Totally chlorine-free bleaching sequences for paper and dissolving - - PowerPoint PPT Presentation

Totally chlorine-free bleaching sequences for paper and dissolving eucalypt pulps

Jordan Perrin, Frédéric Pouyet, Dominique Lachenal

1

Introduction

Why is TCF not developing?

• Quality
• Regulation
• Cost
• ECF bleaching is considered as BAT

2

Introduction

• The efficient TCF sequences contain ozone treatment
• Cellulose is oxidized by HO° radicals during ozone stage
• These radicals are formed by the action of ozone on C=C (HexA, Lignin,
• xidized lignin).

3

Principles for better performance

• C=C have to be lowered as much as possible
• HexA are removed by A stage
• Split of ozone charge
• Muconic acids are removed by E stage
• Final P helps brightness gain and stability

→A(ZE)(ZE)…P type sequences are proposed

4

TCF pulp line

5

Bleaching of Eucalyptus paper pulp

• Properties of TCF pulp similar to those of ECF pulp

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ClO2 charge (%) O3 charge (%) NaOH charge (%) H2O2 charge (%) OXE/T

DA(EP)DP 0.55+0.25 / 1.0+0.8 0.35+0.2 917 ZEP / 0.8 1.0+1.0 0.6 1353 AQ(ZEO)(ZEO)P / 0.25+0.18 1.1+1.0+0.8 0.6 890

Brightness (%ISO) DP

DA(EP)DP 90.5 1180 ZEP 86 800 AQ(ZEO)(ZEO)P 90.6 1000

Mechanical properties

• Good physical properties for TCF pulp

7

Assessment

• Lower OPEX/CAPEX
• Lower water consumption
• Lower COD/BOD
• No AOX
• Similar quality to ECF

8

Dissolving pulps

Difference with paper pulp:

• No HexA
• Low viscosity (viscose grade)

Constraints:

• High reactivity
• Narrow molecular mass distribution

…

9

Bleaching of Eucalyptus dissolving pulp

• Same type of TCF sequences (except A)
• Very low chemical consumption

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ClO2 charge (%) O3 charge (%) NaOH charge (%) H2O2 charge (%) OXE/T

D(EOP)DP 0.40+0.45 / 1.0+0.5 0.1+0.1 747 Qa(ZEO)(ZEO)(ZP) / 0.1+0.1+0.1 1.0+1.0+1.0 0.2 492 (ZEO)(ZEO)(ZP) / 0.1+0.1+0.1 1.0+1.0+1.0 0.2 492

Brightness (%ISO) DP

D(EOP)DP 89.0 745 Qa(ZEO)(ZEO)(ZP) 90.1 640 (ZEO)(ZEO)(ZP) 89.8 620

Properties of dissolving pulp

• Lower DP
• Higher reactivity

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D(EOP)DP Qa(ZEO)(ZEO)(ZP) (ZEO)(ZEO)(ZP) Brightness (%ISO) 89.0 90.1 89.8

• Bright. after ageing (%ISO)

87.9 88.3 87.9 DP 745 640 620 R18 (%) 98.0 98.0 98.0 Fock (%) 75 85

Properties of dissolving pulp (2)

• Similar molecular mass distribution

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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 4.5 5 5.5 6 6.5 7 Differential weight fraction log Mw D(Eop)DP Qa(ZEo)(ZEo)(ZP)

• Lower chemical cost

13

D(EOP)DP (ZEO)(ZEO)(ZP) (ZEO)(ZEO)(ZP) Reagent (%) ClO2: 0.85% H2O2: 0.2% MgSO4: 0.1% NaOH: 1.5% H2SO4: 0.5%

• O3: 0.3%

H2O2: 0.2% MgSO4: 0.3% NaOH: 3% H2SO4: 1.2%

• O3: 0.3%

H2O2: 0.2% MgSO4: 0.1% NaOH: 1% H2SO4: 1.2% OWL: 2% as NaOH Cost ($/T) 17.8 16.2 13.1

Chemical cost

O2 and OWL not taken into account

Assessment

• Lower OPEX/CAPEX
• Lower water consumption
• Lower COD/BOD
• No AOX
• Better reactivity

14

Conclusions

New TCF bleaching sequences are proposed for both paper and dissolving pulps. In these sequences the consumption of ozone by the primary lignin oxidation product are minimized (less

• xidation of cellulose, better ozone efficiency).

These sequences appear attractive in terms of cost and environmental impact. No quality penalty was found so far.

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Thank you for your attention

Acknowledgments:

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