Nitrogen-oxygen separation method based on molecular sieve and hollow fiber membrane

Abstract

The invention provides a nitrogen-oxygen separation method based on a molecular sieve and a hollow fiber membrane, and belongs to the technical field of nitrogen-oxygen separation. According to the technical scheme, the TaON-based modified mesoporous molecular sieve and the hollow fiber membrane are prepared respectively and are combined to realize nitrogen-oxygen separation. Specifically, the preparation method comprises the following steps: firstly, calcining a mesoporous molecular sieve, then reacting with TaCl5 at 80 DEG C to obtain a mesoporous molecular sieve assembled with TaCl5, on the basis, oxidizing TaCl5 into Ta2O5, and then carrying out nitridation reaction to obtain a modified mesoporous molecular sieve; meanwhile, a silicate capillary tube is wrapped by paraffin, sodium chloride particles are attached, when sodium chloride is dissolved in an external solvent, a porous structure is formed on the surface of a wax layer, finally, the wax layer is removed through hydrofluoric acid corrosion and calcination, and the hollow fiber membrane is obtained. The molecular sieve and the hollow fiber membrane prepared by the invention have good nitrogen-oxygen separation performance, and the nitrogen-oxygen separation efficiency can be remarkably improved by combining the molecular sieve and the hollow fiber membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrogen-oxygen separation, and particularly to a nitrogen-oxygen separation method based on molecular sieve and hollow fiber membrane. Background Art

[0002] In the prior art, the methods for nitrogen-oxygen separation mainly include the following: Cryogenic air separation method: This method separates oxygen and nitrogen in air based on their different boiling points after liquefaction (the boiling point of liquid oxygen is -183°C, and the boiling point of liquid nitrogen is -196°C). By compressing and purifying air to liquefy it, and then separating liquid oxygen and liquid nitrogen through a rectification process, pure nitrogen is finally obtained. The cryogenic air separation method has complex equipment and a large floor area, and is suitable for large-scale industrial nitrogen production, but not for medium and small-scale nitrogen production. Pressure swing adsorption method (PSA): It separates based on the selective adsorption characteristics of carbon molecular sieve for oxygen and nitrogen. Under high pressure, the carbon molecular sieve adsorbs oxygen, and nitrogen passes through; when the adsorbent is saturated, the pressure is reduced to desorb oxygen, thereby achieving separation. The PSA method has simple equipment, high automation, fast gas production, and low operating cost, and is particularly suitable for medium and small-scale nitrogen production. Membrane separation method: It separates based on the different permeation rates of special polymer membranes for oxygen and nitrogen. Oxygen molecules are smaller and more active, and can pass through the membrane faster, while nitrogen molecules pass through more slowly. The membrane separation method is simple to operate and has a lower cost, but the separation effect is slightly worse than other methods. Pressure swing adsorption method: It separates based on the different adsorption selectivities of oxygen and nitrogen in the adsorbent, and realizes separation by adjusting temperature and pressure changes. Commonly used adsorbents include activated carbon and molecular sieve. The pressure swing adsorption method has a good separation effect, but requires more energy consumption and the adsorbent has a limited service life. Pressure friction fractionation method: It separates based on the difference in the permeability of oxygen and nitrogen in different permeable membranes. Commonly used permeable membranes include polymer membranes and ceramic membranes. This method has simple equipment and is suitable for large-scale continuous separation, but the cost of the permeable membrane is high and energy consumption is required. Molecular sieve adsorption method: It separates based on the difference in the adsorption capacity of molecular sieve for different gas molecules. The molecular sieve has a specific pore size and selectively adsorbs gas molecules of different sizes to achieve separation. Continuous liquefaction method: Air is cooled and gradually liquefied through multiple condensers, nitrogen is liquefied first and collected, while oxygen remains in the last condenser for collection. Atmospheric distillation method: Liquid air is gradually heated, and nitrogen and oxygen are separated using the difference in gas boiling points. Nitrogen has a lower boiling point and is first collected at the top of the condenser, while oxygen is collected at the bottom. Currently, the separation efficiency of nitrogen and oxygen in air by a single technical means is not high. In this case, how to develop a more efficient nitrogen-oxygen separation method is a technical problem to be solved. Summary of the Invention

[0003] The technical problem to be solved by the present invention is how to integrate different technical means to achieve more efficient nitrogen-oxygen separation.

[0004] To achieve the above technical objectives, the present invention adopts the following technical solutions: A method for separating nitrogen and oxygen based on molecular sieve and hollow fiber membrane, comprising the following steps: 1) Add TaCl5 to absolute ethanol, stir and dissolve to make a TaCl5 ethanol solution; add the calcined mesoporous molecular sieve and the above TaCl5 ethanol solution, and reflux in an 80°C oil bath for 20 hours; wash the precipitate thoroughly with absolute ethanol, and then dry the precipitate; then calcine in an air atmosphere to oxidize TaCl5 fixed in the pores to Ta2O5; nitride Ta2O5 assembled in the molecular sieve pores with ammonia to obtain a modified mesoporous molecular sieve; 2) Mix liquid paraffin and solid paraffin, and then melt them; put a silicate capillary into the melt, and take it out from the melt after its surface is completely wrapped by a wax layer to obtain a capillary with a surface wax layer thickness of 0.1 - 1 mm; sieve sodium chloride particles, take particles with a particle size range of 20 - 200 mesh, and adhere them to the wax layer on the surface of the capillary; immerse the capillary with the wax layer and sodium chloride particles adhered to its surface in water, and take it out after the sodium chloride is completely dissolved to obtain a porous wax layer on the surface of the capillary; immerse the capillary with the porous wax layer adhered to its surface in an aqueous hydrogen fluoride solution; calcine the capillary to remove the wax layer to obtain a hollow fiber membrane; 3) Pass the nitrogen-oxygen mixed gas successively through the mesoporous molecular sieve and the hollow fiber membrane, take the retained part to obtain oxygen, and take the passed part to obtain nitrogen.

[0005] Preferably, in step 1), the concentration of TaCl5 in the TaCl5 ethanol solution is 0.3 M.

[0006] Preferably, in step 1), the calcination temperature of the mesoporous molecular sieve is 900 - 950°C, and the heat preservation time is 2 - 3 h.

[0007] Preferably, in step 1), the drying temperature of the precipitate is 95 - 105°C, and the drying time is 12 - 16 h.

[0008] Preferably, in step 1), the calcination temperature in an air atmosphere is 800 - 860°C, and the heat preservation time is 60 - 80 min.

[0009] Preferably, in step 2), the weight percentage of liquid paraffin is 10 wt% - 80 wt%, and the weight percentage of solid paraffin is 20 wt% - 90 wt%.

[0010] Preferably, in step 2), the melting temperature is 60 - 65°C, and continuous stirring is carried out during the melting process until all are integrated, so that the viscosity of the melt is 0.1 - 10 poise.

[0011] Preferably, the concentration of the hydrogen fluoride aqueous solution in step 2) is 5wt% - 30wt%, and the duration of maintenance is 5 - 8h.

[0012] Preferably, the temperature for calcining the capillary in step 2) is 300 - 600°C, and the duration of heat preservation is 0.5 - 2 hours.

[0013] Preferably, the operating pressure for passing through the mesoporous molecular sieve in step 3) is 0.3 - 0.6MPa, and the operating pressure for passing through the hollow fiber membrane is 2.5 - 4.5 MPa.

[0014] In the present invention, the mesoporous molecular sieve is a conventional product, and MCM-41 or SBA-15 can be used. The acquisition method can be direct procurement or self-preparation by conventional methods.

[0015] The present invention provides a method for separating nitrogen and oxygen based on molecular sieves and hollow fiber membranes. This technical solution separately prepares a modified mesoporous molecular sieve based on TaON and a hollow fiber membrane, and the two are used together to achieve nitrogen-oxygen separation. Specifically, the present invention first calcines the mesoporous molecular sieve, and then reacts it with TaCl5 at 80°C to obtain a mesoporous molecular sieve assembled with TaCl5. On this basis, TaCl5 is oxidized to Ta2O5, and then a nitridation reaction is carried out to obtain a modified mesoporous molecular sieve; at the same time, paraffin is used to wrap the silicate capillary and sodium chloride particles are attached. When sodium chloride dissolves in the external solvent, a porous structure is formed on the surface of the wax layer. Finally, the wax layer is removed by hydrofluoric acid corrosion and calcination to obtain a hollow fiber membrane. The molecular sieve and hollow fiber membrane prepared by the present invention have good nitrogen-oxygen separation performance, and the combination of the two can significantly improve the nitrogen-oxygen separation efficiency. Specific Embodiments

[0016] The specific embodiments of the present invention will be described in detail below. To avoid excessive unnecessary details, the well-known structures or functions will not be described in detail in the following embodiments. The approximate language used in the following embodiments can be used for quantitative expression, indicating that a certain change in quantity is allowed without changing the basic function. Unless otherwise defined, the technical and scientific terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0017] Example 1 A method for separating nitrogen and oxygen based on molecular sieves and hollow fiber membranes, characterized by comprising the following steps: 1) Add TaCl5 to absolute ethanol, stir and dissolve it to make a TaCl5 ethanol solution; add the calcined mesoporous molecular sieve and the above TaCl5 ethanol solution, and reflux in an 80 °C oil bath for 20 hours; wash the precipitate thoroughly with absolute ethanol, and then dry the precipitate; then calcine in an air atmosphere to oxidize the TaCl5 fixed in the pores to Ta2O5; nitride the Ta2O5 assembled in the molecular sieve pores with ammonia to obtain a modified mesoporous molecular sieve; 2) Mix liquid paraffin and solid paraffin and then melt them; place the silicate capillary into the melt, and take it out from the melt after its surface is completely wrapped by the wax layer to obtain a capillary with a surface wax layer thickness of 0.1 mm; sieve the sodium chloride particles, take the particles with a particle size range of 20 mesh, and adhere them to the wax layer on the surface of the capillary; immerse the capillary with the wax layer and sodium chloride particles adhered to its surface into water, and take it out after the sodium chloride is completely dissolved to obtain a porous wax layer on the surface of the capillary; immerse the capillary with the porous wax layer adhered to its surface into an aqueous hydrogen fluoride solution; calcine the capillary to remove the wax layer to obtain a hollow fiber membrane; 3) Pass the nitrogen-oxygen mixed gas through the mesoporous molecular sieve and the hollow fiber membrane in sequence, take the retained part to obtain oxygen, and take the passed part to obtain nitrogen; In step 1), the concentration of TaCl5 in the TaCl5 ethanol solution is 0.3 M; in step 1), the calcination temperature of the mesoporous molecular sieve is 900 °C, and the heat preservation time is 2 h; in step 1), the drying temperature of the precipitate is 95 °C, and the drying time is 12 h; in step 1), the calcination temperature in an air atmosphere is 800 °C, and the heat preservation time is 60 min; in step 2), the weight percentage of liquid paraffin is 10 wt%, and the weight percentage of solid paraffin is 90 wt%; in step 2), the melting temperature is 60 °C, and continuous stirring is carried out during the melting process until all are integrated, so that the viscosity of the melt is 0.1 poise; in step 2), the concentration of the aqueous hydrogen fluoride solution is 5 wt%, and the retention time is 5 h; in step 2), the calcination temperature of the capillary is 300 °C, and the heat preservation time is 0.5 hours; in step 3), the operating pressure for passing through the mesoporous molecular sieve is 0.3 MPa, and the operating pressure for passing through the hollow fiber membrane is 2.5 MPa. After testing, the O2 permeation rate of the separation system in this example reaches 3100 GPU, and the O2 / N2 separation factor is 25.

[0018] Example 2 A nitrogen-oxygen separation method based on a molecular sieve and a hollow fiber membrane, which is characterized by including the following steps: 1) Add TaCl5 to absolute ethanol, stir to dissolve it to make a TaCl5 ethanol solution; add the calcined mesoporous molecular sieve and the above TaCl5 ethanol solution, and reflux in an 80 °C oil bath for 20 hours; wash the precipitate thoroughly with absolute ethanol, and then dry the precipitate; then calcine in an air atmosphere to oxidize TaCl5 fixed in the pores to Ta2O5; nitride Ta2O5 assembled in the molecular sieve pores with ammonia to obtain a modified mesoporous molecular sieve; 2) Mix liquid paraffin and solid paraffin, and then melt them; place a silicate capillary into the melt, and take it out from the melt after its surface is completely wrapped by a wax layer to obtain a capillary with a surface wax layer thickness of 1 mm; sieve sodium chloride particles, take particles with a particle size range of 200 mesh, and adhere them to the wax layer on the surface of the capillary; immerse the capillary with a wax layer and sodium chloride particles adhered to its surface into water, and take it out after the sodium chloride is completely dissolved to obtain a porous wax layer on the surface of the capillary; immerse the capillary with a porous wax layer adhered to its surface into an aqueous hydrogen fluoride solution; calcine the capillary to remove the wax layer to obtain a hollow fiber membrane; 3) Pass the nitrogen-oxygen mixed gas through the mesoporous molecular sieve and the hollow fiber membrane in sequence, take the retained part to obtain oxygen, and take the passed part to obtain nitrogen; In step 1), the concentration of TaCl5 in the TaCl5 ethanol solution is 0.3 M; in step 1), the calcination temperature of the mesoporous molecular sieve is 950 °C, and the heat preservation duration is 3 h; in step 1), the drying temperature of the precipitate is 105 °C, and the drying duration is 16 h; in step 1), the calcination temperature in an air atmosphere is 860 °C, and the heat preservation duration is 80 min; in step 2), the weight percentage of liquid paraffin is 80 wt%, and the weight percentage of solid paraffin is 20 wt%; in step 2), the melting temperature is 65 °C, and continuous stirring is carried out during the melting process until all are integrated, so that the viscosity of the melt is 10 poises; in step 2), the concentration of the aqueous hydrogen fluoride solution is 30 wt%, and the holding duration is 8 h; in step 2), the calcination temperature of the capillary is 600 °C, and the heat preservation duration is 2 hours; in step 3), the operating pressure for passing through the mesoporous molecular sieve is 0.6 MPa, and the operating pressure for passing through the hollow fiber membrane is 4.5 MPa. After testing, the O2 permeation rate of the separation system in this example reaches 2900 GPU, and at the same time, the O2 / N2 separation factor is 28.

[0019] Example 3 A nitrogen-oxygen separation method based on a molecular sieve and a hollow fiber membrane, which is characterized by including the following steps: 1) Add TaCl5 to absolute ethanol, stir to dissolve, and prepare a TaCl5 ethanol solution; add the calcined mesoporous molecular sieve and the above TaCl5 ethanol solution, and reflux in an 80 °C oil bath for 20 hours; wash the precipitate thoroughly with absolute ethanol, and then dry the precipitate; then calcine in an air atmosphere to oxidize TaCl5 fixed in the pores to Ta2O5; nitride Ta2O5 assembled in the molecular sieve pores with ammonia to obtain a modified mesoporous molecular sieve; 2) Mix liquid paraffin and solid paraffin, and then melt them; place the silicate capillary into the melt, and take it out from the melt after its surface is completely wrapped by the wax layer to obtain a capillary with a surface wax layer thickness of 0.5 mm; sieve the sodium chloride particles, take the particles with a particle size range of 100 mesh, and adhere them to the wax layer on the surface of the capillary; immerse the capillary with the wax layer and sodium chloride particles adhered to its surface into water, and take it out after the sodium chloride is completely dissolved to obtain a porous wax layer on the surface of the capillary; immerse the capillary with the porous wax layer adhered to its surface into an aqueous hydrogen fluoride solution; calcine the capillary to remove the wax layer to obtain a hollow fiber membrane; 3) Pass the nitrogen-oxygen mixed gas through the mesoporous molecular sieve and the hollow fiber membrane in sequence, take the retained part to obtain oxygen, and take the passed part to obtain nitrogen; In step 1), the concentration of TaCl5 in the TaCl5 ethanol solution is 0.3 M; in step 1), the calcination temperature of the mesoporous molecular sieve is 920 °C, and the heat preservation duration is 2.5 h; in step 1), the drying temperature of the precipitate is 100 °C, and the drying duration is 14 h; in step 1), the calcination temperature in an air atmosphere is 830 °C, and the heat preservation duration is 70 min; in step 2), the weight percentage of liquid paraffin is 50 wt%, and the weight percentage of solid paraffin is 50 wt%; in step 2), the melting temperature is 63 °C, and continuous stirring is carried out during the melting process until all are integrated, so that the viscosity of the melt is 5 poises; in step 2), the concentration of the aqueous hydrogen fluoride solution is 18 wt%, and the holding duration is 6.5 h; in step 2), the calcination temperature of the capillary is 450 °C, and the heat preservation duration is 1.3 hours; in step 3), the operating pressure for passing through the mesoporous molecular sieve is 0.5 MPa, and the operating pressure for passing through the hollow fiber membrane is 3.5 MPa. After testing, the O2 permeation rate of the separation system in this example reaches 3300 GPU, and at the same time, the O2 / N2 separation factor is 22.

[0020] The above has described the embodiments of the present invention in detail, but the above content is only the preferred embodiments of the present invention and is not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the scope of the application of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for nitrogen-oxygen separation based on molecular sieve and hollow fiber membrane, characterized in that It includes the following steps: 1) Add TaCl5 to absolute ethanol, stir and dissolve to make a TaCl5 ethanol solution; add the calcined mesoporous molecular sieve and the above TaCl5 ethanol solution, reflux in an 80°C oil bath for 20 hours; wash the precipitate thoroughly with absolute ethanol, and then dry the precipitate; then calcine in an air atmosphere to oxidize TaCl5 fixed in the pores to Ta2O5; nitride Ta2O5 assembled in the molecular sieve pores with ammonia to obtain a modified mesoporous molecular sieve; 2) Mix liquid paraffin and solid paraffin, and then melt them; place the silicate capillary into the melt, and take it out from the melt after its surface is completely wrapped by a wax layer to obtain a capillary with a surface wax layer thickness of 0.1 - 1 mm; sieve the sodium chloride particles, take the particles with a particle size range of 20 - 200 mesh, and adhere them to the wax layer on the surface of the capillary; immerse the capillary with the wax layer and sodium chloride particles adhered to its surface into water, and take it out after the sodium chloride is completely dissolved to obtain a porous wax layer on the surface of the capillary; immerse the capillary with the porous wax layer adhered to its surface into an aqueous hydrogen fluoride solution; calcine the capillary to remove the wax layer to obtain a hollow fiber membrane; 3) Pass the nitrogen-oxygen mixed gas successively through the mesoporous molecular sieve and the hollow fiber membrane, take the retained part to obtain oxygen, and take the passed part to obtain nitrogen.

2. The nitrogen-oxygen separation method based on molecular sieve and hollow fiber membrane according to claim 1, wherein, In step 1), the concentration of TaCl5 in the TaCl5 ethanol solution is 0.3 M.

3. The nitrogen-oxygen separation method based on molecular sieve and hollow fiber membrane according to claim 1, wherein In step 1), the calcination temperature of the mesoporous molecular sieve is 900 - 950°C, and the heat preservation duration is 2 - 3 h.

4. A method for nitrogen-oxygen separation based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 1), the drying temperature of the precipitate is 95 - 105°C, and the drying duration is 12 - 16 h.

5. A method for nitrogen-oxygen separation based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 1), the calcination temperature in an air atmosphere is 800 - 860°C, and the heat preservation duration is 60 - 80 min.

6. The nitrogen-oxygen separation method based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 2), the weight percentage of liquid paraffin is 10 wt% - 80 wt%, and the weight percentage of solid paraffin is 20 wt% - 90 wt%.

7. A method for nitrogen-oxygen separation based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 2), the melting temperature is 60 - 65°C, and continuous stirring is carried out during the melting process until all are integrated, so that the viscosity of the melt is 0.1 - 10 poise.

8. A method for nitrogen-oxygen separation based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 2), the concentration of the aqueous hydrogen fluoride solution is 5 wt% - 30 wt%, and the retention duration is 5 - 8 h.

9. A method for separating nitrogen and oxygen based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 2), the calcination temperature of the capillary is 300 - 600°C, and the heat preservation duration is 0.5 - 2 hours.

10. A method for nitrogen-oxygen separation based on molecular sieve and hollow fiber membrane according to claim 1, characterized in that, In step 3), the operating pressure for passing through the mesoporous molecular sieve is 0.3 - 0.6 MPa, and the operating pressure for passing through the hollow fiber membrane is 2.5 - 4.5 MPa.