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Progress in the synthesis of white carbon black
Jun 26, 2018

             

                                     Progress in the synthesis of white carbon black(Silicon Dioxide/SiO2)


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White carbon black is the general name of white powder amorphous silicic acid and silicate products, mainly refers to precipitated silica, gas phase silica, ultrafine silica gel and silica gel, including synthetic aluminum silicate and calcium silicate.


1. Use of white carbon black

White carbon black is widely used in the synthesis of rubber, synthetic oil, paint, light agent, insulation paint, electronic components, thixotropic agent, phosphor precipitant, color printing plate filler, casting mold release agent, and so on. Carbon black can be used as filling material in polyethylene and other plastics. It can significantly improve the electrical insulation of cable on cable. As a glue on paper, it can increase the whiteness and opacity of paper and improve its mechanical properties and ornamentability. In the manufacture of agricultural chemicals, white carbon black is used as a carrier or dilute thinner to be added to agriculture. Because of its high absorbability, easy suspension, good affinity and chemical stability, it can maintain the efficacy of the product.


2,synthesis process of white carbon black 

The main production methods of white carbon black are precipitation and gas phase, and white carbon black in gas phase is white amorphous and translucent solid colloidal nanoparticles (particle size less than 100nm), but the preparation process is complex and the product is expensive, the precipitation method has traditional precipitation method and special precipitation method, the former refers to sulfuric acid, hydrochloric acid, CO: water. The white carbon black produced by the glass is used as the basic raw material. The latter refers to the white carbon black produced by the special methods, such as supergravity technology, sol gel method, chemical crystal method, two crystallization method or reverse micelle microemulsion method.

2.1 fumed silica

China started small-scale production of fumed silica in the 2O century 60s. Only 3 companies produced gas phase white carbon black before 2002, of which two of them were four silicon chloride, and the other was first realized by methyl three chlorosilane, a by-product of organosilicon, to produce gas phase black carbon black, commonly known as "nano silica black".

Chemical vapor deposition (CAV), also known as pyrolysis, dry method or combustion method, is usually made of siloxane, four silicon chloride, six ethyl siloxane, oxygen (or air) and hydrogen, which react at high temperature.

The air and hydrogen are sent to a synthetic hydrolysate after pressure, separation, cooling, dehydration, silica gel drying, and dust filtration. After the four silicon chloride materials are sent to the distillation column, the evaporator is heated and evaporated, and the drying and filtered air is used as the carrier to the synthetic hydrolysate, and the four silicon chloride is vaporized at high temperature. When the temperature is 1000 - 1800 C, the gas phase is hydrolyzed with a certain amount of hydrogen and oxygen (or air) at a high temperature of about 1800 degrees C. The gas phase silica particles are very thin, and the gas formed aerosol, which is not easy to capture, so that the particles are gathered in the aggregator first and then collected through a cyclone separator and then sent off. The acid furnace uses air containing ammonia to purge the fumed silica to pH value of 4 - 6, that is finished product.

2.2 precipitated silica

At present, precipitation method is commonly used in industry, and its process route is generally as follows: at a certain temperature, the industrial water glass is prepared by the reaction of quartz (sand) and sodium hydroxide to make a dilute solution, and then the silica is precipitated under certain conditions and then cleaned, filtered, dried and crushed to make the product white carbon black. There are many methods for precipitation, and acid method is the main method in China.

2.2.1 acid method

Acid method is the reaction of soluble silicate with sulfuric acid or other acid. When the reaction reaches a certain pH value, it stops adding acid, aging, filtering, washing, and removing N%S O, and get the product after drying and crushing.

A schematic diagram of the process of preparing white carbon black by acid method

The key step in the acid process is the acid addition process, which requires the simultaneous processing of several parameters. It can be seen from the material changes in the reaction process that the properties of the product are related to the technological control conditions. The soluble silicate first turns into a monomer silicic acid, one part continues to produce loose floc (aggregation), and the other produces dense colloid (gel action).

2.2.2 carbonization

The production of silica by carbonization is based on the reaction of carbon dioxide and soluble silicate solution to produce water solid SiO 2 after filtration, drying, crushing and packaging.

A schematic diagram of carbonization process for preparing white carbon black

In this process, the conversion rate of sodium silicate is low, and the filtration device is generally needed to recover soda ash from by-products to reduce the cost. The surface active agent also has an effect on the performance of white carbon black. It is better to use polyethylene glycol (6ooo) as a surface active agent in carbonized black carbon black.

The new technology of spray carbonization is made of CO mixed gas and water glass as raw material, using the advanced technology and equipment such as spray carbonization, automatic press filter press, rotary flash drying and other advanced technology and equipment to make active (or transparent grade) white carbon black. This process has large contact area, fast reaction speed, low production cost and continuous production cost. The characteristics of production, low labor intensity, good product quality, large visual capacity, good airtight, high thermal efficiency, obvious energy saving and electricity saving, environmental benefit and economic benefit are remarkable.

2.2.3 mineral dissociation and other new processes

Non metal ore as raw material for making white carbon black are diatomite, protein soil, serpentine, clay, moistening soil, kaolin, wollastonite, quartz sand, sepiolite, attapulgite, fly ash, zircon, coal gangue, yellow phosphorus ore and so on. It is reported in the literature that the production of white carbon black from non-metallic ore shows that it is economically and technically feasible, and provides a new way for its resource utilization.


3. Conclusion

(1) silica has a wide range of uses and different products have different uses. It is urgent to adopt a simpler and more economical way to produce and prepare white carbon black.

(2) it is necessary to carry out systematic research on the preparation of silica from industrial waste (such as yellow phosphorus slag), and develop a technology and economically feasible process.