Process and system for preparing monosilane through fixed bed catalytic cracking of polycrystalline silicon high-boiling residues

Abstract

The invention belongs to the field of polycrystalline silicon preparation, and particularly relates to a technology and system for preparing monosilane through fixed bed catalytic cracking of polycrystalline silicon high-boiling residues, the system comprises a feeding unit, a reaction unit and a condensation recovery unit which are connected in sequence, the feeding unit comprises a storage tank, a feeding pump and a preheating mixer which are connected in sequence, and the reaction unit comprises a reaction unit and a condensation recovery unit which are connected in sequence. The preheating mixer is also connected with a hydrogen feeding pipeline, the reaction unit is a fixed bed catalytic reactor filled with a catalyst, and the condensation recovery unit comprises at least one stage of cooler and a recovery tank. By adopting the system, the process disclosed by the invention has the advantages of extremely simple process, high yield, capability of realizing long-term, continuous and stable production, environmental friendliness, easiness in material separation, high conversion rate, good target product selectivity and high trichlorosilane content in a final product.

Description

Technical Field

[0001] The invention relates to the technical field of polysilicon monomer production, in particular to a process and system for preparing monosilane by catalytic cracking of polysilicon high boiling points in a fixed bed. Background Art

[0002] Polysilicon is an important chemical intermediate, widely used in industries such as integrated circuits and photovoltaics. Due to the rapid development of China's photovoltaic industry, there is also a considerable demand for polysilicon. China is the global center of the polysilicon industry. By the end of 2023, 21 domestic manufacturers have built a polysilicon production capacity of 2.658 million tons, and there is still 1.28 million tons of production capacity to be put into use.

[0003] At present, the main production method of polysilicon is the "modified Siemens process". In this process, in addition to the main product trichlorosilane, by-products such as silicon tetrachloride, low-boiling impurities and polysilicon high-boiling products are often produced.

[0004] Polysilicon high boiling products account for 1-5% of the chlorosilane monomer production, mainly SiCl 3 -SiCl 3 , SiCl 4 , SiCl 3 -O-SiCl 3 And a small amount of trichlorosilane and other substances. The high-boiling substances of polysilicon are unstable in nature. When they come into contact with air and water, they will undergo hydrolysis reactions to generate substances such as hydrogen chloride and silicone oil, while producing a pungent odor, which will cause serious harm to the environment. In addition, the high-boiling substances of polysilicon are highly corrosive and require very high storage materials. With the annual expansion of polysilicon production capacity, the large accumulation of polysilicon chlorosilane has increased the company's hazardous waste treatment costs, causing huge environmental safety risks, and gradually becoming an obstacle to the development of the polysilicon industry.

[0005] At present, there have been related studies reporting on methods for preparing monosilane by cracking high-boiling products of polysilicon, such as CN108658082A, which discloses a process for cracking high-boiling products in polysilicon production, characterized in that it includes: pretreatment: removing solid impurities and metal halides in high-boiling products to obtain a first mixture; first separation: separating the first mixture in a degassing tower at 50-150°C to obtain silicon tetrachloride and chlorosilane oligomers; cracking: cracking the chlorosilane oligomers under the action of a catalyst to obtain a chlorosilane mixture; second separation: sending the chlorosilane mixture back to the degassing tower to remove uncracked chlorosilane oligomers to obtain monosilicon chlorosilane and non-condensable gas. For another example, CN 111498853 provides a process for cracking high-boiling products of chlorosilane produced as a by-product in polysilicon production. The cracking process comprises: filtering high-boiling chlorosilane by-products of polysilicon production to remove amorphous silicon therein to obtain purified high-boiling products; using a catalyst to crack hydrogen chloride and the purified high-boiling products to obtain a cracking product system, wherein the catalyst comprises a macroporous resin and an organic amine supported on the macroporous resin, and the organic amine is selected from any one or more of tri-n-butylamine, tri-n-octylamine, N, N-dimethylaniline, dioctadecyl secondary amine and perfluorotriethylamine.

[0006] The above technical solution has the following problems: 1) The catalyst used is usually tri-n-butylamine or its analogs, but tri-n-butylamine is a highly toxic chemical and does not meet the requirements of green chemistry. 2) The kettle semi-continuous reaction process is used, which has the problems of inability to produce continuously, limited output, difficulty in separating homogeneous catalysis, high output of hazardous waste, and poor selectivity of target products.

[0007] At present, the fixed bed catalytic process has not been applied in the field of polysilicon high boiling point cracking. This is mainly because green, efficient and long-term stable catalysts have not yet been developed. In addition, the fixed bed process requires a variety of processing units, and the initial investment is more expensive than the autoclave reaction process. Summary of the invention

[0008] The purpose of the present invention is to solve the above technical problems and provide a process for preparing monosilane by fixed-bed catalytic cracking of high-boiling polysilicon, which has the advantages of extremely simple process, high yield, long-term, continuous and stable production, environmental friendliness, easy material separation, high conversion rate, good target product selectivity and high trichlorosilane content in the final product.

[0009] The present invention also provides a system for preparing monosilane by catalytic cracking of high boiling polysilicon in a fixed bed for the above process, which has a simple system, low equipment investment and operation cost and good reliability.

[0010] The system for preparing monosilane by catalytic cracking of high-boiling-point polysilicon in a fixed bed comprises a feed unit, a reaction unit and a condensation recovery unit connected in sequence, wherein the feed unit comprises a storage tank, a feed pump and a preheating mixer connected in sequence, and the preheating mixer is also connected to a hydrogen feed pipeline; the reaction unit is a fixed-bed catalytic reactor filled with a catalyst, and the condensation recovery unit comprises at least one stage cooler and a recovery tank.

[0011] The storage tank and the preheating mixer are also connected to a nitrogen purge line.

[0012] It also includes an online detection unit, and the material outlet of the fixed bed catalytic reactor is also connected to the recovery tank via the online detection unit.

[0013] The catalyst filled in the fixed bed catalytic reactor comprises a silicon aluminum molecular sieve, an aluminum oxide carrier and a non-precious metal.

[0014] The process for preparing monosilane by catalytic cracking of high-boiling-point polysilicon in a fixed bed is as follows: a raw liquid of high-boiling-point polysilicon is loaded into a storage tank, and then fed into a preheating mixer via a feed pump, mixed with hydrogen entering the preheating mixer and preheated, and then fed into a fixed bed catalytic reactor for catalytic cracking reaction; the reacted material is cooled to a liquid state via a cooler and then fed into a recovery tank to obtain a product.

[0015] The polysilicon high boiling point raw liquid is mixed with hydrogen and preheated to 300-500°C.

[0016] The catalyst filled in the fixed bed catalytic reactor includes a silicon-aluminum molecular sieve, an alumina carrier and a non-precious metal.

[0017] The topological structure of the silica-alumina molecular sieve is at least one of FAU (zeolite Y-type structure, such as X-type zeolite and Y-type zeolite, such as HY), *BEA (Beta zeolite, β zeolite), MFI (ZSM-5 molecular sieve, pentacyclic zeolite), MOR (mordenite), TON (ZSM-22 molecular sieve, TON type molecular sieve), MWW (MCM-22 molecular sieve, MWW type molecular sieve) and CHA (zeolite A type, small pore CHA type zeolite, such as SAPO-34); the alumina carrier is at least one of pseudo-boehmite, SB powder (powdered silica-alumina molecular sieve), dry gel powder, and aluminum sol; the non-precious metal is at least one of Ni, Mo, Fe, Co, Zn, and Cu.

[0018] The catalyst at least comprises: a silicon-alumina molecular sieve accounting for 40-70wt% by weight, an alumina carrier accounting for 20-40wt% by weight, and a non-precious metal accounting for 1-10wt% by weight.

[0019] The reaction temperature in the fixed bed catalytic reactor is controlled to be 300-500°C, the reaction pressure to be 0.1-2.0MPa, the hydrogen flow rate to be 50-400mL / min, the volume space velocity of the polysilicon high boiling point feed to be 0.1-2.0h-1, and the height-to-diameter ratio of the catalyst loading to be 5-20.

[0020] The material exiting the fixed bed catalytic reactor is cooled to -10°C to -2°C via a cooler.

[0021] The material of the fixed bed catalytic reactor is divided into two streams, one stream is sent to the cooler, and the other stream is sent back to the recovery tank after being detected by the line detection unit. The amount of the other stream is the amount that meets the detection requirements of the line detection unit.

[0022] The main component of the polysilicon high boiling point solution is SiH m Cl n -SiH x Cl y (m+n=3; m, n=0, 1, 2, 3), SiH m Cl n -O-SiH x Cl y (m+n=3; m, n=0, 1, 2, 3), SiCl 4 And a small amount of SiHCl 3 Among them, SiCl 3 -SiCl 3 Accounting for more than 50%, SiCl 4 The proportion is 5% to 30%, SiCl 3 -O-SiCl 3 The proportion is more than 5wt%.

[0023] Further preferably, the above stock solution can be filtered, distilled or rotary evaporated to remove solid residue components and high boiling point impurities. High boiling products often contain a small amount of copper catalyst residues, hydrolysis products, AlCl 3 、FeCl 3 、TiCl 4 、Si、PCl 3 and AsCl 3 If solid materials such as solids are not treated, they will clog the pump or catalyst bed, causing feed fluctuations, pump damage, system pressure fluctuations and even overpressure. Therefore, the removal of solid residues can stabilize the system and extend the start-up cycle.

[0024] In view of the problems existing in the background technology, the inventor has made the following improvements:

[0025] 1) A fixed-bed catalytic reactor is used. Based on the principle of efficient cracking and rearrangement of high-boiling products of polysilicon using efficient, green and stable metal-loaded catalysts, the high-boiling product stock solution of polysilicon is mixed with hydrogen and preheated before being sent into a fixed-bed catalytic reactor for catalytic cracking. This fixed-bed catalytic process can achieve continuous production and can be operated continuously for more than 3 months, reducing the problems of the original kettle cracking process such as difficulty in judging the reaction endpoint, low conversion rate, and inability to produce continuously. It has a large output and is suitable for large-scale promotion and utilization.

[0026] 2) The fixed bed catalytic reactor is filled with non-toxic catalysts to truly achieve source control of environmental hazards, comply with the principles of green chemistry, and reduce the problem of difficulty in separating materials caused by homogeneous reactions, reduce the generation of hazardous waste, improve product quality, and increase the economic benefits of the enterprise. The catalyst includes a silicon-aluminum molecular sieve, an alumina carrier and non-precious metals. The silicon-aluminum molecular sieve has Lewis acidity and can catalyze the breaking of Si-Si bonds in polysilicon high-boiling products, which is beneficial to promote the conversion of polysilicon high-boiling products into chlorosilane monomers. The silicon-aluminum ratio of the silicon-aluminum molecular sieve is preferably SiO 2 / Al 2 O 3 =50-200 (molar ratio), various components are loaded on the molecular sieve, which can effectively improve the catalytic performance and have a certain strength to meet the needs of the fixed bed catalyst bed filling, and non-precious metals can be loaded on the silicon aluminum molecular sieve to form active sites, which can promote the dissociation of hydrogen, thereby promoting the hydrocracking of high-boiling products of polysilicon. In addition, the metal site can also promote the disproportionation of chlorosilanes, effectively improving the selectivity of trichlorosilane; the alumina carrier can effectively improve the catalyst strength, and the catalyst can be prepared by including but not limited to physical mixing, impregnation, encapsulation, etc., which is a prior art and will not be described in detail. The catalyst thus obtained has high strength, high specific surface area, and high stability, and is particularly suitable for use as a catalyst for filling a fixed bed catalytic reactor. Here, it is preferred that the mass proportion of silicon aluminum molecular sieve is 40-70wt%, too much will lead to a decrease in catalyst strength, and too little will lead to a decrease in catalyst catalytic activity; the mass proportion of the non-precious metal is 1-10wt%, too much will increase the catalyst cost, and too little will reduce the catalyst reaction activity.

[0027] 3) Based on the fixed bed catalytic reactor, the reaction conditions are optimized, the reaction temperature is 300-500°C, the reaction pressure is 0.1-2.0MPa, preferably 350-450°C, and the reaction pressure is 0.3-1.0MPa. Through pressure control, the hydrogen concentration in the fixed bed catalytic reactor can be effectively controlled, the degree of hydrogen dissociation can be improved, and the positive cracking reaction of polysilicon high boiling products can be promoted. Controlling the hydrogen flow rate of 50-400mL / min to ensure the residence time of the material in the bed is conducive to the complete conversion of polysilicon high boiling products, improving the selectivity of trichlorosilane, and improving production efficiency.

[0028] 4) The storage tank and preheating mixer are also connected to the nitrogen purge pipeline. The nitrogen purge pipeline is purged before each start-up to prevent air and water residue. The material of the fixed bed catalytic reactor is cooled to -10°C to -2°C by a cooler to ensure that the gaseous product is quickly condensed into a liquid state. The fixed bed catalytic reactor is top-fed and bottom-discharged. The outlet material is divided into two streams (controlled by a valve). One stream of material (most of it) is sent to the cooler, and the other stream of material (a small amount) is sent back to the recovery tank after detection by the line detection unit. The amount of the other stream of material is the amount that meets the detection requirements of the line detection unit. The components of the material after the reaction can be detected synchronously by the online detection unit, and the online detection unit can use various existing detection equipment, such as gas chromatographs.

[0029] In summary, the process of the present invention is extremely simple, has high yield, can realize long-term, continuous and stable production, is environmentally friendly, is easy to separate materials, has high conversion rate, good selectivity for the target product, and has a high content of trichlorosilane in the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a process flow chart and system diagram of the present invention.

[0031] Among them, 1-storage tank, 2-feed pump, 3-preheating mixer, 4-fixed bed catalytic reactor, 4.1-catalyst bed, 5-cooler, 6-nitrogen purge pipeline, 7-hydrogen feed pipeline, 8-polysilicon high boiling point feed pipeline, 9-recovery tank, 10-online detection unit. DETAILED DESCRIPTION

[0032] The system of the present invention is further explained below in conjunction with the accompanying drawings:

[0033] See also Figure 1 , including a feed unit, a reaction unit and a condensation recovery unit connected in sequence,

[0034] The feed unit comprises a storage tank 1, a feed pump 2 and a preheating mixer 3 connected in sequence, and the preheating mixer 3 is also connected to a hydrogen feed pipeline 7, and hydrogen and polysilicon high boiling products are premixed and preheated in the preheating mixer 3;

[0035] The reaction unit is a fixed bed catalytic reactor 4 filled with catalyst, and the condensation recovery unit includes at least one stage cooler 5 and a recovery tank 9. The cooler 5 can be set in one or more stages in series as needed.

[0036] The storage tank 1 and the preheating mixer 3 are also connected to the nitrogen purge pipeline 6. An online detection unit 10 is also included, and the material outlet of the fixed bed catalytic reactor 4 is also connected to the recovery tank 9 via the online detection unit 10. The fixed bed catalytic reactor 4 is provided with a catalyst bed 4.1 filled with a fixed bed catalyst, and the catalyst is made of raw materials including at least a silicon aluminum molecular sieve, an alumina carrier and non-precious metals.

[0037] Process:

[0038] Before starting, nitrogen is used to purge and replace the pipeline 5-10 times through the nitrogen purge pipeline 6, and then the polysilicon high-boiling product stock solution (specific composition is shown in Table 1) after filtering, distillation or rotary evaporation to remove solid residue components and high-boiling impurities is sent to the storage tank 1, sent to the preheating mixer 3 through the feed pump 2, mixed with the hydrogen entering the preheating mixer 3 through the hydrogen feed pipeline 9 and preheated to 300-500°C, and then enter the fixed bed catalytic reactor 4 from the top to carry out catalytic cracking reaction in the catalyst bed 4.1, and the reacted materials are drawn out from the bottom of the fixed bed catalytic reactor 4. The material is divided into two streams, most of which is cooled to -10°C to -2°C liquid by the cooler 5 and then sent to the recovery tank 8 to obtain the product, and the remaining small amount (the detection amount that meets the detection requirements of the line detection unit 10, and the temperature is kept at 200°C) is sent back to the recovery tank 9 after the line detection unit detection 10.

[0039] The catalyst filled in the catalyst of the fixed bed catalytic reactor 4 is made of 40-70wt% of silica-alumina molecular sieve, 20-40wt% of alumina carrier and 1-10wt% of non-precious metal as main raw materials.

[0040] Control the reaction temperature in the fixed bed catalytic reactor to 300-500°C, the reaction pressure to 0.1-2.0MPa, the hydrogen flow rate to 50-400mL / min, and the feed volume space velocity to 0.1-2.0h for polysilicon high boiling liquid. -1 , the height-to-diameter ratio of the catalyst loading is 5-20. Preferably, the reaction temperature in the fixed bed catalytic reactor is controlled to be 350-450°C, the reaction pressure is 0.3-1.0 MPa, and the feed volume space velocity of the polysilicon high boiling liquid is 0.3-1.0 h -1 .

[0041] Catalyst Example:

[0042] (1) Synthesis of NiHY core catalytic component: First, nickel nitrate (metallic nickel precursor) was dissolved in deionized water to form a transparent solution A. Then, the obtained solution A, HY silicon aluminum molecular sieve, and deionized water were mixed to obtain a mixture B, which was stirred in an 80°C water bath for 4 h. The mass ratio of the mixture B was 0.03Ni:1HY:10H 2O; finally, the mixture B was filtered, dried, and calcined at 550°C for 3h to obtain the NiHY core catalytic component;

[0043] (2)NiHY / Al 2 O 3 Preparation of catalyst: The NiHY catalytic active component obtained in step 1), the carrier pseudo-boehmite, sesbania powder, deionized water and nitric acid were mixed evenly, extruded into strips, dried, calcined at 550°C for 3h, and reduced at 500°C in a pure hydrogen atmosphere for 10h to obtain the catalyst, named NiHY / Al 2 O 3 The mass ratio of the NiHY catalytic active component to the carrier pseudo-boehmite (Al2O3) is 60:40, and the content of the metal oxide NiO is 7.82wt% of the total mass of the catalyst.

[0044] The fixed bed catalytic reactor 4 is filled with the catalyst filled in the above catalyst embodiment, and the fixed bed reaction process experiment is carried out using the above process. The effect description is shown in the following experimental example.

[0045] Experimental Example 1

[0046] Reaction temperature 400℃, reaction pressure 0.5MPa, polysilicon high boiling point feed rate 0.5h -1 The circulating cooling device is set at a temperature of -15°C. According to calculations, the conversion rate of polysilicon high boiling products is 96.5%, the selectivity of chlorosilane monomer is 98.4%, and the selectivity of trichlorosilane is 35.8%, as shown in Table 1-A1.

[0047] Experimental Example 2

[0048] Reaction temperature 400℃, reaction pressure 0.3MPa, polysilicon high boiling point feed rate 0.3h -1 , the circulating cooling device is set at -15°C. According to calculations, the conversion rate of high-boiling products of polysilicon is 97.8%, the selectivity of chlorosilane monomer is 99.7%, and the selectivity of trichlorosilane is 35.3%, as shown in Table 1-A2.

[0049] Experimental Example 3

[0050] Reaction temperature 500℃, reaction pressure 0.5MPa, polysilicon high boiling point feed rate 1.0h -1 The circulating cooling device is set at a temperature of -15°C. According to calculations, the conversion rate of high-boiling products of polysilicon is 98.6%, the selectivity of chlorosilane monomer is 98.4%, and the selectivity of trichlorosilane is 41.3%, as shown in Table 1-A3.

[0051] Experimental Example 4

[0052] Reaction temperature: 350℃, reaction pressure: 0.5MPa, polysilicon high boiling point feed rate: 0.2h -1 The circulating cooling device is set at -15°C. According to calculations, the conversion rate of high-boiling products of polysilicon is 96.1%, the selectivity of chlorosilane monomer is 99.4%, and the selectivity of trichlorosilane is 36.3%, as shown in Table 1-A4.

[0053] Comparative Experiment Example 1

[0054] Reaction temperature: 200℃, reaction pressure: 0.5MPa, polysilicon high boiling point feed rate: 0.5h -1 , the circulating cooling device is set at -15°C. According to calculations, the conversion rate of high-boiling products of polysilicon is 51.0%, the selectivity of chlorosilane monomer is 100%, and the selectivity of trichlorosilane is 12.7%, as shown in Table 1-D1.

[0055] Comparative Experiment Example 2

[0056] Reaction temperature 400℃, reaction pressure 0.05MPa, polysilicon high boiling point feed rate 0.5h -1 The circulating cooling device is set at -15°C. According to calculations, the conversion rate of high-boiling products of polysilicon is 36.4%, the selectivity of chlorosilane monomer is 100%, and the selectivity of trichlorosilane is 5.9%, as shown in Table 1-D2.

[0057] Comparative Experiment 3

[0058] Reaction temperature 200℃, reaction pressure 0.5MPa, polysilicon high boiling point feed rate 3.0h -1 The circulating cooling device is set at -15°C. According to calculations, the conversion rate of high-boiling products of polysilicon is 48.3%, the selectivity of chlorosilane monomer is 100%, and the selectivity of trichlorosilane is 19.6%, as shown in Table 1-D3.

[0059] Comparative Experiment Example 4

[0060] Preparation of comparative experimental catalyst:

[0061] (1)HY / Al 2 O 3 Preparation of catalyst: HY silica-alumina molecular sieve, carrier pseudo-boehmite, sesbania powder, deionized water and nitric acid were mixed evenly, extruded into strips, dried, and calcined at 550°C for 3h to obtain the catalyst, named HY / Al 2 O 3 . The mass ratio of the catalytically active component to the carrier is 60:40, and there is no metal oxide. (Except for not containing metal oxide, the rest is the same as the catalyst example)

[0062] (2) The catalyst prepared above was used to carry out a fixed bed catalytic reaction process experiment. The process parameters were consistent with those in Example 4. The catalytic reaction results obtained were: the conversion rate of high boiling points of polysilicon was 78.3%, the selectivity of chlorosilane monomer was 94.5%, and the selectivity of trichlorosilane was 29.6%.

[0063] Comparative Experiment Example 5

[0064] Preparation of comparative experimental catalyst:

[0065] (1)Ni / Al 2 O 3 Preparation of the catalyst: Nickel nitrate was dissolved in deionized water to form a transparent solution A, the transparent solution A, carrier pseudo-boehmite, sesbania powder, deionized water and nitric acid were mixed evenly, extruded into strips, dried, and calcined at 550°C for 3h to obtain the catalyst, named Ni / Al 2 O 3 Among them, the mass of NiO accounts for 8.1wt% of the total mass of the catalyst.

[0066] (2) The catalyst prepared above was used to carry out a fixed bed catalytic reaction process experiment. The process parameters were consistent with those in Example 4. The catalytic reaction effect obtained was: the conversion rate of high boiling points of polysilicon was 99.9%, the selectivity of chlorosilane monomer was 92.5%, and the selectivity of trichlorosilane was 8.1%.

[0067] Table 1

[0068]

[0069]

Claims

1. A system for preparing monosilane by catalytic cracking of high boiling points of polysilicon in a fixed bed, characterized in that: It includes a feed unit, a reaction unit and a condensation recovery unit connected in sequence, wherein the feed unit includes a storage tank, a feed pump and a preheating mixer connected in sequence, and the preheating mixer is also connected to a hydrogen feed pipeline; the reaction unit is a fixed bed catalytic reactor filled with a catalyst, and the condensation recovery unit includes at least one stage cooler and a recovery tank.

2. The system for preparing monosilane by catalytic cracking of polysilicon high boiling points in a fixed bed as claimed in claim 1, characterized in that: The storage tank and the preheating mixer are also connected to a nitrogen purge line.

3. The system for preparing monosilane by catalytic cracking of high boiling polysilicon in a fixed bed as claimed in claim 1, characterized in that: It also includes an online detection unit, and the material outlet of the fixed bed catalytic reactor is also connected to the recovery tank via the online detection unit.

4. The system for preparing monosilane by catalytic cracking of polysilicon high boiling points in a fixed bed according to any one of claims 1 to 3, characterized in that: The catalyst filled in the fixed bed catalytic reactor comprises a silicon-aluminum molecular sieve, an alumina carrier and a non-precious metal.

5. A process for preparing monosilane by catalytic cracking of high boiling products of polysilicon in a fixed bed, characterized in that: The polysilicon high-boiling product liquid is loaded into a storage tank, and then sent to the preheating mixer through a feed pump, mixed with the hydrogen entering the preheating mixer and preheated, and then enters the fixed bed catalytic reactor for catalytic cracking reaction. The reacted material is cooled to liquid through a cooler and sent to a recovery tank to obtain the product.

6. The process for preparing monosilane by catalytic cracking of high boiling points of polysilicon in a fixed bed as claimed in claim 5, characterized in that: The polysilicon high boiling point raw liquid is mixed with hydrogen and preheated to 300-500°C.

7. The process for preparing monosilane by catalytic cracking of high boiling points of polysilicon in a fixed bed as claimed in claim 5, characterized in that: The catalyst filled in the fixed bed catalytic reactor includes a silicon-aluminum molecular sieve, an alumina carrier and a non-precious metal.

8. The process for preparing monosilane by catalytic cracking of polysilicon high boiling points in a fixed bed as claimed in claim 7, characterized in that: The topological structure of the silica-alumina molecular sieve is at least one of FAU, *BEA, MFI, MOR, TON, MWW and CHA; the alumina carrier is at least one of pseudo-boehmite, SB powder, dry gel powder and aluminum sol; the non-precious metal is at least one of Ni, Mo, Fe, Co, Zn and Cu.

9. The system for preparing monosilane by catalytic cracking of high boiling polysilicon in a fixed bed as claimed in claim 7, characterized in that: The catalyst at least comprises: a silicon-alumina molecular sieve accounting for 40-70wt% by weight, an alumina carrier accounting for 20-40wt% by weight, and a non-precious metal accounting for 1-10wt% by weight.

10. The process for preparing monosilane by catalytic cracking of high boiling points of polysilicon in a fixed bed according to any one of claims 5 to 9, characterized in that: Control the reaction temperature in the fixed bed catalytic reactor to 300-500°C, the reaction pressure to 0.1-2.0MPa, the hydrogen flow rate to 50-400mL / min, and the volumetric space velocity of the polysilicon high boiling point feed to 0.1-2.0h -1 The height-to-diameter ratio of the catalyst loading is 5-20.

11. The process for preparing monosilane by catalytic cracking of polysilicon high boiling points in a fixed bed according to any one of claims 5 to 9, characterized in that: The material exiting the fixed bed catalytic reactor is cooled to -10°C to -2°C via a cooler.

12. The process for preparing monosilane by catalytic cracking of high boiling points of polysilicon in a fixed bed according to any one of claims 5 to 9, characterized in that: The material of the fixed bed catalytic reactor is divided into two streams, one stream is sent to the cooler, and the other stream is sent back to the recovery tank after being detected by the line detection unit. The amount of the other stream is the amount that meets the detection requirements of the line detection unit.

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