Canadian Patents Database / Patent 2230315 Summary
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|(12) Patent Application:||(11) CA 2230315|
|(54) English Title:||PROCESS FOR INCREASING MECHANICAL WOOD PULP BRIGHTNESS IN A REFINER|
|(54) French Title:||METHODE POUR AUGMENTER LE DEGRE DE BLANCHEUR DE LA PATE MECANIQUE DANS UN RAFFINEUR|
|(51) International Patent Classification (IPC):||
|(72) Inventors (Country):||
|(73) Owners (Country):||
|(71) Applicants (Country):||
|(22) Filed Date:||1998-02-17|
|(41) Open to Public Inspection:||1999-08-17|
|(30) Availability of licence:||N/A|
|(30) Language of filing:||English|
A pulp refining and bleaching process for increasing the pulp brightness of a
wood pulp prepared from softwood chips wherein the pulp is treated in one or
more stages in
refiner by adding sodium perborate or peracetic acid generated in a bleach
generating unit by
reacting sodium perborate or hydrogen peroxide with an activating agent such
tetraacetylethylenediamine in the presence or absence of caustic solution and
discharged from the refiner is subjected to another bleaching stage in a
bleach tower by
separate addition of sodium perborate or hydrogen peroxide with or without a
activator. The process is preferably carried out by passing the pulp through a
at elevated pressure and optionally to a bleaching tower, a solution of sodium
in-situ generated peracetic acid from a mixture of sodium perborate or
hydrogen peroxide and an
activator, tetraacetylethylenediamine being fed in the refiner and sodium
hydrogen peroxide with an activator, tetraacetylethylenediamine, being fed in
tower. The pulp after refining has improved brightness and pulp brightness
after an optional
tower bleaching has exceeded 75 ISO% points.
1. A process for simultaneously refining wood pulp in a refiner to produce
improved brightness and mechanical properties comprising concurently
chelating agent. bleach liquor and wood chips or pulp in one or more stages
primary refiner at high temperatures achieved by increasing steam pressures
the bleach liquor comprises a solution of sodium perborate without any alkali
generated peracetic acid from peroxide or perborate and TAED with NaOH
other chemicals such as sodium silicate and magnesium suphate. said solution
alkaline pH of from pH about 10 to about 12 and wherein not more than about
weight of sodium perborate or weight equivalent amount of hydrogen peroxide
molar ratio of TAED generated peracetic acid. based on the total weight of the
dry pulp or
wood chips. is added. and the pulp is discharged from the refiner at a pH less
than 7.0 and
whereby the primary refiner bleaching process produces a brightness gain of at
ISO points in the refiner and improved the mechanical properties of pulp.
pulp obtained after refining is optionally subjected to another tower
2. A process as claimed in claim 1 where pulp leaving said pressurized refiner
to further bleaching in a bleaching tower to produce pulp with ISO brightness
and above in a single post bleaching stage comprising concurrent treatment of
refined pulp or in-refiner bleached pulp with a chealting agent and then with
liquor at a temperature not above 50°C and for a time period not
exceeding 90 min. and
where the bleach liquor comprises either a solution of sodium perborate and
sodium silicate or a solution of hydrogen peroxide and TAED with NaOH and
silicate. said solution having an alkaline pH of from 9.6 to 11.2 and wherein
than 12% by weight of sodium perborate and 8% of TAED or 5% of perxide and 10%
TAED. based on the total weight of the pulp. is added and the pulp is
the tower with a pH not below 7.0 and where tower bleaching of refiner pulp
pulp with ISO brightness above 75%.
3. A process in claim 1 where no alkali is added with sodium perborate or
generated from sodium perborate and TAED.
4. A process in claim 2 where no alkali is added with sodium perborate or
and TAED mixture.
5. A process in claim 1 wherein a perborate concentration more than 5% by
weight of dry
wood chips have been added to the refiner.
6. A process is claim 1 where peracetic acid has been generated ex-situ of the
treating separately hydrogen peroxide with TAED or sodium perborate and TAED.
7. A process in claim 1 wherein a refiner temperature between 115 to
145°C. has been used
by adjusting the steam pressure.
8. A process in claim 1 wherein the chelating agent is selected from the group
ethylenediamine tetraacetic acid (EDTA). dipentamethylenetetramine
(DTPA) and dipentamethylenetriaminephosphonates (DTPMPA).
9. A process in claim 1, wherein the liquor solution has a pH of about pH 9.8
10. A simultaneous wood pulp refining and bleaching process which comprises
steps of: feeding wood chips to a primary presurrized refiner and milling said
at elevated temperature using steam pressure to produce a high concentration
feeding to said presurrized refiner, during milling, a bleach liquor of sodium
Sodium silicate and magnesium sulphate solution having a pH of from about 9.8
12 and discharging the said high concentration pulp from the refiner at a pH
about 7.0 and optionally bleaching the said refined pulp in a bleaching tower
11. A process in claim 2 wherein the bleach liquor is a mixture of hydrogen
12. A process in claim 2 wherein the molar proportion of peroxide to TAED is
0.05 to about 0.5.
13. A process in claim 2. wherein the concentration of hydrogen peroxide is
from about 2.0%
to about 5% by weight of dry pulp.
14. A process in claim 2 wherein the bleach liquor is a mixture of sodium
15. A process in claim 2 wherein the molar proportion of peroxide to TAED is
0.05 to about 0.5.
16. A process in claim 2. wherein the concentration of sodium perborate is
from about 6.0%
to about 15% by weight of dry pulp.
17. A process in claim 2. wherein no alkali has been added with perborate and
18. A process in claim 2. where the pH of the bleach solution is from about
9.8 to about 11.
19. A process in claim 2. wherein the bleaching temperature does not exceed
20. A process in claim 2. wherein the bleaching time does not exceed above 90
21. A process in claim 2. wherein a chelating stage has been introduced before
22. A process in claim 2. wherein the chelating agent is selected from the
of ethylenediamine tetraacetic acid (EDTA). dipentamethylenetetramine
(DTPA) and dipentamethylenetriaminephosphonates (DTPMPA).
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|(41) Open to Public Inspection||1999-08-17|
|Fee Type||Anniversary Year||Due Date||Amount Paid||Paid Date|
|Request for Examination||$200.00||1998-02-17|
|Maintenance Fee - Application - New Act||2||2000-02-17||$50.00||1999-12-21|
|Maintenance Fee - Application - New Act||3||2001-02-19||$50.00||2000-12-12|
|Maintenance Fee - Application - New Act||4||2002-02-18||$50.00||2001-12-12|