阅读说明：本技术 一种提高聚丙烯腈正渗透膜耐氯性能的改性方法 (Modification method for improving chlorine resistance of polyacrylonitrile forward osmosis membrane ) 是由 李英华 邓文贺 张诗杰 李海波 苏菲 于 2020-12-29 设计创作，主要内容包括：本发明属于水处理技术领域,公开了一种提高聚丙烯腈正渗透膜耐氯性能的改性方法。包括：将聚丙烯腈溶解在有机溶剂N-甲基吡咯烷酮中,加入致孔剂,待完全溶解后放入超声波清洗机中进行脱气处理,去除搅拌过程中产生的气体,形成铸膜液；将铸膜液倒在玻璃板上,用涂膜器进行刮膜,然后将其立即投入去离子水凝固浴中,通过浸没-沉淀相转化法得到聚丙烯腈支撑膜；通过界面聚法制备聚酰胺功能层,然后用正己烷清洗,去除表面未反应的1,3,5-均苯三甲基酰氯,即得到环己胺改性的聚丙烯腈正渗透膜。本发明在保证聚丙烯腈正渗透膜通量的前提下,大幅度提高膜的耐氯性能。(The invention belongs to the technical field of water treatment, and discloses a modification method for improving chlorine resistance of a polyacrylonitrile forward osmosis membrane. The method comprises the following steps: dissolving polyacrylonitrile in an organic solvent N-methyl pyrrolidone, adding a pore-forming agent, placing the mixture into an ultrasonic cleaning machine for degassing after the mixture is completely dissolved, and removing gas generated in the stirring process to form a membrane casting solution; pouring the membrane casting solution on a glass plate, scraping the membrane by using a membrane coater, immediately putting the membrane casting solution into a deionized water coagulating bath, and obtaining a polyacrylonitrile support membrane by an immersion-precipitation phase conversion method; preparing a polyamide functional layer by an interfacial polymerization method, cleaning the polyamide functional layer by using n-hexane, and removing unreacted 1,3, 5-mesitylene trimethyl acyl chloride on the surface to obtain the cyclohexylamine modified polyacrylonitrile forward osmosis membrane. The invention greatly improves the chlorine resistance of the polyacrylonitrile forward osmosis membrane on the premise of ensuring the flux of the polyacrylonitrile forward osmosis membrane.)

1. A modification method for improving chlorine resistance of a polyacrylonitrile forward osmosis membrane is characterized by comprising the following steps:

s1, dissolving polyacrylonitrile in an organic solvent, and uniformly stirring to obtain a polyacrylonitrile solution;

s2, adding a pore-foaming agent into the polyacrylonitrile solution in the step S1, placing the polyacrylonitrile solution into an ultrasonic cleaning machine for degassing after the polyacrylonitrile solution is completely dissolved, and removing gas generated in the stirring process to form a membrane casting solution;

s3, pouring the casting film liquid obtained in the step S2 on a glass plate, scraping the film by using a film coater, immediately putting the film into a deionized water coagulating bath, and obtaining a polyacrylonitrile support film by an immersion-precipitation phase conversion method;

s4, preparing a polyamide functional layer by an interfacial polymerization method, dissolving cyclohexylamine and m-phenylenediamine in water to form an amine solution, soaking the polyacrylonitrile support membrane in the amine solution in the step S3 for 5min, removing the redundant amine solution on the surface of the membrane, immediately soaking the polyacrylonitrile support membrane in a 1,3, 5-mesitylene trimethyl acyl chloride solution, reacting for 3min to generate the polyamide functional layer, cleaning the polyamide functional layer by n-hexane, and removing the unreacted 1,3, 5-mesitylene trimethyl acyl chloride on the surface to obtain the cyclohexylamine modified polyacrylonitrile forward osmosis membrane.

2. The modification method for improving the chlorine resistance of the polyacrylonitrile forward osmosis membrane according to the claim 1, wherein the mass fraction of the polyacrylonitrile in the step S1 is 16% -18%, and the stirring temperature is 60 ℃.

3. The modification method for improving the chlorine resistance of the polyacrylonitrile forward osmosis membrane according to the claim 1, wherein the organic solvent in the step S1 is N-methyl pyrrolidone or N, N-dimethylformamide.

4. The modification method for improving the chlorine resistance of the polyacrylonitrile forward osmosis membrane according to claim 1, wherein in the step S2, the mass fraction of the pore-forming agent in the polyacrylonitrile solution is 0.5% -1.0%.

5. The modification method for improving the chlorine resistance of the polyacrylonitrile forward osmosis membrane according to the claim 1, wherein in the step S2, the pore-forming agent is lithium chloride or zinc chloride.

6. The modification method for improving the chlorine resistance of the polyacrylonitrile forward osmosis membrane according to the claim 1, wherein in the step S3, the thickness of the scraped membrane is 30-100 μm.

7. The modification method for improving the chlorine resistance of the polyacrylonitrile forward osmosis membrane according to the claim 1, characterized in that in the step S4, the mass fraction of cyclohexylamine in the amine solution is 0.2% -1.2%, the mass fraction of m-phenylenediamine is 4.5% -5.0%, the mass fraction of 1,3, 5-trimesoyl chloride solution is n-hexane as the solvent, and the mass fraction of 1,3, 5-trimesoyl chloride is 0.5% -0.8%.

Technical Field

The invention belongs to the technical field of water treatment, and particularly relates to a modification method for improving chlorine resistance of a polyacrylonitrile forward osmosis membrane.

Background

At present, the shortage of fresh water resources has become a significant problem restricting the development of human society. Reverse Osmosis (RO) technology has been widely used in brackish water desalination and pure water production as a conventional pressure driven separation technology. However, RO has too high energy consumption and has certain limitation in energy shortage areas. In contrast, Forward Osmosis (FO) technology has received attention due to its advantages of low energy consumption, low fouling tendency, high stability, etc., and FO has become one of the most valuable and potential technologies in the field of brackish water desalination.

FO membranes are typically composed of two layers: a non-woven fabric support layer (thickness 100-. The compact functional layer is mainly a Polyamide (PA) structure formed by m-phenylenediamine (MPD) and trimesoyl chloride (TMC) through Interfacial Polymerization (IP), and is responsible for regulating and controlling the separation performance of the membrane. It was investigated that the separation performance of the PA layer is significantly reduced when it is contacted with an oxidizing agent (particularly NaClO) for disinfection and inhibition of microorganisms. Cl attacks the original amide N site primarily through N-chlorination, resulting in direct hydrolysis or the development of an Orton rearrangement. The destruction of the polyamide functional layer by active chlorine causes the membrane to lose its salt-trapping function.

In the past decades, chlorine resistance of polyamide forward osmosis membranes has been improved mainly by chemical grafting or surface coating. Some alicyclic and aliphatic compounds are applied to the modification of the polyamide membrane, and researches prove that both compounds can obviously improve the chlorine resistance of the polyamide membrane. However, in any modification method, the addition of the modifying substance increases the mass transfer resistance of the membrane surface, resulting in a decrease in the membrane flux. Therefore, in developing a modification method for improving the chlorine resistance of the forward osmosis membrane, attention should also be paid to the control of the flux.

Disclosure of Invention

In order to overcome the defect that the addition of the existing modified substance increases the mass transfer resistance of the membrane surface and causes the reduction of the membrane flux, the invention provides a modification method for improving the chlorine resistance of a polyacrylonitrile forward osmosis membrane, which comprises the following steps:

s1, dissolving a predetermined amount of polyacrylonitrile in an organic solvent, and uniformly stirring to obtain a polyacrylonitrile solution;

s2, adding a pore-foaming agent into the polyacrylonitrile solution in the step S1, placing the polyacrylonitrile solution into an ultrasonic cleaning machine for degassing after the polyacrylonitrile solution is completely dissolved, and removing gas generated in the stirring process to form a membrane casting solution;

s3, pouring the casting film liquid obtained in the step S2 on a glass plate, scraping the film by using a film coater, immediately putting the film into a deionized water coagulating bath, and obtaining a polyacrylonitrile support film by an immersion-precipitation phase conversion method;

s4, preparing a polyamide functional layer by an interfacial polymerization method, dissolving cyclohexylamine and m-phenylenediamine in water to form an amine solution, soaking the polyacrylonitrile support membrane in the amine solution in the step S3 for 5min, removing the redundant amine solution on the surface of the membrane, immediately soaking the polyacrylonitrile support membrane in a 1,3, 5-mesitylene trimethyl acyl chloride solution, reacting for 3min to generate the polyamide functional layer, cleaning the polyamide functional layer by n-hexane, and removing the unreacted 1,3, 5-mesitylene trimethyl acyl chloride on the surface to obtain the cyclohexylamine modified polyacrylonitrile forward osmosis membrane.

Further, in the step S1, the mass fraction of polyacrylonitrile is 16% -18%, the organic solvent is N-methyl pyrrolidone or N, N-dimethyl formamide, and the stirring temperature is 60 ℃.

Further, in step S2, the mass fraction of the pore-forming agent in the polyacrylonitrile solution is 0.5% to 1.0%, and the pore-forming agent is lithium chloride or zinc chloride.

Further, in step S3, the thickness of the scratch film is 30-100 μm.

Further, in step S4, the mass fraction of cyclohexylamine in the amine solution is 0.2% to 1.2%, the mass fraction of m-phenylenediamine is 4.5% to 5.0%, the mass fraction of 1,3, 5-trimesoyl chloride solution is 0.5% to 0.8% with n-hexane as a solvent, and the mass fraction of 1,3, 5-trimesoyl chloride is 0.5% to 0.8%.

According to the invention, the cyclohexylamine is in a monoamine structure and cannot form long-chain polyamide, and a large amount of short-chain polyamide structures are formed after the cyclohexylamine with a certain concentration is added into the functional layer of the forward osmosis membrane, so that a chlorine-resistant sacrificial layer is formed; meanwhile, the alicyclic group belongs to an electron-donating group, and the electron cloud density of the polyamide chain can be increased, so that the chlorine resistance of the polyamide is improved. In addition, the steric effect on water is reduced due to the generation of a large number of short-chain polyamide structures, and the water flux of the membrane is promoted, so that the problem of flux reduction caused by chemical grafting is solved.

Compared with the prior art, the invention has the beneficial effects that: the chlorine-resistant layer is constructed through the grafting modification of cyclohexylamine, the chlorine-resistant performance of the forward osmosis membrane is improved, the modification method is simple and cheap, and the cost of the modified membrane is reduced; meanwhile, the flux of the membrane is not greatly reduced due to chemical grafting on the surface of the membrane, and the treatment efficiency of the membrane is effectively ensured. The invention greatly improves the chlorine resistance of the polyacrylonitrile forward osmosis membrane on the premise of ensuring the flux of the polyacrylonitrile forward osmosis membrane.

Description of the drawings:

FIG. 1 is an SEM image (magnification of 10000) of a modified forward osmosis membrane of the present invention;

FIG. 2 is an SEM photograph (100000 times) of a modified forward osmosis membrane according to the present invention;

FIG. 3 is an AFM image of a modified forward osmosis membrane of the present invention;

FIG. 4 is an XPS plot of a modified forward osmosis membrane of the present invention;

FIG. 5 is a schematic diagram of a modification of the present invention.

Detailed Description

The invention is described in more detail below with reference to specific examples, without limiting the scope of the invention. Unless otherwise specified, the experimental methods adopted by the invention are all conventional methods, and experimental equipment, materials, reagents and the like used in the experimental method can be obtained from commercial sources.

The present invention tests the water flux (Jw) and salt rejection (R) of a forward osmosis membrane, as well as the salt rejection (R) of the membrane after 1 hour of soaking in 20000ppm NaClO solution.

The determination of the water flux (Jw) is calculated by measuring the volume change (Δ V) and the effective membrane area (Am) of the feed liquid and the given time interval (Δ t) as follows:

the retention rate of the salt, R, is calculated as follows:

wherein C is_p(mg·L^-1) Is the mass concentration of the draw solution, C_f(mg·L^-1) Is the mass concentration of the feed liquid.

The detection method of the performance of the normal osmosis membrane comprises the following steps: using 0.5mol/L sodium chloride solution as a feeding liquid, and circulating by a peristaltic pump at the flow rate of 6L/h; 2mol/L of Mg is taken as a drawing liquid₂And weighing the Cl solution, and testing the quality and the conductivity of the Cl solution to obtain the water flux and the salt rejection rate of the forward osmosis membrane.

Example 1

A non-solvent induced phase separation (NIPS) method was used to prepare porous PAN supports. Firstly, polyacrylonitrile with the mass fraction of 16.7 percent is dissolved in N-methyl pyrrolidone solution, a pore-foaming agent lithium chloride with the mass fraction of 0.8 percent is added, and the mixture is stirred for 12 hours at the temperature of 60 ℃. And after the casting film is completely dissolved, putting the casting film solution into an ultrasonic cleaning machine for degassing treatment to remove bubbles generated in the stirring process. And after 24 hours, pouring the casting solution on a glass plate, scraping the film by using a film coater, controlling the thickness to be about 60 mu m, and immediately putting the film into a deionized water coagulation bath to obtain the support film. And then preparing a functional layer on the prepared carrier by an IP (interfacial polymerization) method. Firstly, the prepared support membrane is placed in a m-phenylenediamine solution (water is used as a solvent, the mass fraction of m-phenylenediamine is 5%, and the mass fraction of cyclohexylamine is 0.5%) to be soaked for 5min, and then the redundant m-phenylenediamine solution is removed from the surface. Immediately immersing the membrane into 1,3, 5-mesitylene trimethyl acyl chloride solution (normal hexane is used as a solvent, 0.5 percent) and reacting for 3min to form a functional layer.

The water flux of the cyclohexylamine modified forward osmosis membrane obtained in the example is 13.2L/(m)²H), the salt rejection was 98.3%, after chlorination the salt rejection was 66.3%.

Example 2

A non-solvent induced phase separation (NIPS) method was used to prepare porous PAN supports. Firstly, polyacrylonitrile with the mass fraction of 17.0 percent is dissolved in N, N-dimethyl formamide solution, a pore-foaming agent lithium chloride with the mass fraction of 1.0 percent is added, and the mixture is stirred for 12 hours at the temperature of 60 ℃. And after the casting film is completely dissolved, putting the casting film solution into an ultrasonic cleaning machine for degassing treatment to remove bubbles generated in the stirring process. And after 24 hours, pouring the casting solution on a glass plate, scraping the film by using a film coater, controlling the thickness to be about 60 mu m, and immediately putting the film into a deionized water coagulation bath to obtain the support film. And then preparing a functional layer on the prepared carrier by an IP (interfacial polymerization) method. First, the prepared support film was immersed in a m-phenylenediamine solution (water as a solvent, the mass fraction of m-phenylenediamine was 4.8%, and the mass fraction of cyclohexylamine was 0.8%) for 5min, and then the excess m-phenylenediamine solution was removed from the surface. Immediately immersing the membrane into 1,3, 5-mesitylene trimethyl acyl chloride solution (normal hexane is used as a solvent, 0.5 percent) and reacting for 3min to form a functional layer.

The water flux of the cyclohexylamine modified forward osmosis membrane obtained in the embodiment is 8.0L/(m)²H), the salt rejection was 99.3%, after chlorination the salt rejection was 77.2%.

Example 3

A non-solvent induced phase separation (NIPS) method was used to prepare porous PAN supports. Firstly, polyacrylonitrile with the mass fraction of 16.8 percent is dissolved in N-methyl pyrrolidone solution, a pore-foaming agent zinc chloride with the mass fraction of 0.8 percent is added, and the mixture is stirred for 12 hours at the temperature of 60 ℃. And after the casting film is completely dissolved, putting the casting film solution into an ultrasonic cleaning machine for degassing treatment to remove bubbles generated in the stirring process. And after 24 hours, pouring the casting solution on a glass plate, scraping the film by using a film coater, controlling the thickness to be about 60 mu m, and immediately putting the film into a deionized water coagulation bath to obtain the support film. And then preparing a functional layer on the prepared carrier by an IP (interfacial polymerization) method. Firstly, the prepared support membrane is placed in a m-phenylenediamine solution (water is used as a solvent, the mass fraction of the m-phenylenediamine is 5.0%, and the mass fraction of the cyclohexylamine is 1.0%) to be soaked for 5min, and then the redundant m-phenylenediamine solution is removed from the surface. Immediately immersing the membrane into 1,3, 5-mesitylene trimethyl acyl chloride solution (normal hexane is used as a solvent, 0.8 percent) and reacting for 3min to form a functional layer.

The water flux of the cyclohexylamine modified forward osmosis membrane obtained in the example is 4.6L/(m)²H), the salt rejection is 99.7%, and the salt rejection after chlorination is 80.0%.

Example 4

A non-solvent induced phase separation (NIPS) method was used to prepare porous PAN supports. Firstly, polyacrylonitrile with the mass fraction of 16.8 percent is dissolved in N, N-dimethyl formamide solution, a pore-foaming agent zinc chloride with the mass fraction of 0.5 percent is added, and the mixture is stirred for 12 hours at the temperature of 60 ℃. And after the casting film is completely dissolved, putting the casting film solution into an ultrasonic cleaning machine for degassing treatment to remove bubbles generated in the stirring process. And after 24 hours, pouring the casting solution on a glass plate, scraping the film by using a film coater, controlling the thickness to be about 60 mu m, and immediately putting the film into a deionized water coagulation bath to obtain the support film. And then preparing a functional layer on the prepared carrier by an IP (interfacial polymerization) method. Firstly, the prepared support membrane is placed in a m-phenylenediamine solution (water is used as a solvent, the mass fraction of the m-phenylenediamine is 5.0%, and the mass fraction of the cyclohexylamine is 1.2%) to be soaked for 5min, and then the redundant m-phenylenediamine solution is removed from the surface. Immediately immersing the membrane into 1,3, 5-mesitylene trimethyl acyl chloride solution (normal hexane is used as a solvent, 0.5 percent) and reacting for 3min to form a functional layer.

The water flux of the cyclohexylamine modified forward osmosis membrane obtained in the example is 4.0L/(m)²H), the salt rejection was 99.7%, and the salt rejection after chlorination was 81.2%.

Example 5

A non-solvent induced phase separation (NIPS) method was used to prepare porous PAN supports. Firstly, polyacrylonitrile with the mass fraction of 16.2 percent is dissolved in N-methyl pyrrolidone solution, a pore-foaming agent zinc chloride with the mass fraction of 1.0 percent is added, and the mixture is stirred for 12 hours at the temperature of 60 ℃. And after the casting film is completely dissolved, putting the casting film solution into an ultrasonic cleaning machine for degassing treatment to remove bubbles generated in the stirring process. And after 24 hours, pouring the casting solution on a glass plate, scraping the film by using a film coater, controlling the thickness to be about 60 mu m, and immediately putting the film into a deionized water coagulation bath to obtain the support film. And then preparing a functional layer on the prepared carrier by an IP (interfacial polymerization) method. First, the prepared support film was immersed in a m-phenylenediamine solution (water as a solvent, the mass fraction of m-phenylenediamine was 4.5%, and the mass fraction of cyclohexylamine was 0.2%) for 5min, and then the excess m-phenylenediamine solution was removed from the surface. Immediately immersing the membrane into 1,3, 5-mesitylene trimethyl acyl chloride solution (normal hexane is used as a solvent, 0.5 percent) and reacting for 3min to form a functional layer.

The water flux of the cyclohexylamine modified forward osmosis membrane obtained in the example is 13.0L/(m)²H), the salt rejection was 98.8%, after chlorination the salt rejection was 66.4%.

The embodiments described above are merely preferred embodiments of the invention, rather than all possible embodiments of the invention. Any obvious modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the spirit and scope of the present invention.