Mixed matrix membrane for propylene / propane gas separation and preparation method thereof

Abstract

The invention belongs to the technical field of gas separation materials, and particularly discloses a mixed matrix membrane for C3H6 / C3H8 gas separation and a preparation method of the mixed matrix membrane. Wherein SCA6 calixarene is dispersed in an organic solvent and mixed with an organic solvent of a 6FDA-TMPDA polymer to serve as a membrane casting solution for membrane preparation, and the mixed matrix membrane is obtained. According to the invention, 6FDA-TMPDA is taken as a polymer matrix, and SCA6 filler is introduced, so that the dissolution coefficient of C3H6 gas in the membrane is increased, and the obtained gas separation membrane realizes higher C3H6 / C3H8 separation selectivity. Meanwhile, after the mixed matrix membrane provided by the invention continuously operates for a period of time, the separation performance of the mixed matrix membrane can still be basically unchanged.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas separation, and in particular relates to a mixed matrix membrane for C3H6 / C3H8 gas separation and a preparation method thereof. Background Art

[0002] As an important raw material in the field of chemical energy, propylene is often accompanied by impurities such as propane during its production process, and needs to be separated and purified to remove propane to achieve polymerization grade purity. Since the boiling points and relative volatilities of the two components are very similar, in order to obtain high-purity C3H6, cryogenic distillation technology is usually required to separate C3H6 / C3H8 under low temperature and high pressure conditions. However, cryogenic distillation technology is an extremely energy-consuming and cost-intensive separation process. In order to solve this problem, researchers have made a lot of efforts in the development of new C3H6 / C3H8 separation technologies in order to improve separation efficiency and reduce operating costs.

[0003] Compared with traditional cryogenic distillation technology, new gas separation membrane technology has the potential for more efficient separation. At present, polymer membranes have been greatly developed and widely used in the market due to their good mechanical properties, easy processing, economy, and small footprint. However, the trade-off effect between permeability and selectivity of polymer membranes has greatly restricted their further development. Based on this, the preparation of mixed matrix membranes by combining organic / inorganic fillers with polymers is expected to break through the permeability-selectivity limitation and has good development prospects in the industrial field.

[0004] At present, most researchers use 6FDA-TMPDA as the polymer matrix to improve the separation performance of gas separation membranes by introducing different inorganic fillers, such as MOFs, zeolites, carbon nanotubes, etc. However, the introduction of these inorganic fillers often affects the stability of the membrane, resulting in a decrease in the separation performance of the membrane after long-term operation. Summary of the invention

[0005] In view of the defects of low selectivity of current polymer membranes and the degradation of separation performance of the membranes after long-term operation, the present invention provides a new mixed matrix membrane for propylene / propane gas separation and a preparation method thereof. The obtained mixed matrix membrane has high gas separation selectivity, can effectively separate C3H6 / C3H8, and can maintain its separation performance basically unchanged after long-term operation.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical effects:

[0007] A method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation. The mixed matrix membrane is prepared by first mixing a SCA6 calixarene dispersion with a 6FDA-TMPDA polymer solution at room temperature to obtain a casting solution, and then forming a membrane with the obtained casting solution.

[0008] As a further preferred embodiment of the present invention, in the SCA6 calixarene dispersion, the mass concentration of SCA6 is 0.5-2%; in the 6FDA-TMPDA polymer solution, the mass concentration of 6FDA-TMPDA is 56.2%; in the casting solution, the volume mixing ratio of the SCA6 calixarene dispersion and the 6FDA-TMPDA solution is 1:2.

[0009] As a further preferred embodiment of the present invention, the SCA6 dispersion is obtained by adding SCA6 to a tetrahydrofuran solution and continuously stirring with magnetic force at room temperature for 8 hours.

[0010] As further preferred embodiment of the present invention, the 6FDA-TMPDA polymer solution is obtained by adding 6FDA-TMPDA polymer to tetrahydrofuran solution, stirring continuously for 12 hours at room temperature, and filtering.

[0011] As a further preferred embodiment of the present invention, the SCA6 calixarene is synthesized from calix[6]arene and concentrated sulfuric acid; and the 6FDA-TMPDA polymer is synthesized from 2,3,5,6-tetramethyl-1,4-phenylenediamine and 4,4'-hexafluoroisopropylidene-phthalic anhydride.

[0012] As a further preferred embodiment of the present invention, the film is formed by a solution casting evaporation method.

[0013] As a further preferred embodiment of the present invention, the specific operation of the solution casting evaporation method is as follows: the obtained casting solution is ultrasonically removed of small bubbles, poured into a dry and clean glass culture dish, first dried at room temperature for 12-36 hours to ensure that the solvent evaporates slowly and reduce the formation of defects in the membrane, and then vacuum dried to remove the residual organic solvent in the membrane to obtain a mixed matrix membrane for C3H6 / C3H8 gas separation;

[0014] As further preferred embodiment of the present invention, the vacuum drying temperature is 100° C. and the drying time is 24 h.

[0015] The present invention further discloses a mixed matrix membrane for C3H6 / C3H8 gas separation obtained by the above preparation method.

[0016] In the present invention, SCA6 calixarene is a pure organic substance, containing abundant hydroxyl and sulfonic acid groups, and its chemical structure is:

[0017]

[0018] 6FDA-TMPDA polymer, its chemical structure is:

[0019]

[0020] SCA6 calixarene was introduced into 6FDA-TMPDA polymer to prepare mixed matrix membranes. The strong interaction between SCA6 and 6FDA-TMPDA reduced the mobility of the polymer chains and the diffusion rate of the gas, especially for larger C3H8 molecules. On the other hand, adsorption and dissolution dominated the interaction between C3H6 molecules and SCA6 filler, resulting in highly selective separation of C3H6 / C3H8.

[0021] The present invention mixes a SCA6 calixarene dispersion containing rich groups with a 6FDA-TMPDA polymer solution at room temperature to obtain a casting solution; the casting solution is poured into a dry and clean glass culture dish, and after room temperature drying and high-temperature vacuum drying, a gas separation mixed matrix membrane is obtained. The strong interaction between SCA6 and 6FDA-TMPDA reduces the fluidity of the polymer chain and reduces the diffusion rate of the gas, especially for larger C3H8 molecules; on the other hand, adsorption and dissolution dominate between C3H6 molecules and SCA6 fillers, thereby producing highly selective separation of C3H6 / C3H8. Therefore, the effective separation of C3H6 / C3H8 can be achieved by regulating the loading amount of SCA6 calixarene filler in the membrane. The mixed matrix membrane of the present invention has a good permeability to C3H6. C3H6 51.8-90.6 Barrer, α C3H6 / C3H8 In 13.1-17.3.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The present invention uses 6FDA-TMPDA as a polymer matrix and introduces SCA6 filler to increase the solubility coefficient of C3H6 gas in the membrane, and the obtained gas separation membrane achieves a higher C3H6 / C3H8 separation selectivity. At the same time, the mixed matrix membrane provided by the present invention can maintain its separation performance basically unchanged after continuous operation for a period of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the preparation process of the mixed matrix membrane obtained in Examples 1-3;

[0025] Figure 2 The Fourier infrared test spectra of the mixed matrix membranes obtained in Examples 1-3 and Comparative Example 1;

[0026] Figure 3 Gas separation performance diagram of the mixed matrix membrane obtained in Examples 1-3 and Comparative Example 1;

[0027] Figure 4 is a gas separation performance diagram of the mixed matrix membrane prepared in Comparative Example 2;

[0028] Figure 5 The gas separation performance diagram is obtained by operating the mixed matrix membrane obtained in Example 2 at a certain pressure and temperature for a period of time. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the invention are fully described, however, the described embodiments only represent a part of the embodiments of the invention. Based on the embodiments of the invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the invention.

[0030] In the present invention, room temperature refers to 25-30°C.

[0031] In the present invention, the synthesis method of SCA6 is as follows: 1.91 g of cup[6]arene is weighed into a three-necked round-bottom flask, 10 mL of concentrated sulfuric acid is slowly dripped into the flask, and the mixture is heated at 80°C and stirred to fully react. After about 4 hours, the solution in the flask is reddish brown and a precipitate is precipitated. An aliquot of the precipitate is added to deionized water, and the absence of water-insoluble substances indicates that the reaction is complete. After cooling to room temperature, the reaction mixture is added to an ether solution to precipitate SCA6. After vacuum filtration, the mixture is washed with cold acetone for 3 to 5 times, placed in a vacuum drying oven, and dried at 80°C for 24 hours (in other embodiments, drying for 24 hours may also be selected, and the maximum may not exceed 36 hours), to obtain a light yellow powder, namely SCA6.

[0032] Synthesis of 6FDA-TMPDA: Before synthesis, all monomers must be purified. The purification steps are as follows: weigh 3g of 2,3,5,6-tetramethyl-1,4-phenylenediamine monomer in a 250mL beaker, measure 50mL of ethyl acetate and add it to the beaker, ultrasonicate until completely dissolved, then add 120mL of petroleum ether, seal the beaker with plastic wrap and put it in the refrigerator to cool and crystallize. After sufficient precipitation, vacuum filtration is performed, and the sample is placed in a 60℃ vacuum drying oven and dried to obtain a purified amine monomer. 4,4'-Hexafluoroisopropyl-phthalic anhydride monomer is placed in a 150℃ vacuum drying oven and dried for use.

[0033] Synthesis steps: First, the two monomers were dissolved in an ultra-dry DMAc solvent at a molar ratio of 1:1, and stirred at room temperature for 24 hours under a nitrogen atmosphere to obtain a uniform polyamic acid (PAA) solution. Then, acetic anhydride and triethylamine solvents were added to the PAA solution at a molar ratio of 3:1, used as a dehydrating agent and catalyst, respectively, and stirred for 24 hours under the same conditions to complete the chemical imidization reaction. The polymer solution was precipitated with methanol solvent, washed alternately with chloroform and methanol for 3 to 5 times, and dried in a vacuum oven at 180°C for 24 hours.

[0034] Embodiment 1:

[0035] A mixed matrix membrane for C3H6 / C3H8 gas separation in this embodiment is prepared according to the following method:

[0036] 1) Preparation of SCA6 calixarene dispersion:

[0037] Weigh SCA6 calixarene in a vial, add 2 mL of tetrahydrofuran solution, and continuously stir magnetically at room temperature for 8 h to obtain a calixarene dispersion with a content of 0.5 wt%;

[0038] 2) Prepare 6FDA-TMPDA polymer solution:

[0039] Weigh 0.2 g of 6FDA-TMPDA and dissolve it in 4 mL of tetrahydrofuran solvent to a mass concentration of 56.2%. After stirring at room temperature for 12 h, the polymer solution is filtered through a 0.45 μm PTFE filter to remove impurities to obtain a pure polymer solution for later use;

[0040] 3) Preparation process Figure 1 As shown, 0.5wt% SCA6 calixarene dispersion was added to 6FDA-TMPDA polymer solution, stirred and mixed at room temperature overnight to obtain a casting solution, and then the casting solution was ultrasonicated for 30 minutes to remove small bubbles by solution casting evaporation method, and then slowly poured into a dry and clean glass culture dish, dried at room temperature for 12 hours, and then placed in a 100°C vacuum oven for 24 hours to remove the residual organic solvent in the membrane, and a mixed matrix membrane for C3H6 / C3H8 gas separation was obtained. The data of the membrane are P C3H6 =90.6 Barrer, α C3H6 / C3H8 =13.7.

[0041] There is no requirement for the order of operation of step 1) and step 2) described in this embodiment, and they can be performed simultaneously.

[0042] Embodiment 2:

[0043] The mixed matrix membrane for C3H6 / C3H8 gas separation and its preparation method in this embodiment are the same as those in Example 1, except that: in step 1), a 1wt% calixarene dispersion is prepared; in step 3), 1wt% SCA6 calixarene dispersion is added to 6FDA-TMPDA polymer solution, and stirred and mixed at room temperature overnight to obtain a casting solution. The casting solution is ultrasonicated for 30 minutes to remove small bubbles by solution casting evaporation method, and then slowly poured into a dry and clean glass culture dish, dried at room temperature for 12 hours, and placed in a 100°C vacuum oven for 24 hours to remove the residual organic solvent in the membrane to obtain a mixed matrix membrane for C3H6 / C3H8 gas separation. The data of the membrane are P C3H6 =69.3 Barrer, α C3H6 / C3H8 =17.3.

[0044] Embodiment 3:

[0045] The mixed matrix membrane for C3H6 / C3H8 gas separation and its preparation method of this embodiment are the same as those of Example 1, except that in step 1), a 2wt% calixarene dispersion is prepared; in step 3), a 2wt% SCA6 calixarene dispersion is added to a 6FDA-TMPDA polymer solution, and the mixture is stirred and mixed at room temperature overnight to obtain a casting solution. The casting solution is ultrasonicated for 30 minutes to remove small bubbles by solution casting evaporation method, and then slowly poured into a dry and clean glass culture dish, dried at room temperature for 12-36 hours, and placed in a 100°C vacuum oven for 24 hours to remove the residual organic solvent in the membrane to obtain a mixed matrix membrane for C3H6 / C3H8 gas separation. The data of the membrane are P C3H6 =51.8 Barrer, α C3H6 / C3H8 =13.1.

[0046] Comparative Example 1:

[0047] This comparative example prepares pure 6FDA-TMPDA polymer membrane as a comparison. The preparation method is the same as Example 1 except that the SCA6 dispersion is not added. The data of the obtained membrane are P C3H6 =108.7 Barrer, α C3H6 / C3H8 =6.4.

[0048] Comparative Example 2

[0049] This comparative example is the same as Example 1, except that PgC3 (C-propylpyrogallolcalix[4]arene, the preparation method of which can refer to the synthesis of PgC3 in PgC3Mg metal-organic cages functionalized hydrogels with enhanced bioactive andros scavenging capabilities for accelerated bone regeneration[J]. Journal of Materials Chemistry B, 2022, 10(28): 5375-5387) is used to replace the SCA6calixarene in Example 1, and mixed matrix membranes with different PgC3 contents are prepared respectively.

[0050] The SCA6 / 6FDA-TMPDA mixed matrix membranes for efficient separation of C3H6 / C3H8 prepared in Examples 1-3 and the pure 6FDA-TMPDA polymer membrane prepared in Comparative Example 1 were subjected to infrared detection and gas separation performance tests. The results are shown in Table 1. Figure 2-4As shown, the results indicate that the addition of SCA6 and the appropriate increase in the loading amount of SCA6 can result in the high selectivity separation of C3H6 / C3H8.

[0051] Figure 2 The Fourier transform infrared test spectra of the mixed matrix membranes prepared in Examples 1-3 and Comparative Example 1 show that after SCA6 is introduced into the 6FDA-TMPDA polymer, the mixed matrix membrane has a high -1 The signal of -CF3 at 1723cm -1 and 1785cm -1 The vibration of the C=O absorption peak in the imide ring at 980~1160cm -1 In the range of 40 nm, the stretching vibration of S=O=S groups in SCA6 / 6FDA-TMPDA membrane was observed, which was attributed to the sulfonic acid group peak of the filler, which was consistent with the infrared spectrum of SCA6, confirming that SCA6 was successfully introduced into 6FDA-TMPDA membrane.

[0052] Figure 3 The C3H6 / C3H8 gas separation performance diagram of the mixed matrix membrane prepared in Examples 1-3 and Comparative Example 1 is shown in the figure. As the SCA6 loading increases, the permeability of C3H6 and C3H8 both show a downward trend, and the ideal selectivity of C3H6 / C3H8 first increases and then decreases.

[0053] The SCA6 / 6FDA-TMPDA membrane has the highest selectivity, and the separation selectivity of C3H6 / C3H8 increases from 6.4 to 17.3. The C3H6 / C3H8 selectivity of the 0.5wt% SCA6 / 6FDA-TMPDA membrane and the 2wt% SCA6 / 6FDA-TMPDA membrane is comparable, about 13. However, the permeability coefficient of C3H6 when the filler loading is 0.5wt% is about 39 Barrer higher than that of 2wt%. The reason for this difference may be that the less SCA6 loading may play a lesser role, and the gas still mainly relies on 6FDA-TMPDA for transport. When the loading is high, the gas separation performance changes due to the enhanced interaction between SCA6 and the polymer, which slows down the diffusion of C3H6 and leads to a decrease in gas permeability. Further increasing the SCA6 loading to 2wt%, the hardening of the polymer chain has a stronger inhibitory effect on the fast-diffusing C3H6 molecules than C3H8, thereby reducing the C3H6 / C3H8 separation selectivity.

[0054] Figure 4is a gas separation performance diagram of the mixed matrix membrane prepared in Comparative Example 2; Figure 4 It can be seen from the figure that although the addition of PgC3 can improve the separation performance, the gas permeability decreases significantly, and when the separation performance reaches 19, the addition amount of PgC3 is much higher than the addition amount of SCA6 calixarene of the present invention. Therefore, the present invention selects SCA6 calixarene to prepare a mixed matrix membrane with a C3H6 permeability P C3H6 51.8-90.6 Barrer, α C3H6 / C3H8 In 13.1-17.3. Figure 5 The mixed matrix membrane prepared in Example 2 was operated at 1 bar and 298 K for a period of time to obtain a gas separation performance diagram. After 20 days of operation test, the membrane still maintained the best C3H6 / C3H6 separation performance, the permeability coefficient of propylene varied in the range of 67 to 72 Barrer, and the separation selectivity of C3H6 / C3H8 was stable at about 17. This shows that the addition of calixarene material still retains the structure of the 6FDA-TMPDA membrane, and the separation performance of MMMs is in a very stable operating state for up to 20 days.

[0055] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation, characterized in that: The mixed matrix membrane is prepared by first mixing SCA6 calixarene dispersion and 6FDA-TMPDA polymer solution at room temperature with stirring to obtain a casting solution, and then forming a membrane with the obtained casting solution.

2. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 1, characterized in that: In the SCA6 calixarene dispersion, the mass concentration of SCA6 is 0.5-2%; in the 6FDA-TMPDA polymer solution, the mass concentration of 6FDA-TMPDA is 56.2%; in the casting solution, the volume mixing ratio of the SCA6 calixarene dispersion and the 6FDA-TMPDA solution is 1:

2.

3. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 2, characterized in that: The SCA6 dispersion is obtained by adding SCA6 to a tetrahydrofuran solution and continuously stirring with magnetic stirring at room temperature for 8 hours.

4. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 2, characterized in that: The 6FDA-TMPDA polymer solution is obtained by adding 6FDA-TMPDA polymer to a tetrahydrofuran solution, stirring continuously for 12 h at room temperature, and filtering.

5. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 1, characterized in that: The SCA6 calixarene is synthesized from calix[6]arene and concentrated sulfuric acid; and the 6FDA-TMPDA polymer is synthesized from 2,3,5,6-tetramethyl-1,4-phenylenediamine and 4,4'-hexafluoroisopropylidene-phthalic anhydride.

6. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 1, characterized in that: The film was prepared by solution casting evaporation method.

7. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 6, characterized in that: The specific operation of the solution casting evaporation method is as follows: the obtained casting solution is ultrasonically removed of small bubbles, poured into a dry and clean glass culture dish, first dried at room temperature for 12-36 hours, and then vacuum dried to remove the residual organic solvent in the membrane to obtain a mixed matrix membrane for C3H6 / C3H8 gas separation.

8. The method for preparing a mixed matrix membrane for C3H6 / C3H8 gas separation according to claim 7, characterized in that: The vacuum drying temperature was 100°C and the drying time was 24 h.

9. A mixed matrix membrane for C3H6 / C3H8 gas separation obtained by the preparation method according to any one of claims 1 to 8.

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