CN114174589B - Method for producing bleached pulp - Google Patents
Method for producing bleached pulp Download PDFInfo
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- CN114174589B CN114174589B CN202080054157.6A CN202080054157A CN114174589B CN 114174589 B CN114174589 B CN 114174589B CN 202080054157 A CN202080054157 A CN 202080054157A CN 114174589 B CN114174589 B CN 114174589B
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
- D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
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Abstract
The present invention provides a novel method for producing bleached pulp having excellent overall performance such as whiteness and discoloration resistance. The above-described problems are solved by the following method for producing bleached pulp. That is, the method for producing bleached pulp of the present invention comprises: a cooking step of cooking a lignocellulosic material; an oxygen-alkali bleaching step of subjecting the unbleached pulp obtained by the cooking step to oxygen-alkali bleaching; and a chlorine dioxide treatment step of treating the pulp obtained in the oxygen-alkali bleaching step with chlorine dioxide under conditions using monopersulfuric acid, wherein the pH of the treatment liquid in the chlorine dioxide treatment step is in the range of 2 to 8.
Description
Technical Field
The present invention relates to a method for producing bleached pulp using a lignocellulose substance derived from wood or the like as a material.
Background
A method for producing bleached pulp for papermaking is known in the art (for example, patent documents 1 to 5). In conventional methods for producing bleached pulp, unbleached pulp is subjected to various treatments to produce bleached pulp.
Documents of the prior art
Patent document
Patent document 1: WO2009/081714 publication
Patent document 2: WO2007/132836 publication
Patent document 3: japanese unexamined patent publication No. 2010-270410
Patent document 4: japanese unexamined patent publication No. 2010-265564
Patent document 5: japanese patent laid-open No. 2008-088606
Disclosure of Invention
Technical problems to be solved by the invention
In the conventional method for producing bleached pulp, there are various methods for treating unbleached pulp, and various combinations thereof are available. Accordingly, development of a novel method for producing bleached pulp having excellent various performances such as whiteness and discoloration properties as a whole has been desired.
Means for solving the problems
The present invention provides the following method for producing bleached pulp.
(1) A method of making bleached pulp comprising:
a cooking step of cooking a lignocellulosic material;
an oxygen-alkali bleaching step of subjecting the unbleached pulp obtained by the above cooking step to oxygen-alkali bleaching; and
a chlorine dioxide treatment step of treating the pulp obtained by the oxygen-alkali bleaching step with chlorine dioxide under the condition of monopersulfuric acid,
the pH of the treatment liquid in the chlorine dioxide treatment step is in the range of 2 to 8.
(2) The method for producing bleached pulp according to (1) above, wherein in the chlorine dioxide treatment step, the addition amount of monopersulfuric acid is 0.01 to 2.00 mass% per unit mass of the oven dry pulp, and the addition amount of chlorine dioxide is 0.01 to 2.00 mass% per unit mass of the oven dry pulp.
(3) The method for producing bleached pulp according to the item (1) or (2), wherein the time of the chlorine dioxide treatment step is 20 to 200 minutes, and the temperature of the chlorine dioxide treatment step is 40 to 70 ℃.
(4) The method for producing bleached pulp according to any one of (1) to (3) above, wherein the bleached pulp is paper pulp.
(5) The method for producing bleached pulp according to any one of (1) to (4) above, further comprising a pH measurement step of measuring a pH value of a treatment liquid to be treated in the chlorine dioxide treatment step.
(6) The method for producing bleached pulp according to any one of (1) to (5) above, wherein the pH value before treatment, which is the pH value of the treatment liquid before treatment in the chlorine dioxide treatment step, and the pH value after treatment, which is the pH value of the treatment liquid after treatment, are both in the range of 2 to 8.
(7) The method for producing bleached pulp according to any one of (1) to (6) above, wherein a difference between a pre-treatment pH that is a pH of the treatment liquid before treatment in the chlorine dioxide treatment step and a post-treatment pH that is a pH of the treatment liquid after treatment in the chlorine dioxide treatment step is 3.0 or less.
(8) The method for producing bleached pulp according to (7) above, wherein the difference between the pH before the treatment and the pH after the treatment is 2.0 or less.
(9) A method of making bleached pulp comprising:
a cooking step of cooking a lignocellulosic material;
an oxygen-alkali bleaching step of subjecting the unbleached pulp obtained by the above cooking step to oxygen-alkali bleaching; and
a chlorine dioxide treatment step of treating the pulp obtained by the oxygen-alkali bleaching step with chlorine dioxide under the condition of monopersulfuric acid,
the pH value of the treating liquid in the chlorine dioxide treating step is in the range of 2 to 8,
when the pH value before treatment, which is the pH value of the treatment liquid before treatment in the chlorine dioxide treatment step, is 3.0 or less, the difference between the pH value before treatment and the pH value after treatment, which is the pH value of the treatment liquid after treatment in the chlorine dioxide treatment step, is 1.0 or less,
when the pre-treatment pH is higher than 3.0 and not more than 5.5, the difference between the pre-treatment pH and the post-treatment pH is not more than 2.0,
when the pre-treatment pH is higher than 5.5 and not higher than 8.0, the difference between the pre-treatment pH and the post-treatment pH is not higher than 2.5.
(10) The process for producing bleached pulp according to (9) above, wherein when the pH value before the treatment is 3.0 or less, the difference between the pH value before the treatment and the pH value after the treatment is 0.5 or less,
when the pre-treatment pH value is higher than 3.0 and not more than 5.5, the difference between the pre-treatment pH value and the post-treatment pH value is not more than 1.6,
when the pre-treatment pH is higher than 5.5 and not higher than 8.0, the difference between the pre-treatment pH and the post-treatment pH is not higher than 2.0.
(11) The method for producing bleached pulp according to any one of (1) to (10) above, wherein the ISO brightness of the bleached pulp after the chlorine dioxide treatment step is 60% or more.
(12) The method for producing bleached pulp according to any one of (1) to (11) above, wherein the K value of the bleached pulp after the chlorine dioxide treatment step is 1.50 to 4.50.
(13) The method for producing bleached pulp according to any one of (1) to (12) above, further comprising a K value measurement step of measuring a K value before treatment, which is a K value before treatment of the pulp to be treated in the chlorine dioxide treatment step, and a K value after treatment, which is a K value after treatment of the bleached pulp after treatment in the chlorine dioxide treatment step.
(14) The method for producing bleached pulp according to the above (13), wherein the K value K is determined based on the pre-treatment K value 1 And the above-mentioned treated K value K 2 Calculated residual rate K of K value 2 /K 1 The value of x 100 is 80% or less.
(15) The method for producing bleached pulp according to any one of (1) to (14) above, wherein the content of hexenuronic acid in the bleached pulp after the chlorine dioxide treatment step is 30.00. Mu. Mol/g or less.
(16) The method for producing bleached pulp according to any one of (1) to (15) above, wherein the value H of the content of hexenuronic acid before treatment of the pulp to be treated in the chlorine dioxide treatment step is used as the value 1 (mu mol/g) and the value H of the content of hexenuronic acid in the bleached pulp after the treatment in the chlorine dioxide treatment step 2 (μmol/g) calculated residual ratio H of hexenuronic acid content 2 /H 1 The value of x 100 is 90% or less.
(17) The method for producing bleached pulp according to any one of (1) to (16) above, wherein the chlorine dioxide treatment is performed on the pulp at a predetermined ratioThe value W of ISO whiteness of the pulp to be treated in the treatment step before treatment 1 (%), and the value W of ISO brightness of the bleached pulp after treatment in the chlorine dioxide treatment step 2 (percent) calculated whiteness degree increase W 2 /W 1 The value of x 100 is 115% or more.
(18) The method for producing bleached pulp according to any one of (1) to (17) above, wherein the viscosity value A before treatment of the pulp to be treated in the chlorine dioxide treatment step is determined based on the value A of viscosity before treatment 1 (cP) and the value A of the viscosity of the bleached pulp after the treatment in the chlorine dioxide treatment step 2 Viscosity Retention ratio A calculated from (cP) 2 /A 1 The value of x 100 is 60% or more.
(19) The method for producing bleached pulp according to any one of (1) to (18) above, wherein the weight ratio of chlorine dioxide to monopersulfuric acid used in the chlorine dioxide treatment step is 1 or more.
(20) The method for producing bleached pulp according to any one of (1) to (19) above, further comprising a hydrogen peroxide treatment step of further treating the chlorine dioxide-treated pulp with hydrogen peroxide after the chlorine dioxide treatment step.
(21) The method for producing bleached pulp according to (5) above, wherein in the pH measuring step, a pre-treatment pH that is a pre-treatment pH of the treatment liquid and a post-treatment pH that is a post-treatment pH of the treatment liquid are measured.
Effects of the invention
According to the method for producing bleached pulp of the present invention, pulp having excellent properties as a whole, such as high whiteness and excellent discoloration resistance, can be obtained by adjusting various conditions of the pulp treatment process.
Drawings
Fig. 1 is a graph showing ISO brightness (%) of bleached pulp of each example and comparative example.
FIG. 2 is a graph showing K values of bleached pulps of each example and comparative example.
Fig. 3 is a graph showing the amount of hexenuronic acid (HexA) in bleached pulps of each example and comparative example.
Detailed Description
The present invention will be described in detail below. However, the present invention is not limited to the following embodiments, and can be implemented by being arbitrarily changed within the scope of the effect of the invention.
[ method for producing bleached pulp ]
The method for producing bleached pulp of the present invention comprises a cooking step for cooking a lignocellulosic material, an oxygen-alkali bleaching step for subjecting a predetermined unbleached pulp to an oxygen-alkali bleaching treatment, and a chlorine dioxide treatment step for subjecting the pulp subjected to the oxygen-alkali bleaching treatment. In the chlorine dioxide treatment step, the pH of the treatment liquid to be treated is adjusted to a predetermined range.
[ lignocellulosic Material ]
The lignocellulosic material used in the present invention is preferably a hardwood material containing a large amount of methylglucuronic acid which produces hexenuronic acid, but may be a coniferous material. The lignocellulose substance may be a non-wood such as bamboo or hemp, or may be a mixture of the above-mentioned hardwood, coniferous and non-wood, and is not particularly limited.
[ cooking Process ]
In the present invention, unbleached pulp is obtained by a cooking step of cooking a lignocellulosic material. As a cooking method used in the cooking step for obtaining unbleached pulp, known cooking methods such as sulfate cooking, polysulfide cooking, alkali cooking, acid sulfite cooking, alkali sulfite cooking and the like can be used, and the sulfate cooking method or polysulfide cooking is preferably used in consideration of pulp quality, energy efficiency and the like.
For example, when 100% hardwood lignocellulose is kraft-cooked, the degree of vulcanization of the kraft cooking liquor is 5 to 75 mass%, preferably 15 to 45 mass%; the effective alkali addition rate is 5 to 30% by mass, preferably 10 to 25% by mass per unit of oven-dried wood mass. The cooking temperature is, for example, 130 to 170 ℃, and the cooking method may be any of a continuous cooking method and a batch cooking method. In the case of using a continuous retort in the cooking, a modified cooking method in which a cooking liquid is added at a plurality of positions can be employed, and the mode is not particularly limited.
In the cooking step of the lignocellulosic material, delignification treatment is performed. When paper pulp is finally obtained as bleached pulp, hemicellulose derived from lignocellulosic matter can be removed together with lignin in the cooking step. When the hemicellulose-removing treatment is desired, for example, a hydrolysis treatment step may be provided to remove hemicellulose in a stage prior to the step of removing lignin by an alkaline cooking method such as a sulfate cooking method. In addition, when lignin is removed by the acid sulfite cooking method, a cooking step using the acid sulfite cooking method is preferably applied in order to remove lignin and hemicellulose together.
The object of the method for producing bleached pulp of the present invention is not particularly limited, and paper pulp is preferable.
The paper pulp used herein includes the items 47.01 to 47.06 of the customs Code (h.s.code) for international trade product name and classification, that is, mechanical wood pulp, chemical wood pulp, wood pulp produced by a combination of mechanical and chemical pulp processes, waste pulp, pulp using other cellulose fibers as a raw material, and the like.
In the cooking step, it is preferable to add 5 to 30 mass% of active alkali per unit mass of the oven-dried pulp. In the cooking step, 10 to 25 mass% of active alkali is preferably used, more preferably 12 to 20 mass% of active alkali is used, and still more preferably 15 to 18 mass% of active alkali is used. The active alkali in the cooking step is not particularly limited, and for example, sodium hydroxide, potassium hydroxide, or the like can be used. In the cooking step, sodium hydroxide is preferably used as the active alkali.
In the cooking step of the lignocellulosic material, as the cooking aid in the cooking liquid to be used, known cyclic ketone compounds, for example, quinone, naphthoquinone, anthraquinone, anthrone, phenanthrenequinone, ring-substituted compounds of the quinone compounds such as alkyl groups and amino groups, or hydroquinone compounds such as reduced anthradiphenol, which is a reduced form of the quinone compounds, can be used. Further, 1 or more than 2 kinds selected from a stable compound 9,10-dioxohydroanthracene (diketohydroanthracene) compound obtained as an intermediate in the synthesis of anthraquinone by the Diels-Alder method may be added. The addition rate of these cooking aids is a normal addition rate, and is, for example, 0.001 to 1.0 mass% per unit mass of the oven-dried pulp of a lignocellulosic substance such as a wood chip.
[ oxygen and alkali bleaching Process ]
The unbleached pulp obtained by the above cooking is subjected to washing, roughing and fine selection as required. Then, delignification treatment is further performed by an oxygen-alkali bleaching step to be bleached.
As the oxygen-alkali bleaching step, a known medium-consistency method or high-consistency method can be applied, and the pulp concentration in the treatment liquid is preferably 8 to 40% by mass, more preferably 10 to 35% by mass.
In the oxygen-alkali bleaching step, as the alkali to be added to the pulp, sodium hydroxide (caustic soda), potassium hydroxide, oxidized kraft white liquor, or the like can be used. In the oxygen-alkali bleaching step, oxygen may be added together with the alkali. As the oxygen gas, oxygen from a cryogenic separation method, oxygen from PSA (Pressure Swing Adsorption method), oxygen from VSA (Vacuum Swing Adsorption method), and the like can be used.
In the oxygen-alkali bleaching step, for example, an alkali and oxygen which may be used in combination are added to the pulp slurry in a mixer, and after sufficiently mixing, the pulp is sent under pressure to a reaction tower capable of holding the pulp, the mixture of oxygen and alkali for a certain period of time, and the pulp is delignified. The reaction conditions in the oxygen-alkali bleaching step are, for example, as follows.
That is, the addition rate of oxygen is 0.5 to 3% by mass, the addition rate of alkali is 0.5 to 4% by mass, the reaction temperature is 80 to 120 ℃, the reaction time is 15 to 100 minutes, and the pulp concentration is 8 to 40% by mass, preferably 10 to 35% by mass, per unit mass of oven dry (BD: bunedry) pulp, and other conditions may be known.
In the oxygen-alkali bleaching step, it is preferable to continuously perform the above-mentioned treatment of oxygen-alkali bleaching a plurality of times to delignify as much as possible and reduce the content of heavy metals in advance. The pulp subjected to the alkali-oxygen treatment, i.e., the raw pulp obtained in the alkali-oxygen treatment step, is preferably sent to a washing step.
[ chlorine dioxide treatment Process ]
In the chlorine dioxide treatment step, the pulp washed in the washing step is preferably subjected to chlorine dioxide treatment as described below. In the chlorine dioxide treatment, monopersulfuric acid and chlorine dioxide are added to the pulp obtained by the oxygen-alkali bleaching step.
In the chlorine dioxide treatment step, the amount of monopersulfuric acid added per unit mass of the oven-dried raw pulp to be treated is preferably 0.01 to 2.00 mass%, more preferably 0.02 to 1.00 mass%, even more preferably 0.05 to 0.80 mass%, and particularly preferably 0.1 to 0.6 mass%.
Of these, monopersulfuric acid, also called peroxomonosulfuric acid (peroxomonosulfuric acid), can be produced by hydrolyzing peroxodisulfuric acid, or can be produced by mixing hydrogen peroxide and sulfuric acid at an arbitrary ratio, and the production method thereof is not particularly limited. In addition, double salts of monopersulfuric acid (2 KHSO) may also be used 5 -KHSO 4 -K 2 SO 4 ) Potassium hydrogen peroxymonosulfate complex salt (Oxone), and the like. Among these, in view of economy, it is preferable to use a mixture of inexpensive high-concentration hydrogen peroxide and inexpensive high-concentration sulfuric acid to produce monopersulfuric acid at low cost.
As a method for producing monopersulfuric acid by mixing high-concentration hydrogen peroxide and high-concentration sulfuric acid, a method is preferred in which concentrated sulfuric acid having a concentration of 80 to 98 mass%, preferably 93 to 98 mass%, is dropped into hydrogen peroxide water having a concentration of 20 to 70 mass%, preferably 35 to 70 mass%, and mixed. The molar ratio of the sulfuric acid to the hydrogen peroxide is preferably 1: 1 to 5: 1, and more preferably 2: 1 to 4: 1. When the hydrogen peroxide solution and the sulfuric acid are used in low concentrations, the production efficiency of monopersulfuric acid is lowered, which is not preferable. Further, when the concentration of these is too high, the risk of ignition or the like increases, which is not preferable. Further, when the molar ratio of the sulfuric acid to the hydrogen peroxide is deviated from 1: 1 to 5: 1, the production efficiency of monopersulfuric acid is also lowered, which is not preferable.
In the chlorine dioxide treatment step, monopersulfuric acid is preferably used together with chlorine dioxide for the washed pulp. In the chlorine dioxide treatment step, the amount of chlorine dioxide used is preferably 0.01 to 2.00 mass%, more preferably 0.05 to 1.50 mass%, even more preferably 0.1 to 1.00 mass%, and particularly preferably 0.3 to 0.80 mass% per unit mass of the oven-dried raw pulp to be treated.
As described above, the chlorine dioxide treatment step used in the present invention is advantageous in terms of cost because the amount of expensive chlorine dioxide used can be controlled. Further, the pulp can be efficiently bleached by using chlorine dioxide and monopersulfuric acid in combination.
In the present invention, not only is molecular chlorine unnecessary, but also the amount of chlorine dioxide as a chlorine-based compound is minimized, and the effect of suppressing environmental load can be confirmed in addition to the effect of ensuring safety.
The value of the mass ratio of chlorine dioxide to monopersulfate used in the chlorine dioxide treatment step (mass of chlorine dioxide/mass of monopersulfate) is preferably 1 or more, that is, it is preferable to use more chlorine dioxide than monopersulfate, and the above ratio is more preferably 2 or more.
In the chlorine dioxide treatment step, the inorganic peroxy acid and/or a salt thereof (monopersulfuric acid and/or a salt thereof) is added to the reaction solution together with chlorine dioxide, and although there is a possibility that both bleaching agents react and become wasted, the amount of expensive chlorine dioxide can be suppressed by adding monopersulfuric acid. Therefore, it is advantageous in terms of cost as a whole. Further, when a treatment process using monopersulfuric acid alone is introduced into an existing facility for a treatment process using only chlorine dioxide, the investment in original facilities such as new facilities of a bleaching tower is enormous, while a method of using monopersulfuric acid and chlorine dioxide together to add them to a reaction solution is easy to introduce by only a small modification such as adding a monopersulfuric acid injection line to an existing facility for chlorine dioxide treatment, and thus can be introduced into many plants.
The time of the chlorine dioxide treatment step is preferably 10 to 200 minutes, more preferably 15 to 180 minutes, still more preferably 20 to 100 minutes, and particularly preferably 25 to 60 minutes. In the chlorine dioxide treatment step, the treatment temperature is preferably 20 to 100 ℃, more preferably 30 to 90 ℃, and particularly preferably 40 to 70 ℃. The concentration of the pulp to be treated in the chlorine dioxide treatment step is not particularly limited, but is usually 5 to 30% by mass, and preferably 8 to 15% by mass from the viewpoint of workability.
[ pH measurement step and pH adjustment ]
In the chlorine dioxide treatment step, the pH of the treatment liquid is preferably maintained in a favorable range. Specifically, the pH of the treatment liquid in the chlorine dioxide treatment step is adjusted to 2 to 8, preferably 3 to 8, more preferably 4 to 8, still more preferably 4.5 to 7.5, and particularly preferably 5 to 7.
Further, since ions having bleaching activity can be efficiently generated from chlorine dioxide when the pH value is within a predetermined range, the chlorine dioxide treatment step is preferably adjusted to the above-mentioned range such as 2 to 8 not only as the pH value during the treatment in the treatment step but also as the pH value before the treatment in the treatment step, in particular, as the pH value at or immediately before the start of the treatment step, and as the pH value after the treatment, in particular, as the pH value immediately after the treatment. Wherein at least either of the pH value before the treatment and the pH value after the treatment may be in the above-mentioned range such as 2 to 8. In addition, it is preferable that the pH of the treatment liquid is always in the above range such as 2 to 8 in the treatment process in the chlorine dioxide treatment step.
Preferably, the chlorine dioxide treatment step further includes a pH measurement step of measuring a pH value of the treatment liquid to be treated.
In the chlorine dioxide treatment step, the pH of the treatment liquid is preferably adjusted to a range of 3.5 to 7.5, for example, a value of 3.5 or more and more than 3.5 and 7 or less, more preferably 4 to 7, for example, a value of 4 or more and more than 4 and 7 or less, from the viewpoint of achieving high whiteness of the treated pulp.
In the chlorine dioxide treatment step, the pH of the treatment liquid is preferably adjusted to a range of 2 to 6.5, more preferably 2.5 to 6, and even more preferably 3 to 5.5, from the viewpoint of suppressing the K value and the value of the content of hexenuronic acid in the treated pulp.
As described above, in the chlorine dioxide treatment process in which the change in pH with time is observed and the pH of the treatment liquid is always adjusted to the preferable range in the treatment process, the pulp does not need to be subjected to unnecessarily severe conditions to achieve efficient bleaching.
In the chlorine dioxide treatment process, it is not necessary to measure the pH several times, and for example, when the pH range can be empirically controlled to be within a desired range, it is not necessary to measure the pH. However, in the pH measurement step, it is preferable to perform measurement a plurality of times, for example, to measure the pre-treatment pH and the post-treatment pH of the treatment liquid, particularly, the post-treatment pH which is the pH immediately after the treatment, and to confirm that an appropriate pH range is secured, and the pH may be measured at any stage at least before the treatment of the chlorine dioxide treatment (immediately before the treatment is started or immediately after the treatment is started), during the treatment (for example, when half of the time required for the chlorine dioxide treatment step has elapsed), and after the treatment (immediately after the treatment is ended or immediately before the contact treatment).
In addition, in order to adjust the pH of the treatment liquid in the chlorine dioxide treatment step, a known base or acid may be added to the treatment liquid.
In the chlorine dioxide treatment step, the difference between the pH before treatment and the pH after treatment is preferably 3.0 or less, and the pH is preferably adjusted as needed. The pH of the treatment liquid may be adjusted by the above-described known method, but it is preferable to use a treatment liquid whose pH is empirically maintained in a preferable range in advance. The difference between the pre-treatment pH and the post-treatment pH is more preferably 2.5 or less, still more preferably 2.0 or less, and particularly preferably 1.5 or less.
The pH value before treatment is 3.0 or less, the difference between the pH value before treatment and the pH value after treatment is preferably 1.0 or less, and the difference between the pH value before treatment and the pH value after treatment is more preferably 0.5 or less.
When the pre-treatment pH is higher than 3.0 and not higher than 5.5, the difference between the pre-treatment pH and the post-treatment pH is preferably not higher than 2.0, and the difference between the pre-treatment pH and the post-treatment pH is more preferably not higher than 1.6.
When the pre-treatment pH is higher than 5.5 and not higher than 8.0, the difference between the pre-treatment pH and the post-treatment pH is preferably not higher than 2.5, and the difference between the pre-treatment pH and the post-treatment pH is more preferably not higher than 2.0, and particularly preferably not higher than 1.6.
[ Properties of pulp ]
The ISO brightness of the bleached pulp after the chlorine dioxide treatment step, that is, the pulp obtained by the chlorine dioxide treatment is preferably 60 (%) or more, more preferably 65 (%) or more, further preferably 70 (%) or more, and particularly preferably 72 (%) or more.
Further, since the ISO brightness of the bleached pulp is preferably high, the upper limit thereof is not important, and the upper limit of the ISO brightness of the bleached pulp after the chlorine dioxide treatment step is, for example, 90 (%) or less.
The chlorine dioxide treatment step is carried out according to the value W of ISO whiteness of the pulp to be treated before treatment 1 (%) and value of ISO brightness W of the treated bleached pulp in chlorine dioxide treatment 2 (percent) calculated whiteness degree increase W 2 /W 1 The value of X100 is preferably 115% or more. The degree of increase in whiteness is more preferably 120% or more, still more preferably 125% or more, particularly preferably 130% or more, for example 135% or more.
Since the degree of increase in whiteness is preferably high, the upper limit value is not critical, and for example, the upper limit value of the degree of increase in whiteness is 160% or less.
Among them, the chlorine dioxide treatment step preferably further includes a whiteness measurement step of measuring a whiteness value of the pulp, and preferably further includes a whiteness measurement step of measuring a pre-treatment ISO whiteness value before (particularly immediately before) treatment of the pulp to be treated and a post-treatment ISO whiteness value after (particularly immediately after) treatment in the chlorine dioxide treatment step.
The K value of the bleached pulp after the chlorine dioxide treatment step, that is, the pulp obtained by the chlorine dioxide treatment, is preferably 1.50 to 4.50, for example, 4.50 or less, more preferably 1.80 to 4.10, for example, 4.10 or less or 4.00 or less, still more preferably 2.10 to 3.80, and particularly preferably 2.50 to 3.50.
The chlorine dioxide treatment step preferably further includes a K value measurement step of measuring a K value before treatment (particularly immediately before the start of treatment) of the pulp to be treated, that is, a K value before treatment, and a K value after treatment (particularly immediately after the end of treatment) in the chlorine dioxide treatment step, that is, a K value after treatment.
In addition, according to the K value K before processing 1 And the processed K value K 2 Calculated residual rate K of K value 2 /K 1 The value of x 100 is preferably 80% or less, more preferably 70% or less. The K value remaining ratio is more preferably 65% or less, still more preferably 60% or less, particularly preferably 50% or less, for example 45% or less.
Since the K value remaining rate is preferably low, the lower limit thereof is not critical, and the K value remaining rate may be 20% or more, for example.
The viscosity value (cP) of the pulp obtained in the chlorine dioxide treatment step is preferably 10 to 30, more preferably 15 to 25.
The content of hexenuronic acid in the bleached pulp after the chlorine dioxide treatment step, i.e., the pulp obtained by the chlorine dioxide treatment, is preferably 30.00. Mu. Mol/g or less. The content of hexenuronic acid is more preferably 25.00. Mu. Mol/g or less, and still more preferably 20.00. Mu. Mol/g or less.
Further, since the content of hexenuronic acid is preferably low, the lower limit is not critical, and the content of hexenuronic acid in the bleached pulp after the chlorine dioxide treatment step is, for example, 10.00. Mu. Mol/g or more.
According to the value H of the hexenuronic acid content before the treatment of the pulp to be treated in the chlorine dioxide treatment step 1 (mu mol/g) and the bleached pulp after the treatment in the chlorine dioxide treatment step, i.e. obtained by the chlorine dioxide treatmentValue H of the hexenuronic acid content in the pulp 2 (mu mol/g) calculated residue ratio H of hexenuronic acid content 2 /H 1 The value of X100 is preferably 90% or less.
Residual rate H of hexenuronic acid content 2 /H 1 The value of x 100 is more preferably 80% or less, still more preferably 75% or less, particularly preferably 70% or less, for example 60% or less or 50% or less.
The lower limit is not critical since the content of hexenuronic acid is preferably low, for example, the content of hexenuronic acid is 20% or more.
Retention rate of pulp viscosity value (cP) in chlorine dioxide treatment step, i.e., pulp viscosity value a obtained in chlorine dioxide treatment step 2 (cP) viscosity number A of pulp immediately before chlorine dioxide treatment 1 (cP) ratio (A) 2 /A 1 X 100 (%)) is preferably 60% or more. The retention ratio is more preferably 80% or more, further preferably 85% or more, particularly preferably 90% or more, for example, 95% or more.
Further, since the retention of the pulp viscosity is preferably high, the upper limit thereof is not important, and the retention of the pulp viscosity after the chlorine dioxide treatment step is, for example, 100% or less.
The chlorine dioxide treatment step preferably further includes a viscosity measurement step of measuring a value of the viscosity of the pulp, and in the chlorine dioxide treatment step, the value of the viscosity of the pulp during the treatment in the treatment step, the value of the viscosity before the treatment in the treatment step, particularly the value of the viscosity at or immediately before the start of the treatment step, and the value of the viscosity after the treatment, particularly the value of the viscosity immediately after the treatment, are preferably measured.
Among these, the pulp obtained in the chlorine dioxide treatment step preferably has a viscosity value (cP) of 10 to 30, more preferably 15 to 25.
[ Hydrogen peroxide treatment Process ]
In the hydrogen peroxide treatment step, hydrogen peroxide is added to the pulp after the preceding stage treatment, preferably after washing. The hydrogen peroxide treatment step is preferably a step subsequent to the chlorine dioxide treatment step, and in this case, the pulp subjected to at least one chlorine dioxide treatment is a target of the hydrogen peroxide treatment step.
The addition rate of hydrogen peroxide in the hydrogen peroxide treatment step is preferably 0.1 to 2.0 mass%, more preferably 0.2 to 1.0 mass%, per unit mass of the oven-dried raw pulp to be treated.
The treatment temperature in the hydrogen peroxide treatment step is preferably 20 to 100 ℃, and more preferably 40 to 90 ℃. In the hydrogen peroxide treatment step, the pH of the reaction system is preferably adjusted to 8 to 14, and more preferably adjusted to 10.5 to 12.0. The pH can be adjusted by using a known base or acid. The pulp concentration in the hydrogen peroxide treatment step is not particularly limited, but is preferably 8 to 15 mass% in view of handling properties.
In the hydrogen peroxide treatment step, it is also preferable to use at least 1 of magnesium salt and sodium silicate (sodium silicate). Magnesium salt is preferably added to pulp, for example, magnesium sulfate. Further, as sodium silicate, for example, it is preferable to add Na to pulp 2 SiO 3 、Na 4 SiO 4 、Na 2 Si 2 O 5 、Na 2 Si 4 O 9 Any sodium silicate of the like. When magnesium salt or sodium silicate is added to a reaction system containing pulp, it is possible to prevent the generation of active oxygen radicals due to the action of heavy metals such as copper, iron, and manganese, and transition metals with oxygen or hydrogen peroxide in an alkaline system, thereby reducing the viscosity of pulp.
The addition rate of the magnesium salt in the hydrogen peroxide treatment step is preferably 0.01 to 1.0 mass% of Mg based on the mass of the oven-dried pulp of the raw pulp to be treated, more preferably 0.02 to 0.5 mass% of Mg based on the mass of the oven-dried pulp, and still more preferably 0.05 to 0.2 mass% of Mg based on the mass of the oven-dried pulp.
The addition rate of the sodium silicate compound in the hydrogen peroxide treatment step is preferably 0.1 to 2.0% by mass based on the mass of the oven-dried raw pulp to be treated, more preferably 0.2 to 1.5% by mass based on the mass of the oven-dried raw pulp, and still more preferably 0.5 to 1.0% by mass based on the mass of the oven-dried raw pulp.
In the hydrogen peroxide treatment step, the reaction system is preferably kept alkaline as described above, and the alkaline component is preferably used in an amount of 0.1 to 5.0 mass%, more preferably 0.2 to 3.0 mass%, and further preferably 0.3 to 2.0 mass%, based on the mass of hydrogen peroxide. As the alkali component, sodium hydroxide (caustic soda), potassium hydroxide, or the like can be used.
[ kinds and number of stages of various steps ]
In the process for producing bleached pulp, it is preferred that the chlorine dioxide treatment step has only one stage. In this case, the steps of the method for producing bleached pulp can be simplified. However, the method for producing bleached pulp may further include a second chlorine dioxide treatment step of subjecting the pulp subjected to the oxygen-alkali bleaching treatment to monopersulfuric acid treatment. In addition to the hydrogen peroxide treatment step described above, the method may further include a second hydrogen peroxide treatment step of further performing hydrogen peroxide treatment. In the method for producing bleached pulp including the second chlorine dioxide treatment step and the second hydrogen peroxide treatment step, it is also preferable that at least one of the hydrogen peroxide treatment steps is a step subsequent to the chlorine dioxide treatment.
The method for producing bleached pulp may further include a treatment step for bleaching other than the hydrogen peroxide treatment step and the chlorine dioxide treatment step, for example, an ozone treatment step of treating unbleached pulp with ozone, a chlorine treatment step, a hypochlorite treatment step, or the like. Among them, from the viewpoint of simplifying the steps of the method for producing bleached pulp and ensuring safety, it is preferable not to include the ozone treatment step, the chlorine treatment step and the hypochlorite treatment step.
Examples
1. Production of monopersulfuric acid
To 15.2g of 45 mass% hydrogen peroxide water (manufactured by Mitsubishi gas chemical corporation), 60.2g of 98% sulfuric acid (special grade reagent, KISHIDACHEMICAL Co., ltd.) was added to produce monopersulfuric acid. The composition of the aqueous monopersulfate solution thus obtained was 23.4% by mass of monopersulfate, 1.8% by mass of hydrogen peroxide, 59.8% by mass of sulfuric acid, and 15.0% by mass of water.
2. Measurement of pulp whiteness
After the bleached pulp has been disintegrated, a 2-piece basis weight of 400g/m was produced in accordance with ISO3688-1977 2 The whiteness (%) of the pulp was measured in accordance with JIS P8148.
3. Determination of potassium permanganate value (K value) of paper pulp
The potassium permanganate number was determined according to TAPPI UM 253.
4. Determination of the amount of HexA in the pulp
0.8g of completely washed pulp in oven dry mass is accurately weighed. The resulting pulp was charged into a pressure-resistant vessel, 80mL of pure water was added, and formic acid was added to adjust the pH to 3. The pressure-resistant vessel was placed in an oven and treated at 120 ℃ for 4 hours to hydrolyze HexA acid. After the treatment, the solution was filtered, and 2-furancarboxylic acid and 5-carboxy-2-furaldehyde, which were acid hydrolysis products of HexA, present in the solution separated by filtration were quantified by HPLC, and the amount of original HexA was determined from the total molar amount thereof.
5. Measurement of pulp viscosity
The measurement of the pulp viscosity was carried out according to method J.TAPPI No. 44.
6. Physical Properties of unbleached pulp
The physical properties of the used unbleached pulp are shown below.
Unbleached pulp: pulp after oxygen-alkali bleaching
Pulp 1: ISO whiteness 48.0%, K value 8.0, hexA content 44.9 mu mol/pulp g, viscosity 24.19cP
Pulp 2: 54.1 percent of ISO whiteness, 6.6 of K value, 37.8 mu mol of HexA content/paper pulp g and 19.07cP of viscosity
7. Cleaning conditions
Pure water was added to each pulp (pulp 1 or pulp 2) after the above bleaching treatment to adjust the pulp concentration to 2.4%, followed by dewatering until the pulp concentration reached 20% (washing rate 90%).
(example 1)
Unbleached pulp 1 of dry mass 16g was taken out of the polyethylene bag. In order to bleach the pulp at a pulp concentration of 12%, after filtering water with a necessary hollow fiber membrane, an aqueous sodium hydroxide solution was added in an amount such that the pH at the start of the reaction became about 4.5, and the mixture was thoroughly mixed. Thereafter, 0.75 mass% of chlorine dioxide and 0.4 mass% of monopersulfuric acid were added to the mass of the pulp and further mixed. The pH at this point was 4.8.
The substrate was immersed in a constant temperature water bath at 60 ℃ for 36 minutes to carry out bleaching treatment (chlorine dioxide treatment step). The bleached pulp washed under the above washing conditions was diluted to 2L with pure water, and then adjusted to ph5.5 with a sulfurous acid aqueous solution, and 2 pulp sheets (acid paper sheets) were produced on a buchner funnel. After air-drying for 12 hours, the ISO whiteness, K value, and HexA amount of the sample subjected to paper making were measured.
(example 2)
Unbleached pulp 1 having a dry mass of 16g was taken absolutely from a polyethylene bag. In order to bleach the pulp at a pulp concentration of 12%, after filtering water with a necessary hollow fiber membrane, an aqueous sodium hydroxide solution was added in an amount such that the pH at the start of the reaction became about 6, and the mixture was thoroughly mixed. Thereafter, 0.75 mass% of chlorine dioxide and 0.4 mass% of monopersulfuric acid were added to the mass of the pulp, and further mixed.
The pH at this point was 6.3. Thereafter, the same operation as in example 1 was performed.
(example 3)
Bleaching treatment was performed by immersing the substrate in a constant temperature water bath at 60 ℃ for 30 minutes (chlorine dioxide treatment step). Thereafter, the same operation as in example 1 was performed.
(example 4)
The pH at this point was 5.2. Thereafter, the same operation as in example 3 was performed.
(example 5)
The pH at this point was 6.6. Thereafter, the same operation as in example 3 was performed.
Comparative example 1
Unbleached pulp 1 of dry mass 16g was taken out of the polyethylene bag. In order to bleach the pulp at a pulp concentration of 12%, after filtering water with a necessary hollow fiber membrane, sulfuric acid was added in an amount such that the pH at the start of the reaction became about 1.5, and the mixture was thoroughly mixed. Thereafter, 0.75 mass% of chlorine dioxide and 0.4 mass% of monopersulfuric acid were added to the mass of the pulp, and further mixed.
The pH at this point was 1.4. Thereafter, the same operation as in example 1 was performed.
Comparative example 2
Unbleached pulp 1 of dry mass 16g was taken out of the polyethylene bag. In order to bleach the pulp at a pulp concentration of 12%, after filtering water with a necessary hollow fiber membrane, an aqueous sodium hydroxide solution was added in an amount such that the pH at the start of the reaction became about 8.0, and the mixture was thoroughly mixed. Thereafter, 0.75 mass% of chlorine dioxide and 0.4 mass% of monopersulfuric acid were added to the mass of the pulp, and further mixed.
The pH at this point was 8.1. Thereafter, the same operation as in example 1 was performed.
Comparative example 3
The pH at this time was 1.3. Thereafter, the same operation as in example 3 was performed.
Comparative example 4
The pH at this point was 8.2. Thereafter, the same operation as in example 3 was performed.
The results of examples 1 and 2 and comparative examples 1 and 2 are shown in table 1, and the results of examples 3 to 5 and comparative examples 3 and 4 are shown in table 2. The results of examples 1 to 5 and comparative examples 1 to 4 are shown in fig. 1 to 3, respectively, with respect to the degree of whiteness, K value, and hexenuronic acid content.
In each of fig. 1 to 3, the points at the left and right ends indicate the results of the comparative example, and the other points indicate the results of the example.
[ Table 1]
[ Table 2]
In each example, the whiteness was maintained at a good level, and the values of K value and hexenuronic acid content were suppressed, confirming that bleached pulp having overall excellent properties was obtained.
Claims (18)
1. A method of producing bleached pulp, comprising:
a cooking step for cooking a lignocellulosic material;
an oxygen-alkali bleaching step of subjecting the unbleached pulp obtained in the cooking step to oxygen-alkali bleaching; and
a chlorine dioxide treatment step of treating the pulp obtained by the oxygen-alkali bleaching step with chlorine dioxide under a condition of monopersulfuric acid in combination,
the pH value of the treating liquid in the chlorine dioxide treating process is in the range of 2-8,
when the pH value before treatment, which is the pH value of the treatment liquid before treatment in the chlorine dioxide treatment step, is 3.0 or less, the difference between the pH value before treatment and the pH value after treatment, which is the pH value of the treatment liquid after treatment in the chlorine dioxide treatment step, is 1.0 or less,
a difference between the pre-treatment pH and the post-treatment pH is 2.0 or less when the pre-treatment pH is higher than 3.0 and 5.5 or less,
when the pre-treatment pH is higher than 5.5 and 8.0 or lower, the difference between the pre-treatment pH and the post-treatment pH is 2.5 or lower.
2. The method of manufacturing bleached pulp according to claim 1,
in the chlorine dioxide treatment step, the amount of monopersulfuric acid added is 0.01 to 2.00 mass% per unit mass of the oven dry pulp, and the amount of chlorine dioxide added is 0.01 to 2.00 mass% per unit mass of the oven dry pulp.
3. The method of producing bleached pulp according to claim 1 or 2, characterized in that,
the time of the chlorine dioxide treatment process is 20-200 minutes, and the temperature of the chlorine dioxide treatment process is 40-70 ℃.
4. The method for producing bleached pulp according to claim 1 or 2, wherein the bleached pulp is a paper-making pulp.
5. The method of producing bleached pulp according to claim 1 or 2, further comprising a pH measuring step of measuring a pH value of a treatment liquid to be treated in the chlorine dioxide treatment step.
6. The method of producing bleached pulp according to claim 1 or 2, wherein,
the pH value before treatment, which is the pH value of the treatment liquid before treatment in the chlorine dioxide treatment step, and the pH value after treatment, which is the pH value of the treatment liquid after treatment, are both within the range of 2 to 8.
7. The method of producing bleached pulp according to claim 1 or 2, wherein,
when the pH value before the treatment is 3.0 or less, the difference between the pH value before the treatment and the pH value after the treatment is 0.5 or less,
a difference between the pre-treatment pH and the post-treatment pH is 1.6 or less when the pre-treatment pH is higher than 3.0 and 5.5 or less,
when the pre-treatment pH is higher than 5.5 and 8.0 or lower, the difference between the pre-treatment pH and the post-treatment pH is 2.0 or lower.
8. The method of producing bleached pulp according to claim 1 or 2, wherein the ISO brightness of the bleached pulp after the chlorine dioxide treatment step is 60% or more.
9. The method for producing bleached pulp according to claim 1 or 2, wherein the K value of the bleached pulp after the chlorine dioxide treatment step is 1.50 to 4.50.
10. The method of producing bleached pulp according to claim 1 or 2, wherein,
further comprising a K value measuring step of measuring a K value before treatment, which is a K value before treatment of the pulp to be treated in the chlorine dioxide treatment step, and a K value after treatment, which is a K value after treatment of the bleached pulp after treatment in the chlorine dioxide treatment step.
11. The method of manufacturing bleached pulp according to claim 10,
according to the pre-processing K value K 1 And said post-treatment K value K 2 Calculated residual rate K of K value 2 /K 1 The value of x 100 is 80% or less.
12. The method for producing bleached pulp according to claim 1 or 2, wherein the content of hexenuronic acid in the bleached pulp after the chlorine dioxide treatment step is 30.00 μmol/g or less.
13. The method of producing bleached pulp according to claim 1 or 2, wherein,
according to the value H of the content of hexenuronic acid before the treatment of the pulp as a treatment object in the chlorine dioxide treatment process 1 (mu mol/g) and the value H of the content of hexenuronic acid in the bleached pulp after treatment in the chlorine dioxide treatment step 2 (μmol/g) calculated residual ratio H of hexenuronic acid content 2 /H 1 The value of x 100 is 90% or less.
14. The method of producing bleached pulp according to claim 1 or 2, wherein,
according to the value W of ISO whiteness of the pulp before treatment in the chlorine dioxide treatment process 1 (%), and the value W of the ISO brightness of the bleached pulp after treatment in the chlorine dioxide treatment step 2 (percent) calculated whiteness degree increase W 2 /W 1 The value of x 100 is 115% or more.
15. The method of producing bleached pulp according to claim 1 or 2, characterized in that,
according to the value A of the viscosity of the pulp before treatment, which is a treatment object in the chlorine dioxide treatment process 1 (cP) and the value A of the viscosity of the bleached pulp after the treatment in the chlorine dioxide treatment step 2 Viscosity Retention ratio A calculated from (cP) 2 /A 1 The value of x 100 is 60% or more.
16. The method of producing bleached pulp according to claim 1 or 2, wherein,
the weight ratio of chlorine dioxide to monopersulfuric acid used in the chlorine dioxide treatment step is 1 or more.
17. The method of producing bleached pulp according to claim 1 or 2, wherein,
further comprising a hydrogen peroxide treatment step of treating the chlorine dioxide-treated pulp with hydrogen peroxide after the chlorine dioxide treatment step.
18. The method of manufacturing bleached pulp according to claim 5, wherein,
in the pH measurement step, a pre-treatment pH that is a pre-treatment pH of the treatment liquid and a post-treatment pH that is a post-treatment pH of the treatment liquid are measured.
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| PCT/JP2020/028356 WO2021020251A1 (en) | 2019-07-29 | 2020-07-22 | Method for producing bleached pulp |
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| JP2004183149A (en) * | 2002-12-04 | 2004-07-02 | Oji Paper Co Ltd | Method for producing bleached pulp |
| JP2007169831A (en) * | 2005-12-22 | 2007-07-05 | Mitsubishi Gas Chem Co Inc | Method for producing chemical pulp |
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| JP2011001636A (en) * | 2009-06-16 | 2011-01-06 | Mitsubishi Gas Chemical Co Inc | Method for producing bleached pulp |
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| US5645687A (en) * | 1995-07-10 | 1997-07-08 | Champion International Corporation | Process for manufacturing bleached pulp with reduced chloride production |
| JP2004124265A (en) * | 2002-03-28 | 2004-04-22 | Nippon Paper Industries Co Ltd | Method for improving chlorine dioxide bleaching efficiency |
| JP5285896B2 (en) * | 2007-12-05 | 2013-09-11 | 大王製紙株式会社 | Process for producing bleached alkaline chemical pulp |
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Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004183149A (en) * | 2002-12-04 | 2004-07-02 | Oji Paper Co Ltd | Method for producing bleached pulp |
| JP2007169831A (en) * | 2005-12-22 | 2007-07-05 | Mitsubishi Gas Chem Co Inc | Method for producing chemical pulp |
| CN101903591A (en) * | 2007-12-20 | 2010-12-01 | 三菱瓦斯化学株式会社 | Process for production of bleached pulp |
| JP2010265564A (en) * | 2009-05-15 | 2010-11-25 | Mitsubishi Gas Chemical Co Inc | Method for producing ecf-bleached pulp |
| JP2010270410A (en) * | 2009-05-21 | 2010-12-02 | Mitsubishi Gas Chemical Co Inc | Ecf (elemental chlorine free) bleaching method |
| JP2011001637A (en) * | 2009-06-16 | 2011-01-06 | Mitsubishi Gas Chemical Co Inc | Method for producing bleached pulp |
| JP2011001636A (en) * | 2009-06-16 | 2011-01-06 | Mitsubishi Gas Chemical Co Inc | Method for producing bleached pulp |
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| JP2021021165A (en) | 2021-02-18 |
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