JPH0748792A - Method for bleaching paper pulp - Google Patents

Abstract

PURPOSE: To enable bleaching of high whiteness without decreasing its own quality of a paper pulp by a process for bleaching treatment contg. an oxygen treatment stage and free from chlorine. CONSTITUTION: When bleaching a paper pulp, the pulp of high whiteness is obtained, while maintaining an excellent quality of the paper pulp, for example, at first by O stage contacting with gaseous oxygen, then preferably X stage using xylanase enzyme produced from a bacterium, Q stage by a metal ion- blocking agent (suitably diethylenetriamine pentaacetic acid), a bleaching stage (P stage) by hydrogen peroxide, a second bleaching stage by ozone and the bleaching stage(PI stage) by hydrogen peroxide in accordance with this order, by bleaching methods free from chlorine, and moreover by treatment stages including O, X and Z stage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for bleaching paper pulp.

[0002]

BACKGROUND OF THE INVENTION It is not possible to apply a series of delignification and bleaching treatment steps involving the use of oxidizing chemicals to unbleached chemical paper pulp obtained by digesting cellulosic material in the presence of chemical reactants. It is known. The purpose of the first step of bleaching a conventional series of chemical pulp is
It is to complete the delignification of the unbleached pulp in the state where the cooking work is finished. This first delignification step treats the unexposed pulp conventionally with chlorine in an acidic medium or with chlorine-chlorine dioxide as a mixture or continuously and reacts with the lignin remaining in the pulp. And chlorolignin which can be extracted from the pulp by dissolving in an alkaline medium in a subsequent treatment step. For various reasons, it has been found useful in some circumstances to replace this first delignification step with a treatment that no longer requires a chlorine-containing reactant. By the first step of the treatment with the enzyme, the subsequent step with ozone and the step with hydrogen peroxide in an alkaline medium, the step with ozone, and the subsequent step with hydrogen peroxide, that is, XZPZP It has already been proposed to process kraft pulp in sequence (see European Patent Application EP-A1-0512978). However, the whitenesses obtained do not reach the values of 89 to 90 ° ISO required to bring the pulp directly to the market as high quality bleached kraft pulp. In order to obtain a high whiteness of 89 ° ISO or more, use a large amount of ozone without deteriorating the inherent quality of pulp when using this known method, especially without deteriorating the degree of polymerization of the cellulose chain. is necessary.

[0003]

The present invention aims to overcome the drawbacks of the known processes by providing a new series of bleaching processes which obtain a high whiteness while retaining the inherent quality of the pulp. .

[0004]

Therefore, the present invention provides a series of treatments including at least three steps OXZ (O: oxygen step; X: enzymatic step; Z: ozone step) in any order. It relates to a first method of bleaching paper pulp by a process. This method comprises a series of treatment steps without chlorine (Cl ₂ ) (ECF) and preferably without chlorine-containing reactants (TCF) (no chlorine at all).
Are particularly suitable for treating paper pulp according to. In addition to the three steps described above, this method comprises at least one step selected from steps Q and P (Q: treatment with sequestering agent; P: step with hydrogen peroxide in alkaline medium). It is advantageous to include. These additional steps can be at any point in the process sequence. For example, it may be inserted between the steps or may be the final step. In these series of steps, steps O and X are carried out first (in any order, but preferably O is followed by X and may optionally include intermediate steps). Step Q is preferably carried out before the first P step. The order in which good results are obtained in treatments without the TCF-type chlorine-containing reactant is OQPZP with step X. This X step is XOQPZP
It may be first so as to be in order. For example, OXQPZP and OQPXZP may be inserted between any two steps.

The present invention also includes a series of TCFs or ECFs.
Applied to bleaching paper pulp by a chlorine-free process of the type (free of elemental chlorine), including at least process P after process XO or OX, and process Q at any position prior to process P , And the meanings of X, O, P and Q are as described above. The order in which good results are obtained in the bleaching of ECF-type and preferably TCF-type paper pulp is the following four orders: OX
QP, OX / QP, XOQP and X / QOP have been reported. In the above order, the symbol / means that the step immediately preceding the symbol and the step after the symbol can be arbitrarily combined into a single step. In ECF or preferably TCF type treatments, the order in which the Q step is immediately before the P step is preferred. A preferred combination of further steps in ECF or preferably TCF type processing is such that the Q step is immediately after the X step. A particularly preferred order is such that there is a Q step after the X step and at the same time there is a Q step before the P step. This method is particularly suitable for treating chemical paper pulp.

Chemical paper pulp means pulp which has been delignified in the presence of a chemical reactant such as sodium sulfide in an alkaline medium, sulfur dioxide or a metal salt of sulfurous acid in an acidic medium (respectively, Kraft or sulfate cooking and sulfite or bisulfite cooking). Semi-chemical pulp (neutral sulfite cooking, also known as NSSC cooking), which was cooked using a salt of sulfite in a neutral medium, is also available from Ullmann's Encyclopedia of Industrial.
Chemistry, 5th Edition, Volume A18, 1991, 568-5
Pulps obtained by solvent-based methods such as Organosolv, Alcell®, Organocell® and Asam pulps described on page 69 can be bleached by the method according to the invention as well as pulp obtained by the method. The invention applies in particular to pulp which has been kraft or sulphite cooked. All kinds of wood used for the production of chemical pulp are suitable for use in the process of the invention, especially those used for kraft and sulphite pulp, i.e. softwood wood such as various pine and fir, and beech, for example. Suitable for deciduous wood such as oak, eucalyptus and hornbeam.

According to the present invention, in the process using oxygen, the weight of the alkali compound relative to the weight of the dry pulp is 0.
It is carried out by contacting the pulp with gaseous oxygen under a pressure of 20 to 1000 kPa in the presence of an alkali compound in an amount such that it is 5 to 5.0%. The temperature of the process with oxygen should generally be above 70 ° C, preferably above 80 ° C. Suitably this step is also usually below 130 ° C, preferably below 120 ° C. The treatment time of the process with oxygen should be sufficient to complete the reaction of oxygen with the lignin present in the pulp. However, this reaction time must not be exceeded excessively as it induces decomposition of the cellulose chain structure of the pulp. In practice it will be longer than 30 minutes, preferably longer than 40 minutes. Further, it is usually 120 minutes, preferably shorter than 80 minutes. Oxygenation of the pulp may also be carried out in the presence of cellulose protectants such as soluble magnesium salts or organosequestering agents such as polycarboxylic or phosphonic acids.
The magnesium salt is preferred. In particular, 0.02 to 1% by weight of magnesium sulphate is used, based on the weight of dry pulp. The consistency of pulp in the O step is generally 8% by weight or more of solid content, preferably 10% or more. This consistency is usually less than 30% by weight solids content, preferably 25%. In another embodiment, the step O is performed in the presence of hydrogen peroxide (step Op). The amount of hydrogen peroxide used in the O step is generally 0.2 g or more, and often 0.5 g or more, per 100 g of dry pulp. Similarly, it is usually 2.5 g or less, and often 2 g or less, per 100 g of dry pulp.

According to the present invention, the step Q comprises the step of treating the pulp in an acidic medium with an inorganic or polyphosphate (for example an alkali metal salt of pyrophosphoric acid or metaphosphoric acid), an organic polycarboxylic acid or an aminopolycarboxylic acid (for example: Tartaric acid, citric acid, gluconic acid, diethylenetriaminepentaacetic acid and cyclohexanediaminetetraacetic acid) and their salts,
Such as poly-α-hydroxyacrylic acid and salts thereof, and organic polyphosphonic acids (eg ethylenediamine (tetramethylenephosphonic) acid, diethylenetriaminepenta (methylenephosphonic) acid or cyclohexanediaminetetra (methylenephosphonic) acid) and salts thereof This is a step of treating with one or more sequestering agents. Excellent results have been obtained with diethylenetriaminepentaacetic acid (DTPA). In another aspect, Step Q is a step of treating with an acid that does not include a sequestering agent. The acid is
Inorganic acid anhydrides or acids such as sulfur dioxide and sulfuric acid, sulfuric acid, hydrochloric acid and nitric acid and their acid salts, and organic acids such as carboxylic acids or phosphonic acids or their acid salts are meant. Sulfur dioxide or alkali or alkaline earth metal bisulfites are suitable. Bisulfite has the formula Me (H
SO ₃ ) _n (In the formula, Me represents a metal atom having a valence of n, and n is 1
Or an integer of 2).

If a sequestering agent is present, a small amount of acid may also be added to step Q. The amount of acid used in the Q process according to the present invention depends on the type of wood and the amount of metal impurities contained therein. Generally, the amount of acid is
The amount is such that the pH is about 5 or more, preferably about 5.5. Similarly, the amount of acid often has a pH below 7 and preferably 6.5.
Adjusted to be: If no sequestrant is present in step Q, the pH is adjusted so that the mixture is slightly acidic, ie less than 5, preferably less than 4.0. Generally, avoiding a pH drop below 1.0, preferably below 1.5, in order not to decompose the pulp. When a sequestrant is present, it is generally used in step Q in an amount of less than 1.5 g per 100 g of dry pulp. Often this amount is less than 1.0 g per 100 g of dry pulp. Process Q is generally under atmospheric pressure and at a temperature sufficient to ensure sufficient consumption of acid and / or sequestrant, while at the same time not decomposing cellulose and used in the above process. It is carried out at a temperature that is not so high that the energy cost of the heating means to be used does not increase. Actually 4
A temperature of 0 ° C. or higher, preferably a temperature of 50 ° C. or higher is suitable. Similarly, temperatures below 100 ° C, preferably below 90 ° C, are advantageous. Best results were obtained at about 50 ° C.

The time of step Q must be sufficient to ensure complete reaction. Even if the time is long, it does not affect the delignification degree of the pulp or its ultimate strength,
It is not advantageous to extend the reaction time beyond that required to complete the reaction to limit capital costs and energy costs to heat the pulp. In practice, the pretreatment time will vary widely depending on the type of equipment used, the choice of acid, the temperature and the pressure, for example from about 15 minutes to several hours. A time of at least 10 minutes, preferably at least 15 minutes is generally sufficient. Similarly, it is important that the pretreatment time is 60 minutes or less, preferably 40 minutes or less. Excellent results were obtained at about 30 minutes. Step Q is generally carried out at a pulp consistency with a solids content of 2% or more, preferably with a solids content of 2.5% or more. In many cases this consistency is below 15%, preferably below 10%. About 5
Excellent results were obtained with a consistency of% solids content.

According to the present invention, the step P is a treatment step using alkaline hydrogen peroxide. The type of alkali should be such that the extraction efficiency of the oxidized lignin is good and the solubility is good at the same time. An example of such an alkali is aqueous sodium hydroxide. The amount of alkali used should be sufficient to keep the pH above 10 and preferably above 11.
The amount of alkali must also be adjusted to ensure a sufficient consumption of peroxide at the end of the reaction. In practice, 1 to 3 g of alkali per 100 g of dry pulp is suitable. In addition to these amounts of alkali, more than 0.3 g per 100 g of dry pulp, preferably 0.
Use more than 5 g of hydrogen peroxide. A suitable amount of hydrogen peroxide is generally less than 5.0 g, preferably less than 4.0 g per 100 g of dry pulp. The temperature of the P step must be adjusted so as to be maintained at 50 ° C or higher, preferably 60 ° C or higher. The temperature of process P is 100 ℃
Below, preferably below 95 ° C. 70
Excellent results have been obtained at a temperature of ° C.

The duration of the P step must be sufficient to complete the bleaching reaction. However, the reaction time should not be exceeded too much. Otherwise, it will induce a reversal of the whiteness of the pulp. In practice, it is 60 minutes or longer, preferably 90 minutes or longer. In many cases, 300 minutes or less,
It is preferably 200 minutes or less. Good results have been obtained with a combination of conditions of temperature and time of 70 ° C. and about 120 minutes. The consistency of P process is generally 4
Choose from a solids content of 0% or less, preferably less than 30%. It is often at least 5%, preferably at least 8%. Good results were obtained with a consistency of 12%.

According to the present invention, the Z step is a treatment step using ozone. This step is the step of exposing the pulp to a gas stream containing a mixture of ozone and oxygen generated from an electric ozone generator fed with dry gaseous oxygen. Output is 50
Generators of ˜100 l / h, preferably 70-90 l / h are advantageously used in the laboratory. The amount of ozone used can be easily adjusted by varying the time that the ozone / oxygen mixture stream contacts the pulp. Generally, 1 to 10 minutes of dry pulp 1
It is sufficient to use 0.2 to 1 g of ozone per 00 g. On an industrial scale, the ozone generator output and treatment time should be adjusted in order to bring the amount of ozone used in the pulp closer to the amount produced in the laboratory. Ozone treatment is preferably carried out in an acidic medium. PH value of 0.5 to 5, preferably 1.5 to 4
Value is suitable. Very good results were obtained with a pH value of 3. The ozone treatment process has a consistency of 2
% Or more, preferably 10% or more of solid content. Generally, a solids content of 50% or less, preferably 45% or less. Excellent results have been obtained with a consistency of 40%.

The temperature of the ozone treatment process must be kept relatively low. Otherwise, the mechanical strength of the treated pulp will be significantly reduced. Generally this temperature is 5
It is 0 ° C or lower, preferably 35 ° C or lower. However, 2 ° C
Higher, often higher than 10 ° C. Good results have been obtained with an ambient temperature of 22 ° C. Another advantageous embodiment of the process according to the invention is for opening the pulp in order to increase the contact surface between the pulp and ozone (referred to in the literature as "fluffing").
This is a step of performing ozone treatment using mechanical treatment.
This work has a consistency of 15% during ozone treatment.
It is especially useful at higher solids contents. Process P is
A process using hydrogen peroxide in an alkaline medium as described above, as well as an alkali extraction process fortified with a small amount of hydrogen peroxide (Ep process) and a process including the use of oxygen mixed with hydrogen peroxide (Eop process). means.

According to the invention, the step X of treating with one or more enzymes is the step of treating pulp with a composition containing one or more enzymes. Enzymes have already been subjected to one or more steps of bleaching using unexposed chemical paper pulp produced by digestion or an oxidizing reactant such as oxygen, hydrogen peroxide and ozone, by a step after the treatment step with an enzyme. Means any enzyme capable of promoting delignification of chemical paper pulp. A very suitable type of enzyme for the method according to the invention is hemicellulase. These enzymes can react with the lignin-bound hemicellulose present in the pulp. The hemicellulase used in the method according to the invention is preferably xylanase. A hemicellulose enzyme capable of cleaving the xylan bonds that make up the bulk of the interface between lignin and other carbohydrates. Examples of xylanase by the method according to the invention are:
4-β-D-Xylanxylanohydrolase, EC 3.2.1.8.

The preferred sources of xylanase in the method according to the invention vary. In particular, it is produced by a wide range of bacteria and fungi. Xylanase produced from bacteria is particularly advantageous. Among the xylanases produced by bacteria, good results were obtained in the case of xylanase produced by bacteria of the genus Bacillus . Excellent results have been obtained with xylanase produced from bacteria of the genus Bacillus and pumilus . Of these, Bacillus
Xylanase produced from pumilus PRL B12 is particularly advantageous. The xylanase produced from Bacillus pumilus PRL B12 according to the present invention is Bacillus pumilus PRL.
It may be produced directly from a strain of B12, or Bacillus pu
It may be produced from a host strain that has already been genetically engineered to represent a gene that specifies the genetic code for the degradation of xylan of milus PRL B12. Preferably, a purified xylanase containing no other enzyme is used. In particular, the xylanase according to the method according to the invention does not contain any cellulase since it does not break the cellulosic polymer chains of the pulp. The method according to the invention is suitable for delignification of any kind of chemical pulp. Also suitable for delignification of kraft and sulfite pulps. Particularly well suited for treating kraft pulp.

[0017]

The following examples are provided to illustrate the present invention, but not to limit its scope. Examples 1R and 2R (not according to the invention) Samples of Kraft cooked deciduous pulp (ISO standard 47).
Initial whiteness of 33.4 ° ISO measured by 0-1977 (F)
, 12.3 and SCA measured by SCAN standard C1-59
Degree of polymerization 1370) represented by the number of glucose units, measured by N standard C15-62, was measured by 5 step OQP under the following conditions.
Processed according to ZP order. The first step: a step using oxygen (O process): Pressure (bar): 6 NaOH content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 90 Consistency (% by weight of solid content): 15 2nd step : Step using DTPA (Step Q): DTPA content (g / 100g dry pulp): 0.2 Temperature (° C): 50 hours (min): 30 Consistency (wt% solids content): 5

Third step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100g dry pulp): 1.5 NaOH content (g / 100g dry pulp): 1.8 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 temperature (° C.): 70 hours (minutes): 120 consistency,% by weight of solids content: 12 4th Process : Process using ozone (process Z): Example 1R Example 2R O ₃ content (g / 100g dry pulp): 0.35 0.52 pH: 3.0 3.0 Temperature (° C): 22 22 hours (min): 2.25 3.5 Consistent Tensency (% by weight of solid content): 40 40 Fifth step : Step using hydrogen peroxide (P step): H ₂ O ₂ content (g / 100g dry pulp): 2.0 NaOH content (g / 100g dry pulp) : 1.6 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 3.0 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 1.0 temperature (° C.): 80 hours (minutes): 24 0 consistency (wt% solids content): 30 The κ number of the pulp was measured at the end of the first P step before the Z step. The degree of polymerization and whiteness were measured after the treatment.

[0019]

[Table 1] Table 1 Example number Final whiteness κ number before Z step Final degree of polymerization ° ISO 1R 88.8 6.4 830 2R 91.0 6.4 810

Examples 3 and 4 : (according to the invention) A sample of the same pulp as in Examples 1R and 2R was prepared in the X step with an amount of Ba corresponding to 10 XU / g dry pulp.
Bleaching was carried out in order of OXQPZP by using xylanase produced from cillus pumilus PRL B12. The unit XU (xylanase unit) is defined as the amount of xylanase that catalyzes the release of reducing sugars corresponding to 1 μmol glucose per minute in reducing capacity under the test conditions. The working conditions were as follows. The first step: a step using oxygen (O process): Pressure (bar): 6 NaOH content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 90 Consistency (% by weight of solid content): 15 Second step : Step using xylanase enzyme (Step X): Xylanase content (XU / g dry pulp): 10 Temperature (° C) : 50 hours (min): 90 Consistency (% by weight of solid content): 5 3rd step : Step using DTPA (Step Q): DTPA content (g / 100g dry pulp): 0.2 Temperature (° C): 50 Time (minutes): 30 Consistency (wt% solids content): 5

Fourth step : Step using hydrogen peroxide (Step P): H ₂ O ₂ content (g / 100g dry pulp): 1.5 NaOH content (g / 100g dry pulp): 1.8 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 temperature (° C.): 70 hours (minutes): 120 consistency (weight percent solids): 12 5 Process : Process using ozone (process Z): Example 3 Example 4 O ₃ content (g / 100g dry pulp): 0.28 0.43 pH: 3.0 3.0 Temperature (° C): 22 22 hours (min): 2.25 3.0 Consistency Tensity (% by weight of solid content): 40 40 Step 6 : Step using hydrogen peroxide (Step P): H ₂ O ₂ content (g / 100g dry pulp): 2.0 NaOH content (g / 100g dry pulp) : 1.6 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 3.0 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 1.0 temperature (° C.): 80 hours (minutes): 240 Consistency (wt% solids content): 30 The results obtained were as follows.

[0022]

[Table 2] Table 2 Example number Final whiteness κ number before Z step Final degree of polymerization ° ISO 3 89.6 5.5 920 4 91.5 5.5 870

Examples 5 and 6 : (according to the invention) Samples of pulp identical to Examples 1R, 2R, 3 and 4,
Same amount of Bacillus as in Examples 3 and 4 in step X
Bleaching was performed in the order XOQPZP by using xylanase produced from pumilus PRL B12. The working conditions were as follows. First Step: a step of using a xylanase enzyme (X step): xylanase content (XU / g of dry pulp): 10 Temperature (° C.): 50 hours (minutes): 90 consistency,% by weight of solids content: 5 second 2 step: oxygen process using the (O step): pressure (bar): 6 NaOH content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 temperature (℃) : 120 hours (min): 90 Consistency (% by weight of solid content): 15 3rd step : DTPA-using step (Q step): DTPA content (g / 100g dry pulp): 0.2 Temperature (° C): 50 Time (minutes): 30 Consistency (wt% solids content): 5

Fourth step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100g dry pulp): 1.5 NaOH content (g / 100g dry pulp): 1.8 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 temperature (° C.): 70 hours (minutes): 120 consistency (weight percent solids): 12 5 Process : Process using ozone (Process Z): Example 5 Example 6 O ₃ content (g / 100g dry pulp): 0.31 0.43 pH: 3.0 3.0 Temperature (° C): 22 22 hours (min): 2.08 3.0 Consistency Tensity (% by weight of solid content): 40 40 Step 6 : Step using hydrogen peroxide (Step P): H ₂ O ₂ content (g / 100g dry pulp): 2.0 NaOH content (g / 100g dry pulp) : 1.6 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 3.0 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 1.0 temperature (° C.): 80 hours (minutes): 240 Consistency (wt% solids content): 30 The results obtained were as follows.

[0025]

[Table 3] Table 3 Example number Final whiteness κ number before Z step Final degree of polymerization ° ISO 5 89.3 5.6 900 6 91.2 5.6 860

Examples 7 and 8 : (according to the invention) Samples of pulp identical to Examples 1R, 2R and 3 to 6 were treated with the same amount of Bacill as in Examples 3 to 6 in the X step.
Bleaching was done in the order OQPXZP by using xylanase produced from us pumilus PRL B12. The working conditions were as follows. The first step: a step using oxygen (O process): Pressure (bar): 6 NaOH content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 90 Consistency (% by weight of solid content): 15 2nd step : Step using DTPA (Step Q): DTPA content (g / 100g dry pulp): 0.2 Temperature (° C): 50 hours (minutes): 30 Consistency (% by weight of solid content): 5 Third step : Step using hydrogen peroxide (P step): H ₂ O ₂ content (g / 100g dry pulp): 1.5 NaOH content (g / 100 g of dry pulp): 1.8 38 ° Be Na silicate content (g / 100 g of dry _{pulp): 2.5 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 temperature (° C.): 70 hours (min) : 120 Consistency (wt% solids content): 12

Fourth step : Step using xylanase enzyme (step X): Xylanase content (XU / g dry pulp): 10 Temperature (° C): 50 hours (min): 90 Consistency (% by weight of solid content) : 5th step : Step using ozone (Step Z): Example 7 Example 8 O ₃ content (g / 100g dry pulp): 0.25 0.38 pH: 3.0 3.0 Temperature (° C): 22 22 hours (min) : 2.16 3.0 Consistency (% by weight of solid content): 40 40 Step 6 : Step using hydrogen peroxide (Step P): H ₂ O ₂ content (g / 100g dry pulp): 2.0 NaOH content (g / 100g of dry pulp): 1.6 38 ° Be Na silicate content (g / 100g of dry _{pulp): 3.0 MgSO 4 · 7H 2} O content (g / 100g dry pulp): 1.0 temperature (° C.): 80 hours (minutes): 240 consistency Tensity (wt% solids content): 30 The results obtained were as follows.

[0028]

[Table 4] Table 4 Example number Final whiteness κ number before X step κ number before Z step Final degree of polymerization ° ISO 7 88.8 6.5 3.1 870 8 91.4 6.5 2.5 860

Claims (10)

[Claims] 1. A method of bleaching paper pulp by a series of treatment steps using no TCF (chlorine-free) type chlorine-containing reactant, wherein at least three steps OXZ (O: oxygen step) are performed in any order. X: a step using an enzyme; Z: an ozone step). 2. A method for bleaching paper pulp by a series of chlorine-free treatment steps of the TCF or ECF (without elemental chlorine) type, comprising at least step P after step XO or OX, wherein A method including a Q step before. 3. The method according to claim 1, wherein the step X includes one or more hemicellulases. 4. The method of claim 3, wherein the hemicellulase is xylanase. 5. The method according to claim 3, wherein the step X is carried out in the absence of cellulase. 6. The method according to claim 4, wherein the xylanase is produced from a bacterium of the genus Bacillus . 7. The method according to claim 6, wherein the Bacillus bacterium is a pumilus species bacterium. 8. The bacterium is Bacillus pumilus PRL B12.
The method according to claim 7, wherein 9. The OQPZP in which the bleaching order includes the X step.
The method according to any one of claims 1 and 3 to 8, in the order of. 10. The method according to claim 1, which is used for bleaching kraft pulp.