Note: Descriptions are shown in the official language in which they were submitted.
1043514
BACKGROUND OF THE I~VENTION
The present invention relates to a ~rocess for the
bleaching of lignocellulosic pulp with oxygen in the presence
of alkali, and more particularly to an oxygen/alkali bleaching
process wherein the rate of delignification is increased while
at the same time protecting the cellulosic portion against
excessive losses in viscosity.
Pulp delignification with alkaline solutions of
molecular oxygen, or "oxygen bleaching", like any other bleach-
ing process, represent a compromise situation, whereby one
seeks to obtain the maximum extent of delignification, while
minimizing the degree of oxidative degradation, i.e,, depoly-
merization of the cellulosic component.
Industrial utilization of oxygen bleaching was
retarded for a number of years because the above-referred to
compromise was heavily weighted on the side of cellulose de-
gradation. m us, though acceptable delignification could be
achieved with oxygen/alkali bleaching, the pulp mechanlcal
properties were uniformly unacceptable. The discovery by
Robert et al., U.S. 3,384,533, that magnesium compounds could
effect a certain degree of cellulose protection against oxida-
tive degradation, provided the impetus for the establishment
of the first commercial oxygen bleaching system at Enstra,
South Africa. While other researchers have from time to time
found that other alkaline earth metals, aside from magnesium,
could achieve a certain degree of cellulose protection, none
have attained commercialization. Indeed, only the potassium
iodide protection disclosed by Minor and Sanyer in the
104;~514
Journal of Polymer Science, Part C, No. 36:73 (1971) affords
the degree of protection which is comparable with that of
magnesium, or the complexes of magnesium.
Use of magnesium as a protection compound for cel-
lulose during oxygen bleaching presents a number of practical
problems. Not the least of these problems is the expense of
the compound. The action of magnesium is purely specific to
cellulose, and appears to have no effect on the rate or extent
of delignification that can be achieved during oxygen bleach-
ing. Another problem associated with the use of magnesium is
its tendency to impart scale on the process equipment thus
resulting in problems of encrustation.
Consequently, the pulp bleaching industry has sought
new and improved methods by which oxygen bleaching can be con-
ducted, preferably without using magnesium compounds. An ad-
ditive which also catalyzes delignification, aside from pro-
ducing non-profit cellulose protection is, accordingly, highly
desirable. A step in that direction was provided by
Roymoulik et al., U.S. 3,832,276, which describes a low con-
sistency oxygen bleaching process that does not require the use
of cellulose protectors. The process reduces cellulose de-
gradation by lowering the concentration of hydroxyl ions through
the use of low pulp consistency and through the use of declin-
ing oxygen pressures during reaction.
Disclosure of catalysts which will increase the rate
of deliqnification have been rather limited to date. Minor
and Landucci have reported, (see International Pulp Bleaching
Conference, 1973, Vancouver, B.C., p. 83) that the rate of
` ~O~Si4
delignification of pulp b~ ox~gen/alkali could be increased by
the use of manganese (the form was not specified). Data was
presented showing that whereas delignification of a southern
pine groundwood pulp was considerably accelerated by the ad-
dition of 0.01% manganese (basis not specified), only a small
effect was noted with a kraft pulP containing an initial lignin
content of 7%. A subsequent publication by Landucci, Minor and
Sanyer, (Fourth Canadian Wood Chemistry Symposium, 1973,
Quebec, Canada, p. 71) concerning the use of manganese to
accelerate delignification of southern pine, stated that
"manganese has no deleterious effect on carbohydrates", pre-
sumably meaning that pulp viscosities were similar to those
obtained when manganese was not used.
Although the catalytic effect of the manganese on
deiignification is not difficult to understand, the finding
that viscosity was unaffected is quite surprising. A number
of investigators have quite conclusively demonstrated that
manganese, like a number of other transition metal ions, has
a very damaging effect on the viscosity of cellulose oxygen
delignification. For example, Ericsson et al. (Svensk Papper-
stidning, Volume 74 (22), November 1971, p. 757) determined
that, whereas 40 parts per million (as manganese, based on pulp
weight,) of manganous sulfate had little in1uence on the vis-
cosity of cotton linters, i.e., pure cellulose, during oxygen/
alkali treatment, repeating the experiment in the presence of
5% lignin (based on pulp weight) physically added to the mix-
ture gave a disastrous decrease in the viscosity of the cotton
linters. Other heavy metals, such as iron and copper were
found to behave in a similar manner. Concern about the presence
`` ~0~35i4
of manganese during oxygen bleaching is of critical industrial
importance. Myburgh, for example, reported (TAPPI: Vol. 57 [5],
p. 131, 1974) that the Enstra, South Africa, oxygen bleach
plant required that unbleached pulp be prewashed with acid to
dissolve out heavy metals, prior to entering the oxygen bleach
reactor. Myburgh states that the unbleached pulp at Enstra
contains 120-160 parts per million of manganese, which must be
reduced blow 30 parts per million, or the metal will have "have
a catalytic degrading effect on cellulose during oxygen bleach-
ing."
To further confuse the seeming discrepancy betweenLanducci's claim on the one hand that manganese had no effect
on pulp viscosity, and Ericsson's and Myburgh's claim on the
other hand that manganese had disastrous consequences on pulp
viscosity, the work of Gilbert, et al. (TAPPI: Vol. 56 [6],
p. 95, 1973) should be cited. This work presented evidence
that oxygen/alkali treatment of cotton linters in the presence
of iron present in small quantities gave the degradation effect
noted elsewhere. But, upon further additions of iron, to a
level of 1,000 ppm. (on pulp basis) no further degradation was
noted. However, upon extending the addition to a level of
greater than 103 ppm., a prounouced increase in the pulp vis-
cosity was observed. The authors further stated that a similar
phenomenon was noted with manganese, though no data were given.
The observation was evidently not believed by the authors to
be of practical im~ortance, due to the discoloration of the
pulp by the heavy metal ions. They state "the orange color
of the pulp samples is, of course, objectionable."
.~ ,
~`
514
It is, accordingly, an object of the present
invention to provide a process for the deiignification and
bleaching of lignocellulosic pulp fibers with oxygen in an
alkaline medium while protecting the pulp against excessive
losses in viscosity.
It is another object of the present invention to
provide a process for the delignification and bleaching of
lignocellulosic pulps with oxygen in an alkaline medium in
the presence of a compound which simultaneous catalyzes the
rate of delignification and protects the pulp against excessive
losses in viscosity.
It is a further object of the present invention to
provide a continuous process for the delignification and
bleaching of lignocellulosic pulps with oxygen in an alkaline
medium in the presence of a compound which simultaneously
catalyzes the rate of delignification and protects the pulp
against excessive losses in viscosity and, also provides for
the regeneration, recovery, recycling and reuse of the compound.
In one aspect of this invention, there is provided
a process for the delignification and bleaching of ligno-
cellulosic pulp fibers with oxygen in an alkaline medium
while protecting the pulp against excessive losses in viscosity,
which comprises the following steps in sequence:
(a) contacting a slurry of lignocellulosic pulp fibers,
having a consistency of less than 50%, by weight of oven-
dried pulp, with a solution of a water-soluble salt of a
divalent transition metal selected from the group consisting
of manganous, nickelous, cobaltous, and vanadous ions having
a concentration of from 0.27% to about 1.10%, by weight of
oven-dried pulp, for a period of time ~ufficient to allow
A
104;~Si4
the divalent metal ion to penetrate the walls of the pulp
fiber7
~ b) delignifying the pulp by mixing the lignocellulosic
pulp slurry containing the divalent transition metal ion
with oxygen, in an alkaline medium resulting in a slurry pH
between about 10 and about 13, while oxidizing the divalent
transition metal salt to a water-insoluble trivalent transition
metal oxide and precipitating a viscosity protective coating
of said trivalent transition metal oxide on the pulp fibers;
and then
(c) washing the pulp with acid to reduce the trivalent
transition metal oxide and thereby regenerating the divalent
transition metal salt.
In another aspect of this invention, there is provided
a continuous process for the delignification and bleaching
of lignocellulosic pulp fibers with ~xygen in an alkaline
medium while protecting the pulp against excessive losses
in viscosity, which comprises the following steps in sequence:
(a) contacting a slurry of lignocellulosic pulp fibers,
having a consistency of less than 50%, by weight of oven-
dried pulp, with a solution of a water-soluble salt of a
divalent transition metal selected from the group consisting
of manganous, nickelous, cobaltous, and vanadous ions having
a concentration of from about 0.27~ to about 1.10%, by
weight of oven-dried pulp, for a period of time sufficient
to allow the divalent metal ion to penetrate the walls of the
pulp fibers;
(b) delignifying the pulp by mixing the lignocellulosic
pulp slurry containing the divalent transition metal ions
with oxygen, in an al~aline medium resulting in a slur~y pH
~ - 6~a) -
`` i()4;~S14
between about 10 and about 13, while oxidizing the divalent
transition metal salt to a water-insoluble trivalent transition
metal oxide and precipitating a viscoslty protective coating
of said trivalent transition metal oxide on the pulp fibers;
(c) washing the pulp to free it of anions;
(d) washing the pulp with acid to reduce the trivalent
transition metal oxide and thereby regenerating the divalent
transition metal salt;
(e) recovering the regenerated divalent transition
metal salt and recycling it for reuse in (a).
Other objects, aspects and advantages of this
invention will be apparent to those skilled in the art from
the present specification when taken in conjunction with the
appended drawings, in which:
FIG. 1 is a flow diagram illustrating the present
invention.
-~FIG. 2 is a graph in which the effect of sodium
hydroxide concentration in the present invention is
shown by plotting the viscosity of the bleached pulp
versus the l~app~ Nomber of the blea~hed pulp.
- 6(b) -
A
~043514
GENERAL DESCRIP~ION OF THE INVENTION
It has been found that during the delignification
and bleaching of lignocellulosic pulp fibers with oxygen in an
alkaline medium that the rate of delignification can be in-
creased, while simultaneously protecting the pulp against
excessive losses in viscosity, by contacting a slurry of ligno-
cellulosic pulp fibers with a solution of a water-soluble salt
of a divalent transition metal selected from the group con-
sisting of manganous, nickelous, cobaltous and vanadous ions
having a concentration at least about 0.27% to about 1.10~,
based on the weight of oven-dried ~O.D.) pulp. These di-
valent metal salts function both as a catalyst of delignifica-
tion and as a protector against excessive losses in viscosity.
This was highly unexpected, since as previously noted, other
investigators have reported losses in viscosity, thus signi-
fying excessive depolymerization of cellulose.
The present invention also provides a continuous pro-
cess in which water-soluble divalent transition metal salts
selected from the group consisting of manganous, nickelous,
cobaltous and vanadous ions function as a catalyst to increase
delignification and as a protector compound against excessive
losses in viscosity during oxygen bleaching in an alkaline
medium and, also, provides for the recovery, regeneration, re-
cycling and reuse of the metal salts. Thus, there is provided
a continuous process which enables the divalent transition
metal salt to be reused effectively and economically and,
further, removes objectionable color, which adversely effects
brightness and interferes with subsequent bleaching stages.
In accordance with the process of the present inven-
tion, a slurry of unbleached lignocellulosic pulp fibers havinga consistency of less than about 50%, based on the weight of
oven-dried pulp, preferably between about 1% ana about 30%,
-- 7 --
10435~4
and most preferably, between about 1% and about 10%, is
brought into intimate contact with a water-soluble salt of a
divalent transition metal for a period of time sufficient to
allow the divalent metal to penetrate the walls of the pulp
fiber.
I~hile it is preferred to use paper grade pulp or dis-
solving grade pulp prepared by the kraft;process, pulps pre-
; pared by other pulping processes, such as alkaline sulfite,
neutral sulfite, soda, or semichemical, can be employed ad-
vantageously. The lignocellulose utilized in the aforementioned
pulping processes to provide the pulp for the process of the
present invention can vary widely and can include hardwoods,
softwoods, bagasse, etc.
The intimate contact between the Pulp and the metal
is effectively achieved by using a soluble solution of the
metal compound which can readily penetrate the walls of the
pulp fibers. It is preferred to employ the sulfate, acetate
and carbonate salts of the manganous, nickelous, cobaltous,
and vanadous ions, since these anions are compatible with the
pulp mill recovery system. It is especially preferred to employ
manganous sulfate in view of the excellent results achieved
with respect to increasing the rate and extent of delignifi-
cation while, also, and most surprisingly, simultaneously
functioning to retard or minimize excessive losses in viscosity,
which reflects the extent of depolymerization or degradation
; caused by the bleaching process.
It is to be understood that while the specification
will hereinafter only make reference to the terms "manganous
sulfate" and "manganous" and "manganese" when referring to the
divalent transition metal salts and the ions of the present
invention, it is done solely in the interest of brevity and
1~435i4
clarity of exposition, and it is to be further understood that
when such terms are used they are also intended to refer to
and include the water-soluble salts of the nickelous, cGbal-
tous, and vanadous ions, the ions themselves, and the other
water-soluble salts of the manganous ion.
The manganous ion is functioning both as a catalyst
of delignification and as a protector of cellulose viscosity.
It has been found that to function effectively in both ca-
pacities, the concentration of manganous ion should be from
about 0.27% to about 1.10%, based on the weight of oven-dried
(o.~) pulp. At lesser concentrations than 0.27%, it has been
found that the degradation of the pulp is actually catalyzed
as measured by losses in viscosity, while at concentrations
greater than 1.10% no added benefits in either viscosity pro-
tection or increased delignification are realized. While con-
centrations greater than 1.10% have no negative effect on vis-
cosity or rate of delignification, an economic penalty is in-
curred by using excessive amounts of manganous sulfate. It is
preferred to employ a manganous ion concentration of about
0.55%, based on O.D. pulp, since maximum benefits are obtained
at that concentration.
The aqueous pulp slurry, whose consistency has been
diluted by the solution of manganous sulfate is then further
diluted with a stream of liquor containing both sodium hydroxide
and dissolved and intimately dispersed oxygen. The latter
solution has been prepared by separately mixing oxygen and sodium
hydroxide in a mixing device, which insures efficient distri-
bution and dispersion of the oxygen and also assures satisfac-
tory reaction with the manganous ion, along with steam, to give
the desired reaction temperature.
la43s~
Upon contacting the puip slurry containing manganous
ions, the oxygenated caustic stream must be mixed with the
pulp slurry. This may take place in a separate mixing vessel,
or it may occur in a small section of the main reactor.
Alkali is present in the oxygenated liquid in suf-
ficient quantity to elevate the pH of the pulp solution to
between about 10 and about 13, preferably above pH 11, and
about 20 to 30 pounds of oxygen are admitted per ton of pulp.
The manganous ion, which has a valence of +2, is
oxidized to a higher valence state after a protecti~e coating
of manganous hydroxide has been deposited by precipitation
onto the surface of the pulp fibers, The precipitation and
oxidation of the manganous ions occurs only after contact of
the pulp slurry with the oxygenated caustic solution. While
various alkaline agents can be employed, such as sodium car-
bonate, sodium hydroxide, ammonia, kraft white liquor, etc.,
it is preferred to employ sodium hydroxide as the alkali.
Then the oxygenated alkaline pulp slurry, is intro-
duced into a reaction vessel. The vessel can be a large, high-
pressure reactor equipped with a mixing or stirring device,
or a downflow tower such as those used for caustic extraction
in a pulp bleach plant, or an upflow tower such as those used
- for chlorination in a pulp bleach plant. The advantages to be
gained by the use of an upflow tower when oxygen bleaching
; pulp having consistencies less than about 10%, are disclosed in
Roymoulik, U.S. 3,832,276. The process of the present invention,
however, is not limited to operating at low pulp consistencies,
since both high and low pulp consistencies can be utilized
advantageously.
When a large, high pressure reactor is employed in
-- 10 --
~043514
accordance with the process of the present invention, 20 to
30 pounds of dissolved and intimately dispersed oxygen per ton
of pulp along with sodium hydroxide having a concentration of
from about 1 gram per liter to about 20 grams per liter, pre-
ferably from about 2 to about 4 grams per liter, are added
to the pulp slurry in the reactor. The contents, which are at
a pH of from about 11 to about 13, with p~ 12 being preferred,
are heated at a temperature of from about 80C. to about
130C., preferably from about 95C. to about 105C., and at
a pressure of from about 10 psig to about 300 psig, preferably
at 150 psig, for a period of from about 1 minute to about Ç0
minutes, with from about 4 minutes to about 10 minutes being
preferred.
It is believed, but it is not known with certainty,
and is therefore only offered as a postulate, that during the
residence time in the reactor there are three separate and
distinct competing oxidation reactions taking place. These
reactions are oxidation of the manganous ion, oxidation of
the lignin, and oxidation of the cellulose. The manganous ion
is oxidized to hydrous manganese (III) oxide which is believed
to be the active species which affords viscosity protection to
the cellulose and acts to catalyze the rate of delignification.
It is also believed that the oxidized metal combines with
alkali and specifically directs its attack on the lignin, since
experimental evidence indicates that the rate of delignifica-
tion is dependent upon alkali concentration. It has unexpec-
tedly been found that use of manganese allows the use of reduced
concentrations of sodium hydroxide to achieve an extent of
delignification that ordinarily coula only be achieved at much
higher sodium hydroxide concentrations in the absence of man-
ganese.
104;~5~4
~ t the discharge of the reactor, oxygen bleached
pulp falls into a washer~ e.~ acuum ~ilter~ which washes
the pulp mat with fresh water, filters the residual alkali,
and recirculates it back into the bleaching system. During
washing, the manganese flock is retained in the mat of pulp
fibers
Since sorbed manganese ion on the pulp gives it a
high degree of coloration, which both diminishes brightness
and interferes with subsequent bleaching stages, it is effec-
tively removed by washing the pulp mat on a filter with an
acid in which manganese is soluble. This can be accomplished
effectively at a pH of about 2 and at a temperature of from
about room temperature up to about 50C. T~hile it is pre-
ferred to employ sulfurous acid, other acids such as sulfuric,
hydrochloric, or acetic can also be used.
The pulp mat which has now been freed of the cation
can, if desired, be bleached in subsequent stages to a higher
degree of brightness by using conventional bleaching sequences,
such as CEHDED, CEDED, CEHD, or DE~.
The washing of t~e pulp mat with sulfurous acid on
the washer reduces the manganese ion to manganous, and re- .
generates manganous sulfate, which is recovered from the fil-
trate from the second washer and recycled for reuse with new
unbleached pulp. Thus, there is provided a complete, contin-
uous and economic process for the use, regeneration, recovery,
recycle, and reuse of the manganous sulfate.
Referring to FIG. 1 of the drawings, describing one
form of apparatus and embodiment of the process, an unbleached
pulp slurry of the desired consistency and a solution of man-
ganous sulfate are admitted into high density storage chest 1.
104~S14
The manganous sulfate solution is desirably regenerated man-
ganous sulfate solution which is recycled from stream 2. The
recycled manganous sulfate is introduced so as to economically
reuse the same in a continuous manner.
After dilution in the high density storage chest,
the manganous sulfate having penetrated the fiber wall of the
unbleached lignocellulose pulp, the pulp slurry and the man-
ganous sulfate liquor are then pumped via stream 3 into
mixer 4.
The mixer is u~ed to pretreat the pulp slurry for a
short period of time with dissolved and intimately dispersed
oxygen and fresh sodium hydroxide uner pressure. Fresh sodium
hydroxide (NaOH) is pumped into and introduced via stream 5
to steam and oxygen mixer 6 where the temperature of the mix-
ture, i.e., sodium hydroxide, oxygen and dissolved organics,
is raised to 220F. to 230F. and then pumped via stream 7 into
mixer 4.
The pulp and liquor then pass from mixer 4 and are
admitted via stream 8 into reactor 9, which, as previously
stated, can be a high pressure reactor, an upflow tower, such
as that used for chlorination in a bleach plant, or a downflow
tower. Dissolved and intimately dispersed oxygen and alkali
are admitted into the reactor and under elevated pressure and
temperature the oxidation of the lignocellulosic pulp proceeds.
Residence time will vary depending upon the type of pulp, the
amount of alkali employed, and the pressure and temperature
employed.
The oxygenated pulp having entrained Na2SO4 and
Mn2O3 is then carried by stream 10 to washer 11 where the pulp
mat is washed with fresh water causing the Na2SO4, NaOH and
- 13 -
10435i~
organic sodium salts to pass into the filtrate, stream 12,
where they are collected in washer seal tank 13. The major
amount of the filtrate containing the above referred to
compounds is pumped to the screen room deckers or the brown
stock washers via stream 14, with a minor portion thereof being
diverted to stream 14' and then to washer 11 and another minor
portion being recycled into the oxygen delignification system
via stream 5.
The washed pulp mat containing the remaining en-
trained Mn2O3 is then transferred via stream 15 to a secondwasher 16 where the pulp mat is washed with an acid at a pH
of about 2. The acid wash reduces the sorbed manganese back
to its original valence state of ~2, and it passes out of
washer 16 as manganous sulfate filtrate via stream 17 and then
passes into seal tan~ 18.
Optionally, stream l9 from seal tank 18, containing
predominately manganous sulfate, can be partially diverted to
stream 20 and the manganous sulfate can be used to dilute the
pulp consistency on the discharge side of washer 11. The main
portion of stream 19 feeds into stream 2 and the manganous sul-
fate is thus recycled for reuse with new unbleached pulp in
high density storage chest l.
One of the unexpected advantages of the present inven-
tion is shown by FIG. 2 of the appended drawings. That figure
represents a graph plotting the pulp viscosity versu~ Kappa
Number for a series of runs showing the effect of sodium hydrox-
ide at varying concentrations, namely, 2, 4, 6, and 8 grams
per liter, in the absence of manganous sulfate and in the
presence of 0.5~% manganous sulfate. FIG. 2 presents a graphical
representation of the results tabulated in Table II hereinafter,
based upon Examples 14-21, inclusive, hereinafter.
- 14 -
1()4;~
Viscosity represents a measurement of the average
degree of polymerization of the cellulose in the pulp sample,
i.e., the average chain length o the cellulose. Thus, de-
creases in viscosity values represent the extent of depoly-
merization or degradation caused by the bleaching process.
Excessive degradation is to be avoided since it provides un-
desirable physical properties in any paper made from the pulp.
Kappa Number is determined by the potassium perman-
ganate consumed by a sample of pulp and represents a measure-
ment of its retained lignin content. The higher the KappaNumber, the less bleached and delignified is the pulp. By
comparing Kappa Numbers of samples before and after bleaching
treatment, one can obtain an evaluation of the extent of de-
lignification which has taken place.
As can be seen from an examination of FIG. 2, as the
concentration of sodium hydroxide is increased from 2 to 8
grams/liter there is, as expected, a decrease both in Kappa
Number and viscosity. However, unexpectedly, with manganese
present the decrease in viscosity is much less drastic, and in
each and every instance where manganese is present the viscosity
at a given Kappa Number is significantly greater. Of even
greater importance, perhaps, is the fact that the amount of
sodium hydroxide required to achieve a given Kappa Number is
less when manganese is present. This reduces the amount of
sodium hydroxide necessary for the process and, hence, the cost
of the process is appreciably reduced.
DETAILED DES~RIPTION OF THE INVENTION
In order to disclose more clearly the nature of the
present invention, the following examples illustrating the in-
vention are given. It should be understood, however, that this
1043514
is done solely by way of example and is intended neither todelineate the scope of the inVention nor limit the ambit of
the appended claims.
EXAMPLES 1-13
15 grams, oven-dried basis, of an unbleached
Southern hardwood pulp was diluted with water to yield 1.5
liters of a pulp slurry, equal to a pulp consistency of 1%.
The pulp slurry was then placed in the reaction chamber of a
Parr reactor. Examples 1-7, inclusive, employed dissolving
grade pulp and Examples 8-13, inclusive, emPloyed paper grade
pulp. The dissolving grade pulp had a brightness of 43.1,
a permanganate number of 8.5 and a viscosity of 37.8. The
paper grade pulp had a brightness of 26.1, a Kappa number of
17.0 and a ViSCOsIty of 42.3.
To the pulp slurry there was then added manganous
sulfate, in solution, in the amounts indicated below in Table 1.
Following this there was then added sufficient sodium hydroxide
- to yield a 2 gram per liter solution. The addition of the
manganous sulfate and the sodium hydroxide to the pulp slurry
was accompanied by gentle stirring to keep the solution as
homogeneous as possible.
The pressure stirring head was then positioned over
the reaction chamber and the entire unit was sealed. The
reactor was then placed in a heating mantle and slowly brought
to a final temperature of 95C. A slow, steady mixing a~com-
panied the temperature rise. When temperature was achieved,
pressurized oxygen gas was introduced at 40 psig. During this
time, the fastest mixing speed possible, approximately 2000 rpm,
was utilized. After one minute of combined rapid mixing and
oxygen pressure at 40 psig, the mixing was stopped and the
reactor was removed from the heating mantle. Oxygen pressure
- 16 -
1l)4;~S14
was maintained for nine minutes before a slow gradual depres-
surization of 1 psig per minute was undertaken for a total
period of 40 minutes. After complete depressurization, the
pulp was withdrawn, washed, filtered, and made into sheets.
The pulp sheets were diluted to a consistency of 5%
with sulfurous acid at pH 2 and were placed in plastic bags
which were maintained in a constan~ temperature bath at 49C.
for one-half hour.
The pulp was then water-washed, filtered and dried
and the brightness, Kappa Number and viscosity were measured
and are tabulated in Table I below.
1043Sl~
dP ~ ~D O CO_i O ~ $;~ 0~7 Ir) C~ N
0 ~1 N r4 ~1 ~ ~I N O rl N ~ ~ N ~ N
~g! . ~
,~
k ~
N 1~1
H ~ ~ ~ N ~ ~. p, . O ~ N ~I N
~7 Rl z ~ i o
.,. ~
~ .,
,C ~; 111 N ~D<J~ ~ S ~ 0~
m ~ ~ dP ~ ~ ~ 1~ ~ er
J ~ ~ ~ N ~ ~I NO
~ h
I.a ~
,1 h
, ,_ ~ tJ
x Z¦ ,' Z¦ o ~I N
- 18 -
~0435~4
In the series of experiments shown in Table I both
delignification catalysis and ~iscosity protection are evident
with both ty~es of pulp. The viscosity protection was ob-
served with a manganese application of 50 ppm and above.
The pulp, as expected, became increasingly dark and
of a highly objectionable color. Contacting the pulp with a
sulfurous acid solution at pH 2, removed the color caused by
the manganese.
EXAMPLES 14-21
15 grams, oven-dried basis, of an unbleached Southern
hardwood paper grade pulp having a Kappa Number of 17.0, and
a viscosity of 42.3, was diluted with water to yield 1.5 liters
of a pulp slurry, equal to a pulp consistency of 1%. The
pulp slurry was then placed in the reaction chamber of a Parr
re6ctor.
To the pulp slurry there was then added manganous
sulfate, in solution, in the concentrations indicated below
in Table II. Following this there was then added sodium hy-
droxide in the concentrations indicated in Table II. The
sodium hydroxide present is also calculated as a percentage of
oven-dried pulp. The addition of the manganous sulfate and
the sodium hydroxide to the pulp slurry was accompanied by
gentle stirring to keep the solution as homogeneous as possible.
The pressure stirring head was then positioned over
the reaction chamber and the entire unit was sealed. The
reactor was then placed in a heating mantle and slowly brought
to a final temperature of 95C. A slow, steady mixing ac-
companied the temperature rise. When temperature was achieved,
pressurized oxygen gas was introduced at 40 psig. During this
time, the fastest mixing speed possible, approximately 2000 rpm,
-- 19 --
~043S14
was utilized. After one minute of combined rapid mixing and
oxygen pressure at 40 psig, the mixing was stopped and the
reactor was removed from the heating mantle. Oxygen pressure
was maintained for nine minutes before a slow gradual depres-
surization of 1 psig per minute was undertaken for a total
period of 40 minutes. After complete depressurization, the
pulp was withdrawn, washed, filtered, and made into sheets.
The pulp sheets were diluted to a consistency of 5%
with sulfurous acid at pH2 and were placed in plastic bags
which were maintained in a constant temperature bath at 49C.
for one-half hour.
The pulp was then water-washed, filtered and dried
and the brightness, Kappa Number and viscosity were measured.
- 20 -
~43S14
~ ~P ~1 0 U~ O U~
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U~ ~ ~ ~ N O ~
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.q
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Z c~ a~ ~ In ~ CD ~ ~ '~
td
P ~ ~ o o --I co a~
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~O
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x z
-- 21 --
i(~4~S~4
~ t can be seen from Table ~I that the decrease in
Kappa Nu~ber and ~iscosity is less pronouncedwith manganese
present as the concentration of sodium hydroxide is increased.
In each case, it should be noted, the viscosity at a given
Kappa Number is superior. Perhaps even more important, the
amount of sodium hydroxide required to achieve a given Kappa
Number is less when manganese is present. This reduces the
expense of sodium hydroxide for the reaction.
It can be seen that the combination of 2.0 grams per
liter of sodium hydroxide and 0.55% manganese gave delignifi-
cation almost equal to that of 4.0 grams per liter, of sodium
hydroxide without manganese, but the viscosity of the manganese
protected run was vastly superior to the controls. The value
of manganese also lies in the reduction of sodium hydroxide
losses in washing the pulp. If only one washer were available
to wash the oxygen bleached pulp, operation at 4.0 grams per
liter would result in a loss of about 35 pounds of sodium
hydroxide, whereas only about 17 pounds would be lost when
manganese is used in combination with 2.0 grams per liter of
sodium hydroxide.
- EXAMPLES 22-23
1100 grams oven-dried basis of an unbleached EBK
("Easy Bleaching Kraft") hardwood aper grade pulp having a
brightness of 19.8, a Kappa number of 13.5, and a viscosity of
18.7 was diluted with water to yield 36 liters of a pulp slurry,
equal to a pul~ consistency of 3%. The pulp slurry was then
placed in the reaction chamber of a Pfaudler reactor.
To the pulp slurry there was then added manganous
sulfate in solution in the amounts indicated below in Table III.
Following this there was then added sodium hydroxide in the
1(~4;~514
amounts indicated below in Table ~II. The addition of the
manganous sulfate and the sodium hydroxide to the pulp slurry
was accompanied by gentle stirring to keep the solution as
homogeneous as possible.
The reactor was then slowly brought up to a final
temperature of 95C. A slow, steady mixing accompanied the
temperature rise. When the temperature was achieved, pres-
surized oxygen gas was introduced at 100 psig. During this
time, the fastest mixing speed possible, approximately 300 rpm
was utilized. After two minutes of combined mixing and oxygen
pressure at 100 psig, the mixing was stopped and the oxygen
pressure was released to 40 psig. Thereafter, over a period
of 40 minutes slow gradual depressurization from 40 psig to
0 psig, at 1 psig per minute, was accomplished. After com-
plete depressurization the pulp was withdrawn, washed with
water, filtered and made into sheets.
The pulp sheets were diluted to a consistency of 5%
with sulfurous acid at pH 2 and were placed in plastic bags
which were maintained in a constant temperature bath at 49C.
for one-half hour.
The pulp was then water-washed, filtered and dried
and the brightness, Kappa Number and viscosity were measured.
10~
~dP O ~
~rl ~
u~ ~ ~ l`
8 '' ,, ~1
~n
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o
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d~
:~: ~ ,~
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o
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'X O O O
P.
X O
Z
-- 24 --
lO'~S~I
The results in Table III indicate that use of
manganese allowed a reduction in the amount of sodium hydro-
xide from 13.3% (based on O.D. pulp) to 6.7% (based on O.D.
pulp), ~hile simultaneously achieving improved pulp viscosity
at virtually the same Kappa number.
The terms and expressions which have been employed
are used as terms of description and not of limitation, and
there is no intention in the use of such terms and expressions
of excluding any equivalents of the features shown and des-
cribed or portions thereof, but it is recognized that various
modifications are possible within the scope of the invention
claimed.
- 25 -
