[0001] The present invention relates to a method in accordance with the preamble of Claim
1 for preparing mechanical pulp.
[0002] Chemical and mechanical pulps possess different chemical and fibre-technical properties
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 properties of the product.
[0003] 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 major part being
converted into heat. Therefore, the total energy economy of the defibration is very
poor.
[0004] Several methods for improving the energy economy of mechanical pulping are suggested
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 consumption of pulping energy. Thus, the Finnish Patent Application No.
895676 describes an experiment in which once-refined pulp was treated with a xylanase enzyme
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 concerned,
in addition to hemicellulases, the interest has been focused on lignin modifying enzymes,
such as laccase enzyme (Jokinen and Savolainen, 1991). A treatment using the laccase
enzyme did not, however, have an effect on the energy consumption (Jokinen and Savolainen,
1991).
[0005] The Patent Specification
EP 0429 422 suggests the use of laccase treatments in mechanical pulping between the first and
the second refining treatments. This specification states that the laccase treatment
decreases the energy consumption of the refining 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 has been said to have an influence on the strength
of paper or board.
[0006] 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 Specifications
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 suggests that an enzyme preparation be used for the same purpose, containing cellobiohydrolase
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 manufacture 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.
[0007] 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 enzymes before the first refining. The specification cites
enzymes, such as pectinase, xylanase, laccase, cellulase or the mixtures thereof.
The specification gives no numerical values of any energy savings obtained.
[0008] 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. Carried 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 difficulty to control
the process and the impaired optical properties.
[0009] Generally, the different enzymatic treatments according to prior art have been applied
to raw wood material, which has been defibred to a certain extent already during the
manufacturing process. According to a general view, the enzymatic treatment 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 material 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).
[0010] 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/cm
2 and a treatment time of 10 - 16s to a pressure of 2 kp/cm
2 and a treatment time of 5 - 6s, the treatment being repeated 6 - 8 times at 1-minute
intervals /Rydholm, 1965).
[0011] 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.
[0012] 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 cellulase 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.
[0013] The Patent Specification
WO 97/40194 suggests changing the structure or the composition 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 purpose 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
enzymes are mentioned. The patent specification describes the absorption of the enzyme
preparation Clariant Cartazyme HS™ (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 NS™ (xylanase) and Sigma porcine pancreas Lipase L-3126
were treated. In that case, the amount of energy consumed was 12.5% less than when
treated with a buffer only. The specification mentions no preservation of the optical
properties of the pulp. According to the specification, 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.
[0014] Eriksson and Heitman (1998) describe tests, wherein pieces of wood (with a size of
1x1x1.5 inches) were treated with a cellulase enzyme mixture, after which the pieces
were ground and the energy consumed by the grinding was studied. The absorption of
the enzyme mixture into the pieces of wood was facilitated by subjecting the pieces
to a vacuum. The treatment was not observed to have any effect on the consumption
of the grinding energy.
[0015] 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 darkening of
the pulp and an impairment in the optical properties (laccase treatment). Furthermore,
it has not always been possible to make the enzyme solution effectively act on the
wood. In some cases, the preparation of the enzyme composition used in the tests may
have included time-consuming stages and/or been otherwise uneconomic.
[0016] 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 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.
[0017] 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 different
enzyme activities can be used directly as the enzyme preparation.
[0018] 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.
[0019] 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 compressed
chips in a liquid phase into contact with the enzyme composition to absorb the enzyme
composition into the chips. The enzyme composition contains both cellobiohydrolase
and endoglucanase. It is particular for the composition to contain an effective amount
of both cellobiohydrolase and endoglucanase.
[0020] According to some preferable embodiments of the invention, the amount of endoglucanase
compared with that of cellobiohydrolase is higher than what is naturally produced
by the industrial production strains of cellulase, such as
Trichoderma, in their growth media.
[0021] 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.
[0022] 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 energy saving can be
as much as 20% compared with a method, wherein the chips are not treated with the
enzyme preparation.
[0023] 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 improved
to some extent. The optical properties also remained good. Thus, when treating the
chips with the methods according to the preferred embodiments of the invention, it
was possible to improve the quality of the pulp.
[0024] According to prior art, treating the raw material by means of a non-optimized cellulase
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 present
invention, it was surprisingly observed that the enzyme preparation containing cellobiohydrolase
and endoglucanase did not necessarily result in a loss of the pulp strength.
[0025] 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.
[0026] 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
invention.
[0027] The enzymes that participate in the modification and degradation of cellulose are
commonly called "cellulases". These enzymes include endo-β-glucanases, cellobiohydrolases
and β-glucosidase. Countless organisms, such as various wood rotting fungi, moulds
and anaerobic bacteria are able to produce some or all of these enzymes. Depending
on the type of organism and cultivation conditions, these enzymes are produced extracellularly
in various ratios and amounts.
[0028] 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 enzyme(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" in this application
means the same as the enzyme preparation. In addition to the enzymes, the enzyme preparation
or the enzyme composition may also contain, for example, buffers, stabilizers, preservatives
or other necessary additives.
[0029] The "cellobiohydrolase activity" in this application refers to an activity that is
capable of modifying the crystalline parts of the cellulose. The cellobiohydrolase
I and II I activities refer to the main activities of the cellobiohydrolase produced
by
Trichoderma or to the corresponding activities produced by some other organism. The endoglucanase
activity in this application refers to an activity capable of modifying the amorphous
parts of the cellulose. The endoglucanase I and the endoglucanase II activities refer
to the main activities of the endoglucanase produced by
Trichoderma or to the corresponding activities produced by another organism.
[0030] 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 refining. The effective
amount of cellobiohydrolase and endoglucanase provides a decrease of at least 3%,
preferably at least 5%, more preferably at least 8%, most preferably at least 10%
in the energy consumption of the refining.
[0031] When so desired, the method 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, additional enzyme preparations
containing β-glucosidase activity can be used in the present processes, because this
kind of β-glucosidase activity prevents the end product inhibition caused by cellobiose.
[0032] Cellobiohydrolase and endoglucanase enzyme preparations are produced by growing 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 necessary trace elements have
been added to (Mandels and Weber, 1969). The production strains can be bacteria, fungi
or moulds. As examples, the micro-organisms belonging 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. digitatum), Streptomyces (e.g. S. olivochromogenes, S. flavogriseus), Humicola (e.g. H. insolens), and Bacillus (e.g. B. subtilis, B. circulans, Ito et al., 1989). Other white rot fungi can also be used, strains belonging to families,
such as Phlebia, Ceriporiopsis and Trametes.
[0033] It is also possible to produce cellobiohydrolases, endoglucanases or their structural
parts by means of strains, which have been genetically improved to produce specifically
these proteins, or by other genetically modified production strains, to which genes
coding for these proteins have been transferred. When the genes of the desired protein
have been cloned (Teeri et al., 1983), it is possible to produce the protein or its
part in a desired host organism. The desired host may be the
Trichoderma mould (
EP 244 234, Mitsuishi et al., 1990), yeast (Penttilä 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.
[0034] According to the preferred embodiments of the invention, the desired cellobiohydrolase
and endoglucanase are produced by means of the mould strain
Trichoderma, preferably the strain
T.
reesei.
[0035] 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 β-glucosidases (Chen et al, 1992). The biochemical properties of these enzymes
on pure cellulosic substrates have been extensively described. Endoglucanases are
typically active on soluble and amorphous substrates (CMC, HEC, β-glucan), whereas
the cellobiohydrolases are able to hydrolyze crystalline 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.
[0036] The cellulases of
T.
reesei (cellobiohydrolases and endoglucanases) do not essentially 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 ability to hydrolyze and modify
cellulose in the raw wood material.
[0037] 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 cellobiohydrolases
to the endoglucanases is more important than the interrelation between the various
cellobiohydrolases or the various endoglucanases.
[0038] 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 following relative amounts of the main cellulases have been proposed: CBH I 60%,
CBH II 20%, EG I 10% and EG II 10% (Ståhlberg, 1991). In that case, the ratio of the
cellobiohydrolases to the endoglucanases is about 4:1.
[0039] In this invention, it was observed that the preferred enzyme mixtures for the method
according to the invention included those containing both cellobiohydrolase enzymes
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 endoglucanase 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 cellobiohydrolases and the endoglucanases
must work in synergy. According to the invention, the ratio of the cellobiohydrolases
to the endoglucanases, indicated as the weight ratio of the proteins, is 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 saving effect can even
be provided by a weight ratio deviating from this, if the endoglucanase used has a
very strong activity so that even a small amount is sufficient to provide the desired
effect.
[0040] 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 portion 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.
[0041] US Patent No. 5,874,293, for example, describes an enzyme preparation that is produced 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 invention include those, wherein the
amount of endoglucanase is higher than what the cellulase-producing micro-organisms,
such as
Trichoderma, especially
T.
reesei, would naturally produce in their growth media.
[0042] The modified cellulase preparation herein refers to a preparation, wherein the ratio
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 organism 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 different cellulase mixtures.
[0043] The host organism can be modified genetically to produce the desired cellobiohydrolases
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 invention 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 preparations according to the preferred embodiments of the invention,
there should be cellobiohydrolase activities; therefore, adding endoglucanase activities
to the enzyme preparations is more advantageous than decreasing cellobiohydrolase
activities or removing the endoglucanases.
[0044] Corresponding enzyme preparations can also be manufactured by purifying suitable
cellobiohydrolase and endoglucanase enzymes and combining the same in advantageous
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.
[0045] The strains, which are capable of overproducing EGI and EGII enzymes, can be constructed,
for example, by transferring genes coding for these enzymes
(egl1 Penttilä 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
cbh1 and
cbh2 genes that code for cellobiohydrolases, as described in the publication Suominen
et al. (1993). The said genes can be expressed under a strong
cbh1 promoter, as described in the publication Paloheimo et al. (1993).
[0046] When manufacturing genetically modified hosts, the
T.
reesei strain QM6a, for example, 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.
[0047] According to the preferred embodiments of the present invention, the enzyme preparation
is manufactured by means of a host organism, which is modified to produce 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 produces 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 preparation, 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.
[0048] The enzyme preparations can be manufactured by means of the mould
Trichoderma or some other production host. Genes that code for cellobiohydrolase and endoglucanase
can originate in
Trichoderma or some other host that produces the preferable cellobiohydrolase and endoglucanase
activities; and the said activities in the enzyme preparation can be from the same
or a different origin.
[0049] 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.
[0050] 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 compresses
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 material. 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 before refining,
including pre-heating with steam before feeding them into the refiner.
[0051] 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
Salicaceae order (e.g., the
Populus family) and the species in the
Betula family.
[0052] 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 compression/absorption
stage should be at least 1 min; the duration is preferably 5 - 100 min and generally
10 - 30 min. After releasing the compression, the chips are allowed to return to their
original volume under the enzyme solution, whereby the enzyme solution is impregnated
into the chips.
[0053] At the compression/absorption stage, the pH and the temperature of the enzyme solution
should be suitable for the functioning of the enzyme preparation. For the cellobiohydrolases
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, preferably 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 conditions 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.
[0054] 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).
[0055] 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 100ml CSF, more preferably 40 - 80ml CSF. Surprisingly, it was observed that
the method according to the invention yielded energy savings of 13%, preferably 15%
and most preferably as much as 20%.
[0056] It seems that the enzymatic treatment according to the present invention is advantageous,
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.
[0057] 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 embodiments 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 processes.
[0058] 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).
[0059] In the following, the invention is described in detail with the aid of a few examples
of application.
Example 1
Enzymatic treatment of chips
[0060] Enzymatic treatments with a cellulase mixture were carried out on sorted spruce sapwood
chips (∅ 7mm), using an enzyme dosage of 6.3mg of protein per g of chips (as dry matter),
[KL1][KL2]a commercial enzyme preparation produced by the
Trichoderma 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 10min. 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 enzyme. In the compression treatment,
neither visual nor microscopic changes were perceived in the chips. After the compression
treatment, the chips (+ the compression 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.
[0061] 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 |
[0062] On the basis of the results, it was stated that the impregnation of the enzyme provided
by means of the compression treatment considerably enhanced the release of soluble
carbohydrates from the chips compared with a case, wherein no compression treatment
was carried out.
Example 2
Effect of the enzymatic treatment on the beatability of chips
[0063] 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 equipment
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 refining time (3 -
12min) and, thus, also the energy level of the refining. The total energy 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.
[0064] The defibration times for the treated spruce sapwood chips were 3 - 12min. The treatments
were carried out as described in Example 3 (45°C, 22h). The compression/absorption
treatments were carried out using a treated cellulase mixture, as in Example 1, CBH
I, and an EG-rich enzyme preparation. The dosages for the treated mixture were 0.63
and 6.3 of protein per g of chips (as dry matter). The dosage for CBH I and the EG-rich
enzymes was 5.0mg 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, homogenized and its dry content was defined,
on the basis of which the SEC value could be calculated (kWh/kg).
[0065] The results are shown in Table 2.
Table 2.
Treatment |
CFS, ml |
SEC, kWh/kg |
Buffer treatment (pH5) |
100ml |
4.78 |
Cellulase mixture, 0.63 mg/g |
" |
4.15 |
Cellulase mixture, 6.3 mg/g |
" |
3.79 |
CBH I, protein 5mg/g |
" |
4.94 |
EG-rich, protein 5mg/g |
" |
4.14 |
[0066] 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
[0067] The chips were impregnated and treated with a cellulase mixture (a dosage containing
0.63mg of protein per g of chips (dry matter), 45°C, 22h), as described in Example
1. After this, the chips were refined by the blade refiner in accordance with 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.
Treatment |
SEC, kWh/kg |
CSF, ml |
Density, kg/m3 |
Tensile index, Nm/g |
Tear index, mNm2/g |
Scott Bond, J/m2 |
Opacity, % |
Brightness, % |
Reference |
4.61 |
115 |
361 |
38.5 |
8.24 |
112 |
94.5 |
54.4 |
Cellulase |
4.19 |
108 |
375 |
39.9 |
7.84 |
139 |
93.5 |
56.0 |
[0068] 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.
References
[0069]
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1. Verfahren zur Herstellung von Holzstoff, umfassend:
- Zerspanen des Rohholzmaterials,
- Vorbehandeln der Späne mit einem Enzym, welches zur Zersetzung der strukturellen
Teile des Holzes fähig ist, wonach
- Holzstoff aus den Spänen durch Mahlen hergestellt wird, wobei
- die enzymatische Behandlung ausgeführt wird durch Verdichten der Späne und Inkontaktbringen
der verdichteten Späne in einer flüssigen Phase mit einem Enzympräparat, dadurch gekennzeichnet, dass das Enzympräparat eine wirksame Menge sowohl an Cellobiohydrolase als auch an Endoglucanase
in einem Gewichtsverhältnis der Proteine von 3:1-1:3 enthält.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass ein Enzympräparat verwendet wird, welches 2 - 60 Gewichtsprozent, vorzugsweise 20
- 55 Gewichtsprozent Endoglucanase enthält.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Enzympräparat durch jedweden Produktionsstamm hergestellt wird, der industriell
verwendet wird.
4. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Enzympräparat durch einen Stamm hergestellt wird, der zu einer Familie ausgewählt
aus der folgenden Gruppe gehört: Trichoderma, Aspergillus, Penicillium, Humicola, Phanerochaete, Streptomyces und Bacillus.
5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Enzympräparat in einer Menge von 0,1 - 7 mg Protein pro g Späne, vorzugsweise
3 - 6 mg Protein pro g Späne (Trockenmasse) verwendet wird.
6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der Holzstoff gemahlen wird, um eine Entwässerbarkeit von mindestens 100 ml CSF,
vorzugsweise mindestens etwa 80 ml CSF zu erhalten.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Späne um mindestens 10 %, verdichtet werden.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass die Späne mit einem Verdichtungsverhältnis von 1:2 - 1:10 verdichtet werden.
9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die durchschnittliche Spangröße der Späne, welche dem Verdichtungsbehandlung unterzogen
werden, etwa 15 - 25 mm ist.
10. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Verdichtungsbehandlung in einer Schraubzwinge oder einer hydraulischen Presse
durchgeführt wird.
11. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Dauer der Kompressions-/Absorptionsphase mindestens 1 Minute, vorzugsweise etwa
5 - 100 Minuten ist.
12. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Enzympräparat auf die Späne innerhalb eines Bereichs von 1 bis 24 h, vorzugsweise
1 bis 12 h wirken kann, bevor der Refiner-Holzstoff hergestellt wird.
13. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Späne vor der Verdichtungsbehandlung mit Dampf behandelt werden.
14. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der Holzstoff durch das TMP- oder RMP-Verfahren hergestellt wird.
15. Verfahren nach einem der vorhergehenden Ansprüche zur Herstellung von Holzstoff, welcher
für Papierzellstoff verwendet wird.
1. Procédé pour préparer une pâte mécanique, comprenant :
- le déchiquetage du matériau de bois brut,
- le prétraitement des copeaux avec une enzyme qui est capable de désintégrer les
parties structurelles du bois, après quoi
- la pâte mécanique est préparée à partir des copeaux par raffinage, dans lequel
- le traitement enzymatique est mis en oeuvre par compression des copeaux et mise
des copeaux compressés dans une phase liquide en contact avec une préparation enzymatique,
caractérisé en ce que la préparation enzymatique contient une quantité efficace tant de cellobiohydrolase
que d'endoglucanase en un rapport en poids des protéines de 3/1 à 1/3.
2. Procédé selon la revendication 1, caractérisé en ce qu'est utilisée une préparation enzymatique contenant de 2 à 60 % en poids, de préférence
de 20 à 55 % en poids d'endoglucanases.
3. Procédé selon la revendication 1 ou 2, caractérisé en ce que la préparation enzymatique est produite par une souche productrice quelconque qui
est utilisée dans l'industrie.
4. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la préparation enzymatique est produite par une souche appartenant à une famille
qui est choisie dans le groupe suivant : Trichoderma, Aspergillus, Penicillium, Humicola, Phanerochaete, Streptomyces, et Bacillus.
5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la préparation enzymatique est utilisée en une quantité de 0, à 7 mg de protéine
par g de copeaux, de préférence de 3 à 6 mg de protéine par g de copeaux (matière
sèche).
6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la pâte est raffinée pour que soit obtenue une aptitude à l'égouttage d'au moins
100 ml CSF, de préférence d'au moins environ 80 ml CSF.
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que les copeaux sont compressés d'au moins 10 %.
8. Procédé selon la revendication 7, caractérisé en ce que les copeaux sont compressés avec un rapport de compression de 1/2 à 1/10.
9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la taille moyenne des copeaux qui sont soumis au traitement de compression est d'environ
15 à 25 mm.
10. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le traitement de compression est mis en oeuvre dans une pince à vis ou une presse
hydraulique.
11. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la durée de l'étape de compression / absorption est d'au moins 1 minute, de préférence
d'environ 5 à 100 minutes.
12. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la préparation enzymatique est laissée à agir sur les copeaux pendant une période
de 1 à 24 heures, de préférence de 1 à 12 heures, avant que la pâte mécanique de raffineur
soit préparée.
13. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que les copeaux sont étuvés avant le traitement de compression.
14. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la pâte mécanique est préparée par le procédé TMP ou RMP.
15. Utilisation du procédé selon l'une quelconque des revendications précédentes pour
préparer une pâte mécanique qui est utilisée pour de la pâte à papier.