The method of preparation of activated carbon microwave technology
1 the characteristics of activated
1.1 Characteristics of activated carbon
An amorphous carbon material , a hydrophobic non-polar adsorbent capable of selectively adsorbing non- polar material , the adsorption force . Pores of different pore size , different molecular size can be adsorbed substances. Furthermore , because of its surface and the surface of the role of compounds and ash , activated carbon has good catalytic activity . Activated carbon is also able to be widely used due to its stable chemical properties. It acid, alkali , high temperature , insoluble in water and other solvents, and many in the aqueous solvent. Another feature is activated by the use of its failure, the various methods available renewable, multiple use .
1.2 Quality indicators and application of activated carbon
There are a number of activated carbon quality physical and chemical indicators , the main example: moisture, ash, acid-soluble materials , various metals and acid radical content and its adsorption properties. Activated carbon for different purposes , the different substances and methods used to test its adsorption properties , typically methylene blue adsorption, the iodine adsorption, the caramel adsorption, the adsorption of quinine sulfate , phenol, values, etc. Wherein the adsorption of methylene blue is the most common , it reflects the amount of adsorption of small molecules activated carbon adsorption capacity of activated carbon having a large number of micropores , the higher this value . According to characteristics of the activated carbon adsorption , activated carbon is mainly used to remove contaminants from water , bleaching, filtration and purification of liquids, gases , but also for air purification process , the exhaust gas recycling ( in the chemical industry , such as benzene recovery of the gas ) , precious metal recovery and refining ( eg for gold absorption ) . In recent years, the pharmaceutical industry has also been utilized, along with the development of science , as the country 's attention to the ecological environment , the use of activated carbon has become increasingly widespread .
2 status of domestic and external demand of activated carbon
Domestic production and application of activated carbon than later. Europe and the United States in the early 1900s began to develop production of activated carbon . Of activated carbon industry in the 1950s was really set up in the 1970s have greater development . Currently, the world 's annual production of activated carbon around about 6.5 × 105T . 1997 Americas ( Brazil, Mexico, United States ) is 2.359 × 105T, Europe ( Belgium, France, Britain, the Netherlands ) was 1.124 × l05T, Asia [ China ( including Taiwan ) , India, Indonesia, Japan, South Korea , Malaysia , the Philippines , Sri Lanka, Thailand ] count 3.01 × 105T. Activated carbon production in China in 1997 reached a total of more than 1.2 × 105T , accounting for world output l5%. According to the information reported that in 1998 China's export volume of 1.004 × 105T, with exports amounting to $ 604 million ; 2000 Chinese activated carbon export volume up to 1.192 × 105T, exports of up to $ 685 million . In imports , the 1999 imports amounted to 19,045,000 activated T, imports amounted to $ 5,582,000 ; 2001 carbon imports increased to 25,673,000 T. Imports amounted to $ 7,271,000 . From these data we can see , 2l century Chinese activated carbon industry still has broad prospects for development . However, the domestic industry must focus on Activated Carbon application development trends, strengthen the development of new technologies to promote the sound development of the industry throughout the activated carbon .
3 Preparation of Activated Carbon materials with conventional methods
3.1 Preparation of activated carbon materials
The main raw material used in the production of activated carbon can be divided into the following five categories : a, botanical raw materials, such as wood, sawdust , stone , shell , cotton stalks, furfural residue , slag , etc. sucrose ; b, mineral raw materials , such as various coal and oil residues, etc. ; c, all kinds of waste , such as animal bone and blood , industrial waste plastics , rubber waste , etc. ; d, synthetic materials such as polypropylene and the like ; e, organic fiber materials, such as poly acrylonitrile fibers, viscose rayon , pitch fiber. According to the material used in the production , the major domestic varieties of wood activated carbon , coal activated carbon , shell activated carbon and activated carbon fiber.
3.2 The traditional method for preparing activated carbon
The traditional method for preparing active carbon abroad a gas activation method, a chemical activation method, a chemical physical methods : gas activation method is the carbonization of the raw materials , the use of water vapor, carbon dioxide , air, flue gas , etc., in the 800 ~ 900 ℃ of activating methods . Low yield of carbon and unstable quality , lower specific surface area , the activation temperature is high , a large investment in equipment , but the environmental pollution ; chemical activation method is to add chemical raw materials , then heated in an inert gas , simultaneously carbonized and activation of a method. This method is more corrosive to equipment , environmental pollution , and the residue more; chemical physical method of activated carbon material by adding a certain amount of chemicals (i.e., additives) for chemical activation immersion treatment , the carbon material formed within the transmission channel , a conducive gas activator etched into the pores . Advantages of this approach are: by controlling the impregnation ratio and impregnation time to obtain reasonable activated carbon pore size distribution , surface area and high yield .
4 Carbon Prepared by Microwave
Microwave with a fast, efficient , resource recycling rate is high, will not cause secondary pollution, low cost significant advantages. Activated Carbon Prepared by Microwave therefore domestic and foreign scholars in recent years become one of the focus . Many domestic and foreign researchers experimented with microwave preparation of activated carbon and has made gratifying achievements , such as Kasai, Takakazu and other organic wastes using microwave heating molding , carbonization, activation obtain high quality activated carbon . Peng Jinhui other with beans stalks, rice straw , black -type bark tannin extract waste , seeds shell , wheat straw , corn , beans shells , bagasse , bayberry bark waste , tobacco stalks, pine sawdust , coconut shell as raw materials, preparation of activated carbon microwave . Fan Xian and other microwave radiation bamboo , coconut shell , cotton stalk , the use of phosphoric acid , water vapor, zinc chloride as an activator to obtain high quality activated carbon . Zhang Libo, such as the use of microwave radiation performance of different tobacco stalk was prepared from activated carbon .
The principle of microwave heating 4.1
Microwave frequency of about 300MHZ ~ 300GHZ, i.e. 100cm to 1mm wavelength range of electromagnetic waves . The principle of microwave heating on the microwave encounters different materials , depending on the different nature of the material occurs reflection, absorption , transmission through , depending on the dielectric constant , dielectric loss factor , the specific heat , shape and moisture content . Generally medium heated in the microwave field , there are two mechanisms , namely ion conduction mechanism and dipole rotation mechanism , in the actual heating , two mechanisms of microwave energy dissipation exist. Conventional heating by external heat conduction through the thermal radiation from surface heating , compared to microwave heating has the following characteristics : selective heating , heating speed , high thermal efficiency , easy to control , easy automation.
4.2 of microwave technology in the environmental protection field
Microwave technology in the field of environmental protection in several applications : Microwave butter oil sludge technology ; crude oil sludge removal microwave technology ; microwave carbon reduction - flue gas desulfurization and denitration technology ; microwave incineration of waste circuit board recycling precious metals processing technology ; microwave - Preparation of activated carbon zinc sawdust waste water containing Cr ; microwave Preparation of oil spill treatment with high oil absorption complex technology ; anti-electromagnetic radiation pollution microwave absorber preparation techniques .
4.3 Preparation of activated carbon microwave factors
In the preparation of activated carbon , the different raw materials , finished products are different effects . Coconut shell activated carbon industry, which is recognized as the best kind of activated carbon , whether adsorption rate , adsorption capacity, strength and other indicators as well as in accordance with the water treatment process to select different materials activated carbon products . Activated Carbon Prepared by Microwave factors are: microwave power , irradiation time , concentration of the activator , dipping ratio, pH value, etc.
4.3.1 The effect of microwave power
Take drained sludge material impregnated in a quartz tube , the fixed microwave irradiation time 4min, zinc chloride concentration of 35% , the proportion of dry sludge and zinc 1:3.0 , change the microwave power . When the power is low , the heating temperature does not reach the activation temperature of carbonization , so in this case the adsorption performance is poor; when the power continues to increase , the temperature is too high , due to the high vapor pressure of zinc chloride , pharmaceutical serious loss to the actual play instead, the role of zinc chloride reduction resulting sorbent performance degradation.
4.3.2 Time of irradiation
Take impregnated material drained sludge after peeling a quartz tube , fixed to the microwave cavity , the microwave power of 595W, the activator concentration of 35% zinc chloride , zinc chloride solution, dried sludge a weight ratio of 1:3.0 conditions, changing the irradiation time results shown in Figure 2 , the iodine value of the adsorbent and adsorption of methylene blue changing over time, the performance of the microwave variation of a similar , analysis of the reasons , mainly because activation microwave activation rate and the length of time the impact of fast , short irradiation time charring is not sufficient, for too long will result in some radiation aperture sintering .
4.3.3 The concentration of the activator
The zinc chloride solution with different concentrations of sludge drained impregnated material , put into a quartz tube, fixed in the microwave cavity , the microwave power 595W, irradiation time 4min, zinc chloride in dry weight of sludge and ratio of 1:3.0 experimental conditions , effects of different concentrations of the activator concentration on the prepared carbonaceous adsorbent properties. In general, the higher the concentration of the activator , the greater the dehydration condensation , the resulting structure is more developed porous adsorbent , the adsorption performance is better. On the other hand , zinc chloride is a strong adsorption material , if the concentration is too high, the material to enhance the adsorption capacity and enable the activation temperature, the carbon content decreased composition , ash content increased. In addition , the crystal will block a portion of zinc chloride large holes in the washing process can not be sufficiently removed , so that the adsorbent surface area and adsorption ability.
4.3.4 Ratio of impregnation
Different weight of zinc chloride solution of 40% of sludge drained impregnated raw material into a quartz tube , fixed in the microwave cavity , the microwave power 595W irradiated 4min. Dry sludge and the weight ratio of zinc chloride solution greater activator solution can be fully infiltration granular sludge , zinc chloride during pyrolysis full play to the role , the better the performance of the adsorbent obtained . But too much zinc chloride solution impregnated cause pyrolysis feedstock moisture content is too high , you need a longer heating time and the resulting zinc chloride waste.
4.3.5 Other factors
Preparation of activated carbon in the microwave experiments affecting factors include the soaking time , in general, the longer the soaking time , the more the degree of impregnation sufficient , but the time exceeds a certain level , the adsorption effect decreased. This is because the immersion time and the concentration of zinc chloride directly affect the adsorption amount of sludge , thus affecting the yield of the product and the level of performance . Start impregnated with a solution of zinc chloride , the raw water is very low , making the zinc chloride solution to the rapid swelling of the material , and in the beginning of a period of time, with the immersion time, the material in the rapid adsorption of zinc chloride increased , but the amount of adsorption reaches a certain level , with the immersion time, the raw material in slower absorption of zinc chloride . In the preparation of activated carbon in dry sludge this factor has little effect , but in the natural ingredients in the preparation of activated carbon impregnated Time of effect is more significant. In addition , different activators , their effectiveness is correspondingly different , Libo tobacco stems such as the use of microwave radiation performance of different carbon was prepared , the water vapor with an activator , phosphoric acid, zinc chloride , potassium hydroxide, and sulfuric acid.
5 Summary
Prepared by Microwave Preparation of activated carbon activated carbon has opened up a new way , the microwave method has fast heating, high thermal efficiency, easy to control , equipment, small , pollution, etc. , in addition to preparing excellent performance out of the activated carbon adsorption . But there are also shortcomings, microwave leakage would cause harm to the human body and the surrounding environment should be properly designed microwave reaction chamber and consider the appropriate use of microwave absorbing materials . Microwave -related basic research is still relatively lacking , such as microwave influence mechanism of chemical reactions , material heating in the microwave field characteristics , the temperature distribution in the microwave field , etc., only solves these problems , microwave technology was likely to be large-scale industrial application .

 

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