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Kraft Pulping Kinetics: Initial Phase. Kraft Pulping Kinetics: Initial Phase. Kraft Pulping Kinetics: Bulk Phase. Kraft Pulping Kinetics: Bulk Phase. Kraft Pulping Kinetics: Residual Phase. Kraft Pulping Kinetics: Residual Phase. Kraft Pulping Kinetics: In “Nutshell”. - PowerPoint PPT Presentation
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1
Kraft Pulping Kinetics:Initial Phase
ExtractivesReactions1) Saponification of
Extractivesa) Fatsb) Waxesc) Lignans (Lactones)
2) Neutralizationa) Fatty Acidsb) Resin Acidsc) Monoterpene Acidsd) Lignanse) Phenolic Acids
3) Solubilizationa) Nearly all
extractives areremoved during theinitial phase of thecook.
Kinetics1) Effective Alkali
a) These reactions areso rapid that thelevel of alkali haslittle effect on therate
2) Sulfiditya) Sulfidity has no
effect on thesereactions
ExtractivesReactions1) Saponification of
Extractivesa) Fatsb) Waxesc) Lignans (Lactones)
2) Neutralizationa) Fatty Acidsb) Resin Acidsc) Monoterpene Acidsd) Lignanse) Phenolic Acids
3) Solubilizationa) Nearly all
extractives areremoved during theinitial phase of thecook.
Kinetics1) Effective Alkali
a) These reactions areso rapid that thelevel of alkali haslittle effect on therate
2) Sulfiditya) Sulfidity has no
effect on thesereactions
GlucomannansReactions1) Dissolution
a) A certain small %of Glucommans aresoluble in alkaliand will diffusefrom the wood.
2) Peelinga) Peeling reaction
starts during thisphase @ ~ 100C
3) Deacetylation
Kinetics1) Effective Alkali
a) No effect on rate ofdegradation
2) Sulfide Chargea) No effect on reaction
GlucomannansReactions1) Dissolution
a) A certain small %of Glucommans aresoluble in alkaliand will diffusefrom the wood.
2) Peelinga) Peeling reaction
starts during thisphase @ ~ 100C
3) Deacetylation
Kinetics1) Effective Alkali
a) No effect on rate ofdegradation
2) Sulfide Chargea) No effect on reaction
Compound % RemovedExtractivesCelluloseGlucomannansXylansLignin
Majority<1%60-70%20-30%20-30%
Compound % RemovedExtractivesCelluloseGlucomannansXylansLignin
Majority<1%60-70%20-30%20-30%
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Kraft Pulping Kinetics:Initial Phase
LigninReactions1) Cleavage of -O-4
linkagesa) Units with free
phenolic hydroxylb) Very fast
2) Cleavage of -O-4linkages
a) Units with freephenolic hydroxylor carbonyl.
b) Rapid reaction3) Solubilization
a) Small amount oflignin alkali soluble
4) Condensationa) Limited
Kinetics1) Effective Alkali
a) No affect onrate during thisphase
b) Rate diffusionlimited in thisphase
2) Sulfiditya) Sulfidity has no
effect duringthis phase
LigninReactions1) Cleavage of -O-4
linkagesa) Units with free
phenolic hydroxylb) Very fast
2) Cleavage of -O-4linkages
a) Units with freephenolic hydroxylor carbonyl.
b) Rapid reaction3) Solubilization
a) Small amount oflignin alkali soluble
4) Condensationa) Limited
Kinetics1) Effective Alkali
a) No affect onrate during thisphase
b) Rate diffusionlimited in thisphase
2) Sulfiditya) Sulfidity has no
effect duringthis phase
XylansReactions1) Dissolution
a) Major reaction ofXylans during kraftpulping
2) Peelinga) Very minor reaction
starts @ ~ 100C3) Stopping
a) See 2a4) Deacetylation
Kinetics1) Effective Alkali
a) Higher EA increases therate of dissolution
2) Sulfide Chargea) No effect on reaction
XylansReactions1) Dissolution
a) Major reaction ofXylans during kraftpulping
2) Peelinga) Very minor reaction
starts @ ~ 100C3) Stopping
a) See 2a4) Deacetylation
Kinetics1) Effective Alkali
a) Higher EA increases therate of dissolution
2) Sulfide Chargea) No effect on reaction
CelluloseReactions1) Peeling
a) Loss of cellulose begins@ ~ 120C - 130 C
2) Minor reaction as only 10%of all cellulose lost duringcook.
Kinetics1) Effective Alkali
a) ?2) Sulfide Charge
a) No effect on reaction
CelluloseReactions1) Peeling
a) Loss of cellulose begins@ ~ 120C - 130 C
2) Minor reaction as only 10%of all cellulose lost duringcook.
Kinetics1) Effective Alkali
a) ?2) Sulfide Charge
a) No effect on reaction
3
Kraft Pulping Kinetics:Bulk Phase
LigninReactions1) Cleavage of non
phenolic -O-4followed by:
a) Cleavage of -O-4linkages in unitswith free phenolichydroxyl
b) Cleavage of -O-4linkages in unitswith free phenolichydroxyl Rapidreaction
c) Condensationd) Cleavage of C-C
bonds (double)
Kinetics1) Effective Alkali
a) Higher EA =faster rate ofdegradation
2) Sulfide Chargea) Higher sulfide
charge increasesthe rate of ligninremoval.
b) Higher ligninremoval rateresults in alower lig/carb atend of cook
LigninReactions1) Cleavage of non
phenolic -O-4followed by:
a) Cleavage of -O-4linkages in unitswith free phenolichydroxyl
b) Cleavage of -O-4linkages in unitswith free phenolichydroxyl Rapidreaction
c) Condensationd) Cleavage of C-C
bonds (double)
Kinetics1) Effective Alkali
a) Higher EA =faster rate ofdegradation
2) Sulfide Chargea) Higher sulfide
charge increasesthe rate of ligninremoval.
b) Higher ligninremoval rateresults in alower lig/carb atend of cook
CelluloseReactions1) Peeling
a) Loss of celluloseaccelerates at temperaturedue to glycosidic cleavage
2) Stoppinga) Stopping reactions slow
loss of cellulose3) Glycosidic Cleavage
a) See 1ab) Starts to reduce
cellulose viscosity
Kinetics1) Effective Alkali
a) ?2) Sulfide Charge
a) No effect on reaction
CelluloseReactions1) Peeling
a) Loss of celluloseaccelerates at temperaturedue to glycosidic cleavage
2) Stoppinga) Stopping reactions slow
loss of cellulose3) Glycosidic Cleavage
a) See 1ab) Starts to reduce
cellulose viscosity
Kinetics1) Effective Alkali
a) ?2) Sulfide Charge
a) No effect on reaction
Compound % Removed (total)ExtractivesCelluloseGlucomannansXylansLignin
Majority<10%60-70%30-50%80-85%
Compound % Removed (total)ExtractivesCelluloseGlucomannansXylansLignin
Majority<10%60-70%30-50%80-85%
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Kraft Pulping Kinetics:Bulk Phase
GlucomannansReactions1) Peeling
a) Peeling isextensive untilabout 70% of xylanis lost and thenalmost stops
2) Gylcosidic cleavagea) Increases the rate
of peeling3) Stopping
a) Stops losses due topeeling
Kinetics1) Effective Alkali
b) No effect on rate ofdegradation
2) Sulfide Chargea) No effect on reaction
GlucomannansReactions1) Peeling
a) Peeling isextensive untilabout 70% of xylanis lost and thenalmost stops
2) Gylcosidic cleavagea) Increases the rate
of peeling3) Stopping
a) Stops losses due topeeling
Kinetics1) Effective Alkali
b) No effect on rate ofdegradation
2) Sulfide Chargea) No effect on reaction
XylansReactions1) Dissolution
a) Major reaction ofXylans during thisphase
2) Peelinga) Minor reaction
3) Glycosidic Cleavagea) Will increase rate of
peeling reaction4) Precipitation on fibers
a) Starts as alkaliconsummed
Kinetics1) Effective Alkali
a) Higher EA increases therate of dissolution
2) Sulfide Chargea) No effect on reaction
XylansReactions1) Dissolution
a) Major reaction ofXylans during thisphase
2) Peelinga) Minor reaction
3) Glycosidic Cleavagea) Will increase rate of
peeling reaction4) Precipitation on fibers
a) Starts as alkaliconsummed
Kinetics1) Effective Alkali
a) Higher EA increases therate of dissolution
2) Sulfide Chargea) No effect on reaction
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Kraft Pulping Kinetics:Residual Phase
LigninReactions1) Majority of ether
linkages that willcleave are gone:
2) Cleavage of C-Cbonds (double)
3) Condensationa) Increase the Mw
and lower reactivityof remaining lignin
Kinetics1) Effective Alkali
a) The rate slowsrapidly:
b) amount of ligninremaining afunction of theEA and sulfidecharge duringthe cook
LigninReactions1) Majority of ether
linkages that willcleave are gone:
2) Cleavage of C-Cbonds (double)
3) Condensationa) Increase the Mw
and lower reactivityof remaining lignin
Kinetics1) Effective Alkali
a) The rate slowsrapidly:
b) amount of ligninremaining afunction of theEA and sulfidecharge duringthe cook
CelluloseReactions1) Glycosidic Cleavage
a) Major reaction resulting inlower molecular weightand strength loss
2) Peeling/stoppinga) Minor reactions
Kinetics1) Effective Alkali
a) ?2) Sulfide Charge
a) No effect on reaction
CelluloseReactions1) Glycosidic Cleavage
a) Major reaction resulting inlower molecular weightand strength loss
2) Peeling/stoppinga) Minor reactions
Kinetics1) Effective Alkali
a) ?2) Sulfide Charge
a) No effect on reaction
Compound % Removed (total)ExtractivesCelluloseGlucomannansXylansLignin
Majority~10%70-80%40-50%%85-95%
Compound % Removed (total)ExtractivesCelluloseGlucomannansXylansLignin
Majority~10%70-80%40-50%%85-95%
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Kraft Pulping Kinetics:Residual Phase
GlucomannansReactions1) Peeling
a) Limited2) Gylcosidic cleavage
a) Limited3) Stopping
a) Limited
Kinetics1) Effective Alkali
b) No effect on rate ofdegradation
2) Sulfide Chargea) No effect on reaction
GlucomannansReactions1) Peeling
a) Limited2) Gylcosidic cleavage
a) Limited3) Stopping
a) Limited
Kinetics1) Effective Alkali
b) No effect on rate ofdegradation
2) Sulfide Chargea) No effect on reaction
XylansReactions1) Peeling/stopping/
a) negligible2) Precipitation on fibers
a) Significant amountdeposited as alkalicontinues to beconsummed
Kinetics1) Effective Alkali
a) Lower levels of alkali at endof the cook casusedeposition of xylans
2) Sulfide Chargea) No effect on reaction
XylansReactions1) Peeling/stopping/
a) negligible2) Precipitation on fibers
a) Significant amountdeposited as alkalicontinues to beconsummed
Kinetics1) Effective Alkali
a) Lower levels of alkali at endof the cook casusedeposition of xylans
2) Sulfide Chargea) No effect on reaction
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Kraft Pulping Kinetics:In “Nutshell”
Phase Lignin Carbohydrate Alkali
Initial Rapid delignification
Indep. of [OH-] and [HS-]
Rapid carbohydrate degradation
Some [OH-] dependence
Indep.of [HS-]
Rapid alkali consumption
Bulk Moderate delignification rate
Dep. on [OH-] and [HS-]
Moderate carbohydrate degradation
Moderate consumption of alkali
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Kraft Pulping Kinetics:In “Nutshell”
Phase Lignin Carbohydrate Alkali
Residual Very slow delignification
Some dep. on [OH-] and ? [HS-]
Substantial carbohydrate degradation – especially viscosity
Re-deposition of Xylans
Some alkali consumption
