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Pulping and BleachingPSE 476/Chem E 471
Lecture #11Anthraquinone/Polysulfides
Lecture #11Anthraquinone/Polysulfides
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Kraft Pulping AdditivesAgenda
• Anthraquinone» Reactions with lignin and carbohydrates» Use information
• Polysulfides» Formation chemistry» Reaction chemistry» Use information
• Anthraquinone» Reactions with lignin and carbohydrates» Use information
• Polysulfides» Formation chemistry» Reaction chemistry» Use information
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Pulping Additives:Anthraquinone
• Bach and Fiehn first reacted anthraquinone with hydrocellulose under alkaline conditions in 1972» Degradation of cellulose was
slowed
• When this additive was added to an alkaline cook, not only was the degradation of carbohydrates reduced, the rate of lignin removal was increased.
• Bach and Fiehn first reacted anthraquinone with hydrocellulose under alkaline conditions in 1972» Degradation of cellulose was
slowed
• When this additive was added to an alkaline cook, not only was the degradation of carbohydrates reduced, the rate of lignin removal was increased.
O
O
Anthraquinone 2 Sulfonate
SO3-
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Pulping Additives:Reactions of Anthraquinone
O
O
Anthraquinone (AQ)
O
HO(-)
O
OH
(-)
Anthrahydroquinone (AHQ)
Lignin Reactions
Carbohydrate Reactions
• It was discovered that anthraquinone (AQ) acts as a catalyst under pulping conditions. AQ oxidizes carbohydrates while the reduced form AHQ reacts with lignin.
• It was discovered that anthraquinone (AQ) acts as a catalyst under pulping conditions. AQ oxidizes carbohydrates while the reduced form AHQ reacts with lignin.
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Pulping Additives:Anthraquinone and Lignin
• AHQ reacts with quinone methides; this requires a free phenolic hydroxyl group. This is a rapid reaction.
• Slow alkali cleavage of non phenolic groups follows.
• AHQ reacts with quinone methides; this requires a free phenolic hydroxyl group. This is a rapid reaction.
• Slow alkali cleavage of non phenolic groups follows.
O
OCH3
CH
HC OR
H2COH
OOH
(-)
O-OCH3
HC OR
H2COH
CHOO
(-)O-
OCH3
CH
CH
CH2OH
+
O
O
+OR
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Pulping Additives:Anthraquinone and Carbohydrates
• AQ oxidizes the reducing end of carbohydrate to an aldonic acid.» AQ is reduced to AHQ.» Carbohydrate are stabilized against peeling.
• AQ oxidizes the reducing end of carbohydrate to an aldonic acid.» AQ is reduced to AHQ.» Carbohydrate are stabilized against peeling.
CHO
CHOH
HO- C O(-)
C OH
O
O
CHO
C O
O
OH
(-)
HO- CO2
CHOH
(-)
AQ AHQ
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Pulping Additives:Anthraquinone
• There are a large number of quinone chemicals which will function as catalysts.» In United States, AQ is the most cost effective.
• AQ added at catalytic levels.» 1987 FDA allows max addition of 0.11%.
• AQ works better with hardwoods than softwoods.
• AQ compensates for reduction in:» EA, Sulfidity, H factor.
• There are a large number of quinone chemicals which will function as catalysts.» In United States, AQ is the most cost effective.
• AQ added at catalytic levels.» 1987 FDA allows max addition of 0.11%.
• AQ works better with hardwoods than softwoods.
• AQ compensates for reduction in:» EA, Sulfidity, H factor.
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Pulping Additives:Polysulfides
• Sulfur polymers: Na2Sx
• Polysulfides oxidize carbohydrate reducing end groups to carboxylic acid thus slowing peeling.
• Can be formed through the reaction: Na2S + So Na2S2
Na2S2 + So Na2S3
• The addition of elemental sulfur to white liquor forms polysulfides.» Resulting increase in total sulfur causes sulfidity of
liquor to rise.
• Sulfur polymers: Na2Sx
• Polysulfides oxidize carbohydrate reducing end groups to carboxylic acid thus slowing peeling.
• Can be formed through the reaction: Na2S + So Na2S2
Na2S2 + So Na2S3
• The addition of elemental sulfur to white liquor forms polysulfides.» Resulting increase in total sulfur causes sulfidity of
liquor to rise.
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Pulping Additives:Polysulfides
• It is best to generate polysulfides through the oxidation of white liquor forming elemental sulfur which will further react with Na2S.
2Na2S + 2O2 + H2O 2So + 4NaOH*
Na2S + (x-1)So Na2Sx
*This reaction can be catalyzed using activated carbon
• The oxidation of Na2S to thiosulfate is a competing reaction under these conditions:
2Na2S + 2O2 + H2O Na2S2O3 + 2NaOH
• It is best to generate polysulfides through the oxidation of white liquor forming elemental sulfur which will further react with Na2S.
2Na2S + 2O2 + H2O 2So + 4NaOH*
Na2S + (x-1)So Na2Sx
*This reaction can be catalyzed using activated carbon
• The oxidation of Na2S to thiosulfate is a competing reaction under these conditions:
2Na2S + 2O2 + H2O Na2S2O3 + 2NaOH
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Pulping Additives:Polysulfides
• Polysulfides are unstable at temperatures > 130°C
2Na2S3 + 6NaOH 4Na2S + Na2S2O3 + H2O
• The conditions used in a kraft cook must therefore be modified in order to gain a yield benefit from the reaction of polysulfides.» Use thin or short chips.» Allow for ample impregnation time.» Use a slow rate of heat up.
• Polysulfides are unstable at temperatures > 130°C
2Na2S3 + 6NaOH 4Na2S + Na2S2O3 + H2O
• The conditions used in a kraft cook must therefore be modified in order to gain a yield benefit from the reaction of polysulfides.» Use thin or short chips.» Allow for ample impregnation time.» Use a slow rate of heat up.
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Pulping Additives:Polysulfides
• The use of polysulfides gives a yield gain by reduction of peeling reactions.» Most of the gain through reduced
degradation of glucomannans.
• In 1987, a 3.2% yield increase in a kraft mill corresponded to a 1.7 million dollar savings.
• The use of polysulfides gives a yield gain by reduction of peeling reactions.» Most of the gain through reduced
degradation of glucomannans.
• In 1987, a 3.2% yield increase in a kraft mill corresponded to a 1.7 million dollar savings.
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White Liquor Oxidation System
Chiyoda polysulfide process was developed by Chiyoda and Mitsubishi Paper
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Chiyoda polysulfide process (2)
• This process is a very simple. Major equipment comprises the filter and the reactor. » The unique up flow type filter can remove
substantially all the suspended solid in feed white liquor.
• This process does not affect the operation of existing equipment.
• The catalyst has three to four-year life, and it maintains high polysulfide concentration during the life. » An activated carbon with specific pore structure is
used as the catalyst. The catalyst maintains optimum conversion to maximize polysulfide production and long catalyst life.
• This process is a very simple. Major equipment comprises the filter and the reactor. » The unique up flow type filter can remove
substantially all the suspended solid in feed white liquor.
• This process does not affect the operation of existing equipment.
• The catalyst has three to four-year life, and it maintains high polysulfide concentration during the life. » An activated carbon with specific pore structure is
used as the catalyst. The catalyst maintains optimum conversion to maximize polysulfide production and long catalyst life.
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Chiyoda polysulfide process (3)
• Oxidized carbohydrate becomes stable compound for alkaline liquor and the amount of dissolved carbohydrate in the black liquor is reduced. As a result; » Pulp yield is increased with insignificant
changes to pulp properties. » Black liquor viscosity is decreased. » Recovery boiler load is reduced.
• Oxidized carbohydrate becomes stable compound for alkaline liquor and the amount of dissolved carbohydrate in the black liquor is reduced. As a result; » Pulp yield is increased with insignificant
changes to pulp properties. » Black liquor viscosity is decreased. » Recovery boiler load is reduced.
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