Polysilsesquioxane gas separation membranes, methods of making and use thereof

Abstract

The present application relates to the technical field of gas separation material, and more particularly to a polysilsesquioxane gas separation membrane, a preparation method and application thereof, the polysilsesquioxane gas separation membrane comprises an alpha-Al2O3 support body, an alpha-Al2O3 particle layer, a transition layer and a polysilsesquioxane layer, and the preparation raw material of the polysilsesquioxane layer comprises bridged silsesquioxane monomers and pendant silsesquioxane monomers. The present application designs and prepares the polysilsesquioxane gas separation membrane by the strategy of copolymerization of bridged silsesquioxane precursors and pendant silsesquioxane precursors, and constructs a composite membrane structure with a 'rigid skeleton / soft micropore', and realizes efficient molecular sieving of He / N2 through fine regulation of the polysilsesquioxane network pore size and pore environment, which is very obvious in the effect of helium extraction from liquefied natural gas tail gas, solves the problems of high cost and high energy consumption of traditional methods, and the problem of poor hydrothermal stability of traditional silica membranes which is not conducive to industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas separation materials, in particular to a polysilsesquioxane gas separation membrane and a preparation method and application thereof. BACKGROUND

[0002] Helium (He) is a non-renewable rare gas, which is an important strategic gas resource indispensable for the development of national defense and high technology, and plays an irreplaceable role in the fields of national defense, industry and technology such as aerospace, nuclear weapons, submarines, nuclear magnetic resonance and semiconductors. However, He is mainly distributed in the mantle, rocks, air and natural gas, and the content of He in air is relatively low, which is difficult to be resourcefully utilized. Therefore, an important way for He resource utilization is to extract it from natural gas, especially from the tail gas of liquefied natural gas.

[0003] For the current method of extracting helium from the tail gas of liquefied natural gas, there are cryogenic method, pressure swing adsorption method and absorption method. The development of these methods in the prior art is relatively mature, but there are also some problems, such as high cost, high energy consumption and low operation flexibility. However, due to the difference in kinetic diameter between He (0.26 nm) and N2 (0.364 nm), He can be separated according to its molecular size, and membrane separation technology can be coupled with some traditional technologies to realize He recovery and purification, which is considered to be the most promising scheme for extracting helium from the tail gas of liquefied natural gas in the future. In the prior art, there is already a method of using silicon dioxide to prepare inorganic membrane materials for He separation, but the traditional silicon dioxide membrane is easy to hydrolyze in a hydrothermal environment, which is not conducive to industrial production and is not conducive to the separation and purification of helium.

[0004] The present application relates to the technical field of gas separation materials, in particular to a polysilsesquioxane gas separation membrane and a preparation method and application thereof. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a polysilsesquioxane gas separation membrane and a preparation method and application thereof, which solves the problem that the silicon dioxide membrane in the prior art is easy to hydrolyze in a hydrothermal environment, which is not conducive to industrial production and is not conducive to the separation and purification of helium.

[0006] The present application solves the above technical problems through the following technical means:

[0007] In a first aspect, the present application provides a polysilsesquioxane gas separation membrane, which comprises a polysilsesquioxane layer located at the outermost layer of the gas separation membrane, and the preparation raw material of the polysilsesquioxane layer comprises bridged silsesquioxane monomers and pendant silsesquioxane monomers.

[0008] In combination with the first aspect, in some embodiments, the molar ratio of the bridged silsesquioxane monomers to the pendant silsesquioxane monomers is (5-10):(1-5).

[0009] In combination with the first aspect, in some embodiments, the bridged silsesquioxane monomer is any one of 1,2-bis(triethoxysilyl)ethane, bis(triethoxysilyl)methane, 1,3-bis(triethoxysilyl)propane, 1,2-di(triethoxysilyl)benzene, and the pendant silsesquioxane monomer is any one of N-(trimethoxysilylpropyl)imidazole, methyltrimethoxysilane, methyltriethoxysilane, and phenyltriethoxysilane.

[0010] In combination with the first aspect, in some embodiments, the gas separation membrane comprises, from inside to outside, an α-Al2O3 support body, an α-Al2O3 particle layer, a transition layer, and a polysilsesquioxane layer.

[0011] In combination with the first aspect, in some embodiments, the transition layer is formed by drying and sintering of a boehmite sol and a SiO2-ZrO2 sol.

[0012] In combination with the first aspect, in some embodiments, the α-Al2O3 particle layer comprises α-Al2O3 particles with a particle size of 0.2 μm and 2 μm. The α-Al2O3 particles with different particle sizes can gradually reduce the macropore defects and pore size.

[0013] The second aspect of the present application provides a method for preparing a polysilsesquioxane gas separation membrane, comprising the following steps:

[0014] The bridged silsesquioxane monomer and the pendant silsesquioxane monomer are dissolved in anhydrous ethanol, and then added dropwise into a hydrochloric acid solution under stirring to obtain a mixed solution. Subsequently, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in the mixed solution to 0.01-10%. Then, the solution is stirred at room temperature for 10-15 h to obtain a polysilsesquioxane sol.

[0015] An α-Al2O3 particle sol is coated on the outer surface of the α-Al2O3 support body, and then calcined at 500-1200 °C for 10-20 min. The coating and calcining steps are repeated for 3-5 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body.

[0016] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer, and then dried and sintered to form a transition layer.

[0017] Subsequently, the polysilsesquioxane sol is coated on the transition layer, and then calcined at 100-400 °C under N2 atmosphere for 0.5-2 h. The coating and calcining steps are repeated for 1-3 times to obtain a polysilsesquioxane gas separation membrane.

[0018] In combination with the second aspect, in some embodiments, the concentration of the hydrochloric acid solution is 0.1-10 mmol / g.

[0019] In combination with the second aspect, in some embodiments, the step of coating the alpha-Al2O3 particle sol on the outer surface of the alpha-Al2O3 support body comprises: sequentially and uniformly coating an alpha-Al2O3 small particle sol and an alpha-Al2O3 large particle sol on the outer surface of the alpha-Al2O3 support body, the alpha-Al2O3 small particle sol being prepared by uniformly dispersing alpha-Al2O3 particles with a particle size of 0.2 μm in a SiO2-ZrO2 sol, and the alpha-Al2O3 large particle sol being prepared by uniformly dispersing alpha-Al2O3 particles with a particle size of 2 μm in a SiO2-ZrO2 sol.

[0020] In a third aspect, the present application further provides a use of the polysilsesquioxane gas separation membrane of the first aspect or prepared by the method of the second aspect in helium separation and extraction.

[0021] The polysilsesquioxane gas separation membrane of the present application, by the strategy of copolymerization of bridging-type silsesquioxane precursor and pendant-type silsesquioxane precursor, constructs a composite membrane structure with "rigid skeleton / flexible micropore", thereby realizing the synergistic regulation of membrane pore size and pore microenvironment. The two precursors can be 1,2-bis(triethoxysilyl)ethane (BTESE) and N-(trimethoxysilylpropyl)imidazole (SiIm), respectively. The network structure formed by the bridging-type precursor BTESE is relatively loose, and the steric hindrance effect of the pendant group can effectively and accurately reduce the membrane pore size, finally forming a composite membrane pore structure of "rigid skeleton / flexible micropore", and the prepared polysilsesquioxane gas separation membrane can improve the separation selectivity of He / N2 and He / CH4 while maintaining the permeation flux of He.

[0022] The polysilsesquioxane gas separation membrane of the present application realizes the efficient molecular sieving of He / N2 by fine regulation of the network pore size and pore environment of polysilsesquioxane, and the effect of liquefied natural gas tail gas helium extraction is very obvious, solving the problems of high cost and high energy consumption of traditional methods, and the problem of poor hydrothermal stability of traditional silica membranes which is not conducive to industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a schematic diagram of the molecular structure of the bridging-type silsesquioxane monomer and the pendant-type silsesquioxane monomer;

[0024] Figure 2 It is a schematic diagram of the "rigid skeleton / flexible micropore" structure formed by the polysilsesquioxane gas separation membrane;

[0025] Figure 3 It is a particle size distribution diagram of the polysilsesquioxane sol in Examples 1-5;

[0026] Figure 4 IR spectra of the copolymerized polysilsesquioxane gel powder in Examples 1-5;

[0027] Figure 5 TG curves of the copolymerized polysilsesquioxane sol in Examples 1-5;

[0028] Figure 6 N2 adsorption-desorption isotherms of the polysilsesquioxane gas separation membrane in Examples 1-5;

[0029] Figure 7 Gas permeation performance test results of the polysilsesquioxane gas separation membrane in Examples 1-5 for gases having kinetic diameters;

[0030] Figure 8 Gas separation performance test results of the polysilsesquioxane gas separation membrane in Examples 1-5 for He / N2;

[0031] Figure 9 Gas separation performance test results of the polysilsesquioxane gas separation membrane in Examples 1-5 for He / CH4. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0033] In the following examples, the specific conditions not specified are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The raw materials, equipment or instruments used, if not specified by the manufacturer, are all conventional products that can be purchased on the market.

[0034] Silica is a commonly used inorganic membrane material for He separation, but traditional silica membranes are prone to hydrolysis in a hydrothermal environment, which is not conducive to industrial production and is not conducive to the separation and purification of helium. In the present application, a bridged silsesquioxane precursor is copolymerized with one or more pendant silsesquioxane monomer precursors, a sol-gel method is used, and α-Al2O3 is used as a support to prepare a polysilsesquioxane gas separation membrane. Finally, a "rigid skeleton / flexible micropore" composite membrane pore structure is formed. The composite membrane pore structure is shown in FIG. 1. Figure 2Thus, N2 and CH4 molecules are trapped based on the size exclusion effect in the rigid micropores, and He molecules can selectively pass through the above composite membrane pore structure due to the smaller kinetic diameter. The above composite membrane pore structure has high He / N2 and He / CH4 selectivity, and can be well applied to the field of liquefied natural gas tail gas helium extraction and the like.

[0035] The polysilsesquioxane gas separation membrane of the present application comprises, sequentially from the inside to the outside, an α-Al2O3 support body, an α-Al2O3 particle layer, a transition layer and a polysilsesquioxane layer, and the raw material for preparing the polysilsesquioxane layer comprises bridged silsesquioxane monomers and pendant silsesquioxane monomers. The molar ratio of the bridged silsesquioxane monomers to the pendant silsesquioxane monomers is (5-10):(1-5), the bridged silsesquioxane monomers are any one of 1,2-bis(triethoxysilyl)ethane, bis(triethoxysilyl)methane, 1,3-bis(triethoxysilyl)propane and 1,2-bis(triethoxysilyl)benzene, and the pendant silsesquioxane monomers are any one of N-(trimethoxysilylpropyl)imidazole, methyltrimethoxysilane, methyltriethoxysilane and phenyltriethoxysilane. Preferably, the bridged silsesquioxane monomers are 1,2-bis(triethoxysilyl)ethane (BTESE), and the pendant silsesquioxane monomers are N-(trimethoxysilylpropyl)imidazole (SiIm). The schematic diagram of the molecular structure of the bridged silsesquioxane monomers and the pendant silsesquioxane monomers is shown in FIG. 1. Figure 1 The transition layer is formed by drying boehmite sol and SiO2-ZrO2 sol. The α-Al2O3 particle layer comprises α-Al2O3 particles with a particle size of 0.2 μm and 2 μm.

[0036] The method for preparing the polysilsesquioxane gas separation membrane of the present application comprises the following steps:

[0037] The bridged silsesquioxane monomers and the pendant silsesquioxane monomers are dissolved in anhydrous ethanol, and then dropped into a hydrochloric acid solution under stirring to obtain a mixed solution. Subsequently, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomers and the pendant silsesquioxane monomers in the mixed solution to 0.01-10%, and then the mixed solution is stirred at room temperature for 10-15 h to obtain a polysilsesquioxane sol.

[0038] The outer surface of the α-Al2O3 support body is coated with an α-Al2O3 particle sol, and then calcined at 500-1200 °C for 10-20 min. The coating and calcining steps are repeated for 3-5 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body.

[0039] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer, and then dried and sintered to form a transition layer.

[0040] Subsequently, a polysilsequioxane sol is coated on the transition layer, calcined at 100-400°C under N2atmosphere for 0.5-2 hours, repeated 1-3 times, to obtain a polysilsequioxane gas separation membrane.

[0041] The polysilsequioxane gas separation membrane and the method for preparing the same according to the present application are explained in detail by way of Examples 1-7 below.

[0042] The method for preparing the α-Al2O3 support used in the following examples is as follows: a tubular α-Al2O3 ceramic membrane support is prepared by an extrusion molding method, 82wt% of α-Al2O3 with an average particle size of 6.18 microns and 5wt% of carboxymethyl cellulose, 10wt% of kaolin and 3wt% of titanium dioxide are mixed uniformly under mechanical stirring, then aged in an oven at 25°C for 12h, a green body is prepared by extrusion molding, the green body is dried in an oven at 30°C for 12h, and the dried green body is sintered in an electric furnace at a temperature of 1200-1700°C to obtain an α-Al2O3 support.

[0043] Example 1

[0044] The raw materials for preparing the polysilsequioxane layer in the polysilsequioxane gas separation membrane of the present example include bridged silsesquioxane monomers and pendant silsesquioxane monomers in a molar ratio of 7:3. The bridged silsesquioxane monomers are 1,2-bis(triethoxysilyl)ethane, and the pendant silsesquioxane monomers are N-(trimethoxysilylpropyl)imidazole.

[0045] The method for preparing the polysilsequioxane gas separation membrane of the present example is as follows:

[0046] The bridged silsesquioxane monomers and the pendant silsesquioxane monomers are dissolved in anhydrous ethanol, and a hydrochloric acid solution with a concentration of 5.084mmol / L is added dropwise under vigorous stirring to obtain a mixed solution, and then anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomers and the pendant silsesquioxane monomers in the mixed solution to 5%, and then the reaction is stirred at room temperature for 12h to obtain a clear and transparent polysilsequioxane sol.

[0047] The 0.2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 small particle sol, and the 2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are uniformly coated on the outer surface of the α-Al2O3 support in turn, and then calcined at 550°C for 15 min. The coating and calcining steps are repeated 4 times to form the α-Al2O3 particle layer on the outer surface of the α-Al2O3 support, which covers all the large pores on the surface of the α-Al2O3 support to avoid the appearance of pinholes on the separation membrane.

[0048] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer in turn, and dried to form the transition layer, and the average pore size of the surface of the α-Al2O3 support is further reduced to about 1 nm.

[0049] Then, the 5 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 300°C under N2 atmosphere for 1 h, and the coating and calcining steps are repeated 2 times to obtain the polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0050] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0051] Example 2

[0052] The preparation raw material of the polysilsesquioxane layer in the polysilsesquioxane gas separation membrane of this embodiment includes the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in a molar ratio of 9:1. The bridged silsesquioxane monomer is 1,2-bis(triethoxysilyl)ethane, and the pendant silsesquioxane monomer is N-(trimethoxysilylpropyl)imidazole.

[0053] The preparation method of the polysilsesquioxane gas separation membrane of this embodiment is as follows:

[0054] The bridged silsesquioxane monomer and the pendant silsesquioxane monomer are dissolved in anhydrous ethanol, and then the hydrochloric acid solution with a concentration of 5.084 mmol / L is added dropwise under vigorous stirring to obtain a mixed solution. Then, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in the mixed solution to 5%, and then the reaction is stirred at room temperature for 12 h to obtain a clear and transparent polysilsesquioxane sol.

[0055] The 0.2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 small particle sol, and the 2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are uniformly coated on the outer surface of the α-Al2O3 support in turn, and then calcined at 550°C for 15 min. The coating and calcining steps are repeated 4 times to form the α-Al2O3 particle layer on the outer surface of the α-Al2O3 support, which covers all the large pores on the surface of the α-Al2O3 support to avoid the appearance of pinholes on the separation membrane.

[0056] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer in turn, and dried to form the transition layer, and the average pore size of the surface of the α-Al2O3 support is further reduced to about 1 nm.

[0057] Then, the 5 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 300°C under N2 atmosphere for 1 h, and the coating and calcining steps are repeated 2 times to obtain the polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0058] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0059] Example 3

[0060] The preparation raw material of the polysilsesquioxane layer in the polysilsesquioxane gas separation membrane of this embodiment includes the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in a molar ratio of 8:2. The bridged silsesquioxane monomer is 1,2-bis(triethoxysilyl)ethane, and the pendant silsesquioxane monomer is N-(trimethoxysilylpropyl)imidazole.

[0061] The preparation method of the polysilsesquioxane gas separation membrane of this embodiment is as follows:

[0062] The bridged silsesquioxane monomer and the pendant silsesquioxane monomer are dissolved in anhydrous ethanol, and then the hydrochloric acid solution with a concentration of 5.084 mmol / L is added dropwise under vigorous stirring to obtain a mixed solution. Then, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in the mixed solution to 5%, and then the reaction is stirred at room temperature for 12 h to obtain a clear and transparent polysilsesquioxane sol.

[0063] The α-Al2O3 support body is used as the base film, 0.2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 small particle sol, and 2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are uniformly coated on the outer surface of the α-Al2O3 support body in turn, and then calcined at 550°C for 15 min. The coating and calcining steps are repeated 4 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body, which covers all the large pores on the surface of the α-Al2O3 support body to avoid the appearance of pinholes on the separation membrane.

[0064] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer in turn, and dried to form a transition layer, and the average pore size of the surface of the α-Al2O3 support body is further reduced to about 1 nm.

[0065] Then, 5 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 300°C in N2 atmosphere for 1 h, and the coating and calcining steps are repeated 2 times to obtain the polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0066] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0067] Example 4

[0068] The preparation raw material of the polysilsesquioxane layer in the polysilsesquioxane gas separation membrane of this embodiment includes pendant-type silsesquioxane monomer. The pendant-type silsesquioxane monomer is N-(trimethoxysilylpropyl)imidazole.

[0069] The preparation method of the polysilsesquioxane gas separation membrane of this embodiment is as follows:

[0070] The pendant-type silsesquioxane monomer is dissolved in anhydrous ethanol, and then dropped into a hydrochloric acid solution with a concentration of 5.084 mmol / g under vigorous stirring to obtain a mixed solution. Then, anhydrous ethanol is added to adjust the total mass fraction of the pendant-type silsesquioxane monomer in the mixed solution to 5%, and then stirred at room temperature for 12 h to obtain a clear and transparent polysilsesquioxane sol.

[0071] The α-Al2O3 support body is used as the base film, 0.2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 small particle sol, and 2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are uniformly coated on the outer surface of the α-Al2O3 support body in turn, and then calcined at 550°C for 15 min. The coating and calcining steps are repeated 4 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body, which covers all the large pores on the surface of the α-Al2O3 support body to avoid the appearance of pinholes on the separation membrane.

[0072] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer in turn, and dried to form a transition layer, and the average pore size of the surface of the α-Al2O3 support body is further reduced to about 1 nm.

[0073] Then, 5 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 300°C under N2 atmosphere for 1 h, and the coating and calcining steps are repeated 2 times to obtain the polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0074] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0075] Example 5

[0076] The preparation raw material of the polysilsesquioxane layer in the polysilsesquioxane gas separation membrane of this embodiment includes bridged silsesquioxane monomer. The bridged silsesquioxane monomer is 1,2-bis(triethoxysilyl)ethane.

[0077] The preparation method of the polysilsesquioxane gas separation membrane of this embodiment is as follows:

[0078] The bridged silsesquioxane monomer is dissolved in anhydrous ethanol, and then added dropwise into a hydrochloric acid solution with a concentration of 5.084 mmol / g under vigorous stirring to obtain a mixed solution. Then, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in the mixed solution to 5%, and then stirred at room temperature for 12 h to obtain a clear and transparent polysilsesquioxane sol.

[0079] The α-Al2O3 support body is used as a base film, 0.2 μm α-Al2O3 particles are dispersed in SiO2-ZrO2 sol to prepare α-Al2O3 small particle sol, and 2 μm α-Al2O3 particles are dispersed in SiO2-ZrO2 sol to prepare α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are uniformly coated on the outer surface of the α-Al2O3 support body in turn, and then calcined at 550°C for 15 min. The coating and calcination steps are repeated 4 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body, which covers all the large pores on the surface of the α-Al2O3 support body to avoid the appearance of pinholes on the separation membrane.

[0080] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer in turn, and dried to form a transition layer, and the average pore size of the surface of the α-Al2O3 support body is further reduced to about 1 nm.

[0081] Then, 5 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 300°C in N2 atmosphere for 1 hour, and the coating and calcination steps are repeated 2 times to obtain a polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0082] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0083] The polysilsesquioxane gas separation membranes and the intermediate products prepared in Examples 1-5 are subjected to performance detection, and the details are as follows:

[0084] (1) Particle size detection

[0085] The particle size distribution of the polysilsesquioxane sol in Examples 1-5 is characterized by using a nanoparticle size analyzer. The sample of the polysilsesquioxane sol to be tested is placed in a sample tube after ultrasonic treatment for 5 min, and the test is started. The test results are shown in Table 1. Figure 3 .

[0086] Figure 3 The particle size distribution of the polysilsesquioxane sol in Examples 1-5 is shown in Table 1. In Examples 1-5, the polysilsesquioxane sol has different molar ratios of bridged silsesquioxane monomers and pendant silsesquioxane monomers, Figure 3 The data in Table 1 show that the particle size range of all the sols is 0.7-10 nm, and the average particle size is below 4 nm.

[0087] (2) Infrared spectrum analysis

[0088] The polyhedral silsesquioxane gas separation membrane surface prepared from Examples 1-5 was scraped to obtain a polyhedral silsesquioxane layer powder as a sample, and the structure of the sample powder was characterized by a Fourier transform infrared spectrometer (FTIR). The specific test method is as follows: the powder sample scraped from Examples 1-5 was mixed and ground with spectroscopically pure potassium bromide (KBr) in a mortar, and then the mixture of the sample and KBr was pressed into a circular sheet using a special pressing mold for testing. The scanning range of the test wave number was 4000-400 cm -1 , and the scanning number was 128 times. The test results are shown in Figure 4 .

[0089] As can be seen from Figure 4 , the peak shapes of all the powders are roughly the same, and it is observed that all the polyhedral silsesquioxanes show a strong absorption peak near a wave number of 1010 cm -1 , which is formed by the symmetric stretching vibration of oxygen atoms in Si-O-Si, and the peak near a wave number of 900 cm -1 belongs to the asymmetric stretching vibration of oxygen atoms in Si-OH, and the existence of these two peaks proves that the hydrolysis and condensation reaction of the polyhedral silsesquioxane precursor is successful; there is a strong absorption peak near a wave number of 1650 cm -1 in the spectrum of SiIm, while there is no absorption peak at the same position in the spectrum of BTESE, and with the increase of the content of SiIm, the absorption peak gradually increases from nothing to something, which is caused by the vibration of the C=N group in the structure of SiIm; at the same time, the successful doping of SiIm is verified, which shows that the BTESE-SiIm powder is a polysiloxane structure containing imidazole ring units, and further shows that the surface of the polyhedral silsesquioxane gas separation membrane is a polysiloxane structure containing imidazole ring units.

[0090] (3) Thermal stability analysis

[0091] The polyhedral silsesquioxane sol prepared from Examples 1-5 was used as a sample, and the thermal stability of the polyhedral silsesquioxane sol was tested by a thermal gravimetric analyzer to further confirm the temperature used for preparing the membrane. The polyhedral silsesquioxane sol sample was dried in an oven at 120°C for 4h to remove the physically adsorbed water and anhydrous ethanol in the sample, and then tested by a thermal gravimetric analyzer, with N2 as the test atmosphere, the temperature range being 40-800°C, and the heating rate being 10°C / min. The detection results are shown in Figure 5 .

[0092] From Figure 5It can be seen that the thermal stability of BTESE is good, and the overall weight loss is divided into two stages. The first stage is 200-400°C, and this stage is mainly due to the existence of some unhydrolyzed polycondensation groups in the material, and the temperature is further reacted. The second stage is 400-700°C, mainly the decomposition of carbon and other organic groups. The overall weight loss of SiIm is divided into three stages. The first stage is 150-250°C, and this stage is mainly due to the existence of some unhydrolyzed polycondensation groups in the material, and the temperature is further reacted. The second stage is 250-400°C, mainly the cleavage of imidazole ring. The third stage is 400-700°C, mainly the decomposition of carbon and other organic groups. The thermal decomposition starting temperature of BTESE-SiIm is between the two, closer to BTESE, so the coating film temperature and the calcination temperature are determined to be 100-400°C.

[0093] (4) Specific surface area detection

[0094] The polysilsesquioxane gas separation membrane prepared by Examples 1-5 was used as a detection sample, and the adsorption / desorption isotherm of N2(77K) was determined by a specific surface adsorption instrument to determine the specific surface area and pore volume of the material. Before the gas adsorption test, the sample to be tested was activated and treated at 120°C under vacuum for 10h. The vacuum degree of the polysilsesquioxane gas separation membrane was tested by a full-automatic true density tester at 40°C with He as a probe. The detection results are shown in Table 1. Figure 6 and Table 1.

[0095] Table 1

[0096] Specific surface area S BET (m 2 / g)]]> Pore volume V total (cm 3 / g)]]> True density (g / cm3 3 )]]> BTESE 729 0.49 1.6095 B-S-9:1 438 0.36 1.5922 B-S-8:2 158 0.11 1.5574 B-S-7:3 0 0.05 1.5193 SiIm 0 0.099 -

[0097] From Figure 6The data in Table 1 show that BTESE, B-S-9:1 and B-S-8:2 are typical type I adsorption isotherms, which prove that these materials are microporous materials with rigid pores. The N2adsorption amount of the Silm and B-S-7:3 samples is almost zero, indicating that these two materials are "non-porous" structures. It is speculated that the imidazole ring groups of Silm occupy the pores in the rigid Si-O-Si network, causing the pores in the matrix to be blocked, thus forming a relatively dense structure, i.e., a "rigid skeleton / soft micropore" composite structure. As can be seen from the data in Table 1, the pore volume and specific surface area of the gas separation membrane containing BTESE-Sil m copolymer are smaller than those of the gas separation membrane prepared from pure BTESE, and the pore volume and specific surface area gradually decrease with the increase of the proportion of Silm, thus verifying the above speculation that part of the side chain groups in the Silm structure are stacked and filled in the network, reducing the effective pore size of the pores. When the ratio of BTESE and Silm is 7:3, the specific surface area decreases to zero, indicating that as the proportion of Silm precursor increases, the organic side chain occupies the gap of the rigid Si-O-Si network, and the network tends to be more and more dense. It is proved that the copolymerization of BTESE and Silm can effectively regulate the network structure.

[0098] (5) Gas permeation performance test

[0099] The gas permeation and separation performance of the polysilsesquioxane gas separation membranes prepared in Examples 1-5 was evaluated by using a gas permeation and separation device set up in the laboratory. The temperature range for single gas permeation test was 40-200℃, and the tested gas was a series of gases with kinetic diameters: He (0.26 nm), H2(0.289 nm), CO2(0.33 nm), N2(0.364 nm), CH4(0.38 nm). By adjusting the back pressure valve, the pressure on the gas inlet side of the tubular membrane was maintained at a certain pressure, and the pressure difference between the feed and the permeation was maintained at about 0.2 MPa, and the gas was promoted to permeate by pressure difference. Before testing, the polysilsesquioxane gas separation membrane was installed in the membrane module for pretreatment, and the membrane was heated to 200℃, and at the same time, He with a flow rate of 50 ml / min was used to purge for at least 6 h, the purpose of which was to remove water molecules adsorbed on the surface and inside of the membrane. When the temperature of the membrane and the pressure difference between the inside and outside of the membrane reached a stable state, the permeation test was started.

[0100] The calculation formula of gas permeation rate and ideal selectivity is as follows:

[0101] P i =F i / AΔP i

[0102] α ij =P i / P j

[0103] where P i and P j (mol / (m 2 ·s·Pa)) are the permeation rates of gas components i and j, respectively, F i (mol / s) is the molar flow rate of component i permeating through the membrane, the volume flow rate of the gas permeating through the membrane is measured by an electronic soap film flowmeter, A (m 2 ) is the effective area of the membrane, and ΔP i (Pa) is the pressure difference of component i on both sides of the membrane, and a ij is the ideal selectivity coefficient of component i to j. The test results are shown in Figure 7 where a is the single-gas permeation performance map of the membrane, and b is the non-dimensional gas permeation rate and kinetic diameter relationship map of the membrane.

[0104] As can be seen from Figure 7 , the polyhedral silsesquioxane gas separation membranes prepared in Examples 1-5 have different permeation fluxes for gas molecules of different sizes, and the larger the kinetic diameter of the gas, the smaller the permeation flux. This shows that the BTESE, BTESE-SiIm and SiIm membranes have a size sieving effect on gas molecules of different kinetic diameters. Among all the membranes, BTESE has a higher gas permeation flux, which is determined by its rigid porosity. With the increase of SiIm content, the permeation flux of BTESE-SiIm membranes for various gases decreases, which is the same as the decrease of the specific surface area and pore volume of the corresponding gas separation membranes, proving that with the increase of SiIm content in the precursor, the structure of the membrane becomes more and more dense, and tends to be a non-porous structure in appearance.

[0105] (6) Separation performance test for He / N2 mixed gas

[0106] The polyhedral silsesquioxane gas separation membranes prepared in Examples 1-5 were used as sample membranes, and their separation performance for He / N2 and He / CH4 mixed gas was tested, respectively. The test results are shown in Figure 8 and Figure 9 .

[0107] From Figure 8It can be seen that, with the increase of the proportion of SiIm in the film structure, the permeability of the prepared polysilsesquioxane separation membrane decreases, and the He / N2 and He / CH4 selectivity shows a trend of first increasing and then decreasing. It is speculated that when the SiIm content is low, the side chain fills in the pores formed by Si-O-Si, hindering the passage of macromolecules, but at the same time, the side chain has a certain activity space (free volume) to facilitate the permeation of small molecules, so the He selectivity is improved. When the SiIm content is high, the side chain density increases, the chain segment movement is limited, and the corresponding free volume decreases, so that the permeation of both macromolecules and small molecule gases is hindered, and thus the selectivity decreases. From the above, it can be seen that the B-S-8:2 membrane has a He / N2 ideal separation coefficient of 300 or more and a He / CH4 ideal separation coefficient of 240 or more, which is the highest among all the membranes and is much higher than the corresponding Knudsen diffusion coefficient. It is speculated that the two precursors are hydrolyzed and condensed into a uniform and stable network structure, so that the prepared copolymer polysilsesquioxane gas separation membrane has a relatively uniform and suitable effective pore size, so that molecular sieving can be effectively utilized to realize the separation of He / N2 and He / CH4. Figure 8

[0108] Based on the above detection results, it can be seen that the polysilsesquioxane separation membrane prepared by the application has good separation and purification effect on helium, and can be applied in the separation and purification of helium.

[0109] Example 6

[0110] The preparation raw material of the polysilsesquioxane layer in the polysilsesquioxane gas separation membrane of the present embodiment includes bridged silsesquioxane monomers and pendant silsesquioxane monomers in a molar ratio of 10:5. The bridged silsesquioxane monomers are 1,2-bis(triethoxysilyl)ethane, and the pendant silsesquioxane monomers are N-(trimethoxysilylpropyl)imidazole.

[0111] The preparation method of the polysilsesquioxane gas separation membrane of the present embodiment is as follows:

[0112] The bridged silsesquioxane monomers and the pendant silsesquioxane monomers are dissolved in anhydrous ethanol, and a hydrochloric acid solution with a concentration of 10.0 mmol / L is added dropwise under vigorous stirring to obtain a mixed solution. Then, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomers and the pendant silsesquioxane monomers in the mixed solution to 0.01%, and then the reaction is stirred at room temperature for 10 h to obtain a clear and transparent polysilsesquioxane sol.

[0113] ​The 0.2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 small particle sol, and the 2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are uniformly coated on the outer surface of the α-Al2O3 support in turn, and then calcined at 500°C for 10 min. The coating and calcination steps are repeated three times to form the α-Al2O3 particle layer on the outer surface of the α-Al2O3 support, which covers all the large pores on the surface of the α-Al2O3 support to avoid the appearance of pinholes on the separation membrane.

[0114] The boehmite sol and the SiO2-ZrO2 sol are uniformly coated on the α-Al2O3 particle layer in turn, and dried to form the transition layer, and the average pore size of the surface of the α-Al2O3 support is further reduced to about 1 nm.

[0115] Then, the 0.05 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 100°C under N2 atmosphere for 0.5 h, and the step is repeated once to obtain the polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0116] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0117] Example 7

[0118] The preparation raw material of the polysilsesquioxane layer in the polysilsesquioxane gas separation membrane of this embodiment includes the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in a molar ratio of 5:1. The bridged silsesquioxane monomer is 1,2-bis(triethoxysilyl)ethane, and the pendant silsesquioxane monomer is N-(trimethoxysilylpropyl)imidazole.

[0119] The preparation method of the polysilsesquioxane gas separation membrane of this embodiment is as follows:

[0120] The bridged silsesquioxane monomer and the pendant silsesquioxane monomer are dissolved in anhydrous ethanol, and then the 0.1 mmol / L hydrochloric acid solution is added dropwise under vigorous stirring to obtain a mixed solution. Then, anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomer and the pendant silsesquioxane monomer in the mixed solution to 10%. Then, the mixed solution is stirred at room temperature for 15 h to obtain a clear and transparent polysilsesquioxane sol.

[0121] The 0.2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 small particle sol, and the 2 μm α-Al2O3 particles are dispersed in the SiO2-ZrO2 sol to prepare the α-Al2O3 large particle sol. The α-Al2O3 small particle sol and the α-Al2O3 large particle sol are coated on the outer surface of the α-Al2O3 support in turn, and then calcined at 1200°C for 20 min. The coating and calcining steps are repeated 5 times to form the α-Al2O3 particle layer on the outer surface of the α-Al2O3 support, which covers all the macropores on the surface of the α-Al2O3 support to avoid the appearance of pinholes on the separation membrane.

[0122] The boehmite sol and the SiO2-ZrO2 sol are coated on the α-Al2O3 particle layer in turn, and dried to form the transition layer, and the average pore size of the surface of the α-Al2O3 support is further reduced to about 1 nm.

[0123] Then, the 5 wt% polysilsesquioxane sol is coated on the transition layer, and calcined at 400°C in N2 atmosphere for 2 hours, and the step is repeated 3 times to obtain the polysilsesquioxane gas separation membrane with smooth and uniform surface and no defects.

[0124] In this embodiment, the mass fraction of SiO2 in the SiO2-ZrO2 sol is 2%, and the mass fraction of ZrO2 is 20%. The mass fraction of boehmite in the boehmite sol is 5%.

[0125] The above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the present application, and all of them should be covered in the scope of the claims of the present application. The technical, shape and structure parts not described in detail in the present application are the known technology.

Claims

1. A polysilsesquioxane gas separation membrane, characterized by, The polysilsesquioxane layer includes bridged silsesquioxane monomers and pendant silsesquioxane monomers; The bridged silsesquioxane monomers are any one of 1,2-bis(triethoxysilyl)ethane, bis(triethoxysilyl)methane, 1,3-bis(triethoxysilyl)propane, and 1,2-bis(triethoxysilyl)benzene, and the pendant silsesquioxane monomers are N-(trimethoxysilylpropyl)imidazole. The gas separation membrane includes an α-Al2O3 support body, an α-Al2O3 particle layer, a transition layer, and a polysilsesquioxane layer formed in sequence from the inside to the outside, and the transition layer is formed by drying and sintering boehmite sol and SiO2-ZrO2 sol.

2. The polysilsesquioxane gas separation membrane according to claim 1, wherein, The molar ratio of the bridged silsesquioxane monomers to the pendant silsesquioxane monomers is (5-10):(1-5).

3. The polysilsesquioxane gas separation membrane according to claim 2, wherein, The α-Al2O3 particle layer contains α-Al2O3 particles with a particle size of 0.2 μm and 2 μm.

4. The method for producing a polysilsesquioxane gas separation membrane according to claim 1, characterized by, The method includes the following steps: The bridged silsesquioxane monomers and the pendant silsesquioxane monomers are dissolved in anhydrous ethanol, and then the solution is added dropwise into a hydrochloric acid solution under stirring to obtain a mixed solution, and then anhydrous ethanol is added to adjust the total mass fraction of the bridged silsesquioxane monomers and the pendant silsesquioxane monomers in the mixed solution to 0.01-10%, and then the solution is stirred at room temperature for 10-15 hours to obtain polysilsesquioxane sol; The outer surface of the α-Al2O3 support body is coated with α-Al2O3 particle sol, and then the coated support body is calcined at 500-1200°C for 10-20 minutes, and the coating and calcining steps are repeated 3-5 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body; The outer surface of the α-Al2O3 support body is coated with α-Al2O3 particle sol, and then the coated support body is calcined at 500-1200°C for 10-20 minutes, and the coating and calcining steps are repeated 3-5 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body; The outer surface of the α-Al2O3 support body is coated with α-Al2O3 particle sol, and then the coated support body is calcined at 500-1200°C for 10-20 minutes, and the coating and calcining steps are repeated 3-5 times to form an α-Al2O3 particle layer on the outer surface of the α-Al2O3 support body; 5. The method for producing a polysilsesquioxane gas separation membrane according to claim 4, characterized by, The concentration of the hydrochloric acid solution is 0.1-10 mmol / g.

6. The method for producing a polysilsesquioxane gas separation membrane according to claim 5, characterized by, The step of coating the outer surface of the α-Al2O3 support body with α-Al2O3 particle sol includes sequentially and uniformly coating the outer surface of the α-Al2O3 support body with α-Al2O3 small particle sol and α-Al2O3 large particle sol, the α-Al2O3 small particle sol is prepared by uniformly dispersing α-Al2O3 particles with a particle size of 0.2 μm in SiO2-ZrO2 sol, and the α-Al2O3 large particle sol is prepared by uniformly dispersing α-Al2O3 particles with a particle size of 2 μm in SiO2-ZrO2 sol.

7. The polysilsesquioxane gas separation membrane according to any one of claims 1-3 or prepared by the method according to any one of claims 4-6 in the separation and extraction of helium.

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