Note: Descriptions are shown in the official language in which they were submitted.
53~
TITLE
PROCESS FOR I~æROVED ALRALINE OXIDATIVE
DELIGNIFICATION OF OE LLULOSE PULP
Field of the Invention
The in~ention relates to an improved method
for the alkaline oxidative delignification of
lignocellul~sic pulp. In particular, this invention
relates to the treatment of the pulp with nitrosating
agents in an acidic and oxygen environment under
intense mixing conditions before the alkaline oxidative
stage in a bleach sequence.
sackqround to the Invention
Pulping is the process by which
lignocellulosic materials are converted to a fibrous
mass. The process can be performed by mechanical,
thermal or chemical means or a combination of these
means. In che~ical pulping, lignocellulosic materials
such as wood chips are cooked with appropriate
chemicals in an aqueous solution at elevated
temperatures and pressures. Kraft (alkaline) pulping
and sulfite (acidic) pulping are principal chemical
methods employed. Others inc:Lude soda, bisulfite and
semichemical processes such as high yield Kraft, high
yield sulfite and neutral sulfite (NSSC) processes.
The Kraft process, the most widely used
process, can be used with a wide variety of species and
tolerates bark whereas the sulfite, soda and NSSC
processes are less tolerant. The Kraft process
produces the highest strength pulp while the sulfite
process produces a bright pulp that is easy to bleach
to full brightness.
CH~1~72 35
The pulping and bleach sequence chosen depend
on the available lignocellulosic starting material and
the end use envisioned for the pulp.
Lignocellulosic pulp from a pulping process
is washed and subjected to subsequent treatment (bleach
sequence) to remove residual lignin resulting in
brighter pulp with improved optical and mechanical
properties. Chemical pulping processes remove a major
portion of the original lignin. Most of the subsequent
process (bleach sequence) is directed towards removing
the rest of the lignin, preferably under conditions
that do not significantly degrade the cellulose and
hemicellulose in the lignocellulosic material, to give
the desired qualities in the end products.
Lignin is a complex biopolymer known to
contain phenolic groups. Degrading or modifying these
phenolic groups allows the lignin to be easily
solubilized and removed. Preferably, the means used to
modify the phenolic groups and remove the lignin should
be ones that do not degrade the accompanying cellulose
structures.
Lignin can be removed from chemically
digested lignocellulosic pulps by treatment with strong
oxidizing agents such as active chlorine che~icals
(chlorine gas). But, with the addition of chlorine,
noxious chloro-organics including chloroform,
chlorophenols and chlorodioxins are formed. Since most
chloro-organic wastes cannot be easily destroyed by
biological means or by burning in the recovery boilers
to recover energy because of their corrosivity and
chloro-organic emission potential, they pose serious
and increasing environmental concerns. Because of
these concerns, paper mills desire to minimize the
amount of chlorine used to reduce both toxic liquid
wastes and air emissions.
6~
Chlorine dioxide can replace chlorine gas as
an oxidizing agent but the production of chlorine
dioxide requires three times as much electrical energy
per kilogram of active chlorine as chlorine gas.
oxygen can be used instead of chlorine to
partially delignify the pulp and thereby reduce or
e.liminate the amount of chlorine needed in the
subsequent stages. With the reduction of chlorine, the
formation of toxic and carcinogenic chloro-organics
should be substantially reduced and the environmental
problems associated with the bleaching process would be
less severe. Also, the effluent from the oxygen
delignification step can be incinerated for energy
recovery.
Alkaline oxidative delignification, however,
has required high pressures and results in severe
cellulose degradation (lost selectivity) if the degree
of delignification is carried to beyond about 50% of
the remaining lignin from the pulping stage. Several
processes have been taught to overcome these
deficiencies. The purpose of these processes is to aid
in a more efficient and selective alkaline oxidative
stage by modification of the lignin so that it is more
susceptible to oxidation.
Clarke in ~The Action of Nitrogen Dioxide on
Unbleached Pulp, Part I~ Pap~r Trade Journal, Vol. 118,
No. 8 (TAPPI Section), pp. 62 - 66 (1944) teaches using
nitrogen dioxide (N02) as a direct lignocellulosic pulp
delignifying agent to replace or reduce chlorine. He
30 heats li~uid N02 and the aqueous pulp at 90C for 1 to
1.5 hours and then extracts the lignin with hot
caustic. To avoid considerable damage to the
cellulose, Clarke advises only partially bleaching with
N02. Clarke theorizes that the bleaching occurs from
the combined action of the nitrous and nitric acids
3~
formed when the NO2 reacts with the water. He ~elieves
that the nitrous acid first modifies the lignin so that
it can more easily be attacked by the nitric acid.
In U.S. Patent 4,076,579, Brink reveals prior
treatment of the pulp with aqueous nitric acid or
nitric acid made in situ from nitric oxide, oxygen and
water. The aqueous-nitric acid solutions can include an
array of compounds, ions and radicals such as nitrogen
trioxide, nitrogen tetroxide, nitric oxide, nitrate
ions, nitrite ions, nitronium ions and nitrosonium
ions. Water content is critical to avoid cellulose
degradation but not inhibit penetration of nitric acid
into the lignin.
In U.S. Patent No. 4,406,735, Samuelson
discloses delignifying chemically digested pulp with
oxygen gas in the presencP of an alkali after
activation of the pulp by bringing it into intimate
contact with gaseous NO2 at 20-100C and washing the
activated pulp. NO2 and oxygen is taught as reacting
with the lignocellulosic pulp as opposed to the
reactions with nitric acid that Brink refers to.
In U.S. Patent No. 4,435,271, Samuelson
discloses pretreating chemica] pulp with NO2 and then
delignifying with alkaline oxygen. The NO2 is added to
the chemical pulp in an amount so that the nitrogen
monoxide (NO) formed in the reaction is consumed and
essentially none of the N02 and NO remains at the
conclusion of the activation stage. The pretreatment
step is followed by oxygen treatment of the modified
pulp and extraction in the presence of an alkali.
In U.S. Patent No. 4,445,969, Samuelson
discloses a process for delignifying and bleaching the
lignocellulosic pulp in three stages - (1) an
activation step where the water containing pulp is
mixed with gaseous NO and/or NO2 and oxygen and,
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optionally, with nitric acid; (2) a wash step and
extraction with an alkali such as a carbonate; and (3)
a second alkaline step.
In V.S. Patent No. 4,602,982, Samuelson
improves upon U.S. 4,445,969 with the introduction of
at least 5 weight (wt.%) sodium nitrate with gaseous
NO2, water and oxygen along with, optionally, nitric
acid. The pulp is then washed and treated with an
alkaline solution in the presence of oxygen. Samuelson
lo suggests that nitrolignins are formed in the
pretreatment stage which reacts preferentially with the
reactive oxygen species which would otherwise degrade
the cellulose.
Chemical Abstracts 52:14158e (Kuniak et al.,
"Delignification of Wood with Nitric Acid" PaPir a
Celulosa 12, 6 - 11 (1957)) states that use of l or
less weight percent to 3 weight percent nitric acid can
be used to delignify the pulp without cellulose
degradation.
Summary of the Invention
A process has recently been discovered that
improves delignification and hleaching by intimately
contacting lignocellulosic pulp, particularly
chemically digested lignocellulosic pulp, under high
intensity mixing conditions with sufficient
liquid-phase nitrosating agents in an acidic and oxygen
environment prior to an alkaline oxidative stage in a
bleach sequence.
The nitrosating agent is liquid phase, that
is, a solution or a pure liquid at ambient temperature
and pressure, and includes any compound that will
freely contribute predominantly active nl~rosonium ions
(NO(+)) under reaction conditions. For the purposes of
this invention, nitroacidium ions (~2NO2(~)) are
2~0~i3~3
included in the definition of nitrosonium ions in that
they are hydrated nitrosonium ionsO By predominantly,it
is meant that greater than 60 % of the nitrogen ln ~he
nitrosating compound is contributed as NO(+). Thus,
it comprises NO-X wherein X is a halogen, OH, O-SO3H,
O-SO2H, or other inorganic groups such as
hexafluorobromate, pyrosulfate, phosphate,
hexa1uoroplatinate, hexafluorostanate, trisulfate,
tetrachloroferrate(III), tetrachloroborate,
chlorosulfate, difluorochlorate, fluorosulfate,
tetrachloraluminate and tetraflouroborate, or organic
compounds in wnich the NO is bound to an oxygen or
sulfur in the organic molecule. Liquid nitrosating
agents such as solutions of nitrosylsulfuric ~cid
(NSA), of nitrosyl chloride (NOCl) and of nitrosyl
tetrafluoroborate (NOBF4) are particularly useful.
Alternatively, under appropriate conditions,
the nitrosating agent may be made in situ by adding a
high enough concentration of acid to the pulp before or
concurrently with a water-soluble inorganic nitrite
such as sodium nitrite to acidify the pulp to a pH of
less than 4. Also, the water--soluble inorganic nitrite
may be reacted with sufficient acid to yield an acidic
solution of nitrous acid, which then can be added to
the pulp as a nitrosating agent. The acidity o~ the
nitrous acid solution should be such that the resultant
pH upon addition to the pulp is in the range of about
1.7 to 4, preferably 1.8 to 3.4. Preferably, the pulp
should be preacidified before addition of the nitrous
acid solution to a pH of less than 4.
The nitrosating agent is present in a
sufficient amount to provide about 0.1 to 1.2 wt.%,
preferably 0.1 to 1.0 wt.% active nitrosonium ion NO(+)
on a oven-dried (OD) pulp basis.
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The mixing conditions are such that the
nitrosating agent and the oxygen are intimately,
uniformly and rapidly contacted with the pulp fiber so
that desired reactions occur with the lignin before the
NO(~) becomes inactive, that is, equilibrates to N02-
in the water with the pulp. Mixing is preferably done
in a high-shear mixer at a pulp consistency of at least
5 weight percent in wa'er, more preferably at medium to
high consistency, so as to distribute the agents
uniformly and rapidly in the pulp matrix. Mixing
intensity must be high enough that the reaction mixture
becomes fluidized or fluid-like in behavior in the
mixing zone, the nitrosating agent and pulp being
contacted in the mixing zone.
The pH at which the pretreatment takes place
is 1.7 to 4, preferahly 1.8 to 3.4.
The oxygen, which may be added as molecular
oxygen, as an oxygen-containing gas such as air or as
hydrogen peroxide, must be present at least in a
stoichiometric amount. By stoichiometric, i~ is meant
one gram atom of oxygen per gram mole of NO(~) that is
theoretically added to the system. The theoretical
amount of NO(+) added is the amount o~ NO(+) moiety in
the chemical structure of the nitrosating agent. Thus,
undissociated nitrous acid (NO-OH) will have 100~ of
its nitrogen in the form of NO(+) and 63.8 wt.% NO(~)
in thQ molecule.
After the pretreatment with sufficient
liquid-phase nitrosating agents under the consistency,
acidic, oxygen and mixing conditions o~ this invention,
the treated pulp is optionally washed before treatment
with an alkali and oxidative compound according to
known alkaline oxidative stage conditions~
The present invention has several advantages,
the main advantage being that greater delignification
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of the pulp can be accomplished with lower cellulose
degradation than when the pretreatment is not made.
Also, as compared to the use of nitrogen dioxide and
nitrogen monoxide which are gases under reaction
conditions, improvements in safety and environmental
protection associated with not having to handle gases
are made with the present invention. Further, the
present invention, which requires mixing only liquids
and solids, presents fewer complications associated
with distribution of reagents and handling equipment
than the processes o~ the prior art which require
mixing gases with liquids and solids. Liquid-phase
agents are more reactive and selective since there is
more efficient mass transfer across the aqueous layer
on the pulp fibers.
It is thouqht that use of nitric acid forming
chemicals such as N02, NOx and nitrate ions of the
prior art creates an oxidizing environment that results
in cellulose attack by nitric acid oxidation. Thus,
- both nitration of lignin and degradation of cellulose
occur simultaneously because of the occurrence of both
nitrating and oxidizing chemical reactions.
It is thought that, since the present process
avoids the use of nitric acid forming chemicals and
assures reaction of the active NO(+) before the NO(~)
becomes inactive by equilibrating to N02- in the water
with the pulp, the nitrosating chemicals do not cause
as much cellulose degradation. The nitrosating
chemicals are felt to rapidly nitrosate the lignin
structure by introducing NO groups in the lignin to
form nitrosolignins without the concurrent formation of
nitric acid. The nitrosolignins, in the presence of at
least a stoichiometric amount o~ oxygen, are oxidized
to nitrolignins. The nitrolignins, not removed in the
optional wash step which can follow, are then
~S,3~;~
g
efficiently oxidized, hydrolyzed and solubilized in the
alkaline oxidation stage.
Details of the Invention
A wide range of pulps can be treated by the
methods described in the invention. The
lignocellulosic pulp treated by the process of this
invention is preferably from a Kraft process but may be
from other chemical, semichemical, chemi-mechanical
processes, particularly sulfite, soda, high yield
Kraft, high yield sulfite or NSSC processes. The pulp
may also be from a mechanical or thermomechanical
process. Particularly in the case of chemically
digested pulp, the pulp generally is washed prior to
being fed to subsequent processing (a delignification
and bleach sequence) that includes one or more alkaline
oxidative stages as well as stages using chlorine,
chlorine dioxide, hydrogen peroxide and other bleaching
agents.
The pretreatment stage of this invention is
inserted in the bleach sequence prior to any of the
alkaline oxidative stages, preferably before the first
such stage. The pulp that is to be treated ln this
stage is herein also referred to as "untreated pulp"
and the pulp that has bee~ treated in this stage is
herein also referred to as "treated pulp".
The consistency of the untreated pulp can
vary over a wide range but should be greater than about
5 wt.%. Preferably, the consistency should be in the
range of 5 to 30 wt.%, more preferably 8 to 15 wt.%.
The nitrosating agent is liquid-phase, that
is, a solution or a pure liquid at ambient temperature
and pressure, and is defined as any compound that will
freely contribute predominantly active nitrosonium ions
(~0(+)) under reaction conditions. For the purposes of
~5~
--10--
this invention, nitroacidium ions (H2NO2(+)) are
included in the definition of nitrosonium ions in that
they are hydrated nitrosonium ions. By predominantly,
it is meant that greater than 60 % of the nitrogen in
the nitrosating compound is contributed as NO(+).
Thus, it comprises NO-X wherein X is a halogen, O~,
O-SO3H, O-SO2H, or other inorganic groups such as
hexafluorobromate, pyrosulfate, phosphate,
hexafluoroplatinate, hexafluorostanate, trisulfate,
tetrachloroferrate(III~, tetrachloroborate,
chlorosulfate, difluorochlorate, fluorosulfate,
tetrachloraluminate and tetraflouroborate, or organic
compounds in which the NO i5 bound to an oxygen or
sulfur in the organic molecule.
Liquid nitrosating agents such as solutions
of nitrosy]sulfuric acid (NSA), of nitrosyl chloride
(NOCl) and of nitrosyl tetrafluoroborate (NOBF4) are
particularly useful with NSA being the most preferred.
Preferably, sulfuric acid is used to dissolve the
nitrosating agent.
The pH of the pretreatment must be acidic for
the process to be successful. Preferably, the pH is in
the range of 1.7 to 4, more preferably 1.8 to 3.4 and
most preferably the pH is 1.9 to 3Ø If the pH is too
low, ~ellulose degradation will increase; if too high,
pretreatment effectiveness will decrease.
Alt~rnatively, under appropriate conditions,
the nitrosati~g agent may be made in situ by adding a
high enough concentration of acid to acidify the pulp
to a pH of less than 4, preferably 1.8 to 3.4 and more
preferably 1.9 to 3.0, before or concurrently with
adding a water-soluble inorganic nitrite such as sodium
nitrite. Also, the water-soluble inorganic nitrite may
be reacted with sufficient acid to yield an acidic
solution of nitrous acid/ which then can be added to
--10--
2~5,~39
the pulp as a nitrosating agent. The acidity of the
nitrous acid solution should be such that the resultant
pH upon addition to the pulp is less than 4, preferably
in the range of about 1.8 to 3.4, more pre~erably 1.9
to 3Ø Preferably, the pulp should be preacidified
before addition of the nitrous acid solution to a pH of
less than 4.
Preferably, the acid used to dissolve the
nitrosating agent or to acidify the pulp or react with
the inorganic nitrite should be a strong mineral acid,
more preferably a non-oxidizing mineral acid,
particularly sulfuric acid.
Preferably, if the pulp is preacidified, the
preacidification should be shortly before the
nitrosating agent or inorganic nitrite is added under
the intense mixing and other limitations of the
invention so as to minimize attack of the cellulose by
free acid.
The temperature of the pretreatment can be
adapted to mill conditions but: should be at a
temperature that is low, since high temperatures
contribute to cellulose degradation, but not so low
that the reaction of the active NO(+) with the lignin
is hampered. Preferably the temperature should be in
the range of 5 to 80 C. More preferably, the
temperature should be 20 to 55C.
The concentration of NO(+), the active
ingredient in the process, should be 0.1 to 1.2 wt.%,
preferably 0.1 to 1.0 wt.% on an OD pulp basis. The
upper limit is dictated by the economics of the
process. That is to say, when neaxly all of the
nitrosonium ion receptor moieties in the pulp have
reacted with the nitrosating agent, adding more
nitrosating agent does not servP a use~ul purpose. If
--11--
~05316~
-12
the concentration is too low, pretreatment
effectiveness will be reduced.
The pretreatment must be done under such
high-intensity mixing conditions that intimate, uniform
and rapid contact is achieved between the nitrosating
agent and the lignocellulosic material. Preferably the
equipme~t used should be a high-shear mixer, although
any other device known in the art to provide intense
enough mixing may be used. A high-shear mixer provides
the best way known to the inventors for assuring that
the nitrosating agent intimately, uniformly and rapidly
contacts the fiber so that it can then react with the
lignin that is to be removed before the agent
equilibrates to N02- species in the water present with
the pulp.
When using the high-shear mixer employed in
the experiments set forth herein, a tip speed of the
mixer blades of 5 to 50 ~~eet/second (ft.j~ec.)
assured intense enough mixing. Actual mixing
~ parameters will vary with the mixer employed, but one
skilled in the art will be able to define the
parameters for the particular mixer and the pulp type
and consistency based ~n the following. The mixer must
provide sufficient shear rate that the reaction mixture
becomes fluid-like in behavior so that the chemicals
are added uniformly and as rapidly as the reaction
itself. The chemicals should be introduced so as to
assure unifo~ distribution of the chemicals in the
reactor and preferably at the point of high shear.
The time of mixing can vary over a wide range
according to the pulp properties. The time is normally
1 to 900 seconds. Best results occur when conditions
are such that the nitrosating agent intimately and
uniformly contacts the fiber in the pulp essentially
instantaneously (within less than about 15 seconds)
2~5~6~
upon addition. Additional time to allow full
diffusion in the fiber may be used. The diffusion
stage may be at lower intensity or tip spead than the
initial contacting of the fiber with the nitrosating
agent. High intensity mixing may be prolonged to
include both the reagenk distribution and diffusion
phases of the reaction.
Oxygen must be added to the pretreatment
vessel for the lignin reactions to occur. Oxygen may
be added as molecular oxygen or as an oxygen-containing
gas such as air or as a compound such as hydrogen
peroxide. While oxygen-containing compounds such as
NOX can be used, they are not preferred since they can
cause undesired degradation of the cellulose. The
amount of oxygen to be added should be at least equal
to one gram atom per gram mole of NO(+) present in the
nitrosating agent (stoichiometric amount).
Pressure is not critical to the success of
the pretreatment process. But, the oxygen pressure
must be high enough to assure intimate contact of the
oxygen with the pulp during treatment. For exa~ple, if
the oxygen source is air, then the pressure preferably
should be atmospheric pressure to 100 pounds per square
inch gauge (psiq.). If molecular oxygen is used, a
pressure of atmospheric pressure to 40 psig. should be
used. In the case of hydrogen peroxide, pressure is
not a consideration. The concentration of hydrogen
peroxide (100% basis) should be about 0.2 to 5 wt.
based on the OD weight of pulp~
After the pulp has been pretreated with
nitrosating agents, the m~dified pulp preferably is
washed with water to remove free acid and soluble metal
ions and then is extracted with any oxidative
deligni~ication process known in the art. Magnesium
compounds may be added after the pretreatment to
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inhibit the degradation of the cellulose in the
oxidative delignification stage. In a typical
oxidative d~lignification that can follow the
pretreatment, the pulp can be treated with oxygen at
70 to 120 C for 15 to 60 minutes in the presence of
an alkali, the alkali con~ent based on sodium hydroxide
being about 2 to 8% on an OD pulp basis and the oxygen
pressure being between 50 and 100 psig. The oxygen
stage can then be followed by a peroxide stage, a
second oxygen stage or a dioxide stage to complete
delignification and various washes~
_AMPLES
The reactor in which the following examples
were run was a high shear, baffled, laboratory mixer.
The reactor has four mixing blades (impellers) having
the dimensions of 140 millimeters (mm) in width, 21 mm
in height and 6 mm in thickness. This makes the
diameter of the shaft plus blades about 76 mm tabout 3
inches). There are three hollow baffles positioned
around the reactor facing the center axis of the
reactor. There are 9 holes (1/64 inch diameter) in
each baffle. The inlet to the mixer is connected to
the holes in the baffles through check valves to permit
introduction of liqulds and gases through the holes ~o
facilitate uniform distribution of chemicals at the
point of high shear (where the ~lade tips come in close
proximity to the baffles) while the mixer is running.
The tip speed of the blades is as follows:
Revolutions~Per Minute Tip Speed_(m./sec )
200 0.8 (2.6 ft./sec.
300 1.2 (3.9 ft./sec.)
1000 4.0 (13.1 ft./sec.)
352000 8.0 (26.2 ft./sec.)
3000 12.0 (39.3 ft./sec.)
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2g~536~,~
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All percentages, unless otherwise stated, are
based on the oven-dried (OD) weight of the pulp~
All washings with tap water were repeated
until the bleach liquor was clear. About 2 washings
were required in each case.
Example 1
A. Oxygen Delianification
Unbleached Southern pine softwood pulp (kappa
number of 22.1, viscosity of 24 centipoise (cp)) at a
10 wt.% consistency was placed into the reactor and 0.2
wt.% MgS04 (0.04% Mg++) was introduced into the
reactor. They were mixed at 300 revolutions per minute
(rpm). The temperature of the reactor was maintained
at 100C. NaOH (4wt.%) was introduced into the
reactor along with oxygen at 100 psig. The
delignification took place for 30 minutes. The pH of
the bleach liquor was 12 at the end of thP
delignification. The delignified pulp was washed and
air dried. The kappa number of the resulting pulp was
20 determined to be 12.0 and the viscosity was 16.4 cp,
which amounts to reductions of 45.7% and 31.7%,
respectively.
B. NSA Treatment + Oxyqen Deliqnification
The unbleached pulp of Example l-A at 10 wt.%
consistency was placed in the reactor at 40C~ While
mixing the pulp at lOOo rpm, 1 wt.% NSA (100% weight
basis) was introduced into the reactor along with
oxygen gas at 40 psig. The NSA used was 40 wt.~ NSA
(NOHS04), 52.2 wt.% H2S04 and 7.8 wt.~ water. After 5
minutes at these conditions, the oxygen was released
and the activated pulp was washed. This treated pulp
at 10 wt.~ consistency was then subjected to the oxygen
delignification conditions used in Example l-A. The
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~0~15~
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kappa number of the resultiny pulp was 9.3 and the
viscosity was 19.0 cp, which amounts to reductions of
57.9~ and 20.8%, resp~ctively.
Example 2
A. Oxyqen Deliqnification
Unbleached Southern pine pulp (kappa number
of 26~5 and viscosity of 29O0 cp) at a 10 wt.%
consistency was subjected to oxygen delignification in
a manner similar to Example 1-A. In this case the Mg++
concentration was 0.2% and NaOH concentration was 4%.
The temperature and the oxygen pressure in the reactor
were maintained at 100~C and 100 psig oxygen pressure,
respectively. The pulp was mixed at 300 rpm and the
delignification took place for 30 minutes. The pulp
was washed and air dried. The kappa number and the
viscosity of the delignified pulp were 14.0 and 24.0
cp, respectively. The reductions in kappa number and
viscosity as compared to the unbleached pulp were 47.2%
and 17.2~, respectively.
B. NSA Pretreatment ~ Oxyqen Deliqnification
The unbleached pulp of Example 2-A at 10 wt.%
consis~ency was pretreated with 2.3 wt.% NSA at 40C
and 40 psig. oxygen pressure in the reactor for 5
minutes in the manner indicated in Example l-B. The
pulp was then washed with tap water and subjected to
oxygen delignification at conditions identical to
Example 2-A. The kappa number of the delignified pulp
was 11~8 and its viscosity was 28.0 cp, which amounts
to reductions of 52.5% and 3.4~, respectively.
C. NO2 Pretreatment + Oxyqen eliqnification
Pretreatment of pulp used in Example 2-A was
conducted in the reactor with 2.3~ NO2 gas at 40C and
atmospheric pressure in the manner indicated in Example
2-B. No oxygen was present in the pretreatment stage.
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~153~3~
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The activated pulp was washed with tap water and then
delignified with oxygen at conditions indicated in
Example 2-A. The kappa number of the deligni~ied pulp
was 15.5 and the viscosity was 27.3 cp, a reduction of
27.3% and 5.9%, respectively.
Example 3
Effect of NSA Concentration
Southern pine brownstock pulp (kappa number
of 24.0 and viscosity of 27.8 cp) at 10% consislency
was delignified with oxygen in a manner similar to
Example l-~. The conditions of the oxygen stage were
as follows:
Temperature = 100C
Pressure = 100 psig o~ygen pressure
Impeller speed = 200 rpm
time = 30 minutes
NaOH concentration = 5.5 wt.%
Mg~+ (in the form of MgS04) - 0.16 wt.%
The delignified pulp was washed and air
dried. The kappa number at the end of this stage was
12.9 and the viscosity was 21.5 cp, a 46.3% and a 22.7%
reduction, respectively. The selectivity (change in
viscosity per unit change in kappa number) was O.57.
Experiments in which the untreated pulp
indicated above was pretreated using 0.5%, 1.5% and 2%
NSA were ~hen run. In each case, Oxygen at 40 psig.
was used, the temperature was 40~C and impeller speed
3000 rpm for 5 sec. and 200 rpm for 15 minutes. Each
pretreatment was followed by washing followed by an
identical oxygen delignification stage as indicated
above. The results are summarized in Table 1.
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Table 1
Effect of NSA cOncentratiOn
NSA
Conc. X Vlsc. X Select. = pH a~_End of
RaPpa No. Red~p_ Red cp Pretre~t. OXyRen
~ro~- 24.0 - 27.a - - - ~
stock
0 12.946.3 21.522.70.57 - 11.8
0.5 13.543.8 22.120.50.54 5.7 12.0
11.352.9 24.511.90.26 2.1 12.0
0 2 10.4 56.7 24.910.~ 0.21 1.9 11.7
Example 4
Pretreatments were done on Southern pine
brownstock pulp (kappa number of 26.5 and viscosity of
29.0 cp) at 10% consistency with 1 wt.% NSA the reactor
at conditions similar to that indicated in Example lB
(1000 rpm for 5 minutes). Two identical pretreatments
were carried out and each was subjected to an identical
oxygen stage to determine the reproducibility of the
results. The conditions of the oxygen stage are
summarized below.
Temperature = 100C
Pressure = 100 psig oxygen pressure
time 3 30 minutes
NaOH concentration = 4 wt.%
Mg++ = 0.16 wt.%
impeller speed = 200 rpm
consistency - 10 wt.%
The results are summarized in Table 2.
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Table 2
Reproducibility
~ Viscosity ~ Selectivity
Exper. Kappa No. Red c~ _ Red (cp~
Brown- 26.5 - 29.0 - -
stock
1 13.150.6 27.1 6.6 0.14
2 13.847.~ 26.0 10.3 0.24
Example 5
Effect of Mixinq
In the NSA pretreatment stage, three
different mixing conditions were used to determine the
effect of mixing intensity. Mixing conditions were as
follows:
Experiment 1 - Mixing at 1000 rpm for 5 mins.
Experiment 2 - Mixing at 3000 rpm for 5 secs.
and then at 200 rpm for 15 mins.
Experiment 3 - Mixing at 200 rpm for 5 mins.
In each of the above experiments, 1 wt.% NS~
was used in the pretreatment stage along with oxygen at
40 psig pressure at a temperature of 40C. Each
pretreatment was followed by washing followed by an
identical oxygen delignification stage. Results were
compared with the results from Experiment 4 in which
the same oxygen-stage conditions were used but without
pretreatment. The results are summarized in Table 3.
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~ S3~i~
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Table 3
XVisc. ~ ct. PH a~ End of
PP~ ItRed cp RedCD Pr~reae Ox~ en
B~ovn-27 . 9 - 29 . 4
~ock
1 13.7~0.926.5 9.9 0.:~0 2.0 10.6
2 13.7 50.926.6 9.50.20 2.1 10.5
3 15.3 45.224.6 16.3 0.38 2.1 10.9
4 ~ 15.2 45.S22.6 23.1 0.54 - 11.8
*no pretreatment
Example 6
Variation of Viscosity With Kappa Number
With and Without Pretreatment
NaOH concentrations of 4%, 6% and 8% were
used in the oxygen delignification stage. With the
exception of the alkaline concentration all other
conditions were similar to those used in Example 3.
Three identical pretreatments were done with l wt.% NSA
on Southern Pine pulp as indicated in Experiment 2 of
Example 5. The pretreatments were followed by washing
followed by an oxygen delignification stage with NaO~
concentrations of 4%, 6~ and ~% as done above. The
results are presented in Table 4.
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)S3~3
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Table 4
Variation of Viscosity With Ka~a Number
NaOH ~ Viscosity ~ pH at End of
Conc. Kap~a No. Red (c~) Red Pre-staqe Oxygen
Brown- 27.9- 29.4 - - -
stock
Oxvqen Delianification
15.245.5 22.6 23.1 - 11.8
6% 14.5~8.0 20.7 29.6 - 12.2
8% 13.551.6 16.9 42.5 _ 12.5
NSA Pretreatment/Oxvaen Deliqnification
4% 13.7 50.9 26.~g.5 2.1 10.5
~ 11.0 60.6 24.018.4 2.1 1~.0
8% 10.8 61.3 ~1.526.9 2.1 12.3
Example 7
Pretreatment with Nitrosation Chemicals
The following pretreatments were conducted
witll NaNO2/HNO3, NSA and NaNO2/H2SO4. Each
pretreatment was followed by washing followed by an
identical oxygen delignification stage, according to
conditions indicated in Example 4.
The pretreatments were done according to
conditions indicated in Experiment 2 of Example 5
(mixing at 3000 rpm for 5 seconds and then at 200 rpm
for 15 minutes. In Experiment 3, the pH after the
pretreatment with NSA was 2.1, and the pH after the
oxy~en delignification was 10.5. In Experiment 4, 5, 6
and 8, ~he pulp was first acidified and then the sodium
nitrite was added. In Experiment 7 the sodium nitrite
was premixed with sufficient nitric acid and then added
to the pulp. In Experiment 4, the pH after
pretreatment was 1.9, and the pH after oxygen
delignification was 11.9. In Experiment 5, the pH's,
respectively, were 2.1 and 11.7. In Experiment 6, t~le
3~i9
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pH's, respectively, were 1.8 and 10.3. In Experiment
7, the pH's, respectively, were 1.9 and 11~5. In
Experiment 8, the pH's, respecti~ely~ were 1.9 and
11.4. The results are summarized in Table 5.
Table 5
Nitrosation Followed b~ Oxyqen Deliqniflcation
Visc. %
10 No. ~y~ Kappa # Red cp~ Red _lect.
1 Brownstock 27.9 - 29.4 - -
2 Oxygen 15.245.5 22.6 23.1 0.54
3 1% NSA/Oxygen 13.750.9 26.6 9.50.20
15 4 NaN02/HN03* 16.441.2 23.9 18.7 0.48
(equivalent to NSA in 3)
NaN02/H2S04** 17.7 36.6 25.6 12.9 0.37
(equivalent to NSA in 3)
6 1% NaNO2/3% HNO3 14.7 47.3 2S.5 13.3 0.30
20 7 1% NaNO2/3% HNO3 14.3 48.7 24.6 16.3 0.35
(premixed)
8 1% NaNO2/2.3% H2SO4 14.3 48.7 24.2 17.7 0.38
* 0.544 wt.% NaN02/2.17 wt.% HN03 is equivalent to 1
wt.% NSA in reactive species and normality.
** 0.544 wt.% NaNO2/1.69 wt.% H2SO~ is equivalent to 1
wt.% NSA in reactive species and normality.
Example 8
Effect of Tem~erature in the Pretreatment Staqe
Pretreatments were conducted with 1 wt.% NSA
at 25C, 40-C and 48-C at the conditions indicated in
Experiment 2 of Example 5, except for the temperature.
Each pretreatment was followed by washing followed by
an oxygen stage at the conditions indicated in Example
4. The results are summarized in Table 6.
2~ii36~
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Table 6
Effect of TemPerature in the Pretreatment Sta~e
Pretreat % Visc. % Select. pH at End of
~emp-oC) ~E~_~ Red l~L Red _(c~ Pre OxYqen
Brownstock 27.9 - 23.4
14.9 4~.6 27.2 7.5 0.17 2.0 10.4
13.7 50.9 26.6 9.5 0~20 2.1 10.5
48 16.0 42~7 24.9 15.3 0.38 2.1 10.8
Oxygen 15.2 45.5 22.6 23.1 0.54 - -
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