Note: Descriptions are shown in the official language in which they were submitted.
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1
Process for preparing mechanical pulp
The present invention relates to a process in accordance with the preamble of
Claim
1 for preparing mechanical pulp. The invention also relates to a process for
decreas-
ing the energy consumption of mechanical pulping processes based on refining
chips, according to the preamble of Claim 17.
Chemical and mechanical pulps possess different chemical and fibre-technical
prop-
erties and thus their use in different paper grades can be chosen according to
these
properties. Many paper grades contain both types of pulps in different
proportions
according to the desired properties of the final products. Mechanical pulp is
used,
when necessary, to improve or to increase the stiffness, bulkiness or optical
proper-
ties of the product.
In paper manufacture, the wood material must first be defibred. Mechanical
pulp is
mainly manufactured by means of grinding and refining methods, in which the
raw
wood material is subjected to periodical pressure impulses. Due to friction
heat, the
structure of the wood is softened and its structure loosened, finally leading
to the
separation of the fibres from one another (Virkola, 1983). However, only a
small
part of the energy brought into the system is used for separating the fibres;
the ma
jor part being converted into heat. Therefore, the total energy economy of the
defi
bration is very poor.
Several methods for improving the energy economy of mechanical pulping are sug-
gested in prior art. Some of these are based on the pre-treatment of chips by,
e.g.,
water or acid (FI Patent Specifications Nos. 74493 and 87371). Methods are
also
known, which comprise treating the raw material with enzymes to reduce the con-
sumption of pulping energy. Thus, the Finnish Patent Application No. 895676 de-
scribes an experiment in which once-refined pulp was treated with a xylanase
en-
zyme preparation. It is stated in the application that this enzymatic
treatment would,
to some .extent, decrease the energy consumption of pulping. In the said prior
art
publication, the possibility of using cellulases is also mentioned but no
examples of
these are given nor are their effects shown. As far as isolated enzymes are
con-
cerned, in addition to hemicellulases, the interest has been focused on lignin
modi-
fying enzymes, such as laccase enzyme (Jokinen and Savolainen, 1991). A treat-
ment using the laccase enzyme did not, however, have an effect on the energy
con-
sumption (Jokinen and Savolainen, 1991).
The Patent Specification EP 0429 422 suggests the use of laccase treatments in
me-
chanical pulping between the first and the second refining treatments. This
specifi-
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cation states that the laccase treatment decreases the energy consumption of
the re
fining process. The Patent Specification WO 93/23606, in turn, suggests a
treatment
with phenol oxidase enzymes after the last refining or grinding treatments.
The said
treatment had no effect on the energy consumption of the refining treatment
but it
S has been said to have an influence on the strength of paper or board.
As the energy in defibration is mainly absorbed by the amorphous part of the
paper
furnish only, i.e., hemicellulose and lignin, an increase in the amorphousness
of the
raw material improves the energy economy of the defibration. The Patent
Specifica-
tions WO 94/20666 and WO 94/20667 suggest that the amorphousness of the raw
material be increased in connection with mechanical pulping by treating the
raw
material with a suitable enzyme that reacts with the crystalline, insoluble
cellulose
of the raw material. The Patent Specification WO 94/20666 suggests that the
raw
material be treated with an enzyme preparation, the main cellulase activity of
which
consists of cellobiohydrolase activity. The Patent Specification WO 94/20667
sug-
gests that an enzyme preparation be used for the same purpose, containing
cellobio-
hydrolase activity and mannanase activity. The examples of the said
specifications
deal with rough wood, such as the long-fibre fraction of fractioned TMP spruce
pulp, once-refined TMP spruce pulps (with freeness values of CSF 450 - 550) or
TMP pulps refined to different freeness levels (30 - 300). If a
synergistically acting
cellulase enzyme product, i.e., cellulase, was used in connection with the
manufac-
ture of mechanical pulp, containing both cellobiohydrolase and endoglucanase,
the
treatment resulted in the hydrolysis of the insoluble cellulose and, thus, in
the
weakening of the strength properties of the pulp.
The Patent Specification US 6,267,841 describes a manufacturing method of
thermo-mechanical pulp, wherein the pulp is treated with enzyme between the
first
and the second refining processes. It also suggests the treatment of chips
with en-
zymes before the first refining. The specification cites enzymes, such as
pectinase,
xylanase, laccase, cellulase or the mixtures thereof. The specification gives
no nu-
merical values of any energy savings obtained.
In addition to the afore-mentioned isolated enzymes, the application of
growing
white rot fungi in the manufacture of mechanical pulp has also been studied.
Car-
ried out before defibration, such a treatment with a white rot fungus has been
found
to decrease the specific energy consumption and to improve the strength
properties
of these pulps (Setliff et al., 1990, Leatham et al., 1990 and Akhtar et al.,
1992).
The drawbacks of these treatments with the white rot fungus are, however, the
long
treatment times needed (mostly weeks); the decreased yield (85 to 95 %), the
diffi-
culty to control the process and the impaired optical properties.
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Generally, the different enzymatic treatments according to prior art have been
ap-
plied to raw wood material, which has been defibred to a certain extent
already dur-
ing the manufacturing process. According to a general view, the enzymatic
treat-
ment is not as effective when applied to chips directly, because it is
difficult to
make the enzyme preparation to be effectively absorbed into the fibres of a
raw ma
terial that is in the form of chips. In a native form of chips, the surface
area of the
raw wood material is not sufficient for an effective enzymatic treatment to
take
place. Another reason is that a major part of the capillaries of the wood are
too
small to receive any enzyme molecules (Grethlein, H.E. Biotechnology, February
1985, pp. 155 to 160).
According to prior art, the pulping liquor is made to penetrate the chips used
in pulp
cooking by treating the chips with pressure shocks in the presence of the
pulping
liquor. In the Vilamo method, for example, the chips are treated in the
presence of
the cooking liquor by varying the pressure from a pressure of 4.5 kp/cm2 and a
treatment time of 10 - 16s to a pressure of 2 kp/cm2 and a treatment time of 5
- 6s,
the treatment being repeated 6 - 8 times at 1-minute intervals /Rydholm,
1965).
The Patent Specification WO 95/09267 suggests treating the chips, which are
used
in pulp cooking, with a chemical solution by subjecting the chips to a vacuum
and
making the chemical solution penetrate the wood fibres by means of a pressure
shock. According to the application, the chemical solution can be cooking
liquor
that contains, for example, catalysts and enzymes. The object of the invention
is,
thus, to be able to decrease the amount of lignin in order to diminish the
need of
decreasing the residue lignin at the final stage of cooking. However, the
application
does not describe in detail, whether or not the enzymes penetrate the wood
cells
successfully and whether or not the enzymes have any effect on the decrease of
the
amount of lignin.
The US Patent 5,374,555 suggests the removal of lignin from the lignocellulose
material by means of a protease enzyme. To enhance the enzymatic treatment,
the
patent suggests a mechanical treatment of chips, for example, in a screw
clamp. The
patent specification reminds that cellulase can be used as a pre-treatment
enzyme
for the chips or the pulp, but it does not suggest carrying out a treatment
with cellu-
lase in connection with the mechanical processes. The purpose of the patent is
not to
save energy but to remove lignin, and there are no observations relating to
energy
economy. While the application suggests a protease treatment of the wood
material,
which is used both in the manufacture of mechanical pulp and in that of
chemical
pulp, the main issue is the removal of lignin as a pre-treatment in the
manufacture
of chemical pulp.
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The Patent Specification WO 97/40194 suggests changing the structure or the
com-
position of the wood by adding to the compressed chips fungal or bacterial
cultures
or products, such as enzymes obtained from them, by means of pressure. The pur-
pose of the compression is to make cracks and fractures in the wood. When the
chips are released from the compression, microbes of their products, while the
chips
expand, are absorbed by the structures of the wood partially by the virtue of
under
pressure, partially by the capillary action. The application suggests, among
others,
fungi from the genera Ceriposiophsis, Phanerochaete and Ophiostoma. Regarding
enzymes, lipolytic, proteolytic, linginolytic, cellulolytic and
hemicellulolytic en-
zymes are mentioned. The patent specification describes the absorption of the
en-
zyme preparation Clariant Cartazyme HST"' (xylanase) into the compressed chips
after releasing the pressure. Liquid was removed after the treatment, and
mechanical
pulp was prepared from the chips. In that case, the amount of energy consumed
was
7.5% less than in the case of chips that were treated with a buffer only. In
another
test, the enzyme preparations Clariant Cartazyme NSTM (xylanase) and Sigma por-
cine pancreas Lipase L-3126 were treated. In that case, the amount of energy
con-
sumed was 12.5% less than when treated with a buffer only. The specification
men-
tions no preservation of the optical properties of the pulp. According to the
specifi-
cation, the highest energy savings were made by combining enzyme preparations
originating in different sources, of which the amount of a lipase of a
mammalian
origin, in particular, was considerable. The amount of the other enzymes used
was
also fairly high, which makes one suspect that the energy savings achieved
were not
particularly cost-effective.
Eriksson and Heitman (1998) describe tests, wherein pieces of wood (with a
size of
1 x1 x 1.5 inches) were treated with a cellulase enzyme mixture, after which
the
pieces were ground and the energy consumed by the grinding was studied. The ab-
sorption of the enzyme mixture into the pieces of wood was facilitated by
subject-
ing the pieces to a vacuum. The treatment was not observed to have any effect
on
the consumption of the grinding energy.
One problem with the manufacturing methods of mechanical pulp according to
prior
art is their great energy consumption. While attempts have been made to
improve
the beating degree and the energy economy with the aid of enzymatic
treatments,
hardly any energy savings have been made and, often, they have resulted in the
weakening of the strength properties of the pulp (cellulase treatment) or in
the dark-
ening of the pulp and an impairment in the optical properties (laccase
treatment).
Furthermore, it has not always been possible to make the enzyme solution effec-
tively act on the wood. In some cases, the preparation of the enzyme
composition
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used in the tests may have included time-consuming stages and/or been
otherwise
uneconomic.
The purpose of the present invention is to remove at least some disadvantages
of
prior art and to provide an improved method for the manufacture of mechanical
5 pulp. To be more precise, the object of the invention is to provide a pre-
treatment
method of chips to be used before preparing the mechanical pulp.
In connection with the present invention, it has surprisingly been observed
that
chips can be pre-treated with an enzyme preparation that has synergistically
acting
enzyme activities. In that case, the enzyme preparation does not need to
contain any
certain isolated enzyme activity only, but an enzyme preparation containing
differ-
ent enzyme activities can be used directly as the enzyme preparation.
The treatment according to the method can be applied to the chips directly. As
the
enzymatic treatment takes place at an early stage of the pulping process,
savings in
the refining energy are then as high as possible.
According to the method of the present invention, the chips are pre-treated
with an
enzyme that is capable of degrading the structural parts of the wood, after
which
mechanical pulp is manufactured from the chips by refining. It is preferable
to carry
out the enzymatic treatment by compressing the chips and by bringing the com-
pressed chips in a liquid phase into contact with the enzyme composition to
absorb
the enzyme composition into the chips. The enzyme composition preferably con-
tains both cellobiohydrolase and endoglucanase. It is particularly preferable
for the
composition to contain an effective amount of both cellobiohydrolase and
endoglu-
canase. Enzyme preparations containing cellobiohydrolase and endoglucanase in
a
ratio of 20:1 - 1:20, indicated as the weight ratio of the proteins, are
preferable.
According to some preferable embodiments of the invention, the amount of en-
doglucanase compared with that of cellobiohydrolase is higher than what is
natu-
rally produced by the industrial production strains of cellulase, such as
Tricho-
derma, in their growth media.
To be more precise, the method according to the invention is mainly
characterized
in that which is presented in the characterizing part of Claim 1.
The method according to the invention is also characterized in that which is
pre-
sented in the characterizing part of Claim 17.
The invention provides several considerable advantages. When using the methods
according to the preferable embodiments of the invention, considerably lower
amounts of energy are consumed than in the methods according to prior art. The
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energy saving can be as much as 20% compared with a method, wherein the chips
are not treated with the enzyme preparation.
When treating the chips by the methods according to the preferable embodiments
of
the invention, the strength of the pulp was not weakened; on the contrary, it
im-
proved to some extent. The optical properties also remained good. Thus, when
treat-
ing the chips with the methods according to the preferred embodiments of the
in-
vention, it was possible to improve the quality of the pulp.
According to prior art, treating the raw material by means of a non-optimized
cellu-
lase enzyme product resulted in the hydrolysis of the insoluble cellulase and,
thus,
in the weakening of the strength properties of the pulp. In connection with
the pre-
sent invention, it was surprisingly observed that the enzyme preparation
containing
cellobiohydrolase and endoglucanase did not necessarily result in a loss of
the pulp
strength.
According to the preferred embodiments of the invention, the enzyme
preparation is
produced in a host organism, which excretes the enzyme preparation out of the
cell,
whereby the enzyme preparation does not need to be isolated from the cell. It
is also
especially advantageous to use a genetically modified organism as the
production
host, producing the desired enzyme preparation directly in the growth medium.
This
provides the considerable advantage that the used enzyme activity does not
need to
be isolated from the host organism or its growth medium but, for example, the
growth medium of the host organism can be directly used.
In the following, the invention is described with the aid of a detailed
description and
some examples, the purpose of which, however, is not to limit the scope of the
in-
vention.
The enzymes that participate in the modification and degradation of cellulose
are
commonly called "cellulases". These enzymes include endo-(3-glucanases,
cellobio
hydrolases and ~i-glucosidase. Countless organisms, such as various wood
rotting
fungi, moulds and anaerobic bacteria are able to produce some or all of these
en
zymes. Depending on the type of organism and cultivation conditions, these en
zymes are produced extracellularly in various ratios and amounts.
The term "enzyme preparation" used in this application refers to any product
that
contains at least one enzyme or a structural part of the enzyme. Accordingly,
the
enzyme preparation can be, for example, a growth medium containing the en-
zyme(s), an isolated enzyme or a mixture of two or more enzymes. "Cellulase"
or
"cellulase enzyme preparation", in turn, refers to an enzyme preparation
containing
at least one of the above-mentioned cellulase enzymes. The "enzyme
composition"
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in this application means the same as the enzyme preparation. In addition to
the en-
zymes, the enzyme preparation or the enzyme composition may also contain, for
example, buffers, stabilizers, preservatives or other necessary additives.
The "cellobiohydrolase activity" in this application refers to an activity
that is capa-
S ble of modifying the crystalline parts of the cellulose. The
cellobiohydrolase I and II
activities refer to the main activities of the cellobiohydrolase produced by
Tricho-
derma or to the corresponding activities produced by some other organism. The
en-
doglucanase activity in this application refers to an activity capable of
modifying
the amorphous parts of the cellulose. The endoglucanase I and the
endoglucanase (I
activities refer to the main activities of the endoglucanase produced by
Trichoderma
or to the corresponding activities produced by another organism.
An enzyme preparation containing "an effective amount" of cellobiohydrolase
and
endoglucanase refers to an enzyme preparation, in which the effect of each
enzyme
on the chips can be measured as a reduction in the energy consumption of the
refin-
ing. The effective amount of cellobiohydrolase and endoglucanase provides a de-
crease of at least 3%, preferably at least 5%, more preferably at least 8%,
most pref
erably at least 10% in the energy consumption of the refining.
When so desired, the methods according to the invention can be combined with
treatments carried out with other enzymes, such as hemicellulases (e.g.,
xylanases,
glucuronidases and mannanases) or esterases. In addition to these enzymes,
addi
tional enzyme preparations containing (3-glucosidase activity can be used in
the pre-
sent processes, because this kind of (3-glucosidase activity prevents the end
product
inhibition caused by cellobiose.
Cellobiohydrolase and endoglucanase enzyme preparations are produced by grow
ing suitable micro-organism strains, known to produce cellulase. The strains
are
preferably production strains that are used industrially. The growth medium
used
can be, for example, a simple cellulosic substrate (1% Solka floc), which the
neces
sary trace elements have been added to (Mandels and Weber, 1969). The
production
strains can be bacteria, fungi or moulds. As examples, the micro-organisms
belong
ing to the following families can be mentioned:
Trichoderma (e.g. T. reesei), Aspergillus (e.g. A. niger), Phanerochaete (e.g.
P.
chrysosporium; Covert et al., 1992), Penicillium (e.g. P. janthinellum, P.
digi-
tatum), Streptomyces (e.g. S. olivochromogenes, S. flavogriseus), Humicola
(e.g. H.
insolens), and Bacillus (e.g. B. subtilis, B. circulars, Ito et al., 1989).
Other white
rot fungi can also be used, strains belonging to families, such as Phlebia,
Ceri-
poriopsis and Trametes.
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It is also possible to produce cellobiohydrolases, endoglucanases or their
structural
parts by means of strains, which have been genetically improved to produce
specifi-
cally these proteins, or by other genetically modified production strains, to
which
genes coding for these proteins have been transferred. When the genes of the
de-
sired protein have been cloned (Teeri et al., 1983), it is possible to produce
the pro-
tein or its part in a desired host organism. The desired host may be the
Trichoderma
mould (EP 244 234, Mitsuishi et al., 1990), yeast (Penttila et al., 1988),
some other
mould, from families such as Aspergillus (van den Hondel et al., 1992), a
bacterium
or any other micro-organism, whose genetics are sufficiently well-known.
According to the preferred embodiments of the invention, the desired
cellobiohy-
drolase and endoglucanase are produced by means of the mould strain
Trichoderma,
preferably the strain T. reesei.
The said strain is a generally used production organism and its cellulases are
fairly
well known. T. reesei synthesizes two cellobiohydrolases, which are later
referred
to as CBH I and CBH II, several endoglucanases, of which EGI and EGII are the
main activities, and at least two ~-glucosidases (Chen et al, 1992). The
biochemical
properties of these enzymes on pure cellulosic substrates have been
extensively de-
scribed. Endoglucanases are typically active on soluble and amorphous
substrates
(CMC, HEC, ~i-glucan), whereas the cellobiohydrolases are able to hydrolyze
crys-
talline cellulose. The cellobiohydrolases act clearly synergistically on
crystalline
cellulose, but their hydrolysis mechanisms are supposed to be different from
each
other. The present knowledge of the hydrolysis mechanisms of cellulases is
based
on results obtained on pure cellulase preparations, and may not be valid in
cases,
where the substrate also contains other components, such as lignin or
hemicellulose.
The cellulases of T. reesei (cellobiohydrolases and endoglucanases) do not
essen-
tially differ from each other with respect to their optimal external
conditions, such
as pH or temperature. Instead, they differ from each other with respect to
their abil-
ity to hydrolyze and modify cellulose in the raw wood material.
As far as their activities are concerned, the cellobiohydrolases I and II also
differ to
some extent from each other, and so do the endoglucanases I and II. In the
preferred
embodiments of this invention, however, it seems that the ratio of the
cellobiohy-
drolases to the endoglucanases is more important than the interrelation
between the
various cellobiohydrolases or the various endoglucanases.
Trichoderma reesei naturally produces various cellulase components in its
growth
medium, the amount and the interrelation of them depending on the production
strain and the external conditions used. For the wild type of Trichoderma
reesei, the
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9
following relative amounts of the main cellulases have been proposed: CBH I
60%,
CBH II 20%, EG I 10% and EG II 10% (Stahlberg, 1991 ). In that case, the ratio
of
the cellobiohydrolases to the endoglucanases is about 4:1.
In this invention, it was observed that the preferred enzyme mixtures for the
method
according to the invention included those containing both cellobiohydrolase en-
zymes and endoglucanase enzymes. While not wanting to commit ourselves to any
theories, it very strongly seems that the method according to the invention
needs
both cellobiohydrolase enzymes and endoglucanase enzymes, because the endoglu-
canase is capable of preparing, in the chips, objects that the
cellobiohydrolase is
able to act on. As neither activity alone is able to provide the desired
effect, the cel-
lobiohydrolases and the endoglucanases must work in synergy. According to the
preferred embodiments of the invention, the ratio of the cellobiohydrolases to
the
endoglucanases, indicated as the weight ratio of the proteins, is preferably
20:1 -
1:20, more preferably 9:1 - 1:9, more preferably 5:1 - 1:5, and more
preferably 3:1
- 1:3, most preferably 2:1 - 1:2, and even more preferably about 1:1.
Accordingly,
the most preferable cellulase compositions are those, wherein the weight ratio
of the
cellobiohydrolases and the endoglucanases is close to 1:1. However, an energy
sav
ing effect can even be provided by a weight ratio deviating from this, if the
en
doglucanase used has a very strong activity so that even a small amount is
sufficient
to provide the desired effect.
The preferred embodiments of the invention also include an enzyme preparation,
wherein the portion of endoglucanases in the preparation is 2 - 60% by weight.
Even more preferred is a preparation, wherein the portion of endoglucanases in
the
preparation is 20 - 55% by weight and the most preferred is one, wherein the
por-
tion of endoglucanases is 45 - 50% by weight. Such an amount of endoglucanases
can be reached by increasing the amount of either EGI or EGII, or both, in the
preparation. If the amount of EGI is increased exclusively, the amount of EGI
in the
preparation should reach a level of 15 - 45% by weight. This is also true, if
only the
amount of EGII is increased.
US Patent No. 5,874,293, for example, describes an enzyme preparation that is
pro-
duced by the strain Trichoderma (ALKO 3529) that overproduces EGII. The ratio
of CBH:EG in the growth medium produced by the strain is estimated to be 1 -
1.4:1. It would be advantageous to use the growth medium produced by such a
strain, for example, in the present invention. The publication Karhunen et al.
(1993)
describes a Trichoderma host that is modified to overproduce the EGI enzyme.
The
growth medium of this host could also be used in the present invention.
Generally,
preferable enzyme mixtures according to the preferred embodiments of this
inven-
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tion include those, wherein the amount of endoglucanase is higher than what
the
cellulase-producing micro-organisms, such as 7richoderma, especially T.
reesei,
would naturally produce in their growth media.
The modified cellulase preparation herein refers to a preparation, wherein the
ratio
5 of CBH and EG components has been changed by methods that are well-known to
average experts. Such methods include, e.g., the genetic modification of a
host or
ganism so that the host organism produces a novel cellulase compound in its
growth
medium. Other viable methods of manufacturing modified cellulase preparations
include the fractioning of a cellulase-containing growth medium or combining
dif
10 ferent cellulase mixtures.
The host organism can be modified genetically to produce the desired
cellobiohy-
drolases and endoglucanases in a desired proportion. For example, the genetic
modification of the strains of the family Trichoderma can be carried out by
the
methods described in the patent EP 244234 or in the publication Suominen et
al.,
1993. Preferable enzyme preparations to be used in the embodiments of this
inven-
tion include those, wherein the mould T. reesei is modified to overproduce EG
I
and/or EG II enzymes. The overproduction host may also have been modified so
as
to produce less of some cellobiohydrolase activities, especially the CBH I or
CBH
II activities, if any, or to produce less endoglucanases, if any, especially
the EG I
and/or EG II activities. However, it should be noticed that in the enzyme
prepara-
tions according to the preferred embodiments of the invention, there should be
cel-
lobiohydrolase activities; therefore, adding endoglucanase activities to the
enzyme
preparations is more advantageous than decreasing cellobiohydrolase activities
or
removing the endoglucanases.
Corresponding enzyme preparations can also be manufactured by purifying
suitable
cellobiohydrolase and endoglucanase enzymes and combining the same in advanta-
geous proportions, or by adding to an enzyme preparation, which is produced by
a
non-modified host, the desired enzyme activities, for example, the EGI and
EGII
activities.
The strains, which are capable of overproducing EGI and EGII enzymes, can be
constructed, for example, by transferring genes coding for these enzymes (egll
Penttila et al. 1986 and egl2 Saloheimo et al. 1988) to a selected Trichoderma
host
as several copies or to replace some genes of Trichoderma, such as the cbhl
and
cbh2 genes that code for cellobiohydrolases, as described in the publication
Suomi-
nen et al. (1993). The said genes can be expressed under a strong cbhl
promoter, as
described in the publication Paloheimo et al. (1993).
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11
When manufacturing genetically modified hosts, the T. reesei strain QM6a, for
ex-
ample, can be used as a host, especially the strains QM9414 and Rut C - 30,
which
are developed from the same for the production of cellulase, or strains
developed
from them, which produce less protease.
According to the preferred embodiments of the present invention, the enzyme
preparation is manufactured by means of a host organism, which is modified to
pro-
duce cellobiohydrolases and endoglucanases in a desired proportion in its
growth
medium. Alternatively, endoglucanase I and/or II enzymes are added to a growth
medium, which is produced by a non-modified host organism that naturally pro-
duces cellulases in its growth medium, the enzymes having either been produced
by
a micro-organism that is modified to overproduce these enzymes, or isolated
and
possibly purified from the growth medium. In the manufacture of the enzyme
prepa-
ration, the above-mentioned methods can also be combined. The
cellobiohydrolase
and the endoglucanase can be separated from the growth medium of the
production
host by means of several known methods. In these methods of separation,
typically,
various purifying techniques are combined, such as precipitation, ion exchange
chromatographic and affinity chromatographic as well as gel chromatographic
methods.
The enzyme preparations can be manufactured by means of the mould Trichoderma
or some other production host. Genes that code for cellobiohydrolase and
endoglu
canase can originate in Trichoderma or some other host that produces the
preferable
cellobiohydrolase and endoglucanase activities; and the said activities in the
en
zyme preparation can be from the same or a different origin.
The treatment according to the present invention is applied to chips. The raw
wood
material is chipped in a normal manner so that the chip length is about 15 -
25 mm.
Before the treatment, the chips can be graded by removing oversize and too
thick
chips and fines.
In the method according to the invention, the chip material is typically
compressed
by at least 10%, generally 10 - 30% of its original bulk volume. The chips are
com
presses in a ratio of 1:2 - 1:10. A ratio of compression of at least 1:4 is
preferably
used. The compression treatment is preferably carried out by a method, wherein
the
chips are compressed without a considerable circular motion, because the
object is
not to crush the pieces of chips but make microscopic cracks in the raw wood
mate-
rial. In terms of technicality, the compression can be implemented by various
means, e.g., in a screw clamp or by a hydraulic press. In the compression
treatment,
the impregnated chips are treated for a sufficient time in conditions
favourable for
the activity of the enzyme, after which the chips are processed in a normal
manner
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12
before refining, including pre-heating with steam before feeding them into the
re-
fi ner.
The method according to the invention is not limited to a certain raw wood
material
but can generally be applied to both softwood and hardwood, such as the
species of
the Pinaceae order (e.g., the Picea and Pinus families), the species of the
Salica-
ceae order (e.g., the Populus family) and the species in the Betula family.
The compressed chips are brought into contact with the enzyme preparation in a
liquid phase. This is best carried out so that the chips are compressed in an
enzyme
solution. The proportion of the liquid and the chips is preferably selected so
that the
liquid is able to effectively act on the chips. Thus, the proportion of liquid
to the
chips can be 10:1 - 2:1, and it is preferably 6 - 8:1. The compression
pressure can
be 10 - 20 MPa, and it is preferably 12 - 15 MPa. The duration of the compres-
sion/absorption stage should be at least I min; the duration is preferably 5 -
100
min and generally 10 - 30 min. After releasing the compression, the chips are
al-
lowed to return to their original volume under the enzyme solution, whereby
the
enzyme solution is impregnated into the chips.
At the compression/absorption stage, the pH and the temperature of the enzyme
so-
lution should be suitable for the functioning of the enzyme preparation. For
the cel-
lobiohydrolases and the endoglucanases, the pH should preferably be within a
range
of pH 3 - 10, preferably pH 4 - 8, and the temperature should be 20 -
55°C, pref
erably 30 - 45°C. In order for the enzyme to act on the chips before
refining, the
chips are treated for a sufficiently long time in the conditions mentioned
above. The
treatment time greatly varies depending on the properties (size, thickness) of
the
chips, sort of wood, compression treatment, enzyme preparation, operational
condi-
dons etc., and a suitable treatment time must be specified for each case
separately.
In terms of costs, as short a time as possible is advantageous but in terms of
process
technology, there are no obstacles for a treatment of several hours.
Typically, the
treatment time can be within a range of 1 - 24h, preferably 1 - 12h.
The amount of enzyme preparation used in the invention in the treatment of
chips is
selected so that the amount of free sugars released in the solution is
preferably about
0.1 - 1.0% of the original dry matter. A suitable dosage, determined as total
protein,
is 0.1 - 7mg of protein per g of chips, preferably 3 - 6mg of protein per g of
chips
(as dry matter).
In the present invention, mechanical pulp is manufactured by refining chips
that are
treated with an enzyme to obtain a drainability value, which is preferably at
least
100m1 CSF, more preferably 40 - 80m1 CSF. Surprisingly, it was observed that
the
CA 02549469 2006-06-09
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13
method according to the invention yielded energy savings of 13%, preferably
15%
and most preferably as much as 20%.
It seems that the enzymatic treatment according to the present invention is
advanta-
geous, when combined with the manufacture of mechanical pulp by the refining
method, in particular, and when refining the pulp into drainability of 100 CSF
or
lower.
The invention provides considerable advantages. Accordingly, it can be used to
considerably reduce the specific energy consumption of refining; in accordance
with the preferred embodiments of the invention, as much as 20% lower energy
consumption can be achieved than with untreated source materials, as the
examples
below indicate. By means of a suitable enzyme preparation, the properties of
the
mass can also be improved. Using the solutions according to the preferred
embodi-
ments of the invention, a high yield is obtained in the manufacture of
mechanical
pulp by refining, the quality of the pulp is good, the strengths are
maintained, the
optical properties are good, and the method is easy to connect to the present
proc-
esses.
The invention can be applied to all manufacturing methods of mechanical pulp,
such as the manufacture of thermo-mechanical pulp (TMP) and refined mechanical
pulp (RMP).
In the following, the invention is described in detail with the aid of a few
examples
of application.
Example 1
Enzymatic treatment of chips
Enzymatic treatments with a cellulase mixture were carried out on sorted
spruce
sapwood chips (0 7mm), using an enzyme dosage of 6.3mg of protein per g of
chips
(as dry matter), ~KLn~Kra~a commercial enzyme preparation produced by the
Tricho-
derma strain, wherein the weight proportions of CBH:EG were defined as 1:1. To
enhance the enzymatic treatment, a compression treatment was exerted on the
chips
using a PREX hydraulic press. In the hydraulic compression, a chip lot (200g)
was
compressed in the enzyme solution into a volume that was about 20% smaller
than
the original, using a compression load of 48t (14 Mpa). The ratio of liquid to
wood
was 11:4 and the duration of the compression/absorption stage was lOmin. After
releasing the compression, the chips were allowed to return to their original
volume
under the enzyme solution, whereby the enzyme solution was impregnated into
the
chips. As a reference, an otherwise similar treatment was used, but without
the en-
zyme. In the compression treatment, neither visual nor microscopic changes
were
CA 02549469 2006-06-09
WO 2005/056915 PCT/FI2004/000759
14
perceived in the chips. After the compression treatment, the chips (+ the
compres-
sion solution) were transferred into a rotary air oven for further processing.
The
treatment was carried out in atmospheric pressure and at a temperature of
45°C. The
amount of carbohydrates released in the treatment solution, as reducing
sugars, was
defined after 6 and 22 h. The result obtained was compared with a treatment,
wherein the compression treatment of chips was omitted. The results are shown
in
Table 1.
Table 1. The amount of carbohydrates released in the solution (after 6 and
22h)
from spruce sapwood chips in the enzymatic treatment. The amount of dissolved
carbohydrates is calculated as per cent of the original dry matter.
Treatment Dissolved carbohydrates,
%, dry matter
6h 22h
Compression treatment 0.71 1.06
No compression treatment 0.04 0.26
1 S On the basis of the results, it was stated that the impregnation of the
enzyme pro-
vided by means of the compression treatment considerably enhanced the release
of
soluble carbohydrates from the chips compared with a case, wherein no compres-
sion treatment was carried out.
Example 2
Effect of the enzymatic treatment on the beatability of chips
The effects of the combined compression/absorption and enzymatic treatments on
the beatability of the chips were examined by means of a blade refiner. The
equip-
ment used in the tests contained the actual refiner and an accurate energy
measuring
system connected thereto. The refiner chamber of the blade refiner consisted
of a
cylinder provided with counter blades (20 in number) and a rotary rotor having
four
wing-like blades. Several refining operations (125g dry matter per refining)
were
carried out for each specific energy consumption curve (SEC) by varying the
refin-
ing time (3 - l2min) and, thus, also the energy level of the refining. The
total en-
ergy consumption of the refining was obtained from a watt-hour meter by means
of
a cumulative pulse counter. The energy consumption value obtained per amount
of
defibred chips was corrected by a zero load.
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The defibration times for the treated spruce sapwood chips were 3 - l2min. The
treatments were carried out as described in Example 3 (45°C, 22h). The
compres-
sion/absorption treatments were carried out using a treated cellulase mixture,
as in
Example l, CBH l, and an EG-rich enzyme preparation. The dosages for the
treated
5 mixture were 0.63 and 6.3 of protein per g of chips (as dry matter). The
dosage for
CBH 1 and the EG-rich enzymes was S.Omg of protein per g of chips (dry
matter).
Reference refining operations were carried out on untreated chips and chips
that
were treated otherwise similarly to the others but without the enzyme (a
buffer
treatment). After refining, the pulp was removed from the refiner, filtered,
homoge-
10 nized and its dry content was defined, on the basis of which the SEC value
could be
calculated (kWh/kg).
The results are shown in Table 2.
Table 2.
Treatment CFS, ml SEC, kWh/kg
Buffer treatment 1 OOmI 4.78
(pH5)
Cellulase mixture, " 4.15
0.63
mg/g
Cellulase mixture, " 3.79
6.3
mg/g
CBH I, protein Smg/g" 4.94
EG-rich, protein " 4.14
Smglg
15 According to the results, it could be stated that the pre-treatment of
chips with the
treated cellulase mixture considerably enhanced the beatability, compared with
the
other cellulase preparations (CBH I and the EG-rich): depending on the enzyme
dosage used, energy savings of 10 - 20% were achieved with the cellulase
mixture
compared with the corresponding buffer treatment.
Example 3
Effect of the enzymatic treatment on the sheet properties of the pulp
The chips were impregnated and treated with a cellulase mixture (a dosage
contain-
ing 0.63mg of protein per g of chips (dry matter), 45°C, 22h), as
described in Ex-
ample 1. After this, the chips were refined by the blade refiner in accordance
with
CA 02549469 2006-06-09
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16
Example 2. Laboratory sheets were prepared from the refined pulps and tested
in
accordance with SCAN methods. The sheet properties are shown in Table 3.
Table 3.
TreatmentSEC, CSF, Density,TensileTear Scott Opacity,Brightness,
kWh/kg ml kg/m' index,index, Bond,
N m/g mN mz/g J/m2
Reference4.61 115 361 38.5 8.24 112 94.5 54.4
Cellulase4.19 108 375 39.9 7.84 139 93.5 56.0
According to the results, the cellulase treatment, which was applied to the
chips,
improved the strength properties of the pulp; the tensile strength and the z-
strength
(Scott Bond) in particular. Also the optical properties were well-preserved.
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