White carbon black and white carbon black is the general term for white powder X-ray amorphous silicic acid and silicate products, mainly refers to precipitated silica, fumed silica, ultrafine silica gel and aerogel, also including powder Synthetic aluminum silicate and calcium silicate. White carbon black is a porous substance, and its composition can be expressed by SiO2 • nH2O, where nH2O exists in the form of surface hydroxyl groups. It is soluble in caustic alkali and hydrofluoric acid, but insoluble in water, solvents and acids (except hydrofluoric acid). High temperature resistance, non-combustible, odorless, odorless, with good electrical insulation.
According to the production method, white carbon black is roughly divided into precipitation white carbon black and gas phase white carbon black. The gas phase method of white carbon black is normally white amorphous flocculent translucent solid colloidal nanoparticles (particle size less than 100nm), non-toxic, and has a huge specific surface area (100 ~ 400m2 / g) (using fully automatic F-Sorb 2400 Specific surface area instrument BET method test). The gas-phase method silica is all nano-silica, the product purity can reach 99%, the particle size can reach 10 ~ 20nm, but the preparation process is complicated and the price is expensive; the precipitation method silica is divided into the traditional precipitation method silica and Special precipitation method for white carbon black, the former refers to silica produced with sulfuric acid, hydrochloric acid, CO2 and water glass as the basic raw materials, the latter refers to the use of hypergravity technology, sol-gel method, chemical crystal method, secondary crystallization Silica produced by special methods such as the method or reverse micelle microemulsion method. The study of the specific surface area of ​​silica is very important. Only the results of the BET method can be used to detect the specific surface area of ​​silica, and there are many domestic instruments that can only be tested by the direct comparison method. eliminated. 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. Only truly fully automated intelligent specific surface area tester products can meet the international standards of the test instrument industry. All similar international products are fully automated. Manually operated instruments have long been eliminated abroad. A truly fully automated intelligent specific surface area analyzer product frees testers from repeated mechanical operations, greatly reducing their work intensity, training is simple, and working efficiency is improved. The truly fully automated intelligent specific surface area analyzer product greatly reduces errors caused by human operations and improves test accuracy. 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. Detailed information on specific standards can be found on the relevant website to check the precipitated silica is mainly used as a natural rubber and synthetic rubber reinforcement, toothpaste friction agent, etc. Fumed silica is mainly used as a reinforcing agent for silicone rubber, paint and thickener for unsaturated resins, and ultrafine silica gel and aerogel are mainly used as paint matting agent, thickener, plastic film opening agent, etc.
2. Production method The traditional method for preparing white carbon black is to use sodium silicate, silicon tetrachloride, ethyl orthosilicate as the silicon source. In addition to sodium silicate, other costs are very high. The new method uses cheap non-metallic ore as the silicon source, which greatly reduces the production cost of silica.
2.1 Traditional methods (1) The gas phase method is mainly chemical vapor deposition (CAV) method, also known as pyrolysis method, dry method or combustion method. The raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which are reacted at high temperature. The reaction formula is:
SiCl4 ＋ 2H2 ＋ O2—> SiO2 ＋ 4HCl
Air and hydrogen are sent to the synthetic hydrolysis furnace after pressurization, separation, cooling and dehydration, silica gel drying, dust removal and filtration. After the silicon tetrachloride raw material is sent to the rectification tower for rectification, it is heated and evaporated in an evaporator, and the dried and filtered air is used as a carrier to the synthetic hydrolysis furnace. After gasification of silicon tetrachloride at high temperature (flame temperature 1000 ~ 1800 ° C), gas phase hydrolysis is carried out at a high temperature of about 1800 ° C with a certain amount of hydrogen and oxygen (or air); fumed silica particles generated at this time It is extremely fine and forms an aerosol with the gas, which is not easy to trap, so it is first aggregated into larger particles in the accumulator, then collected by the cyclone separator, and then sent to the deacidification furnace, and the fumed silica is flushed with nitrogen-containing air Until the PH value is 4 ~ 6, it is the finished product.
Germany Degussa (Degussa) company and the United States Cabot (Cabot) company's gas-phase production technology is leading the world. Their production equipment is large in scale, high in automation, low in product cost, and has many grades (especially functional special product grades used in special fields). They have good quality, such as uniform surface area distribution and low water content. China's Shenyang Chemical Co., Ltd. and Shanghai Chlor-Alkali Chemical Co., Ltd. also use the gas phase method of production, but they are far inferior to large foreign companies in terms of production scale, production technology, degree of automation, and product brand. Guangzhou Ji Bi Sheng Technology Industrial Co., Ltd. is currently the largest domestic supplier, the most complete brand, the most advanced fumed silica supplier, and is the responsible drafting unit of fumed silica national standard GB20020-2005.
(2) Precipitation method Precipitation method, also called sodium silicate acidification method, uses water glass solution to react with acid, and obtains white carbon black through precipitation, filtration, washing, drying and calcination. The reaction formula is:
Na2SiO3 + 2H + —> Silica + 2Na + + H20
Most domestic manufacturing enterprises adopt the precipitation method.
2.2 New method The new method mainly uses non-metallic ore and its extensions as the silicon source, and uses the precipitation method to prepare the white carbon black. The technical key is to convert crystalline silica and silicate into amorphous silica. The raw materials are mainly wollastonite, opal, halloysite, olivine, snake stone, kaolin, hard kaolin, coal gangue, fly ash, etc.
This report focuses on the process technology for preparing white carbon from kaolin or hard kaolin, coal gangue or fly ash.
(1) Using kaolin or hard kaolin as raw material, first pulverize kaolin or hard kaolin to 50 ~ 60 mesh, then roast at 500 ~ 600 ℃ for 2 hours, and then press the roasted clay and 30% concentration of industrial hydrochloric acid by 1 : 2.5 (weight) ingredients, acid immersed at about 90 ℃ for 7 hours, neutralized, filtered, washed and dried to obtain white carbon black, the product quality meets the GB10507-89 standard; at the same time, a high-efficiency water purifier polyaluminum chloride is obtained. The roasting and acid leaching reaction formula is as follows:
Roasting: Al2O3 • 2Si02 • 2H20 —> Al2O3 • 2Si02 + 2H20
Acid leaching: Al2O3 • 2Si02 + 6HCl + 9H20 —> 2AlCl3 • 6H20 + 2SiO2
(2) Using coal gangue or fly ash as the raw material, first crush the coal gangue or fly ash to a particle size of less than 120 mesh, and then divide it into two steps:
The first step is to produce sodium silicate: mix the crushed coal gangue or fly ash with soda ash at a weight ratio of 1:50, mix it at high temperature (1400 ~ 1500 ℃, 1 hour), and extract with water (more than 100 ℃) , 4 ~ 5 hours), filter to remove impurities, concentrate the filtrate to 45 ~ 46 Baume degree to obtain sodium silicate.
The second step is to produce white carbon black: firstly mix sodium silicate into water glass solution (modulus is 2.4 ~ 3.6, SiO2 content is 4 ~ 10%), then pickle in 5 ~ 20% sulfuric acid (28 ~ 32 ℃, 8 ~ 16 hours), then increase the temperature to 80 ° C, stir, adjust the PH value to 5 ~ 7, ripen for 20 minutes, then filter, wash, dry, and sort to obtain white carbon black. The white carbon black is active and has high purity.
3. Production capacity / output Domestically, precipitation-based silica is mainly used. Industrial production of precipitation-based silica was realized in 1958, but the output was small and the development was slow. In 1987, the output was only 2687 tons; in 1990, it exceeded 10,600 tons; it increased to 28,100 tons in 1994, an increase of 9.4 times compared with 1987; in 1997, China's white carbon black output reached about 80,000 tons; in 2004 Rose to nearly 300,000 tons. It can be seen that the output of China's white carbon black has advanced by leaps and bounds in the past decade.
The production of silica in China is widely distributed, with a total of dozens of provinces and cities, among which Fujian, Shandong, Jiangsu, Jiangxi and other provinces have the largest output. At present, there are dozens of white carbon black production enterprises in China, with a total production capacity of about 400,000 tons / year. Among the large-scale precipitation white carbon black production enterprises are Fujian Nanping Jialian Chemical Co., Ltd., Shanghai Jiuchen Fine Chemical Co., Ltd., Zhuzhou Xinglong Chemical Industry Co., Ltd., Rhodia White Carbon (Qingdao) Co., Ltd., and Wuxi Heng Hengbai Carbon Black Co., Ltd., Tengzhou Xinxu Chemical Co., Ltd. etc. In terms of fumed silica, Guangzhou Jibisheng Technology Industrial Co., Ltd. has a production capacity of 6,000 tons per year and is the largest supplier of fumed silica in China.
Due to the optimistic prospects of the white carbon black market, some domestic enterprises are currently constructing or planning to build white carbon black projects, with some expansions and new constructions. Such as Shanghai Jiuchen Fine Chemical Co., Ltd., Puyang Guangpu Petrochemical Company, Hubei Xingfa Group, etc.
It is expected that China's white carbon black production capacity will exceed the 1 million ton / year mark in 2010.
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