TW201641518A - Method for producing cellulose - Google Patents

Abstract

One embodiment of the present invention provides a method for producing a cellulose from chemical pulp, which comprises the steps (a)-(c) described below. (a) a step for disintegrating chemical pulp (b) a step for washing the disintegrated pulp, which is obtained in step (a), with water (c) a step for obtaining a cellulose by lowering the degree of polymerization of the disintegrated pulp, which has been washed with water in step (b), by means of hydrolysis using a treatment liquid that is composed of an aqueous solution containing a mineral acid.

Description

Cellulose manufacturing method

The present invention relates to a method of producing cellulose.

Cellulose is used in various applications such as foods, pharmaceuticals, and industrial applications. For example, in food use, since cellulose is added to a food, a viscosity-increasing and dispersing effect can be obtained, and it is effective in improving a mouthfeel. Cellulose has high water absorption and oil absorption, and is particularly effective for improving the taste of fried foods and the like.

In the pharmaceutical use, a solid preparation such as a tablet, a powder (powder) or a granule is added as an excipient for the purpose of molding, incrementing, dilution, and the like.

The crystallites or crystalline cellulose used in the above applications are generally required to comply with the legal specifications of food additives or pharmaceutical additives in the country of use.

The amount of burnout in one of the above specifications is an index of the concentration of inorganic impurities contained in the product. For example, in Japan, the amount of microcrystalline cellulose as a food additive is 0.05% or less, and the amount of crystalline cellulose as a pharmaceutical additive is 0.1% or less.

The chemical pulp used for the production of cellulose raw materials is obtained by chemically treating wood chips such as broadleaf wood chips or coniferous trees. Usually, the wood chips contain a metal inorganic substance such as iron, aluminum, manganese, barium, magnesium or calcium (Non-Patent Document 1).

Further, in the pulping process of wood, a large amount of talc is sometimes added as a resin precipitation controlling agent (Patent Document 3). The talc is an inorganic powder obtained by grinding ore, and the main component is an inorganic substance such as hydrated magnesium silicate.

The chemical pulp is generally produced by decomposing and removing lignin and a resin component in wood by a sulfite evaporation method, a kraft distillation method, or a combination of these methods. In order to produce cellulose excellent in whiteness, the content of hemicellulose and lignin is preferably low. In particular, as a raw material pulp for producing microcrystalline or crystalline cellulose, a pulp obtained by using cotton linters having a small amount of inorganic impurities and having a high cellulose purity, and a special grade of chemistry which is refined to improve the purity of cellulose is referred to as dissolving pulp. Pulp (Non-Patent Document 2).

The cellulose is usually produced by subjecting a pulp such as wood pulp to a low degree of polymerization (hydrolysis, etc.) using mineral acid or iron (III) chloride, followed by washing, purification, and drying. In Patent Document 1, in the method for producing microcrystalline or crystalline cellulose, it is disclosed that a special grade pulp such as high-purity dissolving pulp or cotton linters pulp is used, and a rare concentration of mineral acid such as dilute hydrochloric acid or dilute sulfuric acid is used. A method of lowering the degree of polymerization by a hydrolysis reaction. However, these special grades of pulp have a problem in that the degree of freedom of selection is limited as a raw material because it is more expensive than a chemical pulp for papermaking which is generally distributed and has a small amount of flow.

The chemical pulp other than the above is mainly used for paper pulp chemical pulp for paper use. However, chemical pulp for papermaking has a lower cellulose concentration and a lower fineness than a special grade of pulp, so it is not suitable as a cellulose raw material for food or pharmaceutical use. For example, Patent Document 2 discloses a method of producing powdered cellulose from a kraft pulp of chemical pulp which is generally distributed, but it is difficult to say that cellulose which can be used for food or pharmaceutical use can be obtained. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] US Pat. No. 2,978,446 [Patent Document 2] JP-A-2013-60544 [Patent Document 3] Japanese Patent Publication No. 2010-521595 [Non-Patent Document]

[Non-Patent Document 1] Japan Technical Association of the Pulp and Paper Industry, July 2004, Vol. 58, No. 7, 38-41 [Non-Patent Document 2] Cellulose Commun., 2010, Vo.17, No. 2

[Problems to be Solved by the Invention] The inventors of the present invention analyzed the inorganic substances contained in the kraft pulp which is one of the commercially available paper pulps, and as a result, iron, aluminum, barium, magnesium, calcium, and sodium were detected. It is known that iron, aluminum, calcium, and sodium are dissolved in mineral acid during the production of cellulose, and can be relatively easily removed by washing with water, but strontium and magnesium remain almost as they are. Therefore, when we manufacture microcrystalline or crystalline cellulose from commercially available paper pulp, it is necessary to reduce the amount of the above-mentioned metals and the like derived from inorganic impurities, particularly from strontium and magnesium.

However, the method of removing inorganic substances in the production process of the dissolving pulp has been developed in the past, but it is not known to remove the inorganic substances contained in the chemical pulp for papermaking, which is generally used as a product, and to reduce the amount of burn-in.

As described above, Patent Document 2 discloses a method of producing powdered cellulose from kraft pulp which is a chemical pulp which is generally distributed, but there is no description about the reduction in the amount of burn-in. In fact, the inventors of the present invention have attempted to produce cellulose by hydrolyzing kraft pulp with mineral acid, and found that the obtained cellulose does not conform to the specifications of the food additive and the specifications of the pharmaceutical additive. Balance test.

On the other hand, it is also conceivable to reduce the amount of burn-in by washing the obtained cellulose. However, the crystallites or crystalline cellulose obtained by subjecting the pulp to a low degree of polymerization treatment have good affinity with water and have water retention property, and the primary particles have particle diameters of several μm to several 100 μm. Therefore, when the cellulose itself is washed and filtered, the workability is extremely poor, and it is not suitable for industrialization.

Therefore, it is required to efficiently remove the inorganic impurities contained in the commercially available chemical pulp, in particular, mineral acid-insoluble impurities represented by cerium and magnesium, thereby producing crystallites or crystalline cellulose having a small amount of burn-off. method.

The problem to be solved by the present invention is to provide a method for producing cellulose which is low in residual amount of crystallites or crystalline cellulose from chemical pulp and which can be used as an additive for foods and/or pharmaceuticals. That is, a method for producing a cellulose having a residual amount of 0.1% or less from a commercially available chemical pulp including kraft pulp is provided. [Means for solving the problem]

As a result of research conducted on the method for producing cellulose, the inventors of the present invention found a method for producing cellulose having a residual amount of 0.1% or less from chemical pulp, and completed the present invention. That is, the present application includes the following inventions. <1> A method for producing cellulose, which is a method for producing cellulose from chemical pulp, comprising the following steps (a) to (c); (a) desulfurizing chemical pulp; (b) step (a) The obtained defibrated pulp is washed with water; (c) The defibrated pulp which has been washed with water in the step (b) is hydrolyzed by a treatment liquid composed of an aqueous solution containing mineral acid to have a low degree of polymerization, thereby obtaining cellulose. <2> The method for producing cellulose according to <1>, wherein the ultrasonic wave is irradiated in the step (a) and/or the step (b). <3> The method for producing cellulose according to <1> or <2>, wherein the amount of the obtained cellulose is 0.1% or less. The method for producing cellulose according to any one of <1> to <3> wherein the cellulose obtained has an average degree of polymerization of 350 or less. The method for producing cellulose according to any one of <1> to <3-1, wherein the mineral acid is sulfuric acid or hydrochloric acid. <5> The method for producing cellulose according to <4>, wherein the content of the sulfuric acid or hydrochloric acid in the treatment liquid is 0.05 to 30% by weight. The method for producing cellulose according to any one of <1> to <5> wherein the treatment liquid further contains a peroxide. <7> The method for producing cellulose according to <6>, wherein the peroxide is hydrogen peroxide. <8> The method for producing cellulose according to <7>, wherein the content of the hydrogen peroxide in the treatment liquid is 0.05 to 15% by weight. The method for producing cellulose according to any one of <1> to <8> wherein the chemical pulp is pulp for papermaking. [Effects of the Invention]

According to the production method of the present invention, it is possible to produce cellulose having a residual amount of 0.1% or less by using inexpensive chemical pulp as a raw material.

According to one embodiment, the method for producing cellulose of the present invention comprises defibrating the chemical pulp, washing the defibrated pulp with water, and hydrolyzing the washed pulp by a known method.

According to the method of the present embodiment, cellulose having a reduced amount of burn-in (i.e., meaning inorganic impurities) can be obtained. These celluloses can be used as additives for foods and/or pharmaceuticals having a predetermined amount of burn-off. The reason why the amount of burn-off of the cellulose obtained by the method of the present embodiment is reduced is not clear, but it is considered that the step of washing the pulp with water before the low degree of polymerization treatment has significance. That is, according to the method of the present embodiment, the metal inorganic substance (for example, iron, aluminum, calcium, sodium, etc.) dissolved in the mineral acid is removed by the low polymerization degree treatment of the aqueous solution containing the mineral acid, and The inorganic acid insoluble in mineral acid (for example, from strontium, magnesium, specifically talc) may also be removed in advance before the water washing step. Thereby, it is considered that the amount of burn-in in the cellulose finally obtained becomes low.

In addition, the microcrystalline or crystalline cellulose obtained by the low degree of polymerization of the pulp as described above is obtained by the use of fine particles having a particle diameter of several μm to several 100 μm, and the obtained cellulose itself is washed with water and filtered. Poor workability, and moisture and burn-up are likely to remain in the cellulose. Therefore, it is not practical to wash the crystallites or crystalline cellulose obtained by the low degree of polymerization of the pulp, and further, the amount of burn-up in the cellulose tends to be relatively high. On the other hand, when the pulp before the low polymerization degree treatment is washed with water according to the method of the present embodiment, the water washing and the filtration step can be easily performed, and the cellulose having a low amount of combustion can be obtained. Therefore, according to the method of the present embodiment, it can be said that cellulose having a low amount of burn-off can be obtained by a simple method.

Hereinafter, constituent elements of the method according to the present embodiment will be described in order. <Materials> Chemical pulp is made from pulp chips. Examples of the raw material of the pulp scrap include a coniferous tree represented by radiata pine, spruce, and hemlock, and a broad-leaved tree represented by eucalyptus and locust. The pulp of the conifer and the broadleaf tree may be used singly or in combination. When used in various combinations, the combination thereof is not limited at all.

The chemical pulp is produced by using the above-mentioned pulp crumb as a raw material by a sulfite evaporation method, a cowhide evaporation method, or a combination thereof. The chemical pulp obtained by the above method may be either non-bleached pulp or bleached pulp, or a combination thereof.

Further, chemical pulp may be used in paper pulp and high-purity dissolving pulp, and these may be used in combination.

The chemical pulp can be used in a hydrated state after evaporation or bleaching, and a dried platy pulp can also be used. The chemical pulp used in the method according to the present embodiment may be any of the above types of pulp, and bleached pulp is preferably used.

<Manufacturing Step> Hereinafter, the manufacturing steps (a) to (c) will be sequentially described. (a) defibrating the chemical pulp (defibration step); (b) washing the defibrated pulp obtained in the step (a) with water (water washing step); (c) defibrating after washing in the step (b) The pulp is hydrolyzed by a treatment liquid composed of an aqueous solution containing mineral acid to have a low degree of polymerization, and cellulose is obtained (low polymerization degree treatment step).

(a) Desulfurization of chemical pulp (defibration step) In this step, the chemical pulp of the raw material is stirred in water or an aqueous solution to decompose the fibers of the pulp, and then the chemical pulp is mixed with water or an aqueous solution by filtration or the like. Separation to obtain a defibrated pulp.

The defibration of the pulp may be carried out to the extent that the undissolved fibers of the pulp disappear. The degree of defibration can be expressed in terms of Canadian standard freeness, preferably from 100 to 800 mL, more preferably from 300 to 800 mL, and particularly preferably from 500 to 800 mL. If it is higher, the defibration is insufficient, and if it is lower, the defibration is excessive, and as a result, the filterability of the pulp deteriorates, and it becomes difficult to remove inorganic impurities in the subsequent steps.

The ratio of the pulp in the slurry containing water or an aqueous solution to the chemical pulp is preferably in the range of 0.1 to 25% by weight, more preferably 1 to 20% by weight, still more preferably 1 to 15% by weight. When the amount of the pulp is less than the above range, the amount of treatment per one time or per unit time is small, which is uneconomical. On the other hand, when the amount of the pulp is more than the above range, the water or the aqueous solution does not sufficiently permeate the pulp, and the efficiency of defibrating the chemical pulp is lowered, which is not preferable.

The treatment temperature is not particularly limited. Further, in the case of water, water which does not contain an insoluble solid component and is easily obtained can be used as it is. As the aqueous solution, an aqueous solution of an inorganic acid and a salt thereof, an aqueous solution of an organic acid or a salt thereof, or the like can be used, and as the organic acid or a salt thereof, an organic acid having a high solubility in water and a salt thereof are preferred. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of the organic acid include carboxylic acids such as acetic acid, propionic acid, succinic acid, gluconic acid, citric acid, glycolic acid, lactic acid, malonic acid, oxalic acid, and malic acid; ethylenediaminetetraacetic acid, nitrogen triacetic acid, and Aminocarboxylic acid such as ethylene triamine pentaacetic acid or hydroxyethyl ethylenediamine triacetic acid; hydroxyethylidene diphosphonic acid, nitrogen-based ginseng (methylene phosphonic acid), phosphonic acid butane tricarboxylic acid, etc. Phosphonic acid, etc. Amine sulphuric acid may also be used. Examples of the salt include a sodium salt, a potassium salt, a calcium salt, and an ammonium salt. It is better to use water in the defibration step. Ultrasonic waves can also be applied when the chemical pulp is stirred in water or an aqueous solution. By irradiating the ultrasonic waves, the time of the defibrating step can be shortened.

(b) Water-washing of the defibrated pulp obtained in the step (a) (water washing step) This step includes a step of washing the defibrated pulp with water, and a dehydrating step.

In this step, water is first added to the defibrating pulp. The ratio of the pulp in the slurry containing water and defibrated pulp is preferably in the range of 0.1 to 25% by weight, more preferably 1 to 20% by weight. When the amount of the pulp is less than the above range, the amount of treatment per one time or per unit time is small, which is uneconomical. On the other hand, when the amount of the pulp is more than the above range, the water does not sufficiently permeate the pulp, and the efficiency of removing the inorganic impurities is lowered, which is not preferable.

The slurry was then stirred. In the defibrated pulp obtained in the step (a), inorganic impurities mainly composed of magnesium and strontium remain. This step is carried out in order to remove the inorganic impurities. The water washing of the defibrated pulp can be carried out using the same equipment as the (a) step (defiling step). For example, adding water to the general-purpose tanks such as drums and the defibrating pulp obtained in the step (a), and stirring them by using a general stirring blade such as a paddle wing, a turbine wing, a fixed wing, and a propeller wing. . A commercially available beater, refiner, or the like can also be used. Further, the ultrasonic waves can be irradiated while stirring. By irradiating the ultrasonic waves, the time of the water washing step can be shortened. The water washing step can be carried out while stirring, because the diffusion of the defibrated pulp in water is improved by the irradiation of the ultrasonic waves, and the water washing efficiency is improved. The temperature of the system in the water washing step is not particularly limited, and is preferably economical when it is carried out at room temperature where heating or cooling is not required.

Then, the slurry containing the defibrated pulp is subjected to dehydration by a centrifugal separator, a filter press, a belt press, an Aureus type filter, a Young's filter, a barrel filter, a belt filter, or the like. Here, the amount of burn-in in the finally obtained cellulose can be further lowered by dehydration. The degree of dehydration may be appropriately determined depending on the type of pulp to be used, and it is generally preferred to dehydrate to a solid content of about 40 to 50% by weight. When the ratio of the solid content is more than the above range, there is a concern that the dehydration time is too long (that is, the productivity is deteriorated). On the other hand, if the ratio is less than or equal to the above range, the removal of impurities may be insufficient. Washing and dehydration can be carried out only once or multiple times.

(c) The defibrated pulp which has been washed with water in the step (b) is hydrolyzed by a treatment liquid composed of an aqueous solution containing mineral acid to obtain a degree of polymerization to obtain cellulose (low polymerization degree treatment step). In the process, the defibrated pulp which has been washed with water in the step (b) is hydrolyzed by a treatment liquid to carry out a low polymerization degree treatment to produce cellulose having a target average degree of polymerization.

The treatment liquid used in the low polymerization degree treatment is composed of an aqueous solution containing mineral acid. Examples of the mineral acid include sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, phosphoric acid, etc., and they may be used alone or in combination of two or more kinds of mineral acids. The preferred mineral acid is sulfuric acid or hydrochloric acid. In the case of mineral acid, the concentration of the mineral acid in the treatment liquid can be adjusted to a desired concentration, and the concentration of the mineral acid to be used is not limited. In order to make the concentration of the mineral acid in the treatment liquid to a specified concentration, commercially available mineral acid may be diluted and used. The concentration of the mineral acid in the treatment liquid is preferably from 0.05 to 30% by weight, more preferably from 1.0 to 30% by weight, still more preferably from 1.0 to 20% by weight.

The treatment liquid may further contain a peroxide. Examples of the peroxide that can be used include hydrogen peroxide, peracetic acid, organic peroxide, peroxymonosulfuric acid, and chlorine dioxide. These may be used alone or in combination of two or more. The preferred peroxide is hydrogen peroxide. The peroxide can be added in the state of an aqueous solution. For example, hydrogen peroxide water generally flows at a concentration of 30 to 70% by weight, and the concentration of the peroxide used in the treatment liquid can be adjusted to a desired concentration, and the concentration of the hydrogen peroxide water to be used is not limited. . In order to make the concentration of the peroxide in the treatment liquid to a specified concentration, commercially available hydrogen peroxide water can be diluted and used.

The concentration of the peroxide in the treatment liquid is preferably from 0.05 to 15.0% by weight, more preferably from 0.1 to 15.0% by weight, still more preferably from 1.0 to 5.0% by weight. Here, the concentration of mineral acid and peroxide means undiluted, that is, 100% of the ratio of mineral acid and peroxide to the entire treatment liquid (% by weight). Further, the components other than the demineral acid and the peroxide in the treatment liquid are substantially water. The water used for the treatment liquid is preferably water having less impurities such as deionized water.

The low polymerization degree treatment can be carried out by a known method. For example, the chemical pulp may be immersed in the treatment liquid at a predetermined time or a predetermined temperature, but is not limited thereto.

The ratio of the pulp in the slurry containing the treatment liquid and the pulp is preferably from 1 to 20% by weight, more preferably from 3 to 10% by weight. When it is higher than 20% by weight, it is difficult for the treatment liquid to sufficiently permeate the pulp. On the other hand, when it is lower than 1% by weight, the reaction efficiency is poor and the economy is lacking.

The reaction temperature is preferably from 80 to 100 ° C, more preferably from 85 to 95 ° C. The reaction time is preferably from 30 minutes to 3 hours, more preferably from 1 to 2 hours.

The low polymerization degree treatment can be carried out by using a reaction tube, a continuous apparatus of a column, or a batch type reaction tank. In order to sufficiently circulate the treatment liquid, a stirring blade may be used, or the treatment liquid may be circulated through the extraction line.

In order to accelerate the penetration of the treatment liquid into the pulp, a surfactant may be used as the penetrating agent. The surfactant is not particularly limited as long as it is cationic, anionic, amphoteric or nonionic. Any of these may be used alone or in combination.

After the low polymerization degree treatment, the cellulose having a low degree of polymerization is separated from the used treatment liquid by a centrifugal separator, a filter press, a belt press, an Aureus type filter, a Young's filter, or the like. Further, a neutralization step, a washing step, a drying step, a pulverizing step, a classification step, and the like of the obtained cellulose may be carried out as necessary.

The residual amount of the cellulose obtained by the above method is preferably 0.1% or less and 0.05% or less. Further, the average degree of polymerization of the cellulose obtained by the above method is preferably 350 or less, more preferably 300 or less, and particularly preferably 250 or less. [Examples]

The present invention will be specifically described below by way of examples and comparative examples, but the present invention is not limited to the examples.

(1) Test conditions <Water used> In the following examples and comparative examples, deionized water obtained by an ultrapure water production apparatus AutoPure WR-7000 manufactured by Yamato Scientific Co., Ltd. was used. The deionized water has a conductivity of 18.2 MΩ (25.0 ° C) and a TOC content of 5 ppb.

<Method for measuring Canadian standard freeness> The Canadian standard freeness of the defibrated pulp obtained in the above step (a) is according to Japanese Industrial Standard JIS P-8121, "Pulp-Freeness Test Method - Part 2: Canadian Standard Free The method is carried out by a method using a Canadian Standard Freeness Tester. When the measured value exceeds 700 mL, a calibration table for a standard temperature of 20 ° C and a value of 700 mL for a calibration table of a standard concentration of 0.30% are used.

<The amount of burn-off> The amount of burn-off was measured according to the eighth edition of the Food Additives Booklet and the "Microcrystalline Cellulose Burning Test Method".

<Average degree of polymerization> The average degree of polymerization was measured by the viscosity measurement method using copper ethylenediamine described in the 16th revised Japanese Pharmacopoeia Commentary and the "Crystalline Confirmation Test (3)".

(2) Examples and Comparative Examples <Example 1> Bleached conifer pulp (burning amount 0.240%, average polymerization degree 1,254) of 944 g (absolute dry weight) and water 37L were cut by a cutter. The mixture was stirred at 850 rpm for 10 minutes to a stirring tank of 100 L with stirring wings. After stirring, suction filtration was carried out with a mesh having a pore size of 2 mm to obtain a defibrated pulp (defibration step). After the obtained defibrated pulp was added to 37 L of water and stirred for 3 minutes, filtration (water washing step) was carried out. This water washing step was repeated 5 times to obtain a water-washed defibrated pulp. The water-washed defibrated pulp had a Canadian standard freeness of 762 mL and a burn-off of 0.10%. 100 g (absolute dry weight) of the defibrated pulp after washing with water and 1800 g of a 16 wt% sulfuric acid aqueous solution were placed in a 2 L separation flask, and immersed in a constant temperature water tank at 90 ° C for 180 minutes to carry out a low polymerization degree treatment. After the reaction, suction filtration was carried out, and after washing with water for 5 times, suction filtration was carried out to obtain cellulose (low polymerization degree treatment step). The obtained cellulose had an average degree of polymerization of 233 and a burn-off amount of 0.03%.

<Example 2> Bleached conifer pulp (burning amount 0.397%, average degree of polymerization 1,497) 12.5 g (absolute dry weight) and 487.5 g of water were cut into a household mix by a chopper to a length of 40 mm and a width of 5 mm. (FMI (share) company, RM-5200V), stir for 5 minutes. After stirring, suction filtration was carried out with a nylon filter having a pore size of 30 μm to obtain a defibrated pulp (defibration step). To the defibrated pulp, water of 20 times the absolute dry weight of the defibrated pulp was added, and the mixture was stirred in a 1000 mL polypropylene container by a Sany motor (manufactured by Shinto Scientific Co., Ltd., BL600) at 500 rpm for 10 minutes, and then filtered (water washing step). . This water washing step was repeated 5 times to obtain a water-washed defibrated pulp. The water-washed defibrated pulp had a Canadian standard freeness of 720 mL. 6 g (absolute dry weight) of the defibrated pulp after washing was added to a 300 mL separation flask, and 54 g of an aqueous solution containing 16% by weight of sulfuric acid and 2% by weight of hydrogen peroxide was further added. The 300 mL separation flask was immersed in a constant temperature water bath at 90 ° C for 120 minutes to carry out a low polymerization degree treatment. After the reaction, suction filtration was carried out, and after washing with water for 5 times, suction filtration was carried out to obtain cellulose (low polymerization degree treatment step). The obtained cellulose had an average degree of polymerization of 216 and a burn-off amount of 0.04%.

<Example 3> Bleached conifer pulp (burning amount 0.234%, average degree of polymerization 1,254) 944 g (absolute dry weight) and water 37L, which were cut into a length of 5 mm and a width of 5 mm, were placed in a 100 L stirring tank with a cutter. A hand-held mixer (PM-851 manufactured by Ryobi Co., Ltd.) was stirred at 850 rpm for 10 minutes. After stirring, the mixture was filtered through a mesh having a pore size of 2.0 mm to obtain a defibrated pulp (defibration step). 944 g (absolute dry weight) of the defibrated pulp and 37 L of water were placed in a 100 L stirring tank, and stirred at 850 rpm for 3 minutes using a hand-held mixer, followed by filtration (water washing step). After the water washing step was repeated 5 times, the mixture was dehydrated by a centrifugal separator to obtain a water-washed defibrated pulp. The water-washed defibrated pulp had a Canadian standard freeness of 758 mL. 2 kg of a 1.4% by weight aqueous hydrochloric acid solution was added to a 2200 mL separation flask, and 100 g of water-washed defibrated pulp (absolute dry weight) was added. The 2200 mL separation flask was immersed in an oil bath at 130 ° C, and refluxed for 2 hours to carry out a low polymerization degree treatment. After the reaction, the mixture was subjected to suction filtration, washed twice, neutralized once, and washed once, and then subjected to suction filtration to obtain cellulose (low polymerization degree treatment step). The obtained cellulose had an average degree of polymerization of 254 and a burn-off amount of 0.07%.

<Example 4> Bleached conifer pulp (burning amount 0.240%, average degree of polymerization 1,254) having a length of 40 mm and a width of 5 mm (12.5 g (absolute dry weight)) and water (487.5 g) were added to 1000 mL of polypropylene by a chopper. The vessel was stirred at 500 rpm for 2 hours using a propeller with a wing diameter of 40 mm. After stirring, suction filtration was performed using a quantitative filter paper (No. 5C) to obtain a defibrated pulp (defibration step). 20 times by weight of the absolute dry weight of the defibrated pulp and the defibrated pulp was added to a 1000 mL polypropylene container, and the mixture was stirred at 500 rpm for 10 minutes using a Sany motor (manufactured by Shinto Scientific Co., Ltd., BL600), followed by filtration (water washing step). ). This water washing step was repeated 25 times to obtain a water-washed defibrated pulp. The water-washed defibrated pulp had a Canadian standard freeness of 735 mL. 10 g (absolute dry weight) of the water-washed defibrated pulp and 100 g of a 16% by weight sulfuric acid aqueous solution were placed in a 300 mL separation flask, and immersed in a constant temperature water bath at 90 ° C for 180 minutes to carry out a low polymerization degree treatment. After the reaction, suction filtration was carried out, and after washing with water for 5 times, suction filtration was carried out to obtain cellulose (low polymerization degree treatment step). The amount of burned cellulose obtained was 0.02%.

<Example 5> A bleached hardwood pulp (burning amount 0.358, average degree of polymerization 1,556) 11.5 g (absolute dry weight) and 988.5 g of water were cut into a 2000 mL beaker by a chopper to a length of 40 mm and a width of 5 mm, and used. The propeller blade with a wing diameter of 40 mm was stirred at 50 rpm for 1 hour while irradiating ultrasonic waves. After stirring, the mixture was filtered with a quantitative filter paper (No. 5C), and the same operation was repeated twice to obtain a defibrated pulp (defibration step and water washing step). The defibrated pulp was subjected to a low degree of polymerization treatment in the same manner as in Example 2 to obtain cellulose. The amount of burned cellulose obtained was 0.02%.

<Comparative Example 1> A defibrated pulp was produced in the same manner as in Example 2, except that bleached conifer pulp having a length of 40 mm and a width of 5 mm was cut by a chopper (burning amount: 0.397%, average polymerization degree: 1,497). Thereafter, the defibrated pulp was not washed with water, and the polymerization treatment was carried out in the same manner as in Example 2 to obtain cellulose. The amount of burned cellulose obtained was 0.12%.

<Comparative Example 2> A defibrated pulp was produced in the same manner as in Example 2 except that a bleached hardwood pulp having a length of 40 mm and a width of 5 mm was cut by a chopper (burning amount: 0.368%, average polymerization degree: 1,566). Thereafter, the defibrated pulp was not washed with water, and the polymerization treatment was carried out in the same manner as in Example 2 to obtain cellulose. The amount of burned cellulose obtained was 0.14%.

As is clear from the results of Comparative Example 1 and Comparative Example 2, when the water washing step was not performed before the low polymerization degree treatment, the removal of inorganic impurities in the pulp was insufficient, and the amount of the obtained cellulose was larger than 0.10%.

<Comparative Example 3> 2 g of cellulose (absolute dry weight) obtained in Comparative Example 2 and 400 g of water were placed in a 500 mL polypropylene container, and stirred at 500 rpm for 10 minutes using a Sany motor (manufactured by Shinto Scientific Co., Ltd., BL600), followed by filtration. . Repeat this operation 5 times. The amount of fiber burned by this operation was 0.12%.

As shown in Comparative Example 3, even if the cellulose obtained after the water washing step was not subjected to the low polymerization degree treatment was washed with water, the inorganic impurities could not be removed.

The embodiments of the present invention have been described, but are not intended to limit the scope of the invention. The present invention may be embodied in various other forms, and various omissions, substitutions and changes may be made without departing from the scope of the invention. The invention and its modifications are intended to be included within the scope and spirit of the invention and are included in the scope of the invention as claimed.

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Claims (8)

A method for producing cellulose, which is a method for producing cellulose from chemical pulp, comprising the following steps (a) to (c); (a) defibrating the chemical pulp; (b) step (a) The obtained defibrated pulp is washed with water; (c) The defibrated pulp which has been washed with water in the step (b) is hydrolyzed by a treatment liquid composed of an aqueous solution containing mineral acid to have a low degree of polymerization to obtain cellulose. The method for producing cellulose according to the first aspect of the invention, wherein the ultrasonic wave is irradiated in the steps (a) and/or (b). The method for producing cellulose according to the first or second aspect of the invention, wherein the amount of the obtained cellulose is 0.1% or less. The method for producing cellulose according to any one of claims 1 to 3, wherein the mineral acid is sulfuric acid or hydrochloric acid. The method for producing a cellulose according to the fourth aspect of the invention, wherein the content of the sulfuric acid or hydrochloric acid in the treatment liquid is 0.05 to 30% by weight. The method for producing cellulose according to any one of claims 1 to 5, wherein the treatment liquid further contains a peroxide. The method for producing cellulose according to claim 6, wherein the peroxide is hydrogen peroxide. The method for producing cellulose according to claim 7, wherein the hydrogen peroxide is contained in the treatment liquid in an amount of 0.05 to 15% by weight.