CN115364668A

CN115364668A - Preparation method of high-permeability composite reverse osmosis membrane for seawater desalination

Info

Publication number: CN115364668A
Application number: CN202210812923.1A
Authority: CN
Inventors: 周勇; 何金; 高从堦
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2022-07-11
Filing date: 2022-07-11
Publication date: 2022-11-22

Abstract

The invention discloses a preparation method of a high-permeability composite reverse osmosis membrane for seawater desalination, which is compounded on a polysulfone ultrafiltration membrane by interfacial polymerization of an amine monomer in a water phase solution and an acyl chloride monomer in an oil phase solution. In the aqueous phase solution, the addition concentration of an amine monomer is 0.25-5wt%, the addition concentration of an organic weak acid is 4-7wt%, an organic base is added to adjust the pH value, and finally DMF with different concentrations is added.

Description

Preparation method of high-permeability composite reverse osmosis membrane for seawater desalination

Technical Field

The invention belongs to the technical field of membrane preparation, and particularly relates to a preparation method of a high-permeability composite reverse osmosis membrane for seawater desalination

Background

Over the past few decades, the rapid growth of the global population and the lack of proper wastewater management have led to a dramatic increase in fresh water demand throughout the world, with 97.5% of the global water resources not being occupied by directly potable seawater. In the rest 2.5% of fresh water, 87% of ice and snow in glaciers cannot be directly utilized by human beings. In addition, the fresh water reserve of the underground water is very large, but most of the underground water is too deep from the ground surface, so that the underground water is not beneficial to mining and use. By 2025, reported by the united nations, approximately 52 hundred million people worldwide will have no safe drinking water and 18 hundred million people will face serious water shortage problems. Desalination of sea water, i.e. the process of separating dissolved salts from brine to obtain clean water for various human consumption and industrial applications, provides an important solution to this serious problem.

The reverse osmosis method is one of the most effective seawater desalination technologies at present, because the operation is simple, the investment cost and the energy consumption are relatively low, the Polyamide (PA) thin film composite membrane (TFC) membrane commonly used in the market at present is firstly developed by John Cadotte in 1981, and the composite reverse osmosis membrane is generally composed of three layers: the polyester non-woven fabric serving as a supporting structure, the ultrafiltration intermediate layer and the functional separation layer can be respectively and independently optimized in structure, so that the separation performance of the membrane is improved. Wherein the functional separation layer is formed on the surface of the polysulfone layer by utilizing the interfacial polymerization reaction between the aqueous phase monomer m-phenylenediamine (MPD) and the organic phase monomer trimesoyl chloride (TMC). However, this results in a reverse osmosis membrane having a rather limited water flux due to the insufficient hydrophilicity of the highly cross-linked network formed by the aromatic compounds of MPD and TMC. The addition of hydrophilic additives or the substitution of monomers with more hydrophilic chemicals is an effective way to increase the flux of composite membranes. For example, kwak et al (Kwak S Y, jung S G, kim S H.Structure-motion-performance relationship of flux-enhanced Reversed Osmosises (RO) membranes compounded of aromatic polyamine films [ J ]. Environ. Sci.Technol.,2001, 35 4334-4340.) add dimethyl sulfoxide to the aqueous phase, which improves the interfacial compatibility of oil and water phases, increases the surface roughness and specific surface area of the composite membrane, and greatly improves flux. Kim et al (j.h.kim, e.j.moon, c.k.kim, composite membranes prepared from poly (m-aminostyrene-co-vinyl alcohol) polymers for the reverse osmosis process, j.membr.sci.216 (2003) 107-120.) added poly (aminostyrene-co-vinyl alcohol) to the aqueous phase during membrane preparation, due to the hydrophilicity and flexibility of poly (vinyl alcohol), the water flux of the prepared membrane was increased.

Disclosure of Invention

The invention aims to provide a high-permeability composite reverse osmosis membrane and a preparation method thereof, aiming at the defects of the existing reverse osmosis membrane for seawater desalination. The hydrophilic solvent DMF is added into the water phase, so that the flux of the composite membrane is improved, and then the composite membrane is subjected to post-treatment by using an aqueous solution containing glycerol and SDS.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized by comprising the following steps of:

(1) Preparation of aqueous phase solution: adding an amine monomer and an organic weak acid with a hydrophilic group into ultrapure water, adding an organic base to adjust the pH value to 4-8, adding N-N Dimethylformamide (DMF), and uniformly mixing to obtain an aqueous phase solution; wherein in the prepared aqueous phase solution, the addition concentration of the amine monomer is 0.25-5wt%, and the addition concentration of the organic weak acid is 3-5 wt%; the concentration of DMF is 2-8 wt%.

(2) Preparation of oil phase solution: dissolving acyl chloride monomer in a petroleum spirit (Isopar-G) solvent, and uniformly mixing by ultrasonic waves to obtain an oil phase solution; wherein the mass concentration of the acyl chloride monomer in the oil phase solution is 1/40-1/30 of the mass concentration of the amine monomer in the water phase solution obtained in the step (1).

(3) Preparing a soaking solution: adding Sodium Dodecyl Sulfate (SDS) into ultrapure water, then adding a glycerol solution, and uniformly mixing; wherein the concentration of SDS is 0.3wt%, and the adding concentration of glycerol is 1-5 wt%.

(4) Pouring the solution prepared in the step (1) on a polysulfone membrane for 1-8 minutes, then pouring the aqueous phase solution on the surface of the polysulfone membrane, and then drying the surface of the membrane until no obvious liquid drops are formed on the surface of the membrane.

(5) Pouring the solution prepared in the step (2) onto the dried polysulfone membrane obtained in the step (4), reacting for 40-100 seconds, and pouring out the oil phase solution.

(6) And (3) soaking the membrane obtained in the step (5) in the solution prepared in the step (3) for 1-3 minutes, and then putting the membrane into a blast oven for drying treatment to obtain the composite reverse osmosis membrane product.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized in that in the step (1), the amine monomer is m-phenylenediamine, and the concentration of the amine monomer in an aqueous phase solution is 2.2wt%; the organic weak acid is camphorsulfonic acid, the added organic base is triethylamine, and the adding concentration of the triethylamine in the aqueous phase solution is 2.0-2.5 wt%.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized in that in the step (2), the acyl chloride monomer is trimesoyl chloride.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized in that the concentration of SDS in the step (3) is 0.3wt%, and the concentrations of glycerol are 1wt%, 3wt% and 5wt% respectively.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized in that the polysulfone membrane surface is dried in the manner of natural drying in air, fume hood forced air drying, roller spreading drying or air knife blowing drying in the step (4). The aqueous solution was poured onto the polysulfone membrane for 2 minutes.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized in that the reaction time in the step (5) is 1 minute.

The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination is characterized in that the drying temperature in the oven in the step (6) is 90-95 ℃, and the drying time is 8min.

The invention achieves the following beneficial effects:

(1) The permeability of the reverse osmosis membrane prepared by improving the hydrophilicity of the membrane surface is greatly improved.

(2) DMF with different concentrations is added into the water phase to enhance the hydrophilicity of the membrane and reduce the thickness of the separation layer, and the reverse osmosis membrane prepared by the hydrophilicity of the enhanced membrane is soaked by glycerol, so that the flux of the composite membrane is improved, and the rejection rate is prevented from being greatly reduced.

(3) Starting from the introduction of hydrophilic additives and soaking treatment, a new guiding idea is provided for preparing the ideal film composite reverse osmosis membrane.

Drawings

FIG. 1 is SEM pictures of the surfaces of the reverse osmosis membranes prepared in example 1 (M0), example 2 (M1), example 3 (M2), (M3) and (M4).

Fig. 2 is SEM images of the surfaces of the reverse osmosis membranes prepared in example 4 (M5), example 5 (M6), and example 7.

FIG. 3 shows the dynamic water contact angles of the surfaces of the reverse osmosis membranes prepared in example 1 (M0), example 2 (M1), example 3 (M2), (M3) and (M4).

FIG. 4 shows the dynamic water contact angles of the surfaces of the reverse osmosis membranes prepared in example 3 (M3), example 4 (M5), example 5 (M6) and example 7.

Detailed Description

According to the invention, the hydrophilic solvent DMF is added into the water phase, so that the flux of the composite membrane is greatly improved, the interception is prevented from being greatly reduced, and the composite membrane is subjected to post-treatment by using the water solution containing glycerol and SDS, so that the flux of the composite membrane is further improved.

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to the following examples, and all the examples are within the scope of the present invention.

Example 1

Fully dissolving 6G of camphorsulfonic acid and 2.2G of M-phenylenediamine in 98ml of deionized water in sequence, then adjusting the pH value by using 2ml of triethylamine, pouring the solution onto the upper surface of a prepared polysulfone porous supporting layer for 2 minutes, then pouring excessive aqueous phase solution on the surface of a polysulfone membrane, blowing the surface of the membrane by using a nitrogen air knife to remove water drops and liquid drops, pouring 0.11G of Isopar G solution of 100ml of trimesoyl chloride into the prepared polysulfone porous supporting layer for interfacial polymerization when the surface of the membrane has no liquid visible to the naked eye, after 60 seconds of reaction, pouring excessive oil phase on the surface of the polysulfone ultrafiltration membrane, standing and draining for 20 seconds, drying in an oven at the temperature of 95 ℃ for 8 minutes, then taking out the prepared membrane, and storing in ultrapure water for later representation of the osmotic selectivity of the membrane, and marking as an M0 membrane.

Example 2

Fully dissolving 6G of camphorsulfonic acid and 2.2G of M-phenylenediamine in 98ml of deionized water in sequence, then adjusting the pH value by using 2ml of triethylamine, finally adding 1ml of N-Dimethylformamide (DMF), pouring the solution onto the upper surface of a prepared polysulfone porous supporting layer for 2 minutes, then pouring excessive aqueous phase solution on the surface of a polysulfone membrane, blowing the surface of the membrane by using a nitrogen air knife to remove water drops and liquid drops, pouring 0.11G of Isopar G solution of 100ml of trimesoyl chloride into the membrane to generate interfacial polymerization when the surface of the membrane just has no liquid visible to the naked eye, pouring excessive oil phase on the surface of the polysulfone ultrafiltration membrane after reacting for 60 seconds, standing and draining for 20 seconds, placing the membrane into an oven with the temperature set to 95 ℃ to dry for 8 minutes, then taking out the prepared membrane, and storing the membrane in ultrapure water to be used for the subsequent representation of the osmotic selectivity of the membrane, and marking the membrane as an M1 membrane.

Example 3

Except that the above-mentioned N-N Dimethylformamide (DMF) concentration was 3, 5, 7ml in this order. The other conditions were identical to those of example 2 and were designated as M2, M3, M4 films.

Example 4

6G of camphorsulfonic acid and 2.2G of M-phenylenediamine are fully dissolved in 98ml of deionized water in sequence, then 2ml of triethylamine is used for adjusting the pH value, finally 5ml of N-Dimethylformamide (DMF) is added, the solution is poured onto the upper surface of a polysulfone porous supporting layer prepared in advance for 2 minutes, then the excessive aqueous solution on the surface of the polysulfone membrane is poured off, the membrane surface is blown by a nitrogen air knife to remove water drops and liquid drops, when the membrane surface has no liquid visible to the naked eye, 0.11G of Isopar G solution of 100ml of trimesoyl chloride is poured into an ultrapure membrane for interfacial polymerization, after 60 seconds of reaction, the excessive oil phase on the surface of the ultrafiltration membrane is poured off, after standing and draining for 20 seconds, an aqueous solution containing 0.3wt% of Sodium Dodecyl Sulfate (SDS) and 1wt% of glycerol is poured onto the membrane surface for 2 minutes, then the ultrapure membrane is placed into an oven set at the temperature of 95 ℃ for drying for 8 minutes, then the prepared membrane is taken out, and the prepared membrane is stored in an oven for preparing the subsequent membrane for characterization of the osmotic selectivity and is marked as M5 membrane.

Example 5

Except that the glycerol concentrations were 3wt%, 5wt% in this order. The other conditions were identical to those of example 4 and were calculated as M6, M7 films.

The membrane separation performance was measured at 25 ℃ under 5.5MPa using 32000ppm,20L NaCl solution, as shown in the following table:

kind of membrane	Saline flux (L m) ^-2 h ^-1 )	Salt rejection (%)
			M0	36.07	99.12
M1	37.69	99.15
			M2	45.26	99.13
M3	52.00	99.10
			M4	53.50	97.43
M5	35.90	98.55
			M6	37.10	98.12
M7	66.01	98.08

Fig. 1 shows SEM pictures of the surfaces of the reverse osmosis membranes prepared in example 1 (M0), example 2 (M1), example 3 (M2), (M3), and (M4).

Fig. 2 shows SEM pictures of the surfaces of the reverse osmosis membranes prepared in example 4 (M5), example 5 (M6), and example 7.

The dynamic water contact angles on the surfaces of the reverse osmosis membranes prepared in example 1 (M0), example 2 (M1), example 3 (M2), (M3), and (M4) are shown in fig. 3.

The dynamic water contact angles on the surfaces of the reverse osmosis membranes prepared in example 3 (M3), example 4 (M5), example 5 (M6) and example 7 are shown in fig. 4.

As can be seen from fig. 1 and 3, the number of leaf-like structures on the surface of the film increases, and the water contact angle on the surface of the film is M4> M2> M1> M3> M0 in the order of magnitude, which tends to increase first and then decrease. With the addition of DMF, the polymerization reaction is promoted, the release of the limited nano bubbles is accelerated, the nano vesicles in the PA membrane are larger, and more leaf-shaped structures appear on the surface of the PA membrane. The water contact angle of the membrane surface is related to the hydrophilicity of the membrane surface, and the hydrophilicity is reduced, but the permeability of the membrane is not reduced, but is improved. This is probably because the increased leaf-like structure of the membrane surface greatly increases the water permeation area and thus the positive effect of the increased water flux counteracts the negative effect of the decreased hydrophilicity of the membrane surface.

As can be seen from fig. 2 and 4, the leaf-like structure of the membrane surface increases, and the water contact angle of the membrane surface shows a tendency to decrease, confirming that the hydrophilicity of the membrane surface gradually increases with the increase of the concentration of glycerol. So that the membrane flux is highest at a glycerol concentration of 5wt%. The reason why the flux is rather decreased after adding glycerol to M4 and M5 may be due to the coalescence or fusion of the pores of the nanoporous polysulfone skin caused by the heat during the drying process.

The above description is merely illustrative of preferred embodiments of the present invention and the scope of the present invention should not be limited thereto.

Claims

1. A preparation method of a high-permeability composite reverse osmosis membrane for seawater desalination is characterized by comprising the following steps:

(1) Preparation of aqueous phase solution: adding an amine monomer and an organic weak acid with a hydrophilic group into ultrapure water, adding an organic base to adjust the pH value to 4-8, adding N-N dimethylformamide DMF, and uniformly mixing to obtain an aqueous phase solution; wherein in the prepared aqueous phase solution, the addition concentration of the amine monomer is 0.25-5wt%, and the addition concentration of the weak organic acid is 3-5 wt%; the concentration of DMF is 2-8 wt%;

(2) Preparation of oil phase solution: dissolving acyl chloride monomers in a petroleum spirit Isopar-G solvent, and uniformly mixing by ultrasonic waves to obtain an oil phase solution; wherein the mass concentration of the acyl chloride monomer in the oil phase solution is 1/40-1/30 of the mass concentration of the amine monomer in the water phase solution obtained in the step (1);

(3) Preparing a soaking solution: adding Sodium Dodecyl Sulfate (SDS) into ultrapure water, adding a glycerol solution, and uniformly mixing; wherein the concentration of SDS is 0.3wt%, and the adding concentration of glycerol is 1-5 wt%;

(4) Pouring the solution prepared in the step (1) on a polysulfone membrane for 1-8 minutes, then pouring the aqueous phase solution on the surface of the polysulfone membrane, and then drying the surface of the membrane until no obvious liquid drops are on the surface of the membrane;

(5) Pouring the solution prepared in the step (2) onto the polysulfone membrane dried in the step (4), reacting for 40-100 seconds, and pouring out the oil phase solution;

2. The method for preparing a high permeability composite reverse osmosis membrane for seawater desalination as claimed in claim 1, wherein the amine monomer in step (1) is m-phenylenediamine, and the concentration of the amine monomer in the aqueous solution is 2.2wt%; the organic weak acid is camphorsulfonic acid, the added organic base is triethylamine, and the adding concentration of the triethylamine in the aqueous phase solution is 2.0-2.5 wt%.

3. The method for preparing a high permeability composite reverse osmosis membrane for seawater desalination as claimed in claim 1, wherein the acyl chloride monomer in step (2) is trimesoyl chloride.

4. The method for preparing a high-permeability composite reverse osmosis membrane for seawater desalination as claimed in claim 1, wherein the concentration of SDS in the step (3) is 0.3wt%, and the concentration of glycerol is 1wt%, 3wt%, 5wt%, respectively.

5. The method for preparing a high-permeability composite reverse osmosis membrane for seawater desalination according to claim 1, wherein the polysulfone membrane surface dried in the step (4) is air-dried, fume hood-blown, roller spreading-dried or air-knife blowing-dried. The aqueous solution was poured onto the polysulfone membrane surface for 2 minutes.

6. The method for preparing a high permeability composite reverse osmosis membrane for seawater desalination as claimed in claim 1, wherein the reaction time of step (5) is 1 minute.

7. The preparation method of the high-permeability composite reverse osmosis membrane for seawater desalination as claimed in claim 1, wherein the drying temperature in the oven in the step (6) is 90-95 ℃, and the drying time is 8min.