WO2016143761A1

WO2016143761A1 - Method for producing cellulose

Info

Publication number: WO2016143761A1
Application number: PCT/JP2016/057050
Authority: WO
Inventors: 裕哉佐藤; 小柳　賢司; 高嘉濱口; 貴光敦賀
Original assignee: 三菱瓦斯化学株式会社
Priority date: 2015-03-09
Filing date: 2016-03-08
Publication date: 2016-09-15
Also published as: TW201641779A; JP2018070664A

Abstract

One embodiment of the present invention provides a method for producing a cellulose from chemical pulp by means of a treatment liquid that is composed of an aqueous solution containing a mineral acid and a peroxide, which is characterized by comprising at least the steps (a)-(c) described below, and which is also characterized in that a regenerated treatment liquid prepared in the step (c) is reused as a treatment liquid in the step (a). (a) a step for obtaining a cellulose by lowering the degree of polymerization of chemical pulp by means of hydrolysis using a treatment liquid that is composed of an aqueous solution containing a mineral acid and a peroxide (b) a step for separating the cellulose obtained in the step (a) and the used treatment liquid from each other (c) a step for preparing a regenerated treatment liquid by adding a mineral acid and/or a peroxide into the used treatment liquid, which has been separated in the step (b)

Description

Method for producing cellulose

The present invention relates to a method for producing cellulose.

Cellulose is used in various applications such as foods, pharmaceuticals, and industrial applications.
For example, in food applications, the addition of cellulose provides a thickening and dispersing effect, thus improving the texture. Further, the water absorbency and oil absorbency are effective for improving the texture of fried foods.

In pharmaceutical applications, it is added to excipients for the purpose of molding, increasing the amount and diluting into solid preparations such as tablets, powders (powder) and granules.

In industrial applications, it is also used as a filter aid to improve filterability by adding to a slurry.
Furthermore, cellulose may be added to give excellent mechanical properties such as improving the welding workability of the coated arc welding rod. Cellulose is sometimes used as a base material for automobile friction materials as an alternative to asbestos.

As a characteristic of cellulose used in the above-mentioned applications, it is required to be a white powder excellent in fluidity and disintegration. It is known that the fluidity and disintegration of cellulose are affected by the degree of polymerization.

As a method for producing cellulose, for example, methods described in Patent Documents 1 to 3 and Non-Patent Document 1 are known.

Patent Document 1 discloses a method for producing a cellulose product having a level-off polymerization degree by subjecting refined wood pulp or the like to hydrolysis treatment called mineralization, ferric chloride, or the like, which is called low polymerization treatment.

Non-Patent Document 1 discloses a method for obtaining microcrystalline cellulose by subjecting high-purity natural cellulose to a treatment for reducing the degree of polymerization with a mineral acid, purifying and drying.

Patent Document 2 discloses a method for producing microcrystalline cellulose having high whiteness using unbleached kraft pulp or bleached kraft pulp as a raw material. This method uses treatment with a peroxy acid rather than treatment with only a mineral acid such as hydrochloric acid or sulfuric acid. For example, peroxymonosulfuric acid is produced by mixing sulfuric acid and hydrogen peroxide and is in equilibrium with sulfuric acid and hydrogen peroxide. The technology of this patent document generates high-concentration peroxymonosulfuric acid by mixing high-concentration sulfuric acid and hydrogen peroxide, and dilutes with water before reaching the equilibrium state, and is used to reduce the degree of polymerization of pulp. To do. When such a treatment liquid is used, the treatment liquid containing peroxymonosulfuric acid after separating the produced microcrystalline cellulose has been diluted and has already reached equilibrium. Even if high-concentration sulfuric acid or hydrogen peroxide is further added to such a solution, the concentration of newly produced peroxymonosulfuric acid is low and cannot be reused for the treatment for reducing the degree of polymerization of pulp.

In Patent Document 3, as a method for producing powdered cellulose, a mineral acid such as sulfuric acid is used, and when pulp cellulose is subjected to a low polymerization degree treatment, peroxide treatment such as ozone treatment or hydrogen peroxide is performed. A method is described. However, there is no description regarding the technique of reusing the mineral acid solution after the low polymerization degree treatment, and the method of Patent Document 3 cannot obtain crystalline cellulose having a polymerization degree of 350 or less.

On the other hand, in Patent Document 4, ozone generated by an ozone generator or ozone exhaust gas discharged from the ozone bleaching stage of the pulp bleaching process is added to the mineral acid solution used for the process of lowering the degree of polymerization of pulp, A method for regenerating a mineral acid solution is disclosed. Patent Document 5 discloses that the mineral acid solution is decolorized by adding ozone to the mineral acid solution that has been used for the degree-of-polymerization treatment while irradiating ultraviolet rays, and reused in the degree-of-polymerization treatment. A method is also disclosed. However, these methods require relatively large energy for ozone generation and are not suitable for producing cellulose on an industrial scale.

U.S. Pat. No. 2,978,446 Special table 2003-504427 gazette JP 2005-029627 A JP 2003-342301 A JP 2004-11071 A

Referring to Patent Document 2, an attempt was made to produce cellulose by reducing the degree of polymerization of unbleached kraft pulp or bleached pulp with active oxygen, and the following problems were found. In the method of Patent Document 2, active oxygen is derived from, for example, peroxy acid, and peroxy acid is obtained, for example, by reacting high concentration sulfuric acid with high concentration hydrogen peroxide. When using a diluted solution of hydrogen peroxide, the concentration is required to be 50% or more. Hydrogen peroxide is distributed from a high concentration to a low concentration from the viewpoint of safety, transportability, storage stability, and the like. For this reason, it is inconvenient if various concentrations of hydrogen peroxide cannot be used. In addition, since a high concentration of peroxyacid is recognized as corrosive to a stainless steel material, there is also a problem that a material generally used in preparing peroxyacid cannot be used.

Further, the case where the active oxygen in Patent Document 2 is derived from peroxymonosulfuric acid, for example, was examined. Peroxymonosulfuric acid is present in an equilibrium mixture of sulfuric acid and hydrogen peroxide. If the treatment liquid containing peroxymonosulfuric acid used in the pulp lowering treatment in this patent document has an equilibrium composition, the concentration of sulfuric acid and hydrogen peroxide, which are raw materials for peroxymonosulfuric acid, is low. Only the concentration of sulfuric acid and hydrogen peroxide after dilution with water should affect the degree of polymerization treatment. Therefore, the present inventors have examined that hydrogen peroxide solution of high concentration (for example, concentration of 50% or more) and concentrated sulfuric acid are reacted to produce peroxymonosulfuric acid, and then diluted with water. It was found that the composition of peroxymonosulfuric acid does not immediately become an equilibrium composition, and that the amount of peroxymonosulfuric acid produced increases as the concentration of the raw material hydrogen peroxide solution increases. That is, it has been found that the technique described in this patent document uses a high concentration of peroxymonosulfuric acid present in a non-equilibrium mixed solution for the treatment for reducing the degree of polymerization of pulp. Such a treatment solution containing a high concentration of peroxymonosulfuric acid has a drawback that it is difficult to produce stable cellulose because it gradually changes to an equilibrium composition.

Also, there is a problem that it is difficult to reuse a treatment solution containing peroxymonosulfuric acid that has reached an equilibrium composition during the treatment for reducing the degree of polymerization. That is, in the method of Patent Document 2, a high concentration of peroxy acid obtained by a reaction between a high concentration of peroxide and a high concentration of acid is required for the treatment for reducing the degree of polymerization of pulp. Such a treatment liquid containing a high concentration of peroxyacid is diluted with water and used, and has reached an equilibrium state after use. Therefore, the treatment liquid after use in the low polymerization degree treatment is increased again. Even if high-concentration sulfuric acid and high-concentration hydrogen peroxide water are added, high-concentration peroxymonosulfuric acid is not generated and cannot be reused in the low polymerization degree treatment described in Patent Document 2. In order to reuse, each component is separated and recovered from the treatment liquid containing peroxymonosulfuric acid after use in the low polymerization degree treatment with a distillation facility, etc., and the treatment liquid containing peroxymonosulfuric acid is prepared again using them. Need to be, not economical.

In general, the treatment liquid used for lowering the degree of polymerization of pulp contains a high concentration of mineral acid, so it has to be neutralized with a large amount of an alkaline agent for disposal, which increases the production cost. There is. Therefore, it has been economically desired to reuse the treatment liquid. In addition, when trying to reuse the treatment liquid after the degree-of-polymerization treatment, since the original whiteness of cellulose cannot be maintained and the coloring is performed, the methods of Patent Document 4 and Patent Document 5 are disclosed, As described above, a large amount of energy is required for ozone generation, which is not economical and economically advantageous.

The problem to be solved by the present invention is a method for producing cellulose from chemical pulp using a treatment liquid comprising an aqueous solution containing a mineral acid and a peroxide, wherein the recovered used treatment liquid is reused. Thus, it is to provide a method for producing cellulose having an average degree of polymerization of 350 or less and high whiteness.

In the method for producing cellulose by reducing the degree of polymerization of chemical pulp with a treatment liquid comprising an aqueous solution containing a mineral acid and a peroxide, the present inventors reused the treated liquid as a regeneration treatment liquid, and Provided is a method for producing cellulose having an average degree of polymerization of 350 or less and a Hunter whiteness of 92 or more and high whiteness. That is, this application includes the following inventions.
<1>
A method for producing cellulose from chemical pulp by a treatment solution comprising an aqueous solution containing a mineral acid and a peroxide, comprising at least the following steps (a) to (c), wherein the regeneration prepared in step (c) A method for producing cellulose, comprising reusing a treatment liquid as a treatment liquid in step (a).
(A) Step of obtaining cellulose by hydrolyzing chemical pulp with a treatment solution comprising an aqueous solution containing mineral acid and peroxide to obtain cellulose (b) Cellulose obtained in step (a) and treated solution (C) A step (2) of preparing a regenerated treatment liquid by adding at least either a mineral acid or a peroxide to the treated liquid separated in the steps (c) and (b).
The method for producing cellulose according to <1>, wherein the concentration of the peroxide in the treatment liquid is 0.05 to less than 40% by weight.
<3>
The method for producing cellulose according to <1> or <2>, wherein the concentration of the mineral acid in the treatment liquid is 0.05 to 35% by weight.
<4>
The cellulose according to any one of claims 1 to 3, wherein the aqueous solution containing a mineral acid and a peroxide is prepared by mixing a mineral acid, an aqueous peroxide solution having a concentration of less than 50% by weight, and water. How to manufacture.
<5>
The method for producing cellulose according to any one of <1> to <4>, wherein the mineral acid is sulfuric acid.
<6>
The method for producing cellulose according to any one of <1> to <5>, wherein the peroxide is hydrogen peroxide.
<7>
The method for producing cellulose according to any one of <1> to <6>, wherein the chemical pulp is bleached pulp.
<8>
The method for producing cellulose according to any one of <1> to <7>, wherein the cellulose has an average degree of polymerization of 350 or less and a Hunter whiteness of 92 or more.
<9>
Furthermore, the method for producing cellulose according to any one of <1> to <8>, further comprising any one or more of the following steps (d) to (h):
(D) The step of neutralizing the obtained cellulose (e) The step of washing the obtained cellulose (f) The step of drying the obtained cellulose (g) The step of crushing the obtained cellulose (h) Obtained Steps for classifying cellulose

According to the present invention, there is provided a method for producing cellulose from chemical pulp using a treatment liquid comprising an aqueous solution containing a mineral acid and a peroxide, wherein the recovered spent treatment liquid is reused to obtain an average degree of polymerization. Can provide a method for producing cellulose having a whiteness of 350 or less.

The method for producing cellulose according to the embodiment includes the following steps (a), (b) and (c), and further includes the following steps (d), (e), (f), (g) and (h): Either step may be included.
(A) Step of producing cellulose by hydrolyzing chemical pulp with a treatment solution comprising an aqueous solution containing a mineral acid and peroxide to produce cellulose (b) Processed with cellulose obtained in step (a) Steps (d) and (b) for preparing a regenerated processing liquid by adding at least one of mineral acid or peroxide to the processed liquid separated in the steps (c) and (b) The step of neutralizing the cellulose obtained in the step (e) The step of washing the obtained cellulose (f) The step of drying the obtained cellulose (g) The step of pulverizing the obtained cellulose (h) Step of classifying cellulose Recycled processing solution in which the mineral acid and peroxide concentrations are adjusted in step (c) is reused as the processing solution in step (a).

<Raw materials>
(1) Mineral acids that can be used in the steps (a) and (c) include sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, phosphoric acid, etc., and one kind may be used alone, or 2 You may mix and use the mineral acid more than a kind. Of these, the preferred mineral acid is sulfuric acid.

As a method for producing sulfuric acid, there are a production from sulfur dioxide, a nitric acid type production method, and a contact type production method, any of which may be used.

Concentrated sulfuric acid with a concentration of 90 to 98% by weight and dilute sulfuric acid with a concentration of less than 90% by weight are available as sulfuric acid. If the concentration of sulfuric acid in the treatment liquid can be adjusted to a desired concentration, it can be used. The concentration of sulfuric acid to be used is not limited. In order to set the concentration of sulfuric acid in the treatment liquid to a predetermined concentration, commercially available sulfuric acid may be diluted and used. In addition, there exist industrial sulfuric acid and refined sulfuric acid in the distribution | circulation goods of a sulfuric acid, Any can be used and these liquid mixture can also be used.

(2) Peroxides that can be used in the steps (a) and (c) include hydrogen peroxide, peracetic acid, organic peroxides, monopersulfuric acid, chlorine peroxide and the like. May be used alone, or two or more peroxides may be mixed. Among these, a preferred peroxide is hydrogen peroxide.

As a method for producing hydrogen peroxide, there are an organic method using anthraquinone or the like as a starting material, an electrolytic method using sulfuric acid as a raw material, and a direct method using oxygen and hydrogen. May be used in combination.

The peroxide can be added in the form of an aqueous solution. For example, hydrogen peroxide solution is generally distributed at a concentration of 30 to 70% by weight, but the concentration of hydrogen peroxide solution to be used is limited if the peroxide concentration in the treatment liquid can be adjusted to a desired concentration. Not. In order to set the concentration of peroxide in the treatment liquid to a predetermined concentration, commercially available hydrogen peroxide solution may be diluted and used.
In addition, the distribution product of hydrogen peroxide water includes industrial use, electronic industry use, and food additive use, and any of them can be used, and a plurality of kinds can be used in combination. When a plurality of types are used in combination, the combination is not limited at all.

(3) Treatment liquid / treated liquid / regenerated treatment liquid The treatment liquid, treated liquid (that is, used treatment liquid), and regenerated treatment liquid in the present specification contain mineral acid, peroxide and water. Refers to a mixture. For the preparation of the treatment liquid, it is preferable to use an aqueous peroxide solution having a concentration of less than 50% by weight (the amount of peroxide in the aqueous peroxide solution is less than 50% by weight). Originally, an aqueous peroxide solution of less than 50% by weight may be used, or an aqueous peroxide solution diluted to less than 50% by weight may be used. More preferred is an aqueous peroxide solution having a concentration of 20% by weight or more and less than 50% by weight, particularly preferably 30% by weight or more and less than 50% by weight. Depending on the concentration of mineral acid and peroxide, peroxyacid may be generated. Regardless of the concentration of peroxyacid, the mineral acid and peroxide concentration in the treatment liquid should be within the specified concentration range. Add acid and peroxide. The order of mixing the mineral acid, peroxide and water is not particularly limited. Moreover, there is no restriction | limiting in particular in a mixing apparatus, You may mix using a stirrer for a tank-type container, and the external circulation system which connects an external circulation apparatus to a container may be sufficient. Moreover, you may mix using a line mixer. The mixing temperature is in a range where heat is generated when mineral acid, peroxide, and water are mixed but does not boil. In addition, the mixing time is not limited as long as it can be uniformly mixed in an economical time.

In addition, at least one of a mineral acid or a peroxide is added to the treated liquid recovered in the separation step after the degree of polymerization treatment, and the mineral acid and the peroxide are adjusted to a predetermined concentration range, and the regeneration treatment is performed. Prepare the solution. It is preferable to use the same materials as the mineral acid and peroxide used in the preparation of the first treatment liquid as the mineral acid and peroxide added when preparing the regenerating treatment liquid. This regeneration treatment solution is used again for the treatment for reducing the degree of polymerization. That is, the regeneration processing solution prepared in the step (c) is reused as the processing solution in the step (a). The greater the number of reuses, the more economically advantageous and there is no particular limitation, but the reuse is performed 50 times or more, preferably 100 times or more, more preferably 1000 times or more.

(4) Chemical pulp Chemical pulp is produced from pulp chips. Examples of the raw material of the pulp chip include conifers represented by radiata pine and spruce, and broad-leaved trees represented by eucalyptus and acacia. These coniferous and hardwood pulps can be used alone or in combination of two or more. When a plurality of types are used in combination, the combination is not limited at all.

The chemical pulp is produced by using the above-mentioned pulp chip as a raw material, a sulfite cooking method, a kraft cooking method, or a combination of these methods.
The chemical pulp produced by the above method may be either non-bleached pulp or bleached pulp, or a combination thereof.
Chemical pulp includes papermaking pulp and high-precision dissolving pulp, both of which can be used, and these can also be used in combination.

The chemical pulp may be used in a water-containing state after cooking or bleaching, and a dried plate-like pulp may be used.
The chemical pulp used in the present invention may be any of the above types of pulp, but preferably bleached pulp produced by further performing at least one of an oxygen bleaching step or a bleaching step after cooking.

<Manufacturing process>
Hereinafter, the manufacturing steps (a) to (h) will be described in order.
Step (a) In step (a), chemical pulp as a raw material is subjected to a treatment for reducing the degree of polymerization with a treatment liquid to produce cellulose having a desired degree of polymerization.

(1) Composition of treatment liquid The treatment liquid is prepared from mineral acid, peroxide and water. Each of the mineral acid and the peroxide may be used alone or in combination of two or more. The mineral acid concentration in the treatment liquid is 0.05 to 35.0% by weight, preferably 1.0 to 30.0% by weight, more preferably 5.0 to 24.0% by weight, and particularly preferably 10.0. ~ 20.0% by weight. The peroxide concentration in the treatment liquid is 0.05 to 40.0% by weight, preferably 0.05 to 24.0% by weight, more preferably 0.05 to 10.0% by weight, and particularly preferably 0. .1 to 5.0% by weight. Here, the concentration of the mineral acid and the peroxide means a ratio (% by weight) with respect to the whole treatment liquid as undiluted, that is, as 100% mineral acid and peroxide. In addition, the component excluding the mineral acid and peroxide in the treatment liquid is basically water.

When using a treatment liquid prepared with a ratio of mineral acid and peroxide as indicated by the above range, cellulose having an average polymerization degree of 350 or less and a Hunter whiteness of 92 or more can be produced. .

(2) Preparation method of treatment liquid containing mineral acid, peroxide and water Mineral acid, peroxide, and water so that the concentration of mineral acid and peroxide in the treatment liquid is in the range as described above. In a reactor and mix. The order of input is not particularly limited. The mixing temperature may be 0 to 100 ° C. or less, preferably 20 to 90 ° C.

Mineral acid, peroxide and water may be mixed in the reaction tank used for the treatment for reducing the degree of polymerization, or after mixing in another tank, the mixture may be transferred to the reaction tank. Moreover, the chemical pulp used for the low polymerization degree treatment may be put into the reaction tank after preparing the treatment liquid, or may be put into the reaction tank from the beginning, and the treatment liquid may be put there. Further, it can be added during the preparation of the treatment liquid, and may be added before or after the addition of any chemical.

When sulfuric acid is used as the mineral acid and hydrogen peroxide is used as the peroxide, and the peroxymonosulfuric acid produced by mixing sulfuric acid and hydrogen peroxide is added, the initial concentration of peroxymonosulfuric acid is water, sulfuric acid, As well as the amount and concentration of hydrogen peroxide, it is affected by the mixing method. For example, when using at least one of a relatively high concentration sulfuric acid or a relatively high concentration hydrogen peroxide solution, and diluting with water after mixing sulfuric acid and hydrogen peroxide solution, the initial concentration of peroxymonosulfuric acid (That is, the concentration immediately after mixing) tends to be higher than the concentration of peroxymonosulfuric acid in the equilibrium solution. On the other hand, for example, when sulfuric acid and hydrogen peroxide are mixed using at least one of dilute sulfuric acid or prediluted hydrogen peroxide, the initial concentration of peroxymonosulfuric acid is the peroxymonosulfuric acid in the equilibrium solution. It tends to be lower than the concentration of. The composition of these mixed solutions begins to change towards the equilibrium composition depending on subsequent processing conditions. By mixing at a sufficient temperature for a sufficient time, the mixed solution is in an equilibrium state. For example, when the temperature of the mixed solution is 60 ° C., it is mixed for 10 to 180 minutes, when the temperature is 70 ° C., it is 10 to 120 minutes, and when the temperature is 90 ° C., it is mixed for 10 to 90 minutes. As a result, the mixed solution is in an equilibrium state.

In the method of the present invention, when sulfuric acid is used as the mineral acid and hydrogen peroxide is used as the peroxide, it can be carried out regardless of the concentration of peroxymonosulfuric acid produced.

The pH of the treatment liquid containing water, mineral acid and peroxide is determined by the weight ratio of each component in the treatment liquid, but the pH is preferably 2 or less, more preferably 1 or less.

(3) Low polymerization degree treatment The low polymerization degree treatment is a treatment for reducing the polymerization degree of pulp using a treatment liquid. Preferably, the chemical pulp is treated at a predetermined temperature for a predetermined time at a predetermined temperature (for example, sulfuric acid: 0.05 to 35.0% by weight, hydrogen peroxide: 0.05 to 40.0% by weight). %, Water: 50.0 to 94.0% by weight). Although a processing method is not specifically limited, For example, it can carry out by immersing a chemical pulp in a processing liquid at predetermined temperature for predetermined time.

The proportion of the pulp in the reaction solution containing the treatment liquid and the pulp is preferably in the range of 0.1 to 20% by weight, more preferably 1 to 15% by weight. When it is higher than 20% by weight, the treatment liquid does not sufficiently penetrate into the pulp, which is not preferable. If it is lower than 0.1% by weight, the reaction efficiency is poor and there is an economical problem.

The reaction temperature is preferably in the range of 20 ° C to 130 ° C, more preferably 50 ° C to 120 ° C, still more preferably 60 ° C to 110 ° C.
The reaction time is preferably in the range of 5 minutes to 240 minutes, more preferably 15 minutes to 180 minutes, and even more preferably 30 to 120 minutes.

(Facility)
The degree-of-polymerization treatment can be carried out using a continuous apparatus using a reaction tube or a tower, or a batch reaction tank. A stirring blade may be used so that the treatment liquid can be sufficiently circulated, and the treatment liquid may be circulated through the extraction line.

(Additives, other)
In order to accelerate the penetration of the treatment liquid into the pulp, a surfactant can be used as a penetrant. Surfactants include, but are not limited to, cationic, anionic, zwitterionic and nonionic. Any of these may be used alone or in combination.

(B) Step (b) Step is a step of separating the cellulose after the degree of polymerization treatment and the treated liquid, and the method is not particularly limited as long as they can be separated, but for example, filtration may be performed. it can. Specifically, in step (b), separation is performed using a centrifuge, a filter press, a belt press, an Oliver filter, a Young filter, or the like. The separated cellulose is sent to step (d), and the separated treated liquid is recovered and used in step (c).

(C) Step (c) In step (c), at least one of the mineral acid or peroxide consumed in step (a) is added to the treated liquid separated in step (b) to prepare a reclaimed processing solution. .

In step (c), mineral acid, peroxide and / or water exceeding the amount consumed in step (a) may be added as necessary. In addition to the mineral acid, peroxide and / or water consumed in the step (a), the mineral acid, peroxide and water in the treated liquid lost due to the separation from the cellulose in the step (b) are also included. In addition, it is for securing a necessary liquid amount in the second and subsequent steps (a). The ratio of the treated liquid in the regenerated liquid prepared in this step is 10% by weight or more, more preferably 50% by weight or more, still more preferably 70% by weight or more, and particularly preferably 80% by weight or more. (B) If the amount of the treated liquid recovered in the step is small, the amount of the chemical that must be newly added increases, which is not economical. Particularly important here is that the peroxide concentration in the treatment liquid used in step (a) is 0.05 to 40% by weight.

In step (c), in order to add an appropriate amount of mineral acid, peroxide and water, the mineral acid and peroxide concentrations in the treated liquid recovered in step (b) are analyzed. Is preferred. For example, the mineral acid concentration can be calculated by performing neutralization titration with a sodium hydroxide standard solution, and the peroxide concentration can be calculated by oxidation-reduction titration with a potassium permanganate standard solution or by adding potassium iodide. The free iodine can be calculated by titrating with a sodium thiosulfate standard solution.

(D) Neutralization step Mineral acid and peroxide still remain in the cellulose obtained in step (b). In order to remove these, a neutralization step is performed.
This step is a step of neutralizing the acid remaining in the cellulose using an alkali agent. The alkali agent used for neutralization is preferably used in an aqueous solution concentration of 0.01 wt% to 50 wt%, more preferably 0.1 wt% to 25 wt%. The ratio of the cellulose to the total weight of the alkali agent aqueous solution and the cellulose to be neutralized is preferably 1 to 15% by weight. As the alkaline agent, inorganic alkaline substances such as NaOH, KOH, and ammonia water, and organic alkaline substances such as trimethylammonium hydroxide can be used, but inorganic alkaline substances are preferred because of the ease of treatment of the alkaline aqueous solution after neutralization treatment. used. In order to reduce the amount of the alkaline agent to be used, the step (e) may be performed several times prior to this step.

(E) Washing step The (e) step is a step of removing the drug adhering to the cellulose by bringing the cellulose into contact with water. The apparatus which can be used is not specifically limited, For example, the stirring tank which has an impeller type stirrer can be used. You may wash | clean the cellulose obtained at the (b) process directly, without passing through the (d) process. In addition, it can wash | clean simultaneously with spin-drying | dehydration by using a centrifugal filtration, an Oliver type filter, a Young filter, etc. The cleaning process may be repeated.

(F) Drying step As a drying method, not only a method using a general dryer but also a method of substituting with a solvent can be used. As a method using a dryer, a hot air dryer, a steam tube dryer, an aeration dryer, a spray dryer, an air dryer, a drum dryer, a continuous fluidized bed dryer, an infrared dryer, a high-frequency heat dryer, a freezer Examples thereof include a method using a dryer, a rapid dryer, or the like. Examples of the method of replacing with a solvent include a method of replacing the moisture in cellulose with ethanol and then air drying.
The drying temperature is preferably 30 to 220 ° C. When drying at a temperature exceeding 220 ° C., the thermal decomposition of cellulose may proceed, which is not preferable. Drying may be performed under pressure, normal pressure, or reduced pressure.

(G) Pulverization process The pulverization process is performed by a mechanical treatment, and can be performed by, for example, using at least one of an impact mill and an airflow mill, and further by performing the treatment multiple times with the same model.

(H) Classification process A classification process is operation which classifies a cellulose according to a particle size by dry classification, wet classification, or a sieve classification method. The cellulose obtained in the step (g) can be classified and used as necessary. When a spray dryer is used, drying, refinement, and classification can be performed simultaneously.

<Cellulose>
(1) Hunter whiteness Hunter whiteness of the cellulose produced by the above method is 92 or more, more preferably 95 or more, and particularly preferably 97 or more.

(2) Average degree of polymerization The average degree of polymerization of the cellulose produced by the method of the present invention is 350 or less, preferably 300 or less, particularly preferably 250 or less.

Hereinafter, the present invention will be specifically described with reference to examples, comparative examples, and reference examples, but the present invention is not limited to these examples.

(1) Test conditions <Water used>
In the following examples and comparative examples, ion-exchanged water obtained with an ultrapure water production apparatus Autopure WR-7000 manufactured by Yamato Scientific was used. The electric conductivity of the ion exchange water was 18.2 MΩ (25.0 ° C.), and the TOC content was 5 ppb.

<PH measurement>
Unless otherwise specified, the pH was measured using a main body (Horiba, D-51) and a pH electrode (Horiba, 9615-10D).

<Quantification method of hydrogen peroxide>
The hydrogen peroxide contained in the treated liquid was quantified by an iodine reduction titration method. Specifically, 1 g of the recovered treated liquid after the low polymerization degree treatment was weighed and added to a 20 wt% sulfuric acid solution to make about 20 mL, and then potassium iodide powder was added to liberate iodine. . A 0.1 mol / L sodium thiosulfate standard solution was added dropwise thereto, and starch was used as an indicator, and the blue-purple color of the solution disappeared and became colorless, and the released iodine was quantified. From the iodine amount, the hydrogen peroxide amount was calculated.

<Quantification method of sulfuric acid>
The sulfuric acid contained in the treated liquid was quantified by neutralization titration. After the polymerization degree-reducing treatment, 0.5 g of the collected treated solution was weighed and diluted with ion-exchanged water to about 10 mL, and then a few drops of an indicator phenolphthalein solution were added. The 0.1 mol / L sodium hydroxide standard solution was dripped there, and it titrated until the solution became reddish purple, and calculated the quantity of sulfuric acid.

<Chromaticity of treated liquid>
After the treatment for reducing the degree of polymerization, the collected treated liquid was measured for absorbance at a wavelength of 420 nm using an ultraviolet-visible spectrophotometer.
(conditions)
Equipment: UV-2450 (Shimadzu Corporation)
Photometric mode: Absorbance Slit width: 2.0 mm
Scan mode: High speed Cell: Quartz cell 10mm
Reference cell: 16% by weight sulfuric acid Sample cell: treated liquid recovered in step (b) Dilution rate: 1

<Hunter whiteness of cellulose>
Using a color difference meter, the cellulose obtained in Examples and Comparative Examples was placed on a powder and paste sample stage, the surface color was measured, and Hunter whiteness was determined. The following formula was used for calculation of Hunter whiteness.
W (Lab) = 100 − [(100−L) ² + a ² + b ² ] ^1/2
W (Lab): Hunter whiteness of cellulose L: Lightness index a: Color coordinate indicating blue-yellow dimension b: Color coordinate indicating green-red dimension

<Average degree of polymerization of cellulose>
The average degree of polymerization was measured by a viscosity measurement method using copper ethylenediamine described in the 16th revised Japanese Pharmacopoeia Manual, crystalline cellulose confirmation test (3).

(2) Examples and Comparative Examples Table 1 shows the treatment solution compositions of sulfuric acid / hydrogen peroxide / water used in the Examples and Comparative Examples. The values of sulfuric acid (wt%) and hydrogen peroxide (wt%) in Table 1 are the concentrations of sulfuric acid and hydrogen peroxide in the treatment solution containing sulfuric acid, hydrogen peroxide, and water, and are not diluted ( That is, the concentration as sulfuric acid and hydrogen peroxide (100%).

<Example 1>
To 354.2 g of ion-exchanged water, 75.8 g of 95% by weight sulfuric acid (substantially sulfuric acid weight 72.0 g) and 20.0 g of 45% by weight hydrogen peroxide water (substantially hydrogen peroxide weight 9.0 g) were sequentially added. 450 g of a treatment liquid containing 16% by weight and 2.0% by weight of hydrogen peroxide was prepared. 30 g (absolute dry weight) of bleached softwood pulp (whiteness 95.1%, polymerization degree 1,566) chopped into 4 mm squares was added to this treatment solution, and the reaction vessel was placed in a 91 ± 1 ° C. hot water bath. It was immersed and heated for 120 minutes to reduce the degree of polymerization. In this treatment, a 500 mL separable flask equipped with a stirrer was used as the reaction vessel, and the stirring speed was 700 ± 50 rpm. After the treatment, the reaction vessel was cooled by immersion in an ice water bath for 30 minutes, and suction filtration was performed using a filter paper (No. 5C) with a Buchner funnel to recover 400 g of the treated liquid (No. 1-1). The cellulose obtained by filtration was washed three times with ion exchange water. In the third water washing, 1% ammonia water was added dropwise to the suspension containing cellulose to adjust the pH of the suspension to 7.0 ± 0.5, followed by suction filtration. The cellulose washed with water as described above was dried at 70 ° C. and 13.3 kPa or less with a vacuum dryer, and then pulverized with an impact type small pulverizer (Osaka Chemical Co., Ltd. Wonder Blender) to obtain a cellulose powder. . Hunter whiteness and polymerization degree were measured for the obtained cellulose powder, and hydrogen peroxide concentration, sulfuric acid concentration and chromaticity were analyzed for the treated liquid, and the results are shown in Table 2 (No. 1-1).

To the above-treated liquid (No. 1-1) 360 g (containing 59.8 g sulfuric acid and 6.2 g hydrogen peroxide), 12.9 g 95 wt% sulfuric acid (substantially 12.3 g sulfuric acid), 45 wt% Add hydrogen peroxide water 6.2g (substantially hydrogen peroxide weight 2.8g) and ion exchange water 70.9g to prepare 450g of reprocessing solution containing 16wt% sulfuric acid and 2.0wt% hydrogen peroxide. did. 30 g (absolute dry weight) of bleached softwood pulp (whiteness 95.1%, polymerization degree 1,566) chopped into 4 mm squares was put into the regenerated treatment solution, and the reaction vessel was bathed at 91 ± 1 ° C. Then, it was heated for 120 minutes to reduce the degree of polymerization. In this treatment, a 500 mL separable flask equipped with a stirrer was used as the reaction vessel, and the stirring speed was 700 ± 50 rpm. After the treatment, the reaction vessel was immersed in an ice water bath for 30 minutes to cool, and suction filtration was performed using a filter paper (No. 5C) with a Buchner funnel to recover 400 g of the treated liquid (No. 1-2). The cellulose obtained after filtration was washed three times with ion exchange water. In the third water washing, 1% ammonia water was added dropwise to the suspension containing cellulose to adjust the pH of the suspension to 7.0 ± 0.5, followed by suction filtration. The cellulose washed with water as described above was dried at 70 ° C. and 13.3 kPa or less with a vacuum dryer, and then pulverized with an impact type small pulverizer (Wonder Blender manufactured by Osaka Chemical Co., Ltd.) to obtain a cellulose powder. . For the obtained cellulose, Hunter whiteness and polymerization degree were measured, and for the treated liquid, hydrogen peroxide concentration, sulfuric acid concentration and chromaticity were analyzed, and the results are shown in Table 2 (No. 1-2).

To the above-treated liquid (No. 1-2) 360 g (containing 59.4 g sulfuric acid and 5.2 g hydrogen peroxide), 13.3 g 95% sulfuric acid (substantially 12.6 g sulfuric acid), 45% by weight Add 8.4 g of hydrogen peroxide water (substantially hydrogen peroxide weight 3.8 g) and 68.3 g of ion-exchanged water to prepare 450 g of reprocessing solution containing 16 wt% sulfuric acid and 2.0 wt% hydrogen peroxide. did. 30 g (absolute dry weight) of bleached softwood pulp (whiteness 95.1%, polymerization degree 1,566) chopped into 4 mm squares was put into the regenerated treatment solution, and the reaction vessel was bathed at 91 ± 1 ° C. Then, it was heated for 120 minutes to reduce the degree of polymerization. In this treatment, a 500 mL separable flask equipped with a stirrer was used as the reaction vessel, and the stirring speed was 700 ± 50 rpm. After the treatment, the reaction vessel was cooled by immersion in an ice water bath for 30 minutes, and suction filtration was performed using a filter paper (No. 5C) with a Buchner funnel to recover 400 g of the treated liquid (No. 1-3). The cellulose obtained by filtration was washed three times with ion exchange water. In the third water washing, 1% ammonia water was added dropwise to the suspension containing cellulose to adjust the pH of the suspension to 7.0 ± 0.5, followed by suction filtration. The cellulose washed with water as described above was dried at 70 ° C. and 13.3 kPa or less with a vacuum dryer, and then pulverized with an impact type small pulverizer (Osaka Chemical Co., Ltd. Wonder Blender) to obtain a cellulose powder. . For the obtained cellulose, Hunter whiteness and polymerization degree were measured, and for the treated liquid, hydrogen peroxide concentration, sulfuric acid concentration and chromaticity were analyzed, and the results are shown in Table 2 (No. 1-3).
Further, the same operation was repeated (Nos. 1-4 to 1-17).

<Example 2>
To 369.2 g of ion-exchanged water, 75.8 g of 95% by weight sulfuric acid (substantially sulfuric acid weight 72.0 g) and 5.0 g of 45% by weight hydrogen peroxide water (substantially hydrogen peroxide weight 2.3 g) were sequentially added. 450 g of a treatment liquid containing 16% by weight and 0.5% by weight of hydrogen peroxide was prepared. The same treatment as in Example 1 was performed except that this treatment liquid was used. The repeated process was performed twice. Hunter whiteness and polymerization degree were measured for the obtained cellulose powder, and hydrogen peroxide concentration, sulfuric acid concentration and chromaticity analysis were performed on the treated liquid, and the results are shown in Table 2 (No. .2-1 to 2-3).

<Example 3>
To 373.2 g of ion-exchange water, 75.8 g of 95% by weight sulfuric acid (substantially sulfuric acid weight 72.0 g) and 1.0 g of 45% by weight hydrogen peroxide water (substantially hydrogen peroxide weight 0.5 g) were sequentially added. 450 g of a treatment liquid containing 16% by weight and 0.1% by weight of hydrogen peroxide was prepared. The same treatment as in Example 1 was performed except that this treatment liquid was used. The repeated process was performed twice. Hunter whiteness and polymerization degree were measured for the obtained cellulose powder, and hydrogen peroxide concentration, acid concentration and chromaticity analysis were performed on the treated liquid, and the results are shown in Table 2 (No. .3-1 to 3-3).

Table 2 shows the Hunter whiteness of cellulose (No. 1-1, No. 2-1, No. 3-1) produced using the first treatment liquid, that is, the treatment liquid not containing the regeneration treatment liquid. Cellulose (No. 1-2 to No. 1-17, No. 2-2 and No. 2-3, No. 3-2 and The Hunter whiteness of No. 3-3) was shown as relative whiteness. From the results of Examples 1 to 3, it can be said that when the regenerated processing solution is used, the relative whiteness is not lowered and the processing solution can be used repeatedly.

<Comparative Example 1>
To 374.2 g of ion-exchanged water, 75.8 g of 95% by weight sulfuric acid (substantially sulfuric acid weight 72.0 g) was added, and 450 g of a treatment liquid containing no hydrogen peroxide and 16% by weight sulfuric acid was prepared. The same treatment as in Example 1 was performed except that this treatment liquid was used. Only sulfuric acid was added to regenerate the treated solution. The repeated treatment was performed twice. Hunter whiteness and polymerization degree were measured for the obtained cellulose powder, and acid concentration and chromaticity analysis were performed on the treated liquid, and the results are shown in Table 2 (No. 4-1 to 4-3).

From the result of the relative whiteness of Comparative Example 1, it is found that when the regenerated processing liquid without adding peroxide is repeatedly used as the processing liquid, the Hunter whiteness of cellulose is lowered and the processing liquid cannot be used repeatedly. It was.

<Comparative example 2>
To 1497 g of ion-exchanged water, 303 g of 95 wt% sulfuric acid (substantial sulfuric acid weight 288 g) was added to prepare 1800 g of a processing solution containing 16 wt% sulfuric acid without hydrogen peroxide. To this treatment solution, 120 g of bleached softwood pulp (whiteness 95.1%, polymerization degree 1,566) chopped into 4 mm squares was added, and the reaction vessel was immersed in a 90 ± 1 ° C. hot water bath. For 180 minutes to reduce the degree of polymerization of the pulp. In this treatment, a 2000 mL separable flask equipped with a stirrer was used as a reaction vessel, and the stirring speed was 700 ± 50 rpm. After the heat treatment, the reaction vessel was immersed in an ice-water bath for 30 minutes to cool, and suction filtration was performed using a filter paper (No. 5C) on a Buchner funnel to recover 1600 g of the treated liquid (No. 5-1). The operation of washing with water with ion-exchanged water and suction filtration was repeated twice for the pulp-decomposed material containing cellulose. In the second washing with water, 1% ammonia water was added dropwise during washing to adjust the pH of the suspension containing cellulose and ion-exchanged water to 7.0 ± 0.5, followed by suction filtration. The obtained cellulose was dried with a vacuum dryer at 70 ° C. and 13.3 kPa or less, and then pulverized with an impact type small pulverizer (sample mill manufactured by Seishin Co., Ltd.) to obtain a cellulose powder. Hunter whiteness and polymerization degree were measured for the obtained cellulose powder, and chromaticity was analyzed for the treated liquid, and the results are shown in Table 2 (No. 5-1).

A solution containing 0.5% by weight of hydrogen peroxide is prepared by adding 5.0 g of 45% by weight hydrogen peroxide water (substantially hydrogen peroxide weight 2.3g) to 450g of the treated liquid (No. 5-1). did. This solution was heated at 90 ± 1 ° C. for 120 minutes. In the treatment, a 500 mL separable flask with a stirrer was used as a container, and the stirring speed was 300 ± 50 rpm. After the treatment, the solution was allowed to cool to room temperature, and then the hydrogen peroxide remaining in the solution was decomposed using platinum (the concentration of hydrogen peroxide in the solution after the decomposition treatment was 0.014 ppm). Further, the chromaticity of this solution was measured and shown in (No. 5-2) of Table 2.

To this solution (No. 5-2) 360 g, 95% by weight sulfuric acid 14.4 g (substantial sulfuric acid weight 13.7 g) and ion-exchanged water 75.6 g are added to prepare 450 g of a regeneration treatment solution containing 16% by weight sulfuric acid. did. Using this regenerated treatment liquid as a treatment liquid, 30 g (absolute dry weight) of bleached softwood pulp (whiteness 95.1%, polymerization degree 1,566) chopped into 4 mm squares was charged, and the reaction vessel was 91 ±±. It was immersed in a 1 ° C. hot water bath and heated for 120 minutes to perform a low polymerization degree treatment. In this treatment, a 500 mL separable flask equipped with a stirrer was used as the reaction vessel, and the stirring speed was 700 ± 50 rpm. After the treatment, the reaction vessel was cooled by immersion in an ice water bath for 30 minutes, and suction filtration was performed using a filter paper (No. 5C) with a Buchner funnel to recover 400 g of the treated liquid (No. 5-3). The cellulose obtained after filtration was washed 3 times with ion exchange water. In the third water washing, 1% ammonia water was added dropwise to the suspension containing cellulose to adjust the pH of the suspension to 7.0 ± 0.5, followed by suction filtration. The cellulose washed with water as described above was dried at 70 ° C. and 13.3 kPa or less with a vacuum dryer, and then pulverized with an impact type small pulverizer (Wonder Blender manufactured by Osaka Chemical Co., Ltd.) to obtain a cellulose powder. . For the obtained cellulose powder, Hunter whiteness and polymerization degree were measured, and for the treated liquid, chromaticity analysis was performed and the results are shown in Table 2 (No. 5-3).

Even when the colored treated solution is decolored, when a regenerated treatment solution to which hydrogen peroxide is not added is reused as the treatment solution, the relative whiteness decreases, and the treatment solution cannot be used repeatedly.

Claims

A method for producing cellulose from chemical pulp by a treatment solution comprising an aqueous solution containing a mineral acid and a peroxide, comprising at least the following steps (a) to (c), wherein the regeneration prepared in step (c) A method for producing cellulose, comprising reusing a treatment liquid as a treatment liquid in step (a).
(A) Step of obtaining cellulose by hydrolyzing chemical pulp with a treatment solution comprising an aqueous solution containing mineral acid and peroxide to obtain cellulose (b) Cellulose obtained in step (a) and treated solution (C) A step of preparing a regenerated treatment liquid by adding at least one of a mineral acid or a peroxide to the treated liquid separated in the steps (c) and (b)
The method for producing cellulose according to claim 1, wherein the concentration of the peroxide in the treatment liquid is 0.05 to less than 40% by weight.
The method for producing cellulose according to claim 1 or 2, wherein the concentration of the mineral acid in the treatment liquid is 0.05 to 35% by weight.
The cellulose according to any one of claims 1 to 3, wherein the aqueous solution containing a mineral acid and a peroxide is prepared by mixing a mineral acid, an aqueous peroxide solution having a concentration of less than 50% by weight, and water. How to manufacture.
The method for producing cellulose according to any one of claims 1 to 4, wherein the mineral acid is sulfuric acid.
The method for producing cellulose according to any one of claims 1 to 5, wherein the peroxide is hydrogen peroxide.
The method for producing cellulose according to any one of claims 1 to 6, wherein the chemical pulp is bleached pulp.
The method for producing cellulose according to any one of claims 1 to 7, wherein the average polymerization degree of the cellulose is 350 or less and the Hunter whiteness is 92 or more.
The method for producing cellulose according to any one of claims 1 to 8, further comprising any one or more of the following steps (d) to (h):
(D) The step of neutralizing the obtained cellulose (e) The step of washing the obtained cellulose (f) The step of drying the obtained cellulose (g) The step of crushing the obtained cellulose (h) Obtained Steps for classifying cellulose