Coal-carbon conversion
Number 24. 2A PR. 200 1
Research progress in preparation, structure and properties of super activated carbon
Song Yan Li Lvlang
1)
2)
3)
3)
4)
X
Super activated carbon is a new type of high-efficiency adsorption functional material. Because of its high specific surface area, dense micropore distribution and excellent adsorption performance, it is attracting more and more attention and is widely used in many fields. The preparation, structure and properties of super activated carbon are reviewed.
Keywords super activated carbon, specific surface area, chemical activation method, pore structure, surface chemical structure, adsorption performance
China library classification number TQ 424. 1
Chemical method, chemical activation method and physical-chemical combined activation method. Among them, it is more common
0 quotation
Activated carbon is a broad-spectrum adsorbent, and its adsorption capacity is mainly
This depends on the specific surface area and pore size distribution of activated carbon. Conventional activated carbon has been widely used in medicine, catalysis, gas separation and storage, electric double layer capacitors and other fields because of its small specific surface area (2200m /g), concentrated micropore distribution and excellent adsorption performance. The research progress of super activated carbon in preparation, structure and properties is reviewed.
2
Use the latter two activation methods. 1. 1 physical activation method.
The physical activation method usually includes two steps: firstly, the raw materials are carbonized to remove volatile components to generate solid pyrolysis products rich in carbon, and then appropriate oxidizing gases (such as:
Steam, carbon dioxide, oxygen or air) to activate carbonized materials, and a developed pore structure is formed by opening, reaming and generating new pores. Generally, the following reactions will occur during activation:
c+H2O = H2+CO($ H =+ 1 17kJ/m ol)
C +CO 2=2CO ($H =+ 159kJ /m ol) removes carbon atoms from carbon materials through the above two reactions, thus producing abundant micropores.
There are many factors that affect physical activation. The porosity of activated carbon is not only related to the properties of raw materials for preparing activated carbon, but also closely related to carbonization and activation conditions (such as carbonization temperature, carbonization time, activation temperature, activation time, activator type, live load ratio, etc.). ). When preparing super activated carbon by physical activation method, catalysts are often added for catalytic activation. For example, Japanese patent [8] uses a group VIII metal element as a catalyst. The reaction time was shortened and the super activated carbon with specific surface area of 2000 ~ 2500 m/g/g was obtained. Representative transition metal compounds include Fe (NO 3) 3, Fe (OH) 3, FePO 4, FeBr 3, Fe 2 (SO 4) 3, Fe 2O 3, etc.
2
2
Preparation of 1 super activated carbon
Super activated carbon first appeared in the 1970 s, and the United States industrialized in the mid-1980 s, with the commodity code AX series; Japan was industrialized in the early 1990s, and its commodity code was M AXSORB. The raw materials for preparing super activated carbon are quite rich, including petroleum coke or pitch coke, coal, pitch shell [6] and mesophase carbon microspheres [7].
[ 1, 2]
[3]
[4, 5]
, lignin,
There are basically three methods to prepare super activated carbon: physical activity
Project supported by the National Natural Science Foundation of China (5977025).
1) doctoral students; 2) Researcher and doctoral supervisor, State Key Laboratory of Coal Conversion, Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, 03000 1 Taiyuan; 3) Associate researcher; 4) Researcher Taiyuan Bo:
28
Coal-charcoal conversion year 200 1
1.2 chemical activation method
Chemical activation method is to add additives to raw materials that affect pyrolysis reaction.
The dehydrating agent for inhibiting tar formation is carbonized and activated in one step. Chemical activation method is different due to different raw material manufacturing methods, but its process flow is basically the same (see figure
1).
Figure 1 Process Flow Chart of Preparation of Activated Carbon with High Specific Surface Area
F ig。 Preparation technology of 1 high surface area activated carbon
The activators commonly used in chemical activation method are hydroxides, inorganic salts and some acids of alkali metals and alkaline earth metals. At present, the widely used and mature chemical activators are KOH, NaOH, ZnCl _ 2, CaCl _ 2, 3PO _ 4, etc. Among them, the super activated carbon prepared with KOH as activator has the best performance.
When KOH is activated, on the one hand, KOH reacts with carbon to generate K 2CO 3, which makes pores develop, and K 2O and CO 2 generated by K 2CO 3 decomposition also contribute to micropore development; On the other hand, K2CO3 and K2O react with carbon to produce metallic potassium. When the activation temperature exceeds the boiling point of metallic potassium (762℃), metallic potassium will diffuse into the carbon layer, which will affect the development of pore structure, but it has different effects on different carbon materials. In the process of KOH activation, the following reactions mainly occur [9]:
4KOH +CK 2O +C
2CO 3+K 2O+3H 2K +CO
[9]
2222
M/g, 2666 m/g ~ 3646 m/g and 3880 m/g.
[9- 1 1][ 12]
Grade activated carbon. 1996 Xu Bin and others were condensed with solvent.
Super activated carbon with specific surface area of 3464m 2/g was prepared from mesophase pitch by KOH activation treatment, and its total pore volume was as high as 2. 14cm /g, benzene adsorption value is 16 100 mg/g, and pore size is mainly concentrated in the range of 1nm ~4nm ~ 4 nm. The average pore size is about 2. 6nm。 65438+ 1996 Zhang et al. of Dalian University of Technology [6] activated walnut shells and petroleum coke at 900℃ and 800℃ respectively, and prepared super activated carbons with specific surfaces of 2840m 2/g and 2200 m2/g respectively. 1997 et al. used Changling petroleum coke as raw material, and prepared super activated carbons with specific surfaces of. The adsorption values of 438+0m2/g super activated carbon are 2,765,438+08mg/g for iodine, 850mg /g for methylene blue and 65,438+0,480m2/g for benzene.
In a word, the type of activator, activation temperature, activation time and particle size of raw materials will affect the structure and properties of the final product during chemical activation, so it should be selected according to needs in practical application. For example, KOH activation produces new micropores, while H 3PO 4 or phosphate activation mainly produces mesopores. The surface affinity of activated carbon activated by KOH and H 3PO 4 is also different. The activated carbon prepared by KOH activation is phenol-philic, and the surface of activated carbon prepared by H 3PO 4 activation is acidic and hydrophilic, which is suitable for liquid phase adsorption and hydrogen storage. Physical and chemical combined activation method +0.3
The combined physical and chemical activation method is a combination of physical activation and chemical activation. Generally speaking, super activated carbon can be successfully prepared by chemical activation and then physical activation. For example, peach pit [13] is chemically activated with ZnCl _ 2, and after the specific surface area reaches 1000 m2/g ~ 2000 m2/g, it is physically activated with carbon dioxide.
three
Potassium carbonate +2C +3CO
The preparation of super activated carbon by KOH chemical activation method was first developed by American AM OCO company, and then commercialized by Anderson Development-ment company, and the super activated carbon with specific surface area greater than 2500m /g was prepared. KOH activated petroleum coke for super activated carbon prepared by Kansai Thermochemical Co., Ltd. of Japan, with the trade name of M AXSORB, has a specific surface area of 2800M/g ~ 3200M/g/g.. Japanese Otoha Li Lang activated coconut shells, petroleum coke and other raw materials with KOH, dehydrated at 400℃ and activated at 600℃ ~ 800℃, and super activated carbon with specific surface area greater than 3000m /g was obtained. Super activated carbon with specific surface area as high as 4000m 2/g was prepared by KOH activation method from mesophase carbon microspheres in Osaka Gas Company of Japan. The preparation and research of super activated carbon in China started late. Mesophase pitch, oxidized pitch and petroleum coke were used as raw materials in 1993, 1994 and 1998 respectively.
[8]
2
2
2
The temperature is around 0. 37g /mL, granular, very wear-resistant. This is very useful for natural gas storage and other processes. M olina -Sabio et al. used H2PO4 and H2PO4.
[ 14]
CO2 mixing activation of lignocellulose raw materials, that is, soaking lignocellulose with 68% ~ 85% h3po 4 at 85℃.
The fine structure consists of a wavy layer and a stack of two or three layers, and the size is 1nm ~2nm ~ 2 nm. Macropores of tens of nanometers can still be formed in activated carbon with the size of 800 m2/g ~ 1500 m2/g, and there are still slit-like holes between piles. However, the microstructure of super activated carbon with a specific surface area of more than 3000m /g is completely composed of a single wavy layer and small piles.
M arsh et al.
[ 17]
2
2h, then carbonized at 450℃ for 4h, then washed with distilled water and partially gasified with carbon dioxide at 825℃. Results Super activated carbon with specific surface area of 3700m /g and total pore volume of 2mL /g was obtained.
To sum up, the above three activation methods have their own advantages and disadvantages. Although the production process of preparing super activated carbon by chemical activation method is mature and commercialized, it has high cost, serious equipment corrosion and environmental pollution. Although the physical activation method is simple and has little pollution, the reaction time is long. The production process of super activated carbon prepared by this method is still being explored in laboratory scale, and there are few reports in this regard.
2
The activation of KOH was studied by infrared spectroscopy.
It is considered that KOH activation reaction may produce C, aromatic nucleus C and phenolic hydroxyl. Qiao et al. [18] studied the surface chemical structure of super activated carbon with high softening point pitch as raw material and KOH as activator by X-ray photoelectron spectroscopy, and thought that there were C O, C OH and C on the surface of super activated carbon.
Oxygen-containing functional groups such as o, O C and COOH. Otow a et al. [1] found that super activated carbon MAXSORB contains
Study on the Structure of Super Activated Carbon
2. Microstructure and surface chemical structure of1super activated carbon
[ 15]
M ar sh et al. studied KOH activation in Amo co research center by scanning electron microscope (SEM) and transmission electron microscope (T EM).
The number of oxygen-containing functional groups such as R, R, R OH and R O is far more than the number of surface functional groups in activated carbon prepared by steam activation, and the number of oxygen-containing functional groups has a great relationship with the specific surface area of activated carbon.2.2 Pore structure of super activated carbon.
According to IUPAC classification method, the pore structure of activated carbon is divided into micropores (50nm).
Ordinary granular activated carbon has a three-dispersed pore structure (see Figure 2). For adsorption, micropores play a major role, and the function of transition holes is to absorb steam in transition holes according to the mechanism of capillary condensation at a sufficiently high pressure. Like macropores, it acts as a channel for adsorbents to enter micropores.
Super activated carbon has a very developed pore structure, and the pore distribution is mainly concentrated in micropores, which belongs to monodisperse pore structure [6] (see Figure 3 on page 30). With the deepening of the activation degree of raw materials, the pore distribution center of the prepared activated carbon moves to the direction of macropores [18] (see paragraph 10).
Figure 4 on page 30).
The microstructures of two kinds of super activated carbons, PX-2 1 and PX-22, were obtained by chemical methods. The results show that the surface of these activated carbons is flat and the structure is uniform, and their ultramicropore structure consists of cage-like structures with a diameter of1nm ~ 5 nm, separated by carbon layers with a thickness of 1 ~ 3.
Minoru Shiraishi et al. [16] studied the microstructure of activated carbon with specific surface area of 800 m/g ~ 4 000 m/g prepared by activating mesophase carbon microspheres with KOH by transmission electron microscope and X-ray diffraction. The results show that with the increase of specific surface area, the microstructure of activated carbon changes from isotropic disc structure to single structure.
2
2
Fig. 2 pore structure of ordinary activated carbon
F ig。 2 Activate the structure of automobile body
Study on properties of three kinds of super activated carbon
Super activated carbon has large specific surface area and concentrated pores.
Diameter distribution, so it has strong adsorption capacity. Several kinds of research and development at home and abroad
The performance of super activated carbon is shown in table 1[ 19], and the comparison of adsorption performance between super activated carbon and other activated carbons is shown in table 2. [ 1 1]
Table 1 properties of super activated carbon
Table 1 characteristics of high surface activated carbon
Raw petroleum m coke petroleum m coke shell M CM B L asphalt
Asphalt petroleum coke
Activator potassium hydroxide potassium hydroxide alkaline aluminum compound potassium hydroxide potassium hydroxide potassium hydroxide.
s BE T/m2/g & gt； [ 1**********]0~5000
28002600~3646
36463230
V po re /cm 3/g 1。 4~2.0 1.5~2.0
— 1.3 1.5~2.52. 14 1.67
The adsorption capacity of iodine is 2800 ~ 3600 mg/g.
2500—25 142600~3 100
—27 18
Benzene adsorption capacity e/mg/g
——850—990~[ 1**********]0
Adsorption capacity of methylene blue/mg/g 400 ~ 600400 ~ 600620ml/g 353ml/g.
——850
Compared with pitch-based activated carbon fiber and spherical activated carbon, the adsorption value and benzene adsorption value are 2 times and 3 times higher respectively, and nearly 6 times higher than ordinary granular activated carbon. Its excellent adsorption performance makes it have great potential in the application field of adsorption materials.
Table 2 The adsorption properties of super activated carbon and conventional activated carbon are higher than those in Table 2.
Surface area activated automobile bo n and conv activated automobile bon
Fig. 3 pore distribution of activated carbon with high specific surface area
Fig. 3 Microstructure of high surface active carbon fiber
1-m-20 (s bet = 2000m/g); 2——M -30(S is t = 3000m2/g); 3——M -40 (assuming T = 4000m/g
)
2
Active carbohydrates on s hsac pacf psaac
S is ton/square meter/gram.
Adsorption capacity of iodine/mg/g
[ 1**********]8 480
Benzene adsorption capacity e/mg/g
1200 4 12 4 1 1 264
Note: hasc-high surface area activated carbon; Pacf-pitch-based spherical pitch-based activated carbon fiber: PSAC-activated carbon; Ac-granular activated carbon.
4 conclusion
Super activated carbon has attracted more and more attention because of its excellent adsorption performance.
Fig. 4 pore structure of several activated carbon samples
F ig。 4. Partial structure of activated carbon sample
a——S BE T = 2666 m2/g； B——S B ET = 683 m2/g； C-s b et = 619 m2/g.
People's favor, but the production and application of super activated carbon still need to be improved or further studied, such as how to further save energy, reduce consumption and reduce pollution in the production process; How to use effective molding methods to shape powdered super activated carbon to improve its packing density; Further develop new uses of super activated carbon.
It can be seen from Table 1 and Table 2 that the specific surface area of super activated carbon is 2 ~ 3 times higher than that of ordinary granular activated carbon, spherical activated carbon and activated carbon fiber, and it has a very developed micropore structure, so it adsorbs iodine.
Take the exam and contribute.
[1] development of high surface area activated carbon by otow a t, Nojina Y and M iyazaki T and its application in drinking water.
Water purification. Carb on， 1997，35(9): 13 15- 13 19
Liu Hongbo, Zhang Hongbo, Wu Huihe, et al. Preparation of petroleum coke-based activated carbon with high specific surface area. Carbon Science and Technology, 1997 (IV): 15- 19.
[3] Ahmadpour A, D. Preparation of activated carbon from coal by chemical and physical activation. Chebang, 1996,
34(4) :47 1-479
Qiao, Ling Liying, Zhang Hua et al. Preparation of an asphalt-based activated carbon binder with high specific surface area. Journal of Computer Science,1997,32 (16): 4447-4453.
Ouyang Shuguang, Zhou Juwu, Yu Jishun. Study on activated carbon with high specific surface area based on coal tar pitch. Carbon, 1996( 1) :28-32[6] Zhang, Guo Shucai, Deng. Preparation of activated carbon with high specific surface area. Materials Science and Engineering, 196.
A few. Chemical industry H,1990,43 (3):102-[7] Yuji Matsumura. Deng Kai 104 Z activated carbon.
Joe. Study on preparation, structure and properties of super activated carbon. Taiyuan: Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, 1993[9] Yao Jinhua, Bian Shoujun, Li Ming. Research progress of super activated carbon. Chemical Propellants and Polymer Materials,1999 (5):15-18 [10] Yang Jun, Huang Zhier, Wang Dingzhu. Preparation and adsorption characteristics of carbon molecular sieves with high specific surface area. Carbon science and technology, 1993 (2): 1.
[1 1] Liu Haiyan, Ling Yu Cheng, Liu zhichang, et al. Preparation of activated carbon with high specific surface area and preliminary study on its adsorption performance. New carbon materials, 1999,14 (2): 21-25 [12] Kuang Jianhua.
[13] Catur la F, M olina-Sabio M, Rodriguez-Noso F. Activated carbon black was prepared by chemical activation with ZnCl 2. Chebang, 199 1, 29(7) :999- 1007
[14] M olina-S abio M, Rodrig uez -Reinoso F, Caturrla f, etc. Porosity development of combined acid-carbon dioxide activation. Carbon,1996,34 (4): 457-462
[15] M arsh H, Craw for d D, Grady T M O, etc. High surface area carbon. Adsorption and high resolution research
Electron microscope Y. Carbon,1982,20 (5): 419-426.
[16] Minoru Shiraishi, Ji Ze Tuozi, Katsumi Nana Ogawa, et al. Microstructure of activated carbon n with high specific surface area. Carbon (Japan), 1992, 155:295-300.
[17] M arsh H, Yan D. Using potassium hydroxide to form activated carbon from coke. Carbon,1984,22 (6): 603-611[18] Joe, Cha, Liu Lang. Physical and chemical structure of pitch-based activated carbon with high specific surface area. Materials Science and Engineering, 195, 13 (1
Liu Haiyan. Preparation of activated carbon with high specific surface area and its methane adsorption performance. Master's degree thesis. Taiyuan: Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences,
1999
Preparation, Structure and Properties of High Density Polyethylene
Surface activated carbon
**
Institute of Coal Chemistry, China Academy of Sciences, 0300065438;
Activated carbon with high specific surface area is a new type of high functional adsorption material. It has been applied in many fields of modern industry. This paper briefly introduces the manufacture, structure and properties of activated carbon with high specific surface area. Keywords high surface area activated carbon, specific surface area, chemical activation, pore structure, chemical structure, adsorption performance.