U.S. patent application number 11/062534 was filed with the patent office on 2005-07-14 for methods of processing lignocellulosic pulp with cavitation.
Invention is credited to Hudson, Kelly, Kazem, Bijan.
Application Number | 20050150618 11/062534 |
Document ID | / |
Family ID | 34743838 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050150618 |
Kind Code |
A1 |
Kazem, Bijan ; et
al. |
July 14, 2005 |
Methods of processing lignocellulosic pulp with cavitation
Abstract
Methods of treating lignocellulosic pulp with cavitation are
disclosed. The methods include delignifying a slurry comprising
lignocellulos pulp in the presence of cavitation and bleaching a
delignified pulp in the presence of cavitation. Delignification can
be done by contacting a lignocellulosic pulp slurry with an
oxidizing agent in a cavitation zone. Bleaching can be carried out
by contacting a delignified pulp slurry with a bleaching agent in a
cavitation zone.
Inventors: |
Kazem, Bijan; (Woodstock,
GA) ; Hudson, Kelly; (Rome, GA) |
Correspondence
Address: |
WOMBLE CARLYLE SANDRIDGE & RICE, PLLC
P.O. BOX 7037
ATLANTA
GA
30357-0037
US
|
Family ID: |
34743838 |
Appl. No.: |
11/062534 |
Filed: |
February 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11062534 |
Feb 22, 2005 |
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10932604 |
Sep 2, 2004 |
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10932604 |
Sep 2, 2004 |
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10618119 |
Jul 11, 2003 |
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10618119 |
Jul 11, 2003 |
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09747469 |
Dec 20, 2000 |
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6627784 |
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60204838 |
May 17, 2000 |
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Current U.S.
Class: |
162/50 ; 162/65;
162/66; 162/67; 162/78; 162/83; 162/87; 162/90 |
Current CPC
Class: |
B01F 2003/04879
20130101; B01J 19/008 20130101; B01F 3/0807 20130101; B01J 19/1887
20130101; B01J 19/1806 20130101; B01F 3/04099 20130101; B01F
7/00816 20130101; B01J 2219/00121 20130101 |
Class at
Publication: |
162/050 ;
162/065; 162/090; 162/078; 162/083; 162/066; 162/067; 162/087 |
International
Class: |
D21C 009/10; D21C
009/147; D21C 009/14; D21C 009/153; D21C 009/16 |
Claims
What is claimed is:
1. A method of processing lignocellulosic pulp comprising:
producing a delignified pulp slurry; and contacting a bleaching
agent with the delignified pulp slurry in a first cavitation region
to produce a bleached, delignified pulp.
2. The method of claim 1, wherein the slurry contains about 15% or
less by weight dry pulp material.
3. The method of claim 1, wherein the first cavitation region
comprises a plurality of cavitation zones, each cavitation zone
having a void zone adjacent thereto.
4. The method of claim 1, wherein the first cavitation region
comprises a chamber having a rotor formed with a plurality of
irregularities.
5. The method of claim 1, wherein the delignified pulp slurry is
produced by contacting a slurry comprising lignocellulosic pulp
with at least one oxidizing agent.
6. The method of claim 5, wherein the slurry and oxidizing agent
are contacted in a second cavitation region.
7. The method of claim 6, wherein the second cavitation region
comprises a plurality of cavitation zones, each cavitation zone
having a void zone adjacent thereto.
8. The method of claim 6, wherein the second cavitation region
comprises a chamber having a rotor formed with a plurality of
irregularities.
9. The method of claim 5, wherein the slurry further comprises
black liquor.
10. The method of claim 7, wherein the oxidizing agent comprises an
oxygen-containing material.
11. The method of claim 10, wherein the oxygen-containing material
is air, ozone, molecular oxygen, sodium hydroxide, hydrogen
peroxide, or any combination thereof.
12. A method according to claim 1, wherein the bleaching agent is
air, oxygen, ozone, hydrogen peroxide, sodium hydrosulfite,
chlorine, chlorine dioxide, or any combination thereof.
13. A method according to claim 1, wherein the delignified pulp
slurry contains about 15% or less dry pulp material by weight.
14. The method of claim 1, wherein the lignocellulosic pulp is
produced by mechanical pulping, chemical pulping, or semichemical
pulping.
15. The method of claim 1, wherein the lignocellulosic pulp is a
secondary pulp.
16. A method of processing lignocellulosic pulp comprising:
contacting a bleaching agent with a slurry comprising
lignocellulosic pulp in a first cavitation region to produce a
bleached pulp.
17. The method of claim 16, wherein the first cavitation region
comprises a plurality of cavitation zones, each cavitation zone
having a void zone adjacent thereto.
18. The method of claim 16, wherein the first cavitation region
comprises a chamber having a rotor formed with a plurality of
irregularities.
19. The method of claim 16, wherein the slurry further comprises
black liquor.
20. A method according to claim 16, wherein the bleaching agent is
air, oxygen, ozone, hydrogen peroxide, sodium hydrosulfite,
chlorine, chlorine dioxide, or any combination thereof.
21. The method of claim 16, wherein the slurry contains about 15%
or less dry pulp material by weight.
22. The method of claim 16, wherein the lignocellulosic pulp is
produced by mechanical pulping, chemical pulping, or semichemical
pulping.
23. The method of claim 16, wherein the lignocellulosic pulp is a
secondary pulp.
24. The method of claim 16, wherein a first handsheet is produced
from the lignocellulosic pulp and a second handsheet is produced
from the bleached pulp; the first handsheet exhibits a first tear
strength and the second handsheet exhibits a second tear strength;
and the second tear strength is at least 10% greater than the first
tear strength.
25. The method of claim 16, wherein a first handsheet is produced
from the lignocellulosic pulp and a second handsheet is produced
from the bleached pulp; the first handsheet exhibits a first
tensile strength and the second handsheet exhibits a second tensile
strength; and the second tensile strength is at least 15% greater
than the first tensile strength.
26. A process to produce a paper product from wood comprising: (a)
providing wood chips; (b) pulping the wood chips to produce a
lignocellulosic pulp slurry; (c) delignifying the lignocellulosic
pulp slurry to produce a delignified pulp slurry; (d) bleaching the
delignified pulp slurry by contacting a bleaching agent with the
delignified pulp slurry in the presence of cavitation to produce a
bleached, delignified pulp; (e) forming the bleached, delignified
pulp into a paper product.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending
U.S. patent application Ser. No. 10/932,604, filed Sep. 2, 2004,
which is a continuation in-part-of patent application Ser. No.
10/618,119, filed Jul. 11, 2003, which is a continuation
application of U.S. patent application Ser. No. 09/747,469, filed
Dec. 20, 2000, now U.S. Pat. No. 6,627,784, which claims priority
to U.S. Provisional Patent Application Ser. No. 60/204,838, filed
May 17, 2000; all of which are incorporated herein by reference in
their entireties.
TECHNICAL FIELD
[0002] The present invention generally relates to methods for
processing lignocellulosic pulp, and more particularly to
delignifying and bleaching lignocellulosic pulp.
BACKGROUND
[0003] Wood is comprised of two main components, a fibrous
cellulose and a non-fibrous component. The polymeric chains forming
the fibrous cellulose portion of the wood are aligned with one
another and form strong associated bonds with adjacent chains. The
non-fibrous portion of the wood comprises a three-dimensional
polymeric material formed primarily of phenylpropane units, known
as lignin. The lignin is interspersed both between and in the
cellulosic fibers, bonding them into a solid mass.
[0004] Processes for the production of paper and paper products
generally includes a pulping stage in which wood, usually in the
form of wood chips, is reduced to a fibrous mass by removing a
substantial portion of the lignin. Some of these processes include
digestion of the wood by a Kraft or modified Kraft process
resulting in the formation of a dark colored slurry of cellulose
fibers known as "brownstock." The dark color of the brownstock is
attributable to the presence in the pulp after digestion of lignin
that has been chemically modified during pulping to form
chromophoric groups. In order to lighten the color of the
brownstock pulp sufficiently to make it suitable for use in various
paper applications, it is necessary to remove much of the remaining
lignin.
[0005] Further reduction of the concentration of lignin in the
lignocelluosic pulp is carried out in specific delignification
processes, bleaching processes, or combinations of the two.
Delignification processes include, for example, chemical treatment
with chlorine-containing compounds, such as sodium hypochlorite in
a caustic medium, or oxygen delignification with oxygen-containing
compounds. Both types of delignification processes typically are
followed by bleaching operations in which the delignified pulp is
bleached or brightened with ozone, chlorine, or chlorine
dioxide.
[0006] The use of chlorine or chlorinated compounds in paper making
processes is common. The use of such compounds usually result in
the production of effluent containing substantial quantities of
color, BOD (biological oxygen demand), COD (chemical oxygen demand)
and chlorides, which require additional processing before being
discharged. Therefore, reductions in the amount of chlorinated
compounds used the paper making processes can reduce the amount of
pollutants produced by the processes.
[0007] Conventional oxygen delignification processes, in some
cases, have produced smaller amounts of chlorinated organic
compounds and reduced levels of pollutant discharge, as compared
with other types of delignification processes. However,
conventional oxygen delignification processes typically require
significant amounts of oxygen-containing materials and significant
processing time to produce desired levels of delignification. The
overall delignification rate for conventional oxygen
delignification processes is controlled by the mass transfer
limitations associated with the three-phase nature of the system.
In order to react with the lignin inside the lignocellulosic
fibers, oxygen must cross the gas-liquid interface, diffuse through
the liquid film surrounding the fiber and then through the fiber
wall itself. Conventional processes have been found to be
ineffective at sufficiently dissolving oxygen, even at the highest
power input, to overcome these mass transfer limitations.
Furthermore, these oxygen delignification processes usually require
that the concentration of lignocellulosic pulp in the pulp slurry
that is produced in the initial stages of the paper making process
be increased so that the oxygen-containing materials can diffuse
sufficiently through the pulp to effect delignification. The
concentration of pulp usually must be lowered again for further
processing. The concentration manipulations are time-consuming and
energy intensive.
[0008] Conventional ozone bleaching processes are typically costly
as compared to other bleaching processes due to the high cost of
ozone and the large amounts of ozone needed to achieve the desired
pulp brightness.
[0009] Accordingly, alternative delignification processes are
needed that have the potential to reduce or eliminate some or all
of the above disadvantages.
SUMMARY
[0010] Methods for treating lignocellulosic pulp with cavitation
are disclosed. The methods generally include delignifying and/or
bleaching lignocellulosic pulp in the presence of cavitation.
[0011] In one aspect of the present invention, a method of
processing lignocellulosic pulp is provided that comprises
contacting an oxidizing agent with a slurry comprising pulp in the
presence of cavitation to produce a delignified pulp.
[0012] In another aspect of the present invention, a method for
processing lignocellulosic pulp is provided that comprises
delignifying a lignocellulosic pulp in a cavitation zone to produce
a delignified pulp.
[0013] In a further aspect of the present invention, a method of
treating lignocellulosic pulp is provided that comprises mixing a
slurry comprising pulp with a non-alkaline oxidizing agent in the
presence of cavitation to produce a delignified pulp.
[0014] In still a further aspect of the present invention, a method
of treating lignocellulosic pulp is provided that comprises mixing
an oxidizing agent and a slurry containing lignocellulosic pulp in
the presence of cavitation to produce a delignified pulp, wherein
the mixture of the oxidizing agent and the slurry exhibits a pH
above 7.
[0015] In another aspect of the present invention, a method of
making paper is provided that comprises pulping a lignocellulosic
feedstock to produce a lignocellulosic pulp and preparing a slurry
of the lignocellulosic pulp. The method also comprises delignifying
the lignocellulosic pulp in the presence of cavitation to produce a
delignified pulp, and forming paper from the delignified pulp.
[0016] In one aspect of the present invention, a method of treating
lignocellulosic pulp is provided that comprises mixing a bleaching
agent and delignified pulp in a cavitation region to produce a
bleached, delignified pulp.
[0017] In another aspect of the present invention, a method of
treating lignocellulosic pulp is provided that comprises mixing a
bleaching agent and a lignocellulosic pulp in a cavitation region
to produce a bleached pulp.
[0018] In yet another aspect of the present invention, a method of
treating lignocellulosic pulp is provided that comprises mixing a
bleaching agent and a secondary pulp in a cavitation region to
produce a bleached secondary pulp.
[0019] In a further aspect of the present invention, a method of
making paper is provided that comprises delignifying a
lignocellulosic pulp to form a delignified pulp, bleaching the
delignified pulp in a cavitation region, and forming paper from the
bleached, delignified pulp.
[0020] In yet another aspect of the present invention, a method of
making paper is provided that comprises delignifying a
lignocellulosic pulp in a cavitation region to form a delignified
pulp, bleaching the delignified pulp in a cavitation region, and
forming paper from the bleached, delignified pulp.
[0021] In yet another aspect of the present invention, a method of
making paper is provided that comprises bleaching a secondary pulp
in a cavitation region to form a bleached secondary pulp.
[0022] These and other aspects of the present invention are set
forth in greater detail in the description below and in the
accompanying drawings which are briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a flow diagram showing a typical processing scheme
for making paper from wood chips.
[0024] FIG. 2 illustrates a system in which lignocellulosic pulp
can be delignified in the presence of cavitation.
[0025] FIG. 3 is a cross-sectional view of the reactor shown in
FIG. 2.
[0026] FIG. 4 is a diagram showing results of delignification
trials charted as percent delignification versus residence
time.
[0027] FIG. 5 is a diagram showing results of delignification
trials charted as percent delignification versus residence
time.
[0028] FIG. 6 is a diagram illustrating ozone delignification
efficiency as a function of reactor speed at ambient temperatures
(about 20.degree. C. to about 30.degree. C.) for different ozone
charges.
[0029] FIG. 7 is a diagram illustrating ozone delignification
efficiency as a function of reactor speed at higher temperatures
(about 50.degree. C. to about 60.degree. C.) for different ozone
charges.
[0030] FIG. 8 is a diagram illustrating the reduction of pulp
viscosity as a function of Kappa number reduction.
DETAILED DESCRIPTION
[0031] The present invention includes methods for delignifying
lignocellulosic pulp. The delignification generally is carried out
by oxidizing the lignocellulosic pulp contained within a slurry in
the presence of cavitation to produce a delignified pulp.
[0032] As used herein, the term "delignification" refers to a
process of reducing the amount of lignin contained within a
material, particularly by a chemical reaction, such as oxidation,
which can be carried out in conjunction with one or more other
mechanical process or chemical reactions. The term "delignified
pulp" refers to a pulp derived from lignocellulosic material that,
as a result of delignifying, exhibits a smaller Kappa Number than
the pulp exhibited prior to delignification. The amount of
delignification that occurs typically is determined by comparing
the Kappa number of the pulp slurry before delignification and the
Kappa Number of the delignified pulp. As used herein, the term
"Kappa Number" refers to the volume (in millimeters) of 0.1N
potassium permanganate solution consumed by one gram of moisture
free pulp. The amount of delignification can be expressed as a
percent reduction in the two Kappa Numbers. The methods of the
present invention can effectuate delignifications of greater than
5% and, in some instances, about 5% to about 55% and above.
[0033] While a variety of oxidants, such as sodium hydroxide
(NaOH), sodium hydrosulfite, chlorine, chlorine dioxide, and
hydrogen peroxide (H.sub.2O.sub.2), can be used in delignifying the
pulp, the methods particularly are directed to the use of gaseous
oxidizing agents, such as air, molecular oxygen (O.sub.2), ozone
(O.sub.3) and combinations thereof to carry out the
delignification.
[0034] The methods of the present invention generally are directed
to delignifying lignocellulosic pulp in a slurry at any
consistency, but particularly at medium or low consistencies. As
used herein, the term "consistency" refers to the concentration by
weight of pulp in a pulp slurry on a dry weight basis. The term
"high consistency" refers to pulp slurry containing greater than
about 15% by weight pulp. The term "medium consistency" refers to
pulp slurry containing about 6% to about 15% by weight pulp. The
term "low consistency" refers to pulp slurry containing about 0.1%
to about 6% by weight pulp. Consequently, pulp being processed to
make paper can be maintained at or near the consistency level in
previous steps, delignified and further processed without raising
the consistency prior to delignification and then lowering the
consistency for further processing.
[0035] The methods generally include contacting an oxidizing agent
with a slurry comprising pulp in the presence of cavitation to
produce a delignified pulp. The oxidizing agent can be a
non-alkaline agent, such as gaseous oxidants, air, molecular
oxygen, and ozone, an alkaline agent such as sodium hydroxide, or a
combinations thereof. The oxidizing agent can be added to the pulp
slurry during mixing, immediately before mixing, or can be
remaining in the slurry from a previous process. Contacting the
slurry and oxidizing agent in the presence of cavitation can be
done under pressure. In one example, contacting is done under
pressure in the range of about 480 kPa to about 1035 kPa.
[0036] Furthermore, the contacted oxidizing agent and slurry also
can be heated, either in the presence of cavitation or before being
exposed to cavitation, to further effectuate delignification. In
one aspect, either one or both of the oxidizing agent and slurry,
or the mixture of the two, can be heated to a range of about
50.degree. C. to about 120.degree. C. In another aspect, either one
or both of the oxidizing agent and slurry, or the mixture of the
two, can be heated to a range of about 80.degree. C. to about
100.degree. C. This contacting also can take place in a pH range of
about 9 to about 12.
[0037] The methods also can include directing the delignified pulp
to a retention tank and holding the oxidant/slurry mixture
containing delignified pulp in the retention tank for a
predetermined period of time to effectuate additional
delignification. The oxidant/slurry mixture can be held under
pressure, for example in the range of about 480 kPa to about 1035
kPa, for a period of time. The time period in which the mixture can
be held, either under pressure or otherwise to effectuate further
delignification, can be in the range of about 1 minute to about 2
hours. In another aspect of the present invention, the time period
is about 1 minute to about 30 minutes. In yet another aspect of the
present invention, the time period is about 1 minute to about 20
minutes.
[0038] The amount of oxidant used to delignify the pulp depends on
the type of lignocellulosic material that is being treated. For
example, when molecular oxygen is being used to delignify pulp
before washing, molecular oxygen is combined with the slurry in a
range of about 3% to about 15% by weight based on the weight of the
dry pulp fiber in the slurry. For delignification of pulp after
washing, molecular oxygen is added in a range of about 1% to about
4% by weight. The specific amount of oxidant that is used to
delignify the lignocellulosic pulp can be affected by the type of
material it is, whether softwood or hardwood, and the amount of
sodium sulfide (Na.sub.2S) that remains in the slurry from previous
process steps. In one aspect, the methods of the present invention
generally include adding oxidant to the slurry in the range of
about 1% to about 20% by weight on a dry pulp fiber basis. In
another aspect of the present invention, the methods include adding
oxidant to the slurry in the range of about 5% to about 15% by
weight on a dry pulp fiber basis. In yet another aspect of the
present invention, the methods include adding oxidant to the slurry
in the range of about 1% to about 4% by weight of the dry pulp
fiber.
[0039] The slurry to which the oxidant is added can have a
consistency in the range of about 0.1% to about 15%. In another
aspect of the present invention, the slurry can have a consistency
in the range of about 0.1% to about 12%. In yet another aspect of
the present invention, the slurry can have a consistency of less
than about 6%. In still another aspect of the present invention,
the slurry can have a consistency of about 0.1 to about 6%.
[0040] A variety of bleaching agents, such as air, oxygen, ozone,
hydrogen peroxide, sodium hydrosulfite, chlorine, chlorine dioxide,
or any combination thereof can be used in bleaching the delignified
pulp.
[0041] In one aspect of the present invention, the bleaching agent
may be contacted with a delignified pulp slurry of any consistency,
for example, a pulp slurry containing from about 0.5 to about 15
weight % pulp on a dry weight basis. Accordingly, delignified pulp
exiting the delignifying stage can be introduced into the bleaching
stage without changing the consistency of the pulp. Alternatively,
the consistency of the delignified pulp can be raised or lowered
before the pulp is introduced into the bleaching stage.
[0042] In another aspect of the present invention, a
lignocellulosic pulp is contacted with a bleaching agent in the
presence of cavitation. In yet another aspect of the present
invention, a secondary pulp is contacted with the bleaching agent
in the presence of cavitation. As defined herein, secondary pulp
comprises any fibrous material that has undergone a manufacturing
process and is being recycled as the raw material to produce a new
manufactured product.
[0043] The pulp (delignified, lignocellulosic, or secondary pulp)
and bleaching agent may be contacted together in the presence of
cavitation under any range of reactor conditions. For example, the
pulp and bleaching agent may be contacted for about one second to
about 120 seconds. The bleaching agent can be added to the pulp
during mixing or immediately before mixing. Typically, the
bleaching agent, for example, as ozone, is introduced into the
reactor in an amount up to 16 kg/ton of pulp. The contacting can
take place at any pH, for example, a pH range of about 1.5 to about
4. Suitable reactor temperatures include, but are not limited to,
ambient temperatures, for example, temperatures ranging from about
70 to about 85.degree. F., or higher and lower temperatures, for
example, temperatures ranging from about 60 to about 135.degree. F.
Suitable reactor pressures include, but are not limited to, from
about 30 to about 100 psig.
[0044] Referring now in more detail to the drawings, in which like
numerals refer to like parts throughout the several views, FIG. 1
is a flow diagram of a typical processing scheme for producing
paper from wood chips 105. First, the wood chips 105 are converted
into lignocellulosic pulp 115 in a digesting stage 110. The
lignocellulosic pulp 115 is subsequently delignified in a
delignifying stage 120 to produce a delignified pulp 125. The
delignified pulp 125 can optionally be bleached or brightened in a
bleaching stage 130 to form a bleached, delignified pulp 135. The
bleached, delignified pulp 135 can subsequently be rolled into
sheets at a paper plant 140.
[0045] The digesting stage 110 typically consists of a conventional
wood chip cooker where the wood is reduced to a fibrous mass.
Examples of conventional digesting processes are mechanical,
chemical, and semichemical pulping processes. Mechanical pulping
comprises a process wherein wood is pressed lengthwise against a
rough, revolving grinding stone or other suitable material for
reducing the wood into a fibrous mass. Other typical mechanical
pulping processes involve the shredding or grinding of wood chips
between the rotating discs of a refiner device. The resulting
fibrous mass is typically known as a refined mechanical pulp (RMP).
Optionally, a thermal pre-softening step is employed before the
grinding step to reduce the amount of energy required to grind the
wood and to modify the resultant pulp properties. The combination
of pre-softening and mechanical grinding is known in the art as
thermo-mechanical pulping.
[0046] Chemical pulping comprises a process to degrade and dissolve
away the lignin in wood such that the cellulose and hemicellulose
remain in the form of substantially intact fibers. Chemical pulping
typically involves cooking wood chips with the appropriate
chemicals in an aqueous solutaion at elevated temperatures and
pressures. Kraft chemical processing comprises cooking the wood
chips with sodium hydroxide (NaOH) and sodium sulfide (Na.sub.2S).
Alternative chemical processes comprise cooking the wood chips with
sulphurous acid (H.sub.2SO.sub.3) and hydrogen sulfite (HSO.sub.3).
Semichemical pulping comprises a combination of chemical and
mechanical pulping processes. For example, the wood chips are
partially softened or digested with chemicals and then further
digested using a mechanical pulping device.
[0047] The delignifying stage 120 and bleaching stage 130 may
comprise a cavitation reactor or a conventional reactor. For
example, the lignocellulosic pulp 115 may be delignified in the
presence of cavitation, followed by a conventional bleaching stage
130. In another aspect, the lignocellulosic pulp 115 may be
processed in a delignification stage 120 comprising a conventional
delignification reactor, followed by a bleaching stage 130
comprising a cavitation reactor. In yet another aspect, the
lignocellulosic pulp 115 may be delignified in the presence of
cavitation, followed by bleaching in the presence of
cavitation.
[0048] FIG. 2 illustrates a system 100 comprising an apparatus in
which a lignocellulosic pulp slurry can be delignified and/or
bleached. The system 100 includes a reactor 11 in which the slurry
is exposed to cavitation. The system 100 also includes a feed tank
50 which contains the pulp slurry that is to be delignified and/or
bleached. The pulp slurry can be low or medium consistency. The
feed tank 50 is in flow communication with the reactor 11 by
delivery line 55, which has a flow meter 60 disposed therein for
monitoring the flow rate and/or amount of slurry flowing through
the delivery line 55. A feed pump 65 also is provided in flow
communication with the delivery line 55 to pump the slurry from the
feed tank 50 to the reactor 11. A gas inlet 28 is provided in flow
communication with the delivery line 55 to allow the introduction
of gaseous oxidizing and/or bleaching agents into the slurry stream
as it flows to the reactor 11.
[0049] An electric motor 70 is operably connected to the shaft 18
of the cavitator 20 so as to provide the driving force for rotating
the rotor 17 of the cavitator 20. As used herein, the term
"cavitator" refers to a device that can induce cavitation in a
fluid. Also, as used herein, the term "mechanical cavitator" refers
to a device that can induce cavitation in a fluid by moving a body
through the fluid. An exit line 73 is in flow communication with
the reactor 11 and routes the mixture of slurry and oxidizing
and/or bleaching agent to a retention tank 80. The mixture of
slurry and oxidizing and/or bleaching agent can be retained in the
retention tank for a predetermined period of time or simply until
an appropriate amount of delignification and/or bleaching has
occurred, as can be calculated from determining the Kappa Numbers
of the slurry over time. Sample lines 77 can be provided in-line
with the exit line 73 and the product line 75 to allow samples to
be taken to determine Kappa Numbers of the slurry and monitor
quality.
[0050] As shown in FIGS. 2 and 3, the reactor 11 comprises a
cylindrical housing 12 defining an internal cylindrical chamber 15.
In the figures, the housing 12 is formed of a wall 13 capped by end
plates 14 secured to each other by bolts 16. The wall 13 is
sandwiched between the plates 14.
[0051] The cylindrical rotor 17 is disposed within the cylindrical
chamber 15 of the housing and is mounted on the axially extending
shaft 18. The shaft 18 is journaled on either side of the rotor
within bearing assemblies 19 that, in turn, are mounted within
bearing assembly housings 21. The bearing assembly housings 21 are
secured to the housing 12 by means of appropriate fasteners such as
bolts 22. The shaft 18 projects from one of the bearing housings 21
and is coupled to the electric motor 70 or other motive means. It
will thus be seen that the rotor 17 may be spun or rotated within
the cylindrical chamber 15 in the direction of arrows 23 by
activating the motor 70 coupled to the shaft 18.
[0052] The rotor 17 has a peripheral surface that is formed with
one or more circumferentially extending arrays of irregularities in
the form of relatively shallow holes or bores 24. As shown in FIG.
3, the rotor 17 is provided with five arrays of bores 24 separated
by voids 26, the purpose of which is described in more detail
below. It should be understood, however, that fewer or more than
five arrays of bores may be provided in the peripheral surface of
the rotor as desired depending upon the intended fluids and
flowrates. Further, irregularities other than holes or bores also
may be provided. The rotor 17 is sized relative to the cylindrical
chamber 15 in which it is housed to define a space, referred to
herein as a cavitation zone 32, between the peripheral surface of
the rotor and the cylindrical chamber wall 13 of the chamber
15.
[0053] An inlet port 25 is provided in the housing 12 for supplying
from the delivery line 55 the slurry to be delignified and/or
bleached in the interior chamber 15. Gaseous oxidizing and/or
bleaching agents, such as air, molecular oxygen, ozone, chlorine,
chlorine dioxide, or any combination thereof, can be introduced
into the delivery line 55 through the gas supply conduit 28 and
entrained in the form of bubbles within the stream of slurry
flowing through the delivery line 55, if desired. Alternatively,
the oxidizing and/or bleaching agent can be introduced into the
slurry in liquid form. Oxidants such as sodium hydrosulfite,
chlorine, chlorine dioxide, hydrogen peroxide, or any combination
thereof can be introduced into the delivery line 55.
[0054] At the junction of the delivery line 55 and the gas supply
conduit 28, the slurry and oxidizing and/or bleaching agent form a
gas/slurry mixture in the form of relatively large gas bubbles 31
entrained within the flow of slurry 29. This mixture of slurry and
gas bubbles is directed into the cylindrical chamber 15 of the
housing 12 through the inlet port 25 as shown.
[0055] An outlet port 35 is provided in the housing 12 and is
located in the cap 14 of the housing opposite to the location of
the inlet port 25. Location of the outlet port 35 in this way
ensures that the entire volume of the gas/slurry mixture traverses
at least one of the arrays of bores 24 and thus moves through a
cavitation zone prior to exiting the hydrosonic mixer 11. The
outlet port 35 is in fluid communication with the exit line 73,
which directs the gas/slurry mixture to the retention tank 80.
[0056] In operation, the reactor 11 functions to mix the pulp
slurry with the oxidizing and/or bleaching agent and induce
cavitation in the slurry to effectuate thorough mixing. A slurry
containing lignocellulosic pulp exhibiting a first Kappa number is
pumped from the feed tank 50 through the delivery line 55. A
gaseous oxidant is supplied through the gas supply conduit 28 to
the slurry stream, which then form a mixture comprised of
relatively large gas bubbles 31 entrained within the slurry 29. The
slurry/gas bubble mixture moves through the delivery line 55 and
enters the chamber 15 through the supply port 25.
[0057] From the supply port 25, the mixture moves toward the
periphery of the rapidly rotating rotor 17 and enters the
cavitation zones 32 in the region of the bores 24. As described in
substantial detail in U.S. Pat. No. 5,188,090, the disclosure of
which is hereby incorporated by reference, within the cavitation
zones 32, millions of microscopic cavitation bubbles are formed in
the mixture within and around the rapidly moving bores 24 on the
rotor. Since these cavitation bubbles are unstable, they collapse
rapidly after their formation. As a result, the millions of
microscopic cavitation bubbles continuously form and collapse
within and around the bores 24 of the rotor, creating cavitation
induced shock waves that propagate through the mixture in a violent
albeit localized process.
[0058] As the mixture of slurry and relatively large gas bubbles
moves into and through the cavitation zones 32, the gas bubbles in
the mixture are bombarded by the microscopic cavitation bubbles as
they form and further are impacted by the cavitation shock waves
created as the cavitation bubbles collapse. This results in a
"chopping up" of the relatively large gas bubbles into smaller gas
bubbles, which themselves are chopped up into even smaller gas
bubbles and so on in a process that occurs very quickly. Thus, the
original gas bubbles are continuously chopped up and reduced to
millions of tiny microscopic gas bubbles within the cavitation
zone.
[0059] The dispersement and random flow patterns within the
cavitation zone 32 provide a high degree of mixing of the oxidant
and slurry. Some conventional systems do not achieve a thorough
mixing of the oxidant and slurry, thus requiring the addition of
substantially more oxidant into the slurry, resulting in increased
costs and still not guaranteeing even mixing of the combination.
The turbulence of the fluids within the cavitation zone 32 leads to
more complete mixing of the oxidant with the slurry.
[0060] The term "cavitation zone" is used herein to refer to any
region in which cavitation is induced in the lignocellulosic pulp
slurry, and, more particularly, a region specifically established
for the generation of cavitation within the slurry. In regards to
the reactor 11, shown in FIGS. 2 and 3, the term "cavitation zone"
refers to the region between the outer periphery of the rotor
wherein the bores are formed and the cylindrical wall of the
housing chamber. This area is where the most intense cavitation
activity occurs. It should be understood, however, that cavitation
may occur, albeit with less intensity, in regions other than this
space such as, for example, in the reservoir or region between the
sides or faces of the rotor and the housing.
[0061] The term "cavitation region" is used herein to refer to a
region comprising a plurality of cavitation zones, wherein each
cavitation zone has a void zone adjacent thereto. For example, in
the apparatus shown in FIGS. 2 and 3, the cavitation zone may be
the area between the outer periphery of the rotor 17 where the
bores 24 are formed and the cylindrical wall of the housing
chamber, while the void zone may be the area between the outer
periphery of the rotor 17 where the voids 26 are formed and the
cylindrical wall of the housing chamber. However, any apparatus
which provides a cavitaiton region as described herein is intended
to be within the scope of the present invention.
[0062] The process of cavitating the oxidant/slurry mixture can be
on a substantially continuous basis in that a continuous flow of
slurry is pumped into the hydrosonic mixer 11, treated by
cavitation and then discharged from the reactor 11. Alternatively,
the process can be conducted on a batchwise basis, wherein a
specified amount of slurry and oxidant is charged to the reactor
11, cavitated, and then discharged before any additional material
is charged to the mixer.
[0063] Delignification and/or bleaching occurs within the
cavitation zone of the reactor 11 and can continue in the retention
tank 80 if so desired. The oxidizing and/or bleaching agent and
slurry are mixed within the reactor 11 under pressure, typically in
the range of about 480 kPa to about 1035 kPa. The residence time of
the slurry within the reactor generally is within the range of
about 20 seconds to about 60 seconds, although this range can vary
depending upon the flowrate and size of the mixer.
[0064] The pulp contained within the slurry is delignified and/or
bleached within the mixer. In one example, a delignified pulp
exhibiting about 20% to about 25% delignification can be produced
within the reactor. If additional delignification is desired, the
delignified oxidant/slurry mixture can be discharged from the
reactor 11 through outlet port 35, exit line 73 and into retention
tank 80. The mixture can be retained in the retention tank for a
period of time under pressure to further delignify the pulp. In one
example, further delignification in the range of up to about 52%
can be effectuated by retaining the mixture in the retention tank
80 for a time period in the range of about 5 to about 30.
[0065] When the desired amount of delignification is achieved, the
slurry can be directed through the product line 75 for further
processing, such as washing, bleaching, etc.
[0066] Although the methods of the present invention have been
illustrated being carried out using a reactor as shown in FIGS. 2
and 3 and additionally described in the incorporated references,
the methods for delignifying lignocellulosic pulp in the presence
of cavitation are not limited to being carried out only with such
devices. Rather, any apparatus or system that can generate
cavitation in the pulp slurry can be used in conjunction with the
methods of the present invention. For example, systems employing
venturiz nozzles, sonic wave generators, or other mechanical mixers
that produce cavitation in the slurry can be used.
EXAMPLES
Example 1
[0067] Oxygen Delignification
[0068] Softwood slurry with consistency of 5% was heated to
195.degree. F. Either black liquor or sodium hydroxide was added to
the slurry to adjust the pH of the slurry to about 12, so as to
mimic process conditions for before and after washing,
respectively. Hot slurry was pumped through the cavitating reactor
and the line pressure was increased to about 95 psig. Oxygen was
added to the slurry before it entered the cavitating reactor. The
rotor of the reactor included thirty holes or bores per row and was
driven by a variable electric motor. The cavitating reactor was
made of 316 stainless steel and was sixteen inches in length and
three inches in width. The rotor was set at about 1200 rpm during
the trials. The slurry went to a retention tank for residence time
after leaving the reactor. Samples were taken at the feed tank and
after the retention tank.
1TABLE 1 Slurry Slurry Slurry Kappa % Kappa Source of Consistency
Slurry Pressure Temperature O.sub.2 O.sub.2 Kappa # # Final Drop
Alkalinity % wt pH # Psig .degree. C./.degree. F. SCFM psig Initial
5 Min 5 min Sodium 5% 11.6 93 95.2/203 3 105 34.5 24.3 29.6
hydroxide Sodium 5% 11.6 94 69.5/157 3 105 34.5 23.5 31.9 hydroxide
Black 5% 11.62 92 69.1/156 5 105 34.5 24.5 29% Liquor Black 5% 11.6
98 88.5/191 5 105 34.5 21.22 38.50% Liquor
Example 2
[0069] Oxygen Delignification of Softwood Pulp Before Washers
[0070] Trials were run in the cavitating reactor of Example 1 to
determine the amount of oxygen necessary to achieve desired
delignification. Before washing of lignocellulosic pulp slurry
using cavitation, pulp slurries typically carry black liquor solids
that are oxidizable by the oxidant intended for delignification.
Consequently, the amount of oxygen provided to delignify the pulp
should be sufficient to allow for the competing reaction of the
oxidation of the black liquor.
[0071] Table 2 shows the process conditioning for the trials to
determine oxygen requirement for other oxidizeable compounds in
black liquor. FIG. 4 shows the results of the trial.
2 TABLE 2 Property Range Slurry Flow gpm 12-52 Consistency 2.5%
Softwood Slurry Inlet Temperature .degree. C. 81-88 Pressure Psig
85-110 Slurry pH 9-12 Reaction Temperature .degree. C. 89-93
Reaction Pressure 90 psig End pH >11.5
[0072] Results show that black liquor solids (excluding fiber)
oxidize in the presence of oxidizing agent as does the lignin. The
results shown in FIG. 4 indicate that the rate of delignification
is independent of the competing reaction as long as there is enough
oxidant for all the reactions to occur.
Example 3
[0073] Oxygen Delignification
[0074] In this example about 2.5% hardwood slurry after washers was
sent through the reactor and then to the retention tank. The slurry
temperature was about 90.degree. C. and the pH was about 11.8. The
starting Kappa Number was about 13. Oxygen was added to the slurry
prior to the slurry entering the cavitating reactor, which was the
same as described in Example 1. Samples were taken at the feed
tank, after the reactor and before the retention tank, and after
the retention tank. The results shown in FIG. 5 indicate that
during the brief time period of about one minute in the reactor,
the slurry exhibited up to about 20% of delignification.
Example 4
[0075] Ozone Delignification
[0076] A well-washed kraft hardwood pulp slurry with about a 3%
pulp consistency and an initial Kappa number of about 13.5 was
obtained and used at ambient temperatures and an initial pH of
about 2.5. The pH was adjusted with sulfuric acid and the
temperature was adjusted using direct steam. The slurry was pumped
through a cavitation reactor at a rate of about 2.5 to about 3
Tons/Day and the speed of the cavitation rotor was varied from 900
to 3600 rpm. The cavitation reactor was a ShockWave Power Generator
with a 15.4".times.2" rotor, 150 HP motor, and an
adjustable-frequency AC drive. The ozone charge was kept constant
at about 0.53%.
[0077] Ozonated pulp from the reactor went into an upflow column
(0.25.times.2.7 m) with a pressure control valve at the top. Pulp
was discharged from the column to an enclosed tank with a gas
separator. The ozone concentration of the separated gas was
determined with a PCI monitor. Pulp samples for testing were
collected from a sampling valve in the discharge piping following
the upflow column. The ozonated pulp samples were caustic extracted
at 10% consistency with about 1.25% NaOH for about 60 minutes at
about 70.degree. C. in plastic bags in a water bath. The Kappa
number was measured using standard method TAPPI UM246. The
delignification efficiency from the ZE (ozone delignification "Z"
followed by caustic extraction "E") partial sequence was calculated
as the decrease in Kappa number per kg of ozone applied. Inlet and
outlet temperatures and pressures were measured in the feed and
discharge lines. The results are shown in Table 3.
[0078] The delignification efficiency was in a range of about 1.8
to about 2.1 kappa unit decrease per kg ozone charged. A systematic
effect on the efficiency was not observed with an increase in
reactor speed, since the lowest efficiency appeared to be obtained
at the intermediate speed of 1800 rpm.
3TABLE 3 Reactor Inlet Outlet .DELTA. Kappa O.sub.3 charged Speed
Pressure Temp. Temp. ZE Kappa No./kg Sample No. (wt %) (rpm) (kPa)
(.degree. C.) (.degree. C.) No. O.sub.3 B107 0.54 900 317 23 23 2.2
2.09 B108 0.53 900 317 23 23 2.3 2.11 B105 0.53 1800 317 23 24 3.9
1.81 B106 0.53 1800 317 23 24 3.4 1.91 B104 0.53 3600 317 25 31 3.3
2.11
Example 5
[0079] Ozone Delignification
[0080] A well-washed kraft hardwood pulp slurry with about a 2.9%
pulp consistency, an initial Kappa number of about 11, and an
initial pH of about 2.5 was processed as in Example 4. The rotor
speed was varied from 900 to 3600 rpm, and the temperature was
maintained at either about 28.degree. C. or about 50.degree. C.
Black liquor carryover was about 2.1 kg COD/Oven Dried Metric Ton.
These results are shown in Table 4. An increase in efficiency was
observed as the reactor speed was increased from 900 to 3600 rpm.
There also appeared to be a decrease in efficiency at higher
temperatures for a given ozone charge.
4TABLE 4 Reactor Inlet Outlet .DELTA. Kappa O.sub.3 charged Speed
Pressure Temp. Temp. ZE Kappa No./kg Sample No. (wt %) (rpm) (kPa)
(.degree. C.) (.degree. C.) No. O.sub.3 B206 0.34 900 331 52 51 9.0
0.53 B203 0.41 900 331 28 28 7.8 0.74 B205 0.35 1800 306 51 51 8.0
0.81 B209 0.39 1800 324 50 51 7.9 0.74 B202 0.41 1800 324 28 28 7.0
0.93 B208 0.35 3600 379 50 56 6.0 1.37 B204 0.42 3600 303 51 54 6.8
0.96 B201 0.44 3600 310 28 32 6.0 1.09
Example 6
[0081] Ozone Delignification
[0082] A well-washed kraft hardwood pulp slurry with about a 2.7%
pulp consistency, an initial Kappa number of about 14.9, an initial
viscosity of about 33.0 cps (as determined by standard method TAPPI
T230), and an initial pH of about 2.5 was processed as in Example
4. The rotor speed was varied from 900 to 3600 rpm, and the
temperature was maintained at about 28.degree. C. Black liquor
carryover was about 14 kg COD/ODMT. These results are shown in
Table 5.
5TABLE 5 .DELTA. O.sub.3 Reactor Inlet Outlet ZE ZE Kappa Sample
charged Speed Pressure Temp. Temp. Kappa Viscosity No./kg No. (wt
%) (rpm) (kPa) (.degree. C.) (.degree. C.) No. (cps) O.sub.3 A209
0.49 900 315 28 28 11.2 28.5 0.76 A208 0.50 1800 315 28 29 9.9 26.4
1.00 A203 0.57 1800 329 29 30 8.1 20.0 1.19 A206 0.66 1800 322 28
29 8.4 20.8 0.98 A207 0.50 3600 322 28 35 9.8 23.6 1.02 A202 0.60
3600 329 29 34 8.2 19.3 1.12 A205 0.64 3600 329 28 35 8.2 20.0
1.05
Example 7
[0083] Ozone Delignification
[0084] A well-washed kraft hardwood pulp slurry with about a 2.8%
pulp consistency, an initial Kappa number of about 12.7, and an
initial pH between about 2.0 to about 2.8 was processed as in
Example 4. The rotor speed was varied from 900 to 3600 rpm, and the
inlet temperature ranged from about 21.degree. C. or about
55.degree. C. These results are shown in Table 6.
6TABLE 6 .DELTA. O.sub.3 Reactor Inlet Outlet ZE ZE Kappa Sample
charged Speed Pressure Temp. Temp. Kappa Viscosity No./kg No. (wt
%) (rpm) (kPa) (.degree. C.) (.degree. C.) No. (cps) O.sub.3 A306
0.52 900 310 49 49 9.0 31.3 0.72 A303 0.65 900 308 21 21 8.0 24.8
0.72 A305 0.54 1800 310 52 52 7.5 25.0 0.96 A302 0.66 1800 301 21
21 5.8 20.6 1.05 A301 0.58 3600 296 23 27 5.7 22.2 1.21 A304 0.61
3600 303 55 59 6.1 21.4 1.08 A307 0.86 3600 303 38 42 3.1 14.9
1.11
[0085] A statistical analysis of the ozone delignifiaction data,
excluding the data set from Example 4, showed that the
delignification efficiency increased with the reactor speed. There
was no clear trend in the effect of ozone charge or temperature on
delignification efficiency at any given speed. The delignification
efficiency as a function of speed at ambient temperatures (about
20.degree. C. to about 30.degree. C.) for different ozone charges
is shown in FIG. 6. The delignification efficiency at higher
temperatures (about 50.degree. C. to about 60.degree. C.) is shown
in FIG. 7.
Example 8
[0086] Ozone Delignification
[0087] A well-washed kraft hardwood pulp slurry with about a 2.0%
pulp consistency and an initial Kappa number of about 14.4 was
obtained and used at temperatures ranging between about 51 to about
56.degree. C. and an initial pH of between about 2.2 to about 2.6.
Black liquor carryover was increased to either about 30 or about 73
kg COD/Metric Ton. The slurry was pumped through a cavitation
reactor and the speed of the cavitation rotor was maintained at
about 1800 rpm. A reinforced extraction (EP.sub.O) stage was used
following the ozone delignification stage. EP.sub.O stages were
carried out in a pressurized peg mixer at about 10% consistency for
about 60 minutes at about 77.degree. C. with about 1.50% NaOH and
about 0.25% H.sub.2O.sub.2. The initial pressure was about 60 psig
O.sub.2 which was decreased to about 0 psig over the course of the
reaction. The delignification efficiency from the Z(EP.sub.O)
partial sequence was calculated as the decrease in Kappa number per
kg of ozone applied. The results are shown in Table 7. The higher
ozone charges used and use of the (EP.sub.O) stage indicates that
the ozone is somewhat less efficient with the higher carryover.
7TABLE 7 Black .DELTA. Liquor O.sub.3 Reactor Inlet Outlet ZE Kappa
Sample Carryover charged Speed Pressure Temp. Temp. Kappa No./kg
No. (kg COD/MT) (wt %) (rpm) (kPa) (.degree. C.) (.degree. C.) No.
O.sub.3 A401 30 0.73 1800 303 56 56 6.6 1.07 A406 30 1.1 1800 358
52 52 3.9 0.97 A408 73 0.84 1800 345 51 51 5.4 1.07
Example 9
[0088] Pulp Quality Improvement
[0089] The pulp viscosity was measured for each of the hardwood
pulps in Examples 6 and 7, before and after ozone delignification.
A reduction in viscosity following the ZE stages was observed as a
function of the reduction in Kappa number, as shown in FIG. 8.
Handsheets were prepared from the hardwood pulps in Examples 6 and
7, before and after ozone delignification using standard method
TAPPI T205. The reduction in pulp viscosity did not result in a
loss in handsheet tear and tensile strengths (as determined by
standard method TAPPI T220), as shown in Table 8. A refining effect
was observed based on the 25-30% reduction in freeness. There was a
corresponding increase in tear strength of about 10% and in tensile
strength of 15-20%.
8TABLE 8 O.sub.3 Reactor Charged Speed ZE Tensile Sample No. (%)
(rpm) Viscosity CSF Tear Index Index Initial 33.0 547 6.07 32.4
A209 0.49 900 28.5 417 7.93 37.0 A208 0.50 1800 26.4 412 6.50 37.1
A203 0.57 1800 20.0 402 6.45 40.3 A206 0.66 1800 20.8 426 6.73 38.9
A207 0.50 3600 23.6 403 6.74 38.1 A202 0.60 3600 19.3 389 6.63 38.6
A205 0.64 3600 20.0 411 6.77 39.2 Initial 39.6 611 7.13 35.3 A306
0.52 900 31.3 448 7.45 38.0 A303 0.65 900 24.8 460 7.66 38.4 A305
0.54 1800 25.0 410 7.97 40.7 A302 0.66 1800 20.6 421 7.74 39.3 A301
0.58 3600 22.2 427 7.41 39.6 A304 0.61 3600 21.4 417 7.70 39.6 A307
0.86 3600 14.9 416 7.34 38.8
Example 10
[0090] Improved Gas/Liquid Mixing
[0091] Oxygen and water were mixed together using various types of
reactors and the K.sub.La constant (volumetric gas/liquid mass
transfer coefficient) was measured. As shown below in Table 9, the
cavitating Shockwave Power Generator exhibits significantly higher
K.sub.La values (i.e., improved mass transfer properties) as
compared to conventional reactors. Although not wishing to be bound
by theory, it is believed that the improved K.sub.La values
obtained using the Shockwave Power Generator are due to the
reactor's ability to significantly reduce the size of the oxygen
bubbles within the oxygen/water mixture.
9 TABLE 9 Reactor K.sub.La Mechanically Agitated Tank 0.02-0.2 Jet
Loop 0.01-2.2 Tubular/Venturi Ejector 0.1-3 Quantum .TM. Mixer
0.05-1.1 Shockwave Power Generator (5" .times. 4" rotor) 0.28-2.2
Shockwave Power Generator (10" .times. 2" rotor) 0.9-5.2
Example 11
[0092] Ultrasonic Effect
[0093] Softwood slurry with consistency of 4 wt % pulp and an
initial Kappa number of about 27.2 was pumped through the
cavitating reactor with a rotor set at about 1200 rpm during the
trials. In Trial A, the slurry was pumped through the cavitating
reactor in the absence of additional components. NaOH was added to
the slurry in an amount sufficient to reach a pH of about 11.5, and
this mixture was pumped through the cavitating reactor in the
presence of NaOH for Trial B. In Trial C, oxygen and NaOH were
added to the slurry to obtain a mixture and the mixture was pumped
through the cavitating reactor. The mixture contained about 1.5 wt
% oxygen and had an initial pH of about 11.5. Samples were taken
for each trial and the final Kappa number was measured. The results
are shown below in Table 10.
10 TABLE 10 Trial Kappa Number Initial 27.2 Trial A 25.7 Trial B
25.6 Trial C 19
[0094] As shown in Table 10, the slurry exhibits a decrease of
about 1.5 in the Kappa number, even in the absence of oxidizing
agents. This decrease can be attributed to the ultrasonic effect of
the cavitation on the lignocellulosic fiber, resulting in the
opening of the fiber pores and the removal of fragmented lignin
from the fiber. Further, because of the pore-opening effect, when
oxidizing and/or bleaching agents are used in combination with the
cavitating reactor, the chemicals have easier access to the lignin
in the lignocellulosic fiber.
[0095] Although certain aspects of the invention have been
described and illustrated, it should be understood by those skilled
in the art that the foregoing and various other changes, omissions
and additions may be made therein and thereto, without parting from
the spirit and scope of the present invention.
* * * * *