JP5733733B2 - Production method of oxidized polysaccharides - Google Patents

Description

  The present invention relates to a process for producing an oxidized polysaccharide that is modified by oxidizing a polysaccharide in the presence of an N-oxyl compound catalyst (hereinafter sometimes referred to simply as “N-oxyl compound”). The present invention relates to a method for producing an oxidized polysaccharide capable of recovering and reusing an N-oxyl compound catalyst.

  Since polysaccharides such as cellulose and starch are present in a large amount in the natural world as structural polysaccharides and storage polysaccharides of living organisms, they have been conventionally used in various materials. In recent years, in particular, from the viewpoint of safety and the environment, research on the effective use of polysaccharides as a material to replace synthetic polymers derived from petroleum raw materials has become active.

  In addition, for the purpose of effectively using polysaccharides, polysaccharides are also oxidized and modified. For example, polysaccharides are converted to hypohalous acid, halous acid, perhalogen acid, hydrogen peroxide, Oxidized polysaccharides that are oxidized using an oxidizing agent such as a perorganic acid have been produced. In that case, as a catalyst, an N-oxyl compound is preferably used from a viewpoint of catalyst activity and reaction selectivity. Specifically, as a method for producing an oxidized polysaccharide using such an N-oxyl compound as a catalyst, a polysaccharide material mainly composed of a polysaccharide is oxidized in water in the presence of an N-oxyl compound catalyst. A method for producing an oxidized polysaccharide material (Patent Document 1) for treating and modifying the surface of the polysaccharide material, or by using natural cellulose as a raw material, using an N-oxyl compound as an oxidation catalyst in water, and allowing an oxidizing agent to act. A method for producing a fine cellulose fiber dispersion that oxidizes natural cellulose to obtain a reaction product fiber (Patent Document 2) has been proposed.

JP 2003-183302 A JP 2008-1728 A

  However, in the production methods of Patent Document 1 and Patent Document 2, there is no idea of recovering the N-oxyl compound catalyst, and this has become common technical knowledge in this field. Unless such N-oxyl compound is recovered and reused, an expensive catalyst cannot be effectively used, which is uneconomical.

  The present invention has been made in view of such circumstances, and is capable of producing an oxidized polysaccharide having excellent economic efficiency and stable quality by collecting and reusing an N-oxyl compound catalyst. The purpose is to provide a method for producing polysaccharides.

In order to achieve the above object, a method for producing an oxidized polysaccharide of the present invention is a method for producing an oxidized polysaccharide that oxidizes a polysaccharide in an aqueous medium containing an N-oxyl compound catalyst and an oxidizing agent. Including a step of recovering the N-oxyl compound catalyst from the reaction liquid after completion of the saccharide oxidation reaction by distillation, and the distillation is performed by an evaporator at a pressure of 0.03 MPa to normal pressure. The temperature is 70 to 101 ° C., the N-oxyl compound catalyst is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), the polysaccharide is cellulose, and the oxidizing agent is Hypohalous acid or a salt thereof, the addition amount of the oxidizing agent is in the range of 5.4 to 18 mmol with respect to 1 g of the polysaccharide, and the carboxyl group amount of the oxidized polysaccharide is 1.00 mmol / g to 6.2 mmol. g is in the range of, N- oxyl compound by distillation N- oxyl compound recovery of the catalyst of the catalyst from the aqueous medium containing a is not less than 98%, and the oxidized polysaccharide is a cosmetic material, coating the substrate, functional It is configured to be used for additives, medical / pharmaceutical materials, electronic materials, or resin materials.

  That is, the present inventors have obtained a method for producing an oxidized polysaccharide capable of producing an oxidized polysaccharide having excellent economic efficiency and stable quality by collecting and reusing the N-oxyl compound catalyst. The recycling of the catalyst was examined. Usually, the oxidation reaction of a polysaccharide using an N-oxyl compound as a catalyst is carried out in an aqueous medium (water or an aqueous medium), and after completion of the oxidation reaction, it is separated and purified into an oxidized polysaccharide and an aqueous medium. In the separated aqueous medium, the N-oxyl compound catalyst is present in a dilute concentration together with the neutralizing salt derived from the oxidizing agent. The present inventors pay attention to this point, and for the purpose of recovering and reusing the N-oxyl compound catalyst, the diluted N-oxyl in which the neutralized salt derived from the oxidant separated after the oxidation reaction coexists is present. An attempt was made to repeatedly use the aqueous medium (reaction solution) containing the compound catalyst for the next oxidation reaction as it is. However, the recovered catalyst contains neutralized salts derived from the oxidizing agent generated in the previous reaction and low molecular weight compounds derived from polysaccharides, so the catalytic activity does not increase and the polysaccharides are oxidized. Has not been fully developed, and the quality of the resulting oxidized polysaccharide is not satisfactory. That is, the above-described catalyst recovery method has a problem in that a decrease in catalyst activity is inevitable because the amount of neutralized salt derived from the oxidizing agent increases each time the catalyst is recovered and reused. It was. Therefore, the present inventors conducted further experiments to solve this problem. As a result, the reaction solution (in the separated aqueous medium) after completion of the polysaccharide oxidation reaction was not used as it was, but was reacted. It was recalled that the liquid was distilled by an evaporator or the like. Distillation of the reaction solution can remove impurities (such as neutralizing salts derived from oxidizing agents and low molecular weight compounds derived from polysaccharides) from the reaction solution, and effectively removes only the N-oxyl compound catalyst. It can be recovered. Therefore, even if the recovery and reuse of the catalyst are repeated, there is almost no decrease in the activity of the N-oxyl compound catalyst, and the N-oxyl compound, which is an expensive catalyst, can be recovered at an extremely high recovery rate. Since it can be reused repeatedly, it becomes economically superior. In addition, the purity of the recovered catalyst is high, and the recovered catalyst contains almost no contaminants. Therefore, the recovered catalyst has high activity, and even when the catalyst is repeatedly recovered and reused, the reactivity does not decrease and is stable. It has been found that oxidized polysaccharides of the same quality can be produced, and the present invention has been achieved.

  As described above, in the method for producing an oxidized polysaccharide of the present invention, the reaction solution after completion of the polysaccharide oxidation reaction is not used as it is, but the reaction solution is distilled by an evaporator or the like. By removing impurities (neutralized salts derived from oxidizing agents, low molecular compounds derived from polysaccharides, etc.), only the N-oxyl compound catalyst can be recovered. Therefore, even if the recovery and reuse of the catalyst are repeated, there is almost no decrease in the activity of the N-oxyl compound catalyst, and the N-oxyl compound, which is an expensive catalyst, can be recovered at an extremely high recovery rate. Because it can be reused repeatedly, it is economically superior. In addition, the purity of the recovered catalyst is quite high, and since the recovered catalyst contains almost no impurities, the recovered catalyst has high activity, and even when the catalyst is repeatedly recovered and reused, the reactivity does not decrease, Stable quality oxidized polysaccharides can be produced.

Further, the distillation is carried out by evaporator pressure 0.03 MPa ~ normal pressure, the temperature of the distillate in the distillation is 70 ~ 101 ° C., the recovery of the N- oxyl compound catalyst from the reaction solution more effectively Can be done automatically.

Then, the N- oxyl compound catalyst, because it is 2,2,6,6-tetramethyl-1-piperidine -N- oxyl (TEMPO), high catalytic activity, further performed efficiently oxidation of polysaccharides be able to.

Further, the polysaccharide, since a cellulose scan, superior safety and environmental properties, as a material to replace the synthetic polymers derived from petroleum feedstock, can be effectively utilized in a variety of materials.

Then, the oxidizing agent is, for a hypohalous acid or a salt thereof can be carried out the oxidation of polysaccharides more efficiently.

  Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

  The method for producing an oxidized polysaccharide of the present invention is a method for producing an oxidized polysaccharide that oxidizes a polysaccharide in an aqueous medium (water or an aqueous medium) containing an N-oxyl compound catalyst and an oxidizing agent. The greatest feature of the present invention is that it includes a step of recovering the N-oxyl compound catalyst by distillation from the reaction solution after completion of the polysaccharide oxidation reaction.

<Oxidation reaction process>
The polysaccharide oxidation reaction step can be performed, for example, as follows. That is, a polysaccharide is dissolved or dispersed in an aqueous medium (water or an aqueous medium) to form a slurry, and an N-oxyl compound catalyst is added as a catalyst to this and sufficiently stirred to disperse and dissolve. Next, an oxidizing agent is added, and the reaction is carried out while dripping the alkaline aqueous solution so as to maintain pH 8-11, preferably pH 10-11, until there is no pH change.

The polysaccharide to be the process of the present invention, ease of availability, from the viewpoint of economy, cellulose scan is used. The polysaccharide may be chemically modified. Examples of the chemical modification method include methylation, ethylation, alkylation, hydroxyethylation, hydroxypropylation, hydroxyalkylation, carboxymethylation, sulfation, and nitration.

  Examples of the polysaccharides that can be used include powders, granules, pellets, sheets, fibers, and the like. Further, if necessary, the polysaccharides having various shapes may be subjected to treatment such as grinding, grinding, cutting, and crushing.

  The polysaccharide concentration in the reaction solution varies depending on the type of polysaccharide, but is usually in the range of 0.1 to 10% by weight (hereinafter simply referred to as “%”), preferably in the range of 1 to 7%. is there. That is, if the concentration is too low, it is not economical, and conversely if the concentration is too high, the operability of the reaction tends to deteriorate.

Then, as the use as a catalyst N- oxyl compound, from the viewpoint of excellent economic efficiency and catalyst activity, 2,2,6,6-tetramethyl-1-piperidine -N- oxyl (TEMPO) is used.

  The addition amount of the N-oxyl compound as the catalyst is preferably in the range of 0.1 to 4 mmol / l, particularly preferably in the range of 0.2 to 2 mmol / l as the concentration in the reaction solution.

As the oxidizing agent used together with the catalyst, hypohalous acid or its salt is used. These may be used alone or in combination of two or more. Among these, alkali hypohalites such as sodium hypochlorite and sodium hypobromite are preferable from the viewpoint of economy and oxidation efficiency.

The addition amount of the oxidizing agent varies depending polysaccharide type, with respect to the polysaccharide 1g, in the range of 5.4 ~ 18 mmo l. The amount of carboxyl groups of the oxidized polysaccharide can be adjusted by the amount of the oxidizing agent added. That is, the amount of carboxyl groups tends to increase as the amount of oxidant added increases. The number of moles of carboxyl groups in oxidized polysaccharides thus obtained is in the range of the average per acid polysaccharide 1g 1.00 ~ 6.2 mmol / g.

  In addition, when using sodium hypochlorite as said oxidizing agent, it is preferable in terms of reaction rate to advance the reaction in the presence of an alkali metal bromide such as sodium bromide. The addition amount of the alkali metal bromide is about 1 to 40 times mol, preferably about 10 to 20 times mol for the N-oxyl compound.

  Examples of the alkaline aqueous solution for adjusting the pH include 1 to 50% aqueous solutions such as sodium hydroxide and potassium hydroxide.

  The reaction temperature for oxidizing the polysaccharide is usually 0 to 60 ° C, preferably 5 to 40 ° C. Note that the oxidation reaction may be performed at room temperature without controlling the temperature. The completion of the oxidation reaction can be confirmed by eliminating the pH change of the reaction solution. The reaction time for the oxidation reaction is usually in the range of 5 to 600 minutes.

  In the present invention, after the oxidation step is completed, it is preferable to carry out a purification step for purifying the oxidized polysaccharide by separating impurities and oxidized polysaccharide from the reaction solution after the end of the oxidation reaction.

<Purification process>
Since the reaction solution after completion of the oxidation reaction contains salts, residual oxidant, N-oxyl compound as a catalyst, etc. as impurities, these impurities are separated from the oxidized polysaccharide to purify the oxidized polysaccharide. It is preferable to do. Examples of the purification method include filtration, washing, and dialysis.

  For example, when the oxidized polysaccharide is insoluble in water, the reaction-terminated liquid is solid-liquid separated by filtration or centrifugation, and the oxidized polysaccharide is recovered as a solid content. Further, the solid content can be purified until the desired degree of purification is obtained by repeating the reslurry and solid-liquid separation. This purification can be carried out continuously. Usually, water or an aqueous medium is used as a purification solvent, and water is preferable in consideration of economy. In addition, it does not interfere with dialysis using a membrane.

  On the other hand, when the oxidized polysaccharide is water-soluble, the oxidation reaction completion solution may be dialyzed with a membrane, or the oxidized polysaccharide may be purified by precipitating the oxidized polysaccharide with a hydrous solvent and further washing with the hydrous solvent. Absent. In addition, divalent or higher valent metal ions or acids may be added to the oxidation reaction end solution to make the oxidized polysaccharide water insoluble, washed with a water-containing solvent or water, and purified, adsorbent, ion exchange resin, size It may be purified by exclusion column chromatography or the like.

  Next, a catalyst recovery step for recovering the N-oxyl compound catalyst by distillation from the reaction solution after completion of the polysaccharide oxidation reaction will be described. In the present invention, this catalyst recovery step is the greatest feature.

<Catalyst recovery process>
The high-purity N-oxyl compound catalyst can be recovered as a distillate by distilling the oxidation reaction-terminated liquid as it is or by distilling the aqueous medium containing the N-oxyl compound catalyst after the purification step.

In the production method of the present invention, the recovery rate of the N-oxyl compound catalyst by distillation from the aqueous medium containing the N-oxyl compound catalyst is 98% or more .

  If the oxidant used in the oxidation reaction process remains in the liquid to be distilled (reaction liquid), before the distillation, add a reducing agent such as sodium thiosulfate to the liquid to be distilled, Can be reduced. Note that the pH may be adjusted in advance.

  As the distillation method, distillation can be performed by either a batch method or a continuous method. Examples of the heating method include a reboiler type and a jacket type, and steam distillation, equilibrium flash distillation, and the like can also be used. In addition, either simple distillation or multistage distillation may be used. In the present invention, it is possible to recover the N-oxyl compound catalyst with practically no problem by batch distillation, but it is preferable to use a multistage distillation or a distillation column in order to increase efficiency.

The distillation pressure is set at a pressure and a temperature so that the liquid to be distilled will boil in the evaporator . Distillation is preferred at atmospheric pressure or reduced pressure.

Temperature of the distillate at evaporator (evaporator in temperature) is the range of 70 ~ 101 ° C.. That is, if the temperature of the liquid to be distilled is too low, boiling is difficult, whereas if it is too high, energy efficiency tends to deteriorate.

The pressure of the evaporator is in the range of 0.03 MPa ~ normal pressure, preferably from 0.03 MPa~0.1MPa. When ie, the pressure in the evaporator is too low, not vacuum equipment is economical, and an excessively high, because there is a tendency pressurized equipment is not economically seen.

  The temperature of the distillate may be set below the temperature at which condensation occurs under the operating pressure. At that time, for the purpose of preventing the N-oxyl compound from precipitating in the distillate, the temperature of the distillate is preferably equal to or higher than the melting point of the N-oxyl compound. For example, when the N-oxyl compound is TEMPO, when distillation is performed under atmospheric pressure, the temperature of the distillate is preferably 30 to 90 ° C, particularly preferably 40 to 80 ° C.

  The end point of the distillation is when the N-oxyl compound concentration in the evaporation residue becomes 10 to 0.1% or less of the N-oxyl compound concentration of the feed liquid to be distilled, preferably 1 to 0.1% or less. Time points can be used as a guide. In the case of simple distillation, the time when 5 to 20% of the weight of the liquid to be distilled evaporates can be used as a guide.

  The oxidized polysaccharide obtained by the method for producing an oxidized polysaccharide of the present invention can be used, for example, as follows.

  When the obtained oxidized polysaccharide is water-soluble, the purified oxidized polysaccharide can be used as a wet cake, an aqueous solution, a dry powder, or the like. On the other hand, when the obtained oxidized polysaccharide is insoluble in water, the purified oxidized polysaccharide can be used as a wet cake, an aqueous dispersion, a dry powder, or the like. When the oxidized polysaccharide is used as an aqueous dispersion, as a mixing / dispersing device, a propeller type, paddle type, anchor type mixer, homomixer, homodisper, homogenizer, high pressure homogenizer, ultrahigh pressure homogenizer, ultrasonic homogenizer, vibration A dispersing machine such as a mill, a ball mill, a planetary ball mill, a sand mill, a vacuum emulsifier, or a paint shaker can be used. Then, by appropriately changing the dispersion strength of these mixing / dispersing devices, it is possible to obtain a dispersion of oxidized polysaccharides having different sizes of several nanometers to several hundreds of micrometers.

Oxidized polysaccharide obtained by the process of the present invention, cosmetics materials, coated substrate, various functional additives (gelling agents, emulsifiers and the like), used medical and pharmaceutical materials, electronic materials, resin materials applications be able to.

  Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples.

[Example 1]
<Oxidation reaction step (first time)>
Add 150 g of water, 0.025 g of sodium bromide, 0.025 g of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) to 2 g (dry weight) of cellulose (conifer pulp) and stir well. Then, 13% by weight aqueous sodium hypochlorite solution was added to 1 g of pulp so that the amount of sodium hypochlorite was 5.4 mmol / g-cellulose, and the pH was adjusted to 10-11. A 0.5 N sodium hydroxide solution was added dropwise so as to maintain the reaction, and the reaction was continued at room temperature until no pH change was observed. The reaction time was 120 minutes.

<Purification process (first time)>
The reaction-terminated liquid was filtered and solid-liquid separated to obtain 140 g of recovered filtrate water containing 12 g of crude oxidized cellulose wet cake and TEMPO. Furthermore, filtration and water washing were repeated 3 times with 170 g of water, and purification was carried out to obtain 12 g of a wet cake of cellulose fibers whose fiber surface was oxidized. The amount of carboxyl groups of the obtained cellulose fibers was measured as follows. That is, 0.3 g of dried cellulose fiber was dispersed in 55 ml of water, 5 ml of 0.01N sodium chloride aqueous solution was added, and the mixture was sufficiently stirred to disperse the cellulose fiber. Next, 0.1N hydrochloric acid solution is added until the pH reaches 2.5 to 3.0, and 0.04N aqueous sodium hydroxide solution is added dropwise at a rate of 0.1 ml / min. The amount of carboxyl groups was calculated from the difference between the neutralization point of excess hydrochloric acid and the neutralization point of carboxyl groups derived from cellulose fibers. As a result, the amount of carboxyl groups per cellulose fiber solid content was 1.00 mmol / g.

<Catalyst recovery process (first time)>
The recovered filtrate containing TEMPO obtained in the purification step (weight: 140 g, TEMPO concentration 143 ppm) was simply distilled at an evaporator internal temperature of 101 ° C., a distillate temperature of 50 ° C., and atmospheric pressure. Distillation was terminated when the weight of the distillate reached 15 g. As a distillate, 15 g of a recovered TEMPO aqueous solution (TEMPO concentration of 1320 ppm) was obtained. As a result, the TEMPO recovery rate from the recovered filtrate was 99%.

<Attachment process (first time)>
Water was added to the oxidized cellulose wet cake after purification to give a solid concentration of 0.7%. When a dispersion treatment was performed at 13000 rpm for 20 minutes using a homomixer, a transparent and viscous nano-aqueous dispersion of oxidized cellulose was obtained. When this was diluted and cast on a carbon film-coated grid that had been hydrophilized, and observed with a transmission electron microscope (TEM), cellulose nanofibers having a fiber width of 7 nm were observed.

  Next, using the catalyst recovered as described above, the same operation was performed for the cellulose used in the first time.

<Oxidation reaction step (second time)>
Using the recovered TEMPO aqueous solution obtained in the above-mentioned catalyst recovery step (first time) as a catalyst, the reaction is performed in the same manner as the first time with a charge of 3/4 when described in the above-mentioned oxidation reaction step (first time). I let you. The reaction time was 120 minutes as in the first time. As a result, it was confirmed that the reactivity of the TEMPO recovered by distillation was not lowered.

<Purification step (second time)>
It refine | purified similarly to the 1st time with the preparation amount of 3/4 at the time of describing in the above-mentioned refinement | purification process (1st time). The amount of carboxyl groups per cellulose fiber solid was 1.00 mmol / g, which was the same as the first time. As a result, it was confirmed that the reactivity of the TEMPO recovered by distillation was not lowered.

<Catalyst recovery process (second time)>
As described in the above catalyst recovery step (first time), the catalyst was recovered in the same manner as in the first time with a charge of 3/4, and 11.25 g of a recovered TEMPO aqueous solution (TEMPO concentration 1320 ppm) was obtained as a distillate. . The TEMPO recovery rate from the recovered filtrate was 99%.

<Attachment process (second time)>
The operation was performed in the same manner as the first time with a charge of 3/4 as described in the above-mentioned incidental process (first time). As a result, the number average fiber diameter of the cellulose nanofibers was 7 nm, which was not changed from the first time.

  The same operation was performed using the TEMPO recovered by distillation, and the third, fourth, and fifth productions were performed. The reaction time, the amount of carboxyl groups, and the fiber width were not changed, and the TEMPO recovered by distillation was repeatedly used. Stable quality oxidized cellulose could be produced.

[Comparative Example 1]
The recovered filtrate containing TEMPO obtained in the purification step (weight: 140 g, TEMPO concentration 143 ppm) was used in the same manner as in Example 1 except that the next reaction catalyst was used to the same concentration as in Example 1. did. However, since the recovered filtrate containing TEMPO contains sodium bromide, the concentration was adjusted so that the sodium bromide concentration in the oxidation reaction solution was the same as in Example 1. As a result, in the second production, the reaction time was 180 minutes, the carboxyl group amount was 0.75 mmol / g, and the fiber width was 30 nm. In the third production, the reaction time was 250 minutes, the carboxyl group amount was 0.50 mmol / g, and the fiber width was 140 nm. Furthermore, in the fourth production, the reaction time was 400 minutes or more, and it was difficult to complete the reaction. That is, each time the reaction was repeated, the reactivity of the catalyst was lowered, and the quality of the oxidized cellulose obtained was also lowered. This is because the recovered TEMPO catalyst is the recovered filtrate as it is, and it contains sodium chloride generated during the reaction and a cellulose-derived substance having a low molecular weight, which reduces the reactivity.

[Example 2]
<Oxidation reaction step (first time)>
Add 160 g of water, 0.5 g of sodium bromide, 0.055 g of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) to 4 g (dry weight) of cellulose (rayon) and stir well. After being dispersed, 13% by weight aqueous sodium hypochlorite solution is added to 1 g of pulp so that the amount of sodium hypochlorite is 18 mmol / g-cellulose, and the pH is maintained at 10-11. While adding 0.5N sodium hydroxide solution dropwise, the reaction was continued at room temperature until no pH change was observed. The reaction time was 300 minutes.

<Purification process (first time)>
The reaction-terminated solution was dialyzed against 500 g of water to obtain a recovered solution 500 g containing a crude oxidized cellulose aqueous solution 220 g and TEMPO. Further, it was purified by dialysis overnight in running water to obtain 210 g of an oxidized cellulose aqueous solution. As a result of measuring the amount of carboxyl groups by the same method as in Example 1, the amount of carboxyl groups per 1 g of oxidized cellulose was 6.2 mmol / g. So-called sodium cellulonate was obtained.

<Catalyst recovery process (first time)>
The recovered liquid (weight: 500 g, TEMPO concentration 58 ppm) obtained in the purification step was simply distilled at an evaporator internal temperature of 70 ° C., a distillate temperature of 50 ° C., and a pressure of 0.03 MPa. Distillation was terminated when the weight of the distillate reached 75 g. As a distillate, 75 g of a recovered TEMPO aqueous solution (TEMPO concentration of 379 ppm) was obtained. The TEMPO recovery rate from the recovered filtrate was 98%.

<Attachment process (first time)>
The obtained oxidized cellulose has a high amount of carboxyl groups and is so-called sodium seuroronate, which is water-soluble. The aqueous sodium ceuronate solution obtained in the purification step was spray-dried to obtain 3.5 g of sodium ceurouronate powder.

  Next, using the catalyst recovered as described above, the same operation was performed for the cellulose used in the first time.

<Oxidation reaction step (second time)>
Using the recovered TEMPO aqueous solution obtained in the above-mentioned catalyst recovery step (first time) as a catalyst, the reaction is performed in the same manner as the first time with a charge of 3/4 when described in the above-mentioned oxidation reaction step (first time). I let you. The reaction time was 300 minutes as in the first time. As a result, it was confirmed that the reactivity of the TEMPO recovered by distillation was not lowered.

<Purification step (second time)>
It refine | purified similarly to the 1st time with the preparation amount in the case of 3/4 when describing in the above-mentioned refinement | purification process (the 1st time). The amount of carboxyl groups per cellulose fiber solid content was 6.2 mmol / g, which was the same as the first time. As a result, it was confirmed that the reactivity of the TEMPO recovered by distillation was not lowered.

<Catalyst recovery process (second time)>
The catalyst was recovered in the same manner as the first time with a charge of 3/4 as described in the catalyst recovery step (first time). As a distillate, 56 g of a recovered TEMPO aqueous solution (TEMPO concentration of 379 ppm) was obtained. The TEMPO recovery rate from the recovered filtrate was 98%.

<Attachment process (second time)>
The operation was performed in the same manner as in the first time with a charge of 3/4 as described in the above-mentioned incidental process (first time) to obtain 2.6 g of sodium seuroronate powder.

  The same operation was performed using the TEMPO recovered by distillation, and the third, fourth, and fifth productions were performed. The reaction time, the amount of carboxyl groups, and the yield were not changed, and the TEMPO recovered by distillation was repeatedly used. Stable quality oxidized cellulose (sodium cellulonate) could be produced.

[ Reference Example 1 ]
<Oxidation reaction step (first time)>
Add 180g of water, 0.4g of sodium bromide, 0.05g of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) to 4g (dry weight) of starch (derived from potato) and stir well Then, a 13% by weight aqueous sodium hypochlorite solution is added so that the amount of sodium hypochlorite is 20 mmol / g-cellulose with respect to 1 g of starch, and the pH is maintained at 10-11. The reaction was continued at 8 ° C. until no pH change was observed while adding 0.5 N sodium hydroxide solution dropwise. The reaction time was 240 minutes.

<Catalyst recovery process (first time)>
The reaction-terminated liquid was adjusted to pH 6.5 with 5% sulfuric acid and then subjected to simple distillation at an evaporator internal temperature of 70 ° C, a distillate temperature of 50 ° C, and a pressure of 0.03 MPa. Distillation was terminated when the weight of the distillate reached 20 g. As a distillate, 20 g of a recovered TEMPO aqueous solution (TEMPO concentration 2250 ppm) was obtained. The TEMPO recovery rate from the reaction completed solution was 90%.

<Purification process (first time)>
The distillation residue obtained in the catalyst recovery step was added to 10 times the amount of cold acetone to precipitate oxidized starch, and filtered to obtain crude oxidized starch. Furthermore, washing with cold 10% water-containing acetone and filtration were repeated three times for purification, and an oxidized starch wet cake was obtained. As a result of measuring the amount of carboxyl groups by the same method as in Example 1, the amount of carboxyl groups per 1 g of oxidized starch was 5.6 mmol / g. So-called sodium polyglucuronic acid was obtained.

<Attachment process (first time)>
The obtained oxidized starch has a high amount of carboxyl groups, is so-called sodium polyglucuronate, and is water-soluble. The aqueous cellulonate solution obtained in the purification step was vacuum-dried to obtain 3.8 g of sodium polyglucuronate.

  Next, using the catalyst recovered as described above, the same operation was performed on the starch used in the first time.

<Oxidation reaction step (second time)>
Using the recovered TEMPO aqueous solution obtained in the above-mentioned catalyst recovery step (first time) as a catalyst, the reaction is performed in the same manner as the first time with a charge of 3/4 when described in the above-mentioned oxidation reaction step (first time). I let you. The reaction time was 240 minutes as in the first time. As a result, it was confirmed that the reactivity of the TEMPO recovered by distillation was not lowered.

<Catalyst recovery process (second time)>
The catalyst was recovered in the same manner as the first time with a charge of 3/4 as described in the catalyst recovery step (first time). As a distillate, 15 g of a recovered TEMPO aqueous solution (TEMPO concentration: 2250 ppm) was obtained. The TEMPO recovery rate from the recovered filtrate was 90%.

<Purification step (second time)>
It refine | purified similarly to the 1st time with the preparation amount of 3/4 at the time of describing in the above-mentioned refinement | purification process (1st time). The amount of carboxyl groups per cellulose fiber solid content was 5.8 mmol / g, which was the same as the first time. It was confirmed that the reactivity of TEMPO recovered by distillation did not decrease.

<Attachment process (second time)>
When described in the above-mentioned incidental process (first time), operation was performed in the same manner as the first time with a charge of 3/4 to obtain 2.9 g of sodium polyglucuronate powder.

  The same operation was performed using the TEMPO recovered by distillation, and the third, fourth, and fifth productions were performed. The reaction time, the amount of carboxyl groups, and the yield were not changed, and the TEMPO recovered by distillation was repeatedly used. Stable quality oxidized starch (sodium polyglucuronate) could be produced.

Oxidized polysaccharide obtained by the process of the present invention, cosmetics materials, coated substrate, various functional additives (gelling agents, emulsifiers and the like), used medical and pharmaceutical materials, electronic materials, resin materials applications be able to.

Claims (1)

A method for producing an oxidized polysaccharide that oxidizes a polysaccharide in an aqueous medium containing an N-oxyl compound catalyst and an oxidizing agent, wherein the N-oxyl compound catalyst is distilled from a reaction solution after completion of the polysaccharide oxidation reaction. And the distillation is performed with an evaporator at a pressure of 0.03 MPa to normal pressure, the temperature of the liquid to be distilled in the distillation is 70 to 101 ° C., and the N-oxyl compound catalyst is 2, 2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), the polysaccharide is cellulose, the oxidizing agent is hypohalous acid or a salt thereof, and the amount of the oxidizing agent added is An aqueous medium containing an N-oxyl compound catalyst in which the amount of carboxyl groups of the oxidized polysaccharide is in the range of 1.00 mmol / g to 6.2 mmol / g in a range of 5.4 to 18 mmol with respect to 1 g of sugar. The recovery rate of N-oxyl compound catalyst by distillation from water is 98% or more, and the oxidized polysaccharide is used for cosmetic materials, coating base materials, functional additives, medical / pharmaceutical materials, electronic materials or resin materials A process for producing an oxidized polysaccharide, characterized in that