JP5953909B2 - Method for producing dissolving pulp - Google Patents

Description

  The present invention relates to a method for producing dissolving pulp from lignocellulosic material. More specifically, the present invention relates to a method for efficiently producing a variety of dissolving pulps having a wide range of pulp viscosities.

In order to produce dissolving pulp from a lignocellulosic material, it is necessary to selectively remove hemicellulose and lignin in the lignocellulosic material to increase the purity of the cellulose. As an index representing cellulose purity, α-cellulose content is generally used, and the higher the value, the higher the quality of dissolved pulp. Two methods of dissolving pulp have been known for a long time: acidic sulfite cooking method and prehydrolysis-kraft cooking method. Acid sulfite cooking method digests many hemicelluloses and lignin in lignocellulosic materials. The pre-hydrolysis-kraft cooking method removes most of the hemicellulose by acid hydrolysis in the pre-hydrolysis step, while removing a small amount of hemicellulose and most of the lignin in the subsequent kraft cooking, whereas the pre-hydrolysis-kraft cooking method removes it in one step. To do. In the prehydrolysis step, simply adding water to the lignocellulosic material and heating, the acetyl group in hemicellulose is eliminated to produce acetic acid, which automatically becomes acidic and acid hydrolysis proceeds. Is carried out without external addition. Comparing acid sulfite cooking with prehydrolysis-kraft cooking, acid sulfite cooking is more efficient because it can remove hemicellulose and lignin in one step when focusing solely on producing dissolved pulp However, the prehydrolysis-kraft cooking method is more advantageous when focusing on separating and effectively utilizing the waste hemicellulose and lignin separately. In recent years, it is called biorefinery to separate cellulose, hemicellulose, and lignin in lignocellulosic material, which is a raw material for biomass, and to produce high-value substances from each. The importance of kraft cooking has been reaffirmed.

  Dissolved pulp differs in pulp viscosity and ash content required depending on the application. This is because dissolved pulp is usually used after being chemically processed, but the processing conditions and required quality of the processed product differ depending on the application. In order to satisfy these requirements, it is reasonable to produce dissolved pulp with relatively high pulp viscosity and ash content, and to perform two treatments to lower pulp viscosity and reduce ash content as required. It is. As a method for reducing pulp viscosity, a method of treating hypochlorite under alkaline conditions is often used, and it is still mainstream. However, when hypochlorite treatment is carried out under alkaline conditions, there is a problem that chloroform is produced as a by-product and adversely affects the environment. On the other hand, as a method for reducing the ash content in the dissolving pulp, a method is generally used in which the ash content is liberated and removed by treatment with an inorganic acid such as sulfuric acid, nitric acid or hydrochloric acid. As described above, the treatment for reducing the viscosity of the pulp and the treatment for reducing the ash are greatly different in pH, and need to undergo a useless neutralization reaction between the two treatments, and is an efficient treatment. I could not say.

In order to solve the above problem, a method of simultaneously reducing the pulp viscosity while reducing the ash content using an acid can be considered. As an example in which the viscosity of the pulp is lowered by using an acid, an unbleached pulp containing hemicellulose for papermaking is used as a target, and the pH is 1.0 to 1. using an inorganic acid for the purpose of decomposing the hemicellulose main chain or side chain. 6. Examples in which viscosity decreases when processing at 80 ° C or higher (Patent Document 1), and cases in which viscosity decreases when processing at pH 2 to 5 and 85 to 150 ° C using inorganic and organic acids (Patent Document 1) 2), etc. are known. However, all of these treatments were for unbleached pulp containing hemicellulose for papermaking, and the effect on the pulp after bleaching was low and it was unclear.

On the other hand, as an example of processing a pulp by adding a peroxide under acidic conditions, a method of decomposing hexeneuronic acid in hemicellulose (Patent Document 3) or bleaching is intended for unbleached pulp containing hemicellulose for papermaking. A method for decomposing hexeneuronic acid in hemicellulose (Patent Document 4) and the like is known. However, all of these treatments were intended for pulp containing hemicellulose for papermaking, and the effect on pulp viscosity was unclear for dissolved pulp with a low hemicellulose content.

Japanese National Patent Publication No. 6-280177 Japanese National Patent Publication No. 10-508346 JP 2003-105684 A JP 2007-169831 A

In the method for producing a dissolving pulp from a lignocellulosic material, the dissolving pulp can be adjusted to a desired pulp viscosity and ash content by a final one-stage treatment after cooking and bleaching the pulp.

  The present inventors have conducted various studies on a method for efficiently producing a wide variety of dissolving pulp using a lignocellulose material as a raw material by a prehydrolysis-alkali digestion method. As a result, prehydrolysis has achieved a desired cellulose purity. While controlling the conditions to control, while producing the dissolving pulp while keeping the subsequent alkaline and bleaching conditions as constant as possible, and finally adding the peroxide under acidic conditions, It discovered that a cellulose purity, a pulp viscosity, and ash content could be controlled to a desired value, and resulted in this invention. More specifically, for example, when hardwood is used as a raw material, pre-hydrolysis is carried out at a P factor of 200 to 1000, and then alkali digestion is carried out so that the kappa number after cooking is 6 to 13; A dissolved pulp having a high pulp viscosity and a high pulp viscosity is obtained, and further, the bleached pulp is bleached to 85 to 92% ISO, and then treated with hydrogen peroxide under an acidic condition. The inventors have found that the viscosity can be lowered to the pulp viscosity, and have reached the present invention.

The present invention includes the following inventions.
(1) A method for producing a dissolving pulp by using a lignocellulosic material as a raw material by a prehydrolysis-alkali digestion method, wherein the P-factor at the time of prehydrolysis is 200 to 1000, A method for producing a dissolving pulp, in which a pulp is bleached and then treated by adding a peroxide under acidic conditions.
(2) A method for producing a dissolving pulp using a lignocellulosic material as a raw material by a prehydrolysis-alkali digestion method, wherein the P-factor at the time of prehydrolysis is 200 to 1,000, A method for producing a dissolving pulp, comprising bleaching the pulp and adding a peroxide under acidity to reduce the ash content in the resulting dissolving pulp.
(3) The method for producing a dissolving pulp according to (1) or (2), wherein the pulp after the prehydrolysis-alkali digestion is bleached to 85 to 92% ISO and then treated by adding a peroxide under acidic conditions. . (4) The method for producing a dissolving pulp according to any one of (1) to (3), wherein the peroxide is hydrogen peroxide.
(5) The method for producing a dissolving pulp according to any one of (1) to (4), wherein the alkali cooking method is a kraft cooking method.
(6) In the case of lignocellulosic material hardwood is 6-13 are kappa number of the pulp after the alkali digestion to be al (1) - (5) The method of producing dissolving pulp according to any one of .

  According to the present inventor, in a method for producing a dissolved pulp by using a lignocellulosic material as a raw material by a prehydrolysis-alkali cooking method, the whiteness of the pulp is previously bleached to 85 to 92% ISO, and finally It became possible to produce various types of dissolving pulp by adding peroxide under acidic conditions.

The lignocellulosic material that can be used in the present invention may be wood or non-wood, but considering production efficiency, wood with high bulk weight is preferably used. Among woods, broad-leaved wood materials are generally preferred because they have a higher bulk weight than conifers, and some eucalyptus and acacia with a higher bulk weight among hardwoods are preferably used. Examples of applicable broad-leaved trees include eucalyptus globulas, eucalyptus grandis, eucalyptus eurograndis, eucalyptus perita, eucalyptus brushana, acacia melanci, etc. It is not particularly limited. Expressed in volume weight value, it is preferably 450~700kg / ^{m 3,} more preferably those of 500~650kg / ^{m 3.} A material having a bulk weight lower than 450 kg / m ³ is disadvantageous from the viewpoint of pulp production efficiency as described above. On the other hand, a material having a bulk weight higher than 700 kg / m ³ is disadvantageous because chemical penetration during pre-hydrolysis or alkali cooking tends to be insufficient, and as a result, pulp quality may be lowered. Needless to say, broad-leaved trees, coniferous trees, and non-woods can be used alone or in combination, and the combination is not limited.

  In the present invention, the lignocellulosic material is first heated in the presence of water and subjected to a prehydrolysis treatment. Here, the amount (liquid ratio) of water relative to the lignocellulosic material is 1.0 to 10, preferably 1.5 to 5.0. When the liquid ratio is less than 1.0, water is insufficient, hydrolysis does not proceed sufficiently, and the reaction becomes non-uniform, which is not suitable. If it is higher than 10, the amount of heat required for heating to a desired temperature increases, which is not economical, which is not suitable. The method of adding water is not particularly limited, and water may be added from the outside, the water originally contained in the lignocellulosic material may be used, or when steam is used during heating. May use water contained in steam. In addition to water, chemicals that directly or indirectly assist the hydrolysis of polysaccharides, such as alkalis, acids, and chelating agents, can also be added. The strength of the prehydrolysis of the present invention is 200 to 1000 as a P factor, the temperature is 140 to 200 ° C., preferably 160 to 170 ° C., and the treatment time is determined according to the treatment temperature. The P factor is the product of temperature and time at the time of prehydrolysis, and is expressed as Chemical Formula 1.

Ｔ：絶対温度（℃＋２７３．５）
ＫＨ（Ｔ）／Ｋ１００℃：グリコシド結合の酸加水分解の相対速度

T: Absolute temperature (° C + 273.5)
KH (T) / K100 ° C .: Relative rate of acid hydrolysis of glycosidic bond

If the P-factor is lower than 200, the acid hydrolysis of hemicellulose is not sufficient, and the subsequent cellulose digestion is not suitable because the cellulose purity of the pulp cannot be sufficiently increased. When the P factor is higher than 1000, acid hydrolysis of cellulose proceeds, and the cellulose purity of the pulp cannot be sufficiently increased. Further, the pulp viscosity is lowered, and the pulp yield is also lowered, which is not suitable. . When the prehydrolysis temperature is lower than 140 ° C., it is necessary to set the reaction time to 10 hours or more, and it is not economical because it is necessary to prepare a huge reaction vessel. On the other hand, when the temperature is higher than 200 ° C., the reaction time may be required to be 0.1 hour or less in some cases, and it becomes difficult to control the reaction, and the material of the apparatus that can withstand such a thermal condition becomes expensive. Therefore, it is not economically suitable.

The apparatus used in the prehydrolysis step is not particularly limited as long as it can hold the lignocellulosic material in a pressurized state in a water-containing state for a desired time. A digester, a batch kettle, etc. are used. In the prehydrolysis step of the present invention, after completion of the reaction, it is dehydrated or diluted and washed, dehydrated, and sent to the next alkali cooking step. The waste water after pre-hydrolysis is sent to a flash tank, divided into a gas layer and a liquid layer, and flurrals contained in the gas layer are extracted and used to extract hemicellulose degradation products contained in the liquid layer. It is possible to use it.

Although the apparatus used for the alkali cooking of this invention is not specifically limited, A general purpose continuous cooking kettle, a batch kettle, etc. are used suitably. As the alkali cooking method, known cooking methods such as kraft cooking, polysulfide cooking, soda cooking, alkali sulfite cooking and the like can be used, but considering pulp quality, energy efficiency, etc., kraft cooking method is preferably used. . For example, in the case of kraft cooking of wood, the sulfidity of the kraft cooking solution is 5 to 75%, preferably 20 to 35%, and the effective alkali addition rate is 5 to 30% by weight, preferably 10 to 25% by weight of the absolutely dry wood. %, The cooking temperature is 140-170 ° C., and the cooking method in which the cooking white liquor is added in portions may be used, and the method is not particularly limited.

In cooking, as a cooking aid in the cooking solution to be used, known cyclic keto compounds, for example, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone, and nuclear substitutes such as alkyl and amino of the quinone compounds, or the quinone series 1 selected from hydroquinone compounds such as anthrahydroquinone, which is a reduced form of the compound, and a 9,10-diketohydroanthracene compound which is a stable compound obtained as an intermediate of an anthraquinone synthesis method by the Diels-Alder method A seed | species or 2 or more types may be added, and the addition rate is 0.001-1.0 mass% per the absolute dry mass of a wood chip.

The kappa number after cooking is not particularly limited, but considering the pulp quality and subsequent bleaching properties, for example, when hardwood is used as the raw material, the kappa number is preferably 6 to 13, and coniferous as the raw material. In some cases, the kappa number is preferably 20 to 35.

In the present invention, unflooded pulp obtained by a known alkali digestion method is subjected to a bleaching process by a known bleaching method after washing, rough selection and selection steps. Preferably, first, delignification is performed by an oxygen delignification method. As the oxygen delignification method used in the present invention, the intermediate concentration method or the high concentration method can be applied as it is, but the intermediate concentration method performed at a pulp concentration of 8 to 15% does not require a special dehydrating apparatus, and the operability is improved. Is preferable. As the alkali used in the oxygen delignification method, caustic soda or oxidized kraft white liquor can be used. As the oxygen gas, oxygen from a cryogenic separation method, oxygen from PSA (Pressure Swing Adsorption), VSA (Vacuum) Oxygen from Swing Adsorption) can be used. The oxygen gas and alkali are added to a medium-concentration pulp slurry in a medium-concentration mixer and mixed sufficiently, and then sent to a reaction tower capable of holding a mixture of pulp, oxygen and alkali for a certain period of time under pressure, and delignified. Is done. The oxygen gas addition rate is 0.5 to 3% by mass per mass of dry pulp, the alkali addition rate is 0.5 to 4% by mass, the reaction temperature is 80 to 120 ° C., the reaction time is 15 to 100 minutes, and the pulp concentration Is 8 to 15% by mass, and other known conditions can be applied. In the present invention, in the oxygen delignification step, it is a preferred embodiment that the oxygen delignification is continuously performed a plurality of times and the delignification proceeds as much as possible. The pulp subjected to oxygen delignification is sent to a washing stage.

In the present invention, it is preferable to provide a washing stage for each bleaching stage, not limited to the washing stage after oxygen delignification, and as a washing machine used in the washing stage, a pressure diffuser, a diffusion washer, a pressure drum washer, a horizontal A long-net type washer, a press washer, etc. can be mentioned, and it is not particularly limited. In each cleaning stage, a single cleaning machine can be used or a plurality of cleaning machines can be used. In the present invention, a cleaning aid such as an alkali, an acid, a chelating agent, and a surfactant can be added to the cleaning water in each cleaning stage. Further, countercurrent cleaning can be performed in which the cleaning wastewater is reused as cleaning water for the preceding cleaning stage.

  In the present invention, the unbleached pulp is preferably sent to a multi-stage bleaching step via an oxygen delignification step. In the multistage bleaching process of the present invention, known ECF bleaching stages such as chlorine dioxide (D), alkali (E), oxygen (O), hydrogen peroxide (P), and ozone (Z) can be used in combination. Later, the aforementioned cleaning stage can be provided. In addition, a high-temperature acid treatment stage (A), an acid washing stage, a high-temperature chlorine dioxide bleaching stage, a chelating agent treatment stage using ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), etc. are introduced during the multistage bleaching process. You can also. In the multistage bleaching process of the present invention, bleaching is preferably performed so that the whiteness of the pulp is 85 to 92% ISO. When the whiteness is less than 85% ISO, the whiteness becomes lower than 90% ISO even if the subsequent peroxide addition treatment is performed under acidic conditions. When the whiteness is higher than 92% ISO, the amount of bleaching chemicals used in the multi-stage bleaching process is excessive and not economical, and in some cases, additional functional groups are introduced into the dissolved pulp, and the dissolved pulp It is not suitable because the quality of

In the present invention, the peroxide addition treatment under acidic conditions is always performed after the multi-stage bleaching step. The peroxide addition treatment under acidic conditions of the present invention has a pulp concentration in the range of 1 to 40% by weight, preferably 8 to 15% by weight, pH of 1 to 5, preferably 2 to 4, and temperature of 30 to 30. It is carried out at 95 ° C, preferably 50 to 90 ° C. If the pulp concentration is less than 1% by weight, too much acid is added for pH adjustment, which is not economical and not suitable. If it is higher than 40% by weight, mixing of the pulp and chemicals becomes insufficient. This is not suitable because the reaction becomes uneven. When the pH is lower than 1, the reaction vessel tends to corrode. When the pH is higher than 5, the ash removal effect becomes insufficient, which is not suitable. When the reaction temperature is lower than 30 ° C., the effect of reducing the viscosity of the pulp becomes insufficient. When the reaction temperature is higher than 95 ° C., a large amount of energy is required to raise the temperature, which is not economical.

In the peroxide addition treatment under acidic conditions of the present invention, an acid can be added in order to obtain an acidic state. The acid may be any of organic acids such as formic acid, succinic acid, and acetic acid, and inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and is not particularly limited. However, relatively inexpensive sulfuric acid, hydrochloric acid, etc. are preferably used. Is done. The peroxide used in the peroxide addition treatment under the acidity of the present invention may be either an organic peracid or an inorganic peracid, and is not particularly limited, but is preferably relatively inexpensive. Hydrogen peroxide, which has no environmental impact even after decomposition, is used. For example, in the case of hydrogen peroxide, the addition rate is 0.01 to 2%, preferably 0.1 to 1.0%, based on the absolute dry weight of pulp. When the addition rate is less than 0.01%, the effect of addition is hardly observed, and when the addition rate is 2% or more, the reaction cannot be completed. The treatment time is 10 minutes or more, preferably 30 minutes to 180 minutes, but the time is not particularly limited. The pulp viscosity reduction effect due to the addition of peroxide is due to the fact that the cellulose purity of the treatment target is high, so that the reaction frequency of the peroxide and cellulose is high, and the depolymerization is easy. This is considered to be due to the fact that such elements are oxidized, dissolved in water, and easily removed.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples. Unless otherwise indicated, the measurement of the bulk weight of the chip, the pulp kappa number, the whiteness, the viscosity, and the α-cellulose was carried out by the following methods. Moreover, the pitch number in the filtrate after prehydrolysis was evaluated visually. In addition, the addition rate of the chemical | medical agent in an Example and a comparative example shows the mass% per absolute dry pulp mass.

1. Pulp kappa number measurement Measured according to JIS P 8211.

2. Measurement of the whiteness of the pulp After the bleached pulp was disaggregated, a sulfuric acid band was added to the pulp slurry at a ratio of 3.0% to the pulp, and a basis weight of 60 g / m ² prepared according to the Tappi test method T205os-71 (JIS P 8209). Using the sheet, the whiteness of the pulp was measured in accordance with JIS P 8123.

3. Viscosity measurement of pulp J TAPPI No. It measured according to 44.

4). Measurement of α-cellulose content of pulp Measured according to JIS P8101.

5. Pulp ash measurement Measured according to JIS P 8251.

Example 1
Eucalyptus / perita material chips (300 g) were collected in an absolutely dry mass and immersed in 10 liters of tap water overnight. Thereafter, the chips are taken out, emptied through a 400 mesh sieve, and filtered. Then, the dehydrated chips are put into a 2.5 liter autoclave, tap water is added so that the liquid ratio becomes 3, and 170 Prehydrolysis treatment was performed at 60 ° C. for 60 minutes. The P factor at this time was 597. After pre-hydrolysis, waste gas was extracted from the deaeration cock of the autoclave, and after confirming that the pressure in the autoclave was zero, the treated chips were evacuated through a 400-mesh sieve and filtered. 200 g of the chips after filtration were collected at an absolute dry mass, and again put into a 2.5 liter autoclave. The liquid ratio was 5, the active alkali was 20% per absolute dry chip mass, the sulfidity of the cooking liquid was 28%, and the cooking temperature was 165 Kraft cooking was performed under the conditions of ℃ and cooking time of 50 minutes. After cooking, the black liquor and the pulp were separated, and the pulp was carefully selected with a flat screen equipped with an 8-cut screen plate to obtain 84.0 g of unbleached pulp having a kappa number of 10.8.

70.0 g was collected from the unbleached kraft pulp by dry weight, 2.0% caustic soda was added to the dry pulp weight, diluted with ion-exchanged water to adjust the pulp concentration to 10%, and heated indirectly. It put into the type | mold autoclave, 99.9% of commercially available compressed oxygen gas was inject | poured, the gauge pressure was 0.5 Mpa, and oxygen delignification was performed for 60 minutes at 100 degreeC. After the oxygen bleaching was completed, the pressure was reduced until the gauge pressure became 0.05 MPa or less, and the pulp was taken out from the autoclave, washed and dehydrated with 7 liters of ion-exchanged water.

60 g of kraft pulp after alkaline oxygen delignification was collected at an absolute dry mass, put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, and then 1.0% of dioxide dioxide per mass of the absolute dry pulp. Chlorine was added and D0 stage treatment was performed by immersing in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. The pulp after the D0 stage is put in a plastic bag, ion-exchanged water is added to adjust the pulp concentration to 10%, 1.0% caustic soda and 0.2% hydrogen peroxide are added per mass of dry pulp. After mixing well, it was immersed for 90 minutes in a constant temperature water bath having a temperature of 70 ° C. to perform E / P stage treatment. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel.

The pulp after the E / P stage is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 0.3% of chlorine dioxide is added per mass of dry pulp, and the temperature is kept at 70 ° C. It was immersed in a water tank for 60 minutes to perform D1 stage bleaching. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A pulp having a whiteness of 90.5%, a viscosity of 14.4 cP, α-cellulose of 97.6%, and an ash content of 0.22% was obtained.

The pulp after stage D1 is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, and then 0.5% sulfuric acid and 0.3% hydrogen peroxide are added per mass of dry pulp, It was immersed in a constant temperature water bath at a temperature of 90 ° C. for 60 minutes, and an acidic peroxide treatment was performed at a treatment pH of 2.5. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having a whiteness of 91.5% ISO, a viscosity of 8.0 cP, α-cellulose of 97.7%, and an ash content of 0.08% was obtained. The above results are shown in Tables 1 and 2.

Example 2
In Example 1, the same operation as in Example 1 was performed except that the temperature at the prehydrolysis was changed to 157 ° C. and 60 minutes (P factor was 214). Tables 1 and 2 show the results. The acidic peroxide treatment pH was 2.5.

Example 3
In Example 1, the same operation as in Example 1 was performed except that the temperature at the prehydrolysis was changed to 165 ° C. and 60 minutes (P factor was 406). Tables 1 and 2 show the results. The acidic peroxide treatment was performed at pH 2.5.

Example 4
In Example 1, the same operation as in Example 1 was performed except that the temperature at the prehydrolysis was changed to 170 ° C. and 100 minutes (P factor was 995). Tables 1 and 2 show the results. The acidic peroxide treatment was performed at pH 2.5.

Example 5
In Example 1, the same operation as in Example 1 was performed, except that the temperature at the prehydrolysis was changed to 170 ° C. and 40 minutes (P factor was 398). Tables 1 and 2 show the results. The acidic peroxide treatment was performed at pH 2.5.

Example 6
In Example 1, the same operation as in Example 1 was performed, except that the hydrogen peroxide addition rate during the treatment with acidic peroxide was changed to 0.1%. Tables 1 and 2 show the results. The acidic peroxide treatment was performed at pH 2.7.

Example 7
In Example 1, the same operation as in Example 1 was performed, except that the hydrogen peroxide addition rate during acidic peroxide treatment was changed to 1.0%. Tables 1 and 2 show the results. The acidic peroxide treatment was performed at pH 2.2.

Example 8
In Example 1, the same operation as in Example 1 was performed except that the sulfuric acid addition rate during the treatment with acidic peroxide was changed to 0.2%. Tables 1 and 2 show the results. The acidic peroxide treatment was performed at pH 3.9.

Example 9
In Example 1, the same operation as in Example 1 was performed except that the sulfuric acid addition rate during the treatment with acidic peroxide was changed to 0.8%. Tables 1 and 2 show the results. The acidic peroxide treatment pH was 1.9.

Example 10
In Example 1, the same operation as in Example 1 except that the active alkali addition rate during kraft cooking was changed to 18% and the hydrogen peroxide addition rate during acidic peroxide treatment was changed to 1.0%. Was done. Tables 1 and 2 show the results. The kappa number after kraft cooking was 12.8, and the acidic peroxide treatment was performed at pH 2.2.

Example 11
In Example 1, the chlorine dioxide addition rate in the D0 stage was changed to 0.6%, and the hydrogen peroxide addition rate during the acidic peroxide treatment was changed to 1.0%. The operation was performed. Tables 1 and 2 show the results. The acidic peroxide treatment pH was 2.2.

Example 12
In Example 1, the same operation as in Example 1 was performed except that the hydrogen peroxide during the acidic peroxide treatment was changed to peracetic acid. Tables 1 and 2 show the results. The acidic peroxide treatment pH was 2.4.

Example 13
In Example 1, the same operation as in Example 1 was performed except that the hydrogen peroxide during the acidic peroxide treatment was changed to persulfuric acid. Tables 1 and 2 show the results. The acidic peroxide treatment pH was 2.2.

Example 14
In Example 1, the same operation as in Example 1 was performed except that the eucalyptus / perita material chip was changed to the eucalyptus / globula material chip. Tables 1 and 2 show the results. The unbleached pulp was kappa number 6.1 and acidic peroxide treatment pH 2.5.

Comparative Example 1
In Example 9, the same operation as in Example 9 was performed except that the acidic peroxide treatment was not performed. Tables 1 and 2 show the results.

Comparative Example 2
In Example 9, the same operation as in Example 9 was performed except that hydrogen peroxide was not added during the acidic peroxide treatment. Tables 1 and 2 show the results. The acidic peroxide treatment pH was 3.0.

Comparative Example 3
In Example 1, the same operation as in Example 1 was performed except that the acidic peroxide treatment was changed immediately after oxygen delignification. Tables 1 and 2 show the results. The acidic peroxide treatment pH was 4.1.

As is clear when comparing Examples 1 to 14 and Comparative Examples 1 to 3 in Tables 1 and 2, after preparing an unbleached pulp by pre-hydrolysis-alkali digestion using a lignocellulosic material as a raw material, bleaching, Furthermore, it turns out that the melt | dissolution pulp which has high alpha-cellulose content, high whiteness, low ash content, and desired pulp viscosity can be manufactured by adding and processing a peroxide under acidity.

Claims (6)

A method for producing a dissolving pulp using a lignocellulosic material as a raw material by a prehydrolysis-alkali digestion method, wherein the P-factor at the time of prehydrolysis is 200 to 1000, and the pulp after the prehydrolysis-alkali digestion is used. A method for producing a dissolving pulp, comprising bleaching and then processing by adding a peroxide under acidic conditions. A method for producing a dissolving pulp using a lignocellulosic material as a raw material by a prehydrolysis-alkali digestion method, wherein the P-factor at the time of prehydrolysis is 200 to 1000, and the pulp after the prehydrolysis-alkali digestion is used. After bleaching, in order to reduce the ash content in the melt | dissolving pulp obtained, the peroxide is added and processed in acidity, The manufacturing method of the melt pulp characterized by the above-mentioned.   The pulp after the pre-hydrolysis-alkali digestion is bleached to 85 to 92% ISO, and then treated by adding a peroxide under acidity. Method.   The said peroxide is hydrogen peroxide, The manufacturing method of the dissolving pulp of any one of Claims 1-3 characterized by the above-mentioned.   The method for producing a dissolving pulp according to any one of claims 1 to 4, wherein the alkali cooking method is a kraft cooking method. The lignocellulosic material is a hardwood, wherein the kappa number of the pulp after A alkali digestion is 6 to 13, the method of producing dissolving pulp according to any one of claims 1 to 5.