Production process of silica by vapor phase method and its application characteristics
Thread Content
Silica produced by the vapor phase method is scientifically known as silica, and it is a unique ultra-fine nanoscale material used in industry. It features a small particle size, an extremely high specific surface area (100–400 m2/g), and high purity, thereby exhibiting excellent dispersion properties, reinforcing effects, thickening capabilities, thixotropic behavior, matting properties, electrical insulation, as well as hydrophobicity after surface treatment. It is widely used in fields such as aerospace, rubber, coatings, electronics and power, automotive industry, construction, agriculture, and pharmaceuticals; developed countries refer to it as the \"industrial Monosodium glutamate \". 1 Production process of silica by gas-phase method. There are two main routes for producing silica: one is high-temperature gas-phase hydrolysis, also known as the gas-phase method or dry method, and the other is the wet method, namely the precipitation method. Due to their different raw material routes and production processes, in practical applications, the performance of silica produced by the vapor phase method is significantly better than that of silica produced by the precipitation method. Vapor-phase silica is produced by the high-temperature vapor-phase hydrolysis of silicon chlorides in a hydrogen-oxygen flame, with a flame temperature of >1,000 °C, and is manufactured through purification processes such as condensation, separation, deacidification, and screening. Overall reaction equation: SiCl4 + 2H2 + O2 → SiO2 + 4HCl. Silica produced by the precipitation method is manufactured by reacting sodium silicate with concentrated sulfuric acid in a liquid phase, followed by processes such as liquid-phase separation, neutralization, dehydration, drying, and mechanical grinding. Due to the low cost of raw materials, the production cost is much lower than that of silica produced by the vapor phase method. Vapor-phase silica possesses unparalleled advantages over precipitated silica, such as dispersibility, thixotropy, thickening properties, as well as reinforcing effects in the rubber industry and insulating properties in the electronics industry. 2 Mechanism of action of fumed silica 2.1 Mechanism of action in liquid systems Due to the presence of numerous hydroxyl groups on the surface of fumed silica, these hydroxyl groups form hydrogen bonds between the aggregates of fumed silica; when it is fully dispersed in a liquid system, a network structure of silica is formed. Its arrangement is shown in Figure 2; such a grid can increase the viscosity of the liquid and induce thixotropic behavior. Thixotropy is a physical phenomenon of liquids: when a shear force is applied to a liquid system, the hydrogen bonds formed between silica aggregates are broken, resulting in a decrease in the viscosity of the liquid system. Once the shear force is removed, the aggregates re-establish a network structure through hydrogen bonds, and when the shear force is completely gone, the viscosity of the liquid system can return to its initial value. Thixotropic behavior plays a valuable role in many application areas, such as coatings, adhesives, and sealants. The increased viscosity resulting from the network structure of silica particles can improve the rheological properties of the liquid system and prevent it from settling. Increasing the flow rate of the liquid phase system can reduce viscosity; however, once stability is restored, fluidity decreases significantly as the network structure reestablishes itself. This property can be widely applied to mechanical spraying of liquid materials to achieve better spraying results. To achieve good rheological properties, appropriate dispersion of silica particles in the liquid phase system is a decisive factor; however, excessive dispersion can completely destroy the network structure between the silica particles, and it is difficult for this network structure to recover even after shear stress is applied for a long time. 2.2 Mechanism of action in drying systems Silica produced by the vapor phase method can exert various effects in drying systems through different mechanisms. For example, adding it to a granular system can promote free flow, while adding it to a coating can increase friction and resistance to sticking. 2.2.1 Free flow: Adding a small amount of fumed silica to powdery or granular materials helps to promote free flow, prevent caking, and avoid blockages. The microstructure of silica aggregates enables them to move easily between the large particles in a dry system. In most cases, silica produced by vapor-phase methods is added to coatings; after the coating forms a film, the silica particles are firmly embedded within that film, while the aggregated particle parts remain exposed on the surface of the coated film. The resulting microstructure makes the surface of the coating non-slippery and resistant to sticking, thereby increasing the coefficient of friction. If surface-treated fumed silica is added to the paint, it can endow the paint with water resistance. 2.2.3 Anti-adhesion: After production, plastic films, plastic sheets, paper, cardboard, and other resin materials usually need to be stored for a period of time before use. Due to the contact between their surfaces, adhesion can occur. Vapor-phase silica prevents complete contact on its surface, thus acting to prevent sticking. 2.3 Mechanism of action in solid systems: Silica produced by the vapor phase method is an extremely effective reinforcing agent for cross-linked polymer systems, as it enhances the cohesiveness of these solid systems. The small particle size of the silica along with its open-branched structure result in a larger contact area between the polymer and this additive. To obtain vulcanized rubber with high mechanical strength, it is not sufficient to rely solely on the cross-linking between the polymer and additives; the hydroxyl groups present on the surface of silica produced by the vapor phase method are also necessary. Students in the chemical process design field, join the QQ group: 76144910. Communicate together.
This post was last edited by lanjing334 on 2010-4-15 at 14:05. Vapor-phase silica is a nanoscale white powder produced by the high-temperature hydrolysis of silicon halides (mainly silicon tetrachloride and methyltrichlorosilane) in a hydrogen-oxygen flame. Its scientific name is vapor-phase silicon dioxide or aerosol silica; it is an important reinforcing filler and multifunctional additive widely used in industries such as silicone rubber, rubber, plastics, coatings, inks, pharmaceuticals, papermaking, food, cosmetics, and chemical mechanical polishing. It can serve functions such as reinforcement, thickening, thixotropy, and matting. It is a truly industrialized nanomaterial used worldwide. I. Current status of the industrial production of fumed silica: Fumed silica has been produced abroad for over 60 years. Countries such as the United States, Germany, and Japan have, through years of development and research, produced and sold large quantities of fumed silica. In 2005, the total global production capacity for fumed silica via vapor-phase methods was around 210,000 tons per year. With the rapid economic growth in our country and Asia, there has emerged a huge market demand. The appeal of low production costs, along with increasing environmental regulations, has prompted foreign manufacturers of vapor-phase silica to relocate to Asia. In 2005, the German company Degussa built a 3,000 t/a vapor-phase silica production facility in Thailand, primarily to support the former General Electric-Shin-Etsu silicone project. Faced with the huge potential for growth in China’s market for vapor-phase silica, foreign manufacturers of vapor-phase silica not only export large quantities of their products to this market but have also begun to build large-scale production facilities in China, considering increasing their investments there in order to strengthen and expand their business operations. Corteva Corporation of the United States and Lanxing (Group) Corporation of China entered into an agreement; together they invested around $30 million to build China’s largest, world-class production facility for fumed silica – Corteva Lanxing (Jiangxi) Chemical Co., Ltd. With an annual production capacity of 4,600 tons, this facility began operations in 2006. The American company Dow Corning and the German company Wacker Chemie AG have announced plans to establish a joint venture in Asia to produce silicone raw materials and fumed silica; this initiative is set to become a leading integrated production facility for silicone intermediates and silica in the Asian region. The production capacity for silica gel via the vapor phase method is 5,000 tons per year; the construction of this facility has been completed, with trial production scheduled for 2008. The Japanese company Tokuyama invested $49.9 million to build a gas-phase silica production facility with an annual capacity of 5,000 tons at Jia Shan Port in Zhejiang Province. Construction began in 2005, and the facility was put into operation in 2007. China began producing fumed silica on a small scale in the 1960s. Currently, fumed silica is manufactured in the country by Shenyang Chemical Co., Ltd., Shanghai Chlor-Alkali Chemical Co., Ltd., as well as Jilin Shuangji Chemical New Materials Co., Ltd. and Kaihua Xingji New Materials Co., Ltd., which are joint ventures. Among them, Shenyang Chemical Co., Ltd. has a production capacity of 1,000 tons per year, Shanghai Chlor-Alkali Chemical Co., Ltd. has a capacity of 100 tons per year, and Guangzhou Jibisheng Technology Industry Co., Ltd. has a capacity of 2,800 tons per year. In addition, there is also a production capacity of 500 tons per year for hydrophobic vapor-phase silica. By 2007, the production capacity of fumed silica in China via gas-phase methods had reached 13,500 tons per year, of which domestic companies accounted for 29% of this capacity. The production capacity of domestic vapor-phase silica plants in 2007 is detailed in Table 1. Table 1: Production capacity of domestic vapor-phase silica manufacturers in 2007
Manufacturer | Location | Production capacity (tons/year) | Plant details
Shenyang Chemical Co., Ltd. | Shenyang | 1,000 | Proprietary technology
Cabot Blue Star Materials Co., Ltd. | Jiangxi | 4,600 | Imported technology
Guangzhou Jibisheng Technology Industry Co., Ltd. | Jilin, Zhejiang, Guangzhou | 2,800 | Proprietary technology
Shanghai Chlor-Alkali Chemical Co., Ltd. | Shanghai | 100 | Domestic technology
Tokuyama Soda Co., Ltd. (Japan) | Jiashan | 5,000 | Foreign technology
Total | — | 13,500 | —
Foreign vapor-phase silica manufacturers are systematically relocating their production facilities to China in an effort to gain better control over the Chinese market; they use their strong technical and economic capabilities to impose production technology restrictions as well as monopolies over markets and raw materials in China. The market development environment for vapor-phase silica in our country is extremely harsh, with the industry facing tremendous pressures and challenges in terms of survival. After half a century of research and development efforts, the development of the vapor-phase silica industry in our country has been achieved through hard work; it is now imperative to vigorously promote and effectively protect this domestic industry. Faced with a tough market environment, if domestic manufacturers fail to step up their efforts and expand their production capacity within a relatively short period of time, without the support of related industries in the country, the silica industry will remain under the heavy monopoly of foreign companies. This will have a direct impact on the development of the silicone monomers and polysilicon industries, as well as on the defense industry and ** security. While developing and applying gas-phase silica technology, domestic and international silica companies place great emphasis on intellectual property protection, filing a series of patent applications. Foreign companies were the first to file invention patents in China, but domestic enterprises did not become discouraged by this challenge from foreign firms; instead, they stepped up their efforts in filing invention patent applications. It is worth mentioning Guangzhou Jibisheng Company, which entered the silica industry relatively late. Yet it has filed a total of 11 invention and utility model patents related to silica, of which 8 have been granted. This figure far exceeds that of other domestic and foreign companies, placing it at the forefront in terms of intellectual property protection. II. Domestic Market Analysis and Forecast for Vapor-Phase Silica In China, vapor-phase silica was previously mainly used in the military industry; it began to be widely utilized in civilian industries such as silicone rubber, polyesters, sealants, coatings, and inks starting in the 1990s. Regarding the domestic market consumption of fumed silica, no official statistical data are available. Opinions among industry professionals vary, but the general view is consistent: it is acknowledged that with the rapid development of the domestic silicone industry in recent years, the usage of fumed silica has been increasing significantly (see Table 2). Table 2 Domestic consumption structure and demand forecast for fumed silica (unit: tons)
Industry: 2006 2008 2010
Silicone rubber: 8,500 12,000 15,000
Polyester products: 1,100 1,300 1,500
Paints: 1,500 1,800 2,000
Inks: 1,000 1,200 1,400
Others: 3,900 5,000 6,500
Total: 16,000 21,300 26,400
Fumed silica is primarily used in room-temperature vulcanizing silicone rubber (RTV) and heat-vulcanizing silicone rubber (HTV); in the latter, its addition level can reach up to 40 parts by weight. Its use in silicone rubber accounts for approximately 60% of its total production. Therefore, the extent and depth of utilization of silicone rubber will directly influence the market demand for fumed silica. The large-scale application of silicone rubber in our country has already begun, and there is huge market potential. The market for silicone rubber in our country is mainly concentrated in regions such as Guangdong, Jiangsu, and Zhejiang, accounting for approximately 85% of the national market at present. In recent years, the market for vapor-phase silica in China has experienced rapid growth, with the net import volume of vapor-phase silica increasing by more than 20% for seven consecutive years (see Table 3) ； In 2007, the import volume reached 12,318 tons. According to incomplete statistics, the demand for vapor-phase silica in China has currently exceeded 20,000 tons per year, with an average annual growth rate of as high as 32% (see Table 4). Table 3: Import volume of vapor-phase silica in China in recent years (unit: tons)
Year: 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
Import volume: 2110, 2787, 3436, 5759, 6961, 9034, 11427, 12318
Average annual growth rate: 36%, 32%, 23%, 67%, 21%, 30%, 26%, 8%
Table 4: Apparent consumption volume in China from 2000 to 2007 (unit: tons)
Year: 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
Apparent consumption volume (tons): 2675, 3367, 4286, 6909, 8861, 11184, 16043, 20000
Average annual growth rate: 27%, 26%, 27%, 61%, 28%, 26%, 43%, 22%
Note: Apparent consumption volume = Import volume – Export volume + Domestic production
III. Opportunities presented by the rapid development of polysilicon for vapor-phase silica
Due to the severe greenhouse effect caused by the extensive use of traditional non-renewable energy sources such as oil, natural gas, and coal, as well as resource depletion resulting from long-term overexploitation, there is now global concern regarding energy security. This has led to a doubling of crude oil prices in recent years, especially in 2007; the problems arising from this situation are even more severe than those during the oil crisis. Figure 1 shows the changes in crude oil futures prices over the past decade. In 2007, the price exceeded $100 per barrel on several trading days, and in 2008 it remained above $100 per barrel, even reaching $110 per barrel at one point in March. This poses a serious threat to the healthy development of the world economy! Renewable energy has received unprecedented attention in this context; among them, wind and solar energy utilization technologies are the most mature. Wind energy has limited application due to geographical constraints, whereas polycrystalline silicon photovoltaic solar technology has received significant attention and vigorous promotion in developed countries and major developing countries. Polycrystalline silicon serves as the cornerstone of the photovoltaic solar industry. Currently, there are roughly 14 companies around the world that are engaged in the development and production of polysilicon materials. Due to the high technical barriers and substantial investment requirements, this industry is highly concentrated. Although there are nearly a dozen different processing techniques such as the improved Siemens method, the metallurgical method, and the silane method for producing high-purity polysilicon, China’s polysilicon industry began to develop in the 1960s. Represented by the Emei Semiconductor Materials Factory, this industry served mainly the military sector, with each company’s annual production volume not exceeding 50 tons. It was not until the beginning of this century that our country began to focus on building large-scale production lines for high-purity polysilicon materials. The establishment of Sichuan Xinguang Silicon Industry Company in 2002 marked a turning point, but the construction progress was very slow, and mass production only started in 2007. With the rapid development of the domestic photovoltaic industry, and thanks to highly favorable subsidy policies, the demand for polysilicon-based photovoltaic products has grown at an exponential rate. This has increased the demand for high-purity polysilicon, causing its price to rise by nearly ten times within a year. Such abnormal price increases have led to the launch of numerous large-scale polysilicon production projects in China. Over the next 2–3 years, the capacity and output of polysilicon in China are set to grow at an exponential pace, and the country is likely to become a major global producer of polysilicon. With the commissioning of a number of large-scale polysilicon projects, it is inevitable that polysilicon prices will drop significantly. This will help reduce the costs of photovoltaic solar products, thereby enabling a substantial decrease in the costs associated with polysilicon-based photovoltaic solar power generation. In turn, this will further promote the development of the polysilicon industry. It can be said that we are currently in a golden age for the development of the polysilicon and photovoltaic solar industries. However, according to the process technology route of the modified Siemens method, while significantly increasing the production capacity of polysilicon, it inevitably leads to the treatment of silicon tetrachloride, a by-product in its reduction reaction, becoming a bottleneck for the industry’s development. At present, the companies in China with the best control over polysilicon production processes generate around 10 tons of silicon tetrachloride as a by-product per ton of polysilicon produced; those with poorer control levels can produce up to 20 tons of such by-product. With the projects that are currently under construction or planned, China’s total polysilicon production capacity will exceed 10 kt/a by 2010, which means that at least 100 kt/a of silicon tetrachloride will need to be dealt with. Silicon tetrachloride, as a highly dangerous chemical, cannot be handled using ordinary methods. The traditional method involves purifying silicon tetrachloride and then using it with anhydrous ethanol (or methanol) in an esterification reaction to produce ethyl silicate (or methyl silicate) under normal temperature and pressure. However, the amount that can be obtained is very limited, and there are also difficulties such as separation, which prevents full utilization of this method. Using silicon tetrachloride, a by-product of the polysilicon industry, as raw material to produce gaseous silica is a technological process that offers both economic and environmental benefits. It not only addresses the bottlenecks that hinder the development of the polysilicon industry, reducing the production costs of polysilicon, but also helps achieve energy savings, environmental protection, and recycling in its production. This approach further enhances the technical capabilities and market competitiveness of polysilicon manufacturers in China, thereby promoting the rapid and healthy development of the country’s polysilicon industry ； It can also provide a large amount of raw materials for the fumed silica industry, thereby promoting the development of this industry in China and facilitating the healthy growth of China’s sectors related to solar energy, as well as other high-tech and new material fields. The integration and recycling of such resources promote the development of each other, creating an industrial chain characterized by complementary resources, mutual utilization, and joint growth. The social and economic benefits are significant, making it the best approach to overcoming the bottlenecks in the polysilicon industry at present. IV. Gas-phase silica will promote the sustainable development of China’s silicone industry. As the prices of non-renewable resources such as oil and natural gas soar, the costs of petroleum-based polymer products inevitably rise significantly, posing a serious challenge to the synthetic materials industry. Silicone rubber raw materials have little connection to petroleum, and their performance is superior to that of many synthetic materials. Due to their high cost, they have long been used only as special synthetic materials. However, with the commissioning of more than a dozen large-scale silicone monomer production facilities in our country, the price of siloxane, the basic raw material for silicone rubber, is likely to continue to fall, further reducing the cost of silicone rubber. It is already cheaper than ethylene propylene diene monomer rubber, and it is predicted that it may even become cheaper than bulk common rubbers such as natural rubber. As a result, silicone rubber will be able to replace some traditional products at the price of ordinary synthetic materials, and its usage volume is set to increase several times over the current level. This presents significant opportunities for the development of the silicone industry. Due to the structure of its base polymer, silicone rubber requires reinforcing fillers in order to be useful. As mentioned earlier, fumed silica is the best reinforcing filler for silicone rubber; however, due to its high cost, alternatives such as precipitated silica have been sought. Yet the use of these alternatives does not allow silicone rubber to exhibit its full performance potential. Due to the widespread use of silicon tetrachloride, a by-product of polysilicon, as the main raw material for vapor-phase silica, the price of vapor-phase silica has dropped significantly. Moreover, as domestic production of vapor-phase silica continues to expand, there is still room for further price reductions. This allows silicone rubber to maintain its excellent properties when using vapor-phase silica as a reinforcing filler without an increase in cost, which is a major advantage for the silicone rubber processing industry. It is expected that such a situation will lead to an increase in the use of silicone rubber, playing an important role in promoting the sustainable development of the silicone industry. Conversely, the development of silicones will also promote the steady progress of fumed silica. V. Conclusions and Recommendations 1. The annual growth rate of domestic consumption of vapor-phase silica is over 32%, while the annual growth rate of imports is over 30%; by 2010, this figure is expected to exceed 25 kt/a. 2. With foreign companies establishing production bases in China, the rapid development of domestic enterprises, and a significant increase in the use of fumed silica, China has become a major producer and consumer of fumed silica worldwide, and is set to soon develop into a global leader in this field. Those in the silica industry, join the QQ group: 76144910 to communicate together
Manufacturer | Location | Production capacity (tons/year) | Plant details
Shenyang Chemical Co., Ltd. | Shenyang | 1,000 | Proprietary technology
Cabot Blue Star Materials Co., Ltd. | Jiangxi | 4,600 | Imported technology
Guangzhou Jibisheng Technology Industry Co., Ltd. | Jilin, Zhejiang, Guangzhou | 2,800 | Proprietary technology
Shanghai Chlor-Alkali Chemical Co., Ltd. | Shanghai | 100 | Domestic technology
Tokuyama Soda Co., Ltd. (Japan) | Jiashan | 5,000 | Foreign technology
Total | — | 13,500 | —
Foreign vapor-phase silica manufacturers are systematically relocating their production facilities to China in an effort to gain better control over the Chinese market; they use their strong technical and economic capabilities to impose production technology restrictions as well as monopolies over markets and raw materials in China. The market development environment for vapor-phase silica in our country is extremely harsh, with the industry facing tremendous pressures and challenges in terms of survival. After half a century of research and development efforts, the development of the vapor-phase silica industry in our country has been achieved through hard work; it is now imperative to vigorously promote and effectively protect this domestic industry. Faced with a tough market environment, if domestic manufacturers fail to step up their efforts and expand their production capacity within a relatively short period of time, without the support of related industries in the country, the silica industry will remain under the heavy monopoly of foreign companies. This will have a direct impact on the development of the silicone monomers and polysilicon industries, as well as on the defense industry and ** security. While developing and applying gas-phase silica technology, domestic and international silica companies place great emphasis on intellectual property protection, filing a series of patent applications. Foreign companies were the first to file invention patents in China, but domestic enterprises did not become discouraged by this challenge from foreign firms; instead, they stepped up their efforts in filing invention patent applications. It is worth mentioning Guangzhou Jibisheng Company, which entered the silica industry relatively late. Yet it has filed a total of 11 invention and utility model patents related to silica, of which 8 have been granted. This figure far exceeds that of other domestic and foreign companies, placing it at the forefront in terms of intellectual property protection. II. Domestic Market Analysis and Forecast for Vapor-Phase Silica In China, vapor-phase silica was previously mainly used in the military industry; it began to be widely utilized in civilian industries such as silicone rubber, polyesters, sealants, coatings, and inks starting in the 1990s. Regarding the domestic market consumption of fumed silica, no official statistical data are available. Opinions among industry professionals vary, but the general view is consistent: it is acknowledged that with the rapid development of the domestic silicone industry in recent years, the usage of fumed silica has been increasing significantly (see Table 2). Table 2 Domestic consumption structure and demand forecast for fumed silica (unit: tons)
Industry: 2006 2008 2010
Silicone rubber: 8,500 12,000 15,000
Polyester products: 1,100 1,300 1,500
Paints: 1,500 1,800 2,000
Inks: 1,000 1,200 1,400
Others: 3,900 5,000 6,500
Total: 16,000 21,300 26,400
Fumed silica is primarily used in room-temperature vulcanizing silicone rubber (RTV) and heat-vulcanizing silicone rubber (HTV); in the latter, its addition level can reach up to 40 parts by weight. Its use in silicone rubber accounts for approximately 60% of its total production. Therefore, the extent and depth of utilization of silicone rubber will directly influence the market demand for fumed silica. The large-scale application of silicone rubber in our country has already begun, and there is huge market potential. The market for silicone rubber in our country is mainly concentrated in regions such as Guangdong, Jiangsu, and Zhejiang, accounting for approximately 85% of the national market at present. In recent years, the market for vapor-phase silica in China has experienced rapid growth, with the net import volume of vapor-phase silica increasing by more than 20% for seven consecutive years (see Table 3) ； In 2007, the import volume reached 12,318 tons. According to incomplete statistics, the demand for vapor-phase silica in China has currently exceeded 20,000 tons per year, with an average annual growth rate of as high as 32% (see Table 4). Table 3: Import volume of vapor-phase silica in China in recent years (unit: tons)
Year: 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
Import volume: 2110, 2787, 3436, 5759, 6961, 9034, 11427, 12318
Average annual growth rate: 36%, 32%, 23%, 67%, 21%, 30%, 26%, 8%
Table 4: Apparent consumption volume in China from 2000 to 2007 (unit: tons)
Year: 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
Apparent consumption volume (tons): 2675, 3367, 4286, 6909, 8861, 11184, 16043, 20000
Average annual growth rate: 27%, 26%, 27%, 61%, 28%, 26%, 43%, 22%
Note: Apparent consumption volume = Import volume – Export volume + Domestic production
III. Opportunities presented by the rapid development of polysilicon for vapor-phase silica
Due to the severe greenhouse effect caused by the extensive use of traditional non-renewable energy sources such as oil, natural gas, and coal, as well as resource depletion resulting from long-term overexploitation, there is now global concern regarding energy security. This has led to a doubling of crude oil prices in recent years, especially in 2007; the problems arising from this situation are even more severe than those during the oil crisis. Figure 1 shows the changes in crude oil futures prices over the past decade. In 2007, the price exceeded $100 per barrel on several trading days, and in 2008 it remained above $100 per barrel, even reaching $110 per barrel at one point in March. This poses a serious threat to the healthy development of the world economy! Renewable energy has received unprecedented attention in this context; among them, wind and solar energy utilization technologies are the most mature. Wind energy has limited application due to geographical constraints, whereas polycrystalline silicon photovoltaic solar technology has received significant attention and vigorous promotion in developed countries and major developing countries. Polycrystalline silicon serves as the cornerstone of the photovoltaic solar industry. Currently, there are roughly 14 companies around the world that are engaged in the development and production of polysilicon materials. Due to the high technical barriers and substantial investment requirements, this industry is highly concentrated. Although there are nearly a dozen different processing techniques such as the improved Siemens method, the metallurgical method, and the silane method for producing high-purity polysilicon, China’s polysilicon industry began to develop in the 1960s. Represented by the Emei Semiconductor Materials Factory, this industry served mainly the military sector, with each company’s annual production volume not exceeding 50 tons. It was not until the beginning of this century that our country began to focus on building large-scale production lines for high-purity polysilicon materials. The establishment of Sichuan Xinguang Silicon Industry Company in 2002 marked a turning point, but the construction progress was very slow, and mass production only started in 2007. With the rapid development of the domestic photovoltaic industry, and thanks to highly favorable subsidy policies, the demand for polysilicon-based photovoltaic products has grown at an exponential rate. This has increased the demand for high-purity polysilicon, causing its price to rise by nearly ten times within a year. Such abnormal price increases have led to the launch of numerous large-scale polysilicon production projects in China. Over the next 2–3 years, the capacity and output of polysilicon in China are set to grow at an exponential pace, and the country is likely to become a major global producer of polysilicon. With the commissioning of a number of large-scale polysilicon projects, it is inevitable that polysilicon prices will drop significantly. This will help reduce the costs of photovoltaic solar products, thereby enabling a substantial decrease in the costs associated with polysilicon-based photovoltaic solar power generation. In turn, this will further promote the development of the polysilicon industry. It can be said that we are currently in a golden age for the development of the polysilicon and photovoltaic solar industries. However, according to the process technology route of the modified Siemens method, while significantly increasing the production capacity of polysilicon, it inevitably leads to the treatment of silicon tetrachloride, a by-product in its reduction reaction, becoming a bottleneck for the industry’s development. At present, the companies in China with the best control over polysilicon production processes generate around 10 tons of silicon tetrachloride as a by-product per ton of polysilicon produced; those with poorer control levels can produce up to 20 tons of such by-product. With the projects that are currently under construction or planned, China’s total polysilicon production capacity will exceed 10 kt/a by 2010, which means that at least 100 kt/a of silicon tetrachloride will need to be dealt with. Silicon tetrachloride, as a highly dangerous chemical, cannot be handled using ordinary methods. The traditional method involves purifying silicon tetrachloride and then using it with anhydrous ethanol (or methanol) in an esterification reaction to produce ethyl silicate (or methyl silicate) under normal temperature and pressure. However, the amount that can be obtained is very limited, and there are also difficulties such as separation, which prevents full utilization of this method. Using silicon tetrachloride, a by-product of the polysilicon industry, as raw material to produce gaseous silica is a technological process that offers both economic and environmental benefits. It not only addresses the bottlenecks that hinder the development of the polysilicon industry, reducing the production costs of polysilicon, but also helps achieve energy savings, environmental protection, and recycling in its production. This approach further enhances the technical capabilities and market competitiveness of polysilicon manufacturers in China, thereby promoting the rapid and healthy development of the country’s polysilicon industry ； It can also provide a large amount of raw materials for the fumed silica industry, thereby promoting the development of this industry in China and facilitating the healthy growth of China’s sectors related to solar energy, as well as other high-tech and new material fields. The integration and recycling of such resources promote the development of each other, creating an industrial chain characterized by complementary resources, mutual utilization, and joint growth. The social and economic benefits are significant, making it the best approach to overcoming the bottlenecks in the polysilicon industry at present. IV. Gas-phase silica will promote the sustainable development of China’s silicone industry. As the prices of non-renewable resources such as oil and natural gas soar, the costs of petroleum-based polymer products inevitably rise significantly, posing a serious challenge to the synthetic materials industry. Silicone rubber raw materials have little connection to petroleum, and their performance is superior to that of many synthetic materials. Due to their high cost, they have long been used only as special synthetic materials. However, with the commissioning of more than a dozen large-scale silicone monomer production facilities in our country, the price of siloxane, the basic raw material for silicone rubber, is likely to continue to fall, further reducing the cost of silicone rubber. It is already cheaper than ethylene propylene diene monomer rubber, and it is predicted that it may even become cheaper than bulk common rubbers such as natural rubber. As a result, silicone rubber will be able to replace some traditional products at the price of ordinary synthetic materials, and its usage volume is set to increase several times over the current level. This presents significant opportunities for the development of the silicone industry. Due to the structure of its base polymer, silicone rubber requires reinforcing fillers in order to be useful. As mentioned earlier, fumed silica is the best reinforcing filler for silicone rubber; however, due to its high cost, alternatives such as precipitated silica have been sought. Yet the use of these alternatives does not allow silicone rubber to exhibit its full performance potential. Due to the widespread use of silicon tetrachloride, a by-product of polysilicon, as the main raw material for vapor-phase silica, the price of vapor-phase silica has dropped significantly. Moreover, as domestic production of vapor-phase silica continues to expand, there is still room for further price reductions. This allows silicone rubber to maintain its excellent properties when using vapor-phase silica as a reinforcing filler without an increase in cost, which is a major advantage for the silicone rubber processing industry. It is expected that such a situation will lead to an increase in the use of silicone rubber, playing an important role in promoting the sustainable development of the silicone industry. Conversely, the development of silicones will also promote the steady progress of fumed silica. V. Conclusions and Recommendations 1. The annual growth rate of domestic consumption of vapor-phase silica is over 32%, while the annual growth rate of imports is over 30%; by 2010, this figure is expected to exceed 25 kt/a. 2. With foreign companies establishing production bases in China, the rapid development of domestic enterprises, and a significant increase in the use of fumed silica, China has become a major producer and consumer of fumed silica worldwide, and is set to soon develop into a global leader in this field. Those in the silica industry, join the QQ group: 76144910 to communicate together
The reinforcing properties of precipitated silica depend primarily on its specific surface area (or particle size), structure, and surface chemical properties; therefore, its specific surface area and oil absorption value are key indicators reflecting the characteristics of the product. This paper investigates the effect of reaction conditions on the specific surface area and oil absorption value of silica. 1 Experimental Section 1.1 Experimental Instruments and Equipment: 20 L stainless steel jacketed reactor, equipped with a temperature display instrument, speed control motor, stirrer, etc.; laboratory vacuum pump and filter flask; three-legged centrifuge; electric heating forced-air drying oven; laboratory analysis instruments, glassware, etc. 1. 2 Main raw materials: liquid sodium silicate, GB/T 4209—1996, first-grade product; industrial sulfuric acid, GB/T 534—2002. 1.3 Experimental Procedures The industrial liquid water glass is diluted with water to achieve a certain concentration; after vacuum filtration, refined liquid water glass is obtained for later use. Industrial sulfuric acid is also diluted with water to reach a specific mass fraction, and it is kept aside for use. A certain amount of water and a certain amount of sodium silicate, which serves as an additional liquid, are added to the reaction vessel. Once the stirring and heating systems are activated, the temperature of the materials is raised to a specified level. After that, liquid sodium silicate and sulfuric acid are added to the reaction vessel; the flow rate is adjusted using a rotameter, and the pH of the reaction mixture is monitored and kept within the specified range. After the reaction is complete, the material is sent to a three-legged centrifuge for washing and drying, resulting in a silica gel filter cake. The filter cake is sent to an oven for drying to obtain the test product. 1.4 Analysis Methods The determination of the oil absorption value is carried out in accordance with HG/T 3072: Determination of the oil absorption value of rubber additives – precipitated hydrated silica, namely the DBP value. The specific surface area is determined using a simple alkaline titration method, and is expressed as a BET value. 2 Results and Discussion The 5 sets of experimental data (see Tables 1–5) represent the results obtained by changing only one experimental factor while keeping all other conditions constant. 1) As can be seen from Table 1, in this experiment, when the stirring speed was set at 50 r/min, the low stirring speed resulted in insufficient mixing of the materials inside the reactor. This led to the formation of gel in the silica sol produced by the reaction, and the dried silica product contained many undispersed lumps, making it an unqualified product. As the reaction stirring speed varies between 100 and 200 r/min, increasing the stirring speed of the reaction can raise the specific surface area of the silica product (i.e., the BET value); simultaneously, it can also increase the degree of structure of the silica product (i.e., the DBP value). 2) As can be seen from Table 2, as the modulus of water glass varies from 3.13 to 3.45, an increase in this modulus has little effect on the specific surface area of the silica aerogel products; instead, it leads to an increase in the degree of structure of these products. 3) As can be seen from Table 3, as the mass fraction of sulfuric acid varies from 20% to 30%, the specific surface area of the silica product increases with rising sulfuric acid content, while the degree of structure in the silica product decreases. 4) As can be seen from Table 4, as the reaction temperature increases, the specific surface area of the silica product first decreases and then increases, reaching its minimum at 90 °C. Meanwhile, the degree of structure of the silica product first increases and then decreases, with the highest degree of structure occurring at 90 °C. 5) As can be seen from Table 5, as the reaction time increases, the specific surface area of the silica product decreases, while its degree of structure increases. 3 Conclusions 1) Among the reaction conditions, the reaction temperature has the greatest impact on the specific surface area of silica products. Therefore, to obtain silica products with a high specific surface area, it is possible to reduce the reaction temperature. However, lowering the reaction temperature inevitably prolongs the reaction time and reduces production efficiency. Thus, methods such as carrying out the reaction in stages at lower temperatures first and then at higher temperatures can be employed to increase the specific surface area of silica products. 2) Under the reaction conditions, the stirring speed and reaction time have the greatest impact on the structural integrity of the silica product. Therefore, the design of the stirrers in the reaction vessels used in silica production, as well as the location at which acids and bases are added to these vessels, are extremely important. It is necessary to ensure thorough and uniform mixing of the materials inside the reaction vessels, in order to prevent localized high acidity from leading to the formation of gels. Moreover, the better the stirring effect, the more it contributes to improving the internal quality of the silica product. 3) There are many factors that can affect the specific surface area and oil absorption value of silica products. This article only discusses some of them, but it can be concluded that by optimizing the reaction conditions, silica products with significantly different properties can be produced, thereby meeting the requirements of a wider range of users. Those in the silica industry, join the QQ group: 76144910 to communicate together