SLIDE 1 The Future of Eucalyptus Pulp Bleaching Technology
Tapani Vuorinen tapani.vuorinen@aalto.fi
May 26-29, 2015 Vitória, ES, Brazil 7th International Colloquium on Eucalyptus Pulp
SLIDE 2 Outline
- Aim
- Advances in pulp bleaching
technology
- Chemistry of ECF bleaching
- Outlook for the future
- Conclusions
SLIDE 3
Aim of the talk
To show the high potential and solution for a revolution in eucalyptus pulp bleaching practice from today’s best available ECF bleaching technology… …in fulfilling the ”more with less” challenge: less chemicals, less water, less energy, lower environmental impact, lower capex
SLIDE 4 Milestones
- 1992-1995: Discovery of the importance
- f hexenuronic acid (HexA) in kraft pulps
- 1995-: Early mill scale implementations of
A-stage to remove HexA
- 2000-: Large scale implementation of A-
stage in hardwood (eucalyptus) pulp mills
- 2000-: Increasing understanding on the
chemistry of pulp bleaching
- 2020-: Revolutionary pulp bleaching?
SLIDE 5 Advances in eucalyptus pulp ECF bleaching technology
– e.g. D-EOP-D-D
– e.g. A/D-EOP-D-P, D/A-EOP-D-P, A-EOP-D-P – Half less ClO2 is needed (1.5-2 % as active chlorine dosage) – A hot acid stage with long retention time is added to remove HexA
SLIDE 6 Main targets of pulp bleaching
– Low lignin chromophore content
- To reach high brightness stability
– Low residual lignin content – Low hexenuronic acid (HexA) content – Low carbonyl content
- To remove most of chromophores, lignin and
HexA without oxidizing polysaccharides
SLIDE 7 Chemistry of ECF pulp bleaching
- Monitoring the bleaching result
– Lignin content, HexA content – Brightness, viscosity, chlorate formation… – Oxidized structures, chromophores…
- Knowledge on chemical reactions involved
– Inorganic reactions – Reactions of lignin and HexA – Structure-reactivity relationships
- Modeling and simulation of complex reaction
systems
– Visit Poster 6 by Anna Kalliola et al.
SLIDE 8 UV Raman spectra of bleached kraft pulps
Kristiina Kellokoski M.Sc. Thesis 2013
SLIDE 9
General reaction scheme of chlorine dioxide bleaching
SLIDE 10 Oxidants in chlorine dioxide bleaching
– Oxidizes phenols and hydroxyquinones (2 equivalents ClO2 per phenol or hydroxyquinone) – Produces ½ equivalents HOCl and ½ equivalents ClO2
– Oxidizes aldehydes (formed in situ) forming equivalent amount of HOCl – Decomposes to chlorate (ClO3
- ) and HOCl (catalysis by HOCl)
– May react with HOCl to regenerate ClO2
– Oxidizes HexA – Chlorinates and oxidizes lignin – Oxidizes cellulose and hemicelluloses
SLIDE 11 Stoichiometry of overall reactions
- 2ArOH + HexA + 4ClO2 2OxLig + OxHexA +
ClO3
– In this simplified (but relevant) scheme HexA and lignin are oxidized in a 1:2 ratio!
- Formation of HOCl in situ
– 0.75-1 equivalents per added ClO2
- Formation of chlorate (ClO3
- )
– 0-0.25 equivalents per added ClO2
SLIDE 12
Production of bleaching chemicals
Hypochlorite: (1) NaCl + H2O → NaOCl + H2 (electrolysis) Chlorate: (2) 3NaOCl → NaClO3 + 2NaCl (3) NaCl + 3H2O → NaClO3 + 3H2 (electrolysis) Chlorine dioxide: (4) NaClO3 + reductant → ClO2 Hydrogen peroxide: (5) H2 + O2 → H2O2 (catalytic)
SLIDE 13
Production of bleaching chemicals and their usage (share of oxidation power)
3.NaCl 3.NaOCl (eq. HOCl, Cl2) NaClO3 ClO2 40 % HOCl, 40 % HClO2, 20 % ≤ 30 %
SLIDE 14 Inefficiency in current ECF bleaching technology
- Long retention times – huge bleaching towers
- Excessive oxidation power needed in removal of
residual lignin and HexA
– 4-6 equivalents of oxidant per C6C3 + HexA – 7-9 equivalents of oxidant per C6C3 + HexA (HexA hydrolyzed by acid calculated out)
⇒ Target should be in doubling the efficiency!
SLIDE 15 Reactivity of HOCl
– Primary oxidation of HexA - OK – Chlorination of lignin – reduces reactivity of residual lignin (by factor of 10 per each substitution) – Oxidation of lignin - OK – Oxidation of cellulose and hemicelluloses – may decrease brightness stability
– Secondary oxidation of HexA – consumes oxidant without promoting removal of HexA – Oxidation of chromophores - OK
SLIDE 16 Derivatives of HOCl (Cl2)
- General reaction (nucleophilic substitution on chlorine):
Nu- + Clδ+-Clδ- Nu-Cl + Cl- Nucleophile Product Name H2O/HO- HOCl Hypochlorous acid ClO- Cl2O Chlorine monoxide ClO2
Dichlorine dioxide RCO2H RCO2Cl Acyl hypochlorite ROH ROCl Alkyl hypochlorite ArOH ArOCl Aryl hypochlorite R3N R3N+Cl Chloroammonium cation
SLIDE 17 Characteristics of R3N catalysis
- The actve form, R3N+Cl is extremely reactive
- R3N+Cl is not a nucleophile like HOCl is
- We targeted at improving the selectivity of HOCl
towards electrophilic reaction thus preventing e.g. overoxidation of HexA
- We found that ozone becomes a highly selective
- xidant after the catalytic treatment
SLIDE 18 UVRR spectra of eucalyptus kraft pulps in A-EOP-D-P bleaching sequence
Leonardo Clavijo M.Sc. Thesis 2010
SLIDE 19
UVRR spectra of eucalyptus kraft pulps in Hcat-Z-P bleaching sequence
SLIDE 20
Production of bleaching chemicals (sum reactions)
Hypochlorite and peroxide: (6) NaCl + O2 + H2O → NaOCl + H2O2 Chlorate and peroxide: (7) NaCl + 3O2 + 3H2O → NaClO3 + 3H2O2
SLIDE 21
Eucalyptus pulp bleaching sequence in the future?
Hcat-Z-P
NaOCl/HOCl: 0.5-0.7 % (as Cl2) Catalyst: 0.01 % O3: < 0.3 % H2O2: 0.25-0.35 % Total reaction time: ≤ 30 min Viscosity loss: < 50 ml/g
SLIDE 22 Conclusions
- Eucalyptus pulp bleaching could and should be
intensified from today’s BAT
- In the future bleaching can be dramatically faster
than today and consume much less chemicals
- In addition to lower investment and production
costs the new technology may better maintain beneficial fiber properties
- Research and collaboration is still needed to
- vercome the remaining challenges and verify the
technology on larger scale
SLIDE 23 Acknowledgements
Long-term financers and idustrial collaborators:
- TEKES (Finnish Funding Agency for Technology and Innovation)
- Finnish Bioeconomy Cluster Ltd (Strategic Centre for Science,
Technology and Innovation)
- Andritz, Metsä Fibre, Kemira, Stora Enso, UPM
Research collaborators during the past years:
- Aalto University
- BOKU
- INPG Pagora
- Universidad de la República
- VTT
