Method for preparing polyamide composite membrane based on liquid paraffin-water interfacial polymerization and application of polyamide composite membrane

Abstract

The invention discloses a method for preparing a polyamide composite membrane based on liquid paraffin-water interfacial polymerization and application of the polyamide composite membrane, and belongs to the technical field of membrane separation. Liquid paraffin is used as an organic phase solvent for preparing the polyamide composite membrane through interfacial polymerization, an acyl chloride monomer is dissolved in the liquid paraffin, an amine monomer is dissolved in a water phase, and the polyamide composite membrane is prepared through an immiscible interface between the liquid paraffin and water. According to the invention, the polymerization speed of two monomers at an interface is reduced, a more uniform membrane structure is formed, and the overall performance and stability of the membrane are improved. The membrane can be used as a nanofiltration membrane and a reverse osmosis membrane; the method is applied to sewage purification and salt-containing wastewater treatment, and is particularly applied to high-concentration saline water treatment, ion separation and antibiotic desalination.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation and technology, specifically relating to a method for preparing polyamide composite membranes based on liquid paraffin-water interfacial polymerization and its application. Background Technology

[0002] Global changes such as population growth, industrialization, socioeconomic shifts, urbanization, and climate change have placed unprecedented pressure on water resources. Faced with severe global water scarcity, there is a huge demand for efficient water treatment technologies, and achieving global water security through new research is crucial for sustainable development. Currently, relatively cost-effective wastewater treatment technologies include activated sludge processes, adsorption, coagulation, electrochemical technologies, trickling filters, bioreactors, and membrane separation technologies. Among these, membrane separation technology has been widely recognized as a promising solution to overcome the current global water scarcity challenge and is one of the most effective technologies for wastewater treatment and water purification, with wide applications in food processing, pharmaceuticals, drinking water treatment, and industrial wastewater treatment.

[0003] Globally, approximately 63.7% of seawater desalination is achieved using membrane separation technology. Membrane separation technology offers advantages such as low energy consumption, low cost, ease of application, and effective reduction of secondary pollution, giving it a significant advantage over other water treatment technologies. Nanofiltration membranes have pore sizes at the nanometer level (typically around 0.5-2 nm), falling between ultrafiltration membranes with pore sizes of 2-100 nm and non-porous reverse osmosis membranes. Developing high-flux and high-retention-rate nanofiltration membranes has always been a crucial goal in the field. Currently, methods such as finding novel monomers, controlling the substrate, adding intermediate layers, and using additives during interfacial polymerization have been applied to prepare high-flux and high-retention-rate nanofiltration membranes. Xu et al. successfully prepared a nanofiltration membrane rich in -NH4+ by in-situ interfacial polymerization of polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a polyethersulfone (PES) ultrafiltration substrate using polyethyleneimine (PEI) as the amine monomer. 3+ and -NH 2+ Positively charged nanofiltration membranes can achieve magnesium-lithium separation at high magnesium-to-lithium ratios, with a lithium-magnesium selectivity as high as 20%. Oh et al. introduced carboxyl groups into the surface of porous substrates, and the ionic bonds formed by carboxyl and amine groups significantly enhanced the chemical stability of polyamide film composite membranes. Wang et al. promoted the diffusion of PEI monomers by adding sodium dodecyl sulfate (SDS) to the aqueous solution, and the obtained nanofiltration membrane had a higher retention effect.

[0004] Liquid paraffin is a colorless and odorless mixture obtained from crude oil fractionation. Based on the fraction, it can be divided into light liquid paraffin (light wax) and heavy liquid paraffin (heavy wax). Alkanes with 14-15 carbon atoms are light waxes, while those with 25-40 carbon atoms are heavy waxes. Generally, mixed liquid paraffins have a C15-C40 carbon distribution. Due to its compositional characteristics, it is relatively stable at room temperature, does not easily volatilize, and is not prone to chemical reactions. Therefore, it is very suitable as an organic phase solvent for interfacial polymerization to prepare polyamide composite films.

[0005] This invention selects liquid paraffin as the organic phase solvent in the polyamide composite membrane because of its non-volatile properties, making it a green and environmentally friendly membrane solvent. Furthermore, its high viscosity helps to slow down the polymerization rate of the two monomers at the interface, resulting in a more uniform membrane structure. Simultaneously, it forms a more defined interface with the aqueous phase, providing an ideal environment for the polymerization reaction and helping to reduce the dissolution and diffusion of monomers in the solvent. This reduces the possibility of side reactions between acyl chloride monomers and water in the solvent phase, increasing water flux while maintaining a high rejection rate, thus achieving effective treatment of saline wastewater and effectively separating monovalent and divalent salts and removing salts from antibiotic wastewater. Summary of the Invention

[0006] The key technical problem to be solved by this invention is to provide a method for preparing polyamide composite membranes based on liquid paraffin-water interfacial polymerization and its application in the treatment of saline wastewater.

[0007] This invention provides a method for preparing polyamide composite membranes based on liquid paraffin-water interfacial polymerization and its application. The method is characterized by using liquid paraffin as the organic phase solvent for interfacial polymerization to prepare polyamide composite membranes, dissolving acyl chloride monomers in liquid paraffin, dissolving amine monomers in the aqueous phase, and utilizing the immiscible interface between liquid paraffin and water to prepare polyamide composite membranes.

[0008] The liquid paraffin mentioned includes one or more of the following: light liquid paraffin, heavy liquid paraffin, and liquid paraffin that does not distinguish between light and heavy types.

[0009] This invention provides a method for preparing polyamide composite films using liquid paraffin as the organic phase, comprising the following steps:

[0010] Step a: Clean the porous substrate surface repeatedly with ethanol and water to remove organic matter and inorganic dust.

[0011] Step b: Accurately weigh a certain amount of acyl chloride monomer and dissolve it in liquid paraffin. Accurately weigh a certain amount of amine monomer and dissolve it in an aqueous solution. Immerse the substrate cleaned in step a into an aqueous solution of amine monomer with a certain mass concentration. After a certain time, take it out, wipe off the surface moisture, and then immerse it in liquid paraffin of acyl chloride monomer with a certain mass concentration to carry out interfacial polymerization reaction to obtain a composite film. Clean the surface of the film with ethanol to remove excess liquid paraffin.

[0012] Step c: After heat treatment for a certain period of time, the composite membrane obtained in step b is obtained as a polyamide composite membrane with liquid paraffin as the organic phase.

[0013] Specifically, the porous substrate mentioned in step a is selected from one or more of polyacrylonitrile membranes, polysulfone membranes, and polyethersulfone membranes, and has an average pore size of 0.05-10 μm.

[0014] Specifically, the liquid paraffin mentioned in step b is one or two of the following: light liquid paraffin, heavy liquid paraffin, and liquid paraffin that does not distinguish between light and heavy types.

[0015] Specifically, the amine monomer mentioned in step b is selected from one or more of piperazine, m-phenylenediamine, and p-phenylenediamine; the concentration of the amine monomer is 0.01-3 wt%; and the immersion time is 5-120 s.

[0016] Specifically, the acyl chloride monomer in step b is selected from one or more of pyromellitic trimethylolpropionate chloride, isophthaloyl chloride, and pyromellitic tetramethylolpropionate chloride; the concentration of the acyl chloride monomer is 0.01-2 wt%; and the interfacial polymerization reaction time is 30-120 s.

[0017] Specifically, the heat treatment temperature in step c is 30-200 ℃, preferably 30-80 ℃; the heat treatment time is 2-120 min.

[0018] This invention relates to the preparation of polyamide composite membranes using liquid paraffin as the organic phase for nanofiltration and reverse osmosis applications; these membranes are used in wastewater purification and saline wastewater treatment, especially for high-concentration brine treatment, ion separation, and antibiotic desalination, such as seawater desalination, sodium and magnesium ion separation, and antibiotic desalination.

[0019] It can also be used for the separation of cations with different valence states, such as the separation of monovalent and divalent cations, the separation of anions with different valence states, such as the separation of monovalent and divalent anions, and the desalting of antibiotics.

[0020] The beneficial effects of the technical solution provided by this invention are as follows: Currently, the commercially available methods for preparing polyamide composite membranes (PA-TFC) are mainly based on polymerization methods at the organic solvent-water interface. In this method, the organic solvent used to dissolve the acyl chloride monomer is generally a volatile organic compound (VOC), such as hexane and toluene, commonly used in industry, which can easily cause serious harm to the environment and human health. In addition, the heat generated by the interfacial polymerization reaction leads to an increase in the interfacial temperature, which will aggravate the volatilization of VOCs, and the gases dissolved in VOCs will also escape, causing interfacial disturbance and affecting the uniformity and density of the separation layer. Therefore, finding a low-volatility green solvent and developing a green polymerization process based on a new solvent-water interface has important scientific and industrial value. This invention selects liquid paraffin as the organic phase solvent in polyamide composite membranes. Its low volatility makes it a suitable environmentally friendly membrane solvent. The viscosity of liquid paraffin is higher than that of hexane, which reduces the mass transfer rate of amine monomers into the organic phase, thus slowing down the polymerization rate of the two monomers at the interface, resulting in a more uniform membrane structure and improving the overall performance and stability of the membrane. Liquid paraffin, composed of long-chain alkanes, forms a more defined interface with the aqueous phase, providing an ideal site for polymerization. This allows monomers to effectively contact and polymerize at the interface, and the immiscible interface helps reduce the dissolution and diffusion of monomers in the solvent, thereby reducing the possibility of side reactions between acyl chloride monomers and water in the solvent phase. This research aims to develop a low-toxicity, low-volatility, and easily recyclable solvent to reduce negative environmental impacts and promote the green transformation of membrane preparation technology. Simultaneously, the high viscosity and water immiscibility of liquid paraffin enhance the performance and quality of the membrane.

[0021] Compared to polyamide membranes prepared using traditional hexane as the organic phase, polyamide composite nanofiltration membranes prepared using light liquid paraffin as the organic phase exhibit a sodium sulfate rejection rate of 98.6% and a flux of 240.6 L·m⁻¹. -1 ·h -1 ·MPa -1 The water flux increased by 1.11-1.35 times, the separation factor for lithium ions / magnesium ions was 9.1, the separation factor for chloride ions / sulfate ions was 31.8, and the separation factor for antibiotics / sodium chloride was 84-336. A polyamide composite reverse osmosis membrane prepared using light liquid paraffin as the organic phase had a sodium chloride rejection rate of 96.6% and a flux of 31.4 L·m⁻¹. -1 ·h -1 Water flux increased by 1.45 times. Attached Figure Description

[0022] Figure 1 Scanning electron microscope (SEM) images of the surface (1-1) and cross section (1-2) of the polyamide composite nanofiltration membrane with liquid paraffin as the organic phase prepared in Example 1 of this invention.

[0023] Figure 2 Scanning electron microscope (SEM) images of the surface (2-1) and cross section (2-2) of the polyamide composite nanofiltration membrane with n-hexane as the organic phase prepared in Comparative Example 1 of this invention.

[0024] Figure 3 The water contact angle (3-1) of the polyamide composite nanofiltration membrane prepared in Example 1 of the present invention and the water contact angle (3-2) of the polyamide composite nanofiltration membrane prepared in Comparative Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings, but the present invention is not limited to the following embodiments.

[0026] This invention provides a method for preparing polyamide composite films based on liquid paraffin-water interfacial polymerization and its application.

[0027] The liquid paraffins mentioned include light liquid paraffins, heavy liquid paraffins, and liquid paraffins that do not distinguish between light and heavy types.

[0028] This invention provides a method for preparing the above-mentioned polyamide composite film using liquid paraffin as the organic phase, comprising:

[0029] Step 101: Clean the porous substrate surface repeatedly with ethanol and water to remove organic matter and inorganic dust.

[0030] Step 102: Accurately weigh a certain amount of acyl chloride monomer and dissolve it in liquid paraffin. Accurately weigh a certain amount of amine monomer and dissolve it in an aqueous solution. Immerse the substrate cleaned in Step 101 into an aqueous solution of a certain mass concentration of the aqueous phase monomer. After a certain time, take it out, wipe off the surface moisture, and then immerse it in liquid paraffin of a certain mass concentration of the oil phase monomer to carry out an interfacial polymerization reaction to obtain a composite film. Clean the surface of the film with ethanol to remove excess liquid paraffin.

[0031] Step 103: After heat treatment for a certain period of time, the composite membrane obtained in step 102 is obtained as a polyamide composite membrane prepared with liquid paraffin as the organic phase.

[0032] Specifically, the porous substrate mentioned in step 101 is selected from one or more of polyacrylonitrile membranes, polysulfone membranes, and polyethersulfone membranes, and has an average pore size of 0.05-10 μm.

[0033] Specifically, the liquid paraffin mentioned in step 102 is one or both of light liquid paraffin and heavy liquid paraffin;

[0034] Specifically, the aqueous phase monomer mentioned in step 102 is selected from one or more of piperazine, m-phenylenediamine, and p-phenylenediamine; the concentration of the aqueous phase monomer is 0.01-3 wt%; and the immersion time is 5-120 s.

[0035] Specifically, the organic phase monomer in step 102 is selected from one or more of pyromellitic trimethylolpropionate chloride, isophthaloyl chloride, and pyromellitic tetramethylolpropionate chloride; the concentration of the oil phase monomer is 0.01-2 wt%; and the interfacial polymerization reaction time is 30-120 s.

[0036] Specifically, the heat treatment temperature in step 103 is 30-200 ℃, preferably 30-80 ℃; the heat treatment time is 2-120 min.

[0037] The present invention will be further described below through specific embodiments.

[0038] In the following specific embodiments, operations without specified conditions are performed under standard conditions or conditions recommended by the manufacturer. Raw materials without specified manufacturers and specifications are all commercially available products.

[0039] Example 1

[0040] Step (1) Clean the surface of the polyacrylonitrile substrate (average pore size 0.04 μm) with ethanol and water multiple times to remove organic matter and inorganic dust.

[0041] Step (2) The polyacrylonitrile substrate treated in step (1) is first immersed in a 0.75 wt% piperazine aqueous solution. After 30 s, it is taken out, the surface moisture is wiped off, and then immersed in a 0.225 wt% light liquid paraffin solution of trimesoyl chloride for interfacial polymerization for 90 s. The excess liquid paraffin on the membrane surface is cleaned with ethanol. Finally, the composite membrane is heat-treated at 60 ℃ for 4 min to obtain a polyamide composite nanofiltration membrane prepared with light liquid paraffin as the organic phase.

[0042] The separation performance of a 1 g / L Na₂SO₄ aqueous solution was tested at an operating pressure of 0.4 MPa, with a rejection rate of 98.6% and a water flux of 240.6 L / m³. -2 h -1 MPa -1 .

[0043] Example 2

[0044] The polyamide composite membrane prepared in Example 1 was used as a nanofiltration membrane for performance testing.

[0045] For the separation of monovalent and divalent cations, the test solution is a mixed solution of 1 g / L NaCl and 1 g / L MgCl2. + / Mg 2+ The separation factor is 9.1.

[0046] For the separation of monovalent and divalent anions, the test solution is a mixed solution of 1 g / L NaCl and 1 g / L Na2SO4, where Cl... - SO4 2- The separation factor is 31.8.

[0047] For antibiotic desalting, the test solution was a mixture of 1 g / L NaCl and 0.1 g / L antibiotic. Chloramphenicol desalting performance: flux 223.6 L / m³. -2 h -1 MPa -1 The separation factor was 4.1. Bacitracin desalting performance: flux was 217.9 L / m³. -2 h -1 MPa -1 The separation factor was 84.9. Tetracycline desalting performance: flux was 208.7 L / m³. -2 h -1 MPa -1 The separation factor was 279.1. Oxytetracycline desalting performance: flux was 238.3 L / m³. -2 h -1 MPa -1 The separation factor is 336.3.

[0048] Example 3

[0049] Step (1) Clean the surface of the polyacrylonitrile substrate (average pore size 0.04 μm) with ethanol and water multiple times to remove organic matter and inorganic dust.

[0050] Step (2) The polyacrylonitrile substrate treated in step (1) is first immersed in an aqueous solution of the monomer piperazine with a mass concentration of 1.1 wv% for 30 s. After wiping off the surface moisture, it is immersed in a liquid paraffin solution of the oil phase monomer pyromellitic chloride with a mass concentration of 0.22 wt% for 70 s for interfacial polymerization. The excess liquid paraffin on the membrane surface is then cleaned with ethanol. Finally, the composite membrane is heat-treated at 60 ℃ for 4 min to obtain a polyamide composite nanofiltration membrane prepared with liquid paraffin (without distinguishing between light and heavy phases) as the organic phase.

[0051] The separation performance of a 1 g / L Na₂SO₄ aqueous solution was tested at an operating pressure of 0.4 MPa, with a rejection rate of 97.76% and a water flux of 234.56 L / m³. -2 h -1MPa -1 .

[0052] Example 4

[0053] Step (1) Clean the surface of the polysulfone substrate (average pore size of 0.04 μm) multiple times with ethanol and water to remove organic matter and inorganic dust.

[0054] Step (2) The polysulfone substrate treated in step (1) is first immersed in an aqueous solution of m-phenylenediamine with a mass concentration of 2 wv% for 2 min. After 2 min, it is taken out, the surface moisture is wiped off, and then immersed in a liquid paraffin solution of oil phase monomer pyromellitic chloride with a mass concentration of 0.15 wt%. The liquid paraffin is heated to 40 ℃ and the interfacial polymerization reaction is carried out for 1.5 min. The excess liquid paraffin on the membrane surface is cleaned with ethanol, and the polyamide composite reverse osmosis membrane prepared with liquid paraffin as the organic phase is obtained.

[0055] The separation performance of a 2 g / L NaCl aqueous solution was tested at an operating pressure of 1.55 MPa, with a rejection rate of 96.9% and a water flux of 33.1 L / m³. -2 h -1 .

[0056] Comparative Example 1

[0057] Step (1) Clean the surface of the polyacrylonitrile substrate (average pore size 0.04 μm) with ethanol and water multiple times to remove organic matter and inorganic dust.

[0058] Step (2) The polyacrylonitrile substrate treated in step (1) is first immersed in a 0.75 wt% piperazine aqueous solution. After 30 s, it is taken out, the surface moisture is wiped off, and then immersed in a 0.225 wt% hexane solution of trimesoyl chloride for interfacial polymerization for 60 s. Pure hexane is used to clean the excess trimesoyl chloride on the membrane surface. Finally, the composite membrane is heat-treated at 60 ℃ for 4 min to obtain a polyamide composite nanofiltration membrane prepared with hexane as the organic phase.

[0059] The separation performance of a 1 g / L sodium sulfate aqueous solution was tested at an operating pressure of 0.4 MPa, with a rejection rate of 96.7% and a water flux of 184.7 L / m³. -2 h -1 MPa -1 .

[0060] Comparative Example 2

[0061] Step (1) Clean the surface of the polysulfone substrate (average pore size of 0.04 μm) multiple times with ethanol and water to remove organic matter and inorganic dust.

[0062] Step (2) The polysulfone substrate treated in step (1) is first immersed in an aqueous solution of m-phenylenediamine with a mass concentration of 2 wv% for 2 min. After 2 min, it is taken out, the surface moisture is wiped off, and then immersed in a hexane solution of the oil phase monomer pyromellitic chloride with a mass concentration of 0.15 wt%. The hexane is heated to 40 ℃ and the interfacial polymerization reaction is carried out for 1.5 min. The excess liquid paraffin on the membrane surface is cleaned with ethanol, and the polyamide composite reverse osmosis membrane prepared with liquid paraffin as the organic phase is obtained.

[0063] The separation performance of a 2 g / L NaCl aqueous solution was tested at an operating pressure of 1.55 MPa, with a rejection rate of 95.9% and a water flux of 13.5 L / m³. -2 h -1 .

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polyamide composite membrane based on liquid paraffin-water interfacial polymerization, characterized by, The application discloses a method for preparing a polyamide composite nanofiltration membrane by using liquid paraffin as an organic phase solvent for interfacial polymerization.

2. The method according to claim 1, characterized in that The method comprises the following steps: Step a: cleaning the surface of a porous substrate with ethanol and water for multiple times to remove surface organic matters and inorganic dust; Step b: dissolving a certain amount of an acid chloride monomer in liquid paraffin and dissolving a certain amount of an amine monomer in an aqueous solution, immersing the substrate cleaned in step a in the amine monomer aqueous solution with a certain mass concentration, taking out the substrate after a certain time, wiping off the surface water, immersing the substrate in the acid chloride monomer liquid paraffin with a certain mass concentration, and performing interfacial polymerization to obtain a composite membrane, and cleaning the surface of the membrane with ethanol to remove the excess liquid paraffin; Step c: performing heat treatment on the composite membrane obtained in step b for a certain time to obtain a polyamide composite membrane prepared by using liquid paraffin as an organic phase.

3. The method of claim 2, wherein, The porous substrate in step a is selected from one or more of polyacrylonitrile membranes, polysulfone membranes and polyethersulfone membranes, and has an average pore size of 0.05-10 μm.

4. The method of claim 2, wherein, The liquid paraffin in step b is one or both of light liquid paraffin, heavy liquid paraffin and liquid paraffin without distinguishing between light and heavy liquid paraffin.

5. The method of claim 2, wherein, The amine monomer in step b is selected from one or more of piperazine, m-phenylenediamine and p-phenylenediamine, the concentration of the amine monomer is 0.01-3 wt%, and the immersion time is 5-120 s.

6. The method of claim 2, wherein, The acid chloride monomer in step b is selected from one or more of trimesoyl chloride, isophthaloyl chloride and pyromellitic acid chloride, the concentration of the acid chloride monomer is 0.01-2 wt%, and the interfacial polymerization time is 30-120 s.

7. The method of claim 2, wherein, The heat treatment temperature in step c is 30-200 ℃, preferably 30-80 ℃, and the heat treatment time is 2-120 min.

8. The composite membrane prepared by the method according to any one of claims 1-7.

9. Application of the composite membrane prepared by the method according to any one of claims 1-7, as a nanofiltration membrane or a reverse osmosis membrane, to sewage purification, salt-containing wastewater treatment, especially to high-concentration brine treatment, ion separation and antibiotic desalination.

10. The application according to claim 9, to separation of cations with different valences, especially separation of monovalent and divalent cations, and separation of anions with different valences, especially separation of monovalent and divalent anions.

Images