A method for preparing dimethyldichlorosilane

Abstract

The present invention provides a method for preparing dimethyldichlorosilane. The method comprises: performing a cracking and disproportionation reaction on high-boiling substances produced as a by-product in the production of an organosilicon monomer dimethyldichlorosilane under the action of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles to prepare dimethyldichlorosilane. The method not only solves the problem of a large amount of excess high-boiling substances in the production process of the organosilicon monomer and realizes high-value utilization of the high-boiling substances, but also has easy-to-control reactions, simple processes, and mild conditions. Moreover, the method has a single-pass conversion rate of the high-boiling substances of ≥90%, and a selectivity for dimethyldichlorosilane of ≥70%, thus having broad prospects for industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of waste utilization, in particular to the technical field of utilization of high-boiling substances in the production of organosilicon monomer dimethyldichlorosilane, and particularly to a method for preparing dimethyldichlorosilane. Background Art

[0002] Organosilicon materials, known as the "industrial MSG," are widely used in aerospace, military technology, construction, chemistry, electronics, and medicine due to their excellent dielectric properties, high-temperature resistance, weather resistance, oxidation resistance, non-toxicity, and physiological inertness. Currently, the organosilicon monomer, methylchlorosilane, is primarily synthesized domestically and internationally via the "direct process" catalytic synthesis using methyl chloride and silicon powder as raw materials. Methylchlorosilane is a crucial platform raw material for the synthesis of organosilicon materials and a key indicator of the development of the organosilicon industry.

[0003] However, the direct process for producing methylchlorosilane involves complex side reactions such as decomposition, disproportionation, and hydrolysis. Besides the target product, dimethyldichlorosilane (M2), there are also 1-2 wt% of low-boiling products with a boiling range below 40°C and 6-10 wt% of high-boiling products such as Si-Si, Si-CH2-Si, Si-O-Si, and Si-Si-Si with a boiling range exceeding 70°C. After cyclone separation, organosilicon slurry and high-boiling products are produced. With the increasing demand for organosilicon monomers, the resource recovery and high-value utilization of organosilicon high-boiling products have gradually become an obstacle to the sustainable development of the organosilicon industry.

[0004] Therefore, the research and development of resource utilization of high-boiling silicone products has a positive effect on environmental protection, economy and society.

[0005] Currently, there are many patent documents related to the technology of preparing dimethyldichlorosilane by cracking high-boiling organic silicon products, which can be mainly divided into the following methods:

[0006] (1) Precious metal catalysts: CN1071927A discloses a method for preparing methylchlorosilane monomer by catalytic cracking of methylchlorodisilane (Si-Si) in high-boiling materials. The catalyst is a precious metal such as Pd or Pt, and HCl is used as the cracking gas source. The product composition formula is (CH3) m SiCl 4-m , m is 1, 2 and 3, but the catalyst is expensive and difficult to apply on a large scale in industry.

[0007] (2) Aluminum-based catalyst: CN1169996A discloses a method for preparing methylchlorosilane monomer using aluminum trichloride (AlCl3) as a catalyst, HCl, methylchlorodisilane (Si-Si) in high-boiling products, and CH3SiCl3 in low-boiling products as raw materials. However, during the reaction, the active component AlCl3 is easily sublimated and lost, making it difficult to regenerate and recycle the catalyst.

[0008] CN1634937A and CN1634936A disclose a method for preparing methylchlorosilane monomer from methyl chloride, high-boiling substances, low-boiling substances or mixtures thereof under the catalytic conditions of aluminum powder and Lewis acid, utilizing a gas-solid heterogeneous reaction in a stirred bed or a stirred bed-fixed bed, but the yield of dimethyldichlorosilane [(CH3)2SiCl2] is low.

[0009] CN1915999A discloses a method for preparing dimethyldichlorosilane using all components of a high-boiling substance as raw materials and concentrated sulfuric acid and aluminum powder as a composite catalyst. However, this method uses concentrated sulfuric acid as a catalyst, which, on the one hand, places stringent requirements on equipment and, on the other hand, causes problems with subsequent environmental protection and recycling.

[0010] (3) Organic amine catalyst: CN101824047A discloses a method for preparing methylchlorosilane from high-boiling organic silicon products, using triethylamine and tri-n-butylamine as catalysts and chloromethane as the gas source. However, the catalyst is difficult to recycle and tri-n-butylamine is a highly toxic chemical. Furthermore, it is reported that the organic amine catalyst is used in large quantities, and although the reaction temperature is low, it can only cleave low-alkyl disilazane components (1-3 carbon atoms) with Si-Si bonds in the high-boiling products. It is difficult to cleave alkyl-rich disilazane components (4-6 carbon atoms), Si-CH2-Si disilazane, Si-Si-Si trisilane, etc., and has low selectivity for dimethyldichlorosilane.

[0011] (4) Molecular sieves and activated carbon catalysts: In 2011, Li Bin recorded that Dow Corning used LZ-Y-74 molecular sieve as a catalyst to crack methylchlorodisilane (Si-Si), with HCl as the cracking gas. To reduce costs, the company chose activated carbon instead of molecular sieves, but the reaction temperature was 500°C higher and the energy consumption was high (see "Resource Utilization of By-Products in the Production of Methylchlorosilane Monomers", Li Bin, Master's thesis of Beijing University of Chemical Technology).

[0012] Therefore, the existing reaction of cracking high-boiling organic silicon products to prepare dimethyldichlorosilane has problems such as low catalyst selectivity, high reaction temperature and difficulty in recycling. It is urgent to develop a new method for cracking high-boiling organic silicon products to prepare dimethyldichlorosilane. Summary of the Invention

[0013] In view of the problems existing in the prior art, the present invention provides a method for preparing dimethyldichlorosilane. The method uses a Ni@ZSM-5 catalyst to react with a specific raw material, a high-boiling-point by-product of the production of the organosilicon monomer dimethyldichlorosilane. This method solves the problems of difficult catalyst recycling and low selectivity in the preparation of dimethyldichlorosilane from existing high-boiling-point by-products, thereby achieving resource recovery and high-value utilization of the high-boiling-point by-products.

[0014] To achieve this object, the present invention adopts the following technical solutions:

[0015] The invention provides a method for preparing dimethyldichlorosilane. The method comprises: subjecting a high-boiling point by-product of producing the organosilicon monomer dimethyldichlorosilane to a cracking and disproportionation reaction under the action of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles to prepare dimethyldichlorosilane.

[0016] The present invention uses high-boiling products produced as a by-product of the production of the organosilicon monomer dimethyldichlorosilane as raw materials and encapsulates metal nickel nanoparticles in ZSM-5 molecular sieve to form a Ni@ZSM-5 bifunctional encapsulated catalyst with better cracking and disproportionation effect. The metal nickel (Ni) nanoparticles have better hydrogenation catalytic activity, while the ZSM-5 molecular sieve provides acidic sites, which are more conducive to improving the selectivity of the target product dimethyldichlorosilane (M2). In the reaction of the present invention, it is relatively difficult to improve the selectivity of dimethyldichlorosilane (M2), among which monomethyltrichlorosilane (M1) and trimethylmonochlorosilane (M3) are easily produced by-products. The inventors found that the Ni@ZSM-5 catalyst, which is originally suitable for conventional hydrogenation and encapsulated nickel nanoparticles, can achieve redistribution of substituent groups on silicon atoms in the disproportionation reaction, and can achieve both the cleavage and disproportionation reactions of low-alkyl Si-Si, Si-Si-S, Si-C and Si-CH2-Si bonds and the cleavage and disproportionation reactions of alkyl-rich Si-Si, Si-Si-Si, Si-C and Si-CH2-Si bonds, significantly improving the conversion rate of high-boiling products and the selectivity of the target product dimethyldichlorosilane.

[0017] The encapsulated nickel nanoparticles described in the present invention refer to the Ni@ZSM-5 bifunctional encapsulated catalyst formed by encapsulating nickel nanoparticles inside ZSM-5 molecular sieve. Compared with ordinary nickel-loaded molecular sieve catalysts, the encapsulated Ni nanoparticles are smaller and more evenly distributed; therefore, they have better catalytic activity and stability.

[0018] Compared to commonly used industrial catalysts such as triethylamine, tri-n-butylamine, and aluminum powder, the Ni@ZSM-5 catalyst encapsulated with nickel nanoparticles described herein achieves both Si-Si bond cleavage and disproportionation reactions for low-alkyl groups, as well as Si-Si, Si-Si-Si, Si-C, and Si-CH2-Si bonds with alkyl-rich groups that cannot be cracked by triethylamine and tri-n-butylamine, and exhibits higher selectivity for dimethyldichlorosilane. Furthermore, the Ni@ZSM-5 catalyst can be recycled and exhibits excellent recycling performance. Compared to precious metal catalysts such as Pd and Pt, the Ni@ZSM-5 catalyst is inexpensive and more readily applicable in industrial applications.

[0019] Preferably, the partial pressure of hydrogen in the cracking and disproportionation reaction is 2 to 5 MPa, for example, it can be 2 MPa, 2.4 MPa, 2.7 MPa, 3 MPa, 3.4 MPa, 3.7 MPa, 4 MPa, 4.4 MPa, 4.7 MPa or 5 MPa, but is not limited to the listed values. Other values ​​not listed within this range are also applicable.

[0020] Preferably, the time of the cleavage disproportionation reaction is 1 to 8 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 5 hours, 6 hours, 7 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0021] Preferably, the temperature of the cracking and disproportionation reaction is 250-350°C, for example, it can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C or 350°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] Preferably, the cleavage and disproportionation reaction is carried out under stirring conditions.

[0023] The cracking and disproportionation reaction of the present invention does not impose any particular limitation on the stirring speed. The speed varies according to the production output. Any stirring speed known to those skilled in the art that can be used to uniformly mix the reaction materials can be used. For example, in the pilot stage, it can be 100 to 700 r / min.

[0024] Preferably, the single-pass dosage of the Ni@ZSM-5 catalyst accounts for 0.1 to 10 wt% of the high boiling point, for example, it can be 0.1 wt%, 1.2 wt%, 2.3 wt%, 3.4 wt%, 4.5 wt%, 5.6 wt%, 6.7 wt%, 7.8 wt%, 8.9 wt% or 10 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0025] Preferably, the Ni@ZSM-5 catalyst is a bifunctional catalyst of sodium-free silica-alumina molecular sieve.

[0026] Preferably, the bifunctional catalyst has both acid catalytic function and hydrogenation function.

[0027] Preferably, the silicon-aluminum ratio in the Ni@ZSM-5 catalyst is SiO2:Al2O3=50:1~500:1, for example, it can be 50:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1 or 500:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0028] Preferably, the particle size of the nickel nanoparticles in the Ni@ZSM-5 catalyst is 1 to 10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0029] The particle size of the nickel nanoparticles in the catalyst of the present invention is preferably within the above range, which can better ensure the catalytic activity and selectivity.

[0030] Preferably, the nickel content in the Ni@ZSM-5 catalyst is 0.5 to 5 wt%, for example, it can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0031] Preferably, the Ni@ZSM-5 catalyst is obtained by an in-situ synthesis method.

[0032] Preferably, the in-situ synthesis method comprises: adding a nickel precursor during the in-situ synthesis of the ZSM-5 molecular sieve, so as to achieve uniform encapsulation of nickel nanoparticles in the ZSM-5 molecular sieve.

[0033] The present invention preferably uses a catalyst prepared by the above encapsulation method, in which the nickel nanoparticles are more evenly distributed and the catalytic performance is better.

[0034] Preferably, the ZSM-5 molecular sieve is a sodium-free aluminosilicate molecular sieve.

[0035] Preferably, the Ni@ZSM-5 catalyst is a Ni@ZSM-5 catalyst prepared by the preparation method of CN109731608B.

[0036] The Ni@ZSM-5 catalyst of the present invention is further preferably prepared by the above-mentioned preparation method, and the nanoparticles are uniformly distributed and have a uniform particle size of about 1 to 10 nm. The encapsulation method can effectively inhibit the migration, agglomeration and loss of nickel nanoparticles, which is more conducive to improving the catalytic effect and selectivity of the catalyst.

[0037] Preferably, the high boilers include disilane and / or trisilane.

[0038] Preferably, the high boiling substances mainly contain Si-Si compounds, Si-Si-Si containing compounds, Si-C containing compounds and Si-CH2-Si containing compounds.

[0039] The Si-Si described in the present invention refers to a compound containing a Si-Si bond in the compound, and there is no special restriction on the groups connected to the other three bonds on the two silicon atoms, for example, it can be any one or a combination of at least two of an alkyl group, a hydrogen atom, a chlorine atom or an alkenyl group. The Si-Si-Si refers to a compound containing three connected silicon atoms, and there is no special restriction on the groups connected to the other bonds on the three silicon atoms, for example, it can be any one or a combination of at least two of an alkyl group, a hydrogen atom, a chlorine atom or an alkenyl group. The Si-C bond refers to the compound containing no special restriction on the other groups connected to the silicon atom and the carbon atom, for example, it can be any one or a combination of at least two of an alkyl group, a hydrogen atom, a chlorine atom or an alkenyl group. The Si-CH2-Si refers to the compound containing two silicon atoms separated by a carbon atom, and there is no special restriction on the other groups connected to the silicon, for example, it can be any one or a combination of at least two of an alkyl group, a hydrogen atom, a chlorine atom or an alkenyl group. Typical but non-limiting combinations include the combination of an alkyl group and a hydrogen atom, the combination of a hydrogen atom and a chlorine atom, the combination of a chlorine atom and an alkenyl group, etc.

[0040] Preferably, the alkyl group includes methyl and / or ethyl, etc. The alkenyl group includes vinyl and / or propenyl, etc.

[0041] Preferably, the typical composition of the high boiling point is shown in Table 1.

[0042] The compounds in the high-boiling products described in the present invention have the above-mentioned chemical bonds. In the catalytic cracking and disproportionation reaction, it is necessary to achieve the breaking of Si-Si bonds, the breaking of Si-Si bonds in Si-Si-Si, and the breaking of C-Si bonds in Si-C and Si-CH2-Si, and then rearrange the chlorine atoms and methyl groups on the silicon atoms to produce dimethyldichlorosilane. Due to the large number of various components in the reaction raw materials, the present invention improves the selectivity of dimethyldichlorosilane by selecting a Ni@ZSM-5 catalyst.

[0043] Preferably, the high boilers include (CH3)3-Si-SiCl-(CH3)2, (CH3)2-SiCl-SiCl-(CH3)2, CH2=CH-CH2-SiCl-(CH3)2, (CH3)2-SiCl-CH2-SiCl-(CH3)2, (CH3)3-Si-CH-Cl2, CH3-SiCl2 -SiCl2-CH3, (CH3)3-Si-Si(CH3)2-SiH-(CH3)2, CH3-SiCl2-CH2-CH2-SiCl2-CH3, Cl-Si(CH3)2-Si(CH3)2-Si(CH3)2-Cl, Cl-CH2-SiClCH3-CH2-Cl, CH3-SiCl2- Any one or a combination of at least two of CH2-CH=CH2 or (CH3)3-Si-CH2-SiCl-(CH3)2, wherein typical but non-limiting combinations are the combination of (CH3)3-Si-SiCl-(CH3)2 and (CH3)2-SiCl-SiCl-(CH3)2, the combination of (CH3)3-Si-CH-Cl2 and (CH3)2-SiCl-SiCl-(CH3)2, the combination of (CH3)3-Si-Si(CH3)2-SiH-(CH3)2 and (CH3)2-SiCl-SiCl-(CH3)2, and the combination of (CH3)3-Si-SiCl-(CH3)2 and (CH3)3-Si-Si(CH3)2-SiH-(CH3)2.

[0044] Preferably, the content of CH2=CH-CH2-SiCl-(CH3)2 in the high boiling point is 15 to 30 wt%, for example, it can be 15 wt%, 17 wt%, 19 wt%, 20 wt%, 22 wt%, 24 wt%, 25 wt%, 27 wt%, 29 wt% or 30 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0045] Preferably, the content of CH3-SiCl2-SiCl2-CH3 in the high boiling point is 20 to 35 wt%, for example, it can be 20 wt%, 22 wt%, 24 wt%, 25 wt%, 27 wt%, 29 wt%, 30 wt%, 32 wt%, 34 wt% or 35 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0046] Preferably, the content of (CH3)2-SiCl-CH2-SiCl-(CH3)2 in the high boiling point is 8 to 25wt%, for example, it can be 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt% or 25wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] Preferably, the method comprises: mixing high-boiling products produced as a byproduct of the organosilicon monomer dimethyldichlorosilane with a Ni@ZSM-5 catalyst; after replacing air with a protective gas, introducing hydrogen and raising the temperature to carry out a cracking and disproportionation reaction. Preferably, the introduction of hydrogen further replaces the protective gas while maintaining the hydrogen partial pressure. The preferred method of replacing the protective gas with hydrogen reduces the overall reaction pressure at the same hydrogen partial pressure, thereby reducing equipment load and equipment selection costs.

[0048] Preferably, the number of times of replacement is at least 3 times, for example, 3 times, 4 times or 5 times.

[0049] Preferably, the shielding gas comprises any one of nitrogen, argon or helium, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of nitrogen and argon, a combination of nitrogen and helium, and a combination of helium and argon.

[0050] Preferably, the number of times of replacing the air is at least 3 times, for example, 3 times, 4 times or 5 times.

[0051] Preferably, the method comprises: mixing a high-boiling product produced as a by-product of the production of the organosilicon monomer dimethyldichlorosilane and a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles, wherein the single-pass usage of the Ni@ZSM-5 catalyst accounts for 0.1 to 10 wt% of the high-boiling product, the silicon-aluminum ratio in the Ni@ZSM-5 catalyst is SiO2:Al2O3=50 to 500:1, the particle size of the nickel nanoparticles is 1 to 10 nm, and the nickel content is 0.5 to 5 wt%. After nitrogen is introduced to replace the air, hydrogen is introduced to 2 to 5 MPa and the temperature is raised to 250 to 350° C., and a cracking and disproportionation reaction is carried out under stirring conditions for 1 to 8 hours to prepare dimethyldichlorosilane.

[0052] The present invention preferably further improves the selectivity of dimethyldichlorosilane and the single-pass conversion rate of high boiling products through the combination of the above parameters.

[0053] Compared with the prior art, the present invention has at least the following beneficial effects:

[0054] (1) The method for preparing dimethyldichlorosilane provided by the present invention uses a Ni@ZSM-5 dual-function encapsulated catalyst, has a high single-pass conversion rate of high boiling points and a high selectivity for dimethyldichlorosilane, the single-pass conversion rate of high boiling points in the first reaction is above 95%, and the selectivity of the target product dimethyldichlorosilane is above 80%;

[0055] (2) The Ni@ZSM-5 bifunctional encapsulated catalyst used in the method for preparing dimethyldichlorosilane provided by the present invention can be recycled. After five single-pass cycles, the high-boiling-substance conversion rate is still over 90%, and the selectivity of the target product dimethyldichlorosilane is still higher than 70%;

[0056] (3) The method for preparing dimethyldichlorosilane provided by the present invention realizes the efficient utilization of high-boiling substances produced as a by-product in the production of the organosilicon monomer dimethyldichlorosilane, thereby improving environmental protection and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is the TEM analysis diagram of the Ni@ZSM-5 dual-function encapsulated catalyst used in Example 1. DETAILED DESCRIPTION

[0058] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0059] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0060] The following specific examples and comparative examples were conducted using high-boiling-point products, a byproduct of the production of the organosilicon monomer dimethyldichlorosilane (CH₃)₂SiCl₂, at a certain plant. GC-MS analysis of the typical composition and relative content of these high-boiling-point products in a Ni@ZSM-5 dual-functional encapsulated catalyst is shown in Table 1.

[0061] Table 1

[0062]

[0063]

[0064] Example 1

[0065] This embodiment provides a method for preparing dimethyldichlorosilane, comprising: mixing 20.1 g of typical high-boiling products in Table 1 and 1.0 g of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles. The Ni@ZSM-5 catalyst is prepared according to the method disclosed in CN109731608B except for adjusting the material ratio. The final silicon-aluminum ratio in the Ni@ZSM-5 catalyst is SiO2:Al2O3=300:1, the particle size of the nickel nanoparticles is 3-7 nm, and the nickel content is 4.1 wt%. After nitrogen is introduced to replace air three times, hydrogen is introduced to replace air three times, hydrogen is introduced to increase the pressure to 5.0 MPa, the temperature is raised to 350° C., and a cracking and disproportionation reaction is carried out at 400 rpm for 2 hours to prepare dimethyldichlorosilane. After the reacted material is cooled to room temperature, it is removed, and the catalyst and liquid product are separated to obtain a product containing dimethyldichlorosilane. The specific results are shown in column A1 of Table 2.

[0066] The TEM diagram of the Ni@ZSM-5 catalyst encapsulating nickel nanoparticles used in this example is shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the outer surface of the catalyst is uniform and nickel nanoparticles are evenly distributed therein.

[0067] Example 2

[0068] This embodiment provides a method for preparing dimethyldichlorosilane, comprising: mixing 20.0 g of typical high-boiling substances in Table 1 and 1.5 g of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles. The Ni@ZSM-5 catalyst is prepared according to the method disclosed in CN109731608B except for adjusting the material ratio. The final silicon-aluminum ratio in the Ni@ZSM-5 catalyst is SiO2:Al2O3=300:1, the particle size of the nickel nanoparticles is 3-7 nm, and the nickel content is 3.1 wt%. After nitrogen is introduced to replace air four times, hydrogen is introduced to replace air four times, hydrogen is introduced to increase the pressure to 4.0 MPa, the temperature is increased to 300° C., and a cracking and disproportionation reaction is carried out at 600 rpm for 6 hours to prepare dimethyldichlorosilane. After the reacted material is cooled to room temperature, it is removed, and the catalyst and liquid product are separated to obtain a product containing dimethyldichlorosilane. The specific results are shown in column A2 of Table 2.

[0069] Example 3

[0070] This embodiment provides a method for preparing dimethyldichlorosilane, comprising: mixing 20.2 g of typical high-boiling substances in Table 1 and 1.0 g of a Ni@HZSM-5 catalyst encapsulating nickel nanoparticles. The Ni@HZSM-5 catalyst was prepared according to the method disclosed in CN109731608B, except for adjusting the material ratio. The final silicon-aluminum ratio in the Ni@HZSM-5 catalyst was SiO2:Al2O3=300:1, the particle size of the nickel nanoparticles was 2-7 nm, and the nickel content was 2.1 wt%. After nitrogen was introduced to replace air three times, hydrogen was introduced to replace air three times, hydrogen was introduced to increase the pressure to 5.0 MPa, and the temperature was raised to 250° C., and a cracking and disproportionation reaction was carried out at 600 rpm for 8 hours to prepare dimethyldichlorosilane. The reacted material was cooled to room temperature, removed, and the catalyst and liquid product were separated to obtain a product containing dimethyldichlorosilane. The specific results are shown in column A3 of Table 2.

[0071] Example 4

[0072] This example provides a method for preparing dimethyldichlorosilane, comprising: mixing 20.0 g of typical high-boiling substances listed in Table 1 and 2.0 g of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles. The Ni@ZSM-5 catalyst was prepared according to the method disclosed in CN109731608B, except for adjusting the material ratio. The final silicon-aluminum ratio in the Ni@ZSM-5 catalyst was SiO2:Al2O3=500:1, the particle size of the nickel nanoparticles was 2-5 nm, and the nickel content was 4.1 wt%. After nitrogen was introduced to replace air five times and hydrogen was introduced three times, hydrogen was introduced to increase the pressure to 4.5 MPa and the temperature was increased to 350° C., and a cracking and disproportionation reaction was carried out at 100 rpm for 3 hours to prepare dimethyldichlorosilane. The reacted material was cooled to room temperature, removed, and the catalyst and liquid product were separated to obtain a product containing dimethyldichlorosilane. The specific results are shown in column A4 of Table 2.

[0073] Example 5

[0074] This embodiment provides a method for preparing dimethyldichlorosilane, comprising: mixing 20.1 g of a typical high-boiling product in Table 1 and 0.1 g of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles. The Ni@ZSM-5 catalyst is prepared according to the method disclosed in CN109731608B except for adjusting the material ratio. The final silicon-aluminum ratio in the Ni@ZSM-5 catalyst is SiO2:Al2O3=80:1, the particle size of the nickel nanoparticles is 4-9 nm, and the nickel content is 1.5 wt%. After nitrogen is introduced to replace air three times, hydrogen is introduced to replace air three times, hydrogen is introduced to increase the pressure to 4.5 MPa and the temperature is increased to 300° C., and a cracking and disproportionation reaction is carried out at 700 rpm for 8 hours to prepare dimethyldichlorosilane. The reacted material is cooled to room temperature and then removed, and the catalyst and liquid product are separated to obtain a product containing dimethyldichlorosilane. The specific results are shown in column A5 of Table 2.

[0075] Example 6

[0076] This example provides a method for preparing dimethyldichlorosilane. The method is the same as Example 3 except that the reaction temperature is 140° C. The specific results are shown in column A6 of Table 2.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing dimethyldichlorosilane. The method is the same as Example 2, except that the Ni / H-ZSM-5 bifunctional catalyst is prepared by the impregnation method of Comparative Example 2 in CN109731608B, wherein the silicon-aluminum ratio of the ZSM-5 molecular sieve is SiO2:Al2O3=300:1. The specific results are shown in column D1 of Table 2.

[0079] Comparative Example 2

[0080] This comparative example provides a method for preparing dimethyldichlorosilane. The method is the same as Example 2 except that the Fe@H-ZSM-5 bifunctional catalyst prepared in Example 5 of CN109731608B is used. The specific results are shown in column D2 of Table 2.

[0081] The products obtained in the above examples and comparative examples were analyzed by GC-MS. The selectivity of each component in the product and the single-pass conversion rate of high boiling points are shown in Table 2, where A1 to A6 represent Examples 1 to 6, respectively, and D1 to D2 represent Comparative Examples 1 to 2, respectively.

[0082] Table 2

[0083] Liquid product selectivity% A1 A2 A3 A4 A5 A6 D1 D2 <![CDATA[Si-(CH3)4]]> 0 0 0 0 0 0 16.1 0 <![CDATA[(CH3)2-SiH-Cl]]> 1.1 0.9 1.1 5.5 0 1.2 4.6 0 <![CDATA[CH3-SiH-Cl2]]> 2.2 1.0 7.5 8.9 2.6 1.4 2.7 0 <![CDATA[(CH3)3-Si-Cl]]> 5.3 3.8 2.5 4.1 8.7 23.6 28.3 8.4 <![CDATA[(CH3)2-Si-Cl2]]> 85 90.1 80.4 81.1 84.7 73.8 37.8 91.6 Other chlorosilane monomers 5.6 4.2 8.5 0.4 4.1 0 10.1 0 High boiling point per pass conversion rate % 96.9 98.2 97.3 95.1 96.9 25.4 35.4 6.4

[0084] As can be seen from Table 2, the methods for preparing dimethyldichlorosilane provided in Examples 1 to 5 are capable of converting high-boiling waste into dimethyldichlorosilane, with the initial selectivity for dimethyldichlorosilane exceeding 80%, and the single-pass conversion rate of high-boiling waste exceeding 95%. Compared with catalysts prepared by the impregnation method or other metal-based catalysts, the selectivity and conversion rate are significantly improved.

[0085] As can be seen from Table 2, the reaction temperature has a significant impact on the reaction. The present invention further improves the conversion rate of high boiling points and the selectivity of the target product dimethyldichlorosilane by optimizing a specific temperature range; wherein, the single-pass conversion rate of high boiling points is above 95%, and the selectivity of dimethyldichlorosilane is above 80%.

[0086] Using Example 2 as an example, a single-pass cycle evaluation was conducted. The single-pass cycle evaluation method included: after the first reaction, filtering and removing the reaction product, drying the catalyst, and then adding high-boiling material to continue the reaction under the same reaction conditions as Example 2. This cycle was repeated five times. The test results of these five cycles are shown in Table 3.

[0087] Table 3

[0088] Liquid product selectivity (%) first Second time The third time Fourth time Fifth <![CDATA[(CH3)2-SiH-Cl]]> 0.9 1.5 1.1 1.9 3.3 <![CDATA[CH3-SiH-Cl2]]> 1.0 2.3 2.5 3.3 1.9 <![CDATA[(CH3)3-Si-Cl]]> 3.8 4.2 8.6 13.1 16.2 <![CDATA[(CH3)2-Si-Cl2]]> 94.3 86.4 81.3 74.8 71.1 Other chlorosilane monomers 4.2 5.6 6.5 6.9 7.5 High boiling point per-pass conversion 98.2 98.4 95.8 90.4 90.9

[0089] The catalyst in Comparative Example 1 was also cycled five times using the above-mentioned single-pass evaluation process. The results showed that after five cycles, the single-pass conversion rate of high-boiling substances was only 5.8%, which was extremely low. This shows that the Ni@ZSM-5 bifunctional encapsulated catalyst selected in this application not only has a high high-boiling substance conversion rate and selectivity for the target product dimethyldichlorosilane, but also has a much higher stability in cyclic use than the catalyst obtained by the impregnation method.

[0090] Based on the above-mentioned single-pass cycle, the catalysts of Example 2 and Comparative Example 1 were evaluated for regeneration stability. The evaluation method included regenerating the catalyst after the fifth reaction and then evaluating it. The reaction conditions were the same as those of Example 2. The regeneration method included drying, calcining, and reducing the catalyst to obtain a regenerated catalyst. In Example 2, the regenerated catalyst had a single-pass conversion rate of 97.5% for high boiling points and a selectivity for dimethyldichlorosilane of 92.1%. In Comparative Example 1, the regenerated catalyst had a single-pass conversion rate of 32.1% for high boiling points and a selectivity for dimethyldichlorosilane of 35.8%. This shows that the catalyst selected by the present invention has almost no decrease in catalytic activity and selectivity after cyclic regeneration compared to the catalyst obtained by the impregnation method, and its regeneration stability is higher than that of the catalyst obtained by the existing impregnation method.

[0091] In summary, the method for preparing dimethyldichlorosilane provided by the present invention uses a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles to catalyze the production of high-boiling products composed of Si-Si, Si-Si-Si, Si-C and Si-CH2-Si as a by-product of the organosilicon monomer dimethyldichlorosilane, thereby achieving high-value utilization. The reaction is easy to control, the conditions are mild, the selectivity and conversion rate are high, and the application prospects are broad.

[0092] The applicant declares that the present invention is intended to illustrate the detailed structural features of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed structural features. This does not mean that the present invention must rely on the above-described detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific embodiments, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing dimethyldichlorosilane, characterized in that: The method comprises: performing a cracking and disproportionation reaction on a high-boiling product produced as a by-product of producing an organic silicon monomer, dimethyldichlorosilane, under the action of a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles to prepare dimethyldichlorosilane; The temperature of the cracking and disproportionation reaction is 250-350° C.; the silicon-aluminum ratio of the Ni@ZSM-5 catalyst is SiO2:Al2O3=50:1-500:1; the nickel content of the Ni@ZSM-5 catalyst is 0.5-5 wt%; The Ni@ZSM-5 catalyst is obtained by an in-situ synthesis method; the in-situ synthesis method includes: adding a nickel precursor during the in-situ synthesis process of the ZSM-5 molecular sieve to achieve uniform encapsulation of nickel nanoparticles in the ZSM-5 molecular sieve; the ZSM-5 molecular sieve is a sodium-free silicoaluminic acid molecular sieve.

2. The method according to claim 1, characterized in that The partial pressure of hydrogen in the cracking and disproportionation reaction is 2-5 MPa.

3. The method according to claim 1, characterized in that The time of the cracking and disproportionation reaction is 1 to 8 hours.

4. The method according to claim 1, wherein The single-pass usage of the Ni@ZSM-5 catalyst accounts for 0.1 to 10 wt % of the high boiling point.

5. The method according to claim 1, characterized in that The particle size of the nickel nanoparticles in the Ni@ZSM-5 catalyst is 1 to 10 nm.

6. The method according to claim 1, characterized in that The components of the high boiling substances include compounds containing Si-Si, compounds containing Si-Si-Si, compounds containing Si-C and compounds containing Si-CH2-Si.

7. The method according to claim 1, characterized in that The method comprises: mixing high-boiling products produced as a by-product of producing dimethyldichlorosilane, a silicone monomer, and a Ni@ZSM-5 catalyst; after replacing air with a protective gas, introducing hydrogen and maintaining the hydrogen partial pressure; raising the temperature to perform a cracking and disproportionation reaction.

8. The method according to claim 7, characterized in that The introduction of hydrogen replaces the protective gas again and maintains the hydrogen partial pressure.

9. The method according to claim 7, characterized in that The protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them.

10. The method according to claim 1, characterized in that The method comprises: mixing a high-boiling product produced as a by-product of producing dimethyldichlorosilane, a silicone monomer, and a Ni@ZSM-5 catalyst encapsulating nickel nanoparticles, wherein the single-pass usage of the Ni@ZSM-5 catalyst accounts for 0.1 to 10 wt% of the high-boiling product, the silicon-aluminum ratio in the Ni@ZSM-5 catalyst is SiO2:Al2O3=50:1 to 500:1, the particle size of the nickel nanoparticles is 1 to 10 nm, and the nickel content is 0.5 to 5 wt%. After nitrogen is introduced to replace air, hydrogen is introduced to 2 to 5 MPa, the temperature is raised to 250 to 350° C., and a cracking and disproportionation reaction is carried out under stirring for 1 to 8 hours.

Images