Hierarchical pore M-coated MFI / Al2O3 catalyst and preparation method and application thereof

Abstract

The invention provides a hierarchical pore M (at) MFI / Al2O3 catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing an MFI parent molecular sieve; carrying out crystallization conversion on a first mixed MFI parent molecular sieve, a non-noble metal precursor and a first structure-directing agent, and then carrying out first roasting and first reduction to obtain a hierarchical pore M (at) MFI; and secondarily mixing the hierarchical pore M-coated MFI, an aluminum oxide source and an auxiliary agent to obtain a mixture, and then carrying out kneading, extrusion molding, drying, secondary roasting and secondary reduction on the mixture to obtain the hierarchical pore M-coated MFI / Al2O3 catalyst, in which M is a non-noble metal element. When the catalyst is applied to the cracking reaction of the polycrystalline silicon high-boiling residues, the cracking rate of the high-boiling residues is larger than or equal to 95%, the selectivity of the chlorosilane monomer is larger than or equal to 95%, the selectivity of trichlorosilane is larger than or equal to 40%, and the application prospect is wide.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and in particular to a multi-level porous M@MFI / Al 2 O 3 The invention relates to a catalyst, a preparation method and an application thereof, and more specifically to a non-precious metal encapsulated catalyst for continuous and efficient cracking of high-boiling substances of polysilicon to prepare chlorosilane monomers, a preparation method and an application thereof. Background Art

[0002] Solar photovoltaic power generation is an inevitable trend in the development of global renewable energy. Polysilicon is the core raw material of the solar photovoltaic industry and the most basic raw material for the electronics, semiconductor and other industries. The demand is increasing year by year. With the rapid development of polysilicon, a large amount of chlorosilane residual liquid is produced as a by-product during the production process.

[0003] Generally speaking, the main components of polysilicon by-product chlorosilane residual liquid include SiCl 4 Monosilane, Si 2 Cl 6 and SiCl 3 -O-SiCl 3 The waste is mainly composed of high-boiling silicon polymers (referred to as high-boiling products), metal chlorides, solid impurity silicon powder, etc., which are highly corrosive and easily hydrolyzed to generate a large amount of hydrogen chloride (HCl), and are listed as hazardous waste liquids. If not handled properly, it will not only cause serious waste of Si and Cl resources, but also increase subsequent environmental protection and treatment costs, and cause serious damage to human health and the surrounding environment. The accumulation and storage will bring great safety hazards.

[0004] It is reported that in the 100,000 tons / year SiCl 4 In the cold hydrogenation treatment unit, about 7,000-8,000 tons / year of chlorosilane residual liquid (accounting for about 7-8% by mass) is produced. The existing cold hydrogenation unit has a processing scale of about 15 million tons / year, and the corresponding chlorosilane residual liquid produced is about 1 million-1.2 million tons / year.

[0005] As the output of polysilicon continues to expand, the output of chlorosilane residual liquid and high-boiling substances will inevitably increase, especially the high-boiling substances contained therein. How to realize the utilization of this part of resources is one of the important problems currently faced by polysilicon companies and one of the important bottlenecks restricting the sustainable development of the industry.

[0006] At present, the in-depth analysis and systematic research on the resource utilization of polysilicon chlorosilane residual liquid and high-boiling silicon polymers, the existing treatment methods are mainly summarized as follows:

[0007] (1) Hydrolysis treatment, but the added value of the hydrolysis product is low, which not only causes a large amount of silicon and chlorine resources to be wasted, but also causes secondary pollution to the environment.

[0008] (2) The distillation method is used to separate and purify the chlorosilane monomers. However, this treatment method cannot completely achieve the harmlessness and resource utilization of the chlorosilane residue, especially the high-boiling substances.

[0009] (3) Organic amine catalytic cracking method: Chlorosilane residual liquid contains a large number of high-boiling substances. Catalytic cracking to prepare chlorosilane monomers is an effective treatment method. In industry, organic amine catalysts are commonly used, with hydrogen chloride as the cracking gas. However, this process consumes a large amount of catalysts, and the catalysts used are mostly highly toxic chemicals, which need to be strictly controlled during production, transportation, and use. What is more serious is that the use of such catalysts further aggravates secondary pollution. Uncracked high-boiling substances mix with it to form hazardous waste, which makes subsequent treatment more complicated and difficult, and the environmental protection cost is huge.

[0010] Therefore, the research and development of efficient, green and environmentally friendly high-boiling-point cracking catalysts is the core and development direction of the technology for preparing chlorosilane monomers by catalytic cracking of high-boiling-points of polysilicon. It can completely avoid secondary pollution, realize silicon-chlorine resource utilization, harmlessness of chlorosilane residual liquid and maximization of enterprise economic benefits in one step, and promote the green development of the polysilicon industry. Summary of the invention

[0011] In view of the shortcomings of the prior art, the present invention aims to provide a multi-level porous M@MFI / Al 2 O 3 The catalyst and its preparation method and application are prepared by first preparing multi-level pore M@MFI, then mixing with an alumina source and calcining and secondly reducing, so as to obtain a catalyst with large pore size and moderate size of non-precious metal nanoparticles. The catalyst not only has excellent hydrogenation performance, but also moderate pore expansion is conducive to improving the diffusion of larger molecular disilane in the MFI pores and the accessibility of active sites, further ensuring the efficient cracking rate of high boiling products of polysilicon and high SiHCl 3 Selectivity and broad application prospects.

[0012] To achieve this object, the present invention adopts the following technical solutions:

[0013] In the first aspect, the present invention provides a multi-level pore M@MFI / Al 2 O 3 A method for preparing a catalyst, the preparation method comprising:

[0014] Preparation of MFI parent molecular sieve; first mixing MFI parent molecular sieve, non-precious metal precursor and first structure directing agent, performing crystallization conversion, and then performing first calcination and first reduction to obtain multi-level pore M@MFI; second mixing multi-level pore M@MFI, alumina source and auxiliary agent, and the obtained mixture is kneaded, extruded, dried, second calcined and second reduced to obtain multi-level pore M@MFI / Al 2 O 3Catalyst, wherein M is a non-precious metal element.

[0015] The present invention provides a multi-level pore M@MFI / Al 2 O 3 Preparation method of catalyst The multi-level porous M@MFI core catalytic component synthesized by post-processing encapsulation method can, on the one hand, prepare 1-10nm non-precious metal nanoparticles with better hydrogenation performance; on the other hand, subsequent mixing with alumina source and adhesive for moderate pore expansion is beneficial to improve the diffusion of larger molecular disilane in the MFI pores and the accessibility of active sites, further ensuring the efficient cracking rate of polysilicon high boiling products and higher SiHCl 3 selectivity; and the catalyst of the present invention can improve the mechanical strength of the overall catalyst, meeting the requirements for its mechanical strength in, for example, a fixed bed catalytic process.

[0016] Compared with the highly toxic organic amine catalysts commonly used in industry, the catalyst prepared by the present invention not only realizes the efficient cleavage of Si-Si and Si-O-Si cleavage bonds, but also realizes the SiHCl 3 The improvement of selectivity and the green and environmentally friendly nature of the entire process will be beneficial to improving the on-site operating environment.

[0017] Preferably, the preparation of the MFI parent molecular sieve includes: uniformly mixing a silicon source, an aluminum source, an alkali source, a second structure directing agent and water to form a gel, and then subjecting the mixture to hydrothermal crystallization, solid-liquid separation, drying and preliminary calcination to obtain the MFI parent molecular sieve.

[0018] Preferably, the silicon-aluminum ratio of the MFI parent molecular sieve is greater than or equal to 20, for example, it can be 20, 50, 100, 200, 300, 400 or 500.

[0019] Preferably, the MFI parent molecular sieve comprises Na-ZSM-5, NH 4 -ZSM-5, HZSM-5 or S-1, any one or a combination of at least two, wherein a typical but non-limiting combination is Na-ZSM-5 and NH 4 - Combination of ZSM-5, HZSM-5 and NH 4 -Combination of ZSM-5, combination of Na-ZSM-5 and HZSM-5.

[0020] Preferably, in the gel, the molar ratio of structure directing agent / SiO 2 0.05~0.5:1, H 2 O / SiO 2 The ratio of structure directing agent / SiO 2The ratio is 0.05 to 0.5:1, for example, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 0.5:1, but is not limited to the values ​​listed, and other values ​​not listed in the range are also applicable; H 2 O / SiO 2 The ratio is 5 to 50:1, for example, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0021] Preferably, the silicon source comprises any one of white carbon, silica sol or tetraethyl orthosilicate or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of white carbon and silica sol, a combination of tetraethyl orthosilicate and silica sol, and a combination of white carbon and tetraethyl orthosilicate.

[0022] Preferably, the aluminum source comprises any one of pseudo-boehmite, SB powder or aluminum sol, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of pseudo-boehmite and SB powder, a combination of aluminum sol and SB powder, and a combination of pseudo-boehmite and aluminum sol.

[0023] Preferably, the auxiliary agent comprises sesbania powder and / or nitric acid.

[0024] Preferably, the alkali source comprises any one of sodium hydroxide, potassium hydroxide or tetrapropylammonium hydroxide or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of sodium hydroxide and potassium hydroxide, a combination of tetrapropylammonium hydroxide and potassium hydroxide, and a combination of sodium hydroxide and tetrapropylammonium hydroxide.

[0025] Preferably, the second structure directing agent comprises any one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetramethylethyldiammonium or dimethyldiethylammonium hydroxide, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of tetraethylammonium hydroxide and tetrapropylammonium hydroxide, a combination of dimethyldiethylammonium hydroxide and tetrapropylammonium hydroxide, a combination of tetraethylammonium hydroxide and tetramethylethyldiammonium, and a combination of tetramethylethyldiammonium and tetrapropylammonium hydroxide.

[0026] Preferably, the temperature of the hydrothermal crystallization is 100-170°C, for example, it can be 100°C, 108°C, 116°C, 124°C, 132°C, 139°C, 147°C, 155°C, 163°C or 170°C, but is not limited to the listed values, and other values ​​not listed in this range are also applicable. The time is 12-72h, for example, it can be 12h, 19h, 26h, 32h, 39h, 46h, 52h, 59h, 66h or 72h, but is not limited to the listed values, and other values ​​not listed in this range are also applicable.

[0027] Preferably, the temperature of the preliminary calcination is 300-600°C, for example, it can be 300°C, 334°C, 367°C, 400°C, 434°C, 467°C, 500°C, 534°C, 567°C or 600°C, but is not limited to the listed values, and other values ​​not listed in the range are equally applicable. The time is 4-12h, for example, it can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or 12h, but is not limited to the listed values, and other values ​​not listed in the range are equally applicable.

[0028] Preferably, the non-noble metal precursor includes a nickel metal precursor and / or a cobalt metal precursor.

[0029] Preferably, the nickel metal precursor and / or the cobalt metal precursor each independently comprises a complex solution formed by a metal salt and ethylenediamine.

[0030] Preferably, the metal salt comprises a cobalt salt and / or a nickel salt.

[0031] Preferably, the nickel salt comprises any one of nickel nitrate, nickel chloride or nickel sulfate, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of nickel nitrate and nickel chloride, a combination of nickel sulfate and nickel chloride, and a combination of nickel nitrate and nickel sulfate.

[0032] Preferably, the cobalt salt comprises any one of cobalt nitrate, cobalt chloride or cobalt sulfate, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of cobalt nitrate and cobalt chloride, a combination of cobalt sulfate and cobalt chloride, and a combination of cobalt nitrate and cobalt sulfate.

[0033] Preferably, the mass ratio of the MFI parent molecular sieve and the non-precious metal precursor is 9 to 95:1, for example, it can be 9:1, 19:1, 29:1, 38:1, 48:1, 57:1, 67:1, 76:1, 86:1 or 95:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the pore size range of the multi-level pores M@MFI is 0.3 to 3.9 nm, for example, it can be 0.3 nm, 0.7 nm, 1.1 nm, 1.5 nm, 1.9 nm, 2.3 nm, 2.7 nm, 3.1 nm, 3.5 nm or 3.9 nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] Preferably, the multi-level pore M@MFI contains non-precious metal nanoparticles.

[0036] Preferably, the particle size range of the non-precious metal nanoparticles in the multi-level porous M@MFI is 1 to 12 nm, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm or 12 nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] Preferably, the non-precious metal content in the multi-level porous M@MFI is 1.0 to 10.0 wt%, for example, it can be 1.0 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10.0 wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0038] The present invention preferably controls the packaging amount of non-precious metals within the above range. When the packaging amount of non-precious metals is low, the catalyst exhibits low activity in the cracking reaction of high-boiling products of polysilicon. When the packaging amount of non-precious metals is high, on the one hand, the required crystallization conversion conditions far exceed the conditions described in the present invention, which will increase the cost of catalyst preparation. On the other hand, the encapsulated metal nickel nanoparticles are aggregated or concentrated on the surface, and the nickel nanoparticles are prone to uneven distribution and metal particle diameters greater than 12 nm, thereby leading to problems such as low catalytic stability and catalytic activity.

[0039] Preferably, the multi-level pores M@MFI are a core-shell structure.

[0040] Preferably, the temperature of the crystallization transformation is 150-170°C, for example, it can be 150°C, 153°C, 155°C, 157°C, 159°C, 162°C, 164°C, 166°C, 168°C or 170°C, but is not limited to the listed values, and other values ​​not listed in the range are also applicable. The time is 6-12h, for example, it can be 6h, 6.7h, 7.4h, 8h, 8.7h, 9.4h, 10h, 10.7h, 11.4h or 12h, but is not limited to the listed values, and other values ​​not listed in the range are also applicable.

[0041] Preferably, the temperature of the first calcination is 300-600°C, for example, it can be 300°C, 334°C, 367°C, 400°C, 434°C, 467°C, 500°C, 534°C, 567°C or 600°C, but is not limited to the listed values, and other values ​​not listed in this range are equally applicable. The time is 4-12h, for example, it can be 4h, 4.9h, 5.8h, 6.7h, 7.6h, 8.5h, 9.4h, 10.3h, 11.2h or 12h, but is not limited to the listed values, and other values ​​not listed in this range are equally applicable.

[0042] Preferably, the temperature of the first reduction is 300-600°C, for example, it can be 300°C, 334°C, 367°C, 400°C, 434°C, 467°C, 500°C, 534°C, 567°C or 600°C, but is not limited to the listed values, and other values ​​not listed in this range are also applicable. The time is 5-24h, for example, it can be 5h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, but is not limited to the listed values, and other values ​​not listed in this range are also applicable.

[0043] Preferably, taking the sum of the multi-level porous M@MFI, the alumina source and other additives as 100%, the mass percentage of the multi-level porous M@MFI is 50-70wt%, for example, it can be 50wt%, 53wt%, 55wt%, 57wt%, 59wt%, 62wt%, 64wt%, 66wt%, 68wt% or 70wt%, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0044] Preferably, taking the sum of the multi-level porous M@MFI, the alumina source and other additives as 100%, the mass percentage of the alumina source is 20-50wt%, for example, it can be 20wt%, 24wt%, 27wt%, 30wt%, 34wt%, 37wt%, 40wt%, 44wt%, 47wt% or 50wt%, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0045] The present invention has no special limitation on other additives in the catalyst, and any other additives that can be used in catalysts and are well known to those skilled in the art can be used, such as sesbania powder, nitric acid, and the like.

[0046] Preferably, the other auxiliary agent comprises nitric acid.

[0047] Preferably, the alumina source comprises any one of dry glue powder, SB powder, aluminum sol or pseudo-boehmite, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of dry glue powder and SB powder, a combination of aluminum sol and SB powder, a combination of dry glue powder and pseudo-boehmite, and a combination of pseudo-boehmite and SB powder.

[0048] Preferably, the temperature of the second calcination is 400-700°C, for example, it can be 400°C, 434°C, 467°C, 500°C, 534°C, 567°C, 600°C, 634°C, 667°C or 700°C, but is not limited to the listed values, and other values ​​not listed within the range are equally applicable. The time is 4-10h, for example, it can be 4h, 4.7h, 5.4h, 6h, 6.7h, 7.4h, 8h, 8.7h, 9.4h or 10h, but is not limited to the listed values, and other values ​​not listed within the range are equally applicable.

[0049] The present invention preferably controls the temperature of the second calcination within the above range. When the temperature of the second calcination is too low, the mechanical strength of the catalyst is poor. During use, the catalyst is easily crushed, resulting in bed blockage. When the temperature of the second calcination is too high, the basic structure of the catalyst is destroyed, which seriously affects the catalytic effect of the active center, resulting in low catalytic activity in the polysilicon high-boiling product cracking reaction.

[0050] Preferably, the temperature of the second reduction is 300-600°C, for example, it can be 300°C, 334°C, 367°C, 400°C, 434°C, 467°C, 500°C, 534°C, 567°C or 600°C, but is not limited to the listed values, and other values ​​not listed in this range are also applicable. The time is 10-24h, for example, it can be 10h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values, and other values ​​not listed in this range are also applicable.

[0051] In the second aspect, the present invention provides a multi-level pore M@MFI / Al 2 O 3 Catalyst, the multi-level pore M@MFI / Al 2 O 3 The catalyst adopts the multi-level pore M@MFI / Al 2 O 3 The catalyst is prepared by a preparation method.

[0052] Preferably, the pore size range of the multi-level pores M@MFI is 0.3 to 3.9 nm, for example, it can be 0.3 nm, 0.7 nm, 1.1 nm, 1.5 nm, 1.9 nm, 2.3 nm, 2.7 nm, 3.1 nm, 3.5 nm or 3.9 nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0053] Preferably, M in the multi-level pores M@MFI is nickel metal and / or cobalt metal.

[0054] Preferably, the MFI structure in the multi-level pore M@MFI comprises ZSM-5 and / or S-1.

[0055] Preferably, the multi-level pores M@MFI and Al 2 O 3 The mass ratio is 2 to 4:1, for example, it can be 2:1, 2.3:1, 2.5:1, 2.7:1, 2.9:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0056] In a third aspect, the present invention provides a multi-level pore M@MFI / Al according to the second aspect. 2 O 3 Application of catalyst in cracking of high boiling products of polysilicon.

[0057] Preferably, the application includes: a high boiling point of polysilicon undergoes a cracking reaction under the action of a catalyst and a cracking gas to obtain a product containing chlorosilane monomers.

[0058] Preferably, the temperature of the cracking reaction is 200-500°C, for example, it can be 200°C, 234°C, 267°C, 300°C, 334°C, 367°C, 400°C, 434°C, 467°C or 500°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0059] Preferably, the pressure of the cracking reaction is 0.1-3.0 MPa, for example, it can be 0.1 MPa, 0.5 MPa, 0.8 MPa, 1.1 MPa, 1.4 MPa, 1.8 MPa, 2.1 MPa, 2.4 MPa, 2.7 MPa or 3.0 MPa, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0060] Preferably, the polysilicon high boiling point comprises a disilane mixture containing Si-Si and Si-O-Si.

[0061] Preferably, the mass proportion of Si-Si-containing disilane in the polysilicon high boiling point exceeds 50%, for example, it may be 51%, 52%, 53%, 55%, 58%, 60%, 62% or 65%.

[0062] Preferably, the cleavage reaction is carried out in a fixed bed reactor.

[0063] Preferably, the mass space velocity of high boiling products of polysilicon in the cracking reaction is 0.05 to 3.0 h -1 , for example, it can be 0.05h -1 、0.06h -1 、0.08h -1 , 0.1h -1 , 0.15h -1 , 0.2h -1 、0.5h -1 , 0.8h -1 , 1.0h -1 , 1.2h -1 , 1.5h -1 , 1.8h -1 , 2.0h -1 , 2.5h -1 or 3.0h -1 wait.

[0064] The present invention uses polysilicon high boiling point as raw material, preferably Ni@MFI / Al 2 O 3 or Co@MFI / Al 2 O 3 The catalyst is used as a catalyst. In a fixed bed reactor, polysilicon high boiling products and cracked gas flow through the catalyst bed to carry out gas-solid continuous catalytic reaction, showing a higher cracking rate and chlorosilane monomer selectivity.

[0065] Preferably, the cracking rate of high-boiling products of polysilicon in the cracking is ≥95%, for example, it can be 95.0%, 95.5%, 95.9%, 96.4%, 96.8%, 97.3%, 97.7%, 98.2%, 98.6% or 99%, etc., but is not limited to the listed values, and other values ​​not listed in the range are equally applicable; the selectivity of chlorosilane monomer is ≥95%, for example, it can be 95.0%, 95.5%, 95.9%, 96.4%, 96.8%, 97.3%, 97.7%, 98.2%, 98.6% or 99.0%, etc., but is not limited to the listed values, and other values ​​not listed in the range are equally applicable.

[0066] Preferably, the cleavage product contains SiHCl 3The selectivity is ≥ 40%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 48%, 50%, 52%, 53%, 55%, 56%, 58% or 60%, etc.

[0067] The present invention has no special limitation on the solid-liquid separation in the above process. Any device and method for solid-liquid separation known to those skilled in the art can be used, and can also be adjusted according to the actual process, such as filtration, centrifugation or sedimentation separation, or a combination of different methods.

[0068] The present invention has no particular limitation on the drying in the above process. Any drying device and method known to those skilled in the art can be used, and can also be adjusted according to the actual process, for example, it can be air drying, vacuum drying, oven drying or freeze drying, or a combination of different methods.

[0069] Compared with the prior art, the present invention has at least the following beneficial effects:

[0070] (1) The multi-level pore M@MFI / Al provided by the present invention 2 O 3 The preparation method of the catalyst realizes efficient cracking of high-boiling products of polysilicon: it not only realizes the cracking of Si-Si bonds, but also can realize the efficient cracking of Si-O-Si bonds that cannot be cracked by the existing organic amine system, with higher cracking efficiency;

[0071] (2) The multi-level pore M@MFI / Al provided by the present invention 2 O 3 The preparation method of the catalyst can ensure the selectivity of chlorosilane monomer ≥ 95% under the optimal conditions, wherein the high value-added monomer SiHCl 3 The selectivity is ≥40%;

[0072] (3) The multi-level pore M@MFI / Al provided by the present invention 2 O 3 In the process of using the catalyst in the cracking of high-boiling products of polysilicon, a fixed bed reactor is preferably used, and the high-boiling products and the cracking gas flow through the catalyst bed to carry out a gas-solid phase continuous catalytic reaction. Under the preferred conditions, the catalyst has a higher high-boiling product cracking rate (≥95%), a higher chlorosilane monomer yield, and better catalytic stability, wherein the strength of the catalyst is preferably above 88N. In the life test experiment, the catalyst stably operates for more than 1000h in the laboratory test, and the cracking rate and chlorosilane selectivity do not change significantly during the whole process; and the fixed bed catalytic process has mild reaction conditions; the catalyst has no loss or addition during use, is green and environmentally friendly, has efficient cracking, and is easy to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 The multi-level porous Ni@MFI / Al prepared in Example 1 2 O 3 Nitrogen adsorption-desorption curves of the catalyst.

[0074] Figure 2 The multi-level porous Ni@MFI / Al prepared in Example 1 2 O 3 HRTEM image of the catalyst.

[0075] Figure 3 The multi-level porous Ni@MFI / Al prepared in Comparative Example 4 2 O 3 Nitrogen adsorption-desorption curves of the catalyst.

[0076] Figure 4 The multi-level porous Ni@MFI / Al prepared in Comparative Example 4 2 O 3 HRTEM image of the catalyst. DETAILED DESCRIPTION

[0077] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0078] It should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly indicate the number of technical features indicated. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0079] Example 1

[0080] This embodiment provides a multi-level porous Ni@MFI / Al 2 O 3 A method for preparing a catalyst, the preparation method comprising the following steps:

[0081] (1) Mix white carbon black (silicon source), SB powder (aluminum source), sodium hydroxide (alkali source), tetrapropylammonium hydroxide (TPAOH) (second structure directing agent) in a mass ratio of 7.5 g: 0.40 g: 0.5 g: 50.84 g: 74.37 g, mix with water, stir in a water bath at 80 ° C for 6 h to mix evenly to form a gel, then hydrothermally crystallize at 150 ° C for 72 h, filter, dry and preliminarily calcine at 550 ° C for 8 h to obtain an MFI parent molecular sieve.

[0082] (2) A first mixed MFI parent molecular sieve, a complex of nickel nitrate and ethylenediamine (the molar ratio of nickel nitrate to ethylenediamine is 1:2), TPAOH and water (wherein: TPAOH / SiO 2 =0.3, H 2 O / SiO 2 =20, Ni encapsulation amount is 6.7%), crystallization conversion is carried out at 170℃ for 12h, then filtration, drying, first calcination at 550℃ for 4h, and first reduction at 500℃ for 10h to obtain multi-level porous Ni@MFI. BET and HRTEM analysis show that it has obvious intracrystalline mesoporous structure and nickel nanoparticles, and the particle size of nickel nanoparticles is 4-8nm, respectively. Figure 1 and Figure 2 shown.

[0083] (3) According to the mass ratio of multi-level porous Ni@MFI to dry rubber powder of 7:3, multi-level porous Ni@MFI, dry rubber powder, water and nitric acid are mixed for the second time, and the obtained mixture is kneaded, extruded, dried, second calcined at 550°C for 3h and second reduced at 500°C for 10h to obtain multi-level porous Ni@MFI / Al 2 O 3 catalyst.

[0084] Example 2

[0085] This embodiment provides a multi-level porous Ni@MFI / Al 2 O 3 A method for preparing a catalyst, the preparation method comprising the following steps:

[0086] (1) Mix solid silica gel (silicon source), NaAlO in a mass ratio of 8.3 g: 0.18 g: 0.2 g: 40.6 g: 37.0 g. 2 (aluminum source), NaOH (alkali source), tetrapropylammonium hydroxide (TPAOH) (second structure directing agent), and mixed with water, stirred in a water bath at 80°C for 6 hours to mix evenly to form a gel, and then hydrothermally crystallized at 170°C for 24 hours, filtered, dried and preliminarily calcined at 550°C for 6 hours to obtain the MFI parent molecular sieve.

[0087] (2) A first mixed MFI parent molecular sieve, a complex of nickel nitrate and ethylenediamine (the molar ratio of nickel nitrate to ethylenediamine is 1:2), TPAOH and water (wherein: TPAOH / SiO 2 =0.3, H 2 O / SiO 2 =20, the Ni encapsulation amount is 5.2%), crystallization conversion is carried out at 170°C for 10h, and then filtration, drying, first calcination at 550°C for 4h, and then first reduction at 500°C for 10h to obtain multi-level porous Ni@MFI.

[0088] (3) According to the mass ratio of multi-level porous Ni@MFI to dry rubber powder of 6:4, multi-level porous Ni@MFI, dry rubber powder, water and nitric acid were mixed for the second time, and the obtained mixture was kneaded, extruded, dried, second calcined at 550°C for 3h and second reduced at 500°C for 10h to obtain multi-level porous Ni@MFI / Al 2 O 3 catalyst.

[0089] Example 3

[0090] This embodiment provides a multi-level porous Ni@MFI / Al 2 O 3 A method for preparing a catalyst, the preparation method comprising the following steps:

[0091] (1) Mix solid silica gel (silicon source), NaAlO in a mass ratio of 8.15 g: 0.05 g: 1.5 g: 30.5 g: 47.5 g. 2 (aluminum source), NaOH (alkali source), tetrapropylammonium hydroxide (TPAOH) (second structure directing agent), and mixed with water, stirred in a water bath at 85°C for 7 hours to mix evenly to form a gel, and then hydrothermally crystallized at 100°C for 72 hours, filtered, dried and preliminarily calcined at 600°C for 4 hours to obtain the MFI parent molecular sieve.

[0092] (2) A first mixed MFI parent molecular sieve, a complex of nickel nitrate and ethylenediamine (the molar ratio of nickel nitrate to ethylenediamine is 1:2), TPAOH and water (wherein: TPAOH / SiO 2 =0.2, H 2 O / SiO 2 =20, the Ni encapsulation amount is 4.7%), crystallization conversion is carried out at 150°C for 10h, and then filtration, drying, first calcination at 300°C for 12h, and then first reduction at 600°C for 8h to obtain multi-level porous Ni@MFI.

[0093] (3) According to the mass ratio of multi-level porous Ni@MFI to pseudo-boehmite of 7:3, multi-level porous Ni@MFI, dry rubber powder, water and nitric acid were mixed for the second time, and the obtained mixture was kneaded, extruded, dried, second calcined at 400°C for 10h and second reduced at 300°C for 20h to obtain multi-level porous Ni@MFI / Al 2 O 3 catalyst.

[0094] Example 4

[0095] This embodiment provides a multi-level porous NiM@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1 except that the packaging amount of Ni is 0.5%, and will not be described again.

[0096] Example 5

[0097] This embodiment provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1 except that the packaging amount of Ni is 12%, and will not be described again.

[0098] Example 6

[0099] This embodiment provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1 except that the temperature of the second calcination in step (3) is 300° C., and will not be described in detail here.

[0100] Example 7

[0101] This embodiment provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1 except that the temperature of the second calcination in step (3) is 800° C., and will not be described again.

[0102] Example 8

[0103] This embodiment provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1 except that nickel nitrate is replaced by an equal amount of cobalt nitrate, and will not be described in detail here.

[0104] Comparative Example 1

[0105] This comparative example provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1 except that step (3) is not performed, and will not be described again.

[0106] The catalyst obtained in this comparative example is not formed and has poor mechanical strength. During use, the catalyst is easily crushed, resulting in bed blockage and difficulty in stable operation.

[0107] Comparative Example 2

[0108] This comparative example provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1, except that the dry rubber powder is directly mixed into step (2) in step (3) and step (3) is not performed, and the details are not repeated here.

[0109] The mechanical strength of the catalyst obtained in this comparative example is poor. During use, the catalyst is easily crushed, resulting in bed blockage and difficulty in stable operation.

[0110] Comparative Example 3

[0111] This comparative example provides a multi-level pore M@MFI / Al 2 O 3 The preparation method of the catalyst is the same as that of Example 1, except that step (2) is not performed separately and the complex of nickel nitrate and ethylenediamine and TPAOH are directly added to step (1) for in-situ preparation, and will not be repeated here.

[0112] The catalyst obtained in this comparative example has no mesoporous structure and cannot achieve the pore expansion effect.

[0113] Comparative Example 4

[0114] This comparative example provides a multi-level pore M@MFI / Al 2 O 3 A method for preparing a catalyst, wherein the preparation method is the same as Example 1 except that step (2) is replaced by a conventional impregnation process. Specifically, the impregnation process comprises: dissolving nickel nitrate in a certain amount of water (the impregnation amount of Ni is 5.1%), adding the MFI parent molecular sieve described in step (1), stirring at room temperature for 6 hours, drying, calcining at 550° C. for 4 hours, and first hydrogen reduction at 500° C. for 10 hours to obtain Ni / MFI. After BET and HRTEM analysis, the results are as follows: Figure 3 and Figure 4 As shown. Figure 3-4 It can be seen that the catalyst obtained by the method of Comparative Example 4 has no mesoporous structure, indicating that this method cannot achieve the pore expansion effect; most of the metal nickel nanoparticles are distributed on the outer surface of the MFI parent molecular sieve, and the distribution is uneven, the particle size is uneven, and the particles are significantly larger than the catalyst non-precious metal nanoparticles obtained by the catalyst preparation method provided by the present invention.

[0115] Test method: BET analysis method was used to test the pore size of the catalyst, and HRTEM analysis method was used to test the multi-level pore Ni@MFI / Al 2 O 3 Nickel nanoparticles, multi-level pore Ni@MFI / Al tested by SEM analysis 2 O 3 The particle size was determined by XRF analysis and the mechanical strength of the catalyst was tested by a strength tester.

[0116] The test results of the above application examples and application comparison examples are shown in Table 1.

[0117] Table 1

[0118]

[0119] Application Example 1

[0120] This application example provides a method for cracking high-boiling polysilicon products. The method comprises: in a fixed bed reactor, high-boiling polysilicon products (composition of 15% SiCl 3 -SiHCl 2 、83% SiCl 3 -SiCl 3 , 2% SiCl 3 -O-SiCl 3 ) was introduced into a fixed bed reactor containing the catalyst in Example 1, and the mass space velocity of the high boiling products of polysilicon was 1.0 h -1 , a cracking reaction is carried out at 350°C and 0.8MPa to obtain a product containing chlorosilane monomer.

[0121] Application Example 2

[0122] This application example provides a method for cracking high-boiling polysilicon products. The method comprises: in a fixed bed reactor, high-boiling polysilicon products (composition of 13% SiCl 3 -SiHCl 2 、72% SiCl 3 -SiCl 3 、15% SiCl 3 -O-SiCl 3 ) was introduced into a fixed bed reactor containing the catalyst in Example 1, and the mass space velocity of the high boiling products of polysilicon was 0.5h -1 , a cracking reaction is carried out at 450°C and 0.8MPa to obtain a product containing chlorosilane monomer.

[0123] Application Example 3

[0124] This application example provides a method for cracking high-boiling polysilicon products. The method comprises: in a fixed bed reactor, high-boiling polysilicon products (composition of 15% SiCl 3 -SiHCl 2 、83% SiCl 3 -SiCl 3 , 2% SiCl 3 -O-SiCl 3 ) was introduced into a fixed bed reactor containing the catalyst in Example 2, and the mass space velocity of the high boiling products of polysilicon was 1.0 h -1 , a cracking reaction is carried out at 350°C and 0.8MPa to obtain a product containing chlorosilane monomer.

[0125] Application Example 4

[0126] This application example provides a method for cracking high-boiling polysilicon products. The method comprises: in a fixed bed reactor, high-boiling polysilicon products (composition of 15% SiCl 3 -SiHCl 2 、83% SiCl 3 -SiCl 3 , 2% SiCl 3 -O-SiCl 3 ) was introduced into a fixed bed reactor containing the catalyst in Example 2, and the mass space velocity of the high boiling products of polysilicon was 0.5h -1 , a cracking reaction is carried out at 450°C and 0.8MPa to obtain a product containing chlorosilane monomer.

[0127] Application Example 5

[0128] This application example provides a method for cracking high-boiling polysilicon products. The method comprises: in a fixed bed reactor, high-boiling polysilicon products (composition of 15% SiCl 3 -SiHCl 2 、83% SiCl 3 -SiCl 3 , 2% SiCl 3 -O-SiCl 3 ) was introduced into a fixed bed reactor containing the catalyst in Example 3, and the mass space velocity of the high boiling products of polysilicon was 3.0 h -1 , a cracking reaction is carried out at 500°C and 3.0MPa to obtain a product containing chlorosilane monomer.

[0129] Application Examples 6 to 10 and Comparative Application Examples 1 to 4

[0130] Application Examples 6 to 10 and Application Comparative Examples 1 to 4 provide a method for cracking high-boiling-point polysilicon products. Except for adopting the preparation methods of the catalysts in Examples 4 to 8 and Comparative Examples 1 to 4, the rest of the method for cracking high-boiling-point polysilicon products is the same as Application Example 1, which will not be repeated here.

[0131] Conversion rate of high boiling products in polysilicon, chlorosilane selectivity and SiHCl 3 The selective evaluation was performed, and the test results of the above application examples and application comparison examples are shown in Table 2.

[0132] Table 2

[0133]

[0134] In Tables 1 and 2, “ / ” indicates that there is no relevant data.

[0135] From Table 1 and Table 2, we can see the following points:

[0136] (1) Based on Examples 1 to 3, Example 8 and Application Examples 1 to 5, it can be seen that the multi-level pore M@MFI / Al provided by the present invention 2 O 3 The catalyst prepared by the preparation method has high strength, the strength is above 88N, and the catalyst has a mesoporous pore size, the pore size range of the catalyst is within the range of 0.55-3.5nm, and the catalyst is applied in the cracking process of polysilicon high boiling products, the conversion rate of polysilicon high boiling products is above 95%, the selectivity of chlorosilane is above 97%, and SiHCl 3 The selectivity is above 44.7%, and the application prospects are broad;

[0137] (2) It can be seen from Application Example 1 and Application Examples 6 to 7 that the packaging amount of non-precious metals will significantly affect the conversion rate of high-boiling products of polysilicon and the selectivity of chlorosilanes. The present invention preferably controls the packaging amount of non-precious metals within a reasonable range, which can significantly improve the conversion rate of high-boiling products of polysilicon and improve the selectivity of chlorosilanes;

[0138] (3) It can be seen from Example 1 and Examples 6 to 7 that the temperature of the second calcination affects both the strength and catalytic activity of the catalyst. In Example 6, the calcination temperature is low, resulting in the strength of the catalyst decreasing to 41N compared with Example 1, while the temperature of the second calcination in Example 7 is high, resulting in low conversion rate and selectivity in Application Example 9. This shows that the present invention controls the temperature of the second calcination within a reasonable range, which can better improve the comprehensive performance of the catalyst.

[0139] (4) Comprehensive application example 1 and application comparative examples 1 to 4 show that in comparative examples 1 to 2, step (3) is not performed, or the dry rubber powder is directly mixed into step (2), which results in the catalyst being basically unformed and having poor mechanical strength. During use, the catalyst is easily crushed, resulting in bed blockage, making it difficult to operate stably. In application comparative example 3, the catalyst has no mesoporous structure, the final conversion rate is low, and the selectivity of chlorosilane is low; in application comparative example 4, the traditional impregnation method is used, the catalyst has no mesoporous structure, and the particle size distribution is uneven, and the final conversion rate and yield are both low.

[0140] The present invention illustrates the detailed features of the present invention through the above embodiments, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of the technical features selected by the present invention, addition of auxiliary technical features, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a multi-level porous M@MFI / Al2O3 catalyst, characterized in that: The preparation method comprises: Preparing MFI parent molecular sieve; A first mixed MFI parent molecular sieve, a non-precious metal precursor and a first structure directing agent are subjected to crystallization transformation, followed by a first calcination and a first reduction to obtain a multi-level porous M@MFI; The multi-level porous M@MFI, alumina source and additives are mixed for the second time, and the obtained mixture is kneaded, extruded, dried, second calcined and second reduced to obtain a multi-level porous M@MFI / Al2O3 catalyst, wherein M is a non-precious metal element.

2. The preparation method according to claim 1, characterized in that: The preparation of the MFI parent molecular sieve includes: mixing a silicon source, an aluminum source, an alkali source, a second structure directing agent and water uniformly to form a gel, and then performing hydrothermal crystallization, solid-liquid separation, drying and preliminary calcination to obtain the MFI parent molecular sieve; Preferably, the silicon-aluminum ratio of the MFI parent molecular sieve is greater than or equal to 20; Preferably, the MFI parent molecular sieve comprises any one or a combination of at least two of Na-ZSM-5, NH4-ZSM-5, HZSM-5 or S-1; Preferably, in the gel, the molar ratio of structure directing agent / SiO2 is 0.05-0.5:1, and H2O / SiO2 is 5-50:1; Preferably, the silicon source includes any one of white carbon black, silica sol or tetraethyl orthosilicate, or a combination of at least two thereof; Preferably, the aluminum source includes any one or a combination of at least two of pseudo-boehmite, SB powder or aluminum sol; Preferably, the alkali source comprises any one of sodium hydroxide, potassium hydroxide or tetrapropylammonium hydroxide or a combination of at least two thereof; Preferably, the second structure directing agent comprises any one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetramethylethyldiammonium or dimethyldiethylammonium hydroxide, or a combination of at least two thereof; Preferably, the temperature of the hydrothermal crystallization is 100-170° C., and the time is 12-72 hours; preferably, the temperature of the preliminary calcination is 300-600° C., and the time is 4-12 hours.

3. The preparation method according to claim 1 or 2, characterized in that: The non-noble metal precursor includes a nickel metal precursor and / or a cobalt metal precursor; Preferably, the nickel metal precursor and / or the cobalt metal precursor each independently comprises a complex solution formed by a metal salt and ethylenediamine; Preferably, the metal salt comprises a cobalt salt and / or a nickel salt; Preferably, the nickel salt comprises any one of nickel nitrate, nickel chloride or nickel sulfate, or a combination of at least two thereof; Preferably, the cobalt salt comprises any one of cobalt nitrate, cobalt chloride or cobalt sulfate, or a combination of at least two thereof; Preferably, the mass ratio of the MFI parent molecular sieve to the non-precious metal precursor is 9 to 95:

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The pore size range of the multi-level pores M@MFI is 0.3 to 3.9 nm; Preferably, the multi-level porous M@MFI contains non-precious metal nanoparticles; Preferably, the particle size of the non-noble metal nanoparticles in the multi-level porous M@MFI is in the range of 1 to 12 nm; Preferably, the non-precious metal content in the multi-level porous M@MFI is 1.0 to 10.0 wt%; Preferably, the multi-level pores M@MFI are a core-shell structure.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The temperature of the crystallization transformation is 150-170°C and the time is 6-12h; Preferably, the first calcination temperature is 300-600°C and the time is 4-12h; Preferably, the temperature of the first reduction is 300-600° C., and the time is 5-24 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Taking the sum of the multi-level porous M@MFI, the alumina source and other additives as 100%, the mass percentage of the multi-level porous M@MFI is 50-70wt%; Preferably, the mass percentage of the alumina source is 20-50wt% based on the sum of the multi-level porous M@MFI, the alumina source and other additives being 100%; Preferably, the alumina source includes any one of dry rubber powder, SB powder, aluminum sol or pseudo-boehmite, or a combination of at least two thereof.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The second calcination temperature is 400-700°C and the time is 4-10h; Preferably, the temperature of the second reduction is 300-600° C., and the time is 10-24 hours.

8. A multi-level porous M@MFI / Al2O3 catalyst, characterized in that: The multi-level porous M@MFI / Al2O3 catalyst is prepared by the preparation method of the multi-level porous M@MFI / Al2O3 catalyst according to any one of claims 1 to 7.

9. The multi-level porous M@MFI / Al2O3 catalyst according to claim 8, characterized in that: The pore size range of the multi-level pores M@MFI is 0.3 to 3.9 nm; Preferably, M in the multi-level pores M@MFI is nickel metal and / or cobalt metal; Preferably, the MFI structure in the multi-level pore M@MFI comprises ZSM-5 and / or S-1; Preferably, the mass ratio of the multi-level pores M@MFI and Al2O3 is 2 to 4:

1.

10. Use of the multi-level porous M@MFI / Al2O3 catalyst according to claim 8 or 9 in cracking of high boiling products of polysilicon; Preferably, the composition of the polysilicon high boiling product includes a mixture of Si-Si and Si-O-Si; Preferably, the content of Si-Si compounds in the polysilicon high boiling point is not less than 50%; Preferably, the cracking reaction temperature is 200-500°C, and the cracking pressure is 0.1-3.0MPa; Preferably, the cracking rate of high-boiling products of polysilicon in the cracking is ≥95%, and the selectivity of chlorosilane monomer is ≥95%; Preferably, the SiHCl3 selectivity in the cracked product is ≥40%.

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