WO1994017237A1 - Pre-bleaching treatment method using enzyme for chemical pulp - Google Patents

Abstract

This invention provides a method of increasing the degree of delignification of chemical pulp without decreasing the viscosity thereof. In this method, unbleached pulp or pulp which has been subjected to oxygen delignification is subjected to a pre-bleaching treatment, in which xylanase having an activity in the range of pH of not more than 4.5 is used, as the pulp is maintained under acidic conditions. This method enables the quantity of use of a medicine of a chlorine compound to be reduced while maintaining such a degree of whiteness of bleached pulp that permits commercial use, whereby the occurrence of an organic chlorine compound which is environmentally harmful can be minimized.

Description

 Description Pretreatment method for bleaching chemical pulp with enzymes

 The present invention provides an enzyme that reduces or uses no molecular chlorine in the bleaching process by introducing a pre-bleaching process for chemical pulp that combines enzyme treatment and acid treatment. Pretreatment method for bleaching chemical pulp by the method. Background art

 When bleaching using molecular chlorine, the bleaching effluent contains dioxin and has been reported to have potential adverse effects on biological systems and the human body. Based on the results of these studies, methods for bleaching chemical pulp that reduce or do not use molecular chlorine are being considered.

 Chemical pulp in a fibrous form is widely and industrially used as a raw material for manufacturing paper and the like. The above-mentioned raw material is usually wood, and its main component is a cell material and a high-molecular substance having a three-dimensional structure, that is, lignin. Lignin is considered to be in the matrix of cellulosic polysaccharides and hemicellulose polysaccharides.

Generally, the bond existing between the above-mentioned different components is considered to be via a chemical bond having a different property. For example, the lignin block is said to have a portion that is bound to the hemicellulose chain. It is considered that the hermetic mouth is a secondary component of chemical pulp. The major hemicellulose in hardwood is glucuronoxylan. This includes D-xylose polymers, hereinafter referred to as xylans and L.

 In order to produce tough and bright white paper pulp, chemical pulp must be treated to remove lignin, and usually the first part of the treatment involves chemicals such as chemicals. NaOH, sodium sulfide (used to make kraft pulp), or sulfite, usually sodium or magnesium salt ( (Used to produce sulphite pulp), or in digesters in the presence of NaOH, anthraquinone (Soda-AQ method). Removal of this lignin is called delignification.

 The lignin content of wood pulp is determined by the permanganate oxidation test method (TAPPI test method T-236M—76) according to the standard method of the Japan Pulp and Paper Industry Association. C The chemical pulp obtained from the digester still contains significant amounts of residual lignin at this stage, and in some cases Suitable for producing paperboard or double-bag paper without further refining. However, in most cases, for example, in the production of printing papers, writing papers and sanitary papers, the chemical pulp must be whitened by bleaching because it is too black in color. The conventional method of further delignifying and bleaching this unbleached pulp uses about 3 to 6 steps, and sometimes involves a washing step between the steps. This is done in a multi-stage bleaching process (bleaching sequence). In the case of chemical pulp, the purpose of bleaching is to provide pulp with sufficient whiteness to make paper and thin paper products. In this case, pulp with a whiteness of 85 to 90% is produced.

Conventionally, the subject of the above bleaching process is based on the use of chlorine and chlorine containing compounds. The chlorine-containing compound used is chlorine (Hereinafter, the place where chlorine is used is also referred to as C or C process), chlorine dioxide (hereafter, place where chlorine dioxide is used is also referred to as D or D process), and hypochlorite (below) When using hypochlorite, it is also indicated as H or HI, usually sodium hypochlorite.

 Chlorine is used, either alone or mixed with chlorine dioxide, to initiate the bleaching of chemical pulp, and then to extract the chlorinated pulp in an alkaline aqueous medium (hereinafter referred to as Alkaline). The extraction process by リ is referred to as E or E process). The chlorine input amount (or the total input amount of chlorine and chlorine dioxide in the above C step, the chlorine dioxide is displayed on the basis of the oxidizable chlorine equivalent) is the lignin amount (copper) of the pulp to be treated. (Displayed at a single value). The extraction process is used to dissolve and remove most of the chlorinated and oxidized residual lignin, and also removes some hemicellulose in the extraction process. You.

 Stricter environmental regulations aimed at reducing water pollution caused by the use of bleach composed of chlorine-containing compounds, and the large scale required to remove chlorine-containing waste to meet those regulations Considering the necessity of large-scale recovery equipment, it is appropriate to reduce the use of chlorine-containing compound-based bleach in the above various bleaching methods, and it is most preferable to avoid the use. Appropriate.

Usually, in chemical pulping, the cooking effluent is burnt and recovered through a recovery facility. Further, in the case of bleached chemical pulp, pulp fiberized by digestion is further subjected to bleaching treatment, and in this treatment, a chlorine compound is used as a bleaching agent as described above. However, when recovering chlorine-containing waste liquid in a furnace that collects cooking waste liquid, it is implemented because chlorine or its compounds in the waste liquid may damage the evaporator and the recovery furnace. Not. For this reason, the pulp industry continues to research alternative bleaching agents that do not contain chlorine.

 One of the technological advances in the pulp industry over the past 20 years for such purposes has been the use of oxygen as a delignifying and bleaching agent.

 One application of oxygen is primarily for delignification immediately after pulping digestion and prior to bleaching. The oxygen used in this method is added to the unbleached pulp in an alkaline medium under pressure and delignifies by oxidative decomposition of the lignin. This step is conventionally referred to as oxygen bleaching (hereinafter also referred to as 0 or 0 step). There are restrictions on the amount of oxygen used in this case. Excessive use of oxygen adversely affects the degree of polymerization of cellulose.

 The degree of polymerization of cellulose is an indicator of pulp strength, and is measured as pulp viscosity according to the TAPPI standard method (TAPPI test method T-230OM-82). It is generally accepted that in this oxygen bleaching process, the limit of delignification to keep the pulp viscosity reduction within an acceptable range is up to about 50%. Oxygen delignification contributes to reducing the use of chlorine-containing compounds in subsequent bleaching. Since the input amount of the chlorine-containing compound in the chlorination step depends on the lignin content in the pulp, the chlorine input amount can be substantially reduced by performing delignification using oxygen. Is reduced.

 After the chlorination process, extraction is usually carried out with Alri to remove the chlorinated lignin. There is known a method of treating this alloy in combination with various oxidizing agents. They have the following methods:

(1) Combination of oxygen gas (0) and alkaline extraction (denoted as Eo) (2) Combination of hydrogen peroxide (P) and alkaline extraction (denoted by Ep)

 (3) Combination of hypochlorite (H) and alkaline extraction (denoted as Eh)

(4) Combination of hydrogen peroxide, oxygen and aluminum extraction (denoted as Eop)

(5) Combination of hypochlorite, oxygen and alkaline extraction (denoted as E oh) These are also called oxidative extraction.

 Recently, there has been research into the use of enzymes for the processing of chemical pulp (hereinafter also referred to as X or XI). For example, lignin-degrading enzymes, particularly enzymes obtained from white-rot fungi, are known to degrade lignin. Cellulase is also known to degrade cellulose. A variety of studies have been reported on the effect of xylanases on wood pulp, focusing on the hemicellulose component of the dani pulp. As a result of these studies, it has been clarified that xylanases selectively react with xylans in hemicellulose. FR Patent Application No. 25557898 (published in 1985) states that hardwood bleached chemical pulp or softwood bleached chemical pulp should be used to reduce the beating power required for papermaking. Is treated with a solution containing xylanases.

Use of the enzyme as a bleaching pre-treatment or bleaching aids, V ii kar i Raniyo Tsu is the first time £ S seen Rireta (Proceedings of International Symposium on Wood and Pulping Chemistry. Paris, 1987) 0 They are strains of Aspergillus awamori (VTT-D-79125) or Streptomyces olivis α-mogenes (Streptomyces olivochromogenes). , VTT-E-82157), the enzyme groups having xylanase and xylosidase activities obtained from the culture of the strains of camp (birch) and pine (pine). The bleached kraft pulp is treated, then treated with hydrogen peroxide, and after this treatment, treated with (D + C)-E, and treated with enzyme rather than the weakened one. Approx. 2 points It has been observed that copper price is reduced. The conditions of this enzyme treatment are 45 ° C. and 24 hours at pH 5.0. Under these treatment conditions, almost no metal salts, especially transition metals, in unbleached pulp could be removed from the pulp, and excessive addition was carried out despite the long enzymatic treatment of 24 hours. Otherwise, the increase in whiteness cannot be obtained and the decrease in viscosity is large.

 Paice, Bernier, Jurasek and colleagues describe unbleached broad-leaved trees produced by enzymes produced by E. coli that incorporate genes that produce endoxylanases and ^ δ-xylosidases. The pulp was treated, followed by alkaline extraction or C-ED treatment and compared to the untreated case (Biotechnology and Bioengaging, vol. 32, July p235-239, 1988). In this method, the power obtained by the treatment of the enzyme and the alcohol is high, and the treatment of chlorine-containing C-ED is required for bleaching to high whiteness. When chlorine is used, the generation of harmful chlorine compounds such as dioxin is inevitable, and the processing wastewater also contains chlorine ion, so it cannot be recovered in the black liquor recovery system.

In Japanese Patent Application Laid-Open No. 2-264807, before or after oxygen bleaching, the lignocellulose material is treated with xylanases that are substantially free of cellulase to reduce the force. Luo C, D, E, P, H, ozone, and treated with N 0 ₂ and one or more additional steps selected from the oxidative a Luke Li extraction, practical whiteness A technique for obtaining pulp is disclosed.

In this method, the conditions of the enzyme treatment are in the range of 20 ° C to 80 ° C, 1 to 48 hr, ρ ~ 4 to 8, and the measurement of the xylanase activity is performed by ρ至 The optimum ρ ら is also around here, that is, neutral or weakly acidic, since it was implemented in 6.0. In each of the examples, the bleaching step after the enzyme treatment is carried out in such a manner that the bleaching step is started with C, D or C-NO-D. It indicates that there is. This is In the case of enzyme treatment under neutral or weakly acidic conditions, metal salts are not removed, and bleaching agents are decomposed by residual metal salts, which means that efficient bleaching cannot be performed.

 In Japanese Unexamined Patent Publication (Kokai) No. H2-29-193486, pulp is treated with an enzyme before or after the first oxidation treatment with oxygen, followed by treatment with chlorine, chlorine dioxide or a mixture of chlorine and chlorine dioxide, and further intermediate treatment. A method is disclosed in which bleaching is carried out by repeating an oxidation treatment including an extraction of an alkaline solution. This method also describes that the enzyme treatment is carried out within the range of pH 3.0 to 10.0, preferably 4.0 to 9.0, which clearly shows that the optimal pH is obtained. This method is based on the premise that a neutral to weakly acidic enzyme is used. Therefore, in continuous bleaching, treatment with chlorine or chlorine dioxide is an essential condition to obtain high brightness pulp.

 In a bleaching method that does not use molecular chlorine at all for bleaching, processing under strong acidic conditions is not performed throughout the entire process, so that metal salts, particularly transition metal salts, remain in the system and bleaching occurs. Decomposition of the oxidizing agent used to reduce the bleaching effect, and active oxygen and the like generated during the decomposition process attack the cellulose chain, lowering the weight and reducing the pulp quality was there. In addition, the efficiency of the oxidizing agent is reduced, so that an excessive amount must be added, which greatly impairs economic efficiency and lowers the quality to an unacceptable level. .

 Prior art techniques for removing or inactivating metal salts include:

 (1) Pretreatment with acid

 (2) Blocking with chelating agent

Has been used. However, these treatments do not have a delignification effect, and the amount of the oxidizing agent used is still too large to cause quality deterioration. A method that uses chlorine dioxide instead of chlorine in the first stage of bleaching is also used; 'In this case, chlorine ion is contained in the bleaching waste liquid and the wastewater cannot be returned to the black liquor recovery system. It is discharged as wastewater and its amount is small, but it cannot prevent pollution by harmful chlorine compounds. Disclosure of the invention

 (Problems to be solved by the invention)

 It is an object of the present invention to use molecular chlorine at a lower weight than is customary, or to omit the use of molecular chlorine altogether, and thus to obtain a more environmentally acceptable chemical pulp. In addition to providing a bleaching method, it provides a means for recovering part or all of the bleaching wastewater in the black liquor combustion process. Another object of the present invention is to provide a method for increasing the degree of delignification of chemical pulp and efficiently increasing whiteness without causing a decrease in viscosity.

(Means for solving the problem)

 In order to achieve the above-mentioned tasks, it is necessary to promote pulp delignification and to remove metal salts that cause viscosity reduction.

We have two processes:

 (1) Removal of metal salts by acid treatment and promotion of delignification

 (2) Promotion of delignification by enzymes

Combined use of pulp in the subsequent bleaching process does not cause a decrease in viscosity, significantly reduces molecular chlorine, or eliminates the use of molecular chlorine at all. And found that it could be bleached.

Furthermore, by using an acid-resistant enzyme, the above two processes can be performed in a single process. The present invention was completed by developing a method for realizing this.

 That is, according to a first aspect of the present invention, there is provided an enzyme characterized in that unbleached chemical pulp is subjected to an acid treatment, washed, and then treated with an enzyme containing xinalase. This is a pretreatment method for bleaching chemical pulp.

 As a second invention, bleaching of chemical pulp by an enzyme characterized by treating unbleached chemical pulp with an enzyme containing xinalase, and then subjecting it to acid treatment and then washing. This is a preprocessing method.

 As a third invention, unbleached chemical pulp is treated with an enzyme containing xylanases having an optimum pH of 4.5 or less under conditions of pH 4.5 or less. This is a pretreatment method for bleaching chemical pulp with an enzyme, which is characterized by washing afterwards.

 Further, in the first and second inventions, the enzyme to be used is an enzyme containing xylanases having an optimum pH of 4.5 or less. This is a pretreatment method for bleaching pulp.

 The unbleached chemical pulp is unbleached pulp or oxygen bleached pulp, and is characterized by adding hydrogen peroxide or ozone to the acid treatment process. This is a pretreatment method for bleaching chemical pulp with enzymes.The acid used to bring pH under acidic conditions is acetic acid, formic acid, oxalic acid, propionic acid, sulfuric acid, sulfurous acid, nitric acid, This is a pretreatment method for bleaching chemical pulp with an enzyme characterized by being one or more acids selected from nitrous acid.

 Furthermore, the liquid desorbed by the solid-liquid separation operation from the washing step after each treatment step is returned to the step before the treatment step, and finally the waste liquid is burned to recover the inorganic salt. This is a pretreatment method for bleaching of chemical pulp by sending enzymes. Further, the following additional processing steps (1) to (7), namely,

(1) In an aqueous medium using chlorine or chlorine dioxide or a mixture thereof Process

 (2) Step of treating in an alkaline aqueous medium using peroxide

 (3) Step of treating in an alkaline aqueous medium using peroxide and oxygen

(4) Step of treating in an aqueous medium using hypochlorous acid

 (5) Step of treating with ozone in gas or aqueous medium

 (6) Step of treating with thiourea dioxide in an alkaline aqueous medium

(7) Process of treating in an alkaline aqueous medium using hydrophyllite

This is a pretreatment method for bleaching chemical pulp with an enzyme that additionally performs

 As the enzyme used in the present invention, any enzyme having a xylanalytic activity can be used. More preferably, the enzyme is used on the acidic side, particularly at pH 4.5 or lower. Hemicellulase, cellulase, actinase, esterase or a mixture thereof having a sylanase activity can be used.

 In the treatment of the chemical pulp with these enzymes, the chemical pulp is adjusted to a concentration of not less than 2% by weight and less than 12% by weight, and the enzyme is used as a xylanase activity. 1 u Z pulp g or more, 100 u u / pulp less than g, preferably 1 u / pulp g or more, less than 100 u / pulp g, 0 ° C or more, preferably Alternatively, the treatment is performed at a temperature of 40 ° C or more for a time of 10 minutes or more.

 The first invention and the second invention of the present invention will be described in detail.

As described above, the enzyme treatment is performed on the unbleached pulp and the oxygen-delignified pulp prior to the conventional chlorine bleaching. However, when the treatment is performed in combination with the acid treatment, the effect is more enhanced. Is done. In other words, the enzyme treatment is performed before and after the acid treatment.If the treatment is performed after the acid treatment, the pH is not required to be adjusted.If the treatment is performed prior to the acid treatment, the acid treatment waste liquid is used. To Thus, the pH is adjusted. In these treatments, the sample is adjusted to a pH of less than 4.5, preferably less than 3.0. Of course, the effect can be obtained to some extent even in the pH range higher than this.

 Enzyme treatment has the function of breaking xylosid bonds in lignocellulose substances to elute lignin into wastewater, but there are some limitations to this function. You. The first is that the size of the enzyme molecules hinders the release of hemicellulose and the lignin that is deeply involved in the cellulosic matrix. It cannot act on the side bond, and its delignification degree is limited. In the study of the present inventors, the degree of delignification by enzymatic treatment was about 2.0 as the monovalent value of copper before and after treatment in hardwood KP, and the delignification degree exceeding this range was higher. Attempting to obtain a high degree of cell loss will result in a significant decrease in the yield of cellulose. Furthermore, such lignocellulose substances and enzymatic reactions require an excessive amount of time, reducing their industrial significance.

 Given the limitations of such enzymes, it is understood that additional processing to provide delignification is required. Therefore, the present inventors have considered applying an acidic treatment (hereinafter, also referred to as A or A step) together with the enzymatic reaction. The chemical pulp cooked mainly by the alkaline medium is structurally porous (alkaline swelling), and this structure In this case, the lignin can be effectively eluted from the pulp using various media effectively.

Addition of acid to this porous pulp can accelerate lignin dissolution. The reason is that in the case of mineral acids, the bond between lignin and sugar is broken by hydrolysis, and the acid hydrolysis of low molecular weight hemicellulose causes lignin. It is intended to make it easy to move. In the case of organic acids, affinity with lignin facilitates elution. The acids that can be used for this purpose are organic acids such as acetic acid, formic acid, oxalic acid and propionic acid, and the inorganic acids are sulfuric acid, sulfurous acid, nitric acid, nitrous acid and the like.

 Treating with an acid also has another effect. The acid dissolves the metal salts in the pulp and is removed in the next washing step. This removes heavy metals, especially transition metals, from the pulp, preventing decomposition of the oxidizing agent in the next hydrogen peroxide stage and the zoning stage, and reducing the amount of hydroxy radical. It can suppress the production of active chemical species that attack fibers. This increases the bleaching effect and prevents a decrease in the degree of polymerization of the pulp.

 The present invention is to improve the bleaching effect without reducing the pulp quality by combining the respective effects of an acid and an enzyme.

 When an acid-resistant enzyme is used together with an acid, these effects can be obtained simultaneously in a single step, which contributes to shortening of the process.

 Attempts to extract lignin with these acids from lignocellulose substances that had been subjected to oxygen bleaching after cooking resulted in a delignification of about 2 as a hopper value before and after the treatment. It became clear that the degree could be given. By subjecting the lignocellulose material thus obtained to an enzymatic treatment, it can be used for general purposes without a decrease in viscosity due to slight additional bleaching after this. It is possible to reach the required whiteness.

The reaction conditions for the acid treatment are 10 minutes or more, preferably 30 minutes or more and less than 3 hours, the temperature is 20 ° C or more, preferably 40 ° C or more, and 80 ° C or less, and the pulp concentration is Performed at 3% or more and less than 20%. This acid treatment provides a unique degree of delignification even after the enzyme treatment, and its effect is comparable to that obtained before the enzyme treatment. By adding peroxide to this acid treatment (hereinafter referred to as Ap or Ap process), delignification and bleaching can be advanced remarkably. Acids and hydrogen peroxide form peracids under certain conditions, It is known that it reacts with lignin differently to decompose it. In this case, it is also effective acidic treatment of _c further this generation of peracid is accelerated by the this adding a small amount of a mineral acid (such as sulfuric acid) is Tsu bets to turn zone phosphorylation of chemical pulp. Ozone reacts with almost all organic substances and water. The reaction proceeds via intermediates such as peroxides, epoxides and hydroxyradicals, some of which have a bleaching action. Ozone preferentially reacts with aromatic core olefin groups, i.e. selectively attacks lignins with these-but with little or no lignin If the probability of is low, it also attacks carbohydrates, ie fibrous. In particular, if the pH is not properly controlled, the fibers will be violently attacked even if lignin is abundant. This is thought to be because the higher the pH, the greater the amount of hydroxyradical produced by ozone degradation. In applying such ozone bleaching, it is essential to adjust the ρH to the acidic side before the application, but as the pretreatment, the acid treatment described above and the It is reasonable to apply an enzyme treatment that is active on the combined acid side. The presence of metals, especially transition metals and their salts, in the system accelerates ozone degradation, increasing carbohydrate attack and impairing pulp quality. To prevent this, removal of metals with an acid or addition of a metal chelate is used.

In addition, hydrosulfite may be used as a reducing bleach. This chemical is susceptible to oxidation, and high concentrations of pulp generally bleach at a pulp concentration of about 4% because they are less likely to be exposed to oxygen in the air. At such a low concentration, even if an attempt is made to increase the amount of hydrosulfite added to achieve high whiteness, the concentration in the liquid should be so high due to the large amount of water. The improvement in whiteness is limited, and the color return after bleaching is large. Thiourea dioxide is a white powder that is stable at room temperature and has no reducing property. It is decomposed by heat or algal force to generate sulphinic acid and exerts a strong reducing power. Therefore, unlike hydrosulfite, there is no danger of oxidative decomposition, and the same reduction bleaching agent can be obtained by adding and heating alkali at the same time as adding urea dioxide and urea. It is possible to obtain pulp with high brightness that cannot be obtained with hydrosulfite.

 Bleaching with thiourea dioxide (hereinafter also referred to as the FAS and FAS steps). The conditions are as follows. In other words, the chemical stability effect of thiourea dioxide on pulp concentration (concentration of pulp in water) is larger than that of hydrosulfite. The whiteness improves because the concentration of the drug solution can be increased. If the concentration is further increased to a high concentration of about 30%, the whiteness will decrease again, so the reaction concentration with pulp is preferably 10 to 20%. The decrease in whiteness at higher concentrations is due to air oxidation, as is the case with hydrosulfite. For this reason, even at this concentration, there is no decrease in whiteness when the air is replaced with nitrogen. The reaction temperature was tested at 40 ° C (: 60 ° C, 80 ° C, and as a result, 80 ° C was the best force. The reaction is not practical as this kind of treatment method, and is practically in the range of 50 to 100 ° C. In the present invention, the reaction time is 15 minutes. Since the whiteness increases in 60 minutes, the whiteness rises sufficiently in 60 minutes, and the whiteness decreases in 24 hours of treatment, so the range of 10 to 90 minutes is a preferable range.

 Further, the third invention of the present invention will be described in detail.

The effect of the xylanases used in the present invention is limited by PH. Departures from that pH range will result in loss of activity accordingly. Such characteristics are considered to be various problems due to pH adjustment when considering application to pulp bleaching pretreatment. This is inconvenient in obtaining the desired delignification effect.

 That is, the first stage of the subsequent bleaching is most often chlorine or chlorine dioxide or a mixture or ozone, both of which are acidic to less than pH 5 to strongly acidic. This is the step in which the reaction takes place. In this way, when the immediately preceding enzymatic treatment step is performed with neutral or alkaline, the wastewater from the subsequent treatment step performed on the acidic side including chlorination is subjected to enzymatic treatment in a countercurrent manner. It cannot be returned to the stage and used effectively. Considering the enzyme treatment as a pre-process of the bleaching treatment performed on the acid side, when the conventional xylanases are used, the optimum pH is too high, and the purpose of enzyme application is sufficiently achieved. I can't do this.

 For this reason, the present inventors have devised to shift the active pH region of the enzymatic reaction to a strongly acidic region, and have reached the present invention.

 The present inventors use a highly acid-resistant xylanases (acid-resistant enzymes) to treat unbleached or oxygen bleached pulp, followed by chlorine or chlorine dioxide or any of these. Post-bleaching was performed under acidic conditions starting with the mixture or ozone to obtain a high whiteness pulp that could be used as a raw material for printing and writing paper. Then, it was confirmed that the waste liquid of the acidic bleaching stage can be used countercurrently in the enzyme treatment stage. The acid-resistant xylanases show sufficient xylanolytic activity even at pH 2.0 or lower, and even when pulp is prepared and treated in this pH range, delignification occurs. It was confirmed that it was effective. That is, the enzyme used in the present invention preferably has an optimum pH of 4.5 or less, and includes, for example, xylanases "Amano" P (manufactured by Amano Pharmaceutical Co., Ltd.). .

According to the present invention, not only is it possible to obtain an easily bleached pulp with a low lignin content in a single treatment, but also it is possible to perform ozone treatment (hereinafter referred to as Z or Z step) in the preceding and subsequent steps. Such acid treatment does not require special acidification. Processing can be performed continuously. In particular, it is said that the ozone treatment is preferably carried out at a pH of less than 3.0, and a bovine cyanase having an activity at a pH of 4.5 or less, or preferably less than pH 3.0, is preferred. The treatment of the present application using the main enzyme is extremely effective and can reduce the amount of ozone used to damage fibers. In addition, if the subsequent process contains hydrogen peroxide, the extraction with acid can remove the substances that decompose hydrogen peroxide such as heavy metals in the system in advance, so the effect of hydrogen peroxide is maximized. Can be withdrawn. In addition, the delignification effect of the enzyme can significantly reduce the addition of expensive hydrogen peroxide.

 In the case of the present invention, most of the washing waste liquid can be recovered in the digestion black liquor recovery system and burned. Various acids, enzymes, hydrogen peroxide, ozone, and urea dioxide are all combustible chemicals in conventional recovery boilers. When ozone is used in the first stage of bleaching, it is known that various organic acids are contained in the washing wastewater of this stage, and sulfuric acid is also included for pH adjustment. . It is possible to use this waste liquid for acid treatment.It is possible to reduce the supply of fresh water from the outside by using the washing waste liquid in these steps in a countercurrent manner, in addition to adjusting the acidity of the enzyme treatment stage. This makes it possible to reduce the load on the vacuum evaporator when it is recovered as cooked black liquor.

Although various waste liquids according to the present invention are substances that can be sufficiently recovered in the recovery system as described above, if they are sent to the recovery system as they are, the combustion solid content will be low, and the entire waste liquid will be recovered. The load on collection increases. Specifically, the capacity of the vacuum evaporator may be insufficient. In addition, the pH of the black liquor may be lowered due to the acid, and the viscosity of the black liquor may increase, which may cause problems such as poor flow. For this reason, in some cases, washing wastewater such as the above-mentioned acid treatment, ozone treatment, enzyme treatment, hydrogen peroxide treatment, etc. separates and concentrates high molecular substances in the wastewater by membrane separation. May be applied. In particular, the various acids used in the acid treatment can be used by distilling and reusing the effective acid by distillation, and then the waste liquid residue can be sent to the combustion treatment.

 In one embodiment of the method of the present invention, the treatment with xylanase active on the acidic side and the acidic treatment applied in the present invention may be performed by selecting one of the following groups (1) to (7): One or more additional processing steps are performed. That is,

 (1) Process of treating in an aqueous medium using chlorine or chlorine dioxide or a mixture thereof

 (2) Step of treating in an alkaline aqueous medium using peroxide

 (3) Step of treating in an alkaline aqueous medium using peroxide and oxygen

(4) Step of treating in an aqueous medium using hypochlorous acid

 (5) Step of treating with ozone in gas or aqueous medium

 (6) Step of treating with thiourea dioxide in an alkaline aqueous medium

(7) The process of treating in an alkaline aqueous medium using hydrophyllite

Selected from the group consisting of

 In practicing the method of the present invention, these additional treatments are conventionally performed in the art of pulp bleaching, or are performed by any known reasonable method. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the bleaching flow of the present invention. The solid line is the tip where pulp is processed. (A), (b) and (c) are processing flows corresponding to claim 1, claim 2 and claim 3, respectively. The dashed line is a flow in which the treatment liquid desorbed by the solid-liquid separation operation from the washing step is returned countercurrently to the previous step. Explanation of reference numerals

 1 Acid treatment

 2 Enzyme treatment

 3 Acid-resistant enzyme treatment

 4 BEST MODE FOR CARRYING OUT THE INVENTION

 The present invention will be described with reference to the following examples, but the present invention is not limited to these examples. In the following, oxygen treatment is 0, acid treatment is Α, enzyme treatment is X, treatment with acid-resistant enzyme is Xa, treatment with hydrogen peroxide is combined with aluminum oxide treatment, Ep is hypochlorite treatment. Is H and chlorine dioxide treatment is D. Parts in Examples and Comparative Examples indicate parts by weight. Unless otherwise specified,% of pulp concentration is the percentage by weight of oven-dried at 105 ° C, and% of addition of chemicals etc. is the percentage by weight based on the pulp.

 Measurement of parameters overnight to characterize and specify the chemical pulp handled in the present invention The test was performed by the following standard method.

Copper monovalent T A P P I test method T—236 M-76

Viscosity T A P P I Test method T-230 0M-82

Whiteness JISP 8127 (Hunter whiteness)

 The xylanase activity of the enzyme used in the method of the present invention was determined by the following method. (Operation)

Xilan (manufactured by Seikagaku Corporation) Add 0.50 g of water to about 30 ml, stir and heat to dissolve.After cooling, add water to make 50 ml, and use this as the substrate. Used. For acid-resistant enzymes, use 0.1 N tartrate buffer (pH 8) Transfer 3 ml and 1 ml of the substrate to a 50 ml stoppered Nesler tube, place in a constant temperature water bath of 40 minutes, leave it for 5 minutes or more, add 1 ml of the sample solution, and immediately Shake. Leave this solution at 40 ° C for 30 minutes, add 2 ml of somogy solution, shake, seal, and heat in a boiling water bath for 20 minutes, then immediately cool. After cooling, add 1 ml of arsenic and ammonium molybdate solution, shake well until the red precipitate of cuprous oxide completely dissolves, leave at room temperature for 20 minutes, and remove water. Add 25 ml and shake well. Approximately 8 ml of this solution was weighed into a 15 ml centrifuge tube, separated by a refrigerated centrifuge (300 rpm, 25 ° C, 10 minutes), and the supernatant was layer-length 10 mm. The absorbance A30 at a wavelength of 500 nm is measured using water as a control solution. Separately, 3 ml of 0.1 N tartrate buffer (pH 1.8) and 1 ml of the substrate are mixed with 2 ml of the somology solution, shaken, and then mixed with 1 ml of the sample solution. Measure AO.

In the case of Xylana cellulase "Amano" CT-4, instead of 0.1 N tartrate buffer (PHI.8), use 0.1 N acetic acid and sodium acetate. Use buffer solution (PH 4.5).

 (Activity calculation method)

 Under the above conditions, the time at which a reducing sugar corresponding to 1 mg of xylose is produced per minute is defined as 100 units, and is calculated by the following equation.

 Xylanase activity u / g = X x (1/30) X 100 Xn

X: The amount of xylose produced (mg), determined from the xylose calibration curve from the (A30-AO) value; n: the sample dilution factor; 1Z30, 100: conversion factor.

Example 1

Bleaching in the order of 0-A-X-Ep-H-D processing steps: 100 parts of hardwood kraft pulp after oxygen delignification was bleached in the process sequence of 0-A-X-Ep-H-D. The amount and conditions of drug addition were as follows.

 Process 0: 1.8 parts of sodium hydroxide was added, and the pulp adjusted to a concentration of 10% was sealed in a closed autoclave equipped with a high-speed stirring mixer (Toshiba Autoclave). 1.6 parts of oxygen was injected into the mixture, and the mixture was stirred at 105 ° C for 1 minute at first, and then kept under pressure and sealed for 1.5 hours to react. After the reaction, the mixture was diluted with water to 1%, and filtered and washed on a Buchner funnel with 5 A filter paper. The pulp after this treatment had a monovalent copper value of 9.4 and a viscosity of 24.4 cps.

 Step A: Pulp prepared by adding 25 parts of acetic acid to a concentration of 10% was reacted at 70 ° C. for 1.5 hours. After the reaction, the mixture was diluted to 1%, and filtered and washed with 5A filter paper on a Buchner funnel.

 After this treatment, the pulp had a monovalent copper value of 8.0 and a viscosity of 22.2 cps.

 Step X: Enzyme (Xylanases with an optimal pH of 5.5 [cellulase “Amano” CT-4): Amano Pharmaceutical: Xylanases activity 100,000 u / g (pH 4.5)]) 0.015 parts was added, and the pulp prepared at a concentration of 10% was reacted at 50 ° C for 3 hours. After the reaction, the mixture was diluted to 1%, and filtered and washed with 5 A filter paper on a Buchner port. After washing, the copper monovalent was 6.4 and the viscosity was 20.8 cps.

Ep process: 0.8 part of sodium hydroxide and 0.15 part of hydrogen peroxide were added, and the pulp prepared at a concentration of 12% was reacted at 65 ° C for 1.5 hours. Let me know. After the reaction, the mixture was diluted to 1%, and filtered and washed with 5A filter paper on a Buchner funnel. Step H: 0.8 part of sodium hypochlorite was added, and the pulp prepared at a concentration of 10% was reacted at 65 ° C for 2 hours. After the reaction, the mixture was diluted to 1%, filtered and washed on a Buchner filter with 5 A filter paper.

 Step D: Pulp prepared by adding 0.6 parts of chlorine dioxide to a concentration of 10% was reacted at 65 ° C for 2 hours. After the reaction, the mixture was diluted to 1%, and filtered and washed with 5A filter paper on a Buchner funnel.

 The pulp after the final treatment obtained after the final chlorine dioxide treatment (D) step had a whiteness of 86.0% and a viscosity of 16.5 cps. The amount of adsorbable chlorinated organic matter (A0X) in the bleaching solution was 0.85 kg per It pulp.

 As described above, it was confirmed that hardwood bleached pulp having standard whiteness and viscosity can be produced without using molecular chlorine. Example 2

 0 — A — X — Ep — H — D bleaching in the order of the processing steps: Cellulase for bleaching pretreatment manufactured by Amano Pharmaceutical in step X The same operation as in Example 1 was carried out except that 0.15 part was added instead of cellulase 90, xylanase activity 100, and oo uZ enzyme g). The pulp obtained after the final treatment obtained after the final chlorine dioxide treatment (D) step had a whiteness of 85.8% and a viscosity of 16.8 cps. The amount of A0X in the bleaching solution was 0.87 kg / t of pulp.

As described above, by using hemicellulase as an enzyme, bleached hardwood pulp having standard whiteness and viscosity can be produced without using molecular chlorine. This was confirmed. Reference Example 1 Bleaching of process sequence of 0_C-Ep-H-D by conventional method: 100 parts of hardwood pulp after oxygen delignification as in Example 1 tried. The treatment was performed in the same manner as in Example 1 except that the acid treatment (A) and the enzyme treatment (X) were not performed, and the chlorination treatment (C) was performed.

 Step C: 1.4 parts of chlorine was added, and the pulp prepared at a concentration of 3% was reacted at 50 ° C for 0.5 hours. After the reaction, the mixture was diluted to 1%, filtered and washed with 5 A filter paper on a Buchner port.

The pulp after the final treatment obtained after the final chlorine dioxide treatment (D) step had a brightness of 84.4% and a viscosity of 16.8 cps. The amount of A0X in the bleaching solution is The weight was 2.1 kg per ton of Norep.

 As described above, when the acid treatment and the enzyme treatment are used in combination (Examples 1 and 2), the same bleaching viscosity is lower than the result obtained by the conventional bleaching method using chlorine (Reference Example 1). It is clear that the amount is A0X. Comparative Example 1

 Bleaching of process sequence of 0-X-Ep-H-D by conventional method: 100 parts of hardwood pulp after oxygen delignification as in Example 1 were tested. The treatment was performed in the same manner as in Example 1 except that the acid treatment (A) was not performed. The copper monovalent after the enzyme treatment (X) was 7.1 and the viscosity was 23.5 cps.

 The pulp after the final treatment obtained after the final chlorine dioxide treatment (D) step had a whiteness of 82.6% and a viscosity of 16.3 cps.

As described above, when chlorine is not used only by the enzyme treatment, a lower whiteness is obtained than in the present invention (Examples 1 and 2) and the method using the conventional chlorine (Reference Example 1). This is clear. Example 3

 Bleaching of O-X-A-Ep-H_D treatment process sequence: The treatment was performed in the same manner as in Example i except that the order of the acid treatment and the enzyme treatment was changed. In the enzyme treatment, pulp was prepared at a pH of 3.0 or less using the waste liquid after washing in the acidic treatment in Example 1.

After the acid treatment (A), the copper monovalent value was 6.4 and the viscosity was 20.8 cps.

 The pulp obtained after the final treatment obtained after the final treatment with chlorine dioxide (D) had the following properties.

 Whiteness 85.8% Viscosity 16.9 cps

 As described above, it is apparent that higher whiteness can be obtained with the same pulp viscosity than Comparative Example 1. Example 4

 Bleaching of processing sequence of 0—Ap—X—Ep—H—D: The treatment was performed in the same manner as in Example 1 except that in the acid treatment (A), hydrogen peroxide was combined (Ap).

 Ap process: 25 parts of acetic acid and 0.3 part of hydrogen peroxide were added, and the pulp prepared at a concentration of 10% was reacted at 70 ° C for 1.5 hours. After the reaction, the mixture was diluted to 1%, and filtered and washed with 5A filter paper on a Buchner port.

After acid treatment (Ap), the monovalent force was 3.8 and the viscosity was 18.8 cps.

The monovalent copper value after the enzyme treatment was 2.4, and the viscosity was 16.4. The pulp after the final treatment obtained after the final chlorine dioxide treatment (D) process had a whiteness of 89.8% and a viscosity of 14.8 cps. As described above, it is clear that significantly higher whiteness can be obtained than in Comparative Example 1. Example 5

 A—X—C—Ep—H—Bleaching of the processing sequence of D: Except for step 0, set the reaction temperature in step A to 40 ° C, and make the copper monovalent after enzyme treatment (X). The procedure was the same as in Example 1 except that step C was introduced accordingly and the amount of chlorine added was adjusted.

 The pulp obtained after the final treatment obtained after the final chlorine dioxide treatment (D) step had a brightness of 86.2% and a viscosity of 16.8 cps. Reference example 2

 Bleaching of the processing sequence of C-Ep-H-D:

 Example 5 was repeated except that steps A and X were omitted and the amount of chlorine added in step C was increased. This comparative example corresponds to the conventional method without oxygen bleaching. The pulp obtained after the final chlorine dioxide step has the following properties:

 As compared with the conventional bleaching method using chlorine (Reference Example 2), the whiteness is 85.5% and the viscosity is 13.5 cps or more. In addition, the use of molecular chlorine required to achieve general whiteness can be reduced by about 40%. Example 6

A-X-C_Ep—H—D bleaching process sequence: Set the reaction temperature of process A to 2 All operations were performed in the same manner as in Example 5 except that the temperature was changed to 0 ° C.

 The pulp after the final treatment obtained after the final chlorine dioxide treatment (D) step had a whiteness of 85.9% and a viscosity of 15.4 cps.

 As can be seen from comparison with Example 5, the reaction temperature in Step A is preferably 40 or more. Example 7

 Bleaching of processing sequence of A—X—C—Ep—H—D: Same as Example 5 except that the reaction time in Step A was 10 minutes except for Step 0.

 The pulp obtained after the final treatment obtained after the final chlorine dioxide treatment (D) step had a brightness of 86.3% and a viscosity of 16.5 cps.

 As described above, even if the time of the step A is shortened to 10 minutes, the steps A and X of the present invention can be incorporated as compared with the conventional bleaching method using chlorine (Reference Example 2). As a result, the amount of molecular chlorine used to obtain general-purpose whiteness can be reduced by about 36%. In Examples 5, 6, and 7, the chlorine addition rate was adjusted so that the final whiteness was the same. Example 8

 Bleaching of A—X—C—Ep—HD—D processing step sequence: The operation was performed in the same manner as in Example 7 except that the reaction time in step A was 3 minutes and the amount of chlorine added was adjusted. The pulp after the completion of the entire treatment, obtained after the final chlorine dioxide treatment (D) step, had a brightness of 86.1% and a viscosity of 14.8 cps.

In comparison with Example 7, the amount of chlorine required to reach the same whiteness was increased, and the reaction time in Step A was preferably 10 minutes or more. Example 9, Comparative Example 2

 All operations were carried out in the same manner as in Example 1 except that the amount of acetic acid added in Step A was changed to 6 parts in Example 9 and 3 parts in Comparative Example 2.

 Under these conditions, the pH of the sample in step A increased from 2.2 in Example 1 to 4.5 in Example 9 and to 7.0 in Comparative Example 2. The pulp after the final treatment obtained after the last chlorine dioxide treatment (D) step had the following characteristics. Example 9 Whiteness 84.1% Viscosity 16.3 cps

 Comparative Example 2 Whiteness 82.6% Viscosity 16.5 cps

Example 10

 Bleaching of processing sequence of 0 — A — X — Ep — H—D: All operations were performed in the same manner as in Example 1 except that the acid added in Step A was changed to sulfuric acid.

 The pulp after the final treatment obtained after the final chlorine dioxide treatment (D) step had a brightness of 86.4% and a viscosity of 16.3 cps.

 Good results were obtained with sulfuric acid as the acid in step A.

 Further, as can be seen from the comparison with Example 9, only a low whiteness pulp can be obtained in Comparative Example 2. From this, the treatment pH in the step A needs to be 4.5 or less, and preferably, 3.0 or less. Example 1 1

 0-Xa—Ep-H-D processing sequence bleaching:

 The hardwood pulp after oxygen delignification was tested. This pulp was bleached in the bleaching process of 0-Xa-Ep-H-D. The amounts and conditions of drug addition were as follows.

Step 0: Performed in the same manner as in Example 1. The pulp strength after this treatment is 9. 4. The viscosity was 24.4 cps.

 Step Xa: Xylanases “Amano” P [Amano Pharmaceutical Acid-Resistant Enzyme: Xylana-Xase Activity 8,000 u / g (Hl.8)] 0.01 5% was added, and 11 was adjusted to 1.8 with acetic acid at a concentration of 10%. A pulp sample was reacted at 50 ° C for 3 hours. After the reaction, the mixture was diluted to 1% and filtered and washed with 5 A filter paper on a Buchner port. After washing, the monovalent copper value was 6.8, and the viscosity was 20.2 cps. Step Ep, Step H, Step D: Performed in the same manner as in Example 1.

 The pulp obtained after the last step of chlorine dioxide treatment (D) had a whiteness of 85.5% and a viscosity of 16.5 cps.

 The A0X of the bleaching wastewater was 0.86 kg per rep.

 As described above, by adding treatment with an enzyme that is active on the acidic side, bleached hardwood pulp with standard whiteness and viscosity can be produced without using molecular chlorine. Was confirmed. Example 1 2

 Bleaching of processing sequence of 0-A-Xa-Ep-H-D: Hardwood pulp after oxygen delignification was tested. This pulp was bleached in a bleaching process using 0—A—Xa_Ep—HD. The addition amount and conditions of the drug were as follows.

 Step 0: Performed in the same manner as in Example 1. After the treatment, the pulp had a power value of 9.4 and a viscosity of 24.4 cps.

 Step A: Performed in the same manner as in Example 1. After this treatment, the pulp had a power value of 8.0 and a viscosity of 22.2 cps.

Step Xa: A pulp sample prepared by adding the same enzyme used in Example 11 (0.015%) and adjusting the pH to 1.8 and 10% with acetic acid at 50 ° C for 3 hours React I let you. After the reaction, the mixture was diluted to 1% and filtered and washed on a Buchner funnel with 5 A filter paper. After washing, the monovalent copper value was 6.1 and the viscosity was 19.8 cps. Step Ep, Step H, Step D: Performed in the same manner as in Example 1.

 The pulp obtained after the last step of chlorine dioxide treatment (D) had the following characteristics.

 Whiteness 86.9% Viscosity 16.3 cps

 A0X of the bleaching effluent was 0.8 lkg per pulp It.

 As described above, it was confirmed that hardwood bleached pulp having standard whiteness and viscosity can be produced without using molecular chlorine. In addition, it was confirmed that the enzyme treatment having an activity of pH 4.5 or lower was used more effectively by being used in combination with the acid treatment. Comparative Example 3

 Bleaching of processing sequence of 0—X—Ep—H—D: The same hardwood pulp as in Example 11 was used. Xylanase with an optimal pH of 5.5 for enzyme treatment [Cellulase "Amano" CT-14: Amano Pharmaceutical: Xylanaase activity 100,000 0 u / g (pH 4.5)]. The monovalent copper value after the enzyme treatment was 8.2, and the viscosity was 22.3 cps.

 The pulp obtained after the final chlorine dioxide step had the following properties:

 Whiteness 83.4% Viscosity 16.1 cps

As is clear from the comparison with Example 11, Comparative Example 3 used the conventional enzyme having an optimum pH of 5.5 and was treated with the enzyme at a lower condition than the pH of 4.5. When chlorine bleaching is omitted, a lower brightness than the conventional one is obtained. Example 13

 Bleaching of O-Xa-A-Ep-H-D treatment process sequence: The order of the acid treatment and the enzyme treatment was changed. 4.5 The treatment was performed in the same manner as in Example 12 except that the pulp was prepared as follows. At this time, the monovalent value after the enzyme treatment was 6.1, and the viscosity was 19.8 cpS.

 The pulp obtained after the final chlorine dioxide step had the following properties:

 Whiteness 86.7% Viscosity 16.7 cps

 As described above, it is clear that pulp with high whiteness can be obtained by the conventional bleaching method using chlorine in this method as well. Example 14

 A—Xa—C—Ep—H—D bleaching in the order of the processing steps: Example 12 except that the reaction temperature in step A was 40 ° C except for step 0, and step C was added. Same as. The amount of chlorine added in step C was adjusted according to the power value after the enzyme treatment.

 The pulp obtained after the final chlorine dioxide step had the following properties:

 Whiteness 87.1% Viscosity 16.6 cps

As described above, compared to the conventional bleaching method using chlorine without using acid treatment and enzyme treatment (Reference Example 2), the method is more versatile by incorporating the steps A and Xa of the present invention. The use of molecular chlorine required to achieve a high degree of whiteness can be reduced by about 35%. Example 15

 Bleaching of O—A—Z—Xa—Ep—H—D processing sequence: Processing was performed in the same manner as in Example 12 except that the ozone treatment was combined.

 Z process: Pulp prepared with ozone (ozone concentration 5%) generated from an ozone generator (Ozon Japan) at a concentration of 10% is referred to as “Tohoku Hi-Shiichi” 0.4% of pulp equivalent is filled in an auto crepe equipped with a late stirring device, and then nitrogen gas is introduced into the auto crepe to adjust the total pressure to 5 bar and the temperature is 35 ° C. And stir for 30 seconds. To complete the reaction, the pulp was then removed, diluted to 1%, and filtered and washed with 5A filter paper on a Buchner outlet. After this ozone treatment, the monovalent copper value was 3.9 and the viscosity was 17.8.

 The pulp obtained after the final chlorine dioxide process had the following characteristics.

 Brightness 88.8% Viscosity 15.6 cps

 As described above, it is clear that pulp with significantly higher whiteness can be obtained in this method than the conventional bleaching method using chlorine.

The above results are summarized in the table.

1

Two

* Caroline so as to obtain the desired PH Three

* Add to the desired pH Table 4 Table 5

 Example 15 Bleaching process OAZXaEpHD Unbleached pulp. Monovalent 18.5 Test si material Viscosity c p S 28.5

0 Oxygen% 1.6

 NaOH% 1.8 Pulp concentration% 10 Temperature ° C 105 hours hr 1.5

Pach. Monovalent 9.4 viscosity c ps 24.4

A Acetic acid% 25 Peroxide% Pulp concentration% 10 Sample PH 2.2 Temperature ° C 70 hours hr 1.5 Mohc monovalent 8.0 Viscosity cp S 22.2

Z ozone% 0.4 pulp concentration% 10 temperature ° C 35 hours hr 0.5 force monovalent 3.9 viscosity cp S 17.8

Xa enzyme% 0.015 acetic acid% *? Pulp concentration% 10 Sample PH 1.8 Temperature ° C 50 hours hr 3 Power 3.2 Viscosity cp S 16.9

C chlorine%

 Pulp concentration%

 * D pH adjustment with A treatment waste liquid and acetic acid Temperature ° C

*? Addition time hr so that desired pH is achieved. * 3 Since the conditions of Ep HD are common to all cases, Ep HD 3

After completion of all treatments, summarized in Table 6 Whiteness% 88.8 Viscosity cp S 15.6 Process Item Value

E p N a 0 H% 0.8

 H 2 0 2% 0.15 Parf concentration% 1 2 Temperature ° C 65 hours hr 1.5

H Hypo% 0.8 pulp concentration% 10 Temperature 65 hours hr 2

D 2 chlorine oxide% 0.6 pulp concentration% 10 temperature ° c 65 hours hr 2

Industrial applicability

 According to the method of the present invention, there is provided a bleached chemical pulp having brightness and viscosity equivalent to those found in pulp bleached by a conventional method. Also, even higher whiteness levels can be practically achieved using the methods described herein. According to the method described herein, bleaching to a level of conventional whiteness is achieved even with the use of further reduced amounts of the chlorine-containing compound and without the use of molecular chlorine. Pulp can be produced, and as a result, pollutants such as dioxin discharged from the pulp step using the method of the present invention are reduced. According to the method of the present invention, an opportunity is provided to recycle the organic substance removed from the bleaching step to the waste liquid collecting step in the pulping step, thereby reducing the degree of contamination.

Claims

The scope of the claims

1. A pretreatment method for bleaching chemical pulp with an enzyme, which comprises subjecting unbleached chemical pulp to an acidic treatment, followed by washing and treatment with an enzyme containing xinalase.

 2. A pretreatment method for bleaching chemical pulp using an enzyme, which comprises treating unbleached chemical pulp with an enzyme containing xinalase, then subjecting it to an acid treatment, and then washing it.

 3. Unbleached chemical pulp should be treated with an enzyme containing xylanases having an optimum pH below pH 4.5 under conditions of pH below 4.5, and then washed. A pretreatment method for bleaching chemical pulp with a characteristic enzyme.

 4. The method according to claim 1 or 2, wherein the enzyme used is an enzyme containing xylanases having an optimum pH of pH 4.5 or lower, and the treatment with the enzymes is carried out at pH 4. .5 A pretreatment method for bleaching chemical pulp with an enzyme, which is performed in the following.

 5. The pretreatment method for bleaching chemical pulp with enzymes according to claim 1, 2, 3, or 4, wherein the unbleached chemical pulp is unbleached pulp or oxygen bleached pulp.

 6. A pretreatment method for bleaching chemical pulp with an enzyme, characterized in that hydrogen peroxide is added to the step of maintaining under acidic conditions according to claim 1, 2 or 4.

 7. A pretreatment method for bleaching chemical pulp with an enzyme, wherein an ozone is added to the step of maintaining under acidic conditions according to claim 1, 2 or 4.

8. Claims 1, 2, 3, 4, 5, 6 or 7 wherein the acid used to bring the pH under acidic conditions is acetic acid, sulfuric acid, oxalic acid, propionic acid, sulfuric acid, A pretreatment method for bleaching chemical pulp with an enzyme, characterized in that it is one or more acids selected from sulfurous acid, nitric acid, and nitrous acid.

 9. In claim 1, 2, 3, 4, 5, 6, or 7, the liquid desorbed by the solid-liquid separation operation from the washing step after the processing in each processing step is a step before the processing step. A method for pretreatment of chemical pulp bleaching with enzymes that is sent back to the process of recovering inorganic salts by burning the waste liquid.

 1 0. Claims 1, 2, 4, 5, 6 in which one or more additional processing steps selected from the group consisting of the following (1) to (7) are additionally performed. A pretreatment method for bleaching chemical pulp with the enzyme according to any one of 7, 8 and 9.

 (1) A step of treating with chlorine or chlorine dioxide or a mixture thereof in an aqueous medium

 (2) Step of treating in an alkaline aqueous medium using peroxide

 (3) Step of treating in an alkaline aqueous medium using peroxide and oxygen

(4) Step of treating in an aqueous medium using hypochlorous acid

 (5) Step of treating with ozone in gas or aqueous medium

 (6) Step of treating with thiourea dioxide in an alkaline aqueous medium

(7) Treatment in an alkaline aqueous medium using hydrophyllite