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The in-situ brightening of pulp by the electro-reduction of oxygen, mediated with anthraquinone-2-sulfonic acid Chen, Margaret Ying Ting
Abstract
A redox cycle involving anthraquinone 2-sulfonic acid - - denoted as AQS, and oxygen in an aqueous alkaline media was investigated for its ability to promote the in-situ electroreduction of oxygen to hydrogen peroxide with the coincident promotion of the brightening of thermo-mechanical pulp. Current applied at a carbon cloth cathode was used to reduce the AQS to hydroanthraquinone - - denoted as H₂AQS. The reaction of H₂AQS with oxygen was shown to produce hydrogen peroxide. Evidence presented in this study indicates the operation of a redox cycle involving AQS/ H₂AQS, oxygen and current to produce hydrogen peroxide. It is thought hydrogen peroxide produced in this redox cycle was responsible for the larger brightness gains and yellowness reduction of the thermomechanical pulp observed in experimental runs employing the AQS/oxygen redox cycle, than in corresponding runs in the absence of the AQS/oxygen redox cycle. The batch electrochemical reactor employed in this study consisted of a platinized titanium anode and carbon cloth cathode. Major modifications of the reactor design, which included increasing the area of the working electrode (the cathode), decreasing the area of the counter electrode (anode), employing membrane/fritted glass separators and providing adequate mixing, were found to suppress undesirable electrochemical reactions and promote even current distribution in the electrochemical cell, resulting in an increased current efficiency and production rate of peroxide. All runs were conducted at 60 °C pH 10.5-11 and at atmospheric pressure. Some other important quantitative findings were: • In a solution containing 0.1 M Na₂SO₄, 4.7mM Na₂SiO₃, 0.32mM MgSO₄, the hydrogen peroxide produced in 3 hours with the use of the 5mM AQS and oxygen redox cycle was approximately 49.5(+/-) 2.5 mM, which is 28(+/-) 2.5mM more than in a corresponding run in the absence of the AQS. • In a solution containing 0.1 M Na₂SO₄, 4.7mM Na₂SiO₃, 0.32mM MgSO₄, with oxygen purged for 3 hours (at 1.5A without pulp), subsequently followed by oxygen purged for 5 hours (at 0 A with 1 wt. % thermomechanical pulp), the presence of 5mM AQS brought about 21 (%ISO) gain and 15 (%) yellowness reduction more than for a corresponding run in the absence of the AQS. • A 2³ factorial experiment was performed to illuminate the three (3) key process variables: current (0.3A to 1.5A), gas (Air-Oxygen), the AQS concentration (OmM to 5mM). From this factorial experiment, it is found that the presence of two key factors, namely oxygen and current, are essential and the presence of catalyst factor, such as AQS, is beneficial in the in-situ electrochemical generation of hydrogen peroxide in the AQS/oxygen system. Although the AQS/oxygen redox cycle, used in this project, generated hydrogen peroxide at a high current efficiency and produced a brightened pulp that is comparable to that obtained using merchant peroxide, this system cannot be realized in the industry due to the severe fouling problems associated with the use of its working electrode. It is thought that the AQS crystallizes and blocks electro-active areas of the carbon cloth electrode, which makes it unsuitable for any subsequent runs. Due to the fouling problems posed by the carbon cloth cathode with the AQS redox couple, the electroreduction of oxygen mediated by AQS is impractical for industrial use without further study.
Item Metadata
Title |
The in-situ brightening of pulp by the electro-reduction of oxygen, mediated with anthraquinone-2-sulfonic acid
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1998
|
Description |
A redox cycle involving anthraquinone 2-sulfonic acid - - denoted as AQS, and oxygen in an
aqueous alkaline media was investigated for its ability to promote the in-situ electroreduction of
oxygen to hydrogen peroxide with the coincident promotion of the brightening of thermo-mechanical
pulp. Current applied at a carbon cloth cathode was used to reduce the AQS to
hydroanthraquinone - - denoted as H₂AQS. The reaction of H₂AQS with oxygen was shown to
produce hydrogen peroxide. Evidence presented in this study indicates the operation of a redox
cycle involving AQS/ H₂AQS, oxygen and current to produce hydrogen peroxide. It is thought
hydrogen peroxide produced in this redox cycle was responsible for the larger brightness gains and
yellowness reduction of the thermomechanical pulp observed in experimental runs employing the
AQS/oxygen redox cycle, than in corresponding runs in the absence of the AQS/oxygen redox
cycle.
The batch electrochemical reactor employed in this study consisted of a platinized titanium anode
and carbon cloth cathode. Major modifications of the reactor design, which included increasing
the area of the working electrode (the cathode), decreasing the area of the counter electrode
(anode), employing membrane/fritted glass separators and providing adequate mixing, were found
to suppress undesirable electrochemical reactions and promote even current distribution in the
electrochemical cell, resulting in an increased current efficiency and production rate of peroxide.
All runs were conducted at 60 °C pH 10.5-11 and at atmospheric pressure.
Some other important quantitative findings were:
• In a solution containing 0.1 M Na₂SO₄, 4.7mM Na₂SiO₃, 0.32mM MgSO₄, the hydrogen
peroxide produced in 3 hours with the use of the 5mM AQS and oxygen redox cycle was
approximately 49.5(+/-) 2.5 mM, which is 28(+/-) 2.5mM more than in a corresponding run in
the absence of the AQS. • In a solution containing 0.1 M Na₂SO₄, 4.7mM Na₂SiO₃, 0.32mM MgSO₄, with oxygen purged
for 3 hours (at 1.5A without pulp), subsequently followed by oxygen purged for 5 hours (at 0 A
with 1 wt. % thermomechanical pulp), the presence of 5mM AQS brought about 21 (%ISO)
gain and 15 (%) yellowness reduction more than for a corresponding run in the absence of the
AQS.
• A 2³ factorial experiment was performed to illuminate the three (3) key process variables:
current (0.3A to 1.5A), gas (Air-Oxygen), the AQS concentration (OmM to 5mM). From this
factorial experiment, it is found that the presence of two key factors, namely oxygen and
current, are essential and the presence of catalyst factor, such as AQS, is beneficial in the in-situ
electrochemical generation of hydrogen peroxide in the AQS/oxygen system.
Although the AQS/oxygen redox cycle, used in this project, generated hydrogen peroxide at a high
current efficiency and produced a brightened pulp that is comparable to that obtained using
merchant peroxide, this system cannot be realized in the industry due to the severe fouling
problems associated with the use of its working electrode. It is thought that the AQS crystallizes
and blocks electro-active areas of the carbon cloth electrode, which makes it unsuitable for any
subsequent runs. Due to the fouling problems posed by the carbon cloth cathode with the AQS
redox couple, the electroreduction of oxygen mediated by AQS is impractical for industrial use
without further study.
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Extent |
4983648 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-05-04
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0058939
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1998-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.