Compared with conventional activated carbon, activated carbon fiber has obvious advantages in physical and chemical properties. As a nano-porous adsorption material, activated carbon fiber has a slender fiber structure with a diameter of about 20μm and high strength, and can be processed into various shapes (such as felt, cloth, etc.). Specific surface area up to 2 000m2 /g, its surface area is one hundred or even one thousand times of activated carbon, thus greatly increasing the adsorption and catalytic capacity; Because its pores are nano-scale surface pores (<2 nm), abundant in quantity and uniform in arrangement, which can not only reduce the diffusion resistance of gas in the adsorption process, but also easily regenerate the activated carbon fiber in the desorption process.
Due to the enrichment of nano-pores on the surface of activated carbon fiber (molecular sieve effect), it can remove ultra-low concentration OF SO2, which even the current wet desulfurization process with the highest desulfurization efficiency can not be done, not only can be used for desulfurization and denitration of power station flue gas, but also can be used to improve the environment at busy intersections, parks and other places. In addition, denitration process does not need to add additional reactants, can achieve simultaneous desulfurization and denitration, comprehensive economy is better than activated carbon. Because of its advantages of simple process, no secondary pollution and renewable utilization of resources, this method has become a hot spot in environmental protection research all over the world.
1.Principle of activated carbon fiber desulfurization
Based on the activated carbon fiber has incomparable adsorption performance of conventional activated carbon, it has a broad application prospect for SO2 removal. The reaction principle of continuous removal of SO2 from flue gas by activated carbon fiber is shown in Figure 1. After adsorption on the activated carbon fiber, SO2 is catalyzed to SO3 in the presence of oxygen. SO3 then reacts with water vapor in flue gas to form sulfuric acid, which is eluted by excessive condensation water on activated carbon fiber, thus vacating the adsorption site of SO2 and making SO2 The cycle of adsorption, oxidative hydration and sulfuric acid desorption continues continuously, which can not only avoid the loss and activity decline of carbon materials due to wear or regeneration, but also avoid the frequent regeneration of carbon materials, thus reducing the operation cost.
2.Removal of NOx
NOx is also one of the main substances of air pollution. The removal of NOx from flue gas by NH3 selective catalytic reduction (SCR) process has been widely used, and the commonly used catalysts are metal oxides, zeolite and activated carbon. In order to ensure a high NOx removal rate, metal oxide catalyst and zeolite catalyst need to be used in the temperature range of 180 ~ 330 ℃, too high temperature,NH is oxidized; Low temperature causes low catalyst activity. The disadvantage of the SCR process is that it is sometimes necessary to reheat the flue gas. After sulfuric acid activation treatment, the asphalt based activated carbon fiber carries out selective catalytic reduction of NOx in flue gas. When the oxygen content in the gas is less than 10%, the activity of selective catalytic reduction of NOx is greatly improved. I. Mochida et al. systematically studied the catalytic performance of a series of asphalt based activated carbon fibers and found that one activated carbon fiber could reduce NO in flue gas to less than 10mL /m3 at room temperature. At the same time, the study also found that after high temperature heating treatment, activated carbon fiber has higher activity.
M. Shirahama et al. loaded urea on activated carbon fiber at room temperature and removed NO in the reducing air, which could reduce NO from 50 to 1 000mL /m3 to nitrogen, and could continue to reduce until urea was completely consumed.
3.Research direction of activated carbon fiber desulfurization out of stock
Compared with other desulfurization and denitrification methods, the desulfurization and denitrification of activated carbon fiber has the advantages of simple process, no secondary pollution, renewable utilization of resources, and has a very broad application prospect. However, there are many basic researches on reaction mechanism, preparation and modification of activated carbon fiber, and simultaneous desulfurization and denitration. In addition, in the practical aspect, the process design is also the content of further research. Therefore, the main research directions of activated carbon fiber desulfurization and denitrification in the future can be summarized as follows:
(1) The internal mechanism of desulfurization and denitration of activated carbon fiber, especially the relationship between surface functional groups and desulfurization and denitration performance;
(2) Modification method of activated carbon fiber;
(3) The interaction between activated carbon fiber desulfurization and denitrification, and the optimization of desulfurization and denitrification conditions.
