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Electro-brightening of mechanical pulp Jung, Joey Chung-Yen
Abstract
The electro-oxidation of sodium carbonate (Na₂C0₃) to percarbonate (C₂O₆²⁻), with its subsequent hydrolysis was investigated as a means to produce peroxide and to drive the in-situ electrochemical brightening of thermo-mechanical pulp. The conditions for the electrochemical production of peroxide and factors that affected the in-situ electrochemical brightening of TMP were studied by conducting variable level experiments. The investigations were performed using a 2-liter batch electrochemical reactor, fabricated of titanium, with a platinum anode. To promote peroxide generation, different types of cathode material and diaphragms were evaluated; and major modifications to the reactor comprising the anode, cooling system, mixer, and position of thermocouple were performed. The important quantitative findings are as follows: • Experiments with uncovered zirconium cathode generated the highest peroxide concentration than other cathode materials with or without a diaphragm. • The pH of the electrolyte dominated the process of peroxide accumulation through its effect on the concentration of CO₃²⁻. High pH (>11) resulted in high peroxide concentration. While brightening, alkali darkening will not negate the brightening responses in high pH (~11.5). • Temperature had a significant effect on peroxide generation and on brightening. Low anode coolant temperature (1°C) resulted in higher peroxide concentration in the early stage of the process; and high electrolyte temperature promoted the production of peroxide and raised the brightening responses. • The investigation of peroxide production (without pulp) indicated that under equipment limitations, the maximum peroxide concentration for 180 minutes was around 0.08M. The experimental conditions were as follows: • Electrolyte: 2M Na₂C0₃ , 400ppm MgS0₄ , 0.002M DTPA (pH = 11.6) • Electrolyte temperature: 60°C • Current set point: 30A (float voltage) • Mixing speed: 200rpm • Anode coolant: 1°C at 6 liter per minute Electro-brightening of 2.5 % consistency TMP achieved a 17.4 % ISO of brightness gain and a 19.2 % of yellowness loss with pulp (initial brightness: 41.6 % ISO; initial yellowness: 36.8 %) and experimental conditions mentioned above. The specific brightening energy for kWh this brightened TMP was 17 x 10² (kWh/ton•%ISO) , which corresponded to an operation cost of approx. $ 1,020 per ton of OD pulp for 20 % ISO brightness gain. The economic reactor sizing factor, brightening space-time yield, was 0.145 (ton•%ISO/m³•hr). A brightness reversion test showed that electro-brightened pulp has the same brightness stability as conventional peroxide brightened pulp. • The 2³ factorial experiment indicated that the combination of high current, high electrolyte temperature, and high sodium carbonate concentration has positive effects on electrobrightening responses. • Long brightening retention time (240 minutes) resulted in less brightness gain and yellowness loss, which means brightening time longer than 180 minutes is not worthwhile. Also, cycling current on/off with a 30-minute interval gave less brightness gain and yellowness loss than that of a comparable standard electro-brightening run. This indicates that the 30-minute interval was too long or there was not enough peroxide available to brighten the pulp. • High pulp consistency (4.5%) had higher brightening responses than low pulp consistency (2.5%), which demonstrates the electro-brightening process is similar to the conventional peroxide brightening process, with respect to pulp consistency. The in-situ electrochemical brightening process could not be optimized in this thesis study, due to limitations of the laboratory reactor. The Teflon coating and non-conductive glue in the reactor were deteriorated under the experimental conditions to the extent that the reactor was unsuitable for further experiments. However, in-situ electrochemical brightening of TMP using sodium carbonate as the source of brightening agent does produce a brightened pulp that is comparable to that obtained using merchant peroxide.
Item Metadata
Title |
Electro-brightening of mechanical pulp
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
2000
|
Description |
The electro-oxidation of sodium carbonate (Na₂C0₃) to percarbonate (C₂O₆²⁻), with its
subsequent hydrolysis was investigated as a means to produce peroxide and to drive the in-situ
electrochemical brightening of thermo-mechanical pulp. The conditions for the electrochemical
production of peroxide and factors that affected the in-situ electrochemical brightening of TMP
were studied by conducting variable level experiments. The investigations were performed
using a 2-liter batch electrochemical reactor, fabricated of titanium, with a platinum anode. To
promote peroxide generation, different types of cathode material and diaphragms were evaluated;
and major modifications to the reactor comprising the anode, cooling system, mixer, and position
of thermocouple were performed. The important quantitative findings are as follows:
• Experiments with uncovered zirconium cathode generated the highest peroxide concentration
than other cathode materials with or without a diaphragm.
• The pH of the electrolyte dominated the process of peroxide accumulation through its effect
on the concentration of CO₃²⁻. High pH (>11) resulted in high peroxide concentration.
While brightening, alkali darkening will not negate the brightening responses in high pH
(~11.5).
• Temperature had a significant effect on peroxide generation and on brightening. Low anode
coolant temperature (1°C) resulted in higher peroxide concentration in the early stage of the
process; and high electrolyte temperature promoted the production of peroxide and raised the
brightening responses.
• The investigation of peroxide production (without pulp) indicated that under equipment
limitations, the maximum peroxide concentration for 180 minutes was around 0.08M. The
experimental conditions were as follows:
• Electrolyte: 2M Na₂C0₃ , 400ppm MgS0₄ , 0.002M DTPA (pH = 11.6)
• Electrolyte temperature: 60°C
• Current set point: 30A (float voltage)
• Mixing speed: 200rpm
• Anode coolant: 1°C at 6 liter per minute
Electro-brightening of 2.5 % consistency TMP achieved a 17.4 % ISO of brightness gain and
a 19.2 % of yellowness loss with pulp (initial brightness: 41.6 % ISO; initial yellowness:
36.8 %) and experimental conditions mentioned above. The specific brightening energy for
kWh
this brightened TMP was 17 x 10² (kWh/ton•%ISO) , which corresponded to an operation cost of
approx. $ 1,020 per ton of OD pulp for 20 % ISO brightness gain. The economic reactor
sizing factor, brightening space-time yield, was 0.145 (ton•%ISO/m³•hr). A brightness reversion
test showed that electro-brightened pulp has the same brightness stability as conventional
peroxide brightened pulp.
• The 2³ factorial experiment indicated that the combination of high current, high electrolyte
temperature, and high sodium carbonate concentration has positive effects on electrobrightening
responses.
• Long brightening retention time (240 minutes) resulted in less brightness gain and
yellowness loss, which means brightening time longer than 180 minutes is not worthwhile.
Also, cycling current on/off with a 30-minute interval gave less brightness gain and
yellowness loss than that of a comparable standard electro-brightening run. This indicates
that the 30-minute interval was too long or there was not enough peroxide available to
brighten the pulp.
• High pulp consistency (4.5%) had higher brightening responses than low pulp consistency
(2.5%), which demonstrates the electro-brightening process is similar to the conventional
peroxide brightening process, with respect to pulp consistency.
The in-situ electrochemical brightening process could not be optimized in this thesis study, due
to limitations of the laboratory reactor. The Teflon coating and non-conductive glue in the
reactor were deteriorated under the experimental conditions to the extent that the reactor was
unsuitable for further experiments. However, in-situ electrochemical brightening of TMP using
sodium carbonate as the source of brightening agent does produce a brightened pulp that is
comparable to that obtained using merchant peroxide.
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Extent |
10846814 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-07-20
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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.
|
DOI |
10.14288/1.0058623
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2000-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
|
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.