Note: Descriptions are shown in the official language in which they were submitted.
WO92/16~7 PCTtFl92/00076
12 1 ~ 9
A method for reducing pitch trouble in mechanical
pulp
The invention relates to a method for reducing
pitch trouble in mechanical pulp and/or papermaking
pulp containing mechanical pulp by a cellulase/hemi-
cellulase treatment.
Mechanical pulps include groundwood pulp,
refiner mechanical pulp, pressure groundwood, thermo-
mechanical pulp and chemi-thermomechanical pulp
(CTMP). In the production of mechanical pulp, fibres
are detached from the wood mainly mechanically by
utilizing heat. The fibre is subjected to stress so
that the lignin binding fibres together is softened,
and the fibres are detached from each other when the
elasticity of lignin fails.
Wood contains about 1 to 10% of pitch and
extractants soluble in organic solvents in addition
to its main components (cellulose, hemicellulose and
lignin). Pitch contains fatty acids, resin acids,
glycerides, etc. It is well-known that the pitch
content in softwood, which is the primary raw
material of mechanical pulp, is high as compared with
hardwood, for instance. At the pulp production stage,
pitch components are separated from the pulp into a
free space, e.g., in the white water. Pitch suspended
in the white water is in the form of particles 0.2 to
2 ~m in diameter, also known as colloidal pitch.
In papermaking, pitch may deposit on pipes,
33 containers, wires or presses, causing such pitch
troubles as inferior paper quality (e.g. holes and
spots) and paper breakages. It may also block felts
and wires, hampering the removal of water from a
paper web. Pitch troubles may also lead to long
production stoppages. They occur frequently
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WO92/16687 PCT/Fl92/00076
2 -
especially when sto~k containing plenty of mechanical
pulp is used as raw material.
Traditionally, wood has been stored outdoors
for long periods of time (3 to 6 months or more) in
an attempt to avoid pitch trouble. In this way, pitch
components are degraded mainly by the oxidizing
effect of air. Such inoryanic substances as talc and
anionic surfactants that disperse pitch particles
have also been used in the prevention of pitch
trouble.
FI Patent Application 870072 discloses a pitch
prevention method which utilizes certain water-
soluble polyquaternary amines. These compounds are
added to the pulp or paper making system to avoid
pitch trouble.
FI Patent Application 900679 discloses a method
for reducing the pitch content of wood by means of
fungi degrading the pitch and resin components
present in wood.
FI Patent Application 895901 discloses a method
for avoiding pitch trouble associated with mechanical
pulp by adding acylglycerol lipase enzyme to the
stock or white water. This enzyme degrades tri-
glycerides contained in pitch.
The use of enzymes, including cellulase and
hemicellulase, for improving the properties of pulp
is known pe~ se. For example, FR Patent Specification
2557894 discloses a method for treating cellulose
pulp by xylanase in order to shorten the beating
time. CA Patent Specification 758488 concerns a
method for improving the beatability of pulp by a
cellulase/pectinase/lipase treatment. FR Patent Spe-
cification 2571738 concerns a method in which pulp is
provided with special pulp properties by cellulase
treatment.
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WO92/16687 PCT/Fl92/00076
FI Patent Application 874113 (corresponds to FR
Patent Application 8613208) relates to a method for
improving the properties of recycled pulp, for
instance, tin this particular case a pulp containing
plenty of chemical pulp) by cellulase/hemicellulase
treatment. FI Published Specification 81394, in turn,
aims at improving the drainability of mechanical pulp
by hemicellulase treatment (no cellulase).
In addition, FI Patent Application 890214
describes treatment of the white water of a paper-
making system by enzymes for degrading components
dissolved or dispersed from the pulp, such as
hemicellulose.
The object of the invention is to develop a
method for reducing pitch trouble associated with the
production of mechanical pulp, especially papermaking
pulp containing mechanical pulp. Methods known from
the prior art have been used with varying success,
and problems have not been completely avoided.
It ha~ now been unexpectedly discovered that
the pitch trouble associated with the production of
mechanical pulp can be reduced substantially by a
cellulase/hemicellulase treatment. In the pulp
filtrate water, there occurred an abrupt decrease in
the extractant concentrations indicating the pitch
content, especially in the fatty acid, resin acid and
sterol concentrations, and the turbidity of the
filtrate water was reduced.
In accordance with the invention, the pitch
trouble associated with the production of mechanical
pulp and/or papermaking pulp containing mechanical
pulp is solved by treating the mechanical pulp,
papermaking pulp containing mechanical pulp and/or
white water by an enzyme preparation containing cel-
lulase/hemicellulase enzyme activity.
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WO92/16687 PCT/F192/00076
~ 3~j .
It was fully unexpected that the cellulase and
hemicellulase enzymes, which, as is well-known, de-
grade cellulose and hemicellulose, also affect the
main components of pitch, that is, fatty acid, resin
acid and sterol type substances.
In practice, the reduction in the pitch trouble
become apparent e.g. in that the runability of the
paper machine was improved, the wires and felts re-
mained clean, and the number of holes and spots in
paper was decreased.
The enzyme treatment had also other
advantageous effects. For example, the drainability
of pulp was improved. The enzyme treatment did not
either deteriorate the optical or printing properties
of the pulp but its brightness, light scattering co-
efficient, compressibility and smoothness were
improved.
The enzyme treatment according to the invention
can be performed at any pulp production stage after
the mechanical detachment of fibres. The enzyme can
be added e.g. to a pulp storing container, storage
tower or metering chest. The enzyme treatment can be
performed before the bleaching of pulp, in connection
with a pulp bleaching process or after the bleaching.
The enzyme can also be added to the white water.
The cellulase/hemicellulase enzymes for the use
in accordance with the invention can be produced in a
known manner by means of actinomycetes, bacteria and
fungi.
It is also possible to use commercial
cellulase/hemicellulase preparations, such as Liftase
A40 (manufacturer Genencor International Europe
Ltd.), produced by the fungus Trichoderma longi-
brachiatum and having a CMCase activity (carboxy-
methyl cellulase activity) of 2,500 U/ml, a filter
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WO92/16687 PCT/Fl92/00076
5 2~
paper activity (FPU activity) of llO U/ml and a
xylanase activity of 500 U/ml. The carboxymethyl cel-
lulase activity and the filter paper activity de-
scribe the cellulolytic activity, and the xylanase
activity describes the hemicellulolytic activity.
The determination of the filter paper activity
is described in Ghose, T.K., Patnak, A.N., Bisaria,
V.S., Symposium of Enzymatic Hydrolysis of Cellulose,
Bailey, M., Enari, T.M., Linko, M., Eds. (SITRA,
Aulanko, Finland, 1975), 111 - 136; the determination
of the CMCase activity is described in Mandels, M.,
Weber, J., Adv. Chem. Ser. 95 (1969) 391-413; and the
determination of the xylanase activity is described
in Khan, A.W., Tremblay, D., LeDuy, A., Enzyme
Microb. Technol., 8 (1986) 373 - 377.
Other cellulase/hemicellulase preparations of
the same manufacturer (Genencor International Europe
Ltd), such as Multifect L250 and Cytolase 123, and
cellulase/hemicellulase preparations from other
manufacturers can also be used.
Suitable enzyme dosages given as enzyme
activities per kg of pulp dry solids are within the
following limits (U = activity unit):
Cellulases:
Filter paper activity 1 - 20,000 U/kg pulp
CMCase activity lO - 500,000 U/kg pulp
Hemicellulases:
Xylanase O - 2,000,000 U/kg pulp
Preferred enzyme dosages are:
Filter paper activity about 20 - 600 U/kg pulp
CMCase activity about 500 - lO,OOO U/kg pulp
Xylanase activity about 500 - lOO,OOO U/kg pulp.
The enzyme treatment is usually carried out
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WO92/16687 PCT/Fl92/00076
2 ~
within the pH range from about 2 to lO, preferably
within the range from about 4 to 8. The temperature
of the enzyme treatment may range from about lO to -
9O~C, preferably from about 25 to 70C.
In the following the invention will be
described more closely by means of working examples
based on laboratory experiments and mill test runs. -
The examples are merely illustrative and they are not
intended to restrict the invention. The measurements
were performed in compliance with the SCAN standards,
if not stated otherwise.
Example 1
Thermomechanical pulp (TMP) produced from
spruce (Picea abies) and having a consistency of 4%,
pH 4.9, a freeness value of 69 ml CSF and ISO bright-
ness of 66% was taken from a mill process and treated
with an enzyme preparation called Liftase A40.
Liftase A40 (manufacturer Genencor International
Europe Ltd.) is produced by means of the Trichoderma
20 longibrachiatum microorganism and the principal
activities contained in it are as follows:
CMCase activity 2,500 U/ml
FPU activity llO U/ml
Xylanase activity 500 U/ml
Liftase A40 enzyme was added under careful
mixing to the pulp at 55C in an amount corresponding
to 2.5 l/ton of pulp dry solids.
The dosages of the added enzyme preparation
given as cellulase/hemicellulase activities per kg
pulp dry solids were as follows:
CMCase activity 6,250 U/kg
FPU activity 275 U/kg
Xylanase activity 1,250 U/kg
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W O 92/16687 PC~r/F192/00076
7 ~ ~ ~ 3 ~
The enzyme was allowed to react with the pulp
at 55C and pH 4.9 while mixing the pulp at lS0 rpm
for one hour altogether. Samples were taken from the
pulp at uniform intervals, and the samples were
determined for turbidity and the final sample also
for extractant concentrations. In the liquid fraction
of TMP, turbidity is caused by extractants ~pitch),
suspended carbohydrates and other small components
detached from the pulp. Accordingly, the turbidity
describes approximately changes associated with all
the above-mentioned components. Separate analysis of
the extractants gives a more accurate result spe-
cifically as far as pitch is concerned. For turbidity
measurement, 250 g of the pulp suspension was centri-
fuged (1,800 rpm, 20 min). The supernatant (liquid
fraction) was recovered and measured immediately for
the turbidity with a Novasine Analite NTM-150
turbidity meter. Extractants pr~sent in the super-
natant were measured by gas chromatography.
A control sample was treated in a similar way
as the enzyme-treated sample but without enzyme.
The measuring results are shown in Table 1.
Table 1
Effect of enzyme treatment on the turbidity and
extractant concentrations of the liquid fraction of
TMP
CONTROLENZYME TREATED
TURBIDITY, NTU
- 0 min 320 320
- 10 min 300 190
- 30 min 310 100
- 60 min 330 25
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W O 92/~6687 PC~r/F192/00076
2~ ~`3 1 ~ ~ 8
EXTRACTANTS, mg/l
60 min
- fatty acids 65 6.2
- resin acids 21 2.5
- sterols 13 1.2
The results show that a significant reduction
in the turbidity of the liquid fraction of the pulp
occurs as soon as after a reaction time of 10
minutes. After a reaction time of 60 min, the liquid
fraction is almost clear, that is, has a turbidity of
25 NTU, and the concentration of extractants in the
liquid fraction has decreased to 1/10 of the original
value. This indicates that the extractants are
deposited on or adhere to the surface of the fibre
due to the enzyme treatment.
Example 2.
The practical significance of the reduction in
the pitch content of the filtrate water of mechanical
pulp was to be determined, that is, a mill test run
was carried out. The test run was carried out on an
LWC machine applying on-machine coating.
The mechanical pulp used in the machine was
peroxide bleached TMP, and as the experiments in
Example 1 were performed on unbleached TMP, a
laboratory check experiment series was performed
before the test run. Peroxide bleached TMP was
derived directly from a process with a consistency of
3.2%. The pH of the pulp was 5.5 and temperature
45C. Under these conditions, the pulp was subjected
to an enzyme treatment by using the Liftase A40
enzyme in an amount of 2 l/t. The pitch content was
estimated by a turbidity measurement. For measure-
ment, the pulp was filtered through a Macherey-Nagel
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W092/]6687 PCT/F~92/00076
9 ~ 3
MN 640 w filter paper, and turbidity was measured
with the meter mentioned in Example 1. The results
with different reaction times are shown in the table
below.
5Reaction time Turbidity
(min) (NTU)
0 323
110
120 28
As is to be seen, the enzyme was extremely
effective, and the mill test run could be started.
The duration of the test run was 6 days and the
enzyme was Liftase A40 with a dosage of 2 l/t TMP.
The enzyme was dosed to the suction side of a pump
pumping peroxide bleached TMP from a stora~e tower
into a so-called refiner mechanical pulp chest. The
enzyme treatment conditions in the chest were as
follows:
- pH 5.5
20- temperature, C 45
- consistency, % 3.5
- reaction time, min 42
After the refiner mechanical pulp chest the
peroxide bleached TMP was mixed with chemical pulp
and reject in a mixing chest. Then the pulp mixture
was pumped into a machine chest and further after
wire water dilution into the head box of a paper
machine. During the test run the pitch content was
estimated by measuring the turbidity of the filtrate
water of TMP, in addition to which the freeness of
TMP was measured. The results are shown in the table
below.
WO92!]6687 PCT/Fl92/00076
210 1~rj~ `
CONTROLENZYME
Filtrate turbidity, NTU
- before refiner pulp chest 370 370
- after refiner pulp chest 420 250
Freeness, ml
- before refiner pulp chest 62 62
- after refiner pulp chest 59 65
It appears from the results that the enzyme is
effective also in mill conditions and the obtained
reduction in turbidity is 170 units, which indicates
a marked decrease in the pitch content in the fil-
trate, i.e. that the pitch has adhered to ordeposited on the fibres. It is also to be seen that
the freeness of TM~ has increased by 6 units, which
means that the removal of water is easier.
During the test run the following observations
suggesting that the pitch trouble was eliminated/
reduced were made on the machine:
- The runability of the machine was
exceptionally good throughout the enzyme period.
- The wires and felts and the entire wire
section remained very clean.
- The number of holes and spots in base paper
decreased clearly as compared with a normal run.
The results of the test run were verified by a
repeat test run having a duration of 10 days. As to
the pitch and runability, the results complied with
those of the first test run. In addition, it was
observed that the enzyme treatment has a positive
effect on the function of the conventional retention
agent, as the target level of retention was achieved
with a dosage of retention agent which was 20 to 30~
:
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W O 92J16687 PC~r/F192/00076
2~
11
smaller than normally.
Example 3
The increase in the freeness of mechanical pulp
observed in the mill test run raised a question about
its effect on the optical and printing properties of
the pulp primarily in view of the use of the enzyme-
treated pulp in uncoated paper qualities, such as SC
paper and newsprint. To study this, a sample was
obtained from a typical mechanical pulp i.e. ground-
wood for SC paper. The pulp was subjected to anenzyme treatment under conditions given in Table 2
with different dosages of Liftase A40. After the
enzyme treatment, laboratory sheets were prepared
from the pulp. Properties measured from the sheets
both immediately and after calendering are also shown
in Table 2. As can be seen from the results, the
enzyme treatment did not deteriorate the optical or
printing properties of the pulp even though the in-
crease in the freeness value was as high as 25 units;
in fact, the effect was the opposite as
- the light absorption coefficient decreased,
which indicates improved brightness,
- the light scattering coefficient improved,
- the compressibility increased (density after
calendering), and
- the smoothness improved (roughness
decreased).
Accordingly, enzyme-treated pulp can well be
used in uncoated paper qualities. The enzyme treat-
ment not only reduces the pitch trouble but it canalso be expected to improve the quality of the pape-
either directly or at least in that the fineness of
the mechanical pulp can be increased and inferio_
water removal can be compensated for by enzyme trea.-
ment.
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W O 92/16687 PC~r/F192/00076
~1~3~ ~9
12
Example 4.
To veri~y the obtained results, tests werecarried out both on unbleached TMP and dithionite
bleached TMP, and not only the effect on the pitch
content (turbidity) but also the effects on the water
removal (freeness), water retention ability (WRV) and
sheet properties were measured. This time the sheets
were prepared by using a so-called white water sheet
mould. The enzyme treatment conditions and the `
obtained results appear from Table 3. As is to be
seen, the effect of the enzyme treatment on pitch
content (turbidity) also became apparent with these
pulps. In addition, the following positive effects
were observed:
15- water removal properties are improved
(freeness increases and WRV decreases);
- optical properties are improved (light
scattering coefficient and brightness increase),
- printing properties are improved (roughness
decreases and compressibility increases, that is,
density after calendering increases).
Example 5.
As it was observed that the enzyme treatment
has a positive effect on the brightness of mechanical
pulp, it was decided to study the effect of enzyme
treatment carried out before bleaching. For this pur-
pose, the pulps described in Example 1 (control and
enzyme-treated) were peroxide bleached with different
amounts of peroxide under normal peroxide bleaching
conditions (consistency 16%, temperature 60C, react-
ion time 90 min, DTPA 0.2%, MgS04 7H20 0.5% and Na-
silicate 5~ on pulp). After bleaching the pulps were
measured for brightness immediately and after ageing.
The results are shown in Figure 1. It can be seen
that the brightness has improved and the improvement
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W092/16~7 PCT/FI92/00076
13 ~'v~
is to be seen also after ageing. As a consequence, itcan be stated that the enzyme treatment has a
positive effect also on the bleachability of
mechanical pulp.
5Example 6.
The positive effect of the enzyme on the
function of the conventional retention agent observed
in the mill test run was verified by a laboratory
experiment. Unbleached TMP from an intermediate con-
tainer of mechanical pulp was treated with LiftaseA40 under the following conditions:
_ pH 5.0
- temperature 50C
- reaction time 1 hour
15- pulp consistency 3.7%
- enzyme dosage 0, 1, 2 and 4 l/t TMP.
Corresponding enzyme dosages given as cel-
lulase/hemicellulase activities per kg pulp dry
solids were as follows:
1 1/t 2 l/t 4 1/t
(U/kg)(U/kg)(U/kg)
CMCase activity 2,5005,000 lO,000
FPR activity 110 220 440
25 Xylanase activity 5001,000 2,000
After the enzyme treatment, TMP was mixed with
chemical pulp and kaolin under the following con-
ditions:
- TMP 42%
- chemical pulp 24%
: - kaolin 33~.
The pulp mixture was diluted to a concentration
of about lO g/l. The dry solids content and fine
solids content of the mixture were determined as well
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W092/]6687 PCT/Fl92/00076
21~ ~rj9 14
as its total, fine solids and ash retention with a
Dynamic Drainage Jar device in accordance with the
TAPPI T261 pm-80 method. The retention measurement
was carried out on the mixture as such and after an
addition of the retention agent.
The obtained results appear from Table 4. It is
seen that the enzyme treatment does improve the
retention, that is, in practice, the function of the
conventional retention agent is made more effective,
and when aiming at constant retention, the amount of
the conventional retention agent can be decreased.
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