Method for electrochemical synthesis of tetraalkoxy n-silane

Abstract

The invention relates to a green synthesis process of tetraethoxysilane. The activated monatomic silicon and catalyst mixture directly reacts with ethanol in an electrolytic cell, the electrolytic cell contains a promoter and an electrolyte, and tetraethoxysilane is synthesized by applying voltage under heating and stirring conditions. Compared with a traditional method, the method has the advantages of being simple in process, low in energy consumption and environmentally friendly. The selectivity of tetraethoxysilane synthesized by the method exceeds 90%, the silicon powder conversion rate exceeds 95%, and the yield is higher than 80%.

Description

Technical Field

[0001] The invention relates to the field of silicon organic monomer synthesis, and a method for directly synthesizing tetraethoxysilane by electrochemical method in which an activated catalyst and a simple silicon mixture are dissolved in an alcohol electrolyte and alcohol. 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 insulation 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% during 2024-2030.

[0003] The current classic synthesis method of TEOS uses industrial crude silicon to directly react with chlorine under heating conditions to produce silicon tetrachloride. When heated to 200~300℃, the reaction begins to produce SiCl4, and silicon tetrachloride is converted into TEOS by alcoholysis. At the same time, a large amount of hydrogen chloride gas is produced by the byproduct, causing equipment corrosion and environmental pollution. The chemical reaction equation for its synthesis is as follows: Si+2Cl2 SiCl4; SiCl4+4ROH Si(OR)4+4HCl 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.

[0004] The direct synthesis of alkoxysilanes was first proposed by Rochow in 1948, and now has a research history of more than 60 years. Trimethoxysilane has been industrialized. The American Witco Company built the world's first "direct synthesis of trimethoxysilane" industrial production equipment in Italy from 1996 to 1997. The direct synthesis of other alkoxysilanes has never been reported to be industrialized. Generally, high-temperature organic solvents are used as suspending agents, and vaporized ethanol is introduced into the synthesis under the action of catalysts. This process consumes a large amount of high-temperature organic solvents, and the separation of products is relatively complicated.

[0005] This patent adopts 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

[0006] Aiming at the shortcomings of the existing tetraethoxysilane production process, the problem of releasing hydrogen chloride gas during alcoholysis of chlorosilane, corroding equipment, polluting the environment, etc., the present invention proposes an electrochemical method for directly synthesizing tetraalkoxysilane from silanol with simple process and environmental friendliness.

[0007] The technical solution adopted to realize the present invention is as follows: Tetraethoxysilane is directly synthesized by using elemental silicon and ethanol in the presence of a catalyst and an electrolyte and applying a suitable voltage.

[0008] A method for electrochemically synthesizing tetraalkoxysilane comprises the following steps: (1) After the elemental silicon and the main catalyst are mixed, the temperature is raised to activate them. (2) Adding alcohol, a co-catalyst and an electrolyte to the activated product, electrochemically synthesizing tetraalkoxysilane under copper electrode conditions; the reaction formula is as follows: Si+4ROH→Si(OR)4+2H2.

[0009] The purity of the elemental silicon described in step (1) is greater than 99%, and the particle size is between 60-500 mesh.

[0010] The main catalyst described 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%.

[0011] 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.

[0012] 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.

[0013] The alcohol includes any one of methanol, ethanol, propanol, isopropanol, butanol, 2-butanol, amyl alcohol and isopentanol.

[0014] 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 further preferably lower than 500 ppm.

[0015] In some embodiments, molecular sieves may be used to dehydrate the alcohol.

[0016] The co-catalyst in step (2) is selected from ammonium fluoride, and the amount of the co-catalyst is 0.3-2.0%.

[0017] 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.

[0018] The voltage of the electrolytic reaction in step (2) is 2-12 V, the reaction temperature is 50-110° C., and the reaction time is 1-10 hours.

[0019] In some embodiments, the electrolytic cell uses copper as an electrode and uses magnetic stirring to suspend silicon powder in an alcohol solvent for electrolytic reaction.

[0020] The method has a selectivity of more than 90% for synthesizing tetraethoxysilane, a silicon conversion rate of more than 95%, and a yield of more than 80%. The reaction process is simple and environmentally friendly, and is a green synthesis process for tetraethoxysilane. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description is given below in conjunction with specific embodiments.

[0022] Example 1 10g of elemental silicon of 60-200 mesh and 0.5g of cuprous oxide were mixed evenly, put into a tube furnace and activated at 300℃ for 2 hours under nitrogen protection, put into an electrolytic cell after cooling, and 100mL of ethanol, 0.1g of ammonium fluoride, 2g of sodium ethoxide, and a copper electrode were added. Air and moisture were removed by nitrogen purge, and a DC voltage of 6V was applied under stirring conditions, heated to 50°C, and stirred for 4 hours for electrochemical reaction to obtain tetraethoxysilane. GC measured the selectivity of tetraethoxysilane to be 95.6%, the product yield to be 82.2%, and the purity to be 99.3%.

[0023] Example 2 10g of elemental silicon with 500 mesh was mixed evenly with a composite catalyst (0.3g of cuprous oxide and 0.2g of cupric oxide were stirred and mixed), put into a tubular furnace and activated at 400°C for 2 hours under nitrogen protection, and then put into an electrolytic cell after cooling, and 110mL of ethanol, 0.12g of ammonium fluoride, 3g of sodium ethoxide, and a copper electrode were added. Air and moisture were removed by nitrogen purge, and a DC voltage of 8V was applied under stirring conditions. The mixture was heated at 40°C and stirred for 5 hours to perform an electrochemical reaction to obtain tetraethoxysilane. GC measured the selectivity of tetraethoxysilane to be 97.5%, the yield to be 84%, and the purity to be 98.7%.

[0024] Example 3 10g of elemental silicon with a mesh size of 60-200 was mixed evenly with 1g of cuprous oxide, placed in a tubular furnace, activated at 200°C for 5 hours under nitrogen protection, and put into an electrolytic cell after cooling. 90mL of ethanol, 0.05g of ammonium fluoride, 4g of sodium methoxide, and a copper electrode were added. Air and moisture were removed by nitrogen purge. Under stirring conditions, a DC voltage of 4V was applied, heated to 60°C, and stirred for reaction for 8 hours to obtain tetraethoxysilane. GC measured the reaction selectivity as 96.2%, the yield of the product as 86.4%, and the purity as 99.1%.

[0025] Example 4 10g of elemental silicon with a mesh size of 60-200 was mixed evenly with a composite catalyst (0.2g of cuprous oxide + 0.2g of cupric oxide + 0.1g of copper powder, stirred and mixed), activated at 500°C for 1 hour in a tubular furnace under nitrogen protection, put into an electrolytic cell after cooling, added with 120mL of ethanol, 0.04g of ammonium fluoride, 4g of sodium hydroxide, and a copper electrode, purged with nitrogen to remove air and moisture, applied a DC voltage of 10V at 70°C, and reacted for 10 hours to obtain tetraethoxysilane. Samples were taken and analyzed by GC, and the selectivity of tetraethoxysilane was 96.3%, the yield of the distilled product was 85.3%, and the purity was 98.2%.

[0026] 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 the elemental silicon and the main catalyst are mixed, the temperature is raised to activate them. (2) Adding alcohol, a co-catalyst and an electrolyte to the activated product, electrochemically synthesizing tetraalkoxysilane under copper electrode conditions; 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 described 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 main catalyst described 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%.

4. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: 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.

5. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The alcohol described in step (2) includes C1-C5 alcohol, and the molar ratio of elemental silicon to alcohol is 1:4-6.

6. The method for electrochemically synthesizing tetraalkoxysilane according to claim 5, characterized in that: 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 further preferably lower than 500 ppm.

7. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The co-catalyst in step (2) is selected from ammonium fluoride, and the amount of the co-catalyst is 0.3-2.0%.

8. 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.

9. The method for electrochemically synthesizing tetraalkoxysilane according to claim 1, characterized in that: The voltage of the electrolytic reaction in step (2) is 2-12 V, the reaction temperature is 30-80° C., and the reaction time is 1-10 hours.

10. A tetraalkoxysilane, characterized in that The method is prepared by the method described in any one of claims 1 to 9, wherein the selectivity of synthesizing tetraethoxysilane by the method is above 90%, the silicon conversion rate exceeds 95%, and the yield is above 80%.