In December 2020, the Central Economic Work Conference listed the carbon peak and carbon neutral work as one of the eight key tasks in 2021.China has been improving its goals in addressing climate change and made positive contributions to the global climate change.The proposal of carbon peak and carbon neutrality goals is also the internal demand for China to achieve sustainable development and the only way to a "beautiful China".At the present stage, China faces complex challenges such as large total carbon emissions, short time for carbon emission reduction, economic transformation and upgrading, and great difficulty of energy system transformation.The main components of the flue gas discharged by coal combustion and power generation after desulfurization and denitration process purification are carbon dioxide and nitrogen gas.Catching CO2 in flue gas is an important link to realizing carbon capture, utilization and sealing, and is of great significance to reducing greenhouse gas emissions and reducing the occurrence of extreme climate.
In December 2020, the Central Economic Work Conference listed the carbon peak and carbon neutral work as one of the eight key tasks in 2021.China has been improving its goals in addressing climate change and made positive contributions to the global climate change.The proposal of carbon peak and carbon neutrality goals is also the internal demand for China to achieve sustainable development and the only way to a "beautiful China".At the present stage, China faces complex challenges such as large total carbon emissions, short time for carbon emission reduction, economic transformation and upgrading, and great difficulty of energy system transformation.The main components of the flue gas discharged by coal combustion and power generation after desulfurization and denitration process purification are carbon dioxide and nitrogen gas.Catching CO2 in flue gas is an important link to realizing carbon capture, utilization and sealing, and is of great significance to reducing greenhouse gas emissions and reducing the occurrence of extreme climate.
Although there are many film materials studied at present, the separation principle is basically the same, that is, using the choice of the membrane permeability, using the driving force, mass transfer between the membrane components to achieve the separation of different components, the driving force is generally concentration difference, pressure difference, potential difference or temperature difference.
1、Membrane material
Most membranes used for CO2 isolation were organic membranes, such as polyethylene, polysulfone, polyester, etc., but the application was limited due to poor separation performance and stability of membrane materials.With the progress of material science, the separation performance and stability of film materials have been continuously improved, and inorganic films (such as metal, zeolite, carbon film, etc.) and mixed matrix films have also been developed to broaden the application field.Mixed matrix membranes can achieve complementary advantages of organic and inorganic materials, have great potential for CO2 separation, and are considered to be one of the most important development directions in the future separation membrane field.
2.1 Organic polymer membrane material
Organic polymer membrane preparation process has the advantages of relatively simple, low energy consumption and easy to expand, and is suitable for large-scale manufacturing.Organic polymer membrane materials can be divided into glass and rubber states according to the form of the polymer.Glass polymers have lower chain mobility and more stable structures than rubber polymers, therefore, glass polymers have better selectivity, but the disadvantage is poor permeability.Rubber-state polymers have good permeability, but are prone to expansion and deformation at high pressure.
The commonly used polymer membrane materials used for gas separation are cellulose acetate, polyimide, polyalum and polyether amide, which all have good gas selectivity, but their gas permeability coefficient is low, while polydimethylxoxane, polySanya methylsilane acetyne have high gas transmission coefficient.
2.2 Inorganic polymer membrane material
Inorganic film is a film made of inorganic materials. Because of its advantages of high temperature resistance, corrosion resistance, good chemical stability, high separation efficiency, easy cleaning, easy disinfection and long film service life, the development and application of inorganic film has become a major research and development hot spot in the current field of film technology.Inorganic film can be divided into ceramic film, metal film, alloy film, molecular screening composite film, zeolite film and glass film, among which the most use is ceramic film.Ceramic separation film is a separation material made of porous ceramics as the carrier. It is mainly based on the "screening" theory and using the pressure difference to realize the separation of the mixture, which is generally used for microfiltration and ultrafiltration.Ceramic films currently developed are titanium dioxide (TiO2), alumina (Al2O3), cobalt oxide (CoO), zinc oxide (ZnO), silicon dioxide (SiO2), silicon carbide (SiC), carbon nanotubes (CNT), and graphene oxide (GO).Among them, GO is an emerging nanomaterials that shows great development prospects in the development of anti-stain nanocomposite membranes.
2.3 Mixed matrix membrane
The hybrid particles (dispersed polymer phase) are filled in a polymer (polymer phase) and a mixed matrix membrane (MMMs)is made by the interaction between inorganic packing and polymer polymer.Mixed matrix membranes have both the advantages of high membranability and unfragmentation of the polymer membrane, and optimize its arrangement by the introduction of inorganic materials in the polymer matrix.Ideally, the mixed matrix membrane combines the advantages of the two phases of the polymer and dispersed particle phases, namely the processing properties of the polymer, the mechanical properties and the special transport properties of the molecular sieve, giving it potential advantages in CO2 separation.Due to the compatibility problem of the polymer and the inorganic phase in the mixed matrix membrane, only an appropriate amount of the inorganic material load is allowed to obtain the optimal dispersion and interface contact.For hybrid membranes filled with porous packing particles, the screening effect of the packing is the most critical factor in improving performance.For the inorganic particle zeolite, the whisker structure formed on the surface provides an additional roughness for the linkage of the polymer chains to the zeolite.
3、Mixed with a matrix membrane filler
For the formation of a mixed substrate membrane, good adhesion between the polymer substrate and the inorganic packing is crucial, especially when the polymer has a high Tg (glass transition temperature), good mechanical properties and performance stability over time.The structural features and interactions of fillers and polymers also face great challenges.These different fillers also have different effects on the separation properties of the mixed matrix membranes.
3.1 Inorganic particle filler
In combination with the polymer matrix, the most studied fillings were zeolite, carbon interporous silica and metal organic skeleton (MOF).Inorganic particles used for hybridization often include carbon nanotubes, molecular screens, silica, etc.The inorganic filler mainly controls the separation performance of the film through its structure.However, because the inorganic packing is poorly compatible with the polymer membrane matrix, the membrane separation performance is reduced.Excavating more inorganic particles with high compatibility with polymer membranes is an urgent problem.
3.2 Organic filler
The advantages of organic packing structure are controllable and good flexibility, excellent compatibility with polymer substrate, but poor solvent resistance and corrosion resistance, and no good gas separation performance under harsh operating conditions.Common organic fillers include porous organic polymers (POPs), covalent organic frames (COFs), etc.
3.3 Metal organic skeleton filler
Metal-organic skeleton materials (MOFs) are 1 porous mesh material formed from self-assembly of organic ligand and certain metal cations through coordination bonds.Most MOFs have a uniform pore size and present a three-dimensional network conformation.In addition, compared to the traditional porous material (zeolite molecular sieve, activated carbon, etc.), the material has a diverse structure, regulation and other advantages.Since the study of MOFs effectively combines the advantages of inorganic and organic fillers, filling the MOFs in the polymer substrate can effectively improve the gas separation properties of the membrane.MOFs materials have excellent affinity with the high molecular substrate to effectively avoid problems such as the nonselective gap between the two phases and greatly improve the membrane separation performance.A class of zeolite imidazole skeleton materials (Z I F) in MOFs as filled particles can effectively improve the performance of the matrix membrane for CO2 gas separation.Summary: The global emissions of CO2 are increasing, bringing a series of environmental problems. Membrane method CO2 trap has shown great development potential due to its advantages of green, high efficiency, energy saving and flexible operation.Mixed matrix membrane can effectively play the synergistic role of organic and inorganic materials, and is becoming the hot spot and focus of permeation and vaporization separation of CO2 membrane materials.However, in current industrial applications, mixed matrix membranes are still restricted by multiple factors.Aggregation of filled particles may lead to increased membrane flux, reduced retention, and poor membrane performance after long-term use.Therefore, improving the stability of the mixed matrix membrane is something to consider.
Source: polyimide online, if there is any infringement, please contact to delete, thank you!
