U.S. patent application number 12/855176 was filed with the patent office on 2011-03-31 for kraft-pulping of hot water extracted woodchips.
This patent application is currently assigned to The Research Foundation of State University of New York. Invention is credited to Thomas E. Amidon, Kathryn E. Gratien, Shijie Liu, Gangesh Mishra, Jennifer A. Putnam.
Application Number | 20110073264 12/855176 |
Document ID | / |
Family ID | 43778982 |
Filed Date | 2011-03-31 |
United States Patent
Application |
20110073264 |
Kind Code |
A1 |
Liu; Shijie ; et
al. |
March 31, 2011 |
Kraft-Pulping of Hot Water Extracted Woodchips
Abstract
The method of the present invention is directed towards a method
to increase the pulp yield of a lignocellulosic material, or
increasing pulp bulk and/or pulp viscosity. This method comprises
the following steps; preparing a lignocellulosic material,
contacting the lignocellulosic material in a vessel with hot water
or steam for a predetermined time, producing acetic acid from the
reaction of the hot water or steam and the lignocellulosic
material, lowering the pH to less than about 4, removing
lignocellulosic material extracts including a large percentage of
hemicellulose, acetic acid and metal ions, exposing contacted
lignocellulosic material to pulping chemicals in a pulping reactor,
forming a contacted lignocellulosic material pulp with a kappa
number below about 19 after about 90 minutes of contact with the
pulping chemicals, exposing the contacted lignocellulosic material
pulp to whitening agents, and producing a whitened hot water
contacted lignocellulosic material pulp.
Inventors: |
Liu; Shijie; (Manlius,
NY) ; Mishra; Gangesh; (Riceboro, GA) ;
Amidon; Thomas E.; (Jamesville, NY) ; Gratien;
Kathryn E.; (Syracuse, NY) ; Putnam; Jennifer A.;
(Syracuse, NY) |
Assignee: |
The Research Foundation of State
University of New York
Albany
NY
|
Family ID: |
43778982 |
Appl. No.: |
12/855176 |
Filed: |
August 12, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61233704 |
Aug 13, 2009 |
|
|
|
Current U.S.
Class: |
162/68 ; 162/70;
162/82; 162/90 |
Current CPC
Class: |
D21C 3/22 20130101; D21C
3/02 20130101; D21C 1/02 20130101 |
Class at
Publication: |
162/68 ; 162/70;
162/82; 162/90 |
International
Class: |
D21C 1/02 20060101
D21C001/02; D21C 3/22 20060101 D21C003/22; D21C 3/02 20060101
D21C003/02 |
Claims
1. A method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material, the method comprising the steps of: a.
preparing a lignocellulosic material; b. contacting the
lignocellulosic material in a vessel with hot water or steam for a
predetermined time; c. lowering the pH to less than about 5 by
producing acetic acid from the reaction of the hot water or steam
and the lignocellulosic material; d. removing lignocellulosic
material extracts including a percentage of hemicellulose, acetic
acid and metal ions from the vessel; e. exposing contacted
lignocellulosic material to pulping chemicals in a pulping reactor;
f. forming a contacted lignocellulosic material pulp with a kappa
number below about 19 after about 90 minutes of contact with the
pulping chemicals; g. exposing the contacted lignocellulosic
material pulp to whitening agents; and h. producing a whitened hot
water contacted lignocellulosic material pulp.
2. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the hot water in the
vessel is between about 20.degree. C. and about 200.degree. C.
3. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 2, wherein the hot water in the
vessel is about 150.degree. C.
4. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the lignocellulosic
material is contacted for between about 1 minute and 7 days.
5. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 4, wherein the lignocellulosic
material is contacted for about 90 minutes.
6. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the pH is lowered to
about 3.5.
7. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the acetic acid
reaches a concentration of about 0.06 M.
8. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the lignocellulosic
material extracts are between about 2% and about 25% of the mass of
the prepared lignocellulosic material.
9. The method of treating lignocellulosic material to increase pulp
yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the lignocellulosic
material extracts are between about 8% and about 15% of the mass of
the prepared lignocellulosic material.
10. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the pulping chemicals
are consumed by about 80% within about 60 minutes by the contacted
lignocellulosic material.
11. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the residual
concentration of pulping chemical in the contacted lignocellulosic
material prior to exposing the contacted lignocellulosic material
to whitening agents is about 10% of initial concentration within
the pulping reactor.
12. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 9, wherein the pulping chemicals
comprise sodium hydroxide and sodium sulfide.
13. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 10, wherein the pulping chemicals
comprise sodium hydroxide and sodium sulfide.
14. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the contacted
lignocellulosic material pulp has a kappa number about 90% lower
than a pulp which has not undergone hot water contact.
15. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 13, wherein the pulping chemicals
are sodium hydroxide at a concentration of 16% and sodium sulfide
at a concentration of 18%.
16. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 13, wherein the pulping reactor
is heated to between about 150.degree. C. and 180.degree. C.
17. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the contacted
lignocellulosic material pulp has a bulk of at least about 2.00
cm.sup.3/g after about 210 minutes of contact with pulping
chemicals.
18. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the contacted
lignocellulosic material pulp has a bulk higher than an
un-contacted lignocellulosic material pulp.
19. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 16, wherein the pulping chemicals
are sodium hydroxide at a concentration of 16% and sodium sulfide
at a concentration of 18%.
20. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 16, wherein the pulping reactor
is heated to between about 150.degree. C. and 180.degree. C.
21. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein about 50% of the
hemicellulose content of the lignocellulosic material is extracted
from the vessel during the removal of lignocellulosic material
extracts step.
22. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the hot water
contacted lignocellulosic material has a residual chemical
concentration from about 25% to about 33% of the residual chemical
concentration of a non hot water contacted lignocellulosic
material.
23. The method of treating lignocellulosic material to increase
pulp yield, pulp bulk and pulp viscosity of hot-water extracted
lignocellulosic material of claim 1, wherein the pulping chemicals
comprise sodium hydroxide.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/233,704 filed on Aug. 13, 2009, the entire
contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates generally to the field of Kraft
pulping of hot-water extracted wood chips. More specifically, the
present invention is directed to treating lignocellulosic materials
with a hot water extraction process to remove a substantial portion
of hemicellulose, Kraft pulping the treated lignocellulosic
material, thereby producing a lighter pulp with a lower lignin
concentration, lower production time and/or lower chemical charge
with lower residual chemical content.
BACKGROUND OF THE INVENTION
[0003] There are a number of processes that convert lignocellulosic
materials to pulp. Lignocellulosic materials comprise cellulose,
lignin and hemicellulose, with conventional pulping operations
recovering the cellulose in the form of long, flexible, natural
linear homopolymer fibers. Lignin acts as a natural phenolic "glue"
which holds the fibers of cellulose together, with the cellulose
fibers and lignin being encrusted with the lower molecular weight
hetero-sugar polymer, hemicellulose.
[0004] Pulp is the fibrous slurry of cellulosic fibers which is fed
to a paper machine to produce paper. Mechanical, chemical and
hybrid methods dominate commercial pulping plants. About 25% of
worldwide pulp production is mechanical pulp. It is a high-yield
process but suffers from high energy costs and damage to the
lignocellulosic fibers. This damage produces lower strength paper.
These disadvantages (cost and quality) limit the number of
applications for pulp.
[0005] The chemical method of pulping lignocellulosic material
produces a chemical pulp. The dominant chemical pulping process is
the Kraft Process. The traditional Kraft Pulping process,
introduced in 1879, is a process in which lignin is removed in the
presence of a high concentration of sodium hydroxide and sodium
sulfide. The Kraft process is the dominant chemical pulping process
being used today. The popularity of the Kraft process is due to the
process's insensitivity to the wood condition, favorable energy
recovery and chemical recovery capabilities. One problem associated
with the Kraft pulping process is non-uniformity of the pulp formed
from the lignocellulosic material. Uniformity of the pulp formed
from the lignocellulosic material is critical to improving the
performances of cooking and downstream operations such as bleaching
and papermaking. Incomplete penetration and inadequate diffusion of
chemicals into lignocellulosic material remain the primary reasons
for improper delignification and lower quality pulp.
[0006] Another problem associated with the Kraft pulping process is
that the harsh chemicals used during the Kraft pulping process
dissolve about 20-30% of the wood weight into the pulping liquor,
this lost wood weight being in the form of lignin and
hemicellulose. During commercial Kraft pulping, about 70% of the
hemicellulose is removed from the fibers. The removed hemicellulose
and lignin is mostly burned in the boilers after the cellulose has
been separated out for pulp production.
[0007] Hemicellulose is a mixture of sugar and sugar acids, a major
component of which are xylans. The prior art has had difficulty in
isolating hemicelluloses, with the majority of hemicelluloses being
dissolved during Kraft pulping and discharged after pulping with
the rest of the pulping liquor. The inability to capture a pure
stream of a hemicellulose has limited the overall economic
efficiency of the pulping process.
[0008] Hemicellulose is a relatively underutilized component of the
wood during the traditional Kraft pulping process, and has
commercial value beyond being burned in a furnace. Namely,
hemicelluloses can be used as a raw material for production of
furfural, ethyl alcohol, hydrogels, barrier films and for yeast
nutrition. Thus, conventional pulping does not address at least one
major aspect of commercial exploitation of lignocellulosic
materials, mainly the use of extracted hemicellulose.
[0009] What is desired is a process which prepares lignocellulosic
materials for a pulping process which will not require the addition
of caustics, and will provide a benefit to the pulping, bleaching
and fiber quality of the pulp produced. Further, what is desired is
an improved pulping process to address the problem of non-uniform
pulp caused by the lack of impregnation of chemicals used in
traditional chemical pulping into the lignocellulosic material.
Further, what is desired is an improved recovery for economically
valuable products, the products being either a higher viscosity
pulp, a lighter (bulkier) pulp, or pulp with a higher pulp
yield.
[0010] Embodiments of the present application provide a method that
addresses the above and other issues.
SUMMARY OF THE INVENTION
[0011] The present invention is directed to an omnibus process of
pulping lignocellulosic materials. The process is directed towards
a method to 1) reduce pulp weight (increase bulk); 2) increase
viscosity; or 3) increase the pulp yield of a lignocellulosic
material. This method comprises the following steps; preparing a
lignocellulosic material, contacting the lignocellulosic material
in a vessel with hot water or steam for a predetermined time,
producing acetic acid from the reaction of the hot water or steam
and the lignocellulosic material, lowering the pH to less than
about 4, removing lignocellulosic material extracts including a
large percentage of hemicellulose, acetic acid and metal ions from
the vessel, exposing contacted lignocellulosic material to pulping
chemicals in a pulping reactor, forming a contacted lignocellulosic
material pulp with a kappa number below about 19 after about 90
minutes of contact with the pulping chemicals, exposing the
contacted lignocellulosic material pulp to whitening agents, and
producing a whitened hot water contacted lignocellulosic material
pulp.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will be better understood by reference
to the following drawings of which:
[0013] FIG. 1 is a schematic flow diagram of the omnibus pulping
process of the present application;
[0014] FIG. 2 is a table of corresponding fiber properties for
exemplary sets of pulps;
[0015] FIG. 3 is a graphical representation of percentage mass
removal during hot water contacting as a function of time;
[0016] FIG. 4 is a graphical representation of the dissolution of
various components as measured in the hot water contacting vessel
during hot water contact as a function of time;
[0017] FIG. 5 is a graphical representation of the light
absorptivity of the liquid in the pulping reactor during pulping as
a function of time;
[0018] FIG. 6 is a graphical representation of residual NaOH
concentration of the liquid in the pulping reactor during pulping
as a function of time;
[0019] FIG. 7 is a graphical representation of residual NaHS
concentration of the liquid in the pulping reactor during pulping
as a function of time;
[0020] FIG. 8 is a table displaying various properties of pulp
obtained with 210 minutes of maintained temperature of 150.degree.
C. in an M/K digester for eucalyptus woodchips;
[0021] FIG. 9 is a table displaying various properties of hot water
contacted, Kraft pulped sugar maple wood chips;
[0022] FIG. 10 is a graphical representation of the effect of hot
water contact on the pulp viscosity of woodchips through variation
of the H-factor for mixed northeast hardwoods;
[0023] FIG. 11 is a graphical representation of the effect of hot
water contact on the pulp viscosity of woodchips through variation
of the active alkali concentration for mixed northeast hardwoods;
and
[0024] FIG. 12 is a graphical representation of the effect mass
removal has on hot water contacted wood chips as a function of bulk
and PFI revolutions, measuring the amount of refining required.
[0025] FIG. 13 is a graphical representation of the effect
temperature during hot water extraction has on the kappa number and
pulp viscosity.
[0026] FIG. 14 is a graphical representation of the effect liquor
to wood ratio has on the kappa number and pulp viscosity during hot
water extraction.
[0027] FIG. 15 is a graphical representation of the effect the
length of time spent in hot water extraction has on kappa number
and pulp viscosity.
DETAILED DESCRIPTION
[0028] The method of the present invention is an improvement over
pulping methods which do not have a hot water contacting stage. The
improvements are, inter alia, an increased pulp yield, pulp bulk
and pulp viscosity, thereby producing a higher quality pulp.
Initially an amount of lignocellulosic material is prepared for
contact with hot water or steam in a vessel. Preparation could
include chipping or cutting to reach a desired size and shape. The
prepared lignocellulosic material is placed in a vessel and
contacted with steam or hot water for a predetermined time, which
could be any amount of time from 1 minute to 7 days. In one
embodiment, the prepared lignocellulosic material is contacted with
steam or hot water for about 90 minutes. The hot water in the
vessel is between about 20.degree. C. and 200.degree. C. In one
embodiment, the hot water in the vessel is about 150.degree. C.
This time period where the lignocellulosic material is being
contacted with hot water causes a lowering of the pH level to less
than about 5 because acetic acid is being produced from a reaction
between the acetyl groups of the lignocellulosic material and the
hot water or steam. In one embodiment the pH is lowered to about
3.5. In one embodiment, the acetic acid concentration reaches about
0.06 M. After the predetermined time for hot water or steam
contact, the lignocellulosic material is removed and the remaining
liquid is extracted from the vessel. This liquid contains
hemicelluloses, the produced acetic acid, metal ions among other
extracts, which can be purified and commercialized. The liquid,
metal ions and other extracts contain from about 2% to about 25% of
the mass the lignocellulosic material had prior to hot water
contact. In one embodiment, the liquid, metal ions and other
extracts contain from about 8% to about 15% of the mass the
lignocellulosic had prior to hot water contact. At this point, the
lignocellulosic material is exposed to pulping chemicals in a
reactor which remove lignin. The pulping chemicals are consumed by
about 80% within about 60 minutes by the treated lignocellulosic
material. The residual concentration of the pulping chemicals in
the contacted lignocellulosic material is about 10% of the initial
concentration of pulping chemicals within the reactor. The pulping
chemicals comprise sodium hydroxide and sodium sulfide. In one
embodiment the initial concentration of sodium hydroxide within the
reactor is 16% and the initial concentration of sodium sulfide
within the reactor is 18%. In one embodiment, the pulping chemicals
comprise sodium hydroxide. In one embodiment, the reactor is heated
to between about 150.degree. C. and about 180.degree. C. The pulp
formed from this exposure has a kappa number below about 19 after
about 90 minutes of exposure to the pulping chemicals in a pulping
reactor. This kappa number after 90 minutes is lower than a kappa
number of an un-treated lignocellulosic material for the same
amount of time because the de-lignification process occurs more
quickly for hot water or steam treated lignocellulosic material. In
one embodiment, the contacted lignocellulosic material pulp has a
kappa number about 90% lower than a pulp which has not undergone
hot water contact. Subsequent to pulping, the formed pulp is
exposed to whitening agents, thereby producing a whitened hot water
or steam contacted lignocellulosic material which can be made into
a paper product. This whitened hot water or steam contacted
lignocellulosic material has a bulk which is higher than a non-hot
water contacted lignocellulosic material. In one embodiment this
whitened hot water or steam contacted lignocellulosic material has
a bulk of at least about 2.00 cm.sup.3/g after about 210 minutes of
contact with the pulping chemicals. A more detailed description
follows.
[0029] The process of the present application begins with the raw
material utilized in the production of pulp and its
by-products--lignocellulosic material. Some exemplary
lignocellulosic materials utilized in pulping are woods, grasses
and the like. Specific tree genus's which can provide
lignocellulosic material for the pulping process include, among
others, fir, hemlock, juniper, pine, spruce, larch, aspen, beech,
alder, wattle, balsa, eucalyptus, maple, oak, birch and willow.
Generally woods not suitable for use as lumber and certain species
of grass are most commonly employed as raw materials in pulp and
subsequent paper production.
[0030] Lignocellulosic materials 1 in accordance with the process
depicted in FIG. 1, are subjected to hot water contact 3, where
extraction of hemicelluloses from the lignocellulosic materials 1
takes place.
[0031] In hot water contact step 3, water, at temperature in the
range of between about 50.degree. C. and about 200.degree. C. and a
pH in the range of between about 1 and 7 contacts the
lignocellulosic material 1 for a period in the range of between
about 1 minute and about 7 days. More preferably, the water is at a
temperature in the range of between about 140.degree. C. and about
180.degree. C., at a pH in the range of between about 3 and about 7
and a contact time between the lignocellulosic material 1 and the
hot water is in the range of between about 30 minutes and about 120
minutes. As the wood is treated with hot water, acetic acid is
produced. Acetic acid is produced as the acetyl group (1-4.5% of
the weight of the original lignocellulosic material 1) in
lignocellulosic material 1 hydrates and dissociates, causing a
subsequent reduction in pH levels. The acetic acid further
catalyzes the de-acetylation and hydrolysis of lignocellulosic
material 1, creating an autocatalytic reaction. The produced acetic
acid also depolymerizes the hemicelluloses present in
lignocellulosic material 1, for example the hemicellulose xylan to
xylose and xylose oligomers, so that an un-damaged hemicellulose
stream can be extracted as described, supra.
[0032] The hot water contacting step 3 mainly removes
hemicelluloses, leaving a substantially uniform material which can
be pulped. Hemicelluloses are extracted as their glycosidic bonds
are broken by the absorption of protons and water molecules to the
glycosidic bond sites during hot water extraction step 3. This
autocatalytic hydrolysis leaves both cellulose and lignin intact as
essentially un-degraded polymers and increases the lignin density
at the surface of the hot water contacted lignocellulosic material
7.
[0033] The mass of the lignocellulosic material 1 which is lost due
to hot water contacting step 3 can be seen in FIG. 3, which mainly
represents the mass lost due to removal of hemicelluloses. An
exemplary embodiment for a process for hot water contacting step 3
is described below in Example 1.
[0034] This hot water contacting step 3, which serves as an
extraction step, represents an advance in the art insofar as this
step not only enhances the quality of pulp for pulping, which is
conducted subsequent to this step, but, in addition, the step that
occurs downstream of the pulping step, pulp bleaching, requires
fewer chemicals. Pulp quality and quantity is measured by several
parameters, several of which the present process enhances. Mainly,
the Kappa number of a pulp, which measures the lignin content or
bleachability is enhanced by the present process. Kappa number is
representative of the lignin content chemical requirement for
bleaching, as the Kappa number decreases, so does the lignin
content and chemical concentration required to achieve a desired
level of whiteness in a paper product. Another pulp quality the
present process enhances is pulp bulk. Pulp bulk is representative
of the amount of volume a unit weight of a pulp will define. As
pulp bulk increases so does the quantity of a paper product the
pulp will be made into.
[0035] The hot water contacting step 3 is an example of
autocatalytic hydrolysis which has advantages over other methods of
extraction including no reduction in value due to caustic or metal
hydroxides, there is no increase in corrosion from mineral acids,
no sludges are generated, capital and operational costs are lowered
and cellulose is not significantly degraded. Further, environmental
and recovery side effects are avoided as caustic or sodium is not
added to the process streams and no byproducts from mineral acid
neutralization are produced. Because there is no caustic addition,
hydrolyzed hemicelluloses produce acetic acid, in addition to
sugars, with the acetic acid further catalyzing the extraction and
hydrolysis reactions.
[0036] The aqueous extract 13 resulting from hot water contact step
3, an aqueous solution, is subject to further processing to recover
chemical values present in the original lignocellulosic materials
charged into the process. Aqueous extract 13 contains about 50% of
the hemicellulose which was originally contained in the
lignocellulosic material 1, which translates to about 8-25% of the
dry weight of lignocellulosic material 1. The aqueous extract 13,
in accordance with this aim is passed into a separation unit 14.
Separation unit 14 can recover the chemical values present in of
aqueous extract 13 through fractionation or concentration with a
membrane.
[0037] This separation permits recovery of material values inherent
in lignocellulosic materials. Acetic acid is a commodity chemical
with commercial value. Hemicellulose sugars, principally xylose,
can, in the absence of the separated acetic acid, be used to
produce other valuable products including processing for bioenergy
applications. Xylose can also be converted polymers.
[0038] As depicted in FIG. 1, the aqueous extract 13 is separated
in separation unit 14 into an acetic acid stream 15 and
hemicellulose sugar aqueous solution stream 16. The hemicellulose
sugar can, in the absence of acetic acid be treated to form
valuable products 17 such as but not limited to ethanol, also the
hemicellulose sugar aqueous solution stream 16 can be converted
polymers 18.
[0039] The hot water extracted lignocellulosic material 7 is next
subjected to chemical pulping step 8. The removal of hemicelluloses
in hot water contact step 3 removes chromophors in fiber with
chemical units such as uronic and hexenuronic acids that are
resistant to pulping and bleaching. Further, because of hot water
contacting step 3, there is an increase in internal porosity of the
lignocellulosic material, rendering lignin bond sites more open and
accessible to pulping chemicals, leaving pulping and bleaching
requirements reduced. Internal porosity is increased because of the
breaking of covalent bonds between lignin and carbohydrate as a
result of hemicellulose removal.
[0040] The acidic conditions created during hot water contacting
step 3 causes the removal of metal ions and carboxyl groups,
especially those associated with hemicelluloses such as uronic acid
in the lignocellulosic material 1. With a hydration transition pH
of about 3.5 for polyvalent cationic species, the association or
adsorption of these heavy metals on fibers is reduced when the
woodchips or pulp is subject to an acidic environment with pH less
than about 3.5.
[0041] This increased porosity and removal of metal ions and
carboxyl groups allows lower chemical concentrations and shorter
cooking times during pulping, in turn resulting in less fiber
damage and a higher quality pulp 10. As an exemplary embodiment,
the de-lignification process is described in Example 2 supra.
[0042] During chemical pulping 8, the hot water extracted
lignocellulosic material 7 is added to a pulping reactor with
water, active alkali and sulfide. Preferably, the initial
concentration of active alkali is about 16%. Preferably, the
initial concentration of sodium sulfide is about 18%. As one
example of the exemplary method, the alkali and sulfide
concentration change with respect to time is described in Examples
3 and 4 supra.
[0043] As can be seen in Example 3, alkali is consumed more quickly
for hot-water extracted lignocellulosic material 7 as compared to
untreated lignocellulosic material, and the residual concentration
of alkali is lower in hot water extracted lignocellulosic material
7 as compared to untreated lignocellulosic material. Because of the
fast consumption of alkali, a pulping facility can benefit by a
higher throughput, which is the result of faster pulping times.
Further, a lower load of alkali is required to reach the same
consumption in a reasonable time, avoiding the use of a larger
amount of costly chemicals.
[0044] As can be seen in example 4, sulfide is consumed more
quickly by hot-water extracted lignocellulosic material 7 as
compared to untreated lignocellulosic material, and the residual
concentration of sulfide is lower in hot water extracted
lignocellulosic material 7 as compared to untreated lignocellulosic
material. Because of the fast consumption of sulfide, a pulping
facility can benefit by a higher throughput, which is a result of
faster pulping times. Further, a lower load of sulfide is required
to reach the same consumption in a reasonable time, avoiding the
use of a larger amount of costly chemicals.
[0045] After treatment in chemical pulping step 8, hot water
extracted lignocellulosic material 7 becomes a pulp 10. The overall
yield of pulp 10 can be similar to the yield of pulp received for
untreated lignocellulosic material and pulp 10 has a lower kappa
number. In one example, shown in FIG. 2, Pulp 10 has a lower kappa
number and an increase in mass removal as compared to pulp which
has not been hot water contacted. Non-hot water contacted pulp is
referred to herein as control pulp. FIG. 2 shows that with an
increase in length of hot water contact step 3, the kappa number
decreases and mass removal increases. Kappa number is an indication
of the lignin content, or bleachability of a lignocellulosic
material pulp, with a lower number being associated with less
lignin content and increased ability to be bleached with a lower
chemical concentration. Pulp 10 has different properties than a
control pulp, for example pulp 10 has a decreased burst strength
and Scott bond, with an increase in bulk. The decrease in burst,
tear, and Scott bond can be recovered by addition of a small amount
of a bonding agent. A non-exhaustive list of examples of bonding
agents includes starch, PHA, and PLA. Therefore, the strength is
not an important factor for the hot-water extracted pulp.
[0046] In one example, shown in FIG. 8, bulk of pulp 10 is
increased. Bulk of pulp 10 can be increased through either
increasing the length of hot water extraction step 3 or increasing
sulfidity. Scott bond, tear, burst strength and bulk are shown in
FIG. 8, bulk is also shown in FIG. 12. As can be seen in FIG. 12,
there is an increased bulk of pulp 10 as mass removal increases as
compared to the bulk of control pulp. Further, the bulk of pulp 10
remains high as the amount of refining increases, which is measured
in revolutions of a PFI mill.
[0047] Pulp 10 has further properties which differentiate it from
control pulp, including viscosity and a lower H factor. FIG. 9
shows the decrease in H factor associated with pulp 10 as compared
to control pulp. H factor is the effective cooking time (or the
time duration if the pulping reaction were conducted at 100.degree.
C.). A lower H factor indicates a pulp which required a shorter
time for lignocellulosic material to be converted to a pulp of a
certain Kappa number.
[0048] FIG. 9 shows the effect of hot water contact step 3 on the
pulping requirements for hot water extracted lignocellulosic
material 7. As can be seen, hot water contacting step 3 results in
viscosity increase of pulp 10. Example 5 below further describes
FIG. 10 and FIG. 11 and the measure of viscosity of pulp 10.
[0049] FIG. 13 shows the effect of hot water contact temperature
during hot water contact step 3 on the Soda pulping of Aspen
woodchips. In this figure, there has been no sulfur addition to the
soda pulping liquor. It can be seen that an increase in contact
temperature increases the pulp viscosity while decreasing the kappa
number.
[0050] FIG. 14 shows the effect of liquor to wood ratio during
hot-water contact step 3 on the soda pulping of Aspen woodchips. In
this figure, there has been no sulfur addition to the soda pulping
liquor. It can be seen that the change in viscosity and kappa
number is small as the liquor to wood ratio is changed during
hot-water extraction step 3.
[0051] FIG. 15 shows the effect of extraction time during hot water
contact step 3 on soda pulping of Aspen woodchips. In this figure,
there has been no sulfur addition to the soda pulping liquor. It
can be seen that while kappa number decreases with an increase of
extraction time during hot water contact step 3, viscosity
initially increases but subsequently begins to decrease. Because of
hemicellulose removal and a subsequent reduced kappa number, there
are positive benefits to pulping, bleaching and fiber quality.
[0052] Once hot water contacted lignocellulosic material 7 has just
been pulped in chemical pulping step 8, it is bleached at bleaching
step 13. In one preferred embodiment, it is preferred that
bleaching step 13 be accomplished by contacting the pulp with a
strong oxidizing agent. This strong oxidizing agent may be selected
from the non-exhaustive group consisting of oxygen, hydrogen
peroxide, ozone, peracetic acid, chlorine, chlorine dioxide, a
hypochlorite anion and mixtures thereof. A particularly preferred
oxidizing agent employed bleaching step 13 is hydrogen
peroxide.
[0053] In another preferred embodiment, during bleaching step 13,
pulp 10 is bleached in two oxygen-contacting stages. In this
embodiment, it is desirable that there by a washing step between
the two oxygen-contacting stages. Alternatively, that preferred
embodiment with oxygen and sodium hydroxide between the two
oxygen-contacting stages.
[0054] In another preferred embodiment, during bleaching step 13,
pulp 10 is contacted with chlorine dioxide in the presence of at
least one additional agent. In one preferred embodiment, the
additional agent is oxygen. In another preferred embodiment, the
additional agent is magnesium hydroxide or another magnesium
containing compound. In yet another preferred embodiment the
additional agents are oxygen and magnesium hydroxide or another
magnesium containing compound. In still another preferred
embodiment, the additional agent is potassium hydroxide or calcium
hydroxide.
Example 1
[0055] In all of the following examples, the lignocellulosic
material used was Eucalyptus wood chips, unless otherwise noted.
Although Eucalyptus wood chips were used as the lignocellulosic
source, any lignocellulosic material could be used.
[0056] A liquor (water) to lignocellulosic material ratio of 4:1
was added to a vessel capable of holding pressure, for example a
high pressure laboratory M/K circulation digester and brought from
about room temperature to about a temperature of 160.degree. C.
over about a 40 minute period. During this hot water contacting
time, acetic acid was produced through an auto-hydrolysis reaction
to reach a concentration of about 0.06M.
[0057] The vessel was maintained at this temperature for about 30
minutes to about 80 minutes. The extracted lignocellulosic material
was then thoroughly washed with water to remove dissolved
substances. The remaining liquor in the vessel was then separated
into its constituents.
[0058] The mass which was removed during hot water contacting step
accounts for the loss due to the hemicellulose and lignin removal,
which depends on the length of time the lignocellulosic material
was exposed to the hot water contact process. As can be seen in
FIG. 3 below, mass removal, based on virgin, un-treated woodchip
dry mass, or control wood chip dry mass, after about 30 minutes at
peak temperature was about 10%, mass removal after 60 minutes was
about 13%, with mass removal after about 80 minutes being about
20%.
[0059] The hot water contacting step produced a hot water extracted
lignocellulosic material product and an aqueous extract. FIG. 4 is
an example of components of the liquid which were within the
reaction vessel as a function of time. The liquid in the reaction
vessel became the aqueous extract.
Example 2
[0060] FIG. 5 shows the UV light absorptivities of the liquid, or
black liquor, within the pulping reactor during the pulping process
at 280 nm during the kraft pulping of hot-water extracted wood
chips and control woodchips. Time zero represents when the reactor
contents, including woodchips, water and an initial concentration
of active alkali at 16% and sulfide at 18%, have been mixed for 15
minutes at room temperature, with the temperature about to be
raised. The active alkali is the percentage of equivalent Na.sub.2O
in the solution and the sulfidity is the ratio of Na.sub.2S (or
specifically its equivalent in Na.sub.2O) to the total Na.sub.2O.
The temperature reached 150.degree. C. in about 30 minutes, and was
maintained at that temperature. Based on FIG. 5, there is a
noticeable increase in UV light absorptivities at 280 nm during the
initial de-lignification periods (from the start of the temperature
raise to around 70 minutes), after which the absorptivity increased
more slowly and leveled off towards the end. This initial increase
in light absorptivity was mainly due to the concentration of lignin
in the reactor liquid. The de-lignification process took a longer
time to reach near completion (approximately 210 minutes) for
control woodchips, as compared to hot-water extracted woodchips
which reached near completion sooner (approximately 120 minutes).
This difference in time is an advantage which reduces energy input
into the pulping system, and increases throughput for a pulping
facility.
Example 3
[0061] FIG. 6 shows the sodium hydroxide concentration in the black
liquor as a function of time during chemical pulping for control
and hot-water extracted wood chips. Initially sodium hydroxide was
added to water in the pulping reactor at a concentration of about
0.956 Molar, followed by the addition of woodchips. The contents of
the pulping reactor were mixed for 15 minutes at room temperature.
The temperature was increased to about 150.degree. C. over about 30
minutes. As can be seen in FIG. 6, during the first 30 minutes, the
drop in alkali concentration in the black liquor was very rapid for
hot-water extracted woodchips. More alkali was consumed at a faster
rate for the pulping of hot-water extracted woodchips as compared
to the control chips, and the residual concentration of alkali was
much higher in the control wood chips as compared to the hot-water
extracted wood chips.
Example 4
[0062] FIG. 7 shows the sodium sulfide concentration in the black
liquor as a function of time during chemical pulping for control
and hot-water extracted wood chips. Initially sodium sulfide was
added to water in the pulping reactor at a concentration of about
0.201 Molar, followed by the addition of woodchips. The contents of
the pulping reactor were mixed for 15 minutes at room temperature.
The temperature was increased to about 150.degree. C. over about 30
minutes. As can be seen in FIG. 7, during the first 30 minutes, the
drop in sulfide concentration in the black liquor was very rapid
for hot-water extracted woodchips. More sulfide was consumed at a
faster rate for the pulping of hot-water extracted woodchips as
compared to the control chips, and the residual concentration of
sulfide was much higher in the control wood chips as compared to
the hot-water extracted wood chips.
Example 5
[0063] FIG. 9 shows the effect of hot water contact on the Kraft
pulping requirements for sugar maple wood chips. To achieve similar
pulp properties of control pulp properties, hot water contacted
wood chips were beneficially exposed to reduced chemical
concentrations and/or cooking times. FIG. 10 shows the effect of
hot water contacting of woodchips on the pulp viscosity by varying
the H factor for mixed northeast hardwoods. FIG. 11 shows the
effect of hot water contacting of woodchips on the pulp viscosity
by varying the active alkali charge for mixed northeast hardwoods.
Pulp viscosity is a measure of chemical damage to the cellulose
fibers of woodchips. A higher viscosity is indicative of less
damage. For both FIG. 10 and FIG. 11 the hot water contacted
woodchips were obtained by extracting mixed Northeast hardwood
chips including maple, oak and birch with hot-water at about
160.degree. C. for times less than 1 hour. Both hot water contacted
and control woodchips were Kraft pulped with similar conditions.
FIG. 10 shows the variation of pulp viscosity with Kappa number
where H-factor, or effective pulping time, was altered while active
alkali charge was maintained. FIG. 11 shows that the Kappa number
changes were achieved by altering the active alkali charge, but
maintaining the same H-factor during pulping. Based on FIG. 9, FIG.
10 and FIG. 11 it can be seen that hot water contacting results in
viscosity increases of resultant pulp. A pulp with a high viscosity
is an advantage because the pulp will produce a higher strength and
quality paper.
Example 6
[0064] FIGS. 13 through 15 show the effect of hot water contact on
the soda pulping for Aspen wood chips. Increase in hot-water
contact time and temperature decreases the kappa number. Increase
in hot-water contact temperature for 90 minutes increases the
resulting pulp viscosity as seen in FIG. 13. A maximum viscosity is
observed at 90 minutes contact when the pulping liquor is
160.degree. C. as seen in FIG. 15. Water to liquor ratio during the
hot-water contact prior to soda pulping has a minor impact on the
kappa number and viscosity as shown in FIG. 14.
* * * * *