U.S. patent application number 15/655555 was filed with the patent office on 2018-02-01 for method and compositions for oxygen delignification 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 | 20180030651 15/655555 |
Document ID | / |
Family ID | 59558456 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180030651 |
Kind Code |
A1 |
Duggirala; Prasad Y. ; et
al. |
February 1, 2018 |
METHOD AND COMPOSITIONS FOR OXYGEN DELIGNIFICATION OF CHEMICAL
PULP
Abstract
The present disclosure provides methods and compositions for
improving the oxygen delignification process. The methods may
include adding low doses of a borohydride stabilized in an alkaline
solution to brownstock pulp. The methods may result in significant
chemical savings, increased pulp brightness, increased pulp yield,
and reduced kappa number.
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: |
59558456 |
Appl. No.: |
15/655555 |
Filed: |
July 20, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62367406 |
Jul 27, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21C 9/147 20130101;
D21C 9/1084 20130101; D21C 9/14 20130101; D21C 3/026 20130101 |
International
Class: |
D21C 3/02 20060101
D21C003/02; D21C 9/14 20060101 D21C009/14 |
Claims
1. A method for pulp delignification in a kraft process comprising:
adding a composition to a brownstock pulp, wherein the composition
comprises a reducing agent in an alkaline solution, and wherein the
composition is added after a pulp digestion stage and before an
oxygen delignification process.
2. The method of claim 1, wherein the reducing agent is a hydride
donor.
3. The method of claim 1, wherein the reducing agent is selected
from the group consisting of lithium borohydride, sodium
borohydride, potassium borohydride, and any combination
thereof.
4. The method of claim 1, wherein the reducing agent is added in an
amount less than about 0.1% by weight relative to an oven dried
amount of brownstock pulp.
5. The method of claim 1, wherein the composition comprises an
amount of about 1% to about 34% by weight of the reducing agent and
an amount of about 1% to about 50% by weight of a base in
water.
6. The method of claim 5, wherein the base is selected from the
group consisting of sodium hydroxide, potassium hydroxide,
magnesium hydroxide, sodium carbonate, calcium carbonate, and any
combination thereof.
7. The method of claim 1, wherein the reducing agent comprises
sodium borohydride, the composition comprises the sodium
borohydride at a concentration of about 12% by weight, and the
composition comprises sodium hydroxide at a concentration of about
40% by weight.
8. The method of claim 1, wherein the alkaline solution comprises
sodium hydroxide.
9. The method of claim 1, wherein the alkaline solution has a pH in
a range of about 10 to about 14.
10. The method of claim 1, further comprising: forming a mixture
comprising the composition and an alkaline liquor; and adding the
mixture to the brownstock pulp prior to a temperature increase in
the oxygen delignification process.
11. The method of claim 1, wherein the oxygen delignification
process excludes adding peroxides.
12. The method of claim 1, wherein the composition further
comprises a surfactant.
13. The method of claim 1, wherein the composition further
comprises a phase transfer catalyst.
14. The method of claim 13, wherein the phase transfer catalyst is
selected from the group consisting of tetra-n-butylammonium
bromide, methyltrioctylammonium chloride, benzyltrimethylammonium
chloride, hexadecyltributylphosphonium bromide, and any combination
thereof.
15. The method of claim 1, wherein the composition further
comprises a chelant.
16. The method of claim 15, wherein the chelant is selected from
the group consisting of diethylene-triamine-pentamethylene
phosphonic acid (DTMPA), salts of DTMPA,
diethylenetriaminepentaacetic acid (DTPA), salts of DTPA,
ethylenediaminetetraacetic acid (EDTA), salts of EDTA, and any
combination thereof.
17. The method of claim 1, wherein the composition further
comprises a polysulfide.
18. The method of claim 1, further comprising: feeding the
brownstock pulp and the composition into a reactor; pressurizing
the reactor with oxygen; and increasing a temperature inside the
reactor to about 80.degree. C. to 110.degree. C., wherein the
method results in a decreasing amount of lignin in the brownstock
pulp.
19. The method of claim 18, further comprising: removing a pulp
material from the reactor; and bleaching the pulp material using a
bleaching solution, wherein the bleaching solution has an enhanced
effect on increasing pulp brightness, and wherein the bleaching the
pulp is performed after the oxygen delignification process.
20. A composition for brownstock pulp delignification comprising: a
gas and an alkaline solution, wherein the gas is pressurized oxygen
and the alkaline solution comprises a reducing agent and a base.
Description
BACKGROUND
1. Field of the Invention
[0001] The present disclosure generally relates to improvements in
oxygen delignification of chemical pulp. More particularly, the
disclosure relates to the use of reducing agents to remove lignin
during an oxygen delignification process.
2. Description of the Related Art
[0002] Chemical pulping of lignocellulosic materials with sodium
sulfide (e.g., the kraft process) and without sodium sulfide (e.g.,
an alkaline or soda process) yields brownstock pulp that may be
further processed through delignification and bleaching stages to
reach the target brightness and lignin content of the final pulp
product. The kraft process is one of the major pulping processes in
the pulp and paper industry. Papermaking typically includes a stock
preparation stage, a pulping stage, a bleaching stage, a wet end
stage, and a dry end stage.
[0003] Lignin is a highly complex polyphenolic compound, which is
an integral part of the secondary cell walls of plants. It is one
of the most abundant organic polymers and typically constitutes
between a quarter and a third of the dry mass of wood. Lignin
contains numerous functional groups, including carbonyls, which are
highly reactive and interfere with numerous chemical processing
steps in papermaking. Lignin content (commonly reported as kappa
number) is negatively correlated with pulp brightness; therefore,
removing lignin from pulp is a central goal of pulp processing.
[0004] Lignin can be removed from pulp through oxygen
delignification. Oxygen delignification is achieved through
exposure of pulp to pressurized oxygen at elevated temperatures
under alkaline conditions. A drawback of oxygen delignification is
carbohydrate depolymerization due to severe process conditions,
such as temperature and alkalinity.
BRIEF SUMMARY
[0005] The present disclosure generally relates to improvements in
oxygen delignification of chemical pulp. Some embodiments of this
disclosure relate to methods for pulp delignification in a kraft
process, which may include adding a composition to brownstock pulp.
The composition added to the pulp may comprise a reducing agent in
an alkaline solution. In certain embodiments, the composition may
be added after a pulp digestion stage and before an oxygen
delignification process.
[0006] In some embodiments, compositions for brownstock pulp
delignification are disclosed. The compositions may include a gas
and an alkaline solution. The gas may be pressurized oxygen and the
alkaline solution may comprise a reducing agent and a base. The
reducing agent may be stable in the composition in the presence of
oxygen and under the process conditions.
[0007] The foregoing has outlined rather broadly the features and
technical advantages of the present disclosure in order that the
detailed description that follows may be better understood.
Additional features and advantages of the disclosure will be
described hereinafter that form the subject of the claims of this
application. It should be appreciated by those skilled in the art
that the conception and the specific embodiments disclosed may be
readily utilized as a basis for modifying or designing other
embodiments for carrying out the same purposes of the present
disclosure. It should also be realized by those skilled in the art
that such equivalent embodiments do not depart from the spirit and
scope of the disclosure as set forth in the appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] A detailed description of the invention is hereafter
described with specific reference being made to the drawings in
which:
[0009] FIG. 1 shows bleaching process stabilization;
[0010] FIG. 2 shows pulp brightness decrease after trial
period;
[0011] FIG. 3 shows bleaching cost/ton increase after trial
period;
[0012] FIG. 4 shows ClO.sub.2 dosage lb/ton increase after trial
period; and
[0013] FIG. 5 shows calculated % O.sub.2 delignification increase
during trial period.
DETAILED DESCRIPTION
[0014] Various embodiments are described below to illustrate
certain aspects of the present disclosure. However, it should be
understood that the present disclosure is not limited to the
embodiments explicitly described.
[0015] In some embodiments of the present disclosure, a composition
is provided comprising a reducing agent in an alkaline solution.
This composition may be added to brownstock pulp. Brownstock pulp
is commonly understood to refer to pulp that may result from
digesting wood chips in a kraft or soda process. A kraft process
may include the treatment of wood chips with a hot mixture of
water, sodium hydroxide, and sodium sulfide to break and remove
lignin. The technology entails several steps, both mechanical and
chemical. In certain embodiments, the composition may be added
after a pulp digestion stage and before an oxygen delignification
process.
[0016] The reducing agent is not limited and numerous reducing
agents may be used in accordance with the embodiments disclosed
herein. In some embodiments, the reducing agent is a hydride donor.
In some embodiments, the reducing agent may be selected from the
group consisting of lithium borohydride, sodium borohydride,
potassium borohydride, and any combination thereof. In one
particular embodiment, the reducing agent is sodium borohydride. A
representative example of a composition containing sodium
borohydride that may be used in accordance with the present
disclosure is Borol.RTM., which comprises 12 wt. % sodium
borohydride and 40 wt. % sodium hydroxide.
[0017] Sodium borohydride (BH) is a strong reducing agent that
reacts with carbonyl groups in lignin and provides additional
avenues for lignin depolymerization. Without wishing to be bound by
theory, it appears that at low dosages, such as below 0.1 wt. %, BH
selectively attacks functional groups in pulp, thus activating
lignin and passivating carbohydrates relative to subsequent
reactions. While BH is a known bleaching chemical that may also
improve pulping at high doses, its unexpected activity at low
dosages, such as lower than 0.1 wt. % discovered by the present
inventors can be explained, for example, by the presence of active
functionalities in pulp that are small in number but high in
importance in terms of directing the bulk pulping process, residual
lignin preservation and carbohydrate preservation.
[0018] In certain embodiments of the present disclosure, the
reducing agent is added to the pulp in an amount less than about
0.1%, by weight, based on oven dried pulp. The pulp may be
brownstock pulp. In some embodiments, the reducing agent may be
added to the brownstock pulp in an amount between about 0.005% and
0.1%, by weight, based on oven dried pulp. The reducing agent may
also be added in an amount between about 0.001% and 0.005%, between
about 0.001% and 0.002%, between about 0.001% and 0.003%, between
about 0.001% and 0.004%, between about 0.0001% and 0.001%, between
about 0.0005% and 0.001%, between about 0.005% and 0.05%, between
about 0.005% and 0.01%, between about 0.05% and 0.1%, between about
0.05% and about 0.08%, between about 0.07% and about 0.1%, and/or
between about 0.00005% and 0.0001%, by weight, based on oven dried
pulp. In some aspects, the dosage of the reducing agent, such as
sodium borohydride, may be sufficiently low to provide no bleaching
to the pulp.
[0019] In some embodiments, the composition comprises an amount of
about 1% to about 34%, by weight, of the reducing agent and an
amount of about 1% to about 50%, by weight, of a base in water.
Suitable bases may include, but are not limited to, sodium
hydroxide, potassium hydroxide, magnesium hydroxide, sodium
carbonate, calcium carbonate, and any combination thereof. Any
reducing agent, or any combination of reducing agents, may be used
in accordance with this embodiment. For example, the reducing agent
may be sodium borohydride. In some embodiments, the composition may
be added to brownstock pulp that may contain black liquor.
[0020] Other compounds, such as 9,10-antraquinone (AQ), used in
delignification processes act as catalysts, unlike BH, which is a
consumed pulp activator. This led to a universal, but incorrect,
assumption that a high dose (>0.1 wt. %) of BH is always
required to achieve the same effect as catalysts. Considering the
cost of the treatment, this led to the belief that the use of BH is
economically unrealistic. Moreover, no convenient, stable product
and no efficient and safe feeding methods have been proposed;
without them the technology would not be feasible. Adding powdered
BH at the paper mill is unsafe because the chemical reacts with
water under neutral pH, thereby releasing hydrogen. The present
disclosure seeks to overcome these problems by using a solution
comprising the reducing agent instead of a solid. The present
inventors determined that a broad range of reducing agents, such as
a borohydride, can be stabilized in alkaline solution and therefore
can be safely used in industrial applications.
[0021] In certain embodiments of this disclosure, the composition
comprises an alkaline solution containing sodium borohydride, which
is a stable, safe and convenient form for transportation, storage
and dosing to the target process. The composition may contain a
base at a concentration from approximately 10 wt. % to
approximately 40 wt. % and from approximately 5 wt. % to
approximately 25 wt. % reducing agent. The reducing agent may be a
borohydride-containing compound and the alkaline solution may
comprise sodium hydroxide.
[0022] In certain embodiments, the composition may consist of a
reducing agent (or combination of reducing agents), a base (or a
combination of bases), and water. In other embodiments, the
composition may consist of sodium borohydride, sodium hydroxide and
water.
[0023] In some embodiments, the oxygen delignification process may
be improved by feeding a composition comprising BH in an aqueous
alkaline solution to the pulp liquor prior to an oxygen
delignification process. The composition may comprise, for example,
Borol.RTM., Venpure.RTM., or any other liquid containing
approximately 10 wt. % to approximately 25 wt. % NaBH.sub.4 in
approximately 20 wt. % to approximately 40 wt. % NaOH.
[0024] In particular embodiments, the reducing agent in the
composition comprises sodium borohydride at a concentration of
about 12 wt. % and the composition additionally comprises sodium
hydroxide at a concentration of about 40 wt. %. In some
embodiments, the alkaline solution may have a pH from about 10 to
about 14. The pH range may be, for example, about 10 to about 13,
about 10 to about 12, or about 10 to about 11.
[0025] In still further embodiments, the method may comprise
forming a mixture of the composition with an alkaline liquor and
adding the mixture to the brownstock pulp prior to a temperature
increase in the oxygen delignification process. The composition may
comprise a stabilized borohydride alkaline solution. Instead of
adding the composition directly to the brownstock pulp, the
composition may be added, for example, to an alkaline liquor prior
to being added to the brownstock pulp being fed into an oxygen
delignification process. The alkaline liquor may comprise sodium
hydroxide. The alkaline liquor may be fed into the oxygen
delignification process to maintain a NaOH to oxygen mass ratio of
about 0.9. In some embodiments, the oxygen delignification process
excludes adding peroxides.
[0026] In some embodiments, the composition may further comprise a
surfactant or a combination of surfactants. The surfactant is not
limited and can be, for example, cationic, anionic, zwitterionic,
nonionic, or amphoteric. An illustrative example of a nonionic
surfactant is a triblock copolymer of PEO-PPO-PEO, where PEO
(polyethylene oxide) is hydrophilic and PPO (polypropylene oxide)
is hydrophobic. Compatibility testing carried out by the inventors
demonstrated that the sodium borohydride in an alkaline solution
can be applied with a surfactant, or combination of surfactants,
without any side reactions.
[0027] In some embodiments, the composition further comprises a
phase transfer catalyst to aid in oxygen transfer into the liquid
phase. The phase transfer catalyst is not limited and may
illustratively be selected from the group consisting of
tetra-n-butylammonium bromide, methyltrioctylammonium chloride,
benzyltrimethylammonium chloride, hexadecyltributylphosphonium
bromide, and any combination thereof.
[0028] In still further embodiments, the composition may comprise a
chelant. The chelant may be selected from the group consisting of
diethylene-triamine-pentamethylene phosphonic acid (DTMPA) and
salts thereof, salts of diethylene-triamine-pentamethylene
phosphonic acid (DTMPA), diethylenetriaminepentaacetic acid (DTPA),
salts of diethylenetriaminepentaacetic acid (DTPA),
ethylenediaminetetraacetic acid (EDTA), salts of
ethylenediaminetetraacetic acid (EDTA), and any combination
thereof.
[0029] In some embodiments, the composition further comprises a
polysulfide. Polysulfides are compounds that comprise chains of
sulfur atoms and can include anions and organic polysulfides.
Anions may have the general formula S2-n, where "n" can be any
number. These anions are the conjugate bases of the hydrogen
polysulfides H2S.sub.n. Organic polysulfides may have the general
formula RS.sub.nR, where R may be, for example, any alkyl group or
any aryl group. The inventors discovered in a stability test that
BH and polysulfides are compatible so they may be combined in an
alkaline solution. The discovery was achieved by keeping a solution
of the two components at elevated temperature and measuring
residual active BH by means of acidification and comparing the
volume of evolved hydrogen with a control sample. The polysulfide
may be sodium polysulfide. The polysulfide may be mixed into the
composition with sodium borohydride and/or fed separately.
[0030] In additional embodiments, the method may further comprise
feeding the brownstock pulp and the composition into a reactor,
pressurizing the reactor with oxygen, and increasing a temperature
inside the reactor to about 80.degree. C. to about 110.degree. C.
The pressure inside the reactor may be approximately 85 psi. The
pressure inside the reactor may range from approximately 80 psi to
approximately 100 psi. The pH inside the reactor may be between
approximately 10 and approximately 14. The consistency of the pulp
slurry may be between about 1% to about 30%. Consistency is a term
used in the art to refer the mass fraction (or percentage) of solid
or filterable material in a given slurry sample. In other
embodiments, the consistency may be from about 9% to about 15%,
from about 1% to about 3%, or from about 3% to about 9%.
[0031] It is counterintuitive to use a reducing chemical in the
oxidative process of oxygen delignification. However, the present
inventors unexpectedly discovered that BH does not react with
oxygen under the process conditions. Reactions of pulp with BH and
oxygen are separated in time while being part of the same
delignification process. Furthermore, addition of BH can be done
without making adjustments to standard process equipment.
[0032] The methods disclosed herein may further comprise bleaching
the pulp material using a bleaching solution. The bleaching
solution may comprise chlorine dioxide. The pulp may be whitened
using doses of chlorine dioxide that would have been insufficient
to reach the brightness target had no BH been added to the pulp.
The methods may further comprise contacting the pulp material with
one or more chelants.
[0033] In some embodiments, the composition added to the brownstock
pulp may comprise a gas and an alkaline solution. The gas may be
pressurized oxygen and the alkaline solution may comprise a
reducing agent and a base. In certain embodiments, the composition
may consist of pressurized oxygen, sodium borohydride, and sodium
hydroxide in water. The alkaline solution may be added to the
composition at low doses, such as from about 0.05 wt. % to about
0.5 wt. %.
[0034] In accordance with the present disclosure, an oxygen
delignification process can be improved by adding an alkaline
solution comprising a reducing agent to brownstock pulp. Applying
the methods disclosed herein results in significant savings in
process chemicals, process stability, decreased kappa number of the
pulp, increased pulp brightness, and higher pulp yield. Less white
liquor is needed during oxygen delignification and less chlorine
dioxide is needed in later bleaching steps. In addition to chemical
savings, the process may be operated at milder conditions, for
example, the temperature during oxygen delignification may be
lowered to prevent degradation of cellulose and hemicellulose. The
alkalinity of the pulp slurry may be reduced as well. These savings
and improvements are completely unexpected at the low doses of BH
disclosed herein. Additionally, the embodiments of the present
disclosure provide increased safety and efficiency that has never
been achieved. Moreover, the embodiments of the present disclosure
make this BH technology viable for kraft pulp applications.
EXAMPLES
[0035] About 10.5 g (based on oven dried pulp) samples of
brownstock pulp were processed through an oxygen delignification
procedure conducted at 3% consistency and with an initial pH of
about 11.9 (adjusted with 10 wt. % NaOH). The BH alkaline solution
(Borol.RTM.) was added to the brownstock pulp slurry at the target
pH. The brownstock pulp slurry and chemicals were added into an
open Parr reactor. The reactor was closed and pressurized with
oxygen to 100 psi. Mixed at the "max" rate, the slurry was heated
to the target temperature in about 15 to about 20 minutes. Time at
the target temperature was measured from the moment the reactor
temperature was within about 5.degree. C. of the target temperature
to the reactor cool-down initiation, which was about 40 min. The
reactor was cooled and depressurized. The pulp was washed in a
Buchner funnel lined with cheesecloth and divided in half. One half
was used for making brightness pads and the other was saved for
second stage bleaching with chlorine dioxide, when needed.
[0036] Chlorine dioxide bleaching was conducted at about 10%
consistency, a pH of about 4 (adjusted with 10 wt. %
H.sub.2SO.sub.4), at about 70.degree. C. for about 60 minutes. The
pulp was washed in a Buchner funnel lined with cheesecloth with
about 3 L of water. Excess water was squeezed from the samples and
brightness pads were prepared. No acidification at this step was
required.
[0037] In order to make brightness pads, the pulp samples were
diluted with water to about 1 L in a plastic beaker and stirred for
about 10 minutes each. To eliminate residual alkalinity, 1 drop of
5 N H.sub.2SO.sub.4 was added. Then, the samples were passed
through filter paper, placed on a metal plate and pressed for about
5 minutes to remove all excess water. After excess water removal,
the samples were left overnight at a constant humidity (about 50%)
and temperature of about 23.degree. C. Brightness was measured with
a Technodyne Color Touch 2 (Model ISO) instrument. Kappa number was
measured according to TAPPI test method T 236.
[0038] Brownstock low-delignified kraft pulp from a Northwest mill
(kappa# 60, brightness 16.48) was used in the test. The ISO
brightness in the control (without BH) was 19.87 and the ISO
brightness was 21.99 when treated with 0.05 wt. % BH. After
bleaching with 3 wt. % chlorine dioxide, the ISO brightness in the
control (without BH) was 39.96 and the ISO brightness was 44.60
using 0.05 wt. % BH.
[0039] In another experiment (Table 1, Experiment B), the chlorine
dioxide content was 2 wt. % and the BH content was 0.5 wt. %. The
ISO brightness in the control (without BH) was 19.67 and the ISO
brightness was 21.29 using BH. After bleaching with 3 wt. %
chlorine dioxide, the ISO brightness in the control (without BH)
was 30.87 and the ISO brightness was 35.68 using BH.
[0040] Thus, the inventors unexpectedly discovered that the effect
of BH does not depend linearly on the dose and a noticeable effect
can be achieved at a low dose. This effect multiplies at the
following bleaching stages.
TABLE-US-00001 TABLE 1 ISO brightness levels for different
treatments of brownstock pulp. After Oxygen Delignification After
D0 Bleaching Experiment Control BH treatment Control BH treatment A
0.05 wt % BH 19.87 21.99 39.96 44.60 B 0.5 wt % BH 19.67 21.29
30.87 35.68
[0041] Oxygen Delignification Mill Trial
[0042] Several single day trials were conducted at a Northeast mill
on Northern hardwood brownstock pulp (.about.50% maple, .about.20%
birch, .about.20% beech, and .about.10% poplar, blended with
.about.3-6% softwood) from a kraft process. The kappa number of the
pulp before oxygen delignification was about 12-14. The stock
temperature entering the O.sub.2 reactor was about 71.degree. C.,
and the temperature and pressure in the reactor was about
82-88.degree. C. and about 85 psi, respectively. At a consistency
of about 4% to about 5% and pH of about 10.5, the brownstock pulp
was in the reactor for about 1.5 to about 2 hours. The NaOH :
oxygen ratio was maintained at about 0.90. The caustic and oxygen
were on a dosage control for production. A 12 wt. % solution of
sodium borohydride in 40 wt. % aqueous alkaline solution was fed at
about 1.0 lb/oven dried ton of brownstock pulp to the sodium
hydroxide feed just before the O.sub.2 reactor.
[0043] The trial data show that the proposed treatment results in
process stabilization, higher brightness, lower bleaching costs,
lower chlorine dioxide consumption, and improved delignification
(FIGS. 1-5).
[0044] FIG. 1 shows that before the trial period the bleach load
had a range of 3.3. However, during the trial period, the
variability dropped to 0.5. After the trial period, the range
increased to 1.4. Applying the composition to the pulp before
oxygen delignification resulted in process stabilization at the
bleaching stages. It also resulted in higher brightness, lower
bleaching costs, lower chlorine dioxide consumption, and improved
delignification (in FIGS. 1-5, the middle line represents an
average and the lines on either side of the middle line represent
+/-1 Sigma).
[0045] FIG. 2 shows a decrease in pulp brightness after the trial
period when the composition was applied to the process. Pulp
brightness averaged 39.7 during the trial period, as measured by a
Technodyne Color Touch 2 instrument. However, after the trial
period, the brightness decreased to an average of 37.7 with greater
variability.
[0046] FIG. 3 shows how bleaching costs increased after the trial
period from an average of 48.1$/ton to an average of 51.3 $/ton.
The disclosed inventive method produces sensitized pulp that
requires less bleaching chemicals to reach target pulp
brightness.
[0047] FIG. 4 shows an increase in chlorine dioxide after the trial
period from 49.6 lb/ton to 53.7 lb/ton. Less chlorine dioxide is
required when using the composition comprising sodium borohydride
in an alkaline solution.
[0048] FIG. 5 shows that the average % delignification of the pulp
increased during the trial period to an average of 23.1 from an
average of 20.2. Activating lignin before oxygen delignification
improved removal of lignin from the pulp.
[0049] All of the compositions and methods disclosed and claimed
herein can be made and executed without undue experimentation in
light of the present disclosure. While this invention may be
embodied in many different forms, there are described in detail
herein specific 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. In addition, unless expressly stated to
the contrary, use of the term "a" is intended to include "at least
one" or "one or more." For example, "a reducing agent" is intended
to include "at least one reducing agent" or "one or more reducing
agents."
[0050] Any ranges given either in absolute terms or in approximate
terms are intended to encompass both, and any definitions used
herein are intended to be clarifying and not limiting.
Notwithstanding that the numerical ranges and parameters setting
forth the broad scope of the invention are approximations, the
numerical values set forth in the specific examples are reported as
precisely as possible. Any numerical value, however, inherently
contains certain errors necessarily resulting from the standard
deviation found in their respective testing measurements. Moreover,
all ranges disclosed herein are to be understood to encompass any
and all subranges (including all fractional and whole values)
subsumed therein.
[0051] Furthermore, the invention encompasses any and all possible
combinations of some or all of the various embodiments described
herein. It should also be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the invention and without diminishing its intended
advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *