Pulp Bleaching Processes

Inactive Publication Date: 2007-10-25
NIPPON PAPER IND CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0069] The concentration of the ozone by-produced in the irradiation reactor is 0.5-100 ppm, depending on the manner of supplying air or oxygen or the concentration of oxygen. A major feature of the second aspect of the first invention is that a high bleaching efficiency can be obtained with even such low-concentration ozone by combination with the irradiation treatment.
[0070] This concept can be further expanded to select and use multiple light sources having a characteristic wavelength range within 100-400 nm and different characteristic wavelengths as light sources in the irradiation reactor. Specifically, a light source having a narrow wavelength characteristic of 135-242 nm providing a high ozone-generating efficiency and a light source having an evenly distributed wavelength range of 100-400 nm suitable for irradiation reaction can be combined, for example, whereby a further higher bleaching efficiency can be obtained.
[0071] In the irradiation treatment of the present invention, the irradiation reaction efficiency can be increased by using a combination of additives such as reducing agents (e.g., NaBH4, hydrazine, hydrogen), oxidizing agents (e.g., oxygen, ozone), peroxides (e.g., hydrogen peroxide, peracetic acid, Na percarbonate, Na perborate), hydr

Problems solved by technology

Under such circumstances, there is a tendency to use limited chemicals such as chlorine dioxide, hydrogen peroxide, oxygen and ozone in ECF bleaching or TCF bleaching.
However, pulp quality, especially brightness obtained by bleaching with only such chemicals is limited even if they are used in combination, or large amounts of expensive chemicals must be used to attain sufficient quality.
It has been known that various metals from pulp promote decomposition of oxygen-based bleaching chem

Method used

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Examples

Experimental program
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Effect test

example 1

[0118] An oxygen-delignified hardwood kraft pulp available from Nippon Paper Group, Inc. (kappa number 11.6, ISO brightness 45.6%) was used.

[0119] An acid treatment was performed under the following conditions to give a pulp having a kappa number of 5.5 and a brightness of 47.5%.

[0120] Acid treatment conditions: pulp consistency 10% by weight, pH 3.0 (adjusted with sulfuric acid), temperature 95° C., treatment period 180 minutes. After the treatment was completed, the pulp was washed with water.

[0121] A 5 g (bone dry weight) portion of the acid-treated pulp thus obtained was collected and diluted to a pulp consistency of 0.25% by weight and then prepared into pulp slurries at pHs over an acidic to alkaline range using NaOH and H2SO4. These slurries were injected into the experimental apparatus shown in FIG. 3, and subjected to an irradiation reaction while stirring under conditions of a temperature of 25° C. for a treatment period of 120 minutes using a low-pressure UV lamp havin...

example 2

[0122] The same oxygen-delignified hardwood-kraft pulp as used in Example 1 was treated with ozone under the following conditions to give a pulp having a kappa number of 3.0 and a brightness of 56.6%.

[0123] Ozone treatment conditions: pulp consistency 10%, ozone feed 7 kg / ADTP, temperature 50° C., treatment period 30 seconds, pH 2.5 (adjusted with sulfuric acid).

[0124] A 5 g (bone dry weight) portion of the ozone-treated pulp thus obtained was collected and prepared into pulp slurries at pHs over an acidic to alkaline range and subjected to an irradiation reaction under similar conditions to those of Example 1, and the resulting pulps were measured for brightness. The results are shown in FIG. 4 and Table 1.

example 3

[0127] A 5 g (bone dry weight) portion of the same acid-treated pulp as used in Example 1 was collected and diluted to a pulp consistency of 0.25% by weight and then prepared into a pulp slurry at pH 11.5 (adjusted with NaOH and H2SO4). This slurry was injected into the experimental apparatus shown in FIG. 3, and subjected to an irradiation reaction while stirring under conditions of a temperature of 25° C. for varying treatment periods using a low-pressure UV lamp having a dominant wavelength at 254 nm. After the reaction was completed, the pulps were washed and then formed into sheets and measured for brightness. The results are shown in FIG. 5 and Table 2.

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Abstract

The present invention aims to further advance the acid treatment or irradiation technology for pulp to develop a bleaching process using smaller amounts of chlorine chemicals with higher efficiency as compared with conventional bleaching processes. It also aims to provide an excellent high brightness pulp having a low environmental impact and no discoloration as well as a paper containing it. The present invention provides a chlorine-free bleaching process with very high efficiency by irradiating a pulp washed after an acid treatment with UV light and/or visible light at a wavelength of 100-400 nm under alkaline conditions, preferably in a pH range of 10-13. The acid treatment can be performed under conditions of pH 1-6 and a temperature of 80° C. or more. The irradiation treatment can be performed in the presence of at least one compound selected from the group consisting of reducing agents, peroxides, and hydrogen-donating organic compounds. The present invention also provides a high brightness chemical pulp having an ISO brightness of 88% or more and a brightness loss of 1.0% or less in a specific fading test.

Description

TECHNICAL FIELD [0001] The present invention relates to a bleaching process for pulp characterized in that a pulp washed after an acid treatment is irradiated with UV light and / or visible light under alkaline conditions; a bleaching process characterized in that a pulp washed after an acid treatment is treated by a combination of irradiation with UV light and / or visible light and ozone feeding, thereby promoting pulp bleaching; and a bleaching process for chemical pulp by which a high brightness chemical pulp can be obtained (herein collectively referred to as the first invention); as well as a high brightness chemical pulp with greatly improved discoloration and a paper containing it, more specifically a novel high brightness chemical pulp with greatly improved discoloration obtained by further treating a bleached chemical pulp with UV light and a paper containing it (herein collectively referred to as the second invention). BACKGROUND ART [0002] The background art of the first inv...

Claims

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Application Information

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IPC IPC(8): D21C9/10D21C9/16
CPCD21C9/1005D21C9/16D21C9/1084
Inventor MIYAWAKI, SHOICHIKUROSU, KAZUHIROOCHI, TAKASHI
Owner NIPPON PAPER IND CO LTD
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