Method for preparing trialkoxysilane by adopting fluidized bed

Abstract

A method for preparing trialkoxysilane by using a fluidized bed comprises the following steps: preheating the fluidized bed in a protective atmosphere; the heating temperature of the bottom of the fluidized bed is higher than that of the middle of the fluidized bed; pushing a silicon powder composition into the preheated fluidized bed by using preheated protective gas, wherein the silicon powder composition is a mixture of silicon powder and a silicon copper contact body; driving alkyl alcohol gas to enter the preheated fluidized bed by using preheated protective gas; under the protective atmosphere, the reaction temperature in the fluidized bed is maintained, the silicon powder composition and alkyl alcohol gas react in the fluidized bed, and trialkoxysilane is generated. According to the method for preparing the trialkoxysilane by adopting the fluidized bed, a water-free and oxygen-free reaction atmosphere is fully created in the whole reaction system, continuous reaction of the trialkoxysilane is avoided due to the integration of reaction and separation, and the subsequent separation difficulty is reduced while the product selectivity is improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering and relates to a method for preparing trialkoxysilanes using a fluidized bed. Background Technology

[0002] Trialkoxysilanes are important intermediates in the organosilicon industry, with the general chemical formula HSi(OR)3. Among them, trimethoxysilane and triethoxysilane are the most widely used. Currently, the industrial production of trialkoxysilanes mainly involves the following two pathways.

[0003] The preparation of trialkoxysilanes by alcoholysis of chlorosilanes is a complicated process with low yield. The reaction uses corrosive hydrogen chloride as a raw material, which not only corrodes the equipment but also generates a large amount of chlorine-containing byproducts, making product purification difficult.

[0004] The direct synthesis of trialkoxysilanes from silicon powder uses silicon powder and alcohols as raw materials, and proceeds in a step-by-step manner with the aid of a copper-based catalyst, thus solving the problem caused by corrosive raw materials. However, the direct synthesis of alkoxysilanes mainly takes place in a stirred tank reactor, and the reaction temperature must reach 160°C or higher to activate the silanol reactivity. Since alkoxy alcohols have low boiling points, high-boiling-point heat transfer oil needs to be added as a solvent to raise the reaction temperature and then synthesize alkoxysilanes. However, the presence of high-boiling-point solvents hinders the direct contact between silicon powder and ethanol, resulting in low silicon conversion. Trialkoxysilanes also have low stability, and in the reactor, they continue to react with alcohols to form tetraalkoxysilanes and other polymers, resulting in low selectivity for trialkoxysilanes. The addition of high-boiling-point solvents also significantly increases the difficulty of separating and purifying multi-product systems.

[0005] In view of this, it is necessary to provide a method for preparing trialkoxysilanes using a fluidized bed to address the aforementioned technical problems. Summary of the Invention

[0006] To address one of the aforementioned problems, the present invention aims to provide a method for preparing trialkoxysilanes using a fluidized bed.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for preparing trialkoxysilanes using a fluidized bed includes the following steps:

[0009] The fluidized bed is preheated under a protective atmosphere; the heating temperature at the bottom of the fluidized bed is higher than that in the middle of the fluidized bed, and the heating temperature in the middle of the fluidized bed is higher than that at the top of the fluidized bed.

[0010] A preheated protective gas is used to push the silicon powder composition into a preheated fluidized bed. The silicon powder composition is a mixture of silicon powder and silicon copper contact, and the silicon copper contact is prepared by the method for preparing silicon copper contact according to any one of claims 1 to 6.

[0011] A preheated protective gas is used to drive alkyl alcohol gas into the preheated fluidized bed;

[0012] Under a protective atmosphere, the reaction temperature in the fluidized bed is maintained, and the silicon powder composition reacts with alkyl alcohol gas in the fluidized bed to generate trialkoxysilane.

[0013] In one optional embodiment, the temperature difference between the heating temperature at the bottom of the fluidized bed and the heating temperature in the middle of the fluidized bed is 10°C to 30°C, and the temperature difference between the heating temperature in the middle of the fluidized bed and the heating temperature at the top of the fluidized bed is 10°C to 30°C.

[0014] In one optional embodiment, the heating temperature at the bottom of the fluidized bed is 220°C to 240°C, the heating temperature in the middle of the fluidized bed is 170°C to 210°C, and the heating temperature at the top of the fluidized bed is 160°C to 180°C.

[0015] In an optional embodiment, "using a preheated protective gas to propel the silicon powder composition into a preheated fluidized bed" includes the following steps:

[0016] The protective gas is preheated and then introduced into the dryer. The temperature of the protective gas after preheating is 100℃~120℃.

[0017] The silicon powder is fed into a dryer for drying.

[0018] After the surface moisture of the silicon powder is separated, the silicon copper catalyst is added into the dryer. The silicon copper catalyst accounts for 3% to 10% of the mass fraction of the silicon powder raw material. The silicon copper catalyst and the silicon powder are mixed through a vibrating screen to form a silicon powder composition.

[0019] Increase the pressure of the protective gas to feed the silicon powder composition into the fluidized bed.

[0020] It also includes the step of preparing silicon-copper contacts: under a protective atmosphere, a catalyst, silicon powder and a pore-forming agent are mixed, the catalyst being a mixture of cuprous chloride and cuprous oxide; under a protective atmosphere, the mixture is calcined and activated to form silicon-copper contacts.

[0021] In one optional implementation, "calcination activation" includes:

[0022] First stage: Heat to the dehydration temperature and calcine within the dehydration temperature range for 15 to 20 minutes to remove free water from the surface of silicon powder and catalyst;

[0023] Second stage: Heat to the opening temperature and calcine within the opening temperature range for 40 min to 60 min to induce the pore-forming agent to slowly decompose and form pores, and form copper oxide co-catalyst;

[0024] The third stage: heat up to the activation temperature and bake for 60 to 90 minutes within the activation temperature range to generate silicon-copper catalysts.

[0025] In one optional implementation,

[0026] Silicon powder accounts for 30-60% of the total mass, cuprous chloride accounts for 20-50% of the total mass, cuprous oxide accounts for 10-30% of the total mass, and / or

[0027] The amount of pore-forming agent added accounts for 5% to 10% of the mass of the silicon copper contact.

[0028] In one optional implementation, the "mixing" process includes the following steps:

[0029] First, put the catalyst and silicon powder into a ball mill and mix for a predetermined time;

[0030] Add a pore-forming agent and continue grinding until the particle size is 5μm to 20μm;

[0031] Preferably, "predetermined mixing time" refers to grinding to a particle size of less than 30 μm.

[0032] In one optional implementation, during the "calcination activation" process, the temperature is increased to the dehydration temperature at a first preset heating rate, to the pore-opening temperature at a second preset heating rate, and to the activation temperature at a third preset heating rate.

[0033] In one optional implementation, the second preset heating rate is less than the first preset heating rate, and the second preset heating rate is less than the third preset heating rate.

[0034] In one optional embodiment, the first preset heating rate is 15℃ / min to 20℃ / min, the second preset heating rate is 10℃ / min to 15℃ / min, and the third preset heating rate is 15℃ / min to 20℃ / min.

[0035] In an optional embodiment, the calcination activation process further includes: after generating the silicon-copper catalyst, heating it to 800°C to 1000°C and calcining it for 10 to 20 minutes within this temperature range to remove the bound water inside the catalyst.

[0036] In one optional embodiment, the temperature is raised to 800°C to 1000°C at a fourth preset heating rate, wherein the second preset heating rate is less than the first preset heating rate, the second preset heating rate is less than the third preset heating rate, and the fourth preset heating rate is greater than the first preset heating rate, the second preset heating rate, and the third preset heating rate.

[0037] In one optional embodiment, liquid alkyl alcohol is converted into alkyl alcohol gas by an alkyl alcohol vaporizer, and a preheated protective gas is introduced into the alkyl alcohol gas to drive the alkyl alcohol gas into the alkyl alcohol superheater, thereby raising the temperature of the alkyl alcohol to the reaction temperature.

[0038] In one alternative implementation, the deactivated catalyst is separated from the outlet at the bottom of the fluidized bed.

[0039] In one optional embodiment, silicon powder is filtered by a silicon powder filter device located at the top of the fluidized bed; and / or silicon powder and catalyst in the reaction product mixture gas are separated by a cyclone separator located at the top of the fluidized bed and returned to the middle or bottom of the fluidized bed.

[0040] In an optional embodiment, the method for preparing trialkoxysilanes using a fluidized bed further includes:

[0041] The reaction product mixture gas discharged from the top of the fluidized bed is sent to a Venturi scrubber. The separated protective gas and reaction gas are sent to a gas separation device, and the separated liquid containing sediment is sent to a solid-liquid separation device to separate silicon powder and catalyst.

[0042] An extractant is added to the liquid separated by the solid-liquid separation device. The extractant is selected from one or more combinations of m-xylene, mesitylene, ethylbenzene, and cumene.

[0043] The product mixture with added extractant is fed into the first extraction column, where the bottom temperature is 100℃~140℃ and the top temperature is 50℃~70℃. The component separated at the top of the column is an alkyl alcohol, and the components separated at the bottom of the column are trialkoxysilane, tetraalkoxysilane and extractant.

[0044] The components separated at the bottom of the first extraction column are fed into the second extraction column. The bottom temperature is set to 125℃~145℃ and the top temperature is set to 75℃~95℃. The components separated at the top are the extractant, and the components separated at the bottom are trialkoxysilane and tetraalkoxysilane.

[0045] The components separated from the bottom of the second extraction column are sent to a distillation column with a bottom temperature of 140℃~160℃ and a top temperature of 100℃~130℃. The components separated at the top are trialkoxysilanes with a purity of 99% or higher, and the components separated at the bottom are tetraalkoxysilanes with a purity of 99% or higher.

[0046] Compared with existing technologies, this invention uses a fluidized bed method to prepare trialkoxysilanes. The entire reaction system fully creates an anhydrous and oxygen-free reaction atmosphere, reducing the generation of other byproducts. Furthermore, the fluidized bed reactor is temperature-controlled in three stages, with the heating temperature gradually decreasing from the bottom up. On the one hand, the middle and upper parts are maintained at the reaction temperature by the exothermic reaction below, which can reduce energy consumption. On the other hand, it can enhance the stability of the reaction and avoid temperature runaway in the fluidized bed.

[0047] Furthermore, through the integrated reaction-separation system, silicon powder and catalyst are separated from the product in a timely manner, and the generated trialkoxysilane is also separated from the reaction in a timely manner. The silicon powder utilization rate can reach 95% or more, and the selectivity of trialkoxysilane is 90% or more, achieving the goal of high conversion rate and high selectivity. Attached Figure Description

[0048] Figure 1 This is a flowchart of a method for preparing trialkoxysilanes using a fluidized bed according to an embodiment of the present invention;

[0049] Figure 2 This is a complete flow diagram of a method for preparing trialkoxysilanes using a fluidized bed according to an embodiment of the present invention;

[0050] Figure 3 This is a flowchart of a method for preparing a silicon-copper contact according to an embodiment of the present invention. Detailed Implementation

[0051] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0052] The inventors discovered that trialkoxysilanes have low stability and are extremely prone to hydrolysis and deterioration. Furthermore, the presence of moisture exacerbates the polymerization reaction of alkoxysilanes during the reaction process, generating byproducts such as hexaethyl pyrosilicate. Providing an anhydrous and oxygen-free reaction environment significantly increases the difficulty of producing trialkoxysilanes.

[0053] This invention aims to create an anhydrous and oxygen-free preparation system for trialkoxysilanes using alcohols and silicon powder as raw materials and a fluidized bed reactor as the core reactor. Based on this preparation system, a method for preparing trialkoxysilanes using a fluidized bed is proposed to improve the utilization rate of silicon powder and the selectivity of trialkoxysilanes, thereby achieving the goals of high conversion rate and high selectivity.

[0054] The silicon powder of this invention is a byproduct of the polycrystalline silicon production process. The alkyl alcohol is a commercially available alkyl alcohol with a concentration of 99.99% or higher; when the target product is triethoxysilane, ethanol is used as the raw material; when the target product is trimethoxysilane, methanol is used as the raw material.

[0055] The preparation system for the trialkoxysilane includes: a raw material pretreatment unit, a fluidized bed unit, and a product separation unit.

[0056] The raw material pretreatment unit includes a protective gas pretreatment unit, a solid raw material pretreatment unit, and an alkyl alcohol pretreatment unit, which remove water from all raw materials in an oxygen-free environment.

[0057] The protective gas pretreatment unit provides anhydrous and oxygen-free protective gas and creates a protective atmosphere for other units. In this invention, the protective gas is selected from one or more combinations of nitrogen and inert gases, including but not limited to argon.

[0058] The solid raw material pretreatment unit includes a dryer. The dryer contains a vibrating screen to vibrate the silicon powder, enabling rapid separation of surface moisture and ensuring more uniform material mixing in subsequent steps. The dryer also includes a moisture detector to monitor the moisture content within the dryer. The functions and usage of each component are described below.

[0059] The alkyl alcohol pretreatment unit includes an alkyl alcohol vaporizer for vaporizing liquid alkyl alcohol, an alkyl alcohol superheater for raising the temperature of the alkyl alcohol to the reaction temperature, and a protective gas preheater for heating the protective gas. The outlet of the protective gas preheater is connected between the alkyl alcohol vaporizer and the alkyl alcohol superheater. Please refer to the following description for the function and usage of each component.

[0060] The fluidized bed unit comprises a multi-stage fluidized bed. A cyclone separator is installed at the top of the fluidized bed to separate silicon powder and catalyst; silicon powder filters are installed at the bottom and top of the fluidized bed to reduce silicon powder carryover and prevent pipeline blockage; additionally, a stirring paddle is installed at the bottom of the fluidized bed to ensure the reaction proceeds fully. Please refer to the following description for the function and usage of each component.

[0061] The following describes a method for preparing trialkoxysilanes using a fluidized bed, based on the aforementioned preparation system for trialkoxysilanes.

[0062] Please refer to Figure 1 and Figure 2 As shown, the method for preparing trialkoxysilanes using a fluidized bed according to the present invention includes the following steps:

[0063] S1 preheats the fluidized bed under a protective atmosphere; wherein the heating temperature at the bottom of the fluidized bed is higher than the heating temperature in the middle of the fluidized bed, and the heating temperature in the middle of the fluidized bed is higher than the heating temperature at the top of the fluidized bed.

[0064] S2 uses a preheated protective gas to push the silicon powder composition into the preheated fluidized bed. The silicon powder composition is a mixture of silicon powder and the above-mentioned silicon copper catalyst.

[0065] S3 uses a preheated protective gas to drive alkyl alcohol gas into a preheated fluidized bed;

[0066] Under a protective atmosphere, the reaction temperature in the fluidized bed is maintained. The silicon powder composition reacts with the alkyl alcohol gas in the fluidized bed to generate trialkoxysilane.

[0067] The order of steps S1 and S2 can be interchanged, and they can be performed simultaneously.

[0068] Step S1, preheating the fluidized bed, includes the following steps:

[0069] S2A is used to purge and dry the fluidized bed.

[0070] The fluidized bed reactor is the core reactor for the silicon powder alcoholysis reaction, with pretreated silicon powder and alkyl alcohol gases injected from the bottom. Before the reaction, the entire reaction system needs to be purged and heated to dry. A protective gas is used for purging to ensure that the silicon powder alcoholysis reaction takes place in an anhydrous and oxygen-free environment.

[0071] Before feeding S2B, the fluidized bed is preheated to the reaction temperature.

[0072] The inventors discovered that the silicon powder alcoholysis reaction is an exothermic and fast reaction. Therefore, the bottom of the fluidized bed needs to be at a high temperature to trigger the reaction chain. Once the reaction chain is triggered, a large amount of heat will be released. The fluidized bed reactor of this invention has a three-stage temperature control. From the bottom up, the heating temperature gradually decreases. On the one hand, the middle and upper parts are maintained at the reaction temperature by the exothermic reaction below, which can reduce energy consumption. On the other hand, it can enhance the stability of the reaction and avoid temperature runaway in the fluidized bed.

[0073] The alcoholysis of silica powder begins at 160℃ and above, with the optimal conversion rate occurring between 220-260℃. Therefore, the reaction temperature throughout the fluidized bed is controlled between 160℃ and 260℃. The heating temperature decreases sequentially from the bottom to the top of the bed by 10℃ to 30℃. The heating temperature should not be reduced too much to ensure that the middle and top sections reach the reaction temperature; conversely, the heating temperature should not be reduced too little to avoid excessively high temperatures in any particular area.

[0074] The heating temperature at the bottom of the fluidized bed is higher than that in the middle of the fluidized bed, and the heating temperature in the middle of the fluidized bed is higher than that at the top of the fluidized bed.

[0075] Preferably, the temperature difference between the heating temperature at the bottom of the fluidized bed and the heating temperature in the middle of the fluidized bed is 10℃ to 30℃, and the temperature difference between the heating temperature in the middle of the fluidized bed and the heating temperature at the top of the fluidized bed is 10℃ to 30℃.

[0076] In one embodiment, the heating temperature at the bottom of the fluidized bed is 220℃~240℃, the heating temperature in the middle is 170℃~210℃, preferably 190℃~210℃, and the heating temperature at the top is 160℃~180℃.

[0077] Additionally, the heating temperature at the top of the fluidized bed is not lower than the boiling point of the target product, so that the product is discharged in gaseous form.

[0078] Before feeding in step S2, the silicon powder is pretreated, mainly including crushing and screening in step S21 and drying in step S22.

[0079] S21 Crushing and screening are not mandatory steps. If fine silicon powder, a byproduct of polysilicon production, is used as raw material, the particle size of the fine silicon powder is generally distributed between 5μm and 50μm, and further crushing and screening are unnecessary. If coarse particles are used as raw material, they need to be crushed and screened to within 50μm using a ball mill or similar device.

[0080] S22 drying of silicon powder is the core step of pretreatment. It mainly dries the surface of silicon powder to prevent water vapor from being adsorbed on the surface of silicon powder and carried into the fluidized bed.

[0081] This invention uses a dryer to dry silicon powder, and the drying steps mainly include:

[0082] S221 preheats the protective gas and then introduces it into the dryer. Preferably, the protective gas is preheated to 100°C to 120°C, which is higher than the boiling point of water.

[0083] S222 sends the silicon powder into the dryer for drying.

[0084] After the surface moisture of the silicon powder is separated, the silicon-copper catalyst is added into the dryer. The silicon-copper catalyst component accounts for 3% to 10% of the mass fraction of the silicon powder raw material. The silicon-copper catalyst can be evenly distributed in the silicon powder raw material through a vibrating screen.

[0085] After drying, the silicon powder mixture is fed into the fluidized bed via a protective gas conveying system. Specifically, the pressure of the protective gas is increased to force the silicon powder composition into the fluidized bed. In one embodiment, the silicon powder composition is fed from the bottom of the fluidized bed.

[0086] Before feeding in step S2, silicon-copper contacts are prepared. Please refer to [reference needed]. Figure 3 As shown, the preparation method of the silicon-copper contact includes the following steps:

[0087] S2A involves mixing a catalyst, silicon powder, and a pore-forming agent under a protective atmosphere. The catalyst is a mixture of cuprous chloride and cuprous oxide.

[0088] S2B is activated by calcination under a protective atmosphere to form silicon-copper contact.

[0089] The "protective atmosphere" creates an anhydrous and oxygen-free environment for the preparation of the silicon-copper catalyst, preventing the catalyst from being oxidized and also preventing the catalyst from adsorbing water vapor. The purpose and materials of the protective gas and protective atmosphere in other stages of this invention are described herein and will not be repeated hereafter.

[0090] This invention selects a copper-based catalyst as the catalyst for the alcoholysis reaction of silicon powder. Current copper-based catalysts include, but are not limited to, cuprous chloride, cuprous oxide, copper oxide, nano-copper, or composite catalysts thereof. This invention preferably uses at least one or more combinations of cuprous chloride or its composite catalysts, and cuprous oxide or its composite catalysts, as the catalyst.

[0091] Compared to zero-valent copper and copper oxide, which require around 220°C to trigger the reaction chain, cuprous chloride or its composite catalyst, and cuprous oxide or its composite catalyst exhibit higher activity, triggering the reaction chain at around 160°C. This results in a rapid, efficient, and high-yield reaction. Compared to nano-copper, the catalysts of this invention are lower in cost and exhibit stable catalytic performance.

[0092] Furthermore, compared to cuprous chloride alone or its composite catalyst, or cuprous oxide or its composite catalyst, the composite catalyst of cuprous chloride and cuprous oxide can reduce the introduction of halogens while enhancing the catalytic effect.

[0093] Silicon powder accounts for 30-60% of the total mass, cuprous chloride accounts for 20-50% of the total mass, and cuprous oxide accounts for 10-30% of the total mass.

[0094] In one specific embodiment, the mass ratio of cuprous chloride, cuprous oxide, and silicon powder is 1:1:2.

[0095] The pore-forming agent is selected from basic copper carbonate to form a porous silicon-copper contact, which increases the specific surface area and surface active sites, thereby improving catalytic activity.

[0096] In one specific embodiment, the pore-forming agent is basic copper carbonate, which can increase the adsorption active sites on the surface of the silicon-copper contact, and the decomposition of basic copper carbonate can generate copper oxide as a co-catalyst, thereby promoting the occurrence of the alcoholysis reaction of silicon powder.

[0097] In this invention, the amount of the pore-forming agent added accounts for 5% to 10% of the mass of the silicon copper contact to form an excellent porous silicon copper contact.

[0098] The "mixing" process in step S2A includes:

[0099] In S2A1, under a protective atmosphere, the catalyst and silicon powder are first placed in a ball mill and mixed for a predetermined time to ensure that the two are mixed to a certain extent and that the mixing is uniform.

[0100] Add a pore-forming agent to S2A2 and continue grinding until the particle size is 5μm to 20μm to ensure that the catalyst, silicon powder and pore-forming agent are fully mixed.

[0101] In one embodiment, "predetermined mixing time" refers to grinding to a particle size of less than 30 μm.

[0102] The calcination and activation process in step S2B can be carried out in, but is not limited to, a tube furnace. A protective gas is introduced into the tube furnace to create an anhydrous and oxygen-free environment. The mixture from step S2A is then placed into the tube furnace for calcination and activation to prepare the silicon-copper active contact.

[0103] The "roasting activation" process includes the following stages.

[0104] First stage: Heat to the dehydration temperature at the first preset heating rate, and calcine within the dehydration temperature range for 15 min to 20 min to remove a small amount of free water from the silicon powder and catalyst surface.

[0105] The dehydration temperature is around the boiling point of water under the current pressure, for example, 90℃~120℃.

[0106] Second stage: Heat to the opening temperature at the second preset heating rate, and calcine within the opening temperature range for 40 min to 60 min to induce the pore-forming agent to slowly decompose and form pores, and form copper oxide co-catalyst.

[0107] Different pore-opening agents have slightly different pore-opening temperatures. For example, basic copper carbonate has an pore-opening temperature of 300℃ to 400℃.

[0108] The third stage: the temperature is increased to the activation temperature at the third preset heating rate, and calcined for 60 min to 90 min within the activation temperature range to generate a trialkoxysilane catalyst active body with abundant active sites—silicon-copper catalyst.

[0109] This invention uses cuprous chloride and cuprous oxide as catalysts, and the activation temperature is 500℃~600℃.

[0110] The “calcination activation process” may also include a fourth stage: heating to 800℃~1000℃ at a fourth preset heating rate, calcining for 10min~20min within this temperature range to ensure complete removal of bound water inside the catalyst, improve the stability of the catalyst, and avoid the introduction of water into the production of polymerization byproducts during the silicon powder alcoholysis reaction.

[0111] The "calcination activation process" can also include a fifth stage: maintaining a protective atmosphere and cooling to room temperature before removal. This can prevent the silicon copper contacts from being oxidized or absorbing moisture from the outside air.

[0112] Finally, the activated silicon-copper contact is ground, passed through a 500-mesh sieve, sealed under a protective atmosphere, and stored for later use.

[0113] In the above steps, the second preset heating rate is less than the first preset heating rate, and the second preset heating rate is less than the third preset heating rate. The slow heating in the second stage is conducive to the slow decomposition and opening of the pores by the pore-opening agent, forming a good pore structure.

[0114] The fourth preset heating rate is greater than the first, second, and third preset heating rates. This stage involves rapid heating, which can improve efficiency.

[0115] In one specific embodiment, the catalyst is cuprous chloride or cuprous oxide, the pore-forming agent is basic copper carbonate, and the calcination activation process includes:

[0116] First stage: Heat to 90℃~120℃ at a heating rate of 15℃ / min~20℃ / min, and bake within this temperature range preferably at a constant temperature for 15min~20min to remove silicon powder and a small amount of free water on the surface of the catalyst.

[0117] In the second stage, the temperature is increased to 300℃ to 400℃ at a heating rate of 10℃ / min to 15℃ / min. Within this temperature range, calcination is preferably carried out at a constant temperature for 40min to 60min to induce the pore-forming agent to slowly decompose and form pores, and to form copper oxide co-catalyst.

[0118] The third stage involves heating the temperature to 500℃ to 600℃ at a rate of 15℃ / min to 20℃ / min, and then calcining within this temperature range, preferably at a constant temperature for 60min to 90min, to generate silicon-copper catalysts.

[0119] Fourth stage: Rapidly heat to 800℃~1000℃ at a heating rate of 20℃ / min~25℃ / min, and calcine within this temperature range preferably at a constant temperature for 10min~20min to ensure complete removal of bound water inside the catalyst, improve the stability of the catalyst, and avoid the introduction of water into the production of polymerization byproducts during the silicon powder alcoholysis reaction.

[0120] The fifth stage, as described above, will not be repeated here.

[0121] This invention uses cuprous chloride and cuprous oxide as catalysts, adding a pore-forming agent to generate a silicon-copper catalyst with a large specific surface area, increasing the number of active sites. Furthermore, through a three-stage calcination activation process—first removing surface-adsorbed water, then creating pores, and finally high-temperature calcination—it ensures complete removal of bound water from the catalyst interior, forming a silicon-copper catalyst with abundant active sites and high stability. When this silicon-copper catalyst is used as a catalyst in the direct synthesis of alkoxysilanes, it can significantly improve conversion rate and product selectivity.

[0122] Step S3 is carried out in the alkyl alcohol vaporization feed unit and mainly includes the following steps:

[0123] S31 alkyl alcohol vaporization.

[0124] The temperature of the alkyl alcohol vaporizer is set to 80℃~120℃. Alkyl alcohols with a purity of 99.99% or higher are selected as the reaction raw materials. The alkyl alcohols in the raw material tank are sent into the alkyl alcohol vaporizer through a raw material pump, where the liquid alkyl alcohols are heated and converted into alkyl alcohol gas.

[0125] S32 protective gas preheating.

[0126] To enhance control over the vaporization flow rate of alkyl alcohols, a protective gas preheated by a protective gas preheater is introduced into the alkyl alcohol gas. The mixing of the protective gas and alkyl alcohol gas dilutes the alkyl alcohols, controls the flow rate, and enhances the conversion efficiency of alkyl alcohols. It also prevents the alkyl alcohol gas from condensing and clogging the pipeline during transport.

[0127] The temperature of the protective gas preheater is set to 100℃~120℃ to ensure that water vapor in the protective gas is discharged.

[0128] S33 heats the alkyl alcohol gas to the reaction temperature.

[0129] The protective gas carries the alkyl alcohol gas into the alkyl alcohol superheater, heating the mixed gas to meet the reaction temperature requirements. After the alkyl alcohol has completed vaporization and heating, it is fed from the bottom of the fluidized bed.

[0130] In one embodiment, the temperature of the alkyl alcohol superheater is set to 180°C to 240°C.

[0131] In addition, flow detectors and control valves are added after the alkyl alcohol vaporizer, alkyl alcohol superheater, and protective gas preheater to jointly control the feed rate of alkyl alcohol gas.

[0132] After the fluidized bed is preheated to the reaction temperature, the feed valve is opened, and the mixture of fine silicon powder and catalyst is transported into the fluidized bed reactor through the protective gas pressure difference. The mixture of alkyl alcohol gas and protective gas heated to 180℃~240℃ enters from the bottom of the fluidized bed to maintain the reaction temperature in the fluidized bed. After passing through the distributor, it reacts with silicon powder and catalyst materials to generate trialkoxysilane and a small amount of tetraalkoxysilane.

[0133] When the target product is triethoxysilane, a small amount of tetraethoxysilane is a byproduct. When the target product is trimethoxysilane, a small amount of tetramethoxysilane is a byproduct.

[0134] Additionally, a stirring paddle is installed at the bottom of the fluidized bed to ensure the reaction proceeds fully. At the same time, silicon powder filtration devices are installed at the bottom and top of the fluidized bed to reduce the amount of silicon powder carried out and thus prevent clogging of the pipeline.

[0135] The inventors discovered that precise catalysis is another way to reduce byproducts. After high-temperature catalysis, the catalyst becomes zero-valent copper, which is the active site for tetraalkoxysilane catalysis. A large amount of zero-valent copper agglomerates and aggregates to form large particles. Timely removal of the zero-valent copper after catalysis from the reactor can also minimize the further reaction of the target product, trialkoxysilane, into the byproduct tetraalkoxysilane.

[0136] The large zero-valent copper particles formed after aggregation will sink to the bottom of the fluidized bed due to gravity and size differences. A separation outlet is set at the bottom of the fluidized bed to separate the deactivated catalyst from the fluidized bed, thus realizing the continuous operation of the reaction.

[0137] After the reaction is complete, the reaction product mixture at the top of the fluidized bed mainly consists of unreacted alkyl alcohol gas, protective gas, hydrogen generated during the reaction, product trialkoxysilane, a small amount of byproduct tetraalkoxysilane, and a small amount of silicon powder catalyst solid mixture entrained.

[0138] This invention incorporates a cyclone separator at the top of the fluidized bed. The mixed gas undergoes preliminary separation by the cyclone separator before entering the separation unit. The silicon powder and catalyst separated by the cyclone separator are returned to the fluidized bed for further reaction via the material leg valve mechanism of the internal cyclone separator. Because the generated triethoxysilane is promptly separated from the reactor during the fluidized bed reaction, its further catalytic conversion to tetraethoxysilane within the reactor is avoided, achieving a target selectivity of 95% or higher for triethoxysilane.

[0139] The method for preparing trialkoxysilanes using a fluidized bed further includes a step of product separation in S25:

[0140] S251 transports the reaction product mixture gas from the top of the fluidized bed to the Venturi scrubber. The separated protective gas and reaction gas are sent to the gas separation device, and the separated liquid containing sediment is sent to the solid-liquid separation device to separate silicon powder and catalyst.

[0141] S252 adds an extractant to the liquid separated by the solid-liquid separation device. The extractant is selected from one or more combinations of m-xylene, mesitylene, ethylbenzene, and cumene.

[0142] S253 feeds the product mixture with added extractant into the first extraction column. The bottom temperature of the column is 100℃~140℃, and the top temperature is 50℃~70℃. The component separated at the top of the column is alkyl alcohol, and the component separated at the bottom of the column is trialkoxysilane, tetraalkoxysilane and extractant.

[0143] S254 introduces the components separated from the bottom of the first extraction column into the second extraction column. The bottom temperature is set to 125℃~145℃, and the top temperature is set to 75℃~95℃. The components separated at the top are the extractant, and the components separated at the bottom are trialkoxysilane and tetraalkoxysilane.

[0144] S255 sends the components separated from the bottom of the second extraction column to a distillation column. The bottom temperature of the column is 140℃~160℃, and the top temperature is 100℃~130℃. The components separated at the top of the column are trialkoxysilanes with a purity of 99% or higher, and the components separated at the bottom of the column are tetraalkoxysilanes with a purity of 99% or higher.

[0145] In one specific embodiment, step S25, product separation, specifically includes:

[0146] S251 gas-liquid separation.

[0147] The product mixture generated in the fluidized bed enters a Venturi scrubber for cooling, dust removal, and gas-liquid separation. The separated protective gas and hydrogen are sent to a gas separation unit. The separated protective gas is recycled as purge gas and conveying gas; the separated hydrogen is sent as a byproduct to a polysilicon production plant for further use.

[0148] S252 solid-liquid separation.

[0149] Because of the low stability of trialkoxysilanes, in the presence of catalysts and silicon powder, the trialkoxysilanes in the product will continue to convert to tetraalkoxysilanes during the distillation separation process, and the unseparated silicon powder will also continue to react, increasing the difficulty of separation.

[0150] This invention feeds the dust-laden liquid, cooled and separated in a Venturi scrubber, into a solid-liquid separation device. The solid-liquid separation device is selected from a settling tank, a high-speed centrifuge, and a membrane filtration device to ensure the separation of silicon powder and catalyst from the product. At this point, the separated liquid phase product mainly consists of trialkoxysilane, a small amount of tetraalkoxysilane, and unreacted alkyl alcohols.

[0151] S253 azeotropic separation.

[0152] Alkyl alcohols and alkoxysilanes readily form azeotropic compounds, which cannot be separated by ordinary distillation. Azeotropic separation, extraction separation, pressure swing distillation, and other methods can be used instead.

[0153] This invention preferably employs extraction separation, which has lower energy consumption and is less difficult to separate. Specifically, an excess of extractant is added to the liquid product separated in the solid-liquid separator for further separation. The extractant can be selected from one or more combinations of m-xylene, mesitylene, ethylbenzene, cumene, etc.

[0154] The product mixture with added extractant is fed into the first extraction column to separate alkyl alcohols. The bottom temperature of the column is set to 100℃~140℃, and the top temperature is set to 50℃~70℃. The component separated at the top of the column is 99% or higher alkyl alcohol, which can be sent to the alkyl alcohol feed tank for further reaction; the component separated at the bottom of the column is a mixture of trialkoxysilane, tetraalkoxysilane, and extractant.

[0155] The components separated at the bottom of the first extraction column are fed into the second extraction column to recover the extractant. The bottom temperature is set to 125℃~145℃, and the top temperature is set to 75℃~95℃. The components separated at the top are 99% or higher extractant (m-xylene extractant), which are recovered and recycled. The components separated at the bottom are trialkoxysilane and tetraalkoxysilane.

[0156] The fraction separated from the bottom of the second extraction column is sent to a distillation column for further separation to separate trialkoxysilanes. The bottom temperature is set to 140℃~160℃, and the top temperature is set to 100℃~130℃. The fraction separated at the top is trialkoxysilane with a purity of 99% or higher, and the fraction separated at the bottom is tetraalkoxysilane with a purity of 99% or higher.

[0157] As a result, 99% or more of the trialkoxysilane products were successfully produced through the fluidized bed reaction-based trialkoxysilane production system.

[0158] In summary, compared with the prior art, the present invention has at least the following beneficial effects:

[0159] This invention provides a system for preparing trialkoxysilanes, including a raw material pretreatment unit, a fluidized bed for silicon powder alcoholysis reaction, and a product separation unit, ultimately yielding trialkoxysilanes with a purity of 99%. Using fine silicon powder, a byproduct of polysilicon production, as raw material significantly increases its added value and provides more references for the utilization of fine silicon powder. The direct alcoholysis reaction of silicon powder is green and environmentally friendly, generating no toxic or harmful substances. The production system recycles nitrogen, extractants, and other materials, saving energy, reducing emissions, and lowering production costs.

[0160] Based on the characteristics of silicon powder alcoholysis reaction, a fluidized bed-based reaction system was designed. The method of preparing trialkoxysilane using a fluidized bed was adopted. Through the integrated reaction-separation system, silicon powder and catalyst were separated from the product in a timely manner, and the generated trialkoxysilane was separated from the reaction in a timely manner. The silicon powder utilization rate can reach 95% or more, and the selectivity of trialkoxysilane is 90% or more, achieving the goal of high conversion rate and high selectivity.

[0161] Considering the unstable nature of trialkoxysilanes, the entire reaction system is designed to create a fully anhydrous and oxygen-free reaction atmosphere, thereby minimizing the generation of other byproducts.

Claims

1. A method for preparing trialkoxysilanes using a fluidized bed, characterized in that, include: The fluidized bed is preheated under a protective atmosphere; the heating temperature at the bottom of the fluidized bed is higher than that in the middle of the fluidized bed, and the heating temperature in the middle of the fluidized bed is higher than that at the top of the fluidized bed. A preheated protective gas is used to push the silicon powder composition into a preheated fluidized bed. The silicon powder composition is a mixture of silicon powder and silicon copper catalyst. A preheated protective gas is used to drive alkyl alcohol gas into the preheated fluidized bed; Under a protective atmosphere, the reaction temperature in the fluidized bed is maintained, and the silicon powder composition reacts with alkyl alcohol gas in the fluidized bed to generate trialkoxysilane.

2. The method for preparing trialkoxysilanes using a fluidized bed according to claim 1, characterized in that, The temperature difference between the bottom and middle sections of the fluidized bed is 10℃~30℃, and the temperature difference between the top and bottom sections of the fluidized bed is 10℃~30℃; or The heating temperature at the bottom of the fluidized bed is 220℃~240℃, the heating temperature in the middle of the fluidized bed is 170℃~210℃, and the heating temperature at the top of the fluidized bed is 160℃~180℃.

3. The method for preparing trialkoxysilanes using a fluidized bed according to claim 1, characterized in that, "Using a preheated protective gas to propel the silicon powder composition into a preheated fluidized bed" includes the following steps: The protective gas is preheated and then introduced into the dryer. The temperature of the protective gas after preheating is 100℃~120℃. The silicon powder is fed into a dryer for drying. After the surface moisture of the silicon powder is separated, the silicon copper catalyst is added into the dryer. The silicon copper catalyst accounts for 3% to 10% of the mass fraction of the silicon powder raw material. The silicon copper catalyst and the silicon powder are mixed through a vibrating screen to form a silicon powder composition. Increase the pressure of the protective gas to feed the silicon powder composition into the fluidized bed.

4. The method for preparing trialkoxysilanes using a fluidized bed according to claim 1, characterized in that, It also includes the step of preparing the silicon-copper catalyst: under a protective atmosphere, the catalyst, silicon powder and pore-forming agent are mixed, and the catalyst is a mixture of cuprous chloride and cuprous oxide; Under a protective atmosphere, calcination activation is performed to form silicon-copper contact; Among them, "calcination activation" includes: First stage: Heat to the dehydration temperature and calcine within the dehydration temperature range for 15 to 20 minutes to remove free water from the surface of silicon powder and catalyst; Second stage: Heat to the opening temperature and calcine within the opening temperature range for 40 min to 60 min to induce the pore-forming agent to slowly decompose and form pores, and form copper oxide co-catalyst; The third stage: heat up to the activation temperature and bake for 60 to 90 minutes within the activation temperature range to generate silicon-copper catalysts.

5. The method for preparing trialkoxysilanes using a fluidized bed according to claim 4, characterized in that, Silicon powder accounts for 30-60% of the total mass, cuprous chloride accounts for 20-50% of the total mass, cuprous oxide accounts for 10-30% of the total mass, and / or The amount of pore-forming agent added accounts for 5% to 10% of the mass of the silicon copper contact.

6. The method for preparing trialkoxysilanes using a fluidized bed according to claim 4, characterized in that, The "mixing" process includes the following steps: First, put the catalyst and silicon powder into a ball mill and mix for a predetermined time; Add a pore-forming agent and continue grinding until the particle size is 5μm to 20μm; Preferably, "predetermined mixing time" refers to grinding to a particle size of less than 30 μm.

7. The method for preparing trialkoxysilanes using a fluidized bed according to claim 4, characterized in that, During the "calcination activation" process, the temperature is increased to the dehydration temperature at the first preset heating rate, to the pore opening temperature at the second preset heating rate, and to the activation temperature at the third preset heating rate. in The second preset heating rate is less than the first preset heating rate, and the second preset heating rate is less than the third preset heating rate. or The first preset heating rate is 15℃ / min to 20℃ / min, the second preset heating rate is 10℃ / min to 15℃ / min, and the third preset heating rate is 15℃ / min to 20℃ / min.

8. The method for preparing trialkoxysilanes using a fluidized bed according to claim 4, characterized in that, The calcination activation process also includes: after generating the silicon-copper catalyst, heating it to 800℃~1000℃ and calcining it for 10min~20min within this temperature range to remove the bound water inside the catalyst.

9. The method for preparing trialkoxysilanes using a fluidized bed according to claim 8, characterized in that, The temperature is raised to 800℃~1000℃ at the fourth preset heating rate. The second preset heating rate is less than the first preset heating rate, the second preset heating rate is less than the third preset heating rate, and the fourth preset heating rate is greater than the first preset heating rate, the second preset heating rate, and the third preset heating rate.

10. The method for preparing trialkoxysilanes using a fluidized bed according to claim 1, characterized in that, Liquid alkyl alcohol is converted into alkyl alcohol gas through an alkyl alcohol vaporizer. Preheated protective gas is then introduced into the alkyl alcohol gas, which carries the alkyl alcohol gas into the alkyl alcohol superheater, raising the temperature of the alkyl alcohol to the reaction temperature.

11. The method for preparing trialkoxysilanes using a fluidized bed according to claim 1, characterized in that, Deactivated catalyst is separated from the outlet at the bottom of the fluidized bed.

12. The method for preparing trialkoxysilanes using a fluidized bed according to claim 1, characterized in that, Silicon powder is filtered by a silicon powder filter device located at the top of the fluidized bed; and / or The cyclone separator at the top of the fluidized bed separates the silicon powder and catalyst from the reaction product mixture and returns them to the middle or bottom of the fluidized bed.

13. The method for preparing trialkoxysilanes using a fluidized bed according to claim 12, characterized in that, The method for preparing trialkoxysilanes using a fluidized bed further includes: The reaction product mixture gas discharged from the top of the fluidized bed is sent to a Venturi scrubber. The separated protective gas and reaction gas are sent to a gas separation device, and the separated liquid containing sediment is sent to a solid-liquid separation device to separate silicon powder and catalyst. An extractant is added to the liquid separated by the solid-liquid separation device. The extractant is selected from one or more combinations of m-xylene, mesitylene, ethylbenzene, and cumene. The product mixture with added extractant is fed into the first extraction column, where the bottom temperature is 100℃~140℃ and the top temperature is 50℃~70℃. The component separated at the top of the column is an alkyl alcohol, and the components separated at the bottom of the column are trialkoxysilane, tetraalkoxysilane and extractant. The components separated at the bottom of the first extraction column are fed into the second extraction column. The bottom temperature is set to 125℃~145℃ and the top temperature is set to 75℃~95℃. The components separated at the top are the extractant, and the components separated at the bottom are trialkoxysilane and tetraalkoxysilane. The components separated from the bottom of the second extraction column are sent to a distillation column with a bottom temperature of 140℃~160℃ and a top temperature of 100℃~130℃. The components separated at the top are trialkoxysilanes with a purity of 99% or higher, and the components separated at the bottom are tetraalkoxysilanes with a purity of 99% or higher.

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