CARBONACEOUS MATERIAL AND METHOD FOR PRODUCING SAME

Abstract

The present invention relates to a carbonaceous material which is derived from a plant, having a specific surface area of 1000 to 1800 m.sup.2/g as measured by a BET method, a hydrogen element content of 0.25% by mass or less and an oxygen element content of 1.5% by mass or less.

Claims

1. A carbonaceous material which is derived from a plant, the carbonaceous material having a specific surface area of 1000 to 1800 m.sup.2/g as measured by a BET method, a hydrogen element content of 0.25% by mass or less and an oxygen element content of 1.5% by mass or less.

2. The carbonaceous material according to claim 1, wherein a potassium element content is 500 ppm or less.

3. The carbonaceous material according to claim 1, wherein an iron element content is 200 ppm or less.

4. A method for producing a carbonaceous material according to claim 1, comprising: attaching an alkali metal hydroxide onto plant-derived activated carbon having an average particle diameter of 100 to 10000 um and a specific surface area of 900 to 2000 m.sup.2/g as measured by a BET method to obtain an alkali-metal-hydroxide-attached activated carbon; and performing a gas-phase demineralizing by heat-treating the alkali-metal-hydroxide-attached activated carbon at 500 to 1250 C. in an inert gas atmosphere comprising a halogen compound to obtain the carbonaceous material.

Description

EXAMPLES

[0077] Hereinbelow, the present invention will be described specifically by way of examples. However, these examples are not intended to limit the scope of the present invention.

[0078] The methods for measuring the values of physical properties of a carbonaceous material and activated carbon will be described below. However, the values of the physical properties mentioned in the present specification including the section EXAMPLES were determined by the following methods.

[Measurement of BET Specific Surface Area]

[0079] A specific surface area was determined by a BET method for measuring a nitrogen adsorption isothermal line of a sample using a nitrogen adsorption amount measurement device BELSORP-MAX manufactured by MicrotracBel Corporation.

[0080] [Elemental Analysis]

[0081] An elemental analysis was carried out using an oxygen-nitrogen-hydrogen analysis device EMGA-930 manufactured by HORIBA, Ltd.

[0082] The detection method of the device was an oxygen: non-dispersive infrared method (NDIR), a nitrogen: thermal conductivity detection method (TCD) or a hydrogen: non-dispersive infrared method (NDIR). The correction was carried out using an (oxygen-nitrogen) Ni capsule, TiH.sub.2 (H standard sample) and SS-3 (N, O standard sample), 20 mg of a sample, of which the water content had been measured as a pretreatment at 250 C. for about 10 minutes, was placed in the Ni capsule, the sample was degassed in an elemental analysis device for 30 seconds, and then the measurement was carried out. In the test, the analysis was carried out for three samples, and an average value was employed as an analysis value.

[Raman Spectra]

[0083] Raman spectra were measured using LabRAM ARAMIS manufactured by HORIBA, Ltd. using a light source having a laser wavelength of 532 nm. In the test, particles were randomly sampled from three areas in each sample, and then the measurement was carried out with respect to the two areas. The conditions for the measurement were as follows: the wavelength range was 50 to 2000 cm.sup.1, the integration frequency was 1000 times, and an average value of values measured in six areas in total was calculated as a measurement value. The G band half-value width was measured after subjecting the spectra obtained under the above-mentioned measurement conditions to the peak separation between a D band (around 1360 cm.sup.1) and a G band (around 1590 cm.sup.1) by Gaussian function fitting. The R value was determined as an intensity ratio I.sub.D/I.sub.G of the intensity of a peak of D band to the intensity of a peak of G band (i.e., a (D band peak intensity)/(G band peak intensity)).

[Measurement of Average Particle Diameter]

[0084] The average particle diameter (particle size distribution) of a sample was measured by a laser scattering method in the following manner. A sample was introduced into an aqueous solution containing 0.3% by mass of a surfactant (ToritonX100 manufactured by Wako Pure Chemical Industries Ltd.), and then the solution was treated with an ultrasonic cleaner for 10 minutes or longer to disperse the sample in the aqueous solution. The particle size distribution was measured using the resultant liquid dispersion. The measurement of the particle size distribution was carried out using a particle diameter-particle size distribution measurement device (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.). The D50 value was a particle diameter at which the cumulative volume became 50%, and this value was employed as an average particle diameter.

[Measurement of Contents of Metal Elements]

[0085] The method for measuring the content of sodium element, the content of potassium element and the content of iron element content was carried out in the following manner. A carbon sample containing sodium element, potassium element and iron element respectively in predetermined amounts was prepared, and then a calibration curve relating to the relationship between the intensities of sodium and potassium K lines and the contents of sodium element and potassium element and a calibration curve relating to the relationship between the intensity of iron K line and the content of iron element were prepared using a fluorescent X-ray analysis device. Subsequently, the sample was subjected to a fluorescent X-ray analysis to measure the intensities of sodium K line, potassium K line and iron K line, and then the sodium element content, the potassium element content and the iron element content were determined from the previously prepared calibration curves.

[0086] The fluorescent X-ray analysis was carried out under the following conditions using LAB CENTER XRF-1700 manufactured by Shimadzu Corporation. A top irradiation-type holder was used, and the sample measurement area was set within a circle having a diameter of 20 mm. The placement of a sample to be measured was carried out as follows: 0.5 g of the sample was placed in a polyethylene-made container having an inner diameter of 25 mm, then the back of the sample was pressed with a plankton net, then the measurement surface of the sample was covered with a polypropylene-made film, and then the measurement was carried out. An X-ray source was set at 40 kV and 60 mA. With respect to potassium, LiF (200) was used as an analyzing crystal, a gas flow-type proportional counter tube was used as a detector, and an area in which the 2e was 90 to 140 was measured at a scanning rate of 8/min. With respect to iron, LiF (200) was used as an analyzing crystal, a scintillation counter was used as a detector, and an area in which the 2 was 56 to 60 was measured at a scanning rate of 8/min.

Production Example

(Preparation of Raw Material Activated Carbon)

[0087] A coconut-shell-derived carbonaceous precursor having a BET specific surface area of 500 m.sup.2/g was activated with water vapor at 900 C. for 90 minutes in an activation gas that was prepared by feeding steam to a kerosene combustion gas (a mixed gas at a mixing ratio of H.sub.2O, CO.sub.2, CO, N.sub.2=20:10:1:100) so as to adjust the water vapor partial pressure to 35% to prepare coconut-shell-derived raw material activated carbon. The BET specific surface area of the raw material activated carbon was 1500 m.sup.2/g.

Example 1

(Preparation of Carbonaceous Material)

[0088] A carbonaceous material was prepared in accordance with the conditions shown in Table 1 in the following manner. The coconut-shell-derived raw material activated carbon produced in Production Example 1 was ground to obtain coconut-shell-derived raw material activated carbon having an average particle diameter of 2.360 to 0.850 mm. An aqueous solution prepared by dissolving 20 g of sodium hydroxide in 100 g of ion-exchanged water was added to 100 g of the ground coconut-shell-derived raw material activated carbon so that the ground coconut-shell-derived raw material activated carbon was immersed in and impregnated with the aqueous solution for 1 hour, and then the resultant product was dried at 80 C. using a hot-air dryer for 12 hours. The activated carbon obtained by the drying was treated at a treatment temperature of 870 C. for 50 minutes while feeding a nitrogen gas containing 2 vol % of a hydrogen chloride gas at a flow rate of 10 L/min. Subsequently, only the feeding of the hydrogen chloride gas was halted, and the activated carbon was heat-treated at a treatment temperature of 870 C. for 50 minutes to obtain a carbonaceous material. The resultant carbonaceous material was crudely pulverized with a ball mill so as to have an average particle diameter 8 m, and the resultant product was pulverized with a compact jet mill (co-jet system -mkIII) and then classified to obtain a carbonaceous material (1) having an average particle diameter of 4 m.

Example 2

[0089] The same procedure as in Example 1 was carried out, except that the treatment time in the gas-phase demineralizing step was set to 150 minutes instead of 50 minutes. As a result, a carbonaceous material (2) having an average particle diameter of 4 m was prepared.

Example 3

[0090] The same procedure as in Example 1 was carried out, except that each of the treatment temperature in the gas-phase demineralizing step and the subsequent heat treatment temperature was set to 1020 C. instead of 870 C. As a result, a carbonaceous material (3) having an average particle diameter of 4 m was prepared.

Example 4

[0091] A carbonaceous material was prepared in accordance with the conditions shown in Table 1 in the following manner. The coconut-shell-derived raw material activated carbon produced in Production Example 1 was ground to obtain coconut-shell-derived raw material activated carbon having an average particle diameter of 2.360 to 0.850 mm. An aqueous solution prepared by dissolving 25 g of sodium hydroxide in 100 g of ion-exchanged water was added to 100 g of the ground coconut-shell-derived raw material activated carbon so that the ground coconut-shell-derived raw material activated carbon was immersed in and impregnated with the aqueous solution for 1 hour, and then the resultant product was dried at 80 C. using a hot-air dryer for 12 hours. The activated carbon obtained by the drying was treated at a treatment temperature of 870 C. for 100 minutes while feeding a nitrogen gas containing 2 vol % of a hydrogen chloride gas at a flow rate of 10 L/min. Subsequently, only the feeding of the hydrogen chloride gas was halted, and the activated carbon was heat-treated at a treatment temperature of 870 C. for 50 minutes to obtain a carbonaceous material. The resultant carbonaceous material was crudely pulverized with a ball mill so as to have an average particle diameter 8 m, and the resultant product was pulverized with a compact jet mill (co-jet system -mkIII) and then classified to obtain a carbonaceous material (4) having an average particle diameter of 3.8 m.

Example 5

[0092] A carbonaceous material was prepared in accordance with the conditions shown in Table 1 in the following manner. The coconut-shell-derived raw material activated carbon produced in Production Example 1 was ground to obtain coconut-shell-derived raw material activated carbon having an average particle diameter of 2.360 to 0.850 mm. An aqueous solution prepared by dissolving 40 g of sodium hydroxide in 100 g of ion-exchanged water was added to 100 g of the ground coconut-shell-derived raw material activated carbon so that the ground coconut-shell-derived raw material activated carbon was immersed in and impregnated with the aqueous solution for 1 hour, and then the resultant product was dried at 80 C. using a hot-air dryer for 12 hours. The activated carbon obtained by the drying was treated at a treatment temperature of 870 C. for 100 minutes while feeding a nitrogen gas containing 2 vol % of a hydrogen chloride gas at a flow rate of 10 L/min. Subsequently, only the feeding of the hydrogen chloride gas was halted, and the activated carbon was heat-treated at a treatment temperature of 870 C. for 50 minutes to obtain a carbonaceous material. The resultant carbonaceous material was crudely pulverized with a ball mill so as to have an average particle diameter 8 m, and the resultant product was pulverized with a compact jet mill (co-jet system -mkIII) and then classified to obtain a carbonaceous material (5) having an average particle diameter of 3.5 m.

Comparative Example 1

[0093] The same procedure as in Example 1 was carried out, except that a nitrogen gas that did not contain a hydrogen chloride gas was used in place of the nitrogen gas containing a 2-vol % hydrogen chloride gas. As a result, a carbonaceous material (6) having an average particle diameter of 4 m was prepared.

Comparative Example 2

[0094] The same procedure as in Example 3 was carried out, except that a nitrogen gas that did not contain a hydrogen chloride gas was used in place of the nitrogen gas containing a 2-vol % hydrogen chloride gas. As a result, a carbonaceous material (7) having an average particle diameter of 4 m was prepared.

Comparative Example 3

[0095] The same procedure as in Example 1 was carried out, except that sodium hydroxide was not attached. As a result, a carbonaceous material (8) having an average particle diameter of 4 m was prepared.

TABLE-US-00001 TABLE 1 Gas-phase demineralizing step Hydrogen Heat treatment step chloride Nitrogen Treatment Nitrogen Treatment gas gas Temperature time gas Temperature time [vol %] [vol %] [ C.] [min] [vol %] [ C.] [min] Example 1 2 98 870 50 100 870 50 2 2 98 870 150 100 870 50 3 2 98 1020 50 100 1020 50 4 2 98 870 100 100 870 50 5 2 98 870 100 100 870 50 Comparative 1 100 870 50 100 870 50 Example 2 100 1020 50 100 1020 50 3 2 98 870 50 100 870 50

<Analysis of Carbonaceous Materials>

[0096] Next, each of the carbonaceous materials (1) to (8) was used as a sample, and the hydrogen element content, the oxygen element content, the metal element (sodium element, potassium element, iron element) content, the BET specific surface area and the R value of the sample were measured. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 BET Hydrogen Oxygen specific Raman element element Na element K element Fe element surface spectrum content content content content content area R value [mass %] [mass %] [ppm] [ppm] [ppm] [m.sup.2/g] [I.sub.D/I.sub.G] Example 1 0.117 1.053 113 164 48 1690 1.21 2 0.143 1.462 31 100 67 1610 1.27 3 0.097 0.866 73 285 25 1600 1.30 4 0.098 0.912 132 166 44 1660 1.22 5 0.096 0.856 211 244 42 1620 1.28 Comparative 1 0.471 1.889 404 13500 90 1310 1.13 Example 2 0.473 1.697 204 13000 90 1280 1.25 3 0.462 1.256 0 171 30 1690 1.19

[Production of Films Each Containing Carbon Material]

[0097] Each of the carbonaceous materials (1) to (8) produced in Examples 1 to 5 and Comparative Examples 1 to 3 was mixed with a styrene butadiene rubber (SBR) manufactured by JSR Corporation and carboxy methyl cellulose (CMC) manufactured by DSK Co., Ltd in water so that the (electrode material):SBR: CMC became 90:3:2 (by mass), thereby producing a slurry. The resultant slurry was applied onto a white glass slide with a bar coater, and then the resultant product was dried with hot air at 80 C. and then dried with a glass tube oven under a pressure-reduced atmosphere at 150 C. for 7 hours. In this manner, carbon-material-containing films (1) to (8) were obtained. The thickness of each of the carbon-material-containing films (1) to (8) was 100 m.

[0098] The sheet resistance of each of the carbon-material-containing films (1) to (8) was measured using Loresta-GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

<Analysis and Results of Tests>

[0099] The results of the sheet resistance measurement of the carbon-material-containing films (1) to (8) are shown in Table 3.

TABLE-US-00003 TABLE 3 Sheet resistance (/) Example 1 172 2 166 3 142 4 169 5 133 Comparative 1 900 Example 2 880 3 570

[0100] As shown in Table 3, when the carbonaceous materials (1) to (5) produced in Examples 1 to 5 were used, the sheet resistance values were greatly reduced and the improvement in electrical conductivity was observed compared with the cases where the carbonaceous materials (6) to (8) produced in Comparative Examples 1 to 3 were used.