WO2019059079A1 - Method for producing anionically modified cellulose nanofibers - Google Patents

Abstract

This method for producing anionically modified cellulose nanofibers comprises: a preparation step for preparing an anionically modified cellulose; a defibration step for obtaining an anionically modified cellulose nanofiber salt by defibrating the anionically modified cellulose obtained in the preparation step; a desalting step for obtaining anionically modified cellulose nanofibers by desalting the anionically modified cellulose nanofiber salt obtained in the defibration step by subjecting the anionically modified cellulose nanofiber salt to a cation exchange reaction using a cation exchange resin; and a recovery step for recovering the cation exchange resin from a mixture that is obtained in the desalting step and contains the anionically modified cellulose nanofibers and the cation exchange resin.

Description

Method for producing anion-modified cellulose nanofibers

The present invention relates to a method of producing anion-modified cellulose nanofibers.

Cellulose base material is processed in the coexistence of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as "TEMPO") and sodium hypochlorite which is an inexpensive oxidizing agent Then, carboxyl groups can be efficiently introduced to the surface of the microfibrils of cellulose (Patent Document 1). In addition, a carboxymethyl group can be introduced into cellulose by reacting a cellulose-based material with mercuric and subsequent reaction with monochloroacetic acid or sodium monochloroacetate (Patent Document 2). In cellulose in which a carboxyl group or a carboxymethyl group has been introduced, these groups are negatively charged in a solvent (hereinafter referred to as "anion-modified cellulose"). It is known that when such anion-modified cellulose is treated with a mixer or the like in a solvent, a cellulose nanofiber dispersion, which is microfibrils of cellulose, can be obtained (Patent Document 3).

Cellulose nanofibers are biodegradable water-dispersible materials. Since the cellulose nanofibers obtained by the above-mentioned method are in the form of a dispersion, they can be blended with various water-soluble polymers, or complexed with organic / inorganic pigments to be modified. In addition, cellulose nanofibers can also be sheeted or fiberized. Based on such characteristics, development of new high-performance products in which cellulose nanofibers are applied to high-performance packaging materials, transparent organic substrate members, high-performance fibers, separation membranes, regenerative medical materials, etc. are being studied.

In the aqueous dispersion of cellulose nanofibers obtained by the above method, anionic groups such as carboxyl groups present on the surface of the cellulose nanofibers form salts such as sodium salts, resulting in high hydrophilicity. Depending on the application, such as forming a complex with a resin, a cellulose nanofiber in which the anionic group is converted to an acid form to reduce the hydrophilicity is required. In order to convert an anionic group to an acid form, an acid treatment using a mineral acid such as hydrochloric acid or sulfuric acid is performed (see Patent Document 4).

JP, 2008-001728, A Japanese Patent Application Laid-Open No. 10-251301 International Publication No. 2011/115154 International Publication No. 2010/116795

When acid treatment with a mineral acid is carried out to convert the anionic group to the acid form, by-products such as sodium chloride are formed, and it is necessary to remove the by-products by washing. In addition, it is necessary to dehydrate and remove the water used for washing, and after dehydration, the filter cloth is passed and the remaining filter material is recovered, but cellulose nanofibers of extremely short fiber length will pass through the filter cloth Therefore, the yield may be greatly reduced.
Therefore, as a method of desalting the anion-modified cellulose nanofiber salt, investigation of a method using a cation exchange resin without generation of by-products has started.

An object of the present invention is to provide a method for producing anion-modified cellulose nanofibers in which the used cation exchange resin does not mix into the cellulose nanofibers.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining that said inventor should solve said subject, it discovers that the said objective can be achieved by collect | recovering used cation exchange resin, and completed this invention.

That is, the present invention provides the following (1) to (12).
(1) A preparation step of preparing anion-modified cellulose, a fibrillation step of disintegrating the anion-modified cellulose obtained in the preparation step to obtain an anion-modified cellulose nanofiber salt, and A desalting process for obtaining an anion-modified cellulose nanofiber by desalting the anion-modified cellulose nanofiber salt by performing a cation exchange reaction using a cation exchange resin, and the desalting process A method for producing anion-modified cellulose nanofibers, comprising a recovery step of recovering the cation exchange resin from a mixture containing the anion-modified cellulose nanofibers obtained above and the cation exchange resin.
(2) The method for producing anion-modified cellulose nanofiber according to (1), wherein pressure filtration at 0.01 MPa or more and 5 MPa or less or vacuum filtration at 0.01 MPa or more and 0.1 MPa or less is performed in the recovery step.
(3) The method for producing anion-modified cellulose nanofibers according to (1) or (2), wherein in the recovery step, a slit-shaped filter medium having an opening of 5 μm to 400 μm or a slit width of 5 μm to 400 μm is used. .
(4) The method for producing anion-modified cellulose nanofiber according to any one of (1) to (3), further comprising a microfiltration step before or after the recovery step.
(5) The anion-modified cellulose nanofiber according to any one of (1) to (4), wherein a regeneration step of a cation exchange resin by acid treatment is performed on the cation exchange resin recovered in the recovery step. Manufacturing method.
(6) A step of using a positive displacement screw pump for sending and pressure filtration of the mixture in the recovery step, or for sending a solution between the desalting step and the recovery step (1) to (5) The manufacturing method of the anion modified cellulose nanofiber in any one of-.
(7) The method for producing anion-modified cellulose nanofibers according to (6), wherein the positive displacement screw pump is a positive displacement uniaxial eccentric screw pump or a positive displacement twin screw pump.
(8) A step of using a positive displacement reciprocating pump in the liquid transfer and pressure filtration of the mixture in the recovery step, or in the liquid transfer between the desalting step and the recovery step (1) to (5) The manufacturing method of the anion modified cellulose nanofiber in any one of these.
(9) The method for producing anion-modified cellulose nanofibers according to (8), wherein the positive displacement reciprocating pump is a positive displacement diaphragm pump.
(10) The preparation step includes the step of oxidizing the cellulose-based raw material with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, and a mixture thereof The method for producing anion-modified cellulose nanofibers according to any one of (1) to (9), wherein the anion-modified cellulose obtained by the preparation step is one obtained by introducing a carboxyl group into cellulose.
(11) The preparation step includes the step of reacting a cellulose-based material with a mercerizing agent followed by reacting with a carboxymethylating agent, and the anion-modified cellulose obtained by the preparation step has a carboxymethyl group to cellulose The method for producing an anion-modified cellulose nanofiber according to any one of (1) to (9), wherein
(12) The preparation step includes the step of adding a phosphoric acid compound to a cellulose-based material, and the anion-modified cellulose obtained by the preparation step is one in which a phosphate group is introduced into cellulose (1) A method for producing the anion-modified cellulose nanofiber according to any one of (9) to (9).

According to the present invention, it is possible to provide a method for producing anion-modified cellulose nanofibers in which the used cation exchange resin is not mixed into the cellulose nanofibers.

Hereinafter, the present invention will be described in detail. In the present invention, "-" includes an end value. That is, “X to Y” includes the values X and Y at its both ends.

The method for producing anion-modified cellulose nanofibers of the present invention comprises a preparation step of preparing anion-modified cellulose, and disintegration of the anion-modified cellulose obtained in the preparation step to obtain anion-modified cellulose nanofiber salt And the anion-modified cellulose nanofiber salt obtained in the defibrating step are subjected to a desalting treatment by performing a cation exchange reaction using a cation exchange resin to obtain anion-modified cellulose nanofibers A desalting step, and a recovery step of recovering the cation exchange resin from a mixture containing the anion-modified cellulose nanofibers obtained in the desalting step and the cation exchange resin.

(Preparation process)
In the preparation process of the present invention, the cellulose-based material is anion-modified to prepare anion-modified cellulose.

(Cellulose-based raw materials)
Examples of cellulosic materials include plants (eg, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp) (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulphite pulp (NUSP), softwood bleached sulphite pulp (NBSP) thermomechanical pulp (TMP), regenerated pulp, waste paper etc., animals (eg ascidians) , Algae, microorganisms (such as acetic acid bacteria (acetobacter)), products of microbial products, etc. are known, and any of them can be used in the present invention, preferably cellulose fibers of plant or microorganism origin, plant origin Cellulose fibers are more preferred.

(Anion modification)
Anion modification is introducing a anion group to cellulose, and specifically introducing an anion group to a pyranose ring by oxidation or substitution reaction. In the present invention, the above-mentioned oxidation reaction means a reaction of oxidizing the hydroxyl group of the pyranose ring directly to the carboxyl group. In the present invention, the substitution reaction is a reaction which introduces an anionic group to the pyranose ring by substitution reaction other than the oxidation.

(Carboxylation)
Carboxylated (oxidized) cellulose can be used as anion-modified cellulose. The carboxy group in the present invention refers to -COOH (acid form) or -COOM (salt form). Here, M is a metal ion, and examples thereof include sodium and potassium. Carboxylated cellulose (also referred to as "oxidized cellulose") can be obtained by carboxylating (oxidizing) the above-mentioned cellulose-based raw material by a known method. Although not particularly limited, the amount of carboxyl group is preferably 0.6 to 3.0 mmol / g, more preferably 1.0 to 2.0 mmol / g, with respect to the dry weight of the anion-modified cellulose nanofiber. As an example of a carboxylation (oxidation) method, the cellulose-based raw material is dissolved in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, and mixtures thereof. A method of oxidation can be mentioned. This oxidation reaction, C6-position primary hydroxyl groups of the glucopyranose ring of the cellulose surface is selectively oxidized, and an aldehyde group on the surface, a carboxyl group (-COOH) or carboxylate groups (-COO ^-) and cellulosic fibers having a You can get The concentration of cellulose at the time of reaction is not particularly limited, but is preferably 5% by mass or less.

The N-oxyl compound refers to a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound may be used as long as it promotes the target oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy TEMPO) can be mentioned. The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing the cellulosic raw material. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.01 to 0.5 mmol is more preferable with respect to 1 g of the cellulose-based raw material which is completely dried. In addition, about 0.1 to 4 mmol / L is preferable to the reaction system.

Bromides are compounds containing bromine, examples of which include alkali metal bromides which can be dissociated and ionized in water. Further, iodide is a compound containing iodine, and examples thereof include alkali metal iodides. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of the bromide and the iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and still more preferably 0.5 to 5 mmol relative to 1 g of the cellulose-based raw material. The modification is modification by oxidation reaction.

As the oxidizing agent, known ones can be used, and for example, halogen, hypohalous acid, halogenous acid, perhalogenated acid or salts thereof, halogen oxides, peroxides and the like can be used. Among these, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferable. An appropriate amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, and still more preferably 2.5 to 25 mmol, per 1 g of the cellulose-based material which is extremely dry. Also, for example, 1 to 40 mol is preferable to 1 mol of the N-oxyl compound.

In the oxidation process of the cellulosic material, the reaction can be efficiently advanced even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 ° C., and may be room temperature of about 15 to 30 ° C. As the reaction proceeds, carboxyl groups are formed in the cellulose, so the pH of the reaction solution is lowered. In order to allow the oxidation reaction to proceed efficiently, an alkaline solution such as an aqueous sodium hydroxide solution is optionally added to the reaction system to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11. The reaction medium is preferably water because of ease of handling and the difficulty of side reaction. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.

The oxidation reaction may be carried out in two stages. For example, by oxidizing oxidized cellulose obtained by filtering off after completion of the first stage reaction again under the same or different reaction conditions, cellulose is not affected by the reaction inhibition by the salt by-produced in the first stage reaction. A carboxyl group can be efficiently introduced into the system raw material.

The amount of carboxyl groups of oxidized cellulose can be adjusted by controlling the reaction conditions such as the addition amount of the above-mentioned oxidizing agent and the reaction time. The amount of carboxyl groups in the anion-modified cellulose nanofibers is preferably the same as the amount of carboxyl groups in the cellulose nanofibers.

In the present invention, in the oxidized cellulose obtained in the above step, the carboxyl group introduced into the cellulose-based material is usually a salt type and is an alkali metal salt such as a sodium salt. Before the fibrillation step, the alkali metal salt of oxidized cellulose may be replaced with other cationic salt such as phosphonium salt, imidazolinium salt, ammonium salt, sulfonium salt and the like. The substitution can be performed by known methods.

(Carboxymethylation)
Preferred anionic groups include carboxyalkyl groups such as carboxymethyl groups. The carboxyalkyl group in the present invention refers to -RCOOH (acid type) or -RCOOM (salt type). Here, R is an alkylene group such as a methylene group or ethylene group, and M is a metal ion. The carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. It is preferred that the degree of carboxyalkyl substitution per anhydrous glucose unit of cellulose is less than 0.60. Furthermore, when the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.60. If the degree of substitution is 0.60 or more, the crystallinity is lowered and the proportion of the dissolved component is increased, so that the function as a nanofiber is lost. The lower limit value of the degree of carboxyalkyl substitution is preferably 0.01 or more. In consideration of operability, the substitution degree is particularly preferably 0.02 to 0.50, and more preferably 0.10 to 0.30. As an example of the method for producing such carboxyalkylated cellulose, a method comprising the following steps can be mentioned. The modification is modification by substitution reaction. Carboxymethylated cellulose will be described as an example.
i) Mix the base material, solvent and mercerizing agent, and mercerize it at reaction temperature 0 to 70 ° C, preferably 10 to 60 ° C, and reaction time 15 minutes to 8 hours, preferably 30 minutes to 7 hours Process,
ii) Then, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mole per glucose residue, the reaction temperature is 30 to 90 ° C., preferably 40 to 80 ° C., and the reaction time is 30 minutes to 10 hours, preferably A step of performing etherification reaction for 1 hour to 4 hours.

The above-mentioned cellulose-based materials can be used as the base material. As the solvent, 3 to 20 times by mass of water or lower alcohol, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc. alone or More than mixed media of species can be used. When lower alcohols are mixed, the mixing ratio is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 moles of alkali metal hydroxide, specifically sodium hydroxide and potassium hydroxide, can be used per anhydroglucose residue of the base stock.

As mentioned above, the degree of carboxymethyl substitution per glucose unit of cellulose is less than 0.04, preferably not less than 0.01 and less than 0.60. By introducing a carboxymethyl substituent into cellulose, the celluloses electrically repel each other. For this reason, the cellulose which introduce | transduced the carboxymethyl substituent can be easily nano-fibrillated. In addition, when the carboxymethyl substituent per glucose unit is smaller than 0.02, nano defibration may not be enough. The degree of substitution in anion-modified cellulose nanofibers and the degree of substitution when made into cellulose nanofibers are generally the same.

In the present invention, in the carboxyalkylated cellulose obtained in the above steps, the carboxyalkyl group introduced into the cellulose-based material is usually in a salt form, and is an alkali metal salt such as a sodium salt. Prior to the defibration step, the alkali metal salt of carboxyalkylated cellulose may be replaced with other cationic salt such as phosphonium salt, imidazolinium salt, ammonium salt, sulfonium salt and the like. The substitution can be performed by known methods.

(Esterification)
Esterified cellulose can also be used as anion-modified cellulose. The method of mixing the powder and aqueous solution of phosphoric acid type compound A with a cellulose type raw material, the method of adding the aqueous solution of phosphoric acid type compound A to the slurry of a cellulose type raw material, etc. are mentioned. The phosphoric acid compound A includes phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters of these. These may be in the form of a salt. Among the above, a compound having a phosphate group is preferable because it is low in cost, easy to handle, and a phosphate group is introduced into cellulose of pulp fiber to improve the disaggregation efficiency. As a compound having a phosphoric acid group, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, phosphorus Examples thereof include tripotassium acid potassium, pyrophosphate potassium, potassium metaphosphate, ammonium dihydrogenphosphate, ammonium dihydrogenphosphate, ammonium triphosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. These may be introduced singly or in combination of two or more kinds to introduce a phosphate group. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of phosphate group introduction, easy disaggregation in the following fibrillation step, and industrial application. Ammonium salts are preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. In addition, the phosphoric acid compound A is preferably used as an aqueous solution because the reaction can proceed uniformly and the efficiency of introducing a phosphoric acid group becomes high. The pH of the aqueous solution of the phosphoric acid type compound A is preferably 7 or less because the efficiency of introducing a phosphoric acid group is increased, but a pH of 3 to 7 is preferable from the viewpoint of suppressing the hydrolysis of pulp fibers.

The following method can be mentioned as an example of the manufacturing method of phosphated cellulose. A phosphoric acid compound A is added to a suspension of a cellulose-based material having a solid content concentration of 0.1 to 10% by mass with stirring to introduce a phosphate group to cellulose. The amount of the phosphoric acid-based compound A added is preferably 0.2 to 500 parts by mass, and more preferably 1 to 400 parts by mass, as the amount of phosphorus element when the amount of the cellulose-based material is 100 parts by mass. . If the ratio of phosphoric acid type compound A is more than the above-mentioned lower limit, the yield of fine fibrous cellulose can be improved more. However, if the above upper limit is exceeded, the effect of improving the yield becomes flat, which is not preferable from the viewpoint of cost.

In addition to the phosphoric acid compound A, a powder or an aqueous solution of the compound B may be mixed. The compound B is not particularly limited, but a nitrogen-containing compound exhibiting basicity is preferable. "Basic" here is defined as the aqueous solution exhibiting a peach to red color in the presence of a phenolphthalein indicator or that the pH of the aqueous solution is greater than 7. The nitrogen-containing compound having basicity used in the present invention is not particularly limited as long as the effects of the present invention are exhibited, but a compound having an amino group is preferable. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like can be mentioned. Above all, urea which is easy to handle at low cost is preferable. The amount of the compound B added is preferably 2 to 1000 parts by mass, and more preferably 100 to 700 parts by mass, with respect to 100 parts by mass of the solid content of the cellulose-based material. The reaction temperature is preferably 0 to 95 ° C., more preferably 30 to 90 ° C. The reaction time is not particularly limited, but is about 1 to 600 minutes, and more preferably 30 to 480 minutes. When the conditions of the esterification reaction are in these ranges, it is possible to prevent the cellulose from being excessively esterified and easily dissolved, and the yield of the phosphated cellulose becomes good. After dehydration of the obtained phosphated cellulose suspension, heat treatment at 100 to 170 ° C. is preferable from the viewpoint of suppressing hydrolysis of the cellulose. Further, during the heat treatment, while water is contained, it is preferable to heat at 130 ° C. or less, preferably 110 ° C. or less, remove water, and then heat treat at 100 to 170 ° C.

The degree of phosphate substitution per glucose unit of the phosphated cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. For this reason, the cellulose which introduce | transduced the phosphate group can be easily nano-fibrillated. If the degree of phosphate substitution per unit of glucose is less than 0.001, nanofibrillation can not be sufficiently achieved. On the other hand, if the degree of phosphate substitution per glucose unit is greater than 0.40, it may swell or dissolve, and may not be obtained as nanofibers. In order to efficiently carry out disintegration, it is preferable that the phosphated cellulose-based raw material obtained above is boiled and then washed with cold water. These esterification modifications are substitution reactions. The degree of substitution in the anion-modified cellulose nanofibers is preferably the same as the degree of substitution when made into cellulose nanofibers.

In the present invention, in the phosphated cellulose obtained in the above steps, the phosphate group introduced into the cellulose-based material is usually in a salt form, and is an alkali metal salt such as a sodium salt. Prior to the defibration step, the alkali metal salt of phosphated cellulose may be substituted with other cationic salt such as phosphonium salt, imidazolinium salt, ammonium salt, sulfonium salt and the like. The substitution can be performed by known methods.

(Disintegration process)
In the fibrillation step of the present invention, anion-modified cellulose is fibrillated. As the defibration treatment, for example, after thoroughly washing the anion-modified cellulose with water, it can be performed using a known device such as a high-speed shear mixer or a high-pressure homogenizer. Examples of the type of defibration apparatus include a high-speed rotation type, a colloid mill type, a high pressure type, a roll mill type, and an ultrasonic type. These devices may be used alone or in combination of two or more.

When using a high speed shear mixer, the shear rate is preferably 1000 sec ^-1 or more. When the shear rate is 1000 sec ⁻¹ or more, the aggregation structure is small and nanofibers can be uniformly formed. When using a high pressure homogenizer, 50 MPa or more is preferable, 100 MPa or more is more preferable, 140 MPa or more is more preferable. When treated with a wet high-pressure or ultra-high-pressure homogenizer at such pressure, the formation of nanofibers can be efficiently proceeded, and when it is made an aqueous dispersion, anion-modified cellulose nanofibers with low viscosity can be efficiently obtained.

Anion-modified cellulose is subjected to disintegration treatment as an aqueous dispersion such as water. When the concentration of the anion-modified cellulose in the aqueous dispersion is high, the viscosity may be excessively increased during the defibration treatment to prevent uniform defibration, or the device may stop. Therefore, the concentration of anion-modified cellulose needs to be set appropriately depending on the processing conditions of anion-modified cellulose. As an example, the concentration of anion-modified cellulose is preferably 0.3 to 50% (w / v), more preferably 0.5 to 10% (w / v), and 1.0 to 5% (w / v) Is more preferred. In the present invention, after defibrillation of the anion-modified cellulose, an anion-modified cellulose nanofiber salt is obtained.

(Desalting process)
In the desalting step of the present invention, the anion-modified cellulose nanofiber salt is desalted by contacting a cation exchange resin and performing a cation exchange reaction to obtain anion-modified cellulose nanofibers. In the anion-modified cellulose nanofiber salt, the cation salt is substituted with a proton by contacting with a cation exchange resin. Since a cation exchange resin is used, unnecessary by-products such as sodium chloride are not generated.

In the anion-modified cellulose nanofiber salt, the aqueous dispersion obtained in the defibration step can be subjected as it is to the desalting step. In addition, water can be added to lower the concentration as needed.

As a cation exchange resin, as long as a counter ion is H ^<+> , both strongly acidic ion exchange resin and weak acid ion exchange resin can be used. Among them, it is preferable to use a strongly acidic ion exchange resin. As a strongly acidic ion exchange resin and weakly acidic ion exchange resin, what introduce | transduced the sulfonic acid group or the carboxy group into styrene resin or acrylic resin is mentioned, for example.
The shape of the cation exchange resin is not particularly limited, and various shapes such as fine particles (particulates), membranes, fibers and the like can be used. Among them, particulate is preferable from the viewpoint of efficiently treating the anion-modified cellulose nanofiber salt and facilitating separation after the treatment. A commercial item can be used as such a cation exchange resin. Commercially available products include, for example, Amberjet 1020, 1024, 1060, 1220 (above, manufactured by Organo Corporation), Amberlite IR-200C, IR-120B (above, manufactured by Tokyo Organic Chemical Co., Ltd.), Levachit SP 112 S100 (above, manufactured by Bayer), GEL CK08P (manufactured by Mitsubishi Chemical), Dowex 50W-X8 (manufactured by Dow Chemical), and the like.

For contacting the anion-modified cellulose nanofiber salt with the cation exchange resin, for example, a particulate cation exchange resin and an aqueous dispersion of the anion-modified cellulose nanofiber salt are mixed, and the anion modification is performed while stirring and shaking as necessary. It can carry out by contacting a cellulose nanofiber salt and a cation exchange resin for a fixed time.

The concentration of the aqueous dispersion and the ratio to the cation exchange resin are not particularly limited, and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing proton substitution. As an example, the concentration of the aqueous dispersion is preferably 0.05 to 10% by mass. If the concentration of the aqueous dispersion is less than 0.05% by mass, it may take too long for proton substitution. If the concentration of the aqueous dispersion is more than 10% by mass, the effect of sufficient proton substitution may not be obtained.
The contact time is also not particularly limited, and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing proton substitution. For example, it can be conducted in contact for 0.2 to 4 hours.

At this time, the desalting treatment can be carried out by contacting the anion-modified cellulose nanofiber salt with a suitable amount of cation exchange resin for a sufficient time.

(Process of sending liquid)
In the present invention, a step of pumping a mixture containing anion-modified cellulose nanofibers and a cation exchange resin is provided between the desalting step and the recovery step described later.

As a pump for feeding a mixture containing anion-modified cellulose nanofibers and a cation exchange resin to a filtration device or the like used in a recovery step, any pump capable of feeding high viscosity cellulose nanofibers can be used. Although it does not matter, it is preferable to use one which does not damage the ion exchange resin as much as possible by shearing by a pump.

Pumps are mainly divided into turbo type (non-positive displacement) pumps and positive displacement pumps. Turbo-type pumps include centrifugal pumps such as spiral pumps, diffuser pumps, and vortex pumps, mixed flow pumps, and axial flow pumps. The positive displacement pump corresponds to a reciprocating pump such as a piston pump, a plunger pump, or a diaphragm pump, or a rotary pump such as a gear pump, a vane pump, or a screw pump. Among these, it is more preferable to use a positive displacement screw pump or a positive displacement reciprocating pump. This type of pump has lower shear force applied to the fluid as compared with a turbo type (non-positive displacement) pump that imparts kinetic energy to the fluid by rotating the impeller at high speed in the casing, and the rotor and stator It is characterized by the fact that it is possible to feed a fluid with a relatively high viscosity and a relatively high viscosity, since there is very little leakage between them.

As a positive displacement screw pump, a positive displacement uniaxial eccentric screw pump (mono pump), a positive displacement twin screw pump, etc. can be exemplified, and it is preferable to use a mono pump. In the mono pump, a metal rotor having a single-threaded structure rotates a space formed between the rotor and the stator continuously by transferring the fluid by rotating in a stator cut with a double-threaded structure. It is a pump. A positive displacement twin screw pump is a pump that transfers fluid confined in a space formed by two screws and a casing in the axial direction of the screw by the rotation of the screw.

More preferably, a positive displacement diaphragm pump (membrane pump) is used as the positive displacement reciprocating pump. The diaphragm pump is composed of a diaphragm and a valve, and is a pump that reciprocates the diaphragm to change its volume, and performs suction and discharge to transfer fluid. The diaphragm pump is superior to the foreign matter in terms of the seal system and the valve system. Since the sliding portion of the positive displacement screw pump is in liquid contact, resin is easily bite in, and since there is usually no check valve, when the sliding portion is exhausted, pressure does not build up. It is difficult for resin to bite into sliding parts of plunger pumps, piston pumps and diaphragm pumps that are positive displacement reciprocating pumps, and foreign substances such as resin bite into sliding parts because sliding parts do not come into contact particularly with diaphragm pumps. In addition, even if the resin is caught in the check valve and the blockage occurs temporarily, the blockage is removed by the discharge from the next time onward, which is more advantageous.

(Recovery process)
In the recovery step of the present invention, a cation exchange resin is recovered from a mixture containing anion-modified cellulose nanofibers and a cation exchange resin. Since a cation exchange resin is used in the above desalting step, unnecessary by-products such as sodium chloride are not generated. Therefore, after acid treatment using a cation exchange resin, the water of the anion-modified cellulose nanofibers as a filtrate is recovered by recovering the cation exchange resin from the mixture containing the anion-modified cellulose nanofibers and the cation exchange resin. A dispersion is obtained.

Although the collection | recovery method of a cation exchange resin is not limited, The method of filtering using a filtration apparatus is preferable. In addition, you may provide the process of performing precision filtration by auxiliary | assistant agent filtration etc. before or after a collection | recovery process.

The shape of the filter medium used in the filtration device is not limited, and any shape such as mesh or slit may be used. Moreover, as a filter medium, what opened the hole may be used. Further, the material of the filter medium is not limited, and any material such as resin, metal or ceramic can be used, but it is preferable to use a material having acid resistance.

The opening or slit width of the filter medium may be a size capable of capturing the cation exchange resin, preferably 500 μm or less, and more preferably 400 μm or less. If the opening is too large, the cation exchange resin will pass through the filter medium and the cation exchange resin can not be recovered. In addition, the minimum diameter of the opening or slit width of the filter medium depends on the amount of fibrous foreign matter contained in the cellulose nanofibers. That is, in the case where microfiltration of cellulose nanofibers in advance is carried out by auxiliary agent filtration or the like, 5 μm or more is preferable, and in the case where microfiltration is not performed in advance, 10 μm or more is preferable, and 50 μm or more is more preferable. If the mesh size is too small, clogging due to unbroken fibers occurs and the amount of filtration processing decreases.

Auxiliaries As filter aids used for filtration, either inorganic compounds or organic compounds may be used, but diatomaceous earth, silica, perlite, finely powdered cellulose, activated carbon etc. may be mentioned as commonly used aids. . Depending on the filtration conditions, the type of auxiliary can be adjusted.

As the filtration device, any device that can perform pressure filtration or vacuum filtration can be used regardless of its type, for example, Nutche type, candle type, leaf disc type, drum type, filter press type, belt filter type Etc. It is preferable to have a mechanism capable of recovering cellulose nanofibers in the filtration container after filtration. From the viewpoint of facilitating recovery and transport of the cellulose nanofibers and the cation exchange resin, it is preferable to use a candle type or leaf disc type filtration device.

Moreover, it is preferable to pressurize with air as needed and have a mechanism capable of taking out the cellulose nanofibers, since the recovery rate is improved. The pressure in the case of air pressurization is preferably 0.01 to 1.0 MPa, and more preferably 0.05 to 0.5 MPa. When the pressure is lower than the above lower limit, it is difficult to transport the high viscosity cellulose nanofibers, and when the pressure is higher than the above upper limit, it is necessary to improve the pressure resistance of the air tank and the filtration device. Not desirable.

The pressure in the case of pressure filtration is preferably 0.01 MPa or more and 5 MPa or less, and the pressure in the case of vacuum filtration is preferably 0.01 MPa or more and 0.1 MPa or less.

The filtration device has a mechanism for recovering the cation exchange resin after filtration. From the viewpoint of facilitating recovery of the cation exchange resin, the opening of the filtration device is preferably large. In order to recover the cation exchange resin, a mechanism for backwashing, a mechanism for scraping with a scraper, or a mechanism capable of tilting and inverting the filtration container may be provided to the filtration device. Moreover, you may provide the mechanism which conveys the collect | recovered cation exchange resin with a conveyor with respect to a filtration apparatus.

A target to be recovered as a filter with a metal mesh or the like is a cation exchange resin, and anion-modified cellulose nanofibers are difficult to be removed by the diameter of the metal mesh or the like, and almost all of them are contained in the filtrate. Therefore, it is considered that the decrease in yield is extremely reduced.

In addition, in the liquid transfer and pressure filtration of the mixture containing the anion-modified cellulose nanofibers and the cation exchange resin in the recovery step, select a method which does not damage the cation exchange resin as much as the liquid transfer step. It is preferable to use, for example, a positive displacement screw pump or a positive displacement reciprocating pump.

If necessary, washing of the cellulose nanofibers mixed in a trace amount to the recovered cation exchange resin, or acid treatment and drainage for regeneration of the recovered cation exchange resin may be performed. These steps may all be performed by one device or may be performed by a plurality of devices. When using a plurality of devices, different types of devices may be combined.

The method for carrying out the step of regenerating the cation exchange resin by acid treatment is not limited to the recovered cation exchange resin, and for example, 5 times the amount of 1 M hydrochloric acid is added to 1 kg of used resin and stirred, A method such as repeating washing four times with ion exchange water can be mentioned. The cation exchange resin that has undergone the recovery step and the regeneration step can be used repeatedly, so the cost can be reduced.

Hereinafter, the present invention will be described in detail by way of examples. The following examples are intended to illustrate the invention but not to limit it. In addition, unless otherwise indicated, the measuring method of physical-property value etc. is a measuring method described below.

(Method of measuring the amount of carboxyl group)
After preparing 60 mL of 0.5 mass% slurry (water dispersion liquid) of carboxylated cellulose, and adding 0.1 M hydrochloric acid aqueous solution to pH 2.5, 0.05 N sodium hydroxide aqueous solution is dropped and pH 11 The electrical conductivity was measured until it became. The amount of carboxyl groups was calculated from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid in which the change in electrical conductivity was gradual:
Carboxyl group [mmol / g carboxylated cellulose] = a [mL] × 0.05 / mass of carboxylated cellulose [g]

(Method for measuring the degree of carboxymethyl group substitution)
About 2.0 g of the sample was precisely weighed and placed in a 300 mL stoppered Erlenmeyer flask. Add 100 mL of methanol nitrate (a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1 liter of anhydrous methanol), shake for 3 hours, and carboxymethylate cellulose (hereinafter also referred to as “Na-CMC”) of carboxymethyl cellulose Hereinafter, it is also referred to as "H-CMC". The dried H-CMC was precisely weighed 1.5 to 2.0 g and placed in a 300 mL stoppered Erlenmeyer flask. The H-CMC was wetted with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added and shaken at room temperature for 3 hours. The excess NaOH was back titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator, and the degree of carboxymethyl group substitution was calculated using the following formula.
[{100 × F ′ − (0.1 N H ₂ SO ₄ (mL)) × F} / (absolute dry mass (g) of H-CMC)] × 0.1 = A carboxymethyl group substitution degree = 0 .162A / (1-0.058A)
A: Amount (mL) of 1N NaOH required to neutralize 1 g of H-CMC
F ': Factor of 0.1 N H ₂ SO ₄ F: Factor of 0.1 N NaOH

(Method of measuring viscosity of B type (mPa · s))
It was measured under the conditions of 20 ° C. and 60 rpm using a TV-10 type viscometer (Toki Sangyo Co., Ltd.).

Example 1
(Preparation of carboxylated cellulose)
Add 5 g (absolutely dried) bleached softwood unbeaten pulp (manufactured by Nippon Paper Industries Co., Ltd.) to 500 mL of an aqueous solution dissolving 78 mg (0.5 mmol) of TEMPO (manufactured by Sigma Aldrich) and 754 mg (7.4 mmol) of sodium bromide Stir until the pulp was uniformly dispersed. After 18 mL of a 2 M aqueous solution of sodium hypochlorite was added to the reaction system, the pH was adjusted to 10.3 with a 0.5 N aqueous solution of hydrochloric acid to initiate an oxidation reaction. During the reaction, the pH in the system decreased, so 0.5 N aqueous sodium hydroxide solution was successively added to maintain pH 10. After reacting for 2 hours, the reaction solution was filtered through a glass filter and thoroughly washed with water to obtain a carboxylated cellulose having a carboxyl group weight of 1.7 mmol / g.

(Disintegration process)
Next, the obtained carboxylated cellulose slurry is adjusted to 1% (w / v) with water, treated five times with an ultrahigh pressure homogenizer (20 ° C., 140 MPa), and a transparent gel carboxylated cellulose nanofiber salt Dispersion of 1% (w / v) was obtained.

(Desalting process)
A cation exchange resin ("Amberjet 1024" manufactured by Organo Corporation) was added to the obtained dispersion of carboxylated cellulose nanofiber salt, and the mixture was contacted by stirring at 20 ° C for 0.3 hours.

(Recovery process)
A 250 μm mesh wire mesh was attached as a filter medium to a stainless steel holder with a tank (KST-47, manufactured by Advantec, filtration area 12.5 cm ² ) to prepare a filtration device. The mixture of the carboxylated cellulose nanofiber dispersion and the cation exchange resin obtained in the above desalting step was filled in a pressure tank of a filtration apparatus, pressurized to 0.35 MPa using nitrogen gas, and filtered. Thirty minutes after the start of filtration, the filtration was terminated, and visual evaluation was performed to determine whether the cation exchange resin was not mixed in the filtrate. In the case where the cation exchange resin was not mixed in the filtrate, the ion exchange resin could be recovered, and the "recovery of ion exchange resin" column was set to "○". In addition, the amount of the obtained filtrate (filtration throughput) was confirmed. The results are shown in Table 1. In addition, a cellulose nanofiber may be called "CNF."

(Example 2)
A mixture of carboxylated cellulose nanofiber dispersion and cation exchange resin is obtained in the same manner as in Example 1 except that the type of cation exchange resin is changed to "Amberlite IR 124" manufactured by Organo Corporation, followed by filtration, and I made an evaluation. The results are shown in Table 1.

(Example 3)
A mixture of a carboxylated cellulose nanofiber dispersion and a cation exchange resin was obtained in the same manner as in Example 1 except that a wire mesh with an aperture of 400 μm was used as a filter medium, and filtration and evaluation were performed. The results are shown in Table 1.

(Example 4)
A mixture of a carboxylated cellulose nanofiber dispersion and a cation exchange resin was obtained in the same manner as in Example 1 except that a metal mesh with an opening of 100 μm was used as a filter medium, and filtration and evaluation were performed. The results are shown in Table 1.

(Example 5)
A mixture of a carboxylated cellulose nanofiber dispersion and a cation exchange resin was obtained in the same manner as in Example 1 except that a nylon mesh with an aperture of 250 μm was used as a filter medium, and filtration and evaluation were performed. The results are shown in Table 1.

(Example 6)
A metal slit filter (slit width: 50 μm) was attached as a filter medium to a candle type filter (manufactured by Shibata, filtration area 0.097 m ² ) to prepare a filtration device. A mixture of carboxylated cellulose nanofiber dispersion and cation exchange resin was obtained in the same manner as in Example 1 except that this filtration apparatus was used, and filtration and evaluation were performed. The results are shown in Table 1.

(Example 7)
A stainless steel holder with a tank (KST-47, manufactured by Advantec, filtration area 12.5 cm ² ) was diluted with pure water by diluting diatomaceous earth (manufactured by Showa Chemical Industry Co., Ltd., Radiolite 3000, particle diameter 74.9 μm) as a filter aid. The solution was precoated and layered with diatomaceous earth. Thereafter, using the dispersion liquid of carboxylated cellulose nanofiber salt before the desalting step of Example 1, the first-stage filtration treatment was performed. The obtained filtrate was desalted in the same manner as in Example 1 to obtain a mixture of a carboxylated cellulose nanofiber dispersion and a cation exchange resin. The second stage filtration was performed using this mixture. In the second stage of filtration, a metal filter with an aperture of 5 μm was attached as a filter medium, and a filtration device was prepared. The mixture was filtered and evaluated in the same manner as in Example 1 except that this filter medium was used. The results are shown in Table 1.

(Comparative example 1)
A mixture of a carboxylated cellulose nanofiber dispersion and a cation exchange resin was obtained in the same manner as in Example 1 except that a metal filter with an aperture of 5 μm was used as a filter medium, and filtration and evaluation were performed. The results are shown in Table 1.

(Comparative example 2)
A mixture of a carboxylated cellulose nanofiber dispersion and a cation exchange resin was obtained in the same manner as in Example 1 except that a PET filter cloth having an air permeability of 12 was used as a filter medium, and filtration and evaluation were performed. The results are shown in Table 1.

As can be seen from Table 1, desalting treatment is carried out using anion-modified cellulose nanofiber salt and cation exchange resin to obtain a mixture containing anion-modified cellulose nanofibers and cation exchange resin, and the resulting mixture is filtered. The cation exchange resin could be recovered by filtration using an apparatus. Moreover, the cation exchange resin was not mixed in the obtained filtrate containing cellulose nanofibers.

Comparative Examples 1 and 2 had small openings of the filter medium and could not obtain good filtration throughput due to clogging, while Examples 1 to 6 were filter media having a large opening or slit width. There was almost no clogging due to unbroken fiber etc. contained. Moreover, in Example 7, by removing in advance unbroken fibers and the like contained in CNF, a good amount of filtration was obtained without clogging.

(Example 8)
A 250 μm-open nylon mesh was attached to the tip of the outlet hose of a mono pump (pump for liquid delivery) with a hopper attached. Into the hopper was charged a mixture of a dispersion and a cation exchange resin obtained in the same manner as in Example 1. Thereafter, the solution was pumped and pressurized filtration was carried out for 30 minutes to filter out the cation exchange resin and the cellulose nanofibers. The pressure at the start of filtration was 0.1 MPa, and the pressure at the end of filtration was 0.3 MPa. Further, the B-type viscosity of a 1% dispersion of the obtained carboxylated cellulose nanofibers was 2500 mPa · s (60 rpm, 20 ° C.).
When the obtained dispersion liquid of cellulose nanofibers was observed with a microscope, mixing of resin fragments was not observed.

(Example 9)
(Preparation of carboxymethylated cellulose)
A dry mass of 250 g of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) was placed in a reactor capable of stirring the pulp, and 112 g of a 50 mass% aqueous solution of sodium hydroxide and 67 g of water were added while stirring. The mixture was stirred at 30 ° C. for 45 minutes and mercerized, and then 364 g of 35% by mass aqueous sodium monochloroacetate solution was added while stirring. The mixture was stirred at 30 ° C. for 60 minutes, heated to 70 ° C. over 30 minutes, and reacted at 70 ° C. for 1 hour. Thereafter, the reaction product was taken out to obtain a carboxymethylated pulp having a degree of carboxymethyl substitution of 0.27 per glucose unit (hereinafter also referred to as "carboxymethylated cellulose").

(Disintegration process)
The carboxymethylated cellulose was adjusted to 1% (w / v) with water, and treated three times with an ultrahigh pressure homogenizer (20 ° C., 140 Mpa) to obtain a dispersion of carboxymethylated cellulose nanofiber salt.

(Desalting process)
A cation exchange resin ("Amberjet 1024" manufactured by Organo Corporation) was added to the obtained dispersion of carboxymethyl cellulose nanofiber salt, and the mixture was brought into contact with stirring at 20 ° C for 0.3 hours.

A 250 μm-open nylon mesh was attached to the tip of the outlet hose of a mono pump (pump for liquid delivery) with a hopper attached. Into the hopper was charged the mixture of the above-obtained carboxymethyl cellulose nanofiber dispersion and cation exchange resin. Thereafter, the solution was pumped and pressurized filtration was carried out for 30 minutes to filter out the cation exchange resin and the cellulose nanofibers. The pressure at the start of filtration was 0.1 MPa, and the pressure at the end of filtration was 0.3 MPa. In addition, the B-type viscosity of a 1% dispersion of the obtained carboxymethyl cellulose nanofibers was 3500 mPa · s (60 rpm, 20 ° C.).
When the obtained dispersion liquid of cellulose nanofibers was observed with a microscope, mixing of resin fragments was not observed.

(Example 10)
A mixture of a cellulose nanofiber dispersion and a cation exchange resin was charged in the same manner as in Example 8 except that the pump of Example 8 was changed to a diaphragm pump, and then it was pumped and pressurized filtration was performed for 30 minutes. The cation exchange resin and cellulose nanofibers were separated by filtration. The pressure at the start of filtration was 0.1 MPa, and the pressure at the end of filtration was 0.3 MPa. The B-type viscosity of a 1% dispersion of the obtained carboxylated cellulose nanofibers was 2600 mPa · s (60 rpm, 20 ° C.).
When the obtained dispersion liquid of cellulose nanofibers was observed with a microscope, mixing of resin fragments was not observed.

(Comparative example 3)
A cation exchange resin and cellulose nanofibers were filtered in the same manner as in Example 10 except that a vortex pump was used as a pump for liquid transfer. The pressure at the start of filtration was 0.1 MPa, and the pressure at the end of filtration was 0.3 MPa. Further, the B-type viscosity of a 1% dispersion of the obtained carboxylated cellulose nanofibers was 2500 mPa · s (60 rpm, 20 ° C.).
The dispersion of the obtained cellulose nanofibers was observed with a microscope, and resin fragments were detected.

(Comparative example 4)
A cation exchange resin and cellulose nanofibers were filtered in the same manner as in Example 11 except that a vortex pump was used as a pump for liquid transfer. The pressure at the start of filtration was 0.1 MPa, and the pressure at the end of filtration was 0.3 MPa. In addition, the B-type viscosity of a 1% dispersion of the obtained carboxymethyl cellulose nanofibers was 3500 mPa · s (60 rpm, 20 ° C.).
The dispersion of the obtained cellulose nanofibers was observed with a microscope, and resin fragments were detected.

As can be seen from Table 2, when a mixture of a cation exchange resin and a cellulose nanofiber dispersion is sent using a mono pump, which is a positive displacement uniaxial eccentric screw pump, and a positive displacement diaphragm pump, which is a positive displacement reciprocating pump, No contamination of cation exchange resin fragments was observed in the filtrate. On the other hand, when the solution was sent using a vortex pump and filtered, fragments of cation exchange resin were detected in the filtrate.

When a mixture containing anion-modified cellulose nanofibers and a cation exchange resin is sent to a recovery step for recovering a cation exchange resin, the positive ion is used to feed the solution using a uniaxial eccentric screw pump or a positive displacement diaphragm pump. It has been found that anion-modified cellulose nanofibers can be obtained without the inclusion of fragments of exchange resin.

Claims (12)

1. Preparing the anion-modified cellulose;
   A fibrillation step of fibrillating the anion-modified cellulose obtained in the preparation step to obtain an anion-modified cellulose nanofiber salt,
   A desalting process to obtain anion-modified cellulose nanofibers by desalting the anion-modified cellulose nanofiber salt obtained in the fibrillation step by performing a cation exchange reaction using a cation exchange resin When,
   A method for producing anion-modified cellulose nanofibers, comprising a recovery step of recovering the cation exchange resin from a mixture containing the anion-modified cellulose nanofibers obtained in the desalting step and the cation exchange resin.
2. The method for producing anion-modified cellulose nanofibers according to claim 1, wherein pressure filtration at 0.01 MPa or more and 5 MPa or less or vacuum filtration at 0.01 MPa or more and 0.1 MPa or less is performed in the recovery step.
3. The method for producing anion-modified cellulose nanofibers according to claim 1 or 2, wherein, in the recovery step, a mesh-shaped mesh having an opening of 5 μm to 400 μm or a slit-shaped filter medium having a slit width of 5 μm to 400 μm is used.
4. The method for producing anion-modified cellulose nanofibers according to any one of claims 1 to 3, further comprising a microfiltration step before or after the recovery step.
5. The method for producing anion-modified cellulose nanofibers according to any one of claims 1 to 4, wherein a regeneration step of a cation exchange resin by acid treatment is carried out on the cation exchange resin recovered in the recovery step. .
6. The liquid transfer and pressure filtration of the mixture in the recovery step, or the liquid transfer between the desalting step and the recovery step includes a step of using a positive displacement screw pump. The manufacturing method of the anion modified cellulose nanofiber as described in 4.
7. The method for producing anion-modified cellulose nanofibers according to claim 6, wherein the positive displacement screw pump is a positive displacement uniaxial eccentric screw pump or a positive displacement twin screw pump.
8. The method according to any one of claims 1 to 5, including the step of using a positive displacement reciprocating pump for liquid feeding and pressure filtration of the mixture in the recovery step, or for liquid feeding between the desalting step and the recovery step. The manufacturing method of the anion modified cellulose nanofiber as described in claim.
9. The method for producing anion-modified cellulose nanofibers according to claim 8, wherein the positive displacement reciprocating pump is a positive displacement diaphragm pump.
10. The preparation step includes the step of oxidizing the cellulosic raw material with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, and a mixture thereof, The method for producing anion-modified cellulose nanofibers according to any one of claims 1 to 9, wherein the anion-modified cellulose obtained by the step is a cellulose in which a carboxyl group is introduced.
11. The preparation step includes the step of mercerizing the cellulose-based raw material with a mercerizing agent and then reacting with a carboxymethylating agent, and the anion-modified cellulose obtained by the preparation step has a carboxymethyl group introduced into the cellulose. The method for producing anion-modified cellulose nanofibers according to any one of claims 1 to 9, wherein
12. 10. The method according to claim 1, wherein the preparation step includes the step of adding a phosphoric acid compound to a cellulose-based material, and the anion-modified cellulose obtained by the preparation step is a cellulose wherein a phosphate group is introduced into the cellulose. The manufacturing method of the anion modified cellulose nanofiber as described in any one.