JP6398388B2 - Dissolving pulp and method for producing the same - Google Patents

Description

  The present invention relates to a method for producing a dissolving pulp from a lignocellulosic material and a dissolving pulp produced by the production method.

  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 cellulose purity. As an index representing cellulose purity, α-cellulose content is generally used, and the higher the value, the higher the quality of the dissolved pulp.

As a method for producing dissolving pulp, two methods of acid sulfite cooking method and prehydrolysis-kraft cooking method have been known for a long time. The acidic sulfite cooking method is a method in which many hemicelluloses and lignin in the lignocellulosic material are removed at a time in the cooking process. The prehydrolysis-kraft cooking method is a method in which most of the hemicellulose is removed by acid hydrolysis in the prehydrolysis step, and a small amount of hemicellulose and most of the lignin are removed by subsequent kraft cooking. 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 It can be said that. However, when the focus is on separating and effectively using the waste hemicellulose and lignin, the prehydrolysis-kraft cooking method is more advantageous. A technology for producing cellulose, hemicellulose, and lignin in a lignocellulosic material that is a raw material for biomass to produce a material having high industrial use value such as resin and biofuel is called biorefinery. In recent years, attention to such techniques has increased, and accordingly, the usefulness of the prehydrolysis-kraft cooking method has been recognized again.

  Dissolved pulp differs in required pulp viscosity, whiteness, and ash content depending on its use. This is because the processing conditions when chemically processing the dissolving pulp into a product and the requirements for the product after processing differ from product to product. In order to satisfy this requirement, a dissolving pulp having a relatively high whiteness and ash content is produced at a desired pulp viscosity, and then the whiteness is increased or the ash content is lowered as required. It is reasonable to perform this process. As a method for increasing the whiteness, a known pulp bleaching method using chlorine dioxide, alkali, hydrogen peroxide, ozone, or hypochlorite is generally used. Further, as a method for reducing the ash content, a method is generally used in which treatment with an inorganic acid such as sulfuric acid, nitric acid, hydrochloric acid, etc., liberates and removes the ash. After the process for increasing the whiteness and the process for decreasing the ash content, a washing step is provided to remove dissolved components such as ash.

As an example of a method for increasing the whiteness and reducing the ash content without performing JP-A-2013-227705, a method is known in which a peroxide is added under acidic conditions in the final stage of the bleaching step ( Patent Document 1). However, the whitening effect of whiteness was limited by this method.

An object of the present invention is to provide a method for producing a dissolving pulp from a lignocellulosic material and a dissolving pulp produced by the method. More specifically, in a method for producing dissolved pulp by a prehydrolysis-alkaline cooking method using a lignocellulosic material as a raw material, the whiteness of the pulp is previously bleached to an ISO whiteness of 85% to 92%, and then alkaline peroxidation. A method for producing dissolved pulp that can be adjusted to desired whiteness and ash content by performing hydrogen treatment, and then performing acid treatment by adding an acid without washing, and a dissolved pulp produced by the production method are provided. This is the issue. Alternatively, in the present invention, since the water used for washing is usually unnecessary, the environmental load due to the drainage is reduced, and further, the equipment investment and running cost are reduced by not requiring the washing machine used for the washing. It is an object of the present invention to provide a method for producing a dissolved pulp and a dissolving pulp produced by the production method.

The inventors of the present invention have made various studies on a method for efficiently producing a wide variety of dissolving pulp by a prehydrolysis-alkali cooking method using a lignocellulosic material as a raw material. As a result, in order to control the cellulose purity to the desired level in the pre-hydrolysis, the dissolved pulp is produced by keeping the subsequent alkaline and bleaching conditions as constant as possible, and then treated with alkaline hydrogen peroxide. After that, it was found that the cellulose purity, the ash content, and the whiteness of the pulp can be controlled to desired values by adding an acid without washing and performing an acid treatment. More specifically, for example, when hardwood is used as a raw material, if pre-hydrolysis is performed under the condition that the P-factor is 200 to 1000, then alkali digestion is performed so that the kappa number after cooking is 6 to 18, A dissolving pulp having a high cellulose purity is obtained. Furthermore, the bleached pulp is bleached until the ISO whiteness becomes 85% to 92%, and then subjected to an alkaline hydrogen peroxide treatment, and then an acid treatment is carried out by adding an acid without washing. By doing in this way, it discovered that ash content was reduced and the dissolving pulp which has high whiteness was obtained, and resulted in this invention.

The present invention includes the following inventions.
(1) A method for producing a dissolving pulp using a lignocellulosic material as a raw material by a prehydrolysis-alkali digestion method, and bleaching the pulp after the prehydrolysis-alkali digestion, followed by an alkaline hydrogen peroxide treatment Then, the dissolving pulp manufacturing method characterized by performing an acid treatment by adding an acid without washing.
(2) The pulp after the prehydrolysis-alkaline digestion is bleached to an ISO whiteness of 85% to 92% in a multi-stage bleaching step, then subjected to alkaline hydrogen peroxide treatment, acid is added without washing, and acid treatment (1) The method for producing a dissolving pulp according to (1).
(3) The method for producing a dissolving pulp according to any one of (1) and (2), wherein the ash content in the dissolving pulp is 0.2% by mass or less per mass of the absolutely dry pulp. .
(4) A dissolving pulp produced by the method for producing a dissolving pulp according to any one of (1) to (3), wherein the ISO whiteness is 88% to 95%, and the viscosity is 1 cP to 45 cP. Dissolving pulp characterized by being.

  According to the present inventor, in a method for producing a dissolving pulp by a prehydrolysis-alkali cooking method using a lignocellulosic material as a raw material, a multi-stage bleaching is performed in advance and bleaching to a specific whiteness is performed, followed by an alkaline excess. Producing high-quality dissolved pulp with high whiteness and low ash content at low cost and low environmental load by performing hydrogen oxide treatment and then adding acid without washing to perform acid treatment Became possible.

Hereinafter, the dissolving pulp manufacturing method of the present invention and the dissolving pulp manufactured by the method will be described in detail.
In the present invention, the “prehydrolysis-alkaline cooking method” includes a treatment for removing a hemicellulose component by treating a lignocellulosic material under acidic conditions in the prehydrolysis step, and the alkaline cooking step under alkaline conditions. Means a process comprising delignification. The method also includes a prehydrolysis-kraft cooking method.
In the present invention, “alkaline hydrogen peroxide treatment” refers to a process of treating bleached pulp with hydrogen peroxide in the presence of alkali. In addition, the said process is distinguished from the E / P bleaching stage (after-mentioned) which can be employ | adopted at a bleaching process in the point that the processing time is as short as 0.1-5 minutes etc., for example.

<Raw material>
(Lignocellulose material)
In the dissolving pulp manufacturing method of the present invention, the lignocellulosic material used as a raw material may be either wood or non-wood, and is not limited at all. However, considering the production efficiency of dissolving pulp, wood having a high bulk weight is suitable. Used. Among woods, broad-leaved wood materials are generally preferred because they have higher bulk weight than coniferous wood materials, and some eucalyptus and acacia with higher bulk weight among hardwood materials are more preferably used. Examples of applicable broad-leaved trees include, but are not limited to, eucalyptus globulas, eucalyptus grandis, eucalyptus eurograndis, eucalyptus perita, eucalyptus brushana, acacia melanci and the like. A eucalyptus perita with high bulk weight is particularly good. Volume weight of wood as lignocellulose substance for use in the present invention ^may include the ^{450kg / m 3 ~700kg / m 3} , more preferably in these ranges at which is that of 500kg ^{/ m 3} ~650kg ^/ m 3 It is not limited. In addition, the material whose volumetric weight is lower than 450 kg / m ³ may be disadvantageous in terms 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. is there. As the lignocellulosic material of the present invention, hardwood, softwood, and non-wood can be used alone or in combination, and the combination is not limited at all.

<Prehydrolysis-Alkaline cooking>
(Prehydrolysis)
The prehydrolysis in the prehydrolysis-alkali cooking method of the present invention includes a treatment for removing the hemicellulose component by treating the lignocellulose material under acidic conditions. The above acidic condition can be usually realized by an acidic component contained in the lignocellulosic material, but it may be realized by adding a known acid, and there is no limitation on means for realizing this.
The prehydrolysis step of the present invention is first performed by heating the lignocellulosic material in the presence of water. Here, the amount (liquid ratio) of water relative to the lignocellulosic material is not limited, but is 1.0 to 10, preferably 1.5 to 5.0. If the liquid ratio is less than 1.0, water may be insufficient, hydrolysis may not proceed sufficiently, and the reaction may become nonuniform, which may not be suitable. If it is higher than 10, the amount of heat required for heating to a desired temperature may increase, which may not be economically suitable. The water may be added from the outside, the water originally contained in the lignocellulosic material may be used, or when using steam during heating, the water contained in the steam may be used, The introduction means is not limited at all. In addition to the lignocellulosic substance and water, chemicals that directly or indirectly assist the hydrolysis of polysaccharides, such as alkalis, acids, and chelating agents, can also be added. The prehydrolysis conditions of the present invention are not limited at all, and can be appropriately selected by those skilled in the art. For example, the hydrolysis strength is preferably such that the P-factor is in the range of 200 to 1000, the temperature is 140 ° C to 200 ° C, preferably 160 ° C to 170 ° C, and the treatment time corresponds to the treatment temperature. In consideration of the P factor. The P factor is the product of temperature and time during pre-hydrolysis and is expressed as Equation 1.

Ｐファクターが２００より低い場合には、ヘミセルロースの酸加水分解が十分となり得るため、その後のアルカリ蒸解を行っても、パルプのセルロース純度を十分に高められない場合がある。Ｐファクターが１０００より高い場合には、セルロースの酸加水分解が過剰となり得るため、パルプのセルロース純度を十分に高められない場合がある上に、パルプ粘度が低くなり、さらにはパルプ収率も低くなる場合がある。前加水分解温度が１４０℃よりも低い場合には反応時間を１０時間以上にする必要が生じ得、巨大な反応容器が必要となることがあるため経済的ではない場合がある。逆に２００℃よりも高くすると、場合によっては反応時間を０．１時間以下にする必要があり、反応の制御が困難となり得る。さらに、そのような熱条件に耐え得る装置の材質は高価になり得るため、経済的でもない場合がある。

When the P-factor is lower than 200, acid hydrolysis of hemicellulose may be sufficient, so that the cellulose purity of the pulp may not be sufficiently increased even after subsequent alkaline digestion. When the P factor is higher than 1000, the acid hydrolysis of cellulose may be excessive, so that the cellulose purity of the pulp may not be sufficiently increased, and the pulp viscosity is lowered and the pulp yield is also lowered. There is a case. When the prehydrolysis temperature is lower than 140 ° C., the reaction time may need to be 10 hours or more, which may not be economical because a huge reaction vessel may be required. On the other hand, when the temperature is higher than 200 ° C., the reaction time needs to be 0.1 hour or less depending on the case, and the control of the reaction may be difficult. Furthermore, the material of the device that can withstand such thermal conditions can be expensive and may not be economical.

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 or batch kettle is used.
In the prehydrolysis step of the present invention, after the completion of the reaction, dehydration, dilution washing and dehydration are performed before being sent to the alkali cooking step. In addition, the waste water after prehydrolysis can be sent to a flash tank and can be divided into a gas layer and a liquid layer. At this time, the furfurals contained in the gas layer and the hemicellulose degradation product contained in the liquid layer are respectively extracted into biomass, and can be used, for example, as a raw material in a biorefinery.

(Alkaline cooking)
Kraft cooking is also used as alkali cooking in the prehydrolysis-alkali cooking method of the present invention, but other known cooking methods such as polysulfide cooking, soda cooking, alkali sulfite cooking, etc. may be used, and cooking performed under alkaline conditions. If so, the specific method is not limited. Considering pulp quality, energy efficiency, etc., the kraft cooking method is preferably used.
The conditions for kraft cooking of wood are not limited, but the sulfidity of the kraft cooking solution is 5% to 75%, the effective alkali addition rate is 5% to 30% by weight per the absolute dry wood weight, and the cooking temperature is 140%. Those having a temperature of from 170 ° C to 170 ° C are preferred. As more preferred conditions, the kraft cooking liquor has a sulfidity of 20% to 35%, and an effective alkali conversion rate of 10% to 25% by mass of the absolutely dry wood mass. The method of adding the cooking white liquor is not particularly limited, but a method of adding in a divided manner may be adopted.

In the cooking liquor, as a cooking aid, a known cyclic keto compound, for example, quinone compounds such as benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone, and nucleophilic substituents such as alkyl and amino of the quinone compound, Selected from hydroquinone compounds such as anthrahydroquinone, which is a reduced form of the quinone compounds, and 9,10-diketohydroanthracene compounds that are stable compounds obtained as intermediates in the anthraquinone synthesis method by the Diels-Alder method One kind or two or more kinds of compounds may be added. Although the addition rate of a cooking aid is selected from the suitable range according to a specific compound, For example, it may be 0.001 mass%-1.0 mass% per the absolute dry mass of a wood chip.
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.

The kappa number after cooking is not particularly limited, but considering pulp quality and subsequent bleaching property, for example, when hardwood is used as a raw material, 6 to 18 is preferable, and when softwood is used as a raw material, Is preferably 20 to 35.

<Prehydrolysis-Oxygen delignification after alkaline cooking>
In the present invention, the unbleached pulp obtained by the prehydrolysis-alkali cooking method is preferably delignified first by the oxygen delignification method. As the oxygen delignification method that can be used in the present invention, for example, a medium concentration method or a high concentration method can be employed. The medium concentration method is preferably performed at a pulp concentration of 8% by mass to 15% by mass because a special dehydrator is not required and the operability is good. As the alkali used in the oxygen delignification method, caustic soda or oxidized kraft white liquor can be used. The oxygen gas used in the oxygen delignification method includes oxygen gas obtained by a cryogenic separation method, oxygen gas obtained by a pressure swing adsorption (PSA) method, and vacuum swing adsorption (VSA) by a vacuum swing adsorption (PSA) method. The resulting oxygen gas can be used.
In one mode in the case of using the medium concentration method, the oxygen gas and alkali are added to a medium concentration pulp slurry in a medium concentration mixer. Next, after the pulp slurry is sufficiently mixed, it is 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.
As a non-limiting example of the conditions of the oxygen delignification method that can be employed in the present invention, the addition rate of oxygen gas is 0.5% by mass to 3% by mass per mass of absolutely dry pulp, and the alkali addition rate is 0.5% by mass. % To 4% by mass, the reaction temperature is 80 ° C. to 120 ° C., the reaction time is 15 minutes to 100 minutes, and the pulp concentration is 8% to 15% by mass. Other known conditions can be applied. In the oxygen delignification method that can be used in the present invention, it is preferable to perform the oxygen delignification multiple times in succession and to proceed as much as possible.

<Prehydrolysis-pulp bleaching after alkali cooking>
In the present invention, the unbleached pulp is subjected to bleaching treatment by a known bleaching method after washing (preferably including the oxygen delignification step), rough selection and selection steps.
(Multi-stage bleaching process)
In the present invention, a multi-stage bleaching step is preferably employed as the known bleaching method. In the multistage bleaching process of the present invention, known ECFs such as chlorine dioxide bleaching stage (D), alkali extraction stage (E), oxygen delignification stage (O), hydrogen peroxide bleaching stage (P), and ozone bleaching stage (Z). Bleaching stages can be used in combination, and the above-described washing stage can be provided after each bleaching stage. When expressing the structure of the multi-stage bleaching process including the order of each stage, the alphabet abbreviations are described in order according to the order of application of the bleaching stages, and each stage is separated by a hyphen, for example, D0- It is described as E / P-D1. In the above example, numbers such as “0” and “1” indicate the order of application of the bleaching stage when the same type of bleaching stage is applied multiple times, and the symbol “/” is written on both sides thereof. It means that two bleaching stages are applied simultaneously.
Further, the multi-stage bleaching step is combined with a high-temperature acid treatment stage (A), an acid washing stage, a high-temperature chlorine dioxide bleaching stage, or a chelating agent treatment stage with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). It can also be introduced.
In the multi-stage bleaching step of the present invention, bleaching can be performed so that the ISO whiteness of the pulp is 85% to 92%. The ISO whiteness is preferably 87% to 92%, more preferably 89% to 92%. If the ISO whiteness is less than 85%, then the alkaline hydrogen peroxide treatment is performed, and then the ISO whiteness may not reach 90% even if the acid treatment is performed by adding an acid without washing. Since the quality as a dissolving pulp may be low, it may not be suitable. If the ISO whiteness is higher than 92%, the amount of bleaching chemicals used in the multi-stage bleaching process may increase, which may not be economical, and additional functional groups may be introduced into the dissolving pulp. The quality of the dissolving pulp may be reduced.

<Washing stage>
In the present invention, after the alkaline hydrogen peroxide treatment, a washing stage is provided for each bleaching stage, not limited to the washing stage after the oxygen delignification, except where the acid is not washed and the acid treatment is performed.
Examples of the washing machine used in the washing stage include a pressure diffuser, a diffusion washer, a pressure drum washer, a horizontal long washer, and a press washing machine, and are not particularly limited. Each washing stage can be provided by a single washing machine, or a plurality of washing 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. In addition, about the washing | cleaning waste_water | drain, it can also be used for the countercurrent washing | cleaning reused as washing water of the preceding washing | cleaning stage.

<Alkaline hydrogen peroxide treatment>
In this invention, after performing bleaching by a multistage bleaching process etc. with respect to an unbleached pulp, an alkaline hydrogen peroxide process is performed.

Although the addition rate of the alkali in the alkaline hydrogen peroxide treatment is not limited, it is, for example, 0.3% by mass to 2.0% by mass, and preferably 0.5% by mass to 1.% by mass based on the mass of the absolutely dry pulp. 5% by mass. If the amount is less than 0.3% by mass, the pH is not sufficiently increased. If the amount is more than 2.0% by mass, the pH becomes too high and the whiteness whitening effect of the pulp may be insufficient. Moreover, although the addition rate of hydrogen peroxide is not limited, For example, it is 0.01 mass%-1.0 mass% per absolute dry pulp mass, Preferably it is 0.05%-0.5%. . If 0.01%, bleaching chemicals may be insufficient, and the whiteness whitening effect of the pulp may be insufficient, and if it is 1.0% or more, the dissolved pulp quality may deteriorate. The reaction temperature of the alkaline hydrogen peroxide treatment is, for example, 30 ° C to 90 ° C, preferably 50 ° C to 80 ° C. If the reaction temperature is lower than 30 ° C., it may take a long reaction time, and the whiteness whitening effect of the pulp may be insufficient. It may not be economical because it can require energy. In addition, the alkaline hydrogen peroxide treatment of the present invention is such that the reaction time is as short as 0.1 to 5 minutes, for example. In this respect, what is the E / P bleaching stage that can be employed in the bleaching process? It is a distinction.

The pulp concentration in the alkaline hydrogen peroxide treatment is not particularly limited, but may be, for example, in the range of 1% by mass to 40% by mass, preferably 8% by mass to 15% by mass. When the pulp concentration is less than 1% by mass, the amount of water used may increase, which may not be economical. When the pulp concentration is higher than 40% by mass, the reaction between the pulp and the chemical may be insufficient. May be non-uniform. The pH of the alkaline hydrogen peroxide treatment is, for example, 8.5 to 12.5, preferably 9.5 to 12.0. If the pH is lower than 8.5, the pulp whiteness whitening effect is insufficient. If it is higher than 12.5, the amount of chemical may increase, which may not be economical.

<Acid treatment>
In the present invention, after the alkaline hydrogen peroxide treatment, the acid treatment is performed by adding an acid without washing. Although the addition amount of the acid in acid treatment is not limited, For example, it is 0.5%-3.0% per bone dry pulp mass, Preferably, it is 1.0%-2.0%. When the amount is less than 0.5%, the acid treatment pH becomes too high, and the ash content is not sufficiently lowered. When the amount is 3.0%, the pH becomes too low and the quality of the dissolved pulp may be lowered. . The reaction temperature for the acid treatment is, for example, normal temperature to 90 ° C, preferably 50 ° C to 80 ° C. When the reaction temperature is lower than room temperature, cooling is required, and when it is higher than 90 ° C., a large amount of energy is required for temperature increase, which may not be economical. The reaction time for the acid treatment is, for example, 0.1 to 180 minutes, but is not particularly limited. Although the pulp density | concentration in an acid treatment is not specifically limited, For example, 1 mass%-40 mass%, Preferably it is performed in the range of 8 mass%-15 mass%. When the pulp concentration is less than 1% by mass, the amount of water used may increase, which may not be economical. When the pulp concentration is higher than 40% by mass, the reaction between the pulp and the chemical may be insufficient. May be non-uniform. The pH of the acid treatment is 1-5, preferably 2-4. When the pH is lower than 1, the reaction vessel may be easily corroded. When the pH is higher than 5, the ash removal effect may be insufficient.

In the acid treatment of the present invention, an acid is added to adjust the reaction pH. 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. used.

<Dissolving pulp of the present invention>
The dissolving pulp of the present invention is obtained by the above-described production method in which the pulp after prehydrolysis-alkali digestion is bleached, and then subjected to an alkaline hydrogen peroxide treatment, and then an acid treatment is performed by adding an acid without washing. Is.
The content of ash content in the dissolving pulp of the present invention is not limited, but is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, and 0.12% by mass or less per mass of absolutely dry pulp. Is particularly preferred. Moreover, although the ISO whiteness of the dissolving pulp of this invention is not limited, For example, 88%-95% are preferable and 90%-94% are especially preferable. Although the viscosity of the dissolving pulp of this invention is not limited, For example, 1 cP-45 cP are preferable and 5 cP-30 cP are especially preferable.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to specific embodiments of these examples. Unless otherwise indicated, the measurement of the pulp kappa number, whiteness, viscosity, α-cellulose content and ash content was carried out by the following method. 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 was prepared according to TAPPI test method T205os-71 (JIS P 8209). Using the sheet, the whiteness of the pulp was measured in accordance with JIS P 8148.

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

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

5). Pulp ash content 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 chip was taken out, passed through a 400 mesh sieve, filtered, and the dehydrated chip was put into a 2.5 liter capacity indirect heating autoclave (Type 700 325 made by MATARI-TUOTE oy). After adding tap water, prehydrolysis treatment was performed at 165 ° C. for 60 minutes. The P factor at this time was 406.
After pre-hydrolysis, waste gas was extracted from the deaeration cock of the autoclave, and after confirming that the pressure in the autoclave became 0 with a pressure gauge, the treated chip was passed through a 400 mesh sieve and filtered. 200 g of the chips after filtration were collected at an absolute dry mass and placed again in an indirect heating autoclave with a capacity of 2.5 liters. Kraft cooking was performed at a cooking temperature of 165 ° C. and a 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 120.0 g of unbleached pulp having a kappa number of 16.6 in an absolutely dry mass.

  70.0 g of the unbleached pulp was collected at an absolute dry mass, and 2.0% of caustic soda was added to the absolute dry pulp mass, and then diluted with ion-exchanged water to adjust the pulp concentration to 10%. The pulp suspension was placed in an indirect heating autoclave, 99.9% of commercially available compressed oxygen gas was injected, and oxygen delignification was performed at 100 ° C. for 60 minutes at a gauge pressure of 0.5 MPa. 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 the oxygen delignification was collected at an absolutely dry mass, put into a plastic bag, and the pulp concentration was adjusted to 10% using ion-exchanged water. Thereafter, 1.0% of chlorine dioxide per mass of absolutely dry pulp was added thereto, and it was immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for D0 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 D0 stage was put in a plastic bag, and ion exchange water was added to adjust the pulp concentration to 10%. Then, 1.0% caustic soda per mass of dry pulp and 0.2% hydrogen peroxide were added and mixed well, then immersed in a constant temperature water bath at a temperature of 70 ° C. for 90 minutes to perform E / P stage treatment. Went. 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 an ISO whiteness of 89.1%, an α-cellulose content of 95.3%, and an ash content of 0.22% per bone dry pulp mass was obtained.

  The pulp after the D1 stage is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 1.0% caustic soda per mass of dry pulp, and 0.1% hydrogen peroxide are added, It was immersed in a constant temperature water bath having a temperature of 70 ° C. for 2 minutes to perform alkaline hydrogen peroxide treatment. Thereafter, 1.5% sulfuric acid was added to the pulp without washing, and the mixture was immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for acid treatment. The pH after treatment was 2.7. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 90.9%, an α-cellulose content of 95.1%, and an ash content of 0.08% per mass of completely dried pulp was obtained. The results are shown in Table 1.

Example 2
The pulp after the E / P stage described in Example 1 is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 0.2% of chlorine dioxide is added per mass of absolutely dry pulp, and the temperature is increased. It was immersed in a constant temperature water bath at 70 ° C. 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 an ISO whiteness of 85.6%, an α-cellulose content of 94.6%, and an ash content of 0.29% per mass of dry pulp was obtained.

  The pulp after the D1 stage is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 1.0% caustic soda per mass of dry pulp, and 0.1% hydrogen peroxide are added, It was immersed in a constant temperature water bath having a temperature of 70 ° C. for 2 minutes to perform alkaline hydrogen peroxide treatment. Thereafter, 1.5% sulfuric acid was added to the pulp without washing, and the mixture was immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for acid treatment. The pH after treatment was 2.7. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 88.3%, an α-cellulose content of 94.9%, and an ash content of 0.09% per mass of completely dried pulp was obtained. The results are shown in Table 1.

Example 3
The pulp after the E / P stage described in Example 1 is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, and then 0.4% of chlorine dioxide per mass of dry pulp is added. It was immersed in a constant temperature water bath at 70 ° C. 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 an ISO whiteness of 91.6%, an α-cellulose content of 95.5%, and an ash content of 0.19% per mass of dry pulp was obtained.

  The pulp after the D1 stage is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 1.0% caustic soda per mass of dry pulp, and 0.1% hydrogen peroxide are added, It was immersed in a constant temperature water bath having a temperature of 70 ° C. for 2 minutes to perform alkaline hydrogen peroxide treatment. Thereafter, 1.5% sulfuric acid was added to the pulp without washing, and the mixture was immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for acid treatment. The pH after the treatment was 2.6. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 93.1%, an α-cellulose content of 96.0%, and an ash content of 0.04% per mass of dry pulp was obtained. The results are shown in Table 1.

Example 4
The pulp after the E / P stage described in Example 1 is put in a plastic bag, adjusted to a pulp concentration of 10% using ion exchange water, 0.1% of chlorine dioxide is added per mass of dry pulp, and the temperature is It was immersed in a constant temperature water bath at 70 ° C. 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 an ISO whiteness of 84.1%, an α-cellulose content of 93.9%, and an ash content of 0.45% per mass of dry pulp was obtained.

  The pulp after the D1 stage is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 1.0% caustic soda per mass of dry pulp, and 0.1% hydrogen peroxide are added, It was immersed in a constant temperature water bath having a temperature of 70 ° C. for 2 minutes to perform alkaline hydrogen peroxide treatment. Thereafter, 1.5% sulfuric acid was added to the pulp without washing, and the mixture was immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for acid treatment. The pH after treatment was 2.7. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 86.6%, an α-cellulose content of 94.0%, and an ash content of 0.25% per mass of completely dried pulp was obtained. The results are shown in Table 1.

Example 5
The pulp after the E / P stage described in Example 1 is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 0.5% of chlorine dioxide is added per mass of absolutely dry pulp, and the temperature is increased. It was immersed in a constant temperature water bath at 70 ° C. 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 an ISO whiteness of 92.4%, an α-cellulose content of 95.5%, and an ash content of 0.11% per mass of dry pulp was obtained.

  The pulp after the D1 stage is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 1.0% caustic soda per mass of dry pulp, and 0.1% hydrogen peroxide are added, It was immersed in a constant temperature water bath having a temperature of 70 ° C. for 2 minutes to perform alkaline hydrogen peroxide treatment. Thereafter, 1.5% sulfuric acid was added to the pulp without washing, and the mixture was immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for acid treatment. The pH after treatment was 2.7. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 92.5%, an α-cellulose content of 95.9%, and an ash content of 0.04% per mass of dry pulp was obtained. The results are shown in Table 1.

Comparative Example 1
The pulp after stage D1 described in Example 1 was placed in a plastic bag and adjusted to a pulp concentration of 10% using ion-exchanged water. Thereafter, 1.0% caustic soda and 0.1% hydrogen peroxide per mass of dry pulp were added thereto, and immersed in a constant temperature water bath having a temperature of 70 ° C. for 2 minutes to perform alkaline hydrogen peroxide treatment. The pH after treatment was 11.3. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 90.2%, an α-cellulose content of 95.0%, and an ash content of 0.53% per mass of dry pulp was obtained. The results are shown in Table 1.

Comparative Example 2
The pulp after stage D1 described in Example 4 was put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, and immersed in a constant temperature water bath having a temperature of 70 ° C. for 60 minutes for treatment. The pH after the treatment was 9.6. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel. A finished pulp having an ISO whiteness of 83.9%, an α-cellulose content of 94.0%, and an ash content of 0.44% per mass of completely dried pulp was obtained. The results are shown in Table 1.

As is clear from comparison of Example 1 and Comparative Examples 1 and 2 in Table 1, for example, an unbleached pulp was prepared by performing a prehydrolysis-alkali digestion using a lignocellulosic material as a raw material, followed by bleaching and further alkalinity. It was found that a dissolved pulp having a high α-cellulose content, a high whiteness, and a low ash content can be produced by performing a hydrogen oxide treatment and then performing an acid treatment by adding an acid without washing.
Further, as apparent from comparison of, for example, Example and Comparative Example 2 in Table 1, after preparing an unbleached pulp by performing prehydrolysis-alkali digestion using a lignocellulosic material as a raw material, ISO whiteness of 85% to 92% % Bleaching, alkaline hydrogen peroxide treatment, unwashed acid is added, and acid treatment is performed to efficiently produce dissolved pulp with high α-cellulose content, high whiteness, and low ash content It turns out that you can.

According to the present invention, it is possible to produce a high-quality dissolving pulp having high whiteness and low ash content from lignocellulose. In addition, according to the present invention, the water used for washing before acid treatment is usually unnecessary, thereby reducing the environmental burden due to drainage, and not requiring the washing machine used for the washing. A method for producing dissolving pulp with reduced running costs is provided.

Claims (3)

A method for producing a dissolving pulp by using a lignocellulosic material as a raw material by a prehydrolysis-alkali digestion method, wherein the pulp after the prehydrolysis-alkali digestion is bleached and then alkaline in a treatment time of 0.1 to 5 minutes. A method for producing a dissolving pulp, characterized by performing a hydrogen peroxide treatment, and then performing an acid treatment by adding an acid without washing. The pre-hydrolyzed and alkali-digested pulp is bleached to ISO whiteness of 85% to 92% in a multi-stage bleaching step, and then subjected to alkaline hydrogen peroxide treatment for a treatment time of 0.1 to 5 minutes. The method for producing a dissolving pulp according to claim 1, wherein acid treatment is performed by adding an acid. The method for producing a dissolving pulp according to any one of claims 1 and 2, wherein an ash content in the dissolving pulp is 0.2% by mass or less per mass of absolutely dry pulp.