JP2593392B2 - Pulp bleaching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for bleaching cellulose pulp with a peroxide, in which a peroxide-added pulp slurry is irradiated with ultraviolet rays as a treatment means to increase the peroxide activation. And a method for efficiently producing bleached pulp having high whiteness.

[0002]

BACKGROUND ART Conventionally, bleaching of cellulose pulp irrespective of mechanical pulp and chemical pulp is typically multi-stage bleaching using a chlorine-based compound.
It was common to obtain bleached pulp of high whiteness by alternately repeating the bleaching step with hypochlorite and the extraction of hemicellulose with an alkaline substance. Alkali treatment means washing to remove lignin chloride generated in the chlorination treatment and effectively perform hypochlorite treatment in the next stage, and depending on how much lignin elution is suppressed, The amount of use is decided by itself. In recent years, as the preservation of the global environment has been called for and stricter water quality standards have been set for effluents, the use of chlorine-based substances in bleaching has been reduced, and a shift to non-chlorine-based substances has been inevitable. Under these circumstances, it is desirable to use oxygen or peroxide as a bleaching agent.However, conventionally, oxygen is mainly used for delignification in the preceding stage of a chlorine-based multi-stage bleaching process. Is used in the later stage of chemical pulp bleaching systems, and is used to limit bleaching whiteness and improve whiteness stability, and peroxide is known as an effective lignin preservative bleach, It is known to be useful for improving whiteness in a region where significant yield loss is suppressed.

[0003] Peroxide is a typical non-chlorine bleaching agent and has good pulp whiteness and retention. Among them, hydrogen peroxide is the one most frequently used in the paper pulp industry. Hydrogen peroxide alone is relatively less stable,
It is stable around pH 5 in the acidic range, decomposes in the alkaline range and releases nascent oxygen, and in the presence of metal ions, the metal ions act as a catalyst and decompose, losing the bleaching ability. Become. Therefore, it is known to use a chelating agent such as sodium silicate or ethylenediaminetetraacetic acid for pH adjustment and inactivation of metal ions. For example, Japanese Patent Publication No. 63-54838 discloses a new chelating agent, and Japanese Patent Publication No. 2-13069 discloses a method of promoting delignification by using a metal salt together with bleaching in chemical pulp, and Japanese Patent Publication No. Sho 63-20953. The publication discloses that the use of a chelating agent in an acidic region increases the whiteness without lowering the viscosity of the pulp slurry, but none of them is satisfactory.

It has been known for a long time that lignin is decomposed when irradiated with ultraviolet light (Nakano Junzo, Lignin Chemistry, p. 124). However, it is the result of irradiating the wood itself or the extracted lignin with ultraviolet light. No example was found in which the pulp was irradiated with ultraviolet light. Also, Journal of the Japan Wood Science Society
Vol.27 No3 p210-215 (1981)
The "Oxidative Decomposition of Lignin (Part 3)" describes irradiating ultraviolet rays in the presence of hydrogen peroxide when decolorizing kraft cooking waste liquid. However, there is no example in the literature and the market where ultraviolet irradiation is used in combination with hydrogen peroxide bleaching of cellulose pulp.

[0005]

According to the conventional method, the whiteness of pulp obtained in the peroxide bleaching step is generally less than 60% (JIS-P8123 Hunter whiteness). A major issue was how to find a method for obtaining bleached pulp having a higher degree of whiteness than the conventional method.

[0006]

As a result of various studies, the present inventor has found that hydrogen peroxide can be efficiently activated by irradiating ultraviolet rays to a pulp slurry to which peroxide, especially hydrogen peroxide, has been added. In addition to further improving the whiteness of the pulp, high quality and high yield,
It has been found as a pulp bleaching tool that far exceeds the range of predictions. According to the present invention, it is possible to obtain a product having excellent whiteness without increasing the amount of added hydrogen peroxide, and it is possible to increase the whiteness to 70% to 80%. In terms of prevention, its contribution is enormous.

[0007] The present invention is not limited to bleached pulp, but is directed to any pulp such as mechanical pulp, chemical pulp and waste paper pulp. In the first stage, the hydrogen peroxide treatment and ultraviolet irradiation are used together at room temperature in the first stage, and the pulp concentration, the hydrogen peroxide concentration, and the treatment temperature (80
(° C) is also raised and normal bleaching is performed . The ultraviolet irradiation treatment promotes the decomposition of the chromophore and also decomposes lignin when exposed for a long time. Although described in the following examples and table for more information, the concentration of the pulp slurry to be bleached may better the highest possible flow rate and flow velocity, stirring force, depends respectively on the type or the like of the pulp, the first stage Considering uniform irradiation of pulp fibers with ultraviolet rays, 1-3 to 5% by weight (good
Preferably 1% by weight) . Increasing the concentration will be an issue to be expected in the future in consideration of the functions required of the equipment and the quality of the pulp. Pulp slurry pH
The region is in a range of about 3 to 13 (preferably 8 to 13) in which hydrogen peroxide can be decomposed to sufficiently release nascent oxygen, and the effect is recognized even in an acidic range. No bleaching reaction occurs. The wavelength (λ) of ultraviolet light (UV) used is in the range of 160 to 400 μm, and the mercury lamp 1 having a peak at a wavelength of 254 μm is used in the present invention.
It is variable from 00 to 400 W and from 7 to 30 w / cm. The irradiation time depends on the degree of lignin removal, but the longer the irradiation time, the better the result. The amount of added hydrogen peroxide is 1 to 3% by weight based on absolute dry pulp
And As the peroxide, hydrogen peroxide, peracetic acid,
Perphthalic acid, sodium peroxide, t-butyl peroxide,
m-chlorobenzoate, cumene hydroperoxide,
Known peroxides such as tetrahydrofuran and hydroperoxide can be used as having an equivalent effect.

Next, a detailed description will be given based on an embodiment.

Example 1 In a two-stage bleaching of hydrogen peroxide with a kappa number of 10.2 after bleaching of oxygen in a multi-stage bleaching process of hardwood unbleached kraft pulp, the first stage was a pulp concentration of 1% and H ₂
After adding O _{2 at} 1%, pH 11.2, and irradiating with ultraviolet rays (λ = 254 μm) at room temperature for 60 minutes, the second stage was subjected to pulp concentration 5.0% and H ₂ O ₂ added 2%. , PH 1
The pulp treated at 1.0 and a temperature of 80 ° C. for 60 minutes was washed, and the whiteness of a hand-made paper having a base weight of 167 g / m ² was measured and found to be as high as 77.0%.
However, all percentages refer to weight%. The amount of H ₂ O ₂ added is% based on absolutely dried pulp. The whiteness is measured by JIS-P-8123 Hunter whiteness meter.

Example 2 Pulp having a kappa number of 10.2 was used in the same manner as in Example 1, and the first stage had a pulp concentration of 3.5% and an added amount of H ₂ O ₂ of 1
%, PH 12.0, and UV irradiation at normal temperature (λ = 2
54 μm) and treated for 30 minutes. The second stage was washed with pulp having a pulp concentration of 5.0%, an added amount of H ₂ O ₂ of 2%, a pH of 11.9 and a temperature of 80 ° C. for 60 minutes, and washed rice The whiteness of the handmade paper having a basis weight of 167 g / m ² was measured and found to be 71.1%.

Example 3 Pulp having a kappa number of 10.2 as in Example 1
In the first stage, pulp concentration 1%, H_TwoO _TwoAddition amount 1%, pH
 12.2, UV irradiation at normal temperature (λ = 254μ)
m) and after 30 minutes of treatment, the second stage is treated with a pulp concentration of 5.0
%, H_TwoO_TwoAdd 2%, pH 12.0, temperature 80 ° C
Wash the pulp treated for 60 minutes, 167g
/ M^TwoThe whiteness of the paper made by hand shows 70.9%.
Was. In Example 3, the first stage hydrogen peroxide treatment
Bubbles in the pulp slurry
The whiteness of the paper increases to 74.2%, resulting in bubbling.
A stirring effect was observed.

[0009]

[Comparative Example 1] The first stage treatment was not carried out (no UV irradiation) and only the second stage treatment was carried out, but the whiteness of the formed paper was as low as 58.1%.

COMPARATIVE EXAMPLE 2 A two-stage treatment was performed in the same manner as in Example 1, but the ultraviolet light was not irradiated during the first-stage treatment, and the whiteness of this paper was 58.8%, which was less than 60.

Comparative Example 3 In the first stage of Example 1, ultraviolet irradiation was performed but hydrogen peroxide was not added. Therefore, the pH of the pulp slurry was adjusted to 7.4 without alkali adjustment. The whiteness of the paper was 63.6%. In that case, the pH of 7.4 was adjusted to 12.0 by alkali adjustment, but the whiteness was as low as 61.1%. As described above, it is clear from the above, Examples and Comparative Examples that the above is considered.
Irradiation at a relatively low pulp concentration where UV irradiation is likely to be uniform and the synergistic effect of combining it with hydrogen peroxide treatment are fully recognized, and excellent effects can be obtained even if each is carried out alone. In view of the fact that they were not used, an unexpected effect was obtained by using them together.

[0010]

[Table 1] Ep1-Ep2: hydrogen peroxide bunk bleaching sequence Ep1UV: stage UV radiation (* by bubbling agitation) Ep1 conditions: PC _{(pulp) = 1%, H 2 O} 2
= 1% addition, room temperature, Ep2 _{conditions: PC = 5%, H 2} O 2 = 2% additives,
80 ° C,

[Table 2] Condition of Ep1: PC = 3.5%, addition of H ₂ O ₂ = 1%, normal temperature, Condition of Ep2: PC = 5.0%, addition of H ₂ O ₂ = 2%, 80 ° C.

[0011]

The pulp slurry in the hydrogen peroxide treatment stage in the cellulose pulp bleaching process is irradiated with ultraviolet rays, so that the effect of active oxygen on lignin and other chromophores is sufficiently strong. By using only hydrogen peroxide treatment, the quality of the bleached pulp is much better than the whiteness of bleached pulp. Uniform hemicellulose removal was performed, and it was possible to obtain a bleached pulp raw material with a high whiteness far beyond the expected range.In addition, the yield was good without the need to increase the amount of hydrogen peroxide added. The above contribution is very high. By adopting this method, it becomes a big clue that can be changed from conventional pulp bleaching with chlorine-based substances, and there are many benefits that it is possible to minimize drainage pollution.

Claims (1)

(57) [Claims] 1. A method for bleaching cellulose pulp with peroxide, comprising adding hydrogen peroxide to a pulp slurry.
When performing multi-stage bleaching, the first stage has a pulp concentration of 1.0 to
3.5 wt%, hydrogen peroxide concentration vs. 1 wt% pulp, pH
A relatively dilute slurry with a value of 8 to 13 and peroxidation at room temperature
Object treatment and ultraviolet irradiation treatment in combination, the second stage,
Pulp concentration of at least 5% by weight and hydrogen peroxide concentration of 2
~ 3% by weight, and the processing temperature was raised to 80 ° C.
Bleaching process of pulp and performing management.