A method for electrochemically synthesizing tetraalkoxysilane

Abstract

The present invention provides a green synthesis process for tetraethoxysilane. Activated elemental silicon reacts directly with a catalyst mixture and ethanol in an electrolytic cell containing a co-catalyst and electrolyte. Tetraethoxysilane is synthesized by applying a voltage under heated and stirred conditions. Compared with traditional methods, this method offers the advantages of simplicity, low energy consumption, and environmental friendliness. The tetraethoxysilane synthesized by this method achieves a selectivity exceeding 90%, a silicon powder conversion exceeding 95%, and a yield exceeding 80%.

Description

Technical Field

[0001] The present invention relates to the field of silicon organic monomer synthesis, and is a method for directly synthesizing tetraethoxysilane by electrochemically dissolving an activated catalyst and a mixture of elemental silicon and alcohol in an alcohol electrolyte. Background Art

[0002] Tetraethoxysilane (TEOS) is an important organosilicon compound with multiple uses. TEOS is the main silicon source for the preparation of silica aerogel, and is formed into high-thermal-insulating silica aerogel through a vapor deposition process. TEOS is an important intermediate in organic synthesis, used to prepare chemical coatings, heat-resistant coatings, electrical insulation materials, optical glass processing machines, organosilicon solvents, and adhesives for precision casting. Tetraethoxysilane, as an auxiliary agent for ceramic materials, can enhance the impact resistance and wear resistance of ceramic materials. TEOS is increasingly used as a special gas material for electronics. In 2023, the global electronic-grade ethyl orthosilicate market size was approximately US$195 million, and is expected to reach US$288 million in 2030, with a compound annual growth rate of 5.8% from 2024 to 2030.

[0003] The current classic synthesis method for TEOS involves directly reacting industrial crude silicon with chlorine under heating conditions to produce silicon tetrachloride. When heated to 200-300°C, the reaction begins to produce SiCl4, which is then converted into TEOS by alcoholysis. This, along with the release of large amounts of hydrogen chloride gas, can cause equipment corrosion and environmental pollution. The chemical reaction equation for its synthesis is as follows:

[0004] Si+2Cl2 SiCl4; SiCl4+4ROH Si(OR)4+4HCl

[0005] The method of directly synthesizing TEOS from silanols has the advantages of simple process, low cost and environmental friendliness, and has become a hot topic in TEOS synthesis research. Currently, most of the literature reports focus on the synthesis of trialkoxysilanes.

[0006] The direct synthesis of alkoxysilanes, first proposed by Rochow in 1948, now boasts a research history spanning over 60 years. While trimethoxysilane has been industrialized, with the US company Witco building the world's first industrial production facility for direct synthesis of trimethoxysilane in Italy between 1996 and 1997, the direct synthesis of other alkoxysilanes has never been commercialized. Typically, a high-temperature organic solvent is used as a suspending agent, followed by the addition of vaporized ethanol in the presence of a catalyst. This process consumes large amounts of high-temperature organic solvent and complicates product separation.

[0007] This patent uses an electrochemical method to directly synthesize TEOS using silanol, which has the significant advantages of low cost, simple process and environmental friendliness. Summary of the Invention

[0008] The present invention addresses the shortcomings of the existing tetraethoxysilane production process, such as the release of hydrogen chloride gas during the alcoholysis of chlorosilane, which corrodes equipment and pollutes the environment. An electrochemical method for directly synthesizing tetraalkoxysilane from silanol is proposed, which is simple in process and environmentally friendly.

[0009] The technical solutions adopted to realize the present invention are as follows:

[0010] Tetraethoxysilane is directly synthesized by using elemental silicon and ethanol in the presence of a catalyst and an electrolyte and applying a suitable voltage.

[0011] A method for electrochemically synthesizing tetraalkoxysilane comprises the following steps:

[0012] (1) After the elemental silicon and the main catalyst are mixed, the temperature is raised to activate them.

[0013] (2) Add alcohol, co-catalyst, and electrolyte to the activated product and electrochemically synthesize tetraalkoxysilane under copper electrode conditions; the reaction formula is as follows:

[0014] Si+4ROH→Si(OR)4+2H2.

[0015] The purity of the elemental silicon in step (1) is greater than 99%, and the particle size is between 60-500 mesh.

[0016] The main catalyst in step (1) comprises a composite composition formed by one or more of cuprous oxide, cupric oxide or copper, and the addition amount of the main catalyst is 2%-10%.

[0017] In step (1), the activation temperature is between 200-500° C., the activation time is 1-6 hours, and the activation is carried out under a nitrogen atmosphere.

[0018] In the reaction formula of step (2), the alcohol of ROH includes C1-C5 alcohol, and the molar ratio of elemental silicon to alcohol is 1:4-6.

[0019] The alcohol includes any one of methanol, ethanol, propanol, isopropanol, butanol, 2-butanol, amyl alcohol and isopentanol.

[0020] The alcohol is dehydrated in a molecular sieve to make the water content of the alcohol lower than 1500 ppm, more preferably lower than 1000 ppm, and even more preferably lower than 500 ppm.

[0021] In some embodiments, molecular sieves may be used to dehydrate the alcohol.

[0022] In step (2), the co-catalyst is selected from ammonium fluoride, and the amount of the co-catalyst is 0.3-2.0%.

[0023] In step (2), the electrolyte includes sodium ethoxide, sodium hydroxide or sodium methoxide; the concentration of the electrolyte is 0.005 g / ml-0.05 g / ml.

[0024] The voltage of the electrolysis reaction in step (2) is 2-12 V, the reaction temperature is 50-110° C., and the reaction time is 1-10 hours.

[0025] In some embodiments, the electrolytic cell uses copper as electrodes and uses magnetic stirring to suspend silicon powder in an alcohol solvent for electrolytic reaction.

[0026] The method for synthesizing tetraethoxysilane has a selectivity of over 90%, a silicon conversion rate of over 95%, and a yield of over 80%. The reaction process is simple and environmentally friendly, making it a green synthesis process for tetraethoxysilane. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description will be given below in conjunction with specific embodiments.

[0028] Example 1

[0029] 10g of 60-200 mesh silicon and 0.5g of cuprous oxide were mixed uniformly and activated in a tube furnace at 300°C for 2 hours under nitrogen. After cooling, the mixture was placed in an electrolytic cell. 100mL of ethanol, 0.1g of ammonium fluoride, 2g of sodium ethoxide, and a copper electrode were added. A nitrogen purge was performed to remove air and moisture. Under stirring, a DC voltage of 6V was applied, and the mixture was heated to 50°C. The reaction was stirred for 4 hours to produce tetraethoxysilane. GC analysis revealed a tetraethoxysilane selectivity of 95.6%, a product yield of 82.2%, and a purity of 99.3%.

[0030] Example 2

[0031] 10 g of 500-mesh silicon was mixed evenly with a composite catalyst (0.3 g of cuprous oxide and 0.2 g of cupric oxide, stirred and evenly mixed). The mixture was activated in a tube furnace at 400°C under nitrogen for 2 hours. After cooling, the mixture was placed in an electrolytic cell and added with 110 mL of ethanol, 0.12 g of ammonium fluoride, 3 g of sodium ethoxide, and a copper electrode. A nitrogen purge was performed to remove air and moisture. Under stirring conditions, a DC voltage of 8 V was applied. The mixture was heated at 40°C with stirring for 5 hours to perform an electrochemical reaction to obtain tetraethoxysilane. GC analysis showed a selectivity of 97.5%, a yield of 84%, and a purity of 98.7% for tetraethoxysilane.

[0032] Example 3

[0033] 10 g of 60-200 mesh elemental silicon and 1 g of cuprous oxide were mixed uniformly, placed in a tube furnace, activated at 200°C under nitrogen protection for 5 hours, cooled, and placed in an electrolytic cell. 90 mL of ethanol, 0.05 g of ammonium fluoride, 4 g of sodium methoxide, and a copper electrode were added. Nitrogen was purged to remove air and moisture. Under stirring conditions, a DC voltage of 4 V was applied, and the mixture was heated at 60°C. The reaction was stirred for 8 hours to obtain tetraethoxysilane. The reaction selectivity measured by GC was 96.2%, the product yield was 86.4%, and the purity was 99.1%.

[0034] Example 4

[0035] 10g of elemental silicon (60-200 mesh) was mixed evenly with a catalyst mixture (0.2g cuprous oxide, 0.2g cupric oxide, and 0.1g copper powder, stirred and mixed). The mixture was activated in a tube furnace at 500°C under nitrogen for 1 hour. After cooling, the mixture was placed in an electrolytic cell, added with 120mL of ethanol, 0.04g of ammonium fluoride, 4g of sodium hydroxide, and a copper electrode. A nitrogen purge was performed to remove air and moisture. A DC voltage of 10V was applied at 70°C, and the reaction was continued for 10 hours to produce tetraethoxysilane. GC analysis of a sample revealed a tetraethoxysilane selectivity of 96.3%, an 85.3% yield of the distilled product, and a purity of 98.2%.

[0036] All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for electrochemically synthesizing tetraalkoxysilane, characterized in that: The steps include: (1) After uniformly mixing elemental silicon and a main catalyst, the temperature is raised for activation. The main catalyst comprises a composite composition formed by one or more of cuprous oxide, cupric oxide or copper. The activation temperature is between 200°C and 500°C. The activation process is carried out under a nitrogen atmosphere. (2) Cooling the activated product and placing it in an electrolytic cell, adding alcohol, a co-catalyst, and an electrolyte, and electrochemically synthesizing tetraalkoxysilane under copper electrode conditions; the alcohol includes a C1-C5 alcohol; the co-catalyst is selected from ammonium fluoride; the voltage of the electrolytic reaction is 2-12V; The reaction formula is as follows: Si+4ROH→Si(OR)4+2H2.

2. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The purity of the elemental silicon in step (1) is greater than 99%, and the particle size is between 60-500 mesh.

3. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The amount of the main catalyst added in step (1) is 2%-10%.

4. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The heating activation time in step (1) is 1-6 hours.

5. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: In step (2), the molar ratio of elemental silicon to alcohol is 1:4-6; and the amount of the co-catalyst is 0.3-2.0%.

6. The method for electrochemically synthesizing tetraalkoxysilane according to claim 5, characterized in that: The alcohol is dehydrated in a molecular sieve to reduce the water content of the alcohol to less than 1500 ppm.

7. The method for electrochemically synthesizing tetraalkoxysilane according to claim 6, characterized in that: The water content of the alcohol is less than 1000 ppm.

8. The method for electrochemically synthesizing tetraalkoxysilane according to claim 7, characterized in that: The water content of the alcohol is less than 500 ppm.

9. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: In step (2), the electrolyte includes sodium ethoxide, sodium hydroxide or sodium methoxide; the concentration of the electrolyte is 0.005 g / ml-0.05 g / ml.

10. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The temperature of the electrolysis reaction in step (2) is 30-80°C, and the reaction time is 1-10 hours.