CN107261871A - A kind of preparation method of polyethyleneimine/sodium lignin sulfonate composite membrane - Google Patents

Abstract

The invention discloses a kind of preparation method of polyethyleneimine/sodium lignin sulfonate composite membrane.The preparation of the composite membrane is to use surface in electronegative polysulphone super-filter membrane as basement membrane, and thereon, self assembly polyethyleneimine and sodium lignin sulfonate form self assembly composite bed successively, form it into constitutionally stable composite bed by glutaraldehyde cross-linking afterwards.It is an advantage of the invention that using the electrostatic interaction between the electrolyte with different electric charges, zwitterion polyelectrolyte successively can be adsorbed on the surface of polysulphone super-filter membrane, so as to realize the LBL self-assembly of polyelectrolyte.When the double-deck number of polyelectrolyte is 7 layers, composite nanometer filtering film shows preferable separating property.

Description

A kind of preparation method of polyethylenimine/sodium lignosulfonate composite membrane

technical field

The invention relates to a layer-by-layer self-assembled polyethyleneimine/sodium lignosulfonate composite nanofiltration membrane and a preparation method thereof, belonging to the technical field of separation membranes.

Background technique

Membrane separation technology is an emerging mixture separation technology, which uses the selective permeability of the membrane to each component in the mixture to separate, purify, concentrate and enrich the target product with external energy or chemical potential difference as the driving force. Compared with traditional separation methods, membrane separation technology has the advantages of mild separation conditions, low energy consumption, continuous separation, easy industrial scale-up, simple operation, high operational stability, and no pollution. There are many types of membrane separation technologies, which can be divided into microfiltration, ultrafiltration, nanofiltration and reverse osmosis according to the diameter of the membrane intercepted particles from large to small. The intercepted particle diameter of nanofiltration membrane is between ultrafiltration and reverse osmosis, so nanofiltration can intercept macromolecules or high-valent ions under relatively low operating pressure, while ensuring high flux. The special selective rejection performance of nanofiltration membrane makes it have special advantages in certain separation processes, such as drinking water softening, sewage treatment, food engineering, biological engineering, etc.

Since the nanofiltration membrane was developed in the 1980s, many researchers have done a lot of research, the most important research is to develop and prepare new membrane materials. At present, nanofiltration membranes can be divided into organic nanofiltration membranes, inorganic nanofiltration membranes and composite nanofiltration membranes. Organic polymer membranes are a type of nanofiltration membrane with a relatively high degree of commercialization at present. Their materials are basically similar to reverse osmosis membrane materials, mainly including sulfonated polysulfone nanofiltration membranes, polyamide nanofiltration membranes, cellulose filter membrane, etc. At present, inorganic nanofiltration membranes mainly include ceramic membranes, metal oxide membranes, etc., which have extremely good chemical stability, mechanical strength and biological tolerance, but organic nanofiltration membranes are brittle, less elastic, and expensive, so they are widely used. Applications. In recent years, research on composite nanofiltration membranes developed on the basis of organic nanofiltration membranes and inorganic nanofiltration membranes has become a hot topic in nanofiltration membrane preparation research.

Composite nanofiltration membranes with special functions or high flux and high rejection can be prepared by polyelectrolyte layer-by-layer self-assembly method. The separation layer is relatively uniform and compact, and the arrangement and assembly are relatively neat. The biggest advantage is that the single-layer film thickness can be controlled at the nanometer level, and the composition and structure of the film can be controlled at the molecular level by changing the self-assembly conditions, thereby changing its separation performance. . Polyelectrolyte refers to a polymer with a charged group on a monomer. When this type of polymer is dissolved in a polar solvent, it will ionize anion and cation corresponding to the charged group, thereby being charged. Therefore, by utilizing the electrostatic interaction between electrolytes with different charges, the anion and cation polyelectrolytes can be adsorbed layer by layer on the surface of the substrate material, thereby realizing the layer-by-layer self-assembly of polyelectrolytes.

Lignin is a non-crystalline, three-dimensional reticular phenolic complex natural polymer. Lignin, cellulose, and hemicellulose are the main components of higher plant cell walls. Lignin is the most abundant natural polymer compound after cellulose. Sodium lignosulfonate (SL) can be mainly extracted from the waste liquor of sulfite pulping and papermaking, that is, the red liquor produced by acid pulping and the black liquor produced by alkaline pulping, and it can also be extracted by alkali lignosulfonate made. The basic components of sodium lignosulfonate are benzyl propane derivatives, and the hydrogen, methoxyl, and hydroxyl groups on the benzene ring or side chain of lignin are replaced by sulfonic acid groups to form lignosulfonate , common lignin sulfonate is yellow-brown powder. The relative molecular weight distribution of sodium lignosulfonate is very uneven, and it varies greatly with the source of raw materials and pulping process. The molecular weight of common sodium lignosulfonate is above 3500-15000 Da. The basic components of sodium lignosulfonate are benzyl propane derivatives, which are non-polar aromatic groups, and contain polar sulfonic acid groups, hydroxyl groups, carboxyl groups and other hydrophilic groups, so it is hydrophilic Strong water, but weak lipophilicity, soluble in water, but insoluble in acetone, ethanol and other organic solvents. Therefore, sodium lignosulfonate has good surface activity and can be used as an anionic surfactant.

If polyethyleneimine (PEI) is used as the polycation electrolyte and sodium ligninsulfonate (Sodium Ligninsulfonate, SL) is used as the polyanion electrolyte to form a self-assembled composite layer on the surface of the polysulfone ultrafiltration membrane, then through glutaraldehyde exchange Combined to form a structurally stable composite layer, thereby making a self-assembled polyelectrolyte layer-by-layer nanofiltration membrane with good separation performance.

Contents of the invention

The object of the present invention is to provide a kind of preparation method of layer by layer self-assembly polyethyleneimine/sodium lignosulfonate composite nanofiltration membrane, by utilizing polyethyleneimine and sodium lignosulfonate on the surface of polysulfone ultrafiltration membrane The electrostatic force adsorption between the positive and negative electrolytes forms a self-assembled composite layer, which is then cross-linked by glutaraldehyde to form a structurally stable composite layer to improve the selectivity of the nanofiltration membrane.

In order to achieve the above object, the invention provides a kind of preparation method of self-assembled layer by layer polyethyleneimine/sodium lignosulfonate composite nanofiltration membrane, which comprises the following steps:

1) Pretreatment of the base membrane, using polysulfone (PSF) ultrafiltration membrane as the base membrane, soaking it in deionized water for a certain period of time, then immersing it in NaOH aqueous solution, and keeping it in a constant temperature water bath for a period of time; then take out the membrane and wash it with deionized water to neutral;

2) Preparation of composite nanofiltration membrane, immerse polysulfone-based membrane in polyethyleneimine solution for a certain period of time, pour out PEI solution, rinse several times with deionized water; then immerse it in sodium lignosulfonate solution Rinse several times with deionized water; so far a double-layer self-assembly is completed, and the above steps are repeated several times to obtain nanofiltration membranes with different layers;

3) Cross-linking of composite nanofiltration membranes, immerse composite nanofiltration membranes of different layers in glutaraldehyde aqueous solution and let them stand for a period of time, take them out, wash the composite membranes with deionized water several times, and complete cross-linking.

As preferred:

In the step 1), the basement membrane is soaked in deionized water for 6-24 h, the mass concentration of NaOH aqueous solution is 0.2-1.0 wt%, the temperature of the constant temperature water bath is 30-60°C, and the time is 15-60 min.

In the step 2), the polysulfone-based membrane is left to stand in the polyelectrolyte solution for 10-60 minutes, and is washed with deionized water for 5-10 times.

In the step 2), the mass concentration of polyethyleneimine aqueous solution is 0.1-1.0 wt%, the mass concentration of sodium lignosulfonate is 0.1-1.6 wt%, and the number of self-assembled double layers is 2-12.

In the step 3), the mass concentration of the glutaraldehyde aqueous solution is 0.2~2.0 wt%, the resting time of the composite nanofiltration membrane in the glutaraldehyde aqueous solution is 0.5~4.5 h, and the number of times of washing with deionized water is 5~15 times .

Beneficial effect:

The self-assembled composite layer is formed by electrostatic adsorption between positive and negative electrolytes between polyethyleneimine and sodium lignosulfonate, and then cross-linked by glutaraldehyde to form a structurally stable composite layer. The polyethyleneimine/sodium lignosulfonate composite nanofiltration membrane prepared by the invention is used for the nanofiltration membrane to separate MgSO ₄ in aqueous solution, and can exhibit excellent separation performance. The membrane-making process of the invention is simple, the separation performance of the prepared composite nanofiltration membrane is improved, the separation efficiency of the nanofiltration can be improved, and the membrane has great development potential.

Description of drawings

Fig. 1 is a surface scanning electron microscope image of a polysulfone base membrane and a seven-layer composite membrane.

detailed description

_The present invention provides a kind of polyethylene imine/lignosulfonate sodium composite nanofiltration membrane and preparation method thereof for separating MgSO aqueous solution by nanofiltration, below in conjunction with embodiment the present invention is described further, but can not be interpreted as to the present invention limitations on the scope of implementation.

Separation performance evaluation: The nanofiltration separation performance of the polyethyleneimine/sodium lignosulfonate composite nanofiltration membrane separation aqueous solution system was measured by using a flat-plate membrane performance evaluation device: MgSO ₄ aqueous solution with a feed concentration of 2.0 g/L, operating temperature 25 °C, the operating pressure difference of nanofiltration is 1.0 MPa.

Evaluation of nanofiltration separation performance, that is, membrane permeation flux and rejection rate;

1) Permeate flux ( J ), the permeability of the reaction membrane, its definition is: J = M / ( A t ) or J = V / ( A t )

In the formula, M and V are the mass (kg) and volume (m ³ ) of permeate permeated through the membrane respectively; A is the membrane area, m ² ; t is the operation time, h;

2) Rejection rate ( R ), the selectivity of the reaction membrane, its definition formula is: R = ( C _f – C _p ) / C _f × 100%

In the formula, C _f and C _p are the concentrations of the solute components in the feed liquid and the permeate, respectively.

Example 1~5

Pretreatment of the basement membrane: the polysulfone membrane was cut to a size of 14×14 cm and soaked in deionized water for 12 h. After soaking, immerse in 0.5 wt% NaOH aqueous solution, and keep in a constant temperature water bath at 50 °C for 1 h. Then the membrane was taken out and washed with deionized water until neutral. Drain the pretreated basement membrane with deionized water, seal it in a ziplock bag and store it in the refrigerator for later use;

Self-assembly of the polyelectrolyte composite layer: the four corners of the polysulfone base membrane were fixed on the bottom of the culture dish with waterproof tape, and the base membrane was cleaned with deionized water. Pour an appropriate amount of 0.15 wt% PEI solution into the Petri dish and let it stand for 30 min. Pour out the PEI solution and rinse it several times with deionized water to remove excess polyelectrolyte adsorbed by weak force on the surface of the membrane. Then pour about an appropriate amount of 0.2 wt% SL solution, let stand for 30 min, pour out the SL solution, and rinse with deionized water several times. So far, a double-layer self-assembly is completed, and the above steps are repeated several times to obtain composite nanofiltration membranes with double-layer numbers of 1, 3, 5, 7, and 11 respectively;

Cross-linking of the polyelectrolyte multilayer film: After the above composite film was washed with deionized water, an appropriate amount of 1.0 wt% glutaraldehyde aqueous solution was poured into a watch glass and left to stand for 1 h. Afterwards, the glutaraldehyde aqueous solution was poured out, and the composite membrane was washed several times with ionized water, and the cross-linking was completed. For the separation of MgSO ₄ aqueous solution, the separation performance is shown in Table 1.

It can be seen from Table 1 that the permeation flux of the polyethyleneimine/sodium lignosulfonate composite membrane decreases with the increase of the number of membrane layers. The reason may be that the thickening of the separation layer makes it more difficult for the feed liquid to pass through Sincerely. The interception performance of the composite membrane increases with the number of membrane layers at the beginning, and gradually tends to be stable after 7 layers. In order to balance flux and interception performance, it can be considered that the optimal number of self-assembled layers of polyethyleneimine/sodium lignosulfonate composite membrane is 7 bilayers. This result is consistent with the smoothest and densest surface of the 7-layer composite membrane observed by SEM, because the smooth and dense surface separation layer can provide a good separation effect.

Table 1 Separation performance of polyethyleneimine/sodium lignosulfonate composite nanofiltration membrane

Claims (8)

1. a kind of preparation of polyethylenimine/sodium lignosulfonate composite film, preparation method comprises the following steps: 1) Pretreatment of the base membrane, using polysulfone (PSF) ultrafiltration membrane as the base membrane, soaking it in deionized water for a certain period of time, then immersing it in NaOH aqueous solution, and keeping it in a constant temperature water bath for a period of time; then take out the membrane and wash it with deionized water to neutral; 2) Preparation of the composite nanofiltration membrane, immerse the polysulfone-based membrane in the polyethyleneimine solution for a certain period of time, pour out the PEI solution, and rinse it with deionized water several times; then immerse it in the sodium lignosulfonate solution for the same Rinse several times with deionized water; so far a double-layer self-assembly is completed, and the above steps are repeated several times to obtain nanofiltration membranes with different layers; 3) Cross-linking of composite nanofiltration membranes, immerse composite nanofiltration membranes of different layers in glutaraldehyde aqueous solution and let them stand for a period of time, take them out, wash the composite membranes with deionized water several times, and complete cross-linking. 2. The pretreatment of the basement membrane according to claim 1, characterized in that: the soaking time of the basement membrane in deionized water is 6-24 hours, and the mass concentration of NaOH aqueous solution is 0.2-1.0 wt%. 3. The pretreatment of the base film according to claim 1, characterized in that: the temperature of the constant temperature water bath is 30-60°C, and the time is 15-60 min. 4. according to the preparation of the described composite nanofiltration membrane of claim 1, it is characterized in that: the time that polysulfone-based membrane stands still in polyelectrolyte solution is 10～60 min, and the number of times of deionized water washing is 5～10 times. 5. according to the preparation of the described composite nanofiltration membrane of claim 1, it is characterized in that: the mass concentration of polyethyleneimine aqueous solution is 0.1～1.0 wt%, and the mass concentration of sodium lignosulfonate is 0.1～1.6 wt%. 6. The preparation of the composite nanofiltration membrane according to claim 1, characterized in that: the self-assembled double-layer number is 0.5-10. 7. The cross-linking of the composite nanofiltration membrane according to claim 1, characterized in that: the mass concentration of the glutaraldehyde aqueous solution is 0.2 to 2.0 wt%. 8. The cross-linking of the composite nanofiltration membrane according to claim 1, characterized in that: the composite nanofiltration membrane is allowed to stand in the glutaraldehyde aqueous solution for 0.5-4.5 h, and the number of times of washing with deionized water is 5-15 times.