CA1249403A - Brightening of high yield and ultra high yield pulps - Google Patents
Brightening of high yield and ultra high yield pulpsInfo
- Publication number
- CA1249403A CA1249403A CA000486331A CA486331A CA1249403A CA 1249403 A CA1249403 A CA 1249403A CA 000486331 A CA000486331 A CA 000486331A CA 486331 A CA486331 A CA 486331A CA 1249403 A CA1249403 A CA 1249403A
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- Canada
- Prior art keywords
- pulp
- high yield
- reaction
- minutes
- pulps
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/16—Bleaching ; Apparatus therefor with per compounds
- D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
There is provided an improved bleaching or brightening sequence for high yield and ultra-high yield pulps using peroxide compounds, the method being characterized by short reaction time at a relatively high reaction temperature and utilizing a minimum amount of stabilizers such as sodium silicate.
There is provided an improved bleaching or brightening sequence for high yield and ultra-high yield pulps using peroxide compounds, the method being characterized by short reaction time at a relatively high reaction temperature and utilizing a minimum amount of stabilizers such as sodium silicate.
Description
~Z~3 ~)3 The present invention relates to an improvement in a method for brightening high yield and ultra-high yield pulps and more par-ticularly, to the process of bleaching such pulps.
Various bleaching or brigh-tening sequences are employed in the pulp and paper industry to bleach high yield and ultra-high yield pulps. Peroxide is the most commonly employed one-stage oxidizing agent for bleaching mechanical type pulps. This alkaline process is normally carried out at a high pulp consis-tency i.e. 15 - 25~;
moderate temperatures - i.e. 60C and retention times of
Various bleaching or brigh-tening sequences are employed in the pulp and paper industry to bleach high yield and ultra-high yield pulps. Peroxide is the most commonly employed one-stage oxidizing agent for bleaching mechanical type pulps. This alkaline process is normally carried out at a high pulp consis-tency i.e. 15 - 25~;
moderate temperatures - i.e. 60C and retention times of
2 - 3 hours. In the art of peroxide bleaching, the requirement for stabilizers in the bleach liquor is well known; the stabilizers preventing decomposition of the oxidizing agent. Mechanical pulps are also normally pre-treated at a low consistency with organic chelating agents such as sodium diethylene triamine pen-ta-ace-tate (DPTA) to remove naturally occuring trace metals. ISO Brightnesses of 73 - 75~ are conventionally achieved using this one-stage process.
The use of sodium silicate as a stabilizer is well known in the ar-t. The use of sodium silica-te is also useful as a partial source of the alkali for the bleaching as well as a buffer agen-t for the hydrogen peroxide bleach 'liquors. In commercial pulping systems, alkaline hydrogen ~$
~Z'~3 ~)3 peroxide solutions re~uire stabilization with large amounts of sodium silicate, these amounts normally running in the 3 to 6% range. This na-turally is an economic cost.
In addition, silicates tend t~ form scale on equipment which is an additional expense. Silicates also limi-t the recycling of -the spent bleaching liquors.
It is known in the art to eliminate the sodium silicate, but a different stabilizer such as diethylene triamine pentamethylene phosphoric acid (DTPMA) (sold under the trade mark DEQUEST 2060) is used.
It is an object of the present invention to provide an improved method for brightening high yield and ultra-high yi~ld pulps u-tilizing peroxygen compounds.
It is a further object of the present invention to provide an improved peroxygen bleaching metho~ wherein the pulp can be bleached while reducing the amount oE
stabilizer.
It is a s-till further object of the present inven-tion to provide an irnproved peroxygen bleaching process wherein ~he reaction time is minimized.
According to the present invention, there is provided a method for bleaching high yield and ultra-high yield pulps which comprises the step of treating the pulp with a peroxygen compound at a charge of between about 0.5 to about 3% by weight of oven dried pulp in the presence -12~:`3 ~3 of sodium hydroxide and magnesium sulphi-te at a reaction temperature of between 60 - 99C, a reaction -time of between 1 minute to about 60 minutes, at a pulp consistency of from 6% to 25%, and a reac-tion pH of about 7.5 to about 9.
In greater detail-, the method of the presen-t invention may be utilized as a single stage bleaching step or, in the alternative, may be utilized in a multi-stage bleaching system wherein the present bleaching s-tep is used for a portion thereof. Thus, for example, the bleaching step of the presen-t invention could be utilized in the sequential bleaching process taught in Canadian Patent Application 470,961-6 filed December 21, 1984 in -the name of Pulp and Paper Research Insti-tu-te of Canada.
The wood pulp which may be utilized can be a high yield or ultra-high yield pulp such as mechanical, chemimechanical, chemithermomechanical, groundwood and high yield sulphite pulps. The peroxygen compound utilized in the process of the present inven-tion may be selected from among those well known to those skilled in the art including for example, conventional inorganic peroxides, such as hydrogen and sodium peroxide and organic peroxides such as benzolperoxide, ditertiarybutyl peroxide and peracetic acid.
~Z~ 3 The peroxygen compound is preferably charged at between 0.5 to 3~ by weight of oven-dried pulp in the presence of sodium hydroxide and magnesium ~ulphate.
The mos-t preferred charge of the peroxygen compound i5 between 1% to 2.5% by weigh-t of oven dried pulp with -the sodium hydroxide and magnesium being added in charges of between about 0.25 - 3~ and 0.01 - 0.05% respectively.
The present invention utilizes substantially higher reaction temperatures and substantially shorter reaction times than conventionally accep-ted in the art.
It has surprisingly been found that the higher reaction temperatures are efficient in bleaching the pulp without requiring the use of a stabilizer such as sodium silicate.
Due to the higher reaction tempera-tures, the reaction times are lower than is conventionally believed to be required.
The reaction temperatures utilized in the presen-t process range from 60C up to the decomposition temperature of the peroxide with a maximum temperature being 99C. In order -to optimize the bleaching efficiency of the process, a temperature range of between 75 - 9SC is preferred.
~ s discussed above, the reaction time can vary between 1 minute to about 60 minutes with preferred reaction times of between 5 minutes to abou-t 20 minutes utilizing the higher temperature range of 75C to 95C.
~2~3 ~3 Al-though it is common practice in a one-s-tage bleaching process to leave about 15% to about 20% of the initial charge of peroxygen compound as a residual to prevent alkali darkening o the pulp, in -the present invention, due to the short reaction time, it is preferred to lower this residual level to between about 1% to about 10% in order to conserve sulphur dioxide and allow a lower initial charge of the peroxygen addition. ~ith the short reaction time, efficient mixing of the reactants is desirable. Utilizing the present invention, a pulp consistency of 10% was found to be as effective as a 30 pulp consistency for brightness improvement.
If desired, one can utilize a two-stage bleaching process utilizing the specific peroxide bleaching step of the present invention.
Having thus generally described the invention, reference will be made to the following examples~
i2~ )3 EX~MPLE I
A 100 grams of a commercial jack pine thermo-mechanical pulp, brightness 50.6% ISO was treated with a solution containing 1~ hydrogen peroxide on O.D. pulp,
The use of sodium silicate as a stabilizer is well known in the ar-t. The use of sodium silica-te is also useful as a partial source of the alkali for the bleaching as well as a buffer agen-t for the hydrogen peroxide bleach 'liquors. In commercial pulping systems, alkaline hydrogen ~$
~Z'~3 ~)3 peroxide solutions re~uire stabilization with large amounts of sodium silicate, these amounts normally running in the 3 to 6% range. This na-turally is an economic cost.
In addition, silicates tend t~ form scale on equipment which is an additional expense. Silicates also limi-t the recycling of -the spent bleaching liquors.
It is known in the art to eliminate the sodium silicate, but a different stabilizer such as diethylene triamine pentamethylene phosphoric acid (DTPMA) (sold under the trade mark DEQUEST 2060) is used.
It is an object of the present invention to provide an improved method for brightening high yield and ultra-high yi~ld pulps u-tilizing peroxygen compounds.
It is a further object of the present invention to provide an improved peroxygen bleaching metho~ wherein the pulp can be bleached while reducing the amount oE
stabilizer.
It is a s-till further object of the present inven-tion to provide an irnproved peroxygen bleaching process wherein ~he reaction time is minimized.
According to the present invention, there is provided a method for bleaching high yield and ultra-high yield pulps which comprises the step of treating the pulp with a peroxygen compound at a charge of between about 0.5 to about 3% by weight of oven dried pulp in the presence -12~:`3 ~3 of sodium hydroxide and magnesium sulphi-te at a reaction temperature of between 60 - 99C, a reaction -time of between 1 minute to about 60 minutes, at a pulp consistency of from 6% to 25%, and a reac-tion pH of about 7.5 to about 9.
In greater detail-, the method of the presen-t invention may be utilized as a single stage bleaching step or, in the alternative, may be utilized in a multi-stage bleaching system wherein the present bleaching s-tep is used for a portion thereof. Thus, for example, the bleaching step of the presen-t invention could be utilized in the sequential bleaching process taught in Canadian Patent Application 470,961-6 filed December 21, 1984 in -the name of Pulp and Paper Research Insti-tu-te of Canada.
The wood pulp which may be utilized can be a high yield or ultra-high yield pulp such as mechanical, chemimechanical, chemithermomechanical, groundwood and high yield sulphite pulps. The peroxygen compound utilized in the process of the present inven-tion may be selected from among those well known to those skilled in the art including for example, conventional inorganic peroxides, such as hydrogen and sodium peroxide and organic peroxides such as benzolperoxide, ditertiarybutyl peroxide and peracetic acid.
~Z~ 3 The peroxygen compound is preferably charged at between 0.5 to 3~ by weight of oven-dried pulp in the presence of sodium hydroxide and magnesium ~ulphate.
The mos-t preferred charge of the peroxygen compound i5 between 1% to 2.5% by weigh-t of oven dried pulp with -the sodium hydroxide and magnesium being added in charges of between about 0.25 - 3~ and 0.01 - 0.05% respectively.
The present invention utilizes substantially higher reaction temperatures and substantially shorter reaction times than conventionally accep-ted in the art.
It has surprisingly been found that the higher reaction temperatures are efficient in bleaching the pulp without requiring the use of a stabilizer such as sodium silicate.
Due to the higher reaction tempera-tures, the reaction times are lower than is conventionally believed to be required.
The reaction temperatures utilized in the presen-t process range from 60C up to the decomposition temperature of the peroxide with a maximum temperature being 99C. In order -to optimize the bleaching efficiency of the process, a temperature range of between 75 - 9SC is preferred.
~ s discussed above, the reaction time can vary between 1 minute to about 60 minutes with preferred reaction times of between 5 minutes to abou-t 20 minutes utilizing the higher temperature range of 75C to 95C.
~2~3 ~3 Al-though it is common practice in a one-s-tage bleaching process to leave about 15% to about 20% of the initial charge of peroxygen compound as a residual to prevent alkali darkening o the pulp, in -the present invention, due to the short reaction time, it is preferred to lower this residual level to between about 1% to about 10% in order to conserve sulphur dioxide and allow a lower initial charge of the peroxygen addition. ~ith the short reaction time, efficient mixing of the reactants is desirable. Utilizing the present invention, a pulp consistency of 10% was found to be as effective as a 30 pulp consistency for brightness improvement.
If desired, one can utilize a two-stage bleaching process utilizing the specific peroxide bleaching step of the present invention.
Having thus generally described the invention, reference will be made to the following examples~
i2~ )3 EX~MPLE I
A 100 grams of a commercial jack pine thermo-mechanical pulp, brightness 50.6% ISO was treated with a solution containing 1~ hydrogen peroxide on O.D. pulp,
3.0% sodium silica-te,.2.0% sodium hydroxide, 0.05%
magnesium sulphate with sufficient water to reduce the pulp consis-tency to 10%. The temperature of this treatment was 60C and the reaction time was 60 minutes. At the end of the reaction, the pH was 10.7. The brigh-tness of the washed sample after this stage was 56.2.
Thre~ 100-gram samples of the same unbleached jack pine TMP were treated wi-th different solutions con-taining the following chemical charges on O.D. pulp:
Solution ~ hydrogen peroxide, 2% sodium silica-te 1% sodium hydroxide and 0.05~ MgSO4.
Solution B 1% hydrogen peroxide, 0% silicate, 2~ NaOH and 0.05% MgSO4.
Solution C 1% hydrogen peroxide, 4% silicate, 0% NaOH and 0.05% MgSO4.
The temperature of these treatments was 82 and the reaction ti.me was 10 minutes. The pH of the pulp at the end of each reaction is listed in Table 1, along wi-th the brightness values.
.
~Z~ )3 BLEACHING OF MECHANICAL PULPS
TREATMENT CONDITIONS*
.
PULP NO. H2O2 NaOH Na2Si03 TEMP. TIME END BRIGHTNESS
TYPE ~ % % C MIN. pH % ISO
_ _ .
Jack - - - - - - 50.6 pine 1.0 2.0 3.0 60 6010.7 56.2 TMP a 1.0 1.0 2.0 82 108.5 57.8 b 1.0 2.0 0~0 82 108.0 57.6, c 1.0 0.0 4.0 82 107.9 57.8 _"~ .. .
*10~ consistency, peroxide solution contained 0.05%
MgSO4 on pulp and 0.2% EDTA
EXAMPLE II
_ - A 100 grams of a commercial western groundwood pulp, hrightness 55.5% ISO was -trea-ted wi-th a bleaching solution containing 2.5% hydrogen peroxide, 4.0% sodium sili.cate, 2O5% sodium hydroxide, and 0.05% magnesium sulphate with sufficient water to reduce the pulp consistency to 10%. The temperature of this treatment was 60C and the reaction time 60 minut~s. At the end of the reaction -the pH was 10.4 and the brightness after washing 69.6%.
~"~
Three 100-gram samples of the same unbleached western groundwood pulp were -treated wi-th different bleaching solutions cont~ining -the following chemicals:
A. 2.5% hydrogen peroxide, 2.0% silicate, 2.5~ NaOH and 0.05~ MgSO4.
B. 2.5% hydrogen peroxide, 0~ silicate, 3.0% NaOh and 0.05~ MgSO4.
C. 2.5% hydrogen peroxide, 1.0~ silicate, 2~5~ NaOH and 0.05% MgSO4.
C. 2.5% hydrogen peroxide, 5.0% silicate, 0~ NaOH and 0.05% MgSO4.
The solutions were added with sufficient water -to reduce the pulp consistency to 10%. The temperature of this treatment was 95C and the reaction time was 10 minutes.
The pH at the end of each reaction is listed in Table 2, along with the brigh-tness values.
BLEACHING OF MECHANICAL PULPS
. . _ TREATMENT CONDITIONS*
PULP NO. ~1202 NaOH Na2Si03 TEMP. TIME END BRIGHTNESS
TYPE % ~ % C. MIN pH % ISO
.. . .. .. .. . . . . _ West~ 55-5 ern 2.5 2.5 4.0 60 6010.4 69.6 Ground-wood a 2.5 2.5 2.0 95 108.0 71.0 b 2.5 3.0 0 95 108.2 70.7 c 2.5 2.5 1.0 95 108.1 70.9 d 2.5 0 5.0 95 107.7 70.8 . . _ .~
*10% consistency, peroxide solution contained 0.05~ MgSO4 on pulp and 0.2% EDTA.
_~_ .
", EXAMPLE III
A 100 grams of a commercial spruce thermo-mechanical pulp, brightness 60.3% ISO was treated wi-th a solution containing 2% hydrogen peroxide on O.D. pulp, 6.0% sodium silicate, 2.0% sodium hydroxide, 0.05%
magnesium sulphate with sufficient water to reduce -the pulp consistency to 10~. The temperature of this treatment was 60C and the reaction time was 60 minutes. At the end of the reaction, the pH was 10.6. The brightness of the washed sample after -this stage was 75.2.
Three 100-gram samples of the same unbleached spruce TMP were treated with different solutions containing the following chemical charges on O.D. pulp:
Solution A. 2% hydrogen peroxide, 1.0% sodium silicate, 2.5% sodium hydroxide and 0.05% MgSO4.
Solution B. 2% hydrogen peroxide, 0% silicate, 3.0%
NaOH and 0.05% MgSO4.
Solution C. 2% hydrogen peroxide, 6% silicate, 0%
NaOH and 0.05% MgSO~.
The temperature of these treatmen-ts was 85 and the reaction time was 10 minutes. The pH of the pulp at the end of each reaction is listed in Table 3, along with the brightness values.
)3 BLEACEIING OF MECHANICAL PULPS
TREATMENT CONDITIONS*
PULP NO. H202 NaOH Na2SiO3 TEMP. TIME END BRIGHTNESS
TYPE % ~ % C. MIN. pH % ISO
.. _ . . .. _ .
Spruce ~ - 63.5 TMP 2.0 2.5 6.0 6060 10.6 75.2 a 2.0 2.5 1.0 8510 8.3 75.2 b 2.0 3.0 0 8510 8.5 75.4 c 2.0 0 6.0 8510 8.1 75.8 . . _ .
*10% consis-tency, peroxide solu-tion contained 0.05% MgSO~
on pulp and 0.2% EDTA.
As will be seen from each of the above examples, the method of the present invention provides a pulp substan-tially equivalent in brightness -to traditional methods, bu-t can accomplish the same with a peroxide bleachiny solu-tion containing very little or no sodium silicate. Also, the method of the present invention, using the hiyher reaction temperature, mlnimixes the reac-tion time.
:, , ~Z~`3 ~
EXAMPLE IV
A commercial spruce balsam chemithermomechanical pulp, brightness 56.1% ISO taken from a disc filter of a mill was trea-ted with a solution containing 2.0% hydrogen peroxide on O.D. pulp, 2.5% sodium silicate, 1.0% sodium hydroxide, 0.5~ magnesium sulphate with sufficient water to reduce the pulp consistency to 10~. The temperature of this treatment was 85C and the reaction time was 10 minutes. At the end of the reaction the pH was 8.5. The residual peroxide concentration was tested and found to be 0.32 H202 on O.D. pulp. The brightness of a washed sample after this s-tage was 71.5 ISO.
To complete the two-stage process, the washed pulp was treated with a solution containing 2.0% hydrogen peroxide on O.D. pulp~ 2.5~ sodium silicate, 2.0% sodium hydroxide and 0.05% magnesium sulpha-te with sufficient water to reduce the pulp consistency to 10%. The reaction temperature was 85C and the reaction time was 30 minutes.
The pH at -the end of -the reaction was 9.5 and the pulp after souring and washing had a brightness of 78.3%.
I'he peroxide residual measured at the end of the reaction was 1.~ H202 on O.D. pulp.
It will be understood that the above-described embodiments are for purposes of illustration only and changes and modifications may be made thereto without departing from the spirit and scope of the invention.
magnesium sulphate with sufficient water to reduce the pulp consis-tency to 10%. The temperature of this treatment was 60C and the reaction time was 60 minutes. At the end of the reaction, the pH was 10.7. The brigh-tness of the washed sample after this stage was 56.2.
Thre~ 100-gram samples of the same unbleached jack pine TMP were treated wi-th different solutions con-taining the following chemical charges on O.D. pulp:
Solution ~ hydrogen peroxide, 2% sodium silica-te 1% sodium hydroxide and 0.05~ MgSO4.
Solution B 1% hydrogen peroxide, 0% silicate, 2~ NaOH and 0.05% MgSO4.
Solution C 1% hydrogen peroxide, 4% silicate, 0% NaOH and 0.05% MgSO4.
The temperature of these treatments was 82 and the reaction ti.me was 10 minutes. The pH of the pulp at the end of each reaction is listed in Table 1, along wi-th the brightness values.
.
~Z~ )3 BLEACHING OF MECHANICAL PULPS
TREATMENT CONDITIONS*
.
PULP NO. H2O2 NaOH Na2Si03 TEMP. TIME END BRIGHTNESS
TYPE ~ % % C MIN. pH % ISO
_ _ .
Jack - - - - - - 50.6 pine 1.0 2.0 3.0 60 6010.7 56.2 TMP a 1.0 1.0 2.0 82 108.5 57.8 b 1.0 2.0 0~0 82 108.0 57.6, c 1.0 0.0 4.0 82 107.9 57.8 _"~ .. .
*10~ consistency, peroxide solution contained 0.05%
MgSO4 on pulp and 0.2% EDTA
EXAMPLE II
_ - A 100 grams of a commercial western groundwood pulp, hrightness 55.5% ISO was -trea-ted wi-th a bleaching solution containing 2.5% hydrogen peroxide, 4.0% sodium sili.cate, 2O5% sodium hydroxide, and 0.05% magnesium sulphate with sufficient water to reduce the pulp consistency to 10%. The temperature of this treatment was 60C and the reaction time 60 minut~s. At the end of the reaction -the pH was 10.4 and the brightness after washing 69.6%.
~"~
Three 100-gram samples of the same unbleached western groundwood pulp were -treated wi-th different bleaching solutions cont~ining -the following chemicals:
A. 2.5% hydrogen peroxide, 2.0% silicate, 2.5~ NaOH and 0.05~ MgSO4.
B. 2.5% hydrogen peroxide, 0~ silicate, 3.0% NaOh and 0.05~ MgSO4.
C. 2.5% hydrogen peroxide, 1.0~ silicate, 2~5~ NaOH and 0.05% MgSO4.
C. 2.5% hydrogen peroxide, 5.0% silicate, 0~ NaOH and 0.05% MgSO4.
The solutions were added with sufficient water -to reduce the pulp consistency to 10%. The temperature of this treatment was 95C and the reaction time was 10 minutes.
The pH at the end of each reaction is listed in Table 2, along with the brigh-tness values.
BLEACHING OF MECHANICAL PULPS
. . _ TREATMENT CONDITIONS*
PULP NO. ~1202 NaOH Na2Si03 TEMP. TIME END BRIGHTNESS
TYPE % ~ % C. MIN pH % ISO
.. . .. .. .. . . . . _ West~ 55-5 ern 2.5 2.5 4.0 60 6010.4 69.6 Ground-wood a 2.5 2.5 2.0 95 108.0 71.0 b 2.5 3.0 0 95 108.2 70.7 c 2.5 2.5 1.0 95 108.1 70.9 d 2.5 0 5.0 95 107.7 70.8 . . _ .~
*10% consistency, peroxide solution contained 0.05~ MgSO4 on pulp and 0.2% EDTA.
_~_ .
", EXAMPLE III
A 100 grams of a commercial spruce thermo-mechanical pulp, brightness 60.3% ISO was treated wi-th a solution containing 2% hydrogen peroxide on O.D. pulp, 6.0% sodium silicate, 2.0% sodium hydroxide, 0.05%
magnesium sulphate with sufficient water to reduce -the pulp consistency to 10~. The temperature of this treatment was 60C and the reaction time was 60 minutes. At the end of the reaction, the pH was 10.6. The brightness of the washed sample after -this stage was 75.2.
Three 100-gram samples of the same unbleached spruce TMP were treated with different solutions containing the following chemical charges on O.D. pulp:
Solution A. 2% hydrogen peroxide, 1.0% sodium silicate, 2.5% sodium hydroxide and 0.05% MgSO4.
Solution B. 2% hydrogen peroxide, 0% silicate, 3.0%
NaOH and 0.05% MgSO4.
Solution C. 2% hydrogen peroxide, 6% silicate, 0%
NaOH and 0.05% MgSO~.
The temperature of these treatmen-ts was 85 and the reaction time was 10 minutes. The pH of the pulp at the end of each reaction is listed in Table 3, along with the brightness values.
)3 BLEACEIING OF MECHANICAL PULPS
TREATMENT CONDITIONS*
PULP NO. H202 NaOH Na2SiO3 TEMP. TIME END BRIGHTNESS
TYPE % ~ % C. MIN. pH % ISO
.. _ . . .. _ .
Spruce ~ - 63.5 TMP 2.0 2.5 6.0 6060 10.6 75.2 a 2.0 2.5 1.0 8510 8.3 75.2 b 2.0 3.0 0 8510 8.5 75.4 c 2.0 0 6.0 8510 8.1 75.8 . . _ .
*10% consis-tency, peroxide solu-tion contained 0.05% MgSO~
on pulp and 0.2% EDTA.
As will be seen from each of the above examples, the method of the present invention provides a pulp substan-tially equivalent in brightness -to traditional methods, bu-t can accomplish the same with a peroxide bleachiny solu-tion containing very little or no sodium silicate. Also, the method of the present invention, using the hiyher reaction temperature, mlnimixes the reac-tion time.
:, , ~Z~`3 ~
EXAMPLE IV
A commercial spruce balsam chemithermomechanical pulp, brightness 56.1% ISO taken from a disc filter of a mill was trea-ted with a solution containing 2.0% hydrogen peroxide on O.D. pulp, 2.5% sodium silicate, 1.0% sodium hydroxide, 0.5~ magnesium sulphate with sufficient water to reduce the pulp consistency to 10~. The temperature of this treatment was 85C and the reaction time was 10 minutes. At the end of the reaction the pH was 8.5. The residual peroxide concentration was tested and found to be 0.32 H202 on O.D. pulp. The brightness of a washed sample after this s-tage was 71.5 ISO.
To complete the two-stage process, the washed pulp was treated with a solution containing 2.0% hydrogen peroxide on O.D. pulp~ 2.5~ sodium silicate, 2.0% sodium hydroxide and 0.05% magnesium sulpha-te with sufficient water to reduce the pulp consistency to 10%. The reaction temperature was 85C and the reaction time was 30 minutes.
The pH at -the end of -the reaction was 9.5 and the pulp after souring and washing had a brightness of 78.3%.
I'he peroxide residual measured at the end of the reaction was 1.~ H202 on O.D. pulp.
It will be understood that the above-described embodiments are for purposes of illustration only and changes and modifications may be made thereto without departing from the spirit and scope of the invention.
Claims (6)
1. A method for the bleaching of a high or ultra high yield pulp comprising the step of treating the pulp with a peroxygen compound at a charge of between about 0.5 to about 3% by weight of oven-dried pulp in the presence of sodium hydroxide and magnesium sulphate at a reaction temperature of between 60°C to about 99°C with a reaction time of between 1 minute to about 60 minutes and a pulp consistency of from about 6% to about 25% with a reaction pH of from about 7.5 to 9.
2. The method of claim 1 wherein said sodium hydroxide and magnesium sulphate are added in charges of between 0.25% to about 3% and 0.01% to about 0.05 respectively based on oven-dried pulp.
3. The method of claim 1 or 2 wherein said reaction temperature is between 75°C to about 95°C and said reaction time is between 5 minutes to about 20 minutes
4. The method of claim 1 or 2 wherein the pulp is selected from the group of pulps consisting of mechanical, chemimechanical, chemithermomechanical, groundwood and high yield sulphite pulps.
5. A method for the bleaching of a high or ultra high yield pulp selected from the group of pulps consisting of mechanical, chemimechanical, chemithermomechanical, groundwood and high yield sulphite pulps, comprising the step of treating the pulp with a peroxygen compound at a charge of between about 0.5 to about 3% by weight of oven-dried pulp in the presence of between 0.25% to 3%
sodium hydroxide and 0.01% to 0.05% magnesium sulphate at a reaction temperature of between 75° to about 95°C with a reaction time of between 5 minutes to about 20 minutes and a pulp consistency of from about 6% to about 25% with a reaction pH of from about 7.5 to about 9.
sodium hydroxide and 0.01% to 0.05% magnesium sulphate at a reaction temperature of between 75° to about 95°C with a reaction time of between 5 minutes to about 20 minutes and a pulp consistency of from about 6% to about 25% with a reaction pH of from about 7.5 to about 9.
6. The method of claim 1 or 5 further including the step of washing the pulp and subsequently treating the pulp a second time with a peroxygen compound at a charge between about 0.5 to about 3% by weight of oven dry pulp in the presence of sodium hydroxide and magnesium sulphate at a reaction temperature of between 60° to about 99°C with a reaction time of between 1 minute to about 60 minutes and a pulp consistency of about 6% to about 25% with a reaction pH of from about 7.5 to 9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000486331A CA1249403A (en) | 1985-07-04 | 1985-07-04 | Brightening of high yield and ultra high yield pulps |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000486331A CA1249403A (en) | 1985-07-04 | 1985-07-04 | Brightening of high yield and ultra high yield pulps |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1249403A true CA1249403A (en) | 1989-01-31 |
Family
ID=4130929
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000486331A Expired CA1249403A (en) | 1985-07-04 | 1985-07-04 | Brightening of high yield and ultra high yield pulps |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1249403A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5205907A (en) * | 1991-11-25 | 1993-04-27 | Macmillan Bloedel Limited | Removal of manganese from pulp using a chelating agent and magnesium sulphate |
-
1985
- 1985-07-04 CA CA000486331A patent/CA1249403A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5205907A (en) * | 1991-11-25 | 1993-04-27 | Macmillan Bloedel Limited | Removal of manganese from pulp using a chelating agent and magnesium sulphate |
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