CN104524990A - Gas separation membrane, preparation method thereof and membrane type gas separation device - Google Patents

Abstract

The invention discloses a gas separation membrane and a preparation method thereof, belonging to the technical field of membrane separation. The gas separation membrane of the present invention includes a porous substrate, on at least one surface of the porous substrate, a composite membrane formed by mixing graphene oxide and polymer branched polyethyleneimine is attached. The preparation method of the gas separation membrane of the present invention utilizes the flaky graphene oxide material to be dispersed in an aqueous solution, and then prepares a single layer on a porous substrate by a layer-by-layer overlapping coating method with a polymer branched polyethyleneimine solution or multilayer composite film. The invention also discloses a membrane type gas separation device using the gas separation membrane in the membrane module unit. The invention utilizes the unique molecular transport characteristics of the layered graphene material, breaks the restrictive relationship between the permeability and the selectivity in the gas separation membrane, and exhibits excellent gas separation performance. The process of the invention is simple and economical, has wide application range and is suitable for large-scale preparation.

Description

Gas separation membrane and preparation method thereof, membrane gas separation device

technical field

The invention relates to a gas separation membrane and a preparation method thereof, belonging to the technical field of membrane separation.

Background technique

Membrane gas separation is widely used in chemical industry, energy, environment, biomedicine and pharmaceutical industry. In energy science, high-purity _H2 and _CH4 are regarded as the basic materials for fuel cells and hydrogen power generation. In environmental science, suppressing the increase of CO ₂ is the main direction to improve the greenhouse effect. The same direct, low-cost, and environmentally friendly extraction of usable gas and oil from waste gas and oil is a new requirement and challenge for the separation technology in the chemical industry.

Compared with traditional refrigerated distillation and pressure swing adsorption separation technologies, membrane separation technology has many advantages such as energy saving, low price, easy installation, operation and maintenance, standardization, space saving and environmental protection. Composite membranes (TFCs) are currently the most widely used materials in gas and liquid phase separation applications. Although TFC has many advantages, it faces a major technical bottleneck under the technical requirements of thinner, more hydrophilic and porous support layers. Secondly, in the process of synthesizing TFC membranes, the interfacial polymerization process has extremely strict requirements on chemicals, solvents, supports, and reaction conditions, and the functional modulation of the membranes is a very big challenge. Such ultra-thin, high thermal stability, and excellent mechanical properties are the main directions of membrane science research and application.

The emerging two-dimensional graphene oxide is one of the hot research objects of many nanomaterials. From a theoretical point of view, compared with traditional inorganic membrane materials, graphene oxide has a thickness of several atomic layers, uniform pore size and interlayer distribution, ultra-high mechanical strength and high thermal conductivity, and is almost an ideal membrane separation material. Graphene oxide, however, is widely considered to be completely impermeable to gas and liquid molecules. Single-layer thickness graphene has a regular two-dimensional planar hexagonal honeycomb network and ^sp2 hybrid structure in the XY direction. The hexagonal pores of graphene are uniformly distributed but the physical size (< 0.2nm) is smaller than the dynamic diameter of all commonly used gas molecules (Ne ~0.26nm, H ₂ ~0.289nm), so that it is almost impermeable to any gas and liquid phase molecules . Graphene oxide membranes in the Z direction are also considered unsuitable as membrane separation materials due to their dense stacking methods and lack of gas and liquid permeation channels. In addition, the graphene oxide has no functional group pore size and the local electronic density of states with metal characteristics between the layers. The infiltrated molecules will be subject to strong Coulomb repulsion when they are close to the graphene oxide pore size and the layer gap, thereby reducing the size of graphene oxide. The "effective" pore size and greatly reduces the chance of molecular penetration.

In summary, the gas separation technology urgently needs gas separation membrane materials with ultra-thin, high thermal stability, excellent mechanical properties, and a good balance between permeability and selectivity, as well as economically feasible membrane materials. Preparation Process.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a gas separation membrane and its preparation method. The gas separation membrane has ultra-thin, high thermal stability and excellent mechanical properties, and can The restrictive relationship between permeability and selectivity is well balanced, and the preparation process is simple and economical, the application range is wide, and it is suitable for large-scale mass production.

The gas separation membrane of the present invention includes a porous substrate and a composite membrane attached to at least one side of the porous substrate, and the composite membrane is formed by mixing graphene oxide and polymer branched polyethyleneimide (PEI for short).

Preferably, the material of the porous substrate includes at least one of the following materials: polyvinylidene fluoride, polyethersulfone, polyetherimide, cellulose acetate, mullite, alumina, zirconia.

Preferably, the average pore diameter of the porous substrate is 20 nm to 2000 nm.

Preferably, the shape of the porous substrate is sheet, tube or hollow fiber.

The method for preparing a gas separation membrane as described in any of the above technical solutions, comprising the following steps:

Step A, preparing graphene oxide dispersion and polymer branched polyethyleneimine solution respectively;

Step B, smoothing the surface of the porous substrate and washing and drying;

Step C, coating the polymer branched polyethyleneimine solution on the surface of the porous substrate, drying it naturally in the air, and then heating and curing;

Step D, coating the graphene oxide dispersion on the surface of the porous substrate obtained in step C, drying naturally in the air, and then heating and curing.

The above technical scheme can prepare a gas separation membrane with a single-layer composite membrane. On this basis, a gas separation membrane with a multi-layer composite membrane can be further obtained by layer-by-layer overlapping coating according to actual needs, that is, the following technology plan:

  As mentioned above, the preparation method also includes:

Step E, repeat step C and step D several times.

Preferably, the method for preparing the graphene oxide dispersion is as follows: graphene oxide is added to deionized water, followed by mechanical stirring and/or ultrasonic stirring.

Preferably, the method for preparing the polymer branched polyethyleneimine solution is as follows: the polymer branched polyethyleneimine is added to the solvent, heated and stirred and subjected to defoaming treatment, and finally left standing; the solution is water, ethanol , DMF, DMSO, toluene, xylene in any one.

The gas separation membrane of the present invention can also be used to obtain the following technical solutions:

A membrane gas separation device, comprising a membrane module unit, and the membrane module unit includes the gas separation membrane described in any of the above technical solutions.

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

1. The present invention can obtain a high-quality and large-area graphene-based composite film through a simple process and low-cost equipment, and this method can be extended to the preparation of other composite film materials;

2. The coating process of the preparation method of the present invention starts from the solution reaction, so that the obtained material can be uniform at the atomic level and molecular level, which is very important for controlling the physical and chemical properties of the material;

3. The layer-by-layer coating process used in the preparation method of the present invention is easy to control. By adjusting solvents, high molecular polymers, graphene materials and different layers of coating films, a series of different microstructures and permeability properties can be obtained. composite film;

4. The material prepared by the preparation method of the present invention has a wide range of doping (including the amount and type of doping), accurate stoichiometry and easy modification;

5. The preparation method of the present invention does not require vacuum conditions and high temperatures, and is easy to form a film on the substrate. It can be coated flexibly by dip coating, spin coating, spray coating or salivation according to the actual situation. The preparation is convenient, and the coating layer The number is easy to control;

6. The gas separation membrane of the present invention has a good screening effect on gas molecules. Experiments show that the gas separation factor of the gas separation membrane of the present invention for H2/N2 and H2/CH4 can reach 200, which is of great significance in terms of energy and environment .

Description of drawings

Fig. 1 is graphene material and PEI polymer long-chain molecular layer self-assembly structure and the schematic diagram of gas separation mechanism;

Fig. 2 is a schematic diagram of the structure and principle of the gas separation device used in the gas separation experiment.

Detailed ways

The technical scheme of the present invention is described in detail below in conjunction with accompanying drawing:

Aiming at the deficiencies of the prior art, the invention provides a gas separation membrane based on a composite membrane of polymer branched polyethyleneimine and graphene oxide materials and a preparation method thereof. In the invention, the flake graphene oxide material is dispersed in an aqueous solution, and then a single-layer or multi-layer composite membrane is prepared on a porous substrate through a layer-by-layer overlapping coating method with a polymer branched polyethyleneimine solution. The doping between graphene oxide material layers changes and the graphene oxide film is densely stacked in the Z direction, resulting in physical channels for separating gases and functional groups for selective chemical adsorption.

The gas separation membrane of the present invention includes a porous substrate, on at least one surface of the porous substrate, a composite membrane composed of graphene oxide and polymer branched polyethyleneimine (referred to as GO-PEI composite membrane) is attached. The material of the porous substrate is preferably composited with one or more of the following materials: polyvinylidene fluoride, polyethersulfone, polyetherimide, cellulose acetate, mullite, alumina, zirconia. The average pore diameter of the porous substrate is preferably in the range of 20 nm to 2000 nm. According to actual needs, the shape of the porous substrate may be a sheet type, a tube type or a hollow fiber type, and other suitable shapes may also be adopted as required.

The present invention specifically adopts the following method to prepare the above-mentioned gas separation membrane:

Step A, preparing graphene oxide dispersion and polymer branched polyethyleneimine solution respectively;

Wherein, the preparation method of graphene oxide dispersion is as follows: add graphene oxide into deionized water, and then carry out mechanical stirring and/or ultrasonic stirring to obtain graphene oxide dispersion; its concentration can be 0.001mg/ml~3.0mg In the range of /ml, the optimal concentration range is 0.01mg/ml~1.0mg/ml. The preparation method of the polymer branched polyethyleneimine solution is as follows: the polymer branched polyethyleneimine is added to the solvent, the concentration range is 0.001wt%~15.0wt%, the optimal concentration range is 0.01wt%~10.0wt%, Heating and stirring, performing defoaming treatment, and then standing for use; the solution is any one of water, ethanol, DMF, DMSO, toluene, and xylene.

Step B, smoothing the surface of the porous substrate and washing and drying;

Porous substrate materials can be selected from polyvinylidene fluoride (PVDF), polyethersulfone (PES), polyetherimide (PEI), cellulose acetate (CA), mullite, Al ₂ O ₃ , ZrO ₂ One of them, or a composite of two or more. The porous base material is soaked in water or organic solvent and dried, and then the surface to be coated with the composite membrane is smoothed and cleaned. When cleaning, ultrasonic cleaning can be used first, and then the surface is rinsed with deionized water and dried.

Step C, coating the polymer branched polyethyleneimine solution on the surface of the porous substrate, drying it naturally in the air, and curing it by heating.

Step D, coating the graphene oxide dispersion on the surface of the porous substrate obtained in step C, drying naturally in the air, and then heating and curing.

 The coating of the above-mentioned polymer branched polyethyleneimine solution and graphene oxide dispersion can use methods such as dip coating, spin coating, spray coating or salivation according to actual needs.

Through the above steps, a gas separation membrane with a single-layer GO-PEI composite membrane attached to the surface can be obtained. It is also possible to repeat step C and step D multiple times on this basis according to the required microstructure and permeability, thereby preparing GO-PEI composite membranes with different overlapping layers on the surface of the porous substrate to meet the required performance Require.

As shown in Figure 1, the graphene material and PEI polymer long-chain molecules are combined by a layer-by-layer self-assembly method to form a film on a porous substrate. The groups on the edge of the graphene material are negatively charged, and the long-chain polymer molecules are positively charged. The two are firmly combined through electrostatic attraction to form a composite membrane structure of tightly packed graphene materials and polymer membrane materials. Such a membrane structure is more stable and has a stronger binding force than the membrane structure of pure graphene materials, and such graphene sheets are more conducive to forming a pore structure with molecular sieving effect, thereby improving separation performance. At the same time, the graphene material forms many hole-like defects during film formation, and these defects have a certain molecular sieving effect. Hydrogen molecules and carbon dioxide molecules, as an example of gas separation, in the process of passing through the membrane material, the kinetic diameter of hydrogen molecules is smaller than that of carbon dioxide molecules, hydrogen molecules can pass through the porous graphene membrane layer faster, while carbon dioxide Due to the molecular sieve effect, the penetration is slow. Secondly, the oxygen-containing groups and amino groups on graphene materials and polymer materials have a stronger adsorption effect on carbon dioxide molecules than the weak adsorption effect of hydrogen molecules, making it difficult for carbon dioxide molecules to pass through the film layer quickly. It is precisely because of the above reasons that the composite membrane of graphene material and polymer membrane material prepared by the method of layer-by-layer self-assembly achieves the gas separation effect.

Hereinafter, a specific example is used to further illustrate the method for preparing a gas separation membrane of the present invention. This implementation includes the following steps:

Step 1. Add 0.01g of graphene oxide powder into 20ml of deionized water, mechanically and ultrasonically stir for 1h to completely disperse it, and prepare a 0.5 mg/ml graphene oxide dispersion.

Step 2. Add 0.2g of organic polymer material (PEI) into 20ml of deionized water to prepare a solution with a concentration of 1.0% by mass, heat and stir at 30°C for 4 hours, and let the obtained PEI solution stand for defoaming. use.

Step 3. Smooth the Al ₂ O ₃ substrate with metallographic sandpaper, then soak it in 200ml deionized water, ultrasonically clean it for 0.5 hours, and then dry it in an oven at 80°C for 2 hours.

Step 4. Coat the PEI solution on one side of the substrate, let it dry naturally in the air, and then heat and cure. The curing temperature is 35°C and the curing time is 10 hours.

Step 5. Coat the graphene oxide dispersion on the upper layer of PEI, let it dry naturally in the air, and then heat and cure. The curing temperature is 35°C and the curing time is 10 hours.

Step 6. Repeat steps D) and E) to obtain gas separation membranes with different layers of GO-PEI composite membranes.

In order to verify the effect of the gas separation membrane of the present invention, a gas separation experiment was carried out using the gas separation device shown in Figure 2, the experimental process is as follows:

1) Install the gas separation membrane prepared by the method of the present invention into the membrane module unit;

2) Put the membrane module unit into the digitally controlled electric furnace, adjust the gas temperature, connect one side to the gas chromatograph, and the other side to the feed port;

3) The feed flow rate is controlled by the mass flow meter, and the solid phase particles are filtered out by the coarse filter before the mass flow meter;

4) System pressure is controlled by pressure regulator and back pressure regulator;

5) Feed and retentate pressure and temperature are monitored by pressure sensor and temperature sensor respectively;

6) For mixing experiments, adjust the ratio of the two gases so that they are fully mixed in the mixing vessel;

7) When the feed temperature reaches the expected value, the feed flow rate is regulated by the mass flow meter and the soap bubble flow meter so that the raw material enters the upstream of the membrane module unit;

8) The final permeated gas content is calculated by gas chromatographic monitoring.

Separation experiments were carried out on H ₂ /N ₂ mixed gas and H ₂ /CH ₄ mixed gas, and it was found that the gas separation factor can reach 200, which shows that the gas separation membrane of the present invention has good gas separation performance.

The performance of gas separation membranes is mainly investigated from the two aspects of membrane permeation flux and gas separation effect. Since the thickness of traditional membranes is on the order of microns, the gas separation performance often takes a long time, and the membrane flux is relatively small; while the flux Larger separation membranes tend to have lower gas separation efficiency. Compared with the previous technology, the present invention improves the gas separation effect while ensuring that the membrane flux is not reduced, breaks through the traditional restrictive relationship between permeability and selectivity to a certain extent, and exhibits excellent gas separation performance. The process of the invention is simple and economical, has wide application range and is suitable for large-scale preparation.

Claims (10)

1. a gas separation membrane, comprise perforated substrate and be attached to described perforated substrate composite membrane at least simultaneously, it is characterized in that, described composite membrane is that graphene oxide and polymer branching polymine mix.

2. gas separation membrane as claimed in claim 1, it is characterized in that, the material of described perforated substrate comprises at least one in following material: Kynoar, polyether sulfone, PEI, cellulose acetate, mullite, aluminium oxide, zirconium dioxide.

3. gas separation membrane as claimed in claim 1, it is characterized in that, the average pore size of described perforated substrate is 20 nm ~ 2000 nm.

4. gas separation membrane as claimed in claim 1, it is characterized in that, the shape of described perforated substrate is chip, tubular type or hollow fiber form.

5. a membrane type gas fractionation unit, comprises membrane module unit, it is characterized in that, described membrane module unit comprises gas separation membrane described in any one of Claims 1 to 4.

6. the preparation method of gas separation membrane as described in any one of Claims 1 to 4, is characterized in that, comprise the following steps:

Steps A, respectively preparation graphene oxide dispersion and polymer branching polyethylenimine solution;

Step B, by smooth for perforated substrate surface finish and cleaning, drying;

Step C, polymer branching polyethylenimine solution is coated on perforated substrate surface, after naturally drying in atmosphere, is heating and curing;

Step D, graphene oxide dispersion is coated on the perforated substrate surface that step C obtains, after naturally drying in atmosphere, is heating and curing.

7. preparation method as claimed in claim 6, is characterized in that, also comprise:

Step e, repeated execution of steps C and step D many times.

8. preparation method as claimed in claims 6 or 7, is characterized in that, the method for preparation graphene oxide dispersion is specific as follows: added by graphene oxide in deionized water, then carries out mechanical agitation and/or ultrasonic wave stirs.

9. preparation method as claimed in claims 6 or 7, it is characterized in that, the method for prepared polymer branched polyethylene imine solution is specific as follows: add in solvent by polymer branching polymine, adds thermal agitation and carries out deaeration process, finally leaving standstill; Described solution is any one in water, ethanol, DMF, DMSO, toluene, dimethylbenzene.

10. preparation method as claimed in claims 6 or 7, is characterized in that, the coating of polymer branching polyethylenimine solution and graphene oxide dispersion uses dip-coating, spin coating, spraying or salivation method.