A method for preparing a forward osmosis membrane based on a modified cellulose buffer layer and a product thereof

Abstract

The application provides a preparation method of a modified cellulose buffer layer-based forward osmosis membrane and a product thereof, and comprises the following steps: 1) dispersing cellulose fibers into an aqueous sodium hydroxide solution to prepare an alkaline dispersion solution of the cellulose fibers; 2) adding 2-chloroacetamide into the alkaline dispersion solution of the cellulose fibers, and continuously heating and stirring to prepare modified cellulose fibers; 3) dissolving the modified cellulose fibers in a solvent to prepare a cellulose solution, and then coating the cellulose solution on the surface of a non-woven fabric; and 4) growing an ultrathin polyamide layer on the surface of the cellulose-non-woven fabric in situ by using m-phenylenediamine and 1,3,5-benzene tris-methyl chloride, so as to prepare the modified cellulose buffer layer-based forward osmosis membrane. The modified cellulose buffer layer-based forward osmosis membrane has excellent water flux and salt retention performance, has good stability of separation performance, has a simple preparation process, can reduce the amount of polyamide, is low in cost, and is suitable for large-scale production.

Description

[Technical Field]

[0001] This invention relates to the fields of membrane separation and seawater desalination technology, specifically to a method for preparing a forward osmosis membrane based on a modified cellulose buffer layer and its product. [Background Technology]

[0002] Currently, the global shortage of freshwater resources seriously threatens and hinders human survival and development. Abundant seawater resources can be effectively converted into sufficient freshwater through membrane desalination strategies, and membrane separation technology, due to its ease of operation and high efficiency, is widely used in seawater desalination. Membrane-induced water separation technologies are mainly divided into reverse osmosis (RO), powered by external pressure difference, and forward osmosis (FO), powered by internal osmotic pressure difference. Compared with reverse osmosis, forward osmosis has superior energy efficiency and fouling resistance.

[0003] The performance of the membrane material itself determines the efficiency of the FO process. According to literature, current FO membranes typically consist of a porous support layer at the bottom and a dense active layer on the surface (i.e., a thin-film composite, TFC). The support layer provides strength and water channels, while the active layer traps salt. Current FO membranes are usually prepared by in-situ growth of aromatic polymers (as the active layer) using petroleum-based polymers as the support layer material. Although FO technology has been commercialized, FO composite membranes based on petroleum-based polymers as the support layer still suffer from drawbacks such as poor interfacial compatibility between the support and active layers, resulting in low water flux and weak antifouling ability. Current research introduces nanomaterials (such as sodium titanate nanotubes, carbon nanotubes, graphene oxide, and metal-organic frameworks) into these FO membranes to enhance their hydrophilicity and desalination efficiency; however, this undoubtedly increases the manufacturing cost of the FO membrane and complicates the manufacturing process.

[0004] Cellulose, chitosan, and other biomass materials possess excellent hydrophilicity, antibacterial properties, and film-forming properties, and have been applied in the field of membrane separation. Chinese patent CN105727768B discloses a method for preparing a self-supporting forward osmosis membrane based on chitosan. This method involves preparing a casting solution using chitosan and some hydrophilic nanomaterials, then pouring the casting solution onto a sieve to obtain a membrane sheet, which is then cross-linked using a cross-linking agent to obtain a chitosan self-supporting forward osmosis membrane. Chinese patent CN114984779A discloses a method for preparing a cellulose forward osmosis membrane, utilizing cellulase to etch cellulose on one side, constructing an asymmetric structure of the cellulose membrane, thereby improving its forward osmosis performance. However, its binding and stability properties are not ideal. [Summary of the Invention]

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a forward osmosis membrane based on a modified cellulose buffer layer and the product thereof. The forward osmosis membrane based on the modified cellulose buffer layer exhibits excellent water flux and salt rejection performance, and its separation performance is stable. The preparation process is simple, can reduce the amount of polyamide used, has low cost, and is suitable for large-scale production.

[0006] This invention is implemented as follows:

[0007] A method for preparing a forward osmosis membrane based on a modified cellulose buffer layer includes the following steps:

[0008] 1) Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers;

[0009] 2) Add 2-chloroacetamide to an alkaline dispersion of cellulose fibers, and continuously heat and stir to prepare modified cellulose fibers;

[0010] 3) Dissolve the modified cellulose fibers in a solvent to prepare a cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0011] 4) An ultrathin polyamide layer can be grown in situ on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-phenyltrimethylacyl chloride to prepare a forward osmosis membrane based on a modified cellulose buffer layer.

[0012] Further, in step 1), the cellulose fiber mass concentration is 0.5% to 3%.

[0013] Further, in step 1), the mass concentration of the alkali is 0.01–0.1%.

[0014] Further, in step 2), the amount of 2-chloroacetamide relative to cellulose fiber is 5% to 25%.

[0015] Furthermore, in step 2), the reaction temperature is 30℃~80℃, and the reaction time is 0.5h~5h.

[0016] Further, in step 3), the mass concentration of the cellulose solution is 0.1% to 1%.

[0017] Furthermore, in step 4), the thickness of the ultrathin polyamide layer is 50–300 nm.

[0018] Furthermore, a product prepared according to the aforementioned method for preparing a forward osmosis membrane based on a modified cellulose buffer layer.

[0019] The present invention has the following advantages:

[0020] This invention constructs a modified cellulose buffer layer between nonwoven fabric and ultrathin polyamide using a phase inversion method. The modified cellulose participates in the polymerization process of the polyamide, forming covalent bonds between the two. Cellulose can also permeate into the porous structure of the nonwoven fabric, initiating a seamless connection between the two. Ultimately, the cellulose acts as a buffer layer, achieving good compatibility between the nonwoven fabric and the ultrathin polyamide. The forward osmosis membrane based on the modified cellulose buffer layer has a dense ultrathin polyamide layer and a porous nonwoven fabric layer. Furthermore, the cellulose buffer layer possesses excellent hydrophilicity, thus enabling seawater desalination and inhibiting the ultrathin polyamide layer from detaching from the nonwoven fabric surface, ensuring the stability of the forward osmosis membrane operation. [Attached Image Description]

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 These are field emission scanning electron microscope images of the surfaces of a forward osmosis membrane without a cellulose buffer layer and a forward osmosis membrane with a 0.5% cellulose concentration.

[0023] Figure 2 This is a field emission scanning electron microscope image of the cellulose buffer layer.

Detailed Implementation Methods

[0024] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] This invention relates to a method for preparing a forward osmosis membrane based on a modified cellulose buffer layer, comprising the following steps:

[0026] 1) Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers;

[0027] 2) Add 2-chloroacetamide to an alkaline dispersion of cellulose fibers, and continuously heat and stir to prepare modified cellulose fibers;

[0028] 3) Dissolve the modified cellulose fibers in a solvent to prepare a cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0029] 4) An ultrathin polyamide layer can be grown in situ on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-phenyltrimethylacyl chloride to prepare a forward osmosis membrane based on a modified cellulose buffer layer.

[0030] Preferably, in step 1), the cellulose fiber mass concentration is 0.5% to 3%.

[0031] Preferably, in step 1), the mass concentration of the alkali is 0.01–0.1%.

[0032] Preferably, in step 2), the amount of 2-chloroacetamide relative to cellulose fiber is 5% to 25%.

[0033] Preferably, the reaction temperature in step 2) is 30℃~80℃, and the reaction time is 0.5h~5h.

[0034] Preferably, the mass concentration of the cellulose solution in step 3) is 0.1% to 1%.

[0035] Preferably, the thickness of the ultrathin polyamide layer in step 4) is 50–300 nm.

[0036] The present invention also relates to a product prepared by the above-mentioned method for preparing a forward osmosis membrane based on a modified cellulose buffer layer.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] 1. Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers, wherein the concentration of cellulose fibers is 3% and the concentration of alkali is 0.1%;

[0040] 2. Add 25% of 2-chloroacetamide to an alkaline dispersion of cellulose fibers, heat at 50°C and stir for 5 hours to prepare modified cellulose fibers;

[0041] 3. Dissolve the modified cellulose fibers in a solvent to prepare a 0.5% cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0042] 4. A 150 nm thick polyamide layer can be grown in situ on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-benzenetrimethylacyl chloride to prepare a forward osmosis membrane based on a modified cellulose buffer layer.

[0043] The cellulose forward osmosis membrane obtained through the above steps exhibits a water flux Jw of 36.38 LMH, a reverse salt flux Js of 6.06 gMH, and a salt-to-water ratio Js / Jw of 0.17 g·L⁻¹ in FO mode. -1 After running for 120 minutes, the performance remained essentially unchanged.

[0044] Example 2

[0045] 1. Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers, wherein the concentration of cellulose fibers is 0.5% and the concentration of alkali is 0.1%;

[0046] 2. Add 5% 2-chloroacetamide to an alkaline dispersion of cellulose fibers, heat to 80°C and stir for 4 hours to prepare modified cellulose fibers;

[0047] 3. Dissolve the modified cellulose fibers in a solvent to prepare a 1% concentration cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0048] 4. A forward osmosis membrane based on a modified cellulose buffer layer can be prepared by in-situ growing a 300 nm thick polyamide layer on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-benzenetrimethylacyl chloride.

[0049] The cellulose forward osmosis membrane obtained through the above steps exhibits a water flux Jw of 18.92 LMH, a reverse salt flux Js of 5.22 gMH, and a salt-to-water ratio Js / Jw of 0.27 g·L⁻¹ in FO mode. -1 After running for 120 minutes, the performance remained essentially unchanged.

[0050] Example 3

[0051] 1. Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers, wherein the concentration of cellulose fibers is 1.5% and the concentration of alkali is 0.01%.

[0052] 2. Add 20% of 2-chloroacetamide to an alkaline dispersion of cellulose fibers, heat at 40°C and stir for 2 hours to prepare modified cellulose fibers;

[0053] 3. Dissolve the modified cellulose fibers in a solvent to prepare a 0.02% cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0054] 4. A forward osmosis membrane based on a modified cellulose buffer layer can be prepared by in-situ growing a 200 nm thick polyamide layer on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-benzenetrimethylacyl chloride.

[0055] The cellulose forward osmosis membrane obtained through the above steps has a water flux Jw of 35.22 LMH, a reverse salt flux Js of 7.67 gMH, and a salt-to-water ratio Js / Jw of 0.22 g·L⁻¹ in PRO mode. -1 After running for 120 minutes, the performance remained essentially unchanged.

[0056] Example 4

[0057] 1. Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers, wherein the concentration of cellulose fibers is 1% and the concentration of alkali is 0.8%.

[0058] 2. Add 10% of 2-chloroacetamide to an alkaline dispersion of cellulose fibers, heat at 30°C and stir for 5 hours to prepare modified cellulose fibers;

[0059] 3. Dissolve the modified cellulose fibers in a solvent to prepare a 0.1% cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0060] 4. A forward osmosis membrane based on a modified cellulose buffer layer can be prepared by in-situ growing a 50 nm thick polyamide layer on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-benzenetrimethylacyl chloride.

[0061] The cellulose forward osmosis membrane obtained through the above steps exhibits a water flux Jw of 34.53 LMH, a reverse salt flux Js of 8.58 gMH, and a salt-to-water ratio Js / Jw of 0.25 g·L⁻¹ in FO mode. -1 After running for 120 minutes, the performance remained essentially unchanged.

[0062] Example 5

[0063] 1. Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers, wherein the concentration of cellulose fibers is 2.5% and the concentration of alkali is 0.7%.

[0064] 2. Add 15% of 2-chloroacetamide to an alkaline dispersion of cellulose fibers, heat to 80°C and stir for 0.5 h to prepare modified cellulose fibers;

[0065] 3. Dissolve the modified cellulose fibers in a solvent to prepare a 0.4% concentration cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0066] 4. A forward osmosis membrane based on a modified cellulose buffer layer can be prepared by in-situ growing a 250 nm thick polyamide layer on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-benzenetrimethylacyl chloride.

[0067] The cellulose forward osmosis membrane obtained through the above steps exhibits a water flux Jw of 17.08 LMH, a reverse salt flux Js of 3.88 gMH, and a salt-to-water ratio Js / Jw of 0.22 g·L⁻¹ in FO mode. -1 After running for 120 minutes, the performance remained essentially unchanged.

[0068] Example 6

[0069] 1. Disperse cellulose fibers in an aqueous solution of sodium hydroxide to prepare an alkaline dispersion of cellulose fibers, wherein the concentration of cellulose fibers is 2.5% and the concentration of alkali is 0.1%;

[0070] 2. Add 20% of 2-chloroacetamide to an alkaline dispersion of cellulose fibers, heat at 30°C and stir for 5 hours to prepare modified cellulose fibers;

[0071] 3. Dissolve the modified cellulose fibers in a solvent to prepare a 0.1% cellulose solution, and then coat it onto the surface of the nonwoven fabric;

[0072] 4. A forward osmosis membrane based on a modified cellulose buffer layer can be prepared by in-situ growing a 50 nm thick polyamide layer on the surface of cellulose-nonwoven fabric using m-phenylenediamine and 1,3,5-benzenetrimethylacyl chloride.

[0073] The cellulose forward osmosis membrane obtained through the above steps exhibits a water flux Jw of 29.71 LMH, a reverse salt flux Js of 7.61 gMH, and a salt-to-water ratio Js / Jw of 0.25 g·L⁻¹ in FO mode. -1 After running for 120 minutes, the performance remained essentially unchanged.

[0074] Compare with Example 1

[0075] A 50 nm thick polyamide layer was directly polymerized in situ on the surface of a nonwoven fabric. In forward osmosis (FO) mode, the water flux Jw was 10.77 LMH, the reverse salt flux Js was 15.46 gMH, and the salt-to-water ratio Js / Jw was 1.43 g·L⁻¹. -1 Furthermore, after running for 30 minutes, the salt ion retention capacity basically disappeared.

[0076] Compare with Example 2

[0077] A 300 nm thick polyamide layer was directly polymerized in situ on the surface of a nonwoven fabric. In forward osmosis (FO) mode, the water flux Jw was 7.92 LMH, the reverse salt flux Js was 8.92 gMH, and the salt-to-water ratio Js / Jw was 1.13 g·L⁻¹. -1 After running for 30 minutes, the salt ion retention capacity basically disappeared.

[0078] The results show that the forward osmosis membrane based on the modified cellulose buffer layer prepared in this invention has a high water flux and a low reverse salt flux, and its salt-to-water ratio is much lower than that of the forward osmosis membrane without a cellulose buffer layer: the salt-to-water ratio Js / Jw of the cellulose forward osmosis membrane is less than 0.3 g·L⁻¹. -1 The saline ratios Js / Jw of forward osmosis membranes without a cellulose buffer layer were both greater than 1.0 g·L⁻¹. -1 .

[0079] Furthermore, the brine separation performance of the forward osmosis membrane based on the modified cellulose buffer layer prepared in this invention is stable, and its performance remains unchanged after 120 minutes of testing; while the brine separation performance of the forward osmosis membrane without the cellulose buffer layer is very unstable, and its brine separation ability basically disappears after 30 minutes of testing.

[0080] Figure 1 Field emission scanning electron microscope images of the surface of a forward osmosis membrane (a) without a modified cellulose buffer layer and a forward osmosis membrane (b) with a modified cellulose concentration of 0.5% wt. It can be seen that without a cellulose buffer layer, the in-situ growth of the ultrathin polyamide layer on the nonwoven fabric surface is poor, and it cannot form a complete and dense membrane structure. Therefore, it is difficult to achieve effective retention of salt ions, and its brine separation performance is poor.

[0081] Figure 2 These are field emission scanning electron microscope images of cellulose-nonwoven fabric-based membranes; in the image, (a) is the surface of the nonwoven fabric, (b) is the nonwoven fabric-based membrane with a modified cellulose concentration of 0.1% wt, (c) is the nonwoven fabric-based membrane with a modified cellulose concentration of 0.5% wt, and (d) is the nonwoven fabric-based membrane with a modified cellulose concentration of 0.5% wt. In this invention, modified cellulose with different concentrations of amino functional groups is coated onto the surface of a nonwoven fabric. The modified cellulose can penetrate into the porous structure of the nonwoven fabric, providing a buffer platform for the growth of ultrathin polyamides; simultaneously, the amino groups of cellulose can participate in the polymerization and growth process of polyamides, ultimately achieving good growth of the ultrathin polyamide layer on the nonwoven fabric substrate, significantly improving the interfacial compatibility between the ultrathin polyamide and the nonwoven fabric. The nonwoven fabric of the forward osmosis membrane with the cellulose buffer layer can effectively transport water molecules, and its dense ultrathin polyamide layer can repel salt ions in the system, resulting in good brine separation performance of the forward osmosis membrane. By observing the morphology of cellulose-nonwoven base membranes by changing the cellulose concentration, it was found that the buffer layer became denser as the cellulose concentration increased.

[0082] In summary, the advantages of this invention are:

[0083] (1) This invention utilizes 2-chloroacetamide to modify cellulose, then coats the modified cellulose onto the surface of a nonwoven fabric, and constructs a cellulose buffer layer on the nonwoven fabric surface using a phase inversion method. Through the participation of the amino groups of the modified cellulose in the polymerization and growth process of the polyamide, an ultrathin polyamide layer is grown in situ on the surface of the cellulose layer, enabling the development of a low-cost chitosan-based forward osmosis membrane with high water flux. The introduction of cellulose improves the hydrophilicity of the forward osmosis membrane and provides a platform for the growth of the ultrathin polyamide layer, achieving good compatibility between the nonwoven fabric and the ultrathin polyamide. The porous nonwoven fabric provides numerous channels, which is beneficial for water transport; the dense ultrathin polyamide active layer is beneficial for retaining salt ions in the system. The cellulose buffer layer ensures the firm adhesion of the ultrathin polyamide to the nonwoven fabric surface, achieving long-term stability of the forward osmosis membrane's separation performance.

[0084] (2) The preparation method of the present invention has the advantages of simple preparation process, reduced polyamide dosage, low cost, and can be used for large-scale production.

[0085] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a modified cellulose buffer layer-based forward osmosis membrane, characterized by: The method comprises the following steps: 1) dispersing cellulose fibers into an aqueous sodium hydroxide solution to prepare an alkaline dispersion of the cellulose fibers; 2) adding 2-chloroacetamide to the alkaline dispersion of the cellulose fibers and continuously stirring under heating to prepare modified cellulose fibers; the amount of 2-chloroacetamide is 5% to 25% relative to the cellulose fibers; 3) dissolving the modified cellulose fibers in a solvent to prepare a cellulose solution, and then coating the solution on a non-woven fabric surface; 4) growing an ultra-thin polyamide layer on the cellulose-non-woven fabric surface in situ using m-phenylenediamine and 1,3,5-benzene tricarboxylic acid chloride, and the thickness of the ultra-thin polyamide layer is 50 to 300 nm, thereby preparing a modified cellulose buffer layer-based forward osmosis membrane.

2. The method for preparing a modified cellulose buffer layer-based forward osmosis membrane according to claim 1, characterized in that: In step 1), the mass concentration of the cellulose fibers is 0.5% to 3%.

3. The method for preparing a modified cellulose based positive osmosis membrane according to claim 1, characterized in that: In step 1), the mass concentration of the alkali is 0.01% to 0.1%.

4. The method for preparing a modified cellulose based positive osmosis membrane according to claim 1, characterized in that: In step 2), the reaction temperature is 30°C to 80°C, and the reaction time is 0.5 h to 5 h.

5. The method for preparing a modified cellulose based positive osmosis membrane according to claim 1, characterized in that: In step 3), the mass concentration of the cellulose solution is 0.1% to 1%.

6. A product prepared by the method of any one of claims 1 to 5.

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