High-temperature-resistant solvent-resistant polyurea-based organic solvent reverse osmosis membrane and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant solvent-resistant polyurea-based organic solvent reverse osmosis membrane as well as a preparation method and application thereof. The organic solvent reverse osmosis membrane comprises a cross-linked polyimide porous support layer and a polyurea separation layer, wherein the polyurea separation layer is formed by an interfacial polymerization reaction of a water-phase mixed monomer and an organic-phase monomer. According to the invention, Cyclen is introduced as a comonomer to regulate and control the microstructure of the polyurea separation layer, so that the separation performance and solvent permeation flux of the membrane are remarkably improved. The retention rate of the prepared membrane on NaCl in an aqueous solution reaches 97.9%-99.3%, and the water flux reaches 13.7 LMH / MPa; and the retention rate of ibuprofen (206 Da) in an ethanol solution reaches 92.6%, and the ethanol flux reaches 4.52 LMH / MPa. The membrane has excellent solvent resistance and high temperature resistance, the retention rate of NaCl is still kept above 95.8% after the membrane is soaked in DMF (Dimethyl Formamide) at 25 DEG C for 30 days, and the separation performance is not obviously reduced after the membrane is soaked in ethanol at 70 DEG C for 12 days. The preparation method is simple and has a wide application prospect in separation of low-molecular-weight organic mixtures in the fields of chemical engineering, pharmacy and the like.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a high-temperature and solvent-resistant polyurea-based organic solvent reverse osmosis membrane and its preparation method, which is suitable for efficient and low-energy separation of low molecular weight organic mixtures, especially in separation processes under high temperature and strong polar solvent environments. Background Technology

[0002] The chemical industry has a significant need for separating small-molecule mixtures of organic systems, such as the separation of organic solutes and solvents with molecular weights less than 200 Da. Traditional separation processes, such as distillation and evaporation, generally suffer from high energy consumption and limited separation efficiency, accounting for over 80% of the total energy consumption in chemical separation. Organic solvent reverse osmosis technology, with its extremely low theoretical separation energy consumption and ability to achieve phase-change-free separation, shows excellent application prospects in the separation of organic mixtures with molecular weights less than 200 Da.

[0003] Currently, research on organic solvent reverse osmosis membranes mainly focuses on polyamide-based thin-layer composite membranes. Professor Matsuyama's team at Kobe University in Japan has conducted extensive pioneering research on polyamide-based organic solvent reverse osmosis membranes, preparing various high-performance organic solvent reverse osmosis membranes through interfacial polymerization. However, traditional polyamide membranes still suffer from insufficient structural and performance stability in high-temperature environments and highly polar solvents, which limits their application in more demanding industrial environments.

[0004] Polyurea is a polymer formed by the reaction of isocyanates and amino compounds, with its core structure being the urea bond (-NH-CO-NH-). Compared to polyamides, polyurea has unique structural advantages: the urea bond is a polar group, capable of forming numerous bidentate hydrogen bonds between polymer molecular chains. Calculations show that the binding energy of bidentate hydrogen bonds between urea molecules (45.6 kJ / mol) is much higher than that of monodentate hydrogen bonds between amide molecules (29.7 kJ / mol). This strong hydrogen bonding endows polyurea with extremely high cohesive energy density and excellent mechanical strength; the urea bond also exhibits higher chemical stability, resisting hydrolysis or degradation in water, acid / alkali, or salt spray environments; and the isocyanate and amino groups have extremely high reactivity, allowing for rapid reaction without the need for catalysts. In recent years, research has explored the application of polyurea membranes in acid and alkali resistant nanofiltration.

[0005] Currently, polyurea membranes are used to prepare nanofiltration membranes for organic solvents, but there are no studies on the separation of solutes with smaller molecular weights in organic solvents using reverse osmosis membranes. Based on the chemical robustness of the polyurea structure and the dense sieving properties of reverse osmosis membranes, applying polyurea materials to the preparation of reverse osmosis membranes using organic solvents holds promise for solving the problem of insufficient stability of traditional polyamide membranes in high temperatures and highly polar solvents. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing polyamide organic solvent reverse osmosis membranes in terms of insufficient stability in high temperatures and highly polar solvents, and provides a high-temperature and solvent-resistant polyurea-based organic solvent reverse osmosis membrane and its preparation method. This method introduces urea groups with higher chemical stability, forming numerous bidentate hydrogen bonds between the polymer molecular chains of the polyurea separation layer, thus endowing the membrane with excellent high-temperature and solvent resistance. Furthermore, by controlling the microstructure of the polyurea separation layer through comonomer regulation, the solvent flux is significantly improved while maintaining high selectivity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A high-temperature resistant and solvent-resistant reverse osmosis membrane for organic solvents includes: a cross-linked polyimide porous support layer, and a polyurea separation layer formed on the cross-linked polyimide porous support layer; wherein the polyurea separation layer is formed by interfacial polymerization of a polyamine compound or a mixture thereof as an aqueous phase monomer and a polyisocyanate or a mixture thereof as an organic phase monomer.

[0008] Preferably, the polyamine compound includes a diamine compound, and the polyisocyanate includes a diisocyanate.

[0009] More preferably, the aqueous phase monomer comprises polyethyleneimine and 1,4,7,10-tetraazacyclododecane, and the organic phase monomer is toluene-2,4-diisocyanate.

[0010] Its preparation method includes the following steps: (1) Preparation and crosslinking of polyimide support membrane: Polyimide is placed in an aprotic polar organic solvent, a pore-forming agent is added, and after stirring to dissolve and degas, it is coated onto a nonwoven fabric. After evaporation in air, it is immersed in a water bath to undergo non-solvent-induced phase separation to form a porous support membrane. The support membrane is then immersed in a crosslinking agent for crosslinking treatment to improve its solvent resistance. (2) Preparation of aqueous monomer solution: Dissolve the polyamine compound or its mixture as an aqueous monomer in water, add a surfactant, and obtain an aqueous monomer solution; (3) Preparation of organic phase monomer solution: Dissolve polyisocyanate or mixture thereof as organic phase monomer in hydrophobic organic solvent to obtain organic phase monomer solution; (4) The cross-linked polyimide porous support membrane is contacted with the aqueous monomer solution for a certain period of time so that the aqueous monomer is loaded on the surface of the support membrane. (5) After removing excess aqueous monomer solution, the support membrane loaded with aqueous monomer is contacted with organic monomer solution for a certain period of time to carry out interfacial polymerization reaction and form polyurea separation layer. (6) The membrane after interfacial polymerization is placed in an oven for heat treatment for a certain period of time to obtain the target organic solvent reverse osmosis membrane.

[0011] Preferably, the aprotic polar organic solvent is N,N-dimethylformamide, the porogen includes polyethylene glycol-400, and the crosslinking agent includes an isopropanol solution of 1,6-hexanediamine.

[0012] Preferably, the polyamine compound includes a diamine compound, and the polyisocyanate includes a diisocyanate.

[0013] More preferably, the aqueous phase monomer comprises polyethyleneimine and 1,4,7,10-tetraazacyclododecane, the organic phase monomer comprises toluene-2,4-diisocyanate, and the hydrophobic organic solvent comprises n-hexane.

[0014] Preferably, the total mass fraction of the aqueous phase monomer is 0.1~3.0 wt%, and the mass fraction of the surfactant is 0.01~0.1 wt%.

[0015] Preferably, the total mass fraction of the organic phase monomers is 0.1~0.5 wt%.

[0016] Preferably, the interfacial polymerization reaction time is 30~90 s.

[0017] Preferably, the oven temperature is 50~80°C and the heat treatment time is 5~20 min.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) Excellent separation performance: For example, when 1,4,7,10-tetraazacyclododecane is added as an aqueous comonomer, the NaCl rejection rate in the aqueous solution system reaches 97.9%~99.3%, and the water flux reaches 13.7 LMH / MPa (L m -2 h -1 MPa -1 The flux of the membrane was increased by about 2.4 times compared to the reference membrane. In the ethanol system, the rejection rate of ibuprofen at 206 Da reached 92.6%, and the ethanol flux reached 4.52 LMH / MPa.

[0019] (2) Outstanding solvent resistance: After soaking in DMF at 25℃ for 30 days, the NaCl rejection rate is still above 95.8%; after soaking in ethanol at 70℃ for 12 days, the separation performance does not decrease significantly; after soaking in DMF at 70℃ for 48 hours, the NaCl rejection rate is still 94.5%.

[0020] (3) Excellent long-term operational stability: When running continuously for 54 h at 3.0 MPa with ibuprofen / ethanol solution, the ethanol flux is stable at around 5.0 LMH / MPa, and the ibuprofen rejection rate remains above 90%.

[0021] (4) Good pressure resistance: The rejection rate of NaCl aqueous solution and ibuprofen / ethanol solution remains stable within the operating pressure range of 1.0~4.0 MPa, and the flux increases linearly with pressure. Detailed Implementation

[0022] To better understand the present invention, the present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0023] Preparation of the support membrane (general steps) Preparation of the supporting membrane: 18 wt% P84 powder and 1.0 wt% PEG-400 were dissolved in DMF and stirred at 60℃ for 4 h until completely dissolved. The mixture was then allowed to stand for 12 h to remove bubbles. The casting solution was uniformly coated onto a polyester nonwoven fabric using a doctor blade with a gap of 140 μm. After evaporation in air for 10 s, the membrane was immersed in a 25℃ deionized water bath to allow phase separation and form a porous membrane, which was then stored in water for later use.

[0024] Crosslinking treatment: Immerse the support membrane in a 10 wt% HDA / IPA solution and react at 60°C for 30 min. After removal, wash repeatedly with IPA and then transfer to water for storage.

[0025] Test methods Water system separation performance test: A laboratory-built cross-flow filtration device was used. The feed solution was a 2000 mg / L NaCl aqueous solution. The operating pressure was 1.5 MPa, the temperature was 25±1°C, and the effective membrane area was 28.26 cm². The membrane was pre-pressurized at 1.7 MPa for 30 minutes before testing. The water flux was calculated using the formula P = Δm / (ρ×A×Δt×Δp), and the NaCl rejection rate was calculated using the formula R = (1 - Cp / Cf) × 100%.

[0026] Separation performance test of organic solvent system: The feed solution was a 100 mg / kg small molecule solute / ethanol solution, the operating pressure was 3.0 MPa, the temperature was 25±1°C, and the effective membrane area was 28.26 cm². The membrane was pre-pressurized at 3.5 MPa for 30 minutes before testing. The solute concentration was determined by UV spectrophotometry and calculated based on the corresponding standard curve.

[0027] Solvent resistance test: The membrane was immersed in different organic solvents at 25°C for 30 days, or in DMF and ethanol at 70°C for 7 days. After removal, it was thoroughly rinsed with deionized water, and the change in its separation performance was tested.

[0028] Long-term operational stability test: Using 100 mg / kg ibuprofen / ethanol solution as feed, the system was continuously operated for 54 h at 3.0 MPa and 25±1°C.

[0029] Comparative example: Polyamide film The supporting membrane and crosslinking treatment were prepared according to general procedures. An aqueous phase solution was prepared: 1.0 wt% PEI and 0.05 wt% SDS. An organic phase solution was prepared: 0.3 wt% TDI / n-hexane. The crosslinked membrane was contacted with a 2.0 wt% MPD (m-phenylenediamine) aqueous solution for 16 s. After removing excess solution, it was contacted with a 0.15 wt% TMC (trimethylammonium chloride) / n-hexane solution for 12 s for interfacial polymerization. The membrane was then heat-treated at 60℃ for 10 min to obtain the control membrane. This membrane had a water flux of 5.25 LMH / MPa, a NaCl rejection rate of 99.2%, an ethanol flux of 0.34 LMH / MPa, and an acetylsalicylic acid rejection rate of 88.7%. At room temperature (25℃), after immersing the membrane prepared in ethanol for 30 days, the water flux of the resulting membrane was 5.03 LMH / MPa, and the NaCl rejection rate decreased to 97.41%, exhibiting good solvent resistance at room temperature. After the membrane was immersed in DMF for 72 hours, the NaCl rejection rate was 45%. Example 1

[0030] The supporting membrane and crosslinking treatment were prepared according to general procedures. An aqueous phase solution was prepared: 1.0 wt% PEI and 0.05 wt% SDS. An organic phase solution was prepared: 0.3 wt% TDI / n-hexane. The crosslinked membrane was contacted with the aqueous phase solution for 1 min, and after removing excess solution, it was contacted with the organic phase solution for 60 s for interfacial polymerization. The membrane was then heat-treated at 60℃ for 10 min to obtain the TFC-0 membrane. This membrane exhibited a water flux of 5.6 LMH / MPa, a NaCl rejection rate of 98.9%, an ethanol flux of approximately 2.53 LMH / MPa, and an ibuprofen rejection rate of approximately 91%. At room temperature (25℃), after immersion in various commonly used industrial organic solvents such as n-hexane, methanol, ethanol, and DMF for 30 days, the NaCl rejection rate remained above 93%, with almost no performance degradation after immersion in non-polar n-hexane. The membrane showed no significant changes in rejection rate and water flux after being immersed in ethanol at 70°C for 12 days. However, after being immersed in highly polar DMF at 70°C for 7 days, it still maintained a 93.9% rejection rate for NaCl. Example 2

[0031] Following the steps of Example 1, the aqueous phase solution was changed to: 0.8 wt% PEI, 0.2 wt% Cyclen, and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane had a water flux of 8.2 LMH / MPa, a NaCl rejection rate of 98.8%, an ethanol flux of approximately 4.58 LMH / MPa, and an ibuprofen rejection rate of approximately 92%. Example 3

[0032] Following the steps of Example 1, the aqueous phase solution was changed to: 0.4 wt% PEI, 0.6 wt% Cyclen, and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane had a water flux of 13.7 LMH / MPa, a NaCl rejection rate of 98.5%, an ethanol flux of 4.52 LMH / MPa, and an ibuprofen rejection rate of 92.6%. The water contact angle on the membrane surface was approximately 65°, the surface roughness was less than 4 nm, and the separation layer thickness was approximately 95 nm. At room temperature (25°C), after immersion in various organic solvents for 30 days, the NaCl rejection rate remained above 93%, especially after immersion in the strongly polar aprotic solvent DMF for 30 days, where the NaCl rejection rate was still as high as 95.8%. The membrane showed almost no fluctuation in rejection rate and flux after being immersed in ethanol at 70°C for 12 days, demonstrating excellent high-temperature alcohol stability. Even after a short-term immersion in DMF at 70°C for 48 hours, the rejection rate for NaCl remained at 94.5%. Example 4

[0033] Following the steps of Example 1, the aqueous phase solution was changed to: 0.2 wt% PEI, 0.8 wt% Cyclen, and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane water flux was 14.2 LMH / MPa, and the NaCl rejection rate was 98.1%. Example 5

[0034] Following the steps of Example 1, the aqueous phase solution was changed to: 1.0 wt% Cyclen and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane water flux was 15.1 LMH / MPa, and the NaCl rejection rate was 95.9%. Example 6

[0035] Following the steps of Example 1, the aqueous phase solution was changed to: 3.0 wt% MPD and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane water flux was 2.1 LMH / MPa, and the NaCl rejection rate was 70.3%. Example 7

[0036] Following the steps of Example 1, the aqueous phase solution was changed to: 0.2~0.8 wt% PEHA (pentaethylenehexamine) and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane water flux was 5.7 LMH / MPa, and the NaCl rejection rate was 98.2%. Example 8

[0037] Following the steps of Example 1, the aqueous phase solution was changed to: 1.0 wt% PEHA and 0.05 wt% SDS, with all other conditions remaining the same. The resulting membrane water flux was 6.1 LMH / MPa, and the NaCl rejection rate was 98.5%. Example 9

[0038] Following the steps of Example 3, keeping the aqueous phase composition unchanged (0.4 wt% PEI + 0.6 wt% Cyclen + 0.05 wt% SDS), the TDI concentration was changed to 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, and 0.5 wt%, respectively. The NaCl retention rate reached over 98.5%. Example 10

[0039] Following the steps of Example 3, while keeping other conditions unchanged, the interface polymerization time was changed to 30 s, 45 s, 60 s, 75 s, and 90 s, respectively. The NaCl retention rate was over 98% in all cases. Example 11

[0040] The TFC-0.6 membrane prepared in Example 3 was immersed in different solvents at 25°C for 30 days, and its separation performance was tested. The results showed that after immersion in DMF for 30 days, the water flux was improved, and the NaCl rejection rate remained above 95.8%, demonstrating excellent solvent resistance.

[0041] After immersing the TFC-0.6 membrane prepared in Example 3 in DMF at 70°C for 48 hours, the NaCl rejection rate was 94.5%; after immersing it in ethanol at 70°C for 12 days, the NaCl rejection rate remained above 97.6%, and the water flux did not change significantly, demonstrating excellent solvent resistance.

[0042] The TFC-0.6 membrane prepared in Example 3 was continuously run at 3.0 MPa with a 100 mg / kg ibuprofen / ethanol solution for 54 h. The results showed that after 8 h of operation, the ethanol flux stabilized at approximately 5.1 LMH / MPa, and the ibuprofen rejection rate remained above 91%; after 54 h of operation, the ethanol flux remained at around 5.0 LMH / MPa, and the ibuprofen rejection rate remained above 90%. Example 12

[0043] The TFC-0.6 membrane prepared in Example 3 was used for a concentration experiment of ethyl cinnamate / ethanol mixture. The initial concentration of the feed solution was approximately 85 mg / kg, the operating pressure was 3.0 MPa, and after 8 h of operation, the concentration of ethyl cinnamate in the retentate increased to approximately 3.5 times the original concentration, the ethanol flux remained at approximately 4.3 LMH / MPa, and the ethyl cinnamate rejection rate remained at approximately 81.5%.

[0044] As can be seen from the above examples and comparative examples, this invention successfully prepared a polyurea-based organic solvent reverse osmosis membrane with both high separation performance and excellent stability. Compared with the reference membrane without Cyclen, the flux of the membrane after adding Cyclen was significantly improved (water flux increased by approximately 2.4 times, and ethanol flux increased by approximately 2.5 times), while maintaining a high rejection rate. This membrane exhibits excellent stability in high-temperature and highly polar solvent environments, overcoming the application limitations of traditional polyamide membranes under harsh conditions.

[0045] The polyurea-based organic solvent reverse osmosis membrane prepared by this invention can be used for the separation and concentration of low molecular weight organic mixtures, and is particularly suitable for organic solvent recovery and product purification in the fields of pharmaceuticals and fine chemicals, as well as separation processes in high temperature and strongly polar solvent environments.

Claims

1. A high-temperature resistant and solvent-resistant reverse osmosis membrane, characterized in that, include: Crosslinked polyimide porous support layer; and A polyurea separation layer formed on the cross-linked polyimide porous support layer; The polyurea separation layer is formed by interfacial polymerization of a polyamine compound or a mixture thereof as an aqueous phase monomer and a polyisocyanate or a mixture thereof as an organic phase monomer.

2. The high-temperature resistant and solvent-resistant reverse osmosis membrane according to claim 1, characterized in that, The polyamine compound includes a diamine compound, and the polyisocyanate includes a diisocyanate.

3. The high-temperature resistant and solvent-resistant reverse osmosis membrane according to claim 1, characterized in that, The polyamine compound comprises polyethyleneimine (PEI), pentaethylenehexamine (PEHA), m-phenylenediamine (MPD), and 1,4,7,10-tetraazacyclododecane (Cyclen), and the polyisocyanate compound comprises toluene-2,4-diisocyanate (TDI) and diphenylmethane diisocyanate (MDI).

4. The high-temperature resistant and solvent-resistant reverse osmosis membrane according to claim 1, characterized in that, The total mass fraction of the mixed monomers in the aqueous phase mixed monomers is 0.1~3.0 wt%.

5. A method for preparing a high-temperature resistant and solvent-resistant reverse osmosis membrane as described in any one of claims 1-4, characterized in that, Includes the following steps: Step (1): Prepare a polyimide porous support membrane and perform crosslinking treatment; Step (2), preparing an aqueous solution: dissolve polyamine polymers in different proportions in water, add surfactants, and obtain an aqueous mixed monomer solution; Step (3), preparing the organic phase solution: dissolve a certain amount of polyisocyanate or its mixture in a hydrophobic organic solvent to obtain an organic phase monomer solution; Step (4): The cross-linked polyimide porous support membrane is brought into contact with an aqueous solution to load the aqueous monomer onto the surface of the support membrane. Step (5): After removing the excess aqueous solution, the support membrane loaded with aqueous monomers is brought into contact with the organic solution to carry out an interfacial polymerization reaction and form a polyurea separation layer. Step (6): Heat treatment to obtain the target organic solvent reverse osmosis membrane.

6. The preparation method according to claim 5, characterized in that, The crosslinking treatment in step (1) uses a 5-15 wt% isopropanol solution of 1,6-hexanediamine and is treated at 50-70°C for 20-40 min.

7. The preparation method according to claim 5, characterized in that, The aqueous phase mixed monomers mentioned in step (2) are polyethyleneimine and 1,4,7,10-tetraazacyclododecane, with a total mass fraction of 0.1~3.0 wt% and sodium dodecyl sulfate with a mass fraction of 0.01~0.1 wt%.

8. The preparation method according to claim 5, characterized in that, The polyisocyanate mentioned in step (3) is toluene-2,4-diisocyanate, with a mass fraction of 0.1~0.5 wt%.

9. The preparation method according to claim 5, characterized in that, The contact time in step (4) is 1~3 min, the interfacial polymerization reaction time in step (5) is 30~90 s, and the heat treatment temperature in step (6) is 50~80°C and the heat treatment time is 5~20 min.

10. The application of a high-temperature resistant and solvent-resistant reverse osmosis membrane as described in any one of claims 1-4, or a high-temperature resistant and solvent-resistant reverse osmosis membrane prepared by any one of claims 5-9, characterized in that, Used for the separation, concentration, or purification of organic solvent mixtures, including the separation of low molecular weight organic solutes in alcohol systems, and separation processes in high-temperature organic solvent environments.