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Transcript of Quantification of hexenuronic acids in E. globuluseucalyptus.com.br/icep04/16_Mendonca.pdf ·...
Quantification of hexenuronic acids in E. globulus kraft pulps by chromatographic and
spectroscopic techniques
Regis Teixeira Mendonça Facultad de Ciencias Forestales y Centro de Biotecnología
Universidad de Concepción
Kraft pulping and HexA
The degradation of some hemicelluloses during kraft pulping led
to the formation of the hexenuronic acids (HexA).
• Arabino-4-O-methylglucuronoxylan (softwoods).
• Acetyl-4-O-methylglucuronoxylan (hardwoods).
Methylglucuronic acid (MeGlcA)
• Not a major problem in kraft pulping of softwoods (SW).
• Most SW have low amount of MeGlcA.
• More important when pulping hardwoods (HW).
• Main hemicellulose in HW is acetyl-4-O-
methylglucuronoxylan (~ 15-30% of wood weight).
Hexenuronic acids
Importance of HexA
• HexA reacts with KMnO4 during kappa number determination overestimating residual lignin in pulp.
• 10 mmol HexA/kg pulp = 0.84-0.86 units in kappa (Li and Gellerstedt, 1997).
• HexA increase consumption of bleaching chemicals (Cl2, ClO2 and O3).
• HexA decreases brightness stability.
There are several techniques for HexA quantification
Vuourinen et al. 1999 UV Spectroscopy
Chai et al. 2001 HgCl2/Na-acetate UV Spectroscopy
Teleman et al. 1996, Tenkanen et al. 1995 y Dahlman et al. 2000
Enzymatic hydrolysis Spectroscopy
Electrophoresis
Formic acid/Na-formate
Gellersted and Li. 1996 Hg acetate/acetic acid
Chromatography
Jiang et al. 2001 Sulfuric acid Chromatography
HYDROLYSIS QUANTIFICATION
NIRS SPECTROSCOPY
• It is also a powerful technique used to estimate wood and pulp properties.
Longitud de onda (nm)
Lo
g (
1/
R)
Longitud de onda (nm)
Lo
g (
1/
R)
• Prediction models were developed by using chemometrics tools such as PCA, PCR and PLS.
Class 1
Class 2
SIMC A-P 10.5 - 19/04/2005 11:29:21
E. globulus
E. nitens
Class 1
Class 2
SIMC A-P 10.5 - 19/04/2005 11:29:21
E. globulus
E. nitens
E. globulus
E. nitens
E. globulus
E. nitens
446.5 500 550 597.2
440.8
500
600
651.4
SpecifiedEstim
ate
d
xx
xx
xxx
xxx
xx
x
xx
xx
x
xx xx
xx
xxxxxx
x
x
xx
x
x
xxxxx
x
xxxxxx
x
x
x
xx
xx
Densidad básican= 61
R2= 0,90
SEP = 17,2
Densid
ad e
stim
ada
Densidad experimental446.5 500 550 597.2
440.8
500
600
651.4
SpecifiedEstim
ate
d
xx
xx
xxx
xxx
xx
x
xx
xx
x
xx xx
xx
xxxxxx
x
x
xx
x
x
xxxxx
x
xxxxxx
x
x
x
xx
xx
Densidad básican= 61
R2= 0,90
SEP = 17,2
Densid
ad e
stim
ada
Densidad experimental
EXAMPLES OF NIRS APPLICATION
Separation of species Estimation of wood density
OBJECTIVES
1. Produce kraft pulps of E. globulus with varied amount of HexA.
2. Evaluate the effect of pulping conditions on HexA formation/degradation.
3. Compare two methodologies for quantification of HexA content in E. globulus kraft pulps:
• UV spectrophotometry (Chai et al., 2001).
• Anion Exchange Chromatography (Jiang et al., 2001).
4. Develop FT-NIR models to estimate HexA composition in E. globulus kraft pulps.
Wood
• Wood chips from 10 years old E. globulus.
• Chemical characterization:
• Extractives (ethanol/toluene)
• Carbohydrates (acid hydrolysis and HPLC)
• Lignin (Klason and soluble)
• Uronic acids (UV: Blumenkrantz and Asboe-Hansen, 1973)
• 50 g wood chips (odb) and 250 mL cooking liquor (1-L Parr
reactor heated at 1.6°C/min).
• Cooking liquor:
• 15% and 20% active alkali (AA)
• 25% sulfidity
• Na2O basis
• Temperature: 155°C and 165°C.
• Cooking at H-factors from 200 to 2500.
• 130 pulps were produced.
Kraft Pulping
Kraft Pulping
• Pulp yield
• Kappa number
• Carbohydrates
• Lignin
• Uronic acids
• Hexenuronic acids (UV, AEC and FT-NIR)
HexA by UV
• Chai et al., J. Pulp Paper Sci., 27(5):165-170, 2001.
• Pulp hydrolysis with HgCl2/Na-acetate.
• CHexA= 0.287(A260-1.2A290)V/m
Á cido 5 - dehidro - 4 - deoxi - D - glucur ó nico Á cido 5 - dehidro - 4 - deoxi - D - glucur ó nico Á cido 5 - dehidro - 4 - deoxi - D - glucur ó nico
5-dehydro-4-deoxy-D-glucuronic acid
λ1 = 260 nm
λ2 = 290 nm
HexA by AEC
Á cido 5 - dehidro - 4 - deoxi - D - glucur ó nico Á cido 5 - dehidro - 4 - deoxi - D - glucur ó nico Á cido 5 - dehidro - 4 - deoxi - D - glucur ó nico
• Jiang et al., J. Pulp Paper Sci., 27(3):92-97, 2001.
• Pulp hydrolysis with H2SO4.
• AEC analysis: 4 mM NaOH (eluent) at 0.7 mL/min; 25°C;
conductivity detector.
HexA by NIRS
• 110 pulps analyzed for models development.
• 20 pulps used as external validation set.
• Perkin Elmer Identcheck FT-NIR.
• Spectra recorded in diffuse reflectance at 2 nm interval
(1000-2500 nm) using 32 scans.
• Software: Spectrum v. 5.0.1 and QUANT+.
• PCR and PLS analysis on baseline corrected and 2nd
derivative spectra.
Chemical composition of E. globulus
• Glucans: 49.6%
• Xylans: 16.1%
• Lignin: 26.3%
• Extractives: 1.2%
• Uronic acids (MeGlcA): 5.3%*
* Similar amount found for E. globulus grown in Portugal (Simão et al., Ind. Eng. Chem. Res., 2005)
Model: 51.3 ± 1.7 mmol/kg pulp
45 min, 5.7 pH y 80°C
Experimental: 50.6 ± 0,3 mmol/kg pulp
Model: 35,5 ± 1,5 mmol/kg pulp
3.1 h, 0.7 pH y 97°C
Experimental: 36.5 ± 0.2 mmol/kg pulp
Determination of optimal conditions for HexA hydrolisys
HgCl2/NaAc/UV H2SO4 /AEC
HexA (quantified by UV)
Pulping at 155°C
MeGlcA: (■)15% AA and (●) 20% AA
HexA: (□) 15% AA and (○) 20% AA
HexA (quantified by UV)
Pulping at 165°C
MeGlcA: (■)15% AA and (●) 20% AA
HexA: (□) 15% AA and (○) 20% AA
Development of FT-NIR models
HexA-UV (mmol/kg)
HexA-AEC (mmol/kg)
Sample number 130 130
Minimal content 10.2 4.7
Maximal content 71.0 59.7
Average content 44.9 34.2
Average SD 0.7 1.2
Minimal SD 0.1 0.1
Maximal SD 2.0 2.0
Sample number and ranges of analytical data for HexA in E. globulus kraft pulps.
2nd derivative espectra of pulps with similar HexA contents but with different kappa numbers.
1000,0 1200 1400 1600 1800 2000 2400 2500,0
0,00
0,0
0,00
nm
K-M
HexA 41.3, Kappa 8.5
HexA 41.0, Kappa 33,0
HexA 41.3, Kappa 8.5
HexA 41.0, Kappa 33.0
K-M
nm
Developed NIR models with statistical values
* A set of 13 samples with kappa number and HexA content lower than 12 and 55 mmol/g pulp, respectively, were excluded from the calibration models.
y = 0,85x + 5,32
R2 = 0,81
Bias= -0,77
SEP y RMSEP= 5,70
20
40
60
80
0 20 40 60 80Valor observado
Va
lor
pre
dic
ho
y = 0,81x + 9,08
R2 = 0,83
Bias= -0,83
SEP y RMSEP= 6,70
20
40
60
80
0 20 40 60 80Valor observado
Valo
r pre
dic
ho
HexA by UV
HexA by AEC
Correlations for PLS-predict model and observed values for HexA
CONCLUSIONS
• Cooking temperature and active alkali have a significant effect in HexA formation and degradation during kraft pulping.
• Good reproducibility were found for both techniques used for HexA quantification (UV and AEC).
• HexA quantification by UV is a fast technique, however chromatography allows direct quantification of degradation products avoiding interference of lignin or products from carbohydrate degradation.
• NIRS models developed for HexA quantification were adequate to estimate HexA in kraft pulps allowing the analysis of several samples in less time when compared with conventional techniques.
Acknowledgements
Co-authors:
• Mariel Monrroy
• Juanita Freer
• José Ruiz
• André Ferraz
• Jaime Rodríguez
• Jaime Baeza
Financial support from:
• FONDECYT grants 1050535 and 7070089.
• CONICYT (M. Monrroy’s PhD Fellowship).