Note: Descriptions are shown in the official language in which they were submitted.
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FREENESS OF PAPER PRODUCTS
FIELD OF INVENTION
The present invention relates to a new refining process for paper pulp.
BACKGROUND OF THE INVENTION
Pulp for making paper, tissues, board or related products may be obtained from
cellulose from wood and other sources (e.g., hemp, straw, cotton). The vast
majority of the raw material is wood pulp, which can be either softwood or
hardwood raw material. Softwood fibres come from needle-bearing conifer trees
such as pine, spruce, alpine fir, Douglas fir. Hardwood fibres are derived
from
deciduous trees of various types, such as birch, eucalyptus, and acacia.
Mechanical pulp contains most of the original lignin, whilst in chemical pulp
most
of the lignin has been removed.
Among the distinguishing differences between softwood (SW) and hardwood
(HW) fibres are the length of the individual cellulosic fibres of the wood,
the
coarseness of the fibres and the stiffness/collapsibility of the fibres.
Hardwood and softwood must be subjected to specific mechanical treatments
(refining) for converting the wood into a fibrous slurry employed in the
formation of
a paper web. The fibres of cellulose pulp suspensions are mechanically treated
to
change the fibres' properties. The cellulose pulp suspension is processed into
a
product having increased tensile/tear strength properties, increased freeness
(Shopper-Riegler) values, increased fines, and improved paper/tissue making
properties over that of the initial cellulose pulp suspension. Increased
freeness
values lead to decreased dewatering capabilities for paper/tissue making,
which
increases the energy required to dry the paper and it will slow down the speed
of
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paper making. On the other hand, too low freeness yields paper/tissues that
are
not strong enough. Refining is of importance to the properties of both
chemical
and mechanical pulp. Apart from the dewatering, it should also be noted that
the
energy consumption during the refining process is high.
A chemical process to modulate the cellulosic fibres by treatment of fibres by
iron
salts and hydrogen peroxide has been disclosed in WO 2005/028744; treatment
of Kraft softwood pulp leads to fibre properties reminiscent to hardwood
fibres.
WO 2004/022842 discloses a reduced energy process for refining mechanical
pulp after treatment with a pectinase enzyme to produce pulp with certain
freeness properties.
EP 0458397 discloses the use manganese 1,4,7-Trim ethyl- 1,4,7-
triazacyclononane (Me3-TACN) complexes as bleaching and oxidation catalysts
and use for textile and pulp bleaching processes.
United States Application 2001/0025695A1, Patt et al, discloses the use of
C104
and PF6 salts of manganese complexes of 1,2,-bis-(4,7,-dimethyl-1,4,7,-
triazacyclonon-1-yl)-ethane (Me4-DTNE) and Me3-TACN respectively for wood-
pulp delignification and bleaching. Whilst a loss of viscosity reported when
using
a manganese compound comprising Me4-DTNE is absent or small, the viscosity
loss when using a manganese compound comprising Me3-TACN is much greater,
It is known that cellulose having a lower viscosity gives a paper of reduced
strength (Pulp Bleaching, Principle and Practice, C.W. Dence, D.W. Reeve ed.,
Tappi, Atlanta, 1996).
WO 2007/125517 discloses the use of 1,2,-bis-(4,7,-dimethyl-1,4,7,-
triazacyclonon-1-yl)-ethane (Me4-DTNE) and Me3-TACN with buffer and
sequestrants for bleaching of cellulosic substrates.
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WO 2008/086937 discloses the use of 1,2,-bis-(4,7,-dimethyl-l,4,7,-
triazacyclonon-1-yl)-ethane (Me4-DTNE) and Me3-TACN for bleaching of
cellulosic
substrates whilst keeping the pH constant.
US 2002/0066542 Al describes transition metal complex compounds of
polydentate ligands, in particular of cobalt, and the use of such compounds in
a
delignifying and bleaching method. Reference experiments conducted with a
manganese complex comprising Me3-TACN showed a market loss in viscosity,
whilst the other compounds described did not show significant changes in
viscosity.
It would be desirable to provide a method that permits a paper/tissue producer
to
use a refining process with a lower level of freeness that yields the same
pulp
strength properties as conventionally provided by mechanical means.
SUMMARY OF THE INVENTION
We have found that treating cellulosic fibers using a preformed transition
metal
complex of azacyclic molecules and hydrogen peroxide, improves the effect of
refining of these fibers. Treatment can be either done before, during or after
the
refining process, typically before or during the refining process. The
improved
refining properties can be observed by increased tensile strength properties
at the
same mechanical energy input and same Shopper-Riegler value (SR).
In addition, despite the facts that within the pulp/paper field it is widely
acknowledged that significant reduction of the viscosity loss of cellulose is
not
desirable for paper-making properties, and that the use of the manganese
catalysts comprising Me3-TACN gives significant viscosity loss, according to
different studies, it is particularly surprising to have found that the use of
such
catalysts leads to an improvement of the effect of refining process on the
fiber
properties.
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The present invention may be applied to chemical and mechanical pulp,
including
recycling pulp, for production of paper, tissue or board.
We have found that energy consumption and time of reaching a cellulose pulp
suspension that may be further processed to a web having improved freeness
may be reduced by the action of a manganese catalyst together with hydrogen
peroxide.
In a first aspect the present invention provides a method for the treatment of
a
cellulose pulp suspension comprising (i) the step of subjecting cellulose
pulp fibres to an aqueous solution of a manganese transition metal catalyst
and
hydrogen peroxide at pH from 6 to 13 and (ii) subjecting the pulp to a
refining
process until a Shopper Riegler (SR) value of from 10 to 900 is reached and
the
resultant pulp is processed into paper, tissue or board, wherein the manganese
transition metal catalyst is present at a concentration from 0.0001 to 1
kg/tonne
oven-dry pulp and the hydrogen peroxide is present at a concentration from 0.1
to
100 kg/tonne oven-dry pulp, the manganese transition metal catalyst is
preformed
and a mononuclear Mn(II), Mn(III), Mn(IV) or dinuclear Mn(II)Mn(II),
Mn(II)Mn(III),
Mn(III)Mn(III), Mn(II)Mn(IV) or Mn(IV)Mn(IV) transition metal catalyst, the
ligand of
the transition metal catalyst of formula (I):
(Q)
(I)
p0
R
I
wherein: Q -N- [ CR1RZCR3R4 )
p is 3;
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R is independently selected from: hydrogen, C1-C6-alkyl, C2OH,
C1000H, and pyridin-2-ylmethyl or one of R is linked to the N of another Q
from
another ring via an ethylene bridge;
R1, R2, R3, and R4 are independently selected from: H, C1-C4-alkyl, and
C1-C4-alkylhydroxy.
In a second aspect, the invention provides the use of an aqueous solution of a
manganese transition metal catalyst and hydrogen peroxide at a pH from 6 to
13,
wherein the manganese transition metal catalyst is preformed and a mononuclear
Mn(II), Mn(III), Mn(IV) or dinuclear Mn(II)Mn(II), Mn(II)Mn(III),
Mn(III)Mn(III),
Mn(III)Mn(IV) or Mn(IV)Mn(IV) transition metal catalyst, the ligand of the
transition
metal catalyst of formula (I):
Q) P (r)
R
I
wherein: Q -N- [ CRIR2CR3R4 )
pis 3;
R is independently selected from: hydrogen, C1-C6-alkyl, C2OH,
C1000H, and pyridin-2-ylmethyl or one of R is linked to the N of another Q
from
another ring via an ethylene bridge;
R1, R2, R3, and R4 are independently selected from: H, C1-C4-alkyl, and
C1-C4-alkylhydroxy,
for increasing the extent to which the Freeness Value of cellulose pulp
fibres is increased in a refining process.
According to particular embodiments of the first and second aspect of the
invention, each R in the ligand of formula (I) is independently selected from:
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hydrogen, C1-C6-alkyl, C2OH, CICOOH, and pyridin-2-ylmethyl. It is
particularly
unexpected for these unbridged ligands, wherein no R is linked to the N of
another
Q from another ring via an ethylene bridge to be suitable for use according to
the
method of the present invention because of the demonstration in the prior art
of
the reduction in viscosity found when conducting delignification reactions
using
transition metal catalysts comprising such a ligand.
In a further aspect, the invention provides paper, tissue or board obtainable
by a
method according to the first aspect of the invention or a use according to
the
second aspect of the invention.
The Freeness value (SR) is a standard measurement as measured by Shopper
Riegler method for Drainability NORM EN ISO 5267-1; the Freeness value (SR)
as used herein has been measured by this method.
The concentration of the catalyst and hydrogen peroxide will have an effect
upon
the time of refining treatment of the pulp that is required as will the ratio
of the
mass of pulp to amount of actives used. In this regard, to optimise the
conditions
the variables of concentration of actives, temperature, pH and time are
variables
that may be changed.
It is preferred that the treatment time of the pulp with the catalyst and
hydrogen
peroxide is from 1 min to 4 h, more preferred 5 min to 3 h, and most preferred
10
min to 2 h. Further, it is preferred that the temperature of the process using
the
catalyst and hydrogen peroxide is from 30 to 95 C and more preferably between
40 to 90 C. The pH of the process using the catalyst and hydrogen peroxide is
preferably between pH 8 and 12.
The transition metal complex and hydrogen peroxide may be added at a
conventional bleaching stage. Alternatively, the transition metal complex and
hydrogen peroxide may be added prior to or during the refining stage, for
example
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to pulp that this already been bleached in one or more delignification and
bleaching stages, i.e. to chemical pulp. Chemical pulp thus treated may have
been delignified/bleached by contact with hydrogen peroxide and a transition
metal catalyst, for example as defined in accordance with the present
invention.
Alternatively, the chemical pulp may be otherwise produced, for example by non-
catalytic bleaching of pulp, for example using ozone, chlorine dioxide or non-
catalytic bleaching with hydrogen peroxide.
Alternatively, the manganese catalyst together with hydrogen peroxide may be
employed both in a bleaching stage, and again after the bleaching stage, prior
to
or during the refining stage.
Often, for mechanical pulp and recycle pulp processing, a bleaching stage, for
example involving use of hydrogen peroxide, is conducted. In such cases, the
manganese transition metal catalyst defined in accordance with the first and
second aspect of the invention could be included as well. Sometimes, a
reductive
bleaching step with dithionite may be used to treat recycle pulp (to which
bleaching step the manganese transition metal catalyst will not be added).
Alternatively, the manganese transition metal catalyst and hydrogen peroxide
may
be used to treat mechanical pulp and recycle pulp, particularly before or
during the
mechanical refining process, after it has been bleached with hydrogen peroxide
and/or with dithionite.
Alternatively, the manganese catalyst together with hydrogen peroxide may be
employed both in a bleaching stage, and again after the bleaching stage, prior
to
or during the refining stage.
These possibilities are discussed in greater detail below. A washing step is
typically but not necessarily carried out between addition of transition metal
catalyst & hydrogen peroxide and the refining process (if the former is
effected
prior to the latter).
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It will be appreciated that the amount of transition metal catalyst/hydrogen
peroxide required per tonne of pulp (oven dry) is essentially that of a molar
ratios
but within the industry it is normal to express amounts in weight. In this
regard, the
range of transition metal catalyst required per tonne of pulp (oven dry) is in
the
range from 0.0001 to 1 kg per tonne of pulp (oven dry) which equates
approximately to 0.1 to 1500 mmol/tonne pulp (oven dry). According to
particular
embodiments of the invention, the transition metal catalyst is present at a
concentration in the range from 0.0005 to 0.2 kg per tonne of pulp (oven dry).
The
hydrogen peroxide (100%) per tonne of pulp (oven dry) is in the range from 0.1
to
100 kg, more preferably 0.5 to 50 kg, most preferably 1 to 30 kg. For example,
the
hydrogen peroxide (100%) per tonne of pulp (oven dry) may be in the range from
0.1 to 25 kg per tonne of pulp (oven dry). It is to be understood that the
each of
the ranges of concentration of transition metal catalyst disclosed herein may
be
combined with each of the ranges of hydrogen peroxide disclosed herein. For
example, according to certain embodiments of the invention, the transition
metal
catalyst is present at a concentration in the range from 0.0005 to 0.2 kg per
tonne
of pulp (oven dry) and the hydrogen peroxide (100%) per tonne of pulp (oven
dry)
is in the range from 0.1 to 25 kg.
The molar ratio of transition metal catalyst: hydrogen peroxide is preferably
in the
range from 1:100 to 1: 10000.
With the above in mind it is then routine for a technician skilled in the art
to
determine the conditions by trial and error to produce the Freeness value (SR)
and apply the conditions to obtain and optimise the pulp having the desired
Freeness value (SR) to a web industrially.
DETAILED DESCRIPTION OF THE INVENTION
Pulp to produce paper or board grades is fed to a paper machine where it is
formed as a paper web and the water is removed from it by pressing and drying.
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Pressing the sheet removes the water by force. Once the water is forced from
the
sheet, felt is used to collect the water. When making paper by hand, a blotter
sheet is used. Pulp for the manufacturing of tissue or kitchen towel grades is
dewatered and dried without pressing, to maintain the appropriate absorbancy
and smoothness properties.
Drying involves using air and or heat to remove water from the paper sheet. In
the
earliest days of papermaking this was done by hanging the paper sheets like
laundry. In more modern times, various forms of heated drying mechanisms are
used. On the paper machine, the most common is the steam-heated can dryer.
These dryers can heat to temperatures above 200 F (93 C) and are used in long
sequences of more than 40 cans. The heat produced by these can easily dry the
paper to less than 6% moisture.
Specific procedures exist to produce tissue paper. Reference is made to Paper
and Board Grades, Book 18, chapter 4, by the Finnish Paper Engineers'
Association and TAPPI (2000).
We have found that treating a cellulose pulp suspension with a manganese
transition metal catalyst and hydrogen peroxide changes the extent to which
the
pulp reacts to a mechanical refining process, as measured by its freeness
value
(Shopper-Riegler - SR), to produce a web made from the cellulose pulp
suspension. Treatment by the manganese catalyst can be either done before the
mechanical refining, during, or after the mechanical refining process. For
example, and as is discussed below, the catalyst/hydrogen peroxide may be
added to a pulp blend or a pulp stock chest, after mechanical refining, where
pulp
may be stored prior to dewatering.
The ratio between tensile strength and freeness is improved, i.e., either an
increased strength at the same freeness value or same strength at a lower
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freeness value. By monitoring the conditions of treatment optimum freeness
value
of a final product is obtained. Further, increased bulk at the same refining
can be
achieved, particularly important for tissue paper.
We have found that treating a cellulose pulp suspension and monitoring the
variables of concentration and time permits an optimum freeness value for
different periods of time.
The term oven dry pulp is one where pulp has been dried at 100-105 C to yield
a
constant weight. Reference is made to TAPPI-test T240 om-93 (1993).
REFINING
Different types of equipment are frequently used to mechanically treat the
cellulosic pulp. Beaters, including Hollander beaters, have been used in many
mills, but have now largely replaced by conical and disk refiners, which can
operate in continuous processes. Conical refiners are of the shallow angle
refiners
(Jordan), medium angle refiners (Conflo) and wide angle refiners (Claflin).
The
group disk refiners comprises three types, single disc, double disc multi-disc
refiners.
Refining can be done at low consistency (2-6%), medium consistency (10-20%) or
high consistency (30-35%). Depending on the requirements of the end product,
different choices for optimal consistency processing can be made. Reference is
made to Paper and Board Grades, Papermaking Part 1. Stock Preparation and
Wet End, Book 18, chapter 4, by the Finnish Paper Engineers' Association and
TAPPI (2000).
Processes can be either batch-wise or in a continuous manner, the latter being
often preferred due to cost reasons and easier control of quality.
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In many cases different types of wood pulp are mixed, such as softwood and
hardwood pulp. One of those or both may be refined independently. Often, more
refiners are employed in series, to enhance the benefits/energy requirements,
to
treat the pulp.
Refining may take place for chemical pulp, mechanical pulp and recycle pulp,
all
objects of the current invention.
Depending on the application, different levels of refining can be done. For
tissue
and kitchen towel grades, a low refining is carried out, to ensure a good
bulk,
softness, absorbancy and brightness. A low refining is beneficial for above
properties, but negatively impacts the strength properties. Therefore, often
wet-
and/or dry-strength agents are added. Shopper-Riegler values of between 10 and
30' are often obtained, after refining.
For printing and writing paper, printability and machine runnability are key
parameters. The paper must be clean and bright, have the appropriate
smoothness, compressibility, ink-penetration capabilities and sufficient
strength for
the printing operations. A minimum opacity is another important feature.
Therefore, these papers need good refining control to develop the internal
bond
strength and to obtain the right level of smoothness and formation for its end
use.
Bleached board grades, used a.o. for packaging frozen foods and liquids, and
for
paper plates and cups, need good stiffness and bulk with proper smoothness and
printability. Also internal bond, creasability and dimensional stability are
important
factors. Therefore sufficient refining to get these properties will also be
needed
(without decreasing the bulk and stiffness too much). Shopper-Riegler values
after
refining of between 15 and 50 0 are often needed for these applications.
Dense papers need significant amount of refining, depending on the particular
product needs. Release-base papers, glassine, and greaseproof paper all
require
extensive refining to get the desired balance of strength and appearance
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properties. Especially if the objective is to make transparent papers,
considerable
energy requirements are needed for the refining processes. SR values as high
900
can be needed.
Mechanical pulp needs often refining to produce the paper or board materials
exhibiting the appropriate physical properties. Shopper-Riegler values of
between
20 and 80 0 are often reached when refining mechanical pulp.
The extent of refining can be monitored on-line. Energy input is the most
important
parameter to determine the extent of refining. Control systems exist to on-
line
monitor the refining process and adjust energy input according the
requirements.
Probes to monitor the refiner load, temperature changes, flow/consistency,
drainage/freeness (SR), etc. Main process variables include temperature, pH,
consistency, additives, pretreatments, production rate, and applied energy.
Treatment of cellulosic fibers by manganese catalyst and hydrogen peroxide
Application of the manganese catalyst and hydrogen peroxide to treat the
cellulosic fibers can be done at different stages during the fiber
treatment/paper
making process. This can be either before the mechanical refining process,
during
the mechanical refining process or after the mechanical refining process,
typically
before or during the mechanical refining process.
Typically pulp that has been bleached in one or more delignification and
bleaching
stage, chemical pulp, can be used to treat further to produce tissue, paper or
board. However, within the scope of this invention, also lignin-containing
pulp
(mechanical pulp) or recycled wood pulp can be used. For integrated mills a
wet
pulp slurry is brought into the paper mill. When paper producers obtain pulp
from
other mills, the pulp sheets are first put into a chest and disintegrated to
obtain a
diluted pulp slurry, which can be further processed.
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In the pulp mills, chemical pulp is commonly bleached by hydrogen peroxide
and/or other bleaching processes using for example ozone or chlorine dioxide.
Mechanical and recycle pulp are often bleached with hydrogen peroxide to
increase brightness of the pulp. During one or more of these bleaching stages,
hydrogen peroxide together with the manganese catalyst can be employed to
obtain cellulose that can be treated in the refining process. The manganese
catalyst and hydrogen peroxide can be added during different stages in the
pulp
mill.
In a pulp mixer, chemicals are added to the pulp, which is then mixed very
thoroughly. Within the scope of this invention, catalyst and hydrogen peroxide
could be added to the pulp mixer to achieve treatment of the pulp. This can be
done in low consistency mixers (continuous stirred mixers, tower mixers,
dynamic
mixers or static mixers), medium consistency mixers (peg mixers, high shear
mixers) or high consistency mixers, including Kneader and disc-type mixers. In
a
steam mixer, steam is added to the pulp to increase the temperature of the
pulp.
The catalyst and hydrogen peroxide may also be added to the pulp in the steam
mixer.
Reference is made to Pulp Bleaching, Principle and Practice, C.W. Dence, D.W.
Reeve ed., Tappi, Atlanta, 1996, infra).
After adding the pulp bleaching chemicals in the mixers, the bulk of the pulp
bleaching takes place in the pulp bleaching tower, after which the pulp is
washed.
As bleaching processes are generally slow (2-4 h are typical), the bleaching
towers tend to be large. However, also smaller pulp retention pipes are
sometimes
employed to allow certain bleaching or treatment reactions to occur. As the
processes are generally continuous, the pulp is either moving slowly upwards
(upflow tower), downwards (downflow tower), or a combination thereof (upflow-
downflow tower). Within the scope of this invention, the treatment by the
catalyst
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and hydrogen peroxide, may be much shorter, allowing relatively small
treatment
towers.
In a pulp washer usually the pulp treated with chemicals in a previous stage
of the
treatment process are washed out. For example, acidic chlorine dioxide is
washed
with NaOH solution, to remove alkaline-soluble lignin residues and make the
pulp
ready for the next stage. Within the scope this invention, the manganese
catalyst
and hydrogen peroxide could be added into an (additional) mixer, making use of
its fast reaction kinetics to treat the pulp with the catalyst.
A pulp storage tower is designed to store pulp to process further after a
period of
time. Usually such storage tower can be found before the processes where the
pulp bleaching stages are taken place or after the final bleaching stage,
before
e.g. transporting to the paper mill. Catalyst and hydrogen peroxide can be
added
together with the pulp entering this storage tower, allowing a slow treatment
process of the pulp.
A pulper is used to dilute waste paper (deinked pulp) and to add alkaline and
hydrogen peroxide for bleaching of deinked pulp. The manganese catalyst could
be added in this pulper to allow the treatment of deinked pulp by the
catalyst.
Also the manganese catalyst and hydrogen peroxide can be added
to the cellulosic pulp before the refining process in the paper mill, such as
in the
pulper, high density pulp chest, pulp latency chest, pulp mixing chest or pulp
levelling chests. The pulper and high density chest are commonly used to
prepare
dry raw material, half stuff and recyle paper into a pumpable state by
addition of
water and then mixing with water. In the pulp mixing chest, two or more
different
types of pulp, optionally refined, are mixed and stored for further
processing, such
as softwood and hardwood pulp. In levelling chests the consistency of wood
pulp
is lowered to desired levels.
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Mechanical pulp is often treated in latency chests to treat the fibers that
are
distorted (kinked, curled, or twisted). Typically mechanical pulp is diluted
to 1-2%
consistency, heated to 70-90 C, agitated for at least 20 minutes, after which
it is
further processed. Pulp stock chests are, similarly to the pulp storage
described
above, used to store the wood pulp. Also the other above-mentioned chests are
often used to store the wood pulp and ensure a constant flow of pulp to be
treated
in the subsequent processes. The wood pulp may be shipped from pulp bleaching
mills or it may have been produced on site (integrated mill).
Alternatively the catalyst/hydrogen peroxide can be added just before the pulp
refiner and be allowed to react with the cellulose during the refining
process. Due
to heat evolution during refining, the additional energy requirement to obtain
an
optimal treatment effect by the catalyst will be reduced or absent. Different
refining
equipment can be used, which includes beaters; Hollander beaters; shallow-
angle
conical refiners; medium-angle conical refiners; wide-angle conical refiners;
single-disc refiners; double-disc refiners; multi-disc refiners. Reference is
made to
Paper and Board Grades, Papermaking Part 1. Stock Preparation and Wet End,
Book 18, chapter 4, by the Finnish Paper Engineers' Association and TAPPI
(2000) and C.F. Baker, Tappi Journal, 78, 147, 1995.
Finally, the catalyst/hydrogen peroxide may be added after the mechanical
refining stage, in for example in the pulp blend chest (where the different
wood
pulp sources are mixed) or pulp stock chest. For example mechanical pulp may
be treated this way.
Alternatively, the manganese catalyst together with hydrogen peroxide may be
employed both in a bleaching stage, and again after the bleaching stage, prior
to
or during the refining stage.
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TRANSITION METAL CATALYST
The manganese transition metal catalyst used may be non-deliquescent by using
counter ions such as PF6 or C104-. However, it is preferred for industrial
substrates that the transition metal complex is water soluble. It is preferred
that
the preformed transition metal is in the form of a salt such that it has a
water
solubility of at least 30 g/l, for example at least 50 g/I at 20 C. Preferred
salts are
those of chloride, acetate, sulphate, and nitrate. These salts are described
in WO
2006/125517.
According to particular embodiments of the invention, each R in the ligand of
formula (I) is independently selected from: hydrogen, C1-C6-alkyl, C2OH,
C1COOH, and pyridin-2-ylmethyl. According to particular embodiments, R is
independently selected from: hydrogen, CH3, C21-15, CH2CH20H and
CH2COOH.
Preferably, R1, R2, R3, and R4 are independently selected from: H and Me.
According to particular embodiments, R, R1, R2, R3, and R4 are independently
selected from: H and Me. Most preferably, the catalyst is derived from 1,4,7-
trimethyl-1,4,7-triazacyclononane (Me3-TACN).
The preformed transition metal catalyst salt is preferably a dinuclear Mn(III)
or
Mn(IV) complex with at least one 02" bridge. According to certain embodiments
of
the invention, the transition metal catalyst may be a salt, such as the salts
described hereinbefore, of the complex [Mn(IV)2( -O)3(Me3TACN)2]2+.
The level of application of the manganese catalysts can vary depending on the
application, but will be typically between 0.0005 and 0.2 kg/t oven-dry pulp
(o.d.p.).
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HYDROGEN PEROXIDE
The hydrogen peroxide is provided as an aqueous solution per se, or as peroxy
salts, such as, percarbonate, etc. However, for cost reasons liquid hydrogen
peroxide is preferred. A preferred level of hydrogen peroxide applied is: 0.1
kg/t to
100 kg/t oven dry pulp (o.d.p.), more preferable 0.3 to 50 kg/t o.d.p. and
most
preferred 0.5 to 25 kg/t o.d.p.
The reagents are preferably provided in an alkali medium, optimally between pH
8
and 13, the alkalinity of which is preferably provided by sodium hydroxide or
sodium carbonate.
The temperature of the treatment process is preferably between 30 C and 95 C
and more preferably between 40 C and 90 C.
The time of the treatment with the catalyst and hydrogen peroxide is between 1
minute and 4 hours, more preferably between 5 minutes and 3 hours, and most
preferably between 10 minutes and 2 hours.
SEQUESTRANT
Many sequestrants are suitable for use with the present invention. Examples
include aminophosphonate and carboxylate sequestrants, for example
aminophosphonate and aminocarboxylate sequestrants. Suitable sequestrants
include ethylenediamine tetra-acetate (EDTA), the polyphosphonates such as
DequestTM and non-phosphate stabilisers such as EDDS (ethylene diamine di-
succinic acid).
The sequestrant used in the treatment step with manganese catalyst and
hydrogen peroxide is preferably an aminocarboxylate sequestrant or mixtures
thereof. The following are preferred examples of aminocarboxylate
sequestrants:
ethylenediaminetetraacetic acid (EDTA), N-hydroxyethylenediaminetetraacetic
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acid (HEDTA), iminodisuccinic acid (IDS), nitrilotriacetic acid (NTA), N-
hyd roxyethylaminodiacetic acid, diethylenetriaminepentaacetic acid (DTPA),
methylglycinediacetic acid (MGDA), ethylenediamine di-succinic acid (EDDS) and
alanine-N,N-diacetic acid. A most preferred aminocarboxylate sequestrant is
diethylenetriaminepentaacetic acid (DTPA).
Phosphonate sequesterents may also be used; a preferred phosphonate
sequestrant is Dequest 2066 (Diethylenetriamine Penta(methylene phosphonic
acid sodium salt).
It will be understood that, where used, a sequestrant may be present in the
free
acid or salt form. For example, were present in salt form, this may be an
alkali
metal, alkaline earth metal, ammonium or substituted ammonium salt. Typically,
a
sequestrant, if present, is in its free acid form or as a sodium, potassium or
magnesium salt. An example of a sodium salt of an aminocarboxylate
sequestrant is the pentasodium salt of diethylenetriamine penta(methylene
phosphonic acid, commercially available under the trade name Dequest 2066A.
The most preferred concentration of the sequestrant used in the method is 0.01
to
50 kg/ton oven dry pulp in the solution containing the manganese catalyst and
hydrogen peroxide, most preferably 0.03 to 20 kg/ton oven dry pulp.
EXPERIMENTAL
Experiment 1: Treatment of softwood pulp with hydrogen peroxide with and
without [Mn2( -O)3(Me3TACN)2](CH3000)2 at pH 11.0 (Me3-TACN = 1,4,7-
Trimethyl-1,4,7-triazacyclononane).
[Mn2( -O)3(Me3TACN)2](CH3000)2 (as 3.5% aqueous solution) was obtained as
disclosed elsewhere (W02006/125517).
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Softwood pulp with a starting ISO-brightness of 49.9 was treated as follows:
To a
polyethylene (PE) bottle containing 250 g of oven-dry pulp at 10% consistency,
was added 10 kg/odtp H202 (odtp=oven-dry ton pulp - equals to 29.4 mM H202)
and 7.2 kg/odtp NaOH (equals to 18 mM NaOH). Depending on the experiments
0.04 kg/odtp [Mn2(4-O)3(Me3TACN)2](CH3000)2 (equals to 6.5 pM [Mn2( -
O)3(Me3TACN)2](CH3000)2)was added and 1.0 kg/odtp DTPA
(Diethylenetriaminepenta-acetic acid, pentasodium salt) - (ex Akzo Nobel;
trade
name Dissolvine D50; purity is 50%). The initial pH-value was pH 11.0
(measured
at 20 C).
Note 1: This softwood pulp has been delignified in a 02-delignification step,
and
partly further bleached by a C102 step.
Note 2: In practice, pulp was used that contained 35.6% dry matter and 64.4%
water (35.6% dry content). Therefore 702.3 g of 'wet' pulp was used for each
experiment.
Note 3: All experiments were carried out at 10% consistency.
The PE bottles are put in a pre-heated water bath (62.5 C) for 1 hour and are
shaken throughout the bleaching process. Subsequently the pulp mixture is
filtrated through a Buchner funnel and washed with copious amounts of
demineralised water. Using the filtrate, the H202 consumption is measured. The
following analyses are carried out on the bleached pulp: kappa number,
brightness and intrinsic viscosity.
The results of the experiments are given in Table 1.
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Table 1 Results of treatment of softwood pulp using [Mn2(.i-
O)3(Me3TACN)2](CH3000)2, [Mn2( -O)3(Me3TACN)2](CH3000)2 and DTPA and
no [Mn2( -O)3(Me3TACN)2](CH3000)2 at an initial pH 11.0 at 60 C for 60
minutes.
No Sample Brightness Intr. Kappa H202
(ISO %) Visc. # consumption
(ml/g) (kg/odtp)
U Untreated (raw) 49.9 764 8.33
P1 Blank (no catalyst, no 67.4 753 4.27 7.5
DTPA)
P2 0.04 kg/odtp [W2( -O)3 68.1 701 4.11 7.8
(Me3TACN)2](CH3000)2
and 1 kg/odtp DTPA
P3 0.04 kg/odtp [Mn2( - 66.8 698 4.17 9.6
O)3(Me3TACN)2](CH3000)2
The results gathered in Table 1 show that the addition of [Mn2( -
O)3(Me3TACN)2](CH3000)2 has some effect on the bleaching and kappa value
and a clear effect on viscosity (degree of cellulose polymerization) of
softwood
pulp.
The treated pulp was desintegrated (DIN EN ISO 5263-1; 2004-12), beaten (PFI-
mill) ((NORM EN ISO 5264-2; 2003-05) and the drainability (Schopper-Riegler
method, ONORM EN ISO 5267-1; 2000-10) was tested.
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Laboratory handsheets were prepared by the Rapid-Kothen method (ONORM EN
ISO 5269-2; 2005-04) and conditioning of the samples, NC 23/50 was carried out
(DIN EN 20187; 1993-11). The following tests were conducted using the
handsheets: grammage (DIN EN ISO 536; 1996-08), thinkness, bulk and density
(DIN EN ISO 534; 2005-05), air permeance (Bendtsen, ISO 5636/3; 1992-09),
tensile force, stretch at break, tensile strength, tensile index, TEA and
elastic
modulus (DIN EN ISO 1924-2; 2009-05), internal bond strength (z-direction,
TAPPI 541 om-05; 2005), tearing resistance, tear index (ONORM EN 21974;
1994-09).
The results are given in the following tables.
Table 2 Results of beating and drainability of bleached softwood pulp after
having
been treated according to the conditions given in Table 1.
P1: no catalyst, no DTPA
P2: [Mn2( -O)3(Me3TACN)2](CH3000)2 and DTPA
P3 [Mn2( -O)3(Me3TACN)2](CH3000)2 without DTPA
Sample P1 P2 P3
Drainability [SR] [SR] [SR]
Unbeaten 14.0 13.8 14.0
PFI 2000 Revolutions 15.9 16.2 16.9
PFI 5000 Revolutions 24.1 24.3 23.2
PFI 7000 Revolutions 32.7 32.8 32.9
PFI 9000 Revolutions 41.6 46.5 45.5
The results gathered in Table 2 show that the pulp samples treated with the
catalyst and hydrogen peroxide exhibit similar SR values till 7000 revolutions
as
the reference, whilst increase SR values are obtained when the pulp is refined
at
9000 revolutions.
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Table 3 Strength and tear values of handsheets prepared using pulp refined at
5000 revolutions as shown in Table 2.
Sample P1 P2 P3
5000rev 5000rev 5000rev
Grammage [g/M21 80.2 81.0 80.2
Thickness [pm] 111 112 113
Density [g/cm ] 0.724 0.725 0.711
Bulk [cm /g] 1.380 1.380 1.407
Air permeance (Bendtsen) [ml/min] 429 435 560
Tensile force [N] 101 111 108
Stretch at break [%] 2.96 2.89 2.89
Tensile strength [kN/m] 6.74 7.42 7.21
Tensile index [Nm/g] 84.1 91.6 89.9
TEA [JIM 2] 136 144 141
Elastic modulus [GPa] 6.33 6.92 6.76
Internal bond strength [N/cm ] 82.6 81.5 84.1
Tearing resistance [mN] 877 827 814
Tear index [mN.m /g] 10.9 10.2 10.2
The results gathered in Table 3 show that the pulp samples treated with the
catalyst and hydrogen peroxide and then refined at 5000 revolutions in the PFI
mill, show increased tensile strength, tensile energy absorption (TEA) and
tensile
index values, decreased tearing resistance and tear index, whilst the other
parameters are largely unaffected by the treatment using the catalyst and
hydrogen peroxide (all with respect to reference without catalyst - P1). A
slight
enhanced of these tensile strength properties when the catalyst was employed
in
combination with DTPA.
