JPH03223105A - Preparation of low density porous carbon granule - Google Patents

Abstract

PURPOSE:To improve the strength of the subject carbon granule by granulating chaff powder with a binder aqueous solution containing lignin, starch, theriac or a mixture thereof, drying the granules, carbonizing the dried granules and subsequently immersing the carbonized granules in an aqueous solution to elute a SiO2 component therefrom. CONSTITUTION:100 pts.wt. of plant powder such as chaff powder which has an average particle size of <=50mum and whose 60% have particle sizes of <=300mum is mixed with <=60 pts.wt. of a binder aqueous solution comprising lignin, a polysaccharide such as water-soluble starch or theriac or a mixture thereof, and the mixture is charged to a granulating machine and then granulated. The prepared granules are dried at approximately 50-300 deg.C, carbonized at a temperature of <1000 deg.C, immersed in a HF aqueous solution having a concentration of approximately 5% to elute a SiO2 component contained in the tissues of the granules therefrom, followed by washing the treated granules with water and drying the granules to provide low density porous carbon granules having a bulk density of <=0.2g/cm<3>, a N2 adsorption specific surface area of 300-500m<2>/g and a granule-crashing strength of >=300g/granule.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing low-density porous carbon particles that are highly effective mainly for soil improvement or water treatment.

[Conventional technology]

Slash-and-burn agriculture has been practiced since ancient times as a means of soil improvement to create an environment in which microorganisms useful for plants can easily grow. This is because the excellent water permeability and water retention properties of the charcoal that remains after slash-and-burn farming operations are suitable for the growth of microorganisms, and because it does not contain organic matter, it does not contain horse-borne microorganisms or pathogenic microorganisms. This is because it has a variety of effects, such as preventing invasion and inhibiting the growth of mold due to its alkaline nature.

Conventionally, charcoal, sawdust charcoal, bark charcoal, coconut husk charcoal, straw charcoal, and rice husk smoked charcoal have been known as carbon materials for the purpose of soil improvement.
It is thought to work to promote the growth of symbiotic microorganisms such as VA mycorrhizal fungi. Some believe that the presence of char increases the infection rate and spore formation of these fungi, increasing their ability to absorb phosphorus and other components, thereby promoting crop growth.

Recent research has shown that autotrophic microorganisms such as aerial nitrogen-fixing bacteria and photosynthetic cyanobacteria first enter carbonaceous materials mixed into the soil, and then commensal microorganisms that are strong in competition enter, and roots that require oxygen become charcoal. When it increases inside, rhizobia and V. coexist with it.
It is said to be related to the proliferation of Bacterium A ["Agricultural technology"]
Volume 41 (9), p400-405 (1986)
).

This type of soil conditioner has the following properties: ■Improves the air permeability and water permeability of the soil; ■Has an appropriate water retention capacity; ■Has a fertilizing capacity in the soil; ■Has a soil acid/alkali adjustment function. be,
■ Items such as high oxygen (air) retention in the soil are required, but if we translate this into the characteristics and properties of a carbon material, we find that it has a low-density porous structure with high porosity and specific surface area. It is a granular material that does not easily break apart, and its internal skeleton is a soft porous structure, and its outer shell is ideally covered with a relatively hard carbon layer.

On the other hand, porous carbon particles are consumed in large quantities as activated carbon for water treatment. In this case, in addition to the physical action of adsorbing and separating the substances to be removed in the treated water, there is also a bioreactor-like action that utilizes microorganisms grown in the tissue bore. Porous carbon grains used as soil conditioners are also required to have the same characteristics and properties as the soil conditioner.

However, none of the conventional porous carbon material manufacturing techniques has been found that satisfies the above characteristics and properties.

That is, when sawdust, straw, etc. are carbonized at low temperatures, a soft porous structure can be formed, but this has the drawback that the complicated bores easily disappear because the skeleton collapses. In this regard, carbonized rice husks and coconut husks are converted into relatively hard carbon bodies, but the problem is that the bores are too small to impart effective functional properties. In addition, tar,
A method is also known in which the material is molded using a binder such as pitch and then carbonized, but this method has the problem of clogging the bore because the binder component is carbonized while remaining inside the skeleton.

In addition, there are examples of mineral-based soil improvement carbon materials such as coal and pitch coke being commercialized, but they appear to be high-density and hard types with a specific gravity of 0.7 g/cc. unfavorable to

[Problem to be solved by the invention]

The present inventors conducted multifaceted research on the components and behavior of binders when plant-based powders are used as raw materials, and found that when granulated using a specific binder that is not compatible with plant-based powders, the drying process It was confirmed that the binder component migrates to the grain surface and finally forms a shell-like carbon film.After first granulating the vegetable powder with an aqueous solution of the binder component consisting of lignin, starch, or a mixture thereof, We have developed and provided a method for producing low-density porous carbon particles by drying and then firing and carbonizing the granules (Special Application Hei!-
No. 159925).

The carbon particles obtained by this method have a soft porous skeleton, have an extremely low density, yet have a strength that does not easily disintegrate, and are recognized to be suitable for soil improvement materials.

The present invention has been developed by adding further improvements to the prior art described above, and its purpose is to develop properties that are even more ideal for use in soil improvement or water treatment using bioreactors.
An object of the present invention is to provide a method for producing low-density porous carbon particles having the following properties.

[Means to solve the problem]

A method for producing low-density porous carbon particles according to the present invention to achieve the above object includes a granulation step of granulating rice hull powder with an aqueous binder solution containing lignin, starch, molasses, or a mixture thereof; It is characterized in that it consists of a carbonization step in which the material is dried and then subjected to firing carbonization, and an elution step in which the carbonized powder is immersed in an aqueous hydrofluoric acid solution to elute the silica component. The present invention will be explained in detail below step by step.

(1) Granulation process As the raw material of the present invention, chaff powder is selected from plant-based powders. The rice hull powder is preferably used after being pulverized to such an extent that the particle size is 500 μm or less and 60% of the total can pass a 300 μm sieve.

As the binder component, polyesters such as lignin, water-soluble starch, and molasses are used, and they are used alone or as a mixture in the form of an aqueous solution. The amount of the binder aqueous solution added is preferably set to 60 parts by weight or less as a binder component per 100 parts by weight of rice hull powder, and 60 parts by weight or less as a binder component.
If the amount added exceeds parts by weight, the transfer of the binder component to the surface layer during drying will be insufficient, resulting in only hard grains and high-density carbon grains being obtained.

Granulation is performed by putting the rice hull powder and binder aqueous solution into a stirring granulator and applying rotational motion.

As a granulator, a pin-type granulator, such as the one commonly used for wet granulation of carbon black, is suitable for mass production.

(2) Carbonization step The granulated material obtained in the granulation step is subsequently subjected to a drying treatment. The drying process is preferably carried out by transferring the granulated material to a rotating drum maintained at a temperature of 50 to 300°C and rolling it, so that the binder component can be efficiently transferred to the surface layer during the rolling process of the granulated material. Proceed to.

On the other hand, in static drying, a phenomenon occurs in which the binder component does not remain on the grain surface but diffuses to the outside, leading to segregation and reduction in grain strength.

For the firing carbonization treatment after drying, either the static carbonization method or the fluidized carbonization method can be applied, and the firing does not require strict control of the heating rate.The carbonization temperature depends on the alkalinity to be imparted. , is set taking into consideration specific surface area, etc., but usually 1
A temperature range of 000°C or less and around 700 to 800°C is mainly used.

(3) Elution step The carbonized grains obtained in the carbonization step are then immersed in an aqueous solution of hydrofluoric acid to elute the silica component present in the grain structure. The concentration of the hydrofluoric acid aqueous solution is preferably about 5%, including workability, and the immersion treatment is continued until the silica component is completely dissolved.

In this case, it is also possible to use an eluent that can elute the silica component, such as a hot alkali, although the efficiency is reduced.

The carbonized particles after the elution treatment are thoroughly washed with water and then dried to obtain the desired low-density porous carbon particles.

[For production]

According to the present invention, rice hull powder, which forms a soft porous structure, is used as a raw material and is granulated by selectively using binder components such as lignin, starch, and molasses, which are not compatible with rice hull powder. During the drying process after granulation, the components move from the inside of the grain skeleton to the surface layer, and are carbonized in that form in the subsequent carbonization process, so that the internal skeleton of the soft porous structure becomes hard carbon. Form an ideal morphology coated with a membrane.

The rice hull powder used as the raw material of the present invention contains a considerable amount of silicon component, which is converted into amorphous silica (SiO□) by heat treatment during carbonization and remains in the carbonized grain structure. In the elution step after the carbonization step, the silica component is removed using an aqueous hydrofluoric acid solution, and this treatment effectively acts to further increase the specific surface area and pore volume of the tissue.

Therefore, the bulk density of the obtained carbon particles is approximately 0.2 g
/cc or less, nitrogen adsorption specific surface area 300-50
The internal volume of grains at 0.27 g is 2.0 to 3.0 cc/g.
It covers more than that. Moreover, the grain crushing strength is maintained at a level of 300 g/grain or higher.

The above unique characteristics and properties function extremely effectively for soil improvement and water treatment. For example, when used for soil improvement purposes, the high specific surface area and porous skeletal structure have oxygen (air) retention and water retention functions. It supports microorganisms and fertilizers, and contributes to the adsorption of soil improvement active ingredients. Furthermore, since the particle surface forms a shell structure with a relatively hard carbon film, it improves fluidity and porosity (air permeability) when mixed into soil.
It works to secure soil and promote soil agglomeration.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 4 Rice husks were finely pulverized using a free crusher (M-3 type, manufactured by Nara Kikai Seisakusho), and the amount that had passed through a 0.3a filter was collected.For 100 parts by weight of this powder, Granulation treatment was carried out using a pin-type granulator using the binder components and additive amounts (parts by weight) shown in Table 1.In this case, the binder component was calcium lignin sulfonate [manufactured by Choyo Kokusaku Valve ■, [
Sunextract CJ] and water-soluble starch (Kanto Kagaku ■, Shika 1 grade) were used.

The granules were placed in a rotating drum dryer and tumble dried at a temperature of 130°C. Next, the granules were carbonized at different firing temperatures (Table 1) to obtain carbon particles.

Table 1 Next, the carbon particles were immersed in a hydrofluoric acid aqueous solution (5χ) of 20W1 per Ig for 45 minutes to elute the silica component, and then washed with water and dried to produce low-density porous carbon particles.

Example 5 Carbon granules were produced under the same conditions as in Example 1, except that the drying process for the granulated product was changed to static drying.

Comparative Example 1 Granulation and carbonization steps were carried out under the same conditions as in Example 1, and carbon particles were produced without performing an elution step.

Comparative Example 2 Granulation and carbonization steps were carried out under the same conditions as in Example 2, and carbon particles were produced without performing the elution step.

(Evaluation of Properties/Properties) Various properties were measured for each of the carbon grains obtained in Examples 1 to 5 and Comparative Examples 1 to 2, and are shown in Table 2 for comparison. In addition, as Comparative Example 3, the characteristic values of a high-performance grade commercially available soil conditioner made of pulp sludge carbide containing wood fiber as the main component (manufactured by Hokoshi Kagaku ■, "Bratsu Kwan") are also listed in Table 2.

FIG. 1 shows pore distribution curves measured for the carbon grains of Example 1, Comparative Example 1, and the soil conditioner of Comparative Example 3.

As considered from the results in Table 2 and Figure 1, the carbon grains produced in Examples had lower density, larger specific surface area and pore volume, and exhibited better grain crushing strength than Comparative Examples. It turns out that

However, the carbon grains of Example 4, in which the amount of binder added exceeds 60 parts by weight, showed a tendency for the bulk density to increase as well as the grain strength, and the grain strength of Example 5, in which the drying process was performed by the standing method, decreased. A decreasing regression characteristic was observed.

2 and 3 are SEM photographs showing the particle structure of the carbon grains according to Example 1 in an enlarged manner, with FIG. 2 at a magnification of 61 times, and FIG. 3 at a magnification of 650 times. FIG. 4 is an SEM photograph of the particle structure of carbon grains according to Comparative Example 1, which is magnified at a magnification of 630 times.

When these SEM photographs are compared, differences in porosity due to the elution process are clearly recognized.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to efficiently produce low-density porous carbon grains that have high porosity and specific surface area and have grain strength that prevents them from easily breaking. These characteristics and properties are particularly ideal as a soil improvement material or a bioreactor for water treatment, and great effects can be expected when applied to these uses.

[Brief explanation of drawings]

FIG. 1 is a graph showing pore distribution curves measured for each carbon particle according to Example 1, Comparative Example 1, and the commercially available soil conditioner of Comparative Example 3. Figures 2 and 3 are SEM photographs (magnification:
FIG. 1: 61 times, FIG. 2: 650 times), and FIG. 4 are SEM photographs (magnification: 2,630 times) showing the particle structure of carbon grains according to Comparative Example 1.

Claims (1)

[Claims] 1. A granulation step of granulating rice hull powder with an aqueous binder solution containing lignin, starch, molasses, or a mixture thereof; a carbonization step of drying the granulated product and then firing and carbonizing it; A method for producing low-density porous carbon particles, comprising an elution step of immersing carbonized particles in an aqueous hydrofluoric acid solution to elute a silica component. 2. The method for producing low-density porous carbon particles according to claim 1, wherein the drying treatment of the granules is carried out while rolling in a rotating drum at 50 to 300°C.