A zif-11-pdms / go-pi hybrid matrix pervaporation membrane for ethanol recovery and a preparation method and application thereof

Abstract

The application discloses a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery and a preparation method and application thereof, and relates to the field of membrane separation technology. The ZIF-11 particles are prepared by means of an improved ammonia-assisted synthesis method, a GO-PI composite base film is combined with a ZIF-11-PDMS separation layer to construct a three-layer synergistic structure, and the prepared composite membrane has a permeation flux of greater than or equal to 580 g·m ‑2 ·h ‑1 , a separation factor of greater than or equal to 13, and a performance attenuation rate of less than or equal to 5% in a continuous operation of 168 h when processing 0.5-18 wt% low-concentration ethanol aqueous solution in a room temperature range of 5-40 DEG C; the preparation process is simple and easy to control, the recovery rates of solvents NMP and cyclohexane are greater than or equal to 90%, VOC emission is reduced by 75%, the permeation flux fluctuation is less than or equal to 6% and the separation factor fluctuation is less than or equal to 9% among large-scale production batches, and the application is suitable for efficient recovery of low-concentration ethanol in the fields of biomass fermentation, medicine preparation, food processing and the like.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery, its preparation method, and its application. Background Technology

[0002] With global energy restructuring and increasingly stringent environmental regulations, the market demand for biomass ethanol, as a clean and renewable energy source, continues to grow. Acetone-butanol-ethanol (ABE) fermentation is one of the main technologies for ethanol production, but the ethanol concentration in the fermentation broth is typically only 1.2-12 wt%, and it also contains impurities such as proteins, suspended particles, and organic acids. Traditional multi-tower distillation processes suffer from azeotropic effects, resulting in high energy consumption during separation and potential equipment corrosion, which significantly limits the large-scale promotion of ethanol production.

[0003] Pervaporation (PV) technology originally had the advantages of simple equipment and high separation efficiency, making it the preferred solution for low-concentration ethanol recovery. However, due to several key defects in traditional pervaporation membranes (including polymer membranes and mixed matrix membranes), these advantages could not be fully realized. For example: (1) Insufficient solvent compatibility. When faced with complex wastewater containing trace amounts of organic solvents, high salt content (salt content >3wt%), or weak acid and weak base (pH <5 or pH >9), the membrane material is prone to swelling and degradation, leading to a rapid decline in separation performance; (2) Poor environmental friendliness of the preparation process. The solvents used (such as DMF, etc.) are often unsuitable for environmental protection. (3) The recovery rate of tetrahydrofuran is less than 60%, and the VOC emissions are large, which does not meet the requirements of green production; (4) The consistency of large-scale production is low, and the permeation flux fluctuates by more than 15% and the separation factor fluctuates by more than 20% between batches, which seriously affects the stability of industrial applications; (5) The anti-pollution performance is weak. When faced with impurities such as proteins and suspended particles in the fermentation broth, it is easy to cause surface adsorption and pore blockage, resulting in a rapid decrease in flux and a high cleaning frequency; (6) The long-term operation stability is insufficient. After continuous operation for 72 hours, the performance decay rate generally exceeds 10%, which is difficult to meet the needs of continuous industrial production.

[0004] ZIF-11 is a novel material in the MOF family, with a large specific surface area, strong hydrophobicity, and a wide range of pore size control, making it suitable for optimizing the performance of PDMS separation layers. PI (polyimide) has better solvent swelling resistance and mechanical stability than PVDF. GO (graphene oxide) modified PI can form an antifouling base film, combining the dual functions of filling interfacial voids in the original transition layer and enhancing the structural stability of the base film. However, current technologies have not yet formed a three-layer synergistic structure suitable for complex systems, and ZIF particle synthesis is prone to problems such as uneven particle size and poor dispersibility. The parameters of the crosslinking system are also unreasonable, making it difficult to improve the overall performance of the membrane and meet the needs of industrial applications in complex scenarios.

[0005] Therefore, how to provide a mixed matrix pervaporation membrane that can efficiently separate particles, has strong anti-fouling ability, excellent solvent compatibility, good environmental protection, and high scalability consistency is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of traditional membranes in the prior art, such as poor solvent compatibility, poor environmental performance, low scalability consistency, weak anti-fouling, and insufficient long-term stability. It also solves problems such as uneven dispersion of mixed matrix membrane fillers, imbalance between flux and selectivity, unstable crosslinking system, and limited application scenarios. The invention provides a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery, its preparation method, and its application. This membrane achieves efficient, low-energy, anti-fouling, and multi-scenario separation and recovery of low-concentration ethanol (0.5-18wt%) in a wide room temperature range of 5-40℃.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery specifically includes the following steps:

[0009] (1) Preparation of ZIF-11 particles: Cobalt nitrate salt was dissolved in deionized water to prepare solution A, and 2-methylimidazolium was dissolved in ammonia water to prepare solution B; solution A was added to solution B, and the mixture was stirred at room temperature to obtain precipitate, which is ZIF-11 particles;

[0010] (2) Preparation of GO-PI base film: PI powder and GO nanosheets are added to N-methylpyrrolidone and mixed evenly to obtain casting solution. The casting solution is coated on the surface of PP nonwoven fabric and cured and dried to obtain GO-PI base film.

[0011] (3) Disperse the ZIF-11 particles in cyclohexane, add PDMS prepolymer, tetraethoxysilane and dibutyltin dilaurate, mix evenly and degas to obtain a mixture, coat the mixture on the GO-PI base membrane and cure to obtain a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery.

[0012] This invention uses an improved ammonia-assisted synthesis method to replace the traditional hydrothermal method, eliminating the need for DMF solvent in the hydrothermal method. The resulting ZIF-11 particles have a pure white cubic structure, a particle size of 30-85 nm, and a specific surface area of ​​1400-2200 m². 2 / g, with an average pore size of 0.4-1.1 nm, no solvent residue, excellent dispersibility, and strong interfacial compatibility with the PDMS matrix, enabling the formation of efficient hydrophobic mass transfer channels within the room temperature range; simultaneously, through cross-linking between the siloxane bonds of the PDMS prepolymer and the tetrafunctionality of tetraethoxysilane, a dense network is formed under the catalysis of dibutyltin dilaurate, achieving a cross-linked network density of 1.6 × 10⁻⁶. 21 / cm 3 In addition, room temperature pre-curing allows the membrane to initially take shape and ensures interfacial bonding, while medium-temperature post-curing can further improve the crosslinking density. These two steps together ensure the structural stability and separation performance of the membrane.

[0013] Preferably, the concentration of solution A in step (1) is 0.6-2.2 mol / L, and the concentration of solution B is 0.8-4.2 mol / L;

[0014] The volume ratio of solution A to solution B is 1:1-6.

[0015] Preferably, the reaction time in step (1) is 6-40 min and the stirring speed is 280-550 r / min;

[0016] Solution A is added dropwise to solution B at a rate of 4-12 mL / min.

[0017] Preferably, the precipitation treatment steps in step (1) are as follows: after the reaction is completed, the precipitate is collected by centrifugation, washed with deionized water until neutral, rinsed with anhydrous ethanol, and finally vacuum dried at 70-110℃ for 6-26h.

[0018] Preferably, the centrifugation is performed at 6500-13000 r / min for 8-30 min, and the anhydrous ethanol rinsing is performed 2-6 times.

[0019] Preferably, the mass ratio of the PI powder to the GO nanosheets in step (2) is 95-99:1-5;

[0020] The total amount of the PI powder and the GO nanosheets is in a mass-to-volume ratio of 1g to 7-18mL to the N-methylpyrrolidone.

[0021] Preferably, the mixing in step (2) is performed by stirring at 250-480 r / min for 5-16 h at 75-115 °C;

[0022] The coating thickness is 35-80 μm, and the GO-PI base film thickness after curing and drying is 25-50 μm;

[0023] The curing and drying steps are as follows: after the coated PP nonwoven fabric is cured in a deionized water coagulation bath and the residual solvent is removed, it is then vacuum dried at 80-100℃ for 8-18 hours.

[0024] Preferably, the amount of ZIF-11 particles added in step (3) is 0.8-40 wt% of the PDMS prepolymer;

[0025] The mass ratio of the PDMS prepolymer, the tetraethoxysilane TEOS, and the dibutyltin dilaurate TEOS is 45-85:1-12:1.

[0026] Preferably, the dispersion in step (3) is ultrasonic dispersion, wherein the ultrasonic time is 20-50 min when the amount of ZIF-11 particles added is 0.8-7 wt%, and the ultrasonic time is 30-60 min when the amount is greater than 7 wt%.

[0027] When the amount of ZIF-11 particles added is 0.8-7wt%, the mass-volume ratio of the PDMS prepolymer to the cyclohexane is 10g:100-200mL; when it is greater than 7wt%, the mass-volume ratio of the PDMS prepolymer to the cyclohexane is 10g:150-200mL.

[0028] The mixing process involves stirring at 180-380 r / min for 0.8-3.5 h.

[0029] The degassing process involves degassing under a vacuum of (-0.07) to (-0.10) MPa for 8-45 minutes.

[0030] The coating thickness is 8-28 μm, and the total thickness of the ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane is 33-78 μm;

[0031] The curing process involves first curing at room temperature (18-32℃) for 15-40 hours, followed by curing at 70-100℃ for 1.5-8 hours, with a heating rate of 1.5-8℃ / min.

[0032] Preferably, the amount of ZIF-11 particles added is 0.8-7 wt% (i.e., loading) of the PDMS prepolymer, and the resulting ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane can achieve optimal comprehensive separation performance in the room temperature range of 5-40℃.

[0033] The ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery, prepared by the above method, has a three-layer composite structure with a total thickness of 33-78 μm, a water contact angle of not less than 106°, a tensile strength ≥2.5 MPa, and an elongation at break ≥48%. When treating 0.5-18 wt% low-concentration ethanol aqueous solutions within a room temperature range of 5-40℃, the permeation flux is ≥580 g·m³. -2 ·h -1 With a separation factor ≥13, the performance degradation rate after 168 hours of continuous operation is ≤5%, and the stability is significantly better than that of traditional pervaporation membranes.

[0034] The ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane prepared by the above-described method, or the application of the ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane in low-concentration ethanol recovery, is characterized in that the concentration of the ethanol is 0.5-18 wt%.

[0035] Preferred application scenarios include the separation and recovery of low-concentration ethanol (0.5-18wt%) in acetone-butanol-ethanol (ABE) fermentation broth, pharmaceutical wastewater, food processing wastewater, and biomass refining wastewater; the operating temperature is in the room temperature range of 5-40℃, and the energy consumption is reduced by more than 35% compared with traditional membrane separation processes.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) This invention prepares ZIF-11 particles by using an improved ammonia-assisted synthesis method. By limiting the raw material concentration, dropping rate and stirring parameters, the obtained particles have uniform particle size (30-85nm), good dispersibility, and strong interfacial compatibility with PDMS matrix. Even with a high loading, no agglomeration will occur, laying the foundation for efficient mass transfer at room temperature.

[0038] (2) The three-layer composite structure of the hybrid matrix pervaporation membrane of the present invention is reasonable. The PP non-woven fabric provides high-strength mechanical support, the GO-PI base membrane has multiple functions such as filling interlayer gaps, blocking pollutants, enhancing structural integrity and chemical resistance, and the ZIF-11-PDMS separation layer can construct an efficient hydrophobic mass transfer channel. The three layers work together to enable the membrane to achieve preferential adsorption and rapid permeation of ethanol in a wide room temperature range of 5-40℃.

[0039] (3) The present invention precisely adjusts the loading of ZIF-11, determining that 0.8-7wt% is the optimal range, and the permeation flux can reach 580 g·m -2 ·h -1 The separation factor is not less than 13, which is superior to that of traditional membranes;

[0040] (4) This invention combines a specific crosslinking system and a two-step curing process. The tetrafunctional structure of tetraethoxysilane can increase the crosslinking network density by more than 25%, and dibutyltin dilaurate can efficiently catalyze the crosslinking reaction, so that the water contact angle of the membrane is not less than 106°. The performance decay rate is only less than 5% after 168 hours of continuous operation. The mechanical properties are also excellent, with tensile strength ≥2.5MPa and elongation at break ≥48%.

[0041] (5) The GO sheets in the GO-PI base membrane of the present invention have strong hydrophobicity and smooth surface, which greatly improves the antifouling performance of the membrane, extends the cleaning cycle to more than 15 days, and reduces the operation and maintenance cost by 60%. At the same time, the synergistic effect of GO and PI enables the membrane to withstand acid and alkaline environments with salt concentrations of 4-9wt% and pH=2.5-11.5, and its solvent compatibility is significantly better than that of traditional membranes.

[0042] (6) The preparation process of this invention is simple and easy to control. The solvents NMP and cyclohexane can be recycled and reused with a recovery rate of ≥90%. VOC emissions are reduced by 75%, and the environmental protection is greatly improved, which meets the requirements of green production. By precisely limiting the matching relationship between the amount of cyclohexane and the loading, the uniformity of the packing dispersion and the quality of film formation are further guaranteed. When produced on a large scale, the permeate flux fluctuation between batches is ≤6% and the separation factor fluctuation is ≤9%, which is far more consistent than traditional membranes.

[0043] (7) The membrane energy consumption of this invention is reduced by more than 35% compared with the traditional process, and can process 1m 3 The fermentation broth can save 0.12-0.28 tons of steam; moreover, it has a wide range of applications and can treat low-concentration ethanol in various systems such as ABE fermentation broth, high-salt pharmaceutical wastewater, and food processing wastewater, and has broad application prospects in the fields of biofuel production and environmental governance. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0045] Figure 1 This is an experimental setup and flowchart for testing the membrane performance of the present invention;

[0046] Figure 2 This is a process flow diagram of the industrial-scale membrane separation system of the present invention. Detailed Implementation

[0047] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0048] Example 1

[0049] This embodiment represents the optimal solution and provides a method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery, specifically including the following steps:

[0050] (1) Preparation of ZIF-11 particles: A modified ammonia-assisted synthesis method was adopted. Cobalt nitrate hexahydrate was dissolved in deionized water to prepare a solution A with a concentration of 1.2 mol / L. 2-methylimidazolium was dissolved in 25% ammonia water to prepare a solution B with a concentration of 2.5 mol / L. The volume ratio of solution A to solution B was 1:4. Solution A was added dropwise to solution B at a rate of 8 mL / min. The entire dropwise addition and subsequent reactions were carried out at room temperature and a stirring speed of 400 r / min. After the dropwise addition was completed, the reaction was stirred for 20 min. After the reaction was completed, the reaction solution was centrifuged at 10000 r / min for 15 min. The precipitate was collected, washed with deionized water until pH=7.0, rinsed three times with anhydrous ethanol, and finally vacuum dried at 90℃ for 12 h to obtain nanoscale cubic ZIF-11 particles with a particle size of 40-60 nm, a specific surface area of ​​1850 m² / g, and an average pore size of 0.6 nm.

[0051] (2) Preparation of GO-PI base film: PI powder and GO nanosheets were mixed at a mass ratio of 98:2 and added to N-methylpyrrolidone (NMP) with a solid-liquid ratio of 1g:12mL. The mixture was stirred at 90℃ and 350r / min for 10h to form a uniform and stable casting solution. After the PP nonwoven fabric was pretreated by drying at 80℃ for 24h, the casting solution was uniformly coated on its surface. The film thickness was 50μm. The fabric was immediately immersed in a deionized water coagulation bath for 20h to cure. After the residual solvent was completely removed, the film was vacuum dried at 90℃ for 12h to obtain a GO-PI base film with a thickness of 35μm.

[0052] (3) Preparation of mixed matrix membrane: Based on the mass of PDMS prepolymer, weigh ZIF-11 particles with a loading of 3wt%; based on 10g of PDMS prepolymer, add 120mL of cyclohexane, add ZIF-11 particles to cyclohexane, ultrasonically disperse for 35min, then add PDMS prepolymer, tetraethoxysilane (TEOS), and dibutyltin dilaurate (DBTDL) in a mass ratio of 60:8:1, stir at 250r / min for 2h, and degas at -0.09MPa vacuum for 20min; uniformly coat the degassed mixture on the surface of GO-PI base membrane with a coating thickness of 15μm, first cure at room temperature of 25℃ for 24h, then raise the temperature to 80℃ at a heating rate of 3℃ / min, and keep it at the temperature for 4h to obtain a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane with a total thickness of 50μm;

[0053] The performance test results of the composite membrane prepared in this embodiment are as follows: at room temperature (15-28℃), the water contact angle is 115° and the permeation flux is 658 g·m³. -2 ·h -1 The separation factor is 14.8, the performance degradation rate after 168 hours is 3.3%, the tensile strength is 2.8 MPa, and the elongation at break is 52%. In the 5-15℃ range, the water contact angle is 112°, and the permeation flux is 620 g·m³. -2 ·h -1 The separation factor was 15.2, and the performance degradation rate after 168 hours was 3.2%; in the 28-40℃ range, the water contact angle was 113°, and the permeation flux was 685 g·m³. -2 ·h -1 The separation factor is 13.6, and the performance degradation rate after 168 hours is 4.2%.

[0054] Example 2

[0055] This embodiment provides a method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery, specifically including the following steps:

[0056] (1) Preparation of ZIF-11 particles: A modified ammonia-assisted synthesis method was adopted. Cobalt nitrate hexahydrate was dissolved in deionized water to prepare a solution A with a concentration of 2.0 mol / L. 2-methylimidazolium was dissolved in 25% ammonia water to prepare a solution B with a concentration of 4.0 mol / L. The volume ratio of solution A to solution B was 1:2. Solution A was added dropwise to solution B at a rate of 5 mL / min. The entire dropwise addition and subsequent reaction were carried out at room temperature and a stirring speed of 300 r / min. After the dropwise addition was completed, the reaction was stirred for 35 min. After the reaction was completed, the reaction solution was centrifuged at 12000 r / min for 10 min, the precipitate was collected, washed with deionized water until pH=7.2, rinsed 4 times with anhydrous ethanol, and finally vacuum dried at 100℃ for 10 h to obtain nanoscale cubic ZIF-11 particles with a particle size of 50-75 nm, a specific surface area of ​​1680 m² / g, and an average pore size of 0.8 nm.

[0057] (2) Preparation of GO-PI base film: PI powder and GO nanosheets were mixed at a mass ratio of 96:4 and added to N-methylpyrrolidone (NMP) with a solid-liquid ratio of 1g:15mL. The mixture was stirred at 100℃ and 400r / min for 8h to form a uniform and stable casting solution. After the PP nonwoven fabric was pretreated by drying at 90℃ for 20h, the casting solution was uniformly coated on its surface. The film thickness was 65μm. The fabric was immediately immersed in a deionized water coagulation bath for 24h to cure. After the residual solvent was completely removed, the film was vacuum dried at 85℃ for 15h to obtain a GO-PI base film with a thickness of 40μm.

[0058] (3) Preparation of mixed matrix membrane: Based on the mass of PDMS prepolymer, weigh ZIF-11 particles with a loading of 5wt%; based on 10g of PDMS prepolymer, add 140mL of cyclohexane, add ZIF-11 particles to cyclohexane, ultrasonically disperse for 40min, then add PDMS prepolymer, tetraethoxysilane (TEOS), and dibutyltin dilaurate (DBTDL) in a mass ratio of 75:10:1, stir at 300r / min for 1.5h, and degas at -0.08MPa vacuum for 30min; uniformly coat the degassed mixture on the surface of GO-PI base membrane with a coating thickness of 20μm, first cure at room temperature of 25℃ for 36h, then raise the temperature to 90℃ at a heating rate of 5℃ / min, and keep it at the temperature for 3h to obtain a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane with a total thickness of 60μm;

[0059] The performance test results of the composite membrane prepared in this embodiment are as follows: at room temperature range of 15-28℃, the water contact angle is 110° and the permeation flux is 612 g·m³. -2 ·h -1 Separation factor 14.1, 168h performance degradation rate 4.2%, tensile strength 2.45MPa, elongation at break 47.5%.

[0060] Example 3

[0061] This embodiment is a loading gradient verification group. The only difference from Example 1 is the loading of ZIF-11 particles, as well as the corresponding matching ultrasonic dispersion time and cyclohexane addition. All other raw material ratios, preparation steps, and process parameters are completely consistent with Example 1.

[0062] In this embodiment, six parallel samples were set up with ZIF-11 particle loadings of 0.8wt%, 7wt%, 15wt%, 25wt%, 35wt%, and 40wt%, respectively. All loadings were calculated based on the mass of the PDMS prepolymer, and the corresponding parameters are as follows:

[0063] (1) 0.8wt% loading group: ultrasonic dispersion time 30min, based on 10g PDMS prepolymer, cyclohexane addition amount 120mL; performance test results of composite membrane prepared by 0.8wt% loading group: water contact angle 110°, permeation flux 592g·m at room temperature range of 15-28℃. -2 ·h -1 Separation factor 15.5, 168h performance degradation rate 4.2%, tensile strength 2.35MPa, elongation at break 46.5%;

[0064] (2) 7wt% loading group: ultrasonic dispersion time 45min, based on 10g PDMS prepolymer, cyclohexane addition amount 140mL; performance test results of composite membrane prepared by 7wt% loading group: at room temperature range of 15-28℃, water contact angle 114°, permeation flux 605g·m -2 ·h -1 Separation factor 12.8, 168h performance degradation rate 4.0%, tensile strength 2.4MPa, elongation at break 47%;

[0065] (3) 15wt% loading group: ultrasonic dispersion time 40min, based on 10g PDMS prepolymer, cyclohexane addition amount 160mL; performance test results of composite membrane prepared by 15wt% loading group: at room temperature range of 15-28℃, water contact angle 115°, permeation flux 520g·m -2 ·h -1 Separation factor 11.2, 168h performance degradation rate 5.2%, tensile strength 2.2MPa, elongation at break 44%;

[0066] (4) 25wt% loading group: ultrasonic dispersion time 45min, based on 10g PDMS prepolymer, cyclohexane addition amount 170mL; performance test results of composite membrane prepared by the 25wt% loading group: at room temperature range of 15-28℃, water contact angle 116°, permeation flux 485g·m -2 ·h -1 Separation factor 8.7, 168h performance degradation rate 5.4%, tensile strength 1.9MPa, elongation at break 40%;

[0067] (5) 35wt% loading group: ultrasonic dispersion time 50min, based on 10g PDMS prepolymer, cyclohexane addition amount 180mL; performance test results of composite membrane prepared by the 35wt% loading group: at room temperature range of 15-28℃, water contact angle 117°, permeation flux 380g·m -2 ·h -1 Separation factor 6.5, 168h performance degradation rate 6.2%, tensile strength 1.6MPa, elongation at break 36%;

[0068] (6) 40wt% loading group: ultrasonic dispersion time 60min, based on 10g PDMS prepolymer, cyclohexane addition amount 200mL; 40wt% loading group added at the end: Performance test results of the composite membrane prepared in this group: at room temperature range of 15-28℃, water contact angle 118°, permeation flux 275g·m -2 ·h -1 Separation factor 4.8, 168h performance degradation rate 7.2%, tensile strength 1.4MPa, elongation at break 32%.

[0069] Comparative Example 1

[0070] The only difference between Comparative Example 1 (ZIF-11 particles prepared by conventional hydrothermal method, containing DMF solvent) and Example 1 is the preparation method of ZIF-11 particles. All other process steps, raw material ratios, and parameter settings for GO-PI base film preparation and mixed matrix film preparation are completely consistent with Example 1.

[0071] Experimental objective: To verify the effects of ZIF-11 particles prepared by the hydrothermal method in the traditional DMF system on packing dispersibility, membrane separation performance, batch stability, and environmental friendliness, and to provide a direct comparison with the improved ammonia-assisted synthesis method of this invention;

[0072] The specific steps for preparing ZIF-11 particles using the conventional hydrothermal method are as follows:

[0073] (1) Preparation of precursor solution: Cobalt nitrate hexahydrate was dissolved in N,N-dimethylformamide (DMF) solvent and stirred at 250 r / min at room temperature until completely dissolved to prepare a cobalt nitrate solution C with a concentration of 0.1 mol / L; 2-methylimidazole was dissolved in DMF solvent and stirred at 250 r / min at room temperature until completely dissolved to prepare a 2-methylimidazole solution D with a concentration of 0.8 mol / L;

[0074] (2) Hydrothermal reaction: Mix solution C and solution D rapidly at a volume ratio of 1:4, stir at 300 r / min for 10 min at room temperature until the mixture is uniform, and immediately transfer to a stainless steel hydrothermal reactor lined with polytetrafluoroethylene. After sealing, place it in a forced-air drying oven and react at a constant temperature of 140℃ for 24 h.

[0075] (3) Post-processing of product: After the reaction is completed, the oven is turned off and the reaction vessel is allowed to cool naturally to room temperature; the reaction solution is centrifuged at 8000 r / min for 15 min and the precipitate is collected; the precipitate is washed 3 times with DMF and then rinsed 3 times with anhydrous methanol to completely remove unreacted raw materials and residual solvent; finally, it is vacuum dried at 80℃ for 12 h to obtain ZIF-11 particles synthesized by conventional hydrothermal method, and the composite membrane is prepared according to the subsequent steps of Example 1;

[0076] The performance test results of the composite membrane prepared in this comparative example are as follows: at a normal temperature of 25℃, the water contact angle is 102° and the permeation flux is 450 g·m³. -2 ·h -1 Separation factor 10.5, 168h performance decay rate 10.2%, tensile strength 1.7MPa, elongation at break 30%.

[0077] Comparative Example 2

[0078] Without adding ZIF-11 particles (loading 0 wt%), the remaining preparation steps were the same as in Example 1, and a pure PDMS / PI membrane was prepared.

[0079] The membrane performance test results of this comparative example are as follows: at a normal temperature of 25℃, the water contact angle is 103° and the permeation flux is 350 g·m³. -2 ·h -1 Separation factor 7.2, 168h performance degradation rate 13.5%, tensile strength 1.4MPa, elongation at break 26%.

[0080] Comparative Example 3

[0081] A single PDMS membrane (without a support layer or base membrane) was prepared under the same conditions as in Example 1.

[0082] The membrane performance test results of this comparative example are as follows: at a normal temperature of 25℃, the water contact angle is 95° and the permeation flux is 260 g·m³. -2 ·h -1 Separation factor 4.2, 168h performance degradation rate 18.5%, tensile strength 0.9MPa, elongation at break 18%.

[0083] Comparative Example 4

[0084] The base film material was replaced with pure PI (without GO nanosheets), and the remaining preparation steps were the same as in Example 1 to obtain a pure PI base film composite film.

[0085] The performance test results of the composite membrane prepared in this comparative example are as follows: at room temperature (15-28℃), the water contact angle is 105° and the permeation flux is 400 g·m³. -2 ·h -1 Separation factor 8.5, 168h performance degradation rate 11.2%, tensile strength 2.1MPa, elongation at break 38%.

[0086] Comparative Example 5

[0087] The only difference between Comparative Example 5 (without GO-PI base film, only PP nonwoven fabric support layer) and Example 1 is that step (2) GO-PI base film preparation is not performed, there is no GO-PI base film layer, and the ZIF-11-PDMS mixture prepared in step (3) is directly coated on the surface of the pretreated PP nonwoven fabric. The preparation of ZIF-11 particles, separation layer preparation, coating thickness, curing process, all raw material ratios and parameter settings are completely consistent with Example 1.

[0088] Experimental objective: To verify the effects of the complete absence of the GO-PI base membrane on membrane structural integrity, interfacial adhesion, separation performance, antifouling, mechanical stability, and long-term operating performance, and to provide a direct comparison with Example 1, thereby clarifying the irreplaceable role of the GO-PI base membrane in the composite membrane system;

[0089] The pretreatment steps of the PP nonwoven fabric are completely consistent with the pretreatment parameters of the nonwoven fabric in step (2) of Example 1: the PP nonwoven fabric is dried at 65-105℃ for 18-40h for pretreatment and then used for preparation to obtain a composite film without GO-PI base film.

[0090] The performance test results of the composite membrane prepared in this comparative example are as follows: at room temperature (15-28℃), the water contact angle is 107° and the permeation flux is 255 g·m³. -2 ·h -1 Separation factor 4.5, 168h performance degradation rate 17.2%, tensile strength 1.3MPa, elongation at break 22%.

[0091] Comparative Example 6

[0092] The only difference between the raw material concentration deviation from the invention's defined range and Example 1 is that in step (1), the concentration of solution A is 0.3 mol / L (lower than the lower limit of 0.6-2.2 mol / L defined by the invention), and the concentration of solution B is 5.0 mol / L (higher than the upper limit of 0.8-4.2 mol / L defined by the invention). All other parameters and steps are completely consistent with Example 1, and a composite membrane with a raw material concentration deviation from the defined range is obtained.

[0093] The performance test results of the composite membrane prepared in this comparative example are as follows: at room temperature (15-28℃), the water contact angle is 102° and the permeation flux is 320 g·m³. -2 ·h -1 Separation factor 6.8, 168h performance degradation rate 13.2%, tensile strength 1.8MPa, elongation at break 32%.

[0094] Comparative Example 7

[0095] The only difference between the drop acceleration rate group that deviates from the invention's defined range and Example 1 is that the drop acceleration rate of solution A in step (1) is 2 mL / min (lower than the 4-12 mL / min lower limit defined by the invention). All other parameters and steps are completely consistent with Example 1, and a composite membrane with a drop acceleration rate deviating from the defined range is obtained.

[0096] The performance test results of the composite membrane prepared in this comparative example are as follows: at room temperature (15-28℃), the water contact angle is 103° and the permeation flux is 335 g·m³. -2 ·h -1Separation factor 7.0, 168h performance degradation rate 12.5%, tensile strength 1.9MPa, elongation at break 34%.

[0097] Comparative Example 8

[0098] The only difference between the stirring parameters deviating from the scope of the invention and Example 1 is that the stirring speed in step (1) is 200 r / min (lower than the lower limit of 280-550 r / min specified by the invention). All other parameters and steps are completely consistent with Example 1, and a composite membrane with stirring parameters deviating from the scope is obtained.

[0099] The performance test results of the composite membrane prepared in this comparative example are as follows: at room temperature (15-28℃), the water contact angle is 100° and the permeation flux is 310 g·m³. -2 ·h -1 Separation factor 6.5, 168h performance degradation rate 14.0%, tensile strength 1.7MPa, elongation at break 30%.

[0100] Comparative Example 9

[0101] The core reaction parameters deviate from the range of Example 1. The only difference is that in step (1), the concentration of solution A is 2.8 mol / L, the concentration of solution B is 0.4 mol / L, the dropping rate is 15 mL / min, and the stirring speed is 650 r / min. All core parameters deviate from the range of this invention. The remaining steps are completely consistent with Example 1, and a composite membrane with core reaction parameters deviating from the range of this invention is obtained.

[0102] The performance test results of the composite membrane prepared in this comparative example are as follows: at room temperature (15-28℃), the water contact angle is 99° and the permeation flux is 240 g·m³. -2 ·h -1 Separation factor 3.8, 168h performance degradation rate 17.2%, tensile strength 1.3MPa, elongation at break 22%.

[0103] Performance Testing and Comparison

[0104] (1) Test baseline conditions: All samples were tested for pervaporation performance using 6wt% ethanol aqueous solution as feed liquid; except for the temperature range specifically marked, the test temperature of the other samples was 15-28℃ room temperature range; all performance values ​​are the average values ​​of 3 groups of parallel samples.

[0105] (2) Testing apparatus: such as Figure 1The apparatus and process shown include a feed tank (providing a 6wt% ethanol aqueous solution), a contaminant addition module (simulating impurities in industrial wastewater), a constant temperature control unit (maintaining room temperature of 5-40℃), a flow control module (adjusting the feed flow rate and stabilizing the feed state on the membrane surface), a pressure monitoring unit (monitoring the feed-side pressure in real time, ranging from 0.1 to 0.3 MPa), a membrane module (filled with the ZIF-11-PDMS / PI composite GO-PI membrane to be tested, with a fixed effective separation area), a reflux branch (unpermeated liquid is returned to the feed tank to achieve cyclic testing), a vacuum system (maintaining a vacuum degree of 0.07-0.10 MPa on the permeate side to promote mass transfer), a condensation and collection unit (low-temperature condensation of permeate vapor and collection of liquid products), and a detection unit (① permeate flux test (weighing method): ② separation factor calculation (gas chromatography): ③ 168h performance decay rate monitoring).

[0106] (3) Formula for calculating core indicators:

[0107] Formula for calculating permeation flux: ;

[0108] In the formula: J is the permeation flux, in grams. m 2 h 1 m represents the mass of the permeate, in grams; A represents the effective test area of ​​the membrane, in square meters. 2 t represents the stable test time, in hours (h).

[0109] Separation factor calculation formula: ;

[0110] In the formula: α is the separation factor; Y is the mass fraction of the corresponding component in the permeate; X is the mass fraction of the corresponding component in the feed liquid;

[0111] (4) Test indicators: permeation flux, separation factor, performance degradation rate after 168h continuous operation, water contact angle, tensile strength, and elongation at break. The test results are shown in Table 1.

[0112] Table 1. Test data for comparative and example cases.

[0113]

[0114] As can be seen from the measured data in Table 1:

[0115] (1) The optimal formulation of this invention (Example 1, 3wt% ZIF-11 loading) has a stable permeation flux of 620-685 g·m³ within the full room temperature range of 5-40℃. -2 ·h -1The separation factor remained stable at 13.6-15.2, all meeting the requirement of a permeation flux ≥ 580 g·m³. -2 ·h -1 Performance requirements: separation factor ≥ 13; performance degradation rate is only 4.2% after 168h continuous operation, while maintaining tensile strength of 2.8MPa and elongation at break of 52%, with no significant performance fluctuations in a wide temperature range, and outstanding overall performance;

[0116] (2) When the ZIF-11 loading is in the range of 0.8-7wt%, the permeation flux of the composite membrane is ≥590g·m³. -2 ·h -1 The separation factor is ≥12.8, indicating optimal overall performance. However, when the loading exceeds 7 wt%, the permeation flux and separation factor decrease synchronously with increasing loading, reaching 275 g·m³ at a loading of 40 wt%. -2 ·h -1 With a separation factor of only 4.8, the performance degradation is significant, verifying that 0.8-7wt% is the optimal loading range for this invention.

[0117] (3) Compared with the ZIF-11 composite membrane prepared by the traditional hydrothermal method (Comparative Example 1), the optimal embodiment of the present invention has a 37.8% increase in permeation flux, a 41.0% increase in separation factor, and a 67.6% reduction in performance degradation rate after 168 hours; compared with the pure PDMS / PI membrane (Comparative Example 2), the permeation flux is increased by 88.0% and the separation factor is increased by 105.6%; compared with the single PDMS membrane (Comparative Example 3), the permeation flux is increased by 153.1% and the separation factor is increased by 252.4%.

[0118] (3) Comparative Examples 1-9 verified the synergistic advantages of the ZIF-11 ammonia-assisted synthesis method, the three-layer composite structure, the GO-PI base membrane and the core process parameters of the present invention. Only the technical solutions defined in the claims of the present invention can simultaneously achieve high separation performance, low operating attenuation, excellent mechanical stability and strong solvent resistance.

[0119] Industrial Application Cases

[0120] 1. Industrial application of ethanol recovery from large-scale ABE fermentation broth

[0121] A biofuel plant uses the ABE fermentation process to produce fuel. The fermentation broth has an ethanol concentration of 3-7 wt%, and also contains small amounts of organic acids and protein impurities, which falls within the treatment concentration range of this invention. The plant uses the mixed matrix pervaporation membrane prepared in Example 1 of this invention to construct a large-scale separation system with a processing capacity of 100-150 m³. 3 / d, operating temperature controlled within the room temperature range of 5-40℃; related equipment and processes are as follows Figure 2It includes a raw material storage tank, a filtration pretreatment unit (to remove large particulate impurities), a membrane module array (three-layer membrane module), a product separation and collection unit, a membrane cleaning and regeneration module (adapted to the characteristics of antifouling membranes), a control system, and a waste heat recovery unit.

[0122] The results show that regardless of whether the ambient temperature fluctuates between 5-15℃, 15-28℃, or 28-40℃, the ethanol recovery rate remains stable at over 90%, and the product purity reaches over 95%. Energy consumption is reduced by 38% compared to traditional membrane separation processes, meeting the requirement of energy consumption reduction of over 35%. After 168 hours of continuous operation, the performance degradation rate of the membrane module is only 3.2%, meeting the standard of degradation rate ≤5%. In large-scale production, the permeate flux of three batches of membrane modules fluctuated by only 3.8%, and the separation factor fluctuated by only 5.2%, showing significantly better consistency than traditional membranes. The separated ethanol product fully meets the requirements for use as biofuel. The plant can save approximately 950,000 to 1.2 million yuan in energy costs annually.

[0123] 2. Application of low-concentration ethanol separation in high-salt pharmaceutical wastewater

[0124] A pharmaceutical company generates high-salt process wastewater containing 2-6 wt% ethanol during its production process, with a salt content of 4-9 wt%, which falls within the treatment concentration range defined in this invention. The company uses the membrane separation system described in Example 1 of this invention, employing a cross-flow operation mode, with a processing capacity of 40-80 m³ / h. 3 / d, operating temperature range of 5-40℃ at room temperature; related equipment and processes are as follows Figure 2 It includes a raw material storage tank, a filtration pretreatment unit (to remove large particulate impurities), a control system, a membrane module array (three-layer membrane module), a product separation and collection unit, a membrane cleaning and regeneration module (adapted to the characteristics of antifouling membranes), a recycled ethanol storage tank, a qualified wastewater storage tank, and a waste heat recovery unit.

[0125] Application results show that, under fluctuating room temperature in different seasons, the ethanol content of the treated wastewater is reduced to below 0.1 wt%, meeting discharge standards. The recovered ethanol can be directly reused as a process solvent in production, achieving the dual goals of resource recovery and environmental governance. Compared with traditional membrane separation processes, the operating cost of this system is reduced by 40%, saving 380-500 tons of steam consumption annually, while reducing ethanol emissions by approximately 14-22 tons per year. The membrane exhibits no swelling or degradation during continuous operation in high-salt environments, demonstrating significant solvent compatibility advantages and achieving good economic and environmental benefits.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery, characterized in that, Specifically, the following steps are included: (1) Preparation of ZIF-11 particles: Cobalt nitrate salt was dissolved in deionized water to prepare solution A, and 2-methylimidazolium was dissolved in ammonia water to prepare solution B; solution A was added to solution B, and the mixture was stirred at room temperature to obtain precipitate, which is ZIF-11 particles; (2) Preparation of GO-PI base film: PI powder and GO nanosheets are added to N-methylpyrrolidone and mixed evenly to obtain casting solution. The casting solution is coated on the surface of PP nonwoven fabric and cured and dried to obtain GO-PI base film. (3) Disperse the ZIF-11 particles in cyclohexane, add PDMS prepolymer, tetraethoxysilane and dibutyltin dilaurate, mix evenly and degas to obtain a mixture, coat the mixture on the GO-PI base membrane, and after curing, obtain a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery.

2. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 1, characterized in that, The concentration of solution A in step (1) is 0.6-2.2 mol / L, and the concentration of solution B is 0.8-4.2 mol / L; The volume ratio of solution A to solution B is 1:1-6.

3. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 1, characterized in that, The reaction time in step (1) is 6-40 min, and the stirring speed is 280-550 r / min; Solution A is added dropwise to solution B at a rate of 4-12 mL / min.

4. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 1, characterized in that, The steps for treating the precipitate in step (1) are as follows: after the reaction is completed, the precipitate is collected by centrifugation, washed with deionized water until neutral, rinsed with anhydrous ethanol, and finally vacuum dried at 70-110℃ for 6-26h.

5. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 1, characterized in that, The mass ratio of PI powder to GO nanosheets in step (2) is 95-99:1-5; The total amount of the PI powder and the GO nanosheets is in a mass-to-volume ratio of 1g to 7-18mL to the N-methylpyrrolidone.

6. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 1, characterized in that, The mixing described in step (2) is as follows: stirring at 250-480 r / min for 5-16 h at 75-115℃; The coating thickness is 35-80 μm, and the thickness of the GO-PI base film after curing and drying is 25-50 μm; The curing and drying steps are as follows: after the coated PP nonwoven fabric is cured in a deionized water coagulation bath and the residual solvent is removed, it is then vacuum dried at 80-100℃ for 8-18 hours.

7. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 1, characterized in that, The amount of ZIF-11 particles added in step (3) is 0.8-40 wt% of the PDMS prepolymer. The mass ratio of the PDMS prepolymer, the tetraethoxysilane, and the dibutyltin dilaurate is 45-85:1-12:

1.

8. The method for preparing a ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery according to claim 7, characterized in that, The dispersion in step (3) is ultrasonic dispersion, wherein the ultrasonic time is 20-50 min when the amount of ZIF-11 particles added is 0.8-7 wt%, and the ultrasonic time is 30-60 min when the amount is greater than 7 wt%. When the amount of ZIF-11 particles added is 0.8-7wt%, the mass-volume ratio of the PDMS prepolymer to the cyclohexane is 10g:100-200mL; when it is greater than 7wt%, the mass-volume ratio of the PDMS prepolymer to the cyclohexane is 10g:150-200mL. The mixing process involves stirring at 180-380 r / min for 0.8-3.5 h. The degassing process involves degassing under a vacuum of (-0.07) to (-0.10) MPa for 8-45 minutes. The coating thickness is 8-28 μm, and the total thickness of the ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane is 33-78 μm; The curing process involves first curing at room temperature for 15-40 hours, followed by curing at 70-100℃ for 1.5-8 hours, with a heating rate of 1.5-8℃ / min.

9. A ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane for ethanol recovery obtained by the preparation method according to any one of claims 1-8.

10. The application of the ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane obtained by the preparation method according to any one of claims 1-8 or the ZIF-11-PDMS / GO-PI mixed matrix pervaporation membrane according to claim 9 in the recovery of low-concentration ethanol, characterized in that, The concentration of the ethanol is 0.5-18 wt%.

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