A system and process for the direct preparation of tetraalkoxysilanes from silicon powder

Abstract

This invention proposes a system and process for the direct preparation of tetraalkoxysilanes from silicon powder. The system includes a silicon powder reactor, a catalyst reactor, a silicon powder slurry feeding tank, a separation tank, and a centrifuge. A catalyst is prepared in the catalyst reactor, a silicon powder slurry is prepared in the silicon powder slurry feeding tank, and the catalyst, silicon powder slurry, and alcohol are added to the silicon powder reactor to react and prepare tetramethoxysilanes. This invention's direct silicon powder method for preparing tetraalkoxysilanes can simultaneously prepare the catalyst and tetraalkoxysilanes, while simultaneously separating silicon slag, tetraalkoxysilanes, and alcohols. The process is simple and can achieve continuous production.

Description

Technical Field

[0001] This invention relates to the field of tetraalkoxysilane preparation technology, and in particular to a system and process for preparing tetraalkoxysilanes directly from silicon powder. Background Technology

[0002] Tetraalkoxysilanes have been widely used in various industrial fields, from the preparation of silica particles and their inorganic materials and organic polymer composites to adhesives and hard coating agents.

[0003] Tetraalkoxysilanes can be obtained via the dehydrochlorination alkoxylation of tetrachlorosilane with alcohols or via the direct reaction of metallic silicon with alcohols in the presence of a base catalyst. The former method for producing tetraethoxysilanes is now commercially available, but it produces acidic HCl as a byproduct. Furthermore, HCl reacts with alcohols to produce water and chloroalkanes as byproducts. Therefore, HCl should be neutralized with a base under inert conditions as soon as possible and then removed as a salt. Additional processes (such as neutralization and filtration) require costly processes and equipment. Therefore, a low-cost, large-scale method for the preparation of tetraalkoxysilanes is of great interest. Summary of the Invention

[0004] The purpose of this invention is to provide a system and process for the direct preparation of tetraalkoxysilanes from silicon powder, which allows the production of the catalyst for tetraalkoxysilanes to be carried out simultaneously with the production of tetraalkoxysilanes, thereby reducing process costs and achieving continuous production.

[0005] One embodiment of this application proposes a system for the direct preparation of tetraalkoxysilanes using silicon powder, comprising a silicon powder reactor, a catalyst reactor, a silicon powder slurry feeding tank, a separation vessel, and a centrifuge. The silicon powder reactor is provided with a silicon powder slurry inlet, a catalyst inlet, an alcohol inlet, a first nitrogen pipeline, a gas outlet, and a discharge port. The silicon powder slurry outlet of the silicon powder feeding tank is connected to the silicon powder slurry inlet of the silicon powder reactor. The catalyst outlet of the catalyst reactor is connected to the catalyst inlet of the silicon powder reactor. The gas outlet of the silicon powder reactor is connected to the gas inlet of the separation vessel. The discharge port of the silicon powder reactor is connected to the centrifuge. The first outlet of the separation vessel is connected to a condenser, which is used to separate alcohol and hydrogen. The bottom of the separation vessel is provided with a tetraalkoxysilane outlet. An alcohol heating coil is provided inside the separation vessel. The inlet of the alcohol heating coil is connected to an alcohol feeding pump through a pipeline, and the outlet of the alcohol heating coil is connected to the alcohol inlet of the silicon powder reactor through a pipeline.

[0006] In some embodiments, a catalyst condenser is also included, which is connected to the catalyst reactor via a steam pipeline and a return pipeline to form a gas circulation pipeline. The catalyst condenser is equipped with a cooling water coil for cooling the distillate, and the catalyst condenser is also connected to a vacuum device for depressurized distillation inside the catalyst condenser.

[0007] In some embodiments, the catalyst reactor is provided with a second nitrogen pipeline, a first feed pipe, a second feed pipe, a steam outlet, a reflux port, and a catalyst outlet. The first feed pipe is used to add any one of alkali metals, alkali metal alkoxides, alcohol solutions of alkali metal hydroxides, and alcohol solutions of alkali metal carbonates. The second feed pipe is used to add alcohol ether compounds or liquid diethylene glycol oligomers. The steam outlet is connected to the catalyst condenser through a steam pipeline. The catalyst condenser is connected to the reflux port through a reflux pipeline. The catalyst outlet is connected to the catalyst inlet of the silicon powder reactor through a pipeline.

[0008] In some embodiments, the silicon powder slurry feeding tank is provided with a tetraalkoxysilane inlet, a silicon powder inlet, and a silicon powder slurry outlet. The silicon powder inlet is connected to the silicon powder tank via a screw feeder, and the silicon powder slurry outlet is connected to the silicon powder slurry inlet of the silicon powder reactor via a pipeline.

[0009] In some embodiments, the condenser is provided with an inlet, an alcohol outlet, and a hydrogen outlet. The first outlet of the separator is connected to the inlet of the condenser via a pipeline, the alcohol outlet is connected to the inlet of the alcohol feed pump via a pipeline, and the hydrogen outlet is connected to the vent pipe.

[0010] In some embodiments, the centrifuge is connected to the silicon powder reactor via a recovery pipeline.

[0011] In some embodiments, the silicon powder reactor, catalyst reactor, and silicon powder slurry feeding tank are all equipped with a stirring device.

[0012] In some embodiments, a filter for filtering filter residue or foam is connected to the connecting pipeline between the gas outlet of the silicon powder reactor and the separation vessel.

[0013] In some embodiments, a bypass pipe is connected to the silicon powder slurry feeding tank to balance the pressure between the silicon powder slurry feeding tank and the silicon powder reactor. One end of the bypass pipe is connected to the silicon powder slurry feeding tank, and the other end is connected to the pipeline between the silicon powder slurry outlet of the silicon powder slurry feeding tank and the silicon powder slurry inlet of the silicon powder reactor.

[0014] Another embodiment of this application proposes a process for preparing tetraalkoxysilanes using a direct silicon powder method. The system for preparing tetraalkoxysilanes using the above-described direct silicon powder method includes the following steps:

[0015] S1. Catalyst preparation in a catalyst reactor: First, the air in the catalyst reactor and condenser is discharged. Then, any one of the following is added through the first feed pipe: alkali metal, alkali metal alkoxide, alkali metal hydroxide alcohol solution, or alkali metal carbonate alcohol solution. The temperature is raised to 60-150°C. Under stirring, heating, and reflux, alcohol ether compounds or liquid diethylene glycol oligomers are gradually added through the second feed pipe. The reflux reaction is carried out for 0.5-10 hours to generate low-boiling alcohol and catalyst. The low-boiling alcohol flows into the catalyst condenser along the steam pipe. After being cooled by the catalyst condenser, the low-boiling alcohol flows back to the catalyst reactor through the reflux pipe. The prepared catalyst is then introduced into the silicon powder reaction vessel.

[0016] Step S2, preparing silicon powder slurry in silicon powder slurry feeding tank: First, tetraalkoxysilane is added to the silicon powder slurry feeding tank as a solvent. Silicon powder is added to the silicon powder slurry feeding tank through the silicon powder tank. After stirring and mixing evenly, silicon powder slurry is obtained and then introduced into the silicon powder reactor.

[0017] Step S3: Preparation of tetraalkoxysilane in a silicon powder reactor: The air in the silicon powder reactor is purged through the first nitrogen pipeline. The catalyst prepared in step S1 and the silicon powder slurry prepared in step S2 are added to the silicon powder reactor and stirred evenly. The temperature is raised to 100℃~200℃. Heated alcohol is added through the alcohol inlet to react and produce alcohol, hydrogen and tetraalkoxysilane. The alcohol, hydrogen and tetraalkoxysilane are passed into the separation vessel to cool and separate the final product tetraalkoxysilane. The alcohol and hydrogen enter the condenser for separation. The hydrogen is vented or collected through the vent pipe. The condensed alcohol is mixed with the newly introduced alcohol and then transported to the silicon powder reactor by the alcohol feed pump to continue the reaction. The alcohol transported by the alcohol feed pump is first heated in the separation vessel and then passed into the silicon powder reactor to participate in the reaction.

[0018] The heating temperature in the silicon powder reactor is set differently depending on the reaction product, which is either tetramethoxysilane or tetraethoxysilane. The temperature for preparing tetramethoxysilane is between 100℃ and 140℃, and to ensure timely distillation of the tetramethoxysilane, a reaction temperature between 125℃ and 135℃ is most suitable. The reaction temperature for preparing tetraethoxysilane is between 160℃ and 175℃, which facilitates timely distillation of the tetraethoxysilane.

[0019] The beneficial effects of the present invention are as follows: the process for preparing tetraalkoxysilane by direct silicon powder preparation of the present invention can simultaneously prepare catalyst and tetraalkoxysilane, and simultaneously separate silicon slag, tetraalkoxysilane and alcohol. The process is simple and can realize continuous production. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0021] in:

[0022] Figure 1 This is a schematic diagram of the system for preparing tetraalkoxysilanes by the direct method of silicon powder according to this application;

[0023] Figure label:

[0024] 1-Discharge pipe; 2-Vacuum device; 3-Catalyst condenser; 4-Steam pipeline; 5-Reflux pipeline; 6-Oil-water separation pipeline; 7-Catalyst reactor; 8-Second nitrogen pipeline; 9-First feed pipe; 10-Second feed pipe; 11-Silicon powder tank; 12-Screw feeder; 13-Tetraalkoxysilane inlet; 14-Bypass pipe; 15-Silicon powder slurry feed tank; 16-Safety valve; 17-Filter; 18-Silicon powder reactor; 19-First nitrogen pipeline; 20-Recovery pipeline; 21-Centrifuge device; 22-Alcohol heating coil; 23-Separation vessel; 24-Tetraalkoxysilane outlet; 25-Condenser; 26-Flow meter; 27-Vent pipe; 28-Alcohol feed pump; 29-Auxiliary pipeline. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The system and process for preparing tetraalkoxysilanes by direct silicon powder preparation according to embodiments of the present invention are described below with reference to the accompanying drawings.

[0027] like Figure 1 As shown, one embodiment of this application proposes a system for the direct preparation of tetraalkoxysilanes using silicon powder, including a silicon powder reactor 18, a catalyst reactor 7, a silicon powder slurry feeding tank 15, a separation tank 23, a centrifuge device 21, a condenser 25, a silicon powder tank 11, and a catalyst condenser 3.

[0028] The silicon powder reactor 18 is used to react the silicon powder slurry prepared in the silicon powder slurry feeding tank 15 with the catalyst prepared in the catalyst reactor 7 to prepare tetraalkoxysilane. The catalyst reactor 7 is used to synthesize the catalyst for preparing tetraalkoxysilane. The silicon powder slurry feeding tank 15 is used to generate the silicon powder slurry. The separation tank 23 is used to separate tetraalkoxysilane and alcohol. The centrifuge device 21 is used to centrifuge the silicon slag produced after the reaction. The condenser 25 is used to condense and separate the alcohol and hydrogen. The silicon powder tank 11 is used to add silicon powder to the silicon powder slurry feeding tank 15. The catalyst condenser 3 is used to reflux the liquid in the catalyst reactor 7 and perform oil-water separation.

[0029] The silicon powder reactor 18 has an internal stirring paddle and a thermometer for measuring the internal temperature. An external jacket for steam or oil bath heating is provided. An overpressure protection safety valve 16 is also connected to the external part of the reactor. The silicon powder reactor 18 has a silicon powder slurry inlet, a catalyst inlet, an alcohol inlet, a first nitrogen pipeline 19, a gas outlet, and a discharge port. The silicon powder slurry inlet of the silicon powder reactor 18 is connected to the silicon powder slurry outlet of the silicon powder slurry feeding tank 15 via a pipeline. The catalyst inlet of the silicon powder reactor 18 is connected to the catalyst outlet of the catalyst reactor 7 via a pipeline. The alcohol inlet is located at the bottom of the reactor and is used for alcohol feeding. The first nitrogen pipeline 19 is connected to the bottom of the reactor and is used to transport nitrogen and to vent or purge air from the silicon powder reactor 18 and connected equipment. The gas outlet of the silicon powder reactor 18 is connected to the inlet of the separation vessel 23 via a pipeline and is used to discharge hydrogen, alcohol, and the product tetraalkoxysilane. The discharge port of the silicon powder reactor 18 is located at the bottom of the tank and is connected to the centrifuge device 21 via a pipeline. The silicon powder slurry inlet, catalyst inlet, and gas outlet are all located at the top of the tank.

[0030] In some specific embodiments, a filter 17 for filtering filter residue or foam is connected to the connecting pipeline between the gas outlet of the silicon powder reactor 18 and the separation vessel 23.

[0031] The catalyst reactor 7 has a heating jacket on its outer wall. Inside the reactor 7, there is a stirrer for agitation and a thermometer for internal temperature measurement. The catalyst reactor 7 is equipped with a second nitrogen pipeline 8, a first feed pipe 9, a second feed pipe 10, a steam outlet, a reflux port, and a catalyst outlet. The second nitrogen pipeline 8 is located at the bottom of the reactor and is used for nitrogen protection and purging. The first feed pipe 9 is used to add any one of the following to the catalyst reactor 7: an alcohol solution of an alkali metal, an alkali metal alkoxide, an alcohol solution of an alkali metal hydroxide, or an alcohol solution of an alkali metal carbonate. The second feed pipe 10 is used to add alcohol ether compounds or liquid diethylene glycol oligomers. The steam outlet of the catalyst reactor 7 is connected to the catalyst condenser 3 via a steam pipeline 4. The catalyst condenser 3 is connected to the reflux port via a reflux pipeline 5, forming a circulation pipeline. The reflux pipeline 5 returns the reflux liquid to the catalyst reactor 7. The catalyst outlet is connected to the catalyst inlet of the silicon powder reactor 18 via a pipeline. The first feed pipe 9, the second feed pipe 10, the steam outlet, and the reflux port are all located above the catalyst reactor 7, while the second nitrogen pipe 8 and the catalyst outlet are located below the catalyst reactor 7.

[0032] The catalyst condenser 3 refluxes and separates the liquid in the catalyst reactor 7, returning it to the catalyst reactor 7 via the reflux pipe 5. The product after oil-water separation flows into the catalyst reactor 7 or into the oil-water separation pipe 6. The oil is an azeotrope that has an azeotropic point with water, such as n-hexane, cyclohexane, toluene, and xylene, and can be separated upon cooling. The catalyst condenser 3 is equipped with a cooling water coil to cool the distillate. The catalyst condenser 3 is connected to the vacuum device 2 via a pipe, which can be used for vacuum distillation to remove solvents and humid air, and the residue is discharged through the discharge pipe 1. The oil-water separation pipe 6 is also used to recover low-boiling-point alcohols after the reaction.

[0033] A silicon powder slurry feeding tank 15 is connected to a silicon powder reactor 18 via a pipeline. The silicon powder slurry feeding tank 15 is equipped with a stirrer for mixing the silicon powder slurry. The silicon powder slurry feeding tank 15 has a tetraalkoxysilane inlet 13, a silicon powder inlet, and a silicon powder slurry outlet. Both the tetraalkoxysilane inlet 13 and the silicon powder inlet are located at the top of the silicon powder slurry feeding tank 15, while the silicon powder slurry outlet is located at the bottom. The tetraalkoxysilane inlet 13 is used to add tetraalkoxysilane as a solvent. The silicon powder inlet is connected to a silicon powder tank 11 via a screw feeder 12. The top of the silicon powder tank 11 has an openable and closable lid, allowing silicon powder to be added into the tank when the lid is opened. The silicon powder slurry outlet is connected to the silicon powder slurry inlet of the silicon powder reactor 18 via a pipeline.

[0034] In some specific embodiments, a bypass pipe 14 is connected to the silicon powder slurry feeding tank 15 to balance the pressure between the silicon powder slurry feeding tank 15 and the silicon powder reactor 18. One end of the bypass pipe 14 is connected to the silicon powder slurry feeding tank 15, and the other end is connected to the pipeline between the silicon powder slurry outlet of the silicon powder slurry feeding tank 15 and the silicon powder slurry inlet of the silicon powder reactor 18.

[0035] The separation vessel 23 has a first outlet, a tetraalkoxysilane outlet 24, and an inlet. The inlet and first outlet of the separation vessel 23 are located at the top of the vessel, while the tetraalkoxysilane outlet 24 is located at the bottom and connected to a discharge pipe. Inside the separation vessel 23 is an alcohol heating coil 22. The inlet of the alcohol heating coil 22 is connected to an alcohol feed pump 28 via a pipe, and the outlet of the alcohol heating coil 22 is connected to the alcohol inlet of the silicon powder reactor 18 via a pipe. The first outlet of the separation vessel 23 is connected to a condenser 25 via a pipe. The condenser 25 is used to condense and separate alcohol and hydrogen.

[0036] The alcohol is fed to the silicon powder reactor 18 via the alcohol feed pump 28 and reused in the silicon powder reaction. The hydrogen is metered by the flow meter 26 and then discharged through the vent pipe 27.

[0037] The condenser 25 has an inlet, an alcohol outlet, and a hydrogen outlet. The first outlet of the separator 23 is connected to the inlet of the condenser 25 via a pipeline. The alcohol outlet is connected to the inlet of the alcohol feed pump 28 via a pipeline. The hydrogen outlet is connected to the vent pipe 27, which is equipped with a flow meter 26. The condenser 25 is equipped with a condensate pipe for condensing the alcohol into a liquid for recycling.

[0038] Centrifuge device 21 is connected to silicon powder reactor 18 via a pipeline. Centrifuge device 21 is connected to silicon powder reactor 18 via recovery pipeline 20. The supernatant obtained after centrifugation can be returned to silicon powder reactor 18 via recovery pipeline 20. The remaining silicon slag is discharged through the slag discharge pipeline of centrifuge device 21.

[0039] In some specific embodiments, the silicon powder used has a particle size of no more than 100 micrometers and a silicon content of more than 97%. The alcohol added to the silicon powder reactor 18 has a water content of less than 0.1%. The outlet of the alcohol feed pump 28 is connected to an auxiliary pipeline 29, which is used to directly connect to the silicon powder reactor 18. The auxiliary pipeline 29 is combined with the pipeline connected to the outlet of the alcohol heating coil 22 of the separation vessel 23, which can adjust the temperature of the alcohol added to the silicon powder reactor 18 and adjust the amount of alcohol added according to the internal temperature of the silicon powder reactor 18. A control switch is connected to the auxiliary pipeline 29 to control the on / off state of the auxiliary pipeline 29.

[0040] In some specific embodiments, the heating medium of the silicon powder reactor 18 can be an oil bath or steam heating, and the reaction inside can be the reaction of silicon powder with methanol to prepare methyl orthosilicate, or the reaction of silicon powder with ethanol to prepare tetraethyl orthosilicate. The catalyst for the reaction of silicon powder can be an alkali metal alkoxide or alkali metal alcohol ether salt of alkali metal lithium, sodium, or potassium.

[0041] In some specific embodiments, the heating medium of the catalyst reactor 7 can be oil bath or steam heating, with a heating temperature between 60-150°C. It can be used to prepare catalysts by reacting alkali metals such as lithium, sodium, and potassium with alcohol ethers, or it can be used for the reaction of alkali metal salts or alkali metal alkoxides with alcohol ether compounds or short-chain diol polymers.

[0042] Another embodiment of this application proposes a process for preparing tetraalkoxysilanes using a direct silicon powder method. The system for preparing tetraalkoxysilanes using the above-described direct silicon powder method includes the following steps:

[0043] S1. Catalyst preparation in catalyst reactor 7: First, air in catalyst reactor 7 and condenser 25 is discharged through second nitrogen pipeline 8. Then, any one of the following is added through first feed pipe 9: alkali metal, alkali metal alkoxide, alkali metal hydroxide alcohol solution, or alkali metal carbonate alcohol solution. The temperature is raised to 60-150℃. Under stirring, heating, and reflux, alcohol ether compound or liquid diethylene glycol oligomer is gradually added through second feed pipe 10. The reflux reaction is carried out for 0.5-10 hours to generate low-boiling alcohol and catalyst. The evaporated low-boiling alcohol flows into catalyst condenser 3 along steam pipeline 4. After being cooled by the cold water coil of catalyst condenser 3, the low-boiling alcohol is returned to catalyst reactor 7 through reflux pipeline 5. After the reaction is completed, the low-boiling alcohol needs to be removed. Vacuum device 2 (vacuum pump) is turned on for reduced pressure distillation. The low-boiling alcohol is recovered through oil-water separation pipeline 6. The prepared catalyst is introduced into silicon powder reaction vessel through pipeline. The catalyst is used to catalyze the reaction between silicon powder and alcohol.

[0044] Step S2: Prepare silicon powder slurry in silicon powder slurry feeding tank 15: First, add tetraalkoxysilane as a solvent to silicon powder slurry feeding tank 15, open the lid of the top of silicon powder tank 11, add silicon powder, and add silicon powder to silicon powder slurry feeding tank 15 through screw feeder 12. After stirring and mixing evenly, silicon powder slurry is obtained and introduced into silicon powder reactor 18.

[0045] Step S3: Preparation of tetraalkoxysilane in silicon powder reactor 18: Air is purged from silicon powder reactor 18 and related equipment through the first nitrogen pipe 19. The catalyst prepared in step S1 and the silicon powder slurry prepared in step S2 are added to silicon powder reactor 18, stirred evenly, and heated to 100℃~200℃. Heated alcohol or vaporized alcohol is added through the alcohol inlet to initiate the reaction. A stirrer is used to agitate the interior of silicon powder reactor 18 to prevent heat accumulation and agglomeration on the reactor wall. The reaction produces alcohol, hydrogen, and tetraalkoxysilane. During the reaction, a large amount of vapor is generated. The alcohol, hydrogen, and tetraalkoxysilane are carried out by the vapor, filtered through filter 17, and then piped into separation vessel 23 for cooling and separation of the final product, tetraalkoxysilane. The alcohol and hydrogen enter condenser 25 through a pipeline, where they separate under the cooling of the condensate water pipe. The hydrogen is recorded by flow meter 26 and then vented or collected through the drain pipe. The condensed alcohol is mixed with newly introduced alcohol and then pumped by alcohol feed pump 28 to silicon powder reactor 18 for further reaction. The alcohol pumped by alcohol feed pump 28 is further heated in separation vessel 23 before being introduced into the silicon powder reactor to participate in the reaction, preventing the reaction rate from decreasing due to low alcohol temperature.

[0046] In some specific embodiments, the reaction in step S1 can be a reaction between an alkali metal and an alcohol ether compound, where the alkali metal includes one or a mixture of two of lithium, sodium, and potassium. Alternatively, a catalyst can be prepared by reacting a methanol or ethanol solution of an alkali metal hydroxide or carbonate compound with an alcohol ether compound, where the alkali metal hydroxide is one or a mixture of potassium hydroxide, sodium hydroxide, and lithium hydroxide, and the carbonate compound is one or a mixture of two of potassium carbonate, sodium carbonate, and lithium carbonate. Alternatively, a catalyst can be prepared by reacting an alkali metal sodium alkoxide compound with an alcohol ether compound, where the alkali metal sodium alkoxide compound is one or a mixture of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, etc.

[0047] In some specific embodiments, the alcohol ether compound involved in step S1 may be one or a mixture of two of ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol butyl ether, triethylene glycol methyl ether, etc., or may be one or a mixture of diethylene glycol, triethylene glycol, PEG200, PEG400.

[0048] In step S1, if an alkali metal catalyst is used, hydrogen gas will be generated. If the internal temperature is too high, it is necessary to reduce the stirring speed, introduce nitrogen gas for cooling, or introduce condensate into the jacket for cooling. If an alkali metal hydroxide methanol or ethanol solution is used, it is necessary to add toluene, xylene, cyclohexane, or other azeotropic substances that have an azeotropic point with water and can be separated after cooling to remove water, thereby reducing the water content in the catalyst. Finally, the catalyst concentration is further increased by vacuum distillation.

[0049] Step S2, preparing the silicon powder slurry, utilizes a method of adding silicon powder to allow the tetraalkoxysilane preparation reaction to proceed continuously. The tetraalkoxysilane added through the tetraalkoxysilane inlet 13 is the same as the prepared product, being either tetramethoxysilane or tetraethoxysilane. The bypass pipe 14 is used to balance the pressure between the silicon powder feeding tank and the silicon powder reaction vessel, maintaining a negative pressure inside the silicon powder feeding tank. A screw feeder 12 is used to add solid silicon powder, providing a good seal to the silicon powder feeding tank while effectively adding solid silicon powder.

[0050] In step S3, the heating temperature in the silicon powder reactor 18 is set differently depending on the reaction product, which is tetramethoxysilane or tetraethoxysilane. The temperature for preparing tetramethoxysilane is between 100℃ and 140℃, and to ensure timely distillation of the tetramethoxysilane, a reaction temperature between 125℃ and 135℃ is most suitable. The reaction temperature for preparing tetraethoxysilane is between 160℃ and 175℃ to facilitate timely distillation of the tetraethoxysilane. The alcohol used in the reaction is methanol liquid or methanol vapor, or ethanol liquid or ethanol vapor, heated to above 60℃.

[0051] In step S3, the reaction can be controlled by adjusting the addition or cessation of alcohol during the preparation of tetraalkoxysilane. Adjusting the amount of alcohol added results in a smaller amount of alcohol distillation, leading to a faster reaction rate and reduced energy consumption. Timely replenishment of silica powder slurry ensures continuous reaction, thus achieving continuous preparation of tetraalkoxysilane.

[0052] In step S3, after the catalyst has reacted continuously for a period of time, the reaction rate will decrease due to the large amount of impurities in the substrate silicon slag. At this point, the substrate needs to be separated and discharged. The substrate silicon slag is centrifuged through a pipeline into centrifuge 21 to separate the liquid catalyst and solid silicon slag. The liquid catalyst can be recycled back into the silicon powder reactor 18 through recovery pipeline 20 for the preparation of tetraalkoxysilane. When the catalyst is deactivated, it can be directly discharged from the reaction system after centrifugation to separate the silicon slag.

[0053] In step S3, the mixture discharged from the gas outlet is clean gas filtered by filter 17. After the alcohol in the alcohol heating coil 22 in the separation vessel 23 is cooled, tetraalkoxysilane is separated. The tetraalkoxysilane product is discharged through the tetraalkoxysilane outlet 24 at the bottom for further distillation and purification or as a raw material for aerogel preparation. The mixture of alcohol and hydrogen gas at a temperature below 100°C enters the condenser 25 through the pipe at the first outlet. Under the cooling of the condensate water pipe, methanol becomes liquid and is recovered, while hydrogen is discharged from the top after being metered by the flow meter 26.

[0054] In existing technologies, the direct preparation of tetraalkoxysilanes primarily yields trialkoxysilanes, resulting in only small quantities of tetraalkoxysilanes. Furthermore, this process requires complex pretreatment with silica powder catalysts and high reaction temperatures. Alternatively, the resulting products are complex, necessitating sophisticated distillation and separation equipment for separation and purification. In contrast, this invention requires only simple separation to prepare tetraalkoxysilanes suitable for silica aerogels, and further product separation and purification processes are straightforward.

[0055] The present application will be further illustrated below through specific embodiments.

[0056] Example 1

[0057] A process for directly preparing tetraalkoxysilane from silicon powder comprises the following three steps. Taking the preparation of tetramethoxysilane in a 200L reactor as an example, step one is to prepare a catalyst in a catalyst reactor 7. Step two is to prepare a silicon powder slurry in a silicon powder slurry feeding tank 15. Step three is to react silicon powder and methanol in a silicon powder reactor 18 to prepare tetramethoxysilane.

[0058] The following is combined with Figure 1The steps of Example 1 will be further explained.

[0059] The process flow diagram of this invention is attached. Figure 1 As shown, it includes the following steps:

[0060] Step S1: Purge the catalyst reactor 7 and condenser 25 with nitrogen to remove internal air. Add 70 kg of 30% sodium methoxide solution to the catalyst reactor 7 and heat and stir until reflux. Slowly add a mixture of 30 kg of diethylene glycol methyl ether and 20 kg of ethylene glycol methyl ether over 1 hour. Heat and reflux at 100°C for 4 hours. Distill off methanol under reduced pressure at 120°C. If no obvious solution is distilled off, continue distillation under reduced pressure for 20 minutes. Cool down to 70°C to obtain a light brown catalyst. Add the catalyst to the silicon powder reactor 18.

[0061] Step S2: Add the silicon powder from the large packaging bag into the silicon powder tank 11, add tetramethoxysilane into the silicon powder slurry feeding tank 15, stir, and add silicon powder using the screw feeder 12. The silicon powder and tetramethoxysilane are mixed in a mass ratio of 1:2 to obtain the silicon powder slurry.

[0062] Step S3: Before adding the catalyst and silicon powder slurry, purge the silicon powder reactor 18, separation vessel 23, condenser 25, and interconnected pipelines with hot nitrogen to remove air and moisture from the reaction system. Turn on the stirring device of the silicon powder reactor 18, add the prepared catalyst from the catalyst reactor 7 to the silicon powder reactor 18, and then add silicon powder slurry of equal mass to the catalyst from the silicon powder slurry feeding tank 15 to the silicon powder reactor 18. Heat the reactor; gas begins to be generated at 70-90°C, consisting of gases generated by nitrogen expansion and some hydrogen. Continue heating to 130°C, and slowly add methanol at 60°C. The methanol is heated by the distilled tetramethoxysilane in the separation vessel 23, and the reaction officially begins, accompanied by heat release. Maintain the reaction temperature at 130°C by adjusting the amount of methanol added.

[0063] In step S3, the tetramethoxysilane, methanol, and hydrogen produced during the reaction pass through filter 17 from the top of the silicon powder reactor 18 to remove silicon powder impurities and then enter the separation reactor 23. After being cooled by the raw material methanol, the tetramethoxysilane is condensed into a liquid state, collected at the bottom of the separation reactor 23, and transported to a storage tank or distillation unit. The methanol and hydrogen mixture at 70-100°C leaves the separation reactor 23 and enters the condenser 25. Unreacted methanol is condensed into a liquid state at a temperature below 50°C and is then transported back to the silicon powder reactor 18 to prepare tetramethoxysilane. The hydrogen is metered by flow meter 26 and discharged through the vent pipe.

[0064] The reaction in step S3 continues. When the gas flow rate is low, silicon powder slurry is added to continue the reaction with methanol in silicon powder reactor 18 to prepare tetramethoxysilane. After the fourth batch of silicon powder is added and the reaction is completed, the bottom slurry is discharged into centrifuge device 21 through a pipeline. Centrifuge device 21 centrifuges and separates the silicon powder and catalyst mixture. The liquid catalyst mixture is reintroduced into silicon powder reactor 18 to continue catalyzing the reaction between silicon powder and methanol. The silicon powder substrate is collected and stored as silicon slag.

[0065] If the efficiency decreases after the catalyst in step S3 continues to react with multiple batches of silicon powder slurry, the catalyst can be separated from the silicon powder and no longer used for catalytic reaction. The silicon slag and catalyst mixture can be separated and discharged separately.

[0066] In step S3, 70-80 kg of silicon powder slurry is added per batch, the reaction time for each batch is 5-7 hours, the yield of tetramethoxysilane is between 20-30 kg per hour, and the hydrogen flow rate is 16 m³ / h. 3 / h-20m 3 Between / h.

[0067] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0068] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0069] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0070] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0071] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A system for the direct preparation of tetraalkoxysilanes from silicon powder, characterized in that, The system includes a silicon powder reactor, a catalyst reactor, a silicon powder slurry feeding tank, a separation vessel, and a centrifuge. The silicon powder reactor is equipped with a silicon powder slurry inlet, a catalyst inlet, an alcohol inlet, a first nitrogen pipeline, a gas outlet, and a discharge port. The silicon powder slurry outlet of the silicon powder slurry feeding tank is connected to the silicon powder slurry inlet of the silicon powder reactor, the catalyst outlet of the catalyst reactor is connected to the catalyst inlet of the silicon powder reactor, the gas outlet of the silicon powder reactor is connected to the gas inlet of the separation vessel, and the discharge port of the silicon powder reactor is connected to the centrifugal device. It also includes a catalyst condenser, which is connected to the catalyst reactor through a steam pipeline and a return pipeline to form a gas circulation pipeline. The catalyst condenser is equipped with a cold water coil for cooling the distillate, and the catalyst condenser is also connected to a vacuum device for depressurized distillation inside the catalyst condenser. The catalyst reactor is equipped with a second nitrogen pipeline, a first feed pipe, a second feed pipe, a steam outlet, a reflux port, and a catalyst outlet. The first feed pipe is used to add any one of the following: an alcohol solution of alkali metal, alkali metal alkoxide, alkali metal hydroxide, or alkali metal carbonate. The second feed pipe is used to add alcohol ether compounds or liquid diethylene glycol oligomers. The steam outlet is connected to the catalyst condenser through a steam pipeline. The catalyst condenser is connected to the reflux port through a reflux pipeline. The catalyst outlet is connected to the catalyst inlet of the silicon powder reactor through a pipeline. The first outlet of the separation vessel is connected to a condenser, which is used to separate alcohol and hydrogen. The bottom of the separation vessel is equipped with a tetraalkoxysilane outlet. An alcohol heating coil is installed inside the separation vessel. The inlet of the alcohol heating coil is connected to an alcohol feed pump through a pipeline. The outlet of the alcohol heating coil is connected to the alcohol inlet of the silicon powder reactor through a pipeline.

2. The system for preparing tetraalkoxysilanes directly from silicon powder according to claim 1, characterized in that, The silicon powder slurry feeding tank is equipped with a tetraalkoxysilane inlet, a silicon powder inlet, and a silicon powder slurry outlet. The silicon powder inlet is connected to the silicon powder tank via a screw feeder, and the silicon powder slurry outlet is connected to the silicon powder slurry inlet of the silicon powder reactor via a pipeline.

3. The system for preparing tetraalkoxysilanes directly from silicon powder according to claim 2, characterized in that, The condenser is equipped with an inlet, an alcohol outlet, and a hydrogen outlet. The first outlet of the separator is connected to the inlet of the condenser via a pipeline, the alcohol outlet is connected to the inlet of the alcohol feed pump via a pipeline, and the hydrogen outlet is connected to the vent pipe.

4. The system for directly preparing tetraalkoxysilanes from silicon powder according to claim 3, characterized in that, The centrifuge device is connected to the silicon powder reactor via a recovery pipeline.

5. The system for preparing tetraalkoxysilanes directly from silicon powder according to claim 4, characterized in that, The silicon powder reactor, catalyst reactor, and silicon powder slurry feeding tank are all equipped with stirring devices.

6. The system for directly preparing tetraalkoxysilanes from silicon powder according to claim 5, characterized in that, The gas outlet of the silicon powder reactor is connected to the separation vessel via a filter for filtering residue or foam.

7. The system for preparing tetraalkoxysilanes directly from silicon powder according to claim 6, characterized in that, The silicon powder slurry feeding tank is connected to a bypass pipe for balancing the pressure between the silicon powder slurry feeding tank and the silicon powder reactor. One end of the bypass pipe is connected to the silicon powder slurry feeding tank, and the other end is connected to the pipeline between the silicon powder slurry outlet of the silicon powder slurry feeding tank and the silicon powder slurry inlet of the silicon powder reactor.

8. A process for preparing tetraalkoxysilanes directly from silicon powder, characterized in that, The system for preparing tetraalkoxysilanes using the direct silicon powder method according to claim 7 comprises the following steps: Step S1: Preparation of catalyst in catalyst reactor: First, exhaust the air from the catalyst reactor and condenser. Add any one of the following through the first feed pipe: alkali metal, alkali metal alkoxide, alkali metal hydroxide alcohol solution, or alkali metal carbonate alcohol solution. Heat to 60-150°C. Under stirring, heating, and reflux, gradually add alcohol ether compound or liquid diethylene glycol oligomer through the second feed pipe. Reflux reaction for 0.5-10 hours to generate low-boiling alcohol and catalyst. The low-boiling alcohol flows into the catalyst condenser along the steam pipe. After being cooled by the catalyst condenser, the low-boiling alcohol flows back into the catalyst reactor through the reflux pipe. The prepared catalyst is then introduced into the silicon powder reactor. Step S2, preparing silicon powder slurry in silicon powder slurry feeding tank: First, tetraalkoxysilane is added to the silicon powder slurry feeding tank as a solvent. Silicon powder is added to the silicon powder slurry feeding tank through the silicon powder tank. After stirring and mixing evenly, silicon powder slurry is obtained and then introduced into the silicon powder reactor. Step S3: Preparation of tetraalkoxysilane in a silicon powder reactor: The air in the silicon powder reactor is purged through the first nitrogen pipeline. The catalyst prepared in step S1 and the silicon powder slurry prepared in step S2 are added to the silicon powder reactor and stirred evenly. The temperature is raised to 100℃~200℃. Heated alcohol is added through the alcohol inlet to react and generate alcohol, hydrogen and tetraalkoxysilane. The alcohol, hydrogen and tetraalkoxysilane are passed into the separation vessel to cool and separate the final product tetraalkoxysilane. The alcohol and hydrogen enter the condenser for separation. The hydrogen is vented or collected through the vent pipe. The condensed alcohol is mixed with the newly introduced alcohol and then transported to the silicon powder reactor by the alcohol feed pump to continue the reaction. The alcohol transported by the alcohol feed pump is first heated in the separation vessel and then passed into the silicon powder reactor to participate in the reaction.

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