Silane purification process

Abstract

The invention discloses a silane purification process which comprises the following steps: under the conditions of 250-350 DEG C and illumination, methane of silane containing methane impurities is cracked into solid carbon and hydrogen under the action of a photo-thermal catalyst reduced by hydrogen; the photo-thermal catalyst is a core-shell bifunctional catalyst and / or a core-shell-photosensitive three-functional catalyst; the core-shell bifunctional catalyst comprises a nickel core and a mesoporous silica shell wrapping the nickel core; the core-shell-photosensitive three-function catalyst comprises a nickel core, a mesoporous silica shell wrapping the nickel core and a CeO2 photosensitive layer distributed on the outer surface of the mesoporous silica shell in a nano island structure; in the photo-thermal catalyst, the pore diameter of the mesoporous silica shell is 2.3-2.7 nm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of special gas purification, in particular to a silane purification process. BACKGROUND

[0002] In many industrial fields such as semiconductor manufacturing and photovoltaic industry, high-purity silane (SiH4) is a crucial raw material.

[0003] The applicant previously applied for an invention patent entitled "Silicon Tetrafluoride Reduction Process", see patent specification CN119409198A, which includes: preparing a sodium aluminum hydride solution: measuring the required amount of sodium aluminum hydride wrapped with a linear polymer resin to isolate external air, dissolving it in an organic solvent to obtain a sodium aluminum hydride solution; silicon tetrafluoride reacts with the sodium aluminum hydride solution.

[0004] However, during the production and storage of silane, a certain amount of methane (CH4) impurities often mixed in. The presence of methane not only reduces the purity of silane, affects product quality, but also may introduce defects in some chemical vapor deposition (CVD) processes, causing safety hazards.

[0005] Traditional silane purification methods include rectification, adsorption, etc., usually using methane removal columns, light removal columns and similar equipment, for example, see patent specifications CN101817527A and CN221797064U. Although these technical means can remove methane to some extent, they have problems such as high energy consumption, low efficiency, and poor removal effect on trace amounts of methane.

[0006] High-purity silane (CH4 content <1 ppm) is a core raw material for semiconductor manufacturing, photovoltaic cells and other industries. The existing purification technology has three major bottlenecks: 1. Physical separation defects: due to the similar molecular kinetic diameters of CH4 and SiH4 (3.8 Å and 4.0 Å respectively), the adsorption / film separation method has a removal efficiency of less than 70% for low-concentration methane (<1%); 2. Thermal catalytic limitations: traditional nickel-based catalysts require high temperatures above 380℃, close to the critical temperature of silane decomposition (>400℃), and are easily deactivated by the formation of NiSi2 due to silicon deposition; 3. Photocatalytic path pollution: light-driven oxidation method converts methane into CO / H2 gas, which is difficult to separate from silane and may introduce oxygen impurities. SUMMARY

[0007] In view of the above technical problems and the deficiencies in the prior art, the silane purification process provided by the present application is a light-heat synergistically driven silane purification method, which catalytically cracks methane (CH4) impurities in silane (SiH4) at low temperature through light-heat synergy, has the characteristics of low temperature, high efficiency, no pollution, etc., adopts a special core-shell dual functional catalyst and / or a core-shell-photosensitive three functional catalyst, is suitable for green industrialized production of electronic grade high purity silane, and can solve the problem of deep removal of methane.

[0008] The specific technical solutions are as follows: The silane purification process comprises the following steps: under the action of a light-heat catalyst reduced by hydrogen, silane containing methane impurities is subjected to methane cracking into solid carbon and hydrogen at 250-350 DEG C (for example, 300 DEG C) under light irradiation. The light-heat catalyst is a core-shell dual functional catalyst and / or a core-shell-photosensitive three functional catalyst. The core-shell dual functional catalyst comprises a nickel core and a mesoporous silica shell wrapped around the nickel core. The core-shell-photosensitive three functional catalyst comprises a nickel core, a mesoporous silica shell wrapped around the nickel core, and a CeO2 photosensitive layer distributed in an island-like structure on the outer surface of the mesoporous silica shell. In the light-heat catalyst, the pore size of the mesoporous silica shell is 2.3-2.7 nm.

[0009] The silane purification process provided by the present application has a CH4 removal rate of >99.99%, and further ≥99.999%, and the energy consumption is reduced by 54%, and is suitable for green manufacturing of electronic grade high purity silane.

[0010] The light-heat catalyst provided by the present application uses a nickel core to provide methane cracking active sites and generate a light-heat effect, the mesoporous silica shell with a pore size of 2.5±0.2 nm realizes CH4 / SiH4 molecular sieving effect, allows CH4 (3.8 Å) to pass through and blocks SiH4 (4.0 Å), and the CeO2 photosensitive layer can further increase the surface acid sites (>0.8 sites / nm 2 ) to enhance methane adsorption and reduce the energy barrier, and can also enhance the visible light response (CeO2 band gap 2.8 eV).

[0011] The light-heat catalyst provided by the present application has a high specific surface area (more than 600 m 2 / g), and the core-shell structure provides a large number of active sites, which is beneficial to the light-heat catalytic reaction.

[0012] The mesoporous silica shell can enhance the light absorption and utilization efficiency of the light-heat catalyst. The photosensitive layer can further improve the light absorption performance of the light-heat catalyst.

[0013] The photo-thermal catalyst has high stability, and the core-shell structure can effectively prevent the agglomeration and sintering of the nickel core nanoparticles, thereby prolonging the service life of the catalyst.

[0014] In the present application, the nickel core can be synthesized by known prior art or obtained by commercial means.

[0015] The present application provides a preferred preparation method of the core-shell dual functional catalyst, which adopts a microemulsion method and comprises the following steps: dispersing nickel cores in a n-hexanol / cyclohexane microemulsion containing cetyltrimethylammonium bromide (CTAB), adding tetraethyl orthosilicate (TEOS), stirring and reacting at 55-65 DEG C (preferably 60 DEG C), and then separating the solid from the liquid (preferably by centrifugation) to obtain the core-shell dual functional catalyst.

[0016] In the preparation method of the core-shell dual functional catalyst, the thickness of the mesoporous silica shell can be adjusted by adjusting the amount of added TEOS.

[0017] In some preferred examples, in the preparation method of the core-shell dual functional catalyst, the mass content of CTAB in the n-hexanol / cyclohexane microemulsion containing CTAB is 8-12%, for example, 10%, etc.

[0018] In some preferred examples, in the preparation method of the core-shell dual functional catalyst, the stirring and reaction time is 6-7 hours.

[0019] In some preferred examples, in the core-shell dual functional catalyst, the nickel core is spherical and / or polyhedral in structure, and has a particle size of 20-40 nm, for example, 25 nm, 30 nm, 35 nm, etc.; and the mesoporous silica shell has a thickness of 4-6 nm, for example, 5 nm, etc. The mesoporous silica shell with a thickness of 4-6 nm can transmit visible light, filter ultraviolet light (especially ultraviolet light with a wavelength of less than 300 nm), and prevent the photolysis of silane.

[0020] The present application provides a preferred preparation method of the core-shell-photoactive triple functional catalyst, which comprises the following steps: S1, preparing a core-shell dual functional catalyst; S2, depositing a CeO2 photoactive layer on the surface of the core-shell dual functional catalyst obtained in step S1 by atomic layer deposition to obtain the core-shell-photoactive triple functional catalyst.

[0021] The core-shell dual functional catalyst in step S1 can be consistent with the core-shell dual functional catalyst described above, and the preparation method can also be consistent with the preparation method described above.

[0022] In some preferred examples, in step S2, the specific operation of depositing CeO2 includes: performing multiple cycles of the following operations at 150℃: Ce(thd)4 pulse→N2 purge→O3 pulse→N2 purge.

[0023] In step S2, the size of the nano-island and the loading of the CeO2 photosensitive layer can be adjusted by adjusting the number of cycles and / or the pulse time of the cerium precursor, and other parameter conditions.

[0024] In some preferred examples, in the core-shell-photosensitive trifunctional catalyst: the nickel core is spherical and / or polyhedral structure, the particle size is 20-40 nm, for example, 25 nm, 30 nm, 35 nm, etc.; the thickness of the mesoporous silica shell is 4-6 nm, for example, 5 nm, etc.; the loading of the CeO2 photosensitive layer is 1%-3% based on the total mass of the core-shell-photosensitive trifunctional catalyst being 100%; and the size of the nano-island is less than 5 nm. The mesoporous silica shell with a thickness of 4-6 nm can transmit visible light, filter ultraviolet light (especially ultraviolet light with a wavelength less than 300 nm), and prevent silane photodissociation.

[0025] The photo-thermal catalyst of the present application has oxygen vacancies after hydrogen reduction, and EPR detection shows a g=2.002-2.003 signal peak.

[0026] The hydrogen reduction can use pure hydrogen or a mixture of hydrogen and carrier gas. Further, in the mixture of hydrogen and carrier gas, the volume percentage of hydrogen can be 5%-10%, etc. The carrier gas can be an inert gas that does not participate in the reaction, such as argon, etc.

[0027] In some preferred examples, the temperature of the hydrogen reduction is 340-350℃, and the time is 2-3 hours.

[0028] In some preferred examples, the purification process of silane, the light is visible-near infrared light.

[0029] In some preferred examples, the purification process of silane, the wavelength of the light is 420-800 nm, for example, 450 nm, etc.

[0030] In some preferred examples, the purification process of silane, the light intensity of the light is ≥100 mW / cm 2 , further 100-300 mW / cm 2 , for example, 200 mW / cm 2 , etc.

[0031] In some preferred examples, the purification process of silane, the light source providing the light is an LED array and / or a xenon lamp.

[0032] In some preferred examples, the purification process of silane, the volume space velocity of silane containing methane impurities through the photo-thermal catalyst is 2000-5000 h -1 , for example, 3000 h -1 , etc.

[0033] In some preferred examples, the purification process of silane, the reaction pressure of methane cracking is 0.1-1 MPa, for example, 0.5 MPa, etc.

[0034] In some preferred examples, the purification process of silane further comprises: removing solid carbon by using a separation unit. Further preferably, the separation unit comprises a 0.22 μm PTFE membrane filter and a high-voltage electrostatic adsorber with a field strength of ≥5 kV / cm.

[0035] In some examples, the purification process of silane, the volume content of methane in silane containing methane impurities is ≤1%, for example, 0.8%, etc.

[0036] In some examples, the purification process of silane, the solid carbon comprises at least one of carbon fibers and carbon nanotubes.

[0037] In some examples, the purification process of silane, the solid carbon comprises one-dimensional carbon materials. Further, in some examples, the one-dimensional carbon materials have a diameter of 30±2 nm and a length of >10 μm, and are easy to separate by filtration, etc.

[0038] In some examples, the purification process of silane uses a fixed bed reactor.

[0039] In some examples, the purification process of silane, the volume content of methane in purified silane is less than 0.1 ppm, for example, 0.08 ppm, etc.

[0040] The present application initiates a photo-thermal driven methane cracking-solid carbon capture path, combines photo-generated carrier activated C-H bond with core-shell catalyst selective cracking, uses photo-thermal catalyst with visible light response electron excitation, reduces the energy barrier of methane cracking, and uses mesoporous silica shell with a pore size of 2.3-2.7 nm to isolate silane and methane cracking active sites.

[0041] Compared with the prior art, the present application has the following beneficial effects: The loss rate of silane is low, less than 0.01%; the solid carbon product is easy to separate.

[0042] Energy efficiency is improved: 60% of light energy replaces thermal energy, energy consumption is reduced to 1.8 kWh / Nm 3 , which is 54% lower than thermal catalysis.

[0043] Environmentally friendly: the entire purification process does not produce harmful by-products, and is pollution-free to the environment; the by-product hydrogen does not need to be removed further, and has no effect on the subsequent cracking of silane to produce silicon.

[0044] Purity breakthrough: CH4 removal rate > 99.99% (outlet concentration < 0.1 ppm), meeting the 3 nm chip standard (SEMIC 7.1-2025).

[0045] Safety redundancy: the operating temperature (not more than 350℃) is lower than the silane decomposition temperature of 400℃.

[0046] Longer life: the core-shell structured photothermal catalyst has good stability and can be reused multiple times; the anti-carbon deposition design makes the catalyst life > 1200 h (carbon deposition rate under light reduced by 76%). DETAILED DESCRIPTION

[0047] The application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application.

[0048] The operating methods in the following examples without specific conditions are generally according to conventional conditions, or according to the conditions recommended by the manufacturers.

[0049] Example 1: A core-shell bifunctional catalyst was prepared by a microemulsion method using CTAB as a template and hydrolyzing tetraethyl orthosilicate to coat nickel nanocrystals, specifically including: dispersing 1 g of nickel cores with a particle size of 30 nm in 40 g of n-hexanol / cyclohexane microemulsion containing 10wt% CTAB, the composition of the n-hexanol / cyclohexane microemulsion being n-hexanol, cyclohexane and water at a mass ratio of 1:1.33:6.67, adding 0.27 g of tetraethyl orthosilicate, stirring at 60℃ for 6 hours, centrifuging after the reaction to obtain the solid, and washing to obtain the core-shell bifunctional catalyst, the specific surface area of the catalyst being 680 m 2 / g. The core-shell bifunctional catalyst includes nickel cores and a mesoporous silica shell wrapping the nickel cores, the thickness of the mesoporous silica shell being 5 nm, and the pore size of the mesoporous silica shell being 2.7 nm.

[0050] The core-shell bifunctional catalyst was heated and reduced in a hydrogen argon mixed gas atmosphere with a hydrogen volume content of 5%, the heating and reduction temperature being 350℃, and the heating and reduction time being 2 hours, to obtain a hydrogen-reduced photothermal catalyst having oxygen vacancies, and EPR detection showed g=2.002-2.003 signal peaks.

[0051] A quartz fixed bed reactor with a diameter of 50 mm was used, and a 450 nm LED array was built in, with a light intensity of 200 mW / cm 2 , at 300℃, under light, with a volume space velocity of 3000 h-1 , under the condition of pressure 0.5 MPa, silane containing 0.8 vol% methane impurities is cracked into oriented carbon nanotubes with a diameter of 30 nm and a length of >10 μm and hydrogen under the action of the photo-thermal catalyst reduced by hydrogen, the oriented carbon nanotubes are removed by a separation unit (0.22 μm PTFE membrane + high-voltage electrostatic adsorber, field strength ≥5 kV / cm), the volume concentration of methane in the outlet gas is 0.08 ppm, the methane removal rate is 99.999%, and the silane loss rate is less than 0.01%.

[0052] Example 2: The core-shell-photo-sensitive trifunctional catalyst was prepared, including: Step S1, the core-shell bifunctional catalyst was prepared according to Example 1.

[0053] Step S2, the CeO2 photo-sensitive layer was deposited on the surface of the core-shell bifunctional catalyst obtained in step S1 by atomic layer deposition, to obtain the core-shell-photo-sensitive trifunctional catalyst. The core-shell-photo-sensitive trifunctional catalyst includes a nickel core, a mesoporous silica shell wrapping the nickel core, and a CeO2 photo-sensitive layer distributed in the form of nano-islands on the outer surface of the mesoporous silica shell.

[0054] In step S2, the specific operation of depositing CeO2 includes: 3 times of the following cycle operation at 150℃: Ce(thd)4 pulse 0.1 s→N2 purge 10 s→O3 pulse 0.05 s→N2 purge 15 s.

[0055] The loading amount of the CeO2 photo-sensitive layer is 3% based on the total mass of the core-shell-photo-sensitive trifunctional catalyst being 100%.

[0056] The size of the nano-island of the CeO2 photo-sensitive layer in the core-shell-photo-sensitive trifunctional catalyst is less than 5 nm.

[0057] The core-shell-photo-sensitive trifunctional catalyst was heated and reduced in a hydrogen argon mixed gas atmosphere with a hydrogen volume content of 5%, the heating and reduction temperature was 350℃, and the heating and reduction time was 2 hours, to obtain the photo-thermal catalyst reduced by hydrogen, which has oxygen vacancies, and the EPR detection shows g=2.002-2.003 signal peak.

[0058] A quartz fixed bed reactor with a diameter of 50 mm was used, and a 450 nm LED array was built in, with a light intensity of 200 mW / cm 2 at 300℃, under light, with a volume space velocity of 3000 h -1Under the condition of pressure 0.5 MPa, silane containing 0.8 vol% of methane impurities is cracked into oriented carbon nanotubes with diameter of 30±2 nm and length of >10 μm and hydrogen by the action of the photo-thermal catalyst reduced by hydrogen, the oriented carbon nanotubes are removed by a separation unit (0.22 μm PTFE membrane + high-voltage electrostatic adsorber, field strength ≥5 kV / cm), the volume concentration of methane in the outlet gas is 0.06 ppm, the removal rate of methane is 99.99925%, and the loss rate of silane is less than 0.01%.

[0059] Furthermore, it is understood that various modifications and changes can be made to the application by those skilled in the art in light of the above description, and that such modifications and changes are intended to fall within the scope of the claims appended hereto.

Claims

1. A purification process of silane, characterized by, The application relates to a purification process of silane containing methane impurities. Under the action of a photo-thermal catalyst reduced by hydrogen, the silane containing methane impurities is cracked into solid carbon and hydrogen under light at 250-350 DEG C; The photo-thermal catalyst is a core-shell dual functional catalyst and / or a core-shell-photo-sensitive three functional catalyst; The core-shell dual functional catalyst comprises a nickel core and a mesoporous silica shell wrapping the nickel core; The core-shell-photo-sensitive three functional catalyst comprises a nickel core, a mesoporous silica shell wrapping the nickel core and a CeO2 photo-sensitive layer distributed in the form of nano-islands on the outer surface of the mesoporous silica shell; The pore size of the mesoporous silica shell in the photo-thermal catalyst is 2.3-2.7 nm.

2. The purification process of silane according to claim 1, characterized in that, The light-thermal catalyst has a specific surface area greater than 600 m 2 / g; In the core-shell dual functional catalyst, the nickel core is in a spherical and / or polyhedral structure, and the particle size is 20-40 nm; the thickness of the mesoporous silica shell is 4-6 nm; In the core-shell-photo-sensitive three functional catalyst, the nickel core is in a spherical and / or polyhedral structure, and the particle size is 20-40 nm; the thickness of the mesoporous silica shell is 4-6 nm; the loading amount of the CeO2 photo-sensitive layer is 1-3% based on the total mass of the core-shell-photo-sensitive three functional catalyst; and the size of the nano-islands is less than 5 nm.

3. The purification process of silane according to claim 1, characterized in that, The photo-thermal catalyst reduced by hydrogen has oxygen vacancies, and EPR detection shows g=2.002-2.003 signal peaks.

4. The purification process of silane according to claim 1, characterized in that, The temperature of the hydrogen reduction is 340-350 DEG C, and the time is 2-3 hours.

5. The purification process of silane according to claim 1, characterized in that, The light is visible-near infrared light, and the wavelength is 420-800 nm; The light intensity of the light illumination is ≥ 100 mW / cm 2 , further 100-300 mW / cm 2 .

6. The purification process of silane according to claim 1, characterized in that, The volume space velocity of silane containing methane impurities through the photo-thermal catalyst is 2000-5000 h -1 .

7. The purification process of silane according to claim 1, characterized in that, The reaction pressure of the methane cracking is 0.1-1 MPa.

8. The purification process of silane according to claim 1, characterized in that, The purification process of the silane further comprises: removing the solid carbon by using a separation unit. The separation unit comprises a 0.22 mu m PTFE membrane filter and a high-voltage electrostatic adsorber with a field strength of greater than or equal to 5 kV / cm.