CN114984779A - Preparation method of high-flux cellulose forward osmosis membrane - Google Patents

Abstract

The invention discloses a preparation method of a high-flux cellulose forward osmosis membrane, and relates to the technical field of membrane separation and seawater desalination. The preparation method of the present invention includes the following steps: 1) dissolving cellulose in a solvent, and preparing a cellulose film by a phase inversion method; 2) using cellulase to perform single-sided etching treatment on the cellulose film to obtain fibers with an asymmetric structure Prime forward osmosis membrane. The cellulose forward osmosis membrane invented in this study has an asymmetric pore structure, exhibits excellent water flux and salt rejection, and has a simple preparation process that is environmentally friendly and can be mass-produced.

Description

A kind of preparation method of high flux cellulose forward osmosis membrane

technical field

The invention discloses a preparation method of a high-flux cellulose forward osmosis membrane, which relates to the technical field of membrane separation and seawater desalination.

Background technique

Currently, a severe shortage of clean water is challenging our existence and further development. Membrane-inspired desalination strategies have been widely recognized as one of the effective methods to obtain clean water due to their simple operation and high separation efficiency. Membrane-induced water separation techniques can be carried out by external pressure differences or internal chemical potential differences, which form the reverse osmosis (RO) and forward osmosis (FO) methods, respectively. Compared with the reverse osmosis process, forward osmosis has the advantages of low energy demand and strong anti-fouling ability.

Membrane material is a key factor affecting the performance of the FO method. According to literature reports, current FO membranes usually have a bilayer structure (i.e., thin film composites, TFCs), consisting of a porous support layer and a dense active layer, where the support layer provides strength and the active layer realizes the separation behavior. Such FO membranes are typically in situ grown aromatic polymers (as the active layer) on a polysulfone support layer material. Although the technology has matured, thin-film composite membranes based on synthetic polymers still suffer from low hydrophilicity, weak antifouling ability, and difficult biodegradation. Therefore, some nanomaterials, such as sodium titanate nanotubes, carbon nanotubes, graphene oxide, and metal organic frameworks, etc., were introduced into the above-mentioned FO membranes to enhance their hydrophilicity and desalination efficiency, however, this behavior increased the The manufacturing cost of FO membranes and complicates the manufacturing process.

Natural cellulose is used to construct separation membranes due to its excellent hydrophilicity, biocompatibility, and relatively low cost. Chinese patent CN106237875A discloses a preparation method and products of a cellulose-based cation selective filtration membrane. The method utilizes a homogeneous dissolving reagent or a heterogeneous reagent to dissolve or disperse cellulose in a solvent to prepare a porous cellulose film, and then use an acid halide reagent to react with the porous cellulose film to obtain surface-modified cellulose-based macromolecules The cellulose-based macromolecular initiator is then subjected to atom transfer radical polymerization with cationic monomers under the action of catalysts and ligands to obtain a cellulose-based cationic selective filtration membrane. Chinese patent CN101007240A discloses a preparation method of cellulose hollow fiber ultrafiltration membrane. The cellulose hollow membrane is obtained by the immersion phase inversion method and the dry-wet method. application prospects. Chinese patent CN103877867A discloses a method for preparing a cellulose ultrafiltration membrane, which is to obtain a cellulose ultrafiltration composite membrane composed of a support layer and a nanoporous cellulose skin layer under low temperature conditions. The above patents all use cellulose materials to prepare cellulose separation membranes, but the preparation process is relatively complex, the operability is poor, and the water flux of the membrane is low. Therefore, it is necessary to develop a simple method to prepare high-pass amount of cellulose separation membrane. In this study, we developed a low-cost yet ultra-high water flux cellulose forward osmosis membrane from green cellulose materials through a simple cellulase etching strategy. We coat the cellulase on one side of the cellulose membrane to react with cellulose. This behavior triggers the unique asymmetric pore structure of cellulose membranes, including loose and dense layers. The porous layer supports high-flux water transport, while the dense structure is conducive to trapping salt ions in the system.

SUMMARY OF THE INVENTION

In view of the above existing problems, the present invention provides a preparation method of a high-flux cellulose forward osmosis membrane.

For achieving the above object, the technical scheme of the present invention is:

A preparation method of a high-flux cellulose forward osmosis membrane, comprising the following steps:

1) Dissolve the dissolving pulp in an aqueous solution of N-methylmorpholine-N-oxide (NMMO), and obtain a cellulose film by a phase inversion method.

2) Coating the cellulase solution on one side of the cellulose membrane, and then placing it in a constant temperature incubator for processing, the cellulose forward osmosis membrane with asymmetric pore structure can be obtained.

Further, the cellulose content of the dissolving pulp in step 1) is higher than 90%.

Further, the polymerization degree of dissolving pulp in step 1) is 400～600.

Further, the phase inversion method in step 1) forms a film by means of blade coating.

Further, in step 2), the cellulase can be coated on the upper surface or the lower surface of the cellulose film.

Further, the consumption of cellulase in step 2) is 0.1～2 ml/m ² .

Further, the coating method of the cellulase in step 2) includes spray coating, blade coating, spin coating and the like.

Further, the processing conditions of the constant temperature incubator in step 2) are that the processing time is 1 min to 30 min.

The cellulose forward osmosis membrane prepared by the above preparation method has an asymmetric pore structure, has excellent seawater desalination performance, has a simple preparation process, is environmentally friendly, and can be produced on a large scale.

The benefits of the present invention are:

(1) The present invention proposes a method for preparing a high-flux cellulose forward osmosis membrane, which has the characteristics of simple operation and low cost.

(2) The cellulose forward osmosis membrane prepared by the present invention is constructed through the strategy of cellulase single-sided etching of the cellulose membrane, has green environmental protection characteristics, and is a low-carbon strategy.

(3) The cellulose forward osmosis membrane constructed by the present invention has an asymmetric structure, including a dense layer and a porous transport layer, which realizes the rapid transmission of water and the effective interception of salt ions, and provides options for efficient seawater desalination.

Description of drawings

Fig. 1 is the field emission scanning electron microscope image of the original cellulose film in implementation 1;

Fig. 2 is the field emission scanning electron microscope picture of cellulose forward osmosis membrane in implementation 1;

Fig. 3 is the filtration performance comparison diagram of original cellulose membrane and cellulose forward osmosis membrane to 1mol/L NaCl solution in implementation 1;

Fig. 4 is the filtration performance figure of cellulose forward osmosis membrane to different salt solutions in implementation 1;

Fig. 5 is the field emission scanning electron microscope image of cellulose forward osmosis membrane under different treatment time;

Fig. 6 is the photograph figure of cellulose forward osmosis membrane under different treatment time;

Figure 7 is the effect of cellulase treatment time on the performance of cellulose forward osmosis membrane.

Detailed ways

The invention provides a preparation method of a high-flux cellulose forward osmosis membrane:

The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

Example 1

a. The dissolving pulp with a degree of polymerization of 400 and a cellulose content of 90 % was dissolved in NMMO/water solution, and then the original cellulose film was prepared by blade coating using phase separation technology.

b. The cellulase solution was coated on the surface of the cellulose film by spraying technology, and the dosage of cellulase was 0.83ml/m ² .

c. Carry out cellulase treatment in an incubator, treatment time: 30 min, treatment temperature: 40 °C, treatment humidity: 60 %.

Compared with the original cellulose membrane (Figure 1), the cellulose forward osmosis membrane obtained by the above steps, the cellulose forward osmosis membrane treated with cellulase presents a stacked structure (Figure 2), which is conducive to the transport of water molecules and retention of salt ions.

Example 2

a. The dissolving pulp with a degree of polymerization of 500 and a cellulose content of 96 % was dissolved in NMMO/water solution, and then the original cellulose film was prepared by blade coating using phase separation technology.

b. The cellulase solution was coated on the surface of the cellulose film by the blade coating technique, and the dosage of cellulase was 1.66ml/m ² .

c. Carry out cellulase treatment in an incubator, treatment time: 10 min, treatment temperature: 30 °C, treatment humidity: 40 %.

Compared with the original cellulose membrane, the cellulose forward osmosis membrane obtained by the above steps has a porous structure on the surface of the cellulose forward osmosis membrane treated with cellulase, which is helpful for the transport of water molecules and the interception of salt ions.

Example 3

a. The dissolving pulp with a degree of polymerization of 600 and a cellulose content of 94 % was dissolved in NMMO/water solution, and then the original cellulose film was prepared by blade coating using phase separation technology.

b. Use spin coating technology to coat the cellulase solution on the surface of the cellulose membrane, and the dosage of cellulase is 1.66ml/m ² .

c. Carry out cellulase treatment in an incubator, treatment time: 10 min, treatment temperature: 60 ℃, treatment humidity: 60 %.

Compared with the original cellulose membrane, the cellulose forward osmosis membrane obtained by the above steps has a porous structure on the surface of the cellulose forward osmosis membrane treated with cellulase, which is helpful for the transport of water molecules and the interception of salt ions.

Example 4

a. The dissolving pulp with a degree of polymerization of 400 and a cellulose content of 90 % was dissolved in NMMO/water solution, and then the original cellulose film was prepared by blade coating using phase separation technology.

b. Use spin coating technology to coat the cellulase solution on the surface of the cellulose membrane, and the dosage of cellulase is 1.66ml/m ² .

c. Carry out cellulase treatment in an incubator, treatment time: 30 min, treatment temperature: 60 ℃, treatment humidity: 60 %.

Compared with the original cellulose membrane, the cellulose forward osmosis membrane obtained by the above steps is over-treated with cellulase, so that the surface of the cellulose forward osmosis membrane presents more macropores.

Example 5

a. The dissolving pulp with a degree of polymerization of 500 and a cellulose content of 96 % was dissolved in NMMO/water solution, and then the original cellulose film was prepared by blade coating using phase separation technology.

b. The cellulase solution was coated on the surface of the cellulose film by spraying technology, and the dosage of cellulase was 0.83ml/m ² .

c. Carry out cellulase treatment in an incubator, treatment time: 30 min, treatment temperature: 60 °C, treatment humidity: 90 %.

The cellulose forward osmosis membrane obtained by the above steps, compared with the original cellulose membrane, the surface of the cellulose forward osmosis membrane treated with cellulase presents pore structures of different sizes.

Example 6

a. The dissolving pulp with a degree of polymerization of 600 and a cellulose content of 94 % was dissolved in NMMO/water solution, and then the original cellulose film was prepared by blade coating using phase separation technology.

b. The cellulase solution was coated on the surface of the cellulose film by spraying technology, and the dosage of cellulase was 0.83ml/m ² .

c. Carry out cellulase treatment in an incubator, treatment time: 10 min, treatment temperature: 30 °C, treatment humidity: 40 %.

Compared with the original cellulose membrane, the cellulose forward osmosis membrane obtained by the above steps has a smaller pore structure on the surface of the cellulose forward osmosis membrane treated with cellulase.

FIG. 1 and FIG. 2 are field emission scanning electron microscope images of the original cellulose membrane and the cellulose forward osmosis membrane in Example 1, respectively. The phase inversion method endows the pristine cellulose membrane with a special structure with dense upper and lower surfaces and a porous center (Figure 1). The cellulase treatment in Example 1 disrupted the dense surface of the cellulose membrane and significantly increased its pore size and porosity (Figure 2).

In the present invention, the cellulase is only coated on the upper surface of the original cellulose film, which destroys the dense structure of the upper surface, but does not affect the dense structure of the lower surface. Such behavior ultimately induces the asymmetric pore structure of the cellulosic material. The porous layer of the cellulose forward osmosis membrane can effectively transport water molecules, and its dense layer can repel salt ions in the system. The water flux of the cellulose forward osmosis membrane reaches 135.75 LMH, which is 17 times that of the original cellulose membrane (Figure 3).

The cellulose forward osmosis membrane also exhibited higher water flux (greater than 120LMH) and lower brine ratio (below 0.53 g⋅L ⁻¹ ) in different concentrations of NaCl solution.

The desalination performance of cellulose forward osmosis membrane is good, and it is also suitable for the separation of other salt solutions. For example, the 1 M Na ₂ SO ₄ and MgCl ₂ systems also exhibited high water fluxes (167.75, 174.25 LMH), while maintaining low brine ratios (0.14 g⋅L ⁻¹ , 0.12 g⋅L ⁻¹ ) (Figure 4).

By observing the morphology of the cellulose forward osmosis membrane with different cellulase treatment time, it was found that with the prolongation of the cellulase treatment time, the pore size of the surface of the cellulose forward osmosis membrane gradually increased (Fig. 5). Cellulase treatment for too long will cause excessive damage to the cellulose forward osmosis membrane (Fig. 6), break the structure of the cellulose forward osmosis membrane, and reduce its working stability.

Proper extension of cellulase treatment time can enhance the permeation performance of cellulose forward osmosis membranes (Fig. 7).

Other reagents used in the present invention are all reagents that can be purchased or prepared in the prior art, and will not be described again.

The above-mentioned embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims (6)

1. A preparation method of a high-flux cellulose forward osmosis membrane is characterized by comprising the following steps: a cellulose forward osmosis membrane with an asymmetric pore structure is constructed by utilizing a cellulase etching method to realize high-performance fresh water collection, and the method comprises the following steps:

1) dissolving cellulose in the solution, and obtaining a cellulose membrane by a phase inversion method;

2) coating a cellulose membrane with a cellulase solution on one side, and then placing the cellulose membrane into a constant-temperature incubator for treatment to obtain the cellulose forward osmosis membrane with the asymmetric pore structure.

2. The method of claim 1, wherein: the phase inversion method of the cellulose membrane in the step 1) adopts a blade coating mode.

3. The method of claim 1, wherein: the cellulase in step 2) may be coated on the upper surface or the lower surface of the cellulose film.

4. The production method according to claim 1, characterized in that: the dosage of the cellulase in the step 2) is 0.1-2 ml/m ² 。

5. The method of claim 1, wherein: the cellulase in the step 2) is coated in a spraying, blade coating or spin coating mode.

6. The method of claim 1, wherein: the treatment condition of the constant-temperature incubator in the step 2) is 30-60 ℃, the treatment time is 1-30 min, and the treatment humidity is 40-90%.

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