JP4603298B2 - Pulp bleaching method - Google Patents

Description

  The present invention relates to a pulp bleaching method characterized by irradiating ultraviolet light and / or visible light under alkaline conditions to a pulp washed after acid treatment.

  While interest has been focused on the environmental impact of substances discharged from the bleaching process of pulp and paper mills, the conventional bleaching method mainly using chlorine and / or chlorine-based chemicals, ECF bleaching without chlorine and further progress TCF bleaching, which does not use any chlorinated chemicals, is becoming the mainstream worldwide. Against this background, chemicals used in ECF bleaching and TCF bleaching have been limited to chemicals such as chlorine dioxide, hydrogen peroxide, oxygen and ozone. However, with these chemicals alone, combinations may naturally be limited, and there is a limit to the pulp quality obtained by bleaching, especially whiteness, or a large amount of expensive chemicals must be used to obtain it. Problems such as having to come out have come out. In order to solve these problems, there has been a demand for the development of a non-chlorine chemical having an unprecedented bleaching performance or a new bleaching method.

  Conventionally, it is known that various metals derived from pulp accelerate the decomposition of oxygen bleaching chemicals and waste oxygen bleaching chemicals. Therefore, as a technique for removing this metal and increasing the bleaching efficiency of oxygen-based bleaching chemicals, a relatively low-temperature acid treatment and / or chelating agent treatment has been proposed. In this acid treatment technique, pulp produced from lignocellulosic material is delignified by oxygen bleaching. First, nitrite and acid are added to the pulp to pretreat the pulp, followed by oxygen bleaching. Or a bleaching method in which delignification with peroxide and pressurized oxygen is performed in an alkaline medium after acid treatment is performed on the chemical pulp that has been digested or treated (for example, Patent Document 1). Or, Patent Document 2). In addition, after the digested chemical pulp is subjected to high-temperature and high-pressure oxygen bleaching treatment, followed by acid treatment or chelating agent treatment, it is treated with peroxide or hydrogen peroxide and oxygen in an alkaline medium. A bleaching method for performing delignification and bleaching is disclosed (for example, Patent Document 3).

  Moreover, it is known that hexeneuronic acid is involved in addition to conventional lignin and its modified products as a recent new finding regarding substances related to fading of ECF or TCF bleached pulp. This hexeneuronic acid is produced by demethylation from methylglucuronic acid in hemicellulose in the cooking process. This hexeneuronic acid is said to be involved in the fading of pulp. As one of the methods for removing this hexeneuronic acid, a relatively high temperature acid treatment technique has been proposed. In this method, the hexeneuronic acid and the lignin-modified product are removed by acid hydrolysis by treating the unbleached pulp under high temperature and acidity. For example, a suspension of cellulose pulp produced by the sulfate or alkaline method is heated and treated at about 85-150 ° C. at a pH of about 2-5 to remove at least about 50% of hexeneuronic acid in the cellulose pulp. However, a technique for reducing the pulp kappa number by 2 to 9 units is disclosed (see Patent Document 4).

  In addition, as a bleaching technique using light irradiation, a technique of irradiating ultraviolet light in hydrogen peroxide bleaching of unexposed KP (see, for example, Non-Patent Document 1 or Patent Document 5), or an ultraviolet light in oxygen bleaching of unexposed KP. A technique for irradiating light (for example, see Non-Patent Document 2) is disclosed.

Alternatively, a technique of irradiating ultraviolet light and / or visible light in a pulp bleaching method using a reducing agent (see Patent Document 6), or in the presence of an organic peroxide represented by ROOR ′ as an oxidizing agent, ultraviolet and A technique for irradiating visible light (see Patent Document 7) is disclosed.
Japanese Patent No. 2895977 JP-A-6-101186 JP-A-6-158573 Japanese National Patent Publication No. 10-508346 JP 2002-88673 A Japanese Patent Laid-Open No. 2002-88671 JP 2002-88672 A B. Marccia, et al. J34-J39, JOURNAL OF PULP AND PAPER SCIENCE: VOL.17, NO.2, March 1991 J. AbBot, et al. p198 ~ 202, Appita Vol, 46, No.3, May 1993

  The object of the present invention is to further develop the acid treatment or light irradiation technology of pulp as described above, to reduce chlorine chemicals, and to develop a more efficient bleaching method compared to conventional bleaching methods. It is in.

  As a result of intensive studies, the inventors of the present invention are very efficient by irradiating ultraviolet light and / or visible light having a wavelength of 100 to 400 nm under alkaline conditions in the range of pH 10 to 13 after the acid-treated pulp is washed. The present inventors have found a non-chlorine bleaching method and have arrived at the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

  The pulp to be subjected to the bleaching method of the present invention is kraft pulp (KP) washed after acid treatment, and unbleached KP, oxygen delignification KP, and ozone bleaching KP are particularly suitable. The pulp raw material is not particularly limited, and plants such as kenaf, hemp, rice, bacus, and bamboo may be used in addition to hardwood wood or softwood wood.

  The acid used for the acid treatment of the present invention may be an inorganic acid or an organic acid. As the inorganic acid, mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, phosphoric acid, and residual acid of chlorine dioxide generator can be used. Sulfuric acid is preferred. As the organic acid, acetic acid, lactic acid, succinic acid, citric acid, formic acid and the like can be used. The pH during the acid treatment is in the range of 1.0 to 6.0, preferably 1.0 to 5.0, more preferably 2.0 to 5.0, optimally 2.5 to 3.5. It is. When the pH is less than 1.0, the removal of hexeneuronic acid and the like and harmful metals is sufficient, but since the acid is excessive, the viscosity decreases greatly. On the other hand, when the pH exceeds 6.0, the acid concentration is low, and the removal of hexeneuronic acid and the like and harmful metals becomes insufficient. In the case of hardwood pulp having a large amount of hexeneuronic acid, if the pH during acid treatment is 2.5 to 3.5, the temperature of the acid treatment can be lowered, and the effect of reducing the acid treatment cost is produced. The acid treatment can be carried out under atmospheric pressure or under pressure, and the treatment temperature is 80 ° C. to 180 ° C., preferably 80 ° C. to 130 ° C. If the temperature is 30 ° C. or higher and lower than 80 ° C., the metal removal is effective, but there is no removal effect of hexeneuronic acid or the like. In addition, if it is less than 100 degreeC, since a pressure-resistant reaction container is not required, it is advantageous at an equipment cost.

The pulp concentration during acid treatment is in the range of 0.1 to 50% by weight, preferably 1.0 to 30% by weight, and more preferably 2.0 to 20% by weight.
The effect of removing hexeneuronic acid and the like and harmful metals is determined by the pH during the acid treatment, the reaction temperature, and the reaction time. From this, the reaction time is appropriately set according to the other two conditions, but the reaction time at a reaction temperature of 90 ° C. is 1.5 to 6 hours, the reaction time at a reaction temperature of 95 ° C. is 50 minutes to 5 hours, the reaction temperature Typical reaction times are 30 minutes to 4.5 hours at 100 ° C., and reaction times 5 to 50 minutes at a reaction temperature of 120 to 130 ° C.

  In addition, ozone bleaching performed under acidic conditions is a form of acid treatment targeted by the present application, and normal acidic ozone bleaching conditions can be applied. By the way, the conditions of general acidic ozone bleaching are: pH 1.0-8.0, pulp concentration 0.1-50% by weight, temperature 25-95 ° C., using ozone gas with ozone concentration 1-20% by weight, Is preferred. Further, the pressure here is not particularly limited from a negative pressure state to a pressurized state.

In addition, in the acid treatment, by using a chelating agent such as EDTA or DPTA in combination, a greater bleaching reaction promoting effect in the light irradiation treatment can be obtained.
The reason why the bleaching effect is promoted in the subsequent UV and / or visible light irradiation treatment as a result of acid treatment is not clear, but residual lignin in the pulp and metal ions, especially iron ions, form metal complexes. However, this is colored by the light irradiation treatment. Therefore, it is presumed that the bleaching effect by the light irradiation treatment is improved by removing the metal ions by the acid treatment.

  In the present invention, after the acid treatment including ozone, the treated pulp is dehydrated and / or washed, and these may be a known dehydrator and / or washer used in pulp production. In addition to fresh water, bleaching wastewater generated in the bleaching process after the acid treatment, papermaking wastewater generated from the papermaking process, and the like can be used for washing.

  In the present invention, the acid-treated pulp is irradiated with ultraviolet light and / or visible light having a wavelength of 100 to 400 nm under alkaline conditions, and the pH is 10 to 13 as alkaline conditions. When treating hardwood pulp, pH 10-12 is particularly preferred, and when treating softwood pulp, pH 11-13 is particularly preferred. In addition, as an alkali used for this pH adjustment, a normal alkaline chemical | medical agent can be used, However NaOH, KOH, silicate Na, and Na carbonate are especially preferable from points, such as easiness of handling.

  The pulp concentration during the light irradiation treatment of the present invention is preferably 0.1 to 12% by weight. If it is less than 0.1% by weight, the efficiency of the bleaching reaction is increased, but the energy efficiency is lowered, which is not preferable. When the content exceeds 12% by weight, the fluidity of the pulp slurry in the irradiation device is deteriorated, so that the bleaching reaction efficiency is lowered, which is not preferable.

  Moreover, the temperature of the pulp slurry at the time of this irradiation treatment is preferably 20 to 95 ° C, and if it is less than 20 ° C, the bleaching reaction efficiency is low. On the other hand, if it exceeds 95 ° C, the pulp quality may be deteriorated. Neither is it preferable to design an apparatus that takes pressure resistance into consideration, or the reactor internal pressure may exceed atmospheric pressure.

  In the irradiation apparatus of the present invention, the wavelength of light to be irradiated is preferably a wavelength of 100 to 400 nm, but a wavelength of 200 to 360 nm is particularly preferable. When the wavelength is less than 100 nm, the pulp strength is remarkably reduced because the photodegradation of cellulose is promoted, and when the wavelength exceeds 400 nm, the photobleaching property is greatly reduced because the photoexcitation of the photo-colored substance is insufficient. Neither is preferred.

  As a light source for irradiation, a light source having a wavelength in the range of 100 to 400 nm can be used. Specifically, a xenon short arc lamp, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a deuterium lamp, a metal halide lamp. Etc. [Kinoshita Shinobu "UV Irradiation Device", Adhesion (2002, Vol. 46, No. 7) p20-27, or Sugimori Akira "Photochemistry Chapter 8, Experimental Method I of Photochemistry", (Suikabo, 1998) p126- 136, see] is an example, and one or more of these can be used in any combination.

  Further, the degree of irradiation received by the pulp in the irradiation reactor can be arbitrarily set by adjusting the residence time of the pulp in the irradiation reactor, adjusting the energy amount of the irradiation light source, or the like. Specific examples of adjusting the residence time of pulp in the irradiation reactor include adjusting the pulp concentration in the irradiation device by diluting with water, or blowing an inert gas such as air or nitrogen into the pulp slurry. For example, adjusting the pulp concentration. These conditions can be appropriately set in accordance with the pulp quality (whiteness etc.) after the target light irradiation reaction.

  In addition, when irradiating light in the wavelength region of 135 to 242 nm, ozone is generated because air usually exists in the air layer around the light source. In the present invention, while continuously supplying air to the periphery of the light source, the generated ozone is continuously extracted and injected into the light irradiation raw material, so that the reaction can be performed without supplying ozone from outside the system. Ozone can be used as an auxiliary agent. Furthermore, a larger amount of ozone can be obtained by supplying oxygen to the gas layer around the light source. Of course, the generated ozone can be used not only as an auxiliary agent in the light irradiation reaction but also in normal ozone bleaching. As described above, in the present invention, it is also a great advantage that ozone generated secondary by the light irradiation reaction apparatus can be used.

  By applying this concept more actively, a plurality of light sources used in the light irradiation reaction apparatus can be selected from light sources having a characteristic wavelength region in the wavelength range of 100 to 400 nm and having different characteristic wavelengths. Specifically, it is a combination of a light source having a narrow wavelength characteristic of 135 to 242 nm, which has high ozone generation efficiency, and a light source having a wavelength region of 100 to 400 nm suitable for light irradiation reaction. Efficiency can be obtained.

In the light irradiation treatment of the present invention, as an auxiliary agent, a reducing agent (NaBH ₄ , hydrazine, hydrogen), an oxidizing agent (oxygen, ozone), a peroxide (hydrogen peroxide, peracetic acid, sodium percarbonate, hydrogen peroxide) Boric acid Na), hydrogen donating organic compound (alcohol, chain amine, ethylamine, diethylamine, cyclic amine, tetramethylpiperidine), organic compound having acetyl group (α-acetyl-γ-butyrolactone, acetol, acetone) ) Can be used in combination to increase the irradiation reaction efficiency.

An example of a system using the light irradiation reaction apparatus in the present invention is shown in FIG.
The acid-treated pulp is received in the light irradiation raw material adjustment tank (10), and is adjusted to a temperature, pH, and pulp concentration suitable for the light irradiation reaction while being stirred here. The adjusted light irradiation raw material 1 is sent to the light irradiation reaction device (12) by the light irradiation reaction device supply pump (11). If necessary, an auxiliary agent such as a reducing agent in the light irradiation reaction is added as a chemical solution before that. In addition to the chemical solution addition site shown in FIG. 1, this auxiliary agent may be added to the light irradiation raw material adjusting tank (10), or both, and may be arbitrarily selected according to the nature of the auxiliary agent or the light irradiation reaction conditions. However, it is preferable to add an auxiliary agent that reacts quickly or an auxiliary agent that is highly decomposable by itself as soon as it enters the light irradiation reactor (12), that is, at the chemical solution addition site in FIG.

  Further, if necessary, a gas can be supplied before entering the light irradiation reactor (12). This makes it possible to adjust the pulp concentration in the light irradiation reactor (12) (in this case, since the density of the gas is small, so it is considered as volume%), so the pulp in the light irradiation reactor (12) The residence time or irradiation reaction time can be arbitrarily adjusted. In addition, as a kind of gas used in this case, inert gas, such as air or nitrogen, is suitable, and these are disperse | distributed and used in a pulp slurry as a fine bubble. Moreover, also when using gas, such as hydrogen, oxygen, ozone, among the assistants of photoreaction, it can supply to the place of FIG. E similarly.

  Next, as for the pulp after the light irradiation reaction that has exited the light irradiation reaction device (12), the light irradiation reaction is terminated and sent to the next process for those for which the target pulp quality is obtained (C1: light irradiation reaction). Later pulp 1). On the other hand, the pulp whose target pulp quality is not obtained is recycled to repeat the light irradiation reaction (C2: pulp 2 after the light irradiation reaction). The ratio between C1 and C2 can be arbitrarily set according to the target pulp quality.

  The irradiation reaction apparatus basically includes an irradiation light source part and a pulp slurry container part, and the irradiation light source part exists inside the pulp slurry container part, and the irradiation light source part is a pulp slurry container part. [See Akira Sugimori “Photochemistry Chapter 8, Experimental Method I for Photochemistry” (Isaka Hanafusa, 1998) p126-136], but in the present invention, it is particularly limited. Not. Moreover, although the light from an irradiation light source part is irradiated to a pulp slurry, since gas, such as air, exists normally around a light source part, a partition is required. At that time, it is important to select a material for the partition wall so that the light energy is transmitted through the partition wall without being attenuated.

  In the present invention, for example, when light having a wavelength longer than 300 nm is used, one made of hard glass can be used. When using light having a wavelength shorter than 254 nm, one made of quartz glass is used. In addition, about the material of the part which does not participate in the light transmission reaction of this pulp slurry container, a suitable thing can be selected from the materials with little deterioration with respect to the wavelength of the light to be used.

  An example of the light irradiation reaction apparatus is shown in FIG. The acid-treated pulp is adjusted to a temperature, pH, and pulp concentration suitable for the light irradiation reaction, and further, if necessary, an auxiliary such as a reducing agent is added to the reaction layer (20) as a slurry (a1). 25). The injected pulp slurry flows in the apparatus (20), undergoes an irradiation reaction with light generated by the light irradiation light source (22) and passed through the partition wall (21: quartz glass tube), and then the apparatus outlet (26 ).

  Moreover, gas can be supplied as needed through the diffuser (24) attached to a light irradiation reaction apparatus (20). This makes it possible to adjust the pulp concentration in the light irradiation reactor (20) (in this case, since the density of the gas is small, so it is considered as volume%), so the pulp in the light irradiation reactor (20) The residence time or irradiation reaction time can be arbitrarily adjusted. In addition, as a kind of gas used for this purpose, inert gas, such as air or nitrogen, is suitable, and these are disperse | distributed and used in a pulp slurry as a fine bubble.

On the other hand, also when using gas, such as hydrogen, oxygen, ozone, among the assistants of photoreaction, gas can be supplied through this diffuser (24).
In addition, as shown in FIG. 2, when light having a wavelength region of 135 to 242 nm is used as a light irradiation light source and air or oxygen is injected as a light source cooling gas (b1), There is ozone. The exhaust gas containing ozone is injected into the pulp slurry in the light irradiation reactor (20) through the air diffuser (24), so that ozone can be used as a reaction aid without supplying ozone from outside the system. Can be used. The generated ozone can also be used for ordinary ozone bleaching other than the auxiliary agent during the light irradiation reaction. In addition, a gas having an effect as an auxiliary agent for the light irradiation reaction such as hydrogen, oxygen and ozone can be injected from outside the system and used in combination. Use of these gases can be arbitrarily set by attaching three-way valves (23a, 23b).

In addition, in the light irradiation reaction apparatus, ancillary equipment such as a temperature / pH adjusting device, a gas concentration detecting device and the like can be arbitrarily attached as necessary.
In addition, the light irradiation treatment of the present invention can be repeated one or more times, but this is in accordance with the situation such as bleaching efficiency, target pulp quality (whiteness), or the relationship with other bleaching methods to be combined. Can be set as appropriate. Examples in which the light irradiation treatment is repeated one or more times are as follows: (1) Two or more light irradiation devices in FIG. 1 can be provided. In this case, it may be a series or parallel. (2) A plurality of irradiation light sources (having the same characteristics or different characteristics) may be provided in the light irradiation apparatus in FIG. (3) The system shown in FIG. 1 can be recirculated.

  The bleaching method of the present invention can be arbitrarily combined with all other known bleaching methods regardless of chlorine or non-chlorine. Specifically, the bleaching method of the present invention can be followed by another bleaching method, or another bleaching method can be performed following the bleaching method of the present invention. In particular, it is preferable to perform a hydrogen peroxide treatment after the bleaching of the present invention. Further, these sequences can be repeated a plurality of times, and at this time, a washing stage can be provided between different bleaching methods. In addition, the bleaching sequence incorporating the light irradiation system can be repeated a plurality of times. In addition, when performing multiple light irradiation processes, it is preferable to wash | clean after a light irradiation process.

EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these.
<Measurement of pulp properties>
Measurement of kappa number Measurement of kappa number: Measured according to JIS P 8211.

Pulp whiteness measurement: After the pulp was disaggregated, a sheet having a basis weight of 60 g / m ² was prepared according to Tappi test method T205os-71 (JIS P 8209).
The whiteness of the pulp was measured according to P8148.
<Experimental device>
The experimental apparatus used in the examples of the present application is shown in FIG.

  A 3 L glass cylinder (100 mmφ × 620 mmH) was used as the light irradiation reaction tank (1). In addition to the agitator (4) and diffuser pipe (5) shown in the figure, the light irradiation reaction tank (1) is provided with a temperature control device and a pH measuring device. A light irradiation light source (16W low-pressure mercury lamp, AY-1 manufactured by Nippon Photo Science Co., Ltd.) is installed in a quartz glass tube (45 mmφ × 470 mmH, thickness 2 mm), and air can be injected around the light irradiation light source. It has a structure.

[Example 1]
Kraft pulp (kappa number 11.6, ISO whiteness 45.6%) after hardwood oxygen delignification manufactured by Nippon Paper Industries Co., Ltd. was used.

Acid treatment was performed under the following conditions to obtain a pulp having a copper number of 5.5 and a whiteness of 47.5%.
Acid treatment conditions: Pulp concentration 10% by weight, pH 3.0 (using sulfuric acid) temperature 95 ° C., treatment time 180 minutes. After completion of the treatment, the pulp was washed with water.

After taking 5 g (absolutely dry) of the acid-treated pulp thus obtained and adjusting the pulp concentration to 0.25% by weight, a pulp slurry having a pH ranging from acidic to alkaline is adjusted using NaOH and H ₂ SO _4. did. These slurries were poured into the experimental apparatus shown in FIG. 3, and a light irradiation reaction was performed under the conditions of using a low-pressure ultraviolet lamp having a main wavelength of 254 nm at a temperature of 25 ° C. and a treatment time of 120 minutes while stirring. After the reaction, the pulp was washed and then a sheet was prepared to measure the whiteness. The results are shown in FIG. In FIG. 4, pulp slurry (3 samples) having a treatment pH in the light irradiation reaction of 10 to 13 was set as Example 1, and pulp slurry of less than 10 was set as Reference Example 1 (4 samples).

[Example 2]
Using the same hardwood oxygen delignified kraft pulp as in Example 1, ozone treatment was performed under the following conditions to obtain a pulp having a copper number of 3.0 and a whiteness of 56.6%.

Ozone treatment conditions: pulp concentration 10%, ozone addition amount 7 kg / ADTP, temperature 50 ° C., treatment time 30 seconds, pH 2.5 (using sulfuric acid).
It was obtained after taking 5 g (absolutely dry) of the ozone-treated pulp thus obtained, adjusting the pulp slurry at a pH ranging from acidic to alkaline under the same conditions as in Example 1, and performing light irradiation reaction. The whiteness of the pulp was measured. The results are shown in FIG. In FIG. 4, pulp slurry (3 samples) having a treatment pH in the light irradiation reaction of 10 to 13 was set as Example 2, and pulp slurry of less than 10 was set as Reference Example 2 (4 samples).

[Comparative Example 1]
After taking 5 g (absolutely dry) of kraft pulp after broad-leaved oxygen delignification as in Example 1, under the same conditions as in Example 1, adjusting the pH slurry slurry in the acidic to alkaline region, and performing a light irradiation reaction, The whiteness of the obtained pulp was measured. The results are shown in FIG.

[Example 3]
After taking 5 g (absolutely dry) of the same acid-treated pulp as in Example 1 and setting the pulp concentration to 0.25% by weight, a pulp slurry having a pH of 11.5 was prepared (using NaOH and H ₂ SO ₄ ). This slurry was poured into the experimental apparatus shown in FIG. 3, and a light irradiation reaction was carried out under stirring at a temperature of 25 ° C. under a condition that a low-pressure ultraviolet lamp having a dominant wavelength at 254 nm was used. After the reaction, the pulp was washed and then a sheet was prepared to measure the whiteness. The results are shown in FIG.

[Example 4]
5 g (absolutely dry) of the same ozone-treated pulp as in Example 2 was taken, and under the same conditions as in Example 3, a light irradiation reaction was performed while changing the treatment time, and the whiteness was measured. The results are shown in FIG.

[Comparative Example 2]
5 g (absolutely dry) of kraft pulp after the broad-leaved tree oxygen delignification as in Comparative Example 1 was taken, and under the same conditions as in Example 3, a light irradiation reaction was performed with varying treatment time, and the whiteness was measured. The results are shown in FIG.

[Example 5]
Kraft pulp (copper number 9.1, ISO whiteness 33.3%) after coniferous oxygen delignification manufactured by Nippon Paper Industries Co., Ltd. was used.

Acid treatment was performed under the following conditions to obtain a pulp having a kappa number of 9.1 and a whiteness of 34.3%.
Acid treatment conditions: Pulp concentration 10% by weight, pH 3 (sulfuric acid addition) temperature 95 ° C., treatment time 180 minutes. After completion of the treatment, the pulp was washed with water.

After taking 5 g (absolutely dry) of the acid-treated pulp thus obtained and adjusting the pulp concentration to 0.25% by weight, a pulp slurry having a pH ranging from acidic to alkaline is adjusted using NaOH and H ₂ SO _4. did. These slurries were poured into the experimental apparatus shown in FIG. 3, and a light irradiation reaction was performed under the conditions of using a low-pressure ultraviolet lamp having a main wavelength of 254 nm at a temperature of 25 ° C. and a treatment time of 120 minutes while stirring. After the reaction, the pulp was washed and then a sheet was prepared to measure the whiteness. The results are shown in FIG.

[Comparative Example 3]
5 g (absolutely dry) of kraft pulp after coniferous oxygen delignification as in Example 5 was taken, and under the same conditions as in Example 5, after adjusting the pH slurry slurry in the acidic to alkaline region, and performing a light irradiation reaction, The whiteness of the obtained pulp was measured. The results are shown in FIG.

[Example 6]
Kraft pulp (kappa number 9.5, ISO whiteness 47.5%) after hardwood oxygen delignification manufactured by Nippon Paper Industries Co., Ltd. was used.

Acid treatment was performed under the following conditions to obtain a pulp having a copper number of 5.5 and a whiteness of 48.6%.
Acid treatment conditions: Pulp concentration 10% by weight, pH 3 (sulfuric acid added), temperature 85 ° C., treatment time 180 minutes. After completion of the treatment, the pulp was washed with water.

  5 g (absolutely dry) of the acid-treated pulp thus obtained was taken and the pulp concentration was adjusted to 0.5% by weight, and then a pH 11.5 pulp slurry was prepared using NaOH. These slurries were poured into the experimental apparatus shown in FIG. 3, and a light irradiation reaction was performed under the conditions of using a low-pressure ultraviolet lamp having a main wavelength of 254 nm at a temperature of 25 ° C. and a treatment time of 120 minutes while stirring. After the reaction, the pulp was washed and then a sheet was prepared to measure the whiteness. The results are shown in Table 4.

[Comparative Example 4]
After taking 15 g (absolutely dry) of the same acid-treated pulp as in Example 6 and setting the pulp concentration to 0.5% by weight, it was poured into the experimental apparatus of FIG. 3 and stirred at a temperature of 25 ° C. and a pH of 11.5. Ozone treatment was performed for 120 minutes (no light irradiation light source was used). During this time, the cumulative amount of ozone added to the pulp was 0.7% by weight. The results are shown in Table 4.

[Example 7]
15 g (absolutely dry) of the same acid-treated pulp as in Example 6 was taken, and the pulp concentration was adjusted to 0.5% by weight. Then, the pulp was poured into the experimental apparatus of FIG. 3 and stirred at a temperature of 25 ° C. and a pH of 11.5. Ozone treatment and light irradiation reaction were simultaneously performed using a low-pressure ultraviolet lamp having a dominant wavelength at 254 nm for 120 minutes. During this time, the cumulative amount of ozone added to the pulp was 0.7% by weight. The results are shown in Table 4.

[Example 8]
The same kraft pulp after broad-leaved oxygen delignification as in Example 1 (kappa number 11.6, ISO whiteness 45.6%) was subjected to ozone treatment under the following conditions, kappa number 3.0, whiteness 56 .6% pulp was obtained.

Ozone treatment conditions: pulp concentration 10%, ozone addition amount 7 kg / ADTP, temperature 55 ° C., treatment time 30 seconds, pH 2.5.
15 g (absolutely dry) of the ozone-treated pulp thus obtained was taken, and the pulp concentration was adjusted to 0.5% by weight. Then, the pulp was poured into the experimental apparatus of FIG. 3 and stirred at a temperature of 25 ° C. and a pH of 11.5. Then, a light irradiation reaction was performed using a low-pressure ultraviolet lamp having a dominant wavelength at 254 nm for 120 minutes. The results are shown in Table 4.

It is a figure which shows an example of the system using the irradiation reaction apparatus in this invention. It is a figure which shows the internal irradiation type irradiation reaction apparatus used by this invention. It is a figure which shows the internal irradiation type | mold irradiation reaction apparatus used by this invention Example. It is the figure which showed the relationship between process pH and whiteness in the light irradiation process using L material pulp. It is the figure which showed the relationship between the light irradiation time in the light irradiation process using L material pulp, and whiteness. It is the figure which showed the relationship between process pH and whiteness in the light irradiation process using N material pulp.

Explanation of symbols

10: Light irradiation raw material adjustment tank 11: Light irradiation reaction apparatus supply pump 12: Light irradiation reaction apparatus 20: Light irradiation reaction tank 21: Quartz glass tube 22: Light irradiation light source 23a, 23b: Three-way valve 24: Air diffuser, diffuser Trachea 25: Pulp slurry inlet 26: Pulp slurry outlet 27: Stirrer

Claims (6)

A pulp bleaching method, wherein a pulp washed after acid treatment is irradiated with ultraviolet light and / or visible light having a wavelength of 100 to 400 nm under alkaline conditions in the range of pH 10 to 13. Bleaching method. The method of bleaching pulp according to claim 1, wherein the acid treatment is performed under conditions of pH 1 to 6 and temperature of 80 ° C or higher. The method for bleaching pulp according to claim 1, wherein the acid treatment is performed under conditions of pH 1.0 to 8.0 and temperature 25 to 95 ° C in the presence of ozone. Light irradiation treatment, a reducing agent, a peroxide, according to claim 1 to 3, wherein any one, characterized in that is carried out in the presence of at least one compound selected from the group of hydrogen-donating organic compound Pulp bleaching method. Claim 1-4 bleaching method of any claimed pulps irradiation light source of the ultraviolet light and / or visible light, characterized in that it consists of different light sources having wavelength characteristics. Bleaching process according to claim 1-5 pulp according to any one of and repeating a plurality of times of light irradiation treatment.

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