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Activated carbon fiber Activated carbon fiber (ACF), also known as fibrous activated carbon, is a highly efficient activated adsorption material and environmentally friendly engineering material with better performance than activated carbon. More than 50% of its carbon atoms are located on the inner and outer surfaces, forming a unique adsorption structure, which is called a surface solid. It is made of fibrous precursor, which is carbonized and activated by a certain procedure. The more developed specific surface area and narrower pore size distribution make it have a faster adsorption and desorption speed and a larger adsorption capacity, and because it can be easily processed into different shapes such as felt, cloth, paper, etc., and has acid resistance The corrosion resistance of alkali makes it get widespread attention and in-depth research as soon as it comes out. It has been widely used in environmental protection, catalysis, medicine, military industry and other fields. The research on the specific surface area of ​​activated carbon fiber is very important. Only the results of the BET method can be used to detect the specific surface area of ​​activated carbon fiber. The domestic instruments have only been tested by direct comparison method. Now it has been eliminated in China. . At present, the multi-point BET method is used uniformly for the specific surface area testing at home and abroad. The specific surface area measurement standards developed at home and abroad are based on the BET test method. Please refer to China's national standard (GB / T 19587-2004)-Gas adsorption BET principle Method for determining the specific surface area of ​​solid materials. The measurement of specific surface area is actually a time-consuming task. Due to the different adsorption capacity of the sample, the test of some samples may take a whole day. If the test process is not fully automated, then the tester ca n’t leave at all times. A high degree of concentration, observing the instrument panel, manipulating the knob, and a little inattention will lead to the failure of the test process, which will waste a lot of precious time of the tester. Among several domestic manufacturers of specific surface area analyzers, only the F-Sorb 2400 specific surface area analyzer of Beijing Jinyi Spectrum Technology Co., Ltd. is an instrument that can truly realize the detection function of the BET method (both with direct comparison method), and the more important Beijing Gold F-Sorb 2400 specific surface area analyzer is the only fully automated and intelligent specific surface area detection equipment in China. Its test results are highly consistent with international standards, and its stability is also very good. At the same time, it reduces human errors. Improve the accuracy of test results.
Since the first US patent in 1962 involved the subsequent use of activated carbon fibers to filter radioactive iodine radiation by ORNL in the United States, the research and application of different precursor organic fibers and activated carbon fibers have developed rapidly. The United States, the United Kingdom, the former Soviet Union, and Japan in particular are major countries that study and use ACF, with an annual output of nearly 1,000 tons. Domestic ACF research started in the late 1980s, and industrialized devices appeared one after another in the late 1990s. Most are in the laboratory research stage.
Manufacturing method: different precursor materials, ACF production process and product structure are also significantly different. The production of ACF generally involves stabilizing the organic precursor fiber at a low temperature of 200 ℃ to 400 ℃, followed by (carbonization) activation. Commonly used activation methods are: physical activation method using CO2 or water vapor and chemical activation method using ZnCI2, H3PO, H2PO4, KOH, the treatment temperature is between 700 ℃ ~ 1 000 ℃, different treatment processes (time, temperature, Activation dose, etc.) The corresponding products have different pore structures and properties. The organic fibers used as ACF precursors are mainly cellulose-based, PAN-based, phenolic-based, pitch-based, polyvinyl alcohol-based, styrene / olefin copolymer and lignin fibers. The main four types of commercialization.
Structural characteristics: Activated carbon fiber is a typical microporous carbon (MPAC), which is considered to be "a combination of ultrafine particles, irregular surface structures and extremely narrow spaces" with a diameter of 10 μm to 30 μm. The pores directly open to the surface of the fiber, and the ultrafine particles are combined in various ways to form a rich nanospace. The size of these spaces is the same order of magnitude as the ultrafine particles, thus creating a large specific surface area. It contains many irregular structures-heterocyclic structures or microstructures containing surface functional groups, which have extremely large surface energy, which also creates micropores and pore wall molecules work together to form a strong molecular field, providing an adsorbed molecular physics And chemically changing high-pressure systems. The diffusion path of the adsorbate to the adsorption site is shorter than that of activated carbon, the driving force is larger, and the pore size distribution is concentrated. This is the main reason for the larger specific surface area of ​​ACF than activated carbon, the faster absorption and desorption rate, and the higher adsorption efficiency.
Functionalization method: Functionalization mainly meets the efficient adsorption and conversion of specific substances through pore structure control and surface chemical modification.
ACF is generally suitable for the adsorption of low molecular weight molecules (MW = 300 or less) in the gas and liquid phases. When the pore size of the adsorbent is about twice the critical size of the adsorbate molecule, the adsorbate is easier to adsorb. The purpose of the pore size adjustment is to make the pore size of the ACF equal to the size of the adsorbate molecules. The following methods are usually used: 1) the activation process or the degree of activation (to the nanometer level); 2) the addition of metal compounds or other substances to the fibrils and carbonization Activation, or use ACF to add metal compound and then activate (medium pore mainly), the raw fiber has a pore diameter (macropore) close to the macropore in advance; 3) Hydrocarbon pyrolysis deposits on the pore wall, high temperature post-treatment (so that The aperture becomes smaller).
Surface chemical modification mainly changes the surface acid and alkalinity of ACF, and introduces or removes some surface functional groups. The oxygen-containing groups on the surface can be removed (reduced) by high temperature or hydrogenation treatment; acidic surface can be obtained by gas phase oxidation and liquid phase oxidation. Modification needs to consider the influence of physical structure and chemical structure.
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