U.S. patent application number 10/590297 was filed with the patent office on 2007-11-29 for method for reducing the extractives content of high-yield pulps and method for producing bleached high-yield pulps.
Invention is credited to Jukka Jakara, Aarto Paren.
Application Number | 20070272378 10/590297 |
Document ID | / |
Family ID | 31725758 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070272378 |
Kind Code |
A1 |
Paren; Aarto ; et
al. |
November 29, 2007 |
Method for Reducing the Extractives Content of High-Yield Pulps and
Method for Producing Bleached High-Yield Pulps
Abstract
The invention relates to a method for reducing the content of
extractives of a high-yield pulp in a peroxide bleaching stage,
said stage including peroxide bleaching and a subsequent dewatering
or washing, said method comprising contacting the pulp in the
peroxide bleaching with an organic stabilizer and in or after the
peroxide bleaching with a surfactant, and thereafter subjecting the
bleached pulp to said dewatering or washing for removing
extractives along with the aqueous phase. The invention also
relates to a method for producing bleached high-yield pulp.
Inventors: |
Paren; Aarto; (Vaasa,
FI) ; Jakara; Jukka; (Siivikkala, FI) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
31725758 |
Appl. No.: |
10/590297 |
Filed: |
February 23, 2005 |
PCT Filed: |
February 23, 2005 |
PCT NO: |
PCT/FI05/00112 |
371 Date: |
June 13, 2007 |
Current U.S.
Class: |
162/78 ; 162/60;
162/70; 162/9 |
Current CPC
Class: |
D21C 9/1036 20130101;
D21C 9/08 20130101; D21C 9/163 20130101 |
Class at
Publication: |
162/078 ;
162/009; 162/070; 162/060 |
International
Class: |
D21C 9/08 20060101
D21C009/08; D21C 9/16 20060101 D21C009/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2004 |
FI |
20040282 |
Claims
1. A method for treating pulp, said method comprising: peroxide
bleaching the pulp; contacting the pulp with an organic stabilizer
before or during the peroxide bleaching: contacting the pulp with a
surfactant before, during or after the peroxide bleaching; said
dewatering and/or washing the peroxide bleached pulp containing the
organic stabilizer and the surfactant to remove extractives along
with the aqueous phase.
2. The method according to claim 1 wherein the organic stabilizer
and the surfactant are added to the pulp during the peroxide
bleaching.
3. The method according to claim 1 wherein the organic stabilizer
and the surfactant are added to the pulp before the peroxide
bleaching.
4. The method according to claim 1 wherein the surfactant is added
to the pulp after the peroxide bleaching.
5. The method according to claim 1 wherein dilution water is added
to the pulp between the peroxide bleaching and the dewatering or
washing.
6. The method according to claim 5 wherein the surfactant is added
to the dilution water.
7. The method according to claim 1 wherein the organic stabilizer
comprises a polymeric stabilizer.
8. The method according to claim 1 wherein the amount of the
organic stabilizer is from 0.1 kg to 5 kg per ton dry pulp.
9. The method according to claim 1 wherein the surfactant comprises
an anionic surfactant.
10. The method according to claim 1 wherein the amount of the
surfactant is from 0.005 kg to 2 kg per ton dry pulp.
11. A method for producing a bleached having a reduced content of
extractives, comprising: bleaching a pulp with a peroxide;
contacting the pulp with an organic, polymeric stabilizer before or
during the peroxide bleaching, in an amount of 0.1 kg to 5 kg) per
ton dry pulp, wherein the stabilizer comprises a
poly-alpha-hydroxyacrylic acid, a salt thereof, the corresponding
polylactone, a homopolymer of acrylic acid, a homopolymer of
methacrylic acid, a homopolymer of malcic acid, a copolymer of
acrylic acid with an unsaturated dicarboxylic acid, a copolymer of
methacrylic acid with an unsaturated dicarboxylic acid, or a
combination comprising at least one of the foregoing organic
stabilizers; contacting the pulp with an anionic or nonionic
surfactant before the peroxide bleaching, during the peroxide
bleaching, or after the peroxide bleaching in an amount of 0.1 kg
to 5 kg per ton dry pulp, wherein the surfactant comprises
naphthalene sulphonate, naphthalene lignosulphonate, an
oil-in-water emulsifier, a fatty alcohol ethoxylate, an alkyl
phenol ethoxylate, or a combination comprising at least one of the
foregoing surfactants; and dewatering and/or washing the bleached
pulp to remove extractives along with the aqueous phase, to produce
a bleached pulp having a reduced content of extractives.
12. The method according to claim 11 wherein the organic stabilizer
and the surfactant are added to the pulp during the peroxide
bleaching.
13. The method according to claim 11 wherein the organic stabilizer
and the surfactant are added to the pulp before the peroxide
bleaching.
14. The method according to claim 11 wherein the surfactant is
added to the pulp after the peroxide bleaching.
15. The method according to claim 11 wherein dilution water is
added to the pulp between the peroxide bleaching and the dewatering
or washing.
16. The method according to claim 15 wherein the surfactant is
added to the dilution water.
17. (canceled)
18. The method according to claim 11 wherein the amount of the
organic stabilizer is from 0.25 kg to 3 kg per ton of dry pulp.
19. (canceled)
20. The method according to claim 11 wherein the amount of the
surfactant is from 0.05 kg t o 1 kg per ton dry pulp.
21. The method according to claim 1 wherein the organic stabilizer
is a poly-alpha-hydroxyacrylic acid, a salt thereof, the
corresponding polylactone, a homopolymer of acrylic acid, a
homopolymer of methacrylic acid, a homopolymer of maleic acid, a
copolymer of acrylic acid with an unsaturated dicarboxylic acid, a
copolymer of methacrylic acid with an unsaturated dicarboxylic
acid, or a mixture comprising at least one of the foregoing
polymers.
22. The method according to claim 1 wherein the surfactant
comprises naphthalene sulphonate, naphthalene lignosulphonate, an
oil-in-water emulsifier, a fatty alcohol ethoxylate, an alkyl
phenol ethoxylate, or a combination comprising at least one of the
foregoing surfactants.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for reducing the
extractives content of high-yield mechanical pulps. The invention
also relates to a method for producing bleached high-yield pulps
having a reduced content of extractives.
DESCRIPTION OF THE PRIOR ART
[0002] Extractives are known constituents of wood and pulp species
that are extractable with organic solvents. The most predominant
chemical groups found in extractives are fatty and resin acids,
terpenes, phytosterols and phenolic compounds. Extractives are
found esterified, glycosylated and nonderivatized. The most
problematic extractives in wood are mainly the oleophilic
compounds. They are fatty acids, resin acids, terpenes and sterols
and their function is to protect the tree by preventing attacks
from germs, funguses etc. Scandinavian softwoods contain
approximately 1.5% extractives by weight while hardwoods of the
temperate zone usually contain 2-2.5% by weight. Generally, the
problematic extractives are commonly referred to as pitch. Problems
are usually found in high shear force areas and when the
temperature, pH or pitch concentration changes.
[0003] Common detrimental effects from pitch in different areas are
as follows. In bleach plants, deposits are formed and may also
increase consumption of chemicals. In the final product spots and
high level of extractives are found.
[0004] A modern bleaching process for mechanical pulps includes
often high-consistency peroxide bleaching (PHC). After peroxide
bleaching the pulp is often diluted with white water coming from
the paper machine and after that the pulp slurry is dewatered. This
washing step reduces carry-over of anionic trash to paper machine
and also allows recirculation of residual peroxide. Alkaline
peroxide oxidizes and removes quite efficiently extractives from
the pulp. However, if the pulp in the bottom of PHC bleach tower or
after PCH bleaching is diluted with white water the extractives can
re-precipitate in the surface of pulp or process equipment due to
lower pH of the water, high hardness or electrolyte (salt)
concentration. Precipitated extractives will be transferred in the
fiber surface to the paper machine leading to problems in wet end
and paper quality. When the PHC wash filtrate is recirculated back
to earlier stages of the process, the extractives, possibly found
in the wash filtrate, can be precipitated in the process equipment
or fibers in acidic or neutral environment.
[0005] U.S. Pat. No. 4 363 699 describes a process for stabilizing
alkaline solutions of peroxidic compounds used for bleaching
wherein an alkaline salt of a poly-alfa-hydroxy-acrylic acid is
added to the solution as a stabilizer. The stabilized solutions can
be used for the bleaching of paper pulps and textiles. When
bleaching textiles, the bleaching solution may contain a wetting
agent which is a surface active agent.
[0006] U.S. Pat. No. 4 963 157 describes a method of bleaching a
cellulosic fiber material, especially cotton with hydrogen
peroxide. The method comprises impregnating the fiber material with
a bleaching solution containing hydrogen peroxide and a stabilizer.
The stabilizer comprises poly-alfa-hydroxyacrylic acid or a salt
thereof or the polylactone corresponding thereto, and an organic
phosphonic acid or a salt thereof.
[0007] DE 3423452 discloses a solution for avoiding the use of
water glass comprising a stabilizing mixture of a
poly-alfa-hydroxyacrylic acid (PHAA) and a water soluble
homopolymer of acrylic or methacrylic acid or a copolymer of
acrylic acid and/or maleic acid. The salts, especially the sodium
salt of PHAA and the sodium salt of the polycarboxylate polymer are
mixed together. Chelating agents can be added to the mixture and
thus an improved stabilizer mixture for bleaching processes is
obtained. According to DE 3423452 the bleaching process is carried
out by using an alkaline peroxide bleaching liquor containing said
stabilizing mixture.
SUMMARY OF THE INVENTION
[0008] The invention is based on the fact that the extractives are
more soluble in alkaline conditions and thus, when the pulp is
diluted with dilution water, for example white water after
bleaching, the extractives may redeposit on the fiber surfaces
especially when the pH of dilution water is lower that that of pulp
coming out from bleaching tower. According to the present invention
it has been found that certain surface-active agents can inhibit
precipitation of extractives and thus keep them in water phase.
Then the extractives can be washed off the pulp at next dewatering
press which in turn leads to reduced extractives content in the
pulp. Since the extractives are dispersed and the particles are
stabilized, there is no re-precipitation of extractives when the
filtrate is re-circulated to the earlier process stages.
[0009] The invention is especially advantageous when the pulp is
bleached without silicate as stabilizer, since it has been noticed
that silica has some dispersing efficiency against extractives.
However, the invention works also well in the presence of
silicate.
DETAILED DESCRIPTION OF THE INVENTION
[0010] According to the present invention there is provided a
method for reducing the content of extractives of a high-yield pulp
in a peroxide bleaching stage, said stage including peroxide
bleaching and a subsequent dewatering or washing, said method
comprising contacting the pulp in the peroxide bleaching with an
organic stabilizer and in or after the peroxide bleaching with a
surfactant, and thereafter subjecting-the bleached pulp to said
dewatering or washing for removing extractives along with the
aqueous phase.
[0011] In this context the peroxide bleaching stage includes
peroxide bleaching of the pulp, optionally dilution of the pulp,
and dewatering or washing of the pulp.
[0012] According to the present invention there is also provided a
method for producing bleached high-yield pulp having a reduced
content of extractives comprising bleaching high-yield pulp with
peroxide, the pulp being contacted with an organic stabilizer
during the peroxide bleaching and with a surfactant during the
peroxide bleaching or after the peroxide bleaching, and dewatering
or washing the bleached pulp for removing extractives along with
the aqueous phase and for producing bleached high-yield pulp having
a reduced content of extractives.
[0013] The extractives to be removed from the pulp according to the
present invention originate from the wood pitch. The extractives
include fatty acids, resin acids, terpenes, phytosterols and
phenolic compounds in esterified, glycosylated and/or
nonderivatized form. The most problematic extractives include fatty
acids, resin acids, triglycerides, steryl esters, sterols and
lignans.
[0014] The organic stabilizer and the surfactant can be added
separately or these chemicals can be mixed beforehand with the
bleaching solution. Furthermore the organic stabilizer and the
surfactant can be added simultaneously or separately as one
chemical mixture, i.e. product.
[0015] The organic stabilizer and the surfactant can be added to
the pulp in the peroxide bleaching or before the peroxide
bleaching.
[0016] It is also possible to add the surfactant to the pulp after
the peroxide bleaching. In that case the surfactant can be added to
dilution water which is added to the pulp between the peroxide
bleaching and the dewatering or washing. The dilution water can be
white water circulated from the paper machine.
[0017] The organic peroxide stabilizer used in the methods of the
invention is preferably a polymeric stabilizer, such as a
poly-alfa-hydroxyacrylic acid or a salt thereof or the
corresponding polylactone, a homopolymer of acrylic acid,
methacrylic acid or maleic acid or a copolymer of acrylic acid
and/or methacrylic acid with an unsaturated dicarboxylic acid. The
polymeric stabilizer can also be a mixture of the
poly-alfa-hydroxyacrylic acid and the homopolymer and/or the
copolymer. The unsaturated dicarboxylic acid is preferably maleic
acid. The salt of the poly-alfa-hydroxyacrylic acid is preferably a
sodium, potassium or ammonium salt. The poly-alfa-hydroxyacrylic
acid can have a molecular weight of at least 5000, preferably at
least 10000, and more preferably at least 15000 (calculated as the
sodium salt of the PHAA). The homopolymer and the copolymer can
have a molecular weight of at least 4000, preferably at least
10000, and more preferably at least 20000.
[0018] The organic stabilizer can also be a phosphonic acid or a
salt thereof. The salt is preferably a sodium, potassium or
ammonium salt. Suitable phosphonic acids are for example the
(poly)aminophosphonic acids, such as aminotri(methylenephosphonic
acid), ethylenediaminetetra(methylenephosphonic acid), i.e. EDTMPA,
or diethylenetriaminepenta(methylenephosphonic acid), i.e.
DTPMPA.
[0019] In addition to said organic stabilizer it is possible to
introduce another stabilizer. This other stabilizer can be an
alkaline earth metal compound such as a magnesium and/or calcium
compound. The alkaline earth metal compound can be in the form of a
salt, such as a sulphate, chloride or any other water soluble salt
or in the form of a complex with a polymer or a chelating agent. A
preferred alkaline earth metal salt is magnesium sulphate.
[0020] The amount of the organic stabilizer is preferably from 0.1
kg to 5 kg per ton dry pulp, more preferably from 0.25 kg to 3 kg
per ton dry pulp, and even more preferably from 0.5 kg to 3 kg per
ton dry pulp.
[0021] The surfactant used in the methods of the invention can be
an anionic surfactant, such as naphthalene sulphonate or
lignosulphonate, or a non-ionic surfactant, such as an O/W
emulsifier, f. ex. a fatty alcohol ethoxylate or alkyl phenol
ethoxylate.
[0022] Also a mixture of the anionic and non-ionic surfactants can
be used. Defoamers can be used in combination with the
surfactant(s) to prevent foaming.
[0023] The amount of the surfactant is preferably from 0.005 kg to
2 kg per ton dry pulp, more preferably from 0.05 kg to 1 kg per ton
dry pulp.
[0024] The methods of the invention are used in bleaching
high-yield mechanical pulps, like groundwood pulps, stone
groundwood pulps, pressure groundwood pulps (GW, SGW, PGW), refiner
mechanical pulps (RMP), thermomechanical pulps (TMP) and
chemithermomechanical pulps (CTMP, APMP).
[0025] In the peroxide bleaching hydrogen peroxide is preferably
used as the bleaching agent. Other chemicals such as bleaching
stabilizers, chelating agents and/or magnesium sulphate can be used
in the bleaching. Especially advantageous is to add the chemicals
before bleaching or at the same time with bleaching chemicals. If
there are several bleaching stages, the chemicals can be added in
any of them or in several stages.
[0026] The residence time in the bleaching can vary within a wide
range, from 30 to 240 minutes, preferably from 45 to 180 minutes
and most preferably from 60 to 120 minutes. The residence time will
also depend on the temperature used in the bleaching.
[0027] The bleaching of high-yield pulps can be carried out at a
temperature of 30-90.degree. C., preferably at a temperature of
50-90.degree. C. The bleaching can be carried out at a consistency
of choice, but it is most preferably to carry out the bleaching at
a high consistency, i.e. about 30% or higher. Bleaching can also be
carried in two stages with a dewatering stage between the
stages.
[0028] The pH in the alkaline bleaching of the invention can be
from 7 to 14, preferably from 8 to 11. The ratio between the
alkali, typically sodium hydroxide, and hydrogen peroxide can vary
in a wide range, depending on raw materials and degree of
bleaching. Also alternative alkali sources, like sodium carbonate,
can be utilized.
[0029] The present invention will be illustrated by following
examples. The percentages are % by weight unless otherwise
specified. "kg/t" means kilograms per ton dry pulp. "Cs" means
consistency. "P" stands for peroxide stage.
EXAMPLES
Comparative Example
[0030] The purpose of this comparative example is to clarify the
problem to be solved by the invention. TMP pulp (spruce) was
bleached in high consistency with peroxide 5 using waterglass or
poly-a-hydroxy acrylate (PHAA) as stabilizer. Subsequently the pulp
was diluted with ion exchanged water and then dewatered to
consistency of 30%. The detailed experimental data is shown in
table below. TABLE-US-00001 ##STR1## ##STR2##
[0031] The high turbidity of the filtrates after dilution can be
attributed to extractives. The analysis of extractives show, that a
major part of extractives was removed in bleaching. The results
show also that silicate (waterglass) has some dispersing ability
against extractives since the extractives content is much higher
with acrylate-based stabilizer. This means that especially in the
case on silicate-free bleaching, pitch dispersants are
advantageous.
Example 1
[0032] A sample of CTMP-pulp (aspen) was taken from a mill and
bleached with peroxide to brightness of 83-84% ISO. The bleaching
conditions were as follows: t=120 min, 70.degree. C., consistency
30%, H.sub.20.sub.2 38 kg/t, NaOH 21 kg/t, Na.sub.2CO.sub.3 8 kg/t.
The pulp was already chelated in the mill and the manganese content
was 1.5 ppm, Fe 5 ppm. The additives were dosed in the peroxide
bleaching stage and after bleaching the pulp was diluted to 10%
consistency at different pH levels, and subsequently dewatered. The
table below shows the turbidity of the filtrate after dewatering.
The experiment according to this invention was done using per ton
dry pulp 2 kg polymer (poly-a-hydroxy acrylate) as stabilizer and
0.1 kg naphthalene sulphonate +0.1 kg non-ionic surfactant (fatty
alcohol ethoxylate 7 mole EO, C12-C14, HLB 12.3). In the
comparative experiments waterglass and poly-a-hydroxy acrylate were
used as stabilizers. The bleaching result and chemicals consumption
was about the same in each case. TABLE-US-00002 Waterglass,
Acrylate polymer According to 25 kg/t 2 kg/t invention Turbidity,
Turbidity, Turbidity, pH NTU pH NTU pH NTU 6.6 1510 6.3 1353 6.5
1464 7.5 1430 7.3 1317 7.2 1440 7.8 1465 7.7 1389 7.5 1481
[0033] As can be seen from the results, silica originating from the
waterglass (sodium silicate) increases turbidity. This may be
attributed to higher extractives content in the filtrate. When
silicate is replaced by a polymer-based stabilizer, turbidity is
lower and thus extractives content in pulp is higher. The chemical
composition according to this invention yields higher turbidity,
which proves that the extractives dissolved in alkaline peroxide
are not re-precipitated after dilution.
Example 2
[0034] A sample of CTMP-pulp (aspen) was taken from a mill and
bleached with peroxide in high consistency. The bleaching
conditions and results are shown in the table below. The
surfactants were added in the bleaching stage, and after bleaching
the pulp was diluted with ion-exchanged water. The composition of
the surfactants here was naphtalene sulfonic acid condensation
product (Na-salt) and fatty-alcohol ethoxylate (same as in previous
example) in weight-ratio 2:1 (dosage as 20% water solution). The
polymer-based stabilizer was a mixture of poly-alfa-hydroxyacrylate
and maleate-acrylate copolymer (1:4 w:w) having a active substance
content of 25%. TABLE-US-00003 ##STR3## ##STR4## * from pulp DCM
stands for dichloromethane
[0035] DCM stands for dichloromethane.
[0036] The results show, that the method according to the invention
reduces extractives in the pulp and does not affect the bleaching
result.
Example 3
[0037] A sample of CTMP-pulp (aspen) was taken from a mill and
bleached with peroxide to brightness on 83-84% ISO. The surfactant
additives were dosed in peroxide bleaching stage and after
bleaching the pulp was diluted to 10% consistency at different pH
levels, and subsequently dewatered. In one experiment a surfactant
additive was also dosed after the dilution. The results are shown
in the table below. The surfactant additives used here were
naphtalenesulphonate condensation product (A) and fatty alcohol
ethoxylate (B, 25 mole EO, C16-C18, HLB 16). The polymer-based
stabilizer was a mixture of poly-alfa-hydroxyacrylate and
maleate-acrylate copolymer (1:4 w:w) having a active substance
content of 25%. TABLE-US-00004 ##STR5## ##STR6##
[0038] The results show that the combination of polymer-based
stabilizer and anionic and/or nonionic surfactant gives lower
extractives content than waterglass.
* * * * *