Preparation method of solvent-induced loose nanofiltration membrane

Abstract

The invention discloses a preparation method of a solvent-induced loose nanofiltration membrane, and belongs to the technical field of nanofiltration membrane preparation. The method comprises the following steps: blending a styrene-maleic anhydride copolymer, a polymer membrane material, a pore-foaming agent and an organic solvent to obtain a homogeneous membrane casting solution; performing phase inversion on the homogeneous membrane casting solution to obtain a base membrane containing anhydride groups on the surface; the preparation method comprises the following steps: dissolving macromolecular polyethyleneimine in a mixed solvent of a good solvent and a poor solvent to obtain a crosslinking solution with controllable macromolecular chains and rich amino groups; and immersing the base membrane into a cross-linking solution for cross-linking of anhydride and amino to obtain the loose nanofiltration membrane. The preparation method provided by the invention has the beneficial effects that the controllability of a macromolecular crosslinking process can be remarkably improved, so that the loose nanofiltration membrane with excellent performance is obtained; the loose nanofiltration membrane prepared by the preparation method provided by the invention has the characteristics of stable structure, narrow pore size distribution and high permeability, and has a good development prospect in the water treatment process with the purposes of decoloration and heavy metal removal.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membrane preparation, and particularly relates to a method for preparing a solvent-induced loose nanofiltration membrane. Background Art

[0002] In recent years, nanofiltration technology, as a core process in the field of wastewater treatment, has been continuously developed and researched. In response to different treatment processes and requirements, corresponding nanofiltration membranes with specific application areas have been prepared, such as acid- and alkali-resistant nanofiltration membranes, solvent-resistant nanofiltration membranes, and anti-pollution nanofiltration membranes. The vast majority of nanofiltration membranes are dedicated to maintaining a high retention rate and good stability for small molecule salts or organic matter in different wastewater environments. Since the molecular weight cutoff of nanofiltration membranes is generally between 100 and 1000 Daltons, and the retention effect of ultrafiltration membranes around 1000 Daltons is very unsatisfactory, substances with a molecular weight of 1000 Daltons cannot be effectively screened. These substances are mainly large molecular pigments and protein compounds, which are common substances in the pharmaceutical and chemical fields. Given that ultrafiltration and nanofiltration technologies cannot effectively treat substances with a molecular weight of around 1000 Daltons, the concept of loose nanofiltration was born.

[0003] Compared to traditional nanofiltration membranes, which have a high rejection rate for small molecular weights, loose nanofiltration membranes are more focused on separating substances with specific molecular weights. During the preparation process, relevant parameters are controlled to synthesize the separation layer within a certain pore size range to achieve the purpose of limiting the molecular weight cut-off. Existing loose nanofiltration membrane preparation methods are mostly similar to traditional nanofiltration membranes, using interfacial polymerization, phase inversion, or phase deposition methods to prepare the separation layer. Although the resulting nanofiltration membranes can control the molecular weight cut-off within the corresponding range to a certain extent, the overall pore size distribution is not uniform and the structure is unstable, which affects the permeability. Summary of the Invention

[0004] The purpose of an embodiment of the present invention is to provide a method for preparing a solvent-induced loose nanofiltration membrane, which controls the chain distribution of PEI macromolecules by regulating the polarity of the PEI solution, thereby achieving structural regulation of the loose functional layer, so that the prepared loose nanofiltration membrane has the characteristics of stable structure, narrow pore size distribution, and high permeability, thereby solving at least one technical problem involved in the background technology.

[0005] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0006] The present invention provides a method for preparing a solvent-induced loose nanofiltration membrane, comprising the following steps:

[0007] Step S1, blending styrene-maleic anhydride copolymer, polymer membrane material, porogen and organic solvent in a mass ratio of 4:20:5:71 to obtain a homogeneous membrane casting solution;

[0008] Step S2, performing phase inversion on the homogeneous casting solution to obtain a base film having anhydride groups on its surface;

[0009] Step S3, dissolving the macromolecular polyethyleneimine in a mixed solvent of a good solvent and a non-good solvent to obtain a cross-linking solution with controllable macromolecular chains and rich in amino groups;

[0010] Step S4: immersing the base membrane in a cross-linking solution to cross-link the acid anhydride and amino groups to obtain a loose nanofiltration membrane.

[0011] Optionally, in step S1, the styrene-maleic anhydride copolymer is a polymer having an anhydride content of more than 10%.

[0012] Optionally, in step S1, the polymer membrane material is one of polyethersulfone, polysulfone, and polyvinylidene fluoride.

[0013] Optionally, in step S1, the porogen is polyethylene glycol and the organic solvent is N,N-dimethylacetamide.

[0014] Optionally, in step S3, the macromolecular polyethyleneimine is a polyethyleneimine polymer with a molecular weight of more than 10,000 Da.

[0015] Optionally, in step S3, the good solvent is water or ethanol, and the non-good solvent is glycerol or liquid paraffin.

[0016] Optionally, in step S3, the mass ratio of the good solvent to the non-good solvent is 2:1.

[0017] Optionally, in step S3, the mass fraction of the macromolecular polyethyleneimine in the cross-linking solution is greater than 2 g / L.

[0018] Optionally, in step S4, the base film is immersed in the cross-linking solution for more than 30 minutes, and the reaction temperature is 60-80°C.

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

[0020] 1. The preparation method provided by the present invention can significantly improve the controllability of the macromolecular cross-linking process, thereby obtaining a loose nanofiltration membrane with excellent performance;

[0021] 2. The loose nanofiltration membrane prepared by the preparation method provided by the present invention has the characteristics of stable structure, narrow pore size distribution and high permeability, and has good development prospects in the water treatment process for the purpose of decolorization and heavy metal removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive work, among which:

[0023] Figure 1 The present invention provides a flow chart of the method for preparing the solvent-induced loose nanofiltration membrane. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0025] The terms "first," "second," and the like in the specification and claims of the present invention are used to distinguish similar objects, and are not used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present invention can be implemented in an order other than that illustrated or described herein, and that the objects distinguished by "first," "second," and the like are generally of a class, and do not limit the number of objects. For example, the first object can be one or more. In addition, the term "and / or" in the specification and claims refers to at least one of the connected objects, and the character " / " generally indicates that the objects connected are in an "or" relationship.

[0026] See Figure 1 As shown, an embodiment of the present invention provides a method for preparing a solvent-induced loose nanofiltration membrane, comprising the following steps:

[0027] Step S1, blending styrene-maleic anhydride copolymer, polymer membrane material, porogen and organic solvent in a mass ratio of 4:20:5:71 to obtain a homogeneous membrane casting solution;

[0028] Step S2, performing phase inversion on the homogeneous casting solution to obtain a base film having anhydride groups on its surface;

[0029] Step S3, dissolving the macromolecular polyethyleneimine in a mixed solvent of a good solvent and a non-good solvent to obtain a cross-linking solution with controllable macromolecular chains and rich in amino groups;

[0030] Step S4: immersing the base membrane in a cross-linking solution to cross-link the acid anhydride and amino groups to obtain a loose nanofiltration membrane.

[0031] In step S1, the styrene-maleic anhydride copolymer is a polymer having an anhydride content of more than 10%.

[0032] The polymer membrane material is one of polyethersulfone, polysulfone and polyvinylidene fluoride.

[0033] The porogen is polyethylene glycol, and the organic solvent is N,N-dimethylacetamide.

[0034] In step S3, the macromolecular polyethyleneimine is a polyethyleneimine polymer with a molecular weight of more than 10,000 Da.

[0035] The good solvent is water or ethanol, and the non-good solvent is glycerol or liquid paraffin. The mass ratio of the good solvent to the non-good solvent is 2:1.

[0036] The mass fraction of the macromolecular polyethyleneimine in the cross-linking solution is above 2 g / L.

[0037] In step S4, the base film is immersed in the cross-linking solution for more than 30 minutes, and the reaction temperature is 60-80°C.

[0038] It should be further explained that after the macromolecular polyethyleneimine is dissolved in a mixed solvent of a good solvent and a non-good solvent, the good solvent causes the macromolecular chains of the macromolecular polyethyleneimine to stretch, and the non-good solvent causes the macromolecular chains of the macromolecular polyethyleneimine to shrink. The combination of the two allows the macromolecular chains to be orderly distributed in solvents of different polarities, so that the macromolecular chains are in a relatively stable state before cross-linking. Then, on the basis of this stable distribution, the polyethyleneimine is cross-linked with the styrene-maleic anhydride copolymer in the base membrane to form a controllable functional layer nanofiltration membrane.

[0039] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0040] Furthermore, it should be noted that the scope of the methods and systems of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in reverse order, depending on the functions involved. For example, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Furthermore, features described with reference to certain examples may be combined in other examples.

[0041] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for preparing a solvent-induced loose nanofiltration membrane, characterized in that: The steps include: Step S1, blending styrene-maleic anhydride copolymer, polymer membrane material, porogen and organic solvent in a mass ratio of 4:20:5:71 to obtain a homogeneous membrane casting solution; Step S2, performing phase inversion on the homogeneous casting solution to obtain a base film having anhydride groups on its surface; Step S3, dissolving the macromolecular polyethyleneimine in a mixed solvent of a good solvent and a non-good solvent to obtain a cross-linking solution with controllable macromolecular chains and rich in amino groups; Step S4: immersing the base membrane in a cross-linking solution to cross-link the acid anhydride and amino groups to obtain a loose nanofiltration membrane.

2. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 1, wherein: In step S1, the styrene-maleic anhydride copolymer is a polymer having an anhydride content of more than 10%.

3. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 2, wherein: In step S1, the polymer membrane material is one of polyethersulfone, polysulfone, and polyvinylidene fluoride.

4. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 3, wherein: In step S1, the porogen is polyethylene glycol, and the organic solvent is N,N-dimethylacetamide.

5. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 1, wherein: In step S3, the macromolecular polyethyleneimine is a polyethyleneimine polymer with a molecular weight of more than 10,000 Da.

6. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 5, wherein: In step S3, the good solvent is water or ethanol, and the non-good solvent is glycerol or liquid paraffin.

7. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 6, wherein: In step S3, the mass ratio of the good solvent to the non-good solvent is 2:

1.

8. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 7, wherein: In step S3, the mass fraction of the macromolecular polyethyleneimine in the cross-linking solution is greater than 2 g / L.

9. The method for preparing a solvent-induced loose nanofiltration membrane according to claim 1, wherein: In step S4, the base film is immersed in the cross-linking solution for more than 30 minutes, and the reaction temperature is 60-80°C.

Images