U.S. patent application number 13/697130 was filed with the patent office on 2014-01-02 for freeness of paper products.
This patent application is currently assigned to CATEXEL LIMITED. The applicant listed for this patent is Ronald Hage, Kimberly Soraya Yang. Invention is credited to Ronald Hage, Kimberly Soraya Yang.
Application Number | 20140000824 13/697130 |
Document ID | / |
Family ID | 42340037 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140000824 |
Kind Code |
A9 |
Hage; Ronald ; et
al. |
January 2, 2014 |
FREENESS OF PAPER PRODUCTS
Abstract
The present invention provides for the optimisation of
conditions for treating pulp with a catalyst and hydrogen peroxide
to produce a Freeness value (SR) in a web produced from the treated
pulp such that the energy required in mechanical agitation of the
pulp is reduced.
Inventors: |
Hage; Ronald; (Leiden,
NL) ; Yang; Kimberly Soraya; (Leiden, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hage; Ronald
Yang; Kimberly Soraya |
Leiden
Leiden |
|
NL
NL |
|
|
Assignee: |
CATEXEL LIMITED
London
UK
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130126111 A1 |
May 23, 2013 |
|
|
Family ID: |
42340037 |
Appl. No.: |
13/697130 |
Filed: |
May 9, 2011 |
PCT Filed: |
May 9, 2011 |
PCT NO: |
PCT/GB2011/000709 PCKC 00 |
371 Date: |
February 1, 2013 |
Current U.S.
Class: |
162/76; 162/100;
162/72; 162/78 |
Current CPC
Class: |
D21C 9/1042 20130101;
D21D 1/00 20130101; D21C 9/1078 20130101; D21F 1/0009 20130101;
D21C 9/10 20130101; D21C 9/163 20130101; D21C 9/001 20130101; D21D
1/20 20130101 |
Class at
Publication: |
162/76; 162/78;
162/72; 162/100 |
International
Class: |
D21D 1/20 20060101
D21D001/20 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2010 |
EP |
10162405.4 |
Claims
1. A method for the treatment of a cellulose pulp suspension
comprising: (i) subjecting cellulose pulp fibres to an aqueous
solution of a preformed manganese transition metal catalyst and
hydrogen peroxide at pH from 6 to 13, 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; (ii)
subjecting the cellulose pulp fibres treated by step (i) to a
refining process until a Shopper Riegler (SR) value of from 10 to
90.degree. is reached and the resultant pulp is processed into
paper, tissue or board; and wherein the manganese transition metal
catalyst is 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, having a ligand of formula
(I): ##STR00003## p is 3; R is independently selected from the
group consisting of: hydrogen, C.sub.1-C.sub.6-alkyl,
CH.sub.2CH.sub.2OH, CH.sub.2COOH, and pyridin-2-ylmethyl; and
R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are independently selected
from the group consisting of: H, C.sub.1-C.sub.4-alkyl, and
C.sub.1-C.sub.4-alkylhydroxy.
2. The method according to claim 1, wherein the manganese
transition metal catalyst is present at a concentration from 0.0005
to 0.2 kg/tonne oven-dry pulp and the hydrogen peroxide is present
at a concentration from 0.1 to 25 kg/tonne oven-dry pulp.
3. The method according to claim 1, wherein R is independently
selected from the group consisting of: hydrogen, CH.sub.3,
C.sub.2H.sub.5, CH.sub.2CH.sub.2OH, and CH.sub.2COOH.
4. The method according to claim 1, wherein R, R.sub.1, R.sub.2,
R.sub.3, and R.sub.4 are independently selected from: H and Me.
5. The method according to claim 1, wherein the catalyst is derived
from 1,4,7-trimethyl-1,4,7-triazacyclononane (Me.sub.3-TACN).
6. The method according to claim 1, wherein the pulp is subjected
to a refining process until a Shopper Riegler (SR) value of from 10
to 30.degree. is reached, to produce tissue paper.
7. The method according to claim 1, wherein the pulp is subjected
to a refining process until a Shopper Riegler (SR) value of from 15
to 50.degree. is reached, to produce printing and writing
paper.
8. The method according to claim 1, wherein the pulp is subjected
to a refining process until a Shopper Riegler (SR) value of from 50
to 90.degree. is reached, to produce tracing and transparent
paper.
9. The method according to claim 1, wherein mechanical pulp is
subjected to a refining process until a Shopper Riegler (SR) value
of from 20 to 80.degree. is reached.
10. The method according to claim 1, wherein the catalyst and
hydrogen peroxide is added to the cellulose pulp fibres in a device
selected from the group consisting of: a pulper, a high density
pulp chest, a pulp washer, a pulp latency chest, a pulp levelling
chest, a pulp mixing chest, a pulp refiner, a pulp dilution tank,
and a pulp stock chest.
11. The method according to claim 10, wherein the pulp refiner is
selected from the group consisting of: beaters, Hollander beaters,
shallow-angle conical refiners, medium-angle conical refiners,
wide-angle conical refiners, single-disc refiners, double-disc
refiners, and multi-disc refiners.
12. The method according to claim 1, further comprising bleaching
the cellulose pulp fibres, wherein the manganese transition metal
catalyst and hydrogen peroxide in step (i) is added during the
bleaching.
13. The method according to claim 12, wherein the manganese
transition metal catalyst and hydrogen peroxide is added to the
cellulose pulp fibres in a device selected from the group
consisting of a pulp mixer, a pulp bleaching tower, a pulp
retention pipe, a pulp washer, a pulp storage tower, a steam mixer,
and a pulper.
14. The method according to claim 1, wherein the cellulose pulp
fibres have been previously subjected to a bleaching stage.
15. The method according to claim 1, wherein the aqueous solution
of step (i) further comprises from 0.01 to 50 kg/ton oven dry pulp
of an organic sequestrant selected from: an aminophosphonate
sequestrant and a carboxylate sequestrant.
16. The method according to claim 15, wherein the organic
sequestrant is selected from the group consisting of:
diethylenetriamine penta(methylene phosphonic acid sodium salt),
MGDA (methylglycindiacetate), GLDA (glutamic acid diacetate), IDS
(iminodissucinate), EDDS (ethylenediaminedisuccinate), EDTA
(ethylenediamine-tetraacetate), and DTPA
(diethylenetriamine-pentaacetate).
17. A method according to claim 1, wherein an energy input into the
refining process is monitored and based upon an energy input
threshold for cellulose pulp fibres to be processed into paper,
tissue, or board.
18. (canceled)
19. (canceled)
20. Paper, tissue or board obtained by a method according to claim
1.
Description
FIELD OF INVENTION
[0001] The present invention relates to a new refining process for
paper pulp.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] 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.
[0004] 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 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.
[0005] 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.
[0006] 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.
[0007] EP 0458397 discloses the use manganese
1,4,7-Trimethyl-1,4,7-triazacyclononane (Me.sub.3-TACN) complexes
as bleaching and oxidation catalysts and use for textile and pulp
bleaching processes.
[0008] United States Application 2001/0025695A1, Patt et al,
discloses the use of ClO.sub.4.sup.- and PF.sub.6.sup.- salts of
manganese complexes of
1,2,-bis-(4,7,-dimethyl-1,4,7,-triazacyclonon-1-yl)-ethane
(Me.sub.4-DTNE) and Me.sub.3-TACN respectively for wood-pulp
delignification and bleaching. Whilst a loss of viscosity reported
when using a manganese compound comprising Me.sub.4-DTNE is absent
or small, the viscosity loss when using a manganese compound
comprising Me.sub.3-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).
[0009] WO 2007/125517 discloses the use of
1,2,-bis-(4,7,-dimethyl-1,4,7,-triazacyclonon-1-yl)-ethane
(Me.sub.4-DTNE) and Me.sub.3-TACN with buffer and sequestrants for
bleaching of cellulosic substrates.
[0010] WO 2008/086937 discloses the use of
1,2,-bis-(4,7,-dimethyl-1,4,7,-triazacyclonon-1-yl)-ethane
(Me.sub.4-DTNE) and Me.sub.3-TACN for bleaching of cellulosic
substrates whilst keeping the pH constant.
[0011] US 2002/0066542 A1 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
Me.sub.3-TACN showed a market loss in viscosity, whilst the other
compounds described did not show significant changes in
viscosity.
[0012] 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
[0013] 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).
[0014] 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
Me.sub.3-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.
[0015] The present invention may be applied to chemical and
mechanical pulp, including recycling pulp, for production of paper,
tissue or board.
[0016] 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.
[0017] 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 90.degree. 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(III)Mn(IV) or
Mn(IV)Mn(IV) transition metal catalyst, the ligand of the
transition metal catalyst of formula (I):
##STR00001## [0018] p is 3; [0019] R is independently selected
from: hydrogen, C1-C6-alkyl, C2OH, C1COOH, and pyridin-2-ylmethyl
or one of R is linked to the N of another Q from another ring via
an ethylene bridge; [0020] R1, R2, R3, and R4 are independently
selected from: H, C1-C4-alkyl, and C1-C4-alkylhydroxy.
[0021] 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):
##STR00002## [0022] p is 3; [0023] R is independently selected
from: hydrogen, C1-C6-alkyl, C2OH, C1COOH, and pyridin-2-ylmethyl
or one of R is linked to the N of another Q from another ring via
an ethylene bridge; [0024] R1, R2, R3, and R4 are independently
selected from: H, C1-C4-alkyl, and C1-C4-alkylhydroxy, [0025] for
increasing the extent to which the Freeness Value of cellulose pulp
fibres is increased in a refining process.
[0026] 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: hydrogen, C1-C6-alkyl, C2OH, C1COOH,
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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.degree. C. and more
preferably between 40 to 90.degree. C. The pH of the process using
the catalyst and hydrogen peroxide is preferably between pH 8 and
12.
[0031] 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 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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).
[0037] 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.
[0038] The molar ratio of transition metal catalyst:hydrogen
peroxide is preferably in the range from 1:100 to 1:10000.
[0039] 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
[0040] 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. 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.
[0041] 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.degree. F. (93.degree.
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.
[0042] 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).
[0043] 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.
[0044] 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 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.
[0045] 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.
[0046] The term oven dry pulp is one where pulp has been dried at
100-105.degree. C. to yield a constant weight. Reference is made to
TAPPI-test T240 om-93 (1993).
[0047] Refining
[0048] 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.
[0049] 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).
[0050] 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.
[0051] 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.
[0052] Refining may take place for chemical pulp, mechanical pulp
and recycle pulp, all objects of the current invention.
[0053] 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.degree. are often obtained, after refining.
[0054] 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.degree. are often needed for these applications.
[0055] 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 properties. Especially if the
objective is to make transparent papers, considerable energy
requirements are needed for the refining processes. SR values as
high 90.degree. can be needed.
[0056] 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.degree. are often
reached when refining mechanical pulp.
[0057] 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.
[0058] Treatment of Cellulosic Fibers by Manganese Catalyst and
Hydrogen Peroxide
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] Reference is made to Pulp Bleaching, Principle and Practice,
C. W. Dence, D. W. Reeve ed., Tappi, Atlanta, 1996, infra).
[0064] 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 and
hydrogen peroxide, may be much shorter, allowing relatively small
treatment towers.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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 recycle 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.
[0069] 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.degree. 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).
[0070] 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.
[0071] 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.
[0072] 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.
[0073] Transition Metal Catalyst
[0074] The manganese transition metal catalyst used may be
non-deliquescent by using counter ions such as PF.sub.6.sup.- or
ClO.sub.4.sup.-. 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/l at 20.degree. C. Preferred salts are those of
chloride, acetate, sulphate, and nitrate. These salts are described
in WO 2006/125517.
[0075] 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, C2H5, CH2CH2OH and CH2COOH.
[0076] Preferably, R1, R2, R3, and R4 are independently selected
from: H and Me.
[0077] 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
(Me.sub.3-TACN).
[0078] The preformed transition metal catalyst salt is preferably a
dinuclear Mn(III) or Mn(IV) complex with at least one O.sup.2-
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).sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2].sup.2+.
[0079] 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.).
[0080] Hydrogen Peroxide
[0081] 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.
[0082] 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.
[0083] The temperature of the treatment process is preferably
between 30.degree. C. and 95.degree. C. and more preferably between
40.degree. C. and 90.degree. C.
[0084] 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.
[0085] Sequestrant
[0086] 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 Dequest.TM. and
non-phosphate stabilisers such as EDDS (ethylene diamine
di-succinic acid).
[0087] 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 acid (HEDTA), iminodisuccinic
acid (IDS), nitrilotriacetic acid (NTA),
N-hydroxyethylaminodiacetic 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).
[0088] Phosphonate sequestrants may also be used; a preferred
phosphonate sequestrant is Dequest 2066 (Diethylenetriamine
Penta(methylene phosphonic acid sodium salt).
[0089] 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.
[0090] 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.
[0091] Experimental
[0092] Experiment 1: Treatment of softwood pulp with hydrogen
peroxide with and without
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2 at
pH 11.0
(Me.sub.3-TACN=1,4,7-Trimethyl-1,4,7-triazacyclononane).
[0093]
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2 (as
3.5% aqueous solution) was obtained as disclosed elsewhere
(WO2006/125517).
[0094] 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
H.sub.2O.sub.2 (odtp=oven-dry ton pulp--equals to 29.4 mM
H.sub.2O.sub.2) and 7.2 kg/odtp NaOH (equals to 18 mM NaOH).
Depending on the experiments 0.04 kg/odtp
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2
(equals to 6.5 .mu.M
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.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.degree. C.).
[0095] Note 1: This softwood pulp has been delignified in a
O.sub.2-delignification step, and partly further bleached by a
ClO.sub.2 step.
[0096] 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.
[0097] Note 3: All experiments were carried out at 10%
consistency.
[0098] The PE bottles are put in a pre-heated water bath
(62.5.degree. 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 H.sub.2O.sub.2
consumption is measured. The following analyses are carried out on
the bleached pulp: kappa number, brightness and intrinsic
viscosity.
[0099] The results of the experiments are given in Table 1.
TABLE-US-00001 TABLE 1 Results of treatment of softwood pulp using
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2,
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2 and
DTPA and no
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2 at
an initial pH 11.0 at 60.degree. C. for 60 minutes. H.sub.2O.sub.2
Intr. con- Brightness Visc. Kappa sumption N.degree. Sample (ISO %)
(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
[Mn.sub.2(.mu.-O).sub.3 68.1 701 4.11 7.8
(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2 and 1 kg/odtp DTPA P3 0.04
kg/odtp [Mn.sub.2(.mu.- 66.8 698 4.17 9.6
O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2
[0100] The results gathered in Table 1 show that the addition of
[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2 has
some effect on the bleaching and kappa value and a clear effect on
viscosity (degree of cellulose polymerization) of softwood
pulp.
[0101] The treated pulp was desintegrated (DIN EN ISO 5263-1;
2004-12), beaten (PFI-mill) (ONORM EN ISO 5264-2; 2003-05) and the
drainability (Schopper-Riegler method, ONORM EN ISO 5267-1;
2000-10) was tested.
[0102] 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).
[0103] The results are given in the following tables.
TABLE-US-00002 TABLE 2 Results of beating and drainability of
bleached softwood pulp after having been treated according to the
conditions given in Table 1. 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 P1: no catalyst, no DTPA
P2:[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2
and DTPA
P3[Mn.sub.2(.mu.-O).sub.3(Me.sub.3TACN).sub.2](CH.sub.3COO).sub.2
without DTPA
[0104] 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.
TABLE-US-00003 TABLE 3 Strength and tear values of handsheets
prepared using pulp refined at 5000 revolutions as shown in Table
2. P1 P2 P3 Sample 5000rev 5000rev 5000rev Grammage [g/m.sup.2]
80.2 81.0 80.2 Thickness [.mu.m] 111 112 113 Density [g/cm.sup.3]
0.724 0.725 0.711 Bulk [cm.sup.3/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 [J/m.sup.2] 136
144 141 Elastic modulus [GPa] 6.33 6.92 6.76 Internal bond strength
[N/cm.sup.2] 82.6 81.5 84.1 Tearing resistance [mN] 877 827 814
Tear index [mN m.sup.2/g] 10.9 10.2 10.2
[0105] 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.
* * * * *