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Hydrogen Peroxide BleachingHighlights
State of the Art and Research Direction
Art J. Ragauskas
Hydrogen Peroxide Bleaching
• Background
• Mill Applications
• Research Directions
Peroxide Bleaching: Background
HOO HOOH HOH + OH 2 H2O O2
- e- H+ - e- H+ + e- H+ + e- H+
perhydroxyl radical water & hydroxyl radical
H+ O2- H+ -OOH H+ O-
superoxide anion perhydroxyl anion oxoanion
pKa 4.8 pKa 11.8 pKa 11.9
-active bleaching species is HOO- and derivatives
Peroxide Bleaching: BackgroundH2O2 + M → HO. + HO- + M+
H2O2 + HO- → HO2- + H2O
HO2- + M+ → HO2
. + M
HO2. + HO- → O2
-. + H2O
O2-. + M+ → O2 + M
O2-. + HO. → O2 + HO-
2O2.- + H2O → O2 + HO2
- + HO-
HO. + HO2- → H2O + O2
-.
HO. + M → HO- + M+
HO. + HO. → H2O2
Peroxide chemistry strongly influenced by metals
Peroxide Bleaching: Background
OCH3
OR
O-
HOO-
OCH3
O-R
O-
OHO
OCH3
O-R
O
O
OCH3
OC
O-
OR
OCH3O-
OH
OR
-O
HO- O2
OCH3O
O
O2-
O2 or OHC OH
O-
OCH3
C OH
OOCH3
C OH
OOCH3
COH
OOCH3
O O-
OOCH3
O
C O
HO--O2-
Dakin reaction
Dakin-like reaction
Lignin fragmentation reactions
Addition to quinone structures
-OOH O
O-
R
OHO
O-
R
OOHHO O--OHO
-O
R
OOHO
O
R
Destruction of color bodies
Peroxide Bleaching: Background
Peroxide Bleaching: Background
OO XylanO
HO
OHO
OH
CO2HH H2O2/NaOH
Formed during pulping
• 30 -50% of Southern HW Kappa #
•10 - 20% of Southern SW Kappa #
NR
Peroxide: Mill Applications
Eop– Peroxide 0.1 - 0.5%– Temp.: 55 - 85oC– Time: 50 - 134 min– O2: 0.5 - 0.7%consumed
– first extraction stage– P is largely brightening
chemistry
• Ep– Peroxide: 0.1 - 0.2%– Temp. 65- 85oC– Time: 45 - 120 min.– second extraction stage– Brightening chemistry
• P– Peroxide: 0.5 - 1.5%– Temp. 65- 85oC– Time: 45 - 120 min.
Peroxide: Mill Applications
• PHT– Pre Q stage preferred– Peroxide 0.5 - 3.0%– Temp.
• 105 - 110oC for 5-15 min• 90 - 98oC for 180 - 240 min
– O2: 70 - 120 psi– Stabilizer– Brightening &
delignifying
• PO– Requires pre Q-stage– Peroxide: 0.5 - 3.0%– Temp: 100 - 110oC– Time: 60 - 120 min– O2: 75 - 120 psi– Stabilizer– Brightening &
delignifying
Peroxide: Mill Applications
• North America– Primarily ECF
• D(Eop)DED• D(Eop)DEpD, • OD(Eop)D or OD(Eop)DEpD• D(Ep)DED
• HD storage (0.1 - 0.2% P, pH approx. 9)
P-Stage Mill Applications
• Europe– Greater bleaching sequence diversity in ECF & TCF
• OD(Eop)DED• O/OD(Eop)DP• OQ(Op)PaaQ(PO)• ODQ(PO)• OAZQ(Eop)(PO)• OQPZP
Peroxide Bleaching: Role of metals2.5% P, Q vs. no Q for SW Kraft Pulp
• P-delignification requires metal management via Q-stage
• Favorable M: Mg2+
• Harmful: Fe, Cr, Ni– Mn favorable/harmful
• Note: C/D or D not M sensitive
0
10
20
30
40
50
70 C no Q 70 C Q
% Delignification
% Brightness
Peroxide Bleaching: Role of Temperature 2.5% P Q HW Kraft Pulp
• P* significantly improves peroxide
• P* not just increase in rates
• Capital intensive• Sensitive to M+
– Q stage– yield
05
1015202530354045
30 70 110
130/
C
% Delignification
P-Stage Future Research Directions
• Peroxide Efficiency
•Improved Conditions
•Catalysis
•Modification of fibers
Brightening After OD(EPO)D Kraft HWBrightening After OD(EPO)D Kraft HW
84
86
88
90
92
0.0 0.5 1.0 1.5 2.0 2.5Chemical Charge, % o.d. pulp
Brig
htne
ss
Chlorine Dioxide
Peroxide
Ozone
Peroxide Brightening Effects
80818283848586878889
0.5 1 1.5 2 2.5 3.5
Peroxide Charge (%)
Tap
pi B
righ
tnes
s DEDPDEPD
• D-stage generates active lignin structures for P-stage
Peroxide Activation - Catalyst
Peroxide Bleaching: Research
• Bleaching properties of PHT and PO suggest that a catalyst could improve delignification and/or brightening
• First generation– HO3SOOH, CH3CO3H
Peroxide Bleaching: Research P-activators
O
O O AcNN Ac
AcN
NAc
Ac
Ac
O
OAc
OAc
AcO
AcO
OAc
OAc
OAc
OH
OAc
OAc
OH
Pentacetyl Glucose Diacetin
Diethyl Pyrocarbonate DAED TAED
+ H-O-O - RH + -O-O-AcRAc
All improve a P-stage by 15 - 40% >>stoichiometrically
Peroxide Bleaching: Research P-catalyst
N
N
V O2-
O2-O2
-
NFe
N N
NO
OO
OO
HH
X
X
Mn O Mn
O
N
N N
NN N
O O
Peroxide Bleaching: Research P-catalyst
Catalytic Peroxide Activation: Use of Mn-catalyst to improve alkaline peroxide bleaching of Do SW kraft.
02468
10121416
Do
SWkr
aft
0.5%
P
0.02
%Pc
at
0.2%
Pca
t
1.0%
P
0.02
%Pc
at
0.2%
Pca
t
Kap
pa #
Peroxide Fiber Modification
Strength Effects of O and (PO) on (OZE) SW Kraft
Use an OZE pulp and apply O or (PO)
Bleaching stage enriched acid groups content of pulp fibers
(PO) increased acid groups by 65%
(O) increased acid groups by 37%
Practical Application - Bleaching
0
0.02
0.04
0.06
0.08
300 350 400 450
Scattering Coefficient (cm2/g)
Control
Oxygen/Peroxide
Oxygen
Scot
t-B
ond
(J)
CONCLUSIONS
• Additional acid groups on or near fiber surfaces increased specific bond strength.
• Strength benefit mechanism is not known, but could be intermolecular diffusion.
• The possibility exists to produce stronger, bulkier sheets than by conventional processes.
Peroxide Summary
• Current peroxide bleaching chemistry has dramatically advanced.
• P-stage delignifies but destroys color bodies more effectively.
• Environmentally compatible.
• Sensitive to certain metals.
• Peroxide research is directed at reducing capital requirements.
• Improved peroxide delignification will be achieved.
• New research opportunities in fiber modification.
AcknowledgmentsAcknowledgmentsMember Companies IPSTMember Companies IPST