Relationship between Residual Lignin
Structure and Reactivity to ClO2 Pulp
Bleachability
Background
• Influence of residual lignin structure on
ClO2 reactivity
– Residual lignin structure is influenced by
pulping conditions and the extent of
g
delignification
– Residual lignin’s structure will influence its
y towards ClO2
reactivity
Germgard (1982)
Objectives
• Determine how the extent of delignification
and pulping process variables influence
bleachability in a D(EO) delignification
sequence
• Relate
Rel te the unbleached
ble hed residual
e id l lignin
li i
structure and residual lignin reactivity
to ards ClO2 to bleachability
towards
bleachabilit
Experimental Approach
• Bleach pulps in a D(EO) sequence and
define a bleachability parameter (TAC/
appa #)
Kappa
• React isolated residual lignins with ClO2
andd monitor
it functional
f ti l group changes
h
in
i
these lignins
Pulps Investigated
Loblolly
L
bl ll Pine
Pi
Chips
• Conventional kraft
– C28
– C18
• Simulated EMCC
– E29
– E18
– E14
Bleaching conditions in the D(EO) partial sequence
D Stage
EO stage
KF
0.1870.005 % NaOH
50% TAC
Time
30 min
Time
60 min
Temp.
p
45C
Temp.
p
70C
Consy.
10%
Consy
10%
Mixer
Quantum
O2 Press.
60 psig (dec 12psi
every 5 min)
Mixer
Peg
Bleachability parameters for CK and EK pulps.
Parameter
CK
EK
Unbleached Kappa
No.
28.0
18.5
29.1
18.5
14.5
Kappa No. after D
11.0
9.2
11.0
7.5
6.0
TAC1/Kappa
0.30
0.37
0.30
0.31
0.33
Kappa No. after
(EO)
3.8
3.5
3.3
3.0
2.3
TAC1/Kappa
0.21
0.23
0.21
0.22
0.23
49 8
49.8
50 2
50.2
53 5
53.5
Brightness after
47 4
47.4
49 9
49.9
(EO)
1TAC-percent total active chlorine consumed
TA
AC/ Kapp
pa for D
D(EO)
0.240
Conventional
0.235
0 230
0.230
0.225
0.220
0.215
EMCC
0.210
0 205
0.205
35
30
25
20
15
Unbleached kappa number
10
Structure Of Residual Kraft Lignin
Aliphatic OH
H content
(mmol/g)
2.0
CK
EK
1.9
E29 r.l.'
A26 rr.l.
l
18
1.8
1.7
1.6
1.5
30
25
20
Unbleached kappa number
15
10
Aliphatic hydroxyl content versus unbleached kappa number for various CK and EK residual
lignins as determined by 31P-NMR. Also included are A26 r.l., E29 r.l.’ and four replicates of C28 r.l.
Structure Of Residual Kraft Lignin
Total phenolic O
T
OH content
(mmol/gg)
2.6
CK
2.5
EK
2.4
E29 r.l.'
A26 r.l.
l
2.3
2.2
2.1
2.0
30
25
20
Unbleached kappa number
15
10
Total phenolic hydroxyl content versus unbleached kappa number for various CK and EK
g
as determined by
y 31P-NMR.
residual lignins
Structure Of Kraft Residual Lignin
1.2
Condensed phenollic OH content
(mmoll/g)
Guaiacyl phenolic content (mmol/g)
1.4
1.3
CK
12
1.2
EK
E29 r.l.'
1.1
A26 r.l.
CK
EK
E29 r.l.'
1.1
A26 r.l.
1.0
0.9
0.8
1.0
30
25
20
Unbleached kappa number
15
10
30
25
20
Unbleached kappa number
Guaiacyl phenolic and C5 Condensed hydroxyl content versus unbleached kappa number
for various CK and EK residual lignins as determined by 31P-NMR.
15
10
Structure Of Kraft Residual Lignin
-O--4 content (mmoll/g)
0.7
CK
CK
EK
EK
E29 r.l.'
A26 r.l.
0.6
0.5
0.4
0.3
0.2
0.1
30
25
20
U bl h d k
Unbleached
kappa number
b
15
-O-4 content versus unbleached kappa number for various
CK and EK residual lignins as determined by 1H-NMR of lignin acetates.
10
TAC
C/ Kaappa ffor D(E
EO)
Bleachability and Structure Of Kraft
Residual Lignin
0.240
Conventional
0.235
0.230
0.225
0.220
0.215
EMCC
0.210
0.205
35
30
25
20
15
10
Unbleached kappa number
Relationship between residual lignin structure
and p
pulp
p bleachability
y
• Lower kappa number pulps are richer in
phenolic content yet harder to bleach
• Bl
Bleachability
h bili seems to be
b related
l d to the
h
content of condensed structures and aryl
ether
h li
linkages
k
Reactivity of residual lignin toward ClO2
• Reacted the isolated residual lignins with
ClO2
• Measured reactivity by quantifying changes
in functional groups
Experimental
Isolated residual lignins
in 9:1 dioxane:water
ClO2 Treatment
0.05 / 0.10 / 0.20 KF
ClO2 reacted lignins
31P-NMR
analysis
Monitor:
o to :
Guaiacyl/Condensed phenols
COOH groups
31P-NMR
E29 0.10 KF
E29 0.05 KF
E29 Untreated
spectra of residual lignin treated with ClO2
Loss of phenolic hydroxyl groups
-2
E14 r.l.
content (mmol/g)
Loss
s of phen
nolic hyd
droxyl
EMCC residual lignins-reactions with ClO2
-1.6
-1.2
E29 r.l.
-0.8
-0.4
0
0
0.05
0.1
Kappa factor
0.15
0.2
Loss of phenolic hydroxyl groups
Lo
oss of gua
aiacyl and
d
conde
ensed phe
enolic gro
oups
(mmo
ol/g)
Various residual lignins-reactions with ClO2
-1.0
Guaiacyl phenolic
-0.8
08
-0.6
-0.4
Condensed phenolic
-0.2
0.0
0
0.05
0.1
0.15
K
Kappa
ffactor
t
0.2
Increase in carboxylic acid groups
Incre
ease in CO
OOH conttent
(mmo
ol/g)
EMCC residual lignins-reactions with ClO2
0.8
E29 r.l.
0.6
0.4
E18 r.l.
0.2
0
0
0.05
0.1
Kappa Factor
0.15
0.2
Increase in carboxylic acid groups
Various residual lignins-reactions with ClO2
In
ncrease in COOH
H
content ((mmol/g))
c
0.25
0.05 KF
EMCC
0.20
Conventional
0.15
0.10
30
25
20
15
Unbleached kappa number
10
Conclusions
• Residual lignin structure and reactivity
toward ClO2 will influence bleaching in a
D(EO) sequence
• Condensed phenolics not as reactive
• B-O-aryl
BO
l ethers
h
• Pulping conditions influence residual lignin
structure and suggests that these conditions
can be optimized to enhance and improve
ECF bleachability