JP2009242590A - Method for producing oxidized cellulose - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently recovering a catalyst containing an N-oxyl compound used for oxidizing cellulose fibers to obtain oxidized cellulose, and economically producing oxidized cellulose by reusing the recovered catalyst.
SOLUTION: A step of obtaining an aqueous dispersion of oxidized cellulose by oxidizing cellulose fibers in the presence of a catalyst containing an N-oxyl compound, and an aqueous dispersion of the obtained oxidized cellulose, or an aqueous dispersion of the oxidized cellulose A method for producing oxidized cellulose comprising a step of adding an organic solvent, an adsorbent or an ion exchange resin to a reaction solution containing a catalyst after separating oxidized cellulose from the solution, and recovering the catalyst or an aqueous solution containing the catalyst.
[Selection figure] None

Description

  The present invention relates to a method for producing oxidized cellulose.

  In industrial products, structural materials, cosmetics, foods, gas barrier materials, etc., it has been studied to produce cellulose whose surface has been modified in order to impart functionality.

  Patent Documents 1 to 3 and Non-Patent Document 1 describe a method of oxidizing a cellulose fiber using an N-oxyl compound as a catalyst and introducing a carboxyl group or an aldehyde group into cellulose. However, none of the documents describes a method for recovering the catalyst and reusing it to produce oxidized cellulose.

Patent Documents 4 to 8 describe a method in which cellulose is oxidized in the presence of a nitroxide and a carboxyl group is introduced into the cellulose. These references may regenerate or recycle (reuse) 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), which is used as an example of nitroxides, from aqueous systems However, there is no specific description of the regeneration method and the recirculation method, and no experiments for actual regeneration or reuse have been conducted.
JP 2008-1728 A JP 2001-49591 A JP 2003-183302 A Bio MACROMOLECULES Volume7, Number6, June 2006, Published by the American Chemical Society JP 2003-73402 A JP 2003-89701 A JP 2003-54349 A JP 2005-68630 A JP-A-2005-97818

  In the oxidation reaction of cellulose fiber using N-oxyl compound such as TEMPO as a catalyst, when the second reaction is performed by recirculating the liquid after the reaction, together with the N-oxyl compound, salts and low molecular weight uronic acid, etc. By-products are mixed into the second reaction. Furthermore, even if the N-oxyl compound is regenerated by simply removing water, such as evaporation, by-products are mixed into the regenerated product, and an N-oxyl compound with extremely low purity can be obtained. When the second reaction is performed using an N-oxyl compound containing a by-product, the amount of the by-product mixed into the product increases, and stable production cannot be performed. Since the amount of by-products increases with the number of reactions, the oxidized cellulose cannot be continuously produced under stable conditions.

  Accordingly, an object of the present invention is to efficiently recover a catalyst containing an N-oxyl compound used when oxidizing cellulose fibers to obtain oxidized cellulose, and economically producing oxidized cellulose by reusing the recovered catalyst. It is to provide a way to do.

  In response to such problems, the present inventors can recover a catalyst having a higher purity by using an organic solvent, an adsorbent or an ion exchange resin, and can efficiently produce oxidized cellulose by reusing the recovered catalyst. The present invention has been completed.

  That is, this invention provides the manufacturing method of an oxidized cellulose including the oxidation treatment process of the following cellulose fiber, and the collection | recovery process of a catalyst.

<Oxidation treatment process of cellulose fiber>
Step of oxidizing cellulose fibers in the presence of a catalyst containing an N-oxyl compound to obtain an aqueous dispersion of oxidized cellulose <Catalyst recovery step>
A process of performing at least one treatment selected from the following treatments a to c on the aqueous dispersion of oxidized cellulose obtained in the oxidation treatment step: an aqueous dispersion of oxidized cellulose, or an aqueous dispersion of this oxidized cellulose An organic solvent is added to the reaction liquid containing the catalyst after separating the oxidized cellulose from the liquid, the catalyst is extracted, the organic solvent is removed from the organic solvent in which the obtained catalyst is dissolved, and a catalyst or an aqueous solution containing the catalyst is obtained. Step b for recovery: An adsorbent is adsorbed by adding an adsorbent to an aqueous dispersion of oxidized cellulose or a reaction liquid containing the catalyst after separating the oxidized cellulose from the aqueous dispersion of oxidized cellulose, and the adsorbent Step c for recovering the catalyst or the solution containing the catalyst from: c: aqueous dispersion of oxidized cellulose, or contact after separating oxidized cellulose from the aqueous dispersion of oxidized cellulose To the reaction solution containing the by-products were removed by addition of ion-exchange resin, and recovering the aqueous solution containing the catalyst or catalyst process

  By the method of the present invention, it is possible to recover a highly pure catalyst, and by reusing the catalyst, it is possible to reduce the amount of catalyst required for the production of oxidized cellulose and to suppress the increase of by-products. The oxidized cellulose can be produced under stable conditions.

  Hereinafter, the manufacturing method of the oxidized cellulose of this invention is demonstrated for every process.

<Oxidation treatment process of cellulose fiber>
The oxidation treatment step of cellulose fiber in the present invention is a step of obtaining an aqueous dispersion of oxidized cellulose by oxidizing cellulose fiber in the presence of a catalyst containing an N-oxyl compound.

  In this step, the cellulose fiber before the oxidation treatment is about 10-1000 times (mass basis) water added to the raw natural cellulose fiber (absolute dry basis) and pre-treated with a mixer or the like. It is preferable to carry out and slurry.

  As natural cellulose fiber used as a raw material, for example, wood pulp, non-wood pulp, cotton, regenerated cellulose, bacterial cellulose and the like can be used.

  Next, the slurryed cellulose fibers are oxidized in the presence of a catalyst containing an N-oxyl compound to obtain an aqueous dispersion of oxidized cellulose.

  As an N-oxyl compound used for this invention, the compound described in patent document 2, ie, the compound represented by following formula (1), is mentioned.

(In the formula, ring A represents a ring composed of a non-aromatic 5- or 6-membered ring which may have another hetero atom together with the nitrogen atom constituting the ring.)
Examples of N-oxyl compounds include 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), 4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N—. Oxyl is preferred.

  The amount of the N-oxyl compound used is preferably 0.1 to 10% by mass, more preferably 0.2 to 8% by mass, and still more preferably 0.4 to 5% by mass with respect to the raw material cellulose fiber (absolute dry basis). If it is 0.1% by mass or more, the oxidation reaction proceeds smoothly, and if it is 10% by mass or less, the removal burden in the subsequent process is reduced.

Examples of the oxidizing agent used in the oxidation treatment step of the present invention include halogens such as chlorine, bromine and iodine; hypochlorous acid, sodium hypochlorite, potassium hypochlorite, lithium hypochlorite and hypobromine. Hypohalous acid such as acid and hypoiodous acid or salts thereof; Chlorous acid, sodium chlorite, potassium chlorite, lithium chlorite, bromite, iodic acid, or salts thereof Perhalogen acids such as perchloric acid, perbromic acid and periodic acid or salts thereof; halogen oxides such as ClO, ClO ₂ , Cl ₂ O ₆ , BrO ₂ , Br ₃ O ₇ , NO, NO ₂ , N Nitrogen oxides such as ₂ O ₃ ; hydrogen peroxide; perorganic acids such as peracetic acid. These oxidizing agents can be used alone or in combination of two or more. Among these oxidizing agents, at least one selected from the group consisting of hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, and a perorganic acid is preferable. Chlorous acid or a salt thereof is more preferable, and sodium hypochlorite is still more preferable.

  The amount of the oxidizing agent used is preferably 0.1 to 10 mmol, more preferably 1 to 7 mmol, still more preferably 1.4 to 5 mmol, and still more preferably 1.7 to 4.5 mmol, with respect to 1 g of the raw material cellulose fiber (absolute dry basis). If it is 0.1 mmol or more, the oxidation reaction proceeds smoothly, and if it is 10 mmol or less, the removal burden in the subsequent process is reduced.

  In the oxidation treatment step of the present invention, it is preferable to coexist bromide or iodide together with the oxidizing agent.

  Examples of the bromide or iodide include ammonium salts such as ammonium bromide and ammonium iodide, and alkali metal bromides such as lithium bromide, potassium bromide, sodium bromide, lithium iodide, potassium iodide, and sodium iodide. Alternatively, alkali metal iodide, calcium bromide, magnesium bromide, strontium bromide, calcium iodide, magnesium iodide, alkaline earth metal bromide such as strontium iodide, or alkaline earth metal iodide can be exemplified. These bromides and iodides can be used alone or in combination of two or more. Of these, sodium bromide is preferred.

  The amount of bromide or iodide used is preferably 0.1 to 10 mmol, more preferably 0.5 to 7 mmol, and still more preferably 0.7 to 5 mmol with respect to 1 g of the raw material cellulose fiber (absolute dry basis). If it is 0.1 mmol or more, the oxidation reaction proceeds smoothly, and if it is 10 mmol or less, the removal burden in the subsequent process is reduced.

  The pH in the oxidation treatment of the present invention is preferably in the range of 9 to 12, more preferably 9.5 to 11.5, from the viewpoint of allowing the oxidation reaction to proceed efficiently.

  The temperature (temperature of the slurry) in the oxidation treatment of the present invention is preferably 1 to 50 ° C., and the time is preferably 1 to 300 minutes.

  In the oxidation treatment step of the present invention, after the cellulose fiber is oxidized, an aqueous dispersion of oxidized cellulose containing a catalyst, an unreacted oxidant, a by-product and the like is obtained.

<Catalyst recovery process>
The catalyst recovery step in the present invention is a step of performing at least one treatment selected from the treatments a to c on the aqueous dispersion of oxidized cellulose obtained in the cellulose fiber oxidation treatment step.

  In the treatments a to c, an organic solvent, an adsorbent, or an ion exchange resin is added to an aqueous dispersion of oxidized cellulose or a reaction liquid containing a catalyst after separating the oxidized cellulose from the aqueous dispersion of oxidized cellulose. However, it is preferable to add these to the reaction liquid containing the catalyst after separating the oxidized cellulose from the aqueous dispersion of oxidized cellulose.

  Examples of a method for separating oxidized cellulose from an aqueous dispersion of oxidized cellulose include a method of separating oxidized cellulose using a device having a sieve or a network structure, a method of separating oxidized cellulose by gravity or centrifugal force, and the like. It is done.

  In order to obtain higher-purity oxidized cellulose from the separated oxidized cellulose, it is preferable to perform a known purification method such as water washing or centrifugal dehydration. Moreover, you may perform a drying process as needed.

  The obtained oxidized cellulose has a structure in which the hydroxyl group at the C6 position of the cellulose structural unit is selectively oxidized to a carboxyl group. The carboxyl group content of oxidized cellulose is preferably 0.1 to 2.0 mmol / g, more preferably 0.4 to 2 mmol / g, still more preferably 0.5 to 1.7 mmol / g, and even more preferably 0.6 to 1.7 mmol / g. The carboxyl group content of oxidized cellulose is determined by the measurement method described in the examples.

  In the treatment a, the organic solvent to be used is not particularly limited as long as it is an organic solvent that dissolves the by-product and dissolves the catalyst. Specific examples of organic solvents include, for example, alcohol solvents such as ethanol, methanol, and propanol; ketone solvents such as acetone; amylbenzene, ethylbenzene, octane, gasoline, xylene, cyclohexane, cyclopentane, dimethylnaphthalene, camphor oil, styrene, Hydrocarbon solvents such as petroleum ether, petroleum benzine, solvent naphtha, decalin, decane, tetralin, turpentine, toluene, naphthalene, nonane, pinene, hexane, heptane, benzene, pentane, mesitylene, ligroin, liquid paraffin; isopropyl chloride, Halogenated hydrocarbon solvents such as naphthalene chloride, butyl chloride, methylene chloride, chloroform, carbon tetrachloride, chlorobenzene, ethyl bromide; supercritical carbon dioxide, supercritical plasma hydrocarbons, supercritical inorganic gases, Supercritical fluid such as supercritical alcohol (subcritical fluid including) and the like. A plurality of these organic solvents may be used, and an entrainer such as ethanol may be added to the supercritical fluid.

  Among these organic solvents, in order to reduce the load of the separation process of the organic solvent in which the catalyst is dissolved, it is preferably a low polarity or nonpolar organic solvent that is phase-separated from water, and a hydrocarbon solvent is more preferable. An aliphatic hydrocarbon solvent is more preferable.

  The amount of the organic solvent to be used is not particularly limited as long as it is an amount capable of sufficiently dissolving the used catalyst. The required amount of organic solvent can be determined by determining the distribution ratio of the catalyst to water and the organic solvent to be used. The distribution ratio can be obtained by, for example, using the method described in the examples of the catalyst concentration in water and the organic solvent.

  In the process a, an organic solvent is added to extract the catalyst, and then the organic solvent in which the catalyst is dissolved is separated from water containing by-products. Separation can be performed by an extractor such as a separatory funnel or a Soxhlet extractor when an organic solvent that is phase-separated from water is used. When an organic solvent that is difficult to phase separate from water is used, the separation can be performed by centrifugation.

  The above extraction operation may be repeated. As an apparatus for performing extraction and separation, for example, a spray tower, a packed tower, a baffle tower, a perforated plate extraction tower, an orifice tower, a non-powered extraction apparatus such as a flow mixer, a mixer-settler extraction apparatus, a shovel tower, a rotating disk extraction Pulsating / vibrating such as tower, Oldshoe-Rushton tower (Mixco tower), ARD tower (Leuwa extractor), stirring extraction device such as Kunii tower, pulsating packed tower, pulsating perforated plate tower, vibrating plate tower (Curl tower) Centrifugal extraction devices such as an extractor, a podvirniak extractor, and a Lewesta extractor, and a supercritical extractor.

  Next, the organic solvent is removed from the organic solvent in which the catalyst is dissolved to obtain a single catalyst or an aqueous catalyst solution. The catalyst can be recovered by evaporating, lowering the temperature, or reducing the pressure of the organic solvent until the catalyst concentration is equal to or lower than the solubility of the catalyst to precipitate the catalyst, and separating the precipitated catalyst and the organic solvent. The catalyst alone may be obtained by completely evaporating the organic solvent.

  Alternatively, an aqueous catalyst solution may be obtained by newly adding water to an organic solvent in which the catalyst is dissolved and distilling the organic solvent. Examples of the distillation method include simple distillation, continuous multistage distillation, and continuous distillation using a packed column. An entrainer may be added and distilled.

  In the treatment b, the adsorbent to be used is not particularly limited as long as it does not adsorb oxidized cellulose and adsorbs the catalyst, but from the viewpoint of the adsorptivity of the N-oxyl compound, it has strong hydrophobic adsorption. Agents are preferred.

  Specific examples of adsorbents include carbon such as activated carbon, silica, zeolite, alumina, other metals, inorganic adsorbents such as oxides, styrene-divinylbenzene, Br introduced styrene-divinylbenzene, acrylic, and methacrylic acid esters. And organic adsorbents such as C18 group-introduced aliphatic type. A plurality of these adsorbents may be used.

  The form of the adsorbent is not particularly limited, and examples thereof include granular shapes and plate shapes. In the case of a granular form, the particle diameter is not particularly limited, but is preferably 0.01 to 50000 μm, and more preferably 0.1 to 20000 μm. From the viewpoint of increasing the adsorption interface, the adsorbent is preferably porous particles. The average pore size of the porous particles is not particularly limited, but is preferably 1/10 or less of the particle size, more preferably 1/100 or less.

  The amount of the adsorbent used is not particularly limited as long as it is an amount that sufficiently adsorbs the used catalyst. The amount of catalyst adsorbed can be determined by measuring the catalyst concentration in the liquid before and after contact with the adsorbent, for example, using the method described in the Examples.

  Examples of the method for adsorbing the catalyst on the adsorbent include methods such as fixed bed adsorption, simulated moving bed adsorption, moving bed adsorption, fluidized bed adsorption, and stirring bed adsorption. When the stirring layer adsorption is performed, the adsorbent on which the catalyst is adsorbed can be separated by a method such as a filter, a sieve, gravity, or centrifugal force. The above adsorption operation may be performed a plurality of times.

  As a method of recovering the catalyst from the adsorbent on which the catalyst is adsorbed, a heat recovery method in which the catalyst is desorbed from the adsorbent by raising the temperature, a reduced pressure recovery method in which the catalyst is desorbed from the adsorbent by reducing the pressure, an inert gas For example, a purge recovery method in which the catalyst is desorbed from the adsorbent and a substitution recovery method in which a solvent is added. Two or more of these recovery methods may be used.

  When the heat recovery method, the reduced pressure recovery method, or the purge recovery method is used, the catalyst can be recovered by desorbing the catalyst alone from the adsorbent. When the substitution recovery method is used, the catalyst is recovered from the solvent used (hereinafter referred to as eluent). The eluent is not particularly limited as long as it does not dissolve the adsorbent and dissolves the catalyst, and examples thereof include solvents such as water, phosphate buffer, citrate buffer, alcohols such as ethanol and methanol. Two or more of these solvents may be mixed and used. The solubility of the catalyst, that is, the concentration of the catalyst in the eluent can be confirmed, for example, by the method described in the examples. The eluent can be recovered by separating the adsorbent and eluent from the adsorbent and eluent mixture by a filter, sieve, gravity, or centrifugal force, or by elution from the adsorbent packed in a column. The liquid may be circulated and collected. Next, in order to recover the catalyst from the eluent in which the catalyst is dissolved, the catalyst is deposited by evaporating or lowering the temperature or reducing the pressure until the catalyst concentration is equal to or lower than the solubility of the catalyst, and the precipitated catalyst and the eluent are separated. Thus, the catalyst simple substance can be recovered. The catalyst may be obtained by completely evaporating the eluent.

  When an aqueous solution such as a phosphate buffer solution or a citrate buffer solution is used, the catalyst aqueous solution may be obtained by removing components other than the catalyst and water by the ion exchange resin shown in the treatment c. When alcohols are used, an aqueous catalyst solution may be obtained by newly adding water to the eluent and distilling the eluent. Examples of the distillation method include simple distillation, continuous multistage distillation, and continuous distillation using a packed column. An entrainer may be added and distilled.

In the process c, the ion exchange resin to be used is not particularly limited as long as it is an ion exchange resin that has a small amount of catalyst adsorption and a large amount of byproduct adsorption. Examples of such ion exchange resins include acidic cation exchange resins and basic anion exchange trees. The acidic cation exchange resins, such as styrene - SO ₃ in cross-linked polymers of divinylbenzene or the like ^- Na ^+, include resins obtained by introducing a functional group such as COOH. Examples of the basic anion exchange resin include N ⁺ (CH ₃ ) ₃ Cl ⁻ , N ⁺ (CH ₃ ) ₂ C ₂ H ₄ OHCl ⁻ , NH (C ₂ H ₄ NH ) Resins into which functional groups such as _n and N (CH ₃ ) ₂ have been introduced. Two or more of these ion exchange resins may be used.

  The average particle size of the ion exchange resin is not particularly limited, but is preferably 0.01 to 50000 μm, and more preferably 0.1 to 20000 μm. From the viewpoint of increasing the surface area, a porous body having pores having a particle size of 1/10 or less, preferably 1/100 or less of the particle size is desirable.

  As a method for adding an ion exchange resin to an aqueous dispersion or reaction solution, a batch method in which an ion exchange resin is added to an aqueous dispersion or reaction solution, a column method in which the aqueous dispersion or reaction solution is circulated by filling a column or the like. (Tower system). Examples of the column method include a fixed bed method, a moving bed method, and a continuous method using a multistage fluidized bed. When the batch method is used, the aqueous catalyst solution can be separated from the ion exchange resin by a method such as a filter, a sieve, gravity, or centrifugal force. The above adsorption operation may be performed a plurality of times.

  The obtained catalyst aqueous solution may be appropriately dried to obtain a catalyst aqueous solution having a desired concentration. The catalyst is precipitated by evaporating or lowering the temperature or reducing the pressure of the eluent until the catalyst concentration is lower than the solubility of the catalyst. A single unit may be collected and stored. The catalyst may be obtained by completely evaporating water.

  In the catalyst recovery step of the present invention, the treatments a to c can be applied individually or in combination of two or more. Moreover, in order to improve the recovery rate of the catalyst, the treatments a to c may be applied to the water used in the purification of the separated oxidized cellulose by washing with water.

  In the above-mentioned treatments a to c, in the case where an organic solvent, an adsorbent or an ion exchange resin is added to the aqueous dispersion of oxidized cellulose for treatment without separating the oxidized cellulose, the above catalyst recovery treatment is performed. After that, the oxidized cellulose is separated. Also at this time, the separated oxidized cellulose can be purified by the above purification method to obtain highly purified oxidized cellulose. In this case, it is preferable to use the method of the process a from the viewpoint of reducing the load for separating the oxidized cellulose from the liquid subjected to the catalyst recovery process.

  The catalyst recovered in the catalyst recovery step as described above or a solution containing the catalyst has a low by-product content and high purity. Therefore, it can be efficiently reused for the oxidation treatment of cellulose fibers.

  When the recovered catalyst or a solution containing the catalyst is reused, the recovered catalyst alone is dissolved in water, or the recovered catalyst aqueous solution is used, and the catalyst aqueous solution contains an oxidizing agent and a raw material cellulose fiber, Further, if necessary, bromide or iodide can be added, and cellulose fibers can be oxidized by the same method as in the oxidation treatment step. If necessary, a catalyst may be newly added to increase the catalyst concentration, or water may be added to dilute the catalyst.

  By performing the same catalyst recovery step as described above from the reaction solution obtained in this reuse step, the catalyst can be recovered again and reused. That is, the catalyst can be used repeatedly thereafter.

  In the following examples, the measurement methods used are as follows.

(1) Carboxyl group content of oxidized pulp (oxidized cellulose) (mmol / g)
The oxidized pulp was dried at room temperature with a vacuum dryer to obtain absolutely dry oxidized pulp. About 0.5 g of the absolutely dry oxidized pulp is put into a 100 ml beaker, and ion exchange water is added to make a total of 55 ml, and 5 ml of 0.01 M sodium chloride aqueous solution is added to make a 0.83 mass% oxidized pulp suspension. Stir with a stirrer until dispersed. Then, 0.1M hydrochloric acid is added to adjust the pH to 2.5 to 3.0, and then 0.05M sodium hydroxide aqueous solution is injected for 60 seconds with a waiting time using an automatic titrator (AUT-501, manufactured by Toa DK Corporation). Then, the electric conductivity and pH value of the oxidized pulp suspension every minute were measured, and the measurement was continued until the pH reached about pH11. And the sodium hydroxide titration amount was calculated | required from the obtained electrical conductivity curve, and carboxyl group content of the oxidized pulp was computed.

(2) TEMPO concentration (ppm)
TEMPO was dissolved in water to prepare a 500 ppm TEMPO aqueous solution. Further, the aqueous solution was diluted to prepare 250 ppm, 100 ppm, and 33 ppm TEMPO aqueous solutions. Measure the absorption spectrum of each aqueous solution in the range of 800nm to 200nm with a UV-visible spectrophotometer (UV-1700, manufactured by Shimadzu Corporation), and calculate a calibration curve from the absorption peak height (absorbance) of TEMPO present at 249nm. Obtained. A quartz cell with an optical path length of 1 mm was used for the measurement.

  TEMPO was dissolved in ethanol and hexane, respectively, and a calibration curve for the ethanol solution and a calibration curve for the hexane solution were obtained in the same manner as the method for preparing the calibration curve for water.

  It is obtained by measuring the absorption spectrum of the reaction solution and the recovered solution by the same method as used in the preparation of the above calibration curve, and measuring the presence or absence of the absorption peak at 249 nm and the absorption peak height (absorbance). The TEMPO concentration contained in each solution was determined from the calibration curve.

  In addition, since low molecular weight uronic acid as a by-product has an absorption at 220 nm or less, the presence or absence of uronic acid in the reaction solution and the recovered solution can be confirmed from the measurement of the spectrum.

(3) Solid content concentration (% by mass) and TEMPO purity (%)
In order to measure the solid content concentration in the reaction solution or the recovery solution, 1.5 g of the reaction solution or the recovery solution was weighed in a container with a precision balance. Next, the solvent was completely dried at 105 ° C. using a vacuum dryer to precipitate a by-product. When the solvent was water, 10 g of sodium sulfate which had been completely dried before drying was added and dried with sodium sulfate in a vacuum dryer (105 ° C.).

  The amount of increase in the weight of the entire container was measured with a precision balance, and this was defined as the solid content that is the sum of the by-product and the catalyst. In addition, the minimum solid content which can be quantified with a precision balance is 1 mg. The solid content concentration is calculated by dividing the solid content amount by the charged weight (1.5 g). The solid content concentration was measured three times from the same solution, and the average value was taken as the measured value.

  The TEMPO concentration in each solution before drying is obtained by the method shown in (2), and the TEMPO concentration in the solid content, that is, the TEMPO purity can be obtained by dividing the TEMPO concentration by the solid content concentration.

Example 1
(1) Oxidation treatment step of cellulose fiber As a cellulose fiber raw material, bleached kraft pulp of coniferous tree (manufacturer: Fletcher Challenge Canada, trade name “Machenzie”, CSF 650 ml) was used.

  First, 40 g of the bleached kraft pulp fiber of the above-mentioned conifer was sufficiently stirred with 3960 g of ion-exchanged water and defibrated to some extent. Thereafter, the amount of TEMPO (manufacturer: ALDRICH, free radical 98% by mass) becomes 3.71% by mass, sodium bromide (Wako Pure Chemical Industries, Ltd.) 3.6 mmol / g-pulp, hypoxia with respect to 40 g of pulp mass. Sodium chlorate (Wako Pure Chemical Industries, Ltd., Cl concentration 5 mass%) 1.88 mmol / g-pulp was added in this order. Then, it was dropped with 0.5M sodium hydroxide using a pH stud, the pH was maintained at 10.5 and the temperature was 25 ° C., and an oxidation reaction was performed for 60 minutes to obtain oxidized pulp. Further, the reaction solution and oxidized pulp were separated using a sieve having an opening of 90 μm.

  The separated oxidized pulp was sufficiently washed with ion-exchanged water and dehydrated. Further, the oxidized pulp was completely dried with a vacuum dryer, and the carboxyl group content was measured by the method described above, whereby it was 0.91 mmol / g-pulp.

  Next, the TEMPO concentration and the solid content concentration in the reaction solution were measured and found to be 327 ppm and 1.27%, respectively. That is, the TEMPO purity contained in the reaction solution was 2.57%. Further, the absorption spectrum of the reaction solution had a large absorption of 220 nm or less, and it was confirmed that uronic acid was present.

(2) Catalyst recovery step Add 300 g of n-hexane (purity 96% or more, manufactured by Wako Pure Chemical Industries, Ltd.) to 300 g of the reaction solution from which the oxidized pulp obtained in (1) was separated, and stir for 30 minutes. And TEMPO was extracted. After stirring, the mixed solution was allowed to stand, and water and hexane were separated into two phases to obtain a hexane phase.

  When the TEMPO concentration in the hexane phase was measured, it was 245 ppm, and almost no absorption derived from uronic acid at 220 nm or less was observed. The solid content in 1.5 g of hexane phase was below the limit of quantification (1 mg). That is, the solid content is 0.067% by mass or less, and the purity of TEMPO recovered with hexane is at least 36.8%.

  In addition, from the absorption spectrum on the water phase side after extraction, the absorption peak at 249 nm derived from TEMPO was not observed, and only the absorption derived from uronic acid at 220 nm or less was observed.

  70 g of ion-exchanged water was added to 280 g of the hexane phase, the temperature of the mixed solution was set to 70 ° C. using a water bath, and hexane was evaporated while stirring the mixed solution to obtain a TEMPO aqueous solution. The TEMPO concentration in the aqueous solution was 919 ppm, and almost no absorption derived from uronic acid at 220 nm or less was observed.

(3) Catalyst recycling step The same raw materials and reagents as those used in the oxidation treatment step (1) were used for the pulp raw materials and reagents shown below.

  First, 2.0 g of bleached kraft pulp fiber was sufficiently stirred with 148 g of ion-exchanged water and defibrated to some extent. Thereafter, 50 g of TEMPO aqueous solution (TEMPO concentration 919 ppm) obtained in the recovery step (2), sodium bromide 3.6 mmol / g-pulp, sodium hypochlorite (Cl concentration 5 mass%) with respect to 2.0 g of pulp mass 1.88 mmol / g-pulp was added in this order. Then, it was dropped with 0.5M sodium hydroxide using a pH stud, the pH was maintained at 10.5 and the temperature was 25 ° C., and an oxidation reaction was performed for 60 minutes to obtain oxidized pulp. The oxidized pulp was separated from the reaction liquid with a sieve having an opening of 90 μm.

  The separated oxidized pulp was sufficiently washed with ion-exchanged water and dehydrated. Further, the oxidized pulp was completely dried with a vacuum dryer, and the carboxyl group content was measured by the method described above. As a result, it was 0.95 mmol / g-pulp.

  Next, the TEMPO concentration and the solid content concentration in the reaction solution were measured and found to be 215 ppm and 1.10% by mass, respectively. That is, the TEMPO purity is 1.95%.

  That is, the oxidized cellulose obtained in the reuse step and the solid content concentration including the by-products in the reaction solution in the reuse step were similar to the value obtained in the oxidation treatment step (1).

Example 2
(1) Oxidation process of cellulose fiber The oxidation process of the cellulose fiber was performed like (1) of Example 1.

(2) Catalyst recovery step A synthetic adsorbent (HP20, manufactured by Mitsubishi Chemical Corporation) was sufficiently washed with ion-exchanged water to activate the surface of the adsorbent. The water content of the synthetic adsorbent containing water obtained after washing was measured with an infrared moisture meter (FD230, manufactured by Kett Science Laboratory Co., Ltd.) and found to be 72%.

  To 300 g of the reaction liquid from which the oxidized pulp obtained in (1) was separated, 105 g of the synthetic adsorbent (water content 72%) was added and sufficiently stirred. Thereafter, the synthetic adsorbent was separated from the reaction solution with a sieve having an opening of 90 μm. From the reaction solution after separating the synthetic adsorbent, the absorption peak at 249 nm derived from TEMPO was not observed, and only the absorption derived from uronic acid at 220 nm or less was observed.

  300 g of ethanol (purity 99.5% or more, manufactured by Kanto Chemical Co., Inc.) was added to 105 g of the separated synthetic adsorbent and stirred well. Thereafter, the liquid was allowed to stand to precipitate the synthetic adsorbent, and the supernatant ethanol solution was recovered. When the TEMPO concentration and the solid content concentration in the recovered ethanol solution were measured, they were 236 ppm and 0.127%, respectively. That is, the TEMPO purity contained in the reaction solution was 18.6%. Further, the absorption spectrum of the reaction solution was found to have a small absorption of 220 nm or less and a decrease in the amount of uronic acid.

Example 3
(1) Oxidation process of cellulose fiber The oxidation process of the cellulose fiber was performed like (1) of Example 1.

(2) Catalyst recovery process A mixed resin of acidic ion exchange resin and basic ion exchange resin (SNMUP, manufactured by Mitsubishi Chemical Corporation) was thoroughly washed with ion exchange water to activate the surface of the ion exchange resin. . When the water content of the ion exchange resin containing water obtained after washing was measured with an infrared moisture meter (FD230, manufactured by Kett Science Laboratory Co., Ltd.), it was 68%.

  To 300 g of the reaction liquid from which the oxidized pulp obtained in (1) was separated, 105 g of the ion exchange resin (68% water content) was added and sufficiently stirred. Thereafter, the liquid was allowed to stand to precipitate the ion exchange resin, and the supernatant liquid was recovered.

  When the TEMPO concentration in the supernatant was measured, it was 217 ppm, and the absorption derived from uronic acid of 220 nm or less was small. The solid content in 1.5 g of the supernatant was below the limit of quantification (1 mg). That is, the solid content is 0.067% by mass or less, and the purity of TEMPO recovered in the supernatant is at least 32.4%.

Comparative Example 1
Using the reaction solution obtained in the oxidation treatment step (1) of Example 1, the recycling step shown below was performed without performing the catalyst recovery step.
In the reuse process, the same raw materials and reagents as those used in (1) of Example 1 were used for the pulp raw materials and reagents.

  First, 3.0 g of bleached kraft pulp fiber was sufficiently stirred with 60 g of ion-exchanged water, and defibrated to some extent. Then, 237 g of the reaction liquid (TEMPO concentration 327 ppm), sodium bromide 3.6 mmol / g-pulp, sodium hypochlorite (Cl concentration 5 mass%) 1.88 mmol / g-pulp with respect to 2.0 g of pulp mass Were added in this order. Then, it was dropped with 0.5M sodium hydroxide using a pH stud, the pH was maintained at 10.5 and the temperature was 25 ° C., and an oxidation reaction was performed for 60 minutes to obtain oxidized pulp. The oxidized pulp was separated from the reaction liquid with a sieve having an opening of 90 μm.

  The separated oxidized pulp was sufficiently washed with ion-exchanged water and dehydrated. Further, the oxidized pulp was completely dried with a vacuum dryer, and the carboxyl group content was measured by the method described above, and it was 0.86 mmol / g-pulp.

  Next, the TEMPO concentration and solid content concentration in the reaction solution were measured and found to be 258 ppm and 2.15%, respectively. That is, the purity of TEMPO contained in the reaction solution was 1.20%. Further, the absorption spectrum of the reaction solution had a large absorption of 220 nm or less, and it was confirmed that uronic acid was present.

  That is, the carboxyl group content of the oxidized pulp obtained in the recycling process was almost the same as the value of the oxidized pulp obtained in the first oxidation treatment process, but the by-product increased about twice. The solid content concentration in the reaction solution increased and the TEMPO purity decreased.

  The results of the reaction conditions of Examples 1 to 3 and Comparative Example 1 are summarized in Table 1.

Claims (5)

The manufacturing method of an oxidized cellulose including the oxidation treatment process of the following cellulose fiber, and the collection | recovery process of a catalyst.
<Oxidation treatment process of cellulose fiber>
Step of oxidizing cellulose fibers in the presence of a catalyst containing an N-oxyl compound to obtain an aqueous dispersion of oxidized cellulose <Catalyst recovery step>
A process of performing at least one treatment selected from the following treatments a to c on the aqueous dispersion of oxidized cellulose obtained in the oxidation treatment step: an aqueous dispersion of oxidized cellulose, or an aqueous dispersion of this oxidized cellulose An organic solvent is added to the reaction liquid containing the catalyst after separating the oxidized cellulose from the liquid, the catalyst is extracted, the organic solvent is removed from the organic solvent in which the obtained catalyst is dissolved, and a catalyst or an aqueous solution containing the catalyst is obtained. Step b for recovery: An adsorbent is adsorbed by adding an adsorbent to an aqueous dispersion of oxidized cellulose or a reaction liquid containing the catalyst after separating the oxidized cellulose from the aqueous dispersion of oxidized cellulose, and the adsorbent Step c for recovering the catalyst or the solution containing the catalyst from: c: aqueous dispersion of oxidized cellulose, or contact after separating oxidized cellulose from the aqueous dispersion of oxidized cellulose To the reaction solution containing the by-products were removed by addition of ion-exchange resin, and recovering the aqueous solution containing the catalyst or catalyst process   The manufacturing method of the oxidized cellulose of Claim 1 which oxidizes a cellulose fiber again using the catalyst or the solution containing a catalyst collect | recovered by the collection process of a catalyst.   The method for producing oxidized cellulose according to claim 1 or 2, wherein the oxidized cellulose is oxidized cellulose having a carboxyl group content of 0.1 to 2.0 mmol / g of cellulose constituting the cellulose fiber.   The method for producing oxidized cellulose according to any one of claims 1 to 3, wherein the N-oxyl compound is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl.   The oxidizing agent for cellulose fibers is at least one selected from the group consisting of hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, and a perorganic acid. The manufacturing method of the oxidized cellulose in any one of 1-4.