Note: Descriptions are shown in the official language in which they were submitted.
~.~7465~
HIGH YIELD PULPING AND BLEACHING PROCESS
BACKGROUND OF THE INVENTION
Pulping processes can be broadly classified into high yield
processes using mechanical fiberizing equipment and low yield pro-
5 cesses using chemical reactions to produce individual fibers or pulpfrom lignocellulosic raw materials, usuaily wood in chip form.
Within the high yield category there are many variations which
involve varying combinations of chemical, mechanical, and thermal
treatments to effect fiber separation, remove some lignin and other
10 chemlcal components from the original fibers, or increase the
brightness and papermaking strength of the resulting fibers. This
invention is directed to the art of high yield pulping in which
mechanical treatment either with or without heat is the primary
- means of fiber separation and mild chemical treatment is used to
15 facilitate fiber separation and to increase the papermaking strength
and brightness. The application of heat may be utilized in
combination with mechanical and chemical treatments to further
assist in fiber separation and to accelerate chemical reactions.
However, the primary goal of this invention is to economically
20 produce pulp in the highest possil~le yield of the original ligno-
cellulosic raw material by retaining and chemically modifying the
lignin in the fibers to obtain the desired papermaking properties.
Mechanically refined pulp without chemical pretreatment results
in extremely high yields ~about 95% or higher) but results in fibers
25 containing almost all of the original lignin in essentially a chemically
unmodified form. Such unmodified lignin imparts relatively low
brightness to the fibers, and, due to its hydrophobic nature, the
lignin inhibits the development of paper strength through fiber to
~iber bonding (hydrogen bonding) and makes the fibers much
30 stiffer than partially or completely delignified fibers from the same
lignocellulosic raw material. Although some high yield pulps
containing high amounts of lignin can be bleached economically to
relatively high brightnesses using oxidizing agents such as alkaline
peroxide and/or reducing agents such as sodium hydrosulfite, such
~ 3~
-- 2 --
post-refining treatments do not increase papermaking strength to
levels required for many end uses because much mechanical damage
has already been done to the fibers.
The papermaking strength of high yield pulps can be increased
5 by sulfonation of the lignin, particularly when the wood chips are
treated with the sulfonation chemicals (usually sodium sulfite and
sodium hydroxide) prior to mechanical defibration (refining). In
some cases, the resulting fibers can also be bleached economically
as with alkaline peroxide andlor sodium hydrosulfite to give both
10 improved brightness and papermaking strength. However, the high
levels of sulfonation required for high strength result in pulps
which respond less to bleaching than similar non-sulfonated Gr
low-sulfonated pulps, and therefore such highly sulfonated pulps
have lower bleached brightnesses although high strength. More-
15 over, sulfonation processes require the removal and disposal ofenvironmentally objectionable sulfur compounds from process waste
streams. In addition, the need for separate sulfonation, refining,
post-refiner bleaching, and effluent treatment equipment makes the
capital equipment and operating costs for such a system very
20 significant.
An alternative to sulfonation of lignin for increasing paper-
making strength of high yield fibers is carboxylation of lignin with
oxidants such as alkaline peroxide prior to and/or during defibra-
tion. As sulfonation results in lignin containing sulfonate groups,
25 likewise, carboxylation results in lignin with carboxylate groups.
Both the sulfonate and the carboxylate groups are capable of parti-
cipating in hydrogen bonding which increases the strength of paper
made from such high yield pulps (papermaking strength).
Similar to the alkaline sulfonation treatment of chips prior to
30 refining, alkaline peroxide pretreatment of chips softens the
lignocellulosic raw material resultin9 in easier fiber separation (less
energy consumption) and less fines generations ~fiber fragmenta-
tion) during refining. In addition, refiner bleaching with alkaline
peroxide can potentially eliminate the need for separate post-refiner
lX7~657
-- 3 --
bleaching equipment, due to the facts that refiners are excellent
mixers of pulp and bleaching agents, and the temperature within
the refiner ~about 1 00C) causes bleaching to occur extremeh~ fast
relative to typical post-refiner alkaline peroxide bleachiny steps
5 ~approximately 50 to 80C).
Offsetting the advantages is the primary drawback to alkaline
peroxide refiner bleaching of peroxide decomposition. Perox~ide
decomposes to form oxygen ~ineffective for lignin-retaining
bleaching) under the highly alkaline conditions required for
10 papermaking strength development. Peroxide decomposition is
hastened by the high temperatures reached in refiners and by metal
contaminants, particularly manganese, iron, and copper, which are
contained in significant quantities in lignocellulosic raw materials
and in lesser quantities in process water. Partial removal or
15 inactivation of such metal contaminants in lignocellulosic raw material
can be effected by introducing chelating agents into the wood chips
and then removing the chelant-metal complexes. However, the
physical entrapment and chemical attraction of such metals by fiber
components within the chips make complete removal of the metals
20 impossible.
The problems associated with prerefiner or in-refiner alkaline
peroxide treatments are partially avoided by post refiner alkaline
peroxide treatments. For example, removal of metal contaminants
from individual fibers with chelating agents after refining and prior
25 to alkaline peroxide bleaching is much more effective because the
particle size of the fiber in pulp is much smaller than chips befcre
refining. The smaller size makes the metal contaminants much more
accessible to the chelant solution. Consequently, in many cases the
individual fibers can be bleached to rluch higher brightresses with
30 alkaline peroxide in a post refiner bleaching treatment without
significant waste of peroxide bleaching agents due to metal
contaminant induced decomposition of peroxide ( U . S . Patent No.
~1,160,693-Lindahl et al.).
~27~ 7
There have been many attempts to overcome such problems
associated with the pre-refiner or in-refiner use of hydrogen
peroxide in the production of high yield pulps. Control of alka-
linity (e.g., see U. S. Patents 3,069,309-Fennell and 4,270,976-
Sandstrom et al., and Canadian Patents 1,078,558 and 1,173,604),
control of the temperature (e.g., U. S. Patent 4,187,141-Ahrel),
and control of tirne at high temperature (e.g., U. S. Patent
L~,270,976-Sandstrom et al. ) have been tried. However, such tech-
niques for reducing peroxide decomposition also reduce the effec-
tiveness of alkaline peroxide in terms of the resulting pulp
properties (papermaking strength) while the presence of deleterious
metal contaminants still results in inefficient utilization of the
peroxide bleaching agent during refiner bleaching.
Alkaline peroxide stabilizers like water soluble sodium sil ca e
and magnesium sulfate are often utilized in the peroxide bleachinc3
of high yield pulps to further reduce peroxide decomposition caused
by metal contaminants. The silicate forms a flock in alkaline
peroxide solutions and this flock attracts and adsorbes the metal
ions on its surface thereby reducing their ability to decompose
peroxide. Magnesium ions also reduce peroxide decomposition by
electronically deactivating the metal ions, thereby reducing the
potential of the metal ions to decompose peroxide. However, the
present invention is based in part upon the belief that flocks or
precipitates formed by silicates and/or magnesium in alkaline
peroxide solutions cannot readily penetrate into the wood chip
structures prior to refining due to the large size of the flock
relative to the pore size of the wood chips. This belief is
reinforced by the fact that such stabilizers effectively stabilize
peroxide against decomposition when pulp is being b!eached with
peroxide but are not as effective when the wood is in chip form
rather than pulp. It is believed that the difference in stabilizer
effectiveness when treating pulp fibers versus wood chips is due to
the alkali and peroxide entering the chip structure while the
stabilizer flock is impeded from penetrating the chip with the result
~7~57
that the peroxide, separated from the stabilizing flock., rapidly
decomposes within the chip thereby reducing the amount of peroxide
available For bleaching during refining. In addition, the pressure
buildup within the chip due to the evolution of oxygen gas during
peroxide decomposition forces alkaline peroxide out of the chip with
the result that insufficient peroxide is retained in the chip as it
enters the refining zone. Furthermore, irreversible alkaline
yetlowing of the pulp occurs if there is insufficient residual
peroxide remaining with the pulp after refining.
t 0 A common method for circumventing the problem of peroxide
decomposition in alkaline peroxide bleaching of chips during refining
is to add the bleaching agent directly to the refining zone to
rrinimize the contact time between the chip and alkaline peroxide,
and in some cases to al low more intimate contact between metal
contaminants and silicate and/or magnesium ion stabilizer f!ocks lSee
for examp le, U . S . Patent Nos . 3,023,140-Textor, 3,069,309-Fennel I,
4,022,965-Goheen et al., 4,270,976-Sandstrom et al., 4,311,553-
Akerlund et al.; Japanese Patent Application No. 80-72091, and
Federal Republic of Germany Patent No. 2818-320). Additionally,
wood chips have been pretreated by impregnation and/or refining
with chelants (U. S. Patent Nos. 3,023,140-Textor, 4,311,553~/
Akerlund et al., Japanese Patent Application No. 80-72091, and
Federal Republic of Germany Patent No. 2818-320) or with sodium
silicate (U.S. Patent Nos. 3,069,309-Fennell, 4,311,553-Akerlund et
al.), or with magnesium salts (U. S. Patent Nos. 3~o23~l4o-Textor~
3,069,309-Fennell, 4,311,553-Akerlund et al. and Japanese Patent
Application 80-72091) and combinations thereof prior to alkaline
peroxide addition into the refiner to reduce peroxide decomposition.
U.S. Patent No. 4,270,976-Sandstrom et al. is the only case in
which brightness comparable to post refiner alkaline peroxide
bleaching was obtained but it utilized lower alkalinity as the means
of reducing the peroxide decomposition rate which sacrificed good
papermaking strength development. The pr~sent invention is based
in part upon the hypothesis that with processes employing alkaline
1f~7~5~7
peroxide addition directly into the refiner, the majority of
defibration occurs before the alkali and peroxicJe contact the fi~ers
and have an opportunity to swell and react with the wood, thereby
reducing the potential for papermaking strength development, alony
5 with requiring more energy for refining and increasing the
generation of fines, all of which could be avoided if alkaline
peroxide could be inserted and stabilized within the chip prior to
defibration .
Impregnation of the chips with alkaline peroxide prior to
refining has also been practiced (U.S. Patents 4,187,141-Ahrel, and
4,270,976-Sandstrom et al., and Canadian Patents 1,078,558, and
1,173,604) . In most cases, the brightness obtained was comparable
to that obtainable with post refiner alkaline peroxide bleaching.
However, with such processes, metal contaminants are not removed
or deactivated; rather, peroxide decomposition is reduced by lower
alkalinity (U.S. Patent Nos. 4,270,976-Sandstrom et al., Canadian
Patent 1,078,558, and 1,173,604) or by minimizing refining tempera-
ture (U.S. Patent No. 4,187,141-Ahrel). However, the lowering of
the alkalinity or temperature causes less papermaking strength to
be developed than sulfonation methods. At higher alkalinity,
strengths comparable to those of post refiner bleached, sulfonated
high yield pulps were obtained but at the expense of lower bright-
ness due to increased peroxide decomposition (Canadian Patent
1,078,558) .
THEORY OF THE INVENTION
The present invention is based in part upon the theory that
refining of chips impregnated with highly alkaline peroxicle can be
practiced to achieve both high brightness and high strength if
stabilizers such as magnesium ions and silicate are impregnated into
the chip in a manner to Form a stabilizer flock "in situ" within the
chip to stabilize alkaline peroxide within the chip. The benefits
derived are:
(a) higher strength than can be achieved with relatively low
sulfonation processes,
~7465~
-- 7 --
(b) higher brightness than can be achieved with high
sulfonation processes or sulfonation/carboxylation processes
that produce pulps with high papermaking strengths;
(c) low refining energy required; and
(d) lower capitai and operating expenses than those associated
with alkaline peroxide bleached sulfonated fibers due to less
ecluipment for strength formation, bleaçhing, and effluent
treatment ~
SUMMARY OF THE INVENTION
_r~
- 10 ~his invention produces novei fibrous pulps from ligno-
cellulose-containing materials such as softwoods, hardwoods,
bagasse, straw, and similar fibrous materials which have been
chopped or cut into pieces suitable for pulping lhereinafter
referred to as "Chips") prior to reduction into individual fiber
15 form. Chips are usually in the size range of less than 3
centimeters average diameter but can vary. Suitable hardwoods
include Aspen, Gmelina, Eucalyptus, Birch, Beech, Oak and Ash.
Suitable softwoods include Pine, Spruce, Fir and Hemlock.
In accordance with the theory of the present invention the
20 lignocellulosic raw material in pieces referred to in the art as chips
is treated to produce novel pulp according to the following
sequence: (A) chips (usually pretreated with steam and/or washed
and soaked in water) are impregnated with a first impregnation
solution containing stabilizing chemicals for peroxide (such as a
25 solution containing silicate or magnesium ions and optionally a
chelating agent) under conditions of pH, temperature, and
concentration for the stabilizing chemicals so that they remain
soluble in the first impregnation solution; (B) the chips are
impregnated with a second impregnation solution containing the
30 additional stabilizing chemicals, e.g., silicate or magnesium ions,
and optionally a chelating agent under conciitions of pH, temper-
ature, and concentration so that the chemicals are soluble in the
second impregnatiOn solution but precipitate andlor form a flock for
stabilizing peroxide when mixed with the first impregnation solution
~X7~37
within khe chips; and (C) the chips are impregnated with
a third impregnation solution containing alkaline
peroxide with or without stabilizers and/or chelating
agents. Impregnation steps can be accomplished b~
squeezing the chips to expel excess liquids and air
followed by allowing the chips to expand into the
impregnation solution. Optionally, impregnation
solutions of steps B and C can be combined into a single
impregnation solution and impregnation step. The
alkaline peroxide impregnated chips are then refined in
one or more stage(s) under atmospheric pressure or
superatmospheric pressure. The refining pressure is
usually associated with steam added to or generated
within the refining device. The resulting pulp is
dewatered and acidified and/or washed to remove
bleaching and stabilizing chemicals to result in a novel
nonsulfonated pulp having a unique combination of
properties including high yield, superior brightness and
papermaking strength, and low fines content. Recyclable
peroxide is obtained from the dewatering of the pulp
after refining and preferably before acidification. The
peroxide obtained from the post refiner dewatering step
can be reused as makeup in the impregnation step in
which peroxide is added to the chips.
Various aspects of this invention are as follows:
A high yield pulping process for lignocellulosic
material in Chip form comprising:
(a) impregnating the chips with a first
impregnation solution containing stabilizing
chemicals for peroxide under conditions of pH,
temperature and concentration for the stabilizing
chemicals such that they are soluble in the first
impregnation solution;
(b) impregnating the chips with a second
impregnation solution containing stabilizing
chemicals for peroxide under conditions of pH,
,~
"
~L~74~.~7
8a
temperature and concentration preselected to
provide:
(i) conditions under which the chemicals in
said second impregnation solution are soluble
in the second impregnation solution; and
(ii) when said second solution is mixed with
; the first impregnation solution within the
chips, the mixture results in conditions under
which one or more of the stabilizing chemicals
in the combination of the first and second
impregnation solutions precipitate or form a
flock for stabilizing peroxide within the
chips;
(c) impregnating the chips with a third
impregnation solution containing alkaline peroxide;
and
(d) mechanically refining the alkaline peroxide
impregnated chips to produce pulp.
A high yield pulping process for lignocellulosic
material in Chip form comprising:
(a) impregnating the chips with a first
impregnation solution containing stabilizing
chemicals for peroxide under conditions of pH,
temperature and concentration for the stabilizing
chemi~als such that they are soluble in the first
impregnation solution;
(b) impregnating the chips with a second
impregnation solution containing alkaline peroxide
and stabilizing chemicals for peroxide under
conditions of pH, temperature and concentration
preselected to provide;
(i~ conditions under which the chemicals in
said second impregnation solution are soluble
in the second impreynation solution, and
(ii) when said second solution is mixed with
the first impregnation solution within the
~4~57
8b
chips, the mixture results in conditions unde-r
which one or more of the stabilizing chemicals
in the combination of ~he first and second
impregnation solutions precipitate or form a
flock for stabilizing peroxide within the
chips; and
(c) mechanically refining the alkaline peroxide
impregnated chips to produce pulp.
A novel non-sulfonated Pine pulp having a Yield of
at least 85%, a Brightness greater than 70% and a
Papermaking Strength of at ].east 3.0 kw at a freeness of
600.
A novel non-sulfonated Aspen pulp having a Yield of
a~ least 80~, a Brightness greater than 80~ and a
Papermaking Strength of at least 4.0 kw at a freeness of
500.
A novel non-sulfonated Eucalyptus pulp having a
Yield of at least 80%, a Brightness greater than 80% and
a Papermaking Strength of at least 3.0 kw at a freeness
of 500.
A novel non-sulfonated Gmelina pulp having a Yield
of at least 80%, a Brightness greater than 75% and a
Papermaking Strength of at least 2.0 kw at a freeness of
500.
DETAILED DESCRIPTION OF THE INVENTION
This invention is useful in producing fibrous pulps
from lignocellulosic raw materials such as softwoods,
hardwoods, bagasse, straw and other similar fibrous
materials which have been chopped or cut into
appropriate sized pieces known in the art as chips for
pulping into individual fiber form. The resulting high
yield (yield of 80% or higher of the original
lignocellulosic raw material) non-sulfonated pulp has
properties equal to or supPrior to sulfonated pulps
prepared in similar yields from the same lignocellulosic
raw materials. These properties are high brightness and
~4~
8c
papermaking strength, and low fines content.
Additionally, the process has the advantages of lower
capital and operating costs to produce pulps of equal or
better quality than comparable sulfonated pulps because
of lower equipment costs for the pulping and waste
1~7~57
treatment processes, and lower operating costs due to less chemical
usage, lower refining energy, and easier treatment of process
effluents. As used herein all parts are by weight unless other~Ji ,e
specified, and all parts based upon the weight of chips are based
5 upon the oven-dried weight of the chips.
Preferred Method for Pretreating and Impregnating Chips
Prior to the first impregnation step, the chips are preferably
saturated with water and/or steam to expel any entrapped air in
accordance with conventional procedures, Before and as a part Df
1 û each impregnation step, the chips are preferably squeezed to expel
liquid and any remaining air, and then allowed to expand into the
impregnation solution so as to absorb the impregnation solution.
The quantity of solution absorbed is influenced by the impregnation
device and the particular material being impregnated. The level of
15 chemical addition into the chips is primarily controlled by the
concentration of the particular chemical in the impregnation solu-
tion, the degree of chip compression in the impregnation device,
and the density of the chips being treated.
The first impregnation solution is an aqueous solution con-
20 sisting of stabilizers for peroxide and optionallv chelating agentsand has a pH, temperature, and concentration so as to avoid preci-
pitation of the solutes in the impregnation solution. If a chelating
agent is used in the first impregnation solution to effectively
chelate deleterious metal ions like manganese, iron, and copper, the
25 pH, temperature and concentration should also be selected to impede
the chelant from combining with or inactivating the stabilizers. In
the first impregnating solution it is preferred to use magnesium
sulfate as the stabilizer but other stabilizers can be used such as
water soluble magnesium salts (e.g., magnesium chloride, magnesium
30 nitrate, magnesium carbonate, and combinations thereof). In
addition, it is preferred to use chelating agents or complexing
agents in the first impre5nation solution such as diethylene
triaminepentaacetic acid (DTPA), ethylene diaminetetraacetic acid
(EDTA), hydroxyethylethylenediaminetriacetic acid (HEEDTA),
1~7~57
-- 1 o --
nitrilotriacetic acid (NTA) sodium tripolyphosphate (STPP), and
phosphonic acid derivatives or other similar compounds known in
the art for such functionality. The concentration of magnesium salt
in the impregnation solution is preferably between 0.01 and 2.0
5 grams per liter calculated based upon the weight of mac~nesium in
the salt so as to result in a magnesium content of the chips
equivalent to preferably from 0. 001% to 0 . 2% of the weight of chips.
If used, the chelating agent concentration in the impregnation
solution should be preferably from 0. 01 gram per liter to 20 grams
1 U per liter ~expressed as 100% chelating agent in the solution) to give
preferably 0. 001% to 2 . Og6 chelant based on the dry weight of chips,
but chelant concentration and addition level may extend beyond
such ranges depending upon the specific chelating agent and the
quantity and species of metal contaminants contained in the chips.
15 The temperature of the first impregnation step is preferably
between 15C and 100C (100F and 212F). The pH is preferably
between 5 and 10 with between 7 and 9 being most preferred.
Adjustments to the solution pH can be made with any suitable acid
or alkaline substance which does not react with peroxide, cause
20 darkening of the chips, or cause any of the ccmponents of the
impregnation solution to be precipitatea or to lose stabilizing and/or
chelating ability. The pH, temperature and concentration ranges
given above were selected to avoid precipitation of magnesium ions
in the solution and to minimize interaction between magnesium ions
25 and the chelant.
The second impregnation solution is an aqueous alkaline solu-
tion which also consists of stabilizers for peroxide and optionally
chelating agents and is at a pH, temperature, and concentratjon so
as to avoid precipitation of the solutes before entering the chip,
30 and if a chelating agent is used, so as to effectively chelate
deleterious metal ions like manganese, iron, and copper but not
combine with or deactivate the stabili~ers to any significant extent.
The critical aspect of the present invention is that the pH,
temperature, and concentration of the components in the second
~7~57
impregnation solution be suitable for formation of a stabilizer flock
after the solution enters the chip and mixes with alreacJy impreg-
nated chemicals from the first impregnation step. This results in
the "in situ" formation of stabilizing flock for the peroxide within
the chips. In the second impregnation solution it is preferred to
use sodium silicate, especially a 40-42 degrees gaume' sodium
silicate solution with 28.79~ SiO2 and 8.9% Na20 although there are
suitable substitutes recommended by silicate manufacturers for
alkaline peroxide bleaching. In addition, it is preferred to use
chelating agents in the second impregnation solution of a type and
in concentration and addition level ranges based upon the weight of
the chips as described previously for the first impregnation
solution. The concentration of sodium silicate in the second
impregation solution is preferably between 1. 0 and 100 grams per
lS liter calculated and expressed as silicon dioxide (SiO2~. The
temperature of the second impregnation step is preferably between
15C and 100C ~60C and 212F), and the pH is higher than the
pH of the first impregnation solution and preferably greater than 9
with from 9 to 12 being particularly preferred and between 10 and
11 being most preferred. Adjustment to the solution pH can be
made in the same manner as described for the first impregnation
solution. Preferably, the second impregnation of the chips results
in between 0.1% and 10% silicates, calculated as SiO2 based upon the
dry weight of the chips.
The third impregnating solution is an aqueous alkaline peroxide
solution which may also contain a combination of the stabilizers
employed in the first and second impregnation solutions primarily
for stabilizing the peroxide outside the chips. Preferably the third
impregnation solution contains magnesium and silicate stabilizers,
and optionally chelating agents of the types and in concentrationS
and addition levels describ~d for the first and second impregnation
solutions. The third impregnation solution contains preferably
hydrogen peroxide or any other peroxy~Jen compound suitable for
bleaching, in the concentration range of preferably between 10 and
~7~ 7
-- 12 --
100 grams per liter ~calculated and expressed as hydrogen
peroxide) to give addition levels of preferably between 0.5~ and 10
of the weight of chips expressed as hydrogen peroxide. In
addition, an alkaline substance (preferably sodium hydroxicle) is
5 added to the third impregnation solution to give a solution pH
preferably in the range between 9 and 13 with between 11 and 12.5
being most preferred. The temperature of the third impregnating
solution is preferably between 15C and 100C (60F and 212F).
The most preferred impregnation sequence is the three stage
10 sequence previously described and presented in more detail in the
examples. However, it should be understood that the invention is
not limited to the generally described three stage sequence. The
second most preferred embodiment of the invention is a two-stage
impregnation sequence in which the first impregnation stage is
15 practiced as previously described and the second impregnation
solution is combined with the third impregnation solution (alkaline
peroxide) and used in a sing le impregnation step at a pH from 9 to
13. Reversing the solutions by using the first impregnation
solution in the second impregnation step and the second impreg-
20 nation solution in the first impregnation step of the threeimpregnation sequence described above is the third most preferred
embodiment of the invention. That is the first impregnation
solution description appearing on pages 9 and 10 becomes the
description of the second impregnation solution and lilcewise the
Z5 description of the second impregnation solution on pages 11 and 12
becomes the description of the first solution.
The ke~ aspect in all the above sequences is that one compo-
nent of the stabilizin9 flock be in the first impregnation solution
and a second component be in the second impregnation solution so
30 that the two components form the flock within the chip when the two
solutions mix durin~ the second impregnation. With some stabilizers,
it is possible for the second component to be a base that results in
a pH adjustment upon mixing of the first and second solutions in the
chip to result in the "in situ" formation of the flock or sol. In
gL~7~57
addition, the invention is not limited to the concentration and
addition level ranges previously described for stabilizers and
chelating agents, since differences in metal contamination levels of
lignocellulosic raw materials andlor process water could Justify
5 stabilizer or chelating agent usages outside of the specified
preferred ranges.
Refining of Chips (Defibration):
The chips are mechanically refined in a suitable defibration
apparatus in one or more stages in accordance with conventional
10 processes and equipment. The pressure during refining is optional
and can be at atmospheric and/or superatmospheric pressure,
depending on the species being pulped and the desired pulp
properties. Superatmospheric pressure refining (particularly usefui
in first stage refining) does increase the papermaking strength,
15 and decrease refining energy and fines generation but at the
expense of higher peroxide usage and lower brightness compared to
atmospheric refining. The effect on papermaking strength and
fines generation is particularly pronounced when the raw material is
softwood as contrasted with hardwood.
20 Post-Refining Steps:
After refining, the pulp may be allowed to continue bleaching
as long as is practical prior to expe!ling the impregnation solutions.
The amount of peroxide used in the impregnation steps is prefer-
ably preselected to result in some residual peroxide remaining after
25 refining in order to maintain high brightness. Preferably the
refined pulp is concentrated, e.g., by compressing or thickening,
to remove residual impregnation solution containing potentially
recyclable alkaline peroxide, then cooled and diluted ~,vith water,
and acidified preferably with sulfur dioxide, sodium bisulfite, or
30 sulfurous acid to a pH between 5 . 5 and 6 . 0, and then washed with
water. The residual peroxide extracted from the pulp after
refining can be recycled as a source of peroxide in one of the
impregnation solutions particularly if the process is practiced
continuously or in sequential batches. The washed pulp is
1~7~5~
-- 1 4 --
preferably screened and cleaned to result in a pulp suitable for the
production of paper products.
Examples A, 1 and 2
Examples A, 1 and 2 compare the process of the present
invention with a single step conventional process utilizing the same
chemicals. The amount of refining was adjusted to result in
comparable pulps in terms of pulp freeness.
Southern U . S, A . Pine wood chips were used in Examples A,
and 2. The chips were of a size that would pass through a 3/4"
circular hole screen ~1.9 cm). Prior to impregnation, the chips
were steamed at atmospheric pressure for 30 minutes and then
washed with water and drained. To accomplish each impregnation
stage in Examples A, 1 and 2, a Sprout-Waldron Model Ll-12
laboratory impregnator was used at a 4:1 compression ratio. The
impregnator has a perforated cyiinder with a movable piston inside
the cylinder and a removable plug at one end of the cylinder. The
impregnator is operated as follows:
( 1 ) Chips are placed inside the cyl inder with the plug in
place and the initial volume of the chips in the cylinder is
determined,
(2) The piston is moved to compress the chip mass from its
initial volume to a final volume. Any liquid squee~ed out of
the chips during this compression is allowed to drain through
the perforated cylinder wall and out of the equipment. The
ratio of the initial volume of chips to the final volume is
defined as the compression ratio and in the following examples
the compression ratio was 4:1 unless otherwise noted,
(3) Impregnation solution is added to cover all of the chips in
the cylinder and the compression piston is moved back and
forth several tirmes to help purge trapped air from the mass of
compressed chips,
(4) The cylinder plug is removed and comprcssed chips are
pushcd out of the cylinder and allowed to expand while still in
contact with the impregnation solution, and the expanded chips
7~57
are allowed to remain in contact with the solution for about 1g
minutes at a temperature of 25C to 30C, and
(5) The impregnated chips are drained of free impregnation
so l ution .
Example 1
For Example 1, two impregnation stages were used.
The first impregnation solution was a water solution sontain-
ing: 5.28 grams/liter of Epsom salts, technical grade (magnesium
sulfate heptahydrate - Mg 5O4.7H2O~; 4.0 grams/liter of the penta
sodium salt of diethylenetriamine pentaacetic acid ( hereinafter DTPA
and available as Versenex 80TM from Dow Chemical Company~ and
sufficient hydrochloric acid to adjust the pH to 9.D. Impregnation
of the Southern pine chips was accomplished with the Sprout-
Waldron impregnator as described above.
The second impregnation solution was a water solution contain-
ing: 5.2a grams/liter of Epsom salt; 0.4 grams/liter of DTPA; 42.2
grams/liter of sodium silicate solution (a 41 Baume' solution, 28,7
SiO2 and 8.99~ Na20, availabie as type "N" frorn P Q Corporation
hereinafter referred to as "sodium silicate"); 50 grams/liter of
sodium hydroxide (technical grade); and 60 grams/liter of hydrogen
peroxide (added as a stabilized 50~ H2O2 solution, technical grade).
The resulting solution had a pH of 11 . 7 .
The chips were then refined at atmospheric pressure in a
Sprout-Waldron 12" laboratory refiner, Model 12-1 CP. The disk
space and the feed rates of chips into the refiner were adjusted as
appropriate for the desired energy input.
After refining, the pulp was dewatered to 25~ to 35~ consist-
ency, diluted to about 3~ consistency, and the pH of the resulting
pulp slurry was adjusted to between 5 . 5 and 6 . 0 with sulfurous
acid iH2SO3) before the pulp properties were tested. The
resulting pulp was tested for brightness and the total amount of
hydrogen peroxide consumed in the Example was determined. The
results are given in Table 1. The dewatering to 25~ to 35
consistency after refining yielded recyclable hydrogen peroxide.
~7~;i57
-- 1 6 --
The "in situ" formation of stabilizing flock within the chips
occurred during the second impregnation of the chips as a result of
the mixing of the first and second impregnation solutions within the
chips .
Example 2
. _
In Example 2 the same impregnation procedures, equipment and
chemicals in the same total quantities were used as in Example 1.
The main change in Example Z versus Example 1 is that the
chemicals were divided among three impregnation steps rather than
10 two. The additional step between the first and second steps of
Example 1 impregnates some of the sodium silicate at an alkaline pH
into the chips to form a stabilizing flock "in situ" prior to the
addition of the hydrogen peroxide in the third impregnation.
The first impregnation solution for Example 2 was identical to
15 the first impregnation solution in Example 1 and the same impreg-
nating conditions, procedures and equipment were employed as in
Example 1 .
The second impregnation solution was a water solution contain-
ing 21.1 grams/liter of sodium silicate and 0.4 grams/liter of DTPA
20 and had a pH of 10.7. The same conditions, procedures and equip-
ment were employed for impregnation as described in Example 1.
The third impregnation solution was an aqueous solution con-
taining 5.28 grams/liter of Epsom salt, 0.4 gramslliter of DTPA,
21.1 grams/liter sodium silicate solution, 50 grams/liter of sodium
25 hydroxide, and 60 grams/liter of hydrogen peroxide (added as a
stabilized 50~6 H202 solution) and had a pH of lt.7.
The chips from the third impregnation step were refined, and
the resulting pulp was treated after refining as in Example 1. The
pulp was tested for brightness and the amount of hydrogen
30 peroxide consumed was determined. The results are given in
Table 1.
Example A
In Example A the same impregnating procedures, chemicals and
equipment were used as in Examples 1 and 2 except that a single
~7~ 7
impregnation step was used containing all of the chemicals used in
Examples 1 and 2 but the amount of DTPA was reduced because the
higher levels of DTPA would be incompatible and react with
hydrogen peroxide when combined in a single solution.
The impregnation solution was a water solution containing 1~ . 56
grams/liter of Epsom salt, 0.4 grams/liter DTPA, 42.2 grams/liter
sodium silicate solution, 50 grams/liter sodium hydroxide and 60
grams/liter of hydrogen peroxide (added as a stabilized 50% H2O2
solution) and had a pH of 11.7.
After the impregnation step, the chips from Example A were
refined, and the resulting pulp was treated after refining as in
Example 1. The pulp was then tested ~or brightness and the
amount of hydrogen peroxide consumed was determined. The
results are given in Table 1.
Comparison of Results from Examples A, 1 and 2
Example A consumed 7.5% hydrogen peroxide based on the dry
weight of the wood chips but achieved a brightness of only 60%
(Elrepho brightness). In contrast, with the same chemicals the
two-step impregnation sequence of Example 1 achieved a brightness
of 72% Elrepho while only consuming 4.2% hydrogen peroxide based
on the dry weight of the wood chips. The preferred method of
practicing the present invention with the three-step impregnation
sequence of Example 2 consumed only 3.7% hydrogen peroxide based
on the dry weight of the wood chips and achieved the highest
brightness of 75% Elrepho,
Examples 3, B and C
Pulp produced from Southern Pine chips using the preferred
three-stage sequence in Example 3 was compared with pulp
produzed by a high sulfonation CMP process (Example B) and puip
produced by a low sulfonation CTMP process (Example C) and
utilizing commercial scaie equipment.
In Examples 3, B and C the sarne source of lignocellulosic
chips (Southern Pine chips passing through 314" circular screens)
was used as in Examples A, 1 and 2. The chips were pretreated
~74~.5~
-- 1 8 --
with atmospheric steam for 30 minutes. For all the impreynations of
Examples 3, B and C, a CE-Bauer Model 560GS Impressafiner was
employed. It is a tapered screw press using a 4:1 compression
ratio and achieves a temperature of 40C to 60CC during impreg-
nation due to heat generated within the equipment. After impreg-
nation, the chips were allowed to drain of free impregnation liquor.
After all the impregnation steps were completed for each Example,
the chips were refined under a steam pressure of 25 Ibs/inch2 gage
(psig) in a CE-Bauer Modei 4~8 pressurized refiner and then
subjected to secondary refining at atmospheric pressure in a
CE-Bauer Model 401 atmospheric refiner. The refiner plate spacing
and feed rates were adjusted as appropriate for the energy input
and degree of refining which was selected to result in comparable
pulps in terms of freeness. After refining the refined pulp was
diluted to about 3~ consistency, and the pH of the resulting pulp
slurry was adjusted to between 5.5 and 6.0 with sodium bisulfite
( NaH503) .
Example 3
A three-stage impregnation sequence was employed. The first
impregnation solution was a water solution containing 4.4 grams/liter
of Epsom salts, 0.4 grams/liter of DTPA and had a pH of 8.3. The
second impregnation solution contained 17.6 grams/liter sodium
silicate and 0.4 gramslliter DTPA, and had a pH of 10.6. The
third impregnation solution contained 4.4 grams/liter of Epsom salt,
0.4 grams/liter of DTPA, 17.6 grams/liter sodium silicate, 60
grams/liter sodium hydroxide and 50 grams/liter hydrogen peroxide
and had a pH of 11 . 9 . The pulp produced was tested for bright-
ness, freeness (Canadian standard freeness) and strength
(breaking length) . Results are given in Tabie I i .
Example B lCMP Process with Post-Refining Peroxide Bleaching)
The liquor used in the impregnation stage contained 58
grams/ liter SO2 (achieved witll a mixture of sodium sulfite and
sodium bisulfite) and had a pH of 7.4. A sufficient amount of
solution was retained in the chips after impregnation to result in
~L~74~57
_ 1 9 --
6.3~ 52 applied to the chips in the Impressafiner. After
impregnating the chips, the chips were cooked in a digester with a
4:1 liquor to wood ratio at 160C for 30 minutes and then the chips
were drained of cooking liquor. The cooking liquor contained 59
5 grams/liter SO2 (achieved with a sodiurn sulfite and sodium bisulfite
mixture) and had a pH of 7.4. This resulted in 6.~ SO2 applied
to the chips in the digester to result in a total SO2 application to
the chips of 12.3% in the impregnation and cooking steps. The
chips were then refined in the same manner as in Example 3 and
10 after refining the pulp was dewatered, washed with water and
bleached. Bleaching consisted of treating the pulp for 10 minutes
at 3% consistency with 0.25g~ DTPA, dewatering to 25% to 30%
consistency, then bleaching at a pH of 11 and at 60C with a
peroxide bleaching solution at a consistency of 12.5g6 for three
15 hours. The bleaching solu~ion had 5.5% hydrogen peroxide, 5.0%
sodium hydroxide, 4.5g~ sodium silicate, 0.059~ Epsom salt and 0.5
DTPA, (all percentages being based upon the dry weight of pulp).
After being bleached, the pulp was dewatered, diluted to a 3%
consistency and the pH adjusted to about 5.5 with sulfurous acid.
20 The bleaching conditions were selected to result in essentially the
same consumption of peroxide as in Example 3. The pulp of
Example B was tested for brightness, both before (initial) and after
bleaching (bleached), freeness and breaking length and the results
are given in Table l l . The amount of energy consumed during
25 refining is also given in Table ll.
Example C (CTMP Process with Post-Refining Peroxide Bleaching)
The Southern Pine wood chips were steamed at atmospheric
pressure for 30 minutes, and then impregnated using the same
equipment as in Example 3 with an impregnation liquor containing 64
30 grams/liter sodium sulfite and having a pH of 9.0 to result in 3.8%
52 applied to the chips based upon the dry weight of chips.
After the impregnation step, the chips were subjected to
atmospheric steam for 30 minutes. After impregnation and
steaming, the chips were refined in the same manner as in
~7a~657
-- 20 --
Example 3 . The resul ting refined pulp was then dewatered, washed
with water and bleached with peroxide. Bleaching consisted of
pretreating the pulp for 10 minutes at 3% consistency with 0. 25
DTPA, dewatering the pulp and then bleaching the pulp at 60~C
and 12 . 5% consistency for two hours with a bleaching solution
having 4% hydrogen peroxide, 3 . 5% sodium hydroxide, 4 . 5% sodium
silicate, 0. 05~ Epsom salt and 0. 5% DTPA, (all percentages based
upon dry weight of the pulp). After bleaching, the pulp was
dewatered, diluted to a 3~ consistency and the pH adjusted to 5.5
with sulfurous acid. The pulp was tested for brightness ~both
before and after bleaching), freeness and breaking length, The
arnount of energy consumed during refining was also determined.
The results are stated in Table l l .
Comparison of Results
The pulp of Example 3 was the brightest and required the
lowest refining energy. It was much stronger than the pulp of
Example C and brighter and almost as strong as the pulp of
Example B.
Examples 4, 5 and D
_ _ _ _ _ . _ _ _
Examples 4, 5 and D, were essentially a repeat of Examples 1,
2 and A (present invention compared with a single stage impreg-
nation process using the same chemicals) but with hard wood
(Aspen) rather than softwood.
In Examples 4, 5 and D, Aspen chips of a size that passes
through a 3/4" circular hole screen were used after being pre-
treated with atmospheric steam for 20 minutes and then washed with
water. For impregnation, the Spro~lt~Waldron Model Ll-12 with the
same procedures and conditions were used as in Examples 1, 2 and
A with the exceptions noted below. The same procedures for
treatments, refining and testing were used in Examples 4, 5 and D
as in Examples 1, 2 and A.
Example 4 (Two-Stage !mpregnation Sequence)
The first impregnation solution contained 3.52 grams/liter
Epsom salt, 4.0 grams/liter DTPA and had a pH of 9 obtained by
~L~7a~ 7
adding hydrochloric acid. The second impregnation stage used an
aqueous impregnation solution containing 3.52 grams/liter Epsorn
salt, 0.4 grams/liter DTPA, 28,16 grams/liter sodium silicate, 55
grams/liter sodium hydroxide, 40 grams/liter hydrogen peroxide. It
5 had a pH of 12 . 5 .
After being subjected to the impregnation steps, the chips
were refined at atmospheric pressure in the Sprout-Walclron 12"
laboratory refiner Model 12-1 CP using the same procedures as in
Example 1. After refining, the pulp was dewatered to a consist-
ency between 25% and 35%, then diluted to about a 396 consistency
and the pH of the resulting pulp slurry adjusted to between 5.5
and 6AO with sulfurous acid. The pulp was then tested and the
results are given in Table i I . The dewatering resulted in a source
of hydrogen peroxide that could be recycled by utilizing it in the
makeup of an impregnation solution.
Example 5
The same procedures, equipment and conditions were used as
in Example 4 with the same chemicals except that the preferred
three-stage impregnation sequence was employed with the following
impregnation solutions:
An aqueous solution identical to the first impregnation solution
of Example 4 was used as the first impregnation solution. An
aqueous solution containing 14.08 grams/liter sodium silicate and 0.4
grams/liter DTPA and having a pH of 10.7 was used as the second
impregnation solution. The third impregnation solution was an
aqueous solution containing 3.52 grams/liter Epsom salt, 0.4
grams/liter DTPA, 14.08 grams/liter sodium silicate, 55 grams/liter
sodium hydroxide and 40 grams/liter hydrogen peroxide. It had a
pH of 12,5.
After the impregnation steps, the pulp was refined, dewatered
and adjusted to a 3% slurry having a pH of between 5.5 and 6.0
with sulfurous acid and tested as in Example 4. The results are
given in Table l l .
~74~7
-- 22 --
Example D
Example D was a .single stage impregnation process using the
same chemicals, procedures and equipment as in Examples 4 and 5
with the following exception. The impregnation stage of Example D
5 employed an aqueous solution containing 7.04 grams/liter Epsom
salt, 0.4 grams/liter DTPA, 28.16 grams/liter sodium silicate, 55
grams/liter sodium hydroxide and 40 grams/liter hydrogen peroxide.
The pH was 12 . 5 .
Comparison o~ Examples D, 4 and 5
. . ~
Example D consumed 4.7% peroxide and achieved a brightness
of 76%. Example 4 (2 stages) consumed 3.4% peroxide and achieved
a brightness of 82% while the preferred three-stage sequence of
Exampie 5 consumed only 1.5g6 peroxide and achieved the highest
brightness (83%).
. Examples E and F
In Examples E and F, compared the preferred three-stage
impregnation process of Example 5 to the CMP process with post
refining peroxide bleaching (Example E) and with the high alkaline
CTMP process with post refining peroxide bleaching (Example F).
Example E (CMP with Post-Refining Peroxide Bleaching)
Aspen chips of the same type used in Example 5 were pre-
soaked in water for 12 hours under vacuum which is equivalent to
the presteaming of Example 5. The soaked chips were then
pretreated in a digester by cooking the chips with a 4:1 liquor to
chip ratio at 150 for 90 minutes in a sodium sulfite and sodium
bisulfite cooking liquor at an initial pH of 6.9 which resulted in 6
52 applied based on the dry weight of the chips. After 90
minutes of cooking, the chips were drained of free liquor and
refined in the Sprout-Waldron laboratory refiner as in Example 5.
After refining, the pulp was washed with water and then subjected
to a post refining peroxide bleaching step which consisted of
pretreating the pulp for 10 minutes at 3% consistency with 0.25~
DTPA, dewatering the pulp and then bleaching the pulp at 60C
and at a consistency of 12 . 5~ for 2 hours in a bleaching solution
~l274~57
- 23 -
containing 2% hydrogen peroxide, 3.3% sodium hydroxide, 5% sodium
silicate, 0.5% DTPA and 0.05% Epsom salt and having a pH of 11.5
(all percentages based upon the dry weiyht of the pulp). After
bleaching, the pulp was dewatered and diluted to 3% consistency
and the pH adjusted to 5 . 5 with sulfurous acid prior to beiny
tested. The test results are given in Table l l .
Example F (High Alkalinity CTMP Process with Post-Refining
P~roxide Bleaching~
The Aspen chips were presoaked as in Example E and then
were impregnated in a digester under vacuum using a 13.3:1 liquor
to wood ratio for 12 hours at a temperature of 30(~. The cooking
liquor impregnated into the chips was an a~ueous solution
containing 15 grams/liter of Na25O3 and 26 grams/liter of sodium
hydroxide and had a pH of 12.9. This resulted in 1.7% SO2 and
9.8% sodium hydroxide applied based on the dry weight of the
chips. The chips were then drained of excess liquid and steamed
at a pressure of 5 Ibslinch gauge lpsig) for 30 minutes. The
treated chips were refined under steam at 15 Ibs/ inch gauge
pressure in the Sprout-Waldron 12" laboratory refiner Model 12-lC
and then subjected to secondary refining in the same refiner at
atmospheric pressure. After refining the pulp was dewatered,
washed with water and subjected to hydrogen peroxide bleaching by
first pretreating the pulp for 10 minutes at 3% consistency with
0.25% DTPA, dewatering the pulp and then bleaching the pulp at
60C for 2 hours at 12 . 5% consistency with a bleaching solution
containing 3% hydrogen peroxide, 3 . 8% sodium hydroxide, 5% sodium
silicate, 0.5% DTPA, and 0.05% Epsom salt and having a pH of 11.5
lall percentages based upon the dry weight of the pulp). The
bleached pulp was then dewatered, diluted to 3% consistency and
the pH adjusted to 5.5 with sulfurous acid.
The pulp from Examples E, F and 5 were tested for bright-
ness, freeness and strength (breaking length) and the energy
consumed during refining was also determined. The resuits are
~L~79~6~7
- 24 -
shown in Table l l . For Examples E and E, the brightness of the
pulp was determined both before and after peroxide bleaching,
The pulp of Example 5 was brighter and stronger than the
pulps of Examples E and F and required substantially less energy
5 to refine than in Example E.
Exampies 6 G and H
The preferred three-stage impregnation process of the present
invention was compared with CMP pulp subjected to post refining
peroxide bleaching and compared with high alkalinity CTMP puip
10 subjected to post refining peroxide bleaching in order to
substantiate ~he improved process of the present invention and its
applicability to a difficult-to-pulp hardwood species ~e,g.,
Eucalyptus Regnans).
IExample 6
Example 5 was repeated using Eucalyptus Regnans chips and
with the impregnating solutions given below.
The first impregnation solution was an aqueous solution
containing 3.96 grams/liter of Epsom salt and 4.0 grams/liter DTPA
and having a pH adjusted to 9 with hydrochloric acid. The second
20 impregnation solution was an aqueous solution containing 15.8
grams/liter of sodium silicate, 0.4 grams/liter DTPA and having a
pH of 10.7. The third impregnation solution was an aqueous
solution containing 3.96 grams/liter of Epsom salt, 15.8 grams/liter
of sodium silicate, 0.4 grams/liter DTPA, 60 grams/liter sodium
25 hydroxide and 45 grams/liter hydrogen peroxide, and having a pH
of 12.5.
Example G
Example E for the CMP proc~ss was repeated with the same
eucalyptus chips as in Example 6. The cooking and bleaching
30 conditions were as follows:
In the digester, a 4:1 liquor to wood ratio was used at 150C
for 90 minutes. The cooking liquor had a pH of 9.5 and resulted
in 6% SO2 applied to the chips based upon the dry weight of the
chips. The post refining peroxide bleaching process employed a
6~7
-- 25 --
pretreatment with 0. 25gc> DTPA at a 3% consistency for 10 minutes .
After pretreatment, the pulp was dewatered and then bleached with
a bleaching solution containing 5~6 hydrogen peroxide, 4 ~g~ sodium
hydroxide, 5% sodium silicate, 0.5~ DTPA, and 0.05% Epsom salt
5 based upon the dry weight of the chips and having a pH of 1~. 9.
Bleaching was at a consistency of 12.5%.
Example H
. _
Example F was repeated but using the same eucalyptus chips
used in Example 6 and with the digestor treatment and bleaching
10 conditions as follows:
The digester liquor contained 17 ~rams/liter of Na25O3 plus 28
grams/liter sodium hydroxide and had a pH of 12,9 which resulted
in 1.3% SO2 and 10.4~ sodium hydroxide applied to the chips based
upon the dry weight of the chip. The impregnation temperature
15 was 30C. After impregnation, the chips were drained and steamed
for 20 minutes with steam at a pressure of 5 Ibs/inch2 gage
(saturated). The post refining bleaching solution contained 6%
hydrogen peroxide, 5.4% sodium hydroxide, 5% sodium silicate, 0.5%
DTPA and 0 . 05% Epsom salt based upon the dry weight of the chips
20 and had a pH of 11.3.
The pulps of Examples G, H and 6 were tested for brightness,
freeness and strength (breaking length) and the results are
reported in Table l l .
The pulp of Example 6 had the highest brightness and
25 required the least refining ener~y while its strength was comparable
to the high alkalinity CTMP pulp and stronger than the CMP pulp.
Examples J, K and 7
The preferred three-stage impregnation process of the present
invention was compared with conventional CMP with post refiner
30 peroxide bleaching and high alkalinity CTMP with post refiner
peroxide bleaching utilizing Gmelina ~a tropical hardwood) chips.
Examples J, K and 7 were repetitions of Examples E, F and 5 with
the exceptions noted below.
-- 26 --
Gmelina chips of a size that would pass through a 3/4" circular
hole screen were pretreated with atmospheric steam for 20 minutes
and then washed with water prior to being utilized in Examples J,
K and 7.
5 Example 7
Example 5 was repeated with the identical solutions as used in
Example 5 but with Gmelina chips rather than Eucalyptus chips.
Example J (CMP Process with Post Peroxide Bleaching)
~ . .
Example E was repeated with the same type of Cmelina chips as
10 in Example 7 and with the following cooking and bleaching
conditions:
The cooking liquor in the digester was used at a ratio of 4:1
of liquor to chips based on the dry weight of the chips. Cooking
was done at 1 50C for 75 minutes and then the cooked chips were
15 drained of free cooking liquor. The cooking liquor contained 37
grams/liter of Na2SO3 plus 7.4 grams/liter of sodium hydroxide and
had a pH of 13 . This resulted in 4. 4% SO2 and 3% sodium
hydroxide applied to the chips based on the dry weight of the
chips. The post refining peroxide bleaching treatment was with a
20 solution that contained 5% peroxide, 4.9% sodium hydroxide, 5%
sodium silicate, 0.5% DTPA and 0.05% Epsom salt based upon the
dry weight of the pulp and had a pH of 11 . 3 . Prior to bleaching,
the pulp was pretreated at a 3% consistency with 0.25% DrPA for 10
minutes and then dewatered. After being bleached for 2 hours at
25 60C, the pulp was dewatered ar,d diluted to 3% consistency and the
pH was adjusted to 5.5 with sulfurous acid.
Example K (High Alkalinity CTMP Process with Post Peroxide Bleachin~)
_
Example F was repeated except that the chips were of the same
type of Gmelina chips as in Example 7 and with cooking and
30 bleaching conditions as stated below.
The cooking liquor contained 15 grams/liter of Na25O3 and 31
grams/liter of sodium hydroxide and had a pH of 13.3. The
cooking liquor used in the digester was used at a ratio of 4:1
liquor to chips. The chips were cooked for 45 minutes at 11 0C
~Lf~ 7
and then the cooked chips were drained free of cooking liquor.
This resulted in 1.3% 52 and 7.8% of sodium hydroxide appliec3
based upon the dry weight of the chips. The peroxide bleaching
solution contained 5% peroxide, 4.9% sodium hydroxide, 5% sodium
silicate, 0.5% DTPA, and 0.05% Epsom salt and at a pH of 11.3.
Prior to bleaching, the pulp was pretreated at a 3% consistency with
0 . 25% DTPA for 10 minutes and then dewatered .
The pulps of Examples J, K and 7 were tested for brightness,
freeness and strength and the energy required to refine the pulps
was also determined. The results are given in Table l l . The pulp
of Exampie 7 was the brightest and required the least refining
energy although all three pulps had comparable tensile strength.
The process of the present invention is capable of achieving noYel
non-sulfonated pulp having properties not previously achievable. A
non-sulfonated pine pulp can be produced for the first time from
Pine having a Yield greater than 85P6, a Brightness greater than 70
and a Papermaking Strength of at least 3 . 0 km when refined to a
Freeness of 600 ml. A non-sulfonated Aspen pulp can be produced
having a Yield greater than 80%, a Brightness greater than 80% and
a Papermaking Strength of at least 4.0 km when refined to a
freeness of 500 ml. A non-sulfonated Eucalyptus pulp can be
produced having a Yield greater than 80%, a Brightness greater
than 80% and a Papermaking Strength of at least 3 . 0 km when
refined to a Freeness of 500 ml. A non-sulfonated Gmelina pulp can
be produced having a Yield greater than 80%, a Brightness greater
than 75% and a Papermaking Strength of at least 2 . 0 km when
refined to a Freeness of 500.
Test Procedures and Definitions
Hydrogen peroxide usage or consumption (expressed as a
weight percent based on the dry weight of the chips) is the
quantity of peroxide consumed from the impregnatiOn solution
(initial peroxide in the impregnating solution minus final peroxide in
the impregnation solution) minus the quantity of residual peroxide
in the pulp after refining if followed by a refining step or after
~7a~57
-- 28 --
bleaching when using post-refiner bleaching. The percentaae
peroxide consumed is calculated as being equal to the guantity of
peroxide consumed times 100 divided by the dry weight of the chips
or pulp fibers. The quantity of peroxide in a solution was
S determined by iodometric titration using starch as an end point
indicator .
"Brightness" is defined as Elrepho brightness in percent units
which is determined by using the sample preparation procedure
given in the Technical Association of the Pulp and Paper Industry
tTAPPI) Officiai Test Method T~18 om-83. The brightness of the
sample was measured using TAPPI Provisional Method T525 su-72.
Refining energy (net refining energy) is expressed in horse-
power days per ton (HPD/T) and is the total energy absorbed by
the fibers and associated fluids during refining. It is determined
by measuring the total energy input into the refiner during refining
and subtracting the energy required to operate the refiner without
chips being fed to the refiner (usually referred to as the idle
energy required for the refiner). In small laboratory equipment,
the idle energy is usually significant and must be taken into
account. In large industrial equipment it is usually insignificant
and not taken into account in determining the energy for refining.
"Freeness" is defined as Canadian Standard Freeness (CSF)
which is measured in milliliters (ml) and was determined in
accordance with TAPPI Official Test Method T227 os-58.
"Papermaking Strength" is defined as breaking lenath (measure
of papermaking tensile strength) which is measured in kilometers
(km) and is a measure of the maximum length of a paper sheet that
is self supporting. The paper sheet was prepared using the sample
preparation procedure given in TAPPI Qfficial Test Method T205
om-81, the test specimen of the paper sheet was prepared using the
sample preparation procedure given in TAPPI Official Test Method
T220 om-83, and the strength measurement of the test specimen was
determined by using the procedure given in TAPPI Official Test
Method T494 om-81.
~274~;~7
-- 29 --
"Yield" is a percentage and is defined as the dry weight of
pulp times 100 divided by the dry weight of the chips from which
the pulp was made.
TABLE I
No. of
Wood ImpregnationTotal H202Elrepho
Ex. No. Type Steps Usage Briqhtness
A Pine 1 7.5 ~~ 60
Pine 2 4.2 72
2 Pine 3 3.7 75
D Aspen 1 4.7 76
4 Aspen 2 3.4 82
Aspen 3 1.5 83
TABLE ll
Canadian
Elrepho Refining Standard Breaking
Bri~h/tness Energy Freeness Length
Ex. No. Process Initial- Bleached Net HPD/T ml. km.Southern Pine
B CMP 59 671/ 66 720 2.8
C CTMP 54 661 / 49 750 *
3 Invention 70 _ 43 730 2.2
Aspen
E C~1P 58 752/ 72 650 1 2
F CTMP 42 60-/ 22 610 2 5
S Invention 83 _ 39 620 2.8
Eucalyptus 3/
G CMP 43 79_ 101 600 1.0
H CTMP 41 673/ 32 530 2 8
6 Invention 82 _ 30 530 2 6
Gmelina 41
J CMP 45 68- 72 510 2 2
K CTMP 38 544/ 67 510 2 2
7 Invention 78 62 490 2 2
1 / Bleached brightness with same peroxide consumption as Ex. 3 3.4
H 2 on dry weight of wood.
2/ B12eached brightness with same peroxide consumption as Ex. 5 1.5%
H 2 on dry weight of wood.
31 B12eached brightness with same peroxide consumption as Ex. 6 3.0%
H 2 on dry weight of wood.
4/ B12eached brightness with same peroxide consumption as Ex. 7 3.0~g
H202 on dry weight of wood.
45 5/ Inltial brightness after refining.
*Too weak to test (less than 0.5).
