A preparation method and application of in-situ MOF gel mixed matrix membrane

Abstract

The present invention provides a preparation method and application of an in-situ MOF gel-based mixed matrix membrane, relating to the field of gas separation membrane materials. The preparation method comprises the following steps: weighing a certain amount of dried Pebax particles and dissolving them in an ethanol-water mixed solvent at 90°C to obtain solution A; dissolving zinc nitrate hexahydrate in the ethanol-water mixed solvent to obtain solution B; dissolving dimethylimidazole in the ethanol-water mixed solvent to obtain solution C; adding a certain amount of triethylamine to solution C and mixing; successively adding solutions B and C to solution A, stirring to react, to obtain a mixed solution; transferring the mixed solution to a dialysis bag for dialysis; transferring the dialyzed mixed solution to a polytetrafluoroethylene culture dish for drying to obtain a mixed matrix membrane. The preparation method provided by the present invention is simple and easy to operate, and the prepared mixed matrix membrane has good interfacial compatibility with the MOF gel, which can increase the MOF loading capacity, thereby improving gas separation performance.

Description

Technical Field

[0001] The present invention relates to the field of gas separation membrane materials, and in particular to a preparation method and application of an in-situ MOF gel mixed matrix membrane Background Art

[0002] With the rapid development of the industrial economy, atmospheric carbon dioxide (CO2) concentrations have been increasing annually. According to a 2017 report, atmospheric CO2 concentrations reached an 800,000-year high of 405 ppm (parts per million), marking one of the hottest years ever, sparking widespread concern worldwide. As a major greenhouse gas, massive CO2 emissions are a major contributor to sea level rise, global warming, and climate change. Furthermore, CO2 has enormous application value in areas such as food processing, industrial production, and oil extraction. Therefore, efficiently separating CO2 from emission sources (such as flue gases from coal-fired power plants and steel mills) is of vital scientific significance and has enormous engineering application value. Compared to other separation technologies, membrane separation technology offers advantages such as low investment and energy consumption, and has gained significant attention and industrial application in recent years. However, conventional gas separation membranes struggle to achieve excellent separation performance by overcoming the trade-off between permeability and selectivity. Therefore, mixed matrix membranes (MMMs), which combine the advantages of organic and inorganic membranes, offer high selectivity, thermomechanical stability, and resistance to plasticization. They offer the best option for breaking through the upper limits of separation performance and have quickly become a research hotspot for high-performance gas separation membranes.

[0003] As a key component of mixed matrix membranes (MMMs), the choice of filler is crucial. While traditional inorganic fillers can improve gas separation performance, excessive loading can lead to the formation of non-selective voids, resulting in decreased separation performance. While mixed matrix membranes based on MOFs offer advantages over traditional inorganic fillers (MMMs), they can also agglomerate at high loadings, compromising separation performance.

[0004] MOF crystallization primarily involves two processes: nucleation and crystal growth. When the rate of nanoparticle aggregation exceeds the rate of crystal growth, a MOF gel forms. MOF gels exhibit a randomly cross-linked gel network structure and possess high permeability. Numerous reports have been published on the preparation of MMMs by mixing MOF fillers with polymers, and a smaller number on MOF gel MMMs. However, further research is needed to develop MOF-based MMMs that can achieve high loadings while maintaining good interfacial compatibility and high separation performance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to increase the interfacial compatibility between MOFs and polymers and improve the gas separation performance of MMMs, thereby providing an in situ MOF gel-based mixed matrix membrane and a preparation method thereof.

[0006] The technical solution of the present invention is: an in-situ MOF gel mixed matrix membrane and a preparation method thereof, comprising the following steps:

[0007] Step 1: Weigh a certain amount of dried Pebax-1657 particles, add an ethanol-water mixed solvent, and heat under reflux at 90°C to obtain solution A;

[0008] Step 2: Prepare the materials for synthesizing the MOF gel: zinc nitrate hexahydrate, dimethylimidazole, and triethylamine. Dissolve the zinc nitrate hexahydrate in an ethanol-water mixture to obtain solution B. Dissolve dimethylimidazole in an ethanol-water mixture and add a certain amount of triethylamine to the mixture to obtain solution C.

[0009] Step 3: Add solutions B and C to solution A successively, stir and react to obtain a mixed solution;

[0010] Step 4: The mixed solution is transferred to a dialysis bag for dialysis, and the dialyzed mixed solution is transferred to a polytetrafluoroethylene culture dish. The culture dish is placed in an oven and a vacuum oven for drying to obtain a mixed matrix membrane.

[0011] As a preferred embodiment, in step 1, the mass fraction of solution A is 3.0 wt.%; and the mass ratio of ethanol to water in the ethanol-water solvent is 9 / 1.

[0012] As a preferred embodiment, in step 2, the mass volume ratio of zinc nitrate hexahydrate to ethanol-water solvent in solution B is 0.024-0.072 g / ml; the mass volume ratio of dimethylimidazole to ethanol-water solvent in solution C is 0.0264-0.0792 g / ml, and the mass volume ratio of dimethylimidazole to triethylamine is 2.64-3.57 g / ml; and the mass ratio of ethanol to water in the ethanol-water mixed solvent is 9 / 1.

[0013] As a preferred embodiment, in step 3, the molar ratio of zinc nitrate hexahydrate in solution B to dimethylimidazole in solution C is 1 / 2; the mass ratio of zinc nitrate hexahydrate in solution B to Pebax-1657 in solution A is 0.15-0.45; and the mass ratio of ethanol to water in the ethanol-water mixed solvent is 9 / 1.

[0014] As a preferred solution, in step 3, solution B is first added to solution A, stirred for 5 minutes, and then solution C is added after mixing. The mixture is stirred and reacted for 60 minutes.

[0015] As a preferred solution, in step 4, the dialysate is a 90 wt.% ethanol-water mixed solution, and the dialysate is performed 4 times, with each dialysis lasting 12 hours.

[0016] As a preferred solution, in step 4, the film drying temperature in the oven is 40° C., and the film drying time is 24 h; the film drying temperature in the vacuum oven is 60° C., and the film drying time is 24 h.

[0017] The present invention also discloses an application of an in-situ MOF gel mixed matrix membrane in the selective separation of CO2 / N2 gases.

[0018] Compared with the prior art, the present invention has the following technical effects:

[0019] (1) The present invention utilizes a one-pot method to in situ grow MOF gel to increase the interfacial compatibility between the filler and the polymer, thereby preparing high-load MMMs with excellent performance.

[0020] (2) The present invention utilizes the network structure of the MOF gel itself to construct through-channels, thereby enhancing the gas separation performance.

[0021] Therefore, the in-situ MOF gel-based mixed matrix membrane of the present invention can be used to separate CO2 from mixed gases to achieve the purpose of reducing the greenhouse effect and alleviating ecological pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart for preparing the mixed matrix membrane of the present invention.

[0023] Figure 2 Schematic diagram of the mixed matrix membrane separation prepared by the present invention. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below with reference to the accompanying drawings and implementation examples. In the present invention, unless otherwise specified, the raw materials required for preparation are all commercially available products well known to those skilled in the art.

[0025] See also Figure 1 In the preparation method of the mixed matrix membrane of the present invention, a zinc salt solution and a mixed solution of dimethylimidazole and triethylamine are successively added to a Pebax solution and stirred to perform an in situ growth reaction; the reacted solution is placed in a dialysis bag for dialysis; after the dialysis is completed, the dialyzed solution is transferred to a polytetrafluoroethylene culture dish, and the mixed solution is dried to form a membrane.

[0026] See also Figure 2 In the mixed matrix membrane prepared by the present invention, a network of MOF gel-penetrating channels is formed, thereby improving the gas permeation selectivity.

[0027] Example Preparation of Mixed Matrix Membranes:

[0028] (1) Preparation of Pebax solution: First, weigh 3.0 g of dried Pbeax-1657 particles and transfer them to a three-necked flask. Add 100 g of a 90 wt.% ethanol-water mixed solvent to the three-necked flask. Insert a condenser into the three-necked flask, place the three-necked flask in an oil bath, and heat and stir at 90°C for 60 min to obtain a 3.0 wt.% Pebax solution.

[0029] (2) Preparation of reactant solutions: 0.12 g, 0.24 g, and 0.36 g of zinc nitrate hexahydrate were weighed and placed in experimental bottles numbered 1, 2, and 3, and 5 ml of a 90 wt.% ethanol-water mixed solvent was added to each of the bottles to prepare zinc nitrate solutions. 0.132 g, 0.264 g, and 0.396 g of dimethylimidazole were weighed and placed in experimental bottles numbered A, B, and C, and 5 ml of a 90 wt.% ethanol-water mixed solvent was added to each of the bottles to prepare dimethylimidazole solutions. 50 μl, 80 μl, and 110 μl of triethylamine were added to bottles A, B, and C, respectively, and the mixture was mixed.

[0030] (3) Synthesis of ZIF-8 gel: Weigh three 15g portions of Pebax solution into reaction bottles numbered I, II, and III. Place the three reaction bottles on a stirring table and start stirring at a speed of 600 rpm. Add the solutions in experimental bottles No. 1, 2, and 3 to reaction bottles No. I, II, and III respectively. After mixing, add the solutions in experimental bottles No. A, B, and C respectively. Stir and react for 60 minutes.

[0031] (4) Preparation of mixed matrix membrane: The reaction solutions in reaction bottles I, II, and III were transferred to dialysis bags and dialysis was started. The dialysate was a 90 wt.% ethanol-water mixed solution. The dialysis time was 12 h and the number of dialysis was 4 times. After the dialysis was completed, 8 ml of the dialyzed solution and the original Pebax solution were transferred to a polytetrafluoroethylene culture dish, dried in a 40°C oven for 24 h, and then the culture dish was transferred to a vacuum oven at 60°C and dried for 24 h to finally obtain the desired mixed matrix membrane.

[0032] Comparative Example: Preparation of mixed matrix membrane by direct blending method:

[0033] (1) Preparation of ZIF-8 gel particles: Weigh 0.96 g of zinc nitrate hexahydrate and 1.056 g of dimethylimidazole and dissolve them in 20 ml of a 90 wt.% ethanol-water mixed solvent to obtain a solution of the two; add 320 μl of triethylamine to the dimethylimidazole solution and mix well to obtain a mixed solution; add the zinc nitrate hexahydrate solution to 60 g of a 90 wt.% ethanol-water mixed solution and stir for 5 min at a stirring speed of 600 rpm; add the dimethylimidazole-triethylamine mixed solution to the zinc nitrate hexahydrate solution and stir for 60 min; the reacted solution is evenly divided into centrifuge tubes and centrifuged twice at a centrifugal speed of 10,000 rpm for 90 min / time; first transfer the centrifuged product to an oven and dry it at 120°C for 12 h, then transfer it to a vacuum oven and dry it at 120°C for 12 h to obtain ZIF-8 gel particles.

[0034] (2) Preparation of mixed matrix membrane: 10 g of the Pebax solution in the example was weighed in a small glass bottle, 0.045 g of ZIF-8 gel particles was added thereto, and the mixture was stirred with a magnetic stirrer for 60 min at a stirring speed of 600 rpm to obtain a mixed solution; the mixed solution was transferred to a polytetrafluoroethylene culture dish and dried in a 40°C oven for 24 h, and then the culture dish was transferred to a 60°C vacuum oven and dried for 24 h to finally obtain the desired mixed matrix membrane.

[0035] The gas permeability coefficient and selectivity test procedures in the following examples and comparative examples are as follows: The prepared mixed matrix membranes were tested under operating conditions of 35°C and 2 bar. Their permeability performance was determined using the Tima-lag method (constant volume-variable pressure method). Upstream gas was controlled by a manual valve and pressure gauge to enter the upper part of the membrane pool and adjusted to the required pressure. To start the test, the manual valve on the upper side of the membrane pool was opened, and the gas permeated through the MMMs in the membrane pool to the lower part. The pressure gauge below displayed the pressure change on the downstream side of the membrane pool. Before testing, all other gases in the pipeline and permeation pool were evacuated using a vacuum pump.

[0036] The permeability coefficient and selectivity of the gas in the membrane are calculated as follows:

[0037]

[0038]

[0039] Where i and j represent different gases. i 、P j is the permeability coefficient of gas i, j in the membrane, the unit is Barrer (1Barrer=1×10 -10 cm 3 (STP)cm / (cm 2·s·cmHg); L is the thickness of the film, in cm; V d is the volume of the downstream side, in cm 3 ; A is the effective membrane area, unit cm 2 ; R is the universal gas constant, unit is Pa·m 3 ·mol -1 ·K -1 ; T is the permeation chamber temperature, unit K; P0 is the upstream pressure, unit cmHg; is the fitting line coefficient of the curve obtained by the time-lag method for gas i, in Pa / s; i / j Select the separation factor for the gases gas i and gas j.

[0040] The gas separation performance of the MMMs prepared in the examples and comparative examples was tested at 35°C and 2 bar. The test results are shown in Table 1.

[0041] Table 1

[0042]

[0043] Results: As shown in Table 1, for the mixed matrix membranes prepared in the examples, as the mass fraction of gelled ZIF-8 in the membrane increased from 0 to 45 wt.%, the permeability coefficients for CO₂ and N₂ gradually increased, while the CO₂ / N₂ selectivity remained essentially unchanged, and the performance of MMMs gradually improved. In contrast, for the mixed matrix membranes prepared in the comparative examples, the selectivity of the membranes decreased significantly at the same gelled ZIF-8 content. This demonstrates that mixed matrix membranes prepared based on in situ gelled MOF can effectively improve the interfacial compatibility between the gelled MOF and the polymer matrix, enhancing the separation performance of MMMs.

[0044] The above-described embodiments are preferred examples of the present invention, but do not limit the scope of application of the present invention. Appropriate improvements can be made without departing from the principles of the present invention, and these improvements should also be considered as the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ MOF gel mixed matrix membrane, characterized in that: The following steps are involved: (1) Weigh a certain amount of dried Pebax-1657 particles, add ethanol-water mixed solvent, and heat under reflux at 90 °C to obtain solution A; (2) Prepare the materials for synthesizing gel MOF: zinc nitrate hexahydrate, dimethylimidazole, and triethylamine. Dissolve zinc nitrate hexahydrate in an ethanol-water mixed solvent to obtain solution B. Dissolve dimethylimidazole in an ethanol-water mixed solvent, and add a certain amount of triethylamine to the mixed solution to obtain solution C. (3) Add solutions B and C to solution A successively, stir and react to obtain a mixed solution; (4) The mixed solution is transferred to a dialysis bag for dialysis, and the dialyzed mixed solution is transferred to a polytetrafluoroethylene culture dish. The culture dish is placed in an oven and a vacuum oven for drying to obtain a mixed matrix membrane.

2. The method according to claim 1, characterized in that In step (1), the mass fraction of the solute Pebax-1657 in solution A is 3.0 wt %; and the mass ratio of ethanol to water in the ethanol-water mixed solvent is 9 / 1.

3. The method according to claim 1, characterized in that In step (2), the mass volume ratio of zinc nitrate hexahydrate to the ethanol-water mixed solvent in solution B is 0.024-0.072 g / ml; the mass volume ratio of dimethylimidazole to the ethanol-water mixed solvent in solution C is 0.0264-0.0792 g / ml, and the mass volume ratio of dimethylimidazole to triethylamine is 2.64-3.57 g / ml; and the mass ratio of ethanol to water in the ethanol-water mixed solvent is 9 / 1.

4. The method according to claim 1, wherein In step (3), the molar ratio of zinc nitrate hexahydrate in solution B to dimethylimidazole in solution C is 1 / 2; and the mass ratio of zinc nitrate hexahydrate in solution B to Pebax-1657 in solution A is 0.15-0.

45.

5. The method according to claim 1, wherein In step (3), solution B was first added to solution A and stirred for 5 min. After mixing, solution C was added and the mixture was stirred for 60 min.

6. The method according to claim 1, characterized in that In step (4), the dialysate is an ethanol-water mixed solvent with 90 wt% ethanol, and the dialysate is performed 4 times, each time for 12 h.

7. The method according to claim 1, characterized in that In step (4), the film drying temperature in the oven is 40°C and the film drying time is 24 h; the film drying temperature in the vacuum oven is 60°C and the film drying time is 24 h.

8. An in situ MOF gel-based mixed matrix membrane prepared according to the method of any one of claims 1 to 7.

9. Use of an in-situ MOF gel mixed matrix membrane prepared according to the method of any one of claims 1 to 7 in selective separation of CO2 / N2 mixed gases.

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