CN102114391A - Method for preparing polyisophthaloyl metaphenylene diamide nanofiltration membrane - Google Patents

Abstract

The invention discloses a method for preparing an asymmetric nanofiltration membrane by using polym-phenylene isophthalamide as a raw material and adopting a phase inversion method. Its main technical features are: after filtering and defoaming the homogeneous casting solution containing polym-phenylene isophthalamide, organic solvents and additives, it is cleaned by salivation method at a certain temperature and humidity. A nascent film with a certain thickness is scraped on a smooth glass plate or non-woven fabric; after a certain period of solvent evaporation, the film is immersed in a gel bath to solidify and form. The aromatic polyamide nanofiltration membrane prepared by the technology of the present invention has the characteristics of excellent high temperature resistance, pressure tightness resistance, pollution resistance, physical and chemical stability and selective permeability, and the film forming process of this method is simple, easy to operate, The operation cost is low, and it is easy to realize industrialized production. It is suitable for the special treatment of industrial wastewater, high-temperature fluid and desalination and softening treatment of water and other fields.

Description

A kind of preparation method of polym-phenylene isophthalamide nanofiltration membrane

technical field

The invention belongs to the field of membrane separation materials, in particular to a method for preparing an asymmetric flat nanofiltration membrane by using polym-phenylene isophthalamide as the main membrane material and adopting a phase inversion method.

Background technique

Nanofiltration membrane is a new type of membrane separation technology between reverse osmosis membrane and ultrafiltration membrane. The removal rate is high, and the investment cost and operation and maintenance costs are relatively low. Since the advent of nanofiltration membranes, it has attracted people's attention and attention for its remarkable separation characteristics, and its application range has rapidly expanded. Decolorization and other fields.

At present, most of the commercial nanofiltration membranes successively developed at home and abroad are prepared by interfacial polymerization (US5152901, CN101352659). The interfacial polymerization is to immerse the microporous base film in the aqueous solution of the hydrophilic monomer, remove the excess monomer solution, and then immerse it in the organic solution of some hydrophobic monomer to carry out the liquid-liquid interfacial polycondensation reaction, so that the porous support form an ultra-thin layer. In order to obtain better membrane performance, post-treatment processes such as hydrolysis charging, ion radiation or heat treatment are generally required. Although this preparation method can be optimized according to the respective needs of the active layer and the support layer, so that the membrane has high separation performance and permeation flux, the preparation process is complicated, there are many influencing factors, the production cycle is long, and the production cost is high. high.

In order to solve the above problems, the present invention proposes a method for preparing a nanofiltration membrane by using polym-phenylene isophthalamide as the membrane material and adopting a phase inversion method. The film-forming process of the method is simple, the production cycle is short, the operation is convenient, and the operation cost is low. At the same time, due to the low price of polym-phenylene isophthalamide, and the presence of benzene rings and amide groups in its macromolecular main chain, it can not only improve the water flux of the membrane, but also improve the pressure and tightness of the membrane. Performance, pollution resistance, high temperature resistance, radiation resistance and chemical stability have also been greatly improved, and have a wide range of application prospects.

Contents of the invention

The object of the present invention is to provide a kind of method that adopts phase inversion method to prepare asymmetric nanofiltration membrane with polym-phenylene isophthalamide as membrane material. Utilize this method to be able to prepare conveniently under lower operating pressure (0.3-0.7MPa) to the retention rate of anionic dyestuff greater than 96%, to the desalination rate of divalent and high price inorganic salt ion more than 50-85%, water A series of nanofiltration membranes with a flux of 33-71L/m ² ·h.

The nanofiltration membrane prepared by this method has superior performance in terms of water permeability, pressure resistance, pollution resistance, physical and chemical stability, and selective permeation, etc., and the film forming process of this method is simple, easy to operate, and low in operating costs. It is easy to realize industrialized production.

Description of drawings

The morphology and structure of the nanofiltration membrane are shown in Fig. 1 electron micrograph. Nanofiltration membrane surface (a) is dense, smooth and uniform, and has excellent anti-pollution performance. The cross-sectional structure (b) of the nanofiltration membrane is composed of a two-layer structure, a thin and dense skin layer and a porous support layer. From top to bottom, the micropores in the porous layer gradually become smaller, with a typical asymmetric structure.

Detailed ways

The present invention is achieved through the following technical solutions:

(1) Preparation of casting solution: dissolve the dried polym-phenylene isophthalamide in an organic solvent, add a certain amount of additives, stir and dissolve at a constant temperature to form a homogeneous casting with a bright amber color. Membrane solution, after static defoaming, the required casting solution is obtained. Said polym-phenylene isophthalamide is a polymer compound with the following structure.

The mass concentration of polym-phenylene isophthalamide in said casting solution is 10-30 wt%, preferably 15-25 wt%.

The mass concentration of additives in said casting solution is 5-40wt%. Additives are important factors to determine the pore size, water flux and retention rate of the prepared membranes, mainly including organic additives and inorganic additives. The organic additives are mainly one or more of ethylene glycol methyl ether, acetone, polyvinylpyrrolidone, dipropylene glycol, polyethylene glycol or triethylene glycol; the inorganic additives are mainly calcium chloride, chloride One or more of lithium, lithium bromide, aluminum nitrate or lithium perchlorate. In order to obtain a high-performance membrane, the preferred concentration of the additive in the casting solution is 15-25wt%.

Said organic solvent can adopt N, one or one in N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP) or dimethylsulfoxide more than one species;

(2) Film formation by phase inversion method

In the film-scraping chamber, the above-mentioned casting solution is poured on a clean glass plate or non-woven fabric, and a nascent film of a certain thickness (150-300 μm) is scraped with a scraper. After the solvent and additives are evaporated at 100-150°C for 1-10 minutes, uniformly immerse in a gel bath with a temperature of 10-30°C to solidify and form, and after a certain period of time (0.5-24 hours) to gel, a 150-300μm Thick asymmetric membrane. After the membrane is taken out, it is fully washed and put into the preservation solution to obtain the nanofiltration membrane of the present invention.

Said gel bath is deionized water or an aqueous solution containing a certain amount of additives, and the additives are one or more of dimethylacetamide, ethanol, glacial acetic acid, sodium chloride, and the mass concentration is 0.5%-5 %.

The temperature of the wiper chamber is 20-30° C., and the relative humidity is 40-60%.

The nanofiltration membrane prepared by the above method has a higher separation efficiency for anionic dyes with a molecular weight of 500-1000 at a lower operating pressure (0.3-0.7MPa), and a desalination rate of 50-500ppm for sodium sulfate solution. 85%, the water flux is 33-71L/(m ² ·h). The membrane has the advantages of strong anti-pollution ability, high separation efficiency and large water flux; at the same time, it also has excellent high temperature resistance, acid and alkali resistance, solvent resistance and mechanical properties, and can be used for special treatment of industrial wastewater, high temperature fluid and water purification. Desalination and softening etc.

The present invention will be further described below in conjunction with embodiment.

Example

Example 1

Dissolve 5 grams of lithium chloride and 15 grams of polyvinylpyrrolidone in dimethylacetamide solution (DMAC), then add 15 grams of polym-phenylene isophthalamide at about 60 ° C, and the mixture is heated at 80 After stirring and dissolving at constant temperature at ℃, keep it airtight and stand for defoaming.

Keep the temperature of the scraping chamber at 25°C and the relative humidity at 50%, completely dissolve and pour the homogeneous casting solution after defoaming on a clean glass plate or non-woven fabric, and use a scraper to scrape a film with a thickness of about 200 μm. Film, after evaporating at 120°C for 10 minutes, uniformly immerse the glass plate or non-woven fabric in an aqueous solution containing 5% ethanol to solidify to form a film, and the temperature of the gel bath is 10°C. After 30 minutes of gelation, the filter membrane is taken out and fully washed with deionized water, and then placed in a preservation solution to obtain the nanofiltration membrane of the present invention.

Under the pressure of 0.5MPa, the rejection rate of the prepared membrane to 500mg/L Na ₂ SO ₄ solution is 63.7%, and the water flux is 67.8L/m ² ·h.

Example 2

As described in Example 1, the mass concentration of casting solution is 15%, the solvent adopts N-methylpyrrolidone (NMP), the organic additive adopts ethylene glycol methyl ether, and the mass concentration is 15%, and the gel bath water temperature is At 15°C, the gel bath is an aqueous solution of ethanol with a mass concentration of 2%. Under the pressure of 0.5MPa, the rejection rate of the prepared membrane to 500mg/L Na ₂ SO ₄ solution is 72.5%, and the water flux is 52.3L/m ² ·h.

Example 3

As described in Example 1, the solvent adopts dimethylacetamide (DMAC), and the mass concentration of casting solution is changed by 20%. Organic additives, forming a mixed system, evaporated at 120°C for 5 minutes, the gel bath was deionized water, and the water temperature was 20°C. The rejection rate of the prepared membrane to 500mg/L Na ₂ SO ₄ solution is 80.5%, and the water flux is 48.6L/m ² ·h.

Example 4

As described in Example 1, the casting solution concentration is 20% constant, the solvent adopts N-methylpyrrolidone (NMP), the type and concentration of organic additives are constant, and the inorganic additives are 8 grams of lithium chloride and calcium chloride according to 3:1 (mass) mixed additives. The gel bath is an aqueous solution containing 5% sodium chloride, and the temperature of the gel bath is 25°C. Under the pressure of 0.7MPa, the desalination rate of the prepared membrane to 500ppm Na ₂ SO ₄ is 78.2%, and the water flux is 56.8L/m ² ·h.

Example 5

As described in Example 1, get 25 grams of polym-phenylene isophthalamide, join 60 grams of dimethylacetamide and N-methylpyrrolidone in the mixed solvent that is made into by 3:1 (mass) , and then add 15 grams of acetone and ethylene glycol dimethyl ether mixed with organic additives at a ratio of 2:1 (mass) to form a mixed system. Evaporate at 140°C for 2 minutes. The gel bath is deionized water with a water temperature of 25°C. Under the pressure of 0.7MPa, the desalination rate of the prepared membrane to 500ppm Na ₂ SO ₄ is 85.7%, and the water flux is 34.9L/m ² ·h.

Claims (5)

1. a preparation method of polym-phenylene isophthalamide nanofiltration membrane, is characterized in that: adopt phase inversion membrane-forming method, will contain polym-phenylene isophthalamide, aprotic polarity After filtering and defoaming the homogeneous casting solution of solvent and additives, scrape it on a clean and smooth glass plate or non-woven fabric by salivation method at a certain temperature and humidity to form a nascent film with a thickness of 150-300 μm , After the solvent is evaporated for a certain period of time, the membrane is immersed in a gel bath to solidify and form, and the polym-phenylene isophthalamide nanofiltration membrane is obtained. The prepared membrane has a good interception effect on small molecule organic matter with a molecular weight between 200 and 1000 under a relatively low pressure (0.3-0.7 MPa), and has a good removal ability on divalent and high-valent ions. 2. the preparation method of a kind of polym-phenylene isophthalamide nanofiltration membrane according to claim 1, is characterized in that: the prepared nanofiltration membrane is asymmetric flat plate or roll type nanofiltration membrane. 3. the preparation method of a kind of poly-m-phenylene isophthalamide nanofiltration membrane according to claim 1, is characterized in that: the poly-m-phenylene isophthalamide containing 15～25wt% in casting solution Diamine, 5-25wt% of additives and the balance of aprotic polar solvent. 4. the aprotic polar solvent according to claim 1, is characterized in that: can be selected from N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2- One or more of pyrrolidone (NMP) or dimethyl sulfoxide; 5. The additive according to claim 1, characterized in that: it comprises organic additives and inorganic additives. The organic additives are one or more of ethylene glycol methyl ether, acetone, glacial acetic acid, dipropylene glycol, polyethylene glycol or triethylene glycol; the inorganic additives are calcium chloride, lithium chloride, lithium bromide One or more of aluminum nitrate or lithium perchlorate.

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