CN117160255A - MOF-303/PIM-1 mixed matrix membrane, preparation method and application thereof - Google Patents

Abstract

The invention relates to the field of gas separation technology and discloses a MOF-303/PIM-1 mixed matrix membrane, a preparation method and its application. In this invention, the metal-organic framework MOF-303 is evenly blended into the PIM-1 matrix through physical blending and ultrasonic dispersion, and the MOF-303/PIM-1 film prepared by the solution casting method has excellent anti-resistance properties. Aging performance and good long-term stability. The mixed matrix membrane with 30 wt.% MOF‑303 particles still has good separation performance for CO ₂ /CH ₄ mixed gas after 150 days of aging ( , ), compared with pure PIM‑1 membrane, it has a higher and more stable gas permeability coefficient and separation selectivity of CO ₂ .

Description

MOF-303/PIM-1 mixed matrix membrane, preparation method and application

Technical field

The invention belongs to the technical field of gas separation membranes, and specifically relates to a MOF-303/PIM-1 mixed matrix membrane and its preparation method and application.

Background technique

The explosive growth of population and the rapid advancement of industrialization have increased the consumption of fossil energy in all walks of life, resulting in a substantial increase in greenhouse gas emissions. The emissions of _CO2 in greenhouse gases are far greater than those of ozone and nitrous oxide. and other gas emissions, so in order to slow down the further intensification of the greenhouse effect, it is necessary to take effective measures to increase the utilization of clean energy such as natural gas and biogas energy and strengthen the capture of CO ₂ . At present, natural gas accounts for about 25% of the total primary energy. During its extraction process, the excessive CO ₂ gas will not only reduce the calorific value of natural gas, but also corrode gas pipelines and increase gas costs. Currently developed decarbonization technologies include chemical absorption, physical adsorption, cryogenic distillation and membrane separation technology. Among them, membrane separation technology has become the most competitive among many CO ₂ separation technologies due to its low investment costs and operating expenses, easy operation and environmental friendliness. According to the different membrane preparation materials, membranes can be divided into the following three categories: inorganic membranes, polymer membranes and mixed matrix membranes (MMMs). Among them, the dense inorganic membrane can have high gas permeation flux and gas separation selectivity at the same time, making its separation performance of mixed gases easily exceed the Robeson limit. However, the texture of finished inorganic membranes is generally brittle and expensive, which limits their development in large-scale applications. Polymer membranes have the advantages of a wide range of materials, low manufacturing costs per unit membrane area, and good mechanical properties. However, their low separation selectivity has become the biggest drawback. Excellent gas separation membrane materials should have both high gas separation performance (permeability and selectivity) and high stability. Therefore, inorganic fillers are incorporated into the polymer matrix to prepare MMMs that overcome the shortcomings of single components and effectively combine the advantages of inorganic membranes and polymer membranes, becoming one of the current research hotspots.

Among many polymer matrices, the free volume fraction (FFV) and CO ₂ permeability coefficient of general glassy polymers are usually relatively low, while intrinsically microporous polymers (PIMs) with rigid microporous structures have low The molecular structure skeleton limits the free rotation of the polymer main chain and hinders the effective stacking between molecular chains, allowing PIMs to exhibit excellent gas separation performance while having high FFV. However, the aging problem has always restricted the further development of PIMs materials. In addition, how to ensure the long-term stability of its internal inherent micropores and achieve the long-term stability of the separation of MMMs using PIMs materials as membrane matrix has also become a key point that this type of membrane materials need to overcome. question.

The introduction of nanoparticles and microporous organic fillers is one of the effective methods to inhibit membrane aging and maintain long-term stability of separation. Among many fillers, MOFs are very suitable as supporting particles for MMMs due to their high specific surface area, superior molecular sieving ability, modifiable pore structure, and good chemical stability. In recent years, a series of MOFs separation membranes prepared with PIM-1 as the matrix have emerged, showing good gas selective separation. For example, MMMs made from PEG-POSS filler and PIM-1 show ultra-high CO ₂ /CH ₄ selective separation, but their CO ₂ permeability coefficient is low and does not have long-term separation stability; some studies have used MUF-15 filler MMMs prepared with PIM-1 have excellent performance in CO ₂ permeability coefficient, but are not outstanding in gas pair selectivity and lack research on anti-aging properties; MMMs prepared from KAUST-7 and PIM-1 Separation membranes are one of the few MMMs that has been studied on anti-aging properties, but there is still room for further improvement in its ability to suppress the decrease in CO ₂ and CH ₄ permeability coefficients. Therefore, even though there are currently MOFs fillers combined with PIM-1 to generate MMMs for selective separation of CO ₂ and CH ₄ gases, they have both high CO ₂ permeability coefficient and high CO ₂ /CH ₄ permeability selectivity, and maintain good MOFs-based MMMs that separate long-term stability and anti-aging properties still need further research and implementation.

Contents of the invention

In order to separate CO ₂ in the mixed gas, the purpose of the present invention is to provide a MOF-303/PIM-1 membrane and its preparation method.

The technical solution of the present invention is: a MOF-303/PIM-1 membrane and its preparation method, which includes the following steps:

Step 1: Evenly disperse MOF-303 in the solvent through ultrasound to obtain MOF-303 suspension;

Step 2: Dissolve polymer PIM-1 in the solvent and filter to obtain PIM-1 polymer solution;

Step 3: Mix the PIM-1 polymer solution and MOF-303 suspension evenly to obtain a casting liquid;

Step 4: After the casting liquid is deaerated, pour it into a mold to form a film, and then dry it to remove the residual solvent to obtain the MOF-303/PIM-1 membrane (MMMs).

As a preferred version, in step 1, the average size of MOF-303 is 50 nm, and the dispersed solvent can be one of chloroform, dichloromethane, N,N-dimethylamide or N-methylpyrrolidone. species, the mass fraction of MOF-303 suspension is 10~40wt.%.

As a preferred embodiment, in step 2, the solvent is selected from one of chloroform, methylene chloride, N,N-dimethylamide or N-methylpyrrolidone.

As a preferred solution, in step 2, the concentration of the PIM-1 polymer solution is 4 to 10 wt.%, and it is filtered through a 0.45 μm polytetrafluoroethylene filter.

As a preferred option, in step 3, add a part of the PIM-1 polymer solution to the MOF-303 suspension, and after it is evenly dispersed, add all the remaining PIM-1 polymer solution into it and disperse it again. After uniformity, the solution was purged in an _N2 atmosphere until all excess solvent was removed, and a casting liquid was obtained.

As a preferred solution, in step 4, the deaeration method adopts one of standing, negative pressure or ultrasonic deaeration.

As a preferred solution, in step 4, drying is divided into two steps. First, the MMMs are evacuated at 40-80°C for 12-48 hours, and then the temperature is raised to 100-150°C and dried for 12-48 hours.

The invention also discloses the application of a MOF-303/PIM-1 membrane in the selective separation of CO ₂ /CH ₄ mixed gas.

Compared with the prior art, the present invention discloses the following technical effects:

(1) The present invention uses MOF-303 nanofiller and PIM-1 intrinsic microporous polymer to strengthen the interfacial compatibility between the two through intermolecular interactions such as charge transfer and hydrogen bonding to form dense and defect-free MMMs, thereby Achieve simultaneous improvement of gas permeability and selectivity.

(2) Since the PIM-1 polymer successfully avoids the collapse of the molecular chain with the help of the rigid support provided by the MOF-303 filler, the MOF-303/PIM-1 mixed matrix membrane prepared by the present invention can be used continuously for 33 hours (h) The separation and selection of CO ₂ /CH ₄ gas shows long-term stable gas separation performance, and the gas permeability coefficient and selectivity do not fluctuate significantly, showing huge industrial application potential.

(3) In the present invention, the metal-organic framework MOF-303 is uniformly incorporated into the PIM-1 matrix through physical blending and ultrasonic dispersion. The MOF-303/PIM-1 film prepared by the solution casting method is produced at 150 It still has good separation performance for CO ₂ /CH ₄ mixed gas after aging. Compared with pure PIM-1 membrane, it has excellent anti-aging properties.

Therefore, the MOF-303/PIM-1 membrane of the present invention can be used to separate CO ₂ in the mixed gas to achieve the purpose of reducing the greenhouse effect and easing ecological pressure.

Picture description:

These and/or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments and comparative examples in conjunction with the accompanying drawings, in which:

Figure 1 is a diagram showing the relationship between the selectivity of CO ₂ /CH ₄ and the permeability coefficient of CO ₂ for the MOF-303/PIM-1 membrane prepared in Example 1 and the mixed matrix membrane prepared by other MOF and PIM-1; where : QD-FCTF-1/PIM-1; ◆PEG-POSS/PIM-1;/> SNW-1/PIM-1;/> NH ₂ -NUS-8/PIM-1;/> KAUST-7/PIM-1; ▲ZIF-67/PIM-1;/> FCTF-1/PIM-1;/> UiO-66/PIM-1;/> gC ₃ N ₄ /PIM-1;/> MUF-15/PIM-1;/> ZIF-71/PIsM-1;/> BNNS/PIM-1;/> NH ₂ -ZIF-7: ★MOF-303/PIM-1.

Figure 2 is a long-term separation performance diagram of the MOF-303/PIM-1 membrane prepared in Example 1.

Figure 3 shows the permeability coefficients of the MOF-303/PIM-1 membrane prepared in Example 1 and the PIM-1 membrane prepared in Comparative Example 1 to CO ₂ (a) and CH ₄ (b) gases after 150 days of aging, as well as to the mixing Selectivity effect diagram of gas (c).

Detailed ways

Exemplary embodiments of the invention will now be described in detail. This detailed description should not be construed as limitations of the invention, but rather as a more detailed description of certain aspects, features and embodiments of the invention.

It should be understood that the terms used in the present invention are only used to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges in the present invention, it should be understood that every intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or value intermediate within a stated range and any other stated value or value intermediate within a stated range is also included within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded from the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only the preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and/or materials in connection with which the documents relate. In the event of conflict with any incorporated document, the contents of this specification shall prevail.

It will be apparent to those skilled in the art that various modifications and changes can be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to the skilled person from the description of the invention. The specification and examples of the present invention are exemplary only.

The words "includes", "includes", "has", "contains", etc. used in this article are all open terms, which mean including but not limited to.

In order to further improve the selective separation performance, long-term stability and anti-aging performance of the MOF-based mixed matrix membrane, the present invention selects a three-dimensional membrane composed of aluminum ions (Al ³⁺ ) and pyrazole dihydroxy acid (H ₃ PDC) chains. Hybrid membrane production of MOF-303 and PIM-1 in network and original cubic topologies. MOF-303 shows higher reactivity than conventional alkyl and imine MOFs. This increase in reactivity is due to the presence of imine groups on the H ₃ PDC chain and the N=N double bond causing the electron cloud density of the pyrazole ring. Obtained from irregular distribution. In addition, MOF-303 with high porosity and fine-tuned pore size can provide nanochannels with superior size screening capabilities to facilitate rapid transport of small molecules. Through the special pore structure of MOF-303 and the synergistic effect of high density of heteroatoms in one-dimensional channels, MOF-303 can potentially be used for the kinetic separation of _CO2 and _CH4 , where _CO2 passes through MOF more easily than _CH4 The microporous channel of -303, in addition, the filler provides rigid support for the PIM-1 matrix, organizes the migration of molecular chains, and provides help for the long-term stability of the separation of the mixed matrix membrane. Therefore, it is of significant practical significance to mix MOF-303 into PIM-1 to make MMMs for CO ₂ separation.

The test process of gas permeability coefficient and selectivity in the following examples and comparative examples is as follows: Under the operating conditions of 35°C and 2bar, the MOF-303/PIM-1 membrane is tested for permeability, and the mixed gas component CO ₂ /CH ₄ =50: 50 volume percentage. Its permeability performance is obtained by the constant pressure-variable volume method. For the test of mixed gas, the upstream mixed gas enters the top of the permeation tank through a pressure reducing valve, a flow meter and a manually operated valve, and the pressure is controlled by a back pressure regulator. The gas permeates to the bottom through the MMMs in the permeation cell. Helium is used as a purge gas to blow the permeated gas into the gas chromatograph to detect the concentration of each component, and a soap bubble flow meter is used to measure the gas flux. Before testing, use a vacuum pump to evacuate all other gases in the pipeline and permeation tank.

The gas permeability coefficient and selectivity in the membrane are calculated as follows:

Among them, i and j represent different gases respectively. P _i is the permeability coefficient of gas i in the membrane, the unit is Barrer (1Barrer=1×10 ^-10 cm ³ (STP)cm/(cm ² sec cmHg)); L is the thickness of the membrane, cm; N _i is the gas Permeation flux, cm ³ /sec; A is the effective membrane area, cm ² ; Δp _i is the partial pressure driving force of component i, that is, the partial pressure difference between the upstream and downstream of the membrane, cmHg; α _i/j is the gas i and The selection separation coefficient of the mixed gas of gas j, y _i and y _j are the mole fractions of gas i and gas j in the permeation measurement respectively; x _i and x _j are the mole fractions of gas i and gas j in the retention measurement respectively.

Example 1

a) Accurately weigh dry MOF-303 nanoparticles (based on Fathieh, F.; Kalmutzki, M.J.; Kapustin, E.A.; Waller, P.J.; Yang, J.; Yaghi, O.M. Practical water production from desert air. Sci. Adv. 2018 , 4, 3198. Literature preparation) 0.1285g was added to 2mL of chloroform solution, dispersed ultrasonically for 20 minutes, and then stirred for 4 hours to make MOF-303 nanoparticles evenly dispersed in the chloroform solution to form a well-dispersed MOF-303 chloroform suspension. ;

b) Accurately weigh 0.3g of dry PIM-1 powder, add it to 2mL of chloroform solution, stir for 4 hours until completely dissolved, and then filter it through a 0.45μm polytetrafluoroethylene filter to obtain a polymer solution;

c) After ultrasonic treatment for 20 minutes in the MOF-303 chloroform suspension in step a), take out a part of the polymer solution in step b) and pour it into the MOF-303 chloroform suspension. Continue stirring for 2 hours and then ultrasonic for 20 minutes to obtain Dissolve the uniform preliminary casting liquid, pour the remaining polymer solution into the preliminary casting liquid, stir for a further 12 hours, and purge the solution in an _N2 atmosphere until all excess solvent is removed to obtain the final The casting liquid is then degassed by ultrasonic;

d) Pour the degassed casting solution into a 6cm diameter Teflon petri dish, place it horizontally, place it with a glass plate on top of the Teflon dish, vacuum at 80°C for 48 hours, and then The temperature was raised to 150°C and dried for 48 hours to obtain MMMs with a MOF-303 particle content of 30 wt.% and a thickness of 40 to 100 μm.

Comparative example 1

a) Accurately weigh 0.3g of dry PIM-1 powder into a clean brown reagent bottle, then use a pipette to accurately measure 4mL of chloroform solution into the brown reagent bottle, and stir magnetically for 12 hours until PIM-1 is completely dissolved. Form a homogeneous transparent solution, and then defoam by ultrasonic;

b) Pour the solution after ultrasonic degassing into a PTFE culture dish with a diameter of 6cm, place it horizontally, place it with a glass plate on top of the PTFE culture dish, vacuum at 80°C for 48 hours, and then The temperature was raised to 150°C and dried for 48 hours to obtain a pure PIM-1 film with a thickness of 40 to 100 μm.

Under the conditions of 35°C and 0.2MPa, the MMMs prepared in Example 1 were tested for gas separation performance, and the permeability coefficients of CO ₂ and CH ₄ were obtained to be 7528.2 Barrer and 272.8 Barrer respectively, and the selectivity of CO ₂ to CH ₄ was :ɑCO ₂ /CH ₄ =27.6. Also under the conditions of 35°C and 0.2MPa, the gas separation performance of the pure PIM-1 membrane prepared in Example 1 was tested, and the permeability coefficients of CO ₂ and CH ₄ were 3945.0 Barrer and _315.6 Barrer respectively. The selectivity of ₄ is: ɑCO ₂ /CH ₄ =12.5. By comparing the gas separation performance of the membranes prepared in Example 1 and Comparative Example 1, it can be found that after adding MOF-303 nanoparticles to the PIM-1 membrane, the separation of CO ₂ and CH ₄ can be effectively achieved.

Example 2

a) Accurately weigh 0.0333g, 0.0750g, and 0.2000g of dry MOF-303 nanoparticles, and add them to 3 dry and clean brown reagent bottles respectively, and then use a pipette to accurately transfer 2mL of chloroform solution into these 3 bottles. In the reagent bottle, ultrasonic disperse for 20 minutes, and then magnetically stir for 4 hours until the MOF-303 nanoparticles are uniformly dispersed in the chloroform solution to form a well-dispersed MOF-303 chloroform suspension;

b) Accurately weigh 3 portions of 0.3g dried PIM-1 powder and add them to 3 dry and clean brown reagent bottles respectively, and then use a pipette to accurately transfer 2mL of chloroform solution into these 3 reagent bottles. After stirring for 4 hours until completely dissolved, filter them through 0.45 μm polytetrafluoroethylene filters to obtain three polymer solutions;

c) After ultrasonic treatment for 20 minutes in the MOF-303 chloroform suspension in step a), take out a portion of the polymer solution in step b) and pour it into the respective MOF-303 chloroform suspension. Continue stirring for 2 hours before ultrasonicating. After 20 minutes, a uniformly dissolved preliminary casting solution was obtained. Pour the remaining polymer solution into the respective preliminary casting solution, stir for a further 12 hours, and purge the solution in an _N2 atmosphere until all excess solvent was removed. After removal, the final casting liquid with MOF-303 nanoparticle content of 10wt.%, 20wt.% and 40wt.% was obtained, and then ultrasonic degassing was performed;

d) Pour the defoamed casting solution into a 6cm diameter Teflon petri dish, place it horizontally, place it on top of the Teflon dish with a glass plate, and vacuum at 80°C for 48 hours. Then the temperature was raised to 150°C and dried for 48 hours, and three types of MMMs with thicknesses of 40 to 100 μm were obtained.

The MMMs prepared in Examples 1 to 2 and Comparative Example 1 were tested for gas separation performance under the conditions of 35°C and 0.2MPa. The test results are shown in Table 1.

Table 1

It can be seen from Table 1 that as the mass fraction of MOF-303 in the membrane increases from 10wt.% to 30wt.%, the permeability coefficient of CO ₂ continues to increase, while the permeability coefficient of CH ₄ decreases slightly. This is due to the fact that MOF-303 nanoparticles have a uniform pore size (0.5nm) similar to the dynamic diameter of gas molecules and the high affinity for _CO2 allows _CO2 to occupy preferential adsorption sites on the membrane, resulting in a permeability coefficient of _CO2 Increase. However, after the limited adsorption sites are preferentially occupied, the migration of CH ₄ is significantly hindered due to the tightness of the membrane, and thus the permeability coefficient of CH ₄ is reduced. In addition, the MOF-303/PIM-1 membrane can greatly improve the selectivity of the CO ₂ /CH ₄ gas separation system, which achieves the goal of simultaneously improving the permeability coefficient and selectivity. The above test results have far exceeded the Robeson upper limit (Figure 1), indicating that the MMMs have very ideal permeation separation performance when separating the above gas systems. The "Robeson upper limit" here is based on a large number of reported permeability data of polymer membranes for specific gas molecules by American scholar Robeson (Robeson L.M. The upper bound revisited. Journal of Membrane Science. 2008, 320, 390-400). A graph formed by data processing with the permeability coefficient of CO ₂ as the abscissa and the selectivity of CO ₂ /CH ₄ as the ordinate.

The long-term separation performance of the MMMs prepared in Example 1 is shown in Figure 2. The (related) permeability coefficients of the MMMs prepared in Examples 1 to 2 and Comparative Example 1 to CO ₂ and CH ₄ gases and to mixed gases after 150 days of aging. Related) The permeation selectivity effect diagram is shown in Figure 3(a~c). Since the MOF-303 filler provides rigid support for the PIM-1 matrix, it effectively prevents the collapse of the molecular chain, thereby improving the overall rigidity of the PIM-1 matrix, which makes the MOF-303/PIM-1 membrane exhibit excellent performance during the separation process. Stable gas permeability performance, with no obvious change in permeability coefficient and selectivity, shows great potential for industrial applications. Figure 3 (a, b) shows the changes in membrane permeability coefficient and related permeability coefficient with time, respectively. It can be seen that the permeability of the PIM-1 membrane to CO ₂ and CH ₄ decreases, which is more obvious for CH ₄ with larger diameter. After 150 days, the _CO2 and _CH4- related permeability coefficients of the PIM-1 membrane were reduced by 67.0% and 72.0%, respectively. As shown in Figure 3(c), the gas selectivity slowly increases with the aging time, which is due to the improvement of the molecular sieving ability of the PIM-1 matrix. It can be seen from Figure 3 (a, b, c) that the permeability coefficient related to CO ₂ of the MOF-303/PIM-1 (30wt.%) membrane decreased by 7.2%, the related permeability coefficient to CH ₄ decreased by 20.9%, and the related permeability coefficient to CO ₂ /CH The associated permeation selectivity of ₄ is improved by 17.4%. In summary, MOF-303/PIM-1 membrane has excellent anti-aging properties and good long-term stability.

Claims (9)

1. A method for preparing a MOF-303/PIM-1 mixed matrix membrane, comprising the steps of:

step 1: uniformly dispersing MOF-303 in a solvent by ultrasonic to obtain MOF-303 suspension;

step 2: dissolving a polymer PIM-1 in a solvent, and filtering to obtain a PIM-1 polymer solution;

step 3: uniformly mixing PIM-1 polymer solution and MOF-303 suspension to obtain casting solution;

step 4: and pouring the defoamed membrane casting solution into a mould to prepare a membrane, and drying to remove residual solvent to obtain the MOF-303/PIM-1 mixed matrix membrane.

2. The method of claim 1, wherein MOF-303 has an average size of 50 nm.

3. The method according to claim 1, wherein in the step 1, the solvent is selected from one of chloroform, dichloromethane, N-dimethylamide or N-methylpyrrolidone, and the mass fraction of the MOF-303 suspension is 10 to 40wt.%.

4. The method according to claim 1, wherein in step 2, the solvent is selected from one of chloroform, dichloromethane, N-dimethylamide or N-methylpyrrolidone, and the PIM-1 polymer solution has a concentration of 4 to 10 wt.%.

5. The method of claim 1, wherein in step 3, a portion of the PIM-1 polymer solution is added to the MOF-303 suspension, after it has been dispersed uniformly, the remaining PIM-1 polymer solution is added thereto in its entirety, and after it has been dispersed uniformly again, the solution is taken up in N ₂ And (5) purging in the atmosphere until all the redundant solvent is removed, and obtaining the casting solution.

6. The method of claim 1, wherein in step 4, the defoaming method is one of standing, negative pressure or ultrasonic defoaming.

7. The method of claim 1, wherein in step 4, the drying is performed in two steps, wherein the MMMs are first between 40 and 80 ^o C, vacuumizing for 12-48 hours, and then raising the temperature to 100-150 ^o C, drying for 12-48 h.

8. A MOF-303/PIM-1 mixed matrix membrane prepared by the method of any one of claims 1-7.

9. The MOF-303/PIM-1 mixed matrix membrane prepared by the method of any one of claims 1-7 for selective separation of CO ₂ /CH ₄ Application of the mixed gas.