JP2014227342A - Method for producing tetraalkoxysilane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of producing a tetraalkoxysilane using silica in a silicicolous plant at a high reaction rate with high yield.SOLUTION: There is provided a method for producing a tetraalkoxysilane, the method comprising: a step of heating silica contained in a silicicolous plant in an alkaline solution to obtain silica containing silanol; and a step of reacting the silica containing silanol and a dialkyl carbonate under a closed system or pressure in the presence of a basic alkali metal hydroxide or a basic alkali metal salt to obtain a tetraalkoxysilane.

Description

  The present invention relates to a method for producing tetraalkoxysilane.

  The synthesis of silicone, which is an organosilicon compound, has been conventionally performed by the following method.

  First, metal silicon and methyl chloride are directly reacted to obtain dichlorodimethylsilane. Alkylchlorosilane such as dichlorodimethylsilane is hydrolyzed to obtain silicone (for example, page 33, right column, lines 2 to 6 of Non-Patent Document 1 below). However, in the method of chlorinating metal silicon with methyl chloride or the like, halogen such as chlorine is used. Therefore, the environmental burden is large. Therefore, as described in Non-Patent Document 1, various attempts have been made to obtain silicon compounds using SiO 2 in rice husks, that is, rice husk silica, instead of metallic silicon.

Science Forum Co., Ltd. “Organic Silicon Strategic Materials-First Collection-” Part 1 Chapter 1 III. (Okutani Takeshi, pages 33-40, published in May 1991)

  In recent years, various attempts have been made to synthesize silicon compounds using silica in silicic acid plants. In particular, a method for producing an organosilicon compound is strongly demanded.

  An object of the present invention is to provide a method that makes it possible to produce tetraalkoxysilane with a high reaction rate and a high yield using silica in a silicate plant as a raw material.

  The present inventor obtains silica containing silanol by heating silica contained in the silicate plant in an alkaline solution, and then the silica containing silanol and the dialkyl carbonate are sealed in a closed system or under pressure. It has been found that tetraalkoxysilane can be produced at high reaction rate and high yield by reacting in the presence of a basic alkali metal hydroxide or basic alkali metal salt as a catalyst.

  The present invention, which has been completed based on the above knowledge, comprises the steps of obtaining silica containing silanol by heating silica contained in a silicic acid plant in an alkaline solution, silica containing silanol, and dialkyl carbonate. And a step of reacting in the presence of a basic alkali metal hydroxide or a basic alkali metal salt as a catalyst in a closed system or under pressure to obtain a tetraalkoxysilane.

  In one embodiment of the method for producing tetraalkoxysilane of the present invention, silica contained in rice husks is used as the silicic acid plant.

  In another embodiment of the method for producing tetraalkoxysilane of the present invention, before the step of obtaining the silica containing silanol, the step of obtaining the silica contained in the rice husk by leaching the rice husk with an acidic solution is performed. To do.

In still another embodiment of the method for producing a tetraalkoxysilane of the present invention, NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ , RbOH or Rb ₂ CO ₃ is used as the catalyst.

  In still another embodiment of the method for producing a tetraalkoxysilane of the present invention, the pressure in the closed system or under pressure is 0.2 MPa or more and 10 MPa or less.

  In still another embodiment of the method for producing a tetraalkoxysilane of the present invention, the reaction temperature in the closed system or under pressure is 200 to 500 ° C.

  In still another embodiment of the method for producing tetraalkoxysilane of the present invention, the dialkyl carbonate is dimethyl carbonate or diethyl carbonate.

  ADVANTAGE OF THE INVENTION According to this invention, the method which makes it possible to manufacture tetraalkoxysilane with a high reaction rate and a high yield can be provided from the silica in a silicic acid plant as a raw material.

It is a graph which shows the reaction rate of the tetramethoxysilane in the reaction temperature of 305 degreeC which concerns on various silica.

1. Generation of Silanol-Containing Silica In the method for producing tetraalkoxysilane according to the present invention, silica containing silanol is first obtained by heating silica contained in a silicate plant in an alkaline solution.

(Silica in silicic acid plants)
Silica in silicic acid plants refers to silica originating from silicic acid ions contained in living organisms of silicic acid plants such as rice, wheat, sugarcane, corn, bamboo, Japanese pampas grass, and horsetail. In particular, rice husks of rice, which is one of the silicate plants, contain about 20% by weight of silica and rice straw contains about 10% by weight of silica. Therefore, silica in silicic acid plants is inexhaustible silica produced every year by cultivation such as rice cultivation and natural cycle.

  Where silica exists in silicate plants, there are cuticles outside the epidermal cells, such as the walls of conduits and rice husks that feed moisture and nutrients absorbed from the roots. Here, the rice husk containing the most silica in the silicic acid plant (silica content is about 20% by weight) will be described. Rice husk is the hull of rice straw. Rice takes silica from soil and irrigation water as water-soluble silicate ions through roots and accumulates in rice husks, stems and leaves.

  Of the silica accumulated in rice, the silica in rice husk is 15% by weight. Silica incorporated into rice from irrigation water is 20% by weight of silica accumulated in rice, and silica incorporated from soil is 80% by weight. When only silica in rice husk is used, silica in soil does not decrease and does not affect annual rice cultivation.

  Silica in rice husk accumulates in the cuticle outside the epidermal cells. Therefore, organic substances such as cellulose in rice husks are difficult to corrode and become fertilizers and are not effectively used. Furthermore, the silica content in the rice husk is about 20% by weight of the rice husk and is present more in the stem and leaves. Thus, rice husks are suitable for obtaining silica in silicate plants.

  In addition, the property of silica is not limited to the kind of rice, and there is no difference even if it is Japonica or Indica.

Rice husk silica can be obtained by removing organic substances such as cellulose, hemicellulose or lignin in the rice husk and inorganic substances other than silica. The rice husk contains about 5% by weight of impurities, but the rice husk silica can be obtained by burning it at a temperature of 500 ° C. or higher. In this case, carbon is 5% by weight, impurities such as potassium oxide and calcium oxide remain 6% by weight or less, the purity of rice husk silica is 89% by weight or more, and the surface area is 100 m ² / g or less. On the other hand, when rice husk is leached with an acidic solution such as hydrochloric acid to remove impurities, carbon 2% or less, impurities such as potassium oxide or calcium oxide remain 0.1% or less, and the purity of rice husk silica is 99%. % And higher purity. Furthermore, the surface area of SiO ₂ produced from the leached rice husk varies depending on the combustion temperature, but it is 100 to 333 m ² / g or less, which is a wider surface area. Silica from which impurities have been removed by leaching with an acidic solution becomes active silica having a larger surface area and a primary particle size of 20 to 300 nm. For this reason, in order to obtain rice husk silica from rice husks, it is preferable to perform rice husk leaching with an acidic solution.

  Further, when active silica contained in 20% by weight of rice husk is used as a silica source, the above-mentioned hydroxyl group can be easily introduced, the later-described silanol can be easily produced, and the production of tetraalkoxysilane is promoted. .

(Silanol production)
In the present invention, silica containing silanol is obtained by heating silica contained in a silicic acid plant in an alkaline solution. Thus, by having a silanol having a hydroxyl group bonded to silica, it is described later. Formation of tetraalkoxysilane is promoted. That is, silica has a network structure composed of Si—O bonds, but in the case of silica having a hydroxyl group (—OH) as in the present invention, a bond between silicon and a hydroxyl group (Si—OH). have. Here, the Si—OH bond is easier to cut than the Si—O bond constituting the network structure, and the presence of the OH group also reduces the SiO ₂ part to be cut. For this reason, the activation energy of the said silica decreases, and the production | generation of the tetraalkoxysilane using this is accelerated | stimulated.

  Specifically, for example, 2 g of rice husk silica and 40 mL of an alkali metal hydroxide solution such as sodium hydroxide of 0.01 to 3 mol / L, preferably 0.01 to 0.15 mol / L, in an autoclave. , 100 to 200 ° C., preferably 100 to 125 ° C. After treatment for 5 minutes to 4 hours, preferably 5 to 30 minutes, the solid matter produced in the autoclave is taken out and washed with distilled water until the filtrate reaches pH 8.0. Then, the rice husk silica which a part of silane became silanol is obtained by vacuum-drying at 60 degreeC. In the present invention, silanol is made part or most of silica by reacting rice husk silica, which is silica in silicic acid plants, with an alkaline solution under hydrothermal reaction conditions.

2. Production of Tetraalkoxysilane The method for producing a tetraalkoxysilane according to the present invention is a method in which silica containing silanol is obtained by the above process, and then silica containing silanol and dialkyl carbonate are catalyzed in a closed system or under pressure. Tetraalkoxysilane is obtained by reacting in the presence of a basic alkali metal hydroxide or basic alkali metal salt.

  At this time, it is desirable to use dialkyl carbonate in a proportion of 2 to 30 mol, preferably in a proportion of 2.1 to 3 mol, with respect to 1 mol of a mixture of rice husk silica and silanol. By blending dialkyl carbonate within this range, tetraalkoxysilane can be produced in high yield, and wasteful consumption of dialkyl carbonate can be reduced.

  In addition, as described above, since an alkali metal hydroxide or alkali metal salt showing basicity is used as a catalyst in a closed system or under pressure, the reaction rate can be increased, and the yield of tetraalkoxysilane. Can be effectively increased.

  The pressure in the closed system or under pressure is preferably 0.2 MPa or more and 10 MPa or less. In this case, all or part of the dialkyl carbonate and the product tetraalkoxysilane can be kept in a liquid phase, thereby melting the catalyst and keeping it in an ionic state, which can easily act on silica. . For this reason, the reaction rate can be further increased. The pressure in the closed system or under pressure is more preferably 0.4 MPa or more and 2 MPa or less. In this case, tetraalkoxysilane can be obtained at a higher reaction rate.

  The temperature during the reaction in the closed system or under pressure is preferably 200 to 500 ° C, more preferably 250 to 350 ° C. Moreover, if the said reaction temperature is 280-325 degreeC, while improving the yield of tetraalkoxysilane, decomposition | disassembly can be suppressed favorably.

  The reaction vessel used for the reaction in the closed system or under pressure is not particularly limited as long as it can react rice husk silica and dialkyl carbonate in the presence of the catalyst under the closed system or under pressure, and batch reaction. System or distribution system may be used. Moreover, when a batch reaction system is used, there is an advantage that it is possible to suppress wasteful consumption of dialkyl carbonate and rice husk silica.

(Dialkyl carbonate)
Although it does not specifically limit as dialkyl carbonate used by this invention, Dimethyl carbonate, diethyl carbonate, dinormal propyl carbonate, diisopropyl carbonate, etc. can be mentioned. Preferably, dimethyl carbonate or diethyl carbonate is used. In that case, tetramethoxysilane and tetraethoxysilane can be obtained quickly and with a high yield.

(catalyst)
As the catalyst, a basic alkali metal hydroxide or salt is used. Among alkali metals, the higher the atomic number, the stronger the alkali metal hydroxides and salts. By using a strongly basic alkali metal hydroxide or carbonate, tetraalkoxysilane can be obtained in high yield. More preferably, NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ , RbOH or Rb ₂ CO ₃ is used. In this case, the reaction rate can be further increased, and tetramer is obtained in a higher yield. An alkoxysilane can be obtained. The addition amount of the catalyst is 0.1 to 10 atomic% (atomic reference concentration), preferably 1 to 7 atomic% as alkali metal ions with respect to silica.

(Tetraalkoxysilane)
In the present invention, for example, tetramethoxysilane or tetraethoxysilane can be obtained as the tetraalkoxysilane by the above reaction. The tetraalkoxysilane thus obtained can be used for surface treatment of inorganic substances, synthesis of ceramics, synthesis of spherical silica by a sol-gel method, hybridization by silicone modification of a resin, catalyst, carrier and the like.

  Next, examples according to the present invention will be described below, but the present invention is not limited thereto.

Example 1
As the rice husk silica, one prepared by the following procedure was prepared.
After adding 3% (v / v) hydrochloric acid solution to the washed rice husk and performing reflux leaching for 2 hours to remove impurities, the temperature was raised at a heating rate of 5 ° C./min in a stream of nitrogen 100 mL / min, It was carbonized by holding at 600 ° C. for 1 hour. Further, rice husk silica was produced by heating in air for 3 hours at the same temperature as that during carbonization. The purity of the obtained rice husk silica was 99.8% by weight, and the surface area was 333 m ² / g.

  Next, a catalyst (potassium carbonate) is added to the rice husk silica prepared as described above so that the alkali metal content is 5 at% with respect to silica, and after mixing for 40 minutes using an agate mortar, 110 A reaction sample was obtained by removing moisture by vacuum drying at 2 ° C. for 2 hours. In order to compare and examine the difference in reactivity depending on the type of silica, a hydrochloric acid solution is added to a silica sand or sodium silicate solution to form a silica hydrosol, and the sol is dried. AEROSIL (registered trademark), which is amorphous silica and fume deerica: Aerosil and four types of those heated at 600 ° C. for 3 hours in the air (Aerosil 600) are used, and the alkali metal content is 5 at% with respect to silica. A catalyst (potassium carbonate) was added so that a reaction sample was obtained.

  Next, n-heptane was used as a standard substance, 0.1 g of silica to which a catalyst (potassium carbonate) was added, and 50 cc of a mixed solution 0.5 mL adjusted to dimethyl carbonate: n-heptane = 5: 2 (volume ratio). In an autoclave. Subsequently, the inside of the autoclave was replaced five times with an inert gas 0.6078 MPa to form an inert gas atmosphere, and heating was performed at 305 ° C. using an electric furnace to react silica and dimethyl carbonate. The liquid sample before and after the reaction was analyzed by gas chromatography to obtain the reaction rate.

  Table 1 shows the crystal form, secondary particle diameter, and specific surface area of each silica. Table 2 shows the mol% of OH groups contained in various silicas. From the TG-DTA curve, the sudden weight loss (adhesion water) up to 120 ° C, and the weight loss when the temperature rises to 120 ° C or higher and 1000 ° C at a temperature rising rate of 5 ° C / min, The amount of OH groups contained in the silica was determined as the weight loss due to the contained OH groups. In FIG. 1, the graph which shows the reaction rate of the tetramethoxysilane in the reaction temperature of 305 degreeC concerning various silica is shown.

  Comparing the reaction rates of rice husk silica, aerosil, amorphous silica, and silica sand, silica sand did not react, and the reaction rate increased in the order of amorphous silica, rice husk silica, and aerosil. This difference in reactivity was not related to the particle diameter and surface area, and it was recognized that there was a correlation in the amount of OH groups in silica shown in Table 2.

  On the other hand, when Aerosil was heat-treated at 600 ° C. for 3 hours (Aerosil 600), the mol% of OH groups in the silica was 9.6 mol%, which is 60% less than that of Aerosil. It can be seen that the diameter is small. For this reason, in this case, it is recognized that the particle size is related to the difference in reactivity.

(Example 2)
Put 0.033 mol of rice husk silica, 0.03 mol of sodium hydroxide, and 40 mL of distilled water in an autoclave, perform heat treatment at 100 ° C. for 15 minutes, and wash the resulting solid with warm water until the filtrate reaches pH = 8. did. Subsequently, the washed solid was vacuum-dried at 60 ° C. for 120 minutes. The OH groups contained in the rice husk silica were contained in 38 mol% with respect to the silica as shown in Table 2 “Cow husk silica treated under hydrothermal conditions”. When this rice husk silica introduced with OH groups was reacted with dimethyl carbonate in the same manner as in Example 1, the reaction rate was 98% after the reaction for 30 minutes, and the more OH groups were contained, the more OH groups were contained. It was observed that the reaction was significantly accelerated.

Claims (7)

A step of obtaining silica containing silanol by heating silica contained in the silicate plant in an alkaline solution;
A step of reacting silica containing silanol and dialkyl carbonate in a closed system or under pressure in the presence of a basic alkali metal hydroxide or basic alkali metal salt as a catalyst to obtain a tetraalkoxysilane; The manufacturing method of the tetraalkoxysilane containing this.   The method for producing tetraalkoxysilane according to claim 1, wherein silica contained in rice husk is used as the silicic acid plant.   The method for producing tetraalkoxysilane according to claim 2, wherein the step of obtaining silica contained in the rice husk by leaching the rice husk with an acidic solution is performed before the step of obtaining silica containing the silanol. The method for producing tetraalkoxysilane according to claim 1, wherein NaOH, Na ₂ CO ₃ , KOH, K ₂ CO ₃ , RbOH or Rb ₂ CO ₃ is used as the catalyst.   The method for producing tetraalkoxysilane according to any one of claims 1 to 4, wherein the pressure in the closed system or under pressure is 0.2 MPa or more and 10 MPa or less.   The method for producing tetraalkoxysilane according to any one of claims 1 to 5, wherein a reaction temperature in the closed system or under pressure is 200 to 500 ° C.   The method for producing tetraalkoxysilane according to any one of claims 1 to 6, wherein the dialkyl carbonate is dimethyl carbonate or diethyl carbonate.