CN111888943B

CN111888943B - Preparation method of reverse osmosis membrane containing buffer layer free interface polymerization

Info

Publication number: CN111888943B
Application number: CN202010668472.XA
Authority: CN
Inventors: 米皓阳; 张青; 经鑫; 刘跃军
Original assignee: Hunan University of Technology
Current assignee: Hunan University of Technology
Priority date: 2020-07-13
Filing date: 2020-07-13
Publication date: 2022-03-11
Anticipated expiration: 2040-07-13
Also published as: CN111888943A

Abstract

The invention discloses a preparation method of a reverse osmosis membrane containing buffer layer free interface polymerization, which is characterized in that a buffer layer is added between a water phase and an organic phase in the reverse osmosis membrane prepared by free interface polymerization to slow down the intensity and heterogeneity of polymerization reaction, so that the reverse osmosis membrane formed by free interface polymerization is uniform and compact, the problems of uneven distribution of reaction monomers and intense local reaction in free interface polymerization are solved, the conditions of wrinkles and accumulation of a dense layer of the reverse osmosis membrane are avoided, the desalting performance and the chlorine resistance of the reverse osmosis membrane are improved, and the effective control of the polymerization reaction at an interface is realized. The method disclosed by the invention is simple to operate and low in cost, and can be used for rapidly preparing the reverse osmosis membrane which is uniform in structure, excellent in desalination performance, good in chlorine resistance and excellent in stability in batches.

Description

Preparation method of reverse osmosis membrane containing buffer layer free interface polymerization

Technical Field

The invention relates to the technical field of reverse osmosis membranes, in particular to a preparation method of a reverse osmosis membrane containing buffer layer free interface polymerization.

Background

The shortage of water resources remains a major challenge for people today, and reverse osmosis technology is an advanced seawater desalination technology today. The reverse osmosis membrane is an artificial semipermeable membrane with certain characteristics and is made by simulating a biological semipermeable membrane, and is a core component of a reverse osmosis technology. The principle of reverse osmosis is that under the action of the osmotic pressure higher than that of the solution, other substances are separated from water based on the fact that the substances cannot permeate a semipermeable membrane. The reverse osmosis membrane has a very small membrane pore size, and thus can effectively remove dissolved salts, colloids, microorganisms, organic substances, and the like in water. The reverse osmosis membrane technology has the advantages of good filtering water quality, low energy consumption, no pollution, simple process, simple and convenient operation and the like.

The most commonly used reverse osmosis membranes at present are composite membranes. The composite membrane is characterized by being mainly made of the two materials and formed by compounding a very thin compact layer and a porous supporting layer. The porous support layer is also called as a base film and plays a role in enhancing the mechanical strength; dense layers, also known as skin layers, serve as desalination and are currently most used are aromatic polyamide membranes. The main performance of the composite membrane is concentrated on the compact layer, so that the preparation of the compact layer with good selective performance and high permeation flux is an important problem in the research of the reverse osmosis membrane. Interfacial polymerization is the most commonly used process for preparing polyamide membranes, and is mainly characterized in that an interface is formed by an organic phase and an aqueous phase which are mutually incompatible, and polyamine and acyl chloride which participate in the reaction are polymerized at the interface to form the polyamide membrane. The free interface polymerization developed in recent years can form an extremely thin polyamide membrane at a water-oil two-phase interface to effectively improve permeation flux, but when an organic phase is added into a water phase, the surface tension of the organic phase is different from that of water, the reaction monomer is uniformly distributed when the organic phase is diffused, and the monomer concentration difference and the nonuniformity of a synthetic functional membrane are easily caused by the flowing of an organic phase solution on a water surface. In addition, diamine and polybasic acyl chloride react at the interface to violently emit a large amount of heat, and the heat cannot diffuse out in time, so that the generation of the membrane is influenced, the membrane is wrinkled and stacked, and the quality stability of the polyamide membrane formed by free interface polymerization is poor. This problem is currently not solved in an effective way.

Disclosure of Invention

The invention aims to solve the technical problem of the prior reverse osmosis membrane free interface polymerization process, which causes the defects of membrane wrinkling and accumulation, and provides a preparation method of a reverse osmosis membrane containing buffer layer free interface polymerization.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a reverse osmosis membrane containing buffer layer free interface polymerization comprises the following preparation steps:

s1, soaking a base film in absolute ethyl alcohol for ultrasonic treatment, then performing ultrasonic treatment in deionized water until water drops on the surface of the base film are gathered, and storing the base film in the deionized water for later use.

S2, dissolving aromatic diamine in a water phase, controlling the concentration of the aromatic diamine to be 0.3% -0.7%, and dissolving polyacyl chloride in an organic phase, wherein the concentration of the polyacyl chloride is controlled to be 0.15% -0.35%.

S3, placing the base film in the S1 at the bottom of the reactor, pouring the aromatic diamine solution in the S2 into the reactor, adding a buffer solution to cover the surface of the water phase by 3-5 mm to serve as a buffer layer, slowly and uniformly adding the polyacyl chloride solution to the buffer layer, and sealing for reaction.

And S4, taking out the base membrane and the film formed by free interface polymerization, cleaning the film by using normal hexane and deionized water, and drying to obtain the reverse osmosis membrane.

According to the preparation method, the buffer layer is added between the water phase and the organic phase in the reverse osmosis membrane prepared by free interface polymerization, when the organic solution containing the polyacyl chloride is contacted with the buffer layer, the organic solution and the buffer layer are mutually dissolved because the solvents are similar or the same, so that a large amount of acyl chloride monomers cannot be accumulated, and meanwhile, due to the existence of the buffer layer, the acyl chloride monomers can be slowly and uniformly diffused, so that interface disturbance caused by the flow of the organic phase on the surface of the water phase is avoided, and the effective control of the polymerization reaction at the interface is realized. When the acyl chloride organic solution is fused with the buffer layer, the acyl chloride monomer is gradually diffused to an interface formed by the water phase and the buffer layer, so that the polymerization reaction is gradually and orderly carried out, the generated heat is less, the problems of folds and accumulation of the reverse osmosis membrane are avoided, the synthesis of a high-quality polyamide membrane is facilitated, and the filtering performance of the polyamide reverse osmosis membrane is improved.

Further, the base film of S1 is any one of nylon, polysulfone, and polyvinylidene fluoride. S1 the aperture of the basement membrane is 0.1-10 μm.

Further, the aromatic diamine in S2 is one or more of m-xylylenediamine, m-phenylenediamine and p-phenylenediamine; the polybasic acyl chloride is trimesoyl chloride.

Further, the water phase is deionized water; s2 the organic phase is one or more of n-hexane, cyclohexane, toluene and benzene.

Further, the concentration of the poly-acid chloride in the S2 is 2 times of that of the aromatic diamine.

Further, the upper surface of the base film described in S3 is more than 1cm from the aqueous phase surface.

Further, the buffer in S3 is one or more of n-hexane, cyclohexane, toluene, and benzene.

Further, the reaction temperature in S3 is 20-30 ℃, and the reaction time is 3-20 min.

Compared with the prior art, the beneficial effects are:

the invention creatively adds the buffer layer at the interface of the organic phase and the water phase of the free interface polymerization, reduces the reaction degree of the aromatic diamine and the polybasic acyl chloride interface polymerization, avoids the inhomogeneous reaction caused by the interface flow of the organic phase and the water phase, solves the problems of uneven distribution and violent reaction of reaction monomers at the interface and avoids the condition that the reverse osmosis membrane generates wrinkles and piles. The invention can realize effective control of free interface polymerization, ensure that the synthesis reaction of the reverse osmosis membrane is relatively slowly and orderly carried out, ensure that the structure of the reverse osmosis membrane is smoother and the thickness is more uniform, and improve the desalting performance, chlorine resistance and excellent stability of the reverse osmosis membrane. The method disclosed by the invention is simple to operate and low in cost, and can realize batch and quick preparation of the reverse osmosis membrane with excellent desalting performance, good chlorine resistance and excellent stability.

Drawings

FIG. 1 is a schematic view of the process of the present invention;

FIG. 2 is an electron micrograph of a reverse osmosis membrane without interfacial polymerization of the buffer layer;

FIG. 3 is an electron micrograph of a reverse osmosis membrane without interfacial polymerization of the buffer layer;

FIG. 4 is an electron micrograph of a reverse osmosis membrane without interfacial polymerization of the buffer layer;

FIG. 5 is an electron micrograph of a free interfacial polymerized reverse osmosis membrane containing a buffer layer according to the present invention;

FIG. 6 is an electron micrograph of a buffer layer-containing free interfacial polymerized reverse osmosis membrane of the present invention;

FIG. 7 is an electron micrograph of a free interfacial polymerized reverse osmosis membrane containing a buffer layer according to the present invention;

FIG. 8 is a schematic representation of the desalination performance of a buffer layer-containing free interface polymerized reverse osmosis membrane of the present invention;

FIG. 9 is a schematic representation of the desalination performance of a buffer layer-containing free interface polymerized reverse osmosis membrane of the present invention;

FIG. 10 is a schematic representation comparing the desalination performance of a free interface polymerized reverse osmosis membrane containing a buffer layer of the present invention to other process reverse osmosis membranes;

FIG. 11 is a schematic representation comparing the desalination performance of a free interface polymerized reverse osmosis membrane containing a buffer layer of the present invention with other process reverse osmosis membranes;

FIG. 12 is a schematic representation of the chlorine resistance of a buffer layer containing free interface polymerized reverse osmosis membrane of the present invention;

FIG. 13 is a graphical representation of the chlorine resistance of a buffer layer containing free interface polymerized reverse osmosis membrane of the present invention.

Detailed Description

The following examples are further explained and illustrated, but the present invention is not limited in any way by the specific examples. Unless otherwise indicated, the methods and equipment used in the examples are conventional in the art and all materials used are conventional commercially available materials.

Example 1

This example provides a method for preparing a buffer layer-containing free interface polymerized reverse osmosis membrane, comprising the steps of:

s1, soaking a nylon 66(PA66) base film in absolute ethyl alcohol, performing ultrasonic treatment at normal temperature for 60s, cleaning with clear water, performing ultrasonic treatment in deionized water for 150s until no water drops are accumulated on the surface of the base film, and storing the base film in the deionized water for later use.

S2, dissolving m-xylylenediamine (m-XDA) in deionized water to prepare a 0.3 wt% m-XDA solution, and dissolving trimesoyl chloride (TMC) in n-hexane to prepare a 0.15 wt% TMC solution.

S3, placing the PA66 base film at the bottom of the reactor, pouring 20mL of m-XDA aqueous solution into the reactor, ensuring that the upper surface of the base film is more than 1cm away from the surface of the water phase, adding n-hexane with the thickness of 3.5mm to cover the surface of the water phase to serve as a buffer layer, finally slowly and uniformly adding 5mL of TMC solution to the buffer layer, and sealing and reacting for 20min at room temperature.

And S4, taking out the base membrane together with the film formed by free interface polymerization to ensure that the film is tiled on the surface of the base membrane and no artificial cracks or accumulation occurs, respectively cleaning the base membrane with n-hexane and deionized water, and drying for 12 hours to obtain the reverse osmosis membrane.

Example 2

This example is the same process as example 1 except that this example employs a 0.4 wt% m-XDA solution and a 0.2 wt% TMC solution.

Example 3

This example is the same process as example 1 except that this example employs a 0.5 wt% m-XDA solution and a 0.25 wt% TMC solution.

Example 4

This example is the same process as example 1 except that this example employs a 0.6 wt% m-XDA solution and a 0.3 wt% TMC solution.

Example 5

This example is the same process as example 1 except that this example employs a 0.7 wt% m-XDA solution and a 0.35 wt% TMC solution.

The reverse osmosis membranes prepared according to examples 1-5 were named as BLIP1, BLIP2, BLIP3, BLIP4, and BLIP5 membranes, respectively.

Example 6

s1, soaking a polysulfone base membrane in absolute ethyl alcohol, performing ultrasonic treatment at normal temperature for 60s, cleaning with clear water, performing ultrasonic treatment in deionized water for 150s until no water drops are accumulated on the surface of the polysulfone base membrane, and storing in the deionized water for later use.

S2, dissolving m-phenylenediamine in deionized water to prepare a 0.6 wt% m-phenylenediamine solution, and dissolving trimesoyl chloride (TMC) in n-hexane to prepare a 0.3 wt% TMC solution.

S3, placing the PA66 base film at the bottom of the reactor, pouring 20mL of m-phenylenediamine aqueous solution into the reactor, ensuring that the distance between the upper surface of the base film and the surface of the water phase is more than 1cm, slowly and uniformly adding 5mL of TMC solution to the buffer layer, and sealing and reacting for 15min at room temperature.

Example 7

S2, dissolving p-phenylenediamine in deionized water to prepare a 0.6 wt% p-phenylenediamine solution, and dissolving trimesoyl chloride (TMC) in n-hexane to prepare a 0.3 wt% TMC solution.

S3, placing the PA66 base film at the bottom of the reactor, pouring 20mL of p-phenylenediamine aqueous solution into the reactor, ensuring that the distance between the upper surface of the base film and the surface of the water phase is more than 1cm, adding n-hexane with the thickness of 3.5mm to cover the surface of the water phase to serve as a buffer layer, finally slowly and uniformly adding 5mL of TMC solution to the buffer layer, and sealing and reacting for 15min at room temperature.

Comparative example 1

S1, soaking the PA66 membrane in absolute ethyl alcohol, performing ultrasonic treatment at normal temperature for 60s, cleaning with clear water, performing ultrasonic treatment in deionized water for 150s until no water drops are accumulated on the surface of the membrane, and storing the membrane in the deionized water for later use.

S2, dissolving m-xylylenediamine (m-XDA) in deionized water to prepare a 0.6 wt% m-XDA solution, and dissolving trimesoyl chloride (TMC) in n-hexane to prepare a 0.3 wt% TMC solution.

S3, placing the PA66 base film at the bottom of the reactor, pouring 20mL of m-XDA aqueous solution into the reactor, and ensuring that the upper surface of the base film is more than 1cm away from the surface of the water phase; slowly adding 5ml TMC solution water phase surface, sealing and reacting for 5 min.

And S4, taking out the film synthesized on the interface together with the base film, ensuring that the film is flatly laid on the surface of the base film and does not have cracks and accumulation caused by human, respectively washing the film by using normal hexane and deionized water, and drying the film for more than 12 hours to obtain the reverse osmosis membrane which is named as UBLIP 4.

Comparative example 2

S1, soaking a nylon 66 membrane in absolute ethyl alcohol, performing ultrasonic treatment at normal temperature for 60s, cleaning with clear water, performing ultrasonic treatment in deionized water for 150s until no water drops are accumulated on the surface of the membrane, and storing the membrane in the deionized water for later use;

s2, dissolving m-phenylenediamine (MPD) in deionized water to prepare 0.6 wt% MPD solution, and dissolving trimesoyl chloride (TMC) in n-hexane to prepare 0.2 wt% TMC solution.

S3, placing the nylon 66 base film at the bottom of the reactor, pouring 20ml of MPD aqueous solution into the reactor, and ensuring that the upper surface of the base film is more than 1cm away from the surface of the water phase. Slowly adding 3ml of TMC solution water phase surface, sealing and reacting for 3 min;

and S4, taking out the base membrane together with the membrane synthesized on the interface, ensuring that the membrane is tiled on the surface of the base membrane without artificial cracks and accumulation, respectively cleaning the membrane by using normal hexane and deionized water, and drying for more than 12 hours to obtain the reverse osmosis membrane, namely the FI-IP membrane.

Performance testing

1. Electron microscope detection

As can be seen from the figures 2 to 7, the reverse osmosis membrane prepared by the buffer layer-containing interfacial polymerization method has a smooth and uniform surface, and the reverse osmosis membrane prepared by the buffer layer-free process has the condition of folds and accumulation on the surface.

2. Test for desalting Performance

At a working pressure of 5bar, a test temperature of 25. + -. 2 ℃ and a feed of 7.0. + -. 0.2 pH. Methyl orange, sodium sulfate, magnesium sulfate and sodium chloride are selected as test medicines, and the concentration of a salt solution is 2 g/L. The membrane is loaded into a filtration device as required, 70ml of pure water is added, and the membrane is pressed under pure water for at least 30 min. And opening the filtering equipment after film pressing is finished, pouring out the residual pure water, and adding the prepared saline solution. When the liquid drops at the mouth of the filtering device are stable, the filtered liquid begins to be received. Calculating the flux (P, L.m) according to the equation²·h^-1·bar^-1) And salt rejection (R,%), the formula is as follows:

where V (L) is the volume of permeated water, A (m)²) Is the effective filtration area of the membrane, t (h) is the time to collect V, Δ P is the pressure difference across the membrane, where C_pAnd C_fThe salt concentrations of the permeate and feed solutions, respectively, were measured with a conductivity meter.

The results of the desalination tests on the buffer layer free interface polymeric reverse osmosis membranes prepared in examples 1-5 are shown in the following table:

TABLE 1 desalting Performance of different membranes on methyl orange

Class of membrane	BLIP1	BLIP2	BLIP3	BLIP4	BLIP5
						Salt rejection (%)	67.91	82.39	86.56	95.16	89.37
Water flux (L.m)²·h^-1·bar^-1)	3.34	3.68	2.23	1.59	1.09

TABLE 2 desalination Performance of sodium sulfate by different membranes

Class of membrane	BLIP1	BLIP2	BLIP3	BLIP4	BLIP5
						Salt rejection (%)	41.22	62.28	70.14	92.55	84.98
Water flux (L.m)²·h^-1·bar^-1)	4.92	3.47	2.78	1.66	1.36

TABLE 3 desalting Performance of different membranes on magnesium sulfate

Class of membrane	BLIP1	BLIP2	BLIP3	BLIP4	BLIP5
						Salt rejection (%)	37.44	48.58	63.16	92.01	84.13
Water flux (L.m)²·h^-1·bar^-1)	4.58	4.34	2.53	2.02	1.48

TABLE 4 desalination Performance of sodium chloride by different membranes

Class of membrane	BLIP1	BLIP2	BLIP3	BLIP4	BLIP5
						Salt rejection (%)	23.94	35.85	46.68	83.99	64.75
Water flux (L.m)²·h^-1·bar^-1)	4.09	4.51	3.17	1.83	1.45

According to the above test results, it can be seen that as the concentration of the reactive monomer increases, the membrane exhibits the same regularity for different salts: the increase is carried out first and then the decrease is carried out, and the BLIP4 film prepared by the method has the best desalting performance for different salts. Meanwhile, the same membrane has the same law for different salts, namely: methyl orange > sodium sulfate > magnesium sulfate > sodium chloride.

The BLIP4 membrane prepared in example 4 and the UBLIP4 membrane prepared in comparative example 1 were subjected to desalination performance tests, and the results of the tests are shown in FIGS. 8 to 9, wherein the results of the tests show that the reverse osmosis membrane containing buffer layer free interface polymerization prepared in the present invention has greatly improved desalination rate compared with the reverse osmosis membrane without buffer layer on the premise of ensuring water flux.

When the BLIP4 membrane prepared in example 4, the UBLIP4 membrane prepared in comparative example 1 and the FI-IP membrane prepared in comparative example 2 were subjected to desalination performance detection, and the detection result shows that sodium sulfate is adopted as a detection drug, and the comparison result shows that the reverse osmosis membrane containing buffer layer free interface polymerization prepared in the invention has more stable desalination rate and water flux than the other two membranes as shown in FIGS. 10-11.

3. Chlorine resistance test

The active chlorine concentration of the sodium hypochlorite solution was set to 1000ppm, and the pH of the solution was adjusted to 7.0 with 0.1mol/L standard hydrochloric acid. The active chlorine treatment intensity was expressed as the product of the concentration (ppm) and the treatment time (h). Different reverse osmosis membranes subjected to the desalination test are soaked in a sodium hypochlorite solution for 12 hours, then are thoroughly cleaned, and are subjected to a chlorine resistance test. To prevent degradation of the active chlorine, it was left in the dark. The testing steps and conditions are consistent with those of the desalting test, and the tested data are subjected to normalization processing.

The chlorine resistance test of the buffer layer free interface polymeric reverse osmosis membranes prepared in examples 3 and 4 showed that the buffer layer free interface polymeric reverse osmosis membranes prepared in the invention showed a decrease in the salt rejection rate of magnesium sulfate, sodium sulfate and sodium chloride, and the water flux showed a decrease in the salt rejection rate, but the decrease was not large, as shown in fig. 12 to 13. The reason why the desalting rate of the treated membrane to salts is not greatly reduced is that methylene exists between amino and benzene rings in the m-XDA molecular structure, so that the activity of amido bonds is reduced, the steric hindrance is increased, and the possibility of Orton rearrangement is reduced. The reason for the decrease in water flux of the membrane after treatment is: firstly, filter cakes on the surface of the membrane are gradually increased after two salt solution filtrations. Second, the salt ions blocked some of the pores of the membrane during the test, thus resulting in a reduction in water flux.

Claims

1. The preparation method of the reverse osmosis membrane containing the buffer layer free interface polymerization is characterized by comprising the following steps:

s1, soaking a base film in absolute ethyl alcohol for ultrasonic treatment, then performing ultrasonic treatment in deionized water until no water drops gather on the surface of the base film, and storing the base film in the deionized water for later use;

s2, dissolving aromatic diamine in a water phase, controlling the concentration of the aromatic diamine to be 0.3-0.7%, and dissolving polyacyl chloride in an organic phase, wherein the concentration of the polyacyl chloride is controlled to be 0.15-0.35%;

s3, placing the base film in the S1 at the bottom of the reactor, pouring the aromatic diamine solution in the S2 into the reactor, adding a buffer solution to cover the surface of the water phase by 3-5 mm to serve as a buffer layer, slowly and uniformly adding the polyacyl chloride solution to the buffer layer, and sealing for reaction;

s4, taking out the base membrane and the film formed by free interface polymerization, cleaning the film by using normal hexane and deionized water, and drying to obtain the reverse osmosis membrane;

the buffer solution in S3 is one or more of n-hexane, cyclohexane, toluene and benzene.

2. The method of claim 1, wherein the base membrane of S1 is any one of nylon, polysulfone, and polyvinylidene fluoride.

3. The method for preparing a buffer layer-containing free interfacial polymerization reverse osmosis membrane according to claim 2, wherein the pore size of the basement membrane S1 is 0.1-10 μm.

4. A method for preparing a free interfacial polymerized reverse osmosis membrane having a buffer layer according to claim 1, wherein the diamine in S2 is one or more of m-xylylenediamine, m-phenylenediamine, and p-phenylenediamine; the polybasic acyl chloride is trimesoyl chloride.

5. The method of claim 1 wherein the aqueous phase is deionized water; s2 the organic phase is one or more of n-hexane, cyclohexane, toluene and benzene.

6. The method of claim 1, wherein the concentration of the poly-acid chloride at S2 is 2 times the concentration of the aromatic diamine.

7. The method of claim 1 wherein the top surface of the base membrane at S3 is greater than 1cm from the surface of the aqueous phase.

8. The method for preparing a buffer layer-containing free interface polymerized reverse osmosis membrane according to claim 1, wherein the reaction temperature in S3 is 20-30 ℃ and the reaction time is 3-20 min.