Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND CHEMICAL COMPOSITION TO IMPROVE EFFICIENCY OF
MECHANICAL PULP
Cross-Reference to Related Applications
None.
Statement Regarding Federally Sponsored Research or Development
Not Applicable.
Background of the Invention
This invention relates to improving fiber quality and process efficiency in
to mechanical pulping. More specifically, the invention relates to using
specialty chemical
compositions such as combinations of a reductive chemical and a chelant in an
alkaline medium
to improve the process efficiency and brightness of a paper product produced
from a pulp
material manufactured in such a process. The invention has particular
relevance for decreasing
freeness, providing energy and chemical savings, and enhancing brightness of
paper products.
Mechanical pulping is a common method to produce pulp. One advantage
mechanical pulping has over other pulping methods is that the pulping process
does not result in
a significant loss of mass. Mechanical pulping operations unfortunately are
very energy-intensive
and they tend to produce pulps with low strength. Chemical treatment, such as
alkalization, is
sometimes used to increase strength and save energy, at the expense of
brightness. Several
technologies are currently practiced in mechanical pulping to manufacture
products such as stone
ground wood (SGW), pressurized ground wood (PGW), refiner mechanical pulp
(RMP),
pressurized RMP (PRMP), thermo-RMP (TRMP), and thermo-mechanical pulp (TMP).
One currently known method of reducing the energy required in mechanical
pulping is through alkalization that leads to reducing the freeness of the
pulp. The common prior
art method of reducing the freeness of pulp is to add alkali to wood chips
during the mechanical
pulping process. Unfortunately, adding alkali to wood chips also causes a drop
in the brightness
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of the resulting paper. To compensate for this brightness drop, additional
bleach must be added
during the bleaching stage of the papermaking process thereby reducing or
eliminating any
overall cost savings.
As a result, papermakers are forced to make an undesirable tradeoff. They must
either choose to reduce energy costs but accept a loss in brightness or they
must use additional
bleach and sacrifice cost savings. Thus there is a clear need for a technology
that provides energy
savings without jeopardizing optical properties of paper made from such pulp.
Brief Summary of the Invention
At least one embodiment of the invention is directed towards a composition and
a
method of its use. The composition improves the papermaking process. The
composition
comprises a base, a small quantity of a strong reductive chemical, and a
chelating agent. The
composition is added to the papermaking process before or during the
mechanical pulping of
wood chips. The composition decreases the energy consumption in pulp
manufacturing but does
not induce a net decrease in brightness of paper produced from the paper pulp
when compared to
paper similarly produced from similar paper pulp that did not have the
composition added to its
wood chips. The composition can be an aqueous solution or slurry capable of
being applied at
any stage of the mechanical pulping process, before or during the refining,
e.g., in a wood chip
washing operation, chip soaking, sprayed over the chips, and may be capable of
being added
directly into a refiner.
At least one embodiment of the invention is directed towards a composition
wherein the base is selected from the list consisting of: an alkali or
alkaline earth metal hydroxide
such as sodium hydroxide, magnesium hydroxide and any combination thereof. One
preferred
composition can induce the resulting pulp to be more effectively bleached by
peroxide or
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hydrosulfite bleaching including but not limited to treatment with magnesium
hydroxide.
Treatment of wood chips before or during mechanical pulping with small
quantities of
magnesium hydroxide, activates the pulp to subsequent bleaching, specifically
peroxide
bleaching.
At least one embodiment of the invention is directed towards a composition in
which the reductive chemical is selected from the list consisting of: water
soluble
hydrosulfites (dithionites), sulfites, bisulfites, metabisulfites,
formidinesulfinic acid, salts of
formidinesulfinic acid, borohydrides, phosphines, phosphonium tertiary salts;
more
specifically, alkali or alkaline earth metal hydrosulfites, borohydrides,
sodium hydrosulfite,
sodium borohydride and any combination thereof. The chelating agent can be a
transitional
metal ion chelant selected from the list consisting of: organic hydroxyacids,
aminophosphonates, aminophosphates, aminocarboxylates; more specifically,
salts of DTPA,
salts of EDTA, salts of DTMPA, and any combination thereof.
In a specific aspect, the present invention relates to a method of improving a
mechanical pulping process, the method comprising: adding a composition
comprising sodium
borohydride, sodium hydroxide, a chelant, magnesium hydroxide, and a reductive
chemical
selected from the group consisting of a hydrosulfite, a dithionite, a sulfite,
a bisulfite, a
metabisulfite, formidinesulfinic acid, a salt of formidinesulfinic acid, a
borohydride, a
phosphine, a tertiary phosphonium salt, an alkali, an alkaline earth metal
hydrosulfite, sodium
hydrosulfite, sodium borohydride, and any combination thereof to a pulp
material prior to the
conclusion of a mechanical pulping process, wherein the magnesium hydroxide is
in a dosage
of 0.05-0.5 wt%; bleaching the pulp material after adding the composition.
Detailed Description of the Invention
The following definitions are provided to determine how terms used in this
application, and in particular how the claims, are to be construed. The
organization of the
definitions is for convenience only and is not intended to limit any of the
definitions to any
particular category.
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"CSF" means Canadian Standard Freeness a described by TAPPI methods and
standards and measured in millimeters.
"Freeness" means the measure of the rate at which a suspension of pulp may be
drained, and is typically measured according to the Canadian Standard Freeness
test, as
defined by TAPPI methods and standards. Changes in freeness can result from
both chemical
and physical changes in pulp.
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"Mechanical pulping" means a physical change caused by converting pulpwood
logs and chips into pulp by the use of mechanical energy.
"Chemimechanical pulping" means a mild chemical change occurring in a wood
grinding or chip refining process. Chemimechanical pulping commonly improves
paper strength
or facilitates paper production.
"Refiner groundwood" means mechanical pulp made with a grinder and put
through a rubbing, brushing, crushing, fraying, or cutting treatment in a pulp
mill processing
machine called a refiner.
"Refiner mechanical pulp" means pulp made by processing untreated wood chips
in mechanical atmospheric refiners.
"Refiner" means a machine for mechanical treating fibers in pulp and paper
mils
when rubbing, brushing, crushing, fraying, or cutting is desired to process or
impart certain
properties to the finished pulp slurry and the sheet web formed on the paper
machine.
"Small Quantity" means a concentration of an additive added to a suspension of
paper pulp, which is insufficient to induce any substantial chemical changes
in the pulp that are
normally associated with chemimechanical pulping.
It has been known that causing a change in freeness, normally caused by
alkalization, can reduce the energy needed in the pulping process (see for
example US Published
Application 2008/0105392). In at least one embodiment, very small quantities
of chemicals are
added to wood chips that results in low energy costs when the wood chips are
mechanically
pulped. The low energy costs are the result of a synergistic combination of
the chemicals that
both reduces pulp freeness and improves brightness of the pulp. Normally,
freeness reduction
results from the changes in physical pulp properties such as swelling of
fibers. Alkaline
environments can cause such swelling. However because alkali environments also
increase
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coddation and cause phenolic group ionization in lignin, which is always
present in a high-yield
(mechanical) pulp, it causes yellowing of the resulting paper. As a result
either the paper has a
lower brightness or more bleaching chemicals must be used, thereby increasing
costs.
In the Invention, this problem is addressed in two ways. First, magnesium
hydroxide is used as a source of alkalinity. The magnesium hydroxide activates
the pulp in the
following peroxide or hydrosulfite bleaching stages, thereby increasing the
degree of brightness
that results from bleaching. Second, the reaction in the refiner is adjusted
to be reductive not
oxidative. This also inhibits any brightness loss that uncontrolled oxidation
would otherwise
cause. In addition, a chelating agent may be added which further reduces any
yellowing because
to it immobilizes transition metal cations that could otherwise catalyze
yellowing reactions. In at
least onc embodiment, magnesium hydroxide is combined with one or more
reducing agents and,
optionally, one or more chelating agents prior to the refining or in the
refiner. In at least one
embodiment, this combination is followed by peroxide bleaching.
In this application the specialty chemicals are used in very small quantities
and are
believed to operate against the pulp only at a mechanical level and not at a
chemimechanical
level. Because of the low quantity used, no significant chemical changes occur
in the pulp. The
low quantity of specialty chemicals, however, is sufficient to cause the
freeness reduction in the
pulp and thereby reduce the energy consumption during the mechanical pulping
process. Because
relatively little chemical changes occur in the pulp, this method can freely
be used with most if
not all currently known techniques used in most operating mills manufacturing
mechanical pulp,
which include but are not limited to TMP, RMP, and/or groundwood based pulps.
In at least one embodiment, small quantities of at least one reductive
chemical and
at least one chelant in an alkaline medium are used to treat wood chips during
manufacturing of
mechanical pulp. When these chemicals are so combined, instead of the
brightness loss that is
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typical of alkaline treatments, a brightness gain occurs.
In at least one embodiment, the small quantity of at least one reductive
chemical
and at least one chelant in an alkaline medium, applied prior to or at the
refining stage, enhances
the bleaching process performed later in the paperrnaking process. In at least
one embodiment,
the specialty chemicals added prior to or at the refining stage (e.g.,
magnesium hydroxide alone
or in a mixture with reductive chemical(s) and, optionally, chelant(s)) induce
pulp activation
towards subsequent bleaching, which then requires less bleaching materials to
achieve the same
degree of brightness. In at least one embodiment, the bleaching is peroxide or
hydrosulfite
bleaching.
to In at least one embodiment, at least one of the sources of alkali is
magnesium
hydroxide (MID. In at least one embodiment, the MH is used by itself, and the
positive effect on
brightness is observed after the peroxide or hydrosulfite bleaching stage. In
at least one
embodiment, the MH is combined with sodium hydrosulfite and a chelant.
In at least one embodiment, at least one of the reductive chemicals is sodium
hydrosulfite (SH). In at least one embodiment, the SH is combined with
magnesium hydroxide
and a chelant. In at least one embodiment, small quantities of a strong
reductive chemical such as
SH with or without sodium borohydride (BH) are combined with MH. In at least
one
embodiment, small quantities of a strong reductive chemical such as SR with or
without BH are
combined with sodium hydroxide.
In at least one embodiment, at least one of the reductive chemicals is very
small
quantity of BH. In at least one embodiment, the BH is combined with sodium
hydrosulfite and a
chelant. In at least one embodiment the source of alkali is MH. In at least
one embodiment, a
small quantity of a strong reductive chemical such as SH with or without BH
are combined with
MH.
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This method makes use of chemicals commonly available in paper mills but uses
them in a novel manner. As shown in the following references, while use of BH
and hydrosulfite
is known in paper manufacture, it has only been used in bleaching processes,
under neutral to
slightly acidic conditions, and in kraft pulping processes, and not in
mechanical pulping
processes. (See for example patents and patent applications: US 5,129,987, EP
141826, US
2004/0000380, EP 485074,WO 88010334, EP 00027369, DE 2826821, JP 48038328 as
well as
journal articles: "Premix": a novel process for improving bleaching of
tnechartical pulps for
using a mixture of reductive agents, Wasshausen, J. et al. PuIp & Paper
Canada, (2006), Volume
107 Issue 3, Pages 44-47 and New hydrosulfite route reduces groundwood bleach
costs, Sellers,
F. G. Pulp & Paper (1973) Volume 47 Issue 12, pages 80-82.
In addition, sodium borohydride assisted peroxide bleaching is disclosed in
Further Understanding of Sodium Borohydricle Assisted Peroxide Bleaching of
Mechanical
Pulps, He, Th., Appita Journal (2005), Volume 58 issue 1, pages 72-76. The
direct use of BH as
a bleaching chemical is disclosed in US 2004/000380 WO 1996/020308, and WO
90011403 and
its use as a pre-bleaching/mulit-stage bleaching chemical is disclosed in WO
01059205. Use of
large amounts (1-3%) of BH on kraft pulping was described in Determination of
kraft NaBH4
pulping condition of Uldag fir, by .Akgul, M., Pakistan Journal of Biological
Sciences (2006)
Volume 9 page 13. Finally, pre-treatment of wood chips with several chemicals
for kraft and
sulfite cooking is described in DE 1955641 and DE 2105324.
The use of magnesium hydroxide in the refiner is described among other places
in
Chinese Patent Application CN 2008-10014053 20080123. This description is
directed to a
process known as refiner bleaching conducted with Mg(OH)2 and hydrogen
peroxide. None of
any of these references describes using magnesium hydroxide in mechanical
pulping, either by
itself or in combination with small amounts of reductive chemicals, or use of
these chemicals in
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mechanical pulping operations in a basic envirorunent.
US 4,324,612 discusses the use of sodium dithionite which is added to a spray
shower applied to a stone surface in preparation of bleached stone groundwood
spruce pulp,
which is then followed by further bleaching of the screened pulp in a peroxide
tower. This
reference however does not include the use of base for energy savings and does
not mention
using magnesium.
US 5,129,987 discusses refiner bleaching with alkaline sodium hydrosulfite.
This
reference however is essentially a high-consistency bleaching process
involving high doses of the
hydrosuIfite typical of bleaching procedures.
WO 9722749 discusses a method of reducing the energy in a pulping process but
it involves adjusting the pH and overall different treatment procedure
targeting thc crystalline
structure of cellulose..
US 5,338,402 utilizes similar chemicals to the invention but only in
quantities
large enough for cheminaechanical pulping, targeting different pulp
properties, and underdifferent
process conditions. For example, it mentions manufacturing CTMP that involves
cooking at a
temperature equal to or greater than 100 C using a reducing agent more
electronegative than the
sulfite ion together with sodium sulfite or bisulfitc or a mixture of sulfur
dioxide and sodium
=hydroxide. The reducing agent may be thiourea dioxide, sodium borohydride, or
sodium
dithionite.
Another prior art source describes a multistage pretreatment process involving
a
reducing agent but is dissimilar to the inventive one step process. The source
describes
= producing bleached pulp from wood chips via a process involving
pretreatment of the chips first
with at least one reducing agent (e.g., with a mixture of sodium sulfite and
sodium borohydride)
and then with an alkaline peroxide solution. The pretreatments were followed
by refiner
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defibration. (Brightening of Douglass-Fir Groundwood , Betz, R. G, Styan G.
E., Pulp Paper
Magazine Canada (1974) Volume 75 Pages 111-114).
In another prior art, the energy expended in the mechanical refining and
beating of
groundwood pulps was proposed to be lowered while improving brightness and
strength
properties by the addition of sodium dithionite directly to the refiner or
beater. (Treatment of
Mechanical Wood Pulp with Reductive Bleaching Chemicals in Refiners, Melzer,
J.; Auhom, W.,
Wochenblatt fur Papierfabrikation (1986), Volume 114, Number 8, pages 257-260_
This method
however is dissimilar to the inventive process because it lacks alkali, uses
much more
hydrosulfite and essentially is a hydrosulfite refiner bleaching.
In at least one embodiment although the specialty chemicals darken the pulp,
the
resulting paper is not dark. The pulp is darkened due to alkalization.
However, because the
specialty chemicals activate the pulp, the process of subsequently bleaching
the darkened
mechanical pulp is enhanced and less bleach is needed. This method is
particularly effective with
magnesium hydroxide as the source of alkali, and when the bleaching is
accomplished by
peroxide bleaching. Pulp activation targeted towards post-refiner bleaching
can be achieved by
application of magnesium hydroxide alone.
In at least one embodiment, prior to the mechanical pulp undergoing peroxide
bleaching or hydrosulfite bleaching, magnesium hydroxide and sodium
hydrosulfite are combined
with the mechanical pulp in a refiner to produce brighter mechanical pulp. In
at least one
embodiment, a chelant is also added to wood chips prior to the refining
operation or in the
refiner.
In at least one embodiment, the specialty chemical is magnesium hydroxide,
optionally with a chelant. We found that, unlike sodium hydroxide, magnesium
hydroxide
improves pulp brightness after hydrosulfite and, especially, peroxide
bleaching by pulp activation
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towards these processes, while immediate post-refining brightness may still
decrease.
In at least one embodiment, the specialty chemicals are in the form of an
aqueous
solution or slurry that can be fed directly to the refiner or sprayed over
wood chips.
In at least one embodiment, the specialty chemicals are in the form of an
aqueous
solution or slurry that can be applied on wood chips during soaking or washing
operations.
The foregoing may be better understood by reference to the following
example, which is presented for purposes of illustration and is not intended
to limit the
scope of the invention.
Several methods presented below, were used to simulate the environment
1.0 in which the invention can be practiced. Pulp samples were obtained
from Midwestern
American mills and from European mills (softwood TMP, TMP 1st and 2nd
rejects). The
doses are based on actives unless stated otherwise. DTPA has always been used
in a form
of a 3 8% solution (normally used in the industry) and the doses refer to this
solution.
Test A. High temperature shock conditions: borohydride-based compositions with
sodium hydroxide
Experimental tests were conducted under wet temperature shock
conditions simulating those in a refiner where to mechanical treatment occurs.
Samples of
TMP were placed in stainless steel digesters and the chemicals added in water
so that the
end consistency was 3-5% dry pulp in slum/. The samples were kept at 150 C for
10
minutes in a rotating digester setup, cooled down, washed, pH measured and had
handsheets made from them. The pH in all the samples went from alkaline to
slightly
acidic, indicating a finished chemical reaction; therefore no acidification of
the slurries
was needed.
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Test B. Moderate temperature shock conditions: hydrosulfite-containing
compositions with sodium hydroxide
Experimental tests were conducted under wet temperature shock
conditions simulating those in a refiner where mechanical treatment occurs.
Samples of
TMP were placed in degassed flasks under septa (soft plastic that protects the
content
from air but can be penetrated with a needle) and chemicals were added via a
syringe in a
flow of nitrogen, to a total consistency of 3.6%. The samples were kept at 80
C for 1 hour
minutes in a water bath, cooled down, washed, pH measured and handsheets were
10 made upon acidification to pH 5. The pH of the samples after the process
was slightly
alkaline. In a test where sodium borohydride was applied, it was used in a
form of
Rolim&Haas' product Borol, which is (39% NaOH, 12% NaBH4). The target
alkalinity
(for example, 0.75% NaOH, 0.25% NaBH4 to o.d. pulp) was maintained by varying
quantities of introduced sodium hydroxide.
Test C. Hydrosulfite treatment with sodium hydroxide followed by bleaching
The samples were prepared as described in Test B, washed, dewatered and
bleached under standard conditions (70 C, 1 h, 1.5% Na0II, 2% H202). The
samples
were washed, and handsheets were made upon acidification to pH 5.
Test D. Freeness improvement
A protocol was developed that simulated both mechanical and temperature
effects of the thennomechanical process better that just a shock temperature
treatment.
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The pulp was mixed with the chemicals at 10% consistency and then beaten in a
PFI-type
laboratory pulp refiner (150 C). Then the pulp was diluted to 3% and exposed
to heat as
described in Test A. Freeness (CSF) of the pulp treated in presence of 035-1%
NaOH
was about 20 ml lower than in the control; borohydride and DTPA did not affect
the
result.
Test E. High temperature shock conditions: hydrosulfite-containing
compositions
with magnesium hydroxide
A brightness test was conducted under wet temperature shock conditions
simulating those in the refiner (no mechanical treatment). Samples of TMP were
placed
in plastic bags and mixed well with magnesium hydroxide and DTPA. The bags
were
opened, and the samples transferred into stainless steel digesters and
degassed with
nitrogen, for 7 minutes each. The remaining chemicals were added via a syringe
into the
volume of the pulp in a nitrogen flow. The 5%-consistency samples were kept at
150 C
for 10 min in a rotating digester setup, cooled down, washed, pH measured and
either
handsheets were made or the pulp was subsequently bleached. The pH in all of
the
samples went from alkaline to slightly acidic, indicating a finished chemical
reaction;
therefore no acidification of the slurries was needed.
Test F. Moderate temperature shock conditions: hydrosulfite-containing
compositions with magnesium hydroxide
The assessment of the effect of reductive chemicals on brightness was
conducted under wet temperature shock conditions simulating those in the
refiner (no
mechanical treatment). Samples of TMP were placed in degassed flasks under
septa and
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chemicals added via a syringe, to total consistency 5%. Magnesium hydroxide as
a dilute
slurry and DTPA were added first, mixed well with the pulp, then reductive
chemicals
added. After mixing, the samples were kept at 80 C for 1 h 15 min in a water
bath, cooled
down, washed, and pH measured and handsheet made (no pH adjustment) or the
pulp
subsequently bleached.
Test G. Hydrosulfite treatment with magnesium hydroxide followed by peroxide
bleaching
Samples were prepared as described in Test E or F, washed with 2L DI
water, dewatered and bleached under standard conditions (70 C, 1 h, 1.5% NaOH,
2%
H202). The samples were washed with 2L DI water and handsheets made upon
acidification to pH 5.
Test H. Hydrosulfite treatment with magnesium hydroxide followed by
hydrosulfite
bleaching
= Samples were prepared as described in Test E or F, washed with 1L DI
water, dewatered and bleached under standard conditions (70 C, 1 h, 1
Na2S204). The
samples were washed with 2L DI water, and handsheets were made.
The results of tests A-H are provided in the following tables 1-18 in which
the
parenthesis next to the table number indicates which data corresponds to which
tests.
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TABLES
Table 1 (A)
Sample Brightness
Control 52.10
0.5% NaOH 49.66
0.5% NaOH + 0.25% NaBH4 52.96
0.5% NaOH + 0.1% NaBila 51.71
Table 2 (A)
Sample Brightness
Control 52.82
0.5% NaOH 49.64
0.5% NaOH + 0.1% NaBH4 51.88
0.5% NaOH + 0.1% NaBH4 + 0.1% DTPA 52.53
1% (CH3)4NOH 50.38
1% (CH3)4NOH + 0.1% NaBH4 51.95
0.5% NaOH + 0.25% RHOCH2)4P12SO4 51.44
The data of Tables 1 and 2 demonstrate that minimal quantities of the
specialty
chemicals can fully compensate for the brightness loss due to alkalization of
the pulp. A chelant
noticeably increases the effect of borohydrate.
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Table 3 (A)
Sample Brightness
Control 52.42
0.75% NaOH 50.02
0.75% NaOH + 0.25% NaBH4 52.88
0.75% NaOH + 0.1% NaBH4 52.10
0.75% NaOH + 0.1% NaBH4 + 0.1% DTPA 53.13
1% NaOH + 0.25% NaBH4 5L92
Table 4 (A)
Sample Brightness
Control 52.30
0.75% NaOH 49.27
0.75% NaOH + 0.23% NaBH4 52.5
0.75% NaOH + 0.1% NaBH4 51.62
0.75% NaOH + 0.05% NaBH4 51.01
0.75% NaOH + 0.05% NaBH4 + 0.05% DTPA 51.47
0.75% NaOH + 0.025% NaBH4 + 0.05% DTPA 50.6
The data in Table 3 and 4 demonstrate that the optimal alkalinity that can be
applied
without a brightness loss is 0.75%.
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Table 5 (B)
Sample Brightness
Control 55.82
0.75% NaOH ' 54.08
0.75% NaOH + 0.2% Na2S204 55.02
0.75% NaOH + 0.5% Na2S204 55.92
0.75% NaOH + 0.2% Na2S204 + 0.05% NaBH4 55.98
0.75% NaOH + 0.2% Na2S204 + 0.05% NaBH4 + 0.05% DTPA 56.21
0.75% NaOH 0.2% Na2S204 + 0.025% NaBH4 + 0.05% DTPA 55.66
Table 5 lists the effect on brightness upon the thermal treatment of the pulp
after
the composition underwent peroxide bleaching.
Tables 6-9 list the effect of the compositions (prototype products, 27% total
solids) on paper products.
Table 6 (C)
Sample Brightness
Control 61.17
0.75% NaOH 59.78
0.75% NaOH + 0.3% Na2S204 + 0.05% DTPA 62.33
0.75% NaOH + 0.3% Na2S204 + 0.025% NaBH4 + 0.05% DTPA (I) 63.79
0.75% NaOH + 0.3% Na2S204 + 0.0125% NaBH4 + 0.05% DTPA (II) 63.81
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Table 7 (C)
Sample Brightness
Control 61.36
0.75% NaOH 58.90
0.75% NaOH + 0.025% NaB114 + 0.05% DTPA 63.46
0.75% NaOH + 0.3% Na2S204 0.025% NaBH4 + 0.05% DTPA (I) 66.38
0.75% NaOH + 0.3% Na2S204 + 0.0125% NaBH4 + 0.05% DTPA 64.22
Table 8 (C)
Sample Brightness
Control 60.34
0.75% NaOH 58.57
0.75% NaOH + 0.3% Na2S204 0.025% NaBH4 + 0.05% DTPA 65.48
0.75% NaOH + 0.3% Na25204 + 0.0125% NaBH4 + 0.05% DTPA 65.74
Tables 9 and 10 provide the effect of one of preferred compositions, 19% NaOH,
0.316% NaBH4, 0.48% DTPA, 6.32% Na2S204 (26.1-27.2% solids, depends on the
impurities in
the solid hydrosulfite). The composition was then diluted in paper pulp slurry
so that the NaOH
was reduced to 0.75% to o.d. pulp.
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Table 9 (B)
Sample Brightness
Control
49.71
0.75% NaOH 48.62
Prototype Product (first try) 50.57
Prototype Product (second try) 49.83
Prototype Product (third try) 50.01
Table 10 (B)
Sample Brightness
Control
49.40
0.75% NaOH 46.68
Prototype Product (first try) 49.45
Prototype Product (second try) 50.15
Prototype Product (third try) 50.06
Table 11 indicates the effect of using magnesium hydroxide as the alkali.
Magnesium hydroxide is less expensive than other alkali. Compositions
containing magnesium
hydroxide requires less energy to undergo the pulping process. When
substituting magnesium
hydroxide for sodium hydroxide the replacement ratio is 0.75% sodium hydroxide
for 0.5%
magnesium hydroxide.
Table 11 (F,G)
Brightness, Brightness,
unbleached bleached
Control 49.09 55.18
0.5% Mg(OH)2 49.05 60.49
0.5% Mg(OH)2+0.05%DTPA 49.67 60.86
0.5% Mg(OH)2+0.05%DTPA 52.28 61.99
+0.25% Na2S204
0.5% Mg(OH)2+0.05%DTPA 54.44 62.42
+0.25% Na2S204+0.0125%NaBH4
0.25% Mg(OH)2+0.05%DTPA 53.56 62.54
+0.125% Na2S204+0.0125%NaBH4
0.25% Mg(OH)2 49.91 61.15
0.05%DTPA 50.45 56.58
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Table 12 (F, G)
Brightness,
bleached
Control 55.41
0.5% Mg(OH)2+0.05%DTPA 62.11
+0.25% Na2S204
0.5% Mg(OH)2+0.05%DTPA 61.07
+0.125% Na2S204
0.5% Mg(OH)2+0.05%DTPA 61.34
+0.125%Na2S204+0.0125%NaBH4
0.125% Mg(OH)2+0.05%DTPA 61.90
+0.125% Na2S204
0.125% Mg(OH)2+0.05%DTPA 62.03
+0.125%Na2S204+0.0125%NaBH4
0.125% Mg(OH)2 61.17
Table 13 (E,G)
Brightness, Brightness,
unbleached bleached
Control 49.67 54.17
0.5% Mg(OH)2 46.92 57.72
0.5% Mg(OH)2+0.05%DTPA 46.50 59.35
0.5% Mg(OH)2+0.05%DTPA+0.25% Na2S204 49.68 59.85
0.5%Mg(OH)2+0.05%DTPA+0.25% 50.27 60.05
Na2S204+0.0125%NaBH4=
0.25% Mg(OH)2+0.05%DTPA+0.125% 52.76 61.48
Na2S204+0.0125%NaBH4
0.25% Mg(OH)2 48.03 59.17
0.05%DTPA 49.46 56.21
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Table 14 (E,G)
Brightness, Brightness,
unbleached bleached
Control 48.58 54.4
0.5% Mg(OH)2 46.95 58.95
0.75% NaOH 47.59 48.55
0.5% Mg(OH)2+0.05%DTPA 51.55 60.74
+0.25% Na2S204+0.0125%NaBH4
0.25% Mg(OH)2+0.05%DTPA 54.33 61.77
+0.25% Na2S204+0.0125%NaBH4
Prototype Product based on NaOH, 50.41 53 .17
see above (0.75% NaOH)
Prototype Product based on NaOH, 50.59 53.36
see above (0.75% NaOH)
Control, bleaching with 0.05% MgSO4 54.61
Control, bleaching with 0.05% MgSO4 55.42
+ 0.05%DTPA*
The data from Tables 11-14 demonstrate why using magnesium hydroxide is
preferred. There is no magnesium-related brightness loss under moderate
conditions (75 C, no
bleaching), while under severe conditions (150 C, no bleaching) better
simulating a refining
process, magnesium-related brightness loss occurs. However, in both cases
there is a significant
magnesium-induced brightness improvement after bleaching. Reductive chemicals
further
significantly improve post-refining brightness: a major effect of
hydrosulfite, less from extra
borohydride. Magnesium-reductive pulp pre-treatment clearly shows performance
in refining
applications. This effect is new and, as shown in Tables 14-16 (alternative
pulps were used in 15
and 16), it cannot be achieved by just presence of magnesium ions in the
pulping slurry. The pre-
treatment is required, and this stage is automatically achieved when the
proposed chemistry is
present at the stage of mechanical pulping.
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Table 15 (G)
Chemistry Application Brightness
Control 56.40
0.05%
MgSO4-1-0.125%DTPA In liquor 57.47
0.125% MgSO4 Mixed with pulp before bleaching 57.95
0.25% MgSO4 Mixed with pulp before bleaching 58.17
0.125% Mg(OH)2 Mixed with pulp before bleaching 58.60
0.25% Mg(OH)2 Mixed with pulp before bleaching 58.84
Mixed with pulp, kept at 50 C
0.125% Mg(OH)2 for 30 min before bleaching 60.18
Mixed with pulp, kept at 50 C
0.25% Mg(OH)2 for 30 min before bleaching 60.36
Mixed with pulp, kept at 70 C
0.125% Mg(OH)2 for 60 min before bleaching 60.23
Mixed with pulp, kept at 70 C
0.25% Mg(OH)2 for 60 min before bleaching 60.07
10 Table 16 (F,G)
Brightness,
bleached
Control 59.50
0.5% Mg(OH)2+0.05%DTPA 66.93
+0.25% Na2S204
0.5% Mg(OH)2+0.05%DTPA 66.12
+0.125% Na2S204
0.125% Mg(OH)2+0.05%DTPA 66.42
+0.125% Na2S204
0.125% Mg(OH)2+0.05%DTPA 67.14
+0.125%Na2S204+0.0125%NaBH4
The positive effect of the specialty chemicals is also observed in the
subsequent
hydrosulfite bleaching as illustrated in Tables 17 (mild conditions, full
compensation) and 18
(severe conditions better simulating the refining process, a significant
brightness gain).
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Table 17 (F,H)
Sample Brightness
Control
59.22
0.5% Mg(011)2 57.79
0.5% Mg(OH)2+0.05%DTPA
+0.25%Na2S204+0.0125%NaBH4 59.68
0.5% Mg(OH)2+0.05%DTPA
+0.125% Na2S204 58.43
Table 18 (E,H)
Sample Brightness
Control
51.42
0.5% Mg(OH)2 51.97
0.5% Mg(OH)2+0.05%DTPA 52.46
0.5% Mg(OH)2+0.05%DTPA
+0:25% Na2S204 56.03
0.5% Mg(OH)2+0.05%DTPA
+0.25%Na2S204+0.0125%NaBH4 55.43
0.5% Mg(OH)2+0.05%DTPA
+0.125%Na2S204+0.0125%NaBH4 53.67
Changes can be made in the composition, operation, and arrangement of the
method of the invention described herein without departing from the concept
and scope of the
invention as defined in the claims. While this invention may be embodied in
many different
forms, there are described in detail herein specific preferred embodiments
of the invention. The
present disclosure is an exemplification of the principles of the invention
and is not intended to
limit the invention to the particular embodiments illustrated. Furthermore,
the invention
encompasses any possible combination of some or all of the various embodiments
described
herein. All patents, patent applications, and other cited materials mentioned
anywhere in this
application or in any cited patent, cited patent application, or other cited
material are hereby
incorporated by reference in their entirety.
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The above disclosure is intended to be illustrative and not exhaustive. This
description will suggest many variations and alternatives to one of ordinary
skill in this art. All
these alternatives and variations are intended to be included within the scope
of the claims where
the term "comprising" means "including, but not limited to". Those familiar
with the art may
recognize other equivalents to the specific embodiments described herein which
equivalents are
also intended to be encompassed by the claims.
This completes the description of the preferred and alternate embodiments of
the
invention. Those skilled in the art may recognize other equivalents to the
specific embodiment
described herein which equivalents are intended to be encompassed by the
claims attached hereto.
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