U.S. patent application number 13/258488 was filed with the patent office on 2012-07-05 for pulping process for quality protection including methods for hemicellulose extraction and treatment of hemicellulose-extracted lignocellulosic materials.
Invention is credited to Harry T. Cullinan, Gopal A. Krishnagopalan, Sung-Hoon Yoon.
Application Number | 20120168102 13/258488 |
Document ID | / |
Family ID | 42828720 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120168102 |
Kind Code |
A1 |
Yoon; Sung-Hoon ; et
al. |
July 5, 2012 |
PULPING PROCESS FOR QUALITY PROTECTION INCLUDING METHODS FOR
HEMICELLULOSE EXTRACTION AND TREATMENT OF HEMICELLULOSE-EXTRACTED
LIGNOCELLULOSIC MATERIALS
Abstract
A method for producing pulp by extracting hemicellulosic
materials from lignocellulosic materials using water in an
extraction stage, wherein the extraction stage is either a single
extraction or a double extraction process; treating the
lignocellulosic materials with an oxidizing agent in a treatment
stage, wherein the treatment stage is selected from the group
consisting of a second extraction process, an agent impregnation
process, and a first pretreatment process; treating the
lignocellulosic materials with a reducing agent in the treatment
stage, wherein the treatment stage is selected from the group
consisting of the second extraction process, the agent impregnation
process, and a second pretreatment process; and then subjecting the
lignocellulosic materials to a modified Kraft pulping process to
produce pulp.
Inventors: |
Yoon; Sung-Hoon; (Auburn,
AL) ; Cullinan; Harry T.; (Opelika, AL) ;
Krishnagopalan; Gopal A.; (Maple Vally, WA) |
Family ID: |
42828720 |
Appl. No.: |
13/258488 |
Filed: |
April 2, 2010 |
PCT Filed: |
April 2, 2010 |
PCT NO: |
PCT/US10/29765 |
371 Date: |
March 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61165995 |
Apr 2, 2009 |
|
|
|
Current U.S.
Class: |
162/37 ; 162/1;
162/233; 162/29; 162/68; 162/72; 162/76; 162/79; 162/80; 162/82;
162/90 |
Current CPC
Class: |
D21C 3/022 20130101;
D21C 1/02 20130101; D21C 1/06 20130101; D21C 11/00 20130101; D21C
3/02 20130101 |
Class at
Publication: |
162/37 ; 162/1;
162/29; 162/68; 162/72; 162/76; 162/79; 162/80; 162/82; 162/90;
162/233 |
International
Class: |
D21C 3/00 20060101
D21C003/00; D21C 7/00 20060101 D21C007/00; D21C 3/02 20060101
D21C003/02; D21C 1/02 20060101 D21C001/02; D21C 3/04 20060101
D21C003/04 |
Claims
1. A method of protecting hemicellulose pre-extracted
lignocellulosic materials against degradation in an alkaline
pulping process comprising: a) extracting organics from
lignocellulosic materials using water or steam; b) treating the
lignocellulosic materials with an oxidizing agent and a reducing
agent or additive, wherein the treating further includes a second
extraction; and c) subjecting the lignocellulosic materials to a
Kraft pulping process in a digester.
2. The method as claimed in claim 1, wherein the extracting further
comprises treating the lignocellulosic materials and the water at a
temperature between about 120.degree. C. and 180.degree. C.
3. The method as claimed in claim 2, wherein the extracted
lignocellulosic materials are added with water to the second
extraction, along with the oxidizing agent and the reducing agent,
and treated at an elevated temperature of between about 120.degree.
C. and 180.degree. C.
4. The method as claimed in claim 3, wherein the double extracted
lignocellulosic materials are added with water to the digester,
along with sodium hydroxide and sodium sulfide to produce the
pulp.
5. The method as claimed in claim 4, wherein the oxidizing agent is
selected from the group consisting of polysulfides and the reducing
agent is selected from the group consisting of sodium borohydride,
sodium dithionate, and in-situ hydrogen.
6. A method of protecting hemicellulose pre-extracted
lignocellulosic materials against degradation in alkaline pulping
processes comprising: a) extracting organics from lignocellulosic
materials using water or steam; b) treating the lignocellulosic
materials with an oxidizing agent and a reducing agent; and c)
subjecting the lignocellulosic materials to a Kraft pulping process
to produce pulp in a digester.
7. The method as claimed in claim 6, wherein the extracting further
comprises treating the lignocellulosic materials and the water at a
temperature between about 120.degree. C. and 180.degree. C.
8. The method as claimed in claim 7, wherein the treating further
comprises adding the lignocellulosic materials with additional
water, along with the oxidizing agent and the reducing agent, and
further treating at an elevated temperature of between about
120.degree. C. and 180.degree. C.
9. The method as claimed in claim 8, wherein the treated
lignocellulosic materials are added to the digester, along with
sodium hydroxide and sodium sulfide to produce the pulp.
10. The method as claimed in claim 9, wherein the oxidizing agent
is selected from the group consisting of polysulfides and the
reducing agent is selected from the group consisting of sodium
borohydride, sodium dithionate, and in-situ hydrogen.
11. A method of protecting hemicellulose pre-extracted
lignocellulosic materials against degradation in alkaline pulping
processes comprising: a) extracting organics from lignocellulosic
materials using water or steam; b) impregnating the hemicellulose
extracted lignocellulosic materials with an oxidizing agent,
wherein the oxidizing agent is an aqueous polysulfide ion
containing solution; c) treating the impregnated lignocellulosic
materials with a reducing agent; and d) subjecting the
lignocellulosic materials to a Kraft pulping process to produce
pulp in a digester to allow the lignocellulosic materials to
separate into fibers.
12. The method as claimed in claim 11, wherein the impregnating is
conducted at a temperature below 180.degree. C.
13. The method as claimed in claim 11, wherein the impregnating is
conducted at a pH of 7.0 to 13.0.
14. The method as claimed in claim 11, wherein in either the
impregnating or the treating, further comprising adding additives
to increase the resulting pulp yield.
16. The method as claimed in claim 14, wherein the additives are
selected from the group consisting of: anthraquinone, anthraquinone
derivatives, and reducing agents.
17. The method as claimed in claim 11, wherein the reducing agent
is selected from the group consisting of lithium aluminum hydride,
alkali metal borohydride, alkali metal dithionite(hydrosulfite),
alkali metal amalgam, diisobutylaluminum hydride, oxalic acid,
formic acid, and/or the presence of hydrogen gas in a hydroxyl ion
containing solution such as Kraft white liquor.
18. The method as claimed in claim 11, wherein a portion of aqueous
extract from the extracting is recycled back for raising the sugar
content of the extract.
19. The method as claimed in claim 11, wherein the treating is
conducted at a temperature between 80.degree. C. to 180.degree.
C.
20. The method as claimed in claim 11, wherein the polysulfide ion
containing solution is withdrawn from the impregnating to a
polysulfide storage tank for recycling.
21. A method of protecting hemicellulose pre-extracted
lignocellulosic materials against degradation in alkaline pulping
processes comprising: a) extracting organics from lignocellulosic
materials using water or steam; b) treating the hemicellulose
extracted lignocellulosic materials with a first oxidizing agent as
a first pretreatment, wherein the oxidizing agent is an aqueous
polysulfide ion containing solution; c) treating the
lignocellulosic materials with a second oxidizing agent and a
reducing agent as a second pretreatment; and d) subjecting the
lignocellulosic materials to a Kraft pulping process to produce
pulp in a digester.
22. The method as claimed in claim 21, wherein the first
pretreatment is conducted at a temperature below 180.degree. C.
23. The method as claimed in claim 21, wherein the first
pretreatment is conducted at a pH of 7.0 to 13.0.
24. The method as claimed in claim 21, wherein in either the first
pretreatment or the second pretreatment, further comprising adding
additives to increase the resulting pulp yield.
25. The method as claimed in claim 24, wherein the additives are
selected from the group consisting of: anthraquinone, anthraquinone
derivatives, and reducing agents.
26. The method as claimed in claim 21, wherein the reducing agent
is selected from the group consisting of lithium aluminum hydride,
alkali metal borohydride, alkali metal dithionite(hydrosulfite),
alkali metal amalgam, diisobutylaluminum hydride, oxalic acid,
formic acid, and/or the presence of hydrogen gas in a hydroxyl ion
containing solution such as Kraft white liquor.
27. The method as claimed in claim 21, wherein a portion of aqueous
extract from the extracting is recycled back for raising the sugar
content of the extract.
28. The method as claimed in claim 21, wherein the polysulfide ion
containing solution is withdrawn from the first pretreatment to a
polysulfide storage tank for recycling.
29. The method as claimed in claim 21, wherein the first
pretreatment is conducted at a temperature between 80.degree. C. to
180.degree. C.
30. The method as claimed in claim 21, wherein in the second
pretreatment the lignocellulosic materials are treated with Kraft
white liquor containing polysulfide and reducing agent.
31. The method as claimed in claim 30, wherein the second
pretreatment is conducted at a temperature below 150.degree. C. for
at least 30 minutes.
32. A system for protecting hemicellulose pre-extracted
lignocellulosic materials against degradation in alkaline pulping
processes, the system comprising: a) means for water extraction,
wherein organics from the lignocellulosic materials are released;
b) means for treatment or impregnation, wherein an oxidizing agent
and a reducing agent are added to the pre-extracted lignocellulosic
materials to compensate for the extracted organics; and c) a
digester, wherein the lignocellulosic materials are separated into
fibers to produce pulp.
33. A method for producing pulp comprising the steps of: a)
extracting hemicellulosic materials from lignocellulosic materials;
b) treating the lignocellulosic materials with an oxidizing agent
by a process selected from the group consisting of an extraction
process, an agent impregnation process, and a first pretreatment
process; c) treating the lignocellulosic materials with a reducing
agent by a process selected from the group consisting of the
extraction process, the agent impregnation process, and a second
pretreatment process; and then d) subjecting the lignocellulosic
materials to a modified Kraft pulping process to produce pulp.
34. The method as claimed in claim 33, wherein the lignocellulosic
materials are treated at a temperature between about 120.degree. C.
and 180.degree. C. in the extraction process.
35. The method as claimed in claim 34, wherein the oxidizing agent
is selected from the group consisting of polysulfides.
36. The method as claimed in claim 35, wherein the reducing agent
is selected from the group consisting of lithium aluminum hydride,
alkali metal borohydride, alkali metal dithionite(hydrosulfite),
alkali metal amalgam, diisobutylaluminum hydride, oxalic acid,
formic acid, and/or the presence of hydrogen gas in a hydroxyl ion
containing solution such as Kraft white liquor.
37. The method as claimed in claim 36, wherein the method comprises
a double extraction process with water in a first extraction stage
and with the oxidizing agent along with an additive in a second
extraction stage or in the first pretreatment process, followed by
the modified Kraft pulping process with anthraquinone in a
digester.
38. The method as claimed in claim 36, wherein the method comprises
a single stage extraction process, followed by a two stage modified
Kraft pulping comprising a pretreatment with the oxidizing
agent.
39. The method as claimed in claim 36, wherein the method is a
single stage oxidizing agent pretreatment process for alkaline
pulping of hemicellulose pre-extracted lignocellulosic materials
with a polysulfide recycle.
40. The method as claimed in claim 39, further comprising the steps
of: a) impregnating hemicellulose extracted lignocellulosic
materials with the oxidizing agent, wherein the oxidizing agent is
an aqueous polysulfide ion containing solution, whereby aldehyde
end groups of the hemicellulose extracted lignocellulosic materials
are oxidized to carboxyl groups; b) treating the impregnated
lignocellulosic materials with a reducing agent, whereby the
aldehyde end groups of the hemicellulose extracted lignocellulosic
materials are reduced to alditols or thioalditols, and subsequently
continuously digesting the lignocellulosic materials to allow the
lignocellulosic materials to separate into fibers without much
mechanical action.
41. The method as claimed in claim 40, further comprising adding
additional additives selected from the group consisting of
anthraquinone, anthraquinone derivatives, and reducing agents.
42. The method as claimed in claim 41, wherein a portion of the
aqueous extract from the extracting process is recycled back to the
extraction process for raising the sugar content of the
hemicellulosic materials.
43. The method as claimed in claim 36, wherein the method is a
single stage dual pretreatment with an oxidizing agent and a
reducing agent for alkaline pulping of hemicellulose pre-extracted
lignocellulosic materials without a polysulfide recycle.
44. The method as claimed in claim 43, further comprising the steps
of: a) impregnating hemicellulose extracted lignocellulosic
materials with the oxidizing agent, wherein the oxidizing agent is
an aqueous polysulfide ion containing solution, whereby aldehyde
end groups of the hemicellulose extracted lignocellulosic materials
are oxidized to carboxyl groups; b) treating the impregnated
lignocellulosic materials with a reducing agent, whereby the
aldehyde end groups of the hemicellulose extracted lignocellulosic
materials are reduced to alditols or thioalditols, and subsequently
continuously digesting the lignocellulosic materials to allow the
lignocellulosic materials to separate into fibers without much
mechanical action.
45. The method as claimed in claim 44, further comprising adding
additional additives selected from the group consisting of
anthraquinone, anthraquinone derivatives, and reducing agents.
46. The method as claimed in claim 45, wherein a portion of the
aqueous extract from the extraction process is recycled back to the
extraction process for raising the sugar content of the
hemicellulosic materials.
47. The method as claimed in claim 36, wherein the process is a two
stage pretreatment process with an oxidizing agent followed by a
reducing agent for alkaline pulping of hemicellulose pre-extracted
lignocellulosic materials with a polysulfide recycle.
48. The method as claimed in claim 47, further comprising the steps
of: a) impregnating hemicellulose extracted lignocellulosic
materials with the oxidizing agent, wherein the oxidizing agent is
an aqueous polysulfide ion containing solution, whereby aldehyde
end groups of the hemicellulose extracted lignocellulosic materials
are oxidized to carboxyl groups; b) treating the impregnated
lignocellulosic materials with a reducing agent, whereby the
aldehyde end groups of the hemicellulose extracted lignocellulosic
materials are reduced to alditols or thioalditols, and subsequently
continuously digesting the lignocellulosic materials to allow the
lignocellulosic materials to separate into fibers without much
mechanical action.
49. The method as claimed in claim 48, further comprising adding
additional additives selected from the group consisting of
anthraquinone, anthraquinone derivatives, and reducing agents.
50. The method as claimed in claim 49, wherein a portion of the
aqueous extract from the extraction process is recycled back to the
extraction process for raising the sugar content of the
hemicellulosic materials.
Description
STATEMENT OF RELATED APPLICATIONS
[0001] This patent application claims priority on and the benefit
of U.S. provisional patent application No. 61/165,995 having a
filing date of 2 Apr. 2009, which is incorporated herein in its
entirety by this reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] This invention is related generally to the field of pulping
processes preceded by hemicellulose extraction, and is related more
specifically to modified pulping processes, and particularly
modified Kraft pulping processes, preceded by a hemicellulose
extraction process, that maintain yield and quality of pulp. This
invention also is related to the field of yield and strength
advantages that can be achieved by modified pulping processes
compared to Kraft pulping processes not preceded by hemicellulose
extraction.
[0004] 2. Prior Art
[0005] Pulping is the process of converting wood or other
lignocellulosic materials into separated pulp fibers for use in,
for example, paper making. Common simple pulping processes, such as
shown in FIG. 1, comprise (a) mechanically grinding the
lignocellulosic material into fibers and (b) chemically degrading
and dissolving the lignin binding the fibers together. Chemical
pulping comprises the cooking of wood chips in an aqueous mixture
of chemicals so as to dissolve the lignin so as to result in the
separated fibers, washing the fibers, and then optionally bleaching
the fibers resulting in a pulp. The wash effluent can be sent to a
recycle and chemical recovery process.
[0006] The Kraft process, such as shown in FIG. 2, is a common
chemical pulping process in which the lignocellulosic material (for
example cellulose, hemicelluloses, and lignin) and a white liquor
(sodium hydroxide, sodium sulfide, and sodium carbonate) are cooked
in a digester, resulting in pulp and a black liquor (dissolved
lignin, unused chemicals in the white liquor, other chemicals, and
cellulose and hemicellulose degradation products). The Kraft
process as well as other current chemical processes can be
inefficient, result in significant waste streams, and produce
chemical wastes that contain otherwise usable components that can
be turned into value added products.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention, briefly stated, includes modified
pulping processes preceded by hemicellulose extraction processes in
which hemicellulosic materials, such as polysaccharides and other
organic compounds, are extracted from the lignocellulosic materials
prior to pulping. The hemicellulosic materials are extracted prior
to pulping and chemicals and/or other compounds are added to the
lignocellulosic materials prior to or during pulping to compensate
for the loss of the hemicellulosic materials. Using the present
invention, the hemicellulosic materials can be removed as value
added byproducts of the pulping process, yet the addition of the
chemicals and/or other compounds to the lignocellulosic materials
results in a yield and quality of pulp similar to conventional
pulping processes, such as Kraft pulping processes. Thus, the
present invention results in more economical pulping process, in
which byproducts can be extracted and sold, while still yielding a
quantity and quality of pulp similar to conventional pulping
processes not having such a byproduct removal and capture.
[0008] The pulp industry has recognized that it has to continue to
produce chemical pulp but also must look for additional revenue
streams form existing technologies. For example, in the present
invention, instead of simply taking wood chips and taking out the
lignin, hemicellulosic materials can be removed and rather than
leaving the hemicellulosic materials in the black liquor to be
disposed of, some of the hemicellulosic materials can be removed
and used to produce higher value byproducts. Most are
polysaccharides (sugars) that have a potentially high value can be
used to make ethanol or other chemicals, for example. However, in a
typical extraction process, pulling out some of the hemicellulosic
materials reduces the amount of wood that can go to pulping. If a
significant amount of hemicellulosic materials are removed, the
pulp may have different characteristics from the prior art pulp.
The present invention addresses this by providing for the
extraction of hemicellulosic materials while maintaining the pulp
yield and the properties of the pulp.
[0009] The present invention comprises continuous processes for
protecting hemicellulose pre-extracted lignocellulosic materials,
such as wood chips, against degradation in alkaline pulping
processes. One aspect of the present invention is the evolution of
existing chemical pulp mills into integrated forest biorefineries
(IFBR) for the production of value added products. For example,
using the present invention, one selectively and efficiently can
pre-extract hemicelluloses before pulping while maintaining the
yield and quality of the pulp. Another aspect of the present
invention is that the modified pulping process can be used in place
of the Kraft process to achieve yield gain at the same level of
lignin removal without any reduction in the pulp properties.
[0010] Several representative processes are disclosed herein. Each
process comprises a pre-extraction of hemicellulosic materials from
the lignocellulosic materials, such as wood chips. The
pre-extraction can be a water extraction or other types of
extraction with added chemicals. After the pre-extraction, the
lignocellulosic materials are pre-treated and/or treated with
certain chemicals prior to the lignocellulosic materials being
subjected to a modified pulping process, such as a modified Kraft
process in a digester.
[0011] A first process is a double extraction process with water in
the first stage followed by alkaline sodium sulfide with additive
(DE or double extraction) plus a modified Kraft pulping with
anthraquinone (SK or single Kraft). A second process is a single
stage extraction with water (SE or single extraction) followed by a
two stage modified Kraft pulping (DK or double Kraft). A third
process is a single stage polysulfide pretreatment process A fourth
process is a single stage polysulfide and sodium borohydride
pretreatment process. A fifth process is a two stage pretreatment
process with a polysulfide first pretreatment stage followed by a
polysulfide/sodium borohydride/anthraquinone second pretreatment
stage, along with a polysulfide recycle in the first pretreatment
stage. A sixth process is a single stage polysulfide/reducing
agent/anthraquinone pretreatment process for alkaline pulping of
hemicellulose pre-extracted lignocellulosic materials with a
polysulfide recycle. A seventh process is a single stage
polysulfide/reducing agent/anthraquinone pretreatment, without a
polysulfide recycle. An eighth process is a two stage pretreatment
process with a polysulfide/anthraquinone first pretreatment stage
followed by a polysulfide/reducing agent/anthraquinone second
pretreatment stage, along with a polysulfide recycle in the first
pretreatment stage. Other processes and variations also are
contemplated.
[0012] According to the present invention, one manner to maintain
the yield and quality of pulp after hemicellulosic materials have
been extracted involves treating the extracted lignocellulosic
materials with a reducing and/or oxidizing agents such as
polysulfide and/or sodium borohydride, and with anthraquinone.
Practically speaking, it is preferable to use polysulfide instead
of sodium borohydride, or greater relative quantities of
polysulfide relative to sodium borohydride, due to the relative
costs of each. The added treatment stages preferably are carried
out between about 120.degree. C.-180.degree. C. at standard
pressure. At temperatures below about 120.degree. C. the process
proceeds too slowly to be economical.
[0013] These and other aspects of the invention will become
apparent from the following description of the preferred
embodiments taken in conjunction with the following drawings. As
would be obvious to one skilled in the art, many variations and
modifications of the invention may be effected without departing
from the spirit and scope of the novel concepts of the
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a representation of a prior art pulping
process.
[0015] FIG. 2 is a representation of a prior art Kraft pulping
process.
[0016] FIG. 3 is a block diagram of a double extraction process
with water in the first stage followed by alkaline sodium sulfide
with additive (DE or double extraction) plus a modified Kraft
pulping with anthraquinone (SK or single Kraft).
[0017] FIG. 4 is a block diagram of a single stage extraction with
water (SE or single extraction) followed by a two stage modified
Kraft pulping (DK or double Kraft).
[0018] FIG. 5 is a block diagram for a single stage polysulfide
pretreatment process for alkaline pulping of hemicellulose
pre-extracted lignocellulosic materials.
[0019] FIG. 6 is a block diagram for a single stage polysulfide and
sodium borohydride pretreatment process for alkaline pulping of
hemicellulose pre-extracted lignocellulosic materials.
[0020] FIG. 7 is a block diagram for a two stage pretreatment
process, the first stage with polysulfide and the second stage with
polysulfide along with sodium borohydride as reducing agents and
with anthraquinone for alkaline pulping of hemicellulose
pre-extracted lignocellulosic materials with polysulfide recycle in
the first pretreatment stage.
[0021] FIG. 8 is a block diagram for a single stage polysulfide
pretreatment process for alkaline pulping of hemicellulose
pre-extracted lignocellulosic materials with polysulfide
recycle.
[0022] FIG. 9 is a block diagram for a single stage dual
pretreatment of polysulfide and a reducing agent for alkaline
pulping of hemicellulose pre-extracted lignocellulosic materials
without polysulfide recycle.
[0023] FIG. 10 is a block diagram for a two stage pretreatment
process of polysulfide followed by a reducing agent for alkaline
pulping of hemicellulose pre-extracted lignocellulosic materials
with polysulfide recycle.
[0024] A table and various graphs are appended to this
specification and are described in more detail in the Detailed
Description of Preferred Embodiments.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] With reference to the figures, embodiments of the present
invention are shown. The figures and the following description are
for a limited number of embodiments for ease of understanding.
However, the invention is not limited to these illustrative
embodiments. Other processes and variations also are contemplated.
For example, FIGS. 3-10 show block diagrams of representative
Processes 1-8, respectively. Table 1 describes the conditions for
various illustrative processes. Graphs 1-28 show results of the
various illustrative processes and comparisons to controls such as
prior art pulp and paper made from prior art pulp.
[0026] The present invention comprises continuous processes for
protecting hemicellulose pre-extracted lignocellulosic materials,
such as wood chips, against degradation in alkaline pulping
processes. After pre-extraction, the lignocellulosic materials are
treated with reducing and/or oxidizing agents before or during the
alkaline pulping process to maintain the yield and quality of the
pulp produced.
[0027] Several representative processes are disclosed herein.
Process 1 is a double extraction process with water in the first
stage followed by alkaline sodium sulfide with additive (DE or
double extraction) plus a modified Kraft pulping with anthraquinone
(SK or single Kraft). Process 2 is a single stage extraction with
water (SE or single extraction) followed by a two stage modified
Kraft pulping (DK or double Kraft). Process 3 is a single stage
polysulfide pretreatment process. Process 4 is a single stage
polysulfide and sodium borohydride pretreatment process. Process 5
is a two stage pretreatment process with a polysulfide first
pretreatment stage followed by a polysulfide/sodium
borohydride/anthraquinone second pretreatment stage, along with a
polysulfide recycle in the first pretreatment stage. Process 6 is a
single stage polysulfide/reducing agent/anthraquinone pretreatment
process for alkaline pulping of hemicellulose pre-extracted
lignocellulosic materials with a polysulfide recycle. Process 7 is
a single stage polysulfide/reducing agent/anthraquinone
pretreatment, without a polysulfide recycle. Process 8 is a two
stage pretreatment process with a polysulfide/anthraquinone first
pretreatment stage followed by a polysulfide/reducing
agent/anthraquinone second pretreatment stage, along with a
polysulfide recycle in the first pretreatment stage.
[0028] One manner to maintain the yield and quality of pulp after
hemicellulosic materials have been extracted involves treating the
extracted lignocellulosic materials with polysulfide optionally
along with a reducing agent such as sodium borohydride, and with
anthraquinone. Practically speaking, it is preferable to use
polysulfide instead of sodium borohydride, or greater relative
quantities of polysulfide relative to sodium borohydride, due to
the relative costs of each. The added treatment stages preferably
are carried out at between about 120.degree. C.-180.degree. C. at
standard pressure. At temperatures below about 120.degree. C. the
process proceeds too slowly to be economical.
[0029] The various representative processes of the invention now
will be disclosed in connection with the appended figures.
[0030] FIG. 3 is a block diagram of Process 1, a double extraction
process with water in the first stage followed by alkaline sodium
sulfide with additive (DE or double extraction) plus a modified
Kraft pulping with anthraquinone (SK or single Kraft). In the first
extraction stage, water is added to the lignocellulosic materials.
The lignocellulosics and water mass is then treated at an elevated
temperature between 120.degree. C. and 180.degree. C. The organics
released from the chips during this operation are mostly plant
polysaccharides, acetic acid and a small amount of lignin and are
removed as sugar stream 1. The extracted lignocellulosic materials
are added with water to a second extraction stage, along with
alkaline sodium sulfide (ASS) and sodium borohydride (SBH), and
treated at an elevated temperature of between 120.degree. C. and
180 C. The double extracted lignocellulosic materials are added
with water to a digester, along with sodium hydroxide and sodium
sulfide to produce pulp. The black liquor released from the
digester comprises, for example, dissolved lignin, sodium sulfide,
sodium borohydride, sodium hydroxide, sodium sulfide, other
chemicals, and cellulose and hemicellulose degradation
products.
[0031] Graph 1 illustrates the double extraction weight loss
produced in Process 1. This graph shows the insensitivity of the
extraction relative to a control, namely, using only a single water
extraction without a second extraction using sodium borohydride or
another reducing agent. In this graph, the weight loss is how much
hemicellulosic material was dissolved and extracted during the
extraction process(es). As can be seen, with the additives, more
organics are extracted than with simple water extraction. The
x-axis shows the severity of the extraction stage, the H-factor,
which is a combination of time and temperature of extraction.
[0032] Graph 2 illustrates the total sugar extracts in Process 1.
This graph shows the amount of sugars extracted during the
extraction process(es) as a function of weight loss. As above, with
the additives, more sugars are extracted than with simple water
extraction. Sugar extraction is of interest as sugars have value as
removed byproducts.
[0033] Graph 3 illustrates the yield gain or loss for water
extraction in the control typical Kraft process with a water
extraction and the double extraction single Kraft process of
Process 1. This graph shows that, compared to a control process
comprising just a water extraction and a Kraft process, the present
process provides a better yield even though hemicellulosic material
is being removed in the extraction process. Specifically, the
intersection of the curves with the horizontal 0 line shows the
different weight loss at the same yield for the control and Process
1. This illustrates that in the general process of the present
invention, hemicellulosic material can be removed without adversely
affecting the yield.
[0034] As disclosed below in conjunction with Graphs 4-10, using
the double extraction single Kraft process of the present invention
as illustrated by Process 1, 19-24% of the wood mass (about 9-13%
sugar) was extracted without a significant loss in pulp yield. With
this process, other chemicals can be recovered and still have a
similar yield of pulp.
[0035] FIG. 4 is a block diagram of Process 2, a single stage
extraction with water (SE or single extraction) followed by a two
stage modified Kraft pulping (DK or double Kraft). In the
extraction stage, water is added to the lignocellulosic materials.
The lignocellosics and water mass is then treated at an elevated
temperature between 120.degree. C. and 180.degree. C. The organics
released from the chips during this operation are mostly plant
polysaccharides, acetic acid and a small amount of lignin and are
removed as a sugar stream. The extracted lignocellulosic materials
are added with water to a combined pretreatment/digester. In the
pretreatment section, alkaline sodium sulfide and sodium
borohydride are added to the lignocellulosic materials and the mass
is treated at an elevated temperature of between 120.degree. C. and
180.degree. C. in the digester section, the pretreated
lignocellulosic materials are digested with sodium hydroxide and
sodium sulfide to produce pulp. The black liquor released from the
digester comprises, for example, dissolved lignin, sodium sulfide,
sodium borohydride, sodium hydroxide, sodium sulfide, other
chemicals, and cellulose and hemicellulose degradation
products.
[0036] Using the single extraction two stage modified Kraft process
of the present invention, 14% of the wood mass (about 10% sugar)
was extracted without a significant loss in pulp yield. It is
expected that from 10-14% extraction (about 7-10% sugar yield) with
preserved pulp yield can be achieved using Process 2. It is further
expected that with 7-8% extraction sugar yield, both the yield and
strength properties of the pulp can be maintained using Process
2.
[0037] The two stage modified Kraft pulping of Process 2 involves
the use of strong reducing agents such as sodium borohydride,
sodium dithionate, in-situ hydrogen, and others under pressure in
the pretreatment stage followed by Kraft pulping with anthraquinone
as an additive in the second stage. The reducing agent helps to
keep remaining hemicellulose in the final pulp, retaining the pulp
properties.
[0038] Graph 3 also illustrates the yield gain or loss for water
extraction in the control typical Kraft process with a water
extraction and the single extraction double Kraft process of
Process 2. This graph shows that, compared to a control process
comprising just a water extraction and a Kraft process, the present
process provides a better yield even though hemicellulosic material
is being removed in the extraction process. Specifically, the
intersection of the curves with the horizontal 0 line shows the
different weight loss at the same yield for the control and Process
2. This illustrates that in the general process of the present
invention, hemicellulosic material can be removed without adversely
affecting the yield.
[0039] Graph 4 illustrates the sodium borohydride pretreatment
effect on single extraction double Kraft pulp yield of Process 2.
Sodium borohydride is added as a reducing agent and, when added in
accordance with the present invention, has been found to maintain
the pulp yield, even with the extraction of hemicellulosic
materials. Specifically, this graph shows the level of sodium
borohydride is needed to regain the yield loss, which is the effect
of sodium borohydride on the pulp yield. By adding more sodium
borohydride, the yield is increased. The Kraft Control is a pure
Kraft process. The three curves illustrate Process 2 conducted at
different water extraction parameters--9%, 12%, and 14% water
extraction.
[0040] Paper products prepared from Processes 1 and 2 were compared
to control paper products. PFI beating response, handsheet density,
tensile strength, bursting strength, tearing resistance, and
folding endurance of pulp prepared by Processes 1 and 2 were
compared to pulp prepared from a pure Kraft process and pulp
prepared from a Kraft process preceded by a water extraction.
Graphs 5-10 illustrate these comparisons and show that paper
products prepared by Processes 1 and 2 are comparable to paper
products prepared by pure Kraft process. Three different method of
the processes were carried out. The parameters of the control
processes and the processes of the present invention can be found
in Table 1.
[0041] Graph 5 illustrates the PFI beating response of pulp
prepared from Processes 1 and 2 as compared to control pulp. Graph
6 illustrates the handsheet density of paper products prepared from
Processes 1 and 2 as compared to control paper products. Graph 7
illustrates the tensile strength of paper products prepared from
Processes 1 and 2 as compared to control paper products. Graph 8
illustrates the bursting strength of paper products prepared from
Processes 1 and 2 as compared to control paper products. Graph 9
illustrates the tearing strength of paper products prepared from
Processes 1 and 2 as compared to control paper products. Graph 10
illustrates the folding endurance of paper products prepared from
Processes 1 and 2 as compared to control paper products.
[0042] As can be seen, the papermaking properties of pulp prepared
from Processes 1 and 2 show faster refining response, slightly
higher density, comparable or higher tensile strength, comparable
or higher bursting strength, comparable or higher folding
endurance, and comparable tearing resistance relative to control
paper. In other words, the characteristics of paper produced from
the pulp produced from Processes 1 and 2 is comparable to prior art
paper. The combined effect of alkaline sodium sulfide and sodium
borohydride also enables Processes 1 and 2 to maintain pulp yield
and paper strength with significant wood sugar extraction.
Specifically, Process 1 extracts 19-24% of wood mass with a minor
change in pulp and paper properties, and Process 2 extracts up to
12% wood substance without a loss in pulp yield and paper
strength.
[0043] The processes of the present invention also can be carried
out with additional pretreatment steps for yield preservation,
several of which are disclosed herein. One pretreatment is an
oxidative pretreatment with polysulfide. Another pretreatment is an
oxidative-reductive dual pretreatment using polysulfide and sodium
borohydride. Another pretreatment is an oxidative and
oxidative-reductive two stage pretreatment using polysulfide and
dual treatment using polysulfide and sodium borohydride with
polysulfide recycling. FIGS. 5-7 illustrate more general
embodiments of polysulfide pretreatment processes and FIGS. 8-10
illustrate more specific embodiments of polysulfide pretreatment
processes according to the present invention.
[0044] FIG. 5 is a block diagram of Process 3, a polysulfide
pretreatment process comprising a water extraction stage, a
polysulfide pretreatment stage, and a digester stage. In the water
extraction stage, which is illustrative of an extraction stage and
can be replaced with other extraction methods, lignocellulosic
materials in the form of wood chips are contacted with pure water
and steam. Extracted hemicellulosic materials in the form of a
sugar stream is removed. Steam is recycled back to the extractor.
The extracted lignocellulosic materials are introduced to a
pretreatment stage along with a polysulfide solution, and the
extracted lignocellulosic materials are pretreated with the
polysulfide solution at a temperature of between 120.degree. C. and
140.degree. C. for a period of up to about 2 hours. After this
pretreatment stage, the lignocellulosic materials are introduced to
a digester where they are treated with a white liquor to produce
pulp and a black liquor. The pretreatment stage and the digester
stage can be carried out in the same vessel. Process 3 was carried
out at a 14% water extraction and at four different concentrations
of polysulfide solution in water--6%, 10%, 15%, and 20%.
[0045] Graph 11 illustrates the polysulfide treatment effect on
yield recovery for Process 3. Control 1 is a simple Kraft process.
Control 2 is a simple water extraction with a Kraft process. The
other four curves are for polysulfide pretreatments according to
Process 3, in the concentrations of polysulfide given above. The
Kappa number is used in the pulp industry to indicate how much
lignin is left in the pulp. This graph shows the pulp yield
compared to various Kappa numbers and indicates Process 3 has a
total pulp yield comparable to, and generally in between, the two
control processes.
[0046] Graph 12 illustrates the polysulfide pretreatment effect on
yield recovery with a control of 44.64% total yield at Kappa 30 for
Process 3. This graph uses the data from Graph 11 and shows how at
a constant Kappa number the yield obtained with the various
polysulfide solution concentrations. Kappa 30 is a typical Kappa
number used in the pulp industry for a pulp that will be
bleached.
[0047] FIG. 6 is a block diagram of Process 4, a polysulfide and
sodium borohydride dual pretreatment process comprising a water
extraction stage, a polysulfide and sodium borohydride pretreatment
stage, and a digester stage. In the water extraction stage, which
is illustrative of an extraction stage and can be replaced with
other extraction methods, lignocellulosic materials in the form of
wood chips are contacted with pure water and steam. Extracted
hemicellulosic materials in the form of a sugar stream is removed.
Steam is recycled back to the extractor. The extracted
lignocellulosic materials are introduced to a pretreatment stage
along with a polysulfide solution and a sodium borohydride
solution, and the extracted lignocellulosic materials are
pretreated with the polysulfide solution and the sodium borohydride
solution at a temperature of between 120.degree. C. and 140.degree.
C. for a period of up to about 2 hours. After this pretreatment
stage, the lignocellulosic materials are introduced to a digester
where they are treated with a white liquor to produce pulp and a
black liquor. The pretreatment stage and the digester stage can be
carried out in the same vessel. Process 4 was carried out at 14%
water extraction and five different concentrations of polysulfide
solution and sodium borohydride: 6% PS+0.5% SBH; 10% PS+0.5% SBH;
15% PS+0.5% SBH; 20% PS+0.5% SBH; and 15% PS+0.4% SBH.
[0048] Graph 13 illustrates the polysulfide sodium borohydride dual
treatment effect on yield recovery of Process 4. As with Graph 11,
Control 1 is a simple Kraft process. Control 2 is a simple water
extraction with a Kraft process. The other five curves are for
polysulfide pretreatments according to Process 4 at the different
concentrations of polysulfide solution in water and sodium
borohydride given above. This graph shows the pulp yield at various
Kappa numbers and indicates Process 4 has a total pulp yield
comparable to, and generally in between, the two control
processes.
[0049] Graph 14 illustrates the polysulfide solution and sodium
borohydride pretreatment effect on yield recovery with a control of
44.64% total yield at Kappa 30 for Process 4. This graph uses the
data from Graph 13 and shows how at a constant Kappa number the
yield obtained with the various polysulfide solution with 0.5%
sodium borohydride addition.
[0050] FIG. 7 is a block diagram of Process 5, a two stage
pretreatment process comprising a water extraction stage, a
polysulfide first pretreatment stage with polysulfide recycle, a
polysulfide and sodium borohydride second pretreatment stage, and a
digester stage. In the water extraction stage, which is
illustrative of an extraction stage and can be replaced with other
extraction methods, lignocellulosic materials in the form of wood
chips are contacted with pure water and steam. Extracted
hemicellulosic materials in the form of a sugar stream is removed.
Steam is recycled back to the extractor. The extracted
lignocellulosic materials are introduced to a first pretreatment
stage along with a polysulfide solution, and the extracted
lignocellulosic materials are pretreated with the polysulfide
solution at a temperature of between 120.degree. C. and 140.degree.
C. for a period of up to about 2 hours. Polysulfide solution
removed from the first pretreatment stage is recycled. In this
example, the feed to the first pretreatment stage comprises 30% by
volume fresh polysulfide solution and 70% by volume recycled
polysulfide solution. The recirculation percentage can be increased
by extracting more liquid from the chips. The first pretreatment
stage must be carried out in a separate vessel as it has a
polysulfide recycle.
[0051] After the first pretreatment stage, the lignocellulosic
materials are introduced to a second pretreatment stage along with
additional polysulfide solution and with white liquor (cooking
liquor in the Kraft process containing sodium hydroxide and sodium
sulfide, and sodium carbonate in the case of industrial system) at
a temperature of about 140.degree. C. for a period of about 1 hour.
Anthraquinone is added to get a slight yield advantage. After the
second pretreatment stage, the lignocellulosic materials are
introduced to a digester to produce pulp and a black liquor. The
second pretreatment stage and the digester stage can be carried out
in the same vessel. Process 5 was carried out at 14% water
extraction and six different concentrations of polysulfide solution
and sodium borohydride: 15% PS and then 0% PS+0.5% SBH; 15% PS and
then 2% PS+0.5% SBH; 15% PS and then 4% PS+0.5% SBH; 15% PS and
then 5% PS+0.5% SBH; 15% PS and then 6% PS+0.5% SBH; and 15% PS and
then 6% PS+0.4% SBH.
[0052] Graph 15 illustrates the polysulfide sodium borohydride two
stage pretreatment effect on yield recovery of Process 5. As with
Graphs 11 and 13, Control 1 is a simple Kraft process. Control 2 is
a simple water extraction with a Kraft process. The other six
curves are for polysulfide first pretreatment and polysulfide and
sodium borohydride second pretreatments according to Process 5 at
different concentrations of polysulfide solution in water and
sodium borohydride given above. This graph shows the pulp yield
compared to various Kappa numbers and indicates Process 5 has a
total pulp yield comparable to, and generally in between, the two
control processes.
[0053] Graph 16 illustrates the two stage pretreatment effect on
the second pretreatment yield recovery with a Control 1 of 44.64%
total yield and a Control 2 of 37.82% total yield at Kappa 30 for
Process 5. The center line at 40.73% yield at Kappa 30 is
representative of the yield obtained by a 15% polysulfide solution
pretreatment with polysulfide solution recycling, namely, the forts
pretreatment. This graph uses the data from Graph 15 and shows how
at a constant Kappa number the yield obtained after the second
pretreatment with the various polysulfide solution and sodium
borohydride concentrations.
[0054] Graph 17 illustrates a 15% polysulfide solution recycling
effect on the pulp yield, with 70% recycled polysulfide and 30%
fresh polysulfide. This graph shows that there is no negative
effect of polysulfide solution recycling, which is a positive
outcome.
[0055] A novel aspect of this invention is that the hemicellulose
pre-extracted lignocellulosic materials are pretreated with
oxidizing agent (OA) such as alkali metal polysulfide (PS) prior to
pulping (Process 3 in FIG. 5), or with oxidizing agent and reducing
agent simultaneously (Process 4 in FIG. 6) or with two stage
process including polysulfide impregnation followed by reducing
agent treatment with or without polysulfide and anthraquinone or
its derivatives in aqueous alkaline white liquor (Process 5 in FIG.
7). In this invention, the combination of oxidizing agent and
reducing agent in the treatment of hemicellulose extracted
lignocellulosic materials for stabilization of residual
carbohydrates prior to alkaline pulping, which leads to preserve
the pulp yield, is also a novel operation.
[0056] Paper products prepared from Processes 3-5 were compared to
control paper products. PFI mill refining response, apparent
density, breaking length, burst index, tear index, and folding
endurance of pulp prepared by Processes 3-5 were compared to pulp
prepared from a pure Kraft process and pulp prepared from a Kraft
process preceded by a water extraction. Graphs 18-28 illustrate
these comparisons and show that paper products prepared by
Processes 3-5 are comparable to paper products prepared by pure
Kraft processes and by Kraft processes preceded by a water
extraction. Paper products from representative versions of each of
Processes 3-5 were compared with the two controls: Process 3 for a
20% PS; Process 4 for a 15% PS+0.5% SBH; and Process 5 for 15% PS
and then 6% PS+0.5% SBH.
[0057] Graph 18 illustrates the PFI mill refining response for
Processes 3-5 relative to a control Kraft process. Graph 19
illustrates the apparent density for Processes 3-5 relative to a
control Kraft process. Graph 20 illustrates in greater detail the
apparent density at 400 ml and 500 ml Canadian Standard Freeness
(CSF) for Processes 3-5 relative to a control Kraft process. Graph
21 illustrates the breaking length versus CSF for Processes 3-5
relative to a control Kraft process. Graph 22 illustrates in
greater detail the breaking length versus CSF at 400 ml and 500 ml
CSF for Processes 3-5 relative to a control Kraft process. Graph 23
illustrates the burst index for Processes 3-5 relative to a control
Kraft process. Graph 24 illustrates in greater detail the burst
index at 400 ml and 500 ml CSF for Processes 3-5 relative to a
control Kraft process. Graph 25 illustrates the tear index versus
the breaking length for Processes 3-5 relative to a control Kraft
process. Graph 26 illustrates in greater detail the tear index
versus the breaking length at 400 ml and 500 ml CSF for Processes
3-5 relative to a control Kraft process. Graph 27 shows the folding
endurance for Processes 3-5 relative to a control Kraft process.
Graph 28 illustrates in greater detail the folding numbers at 400
ml and 500 ml CSF for Processes 3-5 relative to a control Kraft
process.
[0058] Graphs 18-28 show that the present process can produce a
similar paper to the controls in that the papermaking properties of
pulp prepared from Processes 3-5 are comparable to prior art paper,
and show that the present process can produce a paper that is the
same as what was produced before by the prior art, but with the
added benefit that the present process pulls out other valuable
products.
[0059] FIGS. 8-10 illustrate variations on Processes 3-5 involving
the addition of a reducing agent and/or anthraquinone to the
pretreatments.
[0060] FIG. 8 is a block diagram of Process 6, a hemicellulose
extraction stage and polysulfide impregnation stage followed by
alkaline pulping of lignocellulosic materials with polysulfide
recycling. In the extraction stage pure water is added to the fresh
lignocellulosic materials. The lignocellulosics and water mass is
then treated at an elevated temperature between 120.degree. C. and
180.degree. C. The organics released from the chips during this
operation are mostly plant polysaccharides, acetic acid and a small
amount of lignin. The extract is flashed to produce preheating
steam. A portion of the aqueous extract is recycled back to the
extraction vessel for the purpose of raising the sugar content of
the extract. In the pretreatment stage the pre-extracted
lignocellulosic materials are treated with an aqueous alkaline
solution containing sufficient amount of alkali metal polysulfide
with or without anthraquinone (AQ) or its derivatives and with or
without reducing agent (RA) at temperature between 80.degree. C. to
180.degree. C. The polysulfide liquor is then withdrawn to a
polysulfide storage tank for recycling. In this polysulfide
impregnating operation significant part of residual carbohydrates
of hemicellulose extracted lignocellulosic materials are converted
into carboxyl groups which are stable against alkaline peeling
reaction in the subsequent alkaline cooking stage, and thereby
increasing the pulp yield. With a polysulfide recycle, one must
have a separate pretreatment vessel from the digester vessel.
[0061] FIG. 9 is a block diagram of Process 7, a single stage dual
pretreatment using polysulfide and RA together with or without
anthraquinone or its derivatives for the alkaline cooking of
hemicellulose pre-extracted lignocellulosic materials. The
polysulfide in this process is in the alkaline white liquor and no
polysulfide recycle is involved. In the extraction stage pure water
is added to the fresh lignocellulosic materials. The
lignocellulosics and water mass is then treated at an elevated
temperature between 120 and 180.degree. C. The organics released
from the chips during this operation are mostly plant
polysaccharides, acetic acid and a small amount of lignin. The
extract is flashed to produce preheating steam. A portion of the
aqueous extract is recycled back to the extraction vessel for the
purpose of raising the sugar content of the extract. In the
pretreatment stage the pre-extracted lignocellulosic materials are
treated with an aqueous alkaline solution containing sufficient
amount of sodium borohydride and alkali metal polysulfide with or
without anthraquinone (AQ) or its derivatives, with or without
reducing agent (RA) at temperature between 80 to 180.degree. C. In
this pretreatment operation significant part of residual
carbohydrates of hemicellulose extracted lignocellulosic materials
are converted into carboxyl groups which are stable against
alkaline peeling reaction in the subsequent alkaline cooking stage,
and thereby increasing the pulp yield. Without a polysulfide
recycle, the pretreatment and the digester can be in the same
vessel.
[0062] FIG. 10 is a block diagram of Process 8, a two-stage
pretreatment for alkaline pulping of hemicellulose pre-extracted
lignocellulosic materials. In the first pretreatment stage the
hemicellulose pre-extracted lignocellulosic materials are treated
with polysulfide liquor with or without anthraquinone or its
derivatives at an elevated temperature between 120 and 180.degree.
C. The polysulfide liquor is then withdrawn for recycling. In the
second pretreatment stage lignocellulosic materials are treated
with Kraft white liquor containing polysulfide and reducing agent
with or without anthraquinone and its derivatives maintaining at a
temperature below 150.degree. C. for at least 30 minutes, and
subsequently and continuously alkaline cooking to delignify the
lignocellulosic materials into separable fibers. In this second
treatment operation significant part of residual end groups of
lignocellulosic materials are further converted into alditols and
carboxyl groups by reducing agent and polysulfide or anthraquinone,
respectively. Pretreatment 1, with the polysulfide recycle must be
in a separate vessel from pretreatment 2 and the digester, which
can be in the same vessel.
[0063] A representative method of the present invention comprises
the following steps:
[0064] a) in the first impregnation stage where the hemicellulose
extracted lignocellulosic materials are impregnated with an aqueous
polysulfide ion containing solution at an elevated temperature
below 180.degree. C., preferably between 120.degree. C. and
180.degree. C., and a pH of 7.0 to 13.0; whereby the aldehyde end
groups of the hemicellulose extracted lignocellulosic materials are
oxidized to carboxyl groups, followed by withdrawing the
polysulfide ion containing solution for recycling;
[0065] b) treating the first impregnated lignocellulosic materials
with a reducing agent such as lithium aluminum hydride, alkali
metal borohydride, alkali metal dithionite(hydrosulfite), alkali
metal amalgam, diisobutylaluminum hydride, oxalic acid, formic acid
and/or the presence of hydrogen gas in a hydroxyl ion containing
solution, preferably Kraft white liquor, whereby the residual
aldehyde end groups of the hemicellulose extracted lignocellulosic
materials are reduced to alditols or thioalditols, and subsequently
continuously digesting to allow the lignocellulosic materials to
separate into fibers without much mechanical action.
[0066] In either step a) or step b) or both additional additives
such as anthraquinone or its derivatives and reducing agent can
also be added to increase the resulting pulp yield. The method
results in a pulp yield and pulp quality with a minor change in
strength properties similar to that of alkaline cooking of the
lignocellosic materials alone, while the cooking time is
significantly reduced compared to that of traditional alkaline
cooking alone or alkaline cooking of lignocellulosic materials
preceded by hemicellulose extraction. In step b) only a hydroxyl
ion containing solution or Kraft white liquor can be used without
additional chemical additives to maintain slightly lower pulp
yields than conventional alkaline pulping. All of these methods can
also be used to produce quality pulps from the fresh lignocellosic
materials with no pre-extraction of hemicelluloses for the purpose
of obtaining higher pulp yield than conventional alkaline
processes.
[0067] Using the inventive processes disclosed herein, about 5% of
the lost pulp yield (total 7%) caused by hemicellulose
pre-extraction could be recovered with 15-20% polysulfide treatment
prior to pulping. A complete recovery (7%) can be achieved with
simultaneous pre-treatment of 15% polysulfide and 0.5% sodium
borohydride. Using the two stage modified Kraft process using
recycled 15% polysulfide followed by 6% polysulfide and 0.4-0.5%
SBH also achieved 100% yield recovery. Additionally, the continuous
recycling of 15% polysulfide maintains its yield protection
efficiency in the subsequent process
[0068] There are various other methods for carrying out the present
invention. A representative general method for producing pulp
comprises the steps of:
[0069] a) extracting organics from lignocellulosic materials in an
extraction stage, wherein the extraction stage is either a single
extraction or a double extraction process;
[0070] b) treating the lignocellulosic materials with an oxidizing
agent in a treatment stage, wherein the treatment stage is selected
from the group consisting of a second extraction process, an agent
impregnation process, and a first pretreatment process;
[0071] c) treating the lignocellulosic materials with a reducing
agent in the treatment stage, wherein the treatment stage is
selected from the group consisting of the second extraction
process, the agent impregnation process, and a second pretreatment
process; and then
[0072] d) subjecting the lignocellulosic materials to a modified
Kraft pulping process to produce pulp.
[0073] The method can comprise a double extraction process with
water in a first extraction stage and with the oxidizing agent
along with an additive in a second extraction stage or in the first
pretreatment process, followed by the Kraft pulping process with
anthraquinone in a digester. The lignocellulosic materials and the
water can be treated at a temperature between about 120.degree. C.
and 180.degree. C. in the extraction stage. The extracted
lignocellulosic materials can be added with water to the second
extraction stage, along with the oxidizing agent and the reducing
agent, and treated at an elevated temperature of between about
120.degree. C. and 180.degree. C. The double extracted
lignocellulosic materials can be added with water to the digester,
along with sodium hydroxide and sodium sulfide to produce the
pulp.
[0074] The oxidizing agent can be selected from the group
consisting of alkaline sodium sulfide and polysulfides and the
reducing agent is selected from the group consisting of sodium
borohydride, sodium dithionate, and in-situ hydrogen.
[0075] The method alternatively can comprise a single stage
extraction process with water in the extraction stage, followed by
a two stage modified Kraft pulping comprising a pretreatment with
the oxidizing agent. The lignocellulosic materials and the water
can be treated at a temperature between about 120.degree. C. and
180.degree. C. in the extraction stage. The extracted
lignocellulosic materials can be added with additional water to the
treatment stage, along with the oxidizing agent and the reducing
agent, and treated at an elevated temperature of between about
120.degree. C. and 180.degree. C. The lignocellulosic materials can
be added to the digester, along with sodium hydroxide and sodium
sulfide to produce the pulp.
[0076] The method alternatively can be a single stage oxidizing
agent pretreatment process for alkaline pulping of hemicellulose
pre-extracted lignocellulosic materials with a polysulfide recycle
further comprising the steps of:
[0077] a) impregnating hemicellulose extracted lignocellulosic
materials with the oxidizing agent, wherein the oxidizing agent is
an aqueous polysulfide ion containing solution, whereby aldehyde
end groups of the hemicellulose extracted lignocellulosic materials
are oxidized to carboxyl groups; and
[0078] b) treating the impregnated lignocellulosic materials with a
reducing agent, whereby the aldehyde end groups of the
hemicellulose extracted lignocellulosic materials are reduced to
alditols or thioalditols, and subsequently continuously digesting
the lignocellulosic materials to allow the lignocellulosic
materials to separate into fibers without much mechanical
action.
[0079] The method alternatively can be a single stage dual
pretreatment with an oxidizing agent and a reducing agent for
alkaline pulping of hemicellulose pre-extracted lignocellulosic
materials without a polysulfide recycle further comprising the
steps of:
[0080] a) impregnating hemicellulose extracted lignocellulosic
materials with the oxidizing agent, wherein the oxidizing agent is
an aqueous polysulfide ion containing solution, whereby aldehyde
end groups of the hemicellulose extracted lignocellulosic materials
are oxidized to carboxyl groups; and
[0081] b) treating the impregnated lignocellulosic materials with a
reducing agent, whereby the aldehyde end groups of the
hemicellulose extracted lignocellulosic materials are reduced to
alditols or thioalditols, and subsequently continuously digesting
the lignocellulosic materials to allow the lignocellulosic
materials to separate into fibers without much mechanical
action.
[0082] The method alternatively can be a two stage pretreatment
process with an oxidizing agent followed by a reducing agent for
alkaline pulping of hemicellulose pre-extracted lignocellulosic
materials with a polysulfide recycle further comprising the steps
of:
[0083] a) impregnating hemicellulose extracted lignocellulosic
materials with the oxidizing agent, wherein the oxidizing agent is
an aqueous polysulfide ion containing solution, whereby aldehyde
end groups of the hemicellulose extracted lignocellulosic materials
are oxidized to carboxyl groups; and
[0084] b) treating the impregnated lignocellulosic materials with a
reducing agent, whereby the aldehyde end groups of the
hemicellulose extracted lignocellulosic materials are reduced to
alditols or thioalditols, and subsequently continuously digesting
the lignocellulosic materials to allow the lignocellulosic
materials to separate into fibers without much mechanical
action.
[0085] The method can be conducted at a temperature below
180.degree. C., step a) can be conducted at a temperature between
120.degree. C. and 180.degree. C. and at a pH of 7.0 to 13.0, and
step b) can be conducted at a temperature between 80.degree. C. to
180.degree. C. Additional additives can be added in either step a)
or step b) or both to increase the resulting pulp yield. The
additional additives can be selected from the group consisting of
such as anthraquinone, anthraquinone derivatives, and reducing
agents. The reducing agent is selected from the group consisting of
lithium aluminum hydride, alkali metal borohydride, alkali metal
dithionite(hydrosulfite), alkali metal amalgam, diisobutylaluminum
hydride, oxalic acid, formic acid, and/or the presence of hydrogen
gas in a hydroxyl ion containing solution such as Kraft white
liquor. A portion of the extract from the extraction stage can be
recycled back to the extraction stage for raising the sugar content
of the extract. Although preferred embodiments include a water
and/or steam extraction process, the extraction process is not
limited to water or steam. In the second pretreatment process the
lignocellulosic materials can be treated with Kraft white liquor
containing polysulfide and reducing agent with or without
anthraquinone and its derivatives, and the second pretreatment
process can be maintained at a temperature below 150.degree. C. for
at least 30 minutes.
[0086] The above detailed description of the preferred embodiments,
examples, and the appended figures are for illustrative purposes
only and are not intended to limit the scope and spirit of the
invention, and its equivalents, as defined by the appended claims.
One skilled in the art will recognize that many variations can be
made to the invention disclosed in this specification without
departing from the scope and spirit of the invention.
* * * * *