Note: Descriptions are shown in the official language in which they were submitted.
2~23~04
DEINKING AND BLEACHING SECONDARY FIBER
TECHNICAL FIELD
The present invention relates to the deinking and bleaching of
secondary cellulosic fibers and is particularly concerned with improvements
in the methods for treatment of such fibers whereby desired brightness
levels are attained with zero to minimal production of harmful chlorinated
organics.
BACKGROUND OF THE INVENTION
In existing conventional plants for deinking and bleaching of secondary
fibers, such as salvaged old papers and other reused or recycled fiber-con-
taining materials, these materials are collected and segregated in piles
according to type (ledger, newspaper, cardboard, etc.). The fiber materials
from these piles are blended in a hydropulper, pulped and cleaned, followed
when required by a deinking step carried out by water washing or by flota-
tion. The thus treated pulp is then directed to the bleach plant where it
is subjected to a series of delignifying/bleaching and extraction steps,
15 each stage involving distinctively different treating chemicals and process
conditions utilized. The initial pulping and washing is to eliminate ink
present in the fiber (deink) and the subsequent bleaching process serves to
whiten the pulp and to get rid of any residual ink and/or lignin that may
have been left in the initial fiber stock. The effectiveness of the pulp
20 bleaching is measured and designated by parameters of brightness and vis-
cos~ty.
For the deinking and bleaching of recycled waste paper and other
secondary fiber materials, the most common practices employ chlorine-based
chemicals (generally for fine papers) or hydrosulfite (generally for news-
25 paper stock). Various treating sequences are utilized in the bleaching ofthe recycled pulp to attain desired brightness levels, typically above 76
brightness units (ISO) and commonly in the range of 78-82. Over 80X of the
the fine paper (ledger) bleaching is done by either a CEH type sequence or a
,~
~23~4
CH type. As commonly employed in the art these letter designations respec-
tively stand for:
C = Chlorination with chlorine (C12)
E = Alkali extraction with NaOH
H = Alkaline hypochlorite (NaOCl)
Concern over the negative impact on the environment of chlorine-based
bleach plant effluents has accelerated in recent years, particularly since
the discovery of the highly toxic chlorinated dioxins and furans in some
bleach plant effluents, sludge, and pulp products. Today it is generally
accepted that it is critical to reduce the amount of chloro-organics in the
pulp and in the plant effluent.
Since formation of chlorinated organics is strongly related to the use
and consumption level of molecular chlorine in the chlorination and hypo-
chlorite stages of the conventional bleaching sequence, it is of greater
importance to minimize formation of chloro-organics through a cost-effec-
tive means to reduce the amount of chlorine utilized in the chlorination
and hypochlorite stages, rather than rely on post-treatment technologies
such as advanced wastewater treatment systems. Unl~ke the Kraft Paper
Industry (virgin wood processing), the recylced paper industry is ~ust
starting to deal with the issue of chlor~nated tox~ns including the ini-
tiation of pro~ects involving the reduction of chlorine and hypochlorite.
PRIOR ART
All of the more common treating sequences employed or proposed for
- bleaching and delignifying of kraft pulp as well as those concerned with
bleaching of secondary fibers are chlorine based. While some experimental
research has been directed to the use of molecular oxygen in processes for
bleaching of secondary fiber (Markham, L. D., et al., TAPPI 1988 PULPING
CONFERENCE PROCEEDINGS, pp 189-196), these attempts have failed to produce a
pulp having acceptable high brightness without also using comparatively
large amounts of chlorinated chemicals in the bleaching sequence.
2~2~90~
Among the objects of the present invention are:
A. To avoid or minimize the production of harmful chlorinated products
in the deinking and bleaching of secondary fiber materials.
B. To enable deinking and bleaching of secondary celluosic fiber to
target brightness at least as high or even higher than that heretofore
attainable, without necessitating resort to the extensive use of chlorinated
chemicals.
C. To provide a process for deinking and oxygen bleaching of secondary
fiber wherein redeposit of residual ink and/or other contaminants during
washing is avoided.
D. To enable effective bleaching of secondary fiber to desired
brightness notwithstanding high amounts of residual lignin present in the
initial pulp.
SUMMARY OF THE INVENTION
In accordance with the present invention pulped secondary fiber, after
deinking including conventional washing and cleaning, is treated with an
oxygen-containing gas in the presence of added alkali, and by washing in an
aqueous medium containing dissolved surfactant, whlch may be followed if
desired by further treatment in a final bleach stage. It has been found
that such proposed presence of surfactant during the wash prevents
redeposition of residual ink and other contaminants on the fiber. Moreover,
the use of the surfactant wash was found to enhance the bleachability of the
pulp in a subsequent or final chemical bleaching stage.
In accordance with a preferred embodiment of the invention, surfactant-
containtng alkaline liquid washed out from the pulp is recycled to a
selected stage of the deinking sequence, with consequent important savings
in operation and chemicals costs.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more clearly understood and its several advan-
tages appreciated from the description which follows read in connection with
the accompanying drawings, wherein:
~239~4
-
Figure 1 is a process diagram depicting a system for the oxygen stage
and the surfactant wash applied to the secondary fiber pulp in practice of
an embodiment of the invention.
Figure 2 is a graph showing the effect of surfactant wash on attained
br~ghtness under conditions corresponding to Example 1 of the description.
Figure 3 is a series of bar graphs showing the effect of process
variations on attained pulp brightness at various stages of the bleaching
sequence.
Figure 4 is a graph showing the effect of sodium hydroxide dosage on
attained pulp brightness before and after peroxide bleach.
Figure 5 comprises graphs showing the effect on attained brightness
by variations in retention time in the treating sequence at two different
temperatures.
DETAILED DESCRIPTION
In general, practice of the present invention involves the use of oxy-
gen, alkali and surfactant to bleach and deink secondary fiber. As shown
in Figure 1, after the secondary fiber material has been pulped, cleaned,
deinked and washed by conventional procedures it is subjected to an initial
oxygen bleaching stage (10). The treatment with molecular oxygen is
conducted in an aqueous alkaline medium under pressure. The selected
process conditions depend upon the type of recycled or salvaged fiber
starting material supplied. In general, the oxygen reaction is conducted at
a temperature in the range of 60-130C, sodium hydroxide dosage in the range
of 1 to 7% (by weight of air dried pulp), during a retention time of 0.1 to
2 hours at a pressure of 20-150 psig. Following the oxygen treatment the
pulp is diluted (12) and washed (14) on a vacuum filter in water containing
0.1 to 1.0% (by weight of pulp) surfactant. The surfactant wash serves to
keep residual ink and other contaminants from redepositing. The thus washed
pulp may then be subjected to a final bleaching stage (15) and again washed
and dried on a vacuum filter as indicated at (16).
The preferred operating conditions to be employed in individual cases
will depend largely on the particular makeup of the starting recycled fiber,
as to lignin content, amount and type of ink present, content of coatings
202 3g~
and fillers, etc. Treatment at lower than required severity limits on pulp
having high amounts of any of the contaminants above mentioned would result
in smaller than desired increase in brightness. Operation at condit~ons
much beyond the listed upper limits would result in large loss in strength
and viscosity and would entail large capital constraints on the equipment
needed for effective bleaching and deinking of the pulp.
Without relying on any particular theory to account for the unexpected
high improvements in pulp brightness achleved in practice of the inventlon,
it now appears that at least two contributory factors are present. First,
during the oxygen treatment stage delignification of any contained ground
wood (unprocessed f~ber) takes place, thus removing lignin color bod~es by
breaking these down and washing them out of the pulp. Also, residual ~nk
that has not been earlier removed from the fiber, is oxidized and released.
Without the inclusion of surfactant in the washing step the ink and residual
lS color bodies would normally redeposit onto the pulp. The surfactant, on the
other hand, removes or prevents such deposition.
Among the other benefits obtained by the invention is the decrease
or total avoidance in the final bleach of the otherwise needed use of chem-
icals, such as hydrosulfite andlor chlorinated compounds, that are harmful
20 to the environment. Accordingly, it becomes possible that a typical f~ve
stage bleaching sequence can be reduced to a two or three stage sequence
with resulting reduction in capital equipment costs.
A number of experiments were carried out in the laboratory to determine
the effect of washing the pulp in aqueous surfactant solution follow~ng the
25 oxygen bleaching step. Two different procedures were followed. In Pro-
cedure I the sequence designated sP was employed in Procedure II (desig-
nated (CEoP) a moderate chlorination stage was employed preceding the
oxygen treating step.
The operating sequence employed in Procedure I is substantially that
illustrated in Figure 1 of the accompanying drawings.
~23~a4
. _
EXAMPLE 1
Procedure I. - The OSP Process (Oxygen-surfactant, Peroxide)
s A. Standard Oxygen Bleaching Stage (O):
The cleaned and washed pulp was placed in a laboratory oxygen reactor
which consists of a pressurized reactor, mixer, flow controls, and
condition monitors. An amount of water and sodium hydroxide was added
to the pulp at a 10% consistency of pulp to water (sodium hydroxide
amounts varied). Then the reactor was sealed and heated with both
steam and an electric mantle (to 60-130C). Next, the reactor was
pressurized with oxygen to 30-150 psig and the hlgh shear mixer was
turned on for one minute. The pulp was retained in the reactor at
these conditions anywhere from thirty minutes to two hours with peri-
odic mixing at ten-minute intervals.
B. Surfactant Wash (S):
The pulp from the oxygen reactor was diluted and poured into a beaker
where it was mixed w~th .25-2% by weight of pulp of a surfactant. This
mixture was then poured into a vacuum filter and rinsed with
approximately 4000 mls of water per 60 grams of air dried pulp.
C. Peroxide Stage (P):
After being washed and filtered the pulp was placed in a polyester bag
with 1% sodium hydroxide dosage and 1% hydrogen peroxide dosage. Water
was added to make the pulp a 12% consistency. The bag was heat sealed
and placed in a constant temperature bath at 150-180F, and 60-120
minutes. The pulp was then removed from the bath and bag, put into
the vacuum filter, and dried to approximately 25Z consistency.
2~23~
Viscosity (T230), handsheets (T218), and brightness (T217) determina-
tions were made in accordance with the respective TAPPI Standard Test
Procedures. Chemical charges are on a weight percent basis, pulp
weight is air dry basis. The listed test procedures are described in
5TAPPI: Standard Test Methods 1989.
The operating conditions employed in the runs using Procedure I are set
out ~n Table 1 below and the measured brightness of the pulp at the several
treating stages is reported in Table 2.
Table
Oxygen Conditions Peroxide Conditions
Temp., C 130 -65
Alkali dosage (%) 5 1.0
Retention Time (hrs) 1 2
Pressure (psig) 150
Surfactant (%) 0.5
Peroxide (%) - 1.0
Table 2
Stage Brightness (ISO units)
With Without
Surfactant Surfactant Delta
Initial 56.9 56.9
Oxygen 69.0 69.0
Wash 71.4 70.3 1.1
Peroxide 78.0 74.1 3.9
Although the brightness of the pulp showed a measured increase of about
1.56X following the surfactant wash step, the increase ~n brightness measured
30 after the final peroxide bleach was surprisingly over 5%.
2~3~
EXAMPLE 2
Procedure II - The CEoSP Process
s A. Chlorination Stage (C):
Sixty oven-dried grams of pulp at 4% consistency to water was placed in
a polyester bag and an amount of chlorine water added to make a charge
of 2.0% active chlorine. The bag was heat sealed and the chlorination
proceeded at ambient temperature for one hour. The pulp was filtered
and washed with water.
B. Alkali Oxygen Extraction Stage (Eo)
Procedure for (IA) was followed with different conditions within the
reactor (as reported below) being observed. Temperature was set at
65-100C. Pressure was set 30-50 psig, and for a l0-minute retention
time to simulate the upflow tube of an Eo reactor. Total retention
time was set at 60 minutes and the sodium hydroxide dosage was held at
1.5%.
C. Surfactant Wash (S): Same as (IB).
D. Peroxide Stage (P): Same as (IC).
E. Other: Same as (ID).
The data compiled using procedure II (CEoSP) is reported in Table 3
below and the attained Brightness at the several stages is set out in
Table 4.
2~23904
Table 3
Conditions: C12_ E ~ P
Temperature, C 45 65 65
C12 Dosage, (%) 2.0 * *
Consistency (%) 4.0 10.0 12.0
Retention Time (hrs) 0.5 0.83 2.0
Pressure (in upflow tower) psig * 30 *
Retention Time (in upflow
tower) (min) * 10 *
Peroxide Dosage (%) * * 1.0
NaOH Dosage (%) * 1.5 1.0
Surfactant Dosage (in washer * 1.0 *
after Eo) (%)
NOTE: Oxygen was mixed in the reactor for the first ten minutes of the Eo
run, at two one-minute intervals every five minutes.
Table 4
BRIGHTNESS (ISO)
With Without
Stage Surfactant Surfactant Delta
Initial 56.9 56.0 --
C12 61.0 61.0 __
Eo 66.8 66.8 --
Wash 69.2 67.9 1.3
Peroxide 77.6 73.4 4.2
All of the runs in Examples 1 and 2, as well as those hereinafter
reported, were made on commercial, unbleached, recycled paper pulp. The
surfactant used in the runs of Examples 1 and 2 was a nonionic blend of
nonylphenoxy(ethyleneoxy)ethanol, ethylene glycol and water.
From the data observed in the foregoing examples it appears that the
surfactant treatment enhanced the bleachability of the pulp in the final
treating stage thereby accounting for the unexpectedly high increase in
brightness.
2~2~9~
-- 10 --
In following the procedure of Example 2 wherein an initial chlorine
bleaching step is employed, only comparat~vely low to moderate concentra-
tions of act~ve chlorine are required, in the preferred range of about 0.5
to 3.0Z active chlorine in the aqueous medium, and generally at less than 5X.
s
EXAMPLES 3 to 10
A series of experiments were conducted with variations in process
conditions to determine at what stage or stages in the bleaching sequence
the washing with surfactant solution would be most beneficial. The results
are plotted in Figure 2 of the drawings.
Eight experiments were run in all with four being run at (A) set of
conditions (100C, 4% NaOH, RT-60 min, 130 psig), another four exper~ments
at (B) set of the conditions (130C, 5% NaOH, RT-45 min, 130 psig). One
exper~ment from each set was kept as a control, one pair was treated prior
to the oxygen run with a surfactant wash, one pa~r treated after the oxygen
run with a surfactant wash, one pair treated prior and after with a sur-
factant wash. Then brightness was measured, the results of which are
reported in Table 5.
20TABLE 5
~A) Brightness (B) Brightness
Oxygen 1) 62.2 2) 67.9
Surfactant-Oxygen 3) 64.5 4) 68.8
Oxygen-Surfactant 5) 65.1 6) 71.8
Surfactant-Oxygen- 7) 69.0 8) 72.0
Surfactant
From the data shown in Table 5 it appears that surfactant wash~ng
followed by an oxygen reaction, at B conditions, in turn followed by a
further surfactant wash gives the best brightness results (72). What also
must be taken into account ~s oxygen-surfactant conditions do basically as
~Z3 gO~
good a job (71.8) with one less washer and only half the amount of sur-
factant. If one wanted to achieve high brightness at a milder set of
conditions (A), the surfactant-oxygen-surfactant sequence affords the best
route.
As show in Table 5, treatment with surfactant before the oxygen treat-
ment does obtain some improvement in brightness but less than that achieved
by application of surfactant in the washing step following oxygen treatment.
EXAMPLES 11-14 The effect of different types of surfactants
There are basically three different types of surfactants: nonionic,
anionic, and cationic. In the runs reported below one oxygen reaction was
performed and the pulp from that reaction was broken up into four samples;
the tested brightness of each is set out in Table 6.
Table 6
Brightness
11.Washed with DI water (1000 mls/), then bleached 74.5
with peroxide.
12.Washed with nonionic surfactant in a 1000 mls 77.3
of DI water, then bleached with peroxide.
13.Washed with anionic surfactant in a 1000 mls 76.2
of DI water, then bleached with peroxide.
14.Washed with cationic surfactant in a 1000 mls 72.3
of DI water, then bleached with peroxide.
The surfactants employed at 0.5% by weight of pulp, were
Run 11 none
Run 12 nonylphenoxy(ethyleneoxy)ethanol in aqueous
ethylene glycol
Run 13 Adogen 464 (Ashland Chem.) Methyltrialkyl
C8-C10-ammonium chloride
Run 14 Sodiumdioctyl sulfosuccinate (American
Cyanamide)
2~23~
EXAMPLES 15-17 Process Conditions
Numerous experiments were run to determine what range of condit~ons
(temperature, pressure, retention time, caustic dosage) were most appro-
priate for the oxygen stage. Also examined was the effect shifting certain
conditions while holding others constant, would have on the final br~ghtness
of the pulp.
Each of the experiments of these examples addresses a particular condi-
tion or conditions.
EXAMPLE 15
The effect of sodium hydroxide dosage on pulp brightness.
Temperature - 130C, Pressure - 150 psig, Retention Time - 45 m~n.
Table 7
Brightness
NaOH % Dosage After Oxygen StageAfter Oxygen & Peroxide Sta~e
1.5 70.2 74.0
3.0 70.1 74.6
4.0 70.0 75.1
5.0 69.9 78.0
5.5 71.8 79.1
6.0 72.3 80.6
7.0 73-4 82.2
The results are plotted in Figure 3.
- ~a23s~
- 13 -
EXAMPLE 16
The effect of retention time and temperature. Pressure held at 130
psig, NaOH at 4%.
Table 8
Brightness
Retention Time 100C 130C
45 min 65.5 70.0
90 min 67.6 70.1
135 min 69.7 70.8
The results are plotted in Figure 4.
EXAMPLE 17
The effect of pressure on brightness results. Temperature held
constant at 100C, NaOH at 4%, and retention time at 1 hour.
Table 9
Pressure PSIG Brightness
63.4
65.2
67.1
120 68.3
150 69.6
In practice of the present invention desired brightness of the treated
pulp often may be obtained without necessitating a final chemical bleaching
step after the oxygen gas treatment and washing with surfactant. If such
chemical bleaching is used, it is preferred to employ peroxide. The use of
controlled small amounts of hypochlorite in a final bleach sequence is not
ruled out, however, particularly in instances that chlorine or chlorine
compounds have not been earlier employed in the involved pulp treating
sequence as to result in a total amount having a negative impact on the
35environment. !
~023g~
- 14 -
As indicated in Figure 1 of the drawings, the surfactant may be in-
troduced at any one ore more points of the pulp treating sequence, par-
ticularly as indicated by the arrows 20, 21 and 22. In addltion, part of
the surfactants, if desired, may be introduced into the oxygen reactor (10)
as shown at 23. The pulp, after rinsing on the vacuum filter (14), will be
substantially free of applied surfactant.
In accordance with a preferred embodiment of the invention at least
part of the alkaline filtrate from the oxygen stage washer 14 is recycled to
a selected stage of the deinking sequence, whereby costs of energy supplied
and chemical consumption costs are greatly reduced. As shown, by the dotted
lines in Figure 1, the wash liquor filtrate 25 is dischargewd from washer 14
and a controlled portion is recycled to a selected stage of the deinking
sequence. Thus, as shown in the illustrated embodiment (Figure 1), the
withdrawn portion of the filtrate 25 may be returned to the hydropulping
step (line 26) or to the deinking step at the flotation stage (line 27).
Optionally a part of the liquor recovered from line 25 may be returned and
included as part of the wash water employed in the oxygen stage washer 14 as
shown at 28, thus providing useful surfactant at this stage.
The oxygen stage filtrate 25, it should be noted, contains heat, water,
caustlc and surfactant (washed out from the pulp). These resources would
probably be sent to sewer (as waste) in normal operation of a secondary
fiber bleach plant. By the proposed recycling step important savings in
mill operation are attained without sacrifice in product quality.
3521p
