood Chem. Technol., 1994,

17 Part I: Determination of Units Bearing Etherified Phenolic Hydroxyl Groups

18 Application of 31 P NMR for Determining β-aryl Ether Linkages Quantitative 31 P NMR can Determine only TERMINAL -H Terminal H H ß--4 When --4 linkages are selectively cleaved, an equivalent amount of Phenolic -H will be produced.. Quantitative 31 P NMR Enables the Determination of β--4 linkages H H

19 H H H CH3 3 H AcBr Lignin Step 1 Ac Br Br Ac Lignin CH 3 H CH 3 Ac CH 3 31 P NMR Step 2 Zn Ac/Py Ac Ac P CH 3 CH 3 Ac P Lignin Cl P Me Me Me Me Ac Ac H CH 3 CH3 3 Ac H Lignin

20 Arylglycerol- -aryl ether --aryl Ether (mmol/g) Threo Erythro Total arylglycerol- -aryl ether 0 White fir Redwood E. grandis E. globulus E. grandis and E. globulus have more arylglycerol- -aryl ether than the examined softwoods E. globulus is richer in arylglycerol- -aryl ether units than E. grandis ~ 20% The erythro/threo ratios were similar in White fir and Redwood, while the erythro form predominates in Eucalyptus

21 Part I: Molecular Weight Distribution and Propensity to Associate

22 Freshly prepared lignin solutions Association or covalent bonds White fir E. Globulus Redwood E. grandis Molecular Weight x 10 3 (g/mol) Different wood species display different molecular weight distribution The chromatograms of EMAL from softwoods displayed a bimodal behavior, while E. grandis and E. globulus showed only a low-mw peak and a small shoulder extending over 100 x 10 3 g/mol

23 Conclusions (Part I) The combination of enzymatic hydrolysis and mild acid hydrolysis offered the possibility to isolate lignin in high yields from Eucalyptus wood species The structures of different species of Eucalyptus are significantly different

24 Part II: Fundamental Studies of the Chemical Effects of Green Liquor Impregnation (GL) on Eucalyptus

25 Dissolved lignin in liquor g/l Pulping kinetics Conventional KP GL modified KP minutes Cook Time (min) KP = kraft pulping

26 Part II: AA kappa EA Rejects Yield The amount of active alkali required to prepare low-yield Eucalyptus Grandis pulps can be significantly reduced by using GL-modified kraft pulping (saving of up to 14.7%) The amount of rejects were 52.9% lower for GL-treated pulp

27 Lignin time = 0.5, 1, 2, 5, 10, 30, 60 Temperature = C Synthetic Green Liquor NaH 11 g/l; Na 2 S 37.2 g/l; Na 2 C 3 76 g/l Quantitative Recovery Lignin After Impregnation 31 P NMR Scheme 1. Lignin impregnation with synthetic green liquor

28 Part II: E. grandis E. globulus Softw oods Pretreatment Time (min.) For the actual process of scission of the -aryl ether bonds two kinetics regimes operate A significant part of the total -aryl ether bonds were degraded in an initial fast phase that was followed by another slower phase

29 Part II: Table 1. Kinetic data describing the degradation of the arylglycerol- -aryl units in EMAL from different wood species under GL treatment conditions EMAL from Rate Constant (k x 10-2 ) (min) Fast Phase Slow Phase E. Globulus E. Grandis Softwoods The cleavage of arylglycerol -aryl ether linkages during GL impregnation of softwoods is faster than in hardwoods Degradation of such linkages in E. globulus was faster than in E. grandis

30 Part II: Fast phase Slow phase Rate Constant (k) min PhH (mmol/g) The higher the phenolic hydroxyl contents, the faster the degradation of arylglycerol -aryl ether linkages during GL impregnation

31 Conclusions (Part II) Green liquor pretreatment of Eucalyptus wood chips offered significant savings in the total amount of active alkali, besides reducing the rejects and the residual lignin retained on the fibers The higher the amount of free phenolic hydroxyl contents within the lignin, the faster the degradation of arylglycerol- -aryl ether structures under GL impregnation conditions

32 Conclusions (final) The lignin structure of different Eucalyptus species is significantly different, thus affecting their pulping performance