Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ADDITIVE COMPOSITION AND PROCESS FOR REDUCING
ANTHRAQUINONE REQUIREMENTS'IN PULPING OF
LIGNOCELLULOSIC MATERIAL
BACKGROUND OF THE INVENTION
1. Field of the Invention.
This invention relates to an improved additive
composition and process for the delignification of
lignocellulosic material, such as wood, with an alkaline
pulping liquor of the kraft, or sulfate, alkaline pulping
process. More particularly, the invention relates to
lignocellulosic material delignification with kraft
pulping liquors containing a cyclic keto compound
(preferably, anthraquinone), permitting enhanced yield.
Specifically, the invention relates to an improvement of
said additive composition and process wherein said
enhanced yield is achieved at reduced anthraquinone
levels via the inclusion of a surfactant mixture
comprising at least one alkyl alcohol alkoxylate and at
least one polyoxyalkylene glycol ether of an ester of an
acid selected from the group consisting of ricinoleic
acid and 12-hydroxystearic acid.
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2. Descrivtion of the Prior Art.
In the mid-1970s, a significant advance was made in
the delignification of lignocellulosic material for the
production of wood pulps upon the discovery of the
benefits of using anthraquinone as a pulping additive to
alkaline pulping liquors. Among the earliest public
disclosures of such use of anthraquinone was U.S. Patent
No. 3,888.727, which taught treating lignocellulosic
material with an alkaline pulping liquor containing
anthraquinone sulfonic acid followed by oxygen
delignification. More significantly, however, U.S.
Patent No. 4,012,280 taught that the poorer economics of
the environmentally preferable soda pulping process could
be improved to compete with the more environmentally
offensive (in terms of odor) kraft process by
incorporation of anthraquinone as a pulping additive.
Although the benefits of increased yield of cellulosic
pulp and increased rate of delignification (permitting
lower energy consumption and higher throughput) were
shown, the use of the improved, lower pollution potential
soda process was not advanced. First, incorporating the
relatively expensive anthraquinone in the soda process to
make it productively competitive with the kraft process
without anthraquinone reduced its economic
competitiveness. Second, the benefits of anthraquinone
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also were achieved in other (already more commercially
employed) pulping process such as those employing kraft
or polysulfide pulping liquors.
It was soon discovered, as disclosed in U.S. Patent
No. 4,213,821, that anthraquinone also benefitted cooking
wood chips in neutral sulfate pulping liquor (with a
special case disclosed in U.S. Patent No. 5,139,617), as
well as in the alkaline pulping liquors. Methods for
maximizing the benefits of anthraquinone were disclosed
in U.S. Patent Nos.: 4,127,439; 4,178,861; and 4,310,383.
Also, due to anthraquinone's difficult-to-handle, water-
insoluble, fine powder form, discoveries made to
facilitate its dispersion in the pulping liquors are
disclosed in U.S. Patent Nos.: 4,248,663; 4,384,921; and
4,574,032. One disadvantage to anthraquinone use is its
tendency to cause scaling problems in the cooking vessel.
Methods to overcome this problem are disclosed in U.S.
Patent Nos.: 4,481,073 and 4,561,935. Finally, as a
result of the relative high cost of anthraquinone,
methods for recovering and reuse of the chemical are
disclosed in U. S. Patent Nos.: 4,197,168 and 4,310,383.
In spite of the aforementioned advances, there
remains a need to improve the benefits of anthraquinone
pulping (primarily reduction of energy and chemical
requirements while improving yield) and to reduce its
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disadvantages (primarily cost and equipment scaling).
One approach would be to replace a portion of the
anthraquinone with an additive Which provided some of the
benefits of anthraquinone without providing the
disadvantages which accompany its use.
Therefore, an object of this invention is to provide
an improved pulping additive composition and process for
delignification of a lignocellulosic raw material with,a
pulping liquor with anthraquinone for the production of a
predetermined yield of cellulose pulp which composition
and process permit the achievement of said yield, as well
as other aforementioned benefits, with a reduced
requirement of anthraquinone of at least 10~.
SUN>HIARY OF THE INVENTION
The above stated object is provided by the
instant invention which is an improved additive
composition and an improved process for delignification
of lignocellulosic raw material, such as wood chips, for
the production of cellulose pulps for use in the
manufacture of paper or paperboard wherein the wood chips
are treated in a closed reaction vessel with a pulping
liquor with an amount of a cyclic keto compound, such as,
anthraquinone, included therein for achievement of a
determined pulp yield, wherein the improvement comprises
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a reduction in the amount of anthraquinone required to
achieve said yield by the addition to said alkaline
pulping liquor, in addition to a reduced amount of the
anthraquinone, a surfactant mixture comprising at least
one alkyl alcohol alkoxylate and at least one
polyoxyalkylene glycol ether of an ester of an acid
selected from the group consisting of ricinoleic acid and
12-hydroxystearic acid.
DESCRIPTION OF THE PREFERRED E1~ODIMENTLS)
The improved process of this invention comprises the
steps of (1) treating lignocellulosic material in a
closed reaction vessel with an alkaline pulping liquor
containing a cyclic keto compound additive selected from
the group consisting of naphthoquinone, anthraquinone,
enthrone, phenanthrenequinone, the alkyl, alkoxy, and
amino derivatives of said quinones, 6,11-dioxo-1H-anthra
[1,2-c]pyrazole, anthraquinone-1.,2-naphthacrinone, 7,12-
dioxo-7,12-dihydroanthra[1,2-b]pyrazine, 1,2-
benzanthraquinone, and 10-methylene enthrone, the
treatment taking place at a maximum temperature of from
about 150° to about 200°C for a period from about 0.5 to
about 480 minutes to achieve a determined pulp yield, and
(2) displacing the pulping liquor from the
lignocellulosic material with water or an aqueous liquor
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inert to the lignocellulosic material to obtain a
determined yield of a delignified cellulosic material,
wherein the improvement comprises a reduction in the
amount of cyclic keto compound additive required to
achieve said yield by the addition to the alkaline
pulping liquor, in addition to a reduced amount of the
cyclic keto compound, a surfactant mixture comprising at
least one alkyl alcohol alkoxylate and at least one
polyoxyalkylene glycol ether of an ester of an acid
selected from the group consisting of ricinoleic acid and
12-hydroxystearic acid.
The delignified cellulosic material produced by the
above two steps may be used without further treatment or
may be subjected to conventional bleaching steps.
When the lignocellulosic material to be treated is
wood, it is first converted into the form of chips. This
step is not required when the lignocellulosic material is
of fibrous form.
The lignocellulosic material may be refined between
steps (1) and (2). Refining can be carried out with
known equipment, such as a single disc or double disc
refiner.
The process of this invention may be used to
delignify either coniferous or deciduous species of wood.
By coniferous is meant species such as pine, spruce, and
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balsam fir. By deciduous is meant species such as birch,
aspen, eastern cottonwood, maple, beech, and oak.
The alkyl alcohol alkoxylate component of the
surfactant mixture is preferably a C4 Cue. alkyl alcohol
alkoxylate prepared by reacting an alcohol, which may
have either a linear or branched chain and may be either
a primary or secondary alcohol, with from about 5 moles
to about 100 moles of an alkylene oxide selected from the
group of ethylene oxide, propylene oxide, butylene oxide,
and any combination thereof. A particular preferred
alkyl alcohol alkoxylate is oleyl alcohol ethoxylate
prepared with 23 moles ethylene oxide.
The member of the group of polyoxyalkylene glycol
ethers of an ester of an acid selected from the group of
ricinoleic acid and hydroxy stearic acid can be prepared
by reacting an ester of a glycol, selected from the group
of glycerine, neopentyl glycol, trimethylolethane,
trimethylolpropane, pentaerythritol and its polymers,
mannitol, and sorbitol, with from about 5 moles to about
100 moles of an alkylene oxide selected from the group of
ethylene oxide, propylene oxide, butylene oxide, and any
combination thereof. Inasmuch as ricinoleic acid is the
primary component (~90~) of castor oil, although present
as a triglyceride rather than in free acid form, castor
oil may be alkoxylated directly.to form the required
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polyoxyalkylene glycol ethers of the esters of ricinoleic
acid. Therefore, a preferred member of this group is
ricinoleic acid triglyceride ethoxylate.
U.S. Patent Nos. 5,298,120 and 5,501,769 disclose
pulping wood using fatty acid esters of polyoxyalkylene
glycols to enhance pulping uniformity and pulp yield.
While these esters may give the desired performance,
there is an inherent weakness in the molecule when used
in strongly alkaline solutions which are heated to high
temperatures. The ester will cleave and form both a
fatty acid soap and the polyalkylene glycol used to form
the ester. Thus, it ceases to be the ester claimed.
Also, the beneficial results are not being produced by
the disclosed compound, rather the beneficial results
are, in fact, diminished by the products of this
cleavage.
This is not the case with the claimed alkyl alcohol
polyalkylene glycol ethers and the polyalkylene glycol
ether of ricinoleic acid triglyceride (of castor oil),
which can give superior performance in the strong, hot
alkaline solutions used in pulping wood. When the ester
of the polyalkylene glycol ether of ricinoleic acid
triglyceride cleaves, the resultant molecule will be the
sodium salt of polyalkylene glycol ether of ricinoleic
acid, which is a surfactant and which will have
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functionality in the pulping solution. The presence of
the sodium salt of the polyalkylene glycol ether of
ricinoleic acid will assist in solubilizing the alkyl
alcohol polyalkylene glycol ethers in the hot, alkaline
pulping solution as the pulping process is completed.
The solubilization of the other surfactants is of great
benefit since, otherwise, these other surfactants may
precipitate out of solution and be of less benefit.
The composition of the invention is preferably a
microemulsion prepared by combining an oleyl alcohol
ethoxylate with a ricinoleic acid triglyceride ethoxylate
in a weight ratio of from about 4:1 to about 1:4
(preferably, about 1:2), respectively. For combination
with anthraquinone for use in alkaline pulping, an
aqueous solution of the composition is prepared by
blending with from about 10 to about 30~ (preferably,
about 20~) water, producing a clear viscous solution.
This solution is, in turn, diluted with water to form
about 10 to about 30~ (preferably, about 12.5 0 active
when combined with the aqueous dispersion of
anthraquinone. The invention surfactant composition
should exhibit an HLB of from about 5 to about 20
preferably from about 8 to about 16. Upon combination of
the components of the surfactant composition, a
microemulsion is formed which exhibits an average
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particle size of from about 0.5 to about 10 Vim,
preferably from about 1 to about 4 ~m and most preferably
less than 2 Vim.
Evidence that a microemulsion of the proper average
particle size to accomplish the observed synergism with
anthraquinone has been formed is that, upon combination
of the two components at ambient temperature, a
transparent solution is formed, and, upon heating to
about 82°C (180°F), the solution turns a hazy bluish
color.
The cyclic keto compound, preferably anthraquinone,
is preferably prepared as an aqueous dispersion which is
combined with the invention surfactant compound prior to
their addition to the cooking vessel. The anthraquinone
dispersion is preferably prepared by the addition of a
dispersant and by reducing the anthraquinone average
particle size to from about 6 to about 10 Etm in water by
wet grinding or milling. A preferred dispersant may be a
sodium lignosulfonate.
Although the surfactant composition and the
anthraquinone dispersion may be added separately to the
cooking vessel, it is preferred that they be combined
prior to such addition and then added as a single aqueous
blend. The surfactant microemulsion serves to coat the
anthraquinone particles and allows the mixture of
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anthraquinone and pulping liquors to penetrate the wood
chips at a faster rate and saturate them more efficiently
and completely. It is envisioned that it is this
mechanism which results in obtaining the desired kappa
number and lower rejects using significantly less
anthraquinone.
In a preferred embodiment, then, the present
invention relates to an improved wood pulping aid
composition comprising a cyclic keto compound for
addition to pulping liquors in the delignification of
lignocellulosic raw material wherein the improvement
comprises the addition of a surfactant mixture comprising
at least one alkyl alcohol alkoxylate and at least one
polyoxyalkylene glycol ether of an ester of an acid
selected from the group consisting of ricinoleic acid and
12-hydroxystearic acid, wherein the ratio of alkyl
alcohol alkoxylate to polyoxyalkylene glycol ether of an
ester of an acid selected from the group consisting of
ricinoleic acid and 12-hydroxystearic acid is from about
4:1 to about 1:4 respectively, and the composition
exhibits an HLB of about 5 to about 20.
In another preferred embodiment, the present
invention relates to an improved process for the
delignification of lignocellulosic raw material in the
production of cellulose pulps suitable for use in the
manufacture of paper or paperboard comprising treating
the lignocellulosic raw material at from about 150 to
about 200 C in a closed reaction vessel with an alkaline
pulping liquor with an amount of a cyclic keto compound
included therein to achieve a determined pulp yield,
wherein the improvement comprises a reduction in the
amount of the cyclic keto compound required to achieve
said yield by the addition to said alkaline pulping
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liquor a surfactant mixture comprising at least one alkyl
alcohol alkoxylate and at least one polyoxyalkylene
glycol ether of an ester of an acid selected from the
group consisting of ricinoleic acid and 12-hydroxystearic
acid, wherein the ratio of alkyl alcohol alkoxylate to
polyoxyalkylene glycol ether of an ester of an acid
selected from the group consisting of ricinoleic acid and
12-hydroxystearic acid is from about 4:1 to about 1:4
respectively, and the composition exhibits an HLB of
about 5 to about 20.
The benefits of the invention process and
composition are seen in the following examples.
Example 1
For comparison purposes, 59,090 kg (sixty-five wet
tons) of conifer wood chips were loaded into a pulping
digester filled with kraft alkaline pulping liquors
providing an average of about 4,909 kg (about 10,800
pounds) active alkali a liquor to wood ratio of about
3.45, after which 22.7 kg (50 wet pounds) of a 500
anthraquinone dispersion (0.080 by weight, based on the
weight of oven dried wood chips) were added. The
digester contents were heated up to a maximum temperature
of 166°C (332°F) and the wood chips were cooked for 79
minutes to a kappa number of 91. The cook resulted in a
yield of 540, and rejects of 10%.
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Example 2
For use as an additional digestion aid to enhance
the benefits of anthraquinone, several samples of the
invention surfactant were prepared and evaluated for
microemulsion performance. In varying proportions, an
oleyl alcohol ethoxylate prepared with 23 moles ethylene
oxide was combined with a ricinoleic acid triglyceride
ethoxylate and water. In each case, upon blending the
components together, a clear, viscous solution was
formed.
Sample A:
oleyl alcohol ethoxylate - 23 moles EO 20 parts by weight
ricinoleic acid triglyceride etholxylate 60 parts by weight
water 20 parts by Weight
Sample B:
oleyl alcohol etholxylate - 23 moles EO 40 parts by weight
ricinoleic acid triglyceride ethoxylate 40 parts by weight
water 20 parts by weight
Sample C:
oleyl alcohol ethoxylate - 23 moles EO 60 parts by weight
ricinoleic acid triglyceride ethoxylate 20 parts by weight
water 20 parts by weight
Each sample was diluted to 12.5 wt~ with water and
heated to 82°C (180°F). At ambient temperature all
diluted samples gave transparent solutions, and at 82°C
(180°F) each sample turned a hazy bluish color.
Example 3
The process of Example 1 was again conducted;
except, in place of the 0.08$ anthraquinone, 0.06 by
weight based on oven dried wood chips of a digestion aid
comprised of the surfactant blend of Sample A from
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Example 2 and anthraquinone was,added to the white liquor
as the white liquor was simultaneously pumped into the
digester while the wood chips were being added. Upon
completion of the digestion cycle, a pulp having a kappa
number of 90 was produced with rejects of under 10~.
Compared with the performance of anthraquinone alone
in Example 1, it is noted that a reduction by 25$ of
digestion aid (using the invention pulping additive) gave
a lower kappa number and a significantly lower reject
level. Moreover, when a comparison is made based on the
respective anthraquinone content of the respective
digestion aids, a reduction in anthraquinone required of
at least 50~ is permitted by the invention surfactant
composition.
Other advantages of using a digestion aid having
less anthraquinone include:
1. Less tendency for formation of scale on the
evaporator tubes and plugging of the tubes; and
2. Reduced contamination of the crude tall oil,
which lessens problems in the tall oil refinery and
reduces contamination of the tall oil heads fraction.
While the invention has been described and
illustrated herein by references to various specific
materials, procedures, and examples, it is understood
that the invention is not restricted to the particular
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materials, combinations of materials, and procedures
selected for that purpose. Numerous variations of such
details can be employed, as will be appreciated by those
skilled in the art.
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