Hollow fiber ceramic membrane
Ceramic membranes are a type of inorganic membranes. Since formal industrial production in the 1990s, they have been widely used in various fields such as environmental engineering, biopharmaceutical engineering, food and beverage industry, textile printing and dyeing industry, chemical metallurgy and petroleum industry. At present, the forms of ceramic membranes are mainly divided into tube type, multi-channel type, flat plate type and hollow fiber type. In these four, the hollow fiber ceramic membrane has a small outer diameter of the tube (1 ~ 5㎜) and a thin wall (0.1-1.5㎜ ), So it has the advantages of large packing density, large effective membrane area, small thickness and high separation efficiency. The packing density of the general tubular and multi-channel forms is less than 300㎡ / m3, and the hollow fiber is as high as 30,000㎡ / m3.
The hollow fiber ceramic membrane is usually an asymmetric or composite membrane structure composed of a single layer or multiple layers of ceramic materials. The structure generally has a macroporous support layer, one to two intermediate transition layers and a microporous or dense surface. They are the mechanical support, connection layer and effective separation layer (as shown in Figure 1). Compared with ordinary ceramic membranes, it not only has the advantages of high heat, chemical stability, high transmittance, long service life and high mechanical strength of inorganic membranes, but also has large packing density, thin membrane walls and high permeation flux. , High separation efficiency, and the characteristics of saving raw materials and easy to achieve miniaturization of equipment.
Preparation method of hollow fiber ceramic membrane
The preparation methods of the hollow fiber ceramic membrane include a template method, an electrospinning method, an extrusion molding method, and a phase inversion method.
① Template method
The template method refers to using organic polymer hollow fiber or activated carbon fiber as the template, first immersing the pretreated template in the pre-prepared stable oxide precursor sol, and forming a layer of gel on the surface of the fiber template by dipping and coating method The layer is then dried and fired at high temperature to obtain a hollow fiber ceramic membrane. It is worth noting that the preparation of hollow fiber ceramic membranes by the template method requires the use of metal alkoxides to prepare stable polymer sols in advance, and multiple coatings are required to obtain a gel layer of appropriate thickness. And deformation, it is not suitable for large-scale production, so it is mainly used for the preparation of laboratory hollow fiber membranes.
② Electrostatic spinning method
Electrospinning refers to the formation of a metal alkoxide polymer sol through a hollow needle-shaped spinning head with an inner cannula under the action of high-voltage static electricity, and forming a hollow structure by injecting a core fluid. The advantage of this method is that it can be continuously formed, so it is suitable for the preparation of large quantities of ceramic hollow fibers. At present, the electrospinning method has been successfully used for the preparation of nano-ceramic hollow fibers of various materials such as ZrO2, Al2O3, TiO2, BaTiO3, La2CuO4, etc. The prepared nanofibers are used in catalysis, drug release, jet technology, separation and purification, gas storage, energy Conversion and gas sensors and environmental protection have broad application prospects.
③Extrusion molding method
The method and process for preparing hollow fiber ceramic membranes by extrusion molding method are similar to single-channel tubular ceramic membranes, but differ only in the shape and size of the mold. The preparation process is as follows:
(1) Mix ceramic powder, additives (including plasticizers, lubricants, binders, dispersants, etc.) with appropriate quality and water uniformly, and then make plastic mud by vacuum mud training
(2) Put the mud in a closed environment with suitable humidity for more than 24 hours, and use various molding machines for extrusion molding
(3) Carry out drying and high temperature firing.
Extrusion molding method is widely used in the manufacture of various ceramic materials, the technology is mature, suitable for large-scale industrial production. The disadvantage is that the prepared hollow fiber ceramic membrane has a symmetric structure, the tube wall is thick, and the permeation flux is low when used as a microfiltration membrane or an ultrafiltration membrane. Therefore, this method is mostly used for the preparation of hollow fiber composite ceramic membrane support.
④Phase inversion method
Mutual conversion method is to prepare a homogeneous polymer solution with a certain composition. Through certain physical methods, the solvent in the solution and the non-solvent in the surrounding environment undergo mass exchange, changing the thermodynamic state of the solution to make it from a homogeneous The polymer solution undergoes phase separation and eventually transforms into a three-dimensional macromolecular network gel structure, in which the polymer is the continuous phase, and the dispersed phase is the pore-like structure left after the dilute phase of the polymer is eluted. The phase inversion method has the advantages of simple and easy process control, low cost, controllable microstructure of the prepared membrane, and high permeability membrane that can obtain an asymmetric structure through one-step molding. It can be used for the preparation of microfiltration membranes, ultrafiltration membranes and reverse osmosis membranes with asymmetric structure, and can also be applied to the preparation of micropore membranes with symmetric structure or asymmetric structure.
Applications
In April 2015, a hollow-fiber ceramic membrane water filter of the Institute of Advanced Technology of Guangzhou Chinese Academy of Sciences (abbreviation: Guangzhou Institute of Advanced Technology) was phased by the Gates Foundation founded by Microsoft Corporation founder Bill Gates. The 1,000 water filters ordered by the Gates Fund were sent from Nansha to West Africa to solve the drinking water problem of 100,000 people in a long-term drought and high-temperature environment. According to reports, this water filter innovatively uses super-hydrophilic materials as hollow fiber ceramic membranes, which has the advantages of low energy consumption, long life and strong filtration effect. At the same time, the water filter makes the membrane into a hollow tube, and then gathers the tubes into bundles, which greatly increases the area of the membrane in the same volume, and the filtration efficiency is stronger. According to the parameters provided by the laboratory, within a few seconds of the river water passing through the filter, all particulate impurities, heavy metal ions, more than 99% of bacteria and viruses have been filtered, reaching the national drinking water standard.