A mixed matrix membrane containing alcohol-phobic all-silica molecular sieve

Abstract

The present invention provides a mixed matrix membrane containing an alcohol-phobic all-silica molecular sieve. The mixed matrix membrane comprises a porous substrate and a silicone oil membrane supported on the porous substrate. The silicone oil membrane contains an MFI molecular sieve grafted with fluoroalkyl chains. By incorporating the alcohol-phobic all-silica molecular sieve into the silicone oil, the free volume and network structure of the polymer membrane are systematically controlled. This provides a rapid mass transfer channel for DMC molecules to travel within the membrane layer, reduces methanol adsorption and diffusion in the separation membrane, and improves the membrane's resistance to swelling in organic solvents.

Description

Technical Field

[0001] The present invention relates to a mixed matrix membrane containing an alcohol-phobic all-silica molecular sieve. The prepared mixed matrix membrane containing an alcohol-phobic all-silica molecular sieve can be used in environmental protection fields such as organic-organic azeotropic systems, recovery of organic volatile gases, organic solvent nanofiltration, carbon capture, and recovery of low-concentration organic matter in aqueous solutions. Background Art

[0002] The dimethyl carbonate (DMC) / methanol azeotropic system is a common separation system in the chemical industry, and membrane separation technology has become a popular technology for studying this system. Texaco, a US company, has studied the separation of DMC / methanol mixtures using a coupled process (distillation + pervaporation). Taking an annual DMC production of 907 tons as an example, the investment cost and operating expenses of this coupled process are only 40% of those of azeotropic distillation [1].

[0003] Therefore, for the separation of DMC / methanol azeotropic system, the preferential permeation of DMC pervaporation membrane shows the characteristics of energy saving and high efficiency. The research group of Professor Li Jiding of Tsinghua University prepared a polydimethylsiloxane (PDMS) homogeneous membrane that preferentially permeates DMC. When separating a 30 wt% DMC / methanol mixture at 40°C, the membrane flux and separation factor were 1.41 kg / m2h and 3.46 (the DMC concentration on the permeate side was 59.7 wt%) respectively [2]. Professor Zhou Haoli of Nanjing University of Science and Technology used PDMS / PVDF composite membrane to separate DMC / methanol system. At 40°C, PDMS membrane can concentrate 28 wt% DMC in the raw liquid to 60 wt%, with a membrane flux of 8-10 kg / m2h [3]. Lin et al. of Hefei University incorporated silane-modified SiO2 particles into silicone rubber to obtain a highly selective separation membrane. At 30 °C, the membrane flux was 1.2 kg / m2h and the separation factor was 5.60 (DMC concentration on the permeate side was 70 wt%) [4].

[0004] These studies indicate that PDMS has a greater affinity for DMC molecules than for methanol. However, the selectivity of planar PDMS composite membranes for DMC remains low, and the membranes are highly swellable with organic solvents, resulting in poor long-term stability. Therefore, there is an urgent need to optimize the structure and preparation methods of PDMS membranes to meet their application in dimethyl carbonate separation.

[0005] References:

[0006] [1] A. Jonquières, R. Clément, P. Lochon, J. Néel, M. Dresch, B. Chrétie, Industrial state-of-the-art of pervaporation and vapor permeation in the western countries, J. Membr. Sci., 206(2002) 87-117.

[0007] [2] Wang Luying, Li Jiding, Zhan Xia, Lin Yangzheng, Study on pervaporation separation of methanol / dimethyl carbonate mixture using polydimethylsiloxane membrane, Membrane Science and Technology, 29(2009) 7-11.

[0008] [3] HL Zhou, L. Lv, GP Liu, WQ Jin, WH Xing, PDMS / PVDFcomposite pervaporation membrane for the separation of dimethylcarbonate from a methanol solution, J. Membr. Sci., 471(2014) 47-55.

[0009] [4] ZH Liu, WH Lin, Q. Li, Q. Rong, HJ Zua, MH Sang,Separation of dimethyl carbonate / methanol azeotropic mixture by pervaporationwith dealcoholized room temperature-vulcanized silicone rubber / nanosilicahybrid active layer, Sep. Purif. Technol., 248 (2020) 116926. Summary of the Invention

[0010] The present invention aims to provide a mixed matrix membrane containing an alcohol-phobic all-silica molecular sieve, which can enhance DMC separation performance. This method facilitates the practical industrial application of membrane processes in environmental protection fields such as organic-organic azeotropes, organic volatile gas recovery, organic solvent nanofiltration, carbon capture, and recovery of low-concentration organic matter in aqueous solutions. Furthermore, this mixed matrix membrane exhibits significant separation efficiency for binary systems such as ester / alcohol and toluene / alcohol.

[0011] The present invention provides a mixed matrix membrane containing an alcohol-phobic all-silicon molecular sieve. The mixed matrix membrane comprises a porous substrate and a silicone oil membrane supported on the porous substrate. The silicone oil membrane contains a MFI molecular sieve grafted with fluoroalkyl chains.

[0012] Preferably, the porous substrate is a polymer substrate resistant to organic solvents, selected from one of polyimide, polytetrafluoroethylene, polyvinylidene fluoride, and polyacrylonitrile.

[0013] The present invention also provides a method for preparing a mixed matrix membrane containing an alcohol-phobic all-silica molecular sieve, the method comprising the following steps:

[0014] S1: Hydrophobic modification of all-silica molecular sieves: dissolve the perfluorinated reagent in the first organic solvent to prepare a perfluorinated reagent solution of a certain concentration; disperse the nano-scale MFI all-silica molecular sieve into the perfluorinated reagent solution, stir evenly to complete the grafting of fluoroalkyl chains on the surface of the MFI molecular sieve, and then centrifuge, wash with methanol, and vacuum dry;

[0015] S2: Preparation of mixed matrix membrane: prepare a silicone oil solution containing a second organic solvent, add the ground fluoroalkyl chain-grafted MFI molecular sieve into the silicone oil solution to form an alcohol-phobic all-silicon molecular sieve / silicone oil coating liquid, stir and degas at room temperature, pour and spread it in a mold on the surface of hot water, and then move the porous substrate pre-buried in the hot water at a certain speed and angle to pick up the coating liquid spread on the surface of the hot water to form a composite membrane, and finally heat it again to remove the solvent to form a mixed matrix membrane.

[0016] Preferably, the perfluorinated reagent is selected from one of perfluorododecyltrichlorosilane, perfluorooctyltrichlorosilane, tridecafluorooctyltrimethoxysilane (F13) and heptadecafluorodecyltrimethoxysilane (F17).

[0017] Preferably, the concentration of the perfluorinated reagent solution in step S1 is 0.1-5.0 wt%, the centrifugal speed is 10,000-20,000 rpm, and the drying temperature is 80-150°C.

[0018] Preferably, the first organic solvent is selected from one of ethanol, n-heptane and toluene, and the second organic solvent is selected from one of cyclohexanone, tetrahydrofuran and ethyl acetate.

[0019] Preferably, the concentration of the silicone oil solution in step S2 is 5-30 wt%, the doping amount of the alcohol-phobic all-silicon molecular sieve in the alcohol-phobic all-silicon molecular sieve / silicone oil coating solution is 10-70 wt%, the stirring time at room temperature is 0.5-3 h, and the hot water temperature is 60-100°C.

[0020] Preferably, the certain speed and angle in step S2 are respectively 5-20 cm / s, and the angle between the substrate and the horizontal line is in the range of 10-45°.

[0021] The mixed matrix membrane containing the alcohol-phobic all-silica molecular sieve prepared by the present invention is used for separation in a non-alcohol organic solvent / alcohol binary system, wherein the non-alcohol organic solvent preferentially permeates the alcohol.

[0022] Preferably, the non-alcohol organic solvent is dimethyl carbonate, and the alcohol is one of methanol and ethanol.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] First, the present invention incorporates an alcohol-phobic all-silica molecular sieve into silicone oil to orderly regulate the free volume and network structure of the polymer membrane, thereby providing a rapid mass transfer channel for the transmission of DMC molecules in the membrane layer, reducing the adsorption / diffusion of methanol by the separation membrane, and improving the swelling resistance of the separation membrane to organic solvents.

[0025] Secondly, the MFI molecular sieve is super-hydrophobic modified to enhance the interfacial compatibility between the MFI molecular sieve and the preferentially permeable DMC polymer, and the amphiphobic (hydrophobic and oleophobic) properties of the grafted fluorine element are utilized to reduce the solubility coefficient and diffusion coefficient of methanol molecules in the mixed matrix membrane.

[0026] In addition, in the coating liquid floating on the surface of hot water, the polymer wraps the nanoparticles, and the particles themselves also have mass. The hot water temperature promotes the rapid cross-linking and curing of the coating liquid on the surface of the base film, which can achieve the sedimentation and spreading of high-content MFI on the base film, and use a polymer layer of a certain thickness as the outermost skin layer, avoiding the non-selective defects caused by particle agglomeration. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Process flow chart for hot water-assisted rapid film formation of mixed matrix membranes

[0028] 1, 2, 3, 4- pulleys; 5- pointed scraper head (controls film thickness); 6- porous base membrane; 7- partition (the distance between partitions is the width of the base membrane).

[0029] Figure 2 (a) Mixed matrix membrane structure under ideal conditions; (b) Mixed matrix membrane structure at room temperature (the solvent evaporates slowly; the curing speed is slow, and the particles will settle); (c) Mixed matrix membrane structure under heating conditions (the solvent evaporates quickly; the curing speed is fast, and the particles can maintain good dispersion)

[0030] Figure 3 MFI molecular sieve before modification (a) and after modification (e); 50 wt% unmodified MFI / silicone oil mixed matrix membrane (b and f), 50 wt% F13 -MFI / silicone oil mixed matrix membrane (20℃ water) and 50 wt%F 13 -SEM images of the cross section and surface of the MFI / silicone oil mixed matrix membrane (80°C water). DETAILED DESCRIPTION

[0031] The MFI molecular sieve grafted with fluorosilane chains is dispersed into a silicone oil solution to form a silicone oil coating liquid containing MFI at a certain mass concentration. The silicone oil coating liquid containing MFI is poured onto a surface containing hot water to allow the coating liquid to be pre-crosslinked and the solvent to evaporate quickly. The porous polymer base membrane is driven by a continuous roller and the silicone oil containing MFI is compounded. The film thickness is controlled by a sharp scraper head, and the solvent is removed by secondary heating to obtain a mixed matrix composite membrane. The membrane preparation process device used in the present invention is as follows: Figure 1 As shown, it includes 1, 2, 3, 4-pulleys; 5-pointed scraper head (to control the film thickness); 6-porous base membrane; 7-partition (the spacing between the partitions is the width of the base membrane). This device can be used to achieve continuous preparation of flat membrane materials.

[0032] The present invention adopts hot water surface spreading, such as Figure 2 As shown, the solvent of the present invention evaporates quickly; the curing speed is fast, and the particles can maintain good dispersion. Compared with preparation at room temperature, it is closer to the mixed matrix membrane structure under ideal conditions. Example 1

[0033] Coating solution formulation: Dissolve 5g of vinyl silicone oil in tetrahydrofuran, stir directly for half an hour, and ultrasonically degas for 5 minutes. Pour the mixture onto the left side of separator 7. Because silicone oil is immiscible with water and is lighter than water, it can be spread evenly on the surface of 80°C hot water. A PVDF ultrafiltration membrane serves as the base membrane. The membrane is immersed in the 80°C hot water and moved via pulleys 1→2→3→4 at a rate of 3 meters per minute. The base membrane surface is then coated with vinyl silicone oil. A sharp scraper 5 is used to control the thickness of the separation layer with a 30-micron slit, completing the preparation of a vinyl silicone oil / PVDF composite membrane.

[0034] The vinyl silicone oil / PVDF composite membrane prepared in this example was measured to separate 30 wt% DMC-methanol at 40 °C. The average membrane flux and DMC concentration on the permeate side were 19 kg / m 2 h and 55.2 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 1.2 kg / m 2 h and 28.5 wt%. Example 2

[0035] Coating solution formula: 5g of unmodified MFI molecular sieve is added to 5g of vinyl silicone oil, using tetrahydrofuran as the solvent. The mixture is directly blended and stirred for half an hour, ultrasonically degassed for 5 minutes, and then poured onto the left side of the partition 7. Since silicone oil is immiscible with water and is lighter than water, it can be spread flat on the surface of 80°C hot water. PVDF ultrafiltration membrane is used as the base membrane. The base membrane is immersed in 80°C hot water and moved via pulleys 1→2→3→4 at a speed of 3 meters / minute. The surface of the base membrane is brought to the surface of the vinyl silicone oil coating. The separation layer thickness is controlled by a sharp scraper head 5 with a 30 micron slit thickness to complete 50 wt% F 13 -Preparation of MFI / vinyl silicone oil / PVDF composite membrane.

[0036] Determination of the 50 wt% F 13 -MFI / vinyl silicone oil / PVDF composite membrane, at 40 ℃, when separating 30wt% DMC-methanol, the average membrane flux and DMC concentration on the permeate side were 22.0 kg / m 2 h and 45.1 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 1.9 kg / m 2 h and 24.9 wt%. The morphology and size of the unmodified MFI molecular sieve are as follows Figure 3 The cross section and surface SEM images of the 50 wt% unmodified MFI / vinyl silicone oil / PVDF composite membrane precured at 80 °C are shown in a. Figure 3 As shown in (b, f). Example 3

[0037] 10g of ground MFI molecular sieve powder was added to 2 wt% tridecafluorooctyltrimethoxysilane (F 13 ) / methanol solution, stirred at 100 rpm for 12 hours, centrifuged, washed with methanol 3 times, and vacuum dried at 100℃ for 6 hours. After drying, grind and set aside. 13 The morphology and size of the modified MFI molecular sieve are as follows: Figure 3 As shown in e.

[0038] Coating solution formula: grind 5g F 13 The modified MFI molecular sieve was added to 5 g of vinyl silicone oil, and tetrahydrofuran was used as a solvent. The mixture was directly blended and stirred for half an hour, and ultrasonically degassed for 5 minutes. The mixture was then poured on the left side of the partition 7 and spread on the surface of 80 °C hot water. A PVDF ultrafiltration membrane was used as the base membrane. The base membrane was immersed in 80 °C hot water and moved through pulleys 1→2→3→4 at a speed of 3 m / min. The separation layer thickness was controlled by a sharp scraper head 5 with a 30 μm slit thickness to obtain a doping amount of 50 wt% F. 13 -Preparation of MFI / vinyl silicone oil / PVDF composite membrane.

[0039] Determination of the 50 wt% F 13 -MFI / vinyl silicone oil / PVDF composite membrane, at 40 °C, when separating 30 wt% DMC-methanol, the average membrane flux and DMC concentration on the permeate side were 13.6 kg / m 2 h and 69.9 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 1.4 kg / m 2 h and 35.2 wt%. 50 wt% F under 80 ℃ pre-curing 13 -SEM electron microscope images of the cross section and surface of MFI / vinyl silicone oil / PVDF composite membrane Figure 3 As shown in (d, h). Example 4

[0040] 10g of ground MFI molecular sieve powder was added to 2 wt% tridecafluorooctyltrimethoxysilane (F 13 ) / methanol solution, stirred at 100 rpm for 12 hours, centrifuged, washed with methanol 3 times, and vacuum dried at 100℃ for 6 hours. After drying, grind and set aside. 13 The morphology and size of the modified MFI molecular sieve are as follows: Figure 3 As shown in e.

[0041] Coating solution formula: grind 5g F 13 The modified MFI molecular sieve was added to 5 g of vinyl silicone oil, and tetrahydrofuran was used as a solvent. The mixture was directly blended and stirred for half an hour, and ultrasonically degassed for 5 minutes. The mixture was then poured on the left side of the partition 7 and spread on the surface of 20 °C hot water. A PVDF ultrafiltration membrane was used as the base membrane. The base membrane was immersed in 20 °C hot water and moved via pulleys 1→2→3→4 at a speed of 3 m / min. The separation layer thickness was controlled by a sharp scraper head 5 with a 30 μm slit thickness to obtain a doping amount of 50 wt% F. 13 -MFI / vinyl silicone oil / PVDF composite membrane.

[0042] Determination of the 50 wt% F 13 -MFI / vinyl silicone oil / PVDF composite membrane, at 40 °C, when separating 30 wt% DMC-methanol, the average membrane flux and DMC concentration on the permeate side were 10.2 kg / m 2 h and 54.9 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 0.99 kg / m 2 h and 31.0 wt%. 50 wt% F under 20 ℃ pre-curing 13 -SEM electron microscope images of the cross section and surface of MFI / vinyl silicone oil / PVDF composite membrane Figure 3As shown in (c, g). Example 5

[0043] 5g of ground MFI molecular sieve powder was added to 1.5 wt% heptafluorodecyltrimethoxysilane (F 17 The product was stirred at 100 rpm for 8 hours, centrifuged, washed with ethanol three times, and dried in a vacuum oven at 100°C for 6 hours. After drying, the product was ground and set aside.

[0044] Coating solution formula: 1.5g F 17 The modified MFI molecular sieve was added to 8.5 g of hydroxyl-containing silicone oil, cyclohexanone was used as the solvent, and the mixture was directly blended and stirred for 0.2 hours. Ultrasonic degassing was performed for 5 minutes, and then the mixture was poured on the left side of the partition 7 and spread on the surface of 90 °C hot water. The PTFE ultrafiltration membrane was used as the base membrane, and the base membrane was immersed in 80 °C hot water. The mixture was moved via pulleys 1→2→3→4 at a speed of 10 m / min. The separation layer thickness was controlled by a sharp scraper head 5 with a 60 μm slit thickness to obtain a doping amount of 15 wt% F. 17 -MFI / hydroxy silicone oil / PTFE composite membrane.

[0045] Determination of the 15 wt% F 17 -MFI / hydroxy silicone oil / PTFE composite membrane, at 40 ℃, when separating 30 wt% DMC-methanol, the average membrane flux and DMC concentration on the permeate side were 10.5 kg / m 2 h and 72.7 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 0.89 kg / m 2 h and 38.6 wt%. Example 6

[0046] Add 5 g of ground MFI molecular sieve powder to a 1.0 wt% perfluorododecyltrichlorosilane / ethanol solution, stir at 100 rpm for 6 hours, centrifuge, wash three times with ethanol, and dry under vacuum at 100°C for 6 hours. After drying, grind and set aside.

[0047] Coating solution formula: 4.5 g of perfluorododecyltrichlorosilane-modified MFI molecular sieve was added to 5.5 g of hydroxyl-containing silicone oil, ethyl acetate was used as the solvent, and the mixture was directly blended and stirred for 0.4 hour. Ultrasonic degassing was performed for 10 minutes, and then the mixture was poured on the left side of the partition 7 and spread flat on the surface of 100°C hot water. PAN ultrafiltration membrane was used as the base membrane, and the base membrane was immersed in 80°C hot water. The membrane was moved via pulleys 1→2→3→4 at a speed of 5 m / min, and the separation layer thickness was controlled with a 100 μm slit thickness via a sharp knife scraper 5 to obtain a perfluorododecyl-MFI / silicone oil / PAN composite membrane with a doping amount of 45 wt%.

[0048] The 45 wt% perfluorododecyl modified MFI / silicone oil / PAN composite membrane prepared in this example was measured to separate 30 wt% DMC-methanol at 40 °C. The average membrane flux and DMC concentration on the permeate side were 14.5 kg / m 2 h and 74.1 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 1.29 kg / m 2 h and 38.8 wt%. Example 7

[0049] Add 15 g of ground MFI molecular sieve powder to a 3.0 wt% perfluorooctyltrichlorosilane / methanol solution. Stir at 100 rpm for 8 hours, centrifuge, wash three times with methanol, and dry under vacuum at 100°C for 6 hours. After drying, grind and set aside.

[0050] Coating solution formula: 6.0 g of perfluorooctyltrichlorosilane-modified MFI molecular sieve was added to 4.0 g of vinyl silicone oil, toluene was used as the solvent, and the mixture was directly blended and stirred for 1.5 hours. Ultrasonic degassing was performed for 15 minutes, and then the mixture was poured on the left side of the partition 7 and spread flat on the surface of 70°C hot water. PI ultrafiltration membrane was used as the base membrane, and the base membrane was immersed in 80°C hot water. The membrane was moved via pulleys 1→2→3→4 at a speed of 2 m / min. The thickness of the separation layer was controlled by a sharp scraper 5 with a slit thickness of 80 μm to complete the preparation of a perfluorooctyl-MFI / vinyl silicone oil / PI composite membrane with a doping amount of 60 wt%.

[0051] The average membrane flux and DMC concentration on the permeate side of the 60 wt% perfluorooctyl-MFI / vinyl silicone oil / PI composite membrane prepared in this example were 21.7 kg / m2 and 21.7 kg / m3, respectively, when separating 30 wt% DMC-methanol at 40 °C. 2 h and 70.5 wt%; when separating 5 wt% ethanol-water, the average membrane flux and ethanol concentration on the permeate side were 1.66 kg / m 2 h and 39.5 wt%.

Claims

1. A method for preparing a mixed matrix membrane containing an alcohol-phobic all-silica molecular sieve, characterized in that: The mixed matrix membrane comprises a porous substrate and a silicone oil membrane supported on the porous substrate, wherein the silicone oil membrane contains an MFI molecular sieve grafted with a fluoroalkyl chain, wherein the perfluorinated reagent used in the MFI molecular sieve grafted with a fluoroalkyl chain is selected from the group consisting of perfluorododecyltrichlorosilane, perfluorooctyltrichlorosilane, tridecafluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane. The silicone oil coating solution used to prepare the mixed matrix membrane has a silicone oil solution concentration of 5-30 wt %, and the doping amount of the alcohol-phobic all-silica molecular sieve in the silicone oil coating solution is 10-70 wt %. The method comprises the following steps: S1: Hydrophobic modification of all-silica molecular sieves: a perfluorinated reagent is dissolved in a first organic solvent to prepare a perfluorinated reagent solution of a certain concentration; nano-scale MFI all-silica molecular sieves are dispersed in the perfluorinated reagent solution and uniformly stirred to complete the grafting of fluoroalkyl chains on the surface of the MFI molecular sieves, followed by centrifugation, methanol washing, and vacuum drying; S2: Preparation of mixed matrix membrane: prepare a silicone oil solution containing a second organic solvent, add the ground fluoroalkyl chain-grafted MFI molecular sieve into the silicone oil solution to form an alcohol-phobic all-silicon molecular sieve / silicone oil coating liquid, stir and degas at room temperature, pour and spread it in a mold on the surface of hot water, and then move the porous substrate pre-buried in the hot water at a certain speed and angle to pick up the coating liquid spread on the surface of the hot water to form a composite membrane, and finally heat it again to remove the solvent to form a mixed matrix membrane.

2. The method according to claim 1, characterized in that The porous substrate is a polymer substrate resistant to organic solvents, and is selected from one of polyimide, polytetrafluoroethylene, polyvinylidene fluoride, and polyacrylonitrile.

3. The method according to claim 1, characterized in that In step S1, the concentration of the perfluorinated reagent solution is 0.1-5.0 wt %, the centrifugal speed is 10,000-20,000 rpm, and the drying temperature is 80-150° C.

4. The method according to claim 1, characterized in that The first organic solvent is selected from one of ethanol, n-heptane and toluene, and the second organic solvent is selected from one of cyclohexanone, tetrahydrofuran and ethyl acetate.

5. The method according to claim 1, characterized in that In step S2, the stirring time at room temperature is 0.5-3 hours, and the hot water temperature is 60-100°C.

6. The method according to claim 1, characterized in that In step S2, the certain speed and angle are 5-20 cm / s, and the angle between the substrate and the horizontal line is in the range of 10-45°.

7. Use of the mixed matrix membrane containing alcohol-phobic all-silica molecular sieve obtained by the method according to claim 1 in separation in a non-alcohol organic solvent / alcohol binary system.

8. The use according to claim 7, characterized in that The non-alcohol organic solvent is dimethyl carbonate, and the alcohol is one of methanol and ethanol.

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