Note: Descriptions are shown in the official language in which they were submitted.
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I
PAPER PULP DRAINAGE AID
Field of the Invention
- This invention relates to improvements in treating pulp and process water in
paper mills and in particular to a drainage aid for use in recycled paper mills
Background to the Invention
The use of recycled paper to produce paper pulp creates problems in the free
drainage of the paper pulp and the treatment and recycling of the process water
Because of the wide range of source material ,a large range of components are
present in the bacl~water. These include the organic components fibres, fibrils,pitch, starch derivatives. lignin, synthetic polymers and inorganic components to
include clay, titanium dioxide, gypsum, talc, chalk, zinc oxide, aluminium
sulfate, ferrous sulphate, and calcium carbonate. Much of this material is
present as finesl i.e. below 120 micrometresl. It is preferable to retain some of
the fines, which may comprise up to 5% of the paper sheet on the filter mat,
without reducing drainage rates and paper properties and consequently
affecting process times.
Enzyme treatment of paper pulps has been proposed to improve the freeness
and physical properties of paper pulps with some ~l?.iming success with
recycled fibre as well as virgin fibre . The enzymes that have been proposed arexyl~n~ces. cellulases, and other hemicellulases. These are commercially
available as crude mixtures characterised by the dominant presence of the
named enzyme. One defect of these treatments is that careful regulation of the
addition and treatment conditions is required, because excessive treatment can
~ lead to a decline in drainage. Another ~liffic~llty is that paper pulps are usually
neutral and many cellulases are active in the acidic pH range.
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U S A patent 4923565 proposed the use of a cellulase (having cel~ulase and
xylanase activity), as a drainage aid for recycled paper pulp. One shortcoming of
this proposal is that the pH must be adjusted to within the range 3 to 7.
An improvement to this patent is U S A patent 5116474 which utilises cellulases
active in the pH range of 7 to 9.
U S A patents 51~9497 and 5423946 suggest using the drainage aid of the '565
patent with cationic polymers such as acryl~mi-l~s
Patent specification WO 91/17243 discloses that a cellulase having an endo -
gluc~n~.~e component active between pH 6 and 10 can be used as a drainage aid
for paper pulps including waste paper pulp. The purpose of the enzyme is to
reduce h~rshness or clarify colour in cellulose containing fabrics
Brief description of the invention
It is an object of this invention to improve the drainage of recycled paper pulpusing a more effective enzymatic treatment. The term "recycled paper" is
intended to cover paper pulp, which includes a major portion of paper or
paperboard that has been recycled.
To this end the present invention provides, as a drainage aid for improving the
free drainage of recycled paper pulp slurries, a preparation cont~ining a major
portion of a starch hydrolysing enzyme, preferably an amylase and more
2() preferably an alpha-amylase.
The invention also includes a method of improving drainage of recycled paper
pulp which includes the step of adding to the pulp a drainage aid cont~ining a
major portion of a starcb hydrolysing enzyme, preferably amylase, prior to the
separation of the water from the pulp. The drainage aid is added in an amount
2j of at least 0.05% by weight of oven dried paper forming the pulp, ~or a time and
at a temperature sllffi-,ient to produce an improved drainage rate and at a pH at
which the enzymes are active. At the lower coneent~ ation the addition of enzyrne
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will improve drainage to the extent that the p.aper m~rhine speed and
production can be increased by about 5% or more.
In part this invention is predicated on the discovery that drainage of recycled
paper pulps is hampered by co~ti-lgs on solid components in the pulp,
particularly by the fine particles in the pulp. A .qiFnific~nt proportion of recycled
paper contains starch or starch based materials and in part this invention is
based on the realisation that that enzymatic treatment may remove this coating.
This invention is also founded on the discovery that amylase is able to act on the
coatings of particles in the pulp regardless of its inner composition which is not
the case with previously proposed enzymes such as cellulase. It is thought that
the coatings are starch based and cellulases have little effect on the starch, but
are more likely to act on the particles which are pri-n~rily cellulose. This further
discovery also inrlic~tes that amylase is specific in its action on the starch
components. This has the consequence that careful regulation of the tre~t~ent
iS not nece.ss~ry and PYcessive treatment does not decrease the drainage
improvement. The improved effectiveness of a drainage aid having a major
amylase component may be due to the coatings on the fines being largely
composed of starch and thus more susceptible to amylase or other starch
hydrolysing enzyme treatment. Because the amylase has little action on the
2~1 cellulose component of the fibres, excess treatment is unlikely to cause any
deleterious effect. This contrasts with the prior art enzymes which are prim~rily
cellulases which are usually recommended for papers made with a high content
of virgin fibre.
Although amylase is a major component of the drainage aid, other enzymes,
2j particularly cellulases active in the neutral- ~lk~ e pH range, particularly pH
6 to 9 may be present. Some cellulases do improve drainage which is inhibited
by cellulose based materials in the pulp and part of drainage inhibition in
recycled pulps may be reduced with cellulases. For many recycled pulps or
mixed virgin and recycled fibres a mixture of amylase and cellulase may provide
;~) the optimum improvement.
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Detailed description of the invention
Process conditions for dewatering paper pulp using the drainage aid of this
invention are typically:
temperature 40 to 90 oC
pH 6to9
enzyme dosage 2.5x106 to 15X106 IU of activity per tonne of pulp which for
an alpha amylase such as BAN 240L is equivalent to 0.5 to
3 Kg per oven dried tonne of recycled paper.
contact times 15 to 120 minutes
o The International Unit [I U~ of enzyme activity is the amount of enzyme
necess~ry to produce 1 micromole of reducing sugar product per minute.
The enzymes used in the drainage aid can comprise an amvlase alone preferably
a crude amylase or an amylase in comhi~tion with a cellulase such as
endogluc~n~se. xyl~qn~ce, or other hemi cellulases such as m~nn~n~qe, all of
which are preferably active in the neutral to ~Ik~line pH range of 6 to 9. A
preferred crude alpha- amylase is that derived from Bacillus subtilis. Starch
hydrolysing enzymes from other microbial species may also be used inrll~ling
B.licheniformis and Aspergillus oryzae
In addition to the amylase drainage aid the convPntion~l polymeric flocc..l~nts~such as cationic polyacrylamide, which also aid in drainage can be used. The
amylase presence will allow a reduction in the amount of the floccl~lz.ntc
required.
Laboratory scale drainage tests were carried out on backwater samples from a
recycled paper plant. A crude and a purified alpha- amylase was used to treat
2~ the backwater s~mrles. The pl~tific~on was achieved by chrom~toEraphic
foc~c~inE. Drainage pPrfo m~nce was measured using a modified Schopper-
egler drainage jar. A brass woven screen with 50 micron gaps captured the
fines to form a filter cake. This filter cake sllfficiently impeded the backwater to
permit accurate drainage readings to be taken by continuously collecting and
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weighing the filtrate. Drainage improvement was evaluated by comparing the
difference between control and enzyme treated samples over 30 minutes.
Example 1
Experiments were conducted using both crude and purified alpha amylase as
identified in table 1. The backwater characteristics and fines size dist~ibutionare set out in tables 2 and 3.
Table 1
alpha-amylas~characteri.~ tion
alpha- CMC Xylan oat Xylan Starch Amylo-
amylase IU/mg spelts birchwood IU/mg pectin
IU/mg IU/mg IU/mg
crude 0.006 0.649 0.3g5 243.750 291.667
purified 0 19.875 0 175.624 182.500
Table 2
Backwater char~cter-s~tion
Batch pH Conductance micro S/cm Drymass glL Ash
%
7.23 8~0 6.31 18.19
2 , .12 980 6.53 20.55
3 7.34 860 7.08 19.04
, Table 3
Particle ~ ize analvsis
Number density parameters (microns) Batch 1 Batch 2 Batch 3
Median 1.20 0.89 0.96
Mean 1.80 1.35 1.55
SD 2.13 1.56 2.00
Mode 1.25 0.75 0.75
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G
The results of the experiments are set out in.table 4.
Because the fines in the backwater samples are in a higher concentration than
in the pulp the dosage rates are higher because the surface area to volume ratios
for the fines is 20 to 30 times the ratio for pulp. Thus the dosage requirement for
treating pulps will be .si~ific~ntly less than the table suggests.
Table 4
Drair age analysis
Batch amylase amylase amylase Drainage vol. Drainage
purity dosage mg/Ldosage After 30 mins improvement
units/K~ mL %
1 control 0 0 768.57 na
1 pure 0.15 4,171 791.07 2.93
1 crude 0.15 5789 804.56 4.68
1 crude 1.5 57,890 874.g 13.83
1 crude 15.0 578,900 932.71 21.36
2 control 0 0 764.19 na
2 pure 0.15 4032 774.59 1.36
2 crude 0.15 5597 793.86 3.88
2 crude 1.5 55,970 822.92 7.69
2 crude 15.0 559,700 902.34 18.08
3 control 0 0 707.93 na
3 pure 0.15 3720 725.6 2.50
3 crude 0.15 5163 733.87 3.66
3 crude 1.5 51,630 794.06 12.17
3 crude 15.0 516,300 861.49 21.69
These results show that amylase acts on the surface of all the components in thebackwater regardless of inner composition, by removing starch coatings on both
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fines and fibres. F.~rces.~ive treatment with cellulases tends to increase the fines
leading to a decline in drainage performance and paper strength.
The large surface area and particulate nature of the fines is regarded as the
major contributor to poor drainage perform~nce of recycled pulps. By selectivelyhydrolysing the surface m~teri5~1 on fines and fibres, the interaction between
particle surface, retention and drainage aids and water is thought to be
enhanced. This consequently encourages better drainage in the forming section
of the paper plant.
Example 2
o A mill trial was conducted on a twin wire fourdrinier m~(~hine producing liners
and medium for corrugated boxes. The m~(~hine is capable of producing between
12 and 15 tons of paper per hour from furnish consisting of mixed waste paper,
newsprint and OCC.
The enzyme selected for the mill trial was BAN 240L which is an alpha amylase
preparation produced by Novo Nordisk. It is a clear brown watery liquid
obtained from a purified culture of Bacillus subtilis variety amyloliquefaciens.
The enzyme a~ ition comm~nced from 9am on day 1 and ceased 12pm on day
3[appro~cim~tely 48hoursl. The enzyme was dosed at 30 llhr [as received basisl
in at two points in the stock preparation area.
2~) Table 5 shows the mill perform~nce over 7 days with the enzyme a-l-litio~
oc~rring on days 1 to 3. During the period of enzyme atlflition the machine
speed increased by 4.49% compared to the operation without enzyme a-lAitinn
In the table production rates have been extrapolated to remove lost time.
Product output increased 6.5% but when adjusted for trim the increase was
4.48%.
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TABLE 5
Trial Days 1 2 3 4 5 6 7
Av. Dry end speed 516.21 523.4 507.34 4g3.05 490.12 493.28 497.31
mlmin
Production Tlday 314.~1 318.87 319.91 300.38 298.65 296.27 298.43
T~m mm 2788.60 2843.00 2800.46 2717.26 2806.65 2775.48 2729.96
An improvement in the freeness of the pulp as measured by the Schopper-
Reigler [SR~ drainage values in the headbox and m~chine chests, and for both
top and bottom lines was observed.
TABLE 6
Schopper-Reigler Freeness values of pulp
Headbox lleadbox Machine chest Machine chest
top bottom -top - bottom
Dunng trial 35 40 31 40
After tri~ 57 59 51 63
o This shows that the enzyme decreases the SR freeness values by 32% to 39%
depending on the sample origin.
This compares favourably with the performance of the cellulases with recycled
paper pulp disclosed in USA patent 5116474 which obtained decreases in SR
values of between 5% and 23%
This mill trial showed that a cost ~ ;live enzyme treatment produced an
additional 19.4 tonnes of paper per day, increased m~hine speed by 22.14
mJmin and improved the S R values.
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Example 3- Comparative
The enzymes as described in tables 7a 7b and 7c were tested for comparison
purposes.
"na" means the data is not available
TABLE 7a
Name AMG 300L BAN 240L Celluclast D~nim~Y L
1.5 L
Enzyme Amylo- Alpha Cellulase Endo-
glucosidase amylase gll~e~n~ce
Organism ofAspergillus R~cil11~s Trichoderma Non patho-
origin niger subtilis reesei genic mould
Density g/mL 1.2 1.2 1.2 na
p~I optima 4.5 5-7 4.5-6.0 4.5-5.5
Temp.oC 60 50-70 50-60 45-55
React~on time na na na na
Dosage na na na na
TABLE 7b
Name Fungamyl Irgazyme 40 Novozyme Pergalase
800L 342 A40
Enzyme Alpha- Xylanase Cellulase,glu Cellula~e
amylase lno cellulase canase and Pretlnmin~nt
activity] hemir~llulase
Organism ofAspergillus Trichoderma na Trichoderma
ongin oryzae lo-~gibrachiat longibrachiat
um um
Density glmL 1.25 1.01-1.15 na 1.01-1.15
pH optima 4.5-6.0 7.0-8.5 7.5-8.5 5-7
Temp. oC 55-60 50-70 ~0 35-55
Reac~ion time na 0.5-3 hrs lnr 0.5-2 hrs
Dosage na 0.2-0.7 l/t 4~t 0.5-1.811t
I()
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TABLE 7c
NamePromozyme 200L Pulpzyme HB San Super 240L
Enzyme p~ n~se Xylanase Amylogluco~ida~e
Pullan6-glucano- Endo-1,4-beta-D- [and alpha amylase
hydrolase xylanase
Organism ofBacillus B~cteri~l na
origin acidopull~llytics
Density g/mL 1.25 na 1.25
pH optima 4.0-6.0 7-8 5.5
Temp. oC 50-60 5~ 55
RP~ction time na 2-3 na
Dosage na lkg/t na
These enzymes were tested in the laboratory to assess the drainage
improvement with pulp backwater in cimil~r f~chion to example 1. The results
are shown in table 8. The reducing sugar increase is an indication that the
enzyme was active. These results show that the alpha amylases BAN 240L and
FUNGAMYL out p~rformed the other enzyme types with the exception of the
cellulase CELLUCLAST.
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ll
TABLE 8
Trea~ent of backwater con~sinin~ fines
wi~h enzymes listed in tables 7a, 7b and 7c
- Enzyme ! Drainage Reducing sugar I improvement(%) increase (mM)
AMG 300L 0.7 9.2
BAN 240L 4.0 ~ 0.77
CELLUCLAST 1.5L 2.8 1 0.28
DENIMAX L 1.7 ~ 0.94
FUNGAMYL 800L 2.5 2.75
IRGAZYME 40 0.9 0.78
NOVAZYME 342 1.3 0.78
PERGALASE A40 0.4 O.o
PROMOZYME 200L 0.0 1.35
PULPZYME HB 1.0 1 0.31
SANSUPER240L 0.9 1 4.81
Example 4- Flocc~ nts
Backwater samples having a consistency at 0.631%, were treated with alpha
amylase obtained from Bacillus licheniformis, incubations were performed at O
and 300 IU/ml at 500C for 3 hours. High molecular weight cationic
polyacrylamide {CATPAMl was added at a set dosage of 0.3 micrograms per
o lOOOmL of backwater. The backwater cont~ining the polymer was inverted 30
times in a glass measuring cylinder. Particle size analysis was performed in therange 0.2 to 60 micrometres.
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TABLE 9
alpha-~mylase and polymer treated backwater
ParticleMeasurement Volume Volume
No polymer ~llflition polymer addition
¦ CONTROL - Median 19.3 1 23.46
- Mean 20.91 ~ 23.91
- SD 14.30 14.75
alpha-Amylase-
Median 17.21 25.63
- Mean 19.68 '25.31
-SD 14.32 !~5.67
Control particle count decreased from 212056 to 144617 while the a-Amylase
particle count decreased from 178404 to 128787.
In the ~hsence of polymer the particle count of the enzyme treated backwater
decreased by 15% relative to the control. The particle count decreased further
with the ~d~itio~ of polymer to the backwater. The control decreased by 32%.
whereas the enzyme treated backwater decreased by 40% relative to the control
o without polymer. The mean par~cle mass for the enzyme treated backwater,
with polymer, increased by 6% relative to the control with polymer. These
results imply that the enzyme treated fines are more receptive to polymer
inter~rtior ~ as ~monstrated by the greater ~oc size and lower particle count.
These results compare favourably with the data in USA patent 5169497 which
5 show an improvement in freeness when a cationic polyacryl~mid~ is added to a
cellulase treated recycled paper pulp.
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S~lmmnry of benefits
From the above results it can be seen that the present invention by improving
drainage allows the speed of the paper section to improve, increasing the outputof paper from the recycled paper stock.
In addition the following i~n~ill5/ry benefits can also be recognised
Avoids degradation of cellulose
Overdosing does not degrade paper
Iodine can be used to monitor the reaction
The alpha-Amylase ls inactivated in the drying section
. alpha-Amylase is a food grade enzyme and is safe for use in making food
p~k:~ging
alpha-Amylase is commonly available
