Note: Descriptions are shown in the official language in which they were submitted.
CA 02271900 1999-OS-11
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CHEMICAL PULPING PROCESS
The present invention relates to additives useful
for pulping wood chips. More particularly, the invention
relates to the use of at least one oxyalkylene-modified
organopolysiloxane and at least one alkylated sulfonated
diphenyloxide surfactant as additives for digestive
treatments of wood chips in aqueous cooking liquors.
Chemical pulping is the chemical processing of
wood chips and the like to remove significant amounts of
lignin therefrom. These can often be further subjected to
bleaching and purification operations in a bleach plant,
including further delignification of the pulp.
Lignin is the major noncarbohydrate constituent of
wood and, prior to chemical pulping, usually comprises about
one-quarter of the raw material, functioning as a binder for
the cellulosic fibers. The lignin is dissolved by cooking
liquor in the manufacture of wood pulp. The character of
the pulp produced is dependent on the extent of lignin
removal from the wood chips and hence on the residual lignin
content of the final pulp.
Significant quantities of lignin are removed
during chemical pulping to form the fibrous pulp. However,
substantial quantities of lignin often remain after
conventional chemical pulping processes are complete,
generally 2 to 6 weight percent of the pulp. Chemically,
lignin is a complex structure which varies depending on the
CA 02271900 1999-OS-11
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2
species of wood and is characterized by the presence of
repeating phenol propane units.
It is known that in the conventional methods for
manufacturing wood pulp that the wood can be treated with a
variety of chemicals such as alkaline earth metal salts,
weak acids or sulfuric acid in an aqueous solution. These
methods have several disadvantages, in particular the need
to continue cooking the wood chips for 6 to 12 hours for the
lignin digestion to be complete. In order to accelerate the
delignification of the chips, it is necessary to operate at
a temperature of 150°C. to 180°C. and under pressure of
several atmospheres.
It is also known that in conventional methods of
chemical pulping, wood can be treated with chemicals such as
anthraquinone and anthraquinone derivatives in an aqueous
solution.
It has also been disclosed that surface active
agents can be used in the production of wood pulp by the
sulfate pulp process. For example, Parker et al. in U.S.
Patent No. 3,909,345, teach that surface active agents
having the general formula R{(C2H40)n(C3H60)m}yH wherein R
is the nucleus of a reactive hydrogen compound selected from
various glycols, diols, amines, piperazines, amides and
acids, can be used as additives to sulfate cooking liquor
for the purpose of obtaining higher yields of pulp from a
given wood chip charge and that these agents permit a
greater effectiveness of the cooking process relative to
CA 02271900 1999-OS-11
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chips which prior to that invention were considered rejects
and not pulpable.
Blackstone et al. in U.S. Patent No. 4,906,331
disclose that compounds having the general formula
HO(C2H40)a(C3H60)b(C2H40)cH where a, b and c have a value of
at least one, increase the yield of chemical pulping
processes and decrease the level of rejects. Chen et al. in
U.S. Patent No. 4,952,277 disclose a process for making
paper or linerboard, the process comprising cooking wood
chips in a Kraft liquor to form a Kraft pulp, the liquor
excluding anthraquinone and including a surface active agent
having the general formula CnH2n+1-C6H4-O(C2H40)xH where n
is an integer from 8 to 12 and x is a positive integer from
1 to 100, the surface active agent being present in the
cooking liquor in an amount effective to increase the yield
of pulp. Ling et al. in U.S. Patent No. 5,250,152 teach a
method for enhancing the penetration of cooking liquor into
wood chips to form a Kraft pulp which comprises adding to
the cooking liquor specific surfactants such as ethoxylated
dialkylphenols and ethoxylated alcohols.
Pease in U.S. Patent No. 5,464,502 teaches a
method for removing lignin and spent cooking chemicals from
pulp which comprises adding, within the washing operation,
from 0.1 to 1000 parts per million parts of pulp of an
anionic sulfonate surfactant wherein the removal of lignin
and spent cooking chemicals occurs at a temperature of from
30°-100°C.
~
CA 02271900 1999-OS-11
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It has also been disclosed that in chemical
pulping processes which produce wood pulp that the wood can
be treated with various silicones or siloxanes prior to
addition to a digester unit or may be added directly to the
digester before or after the digester has been filled with
wood chips and liquor. For example, Simmons et al., in U.S.
Patent No. 3,147,179, disclose that various silicones and
siloxanes are useful as digestion aids in Kraft, soda or
sulfite chemical pulping processes.
German Patent Application No. DE 4440186 discloses
a process for obtaining pulp from fibrous materials in which
organosilicon compounds such as oxyalkylene-modified
organopolysiloxanes are added to the chemical pulping
process, wherein the fibrous materials are reacted with a
chemical pulping liquor in the presence of the organosilicon
compounds.
WO 96/41915 discloses an improved pulping process
which comprises contacting wood chips with a liquid mixture
comprised of white liquor and at least one surfactant
selected from the group consisting of a polymethylalkyl-
siloxane containing ethylene oxide and optionally propylene
oxide groups, a co- and terpolymer of silicone and a
polyhydric alcohol, an alkoxylated aryl phosphate, an
alkoxylated branched alkyl phosphate, an alkoxylated
branched alcohol, an alkyl polyglycoside, an alkoxylated
alkyl polyglycoside, a mixture of alkali metal salts of
alkyl aromatic sulfate, a sulfosuccinate and a silicone~and
- CA 02271900 1999-OS-11
combinations thereof for a residence time effective to
extract resinous components without substantial degradation
of cellulose and thereafter heating at least a portion of
the resulting mixture and wood chips. However, none of the
references cited above disclose or suggest that the
particular oxyalkylene-modified organopolysiloxanes of the
present invention in combination with at least one alkylated
sulfonated diphenyloxide surfactant would be useful as
digestion aids in such chemical pulping processes.
The present invention relates to the use of at
least one oxyalkylene-modified organopolysiloxane and at
least one alkylated sulfonated diphenyloxide surfactant as
additives for digestive treatments of wood chips in aqueous
cooking liquors.
It has been discovered in chemical pulping
processes which involve the digestion of wood chips in
liquors that the subsequent properties of the wood pulp are
improved if small amounts of at least one oxyalkylene-
modified organopolysiloxane and at least one alkylated
sulfonated diphenyloxide surfactant are added to the liquors
employed in the digestive treatments.
Thus this invention relates to a chemical pulping
process comprising the steps of: (I) forming a mixture
comprising (A) wood chips, (B) an aqueous cooking liquor,
(C) at least one oxyalkylene-modified organopolysiloxane,
and (D) at least one alkylated sulfonated diphenyloxide
surfactant, (II) heating the mixture of step (I) to a
- CA 02271900 1999-OS-11
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temperature of at least 150°C. for a period of time to
substantially delignify the wood chips (A) so as to form a
pulp therefrom, (III) maintaining the heated mixture of step
(II) at a pressure to prevent boiling of aqueous cooking
liquor (B) during step (II), and (IV) recovering the pulp
from said mixture.
It is an object of the present invention to
increase pulp yield, lower the lignin content and improve
the strength of the cooked, washed pulp in chemical pulping
processes by the addition of at least one oxyalkylene-
modified organopolysiloxane and at least one alkylated
sulfonated diphenyloxide surfactant to wood chips, cooking
liquor or a digester.
This invention relates to a chemical pulping
process comprising the steps of: (I) forming a mixture
comprising (A) wood chips, (B) an aqueous cooking liquor,
(C) at least one oxyalkylene-modified organopolysiloxane
compound having the formula RlR2Si0(R2Si0)a(RXSiO)bSiR2R1
wherein R is a monovalent hydrocarbon group having from 1 to
20 carbon atoms, X is a polyoxyalkylene group selected from
the group consisting of -R2(OC2H4)cOR3,
-R2 (OC2H4 ) c (OC3H6 ) dOR3 , -R2 (OC2H4 ) c (OC4Hg ) eOR3 ,
-R2(OC3H6)d(OC4Hg)eOR3 and -R2(OC2H4)c(OC3H6)d(OC4Hg)eOR3,
wherein R1 is R or X, R2 is a divalent group selected from
hydrocarbon groups having from 1 to 20 carbon atoms and
hydrocarbon groups containing oxygen, R3 is selected from a
- CA 02271900 1999-OS-11
hydrogen atom, an alkyl group, an aryl group or an acyl
group, a has an average value from 1 to 500, b has an
average value from 1 to 500, and c, d and a independently
have an average value from 1 to 150; and (D) at least one
alkylated sulfonated diphenyloxide surfactant, (II) heating
the mixture of step (I) to a temperature of at least 150°C.
for a period of time to substantially delignify the wood
chips (A) so as to form a pulp therefrom, (III) maintaining
the heated mixture of step (II) at a pressure to prevent
boiling of aqueous cooking liquor (B) during step (II), and
(IV) recovering the pulp from said mixture.
The term "chemical pulp" as used herein, refers to
the product of manufacture of wood pulp from raw wood
primarily by chemical means. Chemical pulps are formed by
the removal of lignin from raw wood by chemical action to
form a fibrous pulp.
Wood chips (A) can be in the form of whole tree
chips including bark, branches, hardwood chips, softwood
chips, sawdust or combinations thereof. The wood chips can
be prepared by a de-barking operation in which bark is
removed from the logs and the logs are then shredded or cut
into chips of suitable small size to facilitate their
digestion. Whole tree chips do not need to be de-barked
prior to shredding or chipping. The wood chips (A) of this
invention may also be "presteamed". Presteamed wood chips
are prepared by preheating the wood chips in a steaming
vessel to drive out air and open the wood pores of the chips
CA 02271900 1999-OS-11
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which allows the aqueous cooking liquor (B), described
hereinbelow, to more easily penetrate into the wood. This
steaming process can be carried out in a continuous cooking
operation or in a batchwise fashion for batch digester
operations.
The aqueous cooking liquor, Component (B), can be
selected from the group consisting of Kraft cooking liquors,
soda cooking liquors and sulfite cooking liquors. The
aqueous cooking liquor (B) can also further comprise at
least one ingredient selected from the group consisting of
black liquor, polysulfide and anthraquinone-containing
compounds. Thus a combination of two or more of these
optional ingredients can also be used. The anthraquinone-
containing compounds are exemplified by anthraquinone,
anthraquinone-2-carboxylic acid, anthraquinone-1,5-
disulfonic acid disodium salt hydrate, anthraquinone-2,6-
disulfonic acid disodium salt and anthraquinone-2-sulfonic
acid sodium salt monohydrate. It is believed that the
addition of an anthraguinone-containing compound to the
aqueous cooking liquor significantly contributes to the
removal of lignin.
The Kraft cooking liquors generally comprise
sodium hydroxide and sodium sulfide as the active cooking
components of the liquor. It is preferred that the aqueous
cooking liquor to wood ratio is from 2:1 to 6:1. The
percentage of total active alkali in aqueous cooking liquor
(B) depends on the species of wood to be pulped and on the
- CA 02271900 1999-OS-11
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desired degree of delignification of the wood. For example,
if a "board" grade of pulp with moderate delignification is
desired or a "bleaching" grade of pulp with as much
delignification as possible without severe degradation to
the cellulosic components is desired, the concentration
generally varies from 12-25% total active alkali, and
preferably from 10-30% as Na20 based on the oven dry weight
of the wood chips. The Na20 represents both the amount of
NaOH and Na2S to be used. The Na2S used will furnish 15-25%
of the total Na20 while the remainder is furnished by NaOH.
In actual plant practice, some of the aqueous cooking liquor
may be circulated so that the total Na20 content may include
salts such as sodium carbonate, sodium hydrosulfate, sodium
sulfate and sodium thiosulfate. This is due to the addition
of some black liquor to the freshly prepared aqueous cooking
liquor prior to its addition to the wood chips. The black
liquor may comprise 10 to 50 percent of the aqueous cooking
liquor added to a fresh charge of wood chips. The sulfide
content of the aqueous cooking liquor (B) is expressed as
sulfidity, i.e. the percentage ratio of Na2S expressed as
Na20, to the total active alkali is preferably from 10-40%.
As used herein to describe Component (C), the
oxyalkylene-modified organopolysiloxane, it is understood
that the various siloxane units and the oxyethylene,
oxypropylene and oxybutylene units may be distributed
randomly throughout their respective chains or in respective
- CA 02271900 1999-OS-11
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blocks of such units or in a combination of random or block
distributions.
Those skilled in the art will appreciate that the
term "oxyalkylene-modified organopolysiloxane compound,"
standing alone, encompasses a number of compounds, including
those based upon cyclic, branched and resinous siloxane
compounds. While cyclic, branched and resinous oxyalkylene-
modified siloxanes can be used in combination with alkylated
sulfonated diphenyloxide surfactants they are comparatively
expensive and thus, are not as cost effective as the
particular oxyalkylene-modified organopolysiloxane compounds
used in accordance with the present invention.
In the above formula for Component (C), R is a
monovalent hydrocarbon group having from 1 to 20 carbon
atoms exemplified by alkyl groups such as methyl, ethyl,
propyl, butyl, hexyl, octyl and decyl, cycloaliphatic groups
such as cyclohexyl, aryl groups such as phenyl, tolyl and
xylyl and aralkyl groups such as benzyl and phenylethyl. It
is preferred that R is selected from methyl or phenyl. The
several R radicals can be identical or different, as
desired.
The group R2 is a divalent hydrocarbon group
having from 1 to 20 carbon atoms which is exemplified by
alkylene groups exemplified by methylene, ethylene,
propylene, butylene, pentylene, trimethylene, 2-
methyltrimethylene, pentamethylene, hexamethylene, 3-ethyl-
hexamethylene, octamethylene, -CH2(CH3)CH-, -CH2CH(CH3)CH2-,
- CA 02271900 1999-OS-11
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-(CH2)lg- and cycloalkylene radicals such as cyclohexylene,
arylene radicals such as phenylene, combinations of divalent
hydrocarbon radicals such as benzylene (-C6H4CH2-), or R2 is
a divalent hydrocarbon group containing oxygen such as
-CH20CH2-, -CH2CH2CH20CH2-, -CH2CH20CH2CH2-, -COOCH2CH200C-,
-CH2CH20CH(CH3)CH2- and -CH20CH2CH20CH2CH2-. Preferred
alkylene groups have from 2 to 8 carbon atoms.
The group R3 can be a hydrogen atom, an alkyl
group, an aryl group or an acyl group. The alkyl groups are
exemplified by methyl, ethyl, propyl, butyl, hexyl, octyl
and decyl. The aryl groups are exemplified by phenyl, tolyl
and xylyl. The acyl group can have from 1 to 20 carbon
atoms and include groups such as acetyl, propionyl, butyryl,
isobutyryl, lauroyl, myristoyl and stearoyl 3-carboxypenta-
decanoyl. Preferably, the acyl group is a group having the
formula -C(O)R4 wherein R4 denotes a monovalent hydrocarbon
group. The monovalent hydrocarbon groups of R4 are as
delineated above for R. It is preferred that R4 is a lower
alkyl group such as methyl, ethyl or butyl.
In the above formula for Component (C), preferably
a has an average value from 20 to 500, b has an average
value from 1 to 500, and c, d and a independently have an
average value from 1 to 50. It is especially preferred that
a has an average value from 100 to 300, b has an average
value from 5 to 50 and c, d and a independently have an
- CA 02271900 1999-OS-11
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average value from 1 to 36. It is highly preferred that a
has an average value from 150 to 200.
Preferably Component (C) is an oxyalkylene-
modified organopolysiloxane compound having the formula
Me3Si0(Me2Si0)a(MeXSiO)bSiMe3, wherein X is selected from
the group consisting of -(CH2)n(OC2H4)cOH,
- ( CH2 ) n ( OC2H4 ) c (OC3H6 ) dOH, - ( CH2 ) n ( OC2H4 ) cOCH3 ,
- ( CH2 ) n ( OC2H4 ) c ( OC3 H6 ) dOCH3 , - ( CH2 ) n ( OC2H4 ) cOC ( O ) CH3
and
-(CH2)n(OC2H4)c(OC3H6)dOC(O)CH3 wherein Me denotes methyl, a
has an average value from 100 to 300, b has an average value
from 1 to 50, n has a value of 2 to 10, c has an average
value of 1 to 36 and d has an average value of 1 to 36. In
a preferred embodiment of this invention, a has an average
value from 150 to 200. Component (C) can also comprise a
mixture of the above delineated oxyalkylene-modified
organopolysiloxanes.
Component (D) of the present invention is at least
one surfactant from alkylated sulfonated diphenyloxides.
Suitable alkylated sulfonated diphenyloxide surfactants are
exemplified by a compound having the following formula or a
mixture comprising compounds having the following formula:
~RS~m ~R5)n
\ ~\ ~ ~~//
~5~3 M+~x ~5~3 M+~Y
wherein each R5 is independently selected from the group
. CA 02271900 1999-OS-11
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consisting of saturated alkyl radicals, substituted
saturated alkyl radical, unsaturated alkyl radicals and
substituted unsaturated alkyl radicals, each m and n is
independently 0, 1 or 2, each M is independently selected
from the group consisting of hydrogen, an alkali metal, an
alkaline earth metal, ammonium and substituted ammonium and
each x and y are individually 0, 1 or 2. Each R5 group can
be independently an alkyl group having from 3 to 24 carbon
atoms, preferably 10 to 20 carbon atoms and most preferably
12 to 16 carbon atoms, with 16 carbon atoms being especially
preferred. The alkyl groups can be linear, branched or
cyclic, with linear or branched radicals being preferred.
The ammonium ion radicals are of the formula (R')3NH wherein
each R' is independently hydrogen, a Cl-C4 alkyl or a C1-C4
hydroxyalkyl radical. Illustrative C1-C4 alkyl or
hydroxyalkyl radicals include methyl, ethyl, propyl,
isopropyl, butyl, hydroxymethyl and hydroxyethyl. Typical
ammonium ion radicals include ammonium (NH4), methylammonium
(CH3NH3), ethylammonium (C2H5NH3), dimethylammonium
((CH3)2NH2), methylethylammonium (CH3NH2C2H5),
trimethylammonium ((CH3)3NH) dimethylbutylammonium
((CH3)2NHC4H9) hydroxyethylammonium (HOCH2CH2NH3) and
methylhydroxyethylammonium (CH3NH2CH2CH20H). Preferably,
each M is selected from the group consisting of hydrogen,
sodium, potassium or ammonium.
Alkylated diphenyl oxide sulfonates and their
methods of preparation are well-known and reference is made
CA 02271900 1999-OS-11
14
thereto for the purposes of this invention. Representative
methods of preparation of sulfonates are disclosed in U.S.
Patent Nos. 3,264,242, 3,634,272 and 3,945,437. Commercial
methods of preparation of the alkylated diphenyl oxide
sulfonates generally do not produce species which are
exclusively monoalkylated, monosulfonated, dialkylated or
disulfonated. The commercial available species are
predominantly (greater than 90 percent) disulfonated and are
a mixture of mono- and dialkylated with the percentage of
dialkylation being 15 to 25 and the percentage of mono-
alkylation being 75 to 85 percent. Most typically, the
commercially available species are 80 percent monoalkylated
and 20 percent dialkylated.
Commercially available materials suitable as
Component (D) are exemplified by sodium hexyl diphenyloxide
disulfonate, at a concentration of 45%, a liquid anionic
surfactant (available as Dowfax~ C6L from The Dow Chemical
Company, Midland, Mi.), sodium decyl diphenyloxide
disulfonate, at a concentration of 45%, a liquid anionic
surfactant (available as DowfaxTM C10L from The Dow Chemical
Company, Midland, Mi.), sodium dodecyl diphenyloxide
disulfonate, at a concentration of 45%, a liquid anionic
surfactant having an HLB of 16.7 (available as DowfaxTM 2A1
or DowfaxtM 2EP from The Dow Chemical Company, Midland, Mi.),
sodium dodecyl diphenyloxide disulfonate, at a concentration
of 92%, a powdered anionic surfactant having an HLB of 16.7
(available as DowfaxTM 2A1-D from The Dow Chemical Company,
Midland, Mi.), sodium n-decyl diphenyloxide disulfonate,- at
CA 02271900 1999-OS-11
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a concentration of 45%, a liquid anionic surfactant having
an HLB of 17.8 (available as Dowfax~" 3B2 from The Dow
Chemical Company, Midland, Mi.), sodium n-decyl
diphenyloxide disulfonate, at a concentration of 92%, a
powdered anionic surfactant having an HLB of 17.8 (available
as Dowfax~" 3B2-D from The Dow Chemical Company, Midland,
Mi.), DowfaxT""2000, at a concentration of 36%, a proprietary
liquid anionic surfactant (available from The Dow Chemical
Company, Midland, Mi.), sodium n-hexadecyl diphenyloxide
disulfonate, at a concentration of 35%, a liquid anionic
surfactant having an HLB of 14.4 (available as Dowfax~" 8390
Solution Surfactant from The Dow Chemical Company, Midland,
Mi.), and sodium n-hexadecyl diphenyloxide disulfonate, at a
concentration of 92%, a powdered anionic surfactant having
an HLB of 14.4 (available as DowfaxT"" 8390-D from The Dow
Chemical Company, Midland, Mi.).
The wood chips (A), aqueous cooking liquor (B),
oxyalkylene-modified organopolysiloxane compound (C) and
alkylated sulfonated diphenyloxide surfactant (D) may be
added to a digester in any order. For example, the
oxyalkylene-modified organopolysiloxane compound (C) and
alkylated sulfonated diphenyloxide surfactant (D) of this
invention may be added directly to the digester before or
after the digester is charged with chips and liquor or may
be added to the liquor or chips prior to addition of the
liquor or chips to the digester. Preferably, the
oxyalkylene-modified organopolysiloxane (C) and alkylated
sulfonated diphenyloxide surfactant (D) are added to cooking
CA 02271900 1999-OS-11
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liquor (B) before it is circulated through the wood chips
(A) in a digester.
The term ~~digester~~ as used herein, refers to a
cylindrical metal vessel, used chiefly in the preparation of
wood pulp for papermaking, in which lignin is separated from
cellulose by chemical means. Standard commercial digesters
are 12 feet in diameter and 45 feet high with a wall
thickness of 2 inches. These types of digesters hold 20
cords of wood. Elevated pressure and temperature are
applied to the mixture to separate, by dissolution, as
completely as possible, the lignin content of the cellulosic
fibers of the wood. Usually, steam to heat and pressurize
the digester is supplied through a pipe to the digester
(i.e., direct steam injection). The heat can also be
supplied by circulating steam and a heat exchanger. The
oxyalkylene-modified organopolysiloxane (C) and alkylated
sulfonated diphenyloxide surfactant (D) can be used in Kraft
pulping using either a continuous or a batch digester,
continuous digestion Kraft pulping with extended
delignification using staged alkali addition and
countercurrent final cooking, batch digestion Kraft pulping
with extended delignification using rapid liquor
displacement and cold blowing techniques or Kraft-
anthraquinone pulping to achieve enhanced delignification
using either a continuous or batch digestion stage.
Usually the concentration of oxyalkylene-modified
organopolysiloxane compound (C) and alkylated sulfonated
surfactant (D) ranges from 50 to 1,000 weight parts per
CA 02271900 1999-OS-11
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million (based on dry weight of wood chips), more preferably
from 50 to 500 parts per million, and most preferably from
50 to 300 parts per million.
In the preferred embodiment of the invention, the
amount of oxyalkylene-modified organopolysiloxane compound
(C) ranges from 10 parts to 90 parts by weight and the
amount of alkylated sulfonated diphenyloxide surfactant,
Component (D) ranges from 90 parts to 10 parts by weight'per
100 parts of the combined weights of (C) and (D). In the
process of the invention, it is even more preferred that the
amount of Component ,(C) ranges from 25 parts to 75 parts by
weight and Component (D) ranges from 75 parts to 25 parts by
weight per 100 parts of the combined weights of (C) and (D).
Those skilled in the art will appreciate that
commercially available alkylated sulfonated diphenyloxide
surfactants are often diluted with fairly substantial
quantities of water (up to 50%, by weight.) The preferred
ranges for the use of Components (C) and (D) as set forth
above are based upon "solids" content, exclusive of such
water content.
In manufacturing operations, it is preferable to
add the oxyalkylene-modified organopolysiloxane compound (C)
and alkylated sulfonated diphenyloxide surfactant (D) as an
aqueous solution so as to facilitate the admixture of the
additives with the liquor during digestion. The mixture of
Step (I) is generally formed at temperatures of below 80°C.
Step (II) in the chemical pulping process of this
invention comprises heating the mixture of step (I) to a
CA 02271900 1999-OS-11
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temperature of at least 150°C for a period of time to
substantially delignify the wood chips (A) so as to form a
pulp therefrom. Preferably, the mixture of Step (I) is
heated to temperatures of from 150 to 180°C. This
temperature is then maintained for a period of time to
substantially delignify the wood chips (A) so as to form a
pulp therefrom, generally from 0.5 hours to 6 hours,
preferably from 0.5 hours to 3 hours.
Step (III) in the chemical pulping process of this
invention comprises maintaining the heated mixture of step
(II) at a pressure to prevent boiling of aqueous cooking
liquor (B) during step (II). Generally steam is allowed to
enter the digester until a maximum pressure of from 100 to
150 psi is reached. This pressure is then maintained from
0.5 hours to 6 hours, preferably from 0.5 hours to 3 hours.
Step (IV) in the chemical pulping process of this
invention comprises recovering the pulp from said mixture.
The pulp can be recovered by any method known to those
skilled in the art. Typically, the pulp is recovered by a
method comprising discharging the cooked chips from a
digester under pressure, the mechanical force of which
breaks up the wood chips into individual fibers, producing
pulp which contains fiber and exhausted liquor which is
black in color, washing the black liquor from the pulp and
then screening the pulp to remove uncooked chips and other
large fragments.
CA 02271900 1999-OS-11
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It should be pointed out that organopolysiloxanes
are also employed for suppressing foam in the washing stages
of some Kraft mills. As such, and because of normal black
liquor recycle procedures, trace amounts of organopoly-
siloxanes may have been known to inadvertently enter a
digester with the recycled black liquor. The trace amounts
of organopolysiloxane have produced no recognizable benefits
to the Kraft pulps and accordingly the small amounts of
organopolysiloxane compounds employed in accordance with the
present invention are distinguishable from the trace amounts
which inadvertently enter a digester through the normal use
of certain organosilicon compounds for foam control in the
pulp washing phases of the processes.
The combination of oxyalkylene-modified
organopolysiloxane compound (C) and alkylated sulfonated
diphenyloxide surfactant (D) improve the physical
characteristics of pulp treated therewith, especially the
tensile and tear strength of the produced pulp.
The Kappa number associated with a delignified
pulp represents a measure of residual lignin content. Kappa
number are generally measured in accordance with TAPPI
Classical Method T 236 cm-85. Those skilled in the art will
appreciate that the degree of delignification which is
desirable for a given chemical pulping process is directly
related to the desired end product. For instance, if the
desired end product is unbleached Kraft liner, the target
Kappa number generally ranges from 65 to 115, indicating a
~
CA 02271900 1999-OS-11
fairly high level of residual lignin. Whereas in bleached
Kraft pulp, suitable for use in fine paper, such as writing
paper, the desired Kappa number target may be from 25 to 35,
indicating a much higher degree of delignification. Thus,
in accordance with the present invention, the heating step
(II) is limited such that the mixture is heated to a
temperature in excess of 150°C. for a period of time to
substantially delignify the (A) wood chips so as to form a
pulp therefrom. As used herein, the term "substantially
delignify" means that the delignification has taken place to
the desired extent, depending upon the desired end product.
Examples
The performance of the chemical pulping process of
this invention was compared to the performance of Kraft
cooks completed with and without anthraquinone. The test
cooks were carried out under typical Kraft pulp cooking
conditions utilizing a laboratory scale digester equipped
with temperature and pressure monitoring devices. Duplicate
digester runs were completed in each case to measure the
efficacy of the method of the invention.
The wood chips utilized in this study were
conventional Southern Pine softwood chips obtained from a
commercial pulping operation. The moisture content of the
chips was measured and the wood chips were loaded into the
laboratory digester on a dry weight basis. Thereafter, an
aqueous cooking liquor in the form of a white liquor with an
CA 02271900 1999-OS-11
21
effective alkali content of 16.5% by weight (expressed as
Na20) and a sulfidity of 29.9% by weight (expressed as
Na20), in accordance with that hereinabove described, was
added to the digester. The weight ratio of the cooking
liquor to wood chips was 3.7:1.
In the first run series (RUN1), no additions of
oxyalkylene-modified organopolysiloxanes, alkylated
disulfonated diphenyloxide surfactant or anthraquinone or
its derivatives were made to the white liquor. In the
second run series, RUN2, anthraquinone (at 600 ppm) was
added to the white liquor prior to addition to the
laboratory digester. In the third and fourth run series,
RUN3 and RUN4, a mixture of 45 weight parts of oxyalkylene-
modified organopolysiloxane, 45 weight parts of alkylated
disulfonated diphenyloxide surfactant and 10 weight parts of
water were added to the white liquor at a level of 500 ppm
prior to addition to the digester.
The oxyalkylene-modified organopolysiloxane used
in RUN3 was a random rake copolymer having the general
formula Me3Si0(Me2Si0)a(MeXSiO)bSiMe3 wherein Me denotes
methyl and is used hereafter with the same meaning, a is
157, b is 21, X is a polyoxyalkylene group having the
formula -C3H6-(OC2H4)c-(OC3H6)d-OH wherein c is 18 and d is
18.
The oxyalkylene-modified organopolysiloxane used
in RUN4 was a random rake copolymer have the general formula
CA 02271900 1999-OS-11
22
Me3Si0(Me2Si0)a(MeXSiO)bSiMe3 wherein a is 25, b is 6, X is
a polyoxyalkylene group having the formula
-C3H6-(OC2H4)c-(OC3H6)d-OH wherein c is 10 and d is 4.
The alkylated disulfonated diphenyloxide
surfactant was Dowfax~ 8390 Solution Surfactant (sodium n-
hexadecyl diphenyloxide disulfonate, at a concentration pf
35%, a liquid anionic surfactant having an HLB of 14.4, from
The Dow Chemical Company, Midland, Mi.).
All digester cooks reported in the examples were
completed at a cooking temperature of 171°C. The time to
obtain the specified cooking temperature was 60 minutes and
once obtained, the cooking temperature was held constant for
80 minutes such that the H-factor for each of the laboratory
cooks was 1450. The pressure during each digester cook
reached a maximum of 110 psi. The cooking conditions were
to substantially delignify the wood chips and form a pulp
therefrom. After the cooking was complete, the digester was
vented to reduce the pressure to atmospheric conditions.
The pulp was washed, dewatered and screened on a standard
eight cut laboratory flat screen. The screened pulp yield,
percentage pulp rejects and total pulp yield were
determined. The residual effective alkali and residual
active alkali of the spent liquor was measured. These
results are reported in Table 1.
The screened pulp from each run series was
combined to form a composite pulp. Thereafter aliquots of
each composite pulp sample were subjected to mechanical
CA 02271900 1999-OS-11
23
treatment (beating) in accordance with TAPPI classical test
method T 248 cm-85, until Canadian Standard Freeness values
of 725, 675, 575, 425, 300 and 250 mls were obtained. Five
standard 60 g/m2 handsheets were cast from each pulp aliquot
at each Freeness value in accordance with TAPPI official
test method T 205 om-88. The handsheets were then
conditioned and tested for tensile strength and tearing
resistance in accordance with TAPPI official test method T
220 om-88. The strength indices reported in Tables 2-5 were
calculated from the conditioned weight of the handsheet and
represent the numerical average obtained from the five
handsheets.
Table 1
RUN1 RUN2 RUN3 RUN4
Residual Effective
Alkali (g/1 as NaOH) 13.64 11.78 11.78 13.33
Residual Active
Alkali (g/1 as NaOH) 17.05 17.36 16.12 17.67
Total Yield (%) 44.02 44.01 43.68 43.40
Screened Yield (%) 43.45 43.45 43.05 42.65
KAPPA Number 30.4 25.60 28.95 27.80
CA 02271900 1999-OS-11
24
Table 2
RUN1
PFI Revolutions 0 2000 4000 8000 10000 12000
Canadian Standard
Freeness (mls) 736 674 587 444 353 246
Tear Index
(mNm2/g) 23.7 18.8 16.7 14.9 13.5 13.1
Tensile Index
(Nm/g) 39.8 71.4 79.9 83.6 87.5 90.3
Table 3
RUN2
PFI Revolutions 0 2000 4000 8000 10000 12000
Canadian Standard
Freeness (mls) 734 674 596 487 320 256
Tear Index
(mNm2/g) 2 4.9 17.6 14.7 14.0 12.6 12.5
Tensile Index
(Nm/g) 3 8.6 73.7 85.4 81.5 91.4 86.1
- CA 02271900 1999-OS-11
Table 4
RUN3
PFI Revolutions 0 2000 4000 8000 10000 12000
Canadian Standard
Freeness (mls) 734 684 580 430 290 205
Tear Index
(mNm2/g) 27.2 19.1 16.9 14.4 14.4 13.8
Tensile Index
(Nm/g) 41.7 66.8 79.2 80.8 93.0 94.9
Table 5
RUN4
PFI Revolutions 0 2000 4000 8000 10000 12000
Canadian Standard
Freeness (mls) 722 683 602 388 304 232
Tear Index
(mNm2/g) 23.7 17.1 15.6 13.2 12.6 12.4
Tensile Index
(Nm/g) 41.2 66.6 70.3 85.7 95.6 94.2
The remainder of the p from RUN1,
composite pul
RUN2, RUN3 and RUN4 of pulp
were treated in a
series
bleaching processes obtain a minimum target
to TAPPI
brightness (also knownas GE brightness) of 86. TAPPI
brightness is determined dard handsheets
by irradiating stan
with 457nm light at incident angle of 45 degrees and
an
measuring the percentage degrees. The
of reflectance at
0
- CA 02271900 1999-OS-11
26
procedure for calibration and measuring TAPPI brightness is
described in TAPPI Official Test Method T 452 om-92. The
bleaching sequence consisted of an Oxygen treatment stage
followed by a Chlorine Dioxide stage further followed by an
Extraction Stage with oxygen and peroxide applied and
finally an additional Chlorine Dioxide Stage. The industry
designation for this bleaching sequence being: ODIEopD2.
The CED viscosity of each final bleached pulp was also
measured per TAPPI classical test method T 254 cm-85. GE
Brightness and CED Viscosity results are reported in Table
6.
Table 6
RUN1 RUN2 RUN3 RUN4
GE Brightness 87.4 88.1 88.3 87.8
CED Viscosity (cps) 18.5 17.2 19.0 18.6
Thereafter, aliquots of bleached pulp from each
run series were subjected to mechanical treatment (beating)
in accordance with TAPPI classical test method T 248 cm-85
until Canadian Standard Freeness values of 725, 675, 550,
425, 300 and 250 mls, respectively, were obtained. Five
standard 60 g/m2 handsheets were cast from aliquots of pulp
at each Freeness value in accordance with TAPPI official
test method T 205 om-88. The handsheets were then
conditioned and tested for tensile strength and tearing
resistance in accordance with TAPPI official test method T
220 om-88. The bleached strength indices reported in Tables
- CA 02271900 1999-OS-11
27
7 - 10 were calculated from the conditioned weight of the
handsheet and represent the numerical average obtained from
the five handsheets.
Table 7
RUN1
PFI Revolutions0 2000 4000 6000 8000 10000
Canadian Standard
Freeness (mls) 724 626 497 430 319 231
Tear Index
(mNm2/g) 25.7 16.7 14.0 13.5 12.3 13.1
Tensile Index
(Nm/g) 33.3 81.0 86.8 93.6 96.1 99.0
Tab le 8
RUN2
PFI Revolutions0 2000 4000 6000 8000 10000
Canadian Standard
Freeness (mls) 732 618 529 403 374 200
Tear Index
(mNm2/g) 21.9 15.8 14.3 12.9 12.8 12.5
Tensile Index
(Nm/g) 24.5 74.4 81.4 90.8 87.9 94.9
- CA 02271900 1999-OS-11
28
Table 9
RUN3
PFI Revolutions 0 2000 4000 6000 8000 12000
Canadian Standard
Freeness (mls) 722 627 538 408 348 272
Tear Index
(mNm2/g) 27.2 19.1 16.9 14.4 14.4 13.8
Tensile Index
(Nm/g) 26.1 80.4 86.7 88.1 88.4 97.1
Table 10
RUN4
PFI Revolutions 0 2000 4000 6000 8000 10000
Canadian Standard
Freeness (mls) 722 632 544 455 368 279
Tear Index
(mNm2/g) 21.4 16.2 13.6 12.5 13.2 13.3
Tensile Index
(Nm/g) 26.1 76.4 82.8 87.3 90.5 93.2
Referring now to Table 1, be seen that the
it can
chemical pulping process of this invention (RUN and RUN
3 4)
produces pulp having lower KAPPA
a number when
compared to
pulp produced by a prior art chemicalpulping ess
proc
(RUNl).
Referring to Tables 2-5, it can be seen that the
chemical pulping process of this invention (RUN3 and RUN4)
- CA 02271900 1999-OS-11
' ~,
29
produces pulp having improved fiber strength when compared
to the pulp produced by prior art chemical pulping processes
(RUN1 and RUN2). Specifically, the tear indices of the pulp
measured and reported in Table 4 (RUN3) produced by the
chemical pulping process of this invention, is measurably
higher than the tear indices of the pulp reported in Table 2
(RUN1) and Table 3 (RUN2), produced by prior art chemical
pulping processes, at all levels of Canadian Standard
Freeness. In addition, the tensile indices of the pulp
measured and reported in Table 5 (RUN4), produced by the
chemical pulping process of this invention, are measurably
higher than the tensile indices of the pulp reported in
Table 2 (RUN1) and Table 3 (RUN2), produced by prior art
chemical pulping processes, at a Canadian Standard Freeness
of 300 to 500.
Referring to Tables 7-10, where the fiber strength
characteristics of the produced pulp were measured after the
pulp had been bleached, it can be seen that the chemical
pulping process of this invention Table 9 (RUN3) produces
pulp having improved tear indices when compared to pulp
produced by prior art chemical pulping processes Table 7
(RUN1) and Table 8 (RUN2). Further, particularly beneficial
results are noted in the relationship between tensile index
and tear index provided in Table 9 (RUN 3), the chemical
pulping process of this invention, when compared to the
tensile index-tear index relationship of the prior art
chemical pulping processes in Table 7 (RUN 1) and Table~8
CA 02271900 1999-OS-11
~ ', ' ,
(RUN 2). At any specified tensile index, the tear index
obtained on pulp from the chemical pulping process of this
invention Table 9 (RUN 3) is measurably greater than the
tear index obtained at the same tensile index on pulp from
either of the prior art chemical pulping processes Table 7
(RUN 1) and Table 8 (RUN 2).
