CN114870637A - Preparation method of strong hydrophobic composite membrane - Google Patents

Abstract

The invention discloses a preparation method of a strong hydrophobic composite membrane, which comprises the steps of respectively dissolving 2-methylimidazole and zinc salt in anhydrous methanol to obtain a ligand solution and a zinc salt solution; then, quickly pouring the zinc salt solution into the ligand solution, reacting at room temperature, centrifuging, washing and drying to obtain ZIF-8; ultrasonically dispersing the obtained ZIF-8 in absolute methanol to obtain a uniform ZIF-8 dispersion liquid; dissolving imidazole derivatives in absolute methanol, dropwise adding a proper amount of triethylamine, and then quickly pouring the obtained ZIF-8 dispersion liquid into the anhydrous methanol to obtain a mixed solution; transferring to a polytetrafluoroethylene container, placing in an air-blast drying oven, fully reacting, centrifuging, washing and drying to obtain the strongly hydrophobic ZIF-8; dispersing the obtained strongly hydrophobic ZIF-8 in n-butanol to obtain a suspension, mixing and stirring the suspension and the polyether block amide solution for full reaction, and performing ultrasonic treatment and standing degassing to obtain a strongly hydrophobic ZIF-8/polyether block amide mixed solution; and casting to a polyether sulfone supporting layer, scraping a membrane, and drying to obtain the ZIF-8/polyether block amide composite membrane with strong hydrophobicity.

Description

A kind of preparation method of strong hydrophobic composite membrane

technical field

The invention belongs to the technical field of materials, and in particular relates to a preparation method of a strong hydrophobic composite membrane.

Background technique

At present, the shortage of resources and the deterioration of the environment have attracted global attention and become a worldwide problem that urgently needs to be solved. Renewable, new and clean energy has become a research hotspot around the world. As a substitute for petroleum, bioethanol can play an active role in the sustainable development of energy supply, and the use of gasoline blended with 10% ethanol can reduce harmful gas emissions from automobiles. Bioethanol has become a representative of alternative new energy. However, the water content in the biological fermentation broth is as high as 90%, and the energy consumption of enriching and concentrating bioethanol by rectification is too large. In recent years, the development of membrane separation technology has provided the possibility for the purification of bioethanol with low energy consumption. As a typical liquid mixture membrane separation method, pervaporation technology is driven by vapor pressure difference and is not limited by gas-liquid balance. It is widely used in organic matter dehydration and recovery of organic matter.

The development of high-efficiency separation membranes is the key to improving pervaporation performance, and the development of membrane materials is always the core. Metal-organic frameworks (MOFs) materials are a class of porous materials composed of metal ions or ion clusters connected with organic ligands. The channel can be adjusted and other characteristics. In addition, MOFs have the characteristics of selective adsorption to specific liquid molecules, and become emerging separation membrane materials, which play an important role in the separation of gas and liquid mixtures.

As a typical representative of Zeolitic Imidazolate Frameworks (ZIFs) materials, ZIF-8 has a SOD structure. It has good thermal and chemical stability, high specific surface area and porosity, adjustable pore structure and chemical properties, and is often used as a membrane material for gas or liquid separation.

Although the preparation method of ZIF-8 is simple and the overall performance is good, in the actual removal of ethanol from low-concentration ethanol aqueous solutions, the operating conditions have a great impact on the separation factor and permeation flux of the membrane, and other preparation conditions are ignored. .

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method of a strong hydrophobic ZIF-8/polyether block amide composite membrane, by enhancing the hydrophobicity of the filled particle ZIF-8, promoting its compatibility with polymers, eliminating interface defects and improving its separation It can significantly improve the hydrophobicity and alcohol affinity of the composite membrane, and optimize the separation performance of alcohol and water.

In order to achieve the above purpose, the technical solutions are as follows:

A preparation method of a strong hydrophobic composite membrane, comprising the following steps:

(1) Dissolve 2-methylimidazole and zinc salt in anhydrous methanol respectively to obtain a ligand solution and a zinc salt solution; then quickly pour the zinc salt solution into the ligand solution, react at room temperature, and centrifuge and wash , drying to obtain ZIF-8;

(2) ultrasonically dispersing the obtained ZIF-8 in anhydrous methanol to obtain a uniform ZIF-8 dispersion; dissolving the imidazole derivative in anhydrous methanol, adding an appropriate amount of triethylamine dropwise, and then rapidly dispersing the obtained ZIF-8 dispersion Pour it into it to obtain a mixed solution; transfer it to a polytetrafluoroethylene container, place it in a blast drying oven, fully react, and obtain strong hydrophobic ZIF-8 through centrifugation, washing, and drying;

(3) The obtained strong hydrophobic ZIF-8 was dispersed in n-butanol to obtain a suspension, mixed with the polyether block amide solution and stirred to fully react, and the strong hydrophobic ZIF-8/polyether block amide was obtained by ultrasonic and static degassing mixture;

(4) The obtained strong hydrophobic ZIF-8/polyether block amide mixed solution is cast to the polyether sulfone support layer, scraped and dried to obtain a strong hydrophobic ZIF-8/polyether block amide composite membrane.

According to the above scheme, in step (1), the molar ratio of 2-methylimidazole, zinc salt and anhydrous methanol is 1:(7-9):(600-800). The optimization is 1:8:700.

According to the above scheme, the molar ratio of ZIF-8, imidazole derivative, triethylamine and anhydrous methanol in step (2) is 1:(1.5-2.0):(1.8-2.2):(180-200). The optimization is 1:1:2:200.

According to the above scheme, the polyether block amide solution in step (3) is prepared by the following method:

The polyether block amide is dissolved in n-butanol and fully stirred to obtain a 5-8 wt% polyether block amide solution; the polyether block amide is PEBAX 2533.

According to the above scheme, the mass ratio of strongly hydrophobic ZIF-8 to polyether block amide in step (3) is 1:(7-39). Optimized to 1:9.

According to the above scheme, the polyethersulfone support layer in step (4) is prepared by the following method:

The polyethersulfone is dissolved in N,N-dimethylformamide, fully stirred to obtain a 15-20 wt% polyethersulfone solution, and cast to a non-woven fabric to obtain a polyethersulfone support layer.

According to the above scheme, the doping amount of strongly hydrophobic ZIF-8 in the strongly hydrophobic ZIF-8/polyether block amide composite film obtained in step (4) is less than or equal to 10wt%.

According to the above scheme, the zinc salt is zinc nitrate hexahydrate.

According to the above scheme, the imidazole derivative is 5,6-dimethylbenzimidazole.

The method firstly prepares ZIF-8, and then uses imidazole derivative 5,6-dimethylbenzimidazole, an organic ligand with hydrophobic group, to exchange 2-methylimidazole in the outer layer of ZIF-8, thereby Make ZIF-8 more hydrophobic. The strong hydrophobic ZIF-8/polyether block amide composite membrane was prepared by solution blending-casting method. The filler particles in the composite membrane are uniformly dispersed in the polymer without obvious interface defects, which effectively optimizes the pervaporation separation performance.

The present invention mainly from the viewpoints of enhancing the hydrophobicity of ZIF-8, eliminating interface defects and improving separation performance, post-synthesis modification of fresh ZIF-8 is carried out, and hydrophobic groups are introduced to obtain strong hydrophobic ZIF-8. Due to the introduction of various hydrophobic groups into the outer layer of ZIF-8, more ethanol molecules will be adsorbed, and the hydrophobicity of the membrane will also be improved, which will promote the selective adsorption-diffusion of ethanol molecules, and improve its permeability and separation factor.

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

Compared with the original PEBAX membrane, the flux and separation factor of the strong hydrophobic ZIF-8/polyether block amide composite membrane obtained by the present invention are significantly improved, breaking the "trade-off" effect between the flux and the separation factor. The results indicate that the strongly hydrophobic ZIF-8/polyether block amide composite membrane has great potential for application in dealcoholization by pervaporation.

The present invention utilizes the characteristic of rich chemical composition of MOFs, performs chemical post-synthesis modification on the material itself to exchange its ligands, and a composite membrane made of a polyether block amide matrix and a polyether sulfone support layer is used for ethanol in a low-concentration ethanol solution. The removal and recovery of ethanol/water improves the separation performance of ethanol/water. The membrane preparation process of the invention is simple, the separation performance of the composite membrane is optimized, and the application to the separation of ethanol and water has a strong competitive advantage.

Description of drawings

Figure 1: XRD pattern of the strongly hydrophobic ZIF-8 obtained in Example 1.

Figure 2: The water contact angle diagram of the strongly hydrophobic ZIF-8 obtained in Example 1.

FIG. 3 : SEM image of the polyether block amide composite film with a strong hydrophobic ZIF-8 content of 10 wt % obtained in Example 1.

Figure 4: The pervaporation performance diagram of the polyether block amide composite membrane with a strong hydrophobic ZIF-8 content of 10 wt% obtained in Example 1 and the membranes prepared in Comparative Examples 1 and 2 (left), Example 1 contains different strong Pervaporation test plot of hydrophobic ZIF-8 loading (right).

Detailed ways

The following examples further illustrate the technical solutions of the present invention, but are not intended to limit the protection scope of the present invention.

The specific embodiment provides a preparation method of a strong hydrophobic composite membrane, comprising the following steps:

(1) Dissolve 2-methylimidazole and zinc salt in anhydrous methanol respectively to obtain a ligand solution and a zinc salt solution; then quickly pour the zinc salt solution into the ligand solution, react at room temperature, and centrifuge and wash , drying to obtain ZIF-8;

(2) ultrasonically dispersing the obtained ZIF-8 in anhydrous methanol to obtain a uniform ZIF-8 dispersion; dissolving the imidazole derivative in anhydrous methanol, adding an appropriate amount of triethylamine dropwise, and then rapidly dispersing the obtained ZIF-8 dispersion Pour it into it to obtain a mixed solution; transfer it to a polytetrafluoroethylene container, place it in a blast drying oven, fully react, and obtain strong hydrophobic ZIF-8 through centrifugation, washing, and drying;

(3) The obtained strong hydrophobic ZIF-8 was dispersed in n-butanol to obtain a suspension, mixed with the polyether block amide solution and stirred to fully react, and the strong hydrophobic ZIF-8/polyether block amide was obtained by ultrasonic and static degassing mixture;

(4) The obtained strong hydrophobic ZIF-8/polyether block amide mixed solution is cast to the polyether sulfone support layer, scraped and dried to obtain a strong hydrophobic ZIF-8/polyether block amide composite membrane.

Specifically, in step (1), the molar ratio of 2-methylimidazole, zinc salt, and anhydrous methanol is 1:(7-9):(600-800). The optimization is 1:8:700.

Specifically, in step (2), the molar ratio of ZIF-8, imidazole derivative, triethylamine, and anhydrous methanol is 1:(1.5-2.0):(1.8-2.2):(180-200). The optimization is 1:1:2:200.

Specifically, in step (3), the polyether block amide solution is prepared by the following method:

The polyether block amide is dissolved in n-butanol and fully stirred to obtain a 5-8 wt% polyether block amide solution; the polyether block amide is PEBAX 2533.

Specifically, the mass ratio of the strongly hydrophobic ZIF-8 to the polyether block amide in step (3) is 1:(7-39). Optimized to 1:9.

Specifically, in step (4), the polyethersulfone support layer is prepared by the following method:

The polyethersulfone is dissolved in N,N-dimethylformamide, fully stirred to obtain a 15-20 wt% polyethersulfone solution, and cast to a non-woven fabric to obtain a polyethersulfone support layer.

Specifically, the doping amount of the strongly hydrophobic ZIF-8 in the strongly hydrophobic ZIF-8/polyether block amide composite film obtained in step (4) is less than or equal to 10 wt %.

Specifically, the zinc salt is zinc nitrate hexahydrate.

Specifically, the imidazole derivative is 5,6-dimethylbenzimidazole.

Example 1:

Step 1: 2-methylimidazole and zinc nitrate hexahydrate are respectively dissolved in anhydrous methanol, and the molar ratio of the three is 1:8:700. The zinc salt solution was quickly poured into the ligand solution, reacted at room temperature for 1 h, centrifuged, washed and dried to obtain ZIF-8.

Step 2: Disperse the ZIF-8 in step 1 into anhydrous methanol, ultrasonicate for 1 h to obtain a uniform suspension; dissolve 5,6-dimethylbenzimidazole in anhydrous methanol, and add triethylamine dropwise , and then quickly pour the ZIF-8 uniform suspension; transfer the above mixed solution to a polytetrafluoroethylene container, place it in a blast drying oven, fully react, and obtain strong hydrophobic ZIF-8 through centrifugation, washing and drying. The XRD patterns and water contact angle diagrams are shown in Figures 1 and 2.

Step 3: Disperse 8 g of polyethersulfone in N,N-dimethylformamide, heat and stir until completely dissolved, to obtain a casting solution with a mass fraction of 20 wt%, and cast it to a non-woven fabric to obtain a PES support layer.

Step 4: Disperse 2 g of polyether block amide PEBAX 2533 in n-butanol, heat and stir until completely dissolved, to obtain a matrix solution with a mass fraction of 5 wt %.

Step 5: Disperse the strong hydrophobic ZIF-8 of different quality in step 2 in n-butanol, and ultrasonically obtain a uniform suspension. Mix the dispersed suspension with the polyether block amide PEBAX 2533 solution in step 4, stir and mix thoroughly, and let stand for degassing to obtain a film casting liquid.

Step 6: Cast the film casting liquid in step 5 to the PES support layer in step 3, scrape the film and dry to obtain six different strong hydrophobic ZIF-8 contents (respectively 0wt%, 2.5wt%, 5wt%, 7.5 wt%, 10wt%, 12.5wt%) composite membrane. The SEM image of the polyether block amide composite film with the content of strongly hydrophobic ZIF-8 of 10 wt% is shown in Fig. 3 .

Figure 1 shows that the ZIF-8 particles modified with 5,6-dimethylbenzimidazole maintained the original crystal structure of the ZIF-8 particles without destruction.

Figure 2 shows that ZIF-8 particles modified with 5,6-dimethylbenzimidazole have enhanced hydrophobicity.

Figure 3 shows that ZIF-8 particles modified with 5,6-dimethylbenzimidazole have good compatibility with PEBAX 2533 matrix, and the modified ZIF-8 particles have good dispersibility.

Comparative Example 1

The ZIF-8 was ultrasonically dispersed into n-butanol to obtain a suspension; the dispersed suspension was mixed with a 5 wt % solution of polyether block amide PEBAX 2533, stirred and mixed well, and left to stand for degassing to obtain a casting liquid; then It is cast to the support layer in step 3, scraped and dried to obtain a ZIF-8/PEBAX 2533 composite film.

Comparative Example 2

Step 1: Disperse 8 g of polyethersulfone in N,N-dimethylformamide, heat and stir until completely dissolved to obtain a casting solution with a mass fraction of 20 wt%, and cast it to a non-woven fabric to obtain a PES support layer.

Step 2: Disperse 2 g of polyether block amide PEBAX 2533 in n-butanol, heat and stir until completely dissolved to obtain a matrix solution with a mass fraction of 5 wt %, and stand for degassing to obtain a casting solution.

Step 3: Cast the film casting liquid in step 2 to the PES support layer in step 1, scrape the film and dry to obtain a PEBAX2533 film.

The different membranes prepared in Example 1 were subjected to pervaporation tests in a device independently designed by the laboratory, and the downstream of the membrane was a vacuum environment. The operating temperatures were respectively 30°C, and the feed liquid composition was ethanol/water (5/95 wt%). The total flux increased with the content of modified ZIF-8, while the separation factor reached a maximum at 10% loading. See Figure 4 (right) for details.

Figure 4 (left) shows that the total flux of the polyether block amide composite membrane with a strongly hydrophobic ZIF-8 content of 10 wt% prepared in Example 1 is 312 g/m ² h, and the separation factor is 15.95. The total flux of the ZIF-8/polyether block amide composite membrane prepared in Comparative Example 1 was 269 g/m ² h, and the separation factor was 13.85. The total flux of the original polyether block amide composite membrane prepared in Comparative Example 2 was 210 g/m ² h, and the separation factor was 5.83. In addition, the total flux of the strong hydrophobic ZIF-8/polyether block composite membranes with different contents prepared in Example 1 increased with the increase of the loading amount, and the separation factor experienced a process of first increasing and then decreasing. When the loading amount was 10wt% , the separation factor reaches its maximum value.

Claims (9)

1. A preparation method of a strong hydrophobic composite membrane is characterized by comprising the following steps:

(1) respectively dissolving 2-methylimidazole and zinc salt in absolute methanol to obtain a ligand solution and a zinc salt solution; then, quickly pouring the zinc salt solution into the ligand solution, reacting at room temperature, centrifuging, washing and drying to obtain ZIF-8;

(2) ultrasonically dispersing the obtained ZIF-8 in absolute methanol to obtain a uniform ZIF-8 dispersion liquid; dissolving imidazole derivatives in absolute methanol, dropwise adding a proper amount of triethylamine, and then quickly pouring the obtained ZIF-8 dispersion liquid into the anhydrous methanol to obtain a mixed solution; transferring to a polytetrafluoroethylene container, placing in an air-blast drying oven, fully reacting, centrifuging, washing and drying to obtain the strongly hydrophobic ZIF-8;

(3) dispersing the obtained strongly hydrophobic ZIF-8 in n-butanol to obtain a suspension, mixing and stirring the suspension and the polyether block amide solution for full reaction, and performing ultrasonic treatment and standing degassing to obtain a strongly hydrophobic ZIF-8/polyether block amide mixed solution;

(4) and casting the obtained ZIF-8/polyether block amide mixed solution with strong hydrophobicity to a polyether sulfone supporting layer, scraping the membrane, and drying to obtain the ZIF-8/polyether block amide composite membrane with strong hydrophobicity.

2. The method for preparing the strongly hydrophobic composite membrane according to the claim, wherein in the step (1), the molar ratio of the 2-methylimidazole to the zinc salt to the anhydrous methanol is 1 (7-9) to (600-800).

3. The method for preparing the strongly hydrophobic composite membrane according to the claim, wherein the molar ratio of ZIF-8, the imidazole derivative, the triethylamine and the absolute methanol in the step (2) is 1 (1.5-2.0) to (1.8-2.2) to (180-200).

4. The method for preparing the strongly hydrophobic composite membrane according to the claim, wherein the polyether block amide solution in the step (3) is prepared by the following method: dissolving polyether block amide in n-butyl alcohol, and fully stirring to obtain a polyether block amide solution with the weight of 5-8 wt%; the polyether block amide is PEBAX 2533.

5. The preparation method of the strongly hydrophobic composite membrane, according to the claim, wherein the mass ratio of the strongly hydrophobic ZIF-8 to the polyether block amide in the step (3) is 1: (7-39).

6. The method for preparing the strong hydrophobic composite membrane according to the claim, wherein the polyethersulfone supporting layer in the step (4) is prepared by the following method: dissolving the polyether sulfone in N, N-dimethylformamide, fully stirring to obtain a 15-20 wt% polyether sulfone solution, and casting to a non-woven fabric to obtain a polyether sulfone supporting layer.

7. The method for preparing the strongly hydrophobic composite membrane according to the claim, wherein the doping amount of the strongly hydrophobic ZIF-8 in the strongly hydrophobic ZIF-8/polyether block amide composite membrane obtained in the step (4) is less than or equal to 10 wt%.

8. The method for preparing the strongly hydrophobic composite membrane according to claim, wherein the zinc salt is zinc nitrate hexahydrate.

9. The method for preparing a highly hydrophobic composite membrane according to claim, wherein the imidazole derivative is 5, 6-dimethylbenzimidazole.

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