Note: Descriptions are shown in the official language in which they were submitted.
METHOD OF PRODUCING ~IIGH YIELD
CHEMIMECHANICAL P~LPS
Background of the Invention
_
This invention relates to the production of chemi-
mechanical pulps from woody lignocellulosic materials, such
as chips, shavings and sawdust, with ultra high yields and
with improved strength properties. More particularly, this
invention relates to the production of such pulps by means of
the sulfonation of the lignin in the wood, using aqueous sulfite
or bisulfite solutions, followed by mechanical defibering.
The pulp and paper and related industries use many
processes to produce pulp from wood chips and other lignocellu-
losic materials. These processes can be classified, for purposes
of discussion, into four groups, shown below with the represen-
tative yields:
Chemical Pulps - up to 60% yield
Semichemical Pulps - 60 - 80% yield
Chemimechanical Pulps - 80 - 95% yield
Mechanical Pulps - at least 90% yield
The yield ranges shown are approximate only.
Chemical pulps are prepared by cooking the wood chips
(or other lignocellulosic material) at elevated temperatures and
pressures with various chemical agents which dissolve the lignin
and some carbohydrate material to leave relatively pure cellulose
fibers at the 40-45% yield level or cellulose plus some residual ~
lignin at somewhat higher yield levels (45-55%). ~ -
Mechanical pulps at the other extreme use mechanical
means such as grindstones to defiber logs or disc refiners to
defiber wood chips into pulp. These processes use water for cooling
and dilution purposes so that the approximately 5% of the wood
substance that is water soluble is lost for a net yield of about
95%.
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Chemical pulps have many advantages due to their
cleanliness, hicJh streng-~h, and ease of bleaching, but they
are expensive to produce due to the low yield. Their dissolved
solid and gaseous waste products give rise to many environmental
problems.
Mechanical pulps are much cheaper to produce due to
their high yield and constitute an efficient use of forest
resources. Such processes offer no gaseous pollution and rela
tively little BOD5 (biochemical oxygen demand, five-day test)
discharge compare~-to che~i~al pulps.
The semichemical and chemimechanical pulping processes
fall midway between the chemical and mechanical processes in
these respects.
The increasing world-wide demands for pulp, paper and
other forest resource based products are creating an increasing
. need for the us~ of higher yield pulps due to the decreasing
availability of fiber. The present invention produces a hiyh
yield pulp that can replace some types of chemical or semichemical
pulp in many products.
It is known that the treat~ent of wood chips with
relatively small amounts of sulphite and bisulphite, at near
neutral pH, and under relatively mild conditions (100-150C.,
for 2-15 minutes) produces a softening effect on the chips which
makes them easier to defiber and generally produces a cleaner
and better draining pulp than can be produced by mechanical
means alone. See "Ultrahigh Yield NSCM Pulping", by C. A.
Richardson, Tappi, Vol. 45, No. 12, pp. 139A-142A (1962);
Richardson et al., "Supergroundwood from Aspen", Tappi, Vol. 48,
No. 6, pp. 344-346 (1965); Chidester et al. "Chemimechanical
Pulps from Various Softwoods and Hardwoods", Tappi, Vol. 43,
No. 10, pp. 876-880 (1960); Uschmann U. S. patent 3,607,618;
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Aitken et al. U. S. patent 3,013,93~; and Asplllnd et al. U. S.
patent 3,558,428.
However, the pulps produced by such processes, while
being superior to conventional mecha.nical pulps in terms of
cleanliness and drainage properties, do not have sufficiently
good physical properties to justify their increased cost of
production re].ative to the conventional mechanical pulps.
Better properties can be achieved by cooking under
more severe conditions such as increased temperatures in the
1Ø 16Ø-240C.. range, but the strength improvement is always accom-
panied by a loss in yield. Instead of yields of over 90~, the
yields are reduced to about 70-85~. . See most of the above -:
publications and patents and Richardson U. S. patent 2,962,412; ::
Zimmerman U. S. patent 1,821,198; Cederquist U. S. patent
3,078,208; Asplund et al. U. S. patent 3,446,699; Von Hamzburg
U. SO patent 2,949,395; Oison U. S. patent 3,003,909; and Risch
e~ al. U. S. patent 2,847,304. . .
Considerations of cost and environmental protection
make the maintenance of yields in exGess of 90% highly desirable.
2~ It is well lcnown that the physical properties of wood .
pulps are strongly influenced by the flexibility of the indivi~
dual fibers -which flexibility permits the fibers to be brought
into closer contact with each other during the pressing stages
of the paper-making process, which in turn leads to better
bonding and improved strength. Natural wood fibers are rendered
relatively infle~ible by the presence of large amounts (20-30~
by weight) of lignin which is a relatively rigid material at - :
moderate temperatures (less than 100~C.). Fiber flexibility is ~
improved in conventional chemical or semichemical pulping pro- .:
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cesses by removing, chemically, at least part and in some cases
nearly all of the lignin.
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The present invention modifies the lignin by sulfo-
nating it sufficiently to produce a marked change in the physical
and chemical properties of the lignin, but not enough to render
it soluble in water or in the cooking liquor, so it is not sub-
stantially removed from the wood fiber, and yields are consistent
with those of purely mechanical pulps (90-95%).
Many softwood species such as spruce can be sulfonated
up to about 0.65% (expressed as combined sulfur on wood and
measured by the test method, below), usually without reducing `
the yield below 90%. Conventional high yield chemimechanical
pulping processes such as those reported by the Richardson and
Chidester et al. publications and Asplund et al. patent, supra,
achieve a level of about 0.3 to 0.35~ sulfur (on spruce) or only
about 50% of the maximum level of sulfonation that can be reached
without reducing the yield below about 90~ (see comparative prior
art Example 9 below). This low level of sulfonation achieves
some softening of the lignin, which permits the chips to be more .
readily defibered than untreated chips, but the individual fibers
so produced are still relatively stiff and do not give strong
pulps. The stiffness of the fibers also makes them prone to
damage (cutting) in the refining stages and the consequent pro-
duction of fines and debris -- although not to the same extent
as untreated fibers.
It is, accordingly, an object of the present invention
to provide a high yield chemimechanical process for producing
pulp from wood chips and other woody lignocellulosic materials,
including shavings and sawdust, and which . .
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provides a pulp having excellent strength characteristics.
In accordance with one aspect of the present invention, a
method for the production of high yield chemimechanical pulp from
woody lignocellulosic material comprises treating this material
with an aqueous solution of a mixture of sulfite and bisulfite
having a pH of between about 6.0 and about 8.5 at a temperature
of between about 100C. and about 15~C. for a period of between
about 10 and about 90 minutes, the aqueous solution being of
sufficient strength to sulfonate the material to at least about ;
85% of the maximum level of sulfonation that can be achieved on
the material without reducing the yield of pulp below about 90%
by weight. The resulting sulfonated material is subsequently
subjected to mechanical defibration.
Wherever in this specification, including the claims,
reference is made to the maximum level of sulfonation that can be
achieved on a particular material, this means the maximum level
for that material determined by the test described on page 23 -
and under the conditions of the test, i.e. heating at 140C. for ;;
30 minutes. This maximum level is determined without reference
to yield. Thus, in accordance with the invention, the liquor
strength is chosen to be sufficient to give the 85% sulfonation
level, while at the same time being low enough that it does not
reduce the yield below about 90% by weight.
The sulfonated woody lignocellulosic material may be `~
pressed prior to mechanical defibra-tion to remove spent aqueous
solution, the spent solution being recycled and used to treat
fresh material. The volume of spent aqueous solution produced
in this way may be equal to that which, after refortification with
fresh sulfite and bisulfite, is applied to the fresh material to
provide a system in which there is no excess flow of used aqueous
solution.
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In accordance with another aspect of the invention, a
method for the production of high yield chemimechanical pulp
from woody lignocellulosic material derived from softwoods com-
prises treating this woody lignocellulosic material with an aqueous
solution of a mixture of sodium sulfite and sodium bisulfite
having a pH of between about 6.0 and about 8.5 and having a
strength between about 100 g/l and about 200 g/l as sodium sulfite
at a temperature of between about 120C. and about 140C for a
period of between about 20 and about 60 minutes, and subsequently
subjecting the resulting sulfonated material to mechanical defib-
ration.
The term "softwoods" as used herein means wood from coni-
ferous trees, for example spruce, balsam and pine.
Yet another aspect of the invention provides a similar pro-
cess but using woody lignocellulosic material derived from poplar,
in which the material is treated with an aqueous solution of a - -
mixture of sodium sulfite and sodium bisulfite having a strength
of between about 90 g/l and about 115 g/l as sodium sulfite, the
other conditions and steps of the process being as recited above
for softwoods.
A preferred method for carrying out the invention will be
described with reference to the accompanying drawings, in which~
Figures la through le are a series of five graphs where
five physical properties of pulps produced in accordance with
Examples 1 and 2, infra, are plotted against freeness (CSF, ml.).
These properties are breaking length (Fig. la), burst factor (Fig.
lb), tear factor (Fig. lc), bulk (Fig. ld) and wet web strength
(Fig. le).
Figures 2 through 7 are graphs of % yield of pulp and
sulfur content of the pulp vs. liquor concentration (grams per
liter) of Na2SO3 for a series of six woods, as follows:
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Fig. 2 - Spruce
Fig. 3 - salsam
Fig. 4 - Jack Pine
Fig. 5 - Southern Pine
Fig. 6 - Maple
Fig. 7 - Poplar -
Figure 8 is a graph showing the relationship of pulp
yield and sulfur content for maple wood chips carried out under
identical conditions for various time periods as in Example 16,
infra. ;
General Description of the Invention
In the process of the present invention, the wood is
sulfonated to at least about 85% (0.55% sulfur for spruce) and
preferably to about 90% or more (0.58% sulfur for spruce) of
the maximum level of sulfonation for that wood as described,
and under the conditions of the te:t given on p23,
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infra. This level of sulfonation permits the wood chips to be
readily mechanically defibered into individual fibers which
have a flexibility more similar to low yield chemical pulp
fibers than to conventional 90%-plus yield chemimechanlcal fibers.
Indeed, we have discovered that in accordance with the present
invention, the higher the degree of sulfonation of the pulp,
the greater the strength properties of the pulp. This increase
in strength improves dramatically with increase in sulfur content
of the pulp. This effect is shown in Examples 10, 11, 12, 13,
14 and 15, infra, and Table 2, below, where the cooking liquor
strength is varied from 50 g/l (grams per liter) Na2SO3 to
180 g/l Na2SO3 in a series of labora~ory cooks all carried out
at 140C. for 30 minutes. The best strength levels were not
reached until at least about 120 g/l Na2SO3 liquor wasused, which
achieved a level of sulfonation of 0.6% sulfur. Increasing the
liquor strength (and hence the degree of sulfonation) beyond 120
g/l Na2SO3 did not produce substantial further strength improve-
ments. `
The conventional chemimechanical pulp made by a process
reported by C.A. Richardson (Example 9) has inferior strengths -
compared to the pulps of Examples 13, 14 and 15 which employ
the process of the present invention.
Since the nature and content of lignin in wood varies
from species to species, so does the actual sulfur content that
must be achieved in each case. However, in all cases the sul-
fonation level must always be at least about 85% and preferably
about 90% or more of the maximum sulfonation that can be achieved,
the process conditions being also such as do not reduce the yield
below about 90%. Higher sulfur yields can always be achieved by
increasing time or temperature, however this will usually lead
to yields below 90%. The
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following table illustrates the typical levels of sulfonation
that must be achieved for a selection of commonly used wood
species. These values were obtained using the test procedures
for maximum level of sulfonation, l ra.
Wood Species Ma~imum 85% of Maximum
~ S % S ' ' '
Spruce 0.65 0.55
Balsam 0.70 0.60
Jack Pine 0.75 0.64
10 Southern Pine 0.65 0.55
Poplar 0.36 0.31
Maple 0.33 0.28
In order to achieve the 85% level of sulfonation
while maintaining yields in excess of about 90%, it is desirable
to carry out the reaction at temperatures not higher than 150C.
and preferably not higher than 140C., but at least about 100C.
The preferred range is between about 120 and 140C. These
moderate temperatures also help to maintain good brightness.
In order to achieve reasonably short reaction times, e.g., 60
minutes or less, high chemical application levels are used; ;
typically a concentration of at least 120 g/l Na2SO3 in the -
cooking liquor, with a cooking liquor to wood ratio of 3.3:1
[392 kg/t ~kilograms per metric tonne) Na2SO3 on oven dry wood].
The pH of the cooking liquor should be between about 6.0 and
8.5, preferably between about 7.2 and 8Ø
The process of the present invention is applicable ; -
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to woods of all types, both hardwoods and softwoods, particularly
the latter.
Table 1, below, illustrates the properties of some
pulps that have been made using the process of the invention.
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Examples of the pxoperties of a mechanical pulp ~refiner mec~ha-
nical pulp, Example A) and a chemlcal pulp (semibleached kraft,
Example B) have been included for comparison purposes~
Pulps made by this invention may be bleache~ by such
known reagents as sodium hydrosulfite, hydrogen peroxide, or
various co~inations of th~ two~ For example, a pulp (Example
No. 7) with an initial brightness of 52.7 Elr~pho was bleached
as follows:
Bleach Chemical Final Br~ tness
1~ sodium hydrosulfite 61r3% Elrepho
1~ hydrogen peroxide 65.7~ Elr@pho
1% hydrogen peroxide followed by 69.0% Elrepho
1% sodium hydrosulfite
Since the attainment of the high levels of sulfonation
required by the process of the invention will generally involve
the use of relatively high concentrations of cooking chemicals
and relatively heavy applications of cooking liquor on the wood,
it is anticipated that for economic considerations in successful
commercial application of the process o~ the invention, recycling
of the unreacted sulfite from the cooked chips is desirable.
This may be achieved by pressing the cooked chips to remove the
liquor from them and adding fresh chemicals to the liquor to
return it to its original concentration be~ore reuse when recycled
in the process. Recycling also assists in automatically control-
ling the liquor pH to about 7-8, a desirable value. Substantially
lower pH values tend to result in lower yields.
As long as the conditions ~or sufficient sulfonation
are adhered to, the cook can be carried out in a variety of
different ways. In Example 1~ below, a liquid phase process is
used with no pre-impregnation with cooking liquor prior to the
cook. Example 2, belo~, shows a liquid phase process with a
15-minute impregnation prior to the cook. In Examples 3 and 4,
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low, the chips were impregnated for 60 minutes prior to a
vap~r phase ~ook. In each case, the pulps produced were sub-
stantially similar in physical properties. These exampIes
show that the process of the invention can be carried out
using conventional and readily available liquid or vapor phase
cooking equipment.
Example 4, below, illustrates the effect of cooking
at a temperature (148C.) somewhat higher than the optimum
140C. While the strengths are excellent, the brightness, at
47% Elrepho, is lower than the 52-54~ Elrepho that can be
achieved at 1~0C.
The present invention can produce good quality pulps
from a wide variety of raw materials. Examples 5, 6, 7 and 8,
belo~, show the use of southern pine, northern softwoods plus
32% poplar, 55~ northern softwoods and 45% northern hardwoods,
and northern softwood sawdust.
Pulp made by this invention has excellent properties
over a wide freeness range (100-600 ml.~. This is shown in
....
Figures la through le, where a number.of physical properties
are plo~ted against freeness. These regression curves were
taken from over one hundred pulp samples made as in Exzmples 1
and 2. The ability of this pulp to perform well over such a
wide freeness range, serves to distinguish it from mechanical
and conventional chemimechanical pulps which, typically, are
only useful at relatively low freeness levels--usually below
3Q0 ml. In this respect, the pulp made by this invention is
more comparable to low yield chemicàl pulps. As used in Figures
la through le and throughout the present disclosure, freeness is
referr~d to in terms of Canadian Standard Freeness ~CSF) as
defined in Tappi Standard - T 227 (M~58). Freeness is a measure
of the rate at which a dilute suspension of pulp may be dewatered.
3L05~6~13
Example 16, below, shows the effect of increasing the
cooking time. In this e~ample, a very strong cooking liquor
was used to illustrate the upper limit of sulfonation. Such a
strong liquor could not be used in a commercial plant if liquor
recycling was practiced, due to the solubility limit of Na2SO3
in spent liquor. It can be seen that the yield drops rapidly
as the time is increased, and falls below 90% at about 90 minutes.
The operating pH range of this process is governed
by two considerations. A pH substantially below 7.0 would be
environmentally undesirable on a commercial level due to the
presence o free sulfur dioxide. Due to the high concentration
of the liquor, and paxticularly when recycled liquor is used,
the pH does not drop substantially during the cook (see Example 1).
Nevertheless, it is important to maintain the spent liquor no
lower than about pH 6.5 so as to keep the process essentially
odorless.
It is well known that in most cooking processes a pH
substantially greater than about 8.0 will tend to degrade the
liynin and hemicellulose and lead to reduced yield. This is
shown by Example 17 (results in Table 3, below) where it can
be seen that an increase in pH produced a substantial decrease
in yield. It is also well known that a pH substantially above
about 8.0 will tend to produce a discolored pulp which would be
unacceptable in a wide range of products. Thus, this pH con-
sideration would be significant on a commercial scale operation.In the laboratory, under carefully controlled conditions, the
present process may be carried out at any pH over the about
6.0 to 8.5 range without producing odor, discolored pulp, or
too low a yield. However, in a commercial plant, the control
would not be as satisfactory, so that a practical minimum of
above about 7.0, and preferably a pH range of from about 7.2 to
8.0 would be advisable.
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Subsequent to the sulfonation of the ~ood chips,
they are subjected to mechanical defibration by any oE the
conventional mechanical grinding or refining techniques.
These techniques are well known to those skilled ln the art of
mechanical and chemimechanical pulping. One such suitable treat- -
ment is the use of double-disc refinerb whereby tlle sulfonated
chips are passed het~-een rotating grooved discs to apply work
to the chips and thereby defibrate them. The sulfonated chips
may be passed through one or more refiners until the desired
freeness is achieved.
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T~BLE 3
The E~fect of p~-l; from Example 17, below.
% Yield ~ Sulfur
6.0 94.27 0.662
7.0 93.01 0.585
8.0 92.26 0.521
g.0 90.97 ~ 0.670
The pulps made from this invention are useful in such
p~oducts as ~e~sprint, coated papers, book papers, sanitary tis-
sues, corrugating medium, linerboard, paper toweling, diaperfluff, milk carton board, etc.
Speci~ic Description of the Invention
In order to disclose more clearly the nature of the
present invention, the following examples illustrating the
invention are given. It should be understood, however, that
this is done solely by way of example and is intended neither
to delineate the scope of the invention nor l-imit the ambit of
the appended claims. In the examples which follow, and through-
out the specification, the quantities of material are expressed
20. in terms of parts by weight, unless otherwise specified.
In Example 1, below,the wood chips were digested in
a continuous (3-tube Bauer M and D) digester. This type of
digester is described in Paper Trade Journal, pages 36-37,
(September 5~ 1960) in an article by Van Derveer, entitled
"Unique New Continuous Digesters Improve Operations at Two
Mills"; also Pulp and Paper International, May 1971, pages 55
. . .
and 56. The chips pass through the tubes of the continuous
digester by means of a conveyor.
In Example 1 the refiner employed on the chips after ;~
sulfonation was a double-disc refiner manufactured by Bauer
Bros. (now C-E Bauer) ~nown as Model 400. This double-disc
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~5~
refiner employs 36 inch diameter grooved discs and two 110
kilowatt (150 horsepower) motors. Type 36161 plates were
used in the first stage, and 36106 or 36104 plates were
employed in the second stage of the refiner. The feed rate
through the refiner was between two and four tons per day.
In order to reach a final freeness of 400 milliliters CSF,
a refiner power of about 2.5 megajoules per kilogram (35.2
horsepower days per air-dried ton) was applied in the ~irst
stage of the refiner and 2.2 megajoules per kilogram (31.0
horsepower days per air-dried ton) in the second.
Examples 9 through 15, inclusive, represent a series
of controlled experiments which demonstrate a comparison of
the results obtained by the prior art (Example 9) and a series -
of experiments with all conditions the same except that the
concentration of the Na2SO3 in the digestion liquor is gradually -
increased (Examples 10 through 15, inclusive). In all of
Examples 9-15, the same source of wood chips was employed. As
demonstrated by Examples 10-15, at the temperature and cooking
time conditions employed, it was not until the liquor strength
was increased to about 120 g/l Na2SO3 that the desired at least -
about 85% of maximum sulfonation was achieved.
.,: .
EXAMPLE 1
The following method was used to produce pulp at the
rate of about 4 tons per day in a pulping pilot plant.
A mixture of northern softwood chips containing approx-
imately 42% black and white spruce, 35% balsam fir, and 23%
jack pine was presteamed for about 10 minutes, then metered -
into a 3-tube M and D continuous digester along with cooking
liquor at a liquor to wood ratio of 3.3:1 (wt./wt. of dry
chips). The cooking liquor was initially prepared by mixing
sodium hydroxide and sulfur dioxide in a tank to produce
_ 15_
,,, i'
~, . , ' ;': i ,,. , , "~, ,~, ,;,j ;,~""", ,~ " , ~, "
. ~ , , , ~ , , ~
~Ot516~L8
~ concentration of 120 g/l as Na2SO3 at a pH o~ 7.8. As the
run progressed, sp~nt liquor, still containing some unreacted
sodium sulfite, was extracted from the last quadrant of the M
and D tube, fortified with additional sodium hydroxide and
sulfur dioxide to readjust the original liquor concentrations,
and reused. During the course of the run (several weeks) the
liquor concentration varied rom about 115 g/1 to about 125 g!l as
Na2SO3 and the pH varied from about 7.5 to about 8Ø The pH
of the spent liquor covered the range 7.0 to 7.4.
The liquox in each of the three tubes in the digester
was maintained at a temperature of 135C. (range 132-138C.) at
a pressure of 410 kPa (range of from 400 to 500 kPa) (kPa refers
to kilopascals). The residence time of chips in the digester
- was 30 minutes (10 minutes per tube).
The cooked chips were discharged from the digester
into a blow tank at atmospheric pressure, then transferred to
a double-disc refiner. Sufficient water was added to the chips
just before entering the refiner to reduce the consistency to
about 15%. The pulp leaving the refiner had a freeness range
of 650-720 ml., typlcally.
The pulp was diluted to about 2% consistency and
pumped to a horizontal belt washer where it was washed with
hot water to remove residual cooking chemicals and waste pro-
ducts. The pulp left the washer at a consistency of about
15~ and was fed to a second double-disc refiner, at that con-
sistency, where the freeness was reduced to about 350 ml.
After leaving the second refiner, the pulp was diluted
to about 2% consistency and heated by direct steam injection to
at least 75C. (not exceedin~ 100C.) and held above 75C. for
at least 20 minutes, for latency removal. The pulp was then
further diluted to about 0.8~ and passed th~ough a pressure screen
~(:3S~L6~8
,~entriSCree~l) and centrifut3al cleaners before heing ~hic~ened
on a lap machine to about 25% consistency.
The properties oE a typical pulp made in this manner
are shown in Table 1, supra.
A quantity of this pulp was conveyed to a newsprint
manufacturin~ mill, slurried with water and mixed with other
pulps in the following proportions:
25~ pulp of this example
2% refined semibleached kraft
~5% stone groundwood '
28~ refiner mechanical pulp
This mixture was run over a fourdrinier paper machine
twith vacuum pickup) and converted into newsprint with basis
weight avera~ing 4g.8 g/m2. Operation of the machine was normal ';
compared to operation using a conventional pulp mixture containing ~ '
18~ semibleached kraft except that drainage at the wet end was a
little faster than normal. The newsprint was subsequently printed
at the printing plant of a large metropolitan newspaper with ',
excellent results. ''
' " ' . .
~XP~PLE 2
This example is substantially similar to Example 1,
except that the chips were allo~ed to impregnate in the first ;'
tube of the M and D digester for 15 minutes at a temperature of
a,bout 75C., followed by a 30-minute cook (15 minutes in each
of the next two tubes) at about 135C. The pulp produced by
this technique was substantially similar to that made~in Example
1. This pulp was also used for newsprint production trials as
in Example 1 and with substantially similar results.
~.
EXP~PLE 3
This example is similar to Example 2 except that the
chips wexe impregnated in the first tube for 60 minutes at 345
kPa using sodium sulfite, bisulfite liquor with a concentration
516 IL8
f 154 g /1 (as Na2SO3), and that liquor was removed from the
last quadrant of the impregnating tube of the digester at a
sufficient rate so as to prevent liquor from overflowing into
the second tube. The chips, which entered the second tube sub~
stantially free of surface liquor wexe cooked at a temperature
of 132~C. for 30 minutes using direct injection of steam to a
pressure of 240 kPa. The pulp had properties similar to those
of Example 1.
EXAMPLE 4
Example 3 was repeated, except that the chips were
impregnated with 156 g /1 liquor then cooked at a temperature
of 148C. using a pressure of 327 kPa. This pulp has properties
as shown in Table 1, supra.
EXAMPLE 5
Example 2 was repeated, except that southern pine
chips were used. This pulp had properties as shown in Table 1,
supra.
:
EXAMPLE 6
Example 2 was repeated, except that the chips had
~0 the following average composition:
.
Red Spruce 32.9%
Balsam Fir 9.5%
Red Pine 15.9%
White Pine 9.7%
Poplar 32.0~ .
The pulp produced had the properties shown in Table 1,
supra. Approximately 17 tons wexe made and shipped to a paper
mill where the pulp was slurried and bleached using 1.5~ sodium
hydrosulfite and 0.25% sodium tripolyphosphate, to a final bright-
ness of 58.8 to 61.0 (a~erage 59.3) G. E. The pulp was then
blended with other pulps in the following proportions: `
- 1 8-- :
;~
1C~5~6~8
35% pulp of this e~:ample
35% bleaciled, re~ined, softwood kraft
30~ stone groundwood
This mixture was converted into 65 g/m2 (grams per
square meter) coated publication yrade paper (base sheet weight
40.7 g/m2) using a fourdrinier paper machine with two on~machine
coaters (appxoximately 12.2 g/m2 of clay coating per side being
applied~. The sheet was supercalendered. All phases of the
manufacturing process were normal compared to operation with the
normal furnish of 52% bleached, refined softwood kraft and 48% -
stone groundwood, and the sheet performed well on commercial
- printing presses.
XA~SPLE 7 -
Example 1 was repeated, except that a mixture of
lS northern softwoods and hardwoods with the following approximate
composition was used:
Spruce 34.8%
Balsam 12.5%
. Red and White Pine 8.3
Poplar 19.8~
Beech 5.1%
Maple 10.0~
Ash 3.6%
~lm 5.2%
Basswood 0.8~
Sufficient quantities for small scale investigations
only were made. The pulp had the properties shown in Table 1, ;
supra.
EXA~PLE 8 `
Example 2 was repeated, except that mixed northern
softwood sawdust was used and the liquor heating was substan-
tially supplemented by direct steam. All spent liquor was
allowed to discharge into the blow tank with the cooked sawdust.
Sufficient quantities only for small scale investigations were
made. The pulp had properties sho~m in Table 1, supra.
19
-
.. . . : ~ .
~5~6~
X~MPI,E 9
This is a comparative exa~ple illustrating fhe
prior art.
800 g. (dry basis) of a mixture of northern softwood
chips containing approximately 42% black and white spruce, 35%
balsam fir, and 23~ jack pine were placed in a 10-liter laboxa-
tory digester to which was added 6 liters of a liquor consisting
of a sodium sulfite/bisulfite solution with a concentration of
56 g /1 as Na2SO3, and had a pH of 6.8. The digester and
contents were heated, using indirect steam, to a tempe~ature
of 138C., pressurized to 585 kPa with nitrogen and held there
for 15 minutes. After the cook, the chips were drained and
defibered into pulp using three passes through a 50 HP, 12-
inch diameter, Sprout 1~7aldron laboratory refiner using consis-
tencies of about 159~. The pulp was screened ~hrough a 0.0152
cm. slotted screen, then given a 30-minute, 80C., latency
treatment before testing. The pulp had properties as shown
in Table 2.
These cooking conditions sirnulate those reported by
C. A. Richardson in Tappi, December 1962, Vol. 45, No. 12
page 141A.
,
EXAMPLE 10
This is a comparative control example.
Example 9 was repeated, except that the li.quor con-
centration was 50 g/l as Na2SO3 at a pH of 7.8, and the
cooking conditions were 140C. for 30 minutes, at self-generated
pressure only.
The pulp had properties as shown in Table 2.
,
EXAMPLE 11
This is a comparative control example.
Example 10 was repeated, except that the liquor con- ;-
centration was 70 g/l as Na2S3
~OSl~
The pulp had properties as shown in Table 2.
EXA~5P ~ 12
This is a comparative control example.
Example 10 was repeated, except that the liquor con-
centration was 90 g /1 as Na2SO3.
The pulp had properties as shown in Table 2.
EX~MPLE 13
Example 10 was repeated, except that the liquor con-
centration was 120 g /1 as Na2SO3.
The pulp had properties as shown in Table 2.
EX~IPLE 14
Example 10 was repeated, except that the liquor con-
centration was 150 g /1 as Na2SO3.
The pulp had properties as shown in Table 2. .
..
EX~MPLE 15
Example 10 was repeated, except that the liquor con-
centration was 180 g /1 as Na2~O3.
The pulp had pxoperties as shown in Table 2.
EXAMPLE 16 ;;
Maple chips were cooked in small bombs using a tech-
nique substantially similar to that described in the sulfona~
tion test except that the cooking liquor strength was held
constant at 200 g ,/1 Na2SO3 and a series of cooks were carried .
out at various times between 30 minutès and 8 hours.
The results are plotted in Figure 8 of the drawings.
. ,
- EX~5PLE 17
Mixed softwood chips similar to those used in
Example 1 were cooked in small bombs using a technique sub-
stantially similar to that described in the sulfonation test
,, ,
.
,: .
S~611~
`~cept that the coo~iny liquor strength was held constant at
120 g/l and the pll was varied from 6.0 to 9Ø
The xesults are set forth in Table 3, supra~
'
.
'
. 22
-` ~L0~ 8
l~est Procedure for Determining thc Maximum Level of Sulfonation
that can be Achieved for Various ~ood Species
--_ . _ . .. .. .. ... __
2 ky. (dry basis) of screened wood chips are carefully
mixed and 1 kg. is removed and dried to provide an accurate mois-
ture deter~ination. The balance is divided into 100 g. (~ethasis) aliquots and each is carefully weighed. Each aliquot of
chips is placed in a small bomb (capacity 540 ml.) to which is
added sufficient sodium sulfite/bisulfite liquor to just cover
the chips. A series of liquors are used, each being prepared
by adding gaseous SO2 to a solution of sodium sulfite to reduce
the pH to 7.8. The liquors have the following concentrations:
(w/v as Na2SO3) 50, 70, 90, 120, 150, and 180 g/l. At least
two cooks are carried out at each liquor strength. The bombs-
are sealed and placed in an oil bath which has been heated to
140C. The bom~s are mounted on a rotating device that upends
the bombs 2 or 3 times per minute in order to provide some
agitation to the mixture of chips and liquor. The bombs are
removed after 30 minutes.
When each bomb is removed from the oil bath, it is
immediately plunged into cold water to produce rapid cooling.
The cooked chips are removed from the bomb as soon as possible,
the liquor is drained off and discarded, and the chips are
defibered in cold water using an industrial blender (Waring or
Osterizer type) for 15 minutes or until the chips are well
defibered. The pulp is then fiitered, on a filter paper, care~
fully washed with a large volume of cold water, then dried in
an oven and weighed and the yield calculated. After ~eighing,
a sample of pulp is taken and its sulfur content is determined.
The yield and sulfur content data are plotted against
liquor strength as illustrated in Figures 2 to 7 of the drawings.
These graphs show the customary scatter of clata points, xegres-
sion curves were calculated in order to show ~he trend. For
23
, . , . . ,.. ~ : . . ..
~5~
many species the sulfur content will tend to reach a m~ximum
(or plateau) at 15~18% Na2SO3, and usually this maximum will
be reached without reducing the yield below 90%. In the case
of softwoods (Figures 2 to 5) it is probable that the sulfur
content could be increased a little beyond that reached at 18%
Na2SO3 liquor, but higher liquor concentrations are not prac-
tical, particularly when recycled liquors are used due to the
solubility limit of Na2SO3 in the presence of dissolved organic
materials.
10For each of the typical woods to which Figs. 2 to 7
relate, the graphs may be used to determine suitable ranges of
liquor concentration, making reference to the figures for sul-
fonation of the various woods given on page 7. Thus, for spruce,
page 7 shows that 0.55%S is required to provide the desired level
of 85% of maximum sulfonation, and Fig. 2 shows that a concentration
of above about 100 g/l Na2SO3 is required to produce this sulfur
content; this and higher levels up to ak least about 200 g/l will
not reduce yield below 90%. Figs. 3 to 7 likewise give the fol- ;
lowing approximate results for the various woods~
g/l Na2SO
Wood %S equivalent to Graph Min. for Max. for
85% maximum sul-85% sul- at least
fonation (from p7)fonation 90% yield `
salsam .60 Fig.3100 over 200
Jack Pine .64 Fig.4100 over 200
Southern Pine .55Fig.5 100 over 200
r~aple .28 Fig.6105 over 200
Poplar .31 Fig.7 95 115
Accordingly, it may be seen that for the softwoods (balsam,
jack pine, southern pine) a range of about 100 to about 200 g/l
is suitable; for poplar the suitable range is about 90 g/l to about
115 g/l.
The terms and expressions which ha~e been employed
are used as terms of description and not of limitation, and
there is no intention in the use of such terms and expressions
of excluding any equivalents of the features shown and described
or portions thereof, but it is recognized that various modifi-
cations are possible within the scope of the invention claimed.
-24-
. ' ' ' ` ~ ', ` :,
