Note: Descriptions are shown in the official language in which they were submitted.
CA 02214299 1997-12-04
pATF!NT
ATTORNEY DOCRET NO.: CHS~ AN
COMPOSTTION AND METHOD FOR PRODUCING WOOD PUT.P
Field of the Invention
The present invention is generally directed to a
process for producing paper from wood pulp, and more
particularly to a composition containing a castor oil
derivative, such as an ethoxylated castor oil that is
used for producing pulp from wood chips.
Background of the Invention
The majority of corrugated boxes, paper grocery
bags, fine papers, and market pulps are produced by a
sulfate pulping process known as "Kraft" pulping. The
process is characterized by the fact that sodium
sulfide is added to the medium that is used to cook
the wood chips and produce pulp. When this technique
was introduced over a century ago, the addition of
sodium sulfide produced a dramatic improvement in pulp
strength, pulp yield, and durability of the paper made
therefrom.
In the typical Kraft digestion process, wood
chips are added to an aqueous medium consisting mostly
of white liquor which will be transformed into black
liquor during the cook. In general, the liquor in
which the wood chips are cooked, or cooking liquor,
comprises a mixture of black and white liquor, the
black liquor being liquor added back to the cooking
vessel, or digester, from a prior batch of wood chips
and the white liquor being a freshly prepared alkaline
solution. Black liquor varies considerably among
different mills depending on the white liquor used,
the wood employed, and the method of cooking. Typical
white liquor is a solution of sodium hydroxide, sodium
carbonate, sodium sulfate, sodium sulfide and various
inorganic materials. White liquor solubilizes the
pulp and removes the lignin from the wood fibers.
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The largest part of the organic matter removed
from the wood during cooking is combined chemically
with sodium hydroxide in the form of sodium salts.
Some of these compounds are resin and fatty acid soaps
which account for the intense foaming properties of
black liquor. In addition, organic sulfur compounds
and mercaptans, which give the characteristic odor to
the sulfate-containing black liquor, and small amounts
of sodium sulfate, silica and other impurities such as
lime, oxide, alumina, potash, and sodium chloride are
present in the black liquor.
In the pulping process, pre-sized wood chips are
subjected to the alkaline reagents at elevated
temperatures and pressures in a digester vessel.
Generally, temperatures range from about 250~F to
about 350~F and pressures range from about 60 psi/g to
about 130 psi/g. Digestion time may range from 30
minutes to 10 hours, depending on the process
conditions and the desired pulp/paper characteristics.
The reaction conditions present during the cook,
or digestion, cause lignin--the amorphous polymeric
binder found in wood fibers--to be hydrolyzed.
Ideally, wood chips are digested only long enough to
dissolve sufficient lignin to free the cellulosic wood
fibers but maintain sufficient lignin intact to
provide added strength to the paper. The pulping
process attempts to maximize pulp yield, which is
defined as the dry weight of pulp produced per unit
dry weight of wood consumed.
After sufficient lignin has been dissolved to
free the cellulosic wood fibers, the digester charge
is blown into a receiving vessel, or blow tank. The
sudden drop in pressure from the digester to the blow
tank causes additional mechanical breakup of the wood
fibers. In some papermaking applications, the
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residual lignin is removed to produce papers without
the characteristic brown color of Kraft paper. In
producing linerboard or Kraft paper, however, the
lignin residue remains in the papermaking pulp so that
the highest possible strength of wood pulp is
achieved.
Ideally, each of the wood chips blown from the
digester into the blow tank is broken down into
separate wood fibers. In practice, however, some of
the wood chips fail to completely separate due, in
part, to the undissolved lignin remaining in the pulp.
These unseparated particles are removed from the wood
pulp by passing the pulp through a screen having
openings of a predetermined size. In the pulping
industry, the standard test screen employed is flat
with .01 inch slots therethrough.
The materials that are recovered by this
screening process are known as "rejects". The rejects
include wood fibers that could be used to produce
paper. Accordingly, it is highly desirable to
decrease the amount of rejects. One method of
lowering the amount of rejects is by increasing the
digestion time or by creating more severe hydrolysis
conditions. Such conditions, however, increase the
costs involved and cause some of the cellulose in the
wood chips to be hydrolyzed and rendered unusable.
After contact with liquor in the digester,
inorganics, any unused surfactants that may have been
added, and solubilized lignin and resins are removed
from the pulp in one or more washing steps.
Temperatures in the digestion and washing stages
typically vary from about 250~F to 340~F and 100~F to
200~F, respectively. After washing, the pulp may be
subjected to further bleaching or purification
treatments as desired before being sheeted and dried,
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or prepared for sale, or further utilized in making
paper.
A Kappa number corresponds directly to the amount
of lignin remaining in the pulp. Generally, the
higher the Kappa number, the more lignin present in
the pulp and, therefore, the higher the pulp yield.
The Kappa number generally decreases as the digestion
time is increased or the alkalinity of the cooking
liquor is increased. The goal in such Kraft
papermaking processes is to retain as much lignin as
possible in order to enhance strength and to reduce
the cost, while maintaining the uniformity of the
cook. More uniform cooks result in a decreased
percentage of rejects and, thereby, reduce costs for
running paper mills.
Cooking, or digestion, of the pulp may be
terminated when the amount of rejects in the pulp is
reduced to an acceptable level. Substantial yield and
quality advantages are achieved if the wood chips are
cooked to a higher lignin content. As a result, an
increase in a Kappa number target by the use of
thinner chips can result in a substantial cost
savings. However, the thickness of chips obtainable
on a commercial scale is always variable. A major
portion of the total rejects frequently originate from
a relatively small fraction of the chips having the
greatest thickness. The objective in every pulping
process is to achieve a lower percentage of rejects.
In recent years, the focus of the paper making
industry has turned to various conservation efforts
and to other environmentally related concerns. For
instance, efforts have been undertaken to utilize as
much of the wood as possible during the pulping
process. Besides the obvious economic advantages,
increasing the efficiency of wood conversion to pulp
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lowers raw material requirements, preserving the
amount, of trees that need to be harvested for
producing the paper products.
Besides decreasing wood consumption, other
efforts have been undertaken to decrease the quantity
of chemicals added to the wood in order to convert the
wood into pulp. Once these chemicals become used and
exhausted during the pulping process, they accumulate
various waste products. If the chemicals are not
recycled, they must be disposed of according to very
strict governmental regulations. By reducing the
quantity of chemicals added to the wood, less waste is
generated for disposal, which not only provides
economic advantages, but also places less burdens on
the environment.
In one aspect, improvements to the wood pulping
process have been achieved through the inclusion of
chemical additives in the cooking liquor. For
instance, in U.S. Patent No. 5,298,120 to Blackstone
entitled "Composition for Enhancing the Pulping of
Wood Chips" and in U.S. Patent No. 5,501,796 to
Rl~ckstone et al. entitled "Pulping Wood Using Fatty
Acid Esters of Polyoxyalkene Glycols to Enhance
Pulping Uniformity and Pulp Yield", which are both
incorporated herein by reference, various surfactants
are disclosed that are added to the cooking liquor or
to the wood chips in order to enhance cooking
uniformity, to increase the yield of pulp produced, to
reduce the amount of cooking liquor, and to decrease
the amount of rejects. The surfactants are directed
to esters of ethylene oxide-propylene oxide block
copolymers and to esters of polyoxyalkene glycols.
U.S. Patent No. 3,448,004 to Buckman, et al. is
directed to the addition of an N,N-dimethylamide of a
straight chain carboxylic acid to the cooking
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chemicals used in the preparation of chemical pulp
from wood chips. Buckm~n et al. states that the
addition of the N,N-dimethylamide reduces the amount
of cooking chemicals required in the process
S accompanied by increased yield and improved quality of
the chemical pulp.
Other various surfactants and deresinating agents
added to the cooking liquor during the production of
wood pulp are disclosed in U.S. Patent No. 4,426,254
to Wood et al., U.S. Patent No. 2,999,045 to Mitchell
et al., U.S. Patent No. 4,906,331 to Blackstone et
~1~, and U.S. Patent No. 4,952,277 to Chen, et al
The above prior art represents significant
advances and improvements to the wood pulping process.
The particular features of the present invention,
however, have not heretofore been known and remain
absent from the prior art. The present invention is
directed to further improvements and advances in the
process of producing wood pulp and in the process of
producing paper therefrom.
Summary of the Invention
The present invention is directed to further
advantages and improvements over prior art
constructions in the paper making field. Accordingly,
it is an object of the present invention to provide a
composition and process for improving the cooking of
wood chips during the production of pulp for making
paper.
It is an object of the present invention to
provide a composition and process for enhancing
cooking uniformity of wood chips for producing pulp.
It is another object of the present invention to
provide a composition and process for increasing the
yield of pulp produced per ton of wood chips.
It is another object of the present invention to
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provide a composition and process for reducing the
amount of cooking liquor required to produce pulp.
~t is a further object of the present invention
to provide a composition and process for reducing the
amount of solids contained in the black liquor of a
pulping process.
It is another object of the present invention to
provide a composition and process to decrease the
amount of rejects produced during production of pulp.
It is a further object of the present invention
to provide an economical and efficient process for
producing pulp from wood.
Another object of the present invention is to
provide a composition and process to decrease the
impact of the Kraft pulping process on the environment
and reduce the cost of treating waste materials
produced thereby.
Still another object of the present invention is
to provide a process for producing pulp which includes
the steps of adding an alkoxylated castor oil to a
cooking liquor.
Another object of the present invention is to
provide a process for producing pulp which includes
the step of adding to the cooking liquor an
alkoxylated castor oil blended with other surfactants,
such as an ester of a polyoxyalkene glycol.
These and other objects of the invention are
achieved by providing a process for cooking wood in a
cooking liquor medium comprising the steps of
contacting the wood with a cooking liquor containing a
composition comprising an alkoxylated castor oil. The
wood is cooked to produce a pulp. The process can
further include the step of producing paper from the
pulp .
In one embodiment, the alkoxylated castor oil can
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contain from about 5 moles to about 200 moles
alkoxylate (per mole of castor oil), particularly from
about 5 moles to about 80 moles alkoxylate, and in one
preferred embodiment from about 16 moles to about 25
moles alkoxylate. The alkoxylated castor oil can be
the reaction product of ethylene oxide and castor oil,
the reaction product of propylene oxide and castor oil
or mixtures thereof.
In general, the alkoxylated castor oil can be
present in the composition in an amount from about 10
percent to about 100 percent by weight and
particularly from about 40 percent to about 60 percent
by weight. Prior to being diluted with water, the
composition can be added to wood during the pulping
process in an amount from about 0.2 pounds to about
0.4 pounds per ton of wood.
When added to wood chips, the composition of the
present invention can be diluted with water. For
instance, water can be added to the composition in an
amount up to about 95 percent by weight, and
particularly up to about 90 percent by weight. Once
diluted with water, the composition can be added to
the cooking liquor at a rate of from about 2 pounds to
about 4 pounds per ton of wood.
The alkoxylated castor oil can be used alone or
in combination with other surfactants and chemical
agents. For instance, the composition can contain
alkoxylated castor oil mixed with anthraquinone,
esters of polyoxyalkene glycols, esters of ethylene
oxide-propylene oxide block copolymers, and mixtures
thereof. For example, in one embodiment, the
composition can contain esters of block copolymers
having the general formula:
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HO(CH2CH2O)X(CHCH2O)y(CH2CH2O)zH
I
CH3
wherein X, Y and Z each have a value of at least 1.
In an alternative embodiment, the alkoxylated
castor oil is combined with at least one ester of a
polyoxyalkene glycol. For instance, the composition
can contain a blend of esterified polyoxyalkene
glycols, such as an esterified polyoxyethylene glycol
and an esterified polyoxypropylene glycol. In
particular, the esterified polyoxyethylene glycol can
be the reaction product of polyoxyethylene glycol with
stearic acid, while the esterified polyoxypropylene
glycol can be the reaction product of polyoxypropylene
glycol with oleic acid. In general, the esters of the
polyoxyalkene glycols can be present in the
composition in an amount from about 20 percent to
about 70 percent by weight.
These and other objects of the present invention
are also achieved by providing a composition for
adding to an alkaline liquor for cooking wood to
produce pulp. The composition includes an alkoxylated
castor oil that is present in the composition in an
amount of at least 10~ by weight. The alkoxylated
castor oil is contained in the composition in
combination with a surfactant. The surfactant can be,
for instance, a polyoxyalkene glycol and esters
thereof, a block copolymer of a polyethylene oxide and
polypropylene oxide and esters thereof, anthraquinone
and mixtures thereof.
Other objects, features and aspects of the
present invention are discussed in greater detail
below.
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Descr;pt;on of Preferred ~mbodiments
It is to be understood by one of ordinary skill
in ths art that the present discussion is a
description of exemplary embodiments only and is not
intended as limiting the broader aspects of the
invention, which broader aspects are embodied in the
exemplary construction.
In general, the present invention is directed to
a composition and process for producing pulp from
cellulosic materials such as wood chips. The process
employees a chemical agent that acts as a dispersant
and as a surfactant in the cooking liquor that is used
in the digester to produce the pulp. When added to
the cooking liquor, the composition of the present
lS invention enhances cooking uniformity, increases pulp
yield, reduces the amount of cooking liquor needed to
produce the pulp, decreases the amount of rejects, and
improves the quality of the pulp.
Broadly speaking, the composition of the present
invention, in order to achieve the above-described
benefits, contains a castor oil derivative, and in
particular, an alkoxylated castor oil. For instance,
the alkoxylated castor oil can be the reaction product
of castor oil and ethylene oxide, the reaction product
of castor oil and propylene oxide, or mixtures
thereof. The alkoxylated castor oil can contain from
about 5 moles to about 200 moles of alkoxylation, and
particularly from about 5 moles to about 80 moles of
alkoxylation. In one preferred embodiment of the
present invention, the composition contains mixtures
of an ethoxylated castor oil containing 16 moles of
ethoxylation and an ethoxylated castor oil containing
25 of moles ethoxylation.
At the present time, it is unknown why the
addition of an alkoxylated castor oil to the cooking
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liquor produces the above-described benefits and
advantages. It is believed, however, that an
alkoxylated castor oil is well suited for use in wood
pulping processes due to its resiliency and ability to
remain stable within an alkaline cooking liquor at
high temperatures. In particular, an alkoxylated
castor oil contains an ether linkage between the
polyoxyalkylene glycol portion of the molecule and the
fatty acid backbone which does not break down when
exposed to heat in an alkaline composition thus
maintaining the functional part of the compound in
tact.
In general, prior to being diluted with water,
the composition of the present invention can contain
from about 10 percent to about 100 percent by weight
of the alkoxylated castor oil, and preferably from
about 40 percent by weight to about 60 percent by
weight. More particularly, the amount of alkoxylated
castor oil contained within the composition will
depend upon the particular application and the other
ingredients added to the cooking liquor.
Based upon its concentrated form (not containing
any water), the composition of the present invention,
for most applications, can be added to wood chips for
forming pulp in an amount from about 0.2 pounds to
about 0.4 pounds per ton of wood. Additional amounts
of the composition may be added to the cooking liquor.
It has been discovered, however, that additional
amounts typically do not provide any further benefits.
In general, the composition of the present
invention should be diluted with water prior to being
added to the cooking liquor. Water can be added to
the composition in an amount up to about 95 percent by
weight and particularly up to about 90 percent by
weight. Once diluted with water, the resulting
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solution can be added to the cooking liquor in an
amount from about 2 pounds to about 4 pounds per ton
of wood. In adding the composition of the present
invention to the digester, the composition can be
mixed with the alkaline cooking liquor before
contacting the chips or can be fed in line with the
cooking liquor.
Besides being an effective dispersant and
surfactant in its own right, it has also been
unexpectedly discovered that alkoxylated castor oil
synergistically improves the performance of other
surfactants and chemical agents used in wood pulping
processes. In this regard, the present invention is
also directed to the use of alkoxylated castor oil in
combination with other wood pulping agents.
For instance, the composition of the present
invention can contain an alkoxylated castor oil in
combination with such known surfactants as
polyoxyethylene-polyoxypropylene block copolymers as
disclosed in U.S. Patent No. 3,909,345 to Parker, et
al. which is incorporated herein by reference,
anthraquinone, polyoxyalkene glycols, esters of
polyoxyalkene glycols as disclosed in U.S. Patent No.
5,501,769 which was referenced above, and esters of
ethylene oxide-propylene oxide block copolymers as
disclosed in U.S. Patent No. 5,298,120 which was also
referenced above. Alkoxylated castor oil can be
combined with the above surfactants and mixed with the
cooking liquor or can be added separately to the
cooking liquor.
For example, in one embodiment, alkoxylated
castor oil can be used in combination with esters of
ethylene oxide-propylene oxide block copolymers as can
be represented by the following general formula:
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HO(CH2CH20)x(CHCH20)y(CH2CH20)zH
I
CH3
in which X, Y, and Z are integers having a value of 1
or more. The block copolymers can be esterified by
reacting them with, for instance, a fatty acid. In
general, any fatty acid may be used. Particular fatty
acids include saturated and unsaturated fatty
monoacids and diacids having from about 4 to about 22
carbon atoms. Such fatty acids include maleic acid,
stearic acid, adipic acid, palmitic acid, abietic
acid, linoleic acid, and oleic acid. When present in
the composition, the esterified block copolymers can
be present in an amount from about 20 percent to about
70 percent by weight, and particularly from about 40
percent to about 65 percent by weight.
In an alternative embodiment, instead of using
the above esterified block copolymers or in addition
to using the above esterified block copolymers, esters
of polyoxyalkene glycols are combined with the
alkoxylated castor oil. For instance, the composition
can contain blends of esterified polyoxyalkene
glycols, such as an esterified polyoxyethylene glycol
combined with an esterified polyoxypropylene glycol.
In order to esterify the polyoxyalkene glycols, the
polyoxyalkene glycols can be reacted with the above-
described fatty acids.
In one of the preferred embodiments of the
present invention, the composition of the present
invention contains the following ingredients:
30% to 40% by weight of an ethoxylated
castor oil containing 25 moles of
ethoxylation
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14
5% to about 10% by weight of an ethoxylated
castor oil containing 16 moles of
ethoxylation
25% to about 35% by weight of a
polyoxyethylene glycol containing 40 moles
of ethoxylation that has been esterified
with stearic acid
25% to about 35% by weight of a
polyoxypropylene glycol that has been
esterified with oleic acid
Besides polyoxyalkene glycols, as described
above, the alkoxylated castor oil of the present
invention can also be used in combination with
anthraquinone. For instance, in one embodiment, the
composition can contain about 10 percent by weight
alkoxylated castor oil combined with about 25 percent
by weight of anthraquinone.
The present invention may be better understood
with reference to the following examples.
EXAMPLE
The following test was performed in order to
determine the effectiveness of the process and
composition of the present invention.
Specifically, the following composition was
formulated and mixed with a cooking liquor during the
production of wood pulp:
36% by weight ethoxylated castor oil
containing 25 moles of ethoxylation
8% by weight castor oil containing 16 moles
of ethoxylation
28% by weight of the reaction product of a
polyoxyethylene glycol with stearic acid
28% by weight of the reaction product of a
polyoxypropylene glycol reacted with oleic
acid
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The above composition was diluted with 90 percent
by weight water. The resulting aqueous solution was
added to the cooking liquor at a rate of 2 pounds per
ton of wood chips. The wood chips being processed
were pine at a rate of from about 500 to about 550
tons per day. The trial period lasted six days.
During the trial period, it was observed that
digester production increased in comparison to trials
in which the cooking liquor did not contain the
additive. It was also observed that the total
dissolved solids contained in the cooking liquor
declined which further indicates an increase in yield.
During the trial period, viscosity and kappa
number data was collected. This data did not show an
improvement. Chip shute level control problems
occurred during the trial period, however, which is
believed to account for the results. It is believed
that if such problems were not experienced, the kappa
number and the viscosity would have increased.
These and other modifications to the present
invention may be practiced by those of ordinary skill
in the art, without departing from the spirit and
scope of the present invention which is more
particularly set forth in the appended claims. In
addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole
or in part. Furthermore, those of ordinary skill in
the art will appreciate that the foregoing description
is by way of example only, and is not intended to
limit the invention so further described in such
appended claims.
