U.S. patent application number 15/459303 was filed with the patent office on 2017-09-21 for low capital bleaching of chemical pulp.
This patent application is currently assigned to Ecolab USA Inc.. The applicant listed for this patent is Ecolab USA Inc.. Invention is credited to Prasad Y. Duggirala, Sergey M. Shevchenko.
Application Number | 20170268171 15/459303 |
Document ID | / |
Family ID | 58448621 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170268171 |
Kind Code |
A1 |
Duggirala; Prasad Y. ; et
al. |
September 21, 2017 |
Low Capital Bleaching of Chemical Pulp
Abstract
Bleaching methods and formulations for bleaching/delignification
processes for chemical pulp are provided. The bleaching methods
utilize peroxide and an organomanganese complex under aqueous
caustic conditions, increasing bleaching efficiency of the overall
bleaching/delignification process. Chemical pulp having increased
brightness can be obtained at decreased temperatures and with
reduced stage time, resulting in reduced chemical consumption and
improved energy efficiency.
Inventors: |
Duggirala; Prasad Y.;
(Naperville, IL) ; Shevchenko; Sergey M.; (Aurora,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ecolab USA Inc. |
St. Paul |
MN |
US |
|
|
Assignee: |
Ecolab USA Inc.
St. Paul
MN
|
Family ID: |
58448621 |
Appl. No.: |
15/459303 |
Filed: |
March 15, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62309282 |
Mar 16, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21C 9/1078 20130101;
D21C 9/1036 20130101; D21C 9/144 20130101; D21C 9/163 20130101;
D21C 9/14 20130101; D21C 9/02 20130101 |
International
Class: |
D21C 9/10 20060101
D21C009/10; D21C 9/14 20060101 D21C009/14; D21C 9/16 20060101
D21C009/16 |
Claims
1. A method of bleaching alkali oxidized chemical pulp comprising:
treating alkali oxidized chemical pulp with peroxide and an
organomanganese complex under aqueous caustic conditions subsequent
to an acidic oxidative bleaching stage to form an enhanced chemical
pulp.
2. A method of enhancing chemical pulp comprising: treating
chemical pulp under acidic oxidative conditions to form an acidic
oxidized chemical pulp; washing the acidic oxidized chemical pulp
with aqueous caustic solution to form an alkali oxidized chemical
pulp; and treating the alkali oxidized chemical pulp with peroxide
and an organomanganese complex to form an enhanced chemical
pulp.
3. The method of claim 2, wherein the aqueous caustic solution is
at a temperature of from about 40.degree. C. to about 90.degree.
C.
4. The method of claim 2, wherein the washing step is an express
alkali extraction.
5. The method of claim 2, wherein the washing step is performed at
atmospheric pressure.
6. The method of claim 2, wherein the washing step is performed for
about 10 minutes or less.
7. The method of claim 6, wherein the washing step is performed for
about 2 minutes or less.
8. The method of claim 7, wherein the washing step is performed for
about 1 minute or less.
9. The method of claim 2, wherein the treating the alkali oxidized
chemical pulp step is performed at a temperature of about
75.degree. C. or less.
10. The method of claim 2, wherein the treating the alkali oxidized
chemical pulp step is performed at a temperature of about
55.degree. C. or less.
11. The method of claim 2, wherein the treating the alkali oxidized
chemical pulp step is performed in a reaction tube.
12. The method of claim 1, further comprising treating the enhanced
chemical pulp under acidic oxidative conditions.
13. The method of claim 12, wherein the acidic oxidative conditions
of treating the enhanced chemical pulp result from treating the
enhanced chemical pulp with chlorine dioxide.
14. The method of claim 1, wherein the organomanganese complex is
at a concentration of from about 0.0001 ppm to about 20 ppm, and
the peroxide is at a concentration of from about 0.01% to about 5%
by weight, relative to dry pulp in the chemical pulp.
15. The method of claim 1, wherein the organomanganese complex is a
manganese-triazacyclononane complex.
16. The method of claim 1, wherein the organomanganese complex is
Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)b-
is[octahydro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N-
7]]]di-.mu.-oxodi-X.sup.-.
17. A thermally stable aqueous formulation for bleaching of a
chemical pulp comprising an organomanganese complex and water,
wherein the aqueous formulation has a pH of from about 3 to about 7
and the organomanganese complex is at a concentration of from about
0.0001% to about 3% by weight based on weight of the aqueous
formulation.
18. The formulation of claim 17, wherein the organomanganese
complex is Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)b-
is[octahydro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N-
7]]]di-.mu.-oxodi-X.sup.-.
19. The formulation of claim 17, wherein the organomanganese
complex is at a concentration of from about 0.001% to about 2%, by
weight based on the weight of aqueous solution and wherein the
formulation has a pH of from about 4 to about 6.
20. The formulation of claim 17, further comprising peroxide.
Description
[0001] This application is an international (i.e., PCT) application
claiming the benefit of U.S. Provisional Patent Application No.
62/309,282, filed Mar. 16, 2016, the contents of which are
incorporated by reference herein in their entirety.
FIELD OF INVENTION
[0002] The invention is directed to a method of improving
efficiency of a chemical pulp bleaching process.
BACKGROUND OF THE INVENTION
[0003] Chemical pulps such as kraft or sulfite commonly possess
dark color, the extent of which depends on the wood source, degree
of delignification, and the papermaking processes utilized.
Generally, the papermaking industry utilizes bleaching chemicals to
improve the optical properties of finished paper and paper
products. Bleaching involves chemical alteration of the
light-absorbing structures in pulp, as well as removal of residual
lignin (i.e., delignification) and is an extension of the
delignification started in the digestion stage. Multistage
bleaching processes generally include stages such as oxygen-alkali
delignification, oxygen-peroxide alkali extraction, chlorine
dioxide bleaching, and peroxide bleaching. The resulting pulp can
be evaluated using brightness measurements, which are used to
assess the whiteness of paper materials through measurement of the
amount of light reflected by the pulp.
[0004] Many bleaching sequences comprise oxygen delignification, a
first chlorine dioxide stage ("D0") followed by an alkali
extraction stage with hydrogen peroxide and a second chlorine
dioxide stage ("D1"). Chlorine dioxide stages can be used for
bleaching of wood pulp in elemental chlorine-free ("ECF") bleaching
sequences because chlorine dioxide produces few carcinogenic
organochlorine compounds, and thus is currently preferred over the
use of elemental chlorine. However, the use of chlorine dioxide has
disadvantages. For example, chlorine dioxide stages are acutely
toxic. Generally, chlorine dioxide stages are moderately acidic
(e.g., pH 2.5-5), which usually necessitates one or more subsequent
alkali extraction stages to aid in lignin removal from chemical
pulp. Generally, the chlorine dioxide stages utilize hydrogen
peroxide to provide additional brightness to the chemical pulp. A
higher number of bleaching stages results in an increase in process
time and material costs as well as degradation of the chemical
pulp, resulting in a reduction in pulp yield and strength.
BRIEF SUMMARY OF THE INVENTION
[0005] In an embodiment, a method of bleaching alkali oxidized
chemical pulp is provided. The method comprises treating alkali
oxidized chemical pulp with peroxide and an organomanganese complex
under aqueous caustic conditions, which is done subsequent to an
acidic oxidative bleaching stage, to form an enhanced chemical
pulp. In a preferred embodiment, the chemical pulp is a brownstock
chemical pulp.
[0006] In another embodiment, a method of enhancing chemical pulp
is provided. The method comprises treating chemical pulp under
acidic oxidative conditions to form an acidic oxidized chemical
pulp. The acidic oxidized chemical pulp is washed with aqueous
caustic solution to form an alkali oxidized chemical pulp. The
alkali oxidized chemical pulp is treated with peroxide and an
organomanganese complex to form an enhanced chemical pulp.
[0007] In another embodiment, a thermally stable aqueous
formulation for bleaching of a chemical pulp is provided. The
formulation comprises an organomanganese complex and water, wherein
the aqueous formulation has a pH of from about 3 to about 7 and the
organomanganese complex is present at a concentration of from about
0.0001% to about 1% by weight based on weight of the aqueous
formulation.
[0008] In another embodiment, an aqueous formulation for bleaching
of a chemical pulp is provided. The formulation comprises an
organomanganese complex, a peroxide, and water, wherein the
organomanganese complex is present at a concentration of from
0.0001% to about 1% and the peroxide is present at a concentration
of from about 5% to about 60% by weight based on weight of the
aqueous solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a bar graph that illustrates the effect of
temperature on Kappa number and brightness for an embodiment of the
inventive methods.
[0010] FIG. 2 is a bar graph that illustrates the effect of time on
Kappa number and brightness for an embodiment of the inventive
methods.
[0011] FIG. 3 is a bar graph that illustrates brightness, Kappa
number, and viscosity for an embodiment of the inventive
methods.
[0012] FIG. 4 is a bar graph that illustrates the effect of the
peroxide concentration of an embodiment of the inventive methods on
D0 hardwood pulp pre-treated with aqueous caustic solution.
[0013] FIG. 5 is a bar graph that illustrates the effect of various
conditions on a D0EpD1 sequence for an embodiment of the inventive
methods.
[0014] FIG. 6A is a bar graph that illustrates the effect of
aqueous caustic conditions and exposure time on brightness for
hardwood pulp for an embodiment of the inventive methods.
[0015] FIG. 6B is a bar graph that illustrates the effect of
aqueous caustic conditions and exposure time on brightness for
softwood D0 pulp for an embodiment of the inventive methods.
[0016] FIG. 7 is a bar graph that illustrates the effect of
catalyst concentration on brightness for an embodiment of the
inventive methods.
[0017] FIG. 8A is a bar graph that illustrates comparatively the
effects of increased hydroxide concentration as a means to improve
brightness, viscosity and yield in softwood post-D0 pulp for an
embodiment of the inventive methods.
[0018] FIG. 8B is a line graph that illustrates comparatively the
effects of increased hydroxide concentration as a means to improve
brightness and viscosity in softwood post-D0 pulp for an embodiment
of the inventive methods.
[0019] FIG. 9 is a bar graph that illustrates the effect of reagent
and catalyst concentration on brightness of D0 softwood pulp for an
embodiment of the inventive methods.
[0020] FIG. 10 is a bar graph that illustrates the effect of
caustic pre-treatment of a chemical pulp on brightness for an
EoPcD0 sequence for an embodiment of the inventive methods and
illustrates a potential reduction in chlorine dioxide
consumption.
[0021] FIG. 11 is a bar graph that illustrates the effect of an
oxygen delignification stage on brightness before and after a
chlorine dioxide stage for an embodiment of the inventive
methods.
[0022] FIG. 12 is a bar graph that illustrates the effect of
catalyst on a multistage sequence that allows for the elimination
of a chlorine dioxide stage (D2) for an embodiment of the inventive
methods.
[0023] FIG. 13 is a plot that illustrates stability of catalyst
formulations stored for certain periods of time for one or more
embodiment of the inventive methods and/or formulas.
[0024] FIG. 14 is a bar graph that illustrates changes in catalyst
feeding and their effects on brightness at certain
temperatures.
[0025] FIG. 15A is a line graph that illustrates how changes in
catalyst loading affects brightness for one or more embodiments of
the inventive methods in a field trial.
[0026] FIG. 15B is a bar graph that illustrates how changes in
catalyst loading affects brightness for one or more embodiments of
the inventive methods in a field trial.
[0027] FIG. 15C is a bar graph that illustrates how changes in
catalyst loading and temperature affect Eop brightness for one or
more embodiments of the inventive methods in a field trial.
[0028] FIG. 15D is a bar graph that illustrates how changes in
catalyst loading affects pulp brightness before and after a D1
stage in a field trial.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The invention is based on application of a manganese-based
catalyst in pulp bleaching stages involving peroxide. Applicants
have discovered methods of bleaching chemical pulp that either
eliminates the need for certain stages or reduces the amount of
bleaching agent required. The present methods involve exposure of
chemical pulp from a papermaking process to manganese complex-based
catalysis of peroxide bleaching under aqueous caustic conditions,
which generally refers to high-pH (e.g., pH>7) conditions
undertaken in certain steps of bleaching and/or enhancing chemical
pulp. In certain embodiments of the methods provided herein,
chemical pulp (e.g., acidic oxidized chemical pulp) may be washed
with aqueous caustic solution (i.e., under aqueous caustic
conditions) to form alkali oxidized chemical pulp. In certain
embodiments of the methods described herein, the aqueous caustic
conditions have (or aqueous caustic solution has) a pH of from
about 8 to 14, or from about 8 or from about 9, or from about 10,
to 14, or to about 13, or to about 12. In certain embodiments of
the methods described herein, the aqueous caustic solution has a pH
of from about 8 to 14, or from about 8 or from about 9, or from
about 10, to 14, or to about 13, or to about 12. In certain
embodiments of the methods provided herein, the aqueous caustic
conditions are the result of an express alkali extraction. For
purposes of this disclosure, the terms "caustic" and "alkali" are
used interchangeably.
[0030] The methods of the present invention allow for process
modifications that provide higher efficiency and unexpected
benefits as compared to other bleaching methods. Applicants have
surprisingly discovered that the methods described herein provide
benefits including (a) shorter peroxide bleaching stages at lower
temperature that improve yield and provide stronger pulp, (b) a
reduction in the amount of bleaching chemicals across all stages
without sacrificing brightness, (c) substitution of oxygen stages
with the inventive organomanganese-catalyzed bleaching stage, and
(d) elimination of certain stages that are deemed unnecessary to
achieve certain quality metrics, including chlorine dioxide
stages.
[0031] A problem perceived with certain existing catalyst-based
bleaching methods is that, while some improve pulp brightness in
target processes, the brightness gain alone does not justify the
expense. The methods disclosed herein involve manganese-based
catalysis of a pulp bleaching stage involving hydrogen peroxide
with overall process modifications that have been shown to provide
higher efficiency and unexpected benefits. Applicants have
discovered, among other things, that organomanganese-catalyzed
bleaching stages can be performed at lower temperatures than
conventional bleaching stage temperatures. The
organomanganese-catalyzed bleaching stage can be performed at
temperatures as low as about 50.degree. C. without substantial
erosion of pulp brightness. It was surprisingly and unexpectedly
discovered that brightness in some pulps increases or does not
change with a decrease in process temperature to, e.g., from about
5.degree. C. to about 55.degree. C. Thus, the present invention
provides chemical pulp of sufficient brightness under thermally
milder and more energy-efficient conditions than traditional
bleaching stages. This is an important benefit, because reduction
in process temperature can result in a substantial improvement in
energy efficiency. Moreover, the low temperatures of the present
invention can reduce pulp degradation that often occurs at higher
temperatures, resulting in bleaching processes that produce
chemical pulp in higher yield.
[0032] In some instances, the inventive methods can require as
little as 20 minutes or less to reach maximum brightness. By
comparison, additional process time beyond 20 minutes in those
instances resulted in a small increase in pulp brightness. In
certain embodiments, the use of the present bleaching technology
allows for about 10 to about 15 minutes bleaching when utilized in
a bleaching tube. In an embodiment, reaction tubes are used instead
of bleaching tanks. The reaction tubes contain slowly moving pulp,
which effects the bleaching process. This improvement has been
shown to increase throughput without any decrease in
brightness.
[0033] In certain embodiments, the present invention improves the
multistage bleaching/delignification sequence for chemical pulp
based on the application of an organomanganese complex in the
stages of the process that involve hydrogen peroxide under aqueous
caustic conditions. The result is a modification that includes
eliminating and modifying stages of the process based on increased
brightness and efficiency. The examples are: (a) replacing D0ED1
sequence with D0EPc process, where EPc stands for the peroxide
bleaching with the catalyst (Pc) after express alkali extraction
(E), thus eliminating the D1 stage; (b) substituting the
conventional D0EopD1 sequence with D0EPc eliminating oxygen and the
second chlorine dioxide stage; (c) substituting conventional
D0EopD1 sequence with D0EoPc using the Eo stage for activation of
pulp at the following Pc stage that results in sufficient
brightness to eliminate a second chlorine dioxide stage; (d)
substituting oxygen delignification (O) of brownstock pulp with
catalyzed peroxide extraction (Epc) process, thus eliminating
oxygen; (e) activation of pulp toward a first chlorine dioxide
stage (D0) by introducing the catalyst into a preceding alkali
peroxide stage at the medium brightness range (approximately 50-70
ISO brightness units), thus allowing for reduction of chlorine
dioxide load or even elimination of a subsequent chlorine dioxide
stage; (f) activation of D0 pulp towards subsequent alkali peroxide
bleaching, and additional activation of the catalyst via express
alkali extraction (the phrase "express alkali extraction" is used
to describe fast thorough mixing of the D0 pulp with a warm (e.g.,
from about 40.degree. C. to about 90.degree. C.) caustic solution
followed by immediate dewatering and/or washing prior to the Pc
(Epc) stage, and/or washing pulp with warm caustic solution via a
shower); (g) substituting conventional P and Eop stages with
rapid/short retention lower-temperature Pc (Epc) bleaching stages
(e.g., utilizing reaction tubes instead of conventional bleach
towers), which have been shown to result in less damage to the
fiber thus providing higher throughput, improved energy efficiency,
and increased pulp strength (fiber modification).
[0034] The methods disclosed herein can be performed using any
suitable organomanganese complex. In certain preferred embodiments,
the organomanganese complex is a mononuclear or binuclear complex
of Mn (III) and/or Mn (IV) organic complex with one or more
O.sup.2- bridge. In certain preferred embodiments, the
organomanganese complex is an organomanganese-triazacyclononane
complex. In certain preferred embodiments, the manganese complex is
Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-X.sup.-. The aforementioned complex can comprise any
suitable organic or inorganic anion (X.sup.-). In certain
embodiments, the anion is a halogen such as fluoride, chloride,
bromide, and/or iodide. In certain preferred embodiments, X.sup.-
is selected from a halogen, sulfate, acetate, and citrate. In
certain preferred embodiments, the organomanganese complex is
Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-chloride (1:2). The term "catalyst," as used herein,
indicates an organomanganese complex, and when used in the Examples
set forth herein, "catalyst" refers to Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-chloride (1:2).
[0035] The organomanganese complex can be utilized at any suitable
concentration in the organomanganese-catalyzed bleaching stage. In
certain embodiments, the organomanganese complex is at a
concentration of from about 0.001 ppm to about 100 ppm. In certain
embodiments, the organomanganese complex is at a concentration of
from about 0.001 ppm to about 50 ppm. In certain preferred
embodiments, the organomanganese complex is at a concentration of
from about 0.001 ppm to about 20 ppm. Thus, in certain preferred
embodiments, the organomanganese complex is at a concentration of
from about 0.001 ppm to about 20 ppm, from about 0.001 ppm to about
10 ppm, from about 0.01 to about 10 ppm, from about 0.01 ppm to
about 8 ppm, from about 0.01 ppm to about 6 ppm, from about 0.01
ppm to about 5 ppm, from about 0.001 to about 4 ppm, from about
0.001 ppm to about 3 ppm, from about 0.01 ppm to about 3 ppm, or
from about 0.01 ppm to about 2 ppm, or from about 0.1 ppm to about
2 ppm, or from about 1 ppm to about 2 ppm.
[0036] The inventive methods can include any suitable peroxide. In
certain embodiments, the peroxide is an organic peroxide or an
inorganic peroxide. In certain embodiments, the peroxide is
selected from organic peroxides such as benzoyl peroxides, or
inorganic peroxides such as hydrogen peroxide. In certain preferred
embodiments, the peroxide is hydrogen peroxide.
[0037] The peroxide can be added in any suitable form and at any
concentration. In certain preferred embodiments, the peroxide is
added to the chemical pulp as a solution. In certain preferred
embodiments, the peroxide is added as a solution to the chemical
pulp at a concentration of from about 5% to about 60% by weight
based on the weight of solution. Thus, in certain preferred
embodiments, the peroxide is added as a solution to the chemical
pulp at a concentration of from about 5% to about 60%, from about
10% to about 60%, from about 15% to about 60%, from about 20% to
about 60%, from about 25% to about 60%, from about 30% to about
60%, from about 35% to about 60%, from about 40% to about 60%, from
about 45% to about 60%, or from about 50% to about 60% by weight
based on the weight of solution. In certain other preferred
embodiments, the peroxide is added as a solution to the chemical
pulp at a concentration of about 50% or more. Thus, in certain
other preferred embodiments, the peroxide is added as a solution to
the chemical pulp at a concentration of about 50% or more, about
60% or more, or about 70% or more.
[0038] In certain preferred embodiments, the organomanganese
complex and peroxide are added to the chemical pulp together as an
aqueous solution. It has been discovered that higher brightness is
obtained when the manganese complex is added to a peroxide line
comprising a concentrated hydrogen peroxide solution. In
particular, it was found that the efficiency of the treatment
increases when the catalyst is added to a more concentrated
hydrogen peroxide solution. However, in certain other embodiments,
the organomanganese complex and the peroxide are added separately
to the chemical pulp.
[0039] In certain preferred embodiments, an organomanganese
catalyst solution having a concentration of from about 0.0001% to
about 2%, or to about 1%, or to about 0.5%, or to about 0.1%, is
mixed with concentrated hydrogen peroxide prior to contacting with
the chemical pulp. In certain preferred embodiments, an
organomanganese catalyst solution having a concentration of from
about 0.0001% to about 0.05% is mixed with the concentrated
hydrogen peroxide prior to contacting with the chemical pulp. In
certain preferred embodiments, an organomanganese catalyst solution
having a concentration of from about 0.001% to about 0.05% is mixed
with concentrated hydrogen peroxide prior to contacting with the
chemical pulp. In certain preferred embodiments, an organomanganese
catalyst solution having a concentration of from about 0.001% to
about 0.02% is mixed with concentrated hydrogen peroxide prior to
contacting with the chemical pulp. In certain preferred
embodiments, an organomanganese catalyst solution having a
concentration of from about 0.001% to about 0.01% is mixed with
concentrated hydrogen peroxide prior to contacting with the
chemical pulp. In certain preferred embodiments, vigorous mixing is
applied when the solution of the catalyst is mixed with hydrogen
peroxide. In certain preferred embodiments, the time between the
mixing and feeding the mixture to pulp does not exceed 10 minutes.
In certain preferred embodiments, vigorous mixing is applied when
the solution of the catalyst is mixed with hydrogen peroxide. In
certain embodiments, the time between the mixing and feeding the
mixture to pulp does not exceed 1 minute.
[0040] Any suitable caustic can be used in the
organomanganese-catalyzed bleaching stage. In certain embodiments,
the caustic is an inorganic base or an organic base. In certain
embodiments, the base is an alkali metal or alkaline earth metal
hydroxide or salt. In certain embodiments, the base is an alkaline
earth metal hydroxide or salt selected from magnesium hydroxide,
calcium hydroxide, strontium hydroxide, barium hydroxide, and
combinations thereof. In certain preferred embodiments, the base is
an alkali metal hydroxide or salt selected from sodium hydroxide,
potassium hydroxide, lithium hydroxide, rubidium hydroxide, cesium
hydroxide, and combinations thereof.
[0041] The methods of the present invention can be performed in the
presence or absence of oxygen. Oxygen refers to any added oxygen or
oxygen-containing gas. In certain preferred embodiments, an
individual stage or process does not comprise the use of added
oxygen. Such an embodiment may be advantageous, as one can avoid
the challenges associated with the use of oxygen (e.g., safety and
handling).
[0042] The organomanganese-catalyzed bleaching stage of the present
invention can be performed at any suitable temperature necessary to
achieve a requisite brightness. It has been discovered that the
inventive methods are effective at relatively low process
temperatures. In certain embodiments, the organomanganese-catalyzed
bleaching stage is performed at a temperature of about 100.degree.
C. or less. In certain embodiments, the organomanganese-catalyzed
bleaching stage is performed at a temperature of about 90.degree.
C. or less. In certain preferred embodiments, the
organomanganese-catalyzed bleaching stage is performed at a
temperature of about 80.degree. C. or less. Thus, in certain
preferred embodiments, the organomanganese-catalyzed bleaching
stage is performed at a temperature of about 80.degree. C. or less,
about 75.degree. C. or less, about 70.degree. C. or less, about
65.degree. C. or less, about 60.degree. C. or less, about
55.degree. C. or less, or about 50.degree. C. or less.
[0043] The methods of the present invention provide
organomanganese-catalyzed bleaching stages that require residence
times that are much faster than typical residence times required
under standard mill conditions. For example, standard mill
conditions generally require 60-90 minutes. In certain embodiments,
the organomanganese-catalyzed bleaching stage is complete in about
60 minutes or less, or in about 50 minutes or less, or in about 40
minutes or less. In certain preferred embodiments, the
organomanganese-catalyzed bleaching stage is complete in about 30
minutes or less. Thus, in certain embodiments, the
organomanganese-catalyzed bleaching stage is complete in about 30
minutes or less, or in about 25 minutes or less, or in about 20
minutes or less, or in about 15 minutes or less.
[0044] As discussed above, in certain embodiments, the
organomanganese-catalyzed bleaching stages of the present invention
can be performed using express low-temperature bleaching by
replacing bleach towers with reactor tubes, i.e., "bleaching
tubes." In certain embodiments, the target brightness can be
achieved in about 20 minutes or less at temperatures as low as
50.degree. C., thus providing improved energy efficiency, yield,
throughput, and fiber quality (e.g., increased pulp strength).
Thus, conventional P and Eop stages can be substituted with
rapid/short retention lower-temperature organomanganese catalyzed
bleaching stages by, e.g., utilizing one or more reaction tubes
instead of conventional bleach towers.
[0045] In certain embodiments, the chemical pulp is further treated
with a phase transfer agent. In certain embodiments, the phase
transfer agent is selected from quaternary ammonium salt,
phosphonium salt, crown ether, and polyethylene glycol examples of
which being tetra-n-butylammonium bromide, methyltrioctylammonium
chloride, benzyltrimethylammonium chloride, and
hexadecyltributylphosphonium bromide. The phase transfer agent can
be added to the chemical pulp together with the organomanganese
catalyst and/or peroxide or separately.
[0046] The present invention can be used to bleach any chemical
pulp. In certain preferred embodiments, the chemical pulp is kraft
pulp. In certain embodiments, the chemical pulp is selected from
kraft pulp, sulfite pulp, recycled pulp, and any combination of
such pulps. In an embodiment, the invention provides a method for
improving a papermaking process through modification of a
multistage bleaching of chemical pulp. The method comprises an
organomanganese-catalyzed bleaching stage comprising treating
chemical pulp with an organomanganese complex and a peroxide in the
presence of a base and optionally oxygen; a chlorine dioxide stage
performed immediately following the organomanganese-catalyzed
bleaching stage, wherein the chlorine dioxide stage comprises
treating the chemical pulp with chlorine dioxide at a concentration
of from about 0.01% to about 2% by weight based on weight of the
chemical pulp.
[0047] In certain embodiments, the amount of chlorine dioxide
needed to obtain pulp of sufficient brightness is less than would
be required in the absence of a preceding organomanganese-catalyzed
bleaching stage. It has been discovered that an
organomanganese-catalyzed bleaching stage performed prior to a
chlorine dioxide stage can allow for a reduction in the amount of
chlorine dioxide needed by up to about 20% or more while
maintaining sufficient brightness. Thus, in certain embodiments, an
organomanganese-catalyzed bleaching stage performed prior to a
chlorine dioxide stage reduces the overall amount (e.g., total for
all stages) of chlorine dioxide needed by about 20% or more, about
30% or more, about 40% or more, about 50% or more, about 60% or
more, about 70% or more, or about 80% or more.
[0048] As discussed above, the organomanganese-catalyzed bleaching
stage can reduce the amount of chlorine dioxide needed in a
subsequent chlorine dioxide stage. In certain embodiments, the
chlorine dioxide stage comprises chlorine dioxide at a
concentration of about 5% or less by weight based on the weight of
the chemical pulp. Thus, in certain embodiments, the chlorine
dioxide stage comprises chlorine dioxide at a concentration of from
about 0.01% to about 5%, from about 0.01% to about 4%, from about
0.01% to about 3%, from about 0.01% to about 2%, from about 0.01%
to about 1%, from about 0.01% to about 0.08%, from about 0.01% to
about 0.06%, from about 0.01% to about 0.05%, from about 0.01% to
about 0.04%, from about 0.01% to about 0.02%, or from about 0.01%
to about 0.1% by weight based on the weight of the chemical pulp.
In certain preferred embodiments, the method comprises a chlorine
dioxide stage comprising chlorine dioxide at a concentration of
from about 0.01% to about 1% by weight based on weight of the
chemical pulp.
[0049] In certain preferred embodiments, the organomanganese
complex is present in the organomanganese-catalyzed bleach stage at
a concentration of from about 0.001 ppm to about 20 ppm, the
peroxide is present in the organomanganese-catalyzed bleach stage
at a concentration of from about 0.01% to about 5% by weight, and
the organomanganese-catalyzed bleaching stage is performed for
about 60 minutes or less, with ppm concentrations and weight
percentages each based on the weight of the chemical pulp.
[0050] In certain preferred embodiments, the organomanganese
complex and peroxide are added to the chemical pulp as an aqueous
solution comprising organomanganese complex at a concentration of
from about 0.001% to about 5% and peroxide at a concentration of
from about 5% to about 60% by weight based on the weight of
solution.
[0051] In certain preferred embodiments, the
organomanganese-catalyzed bleaching stage is performed in a
bleaching tube at a temperature of about 55.degree. C. or less and
reaches completion in about 20 minutes or less.
[0052] In certain preferred embodiments, the chemical pulp has
medium brightness and the chlorine dioxide stage is not immediately
followed by an additional chlorine dioxide stage.
[0053] In an embodiment, the invention provides a method for
improving a papermaking process through modification of a
multistage bleaching of chemical pulp, the method comprising in the
following order: a chlorine dioxide stage comprising treating
chemical pulp with chlorine dioxide, an express alkali extraction
(an example of washing with aqueous caustic solution) comprising
contacting the chemical pulp with a caustic solution, and an
organomanganese-catalyzed bleaching stage comprising treating the
chemical pulp with an organomanganese complex and a peroxide in the
presence of caustic, which in certain embodiments is under aqueous
caustic conditions.
[0054] The following are non-limiting examples of sequence
modifications that result in pulp having improved properties:
[0055] (A) For a D0-E-D1 sequence, the second chlorine dioxide
stage (D1) can be replaced with an organomanganese-catalyzed
bleaching stage (Epc) and a standard caustic extraction stage (E)
with express extraction (caustic wash, E'). Thus, the resulting
D0-E'-Epc method comprising a chlorine dioxide stage (D0), caustic
wash and an organomanganese-catalyzed bleaching stage (Epc) does
not comprise a second chlorine dioxide stage.
[0056] (B) For a D0-Eop-D1 sequence, employment of express alkali
extraction (caustic wash, E') combined with an
organomanganese-catalyzed bleaching stage allows for the
elimination of the need for the second chlorine dioxide stage (D1)
and oxygen leading to a simplified procedure D0E'Pc.
[0057] It has been surprisingly and unexpectedly discovered that
express alkali extraction of chemical pulp after a D0 stage prior
to an organomanganese-catalyzed bleaching stage improves reactivity
of the D0-treated chemical pulp towards (a) hydrogen peroxide
itself and (b) the manganese catalyst applied with hydrogen
peroxide, resulting in a substantial increase in pulp brightness.
Otherwise, the D0-treated chemical pulp could be insufficiently
reactive in the presence of the catalyst to provide justification
for the use of the catalyst. For example, only a quick (e.g.,
.ltoreq.1 minute) warm caustic wash at 2 wt % sodium hydroxide at
65.degree. C. is needed to provide significant improvement in
brightness. A quick warm caustic wash tends to reduce alkali
brightness loss and provide higher pulp yield, as pulp tends to
degrade in the presence of caustic. Without wishing to be bound by
theory, the experimental results suggest that express alkali
extraction improves the response of pulp through pulp swelling as
well as removal of uronic acids and degraded lignin, which
constitute chromophores and consume peroxide.
[0058] Moreover, it was surprisingly and unexpectedly discovered
that a two-stage alkali process results in higher differentiation
and brightness as compared to a simple increase in hydroxide
concentration in a one-stage process (see, e.g., FIGS. 8 and
9).
[0059] As discuss above, an organomanganese-catalyzed bleaching
stage can allow for the elimination of the need for a second
chlorine dioxide stage (D1) and/or third chlorine dioxide stage
(D2) and/or oxygen. Thus, in certain embodiments, a chlorine
dioxide stage does not immediately follow the
organomanganese-catalyzed bleaching stage. In certain embodiments,
the express alkali extraction and organomanganese-catalyzed
bleaching stage does not comprise the use of oxygen. However, in
certain embodiments, the express alkali extraction is performed in
the presence of oxygen.
[0060] Any suitable caustic solution can be used to perform the
express alkali extraction. In certain embodiments, the caustic
solution comprises an inorganic base or an organic base. In certain
embodiments, the caustic solution comprises an alkali or alkaline
earth metal hydroxide or salt. In certain embodiments, the caustic
solution comprises an alkali metal hydroxide or salt selected from
sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium
hydroxide, cesium hydroxide, and combinations thereof.
[0061] In certain preferred embodiments, the express alkali
extraction is performed by mixing the chemical pulp with an aqueous
caustic solution having a temperature of from about 40.degree. C.
to about 90.degree. C., and optionally dewatering and washing the
chemical pulp before treating the pulp with the organomanganese
complex and peroxide. As discussed above, sufficient brightness can
be obtained with relatively short extraction times (e.g., 10
minutes or less). In certain embodiments, express alkali extraction
is performed by contacting a chemical pulp with an aqueous caustic
solution for about 10 minutes or less. Thus, in certain
embodiments, express alkali extraction is performed by contacting a
chemical pulp with an aqueous caustic solution for about 10 minutes
or less, about 8 minutes or less, about 6 minutes or less, about 5
minutes or less, about 4 minutes or less, about 2 minutes or less,
or about 1 minute or less. In certain preferred embodiments,
express alkali extraction is performed by contacting the chemical
pulp with an aqueous caustic solution for about 1 minute or
less.
[0062] The aqueous caustic solution used in the express alkali
extraction may be re-used. In certain embodiments, the aqueous
caustic solution is reused in one or more express alkali
extractions from two to ten times. In certain embodiments, express
alkali extraction is performed using an aqueous caustic solution
that has been used from two to ten times.
[0063] In certain embodiments, the organomanganese-catalyzed
bleaching stage reduces the amount of chlorine dioxide needed in
the chlorine dioxide stage by 50% or less. Thus, in certain
embodiments, the organomanganese-catalyzed bleaching stage reduces
the amount of chlorine dioxide needed in the chlorine dioxide stage
by about 50% or less, about 40% or less, about 30% or less, about
20% or less, about 10% or less, or about 5% or less. In certain
embodiments, the organomanganese-catalyzed bleaching stage reduces
the amount of chlorine dioxide needed in the chlorine dioxide stage
by 50% or more.
[0064] In another embodiment, the invention provides a method for
improving a papermaking process through modification of a
multistage bleaching of chemical pulp, the method comprising
performing delignification of a chemical pulp (e.g., brownstock
pulp) subsequent to a cooking process and immediately prior to a
bleaching process (e.g., prior to a chlorine dioxide stage),
wherein the delignification is performed by treating the chemical
pulp with a manganese complex and a peroxide in the presence of a
base, and optionally oxygen gas.
[0065] For example, bleaching experiments on Eo chemical pulp
(e.g., hardwood pulp) has demonstrated that a multistage EoPcD0
sequence results in activation of the pulp towards subsequent
stages in the intermediate bleaching range. In other words, a
brightness gain is higher at the following D stage when the
organomanganese complex is applied in a previous alkali peroxide
stage. Generally, "stage synergism" is not expected when both
stages are oxidative. In certain embodiments, a reduction of about
50% chlorine dioxide at a D stage may be obtained without a
consequential loss in brightness. In certain embodiments, the
method does not comprise a chlorine dioxide stage either
immediately following a D stage or later in the bleaching sequence.
Thus, a D-treated (e.g., D0-treated) chemical pulp is an example of
an acidic oxidated chemical pulp.
[0066] In certain embodiments, express alkali extraction is also
achieved through an oxygen delignification stage. Thus, even on
less reactive D0-treated hardwood chemical pulp, an
organomanganese-catalyzed bleaching stage after oxygen
delignification yields an improvement in catalytic brightness (see,
e.g., FIG. 7).
[0067] Generally, oxygen delignification of brownstock pulp
immediately follows cooking and precedes bleaching stages.
Generally, residual lignin is removed in a reactor under aqueous
caustic conditions and pressurized oxygen, with kappa number being
the most important criterion of performance. Kappa number is an
indication of the residual lignin content or the bleachability of
wood pulp. Kappa number is determined by the number of milliliters
of 0.1-N potassium permanganate solution that can be absorbed by 1
gram of oven-dry pulp under conditions specified in the ISO
302:2004 standard.
[0068] It has been found that in the presence of peroxide, the
effect of the organomanganese complex on oxygen delignification can
be significant. Applying the organomanganese complex with hydrogen
peroxide alone could bring about the same effect that is achieved
through application of oxygen, in terms of both brightness and
kappa number. Moreover, application of the organomanganese complex
improves selectivity in bleaching, yielding increased brightness
and decreased kappa number at increased pulp viscosity (see FIG.
3). If peroxide concentration is sufficient, an
organomanganese-catalyzed bleaching process may be utilized in
addition to or instead of oxygen (e.g., Eo or Eop stages). Thus, in
certain embodiments, the method is performed in the absence of
oxygen.
[0069] In another embodiment, the invention provides an aqueous
formulation for bleaching of a chemical pulp comprising an
organomanganese complex and water, wherein the aqueous formulation
has a pH of from about 3 to about 7 and the organomanganese complex
is at a concentration of from about 0.001% to about 5% by weight
based on the weight of the aqueous solution. In certain preferred
embodiments, the formulation comprises about 0.5% to about 3%
organomanganese complex actives and has a pH of from about 4 to
about 6.
[0070] The organomanganese complex can be thermally unstable under
certain weather conditions, which limits its use at some pulp mill
locations. For example, application sites are normally not
protected from outdoor temperatures. Decomposition of
Mn.sup.2+.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bi-
s[octahydro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7-
]]]di-.mu.-oxodi-chloride (1:2) in an aqueous solution can occur at
sustained temperatures of about 35-40.degree. C. for 1-2 days.
Therefore, it is especially important that the organostability of
the organomanganese complex is taken into account. In certain
preferred embodiments, the organomanganese complex is introduced
into pulp in a form of a dilute solution that provides sufficient
storage stability at elevated temperatures. In certain embodiments
of the formulation, the formulation is ready-to-deliver and can be
stored without substantial degradation for an extended period of
time (e.g., 2 months or more) at temperatures of about
35-40.degree. C.
[0071] The proposed combination of concentration and pH ranges is
optimal from the points of feeding, storage and transportation. The
product can be formulated at an external facility or, preferably,
on site. A critical aspect of the formulation's stability is the pH
adjustment to an acidic range using an organic acid and/or an
inorganic acid, which may include, e.g., acetic acid, citric acid,
lactic acid, sulfuric acid, hydrochloric acid, and/or phosphorous
acid. The pH of the formulation is adjusted in view of a continuous
shift typical of the product. The formulation can be at any
suitable pH. In certain preferred embodiments, the formulation has
a pH of from about 4 to about 6. In certain embodiments, the
formulation has a pH of about 4, or of about 5, or of about 6. In
certain preferred embodiments, a strong acid such as sulfuric acid
is used to lower the pH of the formulation to about 4 to about 6.
In certain embodiments, the formulation is given enough time during
preparation for the pH adjustment. In certain preferred
embodiments, the initial pH of the formulation is about 4 so that
it would not exceed 6.5 after exposure to mill conditions.
[0072] In certain embodiments, the formulation comprises an
organomanganese complex and water. In certain embodiments, the
formulation consists essentially of an organomanganese complex and
water. In certain embodiments, the formulation consists of an
organomanganese complex and water.
[0073] Any suitable water source can be used with the present
inventive methods. In certain embodiments, the water is mill white
water. In certain embodiments, the water is tap water or deionized
water.
[0074] The formulation can comprise any suitable organomanganese
complex. In certain embodiments, the manganese complex is a
mononuclear or binuclear complex of Mn(III) and/or Mn(IV) organic
complex with one or more O.sup.2- bridge. In certain preferred
embodiments, the manganese complex is a manganese-triazacyclononane
complex. In certain preferred embodiments, the manganese complex is
Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-X.sup.-. The aforementioned complex can comprise any
suitable organic or inorganic anion (X.sup.-). In certain
embodiments, the anion is a halogen such as fluoride, chloride,
bromide, and/or iodide. In certain preferred embodiments, X.sup.-
is a chloride anion. In certain preferred embodiments, X.sup.- is
selected from a halogen, sulfate, acetate, and citrate. In certain
preferred embodiments, the organomanganese complex is Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-chloride (1:2).
[0075] The formulation can comprise organomanganese complex at any
suitable concentration. In certain embodiments, the organomanganese
complex is present in the formulation at a concentration of from
about 0.001% to about 5%. Thus, in certain preferred embodiments,
organomanganese complex is present in the formulation at a
concentration of from about 0.001% to about 5%, from about 0.001%
to about 4%, from about 0.001% to about 3%, from about 0.001% to
about 2%, from about 0.001% to about 1%, from about 0.001% to about
0.5% by weight based on the weight of formulation. In certain
preferred embodiments, the organomanganese complex is present in
the formulation at a concentration of from about 0.5% to about 3%
by weight of actives based on weight of the formulation.
[0076] In another embodiment, the invention provides an aqueous
formulation for bleaching of a chemical pulp comprising an
organomanganese complex, a peroxide, and water, wherein the
organomanganese complex is at a concentration of from 0.0001% to
about 1% and the peroxide is at a concentration of from about 5% to
about 60% by weight based on weight of the aqueous solution.
[0077] As discussed herein, it has been found that delivery form
and technique can affect the performance of the organomanganese
complex and industrial utility of the methods set forth herein. In
certain embodiments, the organomanganese complex is fed as a dilute
solution into, preferably, a peroxide line. If delivery into a
peroxide line is not possible, then the organomanganese complex can
be delivered into the chemical pulp line after the chemical pulp
has been treated with base and peroxide. If the organomanganese
complex is delivered directly into the pulp, thorough mixing of the
organomanganese complex with pulp slurry is recommended. In certain
embodiments, a high consistency mixer, e.g., an Andritz mixer Model
HCM3HH, is used to provide even distribution of the catalyst in
pulp. In certain preferred embodiments, the peroxide is
concentrated. In certain preferred embodiments, the
ready-to-deliver catalyst formulation comprises about 0.5 to about
3% actives and has pH adjusted to around about 4 to about 6. In
certain preferred embodiments, the deliverable formulation is
prepared on site from the solid product and tap water. In the
absence of the aforementioned steps, faster product decomposition
has been observed under common pulp mill conditions.
[0078] In certain embodiments, it was also found that the
organomanganese complex is preferably introduced into pulp in a
form of a solution into the hydrogen peroxide feeding line, the
higher concentration of peroxide the better. In certain preferred
embodiments, the peroxide is at a concentration of from about 30%
to about 50%. Introducing the organomanganese complex with the
peroxide increases efficiency in the methods set forth herein. The
organomanganese complex can also be introduced into pulp as a
solution. In certain embodiments, the organomanganese catalyst
solution is mixed with pulp before the bleaching process begins. In
certain preferred embodiments, the organomanganese complex is fed
into the peroxide line as a solution. In certain preferred
embodiments, the organomanganese complex is not fed into the
caustic line because the catalyst can be deactivated.
[0079] 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.
[0080] "Reaction tube" refers to a tube containing pulp combined
with a bleaching solution, where pulp moves through the tube at an
elevated temperature (e.g., 50-90.degree. C.). A difference between
a standard bleaching chest and a reaction tube is that the reaction
tube provides for continuous pulp bleaching during the relatively
short time when the pulp moves through the tube.
[0081] "Chemical pulp" refers to a mass of fibers resulting from
the reduction of wood or other fibrous raw material into its
component parts during cooking phases with various chemical
liquors, in such processes as sulfate, sulfite, soda, NSSC,
etc.
[0082] "Chlorine dioxide state" refers to a step or steps in a
multistage bleaching process (i.e., "D-stages") where chlorine
dioxide solution is combined with pulp, allowed to react, and then
washed as one of the operations making up a multistage pulp
bleaching system.
[0083] "Express alkali extraction" refers to the relatively
short-time contacting of pulp with relatively large quantity of
warm aqueous caustic solution followed by dewatering (e.g., 10%
consistency pulp is mixed with 1:5 volume of 1-10% caustic in water
at about 40 to about 90.degree. C., and then dewatered back to
10%). Generally, an express alkali extraction stage is performed in
the absence of peroxide and organomanganese complex.
[0084] "Medium brightness" refers to pulp having a ISO brightness
of about 50 to about 70.
[0085] The following examples further illustrate the inventive
concepts of the present disclosure but should not be construed as
in any way limiting its scope.
EXAMPLES
[0086] All percentages in the Examples are given on a weight
percent of dry pulp basis. In the Examples, the following terms
shall have the indicated meaning. Br for ISO brightness R457 (TAPPI
525); Ye for E313 yellowness; WI for E313 Whiteness. For the
purposes of the examples and procedures set forth herein,
"catalyst" refers to an organomanganese complex, and, specifically
for the Examples, refers to Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-chloride (1:2), which is an example of an organomanganese
complex.
Procedure 1-- Peroxide Bleaching
[0087] Procedure 1 is a procedure for peroxide bleaching of
chemical pulp in accordance with a portion of an embodiment of the
invention. The catalyst (e.g., organomanganese complex) used for
the experimental Examples is Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-chloride (1:2).
[0088] Pulp samples from various mills were tested. Based on
initial pulp consistency, 10 g (based on o.d. pulp) of sample was
taken. Next, samples were put in Kapak bags and diluted to a total
volume of 100 g, which provided pulp of 10% consistency.
[0089] Hydrogen peroxide (3% solution) was dosed at 0.5-2% by
weight, and sodium hydroxide (3% solution) was dosed at 1-3% by
weight based on o.d. pulp. An organomanganese complex sample
diluted to 1:50000 was applied at 1-5 ppm (active base) based on
dry pulp. The order of addition was as follows unless indicated
otherwise. Sodium hydroxide was added to the pulp first, followed
by the catalyst, and then hydrogen peroxide. After a pH measurement
was taken, the bag was sealed and pulp mixed by pounding and
pressing the bag. Subsequently, the samples were placed in a water
bath at 70.degree. C., unless indicated otherwise. After 40 minutes
(unless indicated otherwise), the samples were removed from the
water bath, placed in cold water and allowed to cool. After about
10 minutes, the samples were washed in a Buchner funnel lined with
cheesecloth with 3 L of water. Excess water was squeezed from the
samples. The samples were weighed and divided in half. One half of
each sample was used for making brightness pads; the other half of
each sample was saved for second stage bleaching with chlorine
dioxide, when needed.
[0090] It was discovered that that feeding the organomanganese
complex with caustic can cause decomposition and loss of activity.
The catalyst can be added to pulp before or after peroxide.
Additional benefit was discovered when the catalyst was fed to the
pulp with the peroxide via the peroxide line. In laboratory tests
simulating the latter process, the catalyst was added as a 1:20
solution of the standard formulation (2% actives) in water (total
dilution 0.1%) to concentrated hydrogen peroxide solution at a
target peroxide/catalyst ratio. The solution was held for 1 min and
then diluted to 3% peroxide that was added to alkali oxidized
chemical pulp at the target dosage.
[0091] In order to make brightness pads, the samples were diluted
to 1 L in a plastic beaker and stirred for about 10 minutes each.
One drop of 5-N sulfuric acid was added in order to eliminate
residual hydroxide. Then, the samples were passed through filter
paper, placed on metal plates and pressed for 5 minutes to remove
excess water. The samples were then left in a constant humidity and
temperature room (23.degree. C., 50% humidity) overnight.
Brightness was measured with a Technodyne Color Touch 2 (Model ISO)
instrument.
Procedure 2--Oxygen and Oxygen-Peroxide Delignification
[0092] Procedure 2 is a procedure for oxygen and oxygen-peroxide
delignification of chemical pulp in accordance with a portion of an
embodiment of the invention.
[0093] Pulp samples were prepared as described above based on 3%
consistency, 10.5 g o.d. pulp. The chemicals were added to dilute
pulp in an open Parr reactor, then the reactor was closed and, when
applicable, pressurized with oxygen to 100 psi. The slurry was
mixed at the "max" rate, believed to be about 300-400 rpm, and
heated to the target temperature that took 15-20 min dependent on
the target temperature. Time at the target temperature was counted
from the moment that the temperature was 5.degree. C. less than the
target (e.g., 95.degree. C. for 100.degree. C. target) to 40 min.
Then the reactor was cooled, depressurized, and the pulp processed
as described above.
Procedure 3--Chlorine Dioxide Bleaching
[0094] Procedure 3 is a procedure for chlorine dioxide bleaching of
chemical pulp in accordance with a portion of an embodiment of the
invention. Chlorine dioxide solution prepared in the laboratory was
stored in a refrigerator and titrated before the bleaching. For
chlorine dioxide bleaching, 5 g samples (based on o.d. pulp)
obtained from the previous step (hydrogen peroxide bleaching) were
diluted to 10% consistency in plastic bags. The pH of these pulp
samples was adjusted to about 4.5 with 5-N sulfuric acid before
addition of chlorine dioxide. Chlorine dioxide was dosed (usually,
at 0.5% based on o.d. pulp) and added right after pH adjustment.
The pH of these samples was from 2.5 to 2.9. The bags were sealed;
the samples mixed and kept in a water bath for 1 hour at 70.degree.
C. Subsequently, the samples were cooled to 25.degree. C. and
processed in the same way as described above for Procedure 1.
Procedure 4--Express Alkali Extraction
[0095] Procedure 4 is a procedure for express alkali extraction of
chemical pulp in accordance with a portion of an embodiment of the
invention.
[0096] Express alkali extraction was done in certain samples before
a peroxide bleaching stage. For such certain samples, usually 10 g
samples (based on o.d. pulp) were diluted to 5% consistency in
plastic bags. Then, 2% NaOH, based on dry pulp, was added as a 3%
solution to the bags and the samples mixed. The samples were then
placed in a water bath at 65.degree. C., diluted to 1 L of water
and squeezed with cheesecloth (i.e., no excessive wash). In further
tests, the samples were washed with a warm aqueous caustic
solution. In even further tests, the samples were treated with
caustic and dewatered to the target bleaching consistency without a
wash. Samples prepared according to Procedure 4 were later used in
peroxide bleaching as described in Example 1 herein.
Procedure 5--Brightness Determination
[0097] Procedure 5 provides background information related to
brightness determination of chemical pulp in accordance with a
portion of an embodiment of the invention.
[0098] Generally, brightness measurements are used for pulp
characterization and process assessment. "ISO Brightness" is a term
used to describe the whiteness of pulp or paper, on a scale from 0%
(absolute black) to 100% (relative to an MgO standard, which has an
absolute brightness of about 96%) by the reflectance of blue light
(457 nm wavelength) from the sheet.
Process Modification Examples
[0099] Examples of process modification and corresponding results
are as follows. FIG. 1 shows that, when organomanganese catalyst is
used in peroxide stage, the temperature of the process can be
reduced without negatively affecting brightness. Generally,
standard mill conditions can require between 60 and 90 minutes to
achieve target brightness. FIG. 2 demonstrates that bleaching
develops quickly in the presence of organomanganese catalyst,
resulting in maximum brightness at a much faster rate than under
standard mill conditions. This result is advantageous because
reducing temperature and time leads to increased pulp preservation,
which translates into increased yield and strength (e.g., increased
viscosity) of bleached pulp. FIG. 3 shows that selectivity of
bleaching and delignification are improved, resulting in increased
brightness, decreased kappa numbers, and increased viscosity.
[0100] Express alkali extraction significantly improves response of
D0-treated chemical pulp. FIG. 4 shows that a significant
improvement in brightness is achieved in the presence of catalyst
when D0-treated chemical pulp is subjected to alkali extraction
prior to bleaching, even at relatively low concentrations of
hydrogen peroxide (0.5% vs. 1%) on D0-treated hardwood chemical
pulp.
[0101] FIG. 5 shows that softwood D0-treated chemical pulp is more
responsive the catalyst and alkali activation further increases the
effect.
[0102] FIGS. 6A and 6B demonstrate that a short caustic wash tends
to improve bleachability and reactivity toward the catalyst for
both Eo (hardwood) and D0 (softwood) chemical pulp. It was
discovered that increased time of treatment had no effect on the
result, and 1 min treatment (e.g., washing with a warm aqueous
caustic solution) provided significant improvement in brightness.
Advantageously, washing with a short warm aqueous caustic solution
does not lead to alkali brightness loss. The results described
herein allow for a bleaching scheme of improved efficiency, with an
aqueous caustic wash followed by alkali peroxide bleaching
comprising a catalyst, e.g., an organomanganese complex.
[0103] Express alkali extraction can be achieved also through the
oxygen delignification stage. FIG. 7 demonstrates that, even on
less reactive D0 hardwood pulp, peroxide bleaching that is
post-oxygen delignification and that utilizes a catalyst improves
brightness in a D0EoEpc sequence.
[0104] Generally, express alkali extraction affects catalyst
performance more than the mere pH increase absent the catalyst.
FIGS. 8A and 8B show a comparative study of two- and one-stage Pc
process at the same hydroxide concentration (pre-treatment at 2%
caustic followed by 2% caustic/2% peroxide bleaching vs. 4%
caustic/2% peroxide bleaching). The figures demonstrate a clear
advantage of the two-stage process--higher differentiation and
higher brightness. The results illustrated in FIGS. 8A and 8B show
that a much greater brightness (81.0 versus 75.6 ISO Brightness
units) and shorter stage time (20 versus 90 minutes) is obtained
when compared to control samples. Additionally, reducing bleaching
time provides a benefit in yield and strength (i.e.,
viscosity).
[0105] FIG. 9 shows that improvement in brightness can be achieved
even at a relatively low peroxide dose and catalyst loading, e.g.,
at 0.5% hydrogen peroxide and 1-2 ppm catalyst.
[0106] Generally, oxygen delignification of brownstock pulp
immediately follows cooking and precedes bleaching stages. Under
aqueous caustic conditions and pressurized oxygen in a reactor,
oxygen delignification removes residual lignin, with kappa number
being an important criterion of performance. In the presence of
peroxide, which is optional, catalyst in oxygen delignification can
provide significant benefit. Moreover, the catalyst improves
selectivity of bleaching and delignification, resulting in
increased brightness, decreased kappa number, and increased
viscosity of the pulp, as illustrated in FIG. 3. With sufficient
peroxide concentration (in this particular instance about 2%
hydrogen peroxide), an Epc process may replace oxygen (Eo, Eop), as
oxygen may no longer be necessary in multistage bleaching.
[0107] FIGS. 10 and 11 demonstrate that multistage EoPcD0 bleaching
experiments on Eo hardwood pulp results in pulp activation toward
subsequent stages in an intermediate bleaching range as exemplified
by an increased brightness at the subsequent D-stage than at the
target peroxide stage. As noted herein, "stage synergism" is not
expected when both stages (e.g., peroxide stage and D-stage) are
oxidative. Potential reduction in chlorine dioxide consumption at
the D-stage may exceed 50 wt % based on examples presented
herein.
[0108] Differentiation achieved at the Ep stage remains when D1 has
a relatively high brightness range as well, which allows for
reduced chlorine dioxide consumption, or even possibly the
elimination of one or more chlorine dioxide stages. Elimination of
one or more chlorine dioxide stages would avoid pH readjustment for
the one or more chlorine dioxide stages that would be eliminated.
FIG. 12 shows the effect of the catalyst on an E2 Stage (D1
hardwood chemical pulp) that allows for a modified procedure,
thereby eliminating a D-stage (e.g., Do-Ep-D1-E2-D2 becomes
Do-Ep-D1-Epc).
[0109] A solution of catalyst in water is thermally unstable under
certain conditions and therefore cannot be used in every pulp mill,
particularly in summer months, as decomposition has been shown to
occur at 35.degree. C. to 40.degree. C. in 1-2 days. In certain
embodiments, the catalyst is introduced into pulp via a dilute
solution (e.g., from about 0.5 wt % to about 3 wt % as actives,
having a pH of from about 4 to about 6). FIG. 13 provides examples
of conditions that have been shown to allow for sufficient storage
stability under elevated temperatures.
Efficiency Improvement Examples
[0110] FIGS. 14A-C show that greater brightness is obtained when
catalyst is introduced as a solution into the hydrogen peroxide
feeding line prior to addition to the chemical pulp. It was
discovered that higher concentration of peroxide gives increased
brightness (e.g., 30-50 wt %). Introducing the catalyst with the
peroxide has been shown to provide improved efficiency (e.g.,
improved energy efficiency via decreased process temperatures
and/or improved chemical efficiency via decreased chemical
consumption). Catalyst can also be introduced into pulp in a form
of a solution after the caustic mixed with pulp or after the
caustic and peroxide mixed with pulp.
[0111] Laboratory findings were confirmed in a full-scale week-long
mill trial (kraft pulp, feeding the organomanganese catalyst as a
solution to a peroxide line). Trial data are presented in FIG.
15.
[0112] The following tests demonstrate how catalyst can be used in
specific stages to improve process efficiency, for example, to
allow for shorter reaction time(s), decreased process
temperature(s), reduction in bleaching agent consumption (e.g.,
chlorine dioxide at a subsequent D1 stage up to 50%), and/or allow
for the use of express bleaching (e.g., via reaction tube(s)), in
accordance with embodiments of the present invention. "Program" and
"Test (no.)" refer to samples that include catalyst. The catalyst
utilized was Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-C-o-
xodi-halide (1:2).
[0113] Test 1--Eop Stage
Conditions: Laboratory test, 3 wt % brownstock pulp, 2 wt %
hydrogen peroxide, 100 psi oxygen, 100.degree. C., 40 minutes+18
min ramping, 10 ppm by weight catalyst Data: Control 1 (no
catalyst) versus Test 1 (with catalyst): Brightness of Control 1
54.6 ISO Brightness Units versus brightness of Test 1 63.5 ISO
Brightness Units; Kappa value: Control 1 7.8 versus Test 1 7.3.
Results and Discussion: There was an immediate effect on the
process observed in the presence of the catalyst. In particular,
the Brightness increases and the Kappa number decreases in the
presence of the catalyst. The data suggests potential reduction in
chemical consumption and elimination of oxygen (e.g., replacement
of Eo stage with Epc stage).
[0114] Test 2--Ep (Eop) Stage
Conditions: Laboratory test, 10 wt % brownstock pulp, 2 wt % sodium
hydroxide, 2 wt % hydrogen peroxide, 70.degree. C., 5 ppm catalyst.
Data: Control 2--Brightness (ISO Brightness Units)--41.8 (20 min),
43.3 (40 min), 42.8 (60 min) Test 2--Brightness (ISO Brightness
Units): 47.6 (20 min), 47.6 (40 min), 48.3 (60 min) Control
2--Kappa: 11.9 (20 min), 11.7 (40 min), 11.7 (60 min) Test
2--Kappa: 10.1 (20 min), 10.8 (40 min), 10.4 (60 min) Results and
Discussion: A significant time saving can be achieved
simultaneously with increased brightness and Kappa number; higher
yield and strength are expected due to decreased pulp degradation
because of shorter exposure to hydroxide.
[0115] Test 3--Ep (Eop)
Conditions: lab test, 10 wt % brownstock pulp, 2 wt % sodium
hydroxide, 2 wt % hydrogen peroxide, 40 min, 5 ppm catalyst.
Data: Control 3--Brightness (ISO Brightness Units): 40.4
(70.degree. C.), 39.7 (60.degree. C.)
Test 3--Brightness (ISO Brightness Units): 46.1 (70.degree. C.),
46.3 (60.degree. C.)
Control 3--Kappa: 11.6 (70.degree. C.), 11.3 (60.degree. C.)
Test 3--Kappa: 9.7 (70.degree. C.), 10.1 (60.degree. C.)
[0116] Results and Discussion: Energy efficiency is improved
simultaneously with increased brightness and Kappa number; higher
yield and strength are expected due to decreased pulp degradation
because of milder conditions. Both time and temperature can be
decreased.
[0117] Tests 4a and 4b--EoEp(c)D1
Conditions: lab test, 10 wt % Eo softwood chemical pulp, 1 wt %
hydrogen peroxide, 2 wt % sodium hydroxide, 70.degree. C., 40 min,
5 ppm catalyst, followed by a D1 stage. Data: Control 4a versus
Test 4a: Brightness (ISO Brightness Units) Control 4a 52.0 versus
Test 4a 62.7 (0.5 wt % chlorine dioxide at D1) Control 4b versus
Test 4b: Brightness (ISO Brightness Units) Control 4b 55.9 versus
Test 4b 64.8 (1 wt % chlorine dioxide at D1) Results and
Discussion: A similar increase in brightness is achieved with 50%
reduction of chlorine dioxide consumption. Low-chlorine dioxide D1
or elimination of D1 with proper chemical balance is possible.
[0118] Tests 5a and 5b--EoEp(c)D1
Conditions: lab test, 10 wt % Eo hardwood chemical pulp, 2 wt %
hydrogen peroxide, 2 wt % sodium hydroxide, 70.degree. C., 40 min,
5 ppm catalyst; then followed by a D1 stage (0.6 wt % chlorine
dioxide) Data: Control 5a versus Test 5a: Brightness (ISO
Brightness Units) Control 5a 47.2 versus Test 5a 55.2 (EoEp(c))
Control 5b versus Test 5b: Brightness (ISO Brightness Units)
Control 5b 54.5 versus Test 5b 65.8 (EoEp(c)D1) Results and
Discussion: Brightness gain in the following D1 stage (Test 5b)
exceeds brightness gain in the Ep(c) stage proper (11.3 vs. 8 ISO
Brightness Units)--synergy likely due to lignin activation;
potential reduction in chlorine dioxide consumption.
Modification Examples
[0119] This Example demonstrates how catalyst can be used to
redesign multistage bleaching processes in accordance with
embodiments of the present invention.
[0120] Test 6--Eo/Eop
Conditions: lab test, 3 wt % chemical pulp, 2 wt % hydrogen
peroxide, 100 psi oxygen, 100.degree. C., 40 minutes+18 minutes
ramping, 10 ppm catalyst. Data: Peroxide alone versus
Peroxide+O.sub.2 versus Peroxide+Program: Brightness (ISO
Brightness Units) 43.1:54.6:54.1.
Kappa 9.8:7.8:8.1
[0121] Results and Discussion: Eop can be potentially replaced with
Epc (no oxygen) that would improve strength and yield, and activate
D0-treated chemical pulp towards the next D1 stage.
[0122] Tests 7a and 7b--Ep
Conditions: lab test, 10 wt % D0-treated softwood pulp, 2 wt %
sodium hydroxide, 2 wt % hydrogen peroxide, 70.degree. C., 40
minutes, 5 ppm catalyst. Data: Control 7a versus Test 7a "direct"
(e.g., no pre-treatment): Brightness (ISO Brightness Units) Control
7a 72.5 versus Test 7a 75.8 Control 7b versus Test 7b after 1
minute, 70.degree. C., pre-treatment with 2 wt % sodium hydroxide:
Brightness (ISO Brightness Units) Control 7b 74.1 versus Test 7b
79.0 Results and Discussion: Process modification, EEpc sequence
brings a significant brightness increase that may potentially
either eliminate subsequent D1 stage or allow significant reduction
in chlorine dioxide consumption.
[0123] Tests 8a and 8b--Ep
Conditions: lab test, 10 wt % D0 softwood chemical pulp, 10 minutes
pre-treatment with 2 wt % sodium hydroxide at 70.degree. C., 2 wt %
sodium hydroxide, 2 wt % hydrogen peroxide, 70.degree. C., 5 ppm
catalyst. Data: Control 8a versus Test 8a, 20 minutes bleaching:
Brightness (ISO Brightness Units) Control 8a 73.7 versus Test 8a
81.0; Yield Control 8a 93.1% versus Test 8a 92.3% Control 8b versus
Test 8b, 90 minutes bleaching: Brightness (ISO Brightness Units)
Control 8b 75.6 versus Test 8b 81.8; Yield Control 8b 88.1% versus
Test 8b 87.7% Results and Discussion: Process modification, EEpc
sequence brings increased brightness that may provide for the
elimination of a subsequent D1 stage or allow for a significant
reduction in chlorine dioxide consumption. Test 8a approximately
achieved in 20 min what a "standard" 90-min cycle achieved (e.g.,
Control 8b and Test 8b).
[0124] Test 9--D0EoPc
Conditions: lab test, 10 wt % D0 hardwood pulp, Eo, 1 wt % sodium
hydroxide, 1.5 wt % hydrogen peroxide, varied catalyst
concentration, 70.degree. C., 40 minutes. Data: Brightness (ISO
Brightness Units): Control 9a 70.9, Test 9a1 (1 ppm catalyst) 74.2,
Test 9a2 (3 ppm catalyst) 76.2 Control 9b versus Test 9b (3 ppm
catalyst), 90 minute bleaching: Brightness (ISO Brightness Units)
Control 9b 75.6 versus Test 9b 81.8; Yield Control 9a 88.1% versus
Control 9b 87.7% Results and Discussion: Multistage bleaching with
catalyst at the last stage: a significant improvement in brightness
was achieved, likely because the treated chemical pulp was
activated at Eo stage. As a result, a decreased dose of catalyst
was required.
Example 9--Field Trial
[0125] A one-week trial of catalyst (for this example, Mn.sup.2+
.mu.-(acetato-.kappa.O:.kappa.O')][.mu.-[1,1'-(1,2-ethanediyl)bis[octahyd-
ro-4,7-dimethyl-1H-1,4,7-triazonine-.kappa.N1,.kappa.N4,.kappa.N7]]]di-.mu-
.-oxodi-chloride (1:2)) confirmed the catalytic effect expected
based on laboratory studies. At 0.8 wt % hydrogen peroxide,
application of the catalyst at 4 ppm (2 ppm actives basis) improved
brightness 2.5 ISO Brightness Units. The effect was observed also
at decreased catalyst and peroxide doses. Bleaching at reduced
temperature by 20.degree. F. (i.e., approximately 11.degree. C.) in
presence of catalyst brought brightness better than in the
baseline. Thus, the primary objective of the trial was
satisfied.
[0126] Secondary objectives of the trial were to assess potential
improvements in decreased chlorine dioxide consumption and energy
efficiency. Chlorine dioxide consumption could be reduced to at
least 5 lbs. per ton chemical pulp (dry), with more work on the D1
stage. The improvement in energy efficiency will be more
site-dependent from plant to plant because it is not always
possible to decrease the temperature for each stage of a multistage
bleaching plant.
[0127] The one-week trial was designed to establish the utility of
the technology in a conventional five-stage bleach plant. The
bleach plant sequence is: D0, Ep, D1, E2, and D2. The catalyst was
added to the hydrogen peroxide stream being delivered to the first
extraction stage and fed into the dilution water delivered into the
50 wt % hydrogen peroxide feed line. The final concentration of the
hydrogen peroxide acting on the pulp was 35 wt %.
[0128] Trial data are illustrated in FIG. 15. The trial data
support the assumption that, under trial conditions (i.e., no
process changes, minimal changes of conditions), 2-ISO Brightness
Unit gain at target catalyst doses could be expected.
[0129] Mill trials always include periods of instability, and
averages should be measured through periods of unchanging
conditions to make correct comparisons. Raw brightness data though
are illustrative of the effect of the catalyst subsequent to an
acidic bleaching stage. Average data through consistent periods of
the same trial stages show that the immediate gain increased from
1.9 to 2.5 ISO Brightness Units when catalyst dose is increased.
Brightness decreased when feeding stopped, followed by an increase
upon resuming catalyst feeding. The effect of concentration
remained almost the same. Total gain can reach 3.9 ISO Brightness
Units at 4.4 ppm (2.2 ppm catalyst based on active ingredients).
The ability to reduce temperature when the catalyst was applied
decreased brightness by around 0.5 ISO Brightness Units, which
provided a gain versus baseline at 3.3 ISO Brightness Units.
[0130] The use of the terms "a" and "an" and "the" and "at least
one" and similar referents in the context of describing the
invention (especially in the context of the following claims) are
to be construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by context. The
use of the term "at least one" followed by a list of one or more
items (for example, "at least one of A and B") is to be construed
to mean one item selected from the listed items (A or B) or any
combination of two or more of the listed items (A and B), unless
otherwise indicated herein or clearly contradicted by context. The
terms "comprising," "having," "including," and "containing" are to
be construed as open-ended terms (i.e., meaning "including, but not
limited to,") unless otherwise noted. Recitation of ranges of
values herein are merely intended to serve as a shorthand method of
referring individually to each separate value falling within the
range, unless otherwise indicated herein, and each separate value
is incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0131] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *