Hydrogen Peroxide Bleaching Highlights State of the Art and Research Direction Art J. Ragauskas

Hydrogen Peroxide Bleaching • Background • Mill Applications • Research Directions

Peroxide Bleaching: Background - e- H + O2

- e- H +

+ e- H +

HOO

HOOH

perhydroxyl radical

-

H+ O 2 superoxide anion pK a 4.8

-

+e H

+

HOH + OH water & hydroxyl radical

+

-

H OOH perhydroxyl anion pK a 11.8

-

H+ O oxoanion pK a 11.9

-active bleaching species is HOO- and derivatives

2 H 2O

Peroxide Bleaching: Background H2O2 + M H2O2 + HOHO2- + M+ HO2. + HOO2-. +

M+

O2-. + HO. 2O2.- + H2O HO. + HO2HO. + M HO. + HO.

→ → → → → → → → → →

HO. + HO- + M+ HO2- + H2O HO2. + M O2-. + H2O O2 + M O2 + HOO2 + HO2- + HOH2O + O2-. HO- + M+ H2O2

Peroxide chemistry strongly influenced by metals

Peroxide Bleaching: Background Dakin reaction

z

R R R

R

R O

HO HOO

O

-

-

O

O

-

O

O

-

O -

C O O

OH HO

OCH3 O

-

OCH3

OCH3

O

O

O

-

O2

OCH3

-

O

O

-

OCH3

OCH3 O

Dakin-like reaction

z

C O

C OH

O2 or OH O2

O

-

C OH

C

OH O2

-

O

OH O O - HO-

OCH3

OCH3

OCH3

-

C

O

O

OCH3

OCH3 O

Lignin fragmentation reactions

O

Peroxide Bleaching: Background

z

Addition to quinone structures R

R

-

O O

-

OOH

O

R

R

-

O

OOH OH

O HO

O

-

-

OOH

Destruction of color bodies

O HO

O O

-

Peroxide Bleaching: Background

CO2H

H HO

H2O2/NaOH

O

NR

OH O HO O

O Xylan

Formed during pulping • 30 -50% of Southern HW Kappa # •10 - 20% of Southern SW Kappa #

Peroxide:

Mill Applications

Eop – – – – – –

• Ep 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

– – – – –

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

• PO – – – – – – –

Requires pre Q-stage Peroxide: 0.5 - 3.0% Temp: 100 - 110oC Time: 60 - 120 min O2: 75 - 120 psi Stabilizer Brightening & delignifying

• 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

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 metals 2.5% P, Q vs. no Q for SW Kraft Pulp • P-delignification requires metal management via Qstage • Favorable M: Mg2+ • Harmful: Fe, Cr, Ni – Mn favorable/harmful

• Note: C/D or D not M sensitive

50 40 30 20 10 0 70 C no Q

70 C Q

% Delignification % Brightness

Peroxide Bleaching: Role of Temperature 2.5% P Q HW Kraft Pulp

130/C

110

– Q stage – yield

45 40 35 30 25 20 15 10 5 0

70

• P* significantly improves peroxide • P* not just increase in rates • Capital intensive • Sensitive to M+

30

% Delignification

P-Stage Future Research Directions • Peroxide Efficiency •Improved Conditions •Catalysis •Modification of fibers

Brightening After OD(EPO)D Kraft HW 92

Brightness

90 88

Chlorine Dioxide Peroxide

86

Ozone

84 0.0

0.5

1.0

1.5

2.0

Chemical Charge, % o.d. pulp

2.5

Tappi Brightness

Peroxide Brightening Effects 89 88 87 86 85 84 83 82 81 80

DEDP DEPD

0.5

1

1.5

2

2.5

3.5

Peroxide Charge (%)

• 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 OAc

OAc

AcO

O

AcO

OAc

OAc

OH

OAc OAc

OH

Pentacetyl Glucose

OAc

Diacetin Ac

O

O

AcN

N Ac

O

Ac

N

N

Ac

Ac

Diethyl Pyrocarbonate

DAED

RAc + H-O-O -

TAED RH + -O-O-Ac

All improve a P-stage by 15 - 40% >>stoichiometrically

Peroxide Bleaching: Research P-catalyst H O O

N N O2

-

O

O 2 V

O2

H

N

N

X

Fe

-

N

X

N O

O O N

N N

Mn N

O O

N

Mn O

N

0.2% Pcat

0.02% Pcat

1.0% P

0.2% Pcat

0.02% Pcat

0.5%P

16 14 12 10 8 6 4 2 0 Do SW kraft

Kappa #

Peroxide Bleaching: Research P-catalyst

Catalytic Peroxide Activation: Use of Mn-catalyst to improve alkaline peroxide bleaching of Do SW kraft.

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 0.08

Scott-Bond (J)

0.06 Control 0.04

Oxygen/Peroxide Oxygen

0.02

0 300

350

400

Scattering Coefficient (cm2/g)

450

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.

Acknowledgments Member Companies IPST