JP7656312B2 - Manufacturing method of SiO2-containing hardened material - Google Patents

Description

The present invention relates to a method for efficiently obtaining a hardened body from _SiO2- containing materials such as sand and gravel.

Concrete is the most widely used construction material in the world. Cement is used as the main ingredient in concrete, but there is an issue with the large amount of carbon dioxide emitted during its production. Furthermore, the mineable lifespan of limestone, the main ingredient in cement, is estimated to be at least a few decades in Japan, and at most a hundred and several decades. Other countries that mass-produce concrete, such as China, India, and the United States, have similar mineable lifespans, meaning there are limits to how much can be achieved through imports.

Therefore, the development of a cement-free construction material to replace concrete has become an urgent issue (see, for example, Patent Document 1). Requirements for an alternative material include an almost unlimited supply of raw materials and the ability to be reused. In this regard, the most abundant materials on Earth are sand and gravel, which contain silicon as their main component, and if construction materials could be produced directly from these, they would be considered to be effective concrete substitutes. However, at present, concrete substitutes that are practical enough have not yet been realized.

JP 2019-6610 A

The present invention aims to provide a concrete substitute that does not use cement, which emits a large amount of carbon dioxide during the manufacturing process.

As a result of intensive research to solve the above problems, the present inventors have discovered that a hardened body in which _SiO2- containing materials, such as sand and gravel, are directly bonded to each other can be efficiently obtained by treating the materials at high temperature in an alcohol compound and an _alkali metal compound or an alkaline earth metal compound, and have thus completed the present invention.

That is, in one aspect, the present invention relates to <1> a method for producing a SiO ₂ -containing cured material, the method comprising: a) a step of mixing a raw material containing SiO ₂ , an alcohol compound, and an alkali metal compound or an alkaline earth metal compound; b) a step of heat-treating the mixture obtained in step a) to produce a SiO ₂ -containing cured material; and c) a step of separating the SiO ₂ -containing cured material produced in step b);
<2> The method according to the above <1>, wherein the raw material containing SiO ₂ is 1 to 50 parts by weight per 100 parts by weight of the alcohol compound;
<3> The method according to the above <1> or <2>, wherein the alkali metal compound or alkaline earth metal compound is 1 to 20 parts by weight per 100 parts by weight of the raw material containing _SiO2 ;
<4> The method according to any one of <1> to <3> above, wherein the heat treatment in the step b) is carried out at a temperature in the range of 100 to 300° C.;
<5> The method according to any one of the above <1> to <4>, wherein the raw material containing SiO ₂ has a particle shape with a particle diameter in the range of 1 μm to 10 cm;
<6> The method according to any one of <1> to <5> above, wherein the SiO ₂ -containing raw material includes silica stone, silica sand, diatomaceous earth, quartz, or silica;
<7> The manufacturing method according to any one of the above <1> to <6>, wherein the raw material containing SiO ₂ is gravel or sand;
<8> The method according to any one of the above <1> to <7>, wherein the alcohol compound is ethanol or methanol;
<9> The method according to any one of the above <1> to <8>, wherein the alkali metal compound is at least one selected from the group consisting of hydroxides, halides, sulfates, carbonates, and hydrogencarbonates of alkali metals;
<10> The production method according to any one of <1> to <9>, further comprising adding a basic solution or an aprotic organic solvent in the step a);
<11> The method according to any one of <1> to <10> above, further comprising pressing a solid component in the mixture in the step b);
<12> The manufacturing method according to any one of <1> to <11> above, further comprising subjecting the _SiO2- containing cured body separated in the step c) to a heat drying treatment.

In another aspect, the present invention also relates to a method and agent for treating SiO _2- containing materials, specifically,
<13> A method for treating a SiO ₂ -containing material, comprising: A) a step of mixing a SiO ₂ -containing material, an alcohol compound, and an alkali metal compound or an alkaline earth metal compound; and B) a step of heat-treating the mixture obtained in step A);
<14> The treatment method according to the above <13>, wherein the SiO _2- containing material is gravel or sand having a particle size in the range of 1 μm to 10 cm;
<15> A treatment agent for SiO _2- containing materials, comprising an alcohol compound and an alkali metal compound or an alkaline earth metal compound; and <16> the treatment agent according to the above <15>, wherein the SiO _2- containing material is gravel or sand having a particle size in the range of 1 μm to 10 cm.

According to the present invention, a hardened body in which SiO2 _- containing materials are directly bonded to each other can be obtained without using cement, which emits a large amount of carbon dioxide during the manufacturing process, and a new concrete substitute can be provided efficiently at low cost. The hardened body of the present invention can use a wide range of _SiO2- containing materials such as sand and gravel as raw materials, which are available in almost unlimited quantities on Earth and do not require concern about shortages. Furthermore, since sand and gravel are easily available on the moon and Mars, they can be expected to be used in space development.

Furthermore, since the hardened body of the present invention is hardened without using conventional cement paste, it has the following advantages, for example.
- Small volume change due to drying and wetting;
- Small creep change;
- It can suppress deterioration caused by calcium elution caused by water or acid;
- Deterioration caused by alkali-aggregate reaction (expansion of aggregate in an alkaline environment) can be suppressed;
The time required for strength development can be shortened (compared to about one month for ordinary concrete, the present invention allows for this in as little as 24 hours);
・The alkali metal compound used in the manufacturing process is a catalyst and can be reused repeatedly.
・The alcohol compounds used in the manufacturing process can be recycled after high-temperature treatment.

FIG. 1 is an image showing the pressure reaction vessel used in the examples. FIG. 2 is an image of the cured product of the present invention obtained in the example. FIG. 3 is an image of the cured product obtained after heating for 24 hours in 13.8% KOH/silica (6 g silica sand; 0.83 g KOH). FIG. 4 shows an image of the hardened specimen obtained after heating for 24 hours in 16.5% KOH/silica (6 g silica sand; 1 g KOH).

The following describes embodiments of the present invention. The scope of the present invention is not limited to these descriptions, and other than the following examples, the present invention can be modified and implemented as appropriate without departing from the spirit of the present invention.

1. Manufacturing method of the cured body of the present invention The manufacturing method of the present invention is for manufacturing a cured body of a _SiO2- containing material, and is characterized by including the following steps a) to c):
a) mixing a raw material containing _SiO2 , an alcohol compound, and an alkali metal compound or an alkaline earth metal compound;
b) a step of heat-treating the mixture obtained in step a) to generate a SiO ₂ -containing hardened body; and c) a step of separating the SiO ₂ -containing hardened body generated in step b).

Although not necessarily bound by theory, the mechanism by which a _SiO2- containing hardened body is obtained in the manufacturing method of the present invention is presumed to be as follows. Fukaya et al. have reported that tetraalkoxysilane, an organosilicon compound, can be obtained by decomposing and dehydrating sand ( _SiO2- containing material) with alcohol (Chemistry Letters 2016 45:7, 828-830). This reaction is represented by the following reaction formula (1).

In the paper by Fukaya et al., the reaction product water (H ₂ O) is removed to shift the equilibrium of the reaction formula to the right, and tetraalkoxysilane (Si(OR) ₄ ) is efficiently produced. Here, since formula (1) is a reversible equilibrium reaction, it can be interpreted that the chemical bonds of SiO ₂ are repeatedly cut and regenerated in the reaction. In the present invention, focusing on this point, the above reaction formula (1) is applied to a SiO _2- containing material, and after tetraalkoxysilane is once produced, SiO ₂ on the left side is regenerated, whereby SiO ₂ components present on the surface of the SiO _2- containing material are bonded to each other, and an aggregate (hardened body) in which SiO _2- containing materials are directly bonded to each other is obtained.

From another perspective, it is known that _SiO2 produces a porous silica body through a sol-gel reaction. In the present invention, it is also possible to consider that only the surfaces of SiO2 _- containing substances are converted into a sol, thereby producing a hardened body in which SiO2 _- containing substances are bonded to each other.

In this way, the manufacturing method of the present invention utilizes the fact that the _SiO2 component in the _SiO2- containing material repeatedly cuts and regenerates the chemical bonds of _SiO2 according to the above reaction formula, and has found that a hardened body in which SiO2 _- containing materials are directly bonded to each other can be obtained, and that such a hardened body can actually be obtained.

In the present invention, the term "SiO _2- containing material (or SiO ₂ -containing raw material)" is not particularly limited as long as it is a material that contains a certain amount of SiO ₂ , but may be a material containing natural minerals such as silica stone, silica sand, diatomaceous earth, and quartz, calcined ash of silicon-containing plants, volcanic ash, silicate salts, silica sol-derived silica gel, fumed silica, silica alumina, zeolite, glass, and other artificial materials. Preferably, silica stone, silica sand, diatomaceous earth, quartz, silica, or a combination of one or more of these materials may be mentioned. For example, granite, rhyolite, etc. may also be included. From the viewpoint of availability, etc., the SiO _2- containing material is typically gravel or sand. Such gravel or sand may be used as aggregate when producing concrete or mortar.

In addition, the raw material containing SiO ₂ (SiO ₂ -containing material) used in the present invention is preferably one having a particulate shape or an approximately particulate shape from the viewpoint of efficiency during the curing reaction. The particle size (average particle size) in this case can be in the range of 1 μ to 10 cm, preferably in the range of 10 μ to 5 cm, and more preferably in the range of 100 μm to 3 cm. However, as described above, the SiO _2- containing material does not need to be in a perfect particulate shape, and may be in a non-uniform shape like so-called sand or gravel, so the "particle size" here should be understood to represent an approximate size.

As described above, step a) in the manufacturing method of the present invention is a step of mixing a _SiO2- containing material, an alcohol compound, and an alkali metal compound or an alkaline earth metal compound, thereby obtaining a chemical equilibrium state as shown in the above reaction formula (1).

The alcohol compound used in step a) may be an alcohol having a linear or branched alkyl, and the alkyl portion may be substituted with any substituent. The alcohol compound may be preferably an alcohol having 1 to 10 carbon atoms, and more preferably an alcohol having 1 to 5 carbon atoms. Typically, the alcohol compound is methanol or ethanol. The alcohol compound may be a raw material for obtaining the alkoxysilane on the right side of the above reaction formula (1), but may return to the alcohol on the left side again in the overall equilibrium reaction.

The alkali metal compound or alkaline earth metal compound used in step a) is a component that promotes the cleavage of the silicon-oxygen bond in _SiO2 and functions as a catalyst for the production of alkoxysilane on the right side of the above reaction formula (1).

Examples of the alkali metals and alkaline earth metals in such alkali metal compounds and alkaline earth metal compounds include lithium (Li), sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), and cesium (Cs). Examples of the counter anions include hydroxides, halides, oxides, carbonates, hydrogen carbonates, alkoxides, silicates, aluminates, phosphates, organic acid salts, sulfates, and nitrates. Among these, hydroxides, halides, carbonates, and hydrogen carbonates are preferred, and alkali metal hydroxides, alkali metal halides, alkali metal carbonates, and alkali metal hydrogen carbonates are more preferred.

Specific examples of alkali metal compounds and alkaline earth metal compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, cesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium fluoride, potassium fluoride, cesium fluoride, etc. The alkali metal compounds and alkaline earth metal compounds may be used alone or in combination of two or more.

The alkali metal compound may preferably be at least one selected from the group consisting of alkali metal hydroxides, halides, sulfates, carbonates, and hydrogen carbonates.

The amount of the _SiO2- containing material added in step a) can be appropriately set, but is preferably 1 to 50 parts by weight, more preferably 1 to 15 parts by weight, per 100 parts by weight of the alcohol compound.

In addition, the amount of the alkali metal compound or alkaline earth metal compound added in step a) is preferably 1 to 20 parts by weight, more preferably 13 to 20 parts by weight, per 100 parts by weight of the raw material containing _SiO2 .

In a preferred embodiment, in step a), in addition to the alcohol compound, a basic solution or an aprotic organic solvent can be further added as a solvent. Examples of such a basic solution include aqueous ammonia, and examples of the aprotic organic solvent include acetals such as dimethoxypropane. Other ethers can also be used.

As described above, in the process b) of the present invention, the mixture obtained in process a) is heated to produce a SiO ₂ -containing hardened material. After the reaction is carried out in a high-temperature environment, the SiO ₂ component on the left side of the reaction formula (1) is regenerated by cooling to room temperature, etc., thereby obtaining a hardened material in which the SiO ₂ -containing materials are directly bonded to each other.

The heating temperature in step b) is preferably in the range of 100 to 300°C, more preferably in the range of 150 to 250°C. The heating time can be set appropriately depending on the amount of reactants, etc., but is typically in the range of 12 to 96 hours, more preferably in the range of 24 to 72 hours. Cooling after heating is preferably performed by allowing to cool to around room temperature.

The reactor and operation procedure for carrying out steps a) and b) are not particularly limited and can be appropriately selected depending on the purpose. The reactor is preferably a pressure-resistant and heat-resistant reactor such as an autoclave.

The reaction in steps a) and b) is not particularly limited, but is usually at least 0.1 MPa, preferably at least 0.5 MPa, more preferably at least 1.0 MPa, and is usually at most 60 MPa, preferably at most 30 MPa, more preferably at most 20 MPa.

In a preferred embodiment, step b) may further include pressing the solid components in the mixture. This can increase the strength of the _SiO2- containing hardened body. The pressing is preferably a physical press, i.e., a mechanical stress is applied to compress the mixture. Therefore, the reactor may be provided with a means for pressing in the reactor. As such a pressing means, for example, a metal plate having punch holes that can be driven in the vertical direction is placed in the reactor, and the solid components in the mixture are pressed by this. In this case, the dimensions of the metal plate may be slightly smaller than the inner diameter of the reactor, so that the liquid components in the mixture escape to the top through the gap with the reactor wall, and pressure can be applied only to the solid components.

Step c) in the manufacturing method of the present invention is a step of separating the _SiO2- containing hardened body produced in step b) from the solvent and isolating the hardened body as the target product. For such separation, a method known in the art, such as filtration, can be used. In addition, the alcohol compound and the alkali metal compound or the alkaline earth metal compound separated from the hardened body can be reused in the next reaction process.

In a preferred embodiment, the _SiO2- containing cured body separated in step c) can be further subjected to a heat drying treatment, which can convert the hydrogen bonds on the surface of the cured body into covalent bonds through a dehydration (condensation) reaction, which is suitable for the purpose of further increasing the strength of the cured body.

2. Treatment method and treatment agent of the present invention The manufacturing method of the present invention for obtaining a hardened body from a _SiO2- containing material has been described above, but from another perspective, such a process can also be regarded as a treatment method for a _SiO2- containing material.

That is, in another aspect, the present invention also relates to a method for treating a SiO _2- containing material, comprising the following steps A) and B):
A) a step of mixing a _SiO2- containing material, an alcohol compound, and an alkali metal compound or an alkaline earth metal compound; and B) a step of heat-treating the mixture obtained in step A).

Here, the types and amounts of the SiO2 _- containing material, alcohol compound, alkali metal compound, or alkaline earth metal compound in step A) have already been described. The heating conditions in step B) are similarly described above. In a preferred embodiment, the SiO2 _- containing material to be treated by the present invention is gravel or sand having a particle size in the range of 1 μm to 10 cm.

The present invention also relates to a treatment agent for _SiO2- containing materials, which contains an alcohol compound and an alkali metal compound or an alkaline earth metal compound. The above explanation can be applied to the type and content of the alcohol compound, alkali metal compound, or alkaline earth metal compound in the treatment agent. The _SiO2- containing material to be treated with the treatment agent is preferably gravel or sand having a particle size in the range of 1 μm to 10 cm.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

1. Production of _SiO2- containing hardened body 6 g of silica sand having a particle size of 0.1 mm ("Mikawa-made silica sand No. 8" manufactured by Marutosha Co., Ltd.), 1 g of potassium hydroxide (KOH), 75 ml of ethanol, and 0.9 ml of dimethoxypropane were placed in a small box-shaped container made of copper or stainless steel thin film, and then placed in a pressure reactor. After sealing the reactor, it was heated at 240 ° C for 24 hours. After heating, the reactor was cooled to room temperature, and the obtained hardened body was isolated by filtration. The pressure in the reactor was maintained at 5 MPa.

The reaction vessel used is shown in Figure 1. An image of the resulting cured product is shown in Figure 2.

The same reaction was carried out by varying the heating time and the amount of KOH added (w/w). The results are shown in Table 1.

Figure 3 shows the hardened body obtained by heating for 24 hours in 13.8% KOH/silica (6 g silica sand; 0.83 g KOH). Figure 4 shows the hardened body obtained by heating for 24 hours in 16.5% KOH/silica (6 g silica sand; 1 g KOH).

Furthermore, experiments were also conducted under various other conditions to examine their effect on the formation of the hardened body.

2. Ratio of silica sand to ethanol The ratio (w/w) of silica sand to ethanol was changed in the range of 5.1 to 20.5%, and the hardened body was synthesized. In each condition, 50 ml of ethanol was used, 0.15 ml of dimethoxypropane was used, and KOH was 16.5% KOH/silica. The results are shown in Table 2.

3. Ratio of dimethoxypropane to ethanol The ratio (w/w) of dimethoxypropane to ethanol was changed in the range of 0.06 to 0.24%, and the hardened body was synthesized. In each condition, the amount of ethanol was 75 ml, and the mass ratio of silica sand to dimethoxypropane was fixed at 42%. The results are shown in Table 3.

4. Ratio of dimethoxypropane to silica sand The ratio (w/w) of dimethoxypropane to silica sand was changed in the range of 8 to 44%, and the hardened body was synthesized. In each condition, the amount of ethanol was fixed at 75 ml, the amount of KOH was fixed at 0.66 g, and the amount of silica sand was fixed at 4 g. The results are shown in Table 4.

5. Heating temperature The heating temperature was changed in the range of 180 to 243°C to synthesize a hardened body. In each condition, the amount of ethanol was fixed at 75 ml, KOH at 0.66 g, silica sand at 4 g, and dimethoxypropane at 0.6 ml. The results are shown in Table 5.

Claims (11)

A method for producing a _SiO2- containing cured body, comprising the steps of: a) mixing a raw material containing _SiO2 , an alcohol compound, and an alkali metal compound;
b) a step of generating a SiO ₂ -containing hardened body by heat-treating the mixture obtained in step a) (excluding a step of removing water from the mixture obtained in step a) using a molecular sieve or an organic dehydrating agent ); and c) a step of separating the SiO ₂ -containing hardened body generated in step b);
In the step a), the alkali metal compound is 13 to 20 parts by weight per 100 parts by weight of the raw material containing _SiO2 ;
the alkali metal compound is potassium hydroxide, sodium hydroxide, sodium carbonate, or potassium carbonate;
The _SiO2- containing cured material is an aggregate having a structure in which the _SiO2 components present on the surface of the SiO2 _- containing raw material are bonded to each other, and the SiO2 _- containing raw materials are directly bonded to each other.
The manufacturing method. The method according to claim 1, wherein the raw material containing _SiO2 is 1 to 50 parts by weight per 100 parts by weight of the alcohol compound. The method according to claim 1 or 2, wherein the heat treatment in step b) is carried out at a temperature in the range of 100 to 300°C. The manufacturing method according to any one of claims 1 to 3, wherein the raw material containing _SiO2 has a particle shape with a particle size in the range of 1 μm to 10 cm. The manufacturing method according to any one of claims 1 to 4, wherein the _SiO2 -containing raw material comprises silica stone, silica sand, diatomaceous earth, quartz, or silica. The manufacturing method according to any one of claims 1 to 5, wherein the raw material containing _SiO2 is gravel or sand. The method according to any one of claims 1 to 6, wherein the alcohol compound is ethanol or methanol. The method according to any one of claims 1 to 7, further comprising adding a basic solution or an aprotic organic solvent in step a). The method according to any one of claims 1 to 8, further comprising pressing the solid components in the mixture by mechanical stress in step b). The manufacturing method according to any one of claims 1 to 9, comprising subjecting the _SiO2- containing cured body separated in the step c) to a heat drying treatment. A composition for use in the method for producing a _SiO2- containing cured body according to any one of claims 1 to 10, comprising an alcohol compound and an alkali metal compound.