CA2541229C - Modified method for mechanical pulp production - Google Patents

Abstract

A method of producing a hardwood pulp by mechanical refining is provided. This method comprises mechanically refining hardwood chips to produce a hardwood mechanical pulp and treating the hardwood mechanical pulp with one or more than one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between about 0.5 to about 5.0 kg xylose/t of pulp. The enzyme-treated mechanical pulp is then further mechanically refined with a reduced demand for refining energy.

Description

= CA 02541229 2012-12-03 =
MODIFIED METHOD FOR MECHANICAL PULP PRODUCTION
FIELD OF INVENTION
[0001] The present invention relates to methods of producing pulp. More specifically, the present invention relates to methods of producing mechanical pulp from hardwood using enzymes.
BACKGROUND OF THE INVENTION

[0002] The production of mechanical pulp is a major industry with over 40 million tonnes of pulp produced annually worldwide. Mechanical pulps are used in a wide variety of papers.
Unbleached or slightly bleached mechanical pulps are used in the production of newsprint and constitute the largest single usage of mechanical pulps. Moderately bleached mechanical pulps have been used to manufacture uncoated products such as supercalendered paper, coated products such as light-weight-coated paper, paperboard and tissue products. Highly bleached mechanical pulps are used in tissue products, coated and uncoated fine papers such as photocopy paper and technical grade paper such as carbonless paper. Pulps produced by mechanical refining are characterized by high yields in excess of 80% from wood, favorable mechanical and optical properties, and lower manufacturing costs than kraft pulps.

[0003] The main characteristic of mechanical pulps is that the fibers in the wood chips are separated by mechanical action rather than through chemical action as in kraft pulping. There are several mechanical pulping processes known in the art as taught by Smook, (1992) Handbook for Pulp & Paper Technologists. The majority of mechanical pulps are made using a refiner, in which wood chips or pulp are passed between plates having raised (bars and dams) and depressed (grooves) segments. The plates are installed in a refiner and at least one of the plates is rotated.
The chips or pulp move from the center of the plates to the edges and the chips are converted from chips into coarse pulp or a coarse pulp is further refined by the action of the plates. The process of converting chips into coarse pulp is known as primary refining and the process of converting the coarse pulp produced during primary refining to refined pulp is known as secondary refining.

[0004] Prior to primary refining, softwood or hardwood chips (also known as furnish) are washed to remove dirt and debris. The chips may then be steamed to remove air and to heat them prior to refining. The chips may also be pre-treated by compression in a device such as a screw press, followed by introduction to a chemical solution in which the chips relax, absorbing the solution, which process is known as impregnation to those of skill in the art.

[0005] After pre-treatment, the chips are introduced to either an atmospheric or pressurized primary refiner and converted into coarse pulp as is familiar to those skilled in the art. Secondary refining of the coarse pulp to post-secondary refined pulp is carried out in a secondary refiner as is familiar to those skilled in the art. Pulp leaving the secondary refiner or additional refining stages is typically sent to a latency chest where the fibers relax and straighten in a hot, low consistency suspension prior to screening and/or cleaning. Next, the pulp is passed from the latency chest to a series of cascading screens. Pulp not passing through a screen of defined size, known as screen rejects, is thickened and directed to a rejects refiner and refined as is familiar to those skilled in the art. After the pulp is screened for debris, it is cleaned by introducing the pulp slurry to a tank containing centrifugal cleaners that remove sclereids, debris and poorly refined pulp to produce a clean pulp flow and a rejected flow known as cleaner rejects, as is familiar to those skilled in the art. The cleaner rejects are typically combined with the screen rejects, thickened and then introduced to a rejects refiner and refined as is familiar to those skilled in the art.

[0006] Secondary refined pulp may undergo additional refining stages (post-secondary refining) to further refine the pulp after which it may be screened, cleaned or both.
Occasionally, the reject pulp will be refined in a secondary refiner instead of a rejects refiner. The pulp accepts may be bleached, either reductively and/or oxidatively. Mechanical pulp used in the production of newsprint is frequently refined in a tertiary refiner (also referred to as a post-secondary stage) following the secondary refining. The finished pulp may be dried and baled or sent to storage prior to introduction to a paper machine.

[0007] One problem encountered by the industry is the high, and increasing, cost of electricity.
The refining of one tonne of mechanical pulp typically requires 800 to 3500 kWh of electricity.
For example, at a cost of 5 cents/kWh, the cost of electricity for refining is $40 to $175/tonne of pulp. This high cost reduces the competitiveness of the pulp in some applications and decreases the profitability of the operation. In addition, the limited amounts of electricity available in some regions can make it difficult for a mill to operate while drawing this much electrical power.

= CA 02541229 2012-12-03 Moreover, a high electricity usage correlates to a high energy input that can damage the pulp fibers. This damage can negatively affect the properties of the final product.

[0008] The use of biological products to decrease the refining energy of mechanical pulping has been investigated. This includes the treatment of chips or refined pulp. For example, WO
97/40194 (Eachus et al.) teaches pre-treating Loblolly pine softwood chips with Ceriporiopsis fungi, CLARIANT CARTAZYME HS enzyme (contains xylanase), or mixtures of CLARIANT
CARTAZYME NS enzyme (contains xylanase) and SIGMA lipase enzyme. Enzyme treatment with CLARIANT CARTAZYME HS had no affect on refiner energy when the enzyme was added by submerging the wood chips into a buffered solution, but decreased the refiner energy by 100 kWhit or about 4% when the enzyme was added using an IMPRESSAFINER (a chip impregnation device) which was followed by an incubation period of 48 hours at 50 C. Some of the benefits desired by the industry were obtained using this method (e.g. improved pulp properties); however, the lengths of treatment periods are impractical.

[0009] Viikari et al. (Pretreatments of Wood Chips in Pulp Processing, in Paavilainen, L. ed., Final report - Finnish Forest Cluster Research Programme, WOOD WISDOM, 1998-2001, Report 3, pp. 115-121) disclose pre-treating Norway spruce softwood chips with fungi or enzymes prior to refining. The fungal treated chips used 15% less refining energy than an untreated control and had an improved tensile strength but lower brightness.
The energy consumption for refining was decreased by using enzymes that modify lignin, and by 10-20%
when using enzymes that modify cellulose or hemicellulose. No details of the methods, conditions of pre-treatment, or the enzymes used are provided.

[0010] As an extension of the studies by Viikari et al. (supra), Pere et al.
(Impregnation of Chips with Enzymes for Enhanced Mechanical Pulping, 9th International Conference on Biotechnology in the Pulp and Paper Industry, Durban, South Africa, 10-14 October 2004, pp.
27-28) discuss the use of a cellulase mixture (CBH I + EG) during chip impregnation prior to refining. Treatment of spruce softwood chips with the cellulase mixture prior to refining resulted in an energy reduction of 18-20%. To date, Pere etal. have not demonstrated the applicability of their treatment on any hardwood species.

[0011] The treatment of pulp after primary refining to decrease energy requirements has also been investigated. US 6,267,841 (Burton) teaches treatment of primary refined hardwood or softwood pulp with enzyme to decrease the energy requirements of the secondary refining operation. To do so, Burton teaches that the specific refining energy be separated between the primary and secondary stages in a 1/3 and 2/3 ratio respectively. In reality, this represents a severe limitation to the practice of the method since, in commercial two stage operations, typically at least half of the refining energy is used in the first stage of defibering. Moreover, to practice the method, an energy input of less than 10 hpd/t (-200 kWh/t) in the primary refiner and less than 20 hpd/t (-390 kWh/t) in the secondary refiner is taught; neither condition is used in commercial applications. Additionally, US 6,267,841 teaches that the temperature of the primary refining stage should be greater than 150 C, which may exclude a commercial process known as the Refiner Mechanical Pulping (RMP) process. In the RMP process, primary refining is performed at atmospheric conditions and thus treatment at a temperature as high as 150 C, as taught in US 6,267,841, may not be possible for the practice of this method.

[0012] US 6,099,688 and US 5,865,949 (Pere et al.) disclose treating once refined pulp with cellulase or a cellulase/mannanase mixture prior to secondary refining in order to decrease the refining energy. US 6,099,688 (Pere et al.) teaches that treating coarse pulp with an enzyme preparation having cellobiohydrolase (CBH I) activity derived from T. reesei can reduce the specific energy required to refine the pulp as it changes the crystallinity of the ultrastructure. In an example of a preferred embodiment, the specific energy was reduced by about 15-20%
following a treatment at 45-50 C and pH 5-5.5 at 5% consistency for 2 hours using an enzyme dosage of 0.5 mg/g pulp. US 5,865,949 (Pere et al.) teaches that the treatment of coarse spruce TMP pulp with cellobiohydrolase (CBH I) and mannanase will also reduce specific refining energy. In one example, the treatment involves reducing the pulp stock pH to 4.5 with a reaction time of 2 hours at 45-50 C and a consistency of 5%. The enzyme dosage used was 0.1 mg/g CBH I and 0.1 mg/g mannanase and achieved an energy reduction of about 12%. In both of Pere's teachings, it would be difficult to comply with the recommended treatment conditions in an industrial environment. Problematic areas for the practice of these methods include the long reaction times and the low consistency between the refining stages. In practice, a 2 hour storage capacity acting as a surge for the pulp stock to carry out enzyme treatment may not be available, nor would it be likely that the necessary equipment would be in place to thicken the pulp stock to the required consistency prior to secondary refining. Furthermore, the effect of the treatment was not demonstrated using a hardwood species.

[0013] EP 0 430 915 (Vaheri et al. '915) teaches the use of hydrolytic enzymes from either A.spergillus or Trichoderma fungi, preferably in the presence of suitable oxidation-reduction chemicals to decrease the refining energy of softwood. The enzymes may be mixed with either wood, wood chips or pulp refined at least once prior to subsequent refining. A
sole example is provided involving xylanase treatment (using 2 U/g dosage) of defibered spruce softwood pulp (once refined) at 2.9% consistency and held at 20 C for a 3 hour period.
Following the xylanase treatment, NaOH was added in an amount equivalent to 4% of the pulp mass and left to react, without stirring, for 80 minutes. The pulp was then concentrated, centrifuged, homogenized and frozen. Following this sequence of several treatments, a reduction of 21% in refining energy was obtained. A disadvantage of the method is that the specified conditions and the sequence of treatments are not practical for use in a mill setting. Also, the applicability ofthe method was not demonstrated using hardwood.

[0014] WO 91/11552 (Vaheri et al. '552) discloses a method of treating fibrous material, including wood chips and pulp, simultaneously with hydrolytic and oxidizing enzymes and adjusting the redox potential to less than 200 mV prior to primary or secondary refining to achieve a corresponding reduction in the refining energy. However, the oxidizing enzymes described by Vaheri '552 (WO 91/11552) are not available commercially and adjusting the redox potential is costly. Furthermore, similar to EP 0 430 915 (Vaheri et al.
'915), the applicability of the method was not demonstrated with hardwood.

[0015] W02004/101889 (Taylor et al.) report the use of mannanase or a combination of mannanase and xylanase to treat southern pine softwood TMP pulp with the goal of reducing the energy required for refining. In one example, the pulp was treated with mannanase at 0.171 pounds/ton dry pulp, at a temperature of 85 C and a consistency of 3%. A
valley beater was used to reduce the freeness of the pulp stock of both treated and untreated pulp.
In this case, the freeness of the two pulps did not differ when subjected to similar beating times and, therefore, no reductions in refining energy were observed. In further examples, reject TMP
softwood pulp was treated with mannanase at 1 mg/g of pulp or a combination of mannanase and xylanase (each at 1 mg/g of pulp) at 80 C and pH 5.0 for 30 minutes. A household blender, operating at 2.5%
consistency was used to reduce the freeness of the pulp. When the pulp was treated with mannanase alone, the freeness of the enzyme-treated pulp was lower than the untreated pulp when subjected to similar times in the blender. The combination of mannanase and xylanase reduced the pulp freeness even further than mannanase alone. However, the results from a =
= CA 02541229 2012-12-03 household blender are difficult to correlate with the results one might obtain using industrial refining equipment. A valley beater is more readily correlated with industrial refining operations than a blender. In addition, the examples do not give any indication of the level of energy savings provided by the practice of the method, and the enzyme dosage of 1 mg/g, which is 1000 g protein per tonne of pulp, is far too high to be economically practical in a mill. Moreover, Taylor et al. do not demonstrate the applicability of the method using hardwood species. A
mannanase treatment will be ineffective in reducing the amount of refining energy as the mannan composition in hardwood represents a small fraction of the hemicellulose. The mannan is found as glucomannan and represents only 2-5% of hardwood. By comparison, in softwood, mannan is present in large quantities (-20%) as galactoglucomannan which comprises the principal hemicellulose found in softwood (Wood Chemistry Fundamentals and Applications, Eero Sjostrom, 2nd ed., 1993, Academic Press).

[0016] Therefore, in spite of previous efforts, there is no commercially viable means of using biological products for reducing the energy required for refining hardwood.
There remains a need in the art for novel products that will decrease refining energies and be commercially viable.
SUMMARY OF THE INVENTION

[0017] The present invention relates to methods of producing pulp. More specifically, the present invention relates to methods of producing mechanical pulp from hardwood using enzymes.

[0018] It is an object of the invention to provide an improved method of mechanical pulping.

[0019] According to the present invention, there is provided a method (A) of producing a hardwood pulp by mechanical refining comprising:
a. mechanically refining hardwood chips to produce a hardwood mechanical pulp;
b. treating the hardwood mechanical pulp with one or more than one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between about 0.5 and about 5.0 kg of xylose/t of pulp to produce an enzyme-treated mechanical pulp;
and c. further mechanically refining the enzyme-treated mechanical pulp to produce the hardwood pulp.

[0020] The present invention also pertains to the method (A) as described above, wherein the step of further mechanically refining (step c.) uses at least 20 kWh/t less energy than a non-xylanase treated control refined to a Canadian Standard Freeness value that is the same as the Canadian Standard Freeness value of the treated pulp after said step of further mechanically refining.

[0021] Preferably, the quantity of released xylose is between about 0.5 and about 3.0 kg of xylose/t of pulp.

[0022] The present invention pertains to the method (A) as described above, wherein the step of treating (step b.) is performed for between about 5 min and about 120 min, at a temperature from about 35 C to about 95 C, at a pH between about pH 3 to about pH 11 and at a consistency between about 0.5% and 30%.

[0023] The present invention also pertains to the method (A) as described above, wherein, in the step of treating (step b.), the Family 11 xylanase is present at an amount from about 0.05 to about xylanase units per gram (XU/g) of pulp, preferably at an amount from about 0.2 to about 2 xylanase units per gram (XU/g) of pulp.

[0024] The present invention also pertains to the method (A) as described above, wherein, in the step of treating (step b.), the Family 11 xylanase is present at an amount from about 0.1 to about 100 grams of xylanase protein per tonne of pulp.

[0025] The present invention also relates to the method (A), wherein, in the step of further mechanically refining (step c.), the treated pulp is refined to a Canadian Standard Freeness of greater than about 75 mL.

[0026] The present invention also pertains to the method (A) as described above, wherein the step of treating (step b.) is performed in the absence of an enzyme causing a substantial release of mannose from the hardwood pulp.

[0027] The mechanically refined hardwood pulp may be selected from the group consisting of coarse pulp, post-secondary refined pulp, reject pulp and a combination thereof.

[0028] The present invention also pertains to the method as described above (A), wherein, in the step of mechanically refining (step a.), the hardwood chips are from a hardwood tree species selected from the group consisting of aspen, poplar, birch, maple, oak, chestnut, alder, eucalyptus, acacia and a combination thereof. Preferably, the hardwood chips are from aspen or poplar.

[0029] The present invention also pertains to the method as described above (A), wherein the step of mechanically refining (step a.) comprises primary refining of hardwood chips, wherein the primary refining uses an energy input of at least about 200 kWh/t.

[0030] The present invention also relates to the method (A), wherein the Family 11 xylanase is from a microorganism selected from the group consisting of the genera A.spergillus niger, Bacillus, Cellulomonas, Chainia, Clostridium, Fibrobacter, Neocallimasterix, Nocardiopsis, Rum inococcus, Schizophyllum, Streptomyces, Thermomonaspora, Thermomyces, Trichoderma, Actinomadura, Aureobasidium, Humicola and Chaetomium. Furthermore, the Family xylanase may be a modified xylanase selected from the group consisting of TrX-DS1; TrX-162H-DS1; TrX-162H-DS2; TrX-162H-DS4; TrX-1621-1-DS8; TrX-75A; TrX-HML-105H; TrX-HML-75A-105H; TrX-HML-75C-105R; TrX-HML-75G-105R; TrX-HML-75G-105R-125A-129E;
TrX-HML-75G-105H-125A-129E; TrX-HML-75A-105H-125A-129E; TrX-HML-75A-105R-125A-129E; TrX-157D-161R-162H-165H; TrX-HML-AHAE; TrX-HML-AHAE-R; TrX-HML-AHAE-RR; TrX-HML-AHAE-RRR; TrX-HML-AHA-RR-DRHH; TrX-HML-AHAE-RR-DRHH; TrX-HML-AHAE-RRR-DRHH; TrX-1 l 6G; TrX-118C; TrX- HML-AHCAE-R; TrX-H-11D-ML-AHGAE-RR; TrX-HML-AHGAE-R; TrX-H-11D-ML-AHGCAE-RR; TrX-H-11D-ML-AHCAE-RR; TrX-HML; HTX13; HTX18; ITX1; ITX2; ITX2';1TX3; ITX3';ITX4; ITX4';

ITX5; ITX5'; X1n1-131N; HTX44; HTX44-131N. The Family 11 xylanase may also be wild-type Trichoderma reesei xylanase II.

[0031] The present invention also pertains to the method (A), wherein the step of treating (step b.) is performed in the absence of an added oxidation or reduction chemical or oxidoreductase enzyme.

[0032] The present invention also relates to the method (A) as described above, wherein, in the step of treating (step b.), the xylanase is added to the hardwood pulp by a mixing device. The mixing device may be selected from the group consisting of a refiner, a blow line exiting a refiner, a chemical mixer, a mechanical pump, and an agitator.

[0033] The present invention also pertains to the method (A) as described above, wherein, after addition of the one or more than one xylanase, the hardwood pulp is contacted with the xylanase in a conveying system, a storage vessel or a combination thereof. The storage vessel may be selected from the group consisting of a wash chest, transfer chest, surge tank and a pulp storage tower.

[0034] The present invention also relates to the method (A) as described above, wherein, during the step of treating (step b.), one or more than one chemical agent is added to the mechanical pulp, the chemical agent being selected from the group consisting of acids, bases, chelants, stabilizers, other enzymes and a combination thereof.

[0035] The present invention also pertains to the method (A) as described above, wherein, prior to or after the step of treating (step b.), the hardwood mechanical pulp is treated with one or more than one chemical agent selected from the group consisting of acids, bases, oxidants, reductants, chelants, stabilizers, other enzymes and a combination thereof.

[0036] The present invention also pertains to the method (A) as described above, wherein, in the step of mechanically refining (step a.), the mechanical hardwood pulp is prepared by primary refining of hardwood chips to produce a coarse pulp; secondary refining of a coarse pulp in one or more than one stage to produce a post-secondary refined pulp; or screening and/or cleaning coarse and post-secondary pulp to provide a reject pulp.

[0037] The present invention also relates to the method (A) as defined above, wherein the step of further mechanically refining (step c.) includes secondary refining of a coarse pulp in one or more than one stage to produce a post-secondary refined pulp; additional refining stages performed after secondary refining; or reject refining of reject pulp collected by screening and/or cleaning coarse or post-secondary pulp.

[0038] According to the invention, there is also provided a method (B) of producing a hardwood pulp by mechanical refining, the method comprising a step of treating a hardwood mechanical pulp with one or more than one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between about 0.5 and about 5.0 kg of xylose/t of pulp thereby producing an =
= CA 02541229 2012-12-03 enzyme-treated hardwood pulp. The quantity of xylose released may also be between about 0.5 and about 3.0 kg xylose/t of pulp, or between about 1.0 and about 3.0 kg xylose/t of pulp, or between about 1.2 and about 3.0 kg xylose/t of pulp, or between about 1.5 and about 3.0 kg xylose/t of pulp, or between about 2.2 and about 3.0 kg xylose/t of pulp.

[0039] The methods of the invention replace conventional refining processes that take place without the use of enzymes and require higher refining energies to develop similar desirable hardwood pulp properties. As described herein, in the presence of one or more than one Family 11 xylanase, and optionally other enzymes, hardwood mechanical pulp may be mechanically refined using less refining energy than conventional processes. The energy reductions obtained using the process of the present invention may provide energy reductions of about 20 to about 300 kWh/t compared to a control process in which the pulp has not been treated with Family 11 xylanase. This corresponds to an energy savings of about 3 to about 50%. These optimal energy reductions are achieved by controlling the quantity of xylose released during the xylanase treatment within a predetermined range. A preferred range of xylose that is released is from about 0.5 to about 5.0 kg xylose/t of pulp. The greatest energy savings are obtained when the amount of xylose released during xylanase treatment is between about 0.5 kg xylose/t of pulp and 5.0 kg xylose/t of pulp.

[0040] The method of the present invention may be performed at any mill as part of a refining process. Further, the process may comprise Refiner Mechanical Pulping (RMP), Thermo-mechanical Pulping (TMP), Chemi-thermo-mechanical Pulping (CTMP), Bleached Thermo-mechanical Pulping (BTMP), Bleached Chemi-thermo-mechanical Pulping (BCTMP) or the production of Medium Density Fiberboard (MDF).

[0041] This summary of the invention does not necessarily describe all features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS

[0042] These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:

[0043] FIGURE 1 depicts the amount of xylose released per gram of enzyme protein used as a function of time for Family 10 and Family 11 xylanases applied to aspen pulp at a dosage of 3.7 g of protein per gram of pulp (3.7 grams of protein per tonne of pulp) at conditions of 63 C, pH ¨ 6.5-7.0 and 3.5% consistency.

[0044] FIGURE 2 depicts the amount of xylose released and measured for an aspen RMP pulp treated using varying dosages of BIOBRITE EB xylanase at 63 C, pH ¨ 6.3 and 5% consistency.

[0045] FIGURE 3 depicts the possible application points (X) where the xylanase could be added to the mechanical pulping process in order to achieve energy reduction benefits.

[0046] FIGURE 4 depicts the relationship between the freeness of the pulp and the energy consumption (refining specific energy) for pulp produced from aspen RMP pulp in the absence of enzyme (Control), or pulp that has been treated with BIOBRITE EB enzyme for 1 hr using varying xylanase dosages (0.33, 1.64 and 9.84 XU/g pulp) at pH ¨ 6.3, 63 C and a consistency of 3.5%.

[0047] FIGURE 5 depicts the relationship between the effect of Family 11 xylanase dosage (XU/g; dosage applied to pulp) and the energy reduction observed (refining specific energy) as a result of the Family 11 xylanase treatment for pulp of varying final freeness (aspen RMP pulp treated with BIOBRITE EB enzyme for 1 hr (pH-6.3, 63 C and 3.5%
consistency)).

[0048] FIGURE 6 depicts energy reductions obtained by varying final freeness targets using the method of the present invention as a result of a Family 11 xylanase treatment of reject pulp (aspen RMP pulp treated with 0.33 XU/g BIOBRITE EB enzyme for 1 hr (pH-6.3, 63 C and 3.5% consistency)).

[0049] FIGURE 7 depicts the energy savings in kWh relative to the Family 11 xylanase dosage (million XU) for various freeness levels as a function of the xylose released following BIOBRITE EB xylanase treatment of aspen RMP pulp at 63 C, pH ¨ 6.3 and 3.5%
consistency for 1 hr. The dashed lines represent data extrapolated to zero xylose release and the solid lines represent the range of the actual data.
DETAILED DESCRIPTION

[0050] The following description is of preferred embodiments.

[0051] The present invention relates to methods of producing pulp.
Furthermore, the present invention relates to methods of treating mechanical pulp using enzymes and methods of refining enzyme-treated pulp. More specifically, the invention relates to methods of treating hardwood mechanical pulp with enzymes prior to further refining of the pulp.

[0052] The following description is of an embodiment by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.

[0053] According to the present invention, there is provided a process of treating hardwood mechanical pulp prior to refining, with refiner energy reductions of 20 to 300 kWh/t being attained for pulp processed using the present method over pulp processed without enzyme treatment. The process results in energy reductions that are dependent upon ensuring that the quantity of xylose released during treatment with a xylanase enzyme is within a range of 0.5 kg xylose/t of pulp to 5.0 kg xylose/t of pulp.

[0054] The method of the present invention comprises treating the hardwood mechanical pulp with the enzyme prior to further refining of the pulp. The enzyme treatment of pulp involves the use of a Family 11 xylanase enzyme alone or in combination with other Family 11 enzymes.

[0055] Other enzymes, in addition to Family 11 xylanases, may be used in the treatment of the pulp. These other enzymes include cel lu lases, cell wall enzymes, esterases, other hem icel lulases or combinations thereof. This includes the addition of purified or semi-purified preparations, crude extracts or the addition of a microbe, such as a fungus, that exhibits hemicellulolytic activity on pulp. Preferably, this excludes the simultaneous addition of a mannanase enzyme that exhibits a substantial amount of mannose release from the pulp.

[0056] The hardwood pulp may be selected from the group consisting of coarse pulp, post-secondary refined pulp and reject pulp.

[0057] During treatment of the hardwood pulp with the Family 11 xylanase, the pulp may be treated with one or more than one chemical agent, for example, acids, bases, chelants, stabilizers, other enzymes and a combination thereof. Additionally, prior to or after treatment with the Family 11 xylanase, the pulp may be treated with one or more than one chemical agent, for example, acids, bases, chelants, stabilizers, oxidants, reductants, other enzymes and a combination thereof.

[0058] Therefore, the present invention provides a method of producing a hardwood pulp by mechanical refining, the method comprising a step of treating a hardwood mechanical pulp with one or more than one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between about 0.5 and about 5.0 kg of xylose/t of pulp thereby producing an enzyme-treated mechanical pulp.

[0059] The present invention also provides a method of producing a hardwood pulp by mechanical refining comprising:
a. mechanically refining hardwood chips to produce a hardwood mechanical pulp;
b. treating the hardwood mechanical pulp with one or more than one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between about 0.5 and about 5.0 kg of xylose/t of pulp to produce an enzyme-treated mechanical pulp; and c. further mechanically refining the enzyme-treated mechanical pulp to produce the hardwood pulp.

[0060] The hardwood pulp may be selected from the group consisting of coarse pulp, post-secondary refined pulp and reject pulp. By "coarse pulp", it is meant pulp exiting a primary refiner. By "post-secondary refined pulp", it is meant pulp exiting a secondary and/or post-secondary refiner. By "reject pulp", it is meant pulp rejected by screening and/or cleaning processes.

[0061] By "hardwood", it is meant wood species that are characterized by fibers shorter than 2.5 centimeters, contain vessel elements and have lignin concentrations not exceeding 25% by weight, for example as taught by Smook (1992). Hardwoods can be classified by the scheme published by the United States Department of Agriculture (2004). Examples of hardwoods, that are not meant to be limiting, are provided in Table 1.
Table 1. Hardwoods Sub-class Order Family Genus Species Common Names Dilleniidae Salicales Salicaceae Populus. L. P.
treniuloides Aspen P. tremula Poplar Rosidae Fabales Fabaceae Acacia P. Mill. A. rigidula Acacia Myrtales Myrtaceae Eucalyptus L' Her. E. grandis Eucalyptus Rosales Rosaceae Ma/us P. Mill. M. sylvestris Apple Sapindales Aceraceae Acer L. A. saccharinum Maple A. platano ides Hamamelidai Fagales Betulaceae Betula L. B. papyrifera Birch B. pendula Alnus L. Incana Alder Fagaceae Fagus L. F. grandifoli Beech F. .sylvatica Quercus L. Q. falcate Oak Q. velutina Castanea P. Mill. C. dentate Chestnut

[0062] Preferably, the hardwood species is aspen or poplar.

[0063] By the term "treating" or "enzyme treatment", it is meant adding the one or more than one Family 11 xylanase either alone or in combination with one or more than one other enzyme to the mechanical pulp and then allowing for contact and reaction between the pulp and the xylanase.
Addition of the Family 11 xylanase may include but is not limited to:
- using a mixing device to introduce the xylanase to the pulp prior to introduction to a storage vessel, - injecting the xylanase into a storage vessel or a conveying system used to carry the pulp suspension into the storage vessel, or - spraying the pulp suspension with the xylanase.

[0064] Furthermore, these methods may be combined.

[0065] The mixing device may be a refiner, a blow line exiting a refiner, a chemical mixer, a mechanical pump, or an agitator to introduce the xylanase prior to or during storage in a storage vessel.

[0066] A preferred method of adding the xylanase to the pulp is injecting it at the inlet of a chemical mixer or a mechanical pump, which provides mixing and carries the pulp to the storage vessel. A further preferred method is injecting the xylanase into an agitated storage vessel.
Another preferred method is to inject the xylanase into a conveying system that can provide some mixing and which carries the pulp suspension into the storage vessel.

[0067] By the term "storage vessel", it is meant any vessel or tower where the pulp, following the enzyme addition, will reside for a sufficient length of time allowing for contact and reaction between the pulp and the xylanase. The storage vessel may include, but is not limited to, a wash chest, a latency chest, a transfer tank, a surge tank or a pulp storage tower.

[0068] By the term "conveying system", it is meant a partially or fully enclosed circuit for carrying the pulp suspension from one operation to the next that could also provide for sufficient reaction and contact between the xylanase and the pulp suspension.

[0069] A schematic diagram of typical process equipment usable to practice the present invention is shown in Figure 3. Figure 3 is included as an example of how the present invention can be practised and is not meant to be limiting, and as would be known to one skilled in the art, various combinations of the process equipment shown in Figure 3 are possible. With reference to Figure 3, open-arrows (101-122) depict examples of application points where the xylanase (xylanase or a blend of xylanase and cellulases, other hemicellulases, cell wall enzymes, esterase or combinations of these enzymes) may be added with the intent of reducing the refining energy.
Hardwood chips are fed (1) to a primary refiner (2) where the chips are converted into a coarse pulp. The coarse pulp exits the primary refiner via a blow line (3), wherein xylanase (101) may be added to the pulp prior to conveyance of the pulp to a storage vessel, e.g.
latency chest (4).

The xylanase may also be added (102) to a pump (5) that pumps the pulp to a second storage vessel (6). The coarse pulp is conveyed to the secondary refiner (7) where it is further refined to produce fine pulp. Xylanase may be added (103) in the secondary refiner (7) or added (104) in the blow line (8) conveying the refined pulp to a storage vessel (9).
Additional refining stages are also possible as illustrated by (A) with (n) equal to or greater than two.
Xylanase treatment of the pulp in post-secondary refining stages can be done in refiners of blow lines as illustrated for the xylanase treatment of secondary refined pulp.

[0070] After secondary or post-secondary refining stages have been completed the pulp is transferred by a pump (10), to which xylanase may be added (105), from the storage vessel to the primary screen (11). Pulp of the desired quality, known as screen accepts, is conveyed via the screen accepts line (12) by a pump (13), to which xylanase may be added (106), to the primary cleaner (14). Pulp rejected by the primary screen (11) may be treated with xylanase (111) in the screen rejects line (31) feeding the secondary screen (32). The secondary screen accepts line (33) can transfer secondary screen accepts pulp to the line feeding the primary screen. The secondary screen rejects can be treated with xylanase (112) in the secondary screen rejects line (33) prior to introduction to a storage vessel (34). Other arrangements of screens can be practised with the present art.

[0071] Cleaner accepts are conveyed by the cleaner accepts line (15) to a storage vessel (16), from which the pulp is then conveyed to the next component of the pulp processing operation (17). Primary cleaner rejects may be treated with xylanase (107) prior to conveyance via the primary cleaner rejects line (18) and pump (19) to a secondary cleaner (20).
Secondary cleaner accepts can be recycled via a transfer line (21) to the primary cleaner (14).
The secondary cleaner rejects can be treated in the secondary cleaner rejects line (22) and pump (23) with xylanase (108) prior to introduction to a tertiary cleaner (24). Tertiary cleaner accepts can be recycled via a transfer line (25) to the secondary cleaner (20). Tertiary cleaner rejects can be treated with xylanase (109) in the tertiary cleaner rejects line (26) or pump (27) prior to introduction to a pulp dewatering or thickening device (28). The use of additional cleaning stages and xylanase treatment points will be obvious to one skilled in the art. The thickened pulp slurry can be treated with xylanase (110) prior to a pump (29) feeding a storage vessel, e.g. rejects transfer tank (34). The xylanase treated pulp can be thickened in a thickening device (35) and then introduced to a rejects refiner, from whence it can be conveyed to a storage vessel (9) via a conveying system (37). Xylanase treatment may be combined to include some or all of the locations. Introduction of the xylanase can be done by means of a mixing device or by spraying the pulp suspension with a xylanase preparation.

[0072] Following enzyme addition, the pulp is contacted with the xylanase for a sufficient length of time to allow for reaction between the pulp and the xylanase to produce a treated pulp mixture.
Contact between the pulp and xylanase may be carried out in a conveying system, a storage vessel or a combination thereof.

[0073] A non-limiting example of a suitable treatment condition is given in Example 6. For example, treatment of hardwood pulp with Family 11 xylanase at a dose of 0.98 XU/g of pulp, at 5% consistency and a temperature of 63 C for 1 hr produced a quantity of xylose released of 3.6 kg/t of pulp (see Figure 2).

[0074] During the enzyme treatment of the pulp, xylose and/or xylan oligomers are released into solution due to hydrolysis of the xylan component of the hardwood. With reference to Figure 7, the greatest energy savings relative to the amount of enzyme used are obtained when the amount of xylose released during xylanase treatment is between about 0.5 kg xylose/t of pulp and about 5.0 kg xylose/t of pulp. Thus, the treatment is carried out under conditions so that the quantity of xylose released is between about 0.5 and 5.0 kg xylose/t of pulp, or any quantity therebetween.
Preferably, but not to be considered limiting, the quantity of xylose released may be between about 0.5 and about 3.0 kg xylose/t of pulp, or any amount therebetween, or between about 1.0 and about 3.0 kg xylose/t of pulp, or any amount therebetween, or between about 1.2 and about 3.0 kg xylose/t of pulp, or any amount therebetween, or between about 1.5 and about 3.0 kg xylose/t of pulp, or any amount therebetween, or between about 2.2 and about 3.0 kg xylose/t of pulp, or any amount therebetween. For example, the amount of xylose released may be about 0.5, 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.5, 4.0, 4.5 or 5.0 kg xylose/t of pulp.

[0075] By the expression "quantity of xylose", it is meant the difference between the concentration of xylose in a hydrolyzed aliquot of the xylanase treated pulp and an untreated control pulp using otherwise identical treatment conditions, which include the pH of the pulp mixture, the temperature of the pulp mixture, the reaction time and the pulp consistency. The measured quantity of xylose includes both xylose monomers and xylose contained in soluble xylan oligomers which are liberated during a subsequent acid hydrolysis step.
The amount of xylose released is measured after completion of the enzymatic treatment.
Although the examples describe the measurement of xylose release in both laboratory and mill settings, the method of quantifying the xylose released according to the invention is by performing the assay set out in Example 8 which is carried out in a mill setting.

[0076] The amount of enzyme effective to release between about 0.5 and 5.0 kg/t of hardwood pulp may be between about 0.05 and about 10.0 xylanase units per gram of hardwood pulp (XU/g), or any amount therebetween, or between about 0.15 and about 5.0 XU/g hardwood mechanical pulp, or any amount therebetween, or between about 0.2 and about 4.5 XU/g, or any amount therebetween, or between about 0.25 and about 4.0 XU/g, or any amount therebetween, or between about 3.0 and about 3.5 XU/g, or any amount therebetween, or between about 0.35 and about 3.0 XU/g, or any amount therebetween, or between about 0.4 and 2.5 XU/g, or any amount therebetween, or between 0.45 and 2.0 XU/g, or any amount therebetween, or between about 0.50 and 1.5 XU/g, or any amount therebetween, or between about 0.55 and 1.0 XU/g, or any amount therebetween. One of skill in the art would be able to readily modify the amount of enzyme to pulp ratio as required, and the specific amounts set out above should not be considered limiting. For example, in Example 7, hardwood mechanical pulp is treated over a range of xylanase dosages that includes dosages that would produce a quantity of xylose released that is between 0.5 and 5.0 kg/tonne of pulp. It should be appreciated that other amounts of enzyme may be selected.

[0077] The xylanase dosage may also be represented in terms of grams of xylanase protein per tonne of hardwood pulp. The xylanase dosage may be between about 0.1 to 100 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween, or the xylanase dosage may be between about 1.0 and 50 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween, or between about 1.5 and 20 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween, or between about 2.0 and 15 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween, or between about 2.5 and 12 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween, or between about 3.0 and 10 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween, or between 3.5 and 9 grams of xylanase protein per tonne of hardwood pulp, or any amount therebetween.

= CA 02541229 2012-12-03 =

[0078] The amount of enzyme required is dependent upon the reaction conditions during the enzyme treatment step. The reaction conditions may be adjusted according to conventional techniques known in the art. This includes, but is not limited to, adjusting the pH, the pulp consistency, the treatment time, the treatment temperature, the method of enzyme addition to the pulp and the choice of enzyme. A non-limiting example of a suitable treatment condition is given in Example 6.

[0079] The xylan content of hardwood typically ranges from between about 15%
and 30% of the dry wood mass (Wood Chemistry Fundamentals and Applications, Eero Sjostrom, 2nd ed., 1993, Academic Press). Therefore, without wishing to be limiting, hydrolysis of between about 0.17 and 3.3% of the xylan component of hardwood pulp corresponds to a quantity of xylose release of between about 0.5 and about 5 kg/t of pulp. However, other amounts of hydrolysis may be obtained. For example, from about 0.17 to about 3.3% of the xylan component of hardwood pulp may be hydrolyzed, or any percentage range therebetween, between about 0.25 and 2.5% of the xylan component of hardwood pulp may be hydrolyzed, or any percentage range therebetween, or from about 0.50 to about 2.0% of the xylan component may be hydrolyzed, or any percentage range therebetween.

[0080] Hardwood mechanical pulp may be treated with the Family 11 xylanase for about 5 to about 120 minutes, or any time interval therebetween, or for about 20 to about 100 minutes, or any time interval therebetween, or for about 25 minutes to about 80 minutes, or any time interval therebetween, or for about 30 to 90 minutes, or any time interval therebetween, or for about 30 to 60 minutes or any time interval therebetween.

[0081] Hardwood mechanical pulp may be treated with the Family 11 xylanase at a temperature from about 35 C to about 95 C, or any temperature range therebetween, or at a temperature from about 55 C to about 90 C, or any temperature range therebetween, or at a temperature from about 55 C to about 85 C, or any temperature range therebetween, or at a temperature from about 30 C
to about 60 C, or any temperature range therebetween. For example, hardwood mechanical pulp may be treated with Family 11 xylanase at a temperature from 35, 37, 40, 42, 45, 47, 50, 52, 55, 57, 60, 62, 65, 67, 70, 72, 75, 77, 80, 82, 85, 87, 90, 92 and 95 C, or any amount therebetween.

[0082] Hardwood mechanical pulp may be treated with the Family 11 xylanase at a pH of from about pH 3 to about pH 11, or any pH therebetween, for example, at a pH of 3, 4, 5, 6, 7, 8, 9, 10, or 11, and any pH therebetween.

[0083] The consistency of the hardwood mechanical pulp during Family 11 xylanase treatment may be from about 0.5 to about 30%, or any consistency therebetween, between about 1 to about 10%, or any consistency therebetween, between about 2% to about 5%, or any consistency therebetween, or between about 2.5% and about 4% or any consistency therebetween. For example, the consistency of the hardwood mechanical pulp during Family 11 xylanase treatment may be from 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 7.5, 10.0, 12.0, 15.0, 17.0, 20.0, 22.0, 25.0, 27.0 and 30%, or any amount therebetween.

[0084] It is to be understood that other treatment conditions may be employed that fall within the overall parameters just defined and one of skill in the art may readily adjust the reaction conditions as desired.

[0085] Consistency is defined as the mass percentage of wood fiber in a slurry of wood fiber and water. The wood fiber may comprise either chips or pulp in a consistency measurement. As is well known in the art, consistency is measured by taking a known mass of the pulp slurry and drying it in an oven at 105 C until the sample reaches a constant mass, at which time all of the water has been removed from the pulp/chips. The oven dry mass of wood fiber that remains is then determined. The consistency is calculated as the quotient of oven dry mass of wood fiber divided by the mass of the slurry and expressed as a percentage.

[0086] For example, which is not to be considered limiting, the pulp may be treated with the Family 11 xylanase for about 30 to about 90 minutes, or any time interval therebetween, at a temperature from about 55 C to about 75 C, or any temperature therebetween, a pH from about pH 5 to about pH 8, or any pH therebetween, at a pulp consistency of I to 10%, or any consistency therebetween, to allow the enzymes to react with the hardwood mechanical pulp. In another non-limiting example, the pulp may be treated with enzymes using a xylanase for about 30 to about 60 minutes or any time interval therebetween, at a temperature from about 40 C to about 75 C or any temperature therebetween and a pH from about pH 6 to about pH 8, or any pH
therebetween, at a consistency of 2 to 5%, or any consistency therebetween, to allow the enzymes to react with the hardwood mechanical pulp. However, it is to be understood that other treatment = CA 02541229 2012-12-03 conditions may be employed that fall within the overall parameters just defined and one of skill in the art may readily adjust the reaction conditions as desired.

[0087] Family 11 xylanase (EC 3.2.1.8) includes wild type or modified Family 11 xylanase, for example, but not limited to, those disclosed in WO 03/046169 (Sung et al.). By Family 11 xylanase, it is meant a xylanase comprising amino acids common to other Family 11 xylanases, including two glutamic acid (E) residues which may serve as catalytic residues. The glutamic acid residues are found at positions 86 and 177 (see Figure 1 of WO 03/046169;
Sungbased on Tr2 amino acid numbering (Trichoderma reesei xylanase II enzyme). As can be seen in Figure 1 of WO 03/046169, Family 11 xylanases share extensive amino acid sequence similarity.
Examples of Family 11 include, but are not limited to, wild type or modified enzymes obtained from Aspergillus, Bacillus, Cellulomonas, Chainia, Clostridium, Fibrobacter, Neocallimasterix, Nocardiopsis, Ruminococcus, Schizophyllum, Streptomyces, Thermomonospora,Thermomyces, Trichoderma, Actinomadura, Aureobasidium, Humicola and Chaetomium. Additional examples of Family 11 xylanases that may be used in accordance with the present invention include, but are not limited to:
Aspergillus niger Xyn A
Aspergillus awamori var.kawachi Xyn B
Aspergillus kawachii Xyn C
Aspergillus tubigensis Xyn A
Bacillus circulans Xyn A
Bacillus pumilus Xyn A
Bacillus subtilis Xyn A
Cellulomonas fimi Xyn D
Chainia spp. Xyn Clostridium acetobutylicum Xyn B
Clostridium stercorarium Xyn A
Fibrobacter succinognees Xyn II
Neocallimasterix patriciarum Xyn A

=

Nocardiopsis dassonvillei Xyn II
Ruminococcus flavefaciens Xyn A
Schizophyllum cimmune Xyn Streptomyces lividans Xyn B
Streptomyces lividans Xyn C
Streptomyces sp. No. 36a Xyn Streptomyces thermoviolaceus Xyn II
The rmomonospora fusca Xyn A
Thermomyces lanuginosus Xyn Trichoderma harzianum Xyn Trichoderma reesei Xyn I
Trichoderma reesei Xyn II
Trichoderma viride Xyn

[0088] Structural studies of several Family 11 xylanases indicate that Family 11 xylanases from bacterial and fungal origins share the same general molecular structure (US
patent 5,405,769;
Campbell etal.; Arase etal., 1993, FEBS Lett.). In addition, most Family 11 xylanases identified so far exhibit three types of secondary structure, including beta-sheets, turns and a single alpha helix.

[0089] Any Family 11 xylanase active at conditions employed in the invention may be used in the method. For example, but not to be considered limiting, the Family 11 xylanase may be a modified xylanase that has been altered or genetically engineered. The modified xylanase may be derived from a native or wild-type xylanase, or it may be derived from an already altered Family 11 xylanase that has been mutagenized and selected or genetically engineered using standard protocols as would be known to one of skill in the art. Examples of modified xylanases include those known to one of skill in the art, for example, but not limited to, those disclosed in WO
00/29587, WO 01/92487, WO 03/046169 and co-pending U.S. application No.
60/556,061 and include, but are not limited to, TrX-DS1; TrX-162H-DS1; TrX-162H-DS2; TrX-162H-DS4;
TrX-162H-DS8; TrX-75A; TrX-HML-105H; TrX-HML-75A-105H; TrX-HML-75C-105R; TrX-HML-75G-105R; TrX-HML-75G-105R-125A-129E; TrX-HML-75G-10511-125A-129E; TrX-HML-75A-105H-125A-129E; TrX-HML-75A-105R-125A-129E; TrX-157D-161R-162H-165H;
TrX-HML-AHAE; TrX-HML-AHAE-R; TrX-HML-AHAE-RR; TrX-HML-AHAE-RRR; TrX-HML-AHA-RR-DRHH; TrX-HML-AHAE-RR

DRHH; TrX-HML-AHAE-RRR-DRHH; TrX-116G; TrX-118C; TrX- HML-AHCAE-R; TrX-H-11D-ML-AHGAE-RR; TrX-HML-AHGAE-R; TrX-H-11D-ML-AHGCAE-RR; TrX-H-11D-ML-AHCAE-RR; TrX-HML; HTX13; HTX18; ITX1; ITX2; ITX2'; ITX3; ITX3'; ITX4;
ITX4';
ITX5; ITX5'; X1n1-131N; HTX44; HTX44-131N and S. hvidans xlnC-131N xylanase.
The Family 11 xylanase may also be wild-type xylanase, for example Trichoderrnareesei xylanase II.

[0090] Additional other enzymes that may be added to the hardwood pulp include, for example, cellulases, cell wall enzymes, esterases, other hemicellulases and combinations of these enzymes or chemical agents. By the term "other hemicellulases" or "other enzymes", it is meant hemicellulases and enzymes other than xylanases, although it should be appreciated that the xylanase treatment can be repeated either before or after the step of treating (step b.). Other hemicellulases may include arabinase, galactanase and a combination thereof.
Cell wall enzymes include expansin, swollenin, xyloglucan endotransglycosylase (XET) and a combination thereof, and esterases may comprise lipases, ferulic esterases and combinations thereof. In addition, an oxidoreductase enzyme may be added before or following the xylanase treatment of the pulp.
This includes the addition of purified or semi-purified preparations, crude extracts or the addition of a microbe, such as a fungus, that exhibit hydrolytic activity on oligosaccharides present in pulp.

[0091] Mannanase has limited use in the mechanical refining of hardwood as a result of the low mannan content in the substrate. Thus, the enzyme treatment may be performed in the absence of adding a mannanase enzyme, or in the presence of a mannanase enzyme that does not release a substantial amount of mannose from the pulp during the treatment. By "substantial amount of mannose", it is meant greater than 0.2 kg of mannose/t of pulp. The concentration of mannose in the xylanase treated pulp mixture can be determined according to an assay that is used for measuring mannose. This assay is set out in Example 8.

[0092] In addition to the xylanase, other chemical agents may be added to the mechanical pulp during treatment. The chemical agents may also be added prior to and after the xylanase treatment. The chemical agents may be selected from the group consisting of acids, bases, chelants, oxidants, reductants, stabilizers, surfactants, other enzymes and combinations thereof.

[0093] Acids used before, during and after the enzyme treatment may include hydrochloric acid, sulfuric acid, sodium bicarbonate, formic acid, acetic acid, oxalic acid and hydroxyacetic acid, used at an addition rate of 0.01% (w/w) to 10% (w/w) on pulp (oven dried basis). Hydroxyacetic acid is also known to those skilled in the art as glycolic acid. In a preferred embodiment, sulfuric acid may be used during treatment.

[0094] Bases used before, during and after the enzyme treatment may include sodium hydroxide, magnesium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and sodium silicate, used at an addition rate of 0.01% (w/w) to 10% (w/w) on pulp (oven dried basis). In a preferred embodiment, sodium hydroxide and sodium silicate may be used during treatment.

[0095] Oxidants, reductants, chelants and stabilizers may also be used before, during and after the treatment. In a preferred embodiment, the oxidation and reduction chemicals are added before or after xylanase treatment. Non-limiting examples of oxidants include hydrogen peroxide, chlorine dioxide, added oxygen, perform ic acid, peracetic acid, organic peroxides and ozone, used at an addition rate of 0.01% (w/w) to 10% (w/w) on pulp (oven dried basis). If an oxidant is used, the preferred oxidant is hydrogen peroxide. Non-limiting examples of reductants include sodium sulfite, formamidine sulfinic acid, sodium hydrosulfite (also known as sodium dithionite), and sodium borohydride, used at an addition rate of 0.01% (w/w) to 10% (w/w) on pulp (oven dried basis). The preferred reductants are sodium sulfite and sodium hydrosulfite.
Non-limiting examples of chelants include ethylenediaminetetraacetic acid and its sodium and potassium salts (EDTA), diethylenetriaminepentaacetic acid and its sodium and potassium salts (DTPA), nitrilotriacetic acid and its sodium and potassium salts (NTA), hydroxyacetic acid and its sodium and potassium salts, and oxalic acid and its sodium and potassium salts, used at an addition rate of 0.01% (w/w) to 10% (w/w) on pulp (oven dried basis).
Preferred chelants include EDTA and DTPA. Non-limiting examples of stabilizers include sodium silicate, magnesium sulfate, magnesium chloride, magnesium nitrate and magnesium hydroxide, used at an addition rate of 0.01% (w/w) to 10% (w/w) on pulp (oven dried basis).
Preferred stabilizers are sodium silicate, magnesium sulfate, and combinations thereof. Non-limiting examples of surfactants include nonionic surfactants such as nonylphenol ethoxylate, anionic surfactants such as sodium lauryl sulphate, cationic surfactants such as quaternary amines, and amphoteric surfactants such as betaine.

[0096] By the term "organic peroxides", it is meant organic compounds containing a peroxy group and which are suitable for use as oxidizing agents during pulp production. Examples of suitable organic peroxides include performie acid, peracetic acid and perpropionic acid.

[0097] After enzyme treatment, the hardwood mechanical pulp is fed to a mechanical refining device and is further mechanically refined as is familiar to those skilled in the art. The treated pulp may be refined in a secondary refining operation. Enzyme treated pulp may also be used in additional refining stages to further refine the pulp following the secondary refining process. As well, the treated pulp may be refined in a reject refining operation as is familiar to those skilled in the art. Furthermore, the pulp may undergo additional refining stages.

[0098] By further mechanically refining the treated pulp, it is meant subjecting the pulp to mechanical action to result in a Canadian Standard Freeness value that is lower than that of the treated pulp immediately after enzyme treatment. An example illustrating the measurement of the Canadian Standard Freeness is given in Example 4. Further mechanical refining may include a secondary refining process followed by additional refining processes also known as post-secondary refining, such as is familiar to those skilled in the art. In addition, refining in this case includes screening and/or cleaning coarse and post-secondary pulp to produce a reject pulp which is then processed in a reject refining stage.

[0099] By "secondary refining", it is meant that coarse pulp is introduced to a mechanical refining device, as known to those skilled in the art, where the coarse pulp is passed between plates having raised (bars and dams) and depressed (grooves) segments. The plates are installed in a refiner and at least one of the plates is rotated. The coarse pulp moves from the center of the plates to the edges and is refined by the action of the plates.

[00100] By "additional refining stages" or "post-secondary refining", it is meant that refined pulp (post-secondary pulp) is further introduced to a refining device, as known to those skilled in the art, where the post-secondary pulp is passed between plates having raised (bars and dams) and depressed (grooves) segments. The plates are installed in a refiner and at least one of the plates is rotated. The post-secondary pulp moves from the center of the plates to the edges and is refined by the action of the plates.

[00101] By "reject refining", it is meant that pulp not having passed through a screen of defined size or removed from the main pulp stock by centrifugal cleaners is thickened and further introduced to a refining device, as known to those skilled in the art, where the reject pulp is passed between plates having raised (bars and dams) and depressed (grooves) segments. The plates are installed in a refiner and at least one of the plates is rotated.
The reject pulp moves from the center of the plates to the edges and is refined by the action of the plates.

[00102] The final process of converting xylanase treated pulp into paper or finished pulp is carried out on its own or in combination with other pulps that may or may not have been treated with enzymes.

[00103] The present invention also provides a method of producing a hardwood pulp by mechanical refining, the method comprising a step of treating a hardwood mechanical pulp with one or more than one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between about 0.5 and about 5.0 kg of xylose/t of pulp thereby producing an enzyme-treated (hardwood) mechanical pulp.

[00104] Furthermore, the present invention also provides a method of producing a hardwood pulp by mechanical refining, the method comprising a step of hydrolyzing between about 0.17% and 3.3% of a xylan component of a hardwood mechanical pulp with one or more than one Family 11 xylanase thereby producing an enzyme-treated (hardwood) mechanical pulp.

[00105] The present invention also provides a method of producing a hardwood pulp by mechanical refining, said method comprising:
a. hydrolyzing between about 0.17% and 3.3% of a xylan component of a hardwood mechanical pulp with one or more than one Family 11 xylanase to produce an enzyme-treated mechanical pulp; and b. further mechanically refining the enzyme-treated mechanical pulp to produce the hardwood pulp.

[00106] The methods described herein may be performed at mills as part of any regular refining process. For example, the process may include Refiner Mechanical Pulping (RMP), Thermo-mechanical Pulping (TMP), Chemi-thermo-mechanical Pulping (CTMP), Bleached Thermo-mechanical Pulping (BTMP), Bleached Chemi-thermo-mechanical Pulping (BCTMP) or the production of Medium Density Fiberboard (MDF).

[00107] The present invention may be illustrated in the following examples.
However, it is to be understood that these examples are for illustrative purposes only, and should not be used to limit the scope of the present invention in any manner.

Examples:
EXAMPLE 1: Determination of protein concentration of xylanase solutions

[00108] The protein concentrations of the xylanase preparations are determined by the Bio-Rad/Coomassie method in which the protein in solution is treated with Coomassie Brilliant Blue dye to form a colored complex. The absorption of light at 595 nm is measured and the amount of enzyme is determined in comparison to a standard cellulase enzyme protein solution.
EXAMPLE 2: Standard assay for the measurement of xylanase activity

[00109] The endo xylanase assay is specific for endo-1,4-beta-D-xylanase activity. On incubation of azo-xylan (oat) with xylanase, the substrate is depolymerized to produce low-molecular weight dyed fragments which remain in solution on addition of ethanol to the reaction mixture. High molecular weight material is removed by centrifugation and the colour of the supernatant is measured. Xylanase activity in the assay solution is determined by reference to a standard curve. The method is based on that published by Megazyme International Ireland Limited (2003), and the product name is S-AXYO oat Azo-Xylan.

[00110] The substrate is purified (to remove starch and beta-glucan). The polysaccharide is dyed with Remazolbrilliant Blue R to an extent of about one dye molecule per 30 sugar residues. The powdered substrate is dissolved in water and sodium acetate buffer and the pH
adjusted to 4.5.

[00111] For the assays, unless otherwise indicated, xylanase is diluted in 0.5 M acetate buffer at pH 4.5. Two milliliters of the solution are heated at 40 C for 5 minutes and 0.25 mL of pre-heated azo-xylan is added to the xylanase preparation. The xylanase is incubated for 10 minutes at 40 C. The reaction is terminated and high molecular weight substrate is precipitated by adding 1.0 mL of ethanol (95% v/v) with vigorous stirring for 10 seconds on a vortex mixer. The reaction tubes are allowed to equilibrate to room temperature for 10 minutes and are then centrifuged at 2000 rpm for 6-10 minutes. The supernatant solution is transferred to a spectrophotometer cuvette and the absorbance of blank and reaction solutions measured at 590 nm. Activity is determined by measuring the level of dilution of the enzyme sample to achieve an absorbance of 0.5 Absorbance Units at 590 nm. Blanks are prepared by adding ethanol to the substrate before addition of the enzyme and the absorbance of the blank is subtracted from that of the sample. The xylanase activity of the sample is then calculated by Equation (1):

A = 1.07 D (1) Where A = Enzyme activity, XU/mL
D = Dilution of enzyme sample to reach an absorbance of 0.5

[00112] For enzymes which exhibit little activity (less than 100 XU/mL at a protein concentration of at least 10 mg/mL) at pH 4.5 and 40 C, and optimum activity at some other pH and/or temperature, the assay is carried out at the optimum pH and/or temperature.
EXAMPLE 3: Laboratory determination of the quantity of xylose released by xylanase treatment

[00113] The quantity of xylose released by the treatment of pulp with a xylanase enzyme in laboratory studies is determined as follows. First, a pulp suspension is treated with enzyme in a polyethylene bag for 1 hour at a solids consistency of 3.5%, a temperature of 63 C and a pH of ¨6.5 to 7Ø The pH of the pulp suspension is adjusted adding either 0.1 N
caustic if the suspension is too acidic or 0.1 N sulfuric acid if the solution is too alkaline. Prior to adding the xylanase enzyme to the pulp, the pulp sample is pre-heated to the desired temperature in a thermostatic water bath so as to emulate operation in a mill, where enzyme is added to hot pulp.
A control pulp is treated in exactly the same manner as the xylanase treated pulp, except that water is used in place of a xylanase preparation, which is equivalent to a dosage of 0 XU/g pulp.
After treatment, each pulp suspension is filtered using a funnel having a fine filter paper that retains all of the solid particles, and the filtrate is collected in a vial.
The amount of xylan and xylose released after the treatment of the pulp is determined by converting all of the xylan oligomers in solution into xylose monomers, without destroying xylose monomers. This is achieved by adding 1 mL of 4% w/v sulfuric acid to a 1 mL aliquot of filtrate and then placing the acidified aliquot in an autoclave at 121 C for 1 hour to hydrolyze all xylan oligomers to xylose monomers. The amount of xylose in each hydrolyzed aliquot is determined by using a xylose standard on a Dionex High Performance Liquid Chromatograph using a Carbopac PA1 column and an electrochemical detector. The amount of xylose released is calculated as the difference between the measured quantities of xylose in a hydrolyzed aliquot for an enzyme treated pulp and the untreated control pulp, and is expressed as mg xylose per gram of initial pulp (oven dried basis).

EXAMPLE 4: Measurement of Canadian Standard Freeness

[00114] The Canadian Standard Freeness (CSF) or "freeness" is a measure of the drainability of a pulp, which is the ease with which water is removed from the pulp mass. CSF
was measured using the Standard Test # ISO 5267-2 of the International Standards Organization and its unit is milliliters (mL). The CSF is the parameter that specifies the extent of mechanical pulping.
Mechanical pulping is carried out by refining wood chips and/or pulp to a specified level of CSF.
EXAMPLE 5: Treatment of aspen pulp with xylanase [001 15] Several samples of CTMP aspen pulp were treated separately with xylanase from the fungi or bacteria shown in Table 2. The protein concentrations of the enzyme stock solution were determined using the method of Example 1 and the xylanase activities were determined using the method of Example 2. The protein in the xylanase preparations listed in Table 2 was comprised of at least 70% xylanase protein.
Table 2. Enzymes tested and xylanase activity of each enzyme Source Microbe Family Enzyme MW Name Protein Xylanase (Kd) (mg/mL) Activity (XU/mL) Korsnas, Bacillus stearo- 10 43 Xylanase 16.8 Not Sweden thermophilus T6 determined IAF, Laval, Streptomyces 10 XynA 30 Strain 911- 5.8 800 Quebec lividans A8 1ogen Trichoderma 11 Xyn2 21 Biobrite0 41.6 3280 reesei EB
logen Trichoderma 11 Xyn2 21 Biobritee 74.1 96240 reesei HTX
AB, Ecopulp Chaetomium 11 XynA 25 TX200A 7.65 Not determined thermophylum [00116] The pulp was treated with 0 and 3.7 ug of protein per gram of CTMP
aspen pulp. For all treatments with and without xylanase, the temperature was maintained at 63 C, pH maintained between pH 6.5 and 7.0, pulp consistency maintained at 3.5% and the reaction time maintained up to one hour. The quantity of xylose released during the reaction period was measured using the method of Example 3.
[00117] The quantities of xylose being released for Family 10 and 11 xylanases tested at 3.7 lig protein/g pulp are tabulated in Table 3. All Family 11 xylanases released significant quantities of xylose indicating that all have the potential to reduce refining energy as they have acted upon the fiber surface. The Family 10 xylanases tested released reduced amounts of xylose.
Table 3. Xylose released measured by treating CTMP aspen pulp with 3.7 jig xylanase per g pulp for 1 hr Microbe Family Name Xylose release, mg/g pulp Bacillus stearothermophilus T6 10 Xylanase T6 0.07 Streptomyces lividans 10 Strain 911-A8 0.15 Chaetomium thermophylum 11 TX200A, Ecopulp 2.5 Tricho derm a reese i II Biobrite EB 2.2 Trichoderma reesei 11 Biobrite0 HTX 2.7 [00118] In Figure 1, the xylose being released per kilogram of enzyme protein applied is plotted as a function of reaction time between the xylanase and the pulp and indicates that Family 11 xylanases provide increasing amounts of xylose release over time.
EXAMPLE 6: Xylose release as a function of xylanase dosage applied to an RMP
aspen reject pulp [00119] Varying amounts of BIOBRITE EB xylanase (available from 1ogen Bioproducts Corp.) were applied to aspen RMP reject pulp having an initial CSF of about 300 mL at dosages of 0, 0.16, 0.33, 0.98, 3.28 and 9.85 XU/g pulp, at 5% consistency and a temperature of 63 C for 1 hr.
A filtrate from each of the pulp samples was collected, prepared and analyzed as per the method of Example 3. The xylose released as a result of the xylanase treatment is plotted against the xylanase dosage applied and shown in Figure 2. Increasing the xylanase dosage of the treatment increases the xylose released.

EXAMPLE 7: Refining of aspen pulp following a xylanase treatment [00120] BIOBRITE EB xylanase (available from Iogen Bioproducts Corp.) was applied to aspen RMP reject pulp having an initial CSF of about 300 m L at dosages of 0.33, 1.64 and 9.85 XU/g pulp (or 4, 20 and 125 vig protein/g pulp respectively), at 3.5% consistency and a temperature of 63 C. The treated suspension was allowed to react for 1 hour. A control pulp was treated in exactly the same manner as the xylanase-treated pulp, except that water was used in place of a xylanase preparation. At the end of the treatment, the pulp was thickened to about 15%
consistency, fluffed and refined using a Sunds Defibrator CD300 pilot plant equipped with a single rotating 12 inch disk in a single pass by gradually decreasing the plate gap. The Canadian Standard Freeness (CSF) of the pulp was measured and plotted as a function of the specific energy for refining.
[00121] The refining energy requirements to produce pulp of a desired Canadian Standard Freeness (CSF), using varying xylanase dosages, are shown in Figure 4.
Treating aspen RMP
reject pulp with xylanase prior to refining results in significant energy reductions in order to achieve a desired CSF regardless of the xylanase dosage used. For example, a 0.33 XU/g pulp xylanase treatment of aspen RMP reject pulp, with a 60 minute reaction time would release 2.4 kg of xylose per tonne of pulp prior to refining and result in an energy reduction of at least 103 kWh/t relative to an untreated control for a final pulp CSF of 150 mL. At a similar target CSF, increasing the xylanase dosage to 9.84 XU/g (which would release 6.2 kg of xylose per tonne of pulp) will reduce the refining energy by at least 160 kWh/t. In Figure 5, it is shown that targeting a higher freeness generates greater energy reductions as a result of enzyme treatment over an untreated control. Increasing the enzyme dosage (which will increase the xylose being released), for a target CSF, further increases the energy reduction noted over an untreated control. In Figure 6, the energy reduction obtained as a result of a 0.33 XU/g pulp treatment (or 2.4 kg of xylose per tonne pulp) is plotted as a function of the target CSF and expressed as a percentage savings relative to refining a control pulp.
[00122] These results demonstrate that energy reductions for the refining of hardwood mechanical pulp following enzyme treatment of hardwood mechanical pulp are affected by target CSF as well as enzyme dosage which will affect the amount of xylose released.

[00123] In Figure 7 the energy savings in kWh relative to the xylanase dosage (Million XU) for various freeness levels is plotted as a function of the xylose released during the treatment, for various freeness levels. The quantity "Energy savings per enzyme dosage" is a measure of the efficiency of enzyme treatment. The greatest energy savings per enzyme dosage are obtained when the amount of xylose released during xylanase treatment is between about 0.5 kg xylose/t of pulp and 5 kg xylose/t of pulp. The optimal energy savings relative to the xylanase dosage were obtained when the quantity of xylose released was ¨2.5 kg/t. The[ww quantity of xylose released from the pulp therefore provides a control parameter for the xylanase treatment. Those skilled in the art can choose an enzyme dosage, treatment time, temperature, pH and method of enzyme addition to obtain the necessary level of xylose released from the pulp. By achieving this level of xylose release, the desired savings in refining energy is obtained.
[00124] Figure 7 also demonstrates that a higher freeness generates increased energy reductions relative to the amount of enzyme being used.
EXAMPLE 8: Determination of the quantity of xylose and/or mannose released by xylanase treatment in a mill setting [00125] The quantity of xylose released by the treatment of pulp with a xylanase preparation in a mill setting is determined by the following example. A sample of the treated pulp is collected from a sample point located downstream from the application point of the xylanase preparation (see Figure 3), typically at the exit of a storage vessel. The consistency of the pulp sample is measured and noted. The temperature and pH of the pulp stock at the sampling point may be noted as well. A liquor sample from the treated pulp is collected by squeezing out an aliquot, filtering it using a funnel having a fine filter paper that retains all of the solid particles, and collecting the filtrate into a vial. A control pulp sample is collected from a sampling point that is located immediately upstream of the point of enzyme addition, and is squeezed and filtered in the same manner as the treated sample to obtain an aliquot of filtrate.
Alternatively the control pulp sample may be collected from the sampling point from which the enzyme treated sample is collected, but with the enzyme application turned off and sufficient time being allowed for the enzyme treated pulp to be flushed from the storage vessel. Again, the consistency of the control pulp is measured and noted =
[00126] The amount of xylan and xylose released after the treatment of the pulp is determined by converting all of the xylan oligomers in solution into xylose monomers, without destroying xylose monomers. This is achieved by adding 1 mL of 4% w/v sulfuric acid to a 1 mL aliquot of filtrate and then heating the acidified aliquot in an autoclave at 121 C for 1 hour to hydrolyze all xylan oligomers to xylose monomers. The amount of xylose in each hydrolyzed aliquot is determined by using a xylose standard on a Dionex High Performance Liquid Chromatograph using a Carbopac PA1 column and an electrochemical detector. The amount of xylose released is calculated as the difference between the measured quantities of xylose in a hydrolyzed aliquot for an enzyme treated pulp and the untreated control pulp, and is expressed as kg xylose per tonne of initial pulp (oven dried basis).
[00127] In the event that there was substantial mannanase activity, this would be identified as an increase in the quantity of mannose released of at least 0.2 kg/t by the treatment of pulp with an enzyme. The method for analysis of mannose release is identical to that described for xylose with the exception that the amount of mannose in each hydrolyzed aliquot is determined by using a mannose standard on a Dionex High Performance Liquid Chromatograph using a Carbopac PA1 column and an electrochemical detector. The amount of released mannose is calculated as the difference between the measured quantities of mannose in a hydrolyzed aliquot for an enzyme treated pulp and an untreated control pulp, and is expressed as kg mannose per tonne of initial pulp.

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REFERENCES
Arase, A., Yomo, T., Urabe, I., Hata, Y., Katsube, Y. and Okada, H. (1993) FEBS Lett. 316:123-127.
Megazyme International Ireland Limited, "Assay of endo-1,4-13-Xylanase using azo-xylan (birchwood)", (2003), http://www.megazyme.com.
Smook, G. A. (1992) Handbook for Pulp & Paper Technologists, Angus Wilde Publications, Vancouver, Canada.
United States Department of Agriculture, (2004), plants.usda.gov.

Claims (12)

WHAT IS CLAIMED IS:

1. A method of producing a hardwood pulp by mechanical refining comprising:
a. mechanically refining hardwood chips to produce a hardwood mechanical pulp;
b. treating the hardwood mechanical pulp with at least one Family 11 xylanase at an amount effective to release a quantity of xylose from the pulp between 0.5 and 3.0 kg of xylose/t of pulp to produce an enzyme- treated mechanical pulp; and c. further mechanically refining the enzyme-treated mechanical pulp to produce the hardwood pulp with a Canadian Standard Freeness value of greater than 75 mL, wherein the step of further mechanically refining (step c.) uses at least 20 kWh/t less energy than a non-xylanase treated control refined to a Canadian Standard Freeness value that is the same as the Canadian Standard Freeness value of the treated pulp after said step of further mechanically refining.

2. The method of claim 1, wherein the step of treating (step b.) is performed for 5 min to 120 min.

3. The method of claim 1, wherein the step of treating (step b.) is performed at a temperature from 35°C to 95°C.

4. The method of claim 1, wherein the step of treating (step b.) is performed between pH
3 and pH 11.

5. The method of claim 1, wherein, in the step of treating (step b.), the consistency of the hardwood mechanical pulp is between 0.5% and 30%.

6. The method of claim 1, wherein, in the step of treating (step b.), the Family 11 xylanase is present at an amount from about 0.05 to 10 xylanase units per gram (XU/g) of pulp.

7. The method of claim 1, wherein, in the step of treating (step b.), the Family 11 xylanase is present at an amount from 0.1 to 100 grams of xylanase protein per tonne of pulp.

8. The method of claim 7, wherein, in the step of treating (step b.), the Family 11 xylanase is present at an amount from 0.2 to 2 xylanase units per gram (XU/g) of pulp.

9. The method of claim 1, wherein, in the step of mechanically refining (step a.), the hardwood mechanical pulp is selected from the group consisting of coarse pulp, post-secondary refined pulp, reject pulp and a combination thereof.

10. The method of claim 1, wherein, in the step of mechanically refining (step a.), the hardwood chips are hardwood tree species selected from the group consisting of aspen, poplar, birch, maple, oak, chestnut, alder, eucalyptus, acacia and a combination thereof.

11. The method of claim 1, wherein the step of mechanically refining (step a.) comprises primary refining of the hardwood chips, wherein the primary refining uses an energy input of at least about 200 kWh/t.

12. The method of claim 1, wherein the Family 11 xylanase is produced by a microorganism selected from the group consisting of the genera Aspergillus, Bacillus, Cellulomonas, Chainia, Clostridium, Fibrobacter, Neocallimasterix, Nocardiopsis, Ruminococcus, Schizophyllum, Streptomyces, Thermomonospora, Thermomyces, Trichoderma, Actinomadura, Aureobasidium, Humicola and Chaetomium.