Composite nanofiltration membrane for desalting organic matters and preparation method of composite nanofiltration membrane

Abstract

The invention belongs to the field of separation, and particularly relates to a composite nanofiltration membrane for desalting organic matters and a preparation method of the composite nanofiltration membrane. According to the technical scheme, the method for preparing the composite nanofiltration membrane for desalination of the organic matter based on the reverse mass transfer process of the cross-linking agent is provided for the first time. In the method, an aqueous solution of a cross-linking agent and a hydrophilic macromolecular aqueous solution are separated by a hydrophobic membrane, and the cross-linking agent in the aqueous solution diffuses from one side of the hydrophobic membrane in a volatilization manner, passes through a hydrophobic membrane pore channel, is dissolved into the hydrophilic macromolecular aqueous solution on the other side of the membrane, and reacts with macromolecules at pores in the surface of the membrane, so that a separation layer is formed. Compared with a conventional method, the separation layer of the composite membrane prepared by the novel method provided by the invention is thinner, and the pore size distribution is more uniform, so that the prepared composite membrane has more excellent organic matter desalting performance and anti-pollution performance.

Description

Technical Field

[0001] The invention belongs to the field of separation, and in particular relates to a composite nanofiltration membrane for desalination of organic matter and a preparation method thereof. Background Art

[0002] Membrane separation technology is widely used in water treatment, material separation, purification, concentration and other fields. At present, membrane technology has gradually replaced traditional water treatment processes due to its energy saving, high efficiency, simple process and easy operation.

[0003] At present, interfacial polymerization and coating cross-linking are the most commonly used methods for preparing composite membranes for organic desalination. Compared with the interfacial polymerization method, there is no substance that destroys the cross-linking structure during the coating cross-linking process, and the macromolecular polymers (such as polyethyleneimine, polyvinyl alcohol and polydopamine) used have a large number of reaction sites on the chain segments, which react with small molecule cross-linking agents, making it easier to achieve controllable customization of membrane pore size. In addition, the coating cross-linking method is simpler to operate, usually only water is needed as the reaction solvent, and it has higher safety in large-scale applications. Therefore, based on the above advantages, the coating cross-linking method has received more and more attention.

[0004] The process of preparing composite membrane by conventional coating cross-linking method adopts the following steps: first, the aqueous solution containing hydrophilic macromolecular reactants is circulated into the tube side of the membrane module; after a certain period of time, the liquid inside the membrane fibers is drained, and the cross-linking agent aqueous solution is continued to be introduced into the tube side of the membrane module. After a certain period of reaction, a separation layer with a cross-linked network structure is formed on the inner surface of the membrane, thereby effectively separating the target organic matter / salt.

[0005] However, in order to ensure that the separation layer can completely cover the surface of the membrane substrate, the thickness of the separation layer will inevitably increase, thereby increasing the mass transfer resistance of water molecules. At the same time, since the crosslinking agent aqueous solution flows through the membrane surface in a dynamic manner under the conventional process, part of the macromolecular substances adsorbed on the membrane surface will be dragged away, which correspondingly destroys the uniform distribution of the macromolecular substances on the membrane surface, thereby causing the separation layer formed by the crosslinking reaction to have an uneven structure. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a composite nanofiltration membrane that can be used for desalination of organic matter and a preparation method thereof.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S1, introducing a hydrophilic macromolecular aqueous solution into the tube side of a membrane component; S2, filling the shell side of the membrane component with an aqueous solution of a crosslinking agent and allowing the solution to react for a certain period of time; S3, respectively placing the membrane component after the reaction into ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter; the membrane used in the membrane component is a hydrophobic membrane.

[0009] The hydrophilic macromolecule is one of polyethyleneimine, polyvinyl alcohol, chitosan, or hydroxyethyl cellulose or a mixture thereof.

[0010] The cross-linking agent is a volatile reagent; the cross-linking agent is one of glutaraldehyde, epichlorohydrin, ethylenediamine, or diethylenetriamine, or a mixture thereof.

[0011] The material of the hydrophobic membrane is one of PVC, PVDF, PTFE, and PVDF-CTFE, or a mixture thereof.

[0012] The mass concentration of the aqueous solution of the hydrophilic macromolecular reactant is 0.1-2.5wt%, preferably 0.5-2%, more preferably 0.5%.

[0013] The mass concentration of the aqueous solution of the cross-linking agent is 0.5-3wt%, preferably 1-3%, and more preferably 1%.

[0014] The reaction time in step S2 is 30-150 min.

[0015] It also includes a pre-sequence reaction S0, which is to carry out chemical grafting on the inner surface of the membrane;

[0016] Specifically, the steps include: a grafting solution is circulated through the tube side of the membrane assembly to react; the grafting solution is an aqueous solution of triethylenetetramine, tetraethylenepentamine or polyethyleneimine; and the mass concentration is 5-10wt%.

[0017] The invention includes a preparation method which can obtain a composite nanofiltration membrane used for desalination of organic matter.

[0018] The composite membrane prepared by the method of the present invention can be specifically applied to the removal of dyes in printing and dyeing wastewater, the recovery of inorganic salts, and the purification in the dye production process.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The technical solution of this application proposes for the first time a method for preparing a composite nanofiltration membrane for organic desalination based on a reverse mass transfer process of a cross-linking agent. In this method, a hydrophobic membrane separates an aqueous solution of a cross-linking agent from an aqueous solution of hydrophilic macromolecules. The cross-linking agent in the aqueous solution diffuses from one side of the hydrophobic membrane through the hydrophobic membrane pore channel in a volatilized manner, dissolves into the aqueous solution of hydrophilic macromolecules on the other side of the membrane, and reacts with the macromolecules at the opening of the membrane pore channel, thereby forming a separation layer only at the opening of the membrane surface ( Figure 1 shown).

[0021] The new method proposed by the present invention can repair defective pores of the composite membrane in situ during the reaction process, thereby effectively overcoming the problem of defective macropores that are easily formed during the preparation of the composite membrane under conventional methods. Moreover, for the new method proposed by the present invention, after the perfect separation layer is formed, the reverse mass transfer process of the cross-linking agent is inhibited, and the cross-linking agent is difficult to contact with the macromolecules, resulting in the termination of the reaction. Therefore, the new method has a self-inhibition effect and can easily form an ultra-thin separation layer on the membrane surface.

[0022] The present invention can effectively regulate the crosslinking degree and surface charge characteristics of the composite membrane separation layer by controlling the concentration of hydrophilic macromolecules, the concentration of the crosslinking agent and the reaction time, thereby achieving the purpose of efficient separation of specific organic matter / salts.

[0023] The invention is not only applicable to the internal pressure hollow fiber membrane, but also can be widely used in the preparation of organic matter / salt separation layers on the external pressure hollow fiber membrane, flat membrane and tubular membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the principle of preparing a composite nanofiltration membrane for desalination of organic matter by the reverse mass transfer process of the cross-linking agent proposed in the present invention;

[0025] Figure 2 This is a comparison chart of dye / salt separation performance of the composite membrane prepared in Example 1 and Comparative Example 1 (feed liquid composition: 0.2 g / L Victoria Blue VBB and 1.0 g / L Na2SO4);

[0026] Figure 3 This is a comparison chart of the anti-pollution performance of the composite membrane prepared in Example 1 and Comparative Example 1 (liquid composition: 0.2 g / L Congo Red CR and 1.0 g / L Na2SO4);

[0027] Figure 4 This is a diagram showing the change in water contact angle of the composite films prepared in Example 1 and Example 5 after ultrasonic treatment. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0029] A method for preparing a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S1, circulating a hydrophilic macromolecular aqueous solution in the tube side of a membrane assembly; S2, filling the shell side of a dry membrane assembly with an aqueous solution of a crosslinking agent and allowing the solution to react for a certain period of time; S3, washing the membrane assembly after the reaction in ethanol and deionized water to obtain a composite nanofiltration membrane for desalination of organic matter. The membrane used in the membrane assembly is a hydrophobic membrane.

[0030] The hydrophilic macromolecule is one of polyethyleneimine, polyvinyl alcohol, chitosan, or hydroxyethyl cellulose or a mixture thereof.

[0031] The cross-linking agent is a volatile reagent; the cross-linking agent is one of glutaraldehyde, epichlorohydrin, ethylenediamine, or diethylenetriamine, or a mixture thereof.

[0032] The material of the hydrophobic membrane is one of PVC, PVDF, PTFE, and PVDF-CTFE, or a mixture thereof.

[0033] The mass concentration of the hydrophilic macromolecular aqueous solution is 0.1-2.5wt%, specifically 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%. The mass concentration of the crosslinking agent aqueous solution is 0.5-3%, specifically 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%. The reaction time in step S2 is 30-150min, specifically 30min, 60min, 90min or 150min. The present invention can effectively regulate the crosslinking degree and surface charge characteristics of the composite membrane separation layer by controlling the concentration of the hydrophilic macromolecule, the concentration of the crosslinking agent and the reaction time, thereby achieving the purpose of efficient separation of specific organic matter / salt.

[0034] As one form thereof, it may also include a pre-sequence reaction S0, in which chemical grafting is performed on the inner surface of the membrane;

[0035] Specifically, the process comprises the following steps: a grafting solution is circulated through the tube side of the membrane assembly to react with the inner surface of the membrane by nucleophilic substitution; the grafting solution is an aqueous solution of triethylenetetramine, tetraethylenepentamine or polyethyleneimine; the mass concentration is 5-10wt%, specifically 5wt%, 8wt%, 10wt%.

[0036] The following is an exemplary description using preferred embodiments.

[0037] Example 1

[0038] A method for preparing a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S1, using a peristaltic pump to circulate a hydrophilic macromolecular reactant aqueous solution through the tube side of a hydrophobic PVC membrane component, in this embodiment, a polyethyleneimine (PEI) aqueous solution with a concentration of 0.5wt% and a molecular weight of 25000Da; S2, using a peristaltic pump to pass a crosslinking agent aqueous solution through the shell side of the PVC membrane component to fill it, in this embodiment, a 1.0wt% glutaraldehyde (GA) aqueous solution, and standing at room temperature for reaction for 40 minutes; S3, respectively placing the membrane component after the reaction in ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter.

[0039] Example 2

[0040] A method for preparing a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S1, using a peristaltic pump to circulate a hydrophilic macromolecular aqueous solution in a hydrophobic PVC membrane component tube side, in this embodiment, a polyvinyl alcohol (PVA) aqueous solution with a concentration of 1.0wt%; S2, using a peristaltic pump to pass a crosslinking agent aqueous solution into and fill the shell side of the PVC membrane component, in this embodiment, a 2.0wt% glutaraldehyde (GA) aqueous solution, and standing for reaction for 60 minutes; S3, respectively placing the reacted membrane component in ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter.

[0041] Example 3

[0042] A method for preparing a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S1, using a peristaltic pump to circulate a hydrophilic macromolecular aqueous solution in a hydrophobic PVC membrane component tube side, in this embodiment, a 2.0wt% hydroxyethyl cellulose (HEC) aqueous solution; S2, using a peristaltic pump to pass a crosslinking agent aqueous solution into and fill the shell side of the PVC membrane component, in this embodiment, a 3.0wt% glutaraldehyde (GA) aqueous solution, and standing at room temperature for reaction for 50 minutes; S3, respectively placing the reacted membrane component in ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter.

[0043] Example 4

[0044] A preparation method of a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S1, using a peristaltic pump to circulate a hydrophilic macromolecular aqueous solution in a hydrophobic PVC membrane component pipe side, in this embodiment, a polyacrylic acid (PAA) aqueous solution with a concentration of 1.0wt% containing 3.0wt% EDC and 1.0wt% NHS as an activator; S2, using a peristaltic pump to pass a crosslinking agent aqueous solution into and fill the shell side of the PVC membrane component, in this embodiment, a 2.0wt% ethylenediamine (EDA) aqueous solution, and standing at room temperature for reaction for 60 minutes; S3, respectively placing the membrane component after the reaction in ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter.

[0045] Example 5

[0046] A preparation method of a composite nanofiltration membrane for desalination of organic matter comprises the following steps: S0: using a peristaltic pump to circulate a grafting solution at a temperature of 50°C in the pipe side of a hydrophobic PVC membrane component, in this embodiment, it is an aqueous solution of tetraethylenepentamine with a concentration of 5wt%, and the reaction is carried out for 1h. The tetraethylenepentamine is grafted onto the surface of the PVC hydrophobic membrane through a nucleophilic substitution reaction; S1: using a peristaltic pump to circulate a hydrophilic macromolecular aqueous solution in the pipe side of the hydrophobic PVC membrane component, in this embodiment, it is an aqueous solution of polyethyleneimine (PEI) with a molecular weight of 25000Da with a concentration of 0.5wt%; S2, using a peristaltic pump to pass and fill the shell side of the membrane component with a crosslinking agent aqueous solution, in this embodiment, it is a 1.0wt% glutaraldehyde (GA) aqueous solution, and the reaction is allowed to stand at room temperature for 40min; S3, the membrane component after the reaction is respectively placed in ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter.

[0047] Glutaraldehyde can react with PEI and the amine groups grafted on the membrane surface, and enhance the firmness of the separation layer and the membrane substrate through chemical bonding.

[0048] Comparative Example 1

[0049] A conventional composite membrane preparation method comprises the following steps: S1, using a peristaltic pump to circulate a hydrophilic macromolecular reactant aqueous solution in a hydrophobic PVC membrane component tube side, in this embodiment, a 0.5wt% polyethyleneimine (PEI) aqueous solution with a molecular weight of 25000Da; after a certain period of time, the liquid inside the membrane component is emptied; S2, using a peristaltic pump to pass and fill a crosslinking agent aqueous solution in the shell side of the membrane component, in this embodiment, a 1.0wt% glutaraldehyde (GA) aqueous solution, and react at room temperature for 40 minutes; S3, the membrane component after the reaction is respectively placed in ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter.

[0050] Results test:

[0051] A solution containing 0.2 g / L dye and 1.0 g / L salt (Na2SO4 or NaCl) was prepared. The composite membrane was pre-pressed at 0.40 MPa and 25°C for 1 h by cross-flow filtration. After the flux stabilized, the membrane flux and dye desalination performance were measured at 0.30 MPa.

[0052] Table 1 shows the properties of composite membranes prepared by reverse mass transfer reaction method of crosslinking agent and conventional coating crosslinking method;

[0053] Table 1

[0054]

[0055] Result analysis:

[0056] Comparison of Example 1 and Comparative Example 1: Figure 2 and Figure 3 It is shown that compared with the conventional method of Comparative Example 1, the composite membrane prepared by the cross-linking agent reverse mass transfer reaction method used in Example 1 has a more uniform pore structure, so that it has better organic matter / salt separation performance and more excellent anti-pollution performance. Moreover, the new method proposed in the present invention is similar to the interfacial polymerization process, and there is a self-inhibition effect, which makes the formed separation layer thinner and gives the membrane a higher water flux. The specific results are shown in Table 1.

[0057] The results of Examples 1-4 show that the preparation method of the composite membrane for desalination of organic matter of the present application is not only for the system of PEI and GA. By using different reaction systems, it is proved that the reverse mass transfer reaction method of the cross-linking agent is universal, and a composite membrane that meets specific separation performance can be prepared by selecting different reactants or cross-linking agents.

[0058] Example 1 and Example 5: Figure 4 As shown, in the ultrasonic experiment, the water contact angle of the composite membrane prepared in Example 4 slightly increased from 56° to 58° after 30 minutes of ultrasound, indicating that the separation layer was firmly attached to the surface of the base membrane. The water contact angle of the composite membrane prepared in Example 1 increased from 65° to 80° after 30 minutes of ultrasound. This shows that the separation layer on the membrane surface has obviously fallen off. The experiment proves that by pre-grafting amine groups on the surface of the PVC membrane and then using the reverse mass transfer reaction process of the cross-linking agent, chemical bonding can be generated between the separation layer and the membrane surface, thereby improving the stability of the separation layer.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a composite nanofiltration membrane for desalination of organic matter, characterized in that: The method comprises the following steps: S1, introducing a hydrophilic macromolecular aqueous solution into the tube side of the membrane component; S2, filling the shell side of the membrane component with an aqueous solution of a crosslinking agent and allowing the solution to react for a certain period of time; S3, respectively placing the membrane component after the reaction into ethanol and deionized water for cleaning to obtain a composite nanofiltration membrane for desalination of organic matter; the membrane used in the membrane component is a hydrophobic membrane.

2. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: The hydrophilic macromolecule is one of polyethyleneimine, polyvinyl alcohol, chitosan, or hydroxyethyl cellulose or a mixture thereof.

3. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: The cross-linking agent is a reagent that is easily volatile; the cross-linking agent is one of glutaraldehyde, epichlorohydrin, ethylenediamine, or diethylenetriamine, or a mixture thereof.

4. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: The material of the hydrophobic membrane is one of PVC, PVDF, PTFE, and PVDF-CTFE, or a mixture thereof.

5. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: The mass concentration of the aqueous solution of the hydrophilic macromolecular reactant is 0.1-2.5wt%.

6. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: The mass concentration of the aqueous solution of the cross-linking agent is 0.5-3wt%.

7. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: The reaction time in step S2 is 30-150 min.

8. The method for preparing a composite nanofiltration membrane for desalination of organic matter according to claim 1, characterized in that: It also includes a pre-sequence reaction S0, which is to carry out chemical grafting on the inner surface of the membrane; Specifically, the steps include: a grafting solution is circulated through the tube side of the membrane assembly to react; the grafting solution is an aqueous solution of triethylenetetramine, tetraethylenepentamine or polyethyleneimine; and the mass concentration is 5-10wt%.

9. A composite nanofiltration membrane for desalination of organic matter obtained by the preparation method according to any one of claims 1 to 8.

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