METHOD OF BROWN STOCK WASHING

LEVAGE DE LA PATE BRUTE

English Abstract

Abstract
An improved method of brown stock washing is
disclosed. A nonionic surfactant in combination with a
polyelectrolyte dispersant, and preferably a solvent,
are utilized in the washing step in the pulping of
virgin cellulosic fiber. The methods of the invention
provide for the enhanced removal and recovery of cooking
chemicals and organics from the pulp.

Claims

- 21 -
I CLAIM:
1. An improved method of removing spent or excess
cooking chemical compounds or organic contaminants from
chemically or mechanically prepared virgin pulp, which
comprises:
(a) forming a fiber mat of chemically or
mechanically prepared virgin pulp; and
(b) forcing an aqueous solution comprising a
substituted oxyethylene glycol non-ionic surfactant,
a water soluble low molecular weight polyelec-
trolyte dispersant and solvent into and through
the fiber mat.
2. The method of Claim 1 wherein forcing the
aqueous solution into and through the fiber mat com-
prises applying the aqueous solution to the mat and
drawing the solution into and through the mat with a
vacuum force.
3. The method of Claim 2 wherein applying the
aqueous solution to the mat comprises spraying the
aqueous solution onto a surface of the mat.
4 . The method of Claim 3 wherein the fiber mat is
formed using a rotary drum vacuum washer.
5. The method of Claim 3 wherein the temperature
of the aqueous solution is from about 100° to 212°
F.
6. The method of Claim 1 wherein the solvent
is an ethoxylated solvent.
7. The method of Claim 1 wherein the solvent is
tetrahydrofurfuryl alcohol, ethoxylated derivatives or
mixtures thereof.
8. The method of Claim 6 wherein the substituted
oxyethylene glycol non ionic surfactant, the water
soluble low molecular weight polyelectrolyte disper-
sant, and the solvent together are provided at a total
concentration of from about 0.1 to 50.0 pounds per ton
of oven dried pulp, the total concentration being
composed of 10 to 60% by weight surfactant, 10 to
60% by weight dispersant, and 20 to 50% by weight

-22-
solvent.
9. The method of Claim 8 wherein the total
concentration is from about 0.5 to 5.0 pounds per ton of
oven dried pulp.
10. The method of Claim 1 wherein the polyelec-
trolyte dispersant comprises a co-polymer of maleic acid
and vinyl acetate.
11. The method of Claim 1 wherein the polyelectro-
lyte dispersant comprises a polyacrylate compound.
12. The method of Claim 11 wherein the polyacry-
late compound has a molecular weight in the range of 500
to 25,000.
13. The method of Claim 1 wherein the polyelectro-
lyte dispersant is of the structure:
<IMG>
wherein R1, R2, R4 and R5 are independent and
are selected from the group consisting of hydrogen,
C1-C4 lower alkyl, alkylcarboxy or mixtures thereof,
R3 and R6 are independent and selected from the
group consisting of hydrogen, carboxy, alkylcarboxy, or
mixtures thereof, X is selected from the group consist-
ing of carboxy, salts and derivatives of carboxy,
acetyl, hydrocarbon moieties commonly attached to free
radical monomers, COOZ where Z is H, a monovalent metal
ion or ammonium, or mixtures thereof; and the total of a
+ b falls in the range of 15 to 1,000.
14. The method of Claim 13 wherein R1, R3,
R4 and R6 are hydrogen, R2 and R5 are hydrogen
or methyl, and x is carboxy.
15. A method of recovering excess or spent cooking

- 23 -
chemical compounds or organic contaminants from an
aqueous pulping medium comprising chemically or mechani-
cally prepared virgin pulp and excess or spent chemical
compounds or organic contaminants, which comprises:
(a) combining the aqueous pulping medium with
a substituted oxyethylene glycol non-ionic surfac-
tant, a water soluble low molecular weight
polyelectrolyte dispersant and solvent;
(b) substantially separating the chemically
or mechanically prepared virgin pulp from the
aqueous pulping medium; and
(c) after step (b), removing excess or spent
cooking chemical compounds or organic contaminants
from the aqueous pulping medium.
16. The method of Claim 15 wherein in substantially
separating the chemically or mechanically prepared
virgin pulp from the aqueous pulping medium, the chemi-
cally or mechanically prepared virgin pulp is washed in
a washing step.
17. The method of Claim 16 wherein the chemically
or mechanically prepared virgin pulp is substantially
separated from the aqueous pulping medium and washed by
a rotary vacuum cylinder washer.
18. The method of Claim 17 wherein the solvent
is tetrahydrofurfuryl alcohol, ethoxylated derivative or
mixtures thereof.
19. The method of Claim 18 wherein the substituted
oxyethylene glycol non-ionic surfactant, the water
soluble low molecular weight polyelectrolyte disper-
sant, and the solvent together are provided at a total
concentration of from about 0.1 to 50.0 pounds per ton
of oven dried pulp, the total concentration being
composed of 10 to 60% by weight surfactant, 10 to
60% by weight dispersant, and 20 to 50% by weight
solvent.
20. The method of Claim 19 wherein the total
concentration is from about 0.5 to 5.0 pounds per ton of

- 24 -
oven dried pulp.
21. The method of Claim 15 wherein the polyelec-
trolyte dispersant comprises a copolymer of maleic acid
and vinyl acetate.
22. The method of Claim 15 wherein the polyelec-
trolyte dispersant comprises a polyacrylate compound.
23. The method of Claim 22 wherein the polyacry-
late compound has a molecular weight in the range of 500
to 25,000.
24. The method of Claim 15 wherein the polyelectro-
lyte dispersant is of the structure:
<IMG>
wherein R1, R2, R4 and R5 are independent and
are selected from the group consisting of hydrogen,
C1-C4 lower alkyl, alkylcarboxy or mixtures thereof,
R3 and R6 are independent and selected from the
group consisting of hydrogen, carboxy, alkylcarboxy, or
mixtures thereof, X is selected from the group consist-
ing of carboxy, salts and derivatives of carboxy,
acetyl, hydrocarbon moieties commonly attached to free
radical monomers, COOZ where Z is H, a monovalent metal
ion or ammonium, or mixtures thereof; and the total of a
+ b falls in the range of 15 to 1,000.
25. The method of Claim 24 wherein R1, R3,
R4 and R6 are hydrogen, R2 and R5 are hydrogen
or methyl, and x is carboxy.

Description

~;~S2'~5~3 (
M&G 163.444-US-01
IMPROVED METE~OD C)F BROWN
STOCK WASHING
Field of the Inventioll
This invention relates to a method of removing and
recovering spent or excess cooking chemicals and pitch
from virgin or primary cellulosic fiber. More particu-
larly, the invention relates to an improved method of
brown stock washing to enhance the recovery of spent
cooking chemical residues ~nd excess cooking chemicals,
and remove non-cellulosic materials such as :Lignin,
fatty acid soaps, and resin acids.
Background of the Invention
Virgin cellulosic Eiber typically derivecl Erom log9
of hardwood or softwood, undergoes length~ processing
before it is suitable for use in papermaking. In a
typical pulping process, briefly, logs are reduced to
wood chips, which are fed into a digester. "Liquor", an
aqueous solution obtained from the later described wash
step and containing dissolved and residual cooking
chemicals, spent cooking chemical residue and cellulosic
contaminants, and "white liquor", another by-product of
the pulping process known in the art, are fed into the
digester, primarily for dilution. Cooking chemicals are
also added as required. The cooking chemicals are
described hereinafter.
The contents of the digester are brought to a
relatively high temperature and pressure, for example
about 350 F. at a pressure of about 110 pounds per
square inch. The wood chips are "cooked" in the
digester under these conditions to reduce the wood chips
to pulp. Typically, under these conditions, the wood
chips are cooked from about 1 to 5 hoursO The cooking
can be carried out in batch or continuous digesters.
The cooked wood chips or pulp in the aqueous medium
after digestion is referred to as "brown stock". The
brown stock consists generally of two phases, the pulp,

1~ 5~ (
and the liquor or liquid phase of the digester contents.
However, typically after digesting, oversized chips,
insufficiently cooked chips, or knots remain. These
components are generally removed from the brown stock by
knotters which typically consist of coarse screens.
Before further processing of the pulp, it is
generally considered necessary to separate the pulp from
the liquor. It is also desirable to clean the pulp,
removing and to the greatest extent possible, recovering
spent or excess cooking chemicals, and removing and
recovering pitch contaminants.
After digestion, and ~ollowing removal of oversized
chips and the like, the brown stock is transferred to a
washer Eor a washing step. I'ypically, the washing
process involves a s~ries of washers which separate the
pulp ~rom the liquor, and progressively clean the
pulp by removal of cooking chemicals, cooking chemical
residues, and non-cellulosic contaminants.
Several methods may be used to perform the washing
step. In the past, the brown stock was filtered in a
fa]se bottom tank or diffuser into which the digester
was discharged. The liquor was drained through the
false bottom, and the pulp was washed by gravity dis-
placement of the liquor with wash water. Other types of
washers such as a pressure washer are also known in the
art.
Currently, the rotary vacuum drum or cylinder or
vacuum washer is more typically used~ As is known to
those familiar with the art, the vacuum washer is
generally a wire cylinder or drum that rotates in a vat
containing the brown stock (i.e. the pulp and liquor
mixture)O The lower section of the drum is immersed in
the brown stock. Vacuum is applied inside the drum as
it rotates through the brown stock. The liquor drains
through the surface of the wire drum into the interior,
leaving a layer of pulp on the outside face of the
drum. The layer of pulp is held in place by the vacuum
force inside the drum, from where it is conducted

-~252~S~3 ~
away.
The layer of pulp continues to build, forming a mat
or sheet, as the submerged portion of the drum rotates
through the brown stock in the vat. Liquor continues to
drain from the pulp or fiber mat as a result of the
differential pressure between the external atmosphere
and the vacuum within the cylinder.
Washing action is generally provided by showers
located over the pulp sheet. Water is sprayed onto the
pulp sheet to displace the liquor from the sheet
on the drum as the drum continues to rotate. The vacuum
force draws the water into the sheet, where it displaces
the liquor. The liquor drains out the other side of the
sheet into the inside of the cylinder/ where it drains
away to a filtrate storage tank for reuse, or example
as wash water Eor a mcre contaminated sheet which has
formed on another of the washers in the series.
Finally, the pulp sheet is removed from the face of
the wire by a doctor blade.
The surface of the shee~ where the wash water is
applied becomes cleaner than the pulp adjacent to the
cylinder at the bottom of the sheet, since the wash
water becomes more concentrated in liquor as it passes
through the sheet. Consequently, where a series of
washers is utilized, the pulp sheet obtained from the
first vacuum washer is generally repulped to provide
a more uniEormly clean pulp before traveling over the
second vacuum washer. This repulping step is generally
-epeated between each vacuum washer in the sequence.
In the repulping step, the pulp fibers are agitated
at a low consistency (i.e. the pulp is very dilute) in
order to facilitate scrubbing. ~he low consistency also
aids in a achieving a lowered concentration of dissolved
solids, prior to collection of the pulp on the next
washer in the series. Low consistency promotes diffu-
sion of the contaminated liquor from the pulp in the
repulping step.
In a sequence of washers, the pulp medium and the

~ ~,zS;~258 (
wash water are generally arranged to flow countercurrent
to each other. Fresh water is typically used to wash
the pulp sheet on the last stage washer. The filtrate
that was pulled through pulp sheet on each washer is
used to wash the pulp on the preceeding washer. This
aids in minimizing dilution of the liquor which is
separated from the pulp, and from which cooking chemi-
cals or cooking chemical residues are to be recovered,
as described hereinafter.
The cooking chemicals used in pulping mills are
known in the art. Briefly, the cooking system is
generally either kraft or sulfite. Other cooking systems
are also known in the art.
The kraft system generally involves the use of
sodium hydroxide and sodium sulfide in the digester to
aid in decomposition of the wood ~ibers to produce
pulp. The sodiurn may be added as sodium sul~ate, soclLum
carbonate, or similar sodium compounds. The sulfite
system typically involves the use of SO2 and magne-
sium, calcium, sodium or ammonia. The kraft millgenerates "black liquor", while the counterpart in the
sulfite mills is referred to as "red liquor". For the
purpose of this description, the term "liquor" refers to
both ~red" and "black" liquor, and the aqueous phase of
the pulp mixture resulting from other pulp processing
methods such as those described below.
Some pulping mills form pulp from wood products
without the use of cooking chemicals. Several such
pulping processes are known, including mechanical
processes such as the groundwood process, use of a
refiner to create refiner mechanical pulp, or use of
heat to create thermomechanical pulp. Most such
processes rely on heat and mechanical action to brea~
down the wood fibers. Other processes, such as the NSSC
process, rely on both chemical and mechanical action.
While these mechanical, thermomechanical, or semi-
chemical processes typically do not involve washing
steps, where washing steps are used the methods of this

~252ZS~3 ~
invention can aid in cleaning the pulp and recovering
organic contaminants.
Before washing, the brown stock will contain
many impurities from the pulping process, including
excess cooking chemicals and spent cooking chemicals
(where chemicals are used in the pulping), and also a
variety of organic contaminants such as resin acids,
fatty acid soaps and the like originating in wood. The
contaminants occlude to the pulp fibers,and are also
present in the aqueous phase of the brown stock. It
has been found that in general, the contaminants of
black liquor and the corresponding pulp are principally
alkali lignin, hydroxy acids and lactones, and sodium.
Generally, black liquor is also contaminated with acetic
acid, ~ormic acid, sulfur, extractives, and methanol.
Red liquor (obtained through the sulfite process) and
the corresponding pulp has been found to be contaminated
with lignosulfonate, monosaccharides (mannose, xylos~,
galactose, glucose and arabinose), poly and oligosac-
charides, calcium, aldonic acids, sugar-sulfonates,
extractives, acetic acid, methanol, and glucuronic
acid. These materials are substantially different from
those encountered in deinking or dewaxing repulping
proceseses, where the contaminants are generally inor-
ganic substances and very different organic compounds.
It is highly desirable to recover or reclaim thecooking chemical residues for reuse, to reduce the
amount of chemicals which must be purchased by the
mill. Those residues which remain in the pulp after
the pulping process are generally not recovered, and
contaminate the pulp products. Those residues which are
carried by the liquor tend to be recoverable. There-
fore, it is advantageous to decrease the amount of
chemicals carried by or occluded to the pulp and in~
crease the amount carried by the liquor. In particular,
it is desirable to effect a transfer of chemicals from
the pulp to the liquor.
Such a transfer can be achieved to a great extent

~'~S2'~58 (-
by the washing of the pulp. However, for production
level washing to obtain large quantities of pulp at a
high quality level or level of purity, vast quan~ities
of wash water are required. The wash water dilutes the
liquor and chemicals washed from the pulp. Since
recovery of the chemicals involves distillation, or
evaporation of the aqueous component, it can be signif-
icantly more expensive to recover chemicals from a
more dilute solution, off-setting the cost benefits to
be achieved by recovery. Thus, a substantial need
exists for a method of washing virgin pulp which will
sufficiently remove excess and spent cooking chemicals
from the pulp and otherwise clean the pulp without
causing excessive dilution.
lS In addition to the problems of recovering inorganic
cooking chemical resiclues, another similar set: of second
problems encountered in pulping virgin pulp results rom
the presence of lignin and other organic substances such
as resin acids, fatty acid soaps, etc. in wood chips.
It is desirable to recover these substances because they
are economically or commercially valuable, for example,
when recovered as tall oils. In addition, pulp which
retains a high level of such materials may require the
use of more chemicals in the bleaching step, thus
rendering the bleaching step more costly. A need exists
for a method of washing virgin pulp which will result in
greater recovery of organic substances and lighter
colored pulp while minimizing the amount of dilution or
wash water required to obtain these results.
Brief Description of the Invention
I have found that the addition of a nonionic
surfactant, a dispersant, and preferably a solvent to
the wash water or the brown stock itself will result in
unexpectedly improved washing of virgin pulp. By the
method of this invention, a given quantity of wash water
will result in surprisingly increased removal of spent
or excess cooking chemical compounds and organic
contam:n~nts, thus minimi~ing dilution in the washing

2~
process whi1e providing cleaner, and generally lighter
colored, pulp and facilitating economical recovery of
the cooking chemical residues and organics.
various aspects of the invention are as follows:
S An improved method of removing spent or excess
cooking chemical compounds or organic contaminants ~rom
chemically or mechanically prepared virgin pulp, which
comprises:
(a) forming a fiber mat of chemically or
mechanically prepared virgin pulp; and
(b) forcing an aqueous solution comprising a
substituted oxyethylene glycol non-ionic surfactant
and a water soluble low molecular weight polyelec-
trolyte dispersant into and throug~ the fiber
1.5 mat.
A method of recovering exce~s or spent cooking
chemical compounds or organic contaminants from an
aqueous pulping medium comprising chemically or mechani-
cally prepared virgin pulp and excess or spent chemical
compounds or organic contaminants, which comprises:
(a) combining the aqueous pulping medium with
a substituted oxyethylene glycol non-ionic surfac-
tant and a water soluble low molecular weight
polyelectrolyte dispersant;
(b) substantially separating the chemically
or mechanically prepared virgin pulp ~rom the
aqueous pulping medium; and
(c) after step (b), removing excess or spent
- cooking chemical compounds or organic contaminants
from the aqueous pulping medium.

5~3
- 7a -
Detailed _escri~tion of the Invention
The present invention invol~es use in the wash
process of a nonionic surface acti~e agent or surfactant
in combination with a dispersant, and preferably a
solventO The surfactan~ comprises an oxyethylene glycol
chain, wherein one terminal hydroxyl of the chain has
been replaced with an ether group selected from the
group consisting of an aliphatic eth~r group and an
alkylaromatic ether group, and the other terminal
hydroxyl of the chain has been replaced with an ether
group selected from the group consisting of a polyoxy-
propylene group and a benzyl ether group. A typical
formula ~or preferred surEactants o~ this invention
would be as follows:
LS ~ r)a (C2H~)n (C3~6)1n
wherein a is zero or 1,
Ar represents an aromatic residue, preferably
monocyclic,
R represents an aliphatic group,
n has a value from about 3 to about 50,
m has a value from about zero to about 50,
and
Y is selected from the group consisting of
hydroxy and benzyl ether and is benzyl ether when m
equals 0.
The R group is typically saturated and contains at
least 6 carbons. When a equals zero, R contains from 6
to 24 carbons; when a equals 1, R normally contains no
more than 18 carbon atomsO In short, the R(Ar)a group
contains at least 6 aliphatic carbon atoms and up to a
-total of 24 carbon atoms.
The foregoing structural formula can be considered
to encompass t~o major classes of surfactants, i.e. (a)
alkylene oxide adducts of alkylphenols, and ~b) alkylene

S~
-- 8 --
oxide adducts of higher (greater than Cs) aliphatic
alcohols or acids. Acids which can be utilized in the
formation o~ the surfactant include lauric, myristic,
oleic, linolenic, palmitic and stearic. Where the
adduct o an aliphatic acid is used, typically R will
contain from 6 to 24 carbon atoms, and may contain some
unsaturation.
The surfactants contemplated for use in the inven-
tion are generally low foaming surfactants which do not
significantly contribute to foam problems within the
system.
These surfactants are described in detail in
commonly assigned United States Paten~ 4,518l459
dated May 21, 1985, on behalf
of Richard E. Freis, James E. Maloney and Thomas R.
Oakes, entitled "Methods of Deinking Secondary Fibers".
The present invention also involves the use of
polyelectrolyte dispersants. A '^polyelectrolyte dis-
persant" as the term is intended herein means any homo,
co, ter, etc., polymer of the structure:
~1 R2 R4 R5
-C. - C _ C - C-
R3 X R6 X
_ _ a _ _ b
wherein Rl, R2, R4 and Rs are independent and can be
hydrogen, Cl-C4 lower alkyl, alkylcarboxy (e~g.,
-CH2COOH) or mixtures thereof; R3 and R6 can be
hydrogen, carboxy, alkylcarboxy, or mixtures thereof,
and X can be carboxy (including saîts or derivatives
thereof, e.g~, amide), acetyl, or hydrocarbon moieties
commonly attached to free radical polymerizable monomers
(e.g., -C6Hs in styrene); a + b having a value in

58 ~
9 _
thY range of 15 to about 1,003.
Examples of materials within the scope of the above
formula include polymaleic acid, polyacrylic acid,
polymethacrylic acid, polyacrylic acid/itaconic acid
copolymers, polyacrylic acid/hydrolyzed mal~ic acid
copolymers, polymaleic acid/itaconic acid copolymers,
hydrolyzed polymaleic acid/vinyl ace~ate copolymers,
polyacrylic acid/acrylamide copolymers, ~olyacrylic
acid/methacrylic acid copolymers, styrene/maleic acid
copolymers, sulfonated styrene/maleic acid copolymers,
polymaleic acid/methacrylic acid copolymers, maleic acid
telomers, maleic~alkyl sulfonic copolymers.
A pa ticularly preferred class of water soluble
polyelectrolytes for use in the practices of the
present invention is the polyacrylate compounds. The
polyacrylate compounds comprise polymers and copolymers
of the structure:
L ,a L ] b
and their derivatives, wherein R2, Rs, X, a and b
are defined as above.
In a most preferred practice of the present inven-
tion, X is -COOZ, wherein Z is ~, or a monovalent
cation, e.g. Na+, K~, or NH4. Ihus, typical of the
preferred polyelectrolytes of the present invention are
p~lyacrylic acid, polymethacrylic acid and copoly-
mers of acrylic acid/methacrylic acid (e.g., AQUATREAT*
available from ALCO Chemical).
The polyelectrolytes of this invention must be
water soluble. Generally speaking, to be water soluble,
the polymer must contain sufficient polar groups (e.g.,
COOH) ~or ~he molecule to interact with the polar water
molecules. Thls means that in copolymers, terpolymers,
tetramers, etc., with unsaturated monomers which are
* Trademark

S;Z'~58 ~-
-- 10 --
predominantly or entirely hydrocarbon (e.g., styrene)
there must be sufficient polar functional groups for the
polymer to dissolve in room temperature or below water.
Generally, at least abou' 10 mole percent of the mono-
mers comprising the polymer must contain polar func-
tionality (e.g.,
~0 0
-C -O-C-CH3
NH2
to provide the required water solubility.
The low molecular weight polyelectrolytes of
present invention generally have molecular weights of
less than about 50,000 with preferred molecular weights
in the range of about 500 to 25,000, most preferably of
750 to 5/000. Thus, the sum of a + b above, generally
falls in range of 5 to l,000, preferably 10 to 500 and
most preferably 12 to 450. One skilled in the art will
recognize that the materials within the above molecular
weight ranges are generally o lower molecular weight
than polymers generally referred to in the art as
flocculants which may have molecular weights in the
range of several million or more. Flocculants perform
function of agglomerating suspended particles opposite
the desired function of dispersion described herein.
Thus, these high molecular weight materials operate
in a manner effectively opposite that of the materials
described herein. The lower molecular weight materials
of the present invention are generally referred to in
the art as "dispersants"~
The improvement of the present invention optionally
contemplates the use of various well-known water soluble
solvents or cosolvents, along with the dispersants
and surfactants. ~he solvents unexpectedly provide
increased removal of contaminants of the pulp, when used
in the context of this invention and use of such sol-
vents is recommended. The solvents can be ethoxylated
solvents such as the glycol ethers available under the
trademarks Cellosolve and Carbitol. Preferred examples

of solvents for use in this invention include tetra-
hydrofuran, tetrahydrofurfuryl alcohol, and ethoxylated
and propoxylated derivatives thereof.. It has been found
that tetrahydrofurfuryl alcohol is particularly bene-
ficial in the context of the invention, and it istheorized that this component contributes to the high
recovery of spent cooking chemicals and the improved
level of pulp purity obtained by the method o:E this
invention.
Functionally speaking, the nonionic surfactant,
dispersant, and solvent additives of the invention
should be utilized in sufficient amounts or ratios to
achieve increased recovery of cooking chemicals and
soluble organics, and increased pulp purity after
washing with a given volume of water. I have found that
.. the components produce the best results at a surfactant:
dispersant ratio Erom about O.S:l to 2:1. Where the
solvent is used, I have found the more effective ratios
of surfactant: solvent to be from about 0.5:1 to 1:1.
As used in brown stock washing, I have found the
desired concentration of the nonionic surfactants in the
context of this invention to be generally in the range
of about 0.01 to 30 lbs/ton oven dried pulp, with
concentrations in the range of about 0~15 to 5 lbs/ton
being preferred. ~he concentration5 of the polyelectro-
lyte dispersants should fall generally in the range of
about 0.01 to 30 lbs/ton, or preferrably 0.1 to 4
lbs/ton. With respect to the solvent, the concentration
should fall in the range of about 0-25 lbs/ton, or more
preferably, 0.1 to 4 lbs/ton. As known in the art,
"pounds per ton" refers to the weight of the additives
in pounds, as compared to the weight in tons of oven
dried pulp which is washed.
The additives can be supplied to various locations
within the pulping system, such as any of the shower
heads for the washers, the washer vats, the filtrate
storage tank from where filtrate is recirculatecl through
the washers, the digester, the deknotter, the repulper,

~;~S'~25~
or the like. I have found that the additives are
distributed throughout the washing system particularly
well when they are added to the shower head of an
intermediate washer in a series of washers, such as the
second in a series of threeO
The additives can be added individually, or can be
premixed and added as a mixture. Preferably, for reasons
of convenience and greater effectiveness, the additives
are premixed~ In a preferred embodiment, a mixture of
from 10 to 60~ nonionic surfactant, 10 to 60% polyelec-
trolyte dispersant, and 0 to 50~ solvent ~o total 100%
is utilized at a level of from about 0 1 - 50.0 pounds
per ton of pulp (oven dried) to be washed. More prefer-
ably, the mixture will comprise from 30 to 50~ nonionic
surfactant, from 20 to 40~ polyelectrolyte dispersant,
and from 20 to 40~ solvent to total 100%. With respect
to the concentration, more preferably, to achieve a
suitahle level of effectiveness at greater economy, the
concentration will range from about 0.5 - 5.0 pounds per
ton, with the mixture being added in the shower head of
an intermediate washer in a series of washers.
The temperature of the wash water can range from
about 100 to 212 F., preferably in the range of about
140 to 180 F.
25While not wishing to be limited to any theory, I
theorize the surprisingly beneficial results achieved by
method of this invention may result from the prevention
of channeling within the mat, such that more of the wash
water actually penetrates the mat and more efficiently
displaces the liquor and impurities such as spent
cooking chemicals and organic substances.
The invention will be further understood by refer-
ence to following examples which include the preferred
embodiment.
35Example I
Example I was performed at a typical sulfite
pulping mill having three rotary cylinder vacuum washers
in sequence. Pre-trial, trial and post-trial production

513
- 13 -
runs were monitored. The "pre-trial" data are taken
from the mill during standard production, over a period
of twenty-one days. The trial occurred over a twenty-
seven day period wherein the invention was utilized at
the mill under otherwise standard conditions. Post-
trial data were taken during approximately twenty-one
days following the end of the trial, again during
standard production without use of the invention. The
pre-trial and post-trial data are in the nature of a
control, for comparison with the data obtained from use
of the method of the invention.
The trial procedure was as follows:
Lbs./ton Lbs./ton Lbs./ton Lbs./ton
~ Additive ~ Additive ~ Additive ~ Additive
1 0.5 8 l.S 15 1.5 22 2.0
2 1.0 9 1.5 16 1.5 23 2.0
3 1.0 10 1.0 17 1.0 24 2.0
20 4 1-5 11 1.0 la 1.0 25 0
1.5 12 1.5 19 1.0 26 200
6 1.5 13 1.5 20 1.0 27 2.0
7 1.5 14 1.5 21 1.0
25The additive used during the trial was in all cases
provided to the #2 shower. It comprised a mixture of
40% by weight of a modified alcohol ethoxylate with a
specific gravity of 0.97, and an activity of 100~,
30 wt-% of a low molecular weight polyacrylic acid in
the form of a 48 to 50% aqueous solution, having a pH at
100% of 1.5-2.0, and about 30 wt-% tetrahydrofurfuryl
alcohol having a molecular weight of about 102, a
specific gravity at 20/20 C. of about 1.0543. The
temperature of the #2 shower solution ranged from
120-160 Fo during the trial.
Test results were as follows:

Z5ZZ~ ~
- 1~
TABLE I
Pre-Trial Trial Post-Trial
Daily 385 399 376
Production N=23 N=27 N=21
(tons per day) S=33.2 S=47.9 S=37.93
Cooks (No./day) 6.1 6.8 7.3
Knotter Flow 2504 2750 2568
(gallons per N=10 N=26 N=21
minute) S=l99 S=281 S=226
(98~) (98
Knotter TDS 8.81 9.86 8.71
(~) N=6 N=26 N=21
S=0.43 S=1.10 S=0.45
(97%) (99~)
15 ~tl washer 8.38 9.89 8.63
Filtrate N-6 N=26 N=21
TDS (~ S=0.39 S=1.07 S=0,46
(99~) (99%)
3 Washer Mat 0.475 0.399 0.480
TDS (%) N=6 N=26 N=21
S=0.142 S=0.158 S=0.230
(82%) (82~)
#3 Washer 696 755 736
Shower Flow N=23 N=26 N=21
(gallons per S=8 S=18 S=39
minute) (99%) (99%)
Red Liquor 9.97% 10.27 9.86
Solids (~) N=23 N=27 N=21
S-0.48 S=0.52 S=0.37
(99%) (99%)
Surge Tank 75.74 74.88 71.51
Solids Loss N=23 N=26 N=21
(lb./ton) S=17.08 S=11.34 S=8.85
(~2%) (75%)
35 Overall 95.35~ 96.37~ 94.44%
Efficiency N=6 N=26 N=21
(%) S=1.22 S=1.59 S=3.24
(85~) (99~)

~S'~'~5~ r
#3 Washer Mat 1~197 1~014 lsl40
Extractables N=3 N=13 N=15
S=0.17 S=0.14 S=0.16
(9~%) (90~)
The knotter TDS refers to the total dissolved
solids in the liquid phase from the knotter, before
washing of the pulp.
The #l washer iltrate TDS refers to the total
dissolved solids of the filtrate recovered from the
first rotary cylinder vacuum washer in the series of
three. A higher value indicates that a greater number
of impurities have been washed from the pulp.
Number 3 washer mat TDS refers to the total dis-
solved solids of the mat itself which forms on washer#3. This is calculated by squeezing liquid ~rom the
mat, and testing that liquid Eor total dissolved solids.
It is understood in the art that the composition of the
liquid squeezings corresponds to the composition of the
mat itself. A lower number indicates a more pure mat
and is preferred.
Number 3 washer shower flow refers to the gallons
per minute of wash water flowing from the head of shower
number 3.
2S Red liquor solids refers to the weight percent of
solids compared to the total weight of the red liquor.
This value indicates the presence oE impurities such as
cooking chemicals~ lignin and the like which the pulp
contains after digestion and which are removed during
washing. A higher number indicates that more impurities
have been removed from the pulp and will be recoverable.
Surge tank solids loss reflects the solids,
whether cooking chemicals, lignin and the like, which
are lost to recovery, that is, which have been carried
over with the pulp and are therefore unrecovered. A
lower value is preferred.
Overall efficiency is expressed as a percentage. A
higher percentage for ovèrall efficiency indicates

~ 5~ 5~ (
- 16 -
greater washing efficiency and is more desirable. It
is calculated by the following formula:
Efficiency = (TDS ~1 vat) - (TDS ~3 mat) x 100
(TDS ~1 vat) - (TDS ~3 shower)
In the formula, "TDS" reers to "total diasolved
solids". The TDS $1 vat refers to the total dissolved
solids of the brown stock in the vat of the flrst in the
series of washers. TDS ~3 mat is a value obtained by
analysis of the squeezings of the mat formed on the ~3
washer. TDS #3 shower reflects the total dissolved
solids of the wash water sprayed through the ~3 shower
head.
Number 3 washer mat extractables is expressed as
the weight percent of impurities as compared to the
total weight of the mat. This test was performed
following the TAPPI method but using a mixt~re of
toluene and alcohol for the extraction process, rather
~han benzene and alcohol. A lower number indicates
fewer organic soluble impurities in the pulp or mat.
With respect to the data, N indicates the number of
samples which were tested. The values obtained were
then analyzed via Student T test to provide the value
given in Table I. S represents the standard of deviation
among the values obtained. The percentage given in
parentheses indicates the confidence limits of the
value.
- Discussion of Results
Regression equations were developed using pre-trial
and trial data with addition o the additive mixture as
'30 described in the example at a level of 1.5 lb/ton. All
work was done through multiple linear regression. Terms
included in the equations are significant at a level of
(P ~ 0.05). The regression equations are as follows:
Red Liquor Solids = 9.813 + 1.352 x # Mat TDS
+ 1.190 x lb./ton additive mixture used in Example
+ 0.077 x #1 Vat TDS - 0.167 x Cooks (No./day).
~2 = 0.8102.
Surge Tank Solids Loss = 117.12 ~ (2.68 x

~'~S~'~58 .~'
- 17 -
Cooks (No~/day)) + (0.022 x Knotter flow) ~ 78 x
Efficiency) + (0.120 x daily production). R2 =
Q.5535.
#3 Mat TDS = 6.552 + (0.030 x Knotter TDS) -
(0.066 x Efficiency) - (0.041 x lb./ton additive
mixture used in Example)~ R2 = 0.6658.
Red Liquor solids increased during the trial and
decreased the post-trial period. The regressiorl equa-
tion confirms a positive effect on red liquor solids
equivalent to .1'9~ per 1 pound/ton of the additive
mixture, or approximately 0.30% at the average trial
feed rate of 1.5 pounds/ton.
Results of the #l washer filtrate total dissolved
solids values indicate a significant increase, showing
markedly better washing results with use of the aclditive
- mixture. Knotter total dissolved solids also increased
during the trial.
The total dissolved solids in the ~3 washer mat
decreased 17~ during the trial, compared to the pre-
trial and post-trial average. This value indicates
surprisingly effective solids removal. The regression
equation indicates that the effect of the additive
mixture on #3 washer mat to~al dissolved solids is a
decrease of .0615% when the additive mixture is used at
1.5 pound/ton.
Overall eficiency for the three washers was found
to be ~ignificantly increased during the trial. The
post trial value is considered to be more reliable than
the pre-trial value due to the small sample size for the
pre-trial data. Efficiency was calGulated from oven
dried total dissolved solids.
Number 3 washer mat extractables showed a 12%
decrease during the trial versus post-trial period, an
unexpectedly high decrease particularly in view of the5 high production rates during the trial.
Example II
Example II was performed as was Example I, in
the same sulfite mill using the same standard proce-

~52Z58
- 18 -
dures. The same additive was also used.
The first pre-trial lasted 8 consecutive days,
followed later by an additional 12 day pre-trial period,
where data were collected regarding the standard mill
operation. The trial period immediately followed the 12
day pre-trial, and lasted 5 days, while the post-trial
period immediately followed the trial and lasted 3
days.
The trial procedure for ~xample II was as follows:
DayTime Action
_
110:30 a.m. Sample run
10:45 a~mO Additive in at 0.5 lb./ton
to #2 shower
15 1:15 p.m. Sample run
2:05 p.m. Additive increased to 1.0
lb./ton
3:00 p.m. Sample run
28:00 a.m. Sample run
20 10:00 a.m. Sample run
10:15 a.m. Additive increased to 1.5
lb./ton
1:00 p.m. Sample run
38:30 a.m. Sample run
25 10:30 a.m. Sample run
10:35 a.m. Additive increased to 2.0
lb./ton
12:30 p.m. Sample run
30 48:30 a.m. Sample run
10:30 a.m. Sample run
12:30 p.m. Sample run
58:30 a.m. Sample run
359:00 a.m. Additive off
Squeezings were taken from mat ~3 at various
times during trial and post trial as indicated at

~5;2;~5~ ~
-- 19 --
"sample run", and were in some cases analyzed for water
soluble inorganics using the TAPPI testing procedure,
except that toluene and alcohol were used instead of
benzene and alcohol. The results oE the #3 mat squeez-
ings analysis, in parts per million, is as follows:
Mat Squeezings
Trial Post-Trial
Day: Day 1 Day 2 Day 4 Day 5 of
Time: Afternoon Morning Morning Post Trial
Chloride 9.35.3 4.4 11.6
Sulfate 125 438 398 1350
Aluminum 4 4 4 1~0
Barium 2 2 2 0.7
15 Iron 3.67.0 3.0 6~0
- Silica 17 17 17 16
as SiO2
Calcium 10 l5 20 93
Magnesium 83 200 240 1200
20 Sulfite by 40 10 40 620
iodine
titration
The average of the #3 mat dissolved solids,
expressed as a percentage by weight solids~weight of the
squeezings as a whole, was as follows:
First Average of Second Pre~Trial
Pre-trial and Post Trial _ Trial
30 0.48 0.49 0~42
Results
Dissolved solids in the #3 mat were decreased
from an average of 0.49% to 0.42% during the trial,
indicating a reduction of soluble inorganics and or-
ganics. Water analysis of the ~3 mat confirmed the
significant reduction of inorganics during the trial.
These results show a trend indicating an unexpectedly

~2~ 2S8
- 20 -
high reduction in inorganic and organic solids carried
in the #3 mat during the use of the additive mixture in
the ~2 shower.
The foregoing description and Examples are exemp-
lary of the invention. However, since persons skilled
in the art can devise various embodiments without
departing from the spirit and scope of the invention,
the invention is embodied in the claims hereinafter
appended.