JP6006623B2 - Oxidation method - Google Patents

Description

  The present invention relates to an oxidation treatment method, and more particularly to an oxidation treatment method for wet oxidation treatment of carbon materials such as fibers, powders, and carbon nanotubes, and fibrous and powdery inorganic materials.

  Nanocarbons such as carbon nanotubes and carbon nanofibers are generally used as composite materials in combination with matrix resins, etc., but because of the high cohesiveness of nanocarbons themselves, additives that are usually called dispersion materials And various solvent dispersions are prepared. However, depending on the use of the secondary battery or the like, the added dispersion material may have an adverse effect, and therefore, a dispersion method that does not use the dispersion material is required.

  As a dispersion method that does not use a dispersing material, there is a method of oxidizing nanocarbons themselves, and ozone is attracting attention, and a dry method using ozone gas and a wet method using a solution in which ozone is dissolved are known. . In recent years, as a method for treating nanocarbons at low cost, a wet treatment method in which an ozone solution in which ozone is dissolved in water or an ozone solution in which ozone is dissolved in a fluorine-based solvent is used for oxidation. Are being adopted (see, for example, Patent Documents 1 and 2).

JP 2009-79344 A JP 2012-31559 A

  However, as described in Patent Document 1, in the case of an ozone solution using water as a solvent, since nanocarbons are hydrophobic, ozone and nanocarbons dissolved in water. Cannot be sufficiently brought into contact with each other, and the efficiency of the oxidation reaction is low. In addition, since water has low ozone solubility, it is necessary to set the reaction conditions strictly in order to complete the oxidation reaction, although it is necessary to lower the temperature in order to increase the solubility. Setting is very difficult.

  In addition, as described in Patent Document 2, in the case of an ozone solution using a fluorine-based solvent, the fluorine-based solvent has a high solubility of ozone, and thus the reaction can proceed under mild conditions. The initial oxidation reaction can be performed efficiently because the affinity between the nanocarbons and the fluorinated solvent is high, but if the oxidation proceeds to some extent, the affinity with the fluorinated solvent is lost, so that the further oxidation occurs. There was also a problem that the reaction did not proceed and a problem that the processing cost increased because the fluorinated solvent was more expensive than water.

  Therefore, an object of the present invention is to provide a wet oxidation method that can improve the efficiency of the oxidation reaction, suppress an increase in cost, and have a simple process after the reaction treatment.

In order to achieve the above object, the oxidation treatment method of the present invention is a two-phase solvent consisting of an object to be oxidized that is hydrophobic before the oxidation reaction treatment and becomes hydrophilic after the oxidation reaction treatment, and water and a fluorinated solvent. In the oxidation treatment method of oxidizing the object to be oxidized by contacting with an ozone solution in which ozone is dissolved, after oxidizing the object to be oxidized in a fluorine-based solvent phase, the water-phase side from the fluorine-based solvent tank phase The fluorinated solvent is separated and taken out as an aqueous dispersion in a state where the oxidation target after the oxidation treatment is held in an aqueous phase .

Furthermore, in the oxidation treatment method of the present invention, the mixing ratio in the two-phase solvent is such that the volume of water is 0.1 to 10 when the volume of the fluorinated solvent is 1 , the ozone solution The ozone concentration is in the range of 120 to 500 mg / L, the fluorine-based solvent is perfluorocarbon, and the oxidation target is a carbon nanotube.

  According to the present invention, ozone in the fluorine-based solvent in the ozone solution reacts in a hydrophobic state before the oxidation treatment, and ozone in water in the ozone solution reacts when the oxidation reaction proceeds to some extent and becomes hydrophilic. In addition, an object to be oxidized such as nanocarbons can be efficiently oxidized.

  Moreover, since the oxidation target moves from the fluorine-based solvent phase to the aqueous phase according to the degree of oxidation, the progress of the reaction can be easily observed. Furthermore, after the oxidation treatment is completed, the oxidation is progressing, so that the object to be oxidized moves to the aqueous phase, so that the object to be oxidized is easily separated, and the oxidation treatment is performed simply by separating the fluorine-based solvent. It is possible to recover the later oxidation target as an aqueous dispersion.

It is explanatory drawing which shows one example of the oxidation processing apparatus of this invention.

  An oxidation treatment apparatus 11 shown in FIG. 1 shows a basic apparatus configuration of the present invention, and an ozonizer 12 as ozone generating means for generating ozone, and ozone generated by the ozonizer 12 are dissolved in a solvent. The ozone dissolving means 13, the ozone solution 14 in which ozone is dissolved, and the oxidation target object 15 are brought into contact with each other, an oxidation reaction tank 16 for performing an oxidation reaction treatment, and unreacted ozone in the exhaust gas derived from the oxidation reaction tank 16 And ozone treatment means 17 for detoxifying treatment.

  The ozonizer 12 generates ozone using oxygen as a raw material. For example, the ozonizer 12 generates ozone from oxygen by silent discharge, and generates ozone-containing oxygen containing ozone in oxygen. The ozone concentration in the ozone-containing oxygen used in the present invention is not particularly limited, but it is usually preferable to use ozone-containing oxygen having an ozone concentration in the range of 6 to 10% by volume. The ozonizer 12 may include a flow rate adjusting device that automatically adjusts the flow rate of the ozone-containing oxygen to be supplied.

  The oxidation reaction tank 16 stores an ozone solution in which ozone is dissolved in a mixed solvent (two-phase solvent) of a fluorine-based solvent and water, and the bottom of the oxidation reaction tank 16 contains ozone in the ozone solution. Ozone dissolving means 13 for bubbling oxygen is provided.

  The mixing ratio of the fluorine-based solvent and water in the two-phase solvent is not particularly limited. When the volume of the fluorine-based solvent is 1, the volume of water is 0.01 to 100. In general, it is desirable to use a two-phase solvent in which the volume of water is mixed at a ratio of 0.1 to 10 with respect to the volume 1 of the fluorine-based solvent.

  The fluorine-based solvent selectively dissolves ozone in ozone-containing oxygen. For example, fluorocarbons, fluoroketones, fluoroethers, or a mixture thereof can be used. Moreover, it is preferable to select the fluorine-type solvent to be used that has a boiling point of 40 to 100 ° C. and is in a liquid state at room temperature.

Specific examples of preferred fluorocarbon solvents include the fluorocarbons such as hydrofluorocarbons such as pentafluoropropane (CHF ₂ CH ₂ CF ₃ ), perfluoropentane (C ₅ F ₁₂ ), and perfluorohexane (C _6). Examples thereof include perfluorocarbons such as F ₁₄ ). Examples of the fluoroketones include 1,1,1,2,2,4,5,5,5-nonafluoro-4- (trifluoromethyl) -3-pentanone (C ₆ F ₁₂ O) and the like. Of perfluoroketone. Examples of fluoroethers include C ₄ F ₉ OC ₂ H _{5 and the} like.

Among these fluorine-based solvents, perfluorocarbons such as perfluoropentane (C ₅ F ₁₂ ) and perfluorohexane (C ₆ F ₁₄ ) are particularly preferable because they have a combustion preventing effect. Fluorohexane selectively dissolves ozone because the amount of dissolved ozone is about 2 liters while the amount of dissolved oxygen is about 0.6 liters per liter of liquid at room temperature. Thus, the oxidation reaction of the object to be oxidized by ozone can be effectively performed.

  The ozone concentration in the ozone solution can be set to 120 mg / L or more, which is the highest ozone concentration in the conventionally used ozone water, to improve the reaction efficiency and shorten the reaction time. If the concentration is too high, the decomposition reaction of ozone itself is promoted, so it is usually preferable to set the concentration within the range of 120 to 500 mg / L.

  The oxidation reaction tank 16 includes an introduction path 16a for introducing ozone-containing oxygen into the oxidation reaction tank 16, and a lead-out path 16b for deriving exhaust gas from the oxidation reaction tank 16, and allows the oxidation target to be taken in and out. However, it may be provided with a lid that can be sealed, and may further include an appropriate stirring means, temperature adjusting means, and pressure adjusting means. The stirring means is not particularly defined as long as the object to be oxidized and the ozone solution can be effectively brought into contact with each other, but it is desirable to use a magnet type or mechanical type stirrer.

  When the reaction is performed at normal pressure, the state of the oxidation reaction tank 16 can be visually confirmed by selecting a transparent material such as glass. On the other hand, when the reaction is performed under pressure, stainless steel having pressure resistance and ozone resistance may be selected.

  Further, as the ozone dissolving means 13, in addition to the bubbling, an ozone dissolving tank provided with a bubbling means or a microbubble generating means is provided in the middle of the introduction path 16a, or an ozone dissolver such as a static mixer or an aspirator is provided. Then, ozone can be previously dissolved in a mixed solution of a fluorinated solvent and water and then introduced into the oxidation reaction tank 16. Further, a circulation path for taking out and circulating the ozone solution in the oxidation reaction tank 16 may be provided, and the ozone dissolution tank and the ozone dissolver may be provided in the circulation path. Furthermore, it is possible to provide a conveying means for automatically and continuously taking the object to be oxidized into and out of the oxidation reaction tank 16, and a route for extracting the ozone solution from the oxidation reaction tank 16 and replenishing the oxidation reaction tank 16 with the ozone solution. It is also possible to provide a route for this.

  The oxidation reaction and ozone dissolution in the oxidation reaction tank 16 can be performed at room temperature and normal pressure. However, in order to improve the oxidation reaction efficiency by increasing the amount of ozone dissolved in the ozone solution, 0.05 to It is desirable to carry out under a pressure of 1.0 MPaG, preferably 0.1 to 0.3 MPaG. Maintaining the pressure in the oxidation reaction tank 16 is facilitated by providing a pressure control valve set to a predetermined pressure in the lead-out path 16b and setting the pressure of the ozone-containing oxygen introduced from the introduction path 16a to a predetermined pressure or higher. Can be done.

  The ozone treatment means 17 detoxifies the exhaust gas by decomposing or adsorbing ozone discharged from the oxidation reaction tank 16 because it does not dissolve in the ozone solution or does not contribute to the oxidation reaction. Various processing means conventionally used can be employed. Further, an ozone concentration meter that measures the ozone concentration is provided in the introduction route 16a and the lead-out route 16b, and the amount of ozone-containing oxygen generated in the ozonizer 12 based on the ozone concentration measured by the ozone concentration meter and the ozone content in the oxidation reaction tank 16 By adjusting the supply amount of oxygen, the ozone concentration in the ozone solution in the oxidation reaction tank 16 can be maintained in an optimum range.

  Examples of the oxidation target to be oxidized by the oxidation processing apparatus 11 formed in this way include substances that are difficult to oxidize in the gas phase because they are flammable, such as carbon fibers, nanocarbons, and metal fine powders. Etc. Specifically, examples of carbon fibers include PAN-based fibers, pitch-based fibers, and cellulose-based fibers. Examples of nanocarbons include carbon nanotubes, carbon nanofibers, carbon nanocoils, carbon nanohorns, acetylene black, Graphene etc. can be mentioned, As metal fine powder, fine powder, such as nickel, copper, titanium, cobalt, can be mentioned.

  The oxidation object is put into an ozone solution that is mixed by bubbling ozone-containing oxygen in the oxidation reaction tank 16, and ozone dissolved in the ozone solution comes into contact with the oxidation object. The object to be oxidized is oxidized by ozone. At this time, the object to be oxidized that has hydrophobicity before the oxidation treatment and has affinity for the fluorinated solvent is the fluorinated solvent phase of the two-phase solvent when put into the ozone solution. It comes into contact with the fluorinated solvent and is oxidized by ozone dissolved in the fluorinated solvent, and this oxidation reaction introduces a hydrophilic oxidizing functional group or generates an oxide film. The object to be oxidized in a state in which an oxidized functional group having hydrophilicity is introduced or an oxide film is formed moves to the aqueous phase of the two-phase solvent, and comes into contact with water to form ozone in the water. Therefore, it is possible to introduce a sufficient amount of an oxidizing functional group into the object to be oxidized or to form an oxide film having a sufficient film thickness.

  Since the oxidation target after the oxidation treatment has moved to the aqueous phase side, it can be taken out as an aqueous dispersion simply by separating the fluorinated solvent by a known appropriate method. Thereafter, the oxidized object can be taken out by drying the object to be oxidized by a known appropriate drying means to remove moisture. Furthermore, when using the oxidation target after treatment with an aqueous dispersion, it is only necessary to separate the fluorinated solvent, and the drying step can be omitted. The separated fluorine-based solvent can be reused in the ozone solution.

  An experiment for oxidizing carbon nanotubes using the oxidation processing apparatus shown in FIG. 1 was conducted. Perfluorododecane was used as the fluorine-based solvent, and water was mixed at a volume ratio of 0.25 to 1 of perfluorododecane to obtain a two-phase solvent of fluorine-based solvent and water. The two-phase solvent, the carbon nanotubes to be oxidized, and the magnet type rotor were sealed in the oxidation reaction tank 16. In a state where the pressure in the oxidation reaction tank 16 is set to 0.06 MPaG, ozone-containing oxygen of ozone 7 volume% and oxygen 93 volume% is supplied from the ozonizer 12 and bubbled in the liquid to make ozone into the two-phase solvent. Dissolved.

  While rotating the rotor and stirring the two-phase solvent, bubbling of ozone-containing oxygen was continued at 25 ° C. for 1 hour to advance the oxidation reaction. After completion of the reaction, all the oxidation target substances had moved to the aqueous phase and were dispersed in the aqueous phase, so perfluorododecane was separated and recovered. When the particle size distribution was measured with the treated oxidation target dispersed in water, the D50 (average particle size) was 26.3 nanometers. When this aqueous dispersion was allowed to stand for 24 hours, no precipitation of carbon nanotubes was observed, and it was found that the degree of dispersion in water was improved by oxidation treatment. Further, the oxygen content of the oxidized carbon nanotubes obtained by drying the aqueous dispersion was measured with an oxygen-nitrogen simultaneous analyzer and found to be 5.74% by weight.

  In addition, D50 in the aqueous dispersion of carbon nanotubes before the oxidation treatment was 44.1 nanometers, and all the carbon nanotubes were precipitated in the aqueous dispersion that was allowed to stand for 24 hours. The oxygen content was 1.34% by weight.

  Further, when the same operation was performed using only perfluorododecane without using water, D50 was 33.5 nanometers, and aggregation was started in the aqueous dispersion that was allowed to stand for 24 hours. % Carbon nanotubes were precipitated. The oxygen content was 4.70% by weight.

  The same operation as in Example 1 was performed except that perfluorohexane was used as the fluorine-based solvent. When the particle size distribution was measured after the oxidation treatment, D50 was 26.0 nanometers and the oxygen content was 5.72% by weight.

  The same operation as in Example 1 was performed using each two-phase solvent in which water was mixed at a volume ratio of 1, 5, 10 to 1 of perfluorododecane. As a result, when the water ratio is 1, the D50 is 34.1 nanometers, the oxygen amount is 4.68% by weight, and when the water ratio is 5, the D50 is 36.8 nanometers, and the oxygen amount is 4.65. When the weight percentage and the water ratio were 10, D50 was 38.3 nanometers, and the oxygen amount was 4.50 weight percent.

  The same operation as in Example 1 was performed except that the perfluorododecane recovered in Example 1 was directly used in the second and subsequent experiments. As a result, the second D50 was 25.9 nanometers, oxygen was 5.60% by weight, the third D50 was 25.2 nanometers, the oxygen was 5.60% by weight, and the fourth D50 was 25.6 nanometers. Meter, oxygen was 5.58% by weight, 5th D50 was 27.0 nanometers, oxygen was 5.62% by weight, 6th D50 was 25.4 nanometers, oxygen was 5.57% by weight .

  DESCRIPTION OF SYMBOLS 11 ... Oxidation processing apparatus, 12 ... Ozonizer, 13 ... Ozone dissolution means, 14 ... Ozone solution, 15 ... Oxidation object, 16 ... Oxidation reaction tank, 16a ... Introduction path, 16b ... Derivation path, 17 ... Ozone treatment means

Claims (5)

The object to be oxidized is brought into contact with an oxidation object that is hydrophobic before the oxidation reaction treatment and becomes hydrophilic after the oxidation reaction treatment, and an ozone solution in which ozone is dissolved in a two-phase solvent of water and a fluorine-based solvent. In an oxidation treatment method for oxidizing a product,
After the oxidation object is oxidized in the fluorine-based solvent phase, the oxidation object is further moved by moving from the fluorine-based solvent tank phase to the water phase side, and the oxidation object after the oxidation treatment is held in the water phase. An oxidation treatment method in which the fluorinated solvent is separated and taken out as an aqueous dispersion . The oxidation treatment method according to claim 1, wherein the mixing ratio in the two-phase solvent is such that the volume of water is 0.1 to 10 when the volume of the fluorinated solvent is 1 . The oxidation treatment method according to claim 1 or 2 , wherein the ozone solution has an ozone concentration in a range of 120 to 500 mg / L. The fluorine-based solvent, oxidation processing method according to any one of claims 1 to 3 is a perfluorocarbon. The oxidation object, oxidation processing method according to any one of claims 1 to 4 carbon nanotubes.

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