JP2004224665A - Method of continuously removing residual active hydrogen oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easy method of continuously removing active hydrogen oxide existing in a carbon material (existing as hetero element-containing functional groups, such as, for example, COOH, CHO and OH) at a relatively low temperature, and to provide a removing device used therefor. <P>SOLUTION: In the method where a carbon material is heat-treated in a reducing gas current, so that residual active hydrogen oxide existing in the carbon material is continuously removed, the carbon material is successively sieved off from the upper stage of a sieve made of transition metal and layered in a multistage way in a vertical direction to the lower stage. Further, in the device where a carbon material is heat-treated in a reducing gas current, so that residual active hydrogen oxide existing in the carbon material is continuously removed, a sieve made of transition metal and layered in a multistage way in a vertical direction, a carbon material feed port of feeding the raw material carbon material to the sieve in the highest stage, and a reducing gas feed port of feeding reducing gas to the sieve in the lowest stage are provided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a continuous production method and a continuous production apparatus for a carbon material used as an active material of a negative electrode of a lithium ion secondary battery or a polarizable electrode of an electric double layer capacitor, and more specifically, to form an electrode using these carbon materials. One of the causes of the inability to operate at a high voltage in the case of activated hydrogen oxide is active hydrogen oxide (hydrogen existing in a state bonded to oxygen, such as COOH, CHO, The present invention relates to a method and an apparatus for continuously and efficiently removing hydrogen existing as a hetero element-containing functional group such as OH at a relatively low temperature.
[0002]
[Prior art]
For example, an electric double layer capacitor has a pair of polarizable electrodes opposed to each other in an electrolyte solution via a separator to form a positive electrode and a negative electrode, and an electric double layer formed at an interface between the polarizable electrode and the electrolyte solution. The principle is to accumulate electric charges in the memory. Accordingly, from the idea that the capacitance of the electric double layer capacitor is almost proportional to the area of the polarizable electrode, the specific surface area by the BET method is 1,000 to 2,000 m as the active material of the polarizable electrode.²/ G of porous carbon / activated carbon has been widely used (for example, Kazuya Hiratsuka et al., DENKI KAGAKU, Vol. 59, No. 7, pp. 607-613 (1991)).
[0003]
On the other hand, the specific surface area is 100m²Non-porous coals of no more than 1 g / g have been proposed (M. Takeuchi et al., DENK1 KAGAKU, Vol. 66, No. 12, pp. 1311-1317 (1998)). In such a carbon material, whether it is porous carbon, activated carbon, or non-porous carbon, in any case, many residual functional groups remain on the carbon surface due to the activation treatment. When a polarizable electrode is formed by using these carbon materials, when an organic solvent-based electrolyte solution is used and a voltage of 2.5 V or more is applied between the facing electrodes, the remaining functional groups remaining on the carbon electrode surface are used. In particular, the reaction between the hetero element-containing functional groups and the electrolyte solution reacts to generate gas or form a non-electrically conductive film. Inconveniences such as shrinking occur. High temperature treatment has been considered as a means for removing such residual functional groups, but it has not been sufficient.
[0004]
That is, this high-temperature treatment is carried out in an inert gas stream as shown in the reference book on carbon (“Carbon Black Handbook-New Edition”, pp. 11, FIG. 9 volatile composition of carbon black).₂As O, COOH, CHO, C ＝ O, etc. become hotter, CO₂, H₂It is based on leaving in the form of O and CO. More than 800 ℃₂Withdrawal begins. Therefore, heat treatment at a temperature of 200 ° C. or more and 800 ° C. or less contributes to the removal of residual functional groups, and the higher the temperature, the more kinds of functional groups to be eliminated. That is, at 800 ° C., most of the hetero element-containing functional groups are once removed. However, at the same time, free radicals are generated on the carbon surface. The resulting free radicals are highly reactive, and as soon as carbon is taken out into the air, H₂O or O₂Reacting with to form active hydrogen oxide (eg, COOH, CHO, OH, etc.) again. This is easily confirmed by observing the carbon material artificially added with water vapor by a pulse NMR (Pulse NMR) method described later.
[0005]
In view of the above problems, the present inventor hopes that the above-mentioned high-temperature treatment will be improved to terminate the generated free radicals with hydrogen.₃Fe gas₂O₃3H decomposed with catalyst₂+ N₂A heat treatment method (in a mixed gas) has been proposed (for example, see Patent Document 1).
[0006]
In the high-temperature treatment in the hydrogen stream, the higher the temperature is, the more effective it is.
[0007]
However, when used as a polarizable electrode such as an electric double layer capacitor, unlike activated carbon, it has almost no micropores at the initial stage, and forms an electric double layer by electrochemical intercalation (history). In the case of non-porous charcoal whose effect is to maintain a high capacity thereafter, the inter-layer distance d of the graphitic layer developed in the carbon structure by the temperature of the post heat treatment₀₀₂Changes as shown in FIG. 1, and as the processing temperature becomes higher, the interlayer distance d increases.₀₀₂Tends to decrease. Interlayer distance d₀₀₂, The intercalation starting voltage increases, the hysteresis effect after initial charging decreases, and the capacitance when operating at a low voltage tends to decrease (FIG. 2). This limits the degree of freedom (eg, selection of a solvent for an electrolyte solution having a small molecular volume) in the process.
[0008]
In addition, the voltage applied between the electrodes is set to a maximum of 3.75 to 4.0 V. When a voltage higher than that is applied, the internal resistance rapidly increases, and thereafter, the internal resistance does not decrease even if the voltage is reduced. Cheap. For this reason, the maximum applied voltage must be set to 3.75 V or 4.0 V. The actual operating voltage is a voltage lower than the maximum voltage, for example, 2.7 V or 3.5 V or less, but as shown in FIG.₀₀₂It can be seen that the hysteresis effect is larger than that of a material having a wide intercalation start voltage and a low intercalation start voltage, and the capacitance at a low voltage is large.
[0009]
Therefore, it is required to remove the remaining functional groups as completely as possible at a temperature as low as possible.
[0010]
Also, when carbon materials such as activated carbon, porous carbon and non-porous carbon are industrially heat-treated in a hydrogen stream, oxygen in the air and leaked hydrogen gas (or when oxygen leaks from the outside into the hydrogen stream) Care must be taken to cause a so-called "oxy-hydrogen explosive reaction", in which a mixed gas containing oxyhydrogen is heated to 550 ° C. or more or reacts explosively when ignited. Thus, if it can be carried out at a low temperature, which is well above 550 ° C., the safety will be increased and no excessive equipment costs will be required.
[0011]
In order to solve the above-mentioned problems, the present inventor has proposed that polarizable materials including not only non-porous charcoal but also activated carbon and porous charcoal can be obtained at a temperature as low as 550 ° C. or less, which does not cause an oxyhydrogen detonation reaction. Active hydrogen oxide of the raw material carbon of the carbon electrode, in other words, remaining functional groups such as COOH, CHO, and OH are removed as cheaply, safely and completely as possible by using transition metals or transition metal compounds. Means have been proposed (for example, see Patent Document 2).
[0012]
[Patent Document 1]
JP-A-2002-25867
[Patent Document 2]
JP-A-2002-362912
[0013]
[Problems to be solved by the invention]
However, in the above-described means, the raw material carbon is mixed with a transition metal or a transition metal compound in a powder form or the like, and the heat treatment is performed in a reducing atmosphere. Need to be completely separated. If the separation and removal of the transition metal and the transition metal compound are not sufficient, when the carbon material is used for the carbon active material of the polarizable electrode of the electric double layer capacitor, if the carbon material is used for a long period of time, the capacitance will be increased. , The internal resistance, and the reactive current increase, the charge / discharge efficiency may decrease. Therefore, no transition metals such as Fe, Ni, and Co remain in the carbon material. Is desirable.
[0014]
After the heat treatment, the method of separating the transition metal or the transition metal compound from the carbon material is roughly classified into a “Dry method” and a “Wet method”. The “Dry method” is a separation method of directly separating a carbon powder and a transition metal or a transition metal compound from a mixture of a carbon powder after the heat treatment and a transition metal or a transition metal compound by a method described below. In addition, the “Wet method” means that a mixture of a carbon powder after heat treatment and a transition metal or a transition metal compound is once dispersed in a solvent, and then mixed with a carbon powder by a method described later. After separating a transition metal or a transition metal compound, a separation method comprising a series of steps of removing a solvent and drying, or a transition metal or a transition metal from a mixture of a carbon powder after heat treatment and a transition metal or a transition metal compound. It means a method in which a metal compound is treated with a chemical such as an acid or base solution, and is separated using a liquid medium which is converted into a soluble salt and eluted and removed. However, any of these methods is complicated and is not suitable for mass processing.
[0015]
Accordingly, an object of the present invention is to provide an industrial method for easily and continuously removing active hydrogen oxide remaining on a carbon material at a relatively low temperature and an apparatus used for the method.
[0016]
[Means for Solving the Problems]
In a secondary battery or an electric double layer capacitor using a non-aqueous electrolyte solution, activated carbon or non-porous carbon used as the active material of the polarizable electrode contains COOH, CHO, phenolic OH, etc. on the surface by an activation treatment. Many hetero element functional groups remain. When an electrode is assembled using such activated carbon or non-porous carbon and the operating electrode voltage is operated at a voltage higher than 2.5 V, the electrolyte solution electrochemically reacts with these hetero element-containing functional groups. Therefore, it is necessary to remove these hetero element-containing functional groups present in activated carbon and non-porous carbon.
[0017]
As one of such removal methods, there is a method of performing heat treatment at 500 to 800 ° C. in a reducing gas stream. In the heat treatment in a hydrogen gas stream, which is a reducing gas, the higher the temperature is, the more kinds of desorbed functional groups are increased, and the functional groups can be effectively removed. Such high-temperature treatment does not cause any problem in the case of activated carbon, but non-porous carbon having microcrystalline carbon similar to graphite and having a small specific surface area is treated by high-temperature treatment to form an interlayer in the microcrystalline carbon. Distance d₀₀₂Was observed at the same time.
[0018]
The present inventor has made it possible to reduce the processing temperature by using a transition metal during the heat treatment in the reducing gas stream, and further, by using a removing device described later, continuously. The present inventors have found that heat treatment can be performed efficiently, and have completed the present invention.
[0019]
The present invention is a hydrogen which exists as the above-mentioned hetero element-containing functional group and is combined with oxygen or the like remaining in a carbon material which reacts with an electrolytic solution when a voltage is applied (so-called chemically adsorbed state). This is a method of removing "active hydrogen oxide". First, the carbon material to be treated is sequentially reduced from the upper stage to the lower stage of a transition metal sieve in which a plurality of layers are vertically stacked in a reducing gas stream. This is performed by heat treatment while sieving. By this treatment, the hetero element-containing functional group in the raw carbon material becomes H₂O, CO₂Alternatively, a purified carbon material, which is a purified carbon material that is removed as CO and has no remaining active hydrogen oxide, is obtained. The purified carbon material thus obtained can be used as a carbon active material for a polarizable electrode such as an electric double layer capacitor.
[0020]
The carbon material to be treated is not particularly limited, and the carbon material may be activated carbon, one having pores such as porous carbon, or non-porous carbon having no pores. In order to maximize the effect of the present invention that enables active hydrogen oxide to be removed at a relatively low temperature, it is preferable to use non-porous carbon as the carbon material. Regarding the shape of the carbon material, any shape such as powder, granule, fiber and whisker can be used as the carbon material to be treated. Especially, it is desirable to use a powdery carbon material.
[0021]
The present invention is characterized in that the carbon material to be treated is subjected to a heat treatment under a reducing atmosphere, preferably in a reducing gas stream, while sequentially sifting from the upper stage to the lower stage of a transition metal sieve stacked in multiple stages in the vertical direction. I do. Hydrogen or ammonia is used as reducing gas₂O₃Mixed gas of hydrogen and nitrogen (3H₂+ N₂Mixed gas) can be used.
[0022]
Further, the present invention also includes a continuous removal apparatus for residual active hydrogen oxide suitable for a method of continuously heat-treating a carbon material as described above to efficiently remove residual active hydrogen oxide. Is a transition metal sieve stacked in multiple stages in the vertical direction, a carbon material supply port that supplies the raw material carbon material to the uppermost screen, and a reducing gas supply port that supplies the reducing gas to the lowermost screen. It is characterized by having.
[0023]
Furthermore, from the viewpoint of sufficiently bringing the carbon material to be treated and the transition metal into contact with each other, the above-described apparatus has a cylindrical sieve, a hole is provided in the center of the cylindrical sieve, and a rotating column having a hole therethrough. Preferably, a comb-shaped rotor fixed to the rotating column is provided inside the sieve, and the comb-shaped rotor rotates with the rotation of the rotating column.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the carbon material to be treated includes those used as an active material for a polarizable electrode of an electric double layer capacitor, such as porous carbon such as activated carbon and non-porous carbon. As a carbon material as a starting material in the method for continuously removing hydrogen, a dried product that has been activated (activated) is used in any case. First, non-porous carbon as a carbon material serving as a starting material will be briefly described. In addition, the “non-porous coal” referred to here has microcrystalline carbon similar to graphite, has few pores, and therefore has a small specific surface area (for example, as described in Japanese Patent Application No. 2000-201849). 270m specific surface area measured by BET method²/ G or less, preferably the interlayer distance d₀₀₂Means about 0.36 to 0.38 nm) carbon.
[0025]
FIG. 3 schematically shows a non-porous coal and a method for continuously removing residual active hydrogen oxide using the same as a starting material. The carbon material (non-porous carbon) used as a starting material in the present invention has a needle coke or infusibilized pitch (easily graphitized carbon from which volatile components have been removed by dry distillation at 300 ° C. to 400 ° C.) of 120 μm or less. Pulverization is performed to obtain “coking coal”, and this “coking coal” is heat-treated at 650 ° C. to 900 ° C., preferably 700 ° C. to 800 ° C. for 2 to 4 hours under an inert atmosphere, for example, a nitrogen atmosphere. Heat treatment to obtain "calcined charcoal". Next, the obtained “calcined charcoal” is mixed with caustic alkali (for example, KOH) in a weight ratio of 1.8 to 2.2 times, and preferably about 2 times, and again in an inert atmosphere, for example, nitrogen. In an atmosphere, heating is performed at 800 ° C. to 900 ° C., preferably about 800 ° C., for 2 to 4 hours to perform an activation treatment with a caustic alkali. Thereafter, the alkali remaining in the carbon is removed as follows.
[0026]
The removal of alkali is performed by washing the obtained carbon after alkali activation. For washing, for example, carbon particles having a size of 1 μm or more are collected from the carbon after the alkali treatment, packed in a stainless steel column, and pressurized steam at 120 ° C. to 150 ° C. and 10 to 100 kgf, preferably 10 to 50 kgf is introduced into the column. Then, it can be carried out by continuously introducing pressurized steam until the pH of the wastewater becomes 〜7 (normally 6 to 10 hours). After the completion of the alkali removing step, an inert gas such as argon or nitrogen is passed through the column and dried to obtain the desired non-porous carbon.
[0027]
On the other hand, in order to produce activated carbon, the above-mentioned raw coal is heat-treated directly with KOH at 800 ° C., and pores are formed into activated carbon. After removing alkali in the same manner as above, an inert gas such as argon or nitrogen is produced. The gas is passed through the column and dried to obtain the desired activated carbon.
[0028]
The non-porous carbon or activated carbon thus obtained has a hetero element-containing functional group such as COOH, CHO, or phenolic OH on the carbon surface. The active hydrogen oxide is removed. That is, as shown in FIG. 3, this method for removing active hydrogen oxide is performed by heat-treating non-porous carbon as a starting material in a reducing gas stream to remove residual active hydrogen oxide present in the non-porous carbon. Is obtained by successively sifting the non-porous carbon from the upper stage to the lower stage of a transition metal sieve, which is vertically laminated in multiple stages, to obtain a purified non-porous carbon.
[0029]
The carbon material such as non-porous carbon or activated carbon used as a starting material in the present invention generally has a particle size in the range of 1 μm to 100 μm, preferably in the range of about 20 μm to 60 μm.
[0030]
The method for removing residual active hydrogen oxide of the present invention is a method for continuously removing residual active hydrogen oxide present in a carbon material by heat-treating the carbon material in a reducing gas stream, and removing the carbon material. It is characterized in that the sieve is sequentially sifted down from the upper stage to the lower stage of a transition metal sieve stacked in multiple stages in the vertical direction.
[0031]
Examples of the transition metal used for the sieve include metal elements belonging to each of the groups 3 to 11 in the periodic table, and particularly, Fe, Ni, Co, Cu, Mo, Cr, Mn, and Th are preferable.
[0032]
The transition metal used may be any of these simple metals, or an alloy containing these metal elements, for example, a material such as permalloy (Fe—Ni) or iron cobalt (Fe—Co). .
[0033]
While the carbon material is sequentially sieved from the upper stage to the lower stage of a transition metal sieve stacked in multiple stages in the vertical direction, heat treatment is performed in a reducing atmosphere, and the heat treatment is performed at 200 to 850 ° C, preferably 400 to 500 ° C. At a temperature of After the heat treatment, a carbon material (purified carbon material) from which active hydrogen oxide has been removed is obtained. Note that the above heat treatment is performed in a reducing atmosphere, but the conditions of the reducing atmosphere are preferably a hydrogen gas or a mixed gas obtained by diluting hydrogen with an inert gas, and such a mixed gas is industrially used. If implemented, NH₃Fe gas₂O₃3H decomposed with catalyst₂+ N₂Mixed gas is available. It is sufficient that the flow rate of the hydrogen gas is about 0.2 to 0.5 liter / min per 100 g of carbon.
[0034]
Here, a conventional method for removing residual active hydrogen oxide will be described.
A conventional method for removing residual active hydrogen oxide is to mix a carbon material and a transition metal powder or a transition metal compound in a powder form, sufficiently disperse the mixture, and then perform a heat treatment in a reducing atmosphere. After the heat treatment, the carbon material and the transition metal powder are separated, the transition metal powder is recovered, and a carbon material from which active hydrogen oxide has been removed (refined carbon material) has been obtained.
[0035]
It is not necessary to separate the transition metal and the transition metal compound from the carbon material after the heat treatment. However, in the case where the transition metal and the transition metal compound are used as the carbon active material of the polarizable electrode of the electric double layer capacitor, the assembled polarizable electrode is used. In order to ensure the reliability of the above, it is preferable to separate the remaining transition metal or transition metal compound from the carbon material.
[0036]
That is, even if transition metals such as Fe, Ni, and Co exist in the carbon material in a metal state, no special problem occurs if the electric double layer capacitor is made of an ideal electrolyte solution. In fact, even in the case of an electric double layer capacitor made of a carbon material in which a transition metal remains, no defect is recognized at the beginning of the charge / discharge test. However, when used for a long period of time, a decrease in capacitance, an increase in internal resistance, and a decrease in charge / discharge efficiency due to an increase in reactive current may be observed. This is because electrolyte ions BF₄ ⁻Is known to react slowly in the presence of water to form various fluorine-containing acids including HF. Therefore, the fluorine-containing acid generated by these reactions reacts with the transition metal, and To generate various kinds of electrochemical reactions.
[0037]
In addition, components such as an electric double layer capacitor and a Li-ion battery are designed so as not to contain water as much as possible, but it is difficult to completely remove water. On the other hand, in the case where water that has changed its form, that is, hydrogen contained in COOH, CHO, and OH, is present instead of Free water, an electrochemical reaction occurs when the apparatus is operated at a relatively high voltage (for example, 2.5 V or more). May occur, and as a result, free water may be gradually generated. As described above, it is inevitable that a small amount of water exists in components such as an electric double layer capacitor and a Li-ion battery. Therefore, this small amount of water causes BF₄ ⁻Even if a fluorine-containing acid is generated from, no problem occurs without a transition metal that reacts with the fluorine-containing acid. Therefore, it is desirable that no transition metals such as Fe, Ni, and Co remain in the carbon material.
[0038]
When fine particles of a ferromagnetic material such as Fe, Ni, and Co remain in the carbon material, when the transverse relaxation time is measured by pulse NMR described later, these fine particles of the ferromagnetic material reduce the magnetic field uniformity in the vicinity. Transverse relaxation time T measured by pulsed NMR₂Is observed as a transverse relaxation time shorter than the original value.
[0039]
A method of separating and recovering the transition metal powder may be a method in which the transition metal powder is separated according to a remarkable difference in physical properties between carbon and the transition metal. Generally, differences in density can be exploited. If the transition metal is a ferromagnetic material of Fe, Ni, or Co or an alloy of these ferromagnetic materials, they can be separated by a difference in magnetism.
[0040]
Furthermore, when a transition metal compound is used, it is generally assumed that the transition metal compound is reduced during the heat treatment and is mostly in the state of a transition metal and acts. After the heat treatment, the transition metal compound can be separated by a magnet in the case of a ferromagnetic material as in the case of the transition metal. be able to.
[0041]
That is, in the conventional method of mixing the transition metal powder or the transition metal compound, it is necessary to go through a complicated process for separating the carbon material from the transition metal powder or the transition metal compound after the heat treatment.
[0042]
In the method for continuously removing residual active hydrogen oxide of the present invention, a step of separating and removing a transition metal or a transition metal compound from a carbon material is not required. The present invention is characterized in that in the heat treatment in a reducing gas, a transition metal sieve is used instead of using transition metal powder.
[0043]
In the past cases, it has been found that in the case where fine metal powders of Fe, Ni, and Co, or these compounds are decomposed during high-temperature treatment to precipitate a metal, there is a so-called spill over effect. . The spillover effect is a phenomenon that occurs when a metal such as a transition metal element Co, Ni, Fe, Cu, Mo, Cr, Mn, or a sulfide thereof is used as a carrier in a region of an activated carbon catalyst. And the gaseous molecular H₂Is reversibly dissociated at the metal interface, becomes atomic H, and flows out onto carbon (for example, Science Dictionary, "Spillover"; edited by Yuzo Sanada et al., "New Edition Activated Carbon Basics and Applications", pp. 162 (1995); K. Fujimoto, S. Tokyo, Proceeding of the 7th International Congress on Catalysis Tokyo, pp. 235 (1980)).
[0044]
In the first place, spillover means "spillover" from a dissociation reaction active site where molecular hydrogen on the surface of a transition metal becomes active atomic hydrogen. Thus, for a transition metal powder of the same weight, if the transition metal is better dispersed, the smaller the particle size, the greater the number of active sites and the smaller the spread of spillover to carbon, and consequently the smaller the carbon. Can be supplied with a high concentration of active hydrogen from nearby active points. Then, this active hydrogen is bonded to carbon, and becomes “hydrogen directly bonded to the carbon skeleton” represented by a short relaxation time component amount described later.
[0045]
The spread of the spillover will be described by taking as an example a case where nickel fine particles having a diameter d of 3 μm are used as the transition metal powder. The mixing ratio between the nickel fine particles and the carbon material was 1: 100 by weight. It has been confirmed that when the heat treatment is performed under these conditions, the remaining active hydrogen oxide in the carbon material can be almost completely removed.
[0046]
From the following formula (1), n = 1.01 × 10¹⁰Individual.
1 = (πd³/ 6) × ρ_Ni× n (1)
(Ρ_Ni= 7g / cm³, D = 3 × 10^-4cm)
The volume V of 100 g of the carbon material is V = 143 cm from the following equation.³It is.
V = 100 / ρ_C      ... (2)
(Ρ_C= 0.7g / cm³)
[0047]
From the above, the carbon material capable of receiving the supply of the active hydrogen flowing out from one nickel fine particle is v = V / n = 1.41 × 10^-8cm³Becomes
[0048]
Thus, the reach L of the atomic H that spills over from the nickel fine particles is L = v^1/3= 24.1 μm. However, it is difficult to consider that the nickel fine particles are actually 100% monodispersed in the carbon material. Further, considering that the carbon material having a diameter of about 100 μm is treated, the reaching range L is at least one order of magnitude larger. It seems to be.
[0049]
As can be seen from the above formula (1), in the conventional removal of active hydrogen oxide, the amount of transition metal used is reduced by dispersing the transition metal as finely and uniformly as possible when mixing the carbon material and the transition metal. It was possible to reduce it. From this fact, it is presumed that the transition metal used in the experimental examples of the present invention may be influenced by the particle diameter of the transition metal rather than the activity of the transition metal itself.
[0050]
That is, in the conventional method of mixing the carbon material and the transition metal powder, it was necessary to spatially disperse the transition metal in the carbon material in order to obtain more spillover active sites. On the other hand, in the continuous removal method of the present invention, the carbon material sequentially moves from the upper stage to the lower stage of the transition metal sieve in which the carbon material is stacked in multiple layers in the vertical direction, in other words, the carbon material is moved to the transition metal sieve. By sufficient contact, the purpose of obtaining many spillover active sites has been achieved. This can be interpreted as temporally dispersing the transition metal with respect to the spatial dispersion using the transition metal powder. In order to uniformly generate the spillover phenomenon with respect to the entire amount of the carbon material, that is, to remove the remaining active hydrogen oxide uniformly in the entire amount of the carbon material, increase the contact frequency between the carbon material and the transition metal as much as possible, In addition, it is desirable to use a method in which the entire amount of the carbon material uniformly contacts the transition metal.
[0051]
Next, a pulse NMR method was used to quantitatively evaluate the amount of active hydrogen oxide present on carbon.¹The measurement of H resonance will be described. Lateral relaxation time T obtained by measurement₂= 10 to 50 μsec (Gauss type) short relaxation time component and transverse relaxation time T₂= 55 to 400 µsec (Lorentze type) The amount of active hydrogen oxide can be determined from the amount of the medium relaxation time component as follows.
[0052]
FIG. 4 shows an outline of a method of preparing a carbon sample for obtaining each relaxation time component using the pulse NMR method. That is, in a vacuum heating and baking furnace adjacent to a glove box having a dew point temperature of about -80 ° C, a small amount of a sample is collected in a deep-bottom glass sample bottle, put in a SUS deep-bottom bat, and gently put a lid on and slowly put it. And bake out.
[0053]
After the baking process, the sample is taken out from the inner door of the glove box, and as shown in FIG. 4, the sample is packed in a 10 mmφ NMR sample tube and fixed with a PTFE inner stopper. The center of the inner plug is filled with glass filter fibers to prevent the sample powder from coming out due to the flow of the internal gas during insertion.
[0054]
Plug with a special sample cap, put it in a laminated plastic bag, and clamp.
[0055]
Take out of the glow box and heat seal.
[0056]
Store in the above state, open the seal just before the measurement, take out the sample, and measure. The sample filling length (L) and the net carbon weight (W) are used for sample filling correction.
[0057]
By pulse NMR method¹The measurement of H resonance is performed as follows.
A second pulse having a phase difference of 90 ° is given at a measurement frequency of 25 MHz, a pulse width Pwl: 2.0 μsec, and a pulse interval Pil: 8.0 μsec, and an echo signal after a pulse interval of 2 Pil is observed. This operation is repeated for the number of repetitions Scans: 128 to 512 at a repetition time Rep: 2.0 sec, and the data is accumulated.
[0058]
With the pulsed NMR device in the powder state as described above,¹When H nuclear resonance is performed, an attenuation signal in which two or three components having different relaxation times are superimposed is observed. One is the lateral relaxation time T₂Is a short component of 10 to 50 μsec, which can be approximated by a resonance line showing a Gaussian distribution. This component is a component which does not change even if this carbon is fired at 800 ° C., and is a component consisting of hydrogen directly bonded to the carbon skeleton. In addition, the lateral relaxation time T₂Has a medium relaxation time component having a Lorentze-type distribution of 55 to 400 μsec, which is a component that does not easily disappear even if it is simply dried by heating under vacuum. This corresponds to chemically adsorbed water and is caused by a functional group of oxygen and hydrogen such as COOH, CHO, and OH. Also, the component T having a longer relaxation time₃Hydrogen due to physically adsorbed water of 500 to 2000 μsec is also observed, but is largely removed by the above-mentioned heating and vacuum drying.
[0059]
In the present invention, the above “hydrogen directly bonded to the carbon skeleton” is referred to as “T₂= 10 to 50 μsec (Gauss type) short relaxation time component ”and“ hydrogen attributable to a hetero element-containing functional group containing oxygen and hydrogen such as COOH, CHO, and OH ”, that is, active hydrogen oxide is referred to as“ T₂= Medium relaxation time component of 55 to 400 µsec (Lorentze type) ”.
[0060]
That is, “T₂= 55 to 400 μsec (Lorentze type), and the active site in carbon is terminated or blocked by hydrogen by heat treatment in a reducing atmosphere (such as in a stream of hydrogen). Since “hydrogen directly bonded to the carbon skeleton” is generated, “T₂= 10 to 50 μsec (Gauss type) short relaxation time component ”is estimated to increase. Therefore, as a purified carbon material from which active hydrogen oxide has been removed obtained by the present invention, T₂= 10 to 50 μsec (Gauss type) for a short relaxation time component₂= 55 to 400 μsec (Lorentze type), the ratio of the medium relaxation time components, ie, “[T₂= 55-400 μsec (Lorentze type) medium relaxation time component] / [T₂= 10 to 50 μsec (Gaussian type short relaxation time component)] when it is used as a carbon active material for a polarizable electrode such as an electric double layer capacitor. This is desirable in that a stable product can be obtained without generating gas or forming a non-electrically conductive film and without increasing the internal resistance.
[0061]
In addition, the hydrogen directly bonded to the carbon generated when the active site in the carbon is terminated or blocked by hydrogen is converted into the active carbon in the carbon by oxygen or water in the air when the purified carbon material is taken out into the air after the treatment. The site is prevented from being converted into COOH, CHO, OH, etc. again.
[0062]
Next, an apparatus for continuously removing residual active hydrogen oxide which can be preferably used as a method suitable for the above-described method for continuously removing residual active hydrogen oxide will be described below.
[0063]
FIG. 5 is a diagram showing an outline of an apparatus for continuously removing residual active hydrogen oxide as one embodiment of the present invention. The continuous removal device of the present invention includes a transition metal sieve 2 stacked in multiple stages in the vertical direction, a carbon material supply port 3 for supplying a raw carbon material to the uppermost sieve, and a reducing gas to the lowermost sieve. And a reducing gas supply port 4 for supplying. The carbon material to be treated is supplied from the raw material carbon material supply port 3 to the uppermost sieve, and is sequentially sifted down from the upper stage to the lower stage by the transition metal sieve 2 stacked in multiple stages in the vertical direction. The refined carbon material sieved from the lowermost sieve is discharged from the refined carbon material discharge port 8 to the outside of the processing apparatus.
[0064]
The reducing gas is supplied to the inside of the apparatus from the reducing gas supply port 4, flows from the lowermost screen to the uppermost screen, and finally discharged from the reducing gas discharge port 5 provided at the upper part of the apparatus. Is done. From the reducing gas outlet 5, H₂Together with reducing gas such as CO₂, COOH, CO and the like are also discharged.
[0065]
The sieve 2 is made of a transition metal, and specifically includes metal elements of each of the groups 3 to 11 in the periodic table described above. In particular, Fe, Ni, Co, Cu, Mo, Cr, Mn, and Th Preferably, there is. The transition metal used may be any of these simple metals, or an alloy containing these metal elements, for example, a material such as permalloy (Fe—Ni) or iron cobalt (Fe—Co). .
[0066]
Further, the sieves 2 are vertically stacked in multiple stages. The number of the screens 2 to be stacked is not particularly limited, but is preferably 10 to 15 steps from the viewpoint of maximizing the contact frequency between the carbon material and the transition metal. A heater 6 is provided outside the multi-layered sieve 2.
[0067]
The sieve 2 is preferably cylindrical, and a hole is provided in the center of the cylindrical sieve, and a rotary column 7 penetrating the hole is provided. Inside the sieve, a comb-shaped rotor fixed to the rotary column 7 Preferably, 10 is provided. The comb-shaped rotator 10 rotates with the rotation of the rotating column 7. FIG. 6 is a plan view showing an outline of an embodiment of the sieve 2, and FIG. 7 is a sectional view showing an outline of an embodiment of the comb-shaped rotator 10.
[0068]
The bottom surface of the sieve 2 is constituted by a mesh. The entire bottom surface may be a mesh, but from the viewpoint of sufficiently securing the contact frequency between the carbon material and the transition metal, only a part of the bottom surface is meshed so that the carbon material sufficiently contacts the sieve made of the transition metal. Preferably, the other parts are flat. For example, as shown in FIG. 6, on the bottom surface of the sieve 2, a fan-shaped portion centered on the rotating column is formed by a mesh. In this case, the central angle of the fan-shaped mesh portion 9 is preferably 15 degrees to 90 degrees, and the mesh is preferably a mesh having a size such that a carbon material having a particle diameter of 125 μm or less passes therethrough. The mesh portion 9 is also preferably made of a transition metal, and specific examples thereof include the same elements as those of the sieve 2.
[0069]
It is preferable that a comb-shaped rotor 10 is fixed to the rotating column 7 inside each sieve, and a comb blade is provided so as to face the bottom surface of the cylindrical sieve 2. A plurality of comb rotors 10 can be provided inside each sieve. Further, a comb-shaped projection 11 may be provided on the bottom surface of the cylindrical sieve 2 so as to mesh with a comb blade of the comb-shaped rotor 10. The comb-shaped rotator 10 provided inside the cylindrical sieve 2 at each stage rotates with the rotation of the rotating column 7. It is preferable that all the comb-shaped rotators 10 in each stage rotate simultaneously in one direction, and the speed at which the comb-shaped rotator 10 rotates is 0.05 rpm to 0.2 rpm. The comb-shaped rotator 10 and the comb-shaped protrusions 11 are also preferably made of a transition metal, and specifically include the same elements as those of the sieve 2.
[0070]
When the cylindrical sieves 2 are provided in multiple stages, it is preferable that the mesh positions of the cylindrical sieves 2 are provided so as not to overlap with the mesh positions of the cylindrical sieves 2 vertically adjacent thereto. With such a configuration, the carbon material sieved from the upper stage is not sieved to the lower stage as it is, but at least to some extent inside the sieve of each stage with the rotation of the comb-shaped rotor 10. Move while contacting the bottom surface of the sieve 2.
[0071]
The contact frequency between the carbon material and the transition metal is determined by the number of stages of the sieve 2, the area of the mesh constituting the sieve 2, the diameter of the mesh (mesh), the particle diameter of the raw carbon material, the rotation speed of the comb-shaped rotor 10, and the like. Can be controlled by Economical operating conditions may be determined in consideration of electric power for maintaining the optimal temperature of the heat treatment, the amount of blowing hydrogen gas, and the like. By continuously feeding the raw material carbon material, continuous removal of active hydrogen oxide can be realized. In addition, as a result of quantifying the amount of active hydrogen oxide in the purified carbon material by the pulse NMR method, if the remaining active hydrogen oxide is not sufficiently removed, re-enter the removing device and subsequently perform the removal treatment. Is also possible.
[0072]
In the above, one embodiment of the continuous removing device for residual active hydrogen oxide of the present invention was described. However, the continuous removing device of the present invention is not limited to this. For example, a mesh (mesh) may be used in each sieve. It is also possible to sieve the carbon material by providing a number of small-diameter holes in the bottom of the sieve, and to change the rotation of the comb-shaped rotor and vibrate the sieve to sift the carbon material. It is also possible. In any of the apparatuses, it is important that the transition metal is temporally dispersed in the carbon material, that is, that the transition metal sieve and the carbon material are sufficiently in contact with each other and that the spillover active point is sufficiently ensured. Furthermore, if the time distribution of the transition metal in the carbon material is sufficient, it is possible to provide sieves in multiple stages in the lateral direction.
[0073]
Next, a specific example using the continuous apparatus for removing active hydrogen oxide shown in FIGS.
The particle size of the carbon material to be treated is 100 μm, the sieve is made of nickel, the number of stages is 13, the mesh (mesh) diameter is 125 μm, the central angle of the fan-shaped mesh portion is 60 degrees, and the comb-shaped rotor is When the processing was performed under the condition that the rotation speed was 0.1 rpm, the time required until the entire amount of the raw carbon material charged into the raw material input port was discharged from the purified carbon material discharge port was about 21 hours. This is a time sufficient for the temporal dispersion of the carbon material of the transition metal.
[0074]
The treated carbon material (purified carbon material) obtained according to the method of the present invention from which active hydrogen oxide has been removed can be used as a carbon active material for a polarizable electrode such as an electric double layer capacitor. Such a polarizable electrode can be manufactured by the same method as a conventional polarizable electrode for an electric double layer capacitor. For example, in order to produce a sheet-like electrode, the obtained purified carbon material is crushed to about 5 to 100 μm to adjust the particle size, and then, as a conductive auxiliary for imparting conductivity to carbon powder, for example, carbon. Black and a binder such as polytetrafluoroethylene (PTFE) are added, kneaded, and formed into a sheet by pressure stretching. As the conductive auxiliary agent, powdered graphite or the like can be used in addition to carbon black (for example, acetylene black). As the binder, besides PTFE, PVDF, PE, PP, or the like can be used. Can be. At this time, the mixing ratio of the non-porous carbon, the conductive auxiliary agent (carbon black) and the binder (PTFE) is generally about 10: 0.5 to 1.0: 0.25 to 0.5. It is.
[0075]
A current collector is attached to the polarizable electrode obtained in this way, and a positive electrode and a negative electrode are formed by superimposing via a separator, and then impregnated with an organic solvent containing an electrolyte to assemble into an electric double layer capacitor. Can be.
[0076]
When a non-porous carbon is used as the carbon active material, the resulting electric double layer capacitor has substantially no interface forming the electric double layer at the beginning of the capacitor assembly, but is applied during the initial charging. When the voltage exceeds a certain threshold value, the electrolyte ions enter the carbon structure with the solvent and generate an interface for forming an electric double layer for the first time, and thereafter this interface is maintained by the hysteresis effect, and as an electric double layer capacitor In order to function effectively, it is necessary to first apply and charge a voltage 10 to 20% higher than the rated voltage (normally about 3.5 to 3.75 V). However, when activated carbon is used as the carbon active material, an electric double layer can be formed immediately upon assembling, and the electric double layer capacitor can be used as it is without necessarily performing an operation such as initial charging. can do.
[0077]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the removal method of the residual active hydrogen oxide of this invention, it is not necessary to isolate | separate a transition metal and a transition metal oxide from a carbon material, and it becomes possible to obtain a refined carbon material simply and efficiently. Further, the raw carbon material can be continuously processed, and automation of mass processing of the carbon material is realized.
[Brief description of the drawings]
FIG. 1 Interlayer distance d by post heat treatment of various non-porous coals₀₀₂5 is a graph showing a change in the graph. The vertical axis represents the interlayer distance d obtained by X-ray diffraction (XRD).₀₀₂The heat treatment temperature is shown on the horizontal axis. In addition, at the beginning of the horizontal axis, calcined coal and the interlayer distance d at the time of the KOH activation treatment are shown.₀₀₂Also shown. From the figure, it can be seen that the interlayer distance shows the largest distance after the KOH activation treatment and becomes narrower by the subsequent heat treatment. As a general tendency, the higher the temperature, the more the interlayer distance d₀₀₂Indicates a small value. In addition, each plot shows the following carbon materials. ▼: Non-porous coal D prepared from infusible petroleum pitch as raw coal, ▽: Non-porous coal A prepared from petroleum needle coke as raw coal, ■: Non-porous prepared from petroleum needle coke as raw coal Charcoal C, □, ▲ and ●: Non-porous coal B prepared from petroleum-based needle coke as raw coal, which has different pre-heat treatment conditions and activation treatment conditions.
FIG. 2 is a graph showing initial charging characteristics of a non-porous coal when a heat treatment temperature is changed. The charge / discharge characteristics were measured while gradually increasing the applied voltage from 0.5 V to 3.75 V in increments of 0.5 V to 0.25 V, and similarly measured while gradually decreasing the voltage from 3.75 V to 0.5 V. It shows the results. The measured sample is a non-porous coal B prepared from petroleum-based needle coke as a raw coal and heat-treated in a reducing atmosphere. The meaning of “+ 504H” added to the sample to be measured means at 500 ° C. Indicates that the heat treatment was performed in hydrogen for a time. According to the figure, each sample shows a higher capacitance when the applied voltage is reduced due to the hysteresis effect than when the applied voltage is increased, but the higher the heat treatment at a higher temperature, the higher the rising voltage and the smaller the capacitance. I understand. This is the interlayer distance d₀₀₂It is caused by
FIG. 3 is a diagram schematically illustrating a method for preparing a non-porous carbon and a purified carbon material.
FIG. 4 is a diagram showing an outline of preparation of a sample for pulse NMR measurement.
FIG. 5 is a diagram showing an outline of an apparatus for continuously removing residual active hydrogen oxide as one embodiment of the present invention.
FIG. 6 is a plan view showing an outline of an embodiment of the sieve 2;
FIG. 7 is a cross-sectional view showing an outline of an embodiment of the comb-shaped rotator 10.
[Explanation of symbols]
1 Continuous removal device for residual active hydrogen oxide
2 Cylindrical sieve
3 Raw material carbon material inlet
4 Reducing gas supply port
5 Reducing gas outlet
6 heater
7 rotating column
8 Refined carbon material outlet
9 mesh part
10 Comb-shaped rotor
11 Comb projection

Claims (7)

A method of continuously removing residual active hydrogen oxide present in a carbon material by heat-treating the carbon material in a reducing gas stream, wherein the carbon material is a transition metal sieve in which the carbon material is vertically stacked in multiple stages. A method for continuously removing residual active hydrogen oxide, comprising sequentially sieving from the upper stage to the lower stage. The residual active hydrogen oxide according to claim 1, wherein the carbon material is activated carbon, porous carbon or non-porous carbon, and the carbon material from which residual active hydrogen oxide has been removed is used as a carbon active material for a polarizable electrode. Continuous removal method. Reducing gas, according to claim 1 or 2 continuous method of removing residual activity hydrogen peroxide according a 3H 2 ₊ N ₂ mixed gas obtained by the hydrogen or ammonia cracking with the catalyst. The method for continuously removing residual active hydrogen oxide according to any one of claims 1 to 3, wherein the transition metal is any one of Fe, Ni, Co, Cu, Mo, Cr, Mn, and Th or an alloy containing the element. . The method for continuously removing residual active hydrogen oxide according to any one of claims 1 to 4, wherein the temperature during the heat treatment is from 200C to 850C. An apparatus for continuously removing remaining active hydrogen oxide present in a carbon material by heat-treating the carbon material in a reducing gas stream, comprising a transition metal sieve vertically stacked in multiple stages, and a top stage. A continuous carbon material supply port for supplying a raw material carbon material to a sieve, and a reducing gas supply port for supplying a reducing gas to a lowermost sieve. The sieve has a cylindrical shape, a hole is provided in the center of the cylindrical sieve, and a rotating column penetrating the hole, a comb-shaped rotor fixed to the rotating column is provided inside the sieve, and the comb-shaped 7. The continuous removing device for residual active hydrogen oxide according to claim 6, wherein the rotor rotates with the rotation of the rotary column.

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