CHEMISTRY OF AN OXIDATIVE ALKALINE EXTRACTION …

CHEMISTRY OF AN OXIDATIVE ALKALINE EXTRACTION

BETWEEN CHLORINE DIOXIDE STAGES

Troy Runge, Art J. RagauskasInstitute of Paper Science and Technology

Topics CoveredIntroduction– Project Objectives – Review of Alkaline Extraction and Oxidant

Reinforcement ChemistryResults and Discussion– Pulp Characterization– UV/VIS– Molecular Weight– NMR

Conclusions/Future Research

Why Study Oxidative Extraction Chemistry?

Increased ECF bleaching sequences– Compliance with “Cluster Rules” legislation– >50% of bleached chemical market pulp– Popular ECF sequences

» D(E*)DED E* = oxidant reinforcement» OD(E*)D of O2 and/or H2O2

– D0 stage has received the bulk of research attention

– Opportunities also exist understanding oxidative E1 stage chemistry

Ph.D. Project ObjectivesPh.D. Project ObjectivesExplore the fundamental chemistry of reactions occurring during the alkaline extraction stageFocus on the E1 stage after a D0 delignification stageLook at various oxidant reinforcements– (EAr), E, (EO), (EP), (EPO)

Use NMR spectroscopy to measure functional group changes and GPC to measure MW distribution changesMeasure and correlate bleachability to lignin structural changes

Brief Bleaching Chemistry Review

Reaction schemes based primarily on model compound studies from the literatureBriefly cover main reactions of– ClO2

– NaOH– O2

– H2O2

ClO2 Delignification Chemistry

OCH3OH

OO

OOHO

OCH3

O

OCH3O

Para-quinone Ortho-quinone Muconic Acid Methyl Ester

ClO2 ClO2ClO2

Reacts primarily with phenolic structures

Generates Cl2and HOCl species that further delignify and form AOX

NaOH Chemistry - Neutralization

RCOOH

OH

OCH3

R= aryl or alkyl

HO-

HO-

RCOO- H2O

H2OO-

OCH3

+

+

Ionizes acidic groups - increases solubilityDisassociates lignin complexes allowing greater diffusion out of the fiber cell wall

NaOH Chemistry - Chlorine Elimination

Cl

O

OHO-

Cl

O-

OHO

O

O-

O

-O

O

O

C Cl

CHO

HO-

HCl-

H2O-

C Cl

C-O

Cl--

C

CO

-OHC OH

C-O

Elimination of organically bound Cl– Reduces AOX– Increases lignin

solubility– Increases

reactivity of lignin aromatic group

Alkaline Saponification of Methyl Ester Group in Muconic Acid Methyl Ester

R

OCH3

OO

HO

R

OH

OO

HO

O

R

O

OCH3

O

O

R

O

OH

O

Recent Hypothesis– McKague, Froass,

and Evtguin et al.

Saponification of Methyl Ester– MAME formed in

D0 stage– Increases solubility

Hydroxide Addition to Quinones

O

O

HO-

+

OO

H

HO- H

+

O

O-

HO

-

O

O

-OH

COO-

OH

-

Hydroxide addition to quinones– Increases lignin solubility– Considered minor reaction

Alkali environment can also cause quinone radicals to form and couple

O2 and H2O2 Species

O2oxygen

e- H++ e- H++

perhydroxl radical

e- H++HOH + OHHOOH

hydrogen peroxide

e- H++2 HOH

water & hydroxyl radical water

H+ O2

HOO

OH+ H+

superoxide radical

-OOHperhydroxyl anion oxoanion

pKa 4.8 pKa 11.8 pKa 11.9

O2 and H2O2 form similar reactive species

Oxygen Chemistry - Autoxidation

C

O-OCH3

OCO

O2, HO-

Aliphatic degradation products including methanol and carobxylic acids

O-O

OCH3

C

C

O

C

C

O

OCH3

O-

O

C

C

O-OCH3

O2-C

C

O-OCH3

+ C

C

O-OCH3

C

C

O-OCH3

+O2-

O2 or OH

O2-

O2-

O2-

O2 or OH

+++

O2 reacts primarily with phenolic structures

Hydrogen Peroxide Chemistry - Addition Reactions

OR

OCH3

CHCH

HCO

HOO-

OR

OCH3

CHCH

HCO-

HOO

OR

OCH3

CHCH

HCO

OHOO-

OR

OCH3

CHCH

HCO

-O OOH

OR

OCH3

CHO

HC

HCO

OHO-

-OH

Addition to quinone structures

Michael addition to conjugated carbonyl structures

-OOH O

O-

R

OHO

O-

R

OOHHO O--OHO

-O

R

OOHO

O

R

H2O2 and O2 Reactions that Create Quinones

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

Bleaching Conditions

D0 - 0.20 KF (2.3% charge of ClO2)– 10% solids, 45 min., 45oC, pHi = 2.5

E1 stagesBleachingStage

Bleaching Conditions Employed

E 2.0% NaOH; atmospheric pressure.(EO) 2.5% NaOH; 60 psig O2 initially, -12 psig/5

minutes(EP) 2.5% NaOH; 0.5% hydrogen peroxide(EPO) 2.5% NaO; 0.5% hydrogen peroxide; 60

psig O2 initially, -12 psig/5 minutes(EAr) All O2 was removed from the pulp and

chemicals. 2.0% NaOH ; slight Ar pressure

Bleaching Conditions - continuedD1 - 0.75% ClO2, 0.2% NaOH– 10% solids, 3 hours, 70oC, pHf ~ 4.0

E2 stages - 1.0% NaOH– 10% solids, 75 min., 70oC

D2 - varying ClO2 charge– NaOH charge = 20% of ClO2 charge– 10% solids, 3 hours, 70oC, pHf ~ 4.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

BS D D(EAr) DE D(EO) D(EP) D(EPO) D(EAr)D DED D(EO)D D(EP)D D(EPO)D

Stage

Aci

d-In

solu

ble

Lign

in w

ith 9

5% C

I .

0

5

10

15

20

25

30

Kap

pa N

umbe

r w

ith 9

5% C

I

Acid-Insoluble

Kappa Number

Bleached Pulps - Lignin Content

Oxidant reinforcement increased delignification for E1* stageO2 increased delignification more than H2O2

Kappa more sensitive than acid insoluble lignin

Bleached Pulps - CED Viscosity

15

17

19

21

23

25

27

29

31

33

BS D D(EAr) DE D(EO) D(EP) D(EPO) D(EAr)D DED D(EO)D D(EP)D D(EPO)D

Stage

CED

Visc

osity

with

95%

CI (

cP)

Viscosity is a measure of carbohydrate degradationLoss from D0 -acid hydrolysisLoss from oxidative EO2 cause more damage than H2O2

Bleached Pulps - D1 ISO Brightness

65

70

75

80

85

90

D(EAr)D DED D(EO)D D(EP)D D(EPO)D

Stage

D1 I

SO B

right

ness

with

95%

CI

.

Increased D1brightness with oxidant reinforcementH2O2 > O2

Affected by lignin and chromophore amount

Bleached Pulps - D2 Brightness Ceiling

81

82

83

84

85

86

87

88

89

90

91

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

D2 Charge, %

D2 I

SO B

righ

tnes

s

D(EAr)DED

D(E)DED

D(EO)DED

D(EP)DED

D(EPO)DED

95% LSD value = 1.0 to 1.395% LSD value = 1.0 to 1.3

Used various ClO2charges to generate a D2 brightness ceiling(EAr), E, and (EO) statistically similar(EP) and (EPO) significantly betterAttributed to quinone destruction

AOX and Cl / 100 C atoms of Bleach Effluents

0.0

0.3

0.5

0.8

1.0

1.3

1.5

1.8

2.0

D+D(EAr) D+DE D+D(EO) D+D(EP) D+D(EPO)

Bleach Sequence

AO

X (g

Cl/k

g pu

lp)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Cl /

100

C

AOX Cl/100C

Trend of decreased AOX content with increased oxidantMineralization phenomena -literatureAmount of decrease is not significant

Bleached Pulps - Carboxyl Content

50

55

60

65

70

75

80

85

90

BS D D(EAr) DE D(EO) D(EP) D(EPO) DED D(EPO)D

Stage

Pul

p C

OO

H c

onte

nt (m

eq/k

g) w

ith

95%

CI

.

COOH groups can control physical paper propertiesConductometric titrationTrend of increased COOH groups with oxidant but not significant

Bleachability Fundamentals

To obtain fundamental understanding of changes in delignification and bleachability - understand changes to lignin structure– Lignin color– Lignin size– Lignin functional groups

Lignin Isolation

Characterized pulps and effluents were used to isolate lignin– Residual lignin - Acid Hydrolysis

» 0.1 M HCl in 9:1 dioxane:H2O solution» Remove dioxane & acid precipitate» Wash repeatedly & freeze-dry

– Effluent lignin - Precipitate» Alkaline stages only» Acid precipitate» Wash repeatedly & freeze-dry

VIS Absorbance - Residual Lignins

-1

-0.5

0

0.5

1

1.5

2

350 400 450 500 550 600 650 700Wavelength (nm)

Res

idua

l Lig

nin

Visi

ble

Abs

. ∆ S

pect

ra (A

bs L

/g c

m)

DD(EAr)DED(EO)D(EP)D(EPO)

Measured in 1:1 (v/v) dioxane:waterAcidic solutions to remove ionization effectsGreatest change in 360 to 420 nm region

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Brownstock D D(EAr) DE D(EO) D(EP) D(EPO)

Bleach Stage

Lign

in A

bsor

ptiv

ity a

t 457

nm

(Abs

L/g

cm

)

ResidualEffluent

Lignin Absorptivity at 457 nm

D0 darker in color than BrownstockEAr, E, and EO darker in color than DEP and EPO lighter in color than BrownstockEffluent lighter in color than residual lignin

95% LSD value = 0.058795% LSD value = 0.0587

Effluent Apparent MW Distribution

– Uses 2 Sephadex packed LC columns and 0.1 N LiCl as eluent

– 5 ml of prepared effluent travel through column according to size

– Column exit stream is measured by TOC detector

– MW calculated from calibration standards of PEG and methanol

• Effluent apparent MW were performed using LC procedure

Apparent MW Distributions of Bleach Stage Effluents

0

20

40

60

80

100

120

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Apparent Molecular Weight

TOC

, ppm

D

D(EPO)

D(EPO)D

D0 - low MW fragments onlyE1* -bimodal distributionD1 low amount of organic matter

Alkaline Extraction Oxidant Affect on E* Stage Effluent Apparent MW Distributions

0

20

40

60

80

100

120

140

160

180

200

0 2000 4000 6000 8000 10000 12000 14000 16000 18000


TOC

, ppm

D(EAr)DED(EO)D(EP)D(EPO)

Oxidant reinforcement decreases effluent apparent MWSignifies oxidant is reacting with dissolved effluent lignin

Average Effluent Molecular Weight

Quantify MW decrease with number and weighted averageDecrease in MWW > MWN due to changes occurring mainly in higher MW fraction 0

1000

2000

3000

4000

5000

6000

7000

8000

9000

D D(EAr) DE D(EO) D(EP) D(EPO)

Bleach Sequence

Mol

ecul

ar W

eigh

t Ave

rage

MWn

MWw

MWMWN N 95% LSD = 621; MW95% LSD = 621; MWWW 95% LSD = 71895% LSD = 718

Controlled Experiment of Oxidant Addition on Effluent Lignin Apparent MW Distribution

D(EAr) effluent was treated to (EP), (EO), and (EPO)Oxidants were able to degrade effluent lignin

0

20

40

60

80

100

120

140

160

180

200

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000


TO

C, p

pm (o

n an

orig

inal

D(E

Ar)

bas

is)

D(EAr)D(EAr)(EP)D(EAr)(EO)D(EAr)(EPO)

Hypothesis - Effluent Apparent MW

Hypothesis: Dissolved lignin in effluent of E1* stage reacts with O2 and H2O2reinforcement - consuming chemicals

Test with alternative E1 stages that remove the bulk of the effluent lignin before the O2and H2O2 are applied

Alternative Alkaline Extraction Experiments

E EPOWash

Majority ofeffluent lignin

D Pulp

D(EP)pulp

Effluent

Freshchemicals

CounterCounter--current Extractioncurrent Extraction Double ExtractionDouble Extraction

Results of the Alternative Extraction Stages

Removal of effluent lignin before applying oxidant reinforcement does not significantly improve delignification or brightnessAdditional experiments with increasing H2O2 charges indicated residual lignin was reactive to further oxidant chemicalThis suggests that very little oxidant is wasted reacting with effluent lignin


To obtain fundamental understanding of changes bleachability - understand changes to lignin structure– Lignin color– Lignin size– Lignin functional groups

NMR Spectroscopy on Lignin

Bruker 400 MHzExperiments Performed– 1H NMR – 13C NMR – 31P NMR - Hydroxyl groups– 31P NMR - Quinones– 2H NMR - Alkyl Carbonyls

Typical 1H NMR Spectrum

(ppm) -202468101214

COOHCOOH Phenolic HPhenolic H

D(EO) residual lignin D(EO) residual lignin TSP internal standardTSP internal standard

Methoxy HMethoxy H

Aromatic HAromatic H

Formyl HFormyl H

Aliphatic CHAliphatic CHXX--OO--

DMSODMSO

OC

OOCH3

C

CH2OH

[R]H

H H

CH2

CHOH

OH

CH

CH

CHO

OCH3

OR

HH

H

1H NMR - COOH groups

0.0

0.5

1.0

1.5

2.0

2.5


Bleach Sequence

CO

OH

gro

ups,

mm

ol/g

isol

ated

lign

in .

Residual

Effluent

95% LSD = 0.15995% LSD = 0.159

COOH increase due to alkaliAttributed to MAME saponificationO2 and H2O2do not give appreciable increases

R

OH

OO

HO

1H NMR - Unsubstituted Phenolic Groups

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0


Bleach Sequence

Uns

ubst

itute

d Ph

enol

ic O

H,

mm

ol/g

isol

ated

lign

in .

Residual

Effluent

95% LSD = 0.18395% LSD = 0.183

Significant phenolic decrease in O2 reinforced stagesAttributed to autoxidation reactions

OHOCH3

H

H H

1H NMR - Substituted Phenolic Groups

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


Bleach Sequence

Subs

titut

ed P

heno

lic O

H,

mm

ol/g

isol

ated

lign

in

.

ResidualEffluent

95% LSD = 0.05495% LSD = 0.054

Decrease in O2 reinforced stagesSubstituted phenolic did not decrease as much as unsubstituted - indicating less reactive

OHOCH3H3CO

1H NMR - Other Groups

Formyl – No change during D0

– slight decrease with O2 reinforcementAromatic – decrease during D0

– No change in E1*Methoxyl and Aliphatic CHX-O-– high variability

1H NMR - D1 stage

D1 Stage – Destroys aromatic

nature of lignin – Leaves primarily

aliphatic structures

No differences noted between functional groups from previous E1* stage

ppm 0 2 4 6 8 10 12

DED LigninDED Lignin

Typical 13C NMR Spectrum

(ppm)20406080100120140160180 0

D(EO) residual lignin D(EO) residual lignin

COOH COOH

Aromatic CsAromatic Cs

DMSODMSO

MethoxyMethoxy

ConjugatedConjugated UnconjugatedUnconjugated

Cs on aliphatic ether Cs on aliphatic ether & hydroxyls& hydroxyls

13C NMR Structures– Unconjugated COOH– Conjugated COOH– C3, C4 Aromatic ether or hydroxyl– C1, Aromatic C-C bond– C5, Aromatic C-C bond– C2, Aromatic C-H bond– C5, Aromatic C-H bond– C6, Aromatic C-H bond– Methoxyl OCH3

– Cβ in β-β and Cβ in β-5– Aliphatic C-O bond, Cβ in β-O-4; Cα in β-5 and β-β– Aliphatic C-O bond, Cα in β-O-4– Aliphatic COR– Aliphatic C-O Cγ in β-O-4

CH

CH

CH2OH

OHOCH3

12

3

45

6

α

β

γ

CCC

CC

C

O O

β-β

CCC

O C

O

β-O-4

CC

O

C

C

O

CC

5-5

13C NMR - Unconjugated COOH

0.0

0.2

0.4

0.6

0.8

1.0

1.2


Bleaching Sequence

Unc

onju

gate

d C

OO

H

(C a

tom

s/Aro

mat

ic R

ing)

Residual

Effluent

95% LSD = 0.09595% LSD = 0.095

O

R

O

OH

O

Increase in D0stage and all E1* stageSuggests an increase in COOH groups due to alkali

13C NMR - Conjugated COOH

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Bleaching Sequence

Con

juga

ted

CO

OH

(C

ato

ms/A

rom

atic

Rin

g)

Residual

Effluent

95% LSD = 0.08895% LSD = 0.088

R

OH

OO

HO

Increase in D0

No increase in E1*Suggests the muconic acid structures are in the lactoneform.

20406080100120140160180

13C NMR Spectra Around the E stage

0ppm

Muconic acidOCH3

D residual lignin

DE effluent lignin

DE residual lignin

UnconjugatedUnconjugatedCOOHCOOH

ConjugatedConjugatedCOOHCOOH

13C NMR - Methoxyl

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Bleaching Sequence

Met

hoxy

l OC

H3

(C a

tom

s/Aro

mat

ic R

ing)

Residual

Effluent

95% LSD = 0.09795% LSD = 0.097

OHOCH3

H

H HMethoxyl enrichment relative to aromatic signalNot creating methoxyl groupsDemethylation reactions create phenolic, which react via autoxidation

31P NMR - Hydroxyl Groups

2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane derivatizedLignins used– Preliminary study - small scale

» 33 kappa industrial softwood pulp

– D0 residual lignin» Performed E1* stage reactions» 1:1 (v/v) dioxane:water » Isolated lignin

Similar results

Typical 31P NMR Spectrum

Aliphatic OH

ppm 134136138140142144146148150

Cyclohexanol

Condensedphenolic

Guaiacylphenolic

Carboxylgroups

DE ligninDE lignin

31P NMR - Carboxyl Groups

0.0

0.2

0.4

0.6

0.8

1.0

1.2


Bleach Stage

Car

boxy

lic A

cid

(mm

ol/g

isol

ated

lign

in)

95% LSD = 0.19195% LSD = 0.191

Increase in COOH with alkali - MAME saponificationIncrease with H2O2reinforcement -perhydroxyl addition to quinone structures

31P NMR - Phenolic

0.0

0.1

0.2

0.3

0.4

0.5

0.6


Bleach Stage

Phe

nolic

(mm

ol/g

isol

ated

lign

in)

GuaiacylCondensed

Condensed phenolic 95% LSD = 0.059; Guaiacyl phenolic 95% LSD = Condensed phenolic 95% LSD = 0.059; Guaiacyl phenolic 95% LSD = 0.024 0.024

Phenolic decrease with oxidant reinforcement - autoxidation reactionsCondensed phenolic smaller drop indicating lower reactive than guaiacyl

31P NMR - Aliphatic Hydroxyl Groups

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


Bleach Stage

Alip

hatic

OH

(mm

ol/g

isol

ated

lign

in)

95% LSD = 0.15095% LSD = 0.150

Increase in aliphatic hydroxyl due to alkaliPossibly due to chlorine elimination reactions

Existing NMR Techniques Summary

Existing techniques are able to show some major delignification reactions Measured structures correlated well with delignification but not brightnessNew NMR techniques needed to measure chromophore structures

Lignin Chromophore Structures

Consists primarily of conjugated carbonyls– Quinones– Conjugated

alkyl carbonyls

O

OH

OCH3

coniferaldehyde

O

OOCH3

O

O

para-quinone ortho-quinone

O

CH

OCH3

O

OCH3C

OCH3

OH

O

CH

OCH3

H3CO

CH

O

para-quinone methide ortho-quinone methide

para-para-stilbene quinone

31P NMR - Quinones

Internal Standardtri-m-tolyl-phosphate

05 -5 -10 -15 -20 ppm

Phosphate ester adductLabeled quinone

Procedure developed by Zawadzki et al.Tri-methyl phosphite derivatized

31P NMR - Quinone Content of D0 and E1*

0.00

0.05

0.10

0.15

0.20

0.25


Bleach Stage

Qui

none

Con

tent

(mm

ol/g

isol

ated

lign

in)

Residual Effluent

95% LSD = 0.05395% LSD = 0.053

D0 stage increase quinones -phenolic reaction Alkali decreases quinone -hydroxide addition & BAR O2 and H2O2decreases quinone -perhydroxyl addition

31P NMR - Quinone Content D1 Stage

0.00

0.05

0.10

0.15

0.20

0.25

D(EAr) DE D(EO) D(EP) D(EPO)E1* Bleach Stage

Qui

none

Con

tent

(mm

ol/g

isol

ated

lign

in)

E1* residual ligninD1 residual lignin

95% LSD = 0.05395% LSD = 0.053

D1 stage does not affect quinone contentBrightening of D1 stage possibly from lignin removal and conjugation destruction

Apparent Quinone Content vs D1 Brightness

y = -39.092x + 84.662R2 = 0.8231

70

72

74

76

78

80

82

84

86

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Apparent Quinone (mmol /kg pulp)

ISO

Bri

ghtn

ess

D(EOP)D

DED

D(EO)D

D(EP)D

D(EAr)D

Apparent quinone = quinone content on pulp weight basis (acid -insoluble ligninCorrelates well brightness suggesting it is a major chromophore

Conclusions

First research to compare fundamental differences between oxidant reinforcement in an alkaline extraction stageAble to to show delignification and brightening reactions occur in the oxidative E1 stageStructural changes measured by existing NMR techniques of 1H-, 13C-, and 31P-hydroxyl NMR useful in explaining delignification reactions but do not correlate to brightness

Conclusions - continuedSummary of main effects of each chemical– NaOH

» Dramatic increase in COOH - MAME saponification

– O2» Increases delignification - autoxidation reactions» Unsubstituted phenolics more reactive than

substituted» Ambient O2 increases delignification

– H2O2» Increases brightness - quinone addition reactions

Acknowledgments:Acknowledgments:IPST Member CompaniesIPST Member CompaniesIPST Wood Chemistry GroupIPST Wood Chemistry Group

CHEMISTRY OF AN OXIDATIVE ALKALINE EXTRACTION …

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