South China University of Technology
New Technologies
In Pulp Bleaching
South China University of Technology
Introduction
Oxygen Delignification
Ozone Delignification
Peroxide Bleaching
Peracid Bleaching
Hydrosulfite Bleaching
Chlorination
Chlorine Dioxide Bleaching
Enzyme Treatment of
Pulp(Biobleaching)
South China University of Technology
INTRODUCTION
Objectives
● Brightness ● Cleanliness
● Purification-dissolving grade
Historical background
Major concerns
? Costs ? Environmental ? Energy
Chemical Function Pulp Advantag
e
Disadvantages
Cl2 Oxidize and chlorinate C Effective,economical
delignification;
good particle
removal
Organochlorine
formation;
highly
corrosive
NaOCl
Ca(Ocl)2
Oxidize,
decolorize,and
solubilize lignin
C Easy to make and use; low
cost
Can cause loss of
pulp strength;
chloroform formation
ClO2 1)Oxide,decolorize and
solubilize lignin
2) In small
amounts with Cl2;
protects against
cellulose
degradation
C Achieve high brightness
without loss of
pulp strength;
good particle
bleaching
Must be made on-
site; cost; some
organochlorine
formation; highly
corrosive
Functions,advantages and disadvantages of bleaching chemicals
Chemical Function Pul
p
Advantage
s
disadvantag
es
O2 Oxidize and solubilize lignin C Low chemical cost; provides
chlorine-free
effluent for
recovery
Requires significant
capital equipment
when used in large
amounts; potential
loss of pulp
strength
H2O2 Oxidize and decolorize
lignin
C or
M
Easy to use;
Low capital
cost
High chemical
cost; Poor
particle bleaching;
Can cause loss of
pulp strength
O3 Oxidize,decolorize and
solubilize lignin
C Effective,provides
chlorine-free
effluent for
recovery
Must be made
on-site; cost; poor
particle bleaching
and pulp strength
Functions,advantages and disadvantages of bleaching chemicals
Chemica
l
Function Pul
p
Advantage
s
disadvantag
es
Na2S2O
4
Reduce and
decolorize
lignin in high-
yield pulps
M Easy to use;
Low capital
cost
Decomposes
readily; Limited
brightness gain
Xylanas
e
Catalyze xylan
hydrolysis and
aid in lignin
removal
C Easy to use; Low capital
cost
Limited
effectiveness;
cost
NaOH Hydrolyze chlorolignin
and solubilize
lignin
C Effective
Economic
al
Darkens pulp
EDTA
DTPA
Removal
metal
ions
C Improves peroxide
selectivity and
efficiency
Cost
Functions,advantages and disadvantages of bleaching chemicals
South China University of Technology
Reactions of different oxidants used in
bleaching
Cl2+2e-→2Cl -
NaOCl+H2O+2e-→NaCl+2OH -
ClO2+2H2O+5e-→Cl -+4OH-
O2+2H2O+4e-→4OH -
H2O2+2H++2e-→2H 2O
O3+3H++6e-→3OH -
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Bleaching sequence
Two improtant aspects of establishing the proper
sequence of bleaching,★ Cost ★ Selectivity
Typical bleaching sequences
● CEH ● (C+D)EoDED ● DEoDED ● OZEoD
● OQP
● YP
Coventional sequences for KP
CEDED CEHDED Softwood
CEDED CEHD Hardwood
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New sequences
OCEoDED CDEoDEpD OCDEoD
OZED XEOPDED
New development
ECF—OPDED ODEDD
TCF—OZEP OQPZP OQPP
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Unbleached
pulp
Effluent to
recovery
NaOH
O2
Water &
Steam
Acidic
effluent
ClO2
Water
NaOH
O2
Water &
Steam
Alkaline
effluent
Water &
Steam
O2
ClO2
Bleached
pulpO D Eo D
Typical process conditions for bleaching softwood KP chemical
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Oxygen Delignification
Two factors that dictate process
design of O2 delignification
△ Oxygen reacts only with units having free-
phenolic hydroxyl group only at temperature
above 70℃
△ Solubility of oxygen in water is very low,
especially at temperature above 70℃
Note
Process condition for oxygen delignification
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O2 HOO· HOOH HO·+-OH 2HOH
+e-,H+ +e-,H+ +e-,H+ +e-,H+
+2e-,2H+
Stepwise Reduction of Oxygen
H++·O2-
pKa 4.8
H++-OOH
11.8
H++·O-
11.9
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Reactive Species in Oxygen Bleaching
Electrophiles,O2≡·O2·,HOO·,HO·,(·O2-)(·O-)
Nucleophiles,HOO-,(HOOH)
Reactivity of transients in oxygen/alkali
delignification systems
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Oxygen Bleaching System
△ Complex interplay between radical and ionic reactions
△ Radical (electrophilic) reactions
Fast
Mailnly responsible for lignin fragmentation (delignification)
△ Ionic (nucleophilic) reactions
Slow
Destruction of chromophoric structures
(brightness improvement)
O-stage combines delignification and bleaching
△ Chemistry of oxygen and hydrogen peroxide bleaching
interrelated
△ The main challenge in bleaching with oxygen is to generate
enough hydroxyl radicals to maintain acceptable rates of oxidative
processes without initiating excessive damage to carbohydrates
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Comparison of MC & HC systems
△ MC systems
△ HC systems
Process variables
alkali charge
oxygen pressure
time & temp
consistency
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Advantages of oxygen delignification
? Improves bleaching process efficiency
? Proven technology
? Spent liquor is free of chloride ions
? Effluent can be handled in kraft recovery
system
? Decrease consumption of chemicals used in
bleaching
? Eases effluent discharge
? Oxygen cheaper than chlorine/chlorine
dioxide
? Essential component of future TCF or closed
cycle technologies
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Disadvantages of oxygen delignification
? Lignin selectivity limitations
? Installation cost
? Creates need for extra recovery capacity
New Development to Improve
Effectiveness
△ Om Process △ Peroxide-aided single and
double oxygen stages △ Two oxygen addition
points △ Effect of matal ions △ Lignin activation
before O-stage △ Ultim-O Process △ Low
pressure oxygen delignification technology
△ Two stage oxygen bleaching
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Summary of Oxygen delignification
? extension of pulping
? lignin removal currently at max,of
50%
? excessive lignin removal causes pulp
strength loss
? Less lignin entering bleach plant
? decreases consumption of bleaching
chemical
Ozone Delignification
Sequence Kappa No Brightness,%ISO
OZ 9.9 66.7
OQP 7.1 71.1
OQPP 5.9 77.9
OZQP 3.6 77.5
OQPZ 2.7 77.6
OZQPP 2.8 83.9
OQPZP Not determined 89.9
Kappa number and brightness of softwood kraft pulp
bleached in TCF sequence
South China University of Technology
Ozone Bleaching
Structure of Ozone Molecules,O3
-- O
O
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
+- OO-O+O
+O
.,.,.,
.,
.,
.,.,
.,.,.,.,
.,
.,
.,
+O
O
O
O
OO
O
OO
O
OO
O
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Ozon reactions with olefins(I),Major
reaction
—1,3 dipolar cycloaddition
primary
ozonide
—cleavage of the primary ozonide
C
.
C
O
O
O
.
.
O- O+
C C
O O
O
=
.
.
-O
O
O
+O
C+OC
O
O
O
CC
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Ozone reaction with olefins(II)
—Formation of the final ozonide
—Hydrolysis of the final ozonide
O
C C
O O
H 2 O C O= O = C HOOH+ + +
C O C
O
O
C
O
C
OO
O+
O-
.
.
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Ozone reactions with aromatics
Two mechanisms are operating
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Decomposition of ozone in water
Decomposition of ozone in water is
influenced by
—temperature
—ozone concentration
—PH
—solutes,not limited to transtion metals
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Mechanism of Ozone
Decomposition
O
3
HO
-
O
2
O
3
O
3
.
H
+
HO
.
O
2
O
2
-
.
HOO
.H
+
O
2
P r o m a t i o n
[O
3
,S u b s t r a t e ]
I n h i b i t i o n
Ra d i c a l S c a v e n g e r
S u b s t r a t e H CO
3
,C O
3
-
2 -
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Carbohydrate reactions during
ozone bleaching
Formation of carbonyl groups on cellulose
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Basics of Ozone Bleaching
? An unbleached pulp is degraded less
rapidly by ozone than a bleached pulp
? The formation of carbonyl groups is mainly
due to molecular ozone and not to ·OH
radicals
? The rapid decrease in viscosity when Z is
applied late suggest that molecular ozone
and not ·OH radicals is responsible for most
of the degradation
? ·OH radicals come mainly form the
liberated H2O2,
? Difference between high and low
consistency ozonation
South China University of Technology
Ozone production
● On – site generation
● Produced form oxygen (or air )by corona
arc discharge generators
● Max,concentration now claimed is 14%
ozone in oxygen
● Power required is 8 to 10 KWH/kg O3
(@10% O3 conc.)
● Easily detected in low concentrations
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Bleaching with Ozone
TCF sequences Hardwood kraft OZP
OZQP
OZEoP
Softwood kraft OZQPP
OQZPP
OZPZP
ECF sequences OZDEoP
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Peroxide Bleaching
Reactivity of Hydrogen Peroxide
HOOH H++HOO- pKa=11.8
O
C =O
CH 3
O C H 3
OH
O C H 3
C OH
CH 3
HO O C
CH 3
OH
O C H 3
O -
HOO
-
- H O
-
CH 3
OHO
O C H 3
O
CH 3
C =O
O
O C H 3
OH
OH
OH
O C H 3
+CH 3 C O O
-
HO
-
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Bleaching with alkaline hydrogen peroxide
Aspects,▼ Thermostability up to ~120℃
▼ Control of metal profile
▼ Control of pH
▼ Sensitive towards certain metal surface
Manufacture of Hydrogen Peroxide
O2 + H2O2 + 2e- HOO- + OH-
Properties,Clear,Colorless liquor
System,Medium consistency (MC)
High consistency (HC)
Temperature 80~120℃
Pressure,about 5 bars(employing o2 or air)
Time,up to several hours
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Decomposition of H2O2
? Base catalyzed
? Bacteria catalyzed
? Metal catalyzed
Metal Ion Management
? Magnesium - Stabilizes H2O2
against decomposition Mg/Mn >50
? Methods for controlling metal ions
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ECF Bleaching whit H2O2
OD(EOP)(DQ)P
TCF Bleaching whit H2O2
OQP
OQP(ZQ)P
O(PaQ)P
OQPQPQP
South China University of Technology
Reactions of peroxide with lignin
Ring opening reaction
Reaction with α-ketone
O
O
O
O
-
OO -
+ H O O -
O- O
O
O
-
O
O
O -
O -
CR
O H
O OH
C =OR
OH
O C H 3
O C H 3
O
O C H 3
O
O
C
O H
R C
O
O
R
O
-
O C H 3
HO
-
+ R C O O H
OH
O
-
O C H 3
HOOH
-
H 2 O
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Reaction with β-ketone
+ CH 3 C =O
H
C H O
O C H 3
O C H 3
O C H 3
O C H 3
HC O OH
HC OH
CH 3
HOOH
OH
-
O C H 3
O C H 3
CH
C OH
CH 3
O C H 3
O C H 3
CH 2
C =O
CH 3
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Reaction with unsaturated aldehyde
+ CH C H O
OH
O C H 3
O C H 3
C H O
OHOHC
H 2 C
C H O
O C H 3
O C H 3
O C H 3
O C H 3
CH
CH
C H O
HOOH
OH
-
South China University of Technology
Peracid Bleaching
Preparation of peracids
Performic acid (Pf)
Peracetic acid (Pa)
Peroxymonosulfuric acid (Px) Caro’s acid
H C O O H + H 2 O 2 HC O OH
O
+ H 2 O
CH 3 C O O H + H 2 O 2 CH 3 C
O
O OH + H 2 O
H 2 SO 4 + H 2 O 2 HO S O OH + H
2 O
O
O
South China University of Technology
Mixed peracetic acid and peroxymonsulfuric acid(Pxa)
In calculating the percent active oxygen of a
peracid,only one of oxygen in the O-O linkage of a
peracid is considered ―active‖
Active Oxygen in H2SO5= × 100%=14.0%
Active Oxygen in CH3COOH= × 100%=21.0%
Conversion ration = × 100%
16.0
114.08
16.0
76.05
Peracidsin mixtures as H2O2
Hydrogen peroxide added
South China University of Technology
Chemical safety and handling
Peracid Composition H2O2
Conversion,%CH3COOH H2SO4 H2O2
Pa 3.5 0.03 1.00 70
Px 0 2.75 1.00 70
Pxa1 1.00 1.00 1.00 74
Pxa2 0.75 1.50 1.00 74
Pxa3 0.50 1.50 1.00 65
Preparation of peracids from 50% H2O2
South China University of Technology
Peracid Composition H2O2
Conversion,%CH3COOH H2SO4 H2O2
Pa 2.00 0.03 1.00 71
Px 0 1.50 1.00 70
Pxa1 0.75 0.50 1.00 77
Pxa2 0.75 0.75 1.00 80
Pxa3 0.50 1.00 1.00 73
Praparation of peracids from 70% H2O2
South China University of Technology
Analysis
Conversion ratio %= × 100%
H2O2 g/l=
Na2S2O3 mmol
Cerium Sulfate mmol+Na2S2O3 mmol
(Cerium sulfate mmol + Na2S2O3mmol) × 17
10
South China University of Technology
Benefits of using peroxy acid in TCF
bleaching
? Higher brightness threshold
? Higher viscosity and strength
? Lower cost
Reaction mechanism of peracid and
lignin
Two main mechanisms
? Electrophilic substitution/addition
? Nucleophilic reactions
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O
O C H 3
HC OH
C = O
O C H 3
O
O+
O C H 3O C H 3
CH 3 O
CH 3 OCH 3 O
CH
C OHO
O
CH
C O
HC
HC O
O
-H 2 O HO
O+Electrophilic reactions
South China University of Technology
OR
O C H 3
O C H 3 O C H 3
OR OR
C =O
CH 3
X O
H
.,
H
O+
CO O H
CH 3
CH 3
X O
C =O
CH 3
O
O
O
O
CH 3
O
O
CH 3
H
O X
H O - X
H
O X
R in g -
o p e n e d P r o d u c t s
Nucleophilic reactions
South China University of Technology
Comparing Pa with Px
? Reaction pathways are identical between Pa
and Px
O C H 3
O C H 3 O C H 3
O C H 3
HO O
O
O C H 3
Aromatic Ring
C— OH
O C H 3
O C H 3
O C H 3
C OHH
CH 3
CH 3
C =O
CH 3
OH
O C H 3
O C H 3
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C=O
CH 3
C
O CH 3
O CH 3
=O
CH 3
O CH 3
O CH 3
O
C
O
O CH 3
O CH 3
OH
COOH
O C H 3
O C H 3
C O O H
Very stable
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? The difference in reactivity
Aromatic,Px>Pa
O C H 3
O C H 3
HO
OE
O C H 3
O C H 3
C=O,Px<Pa
O C H 3
O C H 3
O C H 3
O C H 3
C = O
CH 3
O
C = O
CH 3
ON
O C H 3
O C H 3
O C H 3
O C H 3
O C H 3
O C H 3
C OHH
CH 3
C =O
CH 3
OH
ON
OE
C-OH,Px>Pa
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? Relative reactivity of Peracids
pKa=3.8 pKa=4.8
pKa=1.99
Peracid pKa pKa2=7.1 pKa2=8.2
pKa2=7.1
Nucleophilicity High Medium Low
Electrophilicity Medium Low High
HC O OH
O
CH 3 C O OH
O
SOO-
O
O
O OH
South China University of Technology
Comparison between peracids and
hydrogen peroxide
Peracids Hydrogen
Peroxide
(X-O-H) (H-O-O-H)
pKa of peracids/H2O2 7.1~9.4 11.9
pKa of leaving groups 2.0~4.8 16
X-O-H H-O-O-H
Nucleophilicity High Low
Electrophilicity High Very low
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Other Applications of Peracids
? Activating agent for oxygen
? Pxa Eop as replacement for O stage
? Improve peroxide bleaching
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Summary
? High conversion of peroxide to peracids can be
done on site
? Heavy metals decompose peracids,Use of DTPA
necessary
? Peracids are unstable at alkaline pH
? Peracids react with lignin in the same pathways
? Percids are react both as a nucleophile and an
electrophile
? Peracids are better nucleophiles than peroxide
? Peracids may be used as delignigying and
brightening agents
South China University of Technology
QPaQ(PO) bleaching of oxygen
delignified soft wood pulp (in Sweden)
Mn
(ppm)
75
Q
2kg EDTA
/t pulp
Pa
10kg
/t pulp
Q
1kg EDTA
/t pulp
(PO)
40kg H2O2
/t pulp
10 <1
Kappa No 16 12 3.5
Brightness
% ISO 35 48 85.5
Viscosity
Dm3/kg 970 950 750
South China University of Technology
DMD Bleaching
Acetone Peroxymon-
Dimethydioxirane
sulfate
2KHSO5·KHSO4·K 2SO4
C = O
H 3 C
H 3 C
+ H O
O SO 3
-
O O
H 3 C CH 3
_
_
CH 3H 3 C
OO
+ C = C
C C
O
H 3 C
H 3 C
C = O+
South China University of Technology
Hydrosulfite (Dithionite)
Bleaching
Chemistry of hydrosulfite bleaching
Reducing agent
Sulfur dioxide radical anion
Composition of hydrosulfite bleach solutions
-
2 OS, SO
-
2 2 SO
-
2,
2 SO -2, SO 22
-
+ SO
South China University of Technology
·Pulp+Na2S2SO4+H2O Bleached pulp+2NaHSO3
·Na2S2O4+O2 NaHSO4+NaHSO4
·2Na2S2O4+H2O 2NaHSO3+Na2S2O3
·2Fe3++S2O2-+H2O 2Fe2++2HSO-3+2H+
·NaBH4+8NaHSO3 4Na2S2O4+NaBO2+6H2O
Sodium borate
4
} Decomposition
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Process Vasiables
Normal
Range
Hydrosulfite application 1~10kg/t pulp
Temp,40~100℃
Retention time 30~60min
pH 4.5~6.5
Comsistency 3~30%
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Chlorinaton
Hydrolysis reaction of chlorine
Cl2+H2O HOCl+HCl
H++Cl-
Kh= =3.94× 10-4(25℃ ),pKh=3.40
HOCl H++OCl-
Ka= =5.6× 10-8(25℃ ),pKa=7.25
Kh
[ H O C l ] [ H + ] [ C l - ]
[ C l 2 ]
[H + ] [ O C l - ]
[ H O Cl ]
South China University of Technology
Reaction of Chlorine whit Lingnin
A - S u b s t it u t i o n
C - O x i d a t io n B - E l e c t r op hi l i c d i s p l a c e m e n t
H - C - O R
O C H
3
L ig n i n
O x i d a t i o n
A
A
A
B
O
C
C
C
C
H O
O
O
Cl
}
Cl
x
O
xR e d
C
C
C O O H
L ig n i n
}
O x i d a t i o n
C O O H
C O O H
O x i d,
F r a g m e n t s
o f d ic a r b o x y li c
a c id
Cl
Cl
x
OH
OH
Cl
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Organic chlorinated compunds formed
during chlorination &alkaline extraction
Chlorophenols Chlorocatechols
Chloroguaicols Chlorobenzenes
Polychlorinated dibenzo-p-dioxins
2,3,7,8-TCDD 2,3,7,8-TCDF
2,3,7,8-Tetra- 2,3,7,8-
chlorodibenzo-p-dioxins
Tetrachlorodiben-
zofuran
ClCl
Cl Cl
O
O
Cl
Cl Cl
O Cl
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OH
Cl
2
OH
Cl
Cl
Cl
O
O
OCl
Cl
.
.
Cl
Cl
+C l
2
O
O
Cl
Cl
Cl
Cl
OH
Cl Cl
Cl
O
O M e
Cl
ClCl
Cl
O M e
O H
Cl
.
D ip o ly m e r i z a t i o n
Formation of dioxins during chlorination
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NaO
O M e
Cl
Cl
Cl
Cl
OH
O
ClCl
Cl
Cl
Cl
Cl
O
OB a s e c t a ly z e d
r e a c t io n
Na
+
Cl Cl
Formation of dioxins during alkaline extraction
C and E stages— Main generator of dioxins
Detection limitation of dioxins,10-12 (ppt,trillion)
≯ 5000ppt still safe
Dioxins discharge in USA 40kg/year
only 1~3% from paper industry
South China University of Technology
Variables affecting chlorination
Pulp properties—bleach demand
—method of pulping
—CED(cupric-ethylene diamine) viscosity
Operating condition—time/temperature
—available chlorine application
—proportion of ClO2 in application
—sequence of chemical application
—initial pH
—chlorine concentration
—consistency
Process conditions —degree of mixing
Control parameters —stock color
—OPR(oxidation-reduction potential)
—chemical residual concentration
South China University of Technology
Chlorin Dioxide Bleaching
Reactions of ClO2 with lignin
Cl
OH
C
C OR
C
O C H 3
OR
Cl 2
C l O 2
O
O
O C H 3
O x i d a t i o n
C
C OH
C
C O O H
C O O H
C
C OR
C
C
C
O
O
O C H 3
OR
C l O 2
C
C
C
OH
OH
OH
C
C OH
C
O
O
Cl 2,C l O 2
South China University of Technology
Process Conditions for ClO2 Bleaching
D1 D2
Chemical Applied
ClO2 kg/t pulp 5~15 2~8
NaOH kg/t pulp 0~0.9 0
End pH 2.5~4 4~5.5
Temperature ℃ 50~90
Time min 120~300
Consistency % 9~16
Residual g/l Trace ~0.05
South China University of Technology
Steam
Steam
Mixer
Chemical
MC pump MC Mixer
The upflow-downflow tower
South China University of Technology
ClO2 Generation
▲ Mathieson Process
SO2+2NaClO3+H2SO4
2ClO2+2NaHSO4
▲ Solvay Process
CH3OH+2NaClO3+H2SO4
2ClO2+HCHO+Na2SO4+2H2O
▲ R2 Process
NaCl+NaClO3+H2SO4
ClO2+1/2Cl2+Na2SO4+H2O
South China University of Technology
▲ The Kesting Process
NaCl+3H2O+6e NaClO3+3H2
NaClO3+2HCl ClO2+1/2Cl2+NaCl+H2O
Cl2+H2 2HCl
▲ R3/SVP Process
NaClO3+NaCl+H2SO
ClO2+ 1/2Cl2+Na2SO4+H2O
NaClO3+5NaCl+3H2SO4
3Cl2+3Na2SO4+3H2O
South China University of Technology
▲ R8/SVP-LITE and R10
3NaClO3+2H2SO4+0.85CH3OH
3ClO2+Na3H(SO4)2+H2O+0.05CH3OH+0.6CHOOH+0.2CO2
▲ The R11/SVP-HP
2NaClO3+H2SO4+H2O22
ClO2+Na2SO4+2H2O+O2
AOX—Adsorbable Organic Halogen
TOCl—Total Organic Halogen
BOD—Biochemical Oxygen Demand
COD—Chemical Oxygen Demand
South China University of Technology
Enzyme Treatment of Pulp
(Biobleaching)
Cellulase
Hemicellulases,Xylanase
Mananase
Ligninolytic enzymes,Lignin peroxidase
Manganese-dependent
peroxidase
Laccase
South China University of Technology
Proposed mechanism of enzyme action
★ Xylanases catalyze the hydrolysis of
reprecipitated xylan on the surface of
the pulp fibers making the lignin
fragments in and on the fiber easier to
remove in the following bleaching and
alkaline extraction stages
★ Another hypothesis is that xylanases,
by catalyzing the depolymerization of
xylan in the cell walls,allow entrapped
lignin to diffuse more easily out of the
fiber
South China University of Technology
★ Enzymes are catalytically active over
a specified pH and temperature range,
Most of these enzymes are active at
neutral pH
★ Commercial enzymes are generally
stable (typically in a concentrated liquid)
at ambient temperature for 6 months,
Most suppliers recommend that the
product be refrigerated to preserve its
optimum activity
Supplier Product
Trade Name
Optimum
pH
Optimum
Temp,℃
Primalco Ecopulp 4~7.5 55
Ciba-
Geigy
Irgazyme 10 6~7 60
Irgazyme 40 7~8.5 50~70
ICI Ecopulp X-200 4~7.5 55
Iogen Iogen GS 35 5~7.7 45~57
Shivex 5.2~7.8 40~62
Novo-
Nordic
Pulpzyme HA 5~6 55
Pulpzyme HB 7~8 55
Pulpzyme HC
Industrial Xylanase Suppliers
Supplier Product
Trade Name
Optimum
pH
Optimum
Temp,℃
Sandos
Cartazyme HS 3~5.5 40~55
Cartazyme PS 7~10 50~70
Cartzayme SR 3~5.5 50~80
Solvay Xylanase
L8000
6~8.5 40~65
Zeneca Ecozyme 6~9 45~65
Infustrial Xylanase Suppliers
South China University of Technology
★ Xylanase bleaching is well-suited for use in the
bleach plant for the following reasons:
· Xylanases react selectively with xylan
· Xylanase treatment allows higher brightness
ceilings to be achieved with some pulps
· Xylanase treatment allows bleaching
sequences to be used which produce effluents
containing reduced amounts of organochlorine
compounds
· Xylanase treatment is implemented in modern
integrated bleach plants without extensive capital
investment
South China University of Technology
Conventional
XCEDED
X(CD)EDED
OX(CD)ED
ECF
XDED
OXDED
X(EOP)D(EOP)D
OXDP
Bleaching sequence containing a xylanase treatment
South China University of Technology
TCF
X(EP)P
ZX(EP)
XZ(EP)
OXQPZP
OXZP
OX(EP)ZP
Bleaching sequences containing a xylanase treatment
South China University of Technology
Treatment Kappa No,Viscosity
mPa·s
Brightness
%ISO
Unbleached 14.1 49.1 34.3
O 8.3 — —
X 10.8 — —
OX 5.3 26.6 55.9
OX(CD)ED — 25.7 90.5
Effect of oxygen delignification and a xylanase
treatment on softwood kraft pulp properties
New Technologies
In Pulp Bleaching
South China University of Technology
Introduction
Oxygen Delignification
Ozone Delignification
Peroxide Bleaching
Peracid Bleaching
Hydrosulfite Bleaching
Chlorination
Chlorine Dioxide Bleaching
Enzyme Treatment of
Pulp(Biobleaching)
South China University of Technology
INTRODUCTION
Objectives
● Brightness ● Cleanliness
● Purification-dissolving grade
Historical background
Major concerns
? Costs ? Environmental ? Energy
Chemical Function Pulp Advantag
e
Disadvantages
Cl2 Oxidize and chlorinate C Effective,economical
delignification;
good particle
removal
Organochlorine
formation;
highly
corrosive
NaOCl
Ca(Ocl)2
Oxidize,
decolorize,and
solubilize lignin
C Easy to make and use; low
cost
Can cause loss of
pulp strength;
chloroform formation
ClO2 1)Oxide,decolorize and
solubilize lignin
2) In small
amounts with Cl2;
protects against
cellulose
degradation
C Achieve high brightness
without loss of
pulp strength;
good particle
bleaching
Must be made on-
site; cost; some
organochlorine
formation; highly
corrosive
Functions,advantages and disadvantages of bleaching chemicals
Chemical Function Pul
p
Advantage
s
disadvantag
es
O2 Oxidize and solubilize lignin C Low chemical cost; provides
chlorine-free
effluent for
recovery
Requires significant
capital equipment
when used in large
amounts; potential
loss of pulp
strength
H2O2 Oxidize and decolorize
lignin
C or
M
Easy to use;
Low capital
cost
High chemical
cost; Poor
particle bleaching;
Can cause loss of
pulp strength
O3 Oxidize,decolorize and
solubilize lignin
C Effective,provides
chlorine-free
effluent for
recovery
Must be made
on-site; cost; poor
particle bleaching
and pulp strength
Functions,advantages and disadvantages of bleaching chemicals
Chemica
l
Function Pul
p
Advantage
s
disadvantag
es
Na2S2O
4
Reduce and
decolorize
lignin in high-
yield pulps
M Easy to use;
Low capital
cost
Decomposes
readily; Limited
brightness gain
Xylanas
e
Catalyze xylan
hydrolysis and
aid in lignin
removal
C Easy to use; Low capital
cost
Limited
effectiveness;
cost
NaOH Hydrolyze chlorolignin
and solubilize
lignin
C Effective
Economic
al
Darkens pulp
EDTA
DTPA
Removal
metal
ions
C Improves peroxide
selectivity and
efficiency
Cost
Functions,advantages and disadvantages of bleaching chemicals
South China University of Technology
Reactions of different oxidants used in
bleaching
Cl2+2e-→2Cl -
NaOCl+H2O+2e-→NaCl+2OH -
ClO2+2H2O+5e-→Cl -+4OH-
O2+2H2O+4e-→4OH -
H2O2+2H++2e-→2H 2O
O3+3H++6e-→3OH -
South China University of Technology
Bleaching sequence
Two improtant aspects of establishing the proper
sequence of bleaching,★ Cost ★ Selectivity
Typical bleaching sequences
● CEH ● (C+D)EoDED ● DEoDED ● OZEoD
● OQP
● YP
Coventional sequences for KP
CEDED CEHDED Softwood
CEDED CEHD Hardwood
South China University of Technology
New sequences
OCEoDED CDEoDEpD OCDEoD
OZED XEOPDED
New development
ECF—OPDED ODEDD
TCF—OZEP OQPZP OQPP
South China University of Technology
Unbleached
pulp
Effluent to
recovery
NaOH
O2
Water &
Steam
Acidic
effluent
ClO2
Water
NaOH
O2
Water &
Steam
Alkaline
effluent
Water &
Steam
O2
ClO2
Bleached
pulpO D Eo D
Typical process conditions for bleaching softwood KP chemical
South China University of Technology
Oxygen Delignification
Two factors that dictate process
design of O2 delignification
△ Oxygen reacts only with units having free-
phenolic hydroxyl group only at temperature
above 70℃
△ Solubility of oxygen in water is very low,
especially at temperature above 70℃
Note
Process condition for oxygen delignification
South China University of Technology
O2 HOO· HOOH HO·+-OH 2HOH
+e-,H+ +e-,H+ +e-,H+ +e-,H+
+2e-,2H+
Stepwise Reduction of Oxygen
H++·O2-
pKa 4.8
H++-OOH
11.8
H++·O-
11.9
South China University of Technology
Reactive Species in Oxygen Bleaching
Electrophiles,O2≡·O2·,HOO·,HO·,(·O2-)(·O-)
Nucleophiles,HOO-,(HOOH)
Reactivity of transients in oxygen/alkali
delignification systems
South China University of Technology
Oxygen Bleaching System
△ Complex interplay between radical and ionic reactions
△ Radical (electrophilic) reactions
Fast
Mailnly responsible for lignin fragmentation (delignification)
△ Ionic (nucleophilic) reactions
Slow
Destruction of chromophoric structures
(brightness improvement)
O-stage combines delignification and bleaching
△ Chemistry of oxygen and hydrogen peroxide bleaching
interrelated
△ The main challenge in bleaching with oxygen is to generate
enough hydroxyl radicals to maintain acceptable rates of oxidative
processes without initiating excessive damage to carbohydrates
South China University of Technology
Comparison of MC & HC systems
△ MC systems
△ HC systems
Process variables
alkali charge
oxygen pressure
time & temp
consistency
South China University of Technology
Advantages of oxygen delignification
? Improves bleaching process efficiency
? Proven technology
? Spent liquor is free of chloride ions
? Effluent can be handled in kraft recovery
system
? Decrease consumption of chemicals used in
bleaching
? Eases effluent discharge
? Oxygen cheaper than chlorine/chlorine
dioxide
? Essential component of future TCF or closed
cycle technologies
South China University of Technology
Disadvantages of oxygen delignification
? Lignin selectivity limitations
? Installation cost
? Creates need for extra recovery capacity
New Development to Improve
Effectiveness
△ Om Process △ Peroxide-aided single and
double oxygen stages △ Two oxygen addition
points △ Effect of matal ions △ Lignin activation
before O-stage △ Ultim-O Process △ Low
pressure oxygen delignification technology
△ Two stage oxygen bleaching
South China University of Technology
Summary of Oxygen delignification
? extension of pulping
? lignin removal currently at max,of
50%
? excessive lignin removal causes pulp
strength loss
? Less lignin entering bleach plant
? decreases consumption of bleaching
chemical
Ozone Delignification
Sequence Kappa No Brightness,%ISO
OZ 9.9 66.7
OQP 7.1 71.1
OQPP 5.9 77.9
OZQP 3.6 77.5
OQPZ 2.7 77.6
OZQPP 2.8 83.9
OQPZP Not determined 89.9
Kappa number and brightness of softwood kraft pulp
bleached in TCF sequence
South China University of Technology
Ozone Bleaching
Structure of Ozone Molecules,O3
-- O
O
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
+- OO-O+O
+O
.,.,.,
.,
.,
.,.,
.,.,.,.,
.,
.,
.,
+O
O
O
O
OO
O
OO
O
OO
O
South China University of Technology
Ozon reactions with olefins(I),Major
reaction
—1,3 dipolar cycloaddition
primary
ozonide
—cleavage of the primary ozonide
C
.
C
O
O
O
.
.
O- O+
C C
O O
O
=
.
.
-O
O
O
+O
C+OC
O
O
O
CC
South China University of Technology
Ozone reaction with olefins(II)
—Formation of the final ozonide
—Hydrolysis of the final ozonide
O
C C
O O
H 2 O C O= O = C HOOH+ + +
C O C
O
O
C
O
C
OO
O+
O-
.
.
South China University of Technology
Ozone reactions with aromatics
Two mechanisms are operating
South China University of Technology
Decomposition of ozone in water
Decomposition of ozone in water is
influenced by
—temperature
—ozone concentration
—PH
—solutes,not limited to transtion metals
South China University of Technology
Mechanism of Ozone
Decomposition
O
3
HO
-
O
2
O
3
O
3
.
H
+
HO
.
O
2
O
2
-
.
HOO
.H
+
O
2
P r o m a t i o n
[O
3
,S u b s t r a t e ]
I n h i b i t i o n
Ra d i c a l S c a v e n g e r
S u b s t r a t e H CO
3
,C O
3
-
2 -
South China University of Technology
Carbohydrate reactions during
ozone bleaching
Formation of carbonyl groups on cellulose
South China University of Technology
Basics of Ozone Bleaching
? An unbleached pulp is degraded less
rapidly by ozone than a bleached pulp
? The formation of carbonyl groups is mainly
due to molecular ozone and not to ·OH
radicals
? The rapid decrease in viscosity when Z is
applied late suggest that molecular ozone
and not ·OH radicals is responsible for most
of the degradation
? ·OH radicals come mainly form the
liberated H2O2,
? Difference between high and low
consistency ozonation
South China University of Technology
Ozone production
● On – site generation
● Produced form oxygen (or air )by corona
arc discharge generators
● Max,concentration now claimed is 14%
ozone in oxygen
● Power required is 8 to 10 KWH/kg O3
(@10% O3 conc.)
● Easily detected in low concentrations
South China University of Technology
Bleaching with Ozone
TCF sequences Hardwood kraft OZP
OZQP
OZEoP
Softwood kraft OZQPP
OQZPP
OZPZP
ECF sequences OZDEoP
South China University of Technology
Peroxide Bleaching
Reactivity of Hydrogen Peroxide
HOOH H++HOO- pKa=11.8
O
C =O
CH 3
O C H 3
OH
O C H 3
C OH
CH 3
HO O C
CH 3
OH
O C H 3
O -
HOO
-
- H O
-
CH 3
OHO
O C H 3
O
CH 3
C =O
O
O C H 3
OH
OH
OH
O C H 3
+CH 3 C O O
-
HO
-
South China University of Technology
Bleaching with alkaline hydrogen peroxide
Aspects,▼ Thermostability up to ~120℃
▼ Control of metal profile
▼ Control of pH
▼ Sensitive towards certain metal surface
Manufacture of Hydrogen Peroxide
O2 + H2O2 + 2e- HOO- + OH-
Properties,Clear,Colorless liquor
System,Medium consistency (MC)
High consistency (HC)
Temperature 80~120℃
Pressure,about 5 bars(employing o2 or air)
Time,up to several hours
South China University of Technology
Decomposition of H2O2
? Base catalyzed
? Bacteria catalyzed
? Metal catalyzed
Metal Ion Management
? Magnesium - Stabilizes H2O2
against decomposition Mg/Mn >50
? Methods for controlling metal ions
South China University of Technology
ECF Bleaching whit H2O2
OD(EOP)(DQ)P
TCF Bleaching whit H2O2
OQP
OQP(ZQ)P
O(PaQ)P
OQPQPQP
South China University of Technology
Reactions of peroxide with lignin
Ring opening reaction
Reaction with α-ketone
O
O
O
O
-
OO -
+ H O O -
O- O
O
O
-
O
O
O -
O -
CR
O H
O OH
C =OR
OH
O C H 3
O C H 3
O
O C H 3
O
O
C
O H
R C
O
O
R
O
-
O C H 3
HO
-
+ R C O O H
OH
O
-
O C H 3
HOOH
-
H 2 O
South China University of Technology
Reaction with β-ketone
+ CH 3 C =O
H
C H O
O C H 3
O C H 3
O C H 3
O C H 3
HC O OH
HC OH
CH 3
HOOH
OH
-
O C H 3
O C H 3
CH
C OH
CH 3
O C H 3
O C H 3
CH 2
C =O
CH 3
South China University of Technology
Reaction with unsaturated aldehyde
+ CH C H O
OH
O C H 3
O C H 3
C H O
OHOHC
H 2 C
C H O
O C H 3
O C H 3
O C H 3
O C H 3
CH
CH
C H O
HOOH
OH
-
South China University of Technology
Peracid Bleaching
Preparation of peracids
Performic acid (Pf)
Peracetic acid (Pa)
Peroxymonosulfuric acid (Px) Caro’s acid
H C O O H + H 2 O 2 HC O OH
O
+ H 2 O
CH 3 C O O H + H 2 O 2 CH 3 C
O
O OH + H 2 O
H 2 SO 4 + H 2 O 2 HO S O OH + H
2 O
O
O
South China University of Technology
Mixed peracetic acid and peroxymonsulfuric acid(Pxa)
In calculating the percent active oxygen of a
peracid,only one of oxygen in the O-O linkage of a
peracid is considered ―active‖
Active Oxygen in H2SO5= × 100%=14.0%
Active Oxygen in CH3COOH= × 100%=21.0%
Conversion ration = × 100%
16.0
114.08
16.0
76.05
Peracidsin mixtures as H2O2
Hydrogen peroxide added
South China University of Technology
Chemical safety and handling
Peracid Composition H2O2
Conversion,%CH3COOH H2SO4 H2O2
Pa 3.5 0.03 1.00 70
Px 0 2.75 1.00 70
Pxa1 1.00 1.00 1.00 74
Pxa2 0.75 1.50 1.00 74
Pxa3 0.50 1.50 1.00 65
Preparation of peracids from 50% H2O2
South China University of Technology
Peracid Composition H2O2
Conversion,%CH3COOH H2SO4 H2O2
Pa 2.00 0.03 1.00 71
Px 0 1.50 1.00 70
Pxa1 0.75 0.50 1.00 77
Pxa2 0.75 0.75 1.00 80
Pxa3 0.50 1.00 1.00 73
Praparation of peracids from 70% H2O2
South China University of Technology
Analysis
Conversion ratio %= × 100%
H2O2 g/l=
Na2S2O3 mmol
Cerium Sulfate mmol+Na2S2O3 mmol
(Cerium sulfate mmol + Na2S2O3mmol) × 17
10
South China University of Technology
Benefits of using peroxy acid in TCF
bleaching
? Higher brightness threshold
? Higher viscosity and strength
? Lower cost
Reaction mechanism of peracid and
lignin
Two main mechanisms
? Electrophilic substitution/addition
? Nucleophilic reactions
South China University of Technology
O
O C H 3
HC OH
C = O
O C H 3
O
O+
O C H 3O C H 3
CH 3 O
CH 3 OCH 3 O
CH
C OHO
O
CH
C O
HC
HC O
O
-H 2 O HO
O+Electrophilic reactions
South China University of Technology
OR
O C H 3
O C H 3 O C H 3
OR OR
C =O
CH 3
X O
H
.,
H
O+
CO O H
CH 3
CH 3
X O
C =O
CH 3
O
O
O
O
CH 3
O
O
CH 3
H
O X
H O - X
H
O X
R in g -
o p e n e d P r o d u c t s
Nucleophilic reactions
South China University of Technology
Comparing Pa with Px
? Reaction pathways are identical between Pa
and Px
O C H 3
O C H 3 O C H 3
O C H 3
HO O
O
O C H 3
Aromatic Ring
C— OH
O C H 3
O C H 3
O C H 3
C OHH
CH 3
CH 3
C =O
CH 3
OH
O C H 3
O C H 3
South China University of Technology
C=O
CH 3
C
O CH 3
O CH 3
=O
CH 3
O CH 3
O CH 3
O
C
O
O CH 3
O CH 3
OH
COOH
O C H 3
O C H 3
C O O H
Very stable
South China University of Technology
? The difference in reactivity
Aromatic,Px>Pa
O C H 3
O C H 3
HO
OE
O C H 3
O C H 3
C=O,Px<Pa
O C H 3
O C H 3
O C H 3
O C H 3
C = O
CH 3
O
C = O
CH 3
ON
O C H 3
O C H 3
O C H 3
O C H 3
O C H 3
O C H 3
C OHH
CH 3
C =O
CH 3
OH
ON
OE
C-OH,Px>Pa
South China University of Technology
? Relative reactivity of Peracids
pKa=3.8 pKa=4.8
pKa=1.99
Peracid pKa pKa2=7.1 pKa2=8.2
pKa2=7.1
Nucleophilicity High Medium Low
Electrophilicity Medium Low High
HC O OH
O
CH 3 C O OH
O
SOO-
O
O
O OH
South China University of Technology
Comparison between peracids and
hydrogen peroxide
Peracids Hydrogen
Peroxide
(X-O-H) (H-O-O-H)
pKa of peracids/H2O2 7.1~9.4 11.9
pKa of leaving groups 2.0~4.8 16
X-O-H H-O-O-H
Nucleophilicity High Low
Electrophilicity High Very low
South China University of Technology
Other Applications of Peracids
? Activating agent for oxygen
? Pxa Eop as replacement for O stage
? Improve peroxide bleaching
South China University of Technology
Summary
? High conversion of peroxide to peracids can be
done on site
? Heavy metals decompose peracids,Use of DTPA
necessary
? Peracids are unstable at alkaline pH
? Peracids react with lignin in the same pathways
? Percids are react both as a nucleophile and an
electrophile
? Peracids are better nucleophiles than peroxide
? Peracids may be used as delignigying and
brightening agents
South China University of Technology
QPaQ(PO) bleaching of oxygen
delignified soft wood pulp (in Sweden)
Mn
(ppm)
75
Q
2kg EDTA
/t pulp
Pa
10kg
/t pulp
Q
1kg EDTA
/t pulp
(PO)
40kg H2O2
/t pulp
10 <1
Kappa No 16 12 3.5
Brightness
% ISO 35 48 85.5
Viscosity
Dm3/kg 970 950 750
South China University of Technology
DMD Bleaching
Acetone Peroxymon-
Dimethydioxirane
sulfate
2KHSO5·KHSO4·K 2SO4
C = O
H 3 C
H 3 C
+ H O
O SO 3
-
O O
H 3 C CH 3
_
_
CH 3H 3 C
OO
+ C = C
C C
O
H 3 C
H 3 C
C = O+
South China University of Technology
Hydrosulfite (Dithionite)
Bleaching
Chemistry of hydrosulfite bleaching
Reducing agent
Sulfur dioxide radical anion
Composition of hydrosulfite bleach solutions
-
2 OS, SO
-
2 2 SO
-
2,
2 SO -2, SO 22
-
+ SO
South China University of Technology
·Pulp+Na2S2SO4+H2O Bleached pulp+2NaHSO3
·Na2S2O4+O2 NaHSO4+NaHSO4
·2Na2S2O4+H2O 2NaHSO3+Na2S2O3
·2Fe3++S2O2-+H2O 2Fe2++2HSO-3+2H+
·NaBH4+8NaHSO3 4Na2S2O4+NaBO2+6H2O
Sodium borate
4
} Decomposition
South China University of Technology
Process Vasiables
Normal
Range
Hydrosulfite application 1~10kg/t pulp
Temp,40~100℃
Retention time 30~60min
pH 4.5~6.5
Comsistency 3~30%
South China University of Technology
Chlorinaton
Hydrolysis reaction of chlorine
Cl2+H2O HOCl+HCl
H++Cl-
Kh= =3.94× 10-4(25℃ ),pKh=3.40
HOCl H++OCl-
Ka= =5.6× 10-8(25℃ ),pKa=7.25
Kh
[ H O C l ] [ H + ] [ C l - ]
[ C l 2 ]
[H + ] [ O C l - ]
[ H O Cl ]
South China University of Technology
Reaction of Chlorine whit Lingnin
A - S u b s t it u t i o n
C - O x i d a t io n B - E l e c t r op hi l i c d i s p l a c e m e n t
H - C - O R
O C H
3
L ig n i n
O x i d a t i o n
A
A
A
B
O
C
C
C
C
H O
O
O
Cl
}
Cl
x
O
xR e d
C
C
C O O H
L ig n i n
}
O x i d a t i o n
C O O H
C O O H
O x i d,
F r a g m e n t s
o f d ic a r b o x y li c
a c id
Cl
Cl
x
OH
OH
Cl
South China University of Technology
Organic chlorinated compunds formed
during chlorination &alkaline extraction
Chlorophenols Chlorocatechols
Chloroguaicols Chlorobenzenes
Polychlorinated dibenzo-p-dioxins
2,3,7,8-TCDD 2,3,7,8-TCDF
2,3,7,8-Tetra- 2,3,7,8-
chlorodibenzo-p-dioxins
Tetrachlorodiben-
zofuran
ClCl
Cl Cl
O
O
Cl
Cl Cl
O Cl
South China University of Technology
OH
Cl
2
OH
Cl
Cl
Cl
O
O
OCl
Cl
.
.
Cl
Cl
+C l
2
O
O
Cl
Cl
Cl
Cl
OH
Cl Cl
Cl
O
O M e
Cl
ClCl
Cl
O M e
O H
Cl
.
D ip o ly m e r i z a t i o n
Formation of dioxins during chlorination
South China University of Technology
NaO
O M e
Cl
Cl
Cl
Cl
OH
O
ClCl
Cl
Cl
Cl
Cl
O
OB a s e c t a ly z e d
r e a c t io n
Na
+
Cl Cl
Formation of dioxins during alkaline extraction
C and E stages— Main generator of dioxins
Detection limitation of dioxins,10-12 (ppt,trillion)
≯ 5000ppt still safe
Dioxins discharge in USA 40kg/year
only 1~3% from paper industry
South China University of Technology
Variables affecting chlorination
Pulp properties—bleach demand
—method of pulping
—CED(cupric-ethylene diamine) viscosity
Operating condition—time/temperature
—available chlorine application
—proportion of ClO2 in application
—sequence of chemical application
—initial pH
—chlorine concentration
—consistency
Process conditions —degree of mixing
Control parameters —stock color
—OPR(oxidation-reduction potential)
—chemical residual concentration
South China University of Technology
Chlorin Dioxide Bleaching
Reactions of ClO2 with lignin
Cl
OH
C
C OR
C
O C H 3
OR
Cl 2
C l O 2
O
O
O C H 3
O x i d a t i o n
C
C OH
C
C O O H
C O O H
C
C OR
C
C
C
O
O
O C H 3
OR
C l O 2
C
C
C
OH
OH
OH
C
C OH
C
O
O
Cl 2,C l O 2
South China University of Technology
Process Conditions for ClO2 Bleaching
D1 D2
Chemical Applied
ClO2 kg/t pulp 5~15 2~8
NaOH kg/t pulp 0~0.9 0
End pH 2.5~4 4~5.5
Temperature ℃ 50~90
Time min 120~300
Consistency % 9~16
Residual g/l Trace ~0.05
South China University of Technology
Steam
Steam
Mixer
Chemical
MC pump MC Mixer
The upflow-downflow tower
South China University of Technology
ClO2 Generation
▲ Mathieson Process
SO2+2NaClO3+H2SO4
2ClO2+2NaHSO4
▲ Solvay Process
CH3OH+2NaClO3+H2SO4
2ClO2+HCHO+Na2SO4+2H2O
▲ R2 Process
NaCl+NaClO3+H2SO4
ClO2+1/2Cl2+Na2SO4+H2O
South China University of Technology
▲ The Kesting Process
NaCl+3H2O+6e NaClO3+3H2
NaClO3+2HCl ClO2+1/2Cl2+NaCl+H2O
Cl2+H2 2HCl
▲ R3/SVP Process
NaClO3+NaCl+H2SO
ClO2+ 1/2Cl2+Na2SO4+H2O
NaClO3+5NaCl+3H2SO4
3Cl2+3Na2SO4+3H2O
South China University of Technology
▲ R8/SVP-LITE and R10
3NaClO3+2H2SO4+0.85CH3OH
3ClO2+Na3H(SO4)2+H2O+0.05CH3OH+0.6CHOOH+0.2CO2
▲ The R11/SVP-HP
2NaClO3+H2SO4+H2O22
ClO2+Na2SO4+2H2O+O2
AOX—Adsorbable Organic Halogen
TOCl—Total Organic Halogen
BOD—Biochemical Oxygen Demand
COD—Chemical Oxygen Demand
South China University of Technology
Enzyme Treatment of Pulp
(Biobleaching)
Cellulase
Hemicellulases,Xylanase
Mananase
Ligninolytic enzymes,Lignin peroxidase
Manganese-dependent
peroxidase
Laccase
South China University of Technology
Proposed mechanism of enzyme action
★ Xylanases catalyze the hydrolysis of
reprecipitated xylan on the surface of
the pulp fibers making the lignin
fragments in and on the fiber easier to
remove in the following bleaching and
alkaline extraction stages
★ Another hypothesis is that xylanases,
by catalyzing the depolymerization of
xylan in the cell walls,allow entrapped
lignin to diffuse more easily out of the
fiber
South China University of Technology
★ Enzymes are catalytically active over
a specified pH and temperature range,
Most of these enzymes are active at
neutral pH
★ Commercial enzymes are generally
stable (typically in a concentrated liquid)
at ambient temperature for 6 months,
Most suppliers recommend that the
product be refrigerated to preserve its
optimum activity
Supplier Product
Trade Name
Optimum
pH
Optimum
Temp,℃
Primalco Ecopulp 4~7.5 55
Ciba-
Geigy
Irgazyme 10 6~7 60
Irgazyme 40 7~8.5 50~70
ICI Ecopulp X-200 4~7.5 55
Iogen Iogen GS 35 5~7.7 45~57
Shivex 5.2~7.8 40~62
Novo-
Nordic
Pulpzyme HA 5~6 55
Pulpzyme HB 7~8 55
Pulpzyme HC
Industrial Xylanase Suppliers
Supplier Product
Trade Name
Optimum
pH
Optimum
Temp,℃
Sandos
Cartazyme HS 3~5.5 40~55
Cartazyme PS 7~10 50~70
Cartzayme SR 3~5.5 50~80
Solvay Xylanase
L8000
6~8.5 40~65
Zeneca Ecozyme 6~9 45~65
Infustrial Xylanase Suppliers
South China University of Technology
★ Xylanase bleaching is well-suited for use in the
bleach plant for the following reasons:
· Xylanases react selectively with xylan
· Xylanase treatment allows higher brightness
ceilings to be achieved with some pulps
· Xylanase treatment allows bleaching
sequences to be used which produce effluents
containing reduced amounts of organochlorine
compounds
· Xylanase treatment is implemented in modern
integrated bleach plants without extensive capital
investment
South China University of Technology
Conventional
XCEDED
X(CD)EDED
OX(CD)ED
ECF
XDED
OXDED
X(EOP)D(EOP)D
OXDP
Bleaching sequence containing a xylanase treatment
South China University of Technology
TCF
X(EP)P
ZX(EP)
XZ(EP)
OXQPZP
OXZP
OX(EP)ZP
Bleaching sequences containing a xylanase treatment
South China University of Technology
Treatment Kappa No,Viscosity
mPa·s
Brightness
%ISO
Unbleached 14.1 49.1 34.3
O 8.3 — —
X 10.8 — —
OX 5.3 26.6 55.9
OX(CD)ED — 25.7 90.5
Effect of oxygen delignification and a xylanase
treatment on softwood kraft pulp properties
