A method for preparing a polyamide gas separation membrane using a water-in-oil emulsion system

Abstract

The application belongs to the technical field of gas separation membranes, and particularly relates to a method for preparing a polyamide gas separation membrane by using a water-in-oil emulsion system. The application uses a specially designed water-in-oil emulsion system to replace the water phase in the traditional interfacial polymerization technology, effectively improves the interfacial polymerization reaction rate by increasing the active sites of two-phase monomer contact and the early diffusion of amine monomer, and can effectively avoid the hydrolysis of acyl chloride monomer, thereby creating favorable conditions for forming a thin and moderately dense polyamide membrane.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas separation membranes, and in particular relates to a method for preparing a polyamide gas separation membrane by utilizing a water-in-oil emulsion system. Background Art

[0002] At present, among the many technical routes for capturing CO2 from the flue gas of fossil fuel combustion, the membrane separation method that uses membrane materials to selectively separate different gases with different permeation rates is considered by most researchers to be a CO2 capture technology that can be prepared on a large scale and developed sustainably due to its advantages such as simple operation, low separation energy consumption and high separation efficiency.

[0003] Interfacial polymerization technology is an effective method for forming thin films by rapidly reacting two active monomers at the water-oil interface, and has been widely used in the preparation of reverse osmosis membranes and nanofiltration membranes. In the field of gas separation, the development of interfacial polymerization technology is still in its infancy. Therefore, interfacial polymerization technology has far-reaching development significance in the preparation of high-performance carbon capture composite membranes. However, the traditional "water first, oil later" interfacial polymerization process is not suitable for the preparation of gas separation membranes due to severe porosity. To solve the above problem, a hydrophobic intermediate layer is often introduced on the base membrane, and the "oil first, water later" interfacial polymerization process is considered to be a common method for the preparation of carbon capture membranes.

[0004] However, the "oil-first, water-later" interfacial polymerization process does not fundamentally solve the problems of the diffusion rate and diffusion mode of the two-phase monomers in the interfacial polymerization process. One reason is that the interfacial polymerization reaction involving the amine monomers used in the interfacial polymerization is very likely to cause the permeability of the polyamide membrane to drop significantly due to excessive cross-linking. The second reason is that the "oil-first, water-later" process makes it very easy for the first-coated oil phase monomer to undergo rapid hydrolysis when it comes into contact with the subsequent large amount of aqueous phase solution, resulting in insufficient interfacial polymerization reaction and making the prepared film very prone to defects. Therefore, there is an urgent need to optimize the existing preparation process of polyamide gas separation membranes to solve the above problems. Summary of the Invention

[0005] To address the above problems, the present invention adopts a specially designed oil-in-water emulsion system to replace the water phase in traditional interfacial polymerization technology. It effectively improves the interfacial polymerization reaction rate by increasing the active sites for contact between the two phase monomers and by the early diffusion of amine monomers. It can also effectively avoid the hydrolysis of acyl chloride monomers, creating favorable conditions for the formation of thin and moderately dense polyamide films.

[0006] The present invention provides a method for preparing a polyamide gas separation membrane using a water-in-oil emulsion system. The method comprises sequentially coating a base membrane with an organic solution containing polyacyl chloride monomers and a water-in-oil emulsion containing amine monomers, thereby forming a polyamide separation layer on the surface of the base membrane through an interfacial polymerization reaction. The water-in-oil emulsion comprises an amine monomer, a surfactant, water, and an organic solvent. The solvent used in the organic solution containing polyacyl chloride monomers is the same as the organic solvent in the water-in-oil emulsion. For example, if the organic solution containing polyacyl chloride monomers uses n-hexane as the solvent, the organic solvent in the water-in-oil emulsion is also n-hexane.

[0007] Preferably, the organic solvent is selected from one or more of hexane, pentane, heptane, octane, nonane, decane, undecane, dodecane, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M.

[0008] Preferably, the amine monomer is selected from one or more of aromatic amines, aliphatic amines, heterocyclic amines and long-chain polyamines, and the mass fraction of the amine monomer in the water-in-oil emulsion is 0.01-5wt%, preferably, the mass fraction is 0.01-0.5wt%; the surfactant is selected from one or more of ionic surfactants and non-ionic surfactants, preferably, the surfactant is an anionic surfactant, selected from one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate (sulfate), sodium stearate (carboxylate), potassium monododecyl phosphate (phosphate salt), and dioctyl sodium sulfosuccinate (succinate sulfonate); the mass volume ratio of the surfactant to the water-in-oil emulsion is 0.001-5 g:100 mL, preferably, the mass volume ratio is 100-500 mg:300 mL; the volume ratio of water to organic solvent in the water-in-oil emulsion is 1:0.01-100, preferably, 1:2-10.

[0009] Preferably, the water-in-oil emulsion contains / does not contain an acid absorbent.

[0010] Preferably, the water-in-oil emulsion is prepared by dissolving an amine monomer and a surfactant in water to form a mixed solution, and then adding the mixed solution into an organic solvent to form the water-in-oil emulsion.

[0011] Preferably, the base membrane is a microfiltration membrane, an ultrafiltration membrane, or a microfiltration membrane or ultrafiltration membrane coated with a hydrophobic coating on the surface. The material of the microfiltration membrane or ultrafiltration membrane is selected from one of polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polyimide, polyetherimide, polyacrylonitrile, polyphenylene ether, polyphenylene sulfide, polyetherketone, and polyaryletherketone. The hydrophobic coating is selected from one or more of polydimethylsiloxane (PDMS) and poly(trimethylsilyl) propyne (PTMSP).

[0012] Preferably, the coating time of the organic solution containing polyacyl chloride monomer on the base film is 1~300 s, preferably, the coating time is 30~300 s; the coating time of the water-in-oil emulsion on the base film is 1~300 s, preferably, the coating time is 30~180 s.

[0013] Preferably, a drying step is further performed after the interfacial polymerization reaction, wherein the drying temperature is 40-150° C. and the drying time is 0.005-24 h.

[0014] The present invention also provides a polyamide gas separation membrane, which is prepared by the above method for preparing a polyamide gas separation membrane using a water-in-oil emulsion system.

[0015] The polyamide gas separation membrane prepared by the present invention can be used in gas separation.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] First, for the "oil-first, water-later" process for preparing polyamide gas separation membranes, the present invention adopts an oil-in-water emulsion system to replace the water phase in traditional interfacial polymerization technology. By coupling the two methods of pre-diffusing amine monomers from the dispersed phase in the oil-in-water emulsion into the continuous phase and the continuous phase and the oil phase solution belonging to the same organic solvent, the rate of the interfacial polymerization reaction process is accelerated, the membrane thickness is reduced, and the membrane density is significantly enhanced, thereby greatly improving the permeability of the composite membrane while improving its selectivity.

[0018] Secondly, the method of interfacial polymerization proposed by the present invention using a water-in-oil emulsion instead of an aqueous phase solution avoids the problem of hydrolysis of the acyl chloride monomer caused by instantaneous contact with a large amount of water when the interfacial polymerization reaction occurs, because the continuous phase in the water-in-oil emulsion is an organic solvent of the same type as the oil phase solution. This avoids the use of an acid absorbent while achieving efficient utilization of the acyl chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Surface SEM image and water contact angle of the PDMS / PSf base film used in Example 1;

[0020] Figure 2The surface SEM image and water contact angle of membrane No. 1 prepared in Example 1;

[0021] Figure 3 This is a cross-sectional SEM image of membrane No. 1 prepared in Example 1;

[0022] Figure 4 This is a surface SEM image of membrane No. 4 prepared in Comparative Example 1;

[0023] Figure 5 The infrared spectra of the original PDMS / PSf base film, the No. 1 film prepared in Example 1, and the No. 4 film prepared in Comparative Example 1;

[0024] Figure 6 This is a mixed gas separation performance evaluation device used in the present invention. DETAILED DESCRIPTION

[0025] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0026] Example 1

[0027] The steps of preparing membrane No. 1 in Example 1 are as follows:

[0028] (1) The base membrane used was a polysulfone ultrafiltration membrane coated with a PDMS intermediate layer, wherein the PDMS intermediate layer had a thickness of 150 nm. Trimellitoyl chloride and n-hexane were mixed to form an organic solution containing 0.1 wt% trimesoyl chloride. This organic solution was applied to the base membrane for 3 minutes, and then the excess oil phase solution was discarded. The membrane was allowed to air dry to obtain the first coating.

[0029] (2) An aqueous phase solution consisting of 0.15 g piperazine monomer, 0.15 g sodium dodecylbenzenesulfonate and 100 mL water was placed in a three-necked flask with 200 mL of n-hexane and vigorously stirred at a stirring speed of 1000 r / min using a mechanical stirring method to form an oil-in-water emulsion. The emulsion was then applied on the first coating for 30 seconds to form a polyamide separation layer by interfacial polymerization, and then the excess solution was removed.

[0030] (3) Immediately place the membrane forming the polyamide separation layer in an oven for drying at a temperature of 60 °C for 6 h; after drying, membrane No. 1 is obtained.

[0031] Example 2

[0032] The only difference between Example 2 and Example 1 is that in step (2), an aqueous phase solution containing 0.15 g of piperazine monomer, 0.15 g of sodium dodecylbenzenesulfonate, 0.15 g of NaOH and 100 mL of water is vigorously stirred with 200 mL of n-hexane to form a water-in-oil emulsion.

[0033] Example 3

[0034] The only difference between Example 3 and Example 2 is that in step (2), the duration is 180 seconds.

[0035] Comparative Example 1

[0036] The only difference between Comparative Example 1 and Example 3 is that in step (2), an aqueous solution containing 0.15 g of piperazine monomer, 0.15 g of NaOH and 300 mL of water (without adding n-hexane) is applied on the first coating layer.

[0037] Comparative Example 2

[0038] The only difference between Comparative Example 2 and Example 2 is that in step (2), sunflower oil is used instead of n-hexane.

[0039] Comparative Example 3

[0040] The only difference between Comparative Example 3 and Example 2 is that: in step (1), sunflower seed oil is used instead of n-hexane; in step (2), sunflower seed oil is used instead of n-hexane to form a water-in-oil emulsion.

[0041] Comparative Example 4

[0042] The only difference between Comparative Example 1 and Example 1 is that in step (2), an aqueous solution containing 0.15 g of piperazine monomer, 0.15 g of NaOH, and 300 mL of water (without adding n-hexane) is applied on the first coating.

[0043] Performance Testing

[0044] The membrane samples prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests. The membrane mixed gas separation performance evaluation devices used were all independently developed by our laboratory. Figure 6 As shown, the membrane is sealed in the membrane pool, and the effective area of ​​the membrane pool is 19.26 cm 2 The retentate gas was vented, and He was used as the purge gas on the permeate side. The permeate side was maintained at atmospheric pressure. The permeate outlet flow rate was measured by an electronic soap film flowmeter, and the composition was determined by gas chromatography. The permeation rate of each gas component (in GPU) was calculated based on the feed gas composition, feed gas pressure, and permeate outlet flow rate. The separation factor between the two gases is the ratio of the corresponding gas permeation rates.

[0045] Gas separation membranes are often evaluated by permeation performance and selectivity. The permeation performance of separation membranes is usually evaluated by permeation rate ( R ) or the permeability coefficient ( P ) for evaluation, the permeation rate can better reflect the speed of gas passing through the separation membrane. The definition of permeation rate is shown in formula (1-1):

[0046] (1-1)

[0047] In the above formula, R i For components i The permeation rate through the separation membrane, in GPU (1 GPU = 10 -6 cm 3 (STP) cm - 2 s -1 cmHg -1 = 3.35 × 10 -10 mol m -2 s -1 Pa -1 ); Q i For components i The volume flow rate through a gas separation membrane at standard temperature and standard pressure, in cm 3 (STP) / s; P i It is a component i The partial pressure difference on both sides of the gas separation membrane, in cmHg; A is the effective membrane area, in cm 2 .

[0048] At the same time, the selectivity of the separation membrane is usually expressed by the separation factor ( ) to reflect that the size of the separation factor reflects the speed at which different components pass through the separation membrane. i and j The permeability ratio of ) or the permeability ratio ( ) is defined as the ideal separation factor, as shown in formula (1-2):

[0049] (1-2).

[0050] Performance test results

[0051] Table 1 Performance test results of membrane samples of Examples 1-3 and Comparative Examples 1-4

[0052]

[0053]

[0054] Approaching zero, the chromatogram cannot be detected

[0055] Combining Examples 1 and 2, the technical solution of the present invention can effectively avoid hydrolysis of oil phase monomers, thereby improving the gas separation performance of the composite membrane without using an acid absorbent. Combining Example 3 with Comparative Example 1, the composite membrane prepared using the emulsion method is more dense under the same reaction time conditions, and the selectivity is greatly improved compared to the composite membrane prepared by the conventional method without losing much permeability. Combining Examples 1 and 3, it can be seen that after shortening the reaction time to improve the permeability of the composite membrane, the permeability is improved while the selectivity of the composite membrane remains essentially unchanged, which shows that the strategy proposed by the present invention can effectively prepare thin and defect-free composite membranes. Combining Example 1 with Comparative Example 2, when the continuous phase in the oil-water emulsion uses a vegetable oil with a higher viscosity and the oil phase solvent uses n-hexane, the permeability of the prepared composite membrane decreases sharply. Combining Example 1 with Comparative Examples 1 and 2, when a similar strategy as the present invention is adopted, but the oil phase solvent is replaced with a vegetable oil consistent with the continuous phase of the emulsion, the vegetable oil penetrates into the pores of the composite membrane due to capillary action, causing the gas permeability of the prepared composite membrane to approach zero. Combining Example 1 with Comparative Example 4, when other conditions are exactly the same, the composite membrane prepared by the conventional method has defects due to insufficient reaction time.

[0056] Figure 1 The surface SEM image and water contact angle of the PDMS / PSf base membrane used in this study show the presence of a distinct papillary structure on the substrate surface. This rough micro-nanostructure results in a water contact angle of 110.6±2°. Therefore, due to the hydrophobicity of the base membrane, the composite membrane can only be prepared using an "oil-first, water-second" or "oil-first, emulsion" interfacial polymerization process.

[0057] Figure 2 The surface SEM image and water contact angle of membrane No. 1 prepared in Example 1 are shown in Table 1. Figure 2 The papillary structures on the surface of the basement membrane have significantly disappeared, indicating the successful preparation of the polyamide separation layer. Furthermore, the water contact angle of the prepared membrane No. 1 has increased to 10.61±2°, further confirming the successful preparation of the polyamide separation layer.

[0058] Figure 3 The cross-sectional SEM image of the No. 1 membrane prepared in Example 1 is shown in FIG. Figure 3The thickness of the upper layer of the prepared composite membrane is approximately 262 nm. It should be emphasized that the thickness of the polyamide separation layer cannot be measured independently due to its thinness. Therefore, 262 nm is the sum of the thicknesses of the polyamide separation layer and the PDMS intermediate layer.

[0059] Figure 4 The surface SEM image of the No. 4 membrane prepared in Comparative Example 1 is shown in FIG. Figure 4 The prepared polyamide separation layer exhibits significant wrinkles. This is due to the excessive reaction between the aqueous and oil-phase monomers, caused by increasing the reaction time to avoid membrane defects. While these wrinkles do increase the effective area for gas transfer, they also inevitably increase the thickness of the separation layer.

[0060] Figure 5 The infrared spectra of the original PDMS / PSf base film, the No. 1 film prepared in Example 1 and the No. 4 film prepared in Comparative Example 1 are shown in FIG. Figure 5 It can be seen that the original PDMS / PSf base film has a peak at 1256 cm -1 , 1100~1000 cm -1 and 839 cm -1 The characteristic absorption peaks of Si-CH3 bending vibration, Si-O-Si antisymmetric stretching vibration and Si-O-Si symmetric stretching vibration appeared at 1900 cm -1 and 1620 cm -1 The appearance of characteristic peaks indicated the successful preparation of the polyamide separation layer.

[0061] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a polyamide gas separation membrane using a water-in-oil emulsion system, characterized in that: The base film is coated with an organic solution containing polyacyl chloride monomers and an oil-in-water emulsion containing amine monomers in sequence, and a polyamide separation layer is formed on the surface of the base film through interfacial polymerization reaction, wherein the oil-in-water emulsion contains amine monomers, surfactants, water and organic solvents, and the solvent used in the organic solution containing polyacyl chloride monomers is the same as the organic solvent in the oil-in-water emulsion.

2. The method according to claim 1, wherein The organic solvent is selected from one or more of hexane, pentane, heptane, octane, nonane, decane, undecane, dodecane, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M.

3. The method according to claim 1, wherein The amine monomer is selected from one or more of aromatic amines, aliphatic amines, heterocyclic amines and long-chain polyamines, the mass fraction of the amine monomer in the water-in-oil emulsion is 0.01-5wt%, the surfactant is selected from one or more of ionic surfactants and non-ionic surfactants, the mass volume ratio of the surfactant to the water-in-oil emulsion is 0.001-5 g:100 mL; the volume ratio of water to organic solvent in the water-in-oil emulsion is 1:0.01-100.

4. The method according to claim 1, wherein The water-in-oil emulsion may or may not contain an acid absorber.

5. The method according to claim 1, wherein The water-in-oil emulsion is prepared by dissolving an amine monomer and a surfactant in water to form a mixed solution, and then adding the mixed solution into an organic solvent to form the water-in-oil emulsion.

6. The method according to claim 1, characterized in that The base membrane is a microfiltration membrane, an ultrafiltration membrane, or a microfiltration membrane or ultrafiltration membrane coated with a hydrophobic coating on the surface. The material of the microfiltration or ultrafiltration membrane is selected from one of polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polyimide, polyetherimide, polyacrylonitrile, polyphenylene ether, polyphenylene sulfide, polyetherketone, and polyaryletherketone. The hydrophobic coating is selected from one or more of polydimethylsiloxane (PDMS) and poly(trimethylsilyl)propyne (PTMSP).

7. The method according to claim 1, wherein The coating time of the organic solution containing polyacyl chloride monomer on the base film is 1 to 300 s, and the coating time of the water-in-oil emulsion on the base film is 1 to 300 s.

8. The method according to claim 1, wherein After the interfacial polymerization reaction, a drying step is further performed, wherein the drying temperature is 40-150° C. and the drying time is 0.005-24 h.

9. A polyamide gas separation membrane, characterized in that The polyamide gas separation membrane is prepared by the method for preparing a polyamide gas separation membrane using a water-in-oil emulsion system as described in claim 1.

10. Use of the polyamide gas separation membrane according to claim 9 in gas separation.

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