Preparation method of hollow fiber reverse osmosis composite membrane

Abstract

The present invention belongs to the technical field of composite membranes for separation, and in particular to a method for preparing a hollow fiber reverse osmosis composite membrane. The casting liquid is continuously extruded through one or more nozzles of a hollow fiber membrane film-making machine to form an extruded liquid film, and the core liquid is continuously injected through the core liquid cavity and fills the inner cavity of the extruded liquid film; the extruded liquid film filled with the core liquid in the inner cavity is immersed in a coagulation bath L, and then immersed in a coagulation bath S to generate a hollow fiber primary membrane; the hollow fiber primary membrane is immersed in a coagulation-polymerization bath, and then soaked in dilute hydrochloric acid, and then washed with water to obtain a semi-finished composite membrane; the semi-finished composite membrane is heat-treated to obtain a hollow fiber reverse osmosis composite membrane. The hollow fiber reverse osmosis composite membrane can adopt a reverse osmosis operating pressure difference of 4-5MPa for a long time, and maintains a relatively stable performance, is suitable for the desalination process of low-salinity seawater and brackish water, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of composite membranes for separation, and in particular relates to a method for preparing a hollow fiber reverse osmosis composite membrane. Background Art

[0002] Reverse osmosis, also known as reverse osmosis, is a membrane separation operation that uses pressure difference as a driving force to separate solvent from solution. When pressure is applied to the liquid on one side of the membrane, when the pressure exceeds its osmotic pressure, the solvent will reversely permeate in the opposite direction of natural osmosis. As a result, the permeated solvent, i.e., the permeate, is obtained on the low-pressure side of the membrane; and the concentrated solution, i.e., the concentrate, is obtained on the high-pressure side. The osmotic pressure reflects the binding force between the solute particles and the solvent in the liquid, which is generally proportional to the volume molar concentration, weight concentration and absolute temperature of the solution, and is also affected by conditions such as pH value; for example, the osmotic pressure of normal temperature seawater with a salinity of 35 (3.5wt%) is about 2.45MPa.

[0003] The spiral reverse osmosis membrane has a high pressure resistance and can be used in processes such as seawater desalination and high-salinity brackish water desalination that require a high reverse osmosis pressure difference of 5-6MPa. The pressure resistance of the hollow fiber reverse osmosis membrane is usually slightly lower and is generally used in processes with a reverse osmosis pressure difference below 5MPa, such as tap water, brackish water, and low-salinity seawater (estuarine seawater, which has fluctuating salinity and operating pressure differences).

[0004] Compared with spiral reverse osmosis membrane, hollow fiber reverse osmosis membrane has the advantages of high packing density, simple component structure, easy cleaning, and low overall cost, but its disadvantage of low pressure resistance limits its application in the reverse osmosis pressure difference operation process of about 5MPa. During the operation process of hollow fiber reverse osmosis membrane with a pressure difference of more than 4MPa, one of the main manifestations of insufficient pressure resistance is the rapid annual average decay of desalination rate and / or flux, which reflects its lack of stability.

[0005] Hollow fiber reverse osmosis composite membranes include two structures: external pressure membrane and internal pressure membrane. The external pressure membrane usually has better technical performance. The structure of the external pressure membrane usually includes: ① functional cortex, or selective separation layer, located at the outermost layer of the hollow fiber membrane, generally a polyamide layer formed by interfacial polymerization of polyamine monomers and acyl chloride monomers, with a thickness of 80-200nm and a dense structure, but containing a large number of pores with an equivalent pore diameter of less than 1nm and charged, which is a functional layer that separates and selectively blocks macromolecules, ions and trace particles contained in the concentrated liquid; ② hollow fiber support membrane, or hollow fiber base membrane, hollow fiber support layer, generally a hollow fiber ultrafiltration membrane made of polysulfone, polyethersulfone, polyarylsulfone, polycarbonate, polyvinylidene fluoride and other materials, with an outer diameter of 0.8-1.5mm and an inner diameter of 0.4-0.7mm, providing mechanical support for the functional cortex, having good water permeability, and the surface layer combined with the functional cortex has a suitable surface roughness and pore size; it can also include ③ a transition layer, located between the functional cortex and the surface of the hollow fiber support layer.

[0006] Chinese patent CN115245748A discloses a method for preparing a composite membrane, comprising the following steps: 1) the casting liquid is extruded through a spinneret via a membrane making machine, and at the same time, the core liquid flows out through the core liquid cavity. After the casting liquid contacts the core liquid, phase separation occurs to form a preformed membrane; the core liquid is a deionized water solution containing polyamine active monomers; 2) the preformed membrane is immersed in a polymerization bath to form a composite membrane; the polymerization bath is an ethanol solution containing polyacyl chloride active monomers. The casting liquid comprises the following components by weight: 10-40 parts of polycarbonate and 60-90 parts of a composite solvent; the composite solvent is a mixture of polyethylene glycol and DMAC (dimethylacetamide). The polyamine active monomer is one of piperazine, m-phenylenediamine, and diethylenetriamine, and the polyacyl chloride active monomer is trimesoyl chloride. The concentration of the polyacyl chloride active monomer is 1-3wt%, and the concentration of the polyamine active monomer is 5-10wt%. The beneficial effect of this patent is that the process is simple and can quickly produce composite membranes with ultra-thin functional layers; the disadvantage is that the prepared composite membrane has insufficient pressure resistance, the annual average decay of desalination rate and / or flux is relatively fast, and it is difficult to use in reverse osmosis operations with a pressure difference of more than 4MPa.

[0007] Chinese patent CN117298873A discloses an aromatic polyamide hollow fiber reverse osmosis composite membrane, comprising a selection layer, an adhesive layer and a support layer; the selection layer is a metaphenylenediamine / trimethylenediamine chloride aromatic polyamide layer (MPD / TMC); the adhesive layer is a polydopamine-polyethyleneimine co-deposition layer (PDA / PEI); and the support layer is a polyethersulfone hollow fiber ultrafiltration membrane (PES HFUFM). The preparation method comprises the following steps: S1, taking out a polyethersulfone hollow fiber ultrafiltration membrane stored in a glycerol aqueous solution, and hanging it in a cool place to dry; S2, pumping dopamine hydrochloride and polyethyleneimine adhesive into the inner wall of the hollow fiber membrane for a duration of 3-5 minutes, and passing dry air for 3 minutes to blow off residual droplets on the inner wall; S3, pumping an aqueous solution of m-phenylenediamine and triethylamine into the inner wall of the hollow fiber membrane for a duration of 3-5 minutes, and passing dry air for 3 minutes to blow off residual droplets on the inner wall; S4, pumping trimesoyl chloride Isopar L solution into the inner wall of the hollow fiber membrane for a duration of 3-5 minutes, and passing dry air for 1 minute to blow off residual droplets on the inner wall; S5, moving the hollow fiber membrane to a 50-70°C environment for heat treatment for 10-15 minutes. The dopamine hydrochloride and polyethyleneimine adhesive is prepared by dissolving dopamine hydrochloride and polyethyleneimine in a tris(hydroxymethyl)aminomethane buffer solution, and adjusting the pH of the buffer solution to 7.5-9.5 with hydrochloric acid or sodium hydroxide; wherein the concentration of dopamine hydrochloride is 0.1-5.0 g / L, the concentration of polyethyleneimine is the same as that of dopamine hydrochloride, and the molar concentration of tris(hydroxymethyl)aminomethane in the tris(hydroxymethyl)aminomethane buffer solution is 5-50 mmol / L. In the aqueous solution of m-phenylenediamine and triethylamine, the concentration of m-phenylenediamine is 20 g / L, and the concentration of triethylamine is 10-50 g / L. In the solution of trimesoyl chloride, the concentration of trimesoyl chloride is 1.5-2.0 g / L. In the aqueous solution of glycerol, the concentration of glycerol is 150-200 g / L. Under the test conditions of 32000ppm NaCl in feed liquid, 5.5MPa in operating pressure and 25℃ in test temperature, the flux of hollow fiber reverse osmosis composite membrane in Example 1 was 33.4L / m 2 h, and the desalination rate is 99.7%. The disadvantages of this patent include: complex preparation process, low efficiency, and difficulty in quality control; limited by the pressure resistance of the support layer, the annual average attenuation of the desalination rate and / or flux cannot be guaranteed; the composite membrane is an internal pressure membrane, and the area and pressure resistance of the selective separation layer are significantly lower than those of the external pressure membrane, and it cannot be used in conventional reverse osmosis production processes such as desalination of tap water, brackish water, and seawater.

[0008] Chinese patent CN105056773A discloses a method for preparing an in-situ embedded reinforced hollow composite membrane, comprising the following steps: (1) mixing a polymer resin, a porogen, a hydrophilic agent and a solvent in a weight ratio of 15-20:5-20:1-5:55-79, and then stirring, filtering and vacuum degassing to obtain a coating liquid; (2) winding a plurality of yarns flatly and cross-wrap around a rotating mandrel along a guide groove, and bonding the intersections of the yarns by ultrasonic welding to form a network tubular reinforced substrate wrapped around the mandrel; (3) pumping the coating liquid with a metering pump. The coating liquid is continuously transported to the hollow coating head, and the traction force is used to make the network tubular reinforced substrate move downward along the core rod and continuously enter the coating head; while the coating liquid penetrates into the yarn and completely covers the network tubular reinforced substrate, the rotating core rod acts as a scraper to scrape a coating layer on the inner surface of the network tubular reinforced substrate; (4) under the action of the traction force, the network tubular reinforced substrate covered by the coating liquid continuously leaves the coating head and enters the coagulation bath, and the surface liquid of the network tubular reinforced substrate exchanges with the water in the coagulation bath to form a film, and finally an in-situ embedded reinforced hollow composite membrane is obtained. The porogen is two or three of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, ethylene glycol, diethylene glycol or triethylene glycol; the hydrophilic agent is one of sulfonated polyether sulfone, polymethyl methacrylate, polyoxyethylene-polyoxypropylene block copolymer or polyether siloxane; the solvent is one or two of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, trimethyl phosphate or triethyl phosphate; the yarn is a composite with a denier of 200-1000 The material is one of polypropylene, polyester or nylon; the network tubular reinforced substrate is made of 4-32 strands of yarn cross-wrapped and welded, with an inner diameter of 1-12mm, an outer diameter of 1.6-20mm, and a mesh aperture of 0.1-2mm between the yarns; the core liquid is a mixture of one or two of water, N,N-dimethylacetamide, N,N-dimethylformamide or triethyl phosphate; when the outer diameter of the core rod is less than 3mm, the core liquid is not introduced, and only the coating material is used to wrap the network tubular reinforced substrate. The preparation process of this invention is complicated, inefficient and costly; the prepared hollow composite membrane is not competitive in conventional reverse osmosis production processes such as desalination of tap water, brackish water and seawater.

[0009] Therefore, based on the above-mentioned prior art, it is necessary to develop a method for preparing a hollow fiber reverse osmosis composite membrane with simple process and high efficiency, and the prepared hollow fiber reverse osmosis composite membrane has high pressure resistance. When used in a conventional reverse osmosis low-salinity salt water production process (such as desalination of low-salinity seawater and brackish water) with an operating pressure difference of 4-5MPa, its desalination rate, flux and annual average attenuation are all competitive. Summary of the invention

[0010] The object of the present invention is to provide a method for preparing a hollow fiber reverse osmosis composite membrane, wherein the hollow fiber reverse osmosis composite membrane can adopt a reverse osmosis operation pressure difference of 4-5 MPa for a long time and maintain relatively stable performance.

[0011] The method for preparing the hollow fiber reverse osmosis composite membrane of the present invention comprises the following steps:

[0012] (1) The casting liquid is continuously extruded through one or more nozzles of a hollow fiber membrane making machine to form an extruded liquid film, and at the same time, the core liquid is continuously injected through the core liquid cavity to fill the inner cavity of the extruded liquid film; the extruded liquid film with the inner cavity filled with the core liquid is first immersed in a coagulation bath L, and then immersed in a coagulation bath S to form a hollow fiber primary membrane;

[0013] (2) immersing the hollow fiber primary membrane of step (1) into a coagulation-polymerization bath, then soaking it in dilute hydrochloric acid, and then washing it with water to obtain a semi-finished composite membrane;

[0014] (3) The semi-finished composite membrane of step (2) is heat-treated to obtain a hollow fiber reverse osmosis composite membrane.

[0015] in:

[0016] In step (1), the extruded liquid film with the inner cavity filled with core liquid is immersed in a coagulation bath L and stays for 2-4 minutes, and then immersed in a coagulation bath S and stays for 2-4 minutes to generate a hollow fiber primary membrane; the core liquid is an aqueous solution containing 5-8wt% of m-phenylenediamine and 2-3wt% of camphorsulfonic acid; the extrusion temperature of the casting liquid and the injection temperature of the core liquid are both 30-40°C; the coagulation bath L is an aqueous solution containing 20-30wt% of N-methylpyrrolidone, and the temperature is 15-20°C; the coagulation bath S is water, and the temperature is 20-30°C.

[0017] In step (2), the hollow fiber primary membrane of step (1) is immersed in a coagulation-polymerization bath and kept for 3-5 minutes, and then immersed in dilute hydrochloric acid for 15-30 hours; the coagulation-polymerization bath is an n-heptane solution containing 0.3-0.5wt% of trimesoyl chloride and 10-20wt% of isopropanol, and the temperature is 20-30°C; the dilute hydrochloric acid is an aqueous solution containing 0.4-0.6wt% of HCl, and the temperature is 50-60°C; the outer diameter of the semi-finished composite membrane is 1.2-1.6mm, and the ratio of the outer diameter to the inner diameter is 2.4-2.6.

[0018] In step (3), the heat treatment atmosphere of the semi-finished composite film is air containing saturated water vapor or nitrogen containing saturated water vapor, the heat treatment time is 20-40 minutes, and the heat treatment temperature is 75-85°C.

[0019] The inner and outer diameters of the hollow fiber reverse osmosis composite membrane obtained in step (3) are substantially the same as those of the semi-finished composite membrane.

[0020] The casting solution comprises the following components in parts by weight:

[0021] 20-25 parts of base film resin with molecular weight of 30000-150000;

[0022] 1-1.5 parts of poly(p-phenylene terephthalamide) with a molecular weight of 5000-8000, added in the form of a solution of poly(p-phenylene terephthalamide) in N-methylpyrrolidone;

[0023] 2.0-2.5 parts of resol phenolic resin with a molecular weight of 1000-1500, added in the form of a solution of the resol phenolic resin in N-methylpyrrolidone;

[0024] 0.8-1.2 parts of triethylamine;

[0025] 10-15 parts of isopropyl alcohol;

[0026] The total amount of N-methylpyrrolidone (NMP) is 110-130 parts, including the amount of N-methylpyrrolidone used in preparing the N-methylpyrrolidone solution of poly(p-phenylene terephthalamide), the amount of N-methylpyrrolidone used in preparing the N-methylpyrrolidone solution of the ethyl-resin and the amount of N-methylpyrrolidone used in preparing the casting solution.

[0027] The N-methylpyrrolidone solution of poly(p-phenylene terephthalamide) is prepared by the following method:

[0028] N-methylpyrrolidone, lithium chloride and N-methylpyrrolidone solution of p-phenylenediamine are prepared into a mixed solution; the mixed solution is placed in a cold bath at -10 to -5°C, pyridine is added to the mixed solution, stirring is continued, terephthaloyl chloride is added, and the reaction is carried out for 1-2 hours to obtain an N-methylpyrrolidone solution of poly(p-phenylene terephthalamide); wherein the weight ratio of N-methylpyrrolidone, lithium chloride, p-phenylene diamine, pyridine and terephthaloyl chloride is (15-25):(0.3-0.5):1:(0.5-0.7):(1.94-2.01); the amount of N-methylpyrrolidone accounts for 26.5-27.5wt% of the total amount of N-methylpyrrolidone, and the amount of N-methylpyrrolidone in the N-methylpyrrolidone solution of p-phenylene diamine accounts for 6-7wt% of the total amount of N-methylpyrrolidone.

[0029] The N-methylpyrrolidone solution of the resol phenolic resin is prepared by the following method:

[0030] Add phenol and oxalic acid to a 37-40wt% formaldehyde aqueous solution, continue stirring, open reflux, reflux cooling water temperature 10-15°C, heat the liquid to 60-65°C and stir for 0.5-1h, then heat to 75-80°C and react for 5-8h, add sodium hydroxide to neutralize to pH 7.5-8, wash with water, then perform reduced pressure distillation under vacuum conditions of -0.078 to -0.083MPa, heat to 148-152°C at a rate of 1-2°C / min until there is no distillate, close the vacuum and fill with nitrogen to normal pressure, add N-methylpyrrolidone, and control the temperature at 148-152°C After stirring evenly, the mixture is placed for 5-10 minutes, and then the vacuum system is turned on for reduced pressure distillation at a pressure of -0.078 to -0.083 MPa, and distilled under the vacuum condition and a temperature of 148-152° C. until no distillate is produced. Finally, N-methylpyrrolidone is added to obtain a 20-50wt% N-methylpyrrolidone solution of the resol phenolic resin, wherein the molar ratio of formaldehyde, phenol, and oxalic acid is (0.8-1.0):1:(0.006-0.01), and the amount of N-methylpyrrolidone added twice accounts for 17.5-18.5wt% of the total amount of N-methylpyrrolidone. The purpose of the second reduced pressure distillation is to further reduce the water content.

[0031] N-methylpyrrolidone, pyridine, triethylamine and p-phenylenediamine were purified in advance.

[0032] The purity of the NMP (normal pressure boiling point 203°C) should reach above 99.9wt%, and the water content should be less than 100mg / kg, preferably less than 50mg / kg; the recovered crude NMP with a purity of 99%, conventional NMP commercial materials, and high-purity NMP should be dehydrated and refined after long-term storage. The refining method of the NMP solvent is: under the condition of nitrogen protection, the NMP material is subjected to reduced pressure distillation at a temperature of 85-90°C, and 10-20wt% of the feed weight is distilled out at a slight boiling in 1-2h, the residual liquid is cooled to room temperature, 4A molecular sieve accounting for 5-10% of the weight of the residual liquid is added, and it is placed in a sealed manner for 10-30h before use, and solid-liquid separation is performed before use.

[0033] The pyridine (normal pressure boiling point 115°C) and triethylamine (normal pressure boiling point 89°C) are also refined separately. Pyridine can be refined by first distilling at normal pressure and then adding 4A molecular sieve; the specific method is: under the condition of nitrogen protection, pyridine is distilled at normal pressure, and 10-20wt% of the feed weight is distilled out at a slight boiling in 1-2 hours, the residual liquid is cooled to room temperature, 4A molecular sieve accounting for 10-20% of the weight of the residual liquid is added, and it is placed in a sealed manner for 10-30 hours before use, and solid-liquid separation is performed before use. When refining triethylamine, 4A molecular sieve accounting for 20-30% of the weight of the triethylamine material is directly added without distillation, and it is placed in a sealed manner for 10-30 hours before use, and solid-liquid separation is performed before use.

[0034] The p-phenylenediamine (melting point 140°C, boiling point 267°C at normal pressure) is also subjected to dehydration and refining treatment, and the specific method is: under the conditions of nitrogen protection and bubbling purging, the p-phenylenediamine is subjected to reduced pressure distillation at a temperature of 180-200°C, and 10-20wt% of the feed weight is distilled out at a slight boiling in 1-2 hours, and the remaining bottom liquid is transferred to a container protected by nitrogen, and after cooling to room temperature, it is sealed and stored and used; preferably, 3-5 times the weight of NMP is added to prepare an NMP solution of p-phenylenediamine, which is sealed and stored and used.

[0035] The base film resin and lithium chloride are dehydrated and dried before use. The specific method is: the base film resin and lithium chloride are dried at a temperature of 135-150° C. and a vacuum condition of -0.08 to -0.095 MPa for 5-10 hours respectively.

[0036] The isopropanol has a solubilizing effect on the base film resin, and its water content should be lower than 250 mg / kg. If necessary, 4A molecular sieve can be used for dehydration.

[0037] In the refining process of NMP solvent, pyridine, triethylamine and the dehydration process of isopropanol, it is more preferred to use a more efficient 4A molecular sieve fixed bed continuous treatment method. The 4A molecular sieve should be activated before use, and the activation method is: the charging tray containing the 4A molecular sieve is placed in a muffle furnace, warmed to 350-400°C, and moved into a closed material box or dryer after a constant temperature of 4-8h, and used after cooling. The 4A molecular sieve after refining or dehydration can be air-dried or placed in an oven, pre-dried at 80-120°C for 3-10h, most of the liquid components are removed, and then activated in a muffle furnace. During the solid-liquid separation, the supernatant can be directly poured out, preferably filtered under nitrogen protection conditions.

[0038] The base film resin is bisphenol A type polysulfone, polyether sulfone or polyaryl sulfone, and the molecular weight of the base film resin is 50000-80000.

[0039] The preparation method of the casting liquid comprises the following steps: subtracting the amount of N-methylpyrrolidone consumed in preparing the N-methylpyrrolidone solution of poly(p-phenylene terephthalamide) and the N-methylpyrrolidone solution of the resol phenolic resin from the total amount of N-methylpyrrolidone, placing the remaining N-methylpyrrolidone as a solvent in a reactor under nitrogen protection and anhydrous conditions, adding isopropyl alcohol and base film resin, continuously stirring, raising the temperature and controlling it at 50-60° C., adding the N-methylpyrrolidone solution of poly(p-phenylene terephthalamide) and the N-methylpyrrolidone solution of the resol phenolic resin after the base film resin is completely dissolved, controlling the temperature at 50-60° C., adding triethylamine after 5-10 minutes, cooling the feed liquid to 20-30° C. within 10 minutes after 20-30 minutes, stopping stirring, degassing under reduced pressure for 10-30 minutes, and then sealing and placing for more than 10 hours to obtain the casting liquid.

[0040] No suspended matter is generated during the preparation of the casting solution, and the suspended matter introduced by the raw materials can be removed by high-speed centrifugal sedimentation. The isopropanol also has the function of adjusting the pore size and water flux of the support membrane.

[0041] The application of the hollow fiber reverse osmosis composite membrane of the present invention is as follows:

[0042] The hollow fiber reverse osmosis composite membrane is used for desalination of low-salinity seawater and brackish water with a salt content of 1.9-2.7wt%, wherein the reverse osmosis operating pressure difference during desalination is 4-5MPa.

[0043] In the present invention, the molecular weights of the resins and polymers are all viscosity average molecular weights.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) In the preparation process of the casting solution of the present invention, the poly(p-phenylene terephthalamide) (hereinafter referred to as polymer A) introduced by means of a poly(p-phenylene terephthalamide) solution in N-methylpyrrolidone (NMP) is a linear chain with high rigidity and monodispersity, and its molecular length is 30-50nm. Since terephthaloyl chloride is in excess of 3-7% during preparation, both ends of its molecular linear chain are acyl chloride groups; the resol phenolic resin introduced by means of a resol phenolic resin solution in N-methylpyrrolidone (NMP) is a linear oligomer with high monodispersity, and its molecular chain length is about 10nm; In the 20-30 minutes after the introduction of triethylamine, the acyl chloride groups at both ends of the straight chain of the polymer A molecule will react with the phenolic hydroxyl groups in the phenolic resin molecule, and a linear phenolic resin oligomer molecule with a length of about 10 nm will be grafted on both ends of the straight chain of the poly(p-phenylene terephthalamide) molecule through the generated ester group to generate polymer B. The introduced poly(p-phenylene terephthalamide) is converted to generate polymer B. At the same time, the small amount of residual terephthaloyl chloride introduced by the NMP solution of poly(p-phenylene terephthalamide) also reacts with the phenolic hydroxyl groups. The HCl released by these two reactions is combined and removed by triethylamine.

[0046] (2) During the preparation process of steps (1) to (2), the extruded liquid film is basically solidified into a film by the core liquid, the coagulation bath L, the coagulation bath S, and the coagulation-polymerization bath. The polymer B and the remaining phenolic resin are basically solidified into a film with the base film resin (bisphenol A type polysulfone, polyethersulfone or polyarylsulfone); the core liquid is an aqueous solution containing m-phenylenediamine and camphorsulfonic acid, the coagulation bath L is an aqueous solution containing N-methylpyrrolidone, and the coagulation bath S is water. The three together play a phase transformation role on the extruded liquid film of the casting liquid. During the preparation process of step (1), the m-phenylenediamine and camphorsulfonic acid contained in the core liquid gradually diffuse into the inner pores of the hollow fiber primary membrane (solidification polymer layer), a small amount of which dissolves into the coagulation bath L and the coagulation bath S and is lost, but most of it is retained; in step (2), during the process of immersing the hollow fiber primary membrane (the inner pores are filled with aqueous solution containing m-phenylenediamine and camphorsulfonic acid) in the coagulation-polymerization bath, under the catalytic action of the remaining triethylamine contained in the extruded liquid membrane (a part of which is dissolved into the coagulation bath L and the coagulation bath S along with NMP and isopropanol and is lost), the m-phenylenediamine reacts with the coagulation bath L and the coagulation bath S to form a coagulation-polymerization bath. The trimesoyl chloride contained in the solid-polymerization bath reacts to generate a polyamide cortex on the surface and surface layer of the hollow fiber primary membrane; in the process of generating the polyamide cortex, the solidification-polymerization bath (an n-heptane solution containing 0.3-0.5wt% trimesoyl chloride and 10-20wt% isopropanol) is used as an oil phase solution, and the isopropanol contained in the solid-polymerization bath can improve the contact effect with the surface and surface water phase of the hollow fiber primary membrane, thereby promoting the generation and combination of the polyamide cortex on the surface and surface layer of the hollow fiber primary membrane, and finally improving the reverse osmosis performance of the hollow fiber reverse osmosis composite membrane. In step (2), after the hollow fiber primary membrane contacts with the coagulation-polymerization bath and forms a polyamide skin layer, it is immersed in dilute hydrochloric acid containing 0.4-0.6wt% HCl and a temperature of 50-60°C for 15-30h. During this process, polymer B and the remaining ethyl-resin molecules will completely solidify into a membrane with the base membrane resin. The ethyl-resin molecular segments and the remaining ethyl-resin molecules in polymer B will undergo mutual indirect grafting and polymerization reactions under the acidic conditions of the aqueous solution, whereby the ethyl-resin is converted into the propyl-resin, thereby further forming a bulk phenolic resin structure.

[0047] (3) Polymer B plays a major reinforcing role in the base membrane resin because of the high rigidity of the poly(p-phenylene terephthalamide) straight chain segment in its molecule. The phenolic resin segment structure at both ends of the molecule also contributes to the reinforcing effect of polymer B to a certain extent, because it improves the uniform distribution of polymer B. The added ethyl-resin has an auxiliary reinforcing effect after forming a bulk phenolic resin structure. The combined effect of polymer B and the bulk phenolic resin formed in the end significantly improves the compressive strength and creep resistance of the composite membrane under long-term pressure conditions, making the irreversible compression of the composite membrane in the radial direction of the fiber and the uneven compression degree in various microscopic areas on the surface significantly lighter and slower, thereby reducing and delaying the adverse deformation of the polyamide skin layer and the microscopic bonding layer between it and the surface layer of the composite membrane, and ultimately reducing the annual average attenuation rate of the desalination rate and the annual average attenuation rate of the water flux of the hollow fiber reverse osmosis composite membrane.

[0048] (4) In step (3), the surface of the composite membrane serves as the basis for the growth of the polyamide cortex, and the structure and properties of the surface layer have a significant impact on the generation and performance of the polyamide cortex, thereby significantly improving the desalination performance while ensuring a high water flux level; the reason is that the molecular structure of polymer B and the final phenolic resin contains more phenolic hydroxyl groups, which improves the hydrophilicity of the composite membrane layer, thereby improving the bonding strength between the polyamide cortex with high hydrophilicity and the surface of the composite membrane, and to a certain extent improves the performance stability of the bonding layer between the polyamide cortex and the surface of the composite membrane, thereby making the salt retention performance of the hollow fiber reverse osmosis composite membrane more stable, and also plays a significant role in reducing the annual average decay rate of the desalination rate of the hollow fiber reverse osmosis composite membrane.

[0049] (5) NMP solution of poly(p-phenylene terephthalamide), in which the molecular weight or degree of polymerization of polymer A is controlled by using a method of 3-7% excess of terephthaloyl chloride and changing the ratio of reactants. The characteristic is that when other conditions remain unchanged, the molecular weight of polymer A is lower when the excess of terephthaloyl chloride is large, and the molecular weight of polymer A is higher when the excess is small, and the repeatability is good, indicating that the method is feasible. Two steps of reaction occur in the preparation process. The first step is a block polymerization reaction between p-phenylenediamine and terephthaloyl chloride to generate block molecular straight chains with mainly acyl chloride groups at both ends. This reaction basically occurs in the early stage of the preparation process; in the second step, the block molecular straight chains with acyl chloride groups at both ends (the product of the first step reaction) are further connected by the reaction of the terminal acyl chloride groups with p-phenylenediamine to generate polymer A. This step of reaction mainly occurs in the middle and late stages of the preparation process; after the p-phenylenediamine is completely consumed, the polymerization reaction automatically terminates, and the two ends of the polymer A molecular straight chains in the obtained solution should basically be acyl chloride groups, that is, acyl chloride end-capping.

[0050] In summary, the hollow fiber reverse osmosis composite membrane prepared by the present invention has high compressive strength, creep resistance and hydrophilicity, so that the hollow fiber reverse osmosis composite membrane can adopt a reverse osmosis operating pressure difference of 4-5MPa for a long time and maintain relatively stable performance, and is suitable for the desalination process of low-salinity seawater and brackish water.

[0051] In the application of low-salinity seawater desalination and brackish water desalination, the hollow fiber reverse osmosis composite membrane of the present invention can achieve the following technical indicators: service life of 3-5 years, initial water flux, i.e. water production> 40L / m 2 ·h, initial desalination rate> 99.7%, annual average desalination rate attenuation<1%, annual average water flux attenuation<2%; the comprehensive performance is better than the existing technology and has good application prospects. DETAILED DESCRIPTION

[0052] The present invention is specifically described and illustrated below in conjunction with embodiments.

[0053] Example 1

[0054] The hollow fiber reverse osmosis composite membrane of this embodiment has a total length of about 80m and is cut into segments of about 500mm in length. The specific process includes the following steps:

[0055] (1) The casting liquid is continuously and uniformly extruded through a nozzle (single-filament nozzle) of a hollow fiber membrane test machine to form an extruded liquid film. At the same time, the core liquid is continuously injected through the core liquid cavity and fills the inner cavity of the extruded liquid film; the extruded liquid film with the inner cavity filled with the core liquid is continuously and uniformly immersed in a coagulation bath L for an immersion time (i.e., residence time) of 3 minutes, and then continuously and uniformly immersed in a coagulation bath S for an immersion time of 3 minutes to generate a hollow fiber primary membrane; the core liquid is an aqueous solution containing 8wt% of m-phenylenediamine and 3wt% of camphorsulfonic acid; the extrusion temperature of the casting liquid and the injection temperature of the core liquid are both 35°C; the coagulation bath L is an aqueous solution containing 25wt% of NMP at a temperature of 15°C; the coagulation bath S is water at a temperature of 20°C;

[0056] (2) The hollow fiber nascent membrane of step (1) is continuously and uniformly immersed in a coagulation-polymerization bath for 3 min; the hollow fiber nascent membrane is intermittently cut into segments with a length of about 500 mm, immersed in a sufficient amount of dilute hydrochloric acid for 20 h, and then washed with water until the pH value is 5.2 to obtain a semi-finished composite membrane with an outer diameter of 1.2 mm and an inner diameter of 0.5 mm (outer diameter / inner diameter ratio of 2.4); the coagulation-polymerization bath is an n-heptane solution containing 0.3 wt% of trimesoyl chloride and 20 wt% of isopropanol, and the temperature is 20°C; the dilute hydrochloric acid is an aqueous solution containing 0.4 wt% of HCl, and the temperature is 60°C;

[0057] (3) Take the semi-finished composite membrane of step (2), heat treat it at a temperature of 80°C and an air atmosphere containing saturated water vapor for 30 minutes to obtain a hollow fiber reverse osmosis composite membrane, and cool and store it in water at room temperature.

[0058] in:

[0059] The casting solution contains the following ingredients:

[0060] 250 g of base film resin, bisphenol A type polysulfone (Solvay P-3500) with a molecular weight of 80,000;

[0061] 12.4 g of poly(p-phenylene terephthalamide) with a molecular weight of 5050 was added in the form of a NMP solution of poly(p-phenylene terephthalamide);

[0062] 25 g of 1250 molecular weight resol phenolic resin was added in the form of NMP solution of the resol phenolic resin;

[0063] Triethylamine 10 g;

[0064] Isopropyl alcohol 120g;

[0065] The total amount of NMP (N-methylpyrrolidone) is 1200g.

[0066] The NMP solution of poly(p-phenylene terephthalamide) (polymer A) was prepared by the following method: 119.4 g (containing 12.4 g of poly(p-phenylene terephthalamide) and 98.6 g of NMP solvent):

[0067] In a 500mL glass reaction flask (pre-weighed) under nitrogen protection and anhydrous conditions, 325g of NMP solvent, 8.0g of lithium chloride, and 100.0g of NMP solution containing 20.00g of p-phenylenediamine were added, and the mixture was stirred for 15 minutes to prepare a solution; the reactor was placed in a cold liquid bath at -7°C, 12.0g of pyridine was added to the solution, and stirring was continued. 40.24g of terephthaloyl chloride (200 mesh powder, purity 99.9%) was added and the timing was started. After 25 minutes, the solid matter was completely dissolved, and the reaction was carried out for 2 hours to obtain 478.5g of NMP solution containing poly(p-phenylene terephthalamide) (obtained from the total weight of the flask and the solution, minus the weight of the flask), and the molecular weight of polymer A in the solution was measured by sampling, and the molecular weight was 5050; it was calculated that the solution contained approximately 49.7g of polymer A and 395g of NMP solvent; in the ingredients, the molar ratio of p-phenylene diamine to terephthaloyl chloride was 1:1.07;

[0068] The NMP solution of the resol phenolic resin is prepared by taking 50 g (containing 25 g of the resol phenolic resin and 25 g of the NMP solvent) from a solution prepared by the following method for later use:

[0069] In a glass reaction flask (pre-weighed) with cooling reflux and connected to a vacuum system, add 138.5 g of formaldehyde aqueous solution (concentration 39 wt%), 189.0 g of phenol (purity 99.6 wt%) and 1.63 g of oxalic acid (the molar ratio of formaldehyde aqueous solution, phenol and oxalic acid is 0.9:1:0.009 based on formaldehyde), continue stirring, turn on reflux (reflux cooling water temperature 13 ° C), heat the liquid to 62 ° C and stir for 0.8 h, then heat to 78 ° C and react at this temperature 6h, then add 5wt% sodium hydroxide to neutralize to pH 7.5-8, add 100mL of water to wash three times (each washing is to add water and stir for 10min, then stop stirring, let it stand for 20min, and pour off the upper aqueous phase), then connect the flask to the vacuum system, maintain the vacuum condition of -0.080MPa for one distillation, increase the temperature to 150℃ at a rate of 2℃ / min and maintain the temperature, distill until there is no distillate, turn off the vacuum and fill with nitrogen to normal pressure, add NMP to the remaining bottom liquid 33g, control the temperature at 150°C, stir well and let stand for 10min, connect the flask to the vacuum system again, maintain the vacuum condition of -0.080MPa for secondary distillation, heat to 150°C at a rate of 2°C / min and maintain the temperature, distill until there is no distillate, turn off the vacuum and fill with nitrogen to normal pressure to obtain a distillation bottom liquid containing 189g of resol phenolic resin (the total weight of the flask and the resin minus the weight of the flask), add 189g of NMP, stir well and cool to room temperature to obtain an NMP solution containing 50wt% of resol phenolic resin, take a sample to measure the molecular weight of the resol phenolic resin in the solution, and it is 1250.

[0070] The casting liquid is prepared by the following method: subtracting the amount of NMP solvent consumed in preparing the NMP solution of poly(p-phenylene terephthalamide) and the NMP solution of ethylene-based phenolic resin from the total amount of NMP, placing the remaining NMP in a reactor under nitrogen protection and anhydrous conditions, adding isopropyl alcohol and base film resin, continuously stirring, raising the temperature and controlling it at 55° C., after the base film resin is completely dissolved, adding the NMP solution of poly(p-phenylene terephthalamide) and the NMP solution of ethylene-based phenolic resin, controlling the temperature at 55° C., adding triethylamine after 8 minutes, cooling the feed liquid to 25° C. within 10 minutes after 25 minutes, stopping stirring, degassing by decompression and slight boiling for 30 minutes, and then placing it in a sealed state for 10 hours to obtain the casting liquid; under strong light conditions, no visible suspended matter is observed in the casting liquid by naked eye.

[0071] The hollow fiber reverse osmosis composite membrane obtained in step (3) has a consistent and uniform outer diameter, inner diameter and wall thickness in the cross section, and has good roundness of the inner circle and outer circle, which is basically the same as the semi-finished composite membrane.

[0072] Example 2

[0073] The hollow fiber reverse osmosis composite membrane of this embodiment was prepared according to the method of steps (1) to (3) in Example 1, except that in step (1), another core liquid (an aqueous solution containing 5 wt% of m-phenylenediamine and 2 wt% of camphorsulfonic acid) was used; and the cross-sectional dimensions of the semi-finished composite membrane in step (2) and the hollow fiber reverse osmosis composite membrane in step (3) were changed to: outer diameter 1.6 mm, inner diameter 0.62 mm (outer diameter / inner diameter ratio 2.58).

[0074] Example 3

[0075] The hollow fiber reverse osmosis composite membrane of this embodiment is prepared according to the method of steps (1) to (3) in Example 1, except that 10 g of poly(p-phenylene terephthalamide) with a molecular weight of 5050 is used in the casting solution, and is added in the form of an NMP solution of poly(p-phenylene terephthalamide), specifically, it is taken out from the NMP solution of poly(p-phenylene terephthalamide) (polymer A) prepared in Example 1; the NMP solution of the ethyl-resin prepared in Example 1 is directly used.

[0076] Example 4

[0077] The hollow fiber reverse osmosis composite membrane of this embodiment was prepared according to the method of steps (1) to (3) in Example 1, except that 15 g of poly(p-phenylene terephthalamide) with a molecular weight of 7820 was added to the casting solution in the form of an NMP solution of poly(p-phenylene terephthalamide); the NMP solution of the ethyl-resin prepared in Example 1 was directly used.

[0078] The NMP solution of poly(p-phenylene terephthalamide) (polymer A) is prepared by taking 148.3 g (containing 15 g of poly(p-phenylene terephthalamide) and 124.3 g of NMP solvent) from a solution prepared by the following method:

[0079] In a glass reaction flask (pre-weighed) under nitrogen protection and anhydrous conditions, 325 g of NMP solvent, 8.0 g of lithium chloride, and 100.0 g of NMP solution containing 20.00 g of p-phenylenediamine were added, and the mixture was stirred for 15 minutes to prepare a mixed solution; the reactor was placed in a cold bath at -10°C, 12.0 g of pyridine was added to the mixed solution, and stirring was continued. 38.84 g of terephthaloyl chloride (200 mesh powder, purity 99.9%) was added and the timing was started. After 25 minutes, the solid matter was completely dissolved, and the reaction was carried out for 2 hours to obtain 479.5 g of NMP solution containing poly(p-phenylene terephthalamide) (obtained from the total weight of the flask and the solution, minus the weight of the flask), and the molecular weight of polymer A in the solution was measured by sampling, which was 7820; it was calculated that the solution contained approximately 48.4 g of polymer A and 402 g of NMP solvent; in the ingredients, the molar ratio of p-phenylene diamine to terephthaloyl chloride was 1:1.03.

[0080] Example 5

[0081] The hollow fiber reverse osmosis composite membrane of this embodiment was prepared according to the method of steps (1) to (3) in Example 1, except that 12.5 g of poly(p-phenylene terephthalamide) with a molecular weight of 6600 was added to the casting solution in the form of an NMP solution of poly(p-phenylene terephthalamide); and 40 g of an NMP solution of a phenolic resin (containing 20 g of a phenolic resin with a molecular weight of 1250 and 20 g of an NMP solvent) was used.

[0082] The NMP solution of poly(p-phenylene terephthalamide) (polymer A) is prepared by taking 121.5 g (containing 12.5 g of poly(p-phenylene terephthalamide) and 101.0 g of NMP solvent) from a solution prepared by the following method:

[0083] In a glass reaction flask (pre-weighed) under nitrogen protection and anhydrous conditions, 325 g of NMP solvent, 8.0 g of lithium chloride, and 100.0 g of NMP solution containing 20.00 g of p-phenylenediamine were added, and the mixture was stirred for 15 minutes to prepare a mixed solution; the reactor was placed in a cold bath at -7°C, 12.0 g of pyridine was added to the mixed solution, and stirring was continued. 39.54 g of terephthaloyl chloride (200 mesh powder, purity 99.9%) was added and the timing was started. After 25 minutes, the solid matter was completely dissolved, and the reaction was carried out for 2 hours to obtain 478.7 g of NMP solution containing poly(p-phenylene terephthalamide) (obtained from the total weight of the flask and the solution, minus the weight of the flask), and the molecular weight of polymer A in the solution was measured by sampling, which was 6600; it was calculated that the solution contained approximately 49.1 g of polymer A and 398 g of NMP solvent; in the ingredients, the molar ratio of p-phenylene diamine to terephthaloyl chloride was 1:1.05.

[0084] Example 6

[0085] The hollow fiber reverse osmosis composite membrane of this embodiment was prepared according to the method of steps (1) to (3) in Example 5, except that 200 g of another base membrane resin, polyethersulfone (BASF E6020) with a molecular weight of 50,000, was used; in step (2), the coagulation-polymerization bath liquid was an n-heptane solution containing 0.5 wt % of trimesoyl chloride and 10 wt % of isopropanol.

[0086] Comparative Example 1

[0087] The hollow fiber reverse osmosis composite membrane of this comparative example was prepared according to the method of steps (1) to (3) in Example 1, except that the NMP solution of poly(p-phenylene terephthalamide) (polymer A) was not added to the casting solution in step (1); instead, the NMP solution of ethyl-resin prepared according to the method in Example 1 was directly used.

[0088] Comparative Example 2

[0089] The hollow fiber reverse osmosis composite membrane of this comparative example was prepared according to the method of steps (1) to (3) in Example 1, except that the NMP solution of ethyl-resin was not added to the casting solution in step (1); instead, the NMP solution of poly(p-phenylene terephthalamide) (polymer A) prepared according to the method in Example 1 was directly used.

[0090] Comparative Example 3

[0091] The hollow fiber reverse osmosis composite membrane of this comparative example was prepared according to the method of steps (1) to (3) in Example 1, except that the NMP solution of poly(p-phenylene terephthalamide) (polymer A) and the NMP solution of ethyl-resin were not added to the casting solution in step (1).

[0092] Comparative Example 4

[0093] The hollow fiber reverse osmosis composite membrane of this comparative example was prepared according to the method of steps (1) to (3) in Example 1, except that an NMP solution of poly(p-phenylene terephthalamide) with a molecular weight of 13100 was added to the casting solution in step (1); the preparation method of the NMP solution of poly(p-phenylene terephthalamide) used was basically the same as that in Example 1, except that the molar ratio of p-phenylene diamine to terephthaloyl chloride in the ingredients was 1:1, and the molecular weight of the poly(p-phenylene terephthalamide) in the obtained solution was 13100 when sampled; and the NMP solution of ethyl-resin prepared according to the method in Example 1 was directly used.

[0094] Comparative Example 5

[0095] The hollow fiber reverse osmosis composite membrane of this comparative example was prepared according to the method of steps (1) to (3) in Example 1, except that an NMP solution of poly(p-phenylene terephthalamide) with a molecular weight of 23200 was added to the casting solution, and the amount of poly(p-phenylene terephthalamide) used was 37.2 g; the preparation method of the NMP solution of poly(p-phenylene terephthalamide) used was basically the same as that in Example 1, except that lithium chloride was not used in the ingredients. As a result, the molecular weight of the poly(p-phenylene terephthalamide) in the obtained solution was sampled and measured to be 23200; the NMP solution of ethyl-resin prepared according to the method in Example 1 was directly used.

[0096] During the operation of the above Examples 1-6 and Comparative Examples 1-5, the coagulation bath L containing 25 wt% of NMP used in step (1) of Example 1 was not replaced but used continuously in the operation of Examples 2-6 and Comparative Examples 1-5; in Comparative Example 5, the solution was still clear after use, and the solution was still clear after being sampled and diluted 1 and 2 times with water, indicating that the ethyl-resin contained in the extruded liquid film did not enter the coagulation bath L at a temperature of 15°C.

[0097] Example 1 and Comparative Example 5 verify that in the known preparation technology of low molecular weight poly(p-phenylene terephthalamide), the polymer obtained without adding lithium chloride is a parallel bundle-like aggregate of multiple poly(p-phenylene terephthalamide) molecular straight chains, not a single molecular straight chain, and thus has a low enhancement efficiency for the base film layer.

[0098] Comparative Example 6

[0099] The hollow fiber reverse osmosis composite membrane of this comparative example was prepared according to the method of steps (1) to (3) in Example 1, except that in step (2), no immersion treatment in dilute hydrochloric acid containing 0.4wt% HCl and a temperature of 60°C was performed (no polymerization reaction of the ethyl-resin was performed).

[0100] Test Example 1

[0101] The hollow fiber reverse osmosis composite membranes prepared in the above embodiments and comparative examples were sampled and cut into about 800 short tubes with a length of 50 mm, and were stacked in parallel and closely in the 52x23mm inner cavity of the mold along the axis direction of the short tubes. In the direction perpendicular to the axis of the short tubes, pressures of 0.3 MPa, 4 MPa, and 6 MPa were applied successively and maintained for 10 min respectively. The stacking thickness after 0.3 MPa compression (the thickness perpendicular to the axis direction of the short tubes) was used as a reference, and the thickness compression rate at 4 MPa and 6 MPa pressures perpendicular to the axis direction of the short tubes was measured to simulate and compare the pressure resistance of the hollow fiber reverse osmosis composite membrane. The lower the compression rate, the higher the pressure resistance.

[0102] The results show that the 4MPa compression rate and 6MPa compression rate of the composite membrane test blocks of Examples 1-6 are lower than 1.7% and 2.5%, respectively. The 4MPa compression rate of the composite membrane test blocks of Comparative Examples 1-6 are higher than 3%, and the 6MPa compression rate is higher than 5%. The order of compression rate from low to high is Comparative Examples 4, 6, 2, 1, 5, 3.

[0103] Test Example 2

[0104] The hollow fiber reverse osmosis composite membranes prepared in the above embodiments and comparative examples were cut, sampled, assembled, and made into cross-flow reverse osmosis experimental modules (the effective membrane area was 40 cm 2About), in three sets of reverse osmosis evaluation devices with exactly the same configuration, the initial water flux and initial desalination rate at a temperature of 25°C were measured successively. Condition 1 was that the inlet concentration of sodium chloride aqueous solution was 3.0wt%, the outlet concentration was 3.2wt% and the pressure difference was 4.0MPa, and condition 2 was that the inlet concentration of sodium chloride aqueous solution was 5.0wt%, the outlet concentration was 5.3wt% and the pressure difference was 5.0MPa; metering began after stabilization for 10 minutes, and the metering time was 120 minutes; the sodium chloride aqueous solution used was made of pure water (pure water obtained by distillation after reverse osmosis) and recrystallized sodium chloride, and then purified by an ultrafiltration device before use. The concentration of the sodium chloride aqueous solution was determined by the conductivity method, and water was diluted at a fixed multiple during the determination.

[0105] The results show that the initial water flux of the hollow fiber reverse osmosis composite membrane in each embodiment is greater than 40L / m 2 ·h, the initial desalination rate is >99.7%; among them, the overall effect of the hollow fiber reverse osmosis composite membrane in Example 5 is the best (the overall effect based on the effects of Test Examples 1 and 2). The initial water flux of the hollow fiber reverse osmosis composite membranes in each comparative example is <36L / m 2 ·h; Among them, the overall effect of the hollow fiber reverse osmosis composite membrane in Comparative Example 3 is the worst, and the overall effect of the hollow fiber reverse osmosis composite membrane in Comparative Example 4 is the best.

[0106] Test Example 3

[0107] The cross-flow reverse osmosis experimental assembly prepared by the hollow fiber reverse osmosis composite membrane of Example 5 and Comparative Example 4 in Test Example 2 was used in the reverse osmosis evaluation device used in Test Example 2 to examine the initial conditions of desalination rate decay and water flux decay at a temperature of 25°C, and was controlled according to the inlet concentration of sodium chloride aqueous solution of 5.0wt%, the outlet concentration of 5.3wt% and the pressure difference of 5.0MPa of Condition 2; metering was started after stabilization for 10min, and the test time was 300h each; the discharged sodium chloride aqueous solution and desalted water were continuously mixed and recycled.

[0108] The result is that the initial water flux of the hollow fiber reverse osmosis composite membrane of Example 5 is 43.1 L / m 2 ·h, the initial desalination rate was 99.80%, and after 300h of continuous operation, the desalination rate decayed and the water flux decay did not decrease. The initial water flux of the hollow fiber reverse osmosis composite membrane of Comparative Example 4 was 35L / m 2 ·h, the initial desalination rate was 99.65%. After 300h of continuous operation, the desalination rate decayed by 0.18% and the water flux decayed by 0.17%.

[0109] Industrial Application Example 1

[0110] The hollow fiber reverse osmosis composite membrane of Example 5 was scaled up and made into a membrane with an effective membrane area of ​​60m 2The reverse osmosis components were tested in a low-salinity seawater desalination project in a certain estuary bay, and a pressurized water pump and a control system for flow and pressure were specially configured.

[0111] The reverse osmosis module uses low-salinity seawater at room temperature (salinity 1.9-2.7wt%, seasonal fluctuations, boron content <4mg / L) after pre-purification and ultrafiltration to control the reverse osmosis pressure difference at 4.9-5.0MPa; the average flux in the first operating year was 63.5L / m 2 h, the average salt rejection rate was 99.82%, the average boron removal rate was 93%, and the average water recovery rate was 66.1%; during the four-year long-term operation, routine cleaning was carried out.

[0112] During the four years of application, based on the statistical data of each operating year, it was calculated that the average annual decline in desalination rate was 0.5%, the average annual decline in deboronization rate was 0.6%, and the average annual decline in water flux was 1.2%, maintaining a high and stable performance.

[0113] Combined with the results of the above test examples and industrial application examples, it can be seen that the hollow fiber reverse osmosis composite membrane prepared by the present invention has high compressive strength, creep resistance and hydrophilicity, so that the hollow fiber reverse osmosis composite membrane can adopt an operating pressure of 4-5MPa for a long time, and the performance is relatively stable, which is suitable for the desalination process of low-salinity seawater and has good application prospects.

Claims

1. A method for preparing a hollow fiber reverse osmosis composite membrane, characterized in that: The following steps are involved: (1) The casting liquid is continuously extruded through one or more nozzles of a hollow fiber membrane making machine to form an extruded liquid film, and at the same time, the core liquid is continuously injected through the core liquid cavity to fill the inner cavity of the extruded liquid film; the extruded liquid film with the inner cavity filled with the core liquid is first immersed in a coagulation bath L, and then immersed in a coagulation bath S to form a hollow fiber primary membrane; (2) immersing the hollow fiber primary membrane of step (1) into a coagulation-polymerization bath, then soaking it in dilute hydrochloric acid, and then washing it with water to obtain a semi-finished composite membrane; (3) heat treating the semi-finished composite membrane of step (2) to obtain a hollow fiber reverse osmosis composite membrane; The casting solution comprises the following components in parts by weight: 20-25 parts of base film resin with molecular weight of 30000-150000; 1-1.5 parts of poly(p-phenylene terephthalamide) with a molecular weight of 5000-8000, added in the form of a solution of poly(p-phenylene terephthalamide) in N-methylpyrrolidone; 2.0-2.5 parts of resol phenolic resin with a molecular weight of 1000-1500, added in the form of a solution of the resol phenolic resin in N-methylpyrrolidone; 0.8-1.2 parts of triethylamine; 10-15 parts of isopropyl alcohol; The total amount of N-methylpyrrolidone is 110-130 parts, including the amount of N-methylpyrrolidone used to prepare the N-methylpyrrolidone solution of poly(p-phenylene terephthalamide), the amount of N-methylpyrrolidone used to prepare the N-methylpyrrolidone solution of the resol phenolic resin, and the amount of N-methylpyrrolidone used to prepare the casting solution; The N-methylpyrrolidone solution of poly(p-phenylene terephthalamide) was prepared by the following method: N-methylpyrrolidone, lithium chloride and N-methylpyrrolidone solution of p-phenylenediamine are prepared into a mixed solution; the mixed solution is placed in a cold bath at -10 to -5°C, pyridine is added to the mixed solution, stirring is continued, terephthaloyl chloride is added, and the reaction is carried out for 1-2 hours to obtain an N-methylpyrrolidone solution of poly(p-phenylene terephthalamide); wherein the weight ratio of N-methylpyrrolidone, lithium chloride, p-phenylene diamine, pyridine and terephthaloyl chloride is (15-25):(0.3-0.5):1:(0.5-0.7):(1.94-2.01); the amount of N-methylpyrrolidone accounts for 26.5-27.5wt% of the total amount of N-methylpyrrolidone, and the amount of N-methylpyrrolidone in the N-methylpyrrolidone solution of p-phenylene diamine accounts for 6-7wt% of the total amount of N-methylpyrrolidone.

2. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: In step (1), the extruded liquid film with the inner cavity filled with core liquid is immersed in a coagulation bath L and stays for 2-4 minutes, and then immersed in a coagulation bath S and stays for 2-4 minutes to generate a hollow fiber primary membrane; the core liquid is an aqueous solution containing 5-8wt% of m-phenylenediamine and 2-3wt% of camphorsulfonic acid; the extrusion temperature of the casting liquid and the injection temperature of the core liquid are both 30-40°C; the coagulation bath L is an aqueous solution containing 20-30wt% of N-methylpyrrolidone, and the temperature is 15-20°C; the coagulation bath S is water, and the temperature is 20-30°C.

3. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: In step (2), the hollow fiber primary membrane of step (1) is immersed in a coagulation-polymerization bath and kept for 3-5 minutes, and then immersed in dilute hydrochloric acid for 15-30 hours; the coagulation-polymerization bath is an n-heptane solution containing 0.3-0.5wt% of trimesoyl chloride and 10-20wt% of isopropanol, and the temperature is 20-30°C; the dilute hydrochloric acid is an aqueous solution containing 0.4-0.6wt% of HCl, and the temperature is 50-60°C; the outer diameter of the semi-finished composite membrane is 1.2-1.6mm, and the ratio of the outer diameter to the inner diameter is 2.4-2.

6.

4. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: In step (3), the heat treatment atmosphere of the semi-finished composite film is air containing saturated water vapor or nitrogen containing saturated water vapor, the heat treatment time is 20-40 minutes, and the heat treatment temperature is 75-85°C.

5. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: The N-methylpyrrolidone solution of resol phenolic resin was prepared by the following method: Add phenol and oxalic acid to a 37-40wt% formaldehyde aqueous solution, continue stirring, open reflux, reflux cooling water temperature 10-15°C, heat the liquid to 60-65°C and stir for 0.5-1h, then heat to 75-80°C and react for 5-8h, add sodium hydroxide to neutralize to pH 7.5-8, wash with water, then perform reduced pressure distillation under vacuum conditions of -0.078 to -0.083MPa, heat to 148-152°C at a rate of 1-2°C / min until there is no distillate, close the vacuum and fill with nitrogen to normal pressure, add N-methylpyrrolidone, and control the temperature at 148-152°C After stirring evenly, the mixture is allowed to stand for 5-10 minutes, and then the vacuum system is turned on for reduced pressure distillation at a pressure of -0.078 to -0.083 MPa, and distillation is performed under the vacuum condition and a temperature of 148-152° C. until no distillate is produced. Finally, N-methylpyrrolidone is added to obtain a 20-50wt% N-methylpyrrolidone solution of a resol phenolic resin, wherein the molar ratio of formaldehyde, phenol and oxalic acid is (0.8-1.0):1:(0.006-0.01), and the amount of N-methylpyrrolidone added twice accounts for 17.5-18.5wt% of the total amount of N-methylpyrrolidone.

6. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: N-methylpyrrolidone, pyridine, triethylamine and p-phenylenediamine are purified in advance, and the base film resin and lithium chloride are dried.

7. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: The base film resin is bisphenol A type polysulfone, polyethersulfone or polyarylsulfone, and the molecular weight of the base film resin is 50000-80000.

8. The method for preparing a hollow fiber reverse osmosis composite membrane according to claim 1, characterized in that: The preparation method of the casting liquid comprises the following steps: subtracting the amount of N-methylpyrrolidone consumed in preparing the N-methylpyrrolidone solution of poly(p-phenylene terephthalamide) and the N-methylpyrrolidone solution of the resol phenolic resin from the total amount of N-methylpyrrolidone, placing the remaining N-methylpyrrolidone as a solvent in a reactor under nitrogen protection and anhydrous conditions, adding isopropyl alcohol and base film resin, continuously stirring, raising the temperature and controlling it at 50-60 DEG C, adding the N-methylpyrrolidone solution of poly(p-phenylene terephthalamide) and the N-methylpyrrolidone solution of the resol phenolic resin after the base film resin is completely dissolved, controlling the temperature at 50-60 DEG C, adding triethylamine after 5-10 minutes, cooling the feed liquid to 20-30 DEG C within 10 minutes after 20-30 minutes, stopping stirring, decompressing and degassing for 10-30 minutes, and then sealing and placing for more than 10 hours to obtain the casting liquid.