SE526289C2 - Bleaching step using xylanase with hydrogen peroxide, peracids or a combination thereof - Google Patents

Abstract

An optical fiber harness has a unitary plastic body that is formed into a substantially circular member and a straight member. The straight member intersects the circular member forming a chord through the circular member. At least a first attachment member extends from the straight member for securing the optical fiber harness onto a circuit board. Tabs extend outward from the circular member for receiving an optical fiber.

Description

One of the essential purposes of the cooking process is to release lignin, which binds cellulose fibers in the raw material. The pulp cooking dissolves 85-95% of the lignin in the raw material. In the pulp boiling step, the pulp is washed with water to remove dissolved lignin.

While pulp cooking removes most of the lignin in the feedstock, it cannot remove all the lignin without destroying the cellulosic fibers in the feedstock. The remaining lignin is removed from the pulp by bleaching.

A mass creation process can consist of fl your steps. After pulping, a mass bleaching process may comprise, for example, an alkaline oxygen lignification step (O), an enzyme treatment step (X), one or more chlorine dioxide steps (D) and one or more alkaline extraction steps (E). A pulp bleaching process may also comprise one or more of your washes with water or each step may comprise a water wash as the final part of the step. Thus, a typical mass bleaching sequence, in which the pulp is bleached using three chlorine dioxide steps and two alkaline extraction steps, can be denoted by D-E-D-E-D. Similarly, a pulp bleaching sequence in which the pulp is subjected to an alkaline oxygen delignification step, an enzyme treatment step, three chlorine dioxide bleaching steps and two alkaline extraction steps, each step being followed by a water wash, can be represented by O-X-D-E-D-E-D.

It is common for pulp mills to perform an alkaline oxygen lignification step before the chemical bleaching of the pulp is performed. This process consists in bringing the pulp to react with oxygen and alkali at a high temperature (about 100 ° C) for a period of about 1 hour. Alkali oxygen delignification reduces the amount of lignin in the pulp by 35-50%, but this process is demanding on the pulp and is accompanied, among other things, by the fact that some of the cellulose brema in the pulp is destroyed if the degree of delignification is over 50%. After alkali oxygen degeneration, the pulp is washed as described above to remove soluble lignin. 10 15 20 25 30 526 289 The next bleaching step after alkali oxygen degregation is usually chemical bleaching with oxidizing chemicals, the most fi-occurring being chlorine dioxide (C102). However, there are described processes that can bleach, facilitate bleaching or improve bleaching of pulp before bleaching with C102. These include (1) the use of hydrogen peroxide and peracids and (2) the use of xylanase enzyme treatment.

Hydrogen peroxide is a common bleaching chemical. When this is added to the brown suspension before the bleaching plant, it provides the possibility of partial delignification and / or bleaching of the pulp (Bleackley, 1991). However, above a certain low level of hydrogen peroxide, this poses a significant danger of damaging fi brema.

The use of xylanase and manganese peroxidase, lignin peroxidase or laccase enzymes with hydrogen peroxide in combination or added sequentially, increases the efficiency of hydrogen peroxide (Berrnek et al., 2000; Niku-Paavola et al., 1994). Unfortunately, it is not practically possible to produce and use manganese peroxidase, lignin peroxidase or lacquer on an industrial scale. However, there is no description in these reports regarding mixtures comprising only hydrogen peroxide and xylanase.

For the past 40 years, research has focused on the use of peracids as a means of bleaching pulp. Peracids are formed by reacting hydrogen peroxide with the corresponding acid, ie acetic acid with hydrogen peroxide gives peracetic acid.

The advantage of transferring hydrogen peroxide to a peracid is that the peracid has a higher oxidation potential and that it is therefore a more powerful bleaching agent than the hydrogen peroxide. Peracid in the form of peracetic acid (PAA) was used as a bleaching chemical in several pulp mills in Scandinavia. Peroxynetic acid (Milox process) has been used in pilot plants and peroximonosulfuric acid, peroxosalpic acid and peroxophosphoric acid have been extensively studied (Poppius-Levlin et al., 2000). The essential processes for the production of peracid comprise (1) combining hydrogen peroxide with organic acids, such as acetic acid and formic acid, to form a percarboxylic acid. The general formula for a percarboxylic acid is R (CO) OOH, where R is an alkyl group (for peracetic acid, R = CH 3). (2) Combination of hydrogen peroxide with inorganic acids, such as sulfuric acid. The form of peroximonosulfuric acid is HO-SO 2 -OOH, which is known as Caro's acid. (3) Grain binder of hydrogen peroxide and an activator for the formation of peracids. The activator that has received the most attention is tetraacetylethylenediarnin (TAED).

Mass bleaching can be performed using relatively pure peracids or mixtures of two or more peracids. When peracids are used for bleaching pulp, they can be prepared outside the bleaching step and added to the pulp or the reactant chemicals can be added to the pulp and the peracids are generated in situ. An example of external production of peracids is the reaction between acetic acid and hydrogen peroxide to form peracetic acid which is then purified by distillation. A second example of external generation of peracids is the reaction between potassium persulfate and hydrogen phthalate or sulfuric acid to form peroximonosulfate (available as Oxone® du- du du Pont), which was then added to the pulp (Springer and McSweeney, 1993).

In situ production of peracetic acid has been considered for some time. This includes the addition to the pulp of hydrogen peroxide and acetic acid or hydrogen peroxide and acetic anhydride.

Peracetic acid is generated by the reaction between peroxide and acetic acid in the presence of the mass. (Christiansen et al., 1996). As with all bleaching chemicals, the choice of peracid and the process used to form it depend on the cost of the chemicals and the effectiveness of the bleaching. Although interest in and use of peracids by pulp mills is increasing, the relatively high cost of peracids, which stems from the need to combine two or fl your different chemicals, has limited the use of peracids until now. Xylanases are used in the pulp and paper industry to improve the bleaching of pulp and reduce the amount of chlorinating chemicals used in the bleaching steps (Erickson, 1990; Paice et al., 1988; Pommier et al., 1989). There are fl your mechanisms adopted for the bleaching effect of xylanase. One mechanism is that lignin is linked to crystalline cellulose over xylan and that xylanase enzymes facilitate bleaching of pulp by hydrolyzing xylan, thereby releasing colored lignin from the pulp. Another proposed mechanism is that xylanase removes xylan and thereby improves the alkaline extractability of the pulp. Regardless of the mechanism, xylanase treatment for subsequent bleaching chemicals, such as chlorine, chlorine dioxide, hydrogen peroxide or combinations of such chemicals, enables more efficient bleaching of pulp than in the absence of xylanase. Pre-treatment of the pulp with xylanase before the chemical bleaching increases the brightness and quality of the finished paper product and reduces the amount of chlorine-based chemicals that must be used to bleach the pulp. This in turn reduces the chlorine emissions obtained through such process- SBI.

Xylanases have been isolated from a number of different organisms that include bacteria and fungi. In general, xylanases from fungi show optimal activity at acidic pH values, in the range of about 3.5 -5.5, and a temperature above 50 ° C. In contrast, bacterial xylanases show optimal activity at pH 5 to pH 7 and a temperature optimum between 50 ° C and 70 ° C. However, there are other xylanase enzymes that exhibit optimal activity under other conditions. For example, U.S. 5,405,789, Campbell et al., Discloses the formation of heat stable mutants of low molecular weight xylanase from Bacillus circulans. U.S. Pat. No. 5,759,840 to Sung et al. U.S. 5,916,795, Fukunaga et al., Discloses a heat stable xylanase from Bacillus. A publication entitled "Xylanase Treatment of Oxygen-Bleached Hardwood Kraft Pulp at High Temperature and Alkaline pH Levels Gives Substantial Savings in Bleaching Chemicals", Shah et al., (J. of Pulp and Paper Science, Vol. 26, No. 1 January 2000, which is hereby incorporated by reference) describes the treatment of oxygen-ligated hardwood pulp with xylanase from Thermotoga maritima at pH 10 and 90 ° C and subsequent bleaching of the pulp. These documents describe the use of xylanases to enzymatically treat pulp before chemical bleaching.

After treatment with peroxyacids or xylanase, the next step in a typical pulp bleaching process is usually chlorine dioxide bleaching with chlorine dioxide, chlorine or in some cases a combination of chlorine dioxide and other oxidizing bleaches. For example, the first chlorine dioxide step in a chemical bleaching process is often called the Do or D 100 step. Subsequent chlorine dioxide bleaching steps are referred to as DI, D; etc. In plants where pulp is bleached without any alkaline oxygen delignification step, the Do step is the first chemical bleaching step. The do step is usually performed at pH 1.5-3.0. In a small but decreasing number of uses, up to 30-50% chlorine gas can be added to C102 in an attempt to achieve a higher efficiency for lignin removal. Such a step is referred to as a CD step. After the Do or CD step, the pulp is washed with water and alkali treated (alkaline extracted). The alkalization is carried out by adjusting the pH of the pulp to 9.0-122 with sodium hydroxide or sodium carbonate at a temperature between 60 ° C and 120 ° C for a period of 30-90 minutes. After the alkali treatment, the mass is washed with water. The chlorine oxide bleaching step, washing and alkali treatment are repeated until the mass is sufficiently bleached. In some cases, 2 or 3 rounds of bleaching are required, alternating between chlorine dioxide steps and alkaline extraction steps, before the pulp is sufficiently bleached.

In U.S. Pat. 5,645,686 discloses a process for bleaching a chemical pulp by a sequence of treatment steps, comprising at least one step with hydrogen peroxide and at least one step with peroxyacid. The patent also describes a xylanase treatment step in addition to mass bleaching. The patent does not propose treatment of pulp with a simultaneous xylanase treatment step and peroxyacid step. While xylanase treatments in pulp bleaching processes generally result in improved pulp bleaching, compared to similar pulp bleaching processes that do not involve xylanase treatment, there is still a need in the art to increase the effectiveness of xylanase treatment. The pulp industry is under pressure to reduce the use of chlorine-containing bleaching chemicals, such as chlorine and chlorine dioxide, and consequently any process or process which can be integrated with a pulp bleaching process to reduce the use of chlorine-containing bleaching chemicals or the toxic effluents formed by using such chemicals , constitute an important and valuable asset for the pulp industry. The industry would also save money by using smaller amounts of chemicals, such as chlorine dioxide in bleaching steps, and sodium hydroxide and hydrogen peroxide in alkaline extraction steps. Improving the effectiveness of xylanase treatment would address these issues by further reducing the use of chemicals.

There is a need in this technology for new methods and more efficient methods for bleaching pulp. Furthermore, there is a need in the art for methods or processes that can be integrated with existing pulp bleaching processes to increase the efficiency of the bleaching process and reduce the use of chlorine-containing bleaching compounds or the toxic outputs formed by the use of such chemicals. There is also a need to save money by reducing the use of chemicals.

It is an object of the invention to overcome the disadvantages of the prior art.

This object is achieved by a combination of the features of the main claims. The subclaims further describe advantageous embodiments of the invention. 10 15 20 25 30 526 289 8 SUMMARY OF THE INVENTION The invention relates to pulp bleaching processes. More particularly, the invention relates to processes for bleaching pulp using xylanase, together with hydrogen peroxide, peracids or a combination thereof.

The present invention relates to a process for bleaching chemical pulp comprising a bleaching step comprising at least one xylanase enzyme in combination with an oxidizing chemical, the oxidizing chemical comprising hydrogen peroxide, one or more peracids or a mixture of hydrogen peroxide and a or fl your peracids. The bleaching step according to the invention can take place at a pH value between about 5.0 and about 9.0.

The present invention also relates to a process according to the above description, wherein the peracid is selected from the group consisting of peracetic acid, permyric acid, peroximonosulfuric acid, peroximonophosphoric acid, peroxysalpetic acid and a combination thereof. Preferably the peracid is peracetic acid, permyric acid or peroximonosulfuric acid.

The present invention also relates to the process described above, in which the bleaching step is preceded by one or more alkaline oxygen degelling steps. Furthermore, the bleaching step can be preceded by an ozone-peracid treatment.

The present invention also relates to the method according to the above description, where the bleaching step is followed by a bleaching sequence. The bleaching sequence may comprise a chlorine dioxide bleaching sequence and / or an oxygen-peracid bleaching sequence.

The present invention also relates to a process for reducing the kappa number of a chemical pulp, which comprises: iii) 526 289 9 exposing the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with at least one oxidizing chemical, the oxidizing chemical comprising hydrogen peroxide, one or fl your peracids or a combination of hydrogen peroxide and one or fl your peracids, for the preparation of a treated pulp; washes the treated pulp; and bleaches the treated pulp using chlorine dioxide, ozone, oxygen, peracid, alkaline extraction or a combination thereof.

The present invention relates to a process for reducing the amount of chlorine dioxide required during a sequence for bleaching a chemical pulp, which comprises the steps of: iv) V) vi) subjecting the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with at least one oxidizing chemical, the oxidizing chemical comprising hydrogen peroxide, one or fl your peracids or a combination of hydrogen peroxide and one or fl your peracids, for the preparation of a treated pulp; washes the treated pulp; and bleaches the treated pulp using chlorine dioxide.

The present invention further relates to a process for bleaching a chemical pulp, which comprises the steps of: subjecting the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with peracetic acid, the bleaching step being carried out at a pH value between about , 0 and about 9.0 and comprises 0.5 to about 5 kg of peracetic acid / t pulp, for about 20 to about 60 minutes at a temperature from about 40 ° C to about 70 ° C and with a pulp concentration between about 4 and about 12%, to form a treated mass; Ii) washing the treated pulp; and iii) bleaching the treated pulp using a chlorine dioxide bleaching sequence.

The process of the invention is an improvement over the separate treatments with xylanase and peroxyacids. The process according to the invention uses only one bleaching tower instead of two. It has surprisingly been found that the presence of hydrogen peroxide and peracids does not destroy the activity of the xylanase. The benefits obtained in a pulp mill from the use of peracids in combination with xylanase are greater than the benefits obtained with peracids alone. This means that the factory can carry out a less expensive bleaching process or that the use of chlorine-containing bleaching chemicals can be further reduced.

The pulp bleaching process can be performed in a factory as part of a larger pulp bleaching process. Furthermore, the chemical pulp may comprise sulphate pulp (kraft pulp), soda pulp or sulphite pulp.

Likewise, according to the process of the present invention, as described above, the first bleaching step may be preceded by an alkaline oxygen lignification step.

The xylanase may be selected from the group consisting of BioBritem or BioBritem III-IB xylanases, which are commercially available from the lodge Corporation, T-richoderma reesei xylanase II or any other xylanases which are active under the conditions of the mild extraction step.

This summary does not necessarily describe all the required features of the invention, whereby the invention may also lie in a subcombination of the described features. DESCRIPTION OF THE FIGURES Fig. 1 shows the effect of various bleaching treatments at either 60 ° C or 75 ° C on the final brightness of the pulp after a pulp bleaching sequence. Control ClOz treatment (EI); peracetic acid treatment (pH 6.5; 0); peracetic acid treatment (pH 9.8; 6); xylanase (1); and xylanase and peracetic acid (A).

Fig. 2 shows the effect of different bleaching treatments at either 60 ° C or 75 ° C on the final brightness of the pulp after a bleaching sequence. Control C102 treatment (o); peroximonosulfuric acid treatment (pH 5.5; I), peroximonosulfuric acid treatment (pH 6.5; Ü); peroximonosulfuric acid treatment (pH 9; 0); xylanase (A); and xylanase and peroximonosulfuric acid (A).

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention relates to pulp bleaching processes. More particularly, the invention relates to pulp bleaching processes using xylanase in combination with hydrogen peroxide, peracids or a combination thereof.

The following description relates to a preferred embodiment and this is by way of example only and is not intended to limit the invention with respect to the combination of features required for carrying out the invention.

The present invention relates to a process for bleaching chemical pulp comprising a bleaching step comprising at least one xylanase acid in combination with at least one oxidizing chemical, the oxidizing chemical comprising hydrogen peroxide, one or more peracids or a mixture of hydrogen peroxide and one or more fl era persyror. 10 15 20 25 30 526 289 12 The term "chemical pulp" means any type of fresh, recycled, wood or non-wood pulp, softwood, hardwood or mixtures thereof which has been treated by chemical pulping, such as sulphate pulp , soda ash or sulphite pulp, but not limited to these, which are subsequently in a form suitable for bleaching. In a non-limiting example, the chemical mass comprises new. ber.

Chemical pulp also comprises sulphate pulp, soda ash or sulfur pulp which has been subjected to an alkaline oxygen lignification step before the process of the present invention is carried out. The alkaline oxygen ligation step can be followed by a wash with water. Other conditions associated with the production of chemical pulp, including sulphate and salt pulps, are described in Pulp Bleaching: Principles and Practice (published by Dence and Reeve, 1996; incorporated herein by reference).

By the term "bleaching" is meant that the pulp is brought into contact with one or more of its chemicals for a sufficiently long time and at a suitable pH value and temperature for a partial delignification and / or bleaching of the pulp to be effected. Examples of chemicals that can be used for bleaching include, but are not limited to, C102, H2O2, peracids, NO2, or other chemicals as are known to one skilled in the art.

The term "bleaching step" shall mean the common use of the term in industry. This comprises a combination of pipes, pumps and gutters for transferring the pulp from a wash to a bleaching tower, the bleaching tower itself and the pipes, pumps and gutters for transferring the pulp to the next wash for washing solubilized chemicals from the pulp. The bleaching step of the present invention is preferably one of your bleaching steps in a pulp mill. The bleaching step as described herein may be preceded by one or more oxygen delignification steps. In this case, the bleaching step described herein may be located at the end of a typical bleaching sequence, which includes, but is not limited to, chlorine dioxide sequences (CPPA Technical Section; Dence and Reeve, 1996; 10 15 20 25 30 526). Both incorporated herein by reference), ozone, oxygen-peracid (Bouchard et al., 200 L), alkaline extraction or a combination thereof. Alternatively, the bleaching step of the present invention may be performed before a typical bleaching sequence. In this embodiment, the bleaching step described herein is followed by one or more chemical bleaching steps, which include, but are not limited to, chlorine dioxide, ozone, oxygen peracid, alkaline extraction, or a combination thereof.

The xylanase acid present in the bleaching step can be any xylanase that can hydrolyze xylan and enhance the bleaching of pulp under the conditions that can be used in the process of the present invention. The xylanase must be active at the pH and temperature used in the step and be resistant to the oxidizing chemicals present. The xylanase dosage is preferably from about 0.5 to about 2.0 xylanase units per gram of pulp. Methods for measuring xylanase units are described in Example 2.

Both wild-type xylanases and genetically modified xylanases can be used in the process of the present invention. For example, xylanases which may be useful in the process of the present invention, without being limited thereto, comprise xylanases from fungi which exhibit optimal activity at acidic pH values in the range of from about 3.5 to about 5.5 and at temperatures of about 50 ° C. ° C, and bacterial xylanases, which show optimal activity at pH values from about 5 to about 7 and temperatures between about 50 ° C and about 70 ° C. However, it is understood that alternative xylanase enzymes may be used which exhibit different temperature and pH profiles. In this case, the desired temperature and pH ranges will depend on the xylanase enzyme used.

Therefore, according to the present invention, it is conceivable to use xylanase enzymes which may include, but are not limited to, thermostable and alkalostable wild-type xylanases as described in US 5,405,789, which describe low molecular weight mutants from Bacillus circulans, and US Serial No. 60/213 803 10 15 20 25 30 526 289 14 (PCT / CA / O 1/00769; which is hereby incorporated by reference), which describes xylanases with the desired thermoelectricity and alkalinity in relation to wild-type trichodermaxylanase, e.g. , but not limited to, HTX-IS-xylanase (commercially available from Lodge Corporation), or Wild-type trichoderma reesei xylanase II, eg, but not limited to, "BioBrite" (commercially available from Lodge Corporation) , or modified T. reesei xylanase II, for example, but not limited to, EB xylanase (commercially available from Lodge Corporation) Furthermore, other xylanases may be useful in the process of the present invention, including thermostable xylanases, such as Caldocellum saccharolyticum, Thermothermal and Ihermotoga sp. Strain FJ SS-B1 (Lühti et al., 1990; Winterhalter and Leibl, 1995; Simpson et al., 1991; incorporated herein by reference). use xylanases derived from, but not limited to, T richoderma reesei xylanase I, T richoderma viride xylanase, Streptomyces lividans xylanase B, Streptomyces lividans xylanase C, or other xylanases not belonging to the ll-xylanase family, e.g. limited to, Caldocellum saccharolyticum, Thermotoga maritima and Thermotoga sp. strain F J SS- B.1.

Genetically modified variants of xylanase can also be used in combination or alone in the enzyme treatment steps of the present invention provided that they can improve the bleaching of pulp, i.e. improve the removal of lignin - pulp under the conditions of subsequent bleaching steps. Genetically modifying variants may have a superior ability to över act over a wider pH range, temperature range or range for the concentration of oxidizing chemicals than the corresponding wild-type xylanase.

As will be apparent to one skilled in the art, certain native xylanases exhibit both xylanase and cellulase activities. The additional cellulolytic activity is unsuitable for pulp bleaching due to its harmful effect on cellulose, the main material in paper. It is convenient to use in the process of the present invention one or more xylanases which do not show cellulolytic activity or with lower cellulolytic activity. In a non-limiting example, the process of the present invention uses one or more of its xylanases which have reduced or damaged cellulase activity.

The term "oxidizing chemical" refers to a chemical that has the ability to bleach the pulp, i.e., partially delignifies, brightens, or both partially delignifies and brightens the pulp. The oxidizing chemical is present in such an amount and at such a pH and temperature that it can bleach the pulp. Non-limiting examples of oxidizing chemicals include hydrogen peroxide and peracids.

According to the present invention, the bleaching step comprises xylanase in combination with an oxidizing chemical, for example hydrogen peroxide. The hydrogen peroxide may be present at a concentration of about 0.25 to about 10.0 kg / h mass. For example, the hydrogen peroxide may be present in an amount of from about 0.25 to about 5 kg / h mass. During this concentration, hydrogen peroxide is not effective for delignification and / or bleaching of the pulp. Above this concentration, the hydrogen peroxide can damage the mass. When hydrogen peroxide is used in the absence of peracids, it is added to the pulp in a manner well known to one skilled in the art. Agents such as gastric acid sulphate and sodium silicate can be added with the hydrogen peroxide to stabilize it and / or protect the cellulose and thereby the strength of the pulp.

In an alternative embodiment of the present invention, the bleaching step may comprise xylanase in combination with one or more peracids (also referred to as peroxyacids) as oxidizing chemicals. Peracids are formed when hydrogen peroxide is added to an organic acid or an inorganic acid. The bleaching step according to the present invention can use a single peracid or a mixture of peracids. If the peracid is an organic acid, non-limiting examples of peracids that can be used in accordance with the present invention include peracetic acid, permyric acid, peroximonosulfuric acid, peroximonophosphoric acid, peroxysalpetic acid or a combination thereof. One or more of the organic peracids may be, but are not limited to, peracetic acid, permyric acid or a combination thereof. Organic peracids can be present at a molar concentration that is about twice as large as up to 10 times as large as that of the hydrogen peroxide. In particular, the peracid or peracids are present in an amount of about 2 times to about 5 times that of the hydrogen peroxide. When used alone, the peracid or peracids are present in an amount of about 0.5 to about 5 kg / h mass.

If the peracid is an inorganic acid, it is preferably peroximonosulfuric acid, peroxysalpetic acid, peroxyphosphoric acid or a combination thereof. The organic peracid is used at a molar concentration which is about 1-3 times that of the hydrogen peroxide. Combinations of organic and inorganic peracids can also be used in the bleaching step described herein.

The peracid can be produced outside the bleaching plant (eg as described by Spinger and McSWeeney, 1993, which is hereby incorporated by reference) and added directly to the pulp. This can be done by pumping aqueous solutions of the chemicals to the pump, preferably without direct contact with the xylanase. Alternatively, the peracids may be generated in situ by the addition of hydrogen peroxide and one or more acids, or other reactants, to the mass and the generation of the peracids (for example, as described in Christiansen et al., 1996, which is incorporated herein by reference). The mass may already comprise xylanase or the enzyme may be added after in situ production of one or more peracids.

A peroxide activator, for example, but not limited to, TAED (tetraacetylethylenediamine) can be reacted with the hydrogen peroxide either before or during the addition to the pulp (Turner and Mathews, 1998; incorporated herein by reference). .

The product obtained contains peracid with or without hydrogen peroxide.

In another embodiment of the present invention, the bleaching step comprises a mixture of xylanase in combination with hydrogen peroxide and peracids such as oxidizing chemicals. When these are used together, the hydrogen peroxide may be present at a concentration of about 0.25 to about 10.0 kg / h mass and the peracid or peracids may be present at a molar concentration of about 2 to about 10 times that of the hydrogen peroxide. In a non-limiting example, the hydrogen peroxide is present in an amount of about 1 to about 5 kg / h mass and the peracid or peracid is an organic peracid and is present at a molar concentration which is about 1 to about 5 times that of the hydrogen peroxide. .

The combination of xylanase with hydrogen peroxide, peracids or both hydrogen peroxide and peracids leads to increased performance, expressed as kappa and pulp luster, delignification, improvement of downstream bleaching or a combination of these properties.

This is despite the fact that it was generally believed that combining xylanase with an aggressive bleaching chemical would destroy the enzyme.

The bleaching step may comprise xylanase and hydrogen peroxide, peracids or both hydrogen peroxide and peracids and may be carried out at a pH of about 5.0 to about 9.0. For example, the bleaching step according to the invention takes place at a pH value of about 6.5-8.0.

The bleaching step described herein can be performed at a temperature of about 40 ° C to about 70 ° C or from about 50 ° C to about 60 ° C, at a pulp concentration of about 4% to about 12% and for a period of 20-60 minutes. However, longer treatment times can be used if desired. The bleaching step of the present invention may comprise a washing with water as a final step in the step before the next step of bleaching the pulp. The bleaching step according to the present invention can be performed before or after typical bleaching sequences which include, but are not limited to, those using chlorine dioxide, ozone, alkaline extraction, oxygen-peracid treatment or a combination thereof (see Pulp Bleaching: Principles). and Practice, Chapter 4).

After the bleaching step described herein, the amount of lignin associated with the pulp can be estimated by determining the kappa number of the pulp, which can be performed according to Example 1.

The pulp bleaching process of the present invention improves the brightness or reduces the kappa number of the pulp compared to the pulp bleaching processes known in the art. By increasing the brightness (or reducing the kappa number), less chemical treatment of the pulp is required within the remainder of the bleaching sequence, which means a saving in the cost of bleaching and less emissions of chemicals to the environment. For example, as shown in Fig. 1, the amount of C102 required to bleach a pulp sample can be reduced by about 3.9% when peracetic acid is used in a bleaching step and the amount of C102 can be reduced by about 13.6% when xylanase is used in a bleaching step. . The combination of both peracetic acid and xylanase in a bleaching step as described herein, followed by a bleaching sequence, gives a reduction of C102 addition of about 18.5%. A synergistic result, which results from the combination of xylanase and peracetic acid, is observed when determining the brightness of the pulp (eg Fig. 1, Table 2, Example 6) or kappa number (eg Table 1, Example 5). Fig. 2 shows that the amount of C102 required for bleaching a pulp sample can be reduced by about 0.27-0.81% when peroximonosulfuric acid is used in a bleaching step or by about 12.4% when xylanase is used in a bleaching step. A synergistic result is observed when combining peroximonosulfuric acid and xylanase in a bleaching step as described herein, followed by a bleaching sequence, since the amount of C102 required is reduced by about 16.2%. A synergistic result derived from the combination of xylanase and peroximonosulfuric acid is observed when determining the brightness of the pulp (eg Fig. 1) or kappa numbers (eg Tables 1 and 2 and Example 5, respectively).

The pulp bleaching process of the present invention can be easily integrated with the pulp bleaching processes currently practiced in the art. Existing pretreatment towers, eg even those currently used for xylanase treatment, can be adapted for use with hydrogen peroxide, one or more peracids or a combination thereof and xylanase. Similarly, a bleaching blank used at the end of a bleaching sequence can be adapted for use in a bleaching step as described herein.

The above description is not to be construed as limiting the present invention in any way. The present invention is further illustrated in the following examples. It is to be understood, however, that these examples are for illustrative purposes only and should not be used to limit the scope of the present invention in any way.

EXAMPLE 1: Determination of kappa number The kappa number of the pulp is determined according to the protocol described in: TAPPI method for Kappa number of pulp (T 236 cm-85) from TAPPI Test Methods 1996-1997, which is hereby incorporated by reference. Briefly, the kappa number is the volume (in ml) of a 0.1 N potassium permanganate solution consumed by 1 g of non-greasy pulp under the conditions specified in the method. The results are corrected to 50% consumption of added permanganate.

The determination of the kappa number is carried out at a constant temperature of 25 ° C: 0.2 ° C with continuous stirring. However, it is possible to correct for variations in temperature as described below. The mass fi content of the pulp is determined according to TAPPI T 210 "Sampling and Testing Wood Pulp Shipments for Moisture", which is hereby incorporated by reference. Briefly, the pulp sample is fiberized in about 800 ml of distilled water and the whole is stirred. 100 ml of 0.1 N potassium permanganate and 100 ml of 4 N sulfuric acid (giving a total volume of about 1 l) are added to the slurry and the whole is allowed to react for 10 minutes. At the end of the 10 minute period, the reaction is quenched by the addition of 20 ml of 1.0 N potassium iodide and the solution is titrated with 0.2 N sodium thiosulphate.

The kappa number of the pulp can be calculated using the following formula: K = (p x f) / W varip = (b - a) N / 0, 1 and wherein: K is the kappa number; f is the factor for correction to 50% pernanganatefórbnikrajng, which depends on the value of p (f: 10 (o, ooo9s x (p- 50) »W is the weight in grams of moisture-free mass in the sample; p is the amount 0.1 N potassium perananganate solution consumed by the sample in ml; b is the amount of thiosulphate solution consumed in a blank determination in ml; a is the amount of thiosulphate solution consumed by the sample in ml; and N = thiosulphate solution normality and 30 ° C can be performed using the formula: K = pxf (1 + 0,0l3 (25 -t)) / w where t is the actual reaction temperature in ° C.

EXAMPLE 2: Standard Assay for Measurement of Xylanase Activity Xylanase Assay 1: The endo-xylanase assay is specific for endo-1A-β-D-xylanase activity. Upon incubation of azoxylan (oats) with Xylanase, the substrate is depolymerized to form low molecular weight colored fragments which remain in solution upon addition of ethanol to the reaction mixture. High molecular weight materials are removed by centrifugation and the color of the supernatant is measured. The xylanase activity in the assay solution is determined relative to a standard curve.

Substrate: The substrate is purified (to remove starch and ß-glucan). The polysaccharide is colored with Remazolbrilliant Blue R to an extent of about 1 color molecule per 30 sugar residues. The powdered substrate is dissolved in water and sodium acetate buffer and the pH is adjusted to 4.5.

Analysis: Xylanase is diluted with 0.5 M acetate buffer to pH 4.5. 2 ml of the solution is heated to 40 ° C for 5 minutes. 0.25 ml of preheated azoxylan is added to the enzyme solution. The mixture is incubated for 10 minutes. The reaction is terminated and high molecular weight substrates are 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 at room temperature for 10 minutes and then centrifuged at 2,000 rpm for 6-10 minutes. The supernatant solution was transferred to a spectrophotometer cuvette and the absorbance of blank and reaction solutions was measured at 590 nm. Activity is determined by iron transfer with a standard curve. Blank solutions were prepared by adding ethanol to the substrate before adding enzyme.

The following assay can also be used to quantitatively determine xylanase activity. 10 15 20 25 526 289 22 Xylanase Assay 2: The quantitative assay determines the number of reducing sugar ends generated from soluble xylan. The substrate for this analysis is the fraction from birchwood xylan dissolved in water from a 5% suspension of birchwood xylan (Sigma Chemical Co.). After removal of the insoluble fraction, the supernatant is lyophilized and stored in a desiccator. The measurement of specific activity is performed as follows: Realization mixtures containing 100 μl of 30 mg / nil xylan, diluted in advance with assay buffer (50 mM sodium citrate, pH 5.5 or the optimum pH of the xylanase tested), 150 ul of assay buffer and 50 μl of enzyme diluted with assay buffer was incubated at 40 ° C (or the optimum temperature for the xylanase tested).

At various time intervals, 50 μl aliquots were removed and the reaction was stopped by diluting with 1 μl 5 mM NaOH. The amount of reducing sugar is determined using the reactant hydroxybenzoic acid hydrazide GIBAH) (Lever, 1972, Analytical Biochem 47z273-279). One unit of enzyme activity is defined as the amount that produces l ul of reducing sugar in 1 minute at 40 ° C (or at the optimum pH and the optimum temperature of the enzyme).

EXAMPLE 3: Production of chlorine dioxide Chlorine dioxide was produced in the laboratory by the standard procedure of passing a mixture of chlorine gas and nitrogen through a series of columns containing sodium chlorite and collecting the evolved gas in cold water. The chlorine dioxide was stored chilled at a concentration of 10.4 g per liter in water. Further details regarding the production of chlorine dioxide can be found in the Chlorine Dioxide Generation published by Paprican, Pointe Clare, Quebeck (which is hereby incorporated by reference). EXAMPLE 4: Conventional xylanase treatment of pulp This is a process for carrying out conventional xylanase treatment, before bleaching the pulp.

A sample of 15 g of pulp with a predetermined kappa number is adjusted to a concentration of 10% (w / v) with pulp atlrate and the pH value of the pulp is adjusted to between 6.2 and 6.8 with a 1 N solution of sulfuric acid. The pulp sample is heated to 60 ° C before the addition of BioBritem UHB xylanase (commercially available from Iogen Corporation). The enzyme is added to the samples and the pulp samples are incubated at * 60 ° C for 60 minutes at 10% pulp concentration. After the incubation period, the reaction is stopped by washing the mass with 2 l of tap water at 60 ° C, after which the samples are allowed to dry in air overnight. The previous test showed that the overnight incubation did not increase the apparent effects of the enzyme.

The enzyme dose is 500 ml / h pulp, which corresponds to 5.0 units of xylanase activity (measured according to the first xylanase assay described in Example 2) per gram of pulp. For measuring end needles, the control mass samples were sham-treated under conditions lacking xylanase to facilitate comparison between the different bleaching sequences.

EXAMPLE 5: Xylanase Treatment in the Presence of Hydrogen Peroxide and Peracetic Acid Sulphate hardwood pulp from a plant in Quebec (K = 16.7) was treated as follows: Control Pulp: This pulp was treated as broadly described in Example 4, with some addition of xylanase or oxidizing chemicals, however, were not performed.

Xylanase-treated pulp: This pulp was treated with xylanase as described in Example 4. Hydrogen peroxide-treated pulp: This pulp was bleached with 0.045% hydrogen peroxide calculated on the pulp. The pulp was treated as broadly described in Example 4, however, the hydrogen peroxide was added after the pH of the pulp was adjusted and no xylanase was added.

Pulp treated with xylanase and hydrogen peroxide: This pulp was treated as broadly described in Example 4, however, after adjusting the pH of the pulp, 0.045% hydrogen peroxide was added to the pulp, followed by an addition of xylanase.

Treatment with peracetic acid / hydrogen peroxide: A mixture of peracetic acid and hydrogen peroxide was prepared by combining an aqueous solution of 34% hydrogen peroxide, glacial acetic acid and concentrated sulfuric acid in the ratio 3.5: 1.0: 0.3. The reactants were combined at ambient temperature and then left for 60 minutes, after which the whole was cooled. After 1 month of storage, the concentration of hydrogen peroxide was measured by the method of Swern (1970), which involves titration of the sample with ammonia-cerium urn sulphate. The hydrogen peroxide concentration was determined to be 47.6 g / l. The concentration of peracetic acid was then measured by the procedure of Greenspan (1948), which involves titration of the sample with iodide. The peracetic acid concentration was determined to be 158.4 g / l. The mixture of peracetic acid / hydrogen peroxide was added to the pulp in such a way that the concentration of peracetic acid on pulp was 0.15% and the concentration of hydrogen peroxide on pulp was 0.045%. The pH of the pulp was adjusted to pH 6.2-6.8 with sodium hydroxide. The pulp was otherwise treated as schematically described in Example 4, except that no xylanase was added to the pulp.

Xylanase, peracetic acid and hydrogen peroxide: In this pulp treatment, peracetic acid and hydrogen peroxide were added to the pulp as described above (treatment with peracetic acid / hydrogen peroxide) and the pH of the pulp was adjusted to pH 6.2-6.8 with sodium hydroxide. Xylanase was added after the pH adjusting step. The pulp was otherwise treated as schematically described in Example 4. After all treatments, the pulp was washed with water and the kappa number was measured according to Example 1. The results are shown in Table 1.

Table 1: The effect of different bleaching step treatments on the pulp kappa number.

No further bleaching of the pulp was performed.

Treatment K Untreated 16.6, 16.7 Xylanase (500 ml / h) _ 15.2, 15.1 Hydrogen peroxide (0.045%) 16.6, 16.6 Xylanase + H 2 O; 15.1, 15.0 Peracetic acid (0.15%) + H 2 O; (0.045%) 16.1, 16.2 Xylanase + peracetic acid + H 2 O; 14.8, 14.9 The xylanase additive reduced the kappa number (K) of the pulp by about 1.5 units. Under the present conditions, hydrogen peroxide was ineffective in delignifying the pulp.

However, the combination of Xylanase and hydrogen peroxide K decreased by 1.6 units.

This is slightly more than the effect of Xylanase alone and shows that xylanase was still effective in the presence of the hydrogen peroxide.

Peracetic acid with hydrogen peroxide reduced K by about 0.5 units. However, the combination of Xylanase with peracetic acid and hydrogen peroxide K decreased by 1.8 units, which is more than the effect of peracetic acid with hydrogen peroxide and more than the effect of Xylanase alone. These results indicate a synergistic effect of combining xylans, peracids and hydrogen peroxide. Furthermore, these results show that Xylanase is effective in the presence of peracetic acid and hydrogen peroxide. EXAMPLE 6: Treatment of pulp partially bleached with C102 with xylanase and peracetic acid Hardwood pulp taken from the D1 stage of a pulp mill in eastern Canada was treated as follows: Control pulp: This pulp sample was treated as described in Example 4, but without addition of xylanase. Likewise, the pH was adjusted to 6.5 with sodium carbonate (to prevent alkali-induced yellowing) instead of sulfuric acid.

Xylanase treatment. This pulp was treated with xylanase as schematically described in Example 4, with an enzyme dosage of 150 ml / h, except that the pH was adjusted to 6.5 using sodium bicarbonate instead of sulfuric acid.

Peracetic acid treatment. The pulp was treated as schematically described in Example 4, but without the addition of xylanases. The pH of the pulp was also adjusted to 6.5 with sodium carbonate instead of sulfuric acid, after which 1 kg of peracetic acid was added per tonne of pulp.

Treatment with xylanase and peracetic acid. The pulp was treated with xylanase as described in Example 4, at an enzyme dose of 150 ml / h, except that the pH of the pulp was adjusted to 6.5 with sodium carbonate instead of sulfuric acid, after which 1 kg of peracetic acid was added per tonne of pulp.

After all treatments, the pulp was washed with water and the brightness of the pulp was measured according to the procedures of Example 8. The results are shown in Table 2. Table 2: The effect of treating pulp partially bleached with C102 with xylanase and peracetic acid. No further bleaching of the pulp was performed.

Treatment Brightness (% ISO) Control 84.5 Xylanase (150 ml / h) 86.0 Peracetic acid (1 kg / h) 86.4 Xylanase + peracetic acid 86.6 The xylanase treatment increased the brightness by 1.5 units above the control, while per acetic acid increased the brightness 1.9 units above control, meaning that peracetic acid appears to be more effective than xylanase. The treatment with xylanase + peracetic acid gave the largest increase, 2.1 units. The combination of xylanase and peracetic acid indicates a synergistic effect in increasing the brightness of partially bleached pulp compared to xylanase or peracetic acid alone.

EXAMPLE 7: Chlorine dioxide bleaching of hardwood pulp samples Mass samples were subjected to chlorine dioxide bleaching steps similar to those described in the Glossary of Bleaching Terms CPPA technical section (which is hereby incorporated by reference), using optimal conditions of 1.0-2.3% C102 calculated on a mass basis. san, 40-60 ° C, 3-10% mass concentration, 30-60 minutes incubation time, pH 2.5- 3.0.

The pulp consisted of sulphate hardwood pulp from a pulp mill in the western United States, with a K = 15.0. 10 15 20 25 526 289 28 Chlorine dioxide bleaching step (Qo) The: first chlorine dioxide bleaching step is the Do step. C102 is added to the pulp and the system is kept in a heat-sealable plastic bag. The pulp mixture is cooled to 4 ° C to minimize evaporation. Pulp factors of 0.194, 0.217, 0.239 and 0.262 were used to calculate the chlorine dioxide additive required in the bleaching step. The chlorine dioxide additive can be determined using the following formula: Chlorine dioxide additive (kg / tonne mass) = 10 x kappa factor x kappa number / 2.63 Based on a kappa factor of 0.194 and a mass kappa number of 15.0, the corresponding chlorine dioxide use is 11.1 kg / tonne mass . After addition of ClO 2, the pulp has a concentration of 4%, a pH value of 2.5-3.0 and the bags are placed in a 50 ° C in a water bath for 60 minutes. After the incubation period, the pulp samples are washed with 2 l of tap water. In these cases, the Do pulp samples are subjected to a conventional alkaline extraction step (Eop).

Alkaline extraction step (Eon) After the first chlorine dioxide bleaching step (Do), the pulp samples are subjected to an alkaline extraction step (Eop). The EOP step comprises incubating the pulp samples at 77 ° C, 10% (w / v) concentration, with a sodium hydroxide addition of 1.4%, a hydrogen peroxide addition of 0.65% (w / w) and an oxygen overpressure of 34 kPa (5 psig) for consumption of 6 kg of oxygen per ton of pulp, for 90 minutes. The pH of the extraction medium is about 11.0 at the end of the incubation period. After the incubation period, each pulp sample is washed with 2 l of tap water. 10 15 20 526 289 29 Chlorine dioxide bleaching step (21) In the extraction step, all pulps are subjected to D1 steps. The D1 step is performed in a similar manner to the Do step. Briefly, the pulp samples are adjusted to a concentration of 10% (w / v) and incubated at a pH of 3.6 to about 4, a temperature of 75 ° C for 180 minutes. The chlorine dioxide additives in the D1 stages are selected to correspond to kappa factors of 0.09, 0.101, 0.111 and 0.122 corresponding to the order of the masses, from the lowest to the highest kappa factor, in the Do stage. After the incubation period, each pulp sample is washed with 2 l of tap water. After the extraction, the brightness of the pulp can be measured according to Example 8.

This constitutes the D 1 brightness of the mass.

EXAMPLE 8: Measuring the Brightness of the Pulp The brightness of the pulp is measured according to the procedure described by PAPTAC-Standard Testing Methods July, 1997 (Standard Electricity Brightness of Pulp, Paper and Paperboard; which is incorporated herein by reference). Briefly, a 3.75 g sample of oxygen-lignified pulp was used to form a brightness pad. A pulp sample is placed in a 500 ml container and water is added to about 200 ml. About 2 ml of sulfuric acid solution is added to each container and the contents are mixed well. A pad is formed by holding the mass in a funnel under vacuum and consequently pressing the pad with a plunger. Each pad is pressed between blotting paper using a hydraulic press. The pulp pad is allowed to dry overnight at room temperature. 10 15 20 25 30 526 289 30 Determination of ISO brightness Brightness is measured using an Elrephometer. The sample is diffusely illuminated using a higher fl acting, integrated sphere. Re-reflected light is measured at right angles to the sample. The reflectance is compared with absolute reflectance based on a perfectly reflective, perfectly light-scattering surface that is considered to have a brightness of 100%.

Magnesium oxide is a standard used to compare pulp lightness. A blue light with a wavelength of 457 nm was used to read brightness.

EXAMPLE 9: Mass bleaching test using xylanase treatment in the presence of peracetic acid Sulfate hardwood pulp from a pulp mill in the western United States (K = 15.0) was treated as follows: Control pulp: This pulp was treated as described in Example 4, except that no xylanase was added. Furthermore, the procedure of Example 4 was modified by carrying out the treatment procedure at 75 ° C and at a pH of 9.8, for 1 hour.

Xylanase treated pulp. This mass was treated with xylanase as described in Example 4, at an enzyme dose of 150 ml / h, at 60 ° C, pH 6.5, for 1 hour.

Peracetic acid treatment, pH 9.8. This pulp was treated as schematically described in Example 4, however, a mixture of hydrogen peroxide and tetraacetylethylenediamine (TAED) was added after the pH adjusting step. Furthermore, the pH of the pulp was adjusted to pH 9.8 using dilute sodium hydroxide and the pulp was incubated for 1 hour at 75 ° C. The mixture of hydrogen peroxide and TAED was prepared at a concentration of 0.34 g of hydrogen peroxide and 1.14 g of TAED in 100 ml of deionized water. The mixture was adjusted to pH 7 with 10% sodium hydroxide and carefully heated to dissolve the TAED. Once the TAED has dissolved, leave the solution to stand for 15 minutes. At this point, the titration procedure according to Swem (1970) indicated that the hydrogen peroxide concentration was below the limit of detection. The titration procedure according to Greenspan (1948) indicated that the peracetic acid concentration was 6.6 g / l. The solution was stored refrigerated. The peracetic acid was added to the pulp at a level of 0.1% calculated on the pulp.

Peracetic acid treatment, pH 6.5. This pulp is treated with peracetic acid as schematically described above (peracetic acid treatment, Example 9). However, the mass is incubated at 60 ° C, pH 6.5.

Xylanase with peracetic acid. This pulp sample is treated as schematically described in Example 4, however, peracetic acid, prepared according to the above description (peracetic acid treatment, Example 9), was added to the pulp after the pH of the pulp was adjusted to pH 6.5 with sodium hydroxide, followed by of addition of xylanase at an enzyme dose of 150 ml / h. The treatment was performed at 60 ° C, pH 6.5, for 1 hour.

After all the treatments described above, the pulp was washed with water and bleached with DoEopD1 as described in Example 7. After bleaching, the brightness of the pulp was measured according to the procedures of Example 8. The results are shown in Fig. 1.

The target for brightness is an ISO brightness of 87.5. The untreated control sample required 20.6 kg / h C102 to reach this level of brightness.

Xylanase treatment alone reduced the amount of C102 for bleaching the pulp to a brightness of 87.5 to 17.8 kg / h, a decrease of 13.6%. This is consistent with published reports regarding the beneficial effects of xylanase treatment in ClO2 bleaching.

Peracetic acid at its optimum pH (9.8) was effective in reducing the amount of C102 required for bleaching the pulp to 18.1 kg / h, a decrease of 12.1%. The ClO 2 savings of 2.5 kg / h in a 1 kg / h peracetic acid treatment are in accordance with published reports on the effects of peracetic acid in bleaching pulp.

Peracetic acid at lower than optimal pH (6.5) was less effective in reducing ClO 2 use. The ClO 2 savings in this treatment were only 3.9%.

The combination of xylanase and peracetic acid reduced the amount of C102 required for bleaching the pulp by 18.5%. This is more effective than xylanase or peracetic acid alone. This shows the large CIOZ savings that are possible through the use of a combination of xylanase and peracetic acid.

EXAMPLE 10: Mass bleaching test using xylanase treatment in the presence of peroximonosulfuric acid (Oxone®) Sulfate hardwood pulp from a plant in the western United States (K = 16.59) was treated as follows: Control pulp: This pulp was treated as described in Example 4, but without the addition of xylanase. .

Xylanase treated pulp. This pulp sample was treated with xylanase as described in Example 4, at an enzyme dose of 150 ml / h.

Treatment with peroximonosulfuric acid (Oxone®), pH 5.5. This pulp was treated as schematically described in Example 4, but without the addition of xylanases. In addition, 4 kg of Oxone® (a peroximonosulfate complex, Sigrna-Aldrich, St. Louis, MO) were added per tonne of pulp after adjusting the pH of the pulp to 5.5. 10 15 20 25 30 526 289 33 Treatment with peroxymonosulfuric acid (Oxone®), pH 6.5. This pulp was treated as schematically described in Example 4, but without the addition of xylanases.

In addition, 4 kg of Oxone® per tonne of pulp was added after adjusting the pH value of the pulp to 6.5.

Treatment with peroximonosulfuric acid (Oxone®), pH 9. This pulp was treated as schematically described in Example 4, but without the addition of xylanases. In addition, 4 kg of Oxone® per tonne of pulp was added after adjusting the pH of the pulp to 9 and the sample was incubated at 75 ° C.

Xylanase with peroximonosulfuric acid (0xone®). This mass sample was treated as sehematically described in Example 4, with an enzyme dosage of 150 ml / h, except that 4 kg of Oxone® per tonne of pulp was added after adjusting the pH of the pulp to 6.5.

After all the treatments described above, the pulp was washed with water and then bleached DoEopD1 as described in Example 7. For the Do step, coat factors of 0.277, 0.249 and 0.222 were used for the control pulp. For the other masses, D0 coat folders of 0.249, 0.222 and 0.193 were used. All Do samples were incubated at a concentration of 4.3%, 66 ° C and for 40 minutes. The EQP conditions for all pulp samples were: 77 ° C, 10% concentration, sodium hydroxide addition of 1.5-2.5%, hydrogen peroxide addition of 0.75%, 0.6% oxygen and an incubation time of 90 minutes. For the D1 stage, the control masses of kappa factors of 0.146, 0.132 and 0.117 were used, and for the other masses kappa factors of 0.132, 0.1 17 and 0.103 were used. After bleaching, the brightness of the pulp was measured according to the procedures of Example 8. The results are shown in Figs. 2.

The target for brightness was an ISO brightness of 89%. The control mass needed 23.4 kg / h C102 to reach this brightness level.

The xylanase-treated pulp required 20.5 kg / h C102 for bleaching pulp to 89% ISO brightness, a decrease of 12.4%. 526 289 34 The pulp subjected to treatment with peroximonosulfate (Ozone®) at pH 5.5, pH 6.5 and pH 9 required 23.3 kg / h, 23.2 kg / h and . 23.3 kg / h C102 to reach a brightness level of 89%, decreases by only 0.27%, 0.81% resp. 0.54%.

Pulp treated with xylanase and peroximonosulphate (Ozone®) required 19.6 kg / h C102 to reach the brightness level of 89%, which corresponds to a decrease of 16.2% of the amount of C102. This is a more effective reduction than for xylanase or Ozone® alone, indicating that large savings of C102 are possible when using a combination of xylanase and peroximonosulphate.

All references herein are hereby incorporated by reference.

The present invention has been described with respect to preferred embodiments. However, it will be apparent to one skilled in the art that a number of variations and modifications may be made within the scope of the invention as described herein. 20 30 526 289 35 References: Bermck, H., Li, K., - Eriksson, K-E L (2000) Pulp bleaching with manganese peroxidase and xylanase: a synergistic e fi ect TAPPI Journal 83, 69.

Bleackl fl y, C. (1991) Spring Conference Whistler, B.C.

Bouchard, J., ct al. (2001) JPPS 27, 397-40, cnnn fi nnnnn, en., Bnnnwny, GL., And Pam, Wæ. (1966) TAfPI Jnnnnn 49, 49- 52. nnnnn, c.w., nna Rem, n., San. (1996) 1> n1n Blnnnning Pnnnipnn; nnd Pnnn fi nn.

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Ericksson, K. E. L., (1990) Wood Science and Technology 24, 79-101.

Greenspan, FP. and MacKellar, D.G. (1948) Analysis of aliphatic peracids. Analysis fi cal I ChGmíSIIyZO, 1061-1063.

Lmm, a., Jnnnnf, N. B., mn Bergquist, P. I. (mo) Anna. anvnnn. mnfnninL ss, 2677-2683. ~ _ Níkn-Paavola et al. (1994) Biorcs Technol. 50, 7-77 Paíce, M. G., _R. Bemier, and L. .Tm-afsek (1988) Biofcechnql. and Bioeng. 32, 235-239.

Pommier, J. Y. C., I. I. Fuentes, and G. (1989) TAPPI Jonrnal, 187-191.

Poppins-main, K, Jnnskenannn, A-s, A and Fnnnnnnnn (zøoo) A-Pnnnian ån Blraft Pulp Bleachíng: Past, Present, and Future. Proceedings 2000 TAPPI Pulping Conference, Boston, Mass. '526 289 36 Shah et al. (2000) Xylznasc Treatment of Oxygan-Blcached Hndwood Kraft Pulp ai High Tempel-anna .and Alkalins pH Levels Gives Substantial Savings in Bleaching Chemicals. J. Pulp andPapcr 'Science 26,.

Simpson, H. D., Han fl cr, U. R., and Daniel, R. M. (1991) Biochem. I. 277, 413-417. sp fi nsw. EL, ma Mcsweçney, n). (1993) Pmcwasngs 1993 TAPPI min; cønfum, 453,451.

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Claims (24)

10 15 20 25 30 526 289 37 Patent claims A process for bleaching chemical pulp comprising exposing the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with at least one oxidizing chemical, the oxidizing chemical comprising hydrogen peroxide, one or more peracids or a mixture of hydrogen peroxide. and one or fl your peracids. The method of claim 1, wherein the bleaching step takes place at a pH between about 5.0 and about 9.0. A process according to claim 2, wherein the peracid is selected from the group consisting of peracetic acid, permyric acid, peroximonosulfuric acid, peroximonophosphoric acid, peroxysalpetic acid and a combination thereof. A process according to claim 3, wherein the peracid is peracetic acid or permyric acid. A process according to claim 3, wherein the peracid is peroximonosulfuric acid. A process according to claim 3, wherein the peracid is prepared outside the bleaching step and then added to the bleaching step. A process according to claim 3, wherein the peracid is formed within the bleaching step. The method of claim 3, wherein the bleaching step is performed for a period of 20-60 minutes, at a temperature of about 40 ° C to about 70 ° C and at a pulp concentration of about 4% to about 12%. A process according to claim 1, wherein the chemical pulp comprises sulphate pulp, kraft pulp, soda pulp or salt pulp. 10 15 20 25 30 526 289 A process according to claim 1, wherein the process is carried out in a pulp mill. The method of claim 3, wherein the pH is between about 6.5 and about 8. The method of claim 1, wherein the xylanase is selected from the group consisting of BioBritem EB-xylanase, HTX-18 and T richoderma reesei xylanase II of the wild type. The method of claim 1, wherein the bleaching step is preceded by one or more alkaline oxygen lignification steps. The method of claim 1, wherein the bleaching step is preceded by an ozone acid treatment. The method of claim 1, wherein the bleaching step is followed by a bleaching sequence. The method of claim 15, wherein the bleaching sequence comprises a chlorine dioxide bleaching sequence. The method of claim 15, wherein the bleaching sequence comprises an ozone-peracid bleaching sequence. The method of claim 1, wherein the oxidizing chemical is hydrogen peroxide, wherein the hydrogen peroxide is present in an amount between about 1 and about 10 kg / h mass. A process for reducing the kappa number of a chemical pulp, comprising: (vii) subjecting the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with at least one oxidizing chemical, the oxidizing chemical comprising hydrogen peroxide , one or fl your peracids or a combination of hydrogen peroxide and one or fl your peracids, to form a treated mass; viii) washing the treated pulp; and ix) bleaching the treated pulp using chlorine dioxide, ozone, oxygen, peracid, alkaline extraction or a combination thereof. A method of reducing the amount of chlorine dioxide required during a bleaching sequence for bleaching a chemical pulp comprising: X) xi) subjecting the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with at least one oxidizing chemical, wherein the oxidizing chemical comprises hydrogen peroxide, one or more peracids or a combination of hydrogen peroxide and one or more peracids, to form a treated mass; washes the treated pulp; and xii) bleaching the treated pulp using chlorine dioxide. A process for bleaching a chemical pulp comprising: subjecting the chemical pulp to a bleaching step comprising at least one xylanase enzyme in combination with peracetic acid, the bleaching step being carried out at a pH between about 5.0 and about 9.0, and comprises peracetic acid in an amount of 0.5 to about 5 kg / h of pulp, for about 20 to about 60 minutes at a temperature from about 40 ° C to about 70 ° C and at a pulp concentration between about 4% and about 12%, for the preparation of a treated pulp; washes the treated pulp; and bleaches the treated pulp using a chlorine dioxide bleaching sequence. 10 526 289 40 The method of claim 21, wherein the pH of the step of subjecting the chemical pulp to a bleaching step (step i)) is about 6.5. The method of claim 22, wherein the temperature in the step of subjecting the pulp to a bleaching step (step i)) is about 60 ° C. A method according to claim 22, wherein in the step of subjecting the pulp to a bleaching step (step i)) the pH value of the chemical pulp is adjusted, followed by the addition of the peracetic acid, followed by the addition of the xylanase.