JPH06293576A - Porous silica-carbon composite body and its production - Google Patents

Abstract

PURPOSE:To provide a new porous silica-carbon composite body which can be useful as an absorbent with the same ability as or more than activated carbon in order to increase the availability of silicon-accumulated biomass, and to provide the production method of the composite body. CONSTITUTION:This porous silica-carbon composite body is a fired body of carbonized silicon-accumulated biomass and an alkali metal compd. and has >=900m<2>/g BET surface area. The composite body is a porous silica-carbon composite body having >=900m<2>/g BET surface area and is obtd. by firing a mixture of carbonized silicon-accumulated biomass and an alkali metal compd. and then eluting and removing the alkali metal content from the fired body. The mixture of the carbonized silicon-accumulated biomass and the alkali metal compd. is fired at high temp. of >=400 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel porous silica-carbon composite using silicon-accumulated biomass as a raw material and a method for producing the same.

[0002]

[Prior art and its problems] Silicon-accumulated biomass such as rice husks and straw has been turned into industrial waste with the modernization of agriculture, and is returned to the land in the form of compost and other packaging materials and pulp. Raw materials, civil engineering materials, handicraft materials,
It is also used as a charcoal and as an oxygen scavenger in steel mills, but its use has been greatly expanded compared to the amount of emissions from agriculture. The present inventors sought to cultivate the utilization side by developing an adsorbent using silicon-accumulated biomass as a raw material. That is, 200 to 1 of silicon-accumulated biomass
After carbonization at 000 ℃, activated at 600 ~ 1200 ℃ in the atmosphere of steam, carbon dioxide gas, fuel waste gas containing steam, etc., succeeded in obtaining a porous carbonized product of BET surface area 100 ~ 300 m ² / g did. However, since the porous carbonized product obtained here has a significantly smaller BET surface area and the like as compared with the commercially available activated carbon, its adsorption performance is low, and the effective utilization of the silicon-accumulated biomass centered on the adsorbent intended by the present inventors is effective. I couldn't fulfill my purpose.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a novel porous silica-carbon composite which can be used as an adsorbent having an ability equal to or higher than that of activated carbon in order to enhance the utilization of silicon-accumulated biomass, and its composite. It is an object to provide a manufacturing method.

[0004]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, there is provided a porous silica-carbon composite comprising a carbonized product of silicon-accumulated biomass and a calcined product of an alkali metal compound and having a BET surface area of 900 m ² / g or more. Further, according to the present invention,
It is composed of a calcined product of a carbonized product of silicon-accumulated biomass and an alkali metal compound, in which the alkali metal content contained therein is eluted and removed, and the BET surface area is 9
A porous silica-carbon composite having a density of at least 00 m ² / g is provided. Furthermore, according to the present invention, a mixture of a carbonized product of silicon-accumulated biomass and an alkali metal compound is added to 40
Provided is a method for producing a porous silica-carbon composite, which comprises firing at a high temperature of 0 ° C or higher. Furthermore,
According to the present invention, after firing a mixture of a carbonized product of silicon-accumulated biomass and an alkali metal compound at a high temperature of 400 ° C. or higher, it is possible to elute and remove the alkali metal content remaining in the obtained fired product. A method for producing a composite of a characterized porous silica-carbon composite is provided. Furthermore, according to the present invention, after heating the mixture of the silicon-accumulated biomass and the alkali metal compound at 80 to 300 ° C.,
Provided is a method for producing a porous silica-carbon composite, which comprises calcination at a temperature of 300 ° C. or higher and washing the resulting calcination product with water. Furthermore, according to the present invention, there is provided an adsorbent comprising the porous silica-carbon composite. In addition, the silicon-accumulated biomass referred to in the present specification means
Plants containing silica components (silicon-accumulating plants) or parts thereof such as leaves and stems, specifically, rice husks or rice husks or straws, bamboo leaves, bagasse, corn and tokusa leaves or stems. And so on.

In order to obtain the porous silica-carbon composite of the present invention, first, the silicon-accumulated biomass is carbonized.
The carbonization treatment temperature is 300 ° C. or higher, preferably 350 to
It is 1000 ° C. The carbonization treatment atmosphere may be an atmosphere in which combustion of the silicon-accumulated biomass does not substantially occur,
An atmosphere in which air is shut off, an argon atmosphere or a nitrogen atmosphere,
Carbon dioxide gas atmosphere, steam atmosphere, etc. are generally adopted. In this carbonization treatment step, it is possible to suppress as much as possible the disappearance of the organic matter that constitutes the raw material biomass as a low-molecular compound due to thermal decomposition, and the carbon content contained in the raw material biomass remains in the carbonized product at the highest possible rate. It is important to let In the case of the present invention, the carbon content in the carbonized product is 40% by weight with respect to silica (SiO ₂ ).
As described above, it is preferable to set the content in the range of 50 to 60% by weight. When the proportion of carbon content in the carbonized product is less than the above range, the specific surface area of the finally obtained porous silica-carbon composite is significantly reduced. The carbon content in this case includes both volatile carbon content and fixed carbon content. As one method for obtaining a carbonized product having a high carbon content, when heat treating the raw material biomass, the temperature rising rate from room temperature to the heat treatment temperature is as low as possible, usually 1 to 100 ° C./minute, Preferably 1 to 20 ° C /
The heat treatment time after reaching the heat treatment temperature is 0 to
A method of shortening the time to about 5 hours can be shown. In this case, the smaller the rate of temperature rise, the higher the carbon residue rate. In the carbonization treatment of rice husks, when the heat treatment temperature is 400 to 900 ° C., the carbon content residual ratio is 52 to 54% at a temperature increase rate of 1 ° C./min, and the carbon content residual ratio is 40 at a temperature increase rate of 20 ° C./min. Results of ~ 49% can be obtained.

The carbonized product of the silicon-accumulated biomass obtained as described above is calcined in the form of a mixture with an alkali metal compound. Baking temperature is 300 to 1000
C., preferably 400 to 1000.degree. As the alkali metal compound, a sodium compound or a potassium compound is used, but a potassium metal compound is particularly preferable.
As the alkaline compound, hydroxide, carbonate, sulfate,
Various compounds such as halides can be used, but hydroxides are preferably used. Further, it is also a preferred embodiment to use an alkali metal hydroxide and an alkali metal carbon salt together. The alkali metal compound is added and mixed to the carbonized product, but in this case, the alkali metal compound is in the form of powder or
It is added in granular or solution form. Further, the mixture of the carbonized product and the alkali metal compound can be obtained by adding the alkali metal compound to the previously formed carbonized product as described above, or the addition of the alkali metal compound to the silicon accumulated biomass. It can also be obtained by mixing and carbonizing this mixture. If the amount of the alkali metal compound added is too small, the BET surface area is reduced and the adsorption ability is lowered, resulting in a decrease in product quality, and if the amount added is too large, the yield of the porous silica-carbon composite is reduced. In general,
For 1 part by weight of the carbonized product, 0.
The amount is 1 to 7 parts by weight, preferably 3 to 5 parts by weight. The carbonized product to which the alkali metal compound is added, in a firing furnace such as a rotary kiln or a fluidized furnace,
Baking is performed at 300 to 1000 ° C., preferably 700 to 900 ° C. for 0.5 minutes to 5 hours, preferably 3 to 120 minutes.

A preferred method of firing the mixture of the carbonized product and the alkali metal compound is to add 350 to 4 to the mixture.
At least 10 at a temperature of 50 ° C, preferably about 400 ° C
After firing for 70 minutes, preferably 20-40 minutes, 700-
This is a method in which the temperature is raised to 900 ° C. and firing is performed at this temperature for 0 to 200 minutes. The firing atmosphere can be an inert gas such as nitrogen gas, argon gas, carbon dioxide gas, steam, air, combustion waste gas, or the like. When the mixture of the carbonized product and the alkali metal compound is fired, the silicon-accumulated biomass can be present, which can improve the yield of the product. The amount of silicon-accumulated biomass added is in the range of 1 to 20% by weight based on the carbonized product. When the carbonized product is fired in the form of a mixture with the alkali metal compound as described above, the alkali metal compound finally becomes an alkali metal oxide. The part reacts with the carbon content and the silicon content in the carbonized product to be removed by vaporization. Such a calcined product itself has a high surface area, for example, a BET surface area of 900 m ² / g or more, but it is preferable to elute and remove the alkali metal content contained in the calcined product. By that, the surface area can be remarkably improved. Elution of the alkali metal content from the calcined product can be performed by boiling the calcined product with water, immersing the calcined product in water, filling the calcined product in a column, and circulating water in the packed column. It can be carried out. By such elution treatment, the alkali metal content in the fired product can be almost completely removed. Thus fired product eluted removal of alkali metal component and has a very high surface area, typically, 900 meters ² / g or more in BET surface area, in particular with a surface area of 2000~4000m ² / g.

In the present invention, when the carbonized product is fired in the form of a mixture with an alkali metal compound, the carbonized product is molded in advance into a pellet shape, a spherical shape, a plate shape or the like to obtain a molded product. It can also be baked. The carbonized product can be molded according to a conventionally known method by mixing a polymer compound and a viscous liquid as a binder and then performing an arbitrary molding method such as extrusion molding or tablet molding. When the alkali metal compound added to the carbonized product is powdery, it can be molded after the alkali metal compound is added and mixed to the carbonized product. When the alkali metal compound is added as an aqueous solution, a method such as spraying an aqueous solution of the alkali metal compound on the molded product after molding the carbonized product or immersing the molded product in the aqueous solution of the alkali metal compound Thus, a molded product containing an alkali metal compound can be obtained. As another method for obtaining a carbonized product and a molded product composed of an alkali metal compound according to the present invention, sodium hydroxide and / or potassium hydroxide is mixed with the carbonized product, and the mixture is subjected to the hydroxylation. A method of heat-treating at a temperature above the melting point of sodium and / or potassium hydroxide, preferably about 400 ° C. for about 30 minutes, molding the obtained molten mixture, and cooling to room temperature can be shown.

Another preferable method for producing a porous silica-carbon composite according to the present invention is to mix an alkali metal compound with a pulverized product of silicon-accumulated biomass as a raw material, and mix the mixture at a temperature of 80 to 300 ° C. After the heat treatment, it is fired at a temperature of 300 ° C. or higher, and the obtained fired product is washed with water. In this case, the raw material silicon-accumulated biomass is pulverized as it is or in a state where the moisture is removed by heat treatment at 120 to 200 ° C. The addition amount of the alkali metal compound is 1 to 5 parts by weight with respect to 1 part by weight of the raw material silicon-accumulated biomass on a dry matter basis. The temperature of washing the baked product with water is 30 to 100 ° C., preferably 60 to
90 ° C. According to this method, the surface area is 1000-
A 1500 m ² / g porous silica-carbon composite can be obtained. Further, in the case of this method, by using sodium hydroxide as the alkali metal compound, it is possible to obtain an aqueous sodium silicate solution as the washing effluent. This sodium silicate aqueous solution has no color,
It can be used as water glass by adjusting the concentration,
It can be used as a chemical raw material. Furthermore, by using potassium hydroxide as the alkali metal compound, an aqueous solution of potassium silicate can be obtained as the washing effluent. This potassium silicate aqueous solution is not colored and can be used as a hydroponic fertilizer and also as a chemical raw material.

[0010]

The porous silica-carbon composite of the present invention comprises:
Has a high surface area. In this porous silica-carbon composite, one having an alkali metal content elution has a BET surface area of 800 to 1000 m ² / g, while one having an alkali metal content elution has a BET surface area of 2000 to 4000 m ^2.
It has a very high surface area of / g. Since all of these have a high surface area, they are effectively used as adsorbents, pollution control materials, and the like. The eluate containing alkali silicate obtained when the alkali metal component is eluted from the fired product is not colored and can be used for various purposes. For example, the eluate containing sodium silicate can be used as water glass, and the eluate containing potassium silicate can be used as hydroponic fertilizer. Since the porous silica-carbon composite of the present invention is produced by using silicon-accumulated biomass as a raw material, it has an advantage of low cost.

[0011]

EXAMPLES Next, the present invention will be described in more detail by way of examples. In addition, the measurement of the BET surface area shown in the examples was carried out using a Soaptomatic 1800 manufactured by Carlo Erba, Italy or a counter soap manufactured in the United States. The amount of methylene blue adsorbed was measured according to JIS K 1474 (test method for granular activated carbon). That is, 300
After adding 0.2 g of the sample to a mg / l methylene blue solution while thoroughly stirring, the concentration of methylene blue in the solution was measured with a spectrophotometer at a wavelength of 665 mm, and based on the result, the amount of adsorbed methylene blue per 1 g of the sample Was calculated as mg / g.

Example 1 50 g of rice husks containing about 25% by weight of SiO _{2 and} about 75% by weight of organic matter were placed in a nickel crucible with a lid and heated in an electric furnace while passing nitrogen through the crucible and heated at 20 ° C./min. When the temperature inside the crucible is raised to 400 ° C. at a heating rate and the chaff is carbonized by further heat-treating at 400 ° C. for 120 minutes, a carbonized product consisting of carbon content: 57 wt% and SiO ₂ : 43 wt% was gotten. The carbonized product was allowed to cool to room temperature in nitrogen. Into a 500 ml beaker, 20 g of this carbide was added, and 80 g of caustic potash was added and mixed well, and then the mixture was placed in a nickel crucible with a lid, and 10
The temperature was raised to the temperature shown in Table 1 over a period of 0 minutes and then immediately cooled to obtain a porous silica-carbon composite. Next, the calcined product was added to water and boiled to elute the potassium component and the silicic acid component in the calcined product, and then dried.
Table 1 shows the relationship between the BET surface area and the amount of methylene blue adsorbed on the porous silica-carbon composite obtained here and the firing temperature.
Shown in.

[0013]

[Table 1]

Example 2 Rice straw was cut into 2 to 10 mm and then carbonized by heating to 500 ° C. in nitrogen gas at a heating rate of 1 ° C./min to obtain a carbonized product. To 20 g of this carbonized product, 40 g of caustic potash was added, and porous silica was added in the same manner as in Example 1.
A carbon composite was prepared. In this case, the firing temperature is 800 ° C
And The porous silica-carbon composite material thus obtained showed a BET surface area of 2022 m ² / g and a methylene blue adsorption amount of 720 mg / g.

Example 3 The stem portion of rice husk was heat-treated at about 200 ° C. and then pulverized. The pulverized product was carbonized in the same manner as in Example 1 at a temperature of 400 to 700 ° C. 1 part by weight of this carbonized product was mixed with 4 parts by weight of caustic potash, and the mixture was heat-treated at a temperature of 400 ° C. slightly higher than the melting point of potassium caustic for 50 minutes, and then the mixture was treated with potassium as in Example 1. The silicic acid content was eluted. The BET surface area and methylene blue adsorption amount of the obtained product are shown in Table 2.

[0016]

[Table 2]

Example 4 2 parts by weight of caustic potash and 2 parts by weight of potassium carbonate were added and mixed with 1 part by weight of the chaff carbon material obtained in Example 1.
After calcining the obtained mixture in air at 600 to 900 ° C., the silicic acid and potassium components were eluted. The performance of the obtained product is shown in the following table. The benzene gas adsorption amount (% by weight) shown in Table 2 is the% by weight of the adsorbed benzene gas with respect to the sample at a temperature of 30 ° C.

[0018]

[Table 3]

Example 5 0.1 part by weight of rice husks and 4 parts by weight of caustic potash were added and mixed with 1 part by weight of a carbonized product obtained by carbonizing rice husks at 500 ° C., and this mixture was heated at 800 ° C. After baking for 10 minutes at room temperature, silicic acid and potassium were eluted. The product obtained is
The BET surface area was 3461 m ² / g and the amount of methylene blue adsorbed was 950 mg / g.

Example 6 Rice husks were carbonized by heating them to 600 ° C. at a heating rate of 3 ° C./min in nitrogen gas. Next, each solution formed by adding 2 to 4 g of potassium carbonate or caustic potash to 5 ml of distilled water was added to and mixed with 1 g of the carbonized product obtained above, and this mixture was kept at 900 ° C. for 100 minutes by blocking air. Up to temperature,
After baking at this temperature for 0 to 20 minutes, the potassium content and the silicic acid content were eluted. The properties of the obtained product are shown in the following table.

[0021]

[Table 4]

Example 7 Rice straw was cut into pieces each having a length of about 3 mm and then 40
Carbonized product obtained by carbonizing at 0 ° C. was heat-treated at 500 ° C. for 1 hour. 1 part by weight of potassium carbonate or caustic potash was added.
Parts by weight are added and mixed, and the mixture is mixed in nitrogen gas at 800 parts.
Baking was performed at 30 ° C. for 30 minutes or at 800 ° C. for 100 minutes. The performance of the obtained product is shown in the following table.

[0023]

[Table 5]

Example 8 Rice husks were carbonized by heating them to 600 ° C. in nitrogen gas at a heating rate of 3 ° C./min. To 1 part by weight of this carbonized product, 4 parts by weight of caustic potash was added and mixed, and the mixture was baked in nitrogen gas at 400 ° C. for 100 minutes. This baked product was then baked at 800 ° C. for 100 minutes without being washed with water. When the properties of the obtained fired body (without water washing treatment) were examined, the results were BET surface area: 900 m ² / g and methylene blue adsorption amount: 300 mg / g.

Example 9 A product (baking temperature 900 ° C.) was obtained in the same manner as in Example 1, except that caustic soda was used as the alkali in an amount of 4 parts by weight with respect to 1 part by weight of the carbonized product. This product is
The BET surface area was 3010 m ² / g and the amount of methylene blue adsorbed was 900 mg / g.

Example 10 A product was obtained in the same manner as in Example 5 except that caustic soda was used instead of caustic potash. This product has a BET surface area of 2990 m ² / g and a methylene blue adsorption amount of 970.
It showed mg / g.

Example 11 20 g of chaff carbide treated at 500 ° C. was placed in a nickel crucible with a lid, and then 4 parts of KOH was added to 1 part by weight of the carbonized product. This was treated at 400 ° C. for 30 minutes, then calcined at 800 ° C. for 100 minutes and then washed with water, and the internal surface area of the obtained calcined product and the amount of adsorbed methylene blue were examined. Internal surface area 2940m ² / g~3140m ² / g, methylene blue adsorption of 890mg / g~900mg / g results. The effluent from the rinsing obtained during rinsing contained potassium silicate and was usable as a hydroponic fertilizer.

Example 12 An experiment was conducted in the same manner as in Example 11 except that KCl was used instead of KOH. In this case, the internal surface area 1
200m ² / g, methylene blue adsorption amount 380mg / g
The product was obtained.

Example 13 Rice husks were heat treated in air at 200 ° C. and then crushed to a size of 80 mesh under. 1 part by weight of this pulverized product was mixed with 4 parts by weight of sodium hydroxide, and the oxygen concentration was adjusted to 0.
After heat treatment at 100 ° C. for 15 minutes in a nitrogen gas of 1 vol% or less, the temperature was raised to 800 ° C. and heat treatment was performed at this temperature for 10 minutes. Next, the fired product thus obtained is heated to 90 ° C.
And washed with water. The porous silica-carbon composite obtained after this washing with water had a BET surface area of 1100 m ^2.
/ G, methylene blue adsorption amount: 350 mg / g. Further, the effluent of the rinsing obtained during the rinsing was an uncolored sodium silicate aqueous solution, and this aqueous solution could be used as water glass by concentrating it.

Example 14 Rice husks were crushed, and 4 parts of alkali was added to 1 part by weight of this powder.
Part by weight is mixed, and 0.2 part by weight of waste sugar is mixed. Insert the mixture thus obtained into the cylinder,
After compressing at a pressure of 1.5 ton / cm ² and maintaining this compressed state for 3 minutes, a cylindrical molded body was taken out, dried in the sun, and heated at a temperature of 100 ° C. for dehydration. To do. Next, this molded body is subjected to 800 in nitrogen gas.
Baking for 15 minutes at ° C. After the obtained fired product was washed with hot water, its performance was evaluated. The results are shown in the table below.

[Table 6]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C04B 35/52 B 38/06 F (72) Inventor Iji Ishibashi 2 Tsukikanto, Toyohira-ku, Sapporo, Hokkaido Article 172-12-1 Industrial Technology Institute Hokkaido Industrial Development Laboratory (72) Inventor Satoshi Yamada 2-17-17-2 Tsukikanto, Toyohira-ku, Sapporo-shi, Hokkaido Institute of Industrial Technology Hokkaido Industrial Development Laboratory (72) Inventor Yoshio Noda 2-17-1, Tsukikanto, Toyohira-ku, Sapporo-shi, Hokkaido Inside the Industrial Research Institute of Hokkaido Industrial Technology Institute (72) Inventor Yuji Yokota 2-17-1, Tsukikanto, Toyohira-ku, Sapporo-shi, Hokkaido Industrial Technology Institute (72) Inventor Susumu Kumamoto 2-1 at 1-24 Wakakusa, Chitose-shi, Hokkaido (72) Inventor Yoshie Takahashi 2 Minami, Chuo-ku, Sapporo, Hokkaido Article 5 West 12-4-1-503 (72) Inventor Kazufumi Komatsu 4-22-11 Minamiyukitani, Ota-ku, Tokyo (72) Inventor Sei Kuwagaki 2423-8, Enzo, Chigasaki-shi, Kanagawa

Claims (11)

[Claims] 1. BE comprising a calcined product of a mixture of a carbonized product of silicon-accumulated biomass and an alkali metal compound,
A porous silica-carbon composite having a T surface area of 900 m ² / g or more. 2. BE comprising a calcined product of a mixture of a carbonized product of silicon-containing bios and an alkali metal compound, in which an alkali metal component contained therein is eluted and removed.
A porous silica-carbon composite having a T surface area of 900 m ² / g or more. 3. The porous silica-carbon composite according to claim 1, wherein the alkali metal compound is sodium hydroxide and / or potassium hydroxide. 4. An adsorbent comprising the porous silica-carbon composite according to claim 1. 5. A method for producing a porous silica-carbon composite, which comprises firing a mixture of a carbonized product of silicon-accumulated biomass and an alkali metal compound at a high temperature of 300 ° C. or higher. 6. A method of calcining a mixture of a carbonized product of silicon-accumulated biomass and an alkali metal compound at a high temperature of 300 ° C. or higher, and then eluting and removing an alkali metal content remaining in the obtained calcined product. And a method for producing a porous silica-carbon composite. 7. The method according to claim 5, wherein the silicon-accumulated biomass is added to the carbonized product. 8. A mixture of silicon-accumulated biomass and an alkali metal compound is heat treated at 80 to 300 ° C., and then 3
A method for producing a porous silica-carbon composite, which comprises calcination at a temperature of 00 ° C. or higher and washing the resulting calcinated product with water. 9. A method for producing a porous silica-carbon composite, which comprises firing a mixture of crushed rice husks and an alkali metal compound at a temperature of 300 ° C. or higher, and then washing the obtained fired product with water. 10. The method for producing a porous silica-carbon composite according to claim 8 or 9, wherein sodium hydroxide is used as the alkali metal compound, and an aqueous sodium silicate solution is obtained as the washing effluent. 11. The method for producing a porous silica-carbon composite according to claim 8 or 9, wherein potassium hydroxide is used as the alkali metal compound, and an aqueous potassium silicate solution is obtained as the washing effluent.